Abstract
Auditory dysfunction is the most prevalent injury associated with blast overpressure exposure (BOP) in Warfighters and civilians, yet little is known about the underlying pathophysiological mechanisms. To gain insights into these injuries, an advanced blast simulator was used to expose rats to BOP and assessments were made to identify structural and molecular changes in the middle/inner ears utilizing otoscopy, RNA sequencing (RNA-seq), and histopathological analysis. Deficits persisting up to 1 month after blast exposure were observed in the distortion product otoacoustic emissions (DPOAEs) and the auditory brainstem responses (ABRs) across the entire range of tested frequencies (4–40 kHz). During the recovery phase at sub-acute time points, low frequency (e.g. 4–8 kHz) hearing improved relatively earlier than for high frequency (e.g. 32–40 kHz). Perforation of tympanic membranes and middle ear hemorrhage were observed at 1 and 7 days, and were restored by day 28 post-blast. A total of 1,158 differentially expressed genes (DEGs) were significantly altered in the cochlea on day 1 (40% up-regulated and 60% down-regulated), whereas only 49 DEGs were identified on day 28 (63% up-regulated and 37% down-regulated). Seven common DEGs were identified at both days 1 and 28 following blast, and are associated with inner ear mechanotransduction, cytoskeletal reorganization, myelin development and axon survival. Further studies on altered gene expression in the blast-injured rat cochlea may provide insights into new therapeutic targets and approaches to prevent or treat similar cases of blast-induced auditory damage in human subjects.
Highlights
Auditory dysfunction is the most prevalent injury associated with blast overpressure exposure (BOP) in Warfighters and civilians, yet little is known about the underlying pathophysiological mechanisms
Inner ear hemorrhage was not detected at 4 h, but was clearly visible at 1 and 7 days using a dissecting microscope under 20 × magnification (Fig. 1B)
Some genes have been well studied in the development of the middle and inner ear (Gsc) and cochlear hair cells (Atoh[1], Pou4f3 and Myo7A), we found that their readcounts were 0–30 and failed here to be identified by RNA sequencing (RNA-seq) analysis
Summary
Auditory dysfunction is the most prevalent injury associated with blast overpressure exposure (BOP) in Warfighters and civilians, yet little is known about the underlying pathophysiological mechanisms. Middle ear injuries can often be surgically repaired, but structural damage to the inner ear may have a limited ability to recover, due to death of specific associated neuronal cell types, such as hair cells and ganglion cells that can lead to permanent hearing deficits[16,17,18]. Our present study aimed to determine the molecular events in the inner ear along with structural changes in the middle ear that are associated with auditory functional deficits after blast exposure. We have employed RNA-sequencing (RNA-seq), quantitative real-time polymerase chain reaction (qRT-PCR), histopathology and functional assessments to provide a comprehensive profile of post-blast of auditory injury, repair, short- and long-term maladaptive responses
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