Abstract 18753: Dynamic Phenotypic Transition of Smooth Muscle Cells During Human Ascending Thoracic Aortic Disease Progression: From Compensation in Aortic Aneurysm to Decompensation in Aortic Dissection

Abstract

Introduction: Although ascending thoracic aortic aneurysm (ATAA) and ascending thoracic aortic dissection (ATAD) share common pathologic features of aortic degeneration, the specific elements that lead to rapid disease progression in ATAD remain poorly understood. We examined the molecular and cellular dynamics in smooth muscle cells (SMCs) of aortic tissues from ATAA and ATAD patients and further examined mechanisms in a mouse model. Methods: Single-cell RNA sequencing (scRNA-seq) analyses were performed in ascending aortic tissues from individuals without aortic disease (n=8), patients with ATAA without dissection (n=9), and patients with acute ATAD (n=9). Further, scRNA-seq and scATAC-seq were performed in ascending aortic tissues from mice infused with angiotensin II (AngII) or control mice; scRNA-seq analyses were performed on SMC-specific Tgfbr2 -/- mice. Results: Six SMC subtypes were identified in human aortic tissues. Cluster proportion and trajectory analyses indicated a profound SMC transition from contractile in control to extracellular matrix (ECM)-contractile phenotype in ATAA, however, was reduced in ATAD tissues. Instead, ATAD showed significant SMC transition to inflammatory phenotype. Consistently, many genes in ECM organization and muscle contraction, collectively termed compensatory response, were upregulated in ATAA but downregulated in ATAD tissues compared with controls, whereas inflammatory response and cell death pathway genes were significantly upregulated in ATAD compared with control and ATAA tissues. Cell-cell interaction, regulatory network, and motif analysis suggested that TGF-beta-MEF2C signaling contributed to the induction of the ECM-contractile SMC phenotype. MEF2C + SMCs exhibited the capacity of transition towards ECM-producing SMCs in both mouse and human aorta. SMC-specific Tgfbr2 -/- mice showed compromised SMC transition to ECM-producing phenotype. Conclusions: Our study reveals SMC phenotypic transitions to ECM-producing SMCs in ATAA and to inflammatory and pro-death SMCs in ATAD, which represent a compensatory response in ATAA and a decompensatory status in ATAD. TGF-beta-MEF2C, a novel regulatory axis, promoted the compensatory response in SMCs of the ascending aorta.