Central resistin regulates hypothalamic and peripheral lipid metabolism in a nutritional-dependent fashion

Adipose tissue as a therapeutic target for vascular damage in Alzheimer's disease

Adipose tissue has recently been recognized as an important endocrine organ that plays a crucial role in energy metabolism and in the immune response in many metabolic tissues. With this regard, emerging evidence indicates that an important crosstalk exists between the adipose tissue and the brain. However, the contribution of adipose tissue to the development of age-related diseases, including Alzheimer's disease, remains poorly defined. New studies suggest that the adipose tissue modulates brain function through a range of endogenous biologically active factors known as adipokines, which can cross the blood-brain barrier to reach the target areas in the brain or to regulate the function of the blood-brain barrier. In this review, we discuss the effects of several adipokines on the physiology of the blood-brain barrier, their contribution to the development of Alzheimer's disease and their therapeutic potential. LINKED ARTICLES: This article is part of a themed issue From Alzheimer's Disease to Vascular Dementia: Different Roads Leading to Cognitive Decline. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.6/issuetoc.

Associations of adipokines and metabolic hormones with low-density lipoprotein hypercholesterolemia in men and women under 45 years of age

Aim    To study the adipokine profile in young people with hypercholesterolemia and low-density lipoproteins (LDL) and to evaluate the relationship between concentrations of LDL cholesterol (LDL-C) and metabolic hormones in men and women younger than 45 years. Material and methods    This study included 304 subjects (group 1, 56 men with LDL-C concentration <2.1 mmol/l; group 2, 87 men with LDL-C concentration ≥4.2 mmol/l; group 3, 90 women with LDL-C concentration <2.1 mmol/l; and group 4, 71 women with LDL-C concentration ≥4.2 mmol/l). Serum concentrations of total cholesterol (C), triglycerides (TG), high-density lipoprotein C, and glucose were measured by an enzymatic assay with ThermoFisher Scientific kits and a KonelabPrime 30i biochemical analyzer. LDL-C was calculated using the Friedewald’s formula. Concentrations of amylin, C-peptide, ghrelin, glucose-dependent insulinotropic polypeptide, glucagon-like peptide 1 (GLP-1), glucagon, interleukin 6, insulin, leptin, monocyte chemotactic protein 1 (MCP-1), pancreatic polypeptide (PP), peptide YY (PYY), tumor necrosis factor alpha (TNF-α), adiponectin, adipsin, lipocalin-2, plasminogen activator inhibitor 1 (PAI-1), and resistin were measured by multiplex analysis (Human Metabolic Hormone V3 and Human Adipokine Panel 1 panels).Results    The groups differed in traditional cardiometabolic risk factors. In the male and female patient groups with LDL-C ≥4.2 mmol/l, the prevalence of impaired fasting glucose, incidence of insulin resistance, TG, and TC were higher than in subjects with LDL-C <2.1 mmol/l. The odds for the presence of LDL hypercholesterolemia (LDL-C ≥4.2 mmol/l) were significantly associated with increased concentrations of C-peptide and lipocalin-2 in men and with increased concentrations of lipocalin-2 and decreased concentrations of GLP-1 in women (р<0.05).Conclusion    Increased concentrations of LDL-C in young people were associated with changes in the adipokine profile and with the presence of metabolic syndrome components. These results were confirmed by changes in blood concentrations of metabolic markers that characterize disorders of metabolic processes.

Decreased resistin plasmatic concentrations in patients with Alzheimer's disease: A case-control study

Previous studies suggested a role for adipokines in ageing and in several age-related diseases. The purpose of our study was to further elucidate adipokines involvement in neurodegeneration, investigating adiponectin, leptin and resistin in Alzheimer's disease (AD) and Frontotemporal Dementia (FTD). We enrolled for the study 70 subjects: 26 AD, 21 FTD, and 23 with other neurological (but not neurodegenerative) conditions (CTR, control group). According to a standardized protocol, we measured adipokines plasmatic levels, blood parameters of glucidic and lipidic metabolism, ESR, cerebrospinal fluid (CSF) markers of neurodegeneration (beta-amyloid, total-Tau, phosphorylated-Tau) and anthropometric parameters. In comparison with control group, we found lower resistin concentrations in patients with dementia, and in particular in AD (p < 0.001). In multivariate analysis, AD relative risk was reduced by resistin, when controlling for sex, age and anthropometric/metabolic parameters (RR = 0.71, P < 0.0001). Considering CSF biomarkers, we found a direct correlation between resistin and Aβ_1-42 CSF concentration in patients (p < 0.001, r = 0.50). Lower resistin characterized AD patients in our study and AD, but not FTD, diagnosis risk was found to be inversely associated with resistin when controlling for confounders. We hypothesize that resistin-linked metabolic profile has to be reconsidered and further investigated in AD.

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Adipose tissue has an endocrine function, releasing polypeptide hormones, the adipokines.

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Impairment of adipokines circulating levels has been shown in neurodegenerative dementias.

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We found lower resistin levels in Alzheimer's disease patients compared to control group.

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Resistin plasmatic levels correlated with liquoral amyloid β_1-42 concentrations in dementia patients.

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Resistin could interact with amyloid β_1-42 secretion and have a role in Alzheimer's disease pathogenesis.

Circulatory Adipokines and Incretins in Adolescent Idiopathic Scoliosis: A Pilot Study

Adolescent idiopathic scoliosis (AIS) is a three-dimensional malformation of the spine of unknown cause that develops between 10 and 18 years old and affects 2-3% of adolescents, mostly girls. It has been reported that girls with AIS have a taller stature, lower body mass index (BMI), and bone mineral density (BMD) than their peers, but the causes remain unexplained. Energy metabolism discrepancies, including alterations in adipokine and incretin circulatory levels, could influence these parameters and contribute to disease pathophysiology. This pilot study aims to compare the anthropometry, BMD, and metabolic profile of 19 AIS girls to 19 age-matched healthy controls. Collected data include participants' fasting metabolic profile, anthropometry (measurements and DXA scan), nutritional intake, and physical activity level. AIS girls (14.8 ± 1.7 years, Cobb angle 27 ± 10°), compared to controls (14.8 ± 2.1 years), were leaner (BMI-for-age z-score ± SD: -0.59 ± 0.81 vs. 0.09 ± 1.11, p = 0.016; fat percentage: 24.4 ± 5.9 vs. 29.2 ± 7.2%, p = 0.036), had lower BMD (total body without head z-score ± SD: -0.6 ± 0.83 vs. 0.23 ± 0.98, p = 0.038; femoral neck z-score: -0.54 ± 1.20 vs. 0.59 ± 1.59, p = 0.043), but their height was similar. AIS girls had higher adiponectin levels [56 (9-287) vs. 32 (7-74) μg/mL, p = 0.005] and lower leptin/adiponectin ratio [0.042 (0.005-0.320) vs. 0.258 (0.024-1.053), p = 0.005]. AIS participants with a Cobb angle superior to 25° had higher resistin levels compared to controls [98.2 (12.8-287.2) vs. 32.1 (6.6-73.8), p = 0.0013]. This pilot study suggests that adipokines are implicated in AIS development and/or progression, but more work is needed to confirm their role in the disease.

Evidence that resistin acts on the mechanical responses of the mouse gastric fundus

Resistin, among its several actions, has been reported to exert central anorexigenic effects in rodents. Some adipokines which centrally modulate food intake have also been reported to affect the activity of gastric smooth muscle, whose motor responses represent a source of peripheral signals implicated in the control of the hunger-satiety cycle through the gut-brain axis. On this basis, in the present experiments, we investigated whether resistin too could affect the mechanical responses in the mouse longitudinal gastric fundal strips. Electrical field stimulation (EFS) elicited tetrodotoxin- and atropine-sensitive contractile responses. Resistin reduced the amplitude of the EFS-induced contractile responses. This effect was no longer detected in the presence of L-NNA, a nitric oxide (NO) synthesis inhibitor. Resistin did not influence the direct muscular response to methacholine. In the presence of carbachol and guanethidine, EFS elicited inhibitory responses whose amplitude was increased by resistin. L-NNA abolished the inhibitory responses evoked by EFS, indicating their nitrergic nature. In the presence of L-NNA, resistin did not have any effect on the EFS-evoked inhibitory responses. Western blot and immunofluorescence analysis revealed a significant increase in neuronal nitric oxide synthase (nNOS) expression in neurons of the myenteric plexus following resistin exposure. In conclusion, the present results offer the first evidence that resistin acts on the gastric fundus, likely through a modulatory action on the nitrergic neurotransmission.

Association between host genetics of sheep and the rumen microbial composition

A synergy between the rumen microbiota and the host genetics has created a symbiotic relationship, beneficial to the host's health. In this study, the association between the host genetics and rumen microbiome of Damara and Meatmaster sheep was investigated. The composition of rumen microbiota was estimated through the analysis of the V3-V4 region of the 16S rRNA gene, while the sheep blood DNA was genotyped with Illumina OvineSNP50 BeadChip and the genome-wide association (GWA) was analyzed. Sixty significant SNPs dispersed in 21 regions across the Ovis aries genome were found to be associated with the relative abundance of seven genera: Acinetobacter, Bacillus, Clostridium, Flavobacterium, Prevotella, Pseudomonas, and Streptobacillus. A total of eighty-four candidate genes were identified, and their functional annotations were mainly associated with immunity responses and function, metabolism, and signal transduction. Our results propose that those candidate genes identified in the study may be modulating the composition of rumen microbiota and further indicating the significance of comprehending the interactions between the host and rumen microbiota to gain better insight into the health of sheep.

The "Adipo-Cerebral" Dialogue in Childhood Obesity: Focus on Growth and Puberty. Physiopathological and Nutritional Aspects

Overweight and obesity in children and adolescents are overwhelming problems in western countries. Adipocytes, far from being only fat deposits, are capable of endocrine functions, and the endocrine activity of adipose tissue, resumable in adipokines production, seems to be a key modulator of central nervous system function, suggesting the existence of an “adipo-cerebral axis.” This connection exerts a key role in children growth and puberty development, and it is exemplified by the leptin–kisspeptin interaction. The aim of this review was to describe recent advances in the knowledge of adipose tissue endocrine functions and their relations with nutrition and growth. The peculiarities of major adipokines are briefly summarized in the first paragraph; leptin and its interaction with kisspeptin are focused on in the second paragraph; the third paragraph deals with the regulation of the GH-IGF axis, with a special focus on the model represented by growth hormone deficiency (GHD); finally, old and new nutritional aspects are described in the last paragraph.

Roles of leptin and resistin in metabolism, reproduction, and leptin resistance

Increased adipose mass can cause insulin resistance and type 2 diabetes mellitus. This phenomenon is related to adipocyte-secreted signaling molecules that affect glucose balance, such as fatty acids, adiponectin, leptin, interleukin-6, tumor necrosis factor-α, and resistin. Among these hormones, leptin and resistin play important roles in regulating weight and glucose metabolism. Leptin and resistin work in both similar and opposite ways, and they interact with each other. Circulating concentrations of leptin and resistin are elevated in models of obesity and rodents fed a high-fat diet. In addition, leptin and resistin are similarly regulated by nutritional status: they are reduced by fasting and increased by feeding. This effect is mediated partially through insulin receptors and glucose transporters. Our latest data provided the first indication that in sheep, intravenous infusion of resistin increases the mean circulating concentrations of leptin and decreases luteinizing hormone in a dose-dependent manner during both the long-day (LD) and short-day seasons. Furthermore, exogenous resistin increased suppressor of cytokine signaling (SOCS)-3 mRNA expression only during the LD season, when the leptin resistance/insensitivity phenomenon was observed in the arcuate nucleus, preoptic area, and anterior pituitary. We concluded that one factor contributing to central leptin resistance is autosuppression, via which leptin and resistin stimulate the expression of SOCS-3, which inhibits leptin signaling. The increased expression of SOCS-3 in response to leptin and resistin may be a pivotal cause of leptin resistance/insensitivity, a pathological situation in obese individuals and a physiological occurrence in sheep during the LD season.

Impaired hormonal regulation of appetite in schizophrenia: A narrative review dissecting intrinsic mechanisms and the effects of antipsychotics

Cardiometabolic diseases are the main contributor of reduced life expectancy in patients with schizophrenia. It is now widely accepted that antipsychotic treatment plays an important role in the development of obesity and its consequences. However, some intrinsic mechanisms need to be taken into consideration. One of these mechanisms might be related to impaired hormonal regulation of appetite in this group of patients. In this narrative review, we aimed to dissect impairments of appetite-regulating hormones attributable to intrinsic mechanisms and those related to medication effects. Early hormonal alterations that might be associated with intrinsic mechanisms include low levels of leptin and glucagon-like peptide-1 (GLP-1) together with elevated insulin levels in first-episode psychosis (FEP) patients. However, evidence regarding low GLP-1 levels in FEP patients is based on one large study. In turn, multiple-episode schizophrenia patients show elevated levels of insulin, leptin and orexin A together with decreased levels of adiponectin. In addition, patients receiving olanzapine may present with low ghrelin levels. Post mortem studies have also demonstrated reduced number of neuropeptide Y neurons in the prefrontal cortex of patients with schizophrenia. Treatment with certain second-generation antipsychotics may also point to these alterations. Although our understanding of hormonal regulation of appetite in schizophrenia has largely been improved, several limitations and directions for future studies need to be addressed. This is of particular importance since several novel pharmacological interventions for obesity and diabetes have already been developed and translation of these developments to the treatment of cardiometabolic comorbidities in schizophrenia patients is needed.

Changes in Expression of the Genes for the Leptin Signaling in Hypothalamic-Pituitary Selected Areas and Endocrine Responses to Long-Term Manipulation in Body Weight and Resistin in Ewes

Both long-term undernutrition and overnutrition disturb metabolic balance, which is mediated partially by the action of two adipokines, leptin and resistin (RSTN). In this study, we manipulated the diet of ewes to produce either a thin (lean) or fat (fat) body condition and investigated how RSTN affects endocrine and metabolic status under different leptin concentrations. Twenty ewes were distributed into four groups (n = 5): the lean and fat groups were administered with saline (Lean and Fat), while the Lean-R (Lean-Resistin treated) and Fat-R (Fat-Resistin treated) groups received recombinant bovine resistin. Plasma was assayed for LH, FSH, PRL, RSTN, leptin, GH, glucose, insulin, total cholesterol, nonesterified fatty acid (NEFA), high-density lipoprotein (HDL)-cholesterol, low-density lipoprotein (LDL)-cholesterol and triglycerides. Expression levels of a suppressor of cytokine signaling (SOCS-3) and the long form of the leptin receptor (LRb) were determined in selected brain regions, such as the anterior pituitary, hypothalamic arcuate nucleus, preoptic area and ventro- and dorsomedial nuclei. The results indicate long-term alterations in body weight affect RSTN-mediated effects on metabolic and reproductive hormones concentrations and the expression of leptin signaling components: LRb and SOCS-3. This may be an adaptive mechanism to long-term changes in adiposity during the state of long-day leptin resistance.

Cardiovascular responses produced by resistin injected into paraventricular nucleus mediated by the glutamatergic and CRFergic transmissions within rostral ventrolateral medulla

OBJECTIVES

Resistin, as a 12.5 kDa cysteine-rich polypeptide, is expressed in hypothalamus and regulates sympathetic nerve activity. It is associated with obesity, metabolic syndrome and cardiovascular diseases. In this study, we investigated the neural pathway of cardiovascular responses induced by injection of resistin into paraventricular nucleus (PVN) with rostral ventrolateral medulla (RVLM).

MATERIALS AND METHODS

Adult male rats were anesthetized with urethane (1.4 g/kg intraperitoneally). Resistin (3 µg/1 µl/rat) was first injected into PVN, and the glutamatergic, corticotrophin-releasing factor (CRF)-ergic and angiotensinogenic transmission was inhibited by injecting of their antagonist in RVLM. Arterial pressure (AP) and heart rate (HR) were monitored before and after the injection.

RESULTS

The results showed that resistin injection into PVN significantly increased AP and HR compared to control group and prior to its injection (P<0.05). Injection of AP5 ((2R)-amino-5-phosphonovaleric acid; (2R)-amino-5-phosphonopentanoate) (50 nM/rat), losartan (10 nM/rat) and astressin (50 nM/rat) into RVLM reduced cardiovascular responses produced by injected resistin into PVN. Injection of AP5+losartan or astressin+losartan or astressin+AP5 into RVLM could significantly reduce cardiovascular responses produced by resistin compared to before injection (P<0.05). Furthermore, the depressor responses generated by AP5+losartan injected into RVLM were significantly stronger than the depressor responses generated by AP5+astressin and/or astressin+losartan injected into RVLM (P<0.05).

CONCLUSION

It can be concluded that glutamatergic and CRFergic transmissions have crucial contribution to cardiovascular responses produced by resistin. The results provided new and potentially important insight regarding neural transmission when the plasma level of resistin increases; this reveals the role of resistin in cardiovascular responses such as metabolic syndrome and hypertension.

Molecular Mechanisms Underlying Obesity-Induced Hypothalamic Inflammation and Insulin Resistance: Pivotal Role of Resistin/TLR4 Pathways

Low-grade inflammation and insulin resistance are among the clinical features of obesity that are thought to promote the progressive onset of type 2 diabetes. However, the underlying mechanisms linking these disorders remain not fully understood. Recent reports pointed out hypothalamic inflammation as a major step in the onset of obesity-induced insulin resistance. In light of the increasing prevalence of obesity and T2D, two worldwide public health concerns, deciphering mechanisms implicated in hypothalamic inflammation constitutes a major challenge in the field of insulin-resistance/obesity. Several clinical and experimental studies have identified resistin as a key hormone linking insulin-resistance to obesity, notably through the activation of Toll Like Receptor (TLR) 4 signaling pathways. In this review, we present an overview of the molecular mechanisms underlying obesity-induced hypothalamic inflammation and insulin resistance with peculiar focus on the role of resistin/TLR4 signaling pathway.

Ghrelin Causes a Decline in GABA Release by Reducing Fatty Acid Oxidation in Cortex

Lipid metabolism, specifically fatty acid oxidation (FAO) mediated by carnitine palmitoyltransferase (CPT) 1A, has been described to be an important actor of ghrelin action in hypothalamus. However, it is not known whether CPT1A and FAO mediate the effect of ghrelin on the cortex. Here, we show that ghrelin produces a differential effect on CPT1 activity and γ-aminobutyric acid (GABA) metabolism in the hypothalamus and cortex of mice. In the hypothalamus, ghrelin enhances CPT1A activity while GABA transaminase (GABAT) activity, a key enzyme in GABA shunt metabolism, is unaltered. However, in cortex CPT1A activity and GABAT activity are reduced after ghrelin treatment. Furthermore, in primary cortical neurons, ghrelin reduces GABA release through a CPT1A reduction. By using CPT1A floxed mice, we have observed that genetic ablation of CPT1A recapitulates the effect of ghrelin on GABA release in cortical neurons, inducing reductions in mitochondrial oxygen consumption, cell content of citrate and α-ketoglutarate, and GABA shunt enzyme activity. Taken together, these observations indicate that ghrelin-induced changes in CPT1A activity modulate mitochondrial function, yielding changes in GABA metabolism. This evidence suggests that the action of ghrelin on GABA release is region specific within the brain, providing a basis for differential effects of ghrelin in the central nervous system.

Hypothalamic AMPK and energy balance

AMP-activated protein kinase (AMPK) is the main cellular energy sensor. Activated following a depletion of cellular energy stores, AMPK will restore the energy homoeostasis by increasing energy production and limiting energy waste. At a central level, the AMPK pathway will integrate peripheral signals (mostly hormones and metabolites) through neuronal networks. Hypothalamic AMPK is directly implicated in feeding behaviour, brown adipose tissue (BAT) thermogenesis and browning of white adipose tissue (WAT). It also participates in other metabolic functions: glucose and muscle metabolisms, as well as hepatic function. Numerous anti-obesity and/or antidiabetic agents, such as nicotine, metformin and liraglutide, are known to induce their effects through a modulation of AMPK pathway, either at central or at peripheral levels. Moreover, the weight-gaining side effects of antipsychotic drugs, such as olanzapine, are also mediated by hypothalamic AMPK. Therefore, considering hypothalamic AMPK as a therapeutic target in metabolic diseases appears as an interesting strategy due to its implication in feeding and energy expenditure, the two sides of the energy balance equation.

Suppressing Irf2bp2 expressions accelerates metabolic syndrome-associated brain injury and hepatic dyslipidemia

Increasing studies indicate that high fat diet (HFD) induces neuroinflammation in animal models with obesity, yet the pathology of it is unclear. Interferon Regulatory Factor 2 Binding Protein 2 (Irf2bp2) is a key regulator of macrophage polarization, playing an essential role in regulating inflammatory response. This study investigated the effects of Irf2bp2 on HFD-induced brain injury, and explored the possible molecular mechanisms using wild type (WT) and Irf2bp2 knockout (KO) mice. The results indicated that HFD-increased body weight of mice was further elevated by Irf2bp2-knockout. In addition, Irf2bp2-deletion accelerated HFD-induced metabolic syndrome, as evidenced by the promoted fasting glucose and insulin levels. In the results of behavioral measurements, Irf2bp2-knockout intensified cognitive deficit in HFD-fed mice by using Y-maze, passive avoidance, and morris water maze (MWM) tests. Further, Irf2bp2-deficiency accelerated the activation of astrocytes and microglia cells, as evidenced by the promoted expressions of glial fibrillary acidic protein (GFAP) and Iba-1 in hippocampus and hypothalamus of HFD-fed mice. HFD for 16 weeks induced oxidative stress in serum and brain of mice, as proved by the up-regulated malondialdehyde (MDA) levels and down-regulated superoxide dismutase (SOD) activity, which were significantly enhanced due to Irf2bp2 knockout. Moreover, HFD-triggered systematic and central nervous inflammation by increasing the release of interleukin 1β (IL-1β) and tumor necrosis factor (TNF)-α, accompanied with elevated p-nuclear factor-κB (NF-κB) expressions. Notably, HFD-induced inflammation was significantly exacerbated by Irf2bp2 deletion. Intriguingly, HFD-induced dyslipidemia in liver of mice was further aggravated by Irf2bp2 suppression. Our in vitro results verified the effects of Irf2bp2-inhibition on the promotion of inflammatory response in BV2 cells and lipid dysfunction in primary hepatocytes. Therefore, the findings above suggested that inhibiting Irf2bp2 expression provided a potential therapeutic approach for the prevention of metabolic syndrome-associated central nervous injury.

Resistin inhibits neuronal autophagy through Toll-like receptor 4

Autophagy is a non-selective degradation pathway induced in energy-deprived cells and in non-starved cells by participating in cellular inflammatory responses mainly through the elimination of injured and aged mitochondria that constitute an important source of reactive oxygen species. We have previously reported that resistin/TLR4 signaling pathway induces inflammation and insulin resistance in neuronal cell. However, the impact of resistin-induced inflammation on neuronal autophagy is unknown. In the present study, we hypothesized that resistin-induced neuroinflammation could be attributed, at least partially, to the impairment of autophagy pathways in neuronal cells. Our data show that resistin decreases neuronal autophagy as evidenced by the repression of the main autophagy markers in SH-SY5Y human neuroblastoma cell line. Furthermore, the silencing of TLR4 completely abolished these effects. Resistin also inhibits AMPK phosphorylation and increases that of Akt/mTOR contrasting with activated autophagy where AMPK phosphorylation is augmented and mTOR inhibited. In vivo, resistin treatment inhibits the mRNA expression of autophagy markers in the hypothalamus of WT mice but not in Tlr4-/- mice. In addition, resistin strongly diminished LC3 (a marker of autophagy) labeling in the arcuate nucleus of WT mice, and this effect is abolished in Tlr4-/- mice. Taken together, our findings clearly reveal resistin/TLR4 as a new regulatory pathway of neuronal autophagy.

Central s-resistin deficiency ameliorates hypothalamic inflammation and increases whole body insulin sensitivity

S-resistin, a non-secretable resistin isoform, acts as an intracrine factor that regulates adipocyte maduration, inflammatory and insulin response in 3T3-L1 cells. However, its intracellular function in vivo is still unknown. In this study, we analyze the central role of s-resistin, decreasing its hypothalamic expression using an intracerebroventricular injection of lentiviral RNAi. The data present herein support an improvement in the hypothalamic leptin and insulin signaling pathway upon s-resistin downregulation. Furthermore, hypothalamic levels of pro-inflammatory markers decrease, meanwhile those of the anti-inflammatory cytokine IL-10 increases. Interestingly, peripheral NEFA decreases alike circulating leptin and resistin levels. These data demonstrate that hypothalamic s-resistin controls fuel mobilization and adipokines secretion. Importantly, central s-resistin downregulation improves systemic insulin sensitivity, as demonstrated after an IPGTT. Interestingly, our data also indicate that s-resistin downregulation could improve hypothalamic inflammation in aged Wistar rats. Altogether, our findings suggest that hypothalamic s-resistin seems to be a key regulator of the brain-fat axis which links inflammation with metabolic homeostasis.

Analyzing AMPK Function in the Hypothalamus

Hypothalamic AMPK plays a key role in the control of energy homeostasis by regulating energy intake and energy expenditure, particularly modulating brown adipose tissue (BAT) thermogenesis. The function of AMPK can be assayed by analyzing its phosphorylated protein levels in tissues, since AMPK is activated when it is phosphorylated at Thr-172. Here, we describe a method to obtain hypothalamic (nuclei-specific) protein extracts and the suitable conditions to assay AMPK phosphorylation by Western blotting.

Adiponectin and resistin: potential metabolic signals affecting hypothalamo-pituitary gonadal axis in females and males of different species

Adipokines, including adiponectin and resistin, are cytokines produced mainly by the adipose tissue. They play a significant role in metabolic functions that regulate the insulin sensitivity and inflammation. Alterations in adiponectin and resistin plasma levels, or their expression in metabolic and gonadal tissues, are observed in some metabolic pathologies, such as obesity. Several studies have shown that these two hormones and the receptors for adiponectin, AdipoR1 and AdipoR2 are present in various reproductive tissues in both sexes of different species. Thus, these adipokines could be metabolic signals that partially explain infertility related to obesity, such as polycystic ovary syndrome (PCOS). Species and gender differences in plasma levels, tissue or cell distribution and hormonal regulation have been reported for resistin and adiponectin. Furthermore, until now, it has been unclear whether adiponectin and resistin act directly or indirectly on the hypothalamo–pituitary–gonadal axis. The objective of this review was to summarise the latest findings and particularly the species and gender differences of adiponectin and resistin on female and male reproduction known to date, based on the hypothalamo–pituitary–gonadal axis.

EJE PRIZE 2017: Hypothalamic AMPK: a golden target against obesity?

AMP-activated protein kinase (AMPK) is a cellular gauge that is activated under conditions, such as low energy, increasing energy production and reducing energy waste. Centrally, the AMPK pathway is a canonical route regulating energy homeostasis, by integrating peripheral signals, such as hormones and metabolites, with neuronal networks. Current evidence links hypothalamic AMPK with feeding, brown adipose tissue (BAT) thermogenesis and browning of white adipose tissue (WAT), as well as muscle metabolism, hepatic function and glucose homeostasis. The relevance of these data is interesting from a therapeutic point of view as several agents with potential anti-obesity and/or antidiabetic effects, some currently in clinical use, such as nicotine, metformin and liraglutide are known to act through AMPK, either peripherally or centrally. Furthermore, the orexigenic and weight-gaining effects of the worldwide use of antipsychotic drugs (APDs), such as olanzapine, are also mediated by hypothalamic AMPK. Overall, this evidence makes hypothalamic AMPK signaling an interesting target for the drug development, with its potential for controlling both sides of the energy balance equation, namely feeding and energy expenditure through defined metabolic pathways.

Traveling from the hypothalamus to the adipose tissue: The thermogenic pathway

Brown adipose tissue (BAT) is a specialized tissue critical for non-shivering thermogenesis producing heat through mitochondrial uncoupling; whereas white adipose tissue (WAT) is responsible of energy storage in the form of triglycerides. Another type of fat has been described, the beige adipose tissue; this tissue emerges in existing WAT depots but with thermogenic ability, a phenomenon known as browning. Several peripheral signals relaying information about energy status act in the brain, particularly the hypothalamus, to regulate thermogenesis in BAT and browning of WAT. Different hypothalamic areas have the capacity to regulate the thermogenic process in brown and beige adipocytes through the sympathetic nervous system (SNS). This review discusses important concepts and discoveries about the central control of thermogenesis as a trip that starts in the hypothalamus, and taking the sympathetic roads to reach brown and beige fat to modulate thermogenic functions.

Estradiol effects on hypothalamic AMPK and BAT thermogenesis: A gateway for obesity treatment?

In addition to their prominent roles in the control of reproduction, estrogens are important modulators of energy balance, as evident in conditions of deficiency of estrogens, which are characterized by increased feeding and decreased energy expenditure, leading to obesity. AMP-activated protein kinase (AMPK) is a ubiquitous cellular energy gauge that is activated under conditions of low energy, increasing energy production and reducing energy wasting. Centrally, the AMPK pathway is a canonical route regulating energy homeostasis, by integrating peripheral signals, such as hormones and metabolites, with neuronal networks. As a result of those actions, hypothalamic AMPK modulates feeding, as well as brown adipose tissue (BAT) thermogenesis and browning of white adipose tissue (WAT). Here, we will review the central actions of estrogens on energy balance, with particular focus on hypothalamic AMPK. The relevance of this interaction is noteworthy, because some agents with known actions on metabolic homeostasis, such as nicotine, metformin, liraglutide, olanzapine and also natural molecules, such as resveratrol and flavonoids, exert their actions by modulating AMPK. This evidence highlights the possibility that hypothalamic AMPK might be a potential target for the treatment of obesity.

Hypothalamus and thermogenesis: Heating the BAT, browning the WAT

Brown adipose tissue (BAT) has been also considered as the main thermogenic organ responsible of maintenance body temperature through heat production. However, a new type of thermogenic fat has been characterized during the last years, the beige or brite fat, that is developed from white adipose tissue (WAT) in response to different stimuli by a process known as browning. The activities of brown and beige adipocytes ameliorate metabolic disease, including obesity in mice and correlate with leanness in humans. Many genes and pathways that regulate brown and beige adipocyte biology have now been identified, providing a variety of promising therapeutic targets for metabolic disease. The hypothalamus is the main central place orchestrating the outflow signals that drive the sympathetic nerve activity to BAT and WAT, controlling heat production and energy homeostasis. Recent data have revealed new hypothalamic molecular mechanisms, such as hypothalamic AMP-activated protein kinase (AMPK), that control both thermogenesis and browning. This review provides an overview of the factors influencing BAT and WAT thermogenesis, with special focus on the integration of peripheral information on hypothalamic circuits controlling thermoregulation.

Association Study of Arcuate Nucleus Neuropeptide Y Neuron Receptor Gene Variation And Serum Npy Levels in Clozapine Treated Patients With Schizophrenia

Background

Antipsychotic-induced weight gain (AIWG) leads to metabolic consequences and comorbidity, social stigmatization and nonadherence in patients with schizophrenia. Neuropeptide Y (NPY) has an important role in appetite and body weight regulation. Associations between AIWG and serum NPY levels, and genetic polymorphisms (SNPs) associated with its serum levels have been little studied in these patients.

Subjects and methods

Associations between serum NPY concentration and other metabolic and inflammatory markers, and 215 SNPs in 21 genes (NPY gene, NPY receptor genes and genes encoding arcuate nucleus NPY neuron receptors) were studied in 180 patients with schizophrenia on clozapine treatment.

Results

The serum levels of NPY correlated with levels of resistin (r = 0.31, P < 0.001) and age (r = 0.22, P = 0.003). In the general linear univariate model the best-fitting model with explanatory factors age, serum resistin level, serum insulin level, BMI and gender explained 18.0% (P < 0.001) of the variance of serum NPY. Genetic risk score (GRSNPY) analysis found twelve significant (P < 0.05) serum NPY concentration related SNPs among α7 nicotinic acetylcholine receptor gene CHRNA7, insulin receptor gene INSR, leptin receptor gene LEPR, glucocorticoid receptor (GR) gene NR3C1, and NPY gene. However, after permutation test of gene score the predictive value of GRSNPY remained non-significant (P = 0.078).

Conclusions

Serum NPY level does not seem to be a feasible biomarker of AIWG. Serum NPY level alterations are not significantly associated with the candidate gene polymorphisms studied.

Central inhibitory effects on feeding induced by the adipo-myokine irisin

Irisin, the soluble secreted form of fibronectin type III domain containing 5 (FNDC5)-cleaved product, is a recently identified adipo-myokine that has been indicated as a possible link between physical exercise and energetic homeostasis. The co-localization of irisin with neuropeptide Y in hypothalamic sections of paraventricular nucleus, which receives NPY/AgRP projections from the arcuate nucleus, suggests a possible role of irisin in the central regulation of energy balance. In this context, in the present work we studied the effects of intra-hypothalamic irisin (1μl, 50-200nmol/l) administration on feeding and orexigenic [agouti-related peptide (AgRP), neuropeptide Y (NPY) and orexin-A] and anorexigenic [cocaine and amphetamine-regulated transcript (CART) and proopiomelanocortin (POMC)] peptides in male Sprague-Dawley rats. Furthermore, we evaluated the effects of irisin on hypothalamic dopamine (DA), norepinephrine (NE) and serotonin (5-hydroxytryptamine, 5-HT) concentrations and plasma NE levels. Compared to vehicle, irisin injected rats showed decreased food intake, possibly mediated by stimulated CART and POMC and inhibited DA, NE and orexin-A, in the hypothalamus. We also found increased plasma NE levels, supporting a role for sympathetic nervous system stimulation in mediating increased oxygen consumption by irisin.

Hypothalamic AMPK: a canonical regulator of whole-body energy balance

AMP-activated protein kinase (AMPK) has a major role in the modulation of energy balance. AMPK is activated in conditions of low energy, increasing energy production and reducing energy consumption. The AMPK pathway is a canonical route regulating energy homeostasis by integrating peripheral signals, such as hormones and metabolites, with neuronal networks. Current evidence has implicated AMPK in the hypothalamus and hindbrain with feeding, brown adipose tissue thermogenesis and browning of white adipose tissue, through modulation of the sympathetic nervous system, as well as glucose homeostasis. Interestingly, several potential antiobesity and/or antidiabetic agents, some of which are currently in clinical use such as metformin and liraglutide, exert some of their actions by acting on AMPK. Furthermore, the orexigenic and weight-gain effects of commonly used antipsychotic drugs are also mediated by hypothalamic AMPK. Overall, this evidence suggests that hypothalamic AMPK signalling is an interesting target for drug development, but is this approach feasible? In this Review we discuss the current understanding of hypothalamic AMPK and its role in the central regulation of energy balance and metabolism.

Resistin's, obesity and insulin resistance: the continuing disconnect between rodents and humans

PURPOSE

This review aimed to discuss the conflicting findings from resistin research in rodents and humans as well as recent advances in our understanding of resistin's role in obesity and insulin resistance.

METHODS

A comprehensive review and synthesis of resistin's role in obesity and insulin resistance as well as conflicting findings from resistin research in rodents and humans.

RESULTS

In rodents, resistin is increased in high-fat/high-carbohydrate-fed, obese states characterized by impaired glucose uptake and insulin sensitivity. Resistin plays a causative role in the development of insulin resistance in rodents via 5' AMP-activated protein kinase (AMPK)-dependent and AMPK-independent suppressor of cytokine signaling-3 (SOCS-3) signaling. In contrast to rodents, human resistin is primarily secreted by peripheral-blood mononuclear cells (PBMCs) as opposed to white adipocytes. Circulating resistin levels have been positively associated with central/visceral obesity (but not BMI) as well as insulin resistance, while other studies show no such association. Human resistin has a role in pro-inflammatory processes that have been conclusively associated with obesity and insulin resistance. PBMCs, as well as vascular cells, have been identified as the primary targets of resistin's pro-inflammatory activity via nuclear factor-κB (NF-κB, p50/p65) and other signaling pathways.

CONCLUSION

Mounting evidence reveals a continuing disconnect between resistin's role in rodents and humans due to significant differences between these two species with respect to resistin's gene and protein structure, differential gene regulation, tissue-specific distribution, and insulin resistance induction as well as a paucity of evidence regarding the resistin receptor and downstream signaling mechanisms of action.

Central Resistin/TLR4 Impairs Adiponectin Signaling, Contributing to Insulin and FGF21 Resistance

Adiponectin, an insulin-sensitizing hormone, and resistin, known to promote insulin resistance, constitute a potential link between obesity and type 2 diabetes. In addition, fibroblast growth factor (FGF)21 has effects similar to those of adiponectin in regulating glucose and lipid metabolism and insulin sensitivity. However, the interplay between adiponectin, FGF21, and resistin signaling pathways during the onset of insulin resistance is unknown. Here, we investigated whether central resistin promotes insulin resistance through the impairment of adiponectin and FGF21 signaling. We show that chronic intracerebroventricular resistin infusion downregulated both hypothalamic and hepatic APPL1, a key protein in adiponectin signaling, associated with decreased Akt-APPL1 interaction and an increased Akt association with its endogenous inhibitor tribbles homolog 3. Resistin treatment also decreased plasma adiponectin levels and reduced both hypothalamic and peripheral expression of adiponectin receptors. Additionally, we report that intracerebroventricular resistin increased plasma FGF21 levels and downregulated its receptor components in the hypothalamus and peripheral tissues, promoting FGF21 resistance. Interestingly, we also show that resistin effects were abolished in TLR4 knockout mice and in neuronal cells expressing TLR4 siRNAs. Our study reveals a novel mechanism of insulin resistance onset orchestrated by a central resistin-TLR4 pathway that impairs adiponectin signaling and promotes FGF21 resistance.

Carnitine palmitoyltransferase 1C: From cognition to cancer

Carnitine palmitoyltransferase 1 (CPT1) C was the last member of the CPT1 family of genes to be discovered. CPT1A and CPT1B were identified as the gate-keeper enzymes for the entry of long-chain fatty acids (as carnitine esters) into mitochondria and their further oxidation, and they show differences in their kinetics and tissue expression. Although CPT1C exhibits high sequence similarity to CPT1A and CPT1B, it is specifically expressed in neurons (a cell-type that does not use fatty acids as fuel to any major extent), it is localized in the endoplasmic reticulum of cells, and it has minimal CPT1 catalytic activity with l-carnitine and acyl-CoA esters. The lack of an easily measurable biological activity has hampered attempts to elucidate the cellular and physiological role of CPT1C but has not diminished the interest of the biomedical research community in this CPT1 isoform. The observations that CPT1C binds malonyl-CoA and long-chain acyl-CoA suggest that it is a sensor of lipid metabolism in neurons, where it appears to impact ceramide and triacylglycerol (TAG) metabolism. CPT1C global knock-out mice show a wide range of brain disorders, including impaired cognition and spatial learning, motor deficits, and a deregulation in food intake and energy homeostasis. The first disease-causing CPT1C mutation was recently described in humans, with Cpt1c being identified as the gene causing hereditary spastic paraplegia. The putative role of CPT1C in the regulation of complex-lipid metabolism is supported by the observation that it is highly expressed in certain virulent tumor cells, conferring them resistance to glucose- and oxygen-deprivation. Therefore, CPT1C may be a promising target in the treatment of cancer. Here we review the molecular, biochemical, and structural properties of CPT1C and discuss its potential roles in brain function, and cancer.

The brain and brown fat

Brown adipose tissue (BAT) is a specialized organ responsible for thermogenesis, a process required for maintaining body temperature. BAT is regulated by the sympathetic nervous system (SNS), which activates lipolysis and mitochondrial uncoupling in brown adipocytes. For many years, BAT was considered to be important only in small mammals and newborn humans, but recent data have shown that BAT is also functional in adult humans. On the basis of this evidence, extensive research has been focused on BAT function, where new molecules, such as irisin and bone morphogenetic proteins, particularly BMP7 and BMP8B, as well as novel central factors and new regulatory mechanisms, such as orexins and the canonical ventomedial nucleus of the hypothalamus (VMH) AMP- activated protein kinase (AMPK)-SNS-BAT axis, have been discovered and emerged as potential drug targets to combat obesity. In this review we provide an overview of the complex central regulation of BAT and how different neuronal cell populations co-ordinately work to maintain energy homeostasis.

Pregnancy induces resistance to the anorectic effect of hypothalamic malonyl-CoA and the thermogenic effect of hypothalamic AMPK inhibition in female rats

During gestation, hyperphagia is necessary to cope with the metabolic demands of embryonic development. There were three main aims of this study: Firstly, to investigate the effect of pregnancy on hypothalamic fatty acid metabolism, a key pathway for the regulation of energy balance; secondly, to study whether pregnancy induces resistance to the anorectic effect of fatty acid synthase (FAS) inhibition and accumulation of malonyl-coenzyme A (CoA) in the hypothalamus; and, thirdly, to study whether changes in hypothalamic AMPK signaling are associated with brown adipose tissue (BAT) thermogenesis during pregnancy. Our data suggest that in pregnant rats, the hypothalamic fatty acid pathway shows an overall state that should lead to anorexia and elevated BAT thermogenesis: decreased activities of AMP-activated protein kinase (AMPK), FAS, and carnitine palmitoyltransferase 1, coupled with increased acetyl-CoA carboxylase function with subsequent elevation of malonyl-CoA levels. This profile seems dependent of estradiol levels but not prolactin or progesterone. Despite the apparent anorexic and thermogenic signaling in the hypothalamus, pregnant rats remain hyperphagic and display reduced temperature and BAT function. Actually, pregnant rats develop resistance to the anorectic effects of central FAS inhibition, which is associated with a reduction of proopiomelanocortin (POMC) expression and its transcription factors phospho-signal transducer and activator of transcription 3, and phospho-forkhead box O1. This evidence demonstrates that pregnancy induces a state of resistance to the anorectic and thermogenic actions of hypothalamic cellular signals of energy surplus, which, in parallel to the already known refractoriness to leptin effects, likely contributes to gestational hyperphagia and adiposity.

Smoking is associated with reduced leptin and neuropeptide Y levels and higher pain experience in patients with fibromyalgia

Smoking deregulates neuroendocrine responses to pain supporting production of neuropeptide Y (NpY) by direct stimulation of nicotinic receptors or by inhibiting adipokine leptin. Present study addressed the effect of cigarette smoking on adipokines and pain parameters, in 62 women with fibromyalgia (FM) pain syndrome with unknown etiology. Pain was characterized by a visual analogue scale, tender point (TP) counts, pressure pain threshold, and neuroendocrine markers NpY and substance P (sP). Levels of IGF-1, leptin, resistin, visfatin, and adiponectin were measured in blood and cerebrospinal fluid. Current smokers (n = 18) had lower levels of leptin compared to ex-smokers (n = 25, P = 0.002), while the expected NpY increase was absent in FM patients. In smokers, this was transcribed in higher VAS-pain (P = 0.04) and TP count (P = 0.03), lower pain threshold (P = 0.01), since NpY levels were directly related to the pain threshold (rho = 0.414) and inversely related to TP counts (rho = −0.375). This study shows that patients with FM have no increase of NpY levels in response to smoking despite the low levels of leptin. Deregulation of the balance between leptin and neuropeptide Y may be one of the essential mechanisms of chronic pain in FM.

Resistin: insulin resistance to malignancy

Adipose tissue is recognized as an endocrine organ that secretes bioactive substances known as adipokines. Excess adipose tissue and adipose tissue dysfunction lead to dysregulated adipokine production that can contribute to the development of obesity-related co-morbidities. Among the various adipokines, resistin, which was initially considered as a determinant of the emergence of insulin resistance in obesity, has appeared as an important link between obesity and inflammatory processes. Several experimental and clinical studies have suggested an association between increased resistin levels and severe conditions associated with obesity such as cardiovascular disease and malignancies. In this review, we present the growing body of evidence that human resistin is an inflammatory biomarker and potential mediator of obesity-associated diseases. A common pathway seems to involve the combined alteration of immune and inflammatory processes that favor metabolic disturbances, atherosclerosis and carcinogenesis. The mode of action and the signaling pathways utilized by resistin in its interactions with target cells could involve oxidative and nitrosative stress. Therefore, resistin could function as a key molecule in the complications of obesity development and could potentially be used as a diagnostic and prognostic marker.

Energy Balance Regulating Neuropeptides Are Expressed through Pregnancy and Regulated by Interleukin-6 Deficiency in Mouse Placenta

The placenta produces a number of signaling molecules including metabolic and reproductive hormones as well as several inflammatory mediators. Among them, Interleukin-6 (IL-6), a well-known immune and metabolic regulator, acts peripherally modulating metabolic function and centrally increasing energy expenditure and reducing body fat. IL-6 interacts with key hypothalamic neuropeptidergic systems controlling energy homeostasis such as those producing the orexigenic/anabolic: neuropeptide Y (NPY) and agouti-related peptide (AgRP) and anorectic/catabolic neuropeptides: proopiomelanocortin (POMC) and cocaine and amphetamine regulated transcript (CART). Human and rat placenta have been identified as source of these neuropeptides, but their expression and regulation in murine placental tissues remain unknown. Therefore, placental mRNA levels of IL-6, NPY, AgRP, POMC, and CART at different pregnancy stages (gestational days 13, 15, and 18) were analyzed by real time PCR, as were the effect of IL-6 deficiency (IL-6 knockout mice) on their placental expression. Our results showed that placenta-derived neuropeptides were regulated by gestational age and IL-6 throughout the second half of mouse pregnancy. These data suggest that IL-6 may participate in the fine tune control of energy balance during pregnancy by extending its action as a metabolic signal to the main organ at the fetomaternal interface: the placenta.

Regulation of GPR55 in rat white adipose tissue and serum LPI by nutritional status, gestation, gender and pituitary factors

The G protein-coupled receptor GPR55 has been proposed as a new cannabinoid receptor associated with obesity in humans. We have investigated the regulation of GPR55 in rat white adipose tissue (WAT) in different physiological and pathophysiological settings involved in energy balance. We compared GPR55 expression with Cannabinoid Receptor type 1 (CB1), which mediates the metabolic actions of endocannabinoids, by real time PCR and western blotting. Circulating levels of lysophosphatidylinositol (LPI), the endogenous ligand of GPR55, were measured by liquid chromatography-mass spectrometry. Both WAT CB1 and GPR55 levels were increased after fasting and recovered after leptin treatment. Their expression was decreased during gestation and increased throughout lifespan. Orchidectomy diminished WAT CB1 and GPR55 expression whereas ovariectomized rats showed increased GPR55 but decreased CB1 levels. Alterations in pituitary functions also modified WAT CB1 and GPR55 levels. Serum LPI levels were inversely regulated by fasting and gonadectomy in comparison to WAT GPR55. Our findings indicate that GPR55 and LPI are regulated by different physiological and pathophysiological settings known to be associated with marked alterations in energy status.

Regulation of NR4A by nutritional status, gender, postnatal development and hormonal deficiency

The NR4A is a subfamily of the orphan nuclear receptors (NR) superfamily constituted by three well characterized members: Nur77 (NR4A1), Nurr1 (NR4A2) and Nor 1 (NR4A3). They are implicated in numerous biological processes as DNA repair, arteriosclerosis, cell apoptosis, carcinogenesis and metabolism. Several studies have demonstrated the role of this subfamily on glucose metabolism, insulin sensitivity and energy balance. These studies have focused mainly in liver and skeletal muscle. However, its potential role in white adipose tissue (WAT), one of the most important tissues involved in the regulation of energy homeostasis, is not well-studied. The aim of this work was to elucidate the regulation of NR4A in WAT under different physiological and pathophysiological settings involved in energy balance such as fasting, postnatal development, gender, hormonal deficiency and pregnancy. We compared NR4A mRNA expression of Nur77, Nurr1 and Nor 1 and found a clear regulation by nutritional status, since the expression of the 3 isoforms is increased after fasting in a leptin-independent manner and sex steroid hormones also modulate NR4A expression in males and females. Our findings indicate that NR4A are regulated by different physiological and pathophysiological settings known to be associated with marked alterations in glucose metabolism and energy status.

Peripheral chemerin administration modulates hypothalamic control of feeding

Chemerin is a recently identified adipokine that is involved in the regulation of adipogenesis, energy metabolism, and inflammation. The aim of the present study was to investigate the role of chemerin on food intake, body weight and hypothalamic peptidergic and aminergic modulators which play a pivotal role in feeding regulation in rats. Male adult Wistar rats were intraperitoneally injected, daily for 17 days at 9.00am, with either vehicle (saline; N=12) or chemerin (8μg/kg; N=12) and (16μg/kg; N=12). Food intake was recorded 24h after each administration. Animals were sacrificed 24h after the last injection. Total RNA was extracted from hypothalami and reverse transcribed to evaluate gene expression of agouti-related peptide (AgRP), neuropeptide Y (NPY), orexin-A, corticotrophin releasing hormone (CRH), pro-opiomelanocortin (POMC) and cocaine and amphetamine-regulated transcript (CART). Furthermore, we evaluated the effect of chemerin on dopamine, norepinephrine and serotonin steady state concentrations in rat hypothalamus homogenate, and monoamine release from rat hypothalamic synaptosomes. Chemerin administration (8 and 16μg/kg) decreased both food intake and body weight compared to vehicle, possibly associated with a significant increase in serotonin synthesis and release, in the hypothalamus. On the other hand, the pattern of gene expression following chemerin administration indicates a minor role played by chemerin as a peripheral appetite-regulating signal.

Ghrelin requires p53 to stimulate lipid storage in fat and liver

Ghrelin, a stomach-derived peptide, stimulates feeding behavior and adiposity. For its orexigenic action, ghrelin triggers a central SIRT1/p53/AMPK pathway. The tumor suppressor p53 also plays an important role in white adipose tissue (WAT), where it is up-regulated in the adipocytes of obese mice. It is not known, however, whether p53 has any role in mediating the peripheral action of ghrelin. In the present study, chronic peripheral ghrelin treatment resulted in increased body weight and fat-mass gain in wild-type mice. Correspondingly, mRNA levels of several adipogenic and fat-storage-promoting enzymes were up-regulated in WAT, whereas hepatic triglyceride content and lipogenic enzymes were also increased in wild-type mice following ghrelin treatment. In contrast, mice lacking p53 failed to respond to ghrelin treatment, with their body weight, fat mass, and adipocyte and hepatic metabolism remaining unchanged. Thus, our results show that p53 is necessary for the actions of ghrelin on WAT and liver, leading to changes in expression levels of lipogenic and adipogenic genes, and modifying body weight.

Interleukin 6 deficiency modulates the hypothalamic expression of energy balance regulating peptides during pregnancy in mice

Pregnancy is associated with hyperphagia, increased adiposity and multiple neuroendocrine adaptations. Maternal adipose tissue secretes rising amounts of interleukin 6 (IL6), which acts peripherally modulating metabolic function and centrally increasing energy expenditure and reducing body fat. To explore the role of IL6 in the central mechanisms governing dam's energy homeostasis, early, mid and late pregnant (gestational days 7, 13 and 18) wild-type (WT) and Il6 knockout mice (Il6-KO) were compared with virgin controls at diestrus. Food intake, body weight and composition as well as indirect calorimetry measurements were performed in vivo. Anabolic and orexigenic peptides: neuropeptide Y (Npy) and agouti-related peptide (Agrp); and catabolic and anorectic neuropeptides: proopiomelanocortin (Pomc), corticotrophin and thyrotropin-releasing hormone (Crh and Trh) mRNA levels were determined by in situ hybridization. Real time-PCR and western-blot were used for additional tissue gene expression and protein studies. Non-pregnant Il6-KO mice were leaner than WT mice due to a decrease in fat but not in lean body mass. Pregnant Il6-KO mice had higher fat accretion despite similar body weight gain than WT controls. A decreased fat utilization in absence of Il6 might explain this effect, as shown by increased respiratory exchange ratio (RER) in virgin Il6-KO mice. Il6 mRNA levels were markedly enhanced in adipose tissue but reduced in hypothalamus of mid and late pregnant WT mice. Trh expression was also stimulated at gestational day 13 and lack of Il6 blunted this effect. Conversely, in late pregnant mice lessened hypothalamic Il6 receptor alpha (Il6ra), Pomc and Crh mRNA were observed. Il6 deficiency during this stage up-regulated Npy and Agrp expression, while restoring Pomc mRNA levels to virgin values. Together these results demonstrate that IL6/IL6Ra system modulates Npy/Agrp, Pomc and Trh expression during mouse pregnancy, supporting a role of IL6 in the central regulation of body fat in this physiological state.

Peripheral signalling involved in energy homeostasis control

The alarming prevalence of obesity has led to a better understanding of the molecular mechanisms controlling energy homeostasis. Regulation of energy intake and expenditure is more complex than previously thought, being influenced by signals from many peripheral tissues. In this sense, a wide variety of peripheral signals derived from different organs contributes to the regulation of body weight and energy expenditure. Besides the well-known role of insulin and adipokines, such as leptin and adiponectin, in the regulation of energy homeostasis, signals from other tissues not previously thought to play a role in body weight regulation have emerged in recent years. The role of fibroblast growth factor 21 (FGF21), insulin-like growth factor 1 (IGF-I), and sex hormone-binding globulin (SHBG) produced by the liver in the regulation of body weight and insulin sensitivity has been recently described. Moreover, molecules expressed by skeletal muscle such as myostatin have also been involved in adipose tissue regulation. Better known is the involvement of ghrelin, cholecystokinin, glucagon-like peptide 1 (GLP-1) and PYY(3-36), produced by the gut, in energy homeostasis. Even the kidney, through the production of renin, appears to regulate body weight, with mice lacking this hormone exhibiting resistance to diet-induced obesity. In addition, the skeleton has recently emerged as an endocrine organ, with effects on body weight control and glucose homeostasis through the actions of bone-derived factors such as osteocalcin and osteopontin. The comprehension of these signals will help in a better understanding of the aetiopathology of obesity, contributing to the potential development of new therapeutic targets aimed at tackling excess body fat accumulation.

Heterozygous deficiency of endoglin decreases insulin and hepatic triglyceride levels during high fat diet

Endoglin is a transmembrane auxiliary receptor for transforming growth factor-beta (TGF-beta) that is predominantly expressed on proliferating endothelial cells. It plays a wide range of physiological roles but its importance on energy balance or insulin sensitivity has been unexplored. Endoglin deficient mice die during midgestation due to cardiovascular defects. Here we report for first time that heterozygous endoglin deficiency in mice decreases high fat diet-induced hepatic triglyceride content and insulin levels. Importantly, these effects are independent of changes in body weight or adiposity. At molecular level, we failed to detect relevant changes in the insulin signalling pathway at basal levels in liver, muscle or adipose tissues that could explain the insulin-dependent effect. However, we found decreased triglyceride content in the liver of endoglin heterozygous mice fed a high fat diet in comparison to their wild type littermates. Overall, our findings indicate that endoglin is a potentially important physiological mediator of insulin levels and hepatic lipid metabolism.

Female Nur77-deficient mice show increased susceptibility to diet-induced obesity

Adipose tissue is essential in the regulation of body weight. The key process in fat catabolism and the provision of energy substrate during times of nutrient deprivation or enhanced energy demand is the hydrolysis of triglycerides and the release of fatty acids and glycerol. Nur77 is a member of the NR4A subfamily of nuclear receptors that plays an important metabolic role, modulating hepatic glucose metabolism and lipolysis in muscle. However, its endogenous role on white adipose tissue, as well as the gender dependency of these mechanisms, remains largely unknown. Male and female wild type and Nur77 deficient mice were fed with a high fat diet (45% calories from fat) for 4 months. Mice were analyzed in vivo with the indirect calorimetry system, and tissues were analyzed by real-time PCR and Western blot analysis. Female, but not male Nur77 deficient mice, gained more weight and fat mass when compared to wild type mice fed with high fat diet, which can be explained by decreased energy expenditure. The lack of Nur77 also led to a decreased pHSL/HSL ratio in white adipose tissue and increased expression of CIDEA in brown adipose tissue of female Nur77 deficient mice. Overall, these findings suggest that Nur77 is an important physiological modulator of lipid metabolism in adipose tissue and that there are gender differences in the sensitivity to deletion of the Nur77 signaling. The decreased energy expenditure and the actions of Nur77 on liver, muscle, brown and white adipose tissue contribute to the increased susceptibility to diet-induced obesity in females lacking Nur77.

Central resistin overexposure induces insulin resistance through Toll-like receptor 4

Resistin promotes both inflammation and insulin resistance associated with energy homeostasis impairment. However, the resistin receptor and the molecular mechanisms mediating its effects in the hypothalamus, crucial for energy homeostasis control, and key insulin-sensitive tissues are still unknown. In the current study, we report that chronic resistin infusion in the lateral cerebral ventricle of normal rats markedly affects both hypothalamic and peripheral insulin responsiveness. Central resistin treatment inhibited insulin-dependent phosphorylation of insulin receptor (IR), AKT, and extracellular signal-related kinase 1/2 associated with reduced IR expression and with upregulation of suppressor of cytokine signaling-3 and phosphotyrosine phosphatase 1B, two negative regulators of insulin signaling. Additionally, central resistin promotes the activation of the serine kinases Jun NH(2)-terminal kinase and p38 mitogen-activated protein kinase, enhances the serine phosphorylation of insulin receptor substrate-1, and increases the expression of the proinflammatory cytokine interleukin-6 in the hypothalamus and key peripheral insulin-sensitive tissues. Interestingly, we also report for the first time, to our knowledge, the direct binding of resistin to Toll-like receptor (TLR) 4 receptors in the hypothalamus, leading to the activation of the associated proinflammatory pathways. Taken together, our findings clearly identify TLR4 as the binding site for resistin in the hypothalamus and bring new insight into the molecular mechanisms involved in resistin-induced inflammation and insulin resistance in the whole animal.

Central resistin enhances renal sympathetic nerve activity via phosphatidylinositol 3-kinase but reduces the activity to brown adipose tissue via extracellular signal-regulated kinase 1/2

Resistin is an adipokine, originally identified in adipose tissue, and its plasma levels are elevated in obesity. Characteristics of obesity include impaired metabolic regulation and cardiovascular dysfunction, such as increased sympathetic nerve activity (SNA) to the kidney and skeletal muscle vasculature. Resistin can affect energy homeostasis through central mechanisms that include reduced food intake and reduced thermogenesis, and can also increase lumbar SNA via a central action. The present study investigated: (i) the effect of centrally-administered resistin on SNA targeting the kidney and (ii) the intracellular signalling pathways mediating the changes in SNA innervating the kidney and brown adipose tissue (BAT) induced by resistin. Intracerebroventricular resistin (7 μg) injected into overnight fasted, anaesthetised rats induced a significant increase in renal SNA by approximately 40%. This response was prevented when phosphatidylinositol 3-kinase (PI3K) was inhibited by i.c.v. administration of LY294002 (5 μg). Resistin reduced BAT SNA and this response was delayed by 150 min when extracellular-regulated kinase (ERK)1/2 was inhibited by i.c.v. administration of U0126. The findings indicate that resistin increases renal SNA via PI3K and reduces BAT SNA via ERK1/2.

Hypothalamic inflammation: a double-edged sword to nutritional diseases

The hypothalamus is one of the master regulators of various physiological processes, including energy balance and nutrient metabolism. These regulatory functions are mediated by discrete hypothalamic regions that integrate metabolic sensing with neuroendocrine and neural controls of systemic physiology. Neurons and nonneuronal cells in these hypothalamic regions act supportively to execute metabolic regulations. Under conditions of brain and hypothalamic inflammation, which may result from overnutrition-induced intracellular stresses or disease-associated systemic inflammatory factors, extracellular and intracellular environments of hypothalamic cells are disrupted, leading to central metabolic dysregulations and various diseases. Recent research has begun to elucidate the effects of hypothalamic inflammation in causing diverse components of metabolic syndrome leading to diabetes and cardiovascular disease. These new understandings have provocatively expanded previous knowledge on the cachectic roles of brain inflammatory response in diseases, such as infections and cancers. This review describes the molecular and cellular characteristics of hypothalamic inflammation in metabolic syndrome and related diseases as opposed to cachectic diseases, and also discusses concepts and potential applications of inhibiting central/hypothalamic inflammation to treat nutritional diseases.