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Macrophages in the cochlea; an immunological link between risk factors and progressive hearing loss

Macrophages in the cochlea; an immunological link between risk factors and progressive hearing loss
Macrophages in the cochlea; an immunological link between risk factors and progressive hearing loss
Macrophages are abundant in the cochlea; however, their role in hearing loss is not well understood. Insults to the cochlea, such as noise or insertion of a cochlear implant, cause an inflammatory response, which includes activation of tissue-resident macrophages. Activation is characterized by changes in macrophage morphology, mediator expression, and distribution. Evidence from other organs shows activated macrophages can become primed, whereby subsequent insults cause an elevated inflammatory response. Primed macrophages in brain pathologies respond to circulating inflammatory mediators by disproportionate synthesis of inflammatory mediators. This signaling occurs behind an intact blood–brain barrier, similar to the blood-labyrinth barrier in the cochlea. Local tissue damage can occur as the result of mediator release by activated macrophages. Damage is typically localized; however, if it is to structures with limited ability to repair, such as neurons or hair cells within the cochlea, it is feasible that this contributes to the progressive loss of function seen in hearing loss. We propose that macrophages in the cochlea link risk factors and hearing loss. Injury to the cochlea causes local macrophage activation that typically resolves. However, in susceptible individuals, some macrophages enter a primed state. Once primed, these macrophages can be further activated, as a consequence of circulating inflammatory molecules associated with common co-morbidities. Hypothetically, this would lead to further cochlear damage and loss of hearing. We review the evidence for the role of tissue-resident macrophages in the cochlea and propose that cochlear macrophages contribute to the trajectory of hearing loss and warrant further study.
Macrophages, Cochlea, inflammation, Immune response, Priming, Immune memory, Hearing loss
0894-1491
Hough, Kate
4ab6ce34-81be-4bff-bdc1-bdd22bbb0ace
Verschuur, Carl
5e15ee1c-3a44-4dbe-ad43-ec3b50111e41
Cunningham, Colm
3bc1d897-f0f5-4112-abf4-1a10c2e92a6b
Newman, Tracey
322290cb-2e9c-445d-a047-00b1bea39a25
Hough, Kate
4ab6ce34-81be-4bff-bdc1-bdd22bbb0ace
Verschuur, Carl
5e15ee1c-3a44-4dbe-ad43-ec3b50111e41
Cunningham, Colm
3bc1d897-f0f5-4112-abf4-1a10c2e92a6b
Newman, Tracey
322290cb-2e9c-445d-a047-00b1bea39a25

Hough, Kate, Verschuur, Carl, Cunningham, Colm and Newman, Tracey (2021) Macrophages in the cochlea; an immunological link between risk factors and progressive hearing loss. GLIA. (doi:10.1002/glia.24095).

Record type: Review

Abstract

Macrophages are abundant in the cochlea; however, their role in hearing loss is not well understood. Insults to the cochlea, such as noise or insertion of a cochlear implant, cause an inflammatory response, which includes activation of tissue-resident macrophages. Activation is characterized by changes in macrophage morphology, mediator expression, and distribution. Evidence from other organs shows activated macrophages can become primed, whereby subsequent insults cause an elevated inflammatory response. Primed macrophages in brain pathologies respond to circulating inflammatory mediators by disproportionate synthesis of inflammatory mediators. This signaling occurs behind an intact blood–brain barrier, similar to the blood-labyrinth barrier in the cochlea. Local tissue damage can occur as the result of mediator release by activated macrophages. Damage is typically localized; however, if it is to structures with limited ability to repair, such as neurons or hair cells within the cochlea, it is feasible that this contributes to the progressive loss of function seen in hearing loss. We propose that macrophages in the cochlea link risk factors and hearing loss. Injury to the cochlea causes local macrophage activation that typically resolves. However, in susceptible individuals, some macrophages enter a primed state. Once primed, these macrophages can be further activated, as a consequence of circulating inflammatory molecules associated with common co-morbidities. Hypothetically, this would lead to further cochlear damage and loss of hearing. We review the evidence for the role of tissue-resident macrophages in the cochlea and propose that cochlear macrophages contribute to the trajectory of hearing loss and warrant further study.

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glia.24095 - Version of Record
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Accepted/In Press date: 9 September 2021
e-pub ahead of print date: 18 September 2021
Keywords: Macrophages, Cochlea, inflammation, Immune response, Priming, Immune memory, Hearing loss

Identifiers

Local EPrints ID: 451500
URI: http://eprints.soton.ac.uk/id/eprint/451500
ISSN: 0894-1491
PURE UUID: 784c7173-9bb4-499e-86e2-955d62176144
ORCID for Kate Hough: ORCID iD orcid.org/0000-0002-5160-2517
ORCID for Tracey Newman: ORCID iD orcid.org/0000-0002-3727-9258

Catalogue record

Date deposited: 04 Oct 2021 16:31
Last modified: 05 Oct 2021 01:51

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Contributors

Author: Kate Hough ORCID iD
Author: Carl Verschuur
Author: Colm Cunningham
Author: Tracey Newman ORCID iD

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