Role of gut microbiome in aortic aneurysm

BACKGROUND: Large-scale human and mechanistic mouse studies indicate a strong relationship between the microbiome-dependent metabolite trimethylamine N-oxide (TMAO) and several cardio-metabolic diseases. This study aims to investigate TMAOs role in the pathogenesis of AAA and targeting its parent microbes as a potential pharmacologic intervention. METHODS: TMAO and choline metabolites were examined in plasma samples, with associated clinical data, from two independent patient cohorts (n=2,129 total). Mice were fed high choline diet and underwent 2 murine AAA models, angiotensin II (AngII) infusion in low-density lipoprotein receptor deficient (Ldlr-/-) mice or topical porcine pancreatic elastase in C57BL/6J mice. Gut-microbial-production of TMAO was inhibited via broad-spectrum antibiotics, targeted inhibition of the gut microbial enzymatic dyad CutC/D with fluoromethylcholine (FMC), or utilizing mice genetically deficient in FMO3 (Fmo3-/-). Finally, RNAseq of in vitro human VSMCs and in vivo mouse aortas were used to investigate how TMAO impacts AAA. RESULTS: Elevated TMAO was associated with increased AAA incidence and growth in both patient cohorts studied. Dietary choline supplementation augmented plasma TMAO and aortic diameter in both mouse models of AAA, which was suppressed with poorly-absorbed oral broad-spectrum antibiotics. Treatment with FMC ablated TMAO production, attenuated choline-augmented aneurysm initiation, and halted progression of an established aneurysm model. Additionally, Fmo3-/- mice had reduced plasma TMAO, aortic diameters, and were protected from AAA rupture compared to WT mice. RNA sequencing and functional analyses revealed choline supplementation in mice or TMAO treatment of human VSMCs augmented gene pathways associated with the endoplasmic reticulum (ER)-stress response, specifically, the ER stress kinase Perk. CONCLUSIONS: These results define a role for gut microbiota-generated TMAO in AAA formation via upregulation of ER-stress related pathways in the aortic wall. Additionally, inhibition of microbiome-derived TMAO may serve as a novel therapeutic approach for AAA treatment, where none currently exist.