Abstract 259: Phenotype Switch and Altered Mechanosignaling in Vascular Smooth Muscle Cells From Marfan Syndrome Mice

Abstract

Background: Mechanisms whereby fibrillin-1 gene mutations promote aortic aneurysms in Marfan Syndrome (MFS) are complex. Vascular smooth muscle cells (VSMC) are crucial to aneurysm pathophysiology through (1) support of mechanical homeostasis, in which contractile VSMC connect extracellular matrix to shield synthetic VSMC against high mechanical loads and (2) key effects of synthetic VSMC on extracellular matrix organization. However, little is known about VSMC phenotypic adaptation and response to mechanical loading in MFS development. Methods: We investigated phenotypic patterns and response to cyclic stretch in VSMC cultured from aortae of wild-type (WT) mice or MFS mice bearing mgΔ lpn mutation, which develop aortic dilation/thickening from the first month of age, accelerated after 6 months. We studied VSMC from 8-9 week-old mice to focus on early disease stages. VSMC remained either static or underwent 10% cyclic stretching (1Hz, 8h). Protein expression/morphology were evaluated by Western and confocal analyses. We also performed Traction Force Microscopy to assess force distribution profile. Results: There were significant phenotypic changes in MFS-VSMC vs. WT, with loss of fusiform shape and enhanced spreading, promoting ≈7-fold increased in cell area vs. WT (p<0.001, n=5) and >60% decrease in calponin expression vs. WT (p<0.05, n=3). Also, MFS-VSMC had a 10-fold greater expression of endoplasmic reticulum stress marker Grp78 (n=2). Cyclic stretch promoted expected increase in synthetic phenotype markers in WT-VSMC but an opposing contractile phenotype switch in MFS-VSMC, with decreased calponin and pFAK expression and increased stress fiber buildup. Cyclic stretch promoted similar increase in Grp78 expression in WT vs. MFS-VSMC. MFS-VSMC showed ca.60% lower capacity to generate adhesive force and extracellular matrix contractile momentum (p<0.003, n=10), associated with lower deformation energy in vitro (9,16 vs. 1,67 pJ, p<0.004, n=6). Conclusions: MFS associate with important deregulation of VSMC phenotypic adaptations, which may impact on their force development and disrupt force distribution in aorta.