β2-adrenoceptor signaling reduction is involved in the inflammatory response of fibroblast-like synoviocytes from adjuvant-induced arthritic rats

To investigate the effects of β-AR signaling on fibroblast-like synoviocytes (FLS) from adjuvant-induced arthritis (AA) rats and the partial mechanisms focused on β-AR desensitization mediated by GRK2 and β-arrestin2.

Animals were divided into a control group and an AA model group, and FLSs were cultured. Arthritis index, histopathology of joints, epinephrine (Epi) and norepinephrine (NE) were detected in vivo. The effect of the β-AR agonist isoprenaline (ISO) and the β₂-AR agonist salbutamol on FLS cell viability were detected by CCK8. Cytokines TNF-α, IL-1β, OPG and RANKL were examined by ELISA. The expression of β₂-AR was detected by immunofluorescence and flow cytometry. The cytomembrane expression and desensitization of β2-AR, GRK2, and β-arrestin2 were measured by flow cytometry and western blot.

The concentration of NE increased to a peak on day 21, which was consistent with the arthritis index. The levels of Epi and NE in synovial tissues were decreased. ISO inhibited FLS cell viability and TNF-α, IL-1β, and RANKL secretion, and promoted OPG secretion. β₂-AR mediated the effects of ISO on FLS cell viability. β₂-AR signaling was weaker in AA rats compared to the controls. Elevated GRK2 and β-arrestin2 in cytomembranes promoted β₂-AR desensitization and may decrease the anti-inflammatory effect of β₂-AR signaling.

The activation of β₂-AR signaling exerts its anti-inflammatory activities on FLS. β₂-AR signaling decreased in the AA model, which might be related to the increased membrane expression of GRK2 and β-arrestin2, and promoted the excessive desensitization of β₂-AR. Decreased β₂-AR signaling may be relevant to the exacerbation of arthritis inflammation.