Distribution of Malassezia species on the skin of patients with psoriasis

Quinolinic acid, a tryptophan metabolite of the skin microbiota, negatively regulates the NLRP3 inflammasome through the aryl hydrocarbon receptor in psoriasis

Psoriasis is a chronic inflammatory skin disease whose pathogenesis involves skin microbiota dysbiosis. Multiple studies have revealed changes in microbiota abundances between psoriatic lesions and healthy skin. However, the metabolic pathways of skin microbiota (especially tryptophan metabolism, which is closely related to immunosuppression) are far less understood. In this study, we first detected the major microbial metabolites of tryptophan on skin surfaces, finding that the quinolinic acid (QA) were significantly lower in the lesional skin of patients with psoriasis than in that of healthy subjects and correlated negatively with the severity of psoriasis. In vitro and in vivo, applying QA significantly alleviated skin inflammation in an aryl hydrocarbon receptor (AhR)-dependent manner, resulting in the inhibition of the NLRP3 inflammasome activation. Furthermore, in mice with imiquimod-induced psoriasis-like dermatitis, topical application of AhR small-interfering RNA substantially exacerbated the disease severity with increased NLRP3 inflammasome activation. Collectively, our data suggest that QA, a skin microbiota-derived metabolite, negatively regulates AhR-NLRP3 inflammasome signaling activation in patients with psoriasis, providing an insight into the correlation between microbiota metabolism and the host skin in individuals with psoriasis.

Keratinocyte-intrinsic BCL10/MALT1 activity initiates and amplifies psoriasiform skin inflammation

[Figure: see text].