Dual contribution of the spleen tyrosine kinase (SYK) to epidermolysis bullosa acquisita pathogenesis

获得性大疱性表皮病（EBA）是一种典型的器官特异性自身免疫性疾病，由针对VII型胶原（COL 7）的自身抗体引起。在过去的几年里，使用EBA动物模型显着有助于了解疾病的发病机制。相比之下，开发新疗法的高度医疗需求迄今尚未实现。在EBA发病机制的传入阶段，在给定的遗传背景下，抗原呈递细胞诱导CD 4依赖性B细胞应答，导致抗COL 7自身抗体的产生。我们实验室最近的证据表明，中性粒细胞和GM-CSF也参与其中。脾酪氨酸激酶（SYK）是B细胞和中性粒细胞活化的中心。因此，SYK是调节实验EBA中自身抗体产生的潜在药物靶标（本提案的目的1）。传出相由自身抗体与COL 7的结合启动，COL 7主要位于皮肤中的真皮-表皮连接处（DEJ）。DEJ处免疫复合物（IC）的这种形成建立了促炎环境，导致Gr-1阳性效应细胞的CD 18依赖性募集进入皮肤。在皮肤中，这些效应白细胞通过特异性激活Fc γ受体（Fcgr）与DEJ处的IC结合。通过涉及PI 3 K β、AKT、p38和ERK 1/2的信号级联，释放活性氧（ROS）和蛋白酶，最终导致表皮下起泡。由于SYK介导Fcgr信号传导，靶向SYK将最有可能损害实验EBA中IC诱导的Gr-1阳性效应白细胞的活化。EBA小鼠模型中的这些发现也将在新建立的大疱性类天疱疮小鼠模型中得到验证。将在已建立（免疫诱导）EBA的小鼠中评价潜在治疗相关性。作为一个探索性的目标，其他信号分子在实验EBA发病机制的贡献将在体外和体内进行测试。最终，小鼠模型的发现将在患者样本中得到（至少在形态学上）验证。为了解决这些研究问题，完善的模型系统的EBA和BP将被使用。在项目相关的前期工作中，我们已经确定了SYK在体外激活中性粒细胞中的关键作用。此外，使用SYK-floxed和靶细胞-cre小鼠的试验小鼠实验表明SYK对EBA中水疱形成的细胞类型特异性贡献。鉴于我们的假设可以得到验证，SYK -以及可能的其他信号分子-可能成为EBA患者的潜在新治疗选择，也可能是BP。

Epidermolysis bullosa acquisita (EBA) is a prototypical, organ-specific autoimmune disease caused by autoantibodies directed against type VII collagen (COL7). Over the past years, use of EBA animal models has significantly contributed to the understanding of the disease's pathogenesis. In contrast, the high medical need to develop novel treatments, has not been achieved so far. In the afferent phase of EBA pathogenesis, within a given genetic context, antigen-presenting cells induce a CD4-dependent B cell response, leading to the production of anti-COL7 autoantibodies. Recent evidence from our laboratory indicated that neutrophils and GM-CSF are also involved. The spleen tyrosine kinase (SYK) is central for both, B cell and neutrophil activation. Hence, SYK is a potential pharmaceutical target to modulate autoantibody production in experimental EBA (aim 1 of this proposal). The efferent phase is initiated by the binding of the autoantibodies to COL7, mainly located at the dermal-epidermal junction (DEJ) in the skin. This formation of immune-complexes (IC) at the DEJ establishes a pro-inflammatory milieu, resulting in the CD18-dependent recruitment of Gr-1 positive effector cells into the skin. In the skin, these effector leukocytes bind to the IC at the DEJ via specific, activating Fc gamma receptors (Fcgr). Through a signaling cascade involving PI3Kbeta, AKT, p38 and ERK1/2, reactive oxygen species (ROS) and proteases are released, ultimately causing subepidermal blistering. As SYK mediates Fcgr signaling, targeting SYK will most likely impair IC-induced activation of Gr-1 positive effector leukocytes in experimental EBA. These findings in the EBA mouse model will also be validated in a newly established mouse model of bullous pemphigoid. The potential therapeutic relevance will be evaluated in mice with already established (immunization-induced) EBA. As an exploratory aim, the contribution of other signaling molecules in experimental EBA pathogenesis will be tested both in vitro and in vivo. Ultimately, findings from mouse models will be (at least morphologically) validated in patient samples. To address these research questions, well-established models systems of EBA and BP will be used. In project-related preliminary work, we already established a key role of SYK for in vitro activation of neutrophils. Furthermore, pilot mouse experiments, using SYK-floxed and target cell-cre mice, indicate a cell type-specific contribution of SYK to blister formation in EBA. Given, our assumptions can be validated, SYK -and possibly additional signaling molecules- could emerge as potential new treatment options for patients with EBA, and possibly also BP.