Pleiotrophic function of BAFF to promote a senescence-associated secretome and growth arrest

Senescent cells release a variety of cytokines, proteases and growth factors collectively defined as the Senescent Secretory Associated Phenotype (SASP). Sustained SASP induces a pattern of chronic inflammation associated with aging and implicated in multiple age-related diseases. Here, we investigated the expression and function of the immunomodulatory cytokine BAFF (B-cell activating factor), a SASP factor, in multiple senescence models. First, we characterized BAFF production across different senescence models, including senescent human diploid fibroblasts (WI-38, IMR-90) and monocytic leukemia cells (THP-1), and tissues of mice induced to undergo senescence. We identified IRF1 (interferon response factor 1) as a transcription factor required for promoting BAFF mRNA transcription in senescence, and found that suppressing BAFF production decreased the senescent phenotype in both monocytes and fibroblasts. Importantly, the influence of BAFF on the senescence program was cell type-specific: in monocytes, BAFF promoted the early activation of NF-?B and general SASP secretion, while in fibroblasts, BAFF contributed to the production and function of TP53 (p53). Overall, BAFF silencing affected shared senescence-associated phenotypes including IL6 secretion, SA-beta-Gal staining, and ?-H2AX accumulation. We propose that BAFF is a novel biomarker of senescence and a potential target for senotherapy. Overall design: Gene expression analysis of BAFF siRNA vs. Ctrl siRNA transfected cells in senescence.