High glucose induces HGF-independent activation of Met receptor in human renal tubular epithelium

Context: The role of hepatocyte growth factor (HGF) in diabetic kidney damage remains controversial. Objective: To test the hypothesis that high glucose levels activate pathways related to HGF and its receptor Met and that this could participate in glucose-induced renal cell damage. Materials and methods: HK2 cells, a human proximal tubule epithelial cell line, were stimulated with high glucose for 48hours. Levels of pMet/Met, pEGFR/EGFR, pSTAT3/STAT3, pAkt/Akt and pERK1/2/ERK1/2 were studied by immunoblotting. Absence of HGF was verified by qRT-PCR and ELISA. Results: High glucose level activated Met and its downstream pathways STAT3, Akt and ERK independently of HGF. High glucose induced an integrin ligand fibronectin. HGF-independent Met phosphorylation was prevented by inhibition of integrin alpha 5 beta 1, Met inhibitor crizotinib, Src inhibitors PP2 and SU5565, but not by EGFR inhibitor AG1478. High glucose increased the expression of TGF beta-1, CTGF and the tubular damage marker KIM-1 and increased apoptosis of HK2 cells, effects inhibited by crizotinib. Conclusion: High glucose activated Met receptor in HK2 cells independently of HGF, via induction of integrin 51 and downstream signaling. This mode of Met activation was associated with tubular cell damage and apoptosis and it may represent a novel pathogenic mechanism and a treatment target in diabetic nephropathy.