Somatic mtDNA mutations cause progressive hearing loss in the mouse

Mitochondrial dysfunction has been implicated in the commonly occurring age-associated hearing loss (presbyacusis). We have previously generated mtDNA mutator mice with increased levels of somatic mtDNA point mutations causing phenotypes consistent with premature ageing. We have now utilized these mice to investigate whether elevated levels of somatic mtDNA mutations affect the auditory system. The mtDNA mutator mice develop a progressive impairment of hearing (ABR thresholds). Quantitative assessment of hair cell loss in the cochlea did not show any significant difference between the mutator and wild-type mice. The mtDNA mutator mice showed progressive apoptotic cell loss in the spiral ganglion and increased pathology with increasing age in the stria vascularis. The neurons in the cochlear nucleus showed an accelerated progressive degeneration with increasing age in the mutator mice compared to the wild-type mice. Both physiological and histological characterization thus reveals a striking resemblance between the auditory system pathology of mtDNA mutator mice and humans with presbyacusis. Somatic mtDNA mutations accumulate during normal ageing and further studies in humans are now warranted to investigate whether presbyacusis can be linked to mitochondrial dysfunction.