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Jonusaite S, Himmerkus N. Paracellular barriers: Advances in assessing their contribution to renal epithelial function. Comp Biochem Physiol A Mol Integr Physiol 2024; 298:111741. [PMID: 39276851 DOI: 10.1016/j.cbpa.2024.111741] [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: 08/14/2024] [Revised: 09/10/2024] [Accepted: 09/10/2024] [Indexed: 09/17/2024]
Abstract
Regulation of salt and water balance occupies a dominant role in the physiology of many animals and often relies on the function of the renal system. In the mammalian kidney, epithelial ion and water transport requires high degree of coordination between the transcellular and paracellular pathways, the latter being defined by the intercellular tight junctions (TJs). TJs seal the paracellular pathway in a highly specialized manner, either by forming a barrier against the passage of solutes and/or water or by allowing the passage of ions and/or water through them. This functional TJ plasticity is now known to be provided by the members of the claudin family of tetraspan proteins. Unlike mammalian nephron, the renal structures of insects, the Malpighian tubules, lack TJs and instead have smooth septate junctions (sSJs) as paracellular barrier forming junctions. Many questions regarding the molecular and functional properties of sSJs remain open but research on model species have begun to inform our understanding. The goal of this commentary is to highlight key concepts and most recent findings that have emerged from the molecular and functional dissection of paracellular barriers in the mammalian and insect renal epithelia.
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Affiliation(s)
- Sima Jonusaite
- Institute of Physiology, Christian-Albrechts-University of Kiel, Hermann-Rodewald-Straße 5, 24118 Kiel, Germany.
| | - Nina Himmerkus
- Institute of Physiology, Christian-Albrechts-University of Kiel, Hermann-Rodewald-Straße 5, 24118 Kiel, Germany
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2
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Staruschenko A, Alexander RT, Caplan MJ, Ilatovskaya DV. Calcium signalling and transport in the kidney. Nat Rev Nephrol 2024; 20:541-555. [PMID: 38641658 DOI: 10.1038/s41581-024-00835-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/27/2024] [Indexed: 04/21/2024]
Abstract
The kidney plays a pivotal role in regulating calcium levels within the body. Approximately 98% of the filtered calcium is reabsorbed in the nephron, and this process is tightly controlled to maintain calcium homeostasis, which is required to facilitate optimal bone mineralization, preserve serum calcium levels within a narrow range, and support intracellular signalling mechanisms. The maintenance of these functions is attributed to a delicate balance achieved by various calcium channels, transporters, and calcium-binding proteins in renal cells. Perturbation of this balance due to deficiency or dysfunction of calcium channels and calcium-binding proteins can lead to severe complications. For example, polycystic kidney disease is linked to aberrant calcium transport and signalling. Furthermore, dysregulation of calcium levels can promote the formation of kidney stones. This Review provides an updated description of the key aspects of calcium handling in the kidney, focusing on the function of various calcium channels and the physiological stimuli that control these channels or are communicated through them. A discussion of the role of calcium as an intracellular second messenger and the pathophysiology of renal calcium dysregulation, as well as a summary of gaps in knowledge and future prospects, are also included.
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Affiliation(s)
- Alexander Staruschenko
- Department of Molecular Pharmacology and Physiology, University of South Florida, Tampa, FL, USA.
- Hypertension and Kidney Research Center, University of South Florida, Tampa, FL, USA.
- James A. Haley Veterans Hospital, Tampa, FL, USA.
| | - R Todd Alexander
- Department of Paediatrics, University of Alberta, Edmonton, AB, Canada
- Women's and Children's Health Institute, Edmonton, AB, Canada
| | - Michael J Caplan
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT, USA
| | - Daria V Ilatovskaya
- Department of Physiology, Medical College of Georgia, Augusta University, Augusta, GA, USA
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3
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Mak S, Hammes A. Canonical and Non-Canonical Localization of Tight Junction Proteins during Early Murine Cranial Development. Int J Mol Sci 2024; 25:1426. [PMID: 38338705 PMCID: PMC10855338 DOI: 10.3390/ijms25031426] [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: 12/13/2023] [Revised: 01/12/2024] [Accepted: 01/18/2024] [Indexed: 02/12/2024] Open
Abstract
This study investigates the intricate composition and spatial distribution of tight junction complex proteins during early mouse neurulation. The analyses focused on the cranial neural tube, which gives rise to all head structures. Neurulation brings about significant changes in the neuronal and non-neuronal ectoderm at a cellular and tissue level. During this process, precise coordination of both epithelial integrity and epithelial dynamics is essential for accurate tissue morphogenesis. Tight junctions are pivotal for epithelial integrity, yet their complex composition in this context remains poorly understood. Our examination of various tight junction proteins in the forebrain region of mouse embryos revealed distinct patterns in the neuronal and non-neuronal ectoderm, as well as mesoderm-derived mesenchymal cells. While claudin-4 exhibited exclusive expression in the non-neuronal ectoderm, we demonstrated a neuronal ectoderm specific localization for claudin-12 in the developing cranial neural tube. Claudin-5 was uniquely present in mesenchymal cells. Regarding the subcellular localization, canonical tight junction localization in the apical junctions was predominant for most tight junction complex proteins. ZO-1 (zona occludens protein-1), claudin-1, claudin-4, claudin-12, and occludin were detected at the apical junction. However, claudin-1 and occludin also appeared in basolateral domains. Intriguingly, claudin-3 displayed a non-canonical localization, overlapping with a nuclear lamina marker. These findings highlight the diverse tissue and subcellular distribution of tight junction proteins and emphasize the need for their precise regulation during the dynamic processes of forebrain development. The study can thereby contribute to a better understanding of the role of tight junction complex proteins in forebrain development.
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Affiliation(s)
- Shermin Mak
- Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association (MDC), 13125 Berlin, Germany;
- Institute for Biology, Free University of Berlin, 14159 Berlin, Germany
| | - Annette Hammes
- Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association (MDC), 13125 Berlin, Germany;
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4
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Abstract
Sequential expression of claudins, a family of tight junction proteins, along the nephron mirrors the sequential expression of ion channels and transporters. Only by the interplay of transcellular and paracellular transport can the kidney efficiently maintain electrolyte and water homeostasis in an organism. Although channel and transporter defects have long been known to perturb homeostasis, the contribution of individual tight junction proteins has been less clear. Over the past two decades, the regulation and dysregulation of claudins have been intensively studied in the gastrointestinal tract. Claudin expression patterns have, for instance, been found to be affected in infection and inflammation, or in cancer. In the kidney, a deeper understanding of the causes as well as the effects of claudin expression alterations is only just emerging. Little is known about hormonal control of the paracellular pathway along the nephron, effects of cytokines on renal claudin expression or relevance of changes in paracellular permeability to the outcome in any of the major kidney diseases. By summarizing current findings on the role of specific claudins in maintaining electrolyte and water homeostasis, this Review aims to stimulate investigations on claudins as prognostic markers or as druggable targets in kidney disease.
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Affiliation(s)
- Luca Meoli
- Clinical Physiology/Nutritional Medicine, Medical Department, Division of Gastroenterology, Infectiology, Rheumatology, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Dorothee Günzel
- Clinical Physiology/Nutritional Medicine, Medical Department, Division of Gastroenterology, Infectiology, Rheumatology, Charité - Universitätsmedizin Berlin, Berlin, Germany.
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5
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Nyimanu D, Behm C, Choudhury S, Yu ASL. The role of claudin-2 in kidney function and dysfunction. Biochem Soc Trans 2023; 51:1437-1445. [PMID: 37387353 DOI: 10.1042/bst20220639] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2023] [Revised: 06/19/2023] [Accepted: 06/22/2023] [Indexed: 07/01/2023]
Abstract
Claudin-2 is a tight junction protein expressed in leaky epithelia where it forms paracellular pores permeable to cations and water. The paracellular pore formed by claudin-2 is important in energy-efficient cation and water transport in the proximal tubules of the kidneys. Mounting evidence now suggests that claudin-2 may modulate cellular processes often altered in disease, including cellular proliferation. Also, dysregulation of claudin-2 expression has been linked to various diseases, including kidney stone disease and renal cell carcinoma. However, the mechanisms linking altered claudin-2 expression and function to disease are poorly understood and require further investigation. The aim of this review is to discuss the current understanding of the role of claudin-2 in kidney function and dysfunction. We provide a general overview of the claudins and their organization in the tight junction, the expression, and function of claudin-2 in the kidney, and the evolving evidence for its role in kidney disease.
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Affiliation(s)
- Duuamene Nyimanu
- The Jared Grantham Kidney Institute, University of Kansas Medical Center, 3901 Rainbow Blvd, Kansas City, KS 66160, U.S.A
| | - Christine Behm
- The Jared Grantham Kidney Institute, University of Kansas Medical Center, 3901 Rainbow Blvd, Kansas City, KS 66160, U.S.A
| | - Sonali Choudhury
- The Jared Grantham Kidney Institute, University of Kansas Medical Center, 3901 Rainbow Blvd, Kansas City, KS 66160, U.S.A
| | - Alan S L Yu
- The Jared Grantham Kidney Institute, University of Kansas Medical Center, 3901 Rainbow Blvd, Kansas City, KS 66160, U.S.A
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Wang T, Liu T, Xu S, Frindt G, Weinstein AM, Palmer LG. High dietary K + intake inhibits proximal tubule transport. Am J Physiol Renal Physiol 2023; 325:F224-F234. [PMID: 37318989 PMCID: PMC10396284 DOI: 10.1152/ajprenal.00013.2023] [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: 01/27/2023] [Revised: 05/15/2023] [Accepted: 06/14/2023] [Indexed: 06/17/2023] Open
Abstract
The impact of chronic dietary K+ loading on proximal tubule (PT) function was measured using free-flow micropuncture along with measurements of overall kidney function, including urine volume, glomerular filtration rate, and absolute and fractional Na+ and K+ excretion in the rat. Feeding animals a diet with 5% KCl [high K+ (HK)] for 7 days reduced glomerular filtration rate by 29%, increased urine volume by 77%, and increased absolute K+ excretion by 202% compared with rats on a 1% KCl [control K+ (CK)] diet. HK did not change absolute Na+ excretion but significantly increased fraction excretion of Na+ (1.40% vs. 0.64%), indicating that fractional Na+ absorption is reduced by HK. PT reabsorption was assessed using free-flow micropuncture in anesthetized animals. At 80% of the accessible length of the PT, measurements of inulin concentration indicated volume reabsorption of 73% and 54% in CK and HK, respectively. At the same site, fractional PT Na+ reabsorption was 66% in CK animals and 37% in HK animals. Fractional PT K+ reabsorption was 66% in CK and 37% in HK. To assess the role of Na+/H+ exchanger isoform 3 (NHE3) in mediating these changes, we measured NHE3 protein expression in total kidney microsomes as well as surface membranes using Western blots. We found no significant changes in protein in either cell fraction. Expression of the Ser552 phosphorylated form of NHE3 was also similar in CK and HK animals. Reduction in PT transport may facilitate K+ excretion and help balance Na+ excretion by shifting Na+ reabsorption from K+-reabsorbing to K+-secreting nephron segments.NEW & NOTEWORTHY In rats fed a diet rich in K+, proximal tubules reabsorbed less fluid, Na+, and K+ compared with those in animals on a control diet. Glomerular filtration rates also decreased, probably due to glomerulotubular feedback. These reductions may help to maintain balance of the two ions simultaneously by shifting Na+ reabsorption to K+-secreting nephron segments.
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Affiliation(s)
- Tong Wang
- Department of Molecular and Cellular Physiology, Yale University School of Medicine, New Haven, Connecticut, United States
| | - Tommy Liu
- Department of Molecular and Cellular Physiology, Yale University School of Medicine, New Haven, Connecticut, United States
| | - Shuhua Xu
- Department of Molecular and Cellular Physiology, Yale University School of Medicine, New Haven, Connecticut, United States
| | - Gustavo Frindt
- Department of Physiology and Biophysics, Weill-Cornell Medicine, New York, New York, United States
| | - Alan M Weinstein
- Department of Physiology and Biophysics, Weill-Cornell Medicine, New York, New York, United States
| | - Lawrence G Palmer
- Department of Physiology and Biophysics, Weill-Cornell Medicine, New York, New York, United States
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7
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Alexander RT. Kidney stones, hypercalciuria, and recent insights into proximal tubule calcium reabsorption. Curr Opin Nephrol Hypertens 2023; 32:359-365. [PMID: 37074688 DOI: 10.1097/mnh.0000000000000892] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/20/2023]
Abstract
PURPOSE OF REVIEW Most kidney stones are composed of calcium, and the greatest risk factor for kidney stone formation is hypercalciuria. Patients who form kidney stones often have reduced calcium reabsorption from the proximal tubule, and increasing this reabsorption is a goal of some dietary and pharmacological treatment strategies to prevent kidney stone recurrence. However, until recently, little was known about the molecular mechanism that mediates calcium reabsorption from the proximal tubule. This review summarizes newly uncovered key insights and discusses how they may inform the treatment of kidney stone formers. RECENT FINDINGS Studies examining claudin-2 and claudin-12 single and double knockout mice, combined with cell culture models, support complementary independent roles for these tight junction proteins in contributing paracellular calcium permeability to the proximal tubule. Moreover, a family with a coding variation in claudin-2 causing hypercalciuria and kidney stones have been reported, and reanalysis of Genome Wide Association Study (GWAS) data demonstrates an association between noncoding variations in CLDN2 and kidney stone formation. SUMMARY The current work begins to delineate the molecular mechanisms whereby calcium is reabsorbed from the proximal tubule and suggests a role for altered claudin-2 mediated calcium reabsorption in the pathogenesis of hypercalciuria and kidney stone formation.
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Affiliation(s)
- R Todd Alexander
- Department of Pediatrics
- Department of Physiology, University of Alberta
- The Women's & Children's Health Research Institute, Edmonton, Alberta, Canada
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Hempstock W, Nagata N, Ishizuka N, Hayashi H. The effect of claudin-15 deletion on cationic selectivity and transport in paracellular pathways of the cecum and large intestine. Sci Rep 2023; 13:6799. [PMID: 37100833 PMCID: PMC10133298 DOI: 10.1038/s41598-023-33431-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Accepted: 04/12/2023] [Indexed: 04/28/2023] Open
Abstract
The large intestine plays a pivotal role in water and electrolyte balance. Paracellular transport may play a role in ion transport mechanisms in the cecum and large intestine; however, these molecular mechanisms and their physiological roles have not been fully studied. Claudin-15 forms a cation channel in tight junctions in the small intestine, but its role in the cecum and large intestine has not been investigated. This study aimed to explore the physiological role of claudin-15 in the cecum and large intestine using claudin-15 (Cldn15) KO mice. Electrical conductance, short-circuit current, Na+ flux, and dilution potential were assessed in isolated tissue preparations mounted in Ussing chambers. The induced short-circuit current of short-chain fatty acids, which are fermentative products in the intestinal tract, was also measured. Compared to wild type mice, the electrical conductance and paracellular Na+ flux was decreased in the cecum, but not the middle large intestine, while in both the cecum and the middle large intestine, paracellular Na+ permeability was decreased in Cldn15 KO mice. These results suggest that claudin-15 is responsible for Na+ permeability in the tight junctions of the cecum and large intestine and decreased Na+ permeability in the cecum may cause impaired absorption function.
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Affiliation(s)
- Wendy Hempstock
- Laboratory of Physiology, Graduate School of Nutritional and Environmental Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka, Shizuoka, 422-8526, Japan
- Department of Nursing, School of Nursing, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka, 422-8526, Japan
| | - Nozomi Nagata
- Laboratory of Physiology, Graduate School of Nutritional and Environmental Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka, Shizuoka, 422-8526, Japan
| | - Noriko Ishizuka
- Laboratory of Physiology, Graduate School of Nutritional and Environmental Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka, Shizuoka, 422-8526, Japan
| | - Hisayoshi Hayashi
- Laboratory of Physiology, Graduate School of Nutritional and Environmental Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka, Shizuoka, 422-8526, Japan.
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9
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Suzuki K, Yamaga K, Tokumasu R, Katsuno T, Tanaka H, Chiba S, Yagi T, Katayama I, Tamura A, Murota H, Tsukita S. Double mutation of claudin‐1 and claudin‐3 causes alopecia in infant mice. Ann N Y Acad Sci 2023; 1523:51-61. [PMID: 37002535 DOI: 10.1111/nyas.14980] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/03/2023]
Abstract
Hair follicles (HFs) undergo cyclic phases of growth, regression, and rest in association with hair shafts to maintain the hair coat. Nonsense mutations in the tight junction protein claudin (CLDN)-1 cause hair loss in humans. Therefore, we evaluated the roles of CLDNs in hair retention. Among the 27 CLDN family members, CLDN1, CLDN3, CLDN4, CLDN6, and CLDN7 were expressed in the inner bulge layer, isthmus, and sebaceous gland of murine HFs. Hair phenotypes were observed in Cldn1 weaker knockdown and Cldn3-knockout (Cldn1Δ/Δ Cldn3-/- ) mice. Although hair growth was normal, Cldn1Δ/Δ Cldn3-/- mice showed striking hair loss in the first telogen. Simultaneous deficiencies in CLDN1 and CLDN3 caused abnormalities in telogen HFs, such as an aberrantly layered architecture of epithelial cell sheets in bulges with multiple cell layers, mislocalization of bulges adjacent to sebaceous glands, and dilated hair canals. Along with the telogen HF abnormalities, which shortened the hair retention period, there was an enhanced proliferation of the epithelium surrounding HFs in Cldn1Δ/Δ Cldn3-/- mice, causing accelerated hair regrowth in adults. Our findings suggested that CLDN1 and CLDN3 may regulate hair retention in infant mice by maintaining the appropriate layered architecture of HFs, a deficiency of which can lead to alopecia.
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Affiliation(s)
- Koya Suzuki
- Advanced Comprehensive Research Organization Teikyo University Tokyo Japan
- Department of Clinical Laboratory of Medicine, Graduate School of Medicine Juntendo University Tokyo Japan
- Laboratory of Barriology and Cell Biology, Graduate School of Frontier Biosciences Osaka University Osaka Japan
| | - Kosuke Yamaga
- Laboratory of Barriology and Cell Biology, Graduate School of Frontier Biosciences Osaka University Osaka Japan
- Department of Dermatology, Graduate School of Medicine Osaka University Osaka Japan
| | - Reitaro Tokumasu
- Advanced Comprehensive Research Organization Teikyo University Tokyo Japan
| | - Tatsuya Katsuno
- Laboratory of Barriology and Cell Biology, Graduate School of Frontier Biosciences Osaka University Osaka Japan
- Center for Anatomical, Pathological and Forensic Medical Researches Kyoto University Graduate School of Medicine Kyoto Japan
- KOKORO‐Biology Group, Graduate School of Frontier Biosciences Osaka University Osaka Japan
| | - Hiroo Tanaka
- Advanced Comprehensive Research Organization Teikyo University Tokyo Japan
- Laboratory of Barriology and Cell Biology, Graduate School of Frontier Biosciences Osaka University Osaka Japan
- Department of Pharmacology Teikyo University School of Medicine Tokyo Japan
| | - Shuhei Chiba
- Laboratory of Barriology and Cell Biology, Graduate School of Frontier Biosciences Osaka University Osaka Japan
- Laboratory of Molecular and Cellular Biology, Department of Biomolecular Sciences, Graduate School of Life Sciences Tohoku University Sendai Japan
| | - Takeshi Yagi
- KOKORO‐Biology Group, Graduate School of Frontier Biosciences Osaka University Osaka Japan
| | - Ichiro Katayama
- Department of Dermatology, Graduate School of Medicine Osaka University Osaka Japan
- Department of Pigmentation Research and Therapeutics, Graduate School of Medicine Osaka Metropolitan University Osaka Japan
| | - Atsushi Tamura
- Advanced Comprehensive Research Organization Teikyo University Tokyo Japan
- Laboratory of Barriology and Cell Biology, Graduate School of Frontier Biosciences Osaka University Osaka Japan
- Department of Pharmacology Teikyo University School of Medicine Tokyo Japan
| | - Hiroyuki Murota
- Department of Dermatology, Graduate School of Medicine Osaka University Osaka Japan
- Department of Dermatology Nagasaki University Graduate School of Biomedical Sciences Nagasaki Japan
| | - Sachiko Tsukita
- Advanced Comprehensive Research Organization Teikyo University Tokyo Japan
- Laboratory of Barriology and Cell Biology, Graduate School of Frontier Biosciences Osaka University Osaka Japan
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Imputation-powered whole-exome analysis identifies genes associated with kidney function and disease in the UK Biobank. Nat Commun 2023; 14:1287. [PMID: 36890159 PMCID: PMC9995463 DOI: 10.1038/s41467-023-36864-8] [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: 08/14/2022] [Accepted: 02/20/2023] [Indexed: 03/10/2023] Open
Abstract
Genome-wide association studies have discovered hundreds of associations between common genotypes and kidney function but cannot comprehensively investigate rare coding variants. Here, we apply a genotype imputation approach to whole exome sequencing data from the UK Biobank to increase sample size from 166,891 to 408,511. We detect 158 rare variants and 105 genes significantly associated with one or more of five kidney function traits, including genes not previously linked to kidney disease in humans. The imputation-powered findings derive support from clinical record-based kidney disease information, such as for a previously unreported splice allele in PKD2, and from functional studies of a previously unreported frameshift allele in CLDN10. This cost-efficient approach boosts statistical power to detect and characterize both known and novel disease susceptibility variants and genes, can be generalized to larger future studies, and generates a comprehensive resource ( https://ckdgen-ukbb.gm.eurac.edu/ ) to direct experimental and clinical studies of kidney disease.
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Houillier P, Lievre L, Hureaux M, Prot-Bertoye C. Mechanisms of paracellular transport of magnesium in intestinal and renal epithelia. Ann N Y Acad Sci 2023; 1521:14-31. [PMID: 36622354 DOI: 10.1111/nyas.14953] [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] [Indexed: 01/10/2023]
Abstract
Magnesium is the fourth most abundant cation in the body. It plays a critical role in many biological processes, including the process of energy release. Paracellular transport of magnesium is mandatory for magnesium homeostasis. In addition to intestinal absorption that occurs in part across the paracellular pathway, magnesium is reabsorbed by the kidney tubule. The bulk of magnesium is reabsorbed through the paracellular pathway in the proximal tubule and the thick ascending limb of the loop of Henle. The finding that rare genetic diseases due to pathogenic variants in genes encoding specific claudins (CLDNs), proteins located at the tight junction that determine the selectivity and the permeability of the paracellular pathway, led to an awareness of their importance in magnesium homeostasis. Familial hypomagnesemia with hypercalciuria and nephrocalcinosis is caused by a loss of function of CLDN16 or CLDN19. Pathogenic CLDN10 variants cause HELIX syndrome, which is associated with a severe renal loss of sodium chloride and hypermagnesemia. The present review summarizes the current knowledge of the mechanisms and factors involved in paracellular magnesium permeability. The review also highlights some of the unresolved questions that need to be addressed.
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Affiliation(s)
- Pascal Houillier
- Centre de Recherche des Cordeliers, INSERM, Sorbonne Université, Université Paris Cité, Paris, France
- CNRS ERL 8228 - Laboratoire de Physiologie Rénale et Tubulopathies, Paris, France
- Assistance Publique-Hôpitaux de Paris, Hôpital Européen Georges Pompidou, Service de Physiologie, Paris, France
- Centre de Référence des Maladies Rénales Héréditaires de l'Enfant et de l'Adulte (MARHEA), Paris, France
- Centre de Référence des Maladies Rares du Calcium et du Phosphate, Paris, France
| | - Loïc Lievre
- Centre de Recherche des Cordeliers, INSERM, Sorbonne Université, Université Paris Cité, Paris, France
- CNRS ERL 8228 - Laboratoire de Physiologie Rénale et Tubulopathies, Paris, France
| | - Marguerite Hureaux
- Centre de Référence des Maladies Rénales Héréditaires de l'Enfant et de l'Adulte (MARHEA), Paris, France
- Assistance Publique-Hôpitaux de Paris, Hôpital Européen Georges Pompidou, Service de Génétique, Paris, France
- Paris Centre de Recherche Cardio-vasculaire, INSERM, Université Paris Cité, Paris, France
| | - Caroline Prot-Bertoye
- Centre de Recherche des Cordeliers, INSERM, Sorbonne Université, Université Paris Cité, Paris, France
- CNRS ERL 8228 - Laboratoire de Physiologie Rénale et Tubulopathies, Paris, France
- Assistance Publique-Hôpitaux de Paris, Hôpital Européen Georges Pompidou, Service de Physiologie, Paris, France
- Centre de Référence des Maladies Rénales Héréditaires de l'Enfant et de l'Adulte (MARHEA), Paris, France
- Centre de Référence des Maladies Rares du Calcium et du Phosphate, Paris, France
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12
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Ray E, Mohan K, Ahmad S, Wolf MTF. Physiology of a Forgotten Electrolyte-Magnesium Disorders. ADVANCES IN KIDNEY DISEASE AND HEALTH 2023; 30:148-163. [PMID: 36868730 DOI: 10.1053/j.akdh.2022.12.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2022] [Revised: 11/26/2022] [Accepted: 12/06/2022] [Indexed: 03/05/2023]
Abstract
Magnesium (Mg2+) is the second most common intracellular cation and the fourth most abundant element on earth. However, Mg2+ is a frequently overlooked electrolyte and often not measured in patients. While hypomagnesemia is common in 15% of the general population, hypermagnesemia is typically only found in preeclamptic women after Mg2+ therapy and in patients with ESRD. Mild to moderate hypomagnesemia has been associated with hypertension, metabolic syndrome, type 2 diabetes mellitus, CKD, and cancer. Nutritional Mg2+ intake and enteral Mg2+ absorption are important for Mg2+ homeostasis, but the kidneys are the key regulators of Mg2+ homeostasis by limiting urinary excretion to less than 4% while the gastrointestinal tract loses over 50% of the Mg2+ intake in the feces. Here, we review the physiological relevance of Mg2+, the current knowledge of Mg2+ absorption in the kidneys and the gut, the different causes of hypomagnesemia, and a diagnostic approach on how to assess Mg2+ status. We highlight the latest discoveries of monogenetic conditions causing hypomagnesemia, which have enhanced our understanding of tubular Mg2+ absorption. We will also discuss external and iatrogenic causes of hypomagnesemia and advances in the treatment of hypomagnesemia.
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Affiliation(s)
- Evan Ray
- Renal-Electrolyte Division, Department of Internal Medicine, University of Pittsburgh, PA
| | - Krithika Mohan
- Department of Nephrology, Hosmat Hospital, HBR Layout, Bangalore, India
| | - Syeda Ahmad
- Renal-Electrolyte Division, Department of Internal Medicine, University of Pittsburgh, PA
| | - Matthias T F Wolf
- Pediatric Nephrology, Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas, TX.
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13
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Abstract
Mg2+ is essential for many cellular and physiological processes, including muscle contraction, neuronal activity, and metabolism. Consequently, the blood Mg2+ concentration is tightly regulated by balanced intestinal Mg2+ absorption, renal Mg2+ excretion, and Mg2+ storage in bone and soft tissues. In recent years, the development of novel transgenic animal models and identification of Mendelian disorders has advanced our current insight in the molecular mechanisms of Mg2+ reabsorption in the kidney. In the proximal tubule, Mg2+ reabsorption is dependent on paracellular permeability by claudin-2/12. In the thick ascending limb of Henle's loop, the claudin-16/19 complex provides a cation-selective pore for paracellular Mg2+ reabsorption. The paracellular Mg2+ reabsorption in this segment is regulated by the Ca2+-sensing receptor, parathyroid hormone, and mechanistic target of rapamycin (mTOR) signaling. In the distal convoluted tubule, the fine tuning of Mg2+ reabsorption takes place by transcellular Mg2+ reabsorption via transient receptor potential melastatin-like types 6 and 7 (TRPM6/TRPM7) divalent cation channels. Activity of TRPM6/TRPM7 is dependent on hormonal regulation, metabolic activity, and interacting proteins. Basolateral Mg2+ extrusion is still poorly understood but is probably dependent on the Na+ gradient. Cyclin M2 and SLC41A3 are the main candidates to act as Na+/Mg2+ exchangers. Consequently, disturbances of basolateral Na+/K+ transport indirectly result in impaired renal Mg2+ reabsorption in the distal convoluted tubule. Altogether, this review aims to provide an overview of the molecular mechanisms of Mg2+ reabsorption in the kidney, specifically focusing on transgenic mouse models and human hereditary diseases.
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Affiliation(s)
- Jeroen H F de Baaij
- Department of Physiology, Radboud University Medical Center, Nijmegen, The Netherlands
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14
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Günzel D. Is there a molecular basis for solvent drag in the renal proximal tubule? Pflugers Arch 2023; 475:277-281. [PMID: 36418493 PMCID: PMC9849172 DOI: 10.1007/s00424-022-02773-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2022] [Revised: 11/14/2022] [Accepted: 11/14/2022] [Indexed: 11/27/2022]
Abstract
The concept of solvent drag, i.e., water and solutes sharing the same pore and their transport being frictionally coupled, was first proposed in the early 1950s. During the following decades, it was applied to transport processes across cell membranes as well as transport along the paracellular pathway. Water-driven solute transport was proposed as the major mechanism for electrolyte and nutrient absorption in the small intestine and for Cl- and HCO3- reabsorption in the renal proximal tubule. With the discovery of aquaporins as transcellular route for water transport and the claudin protein family as the major determinant of paracellular transport properties, new mechanistic insights in transepithelial water and solute transport are emerging and call for a reassessment of the solvent drag concept. Current knowledge does not provide a molecular basis for relevant solvent drag-driven, paracellular nutrient, and inorganic anion (re-)absorption. For inorganic cation transport, in contrast, solvent drag along claudin-2-formed paracellular channels appears feasible.
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Affiliation(s)
- Dorothee Günzel
- Clinical Physiology/Nutritional Medicine, Department of Gastroenterology, Rheumatology and Infectious Diseases, Charité-Universitätsmedizin Berlin, Hindenburgdamm 30, 12203, Berlin, Germany.
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15
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Alexander RT, Dimke H. Molecular mechanisms underlying paracellular calcium and magnesium reabsorption in the proximal tubule and thick ascending limb. Ann N Y Acad Sci 2022; 1518:69-83. [PMID: 36200584 DOI: 10.1111/nyas.14909] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Calcium and magnesium are the most abundant divalent cations in the body. The plasma level is controlled by coordinated interaction between intestinal absorption, reabsorption in the kidney, and, for calcium at least, bone storage and exchange. The kidney adjusts urinary excretion of these ions in response to alterations in their systemic concentration. Free ionized and anion-complexed calcium and magnesium are filtered at the glomerulus. The majority (i.e., >85%) of filtered divalent cations are reabsorbed via paracellular pathways from the proximal tubule and thick ascending limb (TAL) of the loop of Henle. Interestingly, the largest fraction of filtered calcium is reabsorbed from the proximal tubule (65%), while the largest fraction of filtered magnesium is reclaimed from the TAL (60%). The paracellular pathways mediating these fluxes are composed of tight junctional pores formed by claudins. In the proximal tubule, claudin-2 and claudin-12 confer calcium permeability, while the exact identity of the magnesium pore remains to be determined. Claudin-16 and claudin-19 contribute to the calcium and magnesium permeable pathway in the TAL. In this review, we discuss the data supporting these conclusions and speculate as to why there is greater fractional calcium reabsorption from the proximal tubule and greater fractional magnesium reabsorption from the TAL.
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Affiliation(s)
- R Todd Alexander
- Departments of Physiology & Pediatrics, University of Alberta, Edmonton, Alberta, Canada.,Women's and Children's Health Institute, Edmonton, Alberta, Canada
| | - Henrik Dimke
- Department of Cardiovascular and Renal Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Demark.,Department of Nephrology, Odense University Hospital, Odense, Denmark
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16
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Berselli A, Benfenati F, Maragliano L, Alberini G. Multiscale modelling of claudin-based assemblies: a magnifying glass for novel structures of biological interfaces. Comput Struct Biotechnol J 2022; 20:5984-6010. [DOI: 10.1016/j.csbj.2022.10.038] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Revised: 10/24/2022] [Accepted: 10/24/2022] [Indexed: 11/03/2022] Open
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17
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Gonschior H, Schmied C, Van der Veen RE, Eichhorst J, Himmerkus N, Piontek J, Günzel D, Bleich M, Furuse M, Haucke V, Lehmann M. Nanoscale segregation of channel and barrier claudins enables paracellular ion flux. Nat Commun 2022; 13:4985. [PMID: 36008380 PMCID: PMC9411157 DOI: 10.1038/s41467-022-32533-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2021] [Accepted: 08/04/2022] [Indexed: 11/09/2022] Open
Abstract
The paracellular passage of ions and small molecules across epithelia is controlled by tight junctions, complex meshworks of claudin polymers that form tight seals between neighboring cells. How the nanoscale architecture of tight junction meshworks enables paracellular passage of specific ions or small molecules without compromising barrier function is unknown. Here we combine super-resolution stimulated emission depletion microscopy in live and fixed cells and tissues, multivariate classification of super-resolution images and fluorescence resonance energy transfer to reveal the nanoscale organization of tight junctions formed by mammalian claudins. We show that only a subset of claudins can assemble into characteristic homotypic meshworks, whereas tight junctions formed by multiple claudins display nanoscale organization principles of intermixing, integration, induction, segregation, and exclusion of strand assemblies. Interestingly, channel-forming claudins are spatially segregated from barrier-forming claudins via determinants mainly encoded in their extracellular domains also known to harbor mutations leading to human diseases. Electrophysiological analysis of claudins in epithelial cells suggests that nanoscale segregation of distinct channel-forming claudins enables barrier function combined with specific paracellular ion flux across tight junctions. Meshworks of claudin polymers control the paracellular transport and barrier properties of epithelial tight junctions. Here, the authors show different claudin nanoscale organization principles, finding that claudin segregation enables barrier formation and paracellular ion flux across tight junctions.
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Affiliation(s)
- Hannes Gonschior
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), 13125, Berlin, Germany
| | - Christopher Schmied
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), 13125, Berlin, Germany
| | | | - Jenny Eichhorst
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), 13125, Berlin, Germany
| | - Nina Himmerkus
- Institute of Physiology, Christian-Albrechts-Universität zu Kiel, 24118, Kiel, Germany
| | - Jörg Piontek
- Clinical Physiology/Nutritional Medicine, Medical Department, Division of Gastroenterology, Infectiology, Rheumatology, Charité - Universitätsmedizin Berlin, 12203, Berlin, Germany
| | - Dorothee Günzel
- Clinical Physiology/Nutritional Medicine, Medical Department, Division of Gastroenterology, Infectiology, Rheumatology, Charité - Universitätsmedizin Berlin, 12203, Berlin, Germany
| | - Markus Bleich
- Institute of Physiology, Christian-Albrechts-Universität zu Kiel, 24118, Kiel, Germany
| | - Mikio Furuse
- Division of Cell Structure, National Institute for Physiological Sciences, Okazaki, Aichi, 444-8787, Japan.,Department of Physiological Sciences, School of Life Science, SOKENDAI (Graduate University for Advanced Studies), Okazaki, Aichi, 444-8585, Japan
| | - Volker Haucke
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), 13125, Berlin, Germany.,Faculty of Biology, Chemistry and Pharmacy, Freie Universität Berlin, 14195, Berlin, Germany
| | - Martin Lehmann
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), 13125, Berlin, Germany.
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18
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The importance of kidney calcium handling in the homeostasis of extracellular fluid calcium. Pflugers Arch 2022; 474:885-900. [PMID: 35842482 DOI: 10.1007/s00424-022-02725-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2022] [Revised: 06/09/2022] [Accepted: 06/30/2022] [Indexed: 12/13/2022]
Abstract
Extracellular fluid calcium concentration must be maintained within a narrow range in order to sustain many biological functions, encompassing muscle contraction, blood coagulation, and bone and tooth mineralization. Blood calcium value is critically dependent on the ability of the renal tubule to reabsorb the adequate amount of filtered calcium. Tubular calcium reabsorption is carried out by various and complex mechanisms in 3 distinct segments: the proximal tubule, the cortical thick ascending limb of the loop of Henle, and the late distal convoluted/connecting tubule. In addition, calcium reabsorption is tightly controlled by many endocrine, paracrine, and autocrine factors, as well as by non-hormonal factors, in order to adapt the tubular handling of calcium to the metabolic requirements. The present review summarizes the current knowledge of the mechanisms and factors involved in calcium handling by the kidney and, ultimately, in extracellular calcium homeostasis. The review also highlights some of our gaps in understanding that need to be addressed in the future.
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19
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Aronson PS. New Insights into the Pivotal Roles of Claudins in Proximal Tubule Electrolyte Reabsorption. J Am Soc Nephrol 2022; 33:659-661. [PMID: 35264457 PMCID: PMC8970453 DOI: 10.1681/asn.2022020157] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Affiliation(s)
- Peter S Aronson
- Departments of Internal Medicine and of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut
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