The Neurogenic Inflammation Mediator Endothelin-1 Causes Human Skin Barrier Disruption in Atopic Dermatitis via an ETAR/TRPA1-Axis

Abstract

Background: Atopic dermatitis (AD) is a common, relapsing inflammatory skin disease driven by an immune imbalance, microbial dysbiosis, and skin barrier impairment, culminating in (neurogenic) inflammation and itch. We hypothesized that the neuropeptide and pruritogen endothelin-1 (ET-1) contributes to AD pathology by impeding skin barrier formation via its cognate receptor ETAR and TRPA1, a cation channel involved in neurogenic inflammation, pain, and itch. Methods: We utilized differentiated human keratinocytes and ex vivo human skin organ cultures in vitro to evaluate the impact of ET-1 on human skin barrier function. ET-1 effects were assessed at the RNA level by RT-qPCR and at the protein level by quantitative immunofluorescence microscopy. Barrier integrity was monitored using real-time cell analysis and transwell permeability assays. Results: ET-1 markedly reduced cell resistance in differentiated keratinocytes, an effect abrogated by the ETAR antagonist bosentan. ET-1 significantly decreased expression of skin differentiation markers filaggrin and loricrin, and tight junction proteins occludin, claudin-1, and claudin-4, at mRNA and protein levels. ETAR-specific siRNA in combination with ET-1, rescued ET-1-mediated downregulation of filaggrin. Furthermore, TRPA1 antagonist HC-030031 abrogated the impairing effect of ET-1 on the skin barrier. We observed increased inflammatory responses of ET-1-stimulated keratinocytes, suggesting that the ET-1-initiated barrier disruption could be mediated by IL-6 and IL-1β and induced by TNF-α. Conclusion: Our findings suggest that a neurogenic inflammation axis ET-1/ETAR/TRPA1 contributes to skin barrier impairment in AD by repressing differentiation markers and tight junction proteins. Additionally, we demonstrate ETAR-blockage as a rational therapeutic modality for patients with AD.