CHRONIC HYPOXIA INDUCES PROLIFERATION OF CULTURED MESANGIAL CELLS - ROLE OF CALCIUM AND PROTEIN-KINASE-C

The effect of hypoxia on the proliferation of cultured rat mesangial c ells was examined. To evaluate the underlying signaling mechanisms, th e roles of intracellular calcium ([Ca2+](i)) and protein kinase C (PKC ) were determined. Quiescent cultures were exposed to hypoxia (3% O-2) or normoxia (18% O-2), and [H-3]thymidine incorporation, cell number, [Ca2+](i), and PKC were assessed. Mesangial cells exposed to 28 h of hypoxia exhibited a significant increase in [H-3]thymidine incorporati on followed by a significant increase in cell number at 72 h in compar ison with respective normoxic controls. Hypoxia induced a biphasic act ivation of PKC, reflected by translocation of the enzyme activity from cytosol to membrane at 1 h, a return to baseline at 4 and 8 h, with s ubsequent reactivation from 16 to 48 h. In addition, hypoxia-induced p roliferation was prevented by a PKC inhibitor 1-(5-isoquinolinylsulfon yl)-2-methylpiperazine (H-7). Cells exposed to hypoxia produced progre ssive increases in resting [Ca2+](i) from 15 to 60 min which remain su stained up to 24 h of examination. Verapamil significantly prevented t he hypoxia-induced proliferation, and both verapamil treatment and inc ubations in a calcium-free medium for 1 h blocked the hypoxia-induced stimulation of[Ca2+](i) as well as PKC. These results provide the firs t in vitro evidence that chronic hypoxia induces proliferation of cult ured glomerular mesangial cells, which is mediated by the stimulation of [Ca2+](i) and the subsequent activation of PKC.