Study on the mechanism of excessive apoptosis of nucleus pulposus cells induced by shRNA-Piezo1 under abnormal mechanical stretch stress.

Objective The aim of the study was to explore the mechanism of excessive apoptosis of nucleus pulposus cells induced by short hairpin RNA (shRNA) Piezo type mechanosensitive ion channel component 1 (Piezo1) under abnormal mechanical stretch stress. Methods In vitro mechanical stretch stress model of nucleus pulposus cells in vitro was established, in which the expression of Piezo1 was interfered by transfection of shRNA-Piezo1 interfering vector. Both messenger RNA and protein level of Piezo1 were measured by reverse-transcription polymerase chain reaction and Western blot analysis, respectively. Cytoplasmic Ca2+ was detected by Fluo3-AM kit, and changes of mitochondrial membrane potential in cells were detected using Cell Meter Assay kit. Finally, the apoptosis was evaluated with annexin V-fluorescein isothiocyanate kit. Results The highest transfection efficiency of lentivirus titer was 1 x 10 TU/mL and the nucleus pulposus cells were transfected with plural multiplicity of infection = 50. Homo-3201 sequence exhibited the most effective silencing effect and was used in subsequent experiments as the default sequence of shRNA-Piezo1. The calcium content in the cytoplasm of the tension stress group increased significantly compared with that in the blank control group (q = 3.773; P < 0.05). The level of cytosolic calcium in shRNA-interference group was significantly lower than that in stretch stress group (q = 5.159; P < 0.05). Stretch stress treatment resulted in an elevated ratio of mitochondrial membrane potential turnover as opposed to blank control group (q = 4.332; P < 0.05), while shRNA-interference group showed smaller ratio of mitochondrial membrane potential turnover than that in stretch stress group (q = 4.974; P < 0.05). Similar results were also observed in apoptosis rate analysis (q = 3.175; P < 0.05). Conclusion ShRNA-Piezo1 can protect cells by reducing the level of intracellular Ca2+ and the change of mitochondrial membrane potential.