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

描述（由申请人提供）：青光眼是一种主要的使人衰弱的眼病，影响着这个国家大约300万人。其中，估计每年有10万名患者尽管接受了眼压正常化治疗，但仍部分丧失视力。青光眼的发病率为65岁左右。视神经轴突缺失的发病率高达1 / 20，因此有必要更好地了解视神经轴突缺失的疾病机制，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的上调，涉及受体酪氨酸激酶的EphB家族及其配体ephrin-B蛋白。EphB/ephrin-B信号的上调特别发生在视神经头，这是视神经的无髓鞘区域，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来自人类患者的ONH组织/细胞中，EphB/ephrin-B信号通路的激活增加，从而暗示该信号通路可能是病理的关键组成部分。我们的实验室最近利用具有特定EphB蛋白基因缺失和突变等位基因的动物进行的研究进一步表明，与野生型相比，EphB/ephrin-B信号缺失的动物有更严重的视神经轴突损失，这表明EphB和ephrin-B蛋白参与了内源性轴突保护机制，该机制是由ONH上尚未完全表征的信号触发的。青光眼中EphB/ephrin-B信号的上调作为一种内源性反应，这让人联想到先前的研究，该信号通路在脊髓和视神经损伤后调节轴突存活和再生。限制青光眼轴突损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，在青光眼疾病的离体组织模型中，应用生物活性EphB2蛋白片段引发的EphB/ephrin-B信号通路的增强导致视轴突损失的减缓。在此，我们试图建立在这一发现的基础上，并确定体内EphB和ephrin-B正向和反向信号的增加是否可以挽救激光诱导的青光眼小鼠模型中的视轴突损失。在激光治疗的小鼠和接受多西环素和未接受多西环素治疗的小鼠的视神经轴突存活率比较中，使用诱导的Tet-on策略可以增强EphB和B- ephrin信号。这项工作的结果可能为新的治疗靶点提供支持，并鼓励进一步的发现努力。

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. PUBLIC HEALTH RELEVANCE: The proposed research is directed at investigating the efficacy of augmented Eph and ephrin signaling in salvaging optic nerve axon survival in the blinding disease, glaucoma. Results from these studies may potentially lead to a new therapeutic avenue to mitigate and delay vision loss in the approximately 3 million patients affected by this disability.