Mitochondrial oxidative metabolism contributes to a cancer stem cell phenotype in cholangiocarcinoma

Highlights•The metabolic characteristics of cancer stem cells in cholangiocarcinoma are not known.•Cholangiocarcinoma stem-like cells preferentially use oxidative phosphorylation as a source of energy.•PGC-1α is a key molecule regulating the metabolic features of cholangiocarcinoma stem-like cells.•Interfering with oxidative phosphorylation or PGC-1α limits the development of tumors originating from stem-like cells in vivo.•Expression of PGC-1α or proteins of the mitochondrial respiratory complex correlate with clinical outcomes in patients with cholangiocarcinoma.AbstractBackground & AimsLittle is known about the metabolic regulation of cancer stem cells (CSCs) in cholangiocarcinoma (CCA). We analyzed whether mitochondrial-dependent metabolism and related signaling pathways contribute to stemness in CCA.MethodsThe stem-like subset was enriched by sphere culture (SPH) in human intrahepatic CCA cells (HUCCT1 and CCLP1) and compared to cells cultured in monolayer. Extracellular flux analysis was examined by Seahorse technology and high-resolution respirometry. In patients with CCA, expression of factors related to mitochondrial metabolism was analyzed for possible correlation with clinical parameters.ResultsMetabolic analyses revealed a more efficient respiratory phenotype in CCA-SPH than in monolayers, due to mitochondrial oxidative phosphorylation. CCA-SPH showed high mitochondrial membrane potential and elevated mitochondrial mass, and over-expressed peroxisome proliferator-activated receptor gamma coactivator (PGC)-1α, a master regulator of mitochondrial biogenesis. Targeting mitochondrial complex I in CCA-SPH using metformin, or PGC-1α silencing or pharmacologic inhibition (SR-18292), impaired spherogenicity and expression of markers related to the CSC phenotype, pluripotency, and epithelial-mesenchymal transition. In mice with tumor xenografts generated by injection of CCA-SPH, administration of metformin or SR-18292 significantly reduced tumor growth and determined a phenotype more similar to tumors originated from cells grown in monolayer. In patients with CCA, expression of PGC-1α correlated with expression of mitochondrial complex II and of stem-like genes. Patients with higher PGC-1α expression by immunostaining had lower overall and progression-free survival, increased angioinvasion and faster recurrence. In GSEA analysis, patients with CCA and high levels of mitochondrial complex II had shorter overall survival and time to recurrence.ConclusionsThe CCA stem-subset has a more efficient respiratory phenotype and depends on mitochondrial oxidative metabolism and PGC-1α to maintain CSC features.Lay summaryThe growth of many cancers is sustained by a specific type of cells with more embryonic characteristics, termed 'cancer stem cells'. These cells have been described in cholangiocarcinoma, a type of liver cancer with poor prognosis and limited therapeutic approaches. We demonstrate that cancer stem cells in cholangiocarcinoma have different metabolic features, and use mitochondria, an organelle located within the cells, as the major source of energy. We also identify PGC-1α, a molecule which regulates the biology of mitochondria, as a possible new target to be explored for developing new treatments for cholangiocarcinoma.Graphical abstract