FSGS-associated alpha-actinin-4 (K256E) impairs cytoskeletal dynamics in podocytes.
Mutations in the ACTN4 gene, encoding the actin crosslinking protein alpha-actinin-4, are associated with a familial form of focal segmental glomerulosclerosis (FSGS). Mice with podocyte-specific expression of K256E alpha-actinin-4 develop foot process effacement and glomerulosclerosis, highlighting the importance of the cytoskeleton in podocyte structure and function. K256E alpha-actinin-4 exhibits increased affinity for F-actin. However, the downstream effects of this aberrant binding on podocyte dynamics remain unclear. Wild-type and K256E alpha-actinin-4 were expressed in cultured podocytes via adenoviral infection to determine the effect of the mutation on alpha-actinin-4 subcellular localization and on cytoskeletal-dependent processes such as adhesion, spreading, migration, and formation of foot process-like peripheral projections. Wild-type alpha-actinin-4 was detected primarily in the Triton-soluble fraction of podocyte lysates and localized to membrane-associated cortical actin and focal adhesions, with some expression along stress fibers. Conversely, K256E alpha-actinin-4 was detected predominantly in the Triton-insoluble fraction, was excluded from cortical actin, and localized almost exclusively along stress fibers. Both wild-type and K256E alpha-actinin-4-expressing podocytes adhered equally to an extracellular matrix (collagen-I). However, podocytes expressing K256E alpha-actinin-4 showed a reduced ability to spread and migrate on collagen-I. Lastly, K256E alpha-actinin-4 expression reduced the mean number of actin-rich peripheral projections. Our data suggest that aberrant sequestering of K256E alpha-actinin-4 impairs podocyte spreading, motility, and reduces the number of peripheral projections. Such intrinsic cytoskeletal derangements may underlie initial podocyte damage and foot process effacement encountered in ACTN4-associated FSGS.
Michaud
J-L R
JL
Kidney Research Centre and Molecular Medicine Program, Ottawa Health Research Institute, University of Ottawa, Ottawa, Ontario, Canada.
Chaisson
K M
KM
Parks
R J
RJ
Kennedy
C R J
CR
D000185:Actinin / Q000235:genetics* / Q000378:metabolism; D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D002448:Cell Adhesion / Q000235:genetics; D002461:Cell Line, Transformed; D002465:Cell Movement / Q000235:genetics; D002472:Cell Transformation, Viral; D003599:Cytoskeleton / Q000473:pathology*; D004195:Disease Models, Animal; D015870:Gene Expression; D005923:Glomerulosclerosis, Focal Segmental / Q000235:genetics* / Q000473:pathology / Q000503:physiopathology*; D051379:Mice; D050199:Podocytes / Q000473:pathology*
C491752:Actn4 protein, mouse; D000185:Actinin