Nedd4-2, a member of the Nedd4 E3 family, targets several membrane channels and transporters, including the epithelial sodium channel (ENaC)(1). We have found that Nedd4-2deficiency in kidney results in progressive nephropathy associated with elevated ENaC, epithelial cell apoptosis, kidney injury and fibrosis (2). While this chronic kidney disease (CKD)-like pathology appears to be due to increased Na+uptake via ENaC, the precise mechanism of injury and fibrosis remain unknown.
To analyse this further, we generated several Nedd4-2-deficient renal collecting duct cell lines (unpublished). Proteome analysis suggested that several mesenchymal markers were enriched in KO cells. We also found that KO cells in culture express high levels of vimentin, have greater motility and enhanced sensitivity to TGFβ as assessed by increased vimentin and ZEB2 transcription, loss of adherens and tight junctions, as well as upregulation of N-cadherin, suggesting that Nedd4-2 loss results sensitises cells to epithelial mesenchymal transition (EMT). Surprisingly KO cells did not show any differences in SMAD activation in response to TGFβ, however we did observe an increase in stabilisation of β-catenin as well as decreased expression of the inactive phosphorylated form, indicating that the Wnt/β-catenin pathway may be deregulated in Nedd4-2 KO cells.
The canonical wntpathway is important in renal development and regeneration, however sustained activation leads to renal fibrosis. It has been shown to be activated in several in vivo models of CKD. As sustained activation of the canonical Wnt/β-catenin pathway can result in renal fibrosis, we propose that Nedd4-2 deficiency contributes to renal injury and fibrosis in KO mice via the deregulation of EMT signalling.