Correlation of cochlear blood supply with mitochondrial DNA common deletion in presbyacusis

Objective-To study the relationships between cochlear hypoxia, mitochondrial (mt) DNA(4977) deletion and metabolic features of mtDNA in presbyacusis. Material and Methods-Sixty-seven temporal bones from a presbyacusis group, an age-matched control group and a young and middle-aged control group were involved in the experiment. Nested and tri-nested polymerase chain reactions (PCRs) were applied to test for the presence of the mtDNA(4977) deletion. Computer imaging processing was used to measure blood vessel parameters in the internal acoustic meatus (IAM). Results-The mtDNA(4977) deletion was detected in 17/34 cars in the presbyacusis group, 4/19 ears in the age-matched control group and 0/14 cars in the young and middle-aged control group. In the presbyacusis group, the lumen of the vasa nervorum of the IAM showed a more severe narrowing in cases with than without the mtDNA(4977) deletion. Conclusion-The high incidence of the mtDNA(4977) deletion in the temporal bones of presbyacusis patients suggests a correlation between the mtDNA(4977) deletion and presbyacusis. Hypoxia of the cochlea may cause the mtDNA(4977) deletion and other mtDNA mutants and furthermore may cause a reduction in mitochondrial oxidative phosphorylation and decreased function of the acoustic neural system. The symptoms of presbyacusis may occur when the function of the acoustic neural system is impaired Lis a result of abnormal mtDNA metabolism reaching a particular threshold.