Sirt1, Vascular Aging, and Aortic Aneurysm

描述(申请人提供)：腹主动脉瘤(AAA)是腹主动脉的永久性扩张，破裂后死亡率超过85%。目前，还没有任何治疗策略被证明可以减缓AAA的进展和狂喜，使手术成为唯一可用的选择。人类流行病学数据表明，老龄化是AAA的主要危险因素。随着人口寿命的延长，预计AAA的发病率将变得更加普遍。AAA患病率的上升，加上AAA破裂的高死亡率，显然支持了研究AAA形成和发展机制的必要性。尽管高龄是AAA已知的主要危险因素，但衰老加速AAA形成的分子基础在很大程度上仍不清楚。我们已经获得了令人兴奋的初步数据，表明年龄相关的抑制肾上主动脉血管平滑肌细胞(VSMCs)中的Sirt1(一种依赖NAD+的脱乙酰酶)会加剧Ang II触发的AAA。此外，血管紧张素II(Ang II)的注入显著降低了Sirt1的活性。血管紧张素II是一种具有良好特征的AAA小鼠模型。此外，在Sirt1-VSMC特异性基因敲除(SV-KO)小鼠中，Ang II可加速AAA的形成和破裂。与此同时，我们发现血管老化标记物[p21，p53和衰老相关β-半乳糖苷酶(SA-β-GAL)阳性染色]在SV-KO小鼠的主动脉中显著升高，而在SV-TG小鼠中显著降低。最后，我们发现在Ang II治疗后，Sirt1消融增加了基质金属蛋白酶(MMP2)和MT1-MMP2的蛋白和mRNA水平。从机制上讲，我们发现老年主动脉中p21水平的升高显著增强了血管紧张素Ⅱ激活的转录因子AP2α与基质金属蛋白酶2启动子的结合，从而导致基质金属蛋白酶2的异常表达。因此，我们的中心假设是，老年动脉中Sirt1的氧化失活增加了P53/p21，从而加剧了Ang II诱导的血管平滑肌细胞和动脉瘤中AP2α介导的MMP2表达。为了验证或驳斥这一假说，我们提出了以下具体目标：(1)确定高龄或Ang II输注对Sirt1活性的影响，并在体内评估Sirt1降低是否导致小鼠血管过早衰老；(2)在体内确定与年龄相关的Sirt1降低可加速Ang II诱导的小鼠血管壁的破坏和动脉瘤的形成；以及(3)阐明Sirt1失活如何加速AAA。这项应用具有很高的临床创新和意义，因为我们预计这项应用的完成将有助于确定Sirt1激活作为一种新的潜在治疗靶点，用于预防高龄患者AAA的启动、进展和狂喜。

DESCRIPTION (provided by applicant): Abdominal aortic aneurysms (AAAs) are permanent dilations of the abdominal aorta with over 85% mortality after rupture. Currently, there are no therapeutic strategies proven to blunt AAA progression and rapture, making surgery as the only available option. Human epidemiologic data indicates that aging is a major risk factor in AAAs. As the population lives longer, it is anticipated that AAA incidence will become even more prevalent. The rising prevalence of AAAs, coupled with the high mortality from ruptured AAA, clearly supports the need for research to define mechanisms of AAA formation and progression. Despite that advanced age is a known major risk factor for AAA, the molecular basis underlying aging-accelerated AAA formation remains largely unknown. We have obtained exciting preliminary data showing that age- associated inhibition of Sirt1 (an NAD+-dependent deacetylase) in vascular smooth muscle cells (VSMCs) of suprarenal aortas accentuates Ang II-triggered AAAs. Further, infusion of angiotensin (Ang) II, a well-characterized mouse model of AAA, significantly lowered Sirt1 activity. Moreover, the formation and rupture of AAAs in response to Ang II were accelerated in Sirt1-VSMC-specific knockout (SV-KO) mice. Concomitantly, we found vascular aging markers [p21, p53, and Senescence Associated β-galactosidase (SA-β-gal)-positive staining)] were significantly elevated in the aortas of SV-KO mice but were reduced in those from SV-Tg mice. Finally, we found that Sirt1 ablation increased the protein and mRNA level of matrix metalloproteinases (MMP) 2 and MT1-MMP after Ang II treatment. Mechanically, we found that increased levels of p21 in old aortas significantly enhance the binding of AP2α, a transcriptional factor activated by Ang II, to the MMP2 promoter resulting in aberrant expression of MMP2. Thus, our central hypothesis is that oxidative inactivation of Sirt1 in aged aortas increases p53/p21, which exacerbates Ang II-induced AP2α-mediated MMP2 expression in VSMCs and aneurysm. To validate or refute this hypothesis, we propose the following specific aims: (1) determine the effects of advanced age or Ang II infusion on Sirt1 activity and evaluate if Sirt1 reduction causes premature vascular aging in mouse in vivo; (2) establish that age-related Sirt1 reduction accelerates Ang II-instigated destruction of the vessel wall and aneurysm formation in mice in vivo; and (3) elucidate how Sirt1 inactivation accelerates AAA. This application has high clinically innovations and significance because we anticipate that the completion of this application will help identify Sirt1 activation as a novel potential therapeutic target for preventing AAA initiation, progression, and rapture in patients with advanced ages.