Alpha-actinin-4 is required for normal podocyte adhesion.
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.
Dandapani
Savita V
SV
Department of Genetics, Harvard Medical School, Boston, Massachusetts, USA.
Sugimoto
Hikaru
H
Matthews
Benjamin D
BD
Kolb
Robert J
RJ
Sinha
Sumita
S
Gerszten
Robert E
RE
Zhou
Jing
J
Ingber
Donald E
DE
Kalluri
Raghu
R
Pollak
Martin R
MR
D000185:Actinin / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D001485:Basement Membrane / Q000378:metabolism; D002448:Cell Adhesion; D003593:Cytoplasm / Q000378:metabolism; D005434:Flow Cytometry; D007150:Immunohistochemistry; D019012:Integrin beta1 / Q000378:metabolism; D007668:Kidney / Q000378:metabolism; D007674:Kidney Diseases / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008840:Microfilament Proteins / Q000378:metabolism / Q000502:physiology*; D010766:Phosphorylation; D050199:Podocytes / Q000166:cytology* / Q000378:metabolism; D013997:Time Factors
C491752:Actn4 protein, mouse; D019012:Integrin beta1; D008840:Microfilament Proteins; D000185:Actinin