Impaired cholesterol efflux in retinal pigment epithelium of individuals with juvenile macular degeneration.

Macular degeneration (MD) is characterized by the progressive deterioration of the macula and represents one of the most prevalent causes of blindness worldwide. Abnormal intracellular accumulation of lipid droplets and pericellular deposits of lipid-rich material in the retinal pigment epithelium (RPE) called drusen are clinical hallmarks of different forms of MD including Doyne honeycomb retinal dystrophy (DHRD) and age-related MD (AMD). However, the appropriate molecular therapeutic target underlying these disorder phenotypes remains elusive. Here, we address this knowledge gap by comparing the proteomic profiles of induced pluripotent stem cell (iPSC)-derived RPEs (iRPE) from individuals with DHRD and their isogenic controls. Our analysis and follow-up studies elucidated the mechanism of lipid accumulation in DHRD iRPE cells. Specifically, we detected significant downregulation of carboxylesterase 1 (CES1), an enzyme that converts cholesteryl ester to free cholesterol, an indispensable process in cholesterol export. CES1 knockdown or overexpression of EFEMP1R345W, a variant of EGF-containing fibulin extracellular matrix protein 1 that is associated with DHRD and attenuated cholesterol efflux and led to lipid droplet accumulation. In iRPE cells, we also found that EFEMP1R345W has a hyper-inhibitory effect on epidermal growth factor receptor (EGFR) signaling when compared to EFEMP1WT and may suppress CES1 expression via the downregulation of transcription factor SP1. Taken together, these results highlight the homeostatic role of cholesterol efflux in iRPE cells and identify CES1 as a mediator of cholesterol efflux in MD.

The second Japanese family with Malattia Leventinese/Doyne honeycomb retinal dystrophy.

PURPOSE: To describe the clinical and genetic findings of patients in the second Japanese family with Malattia Leventinese/Doyne honeycomb retinal dystrophy (ML/DHRD). METHODS: Two patients (a 41-year-old male proband and his third son) underwent comprehensive ophthalmic examinations, including full-field and multifocal electroretinography (ERG). Sanger sequencing was performed to detect an EFEMP1 gene variant (p.Arg345Trp), which was identified as the only causative pathogenic variant. RESULTS: Genetic analysis revealed that both patients carried the heterozygous variant, but the other unaffected family members did not. Although the proband exhibited innumerable radially distributed drusen in both the posterior poles and good visual acuity at initial presentation, bilateral choroidal neovascularization (CNV) developed during the 15-year follow-up. The proband received 15 intravitreal anti-vascular endothelial growth factor (VEGF) injections in the left eye (LE) and two injections in the right eye (RE). At 56 years of age, his decimal best-corrected visual acuity was 0.1 and 1.2 in the LE and RE, respectively. Full-field ERG showed that while the rod and combined responses were within normal amplitudes, the cone and 30-Hz flicker responses had slightly decreased amplitudes. Multifocal ERG revealed attenuated central responses in the LE and decreased temporal responses in the RE. In the 20-year-old son, multifocal ERG showed normal responses in both eyes. CONCLUSION: This is the first report of ML/DHRD in a patient who developed bilateral CNV and received anti-VEGF treatment in both eyes. Although multifocal ERG exhibited worsening of macular function, the generalized photoreceptor function was preserved until middle age.

Complement factor H genotypes impact risk of age-related macular degeneration by interaction with oxidized phospholipids.

The rs1061170T/C variant encoding the Y402H change in complement factor H (CFH) has been identified by genome-wide association studies as being significantly associated with age-related macular degeneration (AMD). However, the precise mechanism by which this CFH variant impacts the risk of AMD remains largely unknown. Oxidative stress plays an important role in many aging diseases, including cardiovascular disease and AMD. A large amount of oxidized phospholipids (oxPLs) are generated in the eye because of sunlight exposure and high oxygen content. OxPLs bind to the retinal pigment epithelium and macrophages and strongly activate downstream inflammatory cascades. We hypothesize that CFH may impact the risk of AMD by modulating oxidative stress. Here we demonstrate that CFH binds to oxPLs. The CFH 402Y variant of the protective rs1061170 genotype binds oxPLs with a higher affinity and exhibits a stronger inhibitory effect on the binding of oxPLs to retinal pigment epithelium and macrophages. In addition, plasma from non-AMD subjects with the protective genotype has a lower level of systemic oxidative stress measured by oxPLs per apolipoprotein B (oxPLs/apoB). We also show that oxPL stimulation increases expression of genes involved in macrophage infiltration, inflammation, and neovascularization in the eye. OxPLs colocalize with CFH in drusen in the human AMD eye. Subretinal injection of oxPLs induces choroidal neovascularization in mice. In addition, we show that the CFH risk allele confers higher complement activation and cell lysis activity. Together, these findings suggest that CFH influences AMD risk by modulating oxidative stress, inflammation, and abnormal angiogenesis.

The potential role of amyloid beta in the pathogenesis of age-related macular degeneration.

Drusen are extracellular deposits that lie beneath the retinal pigment epithelium (RPE) and are the earliest signs of age-related macular degeneration (AMD). Recent proteome analysis demonstrated that amyloid beta (Abeta) deposition was specific to drusen from eyes with AMD. To work toward a molecular understanding of the development of AMD from drusen, we investigated the effect of Abeta on cultured human RPE cells as well as ocular findings in neprilysin gene-disrupted mice, which leads to an increased deposition Abeta. The results showed that Abeta treatment induced a marked increase in VEGF as well as a marked decrease in pigment epithelium-derived factor (PEDF). Conditioned media from Abeta-exposed RPE cells caused a dramatic increase in tubular formation by human umbilical vein endothelial cells. Light microscopy of senescent neprilysin gene-disrupted mice showed an increased number of degenerated RPE cells with vacuoles. Electron microscopy revealed basal laminar and linear deposits beneath the RPE layer, but we did not observe choroidal neovascularization (CNV). The present study demonstrates that Abeta accumulation affects the balance between VEGF and PEDF in the RPE, and an accumulation of Abeta reproduces features characteristic of human AMD, such as RPE atrophy and basal deposit formation. Some other factors, such as breakdown of integrity of Bruch membrane, might be necessary to induce CNV of AMD.

Drusen of the optic disc.

Optic disc drusen are acellular calcific deposits occurring in small, crowded optic discs with abnormal vasculature. Evidence suggests axoplasmic transport alteration and axonal degeneration are involved in disc drusen formation. In affected patients, the number and size of disc drusen are highly variable, and the drusen may be visible near the disc surface or buried within the disc, causing them to appear as pseudopapilledema. B-scan echography is the most sensitive method for detecting disc drusen. Most patients with disc drusen are asymptomatic, but progressive visual field loss and vascular complications, including anterior ischemic optic neuropathy and choroidal neovascularization, may occur. Optic disc drusen have no established effective treatment. Diagnosing disc drusen correctly is important to avoid unnecessary work-up and to avoid overlooking potential serious conditions such as true papilledema. Disc drusen patients with more-than-expected visual field defects or progressive visual loss should have work-up to exclude other causes.

[Optic nerve drusen and angioid streaks in pseudoxanthoma elasticum]. / Drusenul papilar si striile angioide în pseudoxantomul elastic.

The clinical study presents the association between optic disc drusen and angioid streaks in the context of pseudoxanthoma elasticum, in 8.5% (4 from 47) of the cases. The values are significantly higher compared to those from the normal population (0.34%). This result can be the consequence of pathogenic correlations between the two diseases, in which a role is attributed to the metabolic changes within the pseudoxanthoma elasticum. The starting point seems to be the accumulation of polyanions in the elastin of the cribriform plate, followed by disruption of axonal transport, mitochondrial extrusion and subsequent formation of optic disc drusen.

Retinal pigment epithelium cell-derived exosomes: Possible relevance to CNV in wet-age related macular degeneration.

Exosomes are small vesicles that are released by almost every cell type and play a crucial role in many physiological and pathological processes associated with different diseases. Specifically, they promote angiogenesis in the pathogenesis of some diseases. According to previous research, the proteins of exosomes taken from the aqueous humor (AH) of patients with wet-age related macular degeneration (AMD) may function as a new diagnostic biomarker of AMD, suggesting that exosomes may play an important role in the occurrence and development of choroidal neovascularization (CNV). Moreover, additional research has revealed that the levels of some protein makers of exosomes are up-regulated in aged retinal pigment epithelium (RPE) and that drusen and oxidative stress may promote the secretion of exosomes derived from RPE cells. Consequently, we hypothesize that RPE cell-derived exosomes may be relevant to CNV in wet AMD. If this hypothesis is proven correct, future studies based on this link may also help to elucidate the molecular mechanisms of wet AMD and to find new therapeutic targets for the treatment of AMD.

NLRP3 inflammasome activation in retinal pigment epithelial cells by lysosomal destabilization: implications for age-related macular degeneration.

PURPOSE: To evaluate the effect of lysosomal destabilization on NLRP3 inflammasome activation in RPE cells and to investigate the mechanisms by which inflammasome activation may contribute to the pathogenesis of age-related macular degeneration (AMD). METHODS: Human ocular tissue sections from patients with geographic atrophy or neovascular AMD were stained for NLRP3 and compared to tissues from age-matched controls. Expression of the IL-1ß precursor, pro-IL-1ß, was induced in ARPE-19 cells by IL-1α treatment. Immunoblotting was performed to assess expression of NLRP3 inflammasome components (NLRP3, ASC, and procaspase-1) and pro-IL-1ß in ARPE-19 cells. Lysosomes were destabilized using the lysosomotropic agent L-leucyl-L-leucine methyl ester (Leu-Leu-OMe). Active caspase-1 was detected using FAM-YVAD-FMK, a fluorescent-labeled inhibitor of caspases (FLICA) specific for caspase-1. IL-1ß was detected by immunoblotting and ELISA, and cytotoxicity was evaluated by LDH quantification. RESULTS: RPE of eyes affected by geographic atrophy or neovascular AMD exhibited NLRP3 staining at lesion sites. ARPE-19 cells were found to express NLRP3, ASC, and procaspase-1. IL-1α dose-dependently induced pro-IL-1ß expression in ARPE-19 cells. Lysosomal destabilization induced by Leu-Leu-OMe triggered caspase-1 activation, IL-1ß secretion, and ARPE-19 cell death. Blocking Leu-Leu-OMe-induced lysosomal disruption with the compound Gly-Phe-CHN(2) or inhibiting caspase-1 with Z-YVAD-FMK abrogated IL-1ß release and ARPE-19 cytotoxicity. CONCLUSIONS: NLRP3 upregulation occurs in the RPE during the pathogenesis of advanced AMD, in both geographic atrophy and neovascular AMD. Destabilization of RPE lysosomes induces NLRP3 inflammasome activation, which may contribute to AMD pathology through the release of the proinflammatory cytokine IL-1ß and through caspase-1-mediated cell death, known as "pyroptosis."

Protective inflammasome activation in AMD.

Age-related macular degeneration (AMD) is the most common cause of blindness in the elderly. AMD progression is associated with alterations in inflammatory pathways and the immune system. A new study identifies a protective role for inflammasomes in AMD, suggesting that inflammasome activation might be manipulated as a potential therapeutic strategy for this condition (pages 791-798).

Complement dysregulation in AMD: RPE-Bruch's membrane-choroid.

The question as to why the macula of the retina is prone to an aging disease (age-related macular degeneration) remains unanswered. This unmet challenge has implications since AMD accounts for approximately 54% of blindness in the USA (Swaroop, Chew, Bowes Rickman and Abecasis, 2009). While AMD has onset in the elder years, it likely develops over time. Genetic discovery to date has accounted for approximately 50% of the inheritable component of AMD. The polymorphism that has been most widely studied is the Y402H allele in the complement factor H gene. The implication of this genetic association is that in a subset of AMD cases, unregulated complement activation is permissive for AMD. Given that this gene variant results in an amino acid substitution, it is assumed that this change will have functional consequences although the precise mechanisms are still unknown. Genetic predisposition is not the only factor however, since in this complex disease there is substantial evidence that lifestyle factors such as diet and smoking contribute to risk. Here we provide an overview of current knowledge with respect to factors involved in AMD pathogenesis. Interwoven with these issues is a discussion of the significant role played by aging processes, some of which are unique to the retina and retinal pigment epithelium. One recurring theme is the potential for disease promotion by diverse types of oxidation products.

NLRP3 has a protective role in age-related macular degeneration through the induction of IL-18 by drusen components.

Age-related macular degeneration (AMD) is the leading cause of central vision loss worldwide. Drusen accumulation is the major pathological hallmark common to both dry and wet AMD. Although activation of the immune system has been implicated in disease progression, the pathways involved are unclear. Here we show that drusen isolated from donor AMD eyes activates the NACHT, LRR and PYD domains-containing protein 3 (NLRP3) inflammasome, causing secretion of interleukin-1b (IL-1b) and IL-18. Drusen component C1Q also activates the NLRP3 inflammasome. Moreover, the oxidative-stress-related protein-modification carboxyethylpyrrole (CEP), a biomarker of AMD, primes the inflammasome. We found cleaved caspase-1 and NLRP3 in activated macrophages in the retinas of mice immunized with CEP-adducted mouse serum albumin, modeling a dry-AMD­like pathology. We show that laser-induced choroidal neovascularization (CNV), a mouse model of wet AMD, is exacerbated in Nlrp3(-/-) but not Il1r1(-/-) mice, directly implicating IL-18 in the regulation of CNV development. These findings indicate a protective role for NLRP3 and IL-18 in the progression of AMD.

Histologic findings after surgical excision of optic nerve head drusen.

PURPOSE: To report the histopathologic findings of a case of bilateral massive optic nerve head (ONH) drusen. METHODS: A 59-year-old man presented with bilateral massive ONH drusen and secondary compromise of the retinal vasculature leading to vision of counting fingers at 1 ft in the left eye and 20/30 in the right eye. The inferior one half of the left ONH druse was excised resulting in no light perception vision postoperatively. RESULTS: Energy-dispersive spectroscopy suggested the composition of the ONH druse to be calcium phosphate (Ca3[PO4]2), which has implications on pathogenesis of neuronal cell death in ONH drusen. Scanning electron microscopy demonstrated embedded metal particles, likely to be remnants of the instruments used. CONCLUSION: Massive ONH drusen are actually one large druse that has multiple excrescences on its surface giving it the variegated appearance. Although surgical excision of ONH drusen may be technically possible, consideration should be given to improvements in instrumentation and patient selection criteria.

Clathrin and adaptin accumulation in drusen, Bruch's membrane and choroid in AMD and non-AMD donor eyes.

Clathrin was identified in a recent proteomic analysis of Bruch's membrane from age-related macular degeneration (AMD) donor eyes. The present study was conducted to determine the localization of clathrin in AMD tissues and to compare this distribution and relative content with that in non-AMD control tissues. The distribution of adaptin, which is functionally linked to clathrin, was also evaluated. Human eyes were from donors between 66 and 94 years of age; 13 eyes were from donors with AMD and 13 from non-AMD donors. Bruch's membrane and choroid from the macula of each donor eye were prepared for immunohistochemistry and Western blotting. Differences in immunoreactivity were quantitated. Drusen, Bruch's membrane and choroid from AMD tissues showed greater immunoreactivity for clathrin and adaptin than did non-AMD tissues. Western blots also showed more intense clathrin and adaptin immunoreactivity in AMD tissues than were present in non-AMD samples. This study suggests that accumulation of clathrin and adaptin in drusen, Bruch's membrane and choroid may reflect a higher rate of clathrin mediated endocytosis in AMD tissues. Alternatively, the accumulation of these proteins in these extracellular compartments may reflect a higher susceptibility to oxidative damage.