Bone morphogenetic protein 4 promotes the survival and preserves the structure of flow-sorted Bhlhb5+ cochlear spiral ganglion neurons in vitro

Muhammad Waqas,Haibo Shi,Renjie Chai,Xia Gao,Shan Sun,Mingliang Tang,Chuanyin Xuan,Huawei Li,Qiaojun Fang,Jieyu Qi,Irum-Us Islam,Xiaoli Zhang,Shasha Zhang

doi:10.1038/s41598-017-03810-w

Abstract

SGNs are the primary auditory neurons, and damage or loss of SGNs leads to sensorineural hearing loss. BMP4 is a growth factor that belongs to the TGF-β superfamily and has been shown to play a key role during development, but little is known about its effect on postnatal cochlear SGNs in mice. In this study, we used the P3 Bhlhb5-cre/tdTomato transgenic mouse model and FACS to isolate a pure population of Bhlhb5+ SGNs. We found that BMP4 significantly promoted SGN survival after 7 days of culture. We observed fewer apoptotic cells and decreased expression of pro-apoptotic marker genes after BMP4 treatment. We also found that BMP4 promoted monopolar neurite outgrowth of isolated SGNs, and high concentrations of BMP4 preserved the number and the length of neurites in the explant culture of the modiolus harboring the SGNs. We showed that high concentration of BMP4 enhanced neurite growth as determined by the higher average number of filopodia and the larger area of the growth cone. Finally, we found that high concentrations of BMP4 significantly elevated the synapse density of SGNs in explant culture. Thus, our findings suggest that BMP4 has the potential to promote the survival and preserve the structure of SGNs.

Highlights

Spiral ganglion neurons (SGNs) are the primary auditory neurons responsible for delivering the sound signals from the hair cells to the central nervous system via the cochlear nerve[1]
Bone morphogenetic protein 4 (BMP4) is expressed during the delamination of neural progenitors from the cranial placode and in the developing otocyst, where it participates in the development of inner ear hair cells and SGNs25, 26
No structural abnormalities are observed in the cochlear hair cells and stereocilia of these heterozygous mice, but the number of SGNs decreases in the spiral ganglion region, which might be the reason for the partial hearing loss in these mice[33]

Summary

Introduction

Spiral ganglion neurons (SGNs) are the primary auditory neurons responsible for delivering the sound signals from the hair cells to the central nervous system via the cochlear nerve[1]. No structural abnormalities are observed in the cochlear hair cells and stereocilia of these heterozygous mice, but the number of SGNs decreases in the spiral ganglion region, which might be the reason for the partial hearing loss in these mice[33]. These studies indicate that BMP4 plays a critical role during the development of SGNs, but little is known about how it affects the survival and structure of mature SGNs

Methods

Results

Conclusion