The role of retinotomy in an experimental rabbit model of proliferative vitreoretinopathy

Comparative Analysis of Single-cell and Single-nucleus RNA-sequencing in a Rabbit Model of Retinal Detachment-related Proliferative Vitreoretinopathy

Purpose

Proliferative vitreoretinopathy (PVR) is the most common cause of failure of retinal reattachment surgery, and the molecular changes leading to this aberrant wound healing process are currently unknown. Our ultimate goal is to study PVR pathogenesis by employing single-cell transcriptomics to dissect cellular heterogeneity.

Design

Here we aimed to compare single-cell RNA sequencing (scRNA-seq)  and single-nucleus RNA-sequencing (snRNA-seq) of retinal PVR samples in the rabbit model.

Participants

Unilateral induction of PVR lesions in rabbit eyes with contralateral eyes serving as controls.

Methods

Proliferative vitreoretinopathy was induced unilaterally in Dutch Belted rabbits. At different timepoints after PVR induction, retinas were dissociated into either cells or nuclei suspension and processed for scRNA-seq or snRNA-seq.

Main Outcome Measures

Single cell and nuclei transcriptomic profiles of retinas after PVR induction.

Results

Single-cell RNA sequencing and snRNA-seq were conducted on retinas at 4 hours and 14 days after disease induction. Although the capture rate of unique molecular identifiers and genes were greater in scRNA-seq samples, overall gene expression profiles of individual cell types were highly correlated between scRNA-seq and snRNA-seq. A major disparity between the 2 sequencing modalities was the cell type capture rate, however, with glial cell types overrepresented in scRNA-seq, and inner retinal neurons were enriched by snRNA-seq. Furthermore, fibrotic Müller glia were overrepresented in snRNA-seq samples, whereas reactive Müller glia were overrepresented in scRNA-seq samples. Trajectory analyses were similar between the 2 methods, allowing for the combined analysis of the scRNA-seq and snRNA-seq data sets.

Conclusions

These findings highlight limitations of both scRNA-seq and snRNA-seq analysis and imply that use of both techniques together can more accurately identify transcriptional networks critical for aberrant fibrogenesis in PVR than using either in isolation.

Financial Disclosures

Proprietary or commercial disclosure may be found after the references.

Transition to Chronic Fibrosis in an Animal Model of Retinal Detachment With Features of Proliferative Vitreoretinopathy

Purpose

Proliferative vitreoretinopathy (PVR) is the most common cause of failure of surgically repaired rhegmatogenous retinal detachment (RRD). Chemically induced and cell injection PVR models do not fully simulate the clinical characteristics of PVR in the post-RRD context. There is an unmet need for translational models in which to study mechanisms and treatments specific to RRD-PVR.

Methods

RRD was induced in adult Dutch Belted rabbits. Posterior segments were fixed or processed for RNA sequencing at 6 hours and 2, 7, 14, and 35 days after induction. Histochemical staining and immunolabeling for glial fibrillary acidic protein, alpha smooth muscle actin, vascular endothelial growth factor receptor 2, CD68, and RPE 65 kDa protein were performed, and labeling intensity was scored. Single cell RNA sequencing was performed.

Results

Acute histopathological changes included intravitreal and intraretinal hemorrhage, leukocytic vitritis, chorioretinitis, and retinal rarefaction. Chronic lesions showed retinal atrophy, gliosis, fibrotic subretinal membranes, and epiretinal fibrovascular proliferation. Fibrillar collagen was present in the fibrocellular and fibrovascular membranes in chronic lesions. Moderate to strong labeling of glia and vasculature was detected in chronic lesions. At day 14, most cells profiled by single cell sequencing were identified as Mϋller glia and microglia, consistent with immunolabeling. Expression of several fibrillar collagen genes was upregulated in chronic lesions.

Conclusions

Histological and transcriptional features of this rabbit model simulate important features of human RRD-PVR, including the transition to chronic intraretinal and periretinal fibrosis. This animal model of RRD with features of PVR will enable further research on targeted treatment interventions.

Characterisation of the inflammatory cytokine and growth factor profile in a rabbit model of proliferative vitreoretinopathy

To clarify the mechanisms and their temporal relationship in the development of proliferative vitreoretinopathy (PVR), we measured vitreous levels of pro-inflammatory cytokines and growth factors in a rabbit model of PVR. PVR was surgically induced in 11 rabbit eyes by vitrectomy, retinotomy, cryotherapy and injection of platelet-rich plasma at baseline. Severity of PVR was assessed on dilated fundal examination with indirect binocular ophthalmoscopy and graded based on the revised experimental PVR classification. Severe PVR was defined as stage 5 or worse. Vitreous concentrations of interleukin 6 (IL-6), interleukin 8 (IL-8), interleukin 1 beta (IL-1 β), tumor necrosis factor beta (TNF-β), granulocyte macrophage colony stimulating factor (GM-CSF), interferon gamma (IFN-γ), C reactive protein; (CRP), placental growth factor (PlGF), platelet derived growth factor BB (PDGF-BB), vascular endothelial growth factor (VEGF) and angiopoietin 2 (Ang-2) at weeks 2, 3 and 4 were compared to baseline and correlations between the cytokines with PVR severity were assessed. Four weeks after PVR induction, 5 eyes (45.5%) had developed severe PVR. IL-8 was raised at 2 weeks post PVR induction (1.46 ± 0.48 pg/ml vs 0.53 ± 0.25 pg/ml, p = 0.04) and remained significantly elevated at week 4 (2.6 ± 3.1 pg/ml, p = 0.03). CRP was significantly raised at week 4 (34.8 ± 12.0 pg/ml vs 13.0 ± 13.1 pg/ml, p < 0.001). Among the growth factors, PDGF-BB was the earliest to show significantly elevated levels, at 3 weeks (50.4 ± 19.0 pg/ml vs 6.2 ± 10.1 pg/ml) and remained elevated at week 4 (p = 0.002), while PlGF (11.2 ± 7.7 pg/ml vs 5.3 ± 3.8 pg/ml, p = 0.002) and Ang2 (13617.0 ± 8170.2 pg/ml vs 38593.8 ± 8313.4, p = 0.02) were significantly raised at week 4. IFN-γ (p = 0.03), PDGF-BB (p = 0.02) and VEGF (p = 0.02) were significantly associated with PVR severity. We demonstrated that inflammatory cytokines IL-6, -8, elevation post PVR induction is followed by elevated levels of fibroproliferative growth factors, Ang2, PlGF, VEGF and PDGF-BB in the development of PVR. These findings will guide future studies targeting appropriate therapeutic strategies for the treatment of PVR.

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.

[Role of Chlamydia trachomatis intraocular infection in the development of proliferative vitreoretinopathy (experimental study)]

OBJECTIVE

To study the influence of C. trachomatis infection on proliferative vitreoretinopathy (PVR) stimulation and development in an experimental model.

MATERIAL AND METHODS

Intravitreal C. trachomatis injection was performed in 17 rabbits (right eyes) out of which 8 developed minimal chlamydial damage (1 was further subjected to histopathological examination with pathogen detection in ocular structures and other 7 were included in the study group). The control group consisted of 7 rabbits with no laboratory evidence of chlamydial infection. PVR was induced by 4 peripheral retinal punctures with a 19 G needle. Follow-up methods included ophthalmoscopy, ultrasonography, and PVR grading according to the Fastenberg classification. Histopathological examination, supplemented with pathogen detection by direct immunofluorescence in the study group, was performed at weeks 7 and 20.

RESULTS

PVR rate and severity were higher in the study group as compared with the controls (5 out of 7 rabbits, grade 2-4 vs. 2 out of 7 rabbits, grade 0-1, p<0.01). In the study group, histopathological examination performed before and after the induction of PVR revealed a pronounced lymphocyte and macrophage infiltration, characteristic of infectious inflammation. Similarly, extra- and intracellular chlamydial inclusions could be found in the retina and/or zones of proliferation throughout the whole study period. Inflammation signs (including those of proliferation) were reliably less significant in the controls.

CONCLUSION

C. trachomatis infection of the posterior segment contributes to PVR development due to associated chronic inflammation.

In vivo models of proliferative vitreoretinopathy

We outline current in vitro and in vivo models for experimental proliferative vitreoretinopathy (PVR) and provide a detailed protocol of our standardized in vivo PVR model. PVR is the leading cause of failed surgical procedures for the correction of rhegmatogenous retinal detachment. The pathogenesis of this multifactorial condition is still not completely understood. Experimental models for PVR help us understand the factors that play a role in the pathogenesis of the disease process in a controlled manner and allow for reproducible preclinical assessment of novel therapeutic interventions. We describe a cell injection model in detail that uses homologous retinal pigment epithelial (RPE) cell cultures to induce PVR over a 2-8 week period.

Experimental model for proliferative vitreoretinopathy by intravitreal dispase: limited by zonulolysis and cataract

BACKGROUND

The intravitreal injection of dispase has been shown to be a valuable method for induction of experimental PVR. The goal of the present study was to gain additional information about potential side effects associated with this method.

METHODS

Twenty-one pigmented rabbits received a single injection of dispase under topical anesthesia to one eye only, contralateral eyes served as untreated control. The animals were injected with doses from 0.045 to 0.065 units of dispase: 8 animals received 0.045 units, 9 animals 0.055 units and 4 animals 0.065 units.

RESULTS

Proliferative vitreoretinopathy occurred in 81% of the treated eyes. In 90% cataract formation was observed. Lens luxation was present in 47.3% of the cataract eyes.

CONCLUSION

Intravitreal injection of dispase resulted in the reproducible induction of PVR in addition to cataract formation and lens luxation. Whether these effects may all be associated with a toxic reaction or whether the proliferative changes are solely triggered by endogenous reactions similar to the pathomechanism of human PVR and whether the cataract formation and the lens luxation may be avoided by changing the method of injection require further investigation.

Proliferative vitreoretinopathy: cytologic findings in vitreous samples

PURPOSE

To compare the cellularity of vitreous samples obtained from patients with rhegmatogenous retinal detachment complicated by proliferative vitreoretinopathy (PVR) and from patients with uncomplicated rhegmatogenous retinal detachment (RD) to detect possible variations in cellularity over time.

METHODS

One hundred and twenty-five vitreous specimens collected from patients with RD (n = 41) and PVR (n = 84) were processed through direct paraffin embedding and cytospin. Different cell types were identified by light-microscopy (hematoxylin-eosin and Papanicolaou stain) according to their morphologic features, and a scale of cellular density was established for each cell type. Student's t test was used to analyze differences in the cellularity of RD versus PVR. A quadratic model was used to identify variations in the density of each cellular type in the PVR group, based on its evolution time.

RESULTS

During the first months after surgery, more macrophages and fibroblast-like cells were observed in the PVR group, but at other times no differences were found.

CONCLUSIONS

There are some differences in vitreous cellularity in PVR specimens when compared with RD. Especially relevant could be the large number of macrophages in earlier stages and their constant presence over time in PVR samples. The cytology of vitreous samples may shed light on the chronology of PVR cell pathobiology.

Combined pharmacologic therapy in a rabbit model of proliferative vitreoretinopathy (PVR)

PURPOSE

This study was designed to evaluate the efficacy of a combined treatment, previously used to prevent fibrosis after glaucoma surgery, to inhibit an experimental model of proliferative vitreoretinopathy (PVR).

METHODS

Two groups of albino rabbits were used. In the control group (group 1, n = 14), experimental PVR was induced using vitrectomy, retinotomies, cryotherapy and intraocular injection of platelet-rich plasma. In the experimental group (group 2, n = 15), after PVR was induced, the following treatment was administered for 4 weeks: systemic methylprednisolone, sodium diclofenac and colchicine combined with topical atropine 1%, adrenaline 10% and dexamethasone phosphate 0.1%. Follow- up consisted of fundus examination for 4 weeks. Results were classified according to Fastenberg's classification. Only retinal detachments were considered to compare the two groups. Nonparametric test was used.

RESULTS

Retinal detachments were observed in 85.7% of group 1 and 33.3% of group 2 at the end of the follow-up (p<0.01). No major systemic complications were observed.

CONCLUSIONS

Combined therapy seems to be useful for treating experimental PVR.

Proliferative vitreoretinopathy: an overview

Proliferative vitreoretinopathy (PVR) is still the most common cause of failure of surgery for rhegmatogenous retinal detachment, despite the substantial effort that has been devoted to better understanding and managing this condition during the past 25 years. Basic research has indicated that PVR represents scarring, the end stage of the wound-healing process that occurs after retinal detachment surgery. Medical treatment has been directed toward preventing inflammation, the first phase of the wound healing process, and inhibiting cell proliferation, the second phase. The 1983 Retina Society classification was modified in 1989 by the Silicone Study Group, whose classification differentiates between posterior and anterior forms of PVR and recognizes three patterns of proliferation: diffuse, focal, and subretinal. The anterior form has a worse prognosis than the posterior form, and its treatment requires more complex surgical procedures. In this review, risk factors and pathobiology of PVR are discussed, and management of PVR of various degrees of severity are considered.

13-cis-retinoic acid in silicone-fluorosilicone copolymer oil in a rabbit model of proliferative vitreoretinopathy

The purpose of this study was to evaluate the effect of 13-cis-Retinoic Acid (RA) in Silicone-Fluorosilicone Copolymer Oil (SiFO) in a rabbit model of proliferative vitreoretinopathy (PVR). Rabbits underwent gas-compression vitrectomy. During gas-SiFO exchange, group 1 was injected with 1 ml (10 microg ml-1) 13-cis-RA in SiFO, group 2 with 1.5 ml (9 microg 1.5 ml-1) all-trans-RA in SiFO, group 3 with 1 ml SiFO alone, and group 4 with balanced salt solution (BSS). Groups 1-4 were also injected with 0.1 ml suspension of fibroblasts (75,000 0.1 ml-1) and 0.05 ml platelet rich plasma (70,000 0.1 ml-1), and were observed for 4 weeks. Group 5 was injected with SiFO alone, group 6 with 1 ml (10 microg ml-1) 13-cis-RA in SiFO, group 7 with 1.5 ml (9 microg 1.5 ml-1) all-trans-RA in SiFO, and group 8 with BSS. After 4 weeks, groups 5-7 underwent SiFO-BSS exchange. ERG and histopathology were performed to test for retinal toxicity in groups 5-8. The incidence of traction retinal detachment at 4 weeks was: group 1, 42.9%; group 2, 36.4%; group 3, 87.5%; and group 4, 88.9%. A significant difference in the incidence of PVR was noted between treated eyes (groups 1 and 2) and control eyes (groups 3 and 4) at 2, 3, and 4 weeks (P<0.05). No significant difference in the incidence of PVR was found between groups 1 and 2 during the same observation periods. ERG and histopathological studies showed no differences between the treated and the control fellow eyes (group 5-7) after 4 weeks. 13-cis-RA in SiFO (10 microg ml-1) is as effective as all-trans-RA in SiFO (9 microg 1.5 ml-1) in controlling the incidence of PVR when used for short term retinal tamponade and does not appear to be associated with retinal toxicity.