Retinal proteomic changes following unilateral optic nerve transection and early experimental glaucoma in non-human primate eyes

In this work we compared proteomic changes in non-human primate (NHP) retinas at the onset of early experimental glaucoma (EEG) and 3 weeks after optic nerve transection (ONT), as a means to identify regulators in the retina’s response to EEG and ONT. Both eyes of 7 NHPs with either unilateral EEG (n = 4) or ONT (n = 3) were enucleated. Proteins were analyzed by a label-free quantitative mass spectrometry system and the abundance of identified retinal proteins was compared between the treated eye and its contralateral control for each NHP. Cellular processes associated with regulated proteins were identified using the MetaCore program.As a result, a total of 209 and 200 proteins were identified in EEG and ONT retinas, respectively. The EEG eyes exhibited two distinguishable levels of maximum IOP: the highest IOP <27 mmHg (n = 2) and >45 mmHg (n = 2), termed mild IOP EEG and high IOP EEG eyes, respectively. A limited overlap of proteins regulated in the same direction was seen between the high IOP EEG and either the mild IOP EEG eyes or ONT eyes. Most of the proteins that were up regulated in the high IOP EEG eyes were down regulated in the mild IOP EEG eyes; the latter showed an overall down regulation that was not seen in the other two conditions. An association with cytoskeleton regulation was recognized for up-regulated proteins in the high IOP EEG eyes.We conclude that mild IOP EEG, high IOP EEG and ONT retinas exhibited condition-specific proteomic changes with little overlap between conditions. Cytoarchitecture regulation appears to be a component of the early retinal response to chronic experimental IOP elevation.     

The effect of experimental glaucoma and optic nerve transection on amacrine cells in the rat retina

PURPOSE: To detect alterations in amacrine cells associated with retinal ganglion cell (RGC) depletion caused by experimental optic nerve transection and glaucoma. METHODS: Intraocular pressure (IOP) was elevated unilaterally in 18 rats by translimbal trabecular laser treatment, and eyes were studied at 1 (n = 6), 2 (n = 5), and 3 (n = 7) months. Complete optic nerve transection was performed unilaterally in nine rats with survival for 1 (n = 4) and 3 (n = 5) months. Serial cryosections (five per eye) were immunohistochemically labeled with rabbit anti-gamma-aminobutyric acid (GABA) and anti-glycine antibodies. Cells in the ganglion cell and inner nuclear layers that labeled for GABA or glycine were counted in a masked fashion under bright-field microscopy. Additional labeling with other RGC and amacrine antigens was also performed. RGC loss was quantified by axon counts. RESULTS: Amacrine cells identified by GABA and glycine labeling were not significantly affected by experimental glaucoma, with a mean decrease of 15% compared with bilaterally untreated control cells (557 +/- 186 neurons/mm [glaucoma] versus 653.9 +/- 114.4 neurons/mm [control] of retina; P = 0.15, t-test). There was no significant trend for amacrine cell counts to be lower in eyes with fewer RGCs (r = -0.39, P = 0.11). By contrast, there was highly significant loss of GABA and glycine staining 3 months after nerve transection, both in the treated and the fellow eyes (P < 0.0001, t-test). However, there was a substantial number of remaining amacrine cells in transected retinas, as indicated by labeling for calretinin and calbindin. CONCLUSIONS: Experimental glaucoma causes minimal change in amacrine cells and their expression of neurotransmitters. After nerve transection, neurotransmitter presence declines, but many amacrine cell bodies remain. Differences among optic nerve injury models, as well as effects on "untreated" fellow eyes, should be recognized.     

Histomorphometric analysis of optic nerve changes in experimental glaucoma

PURPOSE: To assess relative changes in different tissue components of optic nerve and their relationship to nerve fiber loss in the experimental monkey model of glaucoma. METHODS: Chronic intraocular pressure (IOP) elevation was induced by laser trabeculoplasty in the right eye of eight monkeys (Macaca fascicularis). Both experimental right optic nerves and control left optic nerves were studied. Histomorphometric analysis was performed on optic nerve cross-sections using bright field microscopy with camera lucida. Cross-sectional areas of optic nerve tissue components were estimated by point counting. Nerve fiber density was estimated by unbiased random sampling. Nerve fiber number was calculated by multiplying nerve fiber density with neuroglial area. RESULTS: Varying degrees of nerve fiber loss were seen in eight optic nerves with chronic IOP elevation. More than 50% nerve fiber loss was noted in four of eight experimental optic nerves. In these severely affected optic nerves, total optic nerve area was significantly decreased compared with control optic nerves. Among the optic nerve tissue components, only the ratio of myelinated fiber area to total optic nerve area was significantly decreased. The ratio of extraaxonal area to total optic nerve area was significantly increased, whereas the ratio of interfascicular septal area to total optic nerve area did not change significantly. For all optic nerves, differences in nerve fiber count between control and experimental optic nerves showed the strongest correlation with differences in myelinated fiber area, followed by differences in extraaxonal area and total optic nerve area. CONCLUSION: This histomorphometric study suggests the validity of the experimental monkey model of glaucoma in studying changes occurring in the nonaxonal optic nerve tissue components in human glaucomatous optic neuropathy. Glial scar tissue area was significantly increased in optic nerves with severe glaucomatous damage. Although a decrease in total optic nerve area was observed, among the optic nerve tissue components only myelinated nerve fiber area decreased significantly. Myelinated nerve fiber area also showed the strongest association with nerve fiber loss in experimental glaucoma.     

ERG changes in albino and pigmented mice after optic nerve transection

Optic nerve transection (ONT) triggers retinal ganglion cell (RGC) death. By using this paradigm, we have analyzed for the first time in adult albino and pigmented mice, the effects of ONT in the scotopic threshold response (STR) components (negative and positive) of the full-field electroretinogram. Two weeks after ONT, when in pigmented mice approximately 18% of the RGC population survive, the STR-implicit time decreased and the p and nSTR waves diminished approximately to 40% or 55%, in albino or pigmented, respectively, with respect to the values recorded from the non-operated contralateral eyes. These changes were maintained up to 12 weeks post-ONT, demonstrating that the ERG-STR is a useful parameter to monitor RGC functionality in adult mice.     

Intraocular pressure after optic nerve transection

Intraocular pressure response to systemically administered osmotic agents was studied in albino rabbits with one optic nerve transected and the fellow optic nerve left intact. There eas a significant increase in intraocular pressure of both eyes following water ingestion but no significant difference in the pressure rise of the two eyes. There was a significant decrease in intraocular pressure of both eyes following glycerol ingestion but no significant difference in the pressure fall of two eyes. These results do not support the hypothesis that the optic nerve carries fibers which are part of the control system for intraocular pressure.     

Regional optic nerve damage in experimental mouse glaucoma

PURPOSE: To assess the relationship between regional variation of axon loss and optic nerve head anatomy in laser-induced experimental glaucoma in the mouse. METHODS: Experimental glaucoma was induced unilaterally in eight NIH Swiss black mice. Intraocular pressure (IOP) was measured for 12 weeks, and the mice were killed. The eyes were enucleated, and both optic nerves were dissected and processed conventionally for electron microscopy. Low- and high-magnification images of the optic nerve cross sections 300 microm posterior to the globe were collected systematically and masked before analysis. For each nerve, cross-sectional area was measured in low-magnification micrographs. Axon number and density were determined in the high-magnification micrographs. Loss of axonal density was compared between the superior and inferior and nasal and temporal areas of the optic nerve cross section. Additional cross-section micrographs were collected at 10- or 20-microm intervals throughout the optic nerve head. RESULTS: In the treated (glaucoma) eyes, mean IOP was 44% higher than that in the control eyes. The optic nerve cross-sectional area, mean axonal density, and total axonal number were significantly less than those in the control eyes (P < 0.01 for each). Axon loss in the superior optic nerve was greater than in the inferior optic nerve in each glaucomatous eye (P = 0.012). The ratio of axonal density in the superior and inferior optic nerve (superior-to-inferior [S/I] ratio) in all treated eyes was <1.0 and significantly lower than that in the control eyes (P = 0.012). The central retinal vessels occupied approximately 20% of the central optic nerve head cross-sectional area, gradually shifted position ventrally as they progressed toward the scleral foramen (the mouse does not have a lamina cribrosa), and exited the inferior retrobulbar optic nerve adjacent to the posterior of the globe. CONCLUSIONS: Ocular hypertension in the mouse eye sufficient to cause optic nerve damage induces preferential loss of superior optic nerve axons. Optic nerve axon loss appeared less among the axons that were near the major optic nerve blood vessels at the scleral foramen. Topographic differences in optic nerve axon loss should be considered when evaluating optic nerve damage in experimental laser-induced glaucoma in the mouse.     

Expressions of nestin and glial fibrillary acidic protein in rat retina after optic nerve transection

AIM: To assess the expression of nestin and glial fibrillary acidic protein (GFAP) in rat retina after optic nerve transection. METHODS: Rats were randomly divided into normal control group, sham group and operation group, and used for establishing an animal model of optic nerve transection. Retinal specimen of each group was collected at 3, 48h, 7 and 14d postoperative. Nestin and GFAP expressions on sagittal sections were analyzed by immunohistochemical staining, and protein extraction was analyzed by Western blot. RESULTS: Immunohistochemical analysis showed that nestin positive staining was rarely detected in normal control group and sham group, while sham group showed weak positive staining at 3h postoperative, the reaction gradually increased at 48h postoperative, and reached its maximum at 7d postoperative, and then decreased at 14d postoperative. Compared to the expression of GFAP, there was not statistically significant obvious difference among three groups (P>0.05). Result of Western blot method was consistent with that of immunohistochemical method. CONCLUSION: The expression of nestin increased in a time dependent fashion in Müller cells of retina following optic nerve transection, which was statistically significant, but there was no obvious difference in GFAP expression. The results indicate that an increase in colloid synthesis in retina following optic nerve transection can improve the retinal neurons’ environment.     

大鼠视神经横断伤及夹挫伤后视网膜神经节细胞变化及与损伤时间关系

目的 观察大鼠视神经横断伤及夹挫伤后,视网膜神经节细胞(RGCs)形态学变化、区别及在不同时间的计数变化,探讨其与视神经损伤经过时间的关系,为视神经损伤的病理机制及损伤经过时间的推断提供一定的依据.方法 采用大鼠球后视神经横断伤/夹挫伤动物模型,在伤后不同时间处死动物并取材,HE 染色,光镜下观察RGCs的动态变化.结果 视神经损伤后RGCs数日均严重下降,2周内RGCs快速减少,3～7 d为RGCs快速减少期,2周以后缓慢减少;但横断伤组3 d以后各个时期RGCs计数下降幅度与夹挫伤组相比更明显.结论 视神经损伤导致了视网膜形态结构的变化,RGCs丢失的严重程度与损伤类型及时问呈相关性.     

Experimental glaucoma and optic nerve transection induce simultaneous upregulation of proapoptotic and prosurvival genes

PURPOSE: To investigate changes in gene expression induced by elevated intraocular pressure (IOP) and complete optic nerve transsection (ONT) over time. METHODS: A gene array of 18 signal transduction pathways was used to examine the changes in RNA profiles of retinas post-ONT in rats. Among the seven genes that were determined to be upregulated, four were confirmed to have higher expression by semiquantitative RT-PCR analysis: Ei24 and Gadd45a (both associated with apoptosis induced via the p53 pathway), IAP-1 (inhibitor of apoptosis protein 1), and Cdk2 (cell cycle regulation and apoptosis). Their mRNA levels were then studied by quantitative RT-PCR in experimental glaucoma and ONT over time. Levels of the corresponding proteins were evaluated by Western blot analysis and immunohistochemistry. RESULTS: Proapoptotic genes from the p-53 pathway (Ei24 and Gadd45a), Cdk2 and the prosurvival gene IAP-1 (a caspase inhibitor) were simultaneously and significantly upregulated early after ONT, returning to baseline at 2 weeks. In experimental glaucoma, Gadd45a was significantly upregulated 1 week after induction of increased IOP and stayed upregulated for 2 months and long after IOP returned to baseline. The prosurvival gene IAP-1 was simultaneously upregulated but returned to baseline earlier than the proapoptotic gene. Ei24 and Cdk2 were only slightly upregulated in glaucoma. Western blot analysis demonstrated upregulation of Gadd45a and IAP-1 proteins. Immunohistochemistry localized these changes to the retinal ganglion cell layer. CONCLUSIONS: Members of the p-53 signal transduction pathway are significantly involved in glaucoma and ONT. The endogenous caspase inhibitor IAP-1 is upregulated simultaneously, possibly as part of an intrinsic neuroprotective mechanism. Changes in glaucoma are gradual and last long after IOP returns to normal.     

Pit-like changes of the optic nerve head in open-angle glaucoma.

Six patients with open-angle glaucoma and acquired pit-like changes in the optic nerve head are presented. In 1 patient evolution of the pit-like defect is documented. In all 6 patients progression of associated visual field deficits is described. It is suggested that such pit-like changes in selected patients with glaucoma may not represent congenital lesions but rather local, progressive nerve head disease, occurring particularly in response to raised intraocular pressure. The management of patients with optic nerve head pitting and the pathogenesis of glaucomatous optic neuropathy are discussed with respect to this observation.     

巩膜生物力学改变与青光眼性视神经损伤

青光眼的主要病理特征是视网膜神经节细胞(RGC)的丧失,从而导致进行性、不可逆性的视力丧失。目前已有研究表明,巩膜的生物力学性质会影响视神经的生物力学变化,并且在RGC损伤和视力丧失的病理过程中起重要作用。因此,巩膜生物力学与青光眼关系的研究对深入了解青光眼的发病机制有着重要的意义。本文就巩膜的生物力学特性、巩膜胶原纤维结构、巩膜重塑、巩膜刚度及通透性与青光眼性视神经损伤的关系进行综述,以利于更深入地了解青光眼性视神经损害的机制,为青光眼的预防和治疗提供新思路。