Sirt1, Vascular Aging, and Aortic Aneurysm

描述（由申请人提供）：腹主动脉瘤（AAAs）是腹主动脉的永久性扩张，破裂后死亡率超过85%。目前，没有任何治疗策略被证明可以延缓AAA的进展和狂喜，因此手术是唯一可行的选择。人类流行病学资料表明，衰老是AAAs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，清楚地支持了研究AAA形成和进展机制的必要性。尽管高龄是已知的AAA的主要危险因素，但老化加速AAA形成的分子基础仍不清楚。我们已经获得了令人兴奋的初步数据，表明在肾上主动脉血管平滑肌细胞（VSMCs）中，年龄相关的Sirt1（一种NAD+依赖的去乙酰化酶）抑制会加重Ang ii触发的AAAs。此外，输注血管紧张素（Ang） II（一种具有良好特征的AAA小鼠模型）可显著降低Sirt1活性。此外，在sirt1 - vsmc特异性敲除（SV-KO）小鼠中，Ang II响应的AAAs的形成和破裂加速。同时，我们发现血管衰老标志物[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小鼠的主动脉中则降低。最后，我们发现Sirt1消融增加了Ang II治疗后基质金属蛋白酶（MMP） 2和MT1-MMP的蛋白和mRNA水平。机械地，我们发现老年主动脉中p21水平的增加显著增强了AP2α（一种由Ang II激活的转录因子）与MMP2启动子的结合，导致MMP2的异常表达。因此，我们的中心假设是，老化主动脉中Sirt1的氧化失活增加了p53/p21，从而加剧了Ang ii诱导的VSMCs和动脉瘤中ap2 α-介导的MMP2表达。为了验证或反驳这一假设，我们提出以下具体目标：(1)确定高龄或Ang II输注对Sirt1活性的影响，并评估Sirt1减少是否会导致小鼠体内血管过早衰老；(2)在小鼠体内证实年龄相关的Sirt1降低加速了Ang ii诱导的血管壁破坏和动脉瘤形成；(3)阐明Sirt1失活如何加速AAA。该应用具有很高的临床创新和意义，因为我们预计该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的发生、进展和终止。

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.