Hereditary thoracic aortic aneurysm and dissection (HTAAD) is an autosomal dominant disorder characterized by dilatation or dissection of the thoracic aorta in families without Marfan- or related syndromes. ACTA2 gene, encoding alpha-smooth muscle actin, is the most frequent cause of non-syndromic HTAAD (12 to 21%). The penetrance is incomplete, with a dominant negative effect, and probably affected by the mutation location. Thus, the cumulative risk to aortic event ranges from 76% at the age of 85 in the classical form, to 100% by the age of 25 years in the highly penetrant ACTA2 variant at p.R179 which is associated with multisystem smooth muscle cell dysfunction syndrome (SMDS). SMDS is characterized by patent ductus arteriosus or aorto-pulmonary fenestration, early aortic dissection without dilatation, and cerebrovascular or coronary disease (moya-moya, stenosis). In clinical practice, this clinical heterogeneity doesn’t allow a relevant and personalized health care prevention.

We proposed to develop and validate a new cellular model to explore in vitro the functional effects of ACTA2 variants (Class V) and to identify key mediator of vascular smooth muscle cells (VSMCs) dysfunction.

Three patients with different ACTA2 pathogenic variants (p.G.148R, p.Thr212Lys, p.P355G) were included. Their phenotype was aortic dissection before 30-years old, and a more severe phenotype with ischemic stroke at 13-years old mimicking the SMDS for the patient with the pG.148R variant. Peripheric blood mononuclear cells (PBMCs) were collected from patient blood samples and induced pluripotent stem cells (iPSCs) were reprogrammed. Human iPSCs were differentiated toward the neural crest lineage, and subsequently to VSMCs. VSMCs were analyzed for their proliferation rate and migration capacity. Their actin polymerization was examined. To identify phenotypic difference between these three ACTA2 variants we performed RNAseq analysis. Patients VSMCs from healthy controls were used as controls.

We observed difference of proliferation using FACS analysis, and of migration between these three iPSC-derived VSMCs compared to controls. Transcriptomic analysis is currently analysed and results will be presented at the congress.

Our study identifies a robust protocol to obtain iPSC-derived VSMCs and provides novel insight on the genotype-phenotype correlation in patients with ACTA2 mutations.