FSGS-associated α-actinin-4 (K256E) impairs cytoskeletal dynamics in podocytes

• Published in: Kidney international Vol. 70; no. 6; pp. 1054 - 1061
• Main Authors: Michaud, J.-L.R., Chaisson, K.M., Parks, R.J., Kennedy, C.R.J.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.09.2006; Nature Publishing
• Subjects: Actinin - genetics; Actinin - metabolism; Adenoviridae - genetics; Animals; Biological and medical sciences; Cell Adhesion - genetics; Cell Line, Transformed; Cell Movement - genetics; Cell Transformation, Viral; cytoskeleton; Cytoskeleton - pathology; Disease Models, Animal; foot processes; FSGS; Gene Expression; Glomerulosclerosis, Focal Segmental - genetics; Glomerulosclerosis, Focal Segmental - pathology; Glomerulosclerosis, Focal Segmental - physiopathology; Medical sciences; Mice; Nephrology. Urinary tract diseases; podocyte; Podocytes - pathology; α-actinin-4; FSGS; foot processes; cytoskeleton; α-actinin-4; podocyte; Nephrology; Kidney; Urology; Foot; Renal glomerulus; Podocyte; Alpha actinin 4; Urinary system; Dynamics; Cytoskeleton
• ISSN: 0085-2538; 1523-1755
• DOI: 10.1038/sj.ki.5001665

Mutations in the ACTN4 gene, encoding the actin crosslinking protein α-actinin-4, are associated with a familial form of focal segmental glomerulosclerosis (FSGS). Mice with podocyte-specific expression of K256E α-actinin-4 develop foot process effacement and glomerulosclerosis, highlighting the importance of the cytoskeleton in podocyte structure and function. K256E α-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 α-actinin-4 were expressed in cultured podocytes via adenoviral infection to determine the effect of the mutation on α-actinin-4 subcellular localization and on cytoskeletal-dependent processes such as adhesion, spreading, migration, and formation of foot process-like peripheral projections. Wild-type α-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 α-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 α-actinin-4-expressing podocytes adhered equally to an extracellular matrix (collagen-I). However, podocytes expressing K256E α-actinin-4 showed a reduced ability to spread and migrate on collagen-I. Lastly, K256E α-actinin-4 expression reduced the mean number of actin-rich peripheral projections. Our data suggest that aberrant sequestering of K256E α-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.