A gut microbial odd-chain fatty acid alleviates atherosclerosis in mice.

The gut microbiota plays a pivotal part in human health, yet the molecular mechanisms that underlie its effects are largely unexplored. Bacteroides, a dominant genus in the human gut microbiota, is depleted in patients with atherosclerosis1, but its causal relationship with disease remains unclear. Here, using a mouse model, we show that administration of Bacteroides uniformis alleviates atherosclerosis through the upregulation of hepatic low-density lipoprotein receptor expression. Bioactivity-guided screening revealed pentadecanoic acid (PA, C15:0), a saturated odd-chain fatty acid, as a principal bioactive metabolite. PA supplementation reduced atherosclerotic plaque burden by around 50% and significantly improved plasma lipid profiles, a result that underscores its therapeutic potential. Mechanistically, PA enhances cholesterol clearance by directly inhibiting HMG-CoA reductase, suppressing hepatic cholesterol biosynthesis and promoting plasma low-density lipoprotein cholesterol removal. Analyses of 100 gut bacterial strains revealed that PA production occurs across multiple Bacteroidota genera. Notably, PA is markedly depleted in patients with dyslipidaemia. In summary, a Bacteroidota-derived odd-chain fatty acid regulates gut-liver crosstalk, and modulation of the microbial-metabolic axis has atheroprotective potential.