Treatment Of Retinal Degenerative Diseases Research Articles

Safety of intravitreally delivered AAV2 vector-mediated multi-characteristic opsin genetic construct in wild type beagle dogs.

A novel adeno-associated virus 2 (AAV2)-carried multi-characteristic opsin (MCO) (MCO-010) is undergoing several clinical trials as a novel therapeutic modality for the treatment of degenerative retinal diseases including retinitis pigmentosa and Stargardt disease. The present study aimed to determine the ocular and systemic safety of MCO-010 and the AAV2 vehicle in adult Beagle dogs following intravitreal (IVT) injection. The current safety/toxicology studies spanning 13 weeks described here utilized well-documented techniques to assess the effects of IVT injection of MCO-010 up to 2.2 × 1011 genome copies (gc) per eye, or the AAV2 capsid (vehicle control) on gross behavioral and immunogenic changes, alterations in body weights, blood biochemistry, hematology, blood coagulation, gross necropsy lesions, organ weight changes and histopathology in the dogs (n = 4 per group; two males and two females per group). Immunohistochemical and functional electroretinogram studies were also conducted to determine MCO expression in the retina and determine any retinal toxicity associated with MCO-010. There were no significant deleterious effects of the MCO-010 (or the AAV2 at the tested doses) on any of the examined parameters, including the absence of any severe ocular or systemic adverse events. However, as expected, inflammation after IVT delivery of AAV2 and MCO-010 was observed in the conjunctivae of all groups of animals, although this self-resolved within 1week post-injection. Quantitative immunohistochemical analyses of MCO-010-associated mCherry revealed successful delivery of the gene therapy within the inner retina. In summary, MCO-010 demonstrated a favorable safety profile when administered to the eyes of adult Beagle dogs of both sexes at dose levels up to 2.2 × 1011 gc per eye, with no adverse effects observed. This dose was identified as the No Observed Adverse Effect Level (i.e. NOAEL) and guided selection of safe doses for human clinical trials.

Induction of human ESC-derived and adult primary multipotent limbal stem cells into retinal pigment epithelial cells and corneal stromal stem cells

Human embryonic stem cell (hESC)- and human induced pluripotent stem cell (hiPSC)-derived retinal pigment epithelium (RPE) therapies are promising alternatives for the treatment of retinal degenerative diseases caused by RPE degeneration. The generation of autologous RPE cells from human adult donors, which has the advantage of avoiding immune rejection and teratoma formation, is an alternative cell resource to gain mechanistic insight into and test potential therapies for RPE degenerative diseases. Here, we found that limbal stem cells (LSCs) from hESCs and adult primary human limbus have the potential to produce RPE cells and corneal stromal stem cells (CSSCs). We showed that hESC-LSC-derived RPE cells (LSC-RPE) expressed RPE markers, had a phagocytic function, and synthesized tropical factors. Furthermore, during differentiation from LSCs to RPE cells, cells became pigmented, accompanied by a decrease in the level of LSC marker KRT15 and an increase in the level of RPE marker MITF. The Wnt signaling pathway plays a role in LSC-RPE fate transition, promotes MITF expression in the nucleus, and encourages RPE fate transition. In addition, we also showed that primary LSCs (pLSCs) from adult human limbus similar to hESC-LSC could generate RPE cells, which was supported by the co-expression of LSC and RPE cell markers (KRT15/OTX2, KRT15/MITF), suggesting the transition from pLSC to RPE cells, and typical polygonal morphology, melanization, RPE cell marker genes expression (TYR, RPE65), tight junction formation by ZO-1 expression, and the most crucial phagocytotic function. On the other hand, both hESC-LSCs and pLSCs also differentiated into CSSCs (LSC-CSSCs) that expressed stem cell markers (PAX6, NESTIN), presented MSC features, including surface marker expression and trilineage differentiation capability, like those in human CSSCs. Furthermore, the capability of pLSC-CSSC to differentiate into cells expressing keratocyte marker genes (ALDH3A1, PTGDS, PDK4) indicated the potential to induce keratocytes. These results suggest that the adult pLSC is an alternative cell resource, and its application provides a novel potential therapeutic avenue for preventing RPE dysfunction-related retinal degenerative diseases and corneal scarring.

Synergistic effect of mesenchymal stem cells and silver nanoparticles in the treatment of retinal degenerative diseases

Aims/Purpose: Retinal degenerative diseases represent one of the leading causes of visual loss. Mesenchymal stem cells (MSCs) provide potential option for the treatment of several type of pathologies, including ocular diseases. Moreover, silver nanoparticles (AgNPs) are currently widely used in various fields of medicine mainly due to their antibacterial and antiangiogenic properties. Several studies showed their beneficial but also harmful effect. However, there are limited information about the synergistic effect of AgNPs with MSC‐based therapies.Methods: Chronical retinal degeneration was induced in BALB/c mice by repeated intraperitoneal application of sodium iodate (NaIO3). MSCs, AgNPs or MSCs plus AgNPs were intravitreally injected 48 h before the last application of NaIO3. Retinas were isolated after additional 7 days and tested by RT‐PCR for the expression of genes for rhodopsin (photoreceptors), Iba‐1 (microglia/macrophages), IL‐1β and galectin‐3. The presence of MSCs stained with PKH‐26 was analysed by flow cytometry.Results: It was shown that MSCs and MSCs applied with AgNPs were still present in the retina on day 7 after application. In all treated groups, the expression of the gene for galectin‐3 was decreased in contrast to untreated control. However, co‐application of MSCs with AgNPs had limited effect on downregulation of Iba‐1 and IL‐1β in contrast to MSCs or AgNPs treated group.Conclusions: The application of MSCs and AgNPs modulated immune response in chronical retinal degeneration but co‐application of MSCs with AgNPs decreased immunoregulatory effects comparted with single‐component therapy. Thus, there is a need for more investigation focusing on potential changes in MSCs applied with AgNPs.

Multidisciplinary Approaches in the Treatment of Retinal Degenerative Diseases: A Review

AbstractRetinal degenerative diseases (RDDs) cause irreversible blindness and affect ≈285 million individuals worldwide. The unavailability of treatment to stop the progression of RDDs or restore normal visual function necessitated development of novel therapeutic strategies. In recent years, multidisciplinary approaches have shown great potential for the treatment of RDDs, including intraocular delivery systems, retinal scaffolds for cell therapy, and visual prostheses with different stimulation strategies. This review focuses on the development prospects and shortcomings of various multidisciplinary treatment approaches for RDDs. The results of this review will hopefully inspire further innovation in the design of novel multidisciplinary approaches for RDD treatment and accelerate their commercialization.

Modifying treatment of degenerative retinal diseases. Part 2. Conditioning therapy techniques and the problem of maximizing retinal plasticity

In the first part of the review [ROJ, 2023; 16 (2): 160–2], we discussed the common and specific features of adaptive and non-adaptive retinal plasticity characteristic of glaucoma, age-related macular degeneration, retinitis pigmentosa, diabetic retinopathy, and retinopathy of prematurity. The presented part of the review discusses the issues of axon regeneration of retinal ganglion cells and analyzes therapeutic approaches aimed at maximizing the plasticity and stimulating the reparative potential of the retina. The protective effects of "conditioning" stimuli in the modifying treatment of retinal diseases are considered. Some of the present-day visual rehabilitation strategies based on visual perception training and visual fixation training using biofeedback systems are reported.

Therapeutic Extracellular Vesicles from Tonsil-Derived Mesenchymal Stem Cells for the Treatment of Retinal Degenerative Disease.

Retinal degenerative disease (RDD), one of the most common causes of blindness, is predominantly caused by the gradual death of retinal pigment epithelial cells (RPEs) and photoreceptors due to various causes. Cell-based therapies, such as stem cell implantation, have been developed for the treatment of RDD, but potential risks, including teratogenicity and immune reactions, have hampered their clinical application. Stem cell-derived extracellular vesicles (EVs) have recently emerged as a cell-free alternative therapeutic strategy; however, additional invasiveness and low yield of the stem cell extraction process is problematic. To overcome these limitations, we developed therapeutic EVs for the treatment of RDD which were extracted from tonsil-derived mesenchymal stem cells obtained from human tonsil tissue discarded as medical waste following tonsillectomy (T-MSC EVs). To verify the biocompatibility and cytoprotective effect of T-MSC EVs, we measured cell viability by co-culture with human RPE without or with toxic all-trans-retinal. To elucidate the cytoprotective mechanism of T-MSC EVs, we performed transcriptome sequencing using RNA extracted from RPEs. The in vivo protective effect of T-MSC EVs was evaluated using Pde6b gene knockout rats as an animal model of retinitis pigmentosa. T-MSC EVs showed high biocompatibility and the human pigment epithelial cells were significantly protected in the presence of T-MSC EVs from the toxic effect of all-trans-retinal. In addition, T-MSC EVs showed a dose-dependent cell death-delaying effect in real-time quantification of cell death. Transcriptome sequencing analysis revealed that the efficient ability of T-MSC EVs to regulate intracellular oxidative stress may be one of the reasons explaining their excellent cytoprotective effect. Additionally, intravitreally injected T-MSC EVs had an inhibitory effect on the destruction of the outer nuclear layer in the Pde6b gene knockout rat. Together, the results of this study indicate the preventive and therapeutic effects of T-MSC EVs during the initiation and development of retinal degeneration, which may be a beneficial alternative for the treatment of RDD.

Modifying treatment of degenerative retinal diseases. Part 1. Adaptive and non-adaptive retinal plasticity

Retinal structural plasticity is manifested in multiple damages of the retina. In many cases, the response to these damages is identical at both the cellular and molecular levels, involves similar sets of cellular signals, and is associated with a change in the structure of the retina and remodeling of the neural connections. The review discusses the common and specific features of adaptive and non-adaptive retinal plasticity, which characterize glaucoma, age-related macular degeneration, retinitis pigmentosa, diabetic retinopathy, and retinopathy of prematurity. Given the common features of neurodegeneration and retinal plasticity in brain and retinal diseases, similar therapeutic strategies can be used in many cases to preserve the structure connectivity and retinal function, which stop or slow down the clinical evolution of the disease by either suppressing primary events or enhancing compensatory and regenerative mechanisms in the nervous tissue. Part 2 of the review will present neuroplasticity-based modifying therapy methods for retinal degenerative diseases.

Affinity-controlled release of rod-derived cone viability factor enhances cone photoreceptor survival.

Retinitis pigmentosa (RP) is a group of genetic diseases that results in rod photoreceptor cell degeneration, which subsequently leads to cone photoreceptor cell death, impaired vision and eventual blindness. Rod-derived cone viability factor (RdCVF) is a protein which has two isoforms: a short form (RdCVF) and a long form (RdCVFL) which act on cone photoreceptors in the retina. RdCVFL protects photoreceptors by reducing hyperoxia in the retina; however, sustained delivery of RdCVFL remains challenging. We developed an affinity-controlled release strategy for RdCVFL. An injectable physical blend of hyaluronan and methylcellulose (HAMC) was covalently modified with a peptide binding partner of the Src homology 3 (SH3) domain. This domain was expressed as a fusion protein with RdCVFL, thereby enabling its controlled release from HAMC-binding peptide. Sustained release of RdCVFL was demonstrated for the first time as RdCVFL-SH3 from HAMC-binding peptide for 7 d in vitro. To assess bioactivity, chick retinal dissociates were harvested and treated with the affinity-released recombinant protein from the HAMC-binding peptide vehicle. After 6 d in culture, cone cell viability was greater when cultured with released RdCVFL-SH3 relative to controls. We utilized computational fluid dynamics to model release of RdCVFL-SH3 from our delivery vehicle in the vitreous of the human eye. We demonstrate that our delivery vehicle can prolong the bioavailability of RdCVFL-SH3 in the retina, potentially enhancing its therapeutic effects. Our affinity-based system constitutes a versatile delivery platform for ultimate intraocular injection in the treatment of retinal degenerative diseases. STATEMENT OF SIGNIFICANCE: Retinitis pigmentosa (RP) is the leading cause of inherited blindness in the world. Rod-derived cone viability factor (RdCVF), a novel protein paracrine factor, is effective in preclinical models of RP. To extend its therapeutic effects, we developed an affinity-controlled release strategy for the long form of RdCVF, RdCVFL. We expressed RdCVFL as a fusion protein with an Src homology 3 domain (SH3). We then utilized a hydrogel composed of hyaluronan and methylcellulose (HAMC) and modified it with SH3 binding peptides to investigate its release in vitro. Furthermore, we designed a mathematical model of the human eye to investigate delivery of the protein from the delivery vehicle. This work paves the way for future investigation of controlled release RdCVF.

Stem Cells As Potential Regenerative Treatment For Retinal Degenerative Diseases And Diabetic Retinopathy

Stem Cells As Potential Regenerative Treatment For Retinal Degenerative Diseases And Diabetic Retinopathy

Targeting Necroptosis: A Novel Therapeutic Option for Retinal Degenerative Diseases.

The discovery of the necroptosis, a form of regulated necrosis that is mediated by receptor-interacting protein kinase 1 (RIPK1), RIPK3, and mixed-lineage kinase domain-like pseudokinase (MLKL), represents a major breakthrough that has dramatically altered the conception of necrosis - traditionally thought of as uncontrolled cell death - in various human diseases. Retinal cell death is a leading cause of blindness and has been identified in most retinal diseases, e.g., age-related macular degeneration, glaucoma, retinal detachment, retinitis pigmentosa, etc. Increasing evidence demonstrates that retinal degenerative diseases also share a common mechanism in necroptosis. Exacerbated necroptotic cell death hinders the treatment for retinal degenerative diseases. In this review, we highlight recent advances in identifying retinal necroptosis, summarize the underlying mechanisms of necroptosis in retinal degenerative diseases, and discuss potential anti-necroptosis strategies, such as selective inhibitors and chemical agents, for treating retinal degenerative diseases.

Retinal Degeneration: Molecular Mechanisms and Therapeutic Strategies.

Retinal degenerative diseases are the main retinal diseases that threaten vision. Most retinal degenerative diseases are inherited diseases, including autosomal recessive inheritance, autosomal dominant inheritance, X-linked inheritance, and mitochondrial inheritance; therefore, emerging gene therapy strategies may provide an alternative method of treatment. Currently, three viral vectors are usually used in gene therapy studies: adenovirus, lentivirus, and adeno-associated virus. Other gene therapies have their own advantages, such as DNA nanoparticles, antisense oligonucleotides, and gene editing therapies. In addition, retinal degenerative diseases are often accompanied by abnormalities of retinal cells, including photoreceptor and retinal pigment epithelial cells. At present, stem cell transplantation is a promising new treatment for retinal degenerative diseases. Common sources of stem cells include retinal progenitor cells, induced pluripotent stem cells, embryonic stem cells, and mesenchymal stem cells. In addition, retina explant cultures in vitro can be used as an effective platform for screening new therapies for retinal degenerative diseases. Drugs that actually reach the retinal layer are more controlled, more consistent, and less invasive when using retinal explants. Furthermore, studies have shown that the imbalance of the gut microbiota is closely related to the occurrence and development of diabetic retinopathy. Therefore, the progression of diabetic retinopathy may be restrained by adjusting the imbalance of the gut microbiota. The purpose of this review is to discuss and summarize the molecular mechanisms and potential therapeutic strategies of retinal degenerative diseases.

Optogenetic Therapy for Visual Restoration

Optogenetics is a recent breakthrough in neuroscience, and one of the most promising applications is the treatment of retinal degenerative diseases. Multiple clinical trials are currently ongoing, less than a decade after the first attempt at visual restoration using optogenetics. Optogenetic therapy has great value in providing hope for visual restoration in late-stage retinal degeneration, regardless of the genotype. This alternative gene therapy consists of multiple elements including the choice of target retinal cells, optogenetic tools, and gene delivery systems. Currently, there are various options for each element, all of which have been developed as a product of technological success. In particular, the performance of optogenetic tools in terms of light and wavelength sensitivity have been improved by engineering microbial opsins and applying human opsins. To provide better post-treatment vision, the optimal choice of optogenetic tools and effective gene delivery to retinal cells is necessary. In this review, we provide an overview of the advancements in optogenetic therapy for visual restoration, focusing on available options for optogenetic tools and gene delivery methods.

Hydrogen sulfide protects retinal pigment epithelium cells against ferroptosis through the AMPK- and p62-dependent non-canonical NRF2-KEAP1 pathway

Oxidative stress-induced ferroptosis of retinal pigment epithelium (RPE) cells contributes to retinal degenerative diseases. The antioxidant molecule hydrogen sulfide (H2S) regulates oxidative stress response, but its effect on the ferroptosis of RPE cells is unclear. In this study, sodium hydrosulfide (NaHS) was used as an exogenous H2S donor to intervene tert-butyl hydroperoxide (t-BHP)-induced ferroptosis of APRE-19 cells. We found that NaHS pretreatment attenuates t-BHP-induced oxidative stress and ferroptosis. Analysis of mRNA-sequencing coupled with FerrDb database identified nuclear factor erythroid-2-related factor 2 (NRF2) as a primary target for the cytoprotective role of H2S. NRF2 inhibitor ML385 reverses the effects of H2S on ferroptosis. Biochemical analysis revealed that H2S stabilizes NRF2. H2S decreases the interaction between NRF2 and KEAP1, but enhances the interaction between KEAP1 and p62. These results suggest that H2S activates the non-canonical NRF2-KEAP1 pathway. Further study demonstrated that H2S stimulates AMPK to interact and phosphorylate p62. Additionally, inhibiting AMPK or knocking down p62 blocks the effects of H2S. We speculate that targeting the non-canonical NRF2-KEAP1 pathway by H2S-based drug may benefit the treatment of retinal degenerative diseases.

Ginkgo biloba Extract Attenuates Light-Induced Photoreceptor Degeneration by Modulating CAV-1-Redoxosome Signaling.

The clinical potential of Ginkgo biloba extract (GBE) in the prevention and/or treatment of retinal degenerative diseases has been widely explored; however, the underlying molecular mechanism is poorly understood. Photoreceptor degeneration is the hallmark of retinal degenerative diseases and leads to vision impairment or loss. In this study, the effect of GBE against white light (WL) illumination-induced photoreceptor degeneration was investigated, as well as its underlying mechanism. To evaluate the in vitro activity of GBE, analysis of cell viability, cell apoptosis, oxidative stress, NOX (NADH oxidase) activity and mitochondrial membrane potential (MMP), as well as Western blotting and transcriptome sequencing and analysis, were conducted. To evaluate the in vivo activity of GBE, HE staining, electroretinography (ERG), Terminal-deoxynucleoitidyl transferase (TdT)-mediated nick end labeling (TUNEL) assay and immunofluorescence analysis were conducted. Our study showed that GBE treatment significantly attenuated WL illumination-induced oxidative damage in photoreceptor 661W cells—a finding that was also verified in C57BL/6J mice. Further molecular study revealed that WL illumination downregulated caveolin-1 (CAV-1) expression, interrupted CAV-1-NOX2 interaction, re-located NOX2 from the cell membrane to the cytoplasm and induced the formation of redoxosomes, which led to cell death. However, these cytotoxic events were significantly alleviated by GBE treatment. Interestingly, CAV-1 overexpression showed a consistent protective effect with GBE, while CAV-1 silencing impacted the protective effect of GBE against WL illumination-induced oxidative damage in in vitro and in vivo models. Thus, GBE was identified to prevent photoreceptor cell death due to CAV-1-dependent redoxosome activation, oxidative stress and mitochondrial dysfunction resulting from WL illumination. Overall, our study reveals the protective effect of GBE on photoreceptors against WL illumination-induced oxidative damage in in vitro and in vivo models, which effect is mediated through the modulation of CAV-1-redoxosome signaling. Our findings contribute to better understanding the therapeutic effect of GBE in preventing photoreceptor degeneration in retinal degenerative diseases, and GBE may become a novel therapeutic agent that is effective in reducing the morbidity of these diseases.

Somatostatin signalling promotes the differentiation of rod photoreceptors in human pluripotent stem cell-derived retinal organoid.

ObjectivesStem cell‐derived photoreceptor replacement therapy is a promising strategy for the treatment of retinal degenerative disease. The development of 3D retinal organoids has permitted the production of photoreceptors. However, there is no strategy to enrich a specific photoreceptor subtype due to inadequate knowledge of the molecular mechanism underlying the photoreceptor fate determination. Hence, our aim is to explore the uncharacterized function of somatostatin signalling in human pluripotent stem cell‐derived photoreceptor differentiation.Materials and Methods3D retinal organoids were achieved from human embryonic stem cell. The published single‐cell RNA‐sequencing datasets of human retinal development were utilized to further investigate the transcriptional regulation of photoreceptor differentiation. The assays of immunofluorescence staining, lentivirus transfection, real‐time quantitative polymerase chain reaction and western blotting were performed.ResultsWe identified that the somatostatin receptor 2 (SSTR2)‐mediated signalling was essential for rod photoreceptor differentiation at the precursor stage. The addition of the cognate ligand somatostatin in human 3D retinal organoids promoted rod photoreceptor differentiation and inhibited cone photoreceptor production. Furthermore, we found that the genesis of rod photoreceptors was modulated by endogenous somatostatin specifically secreted by developing retinal ganglion cells.ConclusionsOur study identified SSTR2 signalling as a novel extrinsic regulator for rod photoreceptor fate determination in photoreceptor precursors, which expands the repertoire of functional signalling pathways in photoreceptor development and sheds light on the optimization of the photoreceptor enrichment strategy.

Effects of interaction between stem cells and degenerative retinal microenvironment on stem cell fate determination

<p indent=0mm>To date, a substantial amount of experimental data supports the safety and effectiveness of stem cell-based cell therapy in treating retinal degenerative diseases, thus, serving as a foundation for clinical studies. However, its therapeutic effect often declines or even disappears at a later stage. In addition to the characteristics of stem cells, the microenvironment in which stem cells are transplanted is likely a key factor that determines the fate of stem cells. Glial scar, chronic inflammation, and abnormal metabolic microenvironment in the retina often lead to the failure of long-term survival, correct differentiation, and integration of grafted stem cells in the retina, which may be important factors contributing to the failure of long-term therapeutic effect of stem cell treatment for retinal degenerative diseases. Alternatively, grafted stem cells may also actively regulate the degenerating retina through paracrine or material exchange with the host cells, which can help the fate determinant of grafted stem cells in the retina. Thus, the therapeutic effect of stem cell transplantation can be improved by combined-transplantation of different stem cells or by regulating the degenerative retinal microenvironment. This review summarizes the recent progress in interactions between grafted stem cells and degenerative host retina and their impact on stem cell fate determination.

Human primitive mesenchymal stem cell-derived retinal progenitor cells improved neuroprotection, neurogenesis, and vision in rd12 mouse model of retinitis pigmentosa

BackgroundCurrently, there is no treatment for retinal degenerative diseases (RDD) such as retinitis pigmentosa (RP). Stem cell-based therapies could provide promising opportunities to repair the damaged retina and restore vision. Thus far, primarily adult mesenchymal stem cells (MSCs) have been investigated in preclinical and clinical studies, and the results have not been convincing. We applied a new approach in which primitive (p) MSC-derived retinal progenitor cells (RPCs) were examined to treat retinal degeneration in an rd12 mouse model of RP.MethodsWell-characterized pMSCs and RPCs labeled with PKH26 were intravitreally injected into rd12 mice. The vision and retinal function of transplanted animals were analyzed using electroretinography. Animals were killed 4 and 8 weeks after cell transplantation for histological, immunological, molecular, and transcriptomic analyses of the retina.ResultsTransplanted RPCs significantly improved vision and retinal thickness as well as function in rd12 mice. pMSCs and RPCs homed to distinct retinal layers. pMSCs homed to the retinal pigment epithelium, and RPCs migrated to the neural layers of the retina, where they improved the thickness of the respective layers and expressed cell-specific markers. RPCs induced anti-inflammatory and neuroprotective responses as well as upregulated the expression of genes involved in neurogenesis. The transcriptomic analysis showed that RPCs promoted neurogenesis and functional recovery of the retina through inhibition of BMP and activation of JAK/STAT and MAPK signaling pathways.ConclusionsOur study demonstrated that RPCs countered inflammation, provided retinal protection, and promoted neurogenesis resulting in improved retinal structure and physiological function in rd12 mice.

HMGB2 causes photoreceptor death via down-regulating Nrf2/HO-1 and up-regulating NF-κB/NLRP3 signaling pathways in light-induced retinal degeneration model

In the pathogenesis of retinal degenerative diseases, oxidative stress is a key driver leading to photoreceptor death and eventually vision loss. Currently, there are no effective therapies available to rescue photoreceptors in these diseases. High-mobility group box 2 (HMGB2), a pro-inflammatory factor and damage-associated molecular patterns (DAMPs), has been proven to mediate various inflammatory diseases, but its role in retinal degenerative diseases, especially in retinal inflammation and photoreceptor degeneration, still remains unknown. In this study, we assessed the localization and function of HMGB2 under oxidative stress and explored the underlying mechanisms in a mouse model of light-induced retinal damage (LIRD). The results showed that increased oxidative stress, the photoreceptors death, as well as the pyroptosis-related proteins were evidenced in mice retina after light exposure. HMGB2 protein was predominantly expressed in the outer nuclear layer (ONL), which was translocated to the cytoplasm and released after injury. The mechanistic effect of HMGB2 was studied in the 661w cell line treated with H2O2, showing that exogenous recombinant HMGB2 protein reduced the expressions of the antioxidant protein nuclear erythroid factor 2-related factor 2 (Nrf2) and its downstream target heme oxygenase-1 (HO-1), and induced NF-κB/NLRP3 signaling pathway. HMGB2 knockdown increased cell viability, up-regulated the expressions of Nrf2 and HO-1, down-regulated the expressions of pyroptosis-related proteins in H2O2-treated 661w cells; and also prevented photoreceptors loss and maintained ONL in mice model of LIRD. The present study proposed HMGB2 as a potential therapeutic target for treatment of retinal degenerative diseases.

Polyphenols and Visual Health: Potential Effects on Degenerative Retinal Diseases.

Dietary polyphenols are a group of natural compounds that have been proposed to have beneficial effects on human health. They were first known for their antioxidant properties, but several studies over the years have shown that these compounds can exert protective effects against chronic diseases. Nonetheless, the mechanisms underlying these potential benefits are still uncertain and contradictory effects have been reported. In this review, we analyze the potential effects of polyphenol compounds on some visual diseases, with a special focus on retinal degenerative diseases. Current effective therapies for the treatment of such retinal diseases are lacking and new strategies need to be developed. For this reason, there is currently a renewed interest in finding novel ligands (or known ligands with previously unexpected features) that could bind to retinal photoreceptors and modulate their molecular properties. Some polyphenols, especially flavonoids (e.g., quercetin and tannic acid), could attenuate light-induced receptor damage and promote visual health benefits. Recent evidence suggests that certain flavonoids could help stabilize the correctly folded conformation of the visual photoreceptor protein rhodopsin and offset the deleterious effect of retinitis pigmentosa mutations. In this regard, certain polyphenols, like the flavonoids mentioned before, have been shown to improve the stability, expression, regeneration and folding of rhodopsin mutants in experimental in vitro studies. Moreover, these compounds appear to improve the integration of the receptor into the cell membrane while acting against oxidative stress at the same time. We anticipate that polyphenol compounds can be used to target visual photoreceptor proteins, such as rhodopsin, in a way that has only been recently proposed and that these can be used in novel approaches for the treatment of retinal degenerative diseases like retinitis pigmentosa; however, studies in this field are limited and further research is needed in order to properly characterize the effects of these compounds on retinal degenerative diseases through the proposed mechanisms.

PEDF-Mediated Mitophagy Triggers the Visual Cycle by Enhancing Mitochondrial Functions in a H2O2-Injured Rat Model.

Retinal degenerative diseases result from oxidative stress and mitochondrial dysfunction, leading to the loss of visual acuity. Damaged retinal pigment epithelial (RPE) and photoreceptor cells undergo mitophagy. Pigment epithelium-derived factor (PEDF) protects from oxidative stress in RPE and improves mitochondrial functions. Overexpression of PEDF in placenta-derived mesenchymal stem cells (PD-MSCs; PD-MSCsPEDF) provides therapeutic effects in retinal degenerative diseases. Here, we investigated whether PD-MSCsPEDF restored the visual cycle through a mitophagic mechanism in RPE cells in hydrogen peroxide (H2O2)-injured rat retinas. Compared with naïve PD-MSCs, PD-MSCsPEDF augmented mitochondrial biogenesis and translation markers as well as mitochondrial respiratory states. In the H2O2-injured rat model, intravitreal administration of PD-MSCsPEDF restored total retinal layer thickness compared to that of naïve PD-MSCs. In particular, PTEN-induced kinase 1 (PINK1), which is the major mitophagy marker, exhibited increased expression in retinal layers and RPE cells after PD-MSCPEDF transplantation. Similarly, expression of the visual cycle enzyme retinol dehydrogenase 11 (RDH11) showed the same patterns as PINK1 levels, resulting in improved visual activity. Taken together, these findings suggest that PD-MSCsPEDF facilitate mitophagy and restore the loss of visual cycles in H2O2-injured rat retinas and RPE cells. These data indicate a new strategy for next-generation MSC-based treatment of retinal degenerative diseases.