IFN-b mediates drug-induced blockade of macrophage differentiation to osteoclasts

Introduction: Bone fractures are the biggest problem facing most of the ageing people with bone disease, especially those with osteoporosis. Bisphosphonates (BPs) is the most common drug prescribed to treat osteoporosis and to prevent the occurrence of bone fractures. However, such treatments can lead to Medication Related Osteonecrosis of the Jaw (MRONJ), that is defined as prolonged exposure of bone in the maxillofacial region following anti-RANKL and anti-VEGF therapy and appears following combined therapy, like with the BP zoledronic acid (ZOL) and dexamethasone (DEX). In healthy patients, wound healing is associated with secretion of pro-resolving cytokines, as IL-10 and TGF-b, that induce migration/generation of macrophage that promote injured tissue recovery and homeostasis. Recently, we found IFN-β to be a macrophage-derived effector cytokine in resolving inflammation that promotes macrophage reprogramming to anti-inflammatory phenotypes. In addition, IFN-β is a well-established inhibitor of osteoclast differentiation.

Material and method: RAW 264.7 or peritoneal macrophages were treated with ZOL/DEX for 4-24 hrs, and IFN-β expression was examined by Real Time polymerase chain reaction (RT-PCR) and Western blotting. In addition, the RANKL-induced differentiation of RAW 264.7 macrophages to osteoclasts was evaluated by TRAP assay following treatment with ZOL/DEX, IFN-β, anti-IFN-β, and STAT1/3 inhibition.

Results: Here, we found ZOL+DEX increased IFN-β expression by RAW 264.7 macrophages when treated with or without RANKL. Moreover, these drugs and IFN-β blocked RANKL-induced osteoclast differentiation, and IFN-β neutralization by antibodies reversed the ZOL+DEX effect. In addition, we found that early STAT1 or STAT3 inhibition did not affect ZOL+DEX blockade of osteoclastogenesis, while inhibition of STAT1, but not STAT3, partially restored osteoclastogenesis in IFN-β-treated macrophages. Finally, we found ZOL+DEX also induced IFN-β expression in peritoneal resolution phase macrophages, suggesting they might be used to resolve acute inflammation.

Conclusions: Altogether, our findings suggest MRONJ-inducing drugs block macrophage differentiation to osteoclasts through the induction of high IFN-β expression in macrophages. The induction of IFN-β expression is STAT-independent, while the IFN-β-mediated inhibition of osteoclastogenesis is mediated, at least in part by STAT1. Thus, anti-IFN-β agents could serve as therapeutic strategies for MRONJ disease.