CERS1 is a biomarker of Staphylococcus aureus abundance and atopic dermatitis severity

Atopic dermatitis (AD) is an inflammatory skin condition characterized by widely variable cutaneous Staphylococcus aureus abundance that contributes to disease severity and rapidly responds to type 2 immune blockade (ie, dupilumab). The molecular mechanisms regulating S aureus levels between AD subjects remain poorly understood. We investigated host genes that may be predictive of S aureus abundance and correspond with AD severity. We studied data derived from the National Institutes of Health/National Institute of Allergy and Infectious Diseases–funded (NCT03389893 [ADRN-09]) randomized, double-blind, placebo-controlled multicenter study of dupilumab in adults (n = 71 subjects) with moderate-to-severe AD. Bulk RNA sequencing of skin biopsy samples (n = 57 lesional, 55 nonlesional) was compared to epidermal S aureus abundance, lipidomic, and AD clinical measures. S aureus abundance and ceramide synthase 1 (CERS1) expression positively correlated at baseline across both nonlesional (r = 0.29, P = .030) and lesional (r = 0.41, P = .0015) skin. Lesional CERS1 expression also positively correlated with AD severity (ie, SCORAD r = 0.44, P = .0006) and skin barrier dysfunction (transepidermal water loss area under the curve r = 0.31, P = .025) at baseline. CERS1 expression (forms C18:0 sphingolipids) was negatively associated with elongation of very long-chain fatty acids (ELOVL6; C16:0→C18:0) expression and corresponded with a shorter chain length sphingolipid composition. Dupilumab rapidly reduced CERS1 expression (day 7) and ablated the relationship with S aureus abundance and ELOVL6 expression by day 21. CERS1 is a unique molecular biomarker of S aureus abundance and AD severity that may contribute to dysfunctional skin barrier and shorter-chain sphingolipid composition through fatty acid sequestration as a maladaptive compensatory response to reduced ELOVL6.