Neurosecretory Protein GM-Expressing Neurons Participate in Lipid Storage and Inflammation in Newly Developed Cre Driver Male Mice.

Obesity induces inflammation in the hypothalamus and adipose tissue, resulting in metabolic disorders. A novel hypothalamic neuropeptide, neurosecretory protein GM (NPGM), was previously identified in the hypothalamus of vertebrates. While NPGM plays an important role in lipid metabolism in chicks, its metabolic regulatory effects in mammals remain unclear. In this study, a novel Cre driver line, NPGM-Cre, was generated for cell-specific manipulation. Cre-dependent overexpression of Npgm led to fat accumulation without increased food consumption in male NPGM-Cre mice. Chemogenetic activation of NPGM neurons in the hypothalamus acutely promoted feeding behavior and chronically resulted in a transient increase in body mass gain. Furthermore, the ablated NPGM neurons exhibited a tendency to be glucose intolerant, with infiltration of proinflammatory macrophages into the adipose tissue. These results suggest that NPGM neurons may regulate lipid storage and inflammatory responses, thereby maintaining glucose homeostasis.

Immunohistochemical Analysis of Neurotransmitters in Neurosecretory Protein GL-Producing Neurons of the Mouse Hypothalamus.

We recently discovered a novel neuropeptide of 80 amino acid residues: neurosecretory protein GL (NPGL), in the hypothalamus of birds and rodents. NPGL is localized in the lateral posterior part of the arcuate nucleus (ArcLP), and it enhances feeding behavior and fat accumulation in mice. Various neurotransmitters, such as catecholamine, glutamate, and γ-aminobutyric acid (GABA), produced in the hypothalamus are also involved in energy metabolism. The colocalization of neurotransmitters and NPGL in neurons of the ArcLP leads to the elucidation of the regulatory mechanism of NPGL neurons. In this study, we performed double immunofluorescence staining to elucidate the relationship between NPGL and neurotransmitters in mice. The present study revealed that NPGL neurons did not co-express tyrosine hydroxylase as a marker of catecholaminergic neurons and vesicular glutamate transporter-2 as a marker of glutamatergic neurons. In contrast, NPGL neurons co-produced glutamate decarboxylase 67, a marker for GABAergic neurons. In addition, approximately 50% of NPGL neurons were identical to GABAergic neurons. These results suggest that some functions of NPGL neurons may be related to those of GABA. This study provides insights into the neural network of NPGL neurons that regulate energy homeostasis, including feeding behavior and fat accumulation.

Neurosecretory Protein GL Accelerates Liver Steatosis in Mice Fed Medium-Fat/Medium-Fructose Diet.

Sugar consumption can readily lead to obesity and metabolic diseases such as liver steatosis. We previously demonstrated that a novel hypothalamic neuropeptide, neurosecretory protein GL (NPGL), promotes fat accumulation due to the ingestion of sugar by rats. However, differences in lipogenic efficiency of sugar types by NPGL remain unclear. The present study aimed to elucidate the obesogenic effects of NPGL on mice fed different sugars (i.e., sucrose or fructose). We overexpressed the NPGL-precursor gene (Npgl) in the hypothalamus of mice fed a medium-fat/medium-sucrose diet (MFSD) or a medium-fat/medium-fructose diet (MFFD). Food intake and body mass were measured for 28 days. Body composition and mRNA expression of lipid metabolic factors were measured at the endpoint. Npgl overexpression potently increased body mass with fat accumulation in the white adipose tissue of mice fed MFFD, although it did not markedly affect food intake. In contrast, we observed profound fat deposition in the livers of mice fed MFFD but not MFSD. In the liver, the mRNA expression of glucose and lipid metabolic factors was affected in mice fed MFFD. Hence, NPGL induced liver steatosis in mice fed a fructose-rich diet.

Overexpression of the Gene Encoding Neurosecretory Protein GL Precursor Prevents Excessive Fat Accumulation in the Adipose Tissue of Mice Fed a Long-Term High-Fat Diet.

We previously identified a novel small hypothalamic protein, neurosecretory protein GL (NPGL), which induces feeding behavior and fat accumulation in rodents depending on their diet. In the present study, we explored the effects of NPGL on feeding behavior and energy metabolism in mice placed on a long-term high-fat diet with 60% calories from fat (HFD 60). Overexpression of the NPGL precursor gene (Npgl) over 18 weeks increased food intake and weight. The weekly weight gain of Npgl-overexpressing mice was higher than that of controls until 7 weeks from induction of overexpression, after which it ceased to be so. Oral glucose tolerance tests showed that Npgl overexpression maintained glucose tolerance and increased blood insulin levels, and intraperitoneal insulin tolerance tests showed that it maintained insulin sensitivity. At the experimental endpoint, Npgl overexpression was associated with increased mass of the perirenal white adipose tissue (WAT) and decreased mass of the epididymal WAT (eWAT), resulting in little effect on the total WAT mass. These results suggest that under long-term HFD 60 feeding, Npgl overexpression may play a role in avoiding metabolic disturbance both by accelerating energy storage and by suppressing excess fat accumulation in certain tissues, such as the eWAT.

Effects of Overexpression of Neurosecretory Protein GL-Precursor Gene on Glucose Homeostasis and Insulin Sensitivity in Mice.

A high-fat diet (HFD) quickly induces obesity with insulin resistance and hyperglycemia. We previously reported that a novel hypothalamic small protein, named neurosecretory protein GL (NPGL), stimulates feeding and fat accumulation in mice. However, the effects of NPGL on insulin sensitivity and glucose homeostasis remain unknown. Hence, we subjected NPGL-precursor gene (Npgl)-overexpressing mice to the oral glucose tolerance test (OGTT) and intraperitoneal insulin tolerance test (IPITT) under normal chow (NC) and HFD conditions. Npgl overexpression promoted body mass gain and tended to increase food intake of NC-fed mice, whereas it had little effect on HFD-fed mice. The OGTT showed elevated blood glucose and insulin levels in Npgl-overexpressing NC-fed mice 15 min after glucose administration. Both the OGTT and IPITT demonstrated that Npgl overexpression decreased blood glucose levels in HFD-fed mice 60 min after glucose and insulin treatments. Notably, Npgl overexpression increased adipose tissue masses only in NC-fed mice, and it decreased blood glucose and insulin levels in HFD-fed mice at the experimental end point. It also increased the mRNA expression of galanin, one of the feeding and metabolic regulatory neuropeptides, in the hypothalamus of HFD-fed mice. Therefore, NPGL may alleviate HFD-induced hyperglycemia and insulin resistance in mice.

Effects of Chronic Intracerebroventricular Infusion of RFamide-Related Peptide-3 on Energy Metabolism in Male Mice.

RFamide-related peptide-3 (RFRP-3), the mammalian ortholog of avian gonadotropin-inhibitory hormone (GnIH), plays a crucial role in reproduction. In the present study, we explored the other functions of RFRP-3 by investigating the effects of chronic intracerebroventricular infusion of RFRP-3 (6 nmol/day) for 13 days on energy homeostasis in lean male C57BL/6J mice. The infusion of RFRP-3 increased cumulative food intake and body mass. In addition, the masses of brown adipose tissue (BAT) and the liver were increased by the administration of RFRP-3, although the mass of white adipose tissue was unchanged. On the other hand, RFRP-3 decreased O2 consumption, CO2 production, energy expenditure, and core body temperature during a short time period in the dark phase. These results suggest that the increase in food intake and the decrease in energy expenditure contributed to the gain of body mass, including the masses of BAT and the liver. The present study shows that RFRP-3 regulates not only reproductive function, but also energy metabolism, in mice.