EGF Mediates Survival of Rat Cochlear Sensory Cells via an NF-κB Dependent Mechanism In Vitro

The PERK/ATF4/CHOP signaling branch of the unfolded protein response mediates cisplatin-induced ototoxicity in hair cells

Cisplatin is a widely used chemotherapeutic agent. However, its clinical application remains limited due to the high incidence of severe ototoxicity. It has been reported that the unfolded protein response (UPR) is involved in cisplatin-induced ototoxicity. However, the specific mechanism underlying its effect remains unclear. Therefore, the present study aimed to explore the sequential changes in the key UPR signaling branch and its potential pro-apoptotic role in cisplatin-induced ototoxicity. The hair cell-like OC-1 cells were treated with cisplatin for different periods and then the expression levels of the UPR- and apoptosis-related proteins were determined. The results showed that the apoptotic rate of cells was gradually increased with prolonged cisplatin treatment. Furthermore, the sequential changes in three UPR signaling branches were evaluated. The expression levels of activating transcription factor 4 (ATF4) and C/EBP homologous protein (CHOP) were gradually increased with up to 12 h of cisplatin treatment. The aforementioned expression profile was consistent with that observed for the apoptosis-related proteins. Subsequently, the proportion of apoptotic cells was notably decreased in CHOP-silenced hair cell-like OC-1 cells following treatment with cisplatin. Moreover, we found significant hair cells loss and a higher level of CHOP in cisplatin-treated cochlear explants in a time-dependent manner. Overall, the present study demonstrated that the protein kinase RNA‑like endoplasmic reticulum kinase (PERK)/ATF4/CHOP signaling branch could play an important role in cisplatin-induced cell apoptosis. Furthermore, the current study suggested that CHOP may be considered as a promising therapeutic target for cisplatin-induced ototoxicity.

Nrf2 Knockout Affected the Ferroptosis Signaling Pathway against Cisplatin-Induced Hair Cell-Like HEI-OC1 Cell Death

Cisplatin is a well-known and widely used anticancer drug with high therapeutic efficacy in solid tumors; however, side effects are common with its use. Because cisplatin can be retained in the cochlea, ototoxicity leading to hearing loss limits its clinical applications. Here, we report that Nrf2 knockout (KO) strongly increased cisplatin resistance in HEI-OC1 cells, which are immortalized cells from the murine organ of Corti. The underlying mechanism of this phenomenon was uncovered, and an important novel therapeutic target for combating cisplatin-induced hearing loss was identified. Preliminary investigations determined that Nrf2 KO markedly decreased TfR1 protein levels and increased GPX4 protein levels. Thus, ferroptosis may protect organisms from cisplatin-induced cell death. Furthermore, Nrf2 KO cells were resistant to the classical ferroptosis inducers RSL3 and erastin, providing solid evidence that Nrf2 KO inhibits ferroptosis and that knocking out Nrf2 may be a new clinical strategy to prevent cisplatin-induced hearing loss.

Tauroursodeoxycholic acid attenuates cisplatin-induced ototoxicity by inhibiting the accumulation and aggregation of unfolded or misfolded proteins in the endoplasmic reticulum

Cisplatin-induced ototoxicity is one of the important reasons that limit the drug's clinical application, and its mechanism has not been fully elucidated so far. The aim of this study was to explore the attenuate effect of tauroursodeoxycholic acid (TUDCA), a proteostasis promoter, on cisplatin-induced ototoxicity in vivo and in vitro, and to explore its possible mechanism. Auditory brainstem response (ABR) was measured to identify the attenuate effects of TUDCA administered subcutaneously [500 mg/kg/d × 3d, cisplatin: 4.6 mg/kg/d × 3d, intraperitoneal injection (i.p.)] or trans-tympanically (0.5 mg/mL, cisplatin: 12 mg/kg, i.p. with a pump) in Sprague-Dawley (SD) rats subjected to cisplatin-induced hearing loss. The cochlear explants of neonatal rats and OC1 auditory hair cell-like cell lines cultured in vitro were used to observe the number of apoptotic cells and the endoplasmic reticulum (ER) stress in the control, cisplatin (5 μM for 48 h for cochlear explants, 10 μM for 24 h for OC1 cells), and cisplatin + TUDCA (1 mM for 24 h for cochlear explants, 1.6 mM for 24 h for OC1 cells) groups. Differences in the expression of key proteins in the ER protein quality control (ERQC) system were detected. The changes in the attenuate effect of TUDCA on cisplatin-induced ototoxicity after down-regulating calreticulin (CRT), UDP-glucose ceramide glucosyltransferase-like 1 (UGGT1), and OS9 ER lectin (OS9) were also measured. The effect of TUDCA (10 mM) on stabilizing unfolded or misfolded proteins (UFP/MFP) was analyzed in a cell-free 0.2 % bovine serum albumin (BSA) aggregation system in vitro. Both the subcutaneous and trans-tympanic TUDCA administration alleviated cisplatin-induced increase in ABR thresholds in rats. TUDCA was able to reduce cisplatin-induced apoptosis and alleviate ER stress in cochlear explants and OC1 cells. Under the cisplatin treatment, the expression levels of CRT, UGGT1, and OS9 in the auditory hair cell increased, and the expression of total ubiquitinated proteins decreased. TUDCA attenuated the effect of cisplatin on UGGT1 and OS9, and recovered the protein ubiquitination levels. After down-regulating CRT, UGGT1, or OS9, the protective effect of TUDCA decreased. In the cell-free experimental system, TUDCA inhibited the aggregation of denatured BSA molecules. In summary, TUDCA can attenuate cisplatin-induced ototoxicity, possibly by inhibiting the accumulation and aggregation of UFP/MFP and the associated ER stress.

Regulation of bone morphogenetic protein 4 on epithelial tissue

Epithelial tissues provide tissue barriers and specialize in organs and glands. When epithelial homeostasis is physiologically or pathologically stimulated, epithelial cells produce mesenchymal cells through the epithelial-mesenchymal transition, forming new tissues, promoting the cure of diseases or leading to illness. A variety of cytokines are involved in the regulation of epithelial cell differentiation. Bone morphogenetic proteins (BMPs), especially the bone morphogenetic protein 4 (BMP4) has a variety of biological functions and plays a prominent role in the regulation of epithelial cell differentiation. BMP4 is an important regulatory factor of a series of life activities in vertebrates, which is also related to cell proliferation, differentiation and mobility, it also has relation with tumor development. This paper mainly reviews the mechanism of BMP4's regulation on epithelial tissues, as well as its effect on the growth, differentiation, benign lesions and malignant lesions of epithelial tissues, and expounds the function of BMP4 in epithelial tissues, to provide theoretical support for the research on reducing epithelial diseases.

The nuclear transcription factor FoxG1 affects the sensitivity of mimetic aging hair cells to inflammation by regulating autophagy pathways

Inflammation is a self-defense response to protect individuals from infection and tissue damage, but excessive or persistent inflammation can have adverse effects on cell survival. Many individuals become especially susceptible to chronic-inflammation-induced sensorineural hearing loss as they age, but the intrinsic molecular mechanism behind aging individuals' increased risk of hearing loss remains unclear. FoxG1 (forkhead box transcription factor G1) is a key transcription factor that plays important roles in hair cell survival through the regulation of mitochondrial function, but how the function of FoxG1 changes during aging and under inflammatory conditions is unknown. In this study, we first found that FoxG1 expression and autophagy both increased gradually in the low concentration lipopolysaccharide (LPS)-induced inflammation model, while after high concentration of LPS treatment both FoxG1 expression and autophagy levels decreased as the concentration of LPS increased. We then used siRNA to downregulate Foxg1 expression in hair cell-like OC-1 cells and found that cell death and apoptosis were significantly increased after LPS injury. Furthermore, we used d-galactose (D-gal) to create an aging model with hair cell-like OC-1 cells and cochlear explant cultures in vitro and found that the expression of Foxg1 and the level of autophagy were both decreased after D-gal and LPS co-treatment. Lastly, we knocked down the expression of Foxg1 under aged inflammation conditions and found increased numbers of dead and apoptotic cells. Together these results suggest that FoxG1 affects the sensitivity of mimetic aging hair cells to inflammation by regulating autophagy pathways.

Sonic hedgehog (SHH) promotes the differentiation of mouse cochlear neural progenitors via the Math1-Brn3.1 signaling pathway in vitro

Sonic hedgehog (SHH) is essential for the development of the cochlear duct that harbors the organ of Corti. However, little is known about the molecular signaling pathway through which SHH promotes the development of the organ of Corti, especially cochlear sensory epithelial cells. In this study, we demonstrated that SHH contributes to the differentiation of cochlear neural progenitors (CNPs), which are derived from the postnatal day 1 organ of Corti in mice. Addition of SHH to CNPs increased the formation of epithelial cell islands, simultaneously activated the expression of Math1 that is a transcription factor for the initial differentiation of auditory hair cells. The increased expression of Math1 then regulated the promoter activity of Brn3.1, another transcription factor that controls the further differentiation and survival of auditory hair cells. Taken together, our data suggest that SHH plays an important role in the promotion of auditory hair cell differentiation via the Math1-Brn3.1 signaling pathway.