The Dual Effects of Reactive Oxygen Species on the Mandibular Alveolar Bone Formation in SOD1 Knockout Mice: Promotion or Inhibition

The status of reactive oxygen species (ROS) correlates closely with the normal development of the oral and maxillofacial tissues. Oxidative stress caused by ROS accumulation not only affects the development of enamel and dentin but also causes pathological changes in periodontal tissues (periodontal ligament and alveolar bone) that surround the root of the tooth. Although previous studies have shown that ROS accumulation plays a pathologic role in some oral and maxillofacial tissues, the effects of ROS on alveolar bone development remain unclear. In this study, we focused on mandibular alveolar bone development of mice deficient in superoxide dismutase1 (SOD1). Analyses were performed using microcomputerized tomography (micro-CT), TRAP staining, immunohistochemical (IHC) staining, and enzyme-linked immunosorbent assay (ELISA). We found for the first time that slightly higher ROS in mandibular alveolar bone of SOD1(-/-) mice at early ages (2-4 months) caused a distinct enlargement in bone size and increased bone volume fraction (BV/TV), trabecular thickness (Tb.Th), and expression of alkaline phosphatase (ALP), Runt-related transcription factor 2 (Runx2), and osteopontin (OPN). With ROS accumulation to oxidative stress level, increased trabecular bone separation (Tb.Sp) and decreased expression of ALP, Runx2, and OPN were found in SOD1(-/-) mice at 6 months. Additionally, dosing with N-acetylcysteine (NAC) effectively mitigated bone loss and normalized expression of ALP, Runx2, and OPN. These results indicate that redox imbalance caused by SOD1 deficiency has dual effects (promotion or inhibition) on mandibular alveolar bone development, which is closely related to the concentration of ROS and the stage of growth. We present a valuable model here for investigating the effects of ROS on mandibular alveolar bone formation and highlight important roles of ROS in regulating tissue development and pathological states, illustrating the complexity of the redox signal.