The Role of GDNF Family Ligands in Itch

描述（由申请人提供）：慢性瘙痒影响高达15%的人口，但目前可用的治疗方法控制不佳。瘙痒感受器是支配皮肤和瘙痒的小直径神经纤维。虽然已经发现了几种组胺依赖性和组胺非依赖性瘙痒途径，但对慢性瘙痒如何发展知之甚少。对特应性皮炎和银屑病患者的研究表明，可能涉及表皮神经支配增加和神经营养因子水平升高。大多数神经元受体表达Ret，GDNF家族配体（GFLs）的受体，但没有研究调查GFL-Ret信号转导在神经元受体功能中的作用。我们的初步数据表明，Ret+表皮纤维在干燥皮肤瘙痒模型中增加。此外，我们还发现，用artemin（一种GFL）预处理显著增强了抓挠行为和神经元对致敏原氯喹的反应。基于这些发现，我们推测GFLs调节受体的结构和功能。在本提案的目标1中，我们将确定GFLs是否可以诱导瘙痒或调节促纤维素原诱导的抓挠。我们还将确定是否长期治疗GFLs诱导表皮神经支配过度，以及这些变化是否与抓挠行为的增加相关。在目标2中，我们将利用RetEGFP/+报告小鼠和逆行标记，通过记录游离三叉神经节神经元中的钙反应来确定artemin对降钙素原受体表达和功能的直接影响。在目标3中，我们将使用他莫昔芬诱导的感觉神经元特异性Ret条件性基因敲除小鼠（Ret-cKO），以确定内源性Ret信号传导是否对正常受体的表达和功能很重要。我们还将确定Ret表达是否是GFL诱导的瘙痒效应所必需的。这项提议所产生的工作将最终确定GFLs是否是治疗慢性瘙痒症的潜在靶点。

DESCRIPTION (provided by applicant): Chronic itch affects up to 15% of the population but is poorly controlled with currently available treatments. Pruriceptors are small diameter nerve fibers that innervate the skin and transduce itch. While several histamine-dependent and histamine-independent itch pathways have been discovered, little is known about how chronic itch develops. Studies of patients with atopic dermatitis and psoriasis indicate that increased epidermal innervation and increased levels of neurotrophic factors may be involved. Most pruriceptors express Ret, the receptor for GDNF-family ligands (GFLs), but no studies have investigated the role of GFL-Ret signaling in pruriceptor function. Our preliminary data indicate that Ret+ epidermal fibers are increased in a model of dry skin itch. Furthermore, we have found that pretreatment with artemin (a GFL) significantly potentiates scratching behavior and neuronal responses to the pruritogen chloroquine. Based on these findings, we hypothesize that GFLs modulate pruriceptor structure and function. In Aim 1 of this proposal we will determine if GFLs can induce itch or modulate pruritogen-induced scratching. We will also determine if chronic treatment with GFLs induces epidermal hyperinnervation and whether these changes correlate with increases in scratching behavior. In Aim 2, we will utilize RetEGFP/+ reporter mice and retrograde labeling to determine the direct effects of artemin on pruritogen receptor expression and function by recording calcium responses in dissociated trigeminal ganglion neurons. In Aim 3, we will use tamoxifen-inducible sensory neuron-specific Ret conditional knock-out mice (Ret-cKOs) to determine if endogenous Ret signaling is important for normal pruriceptor expression and function. We will also determine if Ret expression is necessary for GFL-induced effects on itch. The work generated by this proposal will ultimately determine whether GFLs are potential targets for the treatment of chronic pruritus.