Enhanced Axon Sparing In Glaucoma Through Augmentation Of EphB/ephrin B Signaling

描述(申请人提供)：青光眼是一种主要的使人衰弱的眼病，在这个国家大约有300万人受到影响。在这些患者中，估计每年有10万名患者尽管接受了眼压正常化的治疗，但仍失去了一些视力。由于65岁以上人群中青光眼的发病率高达1/20，因此很有必要更好地了解视神经轴突丢失的发病机制，并确定潜在的治疗策略。一个快速发展的研究领域是与疾病相关的细胞间信号上调，涉及EphB受体酪氨酸激酶家族及其配体，即ePhin-B蛋白。EphB/Ephin-B信号的上调具体发生在视神经头，这是视神经的一个无髓区域，临床观察和实验数据都指出，这是导致疾病的主要部位。此外，在两种不同的青光眼小鼠模型、实验性青光眼灵长类动物和人类患者的ONH组织/细胞中，EphB/ephin-B信号的激活增加，从而暗示这一信号通路是病理的潜在关键组成部分。我们实验室最近利用特定EphB蛋白的基因缺失和突变等位基因的动物所做的工作进一步表明，EphB/Ephin-B信号缺陷的动物比它们的野生型后代有更严重的视神经轴突丢失，这表明EphB和ePhin-B蛋白参与了ONH中尚未完全表征的信号触发的内源性轴突保护机制。在青光眼中，作为内源性反应的EphB/ephin-B信号上调，这让人想起以前的工作，即这一信号通路参与了脊髓和视神经损伤后轴突存活和再生长的调节。在青光眼中限制轴突丢失的内源性机制为治疗提供了有趣的靶点。目前提出的研究是基于初步证据，即在青光眼体外组织模型中，应用具有生物活性的EphB2蛋白片段触发的EphB/ePhin-B信号的增强导致视轴突丢失的缓和。在这里，我们试图建立在这一发现的基础上，并确定体内增加EphB和ePhin-B正向和反向信号是否可以挽救激光诱导的青光眼小鼠模型的视轴突丢失。在接受激光治疗的小鼠中，将使用可诱导的Tet-on策略来增强EphB和B-ephin信号，并将接受多西环素和不接受多西环素的动物之间的视神经轴突存活率进行比较。这项工作的结果可能为新的治疗靶点提供支持，并鼓励更多的发现努力。

DESCRIPTION (provided by applicant): Glaucoma is a major debilitating eye disease affecting some 3 million individuals in this country. Of these, an estimated 100,000 patients each year lose some vision despite medical treatment for the normalization of intraocular pressure. As the incidence of glaucoma for the 65 yo.+ population segment is as high as 1 in 20, there is a great need to better understand disease mechanisms underlying optic nerve axon loss and to identify potential therapeutic strategies. A rapidly progressing area of research is th disease-linked up-regulation of intercellular signaling involving the EphB family of receptor tyrosine kinases and their ligands the ephrin-B proteins. Up-regulation of EphB/ephrin-B signaling occurs specificaly at the optic nerve head, an unmyelinated region of the optic nerve that clinical observations and experimental data both point to as a major site contributing to disease. In addition, increased activation of EphB/ephrin-B signaling occurs in two separate mouse models of glaucoma, in primates with experimental glaucoma, and in ONH tissues/cells from human patients, thereby implicating this signaling pathway as a potential key component of pathology. Recent work from our laboratory utilizing animals with genetic deletions and mutant alleles of specific EphB proteins has further demonstrated that animals with deficient EphB/ephrin-B signaling have more severe optic nerve axon loss compared to their wild-type littermates, indicating that EphB and ephrin-B proteins participate in an endogenous axon protective mechanism triggered by as yet incompletely characterized signals at the ONH. The up-regulation of EphB/ephrin-B signaling as an endogenous response in glaucoma is reminiscent of previous work implicating this signaling pathway in modulating axon survival and re-growth after spinal cord and optic nerve injury. Endogenous mechanisms that act to limit axon loss in glaucoma present intriguing targets for therapy. The current proposed research is based on preliminary evidence that the augmentation of EphB/ephrin-B signaling triggered by the application of biologically active EphB2 protein fragments results in a moderation of optic axon loss in an ex vivo tissue model of glaucomatous disease. Here we seek to build upon this finding and determine whether increased EphB and ephrin-B forward as well as reverse signaling in vivo can salvage optic axon loss in a laser-induced mouse model of glaucoma. Augmentation of EphB and B- ephrin signaling will be accomplished using an inducible Tet-on strategy in laser treated mice and optic nerve axon survival compared between animals receiving Doxycycline and those that do not. The results from this work potentially provide support for a novel therapeutic target and encourage additional discovery efforts.