Reg3b Alleviates Cisplatin-Induced Apoptosis of Hair Cells in Cochlear Organ of Corti

Background: Cisplatin-induced cochlear damage causes permanent hearing loss, which can hamper social communication and daily lives. Upregulation of gene regenerating islet-derived protein 3-beta (Reg3b) is reported to have a protective role against damage to the organ of Corti and hearing loss. The aim of this study was to elucidate the role of Reg3 beta in cisplatin-induced cochlear damage, both in vitro and in vivo.Method: Sprague-Dawley rats were treated with an intraperitoneal injection of cisplatin (2 mg/kg a day), to generate a cochlear damage model. The hearing thresholds of these rats were measured by auditory brainstem response (ABR) and distortion prod-uct otoacoustic emission (DPOAE) tests. The cochleae of these rats were harvested and cultured in vitro. Adeno-associated virus serotype 1 (AAV1) vectors were employed, to overexpress or knock down Reg3b in the organ of Corti both in vitro and in vivo. Changes in cochlear morphology were checked for, using hematoxylin and eosin staining and immunohistochemistry. A Termi-nal Deoxynucleotidyl Transferase Dutp Nick End Labeling (TUNEL) assay was performed, to evaluate hair cell apoptosis. The levels of apoptosis-related proteins were measured by western blotting. Results: In vitro, Reg3b overexpression reduced cisplatin-induced apoptosis, the level of cleaved caspase-3 and cleaved caspase-9, and the Bax/Bcl-2 ratio in cultured organs of Corti, whereas Reg3b knockdown elicited the opposite effects. In vivo, Reg3b over -expression protected rats from cisplatin-induced hearing damage, by reducing ABR threshold shifts and increasing the DPOAE amplitude, whereas Reg3b knockdown enhanced cisplatin-induced injury. Furthermore, Reg3b overexpression ameliorated the cisplatin-induced necroptotic changes and loss of spiral ganglion neurons in the organ of Corti, which was accompanied by a re-duction in cleavage of caspase-3 and caspase-9 and the Bax/Bcl-2 ratio. In contrast, the level of apoptotic proteins was increased when Reg3b was inhibited.Conclusions: Reg3 beta can alleviate cisplatin-induced apoptosis in the organ of Corti both in vitro and in vivo. Targeting Reg3 beta may be a promising therapy for cisplatin-induced hearing loss.