The role of tight junctions in skin barrier function

皮肤的表皮是多层上皮，其实现保护身体免受外部攻击（例如病原体和环境化合物）以及防止大量水分流失的不可或缺的屏障功能。另一方面，对于经皮药物递送，必须克服该屏障。因此，了解皮肤屏障功能的本质是必不可少的。几十年来，这种屏障几乎完全归因于角质层（SC）的脂质-蛋白质结构，角质层是皮肤的最上层（SC屏障）。然而，在过去的十年中，很明显，紧密连接（TJ）也存在于表皮中，并形成第二个屏障（TJ屏障），这是本地化的颗粒层，下面的SC层。在这个项目中，我们要澄清的贡献紧密连接皮肤屏障功能。为此，我们将（A）研究在皮肤/SC成熟的不同阶段以及离体人和猪皮肤中，从外到内（施加到皮肤表面的物质）和从内到外（从基底侧施加的物质）对不同大小和极性的离子和试剂的皮肤和TJ屏障。为了揭示单个TJ组分的贡献，TJ蛋白敲低（claudin-1、claudin-4、JAM-A）和通过claudin-1肽模拟物和claudin-4特异性cCPE（产气荚膜梭菌肠毒素的C-末端结构域）突变体打开TJ将应用于这些皮肤模型。最重要的是，SC势垒和TJ势垒绝不是独立的，而是可能相互作用的。因此，TJ对皮肤屏障功能的贡献的一个关键部分，除了本身是屏障之外，可能是它们对SC形成和维持的影响。因此，我们项目（B）的第二个目的是阐明TJ对SC的影响。我们将在上述模型中测试claudin-1，claudin-4和JAM-A在SC形成中的作用，并阐明所涉及的机制。最后，我们希望阐明TJ对特应性皮炎患者病理改变的皮肤中受损的皮肤屏障的作用（C）。我们将研究病变，非病变和健康的皮肤。此外，我们将在治疗前、治疗中和治疗后分析病变皮肤。TJ蛋白量和定位的改变将与TJ和皮肤屏障功能以及疾病参数相关。此外，特应性皮炎相关细胞因子的参与将在体外进行研究。

The epidermis of the skin is a multilayered epithelium which fulfills an indispensable barrier function for the protection of the body against external assaults, e.g. pathogens and environmental compounds, as well as against extensive water loss. On the other hand, this barrier has to be overcome for transdermal drug delivery. Thus, knowledge of the nature of skin barrier function is essential. For decades, this barrier was almost exclusively attributed to the lipid-protein structure of the stratum corneum (SC), the uppermost layer of the skin (SC barrier). However, in the last decade it became evident that tight junctions (TJs) are also present in the epidermis and form a second barrier (TJ barrier) which is localized in the stratum granulosum, the layer beneath the SC. In this project, we want to clarify the contribution of tight junctions to skin barrier function. To this end, we will (A) investigate the skin and TJ barrier to ions and agents of different size and polarity from outside to inside (substances applied to the skin surface) and inside to outside (substances applied from the basal side) in reconstructed human skin at different stages of skin/SC maturation and ex-vivo human and porcine skin. To reveal the contribution of individual TJ components, TJ protein knock-down (claudin-1, claudin-4, JAM-A) and opening of TJs by a claudin-1 peptidomimetic and a claudin-4-specific cCPE (C-terminal domain of Clostridium perfringens enterotoxin) mutant will be applied to these skin models. Most importantly, SC barrier and TJ barrier are by no means independent, but are likely to interact with each other. Thus, a pivotal part of the contribution of TJs to skin barrier function, in addition to being a barrier themselves, might be their influence on SC formation and maintenance. Therefore, the second aim of our project (B) is to elucidate the influence of TJs on the SC. We will test the role of claudin-1, claudin-4 and JAM-A in SC formation in the above-mentioned models and clarify the mechanisms involved. Finally, we want to shed light on the contribution of TJs to the impaired skin barrier in the pathologically altered skin of patients with atopic dermatitis (C). We will investigate lesional, non-lesional and healthy skin. Further, we will analyze lesional skin before, during and after treatment. Alterations of TJ protein amount and localization will be correlated to TJ and skin barrier function as well as disease parameters. Furthermore, the involvement of atopic dermatitis-relevant cytokines will be investigated in vitro.