ACTA1 and renal fibrosis: However, the in vitro and in vivo findings that (a) GSK3β is expressed in myofibroblasts, (b) GSK3β activity is crucial for TGF-β signaling and α-SMA expression, and (c) constitutively active GSK3β can increase α-SMA expression in vitro, suggest that GSK3β could play an important role in fibroblast differentiation and renal fibrosis.