Concept: Bruch's membrane
Age-related macular degeneration (AMD) is the most common cause of blindness among the elderly. AMD patients have elevated levels of membrane attack complex (MAC) in their choroidal blood vessels and retinal pigment epithelium (RPE). MAC forms pores in cell membranes. Low levels of MAC result in an elevation of cytokine release such as vascular endothelial growth factor (VEGF) that promotes the formation of choroidal neovascularization (CNV). High levels of MAC result in cell lysis and RPE degeneration is a hallmark of advanced AMD. The current standard of care for CNV associated with wet AMD is intravitreal injection of anti-VEGF molecules every 4 to 12 weeks. Such injections have significant side effects. Recently, it has been found that membrane pore-forming proteins such as α-haemolysin can mediate their toxic effects through auto- and paracrine signaling and that complement-induced lysis is amplified through ATP release followed by P2X receptor activation. We hypothesized that attenuation of P2X receptor activation may lead to a reduction in MAC deposition and consequent formation of CNV. Hence, in this study we investigated topical application of the purinergic P2X antagonist Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) as a potential treatment for AMD. We found that 4.17 µM PPADS inhibited formation of HUVEC master junctions and master segments by 74.7%. In a human complement mediated cell lysis assay, 104 µM PPADS enabled almost complete protection of Hepa1c1c7 cells from 1% normal human serum mediated cell lysis. Daily topical application of 4.17 mM PPADS for 3 days attenuated the progression of laser induced CNV in mice by 41.8% and attenuated the deposition of MAC at the site of the laser injury by 19.7%. Our data have implications for the future treatment of AMD and potentially other ocular disorders involving CNV such as angioid streaks, choroidal rupture and high myopia.
The parapapillary gamma zone has recently been defined as the parapapillary region free of Bruch’s membrane. Although it has been reported the presence of defects in peripapillary gamma zone, hitherto undescribed is the herniation of the retinal nerve fiver layer tissue into the peripapillary gamma zone defect with the resulting localized defects in the retinal nerve fiber layer.
Age-related macular degeneration (AMD) remains a major cause of blindness, with dysfunction and loss of retinal pigment epithelium (RPE) central to disease progression. We engineered an RPE patch comprising a fully differentiated, human embryonic stem cell (hESC)-derived RPE monolayer on a coated, synthetic basement membrane. We delivered the patch, using a purpose-designed microsurgical tool, into the subretinal space of one eye in each of two patients with severe exudative AMD. Primary endpoints were incidence and severity of adverse events and proportion of subjects with improved best-corrected visual acuity of 15 letters or more. We report successful delivery and survival of the RPE patch by biomicroscopy and optical coherence tomography, and a visual acuity gain of 29 and 21 letters in the two patients, respectively, over 12 months. Only local immunosuppression was used long-term. We also present the preclinical surgical, cell safety and tumorigenicity studies leading to trial approval. This work supports the feasibility and safety of hESC-RPE patch transplantation as a regenerative strategy for AMD.
Age-related Macular Degeneration (AMD) is a leading cause of visual loss among the elderly. A key cell-type involved in AMD, the retinal pigment epithelium expresses a g-protein coupled receptor that, in response to its ligand, L-DOPA, upregulates pigment epithelia derived factor, while downregulating vascular endothelial growth factor. In this study we investigated the potential relationship between L-DOPA and AMD.
This study found evidence of a threshold effect in which the presence of bilateral soft drusen and depigmentation of retinal pigment epithelium was associated with substantially low health-related quality of life (HRQoL) in adult Latinos from the United States.
RNA-guided genome surgery using CRISPR-Cas9 nucleases has shown promise for the treatment of diverse genetic diseases. Yet, the potential of such nucleases for therapeutic applications in nongenetic diseases is largely unexplored. Here, we focus on age-related macular degeneration (AMD), a leading cause of blindness in adults, which is associated with retinal overexpression of, rather than mutations in, the VEGFA gene. Subretinal injection of preassembled, Vegfa gene-specific Cas9 ribonucleoproteins (RNPs) into the adult mouse eye gave rise to mutagenesis at the target site in the retinal pigment epithelium. Furthermore, Cas9 RNPs effectively reduced the area of laser-induced choroidal neovascularization (CNV) in a mouse model of AMD. Genome-wide profiling of Cas9 off-target effects via Digenome-seq showed that off-target mutations were rarely induced in the human genome. Because Cas9 RNPs can function immediately after in vivo delivery and are rapidly degraded by endogenous proteases, their activities are unlikely to be hampered by antibody- and cell-mediated adaptive immune systems. Our results demonstrate that in vivo genome editing with Cas9 RNPs has the potential for the local treatment for nongenetic degenerative diseases, expanding the scope of RNA-guided genome surgery to a new dimension.
Age-related macular degeneration (AMD) causes severe visual impairment due in part to age-dependent impairment of retinal pigment epithelium (RPE). It has been suggested that autologous human induced pluripotent stem cells (hiPSCs) may represent a useful cell source for the generation of graft RPE. We generated hiPSC-derived RPE (hiPSC-RPE) cell sheets optimized to meet clinical use requirements, including quality, quantity, consistency, and safety. These cell sheets are generated as a monolayer of cells without any artificial scaffolds, express typical RPE markers, form tight junctions that exhibit polarized secretion of growth factors, and show phagocytotic ability and gene-expression patterns similar to those of native RPE. Additionally, upon transplantation, autologous nonhuman primate iPSC-RPE cell sheets showed no immune rejection or tumor formation. These results suggest that autologous hiPSC-RPE cell sheets may serve as a useful form of graft for use in tissue replacement therapy for AMD.
While increased VEGF-A has been associated with neovascular age-related macular degeneration (AMD), it is not known whether VEGF-A may also promote other age-related eye diseases. Here, we show that an increase in VEGF-A is sufficient to cause multiple distinct common aging diseases of the eye, including cataracts and both neovascular and non-exudative AMD-like pathologies. In the lens, increased VEGF-A induces age-related opacifications that are associated with ERK hyperactivation, increased oxidative damage, and higher expression of the NLRP3 inflammasome effector cytokine IL-1β. Similarly, increased VEGF-A induces oxidative stress and IL-1β expression also in the retinal pigment epithelium (RPE). Targeting NLRP3 inflammasome components or Il1r1 strongly inhibited not only VEGF-A-induced cataract formation, but also both neovascular and non-exudative AMD-like pathologies. Moreover, increased VEGF-A expression specifically in the RPE was sufficient to cause choroidal neovascularization (CNV) as in neovascular AMD, which could be inhibited by RPE-specific inactivation of Flk1, while Tlr2 inactivation strongly reduced CNV. These findings suggest a shared pathogenic role of VEGF-A-induced and NLRP3 inflammasome-mediated IL-1β activation for multiple distinct ocular aging diseases.
Retinal pigment epithelium (RPE) dysfunction and loss are a hallmark of non-neovascular age-related macular degeneration (NNAMD). Without the RPE, a majority of overlying photoreceptors ultimately degenerate, leading to severe, progressive vision loss. Clinical and histological studies suggest that RPE replacement strategies may delay disease progression or restore vision. A prospective, interventional, U.S. Food and Drug Administration-cleared, phase 1/2a study is being conducted to assess the safety and efficacy of a composite subretinal implant in subjects with advanced NNAMD. The composite implant, termed the California Project to Cure Blindness-Retinal Pigment Epithelium 1 (CPCB-RPE1), consists of a polarized monolayer of human embryonic stem cell-derived RPE (hESC-RPE) on an ultrathin, synthetic parylene substrate designed to mimic Bruch’s membrane. We report an interim analysis of the phase 1 cohort consisting of five subjects. Four of five subjects enrolled in the study successfully received the composite implant. In all implanted subjects, optical coherence tomography imaging showed changes consistent with hESC-RPE and host photoreceptor integration. None of the implanted eyes showed progression of vision loss, one eye improved by 17 letters and two eyes demonstrated improved fixation. The concurrent structural and functional findings suggest that CPCB-RPE1 may improve visual function, at least in the short term, in some patients with severe vision loss from advanced NNAMD.
Macular degenerations, inherited and age-related, are important causes of vision loss. Human genetic studies have suggested perturbation of the complement system is important in the pathogenesis of age-related macular degeneration. The mechanisms underlying the involvement of the complement system are not understood, although complement and inflammation have been implicated in drusen formation. Drusen are an early clinical hallmark of inherited and age-related forms of macular degeneration. We studied one of the earliest stages of macular degeneration which precedes and leads to the formation of drusen, ie the formation of basal deposits. The studies were done using a mouse model of the inherited macular dystrophy Doyne Honeycomb Retinal Dystrophy/Malattia Leventinese (DHRD/ML) which is caused by a p.Arg345Trp mutation in EFEMP1. The hallmark of DHRD/ML is the formation of drusen at an early age, and gene targeted Efemp1(R345 W/R345 W) mice develop extensive basal deposits. Proteomic analyses of Bruch’s membrane/choroid and Bruch’s membrane in the Efemp1(R345 W/R345 W) mice indicate that the basal deposits are composed of normal extracellular matrix components present in abnormal amounts. The proteomic analyses also identified significant changes in proteins with immune-related function, including complement components, in the diseased tissue samples. Genetic ablation of the complement response via generation of Efemp1(R345 W/R345 W):C3(-/-) double mutant mice inhibited the formation of basal deposits. The results demonstrate a critical role for the complement system in basal deposit formation, and suggest that complement-mediated recognition of abnormal extracellular matrix may participate in basal deposit formation in DHRD/ML and perhaps other macular degenerations.