Par1 signaling between T cells and keratinocytes mediates Klk6-elicited skin inflammation in a Rock2-independent

Summary: Abstract Body: Kallikrein 6 (KLK6) is increased in lesional epidermis of human psoriasis skin, and keratinocyte-specific overexpression of Klk6 (Klk6+) in mice results in the development of psoriasis-like skin lesions that are eliminated in the global absence of the protease-activated receptor 1 (Par1). Par1 is a G-protein coupled receptor expressed in keratinocytes (KCs) and T cells and signals via phosphorylating Rock2. Klk6+ mice have increases in cutaneous Rock2 activity compared to littermate controls that decreases in the absence of Par1 suggesting a plausible pathogenic pathway involving T cells, KCs, Par1 and Rock2. To define the cellular mechanisms responsible for Klk6-induced skin inflammation we first mated Klk6+ mice with KC (K14cre) or T cell (Lckcre)-specific Par1 knockout mice to identify the cell type responsible for the Klk6-Par1-elicited skin phenotype. Klk6+-Par1△KC and Klk6+Par1△Tcell mice develop less severe skin inflammation than Klk6+ mice, demonstrated by improvement in appearance and decreases in acanthosis, cutaneous T cell numbers and IL-17A. Moreover, Klk6-Par1 signaling in primary mouse T cells and KCs led to increases in Il17a/f, Il22 and Ifng, and Il17c, Ccl20, Il19, Il36, Cxcl1 and Klk13, respectively, which are abrogated in the absence of Par1. Next, to identify Rock2 signaling as a pathogenic downstream molecule of Par1, Klk6+ mice were treated systemically with the Rock2 inhibitor (KD025) for 4-wks. KD025 treated Klk6+ mice showed no improvement in skin inflammation, despite Rock2 activity decreasing to control mouse levels. Increases in phospho-c-Jun and decreases in phospho-Sapk3 were found in Klk6+ skin that reverse in the absence of Par1 suggesting alternative Par1-dependent pathways may be responsible for skin inflammation. Together, these findings demonstrate that Klk6-Par1 signaling between T cells and KCs are critical for skin inflammation and occur in a Rock2 independent manner. Roopesh Singh¹, Vijaya Bharti¹, Ranjitha Uppala², Mrinal K. Sarkar², Johann E. Gudjonsson², Nicole L. Ward¹ 1. Vanderbilt University Medical Center, Nashville, TN, United States. 2. University of Michigan, Ann Arbor, MI, United States. Cell Communication Networks and Stromal Biology