Microcystin-LR Disrupts Bile Acid Homeostasis, Driving Cholestatic Liver Injury and Gallstones via FXR/SHP Antagonism

Bile acids (BAs) are vital for liver health, and their dysregulation causes hepatobiliary disorders. Microcystins (MCs) are pervasive hepatotoxins in freshwaters worldwide that threaten public health; yet, their effects on BA homeostasis─particularly regulation mechanisms─remain poorly defined. Here, we show that chronic exposure to environmentally relevant doses of microcystin-LR (MC-LR) induces not only cholestatic liver injury but also gallstone formation in mice. Targeted metabolomics revealed that MC-LR strikingly altered BA profiles across the liver, gallbladder bile, and serum, characterized by increased hydrophobicity and excessive deconjugation. Crucially, this compositional distortion overrides the quantitative expansion of the gallbladder BA pool, creating a prolithogenic environment. Gene and protein expression analyses further demonstrated dysregulation of BA synthetic enzymes, transporters, and nuclear receptors FXR and SHP, indicative of a disrupted FXR-SHP signaling axis. Microscale thermophoresis and molecular docking confirmed the high-affinity binding of MC-LR to human FXR and SHP. Rescue experiments further showed that pharmacological activation of FXR using GW4064 or obeticholic acid (OCA) effectively reversed MC-LR-induced intracellular BA accumulation in human HepG2 cell line. Collectively, our findings establish MC-LR as an overlooked environmental driver of gallstone disease and highlight direct FXR-SHP antagonism as a key mechanism with therapeutic potential.