Ketone Dysregulation and Muscle Insulin Resistance

描述（由申请人提供）： 令人信服的证据将肌肉胰岛素抵抗的发展与脂肪酸（FA）过度供应联系起来，但关于哪些特定的FA代谢物和调节途径直接负责介导胰岛素脱敏，仍然存在不确定性。我们目前的知识主要基于候选分子方法，其中潜在相关脂质代谢物的选择在很大程度上依赖于特定测定的隐含偏差或可用性。为了克服这一障碍，我们采用了基于质谱的代谢分析，以全面评估多种脂质衍生的代谢产物在肌肉中的大鼠胰岛素抵抗的高脂肪饮食相比，控制。这种无偏见的“代谢组学”方法使我们发现，胰岛素抵抗大鼠表现出明显的酮-β-羟基丁酸（β HB）肌内蓄积，至少有一部分蓄积的酮是在肌肉组织中直接合成的，恢复胰岛素敏感性的遗传操作对应于肌肉HB水平下降55%。这些令人兴奋的发现暗示肌肉酮失调是脂质诱导的胰岛素抵抗的病因学中的一个致病因素。以前的研究支持生酮和葡萄糖耐受不良之间的负相关，但没有考虑到肌肉组织内酮代谢失调可能导致胰岛素抵抗状态的可能性。我们推测，慢性高脂肪喂养和/或营养过剩造成骨骼肌持续和异常的生酮状态，这反过来又直接导致葡萄糖处理和胰岛素敏感性的适应不良变化。我们建议用以下具体目的来检验这些假设：1）确定酮失调是否是多种胰岛素抵抗动物模型的共同特征。这将通过分析肥胖和糖尿病啮齿动物模型中酮代谢的基因表达和代谢标志物来完成。2)确定干扰酮代谢（通过FA过度表达或通过腺病毒介导的生酮基因递送）是否会破坏分离肌肉和/或培养物中肌肉细胞的葡萄糖处理和胰岛素信号传导。3)确定腺病毒介导的抑制肌肉中酮生成和/或增强酮降解的基因的过表达是否可以逆转体内饮食诱导的胰岛素抵抗。这些研究的结果有望对FA诱导的骨骼肌胰岛素抵抗机制产生重要的新见解，对2型糖尿病的治疗具有潜在的治疗意义。

DESCRIPTION (provided by applicant): Compelling evidence links the development of muscle insulin resistance to fatty acid (FA) oversupply, but there is still uncertainty regarding which specific FA metabolite(s) and regulatory pathways are directly responsible for mediating insulin desensitization. Our current knowledge is based largely on a candidate molecule approach in which the selection of potentially relevant lipid metabolites relies heavily on implicit biases or availability of specific assays. To overcome this obstacle, we have employed mass spectroscopy-based metabolic profiling to comprehensively evaluate multiple lipid-derived metabolites in muscle from rats made insulin resistant by a high fat diet compared to controls. This unbiased "metabolomics" approach led to our discoveries that insulin resistant rats exhibit marked intramuscular accumulation of the ketone, beta-hydroxybutyrate (betaHB), at least a portion of this accumulated ketone was synthesized directly in the muscle tissue, and that genetic manipulations that restored insulin sensitivity corresponded with a 55% decrease in muscle (HB levels. These exciting findings implicate muscle ketone dysregulation as a causal factor in the etiology of lipid-induced insulin resistance. Previous research supports an inverse correlation between ketogenesis and glucose intolerance, but no consideration has been given to the possibility that dysregulated metabolism of ketones within muscle tissue could contribute to insulin resistant states. We hypothesize that chronic high fat feeding and/or overnutrition imposes a state of persistent and abnormal ketogenesis in skeletal muscle, which in turn plays a direct role in causing maladaptive changes in glucose handling and insulin sensitivity. We propose to test these hypotheses with the following specific aims: 1) To determine whether ketone dysregulation is a common feature in multiple animal models of insulin resistance. This will be done by profiling gene expression and metabolic markers of ketone metabolism in rodent models of obesity and diabetes. 2) To determine whether perturbing ketone metabolism (by FA overexposure or by adenovirus-mediated delivery of ketogenic genes), disrupts glucose handling and insulin signaling in isolated muscles and/or muscle cells in culture. 3) To determine whether adenovirus-mediated overexpression of genes that suppress ketogenesis and/or enhance ketone degradation in muscle can reverse diet-induced insulin resistance in vivo. The results from these studies are expected to yield important new insights into the mechanism of FA-induced insulin resistance in skeletal muscle, with potential therapeutic implications for treatment of type 2 diabetes.