AlphaSMA

Alpha-smooth muscle actin (alphaSMA) is an actin isoform encoded by the ACTA2 gene. It is a 42-kilodalton cytoskeletal protein that forms part of the contractile apparatus in smooth muscle cells and in myofibroblasts.

Within tissues, alphaSMA is abundant in vascular smooth muscle cells and other smooth muscle–rich tissues. It is also induced in nonmuscle cells such as fibroblasts during activation to myofibroblasts, contributing to the formation of contractile stress fibers that support wound contraction and extracellular matrix remodeling. The presence of alphaSMA is associated with the ability of cells to generate contractile force.

Because of its restricted expression pattern, alphaSMA is widely used as a marker of smooth muscle differentiation and myofibroblast presence in histology and research. Detection is typically by immunohistochemistry or Western blot using anti-alphaSMA antibodies. Its expression can be upregulated during tissue repair and fibrotic diseases, and alphaSMA–positive myofibroblasts are a common feature of desmoplastic stroma in tumors.

Genetic variants in ACTA2 can cause vascular diseases, notably familial thoracic aortic aneurysm and dissection, with variable penetrance and expressivity. Abnormal alphaSMA function or regulation can also impact smooth muscle contractility and cell motility, contributing to disease phenotypes in certain contexts.