Sphingolipid-Mediated Dysregulation of Glucose and Energy Homeostasis in the CNS

 描述（由申请人提供）：该资助评估了下丘脑鞘脂神经酰胺或葡萄糖神经酰胺的蓄积可驱动POMC和AgRP神经元中下丘脑瘦素、胰岛素或5-羟色胺作用的衰减。鞘脂的过度积累可在许多外周组织中引起胰岛素抵抗。下丘脑内的AgRP和POMC神经元是已知响应于胰岛素或瘦素调节体重和葡萄糖稳态的两个不同的神经元亚群。POMC神经元在肥胖状态下积累神经酰胺和葡萄糖神经酰胺，并且这些鞘脂驱动这些细胞对瘦素和胰岛素的葡萄糖调节信号的抗性的假设将被研究。为了测试这一点，触发过表达的诱导酶，降解神经酰胺，酸性神经酰胺酶，将促进成年小鼠的POMC或AgRP神经元。这将与通过葡糖神经酰胺合酶功能的获得或丧失来防止神经酰胺葡糖基化的类似小鼠互补。这些小鼠将被用来询问是否神经酰胺，葡萄糖神经酰胺，或两者都有一个肥胖症和胰岛素抵抗的发病机制中的致病作用。此外，我们将促进神经胶质细胞内神经酰胺的降解，我们假设这将加剧肥胖期间下丘脑神经元的鞘脂过度供应。在每种小鼠模型中特别感兴趣的是，将评估POMC神经元中的鞘脂减少是否以及如何独立于体重变化改善全身胰岛素敏感性。因此，这项工作将证明一种可能的新的药物靶点，以减少肥胖或糖尿病个体的体重增加和血糖。SA 1）检查POMC神经元中神经酰胺或葡糖神经酰胺的过度积累是否有助于高脂肪饮食诱导的肥胖、胰岛素抵抗和葡萄糖耐量受损。为了确定POMC神经元中异常鞘脂积累作为饮食诱导的体重增加和胰岛素抵抗的介质的重要性，我们将迫使鞘脂降解（其降低神经酰胺和葡糖神经酰胺）或阻止葡糖神经酰胺合成。SA 2）确定胶质细胞中酸性神经酰胺酶过表达是否对抗高脂肪饮食诱导的肥胖、胰岛素抵抗和葡萄糖耐量受损。新的四环素诱导的转基因小鼠已经产生过表达神经胶质细胞中的酸性神经酰胺酶。SA 3）检查AgRP神经元中的鞘脂过度积累是否有助于高脂肪饮食诱导的肥胖、胰岛素抵抗和葡萄糖耐量受损。我们将使用过表达神经酰胺降解酶（酸性神经酰胺酶）的tet-on转基因系来减少AgRP鞘脂。将评价AgRP特异性葡糖神经酰胺合酶敲除小鼠的体重增加和血糖控制受损倾向。我们将评估神经鞘脂在这些诱导型小鼠模型中对肥胖、胰岛素抵抗和葡萄糖耐受不良的起始和逆转的重要性。

 DESCRIPTION (provided by applicant): This grant evaluates hypothalamic accumulation of the sphingolipids ceramide or glucosylceramide can drive attenuation of hypothalamic leptin, insulin, or serotonin action in POMC and AgRP neurons. Overaccumulation of sphingolipids can drive insulin resistance in a number of peripheral tissues. AgRP and POMC neurons within the hypothalamus are two distinct subpopulations of neurons that are known to regulate both body weight and glucose homeostasis in response to insulin or leptin. The hypothesis that POMC neurons accumulate ceramide and glucosylceramides in the obese state, and these sphingolipids drive resistance of these cells to leptin and insulin's glucoregulatory signals will e investigated. To test this, triggered overexpression of an inducible enzyme which degrades ceramides, acid ceramidase, will be promoted in POMC or AgRP neurons of adult mice. This will be complemented with similar mice which prevent glucosylation of ceramide via gain or loss of function of glucosylceramide synthase. These mice will be used to interrogate whether ceramides, glucosylceramides, or both have a causative role in the pathogenesis of obesity and insulin resistance. Moreover, we will promote degradation of ceramides within glial cells, which we hypothesize will exacerbate sphingolipid oversupply to hypothalamic neurons during obesity. Of particular interest in each mouse model, evaluating if and how sphingolipid reduction in POMC neurons can improve whole-body insulin sensitivity independently of weight change will be assessed. This work will thus demonstrate a possible novel drug targets to decrease both body weight gain and blood glucose in obese or diabetic individuals, respectively. SA 1) Examine whether ceramide or glucosylceramide overaccumulation in POMC neurons contributes to high fat diet-induced obesity, insulin resistance, and impaired glucose tolerance. In order to determine the importance of abnormal sphingolipid accumulation in POMC neurons as mediators of diet-induced weight gain and insulin resistance we will force sphingolipid degradation (which lowers ceramide and glucosylceramides) or prevent glucosylceramide synthesis. SA 2) Determine if acid ceramidase overexpression in glial cells opposes high fat diet-induced obesity, insulin resistance, and impaired glucose tolerance. Novel tetracycline-inducible transgenic mice have been generated which overexpress acid ceramidase in glial cells. SA3) Examine whether sphingolipid overaccumulation in AgRP neurons contributes to high fat diet-induced obesity, insulin resistance, and impaired glucose tolerance. We will use tet-on transgenic lines overexpressing the ceramide degrading enzymes, acid ceramidase, to decrease AgRP sphingolipid. AgRP-specific glucosylceramide synthase knockout mice will be evaluated for their propensity for weight gain and impaired glycemic control. We will evaluate the importance of neuronal sphingolipids to both the initiation and reversal of obesity, insulin resistance, and glucose intolerance in each of these inducible mouse models.