2007 — 2009 |
Doetzlhofer, Angelika |
R03Activity Code Description: To provide research support specifically limited in time and amount for studies in categorical program areas. Small grants provide flexibility for initiating studies which are generally for preliminary short-term projects and are non-renewable. |
The Function of Hes and Hey Genes in Maintaining a Supporting Cell State
[unreadable] DESCRIPTION (provided by applicant): The Aim of this proposal is to study the function of transcriptional repressor of the Hes and Hey family in supporting cell development and their potential involvement in repressing hair cell regeneration. Mammals do not regenerate lost hair cells and hair cell loss is a leading cause for deafness in humans. In contrast, supporting cells in birds can function as hair cell progenitors and are capable to regenerate lost hair cells. The choice whether to differentiate into a hair cell or a supporting cell, is controlled by Notch signaling. In the inner ear Notch signaling is believed to be mediated by Hes1 and Hes5, two transcriptional repressors belonging to hairy and enhancer of split (HES) family. We recently discovered that HES related Hey genes (Hey1, Hey2, HeyL) are co-expressed with Hes1 and Hes5 in differentiating supporting cells. In Specific Aim 1 we will address the question if the Hes and Hey genes function synergistically to maintain a supporting cells specific state. We will generate based on their expression pattern combinations of Hey Hes mutant mice and analyze the extent of supporting cell to hair cell trans-differentiation in the single mutant and double mutant mice. In Specific Aim 2 we propose to determine if the persistence of Hey and Hes gene expression in the damaged organ of Corti blocks hair cell regeneration. We propose to analyze if Hes and Hey mutant supporting cells have an enhanced capacity to generate hair cells in primary cell culture. Further we propose to test if loss of Hes or Hey function is sufficient to induce hair cell regeneration in the damaged cochlear using organ culture. In this grant proposal, we want to investigate the role of transcriptional repressors of the Hes and Hey gene family in inhibiting hair cell regeneration. Sensory hair cell loss in the inner ear is a leading cause of deafness and balance disorders. Understanding the molecular mechanisms preventing hair cell regeneration in mammals is crucial for developing successful hair cell replacement therapies. [unreadable] [unreadable] [unreadable]
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2011 — 2015 |
Doetzlhofer, Angelika |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Notch Signaling Pathways in Auditory Support Cell Differentiation and Maintenance @ Johns Hopkins University
DESCRIPTION (provided by applicant): In humans and other mammalian species, damage to mechano-sensory hair cells is irreversible, leading to deafness and balance disorders. Remarkably, non-mammalian vertebrates regenerate lost hair cells. In birds, supporting cells have been shown to replace lost hair cells by mechanisms involving either cell division or direct trans-differentiation. In the mammalian auditory sensory organ, supporting cells do not regenerate lost hair cells. Strikingly, our findings suggest that mammalian supporting cells retain the intrinsic ability to function as hair cell progenitors, but their plasticity to regenerate hair cells is actively suppressed by external inhibitory cues. Our long-term goal is to utilize the latent plasticity of supporting cells to develop supporting cell based hair cell replacement strategies. To attain this goal, it is vital to improve our knowledge of the molecular programs active in developing and in mature supporting cells. We reason that to "reprogram" and induce de- differentiation of supporting cells and consequently trans-differentiation of supporting cells into hair cells, we first have to understand the signals that control differentiation and maintenance in the supporting cell lineage. The goal of this proposal is to determine if the Notch signaling pathway, an evolutionary ancient and highly conserved cell-to-cell communication mechanism, functions in supporting cell differentiation and cell maintenance. In Specific Aim 1 of our proposal, we will test if Notch signaling plays an instructive role in supporting cell differentiation. We will test if induction of an activated form of the Notch1 receptor is sufficient to induce supporting cell fate and whether inhibition of Notch signaling with 3-secretase inhibitors effects the onset and progression of supporting cell differentiation. In Specific Aim 2 of our proposal, we will ablate Rbpj, a core component of the canonical Notch signaling pathway, in supporting cells to address if Notch signaling is required for supporting cell maintenance in the intact and hair cell damaged cochlea. To do so we will employ Rbpj conditional mouse mutants in combination with tamoxifen inducible CreERT lines. We anticipate that this analysis will provide valuable insight into the molecular mechanisms that drive supporting cell differentiation and elucidate the function of Notch signaling in supporting cell maintenance in the adult cochlea. In parallel, we will address a longstanding question-"does persistence of Notch signaling in the hair cell damaged cochlea underlie the lack of hair cell regeneration in mammals?" Addressing this question is relevant to human health as inhibiting Notch signaling using 3-secretase inhibitors in mature cochlea could provide a means for restoring a latent capacity to regenerate hair cells. PUBLIC HEALTH RELEVANCE: It is believed that lack of hair cell regeneration in mammals is due to an inability of neighboring supporting cells to regenerate damaged hair cells. In our proposal, we will characterize the molecular mechanisms instructing supporting cell differentiation and maintenance to elucidate why supporting cells fail to de-differentiate and regenerate lost hair cells. We believe that our findings will shed light on the molecular machinery that restrict hair cell regeneration and could provide new targets for future hair cell replacement therapies.
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2016 — 2020 |
Doetzlhofer, Angelika |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Notch Signaling Pathways in Auditory Supporting Cell Differentiation and Maintece @ Johns Hopkins University
Project summary Auditory supporting cells (SCs) are essential for the proper development, survival and function of mechano- sensory hair cells (HCs) and their innervating neurons. Defects in the biophysical properties or function of SCs result in auditory dysfunction and hearing loss. Despite their importance the molecular mechanisms that control their development and function are largely unknown. A main objective of our proposed study is to uncover the molecular mechanisms that guide auditory SCs development and function. We recently uncovered that Notch signaling instructs SC development in the murine cochlea. Here in this proposed study we will determine the Notch ligand(s) and receptor(s) that control SC differentiation and survival (aim1) as well characterize potential novel roles for Notch signaling and its targets in SC-guided cochlear innervation and auditory function (aim2). Our proposed studies will advance our understanding of how Notch signaling operates in differentiating SCs as wells as provide new insights into how SCs guide neuronal innervation as well as control cochlear homeostasis. A second major objective of our proposed study is to uncover the molecular mechanisms that control the developmental decline of SCs plasticity in the mammalian cochlea. HC loss in mammals is permanent and is a leading cause for deafness in humans. In non- mammalian vertebrates SCs regenerate lost HCs throughout the lifetime of the animal. In mammals, young immature SCs can be coaxed into regenerating lost HCs by inhibiting Notch signaling or over-stimulation of wnt signaling; however, the ability of murine auditory SC to respond to such regenerative stimuli rapidly declines after the first postnatal week. We recently uncovered that the RNA binding protein LIN28B enhances HC production in the immature cochlea in response to Notch signaling. In aim3 we will investigate how LIN28B/let- 7 axis modifies the regenerative response of the immature SCs, as well as address whether LIN28B re- expression in mature SCs enhances their ability to respond to Notch inhibition and regenerate lost HCs. Findings from the proposed experiments could identify new therapeutic targets and lead to novel therapeutic approaches in the treatment of HC loss and eventual cure of deafness.
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