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Wood MB, Nowak N, Fuchs PA. Damage-evoked signals in cochlear neurons and supporting cells. Front Neurol 2024; 15:1361747. [PMID: 38419694 PMCID: PMC10899329 DOI: 10.3389/fneur.2024.1361747] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2023] [Accepted: 01/31/2024] [Indexed: 03/02/2024] Open
Abstract
In addition to hearing loss, damage to the cochlea can lead to gain of function pathologies such as hyperacusis. It has been proposed that painful hyperacusis, noxacusis, may be carried to the central nervous system by type II cochlear afferents, sparse, unmyelinated neurons that share morphological and neurochemical traits with nociceptive C-fibers of the somatic nervous system. Also like in skin, damage elicits spreading calcium waves within cochlear epithelia. These are mediated by extracellular ATP combined with IP3-driven release from intracellular calcium stores. Type II afferents are excited by ATP released from damaged epithelia. Thus, the genesis and propagation of epithelial calcium waves is central to cochlear pathology, and presumably hyperacusis. Damage-evoked signals in type II afferents and epithelial cells have been recorded in cochlear explants or semi-intact otic capsules. These efforts have included intracellular electrical recording, use of fluorescent calcium indicators, and visualization of an activity-dependent, intrinsic fluorescent signal. Of relevance to hyperacusis, prior noise-induced hearing loss leads to the generation of prolonged and repetitive activity in type II neurons and surrounding epithelia.
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Affiliation(s)
- Megan Beers Wood
- The Center for Hearing and Balance, Otolaryngology-Head and Neck Surgery, Baltimore, MD, United States
| | - Nate Nowak
- The Center for Hearing and Balance, Otolaryngology-Head and Neck Surgery, Baltimore, MD, United States
- The Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Paul Albert Fuchs
- The Center for Hearing and Balance, Otolaryngology-Head and Neck Surgery, Baltimore, MD, United States
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Hool SA, Jeng J, Jagger DJ, Marcotti W, Ceriani F. Age-related changes in P2Y receptor signalling in mouse cochlear supporting cells. J Physiol 2023; 601:4375-4395. [PMID: 37715703 PMCID: PMC10952729 DOI: 10.1113/jp284980] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2023] [Accepted: 08/16/2023] [Indexed: 09/18/2023] Open
Abstract
Our sense of hearing depends on the function of a specialised class of sensory cells, the hair cells, which are found in the organ of Corti of the mammalian cochlea. The unique physiological environment in which these cells operate is maintained by a syncitium of non-sensory supporting cells, which are crucial for regulating cochlear physiology and metabolic homeostasis. Despite their importance for cochlear function, the role of these supporting cells in age-related hearing loss, the most common sensory deficit in the elderly, is poorly understood. Here, we investigated the age-related changes in the expression and function of metabotropic purinergic receptors (P2Y1 , P2Y2 and P2Y4 ) in the supporting cells of the cochlear apical coil. Purinergic signalling in supporting cells is crucial during the development of the organ of Corti and purinergic receptors are known to undergo changes in expression during ageing in several tissues. Immunolabelling and Ca2+ imaging experiments revealed a downregulation of P2Y receptor expression and a decrease of purinergic-mediated calcium responses after early postnatal stages in the supporting cells. An upregulation of P2Y receptor expression was observed in the aged cochlea when compared to 1 month-old adults. The aged mice also had significantly larger calcium responses and displayed calcium oscillations during prolonged agonist applications. We conclude that supporting cells in the aged cochlea upregulate P2Y2 and P2Y4 receptors and display purinergic-induced Ca2+ responses that mimic those observed during pre-hearing stages of development, possibly aimed at limiting or preventing further damage to the sensory epithelium. KEY POINTS: Age-related hearing loss is associated with lower hearing sensitivity and decreased ability to understand speech. We investigated age-related changes in the expression and function of metabotropic purinergic (P2Y) receptors in cochlear non-sensory supporting cells of mice displaying early-onset (C57BL/6N) and late-onset (C3H/HeJ) hearing loss. The expression of P2Y1 , P2Y2 and P2Y4 receptors in the supporting cells decreased during cochlear maturation, but that of P2Y2 and P2Y4 was upregulated in the aged cochlea. P2Y2 and P2Y4 receptors were primarily responsible for the ATP-induced Ca2+ responses in the supporting cells. The degree of purinergic expression upregulation in aged supporting cells mirrored hearing loss progression in the different mouse strains. We propose that the upregulation of purinergic-mediated signalling in the aged cochlea is subsequent to age-related changes in the hair cells and may act as a protective mechanism to limit or to avoid further damage to the sensory epithelium.
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Affiliation(s)
- Sarah A. Hool
- School of BiosciencesUniversity of SheffieldSheffieldUK
| | - Jing‐Yi Jeng
- School of BiosciencesUniversity of SheffieldSheffieldUK
| | | | - Walter Marcotti
- School of BiosciencesUniversity of SheffieldSheffieldUK
- Neuroscience InstituteUniversity of SheffieldSheffieldUK
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Moysan L, Fazekas F, Fekete A, Köles L, Zelles T, Berekméri E. Ca 2+ Dynamics of Gap Junction Coupled and Uncoupled Deiters' Cells in the Organ of Corti in Hearing BALB/c Mice. Int J Mol Sci 2023; 24:11095. [PMID: 37446272 DOI: 10.3390/ijms241311095] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2023] [Revised: 06/19/2023] [Accepted: 06/30/2023] [Indexed: 07/15/2023] Open
Abstract
ATP, as a paracrine signalling molecule, induces intracellular Ca2+ elevation via the activation of purinergic receptors on the surface of glia-like cochlear supporting cells. These cells, including the Deiters' cells (DCs), are also coupled by gap junctions that allow the propagation of intercellular Ca2+ waves via diffusion of Ca2+ mobilising second messenger IP3 between neighbouring cells. We have compared the ATP-evoked Ca2+ transients and the effect of two different gap junction (GJ) blockers (octanol and carbenoxolone, CBX) on the Ca2+ transients in DCs located in the apical and middle turns of the hemicochlea preparation of BALB/c mice (P14-19). Octanol had no effect on Ca2+ signalling, while CBX inhibited the ATP response, more prominently in the middle turn. Based on astrocyte models and using our experimental results, we successfully simulated the Ca2+ dynamics in DCs in different cochlear regions. The mathematical model reliably described the Ca2+ transients in the DCs and suggested that the tonotopical differences could originate from differences in purinoceptor and Ca2+ pump expressions and in IP3-Ca2+ release mechanisms. The cochlear turn-dependent effect of CBX might be the result of the differing connexin isoform composition of GJs along the tonotopic axis. The contribution of IP3-mediated Ca2+ signalling inhibition by CBX cannot be excluded.
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Affiliation(s)
- Louise Moysan
- Department of Zoology, University of Veterinary Medicine Budapest, H-1078 Budapest, Hungary
| | - Fruzsina Fazekas
- Department of Zoology, University of Veterinary Medicine Budapest, H-1078 Budapest, Hungary
| | - Adam Fekete
- Program in Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada
| | - László Köles
- Department of Oral Biology, Semmelweis University, H-1089 Budapest, Hungary
- Department of Pharmacology and Pharmacotherapy, Semmelweis University, H-1089 Budapest, Hungary
| | - Tibor Zelles
- Department of Oral Biology, Semmelweis University, H-1089 Budapest, Hungary
- Department of Pharmacology and Pharmacotherapy, Semmelweis University, H-1089 Budapest, Hungary
- Laboratory of Molecular Pharmacology, Institute of Experimental Medicine, H-1083 Budapest, Hungary
| | - Eszter Berekméri
- Department of Zoology, University of Veterinary Medicine Budapest, H-1078 Budapest, Hungary
- Department of Pharmacology and Pharmacotherapy, Semmelweis University, H-1089 Budapest, Hungary
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Vlajkovic SM, Thorne PR. Purinergic Signalling in the Cochlea. Int J Mol Sci 2022; 23:ijms232314874. [PMID: 36499200 PMCID: PMC9741428 DOI: 10.3390/ijms232314874] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2022] [Revised: 11/24/2022] [Accepted: 11/25/2022] [Indexed: 11/29/2022] Open
Abstract
The mammalian cochlea is the sensory organ of hearing with a delicate, highly organised structure that supports unique operating mechanisms. ATP release from the secretory tissues of the cochlear lateral wall (stria vascularis) triggers numerous physiological responses by activating P2 receptors in sensory, supporting and neural tissues. Two families of P2 receptors, ATP-gated ion channels (P2X receptors) and G protein-coupled P2Y receptors, activate intracellular signalling pathways that regulate cochlear development, homeostasis, sensory transduction, auditory neurotransmission and response to stress. Of particular interest is a purinergic hearing adaptation, which reflects the critical role of the P2X2 receptor in adaptive cochlear response to elevated sound levels. Other P2 receptors are involved in the maturation of neural processes and frequency selectivity refinement in the developing cochlea. Extracellular ATP signalling is regulated by a family of surface-located enzymes collectively known as "ectonucleotidases" that hydrolyse ATP to adenosine. Adenosine is a constitutive cell metabolite with an established role in tissue protection and regeneration. The differential activation of A1 and A2A adenosine receptors defines the cochlear response to injury caused by oxidative stress, inflammation, and activation of apoptotic pathways. A1 receptor agonism, A2A receptor antagonism, and increasing adenosine levels in cochlear fluids all represent promising therapeutic tools for cochlear rescue from injury and prevention of hearing loss.
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Affiliation(s)
- Srdjan M. Vlajkovic
- Department of Physiology and The Eisdell Moore Centre, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
- Correspondence: ; Tel.: +64-9-9239782
| | - Peter R. Thorne
- Department of Physiology and The Eisdell Moore Centre, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
- Section of Audiology, School of Population Health, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
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Wu Y, Han K, Han W, Fan Z, Zhou M, Lu X, Liu X, Li L, Du L. Low 25-Hydroxyvitamin D Levels Are Associated With Residual Dizziness After Successful Treatment of Benign Paroxysmal Positional Vertigo. Front Neurol 2022; 13:915239. [PMID: 35812091 PMCID: PMC9256914 DOI: 10.3389/fneur.2022.915239] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2022] [Accepted: 05/23/2022] [Indexed: 11/24/2022] Open
Abstract
Objective: Vitamin D (Vit D) regulates calcium and phosphate metabolism and helps to maintain otolith organ function. Residual dizziness (RD) is one of the most common complications after the successful treatment of benign paroxysmal positional vertigo (BPPV). Various theories have been suggested to explain the cause of RD, and otolith organ disorder is the most evident cause of RD. This study aimed to investigate the association between serum levels of Vit D and the occurrence of RD after the successful treatment of BPPV. Methods A prospective study including patients who were diagnosed with de novo posterior semicircular canal-type BPPV (PC-BPPV) was conducted at our institution from May 2017 to May 2019. All the patients underwent canalith repositioning procedures and were followed up. Univariate and multivariate analyses were performed to investigate the relationship between serum 25-hydroxy vitamin D (25(OH)D) levels and RD occurrence after successful BPPV treatment. Results In total, 123 patients with PC-BPPV were enrolled, and 41.5% (51/123) experienced RD. The serum level of 25(OH)D was significantly lower in PC-BPPV patients with RD [median 16.2 ng/ml (IQR 12.9–22.1)] than in patients without RD [median 20.5 ng/ml (IQR 16.5–26.5)] (P = 0.001). In multivariate models comparing the prevalence of RD in the insufficient group [25(OH)D ≥ 20 to <30 ng/ml], deficient group [25(OH)D < 20 ng/ml] and normal group [25(OH)D ≥ 30 ng/ml], the 25(OH)D levels in the deficient group were associated with the occurrence of RD (odds ratio = 5.48, 95% confidence interval = 1.08–27.71; P = 0.04). Conclusion Low 25(OH)D levels are associated with the development of RD in patients with PC-BPPV after successful treatment. Further efforts to validate and elucidate the mechanism are needed.
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Affiliation(s)
- Yunqin Wu
- Department of Neurology, Hwa Mei Hospital, University of Chinese Academy of Science, Ningbo, China
| | - Kun Han
- Department of Neurology, Hwa Mei Hospital, University of Chinese Academy of Science, Ningbo, China
| | - Weiwei Han
- Department of Rehabilitation, Hwa Mei Hospital, University of Chinese Academy of Science, Ningbo, China
| | - Zhenyi Fan
- Department of Neurology, Hwa Mei Hospital, University of Chinese Academy of Science, Ningbo, China
| | - Min Zhou
- Department of Neurology, Hwa Mei Hospital, University of Chinese Academy of Science, Ningbo, China
| | - Xiaoxiong Lu
- Department of Neurology, Hwa Mei Hospital, University of Chinese Academy of Science, Ningbo, China
| | - Xiaoxia Liu
- Department of Neurology, Hwa Mei Hospital, University of Chinese Academy of Science, Ningbo, China
| | - Li Li
- Department of Neurology, Hwa Mei Hospital, University of Chinese Academy of Science, Ningbo, China
| | - Liwen Du
- Department of Emergency, Hwa Mei Hospital, University of Chinese Academy of Science, Ningbo, China
- *Correspondence: Liwen Du
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Kim SH, Choi JY. Purinergic signaling in the peripheral vestibular system. Purinergic Signal 2022; 18:165-176. [PMID: 35344126 DOI: 10.1007/s11302-022-09855-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2021] [Accepted: 02/19/2022] [Indexed: 11/25/2022] Open
Abstract
The inner ear comprises the cochlea and vestibular system, which detect sound and acceleration stimulation, respectively. The function of the inner ear is regulated by ion transport activity among sensory epithelial cells, neuronal cells, non-sensory epithelial cells, and luminal fluid with a unique ionic composition of high [K+] and low [Na+], which enables normal hearing and balance maintenance. One of the important mechanisms regulating ion transport in the inner ear is purinergic signaling. Various purinergic receptors are distributed throughout inner ear epithelial cells and neuronal cells. To date, most studies have focused on the role of purinergic receptors in the cochlea, and few studies have examined these receptors in the vestibular system. As purinergic receptors play an important role in the cochlea, they would likely do the same in the vestibular system, which is fairly similar to the cochlea in cellular structure and function. Based on available studies performed to date, purinergic signaling is postulated to be involved in the regulation of ion homeostasis, protection of hair cells, otoconia formation, and regulation of electrical signaling from the sensory epithelium to vestibular neurons. In this review, the distribution and roles of purinergic receptors in the peripheral vestibular system are summarized and discussed.
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Affiliation(s)
- Sung Huhn Kim
- Department of Otorhinolaryngology, Yonsei University College of Medicine, 50-1 Yonsei-Ro, Seodaemun-Gu, Seoul, 03722, Republic of Korea
| | - Jae Young Choi
- Department of Otorhinolaryngology, Yonsei University College of Medicine, 50-1 Yonsei-Ro, Seodaemun-Gu, Seoul, 03722, Republic of Korea.
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