A convenient protocol for establishing a human cell culture model of the outer retina

Therapeutic potential of adult stem cells-derived mitochondria transfer combined with curcumin administration into ARPE-19 cells in age-related macular degeneration model

OBJECTIVE

Mitochondria transfer from human Wharton's Jelly-derived mesenchymal stem cells (hWJ-MSCs-mt) and human endometrium-derived mesenchymal stem cells (hE-MSCs-mt), along with curcumin, were explored as potential treatments for age-related macular degeneration (AMD) caused by mitochondrial inefficiency, using a retinal model to assess impacts of curcumin and hWJ-MSCs-mt or hE-MSCs-mt on AMD.

METHODS

ARPE-19 cells established an in vitro AMD model. Cells were exposed to 0-50 μM curcumin for 24 hours to determine optimal concentration by assessing their viability. Immunofluorescence examined SOD1, TNF-α, and TGF-β levels at optimal hydrogen peroxide (H2O2) concentration. β-galactosidase staining and DCFH analysis evaluated H2O2-induced cellular senescence. Immunofluorescence assessed REP65, CRALBP1 (RLBP1), Pink1, and Parkin expression, whereas qRT-PCR analyzed Nrf2, Ire1a, ARMS2, HTRA1, RPE65, RLBP1, NOX4, and TOMM20 expression following co-treatment with curcumin and hWJ-MSCs-mt or hE-MSCs-mt.

RESULTS

Curcumin improved ARPE-19 cell survival under H2O2-induced oxidative stress by regulating SOD1, TNF-α, TGF-β, DCFH, and MDA levels. hWJ-MSCs-mt transfer increased RLBP1 and Parkin expression, whereas curcumin reduced Parkin expression. hE-MSCs-mt transfer upregulated Parkin, RPE65, Pink1, and RLBP1 expressions, with curcumin enhancing RPE65 expression. hWJ-MSCs-mt and curcumin combined more effectively downregulated expressions of stress-related genes (Nrf2, Ire1α, NOX4) and improved expression of mitochondrial function gene (TOMM20). hE-MSCs-mt transfer with curcumin synergistically enhanced expression of retinal health markers (RPE65, RLBP1) and downregulated expression of damage-associated genes (HTRA1, ARMS2) in AMD models.

CONCLUSION

Curcumin combined with hWJ-MSCs-mt or hE-MSCs-mt is a potential AMD therapy owing to its anti-inflammatory properties; however, further in vivo and human studies are needed to confirm its efficacy and safety.

Exploring the therapeutic potential of MOTS-c in age-related macular degeneration: from cellular responses to patient-derived cybrids

Age-related macular degeneration (AMD), the leading cause of irreversible vision loss in the US, is on the rise among the elderly. Uncontrolled mitochondria-derived peptide production from mtDNA disruption and 16S or 12S rRNA damage could worsen AMD. Our previous work has shown that Humanin G possesses cytoprotective effects in retinal pigment epithelial (RPE) cells. However, MOTS-c, a highly efficient mitochondrial peptide, has yet to be evaluated on retinal cell survival. In this study, we show that there are differences in effects between wild-type (wt-) and differentiated ARPE19 cells (diff-ARPE19), implying that the cellular differentiation status may influence how cells respond to MOTS-c. MOTS-c has dose-dependent effects on apoptosis, inflammation, and mitochondrial biogenesis in diff-ARPE19 cells. Lower doses (500 nM) have more significant impacts than 5 µM concentrations. In diff-ARPE19 cells, a lower dose of MOTS-c can reduce the negative impact of hypoxia on cellular survival and gene expression, including apoptosis (CASP3, CASP9), mitochondrial biogenesis (TFAM, PGC-1α), and metabolic sensor (AMPK). However, it had no significant effect on ROS levels or NRF1 expression, regardless of MOTS-c dose. Exposing diff-ARPE19 cells to varied MOTS-c dosages before and after therapy in a chemically induced hypoxic environment yields no extra benefits as compared to MOTS-c treatment alone. MOTS-c had different effects on the expression of genes linked with apoptosis, mitochondrial biogenesis, and antioxidant activity in AMD patients versus age-matched control cybrids. The MOTS-c peptide appears to enhance cellular metabolism and regulate gene expression, which could potentially provide therapeutic benefits in AMD.

Sigma-2 receptor modulator CT1812 alters key pathways and rescues retinal pigment epithelium (RPE) functional deficits associated with dry age-related macular degeneration (AMD)

Trafficking defects in retinal pigmented epithelial (RPE) cells contribute to RPE atrophy, a hallmark of geographic atrophy (GA) in dry age-related macular degeneration (AMD). Dry AMD pathogenesis is multifactorial, including amyloid-β (Aβ) accumulation and oxidative stress-common features of Alzheimer's disease (AD). The Sigma-2 receptor (S2R) regulates lipid and protein trafficking, and S2R modulators reverse trafficking deficits in neurodegeneration in vitro models. Given overlapping mechanisms contributing to AD and AMD, S2R modulator effects on RPE function were investigated. The S2R modulator CT1812 is in clinical trials for AD, dementia with Lewy bodies, and GA. Leveraging AD trials testing CT1812, unbiased analyses of patient biofluid proteomes revealed that proteins altered by CT1812 associated with GA and macular degeneration disease ontologies and overlapped with proteins altered in dry AMD. Differential expression analysis of RPE transcripts from APP-Swedish/London mutant transgenic mice, a model featuring Aβ accumulation, revealed reversal of autophagy/trafficking transcripts in S2R modulator-treated animals versus vehicle toward healthy control levels. Photoreceptor outer segment (POS) trafficking in human RPE cells showed deficits in response to Aβ1-42 or hydrogen peroxide compared to vehicle. S2R modulators normalized stressor-induced POS trafficking deficits, resembling healthy control. Taken together, S2R modulation may provide a novel therapeutic strategy for dry AMD.

Complexin vitromodels positioned for impact to drug testing in pharma: a review

Recent years have seen the creation and popularization of various complexin vitromodels (CIVMs), such as organoids and organs-on-chip, as a technology with the potential to reduce animal usage in pharma while also enhancing our ability to create safe and efficacious drugs for patients. Public awareness of CIVMs has increased, in part, due to the recent passage of the FDA Modernization Act 2.0. This visibility is expected to spur deeper investment in and adoption of such models. Thus, end-users and model developers alike require a framework to both understand the readiness of current models to enter the drug development process, and to assess upcoming models for the same. This review presents such a framework for model selection based on comparative -omics data (which we term model-omics), and metrics for qualification of specific test assays that a model may support that we term context-of-use (COU) assays. We surveyed existing healthy tissue models and assays for ten drug development-critical organs of the body, and provide evaluations of readiness and suggestions for improving model-omics and COU assays for each. In whole, this review comes from a pharma perspective, and seeks to provide an evaluation of where CIVMs are poised for maximum impact in the drug development process, and a roadmap for realizing that potential.

ITF2357 regulates NF-κB signaling pathway to protect barrier integrity in retinal pigment epithelial cells

The robust integrity of the retinal pigment epithelium (RPE), which contributes to the outer brain retina barrier (oBRB), is compromised in several retinal degenerative and vascular disorders, including diabetic macular edema (DME). This study evaluates the role of a new generation of histone deacetylase inhibitor (HDACi), ITF2357, in regulating outer blood-retinal barrier function and investigates the underlying mechanism of action in inhibiting TNFα-induced damage to RPE integrity. Using the immortalized RPE cell line (ARPE-19), ITF2357 was found to be non-toxic between 50 nM and 5 μM concentrations. When applied as a pre-treatment in conjunction with an inflammatory cytokine, TNFα, the HDACi was safe and effective in preventing epithelial permeability by fortifying tight junction (ZO-1, -2, -3, occludin, claudin-1, -2, -3, -5, -19) and adherens junction (E-cadherin, Nectin-1) protein expression post-TNFα stress. Mechanistically, ITF2357 depicted a late action at 24 h via attenuating IKK, IκBα, and p65 phosphorylation and ameliorated the expression of IL-1β, IL-6, and MCP-1. Also, ITF2357 delayed IκBα synthesis and turnover. The use of Bay 11-7082 and MG132 further uncovered a possible role for ITF2357 in non-canonical NF-κB activation. Overall, this study revealed the protection effects of ITF2357 by regulating the turnover of tight and adherens junction proteins and modulating NF-κB signaling pathway in the presence of an inflammatory stressor, making it a potential therapeutic application for retinal vascular diseases such as DME with compromised outer blood-retinal barrier.

Gene replacement therapy restores RCBTB1 expression and cilium length in patient-derived retinal pigment epithelium

Biallelic mutations in the RCBTB1 gene cause retinal dystrophy. Here, we characterized the effects of RCBTB1 gene deficiency in retinal pigment epithelial (RPE) cells derived from a patient with RCBTB1‐associated retinopathy and restored RCBTB1 expression in these cells using adeno‐associated viral (AAV) vectors. Induced pluripotent stem cells derived from a patient with compound heterozygous RCBTB1 mutations (c.170delG and c.707delA) and healthy control subjects were differentiated into RPE cells. RPE cells were treated with AAV vectors carrying a RCBTB1 transgene. Patient‐derived RPE cells showed reduced expression of RCBTB1. Expression of NFE2L2 showed a non‐significant reduction in patient RPE cells compared with controls, while expression of its target genes (RXRA, IDH1 and SLC25A25) was significantly reduced. Trans‐epithelial electrical resistance, surface microvillus densities and primary cilium lengths were reduced in patient‐derived RPE cells, compared with controls. Treatment of patient RPE with AAV vectors significantly increased RCBTB1, NFE2L2 and RXRA expression and cilium lengths. Our study provides the first report examining the phenotype of RPE cells derived from a patient with RCBTB1‐associated retinopathy. Furthermore, treatment of patient‐derived RPE with AAV‐RCBTB1 vectors corrected deficits in gene expression and RPE ultrastructure, supporting the use of gene replacement therapy for treating this inherited retinal disease.

A look into retinal organoids: methods, analytical techniques, and applications

Inherited retinal diseases (IRDs) cause progressive loss of light-sensitive photoreceptors in the eye and can lead to blindness. Gene-based therapies for IRDs have shown remarkable progress in the past decade, but the vast majority of forms remain untreatable. In the era of personalised medicine, induced pluripotent stem cells (iPSCs) emerge as a valuable system for cell replacement and to model IRD because they retain the specific patient genome and can differentiate into any adult cell type. Three-dimensional (3D) iPSCs-derived retina-like tissue called retinal organoid contains all major retina-specific cell types: amacrine, bipolar, horizontal, retinal ganglion cells, Müller glia, as well as rod and cone photoreceptors. Here, we describe the main applications of retinal organoids and provide a comprehensive overview of the state-of-art analysis methods that apply to this model system. Finally, we will discuss the outlook for improvements that would bring the cellular model a step closer to become an established system in research and treatment development of IRDs.

Melatonin prevents blood-retinal barrier breakdown and mitochondrial dysfunction in high glucose and hypoxia-induced in vitro diabetic macular edema model

Diabetic macular edema (DME) is a leading cause of blindness in diabetic retinopathy. Prolonged hyperglycemia plus hypoxia contributes to DME pathogenesis. Retinal pigmented epithelial cells comprise the outer blood-retinal barrier and are essential for maintaining physiological functioning of the retina. Melatonin acts as an antioxidant and regulator of mitochondrial bioenergetics and has a protective effect against ocular diseases. However, the role of mitochondrial dysfunction and the therapeutic potential of melatonin in DME remain largely unexplored. Here, we used an in vitro model of DME to investigate blood-retinal barrier integrity and permeability, angiogenesis, mitochondrial dynamics, and apoptosis signaling to evaluate the potential protective efficacy of melatonin in DME. We found that melatonin prevents cell hyper-permeability and outer barrier breakdown by reducing HIF-1α, HIF-1β and VEGF and VEGF receptor gene expression. In addition, melatonin reduced the expression of genes involved in mitochondrial fission (DRP1, hFis1, MIEF2, MFF), mitophagy (PINK, BNip3, NIX), and increased the expression of genes involved in mitochondrial biogenesis (PGC-1α, NRF2, PPAR-γ) to maintain mitochondrial homeostasis. Moreover, melatonin prevented apoptosis of retinal pigmented epithelial cells. Our results suggest that mitochondrial dysfunction may be involved in DME pathology, and melatonin may have therapeutic value in DME, by targeting signaling in mitochondria.

Oligomeric Aβ1-42 Induces an AMD-Like Phenotype and Accumulates in Lysosomes to Impair RPE Function

Alzheimer's disease-associated amyloid beta (Aβ) proteins accumulate in the outer retina with increasing age and in eyes of age-related macular degeneration (AMD) patients. To study Aβ-induced retinopathy, wild-type mice were injected with nanomolar human oligomeric Aβ1-42, which recapitulate the Aβ burden reported in human donor eyes. In vitro studies investigated the cellular effects of Aβ in endothelial and retinal pigment epithelial (RPE) cells. Results show subretinal Aβ-induced focal AMD-like pathology within 2 weeks. Aβ exposure caused endothelial cell migration, and morphological and barrier alterations to the RPE. Aβ co-localized to late-endocytic compartments of RPE cells, which persisted despite attempts to clear it through upregulation of lysosomal cathepsin B, revealing a novel mechanism of lysosomal impairment in retinal degeneration. The rapid upregulation of cathepsin B was out of step with the prolonged accumulation of Aβ within lysosomes, and contrasted with enzymatic responses to internalized photoreceptor outer segments (POS). Furthermore, RPE cells exposed to Aβ were identified as deficient in cargo-carrying lysosomes at time points that are critical to POS degradation. These findings imply that Aβ accumulation within late-endocytic compartments, as well as lysosomal deficiency, impairs RPE function over time, contributing to visual defects seen in aging and AMD eyes.

Development of 3D Printed Bruch's Membrane-Mimetic Substance for the Maturation of Retinal Pigment Epithelial Cells

Retinal pigment epithelium (RPE) is a monolayer of the pigmented cells that lies on the thin extracellular matrix called Bruch's membrane. This monolayer is the main component of the outer blood-retinal barrier (BRB), which plays a multifunctional role. Due to their crucial roles, the damage of this epithelium causes a wide range of diseases related to retinal degeneration including age-related macular degeneration, retinitis pigmentosa, and Stargardt disease. Unfortunately, there is presently no cure for these diseases. Clinically implantable RPE for humans is under development, and there is no practical examination platform for drug development. Here, we developed porcine Bruch's membrane-derived bioink (BM-ECM). Compared to conventional laminin, the RPE cells on BM-ECM showed enhanced functionality of RPE. Furthermore, we developed the Bruch's membrane-mimetic substrate (BMS) via the integration of BM-ECM and 3D printing technology, which revealed structure and extracellular matrix components similar to those of natural Bruch's membrane. The developed BMS facilitated the appropriate functions of RPE, including barrier and clearance functions, the secretion of anti-angiogenic growth factors, and enzyme formation for phototransduction. Moreover, it could be used as a basement frame for RPE transplantation. We established BMS using 3D printing technology to grow RPE cells with functions that could be used for an in vitro model and RPE transplantation.

Nanodelivery of Resveratrol-Loaded PLGA Nanoparticles for Age-Related Macular Degeneration

Age-related macular degeneration, precisely neovascular form, is the leading cause of vision loss and the key treatment includes intravitreal injections of anti-vascular endothelial growth factor (anti-VEGF) agents. A method to increase local concentration of drug at posterior segment of the eye and to reduce the frequency of intravitreal injections is an unmet need. Resveratrol, a naturally occurring antioxidant and anti-inflammatory polyphenol, was loaded in PLGA polymeric nanoparticles to study their sustained release property and effectiveness in reducing expression of VEGF protein in vitro. Nanoparticles were characterized using FTIR, DSC, size, encapsulation efficiency, TEM, and in vitro drug release studies. Using MTT assay, the cytotoxicity of formulation was evaluated on ARPE-19 cells. The cellular uptake and VEGF expression levels were also evaluated in in vitro settings. The optimized formulation had a particle size of 102.7 nm with - 47.30 mV of zeta potential. Entrapment efficiency was found to be 65.21%. The cell viability results suggested compatibility of developed formulation. Cellular uptake and VEGF expression levels for the formulated nanoparticles specified that the developed formulation showed potential cellular uptake and had displayed anti-angiogenic property by inhibiting VEGF expression in vitro. The results showed successful development of resveratrol-loaded nanoparticles which may be used for neovascular AMD treatment alone or in combination with anti-VEGF agents.

An In-Vitro Cell Model of Intracellular Protein Aggregation Provides Insights into RPE Stress Associated with Retinopathy

Impaired cargo trafficking and the aggregation of intracellular macromolecules are key features of neurodegeneration, and a hallmark of aged as well as diseased retinal pigment epithelial (RPE) cells in the eye. Here, photoreceptor outer segments (POS), which are internalized daily by RPE cells, were modified by UV-irradiation to create oxidatively modified POS (OxPOS). Oxidative modification was quantified by a protein carbonyl content assay. Human ARPE-19 cells were synchronously pulsed with POS or OxPOS to study whether oxidatively modified cargos can recapitulate features of RPE pathology associated with blinding diseases. Confocal immunofluorescence microscopy analysis showed that OxPOS was trafficked to LAMP1, LAMP2 lysosomes and to LC3b autophagy vacuoles. Whilst POS were eventually degraded, OxPOS cargos were sequestered in late compartments. Co-localization of OxPOS was also associated with swollen autolysosomes. Ultrastructural analysis revealed the presence of electron-dense OxPOS aggregates in RPE cells, which appeared to be largely resistant to degradation. Measurement of cellular autofluorescence, using parameters used to assess fundus autofluorescence (FAF) in age-related macular disease (AMD) patients, revealed that OxPOS contributed significantly to a key feature of aged and diseased RPE. This in vitro cell model therefore represents a versatile tool to study disease pathways linked with RPE damage and sight-loss.

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.

Oxidative Stress and Dysfunctional Intracellular Traffic Linked to an Unhealthy Diet Results in Impaired Cargo Transport in the Retinal Pigment Epithelium (RPE)

SCOPE

Oxidative stress and dysregulated intracellular trafficking are associated with an unhealthy diet which underlies pathology. Here, these effects on photoreceptor outer segment (POS) trafficking in the retinal pigment epithelium (RPE), a major pathway of disease underlying irreversible sight-loss, are studied.

METHODS AND RESULTS

POS trafficking is studied in ARPE-19 cells using an algorithm-based quantification of confocal-immunofluorescence data supported by ultrastructural studies. It is shown that although POS are tightly regulated and trafficked via Rab5, Rab7 vesicles, LAMP1/2 lysosomes and LC3b-autophagosomes, there is also a considerable degree of variation and flexibility in this process. Treatment with H2 O2 and bafilomycin A1 reveals that oxidative stress and dysregulated autophagy target intracellular compartments and trafficking in strikingly different ways. These effects appear limited to POS-containing vesicles, suggesting a cargo-specific effect.

CONCLUSION

The findings offer insights into how RPE cells cope with stress, and how mechanisms influencing POS transport/degradation can have different outcomes in the senescent retina. These shed new light on cellular processes underlying retinopathies such as age-related macular degeneration. The discoveries reveal how diet and nutrition can cause fundamental alterations at a cellular level, thus contributing to a better understanding of the diet-disease axis.

Study of Intracellular Cargo Trafficking and Co-localization in the Phagosome and Autophagy-Lysosomal Pathways of Retinal Pigment Epithelium (RPE) Cells

The transport and targeting of internalized molecules to distinct intracellular organelles/compartments can prove challenging to visualize clearly, which can contribute to some of the difficulties associated with these studies. By combining several approaches, we show how the trafficking and processing of photoreceptor outer segments in the phagosome and autophagy-lysosomal pathways of the retinal pigment epithelium (RPE) can easily be quantified and visualized as 3D-reconstructed images. This protocol takes advantage of new developments in microscopy and image-analysis software which has the potential to help better understand dynamic intracellular processes that underlie RPE dysfunction associated with irreversible blinding diseases such as age-related macular degeneration. The method described herein can also be used to study the trafficking and co-localization of different intracellular cargos in other cell types and tissues.