ANALYSIS OF GENES AND PROTEINS RELATED TO COCHLEAR DAMAGE USING DNA MICROARRAY AND PROTEOMICS

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We generated a PolgD257A/D257A (D257A) mutant mouse (a transgenic mouse in which point mutations were introduced into exonuclease domain (Proof Reading activity domain) of DNA polymerase gamma) as a presbycusis animal model. The D257A mouse exhibited ABR threshold shifts of an average of 41-52 dBSPL at the age of 9 month, whereas no ABR threshold shifts were observed in a wild type mouse at this age, indicating that hearing loss appeared by aging early in D257A mouse. Histologically, this mutant mouse exhibited severe degeneration of the cochlear hair cells and spiral ganglion cells. DNA microarray analysis of their cochleae showed a decrease in genes related to sound perception, neurotransmission, ion metabolism, energy metabolism, DNA synthesis, and DNA repair and an increase in genes related to inflammation and apoptosis. We also generated another animal model showing mitochondria dysfunction by feeding CBA mouse with germanium dioxide. Within 3 months from starting the germanium fe … More eding, this mouse developed profound hearing loss and severe degeneration of the stria vascularis and an organ of Corti, and DNA microarray analysis revealed gene expression changes similar to those observed in D257A mouse. In another experiment, we examined whether caloric restriction (CR) could prevent presbycusis in C57BL/6 mouse, a presbycusis model mouse. The C57BL/6 mouse not subjected to CR developed hearing loss and degeneration of the cochlear tissues by the age of 17 months, and CR prevented the manifestation of hearing loss and cochlear degeneration until this age. DNA microarray analysis of the cochlea in C57BL/6 mouse both subjected and not subjected to CR revealed that CR prevented age-related changes of gene expression, such as a decrease of genes related to sound perception, neurotransmission, and energy metabolism, and an increase of genes related to inflammation and apoptosis. We confirmed the expression changes of several important genes by means of real time RT-PCR analysis and their related proteins by performing immunohistochemistry. Finally, we did DNA microarray analysis for mouse exposed to intense sound and are currently doing detailed analysis for several genes that are considered keys in the manifestation of noise0-induced hearing loss. Less