A novel model for rapid induction of apoptosis in spiral ganglions of mice.
OBJECTIVE
The survival of the spiral ganglion (SG) is a critical issue in preservation of hearing. Research on topics related to this issue requires a mouse experimental model because such a model has advantages including use of genetic information and knockout or "knockin" mice. Thus, the aim of the study was to establish a mouse model for induction of apoptosis of SG neurons with a definite time course.


METHODS
Laboratory study using experimental animals.


METHODS
C57BL/6 mice were used as experimental animals and were subjected to direct application of cisplatin into the inner ear. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay and immunostaining for Neurofilament 200-kD (NF) and peripherin were used for analysis of SG degeneration. In addition, generation of peroxynitrite in affected spiral ganglions was examined by immunostaining for nitrotyrosine. Cellular location of activated caspase-9 and cytochrome-c in dying SG neurons were examined for analysis of cell death pathway.


RESULTS
The TUNEL assay and immunohistochemical analysis for NF and peripherin indicated that type I neurons in spiral ganglions were deleted through the apoptotic pathway over time. Spiral ganglion neurons treated with cisplatin exhibited expression of nitrotyrosine, indicating induction of peroxynitrite by cisplatin. In dying SG neurons, expression of activated caspase-9 and translocation of cytochrome-c from mitochondria to cytoplasm were observed, indicating the mitochondrial pathway of apoptosis.


CONCLUSIONS
The predictable fashion of induction of apoptosis in SG neurons over a well-defined time course in the model in the study will aid studies of the molecular mechanism of cell death and elucidation of a strategy for prevention of SG degeneration.
Lee
Ji Eun
JE
Department of Otolaryngology-Head and Neck Surgery, Graduate School of Medicine, Kyoto University, Japan.
Nakagawa
Takayuki
T
Kim
Tae Soo
TS
Iguchi
Fukuichiro
F
Endo
Tsuyoshi
T
Dong
Youyi
Y
Yuki
Kazuo
K
Naito
Yasushi
Y
Lee
Sang Heun
SH
Ito
Juichi
J
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D016923:Cell Death / Q000187:drug effects; D002945:Cisplatin / Q000633:toxicity; D004195:Disease Models, Animal; D020287:In Situ Nick-End Labeling; D007381:Intermediate Filament Proteins / Q000032:analysis; D008562:Membrane Glycoproteins; D051379:Mice; D008810:Mice, Inbred C57BL; D008856:Microscopy, Fluorescence; D009410:Nerve Degeneration / Q000139:chemically induced / Q000473:pathology*; D009419:Nerve Tissue Proteins / Q000032:analysis; D009474:Neurons / Q000187:drug effects / Q000473:pathology; D064531:Peripherins; D030421:Peroxynitrous Acid / Q000032:analysis; D013136:Spiral Ganglion / Q000187:drug effects / Q000473:pathology*; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000032:analysis
D007381:Intermediate Filament Proteins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D064531:Peripherins; D030421:Peroxynitrous Acid; C002744:3-nitrotyrosine; D014443:Tyrosine; D002945:Cisplatin