Mitochondrial dysfunction in glaucoma: Understanding genetic influences

Metformin in Glaucoma Treatment

PRCIS

Rigorous trials are essential to develop comprehensive treatment strategies that fully exploit the therapeutic potential of metformin in the treatment of glaucoma.

OBJECTIVE

The objective of this study was to evaluate the potentially beneficial effect of metformin on glaucoma risk factors and to investigate the underlying mechanisms. The aim is to contribute to the development of new treatment strategies for glaucoma.

METHODS

We searched for studies that assessed the effects of metformin on glaucoma risk factors and the associated underlying mechanisms. Our search included electronic databases such as PUBMED, EMBASE, and clinicaltrials.gov.

RESULTS

Unfortunately, we did not find any clinical trials that specifically investigated the impact of metformin on glaucoma. However, data from experimental studies demonstrated the capability of metformin to modulate various pathways that could contribute to neuroprotection in glaucoma.

CONCLUSION

In order to develop comprehensive treatment strategies that fully exploit the therapeutic potential of metformin in the treatment of glaucoma, rigorous trials are essential. These studies are necessary to demonstrate both the safety and efficacy of metformin in the context of glaucoma treatment.

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.

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.

Red Flags in Primary Mitochondrial Diseases: What Should We Recognize?

Primary mitochondrial diseases (PMDs) are complex group of metabolic disorders caused by genetically determined impairment of the mitochondrial oxidative phosphorylation (OXPHOS). The unique features of mitochondrial genetics and the pivotal role of mitochondria in cell biology explain the phenotypical heterogeneity of primary mitochondrial diseases and the resulting diagnostic challenges that follow. Some peculiar features ("red flags") may indicate a primary mitochondrial disease, helping the physician to orient in this diagnostic maze. In this narrative review, we aimed to outline the features of the most common mitochondrial red flags offering a general overview on the topic that could help physicians to untangle mitochondrial medicine complexity.

Paving the way while playing catch up: mitochondrial genetics in African ancestry primary open-angle glaucoma

Glaucoma, the leading cause of irreversible blindness worldwide, disproportionately affects individuals of African descent. Specifically, previous research has indicated that primary open-angle glaucoma (POAG), the most common form of disease, is more prevalent, severe, early-onset, and rapidly-progressive in populations of African ancestry. Recent studies have identified genetic variations that may contribute to the greater burden of disease in this population. In particular, mitochondrial genetics has emerged as a profoundly influential factor in multiple neurodegenerative diseases, including POAG. Several hypotheses explaining the underlying mechanisms of mitochondrial genetic contribution to disease progression have been proposed, including nuclear-mitochondrial gene mismatch. Exploring the fundamentals of mitochondrial genetics and disease pathways within the understudied African ancestry population can lead to groundbreaking advancements in the research and clinical understanding of POAG. This article discusses the currently known involvements of mitochondrial genetic factors in POAG, recent directions of study, and potential future prospects in mitochondrial genetic studies in individuals of African descent.

The Role of Mitophagy in Glaucomatous Neurodegeneration

This review aims to provide a better understanding of the emerging role of mitophagy in glaucomatous neurodegeneration, which is the primary cause of irreversible blindness worldwide. Increasing evidence from genetic and other experimental studies suggests that mitophagy-related genes are implicated in the pathogenesis of glaucoma in various populations. The association between polymorphisms in these genes and increased risk of glaucoma is presented. Reduction in intraocular pressure (IOP) is currently the only modifiable risk factor for glaucoma, while clinical trials highlight the inadequacy of IOP-lowering therapeutic approaches to prevent sight loss in many glaucoma patients. Mitochondrial dysfunction is thought to increase the susceptibility of retinal ganglion cells (RGCs) to other risk factors and is implicated in glaucomatous degeneration. Mitophagy holds a vital role in mitochondrial quality control processes, and the current review explores the mitophagy-related pathways which may be linked to glaucoma and their therapeutic potential.

Low mitochondrial DNA copy number in buffy coat DNA of primary open-angle glaucoma patients

Primary open-angle glaucoma (POAG) is characterized by optic nerve degeneration and irreversible loss of retinal ganglion cells (RGCs). The pathophysiology is not fully understood. Since RGCs have a high energy demand, suboptimal mitochondrial function may put the survival of these neurons at risk. In the present study, we explored whether mtDNA copy number or mtDNA deletions could reveal a mitochondrial component in POAG pathophysiology. Buffy coat DNA was isolated from EDTA blood of age- and sex-matched study groups, namely POAG patients with high intraocular pressure (IOP) at diagnosis (high tension glaucoma: HTG; n = 97), normal tension glaucoma patients (NTG, n = 37), ocular hypertensive controls (n = 9), and cataract controls (without glaucoma; n = 32), all without remarkable comorbidities. The number of mtDNA copies was assessed through qPCR quantification of the mitochondrial D-loop and nuclear B2M gene. Presence of the common 4977 base pair mtDNA deletion was assessed by a highly sensitive breakpoint PCR. Analysis showed that HTG patients had a lower number of mtDNA copies per nuclear DNA than NTG patients (p-value <0.01, Dunn test) and controls (p-value <0.001, Dunn test). The common 4977 base pair mtDNA deletion was not detected in any of the participants. A lower mtDNA copy number in blood of HTG patients suggests a role for a genetically defined, deficient mtDNA replication in the pathology of HTG. This may cause a low number of mtDNA copies in RGCs, which together with aging and high IOP, may lead to mitochondrial dysfunction, and contribute to glaucoma pathology.

Evidence of impaired mitochondrial cellular bioenergetics in ocular fibroblasts derived from glaucoma patients

Glaucoma is a progressive optic neuropathy characterized by the neurodegeneration of the retinal ganglion cells (RGCs) resulting in irreversible visual impairment and eventual blindness. RGCs are extremely susceptible to mitochondrial compromise due to their marked bioenergetic requirements and morphology. There is increasing interest in therapies targeting mitochondrial health as a method of preventing visual loss in managing glaucoma. The bioenergetic profile of Tenon's ocular fibroblasts from glaucoma patients and controls was investigated using the Seahorse XF24 analyser. Impaired mitochondrial cellular bioenergetics was detected in glaucomatous ocular fibroblasts including basal respiration, maximal respiration and spare capacity. Spare respiratory capacity levels reflect mitochondrial bio-energetic adaptability in response to pathophysiological stress. Basal oxidative stress was elevated in glaucomatous Tenon's ocular fibroblasts and hydrogen peroxide (H₂O₂) induced reactive oxygen species (ROS) simulated the glaucomatous condition in normal Tenon's ocular fibroblasts. This work supports the role of therapeutic interventions to target oxidative stress or provide mitochondrial energetic support in glaucoma.

Role of Mitochondrial Mutations in Ocular Aggregopathy

Background Mitochondria are essential cellular organelles that are responsible for oxidative stress-induced damage in age-dependent neurodegenerations such as glaucoma. Previous studies have linked mitochondrial DNA (mtDNA) mutations to cellular energy shortages that result in eye degeneration. Methodology To look for nucleotide variations in mtDNA in exfoliation syndrome/glaucoma (XFS/XFG), we performed a polymerase chain reaction (PCR) to amplify the entire coding region of the mitochondrial genome from peripheral blood of XFS/XFG (n = 25) patients and controls (n = 25). Results This study identified a total of 65 variations in XFS/XFG patients, of which 25 (38%) variations were non-synonymous single-nucleotide polymorphism (nsSNPs). Out of 25 nsSNPs, seven (five nsSNP in MT-ND4 and two in MT-ATP6 gene) were predicted as pathogenic using four different software, namely, SIFT, Polyphene2, mutation taster, and MutPred2. The pathogenic nsSNPs were then subjected to structural change analysis using online tools. Conclusions The pathogenic nsSNPs were found in both proteins' transmembrane domains and were expected to be conserved, but with lower protein stability (ΔΔG <- 0.5), indicating a possibly harmful effect in exfoliation. However, three-dimensional protein analysis indicated that the predicted mutations in MT-ND4 and MT-ATP6 were unlikely to alter the protein function.

Significance of mitochondrial activity in neurogenesis and neurodegenerative diseases

Mitochondria play a multidimensional role in the function and the vitality of the neurological system. From the generation of neural stem cells to the maintenance of neurons and their ultimate demise, mitochondria play a critical role in regulating our neural pathways' homeostasis, a task that is critical to our cognitive health and neurological well-being. Mitochondria provide energy via oxidative phosphorylation for the neurotransmission and generation of an action potential along the neuron's axon. This paper will first review and examine the molecular subtleties of the mitochondria's role in neurogenesis and neuron vitality, as well as outlining the impact of defective mitochondria in neural aging. The authors will then summarize neurodegenerative diseases related to either neurogenesis or homeostatic dysfunction. Because of the significant detriment neurodegenerative diseases have on the quality of life, it is essential to understand their etiology and ongoing molecular mechanics. The mitochondrial role in neurogenesis and neuron vitality is essential. Dissecting and understanding this organelle's role in the genesis and homeostasis of neurons should assist in finding pharmaceutical targets for neurodegenerative diseases.

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

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

Mitochondrial Genome Study Identifies Association Between Primary Open-Angle Glaucoma and Variants in MT-CYB, MT-ND4 Genes and Haplogroups

Background and purpose: Primary open-angle glaucoma (POAG) is an optic neuropathy characterized by death of retinal ganglion cells and atrophy of the optic nerve head. The susceptibility of the optic nerve to damage has been shown to be mediated by mitochondrial dysfunction. In this study, we aimed to determine a possible association between mitochondrial SNPs or haplogroups and POAG.

Methods: Mitochondrial DNA single nucleotide polymorphisms (mtSNPs) were genotyped using the Illumina Infinium Global Screening Array-24 (GSA) 700K array set. Genetic analyses were performed in a POAG case-control study involving the cohorts, Groningen Longitudinal Glaucoma Study-Lifelines Cohort Study and Amsterdam Glaucoma Study, including 721 patients and 1951 controls in total. We excluded samples not passing quality control for nuclear genotypes and samples with low call rate for mitochondrial variation. The mitochondrial variants were analyzed both as SNPs and haplogroups. These were determined with the bioinformatics software HaploGrep, and logistic regression analysis was used for the association, as well as for SNPs.

Results: Meta-analysis of the results from both cohorts revealed a significant association between POAG and the allele A of rs2853496 [odds ratio (OR) = 0.64; p = 0.006] within the MT-ND4 gene, and for the T allele of rs35788393 (OR = 0.75; p = 0.041) located in the MT-CYB gene. In the mitochondrial haplogroup analysis, the most significant p-value was reached by haplogroup K (p = 1.2 × 10⁻⁰⁵), which increases the risk of POAG with an OR of 5.8 (95% CI 2.7–13.1).

Conclusion: We identified an association between POAG and polymorphisms in the mitochondrial genes MT-ND4 (rs2853496) and MT-CYB (rs35788393), and with haplogroup K. The present study provides further evidence that mitochondrial genome variations are implicated in POAG. Further genetic and functional studies are required to substantiate the association between mitochondrial gene polymorphisms and POAG and to define the pathophysiological mechanisms of mitochondrial dysfunction in glaucoma.

Influence of gut microbiota on eye diseases: an overview

The microbiota is a dynamic ecosystem that plays a major role in the host health. Numerous studies have reported that alterations in the intestinal microbiota (dysbiosis) may contribute to the pathogenesis of various common diseases such as diabetes, neuropsychiatric diseases, and cancer. However, emerging findings also suggest the existence of a gut-eye axis, wherein gut dysbiosis may be a crucial factor influencing the onset and progression of multiple ocular diseases, including uveitis, dry eye, macular degeneration, and glaucoma. Currently, supplementation with pre- and probiotics appears is the most feasible and cost-effective approach to restore the gut microbiota to a eubiotic state and prevent eye pathologies. In this review, we discuss the current knowledge on how gut microbiota may be linked to the pathogenesis of common eye diseases, providing therapeutic perspectives for future translational investigations within this promising research field.

Association between Daily Niacin Intake and Glaucoma: National Health and Nutrition Examination Survey

Background and Aims: To determine the relationship between dietary intake of niacin and glaucoma using the data from the 2005 to 2008 National Health and Nutrition Examination Survey (NHANES). Methods: Subjects aged 40 years and older who participated in the dietary intake interview and vision health questionnaire of NHANES were included in the study. Glaucoma diagnosis by self-report was utilized. Additionally, glaucoma diagnosis by fundus imaging and International Society Geographical and Epidemiological Ophthalmology (ISGEO) criteria was used in subjects with available qualified retinal imaging. Survey logistic regression analyses were used to examine the association between daily niacin consumption and glaucoma. Results: A total of 5768 participants were included in the study. There was a significant decrease in the crude odds of self-reported glaucoma in the third (OR 0.57, 95% Cl 0.43–0.76; p < 0.001) and fourth (OR 0.57, 95% Cl 0.37–0.90; p = 0.018) quartiles of daily niacin consumption, which equated to 21.01 to 28.22 mg/day and greater than 28.22 mg/day, respectively. A similar trend was found using fundus imaging of subjects with niacin intake in the third (OR 0.42, 95% Cl 0.25–0.72; p = 0.002) and fourth (OR 0.36, 95% Cl 0.20–0.67; p = 0.002) quartiles. After adjusting for covariates, the odds of glaucoma based on fundus imaging remained significantly lower for niacin intake in the third (OR 0.49, 95% Cl 0.28–0.87; p = 0.016) and fourth (OR 0.48, 95% Cl 0.26–0.89; p = 0.022) quartile levels. Using ISGEO criteria, there was no significant association between glaucoma and daily niacin consumption. Conclusions: Greater niacin intake may be associated with a lower chance of developing glaucoma.

A missense mutation in Pitx2 leads to early-onset glaucoma via NRF2-YAP1 axis

Glaucoma is a leading cause of blindness, affecting 70 million people worldwide. Owing to the similarity in anatomy and physiology between human and mouse eyes and the ability to genetically manipulate mice, mouse models are an invaluable resource for studying mechanisms underlying disease phenotypes and for developing therapeutic strategies. Here, we report the discovery of a new mouse model of early-onset glaucoma that bears a transversion substitution c. G344T, which results in a missense mutation, p. R115L in PITX2. The mutation causes an elevation in intraocular pressure (IOP) and progressive death of retinal ganglion cells (RGC). These ocular phenotypes recapitulate features of pathologies observed in human glaucoma. Increased oxidative stress was evident in the inner retina. We demonstrate that the mutant PITX2 protein was not capable of binding to Nuclear factor-like 2 (NRF2), which regulates Pitx2 expression and nuclear localization, and to YAP1, which is necessary for co-initiation of transcription of downstream targets. PITX2-mediated transcription of several antioxidant genes were also impaired. Treatment with N-Acetyl-L-cysteine exerted a profound neuroprotective effect on glaucoma-associated neuropathies, presumably through inhibition of oxidative stress. Our study demonstrates that a disruption of PITX2 leads to glaucoma optic pathogenesis and provides a novel early-onset glaucoma model that will enable elucidation of mechanisms underlying the disease as well as to serve as a resource to test new therapeutic strategies.

Association analysis of variants rs35934224 in TXNRD2 and rs6478746 in LMX1B in primary angle-closure and pseudoexfoliation glaucoma

OBJECTIVE

Previous genome-wide studies have demonstrated significant pathogenic association between variants rs35934224 within TXNRD2 and rs6478746 near LMX1B in primary open-angle glaucoma. We investigated the association between these variants in primary angle-closure glaucoma (PACG) and pseudoexfoliation glaucoma (PXG) patients of Saudi origin.

METHODS

In a case-control study, DNA samples from 249 controls (135 men and 114 women), 100 PACG cases (44 men and 56 women), and 95 PXG cases (61 men and 34 women) were genotyped by TaqMan^® based real-time PCR. Statistical tests were performed to evaluate genetic association with glaucoma types and related clinical indices.

RESULTS

The allele frequencies of rs35934224 and rs6478746 did not show significant variation in PACG and PXG than controls, except that the rs35934224[T] allele was found to be significantly low among PXG women (0.10) as compared to controls (0.21) (odds ratio = 0.38, 95% confidence interval = 0.16-0.94, p = 0.024). Rs35934224 genotypes showed a nominal-to-borderline protective association with PACG and PXG among women in different genetic models. However, except for the over-dominant model in PACG (p = 0.0095), none of the effects survived Bonferroni's correction (p < 0.01). Rs6478746 showed no significant genotype or allelic association with PACG and PXG. Regression analysis showed no influence on disease outcome, and neither showed any correlation with intraocular pressure and cup/disk ratio in both PACG and PXG.

CONCLUSIONS

Variants rs35934224 in TXNRD2 and rs6478746 near LMX1B are not associated with PACG and PXG in the Saudi cohort, but rs35934224 may confer modest protection among women. Further population-based studies are needed to validate these results.

Lack of Association Between Polymorphisms in TXNRD2 and LMX1B and Primary Open-Angle Glaucoma in a Saudi Cohort

Objective: Recent studies have demonstrated an association of single nucleotide polymorphisms (SNPs) rs35934224 in TXNRD2 and rs6478746 near LMX1B genes in primary open-angle glaucoma (POAG) among Europeans. We performed a retrospective, case-control study to investigate the association between the rs35934224 (TXNRD2) and rs6478746 (LMX1B) and POAG in a middle-eastern population from Saudi Arabia. Methods: DNA from 399 participants consisting of 150 POAG cases (83 males and 67 females) and 249 controls (135 males and 114 females) were genotyped using TaqMan® real-time PCR. Statistical tests were performed to evaluate genetic association with POAG and related clinical indices. Results: The minor allele frequency (MAF) of rs35934224[T] was 0.19 and 0.20 in POAG and controls, respectively. The difference was non-significant (odds ratio [OR] = 1.08, 95% confidence interval [CI] = 0.75-1.55, p = 0.663). Likewise, rs6478746[G] MAF was 0.12 in both cases and controls with no statistical significance (OR = 1.02, 95% CI = 0.67-1.56, p = 0.910). Genotype analysis showed no association with POAG for both the SNPs in combined and gender-stratified groups. Regression analysis showed no significant effect of risk factors such as age, sex, rs35934224, and rs6478746 genotypes on POAG outcome. Furthermore, both the SNPs showed no significant genotype effect on clinical indices such as intraocular pressure (IOP) and cup/disc ratio in POAG patients. Conclusions: Rs35934224 in TXNRD2 and rs6478746 near LMX1B genes are not associated with POAG or related clinical indices such as IOP and cup/disc ratio in a Saudi cohort. Since the study is limited by sample size further investigations are needed to confirm these results in a larger cohort.

Metformin and Glaucoma-Review of Anti-Fibrotic Processes and Bioenergetics

Glaucoma is the leading cause of irreversible blindness globally. With an aging population, disease incidence will rise with an enormous societal and economic burden. The treatment strategy revolves around targeting intraocular pressure, the principle modifiable risk factor, to slow progression of disease. However, there is a clear unmet clinical need to find a novel therapeutic approach that targets and halts the retinal ganglion cell (RGC) degeneration that occurs with fibrosis. RGCs are highly sensitive to metabolic fluctuations as a result of multiple stressors and thus their viability depends on healthy mitochondrial functioning. Metformin, known for its use in type 2 diabetes, has come to the forefront of medical research in multiple organ systems. Its use was recently associated with a 25% reduced risk of glaucoma in a large population study. Here, we discuss its application to glaucoma therapy, highlighting its effect on fibrotic signalling pathways, mitochondrial bioenergetics and NAD oxidation.

Plasma GDF-15 concentration is not elevated in open-angle glaucoma

Aim

Recently, the level of growth differentiation factor 15 (GDF-15) in blood, was proposed as biomarker to detect mitochondrial dysfunction. In the current study, we evaluate this biomarker in open-angle glaucoma (OAG), as there is increasing evidence that mitochondrial dysfunction plays a role in the pathophysiology of this disease.

Methods

Plasma GDF-15 concentrations were measured with ELISA in 200 OAG patients and 61 age-matched controls (cataract without glaucoma). The OAG patient group consisted of high tension glaucoma (HTG; n = 162) and normal tension glaucoma (NTG; n = 38). Groups were compared using the Kruskal-Wallis nonparametric test with Dunn’s multiple comparison post-hoc correction. GDF-15 concentration was corrected for confounders identified with forward linear regression models.

Results

Before correcting for confounders, median plasma GDF-15 levels was significantly lower in the combined OAG group (p = 0.04), but not when analysing HTG and NTG patients separately. Forward linear regression analysis showed that age, gender, smoking and systemic hypertension were significant confounders affecting GDF-15 levels. After correction for these confounders, GDF-15 levels in OAG patients were no longer significantly different from controls. Subgroup analysis of the glaucoma patients did not show a correlation between disease severity and plasma GDF-15, but did reveal that for NTG patients, intake of dietary supplements, which potentially improve mitochondrial function, correlated with lower plasma GDF-15.

Conclusion

The present study suggests that plasma GDF-15 is not suited as biomarker of mitochondrial dysfunction in OAG patients.

Neuroinflammatory Mechanisms of Mitochondrial Dysfunction and Neurodegeneration in Glaucoma

The exact mechanism of retinal ganglion cell loss in the pathogenesis of glaucoma is yet to be understood. Mitochondrial damage-associated molecular patterns (DAMPs) resulting from mitochondrial dysfunction have been linked to Leber's hereditary optic neuropathy and autosomal dominant optic atrophy, as well as to brain neurodegenerative diseases. Recent evidence shows that, in conditions where mitochondria are damaged, a sustained inflammatory response and downstream pathological inflammation may ensue. Mitochondrial damage has been linked to the accumulation of age-related mitochondrial DNA mutations and mitochondrial dysfunction, possibly through aberrant reactive oxygen species production and defective mitophagy. The present review focuses on how mitochondrial dysfunction may overwhelm the ability of neurons and glial cells to adequately maintain homeostasis and how mitochondria-derived DAMPs trigger the immune system and induce neurodegeneration.

Antiglaucoma Potential of β-Glucogallin Is Mediated by Modulating Mitochondrial Responses in Experimentally Induced Glaucoma

BACKGROUND

The use of phytochemicals for the treatment of various bodily ailments has been in practice since ancient days. Even though in practice, scientific studies on the protective effect of β-glucogallin (BG) against glaucoma is limited.

OBJECTIVES

In the present study, the in vitro glaucoma model (hydrostatic pressure) using PC12 neuronal cells exposed to BG were used to elucidate its protective effects.

METHOD

The cultured cells were analyzed for the mitochondrial responses, oxidant-antioxidant status, and expression of caveolin-1, ANGPTL7, the glaucoma markers, and cytokines.

RESULTS

We demonstrated a significant increase in the expression of glial fibrillary acidic protein, ANGPTL7, with altered mitochondrial enzymes in glaucoma cells compared to the control. Moreover, cells predisposed to hydrostatic pressure demonstrated an increase in oxidative stress with augmented (p < 0.01) inflammatory cytokines such as IL-2, CXCR4, IL-6, IL-8, MCP-1, and TNF-α. On the other hand, cells pretreated with BG attenuated the reactive oxygen species levels with improved antioxidant enzymes. Simultaneously, the levels of inflammatory cytokines and ANGPTL7 proteins were found attenuated with restored mitochondrial responses in BG pretreated cells.

CONCLUSION

Thus, the results of the present study demonstrate that the use of BG on retinal cells against relieving the intraocular pressure may be a promising therapeutic for controlling the disease progression.

Girl Power in Glaucoma: The Role of Estrogen in Primary Open Angle Glaucoma

Estrogen is essential in maintaining various physiological features in women, and a decline in estrogen levels are known to give rise to numerous unfortunate symptoms associated with menopause. To alleviate these symptoms hormone replacement therapy with estrogen is often used, and has been shown to be fruitful in improving quality of life in women suffering from postmenopausal discomforts. An often forgotten condition associated with menopause is the optic nerve disorder, glaucoma. Thus, estrogen may also have an impact in maintaining the retinal ganglion cells (RGCs), which make up the optic nerve, thereby preventing glaucomatous neurodegeneration. This review aims to provide an overview of possible associations of estrogen and the glaucoma subtype, primary open-angle glaucoma (POAG), by evaluating the current literature through a PubMed-based literature search. Multiple in vitro and in vivo studies of RGC protection, as well as clinical and epidemiological data concerning the well-defined retinal neurodegenerative disorder POAG have been reviewed. Over all, deficiencies in retinal estrogen may potentially instigate RGC loss, visual disability, and eventual blindness. Estrogen replacement therapy may therefore be a beneficial future treatment. However, more studies are needed to confirm the relevance of estrogen in glaucoma prevention.

Low-carbohydrate-diet scores and the risk of primary open-angle glaucoma: data from three US cohorts

BACKGROUND/OBJECTIVES

To assess the long-term association between low-carbohydrate dietary patterns and incident primary open-angle glaucoma (POAG), and POAG subtypes defined by highest untreated intraocular pressure (IOP) and by pattern of visual field (VF) loss at diagnosis.

SUBJECTS/METHODS

We followed 185,638 participants of three large US prospective cohorts biennially (1976-2016, 1986-2016 and 1991-2017). Deciles of three low-carbohydrate-diet scores were calculated to represent adherence to diets lower in carbohydrate and higher in protein and fat from any source, animal sources or plant sources. We confirmed POAG cases (n = 2112) by medical record review and used Cox proportional hazards models to estimate multivariable-adjusted relative risks (MVRRs) and 95% confidence intervals (CIs).

RESULTS

There was no association between the three types of low-carbohydrate-diet scores and POAG: the MVRR for POAG in the highest vs. lowest deciles was 1.13 (95% CI, 0.91-1.39; Ptrend = 0.40) for the overall score; 1.10 (95% CI, 0.89-1.35; Ptrend = 0.38) for the animal score and 0.96 (95% CI, 0.79-1.18; Ptrend = 0.88) for the vegetable score. No differential associations by IOP level was found (Pheterogeneity ≥ 0.06). However, the vegetable score showed a suggestive inverse association with early paracentral VF loss (highest vs. lowest decile MVRR = 0.78 [95% CI, 0.55-1.10]; Ptrend = 0.12) but not with peripheral VF loss only (MVRR = 1.09 [95% CI, 0.83-1.44]; Ptrend = 0.14; Pheterogeneity = 0.03).

CONCLUSIONS

Low-carbohydrate diets were not associated with risk of POAG. Our data suggested that higher consumption of fat and protein from vegetable sources substituting for carbohydrates was associated with lower risk of the POAG subtype with initial paracentral VF loss.

Lack of correlation between S1 RNA binding domain 1 SNP rs3213787/rs11884064 and normal-tension glaucoma in a population from the Republic of Korea

Previous studies have reported the association of the S1 RNA binding domain 1 (SRBD1) gene with open-angle glaucoma in various ethnic populations. However, in those studies, the definition of the patients differed, as did the results. Therefore, the relevance of the SRBD1 gene to normal tension glaucoma (NTG) appears uncertain at present. Thus, we investigated the relationship between the SRBD1 gene and NTG in a Korean NTG cohort.In total, 159 unrelated Korean patients with NTG and 103 Korean control subjects were recruited. Thus, a total of 262 participants were analyzed for SRBD1 (rs3213787 and rs11884064) gene polymorphisms.The minor allele frequency of rs3213787 was found to be 0.13 and 0.19 in NTG cases and controls, respectively. The genetic association analysis of SNP rs3213787 revealed no significant difference in genotype distribution between NTG cases and controls in allelic (odds ratio [OR] = 0.634, P = .063), dominant (OR = 0.589, P = .066) or recessive models (OR = 0.639, P = .7716). The minor allele frequency of rs11884064 was found to be 0.24 and 0.25 in NTG cases and controls, respectively. For rs11884064, no significant difference in genotype distribution was observed between NTG cases and controls in allelic (OR = 0.938, P = .755), dominant (OR = 0.927, P = .798) or recessive models (OR = 0.920, P = 1.000).The current study suggested that SRBD1 gene polymorphisms (rs3213787 and rs11884064) may not be associated with genetic susceptibility to NTG in a Korean cohort.

Lactate: More Than Merely a Metabolic Waste Product in the Inner Retina

The retina is an extension of the central nervous system and has been considered to be a simplified, more tractable and accessible version of the brain for a variety of neuroscience investigations. The optic nerve displays changes in response to underlying neurodegenerative diseases, such as stroke, multiple sclerosis, and Alzheimer's disease, as well as inner retinal neurodegenerative disease, e.g., glaucoma. Neurodegeneration has increasingly been linked to dysfunctional energy metabolism or conditions in which the energy supply does not meet the demand. Likewise, increasing lactate levels have been correlated with conditions consisting of unbalanced energy supply and demand, such as ischemia-associated diseases or excessive exercise. Lactate has thus been acknowledged as a metabolic waste product in organs with high energy metabolism. However, in the past decade, numerous beneficial roles of lactate have been revealed in the central nervous system. In this context, lactate has been identified as a valuable energy substrate, protecting against glutamate excitotoxicity and ischemia, as well as having signaling properties which regulate cellular functions. The present review aims to summarize and discuss protective roles of lactate in various model systems (in vitro, ex vivo, and in vivo) reflecting the inner retina focusing on lactate metabolism and signaling in inner retinal homeostasis and disease.

Beneficial effects of saffron (Crocus sativus L.) in ocular pathologies, particularly neurodegenerative retinal diseases

Saffron (Crocus sativus L.) has been traditionally used in food preparation and as a medicinal plant. It currently has numerous therapeutic properties attributed to it, such as protection against ischemia, as well as anticonvulsant, antidepressant, anxiolytic, hypolipidemic, anti-atherogenic, anti-hypertensive, antidiabetic, and anti-cancer properties. In addition, saffron has remarkable beneficial properties, such as anti-apoptotic, anti-inflammatory and antioxidant activities, due to its main metabolites, among which crocin and crocetin stand out. Furthermore, increasing evidence underwrites the possible neuroprotective role of the main bioactive saffron constituents in neurodegenerative diseases, such as Parkinson’s and Alzheimer’s diseases, both in experimental models and in clinical studies in patients. Currently, saffron supplementation is being tested for ocular neurodegenerative pathologies, such as diabetic retinopathy, retinitis pigmentosa, age-related macular degeneration and glaucoma, among others, and shows beneficial effects. The present article provides a comprehensive and up to date report of the investigations on the beneficial effects of saffron extracts on the main neurodegenerative ocular pathologies and other ocular diseases. This review showed that saffron extracts could be considered promising therapeutic agents to help in the treatment of ocular neurodegenerative diseases.

Cytoprotective Effects of Dinitrosyl Iron Complexes on Viability of Human Fibroblasts and Cardiomyocytes

Nitric oxide (NO) is an important signaling molecule that plays a key role in maintaining vascular homeostasis. Dinitrosyl iron complexes (DNICs) generating NO are widely used to treat cardiovascular diseases. However, the involvement of DNICs in the metabolic processes of the cell, their protective properties in doxorubicin-induced toxicity remain to be clarified. Here, we found that novel class of mononuclear DNICs with functional sulfur-containing ligands enhanced the cell viability of human lung fibroblasts and rat cardiomyocytes. Moreover, DNICs demonstrated remarkable protection against doxorubicin-induced toxicity in fibroblasts and in rat cardiomyocytes (H9c2 cells). Data revealed that the DNICs compounds modulate the mitochondria function by decreasing the mitochondrial membrane potential (ΔΨ_m). Results of flow cytometry showed that DNICs were not affected the proliferation, growth of fibroblasts. In addition, this study showed that DNICs did not affect glutathione levels and the formation of reactive oxygen species in cells. Moreover, results indicated that DNICs maintained the ATP equilibrium in cells. Taken together, these findings show that DNICs have protective properties in vitro. It was further suggested that DNICs may be uncouplers of oxidative phosphorylation in mitochondria and protective mechanism is mainly provided by the leakage of excess charge through the mitochondrial membrane. It is assumed that the DNICs have the therapeutic potential for treating cardiovascular diseases and for decreasing of chemotherapy-induced cardiotoxicity in cancer survivors.

Mitochondrial DNA Variation and Disease Susceptibility in Primary Open-Angle Glaucoma

Purpose

To determine whether mitochondrial DNA haplogroups or rare variants associate with primary open-angle glaucoma in subjects of European descent.

Methods

A case-control comparison of age- and sex-matched cohorts of 90 primary open-angle glaucoma patients and 95 population controls. Full mitochondrial DNA sequences from peripheral blood were generated by next-generation sequencing and compared to the revised Cambridge Reference Sequence to define mitochondrial haplogroups and variants.

Results

Most subjects were of the major European haplogroups H, J, K, U, and T. Logistic regression analysis showed haplogroup U to be significantly underrepresented in male primary open-angle glaucoma subjects (odds ratio 0.25; 95% confidence interval [CI] 0.09-0.67; P = 0.007; Bonferroni multiple testing P = 0.022). Variants in the mitochondrial DNA gene MT-ND2 were overrepresented in the control group (P = 0.005; Bonferroni multiple testing correction P = 0.015).

Conclusions

Mitochondrial DNA ancestral lineages modulate the risk for primary open-angle glaucoma in populations of European descent. Haplogroup U and rare variants in the mitochondrial DNA-encoded MT-ND2 gene may be protective against primary open-angle glaucoma. Larger studies are warranted to explore haplogroup associations with disease risk in different ethnic groups and define biomarkers of primary open-angle glaucoma endophenotypes to target therapeutic strategies.

The association of mitochondrial DNA haplogroups with POAG in African Americans

Mitochondrial dysfunction has been implicated in the pathogenesis of primary open-angle glaucoma (POAG). However, the potential significance of mitochondrial DNA (mtDNA) haplogroups to POAG has not been evaluated in the overaffected African American population. To investigate the association of mtDNA haplogroups with POAG and its phenotypic characteristics, genotyping data from 4081 African American subjects (1919 cases and 2162 controls) was analyzed using 1293 positions on mtDNA. The overall frequency of mtDNA haplogroups in the Primary Open-Angle African American Glaucoma Genetics (POAAGG) study cohort was 37% L3, 29% L2, 21% L1, 4% L0, and 10% non-African haplogroups (non-L). When all haplogroups (L0, L1, L2, and non-L) were compared against theL3 reference group, after adjusting by age and principal component of ancestry, the non-L3 haplogroups showed higher risk of POAG (OR-1.19, p = 0.02), with a particularly strong association among males (OR = 1.41, p = 0.003). More specifically the non-L group was associated with higher POAG risk than the L3 haplogroup (OR = 1.77, p = 0.007, Bonferroni adjusted p = 0.027) and to the L3e (n = 256, OR = 1.92, p = 0.007, Bonferroni adjusted p = 0.029). No significant association was found when genders were analyzed together or in female only analysis. There were no significant differences in various POAG endophenotypes across mtDNA haplogroups. This study expands our knowledge of mitochondrial genetics and mtDNA haplogroup associations in African American POAG. Further work is needed to better understand the functional role of mtDNA polymorphisms and their interactions with nuclear genes that affect POAG.

Normal-tension glaucoma: Pathogenesis and genetics

Normal-tension glaucoma (NTG) is a multifactorial optic neuropathy which, similar to open-angle glaucomas, is characterized by progressive retinal ganglion cell death and glaucomatous visual field loss. The major distinction of NTG from open-angle glaucomas is that the intraocular pressure (IOP) does not exceed the normal range. Missing the major risk factor and target of therapy, the elevated IOP, NTG poses a clinical challenge. Several insightful reviews have been published on the pathophysiology of NTG describing the possible underlying mechanisms. The current literature available also suggests that a significant percentage of patients with NTG (as high as 21%) have a family history of glaucoma, indicating a genetic predisposition to the disease. These facts strengthen the indication that NTG remains an enigmatic process. The aim of this review was to summarize the vascular, mechanical and genetic components considered to be responsible for NTG development and to discuss the mechanisms through which they are involved in the pathogenesis of NTG.

Investigation of whole mitochondrial genome variation in normal tension glaucoma

Glaucoma is one of the leading causes of visual impairment and blindness worldwide. However, the cause of retinal ganglion cell loss and damage of the optic nerve in its pathogenesis is largely unknown. The high energy demands of these cells may reflect their strong dependence on mitochondrial function and thus sensitivity to mitochondrial defects. To address this issue, we studied whole mitochondrial genome variation in normal tension glaucoma patients and control individuals from the Polish population using next generation sequencing. Our findings indicate that few features of mitochondrial DNA variation are different for glaucoma patients and control subjects. New insights into normal tension glaucoma development are discussed. We provide also a comprehensive approach for mitochondrial DNA analysis and variant evaluation.

Research progress on human genes involved in the pathogenesis of glaucoma (Review)

Glaucoma is the leading cause of irreversible blindness globally. It is known that the incidence of glaucoma is closely associated with inheritance. A large number of studies have suggested that genetic factors are involved in the occurrence and development of glaucoma, and even affect the drug sensitivity and prognosis of glaucoma. In the present review, 22 loci of glaucoma are presented, including the relevant genes (myocilin, interleukin 20 receptor subunit B, optineurin, ankyrin repeat- and SOCS box-containing protein 10, WD repeat-containing protein 36, EGF-containing fibulin-like extracellular matrix protein 1, neurotrophin 4, TANK-binding kinase 1, cytochrome P450 subfamily I polypeptide 1, latent transforming growth factor β binding protein 2 and TEK tyrosine kinase endothelial) and 74 other genes (including toll-like receptor 4, sine oculis homeobox Drosophila homolog of 1, doublecortin-like kinase 1, RE repeats-encoding gene, retinitis pigmentosa GTPase regulator-interacting protein, lysyl oxidase-like protein 1, heat-shock 70-kDa protein 1A, baculoviral IAP repeat-containing protein 6, 5,10-methylenetetrahydrofolate reductase and nitric oxide synthase 3 and nanophthalmos 1) that are more closely associated with glaucoma. The pathogenesis of these glaucoma-associated genes, glaucomatous genetics and genetic approaches, as well as glaucomatous risk factors, including increasing age, glaucoma family history, high myopia, diabetes, ocular trauma, smoking, intraocular pressure increase and/or fluctuation were also discussed.

The MT-CO1 V83I Polymorphism is a Risk Factor for Primary Open-Angle Glaucoma in African American Men

Purpose

We investigate the function of the V83I polymorphism (m.6150G>A, rs879053914) in the mitochondrial cytochrome c oxidase subunit 1 (MT-CO1) gene and its role in African American (AA) primary open-angle glaucoma (POAG).

Methods

This study used Sanger sequencing (1339 cases, 850 controls), phenotypic characterization of Primary Open-Angle African American Glaucoma Genetics study (POAAGG) cases, a masked chart review of CO1 missense cases (V83I plus M117T, n = 29) versus wild type cases (n = 29), a yeast 2-hybrid (Y2H) cDNA library screen, and quantification of protein-protein interactions by Y2H and ELISA.

Results

The association of V83I with POAG in AA was highly significant for men (odds ratio [OR] 6.5; 95% confidence interval [CI] 2.0-21.3, P = 0.0001), but not for women (OR 1.1; 95% CI, 0.62-2.00, P = 0.78). POAG cases having CO1 double missense mutation (V83I + M117T, L1c2 haplogroup) had a higher cup-to-disc ratio (0.77 vs. 0.71, P = 0.04) and significantly worse visual function (average pattern standard deviation, 6.5 vs. 4.3, P = 0.009; average mean deviation -10.4 vs. -4.5, P = 0.006) when compared to matched wild type cases (L1b haplogroup). Interaction of the V83I region of CO1 with amyloid beta peptide (Aβ) was confirmed by ELISA assay, and this interaction was abrogated by V83I. A Y2H screen of an adult human brain cDNA library with the V83 region of CO1 as bait retrieved the UBQLN1 gene.

Conclusions

The V83I polymorphism was associated strongly with POAG in AA men and disrupts Aβ-binding to CO1. This region also interacts with a neuroprotective protein, UBQLN1.

Correlations between Mitofusin 2 Expression in Fibroblasts and Pelvic Organ Prolapse: An In vitro Study

BACKGROUND

Both Mitofusin 2 (Mfn2) and pelvic organ prolapse (POP) are related to aging. The aim of the present study was to investigate the variations of Mfn2 expression in the uterosacral ligaments of patients with and/or without POP and their correlations with the expression of procollagen.

METHODS

Fibroblasts were cultured using tissue specimens that were harvested from the uterosacral ligaments of POP and non-POP (NPOP) patients (n = 10 for each group) from September 2016 to December 2016. The Cell Counting Kit-8 (CCK-8) assay was used to compare the differences in cell proliferation between the two groups. Relative quantitative reverse transcription-polymerase chain reaction and Western blotting assays were employed to assess the differences in the mRNA and protein expression levels of Mfn2 and procollagen 1A1/1A2/3A1 between the two groups. The changes in procollagen expression were assessed following the downregulation of Mfn2 in the POP group using RNAi. The data were assessed with independent sample t- test or general linear model univariate analysis using the SPSS 13.0 software.

RESULTS

The results from CCK-8 assay indicated that cell viability in the POP group was significantly lower compared with that of the NPOP group (td5, 7, 9, 11= -5.925, -6.851, -9.129, and -9.661, respectively, all P < 0.001, from D5 to D11). The mRNA and protein expression levels of Mfn2 in the cultured fibroblasts of the POP group were significantly higher compared with those of the NPOP group (mRNA: t = 2.425, P = 0.032; protein: t = 2.392, P = 0.037, respectively), whereas only the expression levels of procollagen 1A1/1A2/3A1 were significantly higher in the NPOP group (mRNA: t = -2.165, P1A1 = 0.041; t = -2.741, P1A2 = 0.026; t = -2.147, P3A1 = 0.045, respectively; protein: t = -2.418, P1A1 = 0.029; t = -2.405, P1A2 = 0.033; t = -2.470, P3A1 = 0.012, respectively). The expression levels of procollagen in the POP group increased following the downregulation of Mfn2.

CONCLUSIONS

The proliferation rate and cell viability of the fibroblasts in the POP group were significantly lower compared with those in the NPOP group. In the POP fibroblasts, Mfn2 expression was increased, while procollagen expression was decreased.

Glaucoma as a Metabolic Optic Neuropathy: Making the Case for Nicotinamide Treatment in Glaucoma

Mitochondrial dysfunction may be an important, if not essential, component of human glaucoma. Using transcriptomics followed by molecular and neurobiological techniques, we have recently demonstrated that mitochondrial dysfunction within retinal ganglion cells is an early feature in the DBA/2J mouse model of inherited glaucoma. Guided by these findings, we discovered that the retinal level of nicotinamide adenine dinucleotide (NAD, a key molecule for mitochondrial health) declines in an age-dependent manner. We hypothesized that this decline in NAD renders retinal ganglion cells susceptible to damage during periods of elevated intraocular pressure. To replete NAD levels in this glaucoma, we administered nicotinamide (the amide of vitamin B3). At the lowest dose tested, nicotinamide robustly protected from glaucoma (~70% of eyes had no detectable glaucomatous neurodegeneration). At this dose, nicotinamide had no influence on intraocular pressure and so its effect was neuroprotective. At the highest dose tested, 93% of eyes had no detectable glaucoma. This represents a ~10-fold decrease in the risk of developing glaucoma. At this dose, intraocular pressure still became elevated but there was a reduction in the degree of elevation showing an additional benefit. Thus, nicotinamide is unexpectedly potent at preventing this glaucoma and is an attractive option for glaucoma therapeutics. Our findings demonstrate the promise for both preventing and treating glaucoma by interventions that bolster metabolism during increasing age and during periods of elevated intraocular pressure. Nicotinamide prevents age-related declines in NAD (a decline that occurs in different genetic contexts and species). NAD precursors are reported to protect from a variety of neurodegenerative conditions. Thus, nicotinamide may provide a much needed neuroprotective treatment against human glaucoma. This manuscript summarizes human data implicating mitochondria in glaucoma, and argues for studies to further assess the safety and efficacy of nicotinamide in human glaucoma care.

The Role of Microglia in Retinal Neurodegeneration: Alzheimer's Disease, Parkinson, and Glaucoma

Microglia, the immunocompetent cells of the central nervous system (CNS), act as neuropathology sensors and are neuroprotective under physiological conditions. Microglia react to injury and degeneration with immune-phenotypic and morphological changes, proliferation, migration, and inflammatory cytokine production. An uncontrolled microglial response secondary to sustained CNS damage can put neuronal survival at risk due to excessive inflammation. A neuroinflammatory response is considered among the etiological factors of the major aged-related neurodegenerative diseases of the CNS, and microglial cells are key players in these neurodegenerative lesions. The retina is an extension of the brain and therefore the inflammatory response in the brain can occur in the retina. The brain and retina are affected in several neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), and glaucoma. AD is an age-related neurodegeneration of the CNS characterized by neuronal and synaptic loss in the cerebral cortex, resulting in cognitive deficit and dementia. The extracellular deposits of beta-amyloid (Aβ) and intraneuronal accumulations of hyperphosphorylated tau protein (pTau) are the hallmarks of this disease. These deposits are also found in the retina and optic nerve. PD is a neurodegenerative locomotor disorder with the progressive loss of dopaminergic neurons in the substantia nigra. This is accompanied by Lewy body inclusion composed of α-synuclein (α-syn) aggregates. PD also involves retinal dopaminergic cell degeneration. Glaucoma is a multifactorial neurodegenerative disease of the optic nerve, characterized by retinal ganglion cell loss. In this pathology, deposition of Aβ, synuclein, and pTau has also been detected in retina. These neurodegenerative diseases share a common pathogenic mechanism, the neuroinflammation, in which microglia play an important role. Microglial activation has been reported in AD, PD, and glaucoma in relation to protein aggregates and degenerated neurons. The activated microglia can release pro-inflammatory cytokines which can aggravate and propagate neuroinflammation, thereby degenerating neurons and impairing brain as well as retinal function. The aim of the present review is to describe the contribution in retina to microglial-mediated neuroinflammation in AD, PD, and glaucomatous neurodegeneration.

Mitochondrial dysfunction and oxidative stress in corneal disease

The cornea is the anterior transparent surface and the main refracting structure of the eye. Mitochondrial dysfunction and oxidative stress are implicated in the pathogenesis of inherited (e.g. Kearns Sayre Syndrome) and acquired corneal diseases (e.g. keratoconus and Fuchs endothelial corneal dystrophy). Both antioxidants and reactive oxygen species are found in the healthy cornea. There is increasing evidence of imbalance in the oxidative balance and mitochondrial function in the cornea in disease states. The cornea is vulnerable to mitochondrial dysfunction and oxidative stress due to its highly exposed position to ultraviolet radiation and high oxygen tension. The corneal endothelium is vulnerable to accumulating mitochondrial DNA (mtDNA) damage due to the post- mitotic nature of endothelial cells, yet their mitochondrial genome is continually replicating and mtDNA mutations can develop and accumulate with age. The unique physiology of the cornea predisposes this structure to oxidative damage, and there is interplay between inherited and acquired mitochondrial dysfunction, oxidative damage and a number of corneal diseases. By targeting mitochondrial dysfunction in corneal disease, emerging treatments may prevent or reduce visual loss.

High Pressure-Induced mtDNA Alterations in Retinal Ganglion Cells and Subsequent Apoptosis

Purpose: Our previous study indicated that mitochondrial DNA (mtDNA) damage and mutations are crucial to the progressive loss of retinal ganglion cells (RGCs) in a glaucomatous rat model. In this study, we examined whether high pressure could directly cause mtDNA alterations and whether the latter could lead to mitochondrial dysfunction and RGC death. Methods: Primary cultured rat RGCs were exposed to 30 mm Hg of hydrostatic pressure (HP) for 12, 24, 48, 72, 96 and 120 h. mtDNA alterations and mtDNA repair/replication enzymes OGG1, MYH and polymerase gamma (POLG) expressions were also analyzed. The RGCs were then infected with a lentiviral small hairpin RNA (shRNA) expression vector targeting POLG (POLG-shRNA), and mtDNA alterations as well as mitochondrial function, including complex I/III activities and ATP production were subsequently studied at appropriate times. Finally, RGC apoptosis and the mitochondrial-apoptosis pathway-related protein cleaved caspase-3 were detected using a Terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) assay and western blotting, respectively. Results: mtDNA damage was observed as early as 48 h after the exposure of RGCs to HP. At 120 h after HP, mtDNA damage and mutations significantly increased, reaching >40% and 4.8 ± 0.3-fold, respectively, compared with the control values. Twelve hours after HP, the expressions of OGG1, MYH and POLG mRNA in the RGCs were obviously increased 5.02 ± 0.6-fold (p < 0.01), 4.3 ± 0.2-fold (p < 0.05), and 0.8 ± 0.09-fold (p < 0.05). Western blot analysis showed that the protein levels of the three enzymes decreased at 72 and 120 h after HP (p < 0.05). After interference with POLG-shRNA, the mtDNA damage and mutations were significantly increased (p < 0.01), while complex I/III activities gradually decreased (p < 0.05). Corresponding decreases in membrane potential and ATP production appeared at 5 and 6 days after POLG-shRNA transfection respectively (p < 0.05). Increases in the apoptosis of RGCs and cleaved caspase-3 protein expression were observed after mtDNA damage and mutations. Conclusions: High pressures could directly cause mtDNA alterations, leading to mitochondrial dysfunction and RGC death.

Assessing the Association of Mitochondrial Genetic Variation With Primary Open-Angle Glaucoma Using Gene-Set Analyses

PURPOSE

Recent studies indicate that mitochondrial proteins may contribute to the pathogenesis of primary open-angle glaucoma (POAG). In this study, we examined the association between POAG and common variations in gene-encoding mitochondrial proteins.

METHODS

We examined genetic data from 3430 POAG cases and 3108 controls derived from the combination of the GLAUGEN and NEIGHBOR studies. We constructed biological-system coherent mitochondrial nuclear-encoded protein gene-sets by intersecting the MitoCarta database with the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. We examined the mitochondrial gene-sets for association with POAG and with normal-tension glaucoma (NTG) and high-tension glaucoma (HTG) subsets using Pathway Analysis by Randomization Incorporating Structure.

RESULTS

We identified 22 KEGG pathways with significant mitochondrial protein-encoding gene enrichment, belonging to six general biological classes. Among the pathway classes, mitochondrial lipid metabolism was associated with POAG overall (P = 0.013) and with NTG (P = 0.0006), and mitochondrial carbohydrate metabolism was associated with NTG (P = 0.030). Examining the individual KEGG pathway mitochondrial gene-sets, fatty acid elongation and synthesis and degradation of ketone bodies, both lipid metabolism pathways, were significantly associated with POAG (P = 0.005 and P = 0.002, respectively) and NTG (P = 0.0004 and P < 0.0001, respectively). Butanoate metabolism, a carbohydrate metabolism pathway, was significantly associated with POAG (P = 0.004), NTG (P = 0.001), and HTG (P = 0.010).

CONCLUSIONS

We present an effective approach for assessing the contributions of mitochondrial genetic variation to open-angle glaucoma. Our findings support a role for mitochondria in POAG pathogenesis and specifically point to lipid and carbohydrate metabolism pathways as being important.

Risk factors for open-angle glaucoma in Nigeria: results from the Nigeria National Blindness and Visual Impairment Survey

BACKGROUND

The glaucoma-specific blindness prevalence in Nigeria (0.7 %, 95 % CI 0.6-0.9 %) among those aged ≥40 years is one of the highest ever reported. This study determined the risk factors for open-angle glaucoma (OAG) in adults examined in the Nigeria National Blindness and Visual Impairment Survey.

METHODS

A nationally representative sample of 13,591 people aged ≥40 years in 305 clusters in Nigeria were examined (response rate 90.4 %) between January 2005 to June 2007. Everyone had logMAR visual acuity measurement, Frequency Doubling Technology (FDT) visual field testing, autorefraction, A-scan biometry and optic disc assessment. Full ocular examination (n = 6397), included Goldmann applanation tonometry. Values for defining glaucoma using International Society of Geographical and Epidemiological Ophthalmology criteria were derived from the study population. Disc images were graded by Moorfields Eye Hospital Reading Centre. Socio-demographic factors (age, gender, ethnicity, literacy and place of residence), ocular parameters (intraocular pressure [IOP], axial length and mean ocular perfusion pressure [MOPP]) and systemic parameters (blood pressure, blood glucose and body mass index [BMI]) were assessed for association with OAG.

RESULTS

Thirteen thousand eighty-one (96 %) of 13,591 participants had vertical cup:disc ratio measured in at least one eye. 682 eyes of 462 participants were classified as OAG, with 12,738 controls. In univariate analyses the following were associated with OAG: increasing age, male gender, Igbo and Yoruba ethnic groups, illiteracy, longer axial length, higher IOP, lower MOPP, greater severity of hypertension and low BMI (underweight). In multivariate analysis, increasing age (odds ratio [OR] 1.04, 95 % CI 1.03-1.05), higher IOP (OR 1.22, 95 % CI 1.18-1.25) and Igbo ethnicity (OR 1.73, 95 % CI 1.18-2.56) were independent risk factors for OAG.

CONCLUSION

Case detection strategies for OAG should be improved for those aged ≥40 years and for ethnic groups most at risk as a public health intervention.

Association of Common Variants in eNOS Gene with Primary Open Angle Glaucoma: A Meta-Analysis

Purpose. To clarify the association of endothelial nitric oxide synthase (eNOS) polymorphisms and primary open angle glaucoma (POAG). Methods. After a systematic literature search in the MEDLINE, EMBASE, and ISI Web of Science databases, all relevant studies evaluating the association between the polymorphisms (rs2070744 and rs1799983) of eNOS gene and POAG were screened and included. The pooled odds ratios (ORs) and the 95% confidence interval (CI) of each single-nucleotide polymorphism (SNP) in five genetic models were estimated using fixed-effect model if I (2) < 50% in the test for heterogeneity; otherwise the random-effects model was used. Results. Thirty-one records were obtained, with five being suitable for meta-analysis. The overall results showed that both TT genotype in rs2070744 and GG genotype in rs1799983 are associated with decreased risk of POAG susceptibility. Stratified analysis based on ethnicity showed that the association of rs2070744 with POAG remained only in Caucasians. Results of subgroup analysis by sex indicated association between both polymorphisms and POAG in female group, but not in male group. Conclusions. TT genotype and/or T-allele in rs2070744, as well as GG genotype and/or G-allele in rs1799983, was associated with decreased risk for POAG overall and in female group.

Glaucoma: Focus on mitochondria in relation to pathogenesis and neuroprotection

Primary open-angle glaucoma (POAG) is a common form of glaucoma in which retinal ganglion cells (RGCs) die at varying intervals. Primary open-angle glaucoma is often associated with an increased intraocular pressure (IOP), which when reduced, can slow down the progression of the disease. However, it is essential to develop better modes of treatments for glaucoma patients. In this overview, we discuss the hypothesis that RGC mitochondria are affected during the initiation of POAG, by becoming gradually weakened, but at different rates because of their specific receptor profiles. With this in mind, we argue that neuroprotection in the context of glaucoma should focus on preserving RGC mitochondrial function and suggest a number of ways by which this can theoretically be achieved. Since POAG is a chronic disease, any neuroprotective treatment strategy must be tolerated over many years. Theoretically, topically applied substances should have the fewest side effects, but it is questionable whether sufficient compounds can reach RGC mitochondria to be effective. Therefore, other delivery procedures that might result in greater concentrations of neuroprotectants reaching RGC mitochondria are being developed. Red-light therapy represents another therapeutic alternative for enhancing RGC mitochondrial functions and has the advantage of being both non-toxic and non-invasive.

Crocin protects retinal ganglion cells against H2O2-induced damage through the mitochondrial pathway and activation of NF-κB

Glaucoma is a degenerative nerve disorder that results in irreversible blindness. It has been reported that the apoptosis of retinal ganglion cells (RGCs) is a hallmark of glaucoma. Oxidative stress is one of the major factors that cause apoptosis of RGCs. Crocin has many beneficial effects, including antioxidant and anti-apoptotic actions. However, the mechanism by which crocin protects against oxidative stress‑induced damage to RGCs remains unclear. The present study aimed to investigate the mechanism by which crocin protects RGC-5 cells against H2O2-induced damage. H2O2 was used to establish a model of oxidative stress injury in RGC-5 cells to mimic the development of glaucoma in vitro. Different concentrations (0.1 and 1 µM) of crocin were added to test whether crocin was capable of protecting RGCs from H2O2-induced damage. WST-1, lactic dehydrogenase (LDH) release and Annexin V/FITC assays were then performed. Levels of reactive oxygen species (ROS) were detected using a ROS assay kit, mitochondrial membrane potential (ΔΨm) was analyzed by JC-1 staining, caspase-3 activity was examined using a Caspase-3 assay kit, and the protein levels of Bax, Bcl-1 and cytochrome c were measured using western blot analysis. In addition, the protein level of phosphorylated nuclear factor-κB (p-NF-κB) p65 was also evaluated using western blot analysis. The results showed that crocin protected RGC-5 cells from apoptosis, decreased LDH release and enhanced cell viability. Additional experiments demonstrated that crocin decreased ROS levels, increased ΔΨm, downregulated the protein expression of Bax and cytochrome c, promoted Bcl-2 protein expression and activated NF-κB. Taken together, the findings of this study indicate that crocin prevented H2O2‑induced damage to RGCs through the mitochondrial pathway and activation of NF-κB.

Measurement of Systemic Mitochondrial Function in Advanced Primary Open-Angle Glaucoma and Leber Hereditary Optic Neuropathy

Primary Open Angle Glaucoma (POAG) is a common neurodegenerative disease characterized by the selective and gradual loss of retinal ganglion cells (RGCs). Aging and increased intraocular pressure (IOP) are glaucoma risk factors; nevertheless patients deteriorate at all levels of IOP, implying other causative factors. Recent evidence presents mitochondrial oxidative phosphorylation (OXPHOS) complex-I impairments in POAG. Leber Hereditary Optic Neuropathy (LHON) patients suffer specific and rapid loss of RGCs, predominantly in young adult males, due to complex-I mutations in the mitochondrial genome. This study directly compares the degree of OXPHOS impairment in POAG and LHON patients, testing the hypothesis that the milder clinical disease in POAG is due to a milder complex-I impairment. To assess overall mitochondrial capacity, cells can be forced to produce ATP primarily from mitochondrial OXPHOS by switching the media carbon source to galactose. Under these conditions POAG lymphoblasts grew 1.47 times slower than controls, whilst LHON lymphoblasts demonstrated a greater degree of growth impairment (2.35 times slower). Complex-I enzyme specific activity was reduced by 18% in POAG lymphoblasts and by 29% in LHON lymphoblasts. We also assessed complex-I ATP synthesis, which was 19% decreased in POAG patients and 17% decreased in LHON patients. This study demonstrates both POAG and LHON lymphoblasts have impaired complex-I, and in the majority of aspects the functional defects in POAG were milder than LHON, which could reflect the milder disease development of POAG. This new evidence places POAG in the spectrum of mitochondrial optic neuropathies and raises the possibility for new therapeutic targets aimed at improving mitochondrial function.

Resistance to the most common optic neuropathy is associated with systemic mitochondrial efficiency

Glaucomatous optic neuropathy, an important neurodegenerative condition and the commonest optic neuropathy in humans, is the leading cause of irreversible blindness worldwide. Its prevalence and incidence increase exponentially with ageing and raised intraocular pressure (IOP). Using glaucomatous optic neuropathy as an exemplar for neurodegeneration, this study investigates putative factors imparting resistance to neurodegeneration. Systemic mitochondrial function, oxidative stress and vascular parameters were compared from isolated lymphocytes, whole blood and urine samples between 30 patients who have not developed the neuropathy despite being exposed for many years to very high IOP ('resistant'), 30 fast deteriorating glaucoma patients despite having low IOP ('susceptible'), and 30 age-similar controls. We found that 'resistant' individuals showed significantly higher rates of ADP phosphorylation by mitochondrial respiratory complexes I, II and IV, hyperpolarised mitochondrial membrane potential, higher levels of mitochondrial DNA, and enhanced capacity to deal with cytosolic calcium overload and exogenous oxidative stress, as compared to both controls and glaucoma patients. While it has been known for some years that mitochondrial dysfunction is implicated in neurodegeneration, this study provides a fresh perspective to the field of neurodegeneration by providing, for the first time, evidence that systemic mitochondrial efficiency above normal healthy levels is associated with an enhanced ability to withstand optic nerve injury. These results demonstrate the importance of cellular bioenergetics in glaucomatous disease progression, with potential relevance for other neurodegenerative disorders, and raise the possibility for new therapeutic targets in the field of neurodegeneration.