Key roles of Drosophila flavin-containing monooxygenases in lipid metabolism and longevity

Flavin-containing monooxygenases (FMOs) are a highly conserved enzyme family widely distributed across diverse organisms, primarily known for their role in xenobiotic metabolism. However, their endogenous physiological functions in insects remain poorly understood. In this study, we investigated the roles of Drosophila melanogaster FMOs (DmFMO1 and DmFMO2) using RNA interference-mediated knockdown and UAS/GAL4-driven overexpression, combined with LC-MS/MS-based metabolomics and in vivo/vitro biochemical assays. Metabolomics analysis revealed a critical link between DmFMOs and lipid homeostasis, with significant perturbations in glycerophospholipid metabolism, including phosphorylcholine and various phospholipid species. Genetic knockdown of DmFMOs in adult flies led to marked reductions in triglyceride (TG, 24.6 %-24.9 %) and free fatty acid (FFA, 20.3 %-25.9 %) levels, while overexpression elevated FFA levels (32.9 %-60.3 %) and, specifically for DmFMO1, TG level (12.6 %). Consistent in vitro assays confirmed that knockdown of either gene promoted lipid depletion, as reflected by a 53.7 % reduction in cellular lipid droplets. Notably, DmFMOs expression levels significantly affected lifespan-knockdown reduced median survival by 18.9 %-31.1 % and overexpression extended it by 10.8 %-14.3 %. Additionally, DmFMO1 knockdown impaired development, reducing the eclosion rate to 67.7 % compared to controls. These findings uncover novel physiological functions of DmFMOs in regulating lipid metabolism and lifespan, providing new insights into conserved roles of FMOs and their potential relevance to human metabolic disorders.