Sphingolipid-mediated dysregulation of glucose and energy homeostasis by POMC neurons

 描述（由申请人提供）：已经确定的是，在肥胖和糖尿病的演变中，下丘脑体重和葡萄糖调节神经元变得对抑制体重增加和循环葡萄糖增加的信号（包括激素，如瘦素或胰岛素）不敏感。然而，这些不敏感性的具体机制还没有得到很好的理解。我们推测，下丘脑鞘脂神经酰胺的积累可以驱动下丘脑瘦素和胰岛素信号的衰减。神经酰胺的积累已被证明在许多外周组织中驱动胰岛素抵抗，并且一些证据表明它也可能拮抗中枢瘦素/胰岛素受体信号传导。已知下丘脑内的一组神经元调节体重和循环葡萄糖，并且在肥胖状态下变得对瘦素/胰岛素不敏感，其特征在于阿黑皮素原（POMC）的表达。我们假设POMC神经元在肥胖状态下积累神经酰胺，这些神经酰胺驱动这些细胞对瘦素/胰岛素信号转导的抵抗。为了测试这一点，我们将诱导过表达一种酶，降解神经酰胺，酸性神经酰胺酶，在成年小鼠的POMC神经元。所使用的构建体将是四环素应答元件驱动的酸性神经酰胺酶，当与含有β-stop-β-Rosa 26-rtTA和POMC-Cre盒两者的小鼠交配时，其将在食物中施用多西环素后在POMC神经元中产生酸性神经酰胺酶。这将与迫使神经酰胺葡糖基化的类似小鼠或阻止神经酰胺葡糖基化的基因敲除小鼠互补，因为葡糖神经酰胺衍生物可能对葡萄糖和能量稳态具有独立作用。我们将使用这些小鼠来询问神经酰胺是否在肥胖的发病机制中具有致病作用，减少POMC神经元中的神经酰胺是否可以独立于体重变化改善葡萄糖稳态，以及神经酰胺在POMC神经元内调节的分子途径。因此，这项工作将证明大脑中可能的新药物靶点，以分别降低肥胖或糖尿病个体的体重增加和血糖。

 DESCRIPTION (provided by applicant): It has been well-established that in the evolution of obesity and diabetes, hypothalamic weight- and glucose-regulatory neurons become insensitive to signals (including hormones such as leptin or insulin) that work to inhibit incremental weight gain and increased circulating glucose. However, the specific mechanisms of these insensitivities are not well-understood. We postulate that hypothalamic accumulation of the sphingolipid ceramide can drive attenuation of hypothalamic leptin and insulin signaling. Ceramide accumulation has been demonstrated to drive insulin resistance in a number of peripheral tissues, and some evidence suggests it may antagonize central leptin/insulin receptor signaling also. One set of neurons within the hypothalamus known to regulate both body weight and circulating glucose and that become insensitive to leptin/insulin in the obese state are characterized by expression of proopiomelanocortin (POMC). We hypothesize that POMC neurons accumulate ceramides in the obese state, and these ceramides drive resistance of these cells to leptin/insulin signal transduction. To test this, we will inducibly overexpress an enzyme which degrades ceramides, acid ceramidase, in POMC neurons of adult mice. The construct used will be a tetracycline response element- driven acid ceramidase, which when mated to a mouse containing both flox-stop-flox-Rosa26-rtTA and POMC- Cre cassettes, will produce acid ceramidase in the POMC neuron upon administration of doxycycline in the chow. This will be complemented with similar mice which force ceramide glucosylation or knockout mice which prevent ceramide glucosylation, as glucosylceramide derivatives may have independent effects on glucose and energy homeostasis. We will use these mice to interrogate whether ceramides have a causative role in the pathogenesis of obesity, whether reducing ceramides in POMC neurons can improve glucose homeostasis independent of weight change, and the molecular pathways which ceramides modulate within the POMC neuron. This work will thus demonstrate a possible novel drug target in the brain to decrease both body weight gain and blood glucose in obese or diabetic individuals, respectively.