Increasing evidence indicates that changes in the redox system may contribute to the pathogenesis of multiple optic neuropathies. Optic neuropathies are characterized by the neurodegeneration of the inner-most retinal neurons, the retinal ganglion cells (RGCs), and their axons, which form the optic nerve. Often, optic neuropathies are asymptomatic until advanced stages, when visual impairment or blindness is unavoidable despite existing treatments. In this review, we describe systemic and, whenever possible, ocular redox dysregulations observed in patients with glaucoma, ischemic optic neuropathy, optic neuritis, hereditary optic neuropathies (i.e., Leber’s hereditary optic neuropathy and autosomal dominant optic atrophy), nutritional and toxic optic neuropathies, and optic disc drusen. We discuss aspects related to anti/oxidative stress biomarkers that need further investigation and features related to study design that should be optimized to generate more valuable and comparable results. Understanding the role of oxidative stress in optic neuropathies can serve to develop therapeutic strategies directed at the redox system to arrest the neurodegenerative processes in the retina and RGCs and ultimately prevent vision loss.

The main risk factor for primary open-angle glaucoma (POAG) is increased intraocular pressure (IOP). It is of interest that about half of the patients have an IOP within the normal range (normal-tension glaucoma, NTG). Additionally, there is a group of patients with a high IOP but no glaucomatous neurodegeneration (ocular hypertension, OHT). Therefore, risk factors other than IOP are involved in the pathogenesis of glaucoma. Since the retina has a very high oxygen-demand, decreased autoregulation and a fluctuating oxygen supply to the retina have been linked to glaucomatous neurodegeneration. To assess the significance of these mechanisms, we have utilized a human experimental model, in which we stress participants with a fluctuating oxygen supply. Levels of oxidative stress molecules, antioxidants, and lipid mediators were measured in the plasma. Patients with NTG, OHT, and control subjects were found to have similar levels of oxidative stress markers. In contrast, patients with OHT had a higher level of total antioxidant capacity (TAC) and pro-homeostatic lipid mediators. Thus, we suggest that OHT patients manage fluctuating oxygen levels more efficiently and, thus, are less susceptible to glaucomatous neurodegenerations, due to enhanced systemic antioxidant protection.

BACKGROUND Retinal organoids serve as excellent human-specific disease models for conditions affecting otherwise inaccessible retinal tissue from patients. They permit the isolation of key cell types affected in various eye diseases including retinal ganglion cells (RGCs) and Muller glia. AIM To refine human-induced pluripotent stem cells (hiPSCs) differentiated into three-dimensional (3D) retinal organoids to generate sufficient numbers of RGCs and Muller glia progenitors for downstream analyses. METHODS In this study we described, evaluated, and refined methods with which to generate Muller glia and RGC progenitors, isolated them via magnetic-activated cell sorting, and assessed their lineage stability after prolonged 2D culture. Putative progenitor populations were characterized via quantitative PCR and immunocytochemistry, and the ultrastructural composition of retinal organoid cells was investigated. RESULTS Our study confirms the feasibility of generating marker-characterized Muller glia and RGC progenitors within retinal organoids. Such retinal organoids can be dissociated and the Muller glia and RGC progenitor-like cells isolated via magnetic-activated cell sorting and propagated as monolayers. CONCLUSION Enrichment of Muller glia and RGC progenitors from retinal organoids is a feasible method with which to study cell type-specific disease phenotypes and to potentially generate specific retinal populations for cell replacement therapies.

Glaucoma is a neurodegenerative disease that affects the retinal ganglion cells (RGCs). The main risk factor is elevated intraocular pressure (IOP), but the actual cause of the disease remains unknown. Emerging evidence indicates that metabolic dysfunction plays a central role. The aim of the current study was to determine and compare the effect of universal hypoxia on the metabolomic signature in plasma samples from healthy controls (n = 10), patients with normal-tension glaucoma (NTG, n = 10), and ocular hypertension (OHT, n = 10). By subjecting humans to universal hypoxia, we aim to mimic a state in which the mitochondria in the body are universally stressed. Participants were exposed to normobaric hypoxia for two hours, followed by a 30 min recovery period in normobaric normoxia. Blood samples were collected at baseline, during hypoxia, and in recovery. Plasma samples were analyzed using a non-targeted metabolomics approach based on liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS). Multivariate analyses were conducted using principal component analysis (PCA) and orthogonal partial least squares-discriminant analysis (OPLS-DA), and univariate analysis using the Wilcoxon signed-rank test and false discovery rate (FDR) correction. Unique metabolites involved in fatty acid biosynthesis and ketone body metabolism were upregulated, while metabolites of the kynurenine pathway were downregulated in OHT patients exposed to universal hypoxia. Differential affection of metabolic pathways may explain why patients with OHT initially do not suffer or are more resilient from optic nerve degeneration. The metabolomes of NTG and OHT patients are regulated differently from control subjects and show dysregulation of metabolites important for energy production. These dysregulated processes may potentially contribute to the elevation of IOP and, ultimately, cell death of the RGCs.

Aim: Enhance the understanding of intrinsic metabolic and oxidative stress vulnerability in normal-tension glaucoma (NTG) pathophysiology by targeted profiling of skin fibroblasts from NTG and control donors. Background: NTG is a primary open-angle glaucoma subtype characterised by glaucomatous neurodegeneration without elevated intraocular pressure. Increasing evidence links systemic metabolic and oxidative stress vulnerability to NTG pathophysiology, making non-ocular, somatic cells promising surrogate systems for assessing neurodegenerative predisposing mechanisms. Methods: Skin fibroblast cultures were obtained from four female NTG and four age- and gender-matched control donors. Targeted metabolic profiling of mitochondrial function, glycolytic capacity, and glucose and amino acid metabolism was performed using the Seahorse assay, gas chromatography-mass spectrometry, and high-performance liquid chromatography. Oxidative stress resilience to hydrogen peroxide was assessed employing the lactate dehydrogenase release assay. Results: Pure skin fibroblast cultures were obtained for all included donors. NTG and control fibroblast exhibited similar mitochondrial and glycolytic function. No group difference was demonstrated in relative glucose metabolism and absolute amino acid profile. Control and NTG fibroblasts exhibited similar susceptibility to oxidative stress. Conclusion: NTG skin fibroblasts exhibit similar mitochondrial and glycolytic function, glucose metabolisation, amino acid profile, and oxidative stress resiliency compared to controls. Future studies should focus on mapping cell- and tissue-specific differences through combined genetic and transcriptomic profiling to guide and stratify the functional assessment of different endotypes within the NTG disease spectrum. Cell-specific dysregulation and the need for individual mechanistic grouping diminish the applicability of skin fibroblasts as a model system for exploiting NTG pathophysiology.