R168H and V165X mutant podocin might induce different degrees of podocyte injury via different molecular mechanisms

Abstract

A lot of mutations of podocin, a key protein of podocyte slit diaphragm (SD), have been found both in hereditary and sporadic focal segmental glomeruloscleorosis (FSGS). Nevertheless, the mechanisms of podocyte injury induced by mutant podocins are still unclear. A compound heterozygous podocin mutation was identified in our FSGS patient, leading to a truncated (podocinV165X) and a missense mutant protein (podocinR168H), respectively. Here, it was explored whether and how both mutant podocins induce podocyte injury in the in vitro cultured podocyte cell line. Our results showed that podocinR168H induced more significant podocyte apoptosis and expression changes in more podocyte molecules than podocinV165X. Podocyte injury caused by the normal localized podocinV165X was effectively inhibited by TRPC6 knockdown. The abnormal retention of podocinR168H in endoplasmic reticulum (ER) resulted in the mis-localizations of other critical SD molecules nephrin, CD2AP and TRPC6, and significantly up-regulated ER stress markers Bip/grp78, p-PERK and caspase-12. These results implicated that podocinR168H and podocinV165X induced different degrees of podocyte injury, which might be resulted from different molecular mechanisms. Our findings provided some possible clues for further exploring the pharmacological targets to the proteinuria induced by different mutant podocins. © 2009 The Authors Journal compilation © 2009 by the Molecular Biology Society of Japan/Blackwell Publishing Ltd.