Evaluation of visual function in Royal College of Surgeon rats using a depth perception visual cliff test.

Preserving of vision is the main goal in vision research. The presented research evaluates the preservation of visual function in Royal College of Surgeon (RCS) rats using a depth perception test. Rats were placed on a stage with one side containing an illusory steep drop ("cliff") and another side with a minimal drop ("table"). Latency of stage dismounting and the percentage of rats that set their first foot on the "cliff" side were determined. Nondystrophic Long-Evans (LE) rats were tested as control. Electroretinogram and histology analysis were used to determine retinal function and structure. Four-week-old RCS rats presented a significantly shorter mean latency to dismount the stage compared with 6-week-old rats (mean ± standard error, 13.7 ± 1.68 vs. 20.85 ± 6.5 s, P = 0.018). Longer latencies were recorded as rats aged, reaching 45.72 s in 15-week-old rats (P < 0.00001 compared with 4-week-old rats). All rats at the age of 4 weeks placed their first foot on the table side. By contrast, at the age of 8 weeks, 28.6% rats dismounted on the cliff side and at the age of 10 and 15 weeks, rats randomly dismounted the stage to either table or cliff side. LE rats dismounted the stage faster than 4-week-old RCS rats, but the difference was not statistically significant (7 ± 1.58 s, P = 0.057) and all LE rats dismounted on the table side. The latency to dismount the stage in RCS rats correlated with maximal electroretinogram b-wave under dark and light adaptation (Spearman's rho test = -0.603 and -0.534, respectively, all P < 0.0001), outer nuclear layer thickness (Spearman's rho test = -0.764, P = 0.002), and number of S- and M-cones (Spearman's rho test = -0.763 [P = 0.002], and -0.733 [P = 0.004], respectively). The cliff avoidance test is an objective, quick, and readily available method for the determination of RCS rats' visual function.

The effects of the apoE4 genotype on the developing mouse retina.

Apolipoprotein E4 (apoE4), the most prevalent genetic risk factor for Alzheimer's disease (AD), is associated with neuronal and vascular impairments. The retina, which is as an extension of the central nervous system (CNS), is a particularly suitable model for studying developmental and functional aspects of the neuronal and vascular systems. This study investigates the apoE4-dependent developmental effects on the retinal vasculature and neuronal systems and on the levels of apoE and the vascular endothelial growth factor (VEGF) in the retina. This was performed utilizing retinas of 4, 7, 12, and of 120-day-old human-apoE4-targeted replacement mice and of corresponding mice that express the AD benign isoform, apoE3. The results obtained revealed retinal vascular pathology in the apoE4 mice, which started on the early post-natal days. This includes transient increase in vascular branching, and vascular buds which are round vascular elements representing sprouting or retracting vessels. These effects peaked and ended during the neonatal period. Examination of the synaptic system utilizing the pre-synaptic marker synaptophysin revealed a significant decrease of retinal synaptic density in the apoE4 mice, which was detectable by post-natal day 12 (P12). These morphological changes are associated with neonatal age-dependent elevation in the apoE levels in both apoE3 and apoE4 retinas which is more profound in the apoE4 mice and a corresponding increase in VEGF levels, which is less profound in the apoE4 mice. Additionally, we observed lower levels of retinal VEGF in the apoE4 mice compared to the apoE3 mice retinas on P12. These results show that apoE4 has a transient vascular effect during retinal development that ends in the neonatal period, which is accompanied by a synaptic effect that begins at the end of the neonatal period. These findings show that the apoE4 genotype can have distinct developmental effects on both the retinal vasculature and on neurons and suggest that the vascular effects of apoE4 may be related to reduced levels of VEGF.

Protein phosphatase magnesium dependent 1A governs the wound healing-inflammation-angiogenesis cross talk on injury.

Protein phosphatase magnesium dependent 1A (PPM1A) has been implicated in fibrosis and skin wounding. We generated PPM1A knockout mice to study the role of PPM1A in the wound healing-inflammation-angiogenesis cross talk. The role of PPM1A in these processes was studied using the ocular alkali burn model system. In the injured cornea the absence of PPM1A led to enhanced inflammatory response, stromal keratocyte transactivation, fibrosis, increased p38 mitogen-activated protein kinase phosphorylation, elevated expression of transforming growth factor-ß-related genes (including Acta2, TGF-ß, Col1, MMP9, and VEGF) and subsequently to neovascularization. Augmented angiogenesis in the absence of PPM1A is a general process occurring in vivo in PPM1A knockout mice upon subcutaneous Matrigel injection and ex vivo in aortic ring Matrigel cultures. Using primary keratocyte cultures and various experimental approaches, we found that phospho-p38 is a favored PPM1A substrate and that by its dephosphorylation PPM1A participates in the regulation of the transforming growth factor-ß signaling cascade, the hallmark of inflammation and the angiogenic process. On the whole, the studies presented here position PPM1A as a new player in the wound healing-inflammation-angiogenesis axis in mouse, reveal its crucial role in homeostasis on injury, and highlight its potential as a therapeutic mediator in pathologic conditions, such as inflammation and angiogenesis disorders, including cancer.

The effect of nocturnal CPAP therapy on the intraocular pressure of patients with sleep apnea syndrome.

PURPOSE: Few studies have documented that nocturnal continuous positive airway pressure (CPAP) therapy is associated with an increase in intraocular pressure (IOP) in patients with severe obstructive sleep apnea syndrome (OSAS). We re-examined the effect of CPAP therapy on the IOP of OSAS patients. METHODS: The IOP of two different groups of newly diagnosed OSAS patients was compared at their first sleep lab exam without CPAP treatment (non-CPAP treated group; n = 20) and at the second sleep lab exam with CPAP treatment (CPAP treated group; n = 31). The sleep lab exam (sleep period: from 11:00 p.m. until 6:00 a.m.) included IOP measurements, a complete ophthalmologic exam, and nocturnal hemodynamic recordings. The IOP was measured serially using rebound tonometer (IOP; ICARE® PRO) performed while in sitting and supine positions before, during, and after the sleep period. We compared the difference in IOP of CPAP and non-CPAP groups. RESULTS: The mean IOP of the CPAP and non-CPAP groups measured in sitting position before the sleep period was 13.33 ± 2.04 mmHg and 14.02 ± 2.44 mmHg, respectively (p = 0.9). Assuming a supine position for 1 minute significantly increased the IOP by 1.93 mmHg and 2.13 mmHg for both the non-CPAP and CPAP groups (paired t-test; p = 0.02, p = 0.001 respectively), but this IOP rise showed no difference between the two groups. The IOP increased significantly further after 7 hours of sleep in the supine position, and the mean IOP of the CPAP and non-CPAP groups was 19.2 ± 5.68 mmHg and 19.69 ± 5.61 mmHg respectively (independent t-test; p = 0.74). The rise in IOP for both groups was not correlated with any hemodynamic parameters. Three OSAS patients with glaucoma treated with CPAP had mean IOP of 23.75 mmHg after 7 hours of sleep. CONCLUSIONS: OSAS patients have a significant rise in IOP during the sleep period when comparing measurements before and after the sleep period; however, CPAP therapy did not affect the measured IOP. The presented findings suggest that in terms of IOP, CPAP is safe for non-glaucomatous patients, but this may not hold true for glaucomatous patients.

A role for vascular deficiency in retinal pathology in a mouse model of ataxia-telangiectasia.

Ataxia-telangiectasia is a multifaceted syndrome caused by null mutations in the ATM gene, which encodes the protein kinase ATM, a key participant in the DNA damage response. Retinal neurons are highly susceptible to DNA damage because they are terminally differentiated and have the highest metabolic activity in the central nervous system. In this study, we characterized the retina in young and aged Atm-deficient mice (Atm(-/-)). At 2 months of age, angiography revealed faint retinal vasculature in Atm(-/-) animals relative to wild-type controls. This finding was accompanied by increased expression of vascular endothelial growth factor protein and mRNA. Fibrinogen, generally absent from wild-type retinal tissue, was evident in Atm(-/-) retinas, whereas mRNA of the tight junction protein occludin was significantly decreased. Immunohistochemistry labeling for occludin in 6-month-old mice showed that this decrease persists in advanced stages of the disease. Concurrently, we noticed vascular leakage in Atm(-/-) retinas. Labeling for glial fibrillary acidic protein demonstrated morphological alterations in glial cells in Atm(-/-) retinas. Electroretinographic examination revealed amplitude aberrations in 2-month-old Atm(-/-) mice, which progressed to significant functional deficits in the older mice. These results suggest that impaired vascularization and astrocyte-endothelial cell interactions in the central nervous system play an important role in the etiology of ataxia-telangiectasia and that vascular abnormalities may underlie or aggravate neurodegeneration.

Ambient illuminance, retinal dopamine release and refractive development in chicks.

Form deprivation and low illuminance of ambient light are known to induce myopia in chicks. Low concentrations of retinal dopamine, a light-driven neurohormone, was previously shown to be associated with form deprivation myopia. In the present study we examined the dependence of retinal dopamine release in chicks on illuminance during light-dark cycles and in continuous light, and the role of retinal dopamine release in illuminance dependent refractive development. Newly hatched chicks (n = 166) were divided into two experimental groups, a dopamine (n = 88) and a refraction group (n = 78). Both groups were further divided into six illumination groups for exposure of chicks to illuminances of 50, 500 or 10,000 lux of incandescent illumination (referred to throughout as low, medium, and high illuminance, respectively), either under a light-dark cycle with lights on between 7 AM and 7 PM or under continuous illumination. For the dopamine experiment, chicks were euthanized and vitreous was extracted on day 14 post-hatching at 7, 8 AM and 1 PM. Vitreal dihydroxyphenylacetic acid (DOPAC) and dopamine concentrations were quantified by high-performance liquid chromatography coupled to electrochemical detection. For the refraction experiment, chicks underwent refraction, keratometry and A-scan ultrasonography on days 30, 60 and 90 post-hatching, and each of those measurements was correlated with vitreal DOPAC concentration measured at 1 PM (representing the index of retinal dopamine release). The results showed that under light-dark cycles, vitreal DOPAC concentration was strongly correlated with log illuminance, and was significantly correlated with the developing refraction, corneal radius of curvature, and axial length values. On day 90, low vitreal DOPAC concentrations were associated with myopia (-2.41 ± 1.23 D), flat cornea, deep anterior and vitreous chambers, and thin lens. Under continuous light, vitreal DOPAC concentrations measured at 1 PM in the low, medium, and high illuminance groups did not differ from the concentrations measured at 8 AM. On day 90, low DOPAC concentrations were associated with emmetropia (+0.63 ± 3.61), steep cornea, and shallow vitreous chamber. We concluded that ambient light over a log illuminance range of 1.69-4 is linearly related to vitreal DOPAC concentration. Under both light-dark cycles and continuous light, the intensity of ambient light regulates the release of retinal dopamine. Refractive development is associated with illuminance dependent dopamine release.

Dependency between light intensity and refractive development under light-dark cycles.

The emmetropization process involves fine-tuning the refractive state by altering the refractive components toward zero refraction. In this study, we provided light-dark cycle conditions at several intensities and examined the effect of light intensity on the progression of chicks' emmetropization. Chicks under high-, medium-, and low-light intensities (10,000, 500, and 50 lux, respectively) were followed for 90 days by retinoscopy, keratometry, as well as ultrasound measurements. Emmetropization was reached from days 30-50 and from days 50-60 for the low- and medium-intensity groups, respectively. On day 90, most chicks in the low-intensity group were myopic, with a mean refraction of -2.41D (95% confidence interval (CI) -2.9 to -1.8D), whereas no chicks in the high-intensity group developed myopia, but they exhibited a stable mean hyperopia of +1.1D. The medium-intensity group had a mean refraction of +0.03D. The low-intensity group had a deeper vitreous chamber depth and a longer axial length compared with the high-intensity group, and shifted refraction to the myopic side. The low-intensity group had a flatter corneal curvature, a deeper anterior chamber, and a thinner lens compared with the high-intensity group, and shifted refraction to the hyperopic side. In all groups the corneal power was correlated with the three examined levels of log light intensity for all examined times (e.g., day 20 r = 0.6 P < 0.0001, day 90 r = 0.56 P < 0.0001). Thus, under light-dark cycles, light intensity is an environmental factor that modulates the process of emmetropization, and the low intensity of ambient light is a risk factor for developing myopia.

Inhibition of Sema-3A Promotes Cell Migration, Axonal Growth, and Retinal Ganglion Cell Survival.

Purpose: Semaphorin 3A (Sema-3A) is a secreted protein that deflects axons from inappropriate regions and induces neuronal cell death. Intravitreal application of polyclonal antibodies against Sema-3A prevents loss of retinal ganglion cells ensuing from axotomy of optic nerves. This suggested a therapeutic approach for neuroprotection via inhibition of the Sema-3A pathway. Methods: To develop potent and specific Sema-3A antagonists, we isolated monoclonal anti-Sema-3A antibodies from a human antibody phage display library and optimized low-molecular weight Sema-3A signaling inhibitors. The best inhibitors were identified using in vitro scratch assays and semiquantitative repulsion assays. Results: A therapeutic approach for neuroprotection must have a long duration of action. Therefore, antibodies and low-molecular weight inhibitors were formulated in extruded implants to allow controlled and prolonged release. Following release from the implants, Sema-3A inhibitors antagonized Sema-3A effects in scratch and repulsion assays and protected retinal ganglion cells in animal models of optic nerve injury, retinal ischemia, and glaucoma. Conclusions and Translational Relevance: Collectively, our findings indicate that the identified Sema-3A inhibitors should be further evaluated as therapeutic candidates for the treatment of Sema-3A-driven central nervous system degenerative processes.

Sema-3A indirectly disrupts the regeneration process of goldfish optic nerve after controlled injury.

BACKGROUND: Neurons of adult mammalian CNS are prevented from regenerating injured axons due to formation of a non-permissive environment. The retinal ganglion cells (RGC), which are part of the CNS, share this characteristic. In sharp contrast, the RGC of lower vertebrates, such as fish, are capable of re-growing injured optic nerve axons, and achieve, through a complex multi-factorial process, functional vision after injury. Semaphorin-3A (sema-3A), a member of the class 3 semaphorins known for its repellent and apoptotic activities, has previously been shown to play a key role in the formation of a non-permissive environment after CNS injury in mammalians. METHODS: The expression of sema-3A and its effect on regenerative processes in injured gold fish retina and optic nerve were investigated in this study. Unilateral optic nerve axotomy or crush was induced in goldfish. 2 microl sema-3A was injected intraviterally 48 hours post injury. Neuronal viability was measured using the lipophilic neurotracer dye 4-Di-10-Asp. Axonal regeneration was initiated using the anterograde dye dextran. Retinas and optic nerves were collected at intervals of 2, 3, 7, 14 and 28 days after the procedure. Using Western blot and immunohistochemical analysis, the expression levels of semaphorin-3A, axonal regeneration, the removal of myelin debris and macrophage invasion were studied. RESULTS: We found a decrease in sema-3A levels in the retina at an early stage after optic nerve injury, but no change in sema-3A levels in the injured optic nerve. Intravitreal injection of sema-3A to goldfish eye, shortly after optic nerve injury, led to destructive effects on several pathways of the regenerative processes, including the survival of retinal ganglion cells, axonal growth, and clearance of myelin debris from the lesion site by macrophages. CONCLUSIONS: Exogenous administration of sema-3A in fish indirectly interferes with the regeneration process of the optic nerve. The findings corroborate our previous findings in mammals, and further validate sema-3A as a key factor in the generation of a non-permissive environment after transection of the optic nerve.

Mild carotid stenosis creates gradual, progressive, lifelong brain, and eye damage: An experimental laboratory rat model.

In humans, carotid stenosis of 70% and above might be the cause of clinical symptoms such as transient ischemic attack and stroke. No clinical or animal studies have evaluated mild carotid occlusion, and few examined unilateral occlusion. Here, Westar rats underwent bilateral or unilateral carotid occlusion of 28-45%. Long-term effects were evaluated 9-11 months later. We conducted cognitive evaluation using spatial learning in a water maze and exploration behavior in an open field. Morphology of the brain was examined by MRI using diffusion-tensor imaging (DTI) and immunohistochemistry staining of the brain and eyes. Cognitive deficit was found in spatial memory and exploration behavior in both occluded groups. Brain and eyes histology presented severe damage in the bilateral group, compared to the unilateral one. DTI revealed an increase in mean diffusivity (MD) in the ventral thalamus and a decrease in fractional anisotropy in optic nerve and optic tract in bilateral rats, while unilateral rats showed only an increase in MD in the ventral pons. In those areas, a significant change in astrocytes, microglia, and number of apoptotic cells were found. Bilateral occlusion produced severe damage to both retinas, while unilateral occlusion produced damage mainly in the occluded side. We found that mild carotid stenosis, even in a unilateral occlusion, creates behavioral abnormalities presented by brain and eye histopathology. The results support our hypothesis that gradual formation of mild carotid stenosis along the life course leads to progressive damage that may create different degenerative diseases at a later age.

Upregulation of Semaphorin 3A and the associated biochemical and cellular events in a rat model of retinal detachment.

BACKGROUND: Retinal detachment, as a result of injury or disease, is a severe disorder that may ultimately lead to complete blindness. Despite advanced surgical repair techniques, the visual acuity of patients is often limited. We investigated some of the biochemical and morphological alterations following experimental retinal detachment in laboratory animals. METHODS: Unilateral retinal detachment was induced in male Wistar rats; contralateral untreated eyes served as a control. Approximately half of the retinal area was detached by a sub-retinal injection of 5 mul Saline. The incidence and extent of the retinal detachment was evaluated using MRI analysis and fundus images. The retinas were collected at intervals of 24 hours, 7, 14 and 28 days following the procedure. Using Western blot and immunohistochemical analysis, the expression levels of Semaphorin3A, Neuropilin1, GAP43 and NF-H were studied. In addition, morphological changes in Müller and microglial cells were examined. TUNEL staining was used to assess apoptosis. RESULTS: We found that the expression level of Semaphorin3A was up-regulated and reached its peak at two time points: 24 hours and 14 days after surgery. A similar pattern of expression was found for Neuropilin1. TUNEL-positive cells, indicating apoptotic processes, were evident 24 hours post retinal detachment and increased after 7 days. On the other hand, GAP43 expression was up-regulated 14 days after retinal detachment, and further intensified 28 days post-surgery. Microglial cells were activated shortly after detachment and concentrated mostly at the inner plexiform layer. GFAP staining revealed hypertrophy of Müller cells. CONCLUSIONS: The biochemical and morphological changes suggest that apoptosis as well as axonal regrowth take place following retinal detachment. Collectively, these findings may explain the limited success following repair surgery in terms of visual acuity and physiological function of the retina. Our study may open a new approach for treatment of early phase retinal detachment, as well as improve post-operative care that may, in turn, improve the functional result of the surgery. In addition, further study is required on several other factors that may affect visual acuity, such as size and location of the detached area and the time lapse between detachment and surgery.

Spatial visual function in anomalous trichromats: Is less more?

Color deficiency is a common inherited disorder affecting 8% of Caucasian males with anomalous trichromacy (AT); it is the most common type of inherited color vision deficiency. Anomalous trichromacy is caused by alteration of one of the three cone-opsins' spectral sensitivity; it is usually considered to impose marked limitations for daily life as well as for choice of occupation. Nevertheless, we show here that anomalous trichromat subjects have superior basic visual functions such as visual acuity (VA), contrast sensitivity (CS), and stereo acuity, compared with participants with normal color vision. Both contrast sensitivity and stereo acuity performance were correlated with the severity of color deficiency. We further show that subjects with anomalous trichromacy exhibit a better ability to detect objects camouflaged in natural gray scale figures. The advantages of color-deficient subjects in spatial vision performance could explain the relatively high prevalence of color-vision polymorphism in humans.

Epiretinal transplantation of human bone marrow mesenchymal stem cells rescues retinal and vision function in a rat model of retinal degeneration.

Vision incapacitation and blindness associated with incurable retinal degeneration affect millions of people worldwide. In this study, 0.25×10(6) human bone marrow stem cells (hBM-MSCs) were transplanted epiretinally in the right eye of Royal College Surgeons (RCS) rats at the age of 28 days. Epiretinally transplanted cells were identified as a thin layer of cells along vitreous cavity, in close proximity to the retina or attached to the lens capsule, up to 6 weeks following transplantation. Epiretinal transplantation delayed photoreceptor degeneration and rescued retinal function up to 20 weeks following cell transplantation. Visual functions remained close to normal levels in epiretinal transplantation rats. No inflammation or any other adverse effects were observed in transplanted eyes. Our findings suggest that transplantation of hBM-MSCs as a thin epiretinal layer is effective for treatment of retinal degeneration in RCS rats, and that transplanting the cells in close proximity to the retina enhances hBM-MSC therapeutic effect compared with intravitreal injection.

Conditional inactivation of the NBS1 gene in the mouse central nervous system leads to neurodegeneration and disorganization of the visual system.

Nijmegen breakage syndrome (NBS) is a genomic instability disease caused by hypomorphic mutations in the NBS1 gene encoding the Nbs1 (nibrin) protein. Nbs1 is a component of the Mre11/Rad50/Nbs1 (MRN) complex that acts as a sensor of double strand breaks (DSBs) in the DNA and is critical for proper activation of the broad cellular response to DSBs. Conditional disruption of the murine ortholog of the human NBS1, Nbs1, in the CNS of mice was previously reported to cause microcephaly, severe cerebellar atrophy and ataxia. Here we report that conditional targeted disruption of the murine NBS1 gene in the CNS results in mal-development, degeneration, disorganization and dysfunction of the murine visual system, especially in the optic nerve. Nbs1 deletion resulted in reduced diameters of Nbs1-CNS-Delta eye and optic nerve. MRI analysis revealed defective white matter development and organization. Nbs1 inactivation altered the morphology and organization of the glial cells. Interestingly, at the age of two-month-old the levels of the axonal guidance molecule semaphorin-3A and its receptor neuropilin-1 were up-regulated in the retina of the mutant mice, a typical injury response. Electroretinogram analysis revealed marked reduction in a- and b-waves, indicative of decreased retinal function. Our study points to a novel role for Nbs1 in the development, organization and function of the visual system.

MRI evidence of white matter damage in a mouse model of Nijmegen breakage syndrome.

Nijmegen breakage syndrome (NBS) is a genomic instability disease caused by hypomorphic mutations in the NBS1 gene encoding the Nbs1 (nibrin) protein. Nbs1 is a component of the Mre11/Rad50/Nbs1 (MRN) complex that acts as a sensor of double strand breaks (DSBs) in the DNA and is critical for proper activation of the broad cellular response to DSBs. Conditional disruption of the murine ortholog of NBS1, Nbn, in the CNS of mice was previously reported to cause microcephaly, severe cerebellar atrophy and ataxia. In this study we used MRI to study the brain morphology and organization of Nbn deleted mice. Using conventional T(2)-weighted magnetic resonance, we found that the brains of the mutant mice (Nbs1-CNS-del) were significantly smaller than those of the wild-type animals, with marked mal-development of the cerebellum. Region of interest analysis of the T(2) maps revealed significant T(2) increase in the areas of white matter (corpus callosum, internal capsule and midbrain), with minor changes, if any, in gray matter. Diffusion tensor imaging (DTI) data confirmed that fractional anisotropy values were significantly reduced in these areas, mainly due to increased radial diffusivity (water diffusion perpendicular to neuronal fibers). Biochemical analysis showed low and dispersed staining for MBP and GalC in Nbs1-CNS-del brains, indicating defects in myelin formation and oligodendrocyte development. Myelin index and protein levels were significantly reduced in these brains. Our results point to a novel function of Nbs1 in the development and organization of the white matter.

Lymphocytic reaction to ultraviolet radiation on rabbit conjunctiva.

We examined the clinical and histological effects of controlled UV radiation on the conjunctiva and cornea of rabbit eyes by duration of exposure (0.5-4 hours daily for 5 consecutive days). Longer UV exposure (day 1-day 5) was associated with increased conjunctival redness, corneal erosion, edema and opacity. This study shows that UV irradiation leads to clinical and histological changes which may reflect an immune reaction to damaged epithelial cells.

Examination of cellular and molecular events associated with optic nerve axotomy.

PURPOSE: Analyzing cellular behavior during scar formation and determining the expression of growth inhibiting molecules in the optic nerve and retina following acute optic nerve injury. METHODS: A rat model of complete transection of the optic nerve that spares the vascular supply and the neural scaffold was used. The response of the optic nerve and retinas to axotomy was studied by immunological and biochemical approaches. RESULTS: Optic nerve axotomy led to massive cell invasion at the site of injury that spread along both sides of the nerve. The cells were microglia, oligodendrocytes, and to a lesser extent astrocytes. A marked induction of semaphorin 3A was evident, especially in the area of the scar, and persisted up to the 28th day of the experiment. Expression of neuropilin-1, a component of the semaphorin 3A receptor, increased following injury. The molecular events associated with axotomy were studied by measuring the levels of semaphorin 3A, p38 MAPK, and ERK1/2 in the retina. Semaphorin 3A levels and the activated form of p38 were elevated 3 days post-axotomy and then declined; ERK1/2 activation levels reached their peak 14 days post axotomy. Acute nerve injury led to morphological alterations in oligodendrocytes, astrocytes, and the extracellular matrix, disrupting the delicate internal organization of the optic nerve. CONCLUSIONS: We suggest that cell invasion, semaphorin 3A and neuropilin-1 induction, and disruption of the internal organization of the optic nerve contribute to axotomy-induced degenerative processes.

Anti-semaphorin 3A antibodies rescue retinal ganglion cells from cell death following optic nerve axotomy.

Damage to the optic nerve in mammals induces retrograde degeneration and apoptosis of the retinal ganglion cell (RGC) bodies. The mechanisms that mediate the response of the neuronal cells to the axonal injury are still unknown. We have previously shown that semaphorins, axon guidance molecules with repulsive cues, are capable of mediating apoptosis in cultured neuronal cells (Shirvan, A., Ziv, I., Fleminger, G., Shina, R., He, Z., Brudo, I., Melamed, E., and Brazilai, A. (1999) J. Neurochem. 73, 961-971). In this study, we examined the involvement of semaphorins in an in vivo experimental animal model of complete axotomy of the rat optic nerve. We demonstrate that a marked induction of type III semaphorin proteins takes place in ipsilateral retinas at early stages following axotomy, well before any morphological signs of RGC apoptosis can be detected. Time course analysis revealed that a peak of expression occurred after 2-3 days and then declined. A small conserved peptide derived from semaphorin 3A that was previously shown to induce neuronal death in culture was capable of inducing RGC loss upon its intravitreous injection into the rat eye. Moreover, we demonstrate a marked inhibition of RGC loss when axotomized eyes were co-treated by intravitreous injection of function-blocking antibodies against the semaphorin 3A-derived peptide. Marked neuronal protection from degeneration was also observed when the antibodies were applied 24 h post-injury. We therefore suggest that semaphorins are key proteins that modulate the cell fate of axotomized RGC. Neutralization of the semaphorin repulsive function may serve as a promising new approach for treatment of traumatic injury in the adult mammalian central nervous system or of ophthalmologic diseases such as glaucoma and ischemic optic neuropathy that induce apoptotic RGC death.

Up-regulation of semaphorin expression in retina of glaucomatous rabbits.

BACKGROUND: Glaucoma is a term encompassing a variety of diseases that end in the death of retinal ganglion cells (RGC). Although a variety of factors can initiate the disease onset, increased intraocular pressure (IOP) is one of the major risk factors. In our previous study we found that semaphorins were causally involved in RGC death following axotomy. Since a common feature of all retinal neuropathies is axonal damage, we hypothesized that semaphorins are involved in glaucoma-induced RGC death. The purpose of this study was to analyze the effect of increased IOP on RGC viability and to analyze semaphorin expression pattern in glaucomatous retinas. METHODS: Utilizing retrograde-labeled dye (4-Di-10-Asp) and hematoxylin-eosin staining, we investigated the effect of elevated levels of IOP on RGC viability. In addition, immunohistochemical analysis and western blotting were used to study the pattern of semaphorin expression in retinas of rabbits with genetically developed increased IOP and subsequently glaucoma. RESULTS: Using specific anti-semaphorin antibodies, the expression of a single protein with the size of a semaphorin protein, 110 kDa, was detected; its expression was up-regulated in glaucomatous rabbits compared with controls. Time-course analysis revealed that semaphorin expression peaked between 2 and 6 months of age and declined thereafter. Immunohistochemical analysis revealed that semaphorin expression was up-regulated specifically in the ganglion cell layer, which is a structure that is highly affected in glaucoma. CONCLUSION: Deciphering the molecular mechanisms of glaucoma-induced death and its mediators is a crucial step towards designing new therapeutic strategies to treat this incurable disease.