Elastin deposition and stenosis formation in the developing aorta

摘要 弹性蛋白是大动脉的基本成分，提供弹性以减轻心脏工作负荷和 保护下游器官。弹性蛋白仅在胚胎晚期开始的一段时间内表达 青春期阶段和结束阶段。由于弹性蛋白的70年半衰期，这种短的表达窗口是可能的 并使发育期弹性蛋白的正确沉积变得至关重要。弹性蛋白沉积 主要由同心层中的平滑肌细胞(SMC)组成，称为弹性板层。有一种情结 升主动脉壁内来自不同胚胎来源和分化状态的SMC的混合物 这些不同的壁细胞类型如何促进弹性板层的形成尚不清楚。先天突变 弹性蛋白基因的突变会导致弹性蛋白不足，并导致主动脉瓣上狭窄(SVAS)。没有 提高SVAS弹性蛋白水平和预防性手术缓解主动脉狭窄的治疗策略 避免心源性猝死的主要治疗方法。虽然手术有很好的早期效果，但也有 非常需要重新手术，特别是对儿童。弹性蛋白减少引起主动脉病变的机制 对狭窄的认识还不是很清楚。以前的鼠标模型加深了我们对SVAS的理解，但新的 更精确地控制发育过程中弹性蛋白沉积的位置和时间的小鼠模型 需要用来完善有争议的机制。目前提出的生物物理机制涉及到 主动脉弹性、生长、细胞增殖和/或胶原沉积导致狭窄形成。一个计算性的 主动脉生长和重塑模型(G&R)将有助于评估物理可信度和 竞争机制的局限性。计算G&R模型提供了对以下过程的洞察 成人血管疾病中的主动脉重塑，但在正常和正常过程中的应用有限 先天性疾病中的主动脉发育异常。这项建议的总体目标是更好地理解 正常升主动脉发育中弹性蛋白沉积的过程以及弹性蛋白水平降低如何导致 到主动脉发育异常时的狭窄。为实现这一目标提出了三个具体目标：目标1。 确定主动脉壁内不同类型的细胞如何促进弹性板层的形成；目标2.量化 分级弹性蛋白量对主动脉结构和心血管功能的影响；以及目标3。利用 描述和预测弹性蛋白含量和跨壁组织变化的计算模型 通过应力介导的G&R导致主动脉狭窄一种新的弹性蛋白漂浮的小鼠，允许弹性蛋白表达到 当培育到Cre表达系时，将以细胞类型和时间点特定的方式减少 目标1和2。基于非线性弹性、连续介质力学和应力定律的计算模型-- 目标3将使用中介生长和基质沉积。目标3中的模型预测将与 AIMS 1和AIMS 2中正常和异常主动脉发育的实验结果。 这些目标可能导致治疗SVAS中弹性蛋白不足和/或主动脉狭窄的新策略。

ABSTRACT Elastin is a fundamental component of large arteries, providing elasticity to reduce cardiac workload and protect downstream organs. Elastin is expressed only during a narrow timeframe initiating in the late embryonic stage and ending in adolescence. This short expression window is possible due to elastin’s 70-year half-life and makes correct deposition of elastin in the developmental period critically important. Elastin is deposited predominantly by smooth muscle cells (SMCs) in concentric layers called elastic laminae. There is a complex mixture of SMCs from different embryonic origins and differentiation states within the ascending aortic wall, yet how these different mural cell types contribute to elastic laminae formation is unknown. Congenital mutations in the elastin gene lead to elastin insufficiency and cause supravalvular aortic stenosis (SVAS). There are no therapeutic strategies to increase elastin levels in SVAS and preventative surgery to alleviate aortic stenosis is the primary treatment to avoid sudden cardiac death. While surgery has good early results, there is a significant need for reoperation, especially in children. The mechanisms by which reduced elastin causes aortic stenosis are not well understood. Previous mouse models have advanced our understanding of SVAS, but new mouse models with more precise control of the location and timing of elastin deposition during development are needed to refine debated mechanisms. Currently proposed biophysical mechanisms relate changes in aortic elasticity, growth, cellular proliferation, and/or collagen deposition to stenosis formation. A computational model of aortic growth and remodeling (G&R) would be useful to evaluate the physical plausibility and limitations of competing mechanisms. Computational G&R models have provided insight into processes of aortic remodeling in adult vascular disease, but have seen limited application for processes of normal and abnormal aortic development in congenital disease. The overall goal of this proposal is to better understand the process of elastin deposition in normal ascending aortic development and how reduced elastin levels lead to stenosis in abnormal aortic development. Three specific aims are proposed to accomplish this goal: Aim 1. Determine how different cell types within the aortic wall contribute to elastic laminae formation; Aim 2. Quantify the effects of graded elastin amounts on aortic structure and cardiovascular function; and Aim 3. Utilize a computational model to describe and predict how variations in elastin amount and transmural organization lead to aortic stenosis through stress-mediated G&R. A new elastin-floxed mouse that allows elastin expression to be reduced in a cell type and time point specific manner when bred to Cre expressing lines will be used for Aims 1 and 2. A computational model based on laws of nonlinear elasticity, continuum mechanics, and stress- mediated growth and matrix deposition will be used for Aim 3. Model predictions in Aim 3 will be compared to experimental results for normal and abnormal aortic development in Aims 1 and 2. Successful completion of these aims may lead to novel strategies to treat elastin insufficiency and/or aortic stenosis in SVAS.