Alteration of energy metabolism in the pathogenesis of bile duct lesions in primary biliary cirrhosis

Aim: Primary biliary cirrhosis (PBC) is characterised by antimitochondrial antibody against the pyruvate dehydrogenase complex (PDC) and chronic nonsuppurative destructive cholangitis (CNSDC). Pyruvate oxidation to acetyl-CoA by PDC is a key step in the glycolytic system. Oestrogen-related receptor-α (ERRa) is functionally activated by inducible coactivators such as peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) and Bcl-3. Moreover, the PGC-1α-ERRa axis interrupts glycolytic metabolism through the upregulation of pyruvate dehydrogenase kinase, isozyme 4 (PDK4), which functionally inhibits PDC-E1α and stimulates fatty acid oxidation. In this study, we investigated the PGC-1α-ERRa axis to clarify PDC dysfunction in CNSDC of PBC. Methods: The expression of PGC-1α, Bcl-3, ERRa, PDK4 and PDC-E1α was examined by immunohistochemistry in liver sections from patients with PBC and controls. The expression of these molecules, the activity of mitochondrial dehydrogenase and PDC, and their alterations by starvation, a treatment used to induce PGC-1α expression, were examined in cultured human biliary epithelial cells (BECs). Results: The nuclear expression of PGC-1α, Bcl-3 and ERRa was exclusively observed in CNSDC of PBC. Moreover, the expression of PDK4 and PDC-E1α was enhanced in CNSDC of PBC. In cultured BECs, the amplification of Bcl-3 and PDK4 mRNAs by reversetranscription-PCR and mitochondrial dehydrogenase activity were markedly increased but PDC activity was decreased according to the upregulation of PGC-1α. Conclusions: In CNSDC of PBC, the activation of the ERRa-PGC-1α axis was exclusively observed, suggesting the interference of PDC-related glycolytic function and the induction of the fatty acid degradation system. The switching of the cellular energy system is possibly associated with the pathogenesis of CNSDC in PBC.