Degeneration Of Retinal Ganglion Cells Research Articles

Glaucoma - the significant challenge for the healthcare system in Poland

Introduction
 Glaucoma is a group of optic neuropathies characterized by progressive degeneration of retinal ganglion cells (RGCs) and visual field loss. Glaucoma is the leading cause of irreversible blindness in the world. The World Health Organization classifies it as a social and civilization disease and emphasizes the need to improve ophthalmic care systems in order to meet the constantly growing challenge for public health, which is glaucoma. The aim of this article is to identify the main problems that affect the health care system of patients with glaucoma in Poland.
 Review methods
 The review of literature on glaucoma was performed using the PubMed and Google Scholar databases. The latest available epidemiological data and the current legal acts concerning the health care system of patients with glaucoma in Poland were also analyzed.
 Abbreviated description of the state of knowledge
 The incidence of glaucoma in Poland is constantly increasing, due to the aging of the population. The insidious course of the disease, low public awareness and difficulties in access effective ophthalmic services mean that the disease is diagnosed too late, when significant damage to the optic nerve has already occurred. In addition, the poor mental health of patients, treatment difficulties related to the frequent comorbidity of general diseases and the use of other drug therapies, complicate the course of glaucoma and make it difficult to inhibit its progression.
 Summary
 Glaucoma is a significant challenge for public health and the healthcare system in Poland. Therefore, it is very important to take systemic measures as soon as possible that contribute to improve public awareness of eye diseases, increase the availability of ophthalmic care, early detection and appropriate monitoring of the course of glaucoma.

Retinal Glutamate Neurotransmission: From Physiology to Pathophysiological Mechanisms of Retinal Ganglion Cell Degeneration.

Glutamate neurotransmission and metabolism are finely modulated by the retinal network, where the efficient processing of visual information is shaped by the differential distribution and composition of glutamate receptors and transporters. However, disturbances in glutamate homeostasis can result in glutamate excitotoxicity, a major initiating factor of common neurodegenerative diseases. Within the retina, glutamate excitotoxicity can impair visual transmission by initiating degeneration of neuronal populations, including retinal ganglion cells (RGCs). The vulnerability of RGCs is observed not just as a result of retinal diseases but has also been ascribed to other common neurodegenerative and peripheral diseases. In this review, we describe the vulnerability of RGCs to glutamate excitotoxicity and the contribution of different glutamate receptors and transporters to this. In particular, we focus on the N-methyl-d-aspartate (NMDA) receptor as the major effector of glutamate-induced mechanisms of neurodegeneration, including impairment of calcium homeostasis, changes in gene expression and signalling, and mitochondrial dysfunction, as well as the role of endoplasmic reticular stress. Due to recent developments in the search for modulators of NMDA receptor signalling, novel neuroprotective strategies may be on the horizon.

The APOE E4 Allele Is Associated with FasterRates of Neuroretinal Thinning in a Prospective Cohort Study of Suspect and Early Glaucoma.

PurposeTo investigate the association between the apolipoprotein E (APOE) E4 dementia-risk allele and prospective longitudinal retinal thinning in a cohort study of suspect and early manifest glaucoma.DesignRetrospective analysis of prospective cohort data.ParticipantsThis study included all available eyes from participants recruited to the Progression Risk of Glaucoma: Relevant SNPs [single nucleotide polymorphisms] with Significant Association (PROGRESSA) study with genotyping data from which APOE genotypes could be determined.MethodsApolipoprotein E alleles and genotypes were determined in PROGRESSA, and their distributions were compared with an age-matched and ancestrally matched normative cohort, the Blue Mountains Eye Study. Structural parameters of neuroretinal atrophy measured using spectral-domain OCT were compared within the PROGRESSA cohort on the basis of APOE E4 allele status.Main Outcome MeasuresLongitudinal rates of thinning in the macular ganglion cell–inner plexiform layer (mGCIPL) complex and the peripapillary retinal nerve fiber layer (pRNFL).ResultsRates of mGCIPL complex thinning were faster in participants harboring ≥1 copies of the APOE E4 allele (β = –0.13 μm/year; P ≤0.001). This finding was strongest in eyes affected by normal-tension glaucoma (NTG; β = –0.20 μm/year; P = 0.003). Apolipoprotein E E4 allele carriers were also more likely to be lost to follow-up (P = 0.01) and to demonstrate a thinner average mGCIPL complex (70.9 μm vs. 71.9 μm; P = 0.011) and pRNFL (77.6 μm vs. 79.2 μm; P = 0.045) after a minimum of 3 years of monitoring.ConclusionsThe APOE E4 allele was associated with faster rates of mCGIPL complex thinning, particularly in eyes with NTG. These results suggest that the APOE E4 allele may be a risk factor for retinal ganglion cell degeneration in glaucoma.

Influences of Glaucoma on the Structure and Function of Synapses in the Visual System.

Significance: Glaucoma is an age-related neurodegenerative disorder of the visual system associated with sensitivity to intraocular pressure (IOP). It is the leading irreversible cause of vision loss worldwide, and vision loss results from damage and dysfunction of the retinal output neurons known as retinal ganglion cells (RGCs). Recent Advances: Elevated IOP and optic nerve injury triggers pruning of RGC dendrites, altered morphology of excitatory inputs from presynaptic bipolar cells, and disrupted RGC synaptic function. Less is known about RGC outputs, although evidence to date indicates that glaucoma is associated with altered mitochondrial and synaptic structure and function in RGC-projection targets in the brain. These early functional changes likely contribute to vision loss and might be a window into early diagnosis and treatment. Critical Issues: Glaucoma affects different RGC populations to varying extents and along distinct time courses. The influence of glaucoma on RGC synaptic function as well as the mechanisms underlying these effects remain to be determined. Since RGCs are an especially energetically demanding population of neurons, altered intracellular axon transport of mitochondria and mitochondrial function might contribute to RGC synaptic dysfunction in the retina and brain as well as RGC vulnerability in glaucoma. Future Directions: The mechanisms underlying differential RGC vulnerability remain to be determined. Moreover, the timing and mechanisms of RGCs synaptic dysfunction and degeneration will provide valuable insight into the disease process in glaucoma. Future work will be able to capitalize on these findings to better design diagnostic and therapeutic approaches to detect disease and prevent vision loss. Antioxid. Redox Signal. 37, 842-861.

Tools and Biomarkers for the Study of Retinal Ganglion Cell Degeneration.

The retina is part of the central nervous system, its analysis may provide an idea of the health and functionality, not only of the retina, but also of the entire central nervous system, as has been shown in Alzheimer’s or Parkinson’s diseases. Within the retina, the ganglion cells (RGC) are the neurons in charge of processing and sending light information to higher brain centers. Diverse insults and pathological states cause degeneration of RGC, leading to irreversible blindness or impaired vision. RGCs are the measurable endpoints in current research into experimental therapies and diagnosis in multiple ocular pathologies, like glaucoma. RGC subtype classifications are based on morphological, functional, genetical, and immunohistochemical aspects. Although great efforts are being made, there is still no classification accepted by consensus. Moreover, it has been observed that each RGC subtype has a different susceptibility to injury. Characterizing these subtypes together with cell death pathway identification will help to understand the degenerative process in the different injury and pathological models, and therefore prevent it. Here we review the known RGC subtypes, as well as the diagnostic techniques, probes, and biomarkers for programmed and unprogrammed cell death in RGC.

Quantitative BONCAT Allows Identification of Newly Synthesized Proteins after Optic Nerve Injury.

Retinal ganglion cells (RGCs) die after optic nerve trauma or in degenerative disease. However, acute changes in protein expression that may regulate RGC response to injury are not fully understood, and detailed methods to quantify new protein synthesis have not been tested. Here, we develop and apply a new in vivo quantitative measure of newly synthesized proteins to examine changes occurring in the retina after optic nerve injury. Azidohomoalanine, a noncanonical amino acid, was injected intravitreally into the eyes of rodents of either sex with or without optic nerve injury. Isotope variants of biotin-alkyne were used for quantitative BONCAT (QBONCAT) mass spectrometry, allowing identification of protein synthesis and transport rate changes in more than 1000 proteins at 1 or 5 d after optic nerve injury. In vitro screening showed several newly synthesized proteins regulate axon outgrowth in primary neurons in vitro This novel approach to targeted quantification of newly synthesized proteins after injury uncovers a dynamic translational response within broader proteostasis regulation and enhances our understanding of the cellular response to injury.SIGNIFICANCE STATEMENT Optic nerve injury results in death and degeneration of retinal ganglion cells and their axons. The specific cellular response to injury, including changes in new protein synthesis, is obscured by existing proteins and protein degradation. In this study, we introduce QBONCAT to isolate and quantify acute protein synthesis and subsequent transport between cellular compartments. We identify novel candidate protein effectors of the regenerative response and uncover their regulation of axon growth in vitro, validating the utility of QBONCAT for the discovery of novel regulatory and therapeutic candidates after optic nerve injury.

Further advances in the diagnosis and treatment of Leber's Hereditary Optic Neuropathy - a review.

Leber’s Hereditary Optic Neuropathy (LHON), is one of the most frequent mitochondrial diseases characterized by Retinal Ganglion Cells degeneration. Pathogenic gene mutations in LHON induces mitochondrial impairment, which in turn leads to insufficient mitochondrial ATP production. The pathologic hallmark of the disease is primary degeneration of retinal ganglion cells, which results in optic nerve atrophy. The paper reviews some of the recent advances in the understanding of LHON: new genetics discoveries and novel therapeutic approaches.

Retinal Circular RNA hsa_circ_0087207 Expression Promotes Apoptotic Cell Death in Induced Pluripotent Stem Cell-Derived Leber's Hereditary Optic Neuropathy-like Models.

Backgrounds: Leber’s hereditary optic neuropathy (LHON) is known as an inherited retinal disorder characterized by the bilateral central vision loss and degeneration of retinal ganglion cells (RGCs). Unaffected LHON carriers are generally asymptomatic, suggesting that certain factors may contribute to the disease manifestations between carriers and patients who carry the same mutated genotypes. Methods: We first aimed to establish the iPSC-differentiated RGCs from the normal healthy subject, the carrier, and the LHON patient and then compared the differential expression profile of circular RNAs (CircRNAs) among RGCs from these donors in vitro. We further overexpressed or knocked down the most upregulated circRNA to examine whether this circRNA contributes to the distinct phenotypic manifestations between the carrier- and patient-derived RGCs. Results: iPSCs were generated from the peripheral blood cells from the healthy subject, the carrier, and the LHON patient and successfully differentiated into RGCs. These RGCs carried equivalent intracellular reactive oxygen species, but only LHON-patient iPSC-derived RGCs exhibited remarkable apoptosis. Next-generation sequencing and quantitative real-time PCR revealed the circRNA hsa_circ_0087207 as the most upregulated circRNA in LHON-patient iPSC-derived RGCs. Overexpression of hsa_circ_0087207 increased the apoptosis in carrier iPSC-derived RGCs, while knockdown of hsa_circ_0087207 attenuated the apoptosis in LHON-patient iPSC-derived RGCs. Predicted by bioinformatics approaches, hsa_circ_0087207 acts as the sponge of miR-665 to induce the expression of a variety of apoptosis-related genes in LHON patient iPSC-derived RGCs. Conclusions: Our data indicated that hsa_circ_0087207 upregulation distinguishes the disease phenotype manifestations between iPSC-derived RGCs generated from the LHON patient and carrier. Targeting the hsa_circ_0087207/miR-665 axis might hold therapeutic promises for the treatment of LHON.

Mechanistic study of silica nanoparticles on the size-dependent retinal toxicity in vitro and in vivo

BackgroundSilica nanoparticles (SiO2 NPs) are extensively applied in the biomedical field. The increasing medical application of SiO2 NPs has raised concerns about their safety. However, studies on SiO2 NP-induced retinal toxicity are lacking.MethodsWe investigated the retinal toxicity of SiO2 NPs with different sizes (15 and 50 nm) in vitro and in vivo along with the underlying mechanisms. The cytotoxicity of SiO2 NPs with different sizes was assessed in R28 human retinal precursor cells by determining the ATP content and LDH release. The cell morphologies and nanoparticle distributions in the cells were analyzed by phase-contrast microscopy and transmission electron microscopy, respectively. The mitochondrial membrane potential was examined by confocal laser scanning microscopy. The retinal toxicity induced by SiO2 NPs in vivo was examined by immunohistochemical analysis. To further investigate the mechanism of retinal toxicity induced by SiO2 NPs, reactive oxygen species (ROS) generation, glial cell activation and inflammation were monitored.ResultsThe 15-nm SiO2 NPs were found to have higher cytotoxicity than the larger NPs. Notably, the 15-nm SiO2 NPs induced retinal toxicity in vivo, as demonstrated by increased cell death in the retina, TUNEL-stained retinal cells, retinal ganglion cell degeneration, glial cell activation, and inflammation. In addition, The SiO2 NPs caused oxidative stress, as demonstrated by the increase in the ROS indicator H2DCF-DA. Furthermore, the pretreatment of R28 cells with N-acetylcysteine, an ROS scavenger, attenuated the ROS production and cytotoxicity induced by SiO2 NPs.ConclusionsThese results provide evidence that SiO2 NPs induce size-dependent retinal toxicity and suggest that glial cell activation and ROS generation contribute to this toxicity.Graphical

Dysfunctional cGMP Signaling Leads to Age-Related Retinal Vascular Alterations and Astrocyte Remodeling in Mice.

The nitric oxide–guanylyl cyclase-1–cyclic guanylate monophosphate (NO–GC-1–cGMP) pathway is integral to the control of vascular tone and morphology. Mice lacking the alpha catalytic domain of guanylate cyclase (GC1−/−) develop retinal ganglion cell (RGC) degeneration with age, with only modest fluctuations in intraocular pressure (IOP). Increasing the bioavailability of cGMP in GC1−/− mice prevents neurodegeneration independently of IOP, suggesting alternative mechanisms of retinal neurodegeneration. In continuation to these studies, we explored the hypothesis that dysfunctional cGMP signaling leads to changes in the neurovascular unit that may contribute to RGC degeneration. We assessed retinal vasculature and astrocyte morphology in young and aged GC1−/− and wild type mice. GC1−/− mice exhibit increased peripheral retinal vessel dilation and shorter retinal vessel branching with increasing age compared to Wt mice. Astrocyte cell morphology is aberrant, and glial fibrillary acidic protein (GFAP) density is increased in young and aged GC1−/− mice, with areas of dense astrocyte matting around blood vessels. Our results suggest that proper cGMP signaling is essential to retinal vessel morphology with increasing age. Vascular changed are preceded by alterations in astrocyte morphology which may together contribute to retinal neurodegeneration and loss of visual acuity observed in GC1−/− mice.

Intraocular Delivery of a Collagen Mimetic Peptide Repairs Retinal Ganglion Cell Axons in Chronic and Acute Injury Models.

Vision loss through the degeneration of retinal ganglion cell (RGC) axons occurs in both chronic and acute conditions that target the optic nerve. These include glaucoma, in which sensitivity to intraocular pressure (IOP) causes early RGC axonal dysfunction, and optic nerve trauma, which causes rapid axon degeneration from the site of injury. In each case, degeneration is irreversible, necessitating new therapeutics that protect, repair, and regenerate RGC axons. Recently, we demonstrated the reparative capacity of using collagen mimetic peptides (CMPs) to heal fragmented collagen in the neuronal extracellular milieu. This was an important step in the development of neuronal-based therapies since neurodegeneration involves matrix metalloproteinase (MMP)-mediated remodeling of the collagen-rich environment in which neurons and their axons exist. We found that intraocular delivery of a CMP comprising single-strand fractions of triple helix human type I collagen prevented early RGC axon dysfunction in an inducible glaucoma model. Additionally, CMPs also promoted neurite outgrowth from dorsal root ganglia, challenged in vitro by partial digestion of collagen. Here, we compared the ability of a CMP sequence to protect RGC axons in both inducible glaucoma and optic nerve crush. A three-week +40% elevation in IOP caused a 67% degradation in anterograde transport to the superior colliculus, the primary retinal projection target in rodents. We found that a single intravitreal injection of CMP during the period of IOP elevation significantly reduced this degradation. The same CMP delivered shortly after optic nerve crush promoted significant axonal recovery during the two-week period following injury. Together, these findings support a novel protective and reparative role for the use of CMPs in both chronic and acute conditions affecting the survival of RGC axons in the optic projection to the brain.

Quantitative transportomics identifies Kif5a as a major regulator of neurodegeneration.

Many neurons in the adult central nervous system, including retinal ganglion cells (RGCs), degenerate and die after injury. Early axon protein and organelle trafficking failure is a key component in many neurodegenerative disorders yet changes to axoplasmic transport in disease models have not been quantified. We analyzed early changes in the protein 'transportome' from RGC somas to their axons after optic nerve injury and identified transport failure of an anterograde motor protein Kif5a early in RGC degeneration. We demonstrated that manipulating Kif5a expression affects anterograde mitochondrial trafficking in RGCs and characterized axon transport in Kif5a knockout mice to identify proteins whose axon localization was Kif5a-dependent. Finally, we found that knockout of Kif5a in RGCs resulted in progressive RGC degeneration in the absence of injury. Together with expression data localizing Kif5a to human RGCs, these data identify Kif5a transport failure as a cause of RGC neurodegeneration and point to a mechanism for future therapeutics.

Application of advanced magnetic resonance imaging in glaucoma: a narrative review.

Glaucoma is a group of eye diseases characterized by progressive degeneration of the optic nerve head and retinal ganglion cells and corresponding visual field defects. In recent years, mounting evidence has shown that glaucoma-related damage may not be limited to the degeneration of retinal ganglion cells or the optic nerve head. The entire structure of the visual pathway may be degraded, and the degradation may even extend to some non-visual brain regions. We know that advanced morphological, functional, and metabolic magnetic resonance technologies provide a means to observe quantitatively and in real time the state of brain function. Advanced magnetic resonance imaging (MRI) techniques provide additional diagnostic markers for glaucoma, which are related to known potential histopathological changes. Many researchers in China and globally have conducted clinical and imaging studies on glaucoma. However, they are scattered, and we still need to systematically sort out the advanced MRI related to glaucoma. We reviewed literature published in any language and included all studies that were able to be translated into English from 1 January 1980 to 31 July 2021. Our literature search focused on emerging magnetic resonance neuroimaging techniques for the study of glaucoma. We then identified each functional area of the brain of glaucoma patients through the integration of anatomy, image, and function. The aim was to provide more information about the occurrence and development of glaucoma diseases. From the perspective of neuroimaging, our study provides a research basis to explain the possible mechanism of the occurrence and development of glaucoma. This knowledge gained from these techniques enables us to more clearly observe the damage glaucoma causes to the whole visual pathway. Our study provides new insights into glaucoma-induced changes to the brain. Our findings may enable the progress of these changes to be analyzed and inspire new neuroprotective therapeutic strategies for patients with glaucoma in the future.

Acteoside protects retinal ganglion cells from experimental glaucoma by activating the PI3K/AKT signaling pathway via caveolin 1 upregulation.

BackgroundGlaucoma is the second leading cause of blindness in the world and is characterized by optic neuropathy and degeneration of retinal ganglion cells (RGCs). Our preliminary research found that acteoside can inhibit autophagy-induced apoptosis of RGCs via the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway. However, it is unclear how acteoside activates the PI3K/AKT signaling pathway to prevents RGCs autophagic apoptosis.MethodsAnimal and cell models were used in this study. Hematoxylin-eosin staining revealed pathological histology of retinas. The number of RGCs in retinas was counted using immunofluorescence. Malondialdehyde and superoxide dismutase were determined using enzyme-linked immunosorbent assay kits. Flow cytometry and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining were used to detect cell apoptosis. The reactive oxygen species was determined by the Flow cytometry. The proteins were determined by Western blot.ResultsThe results showed that acteoside treatment significantly reduced RGC loss, oxidative stress, and autophagy, thereby preventing glaucoma exacerbation. Acteoside reversed caveolin 1 (Cav1) expression and PI3K/AKT signaling activation, according to Western blot results. Cav1 knockdown also reversed acteoside’s effects on RGC loss, PI3K/AKT signaling pathway activation, autophagy and oxidative stress. Notably, 3-methyladenine, a PI3K inhibitor, reversed the effects of acteoside and Cav1 overexpression on RGC loss, oxidative stress, and autophagy.ConclusionsThese finding imply that acteoside alleviates RGC loss and oxidative stress by activating of the PI3K/AKT signaling pathway by upregulating Cav1.

Long Non-Coding RNAs in Retinal Ganglion Cell Apoptosis.

Traumatic optic neuropathy or other neurodegenerative diseases, including optic nerve transection, glaucoma, and diabetic retinopathy, can lead to progressive and irreversible visual damage. Long non-coding RNAs (lncRNAs), which belong to the family of non-protein-coding transcripts, have been linked to the pathogenesis, progression, and prognosis of these lesions. Retinal ganglion cells (RGCs) are critical for the transmission of visual information to the brain, damage to which results in visual loss. Apoptosis has been identified as one of the most essential modes of RGC death. Emerging evidence suggests that lncRNAs can regulate RGC degeneration by directly or indirectly modulating apoptosis-associated signaling pathways. This review presents a comprehensive overview of the role of lncRNAs in RGC apoptosis at transcriptional, post-transcriptional, translational, and post-translational levels, emphasizing on the potential mechanisms of action. The current limitations and future perspectives of exploring the connection between lncRNAs and RGC apoptosis have been summarized. Understanding the intricate molecular interaction network of lncRNAs and RGC apoptosis will open new avenues for theidentification of novel diagnostic biomarkers, therapeutic targets, and molecules for prognostic evaluation of diseases related to RGC injury.

TrkB Receptor Agonist 7,8 Dihydroxyflavone is Protective Against the Inner Retinal Deficits Induced by Experimental Glaucoma

Glaucoma is an age-related neurodegenerative disorder characterized by retinal ganglion cell (RGC) degeneration and excavation of the optic nerve head (ONH). It is associated with an increase in intraocular pressure (IOP) and progressive decline in the visual field. Reduction in the retrograde axonal transport of neurotrophic factors such as brain-derived neurotrophic factor (BDNF) from the brain to the neuronal cell bodies in retina, has been suggested as one of the key mechanisms underlying selective degeneration of ganglion cells and optic nerve in glaucoma. Multiple studies have indicated that BDNF and its high affinity receptor Tropomyosin receptor kinase B (TrkB) play crucial roles in survival of RGCs and that upregulating BDNF/TrkB signalling using gene therapy can protect the ganglion cells against degeneration. This study corroborates previous findings and demonstrates that glaucoma is associated with downregulation of TrkB downstream signalling and enhanced levels of amyloid β (Aβ 1–42) accumulation in the retina. 7,8 dihydroxyflavone (7,8 DHF) is a TrkB agonist and regular administration of this compound imparted significant protection against loss of GCL density and preserved inner retinal function in experimental glaucoma models. 7,8 DHF treatment stimulated activation of TrkB intracellular signalling as well as ameliorated the increase in the levels of soluble Aβ (1–42) in the retinas of rats and mice exposed to high IOP. The protective effects of 7,8 DHF were also evident in BDNF+/− mice indicating that TrkB agonist mediated activation of TrkB signalling was not altered upon BDNF allelic impairment. These data support BDNF/TrkB axis as a promising therapeutic target in glaucoma and highlight that the detrimental effects of high IOP exposure can be compensated by the exogenous administration of a TrkB agonist.

Full-Circle Cauterization of Limbal Vascular Plexus for Surgically Induced Glaucoma in Rodents.

Glaucoma, the second leading cause of blindness worldwide, is a heterogeneous group of ocular disorders characterized by structural damage to the optic nerve and retinal ganglion cell (RGC) degeneration, resulting in visual dysfunction by interrupting the transmission of visual information from the eye to the brain. Elevated intraocular pressure is the most important risk factor; thus, several models of ocular hypertension have been developed in rodents by either genetic or experimental approaches to investigate the causes and effects of the disease. Among those, some limitations have been reported such as surgical invasiveness, inadequate functional assessment, requirement of extensive training, and highly variable extension of retinal damage. The present work characterizes a simple, low-cost, and efficient method to induce ocular hypertension in rodents, based on low-temperature, full-circle cauterization of the limbal vascular plexus, a major component of aqueous humor drainage. The new model provides a technically easy, noninvasive, and reproducible subacute ocular hypertension, associated with progressive RGC and optic nerve degeneration, and a unique post-operative clinical recovery rate that allows in vivo functional studies by both electrophysiological and behavioral methods.

Neuroprotective Gene Therapy by Overexpression of the Transcription Factor MAX in Rat Models of Glaucomatous Neurodegeneration.

PurposeBased on our preview evidence that reduced nuclear content of the transcription factor Myc-associated protein X (MAX) is an early event associated with degeneration of retinal ganglion cells (RGCs), in the present study, our purpose was to test whether the overexpression of human MAX had a neuroprotective effect against RGC injury.MethodsOverexpression of either MAX or green fluorescent protein (GFP) in the retina was achieved by intravitreal injections of recombinant adenovirus-associated viruses (rAAVs). Lister Hooded rats were used in three models of RGC degeneration: (1) cultures of retinal explants for 30 hours ex vivo from the eyes of 14-day-old rats that had received intravitreal injections of rAAV2-MAX or the control vector rAAV2-GFP at birth; (2) an optic nerve crush model, in which 1-month-old rats received intravitreal injection of either rAAV2-MAX or rAAV2-GFP and, 4 weeks later, were operated on; and (3) an ocular hypertension (OHT) glaucoma model, in which 1-month-old rats received intravitreal injection of either rAAV2-MAX or rAAV2-GFP and, 4 weeks later, were subject to cauterization of the limbal plexus. Cell death was estimated by detection of pyknotic nuclei and TUNEL technique and correlated with MAX immunocontent in an ex vivo model of retinal explants. MAX expression was detected by quantitative RT-PCR. In the OHT model, survival of RGCs was quantified by retrograde labeling with DiI or immunostaining for BRN3a at 14 days after in vivo injury. Functional integrity of RGCs was analyzed through pattern electroretinography, and damage to the optic nerve was examined in semithin sections.ResultsIn all three models of RGC insult, gene therapy by overexpression of MAX prevented RGC death. Also, ON degeneration and electrophysiologic deficits were prevented in the OHT model.ConclusionsOur experiments offer proof of concept for a novel neuroprotective gene therapy for glaucomatous neurodegeneration based on overexpression of MAX.

SARM1 Ablation Is Protective and Preserves Spatial Vision in an In Vivo Mouse Model of Retinal Ganglion Cell Degeneration.

The challenge of developing gene therapies for genetic forms of blindness is heightened by the heterogeneity of these conditions. However, mechanistic commonalities indicate key pathways that may be targeted in a gene-independent approach. Mitochondrial dysfunction and axon degeneration are common features of many neurodegenerative conditions including retinal degenerations. Here we explore the neuroprotective effect afforded by the absence of sterile alpha and Toll/interleukin-1 receptor motif-containing 1 (SARM1), a prodegenerative NADase, in a rotenone-induced mouse model of retinal ganglion cell loss and visual dysfunction. Sarm1 knockout mice retain visual function after rotenone insult, displaying preservation of photopic negative response following rotenone treatment in addition to significantly higher optokinetic response measurements than wild type mice following rotenone. Protection of spatial vision is sustained over time in both sexes and is accompanied by increased RGC survival and additionally preservation of axonal density in optic nerves of Sarm1−/− mice insulted with rotenone. Primary fibroblasts extracted from Sarm1−/− mice demonstrate an increased oxygen consumption rate relative to those from wild type mice, with significantly higher basal, maximal and spare respiratory capacity. Collectively, our data indicate that Sarm1 ablation increases mitochondrial bioenergetics and confers histological and functional protection in vivo in the mouse retina against mitochondrial dysfunction, a hallmark of many neurodegenerative conditions including a variety of ocular disorders.

Mutation profile of neurodegenerative mitochondriopathy – LHON in Southern India

BackgroundLeber’s Hereditary Optic Neuropathy (LHON) is a rare mitochondriopathy causing retinal ganglion cell degeneration resulting in central vision loss. It is caused by mitochondrial DNA (mtDNA) mutations and thus follows maternal inheritance pattern. MethodsWe analysed the whole mitochondrial genome in 100 South Indian LHON patients by utilizing Sanger and Next Generation Sequencing approaches. Haplogroup analysis was performed using HaploGrep2 to predict the risk group. Methylation changes in the mtDNA D-loop region were investigated by performing methylation-specific polymerase chain reaction (MSP). ResultsLHON associated mutations were detected in 55% of the patients of which 42% harboured the primary mutations and 13% harboured potentially pathogenic variants that were previously reported to cause LHON. The candidate mutations identified with confirmed pathogenicity are: m.11778G > A (38%), m.14484 T > C (3%), m.4171C > A (1%) and m.11696G > A (1%). MSP results demonstrated that the D-loop region was unmethylated in all the study subjects including mutation-positive patients, mutation-negative patients, asymptomatic carriers, and controls. Haplogroup-M was prevalent (69%) in the study cohort followed by R (14%), U (9%), N (3%), HV (2%), G (2%), and W (1%). The frequency of the predominant mutation m.11778G > A was found lower (̴ 11%) in haplogroup-U. ConclusionsSouth Indian LHON cohort shows a unique profile of mtDNA mutations and haplogroup association presumably with no role of D-loop methylation. MT-ND4, MT-ND5, and MT-ND1 serve as the hotspot genes in this cohort. The presence of LHON associated mutations in patients lacking the common primary mutations insists on the necessity of mitochondrial genome sequencing in individuals suspected with LHON.