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


OBJECTIVE
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.
Jeong
Sung-Wook
SW
Department of Otolaryngology-Head and Neck Surgery, College of Medicine, Dong-A University, Busan, Korea.
Kim
Lee-Suk
LS
Hur
Daeyoung
D
Bae
Woo-Yong
WY
Kim
Jae-Ryong
JR
Lee
Jae-Hoon
JH
D000818:Animals; D000900:Anti-Bacterial Agents / Q000633:toxicity*; D017209:Apoptosis / Q000187:drug effects*; D053222:Fas Ligand Protein / Q000502:physiology*; D005839:Gentamicins / Q000633:toxicity*; D006168:Guinea Pigs; D006198:Hair Cells, Auditory / Q000187:drug effects / Q000473:pathology; D020287:In Situ Nick-End Labeling; D048031:JNK Mitogen-Activated Protein Kinases / Q000502:physiology*; D016133:Polymerase Chain Reaction; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D013136:Spiral Ganglion / Q000187:drug effects* / Q000473:pathology
D000900:Anti-Bacterial Agents; D053222:Fas Ligand Protein; D005839:Gentamicins; D017382:Reactive Oxygen Species; D048031:JNK Mitogen-Activated Protein Kinases