Reduction of iatrogenic RPE lesions in AMD patients: evidence for wound healing?

Reprogramming of Differentiated Mammalian and Human Retinal Pigment Epithelium: Current Achievements and Prospects

Abstract

Impairment of the homeostatic and functional integrity of the retina and retinal pigment epithelium (RPE) is the main cause of some degenerative diseases of the human eye, which are accompanied by loss of eyesight. Despite the significant progress made over the past decades in the development of new methods for treatment for this pathology, there are still several complications when using surgical methods for correction of eyesight and so far insurmountable limitations in the applications of modern approaches, such as gene therapy and genetic engineering. One of the promising approaches to the treatment of degenerative diseases of the retina may be an approach based on the application of regenerative capacities of its endogenous cells with high plasticity, in particular, of RPE cells and Müller glia. Currently, vertebrate RPE cells are of great interest as a source of new photoreceptors and other neurons in the degrading retina in vivo. In this regard, the possibilities of their direct reprogramming by genetic, epigenetic, and chemical methods and their combination are being investigated. This review focuses on research in gene-directed reprogramming of vertebrate RPE cells into retinal neurons, with detailed analysis of the genes used as the main reprogramming factors, comparative analysis, and extrapolation of experimental data from animals to humans. Also, this review covers studies on the application of alternative approaches to gene-directed reprogramming, such as chemical-mediated reprogramming with the use of cocktails of therapeutic low-molecular-weight compounds and microRNAs. In general, the research results indicate the complexity of the process for direct reprogramming of human RPE cells into retinal neurons. However, taking into account the results of direct reprogramming of vertebrate cells and the accessibility of human RPE cells for various vectors that deliver a variety of molecules to cells, such as transcription factors, chimeric endonucleases, recombinant proteins, and low-weight molecular compounds, the most optimal combination of factors for the successful conversion of human RPE cells to retinal neurons can be suggested.

Retinal pigment epithelial responses based on the irradiation density of selective retina therapy

PURPOSE

We evaluated the response of the retinal pigment epithelium (RPE) to high-density (HD) or low-density (LD)-selective retina therapy (SRT) with real-time feedback-controlled dosimetry (RFD) in rabbits.

METHODS

Sixteen eyes of 8 Chinchilla Bastard rabbits underwent SRT with RFD (527-nm wavelength, 1.7-μs pulse duration), using automatically titrated pulse energy, by using optoacoustic dosimetry or real-time reflectometry. Fifty-six 25-μJ SRT, including LD-SRT (1-spot or 2-spot-spacing) and HD-SRT (4-spot, 7-spot, or 9-spot-no-spacing), were applied per eye. Color fundus photography and fundus fluorescein angiography (FFA) were used to confirm SRT spots 1-h post-SRT. Light microscopy and scanning electron microscopy (SEM) were performed at 2-h, 3-day, 7-day, and 1-month post-treatment.

RESULTS

We tested 896 spots irradiated by SRT with RFD and confirmed that SRT lesions were adequate, based on invisibility on fundoscopy and visibility on FFA. On SEM, at 2-h post-SRT, flattened RPE cells were observed in the center of the SRT lesion. While normal RPE cells were clearly observed between LD-SRT lesions, healthy RPE cells were rare in HD-SRT lesions at 2-h post-treatment. At 7-day post-SRT, SEM revealed completely restored LD-SRT lesions with small or large RPE cells with microvilli, whereas HD-SRT lesions were covered with RPE cells without microvilli. At 1-month post-SRT, SEM revealed restored RPE cells with microvilli in HD-SRT lesions. On light microscopy, both HD- and LD-SRT lesions were completely restored with adjacent RPE cells and spared photoreceptors at 1-month post-treatment.

CONCLUSIONS

Although both HD- and LD-SRT lesions had recovered at 1-month post-SRT, LD-SRT lesions healed faster than HD-SRT lesions.

Retinal pigment epithelium wound healing after traumatic choroidal rupture

PURPOSE

The aim of this study was to investigate wound healing in the retinal pigment epithelium (RPE) after traumatic indirect choroidal rupture using fundus autofluorescence (FAF) and spectral-domain optical coherence tomography (SD-OCT).

METHODS

A total of 14 eyes of 14 patients with traumatic indirect choroidal rupture were included. Baseline and last follow-up FAF images were compared to evaluate the extent of RPE healing after choroidal rupture, and associated morphologic characteristics were examined by SD-OCT.

RESULTS

The size of the RPE lesion was reduced in five eyes. The change occurred in the fovea in four eyes and in the macula in three eyes. The change was noted in both the fovea and the macula in two eyes; in these cases, the changes were more prominent in the fovea than in the macula. Extra-macular lesions and lesions with deep choroidal involvement did not show any reduction in size. Choroidal neovascularization (CNV) developed in seven eyes. There was no extra-macular CNV.

CONCLUSION

Retinal pigment epithelium (RPE) wound healing after traumatic choroidal rupture is affected by location and extent of the lesion.

Localized RPE Removal with a Novel Instrument Aided by Viscoelastics in Rabbits

PURPOSE

We developed a surgical method for localized and atraumatic removal of the retinal pigment epithelium (RPE) with a novel instrument.

METHODS

Bleb retinal detachments (bRD) were raised with balanced salt solution (BSS) following vitrectomy in 27 rabbits. The RPE was scraped with 3 loop variants (polypropylene [PP], 0.1 mm; PP, 0.06 mm; metal, 0.1 mm) of a custom-made instrument. Stabilization of bRDs with BSS or various concentrations (0.1%-0.5%) of hyaluronic acid (HA) was video analyzed. Perfusion-fixed samples of scraped areas and controls were studied by light and transmission electron microscopy.

RESULTS

The bRDs were sufficiently stabilized by ≥0.25% HA. Using the PP 0.1 mm loop with a single forward/backward stroke, an area of ca. 2.5 × 1.5 mm was nearly devoid of RPE, yet did show occasional Bruch's membrane (BM) defects combined with choriocapillaris hemorrhages in 13% of the bRDs. A single scrape with PP 0.06 mm resulted in unsatisfactory RPE denudement, while repeated scraping maneuvers caused more BM defects and hemorrhages. The metal loop resulted in incomplete RPE removal and massive intraoperative subretinal hemorrhages. Histologically, intact photoreceptor outer segments (POS) were observed above the RPE wounds in bRDs. Controls with bRDs alone showed an intact RPE monolayer with microvilli, with few engulfed remains of POS.

CONCLUSIONS

Localized removal of RPE in HA stabilized bRD can be achieved by a PP 0.1 mm loop instrument.

TRANSLATIONAL RELEVANCE

Removal of degenerated RPE may aid RPE cell replacement strategies.

Progression of retinal pigment epithelial atrophy in antiangiogenic therapy of neovascular age-related macular degeneration

Purpose

To monitor retinal pigment epithelial (RPE) atrophy progression during antiangiogenic therapy of neovascular age-related macular degeneration (AMD) over 2 years using polarization-sensitive optical coherence tomography (OCT).

Design

Prospective interventional case series.

Methods

setting: Clinical practice. study population: Thirty patients (31 eyes) with treatment-naïve neovascular AMD. observation procedures: Standard intravitreal therapy (0.5 mg ranibizumab) was administered monthly during the first year and pro re nata (PRN; as-needed) during the second year. Spectral-domain (SD) OCT and polarization-sensitive OCT (selectively imaging the RPE) examinations were performed at baseline and at 1, 3, 6, 12, and 24 months using a standardized protocol. RPE-related changes were evaluated using a semi-automated polarization-sensitive OCT segmentation algorithm and correlated with SD OCT and fundus autofluorescence (FAF) findings. main outcome measures: RPE response, geographic atrophy (GA) progression.

Results

Atrophic RPE changes included RPE thinning, RPE porosity, focal RPE atrophy, and development of GA. Early RPE loss (ie, RPE porosity, focal atrophy) increased progressively during initial monthly treatment and remained stable during subsequent PRN-based therapy. GA developed in 61% of eyes at month 24. Mean GA area increased from 0.77 mm² at 12 months to 1.10 mm² (standard deviation = 1.09 mm²) at 24 months. Reactive accumulation of RPE-related material at the lesion borders increased until month 3 and subsequently decreased.

Conclusions

Progressive RPE atrophy and GA developed in the majority of eyes. RPE migration signifies certain RPE plasticity. Polarization-sensitive OCT specifically images RPE-related changes in neovascular AMD, contrary to conventional imaging methods. Polarization-sensitive OCT allows for precisely monitoring the sequence of RPE-related morphologic changes.

Induction of ectopic retina-like tissue by transgenic expression of neurogenin

Degeneration of retinal neurons is an underlying cause of several major types of blinding diseases, and effective therapies remain to be developed. The suppositive strategy of repopulating a degenerative retina with new cells generated onsite faces serious challenges, because the mammalian retina seems to lack the ability to regenerate itself or replace its lost neurons. We investigated the possibility of using a transcriptional factor with proneural activities to reprogram ocular tissue with regenerative capability to give rise to retinal cells. Transgenic mice were generated with DNA constructs that targeted the expression in the retinal pigment epithelium of proneural gene neurogenin1 from the promoter of Bestrophin1, or neurogenin3 from RPE65 promoter. Here we report the presence of ectopic retina-like tissue in some of the transgenic mice, young and aged. The ectopic retina-like tissue contained cells positive for photoreceptor proteins Crx, recoverin, red opsin, and rhodopsin, and cells positive for proteins that label other types of retinal neurons, including AP2α and Pax6 for amacrine cells, Otx2 for bipolar cells, and Brn3A for ganglion cells. The retina-like tissue often co-existed with darkly pigmented tissue positive for RPE proteins: cytokeratin 18, Otx2, and RPE65. The ectopic retina-like tissue was detected in the subretinal space, including two retinae co-existing in the same eye, and/or in the optic nerve or in the vicinity of the optic nerve head. On rare occasions, it was detected in the choroid and in the vicinity of the ciliary body. The presence of ectopic retina-like tissue in the transgenic mouse supports the possibility of inducing retinal regeneration in the mammalian eyes through gene-directed reprograming.

Photoreceptor-like cells in transgenic mouse eye

PURPOSE

Recent success of rescuing vision by photoreceptor replacement in mouse models of photoreceptor degeneration intensifies the need to identify approaches to generate photoreceptors cells for future replacement therapies. We explored the possibility of whether in the mouse eye photoreceptor-like cells could arise from the RPE experimentally manipulated to express a regulatory gene participating in transcriptional networks leading to photoreceptor genesis during retinal development.

METHODS

Transgenic mice were generated with a DNA construct that would express neurogenin1 from RPE bestrophin-1 promoter or neurogenin3 from RPE65 promoter. Transgenic mice were examined with histology and immunohistology for the presence of photoreceptor-like cells and for the presence of cells that might represent transitional stages in RPE-to-photoreceptor reprogramming. Explant culture of "sclera+choroid+RPE" eyecup was used to examine whether cells with photoreceptor traits could arise from the eyecup derived from transgenic mice.

RESULTS

Transgenic animals showed varied degrees of phenotype manifestation. Approximately 60% of offspring from ∼50% of founders contained photoreceptor-like cells in the subretinal space. These cells expressed photoreceptor proteins recoverin, red opsin, and rhodopsin, and displayed morphologic similarities to photoreceptors. In these eyes, the RPE was maintained. Cells seemingly amid RPE-to-photoreceptor transformation were observed in young and aged mice, suggesting old animals were responsive to the reprogramming scheme. De novo generation of photoreceptor-like cells was detected in "sclera+choroid+RPE" eyecup explants derived from adult animals.

CONCLUSIONS

Our results point to a potential way to generate photoreceptor cells in situ in adult mammalian eyes.