Melatonin enhances mitophagy and mitochondrial biogenesis in rats with carbon tetrachloride-induced liver fibrosis

Liver fibrosis leads to liver cirrhosis and failure, and no effective treatment is currently available. Growing evidence supports a link between mitochondrial dysfunction and liver fibrogenesis and mitochondrial quality control-based therapy has emerged as a new therapeutic target. We investigated the protective mechanisms of melatonin against mitochondrial dysfunction-involved liver fibrosis, focusing on mitophagy and mitochondrial biogenesis. Rats were treated with carbon tetrachloride (CCl4) dissolved in olive oil (0.5 mL/kg, twice a week, i.p.) for 8 wk. Melatonin was administered orally at 2.5, 5, and 10 mg/kg once a day. Chronic CCl4 exposure induced collagen deposition, hepatocellular damage, and oxidative stress, and melatonin attenuated these increases. Increases in mRNA and protein expression levels of transforming growth factor β1 and α-smooth muscle actin in response to CCl4 were attenuated by melatonin. Melatonin attenuated hallmarks of mitochondrial dysfunction, such as mitochondrial swelling and glutamate dehydrogenase release. Chronic CCl4 exposure impaired mitophagy and mitochondrial biogenesis, and melatonin attenuated this impairment, as indicated by increases in mitochondrial DNA and in protein levels of PTEN-induced putative kinase 1 (PINK1); Parkin; peroxisome proliferator-activated receptor-gamma coactivator 1α (PGC-1α); nuclear respiratory factor 1 (NRF1); and transcription factor A, mitochondrial (TFAM). CCl4-mediated decreases in mitochondrial fission- and fusion-related proteins, such as dynamin-related protein 1 (DRP1) and mitofusin 2, were also attenuated by melatonin. Moreover, melatonin induced AMP-activated protein kinase (AMPK) phosphorylation. These results suggest that melatonin protects against liver fibrosis via upregulation of mitophagy and mitochondrial biogenesis, and may be useful as an anti-fibrotic treatment.