Epidermal proteomics demonstrates Elafin as a psoriasis-specific biomarker and highlights increased anti-inflammatory activity around psoriatic plaques.

Abstract

Eczema and psoriasis are common diseases. Despite both showing active epidermal contribution to the inflammatory process, their molecular aetiology and pathological mechanisms are different. Further molecular insight into these differences is therefore needed to enable effective future diagnostic and treatment strategies. The majority of our mechanistic and clinical understanding of psoriasis and eczema is derived from RNA, immunohistology and whole skin biopsy data. In this study, non-invasive epidermal sampling of lesional, perilesional and non-lesional skin from diseased and healthy skin was used to perform an in depth proteomic analysis of epidermal proteins. Our findings confirmed the psoriasis-associated cytokine IL-36γ as an excellent protein biomarker for lesional psoriasis. However, ELISA and ROC curve analysis of 53 psoriasis and 42 eczema derived samples showed that the sensitivity and specificity were outperformed by elastase-specific protease inhibitor, elafin. Of note, elafin was also found upregulated in non-lesional psoriatic skin at non-predilection sites demonstrating inherent differences between the non-involved skin of healthy and psoriatic individuals. Mass spectrometry and ELISA analysis also demonstrated the upregulation of the anti-inflammatory molecule IL-37 in psoriatic perilesional but not lesional skin. The high expression of IL-37 surrounding psoriatic plaque may contribute to the sharp demarcation of inflammatory morphology changes observed in psoriasis. This finding was also specific for psoriasis and not seen in atopic dermatitis or autoimmune blistering perilesional skin. Our results confirm IL-36γ and add elafin as robust, hallmark molecules distinguishing psoriasis and eczema-associated inflammation even in patients under systemic treatment. Overall, these findings highlight the potential of epidermal non-invasive sampling and proteomic analysis to increase our diagnostic and pathophysiologic understanding of skin diseases. Moreover, the identification of molecular differences in healthy-looking skin between patients and healthy controls highlights potential disease susceptibility markers and proteins involved in the initial stages of disease.