Apoptosis and autophagy in Photoreceptors exposed to oxidative stress
Apoptosis and autophagy in Photoreceptors exposed to oxidative stress
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DOI：
10.4161/auto.4294
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发表时间：
2007-09-01
期刊：
影响因子：
13.3
通讯作者：
Rohrer, Baerbel
中科院分区：
文献类型：
--
作者：
Kunchithapautham, Kannan;Rohrer, Baerbel
对人和动物视网膜营养不良模型的研究表明，细胞凋亡可能是光感受器细胞死亡的共同途径。自噬是动物细胞中主要的细胞降解过程，在正常发育和组织重塑以及病理条件下都是重要的。此前，我们提供了证据，证明其产物参与细胞凋亡和自噬的基因可能在退化的光感受器中共表达。在这里，我们研究了氧化应激介导的光感受器细胞死亡中的自噬，分析了光损伤小鼠模型和用过氧化氢攻击的661W光感受器细胞。在体内模型中，我们发现随着自噬小体的形成，TUNEL阳性细胞的数量随时间的增加而增加。在体外，氧化应激增加了凋亡和自噬标记基因的mRNA水平。H_2O_2处理后，TUNEL阳性细胞积聚，其中大部分含有自噬小体。为了确定自噬和细胞凋亡是否可能在彼此之前或同时发生，我们进行了抑制物研究。自噬抑制剂3-甲基腺嘌呤(3-MA)、针对自噬所必需的两个基因(自噬相关基因5和Beclin 1)的沉默RNA(SiRNA)以及泛caspase-3抑制剂zVAD-fmk都被发现部分阻止细胞死亡。阻断自噬也显著降低caspase-3活性，而阻断凋亡则增加自噬小体的形成。3-MA和zVAD-fmk的存活效应不是相加的；相反，两种抑制剂处理都会增加细胞的坏死死亡。综上所述，该研究首次提出自噬可能通过启动视细胞调亡参与感光细胞死亡。其次，它证实了，如果正常途径被阻断，正常情况下死于凋亡的细胞将会死于坏死。第三，这些结果表明，自噬的上游调节因子需要被确定为光感受器退化的潜在治疗靶点。
Studies on human and animal models of retinal dystrophy have suggested that apoptosis may be the common pathway of photoreceptor cell death. Autophagy, the major cellular degradation process in animal cells, is important in normal development and tissue remodeling, as well as under pathological conditions. Previously we provided evidence that genes, whose products are involved in apoptosis and autophagy, may be coexpressed in photoreceptors undergoing degeneration. Here, we investigated autophagy in oxidative stress-mediated cell death in photoreceptors, analyzing the light-damage mouse model and 661W photoreceptor cells challenged with H2O2. In the in vivo model, we demonstrated a time-dependent increase in the number of TUNEL-positive cells, concomitant with the formation of autophagosomes. In vitro, oxidative stress increased mRNA levels of apoptotic and autophagic marker genes. H2O2 treatment resulted in the accumulation of TUNEL-positive cells, the majority of which contain autophagosomes. To determine whether autophagy and apoptosis might precede each other or co-occur, we performed inhibitor studies. The autophagy inhibitor 3-methyladenine (3-MA), silencing RNA (siRNA) against two genes whose products are required for autophagy (autophagy-related (ATG) gene 5 and beclin 1), as well as the pan-caspase-3 inhibitor, zVAD-fmk, were both found to partially block cell death. Blocking autophagy also significantly decreased caspase-3 activity, whereas blocking apoptosis increased the formation of autophagosomes. The survival effects of 3-MA and zVAD-fmk were not additive; rather treatment with both inhibitors lead to increased cell death by necrosis. In summary, the study first suggests that autophagy participates in photoreceptor cell death possibly by initiating opoptosis. Second, it confirms that cells that normally die by apoptosis will execute cell death by necrosis if the normal pathway is blocked. And third, these results argue that the up-stream regulators of autophagy need to be identified as potential therapeutic targets in photoreceptor degeneration.