Differential regulation of mammalian and avian ATOH1 by E2F1 and its implication for hair cell regeneration in the inner ear

AbstractThe mammalian inner ear has a limited capacity to regenerate its mechanosensory hair cells. This lack of regenerative capacity underlies the high incidence of age-related hearing loss in humans. In contrast, non-mammalian vertebrates can form new hair cells when damage occurs, a mechanism that depends on re-activation of expression of the pro-hair cell transcription factor Atoh1. Here, we show that members of the E2F transcription factor family, known to play a key role in cell cycle progression, regulate the expression of Atoh1. E2F1 activates chicken Atoh1 by directly interacting with a cis-regulatory region distal to the avian Atoh1 gene. E2F does not activate mouse Atoh1 gene expression, since this regulatory element is absent in mammals. We also show that E2F1 expression changes dynamically in the chicken auditory epithelium during ototoxic damage and hair cell regeneration. Therefore, we propose a model in which the mitotic regeneration of non-mammalian hair cells is due to E2F1-mediated activation of Atoh1 expression, a mechanism which has been lost in mammals.

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Transcription Factor Reprogramming in the Inner Ear: Turning on Cell Fate Switches to Regenerate Sensory Hair Cells

Frontiers in Cellular Neuroscience ◽

10.3389/fncel.2021.660748 ◽

2021 ◽

Vol 15 ◽

Author(s):

Amrita A. Iyer ◽

Andrew K. Groves

Keyword(s):

Transcription Factor ◽

Transcription Factors ◽

Hair Cell ◽

Inner Ear ◽

Cell Fate ◽

Hair Cells ◽

Cell Regeneration ◽

Cell Type ◽

Hair Cell Regeneration ◽

Supporting Cells

Non-mammalian vertebrates can restore their auditory and vestibular hair cells naturally by triggering the regeneration of adjacent supporting cells. The transcription factor ATOH1 is a key regulator of hair cell development and regeneration in the inner ear. Following the death of hair cells, supporting cells upregulate ATOH1 and give rise to new hair cells. However, in the mature mammalian cochlea, such natural regeneration of hair cells is largely absent. Transcription factor reprogramming has been used in many tissues to convert one cell type into another, with the long-term hope of achieving tissue regeneration. Reprogramming transcription factors work by altering the transcriptomic and epigenetic landscapes in a target cell, resulting in a fate change to the desired cell type. Several studies have shown that ATOH1 is capable of reprogramming cochlear non-sensory tissue into cells resembling hair cells in young animals. However, the reprogramming ability of ATOH1 is lost with age, implying that the potency of individual hair cell-specific transcription factors may be reduced or lost over time by mechanisms that are still not clear. To circumvent this, combinations of key hair cell transcription factors have been used to promote hair cell regeneration in older animals. In this review, we summarize recent findings that have identified and studied these reprogramming factor combinations for hair cell regeneration. Finally, we discuss the important questions that emerge from these findings, particularly the feasibility of therapeutic strategies using reprogramming factors to restore human hearing in the future.

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Delta1 expression during avian hair cell regeneration

Development ◽

10.1242/dev.126.5.961 ◽

1999 ◽

Vol 126 (5) ◽

pp. 961-973 ◽

Cited By ~ 3

Author(s):

J.S. Stone ◽

E.W. Rubel

Keyword(s):

Hair Cell ◽

Inner Ear ◽

Hair Cells ◽

Cell Injury ◽

Basilar Papilla ◽

Cell Regeneration ◽

Mrna Levels ◽

Hair Cell Regeneration ◽

Drug Induced ◽

In Cells

Postembryonic production of hair cells, the highly specialized receptors for hearing, balance and motion detection, occurs in a precisely controlled manner in select species, including avians. Notch1, Delta1 and Serrate1 mediate cell specification in several tissues and species. We examined expression of the chicken homologs of these genes in the normal and drug-damaged chick inner ear to determine if signaling through this pathway changes during hair cell regeneration. In untreated post-hatch chicks, Delta1 mRNA is abundant in a subpopulation of cells in the utricle, which undergoes continual postembryonic hair cell production, but it is absent from all cells in the basilar papilla, which is mitotically quiescent. By 3 days after drug-induced hair cell injury, Delta1 expression is highly upregulated in areas of cell proliferation in both the utricle and basilar papilla. Delta1 mRNA levels are elevated in progenitor cells during DNA synthesis and/or gap 2 phases of the cell cycle and expression is maintained in both daughter cells immediately after mitosis. Delta1 expression remains upregulated in cells that differentiate into hair cells and is downregulated in cells that do not acquire the hair cell fate. Delta1 mRNA levels return to normal by 10 days after hair cell injury. Serrate1 is expressed in both hair cells and support cells in the utricle and basilar papilla, and its expression does not change during the course of drug-induced hair cell regeneration. In contrast, Notch1 expression, which is limited to support cells in the quiescent epithelium, is increased in post-M-phase cell pairs during hair cell regeneration. This study provides initial evidence that Delta-Notch signaling may be involved in maintaining the correct cell types and patterns during postembryonic replacement of sensory epithelial cells in the chick inner ear.

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Macrophages Respond Rapidly to Ototoxic Injury of Lateral Line Hair Cells but Are Not Required for Hair Cell Regeneration

Frontiers in Cellular Neuroscience ◽

10.3389/fncel.2020.613246 ◽

2021 ◽

Vol 14 ◽

Author(s):

Mark E. Warchol ◽

Angela Schrader ◽

Lavinia Sheets

Keyword(s):

Hair Cell ◽

Inner Ear ◽

Lateral Line ◽

Hair Cells ◽

Control Fish ◽

Cell Regeneration ◽

Cellular Interactions ◽

Hair Cell Regeneration ◽

Genetic Ablation ◽

Larval Zebrafish

The sensory organs of the inner ear contain resident populations of macrophages, which are recruited to sites of cellular injury. Such macrophages are known to phagocytose the debris of dying cells but the full role of macrophages in otic pathology is not understood. Lateral line neuromasts of zebrafish contain hair cells that are nearly identical to those in the inner ear, and the optical clarity of larval zebrafish permits direct imaging of cellular interactions. In this study, we used larval zebrafish to characterize the response of macrophages to ototoxic injury of lateral line hair cells. Macrophages migrated into neuromasts within 20 min of exposure to the ototoxic antibiotic neomycin. The number of macrophages in the near vicinity of injured neuromasts was similar to that observed near uninjured neuromasts, suggesting that this early inflammatory response was mediated by “local” macrophages. Upon entering injured neuromasts, macrophages actively phagocytosed hair cell debris. The injury-evoked migration of macrophages was significantly reduced by inhibition of Src-family kinases. Using chemical-genetic ablation of macrophages before the ototoxic injury, we also examined whether macrophages were essential for the initiation of hair cell regeneration. Results revealed only minor differences in hair cell recovery in macrophage-depleted vs. control fish, suggesting that macrophages are not essential for the regeneration of lateral line hair cells.

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Hair Cell Regeneration in the Inner Ear

Otolaryngology ◽

10.1177/01945998941113p118 ◽

1994 ◽

Vol 111 (3P1) ◽

pp. 281-301 ◽

Cited By ~ 3

Author(s):

Edwin W Rubel ◽

Terance T. Tsue ◽

Elizabeth C. Oesterle ◽

Edwin W. Rubel

Keyword(s):

Hair Cell ◽

Inner Ear ◽

Hair Cells ◽

Neck Surgery ◽

Repair Process ◽

Treatment Modalities ◽

Cell Regeneration ◽

Hair Cell Regeneration ◽

Direct Stimulation ◽

Rapid Pace

Hearing and balance disorders caused by the loss of inner ear hair cells Is a common problem encountered in otolaryngology-head and neck surgery. The postembryonic production of hair cells in cold-blooded vertebrates has been known for several decades, and recent studies in the avian inner ear after ototoxic drug and noise damage have demonstrated a remarkable capacity for both anatomic and functional recovery. The regeneration of sensory hair cells has been shown to be integral to this repair process. Current work is focusing on the cellular progenitor source of new hair cells and the trigger mechanism responsible for inducing hair cell regeneration. Preliminary studies suggest that reparative proliferation may also occur in the mammalian inner ear. Work in this field is moving at a rapid pace. The results thus far have yielded optimism that direct stimulation of hair cell production or transplantation of living hair cells may eventually become treatment modalities for the damaged human inner ear. These proposals would have been considered unrealistic less than 10 years ago, but they now have caught the full attention of both clinician and researcher.

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Macrophages respond rapidly to ototoxic injury of lateral line hair cells but are not required for hair cell regeneration

10.1101/2020.09.28.314922 ◽

2020 ◽

Cited By ~ 1

Author(s):

Mark E. Warchol ◽

Angela Schrader ◽

Lavinia Sheets

Keyword(s):

Hair Cell ◽

Inner Ear ◽

Lateral Line ◽

Hair Cells ◽

Control Fish ◽

Cell Regeneration ◽

Cellular Interactions ◽

Hair Cell Regeneration ◽

Genetic Ablation ◽

Larval Zebrafish

AbstractThe sensory organs of the inner ear contain resident populations of macrophages, which are recruited to sites of cellular injury. Such macrophages are known to phagocytose the debris of dying cells but the full role of macrophages in otic pathology is not understood. Lateral line neuromasts of zebrafish contain hair cells similar to those in the inner ear, and the optical clarity of larval zebrafish permits direct imaging of cellular interactions. In this study, we used larval zebrafish to characterize the response of macrophages to ototoxic injury of lateral line hair cells. Macrophages migrated into neuromasts within 20 min of exposure to the ototoxic antibiotic neomycin. The number of macrophages in close proximity of injured neuromasts was similar to that observed near uninjured neuromasts, suggesting that this early inflammatory response was mediated by ‘local’ macrophages. Upon entering injured neuromasts, macrophages actively phagocytosed hair cell debris. Such phagocytosis was significantly reduced by inhibiting Src-family kinases. Using chemical-genetic ablation of macrophages prior to ototoxic injury, we also examined whether macrophages were essential for the initiation of hair cell regeneration after neomycin exposure. Results revealed only minor differences in hair cell recovery in macrophage-depleted vs. control fish, suggesting that macrophages are not essential for the regeneration of lateral line hair cells.

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Hear, Hear for Notch: Control of Cell Fates in the Inner Ear by Notch Signaling

Biomolecules ◽

10.3390/biom10030370 ◽

2020 ◽

Vol 10 (3) ◽

pp. 370 ◽

Cited By ~ 8

Author(s):

Rogers Brown ◽

Andrew K. Groves

Keyword(s):

Hair Cell ◽

Notch Signaling ◽

Inner Ear ◽

Hair Cells ◽

Notch Pathway ◽

Notch Signaling Pathway ◽

Cell Regeneration ◽

Hair Cell Regeneration ◽

Supporting Cells ◽

Fine Grained

The vertebrate inner ear is responsible for detecting sound, gravity, and head motion. These mechanical forces are detected by mechanosensitive hair cells, arranged in a series of sensory patches in the vestibular and cochlear regions of the ear. Hair cells form synapses with neurons of the VIIIth cranial ganglion, which convey sound and balance information to the brain. They are surrounded by supporting cells, which nourish and protect the hair cells, and which can serve as a source of stem cells to regenerate hair cells after damage in non-mammalian vertebrates. The Notch signaling pathway plays many roles in the development of the inner ear, from the earliest formation of future inner ear ectoderm on the side of the embryonic head, to regulating the production of supporting cells, hair cells, and the neurons that innervate them. Notch signaling is re-deployed in non-mammalian vertebrates during hair cell regeneration, and attempts have been made to manipulate the Notch pathway to promote hair cell regeneration in mammals. In this review, we summarize the different modes of Notch signaling in inner ear development and regeneration, and describe how they interact with other signaling pathways to orchestrate the fine-grained cellular patterns of the ear.

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Transcriptomic and epigenetic regulation of hair cell regeneration in the mouse utricle and its potentiation by Atoh1

eLife ◽

10.7554/elife.44328 ◽

2019 ◽

Vol 8 ◽

Cited By ~ 15

Author(s):

Hsin-I Jen ◽

Matthew C Hill ◽

Litao Tao ◽

Kuanwei Sheng ◽

Wenjian Cao ◽

...

Keyword(s):

Transcription Factor ◽

Hair Cell ◽

Cell Fate ◽

Hair Cells ◽

Cell Regeneration ◽

Rna Seq ◽

Hair Cell Regeneration ◽

Supporting Cells ◽

Ability To Regenerate ◽

Accessible Chromatin

The mammalian cochlea loses its ability to regenerate new hair cells prior to the onset of hearing. In contrast, the adult vestibular system can produce new hair cells in response to damage, or by reprogramming of supporting cells with the hair cell transcription factor Atoh1. We used RNA-seq and ATAC-seq to probe the transcriptional and epigenetic responses of utricle supporting cells to damage and Atoh1 transduction. We show that the regenerative response of the utricle correlates with a more accessible chromatin structure in utricle supporting cells compared to their cochlear counterparts. We also provide evidence that Atoh1 transduction of supporting cells is able to promote increased transcriptional accessibility of some hair cell genes. Our study offers a possible explanation for regenerative differences between sensory organs of the inner ear, but shows that additional factors to Atoh1 may be required for optimal reprogramming of hair cell fate.

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