Role of reactive oxygen species-related enzymes in neuropeptide y and proopiomelanocortin-mediated appetite control: a study using atypical protein kinase C knockdown

High-carbohydrate and fat diet consumption causes metabolic deterioration, neuronal damage, and loss of recognition memory in rats

The number of people diagnosed with metabolic syndrome (MetS) has increased dramatically to reach alarming proportions worldwide. The origin of MetS derives from bad eating habits and sedentary lifestyle. Most people consume foods high in carbohydrates and saturated fat. In recent years, it has been reported that alterations in insulin at the brain level could have an impact on the appearance of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, dementia, depression, and other types of disorders that compromise brain function. These alterations have been associated with damage to the structure and function of neurons located in the reptilian and limbic systems, a decrease in dendritic arborization and an exacerbated inflammatory state that impaired learning and memory and increased in the state of stress and anxiety. Although the molecular mechanisms induced by MetS to cause neurodegeneration are not fully understood. The aim of this study is to know the effect of the intake of hypercaloric diets on the structure and function of neurons located in the frontal cortex, hypothalamus and hippocampus and its impact on behavior in rats with metabolic syndrome. In conclusion, the present study illustrated that chronic exposure to hypercaloric diets, with a high content of sugars and saturated fatty acids, induces a proinflammatory state and exacerbates oxidative stress in brain regions such as the hypothalamus, hippocampus, and frontal cortex, leading to dysfunction. metabolism, neuronal damage, and recognition memory loss.

Selenium in Bodily Homeostasis: Hypothalamus, Hormones, and Highways of Communication

The ability of the body to maintain homeostasis requires constant communication between the brain and peripheral tissues. Different organs produce signals, often in the form of hormones, which are detected by the hypothalamus. In response, the hypothalamus alters its regulation of bodily processes, which is achieved through its own pathways of hormonal communication. The generation and transmission of the molecules involved in these bi-directional axes can be affected by redox balance. The essential trace element selenium is known to influence numerous physiological processes, including energy homeostasis, through its various redox functions. Selenium must be obtained through the diet and is used to synthesize selenoproteins, a family of proteins with mainly antioxidant functions. Alterations in selenium status have been correlated with homeostatic disturbances in humans and studies with animal models of selenoprotein dysfunction indicate a strong influence on energy balance. The relationship between selenium and energy metabolism is complicated, however, as selenium has been shown to participate in multiple levels of homeostatic communication. This review discusses the role of selenium in the various pathways of communication between the body and the brain that are essential for maintaining homeostasis.

Female Mice with Selenocysteine tRNA Deletion in Agrp Neurons Maintain Leptin Sensitivity and Resist Weight Gain While on a High-Fat Diet

The role of the essential trace element selenium in hypothalamic physiology has begun to come to light over recent years. Selenium is used to synthesize a family of proteins participating in redox reactions called selenoproteins, which contain a selenocysteine residue in place of a cysteine. Past studies have shown that disrupted selenoprotein expression in the hypothalamus can adversely impact energy homeostasis. There is also evidence that selenium supports leptin signaling in the hypothalamus by maintaining proper redox balance. In this study, we generated mice with conditional knockout of the selenocysteine tRNA^[Ser]Sec gene (Trsp) in an orexigenic cell population called agouti-related peptide (Agrp)-positive neurons. We found that female Trsp^AgrpKO mice gain less weight while on a high-fat diet, which occurs due to changes in adipose tissue activity. Female Trsp^AgrpKO mice also retained hypothalamic sensitivity to leptin administration. Male mice were unaffected, however, highlighting the sexually dimorphic influence of selenium on neurobiology and energy homeostasis. These findings provide novel insight into the role of selenoproteins within a small yet heavily influential population of hypothalamic neurons.

Double immunofluorescent evidence that oxidative stress-associated activation of JNK/AP-1 signaling participates in neuropeptide-mediated appetite control

Amphetamine (AMPH), an appetite suppressant, alters expression levels of neuropeptide Y (NPY) and cocaine- and amphetamine-regulated transcript (CART) in the hypothalamus. This study explored the potential role of cJun-N-terminal kinases (JNK) in appetite control, mediated by reactive oxygen species (ROS) and activator protein-1 (AP-1) in AMPH-treated rats. Rats were given AMPH daily for 4 days. Changes in feeding behavior and expression levels of hypothalamic NPY, CART, cFos, cJun, phosphorylated JNK (pJNK), as well as those of anti-oxidative enzymes, including superoxide dismutase (SOD), glutathione peroxidase (GP) and glutathione S-transferase (GST), were examined and compared. Following AMPH treatment, food intake and NPY expression decreased, whereas the other proteins expression and AP-1/DNA binding activity increased. Both cerebral cJun inhibition and ROS inhibition attenuated AMPH anorexia and modified detected protein, revealing a crucial role for AP-1 and ROS in regulating AMPH-induced appetite control. Moreover, both pJNK/CART and SOD/CART activities detected by double immunofluorescent staining increased in hypothalamic arcuate nucleus in AMPH-treated rats. The results suggested that pJNK/AP-1 signaling and endogenous anti-oxidants participated in regulating NPY/CART-mediated appetite control in rats treated with AMPH. These findings advance understanding of the molecular mechanism underlying the role of pJNK/AP-1 and oxidative stress in NPY/CART-mediated appetite suppression in AMPH-treated rats.

High- and low- selenium diets affect endocrine energy balance during early programming

High- and low- Se diets received by dams during gestation and lactation are related to insulin resistance in their pups. High-Se diet leads to an increase in serum insulin levels, which does not function properly, and an anabolic process. Low-Se diet is related to very low insulin values and an extreme catabolic energy imbalance. Selenoproteins have been implicated directly in the general endocrine regulation of appetite and energy homeostasis. To obtain information concerning how Se intake by dams is involved in regulating endocrine energy balance in progeny, three experimental groups of dam rats were used: control (Se: 0.1 ppm), Se-supplemented (Se: 0.5 ppm) and Se-deficient (Se: 0.01 ppm). At the end of lactation (21d old), the pups' appetite profile, Se levels, peptides from gastrointestinal tract (including pancreas), leptin, thyroid hormones, skeletal growth markers and cytokines in serum were measured. Low-Se diet leads to severe growth retardation, underdeveloped glands, a non-functional pancreas, non-operative high serum leptin levels and low GIT-anorexigenic signals. High-Se diet leads to non-operative high insulin secretion, obesity, inflammation and low leptin levels. These results point to Se as an important marker and a possible dietary supplementation treatment for gestating and lactating mothers in order to avoid metabolic disorders such as gestational diabetes or intrauterine growth retardation which could affect their progeny's future health in adulthood.

Hypothalamic redox balance and leptin signaling - Emerging role of selenoproteins

The hypothalamus is the central neural site governing food intake and energy expenditure. During the past 25 years, understanding of the hypothalamic cell types, hormones, and circuitry involved in the regulation of energy metabolism has dramatically increased. It is now well established that the adipocyte-derived hormone, leptin, acts upon two distinct groups of hypothalamic neurons that comprise opposing arms of the central melanocortin system. These two cell populations are anorexigenic neurons expressing proopiomelanocortin (POMC) and orexigenic neurons that express agouti-related peptide (AGRP). Several important studies have demonstrated that reactive oxygen species and endoplasmic reticulum stress significantly impact these hypothalamic neuronal populations that regulate global energy metabolism. Reactive oxygen species and redox homeostasis are influenced by selenoproteins, an essential class of proteins that incorporate selenium co-translationally in the form of the 21st amino acid, selenocysteine. Levels of these proteins are regulated by dietary selenium intake and they are widely expressed in the brain. Of additional relevance, selenium supplementation has been linked to metabolic alterations in both animal and human studies. Recent evidence also indicates that hypothalamic selenoproteins are significant modulators of energy metabolism in both neurons and tanycytes, a population of glial-like cells lining the floor of the 3rd ventricle within the hypothalamus. This review article will summarize current understanding of the regulatory influence of redox status on hypothalamic nutrient sensing and highlight recent work revealing the importance of selenoproteins in the hypothalamus.

Role of hypothalamic leptin-LepRb signaling in NPY-CART-mediated appetite suppression in amphetamine-treated rats

Leptin is an adipose tissue hormone which plays an important role in regulating energy homeostasis. Amphetamine (AMPH) is a drug of appetite suppressant, which exerts its effect by decreasing the expression of hypothalamic neuropeptide Y (NPY) and increasing that of cocaine- and amphetamine-regulated transcript (CART). This study investigated whether leptin, the leptin receptor (LepRb) and the signal transducer and activator of transcription-3 (STAT3) were involved in NPY/CART-mediated appetite suppression in AMPH-treated rats. Rats were given AMPH daily for four days, and changes in the levels of blood leptin and hypothalamic NPY, CART, LepRb, Janus kinases 2 (JAK2), and STAT3 were assessed and compared. During the AMPH treatment, blood leptin levels and hypothalamic NPY expression decreased, with the largest reduction observed on Day 2. By contrast, the expression of hypothalamic CART, LepRb, JAK2, and STAT3 increased, with the maximum response on Day 2. Furthermore, the binding activity of pSTAT3/DNA increased and was expressed in similar pattern to that of CART, LepRb, and JAK2. An intracerebroventricular infusion of NPY antisense 60min prior to AMPH treatment increased the levels of leptin, as well as the expression in LepRb, JAK2, and CART, whereas an infusion of STAT3 antisense decreased these levels and the expression of these parameters. The results suggest that blood leptin and hypothalamic LepRb-JAK2-STAT3 signaling involved in NPY-CART-regulated appetite suppression in AMPH-treated rats. The findings may aid understanding the role of leptin-LepRb during the treatment of anorectic drugs.

Knockdown of the transcript of ERK in the brain modulates hypothalamic neuropeptide-mediated appetite control in amphetamine-treated rats

BACKGROUND AND PURPOSE

Amphetamine is a releaser of dopamine stored in synaptic terminals, which can suppress appetite by changing the expression levels of neuropeptide Y (NPY) and proopiomelanocortin (POMC) in the hypothalamus. This study explored whether ERKs are involved in appetite control mediated by cAMP response element binding protein (CREB), NPY and POMC in amphetamine-treated rats.

EXPERIMENTAL APPROACH

Rats were given amphetamine for 4 days, and changes in feeding behaviour and expression levels of phosphorylated-ERK (pERK), pCREB, NPY and melanocortin MC₃ receptors were examined and compared.

KEY RESULTS

Following amphetamine treatment, food intake, body weight and NPY expression decreased, whereas the expression of pERK, pCREB, MC₃ receptors and pCREB/DNA binding activity increased. In amphetamine-treated rats, both cerebral ERK knockdown and pretreatment with a peripheral dopamine receptor antagonist decreased NPY but increased pERK, pCREB and MC₃ receptor expression. Moreover, the immunofluorescence of hypothalamic pERK increased following amphetamine treatment.

CONCLUSIONS AND IMPLICATIONS

These results suggest that ERK/CREB signalling participates in the effects mediated by dopamine receptor/NPY/POMC on appetite control in rats treated with amphetamine. These findings advance the knowledge on the involvement of ERK/CREB signalling in the reciprocal regulation by NPY and POMC of appetite after amphetamine treatment.

Acute Heat Stress Alters the Expression of Orexin System in Quail Muscle

Accumulating evidences indicate that the hypothalamic neuropeptide orexins or hypocretins are involved in stress-induced responses in mammals. Recently, we found that orexin is expressed and secreted from avian muscle cells, however its regulation is still unknown. In this study, we investigated the effect of heat and oxidative stress, the most challenging stressors in poultry production, on the expression of orexin system in quail muscle tissues and myoblast cell lines. Four week-old genetically selected susceptible and resistant Japanese quail (Coturnix coturnix Japonica) lines were exposed to acute heat stress (HS, 37°C for 1.5 h) or maintained at thermoneutral conditions (24°C). Quail myoblast (QM7) cell line was exposed to heat stress (45°C) for 0.5, 1, 2, or 4 h. The control cells were maintained at 37°C. The cells were also treated with several doses of hydrogen peroxide (H₂O₂, 10-200 μM) or 4-Hydroxynonenal (4-HNE, 10-30 μM) as oxidative stress. Untreated cells were used as controls. Acute HS significantly induced the expression of HSP70 and down-regulated orexin system in both quail muscle tissue and QM7 cells. Similarly, H₂O₂ but not 4-HNE treatment significantly increased HSP70 protein levels and dysregulated the expression of orexin and its related receptors in a dose-dependent manner in QM7 cells. Transient overexpression of HSP70 down-regulated the expression of orexin system in QM7 cells. Taken together, these data indicate that orexin may be a key player in stress response in avian muscle by demonstrating that heat and oxidative stress alter the expression of orexin system in quail muscle. This effect might be mediated through HSP70. Unraveling the upstream regulators and downstream effectors of orexin in avian muscle merits further in depth investigations.

Intracerebroventricular Catalase Reduces Hepatic Insulin Sensitivity and Increases Responses to Hypoglycemia in Rats

Specialized metabolic sensors in the hypothalamus regulate blood glucose levels by influencing hepatic glucose output and hypoglycemic counterregulatory responses. Hypothalamic reactive oxygen species (ROS) may act as a metabolic signal-mediating responses to changes in glucose, other substrates and hormones. The role of ROS in the brain's control of glucose homeostasis remains unclear. We hypothesized that hydrogen peroxide (H₂O₂), a relatively stable form of ROS, acts as a sensor of neuronal glucose consumption and availability and that lowering brain H₂O₂ with the enzyme catalase would lead to systemic responses increasing blood glucose. During hyperinsulinemic euglycemic clamps in rats, intracerebroventricular catalase infusion resulted in increased hepatic glucose output, which was associated with reduced neuronal activity in the arcuate nucleus of the hypothalamus. Electrophysiological recordings revealed a subset of arcuate nucleus neurons expressing proopiomelanocortin that were inhibited by catalase and excited by H₂O₂. During hypoglycemic clamps, intracerebroventricular catalase increased glucagon and epinephrine responses to hypoglycemia, consistent with perceived lower glucose levels. Our data suggest that H₂O₂ represents an important metabolic cue, which, through tuning the electrical activity of key neuronal populations such as proopiomelanocortin neurons, may have a role in the brain's influence of glucose homeostasis and energy balance.

Mediation of oxidative stress in hypothalamic ghrelin-associated appetite control in rats treated with phenylpropanolamine

Phenylpropanolamine (PPA)-induced appetite control is associated with oxidative stress in the hypothalamus. This study explored whether hypothalamic antioxidants participated in hypothalamic ghrelin system-associated appetite control in PPA-treated rats. Rats were given PPA daily for 4 days, and changes in food intake and the expression of neuropeptide Y (NPY), the cocaine- and amphetamine-regulated transcript (CART), superoxide dismutase, catalase, ghrelin, acyl ghrelin (AG), ghrelin O-acyltransferase (GOAT) and the ghrelin receptor (GHSR1a) were examined and compared. Results showed that both food intake and the expression of NPY and ghrelin/AG/GOAT/GHSR1a decreased in response to PPA treatment with maximum decrease on Day 2 of the treatment. In contrast, the expression of antioxidants and CART increased, with the maximum increase on Day 2, with the expression opposite to that of NPY and ghrelin. A cerebral infusion of either a GHSR1a antagonist or reactive oxygen species scavenger modulated feeding behavior and NPY, CART, antioxidants and ghrelin system expression, showing the involvement of ghrelin signaling and oxidative stress in regulating PPA-mediated appetite control. We suggest that hypothalamic ghrelin signaling system, with the help of antioxidants, may participate in NPY/CART-mediated appetite control in PPA-treated rats.

Trimetazidine attenuates pressure overload-induced early cardiac energy dysfunction via regulation of neuropeptide Y system in a rat model of abdominal aortic constriction

Background

Metabolism remodeling has been recognized as an early event following cardiac pressure overload. However, its temporal association with ventricular hypertrophy has not been confirmed. Moreover, whether trimetazidine could favorably affect this process also needs to be determined. The aim of the study was to explore the temporal changes of myocardial metabolism remodeling following pressure-overload induced ventricular hypertrophy and the potential favorable effect of trimetazidine on myocardial metabolism remodeling.

Methods

A rat model of abdominal aortic constriction (AAC)-induced cardiac pressure overload was induced. These rats were grouped as the AAC (no treatment) or TMZ group according to whether oral trimetazidine (TMZ, 40 mg/kg/d, for 5 days) was administered. Changes in cardiac structures were sequentially evaluated via echocardiography. The myocardial ADP/ATP ratio was determined to reflect the metabolic status, and changes in serum neuropeptide Y systems were evaluated.

Results

Myocardial metabolic disorder was acutely induced as evidenced by an increased ADP/ATP ratio within 7 days of AAC before the morphological changes in the myocardium, accompanied by up-regulation of serum oxidative stress markers and expression of fetal genes related to hypertrophy. Moreover, the serum NPY and myocardial NPY-1R, 2R, and 5R levels were increased within the acute phase of AAC-induced cardiac pressure overload. Pretreatment with TMZ could partly attenuate myocardial energy metabolic homeostasis, decrease serum levels of oxidative stress markers, attenuate the induction of hypertrophy-related myocardial fetal genes, inhibit the up-regulation of serum NPY levels, and further increase the myocardial expression of NPY receptors.

Conclusions

Cardiac metabolic remodeling is an early change in the myocardium before the presence of typical morphological ventricular remodeling following cardiac pressure overload, and pretreatment with TMZ may at least partly reverse the acute metabolic disturbance, perhaps via regulation of the NPY system.

Role of oxidative stress in disrupting the function of negative glucocorticoid response element in daily amphetamine-treated rats

Amphetamine (AMPH)-induced appetite suppression is associated with changes in hypothalamic reactive oxygen species (ROS), antioxidants, neuropeptides, and plasma glucocorticoid. This study explored whether ROS and glucocorticoid response element (GRE), which is the promoter site of corticotropin-releasing hormone (CRH) gene, participated in neuropeptides-mediated appetite control. Rats were treated daily with AMPH for four days, and changes in food intake, plasma glucocorticoid and expression levels of hypothalamic neuropeptide Y (NPY), proopiomelanocortin (POMC), superoxide dismutase (SOD), CRH, and glucocorticoid receptor (GR) were examined and compared. Results showed that food intake decreased and NPY gene down-regulated, while POMC, SOD, and CRH gene up-regulated during AMPH treatment. GR and GRE-DNA bindings were disrupted on Day 1 and Day 2 when glucocorticoid levels were still high. Pretreatment with GR inhibitor or ROS scavenger modulated mRNA levels in NPY, POMC, SOD and CRH in AMPH-treated rats. We suggest that disruptions of negative GRE (nGRE) on Day 1 and Day 2 are associated with an increase in oxidative stress during the regulation of NPY/POMC-mediated appetite control in AMPH-treated rats. These results advance the understanding of molecular mechanism in regulating AMPH-mediated appetite suppression.

Oxidoreductive homeostasis in alcohol-dependent male patients and the risk of alcohol drinking relapse in a 6-month follow-up

Disturbances in the central signaling of reactive oxygen species (ROS) in response to energy intake are recognized as taking part in appetitive and consummative phases of eating disorders. This study aimed to verify the hypothesis that blood oxidoreductive balance can also affect demand for energy substances, such as alcoholic beverages in alcohol-dependent individuals, as well as the severity of their alcohol dependence and risk of drinking relapse. The following values were determined in the blood of 54 alcohol-dependent male patients after alcohol withdrawal, again after 4 weeks and after 6 months: the aldehyde products of lipid peroxidation (malonyl dialdehyde [MDA] and 4-hydroxynonenal [4-HNE]), nitric oxide (NO) metabolites, total antioxidant status (TAS), the blood activities of glutathione peroxidase (GSHpx), superoxide dismutase (SOD), glutathione reductase (GSHred), blood glucose, and lipids. Alcoholics who relapsed during 6 months of observation (n = 31, 57%) compared with patients who maintained alcohol abstinence for 6 months (n = 23, 43%) differed only in relation to initial and final NO metabolite serum concentrations. The risk of alcohol drinking relapse was lower in patients with an above-median initial blood concentration of NO metabolites and TAS. The oxidative stress parameters correlated with alcohol-dependence severity markers. No significant correlations between the studied antioxidant balance parameters and markers of nutritional status, including blood glucose and lipids, were found. Although the results of our study have some limitations and require further investigation, they suggest the role of oxidoreductive balance in the pathomechanisms of alcohol dependence and drinking relapse. In addition, due to a lack of association found between blood oxidative stress parameters and BMI, blood glucose, and lipid concentrations, they show the presence of disturbances in systemic ROS signaling in response to energy availability in alcoholics after alcohol withdrawal.

Involvement of oxidative stress in the regulation of NPY/CART-mediated appetite control in amphetamine-treated rats

Amphetamine (AMPH) treatment can suppress appetite and increase oxidative stress in the brain. AMPH-induced appetite suppression is associated with the regulation of neuropeptide Y (NPY) and cocaine- and amphetamine-regulated transcript (CART) in the hypothalamus. The present study explored whether antioxidants, including glutathione S-transferase (GST) and glutathione peroxidase (GP), were involved in this NPY/CART-mediated appetite control. Rats were treated daily with AMPH for four days. Changes in food intake and expression levels of hypothalamic NPY, CART, GST, and GP were examined and compared. Results showed that, in AMPH-treated rats, (1) food intake and NPY expression decreased, while CART, GST, and GP expression increased; (2) NPY knockdown in the brain enhanced the decrease in NPY and the increases in CART, GST, and GP expression; and (3) central inhibition of reactive oxygen species production decreased GST and GP and modulated AMPH anorexia and the expression levels of NPY and CART. The present results suggest that oxidative stress in the brain participates in regulating NPY/CART-mediated appetite control in AMPH-treated rats. These results may advance the knowledge regarding the molecular mechanism of AMPH-evoked or NPY/CART-mediated appetite suppression.

Impact of hypothalamic reactive oxygen species in the regulation of energy metabolism and food intake

Hypothalamus is a key area involved in the control of metabolism and food intake via the integrations of numerous signals (hormones, neurotransmitters, metabolites) from various origins. These factors modify hypothalamic neurons activity and generate adequate molecular and behavioral responses to control energy balance. In this complex integrative system, a new concept has been developed in recent years, that includes reactive oxygen species (ROS) as a critical player in energy balance. ROS are known to act in many signaling pathways in different peripheral organs, but also in hypothalamus where they regulate food intake and metabolism by acting on different types of neurons, including proopiomelanocortin (POMC) and agouti-related protein (AgRP)/neuropeptide Y (NPY) neurons. Hypothalamic ROS release is under the influence of different factors such as pancreatic and gut hormones, adipokines (leptin, apelin,…), neurotransmitters and nutrients (glucose, lipids,…). The sources of ROS production are multiple including NADPH oxidase, but also the mitochondria which is considered as the main ROS producer in the brain. ROS are considered as signaling molecules, but conversely impairment of this neuronal signaling ROS pathway contributes to alterations of autonomic nervous system and neuroendocrine function, leading to metabolic diseases such as obesity and type 2 diabetes. In this review we focus our attention on factors that are able to modulate hypothalamic ROS release in order to control food intake and energy metabolism, and whose deregulations could participate to the development of pathological conditions. This novel insight reveals an original mechanism in the hypothalamus that controls energy balance and identify hypothalamic ROS signaling as a potential therapeutic strategy to treat metabolic disorders.

Involvement of hypothalamic PI3K-STAT3 signalling in regulating appetite suppression mediated by amphetamine

BACKGROUND AND PURPOSE

Appetite suppression induced by amphetamine has been attributed to its inhibition of neuropeptide Y (NPY) neurons and activation of pro-opiomelanocortin (POMC) neurons in the hypothalamus. This study examined whether STAT3 was involved in these actions of amphetamine.

EXPERIMENTAL APPROACH

Rats were given amphetamine daily for 4 days. Changes in the expression of NPY, POMC, melanocortin MC3 receptors, PI3K and STAT3 in the hypothalamus were assessed by RT-PCR and Western blotting. Antisense oligonucleotides to STAT3 were also used.

KEY RESULTS

Expression of NPY decreased with a maximum effect day 2 of amphetamine treatment. Expression of POMC, MC3 receptors, PI3K and STAT3 increased with a maximum response on day 2. Moreover, phosphorylation of STAT3 and its DNA binding activity increased and was expressed in a similar pattern. Infusion (i.c.v.) of STAT3 antisense at 60 min before amphetamine treatment, partly blocked amphetamine-induced anorexia and modulated expression of NPY, POMC, MC3 receptors and PI3K, indicating the involvement of STAT3 in amphetamine-treated rats.

CONCLUSIONS AND IMPLICATIONS

Hypothalamic PI3K-STAT3 signalling participated in the regulation of NPY- and POMC-mediated appetite suppression. These findings may contribute to a better understanding of anorectic drugs.

Both neuropeptide Y knockdown and Y1 receptor inhibition modulate CART-mediated appetite control

Amphetamine (AMPH)-induced appetite suppression has been attributed to its inhibition of neuropeptide Y (NPY)-containing neurons in the hypothalamus. This study examined whether hypothalamic cocaine- and amphetamine-regulated transcript (CART)-containing neurons and NPY Y1 receptor (Y1R) were involved in the action of AMPH. Rats were treated daily with AMPH for four days, and changes in feeding behavior and expression levels of NPY, CART, and POMC were assessed and compared. The results showed that both feeding behavior and NPY expression decreased during AMPH treatment, with the biggest reduction occurring on Day 2. By contrast, the expression of CART and melanocortin 3 receptor (MC3R), a member of the POMC neurotransmission, increased with the maximum response on Day 2, directly opposite to the NPY expression results. The intracerebroventricular infusion of NPY antisense or Y1R inhibitor both modulated AMPH-induced anorexia and the expression levels of MC3R and CART. The results suggest that in the hypothalamus both POMC- and CART-containing neurons participate in regulating NPY-mediated appetite control during AMPH treatment. These results may advance the knowledge of molecular mechanism of anorectic drugs.

The neuropeptide Y Y1 receptor knockdown modulates activator protein 1-involved feeding behavior in amphetamine-treated rats

BACKGROUND

Hypothalamic neuropeptide Y (NPY) and two immediate early genes, c-fos and c-jun, have been found to be involved in regulating the appetite-suppressing effect of amphetamine (AMPH). The present study investigated whether cerebral catecholamine (CA) might regulate NPY and POMC expression and whether NPY Y1 receptor (Y1R) participated in activator protein-1 (AP-1)-mediated feeding.

METHODS

Rats were given AMPH daily for 4 days. Changes in the expression of NPY, Y1R, c-Fos, c-Jun, and AP-1 were assessed and compared.

RESULTS

Decreased CA could modulate NPY and melanocortin receptor 4 (MC4R) expressions. NPY and food intake decreased the most on Day 2, but Y1R, c-Fos, and c-Jun increased by approximately 350%, 280%, and 300%, respectively, on Day 2. Similarly, AP-1/DNA binding activity was increased by about 180% on Day 2. The expression patterns in Y1R, c-Fos, c-Jun, and AP-1/DNA binding were opposite to those in NPY during AMPH treatment. Y1R knockdown was found to modulate the opposite regulation between NPY and AP-1, revealing an involvement of Y1R in regulating NPY/AP-1-mediated feeding.

CONCLUSIONS

These results point to a molecular mechanism of CA/NPY/Y1R/AP-1 signaling in the control of AMPH-mediated anorexia and may advance the medical research of anorectic and anti-obesity drugs.

Mitochondrial fatty acid oxidation in obesity

SIGNIFICANCE

Current lifestyles with high-energy diets and little exercise are triggering an alarming growth in obesity. Excess of adiposity is leading to severe increases in associated pathologies, such as insulin resistance, type 2 diabetes, atherosclerosis, cancer, arthritis, asthma, and hypertension. This, together with the lack of efficient obesity drugs, is the driving force behind much research.

RECENT ADVANCES

Traditional anti-obesity strategies focused on reducing food intake and increasing physical activity. However, recent results suggest that enhancing cellular energy expenditure may be an attractive alternative therapy.

CRITICAL ISSUES

This review evaluates recent discoveries regarding mitochondrial fatty acid oxidation (FAO) and its potential as a therapy for obesity. We focus on the still controversial beneficial effects of increased FAO in liver and muscle, recent studies on how to potentiate adipose tissue energy expenditure, and the different hypotheses involving FAO and the reactive oxygen species production in the hypothalamic control of food intake.

FUTURE DIRECTIONS

The present review aims to provide an overview of novel anti-obesity strategies that target mitochondrial FAO and that will definitively be of high interest in the future research to fight against obesity-related disorders.

Oxidative Stress in the Hypothalamus: the Importance of Calcium Signaling and Mitochondrial ROS in Body Weight Regulation

A considerable amount of evidence shows that reactive oxygen species (ROS) in the mammalian brain are directly responsible for cell and tissue function and dysfunction. Excessive reactive oxygen species contribute to various conditions including inflammation, diabetes mellitus, neurodegenerative diseases, tumor formation, and mental disorders such as depression. Increased intracellular calcium levels have toxic roles leading to cell death. However, the exact connection between reactive oxygen production and high calcium stress is not yet fully understood. In this review, we focus on the role of reactive oxygen species and calcium stress in hypothalamic arcuate neurons controlling feeding. We revisit the role of NPY and POMC neurons in the regulation of appetite and energy homeostasis, and consider how ROS and intracellular calcium levels affect these neurons. These novel insights give a new direction to research on hypothalamic mechanisms regulating energy homeostasis and may offer novel treatment strategies for obesity and type-2 diabetes.

Inhibiting neuropeptide Y Y1 receptor modulates melanocortin receptor- and NF-κB-mediated feeding behavior in phenylpropanolamine-treated rats

Neuropeptide Y (NPY) and nuclear factor-kappa B (NF-κB) are involved in regulating anorexia elicited by phenylpropanolamine (PPA), a sympathomimetic drug. This study explored whether NPY Y1 receptor (Y1R) is involved in this process, and a potential role for the proopiomelanocortin system was identified. Rats were given PPA once a day for 4days. Changes in the hypothalamic expression of the NPY, Y1R, NF-κB, and melanocortin receptor 4 (MC4R) levels were assessed and compared. The results indicated that food intake and NPY expression decreased, with the largest reductions observed on Day 2 (approximately 50% and 45%, respectively), whereas NF-κB, MC4R, and Y1R increased, achieving maximums on Day 2 (160%, 200%, and 280%, respectively). To determine the role of Y1R, rats were pretreated with Y1R antisense or a Y1R antagonist via intracerebroventricular injection 1h before the daily PPA dose. Y1R knockdown and inhibition reduced PPA anorexia and partially restored the normal expression of NPY, MC4R, and NF-κB. The data suggest that hypothalamic Y1R participates in the appetite-suppression from PPA by regulating MC4R and NF-κB. The results of this study increase our understanding of the molecular mechanisms in PPA-induced anorexia.

Neuropeptide Y Y1 receptor knockdown can modify glutathione peroxidase and c-AMP response element-binding protein in phenylpropanolamine-treated rats

It has been reported that antioxidative enzymes, neuropeptide Y (NPY), and c-AMP response element-binding protein (CREB) are involved in regulating phenylpropanolamine (PPA)-mediated appetite suppression. Here, we investigated whether Y1 receptor (Y1R) might be involved in this regulation. Rats were daily treated with PPA for 4 days. Changes in the contents of NPY, Y1R, glutathione peroxidase (GP), and CREB were assessed and compared. Results showed that Y1R, GP, and CREB increased, with a maximal increase about 100, 200, and 150 %, respectively, on Day 2. By contrast, NPY decreased with a biggest reduction about 48 % on Day 2 and the pattern of expression during PPA treatment was opposite to those of Y1R, GP, and CREB. Central knockdown (using antisense) or inhibition (using antagonist) of Y1R expression modulated the anorectic response of PPA and the reciprocal regulation between NPY and GP (or CREB), revealing an essential role of Y1R in regulating NPY, GP, and CREB. These results suggest that Y1R participates in the reciprocal regulation of NPY, GP, and CREB in the hypothalamus during PPA treatment in conscious rats. The present results may aid the therapeutic research of PPA and related antiobesity drugs.

The anorexigenic effect of serotonin is mediated by the generation of NADPH oxidase-dependent ROS

Serotonin (5-HT) is a central inhibitor of food intake in mammals. Thus far, the intracellular mechanisms for the effect of serotonin on appetite regulation remain unclear. It has been recently demonstrated that reactive oxygen species (ROS) in the hypothalamus are a crucial integrative target for the regulation of food intake. To investigate the role of ROS in the serotonin-induced anorexigenic effects, conscious mice were treated with 5-HT alone or combination with Trolox (a ROS scavenger) or Apocynin (an NADPH oxidase inhibitor) by acute intracerebroventricular injection. Both Trolox and Apocynin reversed the anorexigenic action of 5-HT and the 5-HT-induced hypothalamic ROS elevation. The mRNA and protein expression levels of pro-opiomelanocortin (POMC) were dramatically increased after ICV injection with 5-HT. The anorexigenic action of 5-HT was accompanied by markedly elevated hypothalamic MDA levels and GSH-Px activity, while the SOD activity was decreased. Moreover, 5-HT significantly increased the mRNA expression of UCP-2 but reduced the levels of UCP-3. Both Trolox and Apocynin could block the 5-HT-induced changes in UCP-2 and UCP-3 gene expression. Our study demonstrates for the first time that the anorexigenic effect of 5-HT is mediated by the generation of ROS in the hypothalamus through an NADPH oxidase-dependent pathway.

The identification of neuropeptide Y receptor subtype involved in phenylpropanolamine-induced increase in oxidative stress and appetite suppression

Hypothalamic neuropeptide Y (NPY) and superoxide dismutase (SOD) have been reported to participate in the regulation of appetite-suppressing effect of phenylpropanolamine (PPA), a sympathomimetic agent. This study explored whether Y1 receptor (Y1R) and/or Y5 receptor (Y5R) was involved in this regulation. Wistar rats were treated with PPA for 24 h. Changes in food intake and hypothalamic NPY, Y1R, Y5R, and SOD contents were assessed and compared. Results showed that food intake and NPY contents were decreased following PPA treatment, while Y1R and SOD contents were increased and Y5R contents remained unchanged. Moreover, although Y1R or Y5R knockdown by themselves could modify the food intake, Y1R but not Y5R knockdown could modify PPA-induced anorexia as well as NPY and SOD contents. In addition, selective inhibition of Y1R but not Y5R could modulate PPA-induced anorexia. It is suggested that Y1R but not Y5R participates in the anorectic response of PPA via the modulation of NPY and SOD. Results provide molecular mechanism of NPY-mediated PPA anorexia and may aid the understanding of the toxicology of PPA.

Lysosome vacuolation disrupts the completion of autophagy during norephedrine exposure in SH-SY5Y human neuroblastoma cells

In our current study, we examined the mechanism underlying neuronal cell injuries caused by norephedrine in SH-SY5Y human neuroblastoma cells. Norephedrine was found to induce cytoplasmic vacuolation and a resultant loss of cell viability. In the cells treated with norephedrine also, an autophagic marker LC3 was converted to its LC3-II activated form, suggesting the induction of autophagy. In cells transfected with RFP-LC3 and GFP-LAMP1, a punctate patterning of LC3 expression and colocalization of LAMP1 with the formed vacuoles were observed, highlighting the lysosomal nature of the vacuoles and their association with autophagosomes. An autophagic flux assay using tfLC3 (mRFP-GFP-LC3) indicated the formation of autophagosomes and autolysosomes by norephedrine stimulation at an early timepoint (∼3 h). However, at a later timepoint (∼6 h), both the dilation of autolysosomes/lysosomes and the neutralization of the vacuolar pH were also observed. These results thus indicate that norephedrine induces autophagy at an early timepoint and cell death with lysosomal dysfunction and autophagy disruption at a later timepoint.

Involvement of neuropeptide Y Y1 receptor in the regulation of amphetamine-mediated appetite suppression

Recently, we reported that an initial decrease followed by recovery of food intake was observed during four days of amphetamine (AMPH) treatment and suggested that these changes in response were mediated by changes in neuropeptide Y (NPY) and proopiomelanocortin (POMC). Here we investigated if Y1 receptor (Y1R) and/or Y5 receptor (Y5R) might be involved in this regulation. Rats were treated daily with AMPH for four days. Changes in the expression levels of Y1R, Y5R, melanocortin receptor 3 (MC3R), and NPY were assessed and compared. Results showed that Y1R and MC3R increased, with a maximal increase of about 210% on Day 2 but with a restoration to the normal level on Day 4. In contrast, NPY decreased with a biggest reduction of about 45% on Day 2 and the pattern of expression during AMPH treatment was opposite to those of Y1R and MC3R, while the expression of Y5R was not changed. Central inhibitions of NPY formation or Y1R activity modulated the anorectic response of AMPH and the reciprocal regulation of NPY and MC3R, revealing a crucial role of Y1R in this action. It is suggested that Y1R participates in the reciprocal regulation of NPY- and MC3R-containing neurons in the hypothalamus during the anorectic effect of AMPH. These results may further the understanding of Y1R in the control of eating.

Knocking down the transcript of NF-kappaB modulates the reciprocal regulation of endogenous antioxidants and feeding behavior in phenylpropanolamine-treated rats

It has been reported that oxidative stress, antioxidants, and neuropeptide Y (NPY) are involved in regulating the feeding behavior of phenylpropanolamine (PPA), a sympathomimetic drug. This study explored whether transcription factor NF-κB is involved in this effect. Rats were treated daily with PPA for 4 days. Changes in hypothalamic NF-κB, NPY, superoxide dismutase (SOD), and glutathione peroxidase (GPx) levels during PPA treatment were assessed and compared. Results showed that NF-κB, SOD, and GPx increased, with a maximal response on Day 2, while the food intake and NPY decreased with the biggest reduction on Day 2 during PPA treatment. To further determine whether NF-κB was involved, intracerebroventricular infusion of antisense oligonucleotide was performed at 1 h before daily PPA in free-moving rats. Cerebral NF-κB knockdown could modify PPA anorexia and the expressions of NPY, SOD, and GPx. It is suggested that hypothalamic NF-κB participates in the reciprocal regulation of NPY and antioxidants, which mediated the appetite-suppressing effect of PPA. Results may further the understanding of the molecular mechanisms of PPA.