Brain-derived neurotrophic factor in human subjects with function-altering melanocortin-4 receptor variants

Background

In rodents, hypothalamic brain-derived neurotrophic factor (BDNF) expression appears to be regulated by melanocortin-4 receptor (MC4R) activity. The impact of MC4R genetic variation on circulating BDNF in humans is unknown.

Objective

To compare BDNF concentrations of subjects with loss-of-function (LOF) and gain-of-function (GOF) MC4R variants to those of controls with common sequence MC4R.

Methods

Circulating BDNF was measured in two cohorts with known MC4R sequence: 148 subjects of Pima Indian heritage ([mean±SD]: age 15.7±6.5y, BMI-Z 1.63±1.03), and 69 subjects of Hispanic heritage (10.8±3.6y, BMI-Z 1.57±1.07). MC4R variants were characterized in vitro by cell surface expression, receptor binding, and cAMP response after agonist administration. BDNF single nucleotide polymorphisms (SNPs) rs12291186, rs6265, and rs7124442 were also genotyped.

Results

In the Pima cohort, no significant differences in serum BDNF was observed for 43 LOF-subjects versus 65 LOF-matched controls [age-, sex-, and BMI-matched] (P=0.29), or 20 GOF-subjects versus 20 GOF-matched controls (P=0.40). Serum BDNF was significantly associated with genotype for BDNF rs12291186 (P=0.006) and rs6265 (P=0.009), but not rs7124442 (P=0.99); BDNF SNPs did not interact with MC4R status to predict serum BDNF. In the Hispanic cohort, plasma BDNF was not significantly different among 21 LOF-subjects, 20 GOF-subjects, and 28 controls (P=0.79); plasma BDNF was not predicted by BDNF genotype or BDNF-x-MC4R genotype interaction.

Conclusions

Circulating BDNF concentrations were not significantly associated with MC4R functional status, suggesting that peripheral BDNF does not directly reflect hypothalamic BDNF secretion and/or that MC4R signaling is not a significant regulator of the bulk of BDNF expression in humans.

Epidemiology and genetic determinants of progressive deterioration of glycaemia in American Indians: the Strong Heart Family Study

AIMS/HYPOTHESIS

Type 2 diabetes is a chronic, heterogeneous disease and a major risk factor for cardiovascular diseases. The underlying mechanisms leading to progression to type 2 diabetes are not fully understood and genetic tools may help to identify important pathways of glycaemic deterioration.

METHODS

Using prospective data on American Indians from the Strong Heart Family Study, we identified 373 individuals defined as progressors (diabetes incident cases), 566 individuals with transitory impaired fasting glucose (IFG) and 1,011 controls (normal fasting glycaemia at all visits). We estimated the heritability (h(2)) of the traits and the evidence for association with 16 known variants identified in type 2 diabetes genome-wide association studies.

RESULTS

We noted high h(2) for diabetes progression (h(2) = 0.65 ± 0.16, p = 2.7 × 10(-6)) but little contribution of genetic factors to transitory IFG (h(2) = 0.09 ± 0.10, p = 0.19) for models adjusted for multiple risk factors. At least three variants (in WFS1, TSPAN8 and THADA) were nominally associated with diabetes progression in age- and sex-adjusted analyses with estimates showing the same direction of effects as reported in the discovery European ancestry studies.

CONCLUSIONS/INTERPRETATION

Our findings do not exclude these loci for diabetes susceptibility in American Indians and suggest phenotypic heterogeneity of the IFG trait, which may have implications for genetic studies when diagnosis is based on a single time-point measure.

Olfactomedin-like 3 (OLFML3) gene expression in baboon and human ocular tissues: cornea, lens, uvea, and retina

BACKGROUND

Olfactomedin-like is a family of polyfunctional polymeric glycoproteins. This family has at least four members. One member of this family is OLFML3, which is preferentially expressed in placenta but is also detected in other adult tissues including the liver and heart. However, its orthologous rat gene is expressed in the iris, sclera, trabecular meshwork, retina, and optic nerve.

METHODS

OLFML3 messenger amplification was performed by RT-PCR from human and baboon ocular tissues. The products were cloned and sequenced.

RESULTS

We report OLFML3 expression in human and baboon eye. The full coding DNA sequence has 1221 bp, from which an open reading frame of 406 amino acid was obtained. The baboon OLFML3 gene nucleotidic sequence has 98% and amino acidic 99% similarity with humans.

CONCLUSIONS

OLFML3 gene expression in human and baboon ocular tissues and its high similarity make the baboon a powerful model to deduce the physiological and/or metabolic function of this protein in the eye.

Pleiotropic effects on subclasses of HDL, adiposity, and glucose metabolism in adult Alaskan Eskimos

The aim of this study was to analyze the heritability and the presence of pleiotropic effects on subfractions of high-density lipoproteins (HDLs) as measured by nuclear magnetic resonance (NMR), parameters for adiposity, and glucose metabolism in adult Alaskan Eskimos. The present family study included 1,214 adult Alaskan Eskimos (537 male/677 female). Body weight, height, circumferences, selected skinfolds, and blood pressure were measured in all participants. Blood samples were collected under fasting conditions for the isolation of plasma. Glucose, insulin, subclasses and size of lipoproteins, triglycerides, total, and HDL cholesterol and lipoprotein (a) were measured in plasma. HbA1c was measured in total blood. Univariate and bivariate quantitative genetic analyses were conducted between HDL subclasses and size and the anthropometric and biochemical measures using the variance decomposition approach. Variation in all the analyzed traits exhibits a significant genetic component. Heritabilities ranged between 0.18 +/- 0.11 for LDL(2) (intermediate) and 0.89 +/- 0.07 for small HDL. No common genetic effects were found on the HDL subclasses (small, intermediate, and large). Small HDL particles were genetically correlated with LDL particles and HbA1c. Negative genetic correlations were observed between intermediate and large HDL subfractions, HDL size and measures of adiposity, and LDL and parameters for glucose metabolism (HbA1, insulin). These observations confirm the presence of possible pleiotropic effects on HDL, adiposity, and cardiovascular risk factors and provide novel insight on the relationship between HDL subclasses, adiposity, and glucose regulation.

Cross-species replication of a resistin mRNA QTL, but not QTLs for circulating levels of resistin, in human and baboon

Resistin has been associated with inflammation and risk for cardiovascular disease. We previously reported evidence of a QTL on chromosome 19p13 affecting the abundance of resistin (RETN) mRNA in the omental adipose tissue of baboons (L0D score 3.8). In this study, whole genome transcription levels were assessed in human lymphocyte samples from 1240 adults participating in the San Antonio Family Heart Study, using the Sentrix Human-6 Expression Beadchip. Lymphocytes were surveyed, as it has been proposed that their expression levels may reflect those in harder to ascertain tissues, such as adipose tissue, that are thought to be more directly relevant to disease procesn was conducted to detect loci affecting RETN mRNA levels. We obtained significant evidence for a QTL influencing the RETN expression (LOD score 10.7) on chromosome 19p. This region is orthologous/homologous to the region previously localized on baboon chromosome 19. The strongest positional candidate gene in this region is the structural gene for resistin, itself. We also found evidence for a QTL influencing resistin protein levels (LOD score 5.3) on chromosome 14q. This differs from our previously reported QTL on chromosome 18 in baboons. The different QTLs for circulating protein suggests that post-translational processing and turnover may be influenced by different or multiple genes in baboons and humans. The parallel findings of a cis-eQTL for RETN mRNA in baboon omental tissue and human lymphocytes lends support to the strategy of using lymphocyte gene expression levels as a surrogate for gene expression levels in other tissues.

Genome-wide scan revealed genetic loci for energy metabolism in Hispanic children and adolescents

OBJECTIVE

Genome-wide scans were conducted in search for genetic locations linked to energy expenditure and substrate oxidation in children.

DESIGN

Pedigreed data of 1030 Hispanic children and adolescents were from the Viva La Familia Study which was designed to investigate genetic and environmental risk factors for the development of obesity in Hispanic families. A respiratory calorimeter was used to measure 24-h total energy expenditure (TEE), basal metabolic rate (BMR), sleep metabolic rate (SMR), 24-h respiratory quotient (24RQ), basal metabolic respiratory quotient (BMRQ) and sleep respiratory quotient (SRQ). Protein, fat and carbohydrate oxidation (PROOX, FATOX and CHOOX, respectively) were also estimated. All participants were genotyped for 384 single tandem repeat markers spaced an average of 10 cM apart. Computer program SOLAR was used to perform the genetic linkage analyses.

RESULTS

Significant linkage for TEE was detected on chromosome 1 near marker D1S2841, with a logarithm of the odds (LOD) score of 4.0. SMR, BMRQ and PROOX were associated with loci on chromosome 18, 17 and 9, respectively, with LOD scores of 4.88, 3.17 and 4.55, respectively. A genome-wide scan of SMR per kg fat-free mass (SpFFM) peaked in the same region as SMR on chromosome 18 (LOD, 5.24). Suggestive linkage was observed for CHOOX and FATOX. Several candidate genes were found in the above chromosomal regions including leptin receptor (LEPR).

CONCLUSION

Regions on chromosomes 1, 9, 17 and 18 harbor genes affecting variation in energy expenditure and substrate oxidation in Hispanic children and adolescents.