Role of RNA-mediated danger signals in regulating TAAD development

摘要 胸主动脉瘤和夹层(TAAD)，尤其是A型夹层，是一种毁灭性的疾病， 住院死亡率高达25%。尽管升主动脉瘤和夹层(AAD)可能 由于遗传易感性，70%以上的病例是散发性的。目前，手术修复是唯一的 可用的治疗方法。由于贫困，药物预防药物的开发仍然是一项具有挑战性的任务 了解AADS发病的细胞和分子机制。我们有 有报道称，血管平滑肌细胞转化生长因子-βI型受体的出生后缺失 (Tgfbr1iko)可诱导雄性小鼠AAD的形成。最近，我们开发了一种新型的X连锁Cre系列，它可以驱动 Tgfbr1iko和AAD在雌性小鼠中的形成与其亲本Y连锁的效率和严重程度相似 MYH11-CreerTM菌株。AADS的组织学特征之一是慢性炎症，其特征是 进行性SMC耗竭、免疫细胞浸润和基质降解。这些活动创造了一个完美的 激活先天免疫的环境。具体地说，濒临死亡的SMC产生的分子可以发挥作用 作为损伤相关的分子模式通过自分泌激活病原体识别受体(PRRs) 和/或旁分泌信号，目前正在对其他 慢性疾病。因此，我们探索了我们的AAD模型中天然免疫的激活，并获得了 结果如下。1)AAD的形成与RNA氧化、Toll样受体(TLR)上调有关。 7、SMC坏死性下垂。2)AAD-，但不是正常的主动脉来源的RNA触发炎症反应 免疫细胞。3)更重要的是，用抑制内体TLRs的试剂处理小鼠可减轻AAD 队形。这些新的发现导致了我们的总体假设，即自我RNA触发TLR7介导的危险 促进TAAD发展的信号。这一假设将通过两个相互关联的具体目标来检验。 特定目标1将确定自身RNA在激活先天免疫损伤和AAD中的作用 队形。这一目标下的研究将解决三个关键问题。1)是什么使自身RNA致病？2)如何致病？ 自身RNA调节RIPK3/pMLKL通路诱导SMC坏死性下垂？3)坏死性下垂的作用是什么 AAD阵容中的SMC？具体目标2将确定识别促进AAD形成的自我RNA的PRR(S)。 在具体目标2下提出的实验将回答两个关键问题。1)自身RNA是由 同一内体TLR成员(S)在不同种类的细胞(即小鼠和人)中是遗传的 或对负责的rna感应TLR的药物抑制(S)，足以改变AAD的进程 队形？我们新颖的AAD鼠标模型使我们处于独特的位置来解决这些问题 不同性别的老鼠AADS。该项目的完成将使人们更好地了解这些机制。 在AAD形成过程中滋养慢性炎症，并可能为AAD的发展提供新的方向 对急性呼吸窘迫综合征发生和发展的药理学预防。

ABSTRACT Thoracic aortic aneurysms and dissections (TAAD), particularly type A dissections, are a devastating disease, with an in-hospital mortality rate up to 25%. Although ascending aortic aneurysms and dissections (AADs) may result from genetic predispositions, more than 70% of cases are sporadic. Currently, surgical repair is the only available treatment. Development of pharmacological prevention agents remains a challenging task due to poor understanding of the cellular and molecular mechanisms responsible for pathogenesis of AADs. We have reported that postnatal deletion of smooth muscle cell (SMC) transforming growth factor-β type I receptors (Tgfbr1iko) induces AAD formation in male mice. Recently, we developed a novel X-linked Cre line that drives Tgfbr1iko and AAD formation in female mice with similar efficiency and severity compared to its parental Y-linked myh11-CreERTM strain. One of the histological hallmarks of AADs is chronic inflammation, characterized by progressive SMC depletion, immune cell infiltration, and matrix degradation. These events create a perfect environment for activation of the innate immunity. Specifically, molecules produced by dying SMCs can function as damage-associated molecular patterns to activate pathogen recognition receptors (PRRs) via autocrine and/or paracrine signaling, a scenario currently under rigorous experimental and clinical evaluation for other chronic conditions. Therefore, we explored activation of the innate immunity in our AAD models and obtained results as follows. 1) AAD formation was associated with RNA oxidation, upregulation of toll-like receptor (TLR)- 7, and SMC necroptosis. 2) AAD-, but not normal aorta-derived RNAs triggered inflammatory response in immune cells. 3) More importantly, treatment of mice with reagents inhibiting endosomal TLRs attenuated AAD formation. These novel findings led to our overall hypothesis that self-RNAs trigger TLR7-mediated danger signals to promote TAAD development. This hypothesis will be tested through two interrelated Specific Aims. Specific Aim 1 will determine the contribution of self-RNAs to activation of innate immune injury and AAD formation. Studies under this Aim will address three key issues. 1) What makes self-RNAs pathogenic? 2) How self-RNAs regulate the RIPK3/pMLKL pathway to induce necroptosis of SMCs? 3) What is the role of necroptosis of SMCs in AAD formation? Specific Aim 2 will identify PRR(s) that sense self-RNAs to promote AAD formation. Experiments proposed under Specific Aim 2 will answer two key questions. 1) Are self-RNAs sensed by the same endosomal TLR member(s) in different type of cells across species (i.e. mouse vs. human)? 2) Is genetic or pharmacological inhibition of the responsible RNA-sensing TLR(s) sufficient to alter the course of AAD formation? Our novel AAD mouse models have placed us in a unique position to address these issues with mouse AADs of either gender. Completion of this project will provide a better understanding of the mechanisms that nourish chronic inflammation during AAD formation and may lead to a new direction for the development of pharmacological preventions against initiation and progression of AADs.