232 Identifying the mechanisms underlying the negative feedback loop between tight junction proteins and cutaneous microbial dysbiosis in atopic dermatitis

Abstract

Reduced skin barrier function and dysbiosis of the skin microbiota are hallmarks of atopic dermatitis (AD). Both, reduced cutaneous barrier and dominance of Staphylococcus aureus (S. aureus) are believed to represent entry points of inflammation in AD, but how they regulate each other is not known. Tight junctions (TJs) in the skin are close contacts between plasma membranes of neighboring cells and important for barrier functioning. TJs have also been indicated to be essential for skin barrier function in AD, yet little is known about their interplay with S. aureus. Here, we investigated how skin barrier impairment contributes to the development of AD, focusing on the microbial shift towards S. aureus dominance in a mouse model. We found that barrier impairment induced by repeated tape stripping of the back skin leads to a significant downregulation of several TJ proteins (e.g. claudin-1, occludin) detected by RT-PCR ex vivo. Furthermore, an upregulation of S. aureus-associated pro inflammatory cytokines (e.g. IL-1ß, TNF-α, IL-6) was detected. Analyses of the skin microbiome affirm this finding by pointing to a shift within the microbial homeostasis characterized by a predominance of staphylococci after tape stripping. We applied the FITC dermatitis model to induce AD-like inflammation. As a result, sensitization of the mice at tape stripped skin resulted in a significant increase in ear swelling upon challenge one week later compared to non-tape stripped mice, as well as a more pronounced Th2-dominated immune response associated by an increased CD3+CD4+ cell population and higher levels of IL-4 and IL-13. These findings establish a model of skin barrier disruption which can be applied to study molecular mechanisms of AD pathophysiology. They also indicate an important role of the downregulation of TJs contributing to a staphylococci-dominated dysbiosis of the skin and AD development. To conclude, this model and findings should be used to develop treatment strategies for patients suffer from this disease.