Impaired adipogenesis in insulin resistance: pilot clinical and in-vitro studies

描述（由申请人提供）：肥胖是2型糖尿病（T2DM）最强的获得性危险因素，然而这些条件之间的确切机制尚不清楚。该试点项目的中心假设是，在营养过度的情况下，新的皮下脂肪细胞分化失败，导致肥厚脂肪细胞的发展，脂肪因子的表达和分泌发生改变。这些变化，包括促炎细胞因子的增加和脂联素的减少，通过旁分泌轴和内分泌轴提供反馈，以限制脂肪的进一步增加，以恶化代谢功能障碍为代价。将在肥胖胰岛素抵抗受试者（OIR, N = 15）和肥胖胰岛素敏感受试者（OIS, N = 15）中测试四个特定目标，以确定：1)与OIS相比，OIR在体内是否会损害前脂肪细胞的增殖或分化；2)与OIS相比，OIR在体外是否会损害前脂肪细胞的增殖或分化；3)前脂肪细胞增殖的损害是否与肥厚脂肪细胞和促炎表型有关；4)内源性大麻素系统在调节前脂肪细胞增殖和分化中的作用。受试者将接受体成分测量（DEXA）、口服葡萄糖耐量、胰岛素敏感性（葡萄糖钳）和皮下脂肪穿刺活检。用2H2O标记DNA，通过测定脂肪细胞和基质血管细胞的周转率来测量体内的脂肪形成。体外前脂肪细胞的增殖和分化将在每个受试者的原代培养物中进行测量。将比较OIR和OIS受试者的脂肪细胞大小、促炎细胞因子的表达和内源性大麻素途径相关基因的表达，以及与增殖和分化有关的指标。了解肥胖导致2型糖尿病的机制可以改善风险分层，并可能提出预防和治疗2型糖尿病及其并发症的新方法。

DESCRIPTION (provided by applicant): Obesity is the strongest acquired risk factor for type 2 diabetes (T2DM), however the precise mechanisms linking these conditions are not known. The central hypothesis of this pilot project is that a failure to differentiate new subcutaneous adipocytes in response to over nutrition leads to the development of hypertrophic adipocytes that manifest alterations in the expression and secretion of adipokines. These changes, including increases in pro-inflammatory cytokines and decreases in adiponectin, provide feedback through both paracrine and endocrine axes to limit further fat accretion, at the expense of worsening metabolic dysfunction. Four specific aims will be tested in obese insulin resistant subjects (OIR, N = 15) and obese insulin sensitive subjects (OIS, N = 15) to determine: 1) whether preadipocyte proliferation or differentiation is impaired in vivo in OIR vs. OIS, 2) whether preadipocyte proliferation or differentiation is impaired in vitro in OIR vs. OIS, 3) whether impairments in preadipocyte proliferation are associated with hypertrophic adipocytes and a pro-inflammatory phenotype and 4) the role of the endocannabinoid system in regulating preadipocyte proliferation and differentiation. Subjects will undergo measurement of body composition (DEXA), oral glucose tolerance, insulin sensitivity (glucose clamp) and percutaneous needle biopsies of subcutaneous fat. Adipogenesis will be measured in vivo by determining turnover rates of adipocytes and stromal-vascular cells using 2H2O to label DNA. Proliferation and differentiation of preadipocytes in vitro will be measured in primary cultures derived from each subject. Adipocyte size, expression of pro-inflammatory cytokines and the expression of genes involved in the endocannabinoid pathway will be compared in OIR and OIS subjects and related to measures of proliferation and differentiation. Understanding the mechanisms whereby obesity leads to T2DM may improve risk stratification and may suggest novel approaches to prevent and treat T2DM and its complications. Project Narrative: Obesity is a potent risk factor for developing type 2 diabetes. This study tests whether differences in the growth rates of fat cells are related to the risk for diabetes in obese individuals. Results from this study could suggest new prevention / treatment strategies.