The role of neuropeptide Y in the pathogenesis of the metabolic syndrome : A study of liver metabolism in transgenic mice overexpressing neuropeptide Y in noradrenergic neurons

The metabolic syndrome (MetS) is a set of symptoms related to obesity, predisposing patients to cardiovascular diseases, and recently hepatosteatosis has been shown to play a major role in its pathogenesis. Neuropeptide Y (NPY) is a neurotransmitter found abundantly in the brain, promoting food intake and energy storage, but also the increased NPY levels in the periphery cause fat accumulation and are associated with impaired glucose tolerance. The main aim of this study was to evaluate the influence of excess NPY on the hepatic metabolism of fatty acids, glucose and cholesterol as a cause of the MetS. The study was performed with genetically obese mice overexpressing NPY in central noradrenergic neurons and the peripheral sympathetic nervous system (OE-NPYDβH), which display obesity, impaired glucose tolerance and insulin resistance as they age. This study revealed that obese OE-NPYDβH mice exhibited also hepatic accumulation of triglycerides and glycogen, as well as hypercholesterolemia preceded by decreased hepatic fatty acid oxidation and increased synthesis of glycogen and cholesterol. Due to this phenotype, these mice are more prone to type 2 diabetes. Furthermore, hepatic glycogen metabolism could be inhibited by the anti-hyperglycemic agent, metformin, which suggests that changes in glycogen metabolism may associate with the prediabetes encountered in obese OE-NPYDβH mice. The mechanism of action of NPY inducing the hepatic pathologies seems to involve decreased sympathetic activity in the liver of OE-NPYDβH mice, similar to that previously detected in adipose tissue. However, there seems to be less involvement of NPY directly on the liver via peripheral Y-receptors. Instead, Y2-receptors appear to mediate the obesogenic effects of NPY, and they could be a potential drug target for obesity induced by consuming an unhealthy diet combined with excess NPY

The role of neuropeptide Y in the pathogenesis of the metabolic syndrome : A study of liver metabolism in transgenic mice overexpressing neuropeptide Y in noradrenergic neurons

The metabolic syndrome (MetS) is a set of symptoms related to obesity, predisposing patients to cardiovascular diseases, and recently hepatosteatosis has been shown to play a major role in its pathogenesis. Neuropeptide Y (NPY) is a neurotransmitter found abundantly in the brain, promoting food intake and energy storage, but also the increased NPY levels in the periphery cause fat accumulation and are associated with impaired glucose tolerance. The main aim of this study was to evaluate the influence of excess NPY on the hepatic metabolism of fatty acids, glucose and cholesterol as a cause of the MetS. The study was performed with genetically obese mice overexpressing NPY in central noradrenergic neurons and the peripheral sympathetic nervous system (OE-NPYDβH), which display obesity, impaired glucose tolerance and insulin resistance as they age. This study revealed that obese OE-NPYDβH mice exhibited also hepatic accumulation of triglycerides and glycogen, as well as hypercholesterolemia preceded by decreased hepatic fatty acid oxidation and increased synthesis of glycogen and cholesterol. Due to this phenotype, these mice are more prone to type 2 diabetes. Furthermore, hepatic glycogen metabolism could be inhibited by the anti-hyperglycemic agent, metformin, which suggests that changes in glycogen metabolism may associate with the prediabetes encountered in obese OE-NPYDβH mice. The mechanism of action of NPY inducing the hepatic pathologies seems to involve decreased sympathetic activity in the liver of OE-NPYDβH mice, similar to that previously detected in adipose tissue. However, there seems to be less involvement of NPY directly on the liver via peripheral Y-receptors. Instead, Y2-receptors appear to mediate the obesogenic effects of NPY, and they could be a potential drug target for obesity induced by consuming an unhealthy diet combined with excess NPY

Spinal TRPA1 Contributes to the Mechanical Hypersensitivity Effect Induced by Netrin-1

Netrin-1, a chemoattractant expressed by floor plate cells, and one of its receptors (deleted in colorectal cancer) has been associated with pronociceptive actions in a number of pain conditions. Here, we addressed the question of whether spinal TRPC4/C5 or TRPA1 are among the downstream receptors contributing to pronociceptive actions induced by netrin-1. The experiments were performed on rats using a chronic intrathecal catheter for administration of netrin-1 and antagonists of TRPC4/C5 or TRPA1. Pain sensitivity was assessed behaviorally by using mechanical and heat stimuli. Effect on the discharge rate of rostral ventromedial medullary (RVM) pain control neurons was studied in lightly anesthetized animals. Netrin-1, in a dose-related fashion, induced mechanical hypersensitivity that lasted up to three weeks. Netrin-1 had no effect on heat nociception. Mechanical hypersensitivity induced by netrin-1 was attenuated by TRPA1 antagonist Chembridge-5861528 and by the control analgesic compound pregabalin both during the early (first two days) and late (third week) phase of hypersensitivity. TRPC4/C5 antagonist ML-204 had a weak antihypersensitivity effect that was only in the early phase, whereas TRPC4/C5 antagonist HC-070 had no effect on hypersensitivity induced by netrin-1. The discharge rate in pronociceptive ON-like RVM neurons was increased by netrin-1 during the late but not acute phase, whereas netrin-1 had no effect on the discharge rate of antinociceptive RVM OFF-like neurons. The results suggest that spinal TRPA1 receptors and pronociceptive RVM ON-like neurons are involved in the maintenance of submodality-selective pronociceptive actions induced by netrin-1 in the spinal cord

Spinal TRPA1 Contributes to the Mechanical Hypersensitivity Effect Induced by Netrin-1

Netrin-1, a chemoattractant expressed by floor plate cells, and one of its receptors (deleted in colorectal cancer) has been associated with pronociceptive actions in a number of pain conditions. Here, we addressed the question of whether spinal TRPC4/C5 or TRPA1 are among the downstream receptors contributing to pronociceptive actions induced by netrin-1. The experiments were performed on rats using a chronic intrathecal catheter for administration of netrin-1 and antagonists of TRPC4/C5 or TRPA1. Pain sensitivity was assessed behaviorally by using mechanical and heat stimuli. Effect on the discharge rate of rostral ventromedial medullary (RVM) pain control neurons was studied in lightly anesthetized animals. Netrin-1, in a dose-related fashion, induced mechanical hypersensitivity that lasted up to three weeks. Netrin-1 had no effect on heat nociception. Mechanical hypersensitivity induced by netrin-1 was attenuated by TRPA1 antagonist Chembridge-5861528 and by the control analgesic compound pregabalin both during the early (first two days) and late (third week) phase of hypersensitivity. TRPC4/C5 antagonist ML-204 had a weak antihypersensitivity effect that was only in the early phase, whereas TRPC4/C5 antagonist HC-070 had no effect on hypersensitivity induced by netrin-1. The discharge rate in pronociceptive ON-like RVM neurons was increased by netrin-1 during the late but not acute phase, whereas netrin-1 had no effect on the discharge rate of antinociceptive RVM OFF-like neurons. The results suggest that spinal TRPA1 receptors and pronociceptive RVM ON-like neurons are involved in the maintenance of submodality-selective pronociceptive actions induced by netrin-1 in the spinal cord.Peer reviewe

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 gamma(3)-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

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-OEDβH) 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-OEDβH mice more than in wild-type mice. In addition, gain in the whole body lean mass gain was decreased only in NPY-OEDβH 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-OEDβH and wild-type mice. The results demonstrate that doxorubicin at a relatively low dose caused significant cardiotoxicity. There were differences between NPY-OEDβH 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.</p

Peripherally Administered Y-2-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 Y-2-receptors have anti-obesity effects, but it is not known whether pharmacological blocking of peripheral Y-2-receptors would similarly benefit energy homeostasis. The effects of a peripherally administered Y-2-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-NPYD beta H) represented the situation of elevated NPY levels, while wildtype (WT) mice represented the normal NPY levels. Specific Y-2-receptor antagonist, BIIE0246, was administered (1.3 mg/kg/day, i.p.) for 2 or 4.5 weeks to OE-NPYD beta H and WT mice feeding on chow or Western diet. Treatment with Y-2-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 Y-2-receptors induced obesity in WT mice, whereas OE-NPYD beta H 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 Y-2-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, Y-2-receptor antagonism has beneficial effects on metabolic status

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

The α2A-adrenoceptors (ARs) are Gi-coupled receptors, which prejunctionally inhibit the release of norepinephrine (NE) and epinephrine (Epi), and postjunctionally 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 (DIO) and type 2 diabetes (T2D). In addition, 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 their WT controls, were protected from T2D, and their insulin secretion was unaltered by the diet. Lack of α2A-ARs associated with 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 fecal 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 norepinephrine. 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.

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-NPYD&beta;H 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 were measured in key regulatory tissues, i.e. hypothalamus, pancreas, epididymal white adipose tissue, liver and soleus muscle, over the development of metabolic dysfunctions in OE-NPYD&beta;H mice. The effects of a 5-week treatment with the CB1 receptor inverse agonist AM251 on adiposity and glucose metabolism were studied. Results: 2-arachidonoylglycerol levels were increased in the hypothalamus and epididymal white adipose tissue of pre-obese and obese OE-NPYD&beta;H 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-NPYD&beta;H to the level of vehicle-treated wildtype mice. Conclusions: Altered endocannabinoid tone may underlie some of the metabolic dysfunctions in OE-NPYD&beta;H 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.</p