Vanilloid Receptors in Diabetic Peripheral Neuropathy

描述(申请人提供)：周围神经病变是糖尿病最常见的并发症之一，但导致异常感觉的机制尚不清楚。在1型糖尿病(T1D)患者中，胰岛素和胰岛素样生长因子-1(IGF1)水平降低。血糖升高与糖尿病周围神经病变(DPN)有关，然而，神经病变和高血糖之间缺乏绝对相关性表明，其他机制可能参与了DPN的发病。胰岛素和IGF1已经建立了神经内分泌功能，包括维持突触完整性和对感觉神经元的神经营养作用。我们的研究表明，香草酸受体-1(VR1)是一种传递热痛和炎性疼痛的离子通道，它被胰岛素和IGF1增强。我们假设胰岛素和IGF1是正常的VR1功能所必需的，从而维持感觉神经末梢的完整性。推而广之，缺乏胰岛素和/或IGF1有望减少痛觉，导致神经病变，正如在T1D观察到的那样。在这项研究中，我们将探索允许胰岛素和IGF-1通过VR1增强膜电流和细胞内钙水平的分子机制。胰岛素和胰岛素样生长因子1分别与胰岛素(IR)和胰岛素样生长因子受体(IGFR)结合。然而，每种激素也可以结合对方的受体，尽管亲和力较低，而且两种受体使用相似的第二信使。我们的研究表明，蛋白激酶C(PKC)介导的VR1的磷酸化导致膜电流和钙离子通量增加。我们假设胰岛素和IGF-1作为一种短期效应导致PKC介导的VR1的磷酸化，并促进VR1从胞浆到质膜的转位。作为一种长期效应，胰岛素/IGF1通过激活第二信使分子，特别是p38MAPK，改变VR1的表达水平。因此，我们将确定将IR_GFR信号与VR1磷酸化联系起来的信号转导分子。为了在体内证实这些假设，我们将比较正常和T1D小鼠的VR1功能。这将包括测试外源性胰岛素和IGF1将TID小鼠观察到的异常热痛觉恢复到接近正常值的能力。为了证实VR1的参与，我们将测量这些动物依赖VR的CGRP释放和神经功能的变化。我们假设，由于胰岛素/IGF1缺乏，VR1功能在糖尿病动物中下调。这里获得的信息将提供T1D和周围神经病变之间的机制联系，包括VR1作为周围痛觉的中心参与者，以及胰岛素/IGF1作为调节剂，帮助维持正常的神经功能，但如果缺乏，则会导致神经病变。

DESCRIPTION (provided by applicant): Peripheral neuropathy is one of the most common complications of diabetes, yet the mechanisms responsible for abnormal sensory perception are poorly understood. In individuals with type 1 diabetes (T1D), insulin and insulin-like growth factor-1 (IGF1) levels are reduced. Elevated blood glucose is implicated in diabetic peripheral neuropathy (DPN), however, lack of an absolute correlation between neuropathy and hyperglycemia suggests that other mechanisms likely contribute to the pathogenesis of DPN. Insulin and IGF1 have established neuroendocrine functions that include maintenance of synaptic integrity and neurotrophic effects on sensory neurons. Our studies demonstrate that vanilloid receptor-1 (VR1), an ion channel that functions to transmit thermal and inflammatory pain, is potentiated by insulin and IGF1. We hypothesize that insulin and IGF1 are required for proper VR1 function, thereby maintaining the integrity, of sensory nerve terminals. By extension, a lack of insulin and/or IGF1 is expected to reduce nociception resulting in neuropathy as observed in T1D. In this study we will explore the molecular mechanisms that allow insulin and IGF 1 to potentiate membrane current and intracellular calcium levels through VR1. Insulin and IGF 1 bind the insulin (IR) and IGF (IGFR) receptors, respectively. However, each hormone can also bind the opposing receptor albeit with lower affinity and both receptors use similar second messengers. Our studies show that protein kinase C (PKC)- mediated phosphorylation of VR1 induces an increase in membrane current and calcium flux. We hypothesize that insulin and IGF 1 as a short-term effect cause PKC-mediated phosphorylation of VR1 and promotes translocation of VR1 from cytosol to plasma membrane. As a long-term effect by activating second messenger molecules, particularly p38 MAPK, insulin/IGF1 alter VR1 expression levels,. Thus, we will identify signal transduction molecules that link IR_GFR signaling with VR1 phosphorylation. To confirm these hypotheses in vivo, we will compare VR1 function in normal and T1D mice. This will include testing the ability of exogenous insulin and IGF1 to restore the otherwise abnormal thermal nociception observed in TID mice to near normal values. To confirm the involvement of VR1 we will measure changes in VR-dependent CGRP release and nerve function in these animals. We hypothesize that VR1 function is down regulated in diabetic animals due to insulin/IGF1 deficiency. Information gained here will provide a mechanistic link between T1D and peripheral neuropathy that includes VR1 as a central player in peripheral pain perception and insulin/IGF1 as modifiers that help to maintain normal nerve function, but when absent contribute to neuropathy.