Redox signaling via lipid raft clustering in homocysteine-induced injury of podocytes

Abstract

Our recent studies have indicated that hyperhomocysteinemia (hHcys) may induce podocyte damage, resulting in glomerulosclerosis. However, the molecular mechanisms mediating hHcys-induced podocyte injury are still poorly understood. In the present study, we first demonstrated that an intact NADPH oxidase system is present in podocytes as shown by detection of its membrane subunit (gp91 phox ) and cytosolic subunit (p47 phox ). Then, confocal microscopy showed that gp91 phox and p47 phox could be aggregated in lipid raft (LR) clusters in podocytes treated with homocysteine (Hcys), which were illustrated by their colocalization with cholera toxin B, a common LR marker. Different mechanistic LR disruptors, either methyl-β-cyclodextrin (MCD) or filipin abolished such Hcys-induced formation of LR-gp91 phox or LR-p47 phox transmembrane signaling complexes. By flotation of detergent-resistant membrane fractions we found that gp91 phox and p47 phox were enriched in LR fractions upon Hcys stimulation, and such enrichment of NADPH oxidase subunits and increase in its enzyme activity were blocked by MCD or filipin. Functionally, disruption of LR clustering significantly attenuated Hcys-induced podocyte injury, as shown by their inhibitory effects on Hcys-decreased expression of slit diaphragm molecules such as nephrin and podocin. Similarly, Hcys-increased expression of desmin was also reduced by disruption of LR clustering. In addition, inhibition of such LR-associated redox signaling prevented cytoskeleton disarrangement and apoptosis induced by Hcys. It is concluded that NADPH oxidase subunits aggregation and consequent activation of this enzyme through LR clustering is an important molecular mechanism triggering oxidative injury of podocytes induced by Hcys.