Spiral ligament fibrocyte-derived MCP-1/CCL2 contributes to inner ear inflammation secondary to nontypeable H. influenzae-induced otitis media

<p>Abstract</p> <p>Background</p> <p>Otitis media (OM), one of the most common pediatric infectious diseases, causes inner ear inflammation resulting in vertigo and sensorineural hearing loss. Previously, we showed that spiral ligament fibrocytes (SLFs) recognize OM pathogens and up-regulate chemokines. Here, we aim to determine a key molecule derived from SLFs, contributing to OM-induced inner ear inflammation.</p> <p>Methods</p> <p>Live NTHI was injected into the murine middle ear through the tympanic membrane, and histological analysis was performed after harvesting the temporal bones. Migration assays were conducted using the conditioned medium of NTHI-exposed SLFs with and without inhibition of MCP-1/CCL2 and CCR2. qRT-PCR analysis was performed to demonstrate a compensatory up-regulation of alternative genes induced by the targeting of MCP-1/CCL2 or CCR2.</p> <p>Results</p> <p>Transtympanic inoculation of live NTHI developed serous and purulent labyrinthitis after clearance of OM. THP-1 cells actively migrated and invaded the extracellular matrix in response to the conditioned medium of NTHI-exposed SLFs. This migratory activity was markedly inhibited by the viral CC chemokine inhibitor and the deficiency of MCP-1/CCL2, indicating that MCP-1/CCL2 is a main attractant of THP-1 cells among the SLF-derived molecules. We further demonstrated that CCR2 deficiency inhibits migration of monocyte-like cells in response to NTHI-induced SLF-derived molecules. Immunolabeling showed an increase in MCP-1/CCL2 expression in the cochlear lateral wall of the NTHI-inoculated group. Contrary to the <it>in vitro </it>data, deficiency of MCP-1/CCL2 or CCR2 did not inhibit OM-induced inner ear inflammation <it>in vivo</it>. We demonstrated that targeting MCP-1/CCL2 enhances NTHI-induced up-regulation of MCP-2/CCL8 in SLFs and up-regulates the basal expression of CCR2 in the splenocytes. We also found that targeting CCR2 enhances NTHI-induced up-regulation of MCP-1/CCL2 in SLFs.</p> <p>Conclusions</p> <p>Taken together, we suggest that NTHI-induced SLF-derived MCP-1/CCL2 is a key molecule contributing to inner ear inflammation through CCR2-mediated recruitment of monocytes. However, deficiency of MCP-1/CCL2 or CCR2 alone was limited to inhibit OM-induced inner ear inflammation due to compensation of alternative genes.</p

The Deaf Mouse Mutant Jeff (Jf) is a Single Gene Model of Otitis Media

Otitis media is the most common cause of hearing impairment in children and is primarily characterized by inflammation of the middle ear mucosa. Yet nothing is known of the underlying genetic pathways predisposing to otitis media in the human population. Increasingly, large-scale mouse mutagenesis programs have undertaken systematic and genome-wide efforts to recover large numbers of novel mutations affecting a diverse array of phenotypic areas involved with genetic disease including deafness. As part of the UK mutagenesis program, we have identified a novel deaf mouse mutant, Jeff (Jf). Jeff maps to the distal region of mouse chromosome 17 and presents with fluid and pus in the middle ear cavity. Jeff mutants are 21% smaller than wild-type littermates, have a mild craniofacial abnormality, and have elevated hearing thresholds. Middle ear epithelia of Jeff mice show evidence of a chronic proliferative otitis media. The Jeff mutant should prove valuable in elucidating the underlying genetic pathways predisposing to otitis media