Background: Mesangial cells (MC) are known to secrete various vasoactive substances that may control endothelial and epithelial cell growth. Therefore, the cell-cell interactions among these cells may be important in the control of renal function. However, the exact mechanisms of maintaining the cell-cell interactions are not yet understood. We have focused on the role of hepatocyte growth factor (HGF) in the regulation of cell-cell interactions, since HGF has many protective functions in the kidney. To investigate the role of HGF in renal injury, we examined (1) the effects of HGF on epithelial injury induced by serum deprivation, and (2) the role of local HGF production in the maintenance of renal structure.
Methods: Apoptotic changes in epithelial cells were assessed by nuclear morphology and DNA fragmentation assay. Transfection of human HGF vector into epithelial cells was performed by a highly efficient viral-liposome method. The effects of secreted HGF on the growth of renal cells were examined using a co-culture system.
Results: The addition of recombinant HGF (rHGF) stimulated the growth of rat and porcine epithelial cells. Moreover, the decrease in number of epithelial cells by serum deprivation was significantly attenuated by rHGF. Interestingly, apoptotic changes in epithelial cells induced by serum deprivation were also significantly attenuated by rHGF (P < 0.01). As a model of gene therapy, the effects of overexpression of human HGF gene in epithelial cells on apoptosis induced by serum deprivation were examined. Transfection of human HGF vector into epithelial cells also attenuated epithelial cell death induced by serum deprivation through the inhibition of apoptosis, accompanied by increased HGF production (P < 0.01). In addition, HGF also prevented endothelial injury induced by tumor necrosis factor-alpha and dexamethasone. Given the presence of a local HGF system, we measured local HGF secreted from renal cells. Immunoreactive HGF was observed in the conditioned medium of MC, but not epithelial cells, while the specific receptor of HGF, c-met, was expressed in epithelial cells. Of importance, co-culture of MC with epithelial cells resulted in a significant increase in number of epithelial cells, which was significantly abolished by neutralizing anti-HGF antibody.
Conclusions: Overall, these results demonstrate that local production of HGF in MC may maintain the growth of epithelial and endothelial cells through its anti-apoptotic action.