Induction of heat shock protein 72 protects retinal ganglion cells in a rat glaucoma model

PURPOSE: To investigate whether heat shock protein (Hsp) 72 is induced in retinal ganglion cells (RGCs) in experimental rat glaucoma and whether the induction of Hsp72 by heat stress or zinc (Zn(2+)) administration can increase survival of RGCs in the model. METHODS: Intraocular pressure (IOP) was elevated unilaterally in Wistar rats with argon laser irradiation of the trabecular meshwork 5 days after intracameral injection of india ink. Immunohistochemical staining for Hsp72 was performed. The rats with elevated IOP were treated with heat stress once a week (six rats) or intraperitoneal injection of zinc (10 mg/kg) every two weeks (six rats). Untreated rats with elevated IOP served as a control group (six rats). Quercetin, an inhibitor of Hsp expression was injected in the rats with heat stress (six rats) and zinc injection (seven rats). Subsequent to 4 weeks of IOP elevation, RGCs were counted. RESULTS: The IOP increase compared with the contralateral eyes was 48% +/- 4% throughout the study period. Hsp72 was detected only in the eyes with elevated IOP at 1 and 2 days and was weakly detected at 1 week of IOP elevation. A single administration of zinc strongly induced Hsp72 in RGCs of rats with elevated IOP for 2 weeks. Treatment with heat stress or zinc in rats with elevated IOP increased RGC survival after 4 weeks of IOP elevation, compared with the untreated control group (P = 0.004, n = 6). Quercetin reversed the positive effect of heat stress or zinc injection on RGC survival. CONCLUSIONS: These results demonstrate the possibility of a novel therapeutic approach to glaucoma through an enhanced induction of the endogenous heat shock response.     

替普瑞酮对大鼠慢性高眼压视网膜HSP70表达的影响

目的:研究慢性高眼压大鼠视网膜HSP70表达的变化及替普瑞酮的影响。方法:Wistar大鼠70只随机分为3组:空白对照组10只;慢性高眼压模型组30只;慢性高眼压模型+GGA组30只。采用烧灼巩膜浅层静脉的方法制备大鼠慢性高眼压模型。模型成功后给予替普瑞酮800mg/(kg.d)每日灌胃。应用免疫组织化学方法观察应用及未应用替普瑞酮的慢性高眼压大鼠视网膜不同时点的差异及HSP70表达的变化。结果:平均眼压高于正常眼压40%的手术眼为造模成功。与正常对照组相比,慢性高眼压大鼠应用与未应用替普瑞酮者,视网膜均随着高眼压时间的延长逐渐出现形态学变化,于高眼压的21d和28d视网膜变薄,节细胞数量减少;在此过程中,HSP70表达增多。慢性高眼压大鼠视网膜应用替普瑞酮者与未应用提普瑞酮者相比,其形态学变化较小,而HSP70表达则明显增多,两者差异具有统计学意义(P<0.01)。结论:替普瑞酮通过上调HSP70表达发挥对慢性高眼压视网膜的保护作用。     

Influence of geranylgeranylacetone on the expression of HSP70 in retina of rats with chronic IOP elevation

AIM: To study the effects of geranylgeranylacetone (GGA) on the expression of heat shock protein70 (HSP70) on retinal ganglion cells (RGC) in rats with chronic intraocular pressure (IOP) elevation. · METHODS: Seventy Wistars were divided into blank control group (10 rats), chronic hypertension group (30 rats) and GGA group (30 rats). Chronic hypertension was created by cauterizing the superficial scleral veins. 800mg/kg/d GGA was given by oral daily after cauterization. Immunohis- tochemistry was used respectively to observe the changes of expression of HSP70 in the model rats and GGA interference rats at different time points during the course of chronic IOP elevation. · RESULTS: The successful model was identified as the IOP over 40% of normal rats. The retinal thickness was significantly reduced in model group and model+GGA group compared with normal rats from 21 days through 28 days after cauterization (P <0.05), and that of model rats was obviously decreased in comparison with model+GGA rats (P < 0.05). The number of ganglion cells was significantly decreased in model rats and model+GGA rats compared with normal rats from 21 days and 28 days. The stronger expression intensity (IOD) value was seen for HSP70 in the model+GGA rats by immunochemistry (P <0.01). · CONCLUSION: Systemic administration of GGA protects retina from chronic IOP elevation by regulating the expression of HSP70.     

Downregulation of Thy1 in retinal ganglion cells in experimental glaucoma

PURPOSE: Thy1 is a surface glycoprotein uniquely expressed in retinal ganglion cells (RGCs) in retina. The aim of this study was to investigate the expression change of Thy1 in a model of experimental glaucoma. METHODS: The change of protein and mRNA levels of Thy1 in the retina were studied using stereological counts of back-labeled RGCs, Western blot analysis, immunohistochemistry, and laser capture microdissection (LCM) of RGCs with quantitative PCR analysis of mRNA in a model of experimental glaucoma. LCM after optic nerve crush was also performed to evaluate Thy1 mRNA levels after a different injury. RESULTS: After 10 days of elevated IOP, there was a 34% loss of RGC number, Thy1 protein decreased 60% in eyes with elevated intraocular pressure (IOP), and Thy1 mRNA levels decreased 51% in RGCs. Both protein and mRNA level change of Thy1 is to a much greater extent than RGC number loss. CONCLUSIONS: The current results confirm that Thy 1 mRNA levels do not reflect the number of RGCs present and extend this to include a parallel decrease in Thy1 protein levels. These results suggest that Thy1 serves as an early marker of RGC stress, but not a marker of RGC loss, in models of retinal damage.     

Induction of heat shock proteins 27 and 72 in retinal ganglion cells after acute pressure-induced ischaemia

Background:  We wanted to investigate whether heat shock protein (HSP) 27 and HSP 72 are induced in retinal ganglion cells (RGCs) after acute intraocular pressure (IOP)-induced ischaemia.
Methods:  Retinal ischaemia was induced by acutely increasing IOP to 100–110 mmHg for 30 or 90 min unilaterally in Sprague Dawley rats. A fluorescent tracer (fluorogold, FG) was applied to the superior colliculi to label RGCs. Twenty-four hours, 1 week or 2 weeks after of IOP elevation, rats were killed, RGCs counted, and immunohistochemical labelling of the retina was performed. HSP-positive RGCs were counted and normalized HSP RGC counts determined.
Results:  The ratio of FG-positive labelled RGCs in the experimental to the contralateral eye as a marker of RGC survival remained unchanged after 30 min of ischaemia: 1.09 ± 0.11 at 1 week, and 0.94 ± 0.28 at 2 weeks. After 90 min of ischaemia RGC survival decreased to 0.19 ± 0.14 at 1 week, and 0.20 ± 0.14 at 2 weeks. After 30 min of ischaemia, the normalized HSP 27- and HSP 72-positive RGC count was detected at highest levels (HSP 27: 5.42 ± 1.18; HSP 72: 12.23 ± 1.24) at 2 weeks compared with controls, whereas after 90 min ischaemia it was detected at higher levels at 1 week (HSP 27: 52.63 ± 3.65; HSP 72: 206.84 ± 60.38), as well as at 2 weeks (HSP 27: 89.00 ± 17.21; HSP 72: 191.00 ± 50.05).
Conclusion:  These results demonstrate an enhanced induction of HSP 27 and HSP 72 after 90 min acute IOP-induced ischaemia. In contrast to 30 min ischaemia, we showed time-dependent loss of RGCs after 90 min of ischaemia after 1 week or 2 weeks.     

热休克蛋白72（HSP72）对大鼠青光眼模型视网膜神经节细胞和视神经的保护作用

目的　探讨热休克蛋白72（heat shock protein 72,HSP72）对大鼠青光眼模型视网膜神经节细胞（retinal ganglial cells,RGCs）和视神经的保护作用。方法　选取Wistar大鼠46只，采用随机数字表法将所有大鼠分为正常对照组（6只）和实验组（40只），实验组40只大鼠中8只不作处理（实验对照组），在制作青光眼模型后2 d，给予16只大鼠热休克反应处理（热休克反应组），16只大鼠硫酸锌腹腔注射（硫酸锌注射组）。观察及比较治疗前后各组大鼠眼压、RGCs中HSP72抗体含量、RGCs平均密度。结果　激光后3 d、7 d、14 d、28 d，各组大鼠右眼眼压均较激光前有所上升，且各组间差异均无统计学意义（均为P>0.05）。正常对照组大鼠不同时间点HSP72抗体在RGCs中无表达，激光后3 d实验组各组大鼠RGCs中HSP72抗体含量缓慢上升，7 d、14 d达高峰，此后逐渐下降至接近正常水平。激光后，实验组各组大鼠RGCs中HSP72抗体含量显著高于正常对照组，且热休克反应组RGCs中HSP72抗体含量均高于实验对照组，低于硫酸锌注射组，差异均有统计学意义（均为P<0.05）。激光后3 d、7 d、14 d、28 d实验组各组大鼠RGCs平均密度均明显低于正常对照组，且热休克反应组RGCs平均密度显著高于实验对照组和硫酸锌注射组，差异均有统计学意义（均为P<0.05）。结论　热休克蛋白反应可在青光眼模型大鼠RGCs中诱导HSP72的生成，且对青光眼性RGCs和视神经具有保护作用。     

Induction of Heat Shock Protein 72 in RGCs of Rat Acute Glaucoma Model after Heat Stress or Zinc Administration

Purpose:To investigate the dynamics of heat shock protein 72 (HSP72) expression in retinal ganglion cells (RGCs) in rat model of acute glaucoma treated with heat stress or intraperitoneal injection of zinc sulfate.Methods : Twenty-seven male Wistar rats were used to make acute glaucoma models. Five others served as normal control. Acute glaucoma models were made by intracameral irrigation in the right eyes with balanced salt saline (BSS) at 102 mmHg for 2 hours. Nine model rats were killed at different intervals after intracameral irrigation without treatment, which served as damage control. Ten were treated with heat stress 40℃-42℃, and 8 were used for zinc sulfate administration 2 days posterior to intracameral irrigation.Treated model rats were sacrificed at designed intervals after treatment. Right eyes were enucleated immediately, and the retinas were dissected for Western blot.Results : No HSP72 was found in RGCs of normal Wistar rats. In damage control group,slight HSP72 was detected during 6-36 hours posterior to intracameral irrigation. HSP72 was detected significantly expressed in RGCs of both heat shock group and zinc sulfate group. But the dynamics of HSP72 production were quite different in these two treated groups. In heat shock group, HSP72 appeared at the sixth hour after treatment, and increased gradually until its peak production emerged at the 48th hour. HSP72 vanished 8 days later after treatment. In zinc sulfate group, HSP72 expression began 24 hours later after zinc administration, and reached its highest level at the 72th hour posterior to treatment. HSP72 expression then decreased slowly, and disappeared 21 days later aftertreatment.Conclusion:HSP72 can be induced in RGCs of rat acute glaucoma models with heat stress or zinc sulfate adddministration. But the dynamics of the HSP72 induction in those two groups were quite different.     

Topically administered timolol and dorzolamide reduce intraocular pressure and protect retinal ganglion cells in a rat experimental glaucoma model

AIMS: This study sought to elucidate the effects of timolol and dorzolamide on intraocular pressure (IOP) and retinal ganglion cell (RGC) death in an experimental model of glaucoma in rat. METHODS: Mild elevation of IOP was induced in rats by intracameral injection of India ink and subsequent laser trabecular photocoagulation. IOP was measured before the surgical procedures and weekly thereafter. Timolol (0.5%), timolol XE (0.5%), dorzolamide (1%), and artificial tears (vehicle) were topically applied daily. Retinal sections were prepared for histology to determine RGC number. RESULTS: Timolol, timolol XE, and dorzolamide induced a significant reduction in IOP (p<0.05) and counteracted the reduction in RGC number that occurred in vehicle treated glaucomatous eyes (p<0.05). The coefficient of correlation between RGC number and IOP was significant in the dorzolamide treated group (r = -0.908, p<0.005), but not in other groups (p>0.05). CONCLUSIONS: Both timolol formulation and dorzolamide reduced IOP and protected RGCs in a rat model of experimental glaucoma. It cannot be ruled out that timolol might protect RGCs by additional mechanisms other than simply lowering of IOP.     

Detection of early neuron degeneration and accompanying microglial responses in the retina of a rat model of glaucoma

PURPOSE: To characterize the early reaction of retinal ganglion cells (RGCs) in a rat model of glaucoma using in vivo imaging and to examine the involvement of retinal microglia in glaucomatous neuropathy. METHODS: Glaucoma was induced in adult female Sprague-Dawley rats by cauterizing two episcleral veins, which resulted in a 1.6-fold increase in intraocular pressure (IOP). Retinal ganglion cells were retrogradely labeled with the fluorescent dye, 4-[didecylaminostyryl]-N-methyl-pyridinium-iodide (4-Di-10ASP) and monitored in vivo after elevation of IOP using fluorescence microscopy imaging. The number of RGCs was quantified on retinal flatmounts. Dying RGCs were surrounded by activated microglia that became visible after taking up the fluorescent debris. Immunocytochemistry was conducted to characterize further the ganglion cells and microglia. RESULTS: Cauterizing two of the four episcleral veins resulted in a consistent increase of IOP to 25.3 +/- 2.0 mm Hg, as measured with a handheld tonometer. IOP remained high for at least 3 months in glaucomatous eyes. The earliest sign of RGC death was detected in anesthetized animals 20 hours after induction of glaucoma. RGCs continued to decrease in number over time, with 40% of RGCs having degenerated after 2.5 months. Fundoscopic examination of the optic nerve head revealed cupping 2 months after induction of glaucoma. In addition, microglia were detected on retinal flatmounts as early as 72 hours after induction. Activated microglia and RGCs were also identified immunocytochemically, with an antibody against ionized calcium-binding adaptor molecule (Iba)-1 and an antibody specific to the 200-kDa subunit of the neurofilament protein, respectively. CONCLUSIONS: Occlusion of episcleral veins is a reproducible method that mimics human glaucoma, with chronically elevated IOP-induced RGC loss. This study shows that in vivo imaging permits the detection of ganglion cells in the living animal in the early stages of the disease and highlights the importance of in vivo imaging in understanding ophthalmic disorders such as glaucoma. Secondly, activation of intraretinal microglia coincides with degeneration of RGCs in glaucoma.     

替普瑞酮对大鼠慢性高眼压视网膜HSP70表达的影响

目的：研究慢性高眼压大鼠视网膜HSP70表达的变化及替普瑞酮的影响。方法：Wistar大鼠70只随机分为3组：空白对照组10只;慢性高眼压模型组30只;慢性高眼压模型＋GGA组30只。采用烧灼巩膜浅层静脉的方法制备大鼠慢性高眼压模型。模型成功后给予替普瑞酮800mg／（kg·d）每目灌胃。应用免疫组织化学方法观察应用及未应用替普瑞酮的慢性高眼压大鼠视网膜不同时点的差异及HSP70表达的变化。结果：平均眼压高于正常眼压40％的手术眼为造模成功。与正常对照组相比,慢性高眼压大鼠应用与未应用替普瑞酮者,视网膜均随着高眼压时间的延长逐渐出现形态学变化,于高眼压的21d和28d视网膜变薄,节细胞数量减少;在此过程中,HSP70表达增多。慢性高眼压大鼠视网膜应用替普瑞酮者与未应用提普瑞酮者相比,其形态学变化较小,而HSPT0表达则明显增多,两者差异具有统计学意义（P〈0．01）。结论：替普瑞酮通过上调HSP70表达发挥对慢性高眼压视网膜的保护作用。     

Neuroprotective and intraocular pressure-lowering effects of (-)Delta9-tetrahydrocannabinol in a rat model of glaucoma

In glaucoma, retinal ganglion cell (RGC) death is induced by many risk factors, including ocular hypertension. It has been proposed that glutamate-mediated oxidative stress may also contribute to this RGC death. Cannabinoids are known to possess therapeutic properties including ocular hypotension and antioxidation. In this study, we test the hypothesis that (-)Delta(9)-tetrahydrocannabinol (THC) lowers intraocular pressure (IOP) and prevents RGC death in a rat model of glaucoma. Arat model of experimental glaucoma with chronic, moderately elevated IOP was produced unilaterally by cauterization of episcleral vessels. Rats received weekly injections of THC at a level of 5 mg/kg or vehicle for 20 weeks. IOP of both eyes was measured weekly on anesthetized animals immediately before THC treatment. RGCs were labeled in a retrograde fashion and counted in whole-mounted retinas. IOP was elevated in all operated eyes 1 day after the operation and remained elevated in the vehicle-treated rats throughout 20 weeks. In THC-treated rats, IOP elevation in operated eyes was diminished 2 weeks after operation and remained reduced. IOP in the contralateral control eyes was not affected by THC. In the operated eyes of vehicle-treated animals, there was a loss of approximately 50 and 40% of the RGCs in the peripheral and central retina, respectively. The RGC loss in the operated eyes of the THC-treated animals was reduced to 10-20%. These results demonstrate that THC is a neuroprotectant that preserves RGCs in an experimental model of glaucoma, possibly through a reduction in IOP.     

Retinal ganglion cell neuroprotection in a rat model of glaucoma following brimonidine, latanoprost or combined treatments

The aim of the present study is to evaluate the neuroprotective effect of two antiglaucomatous substances, regardless of their hypotensive effect in the eye. Brimonidine, which does not reduce IOP when administered intraperitoneally, and latanoprost, which has a renowned hypotensive effect topically. We examined rat retinal ganglion cell (RGC) survival and size distribution in experimental glaucoma in response to different glaucomatous agents. IOP was elevated by episcleral vein cauterization (EVC) prior to the application of different treatments: (I) PBS application (control group), (II) intraperitoneal administration of brimonidine (a general hypotensive agent), (III) topical application of latanoprost (an ocular hypotensive agent), and (IV) latanoprost combined with brimonidine. After 12 weeks, RGCs were retrogradely labeled with fluorogold and RGC density was analyzed. EVC caused a significant increase (42%) in IOP in each group before drug treatment. After 12 weeks of EVC, RGC survival in control vs. EVC rats was 78.9 ± 3.2%. No IOP reduction was observed in brimonidine injected rats, but RGC survival at 12 weeks was total (103.7 ± 2.7%). In latanoprost treated rats, IOP dropped by around 22% and 94.7 ± 3.7% of the RGC population survived. Finally in the latanoprost + brimonidine combined group, IOP was significantly reduced by 25% and 94.4 ± 2.2% of RGCs survived. Surprisingly, whereas EVC led to a 6% increase in RGC soma size, brimonidine treatment was associated with a 9% reduction in the soma size of RGCs at 12 weeks. We conclude that brimonidine exerts a neuroprotective effect via a mechanism which is independent of IOP reduction. These findings indicate that cell survival in glaucoma may be enhanced by neuroprotective strategies which are independent of IOP reduction. No synergistic neuroprotective effect was observed when both treatments were applied simultaneously.     

The pig eye as a novel model of glaucoma

We validated the pig eye as a model of glaucoma, based on chronic elevation of intraocular pressure (IOP). IOP was elevated by cauterising three episcleral veins in each of the left eyes of five adult pigs. Right eyes were used as controls. Measurement of IOP was performed during the experiment with an applanation tonometer (Tono-Pen). Five months after episcleral vein occlusion, retinal ganglion cells (RGCs) from both cauterised and control eyes were retrogradely backfilled with Fluoro-Gold. Analysis of RGC loss and morphometric as characterization of surviving RGCs was performed using whole-mounted retinas. Elevation of IOP was apparent after three weeks of episcleral vein cauterisation and it remained elevated for at least 21 weeks (duration of the experiments). Analysis of RGC loss after chronic elevation of IOP revealed that RGC death was significant in the mid-peripheral and peripheral retina, mainly in the temporal quadrants of both retinal regions. Moreover the mean soma area of remaining RGCs was observed to increase and we found a greater loss of large RGCs in the mid-peripheral and peripheral retina. We conclude that the pattern of RGC death induced in the pig retina by episcleral vein cauterisation resembles that found in human glaucoma. On the basis of this study, the pig retina may be considered as a suitable model for glaucoma-related studies, based on its similarity with human and on its affordability.     

灯盏细辛注射液对鼠实验性高眼压视神经轴浆运输的影响

探讨灯盏细辛注射液是否对急性实验性高眼压大鼠视神经浆运输阻滞有促进恢复作用。方法健康ＳＤ大鼠３０只,右眼制作成急性高眼压模型后,随机分成３组。Ａ组６只鼠,做经左侧上丘逆行辣根过氧化物酶（ｈｏｒｓｅ ｒａｄｉｓｈ ｐｅｒｏｘｉｄａｓｅ,ＨＲＰ）标记,并行视网膜神经节细胞（ｒｅｔｉｎａｌ ｇａｎｇｉｏｎ ｃｅｌｌｓ,ＲＧＣｓ）计数。Ｂ组１２只鼠,再分灯盏细辛腹腔注射治疗组与对照组,每组各６只鼠,高眼压     

Retinal damage after 3 to 4 months of elevated intraocular pressure in a rat glaucoma model

PURPOSE: To characterize a long-term elevated intraocular pressure (IOP) glaucoma model in the rat with respect to electroretinographic (ERG) changes and the pattern and mechanism of retinal ganglion cell (RGC) death. METHODS; An approximate doubling of IOP was induced in one eye (G) of female Wistar rats (150-180 g) by cautery of 3 episcleral/limbal veins. At intervals over 3 to 4 months, measurements of IOP and ERG changes (contact-lens electrode) were made in both the G and contralateral normal (N) eyes. At the end of 3 to 4 months of elevated IOP, RGCs were fluorescently labeled with Fluorogold (retrogradely from the superior colliculus), or retinas were labeled by intravitreal injection of a mitochondrial potential indicator dye and stained for apoptotic nuclei with a DNA dye. Flatmounts of fixed, dye-labeled retinas were examined by epifluorescence, confocal, or interference contrast microscopy. RESULTS: Elevated IOP was consistently maintained for up to 4 months in G eyes, but ERG a- and b-waves showed a statistically significant decline, of 30% to 40% in amplitude, after 3 months. Loss of RGCs in G retinas was primarily focal with no statistically significant loss demonstrable outside of the focal areas when assessed by an area sampling method for counting RGCs, which totaled 2% to 3% of the entire retinal area. Mitochondrial membrane potential of cells in the RGC layer was reduced by 17.5% (P: < 0.05) in regions surrounding areas of focal loss compared with comparable locations in control N eyes. After 3.5 months' elevated IOP the G retinas showed cell nuclei at various stages of apoptosis, from initial DNA condensation to fragmentation. CONCLUSIONS: The three-vein episcleral/limbal vein occlusion model for inducing glaucomatous pathology in the rat eye gives a consistent long-term elevation of IOP. After 3 to 4 months of approximately 100% increased IOP, the ERG responses begin to decline, there is a variable focal loss of RGCs, and some of the remaining RGCs show characteristics of stress and apoptosis. These changes seem consistent with retinal damage in human glaucoma (focal field defects), and this rat model appears to mimic some features of primary open-angle glaucoma.     

Effects of elevated intraocular pressure on mouse retinal ganglion cells

We developed and characterized a mouse model of elevated intraocular pressure (IOP) to investigate the underlying cellular and genetic mechanisms of retinal ganglion cell (RGC) death. IOP was unilaterally increased in C57BL/6J mice by photocoagulation of the episcleral and limbal veins. IOP was measured using an indentation tonometer. RGC survival was measured by retrograde labeling using DiI applied to the superior colliculous. The mechanism of RGC death was investigated using TUNEL staining, immunostaining for cleaved caspase-3, and Western blot for Bcl-2 and Bax expression. RT-PCR was used to measure changes in Bcl-2, Bax, Bad, Bak, P53, ICE and Fas. Mean IOP was increased in the treated eyes from 13+/-1.8 to 20.0+/-2.8 mmHg at four weeks and 17+/-2.2 mmHg at eight weeks. RGC loss was 15.6+/-3.4% at two weeks and 27.3+/-4.5% at four weeks after laser photocoagulation. TUNEL staining and caspase-3 positive cells were increased in the ganglion cell layer (GCL) in the treated eyes and seldom found in the control eyes. Bcl-2 expression in control group was higher than in the experimental group, while Bax expression in the control group was less than in experimental group. This mouse model resulted in a consistent, sustained increase in IOP with a reduction in the number of RGCs in the treated eye. The RGCs in eyes with elevated IOP were TUNEL-positive, with increased caspase-3 and decreased Bcl-2, consistent with apoptosis as the mechanism of neuronal cell death.     

Activation of caspase 9 in a rat model of experimental glaucoma

PURPOSE: We investigated retinal ganglion cell (RGC) death and activation of caspase 9 in rats with experimental glaucoma. METHODS: Elevated intraocular pressure (IOP) was induced in rats using the Morrison model. Surviving backlabeled RGC were counted and TUNEL staining detected apoptosis. Procaspase 9 expression and activated caspase 9 were studied by immunoblot and immunohistochemistry. RESULTS: IOP correlated with surviving RGC. TUNEL-positive RGC were observed in animals with elevated IOP. Procaspase 9 levels increased with IOP intensity. Cleaved caspase 9 was detected by immunoblot only in rats with peak IOP above 35 mm Hg for > or =6 days. Cleaved caspase 9 staining was seen only in the ganglion cell layer of retinas from rats with peak IOP > or =32 mm Hg. CONCLUSIONS: RGC loss is correlated with IOP in experimental glaucoma. These results support activation of caspase 9, the intrinsic caspase cascade, in RGC death in experimental glaucoma.     

Heat Shock Protein 72 Protects Retinal Ganglion Cells in Rat Model of Acute Glaucoma

Purpose: To investigate whether the induction of heat shock protein (HSP)72 by heat stress (HS) or zinc (Zn2 ) administration can increase survival of retinal ganglion cells (RGC)in rat model of acute experimental glaucoma. Methods: Acute glaucoma model was made by intracameral irrigation with BSS at 102 mmHg for two hours in right eyes of male Wistar rats. Glaucoma model rats were treated with HS once a week (six rats) or intraperitoneal injection of zinc sulfate (24.6 mg/kg) every two weeks (six rats), and were referred to as HS group and zinc group, respectively. Untreated model rats served as damage group (six rats). In control groups, querc-etin (400 mg/kg) was intraperitoneally injected to inhibit the induction of heat shock proteins 6 hours before HS or zinc administration, and were referred to as HS que group (six rats) and zinc que group (six rats), respectively. Subsequent to 16 days of IOP elevation, the rats were sacrificed. Eyes were quickly enucleated, and the retinas were dissected. RGC were labeled with Nissl staining and counted under microscope. Results: The average RGC density in normal Wistar rats was (2504±181) cells/mm2. In damage group, it decreased to (2015±111) cells/mm2. The RGC densities at 1,2, and 3 mm from the center of the optic nerve head were (2716±215), (2496±168), and (2317±171) cells/mm2, respectively, for normal rats and (2211±133), (1969±154), and (1872±68) cells/mm2, respectively, for damage group. The latter was significantly lower at all locations compared with the former (P=0.027 for each, Mann-Whitney test). The average RGC densities were (2207±200) cells/mm2 for HS group, (2272±155) cells/mm2 for zinc group, (1964±188) cells/mm2 for HS que group, (2051 ±214) cells/mm2 for zinc que group and (2015±111) cells/mm2for damage group. There were significant differences in density of labeled RGCs among the five groups (P=0.040, Kruskal-Wallis test). Both HS and zinc group had higher RGC densities than damage group (P =0.036 between HS and damage group,P=0.019 between zinc and damage group,Mann-Whitney test). There was no significant difference in RGC densitiy between control groups and damage group (P=0.260 between HS que and damage group,P=0.748 between zinc que and damage group, Mann-Whitney test). Conclusions: The results demonstrated that the induction of HSP72 in RGCs by HS or zinc administration plays an important role in the survival of RGCs in rat model of acute glaucoma. A novel therapeutic approach to glaucoma through an enhanced induction of endogenous HSP72 could be possible. Eye Science 2005;21:163-168.     

Characterization of retinal damage in the episcleral vein cauterization rat glaucoma model

Episcleral vein cauterization (EVC) is used in rats to generate a glaucoma model with high intraocular pressure (IOP). The long-term retinal damage in this glaucoma model, however, has not been accurately quantified. We report the location and amount of retinal ganglion cell (RGC) damage caused by (EVC) induced IOP elevation in two rat strains. IOP was raised in one eye of Wistar (N = 5) and Brown-Norway(B-N)(N = 7) rats by EVC and monitored monthly until IOP in contralateral eyes equalized at 5 months post-surgery. Animals were maintained for 3.5-4.5 additional months. B-N rats (N = 7) that had no EVC served as controls for this strain. Scotopic flash ERGs were recorded at baseline and just prior to euthanasia. Automated counts of all retrogradely labeled RGCs in retinal flat-mounts were determined and compared between contralateral eyes. RGC density maps were constructed and RGC size distribution was determined. Oscillatory potentials in the group of eyes which had elevated IOP were decreased at the time of euthanasia, when IOP had returned to normal. The group of normal B-N rats had similar RGC counts between contralateral eyes. In the experimental group the mean number of RGCs was not significantly different between control and experimental eyes, but 1 of 5 Wistar and 2 of 7 B-N experimental eyes had at least 30% fewer RGCs than contralateral control eyes. Total retinal area in B-N experimental eyes was higher compared to contralateral eyes. Cumulative IOP exposure of the experimental eyes was modestly correlated with RGC loss while oscillatory potentials appeared to be inversely related to RGC loss. In retinas with extensive (> 30% RGC loss) but not complete damage, smaller cells were preserved better than larger ones. The above results indicate that RGC loss in both Wistar and B-N strains is variable after a prolonged elevation of IOP via EVC. Such variability despite equivalent IOP levels and ERG abnormalities, suggests unknown factors that can protect IOP-stressed RGCs. Identification and enhancement of such factors could prove useful for glaucoma therapy.     

Chondroitin sulfate-derived disaccharide protects retinal cells from elevated intraocular pressure in aged and immunocompromised rats

PURPOSE: A disaccharide (DS) derived from the naturally occurring compound chondroitin sulfate proteoglycan (CSPG) was recently shown to have neuroprotective activity. The authors examined the ability of this compound (CSPG-DS) to protect retinal ganglion cells (RGCs) from death caused by elevated intraocular pressure (IOP). METHODS: With the use of chronic and acute models of elevated IOP, the authors examined the effects of CSPG-DS on RGC survival in adult ( approximately 2 months old), aged (10-12 months old), and immunocompromised Lewis rats. Systemic, topical, and oral routes of administration were examined. RESULTS: CSPG-DS protected RGCs from IOP-induced death. Treatment was effective in all three examined rat populations (normal adult, aged, and immunocompromised rats) and with all routes of administration, possibly in part through its control of microglial activity. CONCLUSIONS: Results point to the therapeutic potential of CSPG-DS for glaucoma, particularly in elderly populations for whom disease prevalence is high.