Oxidative Stress and Hypoxia Modify Mitochondrial Homeostasis During Glaucoma

MicroRNA-146a-5p protects retinal ganglion cells through reducing neuroinflammation in experimental glaucoma

Neuroinflammation plays important roles in retinal ganglion cell (RGC) degeneration in glaucoma. MicroRNA-146 (miR-146) has been shown to regulate inflammatory response in neurodegenerative diseases. In this study, whether and how miR-146 could affect RGC injury in chronic ocular hypertension (COH) experimental glaucoma were investigated. We showed that in the members of miR-146 family only miR-146a-5p expression was upregulated in COH retinas. The upregulation of miR-146a-5p was observed in the activated microglia and Müller cells both in primary cultured conditions and in COH retinas, but mainly occurred in microglia. Overexpression of miR-146a-5p in COH retinas reduced the levels pro-inflammatory cytokines and upregulated the levels of anti-inflammatory cytokines, which were further confirmed in the activated primary cultured microglia. Transfection of miR-146a-5p mimic increased the percentage of anti-inflammatory phenotype in the activated BV2 microglia, while transfection of miR-146a-5p inhibitor resulted in the opposite effects. Transfection of miR-146a-5p mimic/agomir inhibited the levels of interleukin-1 receptor associated kinase (IRAK1) and TNF receptor associated factor 6 (TRAF6) and phosphorylated NF-κB subunit p65. Dual luciferase reporter gene assay confirmed that miR-146a-5p could directly target IRAK1 and TRAF6. Moreover, downregulation of IRAK1 and TRAF6 by siRNA techniques or blocking NF-κB by SN50 in cultured microglia reversed the miR-146a-5p inhibitor-induced changes of inflammatory cytokines. In COH retinas, overexpression of miR-146a-5p reduced RGC apoptosis, increased RGC survival, and partially rescued the amplitudes of photopic negative response. Our results demonstrate that overexpression of miR-146a-5p attenuates RGC injury in glaucoma by reducing neuroinflammation through downregulating IRAK1/TRAF6/NF-κB signaling pathway in microglia.

Ocular Inflammation and Oxidative Stress as a Result of Chronic Intermittent Hypoxia: A Rat Model of Sleep Apnea

Obstructive sleep apnea (OSA) is a sleep disorder characterized by intermittent complete or partial occlusion of the airway. Despite a recognized association between OSA and glaucoma, the nature of the underlying link remains unclear. In this study, we investigated whether mild OSA induces morphological, inflammatory, and metabolic changes in the retina resembling those seen in glaucoma using a rat model of OSA known as chronic intermittent hypoxia (CIH). Rats were randomly assigned to either normoxic or CIH groups. The CIH group was exposed to periodic hypoxia during its sleep phase with oxygen reduction from 21% to 10% and reoxygenation in 6 min cycles over 8 h/day. The eyes were subsequently enucleated, and then the retinas were evaluated for retinal ganglion cell number, oxidative stress, inflammatory markers, metabolic changes, and hypoxic response modulation using immunohistochemistry, multiplex assays, and capillary electrophoresis. Statistically significant differences were observed between normoxic and CIH groups for oxidative stress and inflammation, with CIH resulting in increased HIF-1α protein levels, higher oxidative stress marker 8-OHdG, and increased TNF-α. Pyruvate dehydrogenase kinase-1 protein was significantly reduced with CIH. No significant differences were found in retinal ganglion cell number. Our findings suggest that CIH induces oxidative stress, inflammation, and upregulation of HIF-1α in the retina, akin to early-stage glaucoma.

Administration of Bicarbonate Protects Mitochondria, Rescues Retinal Ganglion Cells, and Ameliorates Visual Dysfunction Caused by Oxidative Stress

Oxidative stress is a key factor causing mitochondrial dysfunction and retinal ganglion cell (RGC) death in glaucomatous neurodegeneration. The cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) signaling pathway is involved in mitochondrial protection, promoting RGC survival. Soluble adenylyl cyclase (sAC) is a key regulator of the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) signaling pathway, which is known to protect mitochondria and promote RGC survival. However, the precise molecular mechanisms connecting the sAC-mediated signaling pathway with mitochondrial protection in RGCs against oxidative stress are not well characterized. Here, we demonstrate that sAC plays a critical role in protecting RGC mitochondria from oxidative stress. Using mouse models of oxidative stress induced by ischemic injury and paraquat administration, we found that administration of bicarbonate, as an activator of sAC, protected RGCs, blocked AMP-activated protein kinase activation, inhibited glial activation, and improved visual function. Moreover, we found that this is the result of preserving mitochondrial dynamics (fusion and fission), promoting mitochondrial bioenergetics and biogenesis, and preventing metabolic stress and apoptotic cell death. Notably, the administration of bicarbonate ameliorated mitochondrial dysfunction in RGCs by enhancing mitochondrial biogenesis, preserving mitochondrial structure, and increasing ATP production in oxidatively stressed RGCs. These findings suggest that activating sAC enhances the mitochondrial structure and function in RGCs to counter oxidative stress, consequently promoting RGC protection. We propose that modulation of the sAC-mediated signaling pathway has therapeutic potential acting on RGC mitochondria for treating glaucoma and other retinal diseases.

The ketogenic diet and hypoxia promote mitophagy in the context of glaucoma

Mitochondrial homeostasis includes balancing organelle biogenesis with recycling (mitophagy). The ketogenic diet protects retinal ganglion cells (RGCs) from glaucoma-associated neurodegeneration, with a concomitant increase in mitochondrial biogenesis. This study aimed to determine if the ketogenic diet also promoted mitophagy. MitoQC mice that carry a pH-sensitive mCherry-GFP tag on the outer mitochondrial membrane were placed on a ketogenic diet or standard rodent chow for 5 weeks; ocular hypertension (OHT) was induced via magnetic microbead injection in a subset of control or ketogenic diet animals 1 week after the diet began. As a measure of mitophagy, mitolysosomes were quantified in sectioned retina immunolabeled with RBPMS for RGCs or vimentin for Müller glia. Mitolysosomes were significantly increased as a result of OHT and the ketogenic diet (KD) in RGCs. Interestingly, the ketogenic diet increased mitolysosome number significantly higher than OHT alone. In contrast, OHT and the ketogenic diet both increased mitolysosome number in Müller glia to a similar degree. To understand if hypoxia could be a stimulus for mitophagy, we quantified mitolysosomes after acute OHT, finding significantly greater mitolysosome number in cells positive for pimonidazole, an adduct formed in cells exposed to hypoxia. Retinal protein analysis for BNIP3 and NIX showed no differences across groups, suggesting that these receptors were equivocal for mitophagy in this model of OHT. Our data indicate that OHT and hypoxia stimulate mitophagy and that the ketogenic diet is an additive for mitophagy in RGCs. The different response across RGCs and Müller glia to the ketogenic diet may reflect the different metabolic needs of these cell types.

Protection against Oxidative Stress by Coenzyme Q10 in a Porcine Retinal Degeneration Model

Oxidative stress plays an important role in neurodegenerative diseases, including glaucoma. Therefore, we analyzed if the antioxidant coenzyme Q10 (CoQ10), which is also commercially available, can prevent retinal degeneration induced by hydrogen peroxide (H2O2) in a porcine organ culture model. Retinal explants were cultivated for eight days, and H2O2 (500 µM, 3 h) induced the oxidative damage. CoQ10 therapy was applied (700 µM, 48 h). Retinal ganglion cells (RGCs) and microglia were examined immunohistologically in all groups (control, H2O2, H2O2 + CoQ10). Cellular, oxidative, and inflammatory genes were quantified via RT-qPCR. Strong RGC loss was observed with H2O2 (p ≤ 0.001). CoQ10 elicited RGC protection compared to the damaged group at a histological (p ≤ 0.001) and mRNA level. We detected more microglia cells with H2O2, but CoQ10 reduced this effect (p = 0.004). Cellular protection genes (NRF2) against oxidative stress were stimulated by CoQ10 (p ≤ 0.001). Furthermore, mitochondrial oxidative stress (SOD2) increased through H2O2 (p = 0.038), and CoQ10 reduced it to control level. Our novel results indicate neuroprotection via CoQ10 in porcine retina organ cultures. In particular, CoQ10 appears to protect RGCs by potentially inhibiting apoptosis-related pathways, activating intracellular protection and reducing mitochondrial stress.

Hypoxia expedites the progression of papillary thyroid carcinoma by promoting the CPT1A-mediated fatty acid oxidative pathway

Hypoxia has been reported to promote the proliferation and migration of thyroid cancer, while the special mechanism was still unclear. HIF-1α/carnitine palmitoyl-transferase 1A (CPT1A) was found to be associated with papillary thyroid carcinoma (PTC) but the biological role of CPT1A in PTC was not explored. The effects of hypoxia and carnitine palmitoyl-transferase 1A (CPT1A) expression on PTC cells were determined by cell counting kit-8 assay, detection of oxidative stress, inflammation response and mitochondrial membrane motential (MMP). Oil Red O staining and the detection of free fatty acids were performed to assess the status of lipid metabolism. Flow cytometric analysis was performed to assess cell apoptosis. Quantitative polymerase chain reaction (qPCR) and western blot analysis were applied to investigate the expressions of CPT1A and HIF-1α and the molecules involved cell function. The expressions of CPT1A and HIF-1α were significantly increased in PTC cells with or without hypoxia treatment. CPT1A overexpression or silencing promoted or inhibited cell viability, and hypoxia further repressed cell viability. In addition, CPT1A overexpression alleviates hypoxia-induced increased oxidative stress, inflammation response and elevated MMP. CPT1A overexpression enhanced palmitic acid-induced decreased cell growth, enhanced the metabolic capacity of free fatty acid and suppressed cell apoptosis. Animal experiments showed that CPT1A overexpression promoted PTC tumor growth, reduced lipid deposition, oxidative stress and inflammation, as well as enhancing cell function indicators. However, CPT1A silencing showed the opposite effects both in vitro and in vivo. Hypoxia induces the high expression of HIF-1α/CPT1A, thereby reprogramming the lipid metabolism of PTC cells for adapting the hypoxia environment, meanwhile inhibiting the cell damage and apoptosis caused by oxidative stress.

Aging, Cellular Senescence, and Glaucoma

Aging is one of the most serious risk factors for glaucoma, and according to age-standardized prevalence, glaucoma is the second leading cause of legal blindness worldwide. Cellular senescence is a hallmark of aging that is defined by a stable exit from the cell cycle in response to cellular damage and stress. The potential mechanisms underlying glaucomatous cellular senescence include oxidative stress, DNA damage, mitochondrial dysfunction, defective autophagy/mitophagy, and epigenetic modifications. These phenotypes interact and generate a sufficiently stable network to maintain the cell senescent state. Senescent trabecular meshwork (TM) cells, retinal ganglion cells (RGCs) and vascular endothelial cells reportedly accumulate with age and stress and may contribute to glaucoma pathologies. Therapies targeting the suppression or elimination of senescent cells have been found to ameliorate RGC death and improve vision in glaucoma models, suggesting the pivotal role of cellular senescence in the pathophysiology of glaucoma. In this review, we explore the biological links between aging and glaucoma, specifically delving into cellular senescence. Moreover, we summarize the current data on cellular senescence in key target cells associated with the development and clinical phenotypes of glaucoma. Finally, we discuss the therapeutic potential of targeting cellular senescence for the management of glaucoma.

Activating soluble adenylyl cyclase protects mitochondria, rescues retinal ganglion cells, and ameliorates visual dysfunction caused by oxidative stress

Oxidative stress is a key factor causing mitochondrial dysfunction and retinal ganglion cell (RGC) death in glaucomatous neurodegeneration. The cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) signaling pathway is involved in mitochondrial protection, promoting RGC survival. Soluble adenylyl cyclase (sAC) is one of the key regulators of the cAMP/PKA signaling pathway. However, the precise molecular mechanisms underlying the sAC-mediated signaling pathway and mitochondrial protection in RGCs that counter oxidative stress are not well characterized. Here, we demonstrate that sAC plays a critical role in protecting RGC mitochondria from oxidative stress. Using mouse models of oxidative stress, we found that activating sAC protected RGCs, blocked AMP-activated protein kinase activation, inhibited glial activation, and improved visual function. Moreover, we found that this is the result of preserving mitochondrial dynamics (fusion and fission), promoting mitochondrial bioenergetics and biogenesis, and preventing metabolic stress and apoptotic cell death in a paraquat oxidative stress model. Notably, sAC activation ameliorated mitochondrial dysfunction in RGCs by enhancing mitochondrial biogenesis, preserving mitochondrial structure, and increasing ATP production in oxidatively stressed RGCs. These findings suggest that activating sAC enhances the mitochondrial structure and function in RGCs to counter oxidative stress, consequently promoting RGC protection. We propose that modulation of the sAC-mediated signaling pathway has therapeutic potential acting on RGC mitochondria for treating glaucoma and other retinal diseases.

Reduced Zn2+ promotes retinal ganglion cells survival and optic nerve regeneration after injury through inhibiting autophagy mediated by ROS/Nrf2

The molecular mechanism of how reduced mobile zinc (Zn2+) affected retinal ganglion cell (RGC) survival and optic nerve regeneration after optic nerve crush (ONC) injury remains unclear. Here, we used conditionally knocked out ZnT-3 in the amacrine cells (ACs) of mice (CKO) in order to explore the role of reactive oxygen species (ROS), nuclear factor erythroid 2-related factor 2 (NFE2L2, Nrf2) and autophagy in the protection of RGCs and axon regeneration after ONC injury. We found that reduced Zn2+ can promote RGC survival and axonal regeneration by decreasing ROS, activating Nrf2, and inhibiting autophagy. Additionally, autophagy after ONC is regulated by ROS and Nrf2. Visual function in mice after ONC injury was partially recovered through the reduction of Zn2+, achieved by using a Zn2+ specific chelator N,N,N',N'-tetrakis-(2-Pyridylmethyl) ethylenediamine (TPEN) or through CKO mice. Overall, our data reveal the crosstalk between Zn2+, ROS, Nrf2 and autophagy following ONC injury. This study verified that TPEN or knocking out ZnT-3 in ACs is a promising therapeutic option for the treatment of optic nerve damage and elucidated the postsynaptic molecular mechanism of Zn2+-triggered damage to RGCs after ONC injury.

Hypoxia-Inducible Factor and Oxidative Stress in Tendon Degeneration: A Molecular Perspective

Tendinopathy is a debilitating condition marked by degenerative changes in the tendons. Its complex pathophysiology involves intrinsic, extrinsic, and physiological factors. While its intrinsic and extrinsic factors have been extensively studied, the role of physiological factors, such as hypoxia and oxidative stress, remains largely unexplored. This review article delves into the contribution of hypoxia-associated genes and oxidative-stress-related factors to tendon degeneration, offering insights into potential therapeutic strategies. The unique aspect of this study lies in its pathway-based evidence, which sheds light on how these factors can be targeted to enhance overall tendon health.

Antioxidative effects of ghrelin on human trabecular meshwork cells

Glaucoma is a group of neurodegenerative diseases characterized by loss of retinal ganglion cells and visual field defects and is one of the major causes of irreversible blindness worldwide. Primary open-angle glaucoma (POAG) is one of the classifications of glaucoma. Oxidative stress in trabecular reticulated cells is one of the possible mechanisms of the development of glaucoma. At present, there is still a lack of effective methods to treat glaucoma. Ghrelin is characterized by its wide distribution and high potency and has anti-inflammatory, antioxidant, and anti-apoptotic effects, which may be beneficial in the treatment of glaucoma. In this study, we investigated whether ghrelin can protect human trabecular meshwork cells (HTMCs) from oxidative damage induced by hydrogen peroxide (H2O2), as well as the possible mechanism of action. CCK8 and flow cytometry results revealed that treatment of HTMCs with ghrelin showed a dose-dependent protective effect against H2O2-induced damage. Ghrelin significantly decreased the rate of apoptosis and levels of reactive oxygen species (ROS) and malondialdehyde (MDA) and increased the level of superoxide dismutase (SOD) and catalase (CAT) in HTMCs. The difference was statistically significant compared with the H2O2 group. Ghrelin activated Nrf2/HO-1/NQO-1 signaling pathways and decreased HIF-1α level in H2O2-injured HTMCs as shown on qPCR and Western blot. In conclusion, ghrelin can protect HTMCs from oxidative damage induced by H2O2 and reduce apoptosis in HTMCs, which can be a new approach to treating POAG. The underlying therapeutic mechanism may be related to Nrf2/HO-1/NQO-1 signaling pathways and HIF-1α.

Calbindin 2-specific deletion of arginase 2 preserves visual function after optic nerve crush

We previously found that global deletion of the mitochondrial enzyme arginase 2 (A2) limits optic nerve crush (ONC)-induced neuronal death. Herein, we examined the cell-specific role of A2 in this pathology by studies using wild type (WT), neuronal-specific calbindin 2 A2 KO (Calb2cre/+ A2 f/f), myeloid-specific A2 KO (LysMcre/+ A2f/f), endothelial-specific A2 KO (Cdh5cre/+ A2f/f), and floxed controls. We also examined the impact of A2 overexpression on mitochondrial function in retinal neuronal R28 cells. Immunolabeling showed increased A2 expression in ganglion cell layer (GCL) neurons of WT mice within 6 h-post injury and inner retinal neurons after 7 days. Calb2 A2 KO mice showed improved neuronal survival, decreased TUNEL-positive neurons, and improved retinal function compared to floxed littermates. Neuronal loss was unchanged by A2 deletion in myeloid or endothelial cells. We also found increased expression of neurotrophins (BDNF, FGF2) and improved survival signaling (pAKT, pERK1/2) in Calb2 A2 KO retinas within 24-hour post-ONC along with suppression of inflammatory mediators (IL1β, TNFα, IL6, and iNOS) and apoptotic markers (cleavage of caspase3 and PARP). ONC increased GFAP and Iba1 immunostaining in floxed controls, and Calb2 A2 KO dampened this effect. Overexpression of A2 in R28 cells increased Drp1 expression, and decreased mitochondrial respiration, whereas ABH-induced inhibition of A2 decreased Drp1 expression and improved mitochondrial respiration. Finally, A2 overexpression or excitotoxic treatment with glutamate significantly impaired mitochondrial function in R28 cells as shown by significant reductions in basal respiration, maximal respiration, and ATP production. Further, glutamate treatment of A2 overexpressing cells did not induce further deterioration in their mitochondrial function, indicating that A2 overexpression or glutamate insult induce comparable alterations in mitochondrial function. Our data indicate that neuronal A2 expression is neurotoxic after injury, and A2 deletion in Calb2 expressing neurons limits ONC-induced retinal neurodegeneration and improves visual function.

Mitophagy in the retina: Viewing mitochondrial homeostasis through a new lens

Mitochondrial function is key to support metabolism and homeostasis in the retina, an organ that has one of the highest metabolic rates body-wide and is constantly exposed to photooxidative damage and external stressors. Mitophagy is the selective autophagic degradation of mitochondria within lysosomes, and can be triggered by distinct stimuli such as mitochondrial damage or hypoxia. Here, we review the importance of mitophagy in retinal physiology and pathology. In the developing retina, mitophagy is essential for metabolic reprogramming and differentiation of retina ganglion cells (RGCs). In basal conditions, mitophagy acts as a quality control mechanism, maintaining a healthy mitochondrial pool to meet cellular demands. We summarize the different autophagy- and mitophagy-deficient mouse models described in the literature, and discuss the potential role of mitophagy dysregulation in retinal diseases such as glaucoma, diabetic retinopathy, retinitis pigmentosa, and age-related macular degeneration. Finally, we provide an overview of methods used to monitor mitophagy in vitro, ex vivo, and in vivo. This review highlights the important role of mitophagy in sustaining visual function, and its potential as a putative therapeutic target for retinal and other diseases.

Antioxidant nanoemulsion loaded with latanoprost enables highly effective glaucoma treatment

Glaucoma is the third leading cause of blindness worldwide and is primarily characterized by elevated intraocular pressure (IOP). Common risk factors such as age, myopia, ocular trauma, and hypertension all increase the risk of elevated IOP. Prolonged high IOP not only causes physiological discomfort like headaches, but also directly damages retinal cells and leads to retinal ischemia, oxidative imbalance, and accumulation of reactive oxygen species (ROS) in the retina. This oxidative stress causes the oxidation of proteins and unsaturated lipids, leading to peroxide formation and exacerbating retinal damage. While current clinical treatments primarily target reducing IOP through medication or surgery, there are currently no effective methods to mitigate the retinal cell damage associated with glaucoma. To address this gap, we developed a novel nanoemulsion to co-delivery latanoprost and α-tocopherol (referred to as LA@VNE later) that prolongs ocular retention and enhances retinal permeability through localized administration. By encapsulating latanoprost, an IOP-lowering drug, and α-tocopherol, a potent antioxidant, we effectively reduced ROS accumulation (>1.5-fold in vitro and 2.5-fold in vivo), retinal ganglion cell (RGC) apoptosis (>9 fold), and inflammatory cell infiltration (>1.6 fold). Our approach showed strong biocompatibility and significant potential for clinical translation, providing a promising platform for the treatment of glaucoma.

Revisiting Retinal Degeneration Hallmarks: Insights from Molecular Markers and Therapy Perspectives

Visual impairment and blindness are a growing public health problem as they reduce the life quality of millions of people. The management and treatment of these diseases represent scientific and therapeutic challenges because different cellular and molecular actors involved in the pathophysiology are still being identified. Visual system components, particularly retinal cells, are extremely sensitive to genetic or metabolic alterations, and immune responses activated by local insults contribute to biological events, culminating in vision loss and irreversible blindness. Several ocular diseases are linked to retinal cell loss, and some of them, such as retinitis pigmentosa, age-related macular degeneration, glaucoma, and diabetic retinopathy, are characterized by pathophysiological hallmarks that represent possibilities to study and develop novel treatments for retinal cell degeneration. Here, we present a compilation of revisited information on retinal degeneration, including pathophysiological and molecular features and biochemical hallmarks, and possible research directions for novel treatments to assist as a guide for innovative research. The knowledge expansion upon the mechanistic bases of the pathobiology of eye diseases, including information on complex interactions of genetic predisposition, chronic inflammation, and environmental and aging-related factors, will prompt the identification of new therapeutic strategies.

Modulation of Mitochondrial Metabolic Parameters and Antioxidant Enzymes in Healthy and Glaucomatous Trabecular Meshwork Cells with Hybrid Small Molecule SA-2

Oxidative stress (OS)-induced mitochondrial damage is a risk factor for primary open-angle glaucoma (POAG). Mitochondria-targeted novel antioxidant therapies could unearth promising drug candidates for the management of POAG. Previously, our dual-acting hybrid molecule SA-2 with nitric oxide-donating and antioxidant activity reduced intraocular pressure and improved aqueous humor outflow in rodent eyes. Here, we examined the mechanistic role of SA-2 in trabecular meshwork (TM) cells in vitro and measured the activity of intracellular antioxidant enzymes during OS. Primary human TM cells isolated from normal (hNTM) or glaucomatous (hGTM) post-mortem donors and transformed glaucomatous TM cells (GTM-3) were used for in vitro assays. We examined the effect of SA-2 on oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) in vitro using Seahorse Analyzer with or without the oxidant, tert-butyl hydroperoxide (TBHP) treatment. Concentrations of total antioxidant enzymes, catalase (CAT), malondialdehyde (MDA), and glutathione peroxidase (GPx) were measured. We observed significant protection of both hNTM and hGTM cells from TBHP-induced cell death by SA-2. Antioxidant enzymes were elevated in SA-2-treated cells compared to TBHP-treated cells. In addition, SA-2 demonstrated an increase in mitochondrial metabolic parameters. Altogether, SA-2 protected both normal and glaucomatous TM cells from OS via increasing mitochondrial energy parameters and the activity of antioxidant enzymes.

The Need for Glaucoma Management in Glaucoma Patients with Concurrent Obstructive Sleep Apnea: A Population-Based Cohort Study

We try to evaluate glaucoma management numbers in patients with both glaucoma and obstructive sleep apnea (OSA) using the National Health Insurance Research Database (NHIRD) of Taiwan. A retrospective cohort study was conducted and patients with glaucoma were enrolled and divided into the OSA and non-OSA populations. A total of 11,778 participants were selected in both the OSA and non-OSA groups. The primary outcomes were the number of anti-glaucomatous medications each year and the total number of glaucoma laser and glaucoma surgeries. The Cox proportional hazard regression was utilized to produce the adjusted hazard ratios (AHR) with corresponding 95% confidence intervals (CI) between the two groups. After a study period of 18 years, 286 and 352 events of laser and surgeries for glaucoma were found in the OSA and non-OSA groups, respectively. After considering the effect of potential confounders, no significant difference concerning the numbers of laser trabeculoplasty, trabeculectomy and tube shunt surgery, cyclodestructive procedure and eyeball removal were found between the two groups (all 95% CIs included one). In addition, the multiple anti-glaucomatous medication usages were similar between the two groups (all p > 0.05) In the subgroup analyses, glaucoma patients older than 60 years and with OSA received significantly lesser trabeculectomy and tube shunt surgery compared to glaucoma patients older than 60 years without OSA (AHR: 0.774, 95% CI: 0.611−0.981) while other analyses revealed insignificant results (all 95% CIs included one). In conclusion, the presence of OSA does not increase the need for glaucoma management.

Loss of Retinogeniculate Synaptic Function in the DBA/2J Mouse Model of Glaucoma

Retinal ganglion cell (RGC) axons comprise the optic nerve and carry information to the dorsolateral geniculate nucleus (dLGN), which is then relayed to the cortex for conscious vision. Glaucoma is a blinding neurodegenerative disease that commonly results from intraocular pressure (IOP)-associated injury leading to RGC axonal pathology, disruption of RGC outputs to the brain, and eventual apoptotic loss of RGC somata. The consequences of elevated IOP and glaucomatous pathology on RGC signaling to the dLGN are largely unknown yet are likely to contribute to vision loss. Here, we used anatomic and physiological approaches to study the structure and function of retinogeniculate (RG) synapses in male and female DBA/2J (D2) mice with inherited glaucoma before and after IOP elevation. D2 mice showed progressive loss of anterograde optic tract transport to the dLGN and vGlut2 labeling of RGC axon terminals while patch-clamp measurements of RG synaptic function showed that synaptic transmission was reduced in 9-month and 12-month D2 mice because of the loss of individual RGC axon inputs. TC neuron dendrites had reduced Sholl complexity at 12 months, suggestive of delayed reorganization following reduced synaptic input. There was no detectable change in RGC density in 11- to 12-month D2 retinas, quantified as the number of ganglion cell layer-residing somata immuno-positive for NeuN and immuno-negative for the amacrine marker choline acetyltransferase (ChAT). Thus, observed synaptic defects appear to precede RGC somatic loss. These findings identify glaucoma-associated and IOP-associated deficits in an important subcortical RGC projection target, shedding light on processes linking IOP to vision loss.

Nobiletin protects retinal ganglion cells in models of ocular hypertension in vivo and hypoxia in vitro

Glaucoma, a common cause of blindness, is characterized by the progressive loss of retinal ganglion cells (RGCs). Growing evidence suggests that nobiletin (NOB) is a promising neuroprotective drug; however, its effects on glaucomatous neurodegeneration remain unknown. Using rat models of microbead occlusion in vivo and primary RGCs model of hypoxia in vitro, we first demonstrate that NOB reduces RGC apoptosis by a TUNEL assay, Hoechst 33342 staining and FluoroGold (FG) retrograde labeling. This effect does not depend on intraocular pressure (IOP) lowering. Additionally, NOB partially restored the functional and structural damage of inner retinas, attenuated Müller glial activation and oxidative stress caused by ocular hypertension. At 2 weeks after IOP elevation, NOB further enhanced Nrf2/HO-1 pathway in RGCs to withstand the cumulative damage of ocular hypertension. With the administration of HO-1 inhibitor tin-protoporphyrin IX (SnPP), the protective effect of NOB was attenuated. Overall, these results indicate that NOB exerts an outstanding neuroprotective effect on RGCs of glaucomatous neurodegeneration. Besides, interventions to enhance activation of Nrf2/HO-1 pathway can slow the loss of RGCs and are viable therapies for glaucoma.

Impact of Systemic Comorbidities on Ocular Hypertension and Open-Angle Glaucoma, in a Population from Spain and Portugal

Open-angle glaucoma (OAG), the most prevalent clinical type of glaucoma, is still the main cause of irreversible blindness worldwide. OAG is a neurodegenerative illness for which the most important risk factor is elevated intraocular pressure (IOP). Many questions remain unanswered about OAG, such as whether nutritional or toxic habits, other personal characteristics, and/or systemic diseases influence the course of glaucoma. As such, in this study, we performed a multicenter analytical, observational, case–control study of 412 participants of both sexes, aged 40–80 years, that were classified as having ocular hypertension (OHT) or OAG. Our primary endpoint was to investigate the relationship between specific lifestyle habits; anthropometric and endocrine–metabolic, cardiovascular, and respiratory events; and commonly used psychochemicals, with the presence of OHT or OAG in an ophthalmologic population from Spain and Portugal. Demographic, epidemiological, and ocular/systemic clinical data were recorded from all participants. Data were analyzed using the R Statistics v4.1.2 and RStudio v2021.09.1 programs. The mean age was 62 ± 15 years, with 67–80 years old comprising the largest subgroup sample of participants in both study groups. The central corneal thickness (ultrasound pachymetry)-adjusted IOP (Goldman tonometry) in each eye was 20.46 ± 2.35 and 20.1 ± 2.73 mmHg for the OHT individuals, and 15.8 ± 3.83 and 16.94 ± 3.86 mmHg for the OAG patients, with significant differences between groups (both p = 0.001). The highest prevalence of the surveyed characteristics in both groups was for overweight/obesity and daily coffee consumption, followed by psychochemical drug intake, migraine, and peripheral vasospasm. Our data show that overweight/obesity, migraine, asthma, and smoking are major risk factors for conversion from OHT to OAG in this Spanish and Portuguese population.

Emerging evidence for compromised axonal bioenergetics and axoglial metabolic coupling as drivers of neurodegeneration

Impaired bioenergetic capacity of the nervous system is thought to contribute to the pathogenesis of many neurodegenerative diseases (NDD). Since neuronal synapses are believed to be the major energy consumers in the nervous system, synaptic derangements resulting from energy deficits have been suggested to play a central role for the development of many of these disorders. However, long axons constitute the largest compartment of the neuronal network, require large amounts of energy, are metabolically and structurally highly vulnerable, and undergo early injurious stresses in many NDD. These stresses likely impose additional energy demands for continuous adaptations and repair processes, and may eventually overwhelm axonal maintenance mechanisms. Indeed, pathological axon degeneration (pAxD) is now recognized as an etiological focus in a wide array of NDD associated with bioenergetic abnormalities. In this paper I first discuss the recognition that a simple experimental model for pAxD is regulated by an auto-destruction program that exhausts distressed axons energetically. Provision of the energy substrate pyruvate robustly counteracts this axonal breakdown. Importantly, energy decline in axons is not only a consequence but also an initiator of this program. This opens the intriguing possibility that axon dysfunction and pAxD can be suppressed by preemptively energizing distressed axons. Second, I focus on the emerging concept that axons communicate energetically with their flanking glia. This axoglial metabolic coupling can help offset the axonal energy decline that activates the pAxD program but also jeopardize axon integrity as a result of perturbed glial metabolism. Third, I present compelling evidence that abnormal axonal energetics and compromised axoglial metabolic coupling accompany the activation of the pAxD auto-destruction pathway in models of glaucoma, a widespread neurodegenerative condition with pathogenic overlap to other common NDD. In conclusion, I propose a novel conceptual framework suggesting that therapeutic interventions focused on bioenergetic support of the nervous system should also address axons and their metabolic interactions with glia.

Vascular derived endothelin receptor A controls endothelin-induced retinal ganglion cell death

Endothelin (EDN, also known as ET) signaling has been suggested to be an important mediator of retinal ganglion cell (RGC) death in glaucoma. Antagonism of EDN receptors (EDNRA and EDNRB, also known as ET-A and ET-B) prevented RGC death in mouse models of chronic ocular hypertension, and intravitreal injection of EDN ligand was sufficient to drive RGC death. However, it remains unclear which cell types EDN ligands directly affect to elicit RGC death. Multiple cell types in the retina and optic nerve express EDNRA and EDNRB and thus could respond to EDN ligands in the context of glaucoma. Here, we systematically deleted Edn receptors from specific cell types to identify the critical EDN receptor mediating RGC death in vivo. Deletion of both Ednra and Ednrb from retinal neurons (including RGCs) and macroglia did not prevent RGC loss after exposure to EDN1 ligands, suggesting EDN1 ligands cause RGC death via an indirect mechanism involving a secondary cell type. Deletion of Ednra from the full body, and then specifically from vascular mural cells, prevented EDN1-induced vasoconstriction and RGC death. Together, these data suggest EDN ligands cause RGC death via a mechanism initiated by vascular mural cells. It is possible RGC death is a consequence of vascular mural cell-induced vasoconstriction and its pathological sequelae. These results highlight the potential importance of neurovascular dysfunction in glaucoma.

Molecular regulation of neuroinflammation in glaucoma: Current knowledge and the ongoing search for new treatment targets

Neuroinflammation relying on the inflammatory responses of glial cells has emerged as an impactful component of the multifactorial etiology of neurodegeneration in glaucoma. It has become increasingly evident that despite early adaptive and reparative features of glial responses, prolonged reactivity of the resident glia, along with the peripheral immune cells, create widespread toxicity to retinal ganglion cell (RGC) axons, somas, and synapses. As much as the synchronized responses of astrocytes and microglia to glaucoma-related stress or neuron injury, their bi-directional interactions are critical to build and amplify neuroinflammation and to dictate the neurodegenerative outcome. Although distinct molecular programs regulate somatic and axonal degeneration in glaucoma, inhibition of neurodegenerative inflammation can provide a broadly beneficial treatment strategy to rescue RGC integrity and function. Since inflammatory toxicity and mitochondrial dysfunction are converging etiological paths that can boost each other and feed into a vicious cycle, anti-inflammatory treatments may also offer a multi-target potential. This review presents an overview of the current knowledge on neuroinflammation in glaucoma with particular emphasis on the cell-intrinsic and cell-extrinsic factors involved in the reciprocal regulation of glial responses, the interdependence between inflammatory and mitochondrial routes of neurodegeneration, and the research aspects inspiring for prospective immunomodulatory treatments. With the advent of powerful technologies, ongoing research on molecular and functional characteristics of glial responses is expected to accumulate more comprehensive and complementary information and to rapidly move the field forward to safe and effective modulation of the glial pro-inflammatory activities, while restoring or augmenting the glial immune-regulatory and neurosupport functions.

Treatment of Glaucoma with Natural Products and Their Mechanism of Action: An Update

Glaucoma is one of the leading causes of irreversible blindness. It is generally caused by increased intraocular pressure, which results in damage of the optic nerve and retinal ganglion cells, ultimately leading to visual field dysfunction. However, even with the use of intraocular pressure-lowering eye drops, the disease still progresses in some patients. In addition to mechanical and vascular dysfunctions of the eye, oxidative stress, neuroinflammation and excitotoxicity have also been implicated in the pathogenesis of glaucoma. Hence, the use of natural products with antioxidant and anti-inflammatory properties may represent an alternative approach for glaucoma treatment. The present review highlights recent preclinical and clinical studies on various natural products shown to possess neuroprotective properties for retinal ganglion cells, which thereby may be effective in the treatment of glaucoma. Intraocular pressure can be reduced by baicalein, forskolin, marijuana, ginsenoside, resveratrol and hesperidin. Alternatively, Ginkgo biloba, Lycium barbarum, Diospyros kaki, Tripterygium wilfordii, saffron, curcumin, caffeine, anthocyanin, coenzyme Q10 and vitamins B3 and D have shown neuroprotective effects on retinal ganglion cells via various mechanisms, especially antioxidant, anti-inflammatory and anti-apoptosis mechanisms. Extensive studies are still required in the future to ensure natural products' efficacy and safety to serve as an alternative therapy for glaucoma.

Oral Scutellarin Treatment Ameliorates Retinal Thinning and Visual Deficits in Experimental Glaucoma

Purpose: Intraocular pressure (IOP) is currently the only modifiable risk factor for glaucoma, yet glaucoma can continue to progress despite controlled IOP. Thus, development of glaucoma neurotherapeutics remains an unmet need. Scutellarin is a flavonoid that can exert neuroprotective effects in the eye and brain. Here, we investigated the neurobehavioral effects of scutellarin treatment in a chronic IOP elevation model. Methods: Ten adult C57BL/6J mice were unilaterally injected with an optically clear hydrogel into the anterior chamber to obstruct aqueous outflow and induce chronic IOP elevation. Eight other mice received unilateral intracameral injection of phosphate-buffered saline only. Another eight mice with hydrogel-induced unilateral chronic IOP elevation also received daily oral gavage of 300 mg/kg scutellarin. Tonometry, optical coherence tomography, and optokinetics were performed longitudinally for 4 weeks to monitor the IOP, retinal nerve fiber layer thickness, total retinal thickness, visual acuity, and contrast sensitivity of both eyes in all three groups. Results: Intracameral hydrogel injection resulted in unilateral chronic IOP elevation with no significant inter-eye IOP difference between scutellarin treatment and untreated groups. Upon scutellarin treatment, the hydrogel-injected eyes showed less retinal thinning and reduced visual behavioral deficits when compared to the untreated, hydrogel-injected eyes. No significant difference in retinal thickness or optokinetic measures was found in the contralateral, non-treated eyes over time or between all groups. Conclusion: Using the non-invasive measuring platform, oral scutellarin treatment appeared to preserve retinal structure and visual function upon chronic IOP elevation in mice. Scutellarin may be a novel neurotherapeutic agent for glaucoma treatment.

Crosstalk Between Dysfunctional Mitochondria and Inflammation in Glaucomatous Neurodegeneration

Mitochondrial dysfunction and excessive inflammatory responses are both sufficient to induce pathology in age-dependent neurodegenerations. However, emerging evidence indicates crosstalk between damaged mitochondrial and inflammatory signaling can exacerbate issues in chronic neurodegenerations. This review discusses evidence for the interaction between mitochondrial damage and inflammation, with a focus on glaucomatous neurodegeneration, and proposes that positive feedback resulting from this crosstalk drives pathology. Mitochondrial dysfunction exacerbates inflammatory signaling in multiple ways. Damaged mitochondrial DNA is a damage-associated molecular pattern, which activates the NLRP3 inflammasome; priming and activation of the NLRP3 inflammasome, and the resulting liberation of IL-1β and IL-18 via the gasdermin D pore, is a major pathway to enhance inflammatory responses. The rise in reactive oxygen species induced by mitochondrial damage also activates inflammatory pathways, while blockage of Complex enzymes is sufficient to increase inflammatory signaling. Impaired mitophagy contributes to inflammation as the inability to turnover mitochondria in a timely manner increases levels of ROS and damaged mtDNA, with the latter likely to stimulate the cGAS-STING pathway to increase interferon signaling. Mitochondrial associated ER membrane contacts and the mitochondria-associated adaptor molecule MAVS can activate NLRP3 inflammasome signaling. In addition to dysfunctional mitochondria increasing inflammation, the corollary also occurs, with inflammation reducing mitochondrial function and ATP production; the resulting downward spiral accelerates degeneration. Evidence from several preclinical models including the DBA/2J mouse, microbead injection and transient elevation of IOP, in addition to patient data, implicates both mitochondrial damage and inflammation in glaucomatous neurodegeneration. The pressure-dependent hypoxia and the resulting metabolic vulnerability is associated with mitochondrial damage and IL-1β release. Links between mitochondrial dysfunction and inflammation can occur in retinal ganglion cells, microglia cells and astrocytes. In summary, crosstalk between damaged mitochondria and increased inflammatory signaling enhances pathology in glaucomatous neurodegeneration, with implications for other complex age-dependent neurodegenerations like Alzheimer's and Parkinson's disease.