Mitochondrial dysfunction underlying outer retinal diseases

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.

Genetic context modulates aging and degeneration in the murine retina

BACKGROUND

Age is the principal risk factor for neurodegeneration in both the retina and brain. The retina and brain share many biological properties; thus, insights into retinal aging and degeneration may shed light onto similar processes in the brain. Genetic makeup strongly influences susceptibility to age-related retinal disease. However, studies investigating retinal aging have not sufficiently accounted for genetic diversity. Therefore, examining molecular aging in the retina across different genetic backgrounds will enhance our understanding of human-relevant aging and degeneration in both the retina and brain-potentially improving therapeutic approaches to these debilitating conditions.

METHODS

Transcriptomics and proteomics were employed to elucidate retinal aging signatures in nine genetically diverse mouse strains (C57BL/6J, 129S1/SvlmJ, NZO/HlLtJ, WSB/EiJ, CAST/EiJ, PWK/PhK, NOD/ShiLtJ, A/J, and BALB/cJ) across lifespan. These data predicted human disease-relevant changes in WSB and NZO strains. Accordingly, B6, WSB, and NZO mice were subjected to human-relevant in vivo examinations at 4, 8, 12, and/or 18M, including: slit lamp, fundus imaging, optical coherence tomography, fluorescein angiography, and pattern/full-field electroretinography. Retinal morphology, vascular structure, and cell counts were assessed ex vivo.

RESULTS

We identified common molecular aging signatures across the nine mouse strains, which included genes associated with photoreceptor function and immune activation. Genetic background strongly modulated these aging signatures. Analysis of cell type-specific marker genes predicted age-related loss of photoreceptors and retinal ganglion cells (RGCs) in WSB and NZO, respectively. Fundus exams revealed retinitis pigmentosa-relevant pigmentary abnormalities in WSB retinas and diabetic retinopathy (DR)-relevant cotton wool spots and exudates in NZO retinas. Profound photoreceptor dysfunction and loss were confirmed in WSB. Molecular analyses indicated changes in photoreceptor-specific proteins prior to loss, suggesting photoreceptor-intrinsic dysfunction in WSB. In addition, age-associated RGC dysfunction, loss, and concomitant microvascular dysfunction were observed in NZO mice. Proteomic analyses revealed an early reduction in protective antioxidant processes, which may underlie increased susceptibility to DR-relevant pathology in NZO.

CONCLUSIONS

Genetic context is a strong determinant of retinal aging, and our multi-omics resource can aid in understanding age-related diseases of the eye and brain. Our investigations identified and validated WSB and NZO mice as improved preclinical models relevant to common retinal neurodegenerative diseases.

Oleocanthal mitigates CoCl2-induced oxidative damage and apoptosis via regulating MAPK pathway in human retinal pigment epithelial cells

Retinal hypoxia causes severe visual impairment and dysfunction in retinal pigment epithelial (RPE) cells, triggering a cascade of events leading to cellular apoptosis. Oxidative stress induced by hypoxia plays a significant role in the development of retinal diseases; however, the precise pathogenesis remains unclear. Oleocanthal, a phenolic compound in extra virgin olive oil, is known for its diverse biological properties. This study aims to investigate the potential anti-oxidative effects of oleocanthal against CoCl2-induced hypoxia in ARPE-19 cells. The cell culture model enabled the evaluation of apoptosis, DNA damage, and ROS levels using MTT assay, Western blot, Annexin V/PI staining, JC-1 staining, MitoSOX, H2DCFDA, immunocytochemistry, and comet assays. Our results showed that oleocanthal effectively protected RPE cells against CoCl2-induced damage by enhancing cell viability, reducing DNA damage, and decreasing ROS levels. Moreover, oleocanthal attenuated CoCl2-induced MMP loss by elevating the JC-1 aggregate/monomer ratio. Furthermore, CoCl2-induced cell apoptosis via up-regulating MAPK signaling, while oleocanthal mitigated this effect. These findings shed light on the molecular mechanisms underlying oleocanthal's protection against oxidative stress induced by hypoxia, offering potential insights for the development of novel therapeutic agents for retinal hypoxia.

Mitochondrial functional impairment in ARL3-mutation related rod-cone dystrophy

Mitochondria are vital for retinal cell function and survival, and there is growing evidence linking mitochondrial dysfunction to retinal degenerations. Although ARL3 mutations have been linked to multiple forms of retinal degeneration, the relationship between ARL3 and mitochondria remains unexplored. Herein, we investigated the effects of ARL3 T31A , ARL3 C118F , and ARL3 T31A/C118F mutations on mitochondrial function in fibroblasts obtained from patients with ARL3-related rod-cone dystrophy. Our findings revealed that these mutations led to a decrease in mitochondrial respiration, an increase in the accumulation mitochondrial reactive oxygen species (ROS), and induction of apoptosis in fibroblasts. Additionally, we conducted a comparative analysis of the effects of ARL3T31A, ARL3C118F, and ARL3T31A/C118F proteins on mitochondria in ARPE-19 cells. Results showed that ARL3T31A and ARL3T31A/C118F not only affected mitochondrial function but also induced apoptosis in ARPE-19 cells. Conversely, ARL3C118F primarily influenced cell apoptosis with minimal effects on mitochondrial function in ARPE-19 cells. Transcriptome analysis further suggested the involvement of respiratory electron transport, response to ROS, and apoptotic signaling pathways in ARL3T31A/C118F cells. Our study demonstrated that ARL3-related mutations play a significant role in the diversity of mitochondrial function, providing novel insights into the functional analysis of ARL3-related mutations.

A novel homozygous pathogenic missense variant in COX6B1: Further delineation of the phenotype

Cytochrome c oxidase (COX) deficiency is a phenotypically diverse group of diseases caused by variants in over 30 genes. Biallelic pathogenic variants in COX6B1 have been described in four patients to date with varying disease manifestations. We describe the clinical features and follow-up of a patient with a novel homozygous pathogenic variant in COX6B1 who presented acutely with severe encephalomyopathy associated with an infection. New findings include ophthalmological evaluation and follow-up of neuroradiological investigations. The novel p.Trp31Arg variant was predicted to be pathogenic in silico, and further functional analyses with biochemical analysis of mitochondrial function showed isolated COX deficiency. Muscle biopsy showed a specific lack of COX6B1 protein together with complex IV deficiency on western blot, enzyme histochemistry, and immuno-histochemistry.

The toxic effects of polystyrene microplastic/nanoplastic particles on retinal pigment epithelial cells and retinal tissue

The increasing use of contact lenses, artificial tears, and anti-vascular endothelial growth factor (anti-VEGF) drug injections for age-related macular degeneration has heightened the likelihood of eye exposure to microplastic particles. Extensive research has established that microplastic particles can induce oxidative stress on the ocular surface, resulting in damage. However, the impact of these particles on the retina remains unclear. Therefore, this study investigated whether microplastics/nanoplastics (MPs/NPs) cause retinal damage. In vitro human retinal pigment epithelial (RPE) cells were exposed to polystyrene MPs and NPs for 48 h. Assessment of cell viability using WST-8; evaluation of TNF-α and IL-1β expression; observation of cell morphology and particle invasion via TEM; measurement of ROS levels using the DCFDA reagent; and western blot analysis of SOD2, FIS1, Drp1, and LC3B expression were conducted. In vivo experiments involved intravitreal injection of MPs/NPs in rats, followed by retinal H&E staining 24 h later and evaluation of TNF-α and IL-1β expression. Results indicated that exposure to MPs did not significantly alter RPE cell viability, whereas exposure to NPs led to a noticeable decrease. TEM images revealed NPs' penetration into cells, causing increased oxidative stress (SOD2), mitochondrial fission (FIS1, Drp1), and mitochondrial autophagy (LC3B). In vivo experiments demonstrated an increase in inflammatory cells in retinal tissues exposed to NPs, along with elevated levels of TNF-α and IL-1β. Conclusively, both MPs and NPs impact the retina, with NPs displaying greater toxicity. NPs significantly elevate ROS levels in the retina and induce mitochondrial fission and mitophagy in RPE cells compared to MPs.

High-throughput ultrastructural analysis of macular telangiectasia type 2

Introduction

Macular Telangiectasia type 2 (MacTel), is an uncommon form of late-onset, slowly-progressive macular degeneration. Associated with regional Müller glial cell loss in the retina and the amino acid serine synthesized by Müller cells, the disease is functionally confined to a central retinal region - the MacTel zone.

Methods

We have used high-throughput multi-resolution electron microscopy techniques, optimized for disease analysis, to study the retinas from two women, mother and daughter, aged 79 and 48 years respectively, suffering from MacTel.

Results

In both eyes, the principal observations made were changes specific to mitochondrial structure both outside and within the MacTel zone in all retinal cell types, with the exception of those in the retinal pigment epithelium (RPE). The lesion areas, which are a hallmark of MacTel, extend from Bruch's membrane and the choriocapillaris, through all depths of the retina, and include cells from the RPE, retinal vascular elements, and extensive hypertrophic basement membrane material. Where the Müller glial cells are lost, we have identified a significant population of microglial cells, exclusively within the Henle fiber layer, which appear to ensheathe the Henle fibers, similar to that seen normally by Müller cells.

Discussion

Since Müller cells synthesize retinal serine, whereas retinal neurons do not, we propose that serine deficiency, required for normal mitochondrial function, may relate to mitochondrial changes that underlie the development of MacTel. With mitochondrial changes occurring retina-wide, the question remains as to why the Müller cells are uniquely susceptible within the MacTel zone.

Mitochondrial retinopathies and optic neuropathies: The impact of retinal imaging on modern understanding of pathogenesis, diagnosis, and management

Advancements in ocular imaging have significantly broadened our comprehension of mitochondrial retinopathies and optic neuropathies by examining the structural and pathological aspects of the retina and optic nerve in these conditions. This article aims to review the prominent imaging characteristics associated with mitochondrial retinopathies and optic neuropathies, aiming to deepen our insight into their pathogenesis and clinical features. Preceding this exploration, the article provides a detailed overview of the crucial genetic and clinical features, which is essential for the proper interpretation of in vivo imaging. More importantly, we will provide a critical analysis on how these imaging modalities could serve as biomarkers for characterization and monitoring, as well as in guiding treatment decisions. However, these imaging methods have limitations, which will be discussed along with potential strategies to mitigate them. Lastly, the article will emphasize the potential advantages and future integration of imaging techniques in evaluating patients with mitochondrial eye disorders, considering the prospects of emerging gene therapies.

Genetic context modulates aging and degeneration in the murine retina

Background

Age is the principal risk factor for neurodegeneration in both the retina and brain. The retina and brain share many biological properties; thus, insights into retinal aging and degeneration may shed light onto similar processes in the brain. Genetic makeup strongly influences susceptibility to age-related retinal disease. However, studies investigating retinal aging have not sufficiently accounted for genetic diversity. Therefore, examining molecular aging in the retina across different genetic backgrounds will enhance our understanding of human-relevant aging and degeneration in both the retina and brain-potentially improving therapeutic approaches to these debilitating conditions.

Methods

Transcriptomics and proteomics were employed to elucidate retinal aging signatures in nine genetically diverse mouse strains (C57BL/6J, 129S1/SvlmJ, NZO/HlLtJ, WSB/EiJ, CAST/EiJ, PWK/PhK, NOD/ShiLtJ, A/J, and BALB/cJ) across lifespan. These data predicted human disease-relevant changes in WSB and NZO strains. Accordingly, B6, WSB and NZO mice were subjected to human-relevant in vivo examinations at 4, 8, 12, and/or 18M, including: slit lamp, fundus imaging, optical coherence tomography, fluorescein angiography, and pattern/full-field electroretinography. Retinal morphology, vascular structure, and cell counts were assessed ex vivo.

Results

We identified common molecular aging signatures across the nine mouse strains, which included genes associated with photoreceptor function and immune activation. Genetic background strongly modulated these aging signatures. Analysis of cell type-specific marker genes predicted age-related loss of photoreceptors and retinal ganglion cells (RGCs) in WSB and NZO, respectively. Fundus exams revealed retinitis pigmentosa-relevant pigmentary abnormalities in WSB retinas and diabetic retinopathy (DR)-relevant cotton wool spots and exudates in NZO retinas. Profound photoreceptor dysfunction and loss were confirmed in WSB. Molecular analyses indicated changes in photoreceptor-specific proteins prior to loss, suggesting photoreceptor-intrinsic dysfunction in WSB. In addition, age-associated RGC dysfunction, loss, and concomitant microvascular dysfunction was observed in NZO mice. Proteomic analyses revealed an early reduction in protective antioxidant processes, which may underlie increased susceptibility to DR-relevant pathology in NZO.

Conclusions

Genetic context is a strong determinant of retinal aging, and our multi-omics resource can aid in understanding age-related diseases of the eye and brain. Our investigations identified and validated WSB and NZO mice as improved preclinical models relevant to common retinal neurodegenerative diseases.

Piceid Octanoate Protects Retinal Cells against Oxidative Damage by Regulating the Sirtuin 1/Poly-ADP-Ribose Polymerase 1 Axis In Vitro and in rd10 Mice

Retinitis pigmentosa is a common cause of inherited blindness in adults, which in many cases is associated with an increase in the formation of reactive oxygen species (ROS) that induces DNA damage, triggering Poly-ADP-Ribose Polymerase 1 (PARP1) activation and leading to parthanatos-mediated cell death. Previous studies have shown that resveratrol (RSV) is a promising molecule that can mitigate PARP1 overactivity, but its low bioavailability is a limitation for medical use. This study examined the impact of a synthesized new acylated RSV prodrug, piceid octanoate (PIC-OCT), in the 661W cell line against H2O2 oxidative stress and in rd10 mice. PIC-OCT possesses a better ADME profile than RSV. In response to H2O2, 661W cells pretreated with PIC-OCT preserved cell viability in more than 38% of cells by significantly promoting SIRT1 nuclear translocation, preserving NAD+/NADH ratio, and suppressing intracellular ROS formation. These effects result from expressing antioxidant genes, maintaining mitochondrial function, reducing PARP1 nuclear expression, and preventing AIF nuclear translocation. In rd10 mice, PIC-OCT inhibited PAR-polymer formation, increased SIRT1 expression, significantly reduced TUNEL-positive cells in the retinal outer nuclear layer, preserved ERGs, and enhanced light chamber activity (all p values < 0.05). Our findings corroborate that PIC-OCT protects photoreceptors by modulating the SIRT1/PARP1 axis in models of retinal degeneration.

Potential Retinal Biomarkers in Alzheimer's Disease

Alzheimer's disease (AD) represents a major diagnostic challenge, as early detection is crucial for effective intervention. This review examines the diagnostic challenges facing current AD evaluations and explores the emerging field of retinal alterations as early indicators. Recognizing the potential of the retina as a noninvasive window to the brain, we emphasize the importance of identifying retinal biomarkers in the early stages of AD. However, the examination of AD is not without its challenges, as the similarities shared with other retinal diseases introduce complexity in the search for AD-specific markers. In this review, we address the relevance of using the retina for the early diagnosis of AD and the complex challenges associated with the search for AD-specific retinal biomarkers. We provide a comprehensive overview of the current landscape and highlight avenues for progress in AD diagnosis by retinal examination.

A treatment within sight: challenges in the development of stem cell-derived photoreceptor therapies for retinal degenerative diseases

Stem cell therapies can potentially treat various retinal degenerative diseases, including age-related macular degeneration (AMD) and inherited retinal diseases like retinitis pigmentosa. For these diseases, transplanted cells may include stem cell-derived retinal pigmented epithelial (RPE) cells, photoreceptors, or a combination of both. Although stem cell-derived RPE cells have progressed to human clinical trials, therapies using photoreceptors and other retinal cell types are lagging. In this review, we discuss the potential use of human pluripotent stem cell (hPSC)-derived photoreceptors for the treatment of retinal degeneration and highlight the progress and challenges for their efficient production and clinical application in regenerative medicine.

The New Era of Therapeutic Strategies for the Treatment of Retinitis Pigmentosa: A Narrative Review of Pathomolecular Mechanisms for the Development of Cell-Based Therapies

Retinitis pigmentosa, defined more properly as cone-rod dystrophy, is a paradigm of inherited diffuse retinal dystrophies, one of the rare diseases with the highest prevalence in the worldwide population and one of the main causes of low vision in the pediatric and elderly age groups. Advancements in and the understanding of molecular biology and gene-editing technologies have raised interest in laying the foundation for new therapeutic strategies for rare diseases. As a consequence, new possibilities for clinicians and patients are arising due to the feasibility of treating such a devastating disorder, reducing its complications. The scope of this review focuses on the pathomolecular mechanisms underlying RP better to understand the prospects of its treatment using innovative approaches.

Mechanisms of Extraorbital Lacrimal Gland Aging in Mice: An Integrative Analysis of the Temporal Transcriptome

Purpose

This study used high-throughput RNA sequencing (RNA-Seq) and bioinformatics analysis to investigate the altered transcriptome profile of aging lacrimal glands in mice that occurs over the course of a 24-hour cycle.

Methods

Male C57BL/6J mice aged 12 weeks (young) and 20 months (aging) were housed in a pathogen-free setting with a 12-hour light/12-hour dark cycle. Throughout a 24-hour cycle, mouse extraorbital lacrimal glands (ELGs) were collected at eight time points at three-hour intervals. To prepare for the high-throughput RNA-Seq, whole mRNA was extracted. Differentially expressed genes (DEGs) in the young and aging groups were subjected to bioinformatic analysis based on diurnal patterns. Furthermore, the cell populations in which significant DEGs express and signaling pathways occur were validated at the single-cell RNA sequencing (scRNA-seq) level.

Results

The total transcriptome composition was significantly altered in aging ELGs compared with that in young mouse ELGs at eight time points during the 24-hour cycle, with 864 upregulated and 228 downregulated DEGs, which were primarily enriched in inflammatory pathways. Further comparative analysis of the point-to-point transcriptome revealed that aging ELGs underwent alterations in the temporal transcriptome profile in several pathways, including the inflammation-related, metabolism-related, mitochondrial bioenergetic function-associated, synaptome neural activity-associated, cell processes-associated, DNA processing-associated and fibrosis-associated pathways. Most of these pathways occurred separately in distinct cell populations.

Conclusions

Transcriptome profiles of aging lacrimal glands undergo considerable diurnal time-dependent changes; this finding offers a comprehensive source of information to better understand the pathophysiology of lacrimal gland aging and its underlying mechanisms.

Cellular and subcellular optogenetic approaches towards neuroprotection and vision restoration

Optogenetics is defined as the combination of genetic and optical methods to induce or inhibit well-defined events in isolated cells, tissues, or animals. While optogenetics within ophthalmology has been primarily applied towards treating inherited retinal disease, there are a myriad of other applications that hold great promise for a variety of eye diseases including cellular regeneration, modulation of mitochondria and metabolism, regulation of intraocular pressure, and pain control. Supported by primary data from the authors' work with in vitro and in vivo applications, we introduce a novel approach to metabolic regulation, Opsins to Restore Cellular ATP (ORCA). We review the fundamental constructs for ophthalmic optogenetics, present current therapeutic approaches and clinical trials, and discuss the future of subcellular and signaling pathway applications for neuroprotection and vision restoration.

Mitochondria and the eye-manifestations of mitochondrial diseases and their management

Historically, distinct mitochondrial syndromes were recognised clinically by their ocular features. Due to their predilection for metabolically active tissue, mitochondrial diseases frequently involve the eye, resulting in a range of ophthalmic manifestations including progressive external ophthalmoplegia, retinopathy and optic neuropathy, as well as deficiencies of the retrochiasmal visual pathway. With the wider availability of genetic testing in clinical practice, it is now recognised that genotype-phenotype correlations in mitochondrial diseases can be imprecise: many classic syndromes can be associated with multiple genes and genetic variants, and the same genetic variant can have multiple clinical presentations, including subclinical ophthalmic manifestations in individuals who are otherwise asymptomatic. Previously considered rare diseases with no effective treatments, considerable progress has been made in our understanding of mitochondrial diseases with new therapies emerging, in particular, gene therapy for inherited optic neuropathies.

iPSC-derived retinal pigmented epithelial cells from patients with macular telangiectasia show decreased mitochondrial function

Patient-derived induced pluripotent stem cells (iPSCs) provide a powerful tool for identifying cellular and molecular mechanisms of disease. Macular telangiectasia type 2 (MacTel) is a rare, late-onset degenerative retinal disease with an extremely heterogeneous genetic architecture, lending itself to the use of iPSCs. Whole-exome sequencing screens and pedigree analyses have identified rare causative mutations that account for less than 5% of cases. Metabolomic surveys of patient populations and GWAS have linked MacTel to decreased circulating levels of serine and elevated levels of neurotoxic 1-deoxysphingolipids (1-dSLs). However, retina-specific, disease-contributing factors have yet to be identified. Here, we used iPSC-differentiated retinal pigmented epithelial (iRPE) cells derived from donors with or without MacTel to screen for novel cell-intrinsic pathological mechanisms. We show that MacTel iRPE cells mimicked the low serine levels observed in serum from patients with MacTel. Through RNA-Seq and gene set enrichment pathway analysis, we determined that MacTel iRPE cells are enriched in cellular stress pathways and dysregulation of central carbon metabolism. Using respirometry and mitochondrial stress testing, we functionally validated that MacTel iRPE cells had a reduction in mitochondrial function that was independent of defects in serine biosynthesis and 1-dSL accumulation. Thus, we identified phenotypes that may constitute alternative disease mechanisms beyond the known serine/sphingolipid pathway.

Oxidative Stress Induced Dysfunction of Protein Synthesis in 661W Mice Photoreceptor Cells

Photoreceptor cells are highly susceptible to oxidative-stress-induced damage due to their high metabolic rate. Oxidative stress plays a key role in driving pathological events in several different ocular diseases, which lead to retinal degeneration and ultimately blindness. A growing number of studies have been performed to understand downstream events caused by ROS induced oxidative stress in photoreceptor cells; however, the underlying mechanisms of ROS toxicity are not fully understood. To shed light on ROS induced downstream pathological events, we employed a tandem mass tag (TMT) labelling-based quantitative mass-spectrometric approach to determine proteome changes in 661W photoreceptor cells following oxidative stress induction via the application of different concentrations of H2O2 at different time points. Overall, 5920 proteins were identified and quantified, and 450 differentially expressed proteins (DEPs) were identified, which were altered in a dose and time dependent manner in all treatment groups compared to the control group. These proteins were involved in several biological pathways, including spliceosome and ribosome response, activated glutathione metabolism, decreased ECM-receptor interaction, oxidative phosphorylation, abnormally regulated lysosome, apoptosis, and ribosome biogenesis. Our results highlighted ECM receptor interaction, oxidative phosphorylation and spliceosome pathways as the major targets of oxidative stress that might mediate vascular dysfunction and cellular senescence.

Changes in Mitochondrial Size and Morphology in the RPE and Photoreceptors of the Developing and Ageing Zebrafish

Mitochondria are essential adenosine triphosphate (ATP)-generating cellular organelles. In the retina, they are highly numerous in the photoreceptors and retinal pigment epithelium (RPE) due to their high energetic requirements. Fission and fusion of the mitochondria within these cells allow them to adapt to changing demands over the lifespan of the organism. Using transmission electron microscopy, we examined the mitochondrial ultrastructure of zebrafish photoreceptors and RPE from 5 days post fertilisation (dpf) through to late adulthood (3 years). Notably, mitochondria in the youngest animals were large and irregular shaped with a loose cristae architecture, but by 8 dpf they had reduced in size and expanded in number with more defined cristae. Investigation of temporal gene expression of several mitochondrial-related markers indicated fission as the dominant mechanism contributing to the changes observed over time. This is likely to be due to continued mitochondrial stress resulting from the oxidative environment of the retina and prolonged light exposure. We have characterised retinal mitochondrial ageing in a key vertebrate model organism, that provides a basis for future studies of retinal diseases that are linked to mitochondrial dysfunction.

miR-181a/b downregulation: a mutation-independent therapeutic approach for inherited retinal diseases

Inherited retinal diseases (IRDs) are a group of diseases whose common landmark is progressive photoreceptor loss. The development of gene-specific therapies for IRDs is hampered by their wide genetic heterogeneity. Mitochondrial dysfunction is proving to constitute one of the key pathogenic events in IRDs; hence, approaches that enhance mitochondrial activities have a promising therapeutic potential for these conditions. We previously reported that miR-181a/b downregulation boosts mitochondrial turnover in models of primary retinal mitochondrial diseases. Here, we show that miR-181a/b silencing has a beneficial effect also in IRDs. In particular, the injection in the subretinal space of an adeno-associated viral vector (AAV) that harbors a miR-181a/b inhibitor (sponge) sequence (AAV2/8-GFP-Sponge-miR-181a/b) improves retinal morphology and visual function both in models of autosomal dominant (RHO-P347S) and of autosomal recessive (rd10) retinitis pigmentosa. Moreover, we demonstrate that miR-181a/b downregulation modulates the level of the mitochondrial fission-related protein Drp1 and rescues the mitochondrial fragmentation in RHO-P347S photoreceptors. Overall, these data support the potential use of miR-181a/b downregulation as an innovative mutation-independent therapeutic strategy for IRDs, which can be effective both to delay disease progression and to aid gene-specific therapeutic approaches.

The Correlation Between MicroRNAs and Diabetic Retinopathy

Micro ribonucleic acids (miRNAs), as a category of post-transcriptional gene inhibitors, have a wide range of biological functions, are involved in many pathological processes, and are attractive therapeutic targets. Considerable evidence in ophthalmology indicates that miRNAs play an important role in diabetic retinopathy (DR), especially in inflammation, oxidative stress, and neurodegeneration. Targeting specific miRNAs for the treatment of DR has attracted much attention. This is a review focusing on the pathophysiological roles of miRNAs in DR, diabetic macular edema, and proliferative DR complex multifactorial retinal diseases, with particular emphasis on how miRNAs regulate complex molecular pathways and underlying pathomechanisms. Moreover, the future development potential and application limitations of therapy that targets specific miRNAs for DR are discussed.

Increased H3K27 trimethylation contributes to cone survival in a mouse model of cone dystrophy

Inherited retinal diseases (IRDs) are a heterogeneous group of blinding disorders, which result in dysfunction or death of the light-sensing cone and rod photoreceptors. Despite individual IRDs (Inherited retinal disease) being rare, collectively, they affect up to 1:2000 people worldwide, causing a significant socioeconomic burden, especially when cone-mediated central vision is affected. This study uses the Pde6c^cpfl1 mouse model of achromatopsia, a cone-specific vision loss IRD (Inherited retinal disease), to investigate the potential gene-independent therapeutic benefits of a histone demethylase inhibitor GSK-J4 on cone cell survival. We investigated the effects of GSK-J4 treatment on cone cell survival in vivo and ex vivo and changes in cone-specific gene expression via single-cell RNA sequencing. A single intravitreal GSK-J4 injection led to transcriptional changes in pathways involved in mitochondrial dysfunction, endoplasmic reticulum stress, among other key epigenetic pathways, highlighting the complex interplay between methylation and acetylation in healthy and diseased cones. Furthermore, continuous administration of GSK-J4 in retinal explants increased cone survival. Our results suggest that IRD (Inherited retinal disease)-affected cones respond positively to epigenetic modulation of histones, indicating the potential of this approach in developing a broad class of novel therapies to slow cone degeneration.

Restoring the oxidative balance in age-related diseases - An approach in glaucoma

As human life expectancy increases, age-related health issues including neurodegenerative diseases continue to rise. Regardless of genetic or environmental factors, many neurodegenerative conditions share common pathological mechanisms, such as oxidative stress, a hallmark of many age-related health burdens. In this review, we describe oxidative damage and mitochondrial dysfunction in glaucoma, an age-related neurodegenerative eye disease affecting 80 million people worldwide. We consider therapeutic approaches used to counteract oxidative stress in glaucoma, including untapped treatment options such as novel plant-derived antioxidant compounds that can reduce oxidative stress and prevent neuronal loss. We summarize the current pre-clinical models and clinical work exploring the therapeutic potential of a range of candidate plant-derived antioxidant compounds. Finally, we explore advances in drug delivery systems, particular those employing nanotechnology-based carriers which hold significant promise as a carrier for antioxidants to treat age-related disease, thus reviewing the key current state of all of the aspects required towards translation.

Mitigating the pro-oxidant state and melanogenesis of Retinitis pigmentosa: by counteracting mitochondrial dysfunction

Retinitis pigmentosa (RP) is a group of mitochondrial diseases characterized by progressive degeneration of rods and cones leading to retinal loss of light sensitivity and, consequently, to blindness. To date, no cure is available according to the clinical literature. As a disease associated with pigmentation-related, pro-oxidant state, and mitochondrial dysfunction, RP may be viewed at the crossroads of different pathogenetic pathways involved in adverse health outcomes, where mitochondria play a preeminent role. RP has been investigated in a number of experimental and clinical studies aimed at delaying retinal hyperpigmentation by means of a number of natural and synthetic antioxidants, as well as mitochondrial cofactors, also termed mitochondrial nutrients (MNs), such as alpha-lipoic acid, coenzyme Q10 and carnitine. One should consider that each MN plays distinct-and indispensable-roles in mitochondrial function. Thus, a logical choice would imply the administration of MN combinations, instead of individual MNs, as performed in previous studies, and with limited, if any, positive outcomes. A rational study design aimed at comparing the protective effects of MNs, separately or in combinations, and in association with other antioxidants, might foresee the utilization of animal RP models. The results should verify a comparative optimization in preventing or effectively contrasting retinal oxidative stress in mouse RP models and, in prospect, in human RP cases.

Metabolomics in Retinal Diseases: An Update

Retinal diseases are a leading cause of visual loss and blindness, affecting a significant proportion of the population worldwide and having a detrimental impact on quality of life, with consequent economic burden. The retina is highly metabolically active, and a number of retinal diseases are associated with metabolic dysfunction. To better understand the pathogenesis underlying such retinopathies, new technology has been developed to elucidate the mechanism behind retinal diseases. Metabolomics is a relatively new "omics" technology, which has developed subsequent to genomics, transcriptomics, and proteomics. This new technology can provide qualitative and quantitative information about low-molecular-weight metabolites (M.W. < 1500 Da) in a given biological system, which shed light on the physiological or pathological state of a cell or tissue sample at a particular time point. In this article we provide an extensive review of the application of metabolomics to retinal diseases, with focus on age-related macular degeneration (AMD), diabetic retinopathy (DR), retinopathy of prematurity (ROP), glaucoma, and retinitis pigmentosa (RP).

Mutated CCDC51 Coding for a Mitochondrial Protein, MITOK Is a Candidate Gene Defect for Autosomal Recessive Rod-Cone Dystrophy

The purpose of this work was to identify the gene defect underlying a relatively mild rod-cone dystrophy (RCD), lacking disease-causing variants in known genes implicated in inherited retinal disorders (IRD), and provide transcriptomic and immunolocalization data to highlight the best candidate. The DNA of the female patient originating from a consanguineous family revealed no large duplication or deletion, but several large homozygous regions. In one of these, a homozygous frameshift variant, c.244_246delins17 p.(Trp82Valfs*4); predicted to lead to a nonfunctional protein, was identified in CCDC51. CCDC51 encodes the mitochondrial coiled-coil domain containing 51 protein, also called MITOK. MITOK ablation causes mitochondrial dysfunction. Here we show for the first time that CCDC51/MITOK localizes in the retina and more specifically in the inner segments of the photoreceptors, well known to contain mitochondria. Mitochondrial proteins have previously been implicated in IRD, although usually in association with syndromic disease, unlike our present case. Together, our findings add another ultra-rare mutation implicated in non-syndromic IRD, whose pathogenic mechanism in the retina needs to be further elucidated.

Antimycin A-induced mitochondrial dysfunction regulates inflammasome signaling in human retinal pigment epithelial cells

Age-related macular degeneration (AMD) is a severe retinal eye disease where dysfunctional mitochondria and damaged mitochondrial DNA in retinal pigment epithelium (RPE) have been demonstrated to underlie the pathogenesis of this devastating disease. In the present study, we aimed to examine whether damaged mitochondria induce inflammasome activation in human RPE cells. Therefore, ARPE-19 cells were primed with IL-1α and exposed to the mitochondrial electron transport chain complex III inhibitor, antimycin A. We found that antimycin A-induced mitochondrial dysfunction caused caspase-1-dependent inflammasome activation and subsequent production of mature IL-1β and IL-18 in human RPE cells. AIM2 and NLRP3 appeared to be the responsible inflammasome receptors upon antimycin A-induced mitochondrial damage. We aimed at verifying our findings using hESC-RPE cells but antimycin A was absorbed by melanin. Therefore, results were repeated on D407 RPE cell cultures. Antimycin A-induced mitochondrial and NADPH oxidase-dependent ROS production occurred upstream of inflammasome activation, whereas K⁺ efflux was not required for inflammasome activation in antimycin A-treated human RPE cells. Collectively, our data emphasize that dysfunctional mitochondria regulate the assembly of inflammasome multiprotein complexes in the human RPE cells. The present study associates AIM2 with the pathogenesis of AMD.

The Role of MicroRNAs in Mitochondria-Mediated Eye Diseases

The retina is among the most metabolically active tissues with high-energy demands. The peculiar distribution of mitochondria in cells of retinal layers is necessary to assure the appropriate energy supply for the transmission of the light signal. Photoreceptor cells (PRs), retinal pigment epithelium (RPE), and retinal ganglion cells (RGCs) present a great concentration of mitochondria, which makes them particularly sensitive to mitochondrial dysfunction. To date, visual loss has been extensively correlated to defective mitochondrial functions. Many mitochondrial diseases (MDs) show indeed neuro-ophthalmic manifestations, including retinal and optic nerve phenotypes. Moreover, abnormal mitochondrial functions are frequently found in the most common retinal pathologies, i.e., glaucoma, age-related macular degeneration (AMD), and diabetic retinopathy (DR), that share clinical similarities with the hereditary primary MDs. MicroRNAs (miRNAs) are established as key regulators of several developmental, physiological, and pathological processes. Dysregulated miRNA expression profiles in retinal degeneration models and in patients underline the potentiality of miRNA modulation as a possible gene/mutation-independent strategy in retinal diseases and highlight their promising role as disease predictive or prognostic biomarkers. In this review, we will summarize the current knowledge about the participation of miRNAs in both rare and common mitochondria-mediated eye diseases. Definitely, given the involvement of miRNAs in retina pathologies and therapy as well as their use as molecular biomarkers, they represent a determining target for clinical applications.

Paeonol Induces Protective Autophagy in Retinal Photoreceptor Cells

Background: Retinal photoreceptor (RP) cells are widely involved in retina-related diseases, and oxidative stress plays a critical role in retinal secondary damage. Herein, we investigated the effectiveness and potential mechanisms of autophagy of paeonol (Pae) in terms of oxidation resistance. Methods: The animal model was induced by light damage (LD) in vivo, whereas the in vitro model was established by H₂O₂ stimulation. The effectiveness of Pae was evaluated by hematoxylin and eosin, terminal deoxynucleotidyl transferase dUTP nick end labeling assay, immunofluorescence, transmission electron microscopy, electroretinogram, and Western blot analysis in vivo, and the underlying mechanisms of Pae were assessed by Cell Counting Kit-8 assay, reactive oxygen species (ROS) assay, and Western blot analysis in 661W cells. We mainly evaluated the effects of Pae on apoptosis and autophagy. Results: Increased apoptosis of the LD-induced and decreased autophagy of RPs were mitigated by Pae treatment. Pea, which increased the expression of mitochondrial functional protein cytochrome c, reversed the decreased cell viability and autophagy induced by oxidative stress in 661W cells. Experiments showed that autophagy was downregulated in PINK1/Parkin dependent and the BNIP3L/Nix dependent pathways under H₂O₂ stimulation and was upregulated by Pae treatment. Pae increased the cell viability and reduced ROS levels through autophagy. Conclusion: Pretreatment with Pae preserved RP cells by enhancing autophagy, which protected retinal function.

Retinal Manifestations of Mitochondrial Oxidative Phosphorylation Disorders

Purpose

The purpose of this paper was to discuss manifestations of primary mitochondrial dysfunctions and whether the retinal pigment epithelium or the photoreceptors are preferentially affected.

Methods

A retrospective analysis was performed of patients with clinically and laboratory confirmed diagnoses of maternally inherited diabetes and deafness (MIDD) or Kearns–Sayre syndrome (KSS). Patients underwent full ophthalmic examination, full-field electroretinogram, and multimodal imaging studies, including short-wavelength autofluorescence, spectral domain-optical coherence tomography, and color fundus photography.

Results

A total of five patients with MIDD and four patients with KSS were evaluated at two tertiary referral centers. Mean age at initial evaluation was 50.3 years old. Nascent outer retinal tubulations corresponding with faint foci of autofluorescence were observed in two patients with MIDD. Characteristic features of this cohort included a foveal sparing phenotype observed in 13 of 18 eyes (72%), global absence of intraretinal pigment migration, and preserved retinal function on full-field electroretinogram testing in 12 of 16 eyes (75%). One patient diagnosed with MIDD presented with an unusual pattern of atrophy surrounding the parapapillary region and one patient with KSS presented with an atypical choroideremia-like phenotype.

Conclusions

MIDD and KSS are phenotypically heterogeneous disorders. Several features of disease suggest that primary mitochondrial dysfunction may first affect the retinal pigment epithelium followed by secondary photoreceptor loss. Similarities between primary mitochondrial degenerations and retinal disorders, such as age-related macular degeneration may suggest a primary role of mitochondria in the pathogenesis of these oligogenic disorders.

Efficient differentiation of human embryonic stem cells to retinal pigment epithelium under defined conditions

Age-related macular degeneration (AMD) is a highly prevalent form of blindness caused by loss death of cells of the retinal pigment epithelium (RPE). Transplantation of pluripotent stem cell (PSC)-derived RPE cells is considered a promising therapy to regenerate cell function and vision.

OBJECTIVE

The objective of this study is to develop a rapid directed differentiation method for production of RPE cells from PSC which is rapid, efficient, and fully defined and produces cells suitable for clinical use.

DESIGN

A protocol for cell growth and differentiation from hESCs was developed to induce differentiation through screening small molecules which regulated a primary stage of differentiation to the eyefield progenitor, and then, a subsequent set of molecules to drive differentiation to RPE cells. Methods for cell plating and maintenance have been optimized to give a homogeneous population of cells in a short 14-day period, followed by a procedure to support maturation of cell function.

RESULTS

We show here the efficient production of RPE cells from human embryonic stem cells (hESCs) using small molecules in a feeder-free system using xeno-free/defined medium. Flow cytometry at day 14 showed ~ 90% of cells expressed the RPE markers MITF and PMEL17. Temporal gene analysis confirmed differentiation through defined cell intermediates. Mature hESC-RPE cell monolayers exhibited key morphological, molecular, and functional characteristics of the endogenous RPE.

CONCLUSION

This study identifies a novel cell differentiation process for rapid and efficient production of retinal RPE cells directly from hESCs. The described protocol has utility for clinical-grade cell production for human therapy to treat AMD.

Proline metabolism and transport in retinal health and disease

The retina is one of the most energy-demanding tissues in the human body. Photoreceptors in the outer retina rely on nutrient support from the neighboring retinal pigment epithelium (RPE), a monolayer of epithelial cells that separate the retina and choroidal blood supply. RPE dysfunction or cell death can result in photoreceptor degeneration, leading to blindness in retinal degenerative diseases including some inherited retinal degenerations and age-related macular degeneration (AMD). In addition to having ready access to rich nutrients from blood, the RPE is also supplied with lactate from adjacent photoreceptors. Moreover, RPE can phagocytose lipid-rich outer segments for degradation and recycling on a daily basis. Recent studies show RPE cells prefer proline as a major metabolic substrate, and they are highly enriched for the proline transporter, SLC6A20. In contrast, dysfunctional or poorly differentiated RPE fails to utilize proline. RPE uses proline to fuel mitochondrial metabolism, synthesize amino acids, build the extracellular matrix, fight against oxidative stress, and sustain differentiation. Remarkably, the neural retina rarely imports proline directly, but it uptakes and utilizes intermediates and amino acids derived from proline catabolism in the RPE. Mutations of genes in proline metabolism are associated with retinal degenerative diseases, and proline supplementation is reported to improve RPE-initiated vision loss. This review will cover proline metabolism in RPE and highlight the importance of proline transport and utilization in maintaining retinal metabolism and health.

Mitochondrial DNA A3243G variant-associated retinopathy: a meta-analysis of the clinical course of visual acuity and correlation with systemic manifestations

PURPOSE

The mitochondrial DNA A3243G (m.3243A>G) variant causes a wide spectrum of phenotypes, with pigmentary retinopathy as the most common ocular finding. We undertook this meta-analysis to investigate the clinical course of visual acuity (VA) in patients with m.3243A>G variant and provide key clinical correlations with systemic manifestations.

METHODS

A PubMed literature search was performed and studies were selected after satisfying pre-set inclusion criteria. Demographic and clinical data, including retinal findings and systemic manifestations were recorded. Cross-sectional and linear regression analyses were used to investigate the relationship between VA and age, as well as between the age at diagnosis of retinopathy and the mean ages at diagnosis of sensorineural hearing loss or diabetes. The age and prevalence of systemic manifestations among patients with and without retinopathy were studied using t-tests and Mann-Whitney U-tests (performed on binarized data). Likelihood ratios were computed.

RESULTS

The mean VA (average of both eyes) of 90 patients (72.2% female; 65/90) were collected from 18 studies published between 1990 and 2018. The baseline mean age was 45.2 years (range 17 to 92). The mean logMAR VA was 0.10 (- 0.12 to 1.39). There was a statistically significant linear correlation between the logMAR VA and age (p = .008). The VA of patients less than or equal to 50 years of age was significantly better than that of patients older than 50 years (0.06 vs.0.18 logMAR, p = .002). 67 patients (74.4%) showed a characteristic pigmentary retinopathy with a mean age at diagnosis of 47.9 years (17 to 92) and VA of 0.14 logMAR (- 0.12 to 1.24). Age at diagnosis of retinopathy was linearly correlated with age at diagnosis of hearing loss or diabetes (p < .001). Patients with retinopathy were more likely to have hearing loss (83.6% vs. 56.5%, p = .03) or diabetes (56.7% vs. 17.4%, p = .001) than those without retinopathy. Those with both hearing loss and diabetes had an earlier onset of retinopathy than those without (46.4 vs. 60.4 years, p = .01). Patients without both hearing loss and diabetes were 5.3-fold less likely to develop a retinopathy.

CONCLUSIONS

Patients with m.3243A>G variant pigmentary retinopathy maintain highly functional VA until around the fifth decade of life, after which significant visual decline ensues. Patients without hearing loss and diabetes have a lower likelihood of exhibiting a retinopathy, which tends to appear about one decade after hearing loss and diabetes are diagnosed.

Glial Cells in Glaucoma: Friends, Foes, and Potential Therapeutic Targets

Glaucoma is the second leading cause of blindness worldwide, affecting ~80 million people by 2020 (1, 2). The condition is characterized by a progressive loss of retinal ganglion cells (RGCs) and their axons accompanied by visual field loss. The underlying pathophysiology of glaucoma remains elusive. Glaucoma is recognized as a multifactorial disease, and lowering intraocular pressure (IOP) is the only treatment that has been shown to slow the progression of the condition. However, a significant number of glaucoma patients continue to go blind despite intraocular pressure-lowering treatment (2). Thus, the need for alternative treatment strategies is indisputable. Accumulating evidence suggests that glial cells play a significant role in supporting RGC function and that glial dysfunction may contribute to optic nerve disease. Here, we review recent advances in understanding the role of glial cells in the pathophysiology of glaucoma. A particular focus is on the dynamic and essential interactions between glial cells and RGCs and potential therapeutic approaches to glaucoma by targeting glial cells.

Transcriptomic Changes Associated with Loss of Cell Viability Induced by Oxysterol Treatment of a Retinal Photoreceptor-Derived Cell Line: An In Vitro Model of Smith-Lemli-Opitz Syndrome

Smith–Lemli–Opitz Syndrome (SLOS) results from mutations in the gene encoding the enzyme DHCR7, which catalyzes conversion of 7-dehydrocholesterol (7DHC) to cholesterol (CHOL). Rats treated with a DHCR7 inhibitor serve as a SLOS animal model, and exhibit progressive photoreceptor-specific cell death, with accumulation of 7DHC and oxidized sterols. To understand the basis of this cell type specificity, we performed transcriptomic analyses on a photoreceptor-derived cell line (661W), treating cells with two 7DHC-derived oxysterols, which accumulate in tissues and bodily fluids of SLOS patients and in the rat SLOS model, as well as with CHOL (negative control), and evaluated differentially expressed genes (DEGs) for each treatment. Gene enrichment analysis and compilation of DEG sets indicated that endoplasmic reticulum stress, oxidative stress, DNA damage and repair, and autophagy were all highly up-regulated pathways in oxysterol-treated cells. Detailed analysis indicated that the two oxysterols exert their effects via different molecular mechanisms. Changes in expression of key genes in highlighted pathways (Hmox1, Ddit3, Trib3, and Herpud1) were validated by immunofluorescence confocal microscopy. The results extend our understanding of the pathobiology of retinal degeneration and SLOS, identifying potential new druggable targets for therapeutic intervention into these and other related orphan diseases.

Mitochondrial DNA A3243G variant-associated retinopathy: Current perspectives and clinical implications

Cellular function and survival are critically dependent on the proper functionality of the mitochondrion. Neurodegenerative cellular processes including cellular adenosine triphosphate production, intermediary metabolism control, and apoptosis regulation are all mitochondrially mediated. The A to G transition at position 3243 in the mitochondrial MTTL1 gene that encodes for the leucine transfer RNA (m.3243A>G) causes a variety of diseases, including maternally inherited loss of hearing and diabetes syndrome (MIDD), mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes syndrome (MELAS). Ophthalmological findings-including posterior sub-capsular cataract, ptosis, external ophthalmoplegia, and pigmentary retinopathy- have all been associated with the m.3243A>G variant. Pigmentary retinopathy is, however, the most common ocular finding, occurring in 38% to 86% of cases. To date, little is known about the pathogenesis, natural history, and heteroplasmic and phenotypic correlations of m.3243A>G-associated pigmentary retinopathy. We summarize the current understanding of mitochondrial genetics and pathogenesis of some associated diseases. We then review the pathophysiology, histology, clinical features, treatment, and important ocular and systemic phenotypic manifestations of m.3243A>G variant associated retinopathy. Mitochondrial diseases require a multidisciplinary team approach to ensure effective treatment, regular follow-up, and accurate genetic counseling.

Uncoupling proteins in the mitochondrial defense against oxidative stress

Oxidative stress is a major component of most major retinal diseases. Many extrinsic anti-oxidative strategies have been insufficient at counteracting one of the predominant intrinsic sources of reactive oxygen species (ROS), mitochondria. The proton gradient across the inner mitochondrial membrane is a key driving force for mitochondrial ROS production, and this gradient can be modulated by members of the mitochondrial uncoupling protein (UCP) family. Of the UCPs, UCP2 shows a widespread distribution and has been shown to uncouple oxidative phosphorylation, with concomitant decreases in ROS production. Genetic studies using transgenic and knockout mice have documented the ability of increased UCP2 activity to provide neuroprotection in models of a number of diseases, including retinal diseases, indicating that it is a strong candidate for a therapeutic target. Molecular studies have identified the structural mechanism of action of UCP2 and have detailed the ways in which its expression and activity can be controlled at the transcriptional, translational and posttranslational levels. These studies suggest a number of ways in control of UCP2 expression and activity can be used therapeutically for both acute and chronic conditions. The development of such therapeutic approaches will greatly increase the tools available to combat a broad range of serious retinal diseases.

Photobiomodulation preserves mitochondrial redox state and is retinoprotective in a rodent model of retinitis pigmentosa

Photobiomodulation (PBM) by far-red (FR) to near-infrared (NIR) light has been demonstrated to restore the function of damaged mitochondria, increase the production of cytoprotective factors and prevent cell death. Our laboratory has shown that FR PBM improves functional and structural outcomes in animal models of retinal injury and retinal degenerative disease. The current study tested the hypothesis that a brief course of NIR (830 nm) PBM would preserve mitochondrial metabolic state and attenuate photoreceptor loss in a model of retinitis pigmentosa, the P23H transgenic rat. P23H rat pups were treated with 830 nm light (180 s; 25 mW/cm2; 4.5 J/cm2) using a light-emitting diode array (Quantum Devices, Barneveld, WI) from postnatal day (p) 10 to p25. Sham-treated rats were restrained, but not treated with 830 nm light. Retinal metabolic state, function and morphology were assessed at p30 by measurement of mitochondrial redox (NADH/FAD) state by 3D optical cryo-imaging, electroretinography (ERG), spectral-domain optical coherence tomography (SD-OCT), and histomorphometry. PBM preserved retinal metabolic state, retinal function, and retinal morphology in PBM-treated animals compared to the sham-treated group. PBM protected against the disruption of the oxidation state of the mitochondrial respiratory chain observed in sham-treated animals. Scotopic ERG responses over a range of flash intensities were significantly greater in PBM-treated rats compared to sham controls. SD-OCT studies and histological assessment showed that PBM preserved the structural integrity of the retina. These findings demonstrate for the first time a direct effect of NIR PBM on retinal mitochondrial redox status in a well-established model of retinal disease. They show that chronic proteotoxic stress disrupts retinal bioenergetics resulting in mitochondrial dysfunction, and retinal degeneration and that therapies normalizing mitochondrial metabolism have considerable potential for the treatment of retinal degenerative disease.

Glutathione Trisulfide Prevents Lipopolysaccharide-induced Inflammatory Gene Expression in Retinal Pigment Epithelial Cells

We investigated the effects of glutathione trisulfide (GSSSG) on lipopolysaccharide (LPS)-induced inflammatory gene expression in immortalized ARPE-19, and primary human and mouse retinal pigment epithelial (RPE) cells. Sulfane sulfur molecules were significantly increased in GSSSG-treated ARPE-19 cells. GSSSG prevented the LPS-induced upregulation of interleukin (IL)-1β, IL-6, and C-C motif chemokine ligand 2 (CCL2) in ARPE-19/primary RPE cells. Moreover, GSSSG prevented the activation of the nuclear factor-kappa B p65 subunit, and promoted the activation of extracellular signal-regulated kinase 1/2 (ERK1/2) in LPS-treated ARPE-19 cells. ERK1/2 inhibition prevented the GSSSG-mediated inhibition of LPS-induced IL-6 and CCL2 upregulation. Additionally, ERK1/2 activation prevented the upregulation of these genes in the absence of GSSSG. Knockdown of HMOX1 or NRF2, known as anti-oxidative genes, did not affect the activity of GSSSG in the context of LPS stimulation. These findings suggest that GSSSG attenuates LPS-induced inflammatory gene expression via ERK signaling hyperactivation, independently of the NRF2/HMOX1 pathway.

Optical coherence tomography as a possible tool to monitor and predict disease progression in mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes

Optical coherence tomography (OCT) is an imaging technique used to obtain three-dimensional information on the retina. In this article, we evaluated the structural neuro-retinal abnormalities, especially the thickness in the ganglion cell complex (GCC), in patients with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS). The GCC thickness in MELAS patients was significantly thinner than that in normal controls even when they had no history of transient homonymous hemianopia. There was a negative correlation between GCC thickness and disease duration. In conclusion, OCT may be an effective tool to monitor and predict disease progression in MELAS patients.

Daily mitochondrial dynamics in cone photoreceptors

Cone photoreceptors in the retina are exposed to intense daylight and have higher energy demands in darkness. Cones produce energy using a large cluster of mitochondria. Mitochondria are susceptible to oxidative damage, and healthy mitochondrial populations are maintained by regular turnover. Daily cycles of light exposure and energy consumption suggest that mitochondrial turnover is important for cone health. We investigated the three-dimensional (3D) ultrastructure and metabolic function of zebrafish cone mitochondria throughout the day. At night retinas undergo a mitochondrial biogenesis event, corresponding to an increase in the number of smaller, simpler mitochondria and increased metabolic activity in cones. In the daytime, endoplasmic reticula (ER) and autophagosomes associate more with mitochondria, and mitochondrial size distribution across the cluster changes. We also report dense material shared between cone mitochondria that is extruded from the cell at night, sometimes forming extracellular structures. Our findings reveal an elaborate set of daily changes to cone mitochondrial structure and function.

Mutation-Independent Therapies for Retinal Diseases: Focus on Gene-Based Approaches

Gene therapy is proving to be an effective approach to treat or prevent ocular diseases ensuring a targeted, stable, and regulated introduction of exogenous genetic material with therapeutic action. Retinal diseases can be broadly categorized into two groups, namely monogenic and complex (multifactorial) forms. The high genetic heterogeneity of monogenic forms represents a significant limitation to the application of gene-specific therapeutic strategies for a significant fraction of patients. Therefore, mutation-independent therapeutic strategies, acting on common pathways that underly retinal damage, are gaining interest as complementary/alternative approaches for retinal diseases. This review will provide an overview of mutation-independent strategies that rely on the modulation in the retina of key genes regulating such crucial degenerative pathways. In particular, we will describe how gene-based approaches explore the use of neurotrophic factors, microRNAs (miRNAs), genome editing and optogenetics in order to restore/prolong visual function in both outer and inner retinal diseases. We predict that the exploitation of gene delivery procedures applied to mutation/gene independent approaches may provide the answer to the unmet therapeutic need of a large fraction of patients with genetically heterogeneous and complex retinal diseases.

Mitochondrial Markers in Aging and Primary Open-Angle Glaucoma

This review focuses on recent progress in understanding the role of mitochondrial markers in the context of mitochondrial dysfunction in glaucoma and discussing new therapeutic approaches to modulate mitochondrial function and potentially lead to improved outcomes in glaucoma.

Structural and functional insights into CWC27/CWC22 heterodimer linking the exon junction complex to spliceosomes

Human CWC27 is an uncharacterized splicing factor and mutations in its gene are linked to retinal degeneration and other developmental defects. We identify the splicing factor CWC22 as the major CWC27 partner. Both CWC27 and CWC22 are present in published B^act spliceosome structures, but no interacting domains are visible. Here, the structure of a CWC27/CWC22 heterodimer bound to the exon junction complex (EJC) core component eIF4A3 is solved at 3Å-resolution. According to spliceosomal structures, the EJC is recruited in the C complex, once CWC27 has left. Our 3D structure of the eIF4A3/CWC22/CWC27 complex is compatible with the B^act spliceosome structure but not with that of the C complex, where a CWC27 loop would clash with the EJC core subunit Y14. A CWC27/CWC22 building block might thus form an intermediate landing platform for eIF4A3 onto the B^act complex prior to its conversion into C complex. Knock-down of either CWC27 or CWC22 in immortalized retinal pigment epithelial cells affects numerous common genes, indicating that these proteins cooperate, targeting the same pathways. As the most up-regulated genes encode factors involved in inflammation, our findings suggest a possible link to the retinal degeneration associated with CWC27 deficiencies.

Heme Synthesis Inhibition Blocks Angiogenesis via Mitochondrial Dysfunction

The relationship between heme metabolism and angiogenesis is poorly understood. The final synthesis of heme occurs in mitochondria, where ferrochelatase (FECH) inserts Fe²⁺ into protoporphyrin IX to produce proto-heme IX. We previously showed that FECH inhibition is antiangiogenic in human retinal microvascular endothelial cells (HRECs) and in animal models of ocular neovascularization. In the present study, we sought to understand the mechanism of how FECH and thus heme is involved in endothelial cell function. Mitochondria in endothelial cells had several defects in function after heme inhibition. FECH loss changed the shape and mass of mitochondria and led to significant oxidative stress. Oxidative phosphorylation and mitochondrial Complex IV were decreased in HRECs and in murine retina ex vivo after heme depletion. Supplementation with heme partially rescued phenotypes of FECH blockade. These findings provide an unexpected link between mitochondrial heme metabolism and angiogenesis.

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Heme synthesis inhibition changes mitochondrial morphology in endothelial cells

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Loss of heme causes buildup of mitochondrial ROS and depolarized membrane potential

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Endothelial cells have damaged oxidative phosphorylation and glycolysis on heme loss

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Damage is due to loss of heme-containing Complex IV, restored by exogenous heme

Transcriptomic Analysis of the Developmental Similarities and Differences Between the Native Retina and Retinal Organoids

Purpose

We performed a bioinformatic transcriptome analysis to determine the alteration of gene expression between the native retina and retinal organoids in both mice and humans.

Methods

The datasets of mouse native retina (GSE101986), mouse retinal organoids (GSE102794), human native retina (GSE104827), and human retinal organoids (GSE119320) were obtained from Gene Expression Omnibus. After normalization, a principal component analysis was performed to categorize the samples. The genes were clustered to classify them. A functional analysis was performed using the bioinformatics tool Gene ontology enrichment to analyze the biological processes of selected genes and cellular components.

Results

The development of retinal organoids is slower than that in the native retina. In the early stage, cell proliferation predominates. Subsequently, neural differentiation is dominant. In the later stage, the dominant differentiated cells are photoreceptors. Additionally, the fatty acid metabolic process and mitochondria-related genes are upregulated over time, and the glycogen catabolic process and activin receptors are gradually downregulated in human retinal organoids. However, these trends are opposite in mouse retinal organoids. There are two peaks in mitochondria-related genes, one in the early development period and another during the photoreceptor development period. It takes about five times longer for human retinal development to achieve similar levels of mouse retinal development.

Conclusions

Our study reveals the similarities and differences in the developmental features of retinal organoids as well as the corresponding relationship between mouse and human retinal development.

Tunneling Nanotubes and the Eye: Intercellular Communication and Implications for Ocular Health and Disease

Cellular communication is an essential process for the development and maintenance of all tissues including the eye. Recently, a new method of cellular communication has been described, which relies on formation of tubules, called tunneling nanotubes (TNTs). These structures connect the cytoplasm of adjacent cells and allow the direct transport of cellular cargo between cells without the need for secretion into the extracellular milieu. TNTs may be an important mechanism for signaling between cells that reside long distances from each other or for cells in aqueous environments, where diffusion-based signaling is challenging. Given the wide range of cargoes transported, such as lysosomes, endosomes, mitochondria, viruses, and miRNAs, TNTs may play a role in normal homeostatic processes in the eye as well as function in ocular disease. This review will describe TNT cellular communication in ocular cell cultures and the mammalian eye in vivo, the role of TNTs in mitochondrial transport with an emphasis on mitochondrial eye diseases, and molecules involved in TNT biogenesis and their function in eyes, and finally, we will describe TNT formation in inflammation, cancer, and stem cells, focusing on pathological processes of particular interest to vision scientists.

Estrogenic control of mitochondrial function

Sex-based differences in human disease are caused in part by the levels of endogenous sex steroid hormones which regulate mitochondrial metabolism. This review updates a previous review on how estrogens regulate metabolism and mitochondrial function that was published in 2017. Estrogens are produced by ovaries and adrenals, and in lesser amounts by adipose, breast stromal, and brain tissues. At the cellular level, the mechanisms by which estrogens regulate diverse cellular functions including reproduction and behavior is by binding to estrogen receptors α, β (ERα and ERβ) and G-protein coupled ER (GPER1). ERα and ERβ are transcription factors that bind genomic and mitochondrial DNA to regulate gene transcription. A small proportion of ERα and ERβ interact with plasma membrane-associated signaling proteins to activate intracellular signaling cascades that ultimately alter transcriptional responses, including mitochondrial morphology and function. Although the mechanisms and targets by which estrogens act directly and indirectly to regulate mitochondrial function are not fully elucidated, it is clear that estradiol regulates mitochondrial metabolism and morphology via nuclear and mitochondrial-mediated events, including stimulation of nuclear respiratory factor-1 (NRF-1) transcription that will be reviewed here. NRF-1 is a transcription factor that interacts with coactivators including peroxisome proliferator-activated receptor gamma, coactivator 1 alpha (PGC-1α) to regulate nuclear-encoded mitochondrial genes. One NRF-1 target is TFAM that binds mtDNA to regulate its transcription. Nuclear-encoded miRNA and lncRNA regulate mtDNA-encoded and nuclear-encoded transcripts that regulate mitochondrial function, thus acting as anterograde signals. Other estrogen-regulated mitochondrial activities including bioenergetics, oxygen consumption rate (OCR), and extracellular acidification (ECAR), are reviewed.

Introduction to the multi-author review on macular degeneration

Prolonged life expectancies contribute to the increasing prevalence of age-related macular degeneration (AMD) that is already the leading cause of severe vision loss among the elderly in developed countries. In dry AMD, the disease culminates into vast retinal atrophy, whereas the wet form is characterized by retinal edema and sudden vision loss due to neovascularization originating from the choroid beneath the Bruch's membrane. There is no treatment for dry AMD and despite intravitreal injections of anti-vascular endothelial growth factor (VEGF) that suppress the neovessel formation, also wet AMD needs new therapies to prevent the disease progression and to serve patients lacking of positive response to current medicines. Knowledge on disease mechanisms is a prerequisite for the drug development, which is hindered by the multifactorial nature of AMD. Numerous distinguished publications have revealed AMD mechanisms at the cellular and molecular level and in this multi-author review, we take a bit broader look at the topic with some novel aspects.