Autocrine class 3 semaphorin system regulates slit diaphragm proteins and podocyte survival

Abstract

Class 3 semaphorins are guidance proteins that play crucial roles during development. Semaphorins 3A (sema 3A) and 3F are expressed by podocytes in vivo throughout ontogeny and their function is unknown. Here we examined the expression of class 3 semaphorins (3A, 3B, 3C, 3D, 3E, and 3F) and their receptors (neuropilins 1 and 2, plexins A1, A2, A3, B2, and D1) in undifferentiated and differentiated mouse podocytes using reverse transcriptase-polymerase chain reaction (RT-PCR). All class 3 semaphorins, neuropilins 1 and 2 are expressed by undifferentiated and differentiated podocytes at similar levels. Differentiated podocytes expressed 2-4-fold higher plexin A1, A2, and A3 mRNA levels than undifferentiated podocytes. To examine semaphorin regulation, we exposed podocytes to recombinant sema 3A. Sema 3A decreased semaphorin 3B, plexin A1, A3, and D1 >/=50% and reduced plexin A2 mRNA to undetectable levels. To identify sema 3A function in podocytes, we examined whether sema 3A regulates slit diaphragm proteins and podocyte survival. Sema 3A induced a dose-response podocin downregulation and decreased its interaction with CD2-associated protein and nephrin, as determined by Western analysis and co-immunoprecipitation. To evaluate sema 3A role in podocyte survival, we quantified podocyte apoptosis using a caspase 3 activity marker. Sema 3A induced a 10-fold increase in podocyte apoptosis and significantly decreased the activity of the Akt survival pathway. Our data indicate that (1) immortalized podocytes in culture have a functional autocrine semaphorin system that is regulated by differentiation and ligand availability; (2) sema 3A signaling regulates the expression and interactions of slit-diaphragm proteins and decreases podocyte survival.

HIV-1 Upregulates VEGF in Podocytes

“…21 Sema 3A has been recently shown to regulate expression and interactions among several slit-diaphragm proteins. 22 Our study demonstrates that NefSrc/Stat3-HIF-VEGF is a novel pathway for podocyte proliferation and dedifferentiation in HIVAN. In vivo, podocyte-specific expression of Nef in transgenic mice induces an abnormal podocyte phenotype characterized by increased Ki67, loss of synaptopodin, and increased phospho-Stat3.…”

Semaphorin3a regulates endothelial cell number and podocyte differentiation during glomerular development

“…The function of Sema3a during glomerular development is unknown. In cultured podocytes, recombinant SEMA3A downregulates podocin expression, decreases the interaction between SD proteins podocin, nephrin and CD2AP and induces podocyte apoptosis through inhibition of the phosphorylation of AKT (Guan et al, 2006). Moreover, administration of recombinant SEMA3A to wild-type mice induces foot process effacement and fusion, endothelial cell swelling and reversible albuminuria, representing a novel mechanism for proteinuria (Tapia et al, 2008).…”

Regulation of dendritic development by semaphorin 3A through novel intracellular remote signaling

“…Sema3A was reported to decrease Akt phosphorylation and induce apoptosis in cultured phodocytes. 87 This biphasic action of Sema3A might be related to induction of either neurite outgrowth or inhibition. 23,24,88 The involvement of TrkA may well be consistent with a property of Sema3A-induced axonal transport, the dependence on voltage-dependent ion channels.…”