The agouti-related protein and body fatness in humans

Polymorphisms in corticotrophin-releasing hormone-proopiomalanocortin (CRH-POMC) system genes: Neuroimmune contributions to psoriasis disease

BACKGROUND

Skin is a target organ and source of the corticotropin-releasing hormone-proopiomelanocortin (CRH-POMC) system, operating as a coordinator and executor of responses to stress. Environmental stress exacerbates and triggers inflammatory skin diseases through modifying the cellular components of the immune system supporting the importance of CRH-POMC system in the pathogenesis of psoriasis. The aim of this study was to analyse the association of CRH-POMC polymorphisms with psoriasis and evaluate transcript expression of lesional psoriatic and normal skin in RNA-seq data.

METHODS

Samples of 104 patients with psoriasis and 174 healthy controls were genotyped for 42 single nucleotide polymorphisms (SNPs) of CRH-POMC using Applied Biosystems SNPlex™ method. The transcript quantification was performed using Salmon software v1.3.0.

RESULTS

This study demonstrated the associations between melanocortin 1 receptor (MC1R) polymorphisms rs2228479, rs3212369, dopachrome tautomerase (DCT) polymorphisms rs7987802, rs2031526, rs9524501 and psoriasis in the Tatar population. Very strong association was evident for the SNP rs7987802 in the DCT gene (pc  = 5.95е-006) in psoriasis patients. Additionally, the haplotype analysis provided AT DCT (rs7992630 and rs7987802) and AGA MC1R (rs3212358, 2228479 and 885479) haplotypes significantly associated (pc  ˂ 0.05) with psoriasis in the Tatar population, supporting the involvement of DCT and MC1R to the psoriasis susceptibility. Moreover, MC1R-203 and DCT-201 expression levels were decreased in psoriasis lesional skin compared with healthy control skin.

CONCLUSIONS

This study is the first to identify genetic variants of the MC1R and DCT genes significantly associated with psoriasis in Tatar population. Our results support potential roles of CRH-POMC system genes and DCT in the pathogenesis of psoriasis.

The HERITAGE Family Study: A Review of the Effects of Exercise Training on Cardiometabolic Health, with Insights into Molecular Transducers

The aim of the HERITAGE Family Study was to investigate individual differences in response to a standardized endurance exercise program, the role of familial aggregation, and the genetics of response levels of cardiorespiratory fitness and cardiovascular disease and diabetes risk factors. Here we summarize the findings and their potential implications for cardiometabolic health and cardiorespiratory fitness. It begins with overviews of background and planning, recruitment, testing and exercise program protocol, quality control measures, and other relevant organizational issues. A summary of findings is then provided on cardiorespiratory fitness, exercise hemodynamics, insulin and glucose metabolism, lipid and lipoprotein profiles, adiposity and abdominal visceral fat, blood levels of steroids and other hormones, markers of oxidative stress, skeletal muscle morphology and metabolic indicators, and resting metabolic rate. These summaries document the extent of the individual differences in response to a standardized and fully monitored endurance exercise program and document the importance of familial aggregation and heritability level for exercise response traits. Findings from genomic markers, muscle gene expression studies, and proteomic and metabolomics explorations are reviewed, along with lessons learned from a bioinformatics-driven analysis pipeline. The new opportunities being pursued in integrative -omics and physiology have extended considerably the expected life of HERITAGE and are being discussed in relation to the original conceptual model of the study.

The central melanocortin system and human obesity

The prevalence of obesity and the associated comorbidities highlight the importance of understanding the regulation of energy homeostasis. The central melanocortin system plays a critical role in controlling body weight balance. Melanocortin neurons sense and integrate the neuronal and hormonal signals, and then send regulatory projections, releasing anorexigenic or orexigenic melanocortin neuropeptides, to downstream neurons to regulate the food intake and energy expenditure. This review summarizes the latest progress in our understanding of the role of the melanocortin pathway in energy homeostasis. We also review the advances in the identification of human genetic variants that cause obesity via mechanisms that affect the central melanocortin system, which have provided rational targets for treatment of genetically susceptible patients.

The Human Obesity Gene Map: The 2003 Update

This is the tenth update of the human obesity gene map, incorporating published results up to the end of October 2003 and continuing the previous format. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTLs) from human genome-wide scans and animal crossbreeding experiments, and association and linkage studies with candidate genes and other markers is reviewed. Transgenic and knockout murine models relevant to obesity are also incorporated (N = 55). As of October 2003, 41 Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. QTLs reported from animal models currently number 183. There are 208 human QTLs for obesity phenotypes from genome-wide scans and candidate regions in targeted studies. A total of 35 genomic regions harbor QTLs replicated among two to five studies. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 272 studies reporting positive associations with 90 candidate genes. Fifteen such candidate genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, more than 430 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful sites can be found at http://obesitygene.pbrc.edu.

The Human Obesity Gene Map: The 2004 Update

This paper presents the eleventh update of the human obesity gene map, which incorporates published results up to the end of October 2004. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTLs) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2004, 173 human obesity cases due to single-gene mutations in 10 different genes have been reported, and 49 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 166 genes which, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 221. The number of human obesity QTLs derived from genome scans continues to grow, and we have now 204 QTLs for obesity-related phenotypes from 50 genome-wide scans. A total of 38 genomic regions harbor QTLs replicated among two to four studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably with 358 findings of positive associations with 113 candidate genes. Among them, 18 genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, >600 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful publications and genomic and other relevant sites can be found at http://obesitygene.pbrc.edu.

Association of ghrelin receptor promoter polymorphisms with weight loss following Roux-en-Y gastric bypass surgery

BACKGROUND

Ghrelin plays a role in appetite and has been hypothesized to play a role in the mechanism of Roux-en-Y gastric bypass (RYGB) surgery. Single nucleotide polymorphisms (SNPs) in the promoter region of its receptor gene (growth hormone secretagogue receptor type 1a--GHSR) have also been associated with weight loss outcomes following long-term dietary intervention in adults with impaired glucose tolerance. Our objectives were to evaluate changes in serum ghrelin levels and determine the effect of GHSR promoter polymorphisms on post-RYGB surgery weight loss.

METHODS

Preoperative and 6-month postoperative serum ghrelin levels were measured in 37 patients with extreme obesity undergoing RYGB surgery. Total ghrelin was also measured in liver tissue collected intraoperatively. Association analysis between genotypes for SNPs rs9819506 and rs490683 in the promoter region of the GHSR gene and weight loss outcomes in the 30 months following surgery was performed in over 650 RYGB patients.

RESULTS

Serum ghrelin levels increased after RYGB surgery. Weight loss trajectories were significantly different using an additive model for both ghrelin SNPs, with patients homozygous for the rs490683 CC genotype exhibiting the most weight loss. Weight loss trajectories were also different using a dominant model. The rs490683 risk allele demonstrated decreased promoter activity in vitro.

CONCLUSIONS

The role of increased ghrelin levels in weight loss outcomes following RYGB surgery may be influenced by variation in the GHSR gene.

TG-interacting factor (TGIF) downregulates SOX3 gene expression in the NT2/D1 cell line

SOX3 is a member of the Sox gene family implicated in brain formation and cognitive function. It is considered to be one of the earliest neural markers in vertebrates, playing a role in specifying neuronal fate. Recently, we have established the first link between TALE (three-amino-acid loop extension) proteins, PBX1 (pre-B-cell leukemia homeobox 1) and MEIS1 (myeloid ecotropic viral integration site 1 homologue), and the expression of the human SOX3 gene. Here we present the evidence that TGIF (TG-interacting factor) is an additional TALE superfamily member involved in the regulation of human SOX3 gene expression in NT2/D1 cells by direct interaction with the consensus binding site that is conserved in primate orthologue promoters. Functional analysis demonstrated that mutation of the TGIF binding site resulted in the activation of SOX3 promoter. TGIF overexpression downregulates SOX3 promoter activity and decreases endogenous SOX3 protein expression in both uninduced and retinoic acid (RA)-induced NT2/D1 cells. Up to now, this is the first transcription factor identified as a negative regulator of SOX3 gene expression. The obtained results further underscore the significance of TALE proteins as important transcriptional regulators of SOX3 gene expression.

Alternative G protein coupling and biased agonism: new insights into melanocortin-4 receptor signalling

The melanocortin-4 receptor (MC4R) is a prototypical G protein-coupled receptor (GPCR) that plays a considerable role in controlling appetite and energy homeostasis. Signalling initiated by MC4R is orchestrated by multiple agonists, inverse agonism and by interactions with accessory proteins. The exact molecular events translating MC4R signalling into its physiological role, however, are not fully understood. This review is an attempt to summarize new aspects of MC4R signalling in the context of its recently discovered alternative G protein coupling, and to give a perspective on how future research could improve our knowledge about the intertwining molecular mechanisms that are responsible for the regulation of energy homeostasis by the melanocortin system.

Molecular mechanisms for activation of the agouti-related protein and stimulation of appetite

OBJECTIVE

The agouti-related protein (Agrp) is a powerful orexigenic peptide, but little is known about its transcriptional regulation. The objective of this study was to determine molecular mechanisms for the activation of hypothalamic Agrp and identify compounds that stimulate appetite.

RESEARCH DESIGN AND METHODS

We used promoter analyses methods, hypothalamic cell culture and transfection, immunohistochemistry, luciferase-expressing transgenic mice, in vivo bioluminescence, anitisense RNA, mouse feeding studies, indirect calorimetry, real-time PCR, and Western blots.

RESULTS

We found that the Krüppel-like factor 4 (Klf4) is a potent activator of Agrp by binding to a specific CACCC-box in its minimal promoter. We also found that an extract of tarragon, termed PMI-5011, activated hypothalamic Klf4 and Agrp. In vivo, PMI-5011 increased Agrp promoter activity in luciferase-expressing transgenic mice, increased hypothalamic Klf4 and Agrp expression, increased hypothalamic Orexin and melanin-concentrating hormone, increased food intake, reduced circulating insulin and leptin levels, attenuated energy expenditure, and enhanced body weight but only when using a high-fat diet.

CONCLUSIONS

These data show that Klf4 augmented hypothalamic Agrp by binding to a specific CACCC-box onto its minimal promoter. In addition, the tarragon extract PMI-5011 activated Klf4 and orexigenic neuropeptides and reduced peripheral insulin and leptin levels leading to positive energy balance.

Early growth response protein 1 acts as an activator of SOX18 promoter

Sex-determining region Y box 18 (Sox18/SOX18) gene is an important regulator of vascular development playing a role in endothelial cell specification or differentiation, angiogenesis and atherogenesis. The aim of this study was to perform comprehensive functional characterization of the human SOX18 promoter, including determination of transcription start point (tsp) and identification of control elements involved in the regulation of SOX18 gene expression, with an emphasis on angiogenesis-related transcription factors. Analyses were performed in HeLa cells, representing a tumor cell line, and in EA.hy926 cells used as an endothelial model system. We have determined unique tsp of SOX18 gene, located 172 nucleotides upstream from ATG codon. Further, we have shown that SOX18 promoter region, -726 to -89 bp relative to tsp, contains positive cis-regulatory element(s) that stimulates SOX18 promoter activity, while region -89 to+166 represents the minimal promoter. Within this region we have recognized the presence of essential element(s), positioned from -89 to +29, which harbors cluster of three putative early growth response 1 (EGR1) binding sites. By in vitro binding assays and functional analyses we have shown that these three putative binding sites are functionally relevant and sufficient for EGR1-induced SOX18 transcription. Mutations of these binding sites significantly impaired activity of the SOX18 promoter, particularly in EA.hy926 cells, indicating the importance of these regulatory elements for SOX18 promoter activity in endothelial setting. By data presented in this study, we have established SOX18 as a novel target gene regulated by EGR1 transcription factor, thus providing the first functional link between two transcription factors previously shown to be involved in the control of angiogenesis.

Control elements in the neighboring ATPase gene influence spatiotemporal expression of the human agouti-related protein

The agouti-related protein (AgRP) is an orexigenic peptide that plays a significant role in the regulation of energy balance. It is expressed in the hypothalamus, the adrenal glands, and the testis, but sequences determining its spatial and temporal expression have not been identified. Using an elaborate in vitro screening approach, we show here that two adjacent enhancers inside the first intron of the neighboring (1.4 kb downstream) ATPase gene (ATP6V0D1) modulate the human AgRP promoter with profound spatiotemporal variation despite their diminutive sizes (221 and 231 nt). In transgenic mice, the proximal enhancer displayed specificity for the testis, tail, and ears, and the distal one for the testis, front feet, bone, heart, muscle, brain, spinal cord, and tongue, while dietary fat and overnight fasting had differential effects on enhancer activities. AgRP in the testis was localized to pachytene spermatocytes and in the tongue to epithelial cells. Comparative sequence analysis showed that the AgRP-ATP6V0D1 intergenic region is two times longer in humans than in mice and that the two enhancers are conserved in the rhesus monkey genome but not in the mouse genome. These data show that spatiotemporal expression of the human AgRP gene is influenced by diversified primate-specific intronic sequences in its neighboring ATP6V0D1 gene.

African genetic diversity: implications for human demographic history, modern human origins, and complex disease mapping

Comparative studies of ethnically diverse human populations, particularly in Africa, are important for reconstructing human evolutionary history and for understanding the genetic basis of phenotypic adaptation and complex disease. African populations are characterized by greater levels of genetic diversity, extensive population substructure, and less linkage disequilibrium (LD) among loci compared to non-African populations. Africans also possess a number of genetic adaptations that have evolved in response to diverse climates and diets, as well as exposure to infectious disease. This review summarizes patterns and the evolutionary origins of genetic diversity present in African populations, as well as their implications for the mapping of complex traits, including disease susceptibility.

The role of the Agouti-Related Protein in energy balance regulation

The Agouti-Related Protein (AgRP) is a powerful orexigenic peptide that increases food intake when ubiquitously overexpressed or when administered centrally. AgRP-deficiency, on the other hand, leads to increased metabolic rate and a longer lifespan when mice consume a high fat diet. In humans, AgRP polymorphisms have been consistently associated with resistance to fatness in Blacks and Whites and resistance to the development of type-2 diabetes in African Blacks. Systemically administered AgRP accumulates in the liver, the adrenal gland and fat tissue while recent findings suggest that AgRP may also have inverse agonist effects, both centrally and peripherally. AgRP could thus modulate energy balance via different actions. Its absence or reduced functionality may offer a benefit both in terms of bringing about negative energy balance in obesigenic environments, as well as leading to an increased lifespan.

In silico detection of sequence variations modifying transcriptional regulation

Identification of functional genetic variation associated with increased susceptibility to complex diseases can elucidate genes and underlying biochemical mechanisms linked to disease onset and progression. For genes linked to genetic diseases, most identified causal mutations alter an encoded protein sequence. Technological advances for measuring RNA abundance suggest that a significant number of undiscovered causal mutations may alter the regulation of gene transcription. However, it remains a challenge to separate causal genetic variations from linked neutral variations. Here we present an in silico driven approach to identify possible genetic variation in regulatory sequences. The approach combines phylogenetic footprinting and transcription factor binding site prediction to identify variation in candidate cis-regulatory elements. The bioinformatics approach has been tested on a set of SNPs that are reported to have a regulatory function, as well as background SNPs. In the absence of additional information about an analyzed gene, the poor specificity of binding site prediction is prohibitive to its application. However, when additional data is available that can give guidance on which transcription factor is involved in the regulation of the gene, the in silico binding site prediction improves the selection of candidate regulatory polymorphisms for further analyses. The bioinformatics software generated for the analysis has been implemented as a Web-based application system entitled RAVEN (regulatory analysis of variation in enhancers). The RAVEN system is available at http://www.cisreg.ca for all researchers interested in the detection and characterization of regulatory sequence variation.

DNA sequence variations (polymorphisms) that affect the expression levels of genes play important roles in the pathogenesis of many complex diseases. Compared with genetic variations that alter the amino acid sequences of encoded proteins, which are relatively easy to identify, sequence variants that affect the regulation of genes are difficult to pinpoint among the large amount of nonfunctional polymorphisms located in the vicinity of genes. Computational methods to distinguish functional from neutral variations could therefore prove useful to direct limited laboratory resources to sites most likely to exhibit a phenotypic effect. In this paper we present a Web-based tool for the identification of genetic variation in potential transcription factor binding sites. This tool can be used by any scientist interested in the characterization of regulatory polymorphisms. Using experimentally verified regulatory polymorphisms and background data collected from the literature, we evaluate the method's capacity to identify regulatory genetic variation, and we discuss the limitations of its application.

A rare mutation in AgRP, +79G>A, affects promoter activity

The agouti-related protein is a powerful orexigenic peptide. A rare mutation, +79G>A, was identified in its minimal promoter in two white carriers. Comparison of the 45-year-old male proband, who was also a carrier of the common Ala67Thr polymorphism, with an age- and weight-matching wild-type population showed marginal differences for resting metabolic rate (RMR) and body mass index. The second carrier however was an obese 57-year-old female with reduced RMR. Functional analysis in hypothalamus- and periphery-derived cell lines showed reduced promoter activity for the +79A allele in the adrenocortical cells only, suggesting that it could affect the peripheral expression levels of AgRP. The +79G>A mutation could predispose to body weight gain (as suggested by the phenotype of the second carrier), but it could only affect the proband at an older age as he may be protected by the Ala67Thr polymorphism that is associated with resistance to late-onset fatness.

Agouti-related protein promoter variant associated with leanness and decreased risk for diabetes in West Africans

OBJECTIVE

The role of the central melanocortin system in the development of obesity has been extensively studied. Single-nucleotide polymorphisms (SNPs) within several candidate genes have been associated with food intake and obesity-related phenotypes; however, few of these associations have been replicated. SNPs in the agouti-related protein (AGRP) gene coding (Ala67Thr, 199G/A) and promoter (-38C/T) have been reported to be associated with body mass index (BMI), fat mass (FM) and percent body fat, in populations of European and African descent. In this study, we evaluated the association between the functional AGRP -38C/T promoter SNP and weight-related traits, namely BMI, FM and fat-free mass (FFM), as well as diabetes status.

DESIGN

An association study of the AGRP -38C/T SNP and indices of obesity and diabetes status.

SUBJECTS

A well-characterized population of 538 West Africans from Ghana and Nigeria recruited in the AADM (Africa America Diabetes Mellitus) study (mean age 52 years, 41.3% males, 71% diabetic).

MEASUREMENTS

Genotyping of the AGRP -38C/T SNP, BMI, FM, FFM and fasting plasma glucose.

RESULTS

Women carrying two copies of the variant T allele had significantly lower BMI (OR=0.47; 95% CI, 0.25-0.87). Also, men with at least one copy of the variant T allele were over two times less likely to be diabetic than other men (OR=0.44; 95% CI, 0.22-0.89).

CONCLUSION

Our results replicate previous findings and implicate the AGRP -38C/T SNP in the regulation of body weight in West Africans.

AgRP-deficiency could lead to increased lifespan

The Agouti-related protein (AgRP) is a central orexigenic peptide leading to increased food intake when ubiquitously overexpressed. AgRP-deficient (AgRP(-/-)) mice have either no phenotype or present an age-related leanness. In this study, AgRP(-/-) mice were fed alternate high fat or low fat diets in an effort to determine whether AgRP is a mediating factor for the effects of dietary fat on metabolic parameters. There were no striking metabolic differences between AgRP(-/-) and the equally obese wild type littermates but AgRP(-/-) mice displayed a significantly longer lifespan. The point estimate of median survival for the AgRP(-/-) group was 9.8% greater while the significantly low hazard ratio (0.494) suggests that mortality incidence of AgRP(-/-) mice is less than one-half that of the wild type reference population. It is concluded that although AgRP(-/-) mice become morbidly obese consuming a high fat diet (a landmark feature for a shortened lifespan), they seem to overcome obesity- and age-related pathologies and live significantly longer than their metabolically similar wild type littermates.

The MC4 receptor and control of appetite

Mutations in the human melanocortin (MC)4 receptor have been associated with obesity, which underscores the relevance of this receptor as a drug target to treat obesity. Infusion of MC4R agonists decreases food intake, whereas inhibition of MC receptor activity by infusion of an MC receptor antagonist or with the inverse agonist AgRP results in increased food intake. This review addresses the role of the MC system in different aspects of feeding behaviour. MC4R activity affects meal size and meal choice, but not meal frequency, and the type of diet affects the efficacy of MC4R agonists to reduce food intake. The central sites involved in the different aspects of feeding behaviour that are affected by MC4R signalling are being unravelled. The paraventricular nucleus plays an important role in food intake per se, whereas MC signalling in the lateral hypothalamus is associated with the response to a high fat diet. MC4R signalling in the brainstem has been shown to affect meal size. Further genetic, behavioural and brain-region specific studies need to clarify how the MC4R agonists affect feeding behaviour in order to determine which obese individuals would benefit most from treatment with these drugs. Application of MCR agonists in humans has already revealed side effects, such as penile erections, which may complicate introduction of these drugs in the treatment of obesity.

The melanocortins and melanin-concentrating hormone in the central regulation of feeding behavior and energy homeostasis

A number of different neuropeptides exert powerful concerted controls on feeding behavior and energy balance, most of them being produced in hypothalamic neuronal networks under stimulation by anabolic and catabolic peripheral hormones such as ghrelin and leptin, respectively. These peptide-expressing neurons interconnect extensively to integrate the multiple opposing signals that mediate changes in energy expenditure. In the present review I have summarized our current knowledge about two key peptidic systems involved in regulating appetite and energy homeostasis, the melanocortin system (alpha-MSH, agouti and Agouti-related peptides, MC receptors and mahogany protein) and the melanin-concentrating hormone system (proMCH-derived peptides and MCH receptors) that contribute to satiety and feeding-initiation, respectively, with concurrent effects on energy expenditure. I have focused particularly on recent data concerning transgenic mice and the ongoing development of MC/MCH receptor antagonists/agonists that may represent promising drugs to treat human eating disorders on both sides of the energy balance (anorexia, obesity).

The human obesity gene map: the 2005 update

This paper presents the 12th update of the human obesity gene map, which incorporates published results up to the end of October 2005. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTL) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2005, 176 human obesity cases due to single-gene mutations in 11 different genes have been reported, 50 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 244 genes that, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 408. The number of human obesity QTLs derived from genome scans continues to grow, and we now have 253 QTLs for obesity-related phenotypes from 61 genome-wide scans. A total of 52 genomic regions harbor QTLs supported by two or more studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably, with 426 findings of positive associations with 127 candidate genes. A promising observation is that 22 genes are each supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. The electronic version of the map with links to useful publications and relevant sites can be found at http://obesitygene.pbrc.edu.

Selective tissue uptake of agouti-related protein(82-131) and its modulation by fasting

The blood concentration of agouti-related protein (AgRP), a protein related to hyperphagia and obesity, is increased in obese human and fasted lean subjects. Because there is no saturable transport system at the blood-brain barrier for circulating AgRP to reach its central nervous system target, uptake of AgRP by peripheral organs might be physiologically meaningful. Using the biologically active fragment AgRP(82-131), we determined the pharmacokinetics of its radioactively labeled tracer after iv bolus injection and compared it with that of the vascular marker albumin. AgRP enters peripheral organs at different influx rates, all of which were higher than into brain and spinal cord. At 10 min after iv injection, the radioactivity recovered in the liver, which had the fastest influx rate for AgRP, represented intact (125)I-AgRP. The adrenal gland had a moderately fast uptake (but the highest initial volume of distribution), followed by the heart, lungs, and skeletal muscle. By comparison, epididymal fat, testis, and pancreas had low permeability to AgRP. Saturation of influx was determined by coadministration of excess unlabeled AgRP and was shown to be present in the liver and adrenal gland. The influx rate and initial volume of distribution did not show a linear correlation with vascular permeability or regional blood flow. AgRP uptake by the liver and epididymal fat was significantly increased by overnight fasting, whereas that by the adrenal gland was significantly decreased in fasted mice. Thus, the differential uptake of AgRP by peripheral organs could be a regulated process that is modulated by food deprivation.

Two ethnic-specific polymorphisms in the human Agouti-related protein gene are associated with macronutrient intake

BACKGROUND

The Agouti-related protein (AGRP), an appetite modulator, induces hyperphagia when administered intracerebroventricularly or when overexpressed in transgenic mice. Exogenous administration of AGRP in rodents predisposes to high fat and high sugar intakes.

OBJECTIVE

The objective was to examine the potential associations of 2 ethnic-specific polymorphisms in the AGRP gene (Ala67Thr in whites and -38C>T in blacks) in the Health, Risk Factors, Exercise Training, and Genetics (HERITAGE) Family Study.

DESIGN

We examined the effect of the 2 polymorphisms in the AGRP gene on self-reported macronutrient intakes in 478 white and 272 black participants in the HERITAGE Family Study.

RESULTS

Both AGRP polymorphisms showed a significant association with energy intake. In whites, a smaller proportion of total energy was derived from fat by the Ala67Thr heterozygotes (mean +/- SEM: 29.4 +/- 0.7%) than by the Ala67Ala homozygotes (31.5 +/- 0.5%; P = 0.009), mainly because of a lower intake of saturated (P = 0.06) and monounsaturated (P = 0.01) fats by the Ala67Thr heterozygotes. The percentage of energy from carbohydrates was 2.6% greater in the Ala67Thr heterozygotes (55.1 +/- 1.1%) than in the Ala67Ala homozygotes (52.5 +/- 0.6%; P = 0.03). In blacks, protein intake was associated with the -38C>T promoter polymorphism. T/T homozygotes had a significantly lower protein intake than did the C-allele carriers (C/C: 16.8 +/- 0.4%; C/T: 17.2 +/- 0.2%; T/T: 15.4 +/- 0.7%; P = 0.04). No significant differences in total energy and alcohol intakes existed between genotype groups in blacks or whites.

CONCLUSIONS

The present study suggests that 2 ethnic-specific AGRP variants, previously shown to be associated with leanness in the HERITAGE Family Study, are also associated with macronutrient intake.

The agouti-related protein and its role in energy homeostasis

The melanocortin system plays an important role in the regulation of energy homeostasis. The Agouti-related protein (AGRP) is a natural antagonist of the action of alpha-melanocyte stimulating hormone (alpha-MSH) at the melanocortin receptors (MCR). AGRP is upregulated by fasting while intracerebroventricular injections of synthetic AGRP lead to increased appetite and food intake. Transgenic mice overexpressing AGRP are also hyperphagic and eventually become obese. AGRP is, therefore, a significant regulator of energy balance and a candidate gene for human fatness. Indeed, humans with common single nucleotide polymorphisms (SNPs) in the promoter or the coding region are leaner and resistant to late-onset obesity than wild-type individuals. AGRP is also expressed in the periphery. Recent studies show that AGRP in the adrenal gland is upregulated by fasting as much as it is in the hypothalamus. These data open up the possibility for a wider role by AGRP not only in food intake but also in the regulation of energy balance through its actions on peripheral tissues. This review summarizes recent advances in the biochemical and physiological properties of AGRP in an effort to enhance our understanding of the role this powerful neuropeptide plays in mammalian energy homeostasis.

Unveiling Health Attitudes and Creating Good-For-You Foods: The Genomics Metaphor, Consumer Innovative Web-Based Technologies

This article presents an integrated analysis of three emerging knowledge bases in the nutrition and consumer products industries, and how they may effect the food industry. These knowledge bases produce new vistas for corporate product development, especially with respect to those foods that are positioned as 'good for you.' Couched within the current thinking of state-of-the-art knowledge and information, this article highlights how today's thinking about accelerated product development can be introduced into the food and health industries to complement these three research areas. The 3 knowledge bases are: the genomics revolution, which has opened new insights into understanding the interactions of personal needs of individual consumers with nutritionally relevant components of the foods; the investigation of food choice by scientific studies; the development of large scale databases (mega-studies) about the consumer mind. These knowledge bases, combined with new methods to understand the consumer through research, make possible a more focused development. The confluence of trends outlined in this article provides the corporation with the beginnings of a new path to a knowledge-based, principles-grounded product-development system. The approaches hold the potential to create foods based upon people's nutritional requirements combined with their individual preferences. Integrating these emerging knowledge areas with new consumer research techniques may well reshape how the food industry develops new products to satisfy consumer needs and wants.

Central and peripheral interactions between the agouti-related protein and leptin

The agouti-related protein (AgRP) is a powerful appetite modulator expressed in the hypothalamus and the adrenal gland and regulated by leptin. Here we report the robust expression of AgRP in epididymal fat and its upregulation in this tissue by feeding rather than by fasting. This was observed in both the obesity-susceptible C57BL/6J and the obesity-resistant CAST/Ei mouse strains. Surprisingly, AgRP expression was higher in the hypothalamus and the adrenal gland in the leaner and obesity-resistant CAST/Ei strain. In vitro leptin treatment upregulated endogenous AgRP in mouse hypothalamus and adrenal cells, after an acute 6-h exposure, but it downregulated AgRP after a long-term 60-h exposure. AgRP, on the other hand, upregulated its own endogenous expression in the hypothalamus and the adrenal cells and also upregulated endogenous leptin in the adrenal cells. These results reveal a novel feedback loop and reciprocal transcriptional regulation between AgRP and leptin centrally and peripherally.