SMAD3 and idiopathic pulmonary fibrosis: However, SMAD3-KO IPF fibroblasts did show a significant decrease (approx. 25%) in TG2 expression following TGFβ1 treatment, compared to wild-type IPF fibroblasts (Fig. 6c and d), confirming the importance of Smad3 in TGFβ1 regulated TG2 expression.