Regulation of Endothelial Nitric Oxide Synthase and Postnatal Angiogenesis by Rac1

Abstract

Abstract-Diminished bioavailability of nitric oxide is a hallmark of endothelial dysfunction and is associated with a broad spectrum of vascular disorders such as impaired angiogenesis. Because Rac1, a Rho family member, mediates cellular motility and generation of reactive oxygen species, it could be involved in the regulation of endothelial nitric oxide production. However, the pathophysiological consequences of postnatal endothelial Rac1 deletion on endothelial function have not been determined. We generated endothelial-specific Rac1 haploinsufficient mice (EC-Rac1 ϩ/Ϫ ) using Cre-loxP technology. The EC-Rac1 ϩ/Ϫ mice have decreased expression and activity of endothelial nitric oxide synthase (eNOS), impaired endothelium-dependent vasorelaxation, and mild hypertension compared with control (Rac1 ϩ/flox ) mice. Hind limb ischemia model and aortic capillary sprouting assay showed that eNOS activity and angiogenesis was impaired in EC-Rac1 ϩ/Ϫ mice. Indeed, Rac1 promotes eNOS gene transcription through p21-activated kinase but not NADPH oxidase, increases eNOS mRNA stability, and enhances eNOS activity by promoting endothelial uptake of L-arginine. These findings indicate that endothelial Rac1 is essential for endothelium-dependent vasomotor response and ischemia-induced angiogenesis. These effects of Rac1 on endothelial function are largely due to the upregulation of eNOS through multiple mechanisms that are mediated, in part, by p21-activated kinase. Therapeutic strategies to enhance Rac1 function, therefore, may be important for preventing endothelial dysfunction. (Circ Res. 2008;103:360-368.) Key Words: angiogenesis Ⅲ endothelium Ⅲ hypertension Ⅲ nitric oxide synthase Ⅲ signal transduction E ndothelium-derived nitric oxide (NO) is an important determinant of endothelium-dependent vasodilation and contributes to the anti-inflammatory and antithrombotic properties of the endothelium. Endothelial dysfunction is characterized by impaired synthesis, release, and activity of endothelialderived NO and is thought to contribute to the development and progression of various vascular disorders such as vasoconstriction, hypertension, atherosclerosis, and peripheral artery occlusive disease. 1 Therefore, understanding the pathophysiological mechanisms of endothelial dysfunction would provide important insights into therapeutic strategies for preventing cardiovascular disease.Endothelial NO synthase (eNOS) is the primary source of endothelium-derived NO. The steady-state mRNA level of eNOS is one of the principal determinants of eNOS expression and activity and NO bioavailability. 2 Numerous exogenous stimuli and conditions have been shown to alter eNOS mRNA level through both transcriptional and posttranscriptional mechanisms. For example, the eNOS mRNA is upregulated by laminar flow, vascular endothelial growth factor, transforming growth factor-beta and lysophosphatidylcholine and downregulated by tumor necrosis factor-␣ and oxidized low-density lipoprotein. 2 The enzymatic activity of eNOS is further regulated by mul...

Rac1 Modulates Endothelial Function and Platelet Aggregation in Diabetes Mellitus

“…Mechanistically, we demonstrated that amelioration of endothelial function via restoration of eNOS phosphorylation by Rac1 inhibition requires ROCK1 as a crucial component of Rac1 signaling in both isolated cells and vessels. Although previous studies have suggested a reduction in eNOS expression after Rac1 inhibition,36 the modulation of Rac1 activity by NSC23766 in our study was not related to changes in its expression in both mouse vessels and human endothelial cells. Moreover, we were recently able to demonstrate that Rac1 inhibition by NSC23766 exerts a beneficial effect also in human vessels, ameliorating endothelial dysfunction 16.…”

Inducible nitric oxide synthase–nitric oxide signaling mediates the mitogenic activity of Rac1 during endochondral bone growth

“…expression and activity of eNOS (Sawada et al, 2008), whereas eNOS protein levels were not altered in our system. Together, these data indicate that the connections between Rac1 (and possibly other Rho GTPases) and components of the NO signaling pathway act in a cell-type-specific manner.…”

The Rho/Rac exchange factor Vav2 controls nitric oxide–dependent responses in mouse vascular smooth muscle cells

“…For example, a recent report using tissue-specific knockin mice with a 50% reduction of Rac1 in the endothelium has revealed that this GTPase regulates eNOS function at several levels, including the upregulation of ENOS gene transcription, ENOS transcript stability, and eNOS catalytic activity. As a consequence, these mice display reduced NO bioavailability and a mild hypertension (43). Some of these responses have been reported to be Pak1 dependent (43).…”