BNIP3/Bcl-2-mediated apoptosis induced by cyclic tensile stretch in human cartilage endplate-derived stem cells

The present study aimed to investigate the molecular mechanisms of cyclic stretch-induced apoptosis in human intervertebral disc cartilage endplate-derived stem cells (CESCs). CESCs were stretched by the Flexercell-4000^™ Tension Plus system, the effect on cell viability was measured by a Cell Counting Kit-8 assay, while cell apoptosis was detected by flow cytometry. Western blot analysis was used to evaluate the expression of B-cell lymphoma 2 (Bcl-2)/adenovirus E1B 19 kDa interacting protein 3 (BNIP3), Bcl-2, Bcl-2 homologous antagonist killer (Bak), Bcl-2-associated X protein (Bax), Bcl extra large (Bcl-xl) and the activity of caspase-3, while Z-VAD-FMK was used to inhibit caspase-3. Compared with the control group, the cell viability decreased in a time-dependent manner after stretching. Furthermore, cell apoptosis and the activity of caspase-3 were increased in a time-dependent manner. The ratio of pro-death factor BNIP3 to anti-apoptotic protein Bcl-2 was significantly increased. When cells were stretched for 36 h, the apoptosis-associated proteins Bak and Bax were increased, while Bcl-xl was decreased. The viability and apoptotic ratio of stretched cells were significantly restored after caspase-3 was repressed. In conclusion, cyclic tensile stretch induced apoptosis of CESCs, which was probably due to upregulation of the expression of BNIP3.