Ablation of microglial estrogen receptor alpha predisposes to diet-induced obesity in male mice
Estrogen receptor alpha (ER) signaling has metabolic and anti-inflammatory properties in addition to its impact on reproductive function. In male but not female mice, inflammatory activation of microglia, the resident macrophages of the brain, has been implicated in the pathogenesis of diet-induced obesity (DIO), raising the possibility that differences in microglial estrogen signaling may account for the sexual dimorphism. In this study, we assessed metabolic and CNS histopathological properties in a mouse model with inducible microglia-specific ablation of ER (MG-ERKO). Male MG-ERKO mice developed increased weight gain and insulin resistance relative to controls during high-fat diet (HFD) feeding. Indirect calorimetry analysis revealed that reduced energy expenditure was the main driver of the obese phenotype. In contrast, female MG-ERKO mice fed HFD developed mild insulin resistance with no change in body weight gain compared to controls. Immunohistochemical analyses of the microglial activation marker IBA1 in the mediobasal hypothalamus (MBH) revealed that female MG-ERKO mice had an increased number of microglia without showing morphological signs of activation. In contrast, MBH microglial number was unchanged in MG-ERKO male mice, but the cells adopted more activated morphological profiles. Finally, HFD-fed MG-ERKO male mice had increased POMC neuron-microglia interactions but fewer overall hypothalamic POMC neurons, suggesting microglia may disrupt POMC neuron integrity to promote DIO. Together, these findings indicate that sex-specific actions of estrogen in microglia limit the metabolic complications of HFD feeding.