Quantitative measure of mitochondrial DNA deletions in different tissue in wistar rats

Objective: To determine if there is a different mitochondrial DNA （mtDNA） deletion level in different wistar rat tissues, and if the mtDNA is involved in the aging and the development of presbycusis. Methods: Wistar rats from 3 age groups were used. All animals were tested for auditory sensitivity using the auditory brainstem response （ABR）. The cochlea, cochlear nucleus, brain, heart, liver, temporal muscle and blood were harvested and the total DNA was extracted. The presence of mtDNA⁴⁸³⁴ deletions, corresponding to mtDNA⁴⁹⁷⁷ deletions in human, was examined using polymerase chain reaction （PCR）, and the mtDNA⁴⁸³⁴ deletions were quantitated. Results: ①The results showed a progressive reduction in auditory sensitivity with aging.②The mtDNA⁴⁸³⁴ deletion was detected in an age-related manner in all tissues screened except blood.③There was a significant increase in the presence of the mtDNA⁴⁸³⁴ deletions in the aged subjects compared with the young subjects （i>P＜0.01）.④Quantitative measure showed the mtDNA⁴⁸³⁴ deletion level is an age-related manner in all tissues and different tissues have different deletion level. The mtDNA⁴⁸³⁴ deletion was found to be at its highest level in the liver, followed by the brain of old animals. Conclusions: These findings indicated that the mtDNA deletion is associated with presbycusis, as well as with aging, and the mtDNA deletion is heterogeneous.