Dissociation of NEPH1 from nephrin is involved in development of a rat model of focal segmental glomerulosclerosis

Abstract

Focal segmental glomerulosclerosis (FSGS) is a disease showing severe proteinuria, and the disease progresses to end-stage kidney failure in many cases. However, the pathogenic mechanism of FSGS is not well understood. The slit diaphragm (SD), which bridges the neighboring foot processes of glomerular epithelial cells, is understood to function as a barrier of the glomerular capillary wall. To investigate the role of SD dysfunction in the development of FSGS, we analyzed the expression of SD-associated molecules in rat adriamycin-induced nephropathy, a mimic of FSGS. The staining of the SD molecules nephrin, podocin, and NEPH1 had already shifted to a discontinuous dotlike pattern at the initiation phase of the disease, when neither proteinuria nor any morphological alterations were detected yet. The alteration of NEPH1 expression was the most evident among the molecules examined, and NEPH1 was dissociated from nephrin at the initiation phase. On day 28, when severe proteinuria was detected and sclerotic changes were already observed, alteration of the expressions of nephrin, podocin, and NEPH1 worsened, but no alteration in the expression of other SD-associated molecules or other podocyte molecules was detected. It is postulated that the dissociation of NEPH1 from nephrin initiates proteinuria and that the SD alteration restricted in these molecules plays a critical role in the development of sclerotic changes in FSGS.

Inverted Formin 2 Regulates Actin Dynamics by Antagonizing Rho/Diaphanous-related Formin Signaling

“…33,37 Mutations disrupting the raft localization of podocin or the nephrin/podocin interaction disassociate nephrin from the raft-mediated trafficking pathway, disrupt its membrane localization, and cause congenital proteinuria. 33,38 We found that INF2 interacts with podocin and caveolin-1, proteins both involved in lipid raftmediated trafficking; this finding suggests a direct role for INF2 in lipid raft-mediated SD protein trafficking. In addition to podocin and caveolin-1, recent studies have also identified INF2's association with raft proteins MAL and MAL2, which mediate membrane trafficking of functional molecules in Schwann cells, 24 T lymphocytes, 39 Madin-Darby canine kidney cells, and HepG2 hepatocytes.…”

Slit Diaphragm Protein Neph1 and Its Signaling

“…Our previous study suggested that in addition to Neph1 phosphorylation, the extracellular engagement of Neph1 also induces its internalization and subsequent downstream signaling from the cytoplasmic domain of Neph1 (12,42). This led us to hypothesize that selectively targeting the cytoplasmic domain of Neph1 will affect Neph1 phosphorylation and its ability to internalize.…”

“…Retained Its Functionality-We have previously shown that the extracellular engagement of Neph1 induces its activation that includes Neph1 phosphorylation, its internalization, and subsequent downstream signaling mediated by the cytoplasmic domain of Neph1 (12,42). Therefore, we hypothesized that if we selectively target the cytoplasmic domain of Neph1 by competitive inhibition, it may result in the inhibition of Neph1 phosphorylation and therefore Neph1 internalization.…”

An update: the role of Nephrin inside and outside the kidney

“…[33,34]. The dissociation of Neph1 from Nephrin induced proteinuria in FSGS [35]. The Neph1-Nephrin complex cooperate to induce actin filament nucleation and elongation in a tyrosine phosphorylation dependent fashion at the plasma membrane by recruiting the cytoskeletal adaptor protein Nck1/2 and other proteins of the actin polymerization complex [36,37].…”