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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.TGF-β1 (10 or 20 ng/ml) induced EndoMT in HKGECs as shown by morphological changes. In addition, VE-cadherin and CD31 were significantly downregulated, whereas α-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-β1-induced EndoMT. Zymography indicated that MMP-9 was also upregulated in TGF-β1-treated HKGECs. Recombinant MMP-9 (2 μg/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-β1-induced α-SMA and NICD in HKGECs, whereas inhibition of Notch signaling by γ-secretase inhibitor (GSI) blocked rMMP-9-induced EndoMT.Taken together, our results demonstrate that MMP-9 plays an important role in TGF-β1-induced EndoMT via upregulation of Notch signaling in HKGECs.

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-β1 (10 or 20 ng/ml) induced EndoMT in HKGECs as shown by morphological changes. In addition, VE-cadherin and CD31 were significantly downregulated, whereas α-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-β1-induced EndoMT. Zymography indicated that MMP-9 was also upregulated in TGF-β1-treated HKGECs. Recombinant MMP-9 (2 μg/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-β1-induced α-SMA and NICD in HKGECs, whereas inhibition of Notch signaling by γ-secretase inhibitor (GSI) blocked rMMP-9-induced EndoMT. Conclusions Taken together, our results demonstrate that MMP-9 plays an important role in TGF-β1-induced EndoMT via upregulation of Notch signaling in HKGECs.