Hearing loss is a prevalent problem with age, the result of loss of sensory hair cells of the inner ear, or as seems more likely in recent years, damage to those parts of the peripheral nervous system connecting hair cells to the brain. Chronic inflammation is a noted aspect of aging, excessive activity of the immune system, and is very disruptive to tissue function and maintenance throughout the body. Researchers here provide evidence to suggest that this persistent inflammation in older individuals is an important factor in age-related hearing loss.
Age-related hearing loss (AHL) or presbycusis is a universal sensory disorder in modern society and affects about 25-40% of people over 65 years. The underlying mechanisms of AHL include oxidative stress, mitochondrial DNA mutations, autophagy impairment, and non-coding RNA disorders. However, the mechanism of cochlear degeneration during aging is still not fully understood. In recent years, the effects of inflammation on aging-related disorders have been extensively investigated. During aging, the body suffers from chronic low-grade inflammation, a phenomenon also referred to as "inflammaging". Chronic inflammation is a consequence of immunosenescence, the aging of the immune system, and is primarily characterized by increased levels of proinflammatory cytokines in response to various stressors. However, only little research on the potential role of inflammation in AHL has been reported.
The current study was designed to determine the transcriptional changes of cochlear genes and the most significantly affected functions and pathways during aging in C57BL/6 mice using next generation sequencing. Our RNA-sequencing data revealed that transcripts associated with aging, apoptosis, and necroptosis were significantly modulated in aged cochleae. Importantly, numerous genes related to immune responses and inflammation were differentially expressed during aging. Bioinformatics analysis of the upregulated genes also revealed that a large portion of biological processes and pathways are related to immune and inflammatory pathways, such as complement system and macrophage activation. Whereas, lots of the downregulated genes are involved in biological processes and pathways associated with ion channel function and neuronal signaling. These findings suggest chronic inflammation may be associated with aging-related cochlear degeneration.