Costimulation of Murine Osteoblasts with Interferon-γand Tumor Necrosis Factor-αInduces Apoptosis through Downregulation of Bcl-2 and Release of Cytochromecfrom Mitochondria

Abstract

During chronic inflammation from diseases, such as periodontal disease, the proinflammatory cytokines interferon-gamma (IFNγ) and tumor necrosis factor-α(TNFα) alter bone remodeling. To elucidate the underlying molecular mechanisms, we investigated the effect of IFNγand TNFαon the proliferation and survival of clonal MC3T3-E1 mouse osteoblasts. We found that although IFNγor TNFαalone affected cell growth and survival only marginally, costimulation with both synergistically inhibited cell growth and reduced cell viability. The diminished cell viability was due to apoptosis, as indicated by increased TUNEL staining and elevated caspase 3, 8, and 9 activities. Western blot also showed that costimulation with IFNγand TNFαelicited cytochromecrelease and downregulated B cell lymphoma 2 (Bcl-2) expression without affecting Bcl-2-associated X (Bax) protein expression. Furthermore, stable Bcl-2 overexpression significantly alleviated cell death following costimulation. Collectively, these results suggested that IFNγand TNFαelicited osteoblast apoptosis via cytochromecrelease from damaged mitochondria, caspase activation, and Bcl-2 downregulation.