Major arc mitochondrial DNA deletions in cytochrome c oxidase-deficient human cochlear spiral ganglion cells

Abstract

Conclusions: This study suggests that cytochrome c oxidase subunit 3 (COX 3) expression is diminished in spiral ganglion cells from individuals with presbycusis. In addition to the mitochondrial DNA (mtDNA) common deletion (CD), other deletions involving the mtDNA major arc contribute to the observed deficit in COX 3 expression. Objectives: To assess COX 3 deficiency in spiral ganglion cells from individuals with presbycusis and to determine whether deletions other than the CD contribute to this deficiency. Methods: COX 3 immunofluorescence staining of archival human temporal bone tissue sections from individuals with presbycusis and from age-matched normal-hearing individuals was performed and the intensity of spiral ganglion cell immunostaining was measured. Single COX 3-deficient spiral ganglion cells were isolated by laser microdissection (LMD) and the DNA was analyzed with duplex real-time PCR assays to assess the CD level and the total mtDNA major arc deletion level. Results: A statistically significant difference (p = 0.021) in the mean intensity of COX 3 immunofluorescence staining of spiral ganglion cells was observed between individuals with presbycusis and normal-hearing controls. The total mtDNA major arc deletion level was greater than the CD level in COX 3-deficient spiral ganglion cells.

Keywords::

• Presbycusis
• human temporal bones
• laser microdissection

Acknowledgments

This work was supported by the Bloom Temporal Bone Laboratory Endowment and a 2009 Deafness Research Foundation Grant to A.M. We appreciate the participation of Dr Vytas Bindokas at the University of Chicago Microscopy Core Facility and Kristen E. Wroblewski, MS, from the University of Chicago Department of Health Studies, for the statistical analysis of the data in this study. mtDNA from cybrid cell lines was provided by Dr Eric A. Schon at Columbia University, New York.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.