DOP84 Colonic CD4+ T cell senescence is implicated in the progression of experimental colitis in aged mice

Abstract

Abstract Background Evidence from recent epidemiological data suggests that the burden of IBD in the elderly is increasing globally. However, the mechanisms underlying the age-related IBD susceptibility remain elusive. Aging leads to a progressive functional decline of the immune system, rendering the elderly increasingly susceptible to autoimmune disease. Herein, we sought to determine the role of immunosenescence in age-dependent colitis and to explore the underlying mechanisms. Methods Young (2-3 months), middle-aged (10-12 months), and aged (20-24 months) mice were established models of colitis by 2% dextran sulfate sodium salt (DSS) treatment. Weight loss, colon length, disease activity indexes (DAI) and histological scores were evaluated to assess the severity of colitis. Using a second-generation fluorogenic substrate for β-galactosidase and multi-parameter flow cytometry, we detected the senescence-associated β-galactosidase (SA-βGal) activity in lymphocytes isolated from colon, including CD4+ T cells, CD8+ T cells, B cells, natural killer cells, microphages, neutrophils and dendritic cells. Based on the immunocytes that exhibit greatest age-related increases in SA-βGal activity, inflammatory cytokines such as TNF-α、IFN-γ、IL-17 were evaluated in senescent immunocytes through flow cytometry. Single-cell and bulk RNA-seq of colonic immune cells in mice with different ages were performed to further investigate the precise molecular mechanisms. Results Ageing increased the severity of DSS-induced colitis wherein aged mice exhibited worsened weight loss, shortened colon length, higher DAI and histological scores compared to young mice. The greatest age-associated increases of SA-βGal activity were observed in colonic CD4+ T cell populations. Additionally, aging resulted in systemic activation of CD4+ T cells, exhibiting an expansion of CD4+ effector memory T (TEM) cells in colon, as well as in spleen. Aged colonic CD4+ T cells generate higher levels of IFN-γ and IL-17 comparing to young colonic CD4+ T cells, especially in status of colitis. Moreover, the accumulated CD4+ TEM cells in the aged colon were the main source of IL-17 production. Single-cell analysis revealed that aging increased colonic CD4+ TEM cells, which were associated with T cell-mediated cytotoxicity and cytokine-mediated signaling pathway. Splenic CD4+ TEM cells isolated from aged colitis mice were confirmed to involve in cellular senescence, Th17 differentiation and inflammatory signaling pathway through bulk RNA-seq. Conclusion These results provide a significant insight into the contribution of senescent CD4+ T cells to age-dependent colitis and provide an attractive possibility that targeting T cell specifically might be a potential strategy to treat elderly IBD patients.