To subjugate NPY is to improve the quality of life and live longer

The interactive network of neuropeptide Y (NPY) and cohorts is necessary for integrating the hypothalamic regulation of appetite and energy expenditure with the endocrine and neuroendocrine systems on a daily basis. Genetic and environmental factors that produce an insufficiency of leptin restraint on NPY and cognate receptors deregulate the homeostasis to engender various life-threatening risk factors. Recent studies from our laboratory show that neurotherapy consisting of a single central administration of recombinant adeno-associated virus vector encoding the leptin gene can repress the hypothalamic NPY system for the lifetime of rodents. A major benefit of this stable tonic restraint is deceleration of pathophysiologic sequalae that shorten life span. These include suppression of weight gain, fat accumulation, circulating adipokines, amelioration of major symptoms of metabolic syndrome, improved reproduction and bone health. Thus, sustained repression of NPY signaling in the hypothalamus by leptin transgene expression can improve the quality of life and extend longevity.     

Rhythmic,reciprocal ghrelin and leptin signaling: new insight in the development of obesity

The hypothalamus integrates metabolic, neural and hormonal signals to evoke an intermittent appetitive drive in the daily management of energy homeostasis. Three major players identified recently in the feedback communication between the periphery and hypothalamus are leptin, ghrelin and neuropeptide Y (NPY). We propose that reciprocal circadian and ultradian rhythmicities in the afferent humoral signals, anorexigenic leptin from adipocytes and orexigenic ghrelin from stomach, encode a corresponding discharge pattern in the appetite-stimulating neuropeptide Y network in the hypothalamus. An exquisitely intricate temporal relationship among these signaling modalities with varied sites of origin is paramount in sustenance of weight control on a daily basis. Our model envisages that subtle and progressive derangements in temporal communication, imposed by environmental shifts in energy intake, impel a positive energy balance culminating in excessive weight gain and obesity. This conceptual advance provides a new target for designing pharmacologic or gene transfer therapies that would normalize the rhythmic patterns of afferent hormonal and efferent neurochemical messages.     

The distribution and mechanism of action of ghrelin in the CNS demonstrates a novel hypothalamic circuit regulating energy homeostasis

The gastrointestinal peptide hormone ghrelin stimulates appetite in rodents and humans via hypothalamic actions. We discovered expression of ghrelin in a previously uncharacterized group of neurons adjacent to the third ventricle between the dorsal, ventral, paraventricular, and arcuate hypothalamic nuclei. These neurons send efferents onto key hypothalamic circuits, including those producing neuropeptide Y (NPY), Agouti-related protein (AGRP), proopiomelanocortin (POMC) products, and corticotropin-releasing hormone (CRH). Within the hypothalamus, ghrelin bound mostly on presynaptic terminals of NPY neurons. Using electrophysiological recordings, we found that ghrelin stimulated the activity of arcuate NPY neurons and mimicked the effect of NPY in the paraventricular nucleus of the hypothalamus (PVH). We propose that at these sites, release of ghrelin may stimulate the release of orexigenic peptides and neurotransmitters, thus representing a novel regulatory circuit controlling energy homeostasis.     

Hypothalamic neuronal histamine in genetically obese animals: its implication of leptin action in the brain

Leptin regulates feeding behavior and energy metabolism by affecting hypothalamic neuromodulators. The present study was designed to examine hypothalamic neuronal histamine, a recently identified mediator of leptin signaling in the brain, in genetic obese animals. Concentrations of hypothalamic histamine and tele-methylhistamine (t-MH), a major histamine metabolite, were significantly lower in obese (ob/ob) and diabetic (db/db) mice, and Zucker fatty (fa/fa) rats, leptin-deficient and leptin-receptor defective animals, respectively, relative to lean littermates (P < 0.05 for each). A bolus infusion of leptin (1.0 microg) into the lateral ventricle (ilvt) significantly elevated the turnover rate of hypothalamic neuronal histamine, as assessed by pargyline-induced accumulation of t-MH, in ob/ob mice compared with phosphate-buffered saline (PBS) infusions (P < 0.05). However, this same treatment did not affect hypothalamic histamine turnover in db/db mice. In agouti yellow (A(y)/a) mice, animals defective in pro-opiomelanocortin (POMC) signaling, normal levels of histamine, and t-MH were seen in the hypothalamus at 4 weeks of age when obesity had not yet developed. These amine levels in A(y)/a mice showed no change until 16 weeks of age, although the mice were remarkably obese by this time. Infusions of corticotropin releasing hormone (CRH), one of neuropeptide related to leptin signaling, into the third ventricle (i3vt) increased histamine turnover in the hypothalamus of Wistar King A rats (P < 0.05 versus PBS infusion). Infusion of neuropeptide Y (NPY) or alpha-melanocyte stimulating hormone (MSH), a POMC-derived peptide failed to increase histamine turnover. These results indicate that lowered activity of hypothalamic neuronal histamine in ob/ob and db/db mice, and fa/fa rats may be due to insufficiency of leptin action in the brains of these animals. These results also suggest that disruption of POMC signaling in A(y)/a mice may not impact on neuronal histamine. Moreover, CRH but neither POMC-derived peptide nor NPY may act as a signal to neuronal histamine downstream of the leptin signaling pathway.     

Appetite regulation: The central role of melatonin in Danio rerio

Melatonin is the hormonal mediator of photoperiodic information to the central nervous system in vertebrates and allows the regulation of energy homeostasis through the establishment of a proper balance between energy intake and energy expenditure. The aim of this study was to evaluate the role of melatonin in appetite central control analyzing the involvement of this hormone in the regulation of feeding behavior in the zebrafish Danio rerio. For this purpose, the effect of two different melatonin doses (100 nM and 1 μM) administered for 10 days, via water, to zebrafish adults was evaluated at both physiological and molecular level and the effect of melatonin was considered in relation to the most prominent systems involved in appetite regulation. For the first time, in fact, melatonin control of food intake by the modulation of leptin, MC4R, ghrelin, NPY and CB1 gene expression was evaluated.The results obtained indicate that melatonin significantly reduces food intake and the reduction is in agreement with the changes observed at molecular level. A significant increase in genes codifying for molecules involved in feeding inhibition, such as leptin and MC4R, and a significant reduction in the major orexigenic signals including ghrelin, NPY and CB1 are showed here.Taken together these results support the idea that melatonin falls fully into the complex network of signals that regulate food intake thus playing a key role in central appetite regulation.     

Leptin sensitive neurons in the hypothalamus.

A major paradigm in the field of obesity research is the existence of an adipose tissue-brain endocrine axis for the regulation of body weight. Leptin, the peptide mediator of this axis, is secreted by adipose cells. It lowers food intake and body weight by acting in the hypothalamus, a region expressing an abundance of leptin receptors and a variety of neuropeptides that influence food intake and energy balance. Among the most promising candidates for leptin-sensitive cells in the hypothalamus are arcuate nucleus neurons that co-express the anabolic neuropeptides, neuropeptide Y (NPY) and agouti-related peptide (AGRP), and those that express proopiomelanocortin (POMC), the precursor of the catabolic peptide, alphaMSH. These cell types contain mRNA encoding leptin receptors and show changes in neuropeptide gene expression in response to changes in food intake and circulating leptin levels. Decreased leptin signaling in the arcuate nucleus is hypothesized to increase the expression of NPY and AGRP. Levels of leptin receptor mRNA and leptin binding are increased in the arcuate nucleus during fasting, principally in NPY/AGRP neurons. These findings suggest that changes in leptin receptor expression in the arcuate nucleus are inversely associated with changes in leptin signaling, and that the arcuate nucleus is an important target of leptin action in the brain.     

Role of the AMP-activated protein kinase (AMPK) signaling pathway in the orexigenic effects of endogenous ghrelin

Ghrelin, released from the stomach, stimulates food intake through activation of the ghrelin receptor (GHS-R) located on neuropeptide Y (NPY)/agouti-related peptide (AgRP) neurons in the hypothalamus. A role for the energy sensor AMP-activated protein kinase (AMPK) and its downstream effector uncoupling protein 2 (UCP2) in the stimulatory effect of exogenous ghrelin on NPY/AgRP expression and food intake has been suggested. This study aimed to investigate whether a rise in endogenous ghrelin levels is able to influence hypothalamic AMPK activity, pACC, UCP2 and NPY/AgRP expression through activation of GHS-R. An increase in endogenous ghrelin levels was established by fasting (24h) or by induction of streptozotocin(STZ)-diabetes (15 days) in GHS-R(+/+) and GHS-R(-/-) mice. GHS-R(+/+) mice showed a significant increase in AgRP and NPY mRNA expression after fasting, which was not observed in GHS-R(-/-) mice. Fasting did not affect AMPK activity nor ACC phosphorylation in both genotypes and increased UCP2 mRNA expression. The hyperghrelinemia associated with STZ-induced diabetes was accompanied by an increased NPY and AgRP expression in GHS-R(+/+) but not in GHS-R(-/-) mice. AMPK activity and UCP2 expression in GHS-R(+/+) mice after induction of diabetes were decreased to a similar extent in both genotypes. Exogenous ghrelin administration tended to decrease hypothalamic AMPK activity. In conclusion, an increase in endogenous ghrelin levels triggered by fasting or STZ-induced diabetes stimulates the expression of AgRP and NPY via interaction with the GHS-R. The changes in AMPK activity, pACC and UCP2 occur independently from GHS-R suggesting that they do not play a major role in the orexigenic effect of endogenous ghrelin.     

Leptin and neuropeptide Y (NPY) modulate nitric oxide synthase: further evidence for a role of nitric oxide in feeding.

Recent studies have suggested a role for nitric oxide in the regulation of food intake. Neuropeptide Y (NPY) is one of the most potent orexigenic agents. Chronic administration of leptin decreases food intake. This study examined the effects of NPY and leptin on nitric oxide synthase (NOS) in the hypothalamus. Previously it has been demonstrated that obese (ob/ob) mice have elevated NOS levels in the hypothalamus. In this study we demonstrated that the administration of leptin (6 microg/day) subcutaneously (SC) for 3 days decreased body weight (P < 0.001) and food intake P < 0.001) in obese (ob/ob) mice as expected. In addition, leptin decreased NOS in the hypothalamus nu 37% (P < 0.01) and in brown adipose tissue by 69% (P < 0.01) but not in white adipose tissue. NPY was administered intracerebroventricularly to CD-1 mice at doses of 0.25 and 0.50 microg. Mice were sacrificed 15 min after injection and NOS was measured in their hypothalami. NPY at the lower dose increased NOS in the hypothalamus by 147%. These results, taken together, with previously published studies support the concept that nitric oxide may play a role as a mediator of the effects of NPY and leptin on food intake. The alterations of NOS in brown adipose tissue following leptin administration could result in changes in blood flow or metabolism in the brown fat.     

Leptin,a tool of parasites?

One common physiological phenomenon that is involved both in infectious and in malignant processes is the reduction in appetite: disease anorexia. An increase in plasma levels of leptin with inflammation is thought to be involved in this process. However, from an evolutionary perspective, in certain cases, it would be more adaptive for an internal parasite to stimulate the appetite of the host instead of causing its suppression. We tested whether a parasitic infection with the larvae of the helminth parasite Taenia taeniaformis affects the levels of appetite-regulating proteins, such as leptin, ghrelin and neuropeptide-Y (NPY) in wild yellow-necked mouse (Apodemus flavicollis). We found that infected mice had lower plasma levels of leptin and increased levels of NPY than the uninfected subjects. Ghrelin levels were not associated with the occurrence of the parasites; however, these levels strongly correlated with the levels of NPY. This study suggests a possible manipulation by parasitic larvae of appetite regulation in infected subjects.     

Neuroendocrine actions and regulation of hypothalamic neuropeptide Y during lactation

The expression of neuropeptide Y (NPY) and its co-messenger, agouti-related peptide (AgRP), in arcuate neurons of the hypothalamus is increased during lactation in rats. Our research has been addressing the questions of the physiological actions of these peptides during lactation and the physiological signals associated with lactation that result in increased expression of their genes. Our studies indicate that NPY and AgRP exert pleiotropic actions during lactation that help integrate neuroendocrine regulation of energy balance with controls over anterior and posterior pituitary hormone secretion. Further, reciprocal signaling to the NPY/AgRP system by leptin and ghrelin is responsible for the changes in expression of these hypothalamic peptides in lactating animals, and thus, may contribute to regulation of food intake and the various neuroendocrine adaptations of lactation.     

NPY/neuropeptide Y enhances autophagy in the hypothalamus: a mechanism to delay aging?

Aging was recently described as a life event programmed by the hypothalamus, a key brain region that is crucial for the neuroendocrine interaction between the central nervous system and the periphery. Autophagy impairment is a hallmark of aging, contributing to the aging phenotype and to the aggravation of age-related diseases. Since hypothalamic autophagy decreases with age, strategies to promote autophagy in the hypothalamus may be relevant for control of the aging process. NPY (neuropeptide Y) is an endogenous neuropeptide mainly produced by the hypothalamus. We recently reported, for the first time, that NPY stimulates autophagy in rodent hypothalamus and mediates caloric restriction-induced autophagy in hypothalamic neurons. Moreover, we observed that NPY acts through NPY1R (neuropeptide Y receptor Y1) or NPY5R activation involving a concerted action of different signaling pathways. Since both hypothalamic autophagy and NPY levels decrease with age, modulation of NPY levels could provide new putative therapeutic tools to ameliorate age-related deteriorations and extend longevity.     

Changes of plasma obestatin, ghrelin and NPY in anorexia and bulimia nervosa patients before and after a high-carbohydrate breakfast

Peptides ghrelin, obestatin and neuropeptide Y (NPY) play an important role in regulation of energy homeostasis, the imbalance of which is associated with eating disorders anorexia (AN) and bulimia nervosa (BN). The changes in ghrelin, obestatin and NPY plasma levels were investigated in AN and BN patients after administration of a high-carbohydrate breakfast (1604 kJ). Eight AN women (aged 25.4+/-1.9, BMI: 15.8+/-0.5), thirteen BN women (aged 22.0+/-1.05, BMI: 20.1+/-0.41) and eleven healthy women (aged 25.1+/-1.16, BMI: 20.9+/-0.40) were recruited for the study. We demonstrated increased fasting ghrelin in AN, but not in BN patients, while fasting obestatin and NPY were increased in both AN and BN patients compared to the controls. Administration of high-carbohydrate breakfast induced a similar relative decrease in ghrelin and obestatin plasma levels in all groups, while NPY remained increased in postprandial period in both patient groups. Ghrelin/obestatin ratio was lower in AN and BN compared to the controls. In conclusions, increased plasma levels of fasting NPY and its unchanged levels after breakfast indicate that NPY is an important marker of eating disorders AN and BN. Different fasting ghrelin and obestatin levels in AN and BN could demonstrate their diverse functions in appetite and eating suppression.     

Selected hormonal and neurotransmitter mechanisms regulating feed intake in sheep

Appetite control is a major issue in normal growth and in suboptimal growth performance settings. A number of hormones, in particular leptin, activate or inhibit orexigenic or anorexigenic neurotransmitters within the arcuate nucleus of the hypothalamus, where feed intake regulation is integrated. Examples of appetite regulatory neurotransmitters are the stimulatory neurotransmitters neuropeptide Y (NPY), agouti-related protein (AgRP), orexin and melanin-concentrating hormone and the inhibitory neurotransmitter, melanocyte-stimulating hormone (MSH). Examination of messenger RNA (using in situ hybridization and real-time PCR) and proteins (using immunohistochemistry) for these neurotransmitters in ruminants has indicated that physiological regulation occurs in response to fasting for several of these critical genes and proteins, especially AgRP and NPY. Moreover, intracerebroventricular injection of each of the four stimulatory neurotransmitters can increase feed intake in sheep and may also regulate either growth hormone, luteinizing hormone, cortisol or other hormones. In contrast, both leptin and MSH are inhibitory to feed intake in ruminants. Interestingly, the natural melanocortin-4 receptor (MC4R) antagonist, AgRP, as well as NPY can prevent the inhibition of feed intake after injection of endotoxin (to model disease suppression of appetite). Thus, knowledge of the mechanisms regulating feed intake in the hypothalamus may lead to mechanisms to increase feed intake in normal growing animals and prevent the wasting effects of severe disease in animals.     

Hypothalamic CaMKK2 contributes to the regulation of energy balance

Detailed knowledge of the pathways by which ghrelin and leptin signal to AMPK in hypothalamic neurons and lead to regulation of appetite and glucose homeostasis is central to the development of effective means to combat obesity. Here we identify CaMKK2 as a component of one of these pathways, show that it regulates hypothalamic production of the orexigenic hormone NPY, provide evidence that it functions as an AMPK kinase in the hypothalamus, and demonstrate that it forms a unique signaling complex with AMPK and β. Acute pharmacologic inhibition of CaMKK2 in wild-type mice, but not CaMKK2 null mice, inhibits appetite and promotes weight loss consistent with decreased NPY and AgRP mRNAs. Moreover, the loss of CaMKK2 protects mice from high-fat diet-induced obesity, insulin resistance, and glucose intolerance. These data underscore the potential of targeting CaMKK2 as a therapeutic intervention.     

Leptin signaling pathways in the central nervous system: interactions between neuropeptide Y and melanocortins.

No other hormone has drawn more attention than leptin in recent studies on the control of appetite, body weight and obesity. This hormone is produced by adipose tissue and enters the brain via a saturable specific transport mechanism. Leptin acts in the hypothalamus to modulate food intake and heat production as well as several other neuroendocrine pathways. The mechanisms through which leptin exerts its central nervous effects are now better understood. Proopiomelanocortin- and neuropeptide Y-containing neurons in the hypothalamus have emerged as potent candidate mediators of leptin action. These two neuropeptides have been shown to exert opposing effects using different pathways. Recently, Cowley et al. (2001) described a new circuit in the regulation of neuronal activity by leptin with an interaction between these two pathways. These data add complexity to the mechanisms by which leptin achieves its effects in the central nervous system, but they also offer potential mechanisms to explain the phenomenon of leptin resistance observed in obesity.