Schematic model of osteolysis in the psoriatic joint. Extensive erosions observed in the PsA joint are mediated by a bidirectional attack on bone. We propose that circulating OCPs enter the synovium and are induced to become osteoclasts by RANKL expressed by synoviocytes (outside-in). In parallel, OCPs traverse endothelial cells in the subchondral bone and undergo osteoclastogenesis following RANKL stimulation from osteoblasts and stromal cells (inside-out).
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