Injury, dysbiosis, and filaggrin deficiency drive skin inflammation through keratinocyte IL-1α release

Nathan K Archer, Jay-Hyun Jo, Steven K Lee, Dongwon Kim, Barbara Smith, Roger V Ortines, Yu Wang, Mark C Marchitto, Advaitaa Ravipati, Shuting S Cai, Carly A Dillen, Haiyun Liu, Robert J Miller, Alyssa G Ashbaugh, Angad S Uppal, Michiko K Oyoshi, Nidhi Malhotra, Sabine Hoff, Luis A Garza, Heidi H Kong, Julia A Segre, Raif S Geha, Lloyd S Miller

Atopic dermatitis (AD) is associated with epidermal barrier defects, dysbiosis and skin injury from scratching. In particular, the barrier defective epidermis of AD patients with loss-of-function filaggrin mutations has increased IL-1α and IL-1β levels but the mechanisms by which IL-1α and/or IL-1β are induced and whether they contribute to the aberrant skin inflammation in AD is unknown. We sought to determine the mechanisms by which skin injury, dysbiosis and increased epidermal IL-1α and IL-1β contribute to the development of skin inflammation in a mouse model of injury-induced skin inflammation in filaggrin-deficient mice. Skin injury of wild-type, filaggrin-deficient (ft/ft), and MyD88-deficient ft/ft mice was performed and ensuing skin inflammation was evaluated by digital photography, histologic analysis and flow cytometry. IL-1α and IL-1β protein expression was measured by ELISA and visualized by immunofluorescence and immuno-electron microscopy. The composition of skin microbiome was determined by 16S rDNA sequencing. Skin injury of ft/ft mice induced chronic skin inflammation involving dysbiosis-driven intracellular IL-1α release from keratinocytes. IL-1α was necessary and sufficient for skin inflammation in vivo and secreted from keratinocytes by various stimuli in vitro. Topical antibiotics or co-housing of ft/ft mice with unaffected wild-type mice to alter or intermix skin microbiota, respectively, resolved the skin inflammation and restored keratinocyte intracellular IL-1α localization. Taken together, skin injury, dysbiosis and filaggrin deficiency triggered keratinocyte intracellular IL-1α release that was sufficient to drive chronic skin inflammation, which has implications for AD pathogenesis and for potential therapeutic targets.