Novel role of Vav1-Rac1 pathway in actin cytoskeleton regulation in Interleukin-13-induced minimal change-like nephropathy.

Abstract

Our established interleukin-13 ( IL-13 ) overexpression rat model of minimal change-like nephropathy provided a platform to study the molecular signalling pathways in T-helper 2 (Th2) cytokine associated minimal change nephrotic syndrome. We hypothesized that IL-13 may act directly on podocytes, causing podocyte foot process effacement and hence proteinuria in our rat model of minimal change-like nephropathy. This study aimed firstly to delineate the glomerular "gene signature" associated with IL-13-mediated dysregulation of podocyte related proteins, and subsequently to investigate the role of the differentially regulated genes in IL-13-mediated podocyte injury. Glomerular transcriptional profile of IL-13 -overexpressed rats showed characteristic features of podocyte injury with 87% of podocyte related genes being significantly down-regulated. Gene expression of Vav1 was shown to be highly up-regulated in the glomeruli of IL-13 -overexpressed rats and pathway analysis of the differentially expressed genes suggested a possible novel role of Vav1 in podocyte cytoskeleton remodelling. Immunofluorescence examination demonstrated glomerular expression of Vav1 in rats which co-localized with synaptopodin, confirming podocyte expression. However, positive staining for the phosphorylated form of Vav1 (p-Vav1) was only seen in IL-13 -overexpressed rats. Moreover, in-vitro IL-13 stimulation of human podocytes resulted in phosphorylation of Vav1. This was associated with Rac1 activation and actin cytoskeleton rearrangement, which was abrogated in Vav1 knock-down podocytes. In conclusion, we have demonstrated the role of Vav1-Rac1 pathway characterised by phosphorylation of Vav1, activation of Rac1 and the subsequent actin cytoskeleton rearrangement in IL-13 induced podocyte injury, possibly explaining the podocyte foot process effacement seen in our IL-13 overexpression rat model.