Gentamicin-induced spiral ganglion cell death: Apoptosis mediated by ROS and the JNK signaling pathway

Conclusion: Reactive oxygen species (ROS) and the c-Jun N-terminal kinase (JNK) signaling pathway may be involved in secondary apoptosis of spiral ganglion cells (SGCs) induced by intracochlear gentamicin injection. Objectives: The purpose of this study was to ascertain the role of ROS and the JNK signaling pathway in secondary apoptosis of SGCs induced by intracochlear gentamicin treatment. Methods: Gentamicin (40 mg/ml) was injected into the cochlea of guinea pigs (n = 18) to destroy the hair cells and induce secondary apoptosis of SGCs. At 1 (n = 6), 2 (n = 6), and 3 (n = 6) weeks after gentamicin treatment, the cochleas were removed and stained with hematoxylin and eosin, and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling to observe the morphologic changes and apoptosis of SGCs. A dihydroethidium (DHE) assay was performed to detect ROS generation, and RT-PCR and Western blot analysis were used to assess the expression of Fas ligand (FasL), JNK, and c-Jun. Results: After gentamicin was injected into the cochlea, apoptosis and progressive loss of SGCs were observed. RT-PCR and Western blot analysis showed increased expression of FasL after gentamicin treatment. ROS generation detected by DHE fluorescence increased progressively, and the expression of JNK, phospho-JNK, c-Jun, and phospho-c-Jun also increased.