Axonal cytoskeletal changes in experimental glaucoma

项目摘要/摘要： 该项目提出，在青光眼视网膜神经节细胞(RGC)死亡之前，以及在青光眼永久性丧失之前 视觉方面，存在一个以轴突微管(MTS)降解为特征的RGC功能障碍阶段。 新的证据表明，MT的降解最初可以在轴突没有实质性变化的情况下发生 口径。因此，我们认为涉及MT降解的早期RGC功能障碍应该是 优先通过扫描激光偏振仪(SLP)检测视网膜神经纤维层(RNFL) RNFL厚度的变化。这是因为SLP的基本光学原理是基于检测 偏振光的位相延迟，这是由于在RNFL中产生的光学特性双折射 又长又细的圆柱形MTS。初步研究表明，RNFL的延迟性在 在几种不同的RGC损伤实验模型中比RNFL厚度更快，包括实验 青光眼(EG)。在无RNFL厚度变化的情况下，SLP临床检测轴突MT断裂， 可能代表青光眼损害的早期和潜在的可逆性阶段，并在临床上提供 用于治疗调整的可检测标记。因此，这一提议的中心假设是破坏 乳头周围RNFL轴突内的MTS是青光眼损害的早期指标， 轴突口径的变化和这些轴突的物理损失。根据这一假设得出的预测是 使用非人类灵长类动物(NHP)的EG模型进行了三个特定目标的测试。具体目标1：测试 RNFL厚度改变前乳头周围RNFL延迟性下降的预测 光谱域光学相干断层扫描(SD-OCT)及视神经头(ONH)表面改变前的检查 通过共聚焦扫描激光断层扫描(CSLT)对伴有EG的NHP眼进行测量；特定目标2：测试 预测乳头周围RNFL MT破坏的组织学证据将比 组织学定义的RNFL厚度变化和球后视神经轴突丢失；特定目标3：测试 RGC功能异常与RGC中期相关的预测 以轴突MTS异常为特征的退行性变。为了实现这些目标，将通过激光诱导EG 小梁网光凝导致24例NHP患者的中度单侧慢性眼压升高。 每周测量乳头周RNFL延迟性、RNFL厚度和ONH表面形貌 在激光前4周内，分别使用SLP、SD-OCT和CSLT制作每个NHP的双眼 基准期和最长8个月的持续时间(目标1)。对于每个参数，具有统计意义 变化被定义为每只眼睛两次超过基线会话间期变异性的任何变化 确认了。一旦每只动物发展到终点，它就会被牺牲，用于组织数据收集和 分析(目标2)。在AIM 1的活体结构测试的每周期间，RGC功能也将在 双眼使用三种已证实的视网膜电描记术(目标3)。

Project Summary/Abstract: This project proposes that prior to retinal ganglion cell (RGC) death in glaucoma, and before permanent loss of vision, there exists a stage of RGC dysfunction characterized by degradation of axonal microtubules (MTs). Emerging evidence suggests that MT degradation can occur initially without substantial changes in axonal caliber. Therefore, it is proposed that early stage RGC dysfunction involving MT degradation should be preferentially detectable by scanning laser polarimetry (SLP) of the retinal nerve fiber layer (RNFL) prior to changes in RNFL thickness. This is because the fundamental optical principle of SLP is based on detecting phase retardance of polarized light, which is due to the optical property birefringence produced in the RNFL by the long, thin cylindrical MTs. Preliminary studies demonstrate that RNFL retardance declines prior to, and faster than RNFL thickness in several different experimental models of RGC injury, including experimental glaucoma (EG). Clinical detection of axonal MT disruption by SLP, in the absence of RNFL thickness changes, might represent an early and potentially reversible phase of glaucomatous damage and provide a clinically detectable marker for therapeutic adjustment. Thus the central hypothesis of this proposal is that disruption of MTs within the axons of the peripapillary RNFL is an early indicator of glaucomatous damage, preceding both changes in axonal caliber and physical loss of those axons. Predictions arising from this hypothesis are tested in three Specific Aims using a non-human primate (NHP) model of EG. Specific Aim 1: To test the prediction that peripapillary RNFL retardance will decline prior to RNFL thickness changes measured by spectral domain optical coherence tomography (sd-OCT) and prior to optic nerve head (ONH) surface changes measured by confocal scanning laser tomography (CSLT) in NHP eyes with EG; Specific Aim 2: To test the predictions that histological evidence of peripapillary RNFL MT disruption will be more pronounced than histologically-defined RNFL thickness changes and retrobulbar optic nerve axon loss; Specific Aim 3: To test the prediction that RGC functional abnormalities are associated with the intermediate stage of RGC degeneration characterized by abnormal axonal MTs. To achieve these Aims, EG will be induced via laser photocoagulation of the trabecular meshwork to cause moderate, unilateral chronic IOP elevation in 24 NHPs. Weekly measurements of peripapillary RNFL retardance, RNFL thickness and ONH surface topography will be made in both eyes of each NHP using SLP, sd-OCT and CSLT, respectively, during a 4-week pre-laser baseline period and for up to 8 months after onset of EG (Aim 1). For each parameter, statistically significant change is defined as any change exceeding the baseline intersession variability for each individual eye, twice confirmed. Once each animal progresses to its endpoint, it is sacrificed for histological data collection and analysis (Aim 2). During each week of in vivo structural testing for Aim 1, RGC function will also be assessed in both eyes using three proven forms of electroretinography (Aim 3).