Risk Factors and Etiology of Obesity and Type 2 Diabetes

胰岛素作用降低、胰岛素分泌受损和肥胖增加是2型糖尿病发展的重要危险因素。 这些风险因素存在，即使当个体具有正常的空腹和两小时葡萄糖浓度时，也表明胰岛素分泌减少在2型糖尿病发展中的非常早期的作用。 在以前的工作中，我们发现肌肉组织中的双峰表达基因HLA-DRB 1与皮马印第安人患糖尿病的风险降低和胰岛素分泌增加有关。由于这种保护性HLA单倍型系统表明自身免疫参与了皮马印第安人2型糖尿病的进展，我们在具有和不具有HLA-DRB 1位点的个体中进行了一项初步研究，这些个体也与糖尿病状态不一致，检查了超过9，000种潜在蛋白质和T细胞受体基因的免疫谱。从这9,000种蛋白质研究中，我们选择了80种在糖尿病患者中浓度显著增加的抗体，并在一个更大的队列中测试了这些抗体，该队列包括45名糖尿病患者和缺乏HLA-DRB 1的45名患者，以及45名具有HLA-DRB 1等位基因的正常葡萄糖调节的患者。这些人的年龄和性别都是匹配的。在选定的蛋白质中，11种在糖尿病患者中再次具有较高的信号。其中一种抗体是PPARG，一种参与脂肪细胞分化的核受体，也是抗糖尿病药物的靶点。 我们现在正计划在数百名患有和不患有2型糖尿病的受试者中测试这11种潜在的2型糖尿病生物标志物。 我们还对这些相同个体的T细胞受体中的互补定义区3（CDR 3）进行了测序。我们发现几个联合收割机来定义CDR 3区域的基因在糖尿病患者和非糖尿病患者之间的频率显著不同，并且我们发现糖尿病患者的CDR 3区域的长度较短。然后，我们对大量在就诊时没有保护性HLA单倍型和正常葡萄糖调节的个体的CDR 3区域进行测序，这些个体也有胰岛素作用和分泌的测量。在这个更大的共同研究中，我们证实了在初始队列中糖尿病患者中更常见的一个基因（V基因7-8）预测了糖尿病的发展，正如较短的CDR 3长度一样。 先前基于该研究的体重增加的预测因子包括较高的呼吸商、较高的胰岛素介导的葡萄糖摄取、较低的游离T3和相对较低的能量消耗。 能量消耗的变化是体重变化的一个中介，我们继续评估与代谢率相关的因素。我们之前已经证实了相对于身体大小的较低能量消耗之间的这种关联，作为一个更大的队列中体重增加的预测因素，随访时间更长。此外，我们能够证明，较低的能量消耗也预示着脂肪量的增加。在对成年期体重轨迹的不同分析中，我们还能够证明，与所有体重增加的组相比，体重稳定组的24小时能量消耗相对较高，无论起始体重如何。食物的热效应和唤醒的能量消耗是重叠的，很难测量能量消耗的组成部分。通过检查来自我们的代谢室的时间点数据，我们能够估计这些组分（我们称之为清醒进食产热（AFT）），其占总能量消耗的约10%。我们发现，较低的AFT预测体重增加，但仅适用于BMI 29 kg/m的个体。这表明与肥胖相关的绝缘增加会导致代谢大量营养素的成本降低。随着个体体重的增加，他们的能量消耗增加超过了基于他们体重增加的预期。我们发现，空腹血糖升高可能是肝葡萄糖生成增加的标志物，这部分解释了比预期更大的EE增加，并预测体重增加较少。 遗传因素是肥胖症及其危险因素的基础。黑皮质素4受体基因的突变与人类体重指数增加和24小时能量消耗降低有关。具有MC 4 R突变的个体在儿童期体重增加加速，但在成年期没有，这表明这种突变在早期生活中的影响更强。MC 4 R突变的存在预测了儿童期糖尿病的发展，与体重无关。体重增加的分析。MC 4 R导致食欲过盛和体重增加的机制尚不清楚，但不是由于脑源性神经营养因子（BDNF），其是MC 4 R信号传导的下游效应物，其与儿童食欲过盛和体重增加有关。最近，一种更常见的单核苷酸多态性（SNP）已被确定与皮马印第安人的BMI增加有关。这种常见的SNP位于启动子区域附近，也与较低的能量消耗和增加的随意食物摄入有关。

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.