Augmented Th17 Differentiation Leads to Cutaneous and Synovio-Entheseal Inflammation in a Novel Model of Psoriatic Arthritis

Objective. To introduce a novel preclinical animal model of psoriatic arthritis (PsA) in R26Stat3C(stopfl/fl) CD4Cre mice, and to investigate the role of Th17 cytokines in the disease pathogenesis. Methods. We characterized a novel murine model of Th17-driven cutaneous and synovio-entheseal disease directed by T cell-specific expression of a hyperactive Stat3 allele. By crossing R26Stat3C(stopfl/fl) CD4Cre mice onto an interleukin-22 (IL-22)-knockout background or treating the mice with a neutralizing antibody against IL-17, we interrogated how these Th17 cytokines could contribute to the pathogenesis of PsA. Results. R26Stat3C(stopfl/fl) CD4Cre mice developed acanthosis, hyperkeratosis, and parakeratosis of the skin, as well as enthesitis/tendinitis and periarticular bone erosion in different joints, accompanied by osteopenia. T cell-specific expression of a hyperactive Stat3C allele was found to drive the augmented Th17 response in these animals. Careful characterization of the mouse bone marrow revealed an increase in osteoclast progenitor (OCP) and RANKL-producing cells, which contributed to the osteopenia phenotype observed in the mutant animals. Abrogation of the Th17 cytokines IL-17 or IL-22 improved both the skin and bone phenotype in R26Stat3C(stopfl/fl) CD4Cre mice, revealing a central role of Th17 cells in the regulation of OCP and RANKL expression on stromal cells. Conclusion. Perturbation of the IL-23/Th17 axis instigates Th17-mediated inflammation in R26Stat3C(stopfl/fl) CD4Cre mice, leading to cutaneous and synovio-entheseal inflammation and bone pathologic features highly reminiscent of human PsA. Both IL-17A and IL-22 produced by Th17 cells appear to play critical roles in promoting the cutaneous and musculoskeletal inflammation that characterizes PsA.