Vanilloid Receptors in Diabetic Peripheral Neuropathy

描述（由申请人提供）：周围神经病变是糖尿病最常见的并发症之一，但导致感觉知觉异常的机制尚不清楚。在1型糖尿病患者中，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，神经病变与高血糖之间缺乏绝对相关性，这表明DPN的发病机制可能与其他机制有关。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，香草样受体-1 （VR1）是一种离子通道，其功能是传递热疼痛和炎症性疼痛，可通过胰岛素和IGF1增强。我们假设胰岛素和IGF1是VR1正常功能所必需的，从而维持感觉神经末梢的完整性。由此推而广之，胰岛素和/或IGF1的缺乏有望减少在T1D中观察到的伤害感觉导致的神经病变。在这项研究中，我们将探索胰岛素和igf1通过VR1增强膜电流和细胞内钙水平的分子机制。胰岛素和igf1分别结合胰岛素（IR）和IGF （IGFR）受体。然而，每一种激素也可以结合相反的受体，尽管亲和力较低，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磷酸化诱导膜电流和钙通量的增加。我们假设胰岛素和IGF - 1作为短期效应导致pkc介导的VR1磷酸化，并促进VR1从细胞质溶胶转运到质膜。胰岛素/IGF1通过激活第二信使分子，特别是p38 MAPK的长期效应，改变VR1的表达水平。因此，我们将确定IR_GFR信号传导与VR1磷酸化之间的信号转导分子。为了在体内证实这些假设，我们将比较VR1在正常小鼠和T1D小鼠中的功能。这将包括测试外源性胰岛素和IGF1将在TID小鼠中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中vr依赖性CGRP释放和神经功能的变化。我们假设糖尿病动物的VR1功能下调是由于胰岛素/IGF1缺乏。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作为周围疼痛感知的核心参与者和胰岛素/IGF1作为有助于维持正常神经功能的调节剂，但当缺乏时会导致神经病变。

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.