Microglia in retinal angiogenesis and diabetic retinopathy

Telencephalic stab wound injury induces regenerative angiogenesis and neurogenesis in zebrafish: unveiling the role of vascular endothelial growth factor signaling and microglia

JOURNAL/nrgr/04.03/01300535-202510000-00025/figure1/v/2024-11-26T163120Z/r/image-tiff After brain damage, regenerative angiogenesis and neurogenesis have been shown to occur simultaneously in mammals, suggesting a close link between these processes. However, the mechanisms by which these processes interact are not well understood. In this work, we aimed to study the correlation between angiogenesis and neurogenesis after a telencephalic stab wound injury. To this end, we used zebrafish as a relevant model of neuroplasticity and brain repair mechanisms. First, using the Tg( fli1:EGFP × mpeg1.1:mCherry ) zebrafish line, which enables visualization of blood vessels and microglia respectively, we analyzed regenerative angiogenesis from 1 to 21 days post-lesion. In parallel, we monitored brain cell proliferation in neurogenic niches localized in the ventricular zone by using immunohistochemistry. We found that after brain damage, the blood vessel area and width as well as expression of the fli1 transgene and vascular endothelial growth factor ( vegfaa and vegfbb ) were increased. At the same time, neural stem cell proliferation was also increased, peaking between 3 and 5 days post-lesion in a manner similar to angiogenesis, along with the recruitment of microglia. Then, through pharmacological manipulation by injecting an anti-angiogenic drug (Tivozanib) or Vegf at the lesion site, we demonstrated that blocking or activating Vegf signaling modulated both angiogenic and neurogenic processes, as well as microglial recruitment. Finally, we showed that inhibition of microglia by clodronate-containing liposome injection or dexamethasone treatment impairs regenerative neurogenesis, as previously described, as well as injury-induced angiogenesis. In conclusion, we have described regenerative angiogenesis in zebrafish for the first time and have highlighted the role of inflammation in this process. In addition, we have shown that both angiogenesis and neurogenesis are involved in brain repair and that microglia and inflammation-dependent mechanisms activated by Vegf signaling are important contributors to these processes. This study paves the way for a better understanding of the effect of Vegf on microglia and for studies aimed at promoting angiogenesis to improve brain plasticity after brain injury.

Qideng Mingmu Capsules Ameliorates Retinal Neovascularization by Regulating Ang/Tie2 Signaling Pathway

OBJECTIVE

To investigate the inhibitory effects and underlying mechanisms of Qideng Mingmu Capsules (QD) on retinal neovascularization (RNV).

METHODS

Seven-day-old C57BL/6J mice were assigned to the following groups: control, oxygen-induced retinopathy (OIR), low-, medium-, high-dose QD (225, 450, and 900 mg/g daily), and angiopoietin 1 (Ang1), 20 mice in each group. Except for the control group, an OIR model was induced by exposing mice to a hyperoxic environment for 5 d (postnatal days 7-12), followed by a normoxic environment for 5 d (postnatal days 12-17). From day 12, the treatment groups received QD orally or Ang1 via binocular intravitreal injection. On day 17, hematoxylin and eosin staining and fluorescein isothiocyanate-dextran staining were performed to evaluate RNV growth. Immunofluorescence staining, immunohistochemistry, and Western blotting were used to analyze the expressions of Ang/tyrosine kinase with immunoglobulin and epidermal growth factor homology domain-2 (Tie2) signaling pathway, hypoxia-inducible factor-1α (HIF-1α), and retinal vascular maturation markers. In addition, the effects of QD on the viability of rat retinal microvascular endothelial cells (rRMECs) was assessed.

RESULTS

QD significantly inhibited RNV formation, reduced RNV density, increased the expressions of Ang1, Tie2, and phosphorylated protein kinase B, and decreased the expression of Ang2 (P<0.05 or P<0.01). QD also enhanced retinal vascular pericyte coverage, reduced HIF-1α expression, and increased vascular endothelial cadherin levels (P<0.05 or P<0.01). Furthermore, no adverse effects were observed on the viability of rRMECs after QD intervention.

CONCLUSIONS

QD effectively inhibited RNV formation, promoted neovascular maturation and remodeling, and protected retinal function by modulating the Ang/Tie2 signaling pathway. Therefore, QD may serve as a promising therapeutic option for retinal neovascular diseases.

Nitro-Oleic acid protects from neovascularization, oxidative stress, gliosis and neurodegeneration in oxygen-induced retinopathy

Inflammation and oxidative stress are involved in Proliferative Retinopathies (PR). Müller glial cells (MGCs) and microglia play pivotal roles in pathological neovascularization (NV) and neurodegeneration in PR. Nitro-fatty acids are important electrophilic signaling mediators with anti-inflammatory and antioxidant properties. Herein, our goal was to evaluate the cytoprotective effect of nitro-oleic acid (NO2-OA) on neurons, MGCs and microglia in a mouse model of oxygen-induced retinopathy (OIR). NO2-OA induced vascular regrowth and reduced NV at P17 OIR, although no difference in the proangiogenic/antiangiogenic (VEGF-A/PEDF) balance was found between NO2-OA treatment and vehicle. In addition, Western blot and immunofluorescence assays showed that NO2-OA prevented gliosis at P17 OIR and decreased the number and activation of IBA1+ retinal myeloid cells. However, NO2-OA did not restore the decrease in expression of glutamine synthase (GS). Loss of retinal function in OIR mouse model measured by electroretinography was ameliorated, mainly at P26 OIR, after NO2-OA treatment. Western blot analysis of retinas from OIR mice revealed decreased levels of caspase-3 protein and increased number of TUNEL-positive cells at P26 compared to RA. Notably, these alterations were partially prevented after NO2-OA treatment. Besides, NO2-OA attenuates oxidative stress induced in MGCs exposed to aqueous humor from patients with different stages of PR. These findings highlight NO2-OA as a promising therapeutic strategy targeting both vascular and neuroglial components in PR, suggesting its potential clinical relevance.

Update in the molecular mechanism and biomarkers of diabetic retinopathy

Diabetic retinopathy (DR) is a serious complication of diabetes caused by long-term hyperglycemia that leads to microvascular and neuronal damage in the retina. The molecular mechanisms of DR involve oxidative stress, inflammatory responses, neurodegenerative changes, and vascular dysfunction triggered by hyperglycemia. Oxidative stress activates multiple metabolic pathways, such as the polyol, hexosamine, and protein kinase C (PKC) pathways, resulting in the production of, which in turn promote the formation of advanced glycation end products (AGEs). These pathways exacerbate vascular endothelial damage and the release of inflammatory factors, activating inflammatory signaling pathways such as the NF-κB pathway, leading to retinal cell damage and apoptosis. Additionally, DR involves neurodegenerative changes, including the activation of glial cells, neuronal dysfunction, and cell death. Research on the multiomics molecular markers of DR has revealed complex mechanisms at the genetic, epigenetic, and transcriptional levels. Genome-wide association studies (GWASs) have identified multiple genetic loci associated with DR that are involved in metabolic and inflammatory pathways. Noncoding RNAs, such as miRNAs, circRNAs, and lncRNAs, participate in the development of DR by regulating gene expression. Proteomic, metabolomic and lipidomic analyses have revealed specific proteins, metabolites and lipid changes associated with DR, providing potential biomarkers for the early diagnosis and treatment of this disease. This review provides a comprehensive perspective for understanding the molecular network of DR and facilitates the exploration of innovative therapeutic approaches.

SUMOylation is a Translatable Target in Hypoxic MNPs Regulating Retinal Vasculopathy

Retinal vasculopathies pose a devastating threat to human health. While anti-VEGF therapy situates the first-line treatment for patients, the clinical efficacy is limited by suboptimal response and potential risks raised by long-term high-dosage use. Neurovascular unit uncoupling is recognized as a key mechanism contributing to pathological neovascularization, yet how immune components get involved is less appreciated. Here, it is reported that SUMOylation modulates the pro-angiogenic capacity of macrophage, and inhibition of the SUMO-conjugating enzyme UBC9 synergizes with anti-VEGF therapy in preclinical models. Diabetic human retinal mononuclear phagocytes (MNPs) overexpress UBC9. Genetic ablation of UBC9 in MNPs compromises the crosstalk with endothelial cells by reducing Vegfa splicing isoforms, including Vegf120, Vegf144, Vegf164, and Vegf188. Mechanistically, hypoxia facilitates the SUMOylation of fused in sarcoma (FUS) protein at lysine residues K327 and K502. Mutation of the SUMOylation sites enhances FUS binding to the Vegfa 3'-untranslated region (3'UTR), leading to mRNA destabilization and decreased VEGFA production. Intravitreal administration of anti-VEGF elevates UBC9 whereas Ubc9 siRNA-liposomes alleviates retinal vascular leakage and choroidal neovascularization, and a better therapeutic efficacy is yielded when combining with anti-VEGF therapy. Taken together, this study highlights a novel approach for treating retinal vascular diseases by modulating the MNPs-endothelial cell interplay.

The role of microglia in the development of diabetic retinopathy and its potential clinical application

Lately, research on the function of microglia in diabetic retinopathy (DR) is becoming increasingly focused. Microglia are immune cells that dwell in the central nervous system and are crucial to the pathophysiology of DR. According to studies, a hyperglycemic environment can activate microglia, bringing them out of a resting state to an active state. This allows them to release a variety of inflammatory factors and chemokines, which can then cause retinal inflammatory reactions. When it comes to angiogenesis in DR, activated microglia release a variety of angiogenic substances, such as vascular endothelial growth factor (VEGF), to create aberrant new blood vessels. Moreover, microglia contribute to the retina's oxidative stress process by generating and releasing reactive oxygen and nitrogen-free radicals, which exacerbates retinal damage. Researchers have proposed a variety of strategies for the activation of microglia and the inflammatory response it triggers. By inhibiting the excessive activation of microglia and reducing the release of inflammatory factors, the inflammatory response and damage to the retina can be alleviated. Drugs that interfere with retinal microglia can also be used to regulate vascular damage and inhibit the formation of new blood vessels. In addition, antioxidants are used to remove reactive oxygen and free radicals, reduce oxidative stress levels, and protect retinal cells. These therapeutic strategies aim to achieve the purpose of treating DR by regulating the function of microglia. Thus, we highlight the possibility that therapy aimed at microglia could offer fresh ideas for treating DR.

Integrative Analysis and Experimental Validation Reveal FCGR1A and ITGAL as Key Inflammatory Biomarkers in Proliferative Diabetic Retinopathy

Purpose

Diabetic retinopathy (DR), one of the most common severe complications of diabetes, has become a leading cause of blindness among the working population without a fundamental treatment. Proliferative DR (PDR) is the advanced stage of DR. Recent studies have shown that inflammation is closely related to PDR, as it promotes leukocyte adhesion, breakdown of the blood-retinal barrier, and pathological neovascularization, but the key regulatory genes involved remained unclear. We aim to identify inflammation-related biomarkers in PDR.

Methods

We downloaded and merged PDR-related datasets GSE102485, GSE94019, and GSE60436, comprising a total of 13 control samples and 37 samples from PDR patients, and conducted a joint analysis of inflammation-related genes (IRGs). Differential analysis, functional enrichment analysis, WGCNA and LASSO were used to identify key genes and their functions in the pathogenesis of PDR. Dataset GSE241239, which contains retinal sequencing data from mice, was used for external validation. Additionally, single-cell RNA analysis using GSE165784, which includes five human-derived PDR samples, was conducted to investigate the cellular expression of Fc Gamma Receptor IA (FCGR1A) and Integrin Subunit Alpha L (ITGAL). Finally, the expression of FCGR1A and ITGAL was validated in DR mouse models and high glucose-induced cell models.

Results

Nine key genes associated with the pathogenesis of PDR were identified. Further screening identified FCGR1A and ITGAL as potential therapeutic targets, with single-cell analysis showing their primary distribution in microglia. In vivo and in vitro experiments confirmed localization of FCGR1A and ITGAL in microglia and significant elevation within DR mouse models.

Conclusion

Comprehensive analysis indicates, for the first time, that FCGR1A and ITGAL are key inflammation-related genes involved in the pathogenesis of PDR mediated by microglia. FCGR1A and ITGAL are promising therapeutic targets for PDR.

Microglial regulation of the retinal vasculature in health and during the pathology associated with diabetes

The high metabolic demand of retinal neurons requires a precisely regulated vascular system that can deliver rapid changes in blood flow in response to neural need. In the retina, this is achieved via the action of a coordinated group of cells that form the neurovascular unit. While cells such as pericytes, Müller cells, and astrocytes have long been linked to neurovascular coupling, more recently the resident microglial population have also been implicated. In the healthy retina, microglia make extensive contact with blood vessels, as well as neuronal synapses, and are important in vascular patterning during development. Work in the brain and retina has recently indicated that microglia can directly regulate the local vasculature. In the retina, the fractalkine-Cx3cr1 signalling axis has been shown to induce local capillary constriction within the superficial vascular plexus via a mechanism involving components of the renin-angiotensin system. Furthermore, aberrant microglial induced vasoconstriction may be at the centre of early vascular reactivity changes observed in those with diabetes. This review summarizes the recent emerging evidence that microglia play multiple roles in retinal homeostasis especially in regulating the vasculature. We highlight what is known about the role of microglia under normal circumstances, and then build on this to discuss how microglia contribute to early vascular compromise during diabetes. Further understanding of the mechanisms of microglial-vascular regulation may allow alternate treatment strategies to be devised to reduce vascular pathology in diseases such as diabetic retinopathy.

BARD1-mediated stabilization of METTL14 promotes retinal neovascularization by m6A-modifying MXD1 mRNA on a YTHDF2-dependent manner

Retinal vascular diseases are typified by the proliferation of irregular and leaky microvessels, resulting in vision impairment. Although the etiology of retinal angiogenesis is not yet fully understood, it is evident that microglia play a pivotal role in promoting angiogenesis. Methods: In vivo, the METTL14 conditional knockout (cKO) mouse was constructed to investigate the role of METTL14 in oxygen-induced retinopathy (OIR). In vitro, a combination of methylated RNA immunoprecipitation sequencing (MeRIP-seq), RNA-sequencing (RNA-seq), RNA Immunoprecipitation (RIP) assay, dual-luciferase reporter assays, and Chromatin immunoprecipitation-qPCR (ChIP-qPCR), was performed to explore the underlying mechanisms. Results: The proteomic analysis of hypoxic microglia has uncovered a pronounced enrichment in pathways related to RNA modification. Western blot has revealed that N6-methyladenosine (m6A) methyltransferase-like 14 (METTL14) exhibits the most significant increase among the RNA methylases. METTL14 cKO mice within an OIR model showed fewer neovascular formations. Additionally, in co-culture with sh-METTL14 HMC3 cells, HRMECs also exhibited reduced angiogenesis capabilities. Mechanically, E3 ubiquitin-protein ligase BARD1 can directly interact with METTL14, leading to an up-regulation of METTL14 protein level in hypoxic microglia. METTL14 could directly modifies and regulates the transcription factor MAX Dimerization Protein 1 (MXD1), which is subsequently recognized by the m6A "reader" YTH domain-containing family protein 2 (YTHDF2). Consequently, the modified MXD1 modulates the expression of VEGFA and VCAM1, promotes retinal neovascularization. Conclusion: Our study highlights the critical role of METTL14 in the OIR model and suggests a novel therapeutic target for addressing retinal vascular diseases.

Effect of the MIAT/microRNA 130a-3p/Pdgfra axis on retinal microglia activation in mice with chronic retinal hypoperfusion injury

This paper aimed to address the function of the MIAT/miR-130a-3p/Pdgfra axis in retinal microglia activation in chronic retinal hypoperfusion injury (CRHI) mice. CRHI mouse models were constructed through bilateral common carotid artery occlusion (BCCAO). MIAT, Pdgfra, and miR-130a-3p expression levels in retinal tissues and cells were assessed. The expression of genes linked to the Nlrp3 inflammatory vesicle pathway (Gsdmd, Asc, Tlr4, Casp1, and Casp8) was assessed. Serum contents of inflammatory cytokines IL-18 and IL-1β were determined. Iba-1/Casp1/Csdmd expression was tested. Moreover, the interplay between miR-130a-3p and MIAT, as well as associations between Pdgfra and miR-130a-3p were verified. MIAT and Pdgfra expression was enhanced and miR-130a-3p diminished in BCCAO mouse models. MIAT downregulation reduced IL-18 and IL-1β contents and repressed microglia activation in BCCAO mice, and histopathological results also displayed raised mouse retinal thickness and diminished apoptosis. Both inhibiting miR-130a-3p and overexpressing Pdgfra can reverse the delayed effects of MIAT interference on CRHI. MIAT regulates miR-130a-3p to stimulate the expression of Pdgfra, thereby further promoting retinal microglia activation in CRHI mice. This provides potential targets for the development of innovative treatment approaches for retinal disorders.

Single-cell analysis identifies MKI67+ microglia as drivers of neovascularization in proliferative diabetic retinopathy

BACKGROUND

Proliferative diabetic retinopathy (PDR) is among the primary causes of blindness in individuals with diabetes. Elevated lactate levels have been identified as a critical biomarker associated with the prognosis of PDR. While significant lactate accumulation has been observed in the vitreous fluid of PDR patients, the detailed pathways through which lactate impacts pathological neovascularization remain insufficiently elucidated.

METHODS

The study employed single-cell RNA sequencing (scRNA-seq) to identify and characterize lactate-associated cell type in PDR patients. Key gene expression profiles and molecular pathways associated with lactate metabolism were analyzed. In vitro experiments were conducted using microglial cell cultures treated with high-glucose conditions (50 mM) to assess the induction of lactate metabolism-related genes. Additionally, an oxygen-induced retinopathy (OIR) mouse model was used to evaluate the impact of abemaciclib, an FDA-approved proliferation inhibitor, on retinal neovascularization.

RESULTS

To the best of our knowledge, this investigation is the first to delineate a novel microglial subset, designated as MKI67+ microglia, distinguished by robust upregulation of genes implicated in lactate metabolic processes and proliferation, such as MKI67, PARK7 and LDHA, as well as a pronounced enrichment of glycolysis-associated molecular pathways. This unique cell type promotes angiogenesis by interacting with endothelial cells via secreted phosphoprotein 1 (SPP1)-Integrin alpha 4 (ITGA4) signaling. In vitro experiments have shown the use of 50 mM high glucose to simulate microglia in PDR environment and observe its promotion of vascular proliferation. In the in vivo OIR model, treatment with abemaciclib, a FDA-approved proliferation inhibitor, significantly reduced neovascularization.

CONCLUSION

The identification of MKI67+ microglia as a cell type strongly associated with lactate metabolism provides a novel perspective on the mechanisms underlying PDR onset. These findings expand our understanding of the cellular and metabolic dynamics in PDR, emphasizing potential implications for targeted therapeutic interventions.

Enhancing Retinal Resilience: The Neuroprotective Promise of BDNF in Diabetic Retinopathy

Diabetic retinopathy (DR), a leading cause of vision impairment worldwide, is characterized by progressive damage to the retina due to prolonged hyperglycemia. Despite advances in treatment, current interventions largely target late-stage vascular complications, leaving underlying neurodegenerative processes insufficiently addressed. This article explores the crucial role in neuronal survival, axonal growth, and synaptic plasticity and the neuroprotective potential of Brain-Derived Neurotrophic Factor (BDNF) as a therapeutic strategy for enhancing retinal resilience in DR. Furthermore, it discusses innovative delivery methods for BDNF, such as gene therapy and nanocarriers, which may overcome the challenges of achieving sustained and targeted therapeutic levels in the retina, focusing on early intervention to preserve retinal function and prevent vision loss.

The unanticipated contribution of Zap70 in retinal degeneration: Implications for microglial inflammatory activation

Inflammation is a major mechanism of photoreceptor cell death in the retina during macular degeneration leading to the blindness. In this study, we investigated the role of the kinase molecule Zap70, which is an inflammatory regulator of the systemic immune system, to elucidate the control mechanism of inflammation in the retina. We observed activated microglial cells migrated and populated the retinal layer following blue LED-induced photoreceptor degeneration and activated microglial cells in the LED-injured retina expressed Zap70, unlike the inactive microglial cells in the normal retina. Visual function was considerably decreased in blue-LED light-exposed mice, and animals with Zap70 mutations were adversely affected. Furthermore, extensive photoreceptor cell death was observed in the SKG mice, bearing a Zap70 mutation that induces autoimmune disease. In the blue-LED light-exposed groups, SKG retinas had significantly higher levels of inflammatory cytokines than those in wild-type mice. Furthermore, regulating Zap70 activity has a significant influence on microglial inflammatory state. We discovered that active microglial cells expressing Zap70 could modify vascular endothelial growth factor A (Vegfa) signaling in primary retinal pigment epithelial (RPE) cells. Our novel study revealed that the production of Zap70 by retinal microglial cells is responsible for inflammatory signals that promote apoptosis in photoreceptor cells. Furthermore, Zap70-positive microglial cells were capable of regulating Vegfa signaling in RPE cells, which matches the hallmark of macular degeneration. Overall, we discovered Zap70's inflammatory activity in the retina, which is necessary for upregulating multiple inflammatory cytokines and cell death. Zap70 represents a novel therapeutic target for treating retinal degeneration.

Proliferative Diabetic Retinopathy Microenvironment Drives Microglial Polarization and Promotes Angiogenesis and Fibrosis via Cyclooxygenase-2/Prostaglandin E2 Signaling

Diabetic retinopathy (DR) is the leading cause of visual impairment, particularly in the proliferative form (proliferative DR [PDR]). The impact of the PDR microenvironment on microglia, which are the resident immune cells in the central nervous system, and the specific pathological changes it may induce remain unclear. This study aimed to investigate the role of microglia in the progression of PDR under hypoxic and inflammatory conditions. We performed a comprehensive gene expression analysis using human-induced pluripotent stem cell-derived microglia under different stimuli (dimethyloxalylglycine (DMOG), lipopolysaccharide (LPS), and DMOG + LPS) to mimic the hypoxic inflammatory environment characteristic of PDR. Principal component analysis revealed distinct gene expression profiles, with 76 genes synergistically upregulated under combined stimulation. Notably, prostaglandin-endoperoxide synthase 2 (encoding cyclooxygenase (COX)-2) exhibited the most pronounced increase, leading to elevated prostaglandin E2 (PGE2) levels and driving pathological angiogenesis and inflammation via the COX-2/PGE2/PGE receptor 2 signaling axis. Additionally, the upregulation of the fibrogenic genes snail family transcriptional repressor 1 and collagen type I alpha 1 chain suggested a role for microglia in fibrosis. These findings underscore the critical involvement of microglia in PDR and suggest that targeting both the angiogenic and fibrotic pathways may present new therapeutic strategies for managing this condition.

Association between rest-activity rhythm and diabetic retinopathy among US middle-age and older diabetic adults

Background

The disruption of circadian rhythm has been reported to aggravate the progression of diabetic retinopathy (DR). Rest-activity rhythm (RAR) is a widely used method for measuring individual circadian time influencing behavior. In this study, we sought to explore the potential association between RAR and the risk of DR.

Methods

Diabetic participants aged over 40 from 2011-2014 National Health and Nutrition Examination Survey (NHANES) were enrolled. Data from the wearable device ActiGraph GT3X was used to generate RAR metrics, including interdaily stability (IS), intradaily variability (IV), most active 10-hour period (M10), least active 5-hour period (L5), and Relative amplitude (RA). Weighted multivariable logistic regression analysis and restricted cubic spline analysis were conducted to examine the association between RAR metrics and DR risk. Sensitivity analysis was also conducted to examine the robustness of the findings. An unsupervised K-means clustering analysis was conducted to identify patterns in IV and M10.

Results

A total of 1,096 diabetic participants were enrolled, with a DR prevalence of 20.53%. The mean age of participants was 62.3 years, with 49.57% being male. After adjusting covariates, IV was positively associated with DR (β: 3.527, 95%CI: 1.371-9.073). Compared with the lowest quintile of IV, the highest quintile of IV had 136% higher odds of DR. In contrast, M10 was negatively associated with DR (β: 0.902, 95%CI: 0.828-0.982), with participants in the highest M10 quintile showing 48.8% lower odds of DR. Restricted cubic spline analysis confirmed that these associations were linear. Meanwhile, sensitivity analysis confirmed the robustness. K-means clustering identified three distinct clusters, with participants in Cluster C (high-IV, low-M10) had a significantly higher risk of DR comparing with Cluster A (low-IV, high-M10).

Conclusion

A more fragmented rhythm and lower peak activity level might be associated with an increased risk of DR. These findings indicate that maintaining a more rhythmic sleep-activity behavior might mitigate the development of DR. Further research is necessary to establish causality and understand the underlying mechanisms, and focus on whether interventions designed to enhance daily rhythm stability and increase diurnal activity level can effectively mitigate the risk of progression of DR.