Rolling out physical exercise and energy homeostasis: Focus on hypothalamic circuitries.

Energy balance is the fine regulation of energy expenditure and energy intake. Negative energy balance causes body weight loss, while positive energy balance promotes weight gain. Modern societies offer a maladapted way of life, where easy access to palatable foods and the lack of opportunities to perform physical activity are considered the roots of the obesity pandemic. Physical exercise increases energy expenditure and, consequently, is supposed to promote weight loss. Paradoxically, physical exercise acutely drives anorexigenic-like effects, but the mechanisms are still poorly understood. Using an evolutionary background, this review aims to highlight the potential involvement of the melanocortin system and other hypothalamic neural circuitries regulating energy balance during and after physical exercise. The physiological significance of these changes will be explored, and possible signalling agents will be addressed. The knowledge discussed here might be important for clarifying obesity aetiology as well as new therapeutic approaches for body weight loss.

Coupling of GABA Metabolism to Mitochondrial Glucose Phosphorylation.

Glucose and oxygen (O2) are vital to the brain. Glucose metabolism and mitochondria play a pivotal role in this process, culminating in the increase of reactive O2 species. Hexokinase (HK) is a key enzyme on glucose metabolism and is coupled to the brain mitochondrial redox modulation by recycling ADP for oxidative phosphorylation (OXPHOS). GABA shunt is an alternative pathway to GABA metabolism that increases succinate levels, a Krebs cycle intermediate. Although glucose and GABA metabolisms are intrinsically connected, their interplay coordinating mitochondrial function is poorly understood. Here, we hypothesize that the HK and the GABA shunt interact to control mitochondrial metabolism differently in the cortex and the hypothalamus. The GABA shunt stimulated mitochondrial O2 consumption and H2O2 production higher in hypothalamic synaptosomes (HSy) than cortical synaptosomes (CSy). The GABA shunt increased the HK coupled to OXPHOS activity in both population of synaptosomes, but the rate of activation was higher in HSy than CSy. Significantly, malonate and vigabatrin blocked the effects of the GABA shunt in the HK activity coupled to OXPHOS. It indicates that the glucose phosphorylation is linked to GABA and Krebs cycle reactions. Together, these data shed light on the HK and SDH role on the metabolism of each region fed by GABA turnover, which depends on the neurons' metabolic route.

Intense physical exercise potentiates glucose inhibitory effect over food intake of male Wistar rats.

NEW FINDINGS: What is the central question of this study? How does an acute session of exercise affect food intake of male Wistar rats? What is the main finding and its importance? Food intake in male Wistar rats is decreased in the first hour after physical exercise independent of the intensity. Moreover, high-intensity exercise potentiates the anorexic effect of peripheral glucose administration. This work raises new feeding-related targets that would explain how exercise drives body weight loss. ABSTRACT: Obesity has emerged as a critical metabolic disorder in modern society. An adequate lifestyle with a well-oriented programme of diet and physical exercise (PE) can prevent or potentially even cure obesity. Additionally, PE might lead to weight loss by increasing energy expenditure and decreasing hunger perception. In this article, we hypothesize that an acute exercise session would potentiate the glucose inhibitory effects on food intake in male Wistar rats. Our data show that moderate- or high-intensity PE significantly decreased food intake, although no changes in the expression of feeding-related neuropeptide in the arcuate nucleus of the hypothalamus were found. Exercised animals demonstrated a reduced glucose tolerance and increased blood insulin concentration. Intraperitoneal administration of glucose decreased food intake in control animals. In the animals submitted to moderate-intensity PE, the decrease in food intake promoted by glucose was similar to controls; however, an interaction was observed when glucose was injected in the high-intensity PE group, in which food intake was significantly lower than the effect produced by glucose alone. A different pattern of expression was observed for the monocarboxylate transporter isoforms (MCT1, 2 and 4) and 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFBP3) in the hypothalamus, which was dependent on the exercise intensity. In conclusion, PE decreases food intake independently of the intensity. However, an interaction between PE and the anorexic effect of glucose is only observed when a high-intensity exercise is performed. These data show an essential role of exercise intensity in the modulation of the glucose inhibitory effect on food intake.

Type 2 iodothyronine deiodinase is upregulated in rat slow- and fast-twitch skeletal muscle during cold exposure.

During cold acclimation, shivering is progressively replaced by nonshivering thermogenesis. Brown adipose tissue (BAT) and skeletal muscle are relevant for nonshivering thermogenesis, which depends largely on thyroid hormone. Since the skeletal muscle fibers progressively adapt to cold exposure through poorly defined mechanisms, our intent was to determine whether skeletal muscle type 2 deiodinase (D2) induction could be implicated in the long-term skeletal muscle cold acclimation. We demonstrate that in the red oxidative soleus muscle, D2 activity increased 2.3-fold after 3 days at 4°C together with the brown adipose tissue D2 activity, which increased 10-fold. Soleus muscle and BAT D2 activities returned to the control levels after 10 days of cold exposure, when an increase of 2.8-fold in D2 activity was detected in white glycolytic gastrocnemius but not in red oxidative gastrocnemius fibers. Propranolol did not prevent muscle D2 induction, but it impaired the decrease of D2 in BAT and soleus after 10 days at 4°C. Cold exposure is accompanied by increased oxygen consumption, UCP3, and PGC-1α genes expression in skeletal muscles, which were partialy prevented by propranolol in soleus and gastrocnemius. Serum total and free T3 is increased during cold exposure in rats, even after 10 days, when BAT D2 is already normalized, suggesting that skeletal muscle D2 activity contributes significantly to circulating T3 under this adaptive condition. In conclusion, cold exposure is accompanied by concerted changes in the metabolism of BAT and oxidative and glycolytic skeletal muscles that are paralleled by type 2 deiodinase activation.

Mitochondrial Dysfunction Plays a Relevant Role in Heart Toxicity Caused by MeHg.

The effects of methylmercury (MeHg) on exposed populations are a public health problem. In contrast to widely studied neurological damage, few cardiovascular changes have been described. Our group evaluated the cardiotoxicity of a cumulative dose of 70 mg.kg-1 fractioned over a 14-day exposure period in mice (MeHg70 group). The effects of MeHg on proteins relevant to cardiac mitochondrial function were also investigated. The results obtained showed a reduction in oxygen consumption in the two settings. In cardiac tissue samples in oxygraphy studies, this reduction was related to a lower efficiency of complexes II and V, which belong to the oxidative phosphorylation system. In vivo, mice in the MeHg70 group presented lower oxygen consumption and running tolerance, as shown by ergometric analyses. Cardiac stress was evident in the MeHg70 group, as indicated by a marked increase in the level of the mRNA encoding atrial natriuretic peptide. Electrocardiogram studies revealed a lower heart rate at rest in the animals from the MeHg70 group, as well as prolonged left ventricular depolarisation and repolarisation. Through echocardiographic analysis, reductions in the left ventricular ejection fraction and left ventricular wall thickness of approximately 10% and 20%, respectively, were detected. These results indicate that the oral intake of MeHg can decrease cardiac function and oxidative metabolism. This finding highlights the importance of monitoring MeHg levels in humans and animals in contaminated areas, as well as periodically carrying out cardiac function tests.

Hypothalamic AgRP neurons exert top-down control on systemic TNF-α release during endotoxemia.

Loss of appetite and negative energy balance are common features of endotoxemia in all animals and are thought to have protective roles by reducing nutrient availability to host and pathogen metabolism. Accordingly, fasting and caloric restriction have well-established anti-inflammatory properties. However, in response to reduced nutrient availability at the cellular and organ levels, negative energy balance also recruits distinct energy-sensing brain circuits, but it is not known whether these neuronal systems have a role in its anti-inflammatory effects. Here, we report that hypothalamic AgRP neurons-a critical neuronal population for the central representation of negative energy balance-have parallel immunoregulatory functions. We found that when endotoxemia occurs in fasted mice, the activity of AgRP neurons remains sustained, but this activity does not influence feeding behavior and endotoxemic anorexia. Furthermore, we found that endotoxemia acutely desensitizes AgRP neurons, which also become refractory to inhibitory signals. Mimicking this sustained AgRP neuron activity in fed mice by chemogenetic activation-a manipulation known to recapitulate core behavioral features of fasting-results in reduced acute tumor necrosis factor alpha (TNF-α) release during endotoxemia. Mechanistically, we found that endogenous glucocorticoids play an important role: glucocorticoid receptor deletion from AgRP neurons prevents their endotoxemia-induced desensitization, and importantly, it counteracts the fasting-induced suppression of TNF-α release, resulting in prolonged sickness. Together, these findings provide evidence directly linking AgRP neuron activity to the acute response during endotoxemia, suggesting that these neurons are a functional component of the immunoregulatory effects associated with negative energy balance and catabolic metabolism.

Physical exercise improves mitochondrial function in ovariectomized rats.

Estrogen deficiency causes metabolic disorders in humans and rodents, including in part due to changes in energy expenditure. We have shown previously that skeletal muscle mitochondrial function is compromised in ovariectomized (Ovx) rats. Since physical exercise is a powerful strategy to improve skeletal muscle mitochondrial content and function, we hypothesize that exercise training would counteract the deficiency-induced skeletal muscle mitochondrial dysfunction in Ovx rats. We report that exercised Ovx rats, at 60-65% of maximal exercise capacity for 8 weeks, exhibited less fat accumulation and body weight gain compared with sedentary controls. Treadmill exercise training decreased muscle lactate production, indicating a shift to mitochondrial oxidative metabolism. Furthermore, reduced soleus muscle mitochondrial oxygen consumption confirmed that estrogen deficiency is detrimental to mitochondrial function. However, exercise restored mitochondrial oxygen consumption in Ovx rats, achieving similar levels as in exercised control rats. Exercise-induced skeletal muscle peroxisome proliferator-activated receptor-γ coactivator-1α expression was similar in both groups. Therefore, the mechanisms by which exercise improves mitochondrial oxygen consumption appears to be different in Ovx-exercised and sham-exercised rats. While there was an increase in mitochondrial content in sham-exercised rats, demonstrated by a greater citrate synthase activity, no induction was observed in Ovx-exercised rats. Normalizing mitochondrial respiratory capacity by citrate synthase activity indicates a better oxidative phosphorylation efficiency in the Ovx-exercised group. In conclusion, physical exercise sustains mitochondrial function in ovarian hormone-deficient rats through a non-conventional mitochondrial content-independent manner.

Isolation of Mitochondria From Fresh Mice Lung Tissue.

Direct analysis of isolated mitochondria enables a better understanding of lung dysfunction. Despite well-defined mitochondrial isolation protocols applicable to other tissues, such as the brain, kidney, heart, and liver, a robust and reproductive protocol has not yet been advanced for the lung. We describe a protocol for the isolation of mitochondria from lung tissue aiming for functional analyses of mitochondrial O2 consumption, transmembrane potential, reactive oxygen species (ROS) formation, ATP production, and swelling. We compared our protocol to that used for heart mitochondrial function that is well-established in the literature, and achieved similar results.

Granulocyte-colony stimulating factor treatment of chronic myocardial infarction.

PURPOSE: The aim of this study was to investigate the impact of granulocyte-colony stimulating factor (G-CSF) administration on cardiac function of rats with chronic myocardial infarction through two different protocols: high dose short term and low dose long term protocols. METHODS: Wistar rats were submitted to MI surgery and after 4 weeks they received recombinant human G-CSF (Filgrastim) or vehicle subcutaneously. We tested the classical protocol (50 microg/kg/day during 7 days) and the long term low dose treatment (four cycles of 5 days of 10 microg/kg/day). Cardiac performance was evaluated before, 4 and 6 weeks after G-CSF injections by electro- and echocardiography, hemodynamic and treadmill exercise test. RESULTS: All infarcted groups exhibited impaired function compared to sham operated animals. Moreover, all cardiac functional parameter were not different between G-CSF and Vehicle group at resting conditions as well as after treadmill exercise stress test, despite intense white blood cell mobilization in both protocols at all time points. Hypertrophy was not different and infarct size was similar in histological analysis CONCLUSIONS: These data clearly show that G-CSF treatment was unable to restore cardiac function impaired by myocardial infarction either with classical approach or long term low dose administration.

Regulation of substrate utilization and adiposity by Agrp neurons.

The type of nutrient utilized by the organism at any given time-substrate utilization-is a critical component of energy metabolism. The neuronal mechanisms involved in the regulation of substrate utilization in mammals are largely unknown. Here, we found that activation of hypothalamic Agrp neurons rapidly altered whole-body substrate utilization, increasing carbohydrate utilization, while decreasing fat utilization. These metabolic changes occurred even in the absence of caloric ingestion and were coupled to increased lipogenesis. Accordingly, inhibition of fatty acid synthase-a key enzyme that mediates lipogenesis-blunted the effects of Agrp neuron activation on substrate utilization. In pair-fed conditions during positive energy balance, activation of Agrp neurons improved metabolic efficiency, and increased weight gain and adiposity. Conversely, ablation of Agrp neurons impaired fat mass accumulation. These results suggest Agrp neurons regulate substrate utilization, contributing to lipogenesis and fat mass accumulation during positive energy balance.

Mitochondria-Bound Hexokinase (mt-HK) Activity Differ in Cortical and Hypothalamic Synaptosomes: Differential Role of mt-HK in H2O2 Depuration.

Glucose and oxygen are vital for the brain, as these molecules provide energy and metabolic intermediates that are necessary for cell function. The glycolysis pathway and mitochondria play a pivotal role in cell energy metabolism, which is closely related to reactive oxygen species (ROS) production. Hexokinase (HK) is a key enzyme involved in glucose metabolism that modulates the level of brain mitochondrial ROS by recycling ADP for oxidative phosphorylation (OxPhos). Here, we hypothesize that the control of mitochondrial metabolism by hexokinase differs in distinct areas of the brain, such as the cortex and hypothalamus, in which ROS might function as signaling molecules. Thus, we investigated mitochondrial metabolism of synaptosomes derived from both brain regions. Cortical synaptosomes (CSy) show a predominance of glutamatergic synapses, while in the hypothalamic synaptosomes (HSy), the GABAergic synapses predominate. Significant differences of oxygen consumption and ROS production were related to higher mitochondrial complex II activity (succinate dehydrogenase-SDH) in CSy rather than to mitochondrial number. Mitochondrial HK (mt-HK) activity was higher in CSy than in HSy regardless the substrate added. Mitochondrial O2 consumption related to mt-HK activation by 2-deoxyglucose was also higher in CSy. In the presence of substrate for complex II, the activation of synaptosomal mt-HK promoted depuration of ROS in both HSy and CSy, while ROS depuration did not occur in HSy when substrate for complex I was used. The impact of the mt-HK inhibition by glucose-6-phosphate (G6P) was the same in synaptosomes from both areas. Together, the differences found between CSy and HSy indicate specific roles of mt-HK and SDH on the metabolism of each brain region, what probably depends on the main metabolic route that is used by the neurons.

Differential Expression of NADPH Oxidases Depends on Skeletal Muscle Fiber Type in Rats.

NADPH oxidases (NOX) are important sources of reactive oxygen species (ROS) in skeletal muscle, being involved in excitation-contraction coupling. Thus, we aimed to investigate if NOX activity and expression in skeletal muscle are fiber type specific and the possible contribution of this difference to cellular oxidative stress. Oxygen consumption rate, NOX activity and mRNA levels, and the activity of catalase (CAT), glutathione peroxidase (GPX), and superoxide dismutase (SOD), as well as the reactive protein thiol levels, were measured in the soleus (SOL), red gastrocnemius (RG), and white gastrocnemius (WG) muscles of rats. RG showed higher oxygen consumption flow than SOL and WG, while SOL had higher oxygen consumption than WG. SOL showed higher NOX activity, as well as NOX2 and NOX4 mRNA levels, antioxidant enzymatic activities, and reactive protein thiol contents when compared to WG and RG. NOX activity and NOX4 mRNA levels as well as antioxidant enzymatic activities were higher in RG than in WG. Physical exercise increased NOX activity in SOL and RG, specifically NOX2 mRNA levels in RG and NOX4 mRNA levels in SOL. In conclusion, we demonstrated that NOX activity and expression differ according to the skeletal muscle fiber type, as well as antioxidant defense.

Differential glycolytic profile and Warburg effect in papillary thyroid carcinoma cell lines.

Acceleration of glycolysis is a characteristic of neoplasia. Previous studies have shown that a metabolic shift occurs in many tumors and correlates with a negative prognosis. The present study aimed to investigate the glycolytic profile of thyroid carcinoma cell lines. We investigated glycolytic and oxidative parameters of two thyroid carcinoma papillary cell lines (BCPAP and TPC1) and the non-tumor cell line NTHY-ori. All carcinoma cell lines showed higher rates of glycolysis efficiency, when compared to NTHY-ori, as assessed by a higher rate of glucose consumption and lactate production. The BCPAP cell line presented higher rates of growth, as well as elevated intracellular ATP levels, compared to the TPC1 and NTHY-ori cells. We found that glycolysis and activities of pentose phosphate pathway (PPP) regulatory enzymes were significantly different among the carcinoma cell lines, particularly in the mitochondrial hexokinase (HK) activity which was higher in the BCPAP cells than that in the TPC1 cell line which showed a balanced distribution of HK activity between cytoplasmic and mitochondrial subcellular localizations. However, TPC1 had higher levels of glucose­6-phosphate dehydrogenase activity, suggesting that the PPP is elevated in this cell type. Using high resolution respirometry, we observed that the Warburg effect was present in the BCPAP and TPC1 cells, characterized by low oxygen consumption and high reactive oxygen species production. Overall, these results indicate that both thyroid papillary carcinoma cell lines showed a glycolytic profile. Of note, BCPAP cells presented some relevant differences in cell metabolism compared to TPC1 cells, mainly related to higher mitochondrial-associated HK activity.

Thyroid hormone and estrogen regulate exercise-induced growth hormone release.

Growth hormone (GH) regulates whole body metabolism, and physical exercise is the most potent stimulus to induce its secretion in humans. The mechanisms underlying GH secretion after exercise remain to be defined. The aim of this study was to elucidate the role of estrogen and pituitary type 1 deiodinase (D1) activation on exercise-induced GH secretion. Ten days after bilateral ovariectomy, animals were submitted to 20 min of treadmill exercise at 75% of maximum aerobic capacity and tissues were harvested immediately or 30 min after exercise. Non-exercised animals were used as controls. A significant increase in D1 activity occurred immediately after exercise (~60%) in sham-operated animals and GH was higher (~6-fold) 30 min after exercise. Estrogen deficient rats exhibited basal levels of GH and D1 activity comparable to those found in control rats. However, after exercise both D1 activity and serum GH levels were blunted compared to sedentary rats. To understand the potential cause-effect of D1 activation in exercise-induced GH release, we pharmacologically blocked D1 activity by propylthiouracil (PTU) injection into intact rats and submitted them to the acute exercise session. D1 inhibition blocked exercise-induced GH secretion, although basal levels were unaltered. In conclusion, estrogen deficiency impairs the induction of thyroid hormone activating enzyme D1 in the pituitary, and GH release by acute exercise. Also, acute D1 activation is essential for exercise-induced GH response.