The boxes indicate chondrocyte states, solid arrows indicate cell state transitions, dashed arrows indicate promotion of a transition, and dashed barriers indicate suppression of a transition. The affecting cytokine is indicated along the arrow. The variables CU, CT, and CE denote the three healthy-cell populations, resp.: those not yet signaled by DAMPs, those signaled by DAMPS and in the process of becoming catabolic, and those starting to produce EPO. The variables ST and SA denote the two sick-cell populations, resp.: “catabolic” cells that synthesize inflammatory cytokines and ROS, and EPOR-active cells that express a receptor for EPO and can switch back to the healthy state CU when signaled by EPO. Apoptotic and necrotic cell populations are denoted by DA and DN, resp.