Thermal Stimulation of the Retina Reduces Bruch's Membrane Thickness in Age Related Macular Degeneration Mouse Models

Nanosecond laser induces proliferation and improved cellular health within the retinal pigment epithelium

Background

Age-related macular degeneration (AMD) is a leading cause of vision loss in those over 60 years of age. Although there are limited interventions that may prevent the development or progression of disease, more efficacious treatments are required. Short-pulsed laser treatment shows promise in delaying progression of early disease. This work details how nanosecond laser influences the retinal pigment epithelium (RPE), the principal cell type implicated in AMD.

Methods

C57BL/6J mice (3-month-old) underwent monocular nanosecond laser treatment to assess short-term RPE response, while 9-month-old C57BL/6J and ApoEnull mice were similarly treated and longer-term responses investigated after 3 months. Human tissue was also obtained after 2 nanosecond laser treatments (1 month apart). RPE proliferation was assessed using bromodeoxyuridine and RPE gene change explored using qPCR and RNAseq. Melanin and lipofuscin content were quantified using histological techniques.

Results

Nanosecond laser induced RPE proliferation in treated and fellow mouse eyes, with monolayer repair occurring within 3 days. This was replicated in human tissue, albeit over a longer duration (1-4 weeks). Wildtype animals showed no overt change in RPE gene expression after short or longer post-treatment durations, while laser treated ApoEnull animals showed increased Mertk and Pedf expression, and a reduced number of dysregulated aging genes in treated and fellow eyes after 3 months. Furthermore, melanin and lipofuscin content were restored to wildtype levels in laser-treated ApoEnull RPE, while melanolipofuscin granules were reduced within treated regions of human RPE.

Conclusion

This work shows nanosecond laser stimulates RPE proliferation and results in an improved cellular phenotype. These data provide a biological basis for the prophylactic use of nanosecond lasers in AMD.

Regenerative Retinal Laser and Light Therapies (RELITE): Proposal of a New Nomenclature, Categorization, and Trial Reporting Standard

OBJECTIVES

Numerous laser and light therapies have been developed to induce regenerative processes in the choroid/retinal pigment epithelium (RPE)/photoreceptor complex, leaving the neuroretina undamaged. These therapies are applied to the macula for the treatment of various diseases, most prominently diabetic maculopathy, retinal vein occlusion, central serous chorioretinopathy, and age-related macular degeneration. However, the abundance of technologies, treatment patterns, and dosimetry protocols has made understanding these therapies and comparing different approaches increasingly complex and challenging. To address this, we propose a new nomenclature system with a clear categorization that will allow for better understanding and comparability between different laser and light modalities. We propose this nomenclature system as an open standard that may be adapted in future toward new technical developments or medical advancements.

METHODS

A systematic literature review of reported macular laser and light therapies was conducted. A categorization into a standardized system was proposed and discussed among experts and professionals in the field. This paper does not aim to assess, compare, or evaluate the efficacy of different laser or dosimetry techniques or treatment patterns.

RESULTS

The literature search yielded 194 papers describing laser techniques, 50 studies describing dosimetry, 272 studies with relevant clinical trials, and 82 reviews. Following the common therapeutic aim, we propose "regenerative retinal laser and light therapies (RELITE)" as the general header. We subdivided RELITE into four main categories that refer to the intended physical and biochemical effects of temperature increase (photothermal therapy, PTT), RPE regeneration (photomicrodisruption therapy, PMT), photochemical processes (photochemical therapy, PCT), and photobiomodulation (photobiomodulation therapy, PBT). Further, we categorized the different dosimetry approaches and treatment regimens. We propose the following nomenclature system that integrates the most important parameters to enable understanding and comparability: Pattern-Dosimetry-Exposure Time/Frequency, Duty Cycle/Irradiation Diameter/Wavelength-Subcategory-Category.

CONCLUSION

Regenerative retinal laser and light therapies are widely used for different diseases and may become valuable in the future. A precise nomenclature system and strict reporting standards are needed to allow for a better understanding, reproduceable and comparable clinical trials, and overall acceptance. We defined categories for a systematic therapeutic goal-based nomenclature to facilitate future research in this field.

Effects of Fucoidans on Activated Retinal Microglia

Sulfated marine polysaccharides, so-called fucoidans, have been shown to exhibit anti-inflammatory and immunomodulatory activities in retinal pigment epithelium (RPE). In this study, we tested the effects of different fucoidans (and of fucoidan-treated RPE cells) on retinal microglia to investigate whether its anti-inflammatory effect can be extrapolated to the innate immune cells of the retina. In addition, we tested whether fucoidan treatment influenced the anti-inflammatory effect of RPE cells on retinal microglia. Three fucoidans were tested (FVs from Fucus vesiculosus, Fuc1 and FucBB04 from Laminaria hyperborea) as well as the supernatant of primary porcine RPE treated with fucoidans for their effects on inflammatory activated (using lipopolysaccharide, LPS) microglia cell line SIM-A9 and primary porcine retinal microglia. Cell viability was detected with a tetrazolium assay (MTT), and morphology by Coomassie staining. Secretion of tumor necrosis factor alpha (TNFα), interleukin 1 beta (IL1β) and interleukin 8 (IL8) was detected with ELISA, gene expression (NOS2 (Nitric oxide synthase 2), and CXCL8 (IL8)) with qPCR. Phagocytosis was detected with a fluorescence assay. FucBB04 and FVs slightly reduced the viability of SIM-A9 and primary microglia, respectively. Treatment with RPE supernatants increased the viability of LPS-treated primary microglia. FVs and FucBB04 reduced the size of LPS-activated primary microglia, indicating an anti-inflammatory phenotype. RPE supernatant reduced the size of LPS-activated SIM-A9 cells. Proinflammatory cytokine secretion and gene expression in SIM-A9, as well as primary microglia, were not significantly affected by fucoidans, but RPE supernatants reduced the secretion of LPS-induced proinflammatory cytokine secretion in SIM-A9 and primary microglia. The phagocytosis ability of primary microglia was reduced by FucBB04. In conclusion, fucoidans exhibited only modest effects on inflammatorily activated microglia by maintaining their cell size under stimulation, while the anti-inflammatory effect of RPE cells on microglia irrespective of fucoidan treatment could be confirmed, stressing the role of RPE in regulating innate immunity in the retina.

Diverse functions and pathogenetic role of Crumbs in retinopathy

The Crumbs protein (CRB) family plays a crucial role in maintaining the apical-basal polarity and integrity of embryonic epithelia. The family comprises different isoforms in different animals and possesses diverse structural, localization, and functional characteristics. Mutations in the human CRB1 or CRB2 gene may lead to a broad spectrum of retinal dystrophies. Various CRB-associated experimental models have recently provided mechanistic insights into human CRB-associated retinopathies. The knowledge obtained from these models corroborates the importance of CRB in retinal development and maintenance. Therefore, complete elucidation of these models can provide excellent therapeutic prospects for human CRB-associated retinopathies. In this review, we summarize the current animal models and human-derived models of different CRB family members and describe the main characteristics of their retinal phenotypes.

Bioinformatics analysis for constructing a cellular senescence-related age-related macular degeneration diagnostic model and identifying relevant disease subtypes to guide treatment

Age-related macular degeneration (AMD) is a condition causing progressive central vision loss. Growing evidence suggests a link between cellular senescence and AMD. However, the exact mechanism by which cellular senescence leads to AMD remains unclear. Employing machine learning, we established an AMD diagnostic model. Through unsupervised clustering, two distinct AMD subtypes were identified. GO, KEGG, and GSVA analyses explored the diverse biological functions associated with the two subtypes. By WGCNA, we constructed a coexpression network of differential genes between the subtypes, revealing the regulatory role of hub genes at the level of transcription factors and miRNAs. We identified 5 genes associated with inflammation for the construction of the AMD diagnostic model. Additionally, we observed that the level of cellular senescence and pathways related to programmed cell death (PCD), such as ferroptosis, necroptosis, and pyroptosis, exhibited higher expression levels in subtype B than A. Immune microenvironments also differed between the subtypes, indicating potentially distinct pathogenic mechanisms and therapeutic targets. In summary, by leveraging cellular senescence-associated gene expression, we developed an AMD diagnostic model. Furthermore, we identified two subtypes with varying expression patterns of senescence genes, revealing their differential roles in programmed cell death, disease progression, and immune microenvironments within AMD.

Real-Time Temperature-Controlled Retinal Laser Irradiation in Rabbits

Purpose

Subdamaging thermal retinal laser therapy has the potential to induce regenerative stimuli in retinal diseases, but validated dosimetry is missing. Real-time optoacoustic temperature determination and control could close this gap. This study investigates a first in vivo application.

Methods

Two iterations of a control module that were optically coupled in between a continuous-wave commercial laser source and a commercial slit lamp were evaluated on chinchilla rabbits. The module allows extraction of the temperature rise in real time and can control the power of the therapy laser such that a predefined temperature rise at the retina is quickly achieved and held constant. Irradiations with aim temperatures from 45°C to 69°C were performed on a diameter of 200 µm and a heating time of 100 ms.

Results

We analyzed 424 temperature-guided irradiations in nine eyes of five rabbits. The mean difference between the measured and aim temperature was -0.04°C ± 0.98°C. The following ED50 values for visibility thresholds could be determined: 58.6°C for funduscopic visibility, 57.7°C for fluorescein angiography, and 57.0°C for OCT. In all measurements, the correlation of tissue effect was higher to the temperature than to the average heating laser power used.

Conclusions

The system was able to reliably perform temperature-guided irradiations, which allowed for better tissue effect control than simple power control. This approach could enhance the accuracy, safety, and reproducibility of thermal stimulating laser therapy.

Translational Relevance

This study is a bridge between preclinical ex vivo experiments and a pilot clinical study.

Optical Coherence Tomography: Imaging Visual System Structures in Mice

Optical coherence tomography (OCT) enables micron-scale resolution of structural anatomy, thereby making OCT a valuable tool for addressing ophthalmologic and neurologic inquiries. Although the murine eye and its structures are very small and offers challenges for OCT imaging, OCT can be used to monitor retinal layer thickness in healthy and diseased retinas in murine lines in vivo longitudinally. Thus, OCT can provide insights into disease severity and treatment efficacy. This chapter describes the use of OCT as a powerful non-invasive imaging technology for high-resolution retinal imaging and retinal thickness quantification in rodents.

Temperature Increase and Damage Extent at Retinal Pigment Epithelium Compared between Continuous Wave and Micropulse Laser Application

Continuous wave (CW) and microsecond pulse (MP) laser irradiations were compared regarding cell damage and laser-induced temperature rise at retinal pigment epithelium (RPE). The RPE of porcine RPE-choroid-sclera explants was irradiated with a 577 nm laser in CW or MP mode (5% or 15% duty cycle (DC)) for 20 ms or 200 ms at an average laser power of 20−90 mW. Cell viability was investigated with calcein-AM staining. Optoacoustic (OA) technique was employed for temperature measurement during irradiation. For 200 ms irradiation, the dead cell area (DCA) increased linearly (≈1600 µm2/mW) up to the average power of 40 mW for all modes without significant difference. From 50 mW, the increase of DCA of MP-5% significantly dropped to 610 µm2/mW (p < 0.05), likely due to the detected microbubble formation. OA temperature measurement showed a monotonic temperature increase in CW mode and a stepwise increase in MP mode, but no significant difference in the average temperature increase at the same average power, consistent with the temperature modeling. In conclusion, there is no difference in the average temperature rise between CW and MP modes at the same average power regardless of DC. At lower DC, however, more caution is required regarding mechanical damage due to microbubble formation.

Properties of Cephalopod Skin Ommochromes to Inhibit Free Radicals, and the Maillard Reaction and Retino-Protective Mechanisms in Cellular Models Concerning Oxidative Stress, Angiogenesis, and Inflammation

Ommochromes are pigments of invertebrates that exhibit oxidative stress protection. The aim of this study was to investigate ommochromes extracted from cephalopod’s skin for their ability to inhibit age-related-macular degeneration (AMD)-related factors such as H₂O₂-induced and iron-dependent oxidative stress (ferroptosis and erastin), accumulation of advanced glycation end-products (AGEs), as well as vascular endothelial growth factor (VEGF), and inflammatory cytokines (interleukin 6 and interleukin 8) secretion. As cell systems, we used primary porcine retinal pigment epithelium (RPE), human retinal pigment epithelium cell line ARPE-19 and uveal melanoma cell line OMM-1. In vitro, ommochromes produced an antiglycation effect by the inhibition of fructosylation reaction. The ommochromes showed protective effects against erastin- induced cell death in ARPE-19. In addition, in long-term stimulation (7 days) ommochromes decreased constitutively secreted VEGF, as well as interleukin 6 and interleukin 8 induced by Poly I:C in primary RPE. No relevant effects were detected in OMM-1 cells. The effects are dependent on the cell system, time of exposition, and concentration. This substance is of interest for further research concerning age-related macular degeneration.

Selective retina therapy and thermal stimulation of the retina: different regenerative properties - implications for AMD therapy

BACKGROUND

Selective Retina Therapy (SRT), a photodisruptive micropulsed laser modality that selectively destroys RPE cells followed by regeneration, and Thermal Stimulation of the Retina (TSR), a stimulative photothermal continuous wave laser modality that leads to an instant sublethal temperature increase in RPE cells, have shown therapeutic effects on Age-related Macular Degeneration (AMD) in mice. We investigate the differences between both laser modalities concerning RPE regeneration.

METHODS

For PCR array, 6 eyes of murine AMD models, apolipoprotein E and nuclear factor erythroid-derived 2- like 2 knock out mice respectively, were treated by neuroretina-sparing TSR or SRT. Untreated litter mates were controls. Eyes were enucleated either 1 or 7 days after laser treatment. For morphological analysis, porcine RPE/choroid organ cultures underwent the same laser treatment and were examined by calcein vitality staining 1 h and 1, 3 or 5 days after irradiation.

RESULTS

TSR did not induce the expression of cell-mediators connected to cell death. SRT induced necrosis associated cytokines as well as inflammation 1 but not 7 days after treatment. Morphologically, 1 h after TSR, there was no cell damage. One and 3 days after TSR, dense chromatin and cell destruction of single cells was seen. Five days after TSR, there were signs of migration and proliferation. In contrast, 1 h after SRT a defined necrotic area within the laser spot was seen. This lesion was closed over days by migration and proliferation of adjacent cells.

CONCLUSIONS

SRT induces RPE cell death, followed by regeneration within a few days. It is accompanied by necrosis induced inflammation, RPE proliferation and migration. TSR does not induce immediate RPE cell death; however, migration and mitosis can be seen a few days after laser irradiation, not accompanied by necrosis-associated inflammation. Both might be a therapeutic option for the treatment of AMD.

Retinal temperature determination based on photopic porcine electroretinogram

OBJECTIVE

Subthreshold retinal laser therapy (SLT) is a treatment modality where the temperature of the retinal pigment epithelium (RPE) is briefly elevated to trigger the therapeutic benefits of sublethal heat shock. However, the temperature elevation induced by a laser exposure varies between patients due to individual differences in RPE pigmentation and choroidal perfusion. This study describes an electroretinography (ERG)-based method for controlling the temperature elevation during SLT.

METHODS

The temperature dependence of the photopic ERG response kinetics were investigated both ex vivo with isolated pig retinas and in vivo with anesthetized pigs by altering the temperature of the subject and recording ERG in different temperatures. A model was created for ERG-based temperature estimation and the feasibility of the model for controlling SLT was assessed through computational simulations.

RESULTS

The kinetics of the photopic in vivo flash ERG signaling accelerated between 3.6 and 4.7%/C, depending on the strength of the stimulus. The temperature dependence was 5.0%/C in the entire investigated range of 33 to 44C in ex vivo ERG. The simulations showed that the method is suitable for determining the steady-state temperature elevation in SLT treatments with a sufficiently long laser exposure and large spot size, e.g., during > 30 s laser exposures with > 3 mm stimulus spot diameter.

CONCLUSIONS

The described ERG-based temperature estimation model could be used to control SLT treatments such as transpupillary thermotherapy.

SIGNIFICANCE

The introduced ERG-based method for controlling SLT could improve the repeatability, safety, and efficacy of the treatment of various retinal disorders.

Retinal Pigment Epithelium Expressed Toll-like Receptors and Their Potential Role in Age-Related Macular Degeneration

(1) Background: Inflammation is a major pathomechanism in the development and progression of age-related macular degeneration (AMD). The retinal pigment epithelium (RPE) may contribute to retinal inflammation via activation of its Toll-like receptors (TLR). TLR are pattern recognition receptors that detect the pathogen- or danger-associated molecular pattern. The involvement of TLR activation in AMD is so far not understood. (2) Methods: We performed a systematic literature research, consulting the National Library of Medicine (PubMed). (3) Results: We identified 106 studies, of which 54 were included in this review. Based on these studies, the current status of TLR in AMD, the effects of TLR in RPE activation and of the interaction of TLR activated RPE with monocytic cells are given, and the potential of TLR activation in RPE as part of the AMD development is discussed. (4) Conclusion: The activation of TLR2, -3, and -4 induces a profound pro-inflammatory response in the RPE that may contribute to (long-term) inflammation by induction of pro-inflammatory cytokines, reducing RPE function and causing RPE cell degeneration, thereby potentially constantly providing new TLR ligands, which could perpetuate and, in the long run, exacerbate the inflammatory response, which may contribute to AMD development. Furthermore, the combined activation of RPE and microglia may exacerbate neurotoxic effects.

Influence of Retinal Microsecond Pulse Laser Treatment in Central Serous Chorioretinopathy: A Short-Term Optical Coherence Tomography Angiography Study

Background: Central serous chorioretinopathy (CSC) is a common macular condition characterized by detachment of the neuroretina and is a frequent cause of central vision loss in adults. Among the various therapeutic strategies, subthreshold microsecond pulsed laser (SML) treatment has become a useful option. Despite the suggested involvement of choroidal circulatory disturbances in CSC, the effects of this treatment on macular microperfusion have not been fully evaluated yet. Herein, we report the impact of SML on retinal and choroidal microvascular flow using non-invasive optical coherence tomography (OCT) angiography (OCTA). Methods: In this study, CSC patients with persistent subretinal fluid (SRF) with or without secondary choroidal neovascularization (CNV) were included (referred to as the pachychoroid neovasculopathy (PNV) group and the CSC group, respectively). SML was conducted using a yellow (577 nm) laser with a duty cycle of 10%, spot size of 200 µm and duration of 200 ms. Best corrected visual acuity (BCVA) as well as OCT and OCTA images were evaluated at baseline and 4 weeks after SML. OCTA parameters of interest included full retinal perfusion (FRP), choriocapillaris perfusion (CCP), Sattler’s layer perfusion (SLP), and Haller’s layer perfusion (HLP), which were evaluated longitudinally and compared to unaffected fellow eyes. Results: 27 affected eyes and 17 fellow eyes from 27 patients were included. Before treatment, central retinal thickness (CRT) and subfoveal choroidal thickness (SFCT) of affected eyes were significantly larger than in fellow eyes. Four weeks after SML, CRT decreased significantly, whereas perfusion parameters did not change. In subgroup analyses, the CSC group showed a significant decrease in SFCT, whereas the PNV group did not despite the decrease in CRT. Conclusion: Our results suggest that the SML may affect the SFCT of the CSC, but not the PNV patients at least within four weeks following treatment. This effect seems to be independent of the change in choroidal perfusion measured with OCTA.

Fucoidans as Potential Therapeutics for Age-Related Macular Degeneration-Current Evidence from In Vitro Research

Age-related macular degeneration (AMD) is the major reason for blindness in the industrialized world with limited treatment options. Important pathogenic pathways in AMD include oxidative stress and vascular endothelial growth factor (VEGF) secretion. Due to their bioactivities, fucoidans have recently been suggested as potential therapeutics. This review gives an overview of the recent developments in this field. Recent studies have characterized several fucoidans from different species, with different molecular characteristics and different extraction methods, in regard to their ability to reduce oxidative stress and inhibit VEGF in AMD-relevant in vitro systems. As shown in these studies, fucoidans exhibit a species dependency in their bioactivity. Additionally, molecular properties such as molecular weight and fucose content are important issues. Fucoidans from Saccharina latissima and Laminaria hyperborea were identified as the most promising candidates for further development. Further research is warranted to establish fucoidans as potential therapeutics for AMD.

Organ Cultures for Retinal Diseases

The successful development of novel therapies is closely linked with understanding the underlying pathomechanisms of a disease. To do so, model systems that reflect human diseases and allow for the evaluation of new therapeutic approaches are needed. Yet, preclinical animal studies often have limited success in predicting human physiology, pathology, and therapeutic responses. Moreover, animal testing is facing increasing ethical and bureaucratic hurdles, while human cell cultures are limited in their ability to represent in vivo situations due to the lack of the tissue microenvironment, which may alter cellular responses. To overcome these struggles, organ cultures, especially those of complex organs such as the retina, can be used to study physiological reactions to substances or stressors. Human and animal organ cultures are now well established and recognized. This mini-review discusses how retinal organ cultures can be used to preserve tissue architecture more realistically and therefore better represent disease-related changes. It also shows how molecular biological, biochemical, and histological techniques can be combined to investigate how anatomical localization may alter cellular responses. Examples for the use of retinal organ cultures, including models to study age-related macular degeneration (AMD), retinitis pigmentosa (RP), central artery occlusion (CRAO), and glaucoma are presented, and their advantages and disadvantages are discussed. We conclude that organ cultures significantly improve our understanding of complex retinal diseases and may advance treatment testing without the need for animal testing.

Retbindin: A riboflavin Binding Protein, Is Critical for Photoreceptor Homeostasis and Survival in Models of Retinal Degeneration

The large number of inherited retinal disease genes (IRD), including the photopigment rhodopsin and the photoreceptor outer segment (OS) structural component peripherin 2 (PRPH2), has prompted interest in identifying common cellular mechanisms involved in degeneration. Although metabolic dysregulation has been shown to play an important role in the progression of the disease etiology, identifying a common regulator that can preserve the metabolic ecosystem is needed for future development of neuroprotective treatments. Here, we investigated whether retbindin (RTBDN), a rod-specific protein with riboflavin binding capability, and a regulator of riboflavin-derived cofactors flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), is protective to the retina in different IRD models; one carrying the P23H mutation in rhodopsin (which causes retinitis pigmentosa) and one carrying the Y141C mutation in Prph2 (which causes a blended cone-rod dystrophy). RTBDN levels are significantly upregulated in both the rhodopsin (Rho)^P23H/+ and Prph2^Y141C/+ retinas. Rod and cone structural and functional degeneration worsened in models lacking RTBDN. In addition, removing Rtbdn worsened other phenotypes, such as fundus flecking. Retinal flavin levels were reduced in Rho^P23H/+/Rtbdn^−/− and Prph2^Y141C/+/Rtbdn^−/− retinas. Overall, these findings suggest that RTBDN may play a protective role during retinal degenerations that occur at varying rates and due to varying disease mechanisms.

Novel Porcine Retina Cultivation Techniques Provide Improved Photoreceptor Preservation

Age-related macular degeneration (AMD) is the leading cause of blindness in industrialized countries among people over 60 years. It has multiple triggers and risk factors, but despite intense research efforts, its pathomechanisms are currently not completely understood. AMD pathogenesis is characterized by soft drusen in Bruch’s membrane and involves the retinal pigment epithelium–Bruch’s membrane-choroid complex and adjacent structures, like photoreceptors. This study explores the potential of novel cultivation techniques to preserve photoreceptors in retinal explants to gain better insights in AMD pathology. The porcine retina explants were cultured for 4 and 8 days using three different explantation techniques, namely, control (photoreceptors facing down, touching the filter), filter (photoreceptors facing up, turned sample using a filter), and tweezers (photoreceptors facing up, turned sample using tweezers). Optical coherence tomography revealed that the tweezers method had the best capacity to limit thinning of the retinal explants. Both novel methods displayed advantages in maintaining outer segment thickness. Additionally, immunofluorescence evaluation revealed a better preservation of opsin⁺ cells and rhodopsin signal intensity in both novel methods, especially the tweezers method. Furthermore, RT-qPCR analysis demonstrated an upregulation of OPSIN and RHODOPSIN mRNA expression in tweezers samples at 8 days. Amacrine and bipolar cell numbers were not altered at day 4 of cultivation, while cultivation until 8 days led to reduced bipolar cell numbers. At 4 days, CALRETININ mRNA was upregulated in filter samples, but protein kinase C alpha expression was downregulated. Retinal ganglion cells were diminished in both novel techniques due to a direct physical contact with the insert. Remarkably, no difference in TUBB3 mRNA expression was detected among the techniques. Nevertheless, both novel methods exhibited an improved retention of photoreceptor cells. In conclusion, the tweezers technique was the most promising one. Due to the high homology of the porcine to the human retina, it provides a reasonable alternative to in vivo rodent models. Consequently, an adapted coculture system based on the current findings may serve as an ex vivo model suitable to analyze AMD pathomechanisms and novel therapeutic approaches.

Retina in a dish: Cell cultures, retinal explants and animal models for common diseases of the retina

For many retinal diseases, including age-related macular degeneration (AMD), glaucoma, and diabetic retinopathy (DR), the exact pathogenesis is still unclear. Moreover, the currently available therapeutic options are often unsatisfactory. Research designed to remedy this situation heavily relies on experimental animals. However, animal models often do not faithfully reproduce human disease and, currently, there is strong pressure from society to reduce animal research. Overall, this creates a need for improved disease models to understand pathologies and develop treatment options that, at the same time, require fewer or no experimental animals. Here, we review recent advances in the field of in vitro and ex vivo models for AMD, glaucoma, and DR. We highlight the difficulties associated with studies on complex diseases, in which both the initial trigger and the ensuing pathomechanisms are unclear, and then delineate which model systems are optimal for disease modelling. To this end, we present a variety of model systems, ranging from primary cell cultures, over organotypic cultures and whole eye cultures, to animal models. Specific advantages and disadvantages of such models are discussed, with a special focus on their relevance to putative in vivo disease mechanisms. In many cases, a replacement of in vivo research will mean that several different in vitro models are used in conjunction, for instance to analyze and validate causative molecular pathways. Finally, we argue that the analytical decomposition into appropriate cell and tissue model systems will allow making significant progress in our understanding of complex retinal diseases and may furthermore advance the treatment testing.

Celastrol Protects RPE Cells from Oxidative Stress-Induced Cell Death via Activation of Nrf2 Signaling Pathway

PURPOSE

Oxidative stress to retinal pigment epithelial (RPE) cells and inflammation are closely related to the pathogenesis of age-related macular degeneration (AMD). Celastrol is a natural compound isolated from the root of Tripterygium wilfordii. Celastrol has been shown to have potent anti-inflammatory and anti-tumor effects in multiple disease models. The objective of this study was to test the anti-oxidative effects of celastrol in RPE cells and to investigate the underlying mechanisms.

METHODS

ARPE-19 cells were treated with hydrogen peroxide (H2O2) and menadione alone or in combination with celastrol. Cell viability and apoptosis were examined by CCK-8 and TUNEL assay, respectively. The expression of Nrf2 and its target genes, such as GCLM and HO-1 was determined by Western blotting. The knockdown of Nrf2 was done by transfecting ARPE-19 cells with lentivirus encoding shRNA against Nrf2. The knockdown efficiency was determined by real-time quantitative PCR and Western blotting.

RESULTS

Treatment of ARPE-19 cells with celastrol significantly attenuated the toxic effects of both H2O2 and menadione. Treatment with celastrol enhanced the expression of transcription factor Nrf2 and its targets, GCLM and HO-1. Knockdown of Nrf2 expression by shRNA partially abolished the protective effects of celastrol. Chemical inhibition of glutathione synthesis by L-buthionine-S,R-sulfoximine (BSO) completely abolished the protective effects of celastrol against H2O2 and menadione-induced damage. However, chemical inhibition of HO-1 activity by ZnPPIX did not reduce the protective effects of celastrol.

CONCLUSION

This study provides evidence that treatment of RPE cells with celastrol shows potent protective effects against oxidative insults via activation of Nrf2 signaling pathway and upregulation of GCLM expression. This finding suggests that celastrol might be used as a potential therapeutic agent for oxidative stress-related eyes diseases, such as AMD.

Response of Retinal Pigment Epithelium (RPE)-Choroid Explants to Thermal Stimulation Therapy of the RPE (TSR)

BACKGROUND AND OBJECTIVES

The thermal stimulation therapy of the retinal pigment epithelium (TSR) is a sublethal laser technique for thermal stimulation of the retinal pigment epithelium (RPE)-Bruch's membrane (BrM)-complex. The aim of this study was to investigate the influence of TSR on the release of age-related macular degeneration (AMD)-relevant cell mediators.

STUDY DESIGN/MATERIALS AND METHODS

Porcine RPE-BrM-choroid explants were irradiated with a 532 nm continuous wave laser using different spot sizes (100-300 µm, duration 100 milliseconds, 15-100 mW). Cell death was investigated by calcein staining. Explants were treated with grids of sublethal spots and cultivated in modified Ussing chambers. The effect on matrix metalloproteinase-2 (MMP-2) and -9 was investigated by zymography and quantitative reverse transcription polymerase chain reaction. Secretion of vascular endothelial growth factor (VEGF), pigment epithelium derived factor (PEDF), and transforming growth factor-β (TGF-β) was analyzed by enzyme-linked immunosorbent assay and expression of HSP70 was examined by western blot. Integrity of the RPE/BrM-complex was analyzed by scanning electron microscopy.

RESULTS

Laser powers of 15 mW (100 µm) and 45 mW (300 µm) did not induce RPE cell death. The integrity of the RPE/BrM-complex was not impaired after TSR. After TSR with 300 µm spot size, we observed a significant increase of active MMP-2 in the basal compartments. The content of PEDF significantly increased in treated explants in both compartments with 100 and 300 µm spot sizes. VEGF and TGF-β secretion was not triggered by TSR.

CONCLUSIONS

TSR represents a possible RPE stimulating treatment for dry AMD. TSR increases the basal release of active MMP-2, which might reverse age-related thickening of BrM. VEGF secretion was not triggered by TSR while anti-angiogenic PEDF was increased, indicating an induction of an anti-angiogenic and neuroprotective environment. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.

Modulation of inflammatory processes by thermal stimulating and RPE regenerative laser therapies in age related macular degeneration mouse models

Purpose

Inflammatory processes play a major role within the multifactorial pathogenesis of age-related macular degeneration (AMD). Neuroretina sparing laser therapies, thermal stimulation of the retina (TSR) and selective retina therapy (SRT), are known to reduce AMD-like pathology in vitro and in vivo. We investigated the effect of TSR and SRT on inflammatory processes in AMD mouse models.

Methods

One randomized eye of 8 months old apolipoprotein (Apo)E and 9 months old nuclear factor (erythroid-derived 2) -like 2 (NRF2) knock out mice were treated by TSR (10 ms, 532 nm, 50 µm² spot size, mean 4.5 W, ~200 spots) or SRT (~1.4 µs pulses, 532 nm, 50 µm spot size, 100 Hz over 300 ms, mean 2.5 µJ per pulse, ~200 spots). Fellow eyes, untreated knock out mice and wild-type BL/6J mice acted as controls. All mice were examined funduscopically and by optical coherence tomography (OCT) at the day of laser treatment. Mice were euthanized and enucleated either 1 day or 7 days after laser treatment and examined by gene expression analysis of 84 inflammatory genes.

Results

The inflammatory gene expression profile of both knock out models compared to healthy BL/6J mice suggests a regulation of pro- and anti-inflammatory processes especially concerning T-cell activity and immune cell recruitment. TSR resulted in downregulation of several pro-inflammatory cell-mediators both in ApoE -/- and NRF2-/- mice compared to treatment naïve litter mates one day after treatment. In contrast, SRT induced pro-inflammatory cell-mediators connected with necrosis one day after treatment as expected following laser-induced selective RPE cell death. Seven days after laser treatment, both findings were reversed.

Conclusions

Both TSR and SRT influence inflammatory processes in AMD mouse models. However, they act conversely. TSR leads to anti-inflammatory processes shortly after laser therapy and induces immune-cell recruitment one week after treatment. SRT leads to a quick inflammatory response to laser induced RPE necrotic processes. One week after SRT inflammation is inhibited. It remains unclear, if and to what extent this might play a role in a therapeutic or preventive approach of both laser modalities on AMD pathology.

Vault changes after cyclopentolate instillation in eyes with posterior chamber phakic intraocular lens

Posterior chamber phakic intraocular lens (pIOL) implantation is a common option for correcting moderate-to-high ocular refractive defects. Because this pIOL is implanted on ciliary sulcus, the distance between the back surface of the pIOL and the anterior surface of the crystalline lens, that it is known as vault, should be measured in different conditions to ensure the technique's safety. Cyclopentolate is a drug that dilates the pupil and relaxes accommodation (cycloplegia). It is often used for different ocular examinations and for other medical purposes. However, there is no evidence of the effect of this drug on vault. This study quantified central vault changes associated with cyclopentolate instillation. We measured the vault under normal conditions (pre-cycloplegic instillation) and after instilling cyclopentolate on 39 eyes of 39 patients with implanted pIOL. Our results suggest that cyclopentolate instillation may induce changes to vault in eyes with implanted pIOL. These changes seem safe and are mainly associated with vault under normal conditions, but also with anterior chamber depth, pupillary diameter and pIOL size.

CRB1rd8 mutation influences the age-related macular degeneration phenotype of NRF2 knockout mice and favors choroidal neovascularization

PURPOSE

We examined the influence of retinal degeneration 8 (rd8) mutation of crumbs homolog 1 (CRB1) gene on age-related macular degeneration (AMD) phenotype in nuclear factor E2-related factor 2 knock out (NRF2^-/-) mouse model.

METHODS

CRB1^rd8 mutation genotype was determined by polymerase chain reaction from tail clips in 73 NRF2^-/- mice originating from C57BL/6J background on mixed C57BL/6J and C57BL/6N ancestry. The clinical grade of AMD-like fundus alterations was determined by funduscopy, optical coherence tomography (OCT) and fluorescein angiography (FLA) at the age of 9 or 12 months.

RESULTS

Twelve NRF2^-/- mice were wildtype CRB1^+/+, 61 NRF2^-/- were homozygous CRB1^rd8/rd8. NRF2^-/-CRB1^rd8/rd8 mice had a significantly higher probability to show an advanced grade (grade 4 and 5) of AMD-like fundus alterations known to appear in NRF2^-/- mice. Choroidal neovascularization (CNV) was only detected in NRF2^-/-CRB1^rd8/rd8 homozygous mice.

CONCLUSIONS

Homozygous CRB1^rd8/rd8 mutation is common in commercial vendor mice strains of C57BL/6J origin if partly on C57BL/6N ancestry. The mutation has an influence on the extent of AMD-like retinal alterations in NRF2^-/- mice and favors CNV formation.

Selective Retina Therapy Reduces Bruch's Membrane Thickness and Retinal Pigment Epithelium Pathology in Age-Related Macular Degeneration Mouse Models

Purpose

To investigate the effect of selective retina therapy (SRT) on age-related macular degeneration (AMD)-like alterations of retinal pigment epithelium (RPE) and Bruch's membrane (BrM) in AMD mouse models as therapeutic approach for the treatment of dry AMD.

Methods

In B6.129P2-Apoe^tm1Unc/J (ApoE^−/−) and B6.129X1-Nfe2I2^tm1Ywk/J (NRF2^−/−), one randomized eye of each mouse in groups of 15 mice was treated by SRT (532 nm, 300 ms, ∼1.4-μs pulse, 100 Hz, 50-μm spot), the fellow eye and healthy C57BL/6J mice served as controls. Clinical examinations were obtained at treatment day and 1 month later, followed by enucleation to analyze BrM thickness and ultrastructural RPE morphology.

Results

Nearly all ApoE^−/− and NRF2^−/− mice showed AMD-like retinal alterations. BrM thickness was increased in both mouse models, RPE had vacuoles within the cell body and shortened apical microvilli. SRT neither affected neuroretinal anatomy nor function. BrM thickness as well as AMD-like ultrastructural alterations of the RPE were significantly reduced in laser-treated eyes compared with fellow control and untreated control eyes.

Conclusions

SRT reduces BrM thickness and AMD-like RPE alterations in AMD mouse models without damage to structural or functional properties of neuroretina. It may be a prophylactic or therapeutic option for dry AMD.

Translational Relevance

SRT shows therapeutic effectivity in murine AMD models and might therefore become an option for the treatment of dry AMD.

En-Face Optical Coherence Tomography Angiography for Longitudinal Monitoring of Retinal Injury

A customized Optical Coherence Tomography Angiography (OCTA) algorithm and Orthogonal OCT (en-face and B-Scans) were used for longitudinal assessment of retina murine vascular and tissue remodeling comparing photoreceptor ablation and laser-induced Choroidal Neovascularization (CNV). In the mouse model, we utilized a combined OCTA/OCT technique to image and quantify morphological and vascular features of laser lesions over time. This approach enabled us to monitor and correlate the dynamics of retina vascular and tissue remodeling as evidenced by swelling, edema, and scarring. From the OCT B-Scans, three stages of inflammatory progression were identified: the early response occurring within hours to day 3, the transition phase from 3-7 days, and the late stage of 7-21 days entering either the resolving phase or chronic phase, respectively. For the case of CNV, en-face OCTA revealed a transient non-perfusion of inner retina capillaries, specifically Deep Vascular Plexus (DVP), which corresponded to growth in lesions of a height of 200 μm or greater. Non-perfusion first occurred at 24 hours, persisted during edema and CNV formation days 7-14. In contrast, the acute inflammation induced photoreceptor damage, but no detectable alterations to the microvasculature were observed. We demonstrated that the en-face OCTA system is capable of visualizing capillary networks (~5 μm) and the corresponding tissue remodeling and growth dynamics allowing for separating acute injury from CNV. For the first time, by using OCTA we observed the presence of the 5-10 μm capillary non-perfusion present in DVP as part of CNV formation and the associated wound healing in the retina.

In vivo monitoring of mouse retinal temperature by ERG photoresponses

Non-damaging heating of the retina and RPE provides a promising treatment for retinal diseases. However, the lack of proper control over the temperature hinders the development of safe and repeatable procedures. Here, we demonstrate with mice a non-invasive method for estimating the temperature changes in the retina and the RPE during a heating procedure. The method is based on monitoring the temperature dependent properties of retinal photoresponses recorded by electroretinography (ERG). In this study, our aim was to investigate the feasibility of ERG signal for retinal temperature estimation, utilizing a-wave and b-wave kinetics as the source of temperature information. We quantified the temperature dependencies of photoresponse kinetics and developed two linear regression models between the temperature and the photoresponse features, enabling temperature estimation. With the first model, based on the a-wave of a single photoresponse, the RMS error obtained for retinal temperature estimation was <0.9 °C. The second model, applying the b-waves of five dim flash responses, an RMS error of <0.7 °C was achieved. In addition, we tested the sensitivity of the method to small changes in light stimulus strength and investigated suitable stimulus intervals for continuous retinal temperature monitoring. The proposed method provides a convenient technique for monitoring mouse retinal and RPE temperature with ERG recording when studying controlled retinal heating. Similar temperature dependencies exist in human ERG suggesting that this approach could also be applicable in clinical heating treatments.

Effects of Fucoidans from Five Different Brown Algae on Oxidative Stress and VEGF Interference in Ocular Cells

BACKGROUND

Fucoidans are interesting for potential usage in ophthalmology, and especially age-related macular degeneration. However, fucoidans from different species may vary in their effects. Here, we compare fucoidans from five algal species in terms of oxidative stress protection and vascular endothelial growth factor (VEGF) interference in ocular cells.

METHODS

Brown algae (Fucus vesiculosus, Fucus distichus subsp. evanescens, Fucus serratus, Laminaria digitata, Saccharina latissima) were harvested and fucoidans isolated by hot-water extraction. Fucoidans were tested in several concentrations (1, 10, 50, and 100 µg/mL). Effects were measured on a uveal melanoma cell line (OMM-1) (oxidative stress), retinal pigment epithelium (RPE) cell line ARPE19 (oxidative stress and VEGF), and primary RPE cells (VEGF). Oxidative stress was induced by H2O2 or tert-Butyl hydroperoxide (TBHP). Cell viability was investigated with methyl thiazolyl tetrazolium (MTT or MTS) assay, and VEGF secretion with ELISA. Affinity to VEGF was determined by a competitive binding assay.

RESULTS

All fucoidans protected OMM-1 from oxidative stress. However, in ARPE19, only fucoidan from Saccharina latissima was protective. The affinity to VEGF of all fucoidans was stronger than that of heparin, and all reduced VEGF secretion in ARPE19. In primary RPE, only the fucoidan from Saccharina latissima was effective.

CONCLUSION

Among the fucoidans from five different species, Saccharina latissima displayed the most promising results concerning oxidative stress protection and reduction of VEGF secretion.