Ionizing Radiation Induces Disc Annulus Fibrosus Senescence and Matrix Catabolism via MMP-Mediated Pathways

Previous research has identified an association between external radiation and disc degeneration, but the mechanism was poorly understood. This study explores the effects of ionizing radiation (IR) on inducing cellular senescence of annulus fibrosus (AF) in cell culture and in an in vivo mouse model. Exposure of AF cell culture to 10-15 Gy IR for 5 min followed by 5 days of culture incubation resulted in almost complete senescence induction as evidenced by SA-beta gal positive staining of cells and elevated mRNA expression of the p16 and p21 senescent markers. IR-induced senescent AF cells exhibited increased matrix catabolism, including elevated matrix metalloproteinase (MMP)-1 and -3 protein expression and aggrecanolysis. Analogous results were seen with whole body IR-exposed mice, demonstrating that genotoxic stress also drives disc cellular senescence and matrix catabolism in vivo. These results have important clinical implications in the potential adverse effects of ionizing radiation on spinal health.