Central insulin and leptin-mediated autonomic control of glucose homeostasis

Neuron stress-related genes serve as new biomarkers in hypothalamic tissue following high fat diet

Objective

Energy homeostasis is modulated by the hypothalamic is essential for obesity progression, however, the gene expression profiling remains to be fully understood.

Methods

GEO datasets were downloaded from the GEO website and analyzed by the R packages to obtain the DEGs. And, the WGCNA analysis and PPI networks of co-expressed DEGs were designed using STRING to get key genes. In addition, the single-cell sequencing datasets and GTEx database were utilized to receive the neuron-stress genes from the key genes. Further, high-fat diet (HFD)-induced hypothalamic tissue of mice was used as an animal model to validate the mRNA up-regulation of neuron-stress genes. In addition, the Bmi1 gene was identified as a hub gene through the LASSO model and nomogram analysis. Western blot confirmed the high expression of Bmi1 in hypothalamic tissue of HFD mice and PA-stimulated microglia. Immunofluorescence staining showed that HFD induced the activation of microglia and the expression of Bmi1 in hypothalamic tissue.

Results

We found that six genes (Sacm1l, Junb, Bmi1, Erbb4, Dkc1, and Suv39h1) are neuron stress-related genes and increased in the HFD-induced mice obesity model, Bmi1gene was identified as a key genes that can reflect the pathophysiology of obesity.

Conclusions

Our research depicted a comprehensive activation map of cell abnormality in the obese hypothalamus and Bim1 may be a diagnostic marker in the clinic, which provides a new perspective and basis for investigating the pathogenesis of obesity.

The insulin resistant brain: impact on whole-body metabolism and body fat distribution

Insulin exerts its actions not only on peripheral organs but is also transported into the brain where it performs distinct functions in various brain regions. This review highlights recent advancements in our understanding of insulin's actions within the brain, with a specific emphasis on investigations in humans. It summarises current knowledge on the transport of insulin into the brain. Subsequently, it showcases robust evidence demonstrating the existence and physiological consequences of brain insulin action, while also introducing the presence of brain insulin resistance in humans. This pathophysiological condition goes along with an impaired acute modulation of peripheral metabolism in response to brain insulin action, particularly in the postprandial state. Furthermore, brain insulin resistance has been associated with long-term adiposity and an unfavourable adipose tissue distribution, thus implicating it in the pathogenesis of subgroups of obesity and (pre)diabetes that are characterised by distinct patterns of body fat distribution. Encouragingly, emerging evidence suggests that brain insulin resistance could represent a treatable entity, thereby opening up novel therapeutic avenues to improve systemic metabolism and enhance brain functions, including cognition. The review closes with an outlook towards prospective research directions aimed at further elucidating the clinical implications of brain insulin resistance. It emphasises the critical need to establish feasible diagnostic measures and effective therapeutic interventions.

Crosstalk between neurological, cardiovascular, and lifestyle disorders: insulin and lipoproteins in the lead role

Insulin resistance and impaired lipoprotein metabolism contribute to a plethora of metabolic and cardiovascular disorders. These alterations have been extensively linked with poor lifestyle choices, such as consumption of a high-fat diet, smoking, stress, and a redundant lifestyle. Moreover, these are also known to increase the co-morbidity of diseases like Type 2 diabetes mellitus and atherosclerosis. Under normal physiological conditions, insulin and lipoproteins exert a neuroprotective role in the central nervous system. However, the tripping of balance between the periphery and center may alter the normal functioning of the brain and lead to neurological disorders such as Alzheimer's disease, Parkinson's disease, stroke, depression, and multiple sclerosis. These neurological disorders are further characterized by certain behavioral and molecular changes that show consistent overlap with alteration in insulin and lipoprotein signaling pathways. Therefore, targeting these two mechanisms not only reveals a way to manage the co-morbidities associated with the circle of the metabolic, central nervous system, and cardiovascular disorders but also exclusively work as a disease-modifying therapy for neurological disorders. In this review, we summarize the role of insulin resistance and lipoproteins in the progression of various neurological conditions and discuss the therapeutic options currently in the clinical pipeline targeting these two mechanisms; in addition, challenges faced in designing these therapeutic approaches have also been touched upon briefly.

Estrogenic Action in Stress-Induced Neuroendocrine Regulation of Energy Homeostasis

Estrogens are among important contributing factors to many sex differences in neuroendocrine regulation of energy homeostasis induced by stress. Research in this field is warranted since chronic stress-related psychiatric and metabolic disturbances continue to be top health concerns, and sex differences are witnessed in these aspects. For example, chronic stress disrupts energy homeostasis, leading to negative consequences in the regulation of emotion and metabolism. Females are known to be more vulnerable to the psychological consequences of stress, such as depression and anxiety, whereas males are more vulnerable to the metabolic consequences of stress. Sex differences that exist in the susceptibility to various stress-induced disorders have led researchers to hypothesize that gonadal hormones are regulatory factors that should be considered in stress studies. Further, estrogens are heavily recognized for their protective effects on metabolic dysregulation, such as anti-obesogenic and glucose-sensing effects. Perturbations to energy homeostasis using laboratory rodents, such as physiological stress or over-/under- feeding dietary regimen prevalent in today’s society, offer hints to the underlying mechanisms of estrogenic actions. Metabolic effects of estrogens primarily work through estrogen receptor α (ERα), which is differentially expressed between the sexes in hypothalamic nuclei regulating energy metabolism and in extrahypothalamic limbic regions that are not typically associated with energy homeostasis. In this review, we discuss estrogenic actions implicated in stress-induced sex-distinct metabolic disorders.

A multidimensional functional fitness score has a stronger association with type 2 diabetes than obesity parameters in cross sectional data

Objectives

We examine here the association of multidimensional functional fitness with type 2 diabetes mellitus (T2DM) as compared to anthropometric indices of obesity such as body mass index (BMI) and waist to hip ratio (WHR) in a sample of Indian population.

Research design and method

We analysed retrospective data of 663 volunteer participants (285 males and 378 females between age 28 and 84), from an exercise clinic in which every participant was required to undergo a health related physical fitness (HRPF) assessment consisting of 15 different tasks examining 8 different aspects of functional fitness.

Results

The odds of being diabetic in the highest quartile of BMI were not significantly higher than that in the lowest quartile in either of the sexes. The odds of being a diabetic in the highest WHR quartile were significantly greater than the lowest quartile in females (OR = 4.54 (1.95, 10.61) as well as in males (OR = 3.81 (1.75, 8.3). In both sexes the odds of being a diabetic were significantly greater in the lowest quartile of HRPF score than the highest (males OR = 10.52 (4.21, 26.13); females OR = 10.50 (3.53, 31.35)). After removing confounding, the predictive power of HRPF was significantly greater than that of WHR. HRPF was negatively correlated with WHR, however for individuals that had contradicting HRPF and WHR based predictions, HRPF was the stronger predictor of T2DM.

Conclusion

The association of multidimensional functional fitness score with type 2 diabetes was significantly stronger than obesity parameters in a cross sectional self-selected sample from an Indian city.

Immunity and the carotid body: implications for metabolic diseases

Neuro-immune communication has gained enormous interest in recent years due to increasing knowledge of the way in which the brain coordinates functional alterations in inflammatory and autoimmune responses, and the mechanisms of neuron-immune cell interactions in the context of metabolic diseases such as obesity and type 2 diabetes. In this review, we will explain how this relationship between the nervous and immune system impacts the pro- and anti-inflammatory pathways with specific reference to the hypothalamus-pituitary-adrenal gland axis and the vagal reflex and will explore the possible involvement of the carotid body (CB) in the neural control of inflammation. We will also highlight the mechanisms of vagal anti-inflammatory reflex control of immunity and metabolism, and the consequences of functional disarrangement of this reflex in settlement and development of metabolic diseases, with special attention to obesity and type 2 diabetes. Additionally, the role of CB in the interplay between metabolism and immune responses will be discussed, with specific reference to the different stimuli that promote CB activation and the balance between sympathetic and parasympathetic in this context. In doing so, we clarify the multivarious neuronal reflexes that coordinate tissue-specific responses (gut, pancreas, adipose tissue and liver) critical to metabolic control, and metabolic disease settlement and development. In the final section, we will summarize how electrical modulation of the carotid sinus nerve may be utilized to adjust these reflex responses and thus control inflammation and metabolic diseases, envisioning new therapeutics horizons.

[Role of leptin and nuclear receptor PPARγ in PCOS pathogenesis]

Polycystic ovary syndrome (PCOS) is the most common cause of female endocrine infertility. Insulin resistanсе is supposed to be one of the essential factors of this disease pathways. At the same time, the mechanisms of PCOS development in insulin-resistant patients have not been completely established. Leptin and Peroxisome Proliferator-Activated Receptor γ(PPARγ) are involved in carbohydrate metabolism and reproduction function regulation. It indicates that leptin and PPARγ possibly play a role in the pathways of PCOS. This article is a review of publications on this issue. The purpose of this review was to systematize the available information on the molecular mechanisms that determine the role of leptin and PPARγ in the development of PCOS. The literature search was carried out from 04/05/2020 to 05/17/2020 using the scientific literature databases: NCBI PubMed (foreign sources) and Cyberleninka (domestic sources). We analyzed publications for the period 1990-2020.The review presents the current understanding of the possible role of leptin and PPARγ in the regulation of endocrine, immune systems, and reproductive function, as well as in the development of PCOS. Currently, no studies cover the mechanisms of interaction between leptin and PPARγ in the pathways of this syndrome. The available studies indicating the individual contribution and association of leptin and PPARγ with PCOS are conflicting and have many limitations. Therefore, more studies of direct and indirect interaction of leptin and PPARγ, as well as their role in PCOS pathways, are needed.

High Fat Rodent Models of Type 2 Diabetes: From Rodent to Human

Poor dietary habits contribute to increased incidences of obesity and related co-morbidities, such as type 2 diabetes (T2D). The biological, genetic, and pathological implications of T2D, are commonly investigated using animal models induced by a dietary intervention. In spite of significant research contributions, animal models have limitations regarding the translation to human pathology, which leads to questioning their clinical relevance. Important considerations include diet-specific effects on whole organism energy balance and glucose and insulin homeostasis, as well as tissue-specific changes in insulin and glucose tolerance. This review will examine the T2D-like phenotype in rodents resulting from common diet-induced models and their relevance to the human disease state. Emphasis will be placed on the disparity in percentages and type of dietary fat, the duration of intervention, and whole organism and tissue-specific changes in rodents. An evaluation of these models will help to identify a diet-induced rodent model with the greatest clinical relevance to the human T2D pathology. We propose that a 45% high-fat diet composed of approximately one-third saturated fats and two-thirds unsaturated fats may provide a diet composition that aligns closely to average Western diet macronutrient composition, and induces metabolic alterations mirrored by clinical populations.

The endoplasmic reticulum stress-autophagy pathway controls hypothalamic development and energy balance regulation in leptin-deficient neonates

Obesity is associated with the activation of cellular responses, such as endoplasmic reticulum (ER) stress. Here, we show that leptin-deficient ob/ob mice display elevated hypothalamic ER stress as early as postnatal day 10, i.e., prior to the development of obesity in this mouse model. Neonatal treatment of ob/ob mice with the ER stress-relieving drug tauroursodeoxycholic acid (TUDCA) causes long-term amelioration of body weight, food intake, glucose homeostasis, and pro-opiomelanocortin (POMC) projections. Cells exposed to ER stress often activate autophagy. Accordingly, we report that in vitro induction of ER stress and neonatal leptin deficiency in vivo activate hypothalamic autophagy-related genes. Furthermore, genetic deletion of autophagy in pro-opiomelanocortin neurons of ob/ob mice worsens their glucose homeostasis, adiposity, hyperphagia, and POMC neuronal projections, all of which are ameliorated with neonatal TUDCA treatment. Together, our data highlight the importance of early life ER stress-autophagy pathway in influencing hypothalamic circuits and metabolic regulation.

Diet-induced DNA methylation within the hypothalamic arcuate nucleus and dysregulated leptin and insulin signaling in the pathophysiology of obesity

Obesity rates continue to rise in an unprecedented manner in what could be the most rapid population‐scale shift in human phenotype ever to occur. Increased consumption of unhealthy, calorie‐dense foods, coupled with sedentary lifestyles, is the main factor contributing to a positive energy balance and the development of obesity. Leptin and insulin are key hormones implicated in pathogenesis of this disorder and are crucial for controlling whole‐body energy homeostasis. Their respective function is mediated by the counterbalance of anorexigenic and orexigenic neurons located within the hypothalamic arcuate nucleus. Dysregulation of leptin and insulin signaling pathways within this brain region may contribute not only to the development of obesity, but also systemically affect the peripheral organs, thereby manifesting as metabolic diseases. Although the exact mechanisms detailing how these hypothalamic nuclei contribute to disease pathology are still unclear, increasing evidence suggests that altered DNA methylation may be involved. This review evaluates animal studies that have demonstrated diet‐induced DNA methylation changes in genes that regulate energy homeostasis within the arcuate nucleus, and elucidates possible mechanisms causing hypothalamic leptin and insulin resistance leading to the development of obesity and metabolic diseases.

Sympathetic Denervation of the Common Hepatic Artery Lessens Glucose Intolerance in the Fat- and Fructose-Fed Dog

This study assessed the effectiveness of surgical sympathetic denervation of the common hepatic artery (CHADN) in improving glucose tolerance. CHADN eliminated norepinephrine content in the liver and partially decreased it in the pancreas and the upper gut. We assessed oral glucose tolerance at baseline and after 4 weeks of high-fat high-fructose (HFHF) feeding. Dogs were then randomized to sham surgery (SHAM) (n = 9) or CHADN surgery (n = 11) and retested 2.5 or 3.5 weeks later while still on the HFHF diet. CHADN improved glucose tolerance by ∼60% in part because of enhanced insulin secretion, as indicated by an increase in the insulinogenic index. In a subset of dogs (SHAM, n = 5; CHADN, n = 6), a hyperinsulinemic-hyperglycemic clamp was used to assess whether CHADN could improve hepatic glucose metabolism independent of a change in insulin release. CHADN reduced the diet-induced defect in net hepatic glucose balance by 37%. In another subset of dogs (SHAM, n = 4; CHADN, n = 5) the HFHF diet was continued for 3 months postsurgery and the improvement in glucose tolerance caused by CHADN continued. In conclusion, CHADN has the potential to enhance postprandial glucose clearance in states of diet-induced glucose intolerance.

Metabolomic profiles and development of metabolic risk during the pubertal transition: a prospective study in the ELEMENT Project

OBJECTIVES

(1) Examine associations of a branched-chain amino acid (BCAA) metabolite pattern with metabolic risk across adolescence; (2) use Least Absolute Shrinkage and Selection Operator (LASSO) to identify novel metabolites of metabolic risk.

METHODS

We used linear regression to examine associations of a BCAA score with change (∆) in metabolic biomarkers over 5-year follow-up in 179 adolescents 8-14 years at baseline. Next, we applied LASSO, a regularized regression technique well suited for reduction of high-dimensional data, to identify metabolite predictors of ∆biomarkers.

RESULTS

In boys, the BCAA score corresponded with decreasing C-peptide, C-peptide-based insulin resistance (CP-IR), total cholesterol (TC), and low-density-lipoprotein cholesterol (LDL). In pubertal girls, the BCAA pattern corresponded with increasing C-peptide and leptin. LASSO identified asparagine as a predictor of decreasing C-peptide (β = -0.33) and CP-IR (β = -0.012), and acetyl-carnitine (β = 2.098), 4-hydroxyproline (β = -0.050), ornithine (β = -0.353), and α-aminoisobutyric acid (β = -0.793) as determinants of TC in boys. In girls, histidine was a negative determinant of TC (β = -0.033).

CONCLUSIONS

The BCAA pattern was associated with ∆glycemia and ∆lipids in a sex-specific manner. LASSO identified asparagine, which influences growth hormone secretion, as a determinant of decreasing C-peptide and CP-IR in boys, and metabolites on lipid metabolism pathways as determinants of decreasing cholesterol in both sexes.

Autonomic Regulation of Glucose Homeostasis: a Specific Role for Sympathetic Nervous System Activation

PURPOSE OF REVIEW

Cardiometabolic disorders such as obesity, metabolic syndrome and diabetes are increasingly common and associated with adverse cardiovascular outcomes. The mechanisms driving these developments are incompletely understood but likely to include autonomic dysregulation. The latest evidence for such a role is briefly reviewed here.

RECENT FINDINGS

Recent findings highlight the relevance of autonomic regulation in glucose metabolism and identify sympathetic activation, in concert with parasympathetic withdrawal, as a major contributor to the development of metabolic disorders and an important mediator of the associated adverse cardiovascular consequences. Methods targeting sympathetic overactivity using pharmacological and device-based approaches are available and appear as logical additional approaches to curb the burden of metabolic disorders and alleviate the associated morbidity from cardiovascular causes. While the available data are encouraging, the role of therapeutic inhibition of sympathetic overdrive in the prevention of the metabolic disorders and the associated adverse outcomes requires adequate testing in properly sized randomised controlled trials.

Augmented Insulin and Leptin Resistance of High Fat Diet-Fed APPswe/PS1dE9 Transgenic Mice Exacerbate Obesity and Glycemic Dysregulation

Alzheimer's disease (AD), a progressive neurodegenerative disease is highly associated with metabolic syndromes. We previously demonstrated that glycemic dysregulation and obesity are augmented in high fat diet (HFD)-treated APPswe/PS1dE9 (APP/PS1) transgenic mice. In the current study, the underlying mechanism mediating exacerbated metabolic stresses in HFD APP/PS1 transgenic mice was further examined. APP/PS1 mice developed insulin resistance and, consequently, impaired glucose homeostasis after 10 weeks on HFD. [18F]-2-fluoro-2-deoxy-d-glucose ([18F]-FDG) positron emission tomography showed that interscapular brown adipose tissue is vulnerable to HFD and AD-related pathology. Chronic HFD induced hyperphagia, with limited effects on basal metabolic rates in APP/PS1 transgenic mice. Excessive food intake may be caused by impairment of leptin signaling in the hypothalamus because leptin failed to suppress the food intake of HFD APP/PS1 transgenic mice. Leptin-induced pSTAT3 signaling in the arcuate nucleus was attenuated. Dysregulated energy homeostasis including hyperphagia and exacerbated obesity was elicited prior to the presence of the amyloid pathology in the hypothalamus of HFD APP/PS1 transgenic mice; nevertheless, cortical neuroinflammation and the level of serum Aβ and IL-6 were significantly elevated. Our study demonstrates the pivotal role of AD-related pathology in augmenting HFD-induced insulin and leptin resistance and impairing hypothalamic regulation of energy homeostasis.

Central IGF1 improves glucose tolerance and insulin sensitivity in mice

Insulin-like growth factor 1 (IGF1) is a key factor for tissue growth and fuel metabolism. The potential function of central IGF1 remains unclear. We previously observed that IGF1 expression is increased in the hypothalamus of obese mice lacking STAT5 in the central nervous system (CNS). In this study, we explored the potential metabolic function of central IGF1 by intracerebroventricular (ICV) injection of IGF1, over-expression of central IGF1 by administering an adeno-associated virus (AAV), and ICV injection of an anti-IGF1 antibody. Mice that over-expressed central IGF1 displayed increased appetite, improved glucose tolerance and insulin sensitivity, decreased Pomc levels in the hypothalamus, and increased UCP1 expression in brown fat tissue. This is the first study demonstrating that central IGF1 regulates several important metabolic functions.

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.

Hypothalamic inflammation in obesity and metabolic disease

Over the last years, hypothalamic inflammation has been linked to the development and progression of obesity and its sequelae. There is accumulating evidence that this inflammation not only impairs energy balance but also contributes to obesity-associated insulin resistance. Elevated activation of key inflammatory mediators such as JNK and IκB kinase (IKK) occurs rapidly upon consumption of a high-fat diet, even prior to significant weight gain. This activation of hypothalamic inflammatory pathways results in the uncoupling of caloric intake and energy expenditure, fostering overeating and further weight gain. In addition, these inflammatory processes contribute to obesity-associated insulin resistance and deterioration of glucose metabolism via altered neurocircuit functions. An understanding of the contributions of different neuronal and non-neuronal cell types to hypothalamic inflammatory processes, and delineation of the differences and similarities between acute and chronic activation of these inflammatory pathways, will be critical for the development of novel therapeutic strategies for the treatment of obesity and metabolic syndrome.

Nervous System Expression of PPARγ and Mutant PPARγ Has Profound Effects on Metabolic Regulation and Brain Development

Peroxisome proliferator activated receptor (PPARγ) is a nuclear receptor transcription factor that regulates adipogenesis and energy homeostasis. Recent studies suggest PPARγ may mediate some of its metabolic effects through actions in the brain. We used a Cre-recombinase-dependent (using Nestin^Cre) conditionally activatable transgene expressing either wild-type (WT) or dominant-negative (P467L) PPARγ to examine mechanisms by which PPARγ in the nervous system controls energy balance. Inducible expression of PPARγ was evident throughout the brain. Expression of 2 PPARγ target genes, aP2 and CD36, was induced by WT but not P467L PPARγ in the brain. Surprisingly, Nes^Cre/PPARγ-WT mice exhibited severe microcephaly and brain malformation, suggesting that PPARγ can modulate brain development. On the contrary, Nes^Cre/PPARγ-P467L mice exhibited blunted weight gain to high-fat diet, which correlated with a decrease in lean mass and tissue masses, accompanied by elevated plasma GH, and depressed plasma IGF-1, indicative of GH resistance. There was no expression of the transgene in the pancreas but both fasting plasma glucose, and fed and fasted plasma insulin levels were markedly decreased. Nes^Cre/PPARγ-P467L mice fed either control diet or high-fat diet displayed impaired glucose tolerance yet exhibited increased sensitivity to exogenous insulin and increased insulin receptor signaling in white adipose tissue, liver, and skeletal muscle. These observations support the concept that alterations in PPARγ-driven mechanisms in the nervous system play a role in the regulation of growth and glucose metabolic homeostasis.

Diet-Induced Maternal Obesity Alters Insulin Signalling in Male Mice Offspring Rechallenged with a High-Fat Diet in Adulthood

Modern lifestyle has resulted in an increase in the prevalence of obesity and its comorbidities in pregnant women and the young population. It has been well established that the consumption of a high-fat diet (HFD) has many direct effects on glucose metabolism. However, it is important to assess whether maternal consumption of a HFD during critical periods of development can lead to metabolic changes in the offspring metabolism. This study evaluated the potential effects of metabolic programming on the impairment of insulin signalling in recently weaned offspring from obese dams. Additionally, we investigated if early exposure to an obesogenic environment could exacerbate the impairment of glucose metabolism in adult life in response to a HFD. Swiss female mice were fed with Standard Chow (SC) or a HFD during gestation and lactation and tissues from male offspring were analysed at d28 and d82. Offspring from obese dams had greater weight gain and higher adiposity and food intake than offspring from control dams. Furthermore, they showed impairment in insulin signalling in central and peripheral tissues, which was associated with the activation of inflammatory pathways. Adipose tissue was ultimately the most affected in adult offspring after HFD rechallenge; this may have contributed to the metabolic deregulation observed. Overall, our results suggest that diet-induced maternal obesity leads to increased susceptibility to obesity and impairment of insulin signalling in offspring in early and late life that cannot be reversed by SC consumption, but can be aggravated by HFD re-exposure.

Neuroinflammatory and autonomic mechanisms in diabetes and hypertension

Interdisciplinary studies in the research fields of endocrinology and immunology show that obesity-associated overnutrition leads to neuroinflammatory molecular changes, in particular in the hypothalamus, chronically causing various disorders known as elements of metabolic syndrome. In this process, neural or hypothalamic inflammation impairs the neuroendocrine and autonomic regulation of the brain over blood pressure and glucose homeostasis as well as insulin secretion, and elevated sympathetic activation has been appreciated as a critical mediator. This review describes the involved physiology and mechanisms, with a focus on glucose and blood pressure balance, and suggests that neuroinflammation employs the autonomic nervous system to mediate the development of diabetes and hypertension.

Leptin Controls Parasympathetic Wiring of the Pancreas during Embryonic Life

The autonomic nervous system plays a critical role in glucose metabolism through both its sympathetic and parasympathetic branches, but the mechanisms that underlie the development of the autonomic innervation of the pancreas remain poorly understood. Here, we report that cholinergic innervation of pancreatic islets develops during mid-gestation under the influence of leptin. Leptin-deficient mice display a greater cholinergic innervation of pancreatic islets beginning in embryonic life, and this increase persists into adulthood. Remarkably, a single intracerebroventricular injection of leptin in embryos caused a permanent reduction in parasympathetic innervation of pancreatic β cells and long-term impairments in glucose homeostasis. These developmental effects of leptin involve a direct inhibitory effect on the outgrowth of preganglionic axons from the hindbrain. These studies reveal an unanticipated regulatory role of leptin on the parasympathetic nervous system during embryonic development and may have important implications for our understanding of the early mechanisms that contribute to diabetes.

Hypothalamic-autonomic control of energy homeostasis

Regulation of energy homeostasis is tightly controlled by the central nervous system (CNS). Several key areas such as the hypothalamus and brainstem receive and integrate signals conveying energy status from the periphery, such as leptin, thyroid hormones, and insulin, ultimately leading to modulation of food intake, energy expenditure (EE), and peripheral metabolism. The autonomic nervous system (ANS) plays a key role in the response to such signals, innervating peripheral metabolic tissues, including brown and white adipose tissue (BAT and WAT), liver, pancreas, and skeletal muscle. The ANS consists of two parts, the sympathetic and parasympathetic nervous systems (SNS and PSNS). The SNS regulates BAT thermogenesis and EE, controlled by central areas such as the preoptic area (POA) and the ventromedial, dorsomedial, and arcuate hypothalamic nuclei (VMH, DMH, and ARC). The SNS also regulates lipid metabolism in WAT, controlled by the lateral hypothalamic area (LHA), VMH, and ARC. Control of hepatic glucose production and pancreatic insulin secretion also involves the LHA, VMH, and ARC as well as the dorsal vagal complex (DVC), via splanchnic sympathetic and the vagal parasympathetic nerves. Muscle glucose uptake is also controlled by the SNS via hypothalamic nuclei such as the VMH. There is recent evidence of novel pathways connecting the CNS and ANS. These include the hypothalamic AMP-activated protein kinase-SNS-BAT axis which has been demonstrated to be a key modulator of thermogenesis. In this review, we summarize current knowledge of the role of the ANS in the modulation of energy balance.

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.

Residual sympathetic tone is associated with reduced insulin sensitivity in patients with autonomic failure

PURPOSE

Parkinson disease, an α-synucleinopathy, is associated with reduced insulin sensitivity, impaired glucose tolerance, and diabetes mellitus. Importantly, these metabolic alterations have been shown to contribute to disease progression. The purpose of this study was to determine if reduced insulin sensitivity is also present in other α-synucleinopathies associated with autonomic failure.

METHODS

We studied 19 patients with multiple system atrophy and 26 patients with pure autonomic failure. For comparison, we studied 8 healthy controls matched for body mass index. Insulin sensitivity and beta cell function were calculated using fasting glucose and insulin levels according to the homeostatic model assessment 2. A multiple linear regression model was performed to determine factors that predict insulin sensitivity in autonomic failure.

RESULTS

There was a significant difference in insulin sensitivity among groups (P = 0.048). This difference was due to lower insulin sensitivity in multiple system atrophy patients: 64% [interquartile range (IQR), 43 to 117] compared to healthy controls 139% (IQR, 83 to 212), P = 0.032. The main factor that contributed to the reduced insulin sensitivity was the presence of supine hypertension and residual sympathetic tone.

CONCLUSIONS

Multiple system atrophy patients have reduced insulin sensitivity that is associated with residual sympathetic activation and supine hypertension. These patients may therefore be at high risk for development of impaired glucose tolerance and diabetes mellitus.

Leptin-induced mitochondrial fusion mediates hepatic lipid accumulation

BACKGROUND

Leptin alleviates metabolic conditions such as insulin resistance and obesity, although the precise mechanism of action is unclear. Mitochondrial fusion/fission states affect energy balance, but the association between mitochondrial fusion and lipid metabolism is also unknown. The aim of this study was to determine whether mitochondrial fusion/fission state regulates lipid accumulation and to understand the role of leptin in mitochondrial function and its mechanism of action in metabolic regulation.

METHODS

Primary mouse hepatocytes were isolated from C57BL/6J mice and treated with leptin (25 ng ml(-1)) for 3 days before determinations of mitochondrial morphology and fatty acid accumulation. Hyperglycemia in C57BL/6J mice was induced by providing a 30% fructose-rich diet (FRD) for 6 months, followed by intraperitoneal injections of leptin (1 mg kg(-1) per body weight) for 6 weeks (twice per week).

RESULTS

Leptin triggered mitochondrial fusion and alleviated high glucose-induced fatty acid accumulation in primary hepatocytes by promoting mitochondrial fusion-associated transcription factor peroxisome proliferative-activated receptor-α and co-activator peroxisome proliferative-activated receptor-γ co-activator (PGC)-1α. In turn, these activate the fusion protein mitofusin 1 (Mfn-1). RNA silencing of Mfn-1 or PGC-1 blocked the inhibitory effect of leptin. Leptin treatment also elevated liver Mfn-1 and PGC-1α and improved lipid profiles in FRD mice.

CONCLUSIONS

Mitochondrial fusion has a critical role in alleviating hepatic fatty acid accumulation. Leptin switches mitochondrial morphology via a PGC-1α-dependent pathway to improve hyperlipidemia.

Gut-brain connection: The neuroprotective effects of the anti-diabetic drug liraglutide

Long-acting glucagon-like peptide-1 (GLP-1) analogues marketed for type 2 diabetes (T2D) treatment have been showing positive and protective effects in several different tissues, including pancreas, heart or even brain. This gut secreted hormone plays a potent insulinotropic activity and an important role in maintaining glucose homeostasis. Furthermore, growing evidences suggest the occurrence of several commonalities between T2D and neurodegenerative diseases, insulin resistance being pointed as a main cause for cognitive decline and increased risk to develop dementia. In this regard, it has also been suggested that stimulation of brain insulin signaling may have a protective role against cognitive deficits. As GLP-1 receptors (GLP-1R) are expressed throughout the central nervous system and GLP-1 may cross the blood-brain-barrier, an emerging hypothesis suggests that they may be promising therapeutic targets against brain dysfunctional insulin signaling-related pathologies. Importantly, GLP-1 actions depend not only on the direct effect mediated by its receptor activation, but also on the gut-brain axis involving an exchange of signals between both tissues via the vagal nerve, thereby regulating numerous physiological functions (e.g., energy homeostasis, glucose-dependent insulin secretion, as well as appetite and weight control). Amongst the incretin/GLP-1 mimetics class of anti-T2D drugs with an increasingly described neuroprotective potential, the already marketed liraglutide emerged as a GLP-1R agonist highly resistant to dipeptidyl peptidase-4 degradation (thereby having an increased half-life) and whose systemic GLP-1R activity is comparable to that of native GLP-1. Importantly, several preclinical studies showed anti-apoptotic, anti-inflammatory, anti-oxidant and neuroprotective effects of liraglutide against T2D, stroke and Alzheimer disease (AD), whereas several clinical trials, demonstrated some surprising benefits of liraglutide on weight loss, microglia inhibition, behavior and cognition, and in AD biomarkers. Herein, we discuss the GLP-1 action through the gut-brain axis, the hormone’s regulation of some autonomic functions and liraglutide’s neuroprotective potential.

Integrative neurobiology of metabolic diseases, neuroinflammation, and neurodegeneration

Alzheimer's disease (AD) is a complex, multifactorial disease with a number of leading mechanisms, including neuroinflammation, processing of amyloid precursor protein (APP) to amyloid β peptide, tau protein hyperphosphorylation, relocalization, and deposition. These mechanisms are propagated by obesity, the metabolic syndrome and type-2 diabetes mellitus. Stress, sedentariness, dietary overconsumption of saturated fat and refined sugars, and circadian derangements/disturbed sleep contribute to obesity and related metabolic diseases, but also accelerate age-related damage and senescence that all feed the risk of developing AD too. The complex and interacting mechanisms are not yet completely understood and will require further analysis. Instead of investigating AD as a mono- or oligocausal disease we should address the disease by understanding the multiple underlying mechanisms and how these interact. Future research therefore might concentrate on integrating these by “systems biology” approaches, but also to regard them from an evolutionary medicine point of view. The current review addresses several of these interacting mechanisms in animal models and compares them with clinical data giving an overview about our current knowledge and puts them into an integrated framework.

Models and mechanisms for hippocampal dysfunction in obesity and diabetes

Clinical studies suggest that obesity and Type 2 (insulin-resistant) diabetes impair the structural integrity of medial temporal lobe regions involved in memory and confer greater vulnerability to neurological insults. While eliminating obesity and its endocrine comorbidities would be the most straightforward way to minimize cognitive risk, structural barriers to physical activity and the widespread availability of calorically dense, highly palatable foods will likely necessitate additional strategies to maintain brain health over the lifespan. Research in rodents has identified numerous correlates of hippocampal functional impairment in obesity and diabetes, with several studies demonstrating causality in subsequent mechanistic studies. This review highlights recent work on pathways and cell-cell interactions underlying the synaptic consequences of obesity, diabetes, or in models with both pathological conditions. Although the mechanisms vary across different animal models, immune activation has emerged as a shared feature of obesity and diabetes, with synergistic exacerbation of neuroinflammation in model systems with both conditions. This review discusses these findings with reference to the benefits of incorporating existing models from the fields of obesity and metabolic disease. Many transgenic lines with basal metabolic alterations or differential susceptibility to diet-induced obesity have yet to be characterized with respect to their cognitive and synaptic phenotype. Adopting these models, and building on the extensive knowledge base used to generate them, is a promising avenue for understanding interactions between peripheral disease states and neurodegenerative disorders.

Leptin and insulin act on POMC neurons to promote the browning of white fat

The primary task of white adipose tissue (WAT) is the storage of lipids. However, "beige" adipocytes also exist in WAT. Beige adipocytes burn fat and dissipate the energy as heat, but their abundance is diminished in obesity. Stimulating beige adipocyte development, or WAT browning, increases energy expenditure and holds potential for combating metabolic disease and obesity. Here, we report that insulin and leptin act together on hypothalamic neurons to promote WAT browning and weight loss. Deletion of the phosphatases PTP1B and TCPTP enhanced insulin and leptin signaling in proopiomelanocortin neurons and prevented diet-induced obesity by increasing WAT browning and energy expenditure. The coinfusion of insulin plus leptin into the CNS or the activation of proopiomelanocortin neurons also increased WAT browning and decreased adiposity. Our findings identify a homeostatic mechanism for coordinating the status of energy stores, as relayed by insulin and leptin, with the central control of WAT browning.

Apelin-13 enhances arcuate POMC neuron activity via inhibiting M-current

The hypothalamus is a key element of the neural circuits that control energy homeostasis. Specific neuronal populations within the hypothalamus are sensitive to a variety of homeostatic indicators such as circulating nutrient levels and hormones that signal circulating glucose and body fat content. Central injection of apelin secreted by adipose tissues regulates feeding and glucose homeostasis. However, the precise neuronal populations and cellular mechanisms involved in these physiological processes remain unclear. Here we examine the electrophysiological impact of apelin-13 on proopiomelanocortin (POMC) neuron activity. Approximately half of POMC neurons examined respond to apelin-13. Apelin-13 causes a dose-dependent depolarization. This effect is abolished by the apelin (APJ) receptor antagonist. POMC neurons from animals pre-treated with pertussis toxin still respond to apelin, whereas the Gβγ signaling inhibitor gallein blocks apelin-mediated depolarization. In addition, the effect of apelin is inhibited by the phospholipase C and protein kinase inhibitors. Furthermore, single-cell qPCR analysis shows that POMC neurons express the APJ receptor, PLC-β isoforms, and KCNQ subunits (2, 3 and 5) which contribute to M-type current. Apelin-13 inhibits M-current that is blocked by the KCNQ channel inhibitor. Therefore, our present data indicate that apelin activates APJ receptors, and the resultant dissociation of the Gαq heterotrimer triggers a Gβγ-dependent activation of PLC-β signaling that inhibits M-current.

Coexistence of angioedema alone with impaired glucose tolerance

BACKGROUND

Most patients with chronic spontaneous urticaria (CSU) exhibit recurrent angioedema. As of yet, the pathogenesis of angioedema in CSU is largely unclear, especially when angioedema occurs in patients who do not develop wheals. Over the past years, we and others have repeatedly observed that patients with recurrent angioedema alone exhibit impaired glucose tolerance.

AIM

To assess blood glucose levels and glucose tolerance in these patients and to compare the results to those of CSU patients who do not develop angioedema.

METHODS

A total of 29 patients with angioedema alone (15 women, mean age 43.2 ± 12.8 years) and 33 CSU patients (17 women, mean age 41.9 ± 17 years) were investigated and compared for clinical features and laboratory values, including fasting and random blood glucose levels, and glycated hemoglobin (HbA1c%). All patients were subjected to oral glucose tolerance testing (OGTT).

RESULTS

Fasting plasma glucose levels, random blood glucose levels and OGTT glucose levels were significantly higher in patients with angioedema alone as compared to CSU patients. Glucose tolerance was impaired in 17 of 29 patients with angioedema alone (58.6%) and only in 2 of 33 CSU patients (6.1%). Patients were found to have an increased risk of high glucose (OR 1.74) and HbA1c (OR 1.83) blood levels and of developing a high BMI (OR 1.97).

CONCLUSION

Recurrent angioedema in patients who do not develop wheals appears to be associated with impaired glucose tolerance and elevated blood glucose levels. We recommend blood glucose measurements in patients with recurrent angioedema alone.

Hypothalamic microinflammation: a common basis of metabolic syndrome and aging

Chronic microinflammation is a hallmark of many aging-related neurodegenerative diseases as well as metabolic syndrome-driven diseases. Recent research indicates that chronic caloric excess can lead to hypothalamic microinflammation, which in turn participates in the development and progression of metabolic syndrome disorders such as obesity, glucose intolerance, and hypertension. Additionally, it was recently shown that increasing age after young adulthood can cause hypothalamic microinflammation independently of nutritional status, mediating a central mechanism of systemic aging. Taken together, these findings suggest that the hypothalamus has a fundamental role, via hypothalamic microinflammation, in translating overnutrition and aging into complex outcomes. Here we summarize recent work and suggest a conceptual model in which hypothalamic microinflammation is a common mediator of metabolic syndrome and aging.

Central prolactin receptors (PRLRs) regulate hepatic insulin sensitivity in mice via signal transducer and activator of transcription 5 (STAT5) and the vagus nerve

AIMS/HYPOTHESIS

Recent studies have revealed the crucial role of the central nervous system (CNS), especially the hypothalamus, in the regulation of insulin sensitivity in peripheral tissues. The aim of our current study was to investigate the possible involvement of hypothalamic prolactin receptors (PRLRs) in the regulation of hepatic insulin sensitivity.

METHODS

We employed overexpression of PRLRs in mouse hypothalamus via intracerebroventricular injection of adenovirus expressing PRLR and inhibition of PRLRs via adenovirus expressing short-hairpin RNA (shRNA) specific for PRLRs in vivo. Selective hepatic vagotomy was employed to verify the important role of the vagus nerve in mediating signals from the brain to peripheral organs. In addition, a genetic insulin-resistant animal model, the db/db mouse, was used in our study to investigate the role of hypothalamic PRLRs in regulating whole-body insulin sensitivity.

RESULTS

Overexpression of PRLRs in the hypothalamus improved hepatic insulin sensitivity in mice and inhibition of hypothalamic PRLRs had the opposite effect. In addition, we demonstrated that hypothalamic PRLR-improved insulin sensitivity was significantly attenuated by inhibiting the activity of signal transducer and activator of transcription 5 (STAT5) in the CNS and by selective hepatic vagotomy. Finally, overexpression of PRLRs significantly ameliorated insulin resistance in db/db mice.

CONCLUSIONS/INTERPRETATION

Our study identifies a novel central pathway involved in the regulation of hepatic insulin sensitivity, mediated by hypothalamic PRLR/STAT5 signalling and the vagus nerve, thus demonstrating an important role for hypothalamic PRLRs under conditions of insulin resistance.

Dietary intakes and leptin concentrations

BACKGROUND

Leptin, a peptide contained 146 amino-acids, is mostly secreted from adipose tissue and it has a critical role on regulation of body weight, body fat mass, appetite, and food intakes. We tried to review the previous evidence regarding the effects of dietary intakes, including consumption of carbohydrates, fats and protein on concentrations of leptin concentration.

METHODS

We searched in PubMed search engine to January 2013 by using the following key words: dietary intake, diet, dietary fat, high-fat diet, dietary carbohydrate, high carbohydrate diet, dietary protein, high protein diet in combination with leptin, adipokine. Then, we recruited 35 articles to review in the present study.

RESULTS

It seems that beside the amount of fats, type of fatty acids have the key roles on circulating leptin concentration. Energy intake also significantly associated with the hormone. Studies regarding the association between carbohydrate intake and concentration of lepton have been reached to contradictory results. It seems that protein intake can increase the lepton activity.

CONCLUSION

Findings from several studies suggest that a diet display an important role on change the concentration of lepton.

The role of leptin in glucose homeostasis

The fat‐derived hormone, leptin, is well known to regulate body weight. However, there is now substantial evidence that leptin also plays a primary role in the regulation of glucose homeostasis, independent of actions on food intake, energy expenditure or body weight. As such, leptin might have clinical utility in treating hyperglycemia, particularly in conditions of leptin deficiency, such as lipodystrophy and diabetes mellitus. The mechanisms through which leptin modulates glucose metabolism have not been fully elucidated. Leptin receptors are widely expressed in peripheral tissues, including the endocrine pancreas, liver, skeletal muscle and adipose, and both direct and indirect leptin action on these tissues contributes to the control of glucose homeostasis. Here we review the role of leptin in glucose homeostasis, along with our present understanding of the mechanisms involved. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2012.00203.x, 2012)

Hepatic branch vagus nerve plays a critical role in the recovery of post-ischemic glucose intolerance and mediates a neuroprotective effect by hypothalamic orexin-A

Orexin-A (a neuropeptide in the hypothalamus) plays an important role in many physiological functions, including the regulation of glucose metabolism. We have previously found that the development of post-ischemic glucose intolerance is one of the triggers of ischemic neuronal damage, which is suppressed by hypothalamic orexin-A. Other reports have shown that the communication system between brain and peripheral tissues through the autonomic nervous system (sympathetic, parasympathetic and vagus nerve) is important for maintaining glucose and energy metabolism. The aim of this study was to determine the involvement of the hepatic vagus nerve on hypothalamic orexin-A-mediated suppression of post-ischemic glucose intolerance development and ischemic neuronal damage. Male ddY mice were subjected to middle cerebral artery occlusion (MCAO) for 2 h. Intrahypothalamic orexin-A (5 pmol/mouse) administration significantly suppressed the development of post-ischemic glucose intolerance and neuronal damage on day 1 and 3, respectively after MCAO. MCAO-induced decrease of hepatic insulin receptors and increase of hepatic gluconeogenic enzymes on day 1 after was reversed to control levels by orexin-A. This effect was reversed by intramedullary administration of the orexin-1 receptor antagonist, SB334867, or hepatic vagotomy. In the medulla oblongata, orexin-A induced the co-localization of cholin acetyltransferase (cholinergic neuronal marker used for the vagus nerve) with orexin-1 receptor and c-Fos (activated neural cells marker). These results suggest that the hepatic branch vagus nerve projecting from the medulla oblongata plays an important role in the recovery of post-ischemic glucose intolerance and mediates a neuroprotective effect by hypothalamic orexin-A.

Neonatal insulin action impairs hypothalamic neurocircuit formation in response to maternal high-fat feeding

Maternal metabolic homeostasis exerts long-term effects on the offspring's health outcomes. Here, we demonstrate that maternal high-fat diet (HFD) feeding during lactation predisposes the offspring for obesity and impaired glucose homeostasis in mice, which is associated with an impairment of the hypothalamic melanocortin circuitry. Whereas the number and neuropeptide expression of anorexigenic proopiomelanocortin (POMC) and orexigenic agouti-related peptide (AgRP) neurons, electrophysiological properties of POMC neurons, and posttranslational processing of POMC remain unaffected in response to maternal HFD feeding during lactation, the formation of POMC and AgRP projections to hypothalamic target sites is severely impaired. Abrogating insulin action in POMC neurons of the offspring prevents altered POMC projections to the preautonomic paraventricular nucleus of the hypothalamus (PVH), pancreatic parasympathetic innervation, and impaired glucose-stimulated insulin secretion in response to maternal overnutrition. These experiments reveal a critical timing, when altered maternal metabolism disrupts metabolic homeostasis in the offspring via impairing neuronal projections, and show that abnormal insulin signaling contributes to this effect.

Alterations in blood glucose and plasma glucagon concentrations during deep brain stimulation in the shell region of the nucleus accumbens in rats

Deep brain stimulation (DBS) of the nucleus accumbens (NAc) is an effective therapy for obsessive compulsive disorder (OCD) and is currently under investigation as a treatment for eating disorders. DBS of this area is associated with altered food intake and pharmacological treatment of OCD is associated with the risk of developing type 2 diabetes. Therefore we examined if DBS of the NAc-shell (sNAc) influences glucose metabolism. Male Wistar rats were subjected to DBS, or sham stimulation, for a period of 1 h. To assess the effects of stimulation on blood glucose and glucoregulatory hormones, blood samples were drawn before, during and after stimulation. Subsequently, all animals were used for quantitative assessment of Fos immunoreactivity in the lateral hypothalamic area (LHA) using computerized image analysis. DBS of the sNAc rapidly increased plasma concentrations of glucagon and glucose while sham stimulation and DBS outside the sNAc were ineffective. In addition, the increase in glucose was dependent on DBS intensity. In contrast, the DBS-induced increase in plasma corticosterone concentrations was independent of intensity and region, indicating that the observed DBS-induced metabolic changes were not due to corticosterone release. Stimulation of the sNAc with 200 μA increased Fos immunoreactivity in the LHA compared to sham or 100 μA stimulated animals. These data show that DBS of the sNAc alters glucose metabolism in a region- and intensity- dependent manner in association with neuronal activation in the LHA. Moreover, these data illustrate the need to monitor changes in glucose metabolism during DBS-treatment of OCD patients.

Pancreatic islet vasculature adapts to insulin resistance through dilation and not angiogenesis

Pancreatic islets adapt to insulin resistance through a complex set of changes, including β-cell hyperplasia and hypertrophy. To determine if islet vascularization changes in response to insulin resistance, we investigated three independent models of insulin resistance: ob/ob, GLUT4(+/-), and mice with high-fat diet-induced obesity. Intravital blood vessel labeling and immunocytochemistry revealed a vascular plasticity in which islet vessel area was significantly increased, but intraislet vessel density was decreased as the result of insulin resistance. These vascular changes were independent of islet size and were only observed within the β-cell core but not in the islet periphery. Intraislet endothelial cell fenestration, proliferation, and islet angiogenic factor/receptor expression were unchanged in insulin-resistant compared with control mice, indicating that islet capillary expansion is mediated by dilation of preexisting vessels and not by angiogenesis. We propose that the islet capillary dilation is modulated by endothelial nitric oxide synthase via complementary signals derived from β-cells, parasympathetic nerves, and increased islet blood flow. These compensatory changes in islet vascularization may influence whether β-cells can adequately respond to insulin resistance and prevent the development of diabetes.

Relation of leptin, ghrelin and inflammatory cytokines with body mass index in pulmonary tuberculosis patients with and without type 2 diabetes mellitus

BACKGROUND

Pulmonary tuberculosis (TB) patients often suffer from anorexia and poor nutrition, causing weight loss. The peptide hormones leptin and its counterpart ghrelin, acting in the regulation of food intake and fat utilization, play an important role in nutritional balance. This study aimed to investigate the association of blood concentrations of leptin, ghrelin and inflammatory cytokines with body mass index (BMI) in TB patients with and without type 2 diabetes mellitus (T2DM).

METHODS

BMI, biochemical parameters and plasma levels of leptin, ghrelin and inflammatory cytokines were measured before the start of treatment in 27 incident TB patients with T2DM, 21 TB patients and 23 healthy subjects enrolled in this study.

RESULTS

The levels of leptin were significantly higher in TB patients (35.2 ± 19.1 ng/ml) than TB+T2DM (12.6 ± 6.1 ng/ml) and control (16.1 ± 11.1 ng/ml) groups. The level of ghrelin was significantly lower in TB (119.9 ± 46.1 pg/ml) and non-significantly lower in TB+T2DM (127.7 ± 38.6 pg/ml) groups than control (191.6 ± 86.5 pg/ml) group. The levels of TNF-α were higher, while IFN-γ and IL-6 levels were lower in patients than in the control group. Leptin showed a negative correlation with BMI in TB (r=-0.622, p<0.05) and TB+T2DM (r= -0.654, p<0.05) groups, but a positive correlation with BMI in the control group (r=0.521, p<0.05). Contrary ghrelin showed a positive correlation with BMI in TB (r=0.695, p<0.05) and TB+T2DM (r= 0.199, p>0.05) groups, but negative correlation with BMI in the control (r=-0.693, p<0.05) group. Inflammatory cytokines were poorly correlated with BMI in this study. Only IFN-γ showed a significant negative correlation with BMI in the control group (r=-0.545, p<0.05).

CONCLUSIONS

This study may suggest that possible abnormalities in ghrelin and leptin regulation (high levels of leptin and low levels of ghrelin) may be associated with low BMI and may account for the poor nutrition associated with TB and TB+T2DM.

Neuroinflammatory basis of metabolic syndrome

Inflammatory reaction is a fundamental defense mechanism against threat towards normal integrity and physiology. On the other hand, chronic diseases such as obesity, type 2 diabetes, hypertension and atherosclerosis, have been causally linked to chronic, low-grade inflammation in various metabolic tissues. Recent cross-disciplinary research has led to identification of hypothalamic inflammatory changes that are triggered by overnutrition, orchestrated by hypothalamic immune system, and sustained through metabolic syndrome-associated pathophysiology. While continuing research is actively trying to underpin the identity and mechanisms of these inflammatory stimuli and actions involved in metabolic syndrome disorders and related diseases, proinflammatory IκB kinase-β (IKKβ), the downstream nuclear transcription factor NF-κB and some related molecules in the hypothalamus were discovered to be pathogenically significant. This article is to summarize recent progresses in the field of neuroendocrine research addressing the central integrative role of neuroinflammation in metabolic syndrome components ranging from obesity, glucose intolerance to cardiovascular dysfunctions.

Uncovering novel roles of nonneuronal cells in body weight homeostasis and obesity

Glial cells, which constitute more than 50% of the mass of the central nervous system and greatly outnumber neurons, are at the vanguard of neuroendocrine research in metabolic control and obesity. Historically relegated to roles of structural support and protection, diverse functions have been gradually attributed to this heterogeneous class of cells with their protagonism in crescendo in all areas of neuroscience during the past decade. However, this dramatic increase in attention bestowed upon glial cells has also emphasized our vast lack of knowledge concerning many aspects of their physiological functions, let alone their participation in numerous pathologies. This minireview focuses on the recent advances in our understanding of how glial cells participate in the physiological regulation of appetite and systemic metabolism as well as their role in the pathophysiological response to poor nutrition and secondary complications associated with obesity. Moreover, we highlight some of the existing lagoons of knowledge in this increasingly important area of investigation.

Role of the mixed-lineage protein kinase pathway in the metabolic stress response to obesity

Saturated free fatty acid (FFA) is implicated in the metabolic response to obesity. In vitro studies indicate that FFA signaling may be mediated by the mixed-lineage protein kinase (MLK) pathway that activates cJun NH2-terminal kinase (JNK). Here, we examined the role of the MLK pathway in vivo using a mouse model of diet-induced obesity. The ubiquitously expressed MLK2 and MLK3 protein kinases have partially redundant functions. We therefore compared wild-type and compound mutant mice that lack expression of MLK2 and MLK3. MLK deficiency protected mice against high-fat-diet-induced insulin resistance and obesity. Reduced JNK activation and increased energy expenditure contribute to the metabolic effects of MLK deficiency. These data confirm that the MLK pathway plays a critical role in the metabolic response to obesity.

Cellular insulin resistance disrupts leptin-mediated control of neuronal signaling and transcription

Central resistance to the actions of insulin and leptin is associated with the onset of obesity and type 2 diabetes mellitus, whereas leptin and insulin signaling is essential for both glucose and energy homeostasis. Although it is known that leptin resistance can lead to attenuated insulin signaling, whether insulin resistance can lead to or exacerbate leptin resistance is unknown. To investigate the molecular events underlying crosstalk between these signaling pathways, immortalized hypothalamic neuronal models, rHypoE-19 and mHypoA-2/10, were used. Prolonged insulin exposure was used to induce cellular insulin resistance, and thereafter leptin-mediated regulation of signal transduction and gene expression was assessed. Leptin directly repressed agouti-related peptide mRNA levels but induced urocortin-2, insulin receptor substrate (IRS)-1, IRS2, and IR transcription, through leptin-mediated phosphatidylinositol 3-kinase/Akt activation. Neuronal insulin resistance, as assessed by attenuated Akt phosphorylation, blocked leptin-mediated signal transduction and agouti-related peptide, urocortin-2, IRS1, IRS2, and insulin receptor synthesis. Insulin resistance caused a substantial decrease in insulin receptor protein levels, forkhead box protein 1 phosphorylation, and an increase in suppressor of cytokine signaling 3 protein levels. Cellular insulin resistance may cause or exacerbate neuronal leptin resistance and, by extension, obesity. It is essential to unravel the effects of neuronal insulin resistance given that both peripheral, as well as the less widely studied central insulin resistance, may contribute to the development of metabolic, reproductive, and cardiovascular disorders. This study provides improved understanding of the complex cellular crosstalk between insulin-leptin signal transduction that is disrupted during neuronal insulin resistance.

Alzheimer's disease and insulin resistance: translating basic science into clinical applications

Alzheimer's disease (AD) and diabetes are currently considered among the top threats to human health worldwide. Intriguingly, a connection between these diseases has been established during the past decade, since insulin resistance, a hallmark of type 2 diabetes, also develops in Alzheimer brains. In this article, the molecular and cellular mechanisms underlying defective brain insulin signaling in AD are discussed, with emphasis on evidence that Alzheimer's and diabetes share common inflammatory signaling pathways. I put forward here a hypothesis on how a cross-talk between peripheral tissues and the brain might influence the development of AD, and highlight important unanswered questions in the field. Furthermore, I discuss a rational basis for the use of antidiabetic agents as novel and potentially effective therapeutics in AD.

Neuroinflammation and neurodegeneration in overnutrition-induced diseases

Overnutrition-induced diseases such as obesity and type 2 diabetes (T2D) involve neural dysregulation of metabolic physiology. Recently, interdisciplinary research in neuroscience and immunology has linked overnutrition to a non-classical onset of inflammation in the brain, particularly in the hypothalamus. This neuroinflammation impairs central regulatory pathways of energy balance and nutrient metabolism, and leads to obesity, diabetes, and cardiovascular complications. This review describes recent findings on the roles of overnutrition-induced hypothalamic inflammation in neurodegeneration and defective adult neurogenesis, as well as in impaired neural stem cell regeneration, and their relevance to obesity and related diseases. In addition, commonalities in terms of neuroinflammation between neurodegenerative diseases and overnutrition-induced metabolic diseases are discussed. Targeting neuroinflammation and neurodegeneration will provide promising approaches for treating obesity and other overnutrition-related diseases.

Recent Insights into the Role of Hypothalamic AMPK Signaling Cascade upon Metabolic Control

In 2004, two seminal papers focused on the role of AMP-activated protein kinase (AMPK) in the hypothalamus opened new avenues of research in the field of the central regulation of energy homeostasis. Over the following 8 years, hundreds of studies have firmly established hypothalamic AMPK as a key sensor and integrator of hormonal and nutritional signals with neurochemical and neurophysiological responses to regulate whole-body energy balance. In this review article we aim to discuss the most recent findings in this particular area of research, highlighting the function of hypothalamic AMPK in appetite, thermogenesis, and peripheral glucose metabolism. The diversity of mechanisms by which hypothalamic AMPK regulates energy homeostasis illustrates the importance of this evolutionary-conserved energy signaling cascade in the control of this complex and fundamental biological process.

PVN pathways controlling energy homeostasis

Research into the control of energy balance has tended to focus on discrete brain regions, such as the brainstem, medulla, arcuate nucleus of the hypothalamus, and neocortex. Recently, a larger picture has begun to emerge in which the coordinated communication between these areas is proving to be critical to appropriate regulation of metabolism. By serving as a center for such communication, the paraventricular nucleus of the hypothalamus (PVH) is perhaps the most important brain nucleus regulating the physiological response to energetic challenges. Here we review recent advances in the understanding of the circuitry and function of the PVH.