Transcriptomic Analysis of Healthy and Atopic Dermatitis Samples Reveals the Role of IL-37 in Human Skin.

Atopic dermatitis (AD) is a chronic inflammatory skin disease that affects up to one in five children and millions of adults in developed countries. Clinically, AD skin lesions manifest as subacute and/or chronic lichenified eczematous plaques, which are often intensely pruritic and prone to secondary bacterial and viral infections. Despite the emergence of novel therapeutic agents, treatment options and outcomes for AD remain suboptimal. An improved understanding of AD pathogenesis may help improve patient outcomes. Dysregulated Th2-polarized skin inflammation and impaired skin barrier function interact to drive AD pathogenesis; however, much remains to be understood about the molecular mechanisms underlying this interplay. The current study used published clinical trial datasets to define a skin-related AD gene signature. This meta-analysis revealed significant reductions in IL1F7 transcripts (encodes IL-37) in AD patient samples. Reduced IL1F7 correlated with lower transcripts for key skin barrier function genes in the epidermal differentiation complex. Immunohistochemical analysis of normal (healthy) human skin specimens and an in vitro three-dimensional human skin model localized IL-37 protein to the epidermis. In comparison with normal human skin, IL-37 levels were decreased in AD patient skin. Addition of Th2 cytokines to the aforementioned in vitro three-dimensional skin model recapitulates key aspects of AD skin and was sufficient to reduce epidermal IL-37 levels. Image analysis also indicated close relationship between epidermal IL-37 and skin epidermal differentiation complex proteins. These findings suggest IL-37 is intimately linked to normal keratinocyte differentiation and barrier function and implicates IL-37 as a potential biomarker and therapeutic target for AD.