Activation of neural progenitor cells in human eyes with proliferative vitreoretinopathy

Blastocyst-like Structures in the Peripheral Retina of Young Adult Beagles

In this immunohistological study on the peripheral retina of 3-year-old beagle dogs, excised retina specimens were immunostained with antibodies against nestin, Oct4, Nanog, Sox2, CDX2, cytokeratin 18 (CK 18), RPE65, and YAP1, as well as hematoxylin and DAPI, two nuclear stains. Our findings revealed solitary cysts of various sizes in the inner retina. Intriguingly, a mass of small round cells with scant cytoplasms was observed in the cavity of small cysts, while many disorganized cells partially occupied the cavity of the large cysts. The small cysts were strongly positive for nestin, Oct4, Nanog, Sox2, CDX2, CK18, and YAP1. RPE65-positive cells were exclusively observed in the tissue surrounding the cysts. Since RPE65 is a specific marker of retinal pigment epithelial (RPE) cells, the surrounding cells of the peripheral cysts were presumably derived from RPE cells that migrated intraretinally. In the small cysts, intense positive staining for nestin, a marker of retinal stem cells, seemed to indicate that they were derived from retinal stem cells. The morphology and positive staining for markers of blastocyst and RPE cells indicated that the small cysts may have formed structures resembling the blastocyst, possibly caused by the interaction between retinal stem cells and migrated RPE cells.

Predictive values of systemic inflammation biomarkers in proliferative vitreoretinopathy associated with primary rhegmatogenous retinal detachment

CLINICAL RELEVANCE

Proliferative vitreoretinopathy (PVR) is still the leading cause of surgical failure after rhegmatogenous retinal detachment (RRD) repair. The factors that can predict the development of PVR remain to be elucidated.

BACKGROUND

This study evaluates the predictive values of the systemic immune-inflammation index, neutrophil-to-lymphocyte ratio, and platelet-to-lymphocyte ratio in patients with primary RRD with and without PVR.

METHODS

A total of 150 patients with RRD and 51 age- and sex-matched healthy participants were included in the study. Patients who developed PVR within three months after surgery were enrolled as PVR cases (n = 75, Group 1), and those who did not develop PVR were enrolled in RRD without the PVR group (n = 75, Group 2). Ocular examination findings and medical records of all participants were analysed retrospectively. Peripheral blood samples were collected, and systemic immune-inflammation index, neutrophil-to-lymphocyte ratio, and platelet-to-lymphocyte ratios were calculated. The systemic immune-inflammation index calculation formula is: (Neutrophil/lymphocyte) × Platelet.

RESULTS

The median neutrophil-to-lymphocyte ratio and systemic immune-inflammation index levels were significantly higher in Group 1 patients compared to Group 2 and the control groups (p = 0.01, for both). However, the groups were similar regarding median platelet-to-lymphocyte ratio (p = 0.917). The optimal cut-off values of neutrophil-to-lymphocyte ratio and systemic immune-inflammation index were calculated as 1.72 (with 72% sensitivity and 48% specificity) and 407.9 (with 72% sensitivity and 49.3% specificity), respectively, for predicting PVR development in patients with RRD.

CONCLUSION

Neutrophil-to-lymphocyte ratio and systemic immune-inflammation index may be useful biomarkers for predicting the risk of PVR development in RRD patients.

Optical Coherence Tomography Angiography in Macular Holes Autologous Retinal Transplant

In this paper, we compare the post-operative macular microvascular parameters (vascular density and foveal avascular zone) in eyes with refractory macular hole (MH) that underwent pars plana vitrectomy and autologous retinal transplant (ART) with the fellow unoperated eye. We conducted a retrospective case control study of six consecutive patients who underwent pars plana vitrectomy and ART with at least six months of post-operative follow-up. Pre-operatively, all eyes underwent SD-OCT (Spectral Domain Optical Coherence Tomography) examination. Post-operative OCT-A analyses included vascular density (VD) and the foveal avascular zone (FAZ) area. Six patients with a mean age of 63.7 ± 14.3 years were included. The mean follow-up was 24 months (range 6–30 months). The pre-operative BCVA (best-corrected visual acuity) was 0.99 ± 0.46 logMAR and 1.02 ± 0.23 logMAR at the last post-operative visit (p = 1.00). The mean MH diameter was 966 ± 620 µm. VD in the MH group was 28.1 ± 7.3% compared to 20.2 ± 2.9% in the fellow eyes group (p < 0.05). The mean post-operative FAZ area in the MH group was 109.8 ± 114.6 mm2 compared to 41.5 ± 10.4 mm2 in the control group (p < 0.05). In all six eyes, MH closure was obtained. The post-operative visual acuity did not improve after ART. Eyes with a closed MH showed a bigger FAZ with a higher VD compared to the fellow healthy eye.

Activation of adult mammalian retinal stem cells in vivo via antagonism of BMP and sFRP2

Background

The adult mammalian retina does not have the capacity to regenerate cells lost due to damage or disease. Therefore, retinal injuries and blinding diseases result in irreversible vision loss. However, retinal stem cells (RSCs), which participate in retinogenesis during development, persist in a quiescent state in the ciliary epithelium (CE) of the adult mammalian eye. Moreover, RSCs retain the ability to generate all retinal cell types when cultured in vitro, including photoreceptors. Therefore, it may be possible to activate endogenous RSCs to induce retinal neurogenesis in vivo and restore vision in the adult mammalian eye.

Methods

To investigate if endogenous RSCs can be activated, we performed combinatorial intravitreal injections of antagonists to BMP and sFRP2 proteins (two proposed mediators of RSC quiescence in vivo), with or without growth factors FGF and Insulin. We also investigated the effects of chemically-induced N-methyl-N-Nitrosourea (MNU) retinal degeneration on RSC activation, both alone and in combination withthe injected factors. Further, we employed inducible Msx1-Cre^ERT2 genetic lineage labeling of the CE followed by stimulation paradigms to determine if activated endogenous RSCs could migrate into the retina and differentiate into retinal neurons.

Results

We found that in vivo antagonism of BMP and sFRP2 proteins induced CE cells in the RSC niche to proliferate and expanded the RSC population. BMP and sFRP2 antagonism also enhanced CE cell proliferation in response to exogenous growth factor stimulation and MNU-induced retinal degeneration. Furthermore, Msx1-Cre^ERT2 genetic lineage tracing revealed that CE cells migrated into the retina following stimulation and/or injury, where they expressed markers of mature photoreceptors and retinal ganglion cells.

Conclusions

Together, these results indicate that endogenous adult mammalian RSCs may have latent regenerative potential that can be activated by modulating the RSC niche and hold promise as a means for endogenous retinal cell therapy to repair the retina and improve vision.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02630-0.

Retinal Stem/Progenitor Cells Derived From Adult Müller Glia for the Treatment of Retinal Degeneration

Over the past two decades, progress in our understanding of glial function has been revolutionary. Within the retina, a subset of glial cells termed the “Müller glia (MG),” have been demonstrated to play key roles in retinal homeostasis, structure and metabolism. Additionally, MG have also been shown to possess the regenerative capacity that varies across species. In teleost fish, MG respond to injury by reprogramming into stem-like cells capable of regenerating lost tissue. The expression of stem/progenitor cell markers has been demonstrated broadly in mammalian MG, including human MG, but their in vivo regenerative capacity appears evolutionarily limited. Advances in stem cell therapy have progressively elucidated critical mechanisms underlying innate MG reprogramming in teleost fish, which have shown promising results when applied to rodents. Furthermore, when cultured ex vivo, MG from mammals can differentiate into several retina cell types. In this review, we will explore the reparative and regenerative potential of MG in cellular therapy approaches, and outline our current understanding of embryonic retinal development, the stem-cell potential of MG in adult vertebrate retina (including human), and microenvironmental cues that guide MG reprogramming.

SURGICAL RETINAL EXPLANTS AS A SOURCE OF RETINAL PROGENITOR CELLS

PURPOSE

To describe the novel observation of spontaneously migrating retinal cells from living donor surgical retinal explants that express progenitor cell markers in the absence of exogenous growth factors.

METHODS

Surgical retinal explants were harvested from 5 consecutive patients undergoing 23 G pars plana vitrectomy for the management of rhegmatogenous detachment. During surgery, equatorial flap tears were trimmed with the vitreous cutter and aspirated. Excised tissue was then regurgitated into a syringe containing balanced salt solution and immediately transferred to tissue culture. Migrating cells subsequently underwent immunohistochemical staining and their characteristics were compared with those of a spontaneously immortalized Müller stem cell line.

RESULTS

Spontaneously migrating cells were observed from samples taken from all 5 patients from Day 2 to 10 after transfer to culture. These cells were found to express embryonic cell markers, including paired box 6 (Pax6), sex-determining region Y-box 2 (Sox-2), nestin, cone-rod homeobox, and cyclin-dependent kinase inhibitor 1B (p27Kip1) as well as proteins consistent with early or retained differentiation down the Müller cell lineage, including glial fibrillary acidic protein and glutamine synthetase.

CONCLUSION

After injury, the human equatorial retina is capable of spontaneously producing cells that demonstrate migration and that express progenitor cell markers. In addition, these cells express proteins consistent with Müller cell lineage. These initial observations support the assertion that the human retina may possess the potential for regeneration and that surgical retinal explants could also act as a ready source of retinal progenitor cells.

Retinal Stem Cell 'Retirement Plans': Growth, Regulation and Species Adaptations in the Retinal Ciliary Marginal Zone

The vertebrate retina develops from a specified group of precursor cells that adopt distinct identities and generate lineages of either the neural retina, retinal pigmented epithelium, or ciliary body. In some species, including teleost fish and amphibians, proliferative cells with stem-cell-like properties capable of continuously supplying new retinal cells post-embryonically have been characterized and extensively studied. This region, termed the ciliary or circumferential marginal zone (CMZ), possibly represents a conserved retinal stem cell niche. In this review, we highlight the research characterizing similar CMZ-like regions, or stem-like cells located at the peripheral margin, across multiple different species. We discuss the proliferative parameters, multipotency and growth mechanisms of these cells to understand how they behave in vivo and how different molecular factors and signalling networks converge at the CMZ niche to regulate their activity. The evidence suggests that the mature retina may have a conserved propensity for homeostatic growth and plasticity and that dysfunction in the regulation of CMZ activity may partially account for dystrophic eye growth diseases such as myopia and hyperopia. A better understanding of the properties of CMZ cells will enable important insight into how an endogenous generative tissue compartment can adapt to altered retinal physiology and potentially even restore vision loss caused by retinal degenerative conditions.

Autologous neurosensory retinal transplantation for large refractory idiopathic macular hole

PURPOSE

To investigate the structural and functional reconstruction of the macula after autologous neurosensory retinal-free flap transplantation (ANRFFT) in eyes with large refractory idiopathic macular holes (IMHs).

METHODS

Patients with refractory IMHs after multiple surgeries who underwent ANRFFT were retrospectively reviewed. The main outcomes were anatomic closure of MH, change in external limiting membrane (ELM) defect on optical coherence tomography (OCT) and best-corrected visual acuity (BCVA).

RESULTS

A total of 7 patients (4 female and 3 male; mean age 60.6 ± 8.6 years) were included in the study. Mean preoperative largest basal diameter was 1146.7 ± 413.7 µm (range, 653-1768 µm), and mean narrowest inner-opening diameter was 788.9 ± 148.8 µm (range, 644-1100 µm). Mean BCVA (logarithm of the minimum angle of resolution [logMAR]) significantly improved from 1.53 ± 0.16 (range, 1.3-1.7) to 0.89 ± 0.23 (range, 0.6-1.3) at the final follow-up (P < 0.001). OCT revealed complete closure of MH in all eyes. Mean preoperative ELM defect significantly decreased from 1450.3 ± 306.5 µm (range, 1044-1908 mm) to 533.1 ± 399.2 µm (range, 0-1156 µm, P = 0.001). Postoperative complications included retinal detachment (n = 1), cystoid macular edema like changes in the graft (n = 1) and reactive pigment epithelial hyperplasia (n = 1).

CONCLUSION

Although some postoperative complications did occur, ANRFFT seems to be an effective treatment for large refractory IMHs, and can promote recovery of the outer retinal structure resulting in functional improvement.

Autologous neurosensory retinal transplantation for recurrent macular hole retinal detachment in highly myopic eyes

PURPOSE

To investigate the morphological and functional reconstruction of the macular fovea after autologous neurosensory retinal transplantation for recurrent macular hole retinal detachment (MHRD) in highly myopic eyes.

METHODS

Ten consecutive cases of recurrent MHRD with high myopia were retrospectively reviewed. All eyes underwent pars plana vitrectomy combined with autologous neurosensory retinal transplantation and were followed up for at least 3 months after silicone oil extraction. The main outcomes were whether or not the retina was reattached and the macular hole (MH) was closed, morphological changes in the retinal graft, best-corrected visual acuity (BCVA), the sensitivity threshold and blood flow signal in the macula.

RESULTS

At the one month postoperative visit, there was an obvious boundary between the graft and the surrounding retinal tissue, and some retinal structural layers could be seen in the graft on optical coherence tomography scans. At the final follow-up, eight eyes (80%) showed retinal reattachment and closure of the MH. Optical coherence tomography revealed blurring of the boundary between the graft and surrounding retinal tissue and that the retinal structure in the graft was disordered. The MH was not closed in two eyes (20%), in one case because of partial displacement of the graft and in the other because of incomplete coverage of the MH as a result of a smaller graft. The post-BCVA was significantly better than the pre-BCVA (1.32 ± 0.33 versus 2.01 ± 0.29 logMAR; p = 0.000, paired t-test).

CONCLUSION

Autologous neurosensory retinal transplantation can be an effective treatment for recurrent MHRD in highly myopic eyes. 'Fusion' between the neurosensory retinal graft and the original retinal tissue may be the mechanism involved in the closure of the MH and reconstruction of the macular fovea.

Protein Composition of the Subretinal Fluid Suggests Selective Diffusion of Vitreous Proteins in Retinal Detachment

Purpose

To study the proteome of the subretinal fluid (SRF) from rhegmatogenous retinal detachment (RRD) in search for novel markers for improved diagnosis and prognosis of RRD.

Methods

Human undiluted SRF obtained during vitrectomy for primary RRD using a 41-gauge needle (n = 24) was analyzed and compared to vitreous humor from 2-day postmortem eyes (n = 20). Sample preparation underwent nanoflow liquid chromatography–tandem mass spectrometry. Label-free quantification (LFQ) using MaxQuant was used to determine differentially expressed proteins between SRF and vitreous humor. The intensity-based absolute quantification (iBAQ) was used to rank proteins according to their molar fractions within groups. Identification of proteins beyond the quantitative level was performed using the Mascot search engine.

Results

The protein concentration of the control vitreous humor was lower and more consistent (1.2 ± 0.4 mg) than that of the SRF (17.9 ± 22 mg). The iBAQ analysis showed high resemblance between SRF and vitreous humor, except for crystallins solely identified in vitreous humor. The LFQ analysis found 38 protein misregulations between SRF and vitreous humor of which the blood coagulation pathway was found to be enriched using the PANTHER Classification System. Combined, the iBAQ, LFQ, and Mascot analysis found an overlap only in chitinase-3-like protein 1 and galectin-3-binding protein unique to the SRF.

Conclusions

The proteome of the SRF was highly represented by proteins involved in proteolysis. Such proteins can possibly serve as targets in modulating the effects of SRF in RD.

Translational Relevance

To identify potential novel biomarkers for therapeutic targeting in RD.

Autologous Retinal Transplantation for Primary and Refractory Macular Holes and Macular Hole Retinal Detachments: The Global Consortium

PURPOSE

To report the anatomic and functional outcomes of autologous retinal transplantation (ART).

DESIGN

Multicenter, retrospective, interventional, consecutive case series.

PARTICIPANTS

One hundred thirty eyes of 130 patients undergoing ART for the repair of primary and refractory macular holes (MHs), as well as combined MH-rhegmatogenous retinal detachment (MH-RRD), between January 2017 and December 2019.

METHODS

All patients underwent pars plana vitrectomy and ART, with surgeon modification of intraoperative variables. A large array of preoperative, intraoperative, and postoperative data was collected. Two masked reviewers graded OCT images. Multivariate statistical analysis and subgroup analysis were performed.

MAIN OUTCOME MEASURES

Macular hole closure rate, visual acuity (VA), external limiting membrane and ellipsoid zone (EZ) band integrity, and alignment of neurosensory layers (ANL) on OCT.

RESULTS

One hundred thirty ART surgeries were performed by 33 vitreoretinal surgeons worldwide. Patient demographics were: mean age of 63 ± 6.3 years, 58% female, 41% White, 23% Black, 19% Asian, and 17% Latino. Preoperative VA was 1.37 ± 0.12 logarithm of the minimum angle of resolution (logMAR; Snellen equivalent, approximately 20/500), which improved significantly to 1.05 ± 0.09 logMAR (Snellen equivalent, approximately 20/225; P < 0.001) after surgery (mean follow-up, 8.6 ± 0.8 months). Autologous retinal transplantation was performed for primary MH repair in 27% of patients (n = 35), for refractory MH in 58% of patients (n = 76; mean number of previous surgeries, 1.6 ± 0.2), and for MH-RRD in 15% of patients (n = 19). Mean maximum MH diameter was 1470 ± 160 μm, mean minimum diameter was 840 ± 94 μm, and mean axial length was 24.6 ± 3.2 mm. Overall, 89% of MHs closed (78.5% complete; 10% small eccentric defect), with a 95% closure rate in MH-RRD (68.4% complete; 26.3% small eccentric defect). Visual acuity improved by at least 3 lines in 43% of eyes and by at least 5 lines in 29% of eyes. Reconstitution of the EZ (P = 0.02) and ANL (P = 0.01) on OCT were associated with better final VA. Five cases of ART graft dislocation (3.8%), 5 cases of postoperative retinal detachment (3.8%), and 1 case of endophthalmitis (0.77%) occurred.

CONCLUSIONS

In this global experience, patients undergoing ART for large primary and refractory MHs and MH-RRDs achieved good anatomic and functional outcomes, with low complication rates despite complex surgical pathologic features.

Recalcitrant Macular Hole Closure by Autologous Retinal Transplant Using the Peripheral Retina

Purpose

The peripheral adult human retina has been found to contain neuroepithelial stem cells. In this study, we examined the efficacy of an auto-transplant of peripheral retina into refractory macular holes (MH) from both anatomic and physiologic perspectives.

Methods

The population consisted of four female patients aged 72, 82, 65 and 84 years (cases 1–4, respectively) with persistent refractory MH status; internal limiting membrane (ILM) peeling (case 1), ILM transplant (case 2), and inverted ILM (cases 3 and 4 with myopic MH). In all our cases, retinal grafts were harvested beyond the equator from the far retinal periphery using curved horizontal scissors and gently moved toward the MH using a forceps. A 25-G manipulator with a silicone ball tip was used to tuck the trimmed graft into the MH, followed by fluid-air exchange and infusion of silicone oil, which was removed three months later.

Results

Partial restoration and integration of the outer retinal layer were confirmed on an OCT-B scan imaging. The visual acuity (VA) was improved in all cases: 1.2 to 1.0 logMAR (case 1), 2.0 to 1.3 logMAR (case 2), 2.3 to 1.4 logMAR (case 3) and 2.0 to 1.0 logMAR (case 4). Microperimetry showed improved retinal sensitivity in every case. No intra- or post-operative complications were observed.

Conclusion

Under pathological conditions, the Müller glia reportedly serves as a source of neuronal progenitor cells in regenerating retina, continuing to divide and migrate to the outer nuclear layer thus replacing lost photo-receptors. Although the histological findings remain unknown, the positive anatomic and physiologic outcomes of the auto-transplanted retinal flap in our series suggest that this technique may offer an effective option for treating recalcitrant MH. Further studies are warranted.

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Optical coherence tomography findings in a case of macular hole treated with an autologous retinal transplant

A case is presented of a 56-year-old female patient with a long-standing large macular hole who underwent autologous retina transplant surgery. Fundus images and spectral-domain optical coherence tomography images showed the presence of graft oedema with its corresponding hyper-reflectivity of the inner retinal layers in the first weeks of follow-up. Hyper-reflective dots later appeared mainly in the inner retinal layers. The integrity of the outer retinal layers and a woolly-looking material on the surface of the graft were observed. At the end of follow-up, the graft had integrated with the recipient tissue with functional improvement.

Glia of the human retina

The human retina contains three types of glial cells: microglia and two types of macroglia, astrocytes and Müller cells. Macroglia provide homeostatic and metabolic support to photoreceptors and neurons required for neuronal activity. The fovea, the site of the sharpest vision which is astrocyte- and microglia-free, contains two populations of Müller glia: cells which form the Müller cell cone in the foveola and z-shaped Müller cells of the foveal walls. Both populations are characterized by morphological and functional differences. Müller cells of the foveola do not support the activity of photoreceptors and neurons, but provide the structural stability of the foveal tissue and improve the light transmission through the tissue to the photoreceptors. This article gives overviews of the glia of the human retina and the structure and function of both Müller cell types in the fovea, and describes the contributions of astrocytes and Müller cells to the ontogenetic development of the fovea.

Autologous Retinal Transplant for Refractory Macular Holes: Multicenter International Collaborative Study Group

PURPOSE

To report the structural and functional outcomes of autologous neurosensory retinal transplant for closure of refractory large macular holes (MHs).

DESIGN

Multicenter, retrospective, consecutive case series.

PARTICIPANTS

A total of 41 eyes of 41 patients with a full-thickness MH refractory to prior vitrectomy with internal limiting membrane (ILM) peel and tamponade.

METHODS

All patients underwent pars plana vitrectomy, autologous neurosensory retinal transplant with gas, silicone oil tamponade, or short-term perfluoro-n-octane heavy-liquid tamponade. All patients had at least 6 months' follow-up.

MAIN OUTCOME MEASURES

Anatomic closure of MH, change in ellipsoid zone (EZ) and external limiting membrane (ELM) defect on OCT, visual acuity (VA) recovery, and surgical complications were analyzed.

RESULTS

Mean number of prior surgeries was 1.5±0.94 (range, 1-3), and patients were followed for a mean of 11.1±7.7 months (range, 6-36 months). Complete anatomic closure of MH by OCT was achieved in 36 of 41 eyes (87.8%). Mean corrected VA (logarithm of the minimum angle of resolution [logMAR]) improved (P = 0.03) from 1.11±0.66 (range, 0.48-3) to 1.03±0.51 (range, 0.1-2) at the last postoperative visit. The VA improved (≥0.3 logMAR units) in 15 eyes (36.6%), was stable in 17 eyes (41.5%), and worsened in 9 eyes (21.9%). Among eyes with anatomic closure, VA improved in 52.3% and worsened in 13.8%, whereas in those without closure, VA worsened in 40% and improved in none. Mean preoperative largest basal diameter was 1468.1±656.4 μm (range, 621-2600 μm), and mean inner-opening diameter was 825±422.5 μm (range, 336-1649 μm). Mean preoperative EZ defect was 1777.3±513.8 μm (range, 963-2808 μm), which decreased to 1370±556.9 μm (range, 288-2000 μm) at final follow-up (P = 0.007). Mean preoperative ELM was 1681.5±429 μm (range, 1172-2606 μm), which decreased to 1408.5±571.2 μm (range, 200-2000 μm) at final follow-up (P = 0.017). Major postoperative complications were retinal detachment (n = 1) and vitreous hemorrhage (n = 1). There were no cases of proliferative vitreoretinopathy, endophthalmitis, suprachoroidal hemorrhage, or choroidal neovascularization.

CONCLUSIONS

The autologous retinal transplant technique offers a high degree of anatomic success and proved safe in this initial experience for closure of refractory MHs.

Expression of Progenitor Cell Markers in the Glial-Like Cells of Epiretinal Membranes of Different Origins

Purpose

To investigate the expression of progenitor cell markers (Sox2, Nestin, and Pax2) in idiopathic epiretinal membranes (iERMs) and nonidiopathic epiretinal membranes (niERMs) in relation to glial cell marker expression.

Methods

ERMs were obtained from patients with iERMs and niERMs of different origins: proliferative diabetic retinopathy (PDR), proliferative vitreoretinopathy (PVR), and uveitis. The membranes were studied by flat-mount or sectional immunohistochemistry for expression of progenitor cell markers as well as glial (GFAP) and proliferation (Ki-67) markers.

Results

Cells in the ERMs express strong GFAP, with strong Pax2 expression in the cell nuclei. Some of the GFAP-positive glial cells in all epiretinal membrane types colocalized with Sox2, Pax2, and Nestin. NiERMs are much more cellular than iERMs. Glial cells are more densely packed in all analyzed niERMs, whereas glial cells with long branches are found in the internal limiting membrane parts and the iERMs, which appear to form a local network by their processes.

Conclusion

The GFAP-positive glial cells in ERMs are not pure glial cells, and some of them express progenitor cell markers, which indicate that these cells may have potential for self-renewal and differentiation into more glial or neuroglial type of cells.

Adult Stem Cells, Tools for Repairing the Retina

Purpose

Retinal degenerative diseases lead to the death of retinal neurons causing visual impairment and blindness. In lower order vertebrates, the retina and its surrounding tissue contain stem cell niches capable of regenerating damaged tissue. Here we examine these niches and review their capacity to be used as retinal stem/progenitor cells (RSC/RPCs) for retinal repair.

Recent Findings

Exogenous factors can control the in vitro activation of RSCs/PCs found in several niches within the adult eye including cells in the ciliary margin, the retinal pigment epithelium, iris pigment epithelium as well as the inducement of Müller and amacrine cells within the neural retina itself. Recently, factors have been identified for the activation of adult mammalian Müller cells to a RPC state in vivo.

Summary

Whereas cell transplantation still holds potential for retinal repair, activation of the dormant native regeneration process may lead to a more successful process including greater integration efficiency and proper synaptic targeting.

COMBINED AUTOLOGOUS TRANSPLANTATION OF NEUROSENSORY RETINA, RETINAL PIGMENT EPITHELIUM, AND CHOROID FREE GRAFTS

PURPOSE

To evaluate the feasibility and initial functional and anatomical outcomes of transplanting a full-thickness free graft of choroid and retinal pigment epithelium (RPE), along with neurosensory retina in advanced fibrosis and atrophy associated with end-stage exudative age-related macular degeneration with and without a concurrent refractory macular hole.

METHODS

During vitrectomy, an RPE-choroidal and neurosensory retinal free graft was harvested in nine eyes of nine patients. The RPE-choroidal and neurosensory retinal free graft was either placed subretinally (n = 5), intraretinally to cover the foveal area inside an iatrogenically induced macular hole over the RPE-choroidal graft (n = 3) or preretinally (n = 1) without a retinotomy wherein both free grafts were placed over the concurrent macular hole. Silicone oil endotamponade was used in all cases.

RESULTS

Mean follow-up was 7 ± 5.5 months (range 3-19). The mean preoperative visual acuity was ∼count fingers (logarithm of the minimum angle of resolution = 2.11, range 2-3), which improved to ∼20/800 (logarithm of the minimum angle of resolution 1.62 ± 0.48, range 0.7-2, P = 0.04). Vision was stable in 5 eyes (55.6%) and improved in 4 eyes (44.4%). Reading ability improved in 5 eyes (55.6%). Postoperative complications were graft atrophy (n = 1), epiretinal membrane (n = 1), and dislocation of neurosensory retina-choroid-RPE free graft (n = 1).

CONCLUSION

Combined autologous RPE-choroid and neurosensory retinal free graft is a potential surgical alternative in eyes with end-stage exudative age-related macular degeneration, including concurrent refractory macular hole.

Proliferative Cells Isolated from the Adult Human Peripheral Retina only Transiently Upregulate Key Retinal Markers upon Induced Differentiation

Purpose/Aim: The adult human retina has limited regenerative potential, and severe injury will result in permanent damage. Lower vertebrates handle retinal injury by activating neural stem cells (NSCs) in the ciliary marginal zone (CMZ). Müller glia-like cells expressing markers of NSCs are also present in the peripheral retina (PR) of the adult human eye, leading to the hypothesis that a CMZ-like zone might exists also in humans. In order to shed further light on this hypothesis we investigated the in vitro differentiation potential of proliferative cells isolated from the adult human PR towards a retinal phenotype.

MATERIALS AND METHODS

Proliferative cells were isolated from the peripheral retina of human eyes (n = 6) within 24 to 48 hours post mortem and further expanded for 2 or 3 passages before being differentiated for 1-3 weeks. Gene expression was analyzed by microarray and qRT-PCR analysis, while protein expression was identified by immunocytochemistry.

RESULTS

A high density of cells co-staining with markers for progenitor cells and Müller glia was found in situ in the PR. Cells isolated from this region and cultured adherently showed fibrillary processes and were positive for the immature marker Nestin and the glial marker GFAP, while a few co-expressed PAX6. After 7 days of differentiation, there was a transient upregulation of early and mature photoreceptor markers, including NRL, CRX, RHO and RCVRN, as well as the Müller cell and retinal pigmented epithelium (RPE) marker CRALBP, and the early RPE marker MITF. However, the expression of all these markers dropped from Day 14 and onwards.

CONCLUSIONS

Upon exposure of proliferating cells from the adult human PR to differentiating conditions in culture, there is a widespread change in morphology and gene expression, including the upregulation of key retinal markers. However, this upregulation is only transient and decreases after 14 days of differentiation.

The proteomic profile of a mouse model of proliferative vitreoretinopathy

Proliferative vitreoretinopathy (PVR) develops as a complication of retinal detachment surgery and represents a devastating condition leading to serious vision loss. A good animal model that permits extensive functional studies and drug testing is crucial in finding better therapeutic modalities for PVR. A previously established mouse model, using dispase injection, was analyzed from the proteomic point of view, examining global protein profile changes by 2D electrophoresis, image analysis and HPLC–tandem mass spectrometry‐based protein identification. The easy applicability of the mouse model was used to study the role of transglutaminase 2 (TG2) in PVR formation by proteomic examination of dispase‐induced TG2 knockout vitreous samples. Our data demonstrate that, despite the altered appearance of crystallin proteins, the lack of TG2 did not prevent the development of PVR.

Nonsteroid anti-inflammatory therapy suppresses the development of proliferative vitreoretinopathy more effectively than a steroid one

PURPOSE

This study proves the possibility of targeted use of the nonsteroidal anti-inflammatory drug lornoxicam to prevent the development of proliferative vitreoretinopathy (PVR). Triamcinolone acetonide (TA) was selected as a reference substance.

METHODS

Wistar rats (N = 400) were used. PVR was modeled by intravitreal injection of dispase or concanavalin A. Lornoxicam or TA intravitreal administration was performed 20 min later. On the second and the third day, drugs were administrated systemic. Enucleation was performed on the first, third, seventh and 42nd or 56th day of the experiment.

RESULTS

Pro-inflammatory substances led to the development of sub- and epiretinal membranes. Lornoxicam decreased the incidence of membrane formation by 43 and 31% in dispase and concanavalin models, respectively. Membranes, formed during its use, were smaller and contained less fibrotic components. At the end of the experiment, the thickness of retinal and choroidal layers among the animals which had received the therapy was the same as the thickness of the retina and choroid of intact rats. Lornoxicam administration normalized the cyclooxygenases (COXs) expression in the retina and the choroid at the early stages of the experiment. TA application was less effective in both models.

CONCLUSIONS

COXs blocking during the development of PVR, overwhelming inflammation in the eye and reducing its consequences, is proved to be a much more effective and safe influence than the suppression of the entire cascade of arachidonic acid metabolism. Lornoxicam did not only improve the condition of the retina and the choroid but also significantly reduced the frequency of membrane formation.

Current Trends about Inner Limiting Membrane Peeling in Surgery for Epiretinal Membranes

The inner limiting membrane (ILM) is the basement membrane of the Müller cells and can act as a scaffold for cellular proliferation in the pathophysiology of disorders affecting the vitreomacular interface. The atraumatic removal of the macular ILM has been proposed for treating various forms of tractional maculopathy in particular for macular pucker. In the last decade, the removal of ILM has become a routine practice in the surgery of the epiretinal membranes (ERMs), with good anatomical results. However many recent studies showed that ILM peeling is a procedure that can cause immediate traumatic effects and progressive modification on the underlying inner retinal layers. Moreover, it is unclear whether ILM peeling is helpful to improve vision after surgery for ERM. In this review, we describe the current understanding about ILM peeling and highlight the beneficial and adverse effects associated with this surgical procedure.

Long live the stem cell: the use of stem cells isolated from post mortem tissues for translational strategies

The "stem cell" has become arguably one of the most important biological tools in the arsenal of translational research directed at regeneration and repair. It remains to be seen whether every tissue has its own stem cell niche, although relatively recently a large amount of research has focused on isolating and characterizing tissue-specific stem cell populations, as well as those that are able to be directed to transdifferentiate into a variety of different lineages. Traditionally, stem cells are isolated from the viable tissue of embryonic, fetal, or adult living hosts; from "fresh" donated tissues that have been surgically or otherwise removed (biopsies), or obtained directly from tissues within minutes to several hours post mortem (PM). These human progenitor/stem cell sources remain potentially highly controversial, since they are accompanied by various still-unresolved ethical, social, moral and legal challenges. Due to the limited number of "live" donors, the small amount of material obtained from biopsies and difficulties during purification processes, harvesting from cadaveric material presents itself as an alternative strategy that could provide a hitherto untapped source of stem cells. However, PM stem cells are not without their own unique set of limitations including difficulty of obtaining samples, limited supply of material, variations in delay between death and sample collection, possible lack of medication history and suboptimal retrospective assignment of diagnostic and demographic data. This article is part of a Directed Issue entitled: Regenerative Medicine: The challenge of translation.

Reprint of: the ciliary marginal zone (CMZ) in development and regeneration of the vertebrate eye

The ciliary marginal zone (CMZ) is a circumferential ring of cells found at the extreme periphery of the maturing and mature neural retina that consists of retinal stem and progenitor cells. It functions to add retinal neurons to the periphery of the neural retina in larval and adult fish, larval frogs, and birds. Additionally, the CMZ may contribute to regeneration of the damaged retina in frogs and fish. In mammals, cells from the ciliary epithelium can be induced to express retinal stem cell-like characteristics in culture but may not comprise a classically defined CMZ.

Is neutralizing vitreal growth factors a viable strategy to prevent proliferative vitreoretinopathy?

Proliferative vitreoretinopathy (PVR) is a blinding disorder that occurs in eyes with rhegmatogenous retinal detachment and in eyes that have recently undergone retinal detachment surgery. There are presently no treatment strategies to reduce the risk of developing PVR in eyes with retinal detachment, and surgical intervention is the only option for eyes with retinal detachment and established PVR. Given the poor visual outcome associated with the surgical treatment of PVR, considerable work has been done to identify pharmacologic agents that could antagonize the PVR process. Intensive efforts to identify molecular determinants of PVR implicate vitreal growth factors. A surprise that emerged in the course of testing the 'growth factor hypothesis' of PVR was the existence of a functional relationship amongst growth factors that engage platelet-derived growth factor (PDGF) receptor α (PDGFRα), a receptor tyrosine kinase that is key to pathogenesis of experimental PVR. Vascular endothelial cell growth factor A (VEGF), which is best known for its ability to activate VEGF receptors (VEGFRs) and induce permeability and/or angiogenesis, enables activation of PDGFRα by a wide spectrum of vitreal growth factors outside of the PDGF family (non-PDGFs) in a way that triggers signaling events that potently enhance the viability of cells displaced into vitreous. Targeting these growth factors or signaling events effectively neutralizes the bioactivity of PVR vitreous and prevents PVR in a number of preclinical models. In this review, we discuss recent conceptual advances in understanding the role of growth factors in PVR, and consider the tangible treatment strategies for clinical application.

Does the adult human ciliary body epithelium contain "true" retinal stem cells?

Recent reports of retinal stem cells being present in several locations of the adult eye have sparked great hopes that they may be used to treat the millions of people worldwide who suffer from blindness as a result of retinal disease or injury. A population of proliferative cells derived from the ciliary body epithelium (CE) has been considered one of the prime stem cell candidates, and as such they have received much attention in recent years. However, the true nature of these cells in the adult human eye has still not been fully elucidated, and the stem cell claim has become increasingly controversial in light of new and conflicting reports. In this paper, we will try to answer the question of whether the available evidence is strong enough for the research community to conclude that the adult human CE indeed harbors stem cells.

Proliferative vitreoretinopathy after eye injuries: an overexpression of growth factors and cytokines leading to a retinal keloid

Eye injury is a significant disabling worldwide health problem. Proliferative Vitreoretinopathy (PVR) is a common complication that develops in up to 40–60% of patients with an open-globe injury. Our knowledge about the pathogenesis of PVR has improved in the last decades. It seems that the introduction of immune cells into the vitreous, like in penetrating ocular trauma, triggers the production of growth factors and cytokines that come in contact with intra-retinal cells, like Müller cells and RPE cells. Growth factors and cytokines drive the cellular responses leading to PVR's development. Knowledge of the pathobiological and pathophysiological mechanisms involved in posttraumatic PVR is increasing the possibilities of management, and it is hoped that in the future our treatment strategies will evolve, in particular adopting a multidrug approach, and become even more effective in vision recovery. This paper reviews the current literature and clinical trial data on the pathogenesis of PVR and its correlation with ocular trauma and describes the biochemical/molecular events that will be fundamental for the development of novel treatment strategies. This literature review included PubMed articles published from 1979 through 2013. Only studies written in English were included.

New functions of Müller cells

Müller cells, the major type of glial cells in the retina, are responsible for the homeostatic and metabolic support of retinal neurons. By mediating transcellular ion, water, and bicarbonate transport, Müller cells control the composition of the extracellular space fluid. Müller cells provide trophic and anti-oxidative support of photoreceptors and neurons and regulate the tightness of the blood-retinal barrier. By the uptake of glutamate, Müller cells are more directly involved in the regulation of the synaptic activity in the inner retina. This review gives a survey of recently discoved new functions of Müller cells. Müller cells are living optical fibers that guide light through the inner retinal tissue. Thereby they enhance the signal/noise ratio by minimizing intraretinal light scattering and conserve the spatial distribution of light patterns in the propagating image. Müller cells act as soft, compliant embedding for neurons, protecting them in case of mechanical trauma, and also as soft substrate required for neurite growth and neuronal plasticity. Müller cells release neuroactive signaling molecules which modulate neuronal activity, are implicated in the mediation of neurovascular coupling, and mediate the homeostasis of the extracellular space volume under hypoosmotic conditions which are a characteristic of intense neuronal activity. Under pathological conditions, a subset of Müller cells may differentiate to neural progenitor/stem cells which regenerate lost photoreceptors and neurons. Increasing knowledge of Müller cell function and responses in the normal and diseased retina will have great impact for the development of new therapeutic approaches for retinal diseases.

Retinal Pigment Epithelium and Müller Progenitor Cell Interaction Increase Müller Progenitor Cell Expression of PDGFRα and Ability to Induce Proliferative Vitreoretinopathy in a Rabbit Model

Purpose. Proliferative vitreoretinopathy (PVR) is a complication of retinal detachment characterized by redetachment of the retina as a result of membrane formation and contraction. A variety of retinal cells, including retinal pigment epithelial (RPE) and Müller glia, and growth factors may be responsible. Platelet-derived growth factor receptor alpha (PDGFRα) is found in large quantities in PVR membranes, and is intrinsic to the development of PVR in rabbit models. This study explores the expression of PDGFR in cocultures of RPE and Müller cells over time to examine how these two cell types may collaborate in the development of PVR. We also examine how changes in PDGFRα expression alter Müller cell pathogenicity. Methods. Human MIO-M1 Müller progenitor (MPC) and ARPE19 cells were studied in a transmembrane coculture system. Immunocytochemistry and Western blot were used to look at PDGFRα, PDGFRβ, and GFAP expression. A transfected MPC line cell line expressing the PDGFRα (MIO-M1α) was generated, and tested in a rabbit model for its ability to induce PVR. Results. The expression of PDGFRα and PDGFRβ was upregulated in MIO-M1 MPCs cocultured with ARPE19 cells; GFAP was slightly decreased. Increased expression of PDGFRα in the MIO-M1 cell line resulted in increased pathogenicity and enhanced ability to induce PVR in a rabbit model. Conclusions. Müller and RPE cell interaction can lead to upregulation of PDGFRα and increased Müller cell pathogenicity. Müller cells may play a more active role than previously thought in the development of PVR membranes, particularly when stimulated by an RPE-cell-rich environment. Additional studies of human samples and in animal models are warranted.