Glycochenodeoxycholate promotes IL-8 expression through ER-mitochondrial calcium signaling in human hepatocytes

Accumulation of excessive bile acids in the liver contributes to the progression of liver injury; thus, elucidating the bile acid-induced responses remains a critical challenge. Although conjugated bile acids have recently been reported to induce inflammatory responses at non-cytotoxic concentrations, the precise molecular mechanisms involved are not fully understood. The present study investigated the role of intracellular calcium dynamics-focusing particularly on mitochondria-in bile acid-induced inflammatory signaling. Exposure of human hepatocytes isolated from humanized liver chimeric mice (HepaSH cells) to glycochenodeoxycholate (GCDCA), a major component of the human bile acid pool, induced IL-8 mRNA expression at non-cytotoxic concentrations. This induction was significantly suppressed by 2-APB, an inhibitor of inositol 1,4,5-trisphosphate receptors on the endoplasmic reticulum. To clarify the underlying mechanisms, intracellular calcium measurements using fluorescent probes revealed no prominent changes in global cytosolic calcium levels; instead, GCDCA induced a marked increase in mitochondrial calcium levels, which was attenuated by 2-APB co-treatment. Overall, our findings highlight the critical role of mitochondria-centered calcium regulation in bile acid-induced inflammatory responses, providing novel insights into the pathogenesis of cholestatic liver injury.