Shikonin Attenuates Cochlear Spiral Ganglion Neuron Degeneration by Activating Nrf2-ARE Signaling Pathway.

Hongjie Du,Fangyuan Zhu,Pan Zhang,Ming Xia,Xuanchen Zhou,Lei Shi,Zhenxiao Teng,Huiming Yang,Miaoqing Zhao,Chengcheng Liu,Na Guo,Houyang Hu,Yajie Wang

doi:10.3389/fnmol.2022.829642

Abstract

The molecular mechanisms that regulate the proliferation and differentiation of inner ear spiral ganglion cells (SGCs) remain largely unknown. Shikonin (a naphthoquinone pigment isolated from the traditional Chinese herbal medicine comfrey root) has anti-oxidation, anti-apoptosis and promoting proliferation and differentiation effects on neural progenitor cells. To study the protective effect of shikonin on auditory nerve damage, we isolated spiral ganglion neuron cells (SGNs) and spiral ganglion Schwann cells (SGSs) that provide nutrients in vitro and pretreated them with shikonin. We found that shikonin can reduce ouabain, a drug that can selectively destroy SGNs and induce auditory nerve damage, caused SGNs proliferation decreased, neurite outgrowth inhibition, cells apoptosis and mitochondrial depolarization. In addition, we found that shikonin can increase the expression of Nrf2 and its downstream molecules HO-1 and NQO1, thereby enhancing the antioxidant capacity of SGNs and SGSs, promoting cells proliferation, and inhibiting cells apoptosis by activating the Nrf2/antioxidant response elements (ARE) signal pathway. However, knockdown of Nrf2 rescued the protective effect of shikonin on SGNs and SGSs damage. In addition, we injected shikonin pretreatment into mouse that ouabain-induced hearing loss and found that shikonin pretreatment has a defensive effect on auditory nerve damage. In summary, the results of this study indicate that shikonin could attenuate the level of oxidative stress in SGNs and SGSs through the Nrf2-ARE signaling pathway activated, induce the proliferation and differentiation of SGNs, and thereby improve the neurological hearing damage in mice. Therefore, shikonin may be a candidate therapeutic drug for endogenous antioxidants that can be used to treat neurological deafness.

Highlights

Sensorineural hearing loss is a sensorineural disorder that affects human physical and mental health and quality of life
The existence of spiral ganglion Schwann cells (SGSs) is essential to the maintenance of spiral ganglion neuron cells (SGNs) function, and studies have shown that SGN dysfunction and degeneration are the most important causes of hearing loss (Chai et al, 2017)
The results showed that compared with the pretreatment group without shikonin, shikonin at a concentration of 1 μM can increase the cell activity and cell cycle of SGNs inhibited by ouabain, and increase the proportion of S-phase cells (Figures 3C,E)

Summary

Introduction

Sensorineural hearing loss is a sensorineural disorder that affects human physical and mental health and quality of life. H. et al, 2021) and spiral ganglion neuron degeneration subsequently (White et al, 2000; Liu et al, 2019a). Spiral Ganglion Neuron (SGN), as the first afferent neuron in the auditory pathway, transmits mechanical sound signals received from the outside world from hair cells to cochlear sensory neurons for processing, thereby establishing the bridge between physics and perceptual world of sound (Reijntjes and Pyott, 2016; Tan et al, 2019; Wei et al, 2021). Studies have shown that because SGNs cannot regenerate, the loss of cochlear signals can lead to irreversible hearing damage (Liu et al, 2019a; Ding et al, 2020). Spiral ganglion Schwann cells (SGSs) are glial cells responsible for myelination in the peripheral nervous system (Wise et al, 2017; Meas et al, 2018). Schwann cells play an irreplaceable role in the development of the cochlear nervous system, especially in the recovery and protection of the damaged nervous system

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Conclusion