Focal and segmental glomerulosclerosis (FSGS) describes a lesion in the kidney that reflects a common endpoint for a variety of pathologic processes. Recent advances in understanding genetically inherited causes of FSGS, however, suggest that abnormal glomerular podocyte function is likely common to most pathologic states that lead to FSGS. In our laboratory, mutations within the gene encoding alpha-actinin 4 (ACTN4) were identified as one of the genetic causes of inherited FSGS. How mutations in this actin binding molecule lead to the development of FSGS remains the focus of intense investigation. Preliminary evidence suggests that the phenotypic changes in podocytes resulting from the expression of ACTN4 mutants may be mediated through changes in the podocyte's interaction with the extracellular matrix. Specifically, it appears the extracellular matrix receptor alpha3beta1-integrin may be involved via modulation of betal-integrin phosphorylation. Using a cultured podocyte system, the work proposed here will define: 1) The precise changes in integrin phosphorylation caused by mutant ACTN4 expression? 2) If the identified changes in alpha3beta1-integrin phosphorylation sufficient to recapitulate the altered podocyte phenotype typical of the ACTN4 mutants when expressed in the presence of wild-type ACTN4? 3) How mutant forms of alpha-actinin-4 change physical interactions of the alpha3beta1-integrin signaling complex and alter regulation of cell-matrix binding. I anticipate that completion of these studies will provide considerable advancement in our understanding of alpha-actinin-4's role in FSGS and advance the field of glomerular biology as a whole. Relevance: Understanding how genetic mutations lead to kidney disease is the first step toward finding a treatment or cure for the specific inherited disorder. The work outlined in this proposalfocuseson defining how one such genetic mutation leads to a disease process known as focal and segmental glomerular sclerosis and ultimately to kidney failure. We hope that through this research we may learn information that is broadly applicable to this disorder, as well as many common relateddisorders.
