Thermoneutral conditions correct the obese phenotype in female, but not male, Kiss1r knockout mice: Kiss1r knockout mice in thermoneutral conditions

Kisspeptin, a neuropeptide that activates gonadotropin-releasing hormone (GnRH) neurons, has also been implicated as a regulator of energy balance. Kisspeptin receptor (Kiss1r) knockout (KO) mice display an obese phenotype in adulthood compared to wild-type (WT) controls due to reduced energy expenditure. Additionally, experimental evidence shows that the temperature of typical rodent housing conditions (22 °C) increases the metabolism of mice above basal levels. Female Kiss1r KO mice show reduced core temperature and impaired temperature adaptation to an acute cold challenge, suggesting their temperature homeostasis processes are altered. The present study examined the phenotype of gonadectomised Kiss1r KO mice at both sub-thermoneutral and thermoneutral temperature (22 °C and 30 °C). Our results confirmed the obese phenotype in Kiss1r KO mice at 22 °C, and revealed a sexually dimorphic effect of thermal neutrality on the phenotype. In female KO mice, the obesity observed at 22 °C was attenuated at 30 °C. Plasma leptin levels were higher in KO than WT female mice at 22 °C (P < 0.001) but not at 30 °C. Importantly, the expression of Ucp1 mRNA in brown adipose tissue was lower in KO mice compared to WT mice at 22 °C (P < 0.05), but not different from WT at 30 °C. In male KO mice, a metabolic phenotype was observed at 22 °C and 30 °C. These results provide further evidence for kisspeptin-mediated regulation of adiposity via altered energy expenditure. Moreover, thermoneutral housing alleviated the obese phenotype in female Kiss1r KO mice, compared to WT, indicating the impairment in these mice may relate to an inability to adapt to the chronic cold stress that is experienced at 22 °C.