Uncoupling caspase 8-mediated-apotosis from caspase 8-mediated-inflammation in glaucoma.

青光眼中一个重要的未回答的问题是视网膜神经节细胞（RGC）的凋亡和 轴突变性是由分子上不同的途径介导的两个独立的事件，或者它们是否 通过一个共同的途径连接和触发。解决这个问题对于制定有效的 神经保护疗法，保护轴突和RGC胞体。为了支持这一观点，有两种不同的观点。 通路介导轴突变性和RGC凋亡，已经证明， 凋亡BAX基因阻断青光眼小鼠模型中RGCs的凋亡，但不能阻止轴突生长。 退化越来越多的证据表明，轴突变性是由视神经轴突损伤引发的。 神经头，其先于RGC凋亡并与小胶质细胞活化和神经毒性炎症有关。 因此，阻断炎症可能可以防止轴突变性和随后的死亡。 RGC，留下开放的可能性，有一个共同的途径连接轴突变性和RGC 凋亡为了支持炎症可能是连接轴突变性的共同途径的观点， 和RGC凋亡，我们的实验室以前证明，阻断Fas/Fas配体（FasL）信号转导， 在诱导型和慢性小鼠模型中， 这种保护作用与抑制小胶质细胞活化和诱导炎性细胞凋亡相一致。 调解员然而，由于Fas触发凋亡和炎症途径，问题仍然是， 单独阻断炎症是否能防止轴突变性和随后的RGC凋亡。的 解决这一问题的挑战是不能将Fas介导的炎症与Fas介导的炎症分开， 凋亡然而，Fas信号转导需要激活caspase-8来实现凋亡和炎症， 最近研究caspase-8激活的分子机制发现了一个额外的自- 诱导caspase-8介导的细胞凋亡所需的切割步骤，但不是诱导 caspase-8介导的炎症。使用该信息，在2010年10月20日，在小鼠中产生突变小鼠（Casp 8DA/DA）。 自切割位点的点突变阻断了caspase-8介导的细胞凋亡，但没有阻断caspase-8介导的细胞凋亡。 caspase-8介导的炎症。我们将使用这些小鼠来明确地确定caspase-8介导的 炎症和/或凋亡触发青光眼中的轴突变性和RGC凋亡。我们假设 升高的IOP触发caspase-8介导的炎症，其作为触发轴突的共同途径 RGC变性和凋亡。这一假设将在两个目标中进行测试：（1）确定caspase- 8-介导的凋亡导致微珠诱导的小鼠视网膜神经节细胞轴突变性和死亡 （2）证明Fas介导的小胶质细胞活化介导神经毒性 微珠诱导的小鼠青光眼模型中的炎症、轴突变性和RGC死亡。

One important unanswered question in glaucoma is whether apoptosis of retinal ganglion cells (RGCs) and axon degeneration are two separate events mediated by molecularly distinct pathways, or whether they are linked and triggered through a common pathway. Answering this question is critical to developing effective neuroprotective therapies that protect both axons and RGC somas. In support of the idea there are two distinct pathways that mediate axon degeneration and RGC apoptosis, it was demonstrated that deletion of the pro- apoptotic BAX gene blocked apoptosis of RGCs in a mouse model of glaucoma, but did not prevent axon degeneration. There is accumulating evidence that axon degeneration is triggered by axon damage in the optic nerve head, which precedes RGC apoptosis and is linked to microglial activation and neurotoxic inflammation. Therefore, it is possible that blocking inflammation could prevent axon degeneration and subsequent death of RGCs, leaving open the possibility that there is a shared pathway linking axon degeneration and RGC apoptosis. In support of the idea that inflammation may be the shared pathway that links axon degeneration and RGC apoptosis, our laboratory demonstrated previously that blocking the Fas/Fas ligand (FasL) signaling pathway prevents axon degeneration and RGC apoptosis in both inducible and chronic mouse models of glaucoma and this protection coincided with an inhibition of microglia activation and induction of inflammatory mediators. However, since Fas triggers apoptotic and inflammatory pathways, the question remains as to whether blocking inflammation alone would prevent axon degeneration and subsequent RGC apoptosis. The challenge to resolving this issue is the inability to uncouple Fas-mediated inflammation from Fas-mediated apoptosis. However, Fas signaling requires activation of caspase-8 for both apoptosis and inflammation and recent studies examining the molecular mechanism of caspase-8 activation discovered an additional auto- cleavage step that is required for the induction of caspase-8-mediated apoptosis but not required for induction of caspase-8 mediated inflammation. Using this information, a mutant mouse was created (Casp8DA/DA) in which a point mutation in the auto-cleavage site blocked caspase-8-mediated apoptosis, but did not block caspase-8-mediated inflammation. We will use these mice to definitively determine how caspase-8-mediated inflammation and/or apoptosis triggers axon degeneration and RGC apoptosis in glaucoma. We hypothesize that elevated IOP triggers caspase-8-mediated inflammation that acts as a common pathway triggering axon degeneration and RGC apoptosis. This hypothesis will be tested in two aims: (1) Determine whether caspase- 8-mediated apoptosis contributes to axon degeneration and death of RGCs in a microbead-induced mouse model of glaucoma and (2) Demonstrate that Fas-mediated activation of microglia mediates neurotoxic inflammation, axon degeneration, and death of RGCs in the microbead-induced mouse model of glaucoma.