Decreased insulin action, impaired insulin secretion and increased adiposity are important risk factors for development of type 2 diabetes. These risk factors are present even when individuals have both normal fasting and two hour glucose concentrations indicating a very early role for decreased insulin secretion in the development of type 2 diabetes. In previous work we found that a bimodally expressed gene in muscle tissue, HLA-DRB1, was associated with lower risk for diabetes and higher insulin secretion in Pima Indians. As this protective HLA haplotype system indicates involvement of autoimmunity in progression to type 2 diabetes in Pima Indians we performed a pilot study in individuals with and without the HLA-DRB1 locus who were also discordant for diabetes status, examining both immunoprofiling of over 9,000 potential proteins and T-cell receptor genes. From among those 9,000 proteins study we selected 80 antibodies with significantly increased concentrations in those with diabetes and tested these in a larger cohort of 45 individuals with diabetes and lacking HLA-DRB1 and 45 individuals with normal glucose regulation with the HLA-DRB1 allele. These individuals were matched for age and sex. Of the selected proteins, 11 again had higher signals in those with diabetes. One of the identified antibodies was to PPARG, a nuclear receptor involved in adipocyte differentiation and a target of anti-diabetic medications. We are now planning to test these 11 potential biomarkers for type 2 diabetes in a co-hort of several hundred subjects with and without type 2 diabetes. We also sequenced the complementary defining region 3 (CDR3) in the T cell receptor in these same individuals. We found that several genes which combine to define the CDR3 region differed significantly in frequency between those with and without diabetes and we found that the length of the CDR3 region is shorter in those with diabetes. We then sequenced CDR3 regions in a larger number of individuals without the protective HLA haplotype and normal glucose regulation at the time of the visit who also have measures of insulin action and secretion. In this larger co-hort we confirmed that one of the genes more frequent in those with diabetes (V gene 7-8) in the initial cohort predicted development of diabetes, as did shorter CDR3 length. Previous predictors of weight gain based on this study have included, higher respiratory quotient, higher insulin mediated glucose uptake, lower free T3, and relatively lower energy expenditure. Variability in energy expenditure is a mediator of weight change, and we have continued to evaluate factors related to metabolic rate. We had previously confirmed this association between lower energy expenditure relative to body size as a predictor of weight gain in a larger cohort with longer follow-up. Furthermore, we were able to demonstrate that lower energy expenditure also predicted gain in fat mass. In a different analysis of weight trajectories in adulthood, we were also able to demonstrate a weight stable group had relatively higher 24 hour energy expenditure compared to all the groups who gained weight, regardless of starting weight. The thermic effect of food and the energy cost of arousal are overlapping and difficult to measure components of energy expenditure. By examining time point data from our metabolic chambers, we were able to estimate these components (which we termed awake fed thermogenesis (AFT)) which accounted for approximately 10% of total energy expenditure. We found that lower AFT predicted weight gain, but only in individuals with BMI ≥ 29 kg/m. This indicates that increased insulation associated with adiposity leads to lower cost of metabolizing macronutrients. As individuals gain weight, their energy expenditure increases more than would be expected based on their increased weight. We have found that increased fasting plasma glucose which may be a marker for increase hepatic glucose production explains part of the large than expected increased EE, and predicted less weight gain. Genetic factors underlie adiposity and its risk factors. Mutations in the melanocortin 4 receptor gene are associated with increased body mass index and lower 24 hour energy expenditure in humans. Individuals with MC4R mutations have accelerated weight gain in childhood but not in adulthood indicating a more potent effect of this mutation in early life. The presence of MC4R mutations predicted development of diabetes in childhood independent of body weight. In an analysis of weight gain. The mechanism by which MC4R leads to hyperphagia and weight gain is not clear but is not due to brain derived neurotrophic factor (BDNF) a downstream effector of MC4R signaling which has been implicated in childhood hyperphagia and weight gain. Recently a more common single nucleotide polymorphism (SNP) has been identified that is associated with increased BMI in Pima Indians. This common SNP is near the promoter region and is also associated with lower energy expenditure and increased ad libitum food intake.
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