Endoplasmic Reticulum Stress Is Involved in Cochlear Cell Apoptosis in a Cisplatin-Induced Ototoxicity Rat Model

Endoplasmic reticulum (ER) stress arises when excessive improperly folded proteins accumulate in the ER lumen. When ER stress occurs, the unfolded protein response (UPR) is subsequently activated to restore ER proteostasis. However, severe ER stress leads to apoptosis. Recent studies have suggested that cisplatin cytotoxicity may be related to ER stress. The purpose of this study was to determine whether ER stress participates in cochlear cell apoptosis in a cisplatin-induced ototoxicity rat model and to also determine the possible relationship between ER stress and hearing loss. Our results revealed that treatment with cisplatin upregulated the expression of active caspase-12 in cochlear cells, which is indicative of cisplatin-induced activation of ER-specific apoptosis. Increased expression of C/EBP homologous protein (CHOP) and cleaved caspase-9 suggested a close relationship between severe ER stress and mitochondria-dependent apoptosis in the cochlear cells of cisplatin-treated rats. In addition, we found that tauroursodeoxycholic acid (TUDCA), a promoter of ER proteostasis, had a protective effect on cisplatin-induced hearing loss. These results demonstrate that ER stress is involved in the cisplatin-induced apoptosis of cochlear cells in vivo.