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。 在以前的工作中，我们发现了一个在肌肉组织中双峰表达的基因。在皮马印第安人中，HLA-DRB1基因与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。从这项研究中，我们选择了80个在糖尿病患者中浓度显着增加的抗体，以研究与糖尿病和保护性单倍型不一致的更大的队列。。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，在糖尿病患者中，CDR3区域的长度较短，表明他们失去了自我耐受性。随后，我们对大量没有保护性单倍型的个体的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。 我们正在继续研究控制胰岛素分泌和胰岛素作用的其他因素。接受减肥手术的非糖尿病患者使用以下技术：Roux-en-Y胃分流术(RYGBP)、腹腔镜带或胃袖，他们在手术前和手术后一个月接受了胰岛素作用、胰岛素分泌和饮食测试的测量。结果表明，接受RYGBP的患者在胰岛素作用、肝脏胰岛素敏感性以及餐后血糖和胰岛素反应更快方面有所改善。这就解释了为什么接受RYGBP治疗的糖尿病患者的血糖较其他类型的患者有更大的改善。虽然在接受RYGBP治疗的患者中，餐中胰高血糖素样肽-1(GLP-1)的增加也更多，但这一时机并不表明这种增加在胰岛素释放的增加中起作用。除胰腺多肽外，其他胃肠肽在两组之间没有差异，胰腺多肽是迷走神经活动的标志，在RYGBP后的进餐期间，胰腺多肽显著下降。我们继续跟踪这些人，检查身体成分的变化与关系，并确定饮食测试中的血糖和胰岛素反应是否随着体重的进一步下降而变化。 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。我们证实，在较大的队列中，较低的能量消耗与身体大小之间的联系是体重增加的预测因素，并有较长的随访时间。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。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。我们发现，脑脊液中的超长链脂肪酸浓度与24小时的能量消耗呈负相关，这表明特定的长链脂肪酸作为具有重要外周效应的中央信号分子发挥了作用。我们正在计划一项后续研究，在该研究中，我们使用一种特定的长链脂肪酸，并确定其对代谢参数的影响。我们还证实了相对较低的24小时能量消耗作为体重和脂肪质量增加的预测指标的作用。 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。此外，我们发现MC4R突变的存在独立于体重预测儿童糖尿病的发展。MC4R导致过度吞噬和体重增加的机制尚不清楚。一种可能的媒介是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。然而，血清BDNF在有和没有MC4R突变的个体之间没有差别。

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 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 this study we have selected 80 antibodies with significantly increased concentrations in those with diabetes to investigate in a larger co-hort discordant for diabetes and the protective haplotype. . We also sequenced the complementary defining region 3 (CDR3) in the T cell receptor in these same individuals. We found that the length of the CDR3 region is shorter in those with diabetes indicating loss of self tolerance. We have subsequently sequenced CDR3 regions in a larger number of individuals without the protective HLA haplotype who also have measures of insulin action and secretion. We are continuing to investigate additional factors which control insulin secretion and insulin action. Individuals without diabetes who are undergoing bariatric surgery using the following techniques: Roux-en-Y gastric bypass (RYGBP), laporoscopic band, or gastric sleeve have undergone measures of insulin action, insulin secretion and meal tests prior to and one month following the surgery. Results indicate that individuals who underwent RYGBP had improvements in insulin action hepatic insulin sensitivity, and more rapid glucose and insulin responses during meal tests. This explains the greater improvement in glycemia seen in those with diabetes undergoing RYGBP compared with other the laporoscopic band. Although glucagon like peptide-1 (GLP-1) also increased more during the meal in those who underwent RYGBP, the timing did not indicate that this increase played a role in the increase insulin release. Other gastrointestinal peptides did not differ between the groups except for pancreatic polypeptide, a marker of vagal nerve activity, which decreased significantly during the meal following RYGBP. We are continuing to follow these individuals to examine body composition changes with relation, and determine if the glucose and insulin responses during the meals tests change with further weight loss. 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 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. The thermic effect of food and the energy cost of arousal are overlapping and difficult to measure components of energy expenditure. By examining timepoint 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. We found that very long chain fatty acid concentrations in the CSF were inversely associated with 24 hour energy expenditure indicating a role for specific long chain fatty acids as central signaling molecules with important peripheral effects. We are planning a follow-up study in which we administer a specific long chain fatty acid and determines its effect on metabolic parameters. We have also confirmed the role of relatively lower 24 hour energy expenditure as a predictor of weight and fat mass 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. Inidividuals with MC4R mutations have accelerated weight gain in childhood but not in adulthood indicating a more potent effect of this mutation in early life. Furthermore, we found that presence of MC4R mutations predicted development of diabetes in childhood independent of body weight. The mechanism by which MC4R leads to hyperphagia and weight gain is not clear. One possible mediator is brain derived neurotrophic factor (BDNF) a downstream effector of MC4R signaling which has been implicated in childhood hyperphagia and weight gain. However, serum BDNF did not differ between individuals with and without MC4R mutations.