Retinal microglia: just bystander or target for therapy?

Machine learning-assisted design of immunomodulatory lipid nanoparticles for delivery of mRNA to repolarize hyperactivated microglia

Regulating inflammatory microglia presents a promising strategy for treating neurodegenerative and autoimmune disorders, yet effective therapeutic agents delivery to these cells remains a challenge. This study investigates modified lipid nanoparticles (LNP) for mRNA delivery to hyperactivated microglia, particularly those with pro-inflammatory characteristics, utilizing supervised machine learning (ML) classifiers. We developed and screened a library of 216 LNP formulations with varying lipid compositions, N/P ratios, and hyaluronic acid (HA) modifications. The transfection efficiency of eGFP mRNA was assessed in the BV-2 murine microglia cell line under different immunological states, including resting and activated conditions (LPS-activated and IL4/IL13-activated). ML-guided morphometric analysis tracked the phenotypes of various microglia subtypes before and after transfection. Four supervised ML classifiers were investigated to predict transfection efficiency and phenotypic changes based on LNP design parameters. The Multi-Layer Perceptron (MLP) neural network emerged as the best-performing model, achieving weighted F1-scores ≥0.8. While it accurately predicted responses from LPS-activated and resting cells, it struggled with IL4/IL13-activated cells. The MLP model was validated by predicting the performance of four unseen LNP formulations delivering eGFP mRNA to LPS-activated BV2 cells. HA-LNP2 emerged as optimal formulation for delivering target IL10 mRNA, effectively suppressing inflammatory phenotypes, evidenced by shifts in cell morphology, increased IL10 expression, and reduced TNF-α levels. We also evaluated HA-LNP2 on LPS-activated human iPSC-derived microglia, confirming its efficacy in modulating inflammatory responses. This study highlights the potential of tailored LNP design and ML techniques to enhance mRNA therapy for neuroinflammatory disorders by leveraging carrier's immunogenic properties to modulate microglial responses.

Nitric oxide mediates negative feedback on the TXNIP/NLRP3 inflammasome pathway to prevent retinal neurovascular unit dysfunction in early diabetic retinopathy

Diabetic retinopathy (DR) is a leading cause of vision impairment in working-age adults, and is driven by complex neurovascular dysfunction. This study aimed to elucidate whether nitric oxide (NO) can modulate the TXNIP/NLRP3 inflammasome pathway and mitigate retinal neurovascular unit (NVU) damage during early DR. In an in vitro co-culture system, silencing TXNIP or NLRP3 in retinal microglia (RMG) significantly upregulated glial cell-derived neurotrophic factor (GDNF) and downregulated inducible nitric oxide synthase (iNOS) expression in retinal ganglion cells (RGC). Moreover, it resulted in decreased iNOS and vascular endothelial growth factor A (VEGFA) levels and enhanced the expression of tight junction proteins (Occludin and ZO-1) in retinal microvascular endothelial cells (RMEC), while also reducing NO release and inhibiting RMEC tube formation. Treatment with S-nitroso-N-acetyl penicillamine (SNAP), an NO donor, significantly downregulated TXNIP/NLRP3 inflammasome signaling in RMG, decreased RGC apoptosis, and inhibited tube formation in RMEC. It also upregulated GDNF, suppressed iNOS in RGC, decreased VEGFA, and improved tight junction proteins in RMEC. Treatment with 1400W, an iNOS inhibitor, resulted in decreased NO concentration and increased IL-1β levels in the co-culture supernatant, without significantly affecting iNOS expression in RGC or RMEC. In an early DR rat model, Electroretinogram (ERG), Optical Coherence Tomography (OCT), Fluorescein Angiography (FFA), Evans blue assays, Immunofluorescence staining, and TUNEL staining confirmed that sodium nitroprusside (SNP), NO donor administration mitigated retinal neural and vascular dysfunction, and preserved retinal NVU integrity. Concurrently, SNP treatment reduced IL-1β expression and increased GDNF and Occludin levels in the early DR retina. Genetic Association Database (GAD) enrichment analysis and protein-protein interaction (PPI) network validation indicated that NO functions as a downstream mediator of the TXNIP/NLRP3 inflammasome pathway and exhibits a strong association with DR. These findings suggest that NO mediates negative feedback in the TXNIP/NLRP3 inflammasome pathway to exert protective effects against retinal NVU dysfunction in early DR, thereby offering potential therapeutic strategies for early intervention in DR.

Moss-derived human complement factor H modulates retinal immune response and attenuates retinal degeneration

BACKGROUND

AMD is a multifactorial progressive disease of the central retina that leads to severe vision loss among the elderly. Genome-wide association studies in AMD patients and preclinical data have identified a dysregulated complement system and aberrant microglia responses in the pathogenesis of AMD. Specifically, a genetic variant in the complement factor H (CFH) gene, an important inhibitor of the alternative complement pathway, confers the strongest risk for AMD. Here, we investigated whether moss-derived recombinant human CFH proteins, termed CPV-101 and CPV-104, can modulate microglia reactivity and limit retinal degeneration in a murine light damage paradigm mimicking important features of AMD.

METHODS

Two glycosylated human recombinant CFH proteins CPV101, and CPV-104 were produced in moss suspension cultures. In addition, glycans of the CPV-104 variant are sialylated, an optimization that makes CPV-104 an analog of human CFH. BALB/cJ mice received intravitreal injections of 5 µg CPV-101 and CPV-104 or vehicle, starting 1 day prior to exposure to 10,000 lx white light for 30 min. The effects of CPV-101 and CPV-104 treatment on mononuclear phagocyte and Müller cell reactivity were analyzed by immunostainings of retinal sections and flat mounts. Gene expression of microglia markers was analyzed using quantitative real-time PCR (qRT-PCR). Optical coherence tomography (OCT); Blue Peak Autofluorescence (BAF); terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining, and morphometric analyses were used to quantify the extent of retinal degeneration and photoreceptor apoptosis.

RESULTS

Light-exposed mice treated with moss-derived recombinant human full-length CFH showed reduced complement activation and MAC deposition in the retina. Concomitantly, mononuclear phagocyte and Müller cell reactivity in light-exposed retinas were also ameliorated upon CFH substitution. Moreover, attenuated light-induced retinal degeneration was detected in mice that received moss-derived CFH.

CONCLUSION

Modulating the alternative complement pathway using moss-derived recombinant human full-length CFH variant CPV-101 and CPV-104 counter-regulate gliosis and attenuates light-induced retinal degeneration, highlighting a promising concept for the treatment of AMD patients.

Effect of ophthalmic preparation of methyldopa on induced ocular hypertension in rabbits

Glaucoma is a type of ocular disorder with multifaceted etiologies characterized by progressive optic nerve damage and ultimately loss of visual field. This study aimed to evaluate the possible intraocular pressure (IOP) lowering effect of an ophthalmic preparation of methyldopa (MD) in corticosteroid-induced ocular hypertension in rabbits. Forty New Zealand white male rabbits were assigned to the experiment and then randomly divided into five groups (n = 8). Ocular hypertension was induced by weekly subconjunctival injection of betamethasone suspension in both eyes. Animal groups included the control (healthy) group, which received the ophthalmic vehicle only; the standard (timolol) group, which received 0.5% timolol eye drops (ED); and the MD groups, which received 0.5%, 1%, and 2% of methyldopa ophthalmic preparation. Treatments were applied to the right eye twice daily for 7 days, whereas the left eye served as a control and was given only distilled water. IOP was recorded and ocular reflexes were observed. Weekly subconjunctival injections of betamethasone resulted in a significant elevation in the IOP (P ≤ 0.001) that was reduced after treatments with timolol 0.5% and MD at different concentrations. Timolol showed the highest reduction (P ≤ 0.001) in the mean IOP with a 30% reduction. MD showed a concentration-dependent reduction with the highest reduction (P ≤ 0.01) observed at 2% compared to the induced/distilled water (DW) eyes and no significant difference compared to the timolol 0.5% (P ≥ 0.05) with a 24.2% reduction in the mean IOP. Methyldopa managed to reduce the IOP in the chronic model of glaucoma, making MD a promising addition to the anti-glaucoma medications.

Inherited retinal disease-associated uveitis

Inherited retinal diseases (IRDs) are genetic disorders characterized by progressive photoreceptor function loss, often leading to significant visual impairment. Uveitis has been increasingly recognized in the clinical course of some IRDs. Despite advances in understanding the genetic causes and pathophysiology of IRDs, gaps remain in understanding the roles of inflammation and autoimmunity in IRD and IRD-associated uveitis. This review discusses IRD-associated uveitis, including anterior, intermediate, posterior, and panuveitis, as well as complications such as cystoid macular edema and retinal vasculitis. In patients with IRD-associated uveitis, mutations affecting protein function in cilia or photoreceptor outer segments suggest a universal autoimmune mechanism triggered by the immunogenicity of shedding photoreceptor discs. Notably, in patients where uveitis is the initial sign, CRB1 mutations are often implicated, likely due to the compromised blood-retina barrier function or alterations in the external limiting membrane. Other mechanisms leading to uveitis preceding IRD diagnosis include ALPK1 mutations, which activate the proinflammatory NF-κB pathway, CAPN5 mutations, which lead to dysfunction of the innate and adaptive immune systems, and VCAN1 mutations, which elicit immunogenicity due to irregularities in vitreous modeling. Understanding these mechanisms could enhance the development of innovative treatments that target personalized inflammation pathways in IRDs.

Suppression of astrocyte elevated gene-1 protects against light-induced photoreceptor apoptosis and inflammation in retina

PURPOSE

To research the function of astrocyte elevated gene-1 (AEG-1) in light-induced retinal degeneration.

METHODS

The retinas of BALB/c mice and 661W cells damage were induced by exposure to light; Lipopolysaccharide (LPS) was used to stimulate BV2 cells. AEG-1 siRNA transfection was used to inhibit AEG-1. Expressions of AEG-1, TLR4, TNF-α, phosphor-NF-κB (p-NF-κB) and total NF-κB (t-NF-κB) were detected. Photoreceptor apoptosis was evaluated by flow cytometry or TUNEL. Histological analyses were performed by hematoxylin and eosin (HE) staining.

RESULTS

AEG-1 was highly expressed in light damaged (LD) retinas. The photoreceptor apoptosis and the thinning of outer nuclear layer (ONL) were inhibited by AEG-1 siRNA in LD mice retinas. The AEG-1 siRNA pretreatment significantly down-regulated the elevated expression levels of TLR4, p-NF-κB and TNF-α induced by LD in retinas. In vitro, AEG-1 was upregulated in 661W cells induced by LD and in BV2 cells stimulated by LPS. The AEG-1 siRNA prevented light induced apoptosis of 661W cells, and down-regulated the elevated expressions of TLR4, p-NF-κB and pro-inflammatory cytokine TNF-α caused by LPS in BV2 cells.

CONCLUSIONS

AEG-1 is highly expressed in retinal degeneration caused by LD. Suppression of AEG-1 protects against photoreceptor apoptosis and rescues the thinning of ONL in LD retinas. Suppression of AEG-1 also diminishes inflammation in light induced retinal degeneration, which may be regulated through the NF-κB pathway. Therefore, AEG-1 perhaps become a potential therapeutic target for this type of retinal degenerative disease.

Inhibiting HMGB1/AGER/NF-κB pathway prevents pro-inflammatory microglia polarization and protect photoreceptors in retinitis pigmentosa

PURPOSE

Retinitis pigmentosa (RP) is an inherited retinal neurodegenerative disease which is a significant contributor to blindness. Microglia-mediated inflammation plays a crucial role in retinitis pigmentosa. However, the activation mechanisms of microglia and the role of polarized microglia in RP remain unclear. High-mobility group box 1 (HMGB1) is a key contributor to aseptic inflammation, and glycyrrhizin exerts anti-inflammatory effects by targeting HMGB1. This study aimed to investigate the role of HMGB1 and microglia in RP and explore the protective effects of glycyrrhizin on photoreceptors.

METHODS

Male C57BL/6 mice and age-matched rd1 mice were used for in vivo models, while zaprinast-treated 661w cells and HMGB1-treated BV-2 cells were used for in vitro models. In this study, the expression of HMGB1 was analyzed using QPCR and western blot (WB). Immunofluorescence staining and ELISA were performed to assess HMGB1 translocation and secretion. Glycyrrhizin was used to inhibit HMGB1, while FPS-ZM1 served as an inhibitor of the receptor for advanced glycation end products (AGER). Microglial polarization was evaluated by QPCR, and the HMGB1/ AGER/ NF-κB signaling pathway was analyzed through WB. Photoreceptor degeneration and visual function were assessed through H&E staining, electroretinography, and TUNEL staining.

RESULTS

We observed elevated levels of HMGB1 in the retina of rd1 mice and demonstrated in vitro that photoreceptors may serve as a significant source of HMGB1 in the retina. Additionally, HMGB1 was observed to cause microglial polarization via the HMGB1/AGER/ NF-κB pathway and the polarized microglia secrete inflammatory factors including TNF-α and IL-1β which accelerates the degeneration of photoreceptors. Glycyrrhizin reversed the degeneration of photoreceptors and loss of visual function in rd1 mice through the HMGB1/AGER/ NF-κB pathway.

CONCLUSION

Our findings showed that HMGB1 secreted by photoreceptors activated the microglia through the HMGB1/AGER/NF-κB pathway and the polarized microglia accelerates the degeneration of photoreceptors. Glycyrrhizin reversed the polarization caused by HMGB1 in vitro and delayed the progression of RP in vivo, presenting a potential novel approach for treating retinitis pigmentosa.

The adaptive immune system in the retina of diabetics

As the prevalence of diabetes mellitus increases each year, its most common microvascular complication, diabetic retinopathy (DR), is also on the rise. DR is now regarded as an inflammatory disease in which innate immunity plays a crucial role, and a large number of innate immune cells with associated cytokines are involved in the pathologic process of DR. The role of adaptive immunity in DR is seldom mentioned, probably due to the general perception of the immune privileged environment of the retina; however, in recent years there has been a gradual increase in research on the role of adaptive immunity in DR, and with the discovery of the retinal lymphatic system, it seems that the role of adaptive immunity can no longer be ignored. Here, we discuss the immunosuppressive environment of the retina, the phenomenon and potential mechanisms of lymphocyte infiltration in DR, and the role of the adaptive immune system in the diabetic retina, which may point the way for future research.

Integration and functionality of human iPSC-derived microglia in a chimeric mouse retinal model

INTRODUCTION

Microglia, the resident immune cells of the central nervous system, play a pivotal role in maintaining homeostasis, responding to injury, and modulating neuroinflammation. However, the limitations of rodent models in accurately representing human microglia have posed significant challenges in the study of retinal diseases.

METHODS

PLX5622 was used to eliminate endogenous microglia in mice through oral and intraperitoneal administration, followed by transplantation of human induced pluripotent stem cell-derived microglia (hiPSC-microglia, iMG) into retinal explants to create a novel ex vivo chimeric model containing xenotransplanted microglia (xMG). The number and proportion of xMG in the retina were quantified using retinal flat-mounting and immunostaining. To evaluate the proliferative capacity and synaptic pruning ability of xMG, the expression of Ki-67 and the phagocytosis of synaptic proteins SV2 and PSD95 was assessed. The chimeric model was stimulated with LPS, and single-cell RNA sequencing (scRNA-seq) was used to analyze transcriptomic changes in iMG and xMG. Mouse IL-34 antibody neutralization experiments were performed, and the behavior of xMG in retinal degenerative Pde6b-/- mice was examined.

RESULTS

We demonstrated that xenotransplanted microglia (xMG) successfully migrated to and localized within the mouse retina, adopting homeostatic morphologies. Our approach achieved over 86% integration of human microglia, which maintained key functions including proliferation, immune responsiveness, and synaptic pruning over a 14-day culture period. scRNA-seq of xMG revealed a shift in microglial signatures compared to monoculture iMG, indicating a transition to a more in vivo-like phenotype. In retinal degenerative Pde6b-/- mice, xMG exhibited activation and migrated toward degenerated photoreceptors.

CONCLUSION

This model provides a powerful platform for studying human microglia in the retinal context, offering significant insights for advancing research into retinal degenerative diseases and developing potential therapeutic strategies. Future applications of this model include using patient-derived iPSCs to investigate disease-specific microglial behaviors, thereby enhancing our understanding of microglia-related pathogenesis.

The Signature of Serum Modified Nucleosides in Uveitis

Purpose

This study aims to evaluate the metabolism of serum-modified nucleosides in uveitis by using liquid chromatography-tandem mass spectrometry (LC-MS) and to develop potential diagnostic biomarkers for uveitis.

Methods

Forty-two patients with different subtypes of uveitis (idiopathic uveitis, Vogt-Koyanagi-Harada [VKH] disease, and ankylosing spondylitis [AS]) and 32 healthy controls were recruited in this retrospective case-control study. The concentrations of 23 modified nucleosides in patient serum were quantified by LC-MS. The data was statistically analyzed with SPSS and GraphPad Prism.

Results

The data revealed that 13 out of 23 modified nucleosides (m6A, m1A, m6Am, Cm, ac4C, Gm, m1G, m2G, m2,2G, Um, m3U, m5U, and m5Um) effectively showed quantifiable chromatographic peaks. The statistical results indicated that there were extremely significant differences for m2G, Gm, Cm, and m1G between healthy controls and uveitis patients. The differences for Gm, m6A,and m5U were able to further assort idiopathic uveitis and uveitis with systemic inflammation including VKH and AS. Interestingly, each specific subtype of uveitis is characterized by its signature combination of serum-modified nucleotides comparing with healthy controls.

Conclusions

This study revealed that the metabolism of serum-modified nucleosides in uveitis patients display significant differences from healthy controls. The signature combination of serum modified nucleotides for each subtype of uveitis may be applied for the potential diagnosis of uveitis.

High-density lipoprotein alleviates ocular inflammation by downregulating M1 microglia and pyroptosis through regulating lipid accumulation and Caveolin-1 expression

Uveitis encompasses a group of intraocular inflammatory diseases that are often associated with low levels of high-density lipoprotein (HDL). The role of HDL in intraocular inflammatory diseases remains unclear. In our research, we established an endotoxin-induced uveitis (EIU) model to investigate the role of HDL. Our study indicated that HDL could suppress ocular inflammation and restore retinal function in EIU mice. Specifically, HDL intervention effectively inhibited microglial activation and promoted the transformation of microglia from the M1 phenotype to the M2 phenotype. Furthermore, HDL intervention reduced microglial pyroptosis. Additionally, HDL was found to inhibit lipid accumulation in LPS-induced microglia, which is associated with inflammation, M1 polarization, and pyroptosis, by enhancing the expression of Caveolin-1 (CAV-1). Finally, we demonstrated that the function of HDL may be partially dependent on CAV-1 expression. We conclude that HDL inhibits pathological ocular inflammation by regulating M1/M2 phenotype polarization and pyroptosis through the modulation of lipid accumulation and CAV-1 expression. This suggests that HDL may represent a novel therapeutic strategy for ocular inflammation.

C3aR1-Deletion Delays Retinal Degeneration in a White-Light Damage Mouse Model

Purpose

In the aging retina, persistent activation of microglia is known to play a key role in retinal degenerative diseases like age-related macular degeneration (AMD). Furthermore, dysregulation of the alternative complement pathway is generally accepted as the main driver for AMD disease progression and microglia are important producers of local complement and are equipped with complement receptors themselves. Here, we investigate the involvement of anaphylatoxin signaling, predominantly on Iba1+ cell activity, in light-induced retinal degeneration as a model for dry AMD, using anaphylatoxin receptor knockout (KO) mice.

Methods

Bright white light with an intensity of 10,000 lux was applied for 30 minutes to complement component 3a receptor 1 (C3ar1) or complement component 5a receptor 1 (C5ar1) KO and wildtype (WT) mice. Analyses of transcriptome changes and migration activity of Iba1+ cells as well as retinal thickness were performed 4 days after light exposure.

Results

Full body KO mice of either C3aR1 or C5aR1 were tested, but none led to mitigated migration of Iba1+ cells to the subretinal space or decreased expression of complement factors after light damage compared to WT mice. However, a partial rescue of retinal thickness was shown in C3aR1 KO mice, which was mirrored by significant less membrane attack complex (MAC) occurrence in the outer retina.

Conclusions

We conclude that deletion of the anaphylatoxin receptor C3aR1 cannot modulate mononuclear phagocytes but diminishes retinal degeneration through interference with the complement pathway and thus decreased MAC assembling. C3aR1-targeted therapy may be considered for patients with dry AMD.

Physiology and pathophysiology of the retinal neuroglia

Neuroglia of the retina are represented by Müller glia, parenchymal astrocytes, microglia and oligodendrocytes mainly associated with the optic nerve. Müller glia are the most numerous glia, endowed with multiple homeostatic functions and indispensable for the retinal morphofunctional organization. Müller cells integrate retinal neurons into individual functional units (known as retinal columns) and act as a living light guide, transmitting photons to photoreceptors. In pathology, retinal neuroglia undergo complex changes, which include upregulation of neuroprotection, reactive gliosis, and functional asthenia. The balance between all these changes defines the progression and outcome of retinal disorders.

Microglia in retinal diseases: From pathogenesis towards therapeutic strategies

Microglia, a widely dispersed cohort of immune cells in the retina, are intricately involved in a diverse range of pivotal biological processes, including inflammation, vascular development, complement activation, antigen presentation, and phagocytosis. Within the retinal milieu, microglia are crucial for the clearance of dead cells and cellular debris, release of anti-inflammatory agents, and orchestration of vascular network remodeling to maintain homeostasis. In addition, microglia are key mediators of neuroinflammation. Triggered by oxidative stress, elevated intraocular pressure, genetic anomalies, and immune dysregulation, microglia release numerous inflammatory cytokines, contributing to the pathogenesis of various retinal disorders. Recent studies on the ontogeny and broad functions of microglia in the retina have elucidated their characteristics during retinal development, homeostasis, and disease. Furthermore, therapeutic strategies that target microglia and their effector cytokines have been developed and shown positive results for some retinal diseases. Therefore, we systematically review the microglial ontogeny in the retina, elucidate their dual roles in retinal homeostasis and disease pathogenesis, and demonstrate microglia-based targeted therapeutic strategies for retinal diseases.

Decreased sialylation elicits complement-related microglia response and bipolar cell loss in the mouse retina

Sialylation plays an important role in self-recognition, as well as keeping the complement and innate immune systems in check. It is unclear whether the reduced sialylation seen during aging and in mice heterozygous for the null mutant of UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (Gne+/-), an essential enzyme for sialic acid biosynthesis, contributes to retinal inflammation and degeneration. We found a reduction of polysialic acid and trisialic acid expression in several retinal layers in Gne+/- mice at 9 months of age compared to Gne+/+ wildtype (WT) mice, which was associated with a higher microglial expression of the lysosomal marker CD68. Furthermore, the total number of rod bipolar cells was reduced in 12 months old Gne+/- mice in comparison to WT mice, demonstrating loss of these retinal interneurons. Transcriptome analysis showed up-regulation of complement, inflammation, and apoptosis-related pathways in the retinas of Gne+/- mice. Particularly, increased gene transcript levels of the complement factors C3 and C4 and the pro-inflammatory cytokine Il-1β were observed by semi-quantitative real-time polymerase chain reaction (sqRT-PCR) in 9 months old Gne+/- mice compared to WT mice. The increased expression of CD68, loss of rod bipolar cells, and increased gene transcription of complement factor C4, were all prevented after crossing Gne+/- mice with complement factor C3-deficient animals. In conclusion, our data show that retinal hyposialylation in 9 and 12 months old Gne+/- mice was associated with complement-related inflammation and lysosomal microglia response, as well as rod bipolar cells loss, which was absent after genetic deletion of complement factor C3.

Longitudinal Evaluation of the Distribution of Intraretinal Hyper-Reflective Foci in Eyes with Intermediate Age-Related Macular Degeneration

PURPOSE

Intraretinal hyper-reflective foci (IHRF) are optical coherence tomography (OCT) risk factors for progression of age-related macular degeneration (AMD). In this study we assess the change in the number and distribution of IHRF over two years.

METHODS

The axial distribution of IHRF were quantified in eyes with intermediate AMD (iAMD) at baseline and 24 months, using a series of 5 sequential equidistant en face OCT retinal slabs generated between the outer border of the internal limiting membrane (ILM) and the inner border of the retinal pigment epithelium (RPE). Following thresholding and binarization, IHRF were quantified in each retinal slab using ImageJ. The change in IHRF number in each slab between baseline and month 24 was calculated.

RESULTS

Fifty-two eyes showed evidence of IHRF at baseline, and all continued to show evidence of IHRF at 24 months (M24). The total average IHRF count/eye increased significantly from 4.67 ± 0.63 at baseline to 11.62 ± 13.86 at M24 (p < 0.001) with a mean increase of 6.94 ± 11.12 (range: - 9 to + 60). Overall, at M24, 76.9% eyes showed an increase in IHRF whereas 15.4% of eyes showed a decrease (3 eyes [5.7%] showed no change). There was a greater number of IHRF and a greater increase in IHRF over M24 in the outer slabs.

CONCLUSIONS

IHRF are most common in the outer retinal layers and tend to increase in number over time. The impact of the distribution and frequency of these IHRF on the overall progression of AMD requires further study.

Engineered bio-functional material-based nerve guide conduits for optic nerve regeneration: a view from the cellular perspective, challenges and the future outlook

Nerve injuries can be tantamount to severe impairment, standard treatment such as the use of autograft or surgery comes with complications and confers a shortened relief. The mechanism relevant to the regeneration of the optic nerve seems yet to be fully uncovered. The prevailing rate of vision loss as a result of direct or indirect insult on the optic nerve is alarming. Currently, the use of nerve guide conduits (NGC) to some extent has proven reliable especially in rodents and among the peripheral nervous system, a promising ground for regeneration and functional recovery, however in the optic nerve, this NGC function seems quite unfamous. The insufficient NGC application and the unabridged regeneration of the optic nerve could be a result of the limited information on cellular and molecular activities. This review seeks to tackle two major factors (i) the cellular and molecular activity involved in traumatic optic neuropathy and (ii) the NGC application for the optic nerve regeneration. The understanding of cellular and molecular concepts encompassed, ocular inflammation, extrinsic signaling and intrinsic signaling for axon growth, mobile zinc role, Ca2+ factor associated with the optic nerve, alternative therapies from nanotechnology based on the molecular information and finally the nanotechnological outlook encompassing applicable biomaterials and the use of NGC for regeneration. The challenges and future outlook regarding optic nerve regenerations are also discussed. Upon the many approaches used, the comprehensive role of the cellular and molecular mechanism may set grounds for the efficient application of the NGC for optic nerve regeneration.

Immune responses drive chorioretinitis and retinal pathology after neonatal CMV infection

Human cytomegalovirus (CMV) causes a common congenital infection leading to long-term neurological impairments including brain, cochlear, and ocular pathology. Infection of newborn mice with murine (M)CMV is an established model of neuropathology caused by congenital CMV infection, with recent work suggesting that brain pathology may be driven by immune responses. In the eye, however, CMV retinitis is thought to result from virus-driven necrosis in the absence of T cell responses. We found that MCMV infection of newborn mice recapitulates human eye disease after congenital CMV infection, including focal chorioretinitis, inflamed vasculature, and disrupted blood-retinal barriers. Moreover, infection drove extensive T cell infiltration of the retina and marked gliosis. Blocking immune responses generally, or via targeting the chemokine receptor CXCR3, did not exacerbate retinal disease but instead prevented pathology despite retinal MCMV infection. Thus, our data establish this model for studies of congenital retinal disease and show that the immune system drives pathology in the neonatal eye after MCMV infection.

Bridging the gap of vision restoration

Retinitis pigmentosa (RP) and Age-Related Macular Degeneration (AMD) are similar in that both result in photoreceptor degeneration leading to permanent progressive vision loss. This affords the possibility of implementing vision restoration techniques, where light signaling is restored to spared retinal circuitry to recreate vision. There are far more AMD patients (Wong et al., 2014), yet more resources have been put towards researching and developing vision restoration strategies for RP despite it rarity, because of the tractability of RP disease models. The hope is that these therapies will extend to the AMD population, however, many questions remain about how the implementation of prosthetic or optogenetic vision restoration technologies will translate between RP and AMD patients. In this review, we discuss the difference and similarities of RP and AMD with a focus on aspects expected to impact vision restoration strategies, and we identify key gaps in knowledge needed to further improve vision restoration technologies for a broad patient population.

A Novelly-Spatiotemporal Characterization of the Disease Course in the MNU-Induced Retinitis Pigmentosa Model

OBJECTIVE

With the aids of ophthalmic imaging techniques for animals, the spatiotemporal characterization of MNU-induced retinitis pigmentosa (RP) rats were performed.

METHODS

Sprague-Dawley (SD) rats were randomly divided into normal group (N), MNU-low-dose group (L) and MNU-high-dose group (H). Rats in the L and H group were given intraperitoneally injection with 40 and 60 mg/kg of MNU, a kind of alkylating agent, respectively. The body weight, electroretinogram (ERG) and retinal structure were observed on day one (D1), D3, and D7 after MNU administration. FFA, OCT, TUNEL staining, and immunostaining of Iba1 were also performed.

RESULTS

After MNU injection, the weight and ERG amplitudes of rats in both L and H groups decreased gradually, compared to those of the normal group (P < 0.05). Fundus imaging revealed enlargement of the optical disc and slightly reduced shadow of retinal vessels in both L and H groups, which were more obvious on D7. No significant morphological changes of retinal vessels were found under FFA. OCT and retinal histological examination revealed that outer nuclear layers (ONL) became thinner gradually in both L and H groups, and disappeared in H group at D7. MNU administration increased the numbers of apoptotic cells and Iba1-positive cells in the retinas gradually, showing a dose-dependent effect.

CONCLUSION

MNU gradually reduced the ONL thickness and the ERG amplitudes in the MNU-induced RP model revealed by various ophthalmic imaging techniques, along with the increased apoptosis of photoreceptors, the microglia cells activation, which provide indicators for new intervention effect for RP.

Autophagy-dependent ferroptosis may play a critical role in early stages of diabetic retinopathy

Diabetic retinopathy (DR), as one of the most common and significant microvascular complications of diabetes mellitus (DM), continues to elude effective targeted treatment for vision loss despite ongoing enrichment of the understanding of its pathogenic mechanisms from perspectives such as inflammation and oxidative stress. Recent studies have indicated that characteristic neuroglial degeneration induced by DM occurs before the onset of apparent microvascular lesions. In order to comprehensively grasp the early-stage pathological changes of DR, the retinal neurovascular unit (NVU) will become a crucial focal point for future research into the occurrence and progression of DR. Based on existing evidence, ferroptosis, a form of cell death regulated by processes like ferritinophagy and chaperone-mediated autophagy, mediates apoptosis in retinal NVU components, including pericytes and ganglion cells. Autophagy-dependent ferroptosis-related factors, including BECN1 and FABP4, may serve as both biomarkers for DR occurrence and development and potentially crucial targets for future effective DR treatments. The aforementioned findings present novel perspectives for comprehending the mechanisms underlying the early-stage pathological alterations in DR and open up innovative avenues for investigating supplementary therapeutic strategies.

Evaluation of the effect of full-process blood glucose management on T2DM cataract patients based on visual electrophysiology and OCTA

To investigate the difference in preoperative retinal function in patients with type 2 diabetes cataract (DC) without obvious retinopathy and to explore the clinical application of full blood glucose management for improving the postoperative vision in DC patients. This was a retrospective analysis in which we estimated the changes in visual electrophysiology (N75, P100, photopic flash electroretinogram(FERG), and scotopic FERG, paraoptic retinal nerve fibre layer thickness (pRNFL) and paraoptic radial capillary network blood flow density (ppVD) of type 2 diabetes (T2DM) patients at different phases of disease progression along with fasting blood glucose (FBG) and glycosylated haemoglobin (HbAlC) levels before and after DC surgery at Ziyang Central Hospital from January 2020 to December 2022. Additionally, trends in the above data throughout the entire process of glucose management intervention were examined. As the course of T2DM progressed, FBG and HbA1c increased, the N75 and P100 latency periods of patients gradually increased, and the values of photopic FERG, scotopic FERG, pRNFL, and ppVD gradually decreased at each postoperative time point. Moreover, the best corrected visual acuity(BCVA) of patients after surgery gradually decreased (P < 0.05). The BCVA of Group B (with full process blood glucose management) gradually stabilized at 1 month after surgery, and the BCVA of Group B was better than that of Group A at all time points after surgery. The results revealed that N75 and P100 in Group A were greater than those in Group B, whereas the photopic and scotopic FERG, pRNFL, and ppVD (%) values in Group A were lower than those in Group B. In addition, N75 and P100 in Group A gradually increased at various time points after surgery, whereas the photopic FERG, scotopic FERG, pRNFL, and ppVD (%) values gradually decreased. In the state of full blood glucose management, although N75 and P100 both reached their longest durations at one week after surgery, N75, the P100, photopic FERG, scotopic FERG, and pRNFL showed a gradually decreasing trend at 1 month and 3 months after surgery, whereas ppVD (%) gradually increased (P < 0.05). According to the results of the quantitative analysis of visual electrophysiology and OCTA, with the aggravation of diabetes, the retinal function of DC patients without obvious retinopathy tends to decrease, but full-process blood glucose management can effectively recover the retinal function of DC patients and improve visual quality after surgery.

Human-induced pluripotent stem cell-derived microglia integrate into mouse retina and recapitulate features of endogenous microglia

Microglia exhibit both maladaptive and adaptive roles in the pathogenesis of neurodegenerative diseases and have emerged as a cellular target for central nervous system (CNS) disorders, including those affecting the retina. Replacing maladaptive microglia, such as those impacted by aging or over-activation, with exogenous microglia that can enable adaptive functions has been proposed as a potential therapeutic strategy for neurodegenerative diseases. To investigate microglia replacement as an approach for retinal diseases, we first employed a protocol to efficiently generate human-induced pluripotent stem cell (hiPSC)-derived microglia in quantities sufficient for in vivo transplantation. These cells demonstrated expression of microglia-enriched genes and showed typical microglial functions such as LPS-induced responses and phagocytosis. We then performed xenotransplantation of these hiPSC-derived microglia into the subretinal space of adult mice whose endogenous retinal microglia have been pharmacologically depleted. Long-term analysis post-transplantation demonstrated that transplanted hiPSC-derived microglia successfully integrated into the neuroretina as ramified cells, occupying positions previously filled by the endogenous microglia and expressed microglia homeostatic markers such as P2ry12 and Tmem119. Furthermore, these cells were found juxtaposed alongside residual endogenous murine microglia for up to 8 months in the retina, indicating their ability to establish a stable homeostatic state in vivo. Following retinal pigment epithelial cell injury, transplanted microglia demonstrated responses typical of endogenous microglia, including migration, proliferation, and phagocytosis. Our findings indicate the feasibility of microglial transplantation and integration in the retina and suggest that modulating microglia through replacement may be a therapeutic strategy for treating neurodegenerative retinal diseases.

Implantation of biomimetic polydopamine nanocomposite scaffold promotes optic nerve regeneration through modulating inhibitory microenvironment

Optic nerve regeneration remains challenging worldwide due to the limited intrinsic regenerative capacity of retinal ganglion cells (RGCs) and the inhibitory microenvironment. Oxidative stress, induced by excessive reactive oxygen species (ROS) following optic nerve injury, is associated with prolonged neuroinflammation, resulting in a secondary injury of RGCs and the impairment of axon regeneration. Herein, we developed a bionic nanocomposite scaffold (GA@PDA) with immunoregulatory ability for enhanced optic nerve regeneration. The ice-templating method was employed to fabricate biopolymer-based scaffolds with a directional porous structure, mimicking the optic nerve, which effectively guided the oriented growth of neuronal cells. The incorporation of bioinspired polydopamine nanoparticles (PDA NPs) further confers excellent ROS scavenging ability, thereby modulating the phenotype transformation of microglia/macrophages from pro-inflammatory M1 to anti-inflammatory M2. In a rat optic nerve crush model, the implantation of GA@PDA scaffold enhanced survival of RGCs and promoted axonal regeneration. Our study offers novel insights and holds promising potential for the advancement of engineered biomaterials in facilitating optic nerve regeneration.

Exploring the relationship between cathepsin and age-related macular degeneration using Mendelian randomization

Purpose

Age-related macular degeneration (AMD) is the leading cause of low vision and even blindness in the elderly population worldwide. However, no studies have been conducted to analyze the causal relationship between the cathepsin family and AMD. The present study aimed to explore and analyze this potential association using Mendelian randomization (MR).

Methods

In this study, AMD was classified into two types: exudative AMD and atrophic AMD. Inverse-variance weighting (IVW) was used as the main analysis method. The association between nine cathepsins and the two classifications of AMD were analyzed using multivariable Mendelian randomization (MVMR). Sensitivity analysis included Cochran's Q-test and the MR-Egger intercept test.

Results

Two-sample MR analysis showed that higher levels of cathepsin L2 were associated with a delay in the development of atrophic AMD (IVW: p = 0.017; OR = 0.885; 95% CI = 0.799-0.979). Reverse MR analysis indicated that cathepsin E levels were increased in individuals with atrophic (IVW: p = 0.023; OR = 1.058; 95% CI = 1.007-1.111) and exudative AMD (IVW: p = 0.018; OR = 1.061; 95% CI 1 = 1.010-1.115). MVMR analysis indicated a causal relationship between cathepsin G (IVW: p = 0.025; OR = 1.124; 95% CI = 1.014-1.245), cathepsin O (IVW: p = 0.043, OR = 1.158, 95% CI = 1.004-1.336), and exudative AMD after coordinating for other types of cathepsin.

Conclusion

This study demonstrated a potential link between the cathepsin family and the onset of AMD. Elevated serum concentrations of cathepsin L2 may serve as a protective factor for atrophic AMD, while increased levels of serum cathepsin G and O concentrations may promote the development of exudative AMD. Besides, the development of AMD may be associated with elevated serum concentrations of cathepsin E.

Müller Cells Harboring Exosomal lncRNA OGRU Modulate Microglia Polarization in Diabetic Retinopathy by Serving as miRNA Sponges

Diabetic retinopathy (DR) is one of the most common complications of diabetes worldwide and is associated with visual loss and blindness. However, effective treatments for both early- and late-stage DR remain lacking. A streptozotocin-induced diabetic mouse model and high glucose (HG)-treated Müller cell model were established. M1/M2 microglia polarization was assessed by immunofluorescence staining and flow cytometry. Expression of long noncoding RNA (lncRNA) OGRU, cytokines, and other key molecules was detected by quantitative RT-PCR or Western blot. ELISA was used to monitor cytokine secretion. Müller cell-derived exosomes were isolated and characterized by nanopartical tracking analysis, Western blot, and transmission electron microscopy, and exosome uptake assay was used to monitor the intercellular transport of exosomes. Associations among lncRNA-miRNA-mRNA networks were validated by RNA pulldown and RNA immunoprecipitation and dual luciferase assays. Increased M1 polarization but decreased M2 polarization of retinal microglia was observed in DR mice. HG-treated Müller cell-derived exosomes transported OGRU into microglia and promoted microglia polarization toward the M1 phenotype. Mechanistically, OGRU served as a competing endogenous RNA for miR-320-3p, miR-221-3p, and miR-574-5p to regulate aldose reductase (AR), PFKFB3, and glucose transporter 1 (GLUT1) expression in microglia, respectively. Loss of miR-320-3p/miR-221-3p/miR-574-5p or reinforced AR/PFKFB3/GLUT1 abrogated OGRU silencing-mediated microglia polarization in vitro. In vivo studies further showed that OGRU/miR-320-3p/AR, OGRU/miR-221-3p/PFKFB3, and OGRU/miR-574-5p/GLUT1 axes regulated microglia polarization in DR mice. Collectively, Müller cell-derived exosomal OGRU regulated microglia polarization in DR by modulating OGRU/miR-320-3p/AR, OGRU/miR-221-3p/PFKFB3, and OGRU/miR-574-5p/GLUT1 axes.

ARTICLE HIGHLIGHTS

Timed topical dexamethasone eye drops improve mitochondrial function to prevent severe retinopathy of prematurity

Pathological neovascularization in retinopathy of prematurity (ROP) can cause visual impairment in preterm infants. Current ROP treatments which are not preventative and only address late neovascular ROP, are costly and can lead to severe complications. We showed that topical 0.1% dexamethasone eye drops administered prior to peak neovessel formation prevented neovascularization in five extremely preterm infants at high risk for ROP and suppressed neovascularization by 30% in mouse oxygen-induced retinopathy (OIR) modeling ROP. In contrast, in OIR, topical dexamethasone treatment before any neovessel formation had limited efficacy in preventing later neovascularization, while treatment after peak neovessel formation had a non-statistically significant trend to exacerbating disease. Optimally timed topical dexamethasone suppression of neovascularization in OIR was associated with increased retinal mitochondrial gene expression and decreased inflammatory marker expression, predominantly found in immune cells. Blocking mitochondrial ATP synthetase reversed the inhibitory effect of dexamethasone on neovascularization in OIR. This study provides new insights into topical steroid effects in retinal neovascularization and into mitochondrial function in phase II ROP, and suggests a simple clinical approach to prevent severe ROP.

Small Hyperreflective Retinal Foci as in vivo imaging feature of resident microglia activation in geographic atrophy

Geographic atrophy (GA), the atrophic late stage of age-related macular degeneration (AMD), is one of the leading causes of vision loss in developed countries. Based on genetic, histological and preclinical studies, the role of the innate immune system in the development and progression of GA is well established. Microglia, the principal resident immune cells, are recognized as key players in innate immunity and contributors to AMD development. Optical coherence tomography (OCT) allows to identify small hyperreflective retinal foci (HRF) with specific features known as aggregates of activated microglial cells as possible in vivo imaging feature of local neuroretinal inflammation. The purpose of this study was to evaluate the presence and amount of small HRF in the eyes of patients with different macular atrophic phenotypes. Patients with GA in both eyes (bilateral GA: B-GA group), patients with GA in one eye and macular new vessels (MNV) in the fellow-eye (unilateral GA: U-GA group) and patients with extensive macular atrophy with pseudodrusen (EMAP), a rare and aggressive variant of atrophic AMD, were retrospectively analyzed. HRF, defined as isolated punctiform elements of small dimensions (≤30 μm) with intermediate reflectivity (similar to that of the nerve fiber layer) and without a shadow cone, were manually identified and quantified. The amount of HRF was correlated to best corrected visual acuity (BCVA), GA lesion size, measured both at near infrared reflectance (NIR), and blue wavelength fundus autofluorescence (FAF) images, to some GA features (multifocal versus unifocal GA; presence versus absence of foveal sparing) and to central retinal thickness (CRT). Forty-six patients (26 in the B-GA group, 16 in the U-GA group and 4 in the EMAP group) were studied. Patients with EMAP were younger compared to patients with B-GA and to patients with U-GA (63.5 ± 6.8 years vs 80.4 ± 8.4 years B-GA, and vs 83.3 ± 6.1 years U-GA; p = 0.0004 and p= <0.0001, respectively). Mean BCVA, mean GA area at NIR and at FAF images, foveal sparing and multifocal versus unifocal GA distribution and mean CRT were not significantly different among groups. GA area was wider on NIR versus FAF in all groups, significantly in B-GA and U-GA groups (11.7 ± 7.6 mm2 vs 10.6 ± 7.1 mm2, p = 0.0087 in B-GA; 7.8 ± 9.2 mm2 vs 7.7 ± 9.4 mm2, p = 0.004 in U-GA). The number of HRF was significantly higher in U-GA compared to B-GA and to EMAP (47.4 ± 7.1 vs 31.6 ± 7.3 B-GA and 28.0 ± 4.9 EMAP, p < 0.0001 for both), while mean HRF number did not significantly differ between B-GA and EMAP (p = 0.1960). HRF count correlated only to CRT, positively in B-GA and negatively in U-GA group. The increase of small HRF, which mirrors retinal microglial activation, characterizes eyes with unilateral GA (and MNV in the fellow eye) but not eyes with bilateral GA or EMAP. The role of activated microglia in the retina of GA eyes needs to be better investigated, mainly considering the actual and new therapeutic strategies with which to reduce either the development or progression of the atrophic macular changes.

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.

The Role of Immune Cells and Signaling Pathways in Diabetic Eye Disease: A Comprehensive Review

Diabetic eye disease (DED) encompasses a range of ocular complications arising from diabetes mellitus, including diabetic retinopathy, diabetic macular edema, diabetic keratopathy, diabetic cataract, and glaucoma. These conditions are leading causes of visual impairments and blindness, especially among working-age adults. Despite advancements in our understanding of DED, its underlying pathophysiological mechanisms remain incompletely understood. Chronic hyperglycemia, oxidative stress, inflammation, and neurodegeneration play central roles in the development and progression of DED, with immune-mediated processes increasingly recognized as key contributors. This review provides a comprehensive examination of the complex interactions between immune cells, inflammatory mediators, and signaling pathways implicated in the pathogenesis of DED. By delving in current research, this review aims to identify potential therapeutic targets, suggesting directions of research for future studies to address the immunopathological aspects of DED.

Bruton's tyrosine kinase inhibition suppresses pathological retinal angiogenesis

BACKGROUND AND PURPOSE

Pathological retinal angiogenesis is a typical manifestation of vision-threatening ocular diseases. Many patients exhibit poor response or resistance to anti-vascular endothelial growth factor (VEGF) agents. Bruton's tyrosine kinase (BTK) controls the proliferation and function of immune cells. Therefore, we examined the anti-inflammatory and anti-angiogenic effects of BTK inhibition on retinal angiogenesis.

EXPERIMENTAL APPROACH

Retinal neovascularisation and vascular leakage in oxygen-induced retinopathy in C57/BL6J mice were assessed by whole-mount retinal immunofluorescence. PLX5622 was used to deplete microglia and Rag1-knockout mice were used to test the contribution of lymphocytes to the effects of BTK inhibition. The cytokines, activation markers, inflammatory and immune-regulatory activities of retinal microglia/macrophages were detected using qRT-PCR and immunofluorescence. NLRP3 was detected by western blotting, and the effects of BTK inhibition on the co-culture of microglia and human retinal microvascular endothelial cells (HRMECs) were examined.

KEY RESULTS

BTK inhibition suppressed pathological angiogenesis and vascular leakage, and significantly reduced retinal inflammation, which involved microglia/macrophages but not lymphocytes. BTK inhibition increased anti-inflammatory factors and reduced pro-inflammatory cytokines that resulted from NLRP3 inflammasome activation. BTK inhibition suppressed the inflammatory activity of microglia/macrophages, and acted synergistically with anti-VEGF without retinal toxicity. Moreover, the supernatant of microglia incubated with BTK-inhibitor reduced the proliferation, tube formation and sprouting of HRMECs.

CONCLUSION AND IMPLICATIONS

BTK inhibition suppressed retinal neovascularisation and vascular leakage by modulating the inflammatory activity of microglia and macrophages. Our study suggests BTK inhibition as a novel and promising approach for alleviating pathological retinal angiogenesis.

Mesenchymal Stem Cells Regulate Microglial Polarization via Inhibition of the HMGB1/TLR4 Signaling Pathway in Diabetic Retinopathy

Diabetic retinopathy (DR) is recognized as the most prevalent retinal degenerative disorder. Inflammatory response usually precedes microvascular alteration and is the primary factor of diabetic retinopathy. Activated microglia express many pro-inflammatory cytokines that exacerbate retina inflammation and disruption. In the present study, we found that MSCs alleviated blood-retina barrier (BRB) breakdown in diabetic rats, as evidenced by reduced retinal edema, decreased vascular leakage, and increased occludin expression. The MSC-treated retinal microglia exhibited reduced expression of M1-phenotype markers in the diabetic rats, including inducible nitric oxide synthase (iNOS), CD16, and pro-inflammatory cytokines. On the other hand, MSCs increased the expression of M2-phenotype markers, such as arginase-1 (Arg-1), CD206, and anti-inflammatory cytokines. HMGB1/TLR4 signaling pathway is activated in DR and inhibited after MSC treatment. Consistent with in vivo evidence, MSCs drove BV2 microglia toward M2 phenotype in vitro. Overexpression of HMGB1 in microglia reversed the effects of MSC treatment, suggesting HMGB1/TLR4 pathway is necessary for MSCs' regulatory effects on microglia polarization. Collectively, MSCs exert beneficial effects on DR by polarizing microglia from M1 toward M2 phenotype via inhibiting the HMGB1/TLR4 signaling pathway.

Irisin Alleviates Autoimmune Uveitis Through Promoting Retinal Microglial M1 to M2 Phenotypic Polarization Mediated by HIF-1α Pathway

Irisin, proteolytically cleaved from Fndc5 protein, has been identified as an exercise-related hormone. Here, we investigated the irisin levels in aqueous humor and its involvement in the pathogenesis of uveitis. The results revealed that the irisin level in the aqueous humor was significantly decreased in Vogt-Koyanagi-Harada (VKH), and Behcet uveitis (BU) patients, and was negatively correlated with TNF-α in BU patients. Exogenous supplementation of irisin alleviated scores of experimental autoimmune uveitis (EAU) clinically and pathologically and suppressed the proportion of Th1 and Th17 cells in spleen. Fndc5-/- EAU mice exhibited more severe inflammatory manifestations with increased microglial activation in the retina. Irisin could mitigate M1 microglia and promote M2 microglia polarization. RNA sequencing of the retina showed that HIF-1α pathway was significantly enriched in Fndc5-/- EAU mice. HIF-1α pathway inhibitor significantly rescued EAU severity, associated with a decreased M1 microglial polarization in the retina of Fndc5-/- mice. In conclusion, we highlighted that irisin could alleviate uveitis by inhibiting Th1 and Th17 cells and reducing M1 microglial polarization via HIF-1α pathway.

Settings and Clinical Applications of Subthreshold Micropulse Laser Therapy: A Review

Subthreshold lasers operate below the threshold of visible tissue damage, thereby preventing ophthalmoscopically visible thermal damage to the chorio-retinal layers. They could represent a safe and effective alternative and/or adjunctive procedure to conventional lasers in treating diabetic macula edema (DME), central serous chorioretinopathy (CSCR), and branch retina vein occlusion (BRVO). This review focuses on the use of subthreshold micropulse laser (SMPL), its settings, and clinical applications. Despite their widespread use, a standardized protocol for sub-threshold laser settings has not been established yet, and thus, there is uncertainty in selecting effective and safe parameters for any specific situation. We conducted a comprehensive overview of the existing indications for subthreshold laser therapy and their settings for different retinal diseases. The debate revolves around which parameters could guarantee the safety of the procedure for each case, depending on the duty cycle, the laser wavelength, the spot duration, and the power, with laser power titration on one side or choosing a fixed lowered power value on the other side. SMPL therapy for DME, CSCR, and BRVO-associated macular edema has shown significant effectiveness in reducing the macular thickness, facilitating subretinal fluid absorptions, increasing the best corrected visual acuity (BCVA) and reducing the number of intravitreal injections (IVI) required annually. We presented a broad list of the laser parameters reported in the literature, organized into different tables divided based on the specific pathology, with the aim of providing a useful tool for future studies.

Transcription factor EGR2 alleviates autoimmune uveitis via activation of GDF15 to modulate the retinal microglial phenotype

Uveitis is a vision-threatening disease primarily driven by a dysregulated immune response, with retinal microglia playing a pivotal role in its progression. Although the transcription factor EGR2 is known to be closely associated with uveitis, including Vogt-Koyanagi-Harada disease and Behcet's disease, and is essential for maintaining the dynamic homeostasis of autoimmunity, its exact role in uveitis remains unclear. In this study, diminished EGR2 expression was observed in both retinal microglia from experimental autoimmune uveitis (EAU) mice and inflammation-induced human microglia cell line (HMC3). We constructed a mice model with conditional knockout of EGR2 in microglia and found that EGR2 deficiency resulted in increased intraocular inflammation. Meanwhile, EGR2 overexpression downregulated the expression of inflammatory cytokines as well as cell migration and proliferation in HMC3 cells. Next, RNA sequencing and ChIP-PCR results indicated that EGR2 directly bound to its downstream target growth differentiation factor 15 (GDF15) and further regulated GDF15 transcription. Furthermore, intravitreal injection of GDF15 recombinant protein was shown to ameliorate EAU progression in vivo. Meanwhile, knockdown of GDF15 reversed the phenotype of EGR2 overexpression-induced microglial inflammation in vitro. In summary, this study highlighted the protective role of the transcription factor EGR2 in AU by modulating the microglial phenotype. GFD15 was identified as a downstream target of EGR2, providing a unique target for uveitis treatment.

IL-23 Priming Enhances the Neuroprotective Effects of MSC-Derived Exosomes in Treating Retinal Degeneration

Purpose

Neuroinflammation is a characteristic feature of neurodegenerative diseases. Mesenchymal stem cell-derived exosomes (MSC-exo) have shown neuroprotective effects through immunoregulation, but the therapeutic efficacy remains unsatisfactory. This study aims to enhance the neuroprotective capacity of MSC-exo through IL-23 priming for treating retinal degeneration in mice.

Methods

MSC were primed with IL-23 stimulation in vitro, and subsequently, exosomes (MSC-exo and IL-23-MSC-exo) were isolated and characterized. Two retinal degenerative disease models (NaIO3-induced mice and rd10 mice) received intravitreal injections of these exosomes. The efficacy of exosomes was assessed by examining retinal structural and functional recovery. Furthermore, exosomal microRNA (miRNA) sequencing was conducted, and the effects of exosomes on the M1 and M2 microglial phenotype shift were evaluated.

Results

IL-23-primed MSC-derived exosomes (IL-23-MSC-exo) exhibited enhanced capability in protecting photoreceptor cells and retinal pigment epithelium (RPE) cells against degenerative damage and fostering the restoration of retinal neural function in both NaIO3-induced retinal degeneration mice and rd10 mice when compared with MSC-exo. The exosomal miRNA suppression via Drosha knockdown in IL-23-primed MSC would abolish the neuroprotective role of IL-23-MSC-exo, highlighting the miRNA-dependent mechanism. Bioinformatic analysis, along with further in vivo biological studies, revealed that IL-23 priming induced a set of anti-inflammatory miRNAs in MSC-exo, prompting the transition of M1 to M2 microglial polarization.

Conclusions

IL-23 priming presents as a potential avenue for amplifying the immunomodulatory and neuroprotective effects of MSC-exo in treating retinal degeneration.

A New Modulator of Neuroinflammation in Diabetic Retinopathy: USP25

Diabetic retinopathy (DR) is a diabetes-associated complication that poses a threat to vision, distinguished by persistent and mild inflammation of the retinal microvasculature. The activation of microglia plays a crucial role in driving this pathological progression. Previous investigations have demonstrated that ubiquitin-specific peptidase 25 (USP25), a deubiquitinating enzyme, is involved in the regulation of immune cell activity. Nevertheless, the precise mechanisms through which USP25 contributes to the development of DR remain incompletely elucidated. Firstly, we have demonstrated the potential mechanism by which ROCKs can facilitate microglial activation and augment the synthesis of inflammatory mediators through the modulation of NF-κB signaling pathways in a high-glucose milieu. Furthermore, our study has provided novel insights by demonstrating that the regulatory role of USP25 in the secretion of proinflammatory factors is mediated through the involvement of ROCK in modulating the expression of NF-κB and facilitating the nuclear translocation of the phosphatase NF-κB. This regulatory mechanism plays a crucial role in modulating the activation of microglial cells within a high-glycemic environment. Hence, USP25 emerges as a pivotal determinant for the inflammatory activation of microglial cells, and its inhibition exhibits a dual effect of promoting retinal neuron survival while suppressing the inflammatory response in the retina. In conclusion, the promotion of diabetic retinopathy (DR) progression by USP25 is attributed to its facilitation of microglial activation induced by high glucose levels, a process mediated by the ROCK pathway. These findings highlight the importance of considering USP25 as a potential therapeutic target for the management of diabetic neuroinflammation.

Single-cell RNA sequencing in exploring the pathogenesis of diabetic retinopathy

Diabetic retinopathy (DR) is a leading cause of irreversible blindness in the working-age populations. Despite decades of research on the pathogenesis of DR for clinical care, a comprehensive understanding of the condition is still lacking due to the intricate cellular diversity and molecular heterogeneity involved. Single-cell RNA sequencing (scRNA-seq) has made the high-throughput molecular profiling of cells across modalities possible which has provided valuable insights into complex biological systems. In this review, we summarise the application of scRNA-seq in investigating the pathogenesis of DR, focusing on four aspects. These include the identification of differentially expressed genes, characterisation of key cell subpopulations and reconstruction of developmental 'trajectories' to unveil their state transition, exploration of complex cell‒cell communication in DR and integration of scRNA-seq with genome-wide association studies to identify cell types that are most closely related to DR risk genetic loci. Finally, we discuss the future challenges and expectations associated with studying DR using scRNA-seq. We anticipate that scRNA-seq will facilitate the discovery of mechanisms and new treatment targets in the clinical care landscape for patients with DR. KEY POINTS: Progress in scRNA-seq for diabetic retinopathy (DR) research includes studies on DR patients, non-human primates, and the prevalent mouse models. scRNA-seq facilitates the identification of differentially expressed genes, pivotal cell subpopulations, and complex cell-cell interactions in DR at single-cell level. Future scRNA-seq applications in DR should target specific patient subsets and integrate with single-cell and spatial multi-omics approaches.

Microvascular destabilization and intricated network of the cytokines in diabetic retinopathy: from the perspective of cellular and molecular components

Microvascular destabilization is the primary cause of the inner blood-retinal barrier (iBRB) breakdown and increased vascular leakage in diabetic retinopathy (DR). Microvascular destabilization results from the combinational effects of increased levels of growth factors and cytokines, involvement of inflammation, and the changed cell-to-cell interactions, especially the loss of endothelial cells and pericytes, due to hyperglycemia and hypoxia. As the manifestation of microvascular destabilization, the fluid transports via paracellular and transcellular routes increase due to the disruption of endothelial intercellular junctional complexes and/or the altered caveolar transcellular transport across the retinal vascular endothelium. With diabetes progression, the functional and the structural changes of the iBRB components, including the cellular and noncellular components, further facilitate and aggravate microvascular destabilization, resulting in macular edema, the neuroretinal damage and the dysfunction of retinal inner neurovascular unit (iNVU). Although there have been considerable recent advances towards a better understanding of the complex cellular and molecular network underlying the microvascular destabilization, some still remain to be fully elucidated. Recent data indicate that targeting the intricate signaling pathways may allow to against the microvascular destabilization. Therefore, efforts have been made to better clarify the cellular and molecular mechanisms that are involved in the microvascular destabilization in DR. In this review, we discuss: (1) the brief introduction of DR and microvascular destabilization; (2) the cellular and molecular components of iBRB and iNVU, and the breakdown of iBRB; (3) the matrix and cell-to-cell contacts to maintain microvascular stabilization, including the endothelial glycocalyx, basement membrane, and various cell-cell interactions; (4) the molecular mechanisms mediated cell-cell contacts and vascular cell death; (5) the altered cytokines and signaling pathways as well as the intricate network of the cytokines involved in microvascular destabilization. This comprehensive review aimed to provide the insights for microvascular destabilization by targeting the key molecules or specific iBRB cells, thus restoring the function and structure of iBRB and iNVU, to treat DR.

Timed topical dexamethasone eye drops improve mitochondrial function to prevent severe retinopathy of prematurity

Pathological neovascularization in retinopathy of prematurity (ROP) can cause visual impairment in preterm infants. Current ROP treatments which are not preventative and only address late neovascular ROP, are costly and can lead to severe complications. We showed that topical 0.1% dexamethasone eye drops administered prior to peak neovessel formation prevented neovascularization in five extremely preterm infants at high risk for ROP and suppressed neovascularization by 30% in mouse oxygen-induced retinopathy (OIR) modeling ROP. In contrast, in OIR, topical dexamethasone treatment before any neovessel formation had limited efficacy in preventing later neovascularization, while treatment after peak neovessel formation had a non-statistically significant trend to exacerbating disease. Optimally timed topical dexamethasone suppression of neovascularization in OIR was associated with increased retinal mitochondrial gene expression and decreased inflammatory marker expression, predominantly found in immune cells. Blocking mitochondrial ATP synthetase reversed the inhibitory effect of dexamethasone on neovascularization in OIR. This study provides new insights into topical steroid effects in retinal neovascularization and into mitochondrial function in phase II ROP, and suggests a simple clinical approach to prevent severe ROP.

Molecular hydrogen promotes retinal vascular regeneration and attenuates neovascularization and neuroglial dysfunction in oxygen-induced retinopathy mice

BACKGROUND

Retinopathy of Prematurity (ROP) is a proliferative retinal vascular disease occurring in the retina of premature infants and is the main cause of childhood blindness. Nowadays anti-VEGF and retinal photocoagulation are mainstream treatments for ROP, but they develop a variety of complications. Hydrogen (H2) is widely considered as a useful neuroprotective and antioxidative therapeutic method for hypoxic-ischemic disease without toxic effects. However, whether H2 provides physiological angiogenesis promotion, neovascularization suppression and glial protection in the progression of ROP is largely unknown.This study aims to investigate the effects of H2 on retinal angiogenesis, neovascularization and neuroglial dysfunction in the retinas of oxygen-induced retinopathy (OIR) mice.

METHODS

In this study, mice that were seven days old and either wild-type (WT) or Nrf2-deficient (Nrf2-/-) were exposed to 75% oxygen for 5 days and then returned to normal air conditions. Different stages of hydrogen gas (H2) inhalation were administered. Vascular obliteration, neovascularization, and blood vessel leakage were analyzed and compared. To count the number of neovascularization endothelial nuclei, routine HE staining of retinal sections was conducted. Immunohistochemistry was performed using DyLight 594 labeled GSL I-isolectin B4 (IB4), as well as primary antibodies against proliferating cell nuclear antigen (PCNA), glial fibrillary acidic protein (GFAP), and Iba-1. Western blots were used to measure the expression of NF-E2-related factor 2 (Nrf2), vascular endothelial growth factor (VEGF), Notch1, Dll4, and HIF-1α. Additionally, the expression of target genes such as NQO1, HO-1, Notch1, Hey1, Hey2, and Dll4 was measured. Human umbilical vein endothelial cells (HUVECs) treated with H2 under hypoxia were used as an in vitro model. RT-PCR was used to evaluate the mRNA expression of Nrf2, Notch/Dll4, and the target genes. The expression of reactive oxygen species (ROS) was observed using immunofluorescence staining.

RESULTS

Our results indicate that 3-4% H2 does not disturb retinal physiological angiogenesis, but ameliorates vaso-obliteration and neovascularization in OIR mice. Moreover, H2 prevents the decreased density and reverses the morphologic and functional changes in retinal astrocytes caused by oxygen-induced injury. In addition, H2 inhalation reduces microglial activation, especially in the area of neovascularization in OIR mice. H2 plays a protective role in vascular regeneration by promoting Nrf2 activation and suppressing the Dll4-induced Notch signaling pathway in vivo. Also, H2 promotes the proliferation of HUVECs under hypoxia by negatively regulating the Dll4/Notch pathway and reducing ROS levels through Nrf2 pathway aligning with our findings in vivo.Moreover, the retinal oxygen-sensing mechanisms (HIF-1α/VEGF) are also involved in hydrogen-mediated retinal revascularization and neovascularization suppression.

CONCLUSIONS

Collectively, our results indicate that H2 could be a promising therapeutic agent for POR treatment and that its beneficial effect in human ROP might involve the activation of the Nrf2-Notch axis as well as HIF-1α/VEGF pathways.

Multifunctional nano-in-micro delivery systems for targeted therapy in fundus neovascularization diseases

Fundus neovascularization diseases are a series of blinding eye diseases that seriously impair vision worldwide. Currently, the means of treating these diseases in clinical practice are continuously evolving and have rapidly revolutionized treatment opinions. However, key issues such as inadequate treatment effectiveness, high rates of recurrence, and poor patient compliance still need to be urgently addressed. Multifunctional nanomedicine can specifically respond to both endogenous and exogenous microenvironments, effectively deliver drugs to specific targets and participate in activities such as biological imaging and the detection of small molecules. Nano-in-micro (NIM) delivery systems such as metal, metal oxide and up-conversion nanoparticles (NPs), quantum dots, and carbon materials, have shown certain advantages in overcoming the presence of physiological barriers within the eyeball and are widely used in the treatment of ophthalmic diseases. Few studies, however, have evaluated the efficacy of NIM delivery systems in treating fundus neovascular diseases (FNDs). The present study describes the main clinical treatment strategies and the adverse events associated with the treatment of FNDs with NIM delivery systems and summarizes the anatomical obstacles that must be overcome. In this review, we wish to highlight the principle of intraocular microenvironment normalization, aiming to provide a more rational approach for designing new NIM delivery systems to treat specific FNDs.

Subconjunctival injection of rapamycin-loaded polymeric microparticles for effective suppression of noninfectious uveitis in rats

Noninfective uveitis is a major cause of vision impairment, and corticosteroid medication is a mainstay clinical strategy that causes severe side effects. Rapamycin (RAPA), a potent immunomodulator, is a promising treatment for noninfective uveitis. However, because high and frequent dosages are required, it is a great challenge to implement its clinical translation for noninfective uveitis therapy owing to its serious toxicity. In the present study, we engineered an injectable microparticulate drug delivery system based on biodegradable block polymers (i.e., polycaprolactone-poly (ethylene glycol)-polycaprolactone, PCEC) for efficient ocular delivery of RAPA via a subconjunctival injection route and investigated its therapeutic efficacy in an experimental autoimmune uveitis (EAU) rat model. RAPA-PCEC microparticles were fabricated using the emulsion-evaporation method and thoroughly characterized using scanning electron microscopy, fourier transform infrared spectroscopy, X-ray diffraction, and differential scanning calorimetry. The formed microparticles exhibited slow in vitro degradation over 28 days, and provided both in vitro and in vivo sustained release of RAPA over 4 weeks. Additionally, a single subconjunctival injection of PCEC microparticles resulted in high ocular tolerance. More importantly, subconjunctival injection of RAPA-PCEC microparticles significantly attenuated the clinical signs of EAU in a dose-dependent manner by reducing inflammatory cell infiltration (i.e., CD45+ cells and Th17 cells) and inhibiting microglial activation. Overall, this injectable microparticulate system may be promising vehicle for intraocular delivery of RAPA for the treatment of noninfective uveitis.

Hyperoside mitigates photoreceptor degeneration in part by targeting cGAS and suppressing DNA-induced microglial activation

Activated microglia play an important role in driving photoreceptor degeneration-associated neuroinflammation in the retina. Controlling pro-inflammatory activation of microglia holds promise for mitigating the progression of photoreceptor degeneration. Our previous study has demonstrated that pre-light damage treatment of hyperoside, a naturally occurring flavonol glycoside with antioxidant and anti-inflammatory activities, prevents photooxidative stress-induced photoreceptor degeneration and neuroinflammatory responses in the retina. However, the direct impact of hyperoside on microglia-mediated neuroinflammation during photoreceptor degeneration remains unknown. Upon verifying the anti-inflammatory effects of hyperoside in LPS-stimulated BV-2 cells, our results here further demonstrated that post-light damage hyperoside treatment mitigated the loss of photoreceptors and attenuated the functional decline of the retina. Meanwhile, post-light damage hyperoside treatment lowered neuroinflammatory responses and dampened microglial activation in the illuminated retinas. With respect to microglial activation, hyperoside mitigated the pro-inflammatory responses in DNA-stimulated BV-2 cells and lowered DNA-stimulated production of 2'3'-cGAMP in BV-2 cells. Moreover, hyperoside was shown to directly interact with cGAS and suppress the enzymatic activity of cGAS in a cell-free system. In conclusion, the current study suggests for the first time that the DNA sensor cGAS is a direct target of hyperoside. Hyperoside is effective at mitigating DNA-stimulated cGAS-mediated pro-inflammatory activation of microglia, which likely contributes to the therapeutic effects of hyperoside at curtailing neuroinflammation and alleviating neuroinflammation-instigated photoreceptor degeneration.

Cellular communication network factor 1 promotes retinal leakage in diabetic retinopathy via inducing neutrophil stasis and neutrophil extracellular traps extrusion

BACKGROUND

Diabetic retinopathy (DR) is a major cause of blindness and is characterized by dysfunction of the retinal microvasculature. Neutrophil stasis, resulting in retinal inflammation and the occlusion of retinal microvessels, is a key mechanism driving DR. These plugging neutrophils subsequently release neutrophil extracellular traps (NETs), which further disrupts the retinal vasculature. Nevertheless, the primary catalyst for NETs extrusion in the retinal microenvironment under diabetic conditions remains unidentified. In recent studies, cellular communication network factor 1 (CCN1) has emerged as a central molecule modulating inflammation in pathological settings. Additionally, our previous research has shed light on the pathogenic role of CCN1 in maintaining endothelial integrity. However, the precise role of CCN1 in microvascular occlusion and its potential interaction with neutrophils in diabetic retinopathy have not yet been investigated.

METHODS

We first examined the circulating level of CCN1 and NETs in our study cohort and analyzed related clinical parameters. To further evaluate the effects of CCN1 in vivo, we used recombinant CCN1 protein and CCN1 overexpression for gain-of-function, and CCN1 knockdown for loss-of-function by intravitreal injection in diabetic mice. The underlying mechanisms were further validated on human and mouse primary neutrophils and dHL60 cells.

RESULTS

We detected increases in CCN1 and neutrophil elastase in the plasma of DR patients and the retinas of diabetic mice. CCN1 gain-of-function in the retina resulted in neutrophil stasis, NETs extrusion, capillary degeneration, and retinal leakage. Pre-treatment with DNase I to reduce NETs effectively eliminated CCN1-induced retinal leakage. Notably, both CCN1 knockdown and DNase I treatment rescued the retinal leakage in the context of diabetes. In vitro, CCN1 promoted adherence, migration, and NETs extrusion of neutrophils.

CONCLUSION

In this study, we uncover that CCN1 contributed to retinal inflammation, vessel occlusion and leakage by recruiting neutrophils and triggering NETs extrusion under diabetic conditions. Notably, manipulating CCN1 was able to hold therapeutic promise for the treatment of diabetic retinopathy.

IL-10-induced modulation of macrophage polarization suppresses outer-blood-retinal barrier disruption in the streptozotocin-induced early diabetic retinopathy mouse model

Diabetic retinopathy (DR) is associated with ocular inflammation leading to retinal barrier breakdown, vascular leakage, macular edema, and vision loss. DR is not only a microvascular disease but also involves retinal neurodegeneration, demonstrating that pathological changes associated with neuroinflammation precede microvascular injury in early DR. Macrophage activation plays a central role in neuroinflammation. During DR, the inflammatory response depends on the polarization of retinal macrophages, triggering pro-inflammatory (M1) or anti-inflammatory (M2) activity. This study aimed to determine the role of macrophages in vascular leakage through the tight junction complexes of retinal pigment epithelium, which is the outer blood-retinal barrier (BRB). Furthermore, we aimed to assess whether interleukin-10 (IL-10), a representative M2-inducer, can decrease inflammatory macrophages and alleviate outer-BRB disruption. We found that modulation of macrophage polarization affects the structural and functional integrity of ARPE-19 cells in a co-culture system under high-glucose conditions. Furthermore, we demonstrated that intravitreal IL-10 injection induces an increase in the ratio of anti-inflammatory macrophages and effectively suppresses outer-BRB disruption and vascular leakage in a mouse model of early-stage streptozotocin-induced diabetes. Our results suggest that modulation of macrophage polarization by IL-10 administration during early-stage DR has a promising protective effect against outer-BRB disruption and vascular leakage. This finding provides valuable insights for early intervention in DR.

Current understanding of subclinical diabetic retinopathy informed by histology and high-resolution in vivo imaging

The escalating incidence of diabetes mellitus has amplified the global impact of diabetic retinopathy. There are known structural and functional changes in the diabetic retina that precede the fundus photography abnormalities which currently are used to diagnose clinical diabetic retinopathy. Understanding these subclinical alterations is important for effective disease management. Histology and high-resolution clinical imaging reveal that the entire neurovascular unit, comprised of retinal vasculature, neurons and glial cells, is affected in subclinical disease. Early functional manifestations are seen in the form of blood flow and electroretinography disturbances. Structurally, there are alterations in the cellular components of vasculature, glia and the neuronal network. On clinical imaging, changes to vessel density and thickness of neuronal layers are observed. How these subclinical disturbances interact and ultimately manifest as clinical disease remains elusive. However, this knowledge reveals potential early therapeutic targets and the need for imaging modalities that can detect subclinical changes in a clinical setting.

Macrophage activation contributes to diabetic retinopathy

Diabetic retinopathy (DR) is recognized as a neurovascular complication of diabetes, and emerging evidence underscores the pivotal role of inflammation in its pathophysiology. Macrophage activation is increasingly acknowledged as a key contributor to the onset and progression of DR. Different populations of macrophages originating from distinct sources contribute to DR-associated inflammation. Retinal macrophages can be broadly categorized into two main groups based on their origin: intrinsic macrophages situated within the retina and vitreoretinal interface and macrophages derived from infiltrating monocytes. The former comprises microglia (MG), perivascular macrophages, and macrophage-like hyalocytes. Retinal MG, as the principal population of tissue-resident population of mononuclear phagocytes, exhibits high heterogeneity and plasticity while serving as a crucial connector between retinal capillaries and synapses. This makes MG actively involved in the pathological processes across various stages of DR. Activated hyalocytes also contribute to the pathological progression of advanced DR. Additionally, recruited monocytes, displaying rapid turnover in circulation, augment the population of retinal macrophages during DR pathogenesis, exerting pathogenic or protective effect based on different subtypes. In this review, we examine novel perspectives on macrophage biology based on recent studies elucidating the diversity of macrophage identity and function, as well as the mechanisms influencing macrophage behavior. These insights may pave the way for innovative therapeutic strategies in the management of DR.

Translocator protein (18 kDa) (Tspo) in the retina and implications for ocular diseases

Translocator protein (18 kDa) (Tspo), formerly known as peripheral benzodiazepine receptor is a highly conserved transmembrane protein primarily located in the outer mitochondrial membrane. In the central nervous system (CNS), especially in glia cells, Tspo is upregulated upon inflammation. Consequently, Tspo was used as a tool for diagnostic in vivo imaging of neuroinflammation in the brain and as a potential therapeutic target. Several synthetic Tspo ligands have been explored as immunomodulatory and neuroprotective therapy approaches. Although the function of Tspo and how its ligands exert these beneficial effects is not fully clear, it became a research topic of interest, especially in ocular diseases in the past few years. This review summarizes state-of-the-art knowledge of Tspo expression and its proposed functions in different cells of the retina including microglia, retinal pigment epithelium and Müller cells. Tspo is involved in cytokine signaling, oxidative stress and reactive oxygen species production, calcium signaling, neurosteroid synthesis, energy metabolism, and cholesterol efflux. We also highlight recent developments in preclinical models targeting Tspo and summarize the relevance of Tspo biology for ocular and retinal diseases. We conclude that glial upregulation of Tspo in different ocular pathologies and the use of Tspo ligands as promising therapeutic approaches in preclinical studies underline the importance of Tspo as a potential disease-modifying protein.

YY1 Lactylation Aggravates Autoimmune Uveitis by Enhancing Microglial Functions via Inflammatory Genes

Activated microglia in the retina are essential for the development of autoimmune uveitis. Yin-Yang 1 (YY1) is an important transcription factor that participates in multiple inflammatory and immune-mediated diseases. Here, an increased YY1 lactylation in retinal microglia within in the experimental autoimmune uveitis (EAU) group is observed. YY1 lactylation contributed to boosting microglial activation and promoting their proliferation and migration abilities. Inhibition of lactylation suppressed microglial activation and attenuated inflammation in EAU. Mechanistically, cleavage under targets & tagmentation （CUT&Tag） analysis revealed that YY1 lactylation promoted microglial activation by regulating the transcription of a set of inflammatory genes, including STAT3, CCL5, IRF1, IDO1, and SEMA4D. In addition, p300 is identified as the writer of YY1 lactylation. Inhibition of p300 decreased YY1 lactylation and suppressed microglial inflammation in vivo and in vitro. Collectively, the results showed that YY1 lactylation promoted microglial dysfunction in autoimmune uveitis by upregulating inflammatory cytokine secretion and boosting cell migration and proliferation. Therapeutic effects can be achieved by targeting the lactate/p300/YY1 lactylation/inflammatory genes axis.