Anti-inflammatory compounds improve spiral ganglion neuron survival after aminoglycoside-induced hair cell loss in rats

AbstractSpiral ganglion neurons (SGNs) relay auditory information from cochlear hair cells to the central nervous system. After hair cells are destroyed by aminoglycoside antibiotics, SGNs gradually die. However, the reasons for this cochlear neurodegeneration are unclear. We used microarray gene expression profiling to assess transcriptomic changes in the spiral ganglia of kanamycin-deafened and age-matched control rats and found that many of the genes upregulated after deafening are associated with immune/inflammatory responses. In support of this, we observed increased numbers of macrophages in the spiral ganglion of deafened rats. We also found, via CD68 immunoreactivity, an increase in activated macrophages after deafening. An increase in CD68-associated nuclei was observed by postnatal day 23, a time before significant SGN degeneration is observed. Finally, we show that the immunosuppressive drugs dexamethasone and ibuprofen, as well as the NAD salvage pathway activator P7C3, provide at least some neuroprotection post-deafening. Ibuprofen and dexamethasone also decreased the degree of macrophage activation. These results suggest that activated macrophages specifically, and perhaps a more general neuroinflammatory response, are actively contributing to SGN degeneration after hair cell loss.

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Disruption of Hars2 in Cochlear Hair Cells Causes Progressive Mitochondrial Dysfunction and Hearing Loss in Mice

Frontiers in Cellular Neuroscience ◽

10.3389/fncel.2021.804345 ◽

2021 ◽

Vol 15 ◽

Author(s):

Pengcheng Xu ◽

Longhao Wang ◽

Hu Peng ◽

Huihui Liu ◽

Hongchao Liu ◽

...

Keyword(s):

Hearing Loss ◽

Hair Cell ◽

Mitochondrial Dysfunction ◽

Hair Cells ◽

Cell Loss ◽

Outer Hair Cells ◽

Hair Cell Loss ◽

Progressive Hearing Loss ◽

Cochlear Hair Cells ◽

Inner Hair Cells

Mutations in a number of genes encoding mitochondrial aminoacyl-tRNA synthetases lead to non-syndromic and/or syndromic sensorineural hearing loss in humans, while their cellular and physiological pathology in cochlea has rarely been investigated in vivo. In this study, we showed that histidyl-tRNA synthetase HARS2, whose deficiency is associated with Perrault syndrome 2 (PRLTS2), is robustly expressed in postnatal mouse cochlea including the outer and inner hair cells. Targeted knockout of Hars2 in mouse hair cells resulted in delayed onset (P30), rapidly progressive hearing loss similar to the PRLTS2 hearing phenotype. Significant hair cell loss was observed starting from P45 following elevated reactive oxygen species (ROS) level and activated mitochondrial apoptotic pathway. Despite of normal ribbon synapse formation, whole-cell patch clamp of the inner hair cells revealed reduced calcium influx and compromised sustained synaptic exocytosis prior to the hair cell loss at P30, consistent with the decreased supra-threshold wave I amplitudes of the auditory brainstem response. Starting from P14, increasing proportion of morphologically abnormal mitochondria was observed by transmission electron microscope, exhibiting swelling, deformation, loss of cristae and emergence of large intrinsic vacuoles that are associated with mitochondrial dysfunction. Though the mitochondrial abnormalities are more prominent in inner hair cells, it is the outer hair cells suffering more severe cell loss. Taken together, our results suggest that conditional knockout of Hars2 in mouse cochlear hair cells leads to accumulating mitochondrial dysfunction and ROS stress, triggers progressive hearing loss highlighted by hair cell synaptopathy and apoptosis, and is differentially perceived by inner and outer hair cells.

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Ouabain-Induced Apoptosis in Cochlear Hair Cells and Spiral Ganglion NeuronsIn Vitro

BioMed Research International ◽

10.1155/2013/628064 ◽

2013 ◽

Vol 2013 ◽

pp. 1-16 ◽

Cited By ~ 14

Author(s):

Yong Fu ◽

Dalian Ding ◽

Lei Wei ◽

Haiyan Jiang ◽

Richard Salvi

Keyword(s):

Hair Cells ◽

Gene Array ◽

Spiral Ganglion ◽

Spiral Ganglion Neuron ◽

Round Window Membrane ◽

Spiral Ganglion Neurons ◽

Cochlear Hair Cells ◽

Ganglion Neurons

Ouabain is a common tool to explore the pathophysiological changes in adult mammalian cochleain vivo. In prior studies, locally administering ouabain via round window membrane demonstrated that the ototoxic effects of ouabainin vivovaried among mammalian species. Little is known about the ototoxic effectsin vitro. Thus, we prepared cochlear organotypic cultures from postnatal day-3 rats and treated these cultures with ouabain at 50, 500, and 1000 μM for different time to elucidate the ototoxic effects of ouabainin vitroand to provide insights that could explain the comparative ototoxic effects of ouabainin vivo. Degeneration of cochlear hair cells and spiral ganglion neurons was evaluated by hair-cell staining and neurofilament labeling, respectively. Annexin V staining was used to detect apoptotic cells. A quantitative RT-PCR apoptosis-focused gene array determined changes in apoptosis-related genes. The results showed that ouabain-induced damagein vitrowas dose and time dependent. 500 μM ouabain and 1000 μM ouabain were destructively traumatic to both spiral ganglion neurons and cochlear hair cells in an apoptotic signal-dependent pathway. The major apoptotic pathways in ouabain-induced spiral ganglion neuron apoptosis culminated in the stimulation of the p53 pathway and triggering of apoptosis by a network of proapoptotic signaling pathways.

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Inhibition of mTOR by Rapamycin Results in Auditory Hair Cell Damage and Decreased Spiral Ganglion Neuron Outgrowth and Neurite FormationIn Vitro

BioMed Research International ◽

10.1155/2015/925890 ◽

2015 ◽

Vol 2015 ◽

pp. 1-10 ◽

Cited By ~ 8

Author(s):

Katharina Leitmeyer ◽

Andrea Glutz ◽

Vesna Radojevic ◽

Cristian Setz ◽

Nathan Huerzeler ◽

...

Keyword(s):

Hair Cell ◽

Hair Cells ◽

Cell Damage ◽

Spiral Ganglion ◽

Ganglion Neuron ◽

Spiral Ganglion Neuron ◽

Dependent Manner ◽

Auditory Hair Cells ◽

Ganglion Neurons ◽

Dose Dependent

Rapamycin is an antifungal agent with immunosuppressive properties. Rapamycin inhibits the mammalian target of rapamycin (mTOR) by blocking the mTOR complex 1 (mTORC1). mTOR is an atypical serine/threonine protein kinase, which controls cell growth, cell proliferation, and cell metabolism. However, less is known about the mTOR pathway in the inner ear. First, we evaluated whether or not the two mTOR complexes (mTORC1 and mTORC2, resp.) are present in the mammalian cochlea. Next, tissue explants of 5-day-old rats were treated with increasing concentrations of rapamycin to explore the effects of rapamycin on auditory hair cells and spiral ganglion neurons. Auditory hair cell survival, spiral ganglion neuron number, length of neurites, and neuronal survival were analyzedin vitro. Our data indicates that both mTOR complexes are expressed in the mammalian cochlea. We observed that inhibition of mTOR by rapamycin results in a dose dependent damage of auditory hair cells. Moreover, spiral ganglion neurite number and length of neurites were significantly decreased in all concentrations used compared to control in a dose dependent manner. Our data indicate that the mTOR may play a role in the survival of hair cells and modulates spiral ganglion neuronal outgrowth and neurite formation.

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Efr3a Insufficiency Attenuates the Degeneration of Spiral Ganglion Neurons after Hair Cell Loss

Frontiers in Molecular Neuroscience ◽

10.3389/fnmol.2017.00086 ◽

2017 ◽

Vol 10 ◽

Cited By ~ 3

Author(s):

Haixia Hu ◽

Bin Ye ◽

Le Zhang ◽

Quan Wang ◽

Zhiwei Liu ◽

...

Keyword(s):

Hair Cell ◽

Spiral Ganglion ◽

Cell Loss ◽

Spiral Ganglion Neurons ◽

Hair Cell Loss ◽

Ganglion Neurons

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Noise-induced and age-related hearing loss: new perspectives and potential therapies

F1000Research ◽

10.12688/f1000research.11310.1 ◽

2017 ◽

Vol 6 ◽

pp. 927 ◽

Cited By ~ 78

Author(s):

M Charles Liberman

Keyword(s):

Hearing Loss ◽

Hair Cell ◽

Sensorineural Hearing Loss ◽

Hair Cells ◽

Auditory Nerve ◽

Cell Loss ◽

Sensorineural Hearing ◽

Hair Cell Loss ◽

Age Related ◽

Age Related Hearing Loss

The classic view of sensorineural hearing loss has been that the primary damage targets are hair cells and that auditory nerve loss is typically secondary to hair cell degeneration. Recent work has challenged that view. In noise-induced hearing loss, exposures causing only reversible threshold shifts (and no hair cell loss) nevertheless cause permanent loss of >50% of the synaptic connections between hair cells and the auditory nerve. Similarly, in age-related hearing loss, degeneration of cochlear synapses precedes both hair cell loss and threshold elevation. This primary neural degeneration has remained a “hidden hearing loss” for two reasons: 1) the neuronal cell bodies survive for years despite loss of synaptic connection with hair cells, and 2) the degeneration is selective for auditory nerve fibers with high thresholds. Although not required for threshold detection when quiet, these high-threshold fibers are critical for hearing in noisy environments. Research suggests that primary neural degeneration is an important contributor to the perceptual handicap in sensorineural hearing loss, and it may be key to the generation of tinnitus and other associated perceptual anomalies. In cases where the hair cells survive, neurotrophin therapies can elicit neurite outgrowth from surviving auditory neurons and re-establishment of their peripheral synapses; thus, treatments may be on the horizon.

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New insights into glutamate ototoxicity in cochlear hair cells and spiral ganglion neurons

Acta Oto-Laryngologica ◽

10.3109/00016489.2010.495133 ◽

2010 ◽

Vol 130 (12) ◽

pp. 1316-1323 ◽

Cited By ~ 5

Author(s):

Haitao Lu ◽

Xiang Wang ◽

Wenyan Sun ◽

Yao Hu ◽

Shusheng Gong

Keyword(s):

Hair Cells ◽

Spiral Ganglion ◽

Spiral Ganglion Neurons ◽

Cochlear Hair Cells ◽

Ganglion Neurons

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Neurotrophin gene therapy may be able to treat individuals with noise-induced hearing loss or neural presbyacusis

10.31219/osf.io/spkxh ◽

2021 ◽

Author(s):

Moataz Dowaidar

Keyword(s):

Gene Therapy ◽

Hearing Loss ◽

Hair Cell ◽

Hair Cells ◽

Cell Loss ◽

Cell Populations ◽

Noise Induced Hearing Loss ◽

Hair Cell Loss ◽

Functional Impairments ◽

Peripheral Axon

Neurotrophin (NT) cochlear gene therapy might perhaps give a single treatment that might greatly enhance neuronal survival, resulting in CI patients, provided the many challenges described above can be adequately addressed and safety concerns allayed by more animal model investigations. This is particularly crucial for juvenile CI patients, who have to rely on electrical hearing for the remainder of their lives, and whose outcomes are quite different. In addition, NT gene therapy may have the potential to treat patients with noise-induced hearing loss or neural presbyacusis (e.g., age-related cochlear synaptopathy), where primary neuronal loss is a key cause of hearing loss. Animal research into noise-induced hearing loss has shown that even exposures that generate only reversible threshold alterations and no hair cell loss can lead to permanent loss of SGN synapses on hair cells, resulting in functional impairments and ultimately SGN degeneration. Cochlear synapses frequently precede both hair cell loss and threshold increases in human ears, according to current studies. Cochlear synaptopathy is characterized by ears with intact hair cell populations and normal audiograms as "hidden" hearing loss. Many frequent perceptual abnormalities, including speech-in-noise difficulties, tinnitus, and hyperacusis, are likely produced by suppressing affected neurons, which radically alters information processing. Thus, in the future, NT gene therapy may be successful in inducing SGN peripheral axon resprouting and synaptic regeneration into residual (or even regenerated) hair cell populations. We have demonstrated compelling evidence that, in this investigation, BDNF gene therapy can boost SGN survival and enhance peripheral axon maintenance or rerouting. NT-3 has been found in adult animals exposed to acoustic damage to induce synaptic regeneration of these fibers, reconnecting them to hair cells and their ribbon synapses, and restoring hearing function. Combining BDNF and NT-3 gene therapy may be the most effective way to maintain/restore a more normal cochlear neuronal substrate.

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LIN28B/let-7control the ability of neonatal murine auditory supporting cells to generate hair cells through mTOR signaling

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2000417117 ◽

2020 ◽

Vol 117 (36) ◽

pp. 22225-22236

Author(s):

Xiao-Jun Li ◽

Angelika Doetzlhofer

Keyword(s):

Hair Cell ◽

Hair Cells ◽

Rna Binding ◽

Mammalian Target Of Rapamycin ◽

Cell Loss ◽

Supporting Cell ◽

Dependent Manner ◽

Cell Plasticity ◽

Supporting Cells ◽

Cochlear Hair Cells

Mechano-sensory hair cells within the inner ear cochlea are essential for the detection of sound. In mammals, cochlear hair cells are only produced during development and their loss, due to disease or trauma, is a leading cause of deafness. In the immature cochlea, prior to the onset of hearing, hair cell loss stimulates neighboring supporting cells to act as hair cell progenitors and produce new hair cells. However, for reasons unknown, such regenerative capacity (plasticity) is lost once supporting cells undergo maturation. Here, we demonstrate that the RNA binding protein LIN28B plays an important role in the production of hair cells by supporting cells and provide evidence that the developmental drop in supporting cell plasticity in the mammalian cochlea is, at least in part, a product of declining LIN28B-mammalian target of rapamycin (mTOR) activity. Employing murine cochlear organoid and explant cultures to model mitotic and nonmitotic mechanisms of hair cell generation, we show that loss of LIN28B function, due to its conditional deletion, or due to overexpression of the antagonistic miRNAlet-7g, suppressed Akt-mTOR complex 1 (mTORC1) activity and renders young, immature supporting cells incapable of generating hair cells. Conversely, we found that LIN28B overexpression increased Akt-mTORC1 activity and allowed supporting cells that were undergoing maturation to de-differentiate into progenitor-like cells and to produce hair cells via mitotic and nonmitotic mechanisms. Finally, using the mTORC1 inhibitor rapamycin, we demonstrate that LIN28B promotes supporting cell plasticity in an mTORC1-dependent manner.

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