SIRT1 activation confers neuroprotection in experimental optic neuritis

PURPOSE: Axonal damage and loss of neurons correlate with permanent vision loss and neurologic disability in patients with optic neuritis and multiple sclerosis (MS). Current therapies involve immunomodulation, with limited effects on neuronal damage. The authors examined potential neuroprotective effects in optic neuritis by SRT647 and SRT501, two structurally and mechanistically distinct activators of SIRT1, an enzyme involved in cellular stress resistance and survival. METHODS: Experimental autoimmune encephalomyelitis (EAE), an animal model of MS, was induced by immunization with proteolipid protein peptide in SJL/J mice. Optic neuritis developed in two thirds of eyes with significant retinal ganglion cell (RGC) loss detected 14 days after immunization. RGCs were labeled in a retrograde fashion with fluorogold by injection into superior colliculi. Optic neuritis was detected by inflammatory cell infiltration of the optic nerve. RESULTS: Intravitreal injection of SIRT1 activators 0, 3, 7, and 11 days after immunization significantly attenuated RGC loss in a dose-dependent manner. This neuroprotective effect was blocked by sirtinol, a SIRT1 inhibitor. Treatment with either SIRT1 activator did not prevent EAE or optic nerve inflammation. A single dose of SRT501 on day 11 was sufficient to limit RGC loss and to preserve axon function. CONCLUSIONS: SIRT1 activators provide an important potential therapy to prevent the neuronal damage that leads to permanent neurologic disability in optic neuritis and MS patients. Intravitreal administration of SIRT1 activators does not suppress inflammation in this model, suggesting that their neuroprotective effects will be additive or synergistic with current immunomodulatory therapies.     

Long-term suppression of neurodegeneration in chronic experimental optic neuritis: antioxidant gene therapy

PURPOSE: To test in mice with experimental autoimmune encephalomyelitis (EAE) a strategy designed to treat patients at risk for axonal degeneration and persistent visual loss from optic neuritis and multiple sclerosis. METHODS: The authors cloned the human extracellular superoxide dismutase (ECSOD) or catalase (CAT) gene into recombinant adenoassociated virus (AAV). Transgene expression was evaluated by immunochemistry of infected RGC-5 cells and after intravitreal injection of AAV-ECSOD or AAV-CAT, or both, into the right eyes of DBA/1J mice. Control cells and left eyes were inoculated with AAV-GFP. Animals were sensitized for EAE, followed by serial contrast-enhanced MRI for 6 months, and then were euthanatized. The effects of ECSOD and CAT modulation on the EAE optic nerve were gauged by computerized analysis of optic nerve volume, myelin fiber area, axonal cell loss, and retinal ganglion cell (RGC) loss. RESULTS: Western blot analysis of infected RGC-5 cells revealed that expression of ECSOD increased 15-fold and that of CAT increased 3.5-fold. One month after intraocular injections, transgene expression increased 4-fold for AAV-ECSOD and 3.3-fold for AAV-CAT. Six months after intraocular injections and EAE sensitization, combination therapy with ECSOD and catalase decreased RGC loss by 29%, optic nerve demyelination by 36%, axonal loss by 44%, and cellular infiltration by 34% compared with the contralateral control eyes inoculated with AAV-GFP. Compared with the normal optic nerve, it limited RGC loss to 9%. CONCLUSIONS: Viral-mediated delivery of antioxidant genes provides long-lasting suppression against neuronal and axonal loss associated with permanent visual disability in patients with optic neuritis and multiple sclerosis.     

Suppression of mitochondrial oxidative stress provides long-term neuroprotection in experimental optic neuritis

PURPOSE: Axonal loss is thought to contribute to the persistence of visual loss in optic neuritis and multiple sclerosis (MS). The mechanisms of injury are poorly understood. The authors investigated the contribution of mitochondrial oxidative stress and the effects of modulating mitochondrial antioxidant gene expression in the optic nerves of mice induced with experimental allergic encephalomyelitis (EAE), with a focus on long-term neuroprotection. METHODS: Optic nerves from mice with EAE were probed for reactive oxygen species (ROS) with the use of dichlorofluorescein diacetate (DCFDA), dihydroethidium, and cerium chloride. To modulate mitochondrial oxidative stress, recombinant AAV containing the human SOD2 gene or a ribozyme targeting murine SOD2 was injected into the vitreous. Control eyes received the recombinant virus without a therapeutic gene. Mice were sensitized for EAE and were monitored by serial contrast-enhanced MRI. The effects of SOD2 modulation on the EAE optic nerve were gauged by computerized analysis of optic nerve volume, myelin fiber area, and retinal ganglion cell loss at 1, 3, and 12 months after sensitization for EAE. RESULTS: ROS were detected in the EAE optic nerve as early as 3 days after antigenic sensitization. Colocalization suggested mitochondria as the source of ROS activity in the absence of inflammation. The ribozyme suppressing SOD2 gene expression increased myelin fiber injury by 27%. Increasing SOD2 levels twofold in the optic nerve by virally mediated gene transfer ameliorated myelin fiber injury by 51% and RGC loss fourfold, limiting it to 7% in EAE at 1 year. CONCLUSIONS: Amelioration of mitochondrial oxidative stress by SOD2 gene delivery may be a therapeutic strategy for suppressing neurodegeneration in optic neuritis.     

神经生长因子对脱髓鞘性视神经炎小鼠视网膜神经组织保护作用的实验研究

目的 研究神经生长因子（NGF）对脱髓鞘性视神经炎小鼠视网膜神经组织的保护作用.方法 实验研究.50只C57BL/6小鼠按随机数字表法分为对照组（10只）、BSS组（20只）和NGF组（20只）,取右眼为实验眼.后两组应用MOG35-55多肽加完全弗氏佐剂皮下注射建立实验性视神经炎小鼠模型,每天对各组小鼠进行称重及神经功能评分.NGF组和BSS组分别于免疫后的第4天和第10天,对右眼进行玻璃体腔注射3μg/μl NGF或2 μl BSS.分别于免疫当天、免疫后的第7天和免疫后的第14天,对每组小鼠进行闪光视觉诱发电位（f-VEP）和闪光视网膜电图（f-ERG）检查;采用HE染色、LFB染色、Bielschowsky银染分别评估视神经炎性细胞浸润、髓鞘脱失、轴突病理改变;使用TUNEL法检测视网膜神经节细胞凋亡并计算凋亡指数.对两组实验数据采用t检验进行统计学分析.结果 NGF组与BSS组小鼠发病时间和临床评分比较,差异均无统计学意义（t=-1.844,P=0.079;t=-2.012,P=0.059）.在不同时间点,NGF组和BSS组的f-VEP差异均无统计学意义（P＞0.05）.在免疫后的第14天,NGF组f-ERG b波潜伏期较BSS组缩短,振幅较BSS组增大,两组差异有统计学意义（t=5.909,P=0.000;t=3.602,P=0.043）.LFB染色示,NGF组和BSS组视神经的脱髓鞘面积占横截面比例分别为（31.50±8.72）%、（29.91±10.00）%,差异无统计学意义（t=0.298,P=0.709）.TUNEL检测结果示,NGF组小鼠视网膜神经节细胞凋亡指数[（15.18±3.36）%]低于BSS组[（34.14±3.83）%],差异有统计学意义（t=11.790,P=0.000）.结论 NGF可以促进脱髓鞘性视神经炎小鼠视网膜神经节细胞的存活,对其视网膜神经组织可能具有一定的保护作用.     

Optic nerve degeneration in experimental autoimmune encephalomyelitis

The mechanisms of axonal and neuronal degeneration causing disability in optic neuritis and multiple sclerosis are poorly understood. Here we describe the role of mitochondria, oxidative stress and the effects of modulating antioxidant gene expression in the optic nerves of mice induced with experimental autoimmune encephalomyelitis, with a focus on long-term neuroprotection. Oxidative injury to the mitochondrion began prior to inflammatory cell infiltration and continued. It affected subunits of the respiratory chain, glycolysis and a chaperone critical to the stabilization and import of proteins. Oxidative products were associated with loss of membrane potential, mitochondrial degeneration and severe axonal loss. Reductions in ATP synthesis were even greater than those associated with mitochondrial diseases. Increasing SOD2 levels by viral mediated gene transfer rescued ATP synthesis, suppressed myelin fiber injury and increased retinal ganglion cell survival 1 year later.     

Time-course of the retinal nerve fibre layer degeneration after complete intra-orbital optic nerve transection or crush: A comparative study

We examined qualitatively and quantitatively in adult rat retinas the temporal degeneration of the nerve fibre layer after intra-orbital optic nerve transection (IONT) or crush (IONC). Retinal ganglion cell (RGC) axons were identified by their heavy neurofilament subunit phosphorylated isoform (pNFH) expression. Optic nerve injury induces a progressive axonal degeneration which after IONT proceeds mainly with abnormal pNFH-accumulations in RCG axons and after IONC in RGCs somas and dendrites. Importantly, this aberrant pNFH-expression pattern starts earlier and is more dramatic after IONT than after IONC, highlighting the importance that the type of injury has on the time-course of RGC degeneration.     

Understanding glaucomatous damage: anatomical and functional data from ocular hypertensive rodent retinas

Glaucoma, the second most common cause of blindness, is characterized by a progressive loss of retinal ganglion cells and their axons, with a concomitant loss of the visual field. Although the exact pathogenesis of glaucoma is not completely understood, a critical risk factor is the elevation, above normal values, of the intraocular pressure. Consequently, deciphering the anatomical and functional changes occurring in the rodent retina as a result of ocular hypertension has potential value, as it may help elucidate the pathology of retinal ganglion cell degeneration induced by glaucoma in humans. This paper predominantly reviews the cumulative information from our laboratory’s previous, recent and ongoing studies, and discusses the deleterious anatomical and functional effects of ocular hypertension on retinal ganglion cells (RGCs) in adult rodents. In adult rats and mice, perilimbar and episcleral vein photocauterization induces ocular hypertension, which in turn results in devastating damage of the RGC population. In wide triangular sectors, preferentially located in the dorsal retina, RGCs lose their retrograde axonal transport, first by a functional impairment and after by mechanical causes. This axonal damage affects up to 80% of the RGC population, and eventually causes their death, with somal and intra-retinal axonal degeneration that resembles that observed after optic nerve crush. Importantly, while ocular hypertension affects the RGC population, it spares non-RGC neurons located in the ganglion cell layer of the retina. In addition, functional and morphological studies show permanent alterations of the inner and outer retinal layers, indicating that further to a crush-like injury of axon bundles in the optic nerve head there may by additional insults to the retina, perhaps of ischemic nature.     

A model to study differences between primary and secondary degeneration of retinal ganglion cells in rats by partial optic nerve transection

PURPOSE: To use a rat model of optic nerve injury to differentiate primary and secondary retinal ganglion cell (RGC) injury. METHODS: Under general anesthesia, a modified diamond knife was used to transect the superior one third of the orbital optic nerve in albino Wistar rats. The number of surviving RGC was quantified by counting both the number of cells retrogradely filled with fluorescent gold dye injected into the superior colliculus 1 week before nerve injury and the number of axons in optic nerve cross sections. RGCs were counted in 56 rats, with 24 regions examined in each retinal wholemount. Rats were studied at 4 days, 8 days, 4 weeks, and 9 weeks after transection. The interocular difference in RGCs was also compared in five control rats that underwent no surgery and in five rats who underwent a unilateral sham operation. It was confirmed histologically that only the upper optic nerve had been directly injured. RESULTS: At 4 and 8 days after injury, superior RGCs showed a mean difference from their fellow eyes of -30.3% and -62.8%, respectively (P = 0.02 and 0.001, t-test, n = 8 rats/group), whereas sham-operation eyes had no significant loss (mean difference between eyes = 1.7%, P = 0.74, t-test). At 8 days, inferior RGCs were unchanged from control, fellow eyes (mean interocular difference = -4.8%, P = 0.16, t-test). Nine weeks after transection, inferior RGC had 34.5% fewer RGCs than their fellow eyes, compared with 41.2% fewer RGCs in the superior zones of the injured eyes compared with fellow eyes. Detailed, serial section studies of the topography of RGC axons in the optic nerve showed an orderly arrangement of fibers that were segregated in relation to the position of their cell bodies in the retina. CONCLUSIONS: A model of partial optic nerve transection in rats showed rapid loss of directly injured RGCs in the superior retina and delayed, but significant secondary loss of RGCs in the inferior retina, whose axons were not severed. The findings confirm similar results in monkey eyes and provide a rodent model in which pharmacologic interventions against secondary degeneration can be tested.     

Neuron stress and loss following rodent anterior ischemic optic neuropathy in double-reporter transgenic mice

PURPOSE: Nonarteritic anterior ischemic optic neuropathy (NAION) is an optic nerve infarct involving axons of retinal ganglion cell (RGC) neurons. The rodent NAION model (rAION) can use transgenic mouse strains to reveal unique characteristics about the effects of sudden optic nerve ischemia on RGCs and their axons. The impact of rAION on RGC stress patterns, RGC loss, and their axons after axonal infarct were evaluated. METHODS: A double-transgenic mouse strain was used, containing a construct with cyan fluorescent protein (CFP) under Thy-1 promoter control, and a construct with beta-galactosidase (lacZ) linked to the stress gene c-fos promoter. Thy-1 in the retina is expressed predominantly in RGCs, enabling stereologic analysis of CFP(+) RGC numbers and loss post-rAION-using confocal microscopy. RGC loss was correlated with axonal counts using transmission electron microscopy (TEM). LacZ immunohistochemistry was used to evaluate retinal cell stress after rAION. RESULTS: The 45,000 CFP(+) cells in the RGC layer of control animals compared with previous RGC quantitative estimates. rAION produced RGC stress, defined as lacZ expression, in patterns corresponding with later RGC loss. rAION-associated RGC loss correlated with regional nerve fiber layer loss. Axonal loss correlates with stereologically determined RGC loss estimates in transgenic mice retinas. CONCLUSIONS: Post-ON infarct RGC stress patterns correlate with regional RGC loss. Cellular lacZ levels in most RGCs are low, suggesting rAION-affected RGCs express c-fos only transiently. CFP(+) cell loss correlates closely with quantitative axonal loss, suggesting that the Thy-1 (CFP) transgenic mouse strain is appropriate for RGC stereologic analyses.     

Apoptotic retinal ganglion cell death in the DBA/2 mouse model of glaucoma

The DBA/2 mouse has been used as a model for spontaneous secondary glaucoma. We attempted to determine the in vivo time course and spatial distribution of retinal ganglion cells (RGCs) undergoing apoptotic death in DBA/2 mice. Female DBA/2 mice, 3, 9-10, 12, 15, and 18 months of age, received intravitreal injections of Annexin-V conjugated to AlexaFluor 1h prior to euthanasia. Retinas were fixed and flat-mounted. Annexin-V-positive RGCs in the hemiretina opposite the site of injection were counted, and their locations were recorded. Positive controls for detection of apoptotic RGCs by Annexin-V labeling included rats subjected to optic nerve ligation, and C57BL/6 mice subjected to either optic nerve ligation or intravitreal injection of NMDA. To verify that Annexin-V-labeled cells were RGCs, intravitreal Annexin-V injections were also performed on retinas pre-labeled retrogradely with FluoroGold or with DiI. Annexin-V-positive RGC locations were analyzed to determine possible clustering and areas of preferential loss. Annexin-V labeled apoptotic RGCs in eyes after optic nerve ligation, intravitreal NMDA injection, as well as in aged DBA/2 animals. In glaucomatous DBA/2 mice 95-100% of cells labeled with Annexin-V were also FluoroGold- and DiI-positive. This confirms that Annexin-V can be used to specifically detect apoptotic RGCs in rodent retinas. In DBA/2 mice, apoptotic RGC death is maximal from the 12th to the 15th month of age (ANOVA, p<0.001, Fisher's post hoc test) and occurs in clusters. These clusters are initially located in the midperipheral retina and progressively occur closer to the optic nerve head with increasing age. Retrograde axonal transport of FluoroGold in the glaucomatous mouse retina is functional until at least 2-3days prior to initiation of apoptotic RGC death.     

Intrinsic survival mechanisms for retinal ganglion cells

Retinal ganglion cells (RGCs) undergo programmed cell death (apoptosis) after axonal injury. This cell death is mediated by several mechanisms, including deprivation of neurotrophic factors, alterations in gene expression, and production of reactive oxygen species. However, death of RGCs is delayed after axonal injury, and a significant number survive even after several days. This suggests that RGC death is not an immediate result of axonal injury, and that other pro-survival factors may play a role. While we and other researchers have focused on the mechanisms of cell death after axonal injury, it may be that determining the regulation of cell survival mechanisms may lead to innovative methods for neuroprotection. The final common pathway of glaucomatous optic neuropathy is RGC death, probably via damage to their axons occurring at or near the lamina cribrosa. Axonal injury leads directly (1) or indirectly (2) to the death of retinal ganglion cells. We and others have demonstrated that axotomy is associated with RGC apoptosis (3-7) as well as specific changes in expression of certain genes at the mRNA and protein level (8, 9). Reactive oxygen species may also be part of the pathway for RGC death (10, 11). We therefore hypothesize that axotomy leads to molecular events that are potentially destructive to RGCs, but also induces changes that are potentially protective against cellular injury. If this is the case, then RGC death from axonal injury would result not only from initiation of apoptosis, but also from failure of intrinsic neuroprotective mechanisms. It should therefore be theoretically possible to modulate these two classes of responses, and thus improve RGC cell survival after axotomy.     

视网膜下移植睫状神经营养因子编码基因修饰的细胞保护SD大鼠视神经横断伤后视网膜节细胞变性

目的探讨移植表达睫状神经营养因子(CNTF)的细胞对SD大鼠视神经横断伤后视网膜节细胞的保护作用。方法通过脂质体将CNTF表达质粒转移至人胚肺成纤维细胞,建立稳定、高水平表达CNTF的细胞株。采用双侧背外侧膝状体及上丘核团注射3%荧光金逆行标记视网膜节细胞。将标记后的大鼠分为两组,于标记后7d手术切断眶内段视神经其中一组左眼不做手术作为正常对照组,右眼切断视神经作为手术对照组;另一组双眼均手术切断视神经,左眼注射PBS作为治疗对照组,右眼视网膜下移植表达CNTF的细胞作为实验组。术后5、14、17、21及28d取出眼球,铺片后荧光显微镜观察并计数视网膜内存活的节细胞。结果手术切断眶内段视神经后2周,视网膜内节细胞数减少6744%,视网膜下移植表达CNTF的细胞后第5、17、21d视网膜内存活的节细胞数明显多于治疗对照组(P<005)。结论视网膜下移植高水平表达CNTF的细胞对视网膜节细胞有保护作用。     

黄芪注射液对体外培养视网膜神经节细胞的保护作用

目的 视神经由视网膜神经节细胞(retinal ganglion cells,RGCs)轴突构成,一旦损伤难以再生,视神经保护是治疗视神经疾病的关键,本研究拟评价黄芪注射液的视神经保护作用.方法 体外培养RGCs,采用谷氨酸作为细胞凋亡诱导剂建立RGCs凋亡模型,并用不同浓度黄芪注射液加入细胞培养基进行干预,分别用MTT和流式细胞检测的方法进行细胞存活率及细胞凋亡相关检测.结果 黄芪注射液加入DMEM-F12培养基共培养RGCs 24 h后,MTT检测结果示终浓度为(0.10～0.40)×103g·L-1时黄芪注射液均可促进RGCs存活,其中0.20×103g·L-1、0.30×103g·L-1浓度促生长作用最好(P=0.040、0.005,n=10),谷氨酸浓度为3.2 mmol·L-1时可造成理想的RGCs凋亡模型,0.20×103g·L-1黄芪注射液可促进谷氨酸损伤的RGCs存活(P=0.08,n=10)并减少其细胞凋亡率(P=0.36,n=4).结论 黄芪注射液作为视神经保护中药制剂对RGCs具有一定保护作用,黄芪对RGCs的保护作用很可能跟抑制谷氨酸兴奋性毒性作用有关.     

米诺环素对急性视神经炎视神经轴突及Caspase-3表达的影响

目的:探讨米诺环素对急性视神经炎的影响,并与甲基强的松龙比较。方法:雌性Wistar大鼠22只随机分为正常组、EAE组、米诺环素组、甲基强的松龙组(MP组)。观察视神经病理改变,免疫组织化学法检测视网膜神经节细胞(retinal ganglion cells,RGCs)中Caspase-3蛋白表达。结果:EAE组视神经光镜下表现为神经纤维空泡样变性,轴突不规则肿胀,大量炎性细胞浸润。EAE组、米诺环素组、MP组与正常组视神经轴突占横切面积比例相比,差异均有显著统计学意义(P<0.01),米诺环素组、MP组与EAE组间的差异均有统计学意义(P<0.05)。正常大鼠视网膜几乎未见Caspase-3蛋白表达,EAE组、MP组与米诺环素组间的差异均有统计学意义(P<0.05),MP组与EAE组间的差异有统计学意义(P<0.05)。结论:甲基强的松龙可减轻脱髓鞘性视神经炎轴突损伤,但不能减少RGCs中Caspase-3的表达。米诺环素可下调Caspase-3在视网膜中表达,提示米诺环素可通过抑制RGCs中Caspase-3活性,介导对脱髓鞘性视神经炎RGCs的保护作用。     

辅助性T细胞在脱髓鞘性视神经炎发病中的作用

背景 视神经炎是神经眼科临床常见疾病之一,易反复发作并可造成视神经轴索损害及不可逆性视力损伤,且无有效的防治方法,其发病机制被认为与机体免疫调节失衡有关. 目的 研究辅助性T细胞（Th）亚群调节性T细胞（Treg）、Th17特异性细胞因子及其转录因子在脱髓鞘性视神经炎早期发病中的表达,以明确实验性自身免疫性脑脊髓炎（EAE）小鼠脱髓鞘性视神经炎的免疫反应启动及免疫炎症维持机制. 方法 采用随机数字表法将6～9周龄清洁级C57BL/6（H-2b）雌性小鼠84只随机分为正常对照组12只和免疫后7、11、14、19、23、28 d组（模型组亚分）各12只.模型组小鼠分别于背部两侧皮下注射相应抗原200 μg,免疫当天记作第0天,于免疫后第0、2天给予模型组小鼠腹腔内注射百日咳疫苗400 ng,对照组注射生理盐水.观察视神经炎小鼠的眼部表现及闪光视觉诱发电位（F-VEP）变化;苏木精-伊红染色观察视神经的组织学改变;免疫组织化学法检测视神经轴索损伤标志物β-淀粉样前体蛋白（β-APP）表达量的变化;逆转录PCR（RT-PCR）法检测视神经组织中转化生长因子-β（TGF-β）、白细胞介素-1β（IL-1β）、IL-17、IL-10及叉头蛋白3（Foxp3）等的动态表达.结果 免疫后11d,模型组小鼠陆续出现神经系统症状,苏木精-伊红染色可见模型组视神经组织内出现炎性因子浸润,免疫组织化学法检测发现模型组轴索损伤标志物β-APP阳性染色增强;F-VEP检测结果显示,免疫后7、11、14、19、23、28 d组小鼠P1波潜时值较正常对照组小鼠延长,差异均有统计学意义（t=4.487、15.203、16.364、11.540、11.959、16.163,P＜0.05）;免疫后7d,正常对照组与模型组小鼠N1-P1振幅的差异无统计学意义（t=-0.992,P=0.378）;而免疫后11、14、19、23、28 d组小鼠N1-P1振幅明显低于正常对照组,差异均有统计学意义（t=-13.161、-31.401、-16.109、-7.025、-7.257,P＜0.05）.小鼠视神经中TGF-β、IL-1β、IL-17、Foxp3、IL-10 mRNA表达各时间点间整体比较差异有统计学意义（F=12.721、15.015、14.343、69.374、68.290,均P=0.000）,与正常对照组比较,免疫后11d、14d组,TGF-β mRNA水平明显升高,免疫后19d、23 d组,IL-1β mRNA水平明显升高,免疫后7d、11d组IL-17 mRNA水平明显升高,免疫后7、11、14、19、23、28 d组Foxp3 mRNA水平均明显降低,免疫后19、23、28 d组IL-10 mRNA水平明显降低,差异均有统计学意义（P＜0.05）.结论 Th17细胞亚群参与了脱髓鞘性视神经炎免疫损伤的启动,而Th1细胞亚群维持了炎症损伤,Treg亚群较Th2亚群更早出现异常.Th17/Treg比例失衡可能参与了脱髓鞘性视神经炎的发生.     

The molecular basis of retinal ganglion cell death in glaucoma

Glaucoma is a group of diseases characterized by progressive optic nerve degeneration that results in visual field loss and irreversible blindness. A crucial element in the pathophysiology of all forms of glaucoma is the death of retinal ganglion cells (RGCs), a population of CNS neurons with their soma in the inner retina and axons in the optic nerve. Strategies that delay or halt RGC loss have been recognized as potentially beneficial to preserve vision in glaucoma; however, the success of these approaches depends on an in-depth understanding of the mechanisms that lead to RGC dysfunction and death. In recent years, there has been an exponential increase in valuable information regarding the molecular basis of RGC death stemming from animal models of acute and chronic optic nerve injury as well as experimental glaucoma. The emerging landscape is complex and points at a variety of molecular signals - acting alone or in cooperation - to promote RGC death. These include: axonal transport failure, neurotrophic factor deprivation, toxic pro-neurotrophins, activation of intrinsic and extrinsic apoptotic signals, mitochondrial dysfunction, excitotoxic damage, oxidative stress, misbehaving reactive glia and loss of synaptic connectivity. Collectively, this body of work has considerably updated and expanded our view of how RGCs might die in glaucoma and has revealed novel, potential targets for neuroprotection.     

Neuroprotective effect of memantine in different retinal injury models in rats

PURPOSE: To evaluate the neuroprotective effect of memantine, an NMDA receptor channel blocker, in two retinal ganglion cell (RGC) injury models in rats. METHODS: Neuroprotective effect of memantine was tested in partial optic nerve injury and chronic ocular hypertensive models. In the optic nerve injury model, memantine (0.1 - 30 mg/kg) was injected intraperitoneally immediately after injury. Two weeks later, optic nerve function was determined by measuring compound action potential and surviving RGC was determined by retrograde labeling with dextran tetramethyl rhodamine. Chronic ocular hypertension was attained by laser photocoagulation of episcleral and limbal veins. Memantine (5 or 10 mg/kg) was administered continuously each day with an osmotic pump, either immediately after or 10 days after first laser photocoagulation, for 3 weeks, after which RGC survival was determined. RESULTS: Two weeks after partial optic nerve injury, there was approximately 80% reduction in RGC number. Memantine (5 mg/kg) caused a twofold increase in compound action potential amplitude and a 1.7-fold increase in survival of RGCs, respectively. In the chronic ocular hypertension model there was 37% decrease in RGCs after 3 weeks of elevated intraocular pressure. Memantine (10 mg/kg daily) reduced ganglion cell loss to 12% when applied immediately after first laser photocoagulation, and prevented any further loss when applied 10 days after first laser photocoagulation. CONCLUSION: The protective effect of memantine suggests that excessive stimulation of NMDA receptors by glutamate is involved in causing cell damage in these RGC injury models.     

The neurobiology of cell death in glaucoma

Glaucoma is an optic neuropathy in which the optic nerve axons are damaged, resulting in death of retinal ganglion cells (RGCs). The primary region of damage is thought to be the optic nerve head (ONH), with the lateral geniculate nucleus (LGN) and optic radiations to the visual cortex being secondarily affected. Neurotrophin deprivation resulting from optic nerve injury is thought to cause RGCs to die by apoptosis by inhibition of cell survival pathways. However, disruption of retrograde axonal transport is not the only mechanism associated with optic nerve damage and RGC death, and thus, an additional mechanism of injury is likely to be involved in glaucomatous optic neuropathy.     

米诺环素对急性视神经炎大鼠视网膜神经节细胞的保护作用

目的:探讨米诺环素对大鼠视神经炎视网膜神经节细胞(RGCs)的影响,并与甲基强的松龙比较。方法:选取22只雌性Wistar大鼠随机分为正常对照组和实验组,实验组又分为实验对照组(EAE组)、米诺环素组、甲基强的松龙组(MP组)。HE染色观察视神经病理改变,TUNEL法检测RGCs凋亡率。结果:EAE组视神经纤维空泡样变性,轴突不规则肿胀,大量炎性细胞浸润,轴突内空泡样变性,髓鞘松解脱落,微丝微管消失,EAE大鼠视神经病理变化符合脱髓鞘性视神经炎改变。正常大鼠几乎未见RGCs凋亡,EAE组、米诺环素组、MP组较正常组相比,差异均有显著统计学意义(P<0.01),EAE组、MP组较米诺环素组相比,差异均有统计学意义(P<0.05),MP组与EAE组间的差异有统计学意义(P<0.05)。结论:采用豚鼠脊髓匀浆诱导建立大鼠EAE模型,其视神经病理学改变符合脱髓鞘性视神经炎的表现。米诺环素可抑制脱髓鞘性视神经炎RGCs凋亡,而甲基强的松龙对脱髓鞘性视神经炎RGCs无直接保护作用。