Hypoxia and high glucose upregulate AT₁ receptor expression and potentiate ANG II-induced proliferation in VSM cells

We examined the effect of hypoxia and high glucose (HG) on ANG II type 1 (AT₁) receptor expression and proliferation in cultured vascular smooth muscle (VSM) cells. Exposure of quiescent cells to hypoxia in a serum-free DME-Ham's F-12 medium for 6-24 h induced a progressive increase in AT₁ mRNA expression. Exposure of cells to 24 h of hypoxia also resulted in a significant increase in ANG II receptor binding as assessed with ¹²⁵I-labeled ANG II. Treatment with ANG II (1 μM) for 24 h under normoxic conditions caused an ∼1.5-fold increase in both DNA synthesis and cell number, which was enhanced to ∼3.0-fold under hypoxic conditions. An AT₁ receptor antagonist (losartan, 10 μM) blocked the ANG II-induced increase in DNA synthesis under both normoxic and hypoxic conditions. Incubations in HG medium (25 mM) for 12-24 h under normoxic conditions induced an ∼2.5-fold increase in AT₁ mRNA levels, which was markedly enhanced by hypoxia to ∼5.5-fold at 12 h and ∼8.5-fold at 24 h. ANG II under HG-normoxic conditions caused a complete downregulation of AT₁ expression, which was prevented by hypoxia. These results demonstrate an upregulation of AT₁ receptor expression by hypoxia and HG in cultured VSM cells and suggest a mechanism for enhanced ANG II-induced VSM cell proliferation and the development of atherosclerosis in diabetes.