Abstract Body (Do not enter title and authors here): Introduction: Marfan Syndrome (MFS) is a genetic disorder characterized by aortic root aneurysm formation, with risk of dissection and rupture. Proteomic profiling on human Marfan iPSC-derived second heart field (SHF) SMCs revealed decreased Mannose Receptor 2 (MRC2) expression. Given MRC2's role in collagen homeostasis, its reduction is hypothesized to impair collagen turnover and compromise aortic wall integrity, worsening TAA development in MFS.
Methods: In vitro assays were performed on iPSC-derived SMCs from the SHF and cardiac neural crest (cNC) from MFS patients and control. MRC2's impact on collagen dynamics was assessed via western blot following targeted MRC2 knockdown and overexpression using lenti-vector. In vivo, MRC2 conditional SMC-specific knockout mice on WT and MFS backgrounds were generated to explore collagen turnover and its influence on MFS pathology and for single-cell RNA (scRNA) sequencing.
Results: MRC2 expression was significantly lower and COL1a1 levels significantly higher in SHF-derived SMCs from MFS patients compared to cNC-derived and control SHF SMCs. MRC2 knockdown in these cells significantly increased COL1A1 expression, which normalized upon MRC2 overexpression. Longitudinal echocardiographic analysis of SMC-specific Marfan MRC2 KO mice showed significantly larger aortic root diameters at 24 weeks versus control (MFS-MRC2 KO vs. MFS and WT: 2.62±0.27 mm vs. 2.36±0.25 mm, p<0.05 and 1.92±0.12, p<0.05). Histological evaluation revealed increased adventitial collagen in the aortic root of MFS-MRC2 KO mice. scRNA showed MRC2 was primarily expressed in modulated SMCs (modSMCs) and that modSMCs in MFS SMC-specific MRC2 KO versus MFS control had upregulation of pathways involved in translation at the synapse/cytoplasm, ossification and osteoblast differentiation, and peptidase activity. Overall SMC and fibroblast gene expression profiles were similar when MRC2 was knocked out, however, the majority of gene expression appeared to be influenced by the MFS mutation itself.
Conclusion: The study highlights that MRC2 plays a crucial role in aortic wall collagen homeostasis, with its deficiency markedly exacerbating TAA progression in MFS mice.