Interleukin‐27 inhibits human osteoclastogenesis by abrogating RANKL‐mediated induction of nuclear factor of activated T cells c1 and suppressing proximal RANK signaling

Abstract

Objective. Interleukin-27 (IL-27) has stimulatory and regulatory immune functions and is expressed in rheumatoid arthritis (RA) synovium. This study was undertaken to investigate the effects of IL-27 on human osteoclastogenesis, to determine whether IL-27 can stimulate or attenuate the osteoclast-mediated bone resorption that is a hallmark of RA.Methods. Osteoclasts were generated from bloodderived human CD14؉ cells. The effects of IL-27 on osteoclast formation were evaluated by counting the number of tartrate-resistant acid phosphatase-positive multinucleated cells and measuring the expression of osteoclast-related genes. The induction of nuclear factor of activated T cells c1 (NFATc1) and the activation of signaling pathways downstream of RANK were measured by immunoblotting. The expression of key molecules implicated in osteoclastogenesis (NFATc1, RANK, costimulatory receptors, and immunoreceptor tyrosinebased activation motif-harboring adaptor proteins) was measured by real-time reverse transcriptionpolymerase chain reaction. Murine osteoclast precursors obtained from mouse bone marrow and synovial fluid macrophages derived from RA patients were also tested for their responsiveness to IL-27.Results. IL-27 inhibited human osteoclastogenesis, suppressed the induction of NFATc1, downregulated the expression of RANK and triggering receptor expressed on myeloid cells 2 (TREM-2), and inhibited RANKL-mediated activation of ERK, p38, and NF-B in osteoclast precursors. Synovial fluid macrophages from RA patients were refractory to the effects of IL-27. In contrast to the findings in humans, IL-27 only moderately suppressed murine osteoclastogenesis, and this was likely attributable to low expression of the IL-27 receptor subunit WSX-1 on murine osteoclast precursors.Conclusion. IL-27 inhibits human osteoclastogenesis by a direct mechanism that suppresses the responses of osteoclast precursors to RANKL. These findings suggest that, in addition to its well-known antiinflammatory effects, IL-27 plays a homeostatic role in restraining bone erosion. This homeostatic function is compromised under conditions of chronic inflammation such as in RA synovitis.Interleukin-27 (IL-27) is a member of the IL-12 family of heterodimeric cytokines that also includes . IL-27 comprises the Epstein-Barr virus-induced protein 3 and p28 subunits, which share similarity with the p40 and p35 subunits of IL-12, respectively (4). The IL-27 receptor is a heterodimer composed of a WSX-1 subunit (also termed T cell cytokine receptor), which confers ligand specificity, and the gp130 signaling subunit, which is also utilized by the IL-6 family of cytokines (5). IL-27 activates the JAK/STAT signal transduction pathway in a contextdependent manner, since its effects vary depending on Dr.

Interleukin 27 (IL-27) Alleviates Bone Loss in Estrogen-deficient Conditions by Induction of Early Growth Response-2 Gene

“…is reported to inhibit RANKL-mediated osteoclastogenesis (18). In Ovx estrogen-deficient conditions, there is an increased rate of bone resorption.…”

“…A report by Kalliolias et al (18) has also shown the direct effect of IL-27 on osteoclastogenesis by suppressing responses of osteoclast precursors to RANKL. IL-27 inhibits human osteoclastogenesis by abrogating RANKL-mediated induction of NFATc1 and suppressing proximal RANK signaling (18). In osteoblasts, IL-27 stimulated STAT-3 activation but had no significant effect on alkaline phosphatase activity and proliferation of osteoblasts (17).…”

Cytokine measurements in Brazilian postmenopausal osteoporosis patients reveal high levels of IL-8

“…IL-27 is a cytokine that probably acts in the regulation of bone homeostasis. This cytokine is responsible for decreasing bone degradation by suppressing the expression of RANK precursors (e.g., NFATc1) [24]. Therefore, it is possible to suggest that IL-27 makes an important contribution, with a positive balance regarding cytokine-mediated inflammatory diseases (e.g., osteoporosis).…”

NFAT Signaling and Bone Homeostasis

“…In certain conditions, TLRs and certain cytokines inhibited RANK, RANKL and osteoclasts. For example, IL-10, a immune modulator, inhibited osteoclasts by preventing nuclear translocation of NFATc1 and RANKL-induced expression of NFATc1, Jun and Fos [57], IL4 and IL27 shared the similar mechanism in suppressing NFATc1 induced by RANKL [58,59], and TLRs and γ-interferon inhibited RANK and osteoclast precursors [60]. In addition, in osteoclasts, it has been shown that Toll-like receptor 2 (TLR2) that mediates inflammation and bone metabolism by activating RANKL, NFATc1, NF-κB, and others [61]; protein inhibitor of activated STAT3 (PIAS3) inhibits the promoter of NFATc1 [62]; Notch recruits NF-κB p65 to the promoter of NFATc1 for transcription activation [63]; and vitamin D inhibits the NFAT transcriptional activation [64].…”