Association of Proopiomelanocortin Gene Polymorphisms with Obesity in the IRAS Family Study

Fetal alcohol exposure alters proopiomelanocortin gene expression and hypothalamic-pituitary-adrenal axis function via increasing MeCP2 expression in the hypothalamus

Proopiomelanocortin (POMC) is a precursor gene of the neuropeptide β-endorphin in the hypothalamus and is known to regulate various physiological functions including stress response. Several recent reports showed that fetal alcohol exposure programs the hypothalamus to produce lower levels of POMC gene transcripts and to elevate the hypothalamic-pituitary-adrenal (HPA) axis response to stressful stimuli. We investigated the role of methyl CpG binding protein (MeCP2) in the effects of prenatal ethanol on POMC gene expression and hypothalamic-pituitary-adrenal (HPA) axis function. Pregnant Sprague Dawley rats were fed between GD 7 and 21 with a liquid diet containing 6.7% alcohol, pair-fed with isocaloric liquid diet, or fed ad libitum with rat chow, and their male offsprings were used at 60 days after birth in this study. Fetal alcohol exposure reduced the level of POMC mRNA, but increased the level of DNA methylation of this gene in the arcuate nucleus (ARC) of the hypothalamus where the POMC neuronal cell bodies are located. Fetal alcohol exposed rats showed a significant increase in MeCP2 protein levels in POMC cells, MeCP2 gene transcript levels as well as increased MeCP2 protein binding on the POMC promoter in the arcuate nucleus. Lentiviral delivery of MeCP2 shRNA into the third ventricle efficiently reduced MeCP2 expression and prevented the effect of prenatal ethanol on POMC gene expression in the arcuate nucleus. MeCP2-shRNA treatment also normalized the prenatal ethanol-induced increase in corticotropin releasing hormone (CRH) gene expression in the hypothalamus and elevated plasma adrenocorticotrophic hormone (ACTH) and corticosterone hormone responses to lipopolysaccharide (LPS) challenge. These results suggest that fetal alcohol programming of POMC gene may involve recruitment of MeCP2 on to the methylated promoter of the POMC gene to suppress POMC transcript levels and contribute to HPA axis dysregulation.

Investigation of melanocortin system gene variants in antipsychotic-induced weight gain

OBJECTIVES

The use of second-generation antipsychotic medications may result in substantial weight gain in a subset of schizophrenia patients. Distinct populations of neurons expressed in the hypothalamus, including the cocaine- and amphetamine-regulated transcript (CART), the polypeptide pro-opiomelanocortin (POMC) and the agouti-related protein (AGRP), have regulatory roles in weight control and energy homeostasis. Thus, we investigated the potential role of CART, POMC and AGRP genetic variants in antipsychotic-induced weight gain (AIWG).

METHODS

Five CART single nucleotide polymorphisms (SNPs) (rs10515115, rs3763153, rs3857384, rs11575893, rs16871471), three POMC SNPs (rs6713532, rs1047521, rs3754860) and one AGRP SNP (rs1338993), were genotyped in 218 patients treated with antipsychotics for chronic schizophrenia and evaluated for AIWG. We compared weight change (%) across genotypic groups using analysis of covariance.

RESULTS

None of the SNPs in POMC, CART, AGRP were significantly associated with AIWG in the refined samples stratified by ethnicity and medication treatment.

CONCLUSIONS

In this exploratory study, we observed that POMC, CART and AGRP gene variants are not a major contributor to AIWG. However larger samples are required to completely rule out their effect on AIWG.

Transgenerational epigenetic inheritance: focus on soma to germline information transfer

In trangenerational epigenetic inheritance, phenotypic information not encoded in DNA sequence is transmitted across generations. In germline-dependent mode, memory of environmental exposure in parental generation is transmitted through gametes, leading to appearance of phenotypes in the unexposed future generations. The memory is considered to be encoded in epigenetic factors like DNA methylation, histone modifications and regulatory RNAs. Environmental exposure may cause epigenetic modifications in the germline either directly or indirectly through primarily affecting the soma. The latter possibility is most intriguing because it contradicts the established dogma that hereditary information flows only from germline to soma, not in reverse. As such, identification of the factor(s) mediating soma to germline information transfer in transgenerational epigenetic inheritance would be pathbreaking. Regulatory RNAs and hormone have previously been implicated or proposed to play a role in soma to germline communication in epigenetic inheritance. This review examines the recent examples of gametogenic transgenerational inheritance in plants and animals in order to assess if evidence of regulatory RNAs and hormones as mediators of information transfer is supported. Overall, direct evidence for both mobile regulatory RNAs and hormones is found to exist in plants. In animals, although involvement of mobile RNAs seems imminent, direct evidence of RNA-mediated soma to germline information transfer in transgenerational epigenetic inheritance is yet to be obtained. Direct evidence is also lacking for hormones in animals. However, detailed examination of recently reported examples of transgenerational inheritance reveals circumstantial evidence supporting a role of hormones in information transmission.

Male germline transmits fetal alcohol adverse effect on hypothalamic proopiomelanocortin gene across generations

BACKGROUND

Neurons containing proopiomelanocortin (POMC)-derived peptides, known to control stress axis, metabolic, and immune functions, have a lower function in patients with a family history of alcoholism, raising the possibility that alcohol effects on the POMC system may transmit through generations. Here we describe epigenetic modifications of Pomc gene that transmit through generation via male germline and may be critically involved in alcoholism-inherited diseases.

METHODS

Whether an epigenetic mechanism is involved in causing a Pomc expression deficit in fetal alcohol-exposed rats is studied by determining Pomc gene methylation, expression, and functional abnormalities and their normalization following suppression of DNA methylation or histone acetylation. Additionally, transgenerational studies were conducted to evaluate the germline-transmitted effect of alcohol.

RESULTS

Fetal alcohol-exposed male and female rat offspring showed a significant deficit in POMC neuronal functions. Associated with this was an increased methylation status of several CpG dinucleotides in the proximal part of the Pomc promoter region and altered level of histone-modifying proteins and DNA methyltransferases levels in POMC neurons. Suppression of histone deacetylation and DNA methylation normalized Pomc expression and functional abnormalities. Fetal alcohol-induced Pomc gene methylation, expression, and functional defects persisted in the F2 and F3 male but not in female germline. Additionally, the hypermethylated Pomc gene was detected in sperm of fetal alcohol-exposed F1 offspring that was transmitted through F3 generation via male germline.

CONCLUSIONS

Trangenerational epigenetic studies should spur new insight into the biological mechanisms that influence the sex-dependent difference in genetic risk of alcoholism-inherited diseases.

Association study of POMC variants with body composition measures and nutrient choice

Genome linkage scans and candidate gene studies have implicated the pro-opiomelanocortin (POMC) locus in traits related to food intake, metabolic function, and body mass index. Here we investigate single nucleotide polymorphisms at the POMC locus in order to evaluate the influence of its genetic variance on body fat distribution and diet in a sample of middle-aged men from The Netherlands. 366 Dutch males from the Hamlet cohort were asked detailed questions about food choice, nutrient intake and exercise. Furthermore, their weight and body fat composition were measured. Each cohort member was genotyped for a set of single nucleotide polymorphisms (SNPs) at the POMC locus. Regression analysis, adjusted for several covariates, was used to test for the association between genetic variants and the phenotypes measured. POMC variation was associated with waist:hip ratio, visceral fat and abdominal fat (rs6713532, P=0.020, 0.019, and 0.021, respectively), and nutrient choice (rs1042571, P=0.034), but in light of limited power and multiple testing these results should be taken with caution. POMC is a strong candidate for involvement in appetite regulation as supported by animal, physiological, and genetic studies and variation at the POMC locus may affect an individual's energy intake which in turn leads to variation in body composition and body fat.

Admixture mapping of obesity-related traits in African Americans: the Atherosclerosis Risk in Communities (ARIC) Study

Obesity is an important cause of morbidity and mortality worldwide. In the United States, the prevalence of obesity is higher in African Americans than whites, even after adjustment for socioeconomic status (SES). This leads to the hypothesis that differences in genetic background may contribute to racial/ethnic differences in obesity-related traits. We tested this hypothesis by conducting a genome-wide admixture mapping scan using 1,350 ancestry-informative single-nucleotide polymorphisms (SNPs) in 3,531 self-identified blacks from the Atherosclerosis Risk in Communities (ARIC) study. We used these markers to estimate the overall proportions of European ancestry (PEAs) for each individual and then scanned for the association between PEA and obesity-related traits (both continuous and dichotomous) at each locus. The median (interquartile range) PEA was 0.151 (0.115). PEA was inversely correlated with continuous BMI, weight, and subscapular skinfold thickness, even after adjusting for socioeconomic factors. In contrast, PEA was positively correlated with BMI-adjusted waist circumference. Using admixture mapping on dichotomized traits, we identified a locus on 2p23.3 to be suggestively associated with BMI (locus-specific lod = 4.11) and weight (locus-specific lod = 4.07). After adjusting for global PEA, each additional copy of a European ancestral allele at the 2p23.3 peak was associated with a BMI decrease of approximately 0.92 kg/m(2) (P = 2.9 x 10(-5)). Further mapping in this region on chromosome 2 may be able to uncover causative variants underlying obesity, which may offer insights into the control of energy homeostasis.

Pro-opiomelanocortin gene variation related to alcohol or drug dependence: evidence and replications across family- and population-based studies

BACKGROUND

Opioidergic neurotransmission is critical in many, possibly all, forms of substance dependence. Several opioid-system genes have been shown to be associated with substance dependence disorders. The pro-opiomelanocortin gene (POMC) encodes several peptides important for endogenous opioidergic neurotransmission. We tested whether POMC genetic variation affects risk for substance dependence.

METHODS

Five single nucleotide polymorphisms spanning POMC were examined in independent family and case-control samples. Family-based studies included 854 subjects from 319 African American (AA) families and 761 subjects from 313 European American (EA) families. Each family had a pair of siblings affected with cocaine and/or opioid dependence. Case-control studies included 791 cases (455 AAs and 336 EAs) affected with alcohol, cocaine, and/or opioid dependence and 682 control subjects (199 AAs and 483 EAs).

RESULTS

Family-based analyses revealed an association of rs6719226 with opioid dependence in AA families and rs6713532 with cocaine dependence in EA families (p = .010-.044). Case-control analyses demonstrated an association of rs6713532 with alcohol or cocaine dependence in EAs (p(allele-wise) = .003-.008). Moreover, the minor allele of rs1866146 was found to be a risk factor for cocaine or opioid dependence in AAs (p(allele-wise) = .010-.017) and for alcohol, cocaine, or opioid dependence in EAs (p(allele-wise) = .001-.003). Logistic regression analyses in which sex and age were considered and population stratification analyses confirmed these findings. Additionally, specific haplotypes increased risk for cocaine dependence (p = .023) in AAs and opioid dependence (p = .012) in EAs.

CONCLUSIONS

Given these replicated results, we conclude that variation in POMC confers vulnerability to multiple forms of substance dependence.

Medical sequencing at the extremes of human body mass

Body weight is a quantitative trait with significant heritability in humans. To identify potential genetic contributors to this phenotype, we resequenced the coding exons and splice junctions of 58 genes in 379 obese and 378 lean individuals. Our 96-Mb survey included 21 genes associated with monogenic forms of obesity in humans or mice, as well as 37 genes that function in body weight-related pathways. We found that the monogenic obesity-associated gene group was enriched for rare nonsynonymous variants unique to the obese population compared with the lean population. In addition, computational analysis predicted a greater fraction of deleterious variants within the obese cohort. Together, these data suggest that multiple rare alleles contribute to obesity in the population and provide a medical sequencing-based approach to detect them.

INSIG-2 promoter polymorphism and obesity related phenotypes: association study in 1428 members of 248 families

Background

Obesity is a major public health problem. Body mass index (BMI) is a highly heritable phenotype but robust associations of genetic polymorphisms to BMI or other obesity-related phenotypes have been difficult to establish. Recently a large genetic association study showed evidence for association of the single nucleotide polymorphism (SNP) rs7566605, which lies 10 Kb 5' to the first exon of the insulin-induced gene 2 (INSIG-2), with obesity in several cohorts. We tested this polymorphism for association with body mass related phenotypes in a large family study whose mean BMI was consistent with moderate overweight.

Methods

We studied 1428 members of 248 British Caucasian families who had been ascertained through a proband with hypertension. We measured BMI, waist and hip circumference, and plasma levels of leptin. We genotyped the rs7566605 SNP using a restriction fragment length polymorphism assay, and carried out a family-based association test for quantitative traits related to obesity using the statistical programs MERLIN and QTDT.

Results

We observed no significant association between genotype at rs7566605 and covariate-adjusted (for age, sex, alcohol consumption, smoking and exercise habit) log-transformed BMI, waist measurement, hip measurement, waist-to-hip ratio, or plasma levels of leptin.

Conclusion

There was no association between genotype at rs7566605 and obesity-related phenotypes in this British Caucasian population. These families were in general moderately overweight, few members being severely obese. Our result indicates that this polymorphism has little if any effect on BMI within the normal to moderately overweight range. The effects of this polymorphism on body mass may be restricted to those already predisposed to at least moderate obesity as a result of environmental factors and other predisposing genotypes.

Association of the FBXO11 gene with chronic otitis media with effusion and recurrent otitis media: the Minnesota COME/ROM Family Study

OBJECTIVE

The FBXO11 gene is the human homologue of the gene mutated in the novel deaf mouse mutant jeff (Jf), a single gene model of otitis media. We have evaluated single nucleotide polymorphisms (SNPs) in the FBXO11 gene for association with chronic otitis media with effusion/recurrent otitis media (COME/ROM).

DESIGN

A total of 13 SNPs were genotyped across the 98.7 kilobases of genomic DNA encompassing FBXO11. Data were analyzed for single SNP association using generalized estimating equations, and haplotypes were evaluated using Pedigree Disequilibrium Test methods.

PATIENTS

The Minnesota COME/ROM Family Study, a group of 142 families (619 subjects) with multiple affected individuals with COME/ROM.

MAIN OUTCOME MEASURES

Genetic association of COME/ROM with polymorphisms in FBXO11.

RESULTS

The FBXO11 SNPs are contained in a single linkage disequilibrium haplotype block. Ten of the 13 SNPs were sufficiently polymorphic in the sample to permit analysis. In univariate genetic analysis, 1 reference SNP (hereinafter rs) (rs2134056) showed nominal evidence of association to COME/ROM (P = .02), and 2 SNPs approached significance (rs2020911, P = .06; rs3136367, P = .09). In multivariable analyses, including known risk factors for COME/ROM (sex, exposure to smoking, attending day care centers, no prior breastfeeding, and having allergies), the evidence of independent association was reduced for each SNP (eg, rs2134056, from P = .02 to P = .08). In subsequent analyses using the Pedigree Disequilibrium Test, the association of FBXO11 SNP rs2134056 (P = .06) with COME/ROM was confirmed. Incorporating multiple SNPs in 2- and 3-locus SNP haplotypes, those haplotypes containing rs2134056 also exhibited evidence of association of FBXO11 and COME/ROM (P values ranging from .03 to .10).

CONCLUSION

We have observed evidence consistent with an association between polymorphisms in FBXO11, the human homologue of the Jeff mouse model gene, and COME/ROM.