title: Evidence for a role of claudin 2 as a proximal tubular stress responsive paracellular water channel.
abstract: Claudins are the major proteins of the tight junctions and the composition of claudin subtypes is decisive for the selective permeability of the paracellular route and thus tissue specific function. Their regulation is complex and subject to interference by several factors, including oxidative stress. Here we show that exposure of cultured human proximal tubule cells (RPTEC/TERT1) to the immunosuppressive drug cyclosporine A (CsA) induces an increase in transepithelial electrical resistance (TEER), a decrease in dome formation (on solid growth supports) and a decrease in water transport (on microporous growth supports). In addition, CsA induced a dramatic decrease in the mRNA for the pore forming claudins -2 and -10, and the main subunits of the Na(+)/K(+) ATPase. Knock down of claudin 2 by shRNA had no discernable effect on TEER or dome formation but severely attenuated apical to basolateral water reabsorption when cultured on microporous filters. Generation of an osmotic gradient in the basolateral compartment rescued water transport in claudin 2 knock down cells. Inhibition of Na(+)/K(+) ATPase with ouabain prevented dome formation in both cell types. Taken together these results provide strong evidence that dome formation is primarily due to transcellular water transport following a solute osmotic gradient. However, in RPTEC/TERT1 cells cultured on filters under iso-osmotic conditions, water transport is primarily paracellular, most likely due to local increases in osmolarity in the intercellular space. In conclusion, this study provides strong evidence that claudin 2 is involved in paracellular water transport and that claudin 2 expression is sensitive to compound induced cellular stress.
authors.affiliation: Division of Physiology, Department of Physiology and Medical Physics, Innsbruck Medical University, Innsbruck, Austria. Electronic address: Anja.Wilmes@i-med.ac.at.
authors.forename: Anja
authors.initials: A
authors.lastname: Wilmes
authors.affiliation: Division of Physiology, Department of Physiology and Medical Physics, Innsbruck Medical University, Innsbruck, Austria.
authors.forename: Lydia
authors.initials: L
authors.lastname: Aschauer
authors.affiliation: Division of Physiology, Department of Physiology and Medical Physics, Innsbruck Medical University, Innsbruck, Austria.
authors.forename: Alice
authors.initials: A
authors.lastname: Limonciel
authors.affiliation: Division of Physiology, Department of Physiology and Medical Physics, Innsbruck Medical University, Innsbruck, Austria.
authors.forename: Walter
authors.initials: W
authors.lastname: Pfaller
authors.affiliation: Division of Physiology, Department of Physiology and Medical Physics, Innsbruck Medical University, Innsbruck, Austria.
authors.forename: Paul
authors.initials: P
authors.lastname: Jennings
mesh_terms: D018929:Cell Culture Techniques; D002478:Cells, Cultured; D057167:Claudins / Q000235:genetics / Q000378:metabolism*; D016572:Cyclosporine / Q000633:toxicity*; D017097:Electric Impedance; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007166:Immunosuppressive Agents / Q000633:toxicity*; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000378:metabolism; D009997:Osmotic Pressure; D010042:Ouabain / Q000494:pharmacology; D016062:Porosity; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D013312:Stress, Physiological / Q000187:drug effects*; D019108:Tight Junctions / Q000187:drug effects / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D014867:Water / Q000378:metabolism*
chemical_list: C491875:CLDN2 protein, human; D057167:Claudins; D004791:Enzyme Inhibitors; D007166:Immunosuppressive Agents; D012333:RNA, Messenger; D014867:Water; D010042:Ouabain; D016572:Cyclosporine; D000254:Sodium-Potassium-Exchanging ATPase
keywords: Claudin 2; Cyclosporine A; Proximal tubule; Tight junction; Trans-epithelial electrical resistance; Water permeability