Bmi deficiency causes oxidative stress and intervertebral disc degeneration which can be alleviated by antioxidant treatment

The transcriptional repressor Bmi-1 is involved in cell-cycle regulation and cell senescence, the deficiency of which has been shown to cause oxidative stress. This study investigated whether Bmi-1 deficiency plays a role in promoting disc degeneration and the effect of treatment with antioxidant N-acetylcysteine (NAC) on intervertebral disc degeneration. Bmi-1^-/- mice were treated with the antioxidant NAC, supplied in drinking water (Bmi-1^-/- +NAC). For in vitro experiments, mouse intervertebral discs were cultured under low oxygen tension and serum-limiting conditions in the presence of tumour necrosis factor α and interleukin 1β in order to mimic degenerative insult. Disc metabolism parameters in these in vitro and in vivo studies were evaluated by histopathological, immunohistochemical and molecular methods. Bmi-1^-/- mice showed lower collagen Ⅱ and aggrecan levels and higher collagen Ⅹ levels than wild-type and Bmi-1^-/- +NAC mice. Bmi-1^-/- mice showed significantly lower superoxide dismutase (SOD)-1, SOD-2, glutathione peroxidase (GPX)-1 and GPX-3 levels than their wild-type littermates and Bmi-1^-/- + NAC mice. Relative to Bmi-1^-/- mice, the control and Bmi-1^-/- +NAC mice showed significantly lower p16, p21, and p53 levels. These results demonstrate that Bmi-1 plays an important role in attenuating intervertebral disc degeneration in mice by inhibiting oxidative stress and cell apoptosis.