MAPK3 and idiopathic pulmonary fibrosis: The phosphorylation of Erk1/2 MAPK induced by TGF-β1 was significantly reduced after pre-incubation with treprostinil as shown by Western blotting and image analysis in Figure 5B. The TGF-β1-induced activation of Smad2 was only reduced in IPF-derived fibroblasts by treprostinil, but not in control fibroblasts (Figure 5C).