In Vivo Evaluation of the Cidec R46S Polymorphism for an Obesity QTL, tabw2a

OBJECTIVES: A quantitative trait locus (QTL), tabw2a, was linked to obesity in TALLYHO/Jng (TH) mice, a polygenic model of obesity and type 2 diabetes. In combination with fine mapping information, we used whole genome sequencing data of TH mice to search positional candidate genes for tabw2a. From this search, the cell death-inducing DFFA-like effector c (Cidec) gene, containing a SNP identified as deleterious (likely to affect protein function) by both SIFT and PROVEAN, was raised as a potential candidate for tabw2a. CIDEC is a lipid droplet protein involved in the regulation of cellular lipid droplet size and lipid storage in adipocytes. There was one nucleotide substitution in the coding sequence of Cidec in TH mice, 136 C > A, compared to C57BL/6J (B6) reference sequence, that results in an amino acid substitution R46S (Arginine to Serine). The aim of this study was to evaluate the Cidec R46S polymorphism in vivo for the tabw2a QTL. METHODS: We generated knock-in mice where the TH allele (S46) is exchanged for the B6 allele (R46) at the Cidec gene on a B6 background. Targeting, ES clone selection, blastocyst injection, and breeding of ES cell chimeras were performed by Transgenics Core facility at Pennington Biomedical Research Center (Baton Rouge, LA). We bred the chimeras to B6 mice for 10 generation and collected heterozygous mice with germline transmission of the knock-in allele of Cidec S46. We then interbred the heterozygous mice and obtained homozygous mice for the knock-in allele of Cidec S46. Male and female Cidec (R46S) knock-in and B6 mice were weaned onto chow and high fat (HF) diets (D12266B, Research Diets) at 4 weeks of age and maintained on the same diets. At 20 weeks of age, body composition including fat and lean mass was measured using EchoMRI-100 whole body composition analyzer (Houston, TX). RESULTS: On chow, no genotype effects were shown on adiposity between knock-in and B6 mice for both sexes. However, on HF diets, for both males and females, knock-in homozygous mice had significantly larger body fat mass than B6, although their body weights were comparable. CONCLUSIONS: We conclude that the Cidec gene is a likely candidate for the obesity effect of tabw2a, and that Cidec S46 variant contributes to the obesity susceptibility. FUNDING SOURCES: American Heart Association and National Institutes of Health.