AHR-mediated mechanisms to overcome vascular barriers in autoimmunity

多发性硬化症（MS）是中枢神经系统（CNS）最常见的免疫介导的慢性炎症性和神经退行性疾病之一，其发展需要遗传易感性和环境触发因素的组合。其中包括吸烟，空气污染，可能由对紫外线（UV）暴露反应不足引起的低维生素D水平，饮食摄入，肠道微生物组或EB病毒感染。许多这些风险因素，如紫外线，香烟烟雾的成分，饮食或微生物衍生的代谢产物，都是由芳香烃受体（AHR）感知的。感觉经常发生在皮肤中，从而指出皮肤和MS病理学中CNS之间的联系（皮肤-CNS轴）。因此，在实验性自身免疫性脑脊髓炎（EAE）的小鼠模型中，我们能够表明紫外线照射降低了野生型小鼠的疾病严重程度，但在AHR缺陷型小鼠中则不然。在健康个体中，由脑微血管内皮细胞（BMEC）建立的血脑屏障（BBB）阻止免疫细胞迁移到CNS和神经炎症。然而，在MS中，BBB通常被描述为"渗漏的"，并且免疫细胞正在破坏BBB。参与控制血脑屏障完整性的过程尚未完全了解，我们可以表明，药理学抑制BMEC中的AHR限制了T细胞的迁移，这伴随着ICAM-1表达的减少。与此一致，与野生型对照相比，具有内皮细胞（EC）特异性AHR缺失的小鼠发生了不太严重的EAE，表明AHR信号传导直接影响EC功能、BBB完整性和致病性免疫细胞向CNS中的浸润。因此，在这个项目中，我们将研究AHR在皮肤和CNS炎症过程中的作用，特别关注其在皮肤和脑EC中的功能。这将有助于更好地理解介导免疫细胞浸润到靶组织中以及破坏屏障完整性的途径。在这种情况下，我们将集中在三个不同的方面：（1）调查配体特异性功能的AHR在血-皮肤屏障（BSB）和血脑屏障使用皮肤和脑EC培养，特别关注紧密连接蛋白，屏障的完整性，免疫细胞渗透，转录组学分析，蛋白质组学和分泌组学。(2)通过使用具有EC特异性AHR缺失的自身免疫小鼠模型，将体外获得的结果转移到体内环境中。(3)使用血管化的人类皮质脑类器官和皮肤器官培养物将动物模型的发现转化为人类系统。总之，该项目的结果将增加我们对AHR信号如何影响免疫屏障的了解。由于EC完整性与自身免疫的病理生理学有关，这可能会导致新的治疗选择。

The development of Multiple sclerosis (MS), one of the most frequent immune-mediated, chronic inflammatory, and neurodegenerative diseases of the central nervous system (CNS), requires a combination of genetic predisposition and environmental triggers. Among these are cigarette smoking, air pollution, low vitamin D levels potentially caused by an insufficient response to ultraviolet (UV) light exposure, dietary intake, the intestinal microbiome, or Epstein-Barr virus infection. Many of these risk factors like UV light, components of cigarette smoke, dietary or microbiome-derived metabolites are sensed by the aryl hydrocarbon receptor (AHR). Sensing frequently takes place in the skin, thereby pointing to a link between the skin and the CNS in MS pathology (skin-CNS axis). Accordingly, in a mouse model of experimental autoimmune encephalomyelitis (EAE) we were able to show that UV irradiation reduced disease severity in wild-type but not in AHR deficient mice. In healthy individuals the blood-brain barrier (BBB), which is established by brain microvascular endothelial cells (BMEC) prevents immune cell migration to the CNS and neuroinflammation. However, in MS the BBB is often described as “leaky” and immune cells are breaching the BBB. Processes involved in controlling BBB integrity are not completely understood and we could show that pharmacological inhibition of AHR in BMEC limited T cell transmigration, which was accompanied by a reduction in ICAM-1 expression. In line with this, mice with an endothelial cell (EC)-specific deletion of AHR developed a less severe EAE compared to wild-type controls, indicating that AHR signaling directly impacts on EC function, BBB integrity, and the infiltration of pathogenic immune cells into the CNS. Hence, in this project we will investigate the role of AHR in the connection of inflammatory processes in the skin and the CNS with a particular focus on its function in skin and brain EC. This will help to better understand pathways mediating the infiltration of immune cells into target tissues as well as the destruction of barrier integrity. In this context we will focus on three different aspects: (1) Investigating the ligand-specific function of AHR in the blood-skin barrier (BSB) and the BBB using skin and brain EC cultures with a particular focus on tight junction proteins, barrier integrity, immune cell penetration, transcriptomic profiling, proteomics and secretomics. (2) Transferring the results obtained in vitro to in vivo settings by using autoimmune mouse models with EC-specific deletion of AHR. (3) Translating the findings from animal models into the human system using vascularized human cortical brain organoids and skin organ cultures. Together, the results from this project will increase our knowledge on how AHR signaling influences immunological barriers. Since EC integrity is implicated in the pathophysiology of autoimmunity, this could potentially result in novel therapeutic options.