Adiponectin receptor genes: mutation screening in syndromes of insulin resistance and association studies for type 2 diabetes and metabolic traits in UK populations

Aims/hypothesis Adiponectin is an adipokine with insulin-sensitising and anti-atherogenic properties. Several reports suggest that genetic variants in the adiponectin gene are associated with circulating levels of adiponectin, insulin sensitivity and type 2 diabetes risk. Recently two receptors for adiponectin have been cloned. Genetic studies have yielded conflicting results on the role of these genes and type 2 diabetes predisposition. In this study we aimed to evaluate the potential role of genetic variation in these genes in syndromes of severe insulin resistance, type 2 diabetes and in related metabolic traits in UK Europid populations. Materials and methods Exons and splice junctions of the adiponectin receptor 1 and 2 genes (ADIPOR1; ADIPOR2) were sequenced in patients from our severe insulin resistance cohort (n=129). Subsequently, 24 polymorphisms were tested for association with type 2 diabetes in population-based type 2 diabetes case–control studies (n=2,127) and with quantitative traits in a population-based longitudinal study (n=1,721). Results No missense or nonsense mutations in ADIPOR1 and ADIPOR2 were detected in the cohort of patients with severe insulin resistance. None of the 24 polymorphisms (allele frequency 2.3–48.3%) tested was associated with type 2 diabetes in the case–control study. Similarly, none of the polymorphisms was associated with fasting plasma insulin, fasting and 2-h post-load plasma glucose, 30-min insulin increment or BMI. Conclusions/interpretation Genetic variation in ADIPOR1 and ADIPOR2 is not a major cause of extreme insulin resistance in humans, nor does it contribute in a significant manner to type 2 diabetes risk and related traits in UK Europid populations. Electronic supplementary material The online version of this article () contains supplementary material, which is accessible to authorised users.     

Association of sequence variations in the gene encoding adiponectin receptor 1 (ADIPOR1) with body size and insulin levels. The Finnish Diabetes Prevention Study

Aims/hypothesis Adiponectin is a circulating peptide derived from adipose tissue. It mediates its insulin-sensitising and anti-atherogenic effects on target tissues through two known receptors, adiponectin receptors 1 and 2 (ADIPOR1; ADIPOR2), which are encoded by the genes ADIPOR1 and ADIPOR2. Our aim was to study the association of ADIPOR1 gene variations with body size and risk of type 2 diabetes in subjects with impaired glucose tolerance, who participated in the Finnish Diabetes Prevention Study (DPS).Subjects and methods We selected seven single nucleotide polymorphisms (SNPs) of the ADIPOR1 gene to perform association studies with anthropometrics and metabolic parameters at baseline, and with the risk of type 2 diabetes during the 3-year follow-up in the DPS study population. Both single SNP analysis and haplotype effects were studied.Results Three out of seven markers studied (rs10920534, rs22757538 and rs1342387) were significantly associated with various body size measurements including weight, height, waist and hip circumference, sagittal diameter and body mass index. Furthermore, three markers (rs10920534, rs12045862 and rs7539542), of which two were different from those associating with body size, were linked to fasting and 2-h insulin levels, particularly in men at baseline. The haplotype analysis with five markers revealed seven major haplotypes in the DPS study population. The haplotype effects on body size measures were in line with those of single SNP analysis. However, none of the markers were associated with the risk of type 2 diabetes.Conclusions/interpretation Our findings suggest that ADIPOR1 has a putative role in the development of body size, and that traits for central adiposity and insulin resistance may be dissociated from each other.Electronic Supplementary Material Supplementary Material is available in the online version of this article at     

Polymorphisms of ADIPOR1 and ADIPOR2 are associated with phenotypes of type 2 diabetes in Koreans

Objective  Adiponectin receptors 1 and 2 ( ADIPOR1 and ADIPOR2 ) are considered as candidate genes for type 2 diabetes because they mediate the metabolic effects of adiponectin on target tissues. We investigated whether common polymorphisms of ADIPOR1 and ADIPOR2 are associated with type 2 diabetes or its related phenotypes in Koreans.
Design and patients  By sequencing of the DNA samples from 24 unrelated Korean subjects, we selected seven single nucleotide polymorphisms (SNPs) from ADIPOR1 and four SNPs from ADIPOR2 for genotyping in 757 type 2 diabetic patients and 644 nondiabetic subjects.
Results  None of the SNPs were associated with the risk of type 2 diabetes. However, g.−7309A>G (rs75172865) in ADIPOR1 was associated with lower insulin resistance, measured by the homeostasis model assessment of insulin resistance (HOMA-IR). Thereafter, we transfected three different human cell lines with plasmids harbouring g.−7309A>G and found that this variant reduced the promoter activity of ADIPOR1 . In ADIPOR2 , g.−63442G (novel SNP) and g.33447T (rs1044471) were associated with smaller waist circumference.
Conclusions  None of the SNPs in either ADIPOR1 or ADIPOR2 were associated with the risk of type 2 diabetes in Koreans. However, the altered activity of the ADIPOR1 promoter was associated with insulin resistance and SNPs of ADIPOR2 were associated with waist circumference.     

Polymorphisms in adiponectin receptor genes ADIPOR1 and ADIPOR2 and insulin resistance

Adiponectin plays an important role in insulin sensitivity via adiponectin receptor 1 and 2 signalling. To date, six genetic association studies have examined the role of polymorphisms in the adiponectin receptor 1 and 2 genes (ADIPOR1 and ADIPOR2) in insulin resistance and type 2 diabetes. These studies are summarized in this review along with unpublished data from the authors. In addition, these polymorphism studies are used to illustrate some of the potential pitfalls and reasons for poor reproducibility of findings in genetic association studies.     

Polymorphisms of ADIPOQ and ADIPOR1 and prostate cancer risk

Studies have linked prostate cancer risk with insulin resistance and obesity. Circulating levels of adiponectin, a protein involved in insulin resistance and obesity, have been associated with prostate cancer risk. We studied the association of prostate cancer risk with haplotype tagging single nucleotide polymorphisms (SNPs) of the adiponectin (ADIPOQ) and adiponectin receptor 1 (ADIPOR1) chosen based on their functional relevance or association with other types of cancer. DNA samples from 465 cases and 441 healthy volunteers from New York City were genotyped for ADIPOQ rs266729, rs822395, rs822396, rs1501299, and rs2241766 SNPs and ADIPOR1 rs12733285, rs1342387, rs7539542, rs2232853, and rs10920531 SNPs. We performed both single- and multiple-SNP analyses. We found that rs12733285, rs7539452, rs266729, rs822395, rs822396, and rs1501299 were significantly associated with prostate cancer risk. Haplotype analysis confirmed these results and identified 5 ADIPOQ 4-SNP haplotypes and 1 ADIPOR1 2-SNP haplotype tightly associated with prostate cancer risk. Importantly, 2 ADIPOQ SNPs, rs266729 and rs1501299, have been previously associated with colon and breast cancer risk, respectively, in the same direction as in this study. These findings suggest that variants of the adiponectin pathway may be associated with susceptibility to various forms of common cancers and warrant validation studies.     

Adiponectin and adiponectin receptor gene variants in relation to type 2 diabetes and insulin resistance-related phenotypes

BACKGROUND: Alterations in adiponectin-mediated pathways are known to be associated with glucose intolerance, insulin resistance (IR), obesity, and type 2 diabetes (T2D) mellitus. Genetic variations in adiponectin (ADIPOQ) and adiponectin 1 and 2 receptor (ADIPOR1 and ADIPOR2) could have effects on IR-related phenotypes and T2D. Here we examine whether the polymorphic markers rs2241766 (ADIPOQ), rs22753738 (ADIPOR1), rs11061971 and rs16928751 (both in ADIPOR2) are implicated in susceptibility to T2D in a Russian population. METHODS: The polymorphic markers were genotyped in 129 T2D patients, and 117 non-diabetic controls, by polymerase chain reaction (PCR) restriction fragment length polymorphism approach. In the subjects, biochemical characteristics including serum insulin, plasma glucose and serum lipids/lipoproteins were measured and compared for correlation with the genetic variations studied. RESULTS: Allele T of rs11061971 and allele A of rs16928751 showed association with higher risk of diabetes providing odds ratios (OR) of 2.05 (p = 0.0025) and 1.88 (p = 0.018), respectively. Haplotype A-G consisting of allele A of rs11061971 and allele G of rs16928751 was associated with reduced risk of T2D (OR = 0.59, p_c = 0.0224). Compared to other variants, diabetic patients double homozygous for A/A of rs16928751 and G/G of rs16928751 had decreased homeostasis model assessment-insulin resistance (p_c = 0.0375) and serum triglycerides (p_c = 0.0285). CONCLUSIONS: The variants of ADIPOR2 confer susceptibility to T2D and are associated with some IR-related phenotypes in the Russian study population.     

Secretion of adiponectin by human placenta: differential modulation of adiponectin and its receptors by cytokines

Aims/hypothesis Pregnancy, a state of insulin resistance, is associated with elevated levels of cytokines and profound alterations in metabolism. Serum adiponectin, an adipokine with anti-inflammatory and insulin-sensitising properties, has been shown to be lower in patients with gestational diabetes mellitus, a state of greater insulin resistance than normal pregnancies. Hypothesising that the human placenta is a source of adiponectin, we investigated its expression and secretion, and the regulation by cytokines of adiponectin and its receptors.Methods Real-time RT-PCR, radioimmunoassay, Western blotting, radioligand binding and immunofluorescent analyses were applied to demonstrate the expression, secretion and functionality of placental adiponectin.Results Adiponectin gene expression and protein were found in the human term placenta, with expression primarily in the syncytiotrophoblast. RIA of conditioned media from explant experiments revealed that the placenta can secrete adiponectin in vitro. Addition of conditioned media to HEK-293 cells transfected with the gene for adiponectin receptor-1 (ADIPOR1) altered the phosphorylation status of extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase, an effect abolished after preabsorption with adiponectin antibody. Cytokines, including TNF-α, IFN-γ, IL-6 and leptin, differentially modulated placental adiponectin receptors as well as adiponectin gene expression and secretion. Interestingly, in placentae from women with gestational diabetes mellitus, we observed significant downregulation of adiponectin mRNA, significant upregulation of ADIPOR1 expression, and a non-significant increase in ADIPOR2 expression. Conclusions/interpretation Our results indicate that the human placenta produces and secretes adiponectin, and that adiponectin and its receptors are differentially regulated by cytokines and their expression altered in women with gestational diabetes mellitus. Collectively, our novel data suggest that adiponectin may play a role in adapting energy metabolism at the materno-fetal interface.     

Association between variants in the genes for adiponectin and its receptors with insulin resistance syndrome (IRS)-related phenotypes in Mexican Americans

Aims/hypothesis The aim of this study was to examine whether genetic variation in ADIPOQ, ADIPOR1 and ADIPOR2 may contribute to increased susceptibility to components of the insulin resistance syndrome (IRS). Materials and methods We genotyped single-nucleotide polymorphisms (SNPs) in ADIPOQ, ADIPOR1 and ADIPOR2 in Mexican American subjects (N=439) and performed an association analysis of IRS-related traits. Results Of the eight SNPs examined in the ADIPOQ gene, rs4632532 and rs182052 exhibited significant associations with BMI (p=0.029 and p=0.032), fasting specific insulin (p=0.023 and p=0.026), sum of skin folds (SS) (p=0.0089 and p=0.0084) and homeostasis model assessment of insulin sensitivity (HOMA-%S) (p=0.015 and p=0.016). Two other SNPs, rs266729 and rs2241767, were significantly associated with SS (p=0.036 and p=0.013). SNP rs7539542 of ADIPOR1 was significantly associated with BMI, SS and waist circumference (p=0.025, p=0.047 and p=0.0062). Fourteen of the ADIPOR2 SNPs were found to be significantly (p<0.05) associated with fasting plasma triglyceride concentrations. Four of these SNPs (rs10848569, rs929434, rs3809266 and rs12342) were in high pairwise linkage disequilibrium (r ²=0.99) and were strongly associated with fasting triglyceride levels (p=0.00029, p=0.00016, p=0.00027 and p=0.00021). Adjusting for the effects of BMI and HOMA-%S on triglyceride concentrations increased significance to p=0.000060 for SNP rs929434. Bayesian quantitative trait nucleotide analysis was used to examine all possible models of gene action. Again, SNP rs929434 provided the strongest statistical evidence of an effect on triglyceride concentrations. Conclusions/interpretation These results provide evidence for association of SNPs in ADIPOQ and its receptors with multiple IRS-related phenotypes. Specifically, several genetic variants in ADIPOR2 were strongly associated with decreased triglyceride levels.     

Adiponectin receptor 1 and small ubiquitin-like modifier 4 polymorphisms are associated with risk of coronary artery disease without diabetes

Background The genes encoding adiponectin receptor 1 (ADIPOR1) and small ubiquitin-like modifier 4 (SUMO4) have been linked to anti-atherogenic effects, but little is known about whether polymorphisms in the two genes, acting separately or interacting, affect risk of coronary artery disease (CAD) without diabetes. Methods We genotyped 200 CAD patients without diabetes and 200 controls without CAD or diabetes at three single-nucleotide polymorphisms (SNPs) in ADIPOR1 and one SNP in SUMO4, which were chosen based on previous studies. Potential associations were also explored between these SNPs and clinical characteristics of CAD without diabetes. Results Risk alleles at three SNPs in ADIPOR1 (rs7539542-G, rs7514221-C and rs3737884-G) and the G allele at SNP rs237025 in SUMO4 significantly increased risk of CAD without diabetes, with ORs ranging from 1.79 to 4.44. Carriers of any of these four risk alleles showed similar adverse clinical characteristics. Compared with individuals with a CC or GC genotype, those with a GG genotype at rs3737884 were at significantly higher risk of CAD that affected the left anterior descending coronary artery (OR: 6.77, P = 0.009), the right coronary artery (OR: 4.81, P = 0.028) or a relatively large number of vessels (P = 0.04). Individuals carrying a risk allele at one or more of the three SNPs in ADIPOR1 as well as a risk allele at the SNP in SUMO4 were at significantly higher risk of CAD without diabetes than individuals not carrying any risk alleles (OR: 5.82, 95% CI: 1.23?27.7, P = 0.013). Conclusions SNPs in ADIPOR1 and SUMO4 are associated with elevated risk of CAD without diabetes, and SNPs in the two genes may interact to jointly affect disease risk.