Enhanced Hypothalamic Glucose Sensing in Obesity: Alteration of Redox Signaling

1939-327X (Electronic) Journal articleObjective : Recent data demonstrate that glucose sensing in different tissues is initiated by an intracellular redox-signaling pathway in physiological conditions. However, the relevance of such a mechanism in metabolic disease is not known. The aim of the present study was to determine whether brain-glucose hypersensitivity present in obese Zucker rat is related to an alteration in redox signaling. Research design and Methods: Brain glucose sensing alteration was investigated in vivo through the evaluation of electrical activity in arcuate nucleus, changes in ROS levels, and hypothalamic glucose-induced insulin secretion. In basal conditions, modifications of redox state and mitochondrial function were assessed through oxidized glutathione, glutathione peroxidase, manganese superoxide dismutase, aconitase activities and mitochondrial respiration. Results : Hypothalamic hypersensitivity to glucose was characterized by enhanced electrical activity of the arcuate nucleus and increased insulin secretion at a low glucose concentration, which does not produce such an effect in normal rats. It was associated with 1) increased ROS levels in response to this low glucose load, 2) constitutive oxidized environment coupled with lower antioxidant enzyme activity at both the cellular and mitochondrial level, and 3) over-expression of several mitochondrial subunits of the respiratory chain coupled with a global dysfunction in mitochondrial activity. Moreover, pharmacological restoration of the glutathione hypothalamic redox state by reduced-glutathione infusion in the third ventricle fully reversed the cerebral hypersensitivity to glucose. Conclusions : Altogether, these data demonstrate that obese Zucker rats' impaired hypothalamic regulation in terms of glucose sensing is linked to an abnormal redox signaling, which originates from mitochondria dysfunction

Hypothalamic Reactive Oxygen Species Are Required for Insulin-Induced Food Intake Inhibition: An NADPH Oxidase–Dependent Mechanism

1939-327X (Electronic) Journal Article Research Support, Non-U.S. Gov'tOBJECTIVE: Insulin plays an important role in the hypothalamic control of energy balance, especially by reducing food intake. Emerging data point to a pivotal role of reactive oxygen species (ROS) in energy homeostasis regulation, but their involvement in the anorexigenic effect of insulin is unknown. Furthermore, ROS signal derived from NADPH oxidase activation is required for physiological insulin effects in peripheral cells. In this study, we investigated the involvement of hypothalamic ROS and NADPH oxidase in the feeding behavior regulation by insulin. RESEARCH DESIGN AND METHODS: We first measured hypothalamic ROS levels and food intake after acute intracerebroventricular injection of insulin. Second, effect of pretreatment with a ROS scavenger or an NADPH oxidase inhibitor was evaluated. Third, we examined the consequences of two nutritional conditions of central insulin unresponsiveness (fasting or short-term high-fat diet) on the ability of insulin to modify ROS level and food intake. RESULTS: In normal chow-fed mice, insulin inhibited food intake. At the same dose, insulin rapidly and transiently increased hypothalamic ROS levels by 36%. The pharmacological suppression of this insulin-stimulated ROS elevation, either by antioxidant or by an NADPH oxidase inhibitor, abolished the anorexigenic effect of insulin. Finally, in fasted and short-term high-fat diet-fed mice, insulin did not promote elevation of ROS level and food intake inhibition, likely because of an increase in hypothalamic diet-induced antioxidant defense systems. CONCLUSIONS: A hypothalamic ROS increase through NADPH oxidase is required for the anorexigenic effect of insulin

Mitochondrial Reactive Oxygen Species Are Obligatory Signals for Glucose-Induced Insulin Secretion

OBJECTIVE—Insulin secretion involves complex events in which the mitochondria play a pivotal role in the generation of signals that couple glucose detection to insulin secretion. Studies on the mitochondrial generation of reactive oxygen species (ROS) generally focus on chronic nutrient exposure. Here, we investigate whether transient mitochondrial ROS production linked to glucose-induced increased respiration might act as a signal for monitoring insulin secretion

Sensing the fuels: glucose and lipid signaling in the CNS controlling energy homeostasis

The central nervous system (CNS) is capable of gathering information on the body’s nutritional state and it implements appropriate behavioral and metabolic responses to changes in fuel availability. This feedback signaling of peripheral tissues ensures the maintenance of energy homeostasis. The hypothalamus is a primary site of convergence and integration for these nutrient-related feedback signals, which include central and peripheral neuronal inputs as well as hormonal signals. Increasing evidence indicates that glucose and lipids are detected by specialized fuel-sensing neurons that are integrated in these hypothalamic neuronal circuits. The purpose of this review is to outline the current understanding of fuel-sensing mechanisms in the hypothalamus, to integrate the recent findings in this field, and to address the potential role of dysregulation in these pathways in the development of obesity and type 2 diabetes mellitus

Hypothalamus-Olfactory System Crosstalk: Orexin A Immunostaining in Mice

It is well known that olfaction influences food intake, and conversely, that an individual’s nutritional status modulates olfactory sensitivity. However, what is still poorly understood is the neuronal correlate of this relationship, as well as the connections between the olfactory bulb and the hypothalamus. The goal of this report is to analyze the relationship between the olfactory bulb and hypothalamus, focusing on orexin A immunostaining, a hypothalamic neuropeptide that is thought to play a role in states of sleep/wakefulness. Interestingly, orexin A has also been described as a food intake stimulator. Such an effect may be due in part to the stimulation of the olfactory bulbar pathway. In rats, orexin positive cells are concentrated strictly in the lateral hypothalamus, while their projections invade nearly the entire brain including the olfactory system. Therefore, orexin appears to be a good candidate to play a pivotal role in connecting olfactory and hypothalamic pathways. So far, orexin has been described in rats, however, there is still a lack of information concerning its expression in the brains of adult and developing mice. In this context, we revisited the orexin A pattern in adult and developing mice using immunohistological methods and confocal microscopy. Besides minor differences, orexin A immunostaining in mice shares many features with those observed in rats. In the olfactory bulb, even though there are few orexin projections, they reach all the different layers of the olfactory bulb. In contrast to the presence of orexin projections in the main olfactory bulb, almost none have been found in the accessory olfactory bulb. The developmental expression of orexin A supports the hypothesis that orexin expression only appears post-natally.This work was supported by Research grant BFU2010-15564 from the Spanish Ministry of Economy and Competitiveness (MINECO) and by INRA (National Institute for Agronomical Research) and the Burgundy Regional Council (Conseil Régional de Bourgogne).Peer reviewedPeer Reviewe

Early effects of high-fat diet on hypothalamic cell proliferation

International audienceThe hypothalamus is one of the main brain structure involved in the control of. energy homeostasis. Recent reports indicate that hypothalamus exhibits neuroproliferative. potency in adult. Moreover, it has been found that hypothalamic cell. proliferation could be modulated by numerous intrinsic factors such as CNTF, IGF-. 1, bFGF and EGF, and by external and internal conditions such as dehydration,. variation in ambient temperature and during ovarian cycle. Interestingly, experimental. manipulation of neurogenesis can affect body weight. However, whether. nutritional conditions could influence hypothalamic cell proliferation and thereby. modify energy homeostasis is still unknown. To address this question, mice were. subjected to a high fat diet (HFD) for 1 week and hypothalamic cell renewal was. assessed through central chronic infusion of Bromodeoxy-Uridine (BrdU). Using this. approach, we report that hypothalamus constitutively exhibits G2000 BrdUpositive. neo-formed cells per day. This proliferative rate was significantly higher in hypothalamus 3 days after the onset of HFD (+60%) but decreased by 50% on day. 5. To determine whether these HFD-induced modifications of cell renewal were. linked to change in cell proliferation, we counted Ki67 immunoreactive cells. We. found 1937 Ki67 immunoreactive cells in hypothalamus from mice fed with. standard chow. However, the number of such cell was significantly higher in mice. fed with HFD for 1 and 3 days (+30% and 50%, respectively), and returned to basal. value after 5 days. In order to evaluate the role of newborn cells, HFD fed mice were. treated with the anti-mitotic arabinoside cytosine (AraC) for 30 days. Results show. that AraC treatment increased HFD-induced body weight gain, suggesting that. newborn HFD-induced cells produce anorectic function. Altogether these data. demonstrate that a change in diet induces cell proliferation in the hypothalamus. which might be involved in the control of long-term energy homeostasis

Stimulation of proteoglycan synthesis by glucuronosyltransferase-1 gene delivery: a strategy to promote cartilage repair

Osteoarthritis is a degenerative joint disease characterized by a progressive loss of articular cartilage components, mainly proteoglycans (PGs), leading to destruction of the tissue. We investigate a therapeutic strategy based on stimulation of PG synthesis by gene transfer of the glycosaminoglycan (GAG)-synthesizing enzyme, β1,3-glucuronosyltransferase-I (GlcAT-I) to promote cartilage repair. We previously reported that IL-1β down-regulated the expression and activity of GlcAT-I in primary rat chondrocytes. Here, by using antisense oligonucleotides, we demonstrate that GlcAT-I inhibition impaired PG synthesis and deposition in articular cartilage explants, emphasizing the crucial role of this enzyme in PG anabolism. Thus, primary chondrocytes and cartilage explants were engineered by lipid-mediated gene delivery to efficiently overexpress a human GlcAT-I cDNA. Interestingly, GlcAT-I overexpression significantly enhanced GAG synthesis and deposition as evidenced by (35)S-sulfate incorporation, histology, estimation of GAG content, and fluorophore-assisted carbohydrate electrophoresis analysis. Metabolic labeling and Western blot analyses further suggested that GlcAT-I expression led to an increase in the abundance rather than in the length of GAG chains. Importantly, GlcAT-I delivery was able to overcome IL-1β-induced PG depletion and maintain the anabolic activity of chondrocytes. Moreover, GlcAT-I also restored PG synthesis to a normal level in cartilage explants previously depleted from endogenous PGs by IL-1β-treatment. In concert, our investigations strongly indicated that GlcAT-I was able to control and reverse articular cartilage defects in terms of PG anabolism and GAG content associated with IL-1β. This study provides a basis for a gene therapy approach to promote cartilage repair in degenerative joint diseases

Methods for functional study of mitochondria inrat hypothalamus

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