Mitochondrial dysfunction-associated cellular senescence is partially involved in bleomycin-induced pulmonary fibrosis in mice

Accumulating data demonstrate that bleomycin (BLM), a clinically used antineoplastic drug, induces pulmonary interstitial fibrosis. However, the specific mechanism remains unclear. This study was carried out for the purpose of evaluating the effect of mitochondrial dysfunction-associated senescence on BLM-induced pulmonary fibrosis. Adult C57BL/6 J mice were intratracheally instilled with BLM (2.5 mg/kg). Pulmonary α-SMA and Vimentin, two indicators of epithelial-mesenchymal transition (EMT), were increased, and pulmonary collagen deposition was shown in BLM-treated mice. Pulmonary p16 and p21, two biomarkers of cell cycle arrest, were elevated, and pulmonary SASP indicators were up-regulated in BLM-treated mice. The reduction of mitochondrial area in BLM-treated mouse lungs was revealed by transmission electron microscopy. ATP content was reduced in BLM-treated mouse lungs. Pulmonary SOD2 and IDH2, two enzymes located in mitochondria, were decreased in BLM-treated mice. Sirtuin3 (SIRT3), an NAD + -dependent deacetylase located in mitochondria, was down-regulated in BLM-treated mouse lungs. Interestingly, Sirt3 gene knockout aggravated BLM-evoked mitochondrial dysfunction-associated senescence in mouse lungs. Sirt3 gene knockout exacerbated BLM-induced lung fibrosis. Conversely, nicotinamide mononucleotide (NMN), an NAD + precursor, weakened BLM-induced down-regulation of mitochondrial SIRT3 activity in mouse lungs. NMN pretreatment attenuated BLM-induced mitochondrial dysfunction-associated senescence in mouse lungs. Finally, NMN pretreatment alleviated BLM-induced EMT and lung fibrosis. These results indicate that mitochondrial dysfunction-associated senescence partially contributed to BLM-induced pulmonary fibrosis.