Endothelial mesenchymal transition in kidney fibrosis, and the role of MMP-9 dependent Notch signaling

Abstract

Endothelial-mesenchymal transition (EndoMT) has been shown to be a major source of myofibroblast formation in kidney fibrosis. This study investigated whether Notch signaling plays a role in MMP-9-induced EndoMT of kidney endothelial cells in kidney. Mouse kidney peritubular endothelial cells (MKPEC) were isolated and co-cultured with tubular epithelial cell. MKPECs and human kidney glomerular endothelial cells (HKGECs) were treated with TGF-β1 or recombinant human MMP-9 (rhMMP-9) to induce EndoMT. EndoMT was assessed by immunofluorescence staining and Western blot (WB). Notch signaling was examined by WB. MMP-9 expression was examined by zymography. Interstitial fibrosis was assessed by Trichrome stain. EndoMT was evidenced by significant downregulation of VE-cadherin & CD31 and upregulation of α-SMA. Inhibition of MMP-9 or Notch signaling by their inhibitors demonstrated a dose-dependent response in preventing EndoMT. MMP-9 deficiency also led to a significant reduction in EndoMT in MKPECs. MMP-9 KO mice with UUO showed a significant reduction of interstitial fibrosis, α-SMA expression and fibroblasts originating via EndoMT. These findings demonstrate an important role for MMP-9 in causing kidney fibrosis, especially through the induction of EndoMT in different types of endothelial cells, and highlight the importance of the relationship between MMP-9 and the Notch signaling pathway.