Proliferative vitreoretinopathy: pathobiology and therapeutic targets

Comparison of treatment outcomes of 360° intraoperative laser retinopexy and focal laser retinopexy with pars plans vitrectomy in patients with primary rhegmatogenous retinal detachment

BACKGROUND

This study was to compare the outcomes of 360° intra-operative laser retinopexy (ILR) and focal laser retinopexy in treating patients with pars plans vitrectomy (PPV) for primary rhegmatogenous retinal detachment (RRD). To identify other potential risk factors for retinal re-detachment after primary PPV.

METHODS

This was a retrospective cohort study. Three hundred and forty-four consecutive cases of primary rhegmatogenous retinal detachment treated with PPV were included between July 2013 and July 2018. Clinical characteristics and surgical outcomes were compared between focal laser retinopexy and additional 360° intra-operative laser retinopexy groups. Both univariate and multiple variable analysis were used to identify potential risk factors for retinal re-detachment.

RESULTS

Median follow-up was 6.2 months (Q1, Q3:2.0, 17.2). As estimated with survival analysis, the 360º ILR group had the incidence of 9.74% and focal laser 19.54% at 6 months postoperatively. At 12 months postoperatively the difference was 10.78% vs. 25.21%. The difference in survival rates was significant (p = 0.0021). In multivariate Cox regression, the risk factors for retinal re-detachment were without additional 360° ILR, diabetes and macula off before the primary surgery (relatively OR = 0.456, 95%-CI [0.245-0.848], p < 0.05; OR = 2.301, 95% CI [1.130-4.687], p < 0.05; OR = 2.243, 95% CI [1.212-4.149], p < 0.05).

CONCLUSION

Additional 360° ILR group had a significantly lower rate of retinal re-detachment when compared with focal laser retinopexy group. Our study also elucidated that diabetes and macular off before the primary surgery might also be the potential risk factors for higher rate of retinal re-detachment outcome.

TRIAL REGISTRATION

This was a retrospective cohort study.

TGF-β Superfamily Signaling in the Eye: Implications for Ocular Pathologies

The TGF-β signaling pathway plays a crucial role in several key aspects of development and tissue homeostasis. TGF-β ligands and their mediators have been shown to be important regulators of ocular physiology and their dysregulation has been described in several eye pathologies. TGF-β signaling participates in regulating several key developmental processes in the eye, including angiogenesis and neurogenesis. Inadequate TGF-β signaling has been associated with defective angiogenesis, vascular barrier function, unfavorable inflammatory responses, and tissue fibrosis. In addition, experimental models of corneal neovascularization, diabetic retinopathy, proliferative vitreoretinopathy, glaucoma, or corneal injury suggest that aberrant TGF-β signaling may contribute to the pathological features of these conditions, showing the potential of modulating TGF-β signaling to treat eye diseases. This review highlights the key roles of TGF-β family members in ocular physiology and in eye diseases, and reviews approaches targeting the TGF-β signaling as potential treatment options.

Intravitreal Tissue Plasminogen Activator Injection for the Treatment of Proliferative Vitreoretinopathy in a Rabbit Model

INTRODUCTION

The purpose of this study was to evaluate the effect of intravitreal injection of tissue plasminogen activator (tPA) on proliferative vitreoretinopathy (PVR).

METHODS

PVR was induced in a rabbit model by intraocular injection of dispase (0.05 U/0.1 mL). Progression of PVR was followed by indirect ophthalmic examination. Following 6 weeks, 5 animals received intravitreal injection of 25 µg/0.1 mL tPA and four were injected with balanced salt solution (BSS). Animals were euthanized at 48 h following tPA/BSS injection, and eyes were enucleated for histological evaluation and staining with α-smooth muscle actin (αSMA) and Sirius Red.

RESULTS

Following tPA injection, one eye had a reduction in PVR from grade 2 to 1 and three eyes remained stable. Following BSS, PVR grade was unchanged in three eyes. In one eye in each group, the severity of PVR could not be assessed due to limited view. Staining with αSMA showed reduced presence of fibroblasts in eyes injected with tPA compared with those injected with BSS. Collagen type I and III, demonstrated by Sirius Red staining, was reduced in the tPA group in comparison with controls.

CONCLUSION

Our results suggest that intravitreally injected tPA may show an inhibitory effect on PVR progression. Further exploration in clinical trials is desired.

Role of Curcumin in Retinal Diseases-A review

PURPOSE

To review the role of curcumin in retinal diseases, COVID era, modification of the molecule to improve bioavailability and its future scope.

METHODS

PubMed and MEDLINE searches were pertaining to curcumin, properties of curcumin, curcumin in retinal diseases, curcumin in diabetic retinopathy, curcumin in age-related macular degeneration, curcumin in retinal and choroidal diseases, curcumin in retinitis pigmentosa, curcumin in retinal ischemia reperfusion injury, curcumin in proliferative vitreoretinopathy and curcumin in current COVID era.

RESULTS

In experimental models, curcumin showed its pleiotropic effects in retinal diseases like diabetic retinopathy by increasing anti-oxidant enzymes, upregulating HO-1, nrf2 and reducing or inhibiting inflammatory mediators, growth factors and by inhibiting proliferation and migration of retinal endothelial cells in a dose-dependent manner in HRPC, HREC and ARPE-19 cells. In age-related macular degeneration, curcumin acts by reducing ROS and inhibiting apoptosis inducing proteins and cellular inflammatory genes and upregulating HO-1, thioredoxin and NQO1. In retinitis pigmentosa, curcumin has been shown to delay structural defects of P23H gene in P23H-rhodopsin transgenic rats. In proliferative vitreoretinopathy, curcumin inhibited the action of EGF in a dose- and time-dependent manner. In retinal ischemia reperfusion injury, curcumin downregulates IL-17, IL-23, NF_KB, STAT-3, MCP-1 and JNK. In retinoblastoma, curcumin inhibits proliferation, migration and apoptosis of RBY79 and SO-RB50. Curcumin has already proven its efficacy in inhibiting viral replication, coagulation and cytokine storm in COVID era.

CONCLUSION

Curcumin is an easily available spice used traditionally in Indian cooking. The benefits of curcumin are manifold, and large randomized controlled trials are required to study its effects not only in treating retinal diseases in humans but in their prevention too.

Systemic Curcumin-Human Serum Albumin in Proliferative Vitreoretinal Retinopathy: A Pilot Study

Objectives The purpose of this study is to compare the risks of novel postoperative curcumin infusion in patients with increased proliferative vitreoretinal retinopathy (PVR) after retinal detachment with steroid infusion or no treatment. Methods This was a prospective, non-randomized pilot study of 15 eyes of 15 patients (mean age 68 ± 7 years) with retinal detachment, macula off, and flare >15 pc/ms. Postoperatively, the patients received either curcumin-HSA (human serum albumin) infusion (C, n=5), prednisolone infusion (P, n=5), or no therapy (N, n=5) for three days. The outcome measures included postoperative PVR rate, the number of vitreoretinal surgeries (VRS) required, epiretinal membrane development, and visual acuity (VA).  Results All patients had a preoperative VA of hand movements, macula-off detachment situation, and two quadrants rhegmatogenous retinal detachment. Patients underwent VRS at a mean time of 5.6 ± 1.5 (C), 4.9 ± 2.0 (P), 4.7 ± 1.2 (N) days after first recognized symptoms. Postoperative PVR developed just in one eye (P) after 16 days and required VRS due to PVR retinal detachment. The remaining 14 patients of group C and N did not develop PVR. BCVA improved six months post surgery to 0.56 ± 0.31 (P), 0.53 ± 0.19 (D), 0.53 ± 0.17 (N) logMAR. There were no side effects nor complications related to the postoperative infusions.  Conclusions In this pilot study, we demonstrated that a postoperative application of curcumin infusion is a safe option in patients with an increased risk of PVR. Whether or not PVR can be reduced by curcumin infusion would require to be investigated in larger, randomized clinical trials.

LncRNA NEAT1 Recruits SFPQ to Regulate MITF Splicing and Control RPE Cell Proliferation

Purpose

Retinal pigment epithelium (RPE) cell proliferation is precisely regulated to maintain retinal homoeostasis. Microphthalmia-associated transcription factor (MITF), a critical transcription factor in RPE cells, has two alternatively spliced isoforms: (+)MITF and (-)MITF. Previous work has shown that (-)MITF but not (+)MITF inhibits RPE cell proliferation. This study aims to investigate the role of long non-coding RNA (lncRNA) nuclear-enriched abundant transcript 1 (NEAT1) in regulating MITF splicing and hence proliferation of RPE cells.

Methods

Mouse RPE, primary cultured mouse RPE cells, and different proliferative human embryonic stem cell (hESC)-RPE cells were used to evaluate the expression of (+)MITF, (-)MITF, and NEAT1 by reverse-transcription PCR (RT-PCR) or quantitative RT-PCR. NEAT1 was knocked down using specific small interfering RNAs (siRNAs). Splicing factor proline- and glutamine-rich (SFPQ) was overexpressed with the use of lentivirus infection. Cell proliferation was analyzed by cell number counting and Ki67 immunostaining. RNA immunoprecipitation (RIP) was used to analyze the co-binding between the SFPQ and MITF or NEAT1.

Results

NEAT1 was highly expressed in proliferative RPE cells, which had low expression of (-)MITF. Knockdown of NEAT1 in RPE cells switched the MITF splicing pattern to produce higher levels of (-)MITF and inhibited cell proliferation. Mechanistically, NEAT1 recruited SFPQ to bind directly with MITF mRNA to regulate its alternative splicing. Overexpression of SFPQ in ARPE-19 cells enhanced the binding enrichment of SFPQ to MITF and increased the splicing efficiency of (+)MITF. The binding affinity between SFPQ and MITF was decreased after NEAT1 knockdown.

Conclusions

NEAT1 acts as a scaffold to recruit SFPQ to MITF mRNA and promote its binding affinity, which plays an important role in regulating the alternative splicing of MITF and RPE cell proliferation.

Intravitreal Methotrexate

Intravitreal methotrexate (MTX) has been proven to be an effective treatment for various intraocular diseases. In this article, a comprehensive review was performed on intravitreal applications of methotrexate. Different aspects of the administration of intravitreal MTX for various clinical conditions such as intraocular tumors, proliferative vitreoretinopathy, diabetic retinopathy, age-related macular degeneration, and uveitis were reviewed and the adverse effects of intravitreal injection of MTX were discussed. The most common indications are intraocular lymphoma and uveitis. Other applications remain challenging and more studies are needed to establish the role of intravitreal MTX in the management of ocular diseases.

Corneal Toxicity of Intravitreal Methotrexate Used for the Treatment of Proliferative Vitreoretinopathy in Silicone Oil-Filled Eyes: A Case Series

PURPOSE

The purpose of this study was to evaluate the corneal toxicity of intravitreal methotrexate used for the prevention of proliferative vitreoretinopathy (PVR).

METHODS

In this retrospective case series, eyes with recurrent retinal detachment secondary to PVR were treated with intravitreal injections of 400 μg methotrexate at an average frequency of every 7 days after vitrectomy with silicone oil tamponade. Corneas were examined for corneal epitheliopathy by slit-lamp biomicroscopy before each injection.

RESULTS

Thirteen eyes of 12 patients were reviewed. All had a history of recurrent retinal detachment secondary to PVR treated with vitrectomy and silicone oil. The median age was 35 years (range: 9-83). Four patients (33%) were female. The median follow-up duration was 8 weeks (range: 5-10). The median BCVA (logMAR notation) was 2.00 preoperatively, 2.00 at 1 month postoperatively, and 2.00 at the most recent follow-up (P = 0.969). Ten eyes (77%) were pseudophakic. Nine eyes (69%) had a preexisting ocular comorbidity. The median number of injections was 8 (range: 5-10). The median interval time between each injection was 7.0 days (range: 5.8-10.5), and the median follow-up period beyond last injection was 16 weeks (range: 8-28). Two eyes (15.4%) developed mild corneal epitheliopathy during the course of the treatment.

CONCLUSIONS

Most eyes in this small series tolerated methotrexate injections without corneal toxicity. In eyes that developed epitheliopathy, the findings were mild and not treatment-limiting.

Inflammatory mediators of proliferative vitreoretinopathy: hypothesis and review

Purpose

To review the role of inflammatory mediators in proliferative vitreoretinopathy (PVR) development and the current treatment for PVR prevention.

Methods

A PubMed search was carried out using these keywords “PVR,” “inflammatory mediators,” “growth factors,” “cytokines” and “treatment.” Studies regarding inflammatory mediators and PVR therapy were included and published up to December 2019.

Results

Inflammatory mediators, namely growth factors and cytokines, have been implicated in the occurrence and development of PVR. Among various inflammatory mediators, transforming growth factor-β, platelet-derived growth factor, interleukin-6, interleukin-8 and tumor necrosis factor-α are considered to be particularly important. In this review, we focus on the hypothesis that growth factors and cytokines are involved in the development of PVR, and current treatment for the prevention of PVR.

Conclusion

We support the hypothesis that growth factors and cytokines may participate in the complex process of PVR development. More importantly, the identification of inflammatory mediators provides novel and efficacious therapeutic targets for the treatment of PVR.

Blockade of MDM2 with inactive Cas9 prevents epithelial to mesenchymal transition in retinal pigment epithelial cells

Epithelial to mesenchymal transition (EMT) plays an important role in the pathogenesis of proliferative vitreoretinopathy (PVR). We aimed to demonstrate the role of mouse double minute 2 (MDM2) in transforming growth factor-beta 2 (TGF-β2)-induced EMT in human retinal pigment epithelial cells (RPEs). Immunofluorescence was used to assess MDM2 expression in epiretinal membranes (ERMs) from patients with PVR. A single guide (sg)RNA targeting the second promoter of MDM2 was cloned into a mutant lentiviral Clustered Regularly Interspaced Short Palindromic Repeats (lentiCRISPR) v2 (D10A and H840A) vector for expressing nuclease dead Cas9 (dCas9)/MDM2-sgRNA in RPEs. In addition, MDM2-sgRNA was also cloned into a pLV-sgRNA-dCas9-Kruppel associated box (KRAB) vector for expressing dCas9 fused with a transcriptional repressor KRAB/MDM2-sgRNA. TGF-β2-induced expression of MDM2 and EMT biomarkers were assessed by quantitative polymerase chain reaction (q-PCR), western blot, or immunofluorescence. Wound-healing and proliferation assays were used to evaluate the role of MDM2 in TGF-β2-induced responses in RPEs. As a result, we found that MDM2 was expressed obviously in ERMs, and that TGF-β2-induced expression of MDM2 and EMT biomarkers Fibronectin, N-cadherin and Vimentin in RPEs. Importantly, we discovered that the dCas9/MDM2-sgRNA blocked TGF-β2-induced expression of MDM2 and the EMT biomarkers without affecting their basal expression, whereas the dCas9-KRAB/MDM2-sgRNA suppressed basal MDM2 expression in RPEs. These cells could not be maintained continuously because their viability was greatly reduced. Next, we found that Nutlin-3, a small molecule blocking the interaction of MDM2 with p53, inhibited TGF-β2-induced expression of Fibronectin and N-cadherin but not Vimentin in RPEs, indicating that MDM2 functions in both p53-dependent and -independent pathways. Finally, our experimental data demonstrated that dCas9/MDM2-sgRNA suppressed TGF-β2-dependent cell proliferation and migration without disturbing the unstimulated basal activity. In conclusion, the CRISPR/dCas9 capability for blocking TGF-β2-induced expression of MDM2 and EMT biomarkers can be exploited for a therapeutic approach to PVR.

Intra-silicone Oil Injection of Methotrexate in Retinal Reattachment Surgery for Proliferative Vitreoretinopathy

Purpose: To evaluate the role of intrasilicone oil injection of methotrexate (MTX) at the end of vitrectomy surgery for rhegmatogenous retinal detachment (RRD) associated with proliferative vitreoretinopathy (PVR).Methods: In this prospective comparative study, pars plana vitrectomy and retinal reattachment were performed for eyes with RRD with grade C PVR. In the MTX group, 250 µg MTX was injected into the silicone oil at the end of surgery. The rate of retinal redetachment associated with PVR was assessed.Results: In total, 44 eyes of 44 patients (22 in the MTX group and 22 controls) were included. Baseline characteristics were similar between the two groups. Retinal redetachment occurred in one eye (4.5%) in the MTX group and five eyes (22.7%) in the control group (p = 0.18). The change in visual acuity was similar between the two groups at final visit (p = 0.15).Conclusion: The rate of redetachment associated with PVR was lower after intrasilicone injection of MTX at the end of vitrectomy for RRD with severe PVR compared to control group; however, the difference was not statistically significant.

Comparative transcriptomic analysis reveals adriamycin-induced apoptosis via p53 signaling pathway in retinal pigment epithelial cells

OBJECTIVE

This paper applied a transcriptomic approach to investigate the mechanisms of adriamycin (ADR) in treating proliferative vitreoretinopathy (PVR) using ARPE-19 cells.

METHODS

The growth inhibitory effects of ADR on ARPE-19 cells were assessed by sulforhodamine B (SRB) assay and propidium iodide (PI) staining using flow cytometry. The differentially expressed genes between ADR-treated ARPE-19 cells and normal ARPE-19 cells and the signaling pathways involved were investigated by microarray analysis. Mitochondrial function was detected by JC-1 staining using flow cytometry and the Bcl-2/Bax protein family. The phosphorylated histone H2AX (γ-H2AX), phosphorylated checkpoint kinase 1 (p-CHK1), and phosphorylated checkpoint kinase 2 (p-CHK2) were assessed to detect DNA damage and repair.

RESULTS

ADR could significantly inhibit ARPE-19 cell proliferation and induce caspase-dependent apoptosis in vitro. In total, 4479 differentially expressed genes were found, and gene ontology items and the p53 signaling pathway were enriched. A protein-protein interaction analysis indicated that the TP53 protein molecules regulated by ADR were related to DNA damage and oxidative stress. ADR reduced mitochondrial membrane potential and the Bcl-2/Bax ratio. p53-knockdown restored the activation of c-caspase-3 activity induced by ADR by regulating Bax expression, and it inhibited ADR-induced ARPE-19 cell apoptosis. Finally, the levels of the γ-H2AX, p-CHK1, and p-CHK2 proteins were up-regulated after ADR exposure.

CONCLUSIONS

The mechanism of ARPE-19 cell death induced by ADR may be caspase-dependent apoptosis, and it may be regulated by the p53-dependent mitochondrial dysfunction, activating the p53 signaling pathway through DNA damage.

Autophagy resists EMT process to maintain retinal pigment epithelium homeostasis

Proliferative vitreoretinopathy (PVR) is the most serious fibrous complication that causes vision loss after intraocular surgery, and there is currently no effective treatment in clinical. Autophagy is an important cell biological mechanism in maintaining the homeostasis of tissues and cells, resisting the process of EMT. However, it is still unclear whether autophagy could resist intraocular fibrosis and prevent PVR progression. In this study, we investigated the expression of mesenchymal biomarkers in autophagy deficiency cells and found these proteins were increased. The mesenchymal protein transcription factor Twist can bind to autophagy related protein p62 and promote the degradation of Twist, which reduced the expression of mesenchymal markers. By constructing an EMT model of retinal pigment epithelial (RPE) cells in vitro, we found that autophagy was activated in the EMT process of RPE cells. Moreover, in autophagy deficient RPE cell line via knockdown autophagy related protein 7 (Atg7), the expression of epithelial marker claudin-1 was suppressed and the mesenchymal markers were increased, accompanied by an increase in cell migration and contractility. Importantly, RPE epithelial properties can be maintained by promoting autophagy and effectively reversing TFG-β2-induced RPE fibrosis. These observations reveal that autophagy may be an effective way to treat PVR.

Proliferative Vitreoretinopathy: A Review

Proliferative vitreoretinopathy (PVR) is the most common cause for failure of rhegmatogenous retinal detachment repair and is characterized by the growth and contraction of cellular membranes within the vitreous cavity and on both sides of the retinal surface as well as intraretinal fibrosis. Currently, PVR is thought to be an abnormal wound healing response that is primarily driven by inflammatory, retinal, and RPE cells. At this time, surgery is the only management option for PVR as there is no proven pharmacologic agent for the treatment or prevention of PVR. Laboratory research to better understand PVR pathophysiology and clinical trials of various agents to prevent PVR formation are ongoing.

Vitrectomy with scleral buckling versus with inferior retinectomy in treating primary rhegmatogenous retinal detachment with PVR and inferior breaks

PURPOSE

To evaluate anatomic and functional outcomes of patients treated with pars plana vitrectomy (PPV) with scleral buckling versus PPV with inferior retinectomy for treatment of cases of primary rhegmatogenous retinal detachment (RRD) associated with proliferative vitreoretinopathy (PVR) and inferior retinal breaks.

METHODS

Retrospective, comparative, interventional, single-center study. Fifty-one eyes of fifty-one patients with primary RRD associated with inferior breaks and PVR grade C1 or more were reviewed over 3 years. Twenty-one eyes underwent PPV with encircling band 360° and thirty eyes underwent PPV with primary inferior retinectomy. The primary outcome was final anatomic success. Secondary outcomes included change in visual acuity, primary anatomical success, the mean number of operations, and incidence of postoperative complications.

RESULTS

Primary anatomical success of 85.7% was achieved in buckle group compared to 83.3% in retinectomy group (p = 0.82). Mean duration of follow-up and mean number of operations was 9.8 ± 2.26 and 9.97 ± 2.44 months; 1.24 ± 0.62 and 1.3 ± 0.75 in buckle group and retinectomy group, respectively, achieving final anatomical success of 95.2% for the buckle group and 90% for the retinectomy group with no statistical significant difference (p = 0.49). Although visual acuity (logMAR) was better in the buckle group in the 1st month, it became nearly equal thereafter during the follow-up period (p = 0.5).

CONCLUSION

Similar anatomical and functional outcomes were achieved by combining PPV with scleral buckle or inferior retinectomy for treatment of primary RRD with PVR and inferior breaks.

Acquired Resilience: An Evolved System of Tissue Protection in Mammals

This review brings together observations on the stress-induced regulation of resilience mechanisms in body tissues. It is argued that the stresses that induce tissue resilience in mammals arise from everyday sources: sunlight, food, lack of food, hypoxia and physical stresses. At low levels, these stresses induce an organised protective response in probably all tissues; and, at some higher level, cause tissue destruction. This pattern of response to stress is well known to toxicologists, who have termed it hormesis. The phenotypes of resilience are diverse and reports of stress-induced resilience are to be found in journals of neuroscience, sports medicine, cancer, healthy ageing, dementia, parkinsonism, ophthalmology and more. This diversity makes the proposing of a general concept of induced resilience a significant task, which this review attempts. We suggest that a system of stress-induced tissue resilience has evolved to enhance the survival of animals. By analogy with acquired immunity, we term this system 'acquired resilience'. Evidence is reviewed that acquired resilience, like acquired immunity, fades with age. This fading is, we suggest, a major component of ageing. Understanding of acquired resilience may, we argue, open pathways for the maintenance of good health in the later decades of human life.

Periostin in vitreoretinal diseases

Proliferative vitreoretinal diseases such as diabetic retinopathy, proliferative vitreoretinopathy (PVR), and age-related macular degeneration are a leading cause of decreased vision and blindness in developed countries. In these diseases, retinal fibro(vascular) membrane (FVM) formation above and beneath the retina plays an important role. Gene expression profiling of human FVMs revealed significant upregulation of periostin. Subsequent analyses demonstrated increased periostin expression in the vitreous of patients with both proliferative diabetic retinopathy and PVR. Immunohistochemical analysis showed co-localization of periostin with α-SMA and M2 macrophage markers in FVMs. In vitro, periostin blockade inhibited migration and adhesion induced by PVR vitreous and transforming growth factor-β2 (TGF-β2). In vivo, a novel single-stranded RNAi agent targeting periostin showed the inhibitory effect on experimental retinal and choroidal FVM formation without affecting the viability of retinal cells. These results indicated that periostin is a pivotal molecule for FVM formation and a promising therapeutic target for these proliferative vitreoretinal diseases.

Evaluation of the Effect of Everolimus on Retinal Pigment Epithelial Cells and Experimental Proliferative Vitreoretinopathy

PURPOSE

Failure of retinal detachment surgery is most commonly due to the development of proliferative vitreoretinopathy (PVR). Everolimus is an inhibitor of mammalian target of rapamycin (mTOR), and is available as oral tablets. In this study, we investigated the effect of everolimus on retinal pigment epithelial cells and modification of the severity of experimental PVR.

METHODS

In our in vitro studies, primary culture of retinal pigment epithelium (RPE) cells was obtained from pigmented Rex rabbits. Cell proliferation was assayed with the tetrazolium dye cytotoxicity test, and cell migration assay was performed in 24-well transwell units with 8-μm filters. In the in vivo study, pigmented Rex rabbits weighing between 2 and 2.5 kg were used. Each rabbit eye underwent gas compression; one week later, 5 × 10⁴ RPE cells were injected into the vitreous cavity to induce PVR, and each eye was graded with indirect ophthalmoscopy on days 1, 3, 7, 14, 21, and 28. The rabbits were administered everolimus (0.5 mg/day orally) from the day of PVR induction. Total proteins extracted from RPE cells and dissected retinal samples were processed for Western blotting analysis of mTOR and ribosomal protein S6 (RPS6).

RESULTS

The in vitro studies showed that everolimus significantly inhibited the proliferation of RPE cells at 0.1 μg/ml; additionally, at 10 μg/ml, it suppressed the migration of RPE cells and significantly suppressed the expression of mTOR and RPS6 in RPE cells. The in vivo study did not show any benefit of oral everolimus (0.5 mg/day) in suppressing experimental PVR. Thus, everolimus significantly suppressed the expression of mTOR and RPS6 in PVR.

CONCLUSIONS

Everolimus suppressed the proliferation and migration of RPE cells in vitro. Oral everolimus (0.5 mg/day) suppressed the expression of mTOR and RPS6 in the retina, but showed no effect in suppressing experimental PVR.

Regulation of cell proliferation in the retinal pigment epithelium: Differential regulation of the death-associated protein like-1 DAPL1 by alternative MITF splice forms

Vertebrate eye development and homoeostasis critically depend on the regulation of proliferation of cells forming the retinal pigment epithelium (RPE). Previous results indicated that the death-associated protein like-1 DAPL1 cell autonomously suppresses RPE proliferation in vivo and in vitro. Here, we show in human RPE cell lines that the pigment cell transcription factor MITF regulates RPE cell proliferation by upregulating DAPL1 expression. DAPL1 regulation by MITF is, however, mediated predominantly by (-) MITF, one of two alternative splice isoforms of MITF that lacks six residues located upstream of the DNA-binding basic domain. Furthermore, we find that the regulation of DAPL1 by MITF is indirect in that (-) MITF stimulates the transcription of Musashi homolog-2 (MSI2), which negatively regulates the processing of the anti-DAPL1 microRNA miR-7. Our results provide molecular insights into the regulation of RPE cell proliferation and quiescence and may help us understand the mechanisms of normal RPE maintenance and of eye diseases associated with either RPE hyperproliferation or the lack of regenerative proliferation.

DAPL1, a susceptibility locus for age-related macular degeneration, acts as a novel suppressor of cell proliferation in the retinal pigment epithelium

The retinal pigment epithelium (RPE) forms a monolayer at the back of the vertebrate eye and is fundamental to retinal function and homoeostasis. During early development, RPE cells undergo rapid proliferation, but in the adult, they remain normally nonproliferative throughout life. Nevertheless, under pathological conditions such as in proliferative vitreoretinopathy or after retinal ablation, mature RPE cells can re-enter the cell cycle and form nodules or multiple cell layers. Here we show that Dapl1, whose human homolog represents a susceptibility locus for age-related macular degeneration (AMD), is highly up-regulated in quiescent but not proliferating RPE cells and that experimental overexpression of DAPL1 in proliferating RPE cells inhibits their proliferation. Consistent with this observation, the percent of Ki67-positive cells is significantly higher in E11.5 Dapl1 knockout mouse embryos compared to age-matched controls. In adult Dapl1-/- mice, which survive without showing any overt pathology, RPE overgrowth leads to multiple cell layers and/or cellular nodules. The antiproliferative effect of DAPL1 is associated with an increase in CDKN1A protein levels. Reduction of CDKN1A by siRNA in DAPL1-overexpressing RPE cells in vitro partially restores cell proliferation. Hence, we show that DAPL1 is a novel regulator of RPE cell proliferation that is important for the maintenance of the RPE as a monolayer. The findings suggest that DAPL1 dysregulation may be involved in abnormal RPE-related proliferative diseases and corresponding retinal dysfunctions in humans.

The T-Box Transcription Factor TBX2 Regulates Cell Proliferation in the Retinal Pigment Epithelium

PURPOSE

Vertebrate eye development and function critically depend on the regulation of proliferation of retinal pigment epithelium (RPE) cells. Hence, a thorough analysis of the molecular parameters controlling RPE cell proliferation is crucial for our understanding of the physiology of this cell type both in health and in disease. The T-box transcription factor TBX2 is an important cell cycle regulator in development and oncogenesis, but its specific role in RPE cell proliferation is far from clear. The purpose of the present study is to investigate whether TBX2 plays any role in regulating RPE cell proliferation.

MATERIALS AND METHODS

The expression of TBX2 in RPE cells was analyzed in wildtype mice and ARPE-19 cells by co-staining for RPE-specific markers and cell proliferation. In vitro, the role of TBX2 was studied by manipulating its levels using RNAi and analyzing the effects on DNA synthesis and cell growth and on gene expression at the RNA and protein levels.

RESULTS

Here, we find that TBX2 is expressed in RPE cells both in vivo and in vitro. Specific knockdown of TBX2 in the human RPE cell line ARPE-19 leads to an accumulation of cells at G1. This cell cycle arrest is accompanied by changes in the levels of known cell cycle regulators and, in particular, by an increase in the levels of the tumor-suppressor gene CCAAT/enhancer-binding protein delta (CEBPD). In fact, simultaneous knockdown of both TBX2 and CEBPD interferes with the reduction in cell proliferation brought about by TBX2 reduction alone.

CONCLUSIONS

Our results provide novel insights into the regulatory mechanisms of cell proliferation in the RPE and may contribute to our understanding of normal RPE maintenance and its pathology in degenerative and proliferative disorders of the eye.

Inhibition of Proliferation and Epithelial Mesenchymal Transition in Retinal Pigment Epithelial Cells by Heavy Chain-Hyaluronan/Pentraxin 3

Proliferative vitreoretinopathy (PVR) is mediated by proliferation and epithelial mesenchymal transition (EMT) of retinal pigment epithelium (RPE). Because heavy chain-hyaluronic acid/pentraxin 3 (HC-HA/PTX3) purified from human amniotic membrane exerts anti-inflammatory and anti-scarring actions, we hypothesized that HC-HA/PTX3 could inhibit these PVR-related processes in vitro. In this study, we first optimized an ARPE-19 cell culture model to mimic PVR by defining cell density, growth factors, and cultivation time. Using this low cell density culture model and HA as a control, we tested effects of HC-HA/PTX3 on the cell viability (cytotoxicity), proliferation (EGF + FGF-2) and EMT (TGF-β1). Furthermore, we determined effects of HC-HA/PTX3 on cell migration (EGF + FGF-2 + TGF-β1) and collagen gel contraction (TGF-β1). We found both HA and HC-HA/PTX3 were not toxic to unstimulated RPE cells. Only HC-HA/PTX3 dose-dependently inhibited proliferation and EMT of stimulated RPE cells by down-regulating Wnt (β-catenin, LEF1) and TGF-β (Smad2/3, collagen type I, α-SMA) signaling, respectively. Additionally, HA and HC-HA/PTX3 inhibited migration but only HC-HA/PTX3 inhibited collagen gel contraction. These results suggest HC-HA/PTX3 is a non-toxic, potent inhibitor of proliferation and EMT of RPE in vitro, and HC-HA/PTX3’s ability to inhibit PVR formation warrants evaluation in an animal model.

ASSOCIATION STUDY BETWEEN POLYMORPHISMS OF THE p53 AND LYMPHOTOXIN ALPHA (LTA) GENES AND THE RISK OF PROLIFERATIVE VITREORETINOPATHY/RETINAL DETACHMENT IN A MEXICAN POPULATION

PURPOSE

To report the results of an association study between single-nucleotide polymorphisms of the p53 and LTA genes and the risk of proliferative vitreoretinopathy (PVR)/retinal detachment (RD) in a Mexican cohort.

METHODS

A total of 380 unrelated subjects were studied, including 98 patients with primary rhegmatogenous RD without PVR, 82 patients with PVR after RD surgery, and 200 healthy, ethnically matched subjects. Genotyping of single-nucleotide polymorphisms rs1042522 (p53 gene) and rs2229094 (LTA gene) was performed by direct nucleotide sequencing. Allele frequencies, genotype frequencies, and Hardy-Weinberg equilibrium were assessed with HaploView software.

RESULTS

No significant differences in the allelic distributions of the previously identified risk C allele for LTA rs2229094 were observed between RD subjects and controls (odds ratio [95% confidence interval] = 0.8 [0.5-1.2]; P = 0.3). Conversely, the C allele for rs1042522 in p53 was positively associated with an increased risk for RD (odds ratio [95% confidence interval] = 1.4 [1.01-1.9]; P = 0.04). No significant differences were observed when the subgroup of 82 RD + PVR subjects was compared with the subgroup of 98 patients with RD.

CONCLUSION

The C allele for rs1042522 in p53 was genetically associated with a higher risk for RD but not for PVR in this cohort. This is the first association study attempting replication of PVR-associated risk alleles in a nonwhite population.

Proliferative vitreoretinopathy: A new concept of disease pathogenesis and practical consequences

During the last four decades, proliferative vitreoretinopathy (PVR) has defied the efforts of many researchers to prevent its occurrence or development. Thus, PVR is still the major complication following retinal detachment (RD) surgery and a bottle-neck for advances in cell therapy that require intraocular surgery. In this review we tried to combine basic and clinical knowledge, as an example of translational research, providing new and practical information for clinicians. PVR was defined as the proliferation of cells after RD. This idea was used for classifying PVR and also for designing experimental models used for testing many drugs, none of which were successful in humans. We summarize current information regarding the pathogenic events that follow any RD because this information may be the key for understanding and treating the earliest stages of PVR. A major focus is made on the intraretinal changes derived mainly from retinal glial cell reactivity. These responses can lead to intraretinal PVR, an entity that has not been clearly recognized. Inflammation is one of the major components of PVR, and we describe new genetic biomarkers that have the potential to predict its development. New treatment approaches are analyzed, especially those directed towards neuroprotection, which can also be useful for preventing visual loss after any RD. We also summarize the results of different surgical techniques and clinical information that is oriented toward the identification of high risk patients. Finally, we provide some recommendations for future classification of PVR and for designing comparable protocols for testing new drugs or techniques.

Disease pathways in proliferative vitreoretinopathy: an ongoing challenge

Despite remarkable advances in vitreoretinal surgery, proliferative vitreoretinopathy (PVR) remains a common cause of severe visual loss or blindness. One of the critical reasons for PVR-induced blindness is tractional retinal detachment due to the formation of contractile preretinal fibrous membranes. This membrane formation is characterized by the proliferation and migration of cells and the excessive synthesis and deposition of extracellular matrix proteins. Herein we present the disease pathways of PVR, reviewing the role of both systemic and intraocular cells as well as molecular mediators. A chronological sequence of events leading to PVR is also hypothesized. Better understanding of the pathogenesis of PVR is needed in order to improve disease management. Efforts should be oriented towards greater cooperation between basic researchers and clinicians, aimed at matching the different clinical scenarios with the biological markers of the disease.

Curcumin inhibits human retinal pigment epithelial cell proliferation

Proliferative vitreoretinopathy (PVR) is a common cause of intraoperative failure following retinal reattachment surgery and is mediated in part through the migration, de-differentiation and proliferation of retinal pigment epithelial (RPE) cells. Given the cytotoxic effects of curcumin on epithelial and endothelial cells, in this study, we assessed the effects of curcumin on human RPE (hRPE) cell proliferation. WST-1 analysis revealed that curcumin significantly inhibited primary hRPE cell proliferation in a dose- and time-dependent manner (P<0.001) with the greatest inhibition observed at the dose of 15 μg/ml curcumin. Flow cytometric analysis indicated that the cytotoxic effects of curcumin on hRPE cell proliferation were mediated by cell cycle arrest at the G0/G1 phase and the induction of apoptosis (both P<0.001), which was confirmed by ultrastructural analysis using transmission electron microscopy. Furthermore, western blot analysis revealed that curcumin induced p53 and p21^WAF1/CIP1 expression with a concomitant decrease in proliferating cell nuclear antigen protein levels (P<0.05). Curcumin effectively inhibited primary hRPE cell proliferation, which may be mediated by the p53 pathway. Further in vivo studies are required in order to fully explore the therapeutic potential of curcumin for PVR.

Deferred laser photocoagulation of relaxing retinotomies under silicone oil tamponade to reduce recurrent macular detachment in severe proliferative vitreoretinopathy

PURPOSE

This study sought to investigate whether, in patients with retinal detachment complicated by proliferative vitreoretinopathy, we can re-attach the retina with a posterior relaxing retinotomy and silicone oil tamponade while postponing laser retinopexy for several months.

METHODS

In 13 consecutive patients we applied laser coagulation of the retinotomy edge 15 ± 12 weeks after surgery. Silicone oil was removed 9 ± 6 weeks after laser application.

RESULTS

After the retinotomy without laser, some degree of central shifting was seen in all patients, followed by obvious curling in 10 patients. The total follow-up was 24 ± 7 months after retinotomy and 13 ± 9 months after oil removal. The retina was attached in 12 patients at the last visit, with the oil still in situ in three patients. Seven patients, however, required additional surgery. Function remained stable with a mean preoperative and postoperative Snellen visual acuity of 0.09.

CONCLUSIONS

Not anchoring retinotomy edges with a laser at the time of surgery allows inward curling and central slippage of retinal edges under silicone oil. This appears to compensate for the retinal fibrosis occurring in the weeks following surgery and may result in less macula-off re-detachments under oil, and potentially, in better visual outcome.

Expression of IGFBP-6 in a proliferative vitreoretinopathy rat model and its effects on retinal pigment epithelial cell proliferation and migration

AIM

To investigate the expression of insulin-like growth factor binding protein-6 (IGFBP-6) in a proliferative vitreoretinopathy (PVR) model and its effects on proliferation and migration in retinal pigment epithelial (RPE) cells.

METHODS

A PVR Wistar rat model was established by the intravitreal injection of RPE-J cells combined with platelet-rich plasma (PRP). The expression levels of IGFBP-6 were tested by ELISA. ARPE-19 cell proliferation was evaluated by the MTS method, and cell migration was evaluated by wound healing assays.

RESULTS

The success rate of the PVR model was 89.3% (25/28). IGFBP-6 was expressed at higher levels in the vitreous, serum and retina of rats experiencing advanced PVR (grade 3) than in the control group (vitreous: 152.80±15.08ng/mL vs 105.44±24.81ng/mL, P>0.05; serum: 93.48±9.27ng/mL vs 80.59±5.20ng/mL, P<0.05; retina: 3.02±0.38ng/mg vs 2.05±0.53ng/mg, P<0.05). In vitro, IGFBP-6 (500ng/mL) inhibited the IGF-II (50ng/mL) induced ARPE-19 cell proliferation (OD value at 24h: from 1.38±0.05 to 1.30±0.02; 48h: from 1.44±0.06 to 1.35±0.05). However, it did not affect basal or VEGF-, TGF-β- and PDGF-induced cell proliferation. IGFBP-6 (500ng/mL) reduced the IGF-II (50ng/mL)-induced would healing rate [24h: from (43.91±3.85)% to (29.76±2.49)%; 48 h: from (66.09±1.67)% to (59.88±3.43)%].

CONCLUSION

Concentrations of IGFBP-6 increased in the vitreous, serum, and retinas only in advanced PVR in vivo. IGFBP-6 also inhibited IGF-II-induced cell proliferation in a not dose or time dependent manner and migration. IGFBP-6 participates in the development of PVR and might play a protective role in PVR.

Expression of VEGF-A, Otx homeobox and p53 family genes in proliferative vitreoretinopathy

INTRODUCTION

Proliferative vitreoretinopathy (PVR) is a severe inflammatory complication of retinal detachment. Pathological epiretinal membranes grow on the retina surface leading to contraction, and surgery fails in 5% to 10% of the cases. We evaluated the expression of VEGF-A, Otx1, Otx2, Otx3, and p53 family members from PVR specimens to correlate their role in inducing or preventing the pathology.

METHODS

Twelve retinal samples were taken from patients affected by PVR during therapeutic retinectomies in vitreoretinal surgery. Gene expression was evaluated using quantitative real-time reverse transcriptase PCR analysis and immunohistochemistry, using four healthy human retinae as control.

RESULT

Controls showed basal expression of all genes. PVR samples showed little or no expression of Otx1 and variable expression of VEGF-A, Otx2, Otx3, p53, and p63 genes. Significant correlation was found among VEGF-A, Otx2, p53, and p63 and between Otx1 and Otx3.

CONCLUSIONS

Otx homeobox, p53 family, and VEGF-A genes are expressed in PVR human retina. We individuated two possible pathways (VEGF-A, Otx2, p53, p63 and Otx1 and Otx3) involved in PVR progression that could influence in different manners the course of the pathology. Individuating the genetic pathways of PVR represents a novel approach to PVR therapies.

Comparison of gene expression profile of epiretinal membranes obtained from eyes with proliferative vitreoretinopathy to that of secondary epiretinal membranes

BACKGROUND

Proliferative vitreoretinopathy (PVR) is a destructive complication of retinal detachment and vitreoretinal surgery which can lead to severe vision reduction by tractional retinal detachments. The purpose of this study was to determine the gene expression profile of epiretinal membranes (ERMs) associated with a PVR (PVR-ERM) and to compare it to the expression profile of less-aggressive secondary ERMs.

METHODOLOGY/PRINCIPAL FINDINGS

A PCR-amplified complementary DNA (cDNA) library was constructed using the RNAs isolated from ERMs obtained during vitrectomy. The sequence from the 5' end was obtained for randomly selected clones and used to generate expressed sequence tags (ESTs). We obtained 1116 nonredundant clusters representing individual genes expressed in PVR-ERMs, and 799 clusters representing the genes expressed in secondary ERMs. The transcriptome of the PVR-ERMs was subdivided by functional subsets of genes related to metabolism, cell adhesion, cytoskeleton, signaling, and other functions, by FatiGo analysis. The genes highly expressed in PVR-ERMs were compared to those expressed in the secondary ERMs, and these were subdivided by cell adhesion, proliferation, and other functions. Querying 10 cell adhesion-related genes against the STRING database yielded 70 possible physical relationships to other genes/proteins, which included an additional 60 genes that were not detected in the PVR-ERM library. Of these, soluble CD44 and soluble vascular cellular adhesion molecule-1 were significantly increased in the vitreous of patients with PVR.

CONCLUSIONS/SIGNIFICANCE

Our results support an earlier hypothesis that a PVR-ERM, even from genomic points of view, is an aberrant form of wound healing response. Genes preferentially expressed in PVR-ERMs may play an important role in the progression of PVR and could be served as therapeutic targets.

Opticin production is reduced by hypoxia and VEGF in human retinal pigment epithelium via MMP-2 activation

Opticin, a small leucine rich repeat protein (SLRP) contributes to vitreoretinal adhesion. This study was conducted to investigate the effects of hypoxia and vascular endothelial growth factor (VEGF) on matrix metalloproteinase (MMP) mediated opticin production in retinal pigment epithelium (RPE) cells. Primary cultured human RPE cells were treated with hypoxia (low oxygen and cobalt chloride) or VEGF (0-100 ng/mL). The mRNA levels of opticin and the protein levels of intra and extracellular opticin in RPE cells were examined by RT-PCR and Western blot assay, respectively. Furthermore, the MMP activity was analyzed by zymography, and EDTA was used as an MMP inhibitor. Analysis of the effect of MMP-2 on opticin was performed by recombinant human (rh) MMP-2 stimulation in RPE cultures and by human vitreous sample digestion with activated rhMMP-2. Our results showed that opticin was expressed by primary cultured human RPE cells. Hypoxia and VEGF stimulation did not alter opticin mRNA and protein expression in RPE cells, but markedly decreased the protein levels of extracellular opticin following increased latent MMP-2 activity. The VEGF- and hypoxia induced opticin degradation in the culture medium was blocked by EDTA. Together, opticin levels in the culture medium were also reduced after rhMMP-2 treatment. In addition, opticin in human vitreous samples could be cleaved by rhMMP-2. These results reveal that VEGF and hypoxia could decrease opticin protein levels in the human RPE secretome, and that opticin may be an enzymatic substrate for MMP-2.

Regulation of fibronectin-EDA through CTGF domain-specific interactions with TGFβ2 and its receptor TGFβRII

PURPOSE

To investigate the role of fibronectin containing extra domain A (FN-EDA) in the pathogenesis of proliferative vitreoretinopathy (PVR) and the regulation of FN-EDA by transforming growth factor (TGF)-β and connective tissue growth factor (CTGF) in retinal pigment epithelial (RPE) cells.

METHODS

Expression of FN-EDA in normal human retinas and PVR membranes was evaluated by immunohistochemistry. The effects of TGFβ and CTGF on FN-EDA mRNA and protein expression in primary cultures of human RPE cells were analyzed at different time points by real-time PCR and Western blot, respectively. The interaction of CTGF with TGFβ2 or with its type II receptor TGFβRII was examined by ELISA, immunoprecipitation, and solid-phase binding assays.

RESULTS

FN-EDA was abundantly expressed in PVR membranes but absent from the RPE monolayer in normal human retinas. Treatment of RPE cells with TGFβ2 induced FN-EDA expression in a time- and dose-dependent manner, but CTGF alone had no effect. However, CTGF, through its N-terminal half fragment, augmented TGFβ2-induced expression of FN-EDA at the protein level. This effect was blocked by antibodies against TGFβ2 or TGFβRII. Interaction of TGFβ2 or TGFβRII with CTGF was dose dependent and specific. CTGF directly bound TGFβ2 and TGFβRII at its N- and C-terminal domains, respectively.

CONCLUSIONS

These findings suggest that CTGF promotes the profibrotic activities of TGFβ acting as a cofactor through direct protein interactions and complex regulatory mechanisms.

The retinal pigment epithelium in health and disease

Retinal pigment epithelial cells (RPE) constitute a simple layer of cuboidal cells that are strategically situated behind the photoreceptor (PR) cells. The inconspicuousness of this monolayer contrasts sharply with its importance [1]. The relationship between the RPE and PR cells is crucial to sight; this is evident from basic and clinical studies demonstrating that primary dysfunctioning of the RPE can result in visual cell death and blindness. RPE cells carry out many functions including the conversion and storage of retinoid, the phagocytosis of shed PR outer segment membrane, the absorption of scattered light, ion and fluid transport and RPE-PR apposition. The magnitude of the demands imposed on this single layer of cells in order to execute these tasks, will become apparent to the reader of this review as will the number of clinical disorders that take origin from these cells.