Abstract

Mesenchymal stromal cells (MSCs) are an adult derived stem cell-like population that has been shown to mediate repair in a wide range of degenerative disorders. The protective effects of MSCs are mainly mediated by the release of growth factors and cytokines thereby modulating the diseased environment and the immune system. Within the inner ear, MSCs have been shown protective against tissue damage induced by sound and a variety of ototoxins. To better understand the mechanism of action of MSCs in the inner ear, mice were exposed to narrow band noise. After exposure, MSCs derived from human umbilical cord Wharton’s jelly were injected into the perilymph. Controls consisted of mice exposed to sound trauma only. Forty-eight hours post-cell delivery, total RNA was extracted from the cochlea and RNAseq performed to evaluate the gene expression induced by the cell therapy. Changes in gene expression were grouped together based on gene ontology classification. A separate cohort of animals was treated in a similar fashion and allowed to survive for 2 weeks post-cell therapy and hearing outcomes determined. Treatment with MSCs after severe sound trauma induced a moderate hearing protective effect. MSC treatment resulted in an up-regulation of genes related to immune modulation, hypoxia response, mitochondrial function and regulation of apoptosis. There was a down-regulation of genes related to synaptic remodeling, calcium homeostasis and the extracellular matrix. Application of MSCs may provide a novel approach to treating sound trauma induced hearing loss and may aid in the identification of novel strategies to protect hearing.

Highlights

  • Sound trauma can lead to hearing loss with protean manifestations

  • We identified up and down regulated genes in mice exposed to noise and treated with Wharton’s jelly-derived MSCs (WJCs) when compared to mice exposed to noise trauma only

  • Cells were cultured in medium consisting of 1% penicillinstreptomycin (Life Technologies), 10% fetal bovine serum (FBS) mesenchymal stem cell qualified (MSCq) (Life Technologies), and fibroblast basal medium (Lonza Group Ltd., Basel, Switzerland), and expanded to passage 5 for all experiments

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Summary

Introduction

Sound trauma can lead to hearing loss with protean manifestations. With exposures ranging from acute blast injury to chronic noise exposure, a wide range of pathological effects are induced in the cochlea. More recent studies have focused on erythroid two related factor 2 (Nrf2) being a key signal mediator at the center of multiple pathways (Fetoni et al, 2019). This molecule acts as a reactive oxygen species (ROS) sensor and normally exists in a bound state in the cytoplasm. It controls a variety of stress responses and events such as oxidative stress and inflammation can cause it to enter the nucleus and activate a variety of signaling cascades (Fetoni et al, 2019). Antioxidants and anti-inflammatory drugs clearly can protect against noise induced hearing loss given the complexity of the induced reactome, it is unlikely that a single pharmaceutical agent would adequately protect against all aspects of damage (Rajguru, 2013; Maeda et al, 2017)

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