Downregulation of microRNA-125a is involved in intervertebral disc degeneration by targeting pro-apoptotic Bcl-2 antagonist killer 1

OBJECTIVE(S): To investigate the role of the microRNA-125a (miR-125a) and BAK1 in intervertebral disc degeneration (IDD). MATERIALS AND METHODS: Degenerative lumbar nucleus pulposus (NP) tissues were obtained from 193 patients who underwent resection, and normal controls consisted of normal NP tissues from 32 patients with traumatic lumbar fracture in our hospital. All patients were graded according to the Pfirrmann criteria. QRT-PCR was used to detect the expression of miR-125a and BAK1, and apoptosis of NP tissues detected by TUNEL staining. After isolation of non- degenerative and degenerative nucleus pulposus cells (NPCs), the targeting relationship between miR-125a and BAK1 was verified by dual luciferase reporter gene assay. Flow cytometry was determined the NPCs apoptosis, and Western blot to measure the expressions of BAK1, Caspase-3, Bax and Bcl-2. RESULTS: MiR-125a was reduced while BAK1 was elevated in IDD patients with the increase of Pfirrmann grade. Besides, miRNA-125a was negatively correlated to the NPCs apoptosis, while BAK1 mRNA was positively correlated to cell apoptosis. Additionally, BAK1 is the target gene of miRNA-125a. When transfection of miR-125a mimics in vitro, the apoptosis of NPCs were inhibited, with the down-regulation of BAK1, Caspase-3, and Bax, and the upregulation of Bcl-2. In addition, siBAK1 can reverse the pro-apoptosis function of miR-125a inhibitors in NPCs. CONCLUSION: miRNA-125a may regulate the apoptosis status of the NPCs by inhibiting the expression of its target gene BAK1, which provided a potential strategy for further development of IDD therapies.