AJP - Renal Physiology, Vol 273, Issue 6 954-F960, Copyright © 1997 by American Physiological Society
Chronic hypoxia induces proliferation of cultured mesangial cells: role of calcium and protein kinase C
A. Sahai, C. Mei, T. A. Pattison and R. L. Tannen
Division of Renal Diseases and Hypertension, University of Colorado Health Sciences Center, Denver 80262, USA.
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 ([Ca2+]i) and protein kinase C (PKC) were determined.
Quiescent cultures were exposed to hypoxia (3% O2) or normoxia (18% O2),
and [3H]thymidine incorporation, cell number, [Ca2+]i, and PKC were
assessed. Mesangial cells exposed to 28 h of hypoxia exhibited a
significant increase in [3H]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 [Ca2+]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 [Ca2+]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 [Ca2+]i and the subsequent activation of PKC.
