Mechanism of Insulin Resistance in Aged

描述(申请人提供)：60岁以上人群中2型糖尿病的患病率接近25%，但这一群体中糖尿病的发病机制仍然知之甚少。骨骼肌中的胰岛素抵抗是2型糖尿病发生的主要因素，最近的研究表明，由于葡萄糖转运活性降低，肌内脂质(IMCL)含量的积累与胰岛素刺激的肌肉糖原合成缺陷之间存在很强的相关性。同样的机制是否也是导致老年人胰岛素抵抗的原因还不得而知。在这项提案中，我们计划使用最先进的核磁共振技术结合GC/MS和LC/MS/MS技术来探索老年人胰岛素抵抗的机制。具体地说，13C核磁共振波谱将被用来检测健康的瘦身不吸烟受试者(60-75岁)与性别、体重、脂肪质量百分比和体力活动相匹配的健康、年轻(18-30岁)不吸烟受试者中胰岛素刺激的肌肉糖原合成率。这一过程中的速率控制步骤(即葡萄糖转运、己糖激酶、糖原合成酶)将使用31P和13C核磁共振谱来测量细胞内葡萄糖-6-磷酸和葡萄糖的浓度。骨骼肌中定位的IMCL含量将用~1H核磁共振波谱进行评估。由于初步数据显示IMCL含量在老年人中增加，我们还计划通过采用微透析测量外周脂肪释放甘油来评估局部脂解率，以及通过测量[2H]甘油周转率来评估全身脂解率，以检查IMCL含量的增加是否是由于向骨骼肌输送脂肪酸的增加所致。最后，为了确定这些与年龄相关的IMCL含量的增加是否可能归因于线粒体能量代谢的降低，我们将使用一种新的31P/13C核磁共振方法来评估骨骼肌中线粒体ATP合成和三羧酸循环通量的速率。总体而言，预计这些研究的结果将为老年人胰岛素抵抗的发病机制提供新的见解，这反过来将导致潜在的新的治疗目标，以预防或逆转这些人的糖尿病。

DESCRIPTION (provided by applicant): The prevalence of type 2 diabetes in people over 60 years of age approaches 25%, yet the pathogenesis of diabetes in this group remains poorly understood. Insulin resistance in skeletal muscle is a major factor in the development of type 2 diabetes and recent studies have demonstrated a strong relationship between accumulation of intramyocellular lipid (IMCL) content and defects in insulin stimulated muscle glycogen synthesis due to decreased glucose transport activity. Whether this same mechanism is responsible for insulin resistance in the elderly is unknown. In this proposal we plan to use state-of-the-art NMR techniques combined with GC/MS and LC/MS/MS techniques to explore the mechanism of insulin resistance in the elderly. Specifically, 13C NMR spectroscopy will be used to examine rates of insulin stimulated muscle glycogen synthesis in healthy lean non-smoking older (60-75 yrs) subjects compared to healthy, younger (18-30 yrs) non-smoking subjects matched for gender, body weight, percent fat mass and physical activity. Rate controlling steps in this process (i.e. glucose transport, hexokinase, glycogen synthase) will be examined using 31p and 13C NMR spectroscopy to measure intracellular concentrations of glucose-6- phosphate and glucose. Localized IMCL content in skeletal muscle will be assessed with 1H NMR spectroscopy. Since preliminary data suggest that IMCL content is increased in the elderly we also plan to examine whether this increase in IMCL content is due to increased delivery of fatty acids to skeletal muscle, by employing microdialysis measurements of glycerol release from peripheral fat, to assess localized rates of lipolysis, along with [2H] glycerol turnover measurements to assess rates of whole body lipolysis. Finally, to determine whether these age related increases in IMCL content might be attributed to decreased mitochondrial energy metabolism, we will employ a novel 31P/13C NMR method to assess rates of mitochondrial ATP synthesis and tricarboxylic acid cycle flux in skeletal muscle. Overall, it is anticipated that the results from these studies will provide new insights into the pathogenesis of insulin resistance in the elderly, which in turn will lead to potentially new therapeutic targets to prevent or reverse diabetes in these individuals.