Urmeli Joost is a PhD student at the Institute of Family Medicine and Public Health, University of Tartu, Estonia. Her main focus of research is the genetic, environmental and behavioural factors in obesity, dyslipidemia and glucose metabolism.
The prevalence of overweight and obesity has increased worldwide and is affecting millions of adults and children [1]. The development of obesity is complex with factors like genetics, individual metabolism, dietary and physical activity choices, food and water availability, education and culture, playing a role [2]. Several genome-wide association studies have revealed an association between obesity and the gene encoding the transcription factor AP-2 beta (TFAP2B) [3, 4]. TFAP2B plays an important role during the early stages of pregnancy in the development of different parts of the nervous [5]. It has been demonstrated that overexpression of TFAP2B in fat cells causes a decrease in the production and release of adiponectin, a protein hormone that is involved in glucose metabolism [6], and a diminished response to insulin [7]. But how does TFAP2B contribute to the development of obesity?
We have now shown in our ECPBHS study a very clear association between one TFAP2B variation (intron 2 VNTR) and measures of obesity and insulin resistance. Our findings have just recently published in the International Journal of Obesity [8].
We found that men, who inherited the same variant of that gene from both parents (called 5/5 homozygotes), had significantly higher body weight, body mass index, proportion of body fat and insulin resistance, throughout adolescence to young adulthood. Strikingly, women that were 5/5 homozygotes had the same effects, but these appeared later, in young adulthood.
We hypothesized that the people who are TFAP2B 5/5 homozygotes have a higher risk of obesity because they consume more food. But we found the opposite: by age 25 male 5/5 homozygotes had smaller daily calorie intake and consumption of fats and carbohydrates. In females, these differences in caloric and macronutrient intake, were not observed. We therefor think that the risk is not related to increased food intake, but to differences in metabolism.
In conclusion, the gene TFAP2B increases the risk of obesity, abdominal obesity and insulin resistance in this sample, and is probably related to differences in metabolism. We should consider implementing lifestyle interventions already in childhood for individuals who are 5/5 homozygotes, to reduce the effect of TFAP2B on body weight. The physiological role of TFAP2B in body weight regulation and insulin resistance still needs further research.