Mechanisms Underlying Metabolic Syndrome in Obesity

描述（由申请人提供）：肥胖是造成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还不清楚。 在这项提案中，三名独立资助的研究人员-菲利普克恩，医学博士，临床研究员，和夏洛特彼得森，博士和罗伯特麦基希，博士，在肌肉和脂肪细胞生物学方面的重要经验，分别-将正式合作的努力，作为一个自然的延伸，以前的工作和共同利益领域的肥胖，胰岛素抵抗和组织脂质积累。 我们的总体假设是，人类胰岛素抵抗主要源于肥胖发展过程中肌细胞内脂质（IMCL）的异位积累。 此外，我们假设，过量IMCL积累是依赖于分泌蛋白质来自脂肪组织中的脂肪细胞和巨噬细胞之间的复杂相互作用。 为了验证这些假设，我们将研究从中度肥胖伴胰岛素抵抗和糖耐量受损（IGT）但尚未出现空腹高血糖症的受试者中分离和培养的脂肪细胞、巨噬细胞和肌细胞之间的相互作用。 该研究人群IMCL升高，肥胖并发症风险高，但避免了葡萄糖毒性的病理生理并发症。 将这些受试者与葡萄糖耐量正常（NOT）的中度肥胖受试者进行比较。 目的1探讨IMCL的发病机制，阐明其在IGT发生发展中的作用。培养的肌肉细胞将用于确定IGT与NGT肥胖受试者在不同细胞外脂肪酸浓度下是否表现出肌肉基因表达和代谢活性的内在差异。 将评估脂质蓄积和氧化以及胰岛素介导的糖原合成和信号传导。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、成肌细胞和脂肪基质血管细胞的共培养物来检查IMCL和胰岛素抵抗的发展。 目的3将确定来自IGT受试者的基质组分在与肌细胞共培养中是否比来自NGT受试者的基质组分更有效地促进IMCL。 我们将比较基质血管组分的单核细胞/巨噬细胞积聚和细胞因子表达。 目的4将确定吡格列酮治疗10周后葡萄糖耐量的改善是否会导致IMCL降低，并确定相关的细胞机制。 在吡格列酮治疗前后，还将使用肌肉和基质细胞进行共培养研究。 这些实验将为肥胖和肌肉功能导致代谢综合征之间的联系提供机理上的见解。

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.