Alpha-actinin-4 is required for normal podocyte adhesion

J Biol Chem. 2007 Jan 5;282(1):467-77. doi: 10.1074/jbc.M605024200. Epub 2006 Nov 2.

Abstract

Mutations in the alpha-actinin-4 gene ACTN4 cause an autosomal dominant human kidney disease. Mice deficient in alpha-actinin-4 develop a recessive phenotype characterized by kidney failure, proteinuria, glomerulosclerosis, and retraction of glomerular podocyte foot processes. However, the mechanism by which alpha-actinin-4 deficiency leads to glomerular disease has not been defined. Here, we examined the effect of alpha-actinin-4 deficiency on the adhesive properties of podocytes in vivo and in a cell culture system. In alpha-actinin-4-deficient mice, we observed a decrease in the number of podocytes per glomerulus compared with wild-type mice as well as the presence of podocyte markers in the urine. Podocyte cell lines generated from alpha-actinin-4-deficient mice were less adherent than wild-type cells to glomerular basement membrane (GBM) components collagen IV and laminin 10 and 11. We also observed markedly reduced adhesion of alpha-actinin-4-deficient podocytes under increasing shear stresses. This adhesion deficit was restored by transfecting cells with alpha-actinin-4-GFP. We tested the strength of the integrin receptor-mediated linkages to the cytoskeleton by applying force to microbeads bound to integrin using magnetic pulling cytometry. Beads bound to alpha-actinin-4-deficient podocytes showed greater displacement in response to an applied force than those bound to wild-type cells. Consistent with integrin-dependent alpha-actinin-4-mediated adhesion, phosphorylation of beta1-integrins on alpha-actinin-4-deficient podocytes is reduced. We rescued the phosphorylation deficit by transfecting alpha-actinin-4 into alpha-actinin-4-deficient podocytes. These results suggest that alpha-actinin-4 interacts with integrins and strengthens the podocyte-GBM interaction thereby stabilizing glomerular architecture and preventing disease.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Actinin / metabolism
  • Actinin / physiology*
  • Animals
  • Basement Membrane / metabolism
  • Cell Adhesion
  • Cytoplasm / metabolism
  • Flow Cytometry
  • Immunohistochemistry
  • Integrin beta1 / metabolism
  • Kidney / metabolism
  • Kidney Diseases / metabolism
  • Mice
  • Mice, Transgenic
  • Microfilament Proteins / metabolism
  • Microfilament Proteins / physiology*
  • Phosphorylation
  • Podocytes / cytology*
  • Podocytes / metabolism
  • Time Factors

Substances

  • Actn4 protein, mouse
  • Integrin beta1
  • Microfilament Proteins
  • Actinin