Estradiol and proinflammatory cytokines stimulate ISG20 expression in synovial fibroblasts of patients with osteoarthritis.

Interferon stimulated gene 20-kDa (ISG20) has been implicated in the pathology of osteoarthritis (OA) and it has been separately found to be responsive to estrogen stimulation. OA disproportionately affects women, and especially older women, suggesting some role of reproductive hormones in its pathology. The current study characterized the expression of ISG20 following stimulation with estradiol (E2) and proinflammatory cytokines in OA synovial fibroblasts (OASFs). E2 and the proinflammatory cytokines interleukin-6 (IL-6), lipopolysaccharide (LPS), and tumor necrosis factor α (TNF-α) were used to stimulate OASFs in vitro. The expression of ISG20 before and after stimulation was detected using quantitative real-time polymerase chain reaction (RT-qPCR) and Western blotting. E2 and proinflammatory cytokine (IL-6, LPS and TNF-α) stimulation significantly induced the expression of ISG20 both at the messenger RNA (mRNA) and protein level. Moreover, the induction was time- and dose-dependent. Small interfering RNA (siRNA) was transfected into OASFs, and expression of the inflammatory factors interleukin-1α (IL-1α), IL-6, and interleukin-10 (IL-10) was detected using RT-qPCR. Silencing ISG20 with siRNA inhibited the expression of IL-1α, IL-6, and IL-10. Thus, expression of ISG20 was regulated by estradiol and proinflammatory factors, while ISG20 in turn regulated the expression of other inflammatory factors. These data support the contention that ISG20 plays a role in the inflammatory process of OA.