Ventromedial Hypothalamic NPY Y2 Receptor in the Maintenance of Body Weight in Diet-Induced Obesity in Mice

The Neonatal Salivary Transcriptome

The ability to noninvasively assess the physical and developmental status of a neonate is a goal of modern medicine. In recent years, technological advances have permitted the high-throughput analysis of saliva for thousands of genes, proteins, and metabolites from a single sample source. Saliva is an ideal biofluid to assess health, disease, and development in the newborn. It may be harnessed repeatedly, even in the most vulnerable patients, without risk of harm. Translating novel information about an infant's global development and risk of disease to the neonatal bedside through the salivary transcriptome has the potential to significantly improve clinical care and outcomes in this at-risk population.

High fat diet-induced obesity increases the formation of colon polyps induced by azoxymethane in mice

BACKGROUND

Obesity has been found to be associated with colon cancer. However, the mechanism of this relationship is unclear and thus a good animal model is required. Our previous research showed that some mice developed diet-induced obesity (DIO) whilst others were diet-resistant (DR) when fed a high-fat diet.

METHODS

In the present study, we have tested the effects of a high-fat diet on the formation of colon polyps induced by azoxymethane (AOM) in both DIO and DR mice.

RESULTS

We found that the DIO mice have developed 2.5 times of polyps compared to the DR mice (P<0.05) and 3.4 times of polyps compared to the low fat fed mice (P<0.05). Although the DR mice tended to have more polyps than the low-fat diet fed mice, this was not statistically significant. The DIO mice could have an increased polyp formation due to obesity-related cancer risk factors and different gene expression from DR mice.

CONCLUSIONS

DIO mice could be used as an appropriate model for studying obesity-associated colon cancer; however DR mice are not suitable because they don't show any significant weight gains to indicate obesity.

Ginseng panaxoside Rb1 reduces body weight in diet-induced obese mice

Crude extracts from ginseng demonstrated anti-obesity properties. Ginsenoside Rb1 is the main component of ginseng, however, there are only few studies examining its effects in obesity. In the present study, we evaluated its potential anti-obesity effects in the murine model of diet-induced obesity. Seventy male C57BL/6 mice were randomly divided to consume for 12 weeks either chow diet (N = 8) or high-fat (HF) diet (N = 62). The latter mice were then divided into four groups: diet-induced obesity group (DIO; N = 10), obesity-resistant group (OR; N = 10), HF group (N = 5), and the group whose diet was changed from HF to normal diet (DC; N = 5). Intraperitoneal injections of Rb-1 were administered daily to mice in the DIO and OR groups for 3 weeks. Body weight and energy intake were monitored, and fasting blood glucose, lipids, neuropeptide Y, Y2 receptor, and peptide YY were quantified. Compared with HF group, weight gain and food intake of DIO mice with Rb-1 injection was significantly decreased (p < 0.05). Further, levels of blood glucose and some lipids were also decreased in DIO-Rb1 group compared with HF group. Furthermore, Rb1 was also found to modulate serum levels of PYY and NPY, and mRNA expression of NPY, Y2 receptor and PYY in tissue samples of DIO mice. Taken together, ginsenoside Rb1 may be useful in the treatment of obesity via modifying the serum content and mRNA expression of NPY, Y2 receptor and PYY.

The modulatory role of high fat feeding on gastrointestinal signals in obesity

The gastrointestinal (GI) tract is a specialized sensory system that detects and responds to constant changes in nutrient- and bacterial-derived intestinal signals, thus contributing to controls of food intake. Chronic exposure to dietary fat causes morphological, physiological and metabolic changes leading to disruptions in the regulatory feeding pathways promoting more efficient fat absorption and utilization, blunted satiation signals and excess adiposity. Accumulating evidence demonstrates that impaired gastrointestinal signals following long-term high fat consumption are, at least partially, responsible for increased caloric intake. This review focuses on the role of dietary fat in modulating oral and post-oral chemosensory signaling elements responsible for lipid detection and responses, including changes in sensitivity to satiation signals, such as GLP-1, PYY and CCK and their impact on food intake and weight gain. Furthermore, the influence of the gut microbiota on mechanisms controlling energy regulation in the face of excessive fat exposure will be explored. The profound influence of dietary fats on altering complex regulatory feeding pathways can result in dysregulation of body weight and development of obesity, while restoration or manipulation of satiation signaling may prove an effective tool in prevention and treatment of obesity.

Neuropeptide Y2 receptor (NPY2R) expression in saliva predicts feeding immaturity in the premature neonate

Background

The current practice in newborn medicine is to subjectively assess when a premature infant is ready to feed by mouth. When the assessment is inaccurate, the resulting feeding morbidities may be significant, resulting in long-term health consequences and millions of health care dollars annually. We hypothesized that the developmental maturation of hypothalamic regulation of feeding behavior is a predictor of successful oral feeding in the premature infant. To test this hypothesis, we analyzed the gene expression of neuropeptide Y2 receptor (NPY2R), a known hypothalamic regulator of feeding behavior, in neonatal saliva to determine its role as a biomarker in predicting oral feeding success in the neonate.

Methodology/Principal Findings

Salivary samples (n = 116), were prospectively collected from 63 preterm and 13 term neonates (post-conceptual age (PCA) 26 4/7 to 41 4/7 weeks) from five predefined feeding stages. Expression of NPY2R in neonatal saliva was determined by multiplex RT-qPCR amplification. Expression results were retrospectively correlated with feeding status at time of sample collection. Statistical analysis revealed that expression of NPY2R had a 95% positive predictive value for feeding immaturity. NPY2R expression statistically significantly decreased with advancing PCA (Wilcoxon test p value<0.01), and was associated with feeding status (chi square p value  =  0.013).

Conclusions/Significance

Developmental maturation of hypothalamic regulation of feeding behavior is an essential component of oral feeding success in the newborn. NPY2R expression in neonatal saliva is predictive of an immature feeding pattern. It is a clinically relevant biomarker that may be monitored in saliva to improve clinical care and reduce significant feeding-associated morbidities that affect the premature neonate.

Steroidogenic factor 1 directs programs regulating diet-induced thermogenesis and leptin action in the ventral medial hypothalamic nucleus

The transcription factor steroidogenic factor 1 (SF-1) is exclusively expressed in the brain in the ventral medial hypothalamic nucleus (VMH) and is required for the development of this nucleus. However, the physiological importance of transcriptional programs regulated by SF-1 in the VMH is not well defined. To delineate the functional significance of SF-1 itself in the brain, we generated pre- and postnatal VMH-specific SF-1 KO mice. Both models of VMH-specific SF-1 KO were susceptible to high fat diet-induced obesity and displayed impaired thermogenesis after acute exposure to high fat diet. Furthermore, VMH-specific SF-1 KO mice showed significantly decreased LepR expression specifically in the VMH, leading to leptin resistance. Collectively, these results indicate that SF-1 directs transcriptional programs in the hypothalamus relevant to coordinated control of energy homeostasis, especially after excess caloric intake.

Proteomic analysis of rat hypothalamus revealed the role of ubiquitin-proteasome system in the genesis of DR or DIO

Obesity has become a global epidemic, contributing to the increasing burdens of cardiovascular disease and type 2 diabetes. However, the precise molecular mechanisms of obesity remain poorly elucidated. The hypothalamus plays a major part in regulating energy homeostasis by integrating all kinds of nutritional signals. This study investigated the hypothalamus protein profile in diet-induced obese (DIO) and diet-resistant (DR) rats using two dimensional gel electrophoresis (2-DE) combined with MALDI-TOF/TOF–MS analysis. Twenty-two proteins were identified in the hypothalamus of DIO or DR rats. These include metabolic enzymes, antioxidant proteins, proteasome related proteins, and signaling proteins, some of which are related to AMP-activated protein kinase (AMPK) signaling or mitochondrial respiration. Among these proteins, in comparison with the normal-diet group, Ubiquitin was significantly decreased in DR rats but not changed in DIO rats, while Ubiquitin carboxyl-terminal esterase L1 (UCHL-1) was decreased in DIO rats but not changed in DR rats. The expression level of Ubiquitin and UCHL-1 were further validated using Western blot analysis. Our study reveals that Ubiquitin and UCHL-1 are obesity-related factors in the hypothalamus that may play an important role in the genesis of DR or DIO by interfering with the integrated signaling network that control energy balance and feeding.

Effects of simvastatin and 6-hydroxydopamine on histaminergic H1 receptor binding density in rat brains

Statins have been widely used for the treatment of a variety of medical conditions including psychoneurological disorders beyond their original use in lowering cholesterol. Histamine receptors play an important role in the regulation of neural activity, however, it is unknown whether statins act on histamine receptors, particularly for their neural regulatory effects. This study examined the effects of simvastatin and 6-hydroxydopamine (6-OHDA) lesions on histamine H1 receptors using [(3)H] pyrilamine binding autoradiography. Compared to the saline group, simvastatin (1 mg/kg/day) significantly decreased H1 receptor bindings in the primary motor cortex (M1), ventromedial hypothalamic nucleus (VMH), caudate putamen (CPu), accumbens core (AcbC) and prefrontal cortex (PfC) (all p<0.05); however 10 mg/kg/day simvastatin increased H1 receptor density only in the medial amygdaloid nucleus (Mep) (p<0.05), but had no significant effect in other regions examined. The 6-OHDA lesion did not alter H1 receptor binding density in most brain areas, except a trend decrease in the hippocampus (p=0.07) and a trend increase in the cingulate cortex (p=0.06). These results suggested that simvastatin has different effects on the H1 receptors in different rat brain regions depending on the doses. Therefore, simvastatin can modulate histaminergic neurotransmission in the brain, and support the role of H1 receptors in psychoneurological disorders.

Effects of changing dietary fat content on plasma gut hormone concentrations in diet-induced obese and diet-resistant rats

Gut hormones play key roles in the regulation of energy homeostasis. However, little is known about the long- and short-term effects of changing dietary fat content on gut hormones. We aim to examine the effects of changing dietary fat content on plasma gut hormone concentrations in diet-induced obese (DIO) and diet-resistant (DR) rats. After inducing obesity with a high-fat (HF) diet, male Sprague–Dawley rats were divided into three groups according to their body-weight gain: DIO; DR; control (CON). The DIO and DR rats were further divided in random into two groups. One continued on a HF diet and the other switched to a low-fat (LF) diet for an additional 4 weeks. Finally, each group was randomly divided into three subgroups (n 8): fasted; fasted-refed HF; fasted-refed LF diet groups. Replacing a HF diet with a LF diet for 4 weeks resulted in less fat mass, higher fasting and post-HF plasma ghrelin concentration and lower postprandial plasma cholecystokinin concentration in the DIO and DR rats. Acute switching dietary fat resulted in significantly higher post-HF plasma ghrelin concentrations than post-LF ghrelin concentrations in the DR rats on LF diet (DRLF) and DIO rats on LF diet (DIOLF) rats, and significantly higher post-HF obestatin concentrations than post-LF obestatin concentrations in the CON, DR rats on HF diet (DRHF) and DRLF rats. Dietary fat content appears to play a role in the gut hormone profile, which may consequently influence fat mass.

The action of leptin on appetite-regulating cells in the ovine hypothalamus: demonstration of direct action in the absence of the arcuate nucleus

It is widely accepted that leptin acts on first-order neurons in the arcuate nucleus (ARC) with information then relayed to other hypothalamic centers. However, the extent to which leptin mediates its central actions solely, or even primarily, via this route is unclear. We used a model of hypothalamo-pituitary disconnection (HPD) to determine whether leptin action on appetite-regulating systems requires the ARC. This surgical preparation eliminates the ARC. We measured effects of iv leptin to activate hypothalamic neurons (Fos labeling). In ARC-intact animals, leptin increased the percentage of Fos-positive melanocortin neurons and reduced percentages of Fos-positive neuropeptide Y neurons compared with saline-treated animals. HPD itself increased Fos labeling in the lateral hypothalamic area (LHA). Leptin influenced Fos labeling in the dorsomedial nucleus (DMH), ventromedial nucleus, and paraventricular nucleus (PVN) in HPD and normal animals, with effects on particular cell types varying. In the LHA and DMH, leptin decreased orexin cell activation in HPD and ARC-intact sheep. HPD abolished leptin-induced expression of Fos in melanin-concentrating hormone cells in the LHA and in CRH cells in the PVN. In contrast, HPD accentuated activation in oxytocin neurons. Our data from sheep with lesions encompassing the ARC do not suggest a primacy of action of leptin in this nucleus. We demonstrate that first order to second order signaling may not represent the predominant means by which leptin acts in the brain to generate integrated responses. We provide evidence that leptin exerts direct action on cells of the DMH, ventromedial nucleus, and PVN.

Relationship of arousal to circadian anticipatory behavior: ventromedial hypothalamus: one node in a hunger-arousal network

The mechanisms by which animals adapt to an ever-changing environment have long fascinated scientists. Different forces, conveying information regarding various aspects of the internal and external environment, interact with each other to modulate behavioral arousal. These forces can act in concert or, at times, in opposite directions. These signals eventually converge and are integrated to influence a common arousal pathway which, depending on all the information received from the environment, supports the activation of the most appropriate behavioral response. In this review we propose that the ventromedial hypothalamic nucleus (VMN) is part of the circuitry that controls food anticipation. It is the first nucleus activated when there is a change in the time of food availability, silencing of VMN ghrelin receptors decreases food-anticipatory activity (FAA) and, although lesions of the VMN do not abolish FAA, parts of the response are often altered. In proposing this model it is not our intention to exclude parallel, redundant and possibly interacting pathways that may ultimately communicate with, or work in concert with, the proposed network, but rather to describe the neuroanatomical requirements for this circuit and to illustrate how the VMN is strategically placed and connected to mediate this complex behavioral adaptation.

Obese reversal by a chronic energy restricted diet leaves an increased Arc NPY/AgRP, but no alteration in POMC/CART, mRNA expression in diet-induced obese mice

Weight regain after weight loss is a major hurdle for combating obesity. The aim of this study is to examine orexigenic and anorectic neuropeptides of the hypothalamic arcuate nucleus (Arc) in response to weight loss after chronic energy intake restriction. Thirty mice were fed with a high-fat diet for 8 weeks and then classified as diet-induced obese (DIO; n=10) or diet-resistant (DR; n=10) mice according to the highest and lowest body weight gainers. Five mice from DIO and DR groups were placed on an energy restricted diet or continued on their high-fat diet ad libitum for 6 weeks. An additional five mice were on a LF diet throughout the course of this study as controls. Results showed that a six-week energy restricted diet completely reversed the increased body weight, fat mass and leptin in the DIO mice to the levels of the LF and DR mice. Arc neuropeptide Y (NPY) and agouti-related protein (AgRP) mRNA expression in DIO mice after obesity reversal were significantly higher than DIO mice without obesity reversal (17%, 47%, both p<0.05), while the Arc pro-opiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART) mRNA showed no difference. Both NPY and AgRP expression in DIO mice were negatively correlated with plasma leptin (R=-0.78, p<0.05; R=-0.72, p<0.05). In conclusion, while chronic energy restriction will lead to weight loss, it can up-regulate hypothalamic orexigenic peptides, which may be an important contributing factor to weight regain after a weight loss program from an energy restricted diet.

High-fat diet decreases tyrosine hydroxylase mRNA expression irrespective of obesity susceptibility in mice

Tyrosine hydroxylase is the rate-limiting enzyme in the synthesis of dopamine, a key neurotransmitter in the regulation of food intake. This study examined tyrosine hydroxylase mRNA expression in obese mice fed a high-fat diet. After 8 week feeding of high-fat diet mice were classified as diet-induced obese and obese-resistant according to body weight gain. They were then placed on different dietary interventions including a high-fat diet, a low-fat diet and an energy-restricted high-fat diet for six weeks. The control group was fed a low-fat diet. The results revealed that tyrosine hydroxylase mRNA expression was significantly decreased in the ventral tegmental area (VTA), ventromedial hypothalamic nucleus (VMH), and substantia nigra (SN) of the high-fat diet-induced obese (-29%, -26% and -26%) and obese-resistant mice (-21%, -24% and -18%) compared to controls. After switching the diet from high to low-fat diet tyrosine hydroxylase mRNA was increased in the VTA, VMH, and SN of the diet-induced obese mice and in the VMH, and SN of the obese-resistant mice. Energy restriction, even with high-fat feeding, reduced tyrosine hydroxylase mRNA expression in the VTA, VMH, and SN compared to controls. In addition, tyrosine hydroxylase mRNA expression in the VTA, VMH, and SN showed a significant negative correlation with plasma leptin levels. This study suggests that the up- or down-regulation of tyrosine hydroxylase mRNA expression in the VTA, VMH, and SN is mainly due to the intake of macronutrient type rather than body weight.