Abstract 532: Deficiency of CCN3 in Smooth Muscle Cells Perturbs Vascular Homeostasis and Exacerbates Thoracic Aortic Dissection

Introduction: Thoracic aortic dissection (TAD) is a life-threatening aortic disease with a high mortality rate in the event of rupture. Key mechanisms underlying the development of TAD include extracellular matrix (ECM) degradation and vascular smooth muscle cell (SMC) reprograming. Cellular communication network factor 3 (CCN3), a matricellular protein highly expressed in SMC, exerts a myriad of context-dependent biological functions. However, its role in SMC homeostasis and in the development of TAD remains largely undefined. Methods: A single-cell sequencing (Sc-seq) dataset (GSE213740) from human aortic dissection patients was analyzed to determine the association between CCN3 expression and TAD. In newly weaned male CCN3-floxed mice harboring Myh11-driven inducible Cre, 4 consecutive tamoxifen injections induced CCN3 deletion in SMCs. Mice without Cre expression were subjected to the same procedures and were used as controls. After 1 week of washout, 4-week-old mice were given 0.5% BAPN (β-aminopropionitrile monofumarate) in their drinking water to induce TAD. Histologic and protein measurements were performed on TAD tissues from control and CCN3-SMC-KO mice. Sc-seq analysis was performed to recapitulate cell heterogeneities and transcriptome profile changes. The regulatory role of SMC-derived CCN3 in TGFβ signaling was evaluated by western blot and colocalization analyses. Results: Analysis of the human Sc-seq dataset revealed downregulation of CCN3 in aortas from patients with TAD. CCN3-positive SMCs have elevated ECM and elastin gene expression in comparison to CCN3-null SMCs. In vivo, concordant with increased mortality in CCN3-SMC-KO animals, SMC-specific deletion of CCN3 promotes BAPN-induced elastin fibers fragmentation and degradation. In vitro, SMC deficiency of CCN3 diminished TGFβ-induced elastogenesis. CCN3 binds to the TGFβ receptor on SMCs and augments TGFβ receptor phosphorylation, thereby activating Smads, upregulating SMC elastogenesis, and as a consequence, alleviates elastin fiber fragmentation and TAD development. Conclusion: CCN3 is a key determinate of SMC reprogramming and sustains vascular homeostasis. Our findings suggest a novel target for the prevention and treatment of TAD.