Mitochondrial dysfunction as a cause of optic neuropathies

Targeting OPA1 protein for therapeutic intervention in autosomal dominant optic atrophy: In silico drug discovery

Autosomal dominant hereditary optic atrophy (ADOA) is a prevalent hereditary condition characterized by the gradual and simultaneous deterioration of vision. Mutations in Optic atrophy 1 (OPA1) have been linked to ADOA, the prevailing form of inherited optic neuropathy. However, the current therapeutic options are limited. This study aimed to identify a drug-like molecule that can serve as an activator of the OPA1 GTPase domain, using in silico virtual screening and molecular dynamic simulation pipeline. A ligand-based pharmacophore model was generated to identify the important biological entities in natural compounds, followed by virtual screening pipeline. Total 55,96,00 drug-like compounds were screened and then subsequently proceed for molecular docking, molecular dynamics simulation (200ns), MM-PBSA analysis, and ADMET (Swiss ADME server) studies. Virtual screening revealed the top-ranked compound ZINC000009190697 (-8 kcal/mol). Furthermore, the stability of the top hit compound at the active site of OPA1 was demonstrated using molecular dynamics simulations and MM-PBSA calculations. ADMET analysis assisted in the identification of the top hit compound as possible activators of OPA1 with optimal drug-like properties. These results indicated that there is need of further experimental assessment of the top-hit compound ZINC000009190697 in wet lab to confirm its efficacy as a potential OPA1 activator in both in vitro and in vivo studies.

Clinical and genetic landscape of optic atrophy in 826 families: insights from 50 nuclear genes

Hereditary optic neuropathies (HON) comprise a group of diseases caused by genetic defects in either the mitochondrial or nuclear genomes. The increasing availability of genetic testing has expanded the genetic and phenotypic spectrum of HON more broadly than previously recognized. The genetic and phenotypic landscape of HON is attributed to 50 nuclear genes, so we genetically analysed patients with suspected HON from a group of 4776 index cases following our previous study on 1516 probands with Leber's HON (LHON) who had mitochondrial DNA variants. Exome sequencing was performed in 473 probands diagnosed with nuclear gene-related HON (nHON) and 353 cases with unsolved LHON. Sequencing and variant interpretation of the 50 nuclear genes indicated that the diagnostic yield of exome sequencing for nHON was 31.50% (149/473), while it was markedly lower [1.42% (5/353)] for LHON patients without primary mtDNA mutations. The top five genes implicated in nHON in our in-house cohort were OPA1, WFS1, FDXR, ACO2 and AFG3L2, which accounted for 82.46% of probands. Although OPA1 was the most prevalent nHON-causative gene in both our cohort (53.25%) and a literature review (37.09%), the predominance of OPA1, WFS1 and FDXR differed significantly between our in-house cohort and the literature review (P-adjusted < 0.001). Fundus changes in nHON could be stratified into three categories: the most common was optic atrophy at examination (78.79%); the rarest was LHON-like optic atrophy (3.64%); and optic atrophy with concurrent retinal degeneration (17.57%), an independent risk factor for visual prognosis in nHON, occurred at an intermediate frequency. A systematic genotype-phenotype analysis highlighted different genetic contributions for ocular, extraocular neurological and extraocular non-neurological phenotypes. In addition, systemic variant analysis at the individual gene level suggested a revised interpretation of the pathogenicity of a WFS1 heterozygous truncation variant. This study provides a panoramic view of the genetic and phenotypic profiles of HON in a real-world study and the literature. The categories of nHON fundus phenotypes will benefit future studies on the molecular mechanisms underlying HON and targeted therapies. In addition to routine ophthalmic examinations, careful examination of extraocular symptoms and meaningful genetic counselling are warranted for patients with nHON.

Mitochondria in aging and age-associated diseases

Mitochondria, essential for cellular energy, are crucial in neurodegenerative disorders (NDDs) and their age-related progression. This review highlights mitochondrial dynamics, mitovesicles, homeostasis, and organelle communication. We examine mitochondrial impacts from aging and NDDs, focusing on protein aggregation and dysfunction. Prospective therapeutic approaches include enhancing mitophagy, improving respiratory chain function, maintaining calcium and lipid balance, using microRNAs, and mitochondrial transfer to protect function. These strategies underscore the crucial role of mitochondrial health in neuronal survival and cognitive functions, offering new therapeutic opportunities.

Correlation of Structure With Function: Future Utilities for Optical Coherence Tomography Angiography in Neuro-Ophthalmology

Optical coherence tomography angiography is a burgeoning imaging modality in Ophthalmology. In this review, we outline the breadth of potential utility for optical coherence tomography angiography for diagnosis and prognostication in neuro-ophthalmology. Further mapping of the characteristics and natural history of the optic disc vascular network in neuro-ophthalmic conditions is necessary to increase the utility of this imaging modality for neuro-ophthalmic conditions, as the specificity and sensitivity of optical coherence tomography angiography are currently limited by the small pool of available observational data.

Isolated and Syndromic Genetic Optic Neuropathies: A Review of Genetic and Phenotypic Heterogeneity

Nonsyndromic and syndromic hereditary optic neuropathies (HONs) encompass a variety of genetic illnesses that cause progressive optic nerve damage, resulting in considerable vision impairment. These disorders result from pathogenic variants in mitochondrial or nuclear DNA, impacting essential cellular processes like oxidative phosphorylation, mitochondrial dynamics, and neuroprotection. Advances in next-generation sequencing (NGS) have significantly improved the identification of genetic variations, enabling precise diagnoses and genotype-phenotype correlations. This review consolidates current knowledge regarding the classification, molecular pathogenesis, clinical manifestations, diagnostic methodologies, and emerging therapeutic strategies for HONs. The critical role of mitochondrial dysfunction in optic nerve degeneration highlights the necessity for multimodal therapeutic approaches. Recent clinical trials evaluating gene therapy for Leber hereditary optic neuropathy (LHON) and neuroprotective strategies in dominant optic atrophy (DOA) are discussed. Additionally, individualized therapeutic interventions, as demonstrated by recent case studies involving tailored gene therapies, are evaluated. The integration of molecular and imaging biomarkers in future personalized treatment strategies aims to enhance prognosis and therapeutic outcomes.

Alterations in ganglion cell and nerve fiber layer in Leber hereditary optic neuropathy across clinical stages

PURPOSE

LHON leads to gradual, painless, and permanent vision loss in both eyes, often associated with central scotomas. As the condition progresses, there is a decline in visual function, accompanied by noticeable structural alterations. This study focused on evaluating the clinical characteristics of patients with differing LHON stages, with a specific emphasis on optical coherence tomography (OCT) imaging results.

METHODS

This analysis included 22 individuals with LHON. Patients underwent thorough clinical ophthalmologic assessments, including SD-OCT, Visual evoked potentials, and perimetry. When LHON was suspected, blood samples were obtained to test for the three major mitochondrial mutations (G1178A, T14484C, G3460A), with further sequencing to identify additional known mutations. The data were subsequently examined through descriptive statistical methods.

RESULTS

The clinical characteristics of 22 individuals (median age 33, range 9-68) were examined. All participants carried a mutation linked to LHON. The most prevalent mutation was G11778A (55%), followed by G3460A (23%), T14484C (14%), with one instance each of the rare G13042A and C3461T mutations. Fourteen participants experienced acute vision loss (average duration: 5.2 ± 5 months), while eight had chronic LHON. There was no significant difference in visual acuity (VA, logMAR) between the two groups (0.9 vs. 0.9, p = 0.91). However, chronic patients exhibited significantly reduced the retinal nerve fiber layer (RNFL), especially in the temporal region (32 μm vs. 56 μm, p < 0.0001), but not in the nasal region. Ganglion cell layer (GCL) thickness was also notably thinner in the temporal area for chronic patients compared to those with acute LHON (22 μm vs. 28 μm, p = 0.04). Linear regression analysis showed correlations between RNFL and GCL and visual acuity (R² = 0.18, p = 0.007 and R² = 0.1, p = 0.05).

CONCLUSION

In our analysis, we observed an unusual pattern in the genetic mutations, with G3460A being the second most frequent, rather than T14484C, which may be attributed to the limited sample size. 14 patients experienced acute or subacute vision loss, while eight were assessed for chronic disease. Those with chronic LHON demonstrated significantly thinner GCL and RNFL. These results underscore the importance of accelerating both diagnosis and treatment to facilitate prompt intervention for patients.

Remarkable visual improvement in Leber hereditary optic neuropathy

PURPOSE

Leber hereditary optic neuropathy (LHON) typically has a poor visual outcome. In this study, we examined 8 cases of LHON that demonstrated remarkable visual improvement.

STUDY DESIGN

Retrospective observational study, clinical case series METHODS: We analyzed the clinical histories and outcomes of 8 patients (16 eyes) whose best corrected visual acuity (BCVA) improved to 0.7 or higher in at least 1 eye.

RESULTS

The median age of onset of the 7 male patients and 1 female patient was 17 years (range 8-58). Genetic testing revealed m.11778G>A mutations in 6 and m.14484T>C mutations in 2 of the patients. Of the 16 eyes, 15 improved to a BCVA of 0.7 or higher, whilst 1 eye achieved a final BCVA of 0.5. The lowest BCVA was below 0.1 in 12/16 eyes. BCVA improved to 0.1 or better within 1 year in 6/12 eyes and to 0.7 or better within 2 years in 12/15 eyes. In 10 eyes monitored by use of Humphrey Field Analysis (HFA; Fastpac, 30-2 program), the mean deviation improved from - 13.2 dB (- 23.6 to - 4.54) at its lowest to - 5.0 dB (- 15.6 to - 0.9) at the final measurement. Final HFA showed residual defects in the temporal region in 7/16 eyes. In the chronic phase, 10/12 eyes displayed either normal optic disc findings or partial temporal pallor.

CONCLUSION

In LHON cases with remarkable visual improvement, the recovery began earlier, and the visual field defects were relatively mild and tended to persist in the temporal region after improvement. Understanding these cases of notable improvement may inform future treatment strategies.

Macular Oxygen Saturation in Glaucoma Using Retinal Oximetry of Visible Light Optical Coherence Tomography: A Pilot Study

Purpose

A cross-sectional pilot study to compare macular oxygen saturation (sO2) and associated clinical measurements between normal and glaucoma subjects and to evaluate whether macular sO2 can be a diagnostic metric for early-stage glaucoma.

Methods

Forty-eight eyes of 35 subjects from three groups were included: normal subjects (16 eyes, 10 subjects), suspect/pre-perimetric glaucoma (GS/PPG) subjects (17 eyes, 12 subjects), and perimetric glaucoma (PG) subjects (15 eyes, 13 subjects). We performed retinal oximetry of visible light optical coherence tomography (VIS-OCT) in macular vessels, with 512 × 256 sampling points over a 5 × 5 mm2 area. Zeiss Cirrus OCT scans and a 24-2 visual field test (VFT) were conducted. Statistical analysis was conducted.

Results

Significant differences were observed among the three groups for all VIS-OCT, Zeiss OCT, and VFT variables. As glaucoma severity increased, macular AsO2 (arterial sO2) and A-V sO2 (arteriovenous sO2 difference) decreased, whereas macular VsO2 (venous sO2) increased. Macular AsO2 and A-V sO2 were found to be statistically correlated with ganglion cell layer + inner plexiform layer (GCL+IPL) and circumpapillary retinal nerve fiber layer in all eyes, as well as in PG eyes. Within the PG group, a dominant correlation between AsO2 and ganglion cell layer + inner plexiform layer was observed in the more damaged lower hemifield.

Conclusions

Glaucoma subjects showed altered macular sO2, indicating reduced oxygen consumption. The sO2 measured by VIS-OCT could be a potential metric for early glaucoma diagnosis.

Translational Relevance

This study shows macular sO2 measurements via VIS-OCT could bridge advanced imaging technology and clinical glaucoma detection.

The optic nerve in spaceflight: novel concepts in the pathogenesis of optic disc edema in microgravity

PURPOSE OF REVIEW

Spaceflight-associated neuro-ocular syndrome (SANS) encompasses a unique constellation of neuro-ocular findings in astronauts, including optic disc edema (ODE), globe flattening, chorioretinal folds, and hyperopic refractive shift. Although there are numerous neuro-ocular findings in SANS, the purpose of this review is to describe the novel, emerging concepts of the pathogenesis for the ODE specifically in SANS.

RECENT FINDINGS

While the initial hypotheses on the pathogenesis of ODE in SANS focused on possible elevated intracranial pressures (i.e., papilledema), the most prominent current hypothesis is microgravity-induced cephalad fluid shift. More recent studies however suggest that the pathogenesis of the ODE in SANS is likely multifactorial including possible underlying metabolic and genetic components.

SUMMARY

We review the literature on ODE in SANS including recent work integrating the complex physiologic interactions of microgravity-induced disruption in intracerebral and intraocular fluid dynamics, vascular congestion, cellular stress responses, and genetic predisposition. We believe that the development of ODE in SANS is likely multifactorial in origin, and further understanding of the mechanical, cellular, metabolic, and genetic components is of utmost importance to develop future countermeasures in preparation for possible future crewed missions to the moon, the asteroid belt, and Mars.

Sequencing and characterizing human mitochondrial genomes in the biobank-based genomic research paradigm

Human mitochondrial DNA (mtDNA) harbors essential mutations linked to aging, neurodegenerative diseases, and complex muscle disorders. Due to its uniparental and haploid inheritance, mtDNA captures matrilineal evolutionary trajectories, playing a crucial role in population and medical genetics. However, critical questions about the genomic diversity patterns, inheritance models, and evolutionary and medical functions of mtDNA remain unresolved or underexplored, particularly in the transition from traditional genotyping to large-scale genomic analyses. This review summarizes recent advancements in data-driven genomic research and technological innovations that address these questions and clarify the biological impact of nuclear-mitochondrial segments (NUMTs) and mtDNA variants on human health, disease, and evolution. We propose a streamlined pipeline to comprehensively identify mtDNA and NUMT genomic diversity using advanced sequencing and computational technologies. Haplotype-resolved mtDNA sequencing and assembly can distinguish authentic mtDNA variants from NUMTs, reduce diagnostic inaccuracies, and provide clearer insights into heteroplasmy patterns and the authenticity of paternal inheritance. This review emphasizes the need for integrative multi-omics approaches and emerging long-read sequencing technologies to gain new insights into mutation mechanisms, the influence of heteroplasmy and paternal inheritance on mtDNA diversity and disease susceptibility, and the detailed functions of NUMTs.

A bibliometric analysis of optic atrophy from 2003 to 2023: research trends and hot spots

Background

Optic atrophy (OA) is primarily caused by damage to the retinal pathway system, including widespread degeneration of retinal ganglion cells and axons, leading to visual impairment and blindness. Despite its clinical significance and diverse etiological factors, there is currently a lack of comprehensive bibliometric analyses exploring research trends and hotspots within this field.

Method

This study retrieved relevant literature on OA published between 2003 and 2023 from the Web of Science Core Collection database. We conducted a bibliometric analysis using tools such as CiteSpace, VOSviewer, and SCImago Graphica to examine annual publication trends, co-occurrence patterns, collaborative networks among countries and institutions, and the evolution of research hotspots of OA.

Results

A total of 5,274 publications were included in the bibliometric analysis, comprising 4,561 research articles and 713 review articles. The United States emerged as the leading country in OA research, followed by Germany and China. Over the past two decades, the primary research hotspots focused on "mitochondrial dysfunction," "hereditary optic neuropathy," "ocular hypertension" and "diagnostic techniques." Future research trends are likely to revolve around "molecular mechanisms" and "therapeutic targets."

Conclusion

This bibliometric analysis provides an overview of research developments in OA over the past 20 years, highlighting the emphasis on the pathological basis of OA and advancements in diagnostic and therapeutic approaches. Future studies should continue to explore the molecular basis of mitochondrial dysfunction to identify potential gene therapy targets for treating OA.

Visual recovery in a patient with optic neuropathy secondary to copper deficiency

Purpose

To highlight the utility of ganglion cell layer (GCL) analysis in early diagnosis of optic neuropathy secondary to copper deficiency and emphasize the importance of timely repletion for visual recovery.

Observations

A 67-year-old woman presented with four months of gradually decreasing vision bilaterally. Medical history was significant for Stage I duodenal and Stage III colon cancer treated with Whipple surgery and hemicolectomy. Her visual acuity at presentation was counting-fingers vision in both eyes (OU). No relative afferent pupillary defect was noted. Fundus exam revealed a questionable trace temporal optic disc pallor with symmetric cup-to-disk ratio of 0.4 OU. Intraocular pressures were within normal limits OU. On initial optical coherence tomography (OCT) analysis, retinal nerve fiber layer (RNFL) measurements were normal OU; however, GCL loss was noted in both eyes, left eye (OS) being worse than right eye (OD). On subsequent formal visual field testing, she had cecocentral scotoma and large nasal step in both eyes, again worse in OS. Laboratory investigations revealed a significantly depleted copper level at less than 500 μg per liter (normal limit of 810-1990), while levels of B1 (thiamine), B9 (folic acid), and B12 (cobalamin) levels were within normal limits. She was started on oral copper supplementation. At 2-year follow-up, her best corrected visual acuity improved to 20/25 OD and 20/40 OS while maintained on oral copper repletion.

Conclusions and importance

Optic neuropathy secondary to copper deficiency is a rare but treatable cause of vision loss. In early stages of disease, early GCL loss may precede changes in the RNFL thickness or even appearance of obvious disc pallor on fundus exam. Visual recovery post repletion may be favorable if detected in a timely fashion.

Metabolomic Profiling of Open-Angle Glaucoma Etiologic Endotypes: Tohoku Multi-Omics Glaucoma Study

Purpose

The purpose of this study was to investigate biologically meaningful endotypes of open-angle glaucoma (OAG) by applying unsupervised machine learning to plasma metabolites.

Methods

This retrospective longitudinal cohort study enrolled consecutive patients aged ≥20 years with OAG at Tohoku University Hospital from January 2017 to January 2020. OAG was confirmed based on comprehensive ophthalmic examinations. Among the 523 patients with OAG with available clinical metabolomic data, 173 patients were longitudinally followed up for ≥2 years, with available data from ≥5 reliable visual field (VF) tests without glaucoma surgery. We collected fasting blood samples and clinical data at enrollment and nuclear magnetic resonance spectroscopy to profile 45 plasma metabolites in a targeted approach. After computing a distance matrix of preprocessed metabolites with Pearson distance, gap statistics determined the optimal number of OAG endotypes. Its risk factors, clinical presentations, metabolomic profiles, and progression rate of sector-based VF loss were compared across endotypes.

Results

Five distinct OAG endotypes were identified. The highest-risk endotype (endotype B) showed a significant faster progression of central VF loss (P = 0.007). Compared with patients with other endotypes, those with endotype B were more likely to have a high prevalence of dyslipidemia, cold extremities, oxidative stress, and low OAG genetic risk scores. Pathway analysis of metabolomic profiles implicated altered fatty acid and ketone body metabolism in this endotype, with 34 differentially enriched pathways (false discovery rate [FDR] < 0.05).

Conclusions

Integrated metabolomic profiles identified five distinct etiologic endotypes of OAG, suggesting pathological mechanisms related with a high-risk group of central vision loss progression in the Japanese population.

Massively parallel sequencing of mitochondrial genome in primary open angle glaucoma identifies somatically acquired mitochondrial mutations in ocular tissue

Glaucoma is a sight threatening neurodegenerative condition of the optic nerve head associated with ageing and marked by the loss of retinal ganglion cells. Mitochondrial dysfunction plays a crucial role in the pathogenesis of neurodegeneration in the most prevalent type of glaucoma: primary open angle glaucoma (POAG). All previous mitochondrial genome sequencing studies in POAG analyzed mitochondrial DNA (mtDNA) isolated from peripheral blood leukocytes and have not evaluated cells derived from ocular tissue, which better represent the glaucomatous disease context. In this study, we evaluated mitochondrial genome variation and heteroplasmy using massively parallel sequencing of mtDNA in a cohort of patients with POAG, and in a subset assess the role of somatic mitochondrial genome mutations in disease pathogenesis using paired samples of peripheral blood leukocytes and ocular tissue (Tenon's ocular fibroblasts). An enrichment of potentially pathogenic nonsynonymous mtDNA variants was identified in Tenon's ocular fibroblasts from participants with POAG. The absence of oxidative DNA damage and predominance of transition variants support the concept that errors in mtDNA replication represent the predominant mutation mechanism in Tenon's ocular fibroblasts from patients with POAG. Pathogenic somatic mitochondrial genome mutations were observed in people with POAG. This supports the role of somatic mitochondrial genome variants in the etiology of glaucoma.

MSC-mediated mitochondrial transfer restores mitochondrial DNA and function in neural progenitor cells of Leber's hereditary optic neuropathy

Leber's hereditary optic neuropathy (LHON) is a debilitating mitochondrial disease associated with mutations in mitochondrial DNA (mtDNA). Unfortunately, the available treatment options for LHON patients are limited due to challenges in mitochondrial replacement. In our study, we reprogramming LHON urine cells into induced pluripotent stem cells (iPSCs) and differentiating them into neural progenitor cells (NPCs) and neurons for disease modeling. Our research revealed that LHON neurons exhibited significantly higher levels of mtDNA mutations and reduced mitochondrial function, confirming the disease phenotype. However, through co-culturing LHON iPSC-derived NPCs with mesenchymal stem cells (MSCs), we observed a remarkable rescue of mutant mtDNA and a significant improvement in mitochondrial metabolic function in LHON neurons. These findings suggest that co-culturing with MSCs can enhance mitochondrial function in LHON NPCs, even after their differentiation into neurons. This discovery holds promise as a potential therapeutic strategy for LHON patients.

Targeting the PINK1/Parkin pathway: A new perspective in the prevention and therapy of diabetic retinopathy

Diabetic retinopathy (DR) is a microvascular complication of diabetes characterized by neurovascular impairment of the retina. The dysregulation of the mitophagy process occurs before apoptotic cell death and the appearance of vascular damage. In particular, mitochondrial alterations happen during DR development, supporting the hypothesis that mitophagy is negatively correlated to disease progression. This process is mainly regulated by the PTEN-induced putative kinase protein 1 (PINK1)/Parkin pathway whose activation promotes mitophagy. In this review, we will summarize the evidence reported in the literature demonstrating the involvement of the PINK1/Parkin pathway in diabetic retinopathy-induced retinal degeneration.

Ganglion Cell Complex Thickness and Visual Function in Chronic Leber Hereditary Optic Neuropathy

Purpose

To evaluate the correlation between the macular ganglion cell complex (GCC) thickness measured with manually corrected segmentation and visual function in individuals with chronic Leber hereditary optic neuropathy (LHON).

Methods

Twenty-six chronic LHON subjects (60% treated with idebenone or Q10) from the Swedish LHON registry were enrolled. Best-corrected visual acuity (BCVA), visual field tests, and optical coherence tomography (OCT) were performed. Visual field was evaluated with the Haag-Streit Octopus 900 with the Esterman test and a custom 30° test. Canon OCT-HS100 scans were exported to the Iowa Reference Algorithm. GCC thickness was obtained after the segmentation was corrected manually in nine macular sectors.

Results

The GCC thickness was overestimated by 16 to 30 µm in different macular sectors with the automated segmentation compared with the corrected (P < 0.001). GCC thickness in all sectors showed significant correlation with all functional parameters. The strongest correlation was seen for the external temporal sector (BCVA: r = 0.604, P < 0.001; mean defect: r = 0.457, P = 0.001; Esterman score: r = 0.421, P = 0.003). No differences were seen between treated and untreated subjects with regard to GCC and visual field scores (P > 0.05), but BCVA was better among treated subjects (P = 0.017).

Conclusions

The corrected GCC thickness showed correlation with visual function in chronic LHON subjects. The frequently occurring segmentation errors in OCT measurements related to chronic LHON can potentially be misleading in monitoring of disease progression and in evaluating the treatment effects. Precise measurements of GCC could serve as a sensitive tool to monitor structural changes in LHON. We therefore emphasize the importance of careful evaluation of the accuracy of OCT segmentation.

l-Serine Protects Murine Retinal Ganglion Cells from Oxidative Stress via Modulation of Mitochondrial Dysfunction

PURPOSE

This study aimed to investigate the effects of l-serine on mitochondrial dysfunction in retinal ganglion cells after exposure to H2O2-induced oxidative stress.

METHODS

Retinal ganglion cells obtained from C57BL6 mice (postnatal days 1-4) were purified and cultured. A cell viability assay was performed following exposure to H2O2-induced oxidative stress to assess the cytoprotective effects of l-serine on retinal ganglion cells. Flow cytometry with CellROX Deep Red and MitoSOX dyes was performed to analyze the cytoplasmic and mitochondrial reactive oxygen species levels, respectively. Staining with the fluorescent probe JC-1 was used to detect changes in the mitochondrial membrane potential. The oxygen consumption rate and Bioenergetic Health Index were used to evaluate mitochondrial respiration.

RESULTS

H2O2 treatment was found to induce mitochondrial dysfunction in retinal ganglion cells. Pretreatment with l-serine prevented cytotoxicity and significantly increased the viability of retinal ganglion cells following exposure to H2O2-induced oxidative stress (p < .05). l-Serine alleviated reactive oxygen species production in retinal ganglion cells following exposure to H2O2-induced oxidative (p < .05). Further, it successfully mitigated H2O2-induced mitochondrial depolarization in retinal ganglion cells (p < .05) and significantly increased the oxygen consumption rate and Bioenergetic Health Index in retinal ganglion cells following exposure to H2O2-induced oxidative stress (p < .05).

CONCLUSION

Pretreatment with l-serine protected retinal ganglion cells from H2O2-induced oxidative stress by improving mitochondrial function. The findings of the present study suggest that l-serine is a potential candidate for treatment of reactive oxygen species-related ocular diseases such as mitochondrial optic neuropathies.

Spectrum of rare and common mitochondrial DNA variations from 1029 whole genomes of self-declared healthy individuals from India

Mitochondrial disorders are a class of heterogeneous disorders caused by genetic variations in the mitochondrial genome (mtDNA) as well as the nuclear genome. The spectrum of mtDNA variants remains unexplored in the Indian population. In the present study, we have cataloged 2689 high confidence single nucleotide variants, small insertions and deletions in mtDNA in 1029 healthy Indian individuals. We found a major proportion (76.5 %) of the variants being rare (AF<=0.005) in the studied population. Intriguingly, we found two 'confirmed' pathogenic variants (m.1555 A>G and m.14484 T>C) with a frequency of ∼1 in 250 individuals in our dataset. The high carrier frequency underscores the need for screening of the mtDNA pathogenic mutations in newborns in India. Interestingly, our analysis also revealed 202 variants in our dataset which have been 'reported' in disease cases as per the MITOMAP database. Additionally, we found the frequency of haplogroup M (52.2 %) to be the highest among all the 18 top-level haplogroups found in our dataset. In comparison to the global population datasets, 20 unique mtDNA variants are found in the Indian population. We hope the whole genome sequencing based compendium of mtDNA variants along with their allele frequencies and heteroplasmy levels in the Indian population will drive additional genome scale studies for mtDNA. Furthermore, the identification of clinically relevant variants in our dataset will aid in better clinical interpretation of the variants in mitochondrial disorders.

Glaucoma, More than Meets the Eye: Patterns of Demyelination Revealed in Human Postmortem Glaucomatous Optic Nerve

Glaucoma is a neurodegenerative disease affecting millions worldwide, characterised by retinal ganglion cell (RGC) degeneration which leads to blindness in more advanced cases. Although the pathogenesis and underlying mechanisms of glaucoma are not fully understood, there are theories that hint at demyelination playing a role in the disease process. Demyelination, or the degeneration of the myelin sheath surrounding axons, has been found in previous studies using animal models of glaucoma and clinical assessments of glaucoma patients. However, this has not been fully realised or quantified in glaucoma patients. Utilising postmortem optic nerve samples from glaucoma and healthy subjects, various immunohistochemical and morphological assessments were performed to determine the extent, if any, of demyelination in glaucomatous optic nerves. Our findings revealed that alongside nerve shrinkage and degeneration of nerve tissue fascicles, there were significantly less myelin proteins, specifically myelin basic protein (MBP), in glaucoma optic nerves. Additionally, the loss of MBP was correlated with decreased oligodendrocyte (OLG) precursors and increasing glial activity. This further supports previous evidence that demyelination may be a secondary degenerative process associated with glaucoma disease progression. Not only do these results provide evidence for potential disease mechanisms, but this is also the first study to quantify optic nerve demyelination in glaucoma postmortem tissue.

Recognizing Leber's Hereditary Optic Neuropathy to avoid delayed diagnosis and misdiagnosis

Leber's Hereditary Optic Neuropathy (LHON) is a maternally inherited optic nerve disease primarily caused by mutations in mitochondrial DNA (mtDNA). The peak of onset is typically between 15 and 30 years, but variability exists. Misdiagnosis, often as inflammatory optic neuritis, delays treatment, compounded by challenges in timely genetic diagnosis. Given the availability of a specific treatment for LHON, its early diagnosis is imperative to ensure therapeutic appropriateness. This work gives an updated guidance about LHON differential diagnosis to clinicians dealing also with multiple sclerosi and neuromyelitis optica spectrtum disorders-related optic neuritis. LHON diagnosis relies on clinical signs and paraclinical evaluations. Differential diagnosis in the acute phase primarily involves distinguishing inflammatory optic neuropathies, considering clinical clues such as ocular pain, fundus appearance and visual recovery. Imaging analysis obtained with Optical Coherence Tomography (OCT) assists clinicians in early recognition of LHON and help avoiding misdiagnosis. Genetic testing for the three most common LHON mutations is recommended initially, followed by comprehensive mtDNA sequencing if suspicion persists despite negative results. We present and discuss crucial strategies for accurate diagnosis and management of LHON cases.

Leber's Hereditary Optic Neuropathy with Retinal Hemorrhage

Leber's hereditary optic neuropathy (LHON) causes subacute visual loss, and, in the acute phase, the optic disc shows hyperemia, peripapillary telangiectasia, and swelling of the retinal nerve fiber layer (RNFL). Rarely, retinal hemorrhage may be present. In this study, we investigated LHON cases with retinal hemorrhage in the acute phase. Among 82 cases (164 eyes) of LHON who visited the Inoue Eye Hospital, retinal hemorrhage was observed in 5 cases (5 eyes). The age at onset was 36 (27-46) years, with 4 male cases. Mitochondrial DNA analysis revealed the presence of the m.11778G > A variant in four patients and the m.14484T > C variant in one patient. There was no medical history and no excessive smoking or alcohol consumption in any of the cases. In all cases, retinal hemorrhages were observed in the RNFL, accompanying the characteristic optic disc findings of LHON. Fluorescein angiography performed in three cases showed no leakage from the optic disc or blood vessels. While rare, the presence of retinal hemorrhage along the RNFL during the acute phase of LHON should be recognized, as it may warrant consideration of alternative diagnoses.

Generation of an Armcx1 Conditional Knockout Mouse

Armadillo repeat-containing X-linked protein-1 (Armcx1) is a poorly characterized transmembrane protein that regulates mitochondrial transport in neurons. Its overexpression has been shown to induce neurite outgrowth in embryonic neurons and to promote retinal ganglion cell (RGC) survival and axonal regrowth in a mouse optic nerve crush model. In order to evaluate the functions of endogenous Armcx1 in vivo, we have created a conditional Armcx1 knockout mouse line in which the entire coding region of the Armcx1 gene is flanked by loxP sites. This Armcx1fl line was crossed with mouse strains in which Cre recombinase expression is driven by the promoters for β-actin and Six3, in order to achieve deletion of Armcx1 globally and in retinal neurons, respectively. Having confirmed deletion of the gene, we proceeded to characterize the abundance and morphology of RGCs in Armcx1 knockout mice aged to 15 months. Under normal physiological conditions, no evidence of aberrant retinal or optic nerve development or RGC degeneration was observed in these mice. The Armcx1fl mouse should be valuable for future studies investigating mitochondrial morphology and transport in the absence of Armcx1 and in determining the susceptibility of Armcx1-deficient neurons to degeneration in the setting of additional heritable or environmental stressors.

Mitochondrial Parkinsonism: A Practical Guide to Genes and Clinical Diagnosis

BACKGROUND

Primary mitochondrial diseases (PMDs) are the most common inborn errors of energy metabolism, with a combined prevalence of 1 in 4300. They can result from mutations in either nuclear DNA (nDNA) or mitochondrial DNA (mtDNA). These disorders are multisystemic and mainly affect high energy-demanding tissues, such as muscle and the central nervous system (CNS). Among many clinical features of CNS involvement, parkinsonism is one of the most common movement disorders in PMDs.

METHODS

This review provides a pragmatic educational overview of the most recent advances in the field of mitochondrial parkinsonism, from pathophysiology and genetic etiologies to phenotype and diagnosis.

RESULTS

mtDNA maintenance and mitochondrial dynamics alterations represent the principal mechanisms underlying mitochondrial parkinsonism. It can be present in isolation, alongside other movement disorders or, more commonly, as part of a multisystemic phenotype. Mutations in several nuclear-encoded genes (ie, POLG, TWNK, SPG7, and OPA1) and, more rarely, mtDNA mutations, are responsible for mitochondrial parkinsonism. Progressive external opthalmoplegia and optic atrophy may guide genetic etiology identification.

CONCLUSION

A comprehensive deep-phenotyping approach is needed to reach a diagnosis of mitochondrial parkinsonism, which lacks distinctive clinical features and exemplifies the intricate genotype-phenotype interplay of PMDs.

Axonal mitophagy in retinal ganglion cells

Neurons, exhibiting unique polarized structures, rely primarily on the mitochondrial production of ATP to maintain their hypermetabolic energy requirements. To maintain a normal energy supply, mitochondria are transported to the distal end of the axon. When mitochondria within the axon are critically damaged beyond their compensatory capacity, they are cleared via autophagosomal phagocytosis, and the degradation products are recycled to replenish energy. When the mitochondria are dysfunctional or their transport processes are blocked, axons become susceptible to degeneration triggered by energy depletion, resulting in neurodegenerative diseases. As the final checkpoint for mitochondrial quality control, axonal mitophagy is vital for neuronal growth, development, injury, and regeneration. Furthermore, abnormal axonal mitophagy is crucial in the pathogenesis of optic nerve-related diseases such as glaucoma. We review recent studies on axonal mitophagy and summarize the progress of research on axonal mitophagy in optic nerve-related diseases to provide insights into diseases associated with axonal damage in optic ganglion cells.

A computational study to assess the pathogenicity of single or combinations of missense variants on respiratory complex I

Variants found in the respiratory complex I (CI) subunit genes encoded by mitochondrial DNA can cause severe genetic diseases. However, it is difficult to establish a priori whether a single or a combination of CI variants may impact oxidative phosphorylation. Here we propose a computational approach based on coarse-grained molecular dynamics simulations aimed at investigating new CI variants. One of the primary CI variants associated with the Leber hereditary optic neuropathy (m.14484T>C/MT-ND6) was used as a test case and was investigated alone or in combination with two additional rare CI variants whose role remains uncertain. We found that the primary variant positioned in the E-channel region, which is fundamental for CI function, stiffens the enzyme dynamics. Moreover, a new mechanism for the transition between π- and α-conformation in the helix carrying the primary variant is proposed. This may have implications for the E-channel opening/closing mechanism. Finally, our findings show that one of the rare variants, located next to the primary one, further worsens the stiffening, while the other rare variant does not affect CI function. This approach may be extended to other variants candidate to exert a pathogenic impact on CI dynamics, or to investigate the interaction of multiple variants.

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

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

Electroretinographic oscillatory potentials in Leber hereditary optic neuropathy

PURPOSE

Leber hereditary optic neuropathy (LHON) affects retinal ganglion cells causing severe vision loss. Pattern electroretinogram and photopic negative response (PhNR) of the light-adapted (LA) full-field electroretinogram (ERG) are typically affected in LHON. In the present study, we evaluated dark-adapted (DA) and LA oscillatory potentials (OPs) of the flash ERG in genetically characterized LHON patients to dissociate slow from fast components of the response.

METHODS

Seven adult patients (mean age = 28.4 ± 5.6) in whom genetic diagnosis confirmed LHON with mtDNA or nuclear DNAJC30 (arLHON) pathogenic variants were compared to 12 healthy volunteers (mean age = 35.0 ± 12.1). Full-field ERGs were recorded from both eyes. Offline digital filters at 50, 75 and 100 Hz low cutoff frequencies were applied to isolate high-frequency components from the original ERG signals.

RESULTS

ERG a-waves and b-waves were comparable between LHON patients and controls, while PhNR was significantly reduced (p = 0.009) in LHON patients compared to controls, as expected. OPs derived from DA signals (75 Hz low cutoff frequency) showed reduced peak amplitude for OP2 (p = 0.019). LA OP differences between LHON and controls became significant (OP2: p = 0.047, OP3: p = 0.039 and OP4: p = 0.013) when the 100 Hz low-cutoff frequency filter was applied.

CONCLUSIONS

Reduced OPs in LHON patients may represent disturbed neuronal interactions in the inner retina with preserved photoreceptoral (a-wave) to bipolar cell (b-wave) activation. Reduced DA OP2 and high-cutoff LA OP alterations may be further explored as functional measures to characterize LHON status and progression.

Gene therapy for Leber hereditary optic neuropathy

INTRODUCTION

Leber hereditary optic neuropathy (LHON) is among the most frequent inherited mitochondrial disease, causing a severe visual impairment, mostly in young-adult males. The causative mtDNA variants (the three common are m.11778 G>A/MT-ND4, m.3460 G>A/MT-ND1, and m.14484T>C/MT-ND6) by affecting complex I impair oxidative phosphorylation in retinal ganglion cells, ultimately leading to irreversible cell death and consequent functional loss. The gene therapy based on allotopic expression of a wild-type transgene carried by adeno-associated viral vectors (AVV-based) appears a promising approach in mitochondrial disease and its efficacy has been explored in several large clinical trials.

AREAS COVERED

The review work employed basic concepts in mitochondrial diseases, LHON, and gene therapy procedures. Reports from completed trials in LHON (i.e. RESCUE) were reviewed and critically compared.

EXPERT OPINION

New challenges, as the improvement of the contralateral untreated eye or the apparently better outcome in patients treated in later stages (6-12 months), were highlighted by the latest gene therapy trials. A better understanding of the pathogenetic mechanisms of the disease together with combined therapy (medical and gene therapy) and optimization in genetic correction approaches could improve the visual outcome of treated eyes.

[Leber's hereditary optic neuropathy]

Leber's hereditary optic atrophy (LHON) is a genetic optic neuropathy that is more prevalent in young males but can occur from childhood to old age. The primary cause is mitochondrial genetic mutations, which are associated with dysfunction of mitochondrial electron transport chain complex I. It manifests as acute to subacute visual impairment, often starting unilaterally but progressing to involve both eyes within weeks to months. Visual loss is severe, with many patients having corrected visual acuity below 0.1. The differential diagnosis of optic neuritis is essential, and assessments such as pupillary light reflex, fluorescein fundus angiography, and magnetic resonance imaging can be useful for differentiation. LHON should be considered as one of the differential diagnoses for optic neuritis, and collaboration between neurologists and ophthalmologists is crucial for accurate diagnosis and appropriate treatment.

Compartmental Differences in the Retinal Ganglion Cell Mitochondrial Proteome

Among neurons, retinal ganglion cells (RGCs) are uniquely sensitive to mitochondrial dysfunction. The RGC is highly polarized, with a somatodendritic compartment in the inner retina and an axonal compartment projecting to targets in the brain. The drastically dissimilar functions of these compartments implies that mitochondria face different bioenergetic and other physiological demands. We hypothesized that compartmental differences in mitochondrial biology would be reflected by disparities in mitochondrial protein composition. Here, we describe a protocol to isolate intact mitochondria separately from mouse RGC somatodendritic and axonal compartments by immunoprecipitating labeled mitochondria from RGC MitoTag mice. Using mass spectrometry, 471 and 357 proteins were identified in RGC somatodendritic and axonal mitochondrial immunoprecipitates, respectively. We identified 10 mitochondrial proteins exclusively in the somatodendritic compartment and 19 enriched ≥2-fold there, while 3 proteins were exclusively identified and 18 enriched in the axonal compartment. Our observation of compartment-specific enrichment of mitochondrial proteins was validated through immunofluorescence analysis of the localization and relative abundance of superoxide dismutase ( SOD2 ), sideroflexin-3 ( SFXN3 ) and trifunctional enzyme subunit alpha ( HADHA ) in retina and optic nerve specimens. The identified compartmental differences in RGC mitochondrial composition may provide promising leads for uncovering physiologically relevant pathways amenable to therapeutic intervention for optic neuropathies.

Melatonin ameliorates retinal ganglion cell senescence and apoptosis in a SIRT1-dependent manner in an optic nerve injury model

Melatonin is involved in exerting protective effects in aged-related and neurodegenerative diseases through a silent information regulator type 1 (SIRT1)-dependent pathway. However, little was known about the impact of melatonin on retinal ganglion cell (RGC) senescence and apoptosis following optic nerve crush (ONC). Thus, this study aimed to examine the effects of melatonin on RGC senescence and apoptosis after ONC and investigate the involvement of SIRT1 in this process. To study this, an ONC model was established. EX-527, an inhibitor of SIRT1, was injected intraperitoneally into mice. And melatonin was administrated abdominally into mice after ONC every day. Hematoxylin & eosin staining, retina flat-mounts and optical coherence tomography were used to evaluate the loss of retina cells/neurons. Pattern electroretinogram (p-ERG) was performed to evaluate the function of RGCs. Immunofluorescence and western blot were used to evaluate protein expression. SA-β-gal staining was employed to detect senescent cells. The results demonstrated that melatonin partially rescued the expression of SIRT1 in RGC 3 days after ONC. Additionally, melatonin administration partly rescued the decreased RGC number and ganglion cell complex thickness observed 14 days after ONC. Melatonin also suppressed ONC-induced senescence and apoptosis index. Furthermore, p-ERG showed that melatonin improved the amplitude of P50, N95 and N95/P50 following ONC. Importantly, the protective effects of melatonin were reversed when EX-527 was administered. In summary, this study revealed that melatonin attenuated RGC senescence and apoptosis through a SIRT1-dependent pathway after ONC. These findings provide valuable insights for the treatment of RGC senescence and apoptosis.

Association between glaucoma susceptibility with combined defects in mitochondrial oxidative phosphorylation and fatty acid beta oxidation

Glaucoma is one of the leading causes of visual impairment and blindness worldwide, and is characterized by the progressive damage of retinal ganglion cells (RGCs) and the atrophy of the optic nerve head (ONH). The exact cause of RGC loss and optic nerve damage in glaucoma is not fully understood. The high energy demands of these cells imply a higher sensitivity to mitochondrial defects. Moreover, it has been postulated that the optic nerve is vulnerable towards damage from oxidative stress and mitochondrial dysfunction. To investigate this further, we conducted a pooled analysis of mitochondrial variants related to energy production, specifically focusing on oxidative phosphorylation (OXPHOS) and fatty acid β-oxidation (FAO). Our findings revealed that patients carrying non-synonymous (NS) mitochondrial DNA (mtDNA) variants within the OXPHOS complexes had an almost two-fold increased risk of developing glaucoma. Regarding FAO, our results demonstrated that longer-chain acylcarnitines (AC) tended to decrease, while shorter-chain AC tended to increase in patients with glaucoma. Furthermore, we observed that the knocking down cpt1a (a key rate-limiting enzyme involved in FAO) in zebrafish induced a degenerative process in the optic nerve and RGC, which resembled the characteristics observed in glaucoma. In conclusion, our study provides evidence that genes encoding mitochondrial proteins involved in energy metabolisms, such as OXPHOS and FAO, are associated with glaucoma. These findings contribute to a better understanding of the molecular mechanisms underlying glaucoma pathogenesis and may offer potential targets for therapeutic interventions in the future.

Elamipretide Topical Ophthalmic Solution for the Treatment of Subjects with Leber Hereditary Optic Neuropathy: A Randomized Trial

PURPOSE

This study aimed to assess the safety, tolerability, and potential efficacy of topical elamipretide in patients affected with Leber hereditary optic neuropathy (LHON).

DESIGN

This phase II, prospective, randomized, vehicle-controlled, single-center clinical trial involved administration of elamipretide 1% topical ophthalmic solution to patients with LHON over a 52-week double-masked treatment period, followed by an open-label extension (OLE) for up to 108 additional weeks of treatment.

PARTICIPANTS

Twelve patients with LHON were included in this study. Patients aged 18 to 50 years with decreased vision for at least ≥ 1 year and ≤ 10 years, and a genetically confirmed diagnosis of m.11778G>A LHON were eligible for this trial.

METHODS

For the first 52 weeks of the study, patients were randomized to 1 of 3 groups: elamipretide in both eyes or elamipretide in 1 eye (left eye and right eye were considered separate groups) and vehicle in the other eye, followed by an OLE in which both eyes were treated with elamipretide.

MAIN OUTCOME MEASURES

The primary outcome measure was assessment of adverse events (AEs) from the administration of topical elamipretide, and the primary efficacy end point was change in best-corrected visual acuity (BCVA). Secondary outcome measures included changes in color vision, visual field mean deviation, and electrophysiological outcomes.

RESULTS

Elamipretide was well tolerated with the majority of AEs being mild to moderate and resolving spontaneously. The change from baseline in BCVA in elamipretide-treated eyes was not significantly different from the vehicle eyes at any time point. Six of 12 subjects met the criteria for clinically relevant benefit (CRB). In the post hoc analysis, change from baseline in mean deviation in the central visual field was significantly greater in elamipretide-treated eyes versus the vehicle eyes. Compared with baseline, both treatment groups showed improvement in color discrimination and contrast sensitivity in the OLE.

CONCLUSIONS

Elamipretide treatment was generally well tolerated, with no serious AEs reported. Although this study did not meet its primary BCVA efficacy end point, improvements across assessments on visual function during the OLE and the post hoc findings of the Humphrey automated visual field central region were encouraging and require further exploration.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

The Metabolic Shift: Unraveling the Potential of the Ketogenic Diet in Glaucoma Management

How to cite this article: Bhartiya S. The Metabolic Shift: Unraveling the Potential of the Ketogenic Diet in Glaucoma Management. J Curr Glaucoma Pract 2024;18(2):43-44.

Genetic variants affecting NQO1 protein levels impact the efficacy of idebenone treatment in Leber hereditary optic neuropathy

Idebenone, the only approved treatment for Leber hereditary optic neuropathy (LHON), promotes recovery of visual function in up to 50% of patients, but we can neither predict nor understand the non-responders. Idebenone is reduced by the cytosolic NAD(P)H oxidoreductase I (NQO1) and directly shuttles electrons to respiratory complex III, bypassing complex I affected in LHON. We show here that two polymorphic variants drastically reduce NQO1 protein levels when homozygous or compound heterozygous. This hampers idebenone reduction. In its oxidized form, idebenone inhibits complex I, decreasing respiratory function in cells. By retrospectively analyzing a large cohort of idebenone-treated LHON patients, classified by their response to therapy, we show that patients with homozygous or compound heterozygous NQO1 variants have the poorest therapy response, particularly if carrying the m.3460G>A/MT-ND1 LHON mutation. These results suggest consideration of patient NQO1 genotype and mitochondrial DNA mutation in the context of idebenone therapy.

The human OPA1delTTAG mutation induces adult onset and progressive auditory neuropathy in mice

Dominant optic atrophy (DOA) is one of the most prevalent forms of hereditary optic neuropathies and is mainly caused by heterozygous variants in OPA1, encoding a mitochondrial dynamin-related large GTPase. The clinical spectrum of DOA has been extended to a wide variety of syndromic presentations, called DOAplus, including deafness as the main secondary symptom associated to vision impairment. To date, the pathophysiological mechanisms underlying the deafness in DOA remain unknown. To gain insights into the process leading to hearing impairment, we have analyzed the Opa1delTTAG mouse model that recapitulates the DOAplus syndrome through complementary approaches combining morpho-physiology, biochemistry, and cellular and molecular biology. We found that Opa1delTTAG mutation leads an adult-onset progressive auditory neuropathy in mice, as attested by the auditory brainstem response threshold shift over time. However, the mutant mice harbored larger otoacoustic emissions in comparison to wild-type littermates, whereas the endocochlear potential, which is a proxy for the functional state of the stria vascularis, was comparable between both genotypes. Ultrastructural examination of the mutant mice revealed a selective loss of sensory inner hair cells, together with a progressive degeneration of the axons and myelin sheaths of the afferent terminals of the spiral ganglion neurons, supporting an auditory neuropathy spectrum disorder (ANSD). Molecular assessment of cochlea demonstrated a reduction of Opa1 mRNA level by greater than 40%, supporting haploinsufficiency as the disease mechanism. In addition, we evidenced an early increase in Sirtuin 3 level and in Beclin1 activity, and subsequently an age-related mtDNA depletion, increased oxidative stress, mitophagy as well as an impaired autophagic flux. Together, these results support a novel role for OPA1 in the maintenance of inner hair cells and auditory neural structures, addressing new challenges for the exploration and treatment of OPA1-linked ANSD in patients.

Autosomal recessive cerebellar ataxias: a diagnostic classification approach according to ocular features

Autosomal recessive cerebellar ataxias (ARCAs) are a heterogeneous group of neurodegenerative disorders affecting primarily the cerebellum and/or its afferent tracts, often accompanied by damage of other neurological or extra-neurological systems. Due to the overlap of clinical presentation among ARCAs and the variety of hereditary, acquired, and reversible etiologies that can determine cerebellar dysfunction, the differential diagnosis is challenging, but also urgent considering the ongoing development of promising target therapies. The examination of afferent and efferent visual system may provide neurophysiological and structural information related to cerebellar dysfunction and neurodegeneration thus allowing a possible diagnostic classification approach according to ocular features. While optic coherence tomography (OCT) is applied for the parametrization of the optic nerve and macular area, the eye movements analysis relies on a wide range of eye-tracker devices and the application of machine-learning techniques. We discuss the results of clinical and eye-tracking oculomotor examination, the OCT findings and some advancing of computer science in ARCAs thus providing evidence sustaining the identification of robust eye parameters as possible markers of ARCAs.

Optical Coherence Tomography Angiography: Revolutionizing Clinical Diagnostics and Treatment in Central Nervous System Disease

Optical coherence tomography angiography (OCTA), as a new generation of non-invasive and efficient fundus imaging technology, can provide non-invasive assessment of vascular lesions in the retina and choroid. In terms of anatomy and development, the retina is referred to as an extension of the central nervous system (CNS). CNS diseases are closely related to changes in fundus structure and blood vessels, and direct visualization of fundus structure and blood vessels provides an effective "window" for CNS research. This has important practical significance for identifying the characteristic changes of various CNS diseases on OCTA in the future, and plays a key role in promoting early screening, diagnosis, and monitoring of disease progression in CNS diseases. This article reviews relevant fundus studies by comparing and summarizing the unique advantages and existing limitations of OCTA in various CNS disease patients, in order to demonstrate the clinical significance of OCTA in the diagnosis and treatment of CNS diseases.

Mitochondrial DNA D-loop variants correlate with a primary open-angle glaucoma subgroup

Introduction

Primary open-angle glaucoma (POAG) is a characteristic optic neuropathy, caused by degeneration of the optic nerve-forming neurons, the retinal ganglion cells (RGCs). High intraocular pressure (IOP) and aging have been identified as major risk factors; yet the POAG pathophysiology is not fully understood. Since RGCs have high energy requirements, mitochondrial dysfunction may put the survivability of RGCs at risk. We explored in buffy coat DNA whether mtDNA variants and their distribution throughout the mtDNA could be risk factors for POAG.

Methods

The mtDNA was sequenced from age- and sex-matched study groups, being high tension glaucoma (HTG, n=71), normal tension glaucoma patients (NTG, n=33), ocular hypertensive subjects (OH, n=7), and cataract controls (without glaucoma; n=30), all without remarkable comorbidities.

Results

No association was found between the number of mtDNA variants in genes encoding proteins, tRNAs, rRNAs, and in non-coding regions in the different study groups. Next, variants that controls shared with the other groups were discarded. A significantly higher number of exclusive variants was observed in the D-loop region for the HTG group (~1.23 variants/subject), in contrast to controls (~0.35 variants/subject). In the D-loop, specifically in the 7S DNA sub-region within the Hypervariable region 1 (HV1), we found that 42% of the HTG and 27% of the NTG subjects presented variants, while this was only 14% for the controls and OH subjects. As we have previously reported a reduction in mtDNA copy number in HTG, we analysed if specific D-loop variants could explain this. While the majority of glaucoma patients with the exclusive D-loop variants m.72T>C, m.16163 A>G, m.16186C>T, m.16298T>C, and m.16390G>A presented a mtDNA copy number below controls median, no significant association between these variants and low copy number was found and their possible negative role in mtDNA replication remains uncertain. Approximately 38% of the HTG patients with reduced copy number did not carry any exclusive D-loop or other mtDNA variants, which indicates that variants in nuclear-encoded mitochondrial genes, environmental factors, or aging might be involved in those cases.

Conclusion

In conclusion, we found that variants in the D-loop region may be a risk factor in a subgroup of POAG, possibly by affecting mtDNA replication.

Peripapillary hyperreflective ovoid mass-like structures (PHOMS) in patients with acute Leber's hereditary optic neuropathy

PURPOSE

Peripapillary hyperreflective ovoid mass-like structures (PHOMS) represent an optical coherence tomography (OCT) finding that has been characterized in different forms of pseudopapilledema. The aim of this study was to investigate the prevalence of PHOMS in patients affected by acute LHON using structural OCT, and to provide a detailed description of these findings.

METHODS

Patients with a clinical and molecularly confirmed diagnosis of acute LHON (visual loss having occurred less than 6 months) were enrolled from the neuro-ophthalmology clinic at San Raffaele Scientific Institute. Patients had a complete ophthalmologic evaluation, including imaging with structural OCT.

RESULTS

Our analysis included 16 patients (21 eyes-8 males and 8 females) with acute LHON. Structural OCT exhibited PHOMS in 12 eyes from 9 patients with a prevalence rate of 57.1%. In a subsequent topographical assessment in the peripapillary area, the most common location of PHOMS was the temporal region (12 out of 12 eyes), while the nasal region was affected in 2 eyes (16.7%). Considering the 12 eyes with PHOMS, mean ± SD temporal peripapillary RNFL thickness was 87.5 ± 28.4 microns. The temporal peripapillary RNFL thickness was significantly lower in eyes without PHOMS (63.7 ± 32.2 microns; P = 0.40). At the 12-month follow-up visit, PHOMS disappeared in 10 out of 12 eyes.

CONCLUSIONS

Acute LHON eyes have PHOMS which are mainly confined to the temporal peripapillary sector. PHOMS may represent swelled retinal fibers that have herniated or are in stasis.

Gender- and age-related differences in foveal pit morphology

AIMS

To measure the foveal pit morphology parameters and evaluate their correlations with age and sex.

SETTINGS AND DESIGN

A retrospective cross-sectional matched comparison study in a tertiary center.

METHODS AND MATERIALS

Forty men and 40 age-matched women who had normal macular structures and foveal contours were enrolled. Foveal pit parameters including top width, base width, nasal width, temporal width, minimal thickness, nasal thickness, temporal thickness, nasal height, temporal height, nasal slope, and temporal slope were measured on horizontal B-scan macular optical coherence tomography and compared between men and women.

STATISTICAL ANALYSIS USED

Paired t-tests and Pearson's correlation analysis.

RESULTS

The average patient age was 51.4 ± 17.5 (21-84) years. Women had a wider base width (313.1 ± 68.0 μm vs 266.8 ± 70.9 μm, P = 0.006), wider temporal width (1043.1 ± 245.6 μm vs 968.9 ± 261.0 μm, P = 0.006), thinner nasal thickness (345.6 ± 36.2 μm vs 359.7 ± 35.8 μm, P = 0.048), and flatter temporal slope (11.60 ± 2.52° vs 12.98 ± 2.68°, P = 0.016) than men. With age, the base width (r = 0.35, P = 0.025) and temporal width (r = 0.54, P = 0.0003) tended to be wider and the temporal slope was flatter (r = -0.45, P = 0.003) in women but not men. The minimal thickness tended to be thinner in the elderly group (r = 0.038, P = 0.015).

CONCLUSIONS

Women had a significantly wider base width, wider temporal width, thinner nasal thickness, and flatter temporal slope of the foveal pit than age-matched men. The base width and temporal width were wider and the temporal slope was flatter with age in women but not men.

Recessive MECR pathogenic variants cause an LHON-like optic neuropathy

BACKGROUND

Leber's hereditary optic neuropathy (LHON) is a mitochondrial disorder characterised by complex I defect leading to sudden degeneration of retinal ganglion cells. Although typically associated with pathogenic variants in mitochondrial DNA, LHON was recently described in patients carrying biallelic variants in nuclear genes DNAJC30, NDUFS2 and MCAT. MCAT is part of mitochondrial fatty acid synthesis (mtFAS), as also MECR, the mitochondrial trans-2-enoyl-CoA reductase. MECR mutations lead to a recessive childhood-onset syndromic disorder with dystonia, optic atrophy and basal ganglia abnormalities.

METHODS

We studied through whole exome sequencing two sisters affected by sudden and painless visual loss at young age, with partial recovery and persistent central scotoma. We modelled the candidate variant in yeast and studied mitochondrial dysfunction in yeast and fibroblasts. We tested protein lipoylation and cell response to oxidative stress in yeast.

RESULTS

Both sisters carried a homozygous pathogenic variant in MECR (p.Arg258Trp). In yeast, the MECR-R258W mutant showed an impaired oxidative growth, 30% reduction in oxygen consumption rate and 80% decrease in protein levels, pointing to structure destabilisation. Fibroblasts confirmed the reduced amount of MECR protein, but failed to reproduce the OXPHOS defect. Respiratory complexes assembly was normal. Finally, the yeast mutant lacked lipoylation of key metabolic enzymes and was more sensitive to H2O2 treatment. Lipoic Acid supplementation partially rescued the growth defect.

CONCLUSION

We report the first family with homozygous MECR variant causing an LHON-like optic neuropathy, which pairs the recent MCAT findings, reinforcing the impairment of mtFAS as novel pathogenic mechanism in LHON.

The constraints of allotopic expression

Allotopic expression is the functional transfer of an organellar gene to the nucleus, followed by synthesis of the gene product in the cytosol and import into the appropriate organellar sub compartment. Here, we focus on mitochondrial genes encoding OXPHOS subunits that were naturally transferred to the nucleus, and critically review experimental evidence that claim their allotopic expression. We emphasize aspects that may have been overlooked before, i.e., when modifying a mitochondrial gene for allotopic expression━besides adapting the codon usage and including sequences encoding mitochondrial targeting signals━three additional constraints should be considered: (i) the average apparent free energy of membrane insertion (μΔGapp) of the transmembrane stretches (TMS) in proteins earmarked for the inner mitochondrial membrane, (ii) the final, functional topology attained by each membrane-bound OXPHOS subunit; and (iii) the defined mechanism by which the protein translocator TIM23 sorts cytosol-synthesized precursors. The mechanistic constraints imposed by TIM23 dictate the operation of two pathways through which alpha-helices in TMS are sorted, that eventually determine the final topology of membrane proteins. We used the biological hydrophobicity scale to assign an average apparent free energy of membrane insertion (μΔGapp) and a "traffic light" color code to all TMS of OXPHOS membrane proteins, thereby predicting which are more likely to be internalized into mitochondria if allotopically produced. We propose that the design of proteins for allotopic expression must make allowance for μΔGapp maximization of highly hydrophobic TMS in polypeptides whose corresponding genes have not been transferred to the nucleus in some organisms.

Mitophagy in Astrocytes Is Required for the Health of Optic Nerve

Mitochondrial dysfunction in astrocytes has been implicated in the development of various neurological disorders. Mitophagy, mitochondrial autophagy, is required for proper mitochondrial function by preventing the accumulation of damaged mitochondria. The importance of mitophagy, specifically in the astrocytes of the optic nerve (ON), has been little studied. We introduce an animal model in which two separate mutations act synergistically to produce severe ON degeneration. The first mutation is in Cryba1, which encodes βA3/A1-crystallin, a lens protein also expressed in astrocytes, where it regulates lysosomal pH. The second mutation is in Bckdk, which encodes branched-chain ketoacid dehydrogenase kinase, which is ubiquitously expressed in the mitochondrial matrix and involved in the catabolism of the branched-chain amino acids. BCKDK is essential for mitochondrial function and the amelioration of oxidative stress. Neither of the mutations in isolation has a significant effect on the ON, but animals homozygous for both mutations (DM) exhibit very serious ON degeneration. ON astrocytes from these double-mutant (DM) animals have lysosomal defects, including impaired mitophagy, and dysfunctional mitochondria. Urolithin A can rescue the mitophagy impairment in DM astrocytes and reduce ON degeneration. These data demonstrate that efficient mitophagy in astrocytes is required for ON health and functional integrity.

Central retina thickness measured with spectral-domain optical coherence tomography in Parkinson disease: A meta-analysis

BACKGROUND

Optical coherence tomography (OCT) can detect visual alterations associated with Parkinson disease, such as damage to the retinal nerve fiber layer or changes in retinal vasculature. Macula thinning in association with Parkinson disease (PD) remains controversial. Therefore, we conducted a meta-analysis to investigate the central retina thickness in PD measured using spectral-domain OCT (SD-OCT).

METHODS

We searched PubMed and the Excerpta Medica database to identify studies that compared macular thickness between patients with PD and healthy controls published before July 31, 2021. A random-effects model was used to examine PD-associated changes in macular thickness. Meta-regression analysis was performed by assessing heterogeneity, publication bias, and study quality.

RESULTS

Thirty-two studies with a cross-sectional design were selected, including 2118 patients with PD and 2338 controls. We identified significant differences in the thickness of the ganglion cell-inner plexiform layer (standardized mean difference [SMD], -0.41; 95% confidence interval [CI], -0.66 to -0.16; I2 = 80%), ganglion cell complex (SMD, -0.33; 95% CI, -0.50 to -0.17; I2 = 0%), and of all inner and outer sectors of the macula (SMD range, -0.21 to -0.56; all P < .05) between patients with PD and controls.

DISCUSSION

These results corroborate the increased prevalence of changes in OCT measures in individuals with PD, highlighting the efficacy of SD-OCT-determined macular thickness as a biomarker for PD. Our findings may provide helpful guidelines for clinicians in rapidly evolving areas of PD diagnosis.

Neuroprotective effects of idebenone on hydrogen peroxide-induced oxidative damage in retinal ganglion cells-5

PURPOSE

To investigate the neuroprotective effect of idebenone against hydrogen peroxide (H2O2)-induced oxidative damage in retinal ganglion cells-5 (RGC-5 cells).

METHODS

RGC-5 cells were pre-treated with various idebenone concentrations (5, 10, and 20 µM) for 12 h and were then subjected to 300 µM H2O2 for a further 12 h. Apoptosis in RGC-5 was measured by flow cytometry. The changes of mitochondrial membrane potential (MMP) were detected by JC-1 staining. Autophagy in RGC-5 cells was observed by transmission electron microscopy. Western blots were used to measure the expression of autophagy-related protein light chain 3 (LC3), Beclin-1, and the release of Cytochrome c (Cyt-c).

RESULTS

Flow cytometry showed that the apoptosis rates in the normal control group, H2O2 group, and idebenone groups were 6.48 ± 0.55%, 27.3 ± 0.51%, 22.8 ± 0.52%, 15.45 ± 0.81%, and 12.59 ± 0.58%, respectively (F = 559.7, P < 0.0001). After incubation with H2O2, the number of autophagosomes increased significantly, whereas it was decreased in the idebenone groups. After incubation of RGC-5 cells with H2O2, MMP levels were significantly decreased, while idebenone could prevent the decrease in MMP levels. Compared with that in the normal control group, LC3 II/I, the expression levels of Beclin-1 and Cyt-c were increased significantly in the H2O2 group (P < 0.05). Compared with that in the H2O2 group, LC3 II/I, the expression of Beclin-1 and Cyt-c was significantly decreased in idebenone groups (P < 0.05).

CONCLUSIONS

Idebenone protects RGC-5 cells against H2O2-induced oxidative damage by reducing mitochondrial damage and autophagic activity.