Nuclear translocation of the pro-apoptotic protein BNIP3 in cultured spiral ganglion cells of rat with cisplatin insult

Abstract

To observe spiral ganglion cell (SGC) death pattern caused by cisplatin and investigate pro-apoptotic protein BNIP3 involvement in SGC death. Cochlear SGC were isolated from the neonatal rats and cultured in vitro. A cochleas insult model were induced by treatment of 100 µmol/L cisplatin. Real-time PCR were used to determine expression of apoptosis related gene in neonatal rat cochlear cultures after cisplatin treatment. Western blotting was used to detect α-spectrin and indirectly determine caspase-3 activity. Double immunohistochemical staining method was performed to indicated the localization and expression of BNIP3 and NF-200. Morphological finding showed that SGC were smaller, and neurofiber were blebbing and broken at treatment of cisplatin for 12 h. NF-200 marker positive cell number decreased. The transcription level of BNIP3 in cisplatin treatment for 3 h, 6 h and 12 h was higher than the control group (P < 0.05). Western blotting results showed that 120 000 of breakdown products of α-spectrin relative gray level were 0.10 ± 0.05 in the control group, 0.49 ± 0.09 and 0.75 ± 0.08 in cisplatin treatment for 6 h and 12 h group. It increased significantly in the group of cisplatin treatment for 6 h and 12 h than the control group (q = 8.63 and 14.61, P < 0.01). When compared between 6 h of cisplatin treatment and 12 h group, significant difference was detected (q = 5.98, P < 0.05). There was weak BNIP3 positive expression in cytoplasm of the control group. However, strongly BNIP3-positive labeled were seen in the nucleus of SGC and cytoplasm of some stromal cells around SGC after cisplatin treatment. BNIP3 played an important role in cisplatin induced SGC death and followed independent signaling transduction pathway that differ from stromal cells around SGC. It may suggest that BNIP3 enter nucleus to bind DNA and up-regulate apoptotic gene expression to promote cells death.