title: Synaptopodin Limits TRPC6 Podocyte Surface Expression and Attenuates Proteinuria.
abstract: Gain-of-function mutations of classic transient receptor potential channel 6 (TRPC6) were identified in familial FSGS, and increased expression of wild-type TRPC6 in glomeruli is observed in several human acquired proteinuric diseases. Synaptopodin, an actin binding protein that is important in maintaining podocyte function, is downregulated in various glomerular diseases. Here, we investigated whether synaptopodin maintains podocyte function by regulating podocyte surface expression and activity of TRPC6. We show indirect interaction and nonrandom association of synaptopodin and TRPC6 in podocytes. Knockdown of synaptopodin in cultured mouse podocytes increased the expression of TRPC6 at the plasma membrane, whereas overexpression of synaptopodin decreased it. Mechanistically, synaptopodin-dependent TRPC6 surface expression required functional actin and microtubule cytoskeletons. Overexpression of wild-type or FSGS-inducing mutant TRPC6 in synaptopodin-depleted podocytes enhanced TRPC6-mediated calcium influx and induced apoptosis. In vivo, knockdown of synaptopodin also caused increased podocyte surface expression of TRPC6. Administration of cyclosporin A, which stabilizes synaptopodin, reduced LPS-induced proteinuria significantly in wild-type mice but to a lesser extent in TRPC6 knockout mice. Furthermore, administration of cyclosporin A reversed the LPS-induced increase in podocyte surface expression of TRPC6 in wild-type mice. Our findings suggest that alteration in synaptopodin levels under disease conditions may modify intracellular TRPC6 channel localization and activity, which further contribute to podocyte dysfunction. Reducing TRPC6 surface levels may be a new approach to restoring podocyte function.
authors.affiliation: Department of Internal Medicine, Rush University Medical Center, Chicago, Illinois.|Department of Cell Biology, Miller School of Medicine, University of Miami, Miami, Florida.
authors.forename: Hao
authors.initials: H
authors.lastname: Yu
authors.affiliation: Department of Internal Medicine, Cantonal Hospital Frauenfeld, Frauenfeld, Switzerland.
authors.forename: Andreas
authors.initials: A
authors.lastname: Kistler
authors.affiliation: Department of Internal Medicine, Rush University Medical Center, Chicago, Illinois.
authors.forename: Mohd Hafeez
authors.initials: MH
authors.lastname: Faridi
authors.affiliation: Department of Neuroscience, Physiology and Pharmacology, University College London, London, United Kingdom.
authors.forename: James Otto
authors.initials: JO
authors.lastname: Meyer
authors.affiliation: Department of Internal Medicine, Rush University Medical Center, Chicago, Illinois.
authors.forename: Beata
authors.initials: B
authors.lastname: Tryniszewska
authors.affiliation: Department of Pharmacology, University of Illinois at Chicago, Chicago, Illinois.
authors.forename: Dolly
authors.initials: D
authors.lastname: Mehta
authors.affiliation: Department of Cell Biology, University of Connecticut, Farmington, Connecticut; and.
authors.forename: Lixia
authors.initials: L
authors.lastname: Yue
authors.affiliation: Department of Biology and Biochemistry, University of Houston, Houston, Texas.
authors.forename: Stuart
authors.initials: S
authors.lastname: Dryer
authors.affiliation: Department of Internal Medicine, Rush University Medical Center, Chicago, Illinois; jochen_reiser@rush.edu.
authors.forename: Jochen
authors.initials: J
authors.lastname: Reiser
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008840:Microfilament Proteins / Q000502:physiology*; D050199:Podocytes / Q000378:metabolism* / Q000648:ultrastructure; D011507:Proteinuria / Q000378:metabolism*; D050052:TRPC Cation Channels / Q000096:biosynthesis*; D000074287:TRPC6 Cation Channel
chemical_list: D008840:Microfilament Proteins; C503968:Synpo protein, mouse; D050052:TRPC Cation Channels; D000074287:TRPC6 Cation Channel; C492146:Trpc6 protein, mouse
keywords: TRPC6; calcium; podocyte; proteinuria; surface expression; synaptopodin