Hypoxia and high glucose upregulate AT₁receptor expression and potentiate ANG II-induced proliferation in VSM cells

Abstract

We examined the effect of hypoxia and high glucose (HG) on ANG II type 1 (AT 1) 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 AT 1 mRNA expression. Exposure of cells to 24 h of hypoxia also resulted in a significant increase in ANG II receptor binding as assessed with 125 I-labeled ANG II. Treatment with ANG II (1 M) for 24 h under normoxic conditions caused an ϳ1.5-fold increase in both DNA synthesis and cell number, which was enhanced to ϳ3.0-fold under hypoxic conditions. An AT 1 receptor antagonist (losartan, 10 M) 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 ϳ2.5-fold increase in AT 1 mRNA levels, which was markedly enhanced by hypoxia to ϳ5.5-fold at 12 h and ϳ8.5-fold at 24 h. ANG II under HG-normoxic conditions caused a complete downregulation of AT 1 expression, which was prevented by hypoxia. These results demonstrate an upregulation of AT 1 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. vascular smooth muscle cells; diabetes; chronic hypoxia; cell growth; angiotensin II receptor ARTERIAL WALL HYPOXIA and the associated vascular smooth muscle (VSM) cell proliferation have been implicated in the development of atherosclerosis (7, 23). Moreover, we recently reported (43) that hypoxia directly induces the proliferation of cultured rat aortic VSM cells. Others have shown that hypoxia is also mitogenic to cultured pulmonary artery smooth muscle and endothelial cells (12,13,25). Prevalence of tissue hypoxia and increased VSM cell proliferation is also reported in experimental models of diabetes and hypertension (1,10,28,35,40,45). Elevated glucose concentrations in medium have been shown to produce both hypertrophic and hyperplastic effects in cultured porcine aortic smooth muscle cells (32). We found (43, 44) that high medium glucose also induces the proliferation of cultured VSM cells as well as renal glomerular mesangial cells. In addition, hypoxia potentiates the effect of high medium glucose on the proliferation of both VSM and mesangial cells (43,44). Together, these results strongly suggest an important role for local hypoxia in accelerated VSM cell proliferation in diabetes. The mechanisms responsible for the accelerated VSM cell growth and progression into cardiovascular disease in diabetes remain to be clearly defined.Activation of the renin-angiotensin system (RAS) plays an important role in the pathogenesis of vascular complications of diabetes (16). The primary active component of the RAS, ANG II, causes hypertrophy, hyperplasia, and the deposition of extracellular matrix proteins in VSM cells (19,21,36,49). Interestingly, ANG II-induced proliferation of cultured rat ...

AT 1 Blockade Prevents Glucose-Induced Cardiac Dysfunction in Ventricular Myocytes

“…22,23 The AT 1 receptor is a G protein-coupled receptor that mediates most of the known biologic effects of Ang II. Both local production of Ang II and AT 1 receptor expression are significantly increased in cardiac myocytes and vessels in streptozotocin-induced diabetic rats 24 and in vascular smooth muscle cells exposed to high glucose levels, 25 which are consistent with our findings. Activation of the AT 1 receptor might 'turn on" NADPH oxidase and consequently enhance ROS, such as superoxide anion, which can react with nitric oxide, leading to its inactivation by producing peroxynitrite.…”

Inhibition of Prolyl Hydroxylase Domain-Containing Protein Downregulates Vascular Angiotensin II Type 1 Receptor

“…7 It was also reported that AT 1 R mRNA in VSMCs was upregulated under hypoxia (3% O 2 , 24 hours). 32 However, in the present study, both AT 1 R mRNA and protein were downregulated under hypoxia (1% O 2 , 24 hours). Although it is possible that the different oxygen concentration may affect the result, the reason for this discrepancy between the present study and the previous one is not clear at this time.…”

Multivalent ligand–receptor interactions elicit inverse agonist activity of AT1 receptor blockers against stretch-induced AT1 receptor activation

“…Although it remains unclear whether the subtle constitutive activity of the native AT 1 receptor has a pathophysiological role, the enhancement of its constitutive activity olmesartan Inverse agonist activity of olmesartan Y Qin et al through upregulation of receptor expression may promote cardiovascular remodeling. Indeed, the expression level of the AT 1 receptor in vascular cells is upregulated by low-density lipoprotein cholesterol, 13 insulin, 14 glucose, 15 progesterone 16 and inflammatory cytokines, such as interleukin-1a or interleukin-6. 17,18 Analyses of the binding affinity of olmesartan for mutant AT 1 receptors as well as molecular modeling analyses indicated that the ternary interactions between the hydroxyl group and Tyr 113 and between the carboxyl group and Lys 199 and His 256 are critical to the inverse agonist properties of olmesartan, but that the interaction between the tetrazole group and Gln 257 is dispensable.…”