Podocyte Injury Associated with Mutantα-Actinin-4

Abstract

Focal segmental glomerulosclerosis (FSGS) is an important cause of proteinuria and nephrotic syndrome in humans. The pathogenesis of FSGS may be associated with glomerular visceral epithelial cell (GEC; podocyte) injury, leading to apoptosis, detachment, and “podocytopenia”, followed by glomerulosclerosis. Mutations inα-actinin-4 are associated with FSGS in humans. In cultured GECs,α-actinin-4 mediates adhesion and cytoskeletal dynamics. FSGS-associatedα-actinin-4 mutants show increased binding to actin filaments, compared with the wild-type protein. Expression of anα-actinin-4 mutant in mouse podocytesin vivoresulted in proteinuric FSGS. GECs that express mutantα-actinin-4 show defective spreading and motility, and such abnormalities could alter the mechanical properties of the podocyte, contribute to cytoskeletal disruption, and lead to injury. The potential for mutantα-actinin-4 to injure podocytes is also suggested by the characteristics of this mutant protein to form microaggregates, undergo ubiquitination, impair the ubiquitin-proteasome system, enhance endoplasmic reticulum stress, and exacerbate apoptosis.