Department of Ophthalmology, Shanghai General Hospital (Shanghai First People's Hospital), Shanghai Jiao Tong University, School of Medicine, 200080, Shanghai, China.
Shanghai Key Laboratory of Fundus Diseases, 200080, Shanghai, China.
Free Radic Biol Med. 2020 Oct;158:32-43. doi: 10.1016/j.freeradbiomed.2020.06.023. Epub 2020 Jul 15.
Photoreceptor degeneration underlies various retinal disorders that lead to vision impairment. Currently, no effective medication is available to rescue photoreceptors under disease conditions. Elucidation of the molecular pathways involved in photoreceptor degeneration is a prerequisite for the rational design of therapeutic interventions. Photoreceptors are among the most energy-demanding tissues that require highly active oxidative phosphorylation. Therefore, disruption of metabolic support to photoreceptors results in a redox imbalance and subsequent cell death. We hypothesize that the redox regulatory pathway could be a potential therapeutic target to rescue photoreceptors under disease conditions.
Experimental retinal detachment was induced in mice. A murine photoreceptor-derived 661w cell line treated with HO was employed as an in vitro model to study the cellular response to oxidative stress. The expression and functional role of xCT, an upstream regulator of redox homeostasis, was assessed in vivo and in vitro. An xCT expression vector was constructed for an in vivo study to evaluate the therapeutic potential of this molecule.
xCT expression was upregulated in detached retina and HO-stimulated 661w cells compared to the control cells. Pharmacological inhibition of xCT by sulfasalazine (SAS) promoted photoreceptor degeneration after retinal detachment and 661w cell death upon HO treatment. Additionally, SAS treatment induced reactive oxidative species (ROS) accumulation, glutathione (GSH) depletion, and glutamate release in 661w cells. In contrast, xCT overexpression via viral infection protected photoreceptors from degeneration after retinal detachment.
We conclude that xCT expression is upregulated in photoreceptors after retinal detachment and plays a neuroprotective role in preserving photoreceptors. Mechanistically, xCT promotes cellular homeostasis by regulating intracellular ROS and GSH levels, which are critical to photoreceptor survival after retinal detachment. Collectively, our findings identify xCT as a potential therapeutic target for protection of photoreceptors under disease conditions.
光感受器变性是各种导致视力损害的视网膜疾病的基础。目前，在疾病状态下，没有有效的药物可用于挽救光感受器。阐明参与光感受器变性的分子途径是合理设计治疗干预措施的前提。光感受器是对能量需求最高的组织之一，需要高度活跃的氧化磷酸化。因此，光感受器代谢支持的中断会导致氧化还原失衡和随后的细胞死亡。我们假设，氧化还原调节途径可能是在疾病状态下挽救光感受器的潜在治疗靶点。
在小鼠中诱导实验性视网膜脱离。使用 HO 处理的鼠光感受器衍生 661w 细胞系作为体外模型，研究细胞对氧化应激的反应。在体内和体外评估了氧化还原平衡的上游调节剂 xCT 的表达和功能作用。构建了 xCT 表达载体用于体内研究，以评估该分子的治疗潜力。
与对照细胞相比，在脱离的视网膜和 HO 刺激的 661w 细胞中，xCT 的表达上调。用磺胺嘧啶（SAS）抑制 xCT 的药理作用可促进视网膜脱离后的光感受器变性和 HO 处理后的 661w 细胞死亡。此外，SAS 处理可诱导 661w 细胞中活性氧（ROS）积累、谷胱甘肽（GSH）耗竭和谷氨酸释放。相比之下，通过病毒感染过表达 xCT 可防止视网膜脱离后光感受器变性。
我们得出结论，视网膜脱离后光感受器中的 xCT 表达上调，并在维持光感受器中发挥神经保护作用。从机制上讲，xCT 通过调节细胞内 ROS 和 GSH 水平来促进细胞内稳态，这对视网膜脱离后光感受器的存活至关重要。总之，我们的研究结果表明，xCT 是疾病状态下保护光感受器的潜在治疗靶点。
