Inner Ear Tissue Remodeling and Ion Homeostasis Gene Alteration in Murine Chronic Otitis Media

Abstract

Hypothesis Studies were designed to ascertain the impact of chronic middle ear infection on the numerous ion and water channels, transporters and tissue remodeling genes in the inner and middle ear. Background Permanent sensorineural hearing loss is a significant problem resulting from chronic middle ear disease, although the inner ear processes involved are poorly defined. Maintaining a balanced ionic composition of endolymph in the inner ear is crucial for hearing, thus, it was hypothesized this may be at risk with inflammation. Methods Inner and middle ear RNA collected separately from 6 month-old C3H/HeJ mice with prolonged middle ear disease were subjected to qRT-PCR for 8 common inflammatory cytokine genes, 24 genes for channels controlling ion (sodium, potassium, chloride) and water (aquaporin) transport, tight junction claudins, and gap junction connexins, and 32 tissue remodeling genes. Uninfected Balb/c mice were used as controls. Results Significant increase in inner ear inflammatory and ion homeostasis (claudin, aquaporin and gap junction) gene expression, and both up- and down-regulation of tissue remodeling gene expression occurred. Alteration in middle ear ion homeostasis and tissue remodeling gene expression was noted in the setting of uniform upregulation of cytokine genes. Conclusions Chronic inflammatory middle ear disease can impact inner ear ion and water transport functions and induce tissue remodeling. Recognizing these inner ear mechanisms at risk may identify potential therapeutic targets to maintain hearing during prolonged otitis media.

Correlative mRNA and protein expression of middle and inner ear inflammatory cytokines during mouse acute otitis media

“…This would have an impact on K + ion transport and its recycling into endolymph. It also is now known that numerous genes related to tight junctions, gap junctions, aquaporins, and Cl − , K + and Na + transport are also compromised in the inner ear following middle ear inflammation (MacArthur et al, 2013a; MacArthur et al, 2013b). This parallels findings in other tissues that ion homeostasis is compromised by inflammation (Eisenhut, 2006; Al-Sadi and Ma, 2007; Choi et al, 2007; Peng et al, 2012; Petecchia et al, 2012) Therefore, not only is endolymph production and maintenance at risk, but also the endothelial cell tight junctions that are necessary for preservation of the blood labyrinth barrier (Danese et al, 2007; Lemichez et al, 2010; Trune and Canlon, 2012).…”

“…Numerous genes involving growth factors, bone morphogenetic proteins, and matrix metalloproteinases are affected in both the middle ear and inner ear during middle ear disease (MacArthur et al, 2006; Sautter et al, 2011; MacArthur et al, 2013a; MacArthur et al, 2013b). Thus, significant connective tissue and bone reorganization in the inner ear follows acute and chronic middle ear disease.…”

“…However, the mechanisms underlying the transient and permanent sensorineural hearing loss in OM are poorly defined. Previous DNA array screening studies showed cytokine genes are upregulated in the cochleas of BALB/c mice given transtympanic heat-killed bacteria and in cochleas of C3H/HeJ mice with chronic middle ear inflammation (Ghaheri et al, 2007; Ghaheri et al, 2007; MacArthur et al, 2011; Tokarz et al, 2013; MacArthur et al, 2013b). These inflammatory cytokines are predominantly distributed in the cochlear lateral wall as inoculation of middle ears with bacterial components also causes decrease in cochlear blood flow, stria vascularis damage, cytokine expression by spiral ligament fibrocytes, and decreased auditory function (Ichimiya et al, 2003; Sone et al, 2003; MacArthur and Trune, 2006; Moon et al, 2006; Moon et al, 2007; Tsuprun et al, 2008; Woo et al, 2010; Oh et al, 2012).…”

Intratympanic Steroid Treatments May Improve Hearing via Ion Homeostasis Alterations and Not Immune Suppression

“…We have run our own standardization comparisons with other potential housekeeping genes (Mouse 18SrRNA, actin beta, beta-2 microglobulin, glucuronidase beta, lactate dehydrogenase A-like 6B, ribosomal protein L13a, heat shock protein 90 alpha class B member 1, among others) and find this the most consistent and reliable. Its use also permits comparisons with other qRT-PCR results published by our laboratory 1,2,18 …”

“…Cytokine genes were also chosen for analysis in this study and include eight key inflammation related cytokines (IL-1α, IL-1β, IL-6, IL-10, CCl3, Cxcl2, CxCl1, and TNFα). These genes have been shown to be very active in the mouse model of otitis media in both the middle and inner ear 1,2,18,20 . Therefore, they were chosen to measure the inner ear inflammatory response to a middle ear steroid injection.…”