Metabolic and redox signaling in the retina

Bilateral transcranial direct-current stimulation confers neuroprotection through suppression of PKM2 after mouse cerebral ischemia injury

BACKGROUND

In its tetrameric form, pyruvate kinase M2 isoform (PKM2) catalyzes the last step of glycolysis and plays a key role in the metabolic reprogramming via regulating the signaling of pentose phosphate pathway (PPP). But the role of PKM2 in cerebral ischemia-reperfusion (I/R) injury remains unknown.

METHODS

Mice model of middle cerebral artery occlusion (MCAO) and model of oxygen-glucose deprivation (OGD) injury in cultured neurons were established. PKM2 activator or inhibitor were used to test the effects of PKM2 in wild-type and PKM2 (-/-) mice after I/R injury. Biochemical and molecular approach were used to detect the level of PKM2 tetramers and PPP metabolites.

RESULTS

We showed for the first time that ischemia-induced increase of PKM2 activity promoted neuronal death via the suppression of PPP-dependent antioxidant capacity. To identify therapeutic approach that suppresses ischemia-induced increase of PKM2 activity, we tested the effect of bilateral transcranial direct-current stimulation (BtDCS), a newly established BtDCS approach by us, on PKM2 activity after mouse I/R. Our data demonstrated that BtDCS inhibited PKM2 activity in the ischemic neurons. BtDCS also reduced the cerebral infarct volume and the neurological deficits in stroke mice. We found that BtDCS-induced neuroprotection was mediated through the suppression of PKM2 activity after I/R.

CONCLUSIONS

Together, this study provided novel evidence that supported PKM2 as a crucial regulator of neuronal metabolism after cerebral I/R injury, and revealed the molecular mechanism by which BtDCS protects against mouse cerebral I/R injury through regulating PKM2-mediated metabolic reprogramming.

Potential guidelines for cataract surgery and rehabilitation in visually impaired patients: Literature analysis

Cataracts can reduce the quality of vision in visually impaired patients who already have a visual impairment. The most common causes of low vision include age-related macular degeneration (AMD), high myopia (HM), diabetic retinopathy (DR), glaucoma (GL), and inherited degenerative ocular diseases. The surgery aims to improve their independence, quality of life, and ability to engage in daily, social, and work activities. Phacoemulsification and intraocular lens (IOL) implantation, combined with visual rehabilitation, can improve visual acuity of visually impaired patients. Therefore, comprehensive guidelines for cataract surgery in patients with low vision would be beneficial to ensure optimal surgical outcomes by improving surgical planning, execution, and postoperative care, along with a well-coordinated rehabilitation process. In cases of reduced metabolism, such as low vision, oxidative stress can be aggravated by light exposure and surgical interventions. Thus, maintaining redox balance is crucial for stabilizing retinal conditions. Patients with visual impairments rely on retinal regions with the greatest residual function, and cataract surgery aims to enhance focus on these areas, improving reading quality and reducing scotoma perception. Thorough informed consent is crucial, ensuring that patients are fully aware of the potential risks, benefits, and limitations of surgery. Close postoperative follow-up in the first 6 months is crucial to detect and manage any complications promptly, such as reactivation of maculopathy. The aim of this work is to establish potential guidelines for optimal rehabilitation outcomes through careful literature analysis.

Comparative proteomic analysis of human vitreous in rhegmatogenous retinal detachment and diabetic retinopathy reveals a common pathway and potential therapeutic target

BACKGROUND

The vitreous humor serves as a window into the physiological and pathological processes of the eye, particularly the retina. Diabetic retinopathy (DR), a leading cause of blindness, involves hyperglycemia-induced damage to retinal cells, leading to ischemia and elevated nitric oxide levels, culminating in vascular proliferation. Rhegmatogenous retinal detachment (RD) results from a break in the neuroretina, triggering ischemia, photoreceptor death, and cellular proliferation. Proliferative vitreoretinopathy (PVR) further complicates these conditions through fibrous proliferation. Despite their prevalence and potential for blindness, our understanding of the molecular mechanisms underlying these vitreoretinal diseases is incomplete.

METHODS AND RESULTS

To elucidate disease mechanisms and identify potential therapeutic targets, we conducted a comparative proteomic analysis of vitreous samples from DR, RD, and macular pucker (P) patients, which were chosen as controls. LC-MS analysis identified 988 quantifiable proteins, with distinct clustering observed among disease groups. Differential expression analysis revealed 202 proteins in RD vs. P and 167 in DR vs. P, highlighting distinct proteomic signatures. Enrichment analysis identified glucose metabolism as an altered process in both diseases, suggesting common pathways despite differing etiologies. Notably, aldo-keto reductase family 1 member B1 (AKR1B1) has emerged as a potential key player in both DR and RD, indicating its role in glucose metabolism and inflammation. In silico drug screening identified diclofenac, an approved ophthalmic non-steroidal anti-inflammatory drug (NSAID), as a potential therapeutic agent targeting AKR1B1.

CONCLUSION

Our study revealed distinct proteomic signatures and common pathways in vitreoretinal diseases, highlighting AKR1B1 as a potential therapeutic target. Using diclofenac during diagnosis and postoperative care for diabetic retinopathy or rhegmatogenous retinal detachment may reduce complications, lower costs, and improve quality of life. Future research will focus on confirming AKR1B1's role in vitreoretinal diseases and understanding diclofenac's mechanism of action.

Restoration of Rod-Derived Metabolic and Redox Signaling to Prevent Blindness

Vision is initiated by capturing photons in highly specialized sensory cilia known as the photoreceptor outer segment. Because of its lipid and protein composition, the outer segments are prone to photo-oxidation, requiring photoreceptors to have robust antioxidant defenses and high metabolic synthesis rates to regenerate the outer segments every 10 days. Both processes required high levels of glucose uptake and utilization. Retinitis pigmentosa is a prevalent form of inherited retinal degeneration characterized by initial loss of low-light vision caused by the death of rod photoreceptors. In this disease, rods die as a direct effect of an inherited mutation. Following the loss of rods, cones eventually degenerate, resulting in complete blindness. The progression of vision loss in retinitis pigmentosa suggested that rod photoreceptors were necessary to maintain healthy cones. We identified a protein secreted by rods that functions to promote cone survival, and we named it rod-derived cone viability factor (RdCVF). RdCVF is encoded by an alternative splice product of the nucleoredoxin-like 1 (NXNL1) gene, and RdCVF was found to accelerate the uptake of glucose by cones. Without RdCVF, cones eventually die because of compromised glucose uptake and utilization. The NXNL1 gene also encodes for the thioredoxin RdCVFL, which reduces cysteines in photoreceptor proteins that are oxidized, providing a defense against radical oxygen species. We will review here the main steps of discovering this novel intercellular signaling currently under translation as a broad-spectrum treatment for retinitis pigmentosa.

SLC16A8 is a causal contributor to age-related macular degeneration risk

Age-related macular degeneration (AMD), a complex neurodegenerative disease, is a leading cause of visual impairment worldwide with a strong genetic component. Genetic studies have identified several loci, but few causal genes with functional characterization. Here we highlight multiple lines of evidence which show a causal role in AMD for SLC16A8, which encodes MCT3, a retinal pigment epithelium (RPE) specific lactate transporter. First, in an unbiased, genome-wide analysis of rare coding variants we show multiple SLC16A8 rare variants are associated with AMD risk, corroborating previous borderline significant reports from AMD rare variant studies. Second, we report a novel SLC16A8 mutation in a three-generation family with early onset macular degeneration. Finally, mis-expression in multiple model organisms shows functional and anatomic retinal consequences. This study highlights the important role for SLC16A8 and lactate regulation towards outer retina/RPE health and highlights a potential new therapeutic opportunity for the treatment of AMD.

Bi-allelic variants in COQ8B, a gene involved in the biosynthesis of coenzyme Q10, lead to non-syndromic retinitis pigmentosa

Retinitis pigmentosa (RP) is a Mendelian disease characterized by gradual loss of vision, due to the progressive degeneration of retinal cells. Genetically, it is highly heterogeneous, with pathogenic variants identified in more than 100 genes so far. Following a large-scale sequencing screening, we identified five individuals (four families) with recessive and non-syndromic RP, carrying as well bi-allelic DNA changes in COQ8B, a gene involved in the biosynthesis of coenzyme Q10. Specifically, we detected compound heterozygous assortments of five disease-causing variants (c.187C>T [p.Arg63Trp], c.566G>A [p.Trp189Ter], c.1156G>A [p.Asp386Asn], c.1324G>A [p.Val442Met], and c.1560G>A [p.Trp520Ter]), all segregating with disease according to a recessive pattern of inheritance. Cell-based analysis of recombinant proteins deriving from these genotypes, performed by target engagement assays, showed in all cases a significant decrease in ligand-protein interaction compared to the wild type. Our results indicate that variants in COQ8B lead to recessive non-syndromic RP, possibly by impairing the biosynthesis of coenzyme Q10, a key component of oxidative phosphorylation in the mitochondria.

Oxidative damage and cardiotoxicity induced by 2-aminobenzothiazole in zebrafish (Danio rerio)

There is limited information available on cardiovascular toxicity of 2-Aminobenzothiazole (NTH), a derivative of benzothiazole (BTH) commonly used in tire production, in aquatic organisms. In the present study, the zebrafish embryos were exposed to varying concentrations of NTH (0, 0.05, 0.5, and 5 mg/L) until adulthood and the potential cardiovascular toxicity was assessed. NTH exposure resulted in striking aberrations in cardiac development, including heart looping failure and interference with atrioventricular canal differentiation. RNA-sequencing analysis indicated that NTH causes oxidative damage to the heart via ferroptosis, leading to oxygen supply disruption, cardiac malformation, and ultimately, zebrafish death. Quantitative real-time polymerase chain reaction (qPCR) analysis demonstrated the dysregulation of genes associated with early heart development, contraction, and oxidative stress. Additionally, reactive oxygen species accumulation and glutathione/malondialdehyde levels changes suggested a potential link between cardiac developmental toxicity and oxidative stress. In adult zebrafish, NTH exposure led to ventricular enlargement, decreased heart rate, reduced blood flow, and prolonged RR, QRS, and QTc intervals. To the best of our knowledge, this study is the first to provide evidence of cardiac toxicity and the adverse effects of ontogenetic NTH exposure in zebrafish, revealing the underlying toxic mechanisms connected with oxidative stress damage. These findings may provide crucial insights into the environmental risks associated with NTH and other BTHs.

The Effects of STRA6 Regulation of the Circadian Rhythm on Choroidal Neovascularization

Purpose

This study aims to investigate the relationship among STRA6, circadian rhythm, and choroidal neovascularization (CNV) formation, as well as the regulatory mechanism of STRA6 in CNV under circadian rhythm disturbances.

Methods

C57BL/6J male mice (aged 6 weeks) were randomly divided into control and jet lag groups (using a time shift method every 4 days to disrupt the molecular clock's capacity to synchronize with a stable rhythm). A laser-induced CNV model was established in both the control and the jet lag group after 2 weeks of jet lag. The size of CNV lesions and vascular leakage were detected by morphological and imaging examination on the seventh day post laser. STRA6 was screened by full transcriptome sequencing. Bioinformatics analysis was conducted to assess the variation and association of STRA6 in the GSE29801 dataset. The effects of STRA6 were evaluated both in vivo and in vitro. The pathway mechanism was further elucidated and confirmed through immunofluorescence of paraffin sections and Western blotting.

Results

The disturbance of circadian rhythm promotes the formation of CNV. Patients with age-related macular degeneration (AMD) exhibited higher levels of STRA6 expression compared to the control group, and STRA6 was enriched in pathways related to angiogenesis. In addition, CLOCK and BMAL1, which are initiators that drive the circadian cycle, had regulatory effects on STRA6. Knocking down STRA6 reversed the promotion of CNV formation caused by circadian rhythm disturbance in vivo, and it also affected the proliferation, migration, and VEGF secretion of RPE cells without circadian rhythm in vitro, as well as impacting endothelial cells. Through activation of the JAK2/STAT3/VEGFA signaling pathway in unsynchronized RPE cells, STRA6 promotes CNV formation.

Conclusions

This study suggests that STRA6 reduces CNV production by inhibiting JAK2/STAT3 phosphorylation after circadian rhythm disturbance. The results suggest that STRA6 may be a new direction for the treatment of AMD.

The negative association between the docosapentaenoic acid intake and the incidence of AMD based on NHANES 2005-2008

Introduction

Age-related macular degeneration (AMD) is an ophthalmic disease that causes visual impairment and is one of the leading causes of blindness in the elderly. Fatty acids are essential nutrients required by the body and play a cornerstone role in the life activities of the body. Many studies have reported that fatty acids are involved in the development of AMD. To confirm this association, we conducted the present study.

Methods

We analyzed the association between all fatty acid intake and AMD using National Health and Nutrition Examination Survey (NHANES) data from 2005-2008. Quantile regression was performed to assess the effect of fatty acids on AMD at different intake levels.

Results

After adjusting for covariates, only saturated fatty acids showed no significant difference between AMD patients and non-AMD patients (23.64 g vs. 26.03 g, p = 0.052). Total fat (70.88 g vs. 78.86 g, p = 0.024), monounsaturated fatty acids (25.87 g vs. 28.95 g, p = 0.019), polyunsaturated fatty acids (15.10 g vs. 17.07 g, p = 0.017) showed significant differences between the two groups. When AMD was considered as an outcome, the association between AMD and docosaentaenoic acid (DPA) was negative in the multivariate logic model (model 1: OR = <0.001, 95% CI = <0.001 ~ 0.734; model 2: OR = <0.001, 95% CI = <0.001 ~ 0.002; model 3: OR = <0.001, 95% CI = <0.001 ~ 0.002). In the quantile regression, DPA was shown to be negatively associated with the presence of AMD only in the fourth quartile in model 2 and model 3 (model 2: OR = <0.001, 95% CI = <0.001 ~ 0.927; model 3: OR = <0.001, 95% CI = <0.001 ~ 0.775).

Discussion

Therefore, based on above results, we concluded that DPA intake could prevent the development of AMD.

Granulomatosis with polyangiitis, complicated by ocular adnexa lesion and vascular changes in retina and choroid (literature review with a clinical case)

Granulomatosis with polyangiitis (GPA) is manifested as ocular pathology in almost a third of patients, which can either be detected at the onset of the disease or occur in the late stages. The pathological process involves the orbit, sclera, episclera, cornea, conjunctiva, eyelids, nasolacrimal system, optic nerve, retina and choroid. Lesion of eye and its surrounding structures determines the severity of the pathological process, the patient’s quality of life and prognosis. The article presents a clinical case of a 38-year-old man with an unfavorable course of GPA, lesion to upper and lower respiratory tract, kidneys, and musculoskeletal system. The authors consider ocular manifestations in the context of a systemic disease. An ophthalmological examination of the patient revealed changes in sclera and choroid, which had not previously been described in detail in the literature. The patient underwent cataract phacoemulsification in the right eye with implantation of a posterior chamber intraocular lens. The dynamics of clinical manifestations of eye lesion in the near future is positive, but in the long term it remains doubtful due to pronounced changes in the orbit and adnexa of the eye against the background of ongoing small vessels vasculitis. Early consultation with an ophthalmologist and optical coherence tomography in patients with GPA are necessary at any stage of the disease. The clinical case is presented with consideration to the CARE 2021 recommendations.

Therapeutic Application of Dendrobium fimbriatum Hook for Retinopathy Caused by Ultraviolet Radiation and Chemotherapy Using ARPE-19 Cells and Mouse Retina

Retinopathy caused by ultraviolet radiation and cancer chemotherapy has increased dramatically in humans due to rapid environmental and social changes. Therefore, it is very important to develop therapeutic strategies to effectively alleviate retinopathy. In China, people often choose dendrobium to improve their eyesight. In this study, we explored how Dendrobium fimbriatum extract (DFE) protects ARPE-19 cells and mouse retinal tissue from damage of ultraviolet (UV) radiation and chemotherapy. We evaluated the antioxidant capacity of DFE using the 1,1-diphenyl-2-trinitophenylhydrazine (DPPH) assay. The protective effects of DEF from UV- and oxaliplatin (OXA)-induced damage were examined in ARPE-19 cells using 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and immunofluorescence (IF) stains, and in mouse retinal tissue using immunohistochemistry (IHC) stains. Our results show that DFE has excellent antioxidant capacity. The ARPE-19 cell viability was decreased and the F-actin cytoskeleton structure was damaged by UV radiation and OXA chemotherapy, but both were alleviated after the DFE treatment. Furthermore, DFE treatment can alleviate OXA chemotherapy-induced reduced expressions of rhodopsin and SOD2 and increased expressions of TNF-α and caspase 3 in mouse retinal tissue. Thus, we suggest that DFE can act as suitable treatment for retinopathy through reducing oxidative stress, inflammation, and apoptosis.

Optimal Control with RdCVFL for Degenerating Photoreceptors

Both the rod and cone photoreceptors, along with the retinal pigment epithelium have been experimentally and mathematically shown to work interdependently to maintain vision. Further, the theoredoxin-like rod-derived cone viability factor (RdCVF) and its long form (RdCVFL) have proven to increase photoreceptor survival in experimental results. Aerobic glycolysis is the primary source of energy production for photoreceptors and RdCVF accelerates the intake of glucose into the cones. RdCVFL helps mitigate the negative effects of reactive oxidative species and has shown promise in slowing the death of cones in mouse studies. However, this potential treatment and its effects have never been studied in mathematical models. In this work, we examine an optimal control with the treatment of RdCVFL. We mathematically illustrate the potential this treatment might have for treating degenerative retinal diseases such as retinitis pigmentosa, as well as compare this to the results of an updated control model with RdCVF.

Bi-directional electrical recording and stimulation of the intact retina with a screen-printed soft probe: a feasibility study

Introduction

Electrophysiological investigations of intact neural circuits are challenged by the gentle and complex nature of neural tissues. Bi-directional electrophysiological interfacing with the retina, in its intact form, is particularly demanding and currently there is no feasible approach to achieve such investigations. Here we present a feasibility study of a novel soft multi-electrode array suitable for bi-directional electrophysiological study of the intact retina.

Methods

Screen-printed soft electrode arrays were developed and tested. The soft probes were designed to accommodate the curvature of the retina in the eye and offer an opportunity to study the retina in its intact form.

Results

For the first time, we show both electrical recording and stimulation capabilities from the intact retina. In particular, we demonstrate the ability to characterize retina responses to electrical stimulation and reveal stable, direct, and indirect responses compared with ex-vivo conditions.

Discussion

These results demonstrate the unique performances of the new probe while also suggesting that intact retinas retain better stability and robustness than ex-vivo retinas making them more suitable for characterizing retina responses to electrical stimulation.

Human equivalent doses of L-DOPA rescues retinal morphology and visual function in a murine model of albinism

L-DOPA is deficient in the developing albino eye, resulting in abnormalities of retinal development and visual impairment. Ongoing retinal development after birth has also been demonstrated in the developing albino eye offering a potential therapeutic window in humans. To study whether human equivalent doses of L-DOPA/Carbidopa administered during the crucial postnatal period of neuroplasticity can rescue visual function, OCA C57BL/6 J-c2J OCA1 mice were treated with a 28-day course of oral L-DOPA/Carbidopa at 3 different doses from 15 to 43 days postnatal age (PNA) and for 3 different lengths of treatment, to identify optimum dosage and treatment length. Visual electrophysiology, acuity, and retinal morphology were measured at 4, 5, 6, 12 and 16 weeks PNA and compared to untreated C57BL/6 J (WT) and OCA1 mice. Quantification of PEDF, βIII-tubulin and syntaxin-3 expression was also performed. Our data showed impaired retinal morphology, decreased retinal function and lower visual acuity in untreated OCA1 mice compared to WT mice. These changes were diminished or eliminated when treated with higher doses of L-DOPA/Carbidopa. Our results demonstrate that oral L-DOPA/Carbidopa supplementation at human equivalent doses during the postnatal critical period of retinal neuroplasticity can rescue visual retinal morphology and retinal function, via PEDF upregulation and modulation of retinal synaptogenesis, providing a further step towards developing an effective treatment for albinism patients.

Mechanism of action of platinum nanoparticles implying from antioxidant to metabolic programming in light-induced retinal degeneration model

Photoreceptors (PRs) degeneration is central to visual impairment and loss in most blind retinal diseases, including age-related macular disease (AMD) and diabetic retinopathy (DR). PRs are susceptible to oxidative stress owing to their unique metabolic features. Accumulating evidence has demonstrated that the targeting oxidative stress is a promising treatment strategy for PR degeneration. Herein, we introduced potent antioxidative platinum nanoparticles (Pt NPs) to treat PRs degeneration in this study. The Pt NPs exhibited multi-enzymatic antioxidant activity and protected PRs from H2O2-induced oxidative damage in vitro assays. Based on the same mechanism, the intravitreal injection of Pt NPs significantly reduced cell apoptosis, maintained retinal structure and preserved retinal function in a mouse model of light-induced retinal degeneration (LIRD). Most importantly, the results of RNA sequencing showed that the transcription of antioxidative genes was upregulated, and metabolic reprogramming occurred in the LIRD-retina after treatment with Pt NPs, both of which benefited retinal survival from oxidative damage. The results indicated that Pt NPs were indeed potent therapeutic candidates for PRs degeneration in blind retinal diseases.

Mathematical model for glutathione dynamics in the retina

The retina is highly susceptible to the generation of toxic reactive oxygen species (ROS) that disrupt the normal operations of retinal cells. The glutathione (GSH) antioxidant system plays an important role in mitigating ROS. To perform its protective functions, GSH depends on nicotinamide adenine dinucleotide phosphate (NADPH) produced through the pentose phosphate pathway. This work develops the first mathematical model for the GSH antioxidant system in the outer retina, capturing the most essential components for formation of ROS, GSH production, its oxidation in detoxifying ROS, and subsequent reduction by NADPH. We calibrate and validate the model using experimental measurements, at different postnatal days up to PN28, from control mice and from the rd1 mouse model for the disease retinitis pigmentosa (RP). Global sensitivity analysis is then applied to examine the model behavior and identify the pathways with the greatest impact in control compared to RP conditions. The findings underscore the importance of GSH and NADPH production in dealing with oxidative stress during retinal development, especially after peak rod degeneration occurs in RP, leading to increased oxygen tension. This suggests that stimulation of GSH and NADPH synthesis could be a potential intervention strategy in degenerative mouse retinas with RP.

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

The retinal pigment epithelium (RPE) performs a range of necessary functions within the neural layers of the retina and helps ensure vision. The regulation of pro-oxidative and antioxidant processes is the basis for maintaining RPE homeostasis and preventing retinal degenerative processes. Long-term stable changes in the redox balance under the influence of endogenous or exogenous factors can lead to oxidative stress (OS) and the development of a number of retinal pathologies associated with RPE dysfunction, and can eventually lead to vision loss. Reparative autophagy, ubiquitin-proteasome utilization, the repair of damaged proteins, and the maintenance of their conformational structure are important interrelated mechanisms of the endogenous defense system that protects against oxidative damage. Antioxidant protection of RPE cells is realized as a result of the activity of specific transcription factors, a large group of enzymes, chaperone proteins, etc., which form many signaling pathways in the RPE and the retina. Here, we discuss the role of the key components of the antioxidant defense system (ADS) in the cellular response of the RPE against OS. Understanding the role and interactions of OS mediators and the components of the ADS contributes to the formation of ideas about the subtle mechanisms in the regulation of RPE cellular functions and prospects for experimental approaches to restore RPE functions.

Ambra1 haploinsufficiency in CD1 mice results in metabolic alterations and exacerbates age-associated retinal degeneration

Macroautophagy/autophagy is a key process in the maintenance of cellular homeostasis. The age-dependent decline in retinal autophagy has been associated with photoreceptor degeneration. Retinal dysfunction can also result from damage to the retinal pigment epithelium (RPE), as the RPE-retina constitutes an important metabolic ecosystem that must be finely tuned to preserve visual function. While studies of mice lacking essential autophagy genes have revealed a predisposition to retinal degeneration, the consequences of a moderate reduction in autophagy, similar to that which occurs during physiological aging, remain unclear. Here, we described a retinal phenotype consistent with accelerated aging in mice carrying a haploinsufficiency for Ambra1, a pro-autophagic gene. These mice showed protein aggregation in the retina and RPE, metabolic underperformance, and premature vision loss. Moreover, Ambra1^+/gt mice were more prone to retinal degeneration after RPE stress. These findings indicate that autophagy provides crucial support to RPE-retinal metabolism and protects the retina against stress and physiological aging.Abbreviations : 4-HNE: 4-hydroxynonenal; AMBRA1: autophagy and beclin 1 regulator 1, AMD: age-related macular degeneration;; GCL: ganglion cell layer; GFAP: glial fibrillary acidic protein; GLUL: glutamine synthetase/glutamate-ammonia ligase; HCL: hierarchical clustering; INL: inner nuclear layer; IPL: inner plexiform layer; LC/GC-MS: liquid chromatography/gas chromatography-mass spectrometry; MA: middle-aged; MTDR: MitoTracker Deep Red; MFI: mean fluorescence intensity; NL: NH₄Cl and leupeptin; Nqo: NAD(P)H quinone dehydrogenase; ONL: outer nuclear layer; OPL: outer plexiform layer; OP: oscillatory potentials; OXPHOS: oxidative phosphorylation; PCR: polymerase chain reaction; PRKC/PKCα: protein kinase C; POS: photoreceptor outer segment; RGC: retinal ganglion cells; RPE: retinal pigment epithelium; SI: sodium iodate; TCA: tricarboxylic acid.

Review: Emerging Eye-Based Diagnostic Technologies for Traumatic Brain Injury

The study of ocular manifestations of neurodegenerative disorders, Oculomics, is a growing field of investigation for early diagnostics, enabling structural and chemical biomarkers to be monitored overtime to predict prognosis. Traumatic brain injury (TBI) triggers a cascade of events harmful to the brain, which can lead to neurodegeneration. TBI, termed the "silent epidemic" is becoming a leading cause of death and disability worldwide. There is currently no effective diagnostic tool for TBI, and yet, early-intervention is known to considerably shorten hospital stays, improve outcomes, fasten neurological recovery and lower mortality rates, highlighting the unmet need for techniques capable of rapid and accurate point-of-care diagnostics, implemented in the earliest stages. This review focuses on the latest advances in the main neuropathophysiological responses and the achievements and shortfalls of TBI diagnostic methods. Validated and emerging TBI-indicative biomarkers are outlined and linked to ocular neuro-disorders. Methods detecting structural and chemical ocular responses to TBI are categorised along with prospective chemical and physical sensing techniques. Particular attention is drawn to the potential of Raman spectroscopy as a non-invasive sensing of neurological molecular signatures in the ocular projections of the brain, laying the platform for the first tangible path towards alternative point-of-care diagnostic technologies for TBI.

100 years of the Warburg effect: a historical perspective

Otto Warburg published the first paper describing what became known as the Warburg effect in 1923. All that was known about glucose metabolism at that time was that it occurred in two stages: (i) fermentation (glycolysis) in which glucose was converted to lactate, which did not require oxygen, and (ii) oxidative metabolism, in which the carbon atoms derived from glycolysis were fully oxidized to carbon dioxide, which did require oxygen. Warburg discovered that most tumour tissues produced a large amount of lactate that was reduced but not eliminated in the presence of oxygen, while most normal tissues produced a much smaller amount of lactate that was eliminated by the provision of oxygen. These findings were clearly well ahead of their time because it was another 80 years before they were to have any major impact, and even today the mechanisms underlying the Warburg effect are not completely understood.

Modulating antioxidant systems as a therapeutic approach to retinal degeneration

The human retina is facing a big challenge of reactive oxygen species (ROS) from endogenous and exogenous sources. Excessive ROS can cause damage to DNA, lipids, and proteins, triggering abnormal redox signaling, and ultimately lead to cell death. Thus, oxidative stress has been observed in inherited retinal diseases as a common hallmark. To counteract the detrimental effect of ROS, cells are equipped with various antioxidant defenses. In this review, we will focus on the antioxidant systems in the retina and how they can protect retina from oxidative stress. Both small antioxidants and antioxidant enzymes play a role in ROS removal. Particularly, the thioredoxin and glutaredoxin systems, as the major antioxidant systems in mammalian cells, exert functions in redox signaling regulation via modifying cysteines in proteins. In addition, the thioredoxin-like rod-derived cone viability factor (RdCVFL) and thioredoxin interacting protein (TXNIP) can modulate metabolism in photoreceptors and promote their survival. In conclusion, elevating the antioxidant capacity in retina is a promising therapy to curb the progress of inherited retinal degeneration.

The Emergence of Rod-Cone Cellular Interaction

We studied the origin of rod-derived cone viability factor (RdCVF) during evolution. In mammals, the nucleoredoxin-like 1 gene (NXNL1) produces a truncated thioredoxin-like protein, RdCVF, by intron retention in rod photoreceptors of the retina. This protein prevents the secondary cone degeneration in animal models of rod-cone degeneration. Extracellular RdCVF binds to a complex at the surface of the cones, composed of the basigin-1, a photoreceptor specific alternative splicing product of the basigin gene, and GLUT1, the glucose transporter. RdCVF accelerates glucose uptake allosterically. Glucose is either metabolized by aerobic glycolysis to sustain cone outer segment renewal or by the pentose phosphate pathway to support redox power to the thioredoxin RdCVFL. RdCVF signaling predates the appearance of the eye and evolved through two alternative splicing events. RdCVF signaling is observed first in hydra where it regulates an unknown signaling. A scallop RdCVF protein is produced by ciliated photoreceptors of the retina and binds its receptor, BSG1, the first occurrence of RdCVF/BSG1 signaling. In the lamprey, RdCVF metabolic signaling between rod and cones is fully operational. In the mouse, the production of BSG1 is regulated through alternative splicing. This signaling was extended to other regions of the brain, via its paralogue NXNL2.

The Role of Hsp90 in Retinal Proteostasis and Disease

Photoreceptors are sensitive neuronal cells with great metabolic demands, as they are responsible for carrying out visual phototransduction, a complex and multistep process that requires the exquisite coordination of a large number of signalling protein components. Therefore, the viability of photoreceptors relies on mechanisms that ensure a well-balanced and functional proteome that maintains the protein homeostasis, or proteostasis, of the cell. This review explores how the different isoforms of Hsp90, including the cytosolic Hsp90α/β, the mitochondrial TRAP1, and the ER-specific GRP94, are involved in the different proteostatic mechanisms of photoreceptors, and elaborates on Hsp90 function when retinal homeostasis is disturbed. In addition, several studies have shown that chemical manipulation of Hsp90 has significant consequences, both in healthy and degenerating retinae, and this can be partially attributed to the fact that Hsp90 interacts with important photoreceptor-associated client proteins. Here, the interaction of Hsp90 with the retina-specific client proteins PDE6 and GRK1 will be further discussed, providing additional insights for the role of Hsp90 in retinal disease.

A mathematical model of GLUT1 modulation in rods and RPE and its differential impact in cell metabolism

We present a mathematical model of key glucose metabolic pathways in two cells of the human retina: the rods and the retinal pigmented epithelium (RPE). Computational simulations of glucose transporter 1 (GLUT1) inhibition in the model accurately reproduce experimental data from conditional knockout mice and reveal that modification of GLUT1 expression levels of both cells differentially impacts their metabolism. We hypothesize that, under glucose scarcity, the RPE's energy producing pathways are altered in order to preserve its functionality, impacting the photoreceptors' outer segment renewal. On the other hand, when glucose is limited in the rods, aerobic glycolysis is preserved, which maintains the lactate contribution to the RPE.

Curcumin and Wnt/β‑catenin signaling in exudative age‑related macular degeneration (Review)

Curcumin is a natural product widely used due to its pharmacological effects. Nevertheless, only a limited number of studies concerning the effects of curcumin on exudative age‑related macular degeneration (AMD) is currently available. Since ophthalmic diseases, including exudative AMD, have a marked impact on public health, the prevention and therapy of ophthalmic disorders remain of increasing concern. Exudative AMD is characterized by choroidal neovascularization (CNV) invading the subretinal space, ultimately enhancing exudation and hemorrhaging. The exudative AMD subtype corresponds to 10 to 15% of cases of macular degeneration; however, the occurrence of this subtype has been reported as the major cause of vision loss and blindness, with the occurrence of CNV being responsible for 80% of the cases with vision loss. In CNV increased expression of VEGF has been observed, stimulated by the overactivation of Wnt/β‑catenin signaling pathway. The stimulation of the Wnt/β‑catenin signaling pathway is responsible for the activation of several cellular mechanisms, simultaneously enhancing inflammation, oxidative stress and angiogenesis in numerous diseases, including ophthalmic disorders. Some studies have previously demonstrated the possible advantage of the use of curcumin for the inhibition of Wnt/β‑catenin signaling. In the present review article, the different mechanisms of curcumin are described concerning its effects on oxidative stress, inflammation and angiogenesis in exudative AMD, by interacting with Wnt/β‑catenin signaling.

mTORC1 regulates high levels of protein synthesis in retinal ganglion cells of adult mice

Mechanistic target of rapamycin (mTOR) and mTOR complex 1 (mTORC1), linchpins of the nutrient sensing and protein synthesis pathways, are present at relatively high levels in the ganglion cell layer (GCL) and retinal ganglion cells (RGCs) of rodent and human retinas. However, the role of mTORCs in the control of protein synthesis in RGC is unknown. Here, we applied the SUrface SEnsing of Translation (SUnSET) method of nascent protein labeling to localize and quantify protein synthesis in the retinas of adult mice. We also used intravitreal injection of an adeno-associated virus 2 vector encoding Cre recombinase in the eyes of mtor- or rptor-floxed mice to conditionally knockout either both mTORCs or only mTORC1, respectively, in cells within the GCL. A novel vector encoding an inactive Cre mutant (CreΔC) served as control. We found that retinal protein synthesis was highest in the GCL, particularly in RGC. Negation of both complexes or only mTORC1 significantly reduced protein synthesis in RGC. In addition, loss of mTORC1 function caused a significant reduction in the pan-RGC marker, RNA-binding protein with multiple splicing, with little decrease of the total number of cells in the RGC layer, even at 25 weeks after adeno-associated virus-Cre injection. These findings reveal that mTORC1 signaling is necessary for maintaining the high rate of protein synthesis in RGCs of adult rodents, but it may not be essential to maintain RGC viability. These findings may also be relevant to understanding the pathophysiology of RGC disorders, including glaucoma, diabetic retinopathy, and optic neuropathies.

Metabolism Dysregulation in Retinal Diseases and Related Therapies

The human retina, which is part of the central nervous system, has exceptionally high energy demands that requires an efficient metabolism of glucose, lipids, and amino acids. Dysregulation of retinal metabolism disrupts local energy supply and redox balance, contributing to the pathogenesis of diverse retinal diseases, including age-related macular degeneration, diabetic retinopathy, inherited retinal degenerations, and Macular Telangiectasia. A better understanding of the contribution of dysregulated metabolism to retinal diseases may provide better therapeutic targets than we currently have.

Inverse Problem Reveals Conditions for Characteristic Retinal Degeneration Patterns in Retinitis Pigmentosa Under the Trophic Factor Hypothesis

Retinitis pigmentosa (RP) is the most common inherited retinal dystrophy with a prevalence of about 1 in 4,000, affecting approximately 1.5 million people worldwide. Patients with RP experience progressive visual field loss as the retina degenerates, destroying light-sensitive photoreceptor cells (rods and cones), with rods affected earlier and more severely than cones. Spatio-temporal patterns of retinal degeneration in human RP have been well characterised; however, the mechanism(s) giving rise to these patterns have not been conclusively determined. One such mechanism, which has received a wealth of experimental support, is described by the trophic factor hypothesis. This hypothesis suggests that rods produce a trophic factor necessary for cone survival; the loss of rods depletes this factor, leading to cone degeneration. In this article, we formulate a partial differential equation mathematical model of RP in one spatial dimension, spanning the region between the retinal centre (fovea) and the retinal edge (ora serrata). Using this model we derive and solve an inverse problem, revealing for the first time experimentally testable conditions under which the trophic factor mechanism will qualitatively recapitulate the spatio-temporal patterns of retinal regeneration observed in human RP.

Sodium-Iodate Injection Can Replicate Retinal Degenerative Disease Stages in Pigmented Mice and Rats: Non-Invasive Follow-Up Using OCT and ERG

Purpose: The lack of suitable animal models for (dry) age-related macular degeneration (AMD) has hampered therapeutic research into the disease, so far. In this study, pigmented rats and mice were systematically injected with various doses of sodium iodate (SI). After injection, the retinal structure and visual function were non-invasively characterized over time to obtain in-depth data on the suitability of these models for studying experimental therapies for retinal degenerative diseases, such as dry AMD. Methods: SI was injected into the tail vein (i.v.) using a series of doses (0–70 mg/kg) in adolescent C57BL/6J mice and Brown Norway rats. The retinal structure and function were assessed non-invasively at baseline (day 1) and at several time points (1–3, 5, and 10-weeks) post-injection by scanning laser ophthalmoscopy (SLO), optical coherence tomography (OCT), and electroretinography (ERG). Results: After the SI injection, retinal degeneration in mice and rats yielded similar results. The lowest dose (10 mg/kg) resulted in non-detectable structural or functional effects. An injection with 20 mg/kg SI did not result in an evident retinal degeneration as judged from the OCT data. In contrast, the ERG responses were temporarily decreased but returned to baseline within two-weeks. Higher doses (30, 40, 50, and 70 mg/kg) resulted in moderate to severe structural RPE and retinal injury and decreased the ERG amplitudes, indicating visual impairment in both mice and rat strains. Conclusions: After the SI injections, we observed dose-dependent structural and functional pathological effects on the retinal pigment epithelium (RPE) and retina in the pigmented mouse and rat strains that were used in this study. Similar effects were observed in both species. In particular, a dose of 30 mg/kg seems to be suitable for future studies on developing experimental therapies. These relatively easily induced non-inherited models may serve as useful tools for evaluating novel therapies for RPE-related retinal degenerations, such as AMD.

Kinase activity profiling identifies putative downstream targets of cGMP/PKG signaling in inherited retinal neurodegeneration

Inherited retinal diseases (IRDs) are a group of neurodegenerative disorders that lead to photoreceptor cell death and eventually blindness. IRDs are characterised by a high genetic heterogeneity, making it imperative to design mutation-independent therapies. Mutations in a number of IRD disease genes have been associated with a rise of cyclic 3’,5’-guanosine monophosphate (cGMP) levels in photoreceptors. Accordingly, the cGMP-dependent protein kinase (PKG) has emerged as a new potential target for the mutation-independent treatment of IRDs. However, the substrates of PKG and the downstream degenerative pathways triggered by its activity have yet to be determined. Here, we performed kinome activity profiling of different murine organotypic retinal explant cultures (diseased rd1 and wild-type controls) using multiplex peptide microarrays to identify proteins whose phosphorylation was significantly altered by PKG activity. In addition, we tested the downstream effect of a known PKG inhibitor CN03 in these organotypic retina cultures. Among the PKG substrates were potassium channels belonging to the K_v1 family (KCNA3, KCNA6), cyclic AMP-responsive element-binding protein 1 (CREB1), DNA topoisomerase 2-α (TOP2A), 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (F263), and the glutamate ionotropic receptor kainate 2 (GRIK2). The retinal expression of these PKG targets was further confirmed by immunofluorescence and could be assigned to various neuronal cell types, including photoreceptors, horizontal cells, and ganglion cells. Taken together, this study confirmed the key role of PKG in photoreceptor cell death and identified new downstream targets of cGMP/PKG signalling that will improve the understanding of the degenerative mechanisms underlying IRDs.

Insights into pathological mechanisms and interventions revealed by analyzing a mathematical model for cone metabolism

This work analyzes a mathematical model for the metabolic dynamics of a cone photoreceptor, which is the first model to account for energy generation from fatty acids oxidation of shed photoreceptor outer segments (POS). Multiple parameter bifurcation analysis shows that joint variations in external glucose, the efficiency of glucose transporter 1 (GLUT1), lipid utilization for POS renewal, and oxidation of fatty acids affect the cone’s metabolic vitality and its capability to adapt under glucose-deficient conditions. The analysis further reveals that when glucose is scarce, cone viability cannot be sustained by only fueling energy production in the mitochondria, but it also requires supporting anabolic processes to create lipids necessary for cell maintenance and repair. In silico experiments are used to investigate how the duration of glucose deprivation impacts the cell without and with a potential GLUT1 or oxidation of fatty acids intervention as well as a dual intervention. The results show that for prolonged duration of glucose deprivation, the cone metabolic system does not recover with higher oxidation of fatty acids and requires greater effectiveness of GLUT1 to recover. Finally, time-varying global sensitivity analysis (GSA) is applied to assess the sensitivity of the model outputs of interest to changes and uncertainty in the parameters at specific times. The results reveal a critical temporal window where there would be more flexibility for interventions to rescue a cone cell from the detrimental consequences of glucose shortage.

NXNL1 negatively regulates osteoblast differentiation via GDF15-induced PP2A Cα dependent manner in MC3T3-E1 cells

Controlling the level of intracellular reactive oxygen species (ROS) is important for the survival and differentiation of osteoblasts. Intracellular ROS levels are controlled by antioxidant enzymes that modulate the redox state of the cell. Nucleoredoxin-like 1 (NXNL1) is an antioxidant enzyme that increases the viability of rod and cone cells by protecting them from oxidative stress, and is a potential pharmacological target for the treatment of retinitis pigmentosa. The present study investigated the role of NXNL on osteoblast differentiation of MC3T3-E1 preosteoblast cells. Results from qPCR experiments demonstrated that growth differentiation factor 15 (GDF15) increased NXNL1 expression, and that GDF15-induced NXNL1 decreased the expression of osteogenic genes such as distal-less homeobox 5 (Dlx5) and Runt-related transcription factor 2. Furthermore, NXNL1 also inhibits bone morphogenetic protein 2-induced phosphorylation of Smad1/5/9 and alkaline phosphatase activity. The inhibitory effects of NXNL1 on osteoblast differentiation were mediated by protein phosphatase 2A Cα (PP2A Cα). The expression of PP2A Cα was regulated by GDF15, and overexpression of PP2A Cα increased the expression of NXNL1. Taken together, our results demonstrate that NXNL1 inhibits osteoblast differentiation of MC3T3-E1 due to GDF15-induced expression of PP2A Cα.

In depth understanding of retinitis pigmentosa pathogenesis through optical coherence tomography angiography analysis: a narrative review

Retinitis pigmentosa (RP) is the most recognized inherited retinal disorder involving progressive photoreceptors degeneration which eventually causes blindness. However, the pathogenesis of RP is still unclear, making it difficult to establish satisfying treatments. Evidence have been found to support the theory that vascular dysfunction is associated with the progression of RP. Optical coherence tomography angiography (OCTA) is a newly developed technology that enables visualization as well as quantitative assessment of retinal and choroidal vasculature non-invasively. Advances in OCTA have opened a window for in-depth understanding of RP pathogenesis. Here, we propose a hypothesis of RP pathogenesis based on the current OCTA findings in RP, which includes four stages and two important key factors, vascular dysfunction and microglia activation. Further, we discuss the future animal experiments needed and how advanced OCTA technology can help to further verity the hypothesis. The final goal is to explore potential treatment options with enhanced understanding of RP pathogenesis.

Structural changes in retina (Retinal nerve fiber layer) following mild traumatic brain injury and its association with development of visual field defects

BACKGROUND

Mild traumatic brain injury (mTBI)is the most common form of traumatic brain injury accounting for 70-80% of all brain injuries annually. There is increasing evidence that long lasting morphological and functional consequence can be present in visual system following mTBI. Among all the visual manifestation, awareness of Visual field defects is important because it may compromise the social, personal or professional life of any individual. Retinal structural changes such as thinning of Retinal nerve fiber layer (RFNL)captured using optical coherence tomography have emerged as a possible biomarker in many neurological diseases however very little is known in cases with mTBI OBJECTIVE: (I) To demonstrate the structural changes/morphological changes in retina if any following mTBI. (II) Whether the structural changes in retina have any association with the development of Visual field deficits leading to Visual function impairment following mTBI (III) Clinical relevance of structural changes in retina as a possible biomarker for visual function impairment due to visual field deficits.

MATERIALS AND METHODS

Our study included 60 patients with mTBI who fulfilled the inclusion criteria. All patients underwent a detailed ophthalmic evaluation with special focus on temporal recording of Retinal nerve layer thickness using SD- Optical Coherence Tomography and Visual field (Visual field Index) by Humphrey Automated Field Analyser.

RESULTS

30% of eyes had significant thinning of RFNL (> 30% of the base line thickness) at 6 months following mTBI. Visual function impairment due to visual field deficits (VFI < 80%) at 6 months was seen in 40% of the eyes. The structural changes and visual function impairment peaked at 6 months' post injury. A strong Association was noted between RFNL thinning and manifestation of Visual field deficits (VFI < 80%) leading to visual function impairment (P < 0.001). The Correlation Co-efficient between thinning of RFNL and Visual field deficits had a positive correlation(p < 0.001).

CONCLUSION

This novel study has demonstrated that visual functional impairment due to Visual field deficits is a real possibility following mTBI. Monitoring of retinal parameter such as thinning of Retinal nerve fiber layer, using Optical coherence tomography, can be a biomarker for early detection or development of visual field defects in mTBI.

Structural evaluation in inherited retinal diseases

Ophthalmic genetics is a field that has been rapidly evolving over the last decade, mainly due to the flourishing of translational medicine for inherited retinal diseases (IRD). In this review, we will address the different methods by which retinal structure can be objectively and accurately assessed in IRD. We review standard-of-care imaging for these patients: colour fundus photography, fundus autofluorescence imaging and optical coherence tomography (OCT), as well as higher-resolution and/or newer technologies including OCT angiography, adaptive optics imaging, fundus imaging using a range of wavelengths, magnetic resonance imaging, laser speckle flowgraphy and retinal oximetry, illustrating their utility using paradigm genotypes with on-going therapeutic efforts/trials.

The metabolic signaling of the nucleoredoxin-like 2 gene supports brain function

The nucleoredoxin gene NXNL2 encodes for two products through alternative splicing, rod-derived cone viability factor-2 (RdCVF2) that mediates neuronal survival and the thioredoxin-related protein (RdCVF2L), an enzyme that regulates the phosphorylation of TAU. To investigate the link between NXNL2 and tauopathies, we studied the Nxnl2 knockout mouse (Nxnl2-/-). We established the expression pattern of the Nxnl2 gene in the brain using a Nxnl2 reporter mouse line, and characterized the behavior of the Nxnl2-/- mouse at 2 months of age. Additionally, long term potentiation and metabolomic from hippocampal specimens were collected at 2 months of age. We studied TAU oligomerization, phosphorylation and aggregation in Nxnl2-/- brain at 18 months of age. Finally, newborn Nxnl2-/- mice were treated with adeno-associated viral vectors encoding for RdCVF2, RdCVF2L or both and measured the effect of this therapy on long-term potential, glucose metabolism and late-onset tauopathy. Nxnl2-/- mice at 2 months of age showed severe behavioral deficiency in fear, pain sensitivity, coordination, learning and memory. The Nxnl2-/- also showed deficits in long-term potentiation, demonstrating that the Nxnl2 gene is involved in regulating brain functions. Dual delivery of RdCVF2 and RdCVF2L in newborn Nxnl2-/- mice fully correct long-term potentiation through their synergistic action. The expression pattern of the Nxnl2 gene in the brain shows a predominant expression in circumventricular organs, such as the area postrema. Glucose metabolism of the hippocampus of Nxnl2-/- mice at 2 months of age was reduced, and was not corrected by gene therapy. At 18-month-old Nxnl2-/- mice showed brain stigmas of tauopathy, such as oligomerization, phosphorylation and aggregation of TAU. This late-onset tauopathy can be prevented, albeit with modest efficacy, by recombinant AAVs administrated to newborn mice. The Nxnl2-/- mice have memory dysfunction at 2-months that resembles mild-cognitive impairment and at 18-months exhibit tauopathy, resembling to the progression of Alzheimer's disease. We propose the Nxnl2-/- mouse is a model to study multistage aged related neurodegenerative diseases. The NXNL2 metabolic and redox signaling is a new area of therapeutic research in neurodegenerative diseases.

Mathematical Models of Retinitis Pigmentosa: The Trophic Factor Hypothesis

Retinitis pigmentosa (RP) is the term used to denote a group of inherited retinal-degenerative conditions that cause progressive sight loss. Individuals with this condition lose their light-sensitive photoreceptor cells, known as rods and cones, over a period of years to decades; degeneration starting in the retinal periphery, and spreading peripherally and centrally over time. RP is a rod-cone dystrophy, meaning that rod health and function are affected earlier and more severely than that of cones. Rods degenerate due to an underlying mutation, whereas the reasons for cone degeneration are unknown. A number of mechanisms have been proposed to explain secondary cone loss and the spatio-temporal patterns of retinal degeneration in RP. One of the most promising is the trophic factor hypothesis, which suggests that rods produce a factor necessary for cone survival, such that, when rods degenerate, cone degeneration follows. In this paper we formulate and analyse mathematical models of human RP under the trophic factor hypothesis. These models are constructed as systems of reaction-diffusion partial differential equations in one spatial dimension, and are solved and analysed using a combination of numerical and analytical methods. We predict the conditions under which cones will degenerate following the loss of a patch of rods from the retina, the critical trophic factor treatment rate required to prevent cone degeneration following rod loss and the spatio-temporal patterns of cone loss that would result if the trophic factor mechanism alone were responsible for retinal degeneration.

Technological advancements to study cellular signaling pathways in inherited retinal degenerative diseases

Inherited retinal degenerative diseases (IRDs) are rare neurodegenerative disorders with mutations in hundreds of genes leading to vision loss, primarily owing to photoreceptor cell death. This genetic diversity is impeding development of effective treatment options. Gene-based therapies have resulted in the first FDA-approved drug (Luxturna) for RPE65-specific IRD. Although currently explored in clinical trials, genomic medicines are mutation-dependent, hence suitable only for patients harboring a specific mutation. Better understanding of the pathways leading to photoreceptor degeneration may help to determine common targets and develop mutation-independent therapies for larger groups of patients with IRDs. In this review, we discuss the key pathways involved in photoreceptor cell death studied by transcriptomics, proteomics, and metabolomics techniques to identify potential therapeutic targets in IRDs.

Citicoline and Vitamin B12 Eye Drops in Type 1 Diabetes: Results of a 36-Month Pilot Study Evaluating Macular Electrophysiological Changes

Introduction

Our aim was to evaluate the effects of 36 months of treatment with citicoline and vitamin B₁₂ eye drops on macular function in patients with type 1 diabetes (DM1) with mild signs of non-proliferative diabetic retinopathy (NPDR).

Methods

A prospective, randomized, interventional, monocentric, double-masked study was conducted. Twenty patients with DM1 were enrolled and randomly divided into two groups: the DC group (10 patients; mean age ± standard deviation 46.86 ± 8.78 years) in which one eye of each patient was treated with citicoline and vitamin B₁₂ eye drops (OMK2^®, Omikron Italia srl, Italy, one drop thrice daily) for a period of 36 months; the DP group (10 patients; mean age ± standard deviation 47.89 ± 7.74 years) in which one eye of each patient was treated with placebo (eye drops containing hypromellose 0.3%, one drop thrice daily) for a period of 36 months. A total of 18 eyes (10 from the DP and 8 from the DC group, respectively) completed the study. In both groups, multifocal electroretinogram (mfERG) recordings were assessed at baseline and after 36 months. In mfERG analysis, the N1–P1 response amplitude density (RAD) evaluated in the 0–2.5° (ring 1), in the 2.5–5° (ring 2), in the 5–10° (ring 3), and in the 0–10° (ring 1 + ring 2 + ring 3) were considered.

Results

With respect to baseline, after 36 months of follow-up, the mfERG RADs recorded in R1, R2, R3, and R1 + R2 + R3 were significantly increased (i.e., R1 + R2 + R3 RAD from 21.552 ± 2.522 nV/degree² at baseline to 26.912 ± 2.850 nV/degree² at 36 months) in DC eyes, whereas in DP eyes they were significantly reduced (i.e., R1 + R2 + R3 RAD from 21.033 ± 3.574 nV/degree² at baseline to 16.151 ± 3.571 nV/degree² at 36 months).

Conclusions

This study indicates that patients with NPDR treated with citicoline and vitamin B₁₂ eye drops for a 36-month period achieved an improvement of the macular bioelectrical responses detectable by mfERG recordings. By contrast, during the same period of follow-up, patients with NPDR treated with placebo showed a worsening of the macular function.

Central Metabolism in Mammals and Plants as a Hub for Controlling Cell Fate

Significance: The importance of oxidoreductases in energy metabolism together with the occurrence of enzymes of central metabolism in the nucleus gave rise to the active research field aiming to understand moonlighting enzymes that undergo post-translational modifications (PTMs) before carrying out new tasks. Recent Advances: Cytosolic enzymes were shown to induce gene transcription after PTM and concomitant translocation to the nucleus. Changed properties of the oxidized forms of cytosolic glyceraldehyde 3-phosphate dehydrogenase, and also malate dehydrogenases and others, are the basis for a hypothesis suggesting moonlighting functions that directly link energy metabolism to adaptive responses required for maintenance of redox-homeostasis in all eukaryotes. Critical Issues: Small molecules, such as metabolic intermediates, coenzymes, or reduced glutathione, were shown to fine-tune the redox switches, interlinking redox state, metabolism, and induction of new functions via nuclear gene expression. The cytosol with its metabolic enzymes connecting energy fluxes between the various cell compartments can be seen as a hub for redox signaling, integrating the different signals for graded and directed responses in stressful situations. Future Directions: Enzymes of central metabolism were shown to interact with p53 or the assumed plant homologue suppressor of gamma response 1 (SOG1), an NAM, ATAF, and CUC transcription factor involved in the stress response upon ultraviolet exposure. Metabolic enzymes serve as sensors for imbalances, their inhibition leading to changed energy metabolism, and the adoption of transcriptional coactivator activities. Depending on the intensity of the impact, rerouting of energy metabolism, proliferation, DNA repair, cell cycle arrest, immune responses, or cell death will be induced. Antioxid. Redox Signal. 34, 1025-1047.

A Metabolic Landscape for Maintaining Retina Integrity and Function

Neurons have high metabolic demands that are almost exclusively met by glucose supplied from the bloodstream. Glucose is utilized in complex metabolic interactions between neurons and glia cells, described by the astrocyte-neuron lactate shuttle (ANLS) hypothesis. The neural retina faces similar energy demands to the rest of the brain, with additional high anabolic needs to support continuous renewal of photoreceptor outer segments. This demand is met by a fascinating variation of the ANLS in which photoreceptors are the central part of a metabolic landscape, using glucose and supplying surrounding cells with metabolic intermediates. In this review we summarize recent evidence on how neurons, in particular photoreceptors, meet their energy and biosynthetic requirements by comprising a metabolic landscape of interdependent cells.

The daily gene transcription cycle in mouse retina

Many physiological retinal processes, such as outer segment disk shedding and visual sensitivity, exhibit a daily rhythm. However, the detailed transcriptome dynamics and related biological processes of the retina are not fully understood. Retinal tissues were collected from C57BL/6J male mice housed in a 12h light/12h dark (LD) cycle for 4 weeks, at Zeitgeber time (ZT) 0, 4, 8, 12, 16, and 20. Total RNA was extracted from the tissues and used for unique identifier RNA sequencing experiments. The rhythmicity of gene expression was determined using the MetaCycle R package. We found that 1741 genes (10.26%) were rhythmically expressed in the retina. According to the expression patterns, the rhythmically expressed genes were assigned to four clusters, each with about 361-492 genes, using the Mfuzz R package. The Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) analyses were conducted to identify pathways and biological processes of the profiled genes. Genes in Clusters 1 and 4 were associated with glycolysis and energy production, showed higher activity at night (from ZT16 to ZT20), and were enriched in the Hif-1α signaling pathway and low-oxygen-related terms. Genes in Cluster 2 were predominantly involved in cilium assembly and organization and were relatively upregulated during the day. Genes in Cluster 3 were associated with ribosome biosynthesis and were highly expressed during the day-night transition period. Taken together, these results demonstrate that a large proportion of retinal genes are expressed rhythmically. Genes involved in energy production and glycolysis are highly expressed at night, leading to relative hypoxia and activation of the Hif-1α signaling pathway. Genes associated with the formation of photoreceptor cilia are expressed during the day.

Association of Human Plasma Metabolomics with Delayed Dark Adaptation in Age-Related Macular Degeneration

The purpose of this study was to analyze the association between plasma metabolite levels and dark adaptation (DA) in age-related macular degeneration (AMD). This was a cross-sectional study including patients with AMD (early, intermediate, and late) and control subjects older than 50 years without any vitreoretinal disease. Fasting blood samples were collected and used for metabolomic profiling with ultra-performance liquid chromatography-mass spectrometry (LC-MS). Patients were also tested with the AdaptDx (MacuLogix, Middletown, PA, USA) DA extended protocol (20 min). Two measures of dark adaptation were calculated and used: rod-intercept time (RIT) and area under the dark adaptation curve (AUDAC). Associations between dark adaption and metabolite levels were tested using multilevel mixed-effects linear modelling, adjusting for age, gender, body mass index (BMI), smoking, race, AMD stage, and Age-Related Eye Disease Study (AREDS) formulation supplementation. We included a total of 71 subjects: 53 with AMD (13 early AMD, 31 intermediate AMD, and 9 late AMD) and 18 controls. Our results revealed that fatty acid-related lipids and amino acids related to glutamate and leucine, isoleucine and valine metabolism were associated with RIT (p < 0.01). Similar results were found when AUDAC was used as the outcome. Fatty acid-related lipids and amino acids are associated with DA, thus suggesting that oxidative stress and mitochondrial dysfunction likely play a role in AMD and visual impairment in this condition.

Metabolic Analysis of Vitreous/Lens and Retina in Wild Type and Retinal Degeneration Mice

Photoreceptors are the light-sensing cells of the retina and the major cell type affected in most inherited retinal degenerations. Different metabolic pathways sustain their high energetic demand in physiological conditions, particularly aerobic glycolysis. The principal metabolome of the mature retina has been studied, but only limited information is available on metabolic adaptations in response to key developmental events, such as eye opening. Moreover, dynamic metabolic changes due to retinal degeneration are not well understood. Here, we aimed to explore and map the ocular metabolic dynamics induced by eye opening in healthy (wild type) or Pde6b-mutant (retinal degeneration 1, Rd1) mice, in which photoreceptors degenerate shortly after eye opening. To unravel metabolic differences emerging before and after eye opening under physiological and pathophysiological conditions, we performed nuclear magnetic resonance (NMR) spectroscopy-based metabolome analysis of wild type and Rd1 retina and vitreous/lens. We show that eye opening is accompanied by changes in the concentration of selected metabolites in the retina and by alterations in the vitreous/lens composition only in the retinal degeneration context. As such, we identify NAcetylaspartate as a potential novel vitreous/lens marker reflecting progressive retinal degeneration. Thus, our data can help elucidating mechanisms underlying key events in retinal physiology and reveal changes occurring in pathology, while highlighting the importance of the vitreous/lens in the characterization of retinal diseases.

The role of RdCVFL in a mathematical model of photoreceptor interactions

Recent experimental and mathematical work has shown the interdependence of the rod and cone photoreceptors with the retinal pigment epithelium in maintaining sight. Accelerated intake of glucose into the cones via the theoredoxin-like rod-derived cone viability factor (RdCVF) is needed as aerobic glycolysis is the primary source of energy production. Reactive oxidative species (ROS) result from the rod and cone metabolism and recent experimental work has shown that the long form of RdCVF (RdCVFL) helps mitigate the negative effects of ROS. In this work we investigate the role of RdCVFL in maintaining the health of the photoreceptors. The results of our mathematical model show the necessity of RdCVFL and also demonstrate additional stable modes that are present in this system. The sensitivity analysis shows the importance of glucose uptake, nutrient levels, and ROS mitigation in maintaining rod and cone health in light-damaged mouse models. Together, these suggests areas on which to focus treatment in order to prolong the photoreceptors, especially in situations where ROS is a contributing factor to their death such as retinitis pigmentosa.

A Splice Variant in SLC16A8 Gene Leads to Lactate Transport Deficit in Human iPS Cell-Derived Retinal Pigment Epithelial Cells

Age-related macular degeneration (AMD) is a blinding disease for which most of the patients remain untreatable. Since the disease affects the macula at the center of the retina, a structure specific to the primate lineage, rodent models to study the pathophysiology of AMD and to develop therapies are very limited. Consequently, our understanding relies mostly on genetic studies highlighting risk alleles at many loci. We are studying the possible implication of a metabolic imbalance associated with risk alleles within the SLC16A8 gene that encodes for a retinal pigment epithelium (RPE)-specific lactate transporter MCT3 and its consequences for vision. As a first approach, we report here the deficit in transepithelial lactate transport of a rare SLC16A8 allele identified during a genome-wide association study. We produced induced pluripotent stem cells (iPSCs) from the unique patient in our cohort that carries two copies of this allele. After in vitro differentiation of the iPSCs into RPE cells and their characterization, we demonstrate that the rare allele results in the retention of intron 2 of the SLC16A8 gene leading to the absence of MCT3 protein. We show using a biochemical assay that these cells have a deficit in transepithelial lactate transport.

The interplay of oxidative stress and ARMS2-HTRA1 genetic risk in neovascular AMD

Age-related macular degeneration (AMD) is the leading cause of vision loss in adults over 60 years old globally. There are two forms of advanced AMD: “dry” and “wet”. Dry AMD is characterized by geographic atrophy of the retinal pigment epithelium and overlying photoreceptors in the macular region; whereas wet AMD is characterized by vascular penetrance from the choroid into the retina, known as choroidal neovascularization (CNV). Both phenotypes eventually lead to loss of central vision. The pathogenesis of AMD involves the interplay of genetic polymorphisms and environmental risk factors, many of which elevate retinal oxidative stress. Excess reactive oxygen species react with cellular macromolecules, forming oxidation-modified byproducts that elicit chronic inflammation and promote CNV. Additionally, genome-wide association studies have identified several genetic variants in the age-related maculopathy susceptibility 2/high-temperature requirement A serine peptidase 1 (ARMS2-HTRA1) locus associated with the progression of late-stage AMD, especially the wet subtype. In this review, we will focus on the interplay of oxidative stress and HTRA1 in drusen deposition, chronic inflammation, and chronic angiogenesis. We aim to present a multifactorial model of wet AMD progression, supporting HTRA1 as a novel therapeutic target upstream of vascular endothelial growth factor (VEGF), the conventional target in AMD therapeutics. By inhibiting HTRA1’s proteolytic activity, we can reduce pro-angiogenic signaling and prevent proteolytic breakdown of the blood-retina barrier. The anti-HTRA1 approach offers a promising alternative treatment option to wet AMD, complementary to anti-VEGF therapy.

Mitochondria: The Retina's Achilles' Heel in AMD

Strong experimental evidence from studies in human donor retinas and animal models supports the idea that the retinal pathology associated with age-related macular degeneration (AMD) involves mitochondrial dysfunction and consequent altered retinal metabolism. This chapter provides a brief overview of mitochondrial structure and function, summarizes evidence for mitochondrial defects in AMD, and highlights the potential ramifications of these defects on retinal health and function. Discussion of mitochondrial haplogroups and their association with AMD brings to light how mitochondrial genetics can influence disease outcome. As one of the most metabolically active tissues in the human body, there is strong evidence that disruption in key metabolic pathways contributes to AMD pathology. The section on retinal metabolism reviews cell-specific metabolic differences and how the metabolic interdependence of each retinal cell type creates a unique ecosystem that is disrupted in the diseased retina. The final discussion includes strategies for therapeutic interventions that target key mitochondrial pathways as a treatment for AMD.