Risk Factors and Etiology of Obesity and Type 2 Diabetes

胰岛素作用减弱、胰岛素分泌受损和肥胖增加是2型糖尿病发生的重要危险因素。即使在空腹和两小时血糖浓度都正常的情况下，这些危险因素也存在，这表明胰岛素分泌减少在2型糖尿病的发展中起着非常早期的作用。 在之前的工作中，我们发现在肌肉组织中双峰表达的基因，人类白细胞抗原-DRB1，与皮马印第安人较低的糖尿病风险和较高的胰岛素分泌有关。由于这种保护性的HLA单倍型系统表明自身免疫参与了皮马印第安人发展为2型糖尿病的过程，我们对具有和不具有HLADRB1基因的个体进行了一项初步研究，检测了9000多种潜在蛋白质和T细胞受体基因的免疫图谱。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45名糖尿病患者和45名具有HLA-DRB1等位基因的血糖调节正常的患者中进行了测试。这些人在年龄和性别上都是匹配的。在选定的蛋白质中，有11个在糖尿病患者中再次具有更高的信号。已确定的抗体之一是PPARG，它是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型糖尿病生物标记物。 我们还对这些人的T细胞受体中的互补定义区3(CDR3)进行了测序。我们发现，在糖尿病患者和非糖尿病患者中，几个共同定义CDR3区域的基因在频率上存在显着差异，我们发现糖尿病患者CDR3区域的长度较短。然后，我们对访问时没有保护性HLA单倍型和正常血糖调节的更多个体的CDR3区域进行了测序，这些个体也有胰岛素作用和分泌的测量。在这个更大的队列中，我们证实了最初队列中糖尿病患者中更常见的基因之一(V基因7-8)预测了糖尿病的发生，CDR3长度较短也是如此。 先前基于这项研究的体重增加预测因素包括较高的呼吸商、较高的胰岛素介导的葡萄糖摄取量、较低的游离T3和相对较低的能量消耗。能量消耗的可变性是体重变化的中介，我们继续评估与代谢率相关的因素。我们之前已经证实，在较大的队列中，较低的能量消耗与较长的随访期之间的这种相关性是体重增加的预测因素。此外，我们能够证明，较低的能量消耗也预示着脂肪质量的增加。在对成年后体重轨迹的不同分析中，我们还能够证明，与所有体重增加的小组相比，体重稳定的小组比所有增加体重的小组有相对更高的24小时能量消耗，无论开始体重如何。食物的热效应和唤醒的能量成本是重叠的，很难衡量能量消耗的组成部分。通过检查代谢室的时间点数据，我们能够估计出这些成分(我们称之为清醒喂养的生热作用(AFT))，它们约占总能量消耗的10%。我们发现，较低的AFT预测体重增加，但仅在BMI为29公斤/米的个体中。这表明与肥胖相关的隔热增加导致代谢大量营养素的成本较低。随着个人体重的增加，他们的能量消耗会比基于他们增加的体重而预期的增加得更多。我们发现，空腹血糖升高可能是肝脏葡萄糖产量增加的一个标志，这解释了EE高于预期的部分原因，并预测体重增加较少。 遗传因素是肥胖及其危险因素的基础。黑素皮质素4受体基因的突变与人类体重指数的增加和24小时能量消耗的降低有关。携带MC4R突变的个体在儿童时期体重增加速度加快，但在成年后没有，这表明这种突变在早期生活中的影响更大。MC4R突变的存在可独立于体重预测儿童糖尿病的发生。在体重增加的分析中。MC4R导致过度吞噬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)，它是MC4R信号的下游效应因子，与儿童过度吞噬和体重增加有关。最近，一种更常见的单核苷酸多态(SNP)被发现与PIMA印第安人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更多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.