Cellular reprogramming offers tremendous potential for therapeutics, disease studies, and developmental processes. However, direct reprogramming through ectopic expression of defined transcription factors is a slow and inefficient process with most cells failing to reprogram. In the auditory field, ectopic expressionof transcription factors such as Atoh1 has been used to convert mammalian supporting cells into cells that express many endogenous hair cell markers. However, the reprogramming process of transforming supporting cells into hair cells may not be solely about genetic transformation, but also epigenetic transformation. Studies using induced pluripotent stem cells (iPSCs) have shown that they retain the epigenetic memory of their somatic cell of origin. The epigenetic memory retained by iPSCs can interfere with their potential for differentiation into other cell types. Additionally, iPSCs derived from aged mice have a decreased potential for reprograming compared to iPSCs derived from juvenile mice. Although, ectopic expression of transcription factors (Atoh1) can convert neonatal supporting cells into hair cell-like cells, loss of cellular plasticity at later postnatal ages could largely impact clinical application of this method. Presumably, the optimal reprogramming of supporting cells to hair cells would require complete epigenetic reprogramming to that of an endogenous hair cell, but current techniques have not yet been developed for complete epigenetic reprogramming to occur. However, epigenetic therapeutics such as histone deacetylase inhibitors, histone methyltransferase inhibitors, and DNA methylation inhibitors have been used on iPSCs to increase reprogramming efficiency. Further analysis is needed to better understand whether epigenetic reprogramming is required for mammalian hair cell regeneration and whether epigenetic therapeutics may have a role in hair cell regeneration. The long term goal of this research is to better understand the epigenetic modifications that occur during postnatal inner ear development, and ultimately to help increase cellular plasticity in the mature mammalian inner ear. Thus, we propose the following central hypothesis: Epigenetic modifications during neonatal development in the mammalian inner ear cause a loss in cellular plasticity and use of epigenetic therapeutics will increase the trans-differentiation potential of supporting cells to become hair cells. To test this hypothesis, we propose the following specific aims:
Aim 1. Test whether epigenetic factors are differentially expressed during neonatal development in the mouse inner ear;
Aim 2. Test whether DNA methylation is modified in the mouse inner ear during postnatal development or in response to ectopic Atoh1 expression;
and Aim 3. Test whether epigenetic therapeutics affect hair cell regeneration in the mouse inner ear
The results of this research will lead to significant advances in our basic understanding of how epigenetic modifications contribute to auditory tissue maturation and hearing regeneration. The mechanisms that underlie chromatin modifications and transcriptional regulation are likely to be critical for terminal cellular differentiation and cellular plasticity. These results may also contribute to public health in the development of improved therapies for treating hearing loss.