Flavin-containing monooxygenase 3 (FMO3) is the achilles heel in the TMA-TMAO metaorganismal pathway linking the gut and skin fibrosis

Summary: Abstract Body: Intestinal bacteria generate aliphatic amine trimethylamine (TMA), which in the host is converted to trimethylamine N-oxide (TMAO), an enzymatic reaction catalyzed by FMO3 primarily in the liver. This metaorganismal axis linking dietary precursors, microbial metabolism and bioactive TMAO, is implicated in metabolic and cardiovascular diseases. Because we showed that TMAO is elevated in patients with systemic sclerosis (SSc), the present study sought to explore pathogenic role of FMO3 and TMAO. The effect of FMO3-derived TMAO, and of FMO3 silencing, on fibrotic responses was examined in fibroblasts and endothelial cells. FMO3 was quantified in SSc skin biopsies and explanted skin fibroblasts. Fibrosis and inflammation were examined in FMO3-deficient mice. TMAO induced fibroblast activation via ER stress-mediated PERK/ eIF2α/ATF4 signaling, and endothelial-mesenchymal transition. Silencing FMO3 attenuated fibro-inflammatory responses in human fibroblasts and activated PERK. SSc skin biopsies and explanted skin fibroblasts showed elevated FMO3 protein and mRNA expression, which colocalized with markers of ER stress and elevated collagen gene expression. FMO3 deletion in mice led to a decrease in circulating TMAO levels but no spontaneous phenotype. However, FMO3-null mice showed significantly reduced fibro-inflammatory responses and ER stress in a bleomycin-induced multi-organ disease model. FMO3, which catalyzes production of profibrotic TMAO from intestinal microbiome-derived precursor TMA, showed aberrant expression in dermal stromal cells in SSc. Loss of FMO3 markedly attenuated fibrosis in vitro and in vivo. These results for the first time implicate FMO3 as a novel vulnerability in pathological skin fibrosis and a potential target for treatment of SSc. Priyanka Verma¹, Swati Bhattacharyya¹, Mohammad A. Amin¹, Poulami Dey¹, Rakhee Banerjee², Mark Brown², Stanley L. Hazen², Johann E. Gudjonsson¹, John Varga¹ 1. University of Michigan Michigan Medicine, Ann Arbor, MI, United States. 2. Cleveland Clinic, Cleveland, OH, United States. Translational Studies: Cell and Molecular Biology