FTO influences adipogenesis by regulating mitotic clonal expansion

The fat mass and obesity-associated (FTO) gene plays a pivotal role in regulating body weight and fat mass; however, the underlying mechanisms are poorly understood. Here we show that primary adipocytes and mouse embryonic fibroblasts (MEFs) derived from FTO overexpression (FTO-4) mice exhibit increased potential for adipogenic differentiation, while MEFs derived from FTO knockout (FTO-KO) mice show reduced adipogenesis. As predicted from these findings, fat pads from FTO-4 mice fed a high-fat diet show more numerous adipocytes. FTO influences adipogenesis by regulating events early in adipogenesis, during the process of mitotic clonal expansion. The effect of FTO on adipogenesis appears to be mediated via enhanced expression of the pro-adipogenic short isoform of RUNX1T1, which enhanced adipocyte proliferation, and is increased in FTO-4 MEFs and reduced in FTO-KO MEFs. Our findings provide novel mechanistic insight into how upregulation of FTO leads to obesity

FTO, Type 2 Diabetes, and Weight Gain Throughout Adult Life: A Meta-Analysis of 41,504 Subjects From the Scandinavian HUNT, MDC, and MPP Studies

OBJECTIVE—FTO is the most important polygene identified for obesity. We aimed to investigate whether a variant in FTO affects type 2 diabetes risk entirely through its effect on BMI and how FTO influences BMI across adult life span. RESEARCH DESIGN AND METHODS—Through regression models, we assessed the relationship between the FTO single nucleotide polymorphisms rs9939609, type 2 diabetes, and BMI across life span in subjects from the Norwegian population-based HUNT study using cross-sectional and longitudinal perspectives. For replication and meta-analysis, we used data from the Malmö Diet and Cancer (MDC) and Malmö Preventive Project (MPP) cohorts, comprising a total sample of 41,504 Scandinavians.RESULTS—The meta-analysis revealed a highly significant association for rs9939609 with both type 2 diabetes (OR 1.13; P = 4.5 3 1028) and the risk to develop incident type 2 diabetes (OR 1.16; P = 3.2 3 1028). The associations remained also after correction for BMI and other anthropometric measures. Furthermore, we confirmed the strong effect on BMI (0.28 kg/m2 per risk allele; P = 2.0 3 10226), with no heterogeneity between different age-groups. We found no differences in change of BMI over time according to rs9939609 risk alleles, neither overall (ΔBMI = 0.0[20.05, 0.05]) nor in any individual age stratum, indicating no further weight gain attributable to FTO genotype in adults. CONCLUSIONS—We have identified that a variant in FTO alters type 2 diabetes risk partly independent of its observed effect on BMI. The additional weight gain as a result of the FTO risk variant seems to occur before adulthood, and the BMI difference remains stable thereafter

The obesity-associated SNPs in intron 1 of the FTO gene affect primary transcript levels

As shown by genome-wide association studies single-nucleotide polymorphisms (SNPs) within intron 1 of the FTO gene are associated with the body mass index and type II diabetes, although the functional significance of these SNPs has remained unclear. Using primer extension assays, we have determined the ratio of allelic FTO transcript levels in unspliced heterogeneous nuclear RNA preparations from blood of individuals heterozygous for SNP rs9939609. Allelic expression ratios of the neighboring RPGRIP1L gene were investigated in individuals who were heterozygous for SNP rs4784319 and heterozygous or homozygous for rs9939609. In each of five individuals, the FTO transcripts containing the A (risk) allele of rs9939609 were more abundant than those with T allele (mean 1.38; 95% confidence interval 1.31–1.44). Similar results were obtained in a fibroblast sample. We also observed skewed allelic expression of the RPGRIP1L gene in blood, but skewing was independent of the FTO genotype. Our data suggest that increased expression of FTO is associated with increased body mass

Leveraging cross-species transcription factor binding site patterns: from diabetes risk loci to disease mechanisms

Genome-wide association studies have revealed numerous risk loci associated with diverse diseases. However, identification of disease-causing variants within association loci remains a major challenge. Divergence in gene expression due to cis-regulatory variants in noncoding regions is central to disease susceptibility. We show that integrative computational analysis of phylogenetic conservation with a complexity assessment of co-occurring transcription factor binding sites (TFBS) can identify cis-regulatory variants and elucidate their mechanistic role in disease. Analysis of established type 2 diabetes risk loci revealed a striking clustering of distinct homeobox TFBS. We identified the PRRX1 homeobox factor as a repressor of PPARG2 expression in adipose cells and demonstrate its adverse effect on lipid metabolism and systemic insulin sensitivity, dependent on the rs4684847 risk allele that triggers PRRX1 binding. Thus, cross-species conservation analysis at the level of co-occurring TFBS provides a valuable contribution to the translation of genetic association signals to disease-related molecular mechanisms