Peripherally Administered Y2-Receptor Antagonist BIIE0246 Prevents Diet-Induced Obesity in Mice With Excess Neuropeptide Y, but Enhances Obesity in Control Mice.

Neuropeptide Y (NPY) plays an important role in the regulation of energy homeostasis in the level of central and sympathetic nervous systems (SNSs). Genetic silencing of peripheral Y2-receptors have anti-obesity effects, but it is not known whether pharmacological blocking of peripheral Y2-receptors would similarly benefit energy homeostasis. The effects of a peripherally administered Y2-receptor antagonist were studied in healthy and energy-rich conditions with or without excess NPY. Genetically obese mice overexpressing NPY in brain noradrenergic nerves and SNS (OE-NPYDßH) represented the situation of elevated NPY levels, while wildtype (WT) mice represented the normal NPY levels. Specific Y2-receptor antagonist, BIIE0246, was administered (1.3 mg/kg/day, i.p.) for 2 or 4.5 weeks to OE-NPYDßH and WT mice feeding on chow or Western diet. Treatment with Y2-receptor antagonist increased body weight gain in both genotypes on chow diet and caused metabolic disturbances (e.g., hyperinsulinemia and hypercholesterolemia), especially in WT mice. During energy surplus (i.e., on Western diet), blocking of Y2-receptors induced obesity in WT mice, whereas OE-NPYDßH mice showed reduced fat mass gain, hepatic glycogen and serum cholesterol levels relative to body adiposity. Thus, it can be concluded that with normal NPY levels, peripheral Y2-receptor antagonist has no potential for treating obesity, but oppositely may even induce metabolic disorders. However, when energy-rich diet is combined with elevated NPY levels, e.g., stress combined with an unhealthy diet, Y2-receptor antagonism has beneficial effects on metabolic status.

The metabolic syndrome in mice overexpressing neuropeptide Y in noradrenergic neurons.

A gain-of-function polymorphism in human neuropeptide Y (NPY) gene (rs16139) associates with metabolic disorders and earlier onset of type 2 diabetes (T2D). Similarly, mice overexpressing NPY in noradrenergic neurons (OE-NPYDBH) display obesity and impaired glucose metabolism. In this study, the metabolic syndrome-like phenotype was characterized and mechanisms of impaired hepatic fatty acid, cholesterol and glucose metabolism in pre-obese (2-month-old) and obese (4-7-month-old) OE-NPYDBH mice were elucidated. Susceptibility to T2D was assessed by subjecting mice to high caloric diet combined with low-dose streptozotocin. Contribution of hepatic Y1-receptor to the phenotype was studied using chronic treatment with an Y1-receptor antagonist, BIBO3304. Obese OE-NPYDBH mice displayed hepatosteatosis and hypercholesterolemia preceded by decreased fatty acid oxidation and accelerated cholesterol synthesis. Hyperinsulinemia in early obese state inhibited pyruvate- and glucose-induced hyperglycemia, and deterioration of glucose metabolism of OE-NPYDBH mice developed with aging. Furthermore, streptozotocin induced T2D only in OE-NPYDBH mice. Hepatic inflammation was not morphologically visible, but upregulated hepatic anti-inflammatory pathways and increased 8-isoprostane combined with increased serum resistin and decreased interleukin 10 pointed to increased NPY-induced oxidative stress that may predispose OE-NPYDBH mice to insulin resistance. Chronic treatment with BIBO3304 did not improve the metabolic status of OE-NPYDBH mice. Instead, downregulation of beta-1-adrenoceptors suggests indirect actions of NPY via inhibition of sympathetic nervous system. In conclusion, changes in hepatic fatty acid, cholesterol and glucose metabolism favoring energy storage contribute to the development of NPY-induced metabolic syndrome, and the effect is likely mediated by changes in sympathetic nervous system activity.

Neuropeptide Y Overexpressing Female and Male Mice Show Divergent Metabolic but Not Gut Microbial Responses to Prenatal Metformin Exposure.

BACKGROUND: Prenatal metformin exposure has been shown to improve the metabolic outcome in the offspring of high fat diet fed dams. However, if this is evident also in a genetic model of obesity and whether gut microbiota has a role, is not known. METHODS: The metabolic effects of prenatal metformin exposure were investigated in a genetic model of obesity, mice overexpressing neuropeptide Y in the sympathetic nervous system and in brain noradrenergic neurons (OE-NPYDßH). Metformin was given for 18 days to the mated female mice. Body weight, body composition, glucose tolerance and serum parameters of the offspring were investigated on regular diet from weaning and sequentially on western diet (at the age of 5-7 months). Gut microbiota composition was analysed by 16S rRNA sequencing at 10-11 weeks. RESULTS: In the male offspring, metformin exposure inhibited weight gain. Moreover, weight of white fat depots and serum insulin and lipids tended to be lower at 7 months. In contrast, in the female offspring, metformin exposure impaired glucose tolerance at 3 months, and subsequently increased body weight gain, fat mass and serum cholesterol. In the gut microbiota, a decline in Erysipelotrichaceae and Odoribacter was detected in the metformin exposed offspring. Furthermore, the abundance of Sutterella tended to be decreased and Parabacteroides increased. Gut microbiota composition of the metformin exposed male offspring correlated to their metabolic phenotype. CONCLUSION: Prenatal metformin exposure caused divergent metabolic phenotypes in the female and male offspring. Nevertheless, gut microbiota of metformin exposed offspring was similarly modified in both genders.

Neuropeptide Y in noradrenergic neurons induces obesity in transgenic mouse models.

Neuropeptide Y (NPY) in noradrenergic neurons plays an important role in modulating the release and effects of catecholamines in a prolonged stress response. Among other functions, it controls energy metabolism. Transgenic expression of Npy in noradrenergic neurons in mice allowed showing that it is critical for diet- and stress-induced gain in fat mass. When overexpressed, NPY in noradrenergic neurons increases adiposity in gene-dose-dependent fashion, and leads to metabolic disorders such as impaired glucose tolerance. However, the mechanisms of obesity seem to be different in mice heterozygous and homozygous for the Npy transgene. While in heterozygous mice the adipogenic effect of NPY is important, in homozygous mice inhibition of sympathetic tone leading to decreased lipolytic activity and impaired brown fat function, as well as increased endocannabinoid levels contribute to obesity. The mouse model provides novel insight to the mechanisms of human diseases with increased NPY due to chronic stress or gain-of-function gene variants, and a tool for development of novel therapeutics.

Prenatal metformin exposure in a maternal high fat diet mouse model alters the transcriptome and modifies the metabolic responses of the offspring.

AIMS: Despite the wide use of metformin in metabolically challenged pregnancies, the long-term effects on the metabolism of the offspring are not known. We studied the long-term effects of prenatal metformin exposure during metabolically challenged pregnancy in mice. MATERIALS AND METHODS: Female mice were on a high fat diet (HFD) prior to and during the gestation. Metformin was administered during gestation from E0.5 to E17.5. Male and female offspring were weaned to a regular diet (RD) and subjected to HFD at adulthood (10-11 weeks). Body weight and several metabolic parameters (e.g. body composition and glucose tolerance) were measured during the study. Microarray and subsequent pathway analyses on the liver and subcutaneous adipose tissue of the male offspring were performed at postnatal day 4 in a separate experiment. RESULTS: Prenatal metformin exposure changed the offspring's response to HFD. Metformin exposed offspring gained less body weight and adipose tissue during the HFD phase. Additionally, prenatal metformin exposure prevented HFD-induced impairment in glucose tolerance. Microarray and annotation analyses revealed metformin-induced changes in several metabolic pathways from which electron transport chain (ETC) was prominently affected both in the neonatal liver and adipose tissue. CONCLUSION: This study shows the beneficial effects of prenatal metformin exposure on the offspring's glucose tolerance and fat mass accumulation during HFD. The transcriptome data obtained at neonatal age indicates major effects on the genes involved in mitochondrial ATP production and adipocyte differentiation suggesting the mechanistic routes to improved metabolic phenotype at adulthood.

Stress- and diet-induced fat gain is controlled by NPY in catecholaminergic neurons.

Neuropeptide Y (NPY) and noradrenaline are commonly co-expressed in sympathetic neurons. Both are key regulators of energy homeostasis and critical for stress-coping. However, little is known about the specific function of NPY in the catecholaminergic system in these regulations. Here we show that mice with NPY expression only in the noradrenergic and adrenergic cells of the catecholaminergic system (catNPY) exhibited exacerbated diet-induced obesity, lower body and brown adipose tissue temperatures compared to WT and NPY(-/-) mice under a HFD. Furthermore, chronic stress increased adiposity and serum corticosterone level in WT but not NPY(-/-) mice. Re-introducing NPY specifically to the catecholaminergic system in catNPY mice restored stress responsiveness associated with increased respiratory exchange ratio and decreased liver pACC to tACC ratio. These results demonstrate catecholaminergic NPY signalling is critical in mediating diet- and chronic stress-induced fat gain via effects on diet-induced thermogenesis and stress-induced increases in corticosterone levels and lipogenic capacity.

Prenatal metformin exposure in mice programs the metabolic phenotype of the offspring during a high fat diet at adulthood.

AIMS: The antidiabetic drug metformin is currently used prior and during pregnancy for polycystic ovary syndrome, as well as during gestational diabetes mellitus. We investigated the effects of prenatal metformin exposure on the metabolic phenotype of the offspring during adulthood in mice. METHODS: Metformin (300 mg/kg) or vehicle was administered orally to dams on regular diet from the embryonic day E0.5 to E17.5. Gene expression profiles in liver and brain were analysed from 4-day old offspring by microarray. Body weight development and several metabolic parameters of offspring were monitored both during regular diet (RD-phase) and high fat diet (HFD-phase). At the end of the study, two doses of metformin or vehicle were given acutely to mice at the age of 20 weeks, and Insig-1 and GLUT4 mRNA expressions in liver and fat tissue were analysed using qRT-PCR. RESULTS: Metformin exposed fetuses were lighter at E18.5. There was no effect of metformin on the maternal body weight development or food intake. Metformin exposed offspring gained more body weight and mesenteric fat during the HFD-phase. The male offspring also had impaired glucose tolerance and elevated fasting glucose during the HFD-phase. Moreover, the expression of GLUT4 mRNA was down-regulated in epididymal fat in male offspring prenatally exposed to metformin. Based on the microarray and subsequent qRT-PCR analyses, the expression of Insig-1 was changed in the liver of neonatal mice exposed to metformin prenatally. Furthermore, metformin up-regulated the expression of Insig-1 later in development. Gene set enrichment analysis based on preliminary microarray data identified several differentially enriched pathways both in control and metformin exposed mice. CONCLUSIONS: The present study shows that prenatal metformin exposure causes long-term programming effects on the metabolic phenotype during high fat diet in mice. This should be taken into consideration when using metformin as a therapeutic agent during pregnancy.

Diet-induced obesity in mice overexpressing neuropeptide y in noradrenergic neurons.

Neuropeptide Y (NPY) is a neurotransmitter associated with feeding and obesity. We have constructed an NPY transgenic mouse model (OE-NPY(DBH) mouse), where targeted overexpression leads to increased levels of NPY in noradrenergic and adrenergic neurons. We previously showed that these mice become obese on a normal chow. Now we aimed to study the effect of a Western-type diet in OE-NPY(DBH) and wildtype (WT) mice, and to compare the genotype differences in the development of obesity, insulin resistance, and diabetes. Weight gain, glucose, and insulin tolerance tests, fasted plasma insulin, and cholesterol levels were assayed. We found that female OE-NPY(DBH) mice gained significantly more weight without hyperphagia or decreased activity, and showed larger white and brown fat depots with no difference in UCP-1 levels. They also displayed impaired glucose tolerance and decreased insulin sensitivity. OE-NPY(DBH) and WT males gained weight robustly, but no difference in the degree of adiposity was observed. However, 40% of OE-NPY(DBH) but none of the WT males developed hyperglycaemia while on the diet. The present study shows that female OE-NPY(DBH) mice were not protected from the obesogenic effect of the diet suggesting that increased NPY release may predispose females to a greater risk of weight gain under high caloric conditions.