Role of tryptophan metabolism on senescent synovial fibroblasts

Abstract

Abstract Background Cellular senescence is connected to inflammation and altered metabolism. Rheumatoid arthritis (RA) patients show premature senescence and increased Trp metabolism along the kynurenine pathway. We aim to analyze the effect of Trp metabolism on cellular senescence and the expression of the Senescence Associated Secretory Phenotype (SASP) in human synovial fibroblasts (SF). Methods For inflammation-induced senescence, SF were cultured for 14 days after exposure to IL6/sIL6R (100 ng/ml for 72h on day 2). On day 14, senescence and SASP were analyzed. Senescent SF were quantified in cultures by detection of senescence-associated beta-galactosidase (SA b-gal). IDO1, IDO2, p16, ATG3, ATG5 and SASP components (IL6, IL8, MMP3, MCP1), were quantified by qRT-PCR and IL6 and IL8 proteins by ELISA. IDO1 was silenced using lentiviral vectors. IDO1 protein was detected by WB. Quantitative data were statistically analyzed by Pearson or Spearman correlation coefficient or Mann-Whitney test where appropriate. Results IDO1, but not IDO2, was induced by senescence in SF. Conversely, treatment of SF cultures with the IDO1 product kynurenine significantly reduced senescence, as determined by expression of the senescence marker p16 (p=0.018), although the autophagy response and SASP expression were not affected. IDO1 silencing during senescence induction resulted in a significant increase of IL6 expression without affecting other SASP components. Conclusion Upregulation of IDO1 by senescence, together with the reduction of senescence by kynurenine and the increased IL6 production by deficient IDO1 activity suggest that IDO1 and the kynurenine pathway play a negative regulatory role on senescence and SASP expression.