Gut microbiota-derived butyrate induces epigenetic and metabolic reprogramming in myeloid-derived suppressor cells to alleviate primary biliary cholangitis

Background & Aims Gut dysbiosis and myeloid-derived suppressor cells (MDSCs) are implicated in primary biliary cholangitis (PBC) pathogenesis. However, it remains unknown whether gut microbiota or their metabolites can modulate MDSCs homeostasis to rectify immune dysregulation in PBC. Methods We measured fecal short-chain fatty acids (SCFAs) levels by targeted GC-MS and analyzed circulating MDSCs by flow cytometry in two independent PBC cohorts. Human and murine MDSCs were differentiated in vitro in the presence of butyrate, followed by transcriptomic, epigenetic (CUT&Tag-seq and ChIP-qPCR) and metabolic (untargeted LC-MS, mitochondrial stress test, and isotope tracing) analyses. The in vivo role of butyrate-MDSCs was evaluated in 2-octynoic acid-BSA-induced cholangitis murine model. Results Decreased butyrate levels and defective MDSCs function were found in patients with incomplete response to ursodeoxycholic acid (UDCA), compared to those with adequate response. Butyrate induced expansion and suppressive activity of MDSCs in a manner dependent on PPARD-driven fatty acid β-oxidation (FAO). Pharmaceutical inhibition or genetic knockdown of the FAO rate-limiting gene CPT1A abolished the effect of butyrate. Furthermore, butyrate inhibited HDAC3 function, leading to enhanced H3K27ac modifications at promoter regions of PPARD and FAO genes in MDSCs. Therapeutically, butyrate administration alleviated immune-mediated cholangitis in mice via MDSCs, and adoptive transfer of butyrate-treated MDSCs also displayed protective efficacy. Importantly, reduced expression of FAO genes and impaired mitochondrial physiology were detected in MDSCs from UDCA non-responders, and their impaired suppressive function was restored by butyrate. Conclusion We identify a critical role for butyrate in modulation of MDSCs homeostasis by orchestrating epigenetic and metabolic crosstalk, proposing a novel therapeutic strategy for treating PBC.