Mechanisms underlying metabolic syndrome in obesity

描述（由申请人提供）：肥胖是产生胰岛素抵抗和代谢综合征的最常见和最强大的力量，然而，这种关联的分子基础尚不清楚。在这项提案中，三位独立资助的研究人员——philip Kern医学博士，临床研究员，Charlotte Peterson博士和Robert McGehee博士，分别在肌肉和脂肪细胞生物学方面具有丰富的经验——将正式确定合作努力，作为先前工作的自然延伸，并在肥胖，胰岛素抵抗和组织脂质积累领域共享利益。我们的总体假设是，人类的胰岛素抵抗主要源于肥胖发展过程中淀粉细胞内脂质（IMCL）的异位积累。此外，我们假设过量的IMCL积累依赖于脂肪组织中脂肪细胞和巨噬细胞之间复杂相互作用产生的分泌蛋白。为了验证这些假设，我们将研究脂肪细胞、巨噬细胞和肌肉细胞之间的相互作用，这些细胞是从患有胰岛素抵抗和糖耐量受损（IGT）的中度肥胖受试者中分离和培养出来的，但他们还没有空腹高血糖。本研究人群IMCL升高，肥胖并发症风险高，但避免了糖毒性的病理生理并发症。这些受试者将与糖耐量正常（NOT）的中度肥胖受试者进行比较。目的1将探讨促进IMCL的机制，并阐明其在IGT发展中的作用。培养的肌肉细胞将用于确定IGT和NGT肥胖受试者在不同细胞外脂肪酸浓度下，肌肉基因表达和代谢活性是否存在内在差异。脂质积累和氧化，以及胰岛素介导的糖原合成和信号传导将被评估。目的2将确定IMCL积累是否依赖于脂肪组织分泌蛋白。我们将使用脂肪细胞、成肌细胞和脂肪间质血管细胞的共培养来检查IMCL和胰岛素抵抗的发展。目的3将确定在与肌肉细胞共培养时，来自IGT受试者的基质部分是否比来自NGT受试者的基质部分更有效地促进IMCL。我们将比较基质血管中单核细胞/巨噬细胞的积累和细胞因子的表达。目的4将确定10周吡格列酮治疗后葡萄糖耐量的改善是否导致IMCL的降低，并确定其中的细胞机制。在吡格列酮治疗前后，肌肉和基质细胞也将进行共培养研究。这些实验将为肥胖和导致代谢综合征的肌肉功能之间的联系提供机制上的见解。

DESCRIPTION (provided by applicant): Obesity is the most common and powerful force for creating insulin resistance and metabolic syndrome, however, the molecular basis of this association is not well understood. In this proposal, three independently funded researchers-Philip Kern, MD a clinical investigator, and Charlotte Peterson, PhD and Robert McGehee, PhD, with significant experience in muscle and adipocyte biology, respectively- will formalize a collaborative effort as a natural extension of previous work and shared interests in the fields of obesity, insulin resistance, and tissue lipid accumulation. Our overall hypothesis is that insulin resistance in humans stems largely from ectopic accumulation of intramyocellular lipid (IMCL) during the development of obesity. Further, we hypothesize that excess IMCL accumulation is dependent on secretary proteins derived from a complex interplay between adipocytes and macrophages in adipose tissue. To test these hypotheses, we will examine the interactions among adipocytes, macrophages, and muscle cells isolated and cultured from subjects that are moderately obese with insulin resistance and impaired glucose tolerance (IGT), but who do not yet have fasting hyperglycemia. This study population has elevated IMCL and is at high risk for obesity complications, but avoids the pathophysiologic complications of glucotoxicity. These subjects will be compared to moderately obese subjects with normal glucose tolerance (NOT). Aim 1 will explore mechanisms that contribute to IMCL and elucidate its role in the development of IGT. Cultured muscle cells will be used to determine whether obese subjects with IGT versus NGT demonstrate intrinsic differences in muscle gene expression and metabolic activity under differing extracellular fatty acid concentrations. Lipid accumulation and oxidation, and insulin-mediated glycogen synthesis and signaling will be assessed. Aim 2 will determine if the IMCL accumulation is dependent on adipose tissue secretary proteins. We will use co-cultures of adipocytes, myoblasts, and adipose stromal vascular cells to examine IMCL and the development of insulin resistance. Aim 3 will determine whether the stromal fraction from IGT subjects promotes IMCL more effectively than that from NGT subjects in co-cultures with muscle cells. We will compare the stromal vascular fractions with regard to monocyte/macrophage accumulation and cytokine expression. Aim 4 will determine if improved glucose tolerance in response to a 10- week treatment with pioglitazone results in decreased IMCL and identify cellular mechanisms involved. Co-culture studies will also be used with muscle and stromal cells, before and after pioglitazone treatment. These experiments will provide mechanistic insight into the link between obesity and muscle function leading to metabolic syndrome.