Deficiency of Irx5 protects mice from diet-induced obesity and associated metabolic abnormalities

Obesity, a leading cause of several metabolic abnormalities, is mainly due to an imbalance of energy homeostasis. IRX3 and IRX5 have been suggested as determinants of obesity in connection with the intronic variants of FTO, the strongest genetic risk factor of polygenic obesity in humans. Although the causal effects of Irx3 on obesity and its related metabolic consequences have been demonstrated in vivo, the metabolic function of Irx5 remains unclear. In this study, using mice homozygous for an Irx5-knockout (Irx5KO) allele, we show a direct link between Irx5 expression and regulation of body mass/composition and energy homeostasis. Irx5KO mice are leaner and resistant to diet-induced obesity and associated metabolic abnormalities, primarily through the loss of adiposity with an increase in basal metabolic rate with adipose thermogenesis and lower food intake. Furthermore, our long-term feeding analysis found that Irx3 mutant mouse lines also have less food intake, indicating that lower caloric intake also contributes to their lean phenotype. Together, these results demonstrate that Irx5 is critical for energy homeostasis and regulation of body mass/composition and suggest that it likely acts in other tissues beyond adipocytes.