Sex-Specific Appetite Regulation of Lipocalin-2 in High-Fat-Diet-Induced Obese Mice

Abstract

<b><i>Introduction:</i></b> Lipocalin 2 (Lcn2) is a key factor in appetite suppression. However, the effect of Lcn2 on appetite in terms of sex differences has not been thoroughly studied. <b><i>Methods:</i></b> Young (3-month-old) whole-body Lcn2 knockout (Lcn2^−/−) mice were fed a normal diet (ND) or high-fat diet (HFD) for 8 weeks to investigate obesity, food intake, serum metabolism, hepatic lipid metabolism, and regulation of gastrointestinal hormones. <b><i>Results:</i></b> Lcn2 deficiency significantly increased the body weight and food intake of male mice when fed ND instead of HFD and females when fed HFD but not ND. Compared to wild-type (WT) male mice, the adiponectin level and phosphorylated form of adenosine 5′-monophosphate-activated protein kinase (AMPK) in the hypothalamus were both increased in ND-fed Lcn2^−/− male mice but decreased in HFD-fed Lcn2^−/− male mice. However, in female mice, adiponectin and its energy metabolism pathway were not altered. Instead, estradiol was found to be substantially higher in ND-fed Lcn2^−/− female mice and substantially lower in HFD-fed Lcn2^−/− female mice compared with WT female mice. Estradiol alteration also caused similar changes in ERα in the hypothalamus, leading to changes in the PI3K/AKT energy metabolism pathway. It suggested that the increased appetite caused by Lcn2 deficiency in male mice may be due to increased adiponectin expression and promotion of AMPK phosphorylation, while in female mice it may be related to the decrease of circulating estradiol and the inhibition of the hypothalamic ERα/PI3K/AKT energy metabolism pathway. <b><i>Conclusion:</i></b> Lcn2 plays in a highly sex-specific manner in the regulation of appetite in young mice.