Wear Debris Inhibition of Anti-Osteoclastogenic Signaling by Interleukin-6 and Interferon-γ MECHANISTIC INSIGHTS AND IMPLICATIONS FOR

Background: Wear debris challenge of macrophages provokes the generation of proinflammatory cytokines, which con-tribute to periprosthetic osteolysis. However, it is not known whether this effect is accompanied by reprogramming of other cytokines present within the periprosthetic tissue that may be involved in anti-osteoclastogenic activities. In the present study, we examined the ability of wear debris particles to inhibit the signaling of two such cytokines, interleukin-6 and interferon-γ. Methods: Human osteoclast precursor cells were challenged with particles of titanium or polymethylmethacrylate bone cement prior to the addition of the cytokines interleukin-6 or interferon-γ. Interleukin-6 signaling was determined by measuring the activation of STAT3 signal transduction with use of immunoblotting and electrophoretic mobility shift assays. Interferon-γ signaling was determined by measuring the activation of STAT1 with use of immunoblotting and electrophoretic mobility shift assays and by measuring the expression of interferon-γ-inducible genes with use of real-time reverse transcription-polymerase chain reaction assays. Involvement of mitogen-activated protein kinases in cy-tokine signaling was assessed by including mitogen-activated protein kinase inhibitors in these assays and also by means of immunoblot assessment of mitogen-activated protein kinase activation by wear debris particles. Wear de-bris modulation of expression of the cytokine suppressors SOCS1 and SOCS3 (as well as pro-inflammatory media-tors) was assessed with use of real-time reverse transcription-polymerase chain reaction assays