Wan Ching Toy, Jian-Jun Liu, Anton Kui Sing Cheng, Clara Si Hua Tan, Dawn Pingxi Lau, Melvin Deng Sheng Wong, Tavintharan Subramaniam, Chee Fang Sum and Su Chi Lim
Background: Adiponectin is the most abundant circulating adipokine in human that regulates insulin actions. Association of adiponectin gene variations with type 2 diabetes (T2DM) has been reported albeit predominantly in non-Asian populations. Additionally, proof of variant functionality beyond statistical association is often unavailable. We studied six common (minor allele frequency ?0.05) adiponectin single nucleotide polymorphisms (SNPs) in Singaporean Chinese adults with follow-up functional genetic experiments. Methods: In a case-control study (N=588), genotyping of six common adiponectin haplotype tagging SNPs [-3964A>G(rs822396), +45T>G(rs2241766), 276C>A(rs1501299), 973G>A(rs3774262), 4551G>C(rs1063539) and 5852G>A(rs6444175)] was performed using Taqman genotyping assay. Allele-dependent differential efficiency of mRNA expression was tested with quantitative real time PCR using human subcutaneous and omental adipose tissues. Results: Distributions of genotypes for all SNPs among controls were consistent with Hardy-Weinberg Equilibrium. Single locus, genotyped-based analysis suggested borderline significant (P=0.07) association between an exon- 2 coding-synonymous +45T>G(rs2241766) and T2DM. We demonstrated that the relative mRNA expression of adiponectin gene was ~80% lower among carriers of minor G allele in human subcutaneous adipose tissue (N=43, p<0.001). The observed allele-dependent differential expression was replicated (~50% reduction) in an independent sample of human omental adipose tissue (N=52, p<0.005). Conclusions: Our data was indicative of possible association between +45T>G(rs2241766) and T2DM among Singaporean Chinese adults. Functional experiments in both human subcutaneous and omental adipose tissue suggested that polymorphisms in +45T>G(rs2241766) may be associated with differential allelic expression.