Table 3.

Descriptive features of selected studies which investigated DNA methylation in relation to hearing loss in animal models

Animal studies
Author/Year	Country	Disease	Design	Sample Size	Species/age	Main objective	Results
Zhang, X., et al. 2023 [13]	China	Induced intermittent hypoxia	Methylation-Specific PCR	n = 28	Rats/56 days	Determine whether uhrf1 can induce the methylation of gjb2 in cochlea damaged by intermittent hypoxia (IH)	uhrf1 is highly expressed in IH-injured cochlea/hair cells and induces hypermethylation of gjb2 when combined with gjb2
Zheng, Z., et al. 2021 [14]	China	Noise-Induced Hearing Loss	Histology and Immune Fluorescence	no info	Mice/ 12 weeks	Assessing the effects of DNA methylation on noise-induced hearing loss	Inhibition of dnmt1 ameliorates noise-induced hearing loss and indicates that dnmt1 may be a promising therapeutic target
Lin, J., et al. 2018 [15]	China	Prenatal Hypoxia	Methylation-Specific PCR	n = 120	Rat Offspring/ No info	Examine gjb2 promoter methylation in rats exposed to chronic prenatal hypoxia	Significant hypermethylation of CpG sites within the gjb2 promoter region was found in offspring exposed to hypoxia in utero. In addition, subsequent decrease in gjb2 expression as well as inner and outer hair cell defects in the organ of Corti of these Rats
Deng, X. and Z. Hu 2020 [16]	China	Chemically Induced Hearing Loss	Histology and Immune Fluorescence	no info	Mice/ 4–6 weeks	Identify if generic DNA methylation inhibitor can regenerate hair cells	Hair cell damage induced by kanamycin was shown to be regenerated via sox2-positive supporting cells following exposure to DNA methylation inhibitor. Hence global or specific methylation events may prevent re-generation of damaged hair cells
Deng, X., et al. 2019 [17]	China	Chemically Induced Hearing Loss	Histology and Immune Fluorescence	n = 48	Mice/4–6 weeks	Identify if generic DNA methylation inhibitor can regenerate outer hair cells	DNMT inhibitor may promote hair cell regeneration in a chemically deafened mouse model