The role of melanocortin signalling in the control of body weight: evidence from human and murine genetic models

Appetite- and Weight-Regulating Neuroendocrine Circuitry in Hypothalamic Obesity

Since hypothalamic obesity (HyOb) was first described over 120 years ago by Joseph Babinski and Alfred Fröhlich, advances in molecular genetic laboratory techniques have allowed us to elucidate various components of the intricate neurocircuitry governing appetite and weight regulation connecting the hypothalamus, pituitary gland, brainstem, adipose tissue, pancreas, and gastrointestinal tract. On a background of an increasing prevalence of population-level common obesity, the number of survivors of congenital (eg, septo-optic dysplasia, Prader-Willi syndrome) and acquired (eg, central nervous system tumors) hypothalamic disorders is increasing, thanks to earlier diagnosis and management as well as better oncological therapies. Although to date the discovery of several appetite-regulating peptides has led to the development of a range of targeted molecular therapies for monogenic obesity syndromes, outside of these disorders these discoveries have not translated into the development of efficacious treatments for other forms of HyOb. This review aims to summarize our current understanding of the neuroendocrine physiology of appetite and weight regulation, and explore our current understanding of the pathophysiology of HyOb.

Prostaglandin signaling in ciliogenesis and development

Prostaglandin (PG) signaling regulates a wide variety of physiological and pathological processes, including body temperature, cardiovascular homeostasis, reproduction, and inflammation. Recent studies have revealed that PGs play pivotal roles in embryo development, ciliogenesis, and organ formation. Prostaglandin E2 (PGE2) and its receptor EP4 modulate ciliogenesis by increasing the anterograde intraflagellar transport. Many G-protein-coupled receptors (GPCRs) including EP4 are localized in cilia for modulating cAMP signaling under various conditions. During development, PGE2 signaling regulates embryogenesis, hepatocyte differentiation, hematopoiesis, and kidney formation. Prostaglandins are also essential for skeletal muscle repair. This review outlines recent advances in understanding the functions and mechanisms of prostaglandin signaling in ciliogenesis, embryo development, and organ formation.

Depletion of Alpha-Melanocyte-Stimulating Hormone Induces Insatiable Appetite and Gains in Energy Reserves and Body Weight in Zebrafish

The functions of anorexigenic neurons secreting proopiomelanocortin (POMC)/alpha-melanocyte-stimulating hormone (α-MSH) of the melanocortin system in the hypothalamus in vertebrates are energy homeostasis, food intake, and body weight regulation. However, the mechanisms remain elusive. This article reports on zebrafish that have been genetically engineered to produce α-MSH mutants, α-MSH^-7aa and α-MSH^-8aa, selectively lacking 7 and 8 amino acids within the α-MSH region, but retaining most of the other normal melanocortin-signaling (Pomc-derived) peptides. The α-MSH mutants exhibited hyperphagic phenotypes leading to body weight gain, as observed in human patients and mammalian models. The actions of several genes regulating appetite in zebrafish are similar to those in mammals when analyzed using gene expression analysis. These include four selected orexigenic genes: Promelanin-concentrating hormone (pmch), agouti-related protein 2 (agrp2), neuropeptide Y (npy), and hypothalamic hypocretin/orexin (hcrt). We also study five selected anorexigenic genes: Brain-derived neurotrophic factor (bdnf), single-minded homolog 1-a (sim1a), corticotropin-releasing hormone b (crhb), thyrotropin-releasing hormone (trh), and prohormone convertase 2 (pcsk2). The orexigenic actions of α-MSH mutants are rescued completely after hindbrain ventricle injection with a synthetic analog of α-MSH and a melanocortin receptor agonist, Melanotan II. We evaluate the adverse effects of MSH depletion on energy balance using the Alamar Blue metabolic rate assay. Our results show that α-MSH is a key regulator of POMC signaling in appetite regulation and energy expenditure, suggesting that it might be a potential therapeutic target for treating human obesity.

Expression of obesity-related genes in human spermatozoa affects the outcomes of reproductive treatments

OBJECTIVE

To study the abundance of obesity-related gene (ORG) mRNA in human spermatozoa and its association with sperm quality parameters, embryonic development, and pregnancy rates after assisted reproduction treatment (ART).

DESIGN

Cross-sectional study of spermatozoa ORG mRNA expression, and sperm and embryonic development parameters of infertile couples attending a single ART center.

SETTING

University, in collaboration with a medically assisted reproduction center.

PATIENT(S)

One hundred six couples seeking fertility treatment and receiving ART.

INTERVENTION(S)

Expression of spermatozoa ORG mRNA was assessed by quantitative reverse transcription-polymerase chain reaction. Sperm and embryonic development parameters were measured by board-certified embryologists. Serum β-human chorionic gonadotropin levels and fetal heartbeat detection on ultrasound were used to document biochemical and clinical pregnancy, respectively.

MAIN OUTCOME MEASURE(S)

Correlations between the abundance of ORG transcripts in spermatozoa and sperm quality, embryonic development, and achievement of pregnancy.

RESULTS

The abundance of spermatozoa FTO mRNA was positively correlated with total sperm count (r = 0.5030), fertilization rate (r = 0.4854), embryo cleavage rate (r = 0.5705), and high-quality embryo rate (r = 0.6982). The abundance of spermatozoa MC4R transcript was negatively correlated with sperm viability (r = -0.3111) and positively correlated with biochemical pregnancy (r = 0.4420). The abundance of MC4R and GNPDA2 transcripts was higher in spermatozoa of men with asthenozoospermia and teratozoospermia than in those with normozoospermia.

CONCLUSION

To our knowledge, this is the first report showing that the abundance of MC4R and FTO transcripts in spermatozoa is associated with sperm and embryo quality parameters, as well as pregnancy rates. Overall, these results further support the view that male factors beyond classic sperm quality parameters, namely the abundance of ORG transcripts, also affect the outcome of ART.

Obesity-related genes are expressed in human Sertoli cells and modulated by energy homeostasis regulating hormones

The strong hormonal dysregulation associated with obesity is responsible for the disruption of several reproductive events. Sertoli cells (SCs) function is dependent on energetic homeostasis and thus, directly associated with energy homeostasis regulating hormones. To further understand the influence of those hormones with SCs function and obesity, we hypothesize that human SCs express obesity-related genes (ORG; MC4R, GNPDA2, TMEM18, and FTO) and that they respond to energy homeostasis regulating hormones (leptin, ghrelin, and glucagon-like protein 1 [GLP-1]) stimuli. To test our hypothesis, SCs were cultured with increasing doses of leptin (0, 5, 25, or 50 ng/ml, for 24 h), ghrelin (0, 20, 100, and 500 pM, for 24 h), and GLP-1 (10, 1000, or 1 × 105 pM, for 6 h). The presence and abundance of ORG transcripts and proteins in SCs were accessed by polymerase chain reaction techniques, Western blot analysis, and immunofluorescence staining. Our results show that human SCs express MC4R, GNPDA2, TMEM18, and FTO in specific cellular locations. MC4R and FTO expression in human SCs was not responsive to the treatments. However, GNPDA2 and TMEM18 expression increased after exposure to the highest concentration of leptin and ghrelin, respectively. We highlight for the first time that human SCs express ORG and that these are responsive to energy homeostasis hormonal stimuli. GNPDA2 and TMEM18 expression respond in opposite directions according to overall energy status, mediated by energy homeostasis regulating hormones. Leptin and ghrelin control of ORG expression by human SCs can be associated with overweight-related infertility and subfertility in males.

Neuroanatomy of melanocortin-4 receptor pathway in the mouse brain

Objective

Melanocortin-4 receptors (MC4Rs) are key regulators of energy homeostasis and adipose deposition in the central nervous system. Considering that MC4R expression regions and function-related research mainly focus on the paraventricular nucleus (PVN), little is known about their distribution throughout the mouse brain, although its messenger RNA distribution has been analyzed in the rat. Therefore, MC4R protein localization in mouse neurons was the focus of this study.

Methods

MC4R protein distribution was assessed in mice through immunofluorescence and Western blotting.

Results

MC4R was differentially expressed throughout the arcuate nucleus (ARC), nucleus of the solitary tract (NTS), raphe pallidus (RPa), medial cerebellar nucleus, intermediolateral nucleus, and brainstem. The highest MC4R protein levels were found in the ARC and ventromedial hypothalamic nucleus, while they were significantly lower in the parabrachial nucleus and NTS. The lowest MC4R protein levels were found in the PVN; there was no difference in the protein levels between the area postrema and RPa.

Conclusions

These data provide a basic characterization of MC4R-expressing neurons and protein distribution in the mouse brain and may aid further research on its role in energy homeostasis.

Cilia signaling and obesity

An emerging number of rare genetic disorders termed ciliopathies are associated with pediatric obesity. It is becoming clear that the mechanisms associated with cilia dysfunction and obesity in these syndromes are complex. In addition to ciliopathic syndromic forms of obesity, several cilia-associated signaling gene mutations also lead to morbid obesity. While cilia have critical and diverse functions in energy homeostasis including their roles in centrally mediated food intake as well as in peripheral tissues, many questions remain. Here, we briefly discuss the syndromic ciliopathies and monoallelic cilia signaling gene mutations associated with obesity. We also describe potential ways cilia may be involved in common obesity. We discuss how neuronal cilia impact food intake potentially through leptin signaling and changes in ciliary G protein-coupled receptor (GPCR) signaling. We highlight several recent studies that have implicated the potential for cilia in peripheral tissues such as adipose and the pancreas to contribute to metabolic dysfunction. Then we discuss the potential for cilia to impact energy homeostasis through their roles in both development and adult tissue homeostasis. The studies discussed in this review highlight how a comprehensive understanding of the requirement of cilia for the regulation of diverse biological functions will contribute to our understanding of common forms of obesity.

Combined transcriptomics and proteomics forecast analysis for potential genes regulating the Columbian plumage color in chickens

BACKGROUND

Coloration is one of the most recognizable characteristics in chickens, and clarifying the coloration mechanisms will help us understand feather color formation. "Yufen I" is a commercial egg-laying chicken breed in China that was developed by a three-line cross using lines H, N and D. Columbian plumage is a typical feather character of the "Yufen I" H line. To elucidate the molecular mechanism underlying the pigmentation of Columbian plumage, this study utilizes high-throughput sequencing technology to compare the transcriptome and proteome differences in the follicular tissue of different feathers, including the dorsal neck with black and white striped feather follicles (Group A) and the ventral neck with white feather follicles (Group B) in the "Yufen I" H line.

RESULTS

In this study, we identified a total of 21,306 genes and 5,203 proteins in chicken feather follicles. Among these, 209 genes and 382 proteins were differentially expressed in two locations, Group A and Group B, respectively. A total of 8 differentially expressed genes (DEGs) and 9 differentially expressed proteins (DEPs) were found to be involved in the melanogenesis pathway. Additionally, a specifically expressed MED23 gene and a differentially expressed GNAQ protein were involved in melanin synthesis. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis mapped 190 DEGs and 322 DEPs to 175 and 242 pathways, respectively, and there were 166 pathways correlated with both DEGs and DEPs. 49 DEPs/DEGs overlapped and were enriched for 12 pathways. Transcriptomic and proteomic analyses revealed that the following pathways were activated: melanogenesis, cardiomyocyte adrenergic, calcium and cGMP-PKG. The expression of DEGs was validated by real-time quantitative polymerase chain reaction (qRT-PCR) that produced results similar to those from RNA-seq. In addition, we found that the expression of the MED23, FZD10, WNT7B and WNT11 genes peaked at approximately 8 weeks in the "Yufen I" H line, which is consistent with the molting cycle. As both groups showed significant differences in terms of the expression of the studied genes, this work opens up avenues for research in the future to assess their exact function in determining plumage color.

CONCLUSION

Common DEGs and DEPs were enriched in the melanogenesis pathway. MED23 and GNAQ were also reported to play a crucial role in melanin synthesis. In addition, this study is the first to reveal gene and protein variations in in the "Yufen I" H line during Columbian feather color development and to discover principal genes and proteins that will aid in functional genomics studies in the future. The results of the present study provide a significant conceptual basis for the future breeding schemes with the "Yufen I" H line and provide a basis for research on the mechanisms of feather pigmentation.

Defining the caudal hypothalamic arcuate nucleus with a focus on anorexic excitatory neurons

KEY POINTS

Excitatory glutamate neurons are sparse in the rostral hypothalamic arcuate nucleus (ARC), the subregion that has received the most attention in the past. In striking contrast, excitatory neurons are far more common (by a factor of 10) in the caudal ARC, an area which has received relatively little attention. These glutamate cells may play a negative role in energy balance and food intake. They can show an increase in phosphorylated Stat-3 in the presence of leptin, are electrically excited by the anorectic neuromodulator cholecystokinin, and inhibited by orexigenic neuromodulators neuropeptide Y, met-enkephalin, dynorphin and the catecholamine dopamine. The neurons project local axonal connections that excite other ARC neurons including proopiomelanocortin neurons that can play an important role in obesity. These data are consistent with models suggesting that the ARC glutamatergic neurons may play both a rapid and a slower role in acting as anorectic neurons in CNS control of food intake and energy homeostasis.

ABSTRACT

Here we interrogate a unique class of excitatory neurons in the hypothalamic arcuate nucleus (ARC) that utilizes glutamate as a fast neurotransmitter using mice expressing GFP under control of the vesicular glutamate transporter 2 (vGluT2) promoter. These neurons show a unique distribution, synaptic characterization, cellular physiology and response to neuropeptides involved in energy homeostasis. Although apparently not previously appreciated, the caudal ARC showed a far greater density of vGluT2 cells than the rostral ARC, as seen in transgenic vGluT2-GFP mice and mRNA analysis. After food deprivation, leptin induced an increase in phosphorylated Stat-3 in vGluT2-positive neurons, indicating a response to hormonal cues of energy state. Based on whole-cell recording electrophysiology in brain slices, vGluT2 neurons were spontaneously active with a spike frequency around 2 Hz. vGluT2 cells were responsive to a number of neuropeptides related to energy homeostasis; they were excited by the anorectic peptide cholecystokinin, but inhibited by orexigenic neuropeptide Y, dynorphin and met-enkephalin, consistent with an anorexic role in energy homeostasis. Dopamine, associated with the hedonic aspect of enhancing food intake, inhibited vGluT2 neurons. Optogenetic excitation of vGluT2 cells evoked EPSCs in neighbouring neurons, indicating local synaptic excitation of other ARC neurons. Microdrop excitation of ARC glutamate cells in brain slices rapidly increased excitatory synaptic activity in anorexigenic proopiomelanocortin neurons. Together these data support the perspective that vGluT2 cells may be more prevalent in the ARC than previously appreciated, and play predominantly an anorectic role in energy metabolism.

Variation in the Promoter Region of the MC4R Gene Elucidates the Association of Body Measurement Traits in Hu Sheep

The melanocortin 4 receptor (MC4R) gene is expressed in the appetite-regulating areas of the brain and is engaged in the leptin signaling pathway. Although previous studies have identified variants in the coding region of the sheep MC4R gene showing significant associations with birth weight, weaning weight, and backfat thickness, no such associations have been reported for the promoter region. Besides, the essential promoter region of the sheep MC4R has not been delineated. In this study, to better understand the transcriptional regulation of MC4R and to elucidate the association between regulatory variants and haplotypes with body measurement traits in sheep, we cloned and characterized the MC4R promoter. We found that the minimal promoter of the gene is located within the region -1207/-880 bp upstream of the first exon. Real-time quantitative PCR (RT-qPCR) data revealed the mRNA expression of the MC4R gene had a significant difference between sex and age. In the association analysis, eight single nucleotide polymorphisms (SNPs) had a significant association with one or more traits (p < 0.05); of these, two SNPs were novel. Notably, individuals with haplotype H1H2 (CT-GA-GT-GA-GT-GA-GA-CG) were heavier in body weight than other haplotypes. Altogether, variations in the MC4R gene promoter, most notably haplotype H1H2, may greatly benefit marker-assisted selection in sheep.

A novel mutation in the proopiomelanocortin (POMC) gene of a Hispanic child: metformin treatment shows a beneficial impact on the body mass index

Background Proopiomelanocortin (POMC) is a complex polypeptide that produces a variety of biologically active substances via cleavage in a tissue-specific manner [Challis BG, Millington GW. Proopiomelanocortin deficiency. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle, 1993-2018], yielding several products including adrenocorticotrophic (ACTH) and melanocyte stimulating hormones (MSH). These peptides have roles in the regulation of food intake, energy homeostasis, adrenal steroidogenesis, melanocyte stimulation and immune modulation. Rare mutations in the POMC gene can lead to ACTH deficiency and thus isolated hypocortisolism. The first cases of POMC mutation were documented by Krude et al. in 1998 [Krude H, Biebermann H, Luck W, Horn R, Brabant G, et al. Severe early-onset obesity, adrenal insufficiency and red hair pigmentation caused by POMC mutations in humans. Nat Genet 1998;19:155-7]. Mutations in the POMC gene were linked with a clinical phenotype of adrenal insufficiency, red hair pigmentation, early onset and rapidly progressive obesity, early onset type 2 diabetes, hypothyroidism, hypogonadism and growth hormone deficiency. Case presentation We describe a prepubertal Hispanic boy with a novel homozygous POMC mutation with severe obesity, hypothyroidism, adrenal insufficiency and abnormal reddish hair pigmentation. The patient presented as a 2-year-old with exponential weight gain, abnormal thyroid labs and speech delay. Laboratory testing demonstrated central adrenal insufficiency and genetic testing confirmed a homozygous mutation (nucleotide change c.20_21ins25) in exon 3 of the POMC gene. Replacement therapy with thyroid hormone and hydrocortisone was coupled to a slight decrease in the rate of weight gain, although hyperphagia persisted. Parent-directed nutrition and activity education as well as attempts to restrict access to food resulted in a plateau of the body mass index (BMI). At 4 years of age, metformin treatment was initiated with the patient showing evolving signs of insulin resistance and failure of lifestyle/dietary intervention to adequately decrease the BMI. Over a 3-year metformin treatment span, the BMI decreased from 34.9 kg/m2 to 32.9 kg/m2. Conclusions We demonstrate a possible role for metformin in stemming progressive weight gain, thereby impacting the early onset obesity due to hyperphagia.

Thyroid Hormone-Dependent Epigenetic Regulation of Melanocortin 4 Receptor Levels in Female Offspring of Obese Rats

Maternal obesity is a risk factor for offspring obesity. The melanocortin 4 receptor (Mc4r) is one of the mediators of food intake and energy balance. The present study examined the epigenetic mechanisms underlying altered Mc4r levels in the hypothalamic paraventricular nucleus in the offspring of high-fat diet (HFD)-induced obese dams and sought to elucidate the role of thyroid hormones in epigenetic regulation and tagging of their nucleosome at the Mc4r promoter. Female Wistar rats were fed an HFD or standard chow from weaning through gestation and lactation. Epigenetic alterations were analyzed in the offspring on postnatal day 21 at the Mc4r promoter using chromatin immunoprecipitation and bisulfite sequencing. To study the role of triiodothyronine (T3) in Mc4r downregulation, dams received methimazole (MMI), an inhibitor of thyroid hormone production. Offspring of HFD-fed dams had a greater body weight, elevated plasma T3 concentrations, and lower Mc4r messenger RNA levels than controls. At the Mc4r promoter, offspring of HFD-fed mothers demonstrated increased histone 3 lysine 27 acetylation (H3K27ac) with a greater association to thyroid hormone receptor-β (TRβ), an inhibitor of Mc4r transcription. Moreover, TRβ coimmunoprecipitated with H3K27ac, supporting their presence in the same complex. Maternal MMI administration prevented the HFD reduction in Mc4r levels, the increase in TRβ, and the increase in the TRβ-H3K27ac association, providing further support for the role of T3 in downregulating Mc4r levels. These findings demonstrate that a perinatal HFD environment affects Mc4r regulation through a T3 metabolic pathway involving histone acetylation of its promoter.

Effects of melanocortin-4 receptor agonists and antagonists on expression of genes related to reproduction in spotted scat, Scatophagus argus

Melanocortin-4 receptor (Mc4r) function related to reproduction in fish has not been extensively investigated. Here, we report on gene expression changes by real-time PCR following treatment with Mc4r agonists and antagonists in the spotted scat (Scatophagus argus). Using in vitro incubated hypothalamus, the Mc4r nonselective agonist NDP-MSH ([Nle⁴, D-Phe⁷]-α-melanocyte stimulating hormone; 10^-6 M) and selective agonist THIQ (N-[(3R)-1, 2, 3, 4-Tetrahydroisoquinolinium-3-ylcarbonyl]- (1R)-1-(4-chlorobenzyl)-2-[4-cyclohexyl-4-(1H-1,2,4-triazol-1-ylmethyl) piperidin-1-yl]-2-oxoethylamine; 10^-7 M) significantly increased the expression of gnrh (Gonadotropin releasing hormone), while the Mc4r nonselective antagonist SHU9119 (Ac-Nle-[Asp-His-DPhe/DNal(2')-Arg-Trp-Lys]-NH2; 10^-6 M) and selective antagonist Ipsen 5i (compound 5i synthesized in Ipsen Research Laboratories; 10^-6 M) significantly inhibited gnrh expression after 3 h of incubation. In incubated pituitary tissue, NDP-MSH and THIQ significantly increased the expression of fshb (Follicle-stimulating hormone beta subunit) and lhb (Luteinizing hormone beta subunit), while SHU9119 and Ipsen 5i significantly decreased fshb and lhb expression after 3 h of incubation. During the in vivo experiment, THIQ (1 mg/kg bw) significantly increased gnrh expression in hypothalamic tissue, as well as the fshb and lhb expression in pituitary tissue 12 h after abdominal injection. Furthermore, Ipsen 5i (1 mg/kg bw) significantly inhibited gnrh expression in hypothalamic tissue, as well as fshb and lhb gene expression in pituitary tissue 12 h after abdominal injection. In summary, Mc4r singling appears to stimulate gnrh expression in the hypothalamus, thereby modulating the synthesis of Fsh and Lh in the pituitary. In addition, Mc4r also appears to directly regulate fshb and lhb levels in the pituitary in spotted scat. Our study suggests that Mc4r, through the hypothalamus and pituitary, participates in reproductive regulation in fish.

Contribution of adaptive thermogenesis to the hypothalamic regulation of energy balance

Obesity and its related disorders are among the most pervasive diseases in contemporary societies, and there is an urgent need for new therapies and preventive approaches. Given (i) our poor social capacity to correct unhealthy habits, and (ii) our evolutionarily genetic predisposition to store excess energy as fat, the current environment of caloric surplus makes the treatment of obesity extremely difficult. During the last few decades, an increasing number of methodological approaches have increased our knowledge of the neuroanatomical basis of the control of energy balance. Compelling evidence underlines the role of the hypothalamus as a homeostatic integrator of metabolic information and its ability to adjust energy balance. A greater understanding of the neural basis of the hypothalamic regulation of energy balance might indeed pave the way for new therapeutic targets. In this regard, it has been shown that several important peripheral signals, such as leptin, thyroid hormones, oestrogens and bone morphogenetic protein 8B, converge on common energy sensors, such as AMP-activated protein kinase to modulate sympathetic tone on brown adipose tissue. This knowledge may open new ways to counteract the chronic imbalance underlying obesity. Here, we review the current state of the art on the role of hypothalamus in the regulation of energy balance with particular focus on thermogenesis.

Metabolic and hormonal consequencies of the "obesity risk" MC4R variant (rs12970134) in Czech women

Although the mutations in MC4R gene became known as the most common genetic cause of human obesity, the effect of rs12970134 A/G near MC4R gene on insulin resistance has been described. The aim of this study was to determine the effect of rs12970134 on obesity, hormone levels, and glucose metabolism in a cohort of women varying in glucose tolerance: 850 normoglycemic women, 423 diagnosed with polycystic ovary syndrome (PCOS), 402 gestational diabetics (GDM), and 250 type 2 diabetic (T2D) women. We did not confirm the explicit effect of rs12970134 on obesity. However, the influence of the A-allele on body adiposity index was observed in a cohort of women diagnosed with PCOS. In normoglycemic women, the A-allele carriership was associated with lower fasting levels of glucose, insulin, C-peptide, and index of insulin resistance. Furthermore, higher levels of growth hormone, leptin and SHBG, and lower levels of fT3, testosterone, and androstenedione were recorded in normoglycemic A-allele carriers. In conclusion, the study presents the evidence of the impact of rs12970134 on complex hypothalamic regulations.

Ultraviolet B stimulates proopiomelanocortin signalling in the arcuate nucleus of the hypothalamus in mice

We previously found that ultraviolet B (UVB) could stimulate the paraventricular nucleus (PVN) with activation the systemic hypothalamic-pituitary- adrenal (HPA) axis. To investigate whether UVB can also stimulate other hypothalamic nuclei, we tested its effect on the proopiomelanocortin (POMC) related signalling system in the arcuate nucleus (ARC) of female C57BL/6 and FVB albino mice. The shaved back skin of the mice was irradiated with either 100 or 400 mJ/cm2 of UVB. After 1, 3, 6 and 12 h, blood and hypothalamus were collected and processed for gene and protein expression, and measurement of α-MSH and β-endorphin (β-END) levels. An in situ immunohistochemical examination was performed for melanocortin receptor 4 (MC4R) and POMC-derived α-MSH. The expression of Pomc and MC4R mRNAs was stimulated, whereas that of AgRP was inhibited after exposure to UVB. It was accompanied by an increased number of both α-MSH- and MC4R-immunoreactive neurons in the ARC, and by increased levels of α-MSH and β-END (both found in the hypothalamus and plasma). This surprising discovery of UVB stimulating the POMC system in the ARC, accompanied by the increased plasma levels of α-MSH and β-END, paves the way for exciting areas of research on the communication between the skin and the brain, as well as is suggesting a new role for UVB in regulation of body metabolism.

Ring Finger Protein 11 Inhibits Melanocortin 3 and 4 Receptor Signaling

Intact melanocortin signaling via the G protein-coupled receptors (GPCRs), melanocortin receptor 4 (MC4R), and melanocortin receptor 3 (MC3R) is crucial for body weight maintenance. So far, no connection between melanocortin signaling and hypothalamic inflammation has been reported. Using a bimolecular fluorescence complementation library screen, we identified a new interaction partner for these receptors, ring finger protein 11 (RNF11). RNF11 participates in the constitution of the A20 complex that is involved in reduction of tumor necrosis factor α (TNFα)-induced NFκB signaling, an important pathway in hypothalamic inflammation. Mice treated with high-fat diet (HFD) for 3 days demonstrated a trend toward an increase in hypothalamic Rnf11 expression, as shown for other inflammatory markers under HFD. Furthermore, Gs-mediated signaling of MC3/4R was demonstrated to be strongly reduced to 20-40% by co-expression of RNF11 despite unchanged total receptor expression. Cell surface expression was not affected for MC3R but resulted in a significant reduction of MC4R to 61% by co-expression with RNF11. Mechanisms linking HFD, inflammation, and metabolism remain partially understood. In this study, a new axis between signaling of specific body weight regulating GPCRs and factors involved in hypothalamic inflammation is suggested.

An assessment of molecular pathways of obesity susceptible to nutrient, toxicant and genetically induced epigenetic perturbation

In recent years, the etiology of human disease has greatly improved with the inclusion of epigenetic mechanisms, in particular as a common link between environment and disease. However, for most diseases we lack a detailed interpretation of the epigenetic regulatory pathways perturbed by environment and causal mechanisms. Here, we focus on recent findings elucidating nutrient-related epigenetic changes linked to obesity. We highlight studies demonstrating that obesity is a complex disease linked to disruption of epigenetically regulated metabolic pathways in the brain, adipose tissue and liver. These pathways regulate (1) homeostatic and hedonic eating behaviors, (2) adipocyte differentiation and fat accumulation, and (3) energy expenditure. By compiling these data, we illustrate that obesity-related phenotypes are repeatedly linked to disruption of critical epigenetic mechanisms that regulate key metabolic genes. These data are supported by genetic mutation of key epigenetic regulators, and many of the diet-induced epigenetic mechanisms of obesity are also perturbed by exposure to environmental toxicants. Identifying similarly perturbed epigenetic mechanisms in multiple experimental models of obesity strengthens the translational applications of these findings. We also discuss many of the ongoing challenges to understanding the role of environmentally induced epigenetic pathways in obesity and suggest future studies to elucidate these roles. This assessment illustrates our current understanding of molecular pathways of obesity that are susceptible to environmental perturbation via epigenetic mechanisms. Thus, it lays the groundwork for dissecting the complex interactions between diet, genes and toxicants that contribute to obesity and obesity-related phenotypes.

New targets to treat obesity and the metabolic syndrome

Metabolic syndrome (MetS) is a cluster ofassociated metabolic traits that collectively confer unsurpassed risk for development of cardiovascular disease (CVD) and type 2 diabetes compared to any single CVD risk factor. Truncal obesity plays an exceptionally critical role among all metabolic traits of the MetS. Consequently, the prevalence of the MetS has steadily increased with the growing epidemic of obesity. Pharmacotherapy has been available for obesity for more than one decade, but with little success in improving the metabolic profiles. The serotonergic drugs and inhibitors of pancreatic lipases were among the few drugs that were initially approved to treat obesity. At the present time, only the pancreatic lipase inhibitor orlistat is approved for long-term treatment of obesity. New classes of anti-diabetic drugs, including glucagon-like peptide 1 receptor (GLP-1R) agonists and Dipeptidyl-peptidase IV (DPP-IV) inhibitors, are currently being evaluated for their effects on obesity and metabolic traits. The genetic studies of obesity and metabolic syndrome have identified novel molecules acting on the hunger and satiety peptidergic signaling of the gut-hypothalamus axis or the melanocortin system of the brain and are promising targets for future drug development. The goal is to develop drugs that not only treat obesity, but also favorably impact its associated traits.

Evaluation of MC4R [rs17782313, rs17700633], AGRP [rs3412352] and POMC [rs1042571] Polymorphisms with Obesity in Northern India

OBJECTIVE

Genetic variants of the melanocortin-4 receptor gene (MC4R), agouti related protein (AGRP) and proopiomelanocortin (POMC) are reported to be associated with obesity. Therefore, the aim of this study is to examine MC4R rs17782313, MC4R rs17700633, AGRP rs3412352 and POMCrs1042571 for any association with obesity in North Indian subjects.

METHODS

The variants were investigated for association in 300 individuals with BMI ≥30 kg/m(2) and 300 healthy non-obese individuals BMI <30 kg/m(2.) The genotyping were analyzed by Taqman probes. The statistical analysis was performed by the SPSS software, ver.19 and p≤0.05 was considered statistically significant.

RESULTS

The genotypes of MC4R rs17782313 and POMC rs1042571 were significantly associated with obesity (C), (p=0.02; OR=1.7 and p=0.01; OR=1.6, respectively); however, MC4Rrs17700633 (p=0.001; OR=0.55) was associated with low risk. In addition, AGRPrs3412352 (p=0.93; OR=0.96) showed no association with obesity (BMI ≥30 kg/m(2)) in North Indian subjects.

CONCLUSION

This study provides the report about the significant association of MC4R (rs17782313) and POMC (rs1042571) with morbid obesity (BMI ≥30 kg/m(2)), but MC4R (rs17700633) and AGRP (rs34123523) did not show any association with obesity in the studied North Indian population.

Gene × environment interactions in obesity: the state of the evidence

BACKGROUND/AIMS

Obesity is a pervasive and highly prevalent disease that poses substantial health risks to those it affects. The rapid emergence of obesity as a global epidemic and the patterns and distributions of the condition within and between populations suggest that interactions between inherited biological factors (e.g. genes) and relevant environmental factors (e.g. diet and physical activity) may underlie the current obesity epidemic.

METHODS

We discuss the rationale for the assertion that gene × lifestyle interactions cause obesity, systematically appraise relevant literature, and consider knowledge gaps future studies might seek to bridge.

RESULTS

We identified >200 relevant studies, of which most are relatively small scale and few provide replication data.

CONCLUSION

Although studies on gene × lifestyle interactions in obesity point toward the presence of such interactions, improved data standardization, appropriate pooling of data and resources, innovative study designs, and the application of powerful statistical methods will be required if translatable examples of gene × lifestyle interactions in obesity are to be identified. Future studies, of which most will be observational, should ideally be accompanied by appropriate replication data and, where possible, by analogous findings from experimental settings where clinically relevant traits (e.g. weight regain and weight cycling) are outcomes.

Prolyl carboxypeptidase and its inhibitors in metabolism

Proopiomelanocortin (POMC)-expressing neurons in the hypothalamus integrate a variety of central and peripheral metabolic inputs, and regulate energy homeostasis by controlling energy expenditure and food intake. To accomplish this, a precise balance of production and degradation of α-melanocyte-stimulating hormone (α-MSH), an anorexigenic neuropeptide and product of the POMC gene, in the hypothalamus, is crucial. Prolyl carboxypeptidase (PRCP) is a key enzyme that degrades α-MSH to an inactive form unable to inhibit food intake. Because it represents a new therapeutic target for the treatment of metabolic disorders, such as obesity and diabetes, efforts have been made to generate potent, brain-penetrant PRCP inhibitors. Here, we discuss the role of PRCP on energy metabolism and the development of PRCP inhibitors.

Neuropeptide transmission in brain circuits

Neuropeptides are found in many mammalian CNS neurons where they play key roles in modulating neuronal activity. In contrast to amino acid transmitter release at the synapse, neuropeptide release is not restricted to the synaptic specialization, and after release, a neuropeptide may diffuse some distance to exert its action through a G protein-coupled receptor. Some neuropeptides such as hypocretin/orexin are synthesized only in single regions of the brain, and the neurons releasing these peptides probably have similar functional roles. Other peptides such as neuropeptide Y (NPY) are synthesized throughout the brain, and neurons that synthesize the peptide in one region have no anatomical or functional connection with NPY neurons in other brain regions. Here, I review converging data revealing a complex interaction between slow-acting neuromodulator peptides and fast-acting amino acid transmitters in the control of energy homeostasis, drug addiction, mood and motivation, sleep-wake states, and neuroendocrine regulation.

Expression levels of candidate genes for intramuscular fat deposition in two Banna mini-pig inbred lines divergently selected for fatness traits

Intramuscular fat (IMF) content plays an important role in meat quality. Many genes involved in lipid and energy metabolism were identified as candidate genes for IMF deposition, since genetic polymorphisms within these genes were associated with IMF content. However, there is less information on the expression levels of these genes in the muscle tissue. This study aimed at investigating the expression levels of sterol regulating element binding protein-1c (SREBP-1c), diacylglycerol acyltransferase (DGAT-1), heart-fatty acids binding protein (H-FABP), leptin receptor (LEPR) and melanocortin 4 receptor (MC4R) genes and proteins in two divergent Banna mini-pig inbred lines (BMIL). A similar growth performance was found in both the fat and the lean BMIL. The fat meat and IMF content in the fat BMIL were significantly higher than in the lean BMIL, but the lean meat content was lower. The serum triacylglycerol (TAG) and free fatty acid (FFA) contents were significantly higher in the fat than in the lean BMIL. The expression levels of SREBP-1c, DGAT-1 and H-FABP genes and proteins in fat BMIL were increased compared to the lean BMIL. However, the expression levels of LEPR and MC4R genes and proteins were lower.

Early onset obesity and adrenal insufficiency associated with a homozygous POMC mutation

Isolated hypocortisolism due to ACTH deficiency is a rare condition that can be caused by homozygous or compound heterozygous mutations in the gene encoding proopiomelanocortin (POMC). Loss of function mutations of POMC gene typically results in adrenal insufficiency, obesity and red hair. We describe an 18 month old Hispanic female with congenital adrenal insufficiency, a novel POMC mutation and atypical clinical features. The patient presented at the age of 9 months with hypoglycemia and the endocrine evaluation resulted in a diagnosis of ACTH deficiency. She developed extreme weight gain prompting sequence analysis of POMC, which revealed a homozygous c.231C > A change which is predicted to result in a premature termination codon. The case we report had obesity, hypocortisolism but lacked red hair which is typical for subjects with POMC mutations. Mutations of POMC should be considered in individuals with severe early onset obesity and adrenal insufficiency even when they lack the typical pigmentary phenotype.

Lack of cAMP-response element-binding protein 1 in the hypothalamus causes obesity

The melanocortin system in the hypothalamus controls food intake and energy expenditure. Its disruption causes severe obesity in mice and humans. cAMP-response element-binding protein 1 (CREB1) has been postulated to play an important role downstream of the melanocortin-4 receptor (MC4R), but this hypothesis has never been confirmed in vivo. To test this, we generated mice that lack CREB1 in SIM1-expressing neurons, of the paraventricular nucleus (PVN), which are known to be MC4R-positive. Interestingly, CREB1(ΔSIM1) mice developed obesity as a result of decreased energy expenditure and impairment in maintaining their core body temperature and not because of hyperphagia, defining a new role for CREB1 in the PVN. In addition, the lack of CREB1 in the PVN caused a reduction in vasopressin expression but did not affect adrenal or thyroid function. Surprisingly, MC4R function tested pharmacologically was normal in CREB1(ΔSIM1) mice, suggesting that CREB1 is not required for intact MC4R signaling. Thus CREB1 may affect other pathways that are implicated in the regulation of body weight.

New aspects of melanocortin signaling: a role for PRCP in α-MSH degradation

The role of the central melanocortin system in the regulation of energy metabolism has received much attention during the past decade since gene mutations of key components in melanocortin signaling cause monogenic forms of obesity in animals and humans. In the arcuate nucleus of the hypothalamus the prohormone proopiomelanocortin (POMC) is posttranslationally cleaved to produce α-melanocyte stimulating hormone (α-MSH), a peptide with anorexigenic effects upon activation of the melanocortin receptors (MCRs). α-MSH undergoes extensive post-translational processing and its in vivo activity is short lived due to rapid degradation. The enzymatic process that controls α-MSH inactivation is incompletely understood. Recent evidence suggests that prolyl carboxypeptidase (PRCP) is an enzyme responsible for α-MSH degradation. As for many key melanocortin peptides, gene mutation of PRCP causes a change in the metabolic phenotype of rodents. This review summarizes the current knowledge on the melanocortin system with particular focus on PRCP, a newly discovered component of the melanocortin system.

The nutritional induction of COUP-TFII gene expression in ventromedial hypothalamic neurons is mediated by the melanocortin pathway

BACKGROUND

The nuclear receptor chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) is an important coordinator of glucose homeostasis. We report, for the first time, a unique differential regulation of its expression by the nutritional status in the mouse hypothalamus compared to peripheral tissues.

METHODOLOGY/PRINCIPAL FINDINGS

Using hyperinsulinemic-euglycemic clamps and insulinopenic mice, we show that insulin upregulates its expression in the hypothalamus. Immunofluorescence studies demonstrate that COUP-TFII gene expression is restricted to a subpopulation of ventromedial hypothalamic neurons expressing the melanocortin receptor. In GT1-7 hypothalamic cells, the MC4-R agonist MTII leads to a dose dependant increase of COUP-TFII gene expression secondarily to a local increase in cAMP concentrations. Transfection experiments, using a COUP-TFII promoter containing a functional cAMP responsive element, suggest a direct transcriptional activation by cAMP. Finally, we show that the fed state or intracerebroventricular injections of MTII in mice induce an increased hypothalamic COUP-TFII expression associated with a decreased hepatic and pancreatic COUP-TFII expression.

CONCLUSIONS/SIGNIFICANCE

These observations strongly suggest that hypothalamic COUP-TFII gene expression could be a central integrator of insulin and melanocortin signaling pathway within the ventromedial hypothalamus. COUP-TFII could play a crucial role in brain integration of circulating signal of hunger and satiety involved in energy balance regulation.

Alpha-melanocyte stimulating hormone: production and degradation

Proopiomelanocortin (POMC) is a polypeptide hormone precursor that is expressed in the brain and in peripheral tissues such as in the pituitary gland, immune system, and skin. In the brain, POMC is processed to form several peptides including alpha-melanocyte stimulating hormone (α-MSH). alpha-MSH is expressed in the hypothalamic arcuate nucleus and in the nucleus tractus solitarius of the brainstem where it has a crucial role in the regulation of metabolic functions. Specifically, α-MSH is an anorexigenic peptide. Its production and maturation processes have been shown to be regulated according to the metabolic condition of the organism. This review summarizes our current knowledge on α-MSH processing including its maturation and degradation processes and pharmacological aspects of its manipulation.

Identification of domains responsible for specific membrane transport and ligand specificity of the ACTH receptor (MC2R)

The adrenocorticotropic hormone (ACTH) receptor has highly specific membrane expression that is limited to adrenal cells; in other cell types the polypeptide fails to be transported to the cell surface. Unlike other evolutionarily related members of the melanocortin receptor family (MC1R-MC5R) that recognize different melanocortin peptides, ACTHR (MC2R) binds only ACTH. We used a mutagenesis approach involving systematic construction of chimeric ACTHR/MC4R receptors to identify the domains determining the selectivity of ACTHR membrane transport and ACTH binding. In total 15 chimeric receptors were created by replacement of selected domains of human ACTHR with the corresponding regions of human MC4R. We developed an analytical method to accurately quantify cell-membrane localization of recombinant receptors fused with enhanced green fluorescent protein by confocal fluorescence microscopy. The chimeric receptors were also tested for their ability to bind ACTH (1-24) and the melanocyte-stimulating hormone (MSH) analog, Nle4, DPhe7-alpha-MSH, and to induce a cAMP response. Our results indicate that substitution of the MC4R N-terminal segment with the homologous segment of ACTHR significantly decreased membrane transport. We also identified another signal localized in the third and fourth transmembrane regions as the main determinant of ACTHR intracellular retention. In addition, we found that the fourth and fifth transmembrane domains of the ACTHR are involved in ACTH binding selectivity. We discuss the mechanisms involved in bypassing these arrest signals via an interaction with melanocortin 2 receptor accessory protein (MRAP) and the possible mechanisms that determine the high ligand-binding specificity of ACTHR.

5-HT2CRs expressed by pro-opiomelanocortin neurons regulate energy homeostasis

Drugs activating 5-hydroxytryptamine 2C receptors (5-HT_2CRs) potently suppress appetite, but the underlying mechanisms for these effects are not fully understood. To tackle this issue, we generated mice with global 5-HT_2CR deficiency (2C null) and mice with 5-HT_2CRs re-expression only in pro-opiomelanocortin (POMC) neurons (2C/POMC mice). We show that 2C null mice predictably developed hyperphagia, hyperactivity, and obesity and showed attenuated responses to anorexigenic 5-HT drugs. Remarkably, all these deficiencies were normalized in 2C/POMC mice. These results demonstrate that 5-HT_2CR expression solely in POMC neurons is sufficient to mediate effects of serotoninergic compounds on food intake. The findings also highlight the physiological relevance of the 5-HT_2CR-melanocortin circuitry in the long-term regulation of energy balance.

Overview of human obesity and central mechanisms regulating energy homeostasis

Obesity is now regarded as a global epidemic affecting both adults and children, and is associated with significant morbidity and mortality. Thus the effective management of obesity has become an important clinical focus. Therefore, an understanding of the pathways controlling appetite, satiety and food intake is critical for gaining an insight into the pathogenesis of obesity and also for the development of diagnostic tests and therapeutic agents for use in the clinical management of this condition. Over the last decade or more research using both mouse and human genetic models has elucidated the critical role of the leptin-melanocortin pathway in the hypothalamus, in regulating mammalian energy balance. In tandem with this, a clearer understanding of the regulation of gut-derived hormones and their interaction with the central nervous system has further illuminated the complex interplay between central and peripheral aspects of energy regulation. The obesity epidemic and the expanded knowledge base relating to its aetiopathogenesis have specific implications for clinical biochemistry. In particular, an increase in workload may be expected due to biochemical investigation of obesity and its co-morbidities. Moreover, advice on the in-depth investigation of complex cases of obesity may be sought, including information on newer diagnostic tests, such as serum leptin or molecular genetic analysis. There may also be a substantive role for chemical pathologists in establishing and running clinical obesity services. Finally, clinical biochemistry has a role in research pertaining to obesity and cardiometabolic risk.

Maternal nutrition and the programming of obesity: The brain

The increasing incidence of obesity in the developed and developing world in the last decade has led to a need to define our understanding of the physiological mechanisms which can predispose individuals to weight gain in infancy, childhood and adulthood. There is now a considerable body of evidence which has shown that the pathway to obesity may begin very early in life, and that exposure to an inappropriate level of nutrition during prenatal and/or early postnatal development can predispose individuals to obesity in later life The brain is at the heart of the regulation of appetite and food preferences, and it is increasingly being recognized that the development of central appetitive structures is acutely sensitive to the nutritional environment both before and immediately after birth. This review will summarize the body of work which has highlighted the critical role of the brain in the early origins of obesity and presents some perspectives as to the potential application of these research findings in the clinical setting.

G protein-coupled receptors disrupted in human genetic disease

Genetic variation in G protein-coupled receptors (GPCRs) results in the disruption of GPCR function in a wide variety of human genetic diseases. In vitro strategies have been used to elucidate the molecular pathologies that underlie naturally occurring GPCR mutations. Various degrees of inactive, overactive, or constitutively active receptors have been identified. These mutations often alter ligand binding, G protein coupling, receptor desensitization, and receptor recycling. The role of inactivating and activating calcium-sensing receptor (CASR) mutations is discussed with respect to familial hypocalciuric hypercalemia (FHH) and autosomal dominant hypocalemia (ADH). Among ADH mutations, those associated with tonic-clonic seizures are discussed. Other receptors discussed include rhodopsin, thyrotropin, parathyroid hormone, melanocortin, follicle-stimulating hormone, luteinizing hormone, gonadotropin-releasing hormone (GnRHR), adrenocorticotropic hormone, vasopressin, endothelin-beta, purinergic, and the G protein associated with asthma (GPRA). Diseases caused by mutations that disrupt GPCR function are significant because they might be selectively targeted by drugs that rescue altered receptors. Examples of drug development based on targeting GPCRs mutated in disease include the calcimimetics used to compensate for some CASR mutations, obesity therapeutics targeting melanocortin receptors, interventions that alter GnRHR loss from the cell surface in idiopathic hypogonadotropic hypogonadism and novel drugs that might rescue the P2RY12 receptor in a rare bleeding disorder. The discovery of GPRA suggests that drug screens against variant GPCRs may identify novel drugs. This review of the variety of GPCRs that are disrupted in monogenic disease provides the basis for examining the significance of common pharmacogenetic variants.

Pathogenic potential of adipose tissue and metabolic consequences of adipocyte hypertrophy and increased visceral adiposity

When caloric intake exceeds caloric expenditure, the positive caloric balance and storage of energy in adipose tissue often causes adipocyte hypertrophy and visceral adipose tissue accumulation. These pathogenic anatomic abnormalities may incite metabolic and immune responses that promote Type 2 diabetes mellitus, hypertension and dyslipidemia. These are the most common metabolic diseases managed by clinicians and are all major cardiovascular disease risk factors. 'Disease' is traditionally characterized as anatomic and physiologic abnormalities of an organ or organ system that contributes to adverse health consequences. Using this definition, pathogenic adipose tissue is no less a disease than diseases of other body organs. This review describes the consequences of pathogenic fat cell hypertrophy and visceral adiposity, emphasizing the mechanistic contributions of genetic and environmental predispositions, adipogenesis, fat storage, free fatty acid metabolism, adipocyte factors and inflammation. Appreciating the full pathogenic potential of adipose tissue requires an integrated perspective, recognizing the importance of 'cross-talk' and interactions between adipose tissue and other body systems. Thus, the adverse metabolic consequences that accompany fat cell hypertrophy and visceral adiposity are best viewed as a pathologic partnership between the pathogenic potential adipose tissue and the inherited or acquired limitations and/or impairments of other body organs. A better understanding of the physiological and pathological interplay of pathogenic adipose tissue with other organs and organ systems may assist in developing better strategies in treating metabolic disease and reducing cardiovascular disease risk.

Association of the MC4R V103I polymorphism with the metabolic syndrome: the KORA Study

OBJECTIVE

Epidemiological studies showing an association between the melanocortin-4-receptor (MC4R) 103I variant (rs2229616) and decreased BMI are complemented by functional studies; these suggest a mechanism for appetite regulation and a linkage signal for physical activity and dietary intake for the region encompassing the MC4R. This study aims to provide epidemiological evidence for showing the association of this polymorphism with features of the metabolic syndrome and with parameters related to energy expenditure and dietary habits as potential mediators.

METHODS AND PROCEDURES

We analyzed this polymorphism in 7,888 adults of a population-based cross-sectional study applying regression-based statistical models.

RESULTS

Carriers of the MC4R 103I (3.7%) exhibited a significantly decreased waist circumference (-1.46 cm, P = 0.020), decreased glycosylated hemoglobin (HbA(1c)) (-0.09%, P = 0.040), and increased HDL-cholesterol (HDL-C) (+1.76 mg/dl, P = 0.056), but no change in blood pressure. The odds of having three or more components of the metabolic syndrome were substantially reduced among carriers of MC4R 103I (odds ratio (OR) = 0.46, P = 0.003). Controlling for BMI reduced the HbA(1c) and HDL-C association. Mediator analyses revealed a borderline association of MC4R 103I with carbohydrate intake (OR = 1.26, P = 0.059) possibly mediating association with leanness.

DISCUSSION

Our representative study of well-phenotyped Europeans is the first to describe the association of the MC4R V103I with the metabolic syndrome and with a nutrient-related phenotype. Our data support the idea that this polymorphism plays a role in appetite regulation that not only affects BMI, but also other features of the metabolic syndrome. It further establishes that the association of the MC4R V103I with obesity and related phenotypes is genuine.

Obesity and the skin: Skin physiology and skin manifestations of obesity

Obesity is widely recognized as an epidemic in the Western world; however, the impact of obesity on the skin has received minimal attention. The purpose of this article is to highlight the association between obesity and dermatologic conditions. We review the impact of obesity on the skin, including skin physiology, skin manifestations of obesity, and dermatologic diseases aggravated by obesity. Obesity is responsible for changes in skin barrier function, sebaceous glands and sebum production, sweat glands, lymphatics, collagen structure and function, wound healing, microcirculation and macrocirculation, and subcutaneous fat. Moreover, obesity is implicated in a wide spectrum of dermatologic diseases, including acanthosis nigricans, acrochordons, keratosis pilaris, hyperandrogenism and hirsutism, striae distensae, adiposis dolorosa, and fat redistribution, lymphedema, chronic venous insufficiency, plantar hyperkeratosis, cellulitis, skin infections, hidradenitis suppurativa, psoriasis, insulin resistance syndrome, and tophaceous gout. We review the clinical features, evidence for association with obesity, and management of these various dermatoses and highlight the profound impact of obesity in clinical dermatology.

LEARNING OBJECTIVE

After completing this learning activity, participants should be aware of obesity-associated changes in skin physiology, skin manifestations of obesity, and dermatologic diseases aggravated by obesity, and be able to formulate a pathophysiology-based treatment strategy for obesity-associated dermatoses.

The single nucleotide polymorphisms of chicken melanocortin-4 receptor (MC4R) gene and their association analysis with carcass traits

Mutations of the melanocortin-4 receptor (MC4R) gene are associated with the appetite, obesity and growth in pig, mice and human. But little is known about the function of chicken MC4R gene. In this study, F2 chicken resource population derived from broilers crossing to Silky was screened for the polymorphisms of the MC4R gene using PCR-single strand conformation polymorphism (PCR-SSCP) and DNA sequencing methods. Four single nucleotide polymorphisms (SNPs) sites were found. The mutation (C --> T) in the 5' regulation region of chicken MC4R gene results in one more NF-E2 and cap transcription factor binding sites in the mutation allele than in the wild allele. One missense mutation (G --> A) occurs in the coding region (61nt), which changes the glycine to arginine. Moreover, in the coding region there are 2 synonymous mutations, one G --> T mutation at 315nt and one C --> T mutation at 336nt. Least square analysis of the SNPs and carcass traits showed that BB, DD and FF genotypes are significantly associated with body weight, carcass weight (or half carcass weight), and leg muscle weight (P < 0.05 or P < 0.01). But no significant association between the genotypes and abdominal fat weight is found. The results present the evidence that the chicken MC4R gene can be selected as the major candidate gene for the carcass traits such as body weight and growth.

Genetics of obesity in humans

Considerable attention has focused on deciphering the hypothalamic pathways that mediate the behavioral and metabolic effects of leptin. We and others have identified several single gene defects that disrupt the molecules in the leptin-melanocortin pathway causing severe obesity in humans. In this review, we consider these human monogenic obesity syndromes and discuss how far the characterization of these patients has informed our understanding of the physiological role of leptin and the melanocortins in the regulation of human body weight and neuroendocrine function.

How the hypothalamus controls glucose production: an update

Recent evidence highlights a crucial role of the brain in the control of glucose homeostasis. The hypothalamus senses and integrates signals of fuel abundance, such as circulating macronutrients (glucose and fatty acids) and nutrient-induced hormones (insulin and leptin). This, in turn, results in the activation of neural pathways that return circulating nutrients to baseline by reducing hepatic glucose production and food intake. In Type 2 diabetes and obesity, the ability of the brain to sense and respond to circulating signals is impaired. In this review, the neuroendocrine circuits that have recently been involved in the regulation of endogenous glucose production in rodents will be described. The study of these neural pathways promises to unveil new targets for the therapy of Type 2 diabetes and obesity.

Evaluation of the porcine melanocortin 4 receptor (MC4R) gene as a positional candidate for a fatness QTL in a cross between Landrace and Hampshire

Melanocortin 4 receptor (MC4R) is expressed in the appetite-regulating areas of the brain where it is central in the regulation of feed intake and energy balance. A mutation in MC4R causing an Asp298Asn substitution has been associated with fatness, high daily gain and feed intake in the pig. In a previously performed genome scan based on a Hampshire x Landrace cross, we detected one quantitative trait loci (QTL) affecting carcass fat/meat ratio and one QTL affecting the biceps femoris muscle, both close to the position of MC4R on porcine chromosome 1. In this study, the two lines were found to be close to fixation for alternative alleles of the Asp298Asn polymorphism. Additional QTL analyses supported our hypothesis of MC4R as a positional candidate gene but only for the fat/meat QTL. The Asp298Asn polymorphism was also evaluated as a selection target for daily gain in a Danish pig breeding population that included four breeds (Hampshire, Duroc, Landrace and Yorkshire). Over a 12-year period (1990-2002), a significant increase in the allele frequency of 298Asn was found in Landrace and Duroc, whereas a non-significant decrease in the 298Asn allele frequency was observed in Yorkshire. The Hampshire breed was fixed for the 298Asn allele in 1990. The high 298Asn allele frequencies in Hampshire, Landrace and Duroc are most likely due to selection for daily gain, whereas selection for daily gain in the Yorkshire breed apparently focuses on other loci.

Monogenic human obesity syndromes

Over the past decade we have witnessed a major increase in the scale of scientific activity devoted to the study of energy balance and obesity. This explosion of interest has, to a large extent, been driven by the identification of genes responsible for murine obesity syndromes, and the novel physiological pathways revealed by those genetic discoveries. Others and we have also recently identified several single gene defects causing severe human obesity. Many of these defects have been in molecules identical or similar to those identified as a cause of obesity in rodents. I will review the human monogenic obesity syndromes that have been characterised to date and discuss how far such observations support the physiological role of these molecules in the regulation of human body weight and neuroendocrine function.

The G protein-coupled receptors: pharmacogenetics and disease

Genetic variation in G-protein coupled receptors (GPCRs) is associated with a wide spectrum of disease phenotypes and predispositions that are of special significance because they are the targets of therapeutic agents. Each variant provides an opportunity to understand receptor function that complements a plethora of available in vitro data elucidating the pharmacology of the GPCRs. For example, discrete portions of the proximal tail of the dopamine D1 receptor have been discovered, in vitro, that may be involved in desensitization, recycling and trafficking. Similar in vitro strategies have been used to elucidate naturally occurring GPCR mutations. Inactive, over-active or constitutively active receptors have been identified by changes in ligand binding, G-protein coupling, receptor desensitization and receptor recycling. Selected examples reviewed include those disorders resulting from mutations in rhodopsin, thyrotropin, luteinizing hormone, vasopressin and angiotensin receptors. By comparison, the recurrent pharmacogenetic variants are more likely to result in an altered predisposition to complex disease in the population. These common variants may affect receptor sequence without intrinsic phenotype change or spontaneous induction of disease and yet result in significant alteration in drug efficacy. These pharmacogenetic phenomena will be reviewed with respect to a limited sampling of GPCR systems including the orexin/hypocretin system, the beta2 adrenergic receptors, the cysteinyl leukotriene receptors and the calcium-sensing receptor. These developments will be discussed with respect to strategies for drug discovery that take into account the potential for the development of drugs targeted at mutated and wild-type proteins.

Serotonergic pathways converge upon central melanocortin systems to regulate energy balance

Multiple lines of research provide compelling support for an important role for central serotonergic (5-hydroxytryptamine, 5-HT) and melanocortin pathways in the regulation of food intake and body weight. In this brief review, we outline data supporting a model in which serotonergic pathways affect energy balance, in part, by converging upon central melanocortin systems to stimulate the release of the endogenous melanocortin agonist, alpha-melanocyte stimulating hormone (alpha-MSH). Further, we review the neuroanatomical mapping of a downstream target of alpha-MSH, the melanocortin 4 receptor (MC4R), in the rodent brain. We propose that downstream activation of MC4R-expressing neurons substantially contributes to serotonin's effects on energy homeostasis.