Mechanism of High Glucose–Induced Angiotensin II Production in Rat Vascular Smooth Muscle Cells

Abstract

Abstract-Angiotensin II (Ang II), a circulating hormone that can be synthesized locally in the vasculature, has been implicated in diabetes-associated vascular complications. This study was conducted to determine whether high glucose (HG) (Ϸ23.1 mmol/L), a diabetic-like condition, stimulates Ang II generation and the underlying mechanism of its production in rat vascular smooth muscle cells. The contribution of various enzymes involved in Ang II generation was investigated by silencing their expression with small interfering RNA in cells exposed to normal glucose (Ϸ4.1 mmol/L) and HG. Angiotensin I (Ang I) was generated from angiotensinogen by cathepsin D in the presence of normal glucose or HG. Although HG did not affect the rate of angiotensinogen conversion, it decreased expression of angiotensinconverting enzyme (ACE), downregulated ACE-dependent Ang II generation, and upregulated rat vascular chymasedependent Ang II generation. The ACE inhibitor captopril reduced Ang II levels in the media by 90% in the presence of normal glucose and 19% in HG, whereas rat vascular chymase silencing reduced Ang II production in cells exposed to HG but not normal glucose. The glucose transporter inhibitor cytochalasin B, the aldose reductase inhibitor alrestatin, and the advanced glycation end product formation inhibitor aminoguanidine attenuated HG-induced Ang II generation. HG caused a transient increase in extracellular signal-regulated kinase (ERK)1/2 phosphorylation, and ERK1/2 inhibitors reduced Ang II accumulation by HG. These data suggest that polyol pathway metabolites and AGE can stimulate rat vascular chymase activity via ERK1/2 activation and increase Ang II production. In addition, decreased Ang II degradation, which, in part, could be attributable to a decrease in angiotensin-converting enzyme 2 expression observed in HG, contributes to increased accumulation of Ang II in vascular smooth muscle cells by HG. (Circ Res. 2007;101:455-464.)Key Words: ACE Ⅲ vascular chymase Ⅲ angiotensin Ⅲ VSMC Ⅲ high glucose A ngiotensin (Ang) II, a biologically active component of the renin-angiotensin system (RAS), plays an important role in regulating salt, water, and vascular homeostasis. 1 According to the classical view of RAS, Ang II is cleaved from angiotensin I (Ang I) by angiotensin-converting enzyme (ACE), 2 which is localized on the surface of endothelial cells but also has been shown to be present in the media of aorta and to a lesser degree in adventitia. 3 A soluble form of ACE can be found in plasma. 4 Ang I is formed from the circulating precursor angiotensinogen (AGT) secreted from the liver and is cleaved by renin secreted from the juxtaglomerular cells of the kidney. 5 The presence of local RAS has also been demonstrated in several tissues including vascular wall. 6 AGT is the only known precursor of Ang I and Ang II and is synthesized in vascular smooth muscle cells (VSMCs). 7 Evidence for the presence of renin in vascular tissue has been documented, 8 but renin-like activity in aortic tissue falls to very low ...

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