Hypothalamic AMP-activated Protein Kinase Research Articles

Hypothalamic AMP-Activated Protein Kinase as a Whole-Body Energy Sensor and Regulator.

5´-Adenosine monophosphate (AMP)-activated protein kinase (AMPK), a cellular energy sensor, is an essential enzyme that helps cells maintain stable energy levels during metabolic stress. The hypothalamus is pivotal in regulating energy balance within the body. Certain neurons in the hypothalamus are sensitive to fluctuations in food availability and energy stores, triggering adaptive responses to preserve systemic energy equilibrium. AMPK, expressed in these hypothalamic neurons, is instrumental in these regulatory processes. Hypothalamic AMPK activity is modulated by key metabolic hormones. Anorexigenic hormones, including leptin, insulin, and glucagon-like peptide 1, suppress hypothalamic AMPK activity, whereas the hunger hormone ghrelin activates it. These hormonal influences on hypothalamic AMPK activity are central to their roles in controlling food consumption and energy expenditure. Additionally, hypothalamic AMPK activity responds to variations in glucose concentrations. It becomes active during hypoglycemia but is deactivated when glucose is introduced directly into the hypothalamus. These shifts in AMPK activity within hypothalamic neurons are critical for maintaining glucose balance. Considering the vital function of hypothalamic AMPK in the regulation of overall energy and glucose balance, developing chemical agents that target the hypothalamus to modulate AMPK activity presents a promising therapeutic approach for metabolic conditions such as obesity and type 2 diabetes mellitus.

Obesity wars: hypothalamic sEVs a new hope.

There are currently several pharmacological therapies available for the treatment of obesity, targeting both the central nervous system (CNS) and peripheral tissues. In recent years, small extracellular vesicles (sEVs) have been shown to be involved in many pathophysiological conditions. Because of their special nanosized structure and contents, sEVs can activate receptors and trigger intracellular pathways in recipient cells. Notably, in addition to transferring molecules between cells, sEVs can also alter their phenotypic characteristics. The purpose of this review is to discuss how sEVs can be used as a CNS-targeted strategy for treating obesity. Furthermore, we will evaluate current findings, such as the sEV-mediated targeting of hypothalamic AMP-activated protein kinase (AMPK), and discuss how they can be translated into clinical application.

Obesity wars: may the smell be with you.

Classically, the regulation of energy balance has been based on central and peripheral mechanisms sensing energy, nutrients, metabolites, and hormonal cues. Several cellular mechanisms at central level, such as hypothalamic AMP-activated protein kinase (AMPK), integrate this information to elicit counterregulatory responses that control feeding, energy expenditure, and glucose homeostasis, among other processes. Recent data have added more complexity to the homeostatic regulation of metabolism by introducing, for example, the key role of "traditional" senses and sensorial information in this complicated network. In this regard, current evidence is showing that olfaction plays a key and bidirectional role in energy homeostasis. Although nutritional status dynamically and profoundly impacts olfactory sensitivity, the sense of smell is involved in food appreciation and selection, as well as in brown adipose tissue (BAT) thermogenesis and substrate utilization, with some newly described actors, such as olfactomedin 2 (OLFM2), likely playing a major role. Thus, olfactory inputs are contributing to the regulation of both sides of the energy balance equation, namely, feeding and energy expenditure (EE), as well as whole body metabolism. Here, we will review the current knowledge and advances about the role of olfaction in the regulation of energy homeostasis.

A genetic variant of fatty acid amide hydrolase (FAAH) exacerbates hormone-mediated orexigenic feeding in mice.

Fatty acid amide hydrolase (FAAH) degrades the endocannabinoid anandamide. A polymorphism in FAAH (FAAH C385A) reduces FAAH expression, increases anandamide levels, and increases the risk of obesity. Nevertheless, some studies have found no association between FAAH C385A and obesity. We investigated whether the environmental context governs the impact of FAAH C385A on metabolic outcomes. Using a C385A knock-in mouse model, we found that FAAH A/A mice are more susceptible to glucocorticoid-induced hyperphagia, weight gain, and activation of hypothalamic AMP-activated protein kinase (AMPK). AMPK inhibition occluded the amplified hyperphagic response to glucocorticoids in FAAH A/A mice. FAAH knockdown exclusively in agouti-related protein (AgRP) neurons mimicked the exaggerated feeding response of FAAH A/A mice to glucocorticoids. FAAH A/A mice likewise presented exaggerated orexigenic responses to ghrelin, while FAAH knockdown in AgRP neurons blunted leptin anorectic responses. Together, the FAAH A/A genotype amplifies orexigenic responses and decreases anorexigenic responses, providing a putative mechanism explaining the diverging human findings.

Opposing effects of clozapine and brexpiprazole on β-aminoisobutyric acid: Pathophysiology of antipsychotics-induced weight gain

Clozapine is one of the most effective antipsychotics and has the highest risk of weight gain and metabolic complications; however, the detailed pathophysiology of its clinical action and adverse reactions remains to be clarified. Therefore, the present study determined the chronic effects of clozapine (high risk of weight gain) and brexpiprazole (relatively low risk of weight gain) on intracellular and extracellular levels of β-aminoisobutyric acid (BAIBA) enantiomers, which are endogenous activators of AMP-activated protein kinase (AMPK). L-BAIBA is the dominant BAIBA enantiomer in the rat hypothalamus and cultured astrocytes, whereas L-BAIBA accounts for only approximately 5% of the total plasma BAIBA enantiomers. L-BAIBA displayed GABAB receptor agonistic action in the extracellular space and was released through activated astroglial hemichannels, whereas in the intracellular space, L-BAIBA activated AMPK signalling. Chronic administration of the effective doses of clozapine increased intracellular and extracellular levels of L-BAIBA in the hypothalamus and cultured astrocytes, whereas that of brexpiprazole decreased them. These results suggest that enhancing hypothalamic AMPK signalling by increasing intracellular L-BAIBA levels is, at least partially, involved in the pathophysiology of clozapine-induced weight gain and metabolic complications.

Paliperidone-Induced Acute Hyperglycemia Is Caused by Adrenaline Secretion via the Activation of Hypothalamic AMP-Activated Protein Kinase.

Although paliperidone-related hyperglycemia has been extensively examined, the underlying mechanisms have not yet been elucidated. We investigated the effects of a single intravenous injection of paliperidone (0.2, 0.4, or 0.6 mg/kg) on serum concentrations of glucose and other endogenous metabolites in rats. We also examined the effects of a single intravenous injection of paliperidone (0.4 mg/kg) on AMP-activated protein kinase (AMPK) activity in the hypothalamus and liver. To clarify the relationship between AMPK activity and adrenaline secretion, the effects of berberine, which inhibits hypothalamic AMPK, on paliperidone-induced hyperglycemia were assessed. Significant increases were observed in serum glucose, adrenaline, and insulin concentrations following intravenous injections of paliperidone at doses of 0.4 and 0.6 mg/kg. A propranolol pretreatment attenuated paliperidone-induced increases in serum concentrations of glucose, but not adrenaline. Significant increases were also noted in phosphorylated AMPK concentrations in the hypothalamus following the administration of paliperidone at a dose of 0.4 mg/kg. A berberine pretreatment attenuated paliperidone-induced increases in blood concentrations of glucose, adrenaline, and insulin and phosphorylated AMPK concentrations in the hypothalamus. Collectively, the present results demonstrated that an acute treatment with paliperidone induced hyperglycemia, which was associated with the effects of hypothalamic AMPK activation on the secretion of adrenaline.

Ubiquitin-Specific Protease 2 in the Ventromedial Hypothalamus Modifies Blood Glucose Levels by Controlling Sympathetic Nervous Activation.

Ubiquitin-specific protease 2 (USP2) participates in glucose metabolism in peripheral tissues such as the liver and skeletal muscles. However, the glucoregulatory role of USP2 in the CNS is not well known. In this study, we focus on USP2 in the ventromedial hypothalamus (VMH), which has dominant control over systemic glucose homeostasis. ISH, using a Usp2-specific probe, showed that Usp2 mRNA is present in VMH neurons, as well as other glucoregulatory nuclei, in the hypothalamus of male mice. Administration of a USP2-selective inhibitor ML364 (20 ng/head), into the VMH elicited a rapid increase in the circulating glucose level in male mice, suggesting USP2 has a suppressive role on glucose mobilization. ML364 treatment also increased serum norepinephrine concentration, whereas it negligibly affected serum levels of insulin and corticosterone. ML364 perturbated mitochondrial oxidative phosphorylation in neural SH-SY5Y cells and subsequently promoted the phosphorylation of AMP-activated protein kinase (AMPK). Consistent with these findings, hypothalamic ML364 treatment stimulated AMPKα phosphorylation in the VMH. Inhibition of hypothalamic AMPK prevented ML364 from increasing serum norepinephrine and blood glucose. Removal of ROS restored the ML364-evoked mitochondrial dysfunction in SH-SY5Y cells and impeded the ML364-induced hypothalamic AMPKα phosphorylation as well as prevented the elevation of serum norepinephrine and blood glucose levels in male mice. These results indicate hypothalamic USP2 attenuates perturbations in blood glucose levels by modifying the ROS-AMPK-sympathetic nerve axis.SIGNIFICANCE STATEMENT Under normal conditions (excluding hyperglycemia or hypoglycemia), blood glucose levels are maintained at a constant level. In this study, we used a mouse model to identify a hypothalamic protease controlling blood glucose levels. Pharmacological inhibition of USP2 in the VMH caused a deviation in blood glucose levels under a nonstressed condition, indicating that USP2 determines the set point of the blood glucose level. Modification of sympathetic nervous activity accounts for the USP2-mediated glucoregulation. Mechanistically, USP2 mitigates the accumulation of ROS in the VMH, resulting in attenuation of the phosphorylation of AMPK. Based on these findings, we uncovered a novel glucoregulatory axis consisting of hypothalamic USP2, ROS, AMPK, and the sympathetic nervous system.

Activation of Hypothalamic AMP-Activated Protein Kinase Ameliorates Metabolic Complications of Experimental Arthritis.

To investigate whether thermogenesis and the hypothalamus may be involved in the physiopathology of experimental arthritis (EA). EA was induced in male Lewis rats by intradermal injection of Freund's complete adjuvant (CFA). Food intake, body weight, plasma cytokines, thermographic analysis, gene and protein expression of thermogenic markers in brown adipose tissue (BAT) and white adipose tissue (WAT), and hypothalamic AMP-activated protein kinase (AMPK) were analyzed. Virogenetic activation of hypothalamic AMPK was performed. We first demonstrated that EA was associated with increased BAT thermogenesis and browning of subcutaneous WAT leading to elevated energy expenditure. Moreover, rats experiencing EA showed inhibition of hypothalamic AMPK, a canonical energy sensor modulating energy homeostasis at the central level. Notably, specific genetic activation of AMPK in the ventromedial nucleus of the hypothalamus (a key site modulating energy metabolism) reversed the effect of EA on energy balance, brown fat, and browning, as well as promoting amelioration of synovial inflammation in experimental arthritis. Overall, these data indicate that EA promotes a central catabolic state that can be targeted and reversed by the activation of hypothalamic AMPK. This might provide new therapeutic alternatives to treat rheumatoid arthritis (RA)-associated metabolic comorbidities, improving the overall prognosis in patients with RA.

The activation of hypothalamic AMP-activated protein kinase by oxidative stress is related to hyperphagia in diabetic rats.

During diabetes, there are increased blood glucose levels and oxidative stress. The relationship between oxidative stress and the phosphorylation of AMP-activated protein kinase at the hypothalamic level has been little studied. The objective of this study was to analyze the relationship between oxidative stress and AMP-activated protein kinase activation in Wistar rats with hyperphagia and hyperglycemia. Rats at 7, 14, and 28 days with diabetes were used. Control rats were included. Food intake was calculated to determine hyperphagia. The hypothalamus was extracted to evaluate oxidative stress markers by spectrophotometry; phosphorylation of AMP-activated protein kinase, growth hormone receptor 1a, and neuropeptide Y expression were determined by Western blot. There was a significant increase in the consumption of food in the experimental groups. The level of malondialdehyde decreased in the 7-day group (33%) and increased significantly in the 28-day group (90%), glutathione peroxidase activity increased in the 7-day group (70%) and decreased in the 28-day group (34%), and the phosphorylation of AMP-activated protein kinase increased significantly in the 28-day group (86%). Under ex-vivo conditions in animals with 28 days of hyperglycemia, glutathione peroxidase activity increased 195%, the malondialdehyde level decreased 87%, phosphorylation of AMP-activated protein kinase decreased 53%, and growth hormone receptor 1a expression decreased 66%, when treating hyperglycemic hypothalamic tissue with an antioxidant. NPY expression increased in hyperglycemia, and antioxidant treatment did not regulate its expression. The activation of AMP-activated protein kinase is related with an increase in oxidative stress markers in hyperglycemic and hyperphagic rats.

Orally Induced Hyperthyroidism Regulates Hypothalamic AMP-Activated Protein Kinase.

Besides their direct effects on peripheral metabolic tissues, thyroid hormones (TH) act on the hypothalamus to modulate energy homeostasis. However, since most of the hypothalamic actions of TH have been addressed in studies with direct central administration, the estimation of the relative contribution of the central vs. peripheral effects in physiologic conditions of peripheral release (or administration) of TH remains unclear. In this study we used two different models of peripherally induced hyperthyroidism (i.e., T4 and T3 oral administration) to assess and compare the serum and hypothalamic TH status and relate them to the metabolic effects of the treatment. Peripheral TH treatment affected feeding behavior, overall growth, core body temperature, body composition, brown adipose tissue (BAT) morphology and uncoupling protein 1 (UCP1) levels and metabolic activity, white adipose tissue (WAT) browning and liver metabolism. This resulted in an increased overall uncoupling capacity and a shift of the lipid metabolism from WAT accumulation to BAT fueling. Both peripheral treatment protocols induced significant changes in TH concentrations within the hypothalamus, with T3 eliciting a downregulation of hypothalamic AMP-activated protein kinase (AMPK), supporting the existence of a central action of peripheral TH. Altogether, these data suggest that peripherally administered TH modulate energy balance by various mechanisms; they also provide a unifying vision of the centrally mediated and the direct local metabolic effect of TH in the context of hyperthyroidism.

The influence of thyroid state on hypothalamic AMP-activated protein kinase pathways in broilers

To investigate whether there are important interactions in play in broilers between thyroid hormones and the central regulation of energy homeostasis through AMP-activated protein kinase (AMPK), we induced a functional hyperthyroid and hypothyroid state in broiler chicks, and quantified systemic and hypothalamic AMPK related gene expression and related protein. Thyroid state was manipulated through dietary supplementation of triiodothyronine (T3) or methimazole (MMI) for 7 days. A hypothalamic AMPK suppressor, 0.1% α-lipoic acid (α-LA) was used to assess the effects of the T3 and MMI feed formulations on the AMPK pathways. Feed intake and body weight were reduced in both hypothyroid and hyperthyroid conditions. In hyperthyroid conditions (T3 supplementation) expression of the AMPKα1 subunit increased, while in hypothyroid conditions (MMI supplementation) active phosphorylated AMPK levels in the hypothalamus dropped, but gene expression of the AMPKα1 and α2 subunit increased. For FAS and ACC (involved in fatty acid metabolism), and CRH, TRH and CNR1 (anorexigenic neuropeptides stimulating energy expenditure) there were indications that their regulation in response to thyroid state might be modulated through AMPK pathways. Our results indicate that the expression of hypothalamic AMPK as well as that of several other genes from AMPK pathways are involved in thyroid-hormone-induced changes in appetite, albeit differently according to thyroid state.

Hypothalamic regulation of energy homoeostasis when consuming diets of different energy concentrations: comparison between Tibetan and Small-tailed Han sheep.

Seasonal energy intake of Tibetan sheep on the harsh Qinghai-Tibetan Plateau (QTP) fluctuates greatly and is often well below maintenance requirements. The aim of this study was to gain insight into how the hypothalamus regulates energy homoeostasis in Tibetan sheep. We compared Tibetan and Small-tailed Han sheep (n 24 of each breed), which were each allocated randomly into four groups and offered one of four diets that differed in digestible energy densities: 8·21, 9·33, 10·45 and 11·57 MJ/kg DM. Sheep were weighed every 2 weeks, and it was assumed that the change in body weight (BW) reflected the change in energy balance. The arcuate nucleus of the hypothalamus in Tibetan sheep had greater protein expressions of neuropeptide Y (NPY) and agouti-related peptide (AgRP) when in negative energy balance, but lesser protein expressions of proopiomelanocortin (POMC) and cocaine and amphetamine-regulated transcript (CART) when in positive energy balance than Small-tailed Han sheep. As a result, Tibetan sheep had a lesser BW loss when in negative energy balance and stored more energy and gained more BW when in positive energy balance than Small-tailed Han sheep with the same dietary intake. Moreover, in the hypothalamic adenosine monophosphate-activated protein kinase (AMPK) regulation pathway, Tibetan sheep had greater adenosine monophosphate-activated protein kinase-α 2 protein expression than Small-tailed Han sheep, which supported the premise of a better ability to regulate energy homoeostasis and better growth performance. These differences in the hypothalamic NPY/AgRP, POMC/CART and AMPK pathways between breeds conferred an advantage to the Tibetan over Small-tailed Han sheep to cope with low energy intake on the harsh QTP.

Activity-Based Anorexia Induces Browning of Adipose Tissue Independent of Hypothalamic AMPK.

Anorexia nervosa (AN) is an eating disorder leading to malnutrition and, ultimately, to energy wasting and cachexia. Rodents develop activity-based anorexia (ABA) when simultaneously exposed to a restricted feeding schedule and allowed free access to running wheels. These conditions lead to a life-threatening reduction in body weight, resembling AN in human patients. Here, we investigate the effect of ABA on whole body energy homeostasis at different housing temperatures. Our data show that ABA rats develop hyperactivity and hypophagia, which account for a massive body weight loss and muscle cachexia, as well as reduced uncoupling protein 1 (UCP1) expression in brown adipose tissue (BAT), but increased browning of white adipose tissue (WAT). Increased housing temperature reverses not only the hyperactivity and weight loss of animals exposed to the ABA model, but also hypothermia and loss of body and muscle mass. Notably, despite the major metabolic impact of ABA, none of the changes observed are associated to changes in key hypothalamic pathways modulating energy metabolism, such as AMP-activated protein kinase (AMPK) or endoplasmic reticulum (ER) stress. Overall, this evidence indicates that although temperature control may account for an improvement of AN, key hypothalamic pathways regulating thermogenesis, such as AMPK and ER stress, are unlikely involved in later stages of the pathophysiology of this devastating disease.

P-Coumaric Acid Enhances Hypothalamic Leptin Signaling and Glucose Homeostasis in Mice via Differential Effects on AMPK Activation.

AMP-activated protein kinase (AMPK) plays a crucial role in the regulation of energy homeostasis in both peripheral metabolic organs and the central nervous system. Recent studies indicated that p-Coumaric acid (CA), a hydroxycinnamic phenolic acid, potentially activated the peripheral AMPK pathway to exert beneficial effects on glucose metabolism in vitro. However, CA’s actions on central AMPK activity and whole-body glucose homeostasis have not yet been investigated. Here, we reported that CA exhibited different effects on peripheral and central AMPK activation both in vitro and in vivo. Specifically, while CA treatment promoted hepatic AMPK activation, it showed an inhibitory effect on hypothalamic AMPK activity possibly by activating the S6 kinase. Furthermore, CA treatment enhanced hypothalamic leptin sensitivity, resulting in increased proopiomelanocortin (POMC) expression, decreased agouti-related peptide (AgRP) expression, and reduced daily food intake. Overall, CA treatment improved blood glucose control, glucose tolerance, and insulin sensitivity. Together, these results suggested that CA treatment enhanced hypothalamic leptin signaling and whole-body glucose homeostasis, possibly via its differential effects on AMPK activation.

AMPK-Dependent Mechanisms but Not Hypothalamic Lipid Signaling Mediates GH-Secretory Responses to GHRH and Ghrelin.

GH (growth hormone) secretion/action is modulated by alterations in energy homeostasis, such as malnutrition and obesity. Recent data have uncovered the mechanism by which hypothalamic neurons sense nutrient bioavailability, with a relevant contribution of AMPK (AMP-activated protein kinase) and mTOR (mammalian Target of Rapamycin), as sensors of cellular energy status. However, whether central AMPK-mediated lipid signaling and mTOR participate in the regulation of pituitary GH secretion remains unexplored. We provide herein evidence for the involvement of hypothalamic AMPK signaling, but not hypothalamic lipid metabolism or CPT-1 (carnitine palmitoyltransferase I) activity, in the regulation of GH stimulatory responses to the two major elicitors of GH release in vivo, namely GHRH (growth hormone–releasing hormone) and ghrelin. This effect appeared to be GH-specific, as blocking of hypothalamic AMPK failed to influence GnRH (gonadotropin-releasing hormone)-induced LH (luteinizing hormone) secretion. Additionally, central mTOR inactivation did not alter GH responses to GHRH or ghrelin, nor this blockade affected LH responses to GnRH in vivo. In sum, we document here for the first time the indispensable and specific role of preserved central AMPK, but not mTOR, signaling, through a non-canonical lipid signaling pathway, for proper GH responses to GHRH and ghrelin in vivo.

Effects of acute versus recurrent insulin-induced hypoglycemia on ventromedial hypothalamic nucleus metabolic-sensory neuron AMPK activity: Impact of alpha1-adrenergic receptor signaling

Mechanisms that underlie metabolic sensor acclimation to recurring insulin-induced hypoglycemia (RIIH) are unclear. Norepinephrine (NE) regulates ventromedial hypothalamic nucleus (VMN) gluco-stimulatory nitric oxide (NO) and gluco-inhibitory γ-aminobutryic acid (GABA) neuron signaling. Current research addressed the hypothesis that during RIIH, NE suppresses 5′-AMP-activated protein kinase (AMPK) reactivity in both populations and impedes counter-regulation. The brain is postulated to utilize non-glucose substrates, e.g. amino acids glutamine (Gln), glutamate (Glu), and aspartate (Asp), to produce energy during hypoglycemia. A correlated aim investigated whether NE controls pyruvate recycling pathway marker protein (glutaminase, GLT; malic enzyme, ME-1) expression in either metabolic-sensory cell population. Male rats were injected subcutaneously with vehicle or insulin on days 1–3, then pretreated on day 4 by intracerebroventricular delivery of the alpha1-adrenergic receptor (α1-AR) reverse-agonist prazocin (PRZ) or vehicle before final insulin therapy. PRZ prevented acute hypoglycemic augmentation of AMPK activation in each cell group. Antecedent hypoglycemic repression of sensor activity was reversed by PRZ in GABA neurons. During RIIH, nitrergic neurons exhibited α1-AR – dependent up-regulated GLT and α2-AR profiles, while GABA cells showed down-regulated α1-AR. LC-ESI-MS analysis documented a decline in VMN Glu, Gln, and Asp concentrations during acute hypoglycemia, and habituation of the former two profiles to RIIH. PRZ attenuated glucagon and corticosterone secretion during acute hypoglycemia, but reversed decrements in output of both hormones during RIIH. Results implicate adjustments in impact of α1-AR signaling in repressed VMN metabolic-sensory AMPK activation and counter-regulatory dysfunction during RIIH. Antecedent hypoglycemia may up-regulate NO neuron energy yield via α1-AR – mediated up-regulated pyruvate recycling.

Central Injection of Leptin Increases Sympathetic Nerve Outflows to the Stomach and Spleen in Anesthetized Rats.

Leptin, one of the hormones produced in white adipose tissue, is an efferent sympathetic stimulator. Actually, an injection of leptin into the brain has been shown to activate sympathetic nerve activities innervating the kidney, adrenal gland, adipose tissues, liver, and lumbar in rats. This study investigated the effects of an intracerebroventricular injection of leptin on the activities of sympathetic nerves innervating the stomach and spleen in anesthetized rats. Leptin injection activated the neural activities of sympathetic traffic to both the stomach and spleen. In addition, to investigate the role of AMP-activated protein kinase (AMPK), the effects of 5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside (AICAR), an AMPK activator, or compound C, an AMPK inhibitor, on leptin-induced sympathoexcitation, were assessed. Central pretreatment with AICAR or compound C eliminated not only leptin-induced gastric sympathoexcitation but also leptin-induced splenic sympathoexcitation. Leptin stimulates efferent sympathetic outflow to the stomach and spleen through the hypothalamic AMPK.

Hindbrain dorsal vagal complex AMPK controls hypothalamic gluco-regulatory transmitter and counter-regulatory hormone responses to hypoglycemia

Pharmacologic activation of the hindbrain dorsal vagal complex energy sensor 5′-adenosine monophosphate-activated protein kinase (AMPK) causes site-specific adjustments in hypothalamic AMPK activity. DVC A2 noradrenergic neurons are a likely source of metabolo-sensory cues to downstream network components as they express substrate fuel-sensitive AMPK. This study investigated the hypothesis that DVC AMPK controls hypothalamic sensor, metabolic effector transmitter, and counter-regulatory hormone responses to insulin-induced hypoglycemia. Male rats were injected into the caudal fourth ventricle with the AMPK inhibitor compound C (Ccor vehicle before hypoglycemia. Arcuate (ARH), ventromedial (VMN), and dorsomedial (DMN) nuclei and lateral hypothalamic area (LHA) were micropunch-dissected for norepinephrine ELISA and Western blot analyses. Hypoglycemic stimulation of norepinephrine activity in each site was impeded by compound C. Hypoglycemia caused drug-revocable (ARH) or -refractory (VMN, DMN) reductions in AMPK, alongside hindbrain AMPK-dependent augmentation of phospho-AMPK expression in each location. Compound C prevented hypoglycemic augmentation of gluco-stimulatory ARH neuropeptide Y, VMN neuronal nitric oxide synthase, and LHA orexin-A expression, while hypoglycemic suppression of the catabolic neuron protein markers ARH pro-opiomelanocortin and VMN glutamate decarboxylase65/67 was respectively averted or unaffected by drug treatment. DMN RFamide-related peptide-1 and -3 profiles were correspondingly amplified or suppressed hindbrain AMPK-reliant mechanisms during hypoglycemia. Results show that DVC AMPK is required for hypoglycemic intensification of norepinephrine activity in characterized hypothalamic gluco-regulatory structures, and that this sensor regulates AMPK activation and metabolic effector transmission in those sites.

Differential Role of Hypothalamic AMPKα Isoforms in Fish: an Evolutive Perspective.

In mammals, hypothalamic AMP-activated protein kinase (AMPK) α1 and α2 isoforms mainly relate to regulation of thermogenesis/liver metabolism and food intake, respectively. Since both isoforms are present in fish, which do not thermoregulate, we assessed their role(s) in hypothalamus regarding control of food intake and energy homeostasis. Since many fish species are carnivorous and mostly mammals are omnivorous, assessing if the role of hypothalamic AMPK is different is also an open question. Using the rainbow trout as a fish model, we first observed that food deprivation for 5days did not significantly increase phosphorylation status of AMPKα in hypothalamus. Then, we administered adenoviral vectors that express dominant negative (DN) AMPKα1 or AMPKα2 isoforms. The inhibition of AMPKα2 (but not AMPKα1) led to decreased food intake. The central inhibition of AMPKα2 resulted in liver with decreased capacity of use and synthesis of glucose, lipids, and amino acids suggesting that a signal of nutrient abundance flows from hypothalamus to the liver, thus suggesting a role for central AMPKα2 in the regulation of peripheral metabolism in fishes. The central inhibition of AMPKα1 induced comparable changes in liver metabolism though at a lower extent. From an evolutionary point of view, it is of interest that the function of central AMPKα2 remained similar throughout the vertebrate lineage. In contrast, the function of central AMPKα1 in fish relates to modulation of liver metabolism whereas in mammals modulates not only liver metabolism but also brown adipose tissue and thermogenesis.

Hypothalamic AMPK as a Mediator of Hormonal Regulation of Energy Balance.

As a cellular energy sensor and regulator, adenosine monophosphate (AMP)-activated protein kinase (AMPK) plays a pivotal role in the regulation of energy homeostasis in both the central nervous system (CNS) and peripheral organs. Activation of hypothalamic AMPK maintains energy balance by inducing appetite to increase food intake and diminishing adaptive thermogenesis in adipose tissues to reduce energy expenditure in response to food deprivation. Numerous metabolic hormones, such as leptin, adiponectin, ghrelin and insulin, exert their energy regulatory effects through hypothalamic AMPK via integration with the neural circuits. Although activation of AMPK in peripheral tissues is able to promote fatty acid oxidation and insulin sensitivity, its chronic activation in the hypothalamus causes obesity by inducing hyperphagia in both humans and rodents. In this review, we discuss the role of hypothalamic AMPK in mediating hormonal regulation of feeding and adaptive thermogenesis, and summarize the diverse underlying mechanisms by which central AMPK maintains energy homeostasis.