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.