Identification of ganglion cell neurites in human subretinal and epiretinal membranes

Retinal Toxicity Assessment Following Vitreoretinal Surgery: A Comparison of Silicone Oil and Perfluoropropane Tamponade Using Diopsys® NOVA™

PURPOSE

This study aimed to assess and compare the retinal toxicity associated with silicone oil (SO) and perfluoropropane (C3F8) tamponade following vitreoretinal surgery for fresh rhegmatogenous retinal detachment (RRD), utilizing the office-based Diopsys® NOVA™ system for evaluation.

METHODS

Patients who underwent vitreoretinal surgery for fresh RRD and had SO (group 1) or C3F8 (group 2) tamponade were included in a prospective analysis. Flicker full field electroretinography (ffERG) and pattern electroretinography (PERG) tests were performed at 6 months postoperatively.

RESULTS

Postoperative best corrected visual acuity (logMAR) was significantly different in group 1 and group 2 patients, 0.48 ± 0.3 and 0.30 ± 0.2, respectively. No significant disparities were found in demographic variables. Flicker ffERG and PERG recordings revealed notable alterations in retinal function parameters in the group 1 compared to the group 2.

CONCLUSION

Our findings suggest a correlation between SO tamponade and retinal dysfunction, evidenced by office-based ERG measurements. The Diopsys® NOVA™ protocol offers clinical ease in assessing retinal function. Further controlled studies are essential to validate these findings and guide clinical practice effectively.

PDGF as an Important Initiator for Neurite Outgrowth Associated with Fibrovascular Membranes in Proliferative Diabetic Retinopathy

PURPOSE

The formation of fibrovascular membranes (FVMs) is a serious sight-threatening complication of proliferative diabetic retinopathy (PDR) that may result in retinal detachment and eventual blindness. During the formation of these membranes, neurite/process outgrowth occurs in retinal neurons and glial cells, which may both serve as a scaffold and have guiding or regulatory roles. To further understand this process, we investigated whether previously identified candidate proteins, from vitreous of PDR patients with FVMs, could induce neurite outgrowth in an experimental setting.

MATERIALS AND METHODS

Retinal explants of C57BL6/N mouse pups on postnatal day 3 (P3) were cultured in poly-L-lysine- and laminin-coated dishes. Outgrowth stimulation experiments were performed with the addition of potential inducers of neurite outgrowth. Automated analysis of neurite outgrowth was performed by measuring β-tubulin-immunopositive neurites using Image J. Expression of PDGF receptors was quantified by RT-PCR in FVMs of PDR patients.

RESULTS

Platelet-derived growth factor (PDGF) induced neurite outgrowth in a concentration-dependent manner, whilst neuregulin 1 (NRG1) and connective tissue growth factor (CTGF) did not. When comparing three different PDGF dimers, treatment with PDGF-AB resulted in the highest neurite induction, followed by PDGF-AA and -BB. In addition, incubation of retinal explants with vitreous from PDR patients resulted in a significant induction of neurite outgrowth as compared to non-diabetic control vitreous from patients with macular holes, which could be prevented by addition of CP673451, a potent PDGF receptor (PDGFR) inhibitor. Abundant expression of PDGF receptors was detected in FVMs.

CONCLUSION

Our findings suggest that PDGF may be involved in the retinal neurite outgrowth, which is associated with the formation of FVMs in PDR.

Premacular Cells as Source of Neurotrophic Factors in Idiopathic Macular Holes

Purpose: To describe the presence of neurotrophic growth factors and histopathologic characteristics of internal limiting membrane (ILM) specimens obtained from large idiopathic full-thickness macular holes (FTMH). Methods: In 24 eyes of 24 patients with FTMH of diameter >400 µm, ILM specimens were harvested directly at the edge surrounding the macular hole during vitrectomy with peeling. We performed interference and phase contrast microscopy of flat mounts followed by immunostaining and transmission electron microscopy. Primary antigens directed against neurotrophic growth factors as well as antigens to glial and ganglion cells were used. Topographic relationship of cells and collagen was demonstrated by serial ultrathin sectioning. Results: Immunofluorescence microscopy demonstrated the presence of glial-derived neurotrophic factor and ciliary neurotrophic factor. Expression of vimentin, glial fibrillary acidic protein (GFAP), neurofilament, calretinin, and melanopsin was seen positive too. Cellular retinaldehyde-binding protein was seen positive in half of the specimens. Co-localisation of anti-GFAP as well as anti-vimentin with neurotrophic factors was found. Electron microscopy revealed cells exclusively on the vitreal side of the ILM. Cell fragments on the retinal side were rarely seen. Conclusion: In large FTMH, ILM specimens present positive immunolabelling of neurotrophic factors. The co-localization with macroglial cell markers suggests a premacular cell composition as a source of the neurotrophic factors. Ultrastructurally, premacular cells were found on the vitreal side of the ILM and not within the collagen network of the ILM itself.

Persistent remodeling and neurodegeneration in late-stage retinal degeneration

Retinal remodeling is a progressive series of negative plasticity revisions that arise from retinal degeneration, and are seen in retinitis pigmentosa, age-related macular degeneration and other forms of retinal disease. These processes occur regardless of the precipitating event leading to degeneration. Retinal remodeling then culminates in a late-stage neurodegeneration that is indistinguishable from progressive central nervous system (CNS) proteinopathies. Following long-term deafferentation from photoreceptor cell death in humans, and long-lived animal models of retinal degeneration, most retinal neurons reprogram, then die. Glial cells reprogram into multiple anomalous metabolic phenotypes. At the same time, survivor neurons display degenerative inclusions that appear identical to progressive CNS neurodegenerative disease, and contain aberrant α-synuclein (α-syn) and phosphorylated α-syn. In addition, ultrastructural analysis indicates a novel potential mechanism for misfolded protein transfer that may explain how proteinopathies spread. While neurodegeneration poses a barrier to prospective retinal interventions that target primary photoreceptor loss, understanding the progression and time-course of retinal remodeling will be essential for the establishment of windows of therapeutic intervention and appropriate tuning and design of interventions. Finally, the development of protein aggregates and widespread neurodegeneration in numerous retinal degenerative diseases positions the retina as a ideal platform for the study of proteinopathies, and mechanisms of neurodegeneration that drive devastating CNS diseases.

Identification of proteins associated with clinical and pathological features of proliferative diabetic retinopathy in vitreous and fibrovascular membranes

Purpose

To identify the protein profiles in vitreous associated with retinal fibrosis, angiogenesis, and neurite formation in epiretinal fibrovascular membranes (FVMs) in patients with proliferative diabetic retinopathy (PDR).

Methods

Vitreous samples of 5 non-diabetic control patients with vitreous debris and 7 patients with PDR membranes were screened for 507 preselected proteins using the semi-quantitative RayBio® L-series 507 antibody array. From this array, 60 proteins were selected for a custom quantitative antibody array (Raybiotech, Human Quantibody® array), analyzing 7 control patients, 8 PDR patients with FVMs, and 5 PDR patients without FVMs. Additionally, mRNA levels of proteins of interest were measured in 10 PDR membranes and 11 idiopathic membranes and in retinal tissues and cells to identify possible sources of protein production.

Results

Of the 507 proteins screened, 21 were found to be significantly elevated in PDR patients, including neurogenic and angiogenic factors such as neuregulin 1 (NRG1), nerve growth factor receptor (NGFR), placental growth factor (PlGF) and platelet derived growth factor (PDGF). Angiopoietin-2 (Ang2) concentrations were strongly correlated to the degree of fibrosis and the presence of FVMs in patients with PDR. Protein correlation analysis showed PDGF to be extensively co-regulated with other proteins, including thrombospondin-1 and Ang2. mRNA levels of glial-derived and brain/derived neurotrophic factor (GDNF and BDNF) were elevated in PDR membranes. These results were validated in a second study of 52 vitreous samples of 32 PDR patients and 20 control patients.

Conclusions

This exploratory study reveals protein networks that potentially contribute to neurite outgrowth, angiogenesis and fibrosis in the formation of fibrovascular membranes in PDR. We identified a possible role of Ang2 in fibrosis and the formation of FVMs, and of the neurotrophic factors NRG1, PDGF and GDNF in neurite growth that occurs in all FVMs in PDR.

Epiretinal membrane in a subject after transvitreal delivery of palucorcel (CNTO 2476)

Background

A 70-year-old woman with retinitis pigmentosa experienced an epiretinal membrane (ERM) formation and a tractional retinal detachment (RD) following subretinal administration of palucorcel (CNTO 2476), a novel human umbilical tissue-derived cell-based therapy, as part of a Phase I study. The clinical course and results of a histologic examination of the ERM, which was peeled during surgery to repair the RD, are described here.

Methods

In this open-label, first-in-human, Phase I study (NCT00458575), two of seven subjects developed RD, with an ERM formation reported in a woman receiving a targeted dose of 3.0×10⁵ palucorcel administered via a transvitreal route. A sample of the ERM was retained for analysis following the ERM peeling procedure. Clinical outcomes and ERM histology, based on immunocytochemistry analyses and fluorescence in situ hybridization (FISH) staining, were evaluated.

Results

We first noted the RD and formation of the ERM at 26 days after palucorcel administration. The ERM was cellular and contained multiple cell types, including Müller glial cells, immune cells, neurites, retinal pigment epithelial cells, and palucorcel. The majority of cells were not actively dividing. FISH staining showed a subset of Y chromosome-positive cells in the ERM from this woman, supporting the presence of palucorcel (derived from umbilical cord tissue of male neonate). Palucorcel did not differentiate into Müller glia, immune cells, neurites, or retinal pigment epithelial cells.

Discussion

The development of an ERM containing both subject (self) cells and palucorcel suggests that palucorcel egress in the vitreal cavity after retinotomy may contribute to ERM formation and RD and that an alternative delivery method will be required before further studies are conducted. Subsequent clinical research using alternative subretinal delivery methods for palucorcel in other indications suggests that membrane development does not occur when palucorcel is delivered without retinal perforation.

Macromolecular markers in normal human retina and applications to human retinal disease

Macromolecular cell markers are essential for the classification and characterization of the highly complex and cellularly diverse vertebrate retina. Although a plethora of markers are described in the current literature, the immunoreactivity of these markers in normal human tissue has not been fully determined. This is problematic as they are quintessential to the characterization of morphological changes associated with human retinal disease. This review provides an overview of the macromolecular markers currently available to assess human retinal cell types. We draw on immunohistochemical studies conducted in our laboratories to describe marker immunoreactivity in human retina alongside comparative descriptions in non-human tissues. Considering the growing number of eye banks services offering healthy and diseased human retinal tissue, this review provides a point of reference for future human retina studies and highlights key species specific disease applications of some macromolecular markers.

Characterization of ex vivo cultured neuronal- and glial- like cells from human idiopathic epiretinal membranes

Background

Characterization of the neuro-glial profile of cells growing out of human idiopathic epiretinal membranes (iERMs) and testing their proliferative and pluripotent properties ex vivo is needed to better understand the pathogenesis of their formation.

Methods

iERMs obtained during uneventful vitrectomies were cultivated ex vivo under adherent conditions and assessed by standard morphological and immunocytochemical methods. The intracellular calcium dynamics of the outgrowing cells was assessed by fluorescent dye Fura-2 in response to acetylcholine (ACh)- or mechano- stimulation.

Results

The cells from the iERMs formed sphere-like structures when cultured ex vivo. The diameter of the spheres increased by 5% at day 6 and kept an increasing tendency over a month time. The outgrowing cells from the iERM spheres had mainly glial- and some neuronal- like morphology. ACh- or mechano- stimulation of these cells induced intracellular calcium propagation in both cell types; in the neuronal-like cells resembling action potential from the soma to the dendrites. Immunocytochemistry confirmed presence of glial- and neuronal cell phenotype (GFAP and Nestin-1 positivity, respectively) in the iERMs, as well as presence of pluripotency marker (Sox2).

Conclusion

iERMs contain cells of neuronal- and glial- like origin which have proliferative and pluripotent potential, show functionality reflected through calcium dynamics upon ACh and mechano- stimulation, and a corresponding molecular phenotype.

Comparison of morphologic features of macular proliferative vitreoretinopathy and idiopathic epimacular membrane

BACKGROUND

To compare the spectral-domain optical coherence tomography morphologic features and visual characteristics of a series of patients with epimacular membrane with and without a history of retinal breaks.

METHODS

Prospective, comparative case series of patients with epimacular membrane. All patients were evaluated with spectral-domain optical coherence tomography and detailed peripheral retinal examination. Symptomatic patients were treated with pars plana vitrectomy and epimacular membrane removal based on standard visual criteria.

RESULTS

Macular proliferative vitreoretinopathy was present in 21 of 50 patients (42%). Approximately 18 of 21 patients had a previous retinal break, 5 of which were untreated before the initial examination. No retinal breaks were observed in the idiopathic group. Macular proliferative vitreoretinopathy was highly associated with a history of retinal breaks (P < 0.001). Presenting visual acuity was significantly worse (mean, 0.86 ± 0.44) for macular proliferative vitreoretinopathy than for the idiopathic group (mean, 0.44 ± 0.36).

CONCLUSION

Epimacular membrane occurring in the context of previous retinal breaks or macular proliferative vitreoretinopathy has a characteristic morphologic feature in spectral-domain optical coherence tomography. Surgical removal typically results in significant visual improvement.

Cellular responses following retinal injuries and therapeutic approaches for neurodegenerative diseases

Retinal neurodegenerative diseases like age-related macular degeneration, glaucoma, diabetic retinopathy and retinitis pigmentosa each have a different etiology and pathogenesis. However, at the cellular and molecular level, the response to retinal injury is similar in all of them, and results in morphological and functional impairment of retinal cells. This retinal degeneration may be triggered by gene defects, increased intraocular pressure, high levels of blood glucose, other types of stress or aging, but they all frequently induce a set of cell signals that lead to well-established and similar morphological and functional changes, including controlled cell death and retinal remodeling. Interestingly, an inflammatory response, oxidative stress and activation of apoptotic pathways are common features in all these diseases. Furthermore, it is important to note the relevant role of glial cells, including astrocytes, Müller cells and microglia, because their response to injury is decisive for maintaining the health of the retina or its degeneration. Several therapeutic approaches have been developed to preserve retinal function or restore eyesight in pathological conditions. In this context, neuroprotective compounds, gene therapy, cell transplantation or artificial devices should be applied at the appropriate stage of retinal degeneration to obtain successful results. This review provides an overview of the common and distinctive features of retinal neurodegenerative diseases, including the molecular, anatomical and functional changes caused by the cellular response to damage, in order to establish appropriate treatments for these pathologies.

VEGF-production by CCR2-dependent macrophages contributes to laser-induced choroidal neovascularization

Age-related macular degeneration (AMD) is the most prevalent cause of blindness in the elderly, and its exsudative subtype critically depends on local production of vascular endothelial growth factor A (VEGF). Mononuclear phagocytes, such as macrophages and microglia cells, can produce VEGF. Their precursors, for example monocytes, can be recruited to sites of inflammation by the chemokine receptor CCR2, and this has been proposed to be important in AMD. To investigate the role of macrophages and CCR2 in AMD, we studied intracellular VEGF content in a laser-induced murine model of choroidal neovascularisation. To this end, we established a technique to quantify the VEGF content in cell subsets from the laser-treated retina and choroid separately. 3 days after laser, macrophage numbers and their VEGF content were substantially elevated in the choroid. Macrophage accumulation was CCR2-dependent, indicating recruitment from the circulation. In the retina, microglia cells were the main VEGF+ phagocyte type. A greater proportion of microglia cells contained VEGF after laser, and this was CCR2-independent. On day 6, VEGF-expressing macrophage numbers had already declined, whereas numbers of VEGF+ microglia cells remained increased. Other sources of VEGF detectable by flow cytometry included in dendritic cells and endothelial cells in both retina and choroid, and Müller cells/astrocytes in the retina. However, their VEGF content was not increased after laser. When we analyzed flatmounts of laser-treated eyes, CCR2-deficient mice showed reduced neovascular areas after 2 weeks, but this difference was not evident 3 weeks after laser. In summary, CCR2-dependent influx of macrophages causes a transient VEGF increase in the choroid. However, macrophages augmented choroidal neovascularization only initially, presumably because VEGF production by CCR2-independent eye cells prevailed at later time points. These findings identify macrophages as a relevant source of VEGF in laser-induced choroidal neovascularization but suggest that the therapeutic efficacy of CCR2-inhibition might be limited.

Pathophysiology of proliferative vitreoretinopathy in retinal detachment

Because proliferative vitreoretinopathy cannot be effectively treated, its prevention is indispensable for the success of surgery for retinal detachment. The elaboration of preventive and therapeutic strategies depends upon the identification of patients who are genetically predisposed to develop the disease, as well as upon an understanding of the biological process involved and the role of local factors, such as the status of the uveovascular barrier. Detachment of the retina or vitreous activates glia to release cytokines and ATP, which not only protect the neuroretina but also promote inflammation, retinal ischemia, cell proliferation, and tissue remodeling. The vitreal microenvironment favors cellular de-differentiation and proliferation of cells with nonspecific nutritional requirements. This may render a pharmacological inhibition of their growth difficult without causing damage to the pharmacologically vulnerable neuroretina. Moreover, reattachment of the retina relies upon the local induction of a controlled wound-healing response involving macrophages and proliferating glia. Hence, the functional outcome of proliferative vitreoretinopathy will be determined by the equilibrium established between protective and destructive repair mechanisms, which will be influenced by the location and the degree of damage to the photoreceptor cells that is induced by peri-retinal gliosis.

WITHDRAWN: Ultrastructure of the human retina in aging and various pathological states

This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.

Protein changes in the retina following experimental retinal detachment in rabbits

PURPOSE

Retinal detachment leads to the widespread cellular remodeling of the retina. The purpose of this study was to identify protein changes that accompany these cellular alterations by comparing the proteomic profiles of sham and experimentally detached rabbit retina. Elucidation of the proteins most dramatically affected by retinal detachment would add further understanding to the pathophysiology of this condition, and potentially identify therapeutic targets useful in preventing the deleterious effects of detachment, including photoreceptor cell death and the activation of non-neuronal microglial and Müller cells.

METHODS

Retinal detachments were induced in the right eyes of six New Zealand Red pigmented rabbits. Sham surgery was performed in the right eyes of six other rabbits that were used as controls. At seven days, the eyes were enucleated and the retinal tissue was harvested. The individual retinal samples were subjected to high resolution two-dimensional polyacrylamide gel electrophoresis. Differentially expressed protein spots were processed for identification by liquid chromatography-tandem mass spectrometry. Further investigation was undertaken with western blotting, and immunocytochemical studies on a further set of four sham and four detached retinas.

RESULTS

Eighteen protein spots were found to be at least twofold differentially expressed between the sham and detached retinas. These protein spots were identified as: vimentin; tubulin β-2C; fragments of α-enolase; fructose-bisphosphate aldolase A; ATP synthase subunit β; mitochondrial creatine kinase; N-terminal fragments of albumin; prohibitin; and transducin-β(1).

CONCLUSIONS

The differentially expressed proteins determined in this study may play an important role in the cellular responses of the retina after its detachment, subsequent ability to recover following surgical reattachment, as well as in serious complications such as subretinal fibrosis and proliferative vitreoretinopathy.

Periostin, discovered by nano-flow liquid chromatography and mass spectrometry, is a novel marker of diabetic retinopathy

Diabetes can lead to serious microvascular complications including proliferative diabetic retinopathy (PDR), the leading cause of blindness in adults. Recent studies using gene array technology have attempted to apply a hypothesis-generating approach to elucidate the pathogenesis of PDR, but these studies rely on mRNA differences, which may or may not be related to significant biological processes. To better understand the basic mechanisms of PDR and to identify potential new biomarkers, we performed shotgun liquid chromatography (LC)/tandem mass spectrometry (MS/MS) analysis on pooled protein extracts from neovascular membranes obtained from PDR specimens and compared the results with those from non-vascular epiretinal membrane (ERM) specimens. We detected 226 distinct proteins in neovascular membranes and 154 in ERM. Among these proteins, 102 were specific to neovascular membranes and 30 were specific to ERM. We identified a candidate marker, periostin, as well as several known PDR markers such as pigment epithelium-derived factor (PEDF). We then performed RT-PCR using these markers. The expression of periostin was significantly up-regulated in proliferative membrane specimens. Periostin induces cell attachment and spreading and plays a role in cell adhesion. Proteomic analysis by LC/MS/MS, which permits accurate quantitative comparison, was useful in identifying new candidates such as periostin potentially involved in the pathogenesis of PDR.

Abnormal reactivity of muller cells after retinal detachment in mice deficient in GFAP and vimentin

PURPOSE

To determine the roles of glial fibrillary acidic protein (GFAP) and vimentin in Müller cell reactivity.

METHODS

Retinal detachments were created in mice deficient for GFAP and vimentin (GFAP(-/-)vim(-/-)) and age-matched wild-type (wt) mice. The reactivity of the retina was studied by immunofluorescence and electron microscopy.

RESULTS

Müller cell morphology was different and glutamine synthetase immunoreactivity was reduced in the undisturbed GFAP(-/-)vim(-/-) retinas. After retinal detachment, Müller cells formed subretinal glial scars in the wt mice. In contrast, such scars were not observed in GFAP(-/-)vim(-/-) mice. Müller cells, which normally elongate and thicken in response to detachment, appeared compressed, thin, and "spikey" in the GFAP(-/-)vim(-/-) mice. The end foot region of Müller cells in the GFAP(-/-)vim(-/-) mice often sheared away from the rest of the retina during detachment, corroborating earlier results showing decreased resistance of this region in GFAP(-/-)vim(-/-) retinas to mechanical stress. In regions with end foot shearing, ganglion cells showed intense neurite sprouting, as revealed by anti-neurofilament labeling, a response rarely observed in wt mice.

CONCLUSIONS

Müller cells are subtly different in the GFAP(-/-)vim(-/-) mouse retina before detachment. The end foot region of these cells may be structurally reinforced by the presence of the intermediate filament cytoskeleton, and our data suggest a critical role for these proteins in Müller cell reaction to retinal detachment and participation in subretinal gliosis.