The HDAC/HSP90 Inhibitor G570 Attenuated Blue Light-Induced Cell Migration in RPE Cells and Neovascularization in Mice through Decreased VEGF Production

Age-related macular degeneration (AMD) occurs due to an abnormality of retinal pigment epithelium (RPE) cells that leads to gradual degeneration of the macula. Currently, AMD drug pipelines are endowed with limited options, and anti-VEGF agents stand as the dominantly employed therapy. Despite the proven efficacy of such agents, the evidenced side effects associated with their use underscore the need to elucidate other mechanisms involved and identify additional molecular targets for the sake of therapy improvement. The previous literature provided us with a solid rationale to preliminarily explore the potential of selective HDAC6 and HSP90 inhibitors to treat wet AMD. Rather than furnishing single-target agents (either HDAC6 or HSP90 inhibitor), this study recruited scaffolds endowed with the ability to concomitantly modulate both targets (HDAC6 and HSP90) for exploration. This plan was anticipated to accomplish the important goal of extracting amplified benefits via dual inhibition (HDAC6/HSP90) in wet AMD. As a result, G570 (indoline-based hydroxamate), a dual selective HDAC6-HSP90 inhibitor exerting its effects at micromolar concentrations, was pinpointed in the present endeavor to attenuate blue light-induced cell migration and retinal neovascularization by inhibiting VEGF production. In addition to the identification of a potential chemical tool (G570), the outcome of this study validates the candidate HDAC6-HSP90 as a compelling target for the development of futuristic therapeutics for wet AMD.

Chronic Dicer1 deficiency promotes atrophic and neovascular outer retinal pathologies in mice

Degeneration of the retinal pigmented epithelium (RPE) and aberrant blood vessel growth in the eye are advanced-stage processes in blinding diseases such as age-related macular degeneration (AMD), which affect hundreds of millions of people worldwide. Loss of the RNase DICER1, an essential factor in micro-RNA biogenesis, is implicated in RPE atrophy. However, the functional implications of DICER1 loss in choroidal and retinal neovascularization are unknown. Here, we report that two independent hypomorphic mouse strains, as well as a separate model of postnatal RPE-specific DICER1 ablation, all presented with spontaneous RPE degeneration and choroidal and retinal neovascularization. DICER1 hypomorphic mice lacking critical inflammasome components or the innate immune adaptor MyD88 developed less severe RPE atrophy and pathological neovascularization. DICER1 abundance was also reduced in retinas of the JR5558 mouse model of spontaneous choroidal neovascularization. Finally, adenoassociated vector-mediated gene delivery of a truncated DICER1 variant (OptiDicer) reduced spontaneous choroidal neovascularization in JR5558 mice. Collectively, these findings significantly expand the repertoire of DICER1 in preserving retinal homeostasis by preventing both RPE degeneration and pathological neovascularization.

Low-Luminance Blue Light-Enhanced Phototoxicity in A2E-Laden RPE Cell Cultures and Rats

N-retinylidene-N-retinylethanolamine (A2E) and other bisretinoids are components of lipofuscin and accumulate in retinal pigment epithelial (RPE) cells—these adducts are recognized in the pathogenesis of retinal degeneration. Further, blue light-emitting diode (LED) light (BLL)-induced retinal toxicity plays an important role in retinal degeneration. Here, we demonstrate that low-luminance BLL enhances phototoxicity in A2E-laden RPE cells and rats. RPE cells were subjected to synthetic A2E, and the effects of BLL on activation of apoptotic biomarkers were examined by measuring the levels of cleaved caspase-3. BLL modulates the protein expression of zonula-occludens 1 (ZO-1) and paracellular permeability in A2E-laden RPE cells. Early inflammatory and angiogenic genes were also screened after short-term BLL exposure. In this study, we developed a rat model for A2E treatment with or without BLL exposure for 21 days. BLL exposure caused fundus damage, decreased total retinal thickness, and caused neuron transduction injury in the retina, which were consistent with the in vitro data. We suggest that the synergistic effects of BLL and A2E accumulation in the retina increase the risk of retinal degeneration. These outcomes help elucidate the associations between BLL/A2E and angiogenic/apoptotic mechanisms, as well as furthering therapeutic strategies.

Hydrogen sulfide: a gaseous signaling molecule modulates tissue homeostasis: implications in ophthalmic diseases

Hydrogen sulfide (H2S) serves as a gasotransmitter in the regulation of organ development and maintenance of homeostasis in tissues. Its abnormal levels are associated with multiple human diseases, such as neurodegenerative disease, myocardial injury, and ophthalmic diseases. Excessive exposure to H2S could lead to cellular toxicity, orchestrate pathological process, and increase the risk of various diseases. Interestingly, under physiological status, H2S plays a critical role in maintaining cellular physiology and limiting damages to tissues. In mammalian species, the generation of H2S is catalyzed by cystathionine beta-synthase (CBS), cystathionine gamma-lyase (CSE), 3-mercapto-methylthio pyruvate aminotransferase (3MST) and cysteine aminotransferase (CAT). These enzymes are found inside the mammalian eyeballs at different locations. Their aberrant expression and the accumulation of substrates and intermediates can change the level of H2S by orders of magnitude, causing abnormal structures or functions in the eyes. Detailed investigations have demonstrated that H2S donors' administration could regulate intraocular pressure, protect retinal cells, inhibit oxidative stress and alleviate inflammation by modulating the function of intra or extracellular proteins in ocular tissues. Thus, several slow-releasing H2S donors have been shown to be promising drugs for treating multiple diseases. In this review, we discuss the biological function of H2S metabolism and its application in ophthalmic diseases.

CRISPR-LbCpf1 prevents choroidal neovascularization in a mouse model of age-related macular degeneration

LbCpf1, derived from Lachnospiraceae bacterium ND2006, is a CRISPR RNA-guided endonuclease and holds promise for therapeutic applications. Here we show that LbCpf1 can be used for therapeutic gene editing in a mouse model of age-related macular degeneration (AMD). The intravitreal delivery of LbCpf1, targeted to two angiogenesis-associated genes encoding vascular endothelial growth factor A (Vegfa) and hypoxia inducing factor 1a (Hif1a), using adeno-associated virus, led to efficient gene disruption with no apparent off-target effects in the retina and retinal pigment epithelium (RPE) cells. Importantly, LbCpf1 targeted to Vegfa or Hif1a in RPE cells reduced the area of laser-induced choroidal neovascularization as efficiently as aflibercept, an anti-VEGF drug currently used in the clinic, without inducing cone dysfunction. Unlike aflibercept, LbCpf1 targeted to Vegfa or Hif1a achieved a long-term therapeutic effect on CNV, potentially avoiding repetitive injections. Taken together, these results indicate that LbCpf1-mediated in vivo genome editing to ablate pathologic angiogenesis provides an effective strategy for the treatment of AMD and other neovascularization-associated diseases.

Endomucin inhibits VEGF-induced endothelial cell migration, growth, and morphogenesis by modulating VEGFR2 signaling

Angiogenesis is central to both normal and pathologic processes. Endothelial cells (ECs) express O-glycoproteins that are believed to play important roles in vascular development and stability. Endomucin-1 (EMCN) is a type I O-glycosylated, sialic-rich glycoprotein, specifically expressed by venous and capillary endothelium. Evidence has pointed to a potential role for EMCN in angiogenesis but it had not been directly investigated. In this study, we examined the role of EMCN in angiogenesis by modulating EMCN levels both in vivo and in vitro. Reduction of EMCN in vivo led to the impairment of angiogenesis during normal retinal development in vivo. To determine the cellular basis of this inhibition, gain- and loss-of-function studies were performed in human retinal EC (HREC) in vitro by EMCN over-expression using adenovirus or EMCN gene knockdown by siRNA. We show that EMCN knockdown reduced migration, inhibited cell growth without compromising cell survival, and suppressed tube morphogenesis of ECs, whereas over-expression of EMCN led to increased migration, proliferation and tube formation. Furthermore, knockdown of EMCN suppressed VEGF-induced signaling as measured by decreased phospho-VEGFR2, phospho-ERK1/2 and phospho-p38-MAPK levels. These results suggest a novel role for EMCN as a potent regulator of angiogenesis and point to its potential as a new therapeutic target for angiogenesis-related diseases.

Complement activation and choriocapillaris loss in early AMD: implications for pathophysiology and therapy

Age-related macular degeneration (AMD) is a common and devastating disease that can result in severe visual dysfunction. Over the last decade, great progress has been made in identifying genetic variants that contribute to AMD, many of which lie in genes involved in the complement cascade. In this review we discuss the significance of complement activation in AMD, particularly with respect to the formation of the membrane attack complex in the aging choriocapillaris. We review the clinical, histological and biochemical data that indicate that vascular loss in the choroid occurs very early in the pathogenesis of AMD, and discuss the potential impact of vascular dropout on the retinal pigment epithelium, Bruch's membrane and the photoreceptor cells. Finally, we present a hypothesis for the pathogenesis of early AMD and consider the implications of this model on the development of new therapies.

Prediction of retinal pigment epithelial tear in serous vascularized pigment epithelium detachment

PURPOSE

The aim of the study was to identify predictive factors for detection of impending retinal pigment epithelium (RPE) tears in patients under anti-VEGF therapy for treatment of retinal pigment epithelial detachment (PED) due to exudative age-related macular degeneration (AMD) using near-infrared reflectance imaging (NIR), spectral-domain optical coherence tomography (SD-OCT) and fluorescein angiography (FLA).

METHODS

We retrospectively evaluated NIR, SD-OCT and FLA images, number of intravitreal injections as well as demographical data of 103 eyes of 98 patients with vascularized PED [48.5% fibrovascular PED (fPED), 51.5% serous vascularized PED (svPED)] secondary to AMD.

RESULTS

Fifteen eyes with svPED of 103 included eyes (14.6%) developed an RPE tear under anti-VEGF therapy. Prior to RPE tear formation, we could identify radial hyperreflective lines spreading in a funnel-like pattern across the PED lesion in NIR images in 11 eyes correlating with folds in the RPE on corresponding SD-OCT scans (mean observation period: 115.4 ± 66.6 days; mean number of injections: 3.2 ± 1.5; mean PED height 828.2 ± 356.5 μm). In nine RPE tears (81.8%), the edge of the tear could be clearly localized on the opposite side of the PED lesion in relation to the origin of hyperreflective lines. None of the fPED patients showed the described signal.

CONCLUSIONS

Patients under anti-VEGF therapy for treatment of svPED due to AMD frequently show radial hyperreflective lines in NIR images prior to RPE tear development that correspond to wrinkled changes in the RPE. Hyperreflective lines may serve as an indicator for an impending RPE tear in svPED patients.

The noninvasive retro-mode imaging modality of confocal scanning laser ophthalmoscopy in polypoidal choroidal vasculopathy: a preliminary application

PURPOSE

To evaluate the validity of the novel and noninvasive retro-mode imaging modality of confocal scanning laser ophthalmoscopy (cSLO) for detecting the morphological features of polypoidal choroidal vasculopathy (PCV).

DESIGN

Prospective, observational, consecutive case series.

METHODS

Twenty-six patients (29 eyes) with PCV were enrolled in this study. All patients underwent comprehensive ophthalmologic examinations and imaging studies, including retro-mode imaging, fundus autofluorescence (FAF), fundus photography, fundus fluorescein angiography (FFA), indocyanine green angiography (ICGA) and spectral-domain optical coherence tomography (SD-OCT). We investigated the retro-mode images and compared the results with those of SD-OCT, FFA and ICGA.

RESULTS

In the 29 PCV eyes, the retro-mode images clearly revealed polypoidal lesions in 27 (93.1%) eyes as well as branching vascular networks in 16 (55.2%) eyes. Others findings, including pigment epithelial detachment (PED) in 20 (69.0%) eyes, neuroretinal detachment (NRD) in 3 (10.3%) eyes, cystoid macular edema (CME) in 3 (10.3%) eyes, drusen in 4 (13.8%) eyes and minute granular changes of the retinal pigment epithelium (RPE) in 12 (41.3%) eyes, were also clearly visualized. When we compared the results with those of SD-OCT, FFA and ICGA, there was no significant difference between ICGA and retro-mode imaging for finding polypoidal lesions and (or) branching choroidal vascular networks (P>0.05). However, the rate of PED detection was significantly better with retro-mode imaging than with the ICGA (P<0.05). The differences were not statistically significant between SD-OCT and retro-mode imaging for detecting PED, NRD, CME, drusen and minute granular RPE changes (P>0.05). The differences were not statistically significant between FFA and retro-mode imaging for detecting PED, NRD, CME (P>0.05).

CONCLUSIONS

The novel and noninvasive retro-mode imaging by cSLO is able to clearly visualize the morphological features of PCV.

The blood-retina barrier: tight junctions and barrier modulation

The blood-retina barrier (BRB) is composed of both an inner and an outer barrier. The outer BRB refers to the barrier formed at the retinal pigment epithelial (RPE) cell layer and functions, in part, to regulate the movement of solutes and nutrients from the choroid to the sub-retinal space. In contrast, the inner BRB, similar to the blood brain barrier (BBB) is located in the inner retinal microvasculature and comprises the microvascular endothelium which line these vessels. The tight junctions located between these cells mediate highly selective diffusion of molecules from the blood to the retina and the barrier is essential in maintaining retinal homeostasis. In this chapter, we summarize the key differences between the iBRB and oBRB and outline the molecular constituents of the tight junctions associated with the iBRB. We also describe a process for modulation of the iBRB to enhance systemic delivery of therapeutics to the retina, a technology which may pave the way for safer and more effective therapies for retinal diseases.

The inner blood-retinal barrier: molecular structure and transport biology

The inner blood-retinal barrier (inner BRB) is created by complex tight junctions of retinal capillary endothelial cells. Although this barrier prevents the free diffusion of substances between the circulating blood and the neural retina, the inner BRB efficiently supplies nutrients to the retina and removes endobiotics and xenobiotics from the retina to maintain a constant milieu in the neural retina. We review herein the molecular structure and transport mechanism at the inner BRB.

[The value of autofluorescence imaging in diagnosis of retinal diseases]

Results of fundus autofluorescence imaging using confocal scanning laser ophthalmoscope HRA II ("Heidelberg Engeneering", Heidelberg, Germany) are presented. 106 patients with various retinal and optic nerve conditions were examined. The following conditions were diagnosed using autofluorescence imaging: early stage of age-related macular degeneration, macular hard and soft drusen, signs of retinitis pigmentosa, senile macular hole, central serous chorioretinopathy and optic disc drusen.

Rescue and repair during photoreceptor cell renewal mediated by docosahexaenoic acid-derived neuroprotectin D1

Retinal degenerative diseases result in retinal pigment epithelial (RPE) and photoreceptor cell loss. These cells are continuously exposed to the environment (light) and to potentially pro-oxidative conditions, as the retina's oxygen consumption is very high. There is also a high flux of docosahexaenoic acid (DHA), a PUFA that moves through the blood stream toward photoreceptors and between them and RPE cells. Photoreceptor outer segment shedding and phagocytosis intermittently renews photoreceptor membranes. DHA is converted through 15-lipoxygenase-1 into neuroprotectin D1 (NPD1), a potent mediator that evokes counteracting cell-protective, anti-inflammatory, pro-survival repair signaling, including the induction of anti-apoptotic proteins and inhibition of pro-apoptotic proteins. Thus, NPD1 triggers activation of signaling pathway/s that modulate/s pro-apoptotic signals, promoting cell survival. This review provides an overview of DHA in photoreceptors and describes the ability of RPE cells to synthesize NPD1 from DHA. It also describes the role of neurotrophins as agonists of NPD1 synthesis and how photoreceptor phagocytosis induces refractoriness to oxidative stress in RPE cells, with concomitant NPD1 synthesis.

[Autologous choroidal RPE patch transplantation for submacular hemorrhage in age-related macular degeneration]

PURPOSE

To report autologous choroidal RPE patch transplantation for treatment of submacular hemorrhage in a patients with age related macular degeneration.

MATERIAL AND METHODS

A case report of a patient with sudden vision deterioration due to submacular hemorrhage in AMD. The visual acuity was 5/5 in the right eye and 0.5/50 in the left eye. He was treated with autologous choroidal RPE patch transplantation. Outcome measures included preoperative and postoperative visual acuity at 1, 3, 6 months, duration of hemorrhage, hemorrhage size on preoperative fluorescein angiography and thickness of the subretinal hemorrhagic complex on preoperative and postoperative OCT scans.

RESULTS

Visual acuity improved from 0.5/50 to 5/50 in 6 months follow-up. No major intraoperative and postoperative complications were observed. The perfusion of the graft was confirmed in ICG angiography.

CONCLUSIONS

Autologous choroidal RPE patch transplantation is an effective option for submacular hemorrhage treatment in AMD. Unlike macular translocation, the surgery can be performed even in patients with excellent visual acuity in the fellow eye.