Massive retinal gliosis. A reactive proliferation of Müller cells

Smart Contact Lenses as Wearable Ophthalmic Devices for Disease Monitoring and Health Management

The eye contains a complex network of physiological information and biomarkers for monitoring disease and managing health, and ocular devices can be used to effectively perform point-of-care diagnosis and disease management. This comprehensive review describes the target biomarkers and various diseases, including ophthalmic diseases, metabolic diseases, and neurological diseases, based on the physiological and anatomical background of the eye. This review also includes the recent technologies utilized in eye-wearable medical devices and the latest trends in wearable ophthalmic devices, specifically smart contact lenses for the purpose of disease management. After introducing other ocular devices such as the retinal prosthesis, we further discuss the current challenges and potential possibilities of smart contact lenses.

The Importance of Anatomic Configuration and Cystic Changes in Macular Hole: Predicting Surgical Success with a Different Approach

PURPOSE

This study aimed to define a novel metric for the area of the macular hole (MH) and cysts located around the hole using an optical coherence tomography (OCT) device.

METHODS

This study was conducted with 58 eyes of 56 patients. The patients were divided into two groups according to anatomic closure after surgery. Using the metrics of macular hole index (MHI), tractional hole index (THI), hole forming factor (HFF), macular hole area (HA), the cystoid space areas in the inner retinal layers (CA), and our novel metric, the cyst hole area index (CHAI) was calculated. The correlation of the CA, the HA, and the CHAI with other indexes were assessed. Receiver operating characteristic (ROC) curves and cut-off values were derived for indexes predicting type 1 or type 2 closures.

RESULTS

The CA showed a strong positive correlation with the base MH size and the maximum MH height (r = 0.624, p < 0.001; r = 0.722, p < 0.001, respectively). The HA showed a strong positive correlation with basal MH size and minimum MH size (r = 0.934, p < 0.001; r = 0.765, p < 0.001). The HA showed a moderate positive correlation with maximum MH height (r = 0.483, p < 0.001, respectively). CHAI showed a moderate positive correlation with minimum MH size (r = 0.297, p = 0.02). CHAI and HA showed a moderate negative correlation with post-operative BCVA (r = -0.39, p = 0.003; r = -0.357, p = 0.006; respectively). ROC curve analysis showed that MHI (0.823), THI (0.750), and HFF (0.722) predicted type 1 closure and that CHAI (0.769) and HA (0.709) predicted type 2 closures.

CONCLUSION

MHI and our novel index CHAI, which can be calculated without any additional software, could successfully predict type 1 and type 2 closures, respectively.

Statins Inhibit the Gliosis of MIO-M1, a Müller Glial Cell Line Induced by TRPV4 Activation

We characterized Müller cell gliosis induced by the activation of transient receptor potential vanilloid-type 4 (TRPV4) and assessed whether statins could modulate the gliosis. The human Müller cell line, MIO-M1, was used to analyze the gliosis caused by glaucomatous stimulation. To induce Müller gliosis in MIO-M1 cells, GSK101 was used to activate TRPV4, and Müller gliosis was evaluated by analyzing vimentin, nestin, and glial fibrillary acidic protein (GFAP) expression. The expression level of TNF-α was determined by ELISA. To evaluate the GSK101 activation of the NF-κB pathway, p65 phosphorylation was measured by Western blotting, and the nuclear translocation of p65 and IκBα phosphorylation were assessed by immunostaining. To assess the effect of statins on MIO-M1 gliosis, cells were pretreated for 24 h with statins before GSK101 treatment. Vimentin, nestin, and GFAP expression were upregulated by GSK101, while statins effectively inhibited them. The expression of TNF-α was increased by GSK101. The phosphorylation and nuclear translocation of p65 and IκBα phosphorylation, which occurs prior to p65 activation, were induced. Statins suppressed the GSK101-mediated phosphorylation of IκBα and p65 translocation. Statins can mitigate gliosis in the human Müller cell line. Because TRPV4 activation in Müller cells reflects glaucoma pathophysiology, statins may have the potential to prevent RGC death.

Massive Retinal Gliosis in an Infant Microphthalmic Globe: A Case Report

Patient: Male, 11-month-old

Final Diagnosis: Microphthalmos with massive retinal gliosis

Symptoms: Microphthalmos with no useful vision, left eye

Medication: —

Clinical Procedure: Enucleation, left eye

Specialty: Ophthalmology • Pathology

Evolution of oxidative stress, inflammation and neovascularization in the choroid and retina in a subretinal lipid induced age-related macular degeneration model

Oxidative stress, inflammation and neovascularization are the key pathological events that are implicated in human age-related macular degeneration (AMD). There are a limited number of animal models available for evaluating and developing new therapies. Most models represent late exudative or neovascular AMD (nAMD) but there is a relative paucity of models that mimic early events in AMD. The purpose of this study is to characterize the evolution of oxidative stress, inflammation, retinal degeneration and neovascularization in a rat model of AMD, created by subretinal injection of human lipid hydroperoxide (HpODE) that found in the sub-macular region in aged and AMD patients. Subretinal HpODE induced retinal pigment epithelium (RPE) and retinal degeneration resulting in loss of RPE cells, photoreceptors and retinal thinning. RPE degeneration and atrophy were detected by day 5, followed by neural tissue degeneration at day 12 with robust TUNEL positive cells. Western blot analysis confirmed an increase in pro-apoptotic Bak protein at day 12 in retinal tissues. Oxidative damage biomarkers (4-hydroxynonenal, malondialdehyde, 8-hydroxy-2'-deoxyguanosine, and nitrotyrosine) increased in retinal tissue from days 5-12. Müller glial activation was observed in the HpODE injected area at day 5 followed by its remodeling and migration in the outer retina by day 20. RT-qPCR analysis further indicated upregulation of pro-inflammatory genes (TNF-α, IL-1β and IL-6) both in retinal and RPE/choroidal tissue as early as day 2 and persisted until day 12. Upregulation of oxidative stress markers such as NADPH oxidase (NOX and DOUX family) was detected early in retinal tissue by day 2 followed by its upregulation in choroidal tissue at day 5. Neovascularization was demonstrated from day 12 to day 20 post HpODE injection in choroidal tissue. The results from this study indicate that subretinal HpODE induces advanced AMD phenotypes comprising many aspects of both dry/early and late) and neovascular/late AMD as observed in humans. Within 3 weeks via oxidative damage, upregulation of reactive oxygen species and pro-inflammatory genes, pro-apoptotic Bak and pro-angiogenic VEGF upregulation occurs leading to CNV formation. This experimental model of subretinal HpODE is an appropriate model for the study of AMD and provides an important platform for translational and basic research in developing new therapies particularly for early/dry AMD where currently no viable therapies are available.

Retinal microglia signaling affects Müller cell behavior in the zebrafish following laser injury induction

Microglia are the resident tissue macrophages of the central nervous system including the retina. Under pathophysiological conditions, microglia can signal to Müller cells, the major glial component of the retina, affecting their morphological, molecular, and functional responses. Microglia-Müller cell interactions appear to be bidirectional shaping the overall injury response in the retina. Hence, microglia and Müller cell responses to disease and injury have been ascribed both positive and negative outcomes. However, Müller cell reactivity and survival in the absence of immune cells after injury have not been investigated in detail in adult zebrafish. Here, we develop a model of focal retinal injury combined with pharmacological treatments for immune cell depletion in zebrafish. The retinal injury was induced by a diode laser to damage photoreceptors. Two pharmacological treatments were used to deplete either macrophage-microglia (PLX3397) or selectively eliminate peripheral macrophages (clodronate liposomes). We show that PLX3397 treatment hinders retinal regeneration in zebrafish, which is reversed by microglial repopulation. On the other hand, selective macrophage elimination did not affect the kinetics of retinal regeneration. The absence of retinal microglia and macrophages leads to dysregulated Müller cell behavior. In the untreated fish, Müller cells react after injury induction showing glial fibrillary acidic protein (GFAP), Phospho-p44/42 MAPK (Erk1/2), and PCNA upregulation. However, in the immunosuppressed animals, GFAP and phospho-p44/42 MAPK (Erk1/2) expression was not upregulated overtime and the reentry in the cell cycle was not affected. Thus, microglia and Müller cell signaling is pivotal to unlock the regenerative potential of Müller cells in order to repair the damaged retina.

Re-programming immunosurveillance in persistent non-infectious ocular inflammation

Ocular function depends on a high level of anatomical integrity. This is threatened by inflammation, which alters the local tissue over short and long time-scales. Uveitis due to autoimmune disease, especially when it involves the retina, leads to persistent changes in how the eye interacts with the immune system. The normal pattern of immune surveillance, which for immune privileged tissues is limited, is re-programmed. Many cell types, that are not usually present in the eye, become detectable. There are changes in the tissue homeostasis and integrity. In both human disease and mouse models, in the most extreme cases, immunopathological findings consistent with development of ectopic lymphoid-like structures and disrupted angiogenesis accompany severely impaired eye function. Understanding how the ocular environment is shaped by persistent inflammation is crucial to developing novel approaches to treatment.

Infliximab exerts a dose-dependent effect on retinal safety in the albino rabbit

PURPOSE

To assess the retinal toxicity of an intravitreal injection of infliximab, a monoclonal antibody to tumor necrosis factor α, in a rabbit model.

MATERIALS AND METHODS

Two groups of adult albino rabbits (n = 5) received intravitreal injections of infliximab (0.1 ml) in the study eye and balanced salt solution (BSS, 0.1 ml) in the control eye at baseline. Group 1 was administered with 1.5 mg/0.1 ml, and group 2 was injected with 7.5 mg/0.1 ml of infliximab solution. Electroretinography (ERG) was performed at baseline and at 1, 7, 30, and 45 days after the injection. Visual evoked potentials (VEPs) were recorded at 7 and 45 days after the injection. After the last electrophysiological assessment, the rabbits were euthanized and retinal histopathology and immunhistochemistry for glial fibrillary acidic protein (GFAP) were performed.

RESULTS

ERG responses demonstrated no significant deficit in retinal function in eyes injected with infliximab. Mean dark-adapted a-wave and b-wave maximal amplitude and semi-saturation constant values at baseline and throughout the 45 days of follow-up after the injection indicated no remarkable difference in outer retinal function between the control and experimental eyes. VEP responses were similar at each time point (7 and 45 days). No difference was seen in retinal histopathology and immunocytochemistry sections in eyes receiving the 1.5 mg/0.1 ml dose compared to the control eyes. However, increased GFAP labeling in retinal Müller cells was detected in rabbit eyes treated with the 7.5 mg/0.1 ml dose.

CONCLUSIONS

Intravitreal injection of 1.5 mg/0.1 ml infliximab dose has no toxic effect on the integrity (functional or structural) of the retina in rabbits. A higher dose of 7.5 mg/0.1 ml may be slightly toxic as suggested by positive Müller cell GFAP expression. Additional studies of retinal toxicity at higher doses and after multiple injections are needed to establish the retinal safety of intravitreal infliximab therapy in humans.

Cell Proliferation in Retinal Transplants

The MIB-1 antibody against a nuclear protein Ki-67 was used to study the proliferation of cells in the rabbit retinal transplants. Fragmented pieces of embryonic day 15 rabbit retinas were transplanted into the subretinal space of adult rabbits and allowed to survive for different times. Fragmented donor tissue starts organizing in rosettes 1 day after transplantation. The transplanted cells continue to proliferate in the host eye and their pattern of proliferation resembles that of normal developing retina, suggesting that the factors responsible for the proliferation pattern are preserved after transplantation. The dividing cells in metaphase line up in the luminal layers of the rosettes. Certain cells become postmitotic in the regions corresponding to the inner retina first, followed by the cells in the luminal layers of rosettes. Cells in the regions between the rosettes, corresponding to the inner nuclear layer, presumably the Müller cells, proliferate significantly for the equivalent age of postnatal day 2. Few cells in these regions proliferate for at least the equivalent age of postnatal day 11 in transplants. There is a layer of nonproliferating, degenerating cells in the transplant situated close to the host retina. However, some cells in this layer, situated at the host-graft interface, proliferate. These cells proliferate for a long time possibly indicating gliosis.

SOLITARY CIRCUMSCRIBED "PEARL WHITE" RETINAL MASS (SO-CALLED RETINAL ASTROCYTIC PROLIFERATION) RESIDES IN DEEP RETINA OR BENEATH RETINA: FINDINGS ON MULTIMODAL IMAGING IN 4 CASES

PURPOSE

To report novel observations of previously described solitary circumscribed retinal astrocytic proliferation using spectral domain optical coherence tomography that suggests this tumor does not arise in the nerve fiber layer as initially believed, but arises within deep retinal or retinal pigment epithelial structures.

METHODS

Retrospective review of four cases.

RESULTS

Patient age ranged from 46 to 75 years. The tumor was pearl white or yellow-white (n = 4, 100%), located in the macula (n = 1, 25%) or macula to equator (n = 3, 75%) regions, and with mean tumor base of 1.2 mm and thickness of 0.8 mm. There were no feeding vessels, intrinsic vessels, subretinal fluid, or vitreoretinal traction. Mild surrounding retinal pigment epithelial hyperplasia and atrophy rimmed each tumor (n = 4, 100%). Fluorescein angiography depicted the mass with early hypofluorescence (n = 3/3, 100%) and late hypofluorescence (n = 2/3, 67%). Spectral domain optical coherence tomography demonstrated the mass with an abruptly elevated "snowball" configuration (n = 4, 100%), with smooth or slightly irregular surface (n = 4, 100%), and originating from deep retina or retinal pigment epithelial (n = 4, 100%), with overlying compression and draping of retinal tissue (n = 4, 100%).

CONCLUSION

This previously described small yellow-white retinal tumor appears to arise in the outer retinal layers and not from the inner retinal layers as formerly believed. This tumor may not be astrocytic as initially believed since it arises deep within the retina, but it could represent a deep glial or pigment epithelial fibrous mass. The pathogenesis and pathology of this rare lesion remain unknown.

RECOVERY OF FOVEAL PHOTORECEPTOR INTEGRITY AFTER VITRECTOMY IN EYES WITH AN IMPENDING MACULAR HOLE WITH VITREOMACULAR TRACTION SYNDROME

PURPOSE

To identify factors associated with the recovery of foveal photoreceptor disruption in eyes with an impending macular hole (MH) with vitreomacular traction syndrome after surgery.

METHODS

This study comprised 33 consecutive patients who underwent vitrectomy for Stage 1 impending macular hole with disrupted photoreceptor inner segment/outer segment (IS/OS) layer and were followed up for a minimum of 1 year after surgery. Preoperative optical coherence tomography (OCT) parameters were compared between eyes that achieved complete restoration of the IS/OS layer (Group A) and those that did not (Group B). Postoperative serial changes in best-corrected visual acuity (BCVA) and IS/OS disrupted length were also investigated.

RESULTS

Smooth and symmetric foveolar contour was restored in 29 eyes (87.9%). Complete recovery of IS/OS disruption was observed in 11 of 33 cases (33.3%, Group A). Group A exhibited a larger percentage of foveal pseudocysts (54.5% vs. 13.6%, P = 0.033) and a smaller mean aperture size (102.1 ± 182.1 μm vs. 241.5 ± 163.8 μm, P = 0.031) than Group B. Postoperatively, Group A revealed a significantly better visual outcome than Group Be, which was the same as Group B, but with the four eyes that developed a full-thickness macular hole excluded.

CONCLUSION

Restoration of the foveal photoreceptor layer was more likely to occur in eyes with a foveal pseudocyst and smaller aperture size.

So-called massive retinal gliosis: A critical review and reappraisal

Massive retinal gliosis, a nonneoplastic retinal glial proliferation, was first described in detail over 25 years ago, before the era of immunohistochemistry, in a series of 38 cases-to which can be added 30 case reports or small series (no more than 3 cases) subsequently. We analyze a new series of 3 nontumoral intraretinal glioses and 15 cases of tumoral retinal gliosis, not all of which, strictly speaking, were massive. The data from this series are compared with the findings in previously published cases. Included are 2 cases of massive retinal gliosis diagnosed from evisceration specimens. In reviewing all published and current cases, we were able to establish 3 subgroups of retinal tumoral glioses rather than a single "massive" category: focal nodular gliosis, submassive gliosis, and massive gliosis. Among 43 reported cases, including the present series, but excluding the previous large series of 38 cases in which substantial clinical data were omitted, there were 19 men and 24 women. Their mean and median ages were 36.2 years and 36 years, respectively, with a range of 2 to 79 years. All lesions were composed of mitotically quiet, compact spindled fibrous astrocytes devoid of an Alcian blue-positive myxoid matrix. The most common associated ocular conditions were phthisis bulbi and congenital diseases or malformations. Histopathologically, all 3 tumoral categories were accompanied by progressively more extensive fibrous and osseous metaplasia of the pigment epithelium, the latter forming a clinically and diagnostically useful, almost continuous, outer rim of eggshell calcification in the submassive and massive categories that should be detectable with appropriate imaging studies. In decreasing order of frequency, microcysts and macrocysts, vascular sclerosis, exudates, calcospherites, and Rosenthal fibers were observed among the proliferating fibrous astrocytes. Immunohistochemistry was positive for glial fibrillary acidic protein in all cases and nestin in most (an intermediate cytoplasmic filament typically restricted to embryonic and reparative neural tissue). The nonneoplastic nature of all categories of gliosis was confirmed by absent TP53 (tumor suppressor gene) dysregulation, Ki-67 negativity, and intact p16 expression (the protein product of the p16 tumor suppressor gene) in the overwhelming majority of cases. These findings indicate an intrinsic attempt to regulate and maintain a low level of glial cell proliferation that becomes unsuccessful as the disease evolves. The categories of tumoral proliferation appeared to constitute a spectrum. We conclude that focal nodular tumors encompass lesions previously called retinal vasoproliferative lesions, which display the same histopathologic and immunohistochemical findings as 3 major categories of retinal gliosis characterized herein.

Intraocular astrocytoma and its differential diagnosis

Astrocytomas arising within the eye display 2 distinct histologies: one comprises interlacing bundles of spindle-shaped cells mixed with a minority of polygonal cells, and the other consists of large cells with abundant glassy cytoplasm (gemistocytic astrocytes) indistinguishable from cells found in subependymal giant cell astrocytoma. Both histologic patterns express glial fibrillary acid protein diffusely, are biologically benign, and are frequently associated with dysgenic syndromes, particularly tuberous sclerosis complex. Tumors with gemistocytes, however, demonstrate a greater propensity for invasive growth. The clinical history may provide information to guide the pathologist in distinguishing intraocular astrocytoma from reactive astrocytosis, conditions that are histologically similar. It remains to be determined if other types of primary intraocular glioma exist or whether some degree of ependymal or oligodendroglial differentiation can accompany reactive astrocytosis.

Mapping cation entry in photoreceptors and inner retinal neurons during early degeneration in the P23H-3 rat retina

The proline-23-histidine line 3 (P23H-3) transgenic rat carries a human opsin gene mutation leading to progressive photoreceptor loss characteristic of human autosomal dominant retinitis pigmentosa. The aim of the present study was to evaluate neurochemical modifications in the P23H-3 retina as a function of development and degeneration. Specifically, we investigated the ion channel permeability of photoreceptors by tracking an organic cation, agmatine (1-amino-4-guanidobutane, AGB), which permeates through nonspecific cation channels. We also investigated the activity of ionotropic glutamate receptors in distinct populations of bipolar, amacrine, and ganglion cells using AGB tracking in combination with macromolecular markers. We found elevated cation channel permeation in photoreceptors as early as postnatal day 12 (P12) suggesting that AGB labeling is an early indicator of impending photoreceptor degeneration. However, bipolar, amacrine, or ganglion cells displayed normal responses secondary to ionotropic glutamate receptor activation even at P138 when about one half of the photoreceptor layer was lost and apoptosis and gliosis were observed. These results suggest that possible therapeutic windows as downstream neurons in inner retina appear to retain normal function with regard to AGB permeation when photoreceptors are significantly reduced but not lost.

Reactive retinal astrocytic tumors (so-called vasoproliferative tumors): histopathologic, immunohistochemical, and genetic studies of four cases

PURPOSE

To evaluate the cellular nature of and diagnostic terminology used in connection with acquired retinal "vasoproliferative tumors."

DESIGN

Retrospective clinicopathologic study.

METHODS

Clinical records and microscopic slides of 4 enucleated globes were reviewed. Special stains and immunohistochemical probes for CD31, CD34, p53, glial fibrillary acidic protein (GFAP), CD163, and Ki67 (cell replication) were employed; ultrastructural and fluorescence in situ hybridization (FISH) analyses were performed.

RESULTS

Tumors were located inferotemporally in middle-aged patients. They were uniformly composed of compacted elongated, GFAP-positive spindle cells (due to intermediate filaments identified ultrastructurally) with a Ki67 index of less than 1%. Rosenthal fibers and eosinophilic granular bodies were observed. Hyalinized periodic acid-Schiff-positive vessels were widely separated. CD31 and CD34 revealed a sparse microvasculature. Tumor-associated exudate spread predominantly subretinally. The retinal pigment epithelium had undergone extensive placoid fibrous metaplasia with focal ossification. P53 upregulation, BRAF-KIAA gene rearrangement, and IDH1R132H mutation typically associated with low-grade astrocytic neoplasms were absent.

CONCLUSIONS

Retinal "vasoproliferative" tumors have been mischaracterized, because they actually display a paucity of microvessels. Proliferating fibrous astrocytes with a very low proliferation index predominate, without immunohistochemical or genetic evidence favoring a neoplasm. Subretinal exudate appeared capable of provoking widespread fibrous metaplasia of the pigment epithelium that was mainly responsible for secondary retinal damage. The term "reactive retinal astrocytic tumor" is proposed as more appropriate for this entity. In carefully selected progressive lesions, consideration should be given to earlier surgical intervention before extensive subretinal exudate accumulates and pigment epithelial proliferation with fibrous metaplasia ensues.

External limiting membrane and visual outcome in macular hole repair: spectral domain OCT analysis

PURPOSE

To investigate the relationship between postoperative visual acuity and integrity of the external limiting membrane (ELM) and inner segment-outer segment (IS-OS) junction layers, using spectral domain optical coherence tomography (SD-OCT), in eyes with macular holes (MHs) following surgical repair.

METHODS

Medical charts of MH-operated cases were retrospectively identified and reviewed. The primary outcome measures were best-corrected visual acuity (BCVA) and the status of the ELM and IS-OS lines, using SD-OCT, at 6 weeks and 6 months postoperatively.

RESULTS

Sixty-two eyes of 62 patients were included. At 6 weeks following surgery, out of 56 (90.3%) eyes with successful MH closure: 0 eyes showed the combination of disrupted ELM and continuous IS-OS layers; 7 eyes (12.5%) demonstrated continuity of both ELM and IS-OS (ELM(c)/IS-OS(c) group); 29 eyes (51.8%) had continuous ELM with discontinuous IS-OS layers (ELM(c)/IS-OS(d) group); and 20 eyes (35.7%) had discontinuities in both the layers (ELM(d)/IS-OS(d) group). The ELM(d)/IS-OS(d) group had the lowest visual gain at 6 months (P = 0.03). At 6 months, a restoration of the integrity of IS-OS layer was observed in 51.7% eyes in the ELM(c)/IS-OS(d) group and in 5% in the ELM(d)/IS-OS(d) group (P = 0.001).

CONCLUSIONS

When both ELM and IS-OS layers showed disruptions 6 weeks postoperatively, a significantly worse BCVA was measured at 6 months, compared with the eyes with only IS-OS disruptions, detected 6 weeks following surgery. The integrity of the ELM layer appears to be a critical factor for the restoration of the photoreceptor layer and for predicting a successful visual outcome following MH repair.

Massive retinal gliosis: an unusual case with immunohistochemical study

Massive retinal gliosis (MRG) is a rare, benign intraocular condition that results from the proliferation of well-differentiated glial cells. Immunohistochemically, these cells show positivity for glial fibrillary acid protein (GFAP), neuron specific enolase (NSE), and S-100 protein. We encountered a case of a 45-year-old female with loss of vision in the left eye. She had a history of trauma to that eye two years ago. Enucleation was carried out, because malignancy was suspected due to retinal calcification. On the basis of light microscopy and immunohistochemistry (IHC) performed on the enucleated eye, it was diagnosed as massive retinal gliosis.

Bilateral massive retinal gliosis associated with retinopathy of prematurity

Massive retinal gliosis (MRG) is a rare, benign intraocular condition that may develop in association with long-standing eye conditions including chronic inflammation, vascular disorders, glaucoma, trauma, or congenital abnormalities. It is thought to represent a nonneoplastic reactive tissue response to retinal injury. Here, we describe an unusual case of bilateral MRG in association with retinopathy of prematurity. To our knowledge, this may be the first report of such an occurrence. The differential diagnosis of MRG is discussed with specific emphasis on its relationship to vasoproliferative tumor of the retina and presumed acquired retinal hemangiomas. In addition, we hypothesize that MRG, vasoproliferative tumor of the retina, and presumed acquired retinal hemangiomas may represent different phenotypes along a spectrum of the same disease process.

Cellular signaling and factors involved in Müller cell gliosis: neuroprotective and detrimental effects

Müller cells are active players in normal retinal function and in virtually all forms of retinal injury and disease. Reactive Müller cells protect the tissue from further damage and preserve tissue function by the release of antioxidants and neurotrophic factors, and may contribute to retinal regeneration by the generation of neural progenitor/stem cells. However, Müller cell gliosis can also contribute to neurodegeneration and impedes regenerative processes in the retinal tissue by the formation of glial scars. This article provides an overview of the neuroprotective and detrimental effects of Müller cell gliosis, with accounts on the cellular signal transduction mechanisms and factors which are implicated in Müller cell-mediated neuroprotection, immunomodulation, regulation of Müller cell proliferation, upregulation of intermediate filaments, glial scar formation, and the generation of neural progenitor/stem cells. A proper understanding of the signaling mechanisms implicated in gliotic alterations of Müller cells is essential for the development of efficient therapeutic strategies that increase the supportive/protective and decrease the destructive roles of gliosis.

Involvement of Müller glial cells in epiretinal membrane formation

BACKGROUND

Proliferative retinopathies are considered to represent maladapted retinal wound repair processes driven by growth factor- and cytokine-induced overstimulation of proliferation, migration, extracellular matrix production and contraction of retinal cells. The formation of neovascular membranes represents an attempt to reoxygenize non-perfused retinal areas. Müller glial cells play a crucial role in the pathogenesis of proliferative retinopathies. This review summarizes the present knowledge regarding the role of Müller cells in periretinal membrane formation, especially in the early steps of epiretinal membrane formation, which involve an interaction of inflammatory and glial cells, and gives a survey of the factors which are suggested to be implicated in the induction of Müller cell gliosis and proliferation.

CONCLUSIONS

Alterations in the membrane conductance of Müller cells suggest that Müller cells may alter their phenotype into progenitor-like cells in the course of proliferative retinopathies; transdifferentiated Müller cells may have great impact for the development of new cell-based therapies.

Expression of proteins associated with cell-matrix adhesion in proliferative vitreoretinopathy designed by Dispase model

PURPOSE

During recent years, the interaction of cell surface molecule, extracellular matrix proteins, and cytoskeletal elements has been a topic for research for the purpose of understanding the mechanisms of pathologic conditions. This study aims to evaluate the expression of CD44, as a cell surface adhesion molecule; fibronectin (FN), as an extracellular and a cell surface protein; vinculin and actin/á-smooth muscle actin (alfa-SMA), as cytoskeletal elements; and the interactions of these proteins in the microenvironment of proliferative vitreoretinopathy (PVR).

METHODS

This experimental study was designed by the intravitreal Dispase model in rabbits and proteins' expression were evaluated via immunohistochemical staining.

RESULTS

As a cell surface protein, CD44 expression was determined in only four eyes focally and weakly, but in a small number of cells. Among the cytoskeletal proteins, vinculin expression was the most extensive and the strongest in intensity in epi- and subretinal membranes. Alpha-SMA expression was mostly present within small foci of cells. Fibronectin expression was determined in some of the eyes only faintly.

CONCLUSIONS

Vinculin seems to be involved in PVR pathogenesis. Variability in co-distribution of the expression of vinculin, FN, and alfa-SMA reflects the dynamic interactions evolving between cell and extracellular matrix during the epi- and subretinal membrane formations. The results of this study were determined not to be in support of the assumption that CD44 has a functional role in the pathogenesis of PVR.

Infiltrating orbital astrocytic proliferation associated with congenitally malformed eyes

This report describes the clinical and pathologic findings in two adults with orbital infiltration by astrocytic cells associated with congenitally malformed eyes. Both cases had enlarging orbital masses and underwent complete resection. Histopathology revealed proliferation of astrocytes (fibrillary acidic protein-positive) that invaded the orbital tissues. To the best of our knowledge, there are no similar cases in the literature.

Primary glial tumor of the retina with features of myxopapillary ependymoma

We report a primary retinal tumor with features of myxopapillary ependymoma. The lesion occurred in a 33-year-old man with a long history of phthisis bulbi and a more recent history of pain to the right eye. Enucleated ocular globe revealed a lesion occupying most of the retinal surface. Histologically, the retina was replaced by a tumor composed of spindle cells with fibrillary cytoplasm and round to ovoid nuclei forming fascicles, perivascular pseudorosettes, microcysts, and deposition of extracellular mucins. Calcifications, metaplastic bone, and lymphoplasmacytic inflammatory infiltrate were also seen. Tumor cells expressed GFAP and S-100 and to lesser extent carbonic anhydrase II. The immunoreaction for EMA showed diffuse granular positivity, decorated a few extracellular lumina, and highlighted intracytoplasmic lumina in a few cells. Ultrastructurally, there was accumulation of extracellular material between cells and around capillaries, long interdigitating cytoplasmic processes, extracellular lumina packed with microvilli, a few junctions evident around lumina, and some ciliary basal bodies and ciliary basal rootlets. As control cases, we also investigated expression of EMA and carbonic anhydrase II in an ocular globe with retinal gliosis and three cases of myxopapillary ependymoma of the cauda equina. The lesion described here represents the first example of retinal tumor with features of myxopapillary ependymoma. Pathologic features and particularly expression of carbonic anhydrase II suggest a derivation from intrinsic glial cells of retina otherwise known as Muller cells.

Retinal neurons regulate proliferation of postnatal progenitors and Müller glia in the rat retina via TGF beta signaling

The number of proliferating cells in the rodent retina declines dramatically after birth. To determine if extrinsic factors in the retinal micro-environment are responsible for this decline in proliferation, we established cultures of retinal progenitors or Muller glia, and added dissociated retinal neurons from older retinas. The older cells inhibited proliferation of progenitor cells and Muller glia. When these experiments were performed in the presence of TGF(beta)RII-Fc fusion protein, an inhibitor of TGF(beta) signaling, proliferation was restored. This suggests a retina-derived TGF(beta) signal is responsible for the developmental decline in retinal proliferation. TGFbeta receptors I and II are expressed in the retina and are located in nestin-positive progenitors early in development and glast-positive Muller glia later in development. RT-PCR and immunofluorescence data show TGF(beta)2 is the most highly expressed TGF(beta)ligand in the postnatal retina, and it is expressed by inner retinal neurons. Addition of either TGF(beta)1 or TGF(beta)2 to postnatal day 4 retinas significantly inhibited progenitor proliferation, while treatment of explanted postnatal day 6 retinas with TGF(beta) signaling inhibitors resulted in increased proliferation. Last, we tested the effects of TGF(beta) in vivo by injections of TGF(beta) signaling inhibitors: when TGF(beta) signaling is inhibited at postnatal day 5.5, proliferation is increased in the central retina; and when co-injected with EGF at postnatal day 10, TGF(beta)inhibitors stimulate Muller glial proliferation. In sum, these results show that retinal neurons produce a cytostatic TGF(beta) signal that maintains mitotic quiescence in the postnatal rat retina.

Massive gliosis of the retina: report of a case investigated by immunohistochemistry and clonality assays

We report a rare case of massive retinal gliosis that developed in a 32-year-old woman who had been born with bilateral microphthalmia. The patient had recently noticed left ophthalmos and underwent total resection of the affected eyeball. Histologically, the vitreous body had been totally replaced by massively proliferated spindle cells, which had delicate fibrillary cytoplasm without nuclear atypia. Because the attenuated retinal pigment epithelium and intact sclera were preserved at the periphery of the tumor, the tumor was thought to be retinal in origin. Immunohistochemically, the spindle cells were strongly positive for glial fibrillary acidic protein and neuron-specific enolase and partly positive for S-100 protein. These findings led to a diagnosis of massive gliosis of the retina. Clonality analysis of the tumor using a human androgen receptor assay revealed the polyclonal nature of the proliferating spindle cells. This is the first documentation of the polyclonality of this disease.

The activation of IL-8 receptors in cultured guinea pig Müller glial cells is modified by signals from retinal pigment epithelium

Interleukin 8 (IL-8, CXCL8) is a pro-inflammatory chemokine which attracts neutrophils to sites of inflammation via an activation of the G-protein-coupled receptors, CXCR1 and CXCR2. However, both IL-8 and IL-8 receptors are widely expressed in various tissues and cell types, and have been suggested to be involved in other functions such as angiogenesis, tumor growth, or brain pathology. We examined the expression of IL-8 and IL-8 receptors in highly enriched primary cultures of guinea pig Muller glial cells. Immunoreactivity for CXCL8, CXCR1 and CXCR2 was observed in all cultured Muller cells. The expression of CXCL8 was confirmed by PCR, and the secretion of the CXCL8 protein from Muller cells was revealed by ELISA. Western blots showed prominent bands at approximately 40 kDa by using antibodies specific for human CXCR1 and CXCR2, and the expression of a putative CXCR2 receptor in Muller cells was confirmed by PCR. Furthermore, cultured Muller cells responded to application of recombinant human IL-8 with an increase of the cytosolic Ca(2+) concentration. If supernatants of cultured human retinal pigment epithelium (RPE) cells were applied to the Muller cell cultures, no obvious changes were observed in the CXCL8, CXCR1 and CXCR2 expression but (i) Muller cell proliferation was stimulated, and (ii) there was an increased number of CXCL8-responsive Muller cells and the amplitudes of the evoked calcium responses were enhanced. It is concluded that Muller glial cells may participate in the inflammatory response(s) of the retina during ocular diseases, and that this contribution may be modified by interactions with RPE cells.

Differential expression of GFAP in early v late AMD: a quantitative analysis

BACKGROUND/AIMS

Glial fibrillary acidic protein (GFAP) is an established indicator of retinal stress; its expression in retinal astrocytes and Müller cells has been demonstrated to be modulated by cytokines and retinal pathology, including age related macular degeneration (AMD). This study aims to quantify the modulation of GFAP expression in retinas with drusen and atrophic AMD versus normal age matched controls.

METHODS

Following a histopathological survey, 17 donor retinas were classified into four groups: drusen (n=5), geographic atrophy (GA) (n=6), aged normal (n=3), and young normal (n=3). Paramacular cryosections were immunolabelled with GFAP antibody, examined by confocal microscopy, and quantified by NIH digital image analysis. Groups were matched for potential confounding factors including age, sex, and postmortem delay.

RESULTS

A significant increase in GFAP immunolabelling of macroglia was noted in aged normal compared with young normal retinas (p<0.04). Upregulation of GFAP immunoreactivity involving astrocytes was observed in drusen retinas compared with control retinas (p<0.03). GFAP was also upregulated in retinas with GA compared with controls (p<0.05) and in retinas with GA compared with drusen (p<0.04), both involving Müller cells. Discrete regions of GFAP upregulation in Müller cells were associated with drusen formation. In GA specimens atrophied retinal pigment epithelium (RPE) was substituted by GFAP immunoreactive Müller cell processes (gliosis).

CONCLUSION

This study provides a quantitative assessment of GFAP modulation in ageing and AMD affected retinas. Morphological observations were consistent with quantitative analyses indicating differential modulation of GFAP immunoreactivity in inner and outer retina. Upmodulation of GFAP in inner retina and astroglial processes was predominantly associated with drusen, while in outer retina Müller glia upmodulation of GFAP was associated with disruption of the RPE and blood-retinal barrier.

Regulating proliferation during retinal development

Recent studies have shown that components of the cell-cycle machinery can have diverse and unexpected roles in the retina. Cyclin-kinase inhibitors, for example, have been implicated as regulators of cell-fate decisions during histogenesis and reactive gliosis in the adult tissue after injury. Also, various mechanisms have been identified that can compensate for extra rounds of cell division when the normal timing of the cell-cycle exit is perturbed. Surprisingly, distinct components of the cell-cycle machinery seem to be used during different stages of development, and different organisms might rely on distinct pathways. Such detailed studies on the regulation of proliferation in complex multicellular tissues during development have not only advanced our knowledge of the ways in which proliferation is controlled, but might also help us to understand the degenerative disorders that are associated with gliosis and some types of tumorigenesis.

Control of Müller glial cell proliferation and activation following retinal injury

Müller glial cells are the major support cell for neurons in the vertebrate retina. Following neuronal damage, Müller cells undergo reactive gliosis, which is characterized by proliferation and changes in gene expression. We have found that downregulation of the tumor supressor protein p27Kip1 and re-entry into the cell cycle occurs within the first 24 hours after retinal injury. Shortly thereafter, Müller glial cells upregulate genes typical of gliosis and then downregulate cyclin D3, in concert with an exit from mitosis. Mice lacking p27Kip1 showed a constitutive form of reactive gliosis, which leads to retinal dysplasia and vascular abnormalities reminiscent of diabetic retinopathy. We conclude that p27Kip1 regulates Müller glial cell proliferation during reactive gliosis.

Retinal müller cell culture

A mini-review is presented of the current techniques for maintaining Müller cells in a culture. Within the retina, Müller cells are the predominant glial cells. These highly specialised cells extend over the entire neural retina. One of the most important of the various physiological functions of Müller cells is to regulate the balance of ions and neurotransmitters in the retina. Disturbance of these regulatory functions may lead to toxic effects on receptor and other neural cells in the neuroretina, and may be a common mechanism of clinical retinal neuropathy. The main excitatory neurotransmitter in the retina is glutamate. Müller cells regulate the amount of glutamate in the synaptic regions of the neural network in the retina. Accumulation of extra glutamate seems to be an important mechanism for initiating pathological changes leading to retinal damage. Many previous in vitro studies on the role of Müller cells in retinal toxicology have been based on the use of morphological and histochemical methods. In cell toxicology studies, it is important to develop culture techniques able to provide more cells for biochemical determinations.

Na+ channels of Müller (glial) cells isolated from retinae of various mammalian species including man

Within the last few years, the expression of voltage-dependent, TTX-sensitive Na+ channels has been demonstrated in several types of neuroglial cells such as astrocytes and Schwann cells. Recently, we reported the occurrence of such Na+ currents in retinal Müller (glial) cells from dog and cat. This paper deals with the description of the properties of Na+ currents in Müller cells isolated from retinae of several mammalian species, as well as from human retinae. These Na+ currents were eliminated by TTX (1 microM), and by exposure to sodium-free extracellular solution; typically, they were demonstrable only after blocking most of the K+ conductance by Ba2+ (1 mM). Voltage-dependent activation and inactivation characteristics and time constants of the Na+ currents were similar to those of currents carried by neuronal Na+ channels. The estimated number of sodium channels per cell was low (about 1,500 channels per 7,500 microns 2), and the K+ conductance exceeded the peak Na+ conductance by an average factor of 5. Thus, the cells were incapable of generating action-potential-like responses under current clamp. Modelling estimations show that triggering of glial Na+ currents under physiological conditions, if any, can at best occur by emhaptic transmission at perinodal sites of optic axons. It is speculated that glial Na+ channels might be involved in neuroglial signalling events.

Dye-induced photolesion in the mammalian retina: glial and neuronal reactions

Irradiation in the presence of a dye applied to the extracellular space is known to produce degenerative features in irradiated neurones and fibers. In the present study, we confirmed the potential use of this procedure as a lesion technique by showing the removal of degenerating elements as part of the glial reaction to the lesion. The dye Rose Bengal was applied to the vitreous body of a rat eye and a T-shaped irradiation pattern was projected onto the retina within the absorption band of the dye. Degenerative features were restricted to the irradiated area, which could be readily identified from its shape. Retinae examined after various survival times showed that macrophages invaded the damaged area within 1 day, and that mitotic activity of reactive glial cells subsequently occurred in the vicinity of the wound. Both cell types were identified by their structural features. Macrophages were also revealed by a staining technique using the dye Nile Red, whereas reactive glial cells were immunolabeled with an antibody directed against the glial fibrillary acidic protein. Reactive glial cells helped the macrophages to gradually remove injured cells and damaged processes. Their main task, however, appeared to be in scar formation, since their processes seemed to suture the lips of the wound together and restore the limiting membrane at the inner retina. After 2 months' survival time, the parent ganglion cells of most disrupted axon bundles had retrogradely degenerated, but regenerating ganglion cell axons were also observed. These results provide some new data about healing processes in the retina. They demonstrate that the dye-induced photolesion technique can be used to either remove or axotomize selected neurones in neural networks which have been made optically accessible.

Dominantly inherited cystoid macular edema. A histopathologic study

BACKGROUND

Dominantly inherited cystoid macular edema was described as a clinically distinct form of macular dystrophy with an onset at approximately age 30 years with slow progression over the ensuing decades. This is the first report of the light and electron microscopic findings in two donor eyes of one of the patients with this clinical entity.

METHODS

Both eyes were obtained after death and fixed within 24 hours in a buffered 4% formaldehyde-1% glutaraldehyde solution. For light microscopy, tissue was embedded in paraffin and stained with hematoxylin-eosin, periodic acid-Schiff, colloidal iron for mucopolysaccharides, and an antibody to glial fibrillar acidic protein. For ultrastructural investigation, several blocks of choroidal/retinal tissues from the posterior pole, including both maculae, were embedded in epoxy resin and processed for transmission electron microscopy.

RESULTS

Major findings included large retinal cysts in the macula, atrophy and marked disorganization of the inner nuclear layer, advanced degeneration of Müller cells with nodular aggregates of basement membrane-like material, and a preretinal membrane. The retinal vasculature did not show excessive endothelial alterations but was surrounded by deposits of multilayered basement membrane in the perivascular space.

CONCLUSION

The authors believe that the pathologic features of dominantly inherited cystoid macular edema are different from those of macular edema caused by other disease processes. The predominant pathologic changes affected mainly the inner nuclear layer. The possibility of a primary disease of the Müller cell is suggested.

Mitogenic effects of excitatory amino acids in the adult rat retina

We studied the retinas of adult rats after the intravitreal injection of excitatory amino acids and ouabain. Kainic acid, domoic acid, N-methyl D-asparate and ouabain produced swelling and vacuolization of the outer plexiform, inner nuclear and inner plexiform layers and pyknosis. Mitoses were present in retinas treated with all agents other than N-methyl D-asparate. Rompun ketamine anesthesia blocked the mitogenic effects. Immunohistochemical labeling of both glial fibrillary acidic protein and S100 protein would indicate that the mitoses are occurring in glial cells. We suggest that the mitogenic effects are mediated through action on glial cationic channels, and might account for the reactive gliosis observed in some retinal lesions.

Macrophage products IL-1 alpha, TNF alpha and bFGF may mediate multiple cytopathic effects in the developing eyes of GM-CSF transgenic mice

GM-CSF transgenic mice develop eye disease during ontogeny that is mediated by autostimulated macrophages. The ocular pathology is characterized in part by corneal and vitreous neovascularization, pronounced GFAP expression by retinal Müller cells and degeneration of the retinal photoreceptor layer. The invading intraocular macrophages express the genes for the cytokines interleukin-1 alpha, tumor necrosis factor alpha and basic fibroblast growth factor, which may contribute to the multifaceted developmental ocular disorder. These cytokines, suspected to be angiogenic, may be responsible for neovascularization of the cornea in our transgenic animals. GFAP is normally made by astrocytes in the superficial retina and is induced in Müller cells in models of retinal degeneration. This protein is abnormally and copiously produced by Müller cells in the transgenic mice, which we suggest may be due to the release of cytokines from the invading macrophages. We suggest a mechanism by which autostimulated macrophages, through a perturbation of their normal developmental role, may be responsible for photoreceptor cell death in these transgenic animals.