GABA type B receptor signaling in proopiomelanocortin neurons protects against obesity, insulin resistance, and hypothalamic inflammation in male mice on a high-fat diet

Changes of Signaling Pathways in Hypothalamic Neurons with Aging

The hypothalamus is an important regulator of autonomic and endocrine functions also involved in aging regulation. The aging process in the hypothalamus is accompanied by disturbed intracellular signaling including insulin/insulin-like growth factor-1 (IGF-1)/growth hormone (GH), phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/protein kinase B (AKT)/the mammalian target of rapamycin (mTOR), mitogen activated protein kinase (MAPK), janus kinase (JAK)/signal transducer and activator of transcription (STAT), AMP-activated protein kinase (AMPK), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-ĸB), and nitric oxide (NO). In the current review, I have summarized the current understanding of the changes in the above-mentioned pathways in aging with a focus on hypothalamic alterations.

AAV5-mediated manipulation of insulin expression in choroid plexus has long-term metabolic and behavioral consequences

The choroid plexus (CP) is a source of trophic factors for the developing and mature brain. Insulin is produced in epithelial cells of the CP (EChPs), and its secretion is stimulated by Htr2c-mediated signaling. We modulated insulin expression in EChPs with intracerebroventricular injections of AAV5. Insulin overexpression in CP decelerates food intake, whereas its knockdown has the opposite effect. Insulin overexpression also results in reduced anxious behavior. Transcriptomic changes in the hypothalamus, especially in synapse-related processes, are also seen in mice overexpressing insulin in CP. Last, activation of Gq signaling in CP leads to acute Akt phosphorylation in neurons of the arcuate nucleus, indicating a direct action of CP-derived insulin on the hypothalamus. Taken together, our findings signify that CP is a relevant source of insulin in the central nervous system and that CP-derived insulin should be taken into consideration in future work pertaining to insulin actions in the brain.

The metabolic effects of resumption of a high fat diet after weight loss are sex dependent in mice

Dietary restriction is a frequent strategy for weight loss, but adherence is difficult and returning to poor dietary habits can result in more weight gain than that previously lost. How weight loss due to unrestricted intake of a healthy diet affects the response to resumption of poor dietary habits is less studied. Moreover, whether this response differs between the sexes and if the insulin-like growth factor (IGF) system, sex dependent and involved in metabolic control, participates is unknown. Mice received rodent chow (6% Kcal from fat) or a high-fat diet (HFD, 62% Kcal from fat) for 4 months, chow for 3 months plus 1 month of HFD, or HFD for 2 months, chow for 1 month then HFD for 1 month. Males and females gained weight on HFD and lost weight when returned to chow at different rates (p < 0.001), but weight gain after resumption of HFD intake was not affected by previous weight loss in either sex. Glucose metabolism was more affected by HFD, as well as the re-exposure to HFD after weight loss, in males. This was associated with increases in hypothalamic mRNA levels of IGF2 (p < 0.01) and IGF binding protein (IGFBP) 2 (p < 0.05), factors involved in glucose metabolism, again only in males. Likewise, IGF2 increased IGFBP2 mRNA levels only in hypothalamic astrocytes from males (p < 0.05). In conclusion, the metabolic responses to dietary changes were less severe and more delayed in females and the IGF system might be involved in some of the sex specific observations.

Function of the GABAergic System in Diabetic Encephalopathy

Diabetes is a common metabolic disease characterized by loss of blood sugar control and a high rate of complications. γ-Aminobutyric acid (GABA) functions as the primary inhibitory neurotransmitter in the adult mammalian brain. The normal function of the GABAergic system is affected in diabetes. Herein, we summarize the role of the GABAergic system in diabetic cognitive dysfunction, diabetic blood sugar control disorders, diabetes-induced peripheral neuropathy, diabetic central nervous system damage, maintaining diabetic brain energy homeostasis, helping central control of blood sugar and attenuating neuronal oxidative stress damage. We show the key regulatory role of the GABAergic system in multiple comorbidities in patients with diabetes and hope that further studies elucidating the role of the GABAergic system will yield benefits for the treatment and prevention of comorbidities in patients with diabetes.

Protein Tyrosine Phosphatase 1B Deficiency Improves Glucose Homeostasis in Type 1 Diabetes Treated With Leptin

Leptin, a hormone secreted by adipocytes, exhibits therapeutic potential for the treatment of type 1 diabetes (T1D). Protein tyrosine phosphatase 1B (PTP1B) is a key enzyme that negatively regulates leptin receptor signaling. Here, the role of PTP1B in the treatment of T1D was investigated using PTP1B-deficient (knockout [KO]) mice and a PTP1B inhibitor. T1D wild-type (WT) mice induced by streptozotocin showed marked hyperglycemia compared with non-T1D WT mice. KO mice displayed significantly improved glucose metabolism equivalent to non-T1D WT mice, whereas peripheral or central administration of leptin partially improved glucose metabolism in T1D WT mice. Peripheral combination therapy of leptin and a PTP1B inhibitor in T1D WT mice improved glucose metabolism to the same level as non-T1D WT mice. Leptin was shown to act on the arcuate nucleus in the hypothalamus to suppress gluconeogenesis in liver and enhance glucose uptake in both brown adipose tissue and soleus muscle through the sympathetic nervous system. These effects were enhanced by PTP1B deficiency. Thus, treatment of T1D with leptin, PTP1B deficiency, or a PTP1B inhibitor was shown to enhance leptin activity in the hypothalamus to improve glucose metabolism. These findings suggest a potential alternative therapy for T1D.

Gabra5 plays a sexually dimorphic role in POMC neuron activity and glucose balance

Pro-opiomelanocortin (POMC) neurons are important for the regulation of body weight and glucose balance. The inhibitory tone to POMC neurons is mediated primarily by the GABA receptors. However, the detailed mechanisms and functions of GABA receptors are not well understood. The α5 subunit of GABAA receptor, Gabra5, is reported to regulate feeding, and we found that Gabra5 is highly expressed in POMC neurons. To explore the function of Gabra5 in POMC neurons, we knocked down Gabra5 specifically from mature hypothalamic POMC neurons using the clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 strategy. This POMC-specific knock-down of Gabra5 did not affect body weight or food intake in either male or female mice. Interestingly, the loss of Gabra5 caused significant increases in the firing frequency and resting membrane potential, and a decrease in the amplitude of the miniature inhibitory postsynaptic current (mIPSC) in male POMC neurons. However, the loss of Gabra5 only modestly decreased the frequency of mIPSC in female POMC neurons. Consistently, POMC-specific knock-down of Gabra5 significantly improved glucose tolerance in male mice but not in female mice. These results revealed a sexually dimorphic role of Gabra5 in POMC neuron activity and glucose balance, independent of body weight control.

Colchicine stimulates browning via antagonism of GABA receptor B and agonism of β3-adrenergic receptor in 3T3-L1 white adipocytes

Colchicine has been used for therapeutic purposes and has attracted considerable attention because of its association with tubulin and the inhibition of small tubular polymerization. Although several studies have examined the possible preventive role of colchicine in metabolic diseases, its role in adipocytes is largely unknown. This study examined the novel functional role of colchicine in adipocytes demonstrating that colchicine stimulates browning in cultured white adipocytes. Colchicine stimulates browning by increasing the brown- and beige fat-specific markers in 3T3-L1 white adipocytes. Interestingly, colchicine decreased the expression of the main lipolytic proteins (ATGL, p-HSL) while it activated Ces3, suggesting a possibility for supplying essential fatty acids for inducing thermogenesis. Molecular docking analysis showed that colchicine has a strong affinity against GABA-BR and β3-AR, and its binding activity with GABA-BR (-26.52 kJ/mol) was stronger than β3-AR (-20.71 kJ/mol). Mechanistic studies were conducted by treating the cells separately with agonists and antagonists of GABA-BR and β3-AR to understand the molecular mechanism underlying the browning effect of colchicine. The results showed that colchicine stimulates browning via the antagonism of GABA-BR and the agonism of β3-AR in 3T3-L1 white adipocytes. The colchicine-mediated activation of β3-AR stimulated the PKA/p38 MAPK signaling pathway, where consequently ATF2 acted as a positive regulator, but AFT4 was a negative regulator for the induction of browning.

Peripheral combination treatment of leptin and an SGLT2 inhibitor improved glucose metabolism in insulin-dependent diabetes mellitus mice

We investigated whether peripheral combination treatment of a sodium-glucose cotransporter 2 (SGLT2) inhibitor and leptin improves glucose metabolism in insulin-dependent diabetes mellitus (IDDM) model mice. Twelve-week-old male C57BL6 mice were intraperitoneally administered a high dose of streptozotocin to produce IDDM. IDDM mice were then divided into five groups: SGLT2 inhibitor treatment alone, leptin treatment alone, leptin and SGLT2 inhibitor co-treatment, untreated IDDM mice, and healthy mice groups. The blood glucose (BG) level at the end of the dark cycle was measured, and a glucose tolerance test (GTT) was performed and compared between the five groups. Leptin was peripherally administered at 20 μg/day using an osmotic pump, and an SGLT2 inhibitor, ipragliflozin, was orally administered at 3 mg/kg/day. Monotherapy with SGLT2 inhibitor or leptin significantly improved glucose metabolism in mice as evaluated by BG and GTT compared with the untreated group, whereas the co-treatment group with SGLT2 inhibitor and leptin further improved glucose metabolism as compared with the monotherapy group. Notably, glucose metabolism in the co-treatment group improved to the same level as that in the healthy mice group. Thus, peripheral combination treatment with leptin and SGLT2 inhibitor improved glucose metabolism in IDDM mice without the use of insulin.

The Zonulin-transgenic mouse displays behavioral alterations ameliorated via depletion of the gut microbiota

The gut-brain axis hypothesis suggests that interactions in the intestinal milieu are critically involved in regulating brain function. Several studies point to a gut-microbiota-brain connection linking an impaired intestinal barrier and altered gut microbiota composition to neurological disorders involving neuroinflammation. Increased gut permeability allows luminal antigens to cross the gut epithelium, and via the blood stream and an impaired blood-brain barrier (BBB) enters the brain impacting its function. Pre-haptoglobin 2 (pHP2), the precursor protein to mature HP2, is the first characterized member of the zonulin family of structurally related proteins. pHP 2 has been identified in humans as the thus far only endogenous regulator of epithelial and endothelial tight junctions (TJs). We have leveraged the Zonulin-transgenic mouse (Ztm) that expresses a murine pHP2 (zonulin) to determine the role of increased gut permeability and its synergy with a dysbiotic intestinal microbiota on brain function and behavior. Here we show that Ztm mice display sex-dependent behavioral abnormalities accompanied by altered gene expression of BBB TJs and increased expression of brain inflammatory genes. Antibiotic depletion of the gut microbiota in Ztm mice downregulated brain inflammatory markers ameliorating some anxiety-like behavior. Overall, we show that zonulin-dependent alterations in gut permeability and dysbiosis of the gut microbiota are associated with an altered BBB integrity, neuroinflammation, and behavioral changes that are partially ameliorated by microbiota depletion. Our results suggest the Ztm model as a tool for the study of the cross-talk between the microbiome/gut and the brain in the context of neurobehavioral/neuroinflammatory disorders.

VTA MC3R neurons control feeding in an activity- and sex-dependent manner in mice

Increasing evidence indicates that the melanocortin and mesolimbic dopamine (DA) systems interact to regulate feeding and body weight. Because melanocortin-3 receptors (MC3R) are highly expressed in the ventral tegmental area (VTA), we tested whether VTA neurons expressing these receptors (VTA MC3R neurons) control feeding and body weight in vivo. We also tested whether there were sex differences in the ability of VTA MC3R neurons to control feeding, as MC3R -/- mice show sex-dependent alterations in reward feeding and DA levels, and there are clear sex differences in multiple DA-dependent behaviors and disorders. Designer receptors exclusively activated by designer drugs (DREADD) were used to acutely activate and inhibit VTA MC3R neurons and changes in food intake and body weight were measured. Acutely altering the activity of VTA MC3R neurons decreased feeding in an activity- and sex-dependent manner, with acute activation decreasing feeding, but only in females, and acute inhibition decreasing feeding, but only in males. These differences did not appear to be due to sex differences in the number of VTA MC3R neurons, the ability of hM3Dq to activate VTA MC3R neurons, or the proportion of VTA MC3R neurons expressing tyrosine hydroxylase (TH). These studies demonstrate an important role for VTA MC3R neurons in the control of feeding and reveal important sex differences in behavior, whereby opposing changes in neuronal activity in male and female mice cause similar changes in behavior.

Dietary sodium chloride attenuates increased β-cell mass to cause glucose intolerance in mice under a high-fat diet

Excessive sodium salt (NaCl) or fat intake is associated with a variety of increased health risks. However, whether excessive NaCl intake accompanied by a high-fat diet (HFD) affects glucose metabolism has not been elucidated. In this study, C57BL/6J male mice were fed a normal chow diet (NCD), a NCD plus high-NaCl diet (NCD plus NaCl), a HFD, or a HFD plus high-NaCl diet (HFD plus NaCl) for 30 weeks. No significant differences in body weight gain, insulin sensitivity, and glucose tolerance were observed between NCD-fed and NCD plus NaCl-fed mice. In contrast, body and liver weights were decreased, but the weight of epididymal white adipose tissue was increased in HFD plus NaCl-fed compared to HFD-fed mice. HFD plus NaCl-fed mice had lower plasma glucose levels in an insulin tolerance test, and showed higher plasma glucose and lower plasma insulin levels in an intraperitoneal glucose tolerance test compared to HFD-fed mice. The β-cell area and number of islets were decreased in HFD plus NaCl-fed compared to HFD-fed mice. Increased Ki67-positive β-cells, and increased expression levels of Ki67, CyclinB1, and CyclinD1 mRNA in islets were observed in HFD-fed but not HFD plus NaCl-fed mice when compared to NCD-fed mice. Our data suggest that excessive NaCl intake accompanied by a HFD exacerbates glucose intolerance, with impairment in insulin secretion caused by the attenuation of expansion of β-cell mass in the pancreas.

High-fat Feeding Causes Inflammation and Insulin Resistance in the Ventral Tegmental Area in Mice

The reward system plays an important role in the pathogenesis of not only drug addiction, but also diet-induced obesity. Recent studies have shown that insulin and leptin receptor signaling in the ventral tegmental area (VTA) regulate energy homeostasis and that their dysregulation is responsible for obesity and altered food preferences. Although a high-fat diet (HFD) induces inflammation that leads to insulin and leptin resistance in the brain, it remains unclear whether HFD induces inflammation in the VTA. In the present study, we placed male mice on a chow diet or HFD for 3, 7, and 28 days and evaluated the mRNA expression of inflammatory cytokines and microglial activation markers in the VTA. The HFD group showed significantly elevated mRNA expressions of IL1β at 3 days; tumor necrosis factor-alpha (TNFα), IL1β, IL6, Iba1, and CD11b at 7 days; and TNFα, IL1β, Iba1, and CD11b at 28 days. The changes in TNFα were also confirmed in immunohistochemical analysis. Next, after administration of chow or HFD for 7 days, we selected mice with equal weights in both groups. In experiments using these mice, Akt phosphorylation in the VTA was significantly decreased after intracerebroventricular injection of insulin, whereas no change in STAT3 phosphorylation was found with leptin. Taken together, these results suggest that HFD induces inflammation at least partly associated with microglial activation in the VTA leading to insulin resistance, independently of the energy balance. Our data provide new insight into the pathophysiology of obesity caused by a dysfunctional reward system under HFD conditions.

Trappc9 deficiency causes parent-of-origin dependent microcephaly and obesity

Some imprinted genes exhibit parental origin specific expression bias rather than being transcribed exclusively from one copy. The physiological relevance of this remains poorly understood. In an analysis of brain-specific allele-biased expression, we identified that Trappc9, a cellular trafficking factor, was expressed predominantly (~70%) from the maternally inherited allele. Loss-of-function mutations in human TRAPPC9 cause a rare neurodevelopmental syndrome characterized by microcephaly and obesity. By studying Trappc9 null mice we discovered that homozygous mutant mice showed a reduction in brain size, exploratory activity and social memory, as well as a marked increase in body weight. A role for Trappc9 in energy balance was further supported by increased ad libitum food intake in a child with TRAPPC9 deficiency. Strikingly, heterozygous mice lacking the maternal allele (70% reduced expression) had pathology similar to homozygous mutants, whereas mice lacking the paternal allele (30% reduction) were phenotypically normal. Taken together, we conclude that Trappc9 deficient mice recapitulate key pathological features of TRAPPC9 mutations in humans and identify a role for Trappc9 and its imprinting in controlling brain development and metabolism.

Methylation of the LEP gene promoter in blood at 12 months and BMI at 4 years of age-a population-based cohort study

Increasing evidence links epigenetic variation to anthropometric and metabolic measures. Leptin signalling regulates appetite and energy expenditure, and in pregnancy is important for nutrient supply to the foetus. Maternal metabolic health and foetal growth are linked to infant blood leptin gene (LEP) methylation, which has been cross-sectionally associated with adolescent obesity. Despite this, few studies have explored the relationship between infant LEP methylation and childhood anthropometry, or the impact of genetic variation on these relationships. Using a prospective birth cohort, we investigated whether blood LEP promoter methylation at birth and 12 months predicts weight and adiposity at 4-years. Locus-specific methylation data was analysed by partial correlation tests and multivariable linear regression. There was weak evidence of an association of birth LEP methylation with anthropometry measures at 4 years. Methylation at a specific site (cg19594666) at 12 months was inversely associated with 4-year weight (r = -0.11, p = 0.02) and body-mass index (BMI) (r = -0.13, p = 0.007), which persisted following adjustment for weight at birth and at 12 months. Neither association was influenced by genotype. We report the first evidence of an association between LEP methylation in infancy and childhood weight. Replication in additional cohorts is required to determine if this relationship persists.

GABAB Receptor Signaling in the Mesolimbic System Suppresses Binge-like Consumption of a High-Fat Diet

Binge eating could contribute to the development of obesity, and previous studies suggest that gamma-aminobutyric acid (GABA) type B receptor (GABA_BR) signaling is involved in the regulation of binge eating. Here, we show that time-restricted access to a high-fat diet (HFD) induces binge-like eating behavior in wild-type mice. HFD consumption during restricted time was significantly increased in corticostriatal neuron-specific GABA_BR-deficient mice compared with wild-type mice. Furthermore, the GABA_BR agonist baclofen suppressed HFD intake during restricted time in wild-type mice but not in corticostriatal or dopaminergic neuron-specific GABA_BR-deficient mice. In contrast, there were no significant differences in food consumption among genotypes under ad libitum access to HFD. Thus, our data show that the mesolimbic system regulates food consumption under time-restricted but not ad libitum access to HFD and have identified a mechanism by which GABA_BR signaling suppresses binge-like eating of HFD.

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GABA_BR KO in corticostriatal neurons enhances binge-like feeding of HFD

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Baclofen suppresses binge-like feeding of HFD via the mesolimbic system

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GABA_BR signaling in mesolimbic system does not affect energy balance

Brain signalling systems: A target for treating type I diabetes mellitus

From early to later stages of Type I Diabetes Mellitus (TIDM), signalling molecules including brain indolamines and protein kinases are altered significantly, and that has been implicated in the Metabolic Disorders (MD) as well as impairment of retinal, renal, neuronal and cardiovascular systems. Considerable attention has been focused to the effects of diabetes on these signalling systems. However, the exact pathophysiological mechanisms of these signals are not completely understood in TIDM, but it is likely that hyperglycemia, acidosis, and insulin resistance play significant roles. Insulin maintains normal glycemic levels and it acts by binding to its receptor, so that it activates the receptor's tyrosine kinase activity, resulting in phosphorylation of several substrates. Those substrates provide binding/interaction sites for signalling molecules, including serine/threonine kinases and indolamines. For more than two decades, our research has been focused on the mechanisms of protein kinases, CaM Kinase and Serotonin transporter mediated alterations of indolamines in TIDM. In this review, we have also discussed how discrete areas of brain respond to insulin or some of the pharmacological agents that triggers or restores these signalling molecules, and it may be useful for the treatment of specific region wise changes/disorders of diabetic brain.

"Hypothalamic Microinflammation" Paradigm in Aging and Metabolic Diseases

Under conditions leading to aging and metabolic syndrome, the hypothalamus atypically undergoes proinflammatory signaling activation leading to a chronic and stable background inflammation, referred to as "hypothalamic microinflammation." Through the past decade of research, progress has been made to causally link this hypothalamic inflammation to the mechanism of aging as well as metabolic syndrome, promoting the "hypothalamic microinflammation" theory, which helps characterize the consensus of these epidemic health problems. In general, it is consistently appreciated that hypothalamic microinflammation emerges during the early stages of aging and metabolic syndrome and evolves to be multifaceted and advanced alongside disease progression, while inhibition of key inflammatory components in the hypothalamus has a broad range of effects in counteracting these disorders. Herein, focusing on aging and metabolic syndrome, this writing aims to provide an overview of and insights into the mediators, signaling components, cellular impacts, and physiological significance of this hypothalamic microinflammation.

GABA-stimulated adipose-derived stem cells suppress subcutaneous adipose inflammation in obesity

Accumulating evidence suggests that subcutaneous and visceral adipose tissues are differentially associated with metabolic disorders. In obesity, subcutaneous adipose tissue is beneficial for metabolic homeostasis because of repressed inflammation. However, the underlying mechanism remains unclear. Here, we demonstrate that γ-aminobutyric acid (GABA) sensitivity is crucial in determining fat depot-selective adipose tissue macrophage (ATM) infiltration in obesity. In diet-induced obesity, GABA reduced monocyte migration in subcutaneous inguinal adipose tissue (IAT), but not in visceral epididymal adipose tissue (EAT). Pharmacological modulation of the GABA_B receptor affected the levels of ATM infiltration and adipose tissue inflammation in IAT, but not in EAT, and GABA administration ameliorated systemic insulin resistance and enhanced insulin-dependent glucose uptake in IAT, accompanied by lower inflammatory responses. Intriguingly, compared with adipose-derived stem cells (ADSCs) from EAT, IAT-ADSCs played key roles in mediating GABA responses that repressed ATM infiltration in high-fat diet-fed mice. These data suggest that selective GABA responses in IAT contribute to fat depot-selective suppression of inflammatory responses and protection from insulin resistance in obesity.

Olanzapine-induced endoplasmic reticulum stress and inflammation in the hypothalamus were inhibited by an ER stress inhibitor 4-phenylbutyrate

Antipsychotics are the most important treatment for schizophrenia. However, antipsychotics, particularly olanzapine and clozapine, are associated with severe weight gain/obesity side-effects. Although numerous studies have been carried out to identify the exact mechanisms of antipsychotic-induced weight gain, it is still important to consider other pathways. Endoplasmic reticulum (ER) stress signaling and its associated inflammation pathway is one of the most important pathways involved in regulation of energy balance. In the present study, we examined the role of hypothalamic protein kinase R like endoplasmic reticulum kinase- eukaryotic initiation factor 2α (PERK-eIF2α) signaling and the inflammatory IkappaB kinase β- nuclear factor kappa B (IKKβ-NFκB) signaling pathway in olanzapine-induced weight gain in female rats. In this study, we found that olanzapine significantly activated PERK-eIF2α and IKKβ-NFκB signaling in SH-SY5Y cells in a dose-dependent manner. Olanzapine treatment for 8 days in rats was associated with activated PERK-eIF2α signaling and IKKβ-NFκB signaling in the hypothalamus, accompanied by increased food intake and weight gain. Co-treatment with an ER stress inhibitor, 4-phenylbutyrate (4-PBA), decreased olanzapine-induced food intake and weight gain in a dose- and time-dependent manner. Moreover, 4-PBA dose-dependently inhibited olanzapine-induced activated PERK-eIF2α and IKKβ-NFκB signaling in the hypothalamus. These results suggested that hypothalamic ER stress may play an important role in antipsychotic-induced weight gain.

A Multi-omics Approach to Unraveling the Microbiome-Mediated Effects of Arabinoxylan Oligosaccharides in Overweight Humans

The use of dietary fiber food supplementation as a strategy to reduce the burden of diet-related diseases is a matter of study given its cost-effectiveness and the positive results demonstrated in clinical trials. This multi-omics assessment, on different biological samples of overweight subjects with signs of metabolic syndrome, sheds light on the early and less evident effects of short-term AXOS intake on intestinal microbiota and host metabolism. We observed a deep influence of AXOS on gut microbiota beyond their recognized bifidogenic effect by boosting concomitantly a wide diversity of butyrate producers and Prevotella copri, a microbial species abundant in non-Westernized populations with traditional lifestyle and diets enriched in fresh unprocessed foods. A comprehensive evaluation of hundreds of metabolites unveiled new benefits of the AXOS intake, such as reducing the plasma ceramide levels. Globally, we observed that multiple effects of AXOS consumption seem to converge in reversing the glucose homeostasis impairment.

Long-term consumption of dietary fiber is generally considered beneficial for weight management and metabolic health, but the results of interventions vary greatly depending on the type of dietary fibers involved. This study provides a comprehensive evaluation of the effects of a specific dietary fiber consisting of a wheat-bran extract enriched in arabinoxylan-oligosaccharides (AXOS) in a human intervention trial. An integrated multi-omics analysis has been carried out to evaluate the effects of an intervention trial with an AXOS-enriched diet in overweight individuals with indices of metabolic syndrome. Microbiome analyses were performed by shotgun DNA sequencing in feces; in-depth metabolomics using nuclear magnetic resonance in fecal, urine, and plasma samples; and massive lipid profiling using mass spectrometry in fecal and serum/plasma samples. In addition to their bifidogenic effect, we observed that AXOS boost the proportion of Prevotella species. Metagenome analysis showed increases in the presence of bacterial genes involved in vitamin/cofactor production, glycan metabolism, and neurotransmitter biosynthesis as a result of AXOS intake. Furthermore, lipidomics analysis revealed reductions in plasma ceramide levels. Finally, we observed associations between Prevotella abundance and short-chain fatty acids (SCFAs) and succinate concentration in feces and identified a potential protective role of Eubacterium rectale against metabolic disease given that its abundance was positively associated with plasma phosphatidylcholine levels, thus hypothetically reducing bioavailability of choline for methylamine biosynthesis. The metagenomics, lipidomics, and metabolomics data integration indicates that sustained consumption of AXOS orchestrates a wide variety of changes in the gut microbiome and the host metabolism that collectively would impact on glucose homeostasis. (This study has been registered at ClinicalTrials.gov under identifier NCT02215343.)

IMPORTANCE The use of dietary fiber food supplementation as a strategy to reduce the burden of diet-related diseases is a matter of study given its cost-effectiveness and the positive results demonstrated in clinical trials. This multi-omics assessment, on different biological samples of overweight subjects with signs of metabolic syndrome, sheds light on the early and less evident effects of short-term AXOS intake on intestinal microbiota and host metabolism. We observed a deep influence of AXOS on gut microbiota beyond their recognized bifidogenic effect by boosting concomitantly a wide diversity of butyrate producers and Prevotella copri, a microbial species abundant in non-Westernized populations with traditional lifestyle and diets enriched in fresh unprocessed foods. A comprehensive evaluation of hundreds of metabolites unveiled new benefits of the AXOS intake, such as reducing the plasma ceramide levels. Globally, we observed that multiple effects of AXOS consumption seem to converge in reversing the glucose homeostasis impairment.

Mechanisms for Sex Differences in Energy Homeostasis

Sex differences exist in the regulation of energy homeostasis. Better understanding of the underlying mechanisms for sexual dimorphism in energy balance may facilitate development of gender-specific therapies for human diseases, e.g. obesity. Multiple organs, including the brain, liver, fat and muscle, play important roles in the regulations of feeding behavior, energy expenditure and physical activity, which therefore contribute to the maintenance of energy balance. It has been increasingly appreciated that this multi-organ system is under different regulations in male vs. female animals. Much of effort has been focused on roles of sex hormones (including androgens, estrogens and progesterone) and sex chromosomes in this sex-specific regulation of energy balance. Emerging evidence also indicates that other factors (not sex hormones/receptors and not encoded by the sex chromosomes) exist to regulate energy homeostasis differentially in males vs. females. In this review, we summarize factors and signals that have been shown to regulate energy homeostasis in a sexually dimorphic fashion and propose a framework where these factors and signals may be integrated to mediate sex differences in energy homeostasis.

γ-Aminobutyric Acid Attenuates High-Fat Diet-Induced Cerebral Oxidative Impairment via Enhanced Synthesis of Hippocampal Sulfatides

Long-term high-fat diet (HFD) in rats triggered cerebral oxidative stress, reflected by reactive oxygen species accumulation and antioxidant decline in peripheral and cerebral tissues, together with hippocampal lipid disturbance, particularly for triglyceride accumulation and sulfatide deficiency. Hippocampal formation and cerebral cortex also exhibited pathological changes, characterized by neurofibrillary tangle and reduced Nissl bodies. Sulfatides were noted to protect hippocampal neurons from oxidative damage through the clearance of β-amyloid protein, with apolipoprotein E transporting and low-density lipoprotein receptor binding. Delightedly, we found γ-aminobutyric acid (GABA) supplement delivered by rice bran to rats significantly promoted hippocampal sulfatide synthesis and reversed the HFD-induced sulfatide deficiency and oxidative-triggered cerebral impairment. Elevated GABA concentration in hippocampus and the activation of GABA B-type receptors might be the primary contributors. This study demonstrated the potential of GABA-enriched rice bran as a novel dietary supplement to enhance a sulfatide-based therapeutic approach for neurodegenerative diseases in the early stages.

Neurobiological characteristics underlying metabolic differences between males and females

The hypothalamus is the main integrating center for metabolic control. Our understanding of how hypothalamic circuits function to control appetite and energy expenditure has increased dramatically in recent years, due to the rapid rise in the incidence of obesity and the search for effective treatments. Increasing evidence indicates that these treatments will most likely differ between males and females. Indeed, sex differences in metabolism have been demonstrated at various levels, including in two of the most studied neuronal populations involved in metabolic control: the anorexigenic proopiomelanocortin neurons and the orexigenic neuropeptide Y/Agouti-related protein neurons. Here we review what is known to date regarding the sex differences in these two neuronal populations, as well as other neuronal populations involved in metabolic control and glial cells.

Neuroendocrine response to GABA-B receptor agonism in alcohol-dependent individuals: Results from a combined outpatient and human laboratory experiment

Gamma-aminobutyric acid (GABA), the main inhibitory neurotransmitter in the nervous system, plays an important role in biobehavioral processes that regulate alcohol seeking, food intake, and stress response. The metabotropic GABA-B receptor has been investigated as a potential therapeutic target for alcohol use disorder, by using orthosteric agonists (e.g., baclofen) and positive allosteric modulators. Whether and how pharmacological manipulation of the GABA-B receptor, in combination with alcohol intake, may affect feeding- and stress-related neuroendocrine pathways remains unknown. In the present randomized, double-blind, placebo-controlled study, thirty-four alcohol-dependent individuals received baclofen (30 mg/day) or placebo in a naturalistic outpatient setting for one week, and then performed a controlled laboratory experiment which included alcohol cue-reactivity, fixed-dose priming, and self-administration procedures. Blood samples were collected, and the following neuroendocrine markers were measured: ghrelin, leptin, amylin, glucagon-like peptide-1 (GLP-1), insulin, prolactin, thyroid-stimulating hormone, growth hormone, cortisol, and adrenocorticotropic hormone (ACTH). During the outpatient phase, baclofen significantly increased blood concentrations of acyl-ghrelin (p = 0.01), leptin (p = 0.01), amylin (p = 0.004), and GLP-1 (p = 0.02). Significant drug × time-point interaction effects for amylin (p = 0.001) and insulin (p = 0.03), and trend-level interaction effects for GLP-1 (p = 0.06) and ACTH (p = 0.10) were found during the laboratory experiment. Baclofen, compared to placebo, had no effect on alcohol drinking in this study (p's ≥ 0.05). Together with previous studies, these findings shed light on the role of the GABAergic system and GABA-B receptors in the shared neurobiology of alcohol-, feeding-, and stress-related behaviors.

Pyruvate induces torpor in obese mice

Mice subjected to cold or caloric deprivation can reduce body temperature and metabolic rate and enter a state of torpor. Here we show that administration of pyruvate, an energy-rich metabolic intermediate, can induce torpor in mice with diet-induced or genetic obesity. This is associated with marked hypothermia, decreased activity, and decreased metabolic rate. The drop in body temperature correlates with the degree of obesity and is blunted by housing mice at thermoneutrality. Induction of torpor by pyruvate in obese mice relies on adenosine signaling and is accompanied by changes in brain levels of hexose bisphosphate and GABA as detected by mass spectroscopy-based imaging. Pyruvate does not induce torpor in lean mice but results in the activation of brown adipose tissue (BAT) with an increase in the level of uncoupling protein-1 (UCP1). Denervation of BAT in lean mice blocks this increase in UCP1 and allows the pyruvate-induced torpor phenotype. Thus, pyruvate administration induces torpor in obese mice by pathways involving adenosine and GABA signaling and a failure of normal activation of BAT.

Sex differences in the neuroendocrine control of metabolism and the implication of astrocytes

Males and females have distinct propensities to develop obesity and its related comorbidities, partially due to gonadal steroids. There are sex differences in hypothalamic neuronal circuits, as well as in astrocytes, that participate in metabolic control and the development of obesity-associated complications. Astrocytes are involved in nutrient transport and metabolism, glucose sensing, synaptic remodeling and modulation of neuronal signaling. They express receptors for metabolic hormones and mediate effects of these metabolic signals on neurons, with astrogliosis occurring in response to high fat diet and excess weight gain. However, most studies of obesity have focused on males. Recent reports indicate that male and female astrocytes respond differently to metabolic signals and this could be involved in the differential response to high fat diet and the onset of obesity-associated pathologies. Here we focus on the sex differences in response to obesogenic paradigms and the possible role of hypothalamic astrocytes in this phenomenon.

POMC Neurons: From Birth to Death

The hypothalamus is an evolutionarily conserved brain structure that regulates an organism's basic functions, such as homeostasis and reproduction. Several hypothalamic nuclei and neuronal circuits have been the focus of many studies seeking to understand their role in regulating these basic functions. Within the hypothalamic neuronal populations, the arcuate melanocortin system plays a major role in controlling homeostatic functions. The arcuate pro-opiomelanocortin (POMC) neurons in particular have been shown to be critical regulators of metabolism and reproduction because of their projections to several brain areas both in and outside of the hypothalamus, such as autonomic regions of the brain stem and spinal cord. Here, we review and discuss the current understanding of POMC neurons from their development and intracellular regulators to their physiological functions and pathological dysregulation.

PGBR extract ameliorates TNF-α induced insulin resistance in hepatocytes

Pre-germinated brown rice (PGBR) could ameliorate metabolic syndrome, however, not much research estimates the effect of PGBR extract on insulin resistance. The aim of this study is to examine the effects of PGBR extract in TNF-α induced insulin resistance. HepG2 cells, hepatocytes, were cultured in DMEM medium and added with 5 μM insulin or with insulin and 30 ng/ml TNF-α or with insulin, TNF-α and PGBR extract (50, 100, 300 μg/ml). The glucose levels of the medium were decreased by insulin, demonstrating insulin promoted glucose uptake into cell. However, TNF-α inhibited glucose uptake into cells treated with insulin. Moreover, insulin increased the protein expressions of AMP-activated protein kinase (AMPK), insulin receptor substrate-1 (IRS-1), phosphatidylinositol-3-kinase-α (PI3K-α), serine/threonine kinase PI3K-linked protein kinase B (Akt/PKB), glucose transporter-2 (GLUT-2), glucokinase (GCK), peroxisome proliferator activated receptor-α (PPAR-α) and PPAR-γ. TNF-α activated p65 and MAPKs (JNK1/2 and ERK1/2) which worsened the expressions of AMPK, IRS-1, PI3K-α, Akt/PKB, GLUT-2, GCK, glycogen synthase kinase-3 (GSK-3), PPAR-α and PPAR-γ. Once this relationship was established, we added PGBR extract to cell with insulin and TNF-α. We found glucose levels of medium were lowered and that the protein expressions of AMPK, IRS-1, PI3K-α, Akt/PKB, GLUT-2, GCK, GSK-3, PPAR-α, PPAR-γ and p65, JNK1/2 were also recovered. In conclusion, this study found that TNF-α inhibited insulin stimulated glucose uptake and aggravated related proteins expressions, suggesting that it might cause insulin resistance. PGBR extract was found to ameliorate this TNF-α induced insulin resistance, suggesting that it might be used in the future to help control insulin resistance.

Sequestosome 1 (SQSTM1/p62) maintains protein folding capacity under endoplasmic reticulum stress in mouse hypothalamic organotypic culture

Sequestosome 1 (SQSTM1) also known as ubiquitin-binding protein p62 (p62) is a cargo protein involved in the degradation of misfolded proteins via selective autophagy. Disruption of autophagy and resulting accumulation of misfolded proteins in the endoplasmic reticulum (ER) leads to ER stress. ER stress is implicated in several neurodegenerative diseases and obesity. As knockout of p62 (p62KO) reportedly induces obesity in mice, we examined how p62 contributes to ER stress and the ensuing unfolded protein response (UPR) in hypothalamus using mouse organotypic cultures in the present study. Cultures from p62KO mice showed significantly reduced formation of LC3-GFP puncta, an index of autophagosome formation, in response to the chemical ER stressor thapsigargin compared to wild-type (WT) cultures. Hypothalamic cultures from p62KO mice exhibited higher basal expression of the UPR/ER stress markers CHOP mRNA and ATF4 mRNA than WT cultures. Thapsigargin enhanced CHOP, ATF4, and BiP mRNA as well as p-eIF2α protein expression in both WT and p62KO cultures, but all peak values were greater in p62KO cultures. A proteasome inhibitor increased p62 expression in WT cultures and upregulated the UPR/ER stress markers CHOP mRNA and ATF4 mRNA in both genotypes, but to a greater extent in p62KO cultures. Therefore, p62 deficiency disturbed autophagosome formation and enhanced both basal and chemically induced ER stress, suggesting that p62 serves to prevent ER stress in mouse hypothalamus by maintaining protein folding capacity.

Obesity-associated gene TMEM18 has a role in the central control of appetite and body weight regulation

An intergenic region of human chromosome 2 (2p25.3) harbors genetic variants which are among those most strongly and reproducibly associated with obesity. The gene closest to these variants is TMEM18, although the molecular mechanisms mediating these effects remain entirely unknown. Tmem18 expression in the murine hypothalamic paraventricular nucleus (PVN) was altered by changes in nutritional state. Germline loss of Tmem18 in mice resulted in increased body weight, which was exacerbated by high fat diet and driven by increased food intake. Selective overexpression of Tmem18 in the PVN of wild-type mice reduced food intake and also increased energy expenditure. We provide evidence that TMEM18 has four, not three, transmembrane domains and that it physically interacts with key components of the nuclear pore complex. Our data support the hypothesis that TMEM18 itself, acting within the central nervous system, is a plausible mediator of the impact of adjacent genetic variation on human adiposity.

Melanocortin neurons: Multiple routes to regulation of metabolism

The burden of disability, premature death, escalating health care costs and lost economic productivity due to obesity and its associated complications including hypertension, stroke, cardiovascular disease and type 2 diabetes is staggering [1,2]. A better understanding of metabolic homeostatic pathways will provide us with insights into the biological mechanisms of obesity and how to fundamentally address this epidemic [3-6]. In mammals, energy balance is maintained via a homeostatic system involving both peripheral and central melanocortin systems; changes in body weight reflect an unbalance of the energetic state [7-9]. Although the primary cause of obesity is unknown, there is significant effort to understand the role of the central melanocortin pathway in the brain as it has been shown that deficiency of proopiomelanocortin (POMC) [10,11] and melanocortin 4 receptors (MC4R) [12-15] in both rodents and humans results in severe hyperphagia and obesity [16-23]. In this review, we will summarize how the central melanocortin pathway helps regulate body mass and adiposity within a 'healthy' range through the 'nutrient sensing' network [24-28]. This article is part of a Special Issue entitled: Melanocortin Receptors - edited by Ya-Xiong Tao.

PTP1B deficiency improves hypothalamic insulin sensitivity resulting in the attenuation of AgRP mRNA expression under high-fat diet conditions

Hypothalamic insulin receptor signaling regulates energy balance and glucose homeostasis via agouti-related protein (AgRP). While protein tyrosine phosphatase 1B (PTP1B) is classically known to be a negative regulator of peripheral insulin signaling by dephosphorylating both insulin receptor β (IRβ) and insulin receptor substrate, the role of PTP1B in hypothalamic insulin signaling remains to be fully elucidated. In the present study, we investigated the role of PTP1B in hypothalamic insulin signaling using PTP1B deficient (KO) mice in vivo and ex vivo. For the in vivo study, hypothalamic insulin resistance induced by a high-fat diet (HFD) improved in KO mice compared to wild-type (WT) mice. Hypothalamic AgRP mRNA expression levels were also significantly decreased in KO mice independent of body weight changes. In an ex vivo study using hypothalamic organotypic cultures, insulin treatment significantly increased the phosphorylation of both IRβ and Akt in the hypothalamus of KO mice compared to WT mice, and also significantly decreased AgRP mRNA expression levels in KO mice. While incubation with inhibitors of phosphatidylinositol-3 kinase (PI3K) had no effect on basal levels of Akt phosphorylation, these suppressed insulin induction of Akt phosphorylation to almost basal levels in WT and KO mice. The inhibition of the PI3K-Akt pathway blocked the downregulation of AgRP mRNA expression in KO mice treated with insulin. These data suggest that PTP1B acts on the hypothalamic insulin signaling via the PI3K-Akt pathway. Together, our results suggest a deficiency of PTP1B improves hypothalamic insulin sensitivity resulting in the attenuation of AgRP mRNA expression under HFD conditions.

Deficiency of PTP1B Attenuates Hypothalamic Inflammation via Activation of the JAK2-STAT3 Pathway in Microglia

Protein tyrosine phosphatase 1B (PTP1B) regulates leptin signaling in hypothalamic neurons via the JAK2-STAT3 pathway. PTP1B has also been implicated in the regulation of inflammation in the periphery. However, the role of PTP1B in hypothalamic inflammation, which is induced by a high-fat diet (HFD), remains to be elucidated. Here, we showed that STAT3 phosphorylation (p-STAT3) was increased in microglia in the hypothalamic arcuate nucleus of PTP1B knock-out mice (KO) on a HFD, accompanied by decreased Tnf and increased Il10 mRNA expression in the hypothalamus compared to wild-type mice (WT). In hypothalamic organotypic cultures, incubation with TNFα led to increased p-STAT3, accompanied by decreased Tnf and increased Il10 mRNA expression, in KO compared to WT. Incubation with p-STAT3 inhibitors or microglial depletion eliminated the differences in inflammation between genotypes. These data indicate an important role of JAK2-STAT3 signaling negatively regulated by PTP1B in microglia, which attenuates hypothalamic inflammation under HFD conditions.

Can We Selectively Reduce Appetite for Energy-Dense Foods? An Overview of Pharmacological Strategies for Modification of Food Preference Behavior

Excessive intake of food, especially palatable and energy-dense carbohydrates and fats, is largely responsible for the growing incidence of obesity worldwide. Although there are a number of candidate antiobesity drugs, only a few of them have been proven able to inhibit appetite for palatable foods without the concurrent reduction in regular food consumption. In this review, we discuss the interrelationships between homeostatic and hedonic food intake control mechanisms in promoting overeating with palatable foods and assess the potential usefulness of systemically administered pharmaceuticals that impinge on the endogenous cannabinoid, opioid, aminergic, cholinergic, and peptidergic systems in the modification of food preference behavior. Also, certain dietary supplements with the potency to reduce specifically palatable food intake are presented. Based on human and animal studies, we indicate the most promising therapies and agents that influence the effectiveness of appetite-modifying drugs. It should be stressed, however, that most of the data included in our review come from preclinical studies; therefore, further investigations aimed at confirming the effectiveness and safety of the aforementioned medications in the treatment of obese humans are necessary.

Epigenomic and metabolic responses of hypothalamic POMC neurons to gestational nicotine exposure in adult offspring

Background

Epidemiological and animal studies have reported that prenatal nicotine exposure (PNE) leads to obesity and type-2 diabetes in offspring. Central leptin-melanocortin signaling via hypothalamic arcuate proopiomelanocortin (POMC) neurons is crucial for the regulation of energy and glucose balance. Furthermore, hypothalamic POMC neurons were recently found to mediate the anorectic effects of nicotine through activation of acetylcholine receptors. Here, we hypothesized that PNE impairs leptin-melanocortinergic regulation of energy balance in first-generation offspring by altering expression of long non-coding RNAs (lncRNAs) putatively regulating development and/or function of hypothalamic POMC neurons.

Methods

C57BL/6J females were exposed ad libitum to nicotine through drinking water and crossed with C57BL/6J males. Nicotine exposure was sustained during pregnancy and discontinued at parturition. Offspring development was monitored from birth into adulthood. From the age of 8 weeks, central leptin-melanocortin signaling, diabetes, and obesity susceptibility were assessed in male offspring fed a low-fat or high-fat diet for 16 weeks. Nicotine-exposed and non-exposed C57BL/6J females were also crossed with C57BL/6J males expressing the enhanced green fluorescent protein specifically in POMC neurons. Transgenic male offspring were subjected to laser microdissections and RNA sequencing (RNA-seq) analysis of POMC neurons for determination of nicotine-induced gene expression changes and regulatory lncRNA/protein-coding gene interactions.

Results

Contrary to expectation based on previous studies, PNE did not impair but rather enhanced leptin-melanocortinergic regulation of energy and glucose balance via POMC neurons in offspring. RNA-seq of laser microdissected POMC neurons revealed only one consistent change, upregulation of Gm15851, a lncRNA of yet unidentified function, in nicotine-exposed offspring. RNA-seq further suggested 82 cis-regulatory lncRNA/protein-coding gene interactions, 19 of which involved coding genes regulating neural development and/or function, and revealed expression of several previously unidentified metabolic, neuroendocrine, and neurodevelopment pathways in POMC neurons.

Conclusions

PNE does not result in obesity and type 2 diabetes but instead enhances leptin-melanocortinergic feeding and body weight regulation via POMC neurons in adult offspring. PNE leads to selective upregulation of Gm15851, a lncRNA, in adult offspring POMC neurons. POMC neurons express several lncRNAs and pathways possibly regulating POMC neuronal development and/or function.

Electronic supplementary material

The online version of this article (doi:10.1186/s13073-016-0348-2) contains supplementary material, which is available to authorized users.

Pyridoxine Supplementation Improves the Activity of Recombinant Glutamate Decarboxylase and the Enzymatic Production of Gama-Aminobutyric Acid

Glutamate decarboxylase (GAD) catalyzes the irreversible decarboxylation of L-glutamate to the valuable food supplement γ-aminobutyric acid (GABA). In this study, GAD from Escherichia coli K12, a pyridoxal phosphate (PLP)-dependent enzyme, was overexpressed in E. coli. The GAD produced in media supplemented with 0.05 mM soluble vitamin B₆ analog pyridoxine hydrochloride (GAD-V) activity was 154.8 U mL^-1, 1.8-fold higher than that of GAD obtained without supplementation (GAD-C). Purified GAD-V exhibited increased activity (193.4 U mg^-1, 1.5-fold higher than that of GAD-C), superior thermostability (2.8-fold greater than that of GAD-C), and higher k_cat/K_m (1.6-fold higher than that of GAD-C). Under optimal conditions in reactions mixtures lacking added PLP, crude GAD-V converted 500 g L^-1 monosodium glutamate (MSG) to GABA with a yield of 100%, and 750 g L^-1 MSG with a yield of 88.7%. These results establish the utility of pyridoxine supplementation and lay the foundation for large-scale enzymatic production of GABA.

Current concepts regarding developmental mechanisms in diabetic retinopathy in Taiwan

Diabetic retinopathy (DR) is one of the most feared complications of diabetes and is a leading cause of acquired blindness in working adults. The prevalence of undiagnosed diabetes in Taiwan is about 4%, and the annual incidence of T2D (Type 2 Diabetes) in Taiwan is 1.8% following the 1985 WHO criteria. Multiple mechanisms have been shown in T2DR with some signaling pathways, including the polyol pathway, PKC pathway, AGEs pathway, and MAPK pathway. However, the cause of vision loss in diabetic retinopathy is complex and remains incompletely understood. Herein, we try to fully understand the new concepts regarding hyperglycemia-induced biochemical pathways contributing to DR pathophysiology. Our work may be able to provide new strategies for the prevention and treatment of diabetic vascular complications.

Inhibiting neuroinflammation: The role and therapeutic potential of GABA in neuro-immune interactions

The central nervous system, once thought to be a site of immunological privilege, has since been found to harbour immunocompetent cells and to communicate with the peripheral nervous system. In the central nervous system (CNS), glial cells display immunological responses to pathological and physiological stimuli through pro- and anti-inflammatory cytokine and chemokine signalling, antigen presentation and the clearing of cellular debris through phagocytosis. While this neuroinflammatory signalling can act to reduce neuronal damage and comprises a key facet of CNS homeostasis, persistent inflammation or auto-antigen-mediated immunoreactivity can induce a positive feedback cycle of neuroinflammation that ultimately results in necrosis of glia and neurons. Persistent neuroinflammation has been recognised as a major pathological component of virtually all neurodegenerative diseases and has also been a focus of research into the pathology underlying psychiatric disorders. Thus, pharmacological strategies to curb the pathological effects of persistent neuroinflammation are of interest for many disorders of the CNS. Accumulating evidence suggests that GABAergic activities are closely bound to immune processes and signals, and thus the GABAergic neurotransmitter system might represent an important therapeutic target in modulating neuroinflammation. Here, we review evidence that inflammation induces changes in the GABA neurotransmitter system in the CNS and that GABAergic signalling exerts a reciprocal influence over neuroinflammatory processes. Together, the data support the hypothesis that the GABA system is a potential therapeutic target in the modulation of central inflammation.

AgRP Neuron-Specific Deletion of Glucocorticoid Receptor Leads to Increased Energy Expenditure and Decreased Body Weight in Female Mice on a High-Fat Diet

Agouti-related protein (AgRP) expressed in the arcuate nucleus is a potent orexigenic neuropeptide, which increases food intake and reduces energy expenditure resulting in increases in body weight (BW). Glucocorticoids, key hormones that regulate energy balance, have been shown in rodents to regulate the expression of AgRP. In this study, we generated AgRP-specific glucocorticoid receptor (GR)-deficient (knockout [KO]) mice. Female and male KO mice on a high-fat diet (HFD) showed decreases in BW at the age of 6 weeks compared with wild-type mice, and the differences remained significant until 16 weeks old. The degree of resistance to diet-induced obesity was more robust in female than in male mice. On a chow diet, the female KO mice showed slightly but significantly attenuated weight gain compared with wild-type mice after 11 weeks, whereas there were no significant differences in BW in males between genotypes. Visceral fat pad mass was significantly decreased in female KO mice on HFD, whereas there were no significant differences in lean body mass between genotypes. Although food intake was similar between genotypes, oxygen consumption was significantly increased in female KO mice on HFD. In addition, the uncoupling protein-1 expression in the brown adipose tissues was increased in KO mice. These data demonstrate that the absence of GR signaling in AgRP neurons resulted in increases in energy expenditure accompanied by decreases in adiposity in mice fed HFD, indicating that GR signaling in AgRP neurons suppresses energy expenditure under HFD conditions.

Brain signaling systems in the Type 2 diabetes and metabolic syndrome: promising target to treat and prevent these diseases

The changes in the brain signaling systems play an important role in etiology and pathogenesis of Type 2 diabetes mellitus (T2DM) and metabolic syndrome (MS), being a possible cause of these diseases. Therefore, their restoration at the early stages of T2DM and MS can be regarded as a promising way to treat and prevent these diseases and their complications. The data on the functional state of the brain signaling systems regulated by insulin, IGF-1, leptin, dopamine, serotonin, melanocortins and glucagon-like peptide-1, in T2DM and MS, are analyzed. The pharmacological approaches to restoration of these systems and improvement of insulin sensitivity, energy expenditure, lipid metabolism, and to prevent diabetic complications are discussed.

Hypothalamic inflammation and gliosis in obesity

PURPOSE OF REVIEW

Hypothalamic inflammation and gliosis are recently discovered mechanisms that may contribute to obesity pathogenesis. Current research in this area suggests that investigation of these central nervous system responses may provide opportunities to develop new weight loss treatments.

RECENT FINDINGS

In rodents, hypothalamic inflammation and gliosis occur rapidly with high-fat diet consumption prior to significant weight gain. In addition, sensitivity or resistance to diet-induced obesity in rodents generally correlates with the presence or absence of hypothalamic inflammation and reactive gliosis (brain response to injury). Moreover, functional interventions that increase or decrease inflammation in neurons and glia correspondingly alter diet-associated weight gain. However, some conflicting data have recently emerged that question the contribution of hypothalamic inflammation to obesity pathogenesis. Nevertheless, several studies have detected gliosis and disrupted connectivity in obese humans, highlighting the potential translational importance of this mechanism.

SUMMARY

There is growing evidence that obesity is associated with brain inflammation in humans, particularly in the hypothalamus where its presence may disrupt body weight control and glucose homeostasis. More work is needed to determine whether this response is common in human obesity and to what extent it can be manipulated for therapeutic benefit.

Neuroendocrine control of satiation

Abstract Eating is a simple behavior with complex functions. The unconscious neuroendocrine process that stops eating and brings a meal to its end is called satiation. Energy homeostasis is mediated accomplished through the control of meal size via satiation. It involves neural integrations of phasic negative-feedback signals related to ingested food and tonic signals, such as those related to adipose tissue mass. Energy homeostasis is accomplished through adjustments in meal size brought about by changes in these satiation signals. The best understood meal-derived satiation signals arise from gastrointestinal nutrient sensing. Gastrointestinal hormones secreted during the meal, including cholecystokinin, glucagon-like peptide 1, and PYY, mediate most of these. Other physiological signals arise from activation of metabolic-sensing neurons, mainly in the hypothalamus and caudal brainstem. We review both classes of satiation signal and their integration in the brain, including their processing by melanocortin, neuropeptide Y/agouti-related peptide, serotonin, noradrenaline, and oxytocin neurons. Our review is not comprehensive; rather, we discuss only what we consider the best-understood mechanisms of satiation, with a special focus on normally operating physiological mechanisms.

Obesity- and aging-induced excess of central transforming growth factor-β potentiates diabetic development via an RNA stress response

The brain, in particular the hypothalamus, plays a role in regulating glucose homeostasis; however, it remains unclear whether this organ is causally and etiologically involved in the development of diabetes. Here, we found that hypothalamic transforming growth factor-β (TGF-β) production is excessive under conditions of not only obesity but also aging, which are two general etiological factors of type 2 diabetes. Pharmacological and genetic approaches revealed that central TGF-β excess caused hyperglycemia and glucose intolerance independent of a change in body weight. Further, using cell-specific genetic analyses in vivo, we found that astrocytes and proopiomelanocortin neurons are responsible for the production and prodiabetic effect of central TGF-β, respectively. Mechanistically, TGF-β excess induced a hypothalamic RNA stress response, resulting in accelerated mRNA decay of IκBα, an inhibitor of proinflammatory nuclear factor-κB. These results reveal an atypical, mRNA metabolism-driven hypothalamic nuclear factor-κB activation, a mechanism that links obesity as well as aging to hypothalamic inflammation and ultimately to type 2 diabetes.

Hypothalamic Inflammation: Is There Evidence for Human Obesity?

With increasing awareness of the obesity epidemic have come research efforts to understand the pathophysiology of body weight and appetite regulation. Clinical trials of diet-induced weight loss demonstrate the difficulty of achieving long term success in obese and overweight individuals, leading investigators to examine the question of what mechanisms makes weight loss so difficult. This has lead to a greater focus on neurologic and hormonal reasons that could explain why maintenance of lost weight is so challenging. Injury to the hypothalamic areas known to play a role in feeding and body weight regulation is being studied. Mechanisms of hypothalamic injury include increased inflammation, gliosis/scarring, and apoptosis of anorexigenic neurons in rodent models of diet induced obesity. Although there is evidence of hypothalamic damage due to interference of cell signaling and eventual loss of weight regulating neurons in rodent models, there is limited data thus far on whether we can apply this mechanism of injury to human obesity.

Mitogen-activated protein kinase phosphatase 1 negatively regulates MAPK signaling in mouse hypothalamus

Mitogen-activated protein kinase phosphatase 1 (MKP-1) is shown to negatively regulate MAPK signaling in various peripheral tissues as well as the central nervous system such as cortex, striatum and hippocampus. In this study, we examined whether MKP-1 regulates MAPK signaling in the mouse hypothalamus. Intraperitoneal injection of TNFα significantly increased MKP-1 mRNA expression in paraventricular and arcuate nuclei in the hypothalamus. TNFα treatment induced increases in MKP-1 expression at both mRNA and protein levels, accompanied by the inactivation of MAPK signaling in mouse hypothalamic explants. Inhibition of MKP-1 by its inhibitor or siRNA increased MAPK activity in the explants. Our data indicate that MKP-1 negatively regulates MAPK signaling in the mouse hypothalamus.

Hypothalamic eIF2α signaling regulates food intake

The reversible phosphorylation of the α subunit of eukaryotic initiation factor 2 (eIF2α) is a highly conserved signal implicated in the cellular adaptation to numerous stresses such as the one caused by amino acid limitation. In response to dietary amino acid deficiency, the brain-specific activation of the eIF2α kinase GCN2 leads to food intake inhibition. We report here that GCN2 is rapidly activated in the mediobasal hypothalamus (MBH) after consumption of a leucine-deficient diet. Furthermore, knockdown of GCN2 in this particular area shows that MBH GCN2 activity controls the onset of the aversive response. Importantly, pharmacological experiments demonstrate that the sole phosphorylation of eIF2α in the MBH is sufficient to regulate food intake. eIF2α signaling being at the crossroad of stress pathways activated in several pathological states, our study indicates that hypothalamic eIF2α phosphorylation could play a critical role in the onset of anorexia associated with certain diseases.