PROT 1: EFFECT OF PHYSIOLOGIC INCREASE IN FFA ON MITOCHONDRIAL FUNC IN NGT SUBJ

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 目的：2型糖尿病(T2 DM)以胰岛素作用和胰岛素分泌缺陷为特征。游离脂肪酸(FFA)代谢紊乱也是T2 DM的一个特征，在显性糖尿病发病之前就已在遗传易感个体中观察到。这提出了一种有趣的可能性，即FFA作为代谢信使，当释放的量增加时，会削弱胰岛素在异糖靶组织中的作用，即“脂毒性”。许多证据也表明，T2 DM患者的组织脂肪含量增加。我们假设，组织脂质过载降低了PGC-1、NRG-1的表达，并减少了参与氧化磷酸化的多个线粒体基因。 研究计划：在目前的拨款中，我们将研究FFA诱导和高血糖诱导的胰岛素抵抗的机制。利用胰岛素钳夹股外侧肌活检、磁共振波谱、体内和体外线粒体功能评估，我们将检测单独升高血浆FFA、单独增加氨基葡萄糖(葡萄糖)以及联合升高血浆FFA对健康NGT-胰岛素敏感受试者全身(肌肉)胰岛素刺激的葡萄糖处置/葡萄糖氧化/糖原合成、胰岛素信号转导以及线粒体基因表达和功能的影响。我们还将检查阿昔莫司(一种有效的脂解抑制剂)的效果以及一种高度特异的肾小管葡萄糖转运抑制剂(BMS 512148)对T2 DM受试者上述参数的影响。 方法：线粒体功能受损导致底物氧化受损，有毒脂代谢产物积聚，抑制胰岛素信号转导，导致胰岛素抵抗。体内和体外研究也表明，增加的氨基己糖通量抑制PGC-1和参与氧化磷酸化的多个线粒体基因的表达，即“糖毒性”。在高血糖存在的情况下，丙二酰辅酶A的增加预计会通过抑制CPT1而进一步损害肌肉脂肪和葡萄糖的氧化，导致有毒的细胞内脂肪代谢产物增加和胰岛素抵抗的恶化，即“糖脂毒性”。 临床意义：这些治疗方法分别降低血浆FFA/消耗肌肉脂肪和降低血糖水平。因此，我们推测这些干预措施将增加PGC-1/MRF-1/线粒体基因的表达，改善线粒体功能，并增强胰岛素的敏感性/分泌。最后，我们将观察阿昔莫司/BMS 512148联合治疗对T2 DM患者上述指标的影响。我们相信，这些研究将为T2 DM的胰岛素抵抗的病因提供新的见解，并找到新的治疗方法来逆转胰岛素作用的缺陷，恢复正常血糖。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. OBJECTIVE: Type 2 diabetes mellitus (T2DM) is characterized by defects in insulin action and insulin secretion. Disburbances in free fatty acid (FFA) metabolism also are a characteristic feature of T2DM and are observed in genetically predisposed individuals before the onset of overt diabetes. This raises the interesting possibility that FFA act as metabolic messengers which, when released in increased amounts, impair insulin action in isulin target tissues, i.e., "lipotoxicity". Much evidence also indicates that tissue fat content is increased in T2DM. We hypothesize that tissue lipid overload decreases expression of PGC-1, NRG-1, and mutliple mitochondrial genes involved in oxidative phosphorylation. RESEARCH PLAN: In the present grant we shall examine the mechanisms of FFA-induced and hyperglycemia-induced insulin resistance. Using the insulin clamp with vastus lateralis muscle biopsy, magnetic resonance spectroscopy, and in vivo and in vitro evaluation of mitochondrial function, we shall examine the effect of elevated plasma FFA alone, increased glucosamine (glucose) alone, and the combination of elevated plasma glucosamine (glucose) plus elevated plasma FFA on whole body (muscle) insulin-stimulated glucose disposal/glucose oxidation/glycogen synthesis, insluin signaling, and mitochondrial gene expression and function in healthy NGT-insulin sensitive subjects. We also will examine the effect of acipimox (a potent inhibitor of lipolysis) and the effect of a highly specific inhibitor of renal tubular (SGLT2) glucose transport (BMS 512148) on the preceding parameters in T2DM subjects. METHODS: The resulant impairment in mitochondrial function leads to impaired substrate oxidation and accumulation of toxic lipid metabolites that inhibit insulin signaling and cause insulin resistance. In vivo and in vitro studies also suggest that increased hexosamine flux inhibits expression of PGC-1 and multiple mitochondrial genes involved in oxidative phosphorylation, i.e. "glucotoxicity". In the presence of hyperglycemia, an increase in malonyl CoA would be expected to further impair muscle fat and glucose oxidation by inhibiting CPT1, leading to an increase in toxic intracellular lipid metabolits and worsening of the insulin resistance, i.e. "glucolipotoxicity". CLINICAL RELEVANCE: These treatments reduce plasma FFA/deplete lipid from muscle and reduce plasma glucose levels, respectively. Therefore, we hypothesize that these interventions will increase PGC-1/MRF-1/mitochondrial gene expression, improve mitochondrial function, and enhance insulin sensitivity/secretion. Lastly, we will examine the effect of combined acipimox/BMS 512148 therapy on the above parameters in T2DM. We believe that these studies will yield new insights into the etiology of insulin resistance in T2DM and identify novel therapeutic approaches to reverse the defects in insulin action and restore normoglycemia.