Disturbed glucose and pyruvate metabolism in glaucoma with neuroprotection by pyruvate or rapamycin

TLR4 deficiency does not alter glaucomatous progression in a mouse model of chronic glaucoma

Glaucoma is a leading cause of irreversible blindness worldwide. Toll-like receptor 4 (TLR4) is a pattern-recognition transmembrane receptor that induces neuroinflammatory processes in response to injury. Tlr4 is highly expressed in ocular tissues and is known to modulate inflammatory processes in both anterior and posterior segment tissues. TLR4 activation can lead to mitochondrial dysfunction and metabolic deficits in inflammatory disorders. Due to its effects on inflammation and metabolism, TLR4 is a candidate to participate in glaucoma pathogenesis. It has been suggested as a therapeutic target based on studies using acute models, such as experimentally raising IOP to ischemia-inducing levels. Nevertheless, its role in chronic glaucoma needs further evaluation. In the current study, we investigated the role of TLR4 in an inherited mouse model of chronic glaucoma, DBA/2J. To do this, we analyzed the effect of Tlr4 knockout (Tlr4 -/-) on glaucoma-associated phenotypes in DBA/2J mice. Our studies found no significant differences in intraocular pressure, iris disease, or glaucomatous progression in Tlr4 -/- compared to Tlr4 +/+ DBA/2J mice. These data do not identify a role for TLR4 in this chronic glaucoma, but further research is warranted to understand its role in other glaucoma models and different genetic contexts.

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.

Therapeutic Effects of Anti-Inflammatory and Anti-Oxidant Nutritional Supplementation in Retinal Ischemic Diseases

Appropriate nutrients are essential for cellular function. Dietary components can alter the risk of systemic metabolic diseases, including cardiovascular diseases, cancer, diabetes, and obesity, and can also affect retinal diseases, including age-related macular degeneration, diabetic retinopathy, and glaucoma. Dietary nutrients have been assessed for the prevention or treatment of retinal ischemic diseases and the diseases of aging. In this article, we review clinical and experimental evidence concerning the potential of some nutritional supplements to prevent or treat retinal ischemic diseases and provide further insights into the therapeutic effects of nutritional supplementation on retinopathies. We will review the roles of nutrients in preventing or protecting against retinal ischemic diseases.

Addressing neurodegeneration in glaucoma: Mechanisms, challenges, and treatments

Glaucoma is the leading cause of irreversible blindness globally. The disease causes vision loss due to neurodegeneration of the retinal ganglion cell (RGC) projection to the brain through the optic nerve. Glaucoma is associated with sensitivity to intraocular pressure (IOP). Thus, mainstay treatments seek to manage IOP, though many patients continue to lose vision. To address neurodegeneration directly, numerous preclinical studies seek to develop protective or reparative therapies that act independently of IOP. These include growth factors, compounds targeting metabolism, anti-inflammatory and antioxidant agents, and neuromodulators. Despite success in experimental models, many of these approaches fail to translate into clinical benefits. Several factors contribute to this challenge. Firstly, the anatomic structure of the optic nerve head differs between rodents, nonhuman primates, and humans. Additionally, animal models do not replicate the complex glaucoma pathophysiology in humans. Therefore, to enhance the success of translating these findings, we propose two approaches. First, thorough evaluation of experimental targets in multiple animal models, including nonhuman primates, should precede clinical trials. Second, we advocate for combination therapy, which involves using multiple agents simultaneously, especially in the early and potentially reversible stages of the disease. These strategies aim to increase the chances of successful neuroprotective treatment for glaucoma.

Evaluating the effect of rapamycin treatment in Alzheimer's disease and aging using in vivo imaging: the ERAP phase IIa clinical study protocol

BACKGROUND

Rapamycin is an inhibitor of the mechanistic target of rapamycin (mTOR) protein kinase, and preclinical data demonstrate that it is a promising candidate for a general gero- and neuroprotective treatment in humans. Results from mouse models of Alzheimer's disease have shown beneficial effects of rapamycin, including preventing or reversing cognitive deficits, reducing amyloid oligomers and tauopathies and normalizing synaptic plasticity and cerebral glucose uptake. The "Evaluating Rapamycin Treatment in Alzheimer's Disease using Positron Emission Tomography" (ERAP) trial aims to test if these results translate to humans through evaluating the change in cerebral glucose uptake following six months of rapamycin treatment in participants with early-stage Alzheimer's disease.

METHODS

ERAP is a six-month-long, single-arm, open-label, phase IIa biomarker-driven study evaluating if the drug rapamycin can be repurposed to treat Alzheimer's disease. Fifteen patients will be included and treated with a weekly dose of 7 mg rapamycin for six months. The primary endpoint will be change in cerebral glucose uptake, measured using [18F]FDG positron emission tomography. Secondary endpoints include changes in cognitive measures, markers in cerebrospinal fluid as well as cerebral blood flow measured using magnetic resonance imaging. As exploratory outcomes, the study will assess change in multiple age-related pathological processes, such as periodontal inflammation, retinal degeneration, bone mineral density loss, atherosclerosis and decreased cardiac function.

DISCUSSION

The ERAP study is a clinical trial using in vivo imaging biomarkers to assess the repurposing of rapamycin for the treatment of Alzheimer's disease. If successful, the study would provide a strong rationale for large-scale evaluation of mTOR-inhibitors as a potential disease-modifying treatment in Alzheimer's disease.

TRIAL REGISTRATION

ClinicalTrials.gov ID NCT06022068, date of registration 2023-08-30.

miR-196b-5p regulates inflammatory process and migration via targeting Nras in trabecular meshwork cells

Glaucoma, an insidious ophthalmic pathology, is typified by an aberrant surge in intraocular pressure (IOP) which culminates in the degeneration of retinal ganglion cells and optical neuropathy. The mitigation of IOP stands as the principal therapeutic strategy to forestall vision loss. The trabecular meshwork's (TM) integrity and functionality are pivotal in modulating aqueous humor egress. Despite their potential significance in glaucomatous pathophysiology, the implications of microRNAs (miRNAs) on TM functionality remain largely enigmatic. Transcriptomic sequencing was employed to delineate the miRNA expression paradigm within the limbal region of rodent glaucoma models, aiming to elucidate miRNA-mediated mechanisms within the glaucomatous milieu. Analytical scrutiny of the sequencing data disclosed 174 miRNAs with altered expression profiles, partitioned into 86 miRNAs with augmented expression and 88 with diminished expression. Notably, miRNAs such as hsa-miR-196b-5p were identified as having substantial expression discrepancies with concomitant statistical robustness, suggesting a potential contributory role in glaucomatous progression. Subsequent in vitro assays affirmed that miR-196b-5p augments the inflammatory cascade within immortalized human TM (iHTM) and glaucoma-induced human TM (GTM3) cells, concurrently attenuating cellular proliferation, motility, and cytoskeletal architecture. Additionally, miR-196b-5p implicates itself in the regulation of IOP and inflammatory processes in rodent models. At a mechanistic level, miR-196b-5p modulates its effects via the targeted repression of Nras (neuroblastoma RAS viral oncogene homolog). Collectively, these transcriptomic investigations furnish a comprehensive vista into the regulatory roles of miRNAs within the glaucomatous framework, and the identification of differentially expressed miRNAs alongside their targets could potentially illuminate novel molecular pathways implicated in glaucoma, thereby aiding in the development of innovative therapeutic avenues.

IOP and glaucoma damage: The essential role of optic nerve head and retinal mechanosensors

There are many unanswered questions on the relation of intraocular pressure to glaucoma development and progression. IOP itself cannot be distilled to a single, unifying value, because IOP level varies over time, differs depending on ocular location, and can be affected by method of measurement. Ultimately, IOP level creates mechanical strain that affects axonal function at the optic nerve head which causes local extracellular matrix remodeling and retinal ganglion cell death - hallmarks of glaucoma and the cause of glaucomatous vision loss. Extracellular tissue strain at the ONH and lamina cribrosa is regionally variable and differs in magnitude and location between healthy and glaucomatous eyes. The ultimate targets of IOP-induced tissue strain in glaucoma are retinal ganglion cell axons at the optic nerve head and the cells that support axonal function (astrocytes, the neurovascular unit, microglia, and fibroblasts). These cells sense tissue strain through a series of signals that originate at the cell membrane and alter cytoskeletal organization, migration, differentiation, gene transcription, and proliferation. The proteins that translate mechanical stimuli into molecular signals act as band-pass filters - sensing some stimuli while ignoring others - and cellular responses to stimuli can differ based on cell type and differentiation state. Therefore, to fully understand the IOP signals that are relevant to glaucoma, it is necessary to understand the ultimate cellular targets of IOP-induced mechanical stimuli and their ability to sense, ignore, and translate these signals into cellular actions.

Prophylactic nicotinamide treatment protects from rotenone-induced neurodegeneration by increasing mitochondrial content and volume

Leber's hereditary optic neuropathy (LHON) is driven by mtDNA mutations affecting Complex I presenting as progressive retinal ganglion cell dysfunction usually in the absence of extra-ophthalmic symptoms. There are no long-term neuroprotective agents for LHON. Oral nicotinamide provides a robust neuroprotective effect against mitochondrial and metabolic dysfunction in other retinal injuries. We explored the potential for nicotinamide to protect mitochondria in LHON by modelling the disease in mice through intravitreal injection of the Complex I inhibitor rotenone. Using MitoV mice expressing a mitochondrial-tagged YFP in retinal ganglion cells we assessed mitochondrial morphology through super-resolution imaging and digital reconstruction. Rotenone induced Complex I inhibition resulted in retinal ganglion cell wide mitochondrial loss and fragmentation. This was prevented by oral nicotinamide treatment. Mitochondrial ultrastructure was quantified by transition electron microscopy, demonstrating a loss of cristae density following rotenone injection, which was also prevented by nicotinamide treatment. These results demonstrate that nicotinamide protects mitochondria during Complex I dysfunction. Nicotinamide has the potential to be a useful treatment strategy for LHON to limit retinal ganglion cell degeneration.

It's a Trap! Aldolase-Prescribed C4 Deoxyradiofluorination Affords Intracellular Trapping and the Tracing of Fructose Metabolism by PET

Fructose metabolism has been implicated in various diseases, including metabolic disorders, neurodegenerative disorders, cardiac disorders, and cancer. However, the limited availability of a quantitative imaging radiotracer has hindered its exploration in pathology and diagnostic imaging. Methods: We adopted a molecular design strategy based on the catalytic mechanism of aldolase, a key enzyme in fructolysis. We successfully synthesized a radiodeoxyfluorinated fructose analog, [18F]4-fluoro-4-deoxyfructose ([18F]4-FDF), in high molar activity. Results: Through heavy isotope tracing by mass spectrometry, we demonstrated that C4-deoxyfluorination of fructose led to effective trapping as fluorodeoxysorbitol and fluorodeoxyfructose-1-phosphate in vitro, unlike C1- and C6-fluorinated analogs that resulted in fluorolactate accumulation. This observation was consistent in vivo, where [18F]6-fluoro-6-deoxyfructose displayed substantial bone uptake due to metabolic processing whereas [18F]4-FDF did not. Importantly, [18F]4-FDF exhibited low uptake in healthy brain and heart tissues, known for their high glycolytic activity and background levels of [18F]FDG uptake. [18F]4-FDF PET/CT allowed for sensitive mapping of neuro- and cardioinflammatory responses to systemic lipopolysaccharide administration. Conclusion: Our study highlights the significance of aldolase-guided C4 radiodeoxyfluorination of fructose in enabling effective radiotracer trapping, overcoming limitations of C1 and C6 radioanalogs toward a clinically viable tool for imaging fructolysis in highly glycolytic tissues.

Potentially compromised systemic and local lactate metabolic balance in glaucoma, which could increase retinal glucose and glutamate concentrations

To investigate the association between lactate metabolism and glaucoma, we conducted a multi-institutional cross-sectional clinical study and a retinal metabolomic analysis of mice with elevated intraocular pressure (IOP) induced by intracameral microbead injection. We compared lactate concentrations in serum and aqueous humor in age-matched 64 patients each with primary open-angle glaucoma (POAG) and cataract. Neither serum nor aqueous humor lactate concentrations differed between the two groups. Multiple regression analysis revealed that only body mass index showed a significant positive correlation with serum and aqueous humor lactate concentration in POAG patients (rs = 0.376, P = 0.002, and rs = 0.333, P = 0.007, respectively), but not in cataract patients. L-Lactic acid was one of the most abundantly detected metabolites in mouse retinas with gas chromatography and mass spectrometry, but there were no significant differences among control, 2-week, and 4-week IOP elevation groups. After 4 weeks of elevated IOP, D-glucose and L-glutamic acid ranked as the top two for a change in raised concentration, roughly sevenfold and threefold, respectively (ANOVA, P = 0.004; Tukey-Kramer, P < 0.05). Glaucoma may disrupt the systemic and intraocular lactate metabolic homeostasis, with a compensatory rise in glucose and glutamate in the retina.

Glaucoma: neuroprotection with NAD-based therapeutic interventions

Clinical evidence shows that intraocular hypertension is not the primary pathogenetic event of glaucoma, whereas early neurodegeneration of retinal ganglion cells (RGCs) represents a key therapeutic target. Unfortunately, failure of clinical trials with neuroprotective agents, in particular those testing the anti-excitotoxic drug memantine, generated widespread skepticism regarding the possibility of counteracting neurodegeneration during glaucoma. New avenues for neuroprotective approaches to counteract glaucoma evolution have been opened by the identification of a programmed axonal degeneration (PAD) program triggered by increased nicotinamide mononucleotide (NMN)/NAD concentration ratio. Positive results of proof-of-concept clinical studies based on sustaining axonal NAD homeostasis facilitated the design of Phase 2/3 trials. Here, I share my opinion on how neurodegeneration in glaucoma should be put into context, together with an appraisal of the pharmacological rationale of NAD-supporting therapies for use during glaucoma progression.

Novel frontiers in neuroprotective therapies in glaucoma: Molecular and clinical aspects

In the last years, neuroprotective therapies have attracted the researcher interests as modern and challenging approach for the treatment of neurodegenerative diseases, aimed at protecting the nervous system from injuries. Glaucoma is a neurodegenerative disease characterized by progressive excavation of the optic nerve head, retinal axonal injury and corresponding vision loss that affects millions of people on a global scale. The molecular basis of the pathology is largely uncharacterized yet, and the therapeutic approaches available do not change the natural course of the disease. Therefore, in accordance with the therapeutic regimens proposed for other neurodegenerative diseases, a modern strategy to treat glaucoma includes prescription of drugs with neuroprotective activities. With respect to this, several preclinical and clinical investigations on a plethora of different drugs are currently ongoing. In this review, first, the conceptualization of the rationale for the adoption of neuroprotective strategies for retina is summarized. Second, the molecular aspects highlighting glaucoma as a neurodegenerative disease are reported. In conclusion, the molecular and pharmacological properties of most promising direct neuroprotective drugs used to delay glaucoma progression are examined, including: neurotrophic factors, NMDA receptor antagonists, the α2-adrenergic agonist, brimonidine, calcium channel blockers, antioxidant agents, nicotinamide and statins.

Long-term HIF-1α stabilization reduces respiration, promotes mitophagy, and results in retinal cell death

Ocular hypertension during glaucoma can lead to hypoxia, activation of the HIF transcription factors, and a metabolic shift toward glycolysis. This study aims to test whether chronic HIF activation and the attendant metabolic reprogramming can initiate glaucoma-associated pathology independently of ocular hypertension. HIF-1α stabilization was induced in mice for 2 and 4 weeks by inhibiting prolyl hydroxylases using the small molecule Roxadustat. HIF-1α stabilization and the expression of its downstream bioenergetic targets were investigated in the retina by immunofluorescence, capillary electrophoresis, and biochemical enzyme activity assays. Roxadustat dosing resulted in significant stabilization of HIF-1α in the retina by 4 weeks, and upregulation in glycolysis-associated proteins (GLUT3, PDK-1) and enzyme activity in both neurons and glia. Accordingly, succinate dehydrogenase, mitochondrial marker MTCO1, and citrate synthase activity were significantly decreased at 4 weeks, while mitophagy was significantly increased. TUNEL assay showed significant apoptosis of cells in the retina, and PERG amplitude was significantly decreased with 4 weeks of HIF-1α stabilization. A significant increase in AMPK activation and glial hypertrophy, concomitant with decreases in retinal ganglion cell function and inner retina cell death suggests that chronic HIF-1α stabilization alone is detrimental to retina metabolic homeostasis and cellular survival.

Reduced glutathione level in the aqueous humor of patients with primary open-angle glaucoma and normal-tension glaucoma

Glaucoma is a leading cause of blindness worldwide in older people. Profiling the aqueous humor, including the metabolites it contains, is useful to understand physiological and pathological conditions in the eye. In the current study, we used mass spectrometry (MS) to characterize the aqueous humor metabolomic profile and biological features of patients with glaucoma. Aqueous humor samples were collected during trabeculectomy surgery or cataract surgery and analyzed with global metabolomics. We included 40 patients with glaucoma (32 with POAG, 8 with NTG) and 37 control subjects in a discovery study. VIP analysis revealed five metabolites that were elevated and three metabolites that were reduced in the glaucoma patients. The identified metabolomic profile had an area under the receiver operating characteristic curve of 0.953. Among eight selected metabolites, the glutathione level was significantly decreased in association with visual field defects. Moreover, in a validation study to confirm the reproducibility of our findings, the glutathione level was reduced in NTG and POAG patients compared with a cataract control group. Our findings demonstrate that aqueous humor profiling can help to diagnose glaucoma and that various aqueous humor metabolites are correlated with clinical parameters in glaucoma patients. In addition, glutathione is clearly reduced in the aqueous humor of glaucoma patients with both IOP-dependent and IOP-independent disease subtypes. These findings indicate that antioxidant agents in the aqueous humor reflect glaucomatous optic nerve damage and that excessive oxidative stress may be involved in the pathogenesis of glaucoma.

Regulated Cell Death of Retinal Ganglion Cells in Glaucoma: Molecular Insights and Therapeutic Potentials

Glaucoma is a group of diseases characterized by the degeneration of retinal ganglion cells (RGCs) and progressive, irreversible vision loss. High intraocular pressure (IOP) heightens the likelihood of glaucoma and correlates with RGC loss. While the current glaucoma therapy prioritizes lower the IOP; however, RGC, and visual loss may persist even when the IOP is well-controlled. As such, discovering and creating IOP-independent neuroprotective strategies for safeguard RGCs is crucial for glaucoma management. Investigating and clarifying the mechanism behind RGC death to counteract its effects is a promising direction for glaucoma control. Empirical studies of glaucoma reveal the role of multiple regulated cell death (RCD) pathways in RGC death. This review delineates the RCD of RGCs following IOP elevation and optic nerve damage and discusses the substantial benefits of mitigating RCD in RGCs in preserving visual function.

Retinal ganglion cell repopulation for vision restoration in optic neuropathy: a roadmap from the RReSTORe Consortium

Retinal ganglion cell (RGC) death in glaucoma and other optic neuropathies results in irreversible vision loss due to the mammalian central nervous system's limited regenerative capacity. RGC repopulation is a promising therapeutic approach to reverse vision loss from optic neuropathies if the newly introduced neurons can reestablish functional retinal and thalamic circuits. In theory, RGCs might be repopulated through the transplantation of stem cell-derived neurons or via the induction of endogenous transdifferentiation. The RGC Repopulation, Stem Cell Transplantation, and Optic Nerve Regeneration (RReSTORe) Consortium was established to address the challenges associated with the therapeutic repair of the visual pathway in optic neuropathy. In 2022, the RReSTORe Consortium initiated ongoing international collaborative discussions to advance the RGC repopulation field and has identified five critical areas of focus: (1) RGC development and differentiation, (2) Transplantation methods and models, (3) RGC survival, maturation, and host interactions, (4) Inner retinal wiring, and (5) Eye-to-brain connectivity. Here, we discuss the most pertinent questions and challenges that exist on the path to clinical translation and suggest experimental directions to propel this work going forward. Using these five subtopic discussion groups (SDGs) as a framework, we suggest multidisciplinary approaches to restore the diseased visual pathway by leveraging groundbreaking insights from developmental neuroscience, stem cell biology, molecular biology, optical imaging, animal models of optic neuropathy, immunology & immunotolerance, neuropathology & neuroprotection, materials science & biomedical engineering, and regenerative neuroscience. While significant hurdles remain, the RReSTORe Consortium's efforts provide a comprehensive roadmap for advancing the RGC repopulation field and hold potential for transformative progress in restoring vision in patients suffering from optic neuropathies.

Microglial SIRT1 activation attenuates synapse loss in retinal inner plexiform layer via mTORC1 inhibition

BACKGROUND

Optic nerve injury (ONI) is a key cause of irreversible blindness and triggers retinal ganglion cells (RGCs) change and synapse loss. Microglia is the resistant immune cell in brain and retina and has been demonstrated to be highly related with neuron and synapse injury. However, the function of Sirtuin 1 (SIRT1), a neuroprotective molecule, in mediating microglial activation, retinal synapse loss and subsequent retinal ganglion cells death in optic nerve injury model as well as the regulatory mechanism remain unclear.

METHOD

To this end, optic nerve crush (ONC) model was conducted to mimic optic nerve injury. Resveratrol and EX527, highly specific activator and inhibitor of SIRT1, respectively, were used to explore the function of SIRT1 in vivo and vitro. Cx3Cr1-CreERT2/RaptorF/F mice were used to delete Raptor for inhibiting mammalian target of rapamycin complex 1 (mTORC1) activity in microglia. HEK293 and BV2 cells were transfected with plasmids to explore the regulatory mechanism of SIRT1.

RESULTS

We discovered that microglial activation and synapse loss in retinal inner plexiform layer (IPL) occurred after optic nerve crush, with later-development retinal ganglion cells death. SIRT1 activation induced by resveratrol inhibited microglial activation and attenuated synapse loss and retinal ganglion cells injury. After injury, microglial phagocytosed synapse and SIRT1 inhibited this process to protect synapse and retinal ganglion cells. Moreover, SIRT1 exhibited neuron protective effects via activating tuberous sclerosis complex 2 (TSC2) through deacetylation, and enhancing the inhibition effect of tuberous sclerosis complex 2 on mammalian target of rapamycin complex 1 activity.

CONCLUSION

Our research provides novel insights into microglial SIRT1 in optic nerve injury and suggests a potential strategy for neuroprotective treatment of optic nerve injury disease.

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.

Glaucoma-Associated CDR1 Peptide Promotes RGC Survival in Retinal Explants through Molecular Interaction with Acidic Leucine Rich Nuclear Phosphoprotein 32A (ANP32A)

Glaucoma is a complex, multifactorial optic neuropathy mainly characterized by the progressive loss of retinal ganglion cells (RGCs) and their axons, resulting in a decline of visual function. The pathogenic molecular mechanism of glaucoma is still not well understood, and therapeutic strategies specifically addressing the neurodegenerative component of this ocular disease are urgently needed. Novel immunotherapeutics might overcome this problem by targeting specific molecular structures in the retina and providing direct neuroprotection via different modes of action. Within the scope of this research, the present study showed for the first time beneficial effects of the synthetic CDR1 peptide SCTGTSSDVGGYNYVSWYQ on the viability of RGCs ex vivo in a concentration-dependent manner compared to untreated control explants (CTRL, 50 µg/mL: p < 0.05 and 100 µg/mL: p < 0.001). Thereby, this specific peptide was identified first as a potential biomarker candidate in the serum of glaucoma patients and was significantly lower expressed in systemic IgG molecules compared to healthy control subjects. Furthermore, MS-based co-immunoprecipitation experiments confirmed the specific interaction of synthetic CDR1 with retinal acidic leucine-rich nuclear phosphoprotein 32A (ANP32A; p < 0.001 and log2 fold change > 3), which is a highly expressed protein in neurological tissues with multifactorial biological functions. In silico binding prediction analysis revealed the N-terminal leucine-rich repeat (LRR) domain of ANP32A as a significant binding site for synthetic CDR1, which was previously reported as an important docking site for protein-protein interactions (PPI). In accordance with these findings, quantitative proteomic analysis of the retinae ± CDR1 treatment resulted in the identification of 25 protein markers, which were significantly differentially distributed between both experimental groups (CTRL and CDR1, p < 0.05). Particularly, acetyl-CoA biosynthesis I-related enzymes (e.g., DLAT and PDHA1), as well as cytoskeleton-regulating proteins (e.g., MSN), were highly expressed by synthetic CDR1 treatment in the retina; on the contrary, direct ANP32A-interacting proteins (e.g., NME1 and PPP2R4), as well as neurodegenerative-related markers (e.g., CEND1), were identified with significant lower abundancy in the CDR1-treated retinae compared to CTRL. Furthermore, retinal protein phosphorylation and histone acetylation were also affected by synthetic CDR1, which are both partially controlled by ANP32A. In conclusion, the synthetic CDR1 peptide provides a great translational potential for the treatment of glaucoma in the future by eliciting its neuroprotective mechanism via specific interaction with ANP32A's N terminal LRR domain.

Lifestyle Measures for Glaucoma Patients: An Objective Social Media Content Analysis

Aim

In this study, we analyze the content quality and characteristics of the most viewed search results on various internet platforms related to lifestyle measures for patients with glaucoma.

Materials and methods

In this internet-based cross-sectional study, we used search keywords "glaucoma," "lifestyle," "glaucoma," and "exercise" on the most popular internet platforms-Google, Facebook, YouTube, and Reddit. The top 30 Google searches about each of the keyword combinations were identified. We also assessed the first 30 videos on YouTube and Facebook Watch, the first 30 Reddit posts and the first 30 Google images about each of the keyword combinations. The quality of content from the platforms was evaluated by three independent reviewers using the well-established Sandvik score, Health on Net (HON) code, and risk score for different uploaders. The quality of content regarding lifestyle measures in glaucoma uploaded by healthcare professionals (HCPs) was further evaluated.

Results

The established criteria resulted in 48 websites from the Google search engine, 22 videos from YouTube, 37 posts from Reddit, and 28 videos from Facebook Watch, which were included in the final analysis. The mean Sandvik scores were 11.14 ± 1.8 (Google webpages), 10.4 ± 2.19 (YouTube videos), 10.54 ± 2.21 (Facebook Watch), and 4.24 ± 1.18 (Reddit). The mean risk scores were 0.22 ± 0.68 (YouTube videos), 0.18 ± 0.47 (Facebook Watch), and 0.11 ± 0.31 (Reddit). The mean HON code scores were 5.45 ± 1.62 (YouTube), 6.55 ± 1.44 (Google webpages), 5.29 ± 1.04 (Facebook Watch), and 8.27 ± 3.05 (Reddit). The content uploaded by HCPs was primarily from ophthalmologists and had significantly (p < 0.05) higher content quality scores. The majority of the content recommended aerobic exercise as a lifestyle measure in patients with glaucoma as an adjuvant to medical and surgical management.

Conclusion

The majority of the content regarding lifestyle measures in glaucoma was uploaded by HCPs and had medically accurate and well-referenced information, especially on Google and YouTube.

Clinical significance

Primary care physicians and ophthalmologists can reliably use social media content to guide recently diagnosed patients about the requisite lifestyle measures.

How to cite this article

Chahal R, Jindal A, Parmar UPS, et al. Lifestyle Measures for Glaucoma Patients: An Objective Social Media Content Analysis. J Curr Glaucoma Pract 2023;17(3):141-148.

Association of Circulating Metabolites With Racial Disparities in Hypertension and Stroke in the REGARDS Study

BACKGROUND AND OBJECTIVES

In the United States, the risk of stroke is greater among Black compared with that among White individuals. However, the reasons for the difference in stroke incidence are not fully elucidated. We aimed to identify metabolites that account for higher prevalent hypertension and incident ischemic stroke among Black adults.

METHODS

We used a stroke case cohort nested within the REasons for Geographic and Racial Differences in Stroke (REGARDS) study. Targeted metabolomic profiling of 162 plasma metabolites was performed by liquid chromatography-tandem mass spectrometry. We identified metabolites that were associated with prevalent hypertension and incident ischemic stroke and mediated the relationship between hypertension and ischemic stroke by weighted logistic regression, Cox proportional hazard model, and inverse odds ratio weighting mediation analysis.

RESULTS

Incident ischemic stroke cases adjudicated through April 1, 2019 (n = 1,075) were included in the study. The random cohort sample was derived from the full cohort using stratified sampling (n = 968). Among 162 metabolites, gluconic acid was associated with prevalent hypertension in Black adults (odds ratio [OR] 1.86, 95% CI 1.39-2.47, p = 2.58 × 10-5) but not in White adults (OR 1.00, 95% CI 0.80-1.24, p = 0.97; p for interaction = 4.57 × 10-4). Gluconic acid also demonstrated an association with incident ischemic stroke among Black participants (hazard ratio [HR] 1.53, 95% CI 1.28-1.81, p = 1.76 × 10-6) but not White participants (HR 1.16, 95% CI 1.00-1.34, p = 0.057; p for interaction = 0.019). In mediation analysis, gluconic acid mediated 25.4% (95% CI 4.1%-46.8%, p = 0.02) of the association between prevalent hypertension and incident ischemic stroke among Black individuals. Specific socioeconomic factors were linked to elevated gluconic acid level among Black adults in multivariable analysis, including a Southern dietary pattern (β = 0.18, 95% CI 0.08-0.28, p < 0.001), lower educational attainment (β = 0.45, 95% CI 0.19-0.72, p = 0.001), and a lack of exercise (β = 0.26, 95% CI 0.01-0.51, p = 0.045).

DISCUSSION

Gluconic acid is associated with prevalent hypertension and incident ischemic stroke and mediates the relationship between hypertension and ischemic stroke in Black but not White adults. Gluconic acid is a biomarker that is associated with social determinants of health including a Southern diet, low educational attainment, and low physical activity.

Nutritional Factors: Benefits in Glaucoma and Ophthalmologic Pathologies

Glaucoma is a chronic optic neuropathy that can lead to irreversible functional and morphological damage if left untreated. The gold standard therapeutic approaches in managing patients with glaucoma and limiting progression include local drops, laser, and/or surgery, which are all geared at reducing intraocular pressure (IOP). Nutrients, antioxidants, vitamins, organic compounds, and micronutrients have been gaining increasing interest in the past decade as integrative IOP-independent strategies to delay or halt glaucomatous retinal ganglion cell degeneration. In our minireview, we examine the various nutrients and compounds proposed in the current literature for the management of ophthalmology diseases, especially for glaucoma. With respect to each substance considered, this minireview reports the molecular and biological characteristics, neuroprotective activities, antioxidant properties, beneficial mechanisms, and clinical studies published in the past decade in the field of general medicine. This study highlights the potential benefits of these substances in glaucoma and other ophthalmologic pathologies. Nutritional supplementation can thus be useful as integrative IOP-independent strategies in the management of glaucoma and in other ophthalmologic pathologies. Large multicenter clinical trials based on functional and morphologic data collected over long follow-up periods in patients with IOP-independent treatments can pave the way for alternative and/or coadjutant therapeutic options in the management of glaucoma and other ocular pathologies.

Separate lifetime signatures of macaque S cones, M/L cones, and rods observed with adaptive optics fluorescence lifetime ophthalmoscopy

In the retina, several molecules involved in metabolism, the visual cycle, and other roles exhibit intrinsic fluorescence. The overall properties of retinal fluorescence depend on changes to the composition of these molecules and their environmental interactions due to transient functional shifts, especially in disease. This behooves the understanding of the origins and deviations of these properties within the multilayered retina at high lateral and axial resolution. Of particular interest is the fluorescence lifetime, a potential biomarker of function and disease independent of fluorescence intensity that can be measured in the retina with adaptive optics fluorescence lifetime ophthalmoscopy (AOFLIO). This work demonstrates the utility of the phasor method of analysis, an alternate approach to traditional multiexponential fitting, to evaluate photoreceptor two-photon excited AOFLIO data and separate them based on functional differences. Phasor analysis on fluorescence lifetime decay data allowed the repeatable segregation of S from M/L cones, likely from differences in functional or metabolic demands. Furthermore, it is possible to track the lifetime changes in S cones after photodamage. Phasor analysis increases the sensitivity of AOFLIO to functional differences between cells and has the potential to improve our understanding of pathways involved in normal and diseased conditions at the cellular scale throughout the retina.

NAD salvage pathway machinery expression in normal and glaucomatous retina and optic nerve

Glaucoma is the leading cause of irreversible blindness and is a major health and economic burden. Current treatments do not address the neurodegenerative component of glaucoma. In animal models of glaucoma, the capacity to maintain retinal nicotinamide adenine dinucleotide (NAD) pools declines early during disease pathogenesis. Treatment with nicotinamide, an NAD precursor through the NAD salvage pathway, robustly protects against neurodegeneration in a number of glaucoma models and improves vision in existing glaucoma patients. However, it remains unknown in humans what retinal cell types are able to process nicotinamide to NAD and how these are affected in glaucoma. To address this, we utilized publicly available RNA-sequencing data (bulk, single cell, and single nucleus) and antibody labelling in highly preserved enucleated human eyes to identify expression of NAD synthesizing enzyme machinery. This identifies that the neural retina favors expression of the NAD salvage pathway, and that retinal ganglion cells are particularly enriched for these enzymes. NMNAT2, a key terminal enzyme in the salvage pathway, is predominantly expressed in retinal ganglion cell relevant layers of the retina and declines in glaucoma. These findings suggest that human retinal ganglion cells can directly utilize nicotinamide and could maintain a capacity to do so in glaucoma, showing promise for ongoing clinical trials.

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.

Investigations into photoreceptor energy metabolism during experimental retinal detachment

Retinal detachment is a sight-threatening disorder, which occurs when the photoreceptors are separated from their vascular supply. The aim of the present study was to shed light on photoreceptor energy metabolism during experimental detachment in rats. Retinal detachment was induced in the eyes of rats via subretinal injection of sodium hyaluronate. Initially, we investigated whether detachment caused hypoxia within photoreceptors, as evaluated by the exogenous and endogenous biomarkers pimonidazole and HIF-1α, as well as by qPCR analysis of HIF target genes. The results showed no unequivocal staining for pimonidazole or HIF-1α within any detached retina, nor upregulation of HIF target genes, suggesting that any reduction in pO2 is of insufficient magnitude to produce hypoxia-induced covalent protein adducts or HIF-1α stabilisation. Subsequently, we analysed expression of cellular bioenergetic enzymes in photoreceptors during detachment. We documented loss of mitochondrial, and downregulation of glycolytic enzymes during detachment, indicating that photoreceptors have reduced energetic requirements and/or capacity. Given that detachment did not cause widespread hypoxia, but did result in downregulated expression of bioenergetic enzymes, we hypothesised that substrate insufficiency may be critical in terms of pathogenesis, and that boosting metabolic inputs may preserve photoreceptor bioenergetic production and, protect against their degeneration. Thus, we tested whether supplementation with the bioavailable energy substrate pyruvate mitigated rod and cone injury and degeneration. Despite protecting photoreceptors in culture from nutrient deprivation, pyruvate failed to protect against apoptotic death of rods, loss of cone opsins, and loss of inner segment mitochondria, in situ, when evaluated at 3 days after detachment. The regimen was also ineffective against cumulative photoreceptor deconstruction and degeneration when evaluated after 4 weeks. Retinal metabolism, particularly the bioenergetic profiles and pathological responses of the various cellular subtypes still presents a considerable knowledge gap that has important clinical consequences. While our data do not support the use of pyruvate supplementation as a means of protecting detached photoreceptors, they do provide a foundation and motivation for future research in this area.

Covalent Organic Framework (COF): A Drug and Carrier to Attenuate Retinal Ganglion Cells Death in an Acute Glaucoma Mouse Model

Purpose: We aim to investigate the use of covalent organic framework (COF) nanoparticles in the local treatment of glaucoma, both as a means of protecting retinal ganglion cells (RGCs), and as a carrier for delayed release of the medication rapamycin following a single intravitreal injection. Methods: a water-dispersible COF, and a COF-based nanoplatform for rapamycin release (COF-Rapa) was constructed. C57BL/6J mice were randomly divided into four groups: intravitreal injection of 1.5 µL normal saline (NS), COF (0.67 ng/µL), rapamycin (300 µM) or COF-Rapa (0.67 ng/µL-300 µM), respectively. The ischemia–reperfusion (I/R) model was established to mimic high intraocular pressure (IOP)-induced retinal injury in glaucoma. Labeling of RGCs by Fluoro-Gold and retinal electroretinogram were used to evaluate retinal function. Immunohistochemistry and Western blotting analyses of retinas were performed. Results: COF nanoparticles were delivered in vitro and in vivo. Six weeks after the COF injection, the number of RGCs was unaffected. In addition, the number of RBPMS-positive RGCs, GFAP-positive astrocytes and Iba1-positive microglia did not differ from the normal control. COF could effectively reduce RGCs death, improve phototransduction function and alleviate the overactivation of microglia compared to NS control after retinal I/R injury. Within six weeks, the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway in the retinas could be inhibited by a single intravitreal injection of COF-Rapa. Compared with single COF administration, COF-Rapa significantly reduced the inflammatory reaction after retinal I/R injury. Conclusions: COF may act as both an RGC protection agent and a carrier for prolonged rapamycin release. This research may lead to the development of novel RGC protection agents and drug delivery techniques, as well as the creation of multifunctional COF-based biomaterials for glaucoma retinopathy.

Stretch stress propels glutamine dependency and glycolysis in optic nerve head astrocytes

Glaucoma is an optic neuropathy that leads to irreversible blindness, the most common subtype of which is typified by a chronic increase in intraocular pressure that promotes a stretch injury to the optic nerve head. In rodents, the predominant glial cell in this region is the optic nerve head astrocyte that provides axons with metabolic support, likely by releasing lactate produced through astrocytic glycolysis. Our primary hypothesis is that stretching of the optic nerve head astrocytes alters their metabolic activity, thereby advancing glaucoma-associated degeneration by compromising the metabolic support that the astrocytes provide to the axons in the optic nerve head. Metabolic changes in optic nerve head astrocytes were investigated by subjecting them to 24 h of 12% biaxial stretch at 1 Hz then measuring the cells’ bioenergetics using a Seahorse XFe24 Analyzer. We observed significant glycolytic and respiratory activity differences between control and stretched cells, including greater extracellular acidification and lower ATP-linked respiration, yet higher maximal respiration and spare capacity in stretched optic nerve head astrocytes. We also determined that both control and stretched optic nerve head astrocytes displayed a dependency for glutamine over pyruvate or long-chain fatty acids for fuel. The increased use of glycolysis as indicated by the extracellular acidification rate, concomitant with a dependency on glutamine, suggests the need to replenish NAD + for continued glycolysis and provision of carbon for TCA cycle intermediates. Stretch alters optic nerve astrocyte bioenergetics to support an increased demand for internal and external energy.

The Neuroprotective Role of Retbindin, a Metabolic Regulator in the Neural Retina

Dysregulation of retinal metabolism is emerging as one of the major reasons for many inherited retinal diseases (IRDs), a leading cause of blindness worldwide. Thus, the identification of a common regulator that can preserve or revert the metabolic ecosystem to homeostasis is a key step in developing a treatment for different forms of IRDs. Riboflavin (RF) and its derivatives (flavins), flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), are essential cofactors for a wide range of cellular metabolic processes; hence, they are particularly critical in highly metabolically active tissues such as the retina. Patients with RF deficiency (ariboflavinosis) often display poor photosensitivity resulting in impaired low-light vision. We have identified a novel retina-specific RF binding protein called retbindin (Rtbdn), which plays a key role in retaining flavin levels in the neural retina. This role is mediated by its specific localization at the interface between the neural retina and retinal pigment epithelium (RPE), which is essential for metabolite and nutrient exchange. As a consequence of this vital function, Rtbdn's role in flavin utilization and metabolism in retinal degeneration is discussed. The principal findings are that Rtbdn helps maintain high levels of retinal flavins, and its ablation leads to an early-onset retinal metabolic dysregulation, followed by progressive degeneration of rod and cone photoreceptors. Lack of Rtbdn reduces flavin levels, forcing the neural retina to repurpose glucose to reduce the production of free radicals during ATP production. This leads to metabolic breakdown followed by retinal degeneration. Assessment of the role of Rtbdn in several preclinical retinal disease models revealed upregulation of its levels by several folds prior to and during the degenerative process. Ablation of Rtbdn in these models accelerated the rate of retinal degeneration. In agreement with these in vivo studies, we have also demonstrated that Rtbdn protects immortalized cone photoreceptor cells (661W cells) from light damage in vitro. This indicates that Rtbdn plays a neuroprotective role during retinal degeneration. Herein, we discussed the specific function of Rtbdn and its neuroprotective role in retinal metabolic homeostasis and its role in maintaining retinal health.

mTOR Signalling Pathway: A Potential Therapeutic Target for Ocular Neurodegenerative Diseases

Recent advances in the research of the mammalian target of the rapamycin (mTOR) signalling pathway demonstrated that mTOR is a robust therapeutic target for ocular degenerative diseases, including age-related macular degeneration (AMD), diabetic retinopathy (DR), and glaucoma. Although the exact mechanisms of individual ocular degenerative diseases are unclear, they share several common pathological processes, increased and prolonged oxidative stress in particular, which leads to functional and morphological impairment in photoreceptors, retinal ganglion cells (RGCs), or retinal pigment epithelium (RPE). mTOR not only modulates oxidative stress but is also affected by reactive oxygen species (ROS) activation. It is essential to understand the complicated relationship between the mTOR pathway and oxidative stress before its application in the treatment of retinal degeneration. Indeed, the substantial role of mTOR-mediated autophagy in the pathogenies of ocular degenerative diseases should be noted. In reviewing the latest studies, this article summarised the application of rapamycin, an mTOR signalling pathway inhibitor, in different retinal disease models, providing insight into the mechanism of rapamycin in the treatment of retinal neurodegeneration under oxidative stress. Besides basic research, this review also summarised and updated the results of the latest clinical trials of rapamycin in ocular neurodegenerative diseases. In combining the current basic and clinical research results, we provided a more complete picture of mTOR as a potential therapeutic target for ocular neurodegenerative diseases.

A mathematical model of GLUT1 modulation in rods and RPE and its differential impact in cell metabolism

We present a mathematical model of key glucose metabolic pathways in two cells of the human retina: the rods and the retinal pigmented epithelium (RPE). Computational simulations of glucose transporter 1 (GLUT1) inhibition in the model accurately reproduce experimental data from conditional knockout mice and reveal that modification of GLUT1 expression levels of both cells differentially impacts their metabolism. We hypothesize that, under glucose scarcity, the RPE's energy producing pathways are altered in order to preserve its functionality, impacting the photoreceptors' outer segment renewal. On the other hand, when glucose is limited in the rods, aerobic glycolysis is preserved, which maintains the lactate contribution to the RPE.

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.

Intracellular and extracellular untargeted metabolomics reveal the effect of acute uranium exposure in HK-2 cells

Uranium exposure poses a serious threat to the health of occupational populations and the public. Although metabolomics is a promising research approach to study the toxicological mechanisms of uranium exposure, in vitro studies using human cells are scarce. Applying cultured cell metabolomics, we exhaustively analyzed the intracellular and extracellular differential metabolites upon uranium exposure and characterized the possible biological effects of uranium exposure on human kidney cells. Uranium exposure significantly induced disturbance in the amino acid biosynthesis and linoleic acid metabolism of the cells. Cells exposed to uranium produce excessive amounts of arachidonic acid, which has the potential to cause oxidative stress and damage cells. The results provide new evidence for an oxidative stress mechanism of uranium-induced renal cell injury. Cell metabolomics has proven to be a useful diagnostic tool to study the molecular mechanisms of uranium poisoning.

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.

Medical therapy for glaucoma: A review

A number of pharmacological targets are exploited to modify the parameters in the Goldmann equation and reduce the intraocular pressure (IOP). This strategy constitutes the foundation for the medical management of glaucoma, the evolution of which, until only recently, has been in relative stagnation. A burst of innovation has produced new ocular hypotensive drugs and long-acting delivery methods, including intracameral delivery, which are expanding the clinician's medical armamentarium. A number of IOP-independent neuroprotection strategies have shown strong potential in animal models of glaucoma, but translational attempts have been surprisingly limited. However, while pharmacological options are expanding, the traditional role of topical medical therapy is being challenged by selective laser trabeculoplasty, micro-invasive glaucoma surgery, and sustained delivery methods. A scientifically rigorous assessment of new treatments will be critical to empower clinicians with evidence-based information to optimise vision preservation and quality of life outcomes for their patients.

Systemic Treatment with Pioglitazone Reverses Vision Loss in Preclinical Glaucoma Models

Neuroinflammation significantly contributes to the pathophysiology of several neurodegenerative diseases. This is also the case in glaucoma and may be a reason why many patients suffer from progressive vision loss despite maximal reduction in intraocular pressure. Pioglitazone is an agonist of the peroxisome proliferator-activated receptor gamma (PPARγ) whose pleiotrophic activities include modulation of cellular energy metabolism and reduction in inflammation. In this study we employed the DBA2/J mouse model of glaucoma with chronically elevated intraocular pressure to investigate whether oral low-dose pioglitazone treatment preserves retinal ganglion cell (RGC) survival. We then used an inducible glaucoma model in C57BL/6J mice to determine visual function, pattern electroretinographs, and tracking of optokinetic reflex. Our findings demonstrate that pioglitazone treatment does significantly protect RGCs and prevents axonal degeneration in the glaucomatous retina. Furthermore, treatment preserves and partially reverses vision loss in spite of continuously elevated intraocular pressure. These data suggest that pioglitazone may provide treatment benefits for those glaucoma patients experiencing continued vision loss.

Oxidative Stress and Hypoxia Modify Mitochondrial Homeostasis During Glaucoma

Aims: Cellular response to hypoxia can include transition from respiration to glycolysis via upregulation of glycolytic enzymes and transporters, as well as mitophagy induction to eliminate surplus mitochondria. Our purpose was to evaluate the impact of hypoxia-inducible factor-1α (HIF-1α) stabilization on mitochondrial homeostasis and oxidative stress in a chronic model of glaucoma. Results: Retina and optic nerve (ON) were evaluated from young and aged DBA/2J (D2) glaucoma model mice and the control strain, the DBA/2-Gpnmb⁺. Hypoxic retinal ganglion cells (RGCs) were observed in young and aged D2 retina, with a significant increase in HIF-1α protein in the aged D2 retina. Reactive oxygen species observed in young D2 retina and ON were followed by significant decreases in antioxidant capacity in aged D2 retina and ON. HIF-1α targets such as neuron-specific glucose transporter-3 and lactate dehydrogenase were decreased or unchanged, respectively, in aged D2 retina despite an increased hypoxia response in RGCs. Mitochondrial mass was decreased in aged D2 retina concomitant with decreased mitochondrially encoded electron transport chain transcripts despite a stable nuclear-encoded TFAM (mitochondrial transcription factor), suggesting a breakdown in the nuclear-mitochondrial communication. Decreased mitophagy-associated proteins p62 and Rheb were observed in aged D2 retina, although p62 was significantly increased in the aged D2 ON. Innovation and Conclusion: The increased reactive oxygen species concomitant with HIF-1α upregulation despite reduced glucose transporters, mis-match of nuclear- and mitochondrial-encoded transcripts, and signs of reduced mitophagy suggest that retinas from D2 mice with chronic intraocular pressure elevation transition to pseudohypoxia without consistent metabolic reprogramming before significant RGC loss. Antioxid. Redox Signal. 35, 1341-1357.

Metabolic Imbalance Effect on Retinal Müller Glial Cells Reprogramming Capacity: Involvement of Histone Deacetylase SIRT6

Retinal Müller glial cells (MGs) are among the first to demonstrate metabolic changes during retinal disease and are a potential source of regenerative cells. In response to a harmful stimulus, they can dedifferentiate acquiring neural stem cells properties, proliferate and migrate to the damaged retinal layer and differentiate into lost neurons. However, it is not yet known how this reprogramming process is regulated in mammals. Since glucose and oxygen are important regulatory elements that may help directing stem cell fate, we aimed to study the effect of glucose variations and oxidative stress in Müller cells reprogramming capacity and analyze the participation the histone deacetylase SIRT6, as an epigenetic modulator of this process. We found that the combination of high glucose and oxidative stress induced a decrease in the levels of the marker glutamine synthetase, and an increase in the migration capacity of the cells suggesting that these experimental conditions could induce some degree of dedifferentiation and favor the migration ability. High glucose induced an increase in the levels of the pluripotent factor SOX9 and a decrease in SIRT6 levels accompanied by the increase in the acetylation levels of H3K9. Inhibiting SIRT6 expression by siRNA rendered an increase in SOX9 levels. We also determined SOX9 levels in retinas from mice with a conditional deletion of SIRT6 in the CNS. To further understand the mechanisms that regulate MGs response under metabolic impaired conditions, we evaluated the gene expression profile and performed Gene Ontology enrichment analysis of Müller cells from a murine model of Diabetes. We found several differentially expressed genes and observed that the transcriptomic change involved the enrichment of genes associated with glucose metabolism, cell migration, development and pluripotency. We found that many functional categories affected in cells of diabetic animals were directly related to SIRT6 function. Transcription factors enrichment analysis allowed us to predict several factors, including SOX9, that may be involved in the modulation of the differential expression program observed in diabetic MGs. Our results underline the heterogeneity of Müller cells response and the challenge that the study of metabolic impairment in vivo represents.

Nicotinamide and Pyruvate for Neuroenhancement in Open-Angle Glaucoma: A Phase 2 Randomized Clinical Trial

Importance

Open-angle glaucoma may continue to progress despite significant lowering of intraocular pressure (IOP). Preclinical research has suggested that enhancing mitochondrial function and energy production may enhance retinal ganglion cell survival in animal models of glaucoma, but there is scant information on its effectiveness in a clinical setting.

Objective

To test the hypothesis that a combination of nicotinamide and pyruvate can improve retinal ganglion cell function in human glaucoma as measured with standard automated perimetry.

Design, Setting, and Participants

In this phase 2, randomized, double-blind, placebo-controlled clinical trial at a single academic institution, 197 patients were assessed for eligibility. Of these, 42 patients with treated open-angle glaucoma and moderate visual field loss in at least 1 eye were selected for inclusion and randomized. A total of 32 completed the study and were included in the final analysis. The mean (SD) age was 64.6 (9.8) years. Twenty-one participants (66%) were female. Participant race and ethnicity data were collected via self-report to ensure the distribution reflected that observed in clinical practice in the US but are not reported here to protect patient privacy. Recruitment took place in April 2019 and patients were monitored through December 2020. Data were analyzed from January to May 2021.

Interventions

Ascending oral doses of nicotinamide (1000 to 3000 mg) and pyruvate (1500 to 3000 mg) vs placebo (2:1 randomization).

Main Outcomes and Measures

Number of visual field test locations improving beyond normal variability in the study eye. Secondary end points were the rates of change of visual field global indices (mean deviation [MD], pattern standard deviation [PSD], and visual field index [VFI]).

Results

Twenty-two of 29 participants (76%) randomized to the intervention group and 12 of 13 participants (92%) randomized to placebo received their allocation, and 32 participants (32 eyes; ratio 21:11) completed the study (21 from the intervention group and 11 from the placebo group). Median (IQR) follow-up time was 2.2 (2.0-2.4) months. No serious adverse events were reported during the study. The number of improving test locations was significantly higher in the treatment group than in the placebo group (median [IQR], 15 [6-25] vs 7 [6-11]; P = .005). Rates of change of PSD suggested improvement with treatment compared with placebo (median, -0.06 vs 0.02 dB per week; 95% CI, 0.02 to 0.24; P = .02) but not MD (0.04 vs -0.002 dB per week; 95% CI, -0.27 to 0.09; P = .35) or VFI (0.09 vs -0.02% per week; 95% CI, -0.53 to 0.36; P = .71).

Conclusions and Relevance

A combination of nicotinamide and pyruvate yielded significant short-term improvement in visual function, supporting prior experimental research suggesting a role for these agents in neuroprotection for individuals with glaucoma and confirming the need for long-term studies to establish their usefulness in slowing progression.

Trial Registration

ClinicalTrials.gov Identifier: NCT03797469.

Ocular microbial diversity, community structure, and function at high altitude

PURPOSE

To investigate the composition and function of ocular surface microbiome in healthy people from different altitudes.

METHODS

Thirty-two healthy people living in a high altitude region and 30 sex- and age-matched individuals living in a low altitude region were enrolled. Samples were collected from the lower conjunctival sac of one randomly chosen eye for each participant. 16S rRNA sequencing was conducted to study the bacterial community composition and predict gene function using PICRUSt software.

RESULTS

Microbial diversity and richness was significantly decreased in samples from highlanders as calculated by Abundance-based Coverage Estimator (ACE) index, Chao1 index, and observed-species index (all p < 0.01). Principle coordinate analysis (PCoA) suggested significantly distinct clustering of the conjunctival sac bacterial communities between two groups (p = 0.03), especially the dominant genera. The relative abundances of Corynebacterium, Staphylococcus, and Anaerococcus were significantly enriched in highlanders, while those of Pseudomonas and Massilia were significantly decreased as compared with lowlanders (p < 0.01). In the functional annotation analysis, we found that 74 gene pathways, mainly in metabolism, differed in abundance. Pathways related to immune system diseases and infectious diseases were also enriched in highlanders.

CONCLUSION

The composition and function of ocular surface microbiome in highlanders were distinct from those of lowlanders and our study may provide a reference catalog of the healthy conjunctival microbiome in highlanders.

Metabolomics in Retinal Diseases: An Update

Retinal diseases are a leading cause of visual loss and blindness, affecting a significant proportion of the population worldwide and having a detrimental impact on quality of life, with consequent economic burden. The retina is highly metabolically active, and a number of retinal diseases are associated with metabolic dysfunction. To better understand the pathogenesis underlying such retinopathies, new technology has been developed to elucidate the mechanism behind retinal diseases. Metabolomics is a relatively new "omics" technology, which has developed subsequent to genomics, transcriptomics, and proteomics. This new technology can provide qualitative and quantitative information about low-molecular-weight metabolites (M.W. < 1500 Da) in a given biological system, which shed light on the physiological or pathological state of a cell or tissue sample at a particular time point. In this article we provide an extensive review of the application of metabolomics to retinal diseases, with focus on age-related macular degeneration (AMD), diabetic retinopathy (DR), retinopathy of prematurity (ROP), glaucoma, and retinitis pigmentosa (RP).

Metabolomics and health: from nutritional crops and plant-based pharmaceuticals to profiling of human biofluids

During the past decade metabolomics has emerged as one of the fastest developing branches of “-omics” technologies. Metabolomics involves documentation, identification, and quantification of metabolites through modern analytical platforms in various biological systems. Advanced analytical tools, such as gas chromatography–mass spectrometry (GC/MS), liquid chromatography–mass spectroscopy (LC/MS), and non-destructive nuclear magnetic resonance (NMR) spectroscopy, have facilitated metabolite profiling of complex biological matrices. Metabolomics, along with transcriptomics, has an influential role in discovering connections between genetic regulation, metabolite phenotyping and biomarkers identification. Comprehensive metabolite profiling allows integration of the summarized data towards manipulation of biosynthetic pathways, determination of nutritional quality markers, improvement in crop yield, selection of desired metabolites/genes, and their heritability in modern breeding. Along with that, metabolomics is invaluable in predicting the biological activity of medicinal plants, assisting the bioactivity-guided fractionation process and bioactive leads discovery, as well as serving as a tool for quality control and authentication of commercial plant-derived natural products. Metabolomic analysis of human biofluids is implemented in clinical practice to discriminate between physiological and pathological state in humans, to aid early disease biomarker discovery and predict individual response to drug therapy. Thus, metabolomics could be utilized to preserve human health by improving the nutritional quality of crops and accelerating plant-derived bioactive leads discovery through disease diagnostics, or through increasing the therapeutic efficacy of drugs via more personalized approach. Here, we attempt to explore the potential value of metabolite profiling comprising the above-mentioned applications of metabolomics in crop improvement, medicinal plants utilization, and, in the prognosis, diagnosis and management of complex diseases.

Immune Responses in the Glaucomatous Retina: Regulation and Dynamics

Glaucoma is a multifactorial disease resulting in progressive vision loss due to retinal ganglion cell (RGC) dysfunction and death. Early events in the pathobiology of the disease include oxidative, metabolic, or mechanical stress that acts upon RGC, causing these to rapidly release danger signals, including extracellular ATP, resulting in micro- and macroglial activation and neuroinflammation. Danger signaling also leads to the formation of inflammasomes in the retina that enable maturation of proinflammatory cytokines such IL-1β and IL-18. Chronic neuroinflammation can have directly damaging effects on RGC, but it also creates a proinflammatory environment and compromises the immune privilege of the retina. In particular, continuous synthesis of proinflammatory mediators such as TNFα, IL-1β, and anaphylatoxins weakens the blood–retina barrier and recruits or activates T-cells. Recent data have demonstrated that adaptive immune responses strongly exacerbate RGC loss in animal models of the disease as T-cells appear to target heat shock proteins displayed on the surface of stressed RGC to cause their apoptotic death. It is possible that dysregulation of these immune responses contributes to the continued loss of RGC in some patients.

Diabetes Exacerbates the Intraocular Pressure-Independent Retinal Ganglion Cells Degeneration in the DBA/2J Model of Glaucoma

Purpose

Glaucoma is a multifactorial disease, causing retinal ganglion cells (RGCs) and optic nerve degeneration. The role of diabetes as a risk factor for glaucoma has been postulated but still not unequivocally demonstrated. The purpose of this study is to clarify the effect of diabetes in the early progression of glaucomatous RGC dysfunction preceding intraocular pressure (IOP) elevation, using the DBA/2J mouse (D2) model of glaucoma.

Methods

D2 mice were injected with streptozotocin (STZ) obtaining a combined model of diabetes and glaucoma (D2 + STZ). D2 and D2 + STZ mice were monitored for weight, glycemia, and IOP from 3.5 to 6 months of age. In addition, the activity of RGC and outer retina were assessed using pattern electroretinogram (PERG) and flash electroretinogram (FERG), respectively. At the end point, RGC density and astrogliosis were evaluated in flat mounted retinas. In addition, Müller cell reactivity was evaluated in retinal cross-sections. Finally, the expression of inflammation and oxidative stress markers were analyzed.

Results

IOP was not influenced by time or diabetes. In contrast, RGC activity resulted progressively decreased in the D2 group independently from IOP elevation and outer retinal dysfunction. Diabetes exacerbated RGC dysfunction, which resulted independent from variation in IOP and outer retinal activity. Diabetic retinas displayed decreased RGC density and increased glial reactivity given by an increment in oxidative stress and inflammation.

Conclusions

Diabetes can act as an IOP-independent risk factor for the early progression of glaucoma promoting oxidative stress and inflammation-mediated RGC dysfunction, glial reactivity, and cellular death.

AMPK hyperactivation promotes dendrite retraction, synaptic loss, and neuronal dysfunction in glaucoma

BACKGROUND

The maintenance of complex dendritic arbors and synaptic transmission are processes that require a substantial amount of energy. Bioenergetic decline is a prominent feature of chronic neurodegenerative diseases, yet the signaling mechanisms that link energy stress with neuronal dysfunction are poorly understood. Recent work has implicated energy deficits in glaucoma, and retinal ganglion cell (RGC) dendritic pathology and synapse disassembly are key features of ocular hypertension damage.

RESULTS

We show that adenosine monophosphate-activated protein kinase (AMPK), a conserved energy biosensor, is strongly activated in RGC from mice with ocular hypertension and patients with primary open angle glaucoma. Our data demonstrate that AMPK triggers RGC dendrite retraction and synapse elimination. We show that the harmful effect of AMPK is exerted through inhibition of the mammalian target of rapamycin complex 1 (mTORC1). Attenuation of AMPK activity restores mTORC1 function and rescues dendrites and synaptic contacts. Strikingly, AMPK depletion promotes recovery of light-evoked retinal responses, improves axonal transport, and extends RGC survival.

CONCLUSIONS

This study identifies AMPK as a critical nexus between bioenergetic decline and RGC dysfunction during pressure-induced stress, and highlights the importance of targeting energy homeostasis in glaucoma and other neurodegenerative diseases.

Neuroprotection by WldS depends on retinal ganglion cell type and age in glaucoma

BACKGROUND

Early challenges to axonal physiology, active transport, and ultrastructure are endemic to age-related neurodegenerative disorders, including those affecting the optic nerve. Chief among these, glaucoma causes irreversible vision loss through sensitivity to intraocular pressure (IOP) that challenges retinal ganglion cell (RGC) axons, which comprise the optic nerve. Early RGC axonopathy includes distal to proximal progression that implicates a slow form of Wallerian degeneration. In multiple disease models, including inducible glaucoma, expression of the slow Wallerian degeneration (WldS) allele slows axon degeneration and confers protection to cell bodies.

METHODS

Using an inducible model of glaucoma along with whole-cell patch clamp electrophysiology and morphological analysis, we tested if WldS also protects RGC light responses and dendrites and, if so, whether this protection depends upon RGC type. We induced glaucoma in young and aged mice to determine if neuroprotection by WldS on anterograde axonal transport and spatial contrast acuity depends on age.

RESULTS

We found WldS protects dendritic morphology and light-evoked responses of RGCs that signal light onset (αON-Sustained) during IOP elevation. However, IOP elevation significantly reduces dendritic complexity and light responses of RGCs that respond to light offset (αOFF-Sustained) regardless of WldS. As expected, WldS preserves anterograde axon transport and spatial acuity in young adult mice, but its protection is significantly limited in aged mice.

CONCLUSION

The efficacy of WldS in conferring protection to neurons and their axons varies by cell type and diminishes with age.

Modeling Retinal Ganglion Cell Dysfunction in Optic Neuropathies

As in glaucoma and other optic neuropathies cellular dysfunction often precedes cell death, the assessment of retinal ganglion cell (RGC) function represents a key outcome measure for neuroprotective strategies aimed at targeting distressed but still viable cells. RGC dysfunction can be assessed with the pattern electroretinogram (PERG), a sensitive measure of electrical activity of RGCs that is recorded non-invasively in human subjects and mouse models. Here, we offer a conceptual framework based on an intuitive state-transition model used for disease management in patients to identify progressive, potentially reversible stages of RGC dysfunction leading to cell death in mouse models of glaucoma and other optic neuropathies. We provide mathematical equations to describe state-transitions with a set of modifiable parameters that alter the time course and severity of state-transitions, which can be used for hypothesis testing and fitting experimental PERG data. PERG dynamics as a function of physiological stimuli are also used to differentiate phenotypic and altered RGC response dynamics, to assess susceptibility to stressors and to assess reversible dysfunction upon pharmacological treatment.

Multifactorial Pathogenic Processes of Retinal Ganglion Cell Degeneration in Glaucoma towards Multi-Target Strategies for Broader Treatment Effects

Glaucoma is a chronic neurodegenerative disease characterized by apoptosis of retinal ganglion cell (RGC) somas, degeneration of axons, and loss of synapses at dendrites and axon terminals. Glaucomatous neurodegeneration encompasses multiple triggers, multiple cell types, and multiple molecular pathways through the etiological paths with biomechanical, vascular, metabolic, oxidative, and inflammatory components. As much as intrinsic responses of RGCs themselves, divergent responses and intricate interactions of the surrounding glia also play decisive roles for the cell fate. Seen from a broad perspective, multitarget treatment strategies have a compelling pathophysiological basis to more efficiently manipulate multiple pathogenic processes at multiple injury sites in such a multifactorial neurodegenerative disease. Despite distinct molecular programs for somatic and axonal degeneration, mitochondrial dysfunction and glia-driven neuroinflammation present interdependent processes with widespread impacts in the glaucomatous retina and optic nerve. Since dysfunctional mitochondria stimulate inflammatory responses and proinflammatory mediators impair mitochondria, mitochondrial restoration may be immunomodulatory, while anti-inflammatory treatments protect mitochondria. Manipulation of these converging routes may thus allow a unified treatment strategy to protect RGC axons, somas, and synapses. This review presents an overview of recent research advancements with emphasis on potential treatment targets to achieve the best treatment efficacy to preserve visual function in glaucoma.