Mechanism of Insulin Resistance in Aged

描述（由申请人提供）：60岁以上人群中2型糖尿病的患病率接近25%，但该人群的糖尿病发病机制仍知之甚少。骨骼肌中的胰岛素抵抗是2型糖尿病发展的主要因素，最近的研究表明，由于葡萄糖转运活性降低，细胞内脂质（IMCL）含量的积累与胰岛素刺激的肌糖原合成缺陷之间存在密切关系。是否同样的机制导致了老年人的胰岛素抵抗尚不清楚。在本课题中，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。具体来说，13C核磁共振波谱将用于检查胰岛素刺激的肌糖原合成率在健康的精瘦不吸烟老年人（60-75岁）与健康的年轻不吸烟受试者（18-30岁）的性别、体重、脂肪质量百分比和身体活动相匹配。该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核磁共振波谱来测量细胞内葡萄糖-6-磷酸和葡萄糖的浓度。局部骨骼肌IMCL含量将用1H核磁共振光谱评估。由于初步数据表明，IMCL含量在老年人中增加，我们还计划通过使用微透析测量外周脂肪释放的甘油来评估局部脂肪分解率，以及[2H]甘油周转率来评估全身脂肪分解率，来检查IMCL含量的增加是否由于脂肪酸向骨骼肌的输送增加。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减少，我们将采用一种新的31P/13C NMR方法来评估骨骼肌中线粒体ATP合成率和三羧酸循环通量。总的来说，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靶点，以预防或逆转这些个体的糖尿病。

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.