Matrix metalloproteinase 9 induces endothelial-mesenchymal transition via Notch activation in human kidney glomerular endothelial cells

Background: Endothelial-mesenchymal transition (EndoMT) is a major source of myofibroblast formation in kidney fibrosis. Our previous study showed a profibrotic role for matrix metalloproteinase 9 (MMP-9) in kidney fibrosis via induction of epithelial-mesenchymal transition (EMT). Inhibition of MMP-9 activity reduced kidney fibrosis in murine unilateral ureteral obstruction. This study investigated whether MMP-9 also plays a role in EndoMT in human glomerular endothelial cells. Results: TGF-beta 1 (10 or 20 ng/ml) induced EndoMT in HKGECs as shown by morphological changes. In addition, VE-cadherin and CD31 were significantly downregulated, whereas alpha-SMA, vimentin, and N-cadherin were upregulated. RT-PCR revealed that Snail, a known inducer of EMT, was upregulated. The MMP inhibitor GM6001 abrogated TGF-beta 1-induced EndoMT. Zymography indicated that MMP-9 was also upregulated in TGF-beta 1-treated HKGECs. Recombinant MMP-9 (2 mu g/ml) induced EndoMT in HKGECs via Notch signaling, as evidenced by increased formation of the Notch intracellular domain (NICD) and decreased Notch 1. Inhibition of MMP-9 activity by its inhibitor showed a dose-dependent response in preventing TGF-beta 1-induced alpha-SMA and NICD in HKGECs, whereas inhibition of Notch signaling by gamma-secretase inhibitor (GSI) blocked rMMP-9-induced EndoMT. Conclusions: Taken together, our results demonstrate that MMP-9 plays an important role in TGF-beta 1-induced EndoMT via upregulation of Notch signaling in HKGECs.