COL1A1 and pulmonary fibrosis: In cultured stellate cells, it has been demonstrated that ATRA can prevent morphological transition towards a myofibroblast phenotype and decrease collagen 1 synthesis.37 In addition, ATRA can inhibit radiation-induced pulmonary fibrosis.39 The authors report inhibition of COL1A1 mRNA expression by ATRA in irradiated lung tissue.