α-Melanocyte-stimulating hormone alleviates pathological cardiac remodeling via melanocortin 5 receptor

α-Melanocyte-stimulating hormone (α-MSH) regulates diverse physiological functions by activating melanocortin receptors (MC-R). However, the role of α-MSH and its possible target receptors in the heart remain completely unknown. Here we investigate whether α-MSH could be involved in pathological cardiac remodeling. We found that α-MSH was highly expressed in the mouse heart with reduced ventricular levels after transverse aortic constriction (TAC). Administration of a stable α-MSH analog protected mice against TAC-induced cardiac hypertrophy and systolic dysfunction. In vitro experiments revealed that MC5-R in cardiomyocytes mediates the anti-hypertrophic signaling of α-MSH. Silencing of MC5-R in cardiomyocytes induced hypertrophy and fibrosis markers in vitro and aggravated TAC-induced cardiac hypertrophy and fibrosis in vivo. Conversely, pharmacological activation of MC5-R improved systolic function and reduced cardiac fibrosis in TAC-operated mice. In conclusion, α-MSH is expressed in the heart and protects against pathological cardiac remodeling by activating MC5-R in cardiomyocytes. These results suggest that analogs of naturally occurring α-MSH, that have been recently approved for clinical use and have agonistic activity at MC5-R, may be of benefit in treating heart failure.

Melanocortin 1 receptor regulates cholesterol and bile acid metabolism in the liver

Melanocortin 1 receptor (MC1-R) is widely expressed in melanocytes and leukocytes and is thus strongly implicated in the regulation of skin pigmentation and inflammation. MC1-R has also been found in the rat and human liver, but its functional role has remained elusive. We hypothesized that MC1-R is functionally active in the liver and involved in the regulation of cholesterol and bile acid metabolism. We generated hepatocyte-specific MC1-R knock-out (Mc1r LKO) mice and phenotyped the mouse model for lipid profiles, liver histology, and bile acid levels. Mc1r LKO mice had significantly increased liver weight, which was accompanied by elevated levels of total cholesterol and triglycerides in the liver as well as in the plasma. These mice demonstrated also enhanced liver fibrosis and a disturbance in bile acid metabolism as evidenced by markedly reduced bile acid levels in the plasma and feces. Mechanistically, using HepG2 cells as an in vitro model, we found that selective activation of MC1-R in HepG2 cells reduced cellular cholesterol content and enhanced uptake of low- and high-density lipoprotein particles via a cAMP-independent mechanism. In conclusion, the present results demonstrate that MC1-R signaling in hepatocytes regulates cholesterol and bile acid metabolism and its deficiency leads to hypercholesterolemia and enhanced lipid accumulation and fibrosis in the liver.

Treatment with Soluble Activin Type IIB Receptor Ameliorates Ovariectomy-Induced Bone Loss and Fat Gain in Mice

INTRODUCTION

In postmenopausal osteoporosis, hormonal changes lead to increased bone turnover and metabolic alterations including increased fat mass and insulin resistance. Activin type IIB receptors bind several growth factors of the TGF-β superfamily and have been demonstrated to increase muscle and bone mass. We hypothesized that ActRIIB-Fc treatment could improve bone and muscle mass, inhibit fat accumulation, and restore metabolic alterations in an ovariectomy (OVX) model of postmenopausal osteoporosis.

MATERIALS AND METHODS

Female C57Bl/6 N mice were subjected to SHAM or OVX procedures and received intraperitoneal injections of either PBS or ActRIIB-Fc (5 mg/kg) once weekly for 7 weeks. Glucose and insulin tolerance tests (GTT and ITT, respectively) were performed at 7 and 8 weeks, respectively. Bone samples were analyzed with micro-computed tomography imaging, histomorphometry, and quantitative RT-PCR.

RESULTS

Bone mass decreased in OVX PBS mice compared to the SHAM PBS group but ActRIIB-Fc was able to prevent these changes as shown by µCT and histological analyses. This was due to decreased osteoclast numbers and function demonstrated by histomorphometric and qRT-PCR analyses. OVX induced adipocyte hypertrophy that was rescued by ActRIIB-Fc, which also decreased systemic adipose tissue accumulation. OVX itself did not affect glucose levels in GTT but ActRIIB-Fc treatment resulted in impaired glucose clearance in both SHAM and OVX groups. OVX induced mild insulin resistance in ITT but ActRIIB-Fc treatment did not affect this.

CONCLUSION

Our results reinforce the potency of ActRIIB-Fc as a bone-enhancing agent but also bring new insight into the metabolic effects of ActRIIB-Fc in normal and OVX mice.

Single-Cell Proteomics Reveals the Defined Heterogeneity of Resident Macrophages in White Adipose Tissue

Adipose tissue macrophages (ATMs) regulate homeostasis and contribute to the metabolically harmful chronic inflammation in obese individuals. While evident heterogeneity of resident ATMs has been described previously, their phenotype, developmental origin, and functionality remain inconsistent. We analyzed white adipose tissue (WAT) during homeostasis and diet interventions using comprehensive and unbiased single-cell mass cytometry and genetic lineage tracking models. We now provide a uniform definition of individual subsets of resident ATMs. We show that in lean mice, WAT co-harbors eight kinetically evolving CD206⁺ macrophage subpopulations (defined by TIM4, CD163, and MHC II) and two CD206^- macrophage subpopulations. TIM4^-CD163⁺, TIM4^-CD163^- and CD206^- macrophage populations are largely bone marrow-derived, while the proliferating TIM4⁺CD163⁺ subpopulation is of embryonic origin. All macrophage subtypes are active in phagocytosis, endocytosis, and antigen processing in vitro, whereas TIM4⁺CD163⁺ cells are superior in scavenging in vivo. A high-fat diet induces massive infiltration of CD206^- macrophages and selective down-regulation of MHC II on TIM4⁺ macrophages. These changes are reversed by dietary intervention. Thus, the developmental origin and environment jointly regulate the functional malleability of resident ATMs.

The Effects of Neuropeptide Y Overexpression on the Mouse Model of Doxorubicin-Induced Cardiotoxicity

Doxorubicin is a potent anticancer drug with cardiotoxicity hampering its use. Neuropeptide Y (NPY) is the most abundant neuropeptide in the heart and a co-transmitter of the sympathetic nervous system that plays a role in cardiac diseases. The aim of this work was to study the impact of NPY on doxorubicin-induced cardiotoxicity. Transgenic mice overexpressing NPY in noradrenergic neurons (NPY-OE^DβH) and wild-type mice were treated with a single dose of doxorubicin. Doxorubicin caused cardiotoxicity in both genotypes as demonstrated by decreased weight gain, tendency to reduced ejection fraction, and changes in the expression of several genes relevant to cardiac pathology. Doxorubicin resulted in a tendency to lower ejection fraction in NPY-OE^DβH mice more than in wild-type mice. In addition, gain in the whole body lean mass gain was decreased only in NPY-OE^DβH mice, suggesting a more severe impact of doxorubicin in this genotype. The effects of doxorubicin on genes expressed in the heart were similar between NPY-OE^DβH and wild-type mice. The results demonstrate that doxorubicin at a relatively low dose caused significant cardiotoxicity. There were differences between NPY-OE^DβH and wild-type mice in their responses to doxorubicin that suggest NPY to increase susceptibility to cardiotoxicity. This may point to the therapeutic implications as suggested for NPY system in other cardiovascular diseases.

Vimentin regulates Notch signaling strength and arterial remodeling in response to hemodynamic stress

The intermediate filament (IF) cytoskeleton has been proposed to regulate morphogenic processes by integrating the cell fate signaling machinery with mechanical cues. Signaling between endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) through the Notch pathway regulates arterial remodeling in response to changes in blood flow. Here we show that the IF-protein vimentin regulates Notch signaling strength and arterial remodeling in response to hemodynamic forces. Vimentin is important for Notch transactivation by ECs and vimentin knockout mice (VimKO) display disrupted VSMC differentiation and adverse remodeling in aortic explants and in vivo. Shear stress increases Jagged1 levels and Notch activation in a vimentin-dependent manner. Shear stress induces phosphorylation of vimentin at serine 38 and phosphorylated vimentin interacts with Jagged1 and increases Notch activation potential. Reduced Jagged1-Notch transactivation strength disrupts lateral signal induction through the arterial wall leading to adverse remodeling. Taken together we demonstrate that vimentin forms a central part of a mechanochemical transduction pathway that regulates multilayer communication and structural homeostasis of the arterial wall.

Hypothalamic γ-melanocyte stimulating hormone gene delivery reduces fat mass in male mice

γ-Melanocyte stimulating hormone (γ-MSH) is an endogenous agonist of the melanocortin 3-receptor (MC3R). Genetic disruption of MC3Rs increases adiposity and blunts responses to fasting, suggesting that increased MC3R signaling could be physiologically beneficial in the long term. Interestingly, several studies have concluded that activation of MC3Rs is orexigenic in the short term. Therefore, we aimed to examine the short- and long-term effects of γ-MSH in the hypothalamic arcuate nucleus (ARC) on energy homeostasis and hypothesized that the effect of MC3R agonism is dependent on the state of energy balance and nutrition. Lentiviral gene delivery was used to induce a continuous expression of γ-Msh only in the ARC of male C57Bl/6N mice. Parameters of body energy homeostasis were monitored as food was changed from chow (6 weeks) to Western diet (13 weeks) and back to chow (7 weeks). The γ-MSH treatment decreased the fat mass to lean mass ratio on chow, but the effect was attenuated on Western diet. After the switch back to chow, an enhanced loss in weight (−15% vs −6%) and fat mass (−37% vs −12%) and reduced cumulative food intake were observed in γ-MSH-treated animals. Fasting-induced feeding was increased on chow diet only; however, voluntary running wheel activity on Western diet was increased. The γ-MSH treatment also modulated the expression of key neuropeptides in the ARC favoring weight loss. We have shown that a chronic treatment intended to target ARC MC3Rs modulates energy balance in nutritional state-dependent manner. Enhancement of diet-induced weight loss could be beneficial in treatment of obesity.

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-NPY^DβH) 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-NPY^DβH 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-NPY^DβH 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.

Metformin normalizes the structural changes in glycogen preceding prediabetes in mice overexpressing neuropeptide Y in noradrenergic neurons

Hepatic insulin resistance and increased gluconeogenesis are known therapeutic targets of metformin, but the role of hepatic glycogen in the pathogenesis of diabetes is less clear. Mouse model of neuropeptide Y (NPY) overexpression in noradrenergic neurons (OE-NPY^DβH) with a phenotype of late onset obesity, hepatosteatosis, and prediabetes was used to study early changes in glycogen structure and metabolism preceding prediabetes. Furthermore, the effect of the anti-hyperglycemic agent, metformin (300 mg/kg/day/4 weeks in drinking water), was assessed on changes in glycogen metabolism, body weight, fat mass, and glucose tolerance. Glycogen structure was characterized by cytofluorometric analysis in isolated hepatocytes and mRNA expression of key enzymes by qPCR. OE-NPY^DβH mice displayed decreased labile glycogen fraction relative to stabile fraction (the intermediate form of glycogen) suggesting enhanced glycogen cycling. This was supported by decreased filling of glucose residues in the 10th outer tier of the glycogen molecule, which suggests accelerated glycogen phosphorylation. Metformin reduced fat mass gain in both genotypes, but glucose tolerance was improved mostly in wild-type mice. However, metformin inhibited glycogen accumulation and normalized the ratio between glycogen structures in OE-NPY^DβH mice indicating decreased glycogen synthesis. Furthermore, the presence of glucose residues in the 11th tier together with decreased glycogen phosphorylase expression suggested inhibition of glycogen degradation. In conclusion, structural changes in glycogen of OE-NPY^DβH mice point to increased glycogen metabolism, which may predispose them to prediabetes. Metformin treatment normalizes these changes and suppresses both glycogen synthesis and phosphorylation, which may contribute to its preventive effect on the onset of diabetes.

Melanocortin overexpression limits diet-induced inflammation and atherosclerosis in LDLR-/- mice

Atherosclerosis is a chronic inflammatory disease of the arteries. The disease is initiated by endothelial dysfunction that allows the transport of leukocytes and low-density lipoprotein into the vessel wall forming atherosclerotic plaques. The melanocortin system is an endogenous peptide system that regulates, for example, energy homeostasis and cardiovascular function. Melanocortin treatment with endogenous or synthetic melanocortin peptides reduces body weight, protects the endothelium and alleviates vascular inflammation, but the long-term effects of melanocortin system activation on atheroprogression remain largely unknown. In this study, we evaluated the effects of transgenic melanocortin overexpression in a mouse model of atherosclerosis. Low-density lipoprotein receptor-deficient mice overexpressing alpha- and gamma₃-MSH (MSH-OE) and their wild-type littermates were fed either a regular chow or Western-style diet for 16 weeks. During this time, their metabolic parameters were monitored. The aortae were collected for functional analysis, and the plaques in the aortic root and arch were characterised by histological and immunohistochemical stainings. The aortic expression of inflammatory mediators was determined by quantitative PCR. We found that transgenic MSH-OE improved glucose tolerance and limited atherosclerotic plaque formation particularly in Western diet-fed mice. In terms of aortic vasoreactivity, MSH-OE blunted alpha₁-adrenoceptor-mediated vasoconstriction and enhanced relaxation response to acetylcholine, indicating improved endothelial function. In addition, MSH-OE markedly attenuated Western diet-induced upregulation of proinflammatory cytokines (Ccl2, Ccl5 and Il6) that contribute to the pathogenesis of atherosclerosis. These results show that the activation of the melanocortin system improves glucose homeostasis and limits diet-induced vascular inflammation and atherosclerotic plaque formation.

Increased Energy Expenditure, Lipolysis and Hyperinsulinemia Confer Resistance to Central Obesity and Type 2 Diabetes in Mice Lacking Alpha2α-Adrenoceptors

The alpha2A-adrenoceptors (α2A-ARs) are Gi-coupled receptors, which prejunctionally inhibit the release of norepinephrine (NE) and epinephrine (Epi), and postjunctionally inhibit insulin secretion and lipolysis. We have earlier shown that α2A-/- mice display sympathetic hyperactivity, hyperinsulinemia and improved glucose tolerance. Here we employed α2A-/- mice and placed the mice on a high-fat diet (HFD) to test the hypothesis that lack of α2A-ARs protects from diet-induced obesity and type 2 diabetes (T2D). In addition, a high-caloric diet was combined with running wheel exercise to test the interaction of diet and exercise. HFD was obesogenic in both genotypes, but α2A-/- mice accumulated less visceral fat than the wild-type controls, were protected from T2D, and their insulin secretion was unaltered by the diet. Lack of α2A-ARs is associated with an increased sympatho-adrenal tone, which resulted in increased energy expenditure and fat oxidation rate potentiated by HFD. Fittingly, α2A-/- mice displayed enhanced lipolytic responses to Epi, and increased faecal lipids suggesting altered fat mobilization and absorption. Subcutaneous white fat appeared to be thermogenically more active (measured as Ucp1 mRNA expression) in α2A-/- mice, and brown fat showed an increased response to NE. Exercise was effective in reducing total body adiposity and increasing lean mass in both genotypes, but there was a significant diet-genotype interaction, as even modestly increased physical activity combined with lack of α2A-AR signalling promoted weight loss more efficiently than exercise with normal α2A-AR function. These results suggest that blockade of α2A-ARs may be exploited to reduce visceral fat and to improve insulin secretion.

Melanocortin 1 Receptor Deficiency Promotes Atherosclerosis in Apolipoprotein E-/- Mice

OBJECTIVE

The MC1-R (melanocortin 1 receptor) is expressed by monocytes and macrophages where it mediates anti-inflammatory actions. MC1-R also protects against macrophage foam cell formation primarily by promoting cholesterol efflux through the ABCA1 (ATP-binding cassette transporter subfamily A member 1) and ABCG1 (ATP-binding cassette transporter subfamily G member 1). In this study, we aimed to investigate whether global deficiency in MC1-R signaling affects the development of atherosclerosis.

APPROACH AND RESULTS

Apoe^-/- (apolipoprotein E deficient) mice were crossed with recessive yellow (Mc1r^e/e) mice carrying dysfunctional MC1-R and fed a high-fat diet to induce atherosclerosis. Apoe^-/- Mc1r^e/e mice developed significantly larger atherosclerotic lesions in the aortic sinus and in the whole aorta compared with Apoe^-/- controls. In terms of plaque composition, MC1-R deficiency was associated with less collagen and smooth muscle cells and increased necrotic core, indicative of more vulnerable lesions. These changes were accompanied by reduced Abca1 and Abcg1 expression in the aorta. Furthermore, Apoe^-/- Mc1r^e/e mice showed a defect in bile acid metabolism that aggravated high-fat diet-induced hypercholesterolemia and hepatic lipid accumulation. Flow cytometric analysis of leukocyte profile revealed that dysfunctional MC1-R enhanced arterial accumulation of classical Ly6C^high monocytes and macrophages, effects that were evident in mice fed a normal chow diet but not under high-fat diet conditions. In support of enhanced arterial recruitment of Ly6C^high monocytes, these cells had increased expression of L-selectin and P-selectin glycoprotein ligand 1.

CONCLUSIONS

The present study highlights the importance of MC1-R in the development of atherosclerosis. Deficiency in MC1-R signaling exacerbates atherosclerosis by disturbing cholesterol handling and by increasing arterial monocyte accumulation.

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-NPY^DBH) 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-NPY^DBH 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-NPY^DBH 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-NPY^DBH mice developed with aging. Furthermore, streptozotocin induced T2D only in OE-NPY^DBH 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-NPY^DBH mice to insulin resistance. Chronic treatment with BIBO3304 did not improve the metabolic status of OE-NPY^DBH 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.

Diurnal rhythms of blood glucose, serum ghrelin, faecal IgA and faecal corticosterone in rats subjected to restricted feeding using the diet board

Laboratory rats are generally fed ad libitum, although this method is associated with obesity and an increased frequency of spontaneous tumours. It has been challenging looking for ways to limit feed consumption in group-housed rats without any setbacks to animal welfare and scientific results. The diet board, as a method of dietary restriction, was used in the present study. Diet board feeding allows group housing and should result in enhanced welfare compared with traditional methods of dietary restriction. With respect to animal model robustness and translatability of results it is important that the feeding regime does not affect diurnal rhythmicity of biological parameters. In the present study the effects of diet board feeding on diurnal rhythms of blood glucose, serum ghrelin, faecal immunoglobulin A (IgA) and faecal corticosterone were assessed. The diet board did not alter diurnal rhythms, and adds weight to the use of this method for dietary restriction which should benefit animal health and the validity of scientific results generated from the animals.

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-NPY^DβH). 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.

Deficiency in Melanocortin 1 Receptor Signaling Predisposes to Vascular Endothelial Dysfunction and Increased Arterial Stiffness in Mice and Humans

Objective—

The melanocortin 1 receptor (MC1-R) is expressed by vascular endothelial cells and shown to enhance nitric oxide (NO) availability and vasodilator function on pharmacological stimulation. However, the physiological role of MC1-R in the endothelium and its contribution to vascular homeostasis remain unresolved. We investigated whether a lack of functional MC1-R signaling carries a phenotype with predisposition to vascular abnormalities.

Approach and Results—

Recessive yellow mice (MC1R e/e ), deficient in MC1-R signaling, and their wild-type littermates were studied for morphology and functional characteristics of the aorta. MC1R e/e mice showed increased collagen deposition and arterial stiffness accompanied by an elevation in pulse pressure. Contractile capacity and NO-dependent vasodilatation were impaired in the aorta of MC1R e/e mice supported by findings of decreased NO availability. These mice also displayed elevated levels of systemic and local cytokines. Exposing the mice to high-sodium diet or acute endotoxemia revealed increased susceptibility to inflammation-driven vascular dysfunction. Finally, we investigated whether a similar phenotype can be found in healthy human subjects carrying variant MC1-R alleles known to attenuate receptor function. In a longitudinal analysis of 2001 subjects with genotype and ultrasound data (The Cardiovascular Risk in Young Finns Study), weak MC1-R function was associated with lower flow-mediated dilatation response of the brachial artery and increased carotid artery stiffness.

Conclusions—

The present study demonstrates that deficiency in MC1-R signaling is associated with increased arterial stiffness and impairment in endothelium-dependent vasodilatation, suggesting a physiological role for MC1-R in the regulation of arterial tone.

Role of the endocannabinoid system in obesity induced by neuropeptide Y overexpression in noradrenergic neurons

Objective:

Endocannabinoids and neuropeptide Y (NPY) promote energy storage via central and peripheral mechanisms. In the hypothalamus, the two systems were suggested to interact. To investigate such interplay also in non-hypothalamic tissues, we evaluated endocannabinoid levels in obese OE-NPY^DβH mice, which overexpress NPY in the noradrenergic neurons in the sympathetic nervous system and the brain.

Methods:

The levels of the endocannabinoids anandamide and 2-arachidonoylglycerol (2-AG) were measured in key regulatory tissues, that is, hypothalamus, pancreas, epididymal white adipose tissue (WAT), liver and soleus muscle, over the development of metabolic dysfunctions in OE-NPY^DβH mice. The effects of a 5-week treatment with the CB1 receptor inverse agonist AM251 on adiposity and glucose metabolism were studied.

Results:

2-AG levels were increased in the hypothalamus and epididymal WAT of pre-obese and obese OE-NPY^DβH mice. Anandamide levels in adipose tissue and pancreas were increased at 4 months concomitantly with higher fat mass and impaired glucose tolerance. CB1 receptor blockage reduced body weight gain and glucose intolerance in OE-NPY^DβH to the level of vehicle-treated wild-type mice.

Conclusions:

Altered endocannabinoid tone may underlie some of the metabolic dysfunctions in OE-NPY^DβH mice, which can be attenuated with CB1 inverse agonism suggesting interactions between endocannabinoids and NPY also in the periphery. CB1 receptors may offer a target for the pharmacological treatment of the metabolic syndrome with altered NPY levels.

Neuropeptide Y in the noradrenergic neurones induces obesity and inhibits sympathetic tone in mice

AIM

Neuropeptide Y (NPY) co-localized with noradrenaline in central and sympathetic nervous systems seems to play a role in the control of energy metabolism. In this study, the aim was to elucidate the effects and pathophysiological mechanisms of increased NPY in catecholaminergic neurones on accumulation of body adiposity.

METHODS

Transgenic mice overexpressing NPY under the dopamine-beta-hydroxylase promoter (OE-NPY(DβH) ) and wild-type control mice were followed for body weight gain and body fat content. Food intake, energy expenditure, physical activity, body temperature, serum lipid content and markers of glucose homoeostasis were monitored. Thermogenic and lipolytic responses in adipose tissues, and urine catecholamine and tissue catecholamine synthesizing enzyme levels were analysed as indices of sympathetic tone.

RESULTS

Homozygous OE-NPY(DβH) mice showed significant obesity accompanied with impaired glucose tolerance and insulin resistance. Increased adiposity was explained by neither increased food intake or fat absorption nor by decreased total energy expenditure or physical activity. Adipocyte hypertrophy and decreased circulating lipid levels suggested decreased lipolysis and increased lipid uptake. Brown adipose tissue thermogenic capacity was decreased and brown adipocytes filled with lipids. Enhanced response to adrenergic stimuli, downregulation of catecholamine synthesizing enzyme expressions in the brainstem and lower adrenaline excretion supported the notion of low basal catecholaminergic activity.

CONCLUSION

Increased NPY in catecholaminergic neurones induces obesity that seems to be a result of preferential fat storage. These results support the role of NPY as a direct effector in peripheral tissues and an inhibitor of sympathetic activity in the pathogenesis of obesity.

Neuropeptide y attenuates stress-induced bone loss through suppression of noradrenaline circuits

Chronic stress and depression have adverse consequences on many organ systems, including the skeleton, but the mechanisms underlying stress-induced bone loss remain unclear. Here we demonstrate that neuropeptide Y (NPY), centrally and peripherally, plays a critical role in protecting against stress-induced bone loss. Mice lacking the anxiolytic factor NPY exhibit more anxious behavior and elevated corticosterone levels. Additionally, following a 6-week restraint, or cold-stress protocol, Npy-null mice exhibit three-fold greater bone loss compared to wild-type mice, owing to suppression of osteoblast activity. This stress-protective NPY pathway acts specifically through Y2 receptors. Centrally, Y2 receptors suppress corticotropin-releasing factor expression and inhibit activation of noradrenergic neurons in the paraventricular nucleus. In the periphery, they act to control noradrenaline release from sympathetic neurons. Specific deletion of arcuate Y2 receptors recapitulates the Npy-null stress response, coincident with elevated serum noradrenaline. Importantly, specific reintroduction of NPY solely in noradrenergic neurons of otherwise Npy-null mice blocks the increase in circulating noradrenaline and the stress-induced bone loss. Thus, NPY protects against excessive stress-induced bone loss, through Y2 receptor-mediated modulation of central and peripheral noradrenergic neurons.

α-MSH overexpression in the nucleus tractus solitarius decreases fat mass and elevates heart rate

The POMC pathway is involved in the regulation of energy and cardiovascular homeostasis in the hypothalamus and the brain stem. Although the acute effects of POMC-derived peptides in different brain locations have been elucidated, the chronic site-specific effects of distinct peptides remain to be studied. To this end, we used a lentiviral gene delivery vector to study the long-term effects of α-MSH in the nucleus tractus solitarius (NTS) of the brain stem. The α-MSH vector (LVi-α-MSH-EGFP) based on the N-terminal POMC sequence and a control vector (LVi-EGFP) were delivered into the NTS of C57BL/6N male mice fed on a western diet. Effects on body weight and composition, feeding, glucose metabolism, and hemodynamics by telemetric analyses were studied during the 12-week follow-up. The LVi-α-MSH-EGFP-treated mice had a significantly smaller gain in the fat mass compared with LVi-EGFP-injected mice. There was a small initial decrease in food intake and no differences in the physical activity. Glucose metabolism was not changed compared with the control. LVi-α-MSH-EGFP increased the heart rate (HR), which was attenuated by adrenergic blockade suggesting an increased sympathetic activity. Reduced response to muscarinic blockade suggested a decreased parasympathetic activity. Fitting with sympathetic activation, LVi-α-MSH-EGFP treatment reduced urine secretion. Thus, the results demonstrate that long-term α-MSH overexpression in the NTS attenuates diet-induced obesity. Modulation of autonomic nervous system tone increased the HR and most probably contributed to an anti-obesity effect. The results underline the key role of NTS in the α-MSH-induced long-term effects on adiposity and in regulation of sympathetic and parasympathetic activities.

The effects of equal caloric high fat and western diet on metabolic syndrome, oxidative stress and vascular endothelial function in mice

AIM

Nutrition contributes to increased adiposity, but it remains to be determined whether high fat rather than Western diet exacerbates the development of obesity and other characteristics of metabolic syndrome and vascular function.

METHODS

We studied the effects of high fat (45% kcal) diet (HFD) and equal caloric Western diet (WD) high in fat, sucrose and cholesterol for 8 weeks in male C57B1/6N mice.

RESULTS

Mice fed with HFD and WD showed substantially higher body adiposity (body fat %) compared with control mice receiving low fat (10%) diet (LFD). However, total body weight was higher only in HFD mice compared with other groups. The amount of liver triglycerides, cholesterol and oxidative damage was higher in WD mice compared with mice on LFD. There were no significant differences in fasting blood glucose or serum insulin, serum or muscle triglycerides, glucose tolerance or systolic blood pressure between the groups, but serum free fatty acids were increased in HFD mice compared with LFD. Increased levels of tissue and serum diene conjugation as a marker of oxidative stress were evident especially in WD mice. The endothelium-dependent relaxations were significantly impaired in the small mesenteric arteries of HFD mice, but not in the aorta. Maximal relaxations correlated negatively with body adiposity in WD but not in HFD mice.

CONCLUSIONS

The major finding in the present study is that without changing body weight, Western diet induces marked whole-body oxidative stress and elevates body adiposity, which associates with the endothelial function of resistance arteries.

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.

Lentivirus-mediated α-melanocyte-stimulating hormone overexpression in the hypothalamus decreases diet induced obesity in mice

Melanocyte stimulating hormone (MSH) derived from the pro-hormone pro-opiomelanocortin (POMC) has potent effects on metabolism and feeding that lead to reduced body weight in the long-term. To determine the individual roles of POMC derived peptides and their sites of action, we created a method for the delivery of single MSH peptides using lentiviral vectors and studied the long-term anti-obesity effects of hypothalamic α-MSH overexpression in mice. An α-MSH lentivirus (LVi-α-MSH-EGFP) vector carrying the N'-terminal part of POMC and the α-MSH sequence was generated and shown to produce bioactive peptide in an in vitro melanin synthesis assay. Stereotaxis was used to deliver the LVi-α-MSH-EGFP or control LVi-EGFP vector to the arcuate nucleus (ARC) of the hypothalamus of male C57Bl/6N mice fed on a high-fat diet. The effects of 6-week-treatment on body weight, food intake, glucose tolerance and organ weights were determined. Additionally, a 14-day pairfeeding study was conducted to assess whether the weight decreasing effect of the LVi-α-MSH-EGFP treatment is dependent on decreased food intake. The 6-week LVi-α-MSH-EGFP treatment reduced weight gain (8.4 ± 0.4 g versus 12.3 ± 0.6 g; P < 0.05), which was statistically significant starting from 1 week after the injections. The weight of mesenteric fat was decreased and glucose tolerance was improved compared to LVi-EGFP treated mice. Food intake was decreased during the first week in the LVi-α-MSH-EGFP treated mice but subsequently increased to the level of LVi-EGFP treated mice. The LVi-EGFP injected control mice gained more weight even when pairfed to the level of food intake by LVi-α-MSH-EGFP treated mice. We demonstrate that gene transfer of α-MSH, a single peptide product of POMC, into the ARC of the hypothalamus, reduces obesity and improves glucose tolerance, and that factors other than decreased food intake also influence the weight decreasing effects of α-MSH overexpression in the ARC. Furthermore, viral MSH vectors delivered stereotaxically provide a novel tool for further exploration of chronic site-specific effects of POMC peptides.

α-MSH analogue attenuates blood pressure elevation in DOCA-salt hypertensive mice

Melanocyte-stimulating hormones, α-, β- and γ-MSH, regulate important physiological functions including energy homeostasis, inflammation and sodium metabolism. Previous studies have shown that α-MSH increases sodium excretion and promotes vascular function in rodents, but it is unexplored whether these characteristics of α-MSH could translate into therapeutic benefits in the treatment of hypertension. Therefore, we first assessed the diuretic and natriuretic properties of the stable α-MSH analogue [Nle(4), D-Phe(7)]-α-MSH (NDP-α-MSH) and investigated whether it has protective effects in deoxycorticosterone acetate (DOCA)-salt hypertensive mice. Adult male C57Bl/6N mice were subjected to DOCA-salt treatment and randomized to receive intraperitoneal injections of either saline as vehicle or NDP-α-MSH (0.3 mg/kg/day for 14 days) starting 7 days after the DOCA-salt treatment. Systemic hemodynamics, serum and urine electrolytes, and oxidative stress markers were assessed in control sham-operated and DOCA-salt mice. NDP-α-MSH elicited marked diuretic and natriuretic responses that were reversible with the MC3/4 receptor antagonist SHU9119. Chronic NDP-α-MSH treatment attenuated blood pressure elevation in DOCA-salt mice without affecting the blood pressure of normotensive control animals. Owing to the enhanced sodium excretion, NDP-α-MSH-treated mice were protected from DOCA-salt-induced hypernatremia. DOCA-salt treatment mildly increased oxidative stress at the tissue level, but NDP-α-MSH had no significant effects on the oxidative stress markers. In conclusion, treatment with NDP-α-MSH increases urinary sodium excretion and protects against DOCA-salt-induced hypertension. These findings point to the potential future use of α-MSH analogues in the treatment of hypertension.

Bone-specific overexpression of NPY modulates osteogenesis

OBJECTIVES

Neuropeptide Y (NPY) is a peptide involved in the regulation of appetite and energy homeostasis. Genetic data indicates that NPY decreases bone formation via central and peripheral activities. NPY is produced by various cell types including osteocytes and osteoblasts and there is evidence suggesting that peripheral NPY is important for regulation of bone formation. We sought to investigate the role of bone-derived NPY in bone metabolism.

METHODS

We generated a mouse where NPY was over-expressed specifically in mature osteoblasts and osteocytes (Col2.3NPY) and characterized the bone phenotype of these mice in vivo and in vitro.

RESULTS

Trabecular and cortical bone volume was reduced in 3-month-old animals, however bone formation rate and osteoclast activity were not significantly changed. Calvarial osteoblast cultures from Col2.3NPY mice also showed reduced mineralization and expression of osteogenic marker genes.

CONCLUSIONS

Our data suggest that osteoblast/osteocyte-derived NPY is capable of altering osteogenesis in vivo and in vitro and may represent an important source of NPY for regulation of bone formation. However, it is possible that other peripheral sources of NPY such as the sympathetic nervous system and vasculature also contribute to peripheral regulation of bone turnover.

Neuropeptide Y in the noradrenergic neurons induces the development of cardiometabolic diseases in a transgenic mouse model

Neuropeptide Y (NPY) is a neuropeptide widely expressed in the brain and a peptide transmitter of sympathetic nervous system (SNS) co-released with noradrenaline (NA) in prolonged stress. Association of a gain-of-function polymorphism in the human NPY gene with dyslipideamia, diabetes and vascular diseases suggests that increased NPY plays a role in the pathogenesis of the metabolic syndrome in humans. In the hypothalamus, NPY plays an established role in the regulation of body energy homeostasis. However, the effects of NPY elsewhere in the brain and in the SNS are less explored. In order to understand the role of NPY co-expressed with NA in the sympathetic nerves and brain noradrenergic neurons, a novel mouse model overexpressing NPY in noradrenergic neurons was generated. The mouse displays metabolic defects such as increased adiposity, hepatosteatosis, and impaired glucose tolerance as well as stress-related hypertension and increased susceptibility to vascular wall hypertrophy. The mouse phenotype closely reflects the findings of the several association studies with human NPY gene polymorphisms, and fits with the previous work on the effects of stress-induced NPY release on metabolism and vasculature. Thus, in addition of promoting feeding and obesity in the hypothalamus, NPY expressed in the noradrenergic neurons in the brain and in the SNS induces the development of cardiometabolic diseases.

α-Melanocyte-stimulating hormone regulates vascular NO availability and protects against endothelial dysfunction

AIMS

α-Melanocyte-stimulating hormone (α-MSH), derived from the precursor molecule pro-opiomelanocortin, exerts potent anti-inflammatory actions in the vasculature, but its role in circulatory regulation remains unclear. Therefore, we sought to investigate whether α-MSH could regulate the local control of blood vessel tone.

METHODS AND RESULTS

Using in vivo and ex vivo methods to assess vascular reactivity, we found that α-MSH improved endothelium-dependent vasodilatation in the mouse aorta and coronary circulation without directly contracting or relaxing blood vessels. α-MSH promoted vasodilatation by enhancing endothelial nitric oxide (NO) formation and by improving sensitivity to endothelium-independent blood vessel relaxation. Using cultured human endothelial cells to elucidate the involved molecular mechanisms, we show that α-MSH increased the expression and phosphorylation of endothelial NO synthase in these cells. The observed effects were regulated by melanocortin 1 (MC1) receptors expressed in the endothelium. In keeping with the vascular protective role of α-MSH, in vivo treatment with stable analogues of α-MSH ameliorated endothelial dysfunction associated with aging and diet-induced obesity in mice.

CONCLUSION

The present study identifies α-MSH and endothelial MC1 receptors as a new signalling pathway contributing to the regulation of NO availability and vascular function. These findings suggest applicability of α-MSH analogues for therapeutic use in pathological conditions that are characterized by vascular dysfunction.

Hemodynamic actions and mechanisms of systemically administered α-MSH analogs in mice

α-Melanocyte-stimulating hormone (α-MSH) regulates important physiological functions including energy homeostasis and inflammation. Potent analogs of α-MSH, [Nle(4), D-Phe(7)]-α-MSH (NDP-α-MSH) and melanotan-II (MT-II), are widely used in pharmacological studies, but the hemodynamic effects associated with their systemic administration have not been thoroughly examined. Therefore, we investigated the hemodynamic actions of these compounds in anesthetized and conscious C57Bl/6N mice using peripheral routes of administration. NDP-α-MSH and MT-II induced mild changes in blood pressure and heart rate in anesthetized mice compared to the effects observed in conscious mice, suggesting that anesthesia distorts the hemodynamic actions of α-MSH analogs. In conscious mice, NDP-α-MSH and MT-II increased blood pressure and heart rate in a dose-dependent manner, but the tachycardic effect was more prominent than the pressor effect. Pretreatment with the melanocortin (MC) 3/4 receptor antagonist SHU9119 abolished these hemodynamic effects. Furthermore, the blockade of β(1)-adrenoceptors with metoprolol prevented the pressor effect and partly the tachycardic action of α-MSH analogs, while the ganglionic blocker hexamethonium abrogated completely the difference in heart rate between vehicle and α-MSH treatments. These findings suggest that the pressor effect is primarily caused by augmentation of cardiac sympathetic activity, but the tachycardic effect seems to involve withdrawal of vagal tone in addition to sympathetic activation. In conclusion, the present results indicate that systemic administration of α-MSH analogs elevates blood pressure and heart rate via activation of MC(3/4) receptor pathways. These effects and the consequent increase in cardiac workload should be taken into account when using α-MSH analogs via peripheral routes of administration.

Regulation of prolactin in mice with altered hypothalamic melanocortin activity

This study used two mouse models with genetic manipulation of the melanocortin system to investigate prolactin regulation. Mice with overexpression of the melanocortin receptor (MC-R) agonist, α-melanocyte-stimulating hormone (Tg-MSH) or deletion of the MC-R antagonist agouti-related protein (AgRP KO) were studied. Male Tg-MSH mice had lower blood prolactin levels at baseline (2.9±0.3 vs. 4.7±0.7ng/ml) and after restraint stress (68±6.5 vs. 117±22ng/ml) vs. WT (p<0.05); however, pituitary prolactin content was not different. Blood prolactin was also decreased in male AgRP KO mice at baseline (4.2±0.5 vs. 7.6±1.3ng/ml) and after stress (60±4.5 vs. 86.1±5.7ng/ml) vs. WT (p<0.001). Pituitary prolactin content was lower in male AgRP KO mice (4.3±0.3 vs. 6.7±0.5μg/pituitary, p<0.001) vs. WT. No differences in blood or pituitary prolactin levels were observed in female AgRP KO mice vs. WT. Hypothalamic dopamine activity was assessed as the potential mechanism responsible for changes in prolactin levels. Hypothalamic tyrosine hydroxylase mRNA was measured in both genetic models vs. WT mice and hypothalamic dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) content were measured in male AgRP KO and WT mice but neither were significantly different. However, these results do not preclude changes in dopamine activity as dopamine turnover was not directly investigated. This is the first study to show that baseline and stress-induced prolactin release and pituitary prolactin content are reduced in mice with genetic alterations of the melanocortin system and suggests that changes in hypothalamic melanocortin activity may be reflected in measurements of serum prolactin levels.

MMP-13 regulates growth of wound granulation tissue and modulates gene expression signatures involved in inflammation, proteolysis, and cell viability

Proteinases play a pivotal role in wound healing by regulating cell-matrix interactions and availability of bioactive molecules. The role of matrix metalloproteinase-13 (MMP-13) in granulation tissue growth was studied in subcutaneously implanted viscose cellulose sponge in MMP-13 knockout (Mmp13(-/-)) and wild type (WT) mice. The tissue samples were harvested at time points day 7, 14 and 21 and subjected to histological analysis and gene expression profiling. Granulation tissue growth was significantly reduced (42%) at day 21 in Mmp13(-/-) mice. Granulation tissue in Mmp13(-/-) mice showed delayed organization of myofibroblasts, increased microvascular density at day 14, and virtual absence of large vessels at day 21. Gene expression profiling identified differentially expressed genes in Mmp13(-/-) mouse granulation tissue involved in biological functions including inflammatory response, angiogenesis, cellular movement, cellular growth and proliferation and proteolysis. Among genes linked to angiogenesis, Adamts4 and Npy were significantly upregulated in early granulation tissue in Mmp13(-/-) mice, and a set of genes involved in leukocyte motility including Il6 were systematically downregulated at day 14. The expression of Pdgfd was downregulated in Mmp13(-/-) granulation tissue in all time points. The expression of matrix metalloproteinases Mmp2, Mmp3, Mmp9 was also significantly downregulated in granulation tissue of Mmp13(-/-) mice compared to WT mice. Mmp13(-/-) mouse skin fibroblasts displayed altered cell morphology and impaired ability to contract collagen gel and decreased production of MMP-2. These results provide evidence for an important role for MMP-13 in wound healing by coordinating cellular activities important in the growth and maturation of granulation tissue, including myofibroblast function, inflammation, angiogenesis, and proteolysis.

Involvement of α2-adrenoceptor subtypes A and C in glucose homeostasis and adrenaline-induced hyperglycaemia

BACKGROUND AND AIMS

Insulin secretion is controlled by pancreatic α(2A)-adrenoceptors. Mice lacking α(2A)-adrenoceptors (α(2A)AR(-/-) mice) show hyperinsulinaemia, reduced blood glucose levels and improved glucose tolerance.

METHODS

In the present study, we used α(2AC)AR(-/-), α(2C)AR(-/-) and α(2A)AR(-/-) mice and a mouse line with adrenergic cell-specific expression of α(2A)-adrenoceptors (lacking these receptors in non-adrenergic cells), and their wild-type (WT) controls, to assess the glucoregulatory role of the α(2C)-adrenoceptor subtype in vivo. Glucose and insulin tolerance tests were performed and blood glucose and serum insulin levels were determined after fasting and glucose stimulation. Plasma catecholamines were also measured. In addition, the effect of pretreatment with (±)-propranolol was determined in α(2C)AR(-/-) mice.

RESULTS

α(2AC)AR(-/-) mice had a similar glucose and insulin phenotype as α(2A)AR(-/-) mice and mice with restored α(2A)-autoreceptors, suggesting that only deletion of postsynaptic α(2A)-adrenoceptors has major effects on glucose disposition. However, α(2AC)AR(-/-) mice were more sensitive to the glucose-lowering effect of insulin than WT mice. This was not observed in α(2A)AR(-/-) mice. The α(2C)AR(-/-) mice showed impaired glucose tolerance that was reversed by pretreatment with (±)-propranolol. No difference in insulin secretion was observed in α(2C)AR(-/-) mice compared with WT animals.

CONCLUSION

The results underline that depletion of postsynaptic pancreatic α(2A)-adrenoceptors has major effects on the regulation of glucose homeostasis in α(2AC)AR(-/-) and α(2A)AR(-/-) mice. Deletion of the α(2C) subtype leads to increased adrenaline secretion and has the potential to increase blood glucose levels via enhanced glycogenolysis.

Metabolic regulation in progression to autoimmune diabetes

Recent evidence from serum metabolomics indicates that specific metabolic disturbances precede β-cell autoimmunity in humans and can be used to identify those children who subsequently progress to type 1 diabetes. The mechanisms behind these disturbances are unknown. Here we show the specificity of the pre-autoimmune metabolic changes, as indicated by their conservation in a murine model of type 1 diabetes. We performed a study in non-obese prediabetic (NOD) mice which recapitulated the design of the human study and derived the metabolic states from longitudinal lipidomics data. We show that female NOD mice who later progress to autoimmune diabetes exhibit the same lipidomic pattern as prediabetic children. These metabolic changes are accompanied by enhanced glucose-stimulated insulin secretion, normoglycemia, upregulation of insulinotropic amino acids in islets, elevated plasma leptin and adiponectin, and diminished gut microbial diversity of the Clostridium leptum group. Together, the findings indicate that autoimmune diabetes is preceded by a state of increased metabolic demands on the islets resulting in elevated insulin secretion and suggest alternative metabolic related pathways as therapeutic targets to prevent diabetes.

Acute hormonal changes following intravenous glucose challenge in lean and obese human subjects

OBJECTIVE

To study the effects of rapid i.v. glucose bolus on insulin, leptin, ghrelin, peptide YY (PYY), free fatty acids (FFA), glucagon and glucagon-like peptide-1 (GLP-1) concentrations together with self-reported satiety ratings in lean and obese human subjects.

METHODS

Twenty-five healthy subjects were recruited, 12 were lean (mean age = 26 years, BMI range = 19.8-23.9 kg/m(2)) and 13 were obese (mean age = 27 years, BMI range = 27.7-42.2 kg/m(2)). In two separate 55 min counter-balanced blinded sessions (separate days), subjects were administered an i.v. dose of 300 mg/kg glucose or saline. Blood concentrations of several feeding-related hormones were recorded at multiple time points, together with ratings of satiety and euphoria.

RESULTS

Greater increases in glucose concentrations were observed in the obese group compared to the lean group (p < 0.0001). In both lean and obese subjects, glucose injection induced a clear fall in the concentrations of FFA, ghrelin, glucagon and PYY (p < 0.0001) but not in the concentrations of leptin or GLP-1. Obese subjects showed positive correlations between satiety and glucose, but only at time points 30 min (r = 0.73, p = 0.005) and 55 min (r = 0.82, p = 0.0005).

CONCLUSIONS

The directions and the magnitudes of short-term hormonal changes after i.v. glucose challenge are the same in lean and moderately obese subjects. Possible short-term regulatory effects of leptin and GLP-1 can not be induced by acute energy load bypassing the GI-tract.

Sympathetic nervous system-targeted neuropeptide Y overexpression in mice enhances neointimal formation in response to vascular injury

Sympathetic neurotransmitter neuropeptide Y (NPY) is associated with vascular remodelling, neointimal hyperplasia and atherosclerosis in experimental animal models and clinical studies. In order to study the role of sympathetic nerve-produced NPY in vascular diseases, transgenic mouse model overexpressing NPY in central and peripheral noradrenergic neurons under the dopamine-beta-hydroxylase (DBH) promoter was recently created (OE-NPY(DBH) mouse). This study aimed to examine the effect of NPY overexpression on arterial neointimal hyperplasia in an experimental model of vascular injury. Transgenic OE-NPY(DBH) mice and wildtype control mice of two different inbred strains (C57BL/6 and FVB/n) underwent a femoral artery surgery with a transluminar injury by a 0.38-mm guide wire insertion. Arteries were harvested 4 weeks from the surgery, and they were stained for basic morphology. Both strains of OE-NPY(DBH) mice, as compared with wildtype control mice, showed on average 50% greater formation of the neointima (P<0.01) and an increase in the medial area (P=0.05). The results suggest that moderately increased neuronal NPY causes the arteries to be more susceptible to femoral artery thickening after endothelial injury. The OE-NPY(DBH) mouse provides a novel tool to explore the role of NPY in the development of vascular disease related to metabolic disorders.

Stress-induced hypertension and increased sympathetic activity in mice overexpressing neuropeptide Y in noradrenergic neurons

BACKGROUND AND AIMS

Neuropeptide Y (NPY) is a sympathetic neurotransmitter co-stored and co-released with noradrenaline and adrenaline. We have constructed a novel NPY transgenic mouse model (OE-NPY(DBH) mouse) where targeted overexpression results in increased levels of NPY in the brainstem and adrenal glands. The present study was aimed to understand the role of NPY released from sympathetic nerves and brain noradrenergic neurons in regulation of blood pressure, and behavioral responses to stress.

METHODS

Blood pressure was measured by radiotelemetry in conscious male OE-NPY(DBH) and wild-type mice during surgical stress and in baseline conditions. Plasma and adrenal gland catecholamine levels were measured at baseline. Acute immobilization and cold exposure were used to study the plasma levels of NPY and corticosterone in stress, and brown adipose tissue thermogenic activity was measured with [(3)H]GDP binding after cold.

RESULTS

Here, we demonstrate that sympathoadrenal activity is enhanced in the OE-NPY(DBH) mice. Blood pressure during surgical stress was significantly increased in comparison with wild-type controls. Furthermore, OE-NPY(DBH) mice showed sexually dimorphic NPY responses to stress, and an anxiolytic-like behavior in elevated plus-maze and light-dark tests.

CONCLUSION

This study shows that the overactive noradrenergic NPY system plays a role in regulation of blood pressure and adaptive responses to stress, and may be a link between chronic stress and adiposity-associated disturbances in metabolism.

Blood pressure regulation and cardiac autonomic control in mice overexpressing alpha- and gamma-melanocyte stimulating hormone

Melanocyte stimulating hormones (MSH) derived from pro-opiomelanocortin have been demonstrated to participate in the central regulation of cardiovascular functions. The aim of the present study was to elucidate the chronic effects of increased melanocortin activation on blood pressure regulation and autonomic nervous system function. We adapted telemetry to transgenic mice overexpressing alpha- and gamma-MSH and measured blood pressure, heart rate and locomotor activity, and analyzed heart rate variability (HRV) in the frequency-domain as well as baroreflex function by the sequence technique. Transgenic (MSH-OE) mice had increased systolic blood pressure but their heart rate was similar to wild-type (WT) controls. The 24-h mean of systolic blood pressure was 132+/-7mmHg in MSH-OE and 113+/-4mmHg in WT mice. Locomotor activity was decreased in the MSH-OE mice. Furthermore, MSH-OE mice showed slower adaptation to mild environmental stress in terms of blood pressure changes. The low frequency (LF) power of HRV tended to be higher in MSH-OE mice compared to WT mice, without a difference in overall variability. The assessment of baroreflex function indicated enhanced baroreflex effectiveness and more frequent baroreflex operations in MSH-OE mice. Baseline heart rate, increased LF power of HRV and increased baroreflex activity may all reflect maintenance of baroreflex integrity and an increase in cardiac vagal activity to counteract the increased blood pressure. These results provide new evidence that long-term activation of the melanocortin system elevates blood pressure without increasing heart rate.

Transgenic mice overexpressing neuropeptide Y in noradrenergic neurons: a novel model of increased adiposity and impaired glucose tolerance

OBJECTIVE

A functional polymorphism leucine 7 proline in the human neuropeptide Y (NPY) gene leading to increased NPY release from sympathetic nerves is associated with traits of metabolic syndrome. Although hypothalamic NPY neurons play an established role in promoting positive energy balance, the role of NPY colocalized with norepinephrine in sympathetic nervous system and brain noradrenergic neurons remains obscure.

RESEARCH DESIGN AND METHODS

To clarify the role of NPY in noradrenergic neurons, we generated a transgenic mouse overexpressing NPY under dopamine-beta-hydroxylase promoter and characterized the metabolic phenotype of the OE-NPY(DbetaH) mouse.

RESULTS

NPY levels are increased by 1.3-fold in adrenal glands and 1.8-fold in the brainstem but not in the hypothalamus in OE-NPY(DbetaH) mice. They display increased white adipose tissue mass and cellularity and liver triglyceride accumulation without hyperphagia or increased body weight. Hyperinsulinemia and impaired glucose tolerance develop by the age of 6 months in the OE-NPY(DbetaH) mice. Furthermore, circulating ghrelin is significantly increased in comparison with wild-type mice.

CONCLUSIONS

The present study shows that even a moderate increase in NPY levels in noradrenergic neurons leads to disturbances in glucose and lipid metabolism. The OE-NPY(DbetaH) mouse is an interesting new model to investigate the pathophysiology of some key components of the cluster of abnormalities characterizing the metabolic syndrome.

Reduced blood glucose levels, increased insulin levels and improved glucose tolerance in alpha2A-adrenoceptor knockout mice

Alpha(2)-Adrenoceptors regulate insulin secretion and sympathetic output. In the present study, alpha(2A)-adrenoceptor knockout (alpha(2A)-KO) mice and their C57BL/6J wild-type (WT) controls were used to assess the glucoregulatory role of the alpha(2A)-adrenoceptor subtype in vivo. Fasting and glucose-stimulated blood glucose and plasma insulin levels were determined with or without (+/-)-propranolol (5 mg/kg) or atropine (10 mg/kg) pre-treatment. Intraperitoneal glucose (1 g/kg) and insulin (0.5 and 1.0 IU/kg) tolerance tests were performed. Fasting plasma glucagon and corticosterone levels were measured. Blood glucose levels (mean+/-S.E.M.) were lower in alpha(2A)-KO males (7.2+/-0.6 mM) and females (7.2+/-0.2 mM) than in WT males (9.8+/-0.3 mM) and females (9.1+/-0.3 mM). Plasma insulin levels were higher in alpha(2A)-KO males (2.2+/-0.5 microg/l) and females (1.7+/-0.3 microg/l) than in WT males (0.7+/-0.1 microg/l) and females (0.8+/-0.2 microg/l). These differences remained after pharmacological beta-adrenoceptor and muscarinic acetylcholine receptor inhibition. In spite of a tendency for slightly decreased insulin sensitivity in alpha(2A)-KO mice, glucose tolerance in alpha(2A)-KO mice was significantly better than in WT mice. However, glucose-stimulated insulin secretion was not increased in alpha(2A)-KO mice compared to WT controls. Plasma glucagon levels, but not corticosterone levels, were elevated in alpha(2A)-KO mice. These results suggest that lack of inhibitory pancreatic beta-cell alpha(2A)-adrenoceptor function results in hyperinsulinaemia, reduced blood glucose levels and improved glucose tolerance in alpha(2A)-KO mice, and demonstrate a key role for the alpha(2A)-adrenoceptor in adrenergic regulation of blood glucose and insulin homeostasis.

Effects of intravenous glucose on dopaminergic function in the human brain in vivo

Dopamine is known to regulate food intake by modulating food reward via the mesolimbic circuitry of the brain. The objective of this study was to compare the effects of high energy input (i.v. glucose) on striatal and thalamic dopamine release in overweight and lean individuals. We hypothesized that glucose would induce dopamine release and positive ratings (e.g., satiety) in Behavioral Analog Scales, particularly in food-deprived lean subjects. [(11)C]raclopride PET was performed for 12 lean (mean BMI = 22 kg/m(2)) and 12 overweight (mean BMI = 33 kg/m(2)) healthy subjects. Each subject was imaged twice in a blinded counter-balanced setting, after 300 mg/kg i.v. glucose and after i.v. placebo. Dopamine D2 receptor binding potentials (BPs) were estimated. The voxel-based analysis of the baseline scans indicated lower striatal BPs in the overweight group and a negative correlation between BMIs and BPs. Intravenous glucose did not have a significant effect on BPs in overweight or lean subjects (male and female groups combined). However, BP changes were opposite in the two gender groups. In male subjects, significant BP reductions after glucose were seen in the right and left caudate nucleus, left putamen, and right thalamus. In female subjects, increases in BP secondary to glucose were seen in the right caudate nucleus and right and left putamen. The sexually dimorphic effect of glucose was seen in both overweight and lean subjects. Although gender differences were not among the a priori hypotheses of the present study and, therefore, they must be considered to be preliminary findings, we postulate that this observation is a reflection of an interaction between glucose, sex steroids (estrogen), leptin, and dopamine.

Metabolic effects of transgenic melanocyte-stimulating hormone overexpression in lean and obese mice

The proopiomelanocortin-derived peptide, alpha-MSH, inhibits feeding via melanocortin receptors in the hypothalamus and genetic defects inactivating the melanocortin system have been shown to lead to obesity in experimental animals and humans. To determine whether long-term melanocortinergic activation has significant effects on body weight and composition and insulin sensitivity, transgenic mice overexpressing N-terminal proopiomelanocortin, including alpha- and gamma(3)-MSH, under the control of the cytomegalovirus-promoter were generated. The transgene was expressed in multiple tissues including the hypothalamus, in which both alpha-MSH and gamma(3)-MSH levels were increased approximately 2-fold, compared with wild-type controls. Transgene homozygous mice were also crossed with obese leptin receptor-deficient db(3J) and obese yellow A(y) mice. MSH overexpression led to uniform, dose- dependent darkening of coat color. MSH overexpression reduced weight gain and adiposity and improved glucose tolerance in lean male mice. In female transgenic mice, there was no significant effect on body weight, but there was a significant decrease in insulin levels. Obesity was attenuated in obese db(3J)/db(3J) male and female mice, but there was no improvement in glucose metabolism. In contrast, the MSH transgene improved glucose tolerance in male A(y) mice. These results support the hypothesis that long-term melanocortinergic activation could serve as a potential strategy for anti-obesity and/or antidiabetic therapy.

Obesity in transgenic female mice with constitutively elevated luteinizing hormone secretion

Transgenic (TG) female mice, expressing a chimeric bovine luteinizing hormone (LH) beta-subunit/human chorionic gonadotropin beta-subunit COOH-terminal extension (bLHbeta-CTP) gene, produce high levels of circulating LH and serve as a model for functional ovarian hyperandrogenism and follicular cysts. We report here that obesity is a typical feature of these female mice. The mean body weight of the bLHbeta-CTP females was significantly higher than in controls at, and beyond 5 wk of age, and at 5 mo, it was 32% increased. At this age, the amount of white adipose tissue in the bLHbeta-CTP females was significantly increased, as reflected by the weight difference of the retroperitoneal fat pad. In addition, the expression of leptin mRNA in white adipose tissue of the TG females was elevated about twofold. Serum leptin and insulin levels, and food intake, were also increased significantly in the TG females. Brown adipose tissue (BAT) thermogenic activity, as measured by GDP binding to BAT mitochondria, was reduced (P < 0.05). Ovariectomy at the age of 3 wk totally prevented the development of obesity. In summary, the present results show that intact female bLHbeta-CTP mice are obese, have increased food consumption, and reduced BAT thermogenic activity. The weight gain can be explained partly by elevated androgens but is probably also contributed to the increased adrenal steroidogenesis. Hence, the bLHbeta-CTP mice provide a useful model for studying obesity related to elevated LH secretion, with consequent alterations in ovarian and adrenal function.

Effects of adrenalectomy on AGRP, POMC, NPY and CART gene expression in the basal hypothalamus of fed and fasted rats

Glucocorticoids regulate body energy balance through both peripheral and central mechanisms. In order to understand the central mechanisms that mediate these effects of glucocorticoids we studied the effects of adrenalectomy (ADX) and food deprivation on the expression of four neuropeptide genes (measured by S1 nuclease protection assay) in the medial basal hypothalamus (MBH), which are known to regulate energy balance: pro-opiomelanocortin (POMC), agouti-related peptide (AGRP), neuropeptide Y (NPY), and cocaine and amphetamine regulated transcript (CART). Adult male rats were ADX or sham operated (SHAM), and studied 1-2 weeks later. In the first study effects of ADX and corticosterone replacement on POMC and AGRP expression were determined. ADX decreased POMC and AGRP gene expression in the MBH by 27 and 38%, respectively, compared to SHAM rats. Corticosterone treatment increased the expression of POMC by 87% and AGRP by 45% in ADX rats. The second study was designed to determine if glucocorticoids are necessary for the fasting induced changes in POMC, AGRP, NPY and CART in the MBH. ADX caused a 20-30% decrease in the expression of all four neuropeptide genes in the MBH. As expected, fasting suppressed POMC and CART expression and increased AGRP and NPY expression. The fasting-induced increases in AGRP and NPY persisted after ADX but no further significant decreases in POMC or CART were noted after fasting in ADX rats. Plasma leptin and insulin declined significantly after ADX and increased with corticosterone replacement; both leptin and insulin declined further in fasted, ADX animals. In conclusion, ADX decreases both anorexigenic, POMC and CART, and orexigenic, AGRP and NPY, neuropeptide gene expression in the MBH. AGRP and NPY decrease after ADX despite the fall in plasma leptin and insulin concentrations which in other situations would increase these neuropeptides. Furthermore, glucocorticoids are not required for fasting-induced upregulation of AGRP and NPY expression.

Leptin regulation of Agrp and Npy mRNA in the rat hypothalamus

Agouti-related protein (AGRP) is synthesized in the same neurones in the arcuate nucleus as neuropeptide Y (NPY), another potent orexigenic peptide. AGRP antagonizes the action of alpha-melanocyte stimulating hormone, a derivative of pro-opiomelanocortin (POMC) at the hypothalamic MC4 receptor to increase food intake. Although leptin has been shown to regulate Agrp/Npy and Pomc-expressing neurones, there are differences with respect to Agrp regulation in leptin receptor-deficient mice and rats. Unlike the obese leptin receptor-deficient db/db mouse, which exhibits upregulation of Agrp mRNA expression in the medial basal hypothalamus (MBH) compared to lean controls, the obese leptin receptor-deficient (faf; Koletsky) rat does not exhibit upregulation of Agrp expression. To determine whether this represents a general difference between leptin receptor-deficient mice and rats, neuropeptide gene expression was analysed in the MBH of lean and obese rats segregating for a different leptin receptor mutation, Leprfa (Zucker). Fasting in lean rats (+/fa) for 72 h significantly increased Agrp and Npy mRNA expression, and decreased Pomc mRNA expression as detected by a sensitive solution hybridization/S1 nuclease protection assay. Npy mRNA levels were significantly increased in fed obese fa/fa compared to lean rats, and further increased in the obese animals after fasting. In contrast, Agrp mRNA levels did not differ between fed lean and fed obese rats, and fasting did not significantly change Agrp levels in obese rats. To determine whether the change in Agrp expression that occurs with food deprivation in lean rats could be prevented by leptin replacement, Sprague-Dawley rats were fasted and infused via subcutaneous osmotic micropumps for 48 h with either saline or recombinant mouse leptin. Fasting significantly increased Agrp and Npy, and decreased Pomc mRNA levels. Leptin infusion almost completely reversed these changes such that there was no significant difference between the levels in the fasted rats and those that were fed ad libitum. Thus, in fasted lean rats, Agrp and Npy are upregulated in parallel when leptin levels fall and are downregulated by leptin infusion. By contrast, the absence of a functional leptin receptor results in the upregulation of Npy but not Agrp mRNA.

Effects of estrous cycle and steroid replacement on the expression of leptin and uncoupling proteins in adipose tissue in the rat

Among other actions, leptin has been suggested to increase energy expenditure and to modulate the menstrual cycle. In fact, the main effect of leptin seems to be modulating the sympathetic nervous system and gonadotropin-releasing hormone pulsatility. We investigated whether changes in the plasma steroid concentrations during the estrous cycle and after ovariectomy and steroid replacement can modulate plasma leptin levels, adipose tissue leptin mRNA expression, and some of the candidates for mediating energy expenditure (uncoupling proteins (UCP) 1, 2, and 3 mRNA) in white and brown adipose tissue. Rats in estrous cycle or ovariectomized rats with or without estradiol or progesterone replacement therapy for 18 days were studied. Plasma leptin, insulin, estradiol and progesterone were measured with radioimmunoassays. Leptin mRNA expression was measured in subcutaneous, periovarian and mesenteric white adipose tissue and in interscapular brown adipose tissue. Expression of UCP 1, 2, and 3 mRNA in periovarian white and brown adipose tissue was analyzed. Plasma leptin levels were significantly decreased in the estrous (1.1 +/- 0.4 ng/ml) compared with the pro-estrous (1.7 +/- 0.4 ng/ml, F = 3.0, p = 0.046) phase of cycle. UCP1 mRNA levels in brown adipose tissue were more elevated during pro-estrus than during metestrus (F = 3.17, p = 0.039). Gene expressions of leptin, UCP2 or UCP3 mRNA did not change significantly during the cycle. In ovariectomized rats, estradiol and/or progesterone treatment had no effect on plasma leptin levels. Gene expression analysis of leptin and UCP1, 2 and 3 in adipose tissue was not affected by steroid replacement. In conclusion, the estrous cycle appears to have a minor effect on modulation of leptin and uncoupling proteins. Only plasma leptin levels and expression of UCP1 mRNA are modestly elevated during the estrous cycle in the rat. Since estrogen and/or progesterone substitution in ovariectomized rats does not affect circulating leptin concentration or expression of leptin and UCPs in adipose tissue, it is unlikely that steroids play a major role in their regulation.