Serum Amyloid A, Inflammasome Activation, and Abdominal Aortic Aneurysms

最近的估计表明，美国65-79岁的男性中有5-10%和女性中有1-2%是老年人。 患有腹主动脉瘤每年约有15，000人死于AAA破裂。 AAA的治疗仅限于手术干预，因为缺乏其他已证实获益的治疗方法。 虽然大多数AAA患者无症状，但由于破裂导致死亡的风险大大增加， AAA扩展。深入了解有助于AAA进展的机制将对AAA的发展产生重大影响。 通过提供新的生物标志物来预测AAA扩张，从而预测AAA的风险， 主动脉破裂，以及新的干预策略。我们实验室最近发表的研究结果 为详细评估AAA进展中血清淀粉样蛋白A（SAA）提供动力：1）SAA缺乏 在小鼠模型中减弱AAA; 2）在小鼠中，SAA存在于AAA中具有大量弹性蛋白的区域中 降解、巨噬细胞浸润和基质金属蛋白酶（MMP）活性;和3）可检测SAA 在人类AAA中。在未发表的工作中，我们还确定SAA诱导IL-1β和NLRP 3表达， 以及巨噬细胞中IL-1β分泌，这与NLRP 3炎性体的引发和活化一致。 这些发现是值得注意的，因为最近认识到NLRP 3炎性小体激活是一个关键事件 在小鼠AAA的发育中。因此，我们的中心假设是SAA激活NLRP 3炎性体， 从而放大局部炎症反应，所述局部炎症反应增强病理组织重塑并促进 AAA进展。目的1：研究NLRP 3炎性体在SAA促进AAA的能力中的作用。 小鼠目标1a。使用各种炎性体组分缺陷的小鼠（NLRP 3-/-、ASC-/-、半胱天冬酶-1-/-小鼠） 或IL-1β信号（IL-1 R-/-小鼠），我们将确定SAA介导的AAA是否依赖于NLRP 3。 炎性小体我们还将研究是否小分子阴离子磺酸盐，一种治疗， SAA在组织中的沉积，对减少小鼠AAA有效。目标1b。使用巨噬细胞培养， 我们将调查是否有任何已知的生物活动归因于SAA，包括活性氧， 物种产生或与HDL的关联参与SAA介导的NLRP 3炎性体活化。 目的2：检验系统性SAA促进已建立AAA进展的假设。目标2a。 我们的方法是在实验过程中以特定的时间间隔瞬时增加小鼠肝脏中SAA的表达。 通过使用病毒载体和诱导型转基因进行AngII输注的过程。诸如互补 方法，SAA表达将使用反义寡核苷酸抑制。SAA对指数的影响 将确定AAA进展和主动脉炎症和重塑的风险。目标2b。探讨 SAA与炎性小体活化在AAA发病中的作用，SAA与IL-1β的关系 并且将在前瞻性N-TA 3CT试验中确定人类AAA扩张的速率。这些研究 具有确定AAA临床管理新策略的潜力。

Recent estimates indicate that 5-10% of men and 1-2% of women 65-79 years of age in the United States are living with an abdominal aortic aneurysm (AAA). Approximately 15,000 will die each year due to AAA rupture. The treatment for AAA is limited to surgical intervention due to lack of other therapies with proven benefit. Although most patients with AAAs are asymptomatic, the risk of death due to rupture increases greatly as AAAs expand. Insights into mechanisms contributing to AAA progression would have a major impact on the clinical management of AAA by providing new biomarkers that predict AAA expansion and thus the risk for aortic rupture, as well as novel strategies for intervention. Recent published findings from our laboratory provide the impetus for a detailed evaluation of serum amyloid A (SAA) in AAA progression: 1) SAA deficiency attenuates AAA in a mouse model; 2) in mice, SAA is present in AAA in regions with substantial elastin degradation, macrophage infiltration, and matrix metalloproteinase (MMP) activity; and 3) SAA can be detected in human AAA. In unpublished work, we also determined that SAA induces IL-1β and NLRP3 expression, as well as IL-1β secretion, in macrophages, consistent with priming and activation of the NLRP3 inflammasome. These findings are notable, given the recent recognition that NLRP3 inflammasome activation is a critical event in AAA development in mice. Thus, our central hypothesis is that SAA activates the NLRP3 inflammasome, thereby amplifying local inflammatory responses that enhance pathological tissue remodeling and promote AAA progression. AIM 1: Investigate the role of the NLRP3 inflammasome in SAA's ability to promote AAA in mice. Aim 1a. Using mice deficient in various inflammasome components (NLRP3-/-, ASC-/-, caspase-1-/- mice) or IL-1β signaling (IL-1R-/- mice), we will determine whether SAA-mediated AAA is dependent on the NLRP3 inflammasome. We will also investigate whether small-molecule anionic sulphonates, a treatment that blocks the deposition of SAA in tissues, is effective in reducing AAA in mice. Aim 1b. Using macrophage cell cultures, we will investigate whether any of the known biological activities attributed to SAA, including reactive oxygen species generation or association with HDL, are involved in SAA-mediated NLRP3 inflammasome activation. AIM 2: To test the hypothesis that systemic SAA promotes the progression of an established AAA. Aim 2a. Our approach will be to transiently increase SAA expression in livers of mice at specific intervals during the course of AngII infusion through the use of viral vectors and an inducible transgene. As a complementary approach, SAA expression will be suppressed using antisense oligonucleotides. The impact of SAA on indices of AAA progression and aortic inflammation and remodeling will be determined. Aim 2b. To investigate the potential role of SAA and inflammasome activation in human AAA, the relationship between plasma SAA, IL-1β and the rate of AAA expansion in humans will be determined in the prospective N-TA3CT trial. These studies hold the potential for identifying new strategies for the clinical management of AAA.