Differential effects of IL-8, LIF (pro-inflammatory) and IL-11 (anti-inflammatory) on TNF-alpha-induced PGE(2)release and on signalling pathways in human OA synovial fibroblasts

Abstract

Tumour necrosis factor alpha (TNF-alpha) inflammatory activity is mediated, at least in part, by prostaglandin E(2)(PGE(2)). In osteoarthritis (OA), other cytokines are believed to play a role by interacting with TNF-alpha. Using OA synovial fibroblasts, we investigated the effects of interleukin 8 (IL-8), leukaemia inhibitory factor (LIF) and IL-11 on the level of TNF-alpha-induced PGE(2), and their impact on the TNF-alpha-induced cellular signalling cascades including the TNF-receptor (TNF-R), soluble TNF-R (TNF-sR), cytoplasmic phospholipase A2 (cPLA2), cyclooxygenase 2 (COX-2), and the transcription factors NF-kappaB, C/EBP, CREB and AP-1.IL-8 increased in a synergistic manner (282% at 5 ng/ml) and LIF in an additive fashion (69% at 50 ng/ml) the TNF-alpha-induced PGE(2)release, while IL-11 reduced it (52% at 5 ng/ml). IL-8 (5 ng/ml) and LIF (50 ng/ml) alone upregulated (30%) the TNF-R binding level, but significantly downregulated the TNF-alpha-induced levels (P<0.007 and P<0.004, respectively) and the TNF-sR55 level. In contrast, IL-11 reduced the basal level by 18% (P<0.005) and the TNF-alpha-induced level of TNF-R by 51% (P<0.01) as well as decreasing both TNF-sR55 and TNF-sR75. The COX-2 synthesis level was increased by IL-8 and LIF under TNF-alpha treatment but downregulated by IL-11. IL-8 and LIF either alone or under TNF-alpha treatment increased the cPLA2 synthesis, while IL-11 decreased the level under both conditions. Interestingly, IL-8 induced in a synergistic manner and LIF in an additive fashion, the level of cPLA2 activity. IL-8 and LIF had no effect on the TNF-alpha-induced NF-kappaB accumulation, while IL-11 significantly decreased it (P<0. 02). All three cytokines inhibited TNF-alpha-induced C/EBP, but no true effect was noted for AP-1 and CREB in the presence of TNF-alpha. These results indicate that IL-8 synergizes and LIF potentiates the TNF-alpha PGE(2)effect which appears to be mediated mostly by increasing cPLA2 activity level. On the other hand, IL-11 alone had no effect on the PGE(2)release, but in conjunction with TNF-alpha, this cytokine showed anti-inflammatory properties. This study provides a rational foundation to develop therapeutic strategies for the treatment of OA by shedding light on the mechanisms of action of three prominent cytokines at work in articular joint tissues.