Glia-neuron interactions in the mammalian retina

Transcriptional profiling of retinal astrocytes identifies a specific marker and points to functional specialization

Astrocyte heterogeneity is an increasingly prominent research topic, and studies in the brain have demonstrated substantial variation in astrocyte form and function, both between and within regions. In contrast, retinal astrocytes are not well understood and remain incompletely characterized. Along with optic nerve astrocytes, they are responsible for supporting retinal ganglion cell axons and an improved understanding of their role is required. We have used a combination of microdissection and Ribotag immunoprecipitation to isolate ribosome-associated mRNA from retinal astrocytes and investigate their transcriptome, which we also compared to astrocyte populations in the optic nerve. Astrocytes from these regions are transcriptionally distinct, and we identified retina-specific astrocyte genes and pathways. Moreover, although they share much of the "classical" gene expression patterns of astrocytes, we uncovered unexpected variation, including in genes related to core astrocyte functions. We additionally identified the transcription factor Pax8 as a highly specific marker of retinal astrocytes and demonstrated that these astrocytes populate not only the retinal surface, but also the prelaminar region at the optic nerve head. These findings are likely to contribute to a revised understanding of the role of astrocytes in the retina.

Neuroprotective effect of omidenepag on excitotoxic retinal ganglion cell death regulating COX-2-EP2-cAMP-PKA/Epac pathway via Neuron-Glia interaction

Glutamate excitotoxicity is involved in retinal ganglion cell (RGC) death in various retinal degenerative diseases, including ischemia-reperfusion injury and glaucoma. Excitotoxic RGC death is caused by both direct damage to RGCs and indirect damage through neuroinflammation of retinal glial cells. Omidenepag (OMD), a novel E prostanoid receptor 2 (EP2) agonist, is a recently approved intraocular pressure-lowering drug. The second messenger of EP2 is cyclic adenosine monophosphate (cAMP), which activates protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac). In this study, we investigated the neuroprotective effects of OMD on excitotoxic RGC death by focusing on differences in cAMP downstream signaling from the perspective of glia-neuron interactions. We established a glutamate excitotoxicity model in vitro and NMDA intravitreal injection model in vivo. In vitro, rat primary RGCs were used in an RGC survival rate assay. MG5 cells (mouse microglial cell line) and A1 cells (astrocyte cell line) were used for immunocytochemistry and Western blotting to evaluate the expressions of COX-1/2, PKA, Epac1/2, pCREB, cleaved caspase-3, inflammatory cytokines, and neurotrophic factors. Mouse retinal specimens underwent hematoxylin and eosin staining, flat-mounted retina examination, and immunohistochemistry. OMD significantly suppressed excitotoxic RGC death, cleaved caspase-3 expression, and activated glia both in vitro and in vivo. Moreover, it inhibited Epac1 and inflammatory cytokine expression and promoted COX-2, pCREB, and neurotrophic factor expression. OMD may have neuroprotective effects through inhibition of the Epac pathway and promotion of the COX-2-EP2-cAMP-PKA pathway by modulating glia-neuron interaction.

JR5558 mice are a reliable model to investigate subretinal fibrosis

Subretinal fibrosis is a major untreatable cause of poor outcomes in neovascular age-related macular degeneration. Mouse models of subretinal fibrosis all possess a degree of invasiveness and tissue damage not typical of fibrosis progression. This project characterises JR5558 mice as a model to study subretinal fibrosis. Fundus and optical coherence tomography (OCT) imaging was used to non-invasively track lesions. Lesion number and area were quantified with ImageJ. Retinal sections, wholemounts and Western blots were used to characterise alterations. Subretinal lesions expand between 4 and 8 weeks and become established in size and location around 12 weeks. Subretinal lesions were confirmed to be fibrotic, including various cell populations involved in fibrosis development. Müller cell processes extended from superficial retina into subretinal lesions at 8 weeks. Western blotting revealed increases in fibronectin (4 wk and 8 wk, p < 0.001), CTGF (20 wks, p < 0.001), MMP2 (12 wks and 20 wks p < 0.05), αSMA (12 wks and 20 wks p < 0.05) and GFAP (8 wk and 12 wk, p ≤ 0.01), consistent with our immunofluorescence results. Intravitreal injection of Aflibercept reduced subretinal lesion growth. Our study provides evidence JR5558 mice have subretinal fibrotic lesions that grow between 4 and 8 weeks and confirms this line to be a good model to study subretinal fibrosis development and assess treatment options.

Identification of Optic Nerve-Related Biomarkers in Primary Open-Angle Glaucoma Based on Comprehensive Bioinformatics and Mendelian Randomization

Purpose

Glaucoma is the primary cause of permanent vision loss worldwide. However, the pathogenesis of primary open-angle glaucoma (POAG), the main type of glaucoma, has not yet been completely understood.

Methods

In our study, the POAG cohorts were obtained from the Gene Expression Omnibus (GEO) database (GSE45570). Biomarkers with diagnostic utility for POAG were identified through combining differentially expressed analysis, enrichment analysis, machine learning algorithms, and receiver operating characteristic (ROC) analysis. The regulatory networks (including a competing endogenous RNA (ceRNA) regulatory network and a small molecule compounds-mRNA network) were created. In addition, the Mendelian randomization (MR) analysis was used to identify exposures causally associated with POAG. Finally, the expression of the biomarkers was validated via real-time quantitative polymerase chain reaction (RT-qPCR).

Results

The Gene Ontology (GO) items that the differentially expressed genes (DEGs) between POAG and control groups enriched were relevant to light stimulation and DNA methylation. A total of three light stimulation-related biomarkers (RAB8A, PRG3, and SMAD3) were identified, which had diagnostic value for POAG patients. Besides, the ceRNA regulatory network contained 88 nodes and 93 edges, and a small molecule compounds-mRNA network included 66 nodes and 76 edges. The MR results indicated a causal association between DNA methylation GrimAge acceleration and POAG. Additionally, the results of RT-qPCR revealed that the expression trend of RAB8A was consistent with that of GSE45570.

Conclusions

Taken together, this study provides three light stimulation-related biomarkers (RAB8A, PRG3, and SMAD3) for the diagnosis of POAG, providing scientifically valuable insights for further studies of POAG.

Translational Relevance

Discovering biomarkers that possess diagnostic significance for POAG has the potential to offer new insights into the pathogenesis of POAG and present novel objectives for clinical intervention.

Underlying mechanisms of traditional Chinese medicine in the prevention and treatment of diabetic retinopathy: Evidences from molecular and clinical studies

As one of the most serious microvascular complications of diabetes mellitus (DM), diabetic retinopathy (DR) can cause visual impairment and even blindness. With the rapid increase in the prevalence of DM, the incidence of DR is also rising year by year. Preventing and effectively treating DR has become a major focus in the medical field. Traditional Chinese medicine (TCM) has a wealth of experience in treating DR and has achieved significant results with various herbs and TCM prescriptions. Traditional Chinese Medicine (TCM) provides a comprehensive therapeutic strategy for diabetic retinopathy (DR), encompassing anti-inflammatory and antioxidant actions, anti-neovascularization, neuroprotection, regulation of glucose metabolism, and inhibition of apoptosis. This review provides an overview of the current status of TCM treatment for DR in recent years, including experimental studies and clinical researches, to explore the clinical efficacy and the underlying modern mechanisms of herbs and TCM prescriptions. Besides, we also discussed the challenges TCM faces in treating DR, such as drug-drug interactions among TCM components and the lack of high-quality evidence-based medicine practice, which pose significant obstacles to TCM's application in DR.

Mitochondrial transfer between BMSCs and Müller promotes mitochondrial fusion and suppresses gliosis in degenerative retina

Mitochondrial dysfunction and Müller cells gliosis are significant pathological characteristics of retinal degeneration (RD) and causing blinding. Stem cell therapy is a promising treatment for RD, the recently accepted therapeutic mechanism is cell fusion induced materials transfer. However, whether materials including mitochondrial transfer between grafted stem cells and recipient's cells contribute to suppressing gliosis and mechanism are unclear. In present study, we demonstrated that bone marrow mesenchymal stem cells (BMSCs) transferred mitochondria to Müller cells by cell fusion and tunneling nanotubes. BMSCs-derived mitochondria (BMSCs-mito) were integrated into mitochondrial network of Müller cells, improving mitochondrial function, reducing oxidative stress and gliosis, which protected visual function partially in the degenerative rat retina. RNA sequencing analysis revealed that BMSCs-mito increased mitochondrial DNA (mtDNA) content and facilitated mitochondrial fusion in damaged Müller cells. It suggests that mitochondrial transfer from BMSCs remodels Müller cells metabolism and suppresses gliosis; thus, delaying the degenerative progression of RD.

Inhibition of JNK ameliorates rod photoreceptor degeneration in a mouse model of retinitis pigmentosa

Retinitis pigmentosa (RP) is an inherited eye disease that causes progressive vision loss. Microglial activation and inflammation play essential roles in photoreceptor degeneration in RP, although the underlying mechanisms remain unclear. Here, we examined the progressive degeneration of photoreceptors in rd1 mice, a mouse model of RP. We investigated the molecular changes in various retinal cells in rd1 mice using single-cell RNA sequencing and found that potentiation of JNK signaling is associated with photoreceptor degeneration in RP. Moreover, inflammation-related molecules, which function downstream of JNK, are elevated in RP. Furthermore, inhibiting JNK alleviates microglial activation and rescues photoreceptor degeneration in rd1 mice. Thus, our findings suggest that targeting JNK is a promising approach for slowing RP progression.

Epithelial UNC-23 limits mechanical stress to maintain glia-neuron architecture in C. elegans

For an organ to maintain correct architecture and function, its diverse cellular components must coordinate their size and shape. Although cell-intrinsic mechanisms driving homotypic cell-cell coordination are known, it is unclear how cell shape is regulated across heterotypic cells. We find that epithelial cells maintain the shape of neighboring sense-organ glia-neuron units in adult Caenorhabditis elegans (C. elegans). Hsp co-chaperone UNC-23/BAG2 prevents epithelial cell shape from deforming, and its loss causes head epithelia to stretch aberrantly during animal movement. In the sense-organ glia, amphid sheath (AMsh), this causes progressive fibroblast growth factor receptor (FGFR)-dependent disruption of the glial apical cytoskeleton. Resultant glial cell shape alteration causes concomitant shape change in glia-associated neuron endings. Epithelial UNC-23 maintenance of glia-neuron shape is specific both spatially, within a defined anatomical zone, and temporally, in a developmentally critical period. As all molecular components uncovered are broadly conserved across central and peripheral nervous systems, we posit that epithelia may similarly regulate glia-neuron architecture cross-species.

Interleukin-17A in diabetic retinopathy: The crosstalk of inflammation and angiogenesis

Diabetic retinopathy (DR) is a severe ocular complication of diabetes which can leads to irreversible vision loss in its late-stage. Chronic inflammation results from long-term hyperglycemia contributes to the pathogenesis and progression of DR. In recent years, the interleukin-17 (IL-17) family have attracted the interest of researchers. IL-17A is the most widely explored cytokine in IL-17 family, involved in various acute and chronic inflammatory diseases. Growing body of evidence indicate the role of IL-17A in the pathogenesis of DR. However, the pro-inflammatory and pro-angiogenic effect of IL-17A in DR have not hitherto been reviewed. Gaining an understanding of the pro-inflammatory role of IL-17A, and how IL-17A control/impact angiogenesis pathways in the eye will deepen our understanding of how IL-17A contributes to DR pathogenesis. Herein, we aimed to thoroughly review the pro-inflammatory role of IL-17A in DR, with focus in how IL-17A impact inflammation and angiogenesis crosstalk.

Prohibitin 2 deficiency in photoreceptors leads to progressive retinal degeneration and facilitated Müller glia engulfing microglia debris

Müller glia and microglia are capable of phagocytosing fragments of retinal cells in response to retinal injury or degeneration. However, the direct evidence for their mutual interactions between Müller glia and microglia in the progression of retinal degeneration (RD) remains largely unclear. This study aims to construct a progressive RD mouse model and investigate the activated pattern of Müller glia and the interplay between Müller glia and microglia in the early stage or progression of RD. A Prohibitin 2 (Phb2) photoreceptor-specific knockout (RKO) mouse model was generated by crossing Phb2flox/flox mice with Rhodopsin-Cre mice. Optical Coherence Tomography (OCT), histological staining, and Electroretinography (ERG) assessed retinal structure and function, and RKO mice exhibited progressive RD from six weeks of age. In detail, six-week-old RKO mice showed no significant retinal impairment, but severe vision dysfunction and retina thinning were shown in ten-week-old RKO mice. Furthermore, RKO mice were sensitive to Light Damage (LD) and showed severe RD at an early age after light exposure. Bulk retina RNA-seq analysis from six-week-old control (Ctrl) and RKO mice showed reactive retinal glia in RKO mice. The activated pattern of Müller glia and the interplay between Müller glia and microglia was visualized by immunohistology and 3D reconstruction. In six-week-old RKO mice or light-exposed Ctrl mice, Müller glia were initially activated at the edge of the retina. Moreover, in ten-week-old RKO mice or light-exposed six-week-old RKO mice with severe photoreceptor degeneration, abundant Müller glia were activated across the whole retinas. With the progression of RD, phagocytosis of microglia debris by activated Müller glia were remarkably increased. Altogether, our study establishes a Phb2 photoreceptor-specific knockout mouse model, which is a novel mouse model of RD and can well demonstrate the phenotype of progressive RD. We also report that Müller glia in the peripheral retina is more sensitive to the early damage of photoreceptors. Our study provides more direct evidence for Müller glia engulfing microglia debris in the progression of RD due to photoreceptor Phb2 deficiency.

Homer1a reduces inflammatory response after retinal ischemia/reperfusion injury

JOURNAL/nrgr/04.03/01300535-202407000-00042/figure1/v/2023-11-20T171125Z/r/image-tiff

Elevated intraocular pressure (IOP) is one of the causes of retinal ischemia/reperfusion injury, which results in NLRP3 inflammasome activation and leads to visual damage. Homer1a is reported to play a protective role in neuroinflammation in the cerebrum. However, the effects of Homer1a on NLRP3 inflammasomes in retinal ischemia/reperfusion injury caused by elevated IOP remain unknown. In our study, animal models were constructed using C57BL/6J and Homer1flox/ –/Homer1a+/ –/Nestin-Cre+/ – mice with elevated IOP-induced retinal ischemia/reperfusion injury. For in vitro experiments, the oxygen-glucose deprivation/reperfusion injury model was constructed with Müller cells. We found that Homer1a overexpression ameliorated the decreases in retinal thickness and Müller cell viability after ischemia/reperfusion injury. Furthermore, Homer1a knockdown promoted NF-κB P65Ser536 activation via caspase-8, NF-κB P65 nuclear translocation, NLRP3 inflammasome formation, and the production and processing of interleukin-1β and interleukin-18. The opposite results were observed with Homer1a overexpression. Finally, the combined administration of Homer1a protein and JSH-23 significantly inhibited the reduction in retinal thickness in Homer1flox/ –/Homer1a+/ –/Nestin-Cre+/ – mice and apoptosis in Müller cells after ischemia/reperfusion injury. Taken together, these studies demonstrate that Homer1a exerts protective effects on retinal tissue and Müller cells via the caspase-8/NF-κB P65/NLRP3 pathway after I/R injury.

[A case of autoimmune glial fibrillary acidic protein astrocytopathy with various symptoms such as optic disc edema and cerebellar ataxia]

A 59-year-old man had developed visual abnormality, nausea, headache, and weight loss since three months before. The ophthalmologist found severe optic disc edema in both eyes, and referred him to our hospital. The patient had mild cerebellar ataxia. Increased cerebrospinal fluid pressure, increased protein and cell counts, positive oligoclonal band, and contrast-enhanced head MRI showed multiple linear perivascular radial gadolinium enhancement around bilateral lateral ventricles. His subjective and objective findings significantly improved with steroid treatment. The cerebrospinal fluid was found to be positive for glial fibrillary acidic protein (GFAP) antibodies, and a diagnosis of GFAP astrocytopathy was obtained. When optic edema or radial contrast effects was observed on contrast-enhanced MRI, GFAP astrocytopathy should be considerd. Prompt immunotherapy is required to circumvent the development of permanent visual impairment.

Botulinum neurotoxin serotype A inhibited ocular angiogenesis through modulating glial activation via SOCS3

BACKGROUND

Pathological angiogenesis causes significant vision loss in neovascular age-related macular degeneration and other retinopathies with neovascularization (NV). Neuronal/glial-vascular interactions influence the release of angiogenic and neurotrophic factors. We hypothesized that botulinum neurotoxin serotype A (BoNT/A) modulates pathological endothelial cell proliferation through glial cell activation and growth factor release.

METHODS

A laser-induced choroidal NV (CNV) was employed to investigate the anti-angiogenic effects of BoNT/A. Fundus fluorescence angiography, immunohistochemistry, and real-time PCR were used to assess BoNT/A efficacy in inhibiting CNV and the molecular mechanisms underlying this inhibition. Neuronal and glial suppressor of cytokine signaling 3 (SOCS3) deficient mice were used to investigate the molecular mechanisms of BoNT/A in inhibiting CNV via SOCS3.

FINDINGS

In laser-induced CNV mice with intravitreal BoNT/A treatment, CNV lesions decreased > 30%; vascular leakage and retinal glial activation were suppressed; and Socs3 mRNA expression was induced while vascular endothelial growth factor A (Vegfa) mRNA expression was suppressed. The protective effects of BoNT/A on CNV development were diminished in mice lacking neuronal/glial SOCS3.

CONCLUSION

BoNT/A suppressed laser-induced CNV and glial cell activation, in part through SOCS3 induction in neuronal/glial cells. BoNT/A treatment led to a decrease of pro-angiogenic factors, including VEGFA, highlighting the potential of BoNT/A as a therapeutic intervention for pathological angiogenesis in retinopathies.

Comprehensive single-cell atlas of the mouse retina

Single-cell RNA sequencing (scRNA-seq) has advanced our understanding of cellular heterogeneity by characterizing cell types across tissues and species. While several mouse retinal scRNA-seq datasets exist, each dataset is either limited in cell numbers or focused on specific cell classes, thereby hindering comprehensive gene expression analysis across all retina types. To fill the gap, we generated the largest retinal scRNA-seq dataset to date, comprising approximately 190,000 single cells from C57BL/6J mouse retinas, enriched for rare population cells via antibody-based magnetic cell sorting. Integrating this dataset with public datasets, we constructed the Mouse Retina Cell Atlas (MRCA) for wild-type mice, encompassing over 330,000 cells, characterizing 12 major classes and 138 cell types. The MRCA consolidates existing knowledge, identifies new cell types, and is publicly accessible via CELLxGENE, UCSC Cell Browser, and the Broad Single Cell Portal, providing a user-friendly resource for the mouse retina research community.

PCYT1A deficiency disturbs fatty acid metabolism and induces ferroptosis in the mouse retina

BACKGROUND

Inherited retinal dystrophies (IRDs) are a group of debilitating visual disorders characterized by the progressive degeneration of photoreceptors, which ultimately lead to blindness. Among the causes of this condition, mutations in the PCYT1A gene, which encodes the rate-limiting enzyme responsible for phosphatidylcholine (PC) de novo synthesis via the Kennedy pathway, have been identified. However, the precise mechanisms underlying the association between PCYT1A mutations and IRDs remain unclear. To address this knowledge gap, we focused on elucidating the functions of PCYT1A in the retina.

RESULTS

We found that PCYT1A is highly expressed in Müller glial (MG) cells in the inner nuclear layer (INL) of the retina. Subsequently, we generated a retina-specific knockout mouse model in which the Pcyt1a gene was targeted (Pcyt1a-RKO or RKO mice) to investigate the molecular mechanisms underlying IRDs caused by PCYT1A mutations. Our findings revealed that the deletion of Pcyt1a resulted in retinal degenerative phenotypes, including reduced scotopic electroretinogram (ERG) responses and progressive degeneration of photoreceptor cells, accompanied by loss of cells in the INL. Furthermore, through proteomic and bioinformatic analyses, we identified dysregulated retinal fatty acid metabolism and activation of the ferroptosis signalling pathway in RKO mice. Importantly, we found that PCYT1A deficiency did not lead to an overall reduction in PC synthesis within the retina. Instead, this deficiency appeared to disrupt free fatty acid metabolism and ultimately trigger ferroptosis.

CONCLUSIONS

This study reveals a novel mechanism by which mutations in PCYT1A contribute to the development of IRDs, shedding light on the interplay between fatty acid metabolism and retinal degenerative diseases, and provides new insights into the treatment of IRDs.

Agarose disk electroporation method for ex vivo retinal tissue cultured at the air-liquid interface reveals electrical stimulus-induced cell cycle reentry in retinal cells

It is advantageous to culture the ex vivo murine retina along with many other tissue types at the air-liquid interface. However, gene delivery to these cultures can be challenging. Electroporation is a fast and robust method of gene delivery, but typically requires submergence in a liquid buffer to allow electric current flow. We have developed a submergence-free electroporation technique using an agarose disk that allows for efficient gene delivery to the ex vivo murine retina. This method advances our ability to use ex vivo retinal tissue for genetic studies and can easily be adapted for any tissue cultured at an air-liquid interface. We found an increased ability to transfected Muller glia at 14 days ex vivo and an increase in BrdU incorporation in Muller glia following electrical stimulation. Use of this method has revealed valuable insights on the state of ex vivo retinal tissues and the effects of electrical stimulation on retinal cells.

Inhibition of NLRP3 inflammasome by MCC950 under hypoxia alleviates photoreceptor apoptosis via inducing autophagy in Müller glia

NLRP3 inflammasome activation has emerged as a critical initiator of inflammatory response in ischemic retinopathy. Here, we identified the effect of a potent, selective NLRP3 inhibitor, MCC950, on autophagy and apoptosis under hypoxia. Neonatal mice were exposed to hyperoxia for 5 days to establish oxygen-induced retinopathy (OIR) model. Intravitreal injection of MCC950 was given, and then autophagy and apoptosis markers were assessed. Retinal autophagy, apoptosis, and related pathways were evaluated by western blot, immunofluorescent labeling, transmission electron microscopy, and TUNEL assay. Autophagic activity in Müller glia after NLRP3 inflammasome inhibition, together with its influence on photoreceptor death, was studied using western blot, immunofluorescence staining, mRFP-GFP-LC3 adenovirus transfection, cell viability, proliferation, and apoptosis assays. Results showed that activation of NLRP3 inflammasome in Müller glia was detected in OIR model. MCC950 could improve impaired retinal autophagic flux and attenuate retinal apoptosis while it regulated the retinal AMPK/mTOR/ULK-1 pathway. Suppressed autophagy and depressed proliferation capacity resulting from hypoxia was promoted after MCC950 treatment in Müller glia. Inhibition of AMPK and ULK-1 pathway significantly interfered with the MCC950-induced autophagy activity, indicating MCC950 positively modulated autophagy through AMPK/mTOR/ULK-1 pathway in Müller cells. Furthermore, blockage of autophagy in Müller glia significantly induced apoptosis in the cocultured 661W photoreceptor cells, whereas MCC950 markedly preserved the density of photoreceptor cells. These findings substantiated the therapeutic potential of MCC950 against impaired autophagy and subsequent apoptosis under hypoxia. Such protective effect might involve the modulation of AMPK/mTOR/ULK-1 pathway. Targeting NLRP3 inflammasome in Müller glia could be beneficial for photoreceptor survival under hypoxic conditions.

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.

Complement regulation in the eye: implications for age-related macular degeneration

Careful regulation of the complement system is critical for enabling complement proteins to titrate immune defense while also preventing collateral tissue damage from poorly controlled inflammation. In the eye, this balance between complement activity and inhibition is crucial, as a low level of basal complement activity is necessary to support ocular immune privilege, a prerequisite for maintaining vision. Dysregulated complement activation contributes to parainflammation, a low level of inflammation triggered by cellular damage that functions to reestablish homeostasis, or outright inflammation that disrupts the visual axis. Complement dysregulation has been implicated in many ocular diseases, including glaucoma, diabetic retinopathy, and age-related macular degeneration (AMD). In the last two decades, complement activity has been the focus of intense investigation in AMD pathogenesis, leading to the development of novel therapeutics for the treatment of atrophic AMD. This Review outlines recent advances and challenges, highlighting therapeutic approaches that have advanced to clinical trials, as well as providing a general overview of the complement system in the posterior segment of the eye and selected ocular diseases.

Ferroptosis in Glaucoma: A Promising Avenue for Therapy

Glaucoma, a blind-leading disease largely since chronic pathological intraocular high pressure (ph-IOP). Hitherto, it is reckoned incurable for irreversible neural damage and challenges in managing IOP. Thus, it is significant to develop neuroprotective strategies. Ferroptosis, initially identified as an iron-dependent regulated death that triggers Fenton reactions and culminates in lipid peroxidation (LPO), has emerged as a focal point in multiple tumors and neurodegenerative diseases. Researches show that iron homeostasis play critical roles in the optic nerve (ON) and retinal ganglion cells (RGCs), suggesting targeted treatments could be effective. In glaucoma, apart from neural lesions, disrupted metal balance and increased oxidative stress in trabecular meshwork (TM) are observed. These disturbances lead to extracellular matrix excretion disorders, known as sclerotic mechanisms, resulting in refractory blockages. Importantly, oxidative stress, a significant downstream effect of ferroptosis, is also a key factor in cell senescence. It plays a crucial role in both the etiology and risk of glaucoma. Moreover, ferroptosis also induces non-infectious inflammation, which exacerbate glaucomatous injury. Therefore, the relevance of ferroptosis in glaucoma is extensive and multifaceted. In this review, the study delves into the current understanding of ferroptosis mechanisms in glaucoma, aiming to provide clues to inform clinical therapeutic practices.

Transmembrane protein TMEM97 and epigenetic reader BAHCC1 constitute an axis that supports pro-inflammatory cytokine expression

Pro-inflammatory cytokine production by the retinal pigment epithelium (RPE) is a key etiology in retinal degenerative diseases, yet the underlying mechanisms are not well understood. TMEM97 is a scarcely studied transmembrane protein recently implicated in retinal degeneration. BAH domain coiled coil 1 (BAHCC1) is a newly discovered histone code reader involved in oncogenesis. A role for TMEM97 and BAHCC1 in RPE inflammation was not known. Here we found that they constitute a novel axis regulating pro-inflammatory cytokine expression in RPE cells. Transcriptomic analysis using a TMEM97-/- ARPE19 human cell line and the validation via TMEM97 loss- and gain-of-function revealed a profound role of TMEM97 in promoting the expression of pro-inflammatory cytokines, notably IL1β and CCL2, and unexpectedly BAHCC1 as well. Moreover, co-immunoprecipitation indicated an association between the TMEM97 and BAHCC1 proteins. While TMEM97 ablation decreased and its overexpression increased NFκB (p50, p52, p65), the master transcription factor for pro-inflammatory cytokines, silencing BAHCC1 down-regulated NFκB and downstream pro-inflammatory cytokines. Furthermore, in an RPE-damage retinal degeneration mouse model, immunofluorescence illustrated down-regulation of IL1β and CCL2 total proteins and suppression of glial activation in the retina of Tmem97-/- mice compared to Tmem97+/+ mice. Thus, TMEM97 is a novel determinant of pro-inflammatory cytokine expression acting via a previously unknown TMEM97- > BAHCC1- > NFκB cascade. SYNOPSIS: Retinal pigment epithelium (RPE) inflammation can lead to blindness. We identify here a previously uncharacterized cascade that underlies RPE cell production of pro-inflammatory cytokines. Specifically, transmembrane protein TMEM97 positively regulates the recently discovered histone code reader BAHCC1, which in turn enhances pro-inflammatory cytokine expression via the transcription factor NFκB.

Lipid mediators in glaucoma: Unraveling their diverse roles and untapped therapeutic potential

Glaucoma is a complex neurodegenerative disease characterized by optic nerve damage and visual field loss, and remains a leading cause of irreversible blindness. Elevated intraocular pressure (IOP) is a critical risk factor that requires effective management. Emerging research underscores dual roles of bioactive lipid mediators in both IOP regulation, and the modulation of neurodegeneration and neuroinflammation in glaucoma. Bioactive lipids, encompassing eicosanoids, specialized pro-resolving mediators (SPMs), sphingolipids, and endocannabinoids, have emerged as crucial players in these processes, orchestrating inflammation and diverse effects on aqueous humor dynamics and tissue remodeling. Perturbations in these lipid mediators contribute to retinal ganglion cell loss, vascular dysfunction, oxidative stress, and neuroinflammation. Glaucoma management primarily targets IOP reduction via pharmacological agents and surgical interventions, with prostaglandin analogues at the forefront. Intriguingly, additional lipid mediators offer promise in attenuating inflammation and providing neuroprotection. Here we explore these pathways to shed light on their intricate roles, and to unveil novel therapeutic avenues for glaucoma management.

TIMP3/Wnt axis regulates gliosis of Müller glia

BACKGROUND

Previous studies have confirmed the expression of tissue inhibitor of metalloproteinase-3 (TIMP3) in Müller glia (MG). However, the role of TIMP3 in MG remains unknown.

METHODS

A mouse model of laser-induced retinal damage and gliosis was generated using wild-type C57BL/6 mice. TIMP3 and associated proteins were detected using Western blotting and immunofluorescence microscopy. RNA sequencing (GSE132140) of mouse laser-induced gliosis was utilized for pathway analysis. TIMP3 overexpression was induced in human MG. Human vitreous samples were obtained from patients with proliferative diabetic retinopathy (PDR) and healthy controls for protein analysis.

RESULTS

TIMP3 levels increased in mouse eyes after laser damage. Morphology and spatial location of TIMP3 indicated its presence in MG. TIMP3-overexpressing MG showed increased cellular proliferation, migration, and cell nuclei size, suggesting TIMP3-induced gliosis for retinal repair. Glial fibrillary acidic protein (GFAP) and vimentin levels were elevated in TIMP3-overexpressing MG and laser-damaged mouse retinas. RNA sequencing and Western blotting suggested a role for β-catenin in mediating TIMP3 effects on the retina. Human vitreous samples from patients with PDR showed a positive correlation between TIMP3 and GFAP levels, both of which were elevated in patients with PDR.

CONCLUSIONS

TIMP3 is associated with MG gliosis to enhance the repair ability of damaged retinas and is mediated by the canonical Wnt/β-catenin. Changes in TIMP3 could potentially be used to control gliosis in a range of retinal diseases However, given the multifaceted nature of TIMP3, care must be taken when developing treatments that aim solely to boost the function of TIMP3.

FUNDING

National Cheng Kung University Hospital, Taiwan (NCKUH-10604009 and NCKUH-11202007); the Ministry of Science and Technology (MOST 110-2314-B-006-086-MY3).

Sustained Retinal Defocus Increases the Effect of Induced Myopia on the Retinal Astrocyte Template

The aim of this article is to describe sustained myopic eye growth's effect on astrocyte cellular distribution and its association with inner retinal layer thicknesses. Astrocyte density and distribution, retinal nerve fiber layer (RNFL), ganglion cell layer, and inner plexiform layer (IPL) thicknesses were assessed using immunochemistry and spectral-domain optical coherence tomography on seventeen common marmoset retinas (Callithrix jacchus): six induced with myopia from 2 to 6 months of age (6-month-old myopes), three induced with myopia from 2 to 12 months of age (12-month-old myopes), five age-matched 6-month-old controls, and three age-matched 12-month-old controls. Untreated marmoset eyes grew normally, and both RNFL and IPL thicknesses did not change with age, with astrocyte numbers correlating to RNFL and IPL thicknesses in both control age groups. Myopic marmosets did not follow this trend and, instead, exhibited decreased astrocyte density, increased GFAP+ spatial coverage, and thinner RNFL and IPL, all of which worsened over time. Myopic changes in astrocyte density, GFAP+ spatial coverage and inner retinal layer thicknesses suggest astrocyte template reorganization during myopia development and progression which increased over time. Whether or not these changes are constructive or destructive to the retina still remains to be assessed.

BMX deletion mitigates neuroinflammation induced by retinal ischemia/reperfusion through modulation of the AKT/ERK/STAT3 signaling cascade

Aims

Retinal ischemia/reperfusion (I/R) injury is implicated in the etiology of various ocular disorders. Prior research has demonstrated that bone marrow tyrosine kinase on chromosome X (BMX) contributes to the advancement of ischemic disease and inflammatory reactions. Consequently, the current investigation aims to evaluate BMX's impact on retinal I/R injury and clarify its implied mechanism of action.

Main methods

This study utilized male and female systemic BMX knockout (BMX-/-) mice to conduct experiments. The utilization of Western blot assay and immunofluorescence labeling techniques was employed to investigate variations in the expression of protein and tissue localization. Histomorphological changes were observed through H&E staining and SD-OCT examination. Visual function changes were assessed through electrophysiological experiments. Furthermore, apoptosis in the retina was identified using the TUNEL assay, as well as the ELISA technique, which has been utilized to determine the inflammatory factors level.

Key findings

Our investigation results revealed that the knockdown of BMX did not yield a significant effect on mouse retina. In mice, BMX knockdown mitigated the negative impact of I/R injury on retinal tissue structure and visual function. BMX knockdown effectively reduced apoptosis, suppressed inflammatory responses, and decreased inflammatory factors subsequent to I/R injury. The outcomes of the current investigation revealed that BMX knockdown partially protected the retina through downregulating phosphorylation of AKT/ERK/STAT3 pathway.

Significance

Our investigation showed that BMX-/- reduces AKT, ERK, and STAT3 phosphorylation, reducing apoptosis and inflammation. Thus, this strategy protected the retina from structural and functional damage after I/R injury.

Cell-cell interaction in the pathogenesis of inherited retinal diseases

The retina is part of the central nervous system specialized for vision. Inherited retinal diseases (IRD) are a group of clinically and genetically heterogenous disorders that lead to progressive vision impairment or blindness. Although each disorder is rare, IRD accumulatively cause blindness in up to 5.5 million individuals worldwide. Currently, the pathophysiological mechanisms of IRD are not fully understood and there are limited treatment options available. Most IRD are caused by degeneration of light-sensitive photoreceptors. Genetic mutations that abrogate the structure and/or function of photoreceptors lead to visual impairment followed by blindness caused by loss of photoreceptors. In healthy retina, photoreceptors structurally and functionally interact with retinal pigment epithelium (RPE) and Müller glia (MG) to maintain retinal homeostasis. Multiple IRD with photoreceptor degeneration as a major phenotype are caused by mutations of RPE- and/or MG-associated genes. Recent studies also reveal compromised MG and RPE caused by mutations in ubiquitously expressed ciliary genes. Therefore, photoreceptor degeneration could be a direct consequence of gene mutations and/or could be secondary to the dysfunction of their interaction partners in the retina. This review summarizes the mechanisms of photoreceptor-RPE/MG interaction in supporting retinal functions and discusses how the disruption of these processes could lead to photoreceptor degeneration, with an aim to provide a unique perspective of IRD pathogenesis and treatment paradigm. We will first describe the biology of retina and IRD and then discuss the interaction between photoreceptors and MG/RPE as well as their implications in disease pathogenesis. Finally, we will summarize the recent advances in IRD therapeutics targeting MG and/or RPE.

Compensation of inner retina to early-stage photoreceptor degeneration in a RhoP23H/+ mouse model of retinitis pigmentosa

Retinitis pigmentosa (RP) is an inherited retinal disorder characterized by the degeneration of photoreceptors. RhoP23H/+ mice, which carry a Pro23His mutation in the RHODOPSIN (Rho) gene, are one of the most studied animal models for RP. However, except for the photoreceptors, other retinal neural cells have not been fully investigated in this model. Here, we record the temporal changes of the retina by optical coherence tomography (OCT) imaging of the RhoP23H/+ mice, from early to mid-phase of retinal degeneration. Based on thickness analysis, we identified a natural retinal thickness adaption in wild-type mice during early adulthood and observed morphological compensation of the inner retina layer to photoreceptor degeneration in the RhoP23H/+ mice, primarily on the inner nuclear layer (INL). RhoP23H/+ mice findings were further validated via: histology showing the negative correlation of INL and ONL thicknesses; as well as electroretinogram (ERG) showing an increased b-wave to a-wave ratio. These results unravel the sequential morphologic events in this model and suggest a better understanding of retinal degeneration of RP for future studies.

Ferroptosis: underlying mechanisms and involvement in neurodegenerative diseases

Ferroptosis, a mode of cell death that was recently identified in 2012, is driven by iron-dependent lipid peroxidation and distinct from other mechanisms of cell death such as autophagy and apoptosis. Ferroptosis has the unique features of disruptions in iron equilibrium, iron-induced lipid peroxidation, and the accumulation of glutamate-induced cellular toxicity. The regulation of ferroptosis mainly involves the iron, lipid, and amino acid metabolic pathways, which are controlled by system Xc-, voltage-dependent anion channels, p53 and other pathways. Neurodegenerative diseases involve gradual neuronal loss predominantly within the central nervous system and are categorized into both sporadic and rare hereditary disorders. These diseases result in the progressive decline of specific neuron populations and their interconnections. Recent investigations have revealed a strong correlation between the manifestation and progression of neurodegenerative diseases and ferroptosis. The pharmacological modulation of ferroptosis, whether by induction or inhibition, exhibits promising prospects for therapeutic interventions for these diseases. This review aims to examine the literature on ferroptosis and its implications in various neurodegenerative diseases. We hope to offer novel insights into the potential therapies targeting ferroptosis in central nervous system neurodegenerative diseases. However, there are still limitations of this review. First, despite our efforts to maintain objectivity during our analysis, this review does not cover all the studies on ferroptosis and neurodegenerative diseases. Second, cell death in neurodegenerative diseases is not solely caused by ferroptosis. Future research should focus on the interplay of different cell death mechanisms to better elucidate the specific disease pathogenesis.

SIPA1 promotes angiogenesis by regulating VEGF secretion in Müller cells through STAT3 activation

Diabetic retinopathy (DR) is a prevalent complication of diabetes that can lead to vision loss. The chronic hyperglycemia associated with DR results in damage to the retinal microvasculature. Müller cells, as a kind of macroglia, play a crucial role in regulating the retinal vascular microenvironment. The objective of this study was to investigate the role of signal-induced proliferation-associated protein 1 (SIPA1) in regulating angiogenesis in Müller cells. Through proteomics, database analysis, endothelial cell function tests, and Western blot detection, we observed an up-regulation of SIPA1 expression in Müller cells upon high glucose stimulation. SIPA1 expression contributed to VEGF secretion in Müller cells and regulated the mobility of retinal vascular endothelial cells. Further investigation of the dependence of SIPA1 on VEGF secretion revealed that SIPA1 activated the phosphorylation STAT3, leading to its translocation into the nucleus. Overexpression of SIPA1 combined with the STAT3 inhibitor STATTIC demonstrated the regulation of SIPA1 in VEGF expression, dependent on STAT3 activation. These findings suggest that SIPA1 promotes the secretion of pro-angiogenic factors in Müller cells by activating the STAT3 signaling pathway, thereby highlighting SIPA1 as a potential therapeutic target for DR.

Comprehensive single-cell atlas of the mouse retina

Single-cell RNA sequencing (scRNA-seq) has advanced our understanding of cellular heterogeneity at the single-cell resolution by classifying and characterizing cell types in multiple tissues and species. While several mouse retinal scRNA-seq reference datasets have been published, each dataset either has a relatively small number of cells or is focused on specific cell classes, and thus is suboptimal for assessing gene expression patterns across all retina types at the same time. To establish a unified and comprehensive reference for the mouse retina, we first generated the largest retinal scRNA-seq dataset to date, comprising approximately 190,000 single cells from C57BL/6J mouse whole retinas. This dataset was generated through the targeted enrichment of rare population cells via antibody-based magnetic cell sorting. By integrating this new dataset with public datasets, we conducted an integrated analysis to construct the Mouse Retina Cell Atlas (MRCA) for wild-type mice, which encompasses over 330,000 single cells. The MRCA characterizes 12 major classes and 138 cell types. It captured consensus cell type characterization from public datasets and identified additional new cell types. To facilitate the public use of the MRCA, we have deposited it in CELLxGENE, UCSC Cell Browser, and the Broad Single Cell Portal for visualization and gene expression exploration. The comprehensive MRCA serves as an easy-to-use, one-stop data resource for the mouse retina communities.

Combination of blockade of endothelin signalling and compensation of IGF1 expression protects the retina from degeneration

Retinitis pigmentosa (RP) and macular dystrophy (MD) cause severe retinal dysfunction, affecting 1 in 4000 people worldwide. This disease is currently assumed to be intractable, because effective therapeutic methods have not been established, regardless of genetic or sporadic traits. Here, we examined a RP mouse model in which the Prominin-1 (Prom1) gene was deficient and investigated the molecular events occurring at the outset of retinal dysfunction. We extracted the Prom1-deficient retina subjected to light exposure for a short time, conducted single-cell expression profiling, and compared the gene expression with and without stimuli. We identified the cells and genes whose expression levels change directly in response to light stimuli. Among the genes altered by light stimulation, Igf1 was decreased in rod photoreceptor cells and astrocytes under the light-stimulated condition. Consistently, the insulin-like growth factor (IGF) signal was weakened in light-stimulated photoreceptor cells. The recovery of Igf1 expression with the adeno-associated virus (AAV) prevented photoreceptor cell death, and its treatment in combination with the endothelin receptor antagonist led to the blockade of abnormal glial activation and the promotion of glycolysis, thereby resulting in the improvement of retinal functions, as assayed by electroretinography. We additionally demonstrated that the attenuation of mammalian/mechanistic target of rapamycin (mTOR), which mediates IGF signalling, leads to complications in maintaining retinal homeostasis. Together, we propose that combinatorial manipulation of distinct mechanisms is useful for the maintenance of the retinal condition.

Silva H, P. de Carvalho R, Ventura ALM, Calaza KC, Silveira MS, Kubrusly RCC, de Melo Reis RA. The Healthy and Diseased Retina Seen through Neuron-Glia Interactions

The retina is the sensory tissue responsible for the first stages of visual processing, with a conserved anatomy and functional architecture among vertebrates. To date, retinal eye diseases, such as diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa, glaucoma, and others, affect nearly 170 million people worldwide, resulting in vision loss and blindness. To tackle retinal disorders, the developing retina has been explored as a versatile model to study intercellular signaling, as it presents a broad neurochemical repertoire that has been approached in the last decades in terms of signaling and diseases. Retina, dissociated and arranged as typical cultures, as mixed or neuron- and glia-enriched, and/or organized as neurospheres and/or as organoids, are valuable to understand both neuronal and glial compartments, which have contributed to revealing roles and mechanisms between transmitter systems as well as antioxidants, trophic factors, and extracellular matrix proteins. Overall, contributions in understanding neurogenesis, tissue development, differentiation, connectivity, plasticity, and cell death are widely described. A complete access to the genome of several vertebrates, as well as the recent transcriptome at the single cell level at different stages of development, also anticipates future advances in providing cues to target blinding diseases or retinal dysfunctions.

Protective effect of the natural flavonoid naringenin in mouse models of retinal injury

Glaucoma is an eye disease with a high rate of blindness and a complex pathogenesis. Ocular hypertension (OHT) is a critical risk factor, and retinal ischemia/reperfusion (I/R) is an important pathophysiological basis. This study was designed to investigate the retinal neuroprotective effect of oral naringenin in an acute retinal I/R model and a chronic OHT model and the possible mechanism involved. After the I/R and OHT models were established, mice were given vehicle or naringenin (100 mg/kg or 300 mg/kg). Hematoxylin-eosin (HE) staining and immunostaining of RBPMS and glial fibrillary acidic protein (GFAP) were used to evaluate retinal injury. GFAP, CD38, Sirtuin1 (SIRT1), and NOD-like receptor protein 3 (NLRP3) expression levels were measured by Western blotting. In the OHT model, intraocular pressure (IOP) was dynamically maintained at approximately 20-25 mmHg after injury. The retinal structure was damaged, and retinal ganglion cells (RGCs) were lost in both models. Naringenin ameliorated the abovementioned indications but also demonstrated that high concentrations of naringenin significantly inhibited retinal astrocyte activation and inhibited damage-induced increases in the expression of GFAP, NLRP3, and CD38 proteins, while SIRT1 protein expression was upregulated. This study showed for the first time that naringenin can reduce microbead-induced IOP elevation in the OHT model, providing new evidence for the application of naringenin in glaucoma. Naringenin may mediate the CD38/SIRT1 signaling pathway, inhibit astrocyte activation, and ultimately exert an anti-inflammatory effect to achieve retinal neuroprotection.

Cholesterol and oxysterols in retinal neuron-glia interactions: relevance for glaucoma

Cholesterol is an essential component of cellular membranes, crucial for maintaining their structural and functional integrity. It is especially important for nervous tissues, including the retina, which rely on high amounts of plasma membranes for the transmission of the nervous signal. While cholesterol is by far the most abundant sterol, the retina also contains cholesterol precursors and metabolites, especially oxysterols, which are bioactive molecules. Cholesterol lack or excess is deleterious and some oxysterols are known for their effect on neuron survival. Cholesterol homeostasis must therefore be maintained. Retinal glial cells, especially Müller cells, the principal glial cells of the vertebrate retina, provide mechanical, nutritional, and metabolic support for the neighboring neurons. Several pieces of evidence indicate that Müller cells are major actors of cholesterol homeostasis in the retina, as it is known for other glial cells in the brain. This process is based on a close cooperation with neurons, and sterols can be signaling molecules participating in glia-neuron interactions. While some implication of cholesterol in age-related macular degeneration is now recognized, based on epidemiological and laboratory data, evidence for its role in glaucoma is still scarce. The association between cholesterolemia and glaucoma is controversial, but experimental data suggest that sterols could take part in the pathological processes. It has been demonstrated that Müller glial cells are implicated in the development of glaucoma through an ambivalent reactive retinal gliosis process. The early steps contribute to maintaining retinal homeostasis and favor the survival of ganglion cells, which are targeted during glaucoma. If gliosis persists, dysregulation of the neuroprotective functions, cytotoxic effects of gliotic Müller cells and disruption of glia-neuron interactions lead to an acceleration of ganglion cell death. Sterols could play a role in the glial cell response to glaucomatous injury. This represents an understudied but attractive topic to better understand glaucoma and conceive novel preventive or curative strategies. The present review describes the current knowledge on i) sterol metabolism in retinal glial cells, ii) the potential role of cholesterol in glaucoma, and iii) the possible relationships between cholesterol and oxysterols, glial cells and glaucoma. Focus is put on glia-neuron interactions.

Long-Term Quantitative Analysis of Inner Retinal Dimples and Visual Function Post Internal Limiting Membrane Peeling in Macular Diseases

INTRODUCTION

Inner retinal dimples (IRDs) are frequently detected after internal limiting membrane (ILM) peeling. However, the distribution of IRDs and its effect on postoperative visual function remain unclear. We aim to quantify the distribution of IRDs after ILM peeling in different macular diseases and analyze its influence on postoperative visual function.

METHODS

We retrospectively reviewed patients undergoing vitrectomy with ILM peeling and followed up until 12 months in our center. The distribution of IRDs were quantitatively determined using optical coherence tomography (OCT) and OCT angiography in a different sector of Early Treatment Diabetic Retinopathy Study grid. Visual function was evaluated by retinal sensitivity (RS) using microperimetry. Spearman correlation was performed between RS and IRDs within the same sectors. Multivariate linear regression analysis was performed to analyze the association between baseline characteristics and IRDs.

RESULTS

A total of 43 idiopathic macular hole (iMH) cases, 56 idiopathic epiretinal membrane (iERM) cases and 42 myopic foveoschisis (mFS) cases were included. IRDs increased gradually at ILM-peeled area, interrupting ganglion cell layer. Most IRDs were observed in temporal sector. A negative correlation was depicted between the increase of IRDs and the progress of RS at both perifovea and parafovea in iERM, but only at perifovea in iMH. No significant correlation between the change of IRDs and RS was found in mFS. Multivariable linear regression model showed that preoperative axial length was significantly associated with postoperative IRDs in all patients.

CONCLUSIONS

IRDs distributed mostly at temporal sector after ILM peeling, interrupting ganglion cell layer. IRD progression may influence postoperative RS only in iMH and iERM. Ophthalmologists may avoid temporal sector especially in eyes with normal axial length or strong ILM-ERM adherence.

Training in cortically-blind fields confers patient-specific benefit against retinal thinning after occipital stroke

Purpose

Damage to the adult primary visual cortex (V1) causes vision loss in the contralateral hemifield, initiating a process of trans-synaptic retrograde degeneration (TRD). Here, we examined retinal correlates of TRD using a new metric to account for global changes in inner retinal thickness, and asked if perceptual training in the intact or blind field impacts its progression.

Methods

We performed a meta-analysis of optical coherence tomography (OCT) data in 48 participants with unilateral V1 stroke and homonymous visual defects, who completed clinical trial NCT03350919. After measuring the thickness of the macular ganglion cell and inner plexiform layers (GCL-IPL), and the peripapillary retinal nerve fiber layer (RNFL), we computed individual laterality indices (LI) at baseline and after ~6 months of daily motion discrimination training in the intact- or blind-field. Increasingly positive LI denoted greater layer thinning in retinal regions affected versus unaffected by the cortical damage.

Results

Pre-training, the affected GCL-IPL and RNFL were thinner than their unaffected counterparts, generating LI values positively correlated with time since stroke. Participants trained in their intact-field exhibited increased LIGCL-IPL. Those trained in their blind-field had no significant change in LIGCL-IPL. LIRNFL did not change in either group.

Conclusions

Relative shrinkage of the affected versus unaffected macular GCL-IPL can be reliably measured at an individual level and increases with time post-V1 stroke. Relative thinning progressed during intact-field training, but appeared to be halted by training within the blind field, suggesting a potentially neuroprotective effect of this simple behavioral intervention.

Synergic effects of EP2 and FP receptors co-activation on Blood-Retinal Barrier and Microglia

Macular edema (ME) is caused with disruption of the blood-retinal barrier (BRB) followed by fluid accumulation in the subretinal space. Main components of the outer and inner BRB are retinal pigment epithelial (RPE) cells and retinal microvascular endothelial cells, respectively. In addition, glial cells also participate in the functional regulation of the BRB as the member of 'neurovascular unit'. Under various stresses, cells in neurovascular units secrete inflammatory cytokines. Neuroinflammation induced by these cytokines can cause BRB dysfunction by degrading barrier-related proteins and contribute to the pathophysiology of ME. Prostaglandins (PGs) are crucial lipid mediators involved in neuroinflammation. Among PGs, a novel EP2 agonist, omidenepag (OMD) acts on not only the uveoscleral pathway but also the conventional pathway, unlike F prostanoid (FP) receptor agonists. Moreover, the combination use of the EP and the FP agonist is not recommended because of the risk of inflammation. In this study, we investigated effects of OMD and latanoprost acid (LTA), a FP agonist, on BRB and microglia in vitro and in vivo. To investigate the function of outer/inner BRB and microglia, in vitro, ARPE-19 cells, human retinal microvascular endothelial cells (HRMECs), and MG5 cells were used. Cell viability, inflammatory cytokines mRNA and protein levels, barrier morphology/function, and microglial activation were evaluated using proliferation assays, qRT-PCR, ELISA, immunocytochemistry, trans-epithelial electrical resistance, and permeability assay. Moreover, after vitreous injection into the mouse, outer BRB morphology, glial activation, and cytokine expression were assessed. Each OMD and LTA alone did not affect the viability or cytokines expression of the three types of cells. In ARPE-19 cells, the co-stimulation of OMD and LTA increased the mRNA and protein levels of inflammatory cytokines (IL-6, TNF-α, and VEGF-A) and decreased the barrier function and the junction-related protein (ZO-1 and β-catenin). By contrast in HRMECs, the co-stimulation affected significant differences in the mRNA levels of some cytokine (IL-6 and TNF-α) but enhanced the barrier function. In MG5 cells, the cytokines mRNA and size of Iba1-expressed cell were increased. A non-steroidal anti-inflammatory inhibited the barrier dysfunction and the junction-related protein downregulation in ARPE-19 cells and activation of MG5 cells. Also in vivo, the co-stimulation induced outer BRB disruption, cytokine increase, and retinal glial activation. Therefore, the co-stimulation of EP2 and FP induced the inflammatory cytokine-mediated outer BRB disruption, the enhanced inner BRB function, and the microglial activation. The BRB imbalance and the intrinsic prostaglandin production may be involved in OMD-related inflammation.

Signalling pathways and cell death mechanisms in glaucoma: Insights into the molecular pathophysiology

Glaucoma is a complex multifactorial eye disease manifesting in retinal ganglion cell (RGC) death and optic nerve degeneration, ultimately causing irreversible vision loss. Research in recent years has significantly enhanced our understanding of RGC degenerative mechanisms in glaucoma. It is evident that high intraocular pressure (IOP) is not the only contributing factor to glaucoma pathogenesis. The equilibrium of pro-survival and pro-death signalling pathways in the retina strongly influences the function and survival of RGCs and optic nerve axons in glaucoma. Molecular evidence from human retinal tissue analysis and a range of experimental models of glaucoma have significantly contributed to unravelling these mechanisms. Accumulating evidence reveals a wide range of molecular signalling pathways that can operate -either alone or via intricate networks - to induce neurodegeneration. The roles of several molecules, including neurotrophins, interplay of intracellular kinases and phosphates, caveolae and adapter proteins, serine proteases and their inhibitors, nuclear receptors, amyloid beta and tau, and how their dysfunction affects retinal neurons are discussed in this review. We further underscore how anatomical alterations in various animal models exhibiting RGC degeneration and susceptibility to glaucoma-related neuronal damage have helped to characterise molecular mechanisms in glaucoma. In addition, we also present different regulated cell death pathways that play a critical role in RGC degeneration in glaucoma.

Glial metabolic alterations during glaucoma pathogenesis

Glaucoma is the leading cause of irreversible blindness. Current treatment options are limited and often only slow disease progression. Metabolic dysfunction has recently been recognized as a key early and persistent mechanism in glaucoma pathophysiology. Several intrinsic metabolic dysfunctions have been identified and treated in retinal ganglion cells to provide neuroprotection. Growing pre-clinical and clinical evidence has confirmed that metabolic alterations in glaucoma are widespread, occurring across visual system tissues, in ocular fluids, in blood/serum, and at the level of genomic and mitochondrial DNA. This suggests that metabolic dysfunction is not constrained to retinal ganglion cells and that metabolic alterations extrinsic to retinal ganglion cells may contribute to their metabolic compromise. Retinal ganglion cells are reliant on glial metabolic support under normal physiological conditions, but the implications of metabolic dysfunction in glia are underexplored. We highlight emerging evidence that has demonstrated metabolic alterations occurring within glia in glaucoma, and how this may affect neuro-glial metabolic coupling and the metabolic vulnerability of retinal ganglion cells. In other neurodegenerative diseases which share features with glaucoma, several other glial metabolic alterations have been identified, suggesting that similar mechanisms and therapeutic targets may exist in glaucoma.

Schwann cell-derived extracellular vesicles as a potential therapy for retinal ganglion cell degeneration

Optic neuropathy is the leading cause of irreversible blindness and is characterized by progressive degeneration of retinal ganglion cells (RGCs). Several studies have demonstrated that transplantation of Schwann cells (SCs) is a promising candidate therapy for optic neuropathy and that intravitreally transplanted cells exert their effect via paracrine actions. Extracellular vesicle (EV)-based therapies are increasingly recognized as a potential strategy for cell replacement therapy. In this study, we aimed to investigate the neuroprotective and regenerative effects of SC-EVs following optic nerve injury. We found that SC-EVs were internalized by RGCs in vitro and in vivo without any transfection reagents. Intriguingly, SC-EVs significantly enhanced the survival and axonal growth of primary RGCs in a coculture system. In a rat optic nerve crush model, SC-EVs mitigated RGC degeneration, prevented RGC loss, and preserved the thickness of the ganglion cell complex, as demonstrated by the statistically significant improvement in RGC counts and thickness measurements. Mechanistically, SC-EVs activated the cAMP-response element binding protein (CREB) signaling pathway and regulated reactive gliosis in ONC rats, which is crucial for RGC protection and axonal regeneration. These findings provide novel insights into the neuroprotective and regenerative properties of SC-EVs, suggesting their potential as a cell-free therapeutic strategy and natural biomaterials for neurodegenerative diseases of the central nervous system.

Biphasic change in retinal nerve fibre layer thickness from 30 to 60 weeks postmenstrual age in preterm infants

BACKGROUND/AIMS

The optic nerve development during the critical postnatal weeks of preterm infants is unclear. We aimed to investigate the change of retinal nerve fibre layer (RNFL) in preterm infants.

METHODS

We used an investigational handheld optical coherence tomography (OCT) system to serially image awake preterm infants between 30 and 60 weeks postmenstrual age (PMA) at the bedside. We assessed RNFL thickness in the papillomacular bundle and nasal macular ganglion cell layer+inner plexiform layer (GCL+IPL) thickness. We applied a segmented mixed model to analyse the change in the thickness of RNFL and GCL+IPL as a function of PMA.

RESULTS

From 631 OCT imaging sessions of 101 infants (201 eyes), RNFL thickness followed a biphasic model between 30 and 60 weeks, with an estimated transition at 37.8 weeks PMA (95% CI: 37.0 to 38.6). RNFL thickness increased at 1.8 μm/week (95% CI: 1.6 to 2.1) before 37.8 weeks and decreased at -0.3 μm/week (95% CI: -0.5 to -0.2) afterwards. GCL+IPL thickness followed a similar biphasic model, in which the thickness increased at 2.9 μm/week (95% CI: 2.5 to 3.2) before 39.5 weeks PMA (95% CI: 38.8 to 40.1) and then decreased at -0.8 μm/week (95% CI: -0.9 to -0.6).

CONCLUSION

We demonstrate the feasibility of monitoring RNFL and GCL+IPL thickness from OCT during the postnatal weeks of preterm infants. Thicknesses follow a biphasic model with a transition age at 37.8 and 39.5 weeks PMA, respectively. These findings may shed light on optic nerve development in preterm infants and assist future study designs.

Salvianolic acid B ameliorates retinal deficits in an early-stage Alzheimer's disease mouse model through downregulating BACE1 and Aβ generation

Alzheimer's disease (AD) is a neurodegenerative disease with subtle onset, early diagnosis remains challenging. Accumulating evidence suggests that the emergence of retinal damage in AD precedes cognitive impairment, and may serve as a critical indicator for early diagnosis and disease progression. Salvianolic acid B (Sal B), a bioactive compound isolated from the traditional Chinese medicinal herb Salvia miltiorrhiza, has been shown promise in treating neurodegenerative diseases, such as AD and Parkinson's disease. In this study we investigated the therapeutic effects of Sal B on retinopathy in early-stage AD. One-month-old transgenic mice carrying five familial AD mutations (5×FAD) were treated with Sal B (20 mg·kg-1·d-1, i.g.) for 3 months. At the end of treatment, retinal function and structure were assessed, cognitive function was evaluated in Morris water maze test. We showed that 4-month-old 5×FAD mice displayed distinct structural and functional deficits in the retinas, which were significantly ameliorated by Sal B treatment. In contrast, untreated, 4-month-old 5×FAD mice did not exhibit cognitive impairment compared to wild-type mice. In SH-SY5Y-APP751 cells, we demonstrated that Sal B (10 μM) significantly decreased BACE1 expression and sorting into the Golgi apparatus, thereby reducing Aβ generation by inhibiting the β-cleavage of APP. Moreover, we found that Sal B effectively attenuated microglial activation and the associated inflammatory cytokine release induced by Aβ plaque deposition in the retinas of 5×FAD mice. Taken together, our results demonstrate that functional impairments in the retina occur before cognitive decline, suggesting that the retina is a valuable reference for early diagnosis of AD. Sal B ameliorates retinal deficits by regulating APP processing and Aβ generation in early AD, which is a potential therapeutic intervention for early AD treatment.

Hyperglycemia-regulated tRNA-derived fragment tRF-3001a propels neurovascular dysfunction in diabetic mice

Neurovascular dysfunction is a preclinical manifestation of diabetic complications, including diabetic retinopathy (DR). Herein, we report that a transfer RNA-derived RNA fragment, tRF-3001a, is significantly upregulated under diabetic conditions. tRF-3001a downregulation inhibits Müller cell activation, suppresses endothelial angiogenic effects, and protects against high-glucose-induced retinal ganglion cell injury in vitro. Furthermore, tRF-3001a downregulation alleviates retinal vascular dysfunction, inhibits retinal reactive gliosis, facilitates retinal ganglion cell survival, and preserves visual function and visually guided behaviors in STZ-induced diabetic mice and db/db diabetic mice. Mechanistically, tRF-3001a regulates neurovascular dysfunction in a microRNA-like mechanism by targeting GSK3B. Clinically, tRF-3001a is upregulated in aqueous humor (AH) samples of DR patients. tRF-3001a downregulation inhibits DR-induced human retinal vascular endothelial cell and Müller cell dysfunction in vitro and DR-induced retinal neurovascular dysfunction in C57BL/6J mice. Thus, targeting tRF-3001a-mediated signaling is a promising strategy for the concurrent treatment of vasculopathy and neuropathy in diabetes mellitus.

Latent Epigenetic Programs in Müller Glia Contribute to Stress, Injury, and Disease Response in the Retina

Previous studies have demonstrated the dynamic changes in chromatin structure during retinal development that correlate with changes in gene expression. However, a major limitation of those prior studies was the lack of cellular resolution. Here, we integrate single-cell (sc) RNA-seq and scATAC-seq with bulk retinal data sets to identify cell type-specific changes in the chromatin structure during development. Although most genes' promoter activity is strongly correlated with chromatin accessibility, we discovered several hundred genes that were transcriptionally silent but had accessible chromatin at their promoters. Most of those silent/accessible gene promoters were in the Müller glial cells. The Müller cells are radial glia of the retina and perform a variety of essential functions to maintain retinal homeostasis and respond to stress, injury, or disease. The silent/accessible genes in Müller glia are enriched in pathways related to inflammation, angiogenesis, and other types of cell-cell signaling and were rapidly activated when we tested 15 different physiologically relevant conditions to mimic retinal stress, injury, or disease in human and murine retinae. We refer to these as "pliancy genes" because they allow the Müller glia to rapidly change their gene expression and cellular state in response to different types of retinal insults. The Müller glial cell pliancy program is established during development, and we demonstrate that pliancy genes are necessary and sufficient for regulating inflammation in the murine retina in vivo. In zebrafish, Müller glia can de-differentiate and form retinal progenitor cells that replace lost neurons. The pro-inflammatory pliancy gene cascade is not activated in zebrafish Müller glia following injury, and we propose a model in which species-specific pliancy programs underly the differential response to retinal damage in species that can regenerate retinal neurons (zebrafish) versus those that cannot (humans and mice).

Assessment of Inner Blood-Retinal Barrier: Animal Models and Methods

Proper functioning of the neural retina relies on the unique retinal environment regulated by the blood-retinal barrier (BRB), which restricts the passage of solutes, fluids, and toxic substances. BRB impairment occurs in many retinal vascular diseases and the breakdown of BRB significantly contributes to disease pathology. Understanding the different molecular constituents and signaling pathways involved in BRB development and maintenance is therefore crucial in developing treatment modalities. This review summarizes the major molecular signaling pathways involved in inner BRB (iBRB) formation and maintenance, and representative animal models of eye diseases with retinal vascular leakage. Studies on Wnt/β-catenin signaling are highlighted, which is critical for retinal and brain vascular angiogenesis and barriergenesis. Moreover, multiple in vivo and in vitro methods for the detection and analysis of vascular leakage are described, along with their advantages and limitations. These pre-clinical animal models and methods for assessing iBRB provide valuable experimental tools in delineating the molecular mechanisms of retinal vascular diseases and evaluating therapeutic drugs.

Targeting circular RNA-Glra2 alleviates retinal neurodegeneration induced by ocular hypertension

Glaucoma is a leading cause of irreversible vision loss characterized by retinal neurodegeneration. Circular RNAs (circRNAs) have emerged as the potential biomarkers and therapeutic targets for neurodegenerative diseases. However, the expression profiling of circRNAs in glaucomatous neurodegeneration has not been fully understood. In this study, we built a glaucomatous neurodegeneration model via the injection of microbeads into anterior chamber. circRNA expression profile and bioinformatics analysis revealed that compared with normal retinas, 171 circRNAs were dysregulated in the glaucomatous retinas, including 101 up-regulated circRNAs and 70 down-regulated circRNAs. Detecting the level of circular RNA-glycine receptor α2 subunit gene (cGlra2) in aqueous humor made it possible to distinguish glaucoma patients from cataract patients. Silencing of cGlra2 protected against oxidative stress- or hydrostatic pressure-induced retinal ganglion cell (RGC) injury in vitro. Moreover, silencing of cGlra2 retarded ocular hypertension-induced retinal neurodegeneration in vivo as shown by increased TUJ1 staining, reduced reactive gliosis, decreased retinal cell apoptosis, enhanced visual acuity, and improved retinal function. cGlra2 acted as a miRNA sponge to regulate RGC function through cGlra2/miR-144/BCL2L11 signaling axis. Collectively, this study provides novel insights into the underlying mechanism of retinal neurodegeneration and highlights the potential of cGlra2 as a target for the diagnosis and treatment of glaucoma.

Fluctuation of Intraocular Pressure and Vascular Factors Are Associated With the Development of Epiretinal Membrane in Glaucoma

PURPOSE

To identify factors associated with the development of epiretinal membranes (ERM) in glaucoma patients.

DESIGN

Multicenter, propensity-score matched, case-control study.

METHODS

One hundred ninety-two eyes of 192 patients with glaucoma from the Catholic Medical Center Glaucoma Suspect Cohort Study were analyzed. We identified 64 eyes who developed ERM from the cohort, and 128 eyes without ERM were selected by propensity score matching (1:2) according to baseline age and mean deviation (MD) of the visual field (VF). Demographic, systemic, and ocular characteristics were determined at baseline. Intraocular pressure (IOP) was measured, including baseline, mean IOP, and IOP fluctuation. Early-stage ERM, defined as translucent membrane with no underlying retinal distortion, was detected by fundus photography and optical coherence tomography. Central VF progression was considered when new VF defets developed in one either or both hemifields or when there was an increase of 3 or more abnormal points within 12 points of central 10° fixation. Autonomic nervous system status was evaluated by heart rate variability.

RESULTS

Patients who developed ERM were more frequently receiving medication for systemic hypertension and had higher systolic blood pressure, greater IOP fluctuation, more frequent disc hemorrhage (DH), worse VF MD, and a higher rate of central VF progression than patients without ERM. Additionally, patients with early glaucoma who developed ERM had higher rate of autonomic imbalance while patients with moderate-to-advanced glaucoma who developed ERM had greater baseline and peak IOP and worse MD of the last follow-up VF (MD < 6.0 dB). Older age (P = .048), medication for systemic hypertension (P < .001), IOP fluctuation (P < .001), presence of DH (P < .001), and worse last MD of VF (P = .033) were significantly associated with ERM in Cox proportional hazard analysis.

CONCLUSIONS

Early stage of ERMs in glaucomatous eyes are significantly associated with glaucoma progression, medication of systemic hypertension, presence of DH, and IOP fluctuation. These suggest that glaucoma patients who develop early stage of ERMs should be carefully monitored in terms of IOP fluctuation, vascular factors, and glaucoma progression.

Neuroinflammation and gliosis in the injured and contralateral retinas after unilateral optic nerve crush

The main purpose of this study is to analyze the effects of unilateral optic nerve crush in the gene expression of pro- and anti-inflammatory mediators, and gliosis markers in injured and contralateral retinas. Retinas from intact, unilaterally optic nerve injured or sham-operated C57BL/6J mice were analyzed 1, 3, 9 and 30 days after the surgery (n = 5/group and time point) and the relative expression of TGF-β1, IL-1β, TNF-α, Iba1, AQP4, GFAP, MHCII, and TSPO was analyzed in injured and contralateral using qPCR. The results indicated that compared with intact retinas, sham-operated animals showed an early (day 1) upregulation of IL-1β, TNF-α and TSPO and a late (day 30) upregulation of TNF-α. In sham-contralateral retinas, TNF-α and TSPO mRNA expression were upregulated and day 30 while GFAP, Iba1, AQP4 and MHCII downregulated at day 9. Compared with sham-operated animals, in retinas affected by optic nerve crush GFAP and TSPO upregulated at day 1 and TNF-α, Iba1, AQP4 and MHCII at day 3. In the crushed-contralateral retinas, TGF-β1, TNF-α, Iba1 and MHCII were upregulated at day 1. TSPO was upregulated up to day 30 whereas TGF-β1 and Iba1 downregulated after day 9. In conclusion, both sham surgery and optic nerve crush changed the profile of inflammatory and gliosis markers in the injured and contralateral retinas, changes that were more pronounced for optic nerve crush when compared to sham.

Rapid isolation of intact retinal astrocytes: a novel approach

Astrocytes are a major category of glial support cell in the central nervous system and play a variety of essential roles in both health and disease. As our understanding of the diverse functions of these cells improves, the extent of heterogeneity between astrocyte populations has emerged as a key area of research. Retinal astrocytes, which form the direct cellular environment of retinal ganglion cells somas and axons, undergo a reactive response in both human glaucoma and animal models of the disease, yet their contributions to its pathology and progression remain relatively unknown. This gap in knowledge is largely a function of inadequate isolation techniques, driven in part by the sparseness of these cells and their similarities with the more abundant retinal Müller cells. Here, we present a novel method of isolating retinal astrocytes and enriching their RNA, tested in both normal and ocular hypertensive mice, a common model of experimental glaucoma. Our approach combines a novel enzyme assisted microdissection of retinal astrocytes with selective ribosome immunoprecipitation using the Ribotag method. Our microdissection method is rapid and preserves astrocyte morphology, resulting in a brief post-mortem interval and minimizing loss of RNA from distal regions of these cells. Both microdissection and Ribotag immunoprecipitation require a minimum of specialized equipment or reagents, and by using them in conjunction we are able to achieve > 100-fold enrichment of astrocyte RNA.

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.