RabGEF1 in MyD88 signaling, skin immunity, and atopic dermatitis

 描述（由申请人提供）：本项目的长期目标是了解某些角质形成细胞功能的失调如何通过改变细胞与皮肤微生物组的相互作用损害表皮屏障功能，导致类似特应性皮炎（AD）的特征和高血清IgE水平的发展。小鼠RabGEF 1被发现是肥大细胞活化的负调节因子，RabGEF 1全面缺陷的小鼠迅速发展为AD样皮肤[病理学]。然而，小鼠角质形成细胞中Rabgef1特异性的条件性缺失足以驱动AD样皮肤[病理学]和高水平血清IgE的发展（在AD患者中也可见）。此外，在RabGEF1缺陷小鼠中观察到的严重皮肤病严重依赖于MyD88的角质形成细胞内在表达，MyD88是一种通过几种Toll样受体（TLR）介导信号传导的衔接分子。与健康皮肤相比，在AD患者的病变皮肤中[RabGEF 1蛋白的表达]显著降低，而在AD患者的病变皮肤样本中MYD 88 mRNA的表达显著增加。由于皮肤持续暴露于作为TLR配体丰富来源的微生物，我们将评估皮肤微生物组和角质形成细胞TLR在多大程度上有助于角质形成细胞缺乏RabGEF1时观察到的MyD88依赖性AD样皮肤[病理学]。我们将使用RabGEF1缺陷的小鼠和人类角质形成细胞在体外分析RabGEF1调节MyD88依赖性信号通路的分子机制。最后，我们将评估RabGEF1表达的角质形成细胞限制性[完全或部分]减少如何影响通过皮肤对过敏原的全身致敏，以及随后在远处器官（如肺）中发生过敏性炎症。我们提出了三个具体的目标来测试一般假设：RabGEF1缺陷小鼠中特应性皮炎和血清IgE升高的皮肤病理学特征的发展反映了RabGEF1通过下调角质形成细胞中MyD88依赖性信号传导启动的途径来维持皮肤[屏障和免疫]功能的能力。目标1：明确MyD88、Toll样受体（TLR）和皮肤微生物区系在体内角质形成细胞特异性Rabgef1缺失诱导的AD样皮肤[病理学]中的作用。目的2：确定RabGEF 1负调节角质形成细胞中MyD88依赖性功能反应和信号传导的机制。目标3：确定角质形成细胞中RabGEF1缺乏影响皮肤对过敏原的致敏性和特应性进展的机制。该项目将阐明由于RabGEF1减少而导致的角质形成细胞功能的内在损伤如何导致AD样皮肤[病理学]。最终，进行这样的工作可能会发现新的治疗靶点，用于预防或治疗AD和其他特应性或炎症性疾病。

 DESCRIPTION (provided by applicant): The long-term goal of this project is to understand how the dysregulation of certain keratinocyte functions, by altering the cells' interactions with te skin microbiome, can impair epidermal barrier function, leading to features resembling those of atopic dermatitis (AD) and the development of high serum levels of IgE. Mouse RabGEF1 was discovered as a negative regulator of mast cell activation, and mice globally deficient in RabGEF1 rapidly develop AD-like skin [pathology]. However, conditional deletion of Rabgef1 specifically in mouse keratinocytes is sufficient to drive AD-like skin [pathology] and the development of high levels of serum IgE (as is also seen in AD patients). Moreover, the severe skin disease observed in RabGEF1- deficient mice critically depends on keratinocyte-intrinsic expression of MyD88, an adaptor molecule that mediates signaling by several Toll-like receptors (TLRs). [Expression of RabGEF1 protein] is markedly decreased in lesional skin from patients with AD as compared to healthy skin, whereas MYD88 mRNA expression is significantly increased in lesional skin specimens from AD patients. Since skin is continuously exposed to microorganisms that are a rich source of TLR ligands, we will evaluate to what extent the skin microbiome and keratinocyte TLRs can contribute to the MyD88-dependent AD-like skin [pathology] observed when keratinocytes lack RabGEF1. We will use RabGEF1-deficient mouse and human keratinocytes to analyze in vitro the molecular mechanisms by which RabGEF1 regulates MyD88-dependent signaling pathways. Finally, we will assess how keratinocyte-restricted [complete or partial] reductions in RabGEF1 expression can influence systemic sensitization to allergens via the skin, with the later development of allergic inflammation in distant organs such as the lung. We propose three specific aims to test the General Hypothesis: The development of skin pathology with features of atopic dermatitis, and elevated serum IgE, in RabGEF1-deficient mice reflects the ability of RabGEF1 to maintain skin [barrier and immune] functions by down-regulating pathways initiated by MyD88-dependent signaling in keratinocytes. Aim 1: Define the contributions of MyD88, Toll-like receptors (TLRs), and the skin microflora in the AD-like skin [pathology] induced by keratinocyte-specific Rabgef1 deletion in vivo. Aim 2: Determine the mechanisms by which RabGEF1 negatively regulates MyD88-dependent functional responses and signaling in keratinocytes. Aim 3: Determine the mechanisms by which RabGEF1 deficiency in keratinocytes influences skin sensitization to allergens and the development of the atopic march. This project will clarify how an intrinsic impairment in keratinocyte function due to diminished RabGEF1 can contribute to AD-like skin [pathology]. Ultimately, pursuing such work may enable the discovery of novel therapeutic targets for the prevention or treatment of AD and perhaps other atopic or inflammatory disorders.