Type 1 Diabetes Induces Hearing Loss: Functional and Histological Findings in An Akita Mouse Model.

Yun Yeong Lee,Yeon Ju Kim,Jeong Hun Jang,Eun Sol Gil,Yun-Hoon Choung,Hantai Kim

doi:10.3390/biomedicines8090343

Abstract

The relationship between type 1 diabetes and hearing loss is not well known, although based on many pathological studies, type 2 diabetes induced hearing loss is associated with microcirculation problems in the inner ear. The purpose of this study was to investigate the correlation between type 1 diabetes and hearing loss through hearing function and immunohistochemical analyses using type 1 diabetic Akita or wild-type (WT) mice. The Akita mice had a significant increase in hearing thresholds, blood glucose, and insulin tolerance compared to WT mice. Histological analysis showed that the loss of cells and damage to mitochondria in the spiral ganglion neurons of Akita mice were significantly increased compared to WT. Also, the stria vascularis showed decreased thickness, loss of intermediate cells, and disturbance in blood capillary shape in the Akita mice. Moreover, a reduction in type I, II, and IV fibrocytes and Na+/K+-ATPase α1 expression in spiral ligament was also observed. Cleaved caspase-3 expression was highly expressed in spiral ganglion neurons. In conclusion, hearing loss in type 1 diabetes is caused not only by ion imbalance and blood flow disorders of cochlear endolymph, but through the degenerative nervous system via apoptosis-mediated cell death.

Highlights

Hearing loss can be genetic or acquired by exposure to noise, toxic drugs, or systemic diseases such as hypertension, hyperlipidemia, and diabetes [1]
The Akita group had significantly impaired glucose levels (145 ± 12.3 vs. 516 ± 53.2) and insulin sensitivity compared to the WT group at 0, 15, 30, 60, and 120 min after subcutaneous injection of insulin
We demonstrated that loss of stria vascularis (SV), Spiral Ligament (SL), spiral ganglion neurons (SGNs), and Na+ /K+ -ATPase α1 was due mainly to apoptosis

Summary

Introduction

Hearing loss can be genetic or acquired by exposure to noise, toxic drugs, or systemic diseases such as hypertension, hyperlipidemia, and diabetes [1]. Diabetes is classified into types 1 and 2. Type 1 diabetes is caused by gradual loss or dysfunction of insulin-forming β-cells in the pancreas. Type 2 diabetes is mainly caused by increased insulin resistance and decreased insulin secretion [3]. Diabetes can cause sudden increases in blood viscosity as well as microvascular damage and microcirculation disorders such as thrombosis and embolism [4,5]. A Korean cohort study found a 36% higher risk of incident hearing loss among those with diabetes [7]. The hearing impairment was associated with diabetes complications, such as retinopathy and nephropathy [8]

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