Comprehensive analysis on the signaling pathway of Norrie disease protein (Ndp)
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ABSTRACT: Mutations in the gene for Norrie disease protein (Ndp) cause syndromic deafness and blindness. We show that cochlear function in an Ndp knockout (KO) mouse deteriorated with age: at P3-P4, hair cells (HCs) showed progressive loss of Pou4f3 and Gfi1, key transcription factors for HC maturation, and Myo7a, a specialized myosin required for normal function of HC stereocilia. Loss of expression of these genes correlated to increasing HC loss and profound hearing loss by 2 months of age. We show that overexpression of the Ndp gene in neonatal supporting cells or, remarkably, upregulation of canonical Wnt signaling in HCs rescued HCs and cochlear function. We conclude that Ndp secreted from supporting cells orchestrates a transcription factor network for the maintenance and survival of HCs and that increasing the level of b-catenin, the intracellular effector of Wnt signaling, is sufficient to replace the functional requirement for Ndp in the cochlea.
Project description:Ectopic expression of Atoh1 in non-sensory supporting cells (SCs) in mouse cochleae induces their conversion to hair cells (HCs) in vivo. cHCs in multiple intermediate states of the conversion process that most closely resembled neonatal differentiating HCs, but differed from the progenitors. We further identified 52 transcription factors that are differentially expressed in cHCs, SCs, and mature HCs and confirmed that Isl1 synergistically enhanced the efficiency of Atoh1-mediated HC conversion in cochlear explants. Our results demonstrate that direct HC conversion from SCs in vivo follows a different path from normal development and requires multiple factors for maximum efficiency and completion.
Project description:Mutations in miRNA-96, a microRNA expressed within the hair cells (HCs) of the inner ear, result in progressive hearing loss in both mouse models and humans. While previous studies have delved into miR-96 transcriptional cascades via whole organ of Corti microarray experiments of diminuendo (Mir96Dmdo) mice, they face limitations in pinpointing cell type-specific differentially expressed genes. This hinders the ability to conclusively determine if the effects of Mir96Dmdo are specifically within HCs and contribute to the observed abnormal Mir96Dmdo HC phenotype and determine the role of miR-96 in HCs. In this study, we generate the first HC-specific RNA-sequencing (RNA-seq) datasets from Mir96Dmdo; Atoh1/nGFP+ postnatal day 1 wildtype, heterozygous, and homozygous mutant mice. Our differential gene expression analysis between Mir96Dmdo homozygous mutant HCs compared to wildtype HCs identified 215 upregulated and 428 downregulated genes. Many significantly downregulated genes in Mir96Dmdo homozygous mutant HCs have established roles in HC development and/or known roles in deafness such as Myo15, Myo7a, Ush1c Gfi1, and Ptprq, some of which were not previously identified in other miR-96 datasets. In addition, active modules of protein-protein interaction networks of significantly downregulated genes in Mir96Dmdo homozygous mutant HCs reveal enrichment in GO terms with biological functions such as sound perception and endocytosis. Genes significantly upregulated in Mir96Dmdo homozygous mutant HCs, which are more likely to be direct targets of miR-96, show higher expression in wildtype supporting cells compared to wildtype HCs, suggesting a role of miR-96 in suppressing non-HC genes during HC development. Finally, all generated HC-specific Mir96Dmdo RNA-seq datasets from this manuscript are now publicly available in the miR-96 specific gEAR profile (https://umgear.org/p?l=miR96).
Project description:Strategies to overcome irreversible cochlear hair cell (HC) damage and loss are of vital importance to develop a treatment for hearing loss. HC regeneration in adult cochlea relies on a two-phase process: 1) Reprogramming mature cochlear (SCs) to regain the properties of their younger selves; 2) Activating Atoh1, a gene responsible for HC fate-determining, in the reprogrammed adult SCs for HC regeneration. We have shown that, by transient co-activation of Myc and NICD (Notch1 intracellular domain), the adult mouse cochlea can be successfully reprogrammed to a relatively younger stage and regain progenitor capacity, with the regeneration of HCs following Atoh1 overexpression in vitro and in vivo. We identified a combination (the cocktail) of drug-like molecules composing of small molecules and siRNAs to activate the pathways of Myc, Notch1, Wnt and cAMP. To identify molecules to reprogram mature cochlear SCs and HC regeneration, we utilized single-cell RNA sequencing and uncovered the pathways and their target genes underlying chemical-mediated reprogramming. We used an in-house adult cochlea explant culture system and carried out single-cell RNA sequencing to examine the gene expression profiles of cochlear explants, in response to chemical-induced reprogramming. We compared gene expression profiles between Vehicle/ad.Atoh1 activation vs. Cocktail (chemical reprogramming)/ad.Atoh1 activation.
Project description:Myosin-VIIA (MYO7A) in an unconventional myosin responsible for syndromic (Usher 1B) or non-syndromic recessive deafness in humans when mutated. In the cochlea, MYO7A is expressed in the stereocilia of both inner and outer hair cells, where it is believed to act as the motor protein tensioning the mechanoelectrical transducer (MET) channel. Whether this tensioning role is a common feature among both types of cochlear hair cells is unknown. Here we show that MYO7A has a distinct role in adult outer hair cells (OHCs), being crucial for the structural integrity of the MET complex. Postnatal deletion of MYO7A did not affect the staircase structure of the hair bundles but caused a progressive reduction of the size of the MET current without affecting the resting open probability and calcium sensitivity of the MET channel. The hair bundle of OHCs deficient in MYO7A also showed reduced bundle stiffness and was highly susceptible to noise exposure. RNA-sequencing identified the down-regulation of several stereociliary proteins in the Myo7a-deficient cochlea. This study reveals that IHCs and OHCs use different mechanisms to maintain the MET channel in its most sensitive resting open position, and confirms that in OHCs, this mechanism is MYO7A independent.
Project description:Mechanosensory hair cells (HCs) are the primary receptors of our senses of hearing and balance. However, very little is known about the transcriptional regulators involved in HC fate determination and differentiation. In this paper, we show that expression of three HC lineage-specific transcription factors: Gfi1, Pou4f3 and Atoh1, can induce a direct commitment towards HC fate during in vitro embryonic stem cell (ESC) differentiation. Induced HCs (iHCs) express numerous HC-specific genes and exhibit polarized membrane protusions reminiscent of stereociliary bundles. The ability to obtain purified populations of iHCs by virtue of the Myo7:mVenus reporter line (iGPA-Myo7a:mVenus) allowed us to generate highly reproducible gene expression profiles for these cells, at various phases of their development (day 8 and day 12 of cell culture).
Project description:Strategies to overcome irreversible cochlear hair cell (HC) damage and loss are of vital importance to develop a treatment for hearing loss. HC regeneration in adult cochlea relies on a two-phase process: 1) Reprogramming mature cochlear (SCs) to regain the properties of their younger selves; 2) Activating Atoh1, a gene responsible for HC fate-determining, in the reprogrammed adult SCs for HC regeneration. We have shown that, by transient co-activation of Myc and NICD (Notch1 intracellular domain), the adult mouse cochlea can be successfully reprogrammed to a relatively younger stage and regain progenitor capacity, with the regeneration of HCs following Atoh1 overexpression in vitro and in vivo. To identify molecules to reprogram mature cochlear SCs and HC regeneration, we utilized single-cell RNA sequencing and uncovered the pathways and their target genes underlying MYC/NICD-mediated reprogramming. We used an in-house adult cochlea explant culture system and carried out single-cell RNA sequencing to examine the gene expression profiles of cochlear explants from a transgenic mouse model, rtTa/tet-Myc/-tet-NICD, in response to Dox-induced MYC/NICD co-activation. We compared gene expression profiles between Atoh1 activation vs. MYC/NICD/Atoh1 co-activation.
Project description:Strategies to overcome irreversible cochlear hair cell (HC) damage and loss are of vital importance to develop a treatment for hearing loss. HC regeneration in adult cochlea relies on a two-phase process: 1) Reprogramming mature cochlear (SCs) to regain the properties of their younger selves; 2) Activating Atoh1, a gene responsible for HC fate-determining, in the reprogrammed adult SCs for HC regeneration. We have shown that, by transient co-activation of Myc and NICD (Notch1 intracellular domain), the adult mouse cochlea can be successfully reprogrammed to a relatively younger stage and regain progenitor capacity, with the regeneration of HCs following Atoh1 overexpression in vitro and in vivo. To identify molecules to reprogram mature cochlear SCs, we utilized single-cell RNA sequencing and uncovered the pathways and their target genes underlying MYC/NICD-mediated reprogramming. We used an in-house adult cochlea explant culture system and carried out single-cell RNA sequencing to examine the gene expression profiles of cochlear explants from a transgenic mouse model, rtTa/tet-Myc/-tet-NICD, in response to Dox-induced MYC/NICD co-activation. We have shown that a 4-day treatment by Dox in cultured adult rtTa/tetMyc/-tet-NICD cochleae was sufficient to reprogram adult SCs for HC regeneration.
Project description:Through its activity in stereocilia, MYO7A (myosin VIIA) is essential for hair cell function in the inner ear. Utilizing multiple stages of immunoaffinity enrichment, we have developed a strategy that allows us to partially purify stereocilia membranes from thousands of chick inner ears and isolate low-abundance MYO7A protein complexes from those membranes. By analysis of MYO7A and co-purifying molecules with shotgun and targeted mass spectrometry, we demonstrated that MYO7A forms a complex with PDZD7, a paralog of USH1C and DFNB31, which has been shown to localize to the ankle-link region of stereocilia.
Project description:Through its activity in stereocilia, MYO7A (myosin VIIA) is essential for hair cell function in the inner ear. Utilizing multiple stages of immunoaffinity enrichment, we have developed a strategy that allows us to partially purify stereocilia membranes from thousands of chick inner ears and isolate low-abundance MYO7A protein complexes from those membranes. The D10 stereocilia membrane enrichment protocol involves density centrifugation steps and immuno-enrichment of stereocilia using the D10 antibody, directed against the major stereocilia transmembrane protein PTPRQ. The data in this submission document the effectiveness of the enrichment procedure.
Project description:Sensorineural hearing loss (SHL) is a relatively common disease, and studies have suggested viral infection as a major cause. In the inner ear, the blood-labyrinthine barrier prevents access of the peripheral immune system; therefore, the immune system remains poorly understood. Here we found that cochlear accessory supporting cells (SCs), which are anchored by tight junctions, are organized tissue-resident macrophages. Virus-infected supporting cells change into activated macrophages and protect audiosensory receptor hair cells (HCs) against virus infection by producing interferon (IFN)-α/β. Moreover, we also observed bacterial phagocytosis by SCs. However, tumour necrosis factor-related apoptosis-inducing ligand (Trail), produced by virus-infected SCs, induced sensory hair loss and HC death by necroptosis. Notably, corticosteroid, the only effective drug for SHL, inhibited the virus-induced macrophage change of SCs. These results revealed an inner ear immune system, and suggest a possible mechanism for virus-induced SHL.