Immunocytochemical localization of the translocase of the outer mitochondrial membrane (Tom20) in the human cochlea.

Mitochondrial degeneration in the inner ear is likely a contributing factor in age-related hearing loss and other otopathologies such as Meniere's disease. Most mitochondrial proteins are synthesized in the cytosol and imported through the mitochondrial membranes by translocators. The translocase of the outer membrane (Tom) is the universal entry gate for all proteins that are imported into mitochondria. Altered function of the translocator could alter protein transport into the mitochondria, and disrupt function. In this study, we determined the immunolocalization of Tom20, a major mitochondrial protein import receptor, in microdissected human cochlea frozen sections obtained from postmortem autopsy and celloidin-embedded archival specimens. We used affinity purified rabbit polyclonal antibodies against Tom20. We also determined the Tom20 immunolocalization in the mouse inner ear. In the human and mouse cochlea, Tom20 was ubiquitously distributed in the organ of Corti, allowing well-delineated visualization of inner and outer hair cells. Tom20 immunoreactivity localized in the cytoplasm of spiral ganglia neurons. In the inner ear of aged subjects with Meniere's disease, there was decreased expression of Tom20. These results suggest that Tom20 can be used in the inner ear as a marker for mitochondrial protein import.