Autoinflammatory syndromes associated with hidradenitis suppurativa (HS) and/or acne are rare but potentially debilitating disorders if not diagnosed and treated correctly. They share a common pathogenesis involving a dysregulated innate immune system with abnormal interleukin (IL)-1 signaling leading to sterile neutrophilic inflammation. The clinical features are recurrent episodes of fever, painful arthritis, and skin lesions consistent with HS, acne, and pyoderma gangrenosum (PG) accompanied by elevated systemic inflammatory markers in blood. So far, several clinically different syndromes have been reported in the literature including pyoderma gangrenosum, acne, and pyogenic arthritis (PAPA), pyoderma gangrenosum, acne, and hidradenitis suppurativa (PASH), pyoderma gangrenosum, acne, and spondyloarthritis (PASS), pyoderma gangrenosum, acne, pyogenic arthritis, and hidradenitis suppurativa (PAPASH), psoriatic arthritis, pyoderma gangrenosum, acne, and hidradenitis suppurativa (PsAPASH), and pyoderma gangrenosum, acne, and ulcerative colitis (PAC). The rarity of the syndromes complicates the establishment of evidence-based treatment guidelines. Furthermore, treatment can be challenging due to lack of response to standard treatment modalities. Therefore, it is important to increase the awareness about these diseases in order to optimize disease management and ultimately improve the quality of life of patients.

The chronic skin inflammation psoriasis is crucially dependent on the IL-23/IL-17 cytokine axis. Although IL-23 is expressed by psoriatic keratinocytes and immune cells, only the immune cell-derived IL-23 is believed to be disease relevant. Here we use a genetic mouse model to show that keratinocyte-produced IL-23 is sufficient to cause a chronic skin inflammation with an IL-17 profile. Furthermore, we reveal a cell-autonomous nuclear function for the actin polymerizing molecule N-WASP, which controls IL-23 expression in keratinocytes by regulating the degradation of the histone methyltransferases G9a and GLP, and H3K9 dimethylation of the IL-23 promoter. This mechanism mediates the induction of IL-23 by TNF, a known inducer of IL-23 in psoriasis. Finally, in keratinocytes of psoriatic lesions a decrease in H3K9 dimethylation correlates with increased IL-23 expression, suggesting relevance for disease. Taken together, our data describe a molecular pathway where epigenetic regulation of keratinocytes can contribute to chronic skin inflammation.

No abstract