The secondary bile acid, lithocholic acid, inhibits cystic fibrosis transmembrane conductance regulator expression and activity in colonic epithelial cells

Classically known for their roles in facilitating lipid digestion and absorption, bile acids are now also appreciated as enterocrine hormones that modulate many aspects of intestinal physiology. We have previously shown lithocholic acid (LCA), a secondary bile acid, to be protective against colonic inflammation. Here, we investigated whether LCA also regulates colonic epithelial fluid and electrolyte transport. T₈₄ cell monolayers were mounted in Ussing chambers for measurements of transepithelial Cl^- secretion. CFTR mRNA and protein expression were analyzed by qRT-PCR and Western blotting in T₈₄ cells and human-derived colonic organoids. CFTR promoter activity was assessed using a luciferase promoter/reporter assay in HEK293 cells. Pretreatment of T₈₄ cells with LCA inhibited Cl^- secretory responses to the cAMP-dependent agonist, forskolin (FSK), with maximal effects occurring at a concentration of 10 µM after 24 h of treatment. Under these conditions, LCA also inhibited responses to the Ca²⁺-dependent secretagogues, thapsigargin, and histamine. In nystatin-permeabilized T₈₄ monolayers, LCA reduced FSK-stimulated apical Cl^- conductances, an effect that correlated with reduced CFTR Cl^- channel expression. Although LCA activated both farnesoid X receptor (FXR) and vitamin D receptor (VDR), its effects on CFTR expression and Cl^- conductances were mimicked only by an FXR agonist, GW4064, and not by a VDR agonist, calcitriol. Finally, LCA inhibited CFTR promoter activity in HEK3 cells, but only when FXR was expressed. LCA, at physiologically relevant concentrations, chronically inhibits colonic epithelial Cl^- secretion, likely via FXR-induced downregulation of CFTR. These data broaden our knowledge of the regulatory roles of LCA in the colon and highlight its potential as a therapeutic target for intestinal disorders.<b>NEW & NOTEWORTHY</b> This study reveals a previously unrecognized role for lithocholic acid (LCA) in chronically suppressing colonic epithelial chloride secretion. We demonstrate a genomic mechanism of action for LCA that is likely mediated by FXR-induced downregulation of CFTR expression and function. These findings highlight LCA as a key modulator of intestinal fluid and electrolyte transport and underline the therapeutic potential of targeting bile acids and their receptors for the treatment of diarrheal diseases.