Mitochondria-Dependent Metabolic Reprogramming Enhances Myofibroblast Differentiation and Aggravates Bleomycin-Induced Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial lung disease characterized by irreversible fibrosis. Aberrant cell differentiation plays a crucial role in the development of IPF. Although recent studies have suggested that mitochondrial dysfunction may play a role in IPF, its direct impact on fibrosis remains unclear. This study aimed to clarify the role of mitochondria in lung cell differentiation and pulmonary fibrosis development by employing mito-mice ND6M, in which the activity of respiratory chain complex I is decreased due to a mitochondrial DNA mutation (G13997A). Pulmonary fibrosis was induced by administering bleomycin (BLM) to both wild-type and mito-mice ND6M. Bone marrow-derived macrophages and primary lung fibroblasts, generated from both types of mice, were analyzed to evaluate M1/M2 polarization and myofibroblast differentiation, respectively. Compared to wild-type mice, mito-mice ND6M exhibited more severe fibrosis and lower survival rates following BLM inoculation. Lactate production in the lungs after BLM administration was significantly higher in mito-mice ND6M than in wild-type mice. TGF-β1-treated fibroblasts from mito-mice ND6M exhibited increased α-smooth muscle actin expression. While type I collagen expression was not different between these mice, TGF-β1-induced expression of phosphoserine phosphatase and serine hydroxymethyltransferase2, two of the enzymes involved in the serine–glycine pathway, was significantly higher in mito-mice ND6M than in wild-type mice. On the other hand, mitochondrial dysfunction had a small effect on pulmonary inflammation and on M1/M2 macrophage polarization. In conclusion, mitochondrial dysfunction promotes TGF-β1-induced myofibroblast differentiation and BLM-induced pulmonary fibrosis. Mitochondria-dependent metabolic reprogramming may therefore represent a promising therapeutic target in IPF.