Fmo1, flavin containing dimethylaniline monooxygenase 1, is involved in lipid metabolism [2]. It also has a role in detoxifying xenobiotics and is part of the oxidative flavin-containing monooxygenases family [5]. In humans, its expression shows developmental and tissue-specific patterns, being restricted to the fetus in the liver while having extrahepatic expression in adult life [6,7].

In human skin, Fmo1 defines one of the major fibroblast populations, with Fmo1+ fibroblasts being larger and distributed in interstitial and perivascular locations, suggesting a role in matrix deposition, inflammatory cell retention, and connective tissue cell differentiation [1]. In non-alcoholic fatty liver disease (NAFLD), Fmo1 promotes disease progression by regulating PPARα activation and inducing ferroptosis. Knockdown of Fmo1 in an in vitro NAFLD model suppressed lipid accumulation, down-regulation of PPARα expression, and up-regulation of ferroptosis [2]. In classical papillary thyroid cancer, high Fmo1 expression independently predicts favorable recurrence-free survival [3]. In plants, Arabidopsis thaliana Fmo1 is involved in excess light stress-induced signal transduction and cell death signaling, playing a role in systemic acquired acclimation [4].

In conclusion, Fmo1 has diverse functions in different organisms and tissues. In mammals, it is crucial in lipid metabolism, fibroblast-related functions, and has implications in diseases like NAFLD and classical papillary thyroid cancer. Its role in plants in stress-related signaling further showcases its broad biological importance. The studies, including those using in vitro models for NAFLD, contribute to understanding the role of Fmo1 in specific biological processes and disease conditions.