Over-expression of human SIRT1 prevents ageing-induced endothelial dysfunction : eNOS dependent and independent mechanisms

Abstract

In blood vessel of mature animal, endothelial cells remain quiescent for years, before apoptosis and being replaced by newly generated endothelial cells. During aging, this turnover process is accelerated and the fast generated endothelial cells become dysfunctional. Endothelial dysfunction in blood vessel is characterized by the imbalanced production of endothelium-dependent relaxing factors (EDRF) and endothelium-dependent contracting factors (EDCF). The NAD-dependent deacetylase SIRT1 is an anti-aging protein with therapeutic potential for aging related cardiovascular diseases. Endothelium-specific over-expression of human SIRT1 promotes endothelium-dependent vasodilatation and endothelium-selective inhibition of human SIRT1 inhibit it. It is accepted that SIRT1 plays a protective role in endothelium dysfunction. However, the underlying mechanisms remain unclear. In the present study, the endothelial functions of a transgenic mouse model with endothelium-selective over-expression of human SIRT1 (hSIRT1) were evaluated and compared with those of wild type mice. Aging-induced deterioration in endothelium-dependent vasodilatation was observed in wild type but not hSIRT1 mice. Endothelium-specific over-expression of SIRT1 prevented aging-induced reduction of NO bioavailability in aortae, without changing endothelial nitric oxide synthase (eNOS) expression levels. Enhanced phosphorylation of eNOS at serine 1177 was detected in hSIRT1 mice aorta. In the presence of Nω-Nitro-L-arginine methyl ester (L-NAME), the nitric oxide synthase (NOS) inhibitor, EDCF induced contraction to acetylcholine was significantly decreased in carotid arteries of hSIRT1 mice. Cyclooxygenase-2 (COX-2) expression was induced by aging in wild-type mice but not in hSIRT1 mice. Thus, both the augmented NO bioavailability and the reduced production of COX-2-derived EDCF in hSIRT1 mice enhanced their endothelial function. To further explore the eNOS-independent mechanism underlying the vasoprotective role of SIRT1, the eNOS deficient and hSIRT1 endothelium-specific over-expression (eNOS-hSIRT1) mice was generated. Decreased endothelium-dependent contraction to acetylcholine was observed in both the carotid artery and aorta of eNOS-hSIRT1 mice, when compared to the controlled eNOS deficient mice. Besides, ATP induced endothelium-dependent contraction, which was COX-dependent, was also decreased in aortae of eNOS-hSIRT1 mice. Thus, the improved endothelial function induced by the endothelium-selective overexpression of SIRT1 was partly attributed to the reduced COX function, independent of eNOS signaling pathway. In summary, endothelium-selective overexpression of human SIRT1 prevented aging-induced impairment of endothelial function via both eNOS dependent and independent mechanisms.