High fat feeding and intramyocellular lipid abnormality

目前已知肥胖成人骨骼肌肌内甘油三酯(ImcTG)含量增加，这种异常与肌肉中糖代谢受损有关。然而，导致胰岛素升高的途径以及imcTG升高与胰岛素抵抗之间的联系尚未被详细研究。这项应用的目的是确定导致imcTG积累的因素和途径，并确定imcTG脂肪酸的氧化是否也增加，如果是，是否直接影响葡萄糖代谢。假设血浆胰岛素和脂肪酸水平升高独立地刺激imcTG合成，而imcTG合成是导致imcTG积聚增加的主要途径；imcTG池越大，imcTG氧化速度越快，从而干扰肌肉的葡萄糖代谢。为了验证这些假说，将寻求三个特定的目标来回答以下问题：1)胰岛素是一种促进imcTG合成的合成激素吗？2)血浆脂肪酸浓度升高是否通过提供丰富的前体来增加imcTG的合成？3)imcTG池的增加是否与imcTG脂肪酸的加速氧化有关，如果是，这如何影响肌肉的葡萄糖代谢？一种新的一池模型将用于在控制胰岛素和脂肪酸水平的情况下直接(肌肉活检)测定高脂喂养肥胖大鼠的imcTG合成、周转和氧化率。将使用多种示踪剂测定imcTG脂肪酸的氧化和肌肉对葡萄糖的摄取、糖酵解和糖原合成，以确定imcTG氧化对糖代谢的影响。将使用稳定同位素示踪剂(13C)和质谱仪(GC/MS和同位素比值MS)对动力学进行定量。这些研究旨在回答以下问题：放大的imcTG是否是一种对葡萄糖代谢施加负面影响的化学实体，以及血浆胰岛素和脂肪酸是否与imcTG升高有关，如果是，是如何引起的。因此，该研究将加深对肥胖大鼠胰岛素抵抗和imcTG异常机制的认识，为人类肥胖的研究提供有益的帮助。

It is now known that intramyocellular triglycerides (imcTG) content in skeletal muscle of obese adults is increased and this abnormality is associated with impaired glucose metabolism in the muscle. However, the pathways responsible for the increase and the link between the increased imcTG and insulin resistance have not been studied in detail. The objective of this application is to determine the factors and pathways that are responsible for the imcTG accumulation, and to determine whether the oxidation of imcTG fatty acids is also increased and, if so, whether it directly affects glucose metabolism. It is hypothesized that elevated plasma insulin and fatty acid levels, as commonly seen in human obesity, independently stimulate imcTG synthesis and synthesis is the primary pathway leading to the increased imcTG accumulation; and that a larger imcTG pool leads to accelerated imcTG oxidation thereby interfering with muscle glucose metabolism. To test the hypotheses, three specific aims will be pursued to answer following questions: 1) Is insulin an anabolic hormone stimulating imcTG synthesis? 2) Does elevated plasma fatty acid concentration increase imcTG synthesis by providing abundant precursors? 3) Is a larger imcTG pool associated with accelerated oxidation of imcTG fatty acids, and if so, how this affects muscle glucose metabolism? A new one-pool model will be applied to determine the rates of imcTG synthesis, turnover and oxidation directly (muscle biopsy) at controlled insulin and fatty acid levels in rats made obese by high fat feeding. The oxidation of imcTG fatty acids and muscle glucose uptake, glycolysis and glycogen synthesis will be determined using multiple tracers to determine the effect of imcTG oxidation on glucose metabolism. Stable isotopic tracers (13C) and mass spectrometry (GC/MS and isotope ratio MS) will be used to quantitate the kinetics. These studies are designed to answer the questions whether an enlarged imcTG is a chemical entity that imposes a negative effect on glucose metabolism, and whether plasma insulin and fatty acids are responsible for the increased imcTG, and if so, how. Thus, the proposed research will improve the understanding of the mechanism of insulin resistance and imcTG abnormalities in the obese rat that will benefit investigation of human obesity.