Hypothalamic α7 nicotinic acetylcholine receptor (α7nAChR) is downregulated by TNFα-induced Let-7 overexpression driven by fatty acids.

The α7nAChR is crucial to the anti-inflammatory reflex, and to the expression of neuropeptides that control food intake, but its expression can be decreased by environmental factors. We aimed to investigate whether microRNA modulation could be an underlying mechanism in the α7nAchR downregulation in mouse hypothalamus following a short-term exposure to an obesogenic diet. Bioinformatic analysis revealed Let-7 microRNAs as candidates to regulate Chrna7, which was confirmed by the luciferase assay. Mice exposed to an obesogenic diet for 3 days had increased Let-7a and decreased α7nAChR levels, accompanied by hypothalamic fatty acids and TNFα content. Hypothalamic neuronal cells exposed to fatty acids presented higher Let-7a and TNFα levels and lower Chrna7 expression, but when the cells were pre-treated with TLR4 inhibitor, Let-7a, TNFα, and Chrna7 were rescued to normal levels. Thus, the fatty acids overload trigger TNFα-induced Let-7 overexpression in hypothalamic neuronal cells, which negatively regulates α7nAChR, an event that can be related to hyperphagia and obesity predisposition in mice.

Autophagy proteins are modulated in the liver and hypothalamus of the offspring of mice with diet-induced obesity.

Nutritional excess during pregnancy and lactation has a negative impact on offspring phenotype. In adulthood, obesity and lipid overload represent factors that compromise autophagy, a process of lysosomal degradation. Despite knowledge of the impact of obesity on autophagy, changes in offspring of obese dams have yet to be investigated. In this study, we tested the hypothesis that maternal obesity induced by a high fat diet (HFD) modulates autophagy proteins in the hypothalamus and liver of the offspring of mice. At birth (d0), offspring of obese dams (HFD-O) showed an increase in p62 protein and a decrease in LC3-II, but only in the liver. After weaning (d18), the offspring of HFD-O animals showed impairment of autophagy markers in both tissues compared to control offspring (SC-O). Between day 18 and day 42, both groups received a control diet and we observed that the protein content of p62 remained increased in the livers of the HFD-O offspring. However, after 82days, we did not find any modulation in offspring autophagy proteins. On the other hand, when the offspring of obese dams that received an HFD from day 42 until day 82 (OH-H) were compared with the offspring from the controls that only received an HFD in adulthood (OC-H), we saw impairment in autophagy proteins in both tissues. In conclusion, this study describes that HFD-O offspring showed early impairment of autophagy proteins. Although the molecular mechanisms have not been explored, it is possible that changes in autophagy markers could be associated with metabolic disturbances of offspring.

n-3 Fatty Acids Induce Neurogenesis of Predominantly POMC-Expressing Cells in the Hypothalamus.

Apoptosis of hypothalamic neurons is believed to play an important role in the development and perpetuation of obesity. Similar to the hippocampus, the hypothalamus presents constitutive and stimulated neurogenesis, suggesting that obesity-associated hypothalamic dysfunction can be repaired. Here, we explored the hypothesis that n-3 polyunsaturated fatty acids (PUFAs) induce hypothalamic neurogenesis. Both in the diet and injected directly into the hypothalamus, PUFAs were capable of increasing hypothalamic neurogenesis to levels similar or superior to the effect of brain-derived neurotrophic factor (BDNF). Most of the neurogenic activity induced by PUFAs resulted in increased numbers of proopiomelanocortin but not NPY neurons and was accompanied by increased expression of BDNF and G-protein-coupled receptor 40 (GPR40). The inhibition of GPR40 was capable of reducing the neurogenic effect of a PUFA, while the inhibition of BDNF resulted in the reduction of global hypothalamic cell. Thus, PUFAs emerge as a potential dietary approach to correct obesity-associated hypothalamic neuronal loss.

Saturated fatty acids modulate autophagy's proteins in the hypothalamus.

Autophagy is an important process that regulates cellular homeostasis by degrading dysfunctional proteins, organelles and lipids. In this study, the hypothesis that obesity could lead to impairment in hypothalamic autophagy in mice was evaluated by examining the hypothalamic distribution and content of autophagic proteins in animal with obesity induced by 8 or 16 weeks high fat diet to induce obesity and in response to intracerebroventricular injections of palmitic acid. The results showed that chronic exposure to a high fat diet leads to an increased expression of inflammatory markers and downregulation of autophagic proteins. In obese mice, autophagic induction leads to the downregulation of proteins, such as JNK and Bax, which are involved in the stress pathways. In neuron cell-line, palmitate has a direct effect on autophagy even without inflammatory activity. Understanding the cellular and molecular bases of overnutrition is essential for identifying new diagnostic and therapeutic targets for obesity.

Defective regulation of the ubiquitin/proteasome system in the hypothalamus of obese male mice.

In both human and experimental obesity, inflammatory damage to the hypothalamus plays an important role in the loss of the coordinated control of food intake and energy expenditure. Upon prolonged maintenance of increased body mass, the brain changes the defended set point of adiposity, and returning to normal weight becomes extremely difficult. Here we show that in prolonged but not in short-term obesity, the ubiquitin/proteasome system in the hypothalamus fails to maintain an adequate rate of protein recycling, leading to the accumulation of ubiquitinated proteins. This is accompanied by an increased colocalization of ubiquitin and p62 in the arcuate nucleus and reduced expression of autophagy markers in the hypothalamus. Genetic protection from obesity is accompanied by the normal regulation of the ubiquitin/proteasome system in the hypothalamus, whereas the inhibition of proteasome or p62 results in the acceleration of body mass gain in mice exposed for a short period to a high-fat diet. Thus, the defective regulation of the ubiquitin/proteasome system in the hypothalamus may be an important mechanism involved in the progression and autoperpetuation of obesity.

Hypothalamic endoplasmic reticulum stress and insulin resistance in offspring of mice dams fed high-fat diet during pregnancy and lactation.

OBJECTIVE: The goal of this study was to determine the presence early of markers of endoplasmic reticulum stress (ERS) and insulin resistance in the offspring from dams fed HFD (HFD-O) or standard chow diet (SC-O) during pregnancy and lactation. MATERIALS/METHODS: To address this question, we evaluated the hypothalamic and hepatic tissues in recently weaned mice (d28) and the hypothalamus of newborn mice (d0) from dams fed HFD or SC during pregnancy and lactation. RESULTS: Body weight, adipose tissue mass, and food intake were more accentuated in HFD-O mice than in SC-O mice. In addition, intolerance to glucose and insulin was higher in HFD-O mice than in SC-O mice. Compared with SC-O mice, levels of hypothalamic IL1-ß mRNA, NFκB protein, and p-JNK were increased in HFD-O mice. Furthermore, compared with SC-O mice, hypothalamic AKT phosphorylation after insulin challenge was reduced, while markers of ERS (p-PERK, p-eIF2α, XBP1s, GRP78, and GRP94) and p-AMPK were increased in the hypothalamic tissue of HFD-O at d28 but not at d0. These damages to hypothalamic signaling were accompanied by increased triglyceride deposits, activation of NFκB, p-JNK, p-PERK and p-eIF2α. CONCLUSION: These point out lactation period as maternal trigger for metabolic changes in the offspring. These changes may occur early and quietly contribute to obesity and associated pathologies in adulthood. Although in rodents the establishment of ARC neuronal projections occurs during the lactation period, in humans it occurs during the third trimester. Gestational diabetes and obesity in this period may contribute to impairment of energy homeostasis.

Melatonin acts through MT1/MT2 receptors to activate hypothalamic Akt and suppress hepatic gluconeogenesis in rats.

Melatonin can contribute to glucose homeostasis either by decreasing gluconeogenesis or by counteracting insulin resistance in distinct models of obesity. However, the precise mechanism through which melatonin controls glucose homeostasis is not completely understood. Male Wistar rats were administered an intracerebroventricular (icv) injection of melatonin and one of following: an icv injection of a phosphatidylinositol 3-kinase (PI3K) inhibitor, an icv injection of a melatonin receptor (MT) antagonist, or an intraperitoneal (ip) injection of a muscarinic receptor antagonist. Anesthetized rats were subjected to pyruvate tolerance test to estimate in vivo glucose clearance after pyruvate load and in situ liver perfusion to assess hepatic gluconeogenesis. The hypothalamus was removed to determine Akt phosphorylation. Melatonin injections in the central nervous system suppressed hepatic gluconeogenesis and increased hypothalamic Akt phosphorylation. These effects of melatonin were suppressed either by icv injections of PI3K inhibitors and MT antagonists and by ip injection of a muscarinic receptor antagonist. We conclude that melatonin activates hypothalamus-liver communication that may contribute to circadian adjustments of gluconeogenesis. These data further suggest a physiopathological relationship between the circadian disruptions in metabolism and reduced levels of melatonin found in type 2 diabetes patients.

Fructose-induced hypothalamic AMPK activation stimulates hepatic PEPCK and gluconeogenesis due to increased corticosterone levels.

Fructose consumption causes insulin resistance and favors hepatic gluconeogenesis through mechanisms that are not completely understood. Recent studies demonstrated that the activation of hypothalamic 5'-AMP-activated protein kinase (AMPK) controls dynamic fluctuations in hepatic glucose production. Thus, the present study was designed to investigate whether hypothalamic AMPK activation by fructose would mediate increased gluconeogenesis. Both ip and intracerebroventricular (icv) fructose treatment stimulated hypothalamic AMPK and acetyl-CoA carboxylase phosphorylation, in parallel with increased hepatic phosphoenolpyruvate carboxy kinase (PEPCK) and gluconeogenesis. An increase in AMPK phosphorylation by icv fructose was observed in the lateral hypothalamus as well as in the paraventricular nucleus and the arcuate nucleus. These effects were mimicked by icv 5-amino-imidazole-4-carboxamide-1-ß-d-ribofuranoside treatment. Hypothalamic AMPK inhibition with icv injection of compound C or with injection of a small interfering RNA targeted to AMPKα2 in the mediobasal hypothalamus (MBH) suppressed the hepatic effects of ip fructose. We also found that fructose increased corticosterone levels through a mechanism that is dependent on hypothalamic AMPK activation. Concomitantly, fructose-stimulated gluconeogenesis, hepatic PEPCK expression, and glucocorticoid receptor binding to the PEPCK gene were suppressed by pharmacological glucocorticoid receptor blockage. Altogether the data presented herein support the hypothesis that fructose-induced hypothalamic AMPK activation stimulates hepatic gluconeogenesis by increasing corticosterone levels.

Inhibition of hypothalamic inflammation reverses diet-induced insulin resistance in the liver.

Defective liver gluconeogenesis is the main mechanism leading to fasting hyperglycemia in type 2 diabetes, and, in concert with steatosis, it is the hallmark of hepatic insulin resistance. Experimental obesity results, at least in part, from hypothalamic inflammation, which leads to leptin resistance and defective regulation of energy homeostasis. Pharmacological or genetic disruption of hypothalamic inflammation restores leptin sensitivity and reduces adiposity. Here, we evaluate the effect of a hypothalamic anti-inflammatory approach to regulating hepatic responsiveness to insulin. Obese rodents were treated by intracerebroventricular injections, with immunoneutralizing antibodies against Toll-like receptor (TLR)4 or tumor necrosis factor (TNF)α, and insulin signal transduction, hepatic steatosis, and gluconeogenesis were evaluated. The inhibition of either TLR4 or TNFα reduced hypothalamic inflammation, which was accompanied by the reduction of hypothalamic resistance to leptin and improved insulin signal transduction in the liver. This was accompanied by reduced liver steatosis and reduced hepatic expression of markers of steatosis. Furthermore, the inhibition of hypothalamic inflammation restored defective liver glucose production. All these beneficial effects were abrogated by vagotomy. Thus, the inhibition of hypothalamic inflammation in obesity results in improved hepatic insulin signal transduction, leading to reduced steatosis and reduced gluconeogenesis. All these effects are mediated by parasympathetic signals delivered by the vagus nerve.

Hypothalamic action of glutamate leads to body mass reduction through a mechanism partially dependent on JAK2.

Glutamate acts in the hypothalamus promoting region-, and cell-dependent effects on feeding. Part of these effects are mediated by NMDA receptors, which are up regulated in conditions known to promote increased food intake and thermogenesis, such as exposure to cold and consumption of highly caloric diets. Here, we hypothesized that at least part of the effect of glutamate on hypothalamic control of energy homeostasis would depend on the control of neurotransmitter expression and JAK2 signaling. The expression of NMDA receptors was co-localized to NPY/AgRP, POMC, CRH, and MCH but not to TRH and orexin neurons of the hypothalamus. The acute intracerebroventricular injection of glutamate promoted a dose-dependent increase in JAK2 tyrosine phosphorylation. In obese rats, 5 days intracerebroventricular treatment with glutamate resulted in the reduction of food intake, accompanied by a reduction of spontaneous motility and reduction of body mass, without affecting oxygen consumption. The reduction of food intake and body mass were partially restrained by the inhibition of JAK2. In addition, glutamate produced an increased hypothalamic expression of NPY, POMC, CART, MCH, orexin, CRH, and TRH, and the reduction of AgRP. All these effects on neurotransmitters were hindered by the inhibition of JAK2. Thus, the intracerebroventricular injection of glutamate results in the reduction of body mass through a mechanism, at least in part, dependent on JAK2, and on the broad regulation of neurotransmitter expression. These effects are not impaired by obesity, which suggest that glutamate actions in the hypothalamus may be pharmacologically explored to treat this disease.

Taurine enhances the anorexigenic effects of insulin in the hypothalamus of rats.

Taurine is known to modulate a number of metabolic parameters such as insulin secretion and action and blood cholesterol levels. Recent data have suggested that taurine can also reduce body adiposity in C. elegans and in rodents. Since body adiposity is mostly regulated by insulin-responsive hypothalamic neurons involved in the control of feeding and thermogenesis, we hypothesized that some of the activity of taurine in the control of body fat would be exerted through a direct action in the hypothalamus. Here, we show that the intracerebroventricular injection of an acute dose of taurine reduces food intake and locomotor activity, and activates signal transduction through the Akt/FOXO1, JAK2/STAT3 and mTOR/AMPK/ACC signaling pathways. These effects are accompanied by the modulation of expression of NPY. In addition, taurine can enhance the anorexigenic action of insulin. Thus, the aminoacid, taurine, exerts a potent anorexigenic action in the hypothalamus and enhances the effect of insulin on the control of food intake.