Hearing loss is primarily caused by damage to sensory hair cells (HC) in the cochlea of the inner ear. Humans and other mammals cannot replace damaged HCs;however, chicken, fish and amphibians can, by proliferation and transdifferentiation of neighboring supporting cells (SC) (Conwin and Oberholtzer, 1997). Interestingly, the tumor suppressor gene, p16INK4a, is absent in non-mammalian vertebrates that have the capacity to regenerate HCs (Kim et al., 2003;Gil and Peters, 2006). In mammals, p16INK4a acts as a cyclin-dependent kinase inhibitor that keeps cells in a quiescent state. Its expression is induced by age as well as mitogenic signaling (Zindy et al., 1997). p16INK4a is also known to play a critical role in the in vivo regenerative ability of adult cells, including neurons (Janzen et al., 2006;Molofsky et al., 2006). It is commonly thought that damaged HCs release signals that cause SCs to reenter the cell cycle. In non-mammalian vertebrates this results in HC regeneration;however, in mammals, we predict that this mitotic activity induces the expression of p16INK4a which keeps SCs in a quiescent state and thus prevents HC regeneration. Is it possible to give a mouse, the chicken's ability to regenerate HCs by inactivating p16INK4a? To achieve this goal, we propose the following central hypothesis: Inactivation of p16INK4a in mammals will allow SCs: (1) to respond to signals released from HCs damaged by antibiotics or genetic ablation, (2) to reenter the cell cycle and (3) to regenerate HCs. To test this hypothesis, we propose the following specific aims:
Specific Aim 1 : To determine the regenerative capacity of SCs in p161NK4a-null mice after HC damage caused by the aminoglycoside antibiotic, gentamicin.
Specific Aim 2 : To determine the regenerative capacity of SCs in p16INK4a-null mice after HC damage caused by acute inactivation of the retinoblastoma protein in postnatal HCs. Although mammals cannot spontaneously regenerate HCs, a process of HC regeneration similar to what occurs in non-mammalian vertebrates could be induced by genetic and/or therapeutic manipulations of cochlear SCs. This proposal is the first step toward the final goal of restoring hearing in those exposed to ototoxic drugs, loud noise or other environmental agents. In addition, HC damage induced by acute inactivation of the retinoblastoma protein in postnatal HCs is a technological breakthrough for the field.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Postdoctoral Individual National Research Service Award (F32)
Project #
5F32DC010310-02
Application #
8064638
Study Section
Special Emphasis Panel (ZDC1-SRB-L (49))
Program Officer
Cyr, Janet
Project Start
2009-07-01
Project End
2012-06-30
Budget Start
2010-07-01
Budget End
2011-06-30
Support Year
2
Fiscal Year
2010
Total Cost
$50,474
Indirect Cost
Name
St. Jude Children's Research Hospital
Department
Type
DUNS #
067717892
City
Memphis
State
TN
Country
United States
Zip Code
38105
Cox, Brandon C; Dearman, Jennifer A; Brancheck, Joseph et al. (2014) Generation of Atoh1-rtTA transgenic mice: a tool for inducible gene expression in hair cells of the inner ear. Sci Rep 4:6885
Walters, Bradley J; Liu, Zhiyong; Crabtree, Mark et al. (2014) Auditory hair cell-specific deletion of p27Kip1 in postnatal mice promotes cell-autonomous generation of new hair cells and normal hearing. J Neurosci 34:15751-63
Cox, Brandon C; Chai, Renjie; Lenoir, Anne et al. (2014) Spontaneous hair cell regeneration in the neonatal mouse cochlea in vivo. Development 141:816-29
Mellado Lagarde, Marcia M; Cox, Brandon C; Fang, Jie et al. (2013) Selective ablation of pillar and deiters' cells severely affects cochlear postnatal development and hearing in mice. J Neurosci 33:1564-76
Cox, Brandon C; Liu, Zhiyong; Lagarde, Marcia M Mellado et al. (2012) Conditional gene expression in the mouse inner ear using Cre-loxP. J Assoc Res Otolaryngol 13:295-322
Liu, Zhiyong; Walters, Brandon J; Owen, Thomas et al. (2012) Regulation of p27Kip1 by Sox2 maintains quiescence of inner pillar cells in the murine auditory sensory epithelium. J Neurosci 32:10530-40
Liu, Zhiyong; Dearman, Jennifer A; Cox, Brandon C et al. (2012) Age-dependent in vivo conversion of mouse cochlear pillar and Deiters' cells to immature hair cells by Atoh1 ectopic expression. J Neurosci 32:6600-10
Burns, Joseph C; Cox, Brandon C; Thiede, Benjamin R et al. (2012) In vivo proliferative regeneration of balance hair cells in newborn mice. J Neurosci 32:6570-7
Yu, Yiling; Weber, Thomas; Yamashita, Tetsuji et al. (2010) In vivo proliferation of postmitotic cochlear supporting cells by acute ablation of the retinoblastoma protein in neonatal mice. J Neurosci 30:5927-36