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 cells was examined. To evaluate the underlying signaling mechanisms, the roles of intracellular calcium ([Ca(2+)](i)) and protein kinase C (PKC) were determined. Quiescent cultures were exposed to hypoxia (3% O(2)) or normoxia (18% O(2)), and [(3)H]thymidine incorporation, cell number, [Ca(2+)](i), and PKC were assessed. Mesangial cells exposed to 28 h of hypoxia exhibited a significant increase in [(3)H]thymidine incorporation followed by a significant increase in cell number at 72 h in comparison with respective normoxic controls. Hypoxia induced a biphasic activation 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 subsequent reactivation from 16 to 48 h. In addition, hypoxia-induced proliferation was prevented by a PKC inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7). Cells exposed to hypoxia produced progressive increases in resting [Ca(2+)](i) from 15 to 60 min which remain sustained up to 24 h of examination. Verapamil significantly prevented the hypoxia-induced proliferation, and both verapamil treatment and incubations in a calcium-free medium for 1 h blocked the hypoxia-induced stimulation of[Ca(2+)](i) as well as PKC. These results provide the first in vitro evidence that chronic hypoxia induces proliferation of cultured glomerular mesangial cells, which is mediated by the stimulation of [Ca(2+)](i) and the subsequent activation of PKC.