TREX1 and Arthritis: Based on the above in vivo experimental data, the SD rats in both the AIA and TREX1Cre/+ models exhibited the senescence-associated secretory phenotype (SASP), and the arthritis condition and ageing phenotype in these rats were reversed, together with reductions in the expression levels of proinflammatory cytokines (Supplementary Fig. 9A) and ageing markers18 such as IL-1β, IL-6, IL-8, IFN-β, p16 and p21 (Supplementary Fig. 9B and 10-1A), after MTX treatment or AAV-TREX1 injection.