Genetic regulation of the variation of circulating insulin-like growth factors and leptin in human pedigrees

Exploring correlation between bone metabolism markers and densitometric traits in extended families from Spain

Osteoporosis is a common multifactorial disorder characterized by low bone mass and reduced bone strength that may cause fragility fractures. In recent years, there have been substantial advancements in the biochemical monitoring of bone metabolism through the measurement of bone turnover markers. Currently, good knowledge of the genetics of such markers has become an indispensable part of osteoporosis research. In this study, we used the Genetic Analysis of Osteoporosis Project to study the genetics of the plasma levels of 12 markers related to bone metabolism and osteoporosis. Plasma phenotypes were determined through biochemical assays and log-transformed values were used together with a set of covariates to model genetic and environmental contributions to phenotypic variation, thus estimating the heritability of each trait. In addition, we studied correlations between the 12 markers and a wide variety of previously described densitometric traits. All of the 12 bone metabolism markers showed significant heritability, ranging from 0.194 for osteocalcin to 0.516 for sclerostin after correcting for covariate effects. Strong genetic correlations were observed between osteocalcin and several bone mineral densitometric traits, a finding with potentially useful diagnostic applications. In addition, suggestive genetic correlations with densitometric traits were observed for leptin and sclerostin. Overall, the few strong and several suggestive genetic correlations point out the existence of a complex underlying genetic architecture for bone metabolism plasma phenotypes and provide a strong motivation for pursuing novel whole-genome gene-mapping strategies.

Contribution of body composition components and soft-tissue biochemical factors to genetic variation of body mass index (BMI) in an ethnically homogeneous population

OBJECTIVES

Elevated BMI results from an excess of not only fat mass (FM) but also fat-free soft tissue mass (FFM). Both components of body soft tissue, FM, and FFM, are now considered as active endocrine organs. The major aim of this study was to explore the genetic architecture of BMI, considering genetic variations of its major soft tissue components, and the main biochemical factors associated with their corresponding metabolism: leptin, adiponectin, E-selectin, and insulin-like growth factor binding protein, IGFBP-1.

METHODS

A total of 1,502 apparently healthy individuals (783 men, 719 women) from 359 ethnically homogeneous families were assessed anthropometrically for body composition. Model-based quantitative genetic analyses were implemented to reveal genetic and shared environmental factors affecting the variation and covariation of the studied phenotypes.

RESULTS

We found that inter-individual variation in BMI is strongly correlated with both body composition components (r > 0.92, P < 0.001). These correlations are caused by shared genetic and environmental factors that were interpreted to be a direct result of the intimate genetic and environmental correlations between FM and FFM. The latter were also significantly correlated with leptin, E-selectin, and IGFBP-1. However, whereas leptin displayed both genetic and environmental correlations with both FM and FFM, their correlations with E-selectin were caused only by common genes, and with IGFBP-1-only by a shared environment.

CONCLUSIONS

This study clearly suggests that FM and FFM contributed almost equally to BMI variation, and provides evidence that this contribution is caused by common genetic as well as shared environmental and metabolic factors.

Assessment of age-related changes in heritability and IGF-1 gene effect on circulating IGF-1 levels

It is well established that insulin-like growth factor 1 (IGF-1) circulating levels correlate with age and that heritability and influence of IGF-1 gene variation on IGF-1 levels also well-known. However, the influence of age on the genetic factors determining IGF-1 levels is not clear. In this study, we compared heritability estimates between younger (<52 years) and older (>52 years) twins and tested: (a) whether single nucleotide polymorphisms (SNPs) lying within 100 kbp of the IGF-1 gene are also associated with IGF-1 variation and (b) whether associated SNPs show interaction with age on IGF-1 levels. To achieve these aims, we measured plasma levels of IGF-1 and genotyped 18 SNPs with minor allele frequency >0.1 in a large sample, 4,471 UK female twins. Heritability explained 42 % of IGF-1 variation adjusted for age and in unadjusted sample was independent of age. Ten SNPs in four haploblocks showed significant association with IGF-1 levels, with p = 0.01-0.0005. The most distal SNP was located up to 90 kbp from the IGF-1 gene. When their age-dependent effects were examined, one SNP, rs855203, showed significant (p = 0.0009) age-dependent interaction effect on IGF-1 levels variation. This is the first study to test the age × genotype interaction in IGF-1 levels. The genomic region marked by rs855203 may consequently be of significance for further molecular and pharmacogenetic research, in particular in advanced age.

IGFBP1 and IGFBP3 polymorphisms predict circulating IGFBP-3 levels among women from high-risk breast cancer families

The insulin-like growth factor (IGF) pathway has been implicated as risk modifier in premenopausal breast cancer. In this study, associations between single nucleotide polymorphisms (SNPs) and diplotypes in the IGFBP1 and IGFBP3 genes and circulating IGFBP-3 levels, BRCA family status and breast cancer among women from high-risk breast cancer families were investigated. Nine IGFBP1 and IGFBP3 SNPs were genotyped with PCR-based methods in 323 women. Nine IGFBP1 and ten IGFBP3 diplotypes were identified. Plasma IGFBP-3 levels obtained during cycle day 18-23 were available for 231 women, 87 current users of combined oral contraceptives and 144 non-users. IGFBP1 (rs1995051 and rs4988515) and IGFBP3 (rs2471551 and rs2854744) SNPs were associated with circulating IGFBP-3 levels (P < 0.05). IGFBP1 (low) diplotypes were associated with lower IGFBP-3 levels and were more common in BRCA2 families OR 2.05 (95%CI 0.97-4.30). IGFBP3 (high) diplotypes were associated with higher IGFBP-3 levels and were more common in BRCAX families OR 1.68 (95%CI 1.04-2.74). After adjusting the models for BRCA family status, both the BRCA1 and BRCA2 family status (P ≤ 0.006) and the IGFBP1 diplotype GTAC/ACAT (P = 0.004) were associated with lower IGFBP-3 levels. Similarly, both the BRCA1 and BRCA2 family status (P ≤ 0.03) and the IGFBP-3 diplotypes GCA/GCG (P = 0.007) and GCG/CCG (P = 0.002) were significantly associated with lower IGFBP-3 levels, adjusted for age, weight, OC use, and other IGFBP diplotypes. No individual SNP was associated with breast cancer. There were 23 cases of breast cancer and one IGFBP1 diplotype was associated with a decreased risk of breast cancer after age 18 (log rank P=0.05). In conclusion, independent effects from IGFBP1, IGFBP3 diplotypes, and BRCA family status on IGFBP-3 levels were observed. These factors may influence the risk of breast cancer among women from high-risk breast cancer families.

IGF-I and IGFBP-3 polymorphisms in relation to circulating levels among African American and Caucasian women

Circulating insulin-like growth factor-I (IGF-I) and IGF-binding protein-3 (IGFBP-3) levels have been associated with common diseases. Although family-based studies suggest that genetic variation contributes to circulating IGF-I and IGFBP-3 levels, analyses of associations with multiple IGF-I and IGFBP-3 single nucleotide polymorphisms (SNP) have been limited, especially among African Americans. We evaluated 30 IGF-I and 15 IGFBP-3 SNPs and estimated diplotypes in association with plasma IGF-I and IGFBP-3 among 984 premenopausal African American and Caucasian women. In both races, IGFBP-3 rs2854746 (Ala32Gly) was positively associated with plasma IGFBP-3 (CC versus GG mean difference among Caucasians, 631 ng/mL; 95% confidence interval, 398-864; African Americans, 897 ng/mL; 95% confidence interval, 656-1,138), and IGFBP-3 diplotypes with the rs2854746 GG genotype had lower mean IGFBP-3 levels than reference diplotypes with the CG genotype, whereas IGFBP-3 diplotypes with the CC genotype had higher mean IGFBP-3 levels. IGFBP-3 rs2854744 (-202 A/C) was in strong linkage disequilibrium with rs2854746 in Caucasians only, but was associated with plasma IGFBP-3 in both races. Eight additional IGFBP-3 SNPs were associated with >or=5% differences in mean IGFBP-3 levels, with generally consistent associations between races. Twelve IGF-I SNPs were associated with >or=10% differences in mean IGF-I levels, but associations were generally discordant between races. Diplotype associations with plasma IGF-I did not parallel IGF-I SNP associations. Our study supports that common IGFBP-3 SNPs, especially rs2854746, influence plasma IGFBP-3 levels among African Americans and Caucasians but provides less evidence that IGF-I SNPs affect plasma IGF-I levels.

Correlates of serum leptin and insulin-like growth factor-I concentrations in normal weight and overweight/obese Iranian women

BACKGROUND

Leptin and insulin-like growth factor-I (IGF-I) are two interrelated hormones that are implicated in the development or progression of coronary artery disease (CAD) and some cancers. The aim of this study was to investigate the relation between serum leptin and total IGF-I concentrations and to identify their correlations with age or anthropometric and body composition variables in healthy normal weight and overweight/obese Iranian women.

METHODS

The percent of body fat (BF%), fat mass (FM), fat-free mass (FFM), and waist/hip ratio (WHR) were determined in 51 healthy normal weight (body mass index [BMI] 18.5-24.9 kg/m(2)) and 50 overweight/obese (BMI > or = 25 kg/m(2)) Iranian reproductive-age women. Serum leptin and total IGF-I concentrations were measured by double-antibody sandwich assay and enzyme-linked immunosorbent assay (ELISA), respectively. Statistical analysis was performed by Mann-Whitney U test and Spearman's rank-correlation test. Multivariate linear regression analysis was performed with ranked-transformed data to obtain partial correlation coefficient.

RESULTS

In this group of healthy, premenopausal Iranian women, variance of serum leptin concentration was independently explained by FM (partial rho = 0.295, p < 0.01), and variance of the total IGF-I concentration was explained by age (partial rho = -0.214, p = 0.037) and BMI (partial rho = 0.229, p = 0.026). Overweight/obese women had higher leptin and total IGF-I concentrations than normal weight women (p < 0.01). The serum leptin and total IGF-I concentrations were differentially correlated with age and anthropometric and body composition variables in the two groups. Whereas in normal weight women, leptin was negatively related to BMI (partial rho = -0.356, p = 0.015), in overweight/obese women, BMI, BF%, and FM independently contributed to the serum leptin variability (partial rho = 0.370, p = 0.013; partial rho = -0.320, p = 0.034; partial rho = 0.421, p < 0.01, respectively). There was a weak association between age and total IGF-I concentration in normal weight women, which did not reach statistical significance (partial rho = -0.255, p = 0.091). None of the variables was associated with the total IGF-I in overweight/obese women (p > 0.05).

CONCLUSIONS

Although the studied anthropometric and body composition variables could explain approximately half of the leptin variance in Iranian women, they explained only a small proportion of total IGF-I variability. Our results indicated that the serum leptin and total IGF-I concentrations are differentially regulated in healthy normal weight and overweight/obese Iranian women.

Genetic epidemiology of skeletal system aging in apparently healthy human population

The study of our team was driven by a clinical problem of age-dependent chronic degenerative disease of skeleton that includes osteoporosis (OP) and osteoarthritis (OA)-related phenotypes. The major aims of the study included evaluation of the putative genetic factors determining the rate and pattern of the bone and cartilage loss and identification of the specific genes involved in this process. In addition, we examined genetic effects on circulating molecular factors involved in bone and cartilage metabolism. The skeletal phenotypes were assessed from hand radiographs, in total on about 1200 individuals belonging to ethnically homogeneous nuclear and complex three-generational pedigrees of European origin. The results obtained until now can be divided into three sections: (1) genetic analysis of bone mass/size/geometry characteristics (OP) and traits related to hand OA; (2) pedigree-based investigation of circulating levels of calciotropic hormones, growth factors, cytokines, and biochemical indices of bone and cartilage remodelling; (3) linkage and linkage disequilibrium study of several candidate genes, such as estrogen receptor alpha, collagen type I alpha 1, genes related to extracellular inorganic pyrophosphate transport and OP/OA phenotypes, including biochemical variables. The study provides compelling evidence to suggest strong involvement of the genetic factors in determination of variation of the majority of the examined OP- and OA-related phenotypes.