Endogenous and Exogenous Regulation of Redox Homeostasis in Retinal Pigment Epithelium Cells: An Updated Antioxidant Perspective

Tagetes erecta Linn flower extract inhibits particulate matter 2.5-promoted epithelial-mesenchymal transition by attenuating reactive oxygen species generation in human retinal pigment epithelial ARPE-19 cells

BACKGROUND/OBJECTIVES

Particulate matter 2.5 (PM2.5) exposure can promote epithelial-mesenchymal transition (EMT) in human retinal pigment epithelial (RPE) cells. The flowers of Tagetes erecta Linn, commonly known as marigold, are rich in diverse flavonoids and carotenoids and play a significant role in preventing cellular damage induced by oxidative stress, but the role of their extracts in RPE cells has not been reported. This study aimed to evaluate the influence of an ethanol extract of T. erecta Linn flower (TE) on PM2.5-induced EMT processes in RPE ARPE-19 cells.

MATERIALS/METHODS

To investigate the protective effect of TE against ARPE-19 cell damage following PM2.5 treatment, cells were exposed to TE for 1 h before exposure to PM2.5 for 24 h. We investigated whether the efficacy of TE on suppressing PM2.5-induced EMT was related to antioxidant activity and the effect on the expression changes of factors involved in EMT regulation. Additionally, we further explored the role of intracellular signaling pathways associated with EMT inhibition.

RESULTS

TE significantly blocked PM2.5-induced cytotoxicity while effectively preventing mitochondrial dysfunction, increased reactive oxygen species (ROS) generation, and mitochondrial membrane potential disruption. TE inhibited PM2.5-induced EMT and inflammatory response by suppressing the ROS-mediated transforming growth factor-β/suppressor of mothers against decapentaplegic/mitogen-activated protein kinases signaling pathway.

CONCLUSION

Our results suggest that marigold extract is a highly effective in protection against PM2.5-induced eye damage.

Combination of Saffron (Crocus sativus), Elderberry (Sambucus nigra L.) and Melilotus officinalis Protects ARPE-19 Cells from Oxidative Stress

Oxidative stress is considered a common underlying mechanism in many retinal degenerative diseases and is often associated with inflammation. The use of dietary supplements containing Saffron has beneficial effects in ocular diseases, though the molecular mechanisms are still unclear. In this study, we investigated how Saffron can exert protective effects against oxidative damage in retinal pigment epithelial cells (ARPE-19) and whether its combination with Elderberry and Melilotus may have additive beneficial effects. ARPE-19 cells were pretreated with Saffron alone or in a mix containing Saffron, Elderberry and Melilotus, then exposed to hydrogen peroxide (H2O2) for 3 h. Afterwards, we evaluated cell viability, oxidative stress and inflammatory status. Our results showed that H2O2 reduced cell viability and total glutathione levels, while increasing caspase-3, caspase-1 and LDH activity. Moreover, H2O2 triggered ROS production, glutathione oxidation and IL-1β secretion. Pretreatments with Saffron alone or with the mix counteract these damaging effects by improving cell viability, reducing oxidative stress and enhancing SOD2 expression. Pretreatment with the mix activated the NRF2 pathway and was more effective than Saffron alone in preventing caspase-1 activation. These findings suggest that the combination of Saffron, Elderberry and Melilotus could have therapeutic potential in the prevention and treatment of retinal degenerative diseases.

Evidence for a Functional Link Between the Nrf2 Signalling Pathway and Cytoprotective Effect of S-Petasin in Human Retinal Pigment Epithelium Cells Exposed to Oxidative Stress

The retinal pigment epithelium (RPE) is a highly specialised monolayer epithelium subjected to constant oxidative stress, which, in the long term, favours the development of a complex pathological process that is the underlying cause of macular damage. Therefore, counteracting the overproduction of ROS is the best-researched approach to preserve the functional integrity of the RPE. S-Petasin, a secondary metabolite extracted from the plant Petasites hybridus, has numerous biological effects, which highlight its anti-inflammatory and antioxidative properties. The aim of our study is to investigate whether S-Petasin exerts cytoprotective effects by protecting the RPE from oxidative damage. The effects of pretreatment with S-Petasin were assessed by the determination of the cell viability, intracellular ROS levels, activation of the Nrf2 pathway and the resulting post-transcriptional antioxidant/antiapoptotic response. Our results show that S-Petasin pretreatment (1) reduces intracellular ROS levels, improving cell viability of RPE exposed to oxidative damage; (2) activates the Nrf2 signalling pathway, modulating the post-transcriptional response of its antioxidant chemical biomarkers; (3) reduces the Bax levels, and an increase in those of Bcl-2, with a concomitant downregulation of the Bax/Bc-2 ratio. Overall, our results provide the first evidence that S-Petasin is able to protect the RPE from oxidative damage.

Retinal Pigment Epithelium Under Oxidative Stress: Chaperoning Autophagy and Beyond

The structural and functional integrity of the retinal pigment epithelium (RPE) plays a key role in the normal functioning of the visual system. RPE cells are characterized by an efficient system of photoreceptor outer segment phagocytosis, high metabolic activity, and risk of oxidative damage. RPE dysfunction is a common pathological feature in various retinal diseases. Dysregulation of RPE cell proteostasis and redox homeostasis is accompanied by increased reactive oxygen species generation during the impairment of phagocytosis, lysosomal and mitochondrial failure, and an accumulation of waste lipidic and protein aggregates. They are the inducers of RPE dysfunction and can trigger specific pathways of cell death. Autophagy serves as important mechanism in the endogenous defense system, controlling RPE homeostasis and survival under normal conditions and cellular responses under stress conditions through the degradation of intracellular components. Impairment of the autophagy process itself can result in cell death. In this review, we summarize the classical types of oxidative stress-induced autophagy in the RPE with an emphasis on autophagy mediated by molecular chaperones. Heat shock proteins, which represent hubs connecting the life supporting pathways of RPE cells, play a special role in these mechanisms. Regulation of oxidative stress-counteracting autophagy is an essential strategy for protecting the RPE against pathological damage when preventing retinal degenerative disease progression.

Imaging melanin-associated organelles in the retinal pigment epithelium via visible light OCT redshift

The retinal pigment epithelium (RPE) performs a number of functions essential for retinal health. RPE dysregulation and degeneration can occur in diseases. Methods to image the human RPE directly are limited, as it is only about 10 µm thick and situated between the photoreceptor outer segments and Bruch's membrane (BM). Here we propose a visible light optical coherence tomography (OCT) technique to image the spectral redshift as light traverses the apical to basal RPE. Results in mice and human subjects support that the redshift occurs due to melanosomes and melanolipofuscin in the apical and middle RPE cell body.

Extracellular Vesicles Derived from Adipose-Derived Mesenchymal Stem Cells Alleviate Apoptosis and Oxidative Stress of Retinal Pigment Epithelial Cells Through Activation of Nrf2 Signaling Pathway

Purpose: To examine the potential protective effects of adipose-derived mesenchymal stem cell-derived extracellular vesicles (ASC-EVs) on ARPE-19 cells exposed to hydrogen peroxide (H2O2) stress and to evaluate their ability to delay retinal degeneration in Royal College of Surgeons (RCS) rats. Methods: ARPE-19 cells were pre-treated with ASC-EVs for 24 h, followed by exposure to 200 μM H2O2 for an additional 24 h. RCS rats received an intravitreal injection of phosphate-buffered saline in one eye and ASC-EVs in the other eye. Results: ASC-EV pretreatment significantly protected against H2O2 in the Cell Counting Kit-8 assay and was also effective in the lactate dehydrogenase-release assay. It notably reduced early apoptosis (Annexin V-fluorescein isothiocyanate/propidium iodide assay) and late apoptosis (Terminal Deoxynucleotidyl Transferase dUTP Nick End Labeling assay), while significantly decreasing intracellular reactive oxygen species, glutathione levels, and superoxide dismutase activity. NFE2L2, HMOX1, and NQO1 mRNA levels, along with Nrf2, HO-1, and NQO1 protein levels, were significantly elevated with ASC-EV pretreatment. Compared with ARPE-19-derived EVs, 11 miRNAs were upregulated and 34 were downregulated in ASC-EVs. In RCS rats, intravitreal injections of ASC-EVs led to significant preservation of the outer nuclear layer and photoreceptor segments, along with increased nuclear Nrf2 expression and elevated HO-1 and NQO1 levels in the inner retina. Eyes that received intravitreal injections of ASC-EVs demonstrated significantly preserved electroretinography a- and b-wave amplitudes at 1 week post-injection, though this effect faded by 2 weeks. Conclusions: ASC-EVs mitigated apoptosis and oxidative stress in ARPE-19 cells subjected to H2O2 exposure and temporarily slowed retinal degeneration in RCS rats via Nrf2 pathway activation by miRNAs.

Small Extracellular Vesicle-Associated MiRNAs in Polarized Retinal Pigmented Epithelium

Purpose

Oxidative stress in the retinal pigmented epithelium (RPE) has been implicated in age-related macular degeneration by impacting endocytic trafficking, including the formation, content, and secretion of extracellular vesicles (EVs). Using our model of polarized primary porcine RPE (pRPE) cells under chronic subtoxic oxidative stress, we tested the hypothesis that RPE miRNAs packaged into EVs are secreted in a polarized manner and contribute to maintaining RPE homeostasis.

Methods

Small EVs (sEVs) enriched for exosomes were isolated from apical and basal conditioned media from pRPE cells grown for up to four weeks with or without low concentrations of hydrogen peroxide using two sEV isolation methods, leading to eight experimental groups. The sEV miRNA expression was profiled using miRNA-Seq with Illumina MiSeq, followed by quality control and bioinformatics analysis for differential expression using the R computing environment. Expression of selected miRNAs were validated using qRT-PCR.

Results

We identified miRNA content differences carried by sEVs isolated using two ultracentrifugation-based methods. Regardless of the sEV isolation method, miR-182 and miR-183 were enriched in the cargo of apically secreted sEVs, and miR-122 in the cargo of basally secreted sEVs from RPE cells during normal homeostatic conditions. After oxidative stress, miR-183 levels were significantly decreased in the cargo of apically released sEVs from stressed RPE cells.

Conclusions

We curated RPE sEV miRNA datasets based on cell polarity and oxidative stress. Unbiased miRNA analysis identified differences based on polarity, stress, and sEV isolation methods. These findings suggest that miRNAs in sEVs may contribute to RPE homeostasis and function in a polarized manner.

Molecular Network Mechanism Analysis of Urine Stem Cells Against Retinal Aging

To investigate the effect and potential mechanism of human-derived urine stem cells (hUSCs) in inhibiting retinal aging by using experimental and bioinformatics. Retinal pigment epithelial cells cultured in vitro, which were randomly divided into normal group, aging group and supernatant of hUSCs group. Cell counting kit-8 detection, senescence-related β-galactosidase, and Annexin V/PI staining were performed to detect cell viability, senescence, and apoptosis. Subsequently, bioinformatics methods were used to explore the underlying mechanisms, in which, targets both hUSCs and aging retina-related targets were obtained from GeneCards. Then, Gene Ontology, Kyoto Encyclopedia of Genes and Genomes enrichment analysis, and protein-protein interaction network were analysis, and the expressional level of hub gene was validated by q-PCR. Supernatant addition of hUSCs promoted markedly cellular proliferation, improved viability and inhibited senescence and apoptosis in vitro. A total of 1476 hUSCs-related targets (Relevance score > 20), 692 retinal disease-related targets, and 732 targets related to disease of aging were selected from GeneCards database, and 289 common targets of hUSCs against aging retina were confirmed through Venn analysis. Enrichment analysis demonstrated that hUSCs might exert its anti-apoptosis efficacy in multiple biological processes, including oxidative stress, inflammation and apoptosis, and core targets were associated with HIF-1, MAPK and PI3K-Akt signal. hUSCs inhibited retinal senescence by regulating multiply targets and signaling pathways, of these, HIF-1, MAPK, and PI3K may be important candidates.

Regulatory factors of Nrf2 in age-related macular degeneration pathogenesis

Age-related macular degeneration (AMD) is a complicated disease that causes irreversible visual impairment. Increasing evidences pointed retinal pigment epithelia (RPE) cells as the decisive cell involved in the progress of AMD, and the function of anti-oxidant capacity of PRE plays a fundamental physiological role. Nuclear factor erythroid 2 related factor 2 (Nrf2) is a significant transcription factor in the cellular anti-oxidant system as it regulates the expression of multiple anti-oxidative genes. Its functions of protecting RPE cells against oxidative stress (OS) and ensuing physiological changes, including inflammation, mitochondrial damage and autophagy dysregulation, have already been elucidated. Understanding the roles of upstream regulators of Nrf2 could provide further insight to the OS-mediated AMD pathogenesis. For the first time, this review summarized the reported upstream regulators of Nrf2 in AMD pathogenesis, including proteins and miRNAs, and their underlying molecular mechanisms, which may help to find potential targets via regulating the Nrf2 pathway in the future research and further discuss the existing Nrf2 regulators proved to be beneficial in preventing AMD.

Tail and Spinal Cord Regeneration in Urodelean Amphibians

Urodelean amphibians can regenerate the tail and the spinal cord (SC) and maintain this ability throughout their life. This clearly distinguishes these animals from mammals. The phenomenon of tail and SC regeneration is based on the capability of cells involved in regeneration to dedifferentiate, enter the cell cycle, and change their (or return to the pre-existing) phenotype during de novo organ formation. The second critical aspect of the successful tail and SC regeneration is the mutual molecular regulation by tissues, of which the SC and the apical wound epidermis are the leaders. Molecular regulatory systems include signaling pathways components, inflammatory factors, ECM molecules, ROS, hormones, neurotransmitters, HSPs, transcriptional and epigenetic factors, etc. The control, carried out by regulatory networks on the feedback principle, recruits the mechanisms used in embryogenesis and accompanies all stages of organ regeneration, from the moment of damage to the completion of morphogenesis and patterning of all its structures. The late regeneration stages and the effects of external factors on them have been poorly studied. A new model for addressing this issue is herein proposed. The data summarized in the review contribute to understanding a wide range of fundamentally important issues in the regenerative biology of tissues and organs in vertebrates including humans.

Retinal Pigment Epithelium Pigment Granules: Norms, Age Relations and Pathology

The retinal pigment epithelium (RPE), which ensures the normal functioning of the neural retina, is a pigmented single-cell layer that separates the retina from the Bruch's membrane and the choroid. There are three main types of pigment granules in the RPE cells of the human eye: lipofuscin granules (LG) containing the fluorescent "age pigment" lipofuscin, melanoprotein granules (melanosomes, melanolysosomes) containing the screening pigment melanin and complex melanolipofuscin granules (MLG) containing both types of pigments simultaneously-melanin and lipofuscin. This review examines the functional role of pigment granules in the aging process and in the development of oxidative stress and associated pathologies in RPE cells. The focus is on the process of light-induced oxidative degradation of pigment granules caused by reactive oxygen species. The reasons leading to increased oxidative stress in RPE cells as a result of the oxidative degradation of pigment granules are considered. A mechanism is proposed to explain the phenomenon of age-related decline in melanin content in RPE cells. The essence of the mechanism is that when the lipofuscin part of the melanolipofuscin granule is exposed to light, reactive oxygen species are formed, which destroy the melanin part. As more melanolipofuscin granules are formed with age and the development of degenerative diseases, the melanin in pigmented epithelial cells ultimately disappears.

Recent Achievements in the Heterogeneity of Mammalian and Human Retinal Pigment Epithelium: In Search of a Stem Cell

Retinal pigment epithelium (RPE) cells are important fundamentally for the development and function of the retina. In this regard, the study of the morphological and molecular properties of RPE cells, as well as their regenerative capabilities, is of particular importance for biomedicine. However, these studies are complicated by the fact that, despite the external morphological similarity of RPE cells, the RPE is a population of heterogeneous cells, the molecular genetic properties of which have begun to be revealed by sequencing methods only in recent years. This review carries out an analysis of the data from morphological and molecular genetic studies of the heterogeneity of RPE cells in mammals and humans, which reveals the individual differences in the subpopulations of RPE cells and the possible specificity of their functions. Particular attention is paid to discussing the properties of "stemness," proliferation, and plasticity in the RPE, which may be useful for uncovering the mechanisms of retinal diseases associated with pathologies of the RPE and finding new ways of treating them.

Regional Variations in Peucedanum japonicum Antioxidants and Phytochemicals

Peucedanum japonicum has long been a staple in East Asian cuisine. In the context of traditional medicine, various members of the Peucedanum genus have been investigated for potential medicinal properties. In laboratory settings, some compounds derived from this plant have shown antioxidant and anti-inflammatory properties-characteristics often associated with potential medicinal applications. This study aimed to determine which part of the P. japonicum plants cultivated on two Korean islands contains the most antioxidant compounds. This determination was made through assessments of total polyphenol content and total flavonoid content, coupled with evaluation of antioxidant activity via DPPH and ABTS assays. The results showed that the aerial parts contain a richer array of bioactive compounds and demonstrate superior antioxidant activity compared to their root counterparts in the plants from both islands. To characterize the phytochemicals underpinning this bioactivity, LC-MS/MS and HPLC analyses were carried out. These methods detected varying amounts of chlorogenic acid, peucedanol 7-O-glucoside, rutin, and peucedanol, with good separation and retention times. This study addresses the lack of research on the antioxidant activity of different parts of P. japonicum. The findings hold significance for traditional medicine, dietary supplements, and the development of functional foods. Understanding antioxidant distribution aids in the development of medicinal and nutritional applications, influences agricultural practices, and contributes to regional biodiversity-conservation efforts. The study's geographical scope provides insights into how location impacts the concentration of bioactive compounds in plants. Overall, the results contribute valuable data for future research in plant biology, biochemistry, and related fields.

Oxidative stress in the eye and its role in the pathophysiology of ocular diseases

Oxidative stress occurs through an imbalance between the generation of reactive oxygen species (ROS) and the antioxidant defense mechanisms of cells. The eye is particularly exposed to oxidative stress because of its permanent exposure to light and due to several structures having high metabolic activities. The anterior part of the eye is highly exposed to ultraviolet (UV) radiation and possesses a complex antioxidant defense system to protect the retina from UV radiation. The posterior part of the eye exhibits high metabolic rates and oxygen consumption leading subsequently to a high production rate of ROS. Furthermore, inflammation, aging, genetic factors, and environmental pollution, are all elements promoting ROS generation and impairing antioxidant defense mechanisms and thereby representing risk factors leading to oxidative stress. An abnormal redox status was shown to be involved in the pathophysiology of various ocular diseases in the anterior and posterior segment of the eye. In this review, we aim to summarize the mechanisms of oxidative stress in ocular diseases to provide an updated understanding on the pathogenesis of common diseases affecting the ocular surface, the lens, the retina, and the optic nerve. Moreover, we discuss potential therapeutic approaches aimed at reducing oxidative stress in this context.

Cellular and Molecular Triggers of Retinal Regeneration in Amphibians

Understanding the mechanisms triggering the initiation of retinal regeneration in amphibians may advance the quest for prevention and treatment options for degenerating human retina diseases. Natural retinal regeneration in amphibians requires two cell sources, namely retinal pigment epithelium (RPE) and ciliary marginal zone. The disruption of RPE interaction with photoreceptors through surgery or injury triggers local and systemic responses for retinal protection. In mammals, disease-induced damage to the retina results in the shutdown of the function, cellular or oxidative stress, pronounced immune response, cell death and retinal degeneration. In contrast to retinal pathology in mammals, regenerative responses in amphibians have taxon-specific features ensuring efficient regeneration. These include rapid hemostasis, the recruitment of cells and factors of endogenous defense systems, activities of the immature immune system, high cell viability, and the efficiency of the extracellular matrix, cytoskeleton, and cell surface remodeling. These reactions are controlled by specific signaling pathways, transcription factors, and the epigenome, which are insufficiently studied. This review provides a summary of the mechanisms initiating retinal regeneration in amphibians and reveals its features collectively directed at recruiting universal responses to trauma to activate the cell sources of retinal regeneration. This study of the integrated molecular network of these processes is a prospect for future research in demand biomedicine.