ACTA1 and glomerular disorder: TGF-β1 drives differentiation of renal epithelial cells into α-SMA positive myofibroblasts, which also secrete collagen (Fan et al., 1999). In human glomerular disease, TGF-β1 protein expression is positively correlated with interstitial fibrosis severity and ECM production (Goumenos et al., 2001).