ACTA2 and disease of the tendon: Another important gene found to be upregulated in tendinopathy samples, as well as in healthy samples with SP treatment, was ACTA2. ACTA2 is an important cytoskeleton gene that encodes the α-smooth muscle actin [37,38,39], which is a functional marker for a fibroblast subtype that rapidly remodels the extracellular matrix [40].