Mwangi Martin, Kil Sung-Hee, Phak David, Park Hun Yi, Lim David J, Park Raekil, Moon Sung K
Department of Head and Neck Surgery, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States.
Department of Otolaryngology, Ajou University School of Medicine, Suwon, South Korea.
Front Cell Neurosci. 2017 Oct 6;11:314. doi: 10.3389/fncel.2017.00314. eCollection 2017.
Inflammatory reaction plays a crucial role in the pathophysiology of acquired hearing loss such as ototoxicity and labyrinthitis. In our earlier work, we showed the pivotal role of otic fibrocytes in cochlear inflammation and the critical involvement of proinflammatory cytokines in cisplatin ototoxicity. We also demonstrated that otic fibrocytes inhibit monocyte chemoattractant protein 1 (CCL2) upregulation in response to interleukin-10 (IL-10) via heme oxygenase 1 (HMOX1) signaling, resulting in suppression of cochlear inflammation. However, it is still unclear how IL-10 affects inflammation-mediated cochlear injury. Here we aim to determine how hypochlorous acid, a model inflammation mediator affects cochlear cell viability and how IL-10 affects hypochlorous acid-mediated cochlear cell injury. NaOCl, a sodium salt of hypochlorous acid (HOCl) was found to induce cytotoxicity of HEI-OC1 cells in a dose-dependent manner. Combination of hydrogen peroxide and myeloperoxidase augmented cisplatin cytotoxicity, and this synergism was inhibited by N-Acetyl-L-cysteine and ML-171. The rat spiral ligament cell line (RSL) appeared to upregulate the antioxidant response element (ARE) activities upon exposure to IL-10. RSL cells upregulated the expression of NRF2 (an ARE ligand) and NR0B2 in response to CoPP (a HMOX1 inducer), but not to ZnPP (a HMOX1 inhibitor). Adenovirus-mediated overexpression of NR0B2 was found to suppress CCL2 upregulation. IL-10-positive cells appeared in the mouse stria vascularis 1 day after intraperitoneal injection of lipopolysaccharide (LPS). Five days after injection, IL-10-positive cells were observed in the spiral ligament, spiral limbus, spiral ganglia, and suprastrial area, but not in the stria vascularis. IL-10R1 appeared to be expressed in the mouse organ of Corti as well as HEI-OC1 cells. HEI-OC1 cells upregulated Bcl-xL expression in response to IL-10, and IL-10 was shown to attenuate NaOCl-induced cytotoxicity. In addition, HEI-OC1 cells upregulated IL-22RA upon exposure to cisplatin, and NaOCl cytotoxicity was inhibited by IL-22. Taken together, our findings suggest that hypochlorous acid is involved in cochlear injury and that IL-10 potentially reduces cochlear injury through not only inhibition of inflammation but also enhancement of cochlear cell viability. Further studies are needed to determine immunological characteristics of intracochlear IL-10-positive cells and elucidate molecular mechanisms involved in the otoprotective activity of IL-10.
炎症反应在诸如耳毒性和迷路炎等获得性听力损失的病理生理学中起着关键作用。在我们早期的工作中，我们展示了耳纤维细胞在耳蜗炎症中的关键作用以及促炎细胞因子在顺铂耳毒性中的重要参与。我们还证明，耳纤维细胞通过血红素加氧酶1（HMOX1）信号通路抑制单核细胞趋化蛋白1（CCL2）对白细胞介素10（IL-10）的上调反应，从而抑制耳蜗炎症。然而，IL-10如何影响炎症介导的耳蜗损伤仍不清楚。在这里，我们旨在确定次氯酸（一种典型的炎症介质）如何影响耳蜗细胞活力以及IL-10如何影响次氯酸介导的耳蜗细胞损伤。发现次氯酸钠（NaOCl，次氯酸（HOCl）的钠盐）以剂量依赖性方式诱导HEI-OC1细胞的细胞毒性。过氧化氢和髓过氧化物酶的组合增强了顺铂的细胞毒性，并且这种协同作用被N-乙酰-L-半胱氨酸和ML-171抑制。大鼠螺旋韧带细胞系（RSL）在暴露于IL-10后似乎上调了抗氧化反应元件（ARE）的活性。RSL细胞在暴露于钴原卟啉（CoPP，一种HMOX1诱导剂）时上调了NRF2（一种ARE配体）和NR0B2的表达，但在暴露于锌原卟啉（ZnPP，一种HMOX1抑制剂）时未上调。发现腺病毒介导的NR0B2过表达抑制CCL2的上调。在腹腔注射脂多糖（LPS）后1天，IL-10阳性细胞出现在小鼠血管纹中。注射后5天，在螺旋韧带、螺旋缘、螺旋神经节和血管纹上方区域观察到IL-10阳性细胞，但在血管纹中未观察到。IL-10R1似乎在小鼠柯蒂氏器以及HEI-OC1细胞中表达。HEI-OC1细胞在暴露于IL-10时上调Bcl-xL的表达，并且IL-10被证明可减弱NaOCl诱导的细胞毒性。此外，HEI-OC1细胞在暴露于顺铂时上调IL-22RA，并且IL-22可抑制NaOCl的细胞毒性。综上所述，我们的研究结果表明次氯酸参与耳蜗损伤，并且IL-10可能不仅通过抑制炎症而且通过增强耳蜗细胞活力来潜在地减少耳蜗损伤。需要进一步研究以确定耳蜗内IL-10阳性细胞的免疫学特征，并阐明IL-10耳保护活性所涉及的分子机制。
