Seasonal effects of the UCP3 and the RPTOR gene polymorphisms on obesity traits in Japanese adults

Background: Non-shivering thermogenesis (NST) involves a substantial amount of energy expenditure in humans and, thus, contributes to reducing the risk for obesity. Molecular evolutionary studies have reported that SNPs in/near the uncoupling protein 3 gene (UCP3) and the regulatory associated protein of mTOR complex 1 gene (RPTOR) might influence NST and confer adaptive advantages for modern human dispersal into cold environments. In the present study, the impact of these SNPs on obesity-related traits was investigated. Methods: Study subjects consisted of 2,834 Japanese adults (percentage of female: 46%, mean age: 51.5). Associations of the UCP3-55C/T and the RPTOR-26934C/T - the 2 potential genetic variations involved in cold adaptation and thermogenic mechanisms in mammals, with quantitative obesity-related traits including body mass index (BMI), waist circumference, visceral fat area (VFA), VFA adjusted for BMI, and selected blood parameters - were tested using multiple linear regression models. Sliding windowsampling analysis was applied to depict seasonal effects of the SNPs on the obesity-related phenotypes. Results: UCP3-55C/T and the RPTOR-26934C/T did not show any association with obesity traits and blood chemical parameters in multiple linear regression models consisting of the whole subjects. Moreover, sliding window sampling-based association analyses involving seasonality also failed to find associations between these two SNPs and obesity-related traits. Conclusions: UCP3-55C/T and the RPTOR-26934C/T may only have subtle effects on the development of obesity-related traits in the present humans. These two SNPs might be irrelevant to inter-individual variations in energy metabolism and efficiency of NST.