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Vera E, Cornejo I, Henao JC, Tribiños F, Burgos J, Sepúlveda FV, Cid LP. Normal vision and development in mice with low functional expression of Kir7.1 in heterozygosis for a blindness-producing mutation inactivating the channel. Am J Physiol Cell Physiol 2024; 326:C1178-C1192. [PMID: 38406825 DOI: 10.1152/ajpcell.00597.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2023] [Revised: 02/18/2024] [Accepted: 02/19/2024] [Indexed: 02/27/2024]
Abstract
K+ channel Kir7.1 expressed at the apical membrane of the retinal pigment epithelium (RPE) plays an essential role in retinal function. An isoleucine-to-threonine mutation at position 120 of the protein is responsible for blindness-causing vitreo-retinal dystrophy. We have studied the molecular mechanism of action of Kir7.1-I120T in vitro by heterologous expression and in vivo in CRISPR-generated knockin mice. Full-size Kir7.1-I120T reaches the plasma membrane but lacks any activity. Analysis of Kir7.1 and the I120T mutant in mixed transfection experiments, and that of tandem tetrameric constructs made by combining wild type (WT) and mutant protomers, leads us to conclude that they do not form heterotetramers in vitro. Homozygous I120T/I120T mice show cleft palate and tracheomalacia and do not survive beyond P0, whereas heterozygous WT/I120T develop normally. Membrane conductance of RPE cells isolated from WT/WT and heterozygous WT/I120T mice is dominated by Kir7.1 current. Using Rb+ as a charge carrier, we demonstrate that the Kir7.1 current of WT/I120T RPE cells corresponds to approximately 50% of that in cells from WT/WT animals, in direct proportion to WT gene dosage. This suggests a lack of compensatory effects or interference from the mutated allele product, an interpretation consistent with results obtained using WT/- hemizygous mouse. Electroretinography and behavioral tests also show normal vision in WT/I120T animals. The hypomorphic ion channel phenotype of heterozygous Kir7.1-I120T mutants is therefore compatible with normal development and retinal function. The lack of detrimental effect of this degree of functional deficit might explain the recessive nature of Kir7.1 mutations causing human eye disease.NEW & NOTEWORTHY Human retinal pigment epithelium K+ channel Kir7.1 is affected by generally recessive mutations leading to blindness. We investigate one such mutation, isoleucine-to-threonine at position 120, both in vitro and in vivo in knockin mice. The mutated channel is inactive and in heterozygosis gives a hypomorphic phenotype with normal retinal function. Mutant channels do not interfere with wild-type Kir7.1 channels which are expressed concomitantly without hindrance, providing an explanation for the recessive nature of the disease.
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Affiliation(s)
- Erwin Vera
- Centro de Estudios Científicos (CECs), Valdivia, Chile
- Universidad Austral de Chile, Valdivia, Chile
| | - Isabel Cornejo
- Centro de Estudios Científicos (CECs), Valdivia, Chile
- Facultad de Ciencias para el Cuidado de la Salud, Universidad San Sebastián, Valdivia, Chile
| | - Juan Carlos Henao
- Centro de Estudios Científicos (CECs), Valdivia, Chile
- Universidad Austral de Chile, Valdivia, Chile
| | | | | | - Francisco V Sepúlveda
- Centro de Estudios Científicos (CECs), Valdivia, Chile
- Facultad de Medicina y Ciencia, Universidad San Sebastián, Valdivia, Chile
| | - L Pablo Cid
- Centro de Estudios Científicos (CECs), Valdivia, Chile
- Facultad de Medicina y Ciencia, Universidad San Sebastián, Valdivia, Chile
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2
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Hernandez CC, Gimenez LE, Cone RD. Automated Patch Clamp Recordings of GPCR-Gated Ion Channels: Targeting the MC4-R/Kir7.1 Potassium Channel Complex. Methods Mol Biol 2024; 2796:229-248. [PMID: 38856905 DOI: 10.1007/978-1-0716-3818-7_14] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2024]
Abstract
Automated patch clamp recording is a valuable technique in drug discovery and the study of ion channels. It allows for the precise measurement and manipulation of channel currents, providing insights into their function and modulation by drugs or other compounds. The melanocortin 4 receptor (MC4-R) is a G protein-coupled receptor (GPCR) crucial to appetite regulation, energy balance, and body weight. MC4-R signaling is complex and involves interactions with other receptors and neuropeptides in the appetite-regulating circuitry. MC4-Rs, like other GPCRs, are known to modulate ion channels such as Kir7.1, an inward rectifier potassium channel, in response to ligand binding. This modulation is critical for controlling ion flow across the cell membrane, which can influence membrane potential, excitability, and neurotransmission. The MC4-R is the target for the anti-obesity drug Imcivree. However, this drug is known to lack optimal potency and also has side effects. Using high-throughput techniques for studying the MC4-R/Kir7.1 complex allows researchers to rapidly screen many compounds or conditions, aiding the development of drugs that target this system. Additionally, automated patch clamp recording of this receptor-channel complex and its ligands can provide valuable functional and pharmacological insights supporting the development of novel therapeutic strategies. This approach can be generalized to other GPCR-gated ion channel functional complexes, potentially accelerating the pace of research in different fields with the promise to uncover previously unknown aspects of receptor-ion channel interactions.
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Affiliation(s)
- Ciria C Hernandez
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, USA.
- Center for Chemical Genomics, Life Sciences Institute, University of Michigan, Ann Arbor, MI, USA.
| | - Luis E Gimenez
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, USA
| | - Roger D Cone
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, USA
- Department of Molecular and Integrative Physiology, School of Medicine, University of Michigan, Ann Arbor, MI, USA
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3
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Ybañez-Julca RO, Pino-Ríos R, Quispe-Díaz IM, Asunción-Alvarez D, Acuña-Tarrillo EE, Mantilla-Rodríguez E, Minchan-Herrera P, Catalán MA, Zevallos-Escobar L, Vásquez-Corales E, Yáñez O, Gutiérrez-Alvarado WO, Benites J. Antispasmodic Effect of Valeriana pilosa Root Essential Oil and Potential Mechanisms of Action: Ex Vivo and In Silico Studies. Pharmaceutics 2023; 15:2072. [PMID: 37631286 PMCID: PMC10458982 DOI: 10.3390/pharmaceutics15082072] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2023] [Revised: 07/28/2023] [Accepted: 07/30/2023] [Indexed: 08/27/2023] Open
Abstract
Infusions of Valeriana pilosa are commonly used in Peruvian folk medicine for treating gastrointestinal disorders. This study aimed to investigate the spasmolytic and antispasmodic effects of Valeriana pilosa essential oil (VPEO) on rat ileum. The basal tone of ileal sections decreased in response to accumulative concentrations of VPEO. Moreover, ileal sections precontracted with acetylcholine (ACh), potassium chloride (KCl), or barium chloride (BaCl2) were relaxed in response to VPEO by a mechanism that depended on atropine, hyoscine butylbromide, solifenacin, and verapamil, but not glibenclamide. The results showed that VPEO produced a relaxant effect by inhibiting muscarinic receptors and blocking calcium channels, with no apparent effect on the opening of potassium channels. In addition, molecular docking was employed to evaluate VPEO constituents that could inhibit intestinal contractile activity. The study showed that α-cubebene, β-patchoulene, β-bourbonene, β-caryophyllene, α-guaiene, γ-muurolene, valencene, eremophyllene, and δ-cadinene displayed the highest docking scores on muscarinic acetylcholine receptors and voltage-gated calcium channels, which may antagonize M2 and/or M3 muscarinic acetylcholine receptors and block voltage-gated calcium channels. In summary, VPEO has both spasmolytic and antispasmodic effects. It may block muscarinic receptors and calcium channels, thus providing a scientific basis for its traditional use for gastrointestinal disorders.
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Affiliation(s)
- Roberto O. Ybañez-Julca
- Facultad de Farmacia y Bioquímica, Universidad Nacional de Trujillo, Trujillo 13011, Peru; (I.M.Q.-D.); (D.A.-A.); (E.E.A.-T.); (E.M.-R.); (P.M.-H.)
| | - Ricardo Pino-Ríos
- Química y Farmacia, Facultad de Ciencias de la Salud, Universidad Arturo Prat, Casilla 121, Iquique 1100000, Chile;
- Instituto de Estudios de la Salud, Universidad Arturo Prat, Casilla 121, Iquique 1100000, Chile
| | - Iván M. Quispe-Díaz
- Facultad de Farmacia y Bioquímica, Universidad Nacional de Trujillo, Trujillo 13011, Peru; (I.M.Q.-D.); (D.A.-A.); (E.E.A.-T.); (E.M.-R.); (P.M.-H.)
| | - Daniel Asunción-Alvarez
- Facultad de Farmacia y Bioquímica, Universidad Nacional de Trujillo, Trujillo 13011, Peru; (I.M.Q.-D.); (D.A.-A.); (E.E.A.-T.); (E.M.-R.); (P.M.-H.)
| | - Edwin E. Acuña-Tarrillo
- Facultad de Farmacia y Bioquímica, Universidad Nacional de Trujillo, Trujillo 13011, Peru; (I.M.Q.-D.); (D.A.-A.); (E.E.A.-T.); (E.M.-R.); (P.M.-H.)
| | - Elena Mantilla-Rodríguez
- Facultad de Farmacia y Bioquímica, Universidad Nacional de Trujillo, Trujillo 13011, Peru; (I.M.Q.-D.); (D.A.-A.); (E.E.A.-T.); (E.M.-R.); (P.M.-H.)
| | - Patricia Minchan-Herrera
- Facultad de Farmacia y Bioquímica, Universidad Nacional de Trujillo, Trujillo 13011, Peru; (I.M.Q.-D.); (D.A.-A.); (E.E.A.-T.); (E.M.-R.); (P.M.-H.)
| | - Marcelo A. Catalán
- Instituto de Fisiología, Facultad de Medicina, Universidad Austral de Chile, Valdivia 5090000, Chile;
| | - Liz Zevallos-Escobar
- Escuela de Farmacia y Bioquímica, Universidad Católica Los Ángeles de Chimbote, Chimbote 02801, Peru; (L.Z.-E.); (E.V.-C.)
| | - Edison Vásquez-Corales
- Escuela de Farmacia y Bioquímica, Universidad Católica Los Ángeles de Chimbote, Chimbote 02801, Peru; (L.Z.-E.); (E.V.-C.)
| | - Osvaldo Yáñez
- Facultad de Ingeniería y Negocios, Universidad de las Américas, Santiago 7500000, Chile;
| | | | - Julio Benites
- Química y Farmacia, Facultad de Ciencias de la Salud, Universidad Arturo Prat, Casilla 121, Iquique 1100000, Chile;
- Instituto de Estudios de la Salud, Universidad Arturo Prat, Casilla 121, Iquique 1100000, Chile
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4
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García-Llorca A, Ólafsson KH, Sigurdsson AT, Eysteinsson T. Progressive Cone-Rod Dystrophy and RPE Dysfunction in Mitfmi/+ Mice. Genes (Basel) 2023; 14:1458. [PMID: 37510362 PMCID: PMC10379086 DOI: 10.3390/genes14071458] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2023] [Revised: 07/11/2023] [Accepted: 07/15/2023] [Indexed: 07/30/2023] Open
Abstract
Mutations in the mouse microphthalmia-associated transcription factor (Mitf) gene affect retinal pigment epithelium (RPE) differentiation and development and can lead to hypopigmentation, microphthalmia, deafness, and blindness. For instance, an association has been established between loss-of-function mutations in the mouse Mitf gene and a variety of human retinal diseases, including Waardenburg type 2 and Tietz syndromes. Although there is evidence showing that mice with the homozygous Mitfmi mutation manifest microphthalmia and osteopetrosis, there are limited or no data on the effects of the heterozygous condition in the eye. Mitf mice can therefore be regarded as an important model system for the study of human disease. Thus, we characterized Mitfmi/+ mice at 1, 3, 12, and 18 months old in comparison with age-matched wild-type mice. The light- and dark-adapted electroretinogram (ERG) recordings showed progressive cone-rod dystrophy in Mitfmi/+ mice. The RPE response was reduced in the mutant in all age groups studied. Progressive loss of pigmentation was found in Mitfmi/+ mice. Histological retinal sections revealed evidence of retinal degeneration in Mitfmi/+ mice at older ages. For the first time, we report a mouse model of progressive cone-rod dystrophy and RPE dysfunction with a mutation in the Mitf gene.
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Affiliation(s)
- Andrea García-Llorca
- Department of Physiology, Faculty of Medicine, University of Iceland, 101 Reykjavík, Iceland
| | | | - Arnór Thorri Sigurdsson
- Department of Physiology, Faculty of Medicine, University of Iceland, 101 Reykjavík, Iceland
| | - Thor Eysteinsson
- Department of Physiology, Faculty of Medicine, University of Iceland, 101 Reykjavík, Iceland
- Department of Ophthalmology, Landspitali—National University Hospital, 101 Reykjavík, Iceland
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5
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Hernandez CC, Gimenez LE, Dahir NS, Peisley A, Cone RD. The unique structural characteristics of the Kir 7.1 inward rectifier potassium channel: a novel player in energy homeostasis control. Am J Physiol Cell Physiol 2023; 324:C694-C706. [PMID: 36717105 PMCID: PMC10026989 DOI: 10.1152/ajpcell.00335.2022] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2022] [Revised: 01/12/2023] [Accepted: 01/13/2023] [Indexed: 02/01/2023]
Abstract
The inward rectifier potassium channel Kir7.1, encoded by the KCNJ13 gene, is a tetramer composed of two-transmembrane domain-spanning monomers, closer in homology to Kir channels associated with potassium transport such as Kir1.1, 1.2, and 1.3. Compared with other channels, Kir7.1 exhibits small unitary conductance and low dependence on external potassium. Kir7.1 channels also show a phosphatidylinositol 4,5-bisphosphate (PIP2) dependence for opening. Accordingly, retinopathy-associated Kir7.1 mutations mapped at the binding site for PIP2 resulted in channel gating defects leading to channelopathies such as snowflake vitreoretinal degeneration and Leber congenital amaurosis in blind patients. Lately, this channel's role in energy homeostasis was reported due to the direct interaction with the melanocortin type 4 receptor (MC4R) in the hypothalamus. As this channel seems to play a multipronged role in potassium homeostasis and neuronal excitability, we will discuss what is predicted from a structural viewpoint and its possible implications for hunger control.
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Affiliation(s)
- Ciria C Hernandez
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, United States
| | - Luis E Gimenez
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, United States
| | - Naima S Dahir
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, United States
| | - Alys Peisley
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, United States
| | - Roger D Cone
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, United States
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan, United States
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6
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Beverley KM, Pattnaik BR. Inward rectifier potassium (Kir) channels in the retina: living our vision. Am J Physiol Cell Physiol 2022; 323:C772-C782. [PMID: 35912989 PMCID: PMC9448332 DOI: 10.1152/ajpcell.00112.2022] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2022] [Revised: 07/25/2022] [Accepted: 07/25/2022] [Indexed: 11/22/2022]
Abstract
Channel proteins are vital for conducting ions throughout the body and are especially relevant to retina physiology. Inward rectifier potassium (Kir) channels are a class of K+ channels responsible for maintaining membrane potential and extracellular K+ concentrations. Studies of the KCNJ gene (that encodes Kir protein) expression identified the presence of all of the subclasses (Kir 1-7) of Kir channels in the retina or retinal-pigmented epithelium (RPE). However, functional studies have established the involvement of the Kir4.1 homotetramer and Kir4.1/5.1 heterotetramer in Müller glial cells, Kir2.1 in bipolar cells, and Kir7.1 in the RPE cell physiology. Here, we propose the potential roles of Kir channels in the retina based on the physiological contributions to the brain, pancreatic, and cardiac tissue functions. There are several open questions regarding the expressed KCNJ genes in the retina and RPE. For example, why does not the Kir channel subtype gene expression correspond with protein expression? Catching up with multiomics or functional "omics" approaches might shed light on posttranscriptional changes that might influence Kir subunit mRNA translation within the retina that guides our vision.
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Affiliation(s)
- Katie M Beverley
- Endocrinology and Reproductive Physiology Graduate Program, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin
- Department of Pediatrics, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin
- McPherson Eye Research Institute, University of Wisconsin, Madison, Wisconsin
| | - Bikash R Pattnaik
- Endocrinology and Reproductive Physiology Graduate Program, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin
- Department of Pediatrics, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin
- McPherson Eye Research Institute, University of Wisconsin, Madison, Wisconsin
- Department of Ophthalmology and Visual Sciences, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin
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7
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Lv YY, Wang H, Fan HT, Xu T, Xin WJ, Guo RX. SUMOylation of Kir7.1 participates in neuropathic pain through regulating its membrane expression in spinal cord neurons. CNS Neurosci Ther 2022; 28:1259-1267. [PMID: 35633059 PMCID: PMC9253747 DOI: 10.1111/cns.13871] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2022] [Revised: 04/14/2022] [Accepted: 04/18/2022] [Indexed: 11/28/2022] Open
Abstract
Aims Potassium (K+) channels have been demonstrated to play a prominent involvement in nociceptive processing. Kir7.1, the newest members of the Kir channel family, has not been extensively studied in the CNS, and its function remains largely unknown. The present study investigated the role of spinal Kir7.1 in the development of pathological pain. Methods and Results Neuropathic pain was induced by spared nerve injury (SNI). The mechanical sensitivity was assessed by von Frey test. Immunofluorescence staining assay revealed that Kir7.1 was predominantly expressed in spinal neurons but not astrocytes or microglia in normal rats. Western blot results showed that SNI markedly decreased the total and membrane expression of Kir7.1 in the spinal dorsal horn accompanied by mechanical hypersensitivity. Blocking Kir7.1 with the specific antagonist ML418 or knockdown kir7.1 by siRNA led to mechanical allodynia. Co‐IP results showed that the spinal kir7.1 channels were decorated by SUMO‐1 but not SUMO‐2/3, and Kir7.1 SUMOylation was upregulated following SNI. Moreover, inhibited SUMOylation by GA (E1 inhibitor) or 2‐D08 (UBC9 inhibitor) can increase the spinal surface Kir7.1 expression. Conclusion SUMOylation of the Kir7.1 in the spinal cord might contribute to the development of SNI‐induced mechanical allodynia by decreasing the Kir7.1 surface expression in rats.
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Affiliation(s)
- You-You Lv
- Department of Anesthesiology, The Fifth Affiliated Hospital, Sun Yat-Sen University, Zhuhai, China
| | - Han Wang
- Department of Anesthesiology, Changhai Hospital, Naval Medical University, Shanghai, China
| | - Hai-Ting Fan
- Department of Anesthesiology, The Fifth Affiliated Hospital, Sun Yat-Sen University, Zhuhai, China
| | - Ting Xu
- Department of Physiology and Pain Research Center, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, China
| | - Wen-Jun Xin
- Department of Physiology and Pain Research Center, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, China
| | - Rui-Xian Guo
- Department of Physiology and Pain Research Center, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, China
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8
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Jiao X, Ma Z, Lei J, Liu P, Cai X, Shahi PK, Chan CC, Fariss R, Pattnaik BR, Dong L, Hejtmancik JF. Retinal Development and Pathophysiology in Kcnj13 Knockout Mice. Front Cell Dev Biol 2022; 9:810020. [PMID: 35096838 PMCID: PMC8790323 DOI: 10.3389/fcell.2021.810020] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2021] [Accepted: 12/10/2021] [Indexed: 11/22/2022] Open
Abstract
Purpose: We constructed and characterized knockout and conditional knockout mice for KCNJ13, encoding the inwardly rectifying K+ channel of the Kir superfamily Kir7.1, mutations in which cause both Snowflake Vitreoretinal Degeneration (SVD) and Retinitis pigmentosa (RP) to further elucidate the pathology of this disease and to develop a potential model system for gene therapy trials. Methods: A Kcnj13 knockout mouse line was constructed by inserting a gene trap cassette expressing beta-galactosidase flanked by FRT sites in intron 1 with LoxP sites flanking exon two and converted to a conditional knockout by FLP recombination followed by crossing with C57BL/6J mice having Cre driven by the VMD2 promoter. Lentiviral replacement of Kcnj13 was driven by the EF1a or VMD2 promoters. Results: Blue-Gal expression is evident in E12.5 brain ventricular choroid plexus, lens, neural retina layer, and anterior RPE. In the adult eye expression is seen in the ciliary body, RPE and choroid. Adult conditional Kcnj13 ko mice show loss of photoreceptors in the outer nuclear layer, inner nuclear layer thinning with loss of bipolar cells, and thinning and disruption of the outer plexiform layer, correlating with Cre expression in the overlying RPE which, although preserved, shows morphological disruption. Fundoscopy and OCT show signs of retinal degeneration consistent with the histology, and photopic and scotopic ERGs are decreased in amplitude or extinguished. Lentiviral based replacement of Kcnj13 resulted in increased ERG c- but not a- or b- wave amplitudes. Conclusion: Ocular KCNJ13 expression starts in the choroid, lens, ciliary body, and anterior retina, while later expression centers on the RPE with no/lower expression in the neuroretina. Although KCNJ13 expression is not required for survival of the RPE, it is necessary for RPE maintenance of the photoreceptors, and loss of the photoreceptor, outer plexiform, and outer nuclear layers occur in adult KCNJ13 cKO mice, concomitant with decreased amplitude and eventual extinguishing of the ERG and signs of retinitis pigmentosa on fundoscopy and OCT. Kcnj13 replacement resulting in recovery of the ERG c- but not a- and b-waves is consistent with the degree of photoreceptor degeneration seen on histology.
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Affiliation(s)
- Xiaodong Jiao
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, MD, United States
| | - Zhiwei Ma
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, MD, United States
| | - Jingqi Lei
- Genetic Engineering Core, National Eye Institute, National Institute of Health, Bethesda, MD, United States
| | - Pinghu Liu
- Genetic Engineering Core, National Eye Institute, National Institute of Health, Bethesda, MD, United States
| | - Xiaoyu Cai
- Genetic Engineering Core, National Eye Institute, National Institute of Health, Bethesda, MD, United States
| | - Pawan K Shahi
- Departments of Pediatrics and Ophthalmology and Visual Sciences and the McPherson Eye Research Institute, University of Wisconsin, Madison, AL, United States
| | - Chi-Chao Chan
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, MD, United States
| | - Robert Fariss
- Imaging Core, National Eye Institute, National Institutes of Health, Bethesda, MD, United States
| | - Bikash R Pattnaik
- Departments of Pediatrics and Ophthalmology and Visual Sciences and the McPherson Eye Research Institute, University of Wisconsin, Madison, AL, United States
| | - Lijin Dong
- Genetic Engineering Core, National Eye Institute, National Institute of Health, Bethesda, MD, United States
| | - J Fielding Hejtmancik
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, MD, United States
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9
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Akyuz E, Koklu B, Uner A, Angelopoulou E, Paudel YN. Envisioning the role of inwardly rectifying potassium (Kir) channel in epilepsy. J Neurosci Res 2021; 100:413-443. [PMID: 34713909 DOI: 10.1002/jnr.24985] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2021] [Revised: 09/23/2021] [Accepted: 10/01/2021] [Indexed: 01/29/2023]
Abstract
Epilepsy is a devastating neurological disorder characterized by recurrent seizures attributed to the disruption of the dynamic excitatory and inhibitory balance in the brain. Epilepsy has emerged as a global health concern affecting about 70 million people worldwide. Despite recent advances in pre-clinical and clinical research, its etiopathogenesis remains obscure, and there are still no treatment strategies modifying disease progression. Although the precise molecular mechanisms underlying epileptogenesis have not been clarified yet, the role of ion channels as regulators of cellular excitability has increasingly gained attention. In this regard, emerging evidence highlights the potential implication of inwardly rectifying potassium (Kir) channels in epileptogenesis. Kir channels consist of seven different subfamilies (Kir1-Kir7), and they are highly expressed in both neuronal and glial cells in the central nervous system. These channels control the cell volume and excitability. In this review, we discuss preclinical and clinical evidence on the role of the several subfamilies of Kir channels in epileptogenesis, aiming to shed more light on the pathogenesis of this disorder and pave the way for future novel therapeutic approaches.
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Affiliation(s)
- Enes Akyuz
- Faculty of International Medicine, Department of Biophysics, University of Health Sciences, Istanbul, Turkey
| | - Betul Koklu
- Faculty of Medicine, Namık Kemal University, Tekirdağ, Turkey
| | - Arda Uner
- Faculty of Medicine, Yozgat Bozok University, Yozgat, Turkey
| | - Efthalia Angelopoulou
- Department of Biological Chemistry, Medical School, National and Kapodistrian University of Athens, Athens, Greece
| | - Yam Nath Paudel
- Neuropharmacology Research Strength, Jeffrey Cheah School of Medicine and Health Sciences, Monash University Malaysia, Bandar Sunway, Malaysia
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10
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Björkgren I, Mendoza S, Chung DH, Haoui M, Petersen NT, Lishko PV. The epithelial potassium channel Kir7.1 is stimulated by progesterone. J Gen Physiol 2021; 153:212552. [PMID: 34387656 PMCID: PMC8374857 DOI: 10.1085/jgp.202112924] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2021] [Accepted: 07/29/2021] [Indexed: 11/20/2022] Open
Abstract
The choroid plexus (CP) epithelium secretes cerebrospinal fluid and plays an important role in healthy homeostasis of the brain. CP function can be influenced by sex steroid hormones; however, the precise molecular mechanism of such regulation is not well understood. Here, using whole-cell patch-clamp recordings from male and female murine CP cells, we show that application of progesterone resulted in specific and strong potentiation of the inwardly rectifying potassium channel Kir7.1, an essential protein that is expressed in CP and is required for survival. The potentiation was progesterone specific and independent of other known progesterone receptors expressed in CP. This effect was recapitulated with recombinant Kir7.1, as well as with endogenous Kir7.1 expressed in the retinal pigment epithelium. Current-clamp studies further showed a progesterone-induced hyperpolarization of CP cells. Our results provide evidence of a progesterone-driven control of tissues in which Kir7.1 is present.
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Affiliation(s)
- Ida Björkgren
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA
| | - Sarah Mendoza
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA
| | - Dong Hwa Chung
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA
| | - Monika Haoui
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA
| | - Natalie True Petersen
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA
| | - Polina V Lishko
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA
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11
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Kir Channel Molecular Physiology, Pharmacology, and Therapeutic Implications. Handb Exp Pharmacol 2021; 267:277-356. [PMID: 34345939 DOI: 10.1007/164_2021_501] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
For the past two decades several scholarly reviews have appeared on the inwardly rectifying potassium (Kir) channels. We would like to highlight two efforts in particular, which have provided comprehensive reviews of the literature up to 2010 (Hibino et al., Physiol Rev 90(1):291-366, 2010; Stanfield et al., Rev Physiol Biochem Pharmacol 145:47-179, 2002). In the past decade, great insights into the 3-D atomic resolution structures of Kir channels have begun to provide the molecular basis for their functional properties. More recently, computational studies are beginning to close the time domain gap between in silico dynamic and patch-clamp functional studies. The pharmacology of these channels has also been expanding and the dynamic structural studies provide hope that we are heading toward successful structure-based drug design for this family of K+ channels. In the present review we focus on placing the physiology and pharmacology of this K+ channel family in the context of atomic resolution structures and in providing a glimpse of the promising future of therapeutic opportunities.
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12
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Abstract
K+ channels enable potassium to flow across the membrane with great selectivity. There are four K+ channel families: voltage-gated K (Kv), calcium-activated (KCa), inwardly rectifying K (Kir), and two-pore domain potassium (K2P) channels. All four K+ channels are formed by subunits assembling into a classic tetrameric (4x1P = 4P for the Kv, KCa, and Kir channels) or tetramer-like (2x2P = 4P for the K2P channels) architecture. These subunits can either be the same (homomers) or different (heteromers), conferring great diversity to these channels. They share a highly conserved selectivity filter within the pore but show different gating mechanisms adapted for their function. K+ channels play essential roles in controlling neuronal excitability by shaping action potentials, influencing the resting membrane potential, and responding to diverse physicochemical stimuli, such as a voltage change (Kv), intracellular calcium oscillations (KCa), cellular mediators (Kir), or temperature (K2P).
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13
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Haoui M, Petersen NT, Björkgren I, Chung DH, Lishko PV. Choroid plexus epithelial cells as a model to study nongenomic steroid signaling and its effect on ion channel function. Methods Enzymol 2021; 654:297-314. [PMID: 34120718 DOI: 10.1016/bs.mie.2021.03.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The choroid plexus (CP) is an epithelial tissue primarily responsible for the secretion of the cerebrospinal fluid (CSF). Choroid plexuses are found in each of the four brain ventricles: two laterals, third and fourth. They ensure continuous production of CSF to provide nutrients, remove waste products and provide a mechanical buffer to protect the brain. Tight junctions in the CP epithelium form a barrier between the blood plasma and the CSF, which allow channels and transporters in the CP to establish a highly regulated concentration gradient of ions between the two fluids, thereby controlling the composition of CSF. CP plays an important part in healthy brain homeostasis, as its failure to maintain adequate CSF perfusion is implicated in Alzheimer's disease and traumatic brain injury. And yet, the physiology of CP and the mechanism of its age-related functional decline is one of the most understudied areas of neurobiology. Here, we describe a protocol to isolate and identify individual choroid plexus epithelial cells (CPEC) from murine brain for whole-cell patch-clamp recordings and ion channel identification. Using the recording from the inwardly rectifying potassium channel Kir7.1 and TRPM3 that are abundant in CP, we demonstrate a technique to study the regulators of ion channels in the choroid plexus.
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Affiliation(s)
- Monika Haoui
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, United States
| | - Natalie True Petersen
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, United States
| | - Ida Björkgren
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, United States
| | - Dong Hwa Chung
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, United States
| | - Polina V Lishko
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, United States.
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14
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Weaver CD, Denton JS. Next-generation inward rectifier potassium channel modulators: discovery and molecular pharmacology. Am J Physiol Cell Physiol 2021; 320:C1125-C1140. [PMID: 33826405 DOI: 10.1152/ajpcell.00548.2020] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Inward rectifying potassium (Kir) channels play important roles in both excitable and nonexcitable cells of various organ systems and could represent valuable new drug targets for cardiovascular, metabolic, immune, and neurological diseases. In nonexcitable epithelial cells of the kidney tubule, for example, Kir1.1 (KCNJ1) and Kir4.1 (KCNJ10) are linked to sodium reabsorption in the thick ascending limb of Henle's loop and distal convoluted tubule, respectively, and have been explored as novel-mechanism diuretic targets for managing hypertension and edema. G protein-coupled Kir channels (Kir3) channels expressed in the central nervous system are critical effectors of numerous signal transduction pathways underlying analgesia, addiction, and respiratory-depressive effects of opioids. The historical dearth of pharmacological tool compounds for exploring the therapeutic potential of Kir channels has led to a molecular target-based approach using high-throughput screen (HTS) of small-molecule libraries and medicinal chemistry to develop "next-generation" Kir channel modulators that are both potent and specific for their targets. In this article, we review recent efforts focused specifically on discovery and improvement of target-selective molecular probes. The reader is introduced to fluorescence-based thallium flux assays that have enabled much of this work and then provided with an overview of progress made toward developing modulators of Kir1.1 (VU590, VU591), Kir2.x (ML133), Kir3.X (ML297, GAT1508, GiGA1, VU059331), Kir4.1 (VU0134992), and Kir7.1 (ML418). We discuss what is known about the small molecules' molecular mechanisms of action, in vitro and in vivo pharmacology, and then close with our view of what critical work remains to be done.
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Affiliation(s)
- C David Weaver
- Department of Pharmacology, Vanderbilt University, Nashville, Tennessee.,Department of Chemistry, Vanderbilt University, Nashville, Tennessee.,Institute of Chemical Biology, Vanderbilt University, Nashville, Tennessee
| | - Jerod S Denton
- Department of Pharmacology, Vanderbilt University, Nashville, Tennessee.,Institute of Chemical Biology, Vanderbilt University, Nashville, Tennessee.,Department of Anesthesiology, Vanderbilt University Medical Center, Nashville, Tennessee
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15
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Vera E, Cornejo I, Niemeyer MI, Sepúlveda FV, Cid LP. Altered phosphatidylinositol regulation of mutant inwardly rectifying K + Kir7.1 channels associated with inherited retinal degeneration disease. J Physiol 2020; 599:593-608. [PMID: 33219695 DOI: 10.1113/jp280681] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2020] [Accepted: 11/12/2020] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Kir7.1 K+ channel expressed in retinal pigment epithelium is mutated in inherited retinal degeneration diseases. We study Kir7.1 in heterologous expression to test the hypothesis that pathological R162 mutation to neutral amino acids results in loss of a crucial site that binds PI(4,5)P2 . Although R162W mutation inactivates Kir7.1, changes to smaller volume (e.g. Gln) amino acids are tolerated or even enhance function (Ala or Cys). Chemical modification of Kir7.1-R162C confirms that large residues of the size of Trp are incompatible with normal channel function even if positively charged. In addition to R162, K164 (and possibly K159) forms a binding site for the phosphoinositide and is essential for channel activity. R162 substitution with a large, neutral side chain like Trp exerts a dominant negative effect on Kir7.1 activity such that less than one fifth of the full activity is expected in a cell expressing the same amount of mutant and wild-type channels. ABSTRACT Mutations in the Kir7.1 K+ channel, highly expressed in retinal pigment epithelium, have been linked to inherited retinal degeneration diseases. Examples are mutations changing Arg 162 to Trp in snowflake vitreoretinal degeneration (SVD) and Gln in retinitis pigmentosa. R162 is believed to be part of a site that binds PI(4,5)P2 and stabilises the open state. We have tested the hypothesis that R162 mutation to neutral amino acids will result in the loss of this crucial interaction to the detriment of channel function. Our findings indicate that although R612W mutation inactivates Kir7.1, changes to smaller volume (e.g. Gln) amino acids are tolerated or even enhance function (Ala or Cys). Cys chemical modification of Kir7.1-R162C confirms that large residues of the size of Trp are incompatible with normal channel function even if positively charged. Experiments titrating the levels of plasma membrane PI(4,5)P2 with voltage-dependent phosphatase DrVSP reveal that, in addition to R162, K164 (and possibly K159) forms a binding site for the phosphoinositide and ensures channel activity. Finally, the use of a concatemeric approach shows that substitution of R162 with a large, neutral side chain mimicking a Trp residue exerts a dominant negative effect on Kir7.1 activity such that less than one fifth of the full activity is expected in heterozygous cells carrying the SVD mutation. Our results suggest that if mutations in the human KCNJ13 gene resulting in the neutralisation of R162 and Kir7.1 malfunction led to retinal degeneration diseases, their severity might depend on the nature of the side chain of the replacing amino acid.
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Affiliation(s)
- Erwin Vera
- Centro de Estudios Científicos (CECs), Valdivia, Chile
| | | | | | | | - L Pablo Cid
- Centro de Estudios Científicos (CECs), Valdivia, Chile
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16
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Potassium Channel-Associated Bioelectricity of the Dermomyotome Determines Fin Patterning in Zebrafish. Genetics 2020; 215:1067-1084. [PMID: 32546498 PMCID: PMC7404225 DOI: 10.1534/genetics.120.303390] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2019] [Accepted: 06/15/2020] [Indexed: 12/21/2022] Open
Abstract
The roles of bioelectric signaling in developmental patterning remain largely unknown, although recent work has implicated bioelectric signals in cellular processes such as proliferation and migration. Here, we report a mutation in the inwardly rectifying potassium channel (kir) gene, kcnj13/kir7.1, that causes elongation of the fins in the zebrafish insertional mutant Dhi2059. A viral DNA insertion into the noncoding region of kcnj13 results in transient activation and ectopic expression of kcnj13 in the somite and dermomyotome, from which the fin ray progenitors originate. We made an allele-specific loss-of-function kcnj13 mutant by CRISPR (clustered regularly interspaced short palindromic repeats) and showed that it could reverse the long-finned phenotype, but only when located on the same chromosome as the Dhi2059 viral insertion. Also, we showed that ectopic expression of kcnj13 in the dermomyotome of transgenic zebrafish produces phenocopies of the Dhi2059 mutant in a gene dosage-sensitive manner. Finally, to determine whether this developmental function is specific to kcnj13, we ectopically expressed three additional potassium channel genes: kcnj1b, kcnj10a, and kcnk9 We found that all induce the long-finned phenotype, indicating that this function is conserved among potassium channel genes. Taken together, our results suggest that dermomyotome bioelectricity is a new fin-patterning mechanism, and we propose a two-stage bioelectricity model for zebrafish fin patterning. This ion channel-regulated bioelectric developmental patterning mechanism may provide with us new insight into vertebrate morphological evolution and human congenital malformations.
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17
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Sancho M, Welsh DG. K IR channels in the microvasculature: Regulatory properties and the lipid-hemodynamic environment. CURRENT TOPICS IN MEMBRANES 2020; 85:227-259. [PMID: 32402641 DOI: 10.1016/bs.ctm.2020.01.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
Abstract
Basal tone and perfusion control is set in cerebral arteries by the sensing of pressure and flow, key hemodynamic stimuli. These forces establish a contractile foundation within arterial networks upon which local neurovascular stimuli operate. This fundamental process is intimately tied to arterial VM and the rise in cytosolic [Ca2+] by the graded opening of voltage-operated Ca2+ channels. Arterial VM is in turn controlled by a dynamic interaction among several resident ion channels, KIR being one of particular significance. As the name suggests, KIR displays strong inward rectification, retains a small outward component, potentiated by extracellular K+ and blocked by micromolar Ba2+. Cerebrovascular KIR is unique from other K+ currents as it is present in both smooth muscle and endothelium yet lacking in classical regulatory modulation. Such observations have fostered the view that KIR is nothing more than a background conductance, activated by extracellular K+ and which passively facilitates dilation. Recent work in cell model systems has; however, identified two membrane lipids, phosphatidylinositol 4,5-bisphosphate (PIP2) and cholesterol, that interact with KIR2.x, to stabilize the channel in the preferred open or silent state, respectively. Translating this unique form of regulation, recent studies have demonstrated that specific lipid-protein interactions enable unique KIR populations to sense distinct hemodynamic stimuli and set basal tone. This review summarizes the current knowledge of vascular KIR channels and how the lipid and hemodynamic impact their activity.
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Affiliation(s)
- Maria Sancho
- Robarts Research Institute and the Department of Physiology & Pharmacology, University of Western Ontario, London, ON, Canada
| | - Donald G Welsh
- Robarts Research Institute and the Department of Physiology & Pharmacology, University of Western Ontario, London, ON, Canada.
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18
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Garcia DCG, Longden TA. Ion channels in capillary endothelium. CURRENT TOPICS IN MEMBRANES 2020; 85:261-300. [PMID: 32402642 DOI: 10.1016/bs.ctm.2020.01.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Vascular beds are anatomically and functionally compartmentalized into arteries, capillaries, and veins. The bulk of the vasculature consists of the dense, anastomosing capillary network, composed of capillary endothelial cells (cECs) that are intimately associated with the parenchyma. Despite their abundance, the ion channel expression and function and Ca2+ signaling behaviors of capillaries have only recently begun to be explored in detail. Here, we discuss the established and emerging roles of ion channels and Ca2+ signaling in cECs. By mining a publicly available RNA-seq dataset, we outline the wide variety of ion channel genes that are expressed in these cells, which potentially imbue capillaries with a broad range of sensing and signal transduction capabilities. We also underscore subtle but critical differences between cEC and arteriolar EC ion channel expression that likely underlie key functional differences in ECs at these different levels of the vascular tree. We focus our discussion on the cerebral vasculature, but the findings and principles being elucidated in this area likely generalize to other vascular beds.
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Affiliation(s)
- Daniela C G Garcia
- Department of Physiology, School of Medicine, University of Maryland, Baltimore, MD, United States
| | - Thomas A Longden
- Department of Physiology, School of Medicine, University of Maryland, Baltimore, MD, United States.
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19
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Papanikolaou M, Butt AM, Lewis A. A critical role for the inward rectifying potassium channel Kir7.1 in oligodendrocytes of the mouse optic nerve. Brain Struct Funct 2020; 225:925-934. [PMID: 32086565 PMCID: PMC7166203 DOI: 10.1007/s00429-020-02043-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2019] [Accepted: 02/06/2020] [Indexed: 01/27/2023]
Abstract
Inward rectifying potassium channels (Kir) are a large family of ion channels that play key roles in ion homeostasis in oligodendrocytes, the myelinating cells of the central nervous system (CNS). Prominent expression of Kir4.1 has been indicated in oligodendrocytes, but the extent of expression of other Kir subtypes is unclear. Here, we used qRT-PCR to determine expression of Kir channel transcripts in the mouse optic nerve, a white matter tract comprising myelinated axons and the glia that support them. A novel finding was the high relative expression of Kir7.1, comparable to that of Kir4.1, the main glial Kir channel. Significantly, Kir7.1 immunofluorescence labelling in optic nerve sections and in isolated cells was localised to oligodendrocyte somata. Kir7.1 are known as a K+ transporting channels and, using patch clamp electrophysiology and the Kir7.1 blocker VU590, we demonstrated Kir7.1 channels carry a significant proportion of the whole cell potassium conductance in oligodendrocytes isolated from mouse optic nerves. Notably, oligodendrocytes are highly susceptible to ischemia/hypoxia and this is due at least in part to disruption of ion homeostasis. A key finding of this study is that blockade of Kir7.1 with VU590 compromised oligodendrocyte cell integrity and compounds oligodendroglial loss in ischemia/hypoxia in the oxygen-glucose deprivation (OGD) model in isolated intact optic nerves. These data reveal Kir7.1 channels are molecularly and functionally expressed in oligodendrocytes and play an important role in determining oligodendrocyte survival and myelin integrity.
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Affiliation(s)
- Maria Papanikolaou
- Institute of Biomedical and Biomolecular Sciences, School of Pharmacy and Biomedical Science, University of Portsmouth, Portsmouth, PO1 2DT, UK
| | - Arthur M Butt
- Institute of Biomedical and Biomolecular Sciences, School of Pharmacy and Biomedical Science, University of Portsmouth, Portsmouth, PO1 2DT, UK.
| | - Anthony Lewis
- Institute of Biomedical and Biomolecular Sciences, School of Pharmacy and Biomedical Science, University of Portsmouth, Portsmouth, PO1 2DT, UK
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20
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Manis AD, Hodges MR, Staruschenko A, Palygin O. Expression, localization, and functional properties of inwardly rectifying K + channels in the kidney. Am J Physiol Renal Physiol 2020; 318:F332-F337. [PMID: 31841387 PMCID: PMC7052651 DOI: 10.1152/ajprenal.00523.2019] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2019] [Revised: 12/10/2019] [Accepted: 12/10/2019] [Indexed: 12/13/2022] Open
Abstract
Inwardly rectifying K+ (Kir) channels are expressed in multiple organs and cell types and play critical roles in cellular function. Most notably, Kir channels are major determinants of the resting membrane potential and K+ homeostasis. The renal outer medullary K+ channel (Kir1.1) was the first renal Kir channel identified and cloned in the kidney over two decades ago. Since then, several additional members, including classical and ATP-regulated Kir family classes, have been identified to be expressed in the kidney and to contribute to renal ion transport. Although the ATP-regulated Kir channel class remains the most well known due to severe pathological phenotypes associated with their mutations, progress is being made in defining the properties, localization, and physiological functions of other renal Kir channels, including those localized to the basolateral epithelium. This review is primarily focused on the current knowledge of the expression and localization of renal Kir channels but will also briefly describe their proposed functions in the kidney.
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Affiliation(s)
- Anna D Manis
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin
| | - Matthew R Hodges
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin
- Neuroscience Research Center, Medical College of Wisconsin, Milwaukee, Wisconsin
| | - Alexander Staruschenko
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin
- Cardiovascular Center, Medical College of Wisconsin, Milwaukee, Wisconsin
- Clement J. Zablocki Veterans Affairs Medical Center, Milwaukee, Wisconsin
| | - Oleg Palygin
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin
- Cardiovascular Center, Medical College of Wisconsin, Milwaukee, Wisconsin
- Neuroscience Research Center, Medical College of Wisconsin, Milwaukee, Wisconsin
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21
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Toms M, Dubis AM, Lim WS, Webster AR, Gorin MB, Moosajee M. Missense variants in the conserved transmembrane M2 protein domain of KCNJ13 associated with retinovascular changes in humans and zebrafish. Exp Eye Res 2019; 189:107852. [PMID: 31647904 PMCID: PMC6899441 DOI: 10.1016/j.exer.2019.107852] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2019] [Revised: 10/02/2019] [Accepted: 10/19/2019] [Indexed: 01/27/2023]
Abstract
Mutations in KCNJ13 are associated with two retinal disorders; Leber congenital amaurosis (LCA) and snowflake vitreoretinal degeneration (SVD). We describe a novel fibrovascular proliferation in the retina of two affected members of a KCNJ13-related LCA family with a homozygous c.458C > T, p.(Thr153Ile) missense mutation. Optical coherence tomography retinal imaging of the kcnj13 mutant zebrafish (obelixtd15 c.502T > C, p.[Phe168Leu]) revealed a late onset retinal degeneration at 12 months, with retinal thinning and associated retinovascular changes, including increased vessel calibre and vitreous deposits. Both human and zebrafish variants are missense and located within the conserved transmembrane M2 protein domain, suggesting that disruption of this region may contribute to retinovascular changes as an additional feature to the previously described LCA phenotype. Close monitoring of other patients with similar mutations may be required to minimise the ensuing retinal damage.
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Affiliation(s)
- Maria Toms
- UCL Institute of Ophthalmology, London, UK
| | - Adam M Dubis
- UCL Institute of Ophthalmology, London, UK; Moorfields Eye Hospital NHS Foundation Trust, London, UK
| | - Wei Sing Lim
- Moorfields Eye Hospital NHS Foundation Trust, London, UK
| | - Andrew R Webster
- UCL Institute of Ophthalmology, London, UK; Moorfields Eye Hospital NHS Foundation Trust, London, UK
| | - Michael B Gorin
- Department of Ophthalmology, Jules Stein Eye Institute, David Geffen School of Medicine, UCLA Los Angeles, USA
| | - Mariya Moosajee
- UCL Institute of Ophthalmology, London, UK; Moorfields Eye Hospital NHS Foundation Trust, London, UK.
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22
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Burgos J, Villanueva S, Ojeda M, Cornejo I, Cid LP, Sepúlveda FV. Kir7.1 inwardly rectifying K + channel is expressed in ciliary body non pigment epithelial cells and might contribute to intraocular pressure regulation. Exp Eye Res 2019; 186:107723. [PMID: 31319081 DOI: 10.1016/j.exer.2019.107723] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2019] [Revised: 06/26/2019] [Accepted: 07/10/2019] [Indexed: 02/08/2023]
Abstract
Inwardly rectifying K+ channel Kir7.1 is expressed in epithelia where it shares membrane localisation with the Na+/K+-pump. The ciliary body epithelium (CBE) of the eye is a determinant of intraocular pressure (IOP) through NaCl-driven fluid secretion of aqueous humour. In the present study we explored the presence Kir7.1 in this epithelium in the mouse and its possible functional role in the generation of IOP. Use heterozygous animals for total Kir7.1 knockout expressing β-galactosidase under the control of Kir7.1 promoter, identified the expression of Kir7.1 in non-pigmented epithelial cells of CBE. Using conditional, floxed knockout Kir7.1 mice as negative controls, we found Kir7.1 at the basolateral membrane of the same CBE cell layer. This was confirmed using a knockin mouse expressing the Kir7.1 protein tagged with a haemagglutinin epitope. Measurements using the conditional knockout mouse show only a minor effect of Kir7.1 inactivation on steady-state IOP. Transient increases in IOP in response to general anaesthetics, or to water injection, are absent or markedly curtailed in Kir7.1-deficient mice. These results suggest a role for Kir7.1 in IOP regulation through a possible modulation of aqueous humour production by the CBE non-pigmented epithelial cells. The location of Kir7.1 in the CBE, together with the effect of its removal on dynamic changes in IOP, point to a possible role of the channel as a leak pathway preventing cellular overload of K+ during the secretion process. Kir7.1 could be used as a potential therapeutic target in pathological conditions leading to elevated intraocular pressure.
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Affiliation(s)
- Johanna Burgos
- Centro de Estudios Científicos (CECs), Avenida Arturo Prat 514, Valdivia, Chile
| | - Sandra Villanueva
- Centro de Estudios Científicos (CECs), Avenida Arturo Prat 514, Valdivia, Chile; Universidad Austral de Chile, Valdivia, Chile
| | - Margarita Ojeda
- Centro de Estudios Científicos (CECs), Avenida Arturo Prat 514, Valdivia, Chile
| | - Isabel Cornejo
- Centro de Estudios Científicos (CECs), Avenida Arturo Prat 514, Valdivia, Chile
| | - L Pablo Cid
- Centro de Estudios Científicos (CECs), Avenida Arturo Prat 514, Valdivia, Chile
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23
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Papanikolaou M, Lewis A, Butt AM. Glial and neuronal expression of the Inward Rectifying Potassium Channel Kir7.1 in the adult mouse brain. J Anat 2019; 235:984-996. [PMID: 31309576 PMCID: PMC6794205 DOI: 10.1111/joa.13048] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/29/2019] [Indexed: 01/01/2023] Open
Abstract
Inward Rectifying Potassium channels (Kir) are a large family of ion channels that play key roles in ion homeostasis and neuronal excitability. The most recently described Kir subtype is Kir7.1, which is known as a K+ transporting subtype. Earlier studies localised Kir7.1 to subpopulations of neurones in the brain. However, the pattern of Kir7.1 expression across the brain has not previously been examined. Here, we have determined neuronal and glial expression of Kir7.1 in the adult mouse brain, using immunohistochemistry and transgenic mouse lines expressing reporters specific for astrocytes [glial fibrillary acidic protein‐enhanced green fluorescent protein (GFAP‐EGFP], myelinating oligodendrocytes (PLP‐DsRed), oligodendrocyte progenitor cells (OPC, Pdgfra‐creERT2/Rosa26‐YFP double‐transgenic mice) and all oligodendrocyte lineage cells (SOX10‐EGFP). The results demonstrate significant neuronal Kir7.1 immunostaining in the cortex, hippocampus, cerebellum and pons, as well as the striatum and hypothalamus. In addition, astrocytes are shown to be immunopositive for Kir7.1 throughout grey and white matter, with dense immunostaining on cell somata, primary processes and perivascular end‐feet. Immunostaining for Kir7.1 was observed in oligodendrocytes, myelin and OPCs throughout the brain, although immunostaining was heterogeneous. Neuronal and glial expression of Kir7.1 is confirmed using neurone‐glial cortical cultures and optic nerve glial cultures. Notably, Kir7.1 have been shown to regulate the excitability of thalamic neurones and our results indicate this may be a widespread function of Kir7.1 in neurones throughout the brain. Moreover, based on the function of Kir7.1 in multiple transporting epithelia, Kir7.1 are likely to play an equivalent role in the primary glial function of K+ homeostasis. Our results indicate Kir7.1 are far more pervasive in the brain than previously recognised and have potential importance in regulating neuronal and glial function.
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Affiliation(s)
- Maria Papanikolaou
- Institute of Biomedical and Biomolecular Sciences, School of Pharmacy and Biomedical Science, University of Portsmouth, Portsmouth, UK
| | - Anthony Lewis
- Institute of Biomedical and Biomolecular Sciences, School of Pharmacy and Biomedical Science, University of Portsmouth, Portsmouth, UK
| | - Arthur M Butt
- Institute of Biomedical and Biomolecular Sciences, School of Pharmacy and Biomedical Science, University of Portsmouth, Portsmouth, UK
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24
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Vera E, Cornejo I, Burgos J, Niemeyer MI, Sepúlveda FV, Cid LP. A novel Kir7.1 splice variant expressed in various mouse tissues shares organisational and functional properties with human Leber amaurosis-causing mutations of this K + channel. Biochem Biophys Res Commun 2019; 514:574-579. [PMID: 31056263 DOI: 10.1016/j.bbrc.2019.04.169] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2019] [Accepted: 04/24/2019] [Indexed: 01/27/2023]
Abstract
Kir7.1 is an inwardly rectifying K+ channel present in epithelia where it shares membrane localization with the Na+/K+-pump. In the present communication we report the presence of a novel splice variant of Kir7.1 in mouse tissues including kidney, lung, choroid plexus and retinal pigment epithelium (RPE). The variant named mKir7.1-SV2 lacks most of the C-terminus domain but is predicted to have the two transmembrane domains and permeation pathway unaffected. Similarly truncated predicted proteins, Kir7.1-R166X and Kir7.1-Q219X, would arise from mutations associated with Leber Congenital Amaurosis, a rare recessive hereditary retinal disease that results in vision loss at early age. We found that mKir7.1-SV2 and the pathological variants do not produce any channel activity when expressed alone in HEK-293 cells due to their scarce presence in the plasma membrane. Simultaneous expression with the full length Kir7.1 however leads to a reduction in activity of the wild-type channel that might be due to partial proteasome degradation of WT-mutant channel heteromers.
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Affiliation(s)
- Erwin Vera
- Centro de Estudios Científicos (CECs), Avenida Arturo Prat 514, Valdivia, Chile
| | - Isabel Cornejo
- Centro de Estudios Científicos (CECs), Avenida Arturo Prat 514, Valdivia, Chile
| | - Johanna Burgos
- Centro de Estudios Científicos (CECs), Avenida Arturo Prat 514, Valdivia, Chile
| | | | | | - L Pablo Cid
- Centro de Estudios Científicos (CECs), Avenida Arturo Prat 514, Valdivia, Chile.
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25
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Toms M, Burgoyne T, Tracey-White D, Richardson R, Dubis AM, Webster AR, Futter C, Moosajee M. Phagosomal and mitochondrial alterations in RPE may contribute to KCNJ13 retinopathy. Sci Rep 2019; 9:3793. [PMID: 30846767 PMCID: PMC6405871 DOI: 10.1038/s41598-019-40507-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2018] [Accepted: 02/18/2019] [Indexed: 12/29/2022] Open
Abstract
Mutations in KCNJ13 are associated with two retinal disorders; Leber congenital amaurosis (LCA) and snowflake vitreoretinal degeneration (SVD). We examined the retina of kcnj13 mutant zebrafish (obelixtd15, c.502T > C p.[Phe168Leu]) to provide new insights into the pathophysiology underlying these conditions. Detailed phenotyping of obelixtd15 fish revealed a late onset retinal degeneration at 12 months. Electron microscopy of the obelixtd15 retinal pigment epithelium (RPE) uncovered reduced phagosome clearance and increased mitochondrial number and size prior any signs of retinal degeneration. Melanosome distribution was also affected in dark-adapted 12-month obelixtd15 fish. At 6 and 12 months, ATP levels were found to be reduced along with increased expression of glial fibrillary acidic protein and heat shock protein 60. Quantitative RT-PCR of polg2, fis1, opa1, sod1/2 and bcl2a from isolated retina showed expression changes consistent with altered mitochondrial activity and retinal stress. We propose that the retinal disease in this model is primarily a failure of phagosome physiology with a secondary mitochondrial dysfunction. Our findings suggest that alterations in the RPE and photoreceptor cellular organelles may contribute to KCNJ13-related retinal degeneration and provide a therapeutic target.
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Affiliation(s)
- Maria Toms
- UCL Institute of Ophthalmology, London, UK
| | | | | | | | - Adam M Dubis
- UCL Institute of Ophthalmology, London, UK.,Moorfields Eye Hospital NHS Foundation Trust, London, UK
| | - Andrew R Webster
- UCL Institute of Ophthalmology, London, UK.,Moorfields Eye Hospital NHS Foundation Trust, London, UK
| | | | - Mariya Moosajee
- UCL Institute of Ophthalmology, London, UK. .,Moorfields Eye Hospital NHS Foundation Trust, London, UK. .,Great Ormond Street Hospital for Children NHS Foundation Trust, London, UK.
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26
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Shahi PK, Hermans D, Sinha D, Brar S, Moulton H, Stulo S, Borys KD, Capowski E, Pillers DAM, Gamm DM, Pattnaik BR. Gene Augmentation and Readthrough Rescue Channelopathy in an iPSC-RPE Model of Congenital Blindness. Am J Hum Genet 2019; 104:310-318. [PMID: 30686507 DOI: 10.1016/j.ajhg.2018.12.019] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Accepted: 12/21/2018] [Indexed: 12/11/2022] Open
Abstract
Pathogenic variants of the KCNJ13 gene are known to cause Leber congenital amaurosis (LCA16), an inherited pediatric blindness. KCNJ13 encodes the Kir7.1 subunit that acts as a tetrameric, inwardly rectifying potassium ion channel in the retinal pigment epithelium (RPE) to maintain ionic homeostasis and allow photoreceptors to encode visual information. We sought to determine whether genetic approaches might be effective in treating blindness arising from pathogenic variants in KCNJ13. We derived human induced pluripotent stem cell (hiPSC)-RPE cells from an individual carrying a homozygous c.158G>A (p.Trp53∗) pathogenic variant of KCNJ13. We performed biochemical and electrophysiology assays to confirm Kir7.1 function. We tested both small-molecule readthrough drug and gene-therapy approaches for this "disease-in-a-dish" approach. We found that the LCA16 hiPSC-RPE cells had normal morphology but did not express a functional Kir7.1 channel and were unable to demonstrate normal physiology. After readthrough drug treatment, the LCA16 hiPSC cells were hyperpolarized by 30 mV, and the Kir7.1 current was restored. Similarly, we rescued Kir7.1 channel function after lentiviral gene delivery to the hiPSC-RPE cells. In both approaches, Kir7.1 was expressed normally, and there was restoration of membrane potential and the Kir7.1 current. Loss-of-function variants of Kir7.1 are one cause of LCA. Using either readthrough therapy or gene augmentation, we rescued Kir7.1 channel function in iPSC-RPE cells derived from an affected individual. This supports the development of precision-medicine approaches for the treatment of clinical LCA16.
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Affiliation(s)
- Pawan K Shahi
- Division of Neonatology, Department of Pediatrics, University of Wisconsin-Madison, Madison, WI 53706, USA; McPherson Eye Research, University of Wisconsin-Madison, Madison, WI 53705, USA
| | - Dalton Hermans
- Division of Neonatology, Department of Pediatrics, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Divya Sinha
- McPherson Eye Research, University of Wisconsin-Madison, Madison, WI 53705, USA; Waisman Center, University of Wisconsin-Madison, Madison, WI 53705, USA
| | - Simran Brar
- Division of Neonatology, Department of Pediatrics, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Hannah Moulton
- Division of Neonatology, Department of Pediatrics, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Sabrina Stulo
- Division of Neonatology, Department of Pediatrics, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Katarzyna D Borys
- Waisman Center, University of Wisconsin-Madison, Madison, WI 53705, USA
| | - Elizabeth Capowski
- McPherson Eye Research, University of Wisconsin-Madison, Madison, WI 53705, USA; Waisman Center, University of Wisconsin-Madison, Madison, WI 53705, USA
| | - De-Ann M Pillers
- Division of Neonatology, Department of Pediatrics, University of Wisconsin-Madison, Madison, WI 53706, USA; McPherson Eye Research, University of Wisconsin-Madison, Madison, WI 53705, USA; Medical Genetics, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - David M Gamm
- McPherson Eye Research, University of Wisconsin-Madison, Madison, WI 53705, USA; Waisman Center, University of Wisconsin-Madison, Madison, WI 53705, USA; Department of Ophthalmology and Visual Sciences, University of Wisconsin-Madison, Madison, WI 53705, USA
| | - Bikash R Pattnaik
- Division of Neonatology, Department of Pediatrics, University of Wisconsin-Madison, Madison, WI 53706, USA; McPherson Eye Research, University of Wisconsin-Madison, Madison, WI 53705, USA; Department of Ophthalmology and Visual Sciences, University of Wisconsin-Madison, Madison, WI 53705, USA.
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27
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Yu M, Peachey NS. Use of Direct Current Electroretinography for Analysis of Retinal Pigment Epithelium Function in Mouse Models. Methods Mol Biol 2019; 1753:103-113. [PMID: 29564784 DOI: 10.1007/978-1-4939-7720-8_7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/26/2023]
Abstract
A monolayer of pigmented epithelial cells, the retinal pigment epithelium (RPE), supports photoreceptor function in many ways. Consistent with these roles, RPE dysfunction underlies a number of hereditary retinal disorders. To monitor RPE function in vivo models for these conditions, we adapted an electroretinographic (ERG) technique based on direct current amplification (DC-ERG). This chapter describes the main features of this approach and its application to mouse models involving the RPE.
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Affiliation(s)
- Minzhong Yu
- Department of Ophthalmic Research, Cole Eye Institute, Cleveland Clinic Foundation, Cleveland, OH, USA. .,Department of Ophthalmology, Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Cleveland, OH, USA.
| | - Neal S Peachey
- Department of Ophthalmic Research, Cole Eye Institute, Cleveland Clinic Foundation, Cleveland, OH, USA.,Department of Ophthalmology, Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Cleveland, OH, USA.,Louis Stokes Cleveland VA Medical Center, Cleveland, OH, USA
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28
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Piermarini PM, Inocente EA, Acosta N, Hopkins CR, Denton JS, Michel AP. Inward rectifier potassium (Kir) channels in the soybean aphid Aphis glycines: Functional characterization, pharmacology, and toxicology. JOURNAL OF INSECT PHYSIOLOGY 2018; 110:57-65. [PMID: 30196125 PMCID: PMC6173977 DOI: 10.1016/j.jinsphys.2018.09.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2018] [Revised: 09/05/2018] [Accepted: 09/05/2018] [Indexed: 05/21/2023]
Abstract
Inward rectifier K+ (Kir) channels contribute to a variety of physiological processes in insects and are emerging targets for insecticide development. Previous studies on insect Kir channels have primarily focused on dipteran species (e.g., mosquitoes, fruit flies). Here we identify and functionally characterize Kir channel subunits in a hemipteran insect, the soybean aphid Aphis glycines, which is an economically important insect pest and vector of soybeans. From the transcriptome and genome of Ap. glycines we identified two cDNAs, ApKir1 and ApKir2, encoding Kir subunits that were orthologs of insect Kir1 and Kir2, respectively. Notably, a gene encoding a Kir3 subunit was absent from the transcriptome and genome of Ap. glycines, similar to the pea aphid Acyrthosiphon pisum. Heterologous expression of ApKir1 and ApKir2 in Xenopus laevis oocytes enhanced K+-currents in the plasma membrane; these currents were inhibited by barium and the small molecule VU041. Compared to ApKir2, ApKir1 mediated currents that were larger in magnitude, more sensitive to barium, and less inhibited by small molecule VU041. Moreover, ApKir1 exhibited stronger inward rectification compared to ApKir2. Topical application of VU041 in adult aphids resulted in dose-dependent mortality within 24 h that was more efficacious than flonicamid, an established insecticide also known to inhibit Kir channels. We conclude that despite the apparent loss of Kir3 genes in aphid evolution, Kir channels are important to aphid survival and represent a promising target for the development of new insecticides.
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Affiliation(s)
- Peter M Piermarini
- Department of Entomology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster, OH, USA.
| | - Edna Alfaro Inocente
- Department of Entomology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster, OH, USA
| | - Nuris Acosta
- Department of Entomology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster, OH, USA
| | - Corey R Hopkins
- Department of Pharmaceutical Sciences, University of Nebraska Medical Center, Omaha, NE, USA
| | - Jerod S Denton
- Departments of Anesthesiology and Pharmacology, Vanderbilt University Medical Center, Nashville, TN, USA
| | - Andrew P Michel
- Department of Entomology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster, OH, USA
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29
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Conditional loss of Kcnj13 in the retinal pigment epithelium causes photoreceptor degeneration. Exp Eye Res 2018; 176:219-226. [PMID: 30009826 DOI: 10.1016/j.exer.2018.07.014] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Revised: 06/20/2018] [Accepted: 07/11/2018] [Indexed: 12/31/2022]
Abstract
The retina is the light sensing tissue of the eye which contains multiple layers of cells required for the detection and transmission of a visual signal. Loss of the light-sensing photoreceptors leads to defects in visual function and blindness. Previously, we found that mosaic deletion of Kcnj13, and subsequent loss of the potassium channel Kir7.1, in mice leads to photoreceptor degeneration and recapitulates the human retinal disease phenotype (Zhong et al., 2015). Kcnj13 expression in the retinal pigment epithelium (RPE) is essential for normal retinal electrophysiology, function, and survival. Mice with homozygous loss of Kcnj13 die at postnatal day 1 (P1), requiring a tissue-specific approach to study retinal degeneration phenotypes in adult mice. We used the CRISPR-Cas9 system to generate a floxed, conditional loss-of-function (cKO) Kcnj13flox allele to study the pathogenesis of Kcnj13 deficiency in the retina. To investigate if the Kcnj13 is required in the RPE for photoreceptor function and survival, we used Best1-cre, which is specifically expressed in the RPE. We observed complete loss of Kcnj13 expression in Cre-positive RPE cells. Furthermore, our findings show that widespread loss of Kcnj13 in the RPE leads to severe and progressive thinning of the outer nuclear layer and a reduced response to light. Finally, to detect Best1-cre expression in the RPE of live animals without sacrificing the animal for histology, we generated a Cre-reporter-containing Kcnj13 cKO mouse line (cKOR: Kcnj13flox/flox; Best1-cre; Ai9) which can be rapidly screened using retinal fluorescence microscopy. These findings provide new tools for studying the roles of Kcnj13 in retinal homeostasis.
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30
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Yin W, Kim HT, Wang S, Gunawan F, Wang L, Kishimoto K, Zhong H, Roman D, Preussner J, Guenther S, Graef V, Buettner C, Grohmann B, Looso M, Morimoto M, Mardon G, Offermanns S, Stainier DYR. The potassium channel KCNJ13 is essential for smooth muscle cytoskeletal organization during mouse tracheal tubulogenesis. Nat Commun 2018; 9:2815. [PMID: 30022023 PMCID: PMC6052067 DOI: 10.1038/s41467-018-05043-5] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Accepted: 05/25/2018] [Indexed: 12/22/2022] Open
Abstract
Tubulogenesis is essential for the formation and function of internal organs. One such organ is the trachea, which allows gas exchange between the external environment and the lungs. However, the cellular and molecular mechanisms underlying tracheal tube development remain poorly understood. Here, we show that the potassium channel KCNJ13 is a critical modulator of tracheal tubulogenesis. We identify Kcnj13 in an ethylnitrosourea forward genetic screen for regulators of mouse respiratory organ development. Kcnj13 mutants exhibit a shorter trachea as well as defective smooth muscle (SM) cell alignment and polarity. KCNJ13 is essential to maintain ion homeostasis in tracheal SM cells, which is required for actin polymerization. This process appears to be mediated, at least in part, through activation of the actin regulator AKT, as pharmacological increase of AKT phosphorylation ameliorates the Kcnj13-mutant trachea phenotypes. These results provide insight into the role of ion homeostasis in cytoskeletal organization during tubulogenesis.
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Affiliation(s)
- Wenguang Yin
- Department of Developmental Genetics, Max Planck Institute for Heart and Lung Research, Bad Nauheim, 61231, Germany.
| | - Hyun-Taek Kim
- Department of Developmental Genetics, Max Planck Institute for Heart and Lung Research, Bad Nauheim, 61231, Germany
| | - ShengPeng Wang
- Department of Pharmacology, Max Planck Institute for Heart and Lung Research, Bad Nauheim, 61231, Germany
- Cardiovascular Research Center, School of Basic Medical Sciences, Xi'an Jiaotong University, Xi'an, 710061, China
| | - Felix Gunawan
- Department of Developmental Genetics, Max Planck Institute for Heart and Lung Research, Bad Nauheim, 61231, Germany
| | - Lei Wang
- Department of Pharmacology, Max Planck Institute for Heart and Lung Research, Bad Nauheim, 61231, Germany
| | - Keishi Kishimoto
- Laboratory for Lung Development, RIKEN Center for Developmental Biology, Kobe, 650-0047, Japan
| | - Hua Zhong
- Departments of Pathology and Immunology and Molecular and Human Genetics, Integrative Molecular and Biomedical Sciences Program, Baylor College of Medicine, Houston, TX, 77030, USA
| | - Dany Roman
- Departments of Pathology and Immunology and Molecular and Human Genetics, Integrative Molecular and Biomedical Sciences Program, Baylor College of Medicine, Houston, TX, 77030, USA
| | - Jens Preussner
- Max Planck Institute for Heart and Lung Research, ECCPS Bioinformatics and Deep Sequencing Platform, Bad Nauheim, 61231, Germany
| | - Stefan Guenther
- Max Planck Institute for Heart and Lung Research, ECCPS Bioinformatics and Deep Sequencing Platform, Bad Nauheim, 61231, Germany
| | - Viola Graef
- Department of Developmental Genetics, Max Planck Institute for Heart and Lung Research, Bad Nauheim, 61231, Germany
| | - Carmen Buettner
- Department of Developmental Genetics, Max Planck Institute for Heart and Lung Research, Bad Nauheim, 61231, Germany
| | - Beate Grohmann
- Department of Developmental Genetics, Max Planck Institute for Heart and Lung Research, Bad Nauheim, 61231, Germany
| | - Mario Looso
- Max Planck Institute for Heart and Lung Research, ECCPS Bioinformatics and Deep Sequencing Platform, Bad Nauheim, 61231, Germany
| | - Mitsuru Morimoto
- Laboratory for Lung Development, RIKEN Center for Developmental Biology, Kobe, 650-0047, Japan
| | - Graeme Mardon
- Departments of Pathology and Immunology and Molecular and Human Genetics, Integrative Molecular and Biomedical Sciences Program, Baylor College of Medicine, Houston, TX, 77030, USA
| | - Stefan Offermanns
- Department of Pharmacology, Max Planck Institute for Heart and Lung Research, Bad Nauheim, 61231, Germany
- Center for Molecular Medicine, Goethe University, Frankfurt, 60590, Germany
| | - Didier Y R Stainier
- Department of Developmental Genetics, Max Planck Institute for Heart and Lung Research, Bad Nauheim, 61231, Germany.
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31
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Cornejo I, Villanueva S, Burgos J, López-Cayuqueo KI, Chambrey R, Julio-Kalajzić F, Buelvas N, Niemeyer MI, Figueiras-Fierro D, Brown PD, Sepúlveda FV, Cid LP. Tissue Distribution of Kir7.1 Inwardly Rectifying K + Channel Probed in a Knock-in Mouse Expressing a Haemagglutinin-Tagged Protein. Front Physiol 2018; 9:428. [PMID: 29740340 PMCID: PMC5925607 DOI: 10.3389/fphys.2018.00428] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2017] [Accepted: 04/05/2018] [Indexed: 11/13/2022] Open
Abstract
Kir7.1 encoded by the Kcnj13 gene in the mouse is an inwardly rectifying K+ channel present in epithelia where it shares membrane localization with the Na+/K+-pump. Further investigations of the localisation and function of Kir7.1 would benefit from the availability of a knockout mouse, but perinatal mortality attributed to cleft palate in the neonate has thwarted this research. To facilitate localisation studies we now use CRISPR/Cas9 technology to generate a knock-in mouse, the Kir7.1-HA that expresses the channel tagged with a haemagglutinin (HA) epitope. The availability of antibodies for the HA epitope allows for application of western blot and immunolocalisation methods using widely available anti-HA antibodies with WT tissues providing unambiguous negative control. We demonstrate that Kir7.1-HA cloned from the choroid plexus of the knock-in mouse has the electrophysiological properties of the native channel, including characteristically large Rb+ currents. These large Kir7.1-mediated currents are accompanied by abundant apical membrane Kir7.1-HA immunoreactivity. WT-controlled western blots demonstrate the presence of Kir7.1-HA in the eye and the choroid plexus, trachea and lung, and intestinal epithelium but exclusively in the ileum. In the kidney, and at variance with previous reports in the rat and guinea-pig, Kir7.1-HA is expressed in the inner medulla but not in the cortex or outer medulla. In isolated tubules immunoreactivity was associated with inner medulla collecting ducts but not thin limbs of the loop of Henle. Kir7.1-HA shows basolateral expression in the respiratory tract epithelium from trachea to bronchioli. The channel also appears basolateral in the epithelium of the nasal cavity and nasopharynx in newborn animals. We show that HA-tagged Kir7.1 channel introduced in the mouse by a knock-in procedure has functional properties similar to the native protein and the animal thus generated has clear advantages in localisation studies. It might therefore become a useful tool to unravel Kir7.1 function in the different organs where it is expressed.
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Affiliation(s)
| | - Sandra Villanueva
- Centro de Estudios Científicos, Valdivia, Chile.,Universidad Austral de Chile, Valdivia, Chile
| | - Johanna Burgos
- Centro de Estudios Científicos, Valdivia, Chile.,Universidad Austral de Chile, Valdivia, Chile
| | - Karen I López-Cayuqueo
- Centro de Estudios Científicos, Valdivia, Chile.,Institut National de la Santé et de la Recherche Médicale, Unité Mixte de Recherche S970, PARCC, Hôpital Européen Georges Pompidou, Assistance Publique Hôpitaux de Paris, Paris, France
| | - Régine Chambrey
- Institut National de la Santé et de la Recherche Médicale, Unité Mixte de Recherche S970, PARCC, Hôpital Européen Georges Pompidou, Assistance Publique Hôpitaux de Paris, Paris, France
| | | | | | | | | | - Peter D Brown
- School of Medical Sciences, University of Manchester, Manchester, United Kingdom
| | | | - L P Cid
- Centro de Estudios Científicos, Valdivia, Chile
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32
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Jiménez-Vargas JM, Possani LD, Luna-Ramírez K. Arthropod toxins acting on neuronal potassium channels. Neuropharmacology 2017; 127:139-160. [PMID: 28941737 DOI: 10.1016/j.neuropharm.2017.09.025] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Revised: 09/13/2017] [Accepted: 09/15/2017] [Indexed: 01/01/2023]
Abstract
Arthropod venoms are a rich mixture of biologically active compounds exerting different physiological actions across diverse phyla and affecting multiple organ systems including the central nervous system. Venom compounds can inhibit or activate ion channels, receptors and transporters with high specificity and affinity providing essential insights into ion channel function. In this review, we focus on arthropod toxins (scorpions, spiders, bees and centipedes) acting on neuronal potassium channels. A brief description of the K+ channels classification and structure is included and a compendium of neuronal K+ channels and the arthropod toxins that modify them have been listed. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'
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Affiliation(s)
- Juana María Jiménez-Vargas
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Avenida Universidad, 2001, Colonia Chamilpa, Apartado Postal 510-3, Cuernavaca 62210, Mexico
| | - Lourival D Possani
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Avenida Universidad, 2001, Colonia Chamilpa, Apartado Postal 510-3, Cuernavaca 62210, Mexico
| | - Karen Luna-Ramírez
- Illawarra Health and Medical Research Institute, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, Australia.
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33
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Abnormal Electroretinogram after Kir7.1 Channel Suppression Suggests Role in Retinal Electrophysiology. Sci Rep 2017; 7:10651. [PMID: 28878288 PMCID: PMC5587531 DOI: 10.1038/s41598-017-11034-1] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2017] [Accepted: 08/18/2017] [Indexed: 01/13/2023] Open
Abstract
The KCNJ13 gene encodes the inwardly rectifying potassium channel, Kir7.1. Mutations in this gene cause childhood blindness, in which the a- and b-wave responses of electroretinogram (ERG) are abolished. The ERG a-wave is the light-induced hyperpolarization of retinal photoreceptors, and the b-wave is the depolarization of ON-bipolar cells. The Kir7.1 channel is localized to the apical aspects of retinal pigment epithelium (RPE) cells and contributes to a delayed c-wave response. We sought to understand why a defect in an RPE ion-channel result in abnormal electrophysiology at the level of the retinal neurons. We have established the expression of Kir7.1 channels in the mouse RPE. ERGs recorded after mice Kir7.1 suppression by shRNA, or by blocking with VU590, showed reduced a-, b- and c-wave amplitudes. In contrast, the Kir7.1 blocker had no effect on the ex-vivo isolated mouse retina ERG where the RPE is not attached to the isolated retina preparation. Finally, we confirmed the specificity of VU590 action by inhibition of native mouse RPE Kir7.1 current in patch-clamp experiment. We propose that mutant RPE Kir7.1 channels contribute directly to the abnormal ERG associated with blindness via alterations in sub-retinal space K+ homeostasis in the vicinity of the photoreceptor outer segment.
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34
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Kharade SV, Sheehan JH, Figueroa EE, Meiler J, Denton JS. Pore Polarity and Charge Determine Differential Block of Kir1.1 and Kir7.1 Potassium Channels by Small-Molecule Inhibitor VU590. Mol Pharmacol 2017; 92:338-346. [PMID: 28619748 DOI: 10.1124/mol.117.108472] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2017] [Accepted: 06/12/2017] [Indexed: 12/28/2022] Open
Abstract
VU590 was the first publicly disclosed, submicromolar-affinity (IC50 = 0.2 μM), small-molecule inhibitor of the inward rectifier potassium (Kir) channel and diuretic target, Kir1.1. VU590 also inhibits Kir7.1 (IC50 ∼ 8 μM), and has been used to reveal new roles for Kir7.1 in regulation of myometrial contractility and melanocortin signaling. Here, we employed molecular modeling, mutagenesis, and patch clamp electrophysiology to elucidate the molecular mechanisms underlying VU590 inhibition of Kir1.1 and Kir7.1. Block of both channels is voltage- and K+-dependent, suggesting the VU590 binding site is located within the pore. Mutagenesis analysis in Kir1.1 revealed that asparagine 171 (N171) is the only pore-lining residue required for high-affinity block, and that substituting negatively charged residues (N171D, N171E) at this position dramatically weakens block. In contrast, substituting a negatively charged residue at the equivalent position in Kir7.1 enhances block by VU590, suggesting the VU590 binding mode is different. Interestingly, mutations of threonine 153 (T153) in Kir7.1 that reduce constrained polarity at this site (T153C, T153V, T153S) make wild-type and binding-site mutants (E149Q, A150S) more sensitive to block by VU590. The Kir7.1-T153C mutation enhances block by the structurally unrelated inhibitor VU714 but not by a higher-affinity analog ML418, suggesting that the polar side chain of T153 creates a barrier to low-affinity ligands that interact with E149 and A150. Reverse mutations in Kir1.1 suggest that this mechanism is conserved in other Kir channels. This study reveals a previously unappreciated role of membrane pore polarity in determination of Kir channel inhibitor pharmacology.
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Affiliation(s)
- Sujay V Kharade
- Department of Anesthesiology (S.V.K., E.E.F., J.S.D.), Department of Pharmacology (E.E.F., J.S.D.), Department of Biochemistry (J.H.S., J.M.), Center for Structural Biology (J.H.S., J.M.), Department of Chemistry (J.M.), Institute of Chemical Biology (J.S.D.), Vanderbilt University, Nashville, Tennessee
| | - Jonathan H Sheehan
- Department of Anesthesiology (S.V.K., E.E.F., J.S.D.), Department of Pharmacology (E.E.F., J.S.D.), Department of Biochemistry (J.H.S., J.M.), Center for Structural Biology (J.H.S., J.M.), Department of Chemistry (J.M.), Institute of Chemical Biology (J.S.D.), Vanderbilt University, Nashville, Tennessee
| | - Eric E Figueroa
- Department of Anesthesiology (S.V.K., E.E.F., J.S.D.), Department of Pharmacology (E.E.F., J.S.D.), Department of Biochemistry (J.H.S., J.M.), Center for Structural Biology (J.H.S., J.M.), Department of Chemistry (J.M.), Institute of Chemical Biology (J.S.D.), Vanderbilt University, Nashville, Tennessee
| | - Jens Meiler
- Department of Anesthesiology (S.V.K., E.E.F., J.S.D.), Department of Pharmacology (E.E.F., J.S.D.), Department of Biochemistry (J.H.S., J.M.), Center for Structural Biology (J.H.S., J.M.), Department of Chemistry (J.M.), Institute of Chemical Biology (J.S.D.), Vanderbilt University, Nashville, Tennessee
| | - Jerod S Denton
- Department of Anesthesiology (S.V.K., E.E.F., J.S.D.), Department of Pharmacology (E.E.F., J.S.D.), Department of Biochemistry (J.H.S., J.M.), Center for Structural Biology (J.H.S., J.M.), Department of Chemistry (J.M.), Institute of Chemical Biology (J.S.D.), Vanderbilt University, Nashville, Tennessee
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35
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Swale DR, Kurata H, Kharade SV, Sheehan J, Raphemot R, Voigtritter KR, Figueroa EE, Meiler J, Blobaum AL, Lindsley CW, Hopkins CR, Denton JS. ML418: The First Selective, Sub-Micromolar Pore Blocker of Kir7.1 Potassium Channels. ACS Chem Neurosci 2016; 7:1013-23. [PMID: 27184474 DOI: 10.1021/acschemneuro.6b00111] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The inward rectifier potassium (Kir) channel Kir7.1 (KCNJ13) has recently emerged as a key regulator of melanocortin signaling in the brain, electrolyte homeostasis in the eye, and uterine muscle contractility during pregnancy. The pharmacological tools available for exploring the physiology and therapeutic potential of Kir7.1 have been limited to relatively weak and nonselective small-molecule inhibitors. Here, we report the discovery in a fluorescence-based high-throughput screen of a novel Kir7.1 channel inhibitor, VU714. Site-directed mutagenesis of pore-lining amino acid residues identified glutamate 149 and alanine 150 as essential determinants of VU714 activity. Lead optimization with medicinal chemistry generated ML418, which exhibits sub-micromolar activity (IC50 = 310 nM) and superior selectivity over other Kir channels (at least 17-fold selective over Kir1.1, Kir2.1, Kir2.2, Kir2.3, Kir3.1/3.2, and Kir4.1) except for Kir6.2/SUR1 (equally potent). Evaluation in the EuroFins Lead Profiling panel of 64 GPCRs, ion-channels, and transporters for off-target activity of ML418 revealed a relatively clean ancillary pharmacology. While ML418 exhibited low CLHEP in human microsomes which could be modulated with lipophilicity adjustments, it showed high CLHEP in rat microsomes regardless of lipophilicity. A subsequent in vivo PK study of ML418 by intraperitoneal (IP) administration (30 mg/kg dosage) revealed a suitable PK profile (Cmax = 0.20 μM and Tmax = 3 h) and favorable CNS distribution (mouse brain/plasma Kp of 10.9 to support in vivo studies. ML418, which represents the current state-of-the-art in Kir7.1 inhibitors, should be useful for exploring the physiology of Kir7.1 in vitro and in vivo.
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Affiliation(s)
| | | | | | - Jonathan Sheehan
- Department
of Chemistry, Vanderbilt University, Nashville, Tennessee 37232, United States
| | | | | | | | - Jens Meiler
- Department
of Chemistry, Vanderbilt University, Nashville, Tennessee 37232, United States
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36
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Choi EJ, Sloma EA, Miller AD. Kir7.1 immunoreactivity in canine choroid plexus tumors. J Vet Diagn Invest 2016; 28:464-8. [PMID: 27216721 DOI: 10.1177/1040638716650239] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Choroid plexus neoplasms are uncommon brain tumors in dogs. Choroid plexus carcinomas often spread diffusely throughout the ventricular system and subarachnoid space and, in aggressive forms, can mimic histologic patterns of other carcinomas, including being embedded in a desmoplastic reaction. Although choroid plexus tumors (CPTs) heterogeneously express pan-cytokeratin, little is known about other markers to identify choroid plexus and their associated tumors. Kir7.1, an inward-rectifier potassium channel, is reported to have high diagnostic utility in human neuropathology to distinguish CPTs from other primary brain tumors and cerebral metastases. To determine Kir7.1 expression in the dog brain, we analyzed the immunoreactivity of Kir7.1 in normal brain, gliomas, ependymomas, CPTs, meningiomas, and carcinomas. In normal brain tissue, the immunostaining was restricted to the choroid plexus where there was robust membrane immunoreactivity along the apical border of the cells with less intense cytoplasmic staining. Similar strong immunoreactivity was detected in 12 of 12 CPTs, whereas 5 of 5 gliomas, 4 of 5 ependymomas, 5 of 5 meningiomas, and 5 of 6 carcinomas had no immunoreactivity. One ependymoma and 1 nasal carcinoma with squamous metaplasia were up to 75% immunopositive, with moderate cytoplasmic and membranous immunoreactivity, but lacking the robust apical immunoreactivity pattern. Analysis for immunoreactivity in a tissue microarray failed to yield any other locations in which immunoreactivity was detected. These results, including the distinctive pattern of immunostaining in CPTs, suggest that Kir7.1 is an excellent marker for CPTs in the dog.
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Affiliation(s)
- Eun Ju Choi
- Section of Anatomic Pathology, Department of Biomedical Sciences, Cornell University, College of Veterinary Medicine, Ithaca, NY
| | - Erica A Sloma
- Section of Anatomic Pathology, Department of Biomedical Sciences, Cornell University, College of Veterinary Medicine, Ithaca, NY
| | - Andrew D Miller
- Section of Anatomic Pathology, Department of Biomedical Sciences, Cornell University, College of Veterinary Medicine, Ithaca, NY
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37
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Atia J, McCloskey C, Shmygol AS, Rand DA, van den Berg HA, Blanks AM. Reconstruction of Cell Surface Densities of Ion Pumps, Exchangers, and Channels from mRNA Expression, Conductance Kinetics, Whole-Cell Calcium, and Current-Clamp Voltage Recordings, with an Application to Human Uterine Smooth Muscle Cells. PLoS Comput Biol 2016; 12:e1004828. [PMID: 27105427 PMCID: PMC4841602 DOI: 10.1371/journal.pcbi.1004828] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2015] [Accepted: 02/23/2016] [Indexed: 11/28/2022] Open
Abstract
Uterine smooth muscle cells remain quiescent throughout most of gestation, only generating spontaneous action potentials immediately prior to, and during, labor. This study presents a method that combines transcriptomics with biophysical recordings to characterise the conductance repertoire of these cells, the ‘conductance repertoire’ being the total complement of ion channels and transporters expressed by an electrically active cell. Transcriptomic analysis provides a set of potential electrogenic entities, of which the conductance repertoire is a subset. Each entity within the conductance repertoire was modeled independently and its gating parameter values were fixed using the available biophysical data. The only remaining free parameters were the surface densities for each entity. We characterise the space of combinations of surface densities (density vectors) consistent with experimentally observed membrane potential and calcium waveforms. This yields insights on the functional redundancy of the system as well as its behavioral versatility. Our approach couples high-throughput transcriptomic data with physiological behaviors in health and disease, and provides a formal method to link genotype to phenotype in excitable systems. We accurately predict current densities and chart functional redundancy. For example, we find that to evoke the observed voltage waveform, the BK channel is functionally redundant whereas hERG is essential. Furthermore, our analysis suggests that activation of calcium-activated chloride conductances by intracellular calcium release is the key factor underlying spontaneous depolarisations. A well-known problem in electrophysiologal modeling is that the parameters of the gating kinetics of the ion channels cannot be uniquely determined from observed behavior at the cellular level. One solution is to employ simplified “macroscopic” currents that mimic the behavior of aggregates of distinct entities at the protein level. The gating parameters of each channel or pump can be determined by studying it in isolation, leaving the general problem of finding the densities at which the channels occur in the plasma membrane. We propose an approach, which we apply to uterine smooth muscle cells, whereby we constrain the list of possible entities by means of transcriptomics and chart the indeterminacy of the problem in terms of the kernel of the corresponding linear transformation. A graphical representation of this kernel visualises the functional redundancy of the system. We show that the role of certain conductances can be fulfilled, or compensated for, by suitable combinations of other conductances; this is not always the case, and such “non-substitutable” conductances can be regarded as functionally non-redundant. Electrogenic entities belonging to the latter category are suitable putative clinical targets.
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Affiliation(s)
- Jolene Atia
- Division of Reproductive Health, Warwick Medical School, University of Warwick, Coventry, United Kingdom
| | - Conor McCloskey
- Division of Reproductive Health, Warwick Medical School, University of Warwick, Coventry, United Kingdom
| | - Anatoly S. Shmygol
- Division of Reproductive Health, Warwick Medical School, University of Warwick, Coventry, United Kingdom
| | | | | | - Andrew M. Blanks
- Division of Reproductive Health, Warwick Medical School, University of Warwick, Coventry, United Kingdom
- * E-mail:
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Nessa A, Rahman SA, Hussain K. Hyperinsulinemic Hypoglycemia - The Molecular Mechanisms. Front Endocrinol (Lausanne) 2016; 7:29. [PMID: 27065949 PMCID: PMC4815176 DOI: 10.3389/fendo.2016.00029] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Accepted: 03/21/2016] [Indexed: 12/14/2022] Open
Abstract
Under normal physiological conditions, pancreatic β-cells secrete insulin to maintain fasting blood glucose levels in the range 3.5-5.5 mmol/L. In hyperinsulinemic hypoglycemia (HH), this precise regulation of insulin secretion is perturbed so that insulin continues to be secreted in the presence of hypoglycemia. HH may be due to genetic causes (congenital) or secondary to certain risk factors. The molecular mechanisms leading to HH involve defects in the key genes regulating insulin secretion from the β-cells. At this moment, in time genetic abnormalities in nine genes (ABCC8, KCNJ11, GCK, SCHAD, GLUD1, SLC16A1, HNF1A, HNF4A, and UCP2) have been described that lead to the congenital forms of HH. Perinatal stress, intrauterine growth retardation, maternal diabetes mellitus, and a large number of developmental syndromes are also associated with HH in the neonatal period. In older children and adult's insulinoma, non-insulinoma pancreatogenous hypoglycemia syndrome and post bariatric surgery are recognized causes of HH. This review article will focus mainly on describing the molecular mechanisms that lead to unregulated insulin secretion.
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Affiliation(s)
- Azizun Nessa
- Genetics and Genomic Medicine Programme, Department of Paediatric Endocrinology, UCL Institute of Child Health, Great Ormond Street Hospital for Children NHS, London, UK
| | - Sofia A. Rahman
- Genetics and Genomic Medicine Programme, Department of Paediatric Endocrinology, UCL Institute of Child Health, Great Ormond Street Hospital for Children NHS, London, UK
| | - Khalid Hussain
- Genetics and Genomic Medicine Programme, Department of Paediatric Endocrinology, UCL Institute of Child Health, Great Ormond Street Hospital for Children NHS, London, UK
- *Correspondence: Khalid Hussain,
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39
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Cang C, Aranda K, Seo YJ, Gasnier B, Ren D. TMEM175 Is an Organelle K(+) Channel Regulating Lysosomal Function. Cell 2015; 162:1101-12. [PMID: 26317472 DOI: 10.1016/j.cell.2015.08.002] [Citation(s) in RCA: 135] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2015] [Revised: 06/10/2015] [Accepted: 07/13/2015] [Indexed: 12/15/2022]
Abstract
Potassium is the most abundant ion to face both plasma and organelle membranes. Extensive research over the past seven decades has characterized how K(+) permeates the plasma membrane to control fundamental processes such as secretion, neuronal communication, and heartbeat. However, how K(+) permeates organelles such as lysosomes and endosomes is unknown. Here, we directly recorded organelle K(+) conductance and discovered a major K(+)-selective channel KEL on endosomes and lysosomes. KEL is formed by TMEM175, a protein with unknown function. Unlike any of the ∼80 plasma membrane K(+) channels, TMEM175 has two repeats of 6-transmembrane-spanning segments and has no GYG K(+) channel sequence signature-containing, pore-forming P loop. Lysosomes lacking TMEM175 exhibit no K(+) conductance, have a markedly depolarized ΔΨ and little sensitivity to changes in [K(+)], and have compromised luminal pH stability and abnormal fusion with autophagosomes during autophagy. Thus, TMEM175 comprises a K(+) channel that underlies the molecular mechanism of lysosomal K(+) permeability.
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Affiliation(s)
- Chunlei Cang
- Department of Biology, University of Pennsylvania, 415 South University Avenue, Philadelphia, PA 19104, USA
| | - Kimberly Aranda
- Department of Biology, University of Pennsylvania, 415 South University Avenue, Philadelphia, PA 19104, USA
| | - Young-jun Seo
- Department of Biology, University of Pennsylvania, 415 South University Avenue, Philadelphia, PA 19104, USA
| | - Bruno Gasnier
- Paris Descartes University, Sorbonne Paris Cité, Neurophotonics Laboratory, Centre National de la Recherche Scientifique UMR8250, 45 rue des Saints Pères, 75006 Paris, France
| | - Dejian Ren
- Department of Biology, University of Pennsylvania, 415 South University Avenue, Philadelphia, PA 19104, USA.
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40
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Abstract
Genetic studies have linked alterations in Kir7.1 channel to diverse pathologies. We summarize functional relevance of Kir7.1 channel in retinal pigment epithelium (RPE), regulation of channel function by various cytoplasmic metabolites, and mutations that cause channelopathies. At the apical membrane of RPE, K(+) channels contribute to subretinal K(+) homeostasis and support Na(+)/K(+) pump and Na(+)-K(+)-2Cl(-) cotransporter function by providing a pathway for K(+) secretion. Electrophysiological studies have established that barium- and cesium-sensitive inwardly rectifying K(+) (Kir) channels make up a major component of the RPE apical membrane K(+) conductance. Native human RPE expresses transcripts for Kir1.1, Kir2.1, Kir2.2, Kir3.1, Kir3.4, Kir4.2, and Kir6.1, albeit at levels at least 50-fold lower than Kir7.1. Kir7.1 is structurally similar to other Kir channels, consisting of 2 trans-membrane domains, a pore-forming loop that contains the selectivity filter, and 2 cytoplasmic polar tails. Within the cytoplasmic structure, clusters of amino acid sequences form regulatory domains that interact with cellular metabolites and control the opening and closing of the channel. Recent evidence indicated that intrinsic sequence motifs present in Kir7.1 control surface expression. Mutant Kir7.1 channels are associated with inherited eye pathologies such as Snowflake Vitreoretinal Degeneration (SVD) and Lebers Congenital Amaurosis (LCA16). Based on the current evidence, mutations implicated in channelopathies have the potential to be used for genetic testing to diagnose blindness due to Kir7.1.
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Affiliation(s)
- Mohit Kumar
- a Departments of Biotechnology and Bioinformatics ; NIIT University ; Neemrana , Rajasthan , India
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41
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Villanueva S, Burgos J, López-Cayuqueo KI, Lai KMV, Valenzuela DM, Cid LP, Sepúlveda FV. Cleft Palate, Moderate Lung Developmental Retardation and Early Postnatal Lethality in Mice Deficient in the Kir7.1 Inwardly Rectifying K+ Channel. PLoS One 2015; 10:e0139284. [PMID: 26402555 PMCID: PMC4581704 DOI: 10.1371/journal.pone.0139284] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2015] [Accepted: 09/09/2015] [Indexed: 12/15/2022] Open
Abstract
Kir7.1 is an inwardly rectifying K+ channel of the Kir superfamily encoded by the kcnj13 gene. Kir7.1 is present in epithelial tissues where it colocalizes with the Na+/K+-pump probably serving to recycle K+ taken up by the pump. Human mutations affecting Kir7.1 are associated with retinal degeneration diseases. We generated a mouse lacking Kir7.1 by ablation of the Kcnj13 gene. Homozygous mutant null mice die hours after birth and show cleft palate and moderate retardation in lung development. Kir7.1 is expressed in the epithelium covering the palatal processes at the time at which palate sealing takes place and our results suggest it might play an essential role in late palatogenesis. Our work also reveals a second unexpected role in the development and the physiology of the respiratory system, where Kir7.1 is expressed in epithelial cells all along the respiratory tree.
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Affiliation(s)
| | - Johanna Burgos
- Centro de Estudios Científicos (CECs), Valdivia, Chile
- Doctorado en Ciencias Veterinarias de la Universidad Austral de Chile, Valdivia, Chile
| | | | - Ka-Man Venus Lai
- Regeneron Pharmaceuticals, Inc., Tarrytown, New York, United States of America
| | - David M. Valenzuela
- Regeneron Pharmaceuticals, Inc., Tarrytown, New York, United States of America
| | - L. Pablo Cid
- Centro de Estudios Científicos (CECs), Valdivia, Chile
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42
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Glaaser IW, Slesinger PA. Structural Insights into GIRK Channel Function. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2015; 123:117-60. [PMID: 26422984 DOI: 10.1016/bs.irn.2015.05.014] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
G protein-gated inwardly rectifying potassium (GIRK; Kir3) channels, which are members of the large family of inwardly rectifying potassium channels (Kir1-Kir7), regulate excitability in the heart and brain. GIRK channels are activated following stimulation of G protein-coupled receptors that couple to the G(i/o) (pertussis toxin-sensitive) G proteins. GIRK channels, like all other Kir channels, possess an extrinsic mechanism of inward rectification involving intracellular Mg(2+) and polyamines that occlude the conduction pathway at membrane potentials positive to E(K). In the past 17 years, more than 20 high-resolution atomic structures containing GIRK channel cytoplasmic domains and transmembrane domains have been solved. These structures have provided valuable insights into the structural determinants of many of the properties common to all inward rectifiers, such as permeation and rectification, as well as revealing the structural bases for GIRK channel gating. In this chapter, we describe advances in our understanding of GIRK channel function based on recent high-resolution atomic structures of inwardly rectifying K(+) channels discussed in the context of classical structure-function experiments.
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Affiliation(s)
- Ian W Glaaser
- Department of Neuroscience, Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, New York, USA
| | - Paul A Slesinger
- Department of Neuroscience, Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, New York, USA.
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43
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McCloskey C, Rada C, Bailey E, McCavera S, van den Berg HA, Atia J, Rand DA, Shmygol A, Chan YW, Quenby S, Brosens JJ, Vatish M, Zhang J, Denton JS, Taggart MJ, Kettleborough C, Tickle D, Jerman J, Wright P, Dale T, Kanumilli S, Trezise DJ, Thornton S, Brown P, Catalano R, Lin N, England SK, Blanks AM. The inwardly rectifying K+ channel KIR7.1 controls uterine excitability throughout pregnancy. EMBO Mol Med 2015; 6:1161-74. [PMID: 25056913 PMCID: PMC4197863 DOI: 10.15252/emmm.201403944] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Abnormal uterine activity in pregnancy causes a range of important clinical disorders, including preterm birth, dysfunctional labour and post-partum haemorrhage. Uterine contractile patterns are controlled by the generation of complex electrical signals at the myometrial smooth muscle plasma membrane. To identify novel targets to treat conditions associated with uterine dysfunction, we undertook a genome-wide screen of potassium channels that are enriched in myometrial smooth muscle. Computational modelling identified Kir7.1 as potentially important in regulating uterine excitability during pregnancy. We demonstrate Kir7.1 current hyper-polarizes uterine myocytes and promotes quiescence during gestation. Labour is associated with a decline, but not loss, of Kir7.1 expression. Knockdown of Kir7.1 by lentiviral expression of miRNA was sufficient to increase uterine contractile force and duration significantly. Conversely, overexpression of Kir7.1 inhibited uterine contractility. Finally, we demonstrate that the Kir7.1 inhibitor VU590 as well as novel derivative compounds induces profound, long-lasting contractions in mouse and human myometrium; the activity of these inhibitors exceeds that of other uterotonic drugs. We conclude Kir7.1 regulates the transition from quiescence to contractions in the pregnant uterus and may be a target for therapies to control uterine contractility.
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Affiliation(s)
- Conor McCloskey
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Cara Rada
- Division of Basic Science Research, Department of Obstetrics and Gynecology, School of Medicine Washington University in St. Louis,, St. Louis, MO, USA
| | - Elizabeth Bailey
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Samantha McCavera
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Hugo A van den Berg
- Warwick Systems Biology & Mathematics Institute University of Warwick, Coventry, UK
| | - Jolene Atia
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - David A Rand
- Warwick Systems Biology & Mathematics Institute University of Warwick, Coventry, UK
| | - Anatoly Shmygol
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Yi-Wah Chan
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Siobhan Quenby
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Jan J Brosens
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Manu Vatish
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Jie Zhang
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Jerod S Denton
- Vanderbilt Institute of Chemical Biology, Vanderbilt Institute for Global Health Vanderbilt University School of Medicine Medical Center North, Nashville, TN, USA
| | - Michael J Taggart
- Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, UK
| | | | - David Tickle
- Centre for Therapeutics and Discovery, Medical Research Council Technologies, London, UK
| | - Jeff Jerman
- Centre for Therapeutics and Discovery, Medical Research Council Technologies, London, UK
| | - Paul Wright
- Centre for Therapeutics and Discovery, Medical Research Council Technologies, London, UK
| | - Timothy Dale
- BioPark, Essen BioScience Ltd, Welwyn Garden City, Hertfordshire, UK
| | | | - Derek J Trezise
- BioPark, Essen BioScience Ltd, Welwyn Garden City, Hertfordshire, UK
| | | | - Pamela Brown
- MRC Centre for Reproductive Health (CRH), Queen's Medical Research Institute University of Edinburgh, Edinburgh, UK
| | - Roberto Catalano
- MRC Centre for Reproductive Health (CRH), Queen's Medical Research Institute University of Edinburgh, Edinburgh, UK
| | - Nan Lin
- Department of Mathematics, Washington University, St. Louis, MO, USA
| | - Sarah K England
- Division of Basic Science Research, Department of Obstetrics and Gynecology, School of Medicine Washington University in St. Louis,, St. Louis, MO, USA
| | - Andrew M Blanks
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
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44
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Pattnaik BR, Shahi PK, Marino MJ, Liu X, York N, Brar S, Chiang J, Pillers DAM, Traboulsi EI. A Novel KCNJ13 Nonsense Mutation and Loss of Kir7.1 Channel Function Causes Leber Congenital Amaurosis (LCA16). Hum Mutat 2015; 36:720-7. [PMID: 25921210 DOI: 10.1002/humu.22807] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2015] [Accepted: 04/20/2015] [Indexed: 11/08/2022]
Abstract
Mutations in the KCNJ13 gene that encodes the inwardly rectifying potassium channel Kir7.1 cause snowflake vitreoretinal degeneration (SVD) and leber congenital amaurosis (LCA). Kir7.1 controls the microenvironment between the photoreceptors and the retinal pigment epithelium (RPE) and also contributes to the function of other organs such as uterus and brain. Heterologous expressions of the mutant channel have suggested a dominant-negative loss of Kir7.1 function in SVD, but parallel studies in LCA16 have been lacking. Herein, we report the identification of a novel nonsense mutation in the second exon of the KCNJ13 gene that leads to a premature stop codon in association with LCA16. We have determined that the mutation results in a severe truncation of the Kir7.1 C-terminus, alters protein localization, and disrupts potassium currents. Coexpression of the mutant and wild-type channel has no negative influence on the wild-type channel function, consistent with the normal clinical phenotype of carrier individuals. By suppressing Kir7.1 function in mice, we were able to reproduce the severe LCA electroretinogram phenotype. Thus, we have extended the observation that Kir7.1 mutations are associated with vision disorders to include novel insights into the molecular mechanism of disease pathobiology in LCA16.
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Affiliation(s)
- Bikash R Pattnaik
- Department of Pediatrics, University of Wisconsin, Madison, Wisconsin.,Department of Ophthalmology and Visual Sciences, University of Wisconsin, Madison, Wisconsin.,McPherson Eye Research Institute, University of Wisconsin, Madison, Wisconsin
| | - Pawan K Shahi
- Department of Pediatrics, University of Wisconsin, Madison, Wisconsin
| | - Meghan J Marino
- Center for Genetic Eye Diseases and Department of Ophthalmic Research, Cole Eye Institute, Cleveland Clinic Foundation, Cleveland, Ohio
| | - Xinying Liu
- Department of Pediatrics, University of Wisconsin, Madison, Wisconsin
| | - Nathaniel York
- Department of Pediatrics, University of Wisconsin, Madison, Wisconsin
| | - Simran Brar
- Department of Pediatrics, University of Wisconsin, Madison, Wisconsin
| | - John Chiang
- Casey Molecular Diagnostic Laboratory, Oregon Health & Science University, Portland, Oregon
| | - De-Ann M Pillers
- Department of Pediatrics, University of Wisconsin, Madison, Wisconsin.,McPherson Eye Research Institute, University of Wisconsin, Madison, Wisconsin
| | - Elias I Traboulsi
- Center for Genetic Eye Diseases and Department of Ophthalmic Research, Cole Eye Institute, Cleveland Clinic Foundation, Cleveland, Ohio
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45
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Ghamari-Langroudi M, Digby GJ, Sebag JA, Millhauser GL, Palomino R, Matthews R, Gillyard T, Panaro BL, Tough IR, Cox HM, Denton JS, Cone RD. G-protein-independent coupling of MC4R to Kir7.1 in hypothalamic neurons. Nature 2015; 520:94-8. [PMID: 25600267 PMCID: PMC4383680 DOI: 10.1038/nature14051] [Citation(s) in RCA: 132] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2013] [Accepted: 11/10/2014] [Indexed: 02/04/2023]
Abstract
The regulated release of anorexigenic α-melanocyte stimulating hormone (α-MSH) and orexigenic Agouti-related protein (AgRP) from discrete hypothalamic arcuate neurons onto common target sites in the central nervous system has a fundamental role in the regulation of energy homeostasis. Both peptides bind with high affinity to the melanocortin-4 receptor (MC4R); existing data show that α-MSH is an agonist that couples the receptor to the Gαs signalling pathway, while AgRP binds competitively to block α-MSH binding and blocks the constitutive activity mediated by the ligand-mimetic amino-terminal domain of the receptor. Here we show that, in mice, regulation of firing activity of neurons from the paraventricular nucleus of the hypothalamus (PVN) by α-MSH and AgRP can be mediated independently of Gαs signalling by ligand-induced coupling of MC4R to closure of inwardly rectifying potassium channel, Kir7.1. Furthermore, AgRP is a biased agonist that hyperpolarizes neurons by binding to MC4R and opening Kir7.1, independently of its inhibition of α-MSH binding. Consequently, Kir7.1 signalling appears to be central to melanocortin-mediated regulation of energy homeostasis within the PVN. Coupling of MC4R to Kir7.1 may explain unusual aspects of the control of energy homeostasis by melanocortin signalling, including the gene dosage effect of MC4R and the sustained effects of AgRP on food intake.
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Affiliation(s)
- Masoud Ghamari-Langroudi
- Department of Molecular Physiology &Biophysics, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA
| | - Gregory J Digby
- Department of Molecular Physiology &Biophysics, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA
| | - Julien A Sebag
- Department of Molecular Physiology &Biophysics, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA
| | - Glenn L Millhauser
- Department of Chemistry &Biochemistry, University of California, Santa Cruz, California 95064, USA
| | - Rafael Palomino
- Department of Chemistry &Biochemistry, University of California, Santa Cruz, California 95064, USA
| | - Robert Matthews
- Department of Molecular Physiology &Biophysics, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA
| | - Taneisha Gillyard
- 1] Department of Molecular Physiology &Biophysics, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA [2] Department of Pharmacology, Meharry Medical College, Nashville, Tennessee 37208, USA
| | - Brandon L Panaro
- Department of Molecular Physiology &Biophysics, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA
| | - Iain R Tough
- King's College London, Wolfson Centre for Age-Related Diseases, Guy's Campus, London SE1 1UL, UK
| | - Helen M Cox
- King's College London, Wolfson Centre for Age-Related Diseases, Guy's Campus, London SE1 1UL, UK
| | - Jerod S Denton
- 1] Department of Anesthesiology, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA [2] Department of Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA
| | - Roger D Cone
- Department of Molecular Physiology &Biophysics, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA
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46
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Longden TA, Nelson MT. Vascular inward rectifier K+ channels as external K+ sensors in the control of cerebral blood flow. Microcirculation 2015; 22:183-96. [PMID: 25641345 PMCID: PMC4404517 DOI: 10.1111/micc.12190] [Citation(s) in RCA: 102] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2014] [Accepted: 01/16/2015] [Indexed: 12/25/2022]
Abstract
For decades it has been known that external K(+) ions are rapid and potent vasodilators that increase CBF. Recent studies have implicated the local release of K(+) from astrocytic endfeet-which encase the entirety of the parenchymal vasculature-in the dynamic regulation of local CBF during NVC. It has been proposed that the activation of KIR channels in the vascular wall by external K(+) is a central component of these hyperemic responses; however, a number of significant gaps in our knowledge remain. Here, we explore the concept that vascular KIR channels are the major extracellular K(+) sensors in the control of CBF. We propose that K(+) is an ideal mediator of NVC, and discuss KIR channels as effectors that produce rapid hyperpolarization and robust vasodilation of cerebral arterioles. We provide evidence that KIR channels, of the KIR 2 subtype in particular, are present in both the endothelial and SM cells of parenchymal arterioles and propose that this dual positioning of KIR 2 channels increases the robustness of the vasodilation to external K(+), enables the endothelium to be actively engaged in NVC, and permits electrical signaling through the endothelial syncytium to promote upstream vasodilation to modulate CBF.
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Affiliation(s)
- Thomas A Longden
- Department of Pharmacology, College of Medicine, University of Vermont, Burlington, Vermont, USA
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Sepúlveda FV, Pablo Cid L, Teulon J, Niemeyer MI. Molecular aspects of structure, gating, and physiology of pH-sensitive background K2P and Kir K+-transport channels. Physiol Rev 2015; 95:179-217. [PMID: 25540142 DOI: 10.1152/physrev.00016.2014] [Citation(s) in RCA: 77] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
K(+) channels fulfill roles spanning from the control of excitability to the regulation of transepithelial transport. Here we review two groups of K(+) channels, pH-regulated K2P channels and the transport group of Kir channels. After considering advances in the molecular aspects of their gating based on structural and functional studies, we examine their participation in certain chosen physiological and pathophysiological scenarios. Crystal structures of K2P and Kir channels reveal rather unique features with important consequences for the gating mechanisms. Important tasks of these channels are discussed in kidney physiology and disease, K(+) homeostasis in the brain by Kir channel-equipped glia, and central functions in the hearing mechanism in the inner ear and in acid secretion by parietal cells in the stomach. K2P channels fulfill a crucial part in central chemoreception probably by virtue of their pH sensitivity and are central to adrenal secretion of aldosterone. Finally, some unorthodox behaviors of the selectivity filters of K2P channels might explain their normal and pathological functions. Although a great deal has been learned about structure, molecular details of gating, and physiological functions of K2P and Kir K(+)-transport channels, this has been only scratching at the surface. More molecular and animal studies are clearly needed to deepen our knowledge.
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Affiliation(s)
- Francisco V Sepúlveda
- Centro de Estudios Científicos, Valdivia, Chile; UPMC Université Paris 06, Team 3, Paris, France; and Institut National de la Santé et de la Recherche Médicale, UMR_S 1138, Paris, France
| | - L Pablo Cid
- Centro de Estudios Científicos, Valdivia, Chile; UPMC Université Paris 06, Team 3, Paris, France; and Institut National de la Santé et de la Recherche Médicale, UMR_S 1138, Paris, France
| | - Jacques Teulon
- Centro de Estudios Científicos, Valdivia, Chile; UPMC Université Paris 06, Team 3, Paris, France; and Institut National de la Santé et de la Recherche Médicale, UMR_S 1138, Paris, France
| | - María Isabel Niemeyer
- Centro de Estudios Científicos, Valdivia, Chile; UPMC Université Paris 06, Team 3, Paris, France; and Institut National de la Santé et de la Recherche Médicale, UMR_S 1138, Paris, France
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48
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Wright PD, Kanumilli S, Tickle D, Cartland J, Bouloc N, Dale T, Tresize DJ, McCloskey C, McCavera S, Blanks AM, Kettleborough C, Jerman JC. A High-Throughput Electrophysiology Assay Identifies Inhibitors of the Inwardly Rectifying Potassium Channel Kir7.1. ACTA ACUST UNITED AC 2015; 20:739-47. [PMID: 25656238 DOI: 10.1177/1087057115569156] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2014] [Accepted: 12/31/2014] [Indexed: 11/17/2022]
Abstract
Kir7.1 is an inwardly rectifying potassium channel that has been implicated in controlling the resting membrane potential of the myometrium. Abnormal uterine activity in pregnancy plays an important role in postpartum hemorrhage, and novel therapies for this condition may lie in manipulation of membrane potential. This work presents an assay development and screening strategy for identifying novel inhibitors of Kir7.1. A cell-based automated patch-clamp electrophysiology assay was developed using the IonWorks Quattro (Molecular Devices, Sunnyvale, CA) system, and the iterative optimization is described. In total, 7087 compounds were tested, with a hit rate (>40% inhibition) of 3.09%. During screening, average Z' values of 0.63 ± 0.09 were observed. After chemistry triage, lead compounds were resynthesized and activity confirmed by IC50 determinations. The most potent compound identified (MRT00200769) gave rise to an IC50 of 1.3 µM at Kir7.1. Compounds were assessed for selectivity using the inwardly rectifying potassium channel Kir1.1 (ROMK) and hERG (human Ether-à-go-go Related Gene). Pharmacological characterization of known Kir7.1 inhibitors was also carried out and analogues of VU590 tested to assess selectivity at Kir7.1.
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Affiliation(s)
- Paul D Wright
- MRC Technology, Center for Therapeutics Discovery, London, UK
| | | | - David Tickle
- MRC Technology, Center for Therapeutics Discovery, London, UK
| | - Jamie Cartland
- MRC Technology, Center for Therapeutics Discovery, London, UK
| | - Nathalie Bouloc
- MRC Technology, Center for Therapeutics Discovery, London, UK
| | - Timothy Dale
- Essen BioScience Ltd, Welwyn Garden City, Hertfordshire, UK
| | | | - Conor McCloskey
- Division of Reproductive Health, Warwick Medical School, Clinical Sciences Research Laboratory, Coventry, UK
| | - Samantha McCavera
- Division of Reproductive Health, Warwick Medical School, Clinical Sciences Research Laboratory, Coventry, UK
| | - Andrew M Blanks
- Division of Reproductive Health, Warwick Medical School, Clinical Sciences Research Laboratory, Coventry, UK
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49
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Bhoelan BS, Stevering CH, van der Boog ATJ, van der Heyden MAG. Barium toxicity and the role of the potassium inward rectifier current. Clin Toxicol (Phila) 2014; 52:584-93. [DOI: 10.3109/15563650.2014.923903] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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50
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Reuter P, Kohl S, Bernd A, Wissinger B. Erbliche Ionenkanalerkrankungen der Netzhaut. MED GENET-BERLIN 2013. [DOI: 10.1007/s11825-013-0422-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Zusammenfassung
Retinale Ionenkanalerkrankungen sind klinisch und genetisch sehr heterogen. Die bisher identifizierten krankheitsassoziierten Ionenkanäle umfassen zyklisch nukleotidgesteuerte (CNG-)Kanäle, spannungsgesteuerte Kalium- und Kalziumkanäle, einen einwärtsrektifizierenden Kaliumkanal, einen kalziumaktivierten Chloridkanal und den transienten Rezeptorpotenzialionenkanal TRPM1. Dieses breite Spektrum spiegelt sich auch in der resultierenden Pathophysiologie wieder. Mutationen in retinalen Ionenkanälen können die Detektion von Lichtreizen bzw. deren Umwandlung in ein elektrisches Signal oder die Weiterleitung des Signals von den Fotorezeptoren zu nachgeschalteten Neuronen beeinträchtigen. Einige Erkrankungen werden auch durch Mutationen in Ionenkanälen, die im retinalen Pigmentepithel lokalisiert sind, hervorgerufen. Dieses ist mit seinen unterstützenden Aufgaben für eine normale Netzhautfunktion essenziell.
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Affiliation(s)
- P. Reuter
- Aff1 grid.411544.1 0000000101968249 Molekulargenetisches Labor Forschungsinstitut für Augenheilkunde, Universitätsklinikum Tübingen Röntgenweg 11 72076 Tübingen Deutschland
| | - S. Kohl
- Aff1 grid.411544.1 0000000101968249 Molekulargenetisches Labor Forschungsinstitut für Augenheilkunde, Universitätsklinikum Tübingen Röntgenweg 11 72076 Tübingen Deutschland
| | - A. Bernd
- Aff2 grid.411544.1 0000000101968249 Universitätsaugenklinik Tübingen Tübingen Deutschland
| | - B. Wissinger
- Aff1 grid.411544.1 0000000101968249 Molekulargenetisches Labor Forschungsinstitut für Augenheilkunde, Universitätsklinikum Tübingen Röntgenweg 11 72076 Tübingen Deutschland
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