Abstract 12006: Smooth Muscle Cell Embryologic Origin Does Not Define Propensity for Phenotype Modulation in Murine Marfan Syndrome Aortic Root Aneurysm

Abstract

Introduction: Vascular smooth muscle cells (SMC) undergo phenotype modulation (silenced contractile genes and activated proteolytic/synthetic genes) in Marfan syndrome (MFS) aortic aneurysm. Aortic root SMCs develop from the second heart field (SHF) proximally and neural crest (NC) distally. We hypothesize that both developmental lineage and hemodynamic factors dictate SMC vulnerability to phenotype change, promoting focal aortic root aneurysm. Methods/Results: Aortic roots from adult MFS and littermate control mice (n=4 each sex) with a knockin fluorescent SHF tracing construct ( Nkx2-5 cre ) were sorted for lineage-resolved single cell RNA sequencing (scRNAseq). Modulated SMCs (modSMC) were enriched in MFS vs. controls (18.1% of all SMCs vs. 2.2%) and originated from both SHF (15.5%) and NC (20.2%) lineages, ruling out complete lineage specificity. NC-derived modSMCs expressed more aggrecan ( Acan ) and sclerostin ( Sost ) while small proteoglycans decorin ( Dcn ) and lumican ( Lum ) were enriched in SHF modSMCs. Insulin-like growth factor binding protein-2 ( Igfbp2 ) was a lineage-independent modSMC marker. RNA in situ hybridization localized Igfbp2 + SMCs within SHF/NC overlap in the aortic root. To study regional SMC propensity for modulation due to hemodynamic stresses, we generated aortic pressure overload via 27-gauge transverse aortic arch constriction (TAC) or sham surgery on healthy Myh11 cre / Rosa tdT (SMC-traced) mice. TAC induced mild root dilation vs . sham (1.93±0.07 mm vs. 1.69±0.09 mm, n=4, p<0.01). scRNAseq showed SMC phenotype modulation comparable to MFS in TAC mice and spatially concentrated in the aortic root. Conclusions: Embryologic origin does not dictate aortic SMC propensity for pathologic phenotype change in MFS but does promote distinct ECM proteoglycan gene activation. Aortic pressure overload incites root SMC modulation, suggesting hemodynamic effects may promote regional susceptibility to SMC-mediated aortic remodeling.