New Prospects for Retinal Pigment Epithelium Transplantation.

ABSTRACT: Retinal pigment epithelium (RPE) transplants rescue photoreceptors in selected animal models of retinal degenerative disease. Early clinical studies of RPE transplants as treatment for age-related macular degeneration (AMD) included autologous and allogeneic transplants of RPE suspensions and RPE sheets for atrophic and neovascular complications of AMD. Subsequent studies explored autologous RPE-Bruch membrane-choroid transplants in patients with neovascular AMD with occasional marked visual benefit, which establishes a rationale for RPE transplants in late-stage AMD. More recent work has involved transplantation of autologous and allogeneic stem cell-derived RPE for patients with AMD and those with Stargardt disease. These early-stage clinical trials have employed RPE suspensions and RPE monolayers on biocompatible scaffolds. Safety has been well documented, but evidence of efficacy is variable. Current research involves development of better scaffolds, improved modulation of immune surveillance, and modification of the extracellular milieu to improve RPE survival and integration with host retina.

A human model of Batten disease shows role of CLN3 in phagocytosis at the photoreceptor-RPE interface.

Mutations in CLN3 lead to photoreceptor cell loss in CLN3 disease, a lysosomal storage disorder characterized by childhood-onset vision loss, neurological impairment, and premature death. However, how CLN3 mutations cause photoreceptor cell death is not known. Here, we show that CLN3 is required for phagocytosis of photoreceptor outer segment (POS) by retinal pigment epithelium (RPE) cells, a cellular process essential for photoreceptor survival. Specifically, a proportion of CLN3 in human, mouse, and iPSC-RPE cells localized to RPE microvilli, the site of POS phagocytosis. Furthermore, patient-derived CLN3 disease iPSC-RPE cells showed decreased RPE microvilli density and reduced POS binding and ingestion. Notably, POS phagocytosis defect in CLN3 disease iPSC-RPE cells could be rescued by wild-type CLN3 gene supplementation. Altogether, these results illustrate a novel role of CLN3 in regulating POS phagocytosis and suggest a contribution of primary RPE dysfunction for photoreceptor cell loss in CLN3 disease that can be targeted by gene therapy.

Migration of intravitreal dexamethasone implant to anterior chamber.

PURPOSE: To describe two cases of migration of intravitreally injected dexamethasone implant into the anterior chamber. METHODS: Charts were reviewed of two patients who received sustained-release dexamethasone implant intravitreally for chronic intractable cystoid macular edema. RESULTS: Both patients had pseudophakic cystoid macular edema and a complicated clinical course before receiving the implant. Treatments before intravitreal injection of implant included topical nonsteroidal anti-inflammatory drugs, sub-Tenon triamcinolone injections, vitrectomy, and, in one case, intravitreal bevacizumab. Both patients responded well to triamcinolone injections but required repeated injections. This led to the decision to inject the implant. Within 2 weeks of injection, the implant was noted in the anterior chamber causing pain and decreased vision from corneal edema. Both patients underwent successful removal of the implant. CONCLUSION: Sustained-release intravitreal injectable implants can migrate freely in vitrectomized pseudophakic or aphakic eyes. Selection of a scleral-fixated steroid implant might be safer in such cases.

Cell-deposited matrix improves retinal pigment epithelium survival on aged submacular human Bruch's membrane.

PURPOSE: To determine whether resurfacing submacular human Bruch's membrane with a cell-deposited extracellular matrix (ECM) improves retinal pigment epithelial (RPE) survival. METHODS: Bovine corneal endothelial (BCE) cells were seeded onto the inner collagenous layer of submacular Bruch's membrane explants of human donor eyes to allow ECM deposition. Control explants from fellow eyes were cultured in medium only. The deposited ECM was exposed by removing BCE. Fetal RPE cells were then cultured on these explants for 1, 14, or 21 days. The explants were analyzed quantitatively by light microscopy and scanning electron microscopy. Surviving RPE cells from explants cultured for 21 days were harvested to compare bestrophin and RPE65 mRNA expression. Mass spectroscopy was performed on BCE-ECM to examine the protein composition. RESULTS: The BCE-treated explants showed significantly higher RPE nuclear density than did the control explants at all time points. RPE expressed more differentiated features on BCE-treated explants than on untreated explants, but expressed very little mRNA for bestrophin or RPE65. The untreated young (<50 years) and African American submacular Bruch's membrane explants supported significantly higher RPE nuclear densities (NDs) than did the Caucasian explants. These differences were reduced or nonexistent in the BCE-ECM-treated explants. Proteins identified in the BCE-ECM included ECM proteins, ECM-associated proteins, cell membrane proteins, and intracellular proteins. CONCLUSIONS: Increased RPE survival can be achieved on aged submacular human Bruch's membrane by resurfacing the latter with a cell-deposited ECM. Caucasian eyes seem to benefit the most, as cell survival is the worst on submacular Bruch's membrane in these eyes.

Culture-induced increase in alpha integrin subunit expression in retinal pigment epithelium is important for improved resurfacing of aged human Bruch's membrane.

The purpose of this study was to examine the change in integrin expression in adult human retinal pigment epithelium (RPE) after culturing and to characterize the role of integrins in RPE adhesion to aged submacular human Bruch's membrane. Expression of alpha integrin subunits 1 through 6 in adult RPE cells, cultured or uncultured, was examined by reverse transcription/real-time polymerase chain reaction (PCR) and Western blotting. RPE was cultured on bovine corneal endothelial cell-secreted extracellular matrix (BCE-ECM). The role of alpha integrin subunits in RPE attachment was examined by immunofluorescent localization of these subunits at sites of focal adhesions in cultured adult RPE attached to laminin or collagen-I-coated culture dishes. Additionally, the effect of function-blocking antibodies to alpha integrin subunits on RPE attachment to laminin, collagen I, and aged submacular human Bruch's membrane was determined. Cultured adult RPE had increased expression of alpha1-5 integrin subunits by PCR compared to uncultured RPE. Western blots showed that alpha2, 3, and 5 subunit levels were low or absent in uncultured adult RPE. Cultured adult RPE had a substantially higher expression of these integrins. Alpha 1-3 subunits co-localized with phosphorylated focal adhesion kinase (FAK) at focal adhesions in RPE cells spread on laminin. Only alpha2 and alpha3 co-localized with phosphorylated FAK in focal adhesions of RPE on collagen I. Using function blocking antibodies, blocking alpha1 subunit singly or in combination with alpha2 and/or alpha3 significantly decreased RPE adhesion to laminin. Blocking alpha1 and alpha2 or blocking alpha1, alpha2, and alpha3 subunits significantly decreased RPE adhesion to collagen I. Compared to controls, significantly fewer RPE cells were able to spread on aged submacular human Bruch's membrane when alpha1-6 integrin subunits were blocked. These results indicate that alpha 1-5 subunits that are upregulated by culturing on BCE-ECM are necessary for RPE attachment to aged submacular human Bruch's membrane. Relative lack of these integrin subunits in uncultured adult RPE may be responsible for poor resurfacing of aged submacular human Bruch's membrane by these cells.

Impaired RPE survival on aged submacular human Bruch's membrane.

Resurfacing of diseased or iatrogenically damaged Bruch's membrane with healthy retinal pigment epithelium (RPE) has been proposed as adjunctive treatment for age-related macular degeneration (AMD). The purpose of this study was to determine whether cultured fetal human RPE cells can attach and differentiate on aged submacular human Bruch's membrane. Bruch's membrane was debrided to expose native RPE basement membrane, the superficial inner collagenous layer directly below the RPE basement membrane, or the deep inner collagenous layer. These are three surfaces that transplanted RPE cells will encounter in situ. Approximately 3146 cultured fetal RPE cells mm(-2) were seeded onto these three surfaces and grown in organ culture for 1, 7, or 14 days. Explants were bisected and examined histologically or analyzed with a scanning electron microscope. RPE nuclear density was measured on stained sections. Morphology and cell density were compared to cells seeded onto bovine corneal endothelial cell-extracellular matrix (BCE-ECM). In situ submacular RPE nuclear density was also measured in tissue sections of donor eyes ranging from 18 weeks gestation to 88 years of age to determine the effect of age on RPE density. Compared to cells seeded onto BCE-ECM at similar density, RPE cell coverage and cellular morphology on aged submacular human Bruch's membrane was poor at all time points. In contrast to cells on BCE-ECM, RPE cell density on Bruch's membrane decreased with time. In general, cell morphology on all three Bruch's membrane surfaces worsened by day-7 compared to day-1. Although some cells were more pigmented on RPE basement membrane and the deep inner collagenous layer at day-7, poor cellular morphology indicated the remaining cells were not well differentiated. At day-14, the cells were uniform and cuboidal on BCE-ECM, with cell density similar to that at day-7 and similar to in situ density of young donors (

Retinal pigment epithelium resurfacing of aged submacular human Bruch's membrane.

PURPOSE: To determine whether cultured fetal human retinal pigment epithelium (RPE) cells can attach and differentiate on submacular Bruch's membrane from donors over age 55. METHODS: Differential debridements of Bruch's membrane were performed to expose three different surfaces: the RPE basement membrane, the superficial inner collagenous layer (ICL) directly below the RPE basement membrane, and the deeper ICL. Approximately 3,146 cells/mm2 were seeded onto these Bruch's membrane explants and cultured for 1 or 7 days. Explants were bisected and examined histologically or analyzed with scanning electron microscopy. Nuclear density counts were performed on stained sections. Morphology and cell density were compared to those of cells seeded onto bovine corneal endothelial cell-extracellular matrix (BCE-ECM). RESULTS: Compared to cells seeded onto BCE-ECM at similar density, cell coverage and cellular morphology were poor at both time points. Unlike cells on BCE-ECM, cell density remained the same or decreased with time. In general, cell morphology on all surfaces worsened by day 7 compared to day 1. Although cells were more pigmented on RPE basement membrane and deep ICL at day 7, poor cellular morphology indicated the remaining cells were not well differentiated. An explant from a donor with large soft drusen showed the poorest resurfacing at day 7 in organ culture. CONCLUSIONS: These data indicate that aged submacular human Bruch's membrane does not support transplanted RPE survival and differentiation. The formation of localized RPE defects, cell death, and worsening cellular morphology on aged Bruch's membrane suggest that modification of Bruch's membrane may be necessary in patients with age-related macular degeneration receiving RPE transplants to prevent graft failure.