Hypoxia and high glucose cause exaggerated mesangial cell growth and collagen synthesis: role of osteopontin

The effect of hypoxia on the proliferation and collagen synthesis of cultur ed rat mesangial cells was examined under normal-glucose (NG, 5 mM) and hig h-glucose (HG, 25 mM)-media conditions. In addition, a role for osteopontin (OPN) in mediating these processes was assessed. Quiescent cultures were e xposed to hypoxia (3% O-2) and normoxia (18% O-2) in a serum-free medium wi th NG or HG, and cell proliferation, collagen synthesis, and OPN expression were assessed. Cells exposed to hypoxia in NG medium resulted in significa nt increases in [H-3] thymidine incorporation, cell number, and [H-3] proli ne incorporation, respectively. HG incubations also produced significant st imulation of these parameters under normoxic conditions, which were markedl y enhanced in cells exposed to hypoxia in HG medium. In addition, hypoxia a nd HG stimulated the mRNA levels of type IV collagen, and the combination o f hypoxia and HG resulted in additive increases in type IV collagen express ion. Hypoxia and HG also stimulated OPN mRNA and protein levels in an addit ive fashion. A neutralizing antibody to OPN or its beta (3)-integrin recept or significantly blocked the effect of hypoxia and HG on proliferation and collagen synthesis. In conclusion, these results demonstrate for the first time that hypoxia in HG medium produces exaggerated mesangial cell growth a nd type IV collagen synthesis. In addition, OPN appears to play a role in m ediating the accelerated mesangial cell growth and collagen synthesis found in a hyperglycemic and hypoxic environment.