ACTA2 Pathogenic Variants Activating Heat Shock Factor 1 and Increasing Cholesterol Biosynthesis in Smooth Muscle Cells Predispose to Early Onset Atherosclerosis.

BACKGROUND: ACTA2 pathogenic variants predispose to thoracic aortic disease, and a subset of variants lead to early onset atherosclerotic cardiovascular disease (ASCVD). The molecular pathway linking misfolded SMA (α-smooth muscle actin) monomers to augmented atherosclerosis-associated smooth muscle cell phenotypic modulation can be modeled in vitro by stably expressing the ACTA2 p.R149C variant in Acta2-/- smooth muscle cells. METHODS: The Montalcino Aortic Consortium patient registry was used to identify cases with ACTA2 pathogenic/likely pathogenic missense variants. These patients were surveyed, and their medical records were reviewed to identify cases with early onset ASCVD. The variants for these cases, as well as other recurrent ACTA2 missense variants, were individually expressed in Acta2-/- smooth muscle cells, and transcript and protein levels, HSF1 (heat shock factor 1) activation, HMGCR (3-hydroxy-3-methylglutaryl-coenzyme A reductase) expression and activity, cholesteryl ester levels, and downstream smooth muscle cell phenotypic modulation were assessed. RESULTS: Early onset ASCVD included coronary artery disease, peripheral vascular disease, and atherosclerotic plaques identified by imaging in the arch, descending, or abdominal aorta, along with the celiac, iliac, renal, or vertebral arteries. Twelve ACTA2 variants were identified to be associated with early onset ASCVD. Early onset ASCVD was correlated with HSF1 activation (P=0.035), cellular cholesteryl ester levels (P=0.0031), and having one family member with the specific ACTA2 pathogenic variant who had early onset ASCVD (P=0.0001). CONCLUSIONS: Assays assessing the molecular mechanism that leads to early onset ASCVD can identify which ACTA2 pathogenic variants will trigger this condition. Ultimately, this information informs precision medical care for individuals with ACTA2 pathogenic variants, with the ultimate goal of preventing thoracic aortic disease and ASCVD.