Thoracic aortic aneurysm is found in patients withACTA2pathogenic variants.ACTA2missense variants are associated with impaired aortic smooth muscle cell (SMC) contraction. This study tested the hypothesis that theActa2R149C/+variant alters actin isoform expression and decreases integrin recruitment, thus, reducing aortic contractility. Stress relaxation measurements in thoracic aortic rings showed two functional regimes with a reduction of stress relaxation in the aorta fromActa2R149C/+mice at low tension, but not at high tension values. Contractile responses to phenylephrine and potassium chloride were 50% lower inActa2R149C/+mice than in wild-type (WT) mice. Additionally, SMC were immunofluorescently labeled for specific proteins and imaged by confocal or total internal reflection fluorescence microscopy. The quantification of protein fluorescence ofActa2R149C/+SMC showed a downregulation in smooth muscle α-actin (SMα-actin) and a compensatory upregulation of smooth muscle γ-actin (SMγ-actin) compared to WT cells. These results suggest that downregulation of SMα-actin leads to reduced SMC contractility, while upregulation of SMγ-actin may lead to increased SMC stiffness. Decreased α5β1 and α2β1 integrin recruitment at cell-matrix adhesions further reduce the ability of mutant cells to participate in cell-matrix crosstalk. Collectively, the results suggest that mutantActa2R149C/+aortic SMC have reduced contractility and interaction with the matrix, which are potential long-term contributing factors to thoracic aortic aneurysms.