EPHX1 mutations cause a lipoatrophic diabetes syndrome due to impaired epoxide hydrolysis and increased cellular senescence

Epoxide hydrolases (EHs) regulate cellular homeostasis through hydrolysis of epoxides to less reactive diols. The first discovered EH was EPHX1, also known as mEH. EH functions remains partly unknown and no pathogenic variants have been reported in humans. We identified two de novo variants located in EPHX1 catalytic site in patients with a lipoatrophic diabetes characterized by loss of adipose tissue, insulin resistance, and multiple organ dysfunction. Functional analyses revealed that these variants led to the protein aggregation within the endoplasmic reticulum and to a loss of its hydrolysis activity. CRISPR-Cas9-mediated Ephx1 knockout (KO) abolished adipocyte differentiation and decreased insulin response. This KO also promoted oxidative stress and cellular senescence, an observation confirmed in patient-derived fibroblasts. A major beneficial effect of metreleptin therapy was observed. This translational study highlights the importance of epoxide regulation for adipocyte function, and provides new insights into the physiological roles of EHs in humans.