Mature interleukin-36γ induces stratum corneum exfoliation in generalized pustular psoriasis by suppressing corneodesmosin

Loss-of-function mutations in the IL36RN gene encoding IL-36 receptor antagonist (IL-36RA) cause familial generalized pustular psoriasis (GPP), which sometimes begins shortly after birth and is difficult to treat, and its effects on the epidermis are unclear. This study aimed to investigate the involvement of IL-36 receptor agonists in the epidermal formation of GPP. In this study, we found that IL-36 receptor agonists, especially mature IL-36γ, stimulate IL-8 and proIL-36γ production in the epidermis, while down-regulating the genes encoding epidermal cornified envelope-related proteins such as corneodesmosin. IL-36 receptor antagonists and monoclonal anti-IL-36γ antibodies counteract the effect of mature IL-36γ on corneodesmosin in keratinocytes in a dose-dependent manner. In the epidermis of generalized pustular psoriasis patients with IL36RN loss-of-function mutations, proIL-36γ is overproduced in the epidermis and corneodesmosin protein expression is markedly decreased in the region of giant subcorneal pustules called Kogoj’s spongiform pustules with high neutrophil infiltration. IL-8 induced by mature IL-36γ induces several neutrophils in the epidermis, and the newly produced proIL-36γ is cleaved to the mature form by neutrophil proteases. This newly produced mature IL-36γ was predicted to further suppress the gene expression of the granulosa-stratum-associated protein, corneodesmosin, leading to significant stratum corneum exfoliation and formation of giant subcorneal pustules. Overall, our results elucidate the mechanism underlying the formation of Kogoj’s spongiform pustules in generalized pustular psoriasis. Normal human 3D epidermis to which only solvent was added was used as a control and compared with (1) IL-36α-added group, (2) IL-36β-added group, and (3) IL-36γ-added group, respectively.