Abstract
The etiology of hearing impairment following cochlear damage can be caused by many factors, including congenital or acquired onset, ototoxic drugs, noise exposure, and aging. Regardless of the many different etiologies, a common pathologic change is auditory cell death. It may be difficult to explain hearing impairment only from the aspect of cell death including apoptosis, necrosis, or necroptosis because the level of hearing loss varies widely. Therefore, we focused on autophagy as an intracellular phenomenon functionally competing with cell death. Autophagy is a dynamic lysosomal degradation and recycling system in the eukaryotic cell, mandatory for controlling the balance between cell survival and cell death induced by cellular stress, and maintaining homeostasis of postmitotic cells, including hair cells (HCs) and spiral ganglion neurons (SGNs) in the inner ear. Autophagy is considered a candidate for the auditory cell fate decision factor, whereas autophagy deficiency could be one of major causes of hearing impairment. In this paper, we review the molecular mechanisms and biologic functions of autophagy in the auditory system and discuss the latest research concerning autophagy-related genes and sensorineural hearing loss to gain insight into the role of autophagic mechanisms in inner-ear disorders.
Highlights
Cells are continuously exposed to various stresses, including both extracellular oxidative stress as well as intracellular endoplasmic reticulum (ER) stress
These results suggested that the lysosome function via TFEB in autophagy–lysosome fusion step plays an essential role for restoring spiral ganglion neurons (SGNs) and nerve fiber degradation
We summarized the effects of the autophagy process on the genetics of hearing impairment and autophagy–lysosomal function-related genes for hearing impairment (Figure 4)
Summary
Cells are continuously exposed to various stresses, including both extracellular oxidative stress as well as intracellular endoplasmic reticulum (ER) stress. A higher production of ROS may change DNA structure, resulting in cell death, including apoptosis, necrosis, and necroptosis or cellular senescence. Genes 2020, 11, 1331 loss only from the aspect of cell death, apoptosis, necroptosis, or necrosis at the cellular level. Since the autophagic process controls auditory cell fate, protecting against hearing impairment, autophagy-related genes could potentially hold the key to the genetics of hearing impairment. To the best of our knowledge, there is no review article describing the effects of the autophagy process on the genetics of hearing impairment and autophagy–lysosomal function-related genes for hearing impairment. The first part describes the mechanisms and biologic functions of autophagy as a decision factor in auditory cell fate and the role of autophagy in the auditory system (or hearing), while the second part focuses on the relationship between autophagy (elongation and completion steps)- and lysosomal function (fusion step)-related genes and hearing loss, congenital disorder of autophagy with hearing loss, and the effect of autophagy for genetics of hearing loss
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