Schisandrol B protects against lithocholic acid-induced cholestatic liver injury in mice through mitochondrial biogenesis

BACKGROUND: Mitochondrial biogenesis plays a vital role in various types of hepatocyte injury. Schisandrol B (SolB), a bioactive lignan isolated from Schisandra sphenanthera, exerts a significant hepatoprotective effect against lithocholic acid (LCA)-induced cholestatic liver injury. Whether mitochondrial biogenesis is involved in the anti-cholestasis effect of SolB remains unknown. METHODS: A mouse model of cholestatic liver injury was induced by intraperitoneal injection of LCA. SolB was administered orally twice a day. Serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), total bile acids (TBA) and total bilirubin (TBILI), as well as hepatic superoxide dismutase (SOD) activity were measured. Liver pathology was evaluated by toxylin and eosin (H&E) staining. Mitochondrial morphology was examined using electron microscopy. Furthermore, the expression of mitochondrial biogenesis-related genes or proteins was analyzed by RT-qPCR or Western blot. RESULTS: We confirmed that SolB pretreatment (200 mg/kg/d) alleviated LCA-induced liver injury as evidenced by histological and biochemical analyses. SolB alleviated LCA-induced mitochondrial dysfunction in mice, as evidenced by increased mitochondrial DNA (mtDNA) content, superoxide dismutase (SOD) levels, and peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α) and mitochondrially encoded cytochrome c oxidase subunit 1 (MTCO1) expression, together with decreased fibroblast growth factor 21 (Fgf21) and growth differentiation factor 15 (Gdf15) gene levels. Transmission electron microscope analysis showed that LCA elicited small, fragmented mitochondria, which were not reversed after SolB pretreatment. However, western blot analysis showed that the expression of mitochondrial dynamics-related proteins, such as dynamin-related protein1 (DRP1), optic atrophy 1 (OPA1), mitofusin 1 (MFN1), and MFN2, was significantly decreased after LCA treatment. Pretreatment with SolB could significantly upregulate DRP1, mitochondrial fission factor (MFF), and fission1 (FIS1) which are crucial to regulate mitochondrial fission. It is worth noting that the protective effect of SolB against LCA-induced liver injury was independent of parkin RBR E3 ubiquitin-protein ligase (PARKIN)-mediated mitophagy as evidenced by decreased PARKIN and microtubule-associated protein light chain 3 (LC3)-II. CONCLUSION: In summary, this study demonstrated that SolB improved mitochondrial function but had no effect on LCA-induced mitochondrial fragmentation, which provides new insights into better understanding hepatoprotective mechanism of SolB against cholestatic liver injury.