The type III procollagen mRNA expression, the microvascular permeability, the quantitative and qualitative evaluation of pulmonary fibrosis by hydroxyproline assay and Masson's trichrome staining, the positive S100A4/FSP1 staining of epithelium and fibroblasts in the interstitium, and the phosphorylation of Akt and ERK1/2 were significantly reduced after using Akt-deficient mice and pharmacological inhibition with PD98059 and SB203580. Here, MAPK3 is linked to pulmonary fibrosis.