ARHL commonly occurs in old age and brings a bad experience to life. In addition to affecting hearing, some studies have shown a significant correlation between hearing sensitivity and the incidence of Alzheimer's disease[21, 22],as well as the difference between hearing sensitivity and cognitive function among non-demented individuals [23]. Due to the lack of good phenotyping methods and sufficient sample size, several published GWAS data on ARHL have not found reproducible results[24]. We are still unclear about the molecular mechanism of ARHL.
Because of the difficulties in human cohort studies, researchers began to use animal models to help determine the pathogenesis and genetics associated with ARHL. Mice are the main model organisms for studying the auditory function and aging of mammals[25]. For a long time, it has been reported that certain strains have good hearing for the elderly (e.g. CAST, CBA/CaJ, CBA/J, C3H/HeH), while others show a gradual decline in auditory function (e.g. BALB, C57BL/6, DBA/ 2J). The GSE datasets selected in this study are all mouse strains whose hearing loss occurs with age.
Integrating multiple data set displays can improve detection capabilities [26]. Compared with single array analysis, integrating multiple arrays is a better way to improve the reliability of the results. During the GEO search process, we found four chips that study ARHL including GSE45026, GSE6045, GSE62173, and GSE35234. Through analysis, we identified 230 genes (109 up-regulated and 121 down-regulated) co-expressed between GEO data, and screened out 10 up-regulated central genes (MPo, Hp, Cd52, Elane, II1b, H2-K1, Tyrobp, Cd74, Lcp1 and Ptprc) and 10 down-regulated genes (Col3a1, Col4a2, Acan, Postn, Col2a1, Col1a2, Sparc, Lox, Col5a2 and Ctgf).
When conducting GO analysis on up-regulated genes, we found that they mainly focused on defense response to bacterium, ligand − gated ion channel activity, and s receptor complex. For down-gradulated genes, they mainly focused on extracellular structure organization, extracellular matrix structural constituent, cell adhesion molecule binding, etc. the up-regulated DEGs are significantly enriched in certain pathways such as Neuroactive ligand − receptor interaction, Phagosome, Retrograde endocannabinoid signaling, Cell adhesion molecules, etc. For down-regulated important DEGs, these down-regulated DEGs are significantly enriched in certain pathways, such as PI3K-Akt signaling pathway, ECM-receptor interaction, Protein digestion and absorption, Focal adhesion, etc.
Previous studies have shown that hearing loss is mainly due to the loss of internal or external hair cells, which damages IHC ribbon synapses or spiral ganglion neurons [27]. It now appears that the biological processes of gene enrichment, cell composition, and molecular function are consistent with the occurrence of ARHL.
To systematically analyze the relationship and function of the important DEG in ARHL, we mapped DEG to STRING database and obtained PPI network. As we all know, genes with higher node degree in PPI network usually play more roles. To further identify the key genes in ARHL, we selected the top ten up-regulated and down-regulated hub genes for further analysis. The analysis results showed that seven down-regulated genes (Col3a1, Col1a2, Sparc, Col4a2, Col2a1,Lox, Sparc, Ctgf) may be the key genes of ARHL.
We predicted the miRNA targeting the hub gene through miRTarBase, and verified in the difference results of the GSE45026 chip that miR-29a-3p, miR-29b-3p, miR-29c-3p, miR-124-3p were verified, they may play a regulatory role in the process of hearing loss, so we highly suspect that miR-29a-3p, miR-29b-3p, miR-29c-3p, miR-124-3p may be key molecules involved in the occurrence of hearing loss. In the analysis of GSE45026, we only selected C57 mice for analysis, because C57 mice have a clear phenomenon of senile hearing loss. In previous studies, Mun found that the expression of miR-29b-3p was elevated in the cochlea of aged C57BL/6 mice[28], which was consistent with our analysis. For others, miR-29a-3p, miR-29c-3p and miR-124-3p were mainly related to cancer[29–34], AD[35, 36], and miR-124-3p also related to neurogenesis[37, 38] and depression[39], with no research related to hearing loss.
All in all, our study analyzed the GEO database data and found differential genes for age-related hearing loss, and found some key miRNA molecules, which may be potential biological targets for predicting age-related hearing loss.