Effect of histone deacetylase inhibitors trichostatin A and valproic acid on hair cell regeneration in zebrafish lateral line neuromasts.

Yingzi He,Chengfu Cai,Dongmei Tang,Huawei Li,Shan Sun

doi:10.3389/fncel.2014.00382

Abstract

In humans, auditory hair cells are not replaced when injured. Thus, cochlear hair cell loss causes progressive and permanent hearing loss. Conversely, non-mammalian vertebrates are capable of regenerating lost sensory hair cells. The zebrafish lateral line has numerous qualities that make it well-suited for studying hair cell development and regeneration. Histone deacetylase (HDAC) activity has been shown to have an important role in regenerative processes in vertebrates, but its function in hair cell regeneration in vivo is not fully understood. Here, we have examined the role of HDAC activity in hair cell regeneration in the zebrafish lateral line. We eliminated lateral line hair cells of 5-day post-fertilization larvae using neomycin and then treated the larvae with HDAC inhibitors. To assess hair cell regeneration, we used 5-bromo-2-deoxyuridine (BrdU) incorporation in zebrafish larvae to label mitotic cells after hair cell loss. We found that pharmacological inhibition of HDACs using trichostatin A (TSA) or valproic acid (VPA) increased histone acetylation in the regenerated neuromasts following neomycin-induced damage. We also showed that treatment with TSA or VPA decreased the number of supporting cells and regenerated hair cells in response to hair cell damage. Additionally, BrdU immunostaining and western blot analysis showed that TSA or VPA treatment caused a significant decrease in the percentage of S-phase cells and induced p21Cip1 and p27Kip1 expression, both of which are likely to explain the decrease in the amount of newly regenerated hair cells in treated embryos. Finally, we showed that HDAC inhibitors induced no observable cell death in neuromasts as measured by cleaved caspase-3 immunohistochemistry and western blot analysis. Taken together, our results demonstrate that HDAC activity has an important role in the regeneration of hair cells in the lateral line.

Highlights

Loss of sensory hair cells (HCs) in the inner ear as a result of aging, ototoxic drugs, or noise is the primary cause of hearing disorders in humans and most other mammals
We have previously shown that Histone deacetylase (HDAC) activity is necessary for the control of proliferation and migration of the posterior lateral line (PLL) primordium and the concomitant deposition of the neuromasts during the early stages of PLL development in zebrafish (He et al, 2014b)
Our previous study revealed that HDAC activity is involved in lateral line development and might have a role in neuromast formation by altering cell proliferation through the expression of cell cycle regulatory proteins

Summary

Introduction

Loss of sensory hair cells (HCs) in the inner ear as a result of aging, ototoxic drugs, or noise is the primary cause of hearing disorders in humans and most other mammals. Previous studies have reported that newly regenerated HCs in the auditory and vestibular sensory epithelia usually arise through proliferation and differentiation of progenitor cells during the process of proliferative regeneration (Corwin and Cotanche, 1988; Warchol and Corwin, 1996; Stone and Rubel, 2000). These progenitor cells are believed to be non-sensory supporting cells (SCs) that surround HCs in the sensory epithelia. SCs have been shown to have the ability to spontaneously convert into new HCs through an unusual process called direct transdifferentiation, which is the phenotypic conversion of SCs into HCs without cell cycle reentry (Adler and Raphael, 1996; Adler et al, 1997; Baird et al, 2000; Roberson et al, 2004)

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