H2A.J is an epigenetic driver of IL-17-associated inflammation in TH17 cells and keratinocytes

Psoriasis is a common autoinflammatory disease driven by excessive IL-17 expression. While the pathomechanism of the disease has been revealed, epigenetic factors contributing to psoriasis are less well understood. Here, we investigated the role of the poorly studied histone variant H2A.J in psoriasis. We found that H2A.J gets overexpressed in the skin of psoriasis patients, with even non-lesional skin showing increased expression compared to the skin of healthy donors. To gain mechanistic insights, we studied mice with a global H2A.J knockout (KO) and found them to be partially protected against experimentally induced psoriasis, highlighted by reduced immune cell infiltration and less hyperkeratosis. Molecularly, psoriatic skin of H2A.J KO mice showed diminished expression of chemokines and cytokines, including CXCL1, CCL3, and IL-17A. This phenotype could partially be explained by the role of H2A.J as a key regulator of IL-17A-responsive genes in keratinocytes. Furthermore, we uncovered a T-cell-intrinsic function of H2A.J, which specifically promoted the expression of effector molecules such as Il17a and Il17f in T H 17 cells. Our findings from human skin and murine psoriasis models imply that H2A.J acts as a key epigenetic regulator of IL-17-associated inflammation, which controls the (chronic) activation of T H 17 cells and keratinocytes in psoriasis.