The most prominent changes are the loss of sensory hair cells and spiral ganglion neurons (SGNs Makary et al., 2011). Traditionally, ARHL was classified into different types based on distinctive pathological changes of the cochlea and the altered audiogram ( Schuknecht, 1964 Johnsson and Hawkins, 1972 Schuknecht and Gacek, 1993). Its prevalence is expected to continue to climb given an increasing aging population ( US Census Bureau, 2014). Our study suggests that during normal aging, chronic inflammation occurs in both the peripheral and the central auditory system, which may contribute in coordination to the development of ARHL.Īge-related hearing loss (ARHL) is among the most common ailments in the aging population, affecting one in three people over the age of 60 and greater than one in two people over the age of 75 ( Lin et al., 2011). During the process, we further identified significant increases in microglial activation and C1q deposition in the CN, indicating increased neuroinflammation and complement activation in the central auditory system. We found progressive increases in the area covered by Iba1-labeled macrophages and enhanced CD68 staining in the osseous spiral lamina of the cochlea that correlated with elevated ABR threshold across the lifespan. Using immunohistochemistry, confocal microscopy, and quantitative image processing, we measured the accumulation and activation of macrophages in the cochlea and microglia in the CN using their shared markers: ionized calcium binding adaptor molecule 1 (Iba1) and CD68-a marker of phagocytic activity. To address this, we investigated chronic inflammation in both the cochlea and the cochlear nucleus (CN) of CBA/CaJ mice, an inbred mouse strain that undergoes normal aging and develops human, like-late-onset ARHL. However, it remains elusive how chronic inflammation progresses during normal aging in the cochlea, and especially the accompanying changes of neuroinflammation in the central auditory system. Low-grade inflammation was observed in the cochlea of deceased human subjects with ARHL and animal models of early onset ARHL, which suggests that inflammation contributes to the development of ARHL. 2Department of Neuroscience, The Ohio State University, Columbus, OH, United StatesĪge-related hearing loss (ARHL) is a major hearing impairment characterized by pathological changes in both the peripheral and central auditory systems.1Department of Otolaryngology-Head and Neck Surgery, The Ohio State University, Columbus, OH, United States.
Seicol 1,2, Shengyin Lin 1 and Ruili Xie 1,2*
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