Mitsuyoshi Nakao

The high glycolytic activity of cancer cells leads to lactic acidosis (LA) in the tumor microenvironment. LA is not merely a consequence of metabolic activities but also has functional roles in metabolic reprogramming and cancer progression. Cholangiocarcinoma (CCA) cells exhibit a high dependency on glycolysis for survival and growth, but the specific effects of LA on cellular characteristics remain unknown. Here, we demonstrate that long‐term LA (LLA) reprograms the metabolic phenotype of CCA cells from glycolytic to oxidative and enhances their migratory activity. In CCA cell culture, short‐term LA (24 h) showed a growth inhibitory effect, while extended LA exposure for more than 2 weeks (LLA) led to enhanced cell motility. Coincidentally, LLA enhanced the respiratory capacity with an increase in mitochondrial mass. Inhibition of mitochondrial function abolished LLA‐induced cell motility, suggesting that metabolic remodeling affects the phenotypic outcomes. RNA‐sequencing analysis revealed that LLA upregulated genes associated with cell migration and epithelial–mesenchymal transition (EMT), including thrombospondin‐1 ( THBS1 ), which encodes a pro‐EMT‐secreted protein. Inhibition of THBS1 resulted in the suppression of both LLA‐induced cell motility and respiratory capacity. Moreover, high THBS1 expression was associated with poor survival in patients with CCA. Collectively, our study suggests that the increased expression of THBS1 by LLA promotes phenotypic alterations, leading to CCA progression.