Dexamethasone inhibits BAFF expression in fibroblast-like synoviocytes from patients with rheumatoid arthritis

Abstract

Fibroblast-like synoviocytes (FLS) play a major role in the pathogenesis of rheumatoid arthritis (RA). FLS isolated from patients with RA (FLS-RA) express B cell-activating factor belonging to the TNF family (BAFF), a cytokine that has been associated with the onset and progression of RA. Glucocorticoids are powerful anti-inflammatory drugs used in the treatment of RA. In the present study, we examined the effect of dexamethasone (Dex) on constitutive and TNF-α- and IFN-γ-induced BAFF expression in FLS-RA. BAFF mRNA expression and soluble BAFF were determined by RT-PCR and ELISA, respectively. The results showed that constitutive BAFF mRNA expression was inhibited by Dex in a dose- and time-dependent manner. Also, Dex inhibited the secretion of BAFF in a time-dependent manner reaching 76% of inhibition 72 h after treatment. Moreover, Dex suppressed both mRNA and protein BAFF expression induced by TNF-α but had no effect on IFN-γ-induced BAFF expression. In comparison with B cells cultured alone, B cells co-cultured with FLS-RA exhibited a higher survival, which was inhibited when FLS-RA were pretreated with Dex. However, the enhanced B cell survival was reestablished by the addition of rhBAFF. Therefore, Dex is a potent inhibitor of constitutive and TNF-α-induced BAFF expression in FLS-RA.

Introduction

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease characterized by hyperplasia of the synovial lining, composed of fibroblast-like synoviocytes (FLS) and macrophage-like synoviocytes. Growing evidence suggests that FLS play a major role in the pathogenesis of RA. FLS modulate the joint inflammation through the expression of cytokines and chemokines, such as interleukin (IL)-6; IL-8 and monocyte chemoattractant protein (MCP)-1; support myeloid and lymphoid cell growth and angiogenesis by releasing various growth factors including epidermal growth factor (EGF); and promote matrix degradation through the production of matrix metalloproteinases and cathepsins (for review see [1], [2], [3]).

B cell-activating factor belonging to the TNF family (BAFF; also called BlyS, TALL-1, THANK, zTNF4) is a recently described member of the TNF family ligands [4], [5]. BAFF exists as a soluble and a cell surface molecule. Several studies indicate that it is involved both in the maturation and survival of B cells in the periphery (for review see [6], [7], [8]) and the activation and effector functions of T cells [9], [10], [11], [12]. Initially, it was described that the expression of BAFF was highly restricted to cells of the myeloid lineage such as monocytes, macrophages and dendritic cells [13], [14]. However, recently it has been shown that bone marrow stromal cells [15] and follicular dendritic cells [16] express BAFF constitutively. The expression of BAFF can be up-regulated in myeloid cells [14], astrocytes [17] and salivary gland epithelial cells [18] by pro-inflammatory cytokines such as IFN-α, IFN-γ, TNF-α and a combination of them, while that BAFF can be induced in neutrophils by G-CSF [19]. In contrast, stimuli inhibiting BAFF expression are less well known.

Elevated levels of BAFF have been detected in the serum of patients with autoimmune and chronic inflammatory diseases, such as systemic lupus erythematosus (SLE) [20], [21]; Sjögren’s syndrome (SS) [20], [22]; bullous pemphigoid [23]; asthma [24] and chronic hepatitis C virus infection [25], [26].

Evidence suggests that BAFF plays an important role in the pathogenesis of RA. Increased levels of BAFF have been detected in the serum of patients with RA [27] and a positive correlation was established between the intensity of the local inflammatory response and the levels of BAFF in the joint of patients with RA [28]. Moreover, concentrations of BAFF were higher in the synovial fluid that in the serum of RA patients [21], [27], [28], suggesting local production of BAFF by the inflamed synovium. Recently, it has been shown that macrophages [29] and FLS from patients with RA (FLS-RA) [30] express BAFF constitutively and that its expression was up-regulated in FLS-RA upon stimulation by TNF-α and IFN-γ [30]. Besides, increased BAFF production has been related to the onset and progression of disease in a collagen-induced arthritis (CIA) mouse model [31]. In these mice, splenic macrophages and dendritic cells expressed high levels of BAFF during the progression of RA [31]. Interestingly, the treatment with TACI-Fc, a soluble decoy receptor for BAFF, inhibited the production of autoantibodies and delayed the progression of disease in CIA mice [32]. In addition, using a xenogeneic model generated by implanting synovial tissue from RA patients into NOD-SCID mice, it was demonstrated that TACI-Fc abrogated the development of ectopic germinal centers, inhibited the human mRNA production of IgG, IFN-γ and TNF-α and reduced the number of infiltrating B and T lymphocytes in the transplanted tissues graft [29].

Glucocorticoids (GCs) are powerful drugs with strong, albeit non-specific, anti-inflammatory and immunomodulatory effects used in the treatment of RA and many other inflammatory diseases [33], [34]. This effect is mediated in part through down-regulation of inflammatory cytokines expression such as TNF-α and IFN-γ [33], [35]. Previous reports have described that the treatment with GCs induces a marked decrease in BAFF levels in the serum of patients with SLE, asthma and bullous pemphigoid [23], [24], [36]. However, from these studies it is not clear if BAFF expression is directly affected by GCs or if attenuation of BAFF levels could be a consequence of the action of GCs upon others factors regulating BAFF expression, such as TNF-α or IFN-γ.

In this study, we were interested in analyzing the effect of dexamethasone (Dex), a synthetic glucocorticoid, on the constitutive and TNF-α- and IFN-γ-induced BAFF expression in FLS-RA.