Background/Purpose: Inflammation is an important component of most age-related disorders. Cellular changes associated to aging are tightly connected with pro-inflammatory mechanisms. The purpose of this study is to analyze cellular senescence in synovial fibroblasts and its potential influence in the pathogenesis of chronic arthritis, including rheumatoid arthritis (RA) and osteoarthritis (OA).

Methods: The expression of senescence associated markers p16INK4 (p16) and Nanog was analyzed by immunohistochemistry (IHC) and immunofluorescence (IF) in synovial tissues from RA (n=43), OA (n=18), and non-inflammatory synovial tissues (n=15). Senescent synovial fibroblasts (SF) were quantified in cultures by senescence-associated beta-galactosidase (SA-β-gal) staining. For a model of stress-induced senescence, SF were cultured for 14 days after a short course of oxidative stress with H₂O₂ (200 mM for 1h on day 5) or exposure to TNFα (100 ng/ml for 72h on day 2). At 14 days, senescence and further response to stimulation with TNFα 20 ng/ml for 24h were analyzed. RNA was extracted to quantify IL-6, IL-8, MMP-3, MCP-1, p16 and p21 mRNA expression by qRT-PCR and culture supernatants were analyzed for IL-6 and IL-8 production by ELISA. Quantitative data were statistically analyzed by Pearson or Spearman correlation coefficient or Mann-Whitney test where appropriate.

Results: Synovial tissue expression of both p16 and Nanog was detected by IHC and correlated positively with the age of the donors regardless of their origin (p16: p=0.008/r=0.307; Nanog: p=0.001/r=0.413). p16(+) cell density was significantly higher in OA tissues (p=0.01) and Nanog(+) was higher in both RA (p=0.0006) or OA (p<0.0001) tissues compared to controls. p16(+) and Nanog(+) cell density were higher in young (age <40 y/o) RA patients compared to the same group of age in non-inflammatory donors (p= 0.04 and p=0.02 respectively). Double p16 and hsp47 IF labelling confirmed that both hsp47(+) SF and hsp47(-) non-fibroblastic cell fractions contained p16(+) senescent cells. The percentage of SA-β-gal(+) in non-inflammatory control SF after 14 days in culture was positively correlated with age (p=0.008/r=0.75). This fraction was higher in RA (p=0.03) compared to healthy control SF, and increased upon SF exposure to H₂O₂ or TNFα (p=0.004 for both). Stress-induced senescence enhanced the senescence associated secretory phenotype (SASP) in SF, up-regulating the mRNA expression of pro-inflammatory factors such as IL-6, IL-8, MCP-1, and MMP-3. Consistently, senescent SF released more IL-6 and IL-8 than non-senescent SF. Finally, further stimulation with TNFα induced a higher increase in IL-6, IL-8 and MMP-3 mRNA expression in senescent SF compared to non-senescent SF.

Conclusion: Synovial tissues from patients with RA and OA shows an increased proportion of senescent SF. Stress-induced senescence in SF increases the production of pro-inflammatory mediators, and gives rise to an activation state that enhances the responsiveness to TNFα. Our data suggest that SF senescence is linked to the activation of a pro-inflammatory phenotype that may contribute to the pathogenesis of chronic arthritis.

« Back to 2018 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/fibroblasts-senescence-is-observed-in-rheumatoid-and-osteoarthritic-synovial-tissues-and-triggers-a-pro-inflammatory-program-ex-vivo/