Excessive Polyamine Generation in Keratinocytes Promotes Self-RNA Endosomal Sensing by Dendritic Cells in Psoriasis

SUMMARY The mechanisms underlying tissue-specific chronic inflammation are elusive. Here we report that mice lacking Protein Phosphatase 6 in keratinocytes are predisposed to psoriasis-like skin inflammation, with an inordinate urea cycle and enhanced oxidative phosphorylation that supports hyperproliferation. This phenotype is mediated by increased Arginase-1 production resulting from CCAAT/enhancer-binding protein beta activation. Single-cell RNA-seq of the psoriatic epidermis revealed that the rate-limiting enzyme for Arginine biosynthesis, Argininosuccinate synthetase 1, maintains the Arginine pool, which is indispensable for immune responses. Accumulated polyamines branched from the urea cycle promote endosomal Tlr7-dependent self-RNA sensing by myeloid dendritic cells. This process is achieved with the assistance of an RNA-binding peptide that originates from the heterogeneous nuclear ribonucleoprotein A1, a probable autoantigen in psoriasis. Finally, targeting urea cycle wiring with an arginase inhibitor markedly improved skin inflammation in murine and non-human primate models of psoriasis. Our findings suggest that urea cycle alteration and excessive polyamine production by psoriatic keratinocytes promote self-RNA sensing by dendritic cells, which links the hyperproliferation of stationary cells with innate-immune activation in an auto-inflammatory condition.