Sirtuin1 inhibitor attenuates hypertension in spontaneously hypertensive rats: role of Giα proteins and nitroxidative stress.

BACKGROUND: We recently showed that vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHR) exhibit overexpression of Sirtuin1 (Sirt1) that contributes to the enhanced expression of Giα proteins implicated in the development of hypertension in SHR. METHOD: The present study investigated if the inhibition of Sirt1 could also ameliorate hypertension in SHR and explore the underlying molecular mechanisms. For this study, a selective inhibitor of Sirt1, EX-527 (5 mg/kg of body weight), was injected intraperitoneally into 8-week-old SHR and age-matched Wistar Kyoto (WKY) rats twice per week for 3 weeks. The blood pressure (BP) and heart rate was measured twice a week by the CODA noninvasive tail cuff method. RESULTS: The high BP and augmented heart rate in SHR was significantly attenuated by EX-527 treatment, which was associated with the suppression of the overexpression of Sirt1 and Giα proteins in heart, VSMC and aorta. In addition, the enhanced levels of superoxide anion, NADPH oxidase activity, overexpression of NADPH oxidase subunits and FOXO1 were attenuated and the decreased levels of endothelial nitric oxide synthase (eNOS), nitric oxide and increased levels of peroxynitrite (ONOO-) and tyrosine nitration in VSMC from SHR were restored to control levels by EX-527 treatment. Furthermore, knockdown of FOXO1 by siRNA also attenuated the overexpression of Giα-2 and NADPH oxidase subunit proteins and restored the decreased expression of eNOS in VSMC from SHR. CONCLUSION: These results suggest that the inhibition of overexpressed Sirt1 and its target FOXO1 through decreasing the enhanced levels of Giα proteins and nitro-oxidative stress attenuates the high BP in SHR.