Regulation of SIRT1 in Vascular Smooth Muscle Cells from Streptozotocin-Diabetic Rats

Abstract

Sirtuins enzymes are a conserved family of nicotinamide adenine dinucleotide (NAD)-dependent deacetylases and ADP-ribosyltransferases that mediate responses to oxidative stress, fasting and dietary restriction in mammals. Vascular smooth muscle cells (VSMCs) are involved in many mechanisms that regulate vascular biology in vivo but the role of SIRT1 has not been explored in much detail. Therefore, we investigated the regulation of SIRT1 in cultured VSMCs under various stress conditions including diabetes. Sprague-Dawley rats were made diabetic by injecting a single dose of streptozotocin (65 mg/Kg), and aortic VSMCs were isolated after 4 weeks. Immunocytochemistry showed that SIRT1 was localized predominantly in the nucleus, with lower staining in VSMCs from STZ-diabetic as compared with normoglycemic rats. Previous diabetes induction in vivo and high glucose concentrations in vitro significantly downregulated SIRT1 amounts as detected in Western blot assays, whereas TNF-α (30 ng/ml) stimulation failed to induce significant changes. Because estrogen signaling affects several pathways of oxidative stress control, we also investigated SIRT1 modulation by 17β-estradiol. Treatment with the hormone (10 nM) or a selective estrogen receptor-α agonist decreased SIRT1 levels in VSMCs from normoglycemic but not in those from STZ-diabetic animals. 17β-estradiol treatment also enhanced activation of AMP-dependent kinase, which partners with SIRT1 in a signaling axis. SIRT1 downregulation by 17β-estradiol could be observed as well in human peripheral blood mononuclear cells, a cell type in which SIRT1 downregulation is associated with insulin resistance and subclinical atherosclerosis. These data suggest that SIRT1 protein levels are regulated by diverse cellular stressors to a variable extent in VSMCs from diabetic and normoglycemic rats, warranting further investigation on SIRT1 as a modulator of VSMC activity in settings of vascular inflammation.

Estrogen modulates vascular smooth muscle cell function through downregulation of SIRT1

“…During aging, the negative effects associated with natural decline may be exacerbated by the effects of estrogen. There are some controversies regarding the effects of estrogen on the regulation of SIRT1 in the vasculature [ 47 , 48 ]. Our observations may partially explain the negative impact of estrogen replacement therapy on cardiovascular disease in some large-scale clinical trials.…”

Sirtuins Link Inflammation and Metabolism

“…SIRT1 and SIRT3 activation reduces ischemia reperfusion injury in rodents [ 54 – 56 ]; nuclear-cytoplasmic shuttling of SIRT1 plays an important role in this protection [ 57 ]. Thus, accumulating data supports an overall protective effect of SIRT1 activation on the chronic inflammation associated with atherosclerosis [ 58 – 60 ].…”

Diabetes and ageing‐induced vascular inflammation

“…The potential anti-inflammatory effects of SIRT1 in the diabetic vasculature have been proposed (Winnik et al 2012). In this sense, SIRT1 expression is reduced in vascular smooth muscle cells after induction of diabetes in rats (Toniolo et al 2013). As well, SIRT6 has also been suggested to be involved in metabolic disorders (Lombard et al 2008).…”

“…In this sense, SIRT1 expression is reduced in vascular smooth muscle cells after induction of diabetes in rats (Toniolo et al . ). As well, SIRT6 has also been suggested to be involved in metabolic disorders (Lombard et al .…”