The proteoglycan syndecan 4 regulates transient receptor potential canonical 6 channels via RhoA/Rho-associated protein kinase signaling

Arterioscler Thromb Vasc Biol. 2012 Feb;32(2):378-85. doi: 10.1161/ATVBAHA.111.241018. Epub 2011 Dec 8.

Abstract

Objective: Syndecan 4 (Sdc4) modulates signal transduction and regulates activity of protein channels. Sdc4 is essential for the regulation of cellular permeability. We hypothesized that Sdc4 may regulate transient receptor potential canonical 6 (TRPC6) channels, a determinant of glomerular permeability, in a RhoA/Rho-associated protein kinase-dependent manner.

Methods and results: Sdc4 knockout (Sdc4(-/-)) mice showed increased glomerular filtration rate and ameliorated albuminuria under baseline conditions and after bovine serum albumin overload (each P<0.05). Using reverse transcription-polymerase chain reaction and immunoblotting, Sdc4(-/-) mice showed reduced TRPC6 mRNA by 79% and TRPC6 protein by 82% (each P<0.05). Sdc4(-/-) mice showed an increased RhoA activity by 87% and increased phosphorylation of ezrin in glomeruli by 48% (each P<0.05). Sdc4 knockdown in cultured podocytes reduced TRPC6 gene expression and reduced the association of TRPC6 with plasma membrane and TRPC6-mediated calcium influx and currents. Sdc4 knockdown inactivated negative regulatory protein Rho GTPase activating protein by 33%, accompanied by a 41% increase in RhoA activity and increased phosphorylation of ezrin (P<0.05). Conversely, overexpression of Sdc4 reduced RhoA activity and increased TRPC6 protein and TRPC6-mediated calcium influx and currents.

Conclusions: Our results establish a previously unknown function of Sdc4 for regulation of TRPC6 channels and support the role of Sdc4 for the regulation of glomerular permeability.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / physiology
  • Cell Membrane / physiology
  • Cells, Cultured
  • Glomerular Filtration Rate / physiology
  • Kidney Cortex / cytology
  • Mice
  • Mice, Knockout
  • Models, Animal
  • Podocytes / cytology
  • Podocytes / physiology*
  • Signal Transduction / physiology*
  • Syndecan-4 / deficiency
  • Syndecan-4 / genetics
  • Syndecan-4 / physiology*
  • TRPC Cation Channels / physiology*
  • rho GTP-Binding Proteins / physiology*
  • rho-Associated Kinases / physiology*

Substances

  • Sdc4 protein, mouse
  • Syndecan-4
  • TRPC Cation Channels
  • Trpc6 protein, mouse
  • rho-Associated Kinases
  • RhoA protein, mouse
  • rho GTP-Binding Proteins
  • Calcium