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Yuan WQ, Huang WP, Jiang YC, Xu H, Duan CS, Chen NH, Liu YJ, Fu XM. The function of astrocytes and their role in neurological diseases. Eur J Neurosci 2023; 58:3932-3961. [PMID: 37831013 DOI: 10.1111/ejn.16160] [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: 05/30/2023] [Revised: 09/11/2023] [Accepted: 09/13/2023] [Indexed: 10/14/2023]
Abstract
Astrocytes have countless links with neurons. Previously, astrocytes were only considered a scaffold of neurons; in fact, astrocytes perform a variety of functions, including providing support for neuronal structures and energy metabolism, offering isolation and protection and influencing the formation, function and elimination of synapses. Because of these functions, astrocytes play an critical role in central nervous system (CNS) diseases. The regulation of the secretiory factors, receptors, channels and pathways of astrocytes can effectively inhibit the occurrence and development of CNS diseases, such as neuromyelitis optica (NMO), multiple sclerosis, Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease. The expression of aquaporin 4 in AS is directly related to NMO and indirectly involved in the clearance of Aβ and tau proteins in AD. Connexin 43 has a bidirectional effect on glutamate diffusion at different stages of stroke. Interestingly, astrocytes reduce the occurrence of PD through multiple effects such as secretion of related factors, mitochondrial autophagy and aquaporin 4. Therefore, this review is focused on the structure and function of astrocytes and the correlation between astrocytes and CNS diseases and drug treatment to explore the new functions of astrocytes with the astrocytes as the target. This, in turn, would provide a reference for the development of new drugs to protect neurons and promote the recovery of nerve function.
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Affiliation(s)
- Wen-Qin Yuan
- College of Pharmacy, Jiangxi University of Chinese Medicine, Nanchang, China
| | - Wei-Peng Huang
- State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Institute of Materia Medica and Neuroscience Center, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
- College of Pharmacy, Minzu University of China, Beijing, China
| | - Yang-Chao Jiang
- College of Pharmacy, Jiangxi University of Chinese Medicine, Nanchang, China
| | - Hao Xu
- College of Economics and Management, Jiangxi University of Chinese Medicine, Nanchang, China
| | - Chong-Shen Duan
- College of Pharmacy, Jiangxi University of Chinese Medicine, Nanchang, China
| | - Nai-Hong Chen
- State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Institute of Materia Medica and Neuroscience Center, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Ying-Jiao Liu
- College of Pharmacy, Jiangxi University of Chinese Medicine, Nanchang, China
| | - Xiao-Mei Fu
- College of Pharmacy, Jiangxi University of Chinese Medicine, Nanchang, China
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Meng F, Fu J, Zhang L, Guo M, Zhuang P, Yin Q, Zhang Y. Function and therapeutic value of astrocytes in diabetic cognitive impairment. Neurochem Int 2023; 169:105591. [PMID: 37543309 DOI: 10.1016/j.neuint.2023.105591] [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: 06/12/2023] [Revised: 07/25/2023] [Accepted: 08/01/2023] [Indexed: 08/07/2023]
Abstract
Diabetic cognitive impairment (DCI) is a complex complication of diabetes in the central nervous system, and its pathological mechanism is still being explored. Astrocytes are abundant glial cells in central nervous system that perform diverse functions in health and disease. Accumulating excellent research has identified astrocyte dysfunction in many neurodegenerative diseases (such as Alzheimer's disease, aging and Parkinson's disease), and summarized and discussed its pathological mechanisms and potential therapeutic value. However, the contribution of astrocytes to DCI has been largely overlooked. In this review, we first systematically summarized the effects and mechanisms of diabetes on brain astrocytes, and found that the diabetic environment (such as hyperglycemia, advanced glycation end products and cerebral insulin resistance) mediated brain reactive astrogliosis, which was specifically reflected in the changes of cell morphology and the remodeling of signature molecules. Secondly, we emphasized the contribution and potential targets of reactive astrogliosis to DCI, and found that reactive astrogliosis-induced increased blood-brain barrier permeability, glymphatic system dysfunction, neuroinflammation, abnormal cell communication and cholesterol metabolism dysregulation worsened cognitive function. In addition, we summarized effective strategies for treating DCI by targeting astrocytes. Finally, we discuss the application of new techniques in astrocytes, including single-cell transcriptome, in situ sequencing, and prospected new functions, new subsets and new targets of astrocytes in DCI.
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Affiliation(s)
- Fanyu Meng
- Tianjin University of Traditional Chinese Medicine, Tianjin, 301617, China
| | - Jiafeng Fu
- Tianjin University of Traditional Chinese Medicine, Tianjin, 301617, China
| | - Lin Zhang
- Tianjin University of Traditional Chinese Medicine, Tianjin, 301617, China
| | - Mengqing Guo
- Tianjin University of Traditional Chinese Medicine, Tianjin, 301617, China
| | - Pengwei Zhuang
- Tianjin University of Traditional Chinese Medicine, Tianjin, 301617, China; State Key Laboratory of Component-based Chinese Medicine, Tianjin University of Traditional Chinese Medicine, Tianjin, 301617, China; Haihe Laboratory of Modern Chinese Medicine, Tianjin, 301617, China
| | - Qingsheng Yin
- Tianjin University of Traditional Chinese Medicine, Tianjin, 301617, China; State Key Laboratory of Component-based Chinese Medicine, Tianjin University of Traditional Chinese Medicine, Tianjin, 301617, China; Haihe Laboratory of Modern Chinese Medicine, Tianjin, 301617, China.
| | - Yanjun Zhang
- State Key Laboratory of Component-based Chinese Medicine, Tianjin University of Traditional Chinese Medicine, Tianjin, 301617, China; Haihe Laboratory of Modern Chinese Medicine, Tianjin, 301617, China; First Teaching Hospital of Tianjin University of Traditional Chinese Medicine, Tianjin, 300193, China; National Clinical Research Center for Chinese Medicine Acupuncture and Moxibustion, Tianjin, 300193, China.
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3
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Activity of TREK-2-like Channels in the Pyramidal Neurons of Rat Medial Prefrontal Cortex Depends on Cytoplasmic Calcium. BIOLOGY 2021; 10:biology10111119. [PMID: 34827112 PMCID: PMC8614805 DOI: 10.3390/biology10111119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Revised: 10/26/2021] [Accepted: 10/28/2021] [Indexed: 11/22/2022]
Abstract
Simple Summary The pyramidal neurons of rat prefrontal cortex express potassium channels identified as a non-canonical splice variant of the TREK-2 channel. The main function of TREK channels is to regulate the resting membrane potential. We showed that cytoplasmic Ca2+ upregulates the activity of TREK-2-like channels. Previous studies have indicated that the activation of TREK-2 channels is mediated by PI(4,5)P2, a polyanionic lipid in the inner leaflet of the plasma membrane. While TREK channels are believed to not be regulated by calcium, our work shows otherwise. We propose a model in which calcium ions enable the formation of PI(4,5)P2 nanoclusters, which stabilize active conformation of the channel. Abstract TREK-2-like channels in the pyramidal neurons of rat prefrontal cortex are characterized by a wide range of spontaneous activity—from very low to very high—independent of the membrane potential and the stimuli that are known to activate TREK-2 channels, such as temperature or membrane stretching. The aim of this study was to discover what factors are involved in high levels of TREK-2-like channel activity in these cells. Our research focused on the PI(4,5)P2-dependent mechanism of channel activity. Single-channel patch clamp recordings were performed on freshly dissociated pyramidal neurons of rat prefrontal cortexes in both the cell-attached and inside-out configurations. To evaluate the role of endogenous stimulants, the activity of the channels was recorded in the presence of a PI(4,5)P2 analogue (PI(4,5)P2DiC8) and Ca2+. Our research revealed that calcium ions are an important factor affecting TREK-2-like channel activity and kinetics. The observation that calcium participates in the activation of TREK-2-like channels is a new finding. We showed that PI(4,5)P2-dependent TREK-2 activity occurs when the conditions for PI(4,5)P2/Ca2+ nanocluster formation are met. We present a possible model explaining the mechanism of calcium action.
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Rueda-Ruzafa L, Herrera-Pérez S, Campos-Ríos A, Lamas JA. Are TREK Channels Temperature Sensors? Front Cell Neurosci 2021; 15:744702. [PMID: 34690704 PMCID: PMC8526543 DOI: 10.3389/fncel.2021.744702] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2021] [Accepted: 09/08/2021] [Indexed: 11/17/2022] Open
Abstract
Internal human body normal temperature fluctuates between 36.5 and 37.5°C and it is generally measured in the oral cavity. Interestingly, most electrophysiological studies on the functioning of ion channels and their role in neuronal behavior are carried out at room temperature, which usually oscillates between 22 and 24°C, even when thermosensitive channels are studied. We very often forget that if the core of the body reached that temperature, the probability of death from cardiorespiratory arrest would be extremely high. Does this mean that we are studying ion channels in dying neurons? Thousands of electrophysiological experiments carried out at these low temperatures suggest that most neurons tolerate this aggression quite well, at least for the duration of the experiments. This also seems to happen with ion channels, although studies at different temperatures indicate large changes in both, neuron and channel behavior. It is known that many chemical, physical and therefore physiological processes, depend to a great extent on body temperature. Temperature clearly affects the kinetics of numerous events such as chemical reactions or conformational changes in proteins but, what if these proteins constitute ion channels and these channels are specifically designed to detect changes in temperature? In this review, we discuss the importance of the potassium channels of the TREK subfamily, belonging to the recently discovered family of two-pore domain channels, in the transduction of thermal sensitivity in different cell types.
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Affiliation(s)
- Lola Rueda-Ruzafa
- CINBIO, Laboratory of Neuroscience, University of Vigo, Vigo, Spain.,Laboratory of Neuroscience, Galicia Sur Health Research Institute (IISGS), Vigo, Spain
| | - Salvador Herrera-Pérez
- CINBIO, Laboratory of Neuroscience, University of Vigo, Vigo, Spain.,Grupo de Neurofisiología Experimental y Circuitos Neuronales, Hospital Nacional de Parapléjicos, SESCAM, Toledo, Spain
| | - Ana Campos-Ríos
- CINBIO, Laboratory of Neuroscience, University of Vigo, Vigo, Spain.,Laboratory of Neuroscience, Galicia Sur Health Research Institute (IISGS), Vigo, Spain
| | - J A Lamas
- CINBIO, Laboratory of Neuroscience, University of Vigo, Vigo, Spain.,Laboratory of Neuroscience, Galicia Sur Health Research Institute (IISGS), Vigo, Spain
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Zhou M, Du Y, Aten S, Terman D. On the electrical passivity of astrocyte potassium conductance. J Neurophysiol 2021; 126:1403-1419. [PMID: 34525325 DOI: 10.1152/jn.00330.2021] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Predominant expression of leak-type K+ channels provides astrocytes a high membrane permeability to K+ ions and a hyperpolarized membrane potential that are crucial for astrocyte function in brain homeostasis. In functionally mature astrocytes, the expression of leak K+ channels creates a unique membrane K+ conductance that lacks voltage-dependent rectification. Accordingly, the conductance is named ohmic or passive K+ conductance. Several inwardly rectifying and two-pore domain K+ channels have been investigated for their contributions to passive conductance. Meanwhile, gap junctional coupling has been postulated to underlie the passive behavior of membrane conductance. It is now clear that the intrinsic properties of K+ channels and gap junctional coupling can each act alone or together to bring about a passive behavior of astrocyte conductance. Additionally, while the passive conductance can generally be viewed as a K+ conductance, the actual representation of this conductance is a combined expression of multiple known and unknown K+ channels, which has been further modified by the intricate morphology of individual astrocytes and syncytial gap junctional coupling. The expression of the inwardly rectifying K+ channels explains the inward-going component of passive conductance disobeying Goldman-Hodgkin-Katz constant field outward rectification. However, the K+ channels encoding the outward-going passive currents remain to be determined in the future. Here, we review our current understanding of ion channels and biophysical mechanisms engaged in the passive astrocyte K+ conductance, propose new studies to resolve this long-standing puzzle in astrocyte physiology, and discuss the functional implication(s) of passive behavior of K+ conductance on astrocyte physiology.
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Affiliation(s)
- Min Zhou
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, Ohio
| | - Yixing Du
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, Ohio
| | - Sydney Aten
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, Ohio
| | - David Terman
- Department of Mathematics, Ohio State University, Columbus, Ohio
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Méndez-González MP, Rivera-Aponte DE, Benedikt J, Maldonado-Martínez G, Tejeda-Bayron F, Skatchkov SN, Eaton MJ. Downregulation of Astrocytic Kir4.1 Potassium Channels Is Associated with Hippocampal Neuronal Hyperexcitability in Type 2 Diabetic Mice. Brain Sci 2020; 10:brainsci10020072. [PMID: 32019062 PMCID: PMC7071513 DOI: 10.3390/brainsci10020072] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2020] [Accepted: 01/22/2020] [Indexed: 11/16/2022] Open
Abstract
Epilepsy, characterized by recurrent seizures, affects 1% of the general population. Interestingly, 25% of diabetics develop seizures with a yet unknown mechanism. Hyperglycemia downregulates inwardly rectifying potassium channel 4.1 (Kir4.1) in cultured astrocytes. Therefore, the present study aims to determine if downregulation of functional astrocytic Kir4.1 channels occurs in brains of type 2 diabetic mice and could influence hippocampal neuronal hyperexcitability. Using whole-cell patch clamp recording in hippocampal brain slices from male mice, we determined the electrophysiological properties of stratum radiatum astrocytes and CA1 pyramidal neurons. In diabetic mice, astrocytic Kir4.1 channels were functionally downregulated as evidenced by multiple characteristics including depolarized membrane potential, reduced barium-sensitive Kir currents and impaired potassium uptake capabilities of hippocampal astrocytes. Furthermore, CA1 pyramidal neurons from diabetic mice displayed increased spontaneous activity: action potential frequency was ≈9 times higher in diabetic compared with non-diabetic mice and small EPSC event frequency was significantly higher in CA1 pyramidal cells of diabetics compared to non-diabetics. These differences were apparent in control conditions and largely pronounced in response to the pro-convulsant 4-aminopyridine. Our data suggest that astrocytic dysfunction due to downregulation of Kir4.1 channels may increase seizure susceptibility by impairing astrocytic ability to maintain proper extracellular homeostasis.
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Affiliation(s)
- Miguel P. Méndez-González
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR 00960-6032, USA; (M.P.M.-G.); (F.T.-B.)
- Department of Sciences and Technology, Antilles Adventist University, Mayaguez, PR 00680, USA
- Department of Natural Sciences, University of Puerto Rico, Aguadilla, PR 00604-6150, USA
| | - David E. Rivera-Aponte
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR 00960-6032, USA; (M.P.M.-G.); (F.T.-B.)
| | - Jan Benedikt
- Departments of Physiology and Biochemistry Universidad Central del Caribe, Bayamón, PR 00960-6032, USA;
| | | | - Flavia Tejeda-Bayron
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR 00960-6032, USA; (M.P.M.-G.); (F.T.-B.)
| | - Serguei N. Skatchkov
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR 00960-6032, USA; (M.P.M.-G.); (F.T.-B.)
- Departments of Physiology and Biochemistry Universidad Central del Caribe, Bayamón, PR 00960-6032, USA;
- Correspondence: (S.N.S.); (M.J.E.); Tel.: +787-798-3001 (ext. 2057) (S.N.S.); +787-798-3001 (ext. 2034) (M.J.E.); Fax: +787-786-6285 (M.J.E.)
| | - Misty J. Eaton
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR 00960-6032, USA; (M.P.M.-G.); (F.T.-B.)
- Correspondence: (S.N.S.); (M.J.E.); Tel.: +787-798-3001 (ext. 2057) (S.N.S.); +787-798-3001 (ext. 2034) (M.J.E.); Fax: +787-786-6285 (M.J.E.)
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7
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Lamas JA, Rueda-Ruzafa L, Herrera-Pérez S. Ion Channels and Thermosensitivity: TRP, TREK, or Both? Int J Mol Sci 2019; 20:ijms20102371. [PMID: 31091651 PMCID: PMC6566417 DOI: 10.3390/ijms20102371] [Citation(s) in RCA: 53] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2019] [Revised: 05/03/2019] [Accepted: 05/07/2019] [Indexed: 11/16/2022] Open
Abstract
Controlling body temperature is a matter of life or death for most animals, and in mammals the complex thermoregulatory system is comprised of thermoreceptors, thermosensors, and effectors. The activity of thermoreceptors and thermoeffectors has been studied for many years, yet only recently have we begun to obtain a clear picture of the thermosensors and the molecular mechanisms involved in thermosensory reception. An important step in this direction was the discovery of the thermosensitive transient receptor potential (TRP) cationic channels, some of which are activated by increases in temperature and others by a drop in temperature, potentially converting the cells in which they are expressed into heat and cold receptors. More recently, the TWIK-related potassium (TREK) channels were seen to be strongly activated by increases in temperature. Hence, in this review we want to assess the hypothesis that both these groups of channels can collaborate, possibly along with other channels, to generate the wide range of thermal sensations that the nervous system is capable of handling.
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Affiliation(s)
- J Antonio Lamas
- Laboratory of Neuroscience, Biomedical Research Center (CINBIO), University of Vigo, 36310 Vigo, Spain.
| | - Lola Rueda-Ruzafa
- Laboratory of Neuroscience, Biomedical Research Center (CINBIO), University of Vigo, 36310 Vigo, Spain.
| | - Salvador Herrera-Pérez
- Laboratory of Neuroscience, Biomedical Research Center (CINBIO), University of Vigo, 36310 Vigo, Spain.
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8
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Lamas JA, Fernández-Fernández D. Tandem pore TWIK-related potassium channels and neuroprotection. Neural Regen Res 2019; 14:1293-1308. [PMID: 30964046 PMCID: PMC6524494 DOI: 10.4103/1673-5374.253506] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
TWIK-related potassium channels (TREK) belong to a subfamily of the two-pore domain potassium channels family with three members, TREK1, TREK2 and TWIK-related arachidonic acid-activated potassium channels. The two-pore domain potassium channels is the last big family of channels being discovered, therefore it is not surprising that most of the information we know about TREK channels predominantly comes from the study of heterologously expressed channels. Notwithstanding, in this review we pay special attention to the limited amount of information available on native TREK-like channels and real neurons in relation to neuroprotection. Mainly we focus on the role of free fatty acids, lysophospholipids and other neuroprotective agents like riluzole in the modulation of TREK channels, emphasizing on how important this modulation may be for the development of new therapies against neuropathic pain, depression, schizophrenia, epilepsy, ischemia and cardiac complications.
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Affiliation(s)
- J Antonio Lamas
- Laboratory of Neuroscience, Biomedical Research Center (CINBIO), University of Vigo, Vigo, Galicia, Spain
| | - Diego Fernández-Fernández
- Laboratory of Neuroscience, Biomedical Research Center (CINBIO), University of Vigo, Vigo, Galicia, Spain
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Zhao G, Yang L, Wang S, Cai M, Sun S, Dong H, Xiong L. TREK-2 Mediates the Neuroprotective Effect of Isoflurane Preconditioning Against Acute Cerebral Ischemia in the Rat. Rejuvenation Res 2018; 22:325-334. [PMID: 30412001 DOI: 10.1089/rej.2017.2039] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
It is known that preconditional treatment with volatile anesthetics can induce tolerance of the brain to stroke. A previous study demonstrated that the involvement of TREK-1, a two-pore domain K+ channel, in sevoflurane preconditioning induced neuroprotection against focal cerebral ischemia in rats. The present study testified whether TREK-2, another anesthetic-target K+ channel, is also associated with volatile anesthetic-induced neuroprotection, and further explored its potential mechanism. Rats preconditioned with isoflurane were subjected to 1.4vol% isoflurane plus 98% O2 (1.5 L/min) inhalation for 1 hour daily and continuing for 5 consecutive days. Then, these rats were subjected to middle cerebral artery occlusion (MCAO) as focal cerebral ischemia model. The expression of TWIK-related K+ channel 2 (TREK-2) was analyzed by western blotting and quantitative real-time RT-PCR, and its downstream signaling molecules, protein kinase C (PKC) alpha, extracellular signal-regulated kinase 1/2 (ERK1/2), and pERK1/2 were detected by western blotting also. Subsequently, the expression of TREK-2 was regulated by siRNA transfection in the brain to clarify its role in the neuroprotection of isoflurane preconditioning. Neurological scores, infarction volume, and TdT-mediated dUTP Nick-End Labeling (TUNEL) staining were examined to evaluate the outcomes. The impact of TREK-2 on the expression of its downstream signaling molecules was also examined for preliminary analysis of the possible mechanisms. Isoflurane preconditioning reduced the infarct volume, inhibited the cell apoptosis, and improved the neurological outcome in rats subjected to MCAO. These effects were parallel with the increase in TREK-2 protein and inhibition of the ERK1/2 phosphorylation. The downregulation of TREK-2 through siRNA could significantly attenuate the isoflurane preconditioning-induced neuroprotective effects. Isoflurane preconditioning-induced neuroprotective effects against ischemia-reperfusion injury are associated with the increase in TREK-2 channel activation. These effects depend on the attenuation of PKC alpha and inhibition of ERK1/2 phosphorylation. Results enrich our understanding on the mechanism of two-pore domain K+ channel in preconditioning-induced tolerance to focal cerebral ischemia.
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Affiliation(s)
- Guangchao Zhao
- 1Department of Anesthesiology and Perioperative Medicine, Xijing Hospital, Fourth Military Medical University, Xi'an, China
| | - LuJia Yang
- 2Department of Anesthesiology, Chinese PLA General Hospital, Beijing, China
| | - Shiquan Wang
- 1Department of Anesthesiology and Perioperative Medicine, Xijing Hospital, Fourth Military Medical University, Xi'an, China
| | - Min Cai
- 3Department of Psychiatry, Xijing Hospital, Fourth Military Medical University, Xi'an, China
| | - Sisi Sun
- 4The Medical Department of the Emergence Center of Xi'an, Xi'an, Shaanxi, China
| | - Hailong Dong
- 1Department of Anesthesiology and Perioperative Medicine, Xijing Hospital, Fourth Military Medical University, Xi'an, China
| | - Lize Xiong
- 1Department of Anesthesiology and Perioperative Medicine, Xijing Hospital, Fourth Military Medical University, Xi'an, China
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10
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Rivera-Pagán AF, Méndez-González MP, Rivera-Aponte DE, Malpica-Nieves CJ, Melnik-Martínez KV, Zayas-Santiago A, Maldonado-Martínez G, Shuba YM, Skatchkov SN, Eaton MJ. A-Kinase-Anchoring Protein (AKAP150) is expressed in Astrocytes and Upregulated in Response to Ischemia. Neuroscience 2018; 384:54-63. [PMID: 29800717 DOI: 10.1016/j.neuroscience.2018.05.019] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Revised: 05/11/2018] [Accepted: 05/14/2018] [Indexed: 10/16/2022]
Abstract
A-kinase-anchoring proteins, AKAPs, are scaffolding proteins that associate with kinases and phosphatases, and direct them to a specific submembrane site to coordinate signaling events. AKAP150, a rodent ortholog of human AKAP79, has been extensively studied in neurons, but very little is known about the localization and function of AKAP150 in astrocytes, the major cell type in brain. Thus, in this study, we assessed the localization of AKAP150 in astrocytes and elucidated its role during physiological and ischemic conditions. Herein, we demonstrate that AKAP150 is localized in astrocytes and is up-regulated during ischemia both in vitro and in vivo. Knock-down of AKAP150 by RNAi depolarizes the astrocytic membrane potential and substantially reduces by 80% the ability of astrocytes to take up extracellular potassium during ischemic conditions. Therefore, upregulation of AKAP150 during ischemia preserves potassium conductance and the associated hyperpolarized membrane potential of astrocytes; properties of astrocytes needed to maintain extracellular brain homeostasis. Taken together, these data suggest that AKAP150 may play a pivotal role in the neuroprotective mechanism of astrocytes during pathological conditions.
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Affiliation(s)
- Aixa F Rivera-Pagán
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR, United States
| | - Miguel P Méndez-González
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR, United States; University of Puerto Rico, Natural Sciences Department, Aguadilla, PR, United States
| | - David E Rivera-Aponte
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR, United States
| | | | | | - Astrid Zayas-Santiago
- Department of Pathology and Laboratory Medicine, Universidad Central del Caribe, Bayamón, PR, United States
| | | | - Yaroslav M Shuba
- Bogomoletz Institute of Physiology and International Center of Molecular Physiology of the National Academy of Sciences of Ukraine, Kiev, Ukraine
| | - Serguei N Skatchkov
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR, United States; Department of Physiology, Universidad Central del Caribe, Bayamón, PR, United States.
| | - Misty J Eaton
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR, United States.
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11
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Milton M, Smith PD. It's All about Timing: The Involvement of Kir4.1 Channel Regulation in Acute Ischemic Stroke Pathology. Front Cell Neurosci 2018; 12:36. [PMID: 29503609 PMCID: PMC5820340 DOI: 10.3389/fncel.2018.00036] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2017] [Accepted: 01/30/2018] [Indexed: 01/28/2023] Open
Abstract
An acute ischemic stroke is characterized by the presence of a blood clot that limits blood flow to the brain resulting in subsequent neuronal loss. Acute stroke threatens neuronal survival, which relies heavily upon proper function of astrocytes. Neurons are more susceptible to cell death when an astrocyte is unable to carry out its normal functions in supporting the neuron in the area affected by the stroke (Rossi et al., 2007; Takano et al., 2009). For example, under normal conditions, astrocytes initially swell in response to changes in extracellular osmotic pressure and then reduce their regulatory volume in response to volume-activated potassium (K+) and chloride channels (Vella et al., 2015). This astroglial swelling may be overwhelmed, under ischemic conditions, due to the increased levels of glutamate and extracellular K+ (Lai et al., 2014; Vella et al., 2015). The increase in extracellular K+ contributes to neuronal damage and loss through the initiation of harmful secondary cascades (Nwaobi et al., 2016). Reducing the amount of extracellular K+ could, in theory, limit or prevent neuronal damage and loss resulting in an improved prognosis for individuals following ischemic stroke. Kir4.1, an inwardly rectifying K+ channel, has demonstrated an ability to regulate the rapid reuptake of this ion to return the cell to basal levels allowing it to fire again in rapid transmission (Sibille et al., 2015). Despite growing interest in this area, the underlying mechanism suggesting that neuroprotection could occur through modification of the Kir4.1 channel's activity has yet to be described. The purpose of this review is to examine the current literature and propose potential underlying mechanisms involving Kir4.1, specially the mammalian target of rapamycin (mTOR) and/or autophagic pathways, in the pathogenesis of ischemic stroke. The hope is that this review will instigate further investigation of Kir4.1 as a modulator of stroke pathology.
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Affiliation(s)
| | - Patrice D. Smith
- Department of Neuroscience, Carleton University, Ottawa, ON, Canada
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12
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Woo J, Im SK, Chun H, Jung SY, Oh SJ, Choi N, Lee CJ, Hur EM. Functional Characterization of Resting and Adenovirus-Induced Reactive Astrocytes in Three-Dimensional Culture. Exp Neurobiol 2017; 26:158-167. [PMID: 28680301 PMCID: PMC5491584 DOI: 10.5607/en.2017.26.3.158] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2017] [Revised: 06/16/2017] [Accepted: 06/16/2017] [Indexed: 12/14/2022] Open
Abstract
Brain is a rich environment where neurons and glia interact with neighboring cells as well as extracellular matrix in three-dimensional (3D) space. Astrocytes, which are the most abundant cells in the mammalian brain, reside in 3D space and extend highly branched processes that form microdomains and contact synapses. It has been suggested that astrocytes cultured in 3D might be maintained in a less reactive state as compared to those growing in a traditional, two-dimensional (2D) monolayer culture. However, the functional characterization of the astrocytes in 3D culture has been lacking. Here we cocultured neurons and astrocytes in 3D and examined the morphological, molecular biological, and electrophysiological properties of the 3D-cultured hippocampal astrocytes. In our 3D neuron-astrocyte coculture, astrocytes showed a typical morphology of a small soma with many branches and exhibited a unique membrane property of passive conductance, more closely resembling their native in vivo counterparts. Moreover, we also induced reactive astrocytosis in culture by infecting with high-titer adenovirus to mimic pathophysiological conditions in vivo. Adenoviral infection induced morphological changes in astrocytes, increased passive conductance, and increased GABA content as well as tonic GABA release, which are characteristics of reactive gliosis. Together, our study presents a powerful in vitro model resembling both physiological and pathophysiological conditions in vivo, and thereby provides a versatile experimental tool for studying various neurological diseases that accompany reactive astrocytes.
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Affiliation(s)
- Junsung Woo
- Center for Neuroscience, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea.,Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea.,Center for Glia-Neuron Interaction, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea
| | - Sun-Kyoung Im
- Convergence Research Center for Diagnosis, Treatment and Care System of Dementia, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea
| | - Heejung Chun
- Center for Neuroscience, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea.,Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea
| | - Soon-Young Jung
- Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea
| | - Soo-Jin Oh
- Center for Neuroscience, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea.,Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea.,Center for Glia-Neuron Interaction, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea
| | - Nakwon Choi
- Center for Neuroscience, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea.,Division of Bio-Medical Science & Technology, KIST School, Korea University of Science and Technology, Seoul 02792, Korea
| | - C Justin Lee
- Center for Neuroscience, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea.,Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea.,Center for Glia-Neuron Interaction, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea.,Department of Neuroscience, Division of Bio-Medical Science & Technology, KIST School, Korea University of Science and Technology, Seoul 02792, Korea
| | - Eun-Mi Hur
- Center for Neuroscience, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea.,Convergence Research Center for Diagnosis, Treatment and Care System of Dementia, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea.,Department of Neuroscience, Division of Bio-Medical Science & Technology, KIST School, Korea University of Science and Technology, Seoul 02792, Korea
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13
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Kinetic properties and adrenergic control of TREK-2-like channels in rat medial prefrontal cortex (mPFC) pyramidal neurons. Brain Res 2017; 1665:95-104. [PMID: 28438532 DOI: 10.1016/j.brainres.2017.04.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2016] [Revised: 03/03/2017] [Accepted: 04/14/2017] [Indexed: 02/01/2023]
Abstract
TREK-2-like channels were identified on the basis of electrophysiological and pharmacological tests performed on freshly isolated and enzymatically/mechanically dispersed pyramidal neurons of the rat medial prefrontal cortex (mPFC). Single-channel currents were recorded in cell-attached configuration and the impact of adrenergic receptors (α1, α2, β) stimulation on spontaneously appearing TREK-2-like channel activity was tested. The obtained results indicate that noradrenaline decreases the mean open probability of TREK-2-like channel currents by activation of β1 but not of α1- and α2-adrenergic receptors. Mean open time and channel conductance were not affected. The system of intracellular signaling pathways depends on the activation of protein kinase A. We also show that adrenergic control of TREK-2-like channel currents by adrenergic receptors was similar in pyramidal neurons isolated from young, adolescent, and adult rats. Immunofluorescent confocal scans of mPFC slices confirmed the presence of the TREK-2 protein, which was abundant in layer V pyramidal neurons. The role of TREK-2-like channel control by adrenergic receptors is discussed.
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14
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Haenisch S, von Rüden EL, Wahmkow H, Rettenbeck ML, Michler C, Russmann V, Bruckmueller H, Waetzig V, Cascorbi I, Potschka H. miRNA-187-3p-Mediated Regulation of the KCNK10/TREK-2 Potassium Channel in a Rat Epilepsy Model. ACS Chem Neurosci 2016; 7:1585-1594. [PMID: 27609046 DOI: 10.1021/acschemneuro.6b00222] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Regulatory RNAs play a key role in the regulation of protein expression patterns in neurological diseases. Here we studied the regulation of miRNAs in a chronic rat model of temporal lobe epilepsy. The analysis was focused on a putative link with pharmacoresponsiveness as well as the functional implications of the regulation of a selected miRNA. The findings did not reveal a difference in hippocampal miRNA expression between phenobarbital responders and nonresponders. However, when comparing rats following status epilepticus with control rats we identified 13 differentially expressed miRNAs with miRNA-187-3p being most strongly regulated. mRNAs encoding KCNK10/TREK-2 as well as DYRK2 were confirmed as targets of miRNA-187-3p. Expression of the potassium channel protein KCNK10/TREK-2 negatively correlated with hippocampal miRNA-187-3p expression and proved to be upregulated in the chronic phase of the epilepsy model. In conclusion, our data do not suggest a relevant impact of miRNA expression patterns on pharmacoresponsiveness. However, we confirmed regulation of miRNA-187-3p and demonstrated that it impacts the expression of the two-pore domain potassium channel protein KCNK10/TREK-2. Considering evidence from brain ischemia models, KCNK10/TREK-2 upregulation might serve a protective function with a beneficial impact on astrocytic potassium and glutamate homeostasis.
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Affiliation(s)
- Sierk Haenisch
- Institute of Experimental and Clinical Pharmacology, University Hospital Schleswig-Holstein , 24105 Campus Kiel, Germany
| | - Eva-Lotta von Rüden
- Institute of Pharmacology, Toxicology, and Pharmacy, Ludwig-Maximilians-University (LMU) , 80539 Munich, Germany
| | - Hannes Wahmkow
- Institute of Experimental and Clinical Pharmacology, University Hospital Schleswig-Holstein , 24105 Campus Kiel, Germany
| | - Maruja L Rettenbeck
- Institute of Pharmacology, Toxicology, and Pharmacy, Ludwig-Maximilians-University (LMU) , 80539 Munich, Germany
| | - Christina Michler
- Institute of Pharmacology, Toxicology, and Pharmacy, Ludwig-Maximilians-University (LMU) , 80539 Munich, Germany
| | - Vera Russmann
- Institute of Pharmacology, Toxicology, and Pharmacy, Ludwig-Maximilians-University (LMU) , 80539 Munich, Germany
| | - Henrike Bruckmueller
- Institute of Experimental and Clinical Pharmacology, University Hospital Schleswig-Holstein , 24105 Campus Kiel, Germany
| | - Vicki Waetzig
- Institute of Experimental and Clinical Pharmacology, University Hospital Schleswig-Holstein , 24105 Campus Kiel, Germany
| | - Ingolf Cascorbi
- Institute of Experimental and Clinical Pharmacology, University Hospital Schleswig-Holstein , 24105 Campus Kiel, Germany
| | - Heidrun Potschka
- Institute of Pharmacology, Toxicology, and Pharmacy, Ludwig-Maximilians-University (LMU) , 80539 Munich, Germany
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15
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Ryoo K, Park JY. Two-pore Domain Potassium Channels in Astrocytes. Exp Neurobiol 2016; 25:222-232. [PMID: 27790056 PMCID: PMC5081468 DOI: 10.5607/en.2016.25.5.222] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Revised: 09/01/2016] [Accepted: 09/15/2016] [Indexed: 12/23/2022] Open
Abstract
Two-pore domain potassium (K2P) channels have a distinct structure and channel properties, and are involved in a background K+ current. The 15 members of the K2P channels are identified and classified into six subfamilies on the basis of their sequence similarities. The activity of the channels is dynamically regulated by various physical, chemical, and biological effectors. The channels are expressed in a wide variety of tissues in mammals in an isoform specific manner, and play various roles in many physiological and pathophysiological conditions. To function as channels, the K2P channels form dimers, and some isoforms form heterodimers that provide diversity in channel properties. In the brain, TWIK1, TREK1, TREK2, TRAAK, TASK1, and TASK3 are predominantly expressed in various regions, including the cerebral cortex, dentate gyrus, CA1-CA3, and granular layer of the cerebellum. TWIK1, TREK1, and TASK1 are highly expressed in astrocytes, where they play specific cellular roles. Astrocytes keep leak K+ conductance, called the passive conductance, which mainly involves TWIK1-TREK1 heterodimeric channel. TWIK1 and TREK1 also mediate glutamate release from astrocytes in an exocytosis-independent manner. The expression of TREK1 and TREK2 in astrocytes increases under ischemic conditions, that enhance neuroprotection from ischemia. Accumulated evidence has indicated that astrocytes, together with neurons, are involved in brain function, with the K2P channels playing critical role in these astrocytes.
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Affiliation(s)
- Kanghyun Ryoo
- School of Biosystem and Biomedical Science, College of Health Science, Korea University, Seoul 02841, Korea
| | - Jae-Yong Park
- School of Biosystem and Biomedical Science, College of Health Science, Korea University, Seoul 02841, Korea
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16
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Skatchkov SN, Antonov SM, Eaton MJ. Glia and glial polyamines. Role in brain function in health and disease. BIOCHEMISTRY MOSCOW SUPPLEMENT SERIES A-MEMBRANE AND CELL BIOLOGY 2016. [DOI: 10.1134/s1990747816010116] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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Banerjee A, Ghatak S, Sikdar SK. l-Lactate mediates neuroprotection against ischaemia by increasing TREK1 channel expression in rat hippocampal astrocytes in vitro. J Neurochem 2016; 138:265-81. [PMID: 27062641 DOI: 10.1111/jnc.13638] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Revised: 04/04/2016] [Accepted: 04/04/2016] [Indexed: 12/20/2022]
Abstract
Brain ischaemia is a highly debilitating condition where shortage of oxygen and glucose leads to profuse cell death. Lactate is a neuroprotective metabolite whose concentrations increase up to 15-30 mmol/L during ischaemia and TREK1 is a neuroprotective potassium channel which is upregulated during ischaemia. The aim of this study was to investigate the effect of l-lactate on TREK1 expression and to evaluate the role of l-lactate-TREK1 interaction in conferring neuroprotection in ischaemia-prone hippocampus. We show that 15-30 mmol/L l-lactate increases functional TREK1 protein expression by 1.5-3-fold in hippocampal astrocytes using immunostaining and electrophysiology. Studies with transcription blocker actinomycin-D and quantitative PCR indicate that the increase in TREK1 expression is due to enhanced TREK1 mRNA transcription. We further report that l-lactate-mediated increase in TREK1 expression is via protein kinase A (PKA)-dependent pathway. This is the first report of an ischaemic metabolite affecting functional expression of an ion channel. Our studies in an in vitro model of ischaemia using oxygen glucose deprivation show that 30 mmol/L l-lactate fails to reduce cell death in rat hippocampal slices treated with TREK1 blockers, PKA inhibitors and gliotoxin. The above effects were specific to l-lactate as pyruvate failed to increase TREK1 expression and reduce cell death. l-Lactate-induced TREK1 upregulation is a novel finding of physiological significance as TREK1 channels contribute to neuroprotection by enhancing potassium buffering and glutamate clearance capacity of astrocytes. We propose that l-lactate promotes neuronal survival in hippocampus by increasing TREK1 channel expression via PKA pathway in astrocytes during ischaemia. Insufficient blood supply to the brain leads to cerebral ischaemia and increase in extracellular lactate concentrations. We incubated hippocampal astrocytes in lactate and observed increase in TREK1 channel expression via protein kinase A (PKA). Inhibition of TREK1, PKA and metabolic impairment of astrocytes prevented lactate from reducing cell death in ischaemic hippocampus. This pathway serves as an alternate mechanism of neuroprotection. Cover image for this issue: doi: 10.1111/jnc.13326.
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Affiliation(s)
- Aditi Banerjee
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, Karnataka, India
| | - Swagata Ghatak
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, Karnataka, India
| | - Sujit Kumar Sikdar
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, Karnataka, India
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18
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Ghatak S, Banerjee A, Sikdar SK. Ischaemic concentrations of lactate increase TREK1 channel activity by interacting with a single histidine residue in the carboxy terminal domain. J Physiol 2015; 594:59-81. [PMID: 26445100 DOI: 10.1113/jp270706] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2015] [Accepted: 09/21/2015] [Indexed: 02/01/2023] Open
Abstract
KEY POINTS The physiological metabolite, lactate and the two-pore domain leak potassium channel, TREK1 are known neuroprotectants against cerebral ischaemia. However, it is not known whether lactate interacts with TREK1 channel to provide neuroprotection. In this study we show that lactate increases TREK1 channel activity and hyperpolarizes CA1 stratum radiatum astrocytes in hippocampal slices. Lactate increases open probability and decreases longer close time of the human (h)TREK1 channel in a concentration dependent manner. Lactate interacts with histidine 328 (H328) in the carboxy terminal domain of hTREK1 channel to decrease its dwell time in the longer closed state. This interaction was dependent on the charge on H328. Lactate-insensitive mutant H328A hTREK1 showed pH sensitivity similar to wild-type hTREK1, indicating that the effect of lactate on hTREK1 is independent of pH change. A rise in lactate concentration and the leak potassium channel TREK1 have been independently associated with cerebral ischaemia. Recent literature suggests lactate to be neuroprotective and TREK1 knockout mice show an increased sensitivity to brain and spinal cord ischaemia; however, the connecting link between the two is missing. Therefore we hypothesized that lactate might interact with TREK1 channels. In the present study, we show that lactate at ischaemic concentrations (15-30 mm) at pH 7.4 increases TREK1 current in CA1 stratum radiatum astrocytes and causes membrane hyperpolarization. We confirm the intracellular action of lactate on TREK1 in hippocampal slices using monocarboxylate transporter blockers and at single channel level in cell-free inside-out membrane patches. The intracellular effect of lactate on TREK1 is specific since other monocarboxylates such as pyruvate and acetate at pH 7.4 failed to increase TREK1 current. Deletion and point mutation experiments suggest that lactate decreases the longer close dwell time incrementally with increase in lactate concentration by interacting with the histidine residue at position 328 (H328) in the carboxy terminal domain of the TREK1 channel. The interaction of lactate with H328 is dependent on the charge on the histidine residue since isosteric mutation of H328 to glutamine did not show an increase in TREK1 channel activity with lactate. This is the first demonstration of a direct effect of lactate on ion channel activity. The action of lactate on the TREK1 channel signifies a separate neuroprotective mechanism in ischaemia since it was found to be independent of the effect of acidic pH on channel activity.
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Affiliation(s)
- Swagata Ghatak
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, Karnataka, 560012, India
| | - Aditi Banerjee
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, Karnataka, 560012, India
| | - Sujit Kumar Sikdar
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, Karnataka, 560012, India
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19
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Rivera-Aponte DE, Méndez-González MP, Rivera-Pagán AF, Kucheryavykh YV, Kucheryavykh LY, Skatchkov SN, Eaton MJ. Hyperglycemia reduces functional expression of astrocytic Kir4.1 channels and glial glutamate uptake. Neuroscience 2015; 310:216-23. [PMID: 26404875 DOI: 10.1016/j.neuroscience.2015.09.044] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2015] [Revised: 09/11/2015] [Accepted: 09/18/2015] [Indexed: 11/24/2022]
Abstract
Diabetics are at risk for a number of serious health complications including an increased incidence of epilepsy and poorer recovery after ischemic stroke. Astrocytes play a critical role in protecting neurons by maintaining extracellular homeostasis and preventing neurotoxicity through glutamate uptake and potassium buffering. These functions are aided by the presence of potassium channels, such as Kir4.1 inwardly rectifying potassium channels, in the membranes of astrocytic glial cells. The purpose of the present study was to determine if hyperglycemia alters Kir4.1 potassium channel expression and homeostatic functions of astrocytes. We used q-PCR, Western blot, patch-clamp electrophysiology studying voltage and potassium step responses and a colorimetric glutamate clearance assay to assess Kir4.1 channel levels and homeostatic functions of rat astrocytes grown in normal and high glucose conditions. We found that astrocytes grown in high glucose (25 mM) had an approximately 50% reduction in Kir4.1 mRNA and protein expression as compared with those grown in normal glucose (5mM). These reductions occurred within 4-7 days of exposure to hyperglycemia, whereas reversal occurred between 7 and 14 days after return to normal glucose. The decrease in functional Kir channels in the astrocytic membrane was confirmed using barium to block Kir channels. In the presence of 100-μM barium, the currents recorded from astrocytes in response to voltage steps were reduced by 45%. Furthermore, inward currents induced by stepping extracellular [K(+)]o from 3 to 10mM (reflecting potassium uptake) were 50% reduced in astrocytes grown in high glucose. In addition, glutamate clearance by astrocytes grown in high glucose was significantly impaired. Taken together, our results suggest that down-regulation of astrocytic Kir4.1 channels by elevated glucose may contribute to the underlying pathophysiology of diabetes-induced CNS disorders and contribute to the poor prognosis after stroke.
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Affiliation(s)
- D E Rivera-Aponte
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR, USA.
| | - M P Méndez-González
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR, USA.
| | - A F Rivera-Pagán
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR, USA.
| | - Y V Kucheryavykh
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR, USA.
| | - L Y Kucheryavykh
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR, USA.
| | - S N Skatchkov
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR, USA; Department of Physiology, Universidad Central del Caribe, Bayamón, PR, USA.
| | - M J Eaton
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR, USA.
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20
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Rivera-Pagán AF, Rivera-Aponte DE, Melnik-Martínez KV, Zayas-Santiago A, Kucheryavykh LY, Martins AH, Cubano LA, Skatchkov SN, Eaton MJ. Up-regulation of TREK-2 potassium channels in cultured astrocytes requires de novo protein synthesis: relevance to localization of TREK-2 channels in astrocytes after transient cerebral ischemia. PLoS One 2015; 10:e0125195. [PMID: 25886567 PMCID: PMC4401746 DOI: 10.1371/journal.pone.0125195] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2014] [Accepted: 03/12/2015] [Indexed: 11/19/2022] Open
Abstract
Excitotoxicity due to glutamate receptor over-activation is one of the key mediators of neuronal death after an ischemic insult. Therefore, a major function of astrocytes is to maintain low extracellular levels of glutamate. The ability of astrocytic glutamate transporters to regulate the extracellular glutamate concentration depends upon the hyperpolarized membrane potential of astrocytes conferred by the presence of K+ channels in their membranes. We have previously shown that TREK-2 potassium channels in cultured astrocytes are up-regulated by ischemia and may support glutamate clearance by astrocytes during ischemia. Thus, herein we determine the mechanism leading to this up-regulation and assess the localization of TREK-2 channels in astrocytes after transient middle cerebral artery occlusion. By using a cell surface biotinylation assay we confirmed that functional TREK-2 protein is up-regulated in the astrocytic membrane after ischemic conditions. Using real time RT-PCR, we determined that the levels of TREK-2 mRNA were not increased in response to ischemic conditions. By using Western blot and a variety of protein synthesis inhibitors, we demonstrated that the increase of TREK-2 protein expression requires De novo protein synthesis, while protein degradation pathways do not contribute to TREK-2 up-regulation after ischemic conditions. Immunohistochemical studies revealed TREK-2 localization in astrocytes together with increased expression of the selective glial marker, glial fibrillary acidic protein, in brain 24 hours after transient middle cerebral occlusion. Our data indicate that functional TREK-2 channels are up-regulated in the astrocytic membrane during ischemia through a mechanism requiring De novo protein synthesis. This study provides important information about the mechanisms underlying TREK-2 regulation, which has profound implications in neurological diseases such as ischemia where astrocytes play an important role.
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Affiliation(s)
- Aixa F. Rivera-Pagán
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, Puerto Rico, United States of America
- * E-mail: (AFRP); (SNS)
| | - David E. Rivera-Aponte
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, Puerto Rico, United States of America
| | - Katya V. Melnik-Martínez
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, Puerto Rico, United States of America
| | - Astrid Zayas-Santiago
- Department of Physiology, Universidad Central del Caribe, Bayamón, Puerto Rico, United States of America
| | - Lilia Y. Kucheryavykh
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, Puerto Rico, United States of America
| | - Antonio H. Martins
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, Puerto Rico, United States of America
| | - Luis A. Cubano
- Departments of Anatomy and Cell Biology, Universidad Central del Caribe, Bayamón, Puerto Rico, United States of America
| | - Serguei N. Skatchkov
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, Puerto Rico, United States of America
- Department of Physiology, Universidad Central del Caribe, Bayamón, Puerto Rico, United States of America
- * E-mail: (AFRP); (SNS)
| | - Misty J. Eaton
- Department of Biochemistry, Universidad Central del Caribe, Bayamón, Puerto Rico, United States of America
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Abstract
This review focuses on the roles of glia and polyamines (PAs) in brain function and dysfunction, highlighting how PAs are one of the principal differences between glia and neurons. The novel role of PAs, such as putrescine, spermidine, and spermine and their precursors and derivatives, is discussed. However, PAs have not yet been a focus of much glial research. They affect many neuronal and glial receptors, channels, and transporters. They are therefore key elements in the development of many diseases and syndromes, thus forming the rationale for PA-focused and glia-focused therapy for these conditions.
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Affiliation(s)
- Serguei N Skatchkov
- Department of Biochemistry, School of Medicine, Universidad, Central del Caribe, PO Box 60-327, Bayamón, PR 00960-6032, USA; Department of Physiology, School of Medicine, Universidad, Central del Caribe, PO Box 60-327, Bayamón, PR 00960-6032, USA.
| | - Michel A Woodbury-Fariña
- Department of Psychiatry, University of Puerto Rico School of Medicine, 307 Calle Eleonor Roosevelt, San Juan, PR 00918-2720, USA
| | - Misty Eaton
- Department of Biochemistry, School of Medicine, Universidad, Central del Caribe, PO Box 60-327, Bayamón, PR 00960-6032, USA
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22
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Lujia Y, Xin L, Shiquan W, Yu C, Shuzhuo Z, Hong Z. Ceftriaxone pretreatment protects rats against cerebral ischemic injury by attenuating microglial activation-induced IL-1β expression. Int J Neurosci 2014; 124:657-65. [PMID: 24985046 DOI: 10.3109/00207454.2013.856009] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
BACKGROUND Although the neuroprotective effect of ceftriaxone (CTX) has been reported, the underlying mechanisms are still uncertain. In this study, we investigated if rats recover better from CTX pretreatment against cerebral ischemia by inhibiting the inflammatory response. METHODS Rats were pretreated with CTX (200 mg/kg, 1/day, i.p.) for 5 d. At 24 h after the end of the last CTX pretreatment, focal cerebral ischemia was induced by middle cerebral artery occlusion (MCAO) for 120 min in male Sprague Dawley rats. The neurological deficit scores (NDS) and infarct volumes were evaluated. Microglia cells were observed by immunofluorescence staining and IL-1β was assayed by ELISA and Western Blot. RESULTS The results showed that CTX pretreatment improved the neurological deficit scores and decreased the infarct volumes 24 h after reperfusion. The activation of microglia cells was reduced and the expression of IL-1β was partially inhibited 24 h after reperfusion. CONCLUSION These findings demonstrate that CTX pretreatment may provide a neuroprotective effect against transient cerebral ischemic injury, partially inhibit in microglial activation and reduce the expression of IL-1β.
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Affiliation(s)
- Yang Lujia
- 1Department of Anesthesiology, Chinese PLA General Hospital , Beijing , China
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23
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Honsa P, Pivonkova H, Harantova L, Butenko O, Kriska J, Dzamba D, Rusnakova V, Valihrach L, Kubista M, Anderova M. Increased expression of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels in reactive astrocytes following ischemia. Glia 2014; 62:2004-21. [PMID: 25042871 DOI: 10.1002/glia.22721] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Revised: 07/01/2014] [Accepted: 07/02/2014] [Indexed: 12/12/2022]
Abstract
Astrocytes respond to ischemic brain injury by proliferation, the increased expression of intermediate filaments and hypertrophy, which results in glial scar formation. In addition, they alter the expression of ion channels, receptors and transporters that maintain ionic/neurotransmitter homeostasis. Here, we aimed to demonstrate the expression of Hcn1-4 genes encoding hyperpolarization-activated cyclic nucleotide-gated (HCN) channels in reactive astrocytes following focal cerebral ischemia (FCI) or global cerebral ischemia (GCI) and to characterize their functional properties. A permanent occlusion of the middle cerebral artery (MCAo) was employed to induce FCI in adult GFAP/EGFP mice, while GCI was induced by transient bilateral common carotid artery occlusion combined with hypoxia in adult rats. Using FACS, we isolated astrocytes from non-injured or ischemic brains and performed gene expression profiling using single-cell RT-qPCR. We showed that 2 weeks after ischemia reactive astrocytes express high levels of Hcn1-4 transcripts, while immunohistochemical analyses confirmed the presence of HCN1-3 channels in reactive astrocytes 5 weeks after ischemia. Electrophysiological recordings revealed that post-ischemic astrocytes are significantly depolarized, and compared with astrocytes from non-injured brains, they display large hyperpolarization-activated inward currents, the density of which increased 2-3-fold in response to ischemia. Their activation was facilitated by cAMP and their amplitudes were decreased by ZD7288 or low extracellular Na(+) concentration, suggesting that they may belong to the family of HCN channels. Collectively, our results demonstrate that regardless of the type of ischemic injury, reactive astrocytes express HCN channels, which could therefore be an important therapeutic target in poststroke therapy.
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Affiliation(s)
- Pavel Honsa
- Department of Cellular Neurophysiology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague 4, 14220, Czech Republic
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Lu L, Wang W, Peng Y, Li J, Wang L, Wang X. Electrophysiology and pharmacology of tandem domain potassium channel TREK-1 related BDNF synthesis in rat astrocytes. Naunyn Schmiedebergs Arch Pharmacol 2014; 387:303-12. [PMID: 24402080 DOI: 10.1007/s00210-013-0952-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2013] [Accepted: 12/18/2013] [Indexed: 01/06/2023]
Abstract
In the present study, the functional properties and pharmacology of two-pore domain potassium channel (K2P) TREK-1 in primary cultured rat brain astrocytes were investigated. Western blot, patch clamping techniques, and ELISA were used to detect the distribution and function of TREK-1 as well as the expression of brain-derived neurotrophic factor (BDNF) on the primary cultured astrocytes. It was shown that TREK-1 protein expressed in astrocytes was 2.4-fold higher than it was expressed in microglia. Single channel recording via patch clamping showed that the TREK-1 outward currents in astrocytes could be activated by arachidonic acid (AA) or chloroform with the conductance of 113 ± 14 and 120 ± 13 pS, respectively. The current was also sensitive to mechanical stretch and intracellular acidification. Negative pressure (-30 cm H2O) and acidification of intracellular solution (pH 6.8 or 6.3) both enhanced TREK-1 channel open probability significantly. Further pharmacological studies showed that TREK-1 antagonist penfluridol inhibited AA-induced currents, and both penfluridol and methionine (TREK-1 blockers) significantly increased BDNF level in astrocytes by 50 %. These results indicated that TREK-1 channel current was a major component of K2P currents in astrocytes. TREK-1 channels might play important roles in regulating the function of astrocytes and might be used as a drug target for neuroprotection.
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Affiliation(s)
- Li Lu
- State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Institute of Materia Medica, Chinese Academy of Medical Sciences and Peking Union Medical College, No. 1 Xiannongtan Street, Xicheng District, Beijing, 100050, China
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Minieri L, Pivonkova H, Caprini M, Harantova L, Anderova M, Ferroni S. The inhibitor of volume-regulated anion channels DCPIB activates TREK potassium channels in cultured astrocytes. Br J Pharmacol 2013; 168:1240-54. [PMID: 23072356 DOI: 10.1111/bph.12011] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2012] [Revised: 09/10/2012] [Accepted: 09/28/2012] [Indexed: 10/27/2022] Open
Abstract
BACKGROUND AND PURPOSE The ethacrynic acid derivative, 4-(2-butyl-6,7-dichlor-2-cyclopentylindan-1-on-5-yl) oxobutyric acid (DCPIB) is considered to be a specific and potent inhibitor of volume-regulated anion channels (VRACs). In the CNS, DCPIB was shown to be neuroprotective through mechanisms principally associated to its action on VRACs. We hypothesized that DCPIB could also regulate the activity of other astroglial channels involved in cell volume homeostasis. EXPERIMENTAL APPROACH Experiments were performed in rat cortical astrocytes in primary culture and in hippocampal astrocytes in situ. The effect of DCPIB was evaluated by patch-clamp electrophysiology and immunocytochemical techniques. Results were verified by comparative analysis with recombinant channels expressed in COS-7 cells. KEY RESULTS In cultured astrocytes, DCPIB promoted the activation of a K(+) conductance mediated by two-pore-domain K(+) (K(2P) ) channels. The DCPIB effect occluded that of arachidonic acid, which activates K(2P) channels K(2P) 2.1 (TREK-1) and K(2P) 10.1 (TREK-2) in cultured astrocytes. Immunocytochemical analysis suggests that cultured astrocytes express K(2P) 2.1 and K(2P) 10.1 proteins. Moreover, DCPIB opened recombinant K(2P) 2.1 and K(2P) 10.1 expressed in heterologous system. In brain slices, DCPIB did not augment the large background K(+) conductance in hippocampal astrocytes, but caused an increment in basal K(+) current of neurons. CONCLUSION AND IMPLICATIONS Our results indicate that the neuroprotective effect of DCPIB could be due, at least in part, to activation of TREK channels. DCPIB could be used as template to build new pharmacological tools able to increase background K(+) conductance in astroglia and neuronal cells.
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Affiliation(s)
- L Minieri
- Department of Human and General Physiology, University of Bologna, Bologna, Italy
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Mirkovic K, Palmersheim J, Lesage F, Wickman K. Behavioral characterization of mice lacking Trek channels. Front Behav Neurosci 2012; 6:60. [PMID: 22973213 PMCID: PMC3435516 DOI: 10.3389/fnbeh.2012.00060] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2012] [Accepted: 08/23/2012] [Indexed: 11/26/2022] Open
Abstract
Two-pore domain K+ (K2P) channels are thought to underlie background K+ conductance in many cell types. The Trek subfamily of K2P channels consists of three members, Trek1/Kcnk2, Trek2/Kcnk10, and Traak/Kcnk4, all three of which are expressed in the rodent CNS. Constitutive ablation of the Trek1 gene in mice correlates with enhanced sensitivity to ischemia and epilepsy, decreased sensitivity to the effects of inhaled anesthetics, increased sensitivity to thermal and mechanical pain, and resistance to depression. While the distribution of Trek2 mRNA in the CNS is broad, little is known about the relevance of this Trek family member to neurobiology and behavior. Here, we probed the effect of constitutive Trek2 ablation, as well as the simultaneous constitutive ablation of all three Trek family genes, in paradigms that assess motor activity, coordination, anxiety-related behavior, learning and memory, and drug-induced reward-related behavior. No differences were observed between Trek2−/− and Trek1/2/Traak−/− mice in coordination or total distance traveled in an open-field. A gender-dependent impact of Trek ablation on open-field anxiety-related behavior was observed, as female but not male Trek2−/− and Trek1/2/Traak−/− mice spent more time in, and made a greater number of entries into, the center of the open-field than wild-type counterparts. Further evaluation of anxiety-related behavior in the elevated plus maze and light/dark box, however, did not reveal a significant influence of genotype on performance for either gender. Furthermore, Trek−/− mice behaved normally in tests of learning and memory, including contextual fear conditioning and novel object recognition, and with respect to opioid-induced motor stimulation and conditioned place preference (CPP). Collectively, these data argue that despite their broad distribution in the CNS, Trek channels exert a minimal influence on a wide-range of behaviors.
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Affiliation(s)
- Kelsey Mirkovic
- Department of Pharmacology, University of Minnesota Minneapolis, MN, USA
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Wu X, Liu Y, Chen X, Sun Q, Tang R, Wang W, Yu Z, Xie M. Involvement of TREK-1 Activity in Astrocyte Function and Neuroprotection Under Simulated Ischemia Conditions. J Mol Neurosci 2012; 49:499-506. [DOI: 10.1007/s12031-012-9875-5] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2012] [Accepted: 08/08/2012] [Indexed: 10/28/2022]
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Benesova J, Rusnakova V, Honsa P, Pivonkova H, Dzamba D, Kubista M, Anderova M. Distinct expression/function of potassium and chloride channels contributes to the diverse volume regulation in cortical astrocytes of GFAP/EGFP mice. PLoS One 2012; 7:e29725. [PMID: 22253765 PMCID: PMC3256164 DOI: 10.1371/journal.pone.0029725] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2011] [Accepted: 12/02/2011] [Indexed: 11/19/2022] Open
Abstract
Recently, we have identified two astrocytic subpopulations in the cortex of GFAP-EGFP mice, in which the astrocytes are visualized by the enhanced green-fluorescent protein (EGFP) under the control of the human glial fibrillary acidic protein (GFAP) promotor. These astrocytic subpopulations, termed high response- (HR-) and low response- (LR-) astrocytes, differed in the extent of their swelling during oxygen-glucose deprivation (OGD). In the present study we focused on identifying the ion channels or transporters that might underlie the different capabilities of these two astrocytic subpopulations to regulate their volume during OGD. Using three-dimensional confocal morphometry, which enables quantification of the total astrocytic volume, the effects of selected inhibitors of K⁺ and Cl⁻ channels/transporters or glutamate transporters on astrocyte volume changes were determined during 20 minute-OGD in situ. The inhibition of volume regulated anion channels (VRACs) and two-pore domain potassium channels (K(2P)) highlighted their distinct contributions to volume regulation in HR-/LR-astrocytes. While the inhibition of VRACs or K(2P) channels revealed their contribution to the swelling of HR-astrocytes, in LR-astrocytes they were both involved in anion/K⁺ effluxes. Additionally, the inhibition of Na⁺-K⁺-Cl⁻ co-transporters in HR-astrocytes led to a reduction of cell swelling, but it had no effect on LR-astrocyte volume. Moreover, employing real-time single-cell quantitative polymerase chain reaction (PCR), we characterized the expression profiles of EGFP-positive astrocytes with a focus on those ion channels and transporters participating in astrocyte swelling and volume regulation. The PCR data revealed the existence of two astrocytic subpopulations markedly differing in their gene expression levels for inwardly rectifying K⁺ channels (Kir4.1), K(2P) channels (TREK-1 and TWIK-1) and Cl⁻ channels (ClC2). Thus, we propose that the diverse volume changes displayed by cortical astrocytes during OGD mainly result from their distinct expression patterns of ClC2 and K(2P) channels.
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Affiliation(s)
- Jana Benesova
- Department of Cellular Neurophysiology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic
- Second Medical Faculty, Charles University, Prague, Czech Republic
| | - Vendula Rusnakova
- Laboratory of Gene Expression, Institute of Biotechnology, Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Pavel Honsa
- Department of Cellular Neurophysiology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic
- Second Medical Faculty, Charles University, Prague, Czech Republic
| | - Helena Pivonkova
- Department of Cellular Neurophysiology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic
- Second Medical Faculty, Charles University, Prague, Czech Republic
| | - David Dzamba
- Department of Cellular Neurophysiology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic
- Second Medical Faculty, Charles University, Prague, Czech Republic
| | - Mikael Kubista
- Laboratory of Gene Expression, Institute of Biotechnology, Academy of Sciences of the Czech Republic, Prague, Czech Republic
- TATAA Biocenter, Gothenburg, Sweden
| | - Miroslava Anderova
- Department of Cellular Neurophysiology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic
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Activation of TREK currents by the neuroprotective agent riluzole in mouse sympathetic neurons. J Neurosci 2011; 31:1375-85. [PMID: 21273422 DOI: 10.1523/jneurosci.2791-10.2011] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Background K2P channels play a key role in stabilizing the resting membrane potential, thereby modulating cell excitability in the central and peripheral somatic nervous system. Whole-cell experiments revealed a riluzole-activated current (I(RIL)), transported by potassium, in mouse superior cervical ganglion (mSCG) neurons. The activation of this current by riluzole, linoleic acid, membrane stretch, and internal acidification, its open rectification and insensitivity to most classic potassium channel blockers, indicated that I(RIL) flows through channels of the TREK [two-pore domain weak inwardly rectifying K channel (TWIK)-related K channel] subfamily. Whole-ganglia and single-cell reverse transcription-PCR demonstrated the presence of TREK-1, TREK-2, and TRAAK (TWIK-related arachidonic acid-activated K(+) channel) mRNA, and the expression of these three proteins was confirmed by immunocytochemistry in mSCG neurons. I(RIL) was enhanced by zinc, inhibited by barium and fluoxetine, but unaffected by quinine and ruthenium red, strongly suggesting that it was carried through TREK-1/2 channels. Consistently, a channel with properties identical with the heterologously expressed TREK-2 was recorded in most (75%) cell-attached patches. These results provide the first evidence for the expression of K2P channels in the mammalian autonomic nervous system, and they extend the impact of these channels to the entire nervous system.
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Sala-Rabanal M, Kucheryavykh LY, Skatchkov SN, Eaton MJ, Nichols CG. Molecular mechanisms of EAST/SeSAME syndrome mutations in Kir4.1 (KCNJ10). J Biol Chem 2010; 285:36040-8. [PMID: 20807765 PMCID: PMC2975226 DOI: 10.1074/jbc.m110.163170] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2010] [Revised: 08/27/2010] [Indexed: 11/06/2022] Open
Abstract
Inwardly rectifying potassium channel Kir4.1 is critical for glial function, control of neuronal excitability, and systemic K(+) homeostasis. Novel mutations in Kir4.1 have been associated with EAST/SeSAME syndrome, characterized by mental retardation, ataxia, seizures, hearing loss, and renal salt waste. Patients are homozygous for R65P, G77R, C140R or T164I; or compound heterozygous for A167V/R297C or R65P/R199Stop, a deletion of the C-terminal half of the protein. We investigated the functional significance of these mutations by radiotracer efflux and inside-out membrane patch clamping in COSm6 cells expressing homomeric Kir4.1 or heteromeric Kir4.1/Kir5.1 channels. All of the mutations compromised channel function, but the underlying mechanisms were different. R65P, T164I, and R297C caused an alkaline shift in pH sensitivity, indicating that these positions are crucial for pH sensing and pore gating. In R297C, this was due to disruption of intersubunit salt bridge Glu(288)-Arg(297). C140R breaks the Cys(108)-Cys(140) disulfide bond essential for protein folding and function. A167V did not affect channel properties but may contribute to decreased surface expression in A167V/R297C. In G77R, introduction of a positive charge within the bilayer may affect channel structure or gating. R199Stop led to a dramatic decrease in surface expression, but channel activity was restored by co-expression with intact subunits, suggesting remarkable tolerance for truncation of the cytoplasmic domain. These results provide an explanation for the molecular defects that underlie the EAST/SeSAME syndrome.
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Affiliation(s)
- Monica Sala-Rabanal
- Department of Cell Biology and Physiology, Washington University, St Louis, Missouri 63110, USA.
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31
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Es-Salah-Lamoureux Z, Steele DF, Fedida D. Research into the therapeutic roles of two-pore-domain potassium channels. Trends Pharmacol Sci 2010; 31:587-95. [PMID: 20951446 DOI: 10.1016/j.tips.2010.09.001] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2010] [Revised: 09/04/2010] [Accepted: 09/07/2010] [Indexed: 12/27/2022]
Abstract
The K(2P) potassium channels are responsible for the background conductance observed in several tissues. Their ubiquitous localization and thus their potential implications in diseases have led to increased research on these channels over the last few years. In this review, we outline different aspects of the research on K(2P) channels and highlight some of the latest discoveries in this area. We focus on research into K(2P) channels as potential therapeutic targets in ischemia/hypoxia, depression, memory disorders, pain, cardiovascular disease and disorders of the immune system. We address the challenge of developing novel pharmacological compounds to target these channels. We also discuss the regulation of expression of the K(2P) gene in health and disease, as well as the value of assessing the expression of K(2P) channels as potential biomarkers of disease.
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Affiliation(s)
- Zeineb Es-Salah-Lamoureux
- Department of Anesthesiology Pharmacology and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
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32
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Inyushin M, Kucheryavykh LY, Kucheryavykh YV, Nichols CG, Buono RJ, Ferraro TN, Skatchkov SN, Eaton MJ. Potassium channel activity and glutamate uptake are impaired in astrocytes of seizure-susceptible DBA/2 mice. Epilepsia 2010; 51:1707-13. [PMID: 20831751 DOI: 10.1111/j.1528-1167.2010.02592.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
PURPOSE KCNJ10 encodes subunits of inward rectifying potassium (Kir) channel Kir4.1 found predominantly in glial cells within the brain. Genetic inactivation of these channels in glia impairs extracellular K(+) and glutamate clearance and produces a seizure phenotype. In both mice and humans, polymorphisms and mutations in the KCNJ10 gene have been associated with seizure susceptibility. The purpose of the present study was to determine whether there are differences in Kir channel activity and potassium- and glutamate-buffering capabilities between astrocytes from seizure resistant C57BL/6 (B6) and seizure susceptible DBA/2 (D2) mice that are consistent with an altered K(+) channel activity as a result of genetic polymorphism of KCNJ10. METHODS Using cultured astrocytes and hippocampal brain slices together with whole-cell patch-clamp, we determined the electrophysiologic properties, particularly K(+) conductances, of B6 and D2 mouse astrocytes. Using a colorimetric assay, we determined glutamate clearance capacity by B6 and D2 astrocytes. RESULTS Barium-sensitive Kir currents elicited from B6 astrocytes are substantially larger than those elicited from D2 astrocytes. In addition, potassium and glutamate buffering by D2 cortical astrocytes is impaired, relative to buffering by B6 astrocytes. DISCUSSION In summary, the activity of Kir4.1 channels differs between seizure-susceptible D2 and seizure-resistant B6 mice. Reduced activity of Kir4.1 channels in astrocytes of D2 mice is associated with deficits in potassium and glutamate buffering. These deficits may, in part, explain the relatively low seizure threshold of D2 mice.
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Affiliation(s)
- Mikhail Inyushin
- Department of Physiology, Universidad Central del Caribe, School of Medicine, Bayamón, Puerto Rico 00960-6032, USA
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