微生物由来胆汁酸：肝臓修復における内因性再生メディエーター

The liver's extraordinary capacity for self-repair is often compromised by chronic injury, fibrosis, or extensive resection, creating an urgent need for innovative regenerative therapies to restore liver function. Emerging evidence suggests that microbiome-derived bile acid metabolites are potent endogenous mediators of hepatic regeneration. Beyond their canonical role in lipid emulsification, these chemically diverse molecules engage nuclear and membrane receptors, most notably the farnesoid X receptor (FXR) and Takeda G protein-coupled receptor 5 (TGR5), to stimulate hepatocyte proliferation, modulate inflammatory responses, and reactivate quiescent progenitor cells. In this review, we integrate mechanistic insights from partial hepatectomy, germ-free, and antibiotic-treated animal models with early clinical observations to illuminate how primary and secondary bile acids orchestrate cell cycle progression, cytokine balance, and extracellular matrix remodeling. We then examined the therapeutic landscape, from synthetic FXR/TGR5 agonists to live-biotherapeutic approaches, genetically modified probiotic strains, and fecal microbiota transplantation. We highlight the preliminary indicators of efficacy and challenges in manufacturing consistency, safety profiling, and regulatory classification. We address the interindividual variability in microbiome composition, potential biomarkers such as serum FGF19, imaging-based measures of functional liver mass, and considerations for optimal trial design. This is the first comprehensive review to frame microbiome-driven bile acids as direct modulators of liver regeneration and chart a coherent translational development pathway. By integrating stem cell biology, hepatology, microbiology, and bioengineering perspectives, we demonstrate the underexplored therapeutic potential of these approaches to transform the future of hepatic repair.