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%，但对这一人群中糖尿病的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，肌细胞内脂质（IMCL）含量的积累与胰岛素刺激的肌糖原合成缺陷（由于葡萄糖转运活性降低）之间存在密切关系。这一机制是否与老年人的胰岛素抵抗有关尚不清楚。本研究拟采用现代核磁共振技术结合GC/MS和LC/MS/MS技术来探讨老年人胰岛素抵抗的机制。具体而言，将使用13 C NMR光谱检查与健康、年轻（18-30岁）的非吸烟受试者相比，健康、瘦型非吸烟老年受试者（60-75岁）中胰岛素刺激的肌糖原合成速率，这些受试者在性别、体重、脂肪质量百分比和体力活动方面匹配。将使用31 p和13 C NMR光谱法检查该过程中的速率控制步骤（即葡萄糖转运、己糖激酶、糖原合酶），以测量葡萄糖-6-磷酸和葡萄糖的细胞内浓度。将采用1H NMR光谱法评估骨骼肌中的局部IMCL含量。由于初步数据表明老年人IMCL含量增加，我们还计划通过采用外周脂肪甘油释放的微透析测量来评估局部脂解率，沿着[2 H]甘油周转率测量来评估全身脂解率，以检查IMCL含量增加是否是由于脂肪酸向骨骼肌的输送增加所致。最后，为了确定这些年龄相关的IMCL含量增加是否可能归因于线粒体能量代谢降低，我们将采用一种新的31 P/13 C NMR方法来评估骨骼肌中线粒体ATP合成速率和三羧酸循环通量。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，这反过来又将导致潜在的新治疗靶点，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.