Ischaemia-induced retinal neovascularisation and diabetic retinopathy in mice with conditional knockout of hypoxia-inducible factor-1 in retinal Müller cells

Hypoxia-inducible factor activators: a novel class of oral drugs for the treatment of anemia of chronic kidney disease

Anemia is a hallmark of chronic kidney disease (CKD), worsens with disease progression, and profoundly affects a patient's well-being. Major pathogenic factors are inadequate kidney erythropoietin (EPO) production and absolute and functional iron deficiency. The 2 mainstays of current anemia treatment are a) replacement therapy with recombinant EPO or 1 of its glycosylated derivatives, administered subcutaneously or intravenously, and b) intravenous (IV) iron injections. Over the past 5 years, hypoxia-inducible factor (HIF)-prolyl hydroxylase inhibitors (HIF-PHIs) have been approved in many countries for the management of anemia in both nondialysis and dialysis-dependent patients with CKD. Due to cardiovascular safety concerns, only 2 HIF-PHIs, daprodustat and vadadustat, have been approved for marketing in the United States, and only for patients on maintenance dialysis. HIF-PHIs are oral agents that are effective at improving and maintaining hemoglobin levels by activating HIF signaling in anemic patients with CKD. They stimulate the production of endogenous EPO, increase total iron-binding capacity through their direct effects on transferrin gene transcription, lower plasma hepcidin indirectly, and have beneficial effects on red blood cell parameters. Here, we discuss the mechanisms of action and pharmacologic properties of different HIF-PHIs. We discuss unwanted on-target and off-target effects, review cardiovascular and other safety concerns, and provide a benefit/risk-based perspective on how this new class of oral drugs might impact current anemia management in CKD. A clinical case is presented that highlights the clinical complexities and therapeutic challenges in managing anemia in CKD.

Roles of noncoding RNAs in diabetic retinopathy: Mechanisms and therapeutic implications

Diabetic retinopathy (DR) is a microvascular complication of diabetes that leads to vision loss. The striking features of DR are hard exudate, cotton-wool spots, hemorrhage, and neovascularization. The dysregulated retinal cells, encompassing microvascular endothelial cells, pericytes, Müller cells, and adjacent retinal pigment epithelial cells, are involved in the pathological processes of DR. According to recent research, oxidative stress, inflammation, ferroptosis, pyroptosis, apoptosis, and angiogenesis contribute to DR. Recent advancements have highlighted that noncoding RNAs could regulate diverse targets in pathological processes that contribute to DR. Noncoding RNAs, including long noncoding RNAs, microRNAs (miRNA), and circular RNAs, are dysregulated in DR, and interact with miRNA, mRNA, or proteins to control the pathological processes of DR. Hence, modulation of noncoding RNAs may have therapeutic effects on DR. Small extracellular vesicles may be valuable tools for transferring noncoding RNAs and regulating the genes involved in progression of DR. However, the roles of noncoding RNA in developing DR are not fully understood; it is critical to summarize the mechanisms for noncoding RNA regulation of pathological processes and pathways related to DR. This review provides a fundamental understanding of the relationship between noncoding RNAs and DR, exploring the mechanism of how noncoding RNA modulates different signaling pathways, and pave the way for finding potential therapeutic strategies for DR.

Recent Insights into Roles of Hypoxia-Inducible Factors in Retinal Diseases

Hypoxia-inducible factors (HIFs) are transcriptional factors that function as strong regulators of oxygen homeostasis and cellular metabolisms. The maintenance of cellular oxygen levels is critical as either insufficient or excessive oxygen affects development and physiologic and pathologic conditions. In the eye, retinas have a high metabolic demand for oxygen. Retinal ischemia can cause visual impairment in various sight-threating disorders including age-related macular degeneration, diabetic retinopathy, and some types of glaucoma. Therefore, understanding the potential roles of HIFs in the retina is highly important for managing disease development and progression. This review focuses on the physiologic and pathologic roles of HIFs as regulators of oxygen homeostasis and cellular metabolism in the retina, drawing on recent evidence. Our summary will promote comprehensive approaches to targeting HIFs for therapeutic purposes in retinal diseases.

Characterization of the angiomodulatory effects of Interleukin 11 cis- and trans-signaling in the retina

BACKGROUND

The IL-6 cytokine family, with its crucial and pleiotropic intracellular signaling pathway STAT3, is a promising target for treating vasoproliferative retinal diseases. Previous research has shown that IL-6 cis-signaling (via membrane-bound receptors) and trans-signaling (via soluble receptors) can have distinct effects on target cells, leading to their application in various disease treatments. While IL-6 has been extensively studied, less is known about the angiogenic effects of IL-11, another member of the IL-6 family, in the retina. Therefore, the aim of this study was to characterize the effects of IL-11 on retinal angiogenesis.

MAIN TEXT

In vitreous samples from proliferative diabetic retinopathy (PDR) patients, elevated levels of IL-11Rα, but not IL-11, were detected. In vitro studies using vascular endothelial cells revealed distinct effects of cis- and trans-signaling: cis-signaling (IL-11 alone) had antiangiogenic effects, while trans-signaling (IL-11 + sIL-11Rα) had proangiogenic and pro-migratory effects. These differences can be attributed to their individual signaling responses and associated transcriptomic changes. Notably, no differences in cis- and trans-signaling were detected in primary mouse Müller cell cultures. STAT3 and STAT1 siRNA knockdown experiments revealed opposing effects on IL-11 signaling, with STAT3 functioning as an antiproliferative and proapoptotic player while STAT1 acts in opposition to STAT3. In vivo, both IL-11 and IL-11 + sIL-11Rα led to a reduction in retinal neovascularization. Immunohistochemical staining revealed Müller cell activation in response to treatment, suggesting that IL-11 affects multiple retinal cell types in vivo beyond vascular endothelial cells.

CONCLUSIONS

Cis- and trans-signaling by IL-11 have contrasting angiomodulatory effects on endothelial cells in vitro. In vivo, cis- and trans-signaling also influence Müller cells, ultimately determining the overall angiomodulatory impact on the retina, highlighting the intricate interplay between vascular and glial cells in the retina.

ROS-responsive charge reversal mesoporous silica nanoparticles as promising drug delivery system for neovascular retinal diseases

Intravitreal injection of biodegradable implant drug carriers shows promise in reducing the injection frequency for neovascular retinal diseases. However, current intravitreal ocular devices have limitations in adjusting drug release rates for individual patients, thereby affecting treatment effectiveness. Accordingly, we developed mesoporous silica nanoparticles (MSNs) featuring a surface that reverse its charge in response to reactive oxygen species (ROS) for efficient delivery of humanin peptide (HN) to retinal epithelial cells (ARPE-19). The MSN core, designed with a pore size of 2.8 nm, ensures a high HN loading capacity 64.4% (w/w). We fine-tuned the external surface of the MSNs by incorporating 20% Acetyl-L-arginine (Ar) to create a partial positive charge, while 80% conjugated thioketal (TK) methoxy polyethylene glycol (mPEG) act as ROS gatekeeper. Ex vivo experiments using bovine eyes revealed the immobilization of Ar-MSNs-TK-PEG (mean zeta potential: 2 mV) in the negatively charged vitreous. However, oxidative stress reversed the surface charge to -25 mV by mPEG loss, facilitating the diffusion of the nanoparticles impeded with HN. In vitro studies showed that ARPE-19 cells effectively internalize HN-loaded Ar-MSNs-TK, subsequently releasing the peptide, which offered protection against oxidative stress-induced apoptosis, as evidenced by reduced TUNEL and caspase3 activation. The inhibition of retinal neovascularization was further validated in an in vivo oxygen-induced retinopathy (OIR) mouse model.

Pharmacological regulation of HIF-1α, RGC death, and glaucoma

Hypoxia can regulate oxygen-sensitive pathways that could be neuroprotective to compensate for the detrimental effects of low oxygen. However, prolonged hypoxia can activate neurodegenerative pathways. HIF-1α is upregulated/stabilized in hypoxic conditions, promoting alteration of gene expression, and ultimately leading to cell-death. Therefore, regulation of HIF-1α expression pharmacologically is a vital approach to mitigate cell death. In this review, we provide information showing the role of HIF-1α and its associated pathways in ocular retinopathies. We also discuss the beneficial roles of HIF-1α inhibitor, KC7F2, in ocular pathologies. Finally, we provided our own data demonstrating RGC neuroprotection by KC7F2 in glaucomatous animals.

Pathogenesis of diabetic complications: Exploring hypoxic niche formation and HIF-1α activation

Hypoxia is a common feature of diabetic tissues, which highly correlates to the progression of diabetes. The formation of hypoxic context is induced by disrupted oxygen homeostasis that is predominantly driven by vascular remodeling in diabetes. While different types of vascular impairments have been reported, the specific features and underlying mechanisms are yet to be fully understood. Under hypoxic condition, cells upregulate hypoxia-inducible factor-1α (HIF-1α), an oxygen sensor that coordinates oxygen concentration and cell metabolism under hypoxic conditions. However, diabetic context exploits this machinery for pathogenic functions. Although HIF-1α protects cells from diabetic insult in multiple tissues, it also jeopardizes cell function in the retina. To gain a deeper understanding of hypoxia in diabetic complications, we focus on the formation of tissue hypoxia and the outcomes of HIF-1α dysregulation under diabetic context. Hopefully, this review can provide a better understanding on hypoxia biology in diabetes.

Targeting the Mitochondrial Chaperone TRAP1 Alleviates Vascular Pathologies in Ischemic Retinopathy

Activation of hypoxia-inducible factor 1α (HIF1α) contributes to blood-retinal barrier (BRB) breakdown and pathological neovascularization responsible for vision loss in ischemic retinal diseases. During disease progression, mitochondrial biology is altered to adapt to the ischemic environment created by initial vascular dysfunction, but the mitochondrial adaptive mechanisms, which ultimately contribute to the pathogenesis of ischemic retinopathy, remain incompletely understood. In the present study, it is identified that expression of mitochondrial chaperone tumor necrosis factor receptor-associated protein 1 (TRAP1) is essential for BRB breakdown and pathologic retinal neovascularization in mouse models mimicking ischemic retinopathies. Genetic Trap1 ablation or treatment with small molecule TRAP1 inhibitors, such as mitoquinone (MitoQ) and SB-U015, alleviate retinal pathologies via proteolytic HIF1α degradation, which is mediated by opening of the mitochondrial permeability transition pore and activation of calcium-dependent protease calpain-1. These findings suggest that TRAP1 can be a promising target for the development of new treatments against ischemic retinopathy, such as retinopathy of prematurity and proliferative diabetic retinopathy.

Integrated serum pharmacochemistry and serum pharmacology to investigate the active components and mechanism of Bushen Huoxue Prescription in the treatment of diabetic retinopathy

This study aimed to investigate the active components of Bushen Huoxue Prescriptions (BHP), and further clarify the mechanism by the integration of serum pharmacochemistry and serum pharmacology based on spectrum-effect relationship in vivo. In this paper, the components absorbed into serum were analyzed by ultra-high performance liquid chromatography-quadrupole-Exactive Orbitrap-high resolution mass spectrometry (UPLC-Q-Exactive Orbitrap-HRMS). And Müller cells were chosen as target cells to further investigate the mechanism. After cell purification, the well-grown cells were identified by Hematoxylin-eosin staining (HE) staining and immunofluorescence assay, such as glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS). The logarithmic phase cells were divided into normal group, model group and 12 BHP groups. The hyperglycemic and hypoxic model was induced by 50 mmol/L glucose and 1 mmol/L sodium disulfite. Enzyme-linked immunesorbnent assay (ELISA) was used to detect the expressions of five factors closely related to DR, named vascular endothelial growth factor (VEGF), hypoxia-inducible factor1-alpha (HIF-1α), protein kinase C-β (PKC-β), angiopoietin-2 (ANG-2) and transforming growth factor-β (TGF-β). Finally, the spectrum-effect relationship was investigated to screen the active components of BHP by partial least squares regression (PLSR). The results showed that 83 metabolic components, containing 30 prototypes and 53 metabolites were found in BHP serum. 12 characteristic common peaks were chosen to establish spectrum-effect relationship. Significantly, all the 12 BHP serum exhibited stronger inhibition on the expression of VEGF, PKC-β, and ANG-2, and the expression of VEGF, PKC-β, ANG-2 was chosen to establish the spectrum-effect relationship in vivo. The results of PLSR revealed that the content of methylation and sulfuration of caffeic acid, dehydroxylation and sulfation of Danshensu, daidzein, O-demethylangolanolin, cryptotanshinone, tanshinone IIA and protopanaxatriol were inversely correlated with VEGF expression of Müller cells; the areas of dihydrocaffeic acid, methylation and sulfuration of caffeic acid, dehydroxylation and sulfation of Danshensu, daidzein, cryptotanshinone, tanshinone IIA were negative correlation with the expression of PKC-β; while the coefficient of hydroxytyrosol sulfation, R-equol, O-demethylangolanolin, dihydrotanshinone IIA, hydrated cryptotanshinone, protopanaxatriol showed negative correlation with the expression of ANG-2. The above results indicated that cryptotanshinone, tanshinone IIA, daidzein and protopanaxatriol need be focused in our future research. In addition, this research idea provides feasible ways to investigate and determine pharmacodyamic material basis and screen the Q-markers of TCM and its formulas.

Diabetic complications and prospective immunotherapy

The incidence of Diabetes Mellitus is increasing globally. Individuals who have been burdened with diabetes for many years often develop complications as a result of hyperglycemia. More and more research is being conducted highlighting inflammation as an important factor in disease progression. In all kinds of diabetes, hyperglycemia leads to activation of alternative glucose metabolic pathways, resulting in problematic by-products including reactive oxygen species and advanced glycation end products. This review takes a look into the pathogenesis of three specific diabetic complications; retinopathy, nephropathy and neuropathy as well as their current treatment options. By considering recent research papers investigating the effects of immunotherapy on relevant conditions in animal models, multiple strategies are suggested for future treatment and prevention of diabetic complications with an emphasis on molecular targets associated with the inflammation.

Redox Balance in Type 2 Diabetes: Therapeutic Potential and the Challenge of Antioxidant-Based Therapy

Oxidative stress is an important factor in the development of type 2 diabetes (T2D) and associated complications. Unfortunately, most clinical studies have failed to provide sufficient evidence regarding the benefits of antioxidants (AOXs) in treating this disease. Based on the known complexity of reactive oxygen species (ROS) functions in both the physiology and pathophysiology of glucose homeostasis, it is suggested that inappropriate dosing leads to the failure of AOXs in T2D treatment. To support this hypothesis, the role of oxidative stress in the pathophysiology of T2D is described, together with a summary of the evidence for the failure of AOXs in the management of diabetes. A comparison of preclinical and clinical studies indicates that suboptimal dosing of AOXs might explain the lack of benefits of AOXs. Conversely, the possibility that glycemic control might be adversely affected by excess AOXs is also considered, based on the role of ROS in insulin signaling. We suggest that AOX therapy should be given in a personalized manner according to the need, which is the presence and severity of oxidative stress. With the development of gold-standard biomarkers for oxidative stress, optimization of AOX therapy may be achieved to maximize the therapeutic potential of these agents.

Characterization of Diabetic Retinopathy in Two Mouse Models and Response to a Single Injection of Anti-Vascular Endothelial Growth Factor

In this study, we characterized diabetic retinopathy in two mouse models and the response to anti-vascular endothelial growth factor (VEGF) injection. The study was conducted in 58 transgenic, non-obese diabetic (NOD) mice with spontaneous type 1 diabetes (n = 30, DMT1-NOD) or chemically induced (n = 28, streptozotocin, STZ-NOD) type 1 diabetes and 20 transgenic db/db mice with type 2 diabetes (DMT2-db/db); 30 NOD and 8 wild-type mice served as controls. Mice were examined at 21 days for vasculopathy, retinal thickness, and expression of genes involved in oxidative stress, angiogenesis, gliosis, and diabetes. The right eye was histologically examined one week after injection of bevacizumab, ranibizumab, saline, or no treatment. Flat mounts revealed microaneurysms and one apparent area of tufts of neovascularization in the diabetic retina. Immunostaining revealed activation of Müller glia and prominent Müller cells. Mean retinal thickness was greater in diabetic mice. RAGE increased and GFAP decreased in DMT1-NOD mice; GFAP and SOX-9 mildly increased in db/db mice. Anti-VEGF treatment led to reduced retinal thickness. Retinas showed vasculopathy and edema in DMT1-NOD and DMT2-db/db mice and activation of Müller glia in DMT1-NOD mice, with some response to anti-VEGF treatment. Given the similarity of diabetic retinopathy in mice and humans, comparisons of type 1 and type 2 diabetic mouse models may assist in the development of new treatment modalities.

A novel and atypical NF-KB pro-inflammatory program regulated by a CamKII-proteasome axis is involved in the early activation of Muller glia by high glucose

Background

Diabetic retinopathy (DR) is a microvascular complication of diabetes with a heavy impact on the quality of life of subjects and with a dramatic burden for health and economic systems on a global scale. Although the pathogenesis of DR is largely unknown, several preclinical data have pointed out to a main role of Muller glia (MG), a cell type which spans across the retina layers providing nourishment and support for Retina Ganglion Cells (RGCs), in sensing hyper-glycemia and in acquiring a pro-inflammatory polarization in response to this insult.

Results

By using a validated experimental model of DR in vitro, rMC1 cells challenged with high glucose, we uncovered the induction of an early (within minutes) and atypical Nuclear Factor-kB (NF-kB) signalling pathway regulated by a calcium-dependent calmodulin kinase II (CamKII)-proteasome axis. Phosphorylation of proteasome subunit Rpt6 (at Serine 120) by CamKII stimulated the accelerated turnover of IkBα (i.e., the natural inhibitor of p65-50 transcription factor), regardless of the phosphorylation at Serine 32 which labels canonical NF-kB signalling. This event allowed the p65-p50 heterodimer to migrate into the nucleus and to induce transcription of IL-8, Il-1β and MCP-1. Pharmacological inhibition of CamKII as well as proteasome inhibition stopped this pro-inflammatory program, whereas introduction of a Rpt6 phospho-dead mutant (Rpt6-S120A) stimulated a paradoxical effect on NF-kB probably through the activation of a compensatory mechanism which may involve phosphorylation of 20S α4 subunit.

Conclusions

This study introduces a novel pathway of MG activation by high glucose and casts some light on the biological relevance of proteasome post-translational modifications in modulating pathways regulated through targeted proteolysis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00839-x.

High glucose quickly induces an atypical NF-kB pro-inflammatory program.

CamKII phosphorylation of Rpt6 subunit of the proteasome stimulates IkBα turnover and p65-p50 release.

Inhibition of either CamkII or proteasome blocks this pathway.

Spleen Tyrosine Kinase Contributes to Müller Glial Expression of Proangiogenic Cytokines in Diabetes

Purpose

Neuroglial dysfunction occurs early in the progression of diabetic retinopathy. In response to diabetes or hypoxia, Müller glia secrete cytokines and growth factors that contribute to disease progression. This study was designed to examine common signaling pathways activated in Müller glia by both type 1 and pre-/type 2 diabetes.

Methods

RiboTag (Pdgfra-cre;HA-Rpl22) mice were used to compare the impact of streptozotocin (STZ) and a high-fat, high-sucrose (HFHS) diet on ribosome association of mRNAs in Müller glia by RNA sequencing analysis. Human MIO-M1 Müller cells were exposed to either hyperglycemic or hypoxic culture conditions. Genetic manipulation and pharmacologic inhibition were used to interrogate signaling pathways.

Results

Association of mRNAs encoding triggering receptor expressed on myeloid cells 2 (TREM2), DNAX-activating protein 12 kDa (DAP12), and colony stimulating factor 1 receptor (CSF1R) with ribosomes isolated from Müller glia was upregulated in both STZ diabetic mice and mice fed an HFHS diet. The TREM2/DAP12 receptor-adaptor complex signals in coordination with CSF1R to activate spleen tyrosine kinase (SYK). SYK activation was enhanced in the retina of diabetic mice and in human MIO-M1 Müller cell cultures exposed to hyperglycemic or hypoxic culture conditions. DAP12 knockdown reduced SYK autophosphorylation in Müller cells exposed to hyperglycemic or hypoxic conditions. SYK inhibition or DAP12 knockdown suppressed hypoxia-induced expression of the transcription factor hypoxia-inducible factor 1⍺ (HIF1⍺), as well as expression of vascular endothelial growth factor and angiopoietin-like 4.

Conclusions

The findings support TREM2/DAP12 receptor-adaptor complex signaling via SYK to promote HIF1α stabilization and increased angiogenic cytokine production by Müller glia.

Effect of bone marrow mesenchymal stem cells-derived exosomes on diabetes-induced retinal injury: Implication of Wnt/ b-catenin signaling pathway

BACKGROUND

Diabetic retinopathy (DR) is a serious microvascular complication of diabetes mellitus. Mesenchymal stem cells are currently studied as therapeutic strategy for management of DR. Exosomes, considered as a promising cell-free therapy option, display biological functions similar to those of their parent cells. In retinal development, Wnt/b-catenin signaling provides key cues for functional progression. The present study aimed to evaluate the potential efficacy of bone marrow-derived mesenchymal stem cell-derived exosomes (BM-MSCs-Ex) in diabetes-induced retinal injury via modulation of the Wnt/ b-catenin signaling pathway.

METHODS

Eighty-one rats were allocated into 6 groups (control, DR, DR + DKK1, DR + exosomes, DR + Wnt3a and DR + exosomes+Wnt3a). Evaluation of each group was via histopathological examination, assessment of gene and/or protein expression concerned with oxidative stress (SOD1, SOD2, Nox2, Nox4, iNOS), inflammation (TNF-α, ICAM-1, NF-κB) and angiogenesis (VEGF, VE-cadherin).

RESULTS

Results demonstrated that exosomes blocked the wnt/b-catenin pathway in diabetic retina concomitant with significant reduction of features of DR as shown by downregulation of retinal oxidants, upregulation of antioxidant enzymes, suppression of retinal inflammatory and angiogenic markers. These results were further confirmed by histopathological results, fundus examination and optical coherence tomography. Additionally, exosomes ameliorative effects abrogated wnt3a-triggered retinal injury in DR.

CONCLUSION

Collectively, these data demonstrated that exosomes ameliorated diabetes-induced retinal injury via suppressing Wnt/ b-catenin signaling with subsequent reduction of oxidative stress, inflammation and angiogenesis.

Combination of pigment epithelium derived factor with anti-vascular endothelial growth factor therapy protects the neuroretina from ischemic damage

Ocular ischemia is a vision-threatening disease, and is a medical condition associated with many ocular diseases. Anti-VEGF therapy has limitations related to its side effects and suppression of physiological revascularization. Pigment epithelium derived factor (PEDF) has anti-angiogenesis and neurotrophic neuroprotective functions and is a promising agent in the treatment of ischemia-induced retinal neurodegeneration. The purpose of this study is to investigate the effect of PEDF and anti-VEGF and the combined therapy on the ischemic rat eye model ex vivo. In this study, the PEDF protein, anti-VEGF drug (Avastin) or the combination of PEDF and Avastin were intravitreally injected immediately after eye enucleation. Then the eyes were incubated in Dulbecco's modified eagle medium (DMEM) at 4 ℃ for 14 h. After that the eyes were fixed immediately by formalin. VEGF, PEDF and glial fibrillary acidic protein (GFAP) were detected by immunohistochemical (IHC) staining. The IHC staining intensity was evaluated for each eye. Compared to the groups treated by vehicle, PEDF, and anti-VEGF alone, the value of staining intensity of VEGF and GFAP was significantly reduced in the retina and choroidal vessels of the PEDF/Anti-VEGF treatment group. The intravitreally injected PEDF protein can locate in the retina and the choroidal vessels. Compared to the vehicle-treatment group, both the PEDF-treatment and the PEDF/Anti-VEGF treatment groups showed significantly decreased number of TUNEL-positive nuclei, and the PEDF/Anti-VEGF treatment group had the least TUNEL-positive nuclei. Combination of PEDF and an anti-VEGF drug (Avastin) is a possible therapeutic strategy against ischemic retinal and choroidal diseases.

A Mechanistic Exploratory Study on the Therapeutic Efficacy of Astragaloside IV Against Diabetic Retinopathy Revealed by Network Pharmacology

Purpose: Diabetic retinopathy (DR) is a serious complication of diabetes mellitus, which nearly happens to all the diabetic sufferers. This study aims to identify the preliminary molecular regulation involved in the therapeutic efficacy of astragaloside IV (AS- IV) for DR.

Methods: Diabetic rat models were established and treated with AS-IV. Optical coherence tomography (OCT) and Hematoxylin-eosin (HE) staining was employed to demonstrate the histopathological changes. The main targets of AS-IV were identified by searching from public databases of traditional Chinese medicine (GeneCards, PharmMapper and Swiss Target Prediction). Besides, disease targets of DR were also obtained by integrated data from GEO datasets and predicted from public databases. Protein-protein interaction (PPI) network was constructed by Cytoscape with overlapping genes and 10 core targets were selected, on which Gene Ontology (GO) along with Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis were conducted. The interaction between AS-IV and these crucial genes were analyzed using molecular docking. RT-qPCR and western blot were used to verify the expression variation of core targets.

Results: OCT imaging and HE staining demonstrated that AS-IV administration significantly increased retinal thickness in diabetic rats, obviously alleviating DR induced histopathological changes as well as elevated blood glucose levels. 107 common targets of AS-IV and DR were determined after intersection. PPI network analysis filtered 10 hub genes potentially targeted by AS-IV, including VEGFA, CASP3, HIF1α, STAT3, CTNNB1, SRC, AKT1, EGFR, IL1β and IL6. Enrichment analysis indicated that these genes were mainly enriched in biological processes like T cell activation, epithelial cell proliferation and protein kinase B signaling, and involved in oxidative stress, apoptosis and inflammation-related pathways. The molecular docking prediction suggested that AS-IV exhibited stable binding to these core targets. In addition, mRNA levels of core targets in diabetic rats were differentially expressed before and after AS-IV treatment. Western blot further revealed that AS-IV treatment elevated DR-depressed protein levels of PI3K and AKT.

Conclusion: Our study elucidated the effect of AS-IV in attenuating retinopathy induced by diabetes in rats and preliminarily unveiled the therapeutic efficacy of AS-IV in the treatment of DR might be attributed to activation of PI3K-AKT signaling pathway.

A Novel Hypoxia-inducible Factor 1α Inhibitor KC7F2 Attenuates Oxygen-induced Retinal Neovascularization

Purpose

KC7F2 is a novel molecule compound that can inhibit the translation of hypoxia-inducible factor 1α (HIF1α). It has been reported to exhibit potential antiangiogenic effect. We hypothesized that KC7F2 could inhibit oxygen-induced retinal neovascularization (RNV). The purpose of this study was to investigate this assumption.

Methods

Oxygen-induced retinopathy (OIR) models in C57BL/6J mice and Sprague-Dawley rats were used for in vivo study. After intraperitoneal injections of KC7F2, RNV was detected by immunofluorescence and hematoxylin and eosin staining. Retinal inflammation was explored by immunofluorescence. EdU incorporation assay, cell counting kit-8 assay, scratch test, transwell assay, and Matrigel assay were used to evaluate the effect of KC7F2 on the proliferation, migration and tube formation of human umbilical vein endothelial cells (HUVEC) induced by vascular endothelial growth factor (VEGF) in vitro. Protein expression was examined by Western blot.

Results

KC7F2 treatment (10 mg/kg/d) in OIR mice significantly attenuated pathological neovascularization and decreased the number of preretinal neovascular cell nuclei, without changing the avascular area, which showed the same trends in OIR rats. Consistently, after the KC7F2 intervention (10 µM), cell proliferation was inhibited in VEGF-induced HUVEC, which was in agreement with the trend observed in the retinas of OIR mice. Meanwhile, KC7F2 suppressed VEGF-induced HUVEC migration and tube formation, and decreased the density of leukocytes and microglia colocalizing neovascular areas in the retinas. Moreover, the HIF1α–VEGF pathway activated in retinas of OIR mice and hypoxia-induced HUVEC, was suppressed by KC7F2 treatment.

Conclusions

The current study revealed that KC7F2 was able to inhibit RNV effectively via HIF1α–VEGF pathway, suggesting that it might be an effective drug for RNV treatment.

Ocular Hypertension Results in Hypoxia within Glia and Neurons throughout the Visual Projection

The magnitude and duration of hypoxia after ocular hypertension (OHT) has been a matter of debate due to the lack of tools to accurately report hypoxia. In this study, we established a topography of hypoxia in the visual pathway by inducing OHT in mice that express a fusion protein comprised of the oxygen-dependent degradation (ODD) domain of HIF-1α and a tamoxifen-inducible Cre recombinase (CreERT2) driven by a ubiquitous CAG promoter. After tamoxifen administration, tdTomato expression would be driven in cells that contain stabilized HIF-1α. Intraocular pressure (IOP) and visual evoked potential (VEP) were measured after OHT at 3, 14, and 28 days (d) to evaluate hypoxia induction. Immunolabeling of hypoxic cell types in the retina and optic nerve (ON) was performed, as well as retinal ganglion cell (RGC) and axon number quantification at each time point (6 h, 3 d, 14 d, 28 d). IOP elevation and VEP decrease were detected 3 d after OHT, which preceded RGC soma and axon loss at 14 and 28 d after OHT. Hypoxia was detected primarily in Müller glia in the retina, and microglia and astrocytes in the ON and optic nerve head (ONH). Hypoxia-induced factor (HIF-α) regulates the expression of glucose transporters 1 and 3 (GLUT1, 3) to support neuronal metabolic demand. Significant increases in GLUT1 and 3 proteins were observed in the retina and ON after OHT. Interestingly, neurons and endothelial cells within the superior colliculus in the brain also experienced hypoxia after OHT as determined by tdTomato expression. The highest intensity labeling for hypoxia was detected in the ONH. Initiation of OHT resulted in significant hypoxia that did not immediately resolve, with low-level hypoxia apparent out to 14 and 28 d, suggesting that continued hypoxia contributes to glaucoma progression. Restricted hypoxia in retinal neurons after OHT suggests a hypoxia management role for glia.

Biochemical mechanism underlying the pathogenesis of diabetic retinopathy and other diabetic complications in humans: the methanol-formaldehyde-formic acid hypothesis

Hyperglycemia in diabetic patients is associated with abnormally-elevated cellular glucose levels. It is hypothesized that increased cellular glucose will lead to increased formation of endogenous methanol and/or formaldehyde, both of which are then metabolically converted to formic acid. These one-carbon metabolites are known to be present naturally in humans, and their levels are increased under diabetic conditions. Mechanistically, while formaldehyde is a cross-linking agent capable of causing extensive cytotoxicity, formic acid is an inhibitor of mitochondrial cytochrome oxidase, capable of inducing histotoxic hypoxia, ATP deficiency and cytotoxicity. Chronic increase in the production and accumulation of these toxic one-carbon metabolites in diabetic patients can drive the pathogenesis of ocular as well as other diabetic complications. This hypothesis is supported by a large body of experimental and clinical observations scattered in the literature. For instance, methanol is known to have organ- and species-selective toxicities, including the characteristic ocular lesions commonly seen in humans and non-human primates, but not in rodents. Similarly, some of the diabetic complications (such as ocular lesions) also have a characteristic species-selective pattern, closely resembling methanol intoxication. Moreover, while alcohol consumption or combined use of folic acid plus vitamin B is beneficial for mitigating acute methanol toxicity in humans, their use also improves the outcomes of diabetic complications. In addition, there is also a large body of evidence from biochemical and cellular studies. Together, there is considerable experimental support for the proposed hypothesis that increased metabolic formation of toxic one-carbon metabolites in diabetic patients contributes importantly to the development of various clinical complications.

Neurovascular abnormalities in retinopathy of prematurity and emerging therapies

Blood vessels in the developing retina are formed in concert with neural growth, resulting in functional neurovascular network. Disruption of the neurovascular coordination contributes to the pathogenesis of retinopathy of prematurity (ROP), a potentially blinding retinal neovascular disease in preterm infants that currently lacks an approved drug therapy in the USA. Despite vasculopathy as predominant clinical manifestations, an increasing number of studies revealed complex neurovascular interplays among neurons, glial cells and blood vessels during ROP. Coordinated expression of glia-derived vascular endothelial growth factor (VEGF) in spatio-temporal gradients is pivotal to the formation of well-organized vascular plexuses in the healthy retina, whereas uncoordinated VEGF expression triggers pathological angiogenesis with disorganized vascular tufts in ROP. In contrast with VEGF driving both pathological and physiological angiogenesis, neuron-derived angiogenic factor secretogranin III (Scg3) stringently regulates ROP but not healthy retinal vessels in animal models. Anti-VEGF and anti-Scg3 therapies confer similar high efficacies to alleviate ROP in preclinical studies but are distinct in their disease selectivity and safety. This review discusses neurovascular communication among retinal blood vessels, neurons and glial cells during retinal development and ROP pathogenesis and summarizes the current and emerging therapies to address unmet clinical needs for the disease.

Amelioration of endothelial dysfunction by sodium glucose co-transporter 2 inhibitors: pieces of the puzzle explaining their cardiovascular protection

Sodium glucose co‐transporter 2 inhibitors (SGLT‐2is) improve cardiovascular outcomes in both diabetic and non‐diabetic patients. Preclinical studies suggest that SGLT‐2is directly affect endothelial function in a glucose‐independent manner. The effects of SGLT‐2is include decreased oxidative stress and inflammatory reactions in endothelial cells. Furthermore, SGLT2is restore endothelium‐related vasodilation and regulate angiogenesis. The favourable cardiovascular effects of SGLT‐2is could be mediated via a number of pathways: (1) inhibition of the overactive sodium‐hydrogen exchanger; (2) decreased expression of nicotinamide adenine dinucleotide phosphate oxidases; (3) alleviation of mitochondrial injury; (4) suppression of inflammation‐related signalling pathways (e.g., by affecting NF‐κB); (5) modulation of glycolysis; and (6) recovery of impaired NO bioavailability. This review focuses on the most recent progress and existing gaps in preclinical investigations concerning the direct effects of SGLT‐2is on endothelial dysfunction and the mechanisms underlying such effects.

tiRNA-Val promotes angiogenesis via Sirt1–Hif-1α axis in mice with diabetic retinopathy

Background

Diabetic retinopathy (DR) is a specific microvascular complication arising from diabetes, and its pathogenesis is not completely understood. tRNA-derived stress-induced RNAs (tiRNAs), a new type of small noncoding RNA generated by specific cleavage of tRNAs, has become a promising target for several diseases. However, the regulatory function of tiRNAs in DR and its detailed mechanism remain unknown.

Results

Here, we analyzed the tiRNA profiles of normal and DR retinal tissues. The expression level of tiRNA-Val was significantly upregulated in DR retinal tissues. Consistently, tiRNA-Val was upregulated in human retinal microvascular endothelial cells (HRMECs) under high glucose conditions. The overexpression of tiRNA-Val enhanced cell proliferation and inhibited cell apoptosis in HRMECs, but the knockdown of tiRNA-Val decreased cell proliferation and promoted cell apoptosis. Mechanistically, tiRNA-Val, derived from mature tRNA-Val with Ang cleavage, decreased Sirt1 expression level by interacting with sirt1 3'UTR, leading to the accumulation of Hif-1α, a key target for DR. In addition, subretinal injection of adeno-associated virus to knock down tiRNA-Val in DR mice ameliorated the symptoms of DR.

Conclusion

tiRNA-Val enhance cell proliferation and inhibited cell apoptosis via Sirt1/Hif-1α pathway in HRMECs of DR retinal tissues.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40659-022-00381-7.

PAI-1 is a vascular cell-specific HIF-2-dependent angiogenic factor that promotes retinal neovascularization in diabetic patients

For patients with proliferative diabetic retinopathy (PDR) who do not respond adequately to pan-retinal laser photocoagulation (PRP) or anti-vascular endothelial growth factor (VEGF) therapies, we hypothesized that vascular cells within neovascular tissue secrete autocrine/paracrine angiogenic factors that promote disease progression. To identify these factors, we performed multiplex ELISA angiogenesis arrays on aqueous fluid from PDR patients who responded inadequately to anti-VEGF therapy and/or PRP and identified plasminogen activator inhibitor-1 (PAI-1). PAI-1 expression was increased in vitreous biopsies and neovascular tissue from PDR eyes, limited to retinal vascular cells, regulated by the transcription factor hypoxia-inducible factor (HIF)-2α, and necessary and sufficient to stimulate angiogenesis. Using a pharmacologic inhibitor of HIF-2α (PT-2385) or nanoparticle-mediated RNA interference targeting Pai1, we demonstrate that the HIF-2α/PAI-1 axis is necessary for the development of retinal neovascularization in mice. These results suggest that targeting HIF-2α/PAI-1 will be an effective adjunct therapy for the treatment of PDR patients.

DIX domain containing 1 (DIXDC1) modulates VEGFR2 level in vasculatures to regulate embryonic and postnatal retina angiogenesis

Background

In sprouting angiogenesis, VEGFR2 level is regulated via a fine-tuned process involving various signaling pathways. Other than VEGF/VEGFR2 signaling pathway, Wnt/ β-catenin signaling is also important in vascular development. However, the crosstalk between these two signaling pathways is still unknown to date. In this study, we aimed to investigate the role of DIX domain containing 1 (DIXDC1) in vasculature, facilitating the crosstalk between VEGF/VEGFR2 and Wnt/ β-catenin signaling pathways.

Results

In mice, DIXDC1 deficiency delayed angiogenesis at the embryonic stage and suppressed neovascularization at the neonatal stage. DIXDC1 knockdown inhibited VEGF-induced angiogenesis in endothelial cells in vitro by downregulating VEGFR2 expression. DIXDC1 bound Dishevelled Segment Polarity Protein 2 (Dvl2) and polymerized Dvl2 stabilizing VEGFR2 protein via its direct interaction. The complex formation and stability of VEGFR2 was potentiated by Wnt signaling. Moreover, hypoxia elevated DIXDC1 expression and likely modulated both canonical Wnt/β-catenin signaling and VEGFR2 stability in vasculatures. Pathological angiogenesis in DIXDC1 knockout mice was decreased significantly in oxygen-induced retinopathy (OIR) and in wound healing models. These results suggest that DIXDC1 is an important factor in developmental and pathological angiogenesis.

Conclusion

We have identified DIXDC1 as an important factor in early vascular development. These results suggest that DIXDC1 represents a novel regulator of sprouting angiogenesis that links Wnt signaling and VEGFR2 stability and may have a potential role in pathological neovascularization.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01240-3.

Relevance of Peptide Homeostasis in Metabolic Retinal Degenerative Disorders: Curative Potential in Genetically Modified Mice

The mammalian retina contains approximately 30 neuropeptides that are synthetized by different neuronal cell populations, glia, and the pigmented epithelium. The presence of these neuropeptides leaves a mark on normal retinal molecular processes and physiology, and they are also crucial in fighting various pathologies (e.g., diabetic retinopathy, ischemia, age-related pathologies, glaucoma) because of their protective abilities. Retinal pathologies of different origin (metabolic, genetic) are extensively investigated by genetically manipulated in vivo mouse models that help us gain a better understanding of the molecular background of these pathomechanisms. These models offer opportunities to manipulate gene expression in different cell types to help reveal their roles in the preservation of retinal health or identify malfunction during diseases. In order to assess the current status of transgenic technologies available, we have conducted a literature survey focused on retinal disorders of metabolic origin, zooming in on the role of retinal neuropeptides in diabetic retinopathy and ischemia. First, we identified those neuropeptides that are most relevant to retinal pathologies in humans and the two clinically most relevant models, mice and rats. Then we continued our analysis with metabolic disorders, examining neuropeptide-related pathways leading to systemic or cellular damage and rescue. Last but not least, we reviewed the available literature on genetically modified mouse strains to understand how the manipulation of a single element of any given pathway (e.g., signal molecules, receptors, intracellular signaling pathways) could lead either to the worsening of disease conditions or, more frequently, to substantial improvements in retinal health. Most attention was given to studies which reported successful intervention against specific disorders. For these experiments, a detailed evaluation will be given and the possible role of converging intracellular pathways will be discussed. Using these converging intracellular pathways, curative effects of peptides could potentially be utilized in fighting metabolic retinal disorders.

Monoclonal antibodies in diabetic retinopathy

INTRODUCTION

Diabetic retinopathy (DR), as one of the main complications of diabetes, is among the leading causes of blindness and visual impairment worldwide.

AREAS COVERED

Current clinical therapies include photocoagulation, vitrectomy, and anti-vascular endothelial growth factor (VEGF) therapies. Bevacizumab and ranibizumab are two monoclonal antibodies (mAbs) inhibiting angiogenesis. Intravitreal ranibizumab and bevacizumab can decrease the rate of blindness and retinal thickness, and improve visual acuity whether as monotherapy or combined with other treatments. They can increase the efficacy of other treatments and decrease their adverse events. Although administered intravitreally, they also might enter the circulation and cause systemic effects. This study is aimed to review our current knowledge about mAbs, bevacizumab and ranibizumab, in DR including superiorities, challenges, and limitations. Meanwhile, we tried to shed light on new ideas to overcome these limitations. Our latest search was done in April 2021 mainly through PubMed and Google Scholar. Relevant clinical studies were imported.

EXPERT OPINION

Future direction includes detection of more therapeutic targets considering other components of DR pathophysiology and shared pathogenesis of DR and neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease, the treat-and-extend regimen, and new ways of drug delivery and other routes of ocular drug administration.

Comparative Analysis Reveals Novel Changes in Plasma Metabolites and Metabolomic Networks of Infants With Retinopathy of Prematurity

Purpose

Advances in mass spectrometry have provided new insights into the role of metabolomics in the etiology of several diseases. Studies on retinopathy of prematurity (ROP), for example, overlooked the role of metabolic alterations in disease development. We employed comprehensive metabolic profiling and gold-standard metabolic analysis to explore major metabolites and metabolic pathways, which were significantly affected in early stages of pathogenesis toward ROP.

Methods

This was a multicenter, retrospective, matched-pair, case-control study. We collected plasma from 57 ROP cases and 57 strictly matched non-ROP controls. Non-targeted ultra-high-performance liquid chromatography-tandem mass spectroscopy (UPLC-MS/MS) was used to detect the metabolites. Machine learning was employed to reveal the most affected metabolites and pathways in ROP development.

Results

Compared with non-ROP controls, we found a significant metabolic perturbation in the plasma of ROP cases, which featured an increase in the levels of lipids, nucleotides, and carbohydrate metabolites and lower levels of peptides. Machine leaning enabled us to distinguish a cluster of metabolic pathways (glycometabolism, redox homeostasis, lipid metabolism, and arginine pathway) were strongly correlated with the development of ROP. Moreover, the severity of ROP was associated with the levels of creatinine and ribitol; also, overactivity of aerobic glycolysis and lipid metabolism was noted in the metabolic profile of ROP.

Conclusions

The results suggest a strong correlation between metabolic profiling and retinal neovascularization in ROP pathogenesis. These findings provide an insight into the identification of novel metabolic biomarkers for the diagnosis and prevention of ROP, but the clinical significance requires further validation.

The Role of HIF1α-PFKFB3 Pathway in Diabetic Retinopathy

Diabetic retinopathy (DR) is the leading cause of blindness for adults in developed countries. Both microvasculopathy and neurodegeneration are implicated in mechanisms of DR development, with neuronal impairment preceding microvascular abnormalities, which is often underappreciated in the clinic. Most current therapeutic strategies, including anti-vascular endothelial growth factor (anti-VEGF)-antibodies, aim at treating the advanced stages (diabetic macular edema and proliferative diabetic retinopathy) and fail to target the neuronal deterioration. Hence, new therapeutic approach(es) intended to address both vascular and neuronal impairment are urgently needed. The hypoxia-inducible factor 1α (HIF1α)-6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) pathway is critically implicated in the islet pathology of diabetes. Recent evidence highlighted the pathway relevance for pathologic angiogenesis and neurodegeneration, two key aspects in DR. PFKFB3 is key to the sprouting angiogenesis, along with VEGF, by determining the endothelial tip-cell competition. Also, PFKFB3-driven glycolysis compromises the antioxidative capacity of neurons leading to neuronal loss and reactive gliosis. Therefore, the HIF1α-PFKFB3 signaling pathway is unique as being a pervasive pathological component across multiple cell types in the retina in the early as well as late stages of DR. A metabolic point-of-intervention based on HIF1α-PFKFB3 targeting thus deserves further consideration in DR.

Polymorphisms in HIF-1a gene are not associated with diabetic retinopathy in China

BACKGROUND

It has been reported that vascular endothelial growth factor (VEGF) is a susceptibility gene for both type 2 diabetes mellitus (T2DM) and diabetic retinopathy (DR). In response to hypoxia, VEGF mRNA levels are increased, which is mainly mediated by the binding of hypoxia-inducible factor-1 (HIF-1) and hypoxia response element upstream of the transcriptional start site of VEGF. Therefore, HIF-1a is supposed to be involved in pathology of DR.

AIM

To investigate whether the polymorphisms in HIF-1a gene are associated with DR.

METHODS

Two hundred and ninety-nine type 2 diabetic patients (128 males and 171 females) and 144 healthy volunteers were recruited. Mean age was 56.04 ± 21.05 years. According to the results of fundus fluorescein angiography and examination of ophthalmoscopy, patients were divided into two groups, DNR group (diabetes without retinopathy) and DR group (diabetes with retinopathy). There are 150 cases in DNR group and 149 cases in DR group. Two single nucleotide polymorphisms (SNP) of the HIF-1a gene were tested using matrix-assisted laser desorption/Ionization time of flight mass spectrometry. The frequency of genotypes and alleles, and odds ratio were measured.

RESULTS

The mean age of the cases with diabetes was 55.84 ± 3.66 years, the mean age of the cases with DR was 55.97 ± 4.66 years and that of controls was 56.32 ± 4.70 years. Two variations were found in 76 patients. Rs11549465 is the change of C-T base, rs11549467 is the change of G-A base. The rs11549467 G/A genotype was 5.33% in diabetes and 6.04% in DR patients, respectively. The rs11549465 C/T genotype was 10% and 12.75% in patients with diabetes and DR. The rs11549467 A allele frequencies and rs11549465 T frequencies was similar to that of controls. Paired SNP linkage disequilibrium analysis indicated that rs11549467 was in linkage disequilibrium with rs11549465. Haplotype association analysis denoted that the haplotype association exhibited similar distribution in the patients compared to the normal controls.

CONCLUSION

This study suggests that there is no relationship between the genetic variations of HIF1a and diabetes or DR.

Celastrol inhibits the proliferation and angiogenesis of high glucose-induced human retinal endothelial cells

Background

Diabetic retinopathy (DR) is one of the most common microvascular complications of diabetes. Celastrol plays a certain role in the improvement of various diabetes complications. Therefore, this study aimed to explore whether celastrol inhibited the proliferation and angiogenesis of high glucose (HG)-induced human retinal endothelial cells (hRECs) by down-regulating the HIF1/VEGF signaling pathway.

Methods

The viability and proliferation of hRECs treated with glucose, celastrol or dimethyloxallyl glycine (DMOG) were analyzed by MTT assay. The invasion and tube formation ability of hRECs treated with glucose, celastrol or DMOG were in turn detected by transwell assay and tube formation assay. The expression of HIF1α and VEGF in hRECs after indicated treatment was analyzed by Western blot analysis and RT-qPCR analysis and ICAM-1 expression in hRECs after indicated treatment was detected by immunofluorescence assay

Results

HG induction promoted the proliferation, invasion and tube formation ability and increased the expression of HIF-1α and VEGF of hRECs, which were gradually suppressed by celastrol changing from 0.5 to 2.0 μM. DMOG was regarded as a HIF1α agonist, which attenuated the effect of celastrol on HG-induced hRECs.

Conclusion

Celastrol inhibited the proliferation and angiogenesis of HG-induced hRECs by down-regulating the HIF1α/VEGF signaling pathway.

Hypoxia-inducible factor-prolyl hydroxylase inhibitors in the treatment of anemia of chronic kidney disease

Hypoxia-inducible factor-prolyl hydroxylase domain inhibitors (HIF-PHIs) are a promising new class of orally administered drugs currently in late-stage global clinical development for the treatment of anemia of chronic kidney disease (CKD). HIF-PHIs activate the HIF oxygen-sensing pathway and are efficacious in correcting and maintaining hemoglobin levels in patients with non-dialysis- and dialysis-dependent CKD. In addition to promoting erythropoiesis through the increase in endogenous erythropoietin production, HIF-PHIs reduce hepcidin levels and modulate iron metabolism, providing increases in total iron binding capacity and transferrin levels, and potentially reducing the need for i.v. iron supplementation. Furthermore, HIF-activating drugs are predicted to have effects that extend beyond erythropoiesis. This review summarizes clinical data from current HIF-PHI trials in patients with anemia of CKD, discusses mechanisms of action and pharmacologic properties of HIF-PHIs, and deliberates over safety concerns and potential impact on anemia management in patients with CKD.

Retinal hypoxia and angiogenesis with methamphetamine

Central retinal artery occlusion, retinopathy, and retinal neovascularization have been reported in methamphetamine (METH) abusers. In the current study, we investigated whether METH induces retinal neovascularization in a mouse model, and if so, whether the neovascularization is associated with increased hypoxia, hypoxia-inducible factor 1α (HIF-1α), and vascular endothelial growth factor (VEGF). Mice were administrated METH by intraperitoneal injection over a 26-day period, or injected with saline as a vehicle control. The number of retinal arterioles and venules were counted using in vivo live imaging following infusion with fluorescein isothiocyanate-dextran. Excised retinas were stained with griffonia simplicifolia lectin I and flat mounted for a measurement of vascularity (length of vessels per tissue area) with AngioTool. Retinal hypoxia was examined by formation of pimonidazole adducts with an anti-pimonidazole antibody, and HIF-1α and VEGFa protein levels in the retina were detected by immunoblot. METH administration increased vascularity (including the number of arterioles) measured on Day 26. Retinal VEGFa protein level was not changed in METH-treated mice on Day 5, but was increased on Day 12 and Day 26. Hypoxia (pimonidazole adduct formation) was increased in retinas of METH-treated mice on Day 12 and Day 26, as were HIF-1α protein expression levels. These results indicate that METH administration induces hypoxia, HIF-1α, VEGFa, and angiogenesis in the retina.

Lymphocytic microparticles suppress retinal angiogenesis via targeting Müller cells in the ischemic retinopathy mouse model

Retinopathy of prematurity (ROP) is the primary cause of visual impairment and vision loss in premature infants, which results from the formation of aberrant retinal neovascularization (NV). An emerging body of evidence has shown that Müller cells are the predominant source of vascular endothelial growth factor (VEGF), which also serves as a chemoattractant for monocyte/macrophage lineage. The recruitment of macrophages is increased during retinal NV, and they exert a pro-angiogenic role in ROP. We have shown that lymphocytic microparticles (microvesicles; LMPs) derived from apoptotic human T lymphocytes possess strong angiogenesis-inhibiting properties. Here, we investigated the effect of LMPs on the chemotactic capacity of Müller cells in vitro using rat Müller cell rMC-1 and mouse macrophage RAW 264.7. In addition, the impact of LMPs was determined in vivo using a mouse model of oxygen-induced ischemic retinopathy (OIR). The results revealed that LMPs were internalized by rMC-1 and reduced their cell proliferation dose-dependently without inducing cell apoptosis. LMPs inhibited the chemotactic capacity of rMC-1 on RAW 264.7 via reducing the expression of VEGF. Moreover, LMPs attenuated pathological retinal NV and the infiltration of macrophages in vivo. LMPs downregulated ERK1/2 and HIF-1α both in vitro and in vivo. These findings expand our understanding of the effects of LMPs, providing evidence of LMPs as a promising therapeutic approach for the treatment of retinal NV diseases.

Protective effect of metformin on rat diabetic retinopathy involves suppression of toll-like receptor 4/nuclear factor-k B expression and glutamate excitotoxicity

Microvascular complications of diabetes mellitus are progressively significant reasons for mortality. Metformin (MET) is considered as the first-line therapy for type 2 diabetes patients, and may be especially beneficial in cases of diabetic retinopathy although the precise mechanisms of MET action are not fully elucidated. The current study was designed to inspect the antioxidant and modulatory actions of MET on DRET in streptozotocin-induced diabetic rats. The effect of MET on the toll-like receptor 4/nuclear factor kappa B (TLR4/NFkB), inflammatory burden and glutamate excitotoxicity was assessed. Twenty-four male rats were assigned to four experimental groups: (1) Vehicle group, (2) Diabetic control: developed diabetes by injection of streptozotocin (60 mg/kg, i.p.). (3&4) Diabetic + MET group: diabetic rats were left for 9 weeks without treatment and then received oral MET 100 and 200 mg/kg for 6 weeks. Retinal samples were utilized in biochemical, histological, immunohistochemical and electron microscopic studies. MET administration significantly decreased retinal level of insulin growth factor and significantly suppressed the diabetic induced increase of malondialdehyde, glutamate, tumor necrosis factor-α and vascular endothelial growth factor (VEGF). Further, MET decreased the retinal mRNA expression of NFkB, tumor necrosis factor-α and TLR4 in diabetic rats. The current findings shed the light on MET's efficacy as an adjuvant therapy to hinder the development of diabetic retinopathy, at least partly, via inhibition of oxidative stress-induced NFkB/TLR4 pathway and suppression of glutamate excitotoxicity.

Connexin43 hemichannel block inhibits NLRP3 inflammasome activation in a human retinal explant model of diabetic retinopathy

Diabetic retinopathy (DR), the most common ocular complication associated with diabetes, is a chronic vascular and inflammatory disease that leads to vision loss. The inflammasome pathway, a key part of the innate immune system, is required to activate chronic inflammation in DR. Unfortunately, current therapies for DR target pathological signs that are downstream of the inflammasome pathway, making them only partly effective in treating the disease. Using in vitro and in vivo DR models, it was discovered that connexin43 hemichannel blockers can inhibit activation of the inflammasome pathway. However, those studies were conducted using in vitro cell culture and in vivo animal disease models that are predictive but do not, of course, like any model, completely replicate the human condition. Here, we have developed an addition to our armamentarium of useful models, an ex vivo human organotypic retinal culture model of DR by exposing human donor retinal explants to a combination of high glucose (HG) and pro-inflammatory cytokines, interleukin-1 beta (IL-1β) and tumour necrosis factor alpha (TNF-α). We hypothesized that in this model, connexin43 hemichannel block would protect against NLRP3 inflammasome complex assembly which would in turn decrease signs of inflammation characteristic of DR. To test our hypothesis, molecular changes in the inflammatory and inflammasome pathway were assessed using immunohistochemistry and a Luminex cytokine release assay. Our results showed that the human retinal explant DR model was associated with increased inflammation and activation of the inflammasome pathway, characteristic of the human condition. Furthermore, we showed that by blocking connexin43 hemichannels with the hemichannel modulator, tonabersat, we were able to prevent NLRP3 inflammasome complex assembly, Müller cell activation, as well as release of pro-inflammatory cytokines and VEGF. This further supports the possible use of connexin43 hemichannel blockers as potential new therapies for DR.

The G-protein-coupled chemoattractant receptor Fpr2 exacerbates neuroglial dysfunction and angiogenesis in diabetic retinopathy

Diabetic retinopathy (DR) as a retinal neovascularization‐related disease is one of the leading causes of irreversible blindness in patients. The goal of this study is to determine the role of a G‐protein‐coupled chemoattractant receptor (GPCR) FPR2 (mouse Fpr2) in the progression of DR, in order to identify novel therapeutic targets. We report that Fpr2 was markedly upregulated in mouse diabetic retinas, especially in retinal vascular endothelial cells, in associated with increased number of activated microglia and Müller glial cells. In contrast, in the retina of diabetic Fpr2^−/− mice, the activation of vascular endothelial cells and glia was attenuated with reduced production of proinflammatory cytokines. Fpr2 deficiency also prevented the formation of acellular capillary during diabetic progression. Furthermore, in oxygen‐induced retinopathy (OIR) mice, the absence of Fpr2 was associated with diminished neovasculature formation and pathological vaso‐obliteration region in the retina. These results highlight the importance of Fpr2 in exacerbating the progression of neuroglial degeneration and angiogenesis in DR and its potential as a therapeutic target.

Z-Ligustilide Ameliorates Diabetic Rat Retinal Dysfunction Through Anti-Apoptosis and an Antioxidation Pathway

Background

Diabetic retinopathy (DR) is one of the major causes of vision impairment. Z-ligustilide (3-butylidene-4,5-dihydrophthalide; Z-LIG) is an important volatile oil from the Chinese herb Angelica sinensis (Oliv.) Diels. It has been extensively studied and reportedly has anti-inflammatory, antioxidant, antitumor, analgesic, vasodilatory, and neuroprotective effects. Its effects on DR, however, remain obscure. In this study, we attempted to explore the protective effects of Z-LIG on retinal dysfunction and the potential underlying mechanisms.

Material/Methods

A diabetic rat model was constructed with streptozotocin injection. Three study groups were constituted: control (CON), diabetic model (DM), and DM+Z-LIG. The DM+Z-LIG group was injected intraperitoneally with 10 mg/kg of Z-LIG. The other groups received the same volume of 3% solution of polysorbate 80. After a 12-week intervention, a series of assessments were performed, including tests for retinal function, morphology, and molecular biology.

Results

Z-LIG treatment significantly elevated b-wave and OPs2-wave amplitude and thickened the inner layer of the nucleus of the retina, and the outer plexiform and nuclear layers (INL+OPL+ONL). Moreover, the rate of apoptosis and expression of bcl-2- associated X protein (BAX) and cleaved-Caspase-3 were clearly reduced, and the expression of bcl-2 was raised by Z-LIG in retinas of diabetic mice. In addition, the levels of retinal proinflammatory cytokines interleukin-1 and tumor necrosis factor-α were downregulated by Z-LIG. Furthermore, Z-LIG inhibited expression of vascular endothelial growth factor-α (VEGF-α) at the mRNA and protein levels.

Conclusions

Z-LIG can inhibit inflammatory response and cell apoptosis in retinas of diabetic rats by repressing the VEGF-α pathway. Therefore, it may serve as a potential therapeutic agent for DR.

Acetylcholinesterase inhibition ameliorates retinal neovascularization and glial activation in oxygen-induced retinopathy

AIM

To investigate whether inhibition of acetylcholinesterase (AChE) by donepezil ameliorate aberrant retinal neovascularization (RNV) and abnormal glial activation in oxygen-induced retinopathy (OIR).

METHODS

A mouse model of RNV was induced in postnatal day 7 (P7) mice by exposure to 75% oxygen. Donepezil was administrated to P12 mice by intraperitoneal injection. Expression and localization of AChE in mouse retinas were determined by immunofluorescence. RNV was evaluated by paraffin sectioning and hematoxylin and eosin (HE) staining. Activation of retinal Müller glial cells were examined by immunoblot of glial fibrillary acidic protein (GFAP). rMC-1, a retinal Müller cell line, was used for in vitro study. Expression of hypoxia-induced factor 1α (HIF-1α) and vascular endothelial growth factor (VEGF) were determined by Western-blot analysis, enzyme-linked immunosorbent assay (ELISA) or immunostaining.

RESULTS

Aberrant RNV and glial activation was observed after OIR. Of note, retinal AChE was mainly expressed by retinal Müller glial cells and markedly increased in OIR mice. Systemic administration of donepezil significantly reduced RNV and abnormal glial activation in mice with OIR. Moreover, ischemia-induced HIF-1α accumulation and VEGF upregulation in OIR mouse retinas and cultured rMC-1 were significantly inhibited by donepezil intervention.

CONCLUSION

AchE is implicated in RNV with OIR. Inhibition of AChE by donepeizl is likely to be a potential therapeutic approach for retinal neovascular diseases.

A Comparison of Subconjunctival Wound Healing between Different Methods of Dissecting Subconjunctival Tissues

OBJECTIVE

To compare different methods for dissecting subconjunctival tissues by developing subconjunctival wound healing models.

METHODS

New Zealand white rabbits were separated into 3 groups based on the method by which the rabbit subconjunctival wound healing model was generated: subconjunctival tissues were dissected episclerally (EPI) or subepithelially (SUB), with a corresponding blank control (CON). All the cases in the experimental groups were surgically prepared with conjunctival flaps, and they were sacrificed on the third postoperative day. At the surgical sites, the protein levels of hypoxia-inducible factor-1 (HIF-1)-α, vascular endothelial growth factor (VEGF)-A, and matrix metalloproteinase (MMP)-2 were detected by Western blot, morphological vascularity was measured by Adobe Photoshop, and subconjunctival fibrosis was assessed by histology.

RESULTS

Compared with the CON group, both the EPI and SUB groups showed significantly upregulated protein levels of HIF-1α, VEGF-A, and MMP-2. In addition, the protein levels of HIF-1α, VEGF-A, and MMP-2 were higher in the EPI group than in the SUB group. Morphological vascularity was significantly elevated in the EPI group compared with the SUB and CON groups. Collagen content was markedly increased in the EPI group compared with the SUB and CON groups.

CONCLUSIONS

Dissecting subconjunctival tissues subepithelially inhibits subconjunctival fibrosis, which may be instructive in tenonectomy in filtration surgery.

Hypoxia-inducible factor-1α: A promising therapeutic target for vasculopathy in diabetic retinopathy

Diabetic retinopathy (DR) is a serious condition that can cause blindness in diabetic patients. It is a neurovascular disease, but the pathogenesis leading to the onset of this disease is still not completely understood. However, hypoxia with subsequent neovascularization is a characteristic phenomenon observed with DR. Cellular response to hypoxia is mediated by the transcriptional regulator hypoxia-inducible factor (HIF). Long-term research has shown that one isotype of HIF, HIF-1α, may play a pivotal role under hypoxic conditions, and an increasing number of studies have shown that HIF-1α and its target genes contribute to retinal neovascularization. Therefore, targeting HIF-1α may lead to more effective DR treatments. This review describes the possible mechanisms of HIF-1α in neovascularization of DR. Furthermore, various inhibitors of HIF-1α that may have viable potential in the treatment of DR are also discussed.

Glucocorticoid-transactivated TSC22D3 attenuates hypoxia- and diabetes-induced Müller glial galectin-1 expression via HIF-1α destabilization

Galectin‐1/LGALS1, a newly recognized angiogenic factor, contributes to the pathogenesis of diabetic retinopathy (DR). Recently, we demonstrated that glucocorticoids suppressed an interleukin‐1β‐driven inflammatory pathway for galectin‐1 expression in vitro and in vivo. Here, we show glucocorticoid‐mediated inhibitory mechanism against hypoxia‐inducible factor (HIF)‐1α‐involved galectin‐1 expression in human Müller glial cells and the retina of diabetic mice. Hypoxia‐induced increases in galectin‐1/LGALS1 expression and promoter activity were attenuated by dexamethasone and triamcinolone acetonide in vitro. Glucocorticoid application to hypoxia‐stimulated cells decreased HIF‐1α protein, but not mRNA, together with its DNA‐binding activity, while transactivating TSC22 domain family member (TSC22D)3 mRNA and protein expression. Co‐immunoprecipitation revealed that glucocorticoid‐transactivated TSC22D3 interacted with HIF‐1α, leading to degradation of hypoxia‐stabilized HIF‐1α via the ubiquitin‐proteasome pathway. Silencing TSC22D3 reversed glucocorticoid‐mediated ubiquitination of HIF‐1α and subsequent down‐regulation of HIF‐1α and galectin‐1/LGALS1 levels. Glucocorticoid treatment to mice significantly alleviated diabetes‐induced retinal HIF‐1α and galectin‐1/Lgals1 levels, while increasing TSC22D3 expression. Fibrovascular tissues from patients with proliferative DR demonstrated co‐localization of galectin‐1 and HIF‐1α in glial cells partially positive for TSC22D3. These results indicate that glucocorticoid‐transactivated TSC22D3 attenuates hypoxia‐ and diabetes‐induced retinal glial galectin‐1/LGALS1 expression via HIF‐1α destabilization, highlighting therapeutic implications for DR in the era of anti‐vascular endothelial growth factor treatment.

Development and Validation of Analytical Method for SH-1242 in the Rat and Mouse Plasma by Liquid Chromatography/Tandem Mass Spectrometry

SH-1242, a novel inhibitor of heat shock protein 90 (HSP90), is a synthetic analog of deguelin: It was previously reported that the treatment of SH-1242 led to a strong suppression of hypoxia-mediated retinal neovascularization and vascular leakage in diabetic retinas by inhibiting the hypoxia-induced upregulation of expression in hypoxia-inducible factor 1α (HIF-1α) and vascular endothelial growth factor (VEGF). In this study, an analytical method for the quantification of SH-1242 in biological samples from rats and mice was developed/validated for application in pharmacokinetic studies. SH-1242 and deguelin, an internal standard of the assay, in plasma samples from the rodents were extracted with methanol containing 0.1% formic acid and analyzed at m/z transition values of 368.9→151.0 and 395.0→213.0, respectively. The method was validated in terms of accuracy, precision, dilution, matrix effects, recovery, and stability and shown to comply with validation guidelines when it was used in the concentration ranges of 1–1000 ng/mL for rat plasma and of 2–1000 ng/mL for mouse plasma. SH-1242 levels in plasma samples were readily determined using the developed method for up to 480 min after the intravenous administration of 0.1 mg/kg SH-1242 to rats and for up to 120 min to mice. These findings suggested that the current method was practical and reliable for pharmacokinetic studies on SH-1242 in preclinical animal species.

Effects and Mechanism of Action of PX-478 in Oxygen-Induced Retinopathy in Mice

IMPORTANCE

Retinopathy of prematurity (ROP) is an important risk factor for blindness in children due to neovascularization (NV). Hypoxia stimulates the formation of NV, as retinal hypoxia affects the stability and function of hypoxia-inducible factor (HIF) transcription factors. The purpose of this study is to study the mechanism of ROP and provide theoretical basis for clinical treatment of ROP.

OBJECTIVE

In the present study, we used a mouse model of oxygen-induced retinopathy (OIR) to demonstrate the effects of the HIF-1α inhibitor PX-478 on OIR, and to determine its mechanism of action, to provide a theoretical basis for the clinical treatment of ROP.

MATERIALS AND METHODS

The OIR mouse model was induced by exposing neonatal mouse pups and their mothers to 75 ± 5% oxygen from postnatal day 7 (P7) to P12, before being returned to room air from P12 to P17. Flat mount analyses were performed at P12 and P17. Hif1a, Hif2a, Hif3a, and Vegfa mRNA were detected by reverse transcription-polymerase chain reaction in OIR mice at P12 and P17. Hif1a and Vegfa mRNA were detected in OIR mice at P12 and P17 treatment with PX-478. Western blot analyses were used to assess the levels of HIF-1α, VEGF-A, and EPO before and after treatment with PX-478 at P12 and P17.

RESULTS

Hif1a mRNA was increased in OIR mice at P12 and P17, while Vegfa mRNA was increased at P12 and P17. HIF-1α, VEGF-A, and EPO protein levels were increased in OIR mice at P12 and P17, as compared to control mice at the same age (all p < 0.05). Inhibition of HIF-1α by injection of PX-478 in OIR mice (P9-P16) caused a decrease in the retinal avascular area at P12 and P17 (both p < 0.05), NV areas at P17 (p < 0.05), Vegfa mRNA decreased at P12 and P17, as compared to control mice (p < 0.05), and VEGF-A and EPO protein levels at P12 and P17, as compared to control mice. Our study found that there were PX-478 both retina and vitreous body of OIR. Inhibition of HIF-1α by injection of PX-478 in OIR mice caused a decrease in the retinal avascular area at P12 and P17, NV areas decreased at P17, VEGF-A and EPO protein levels at P12 and P17. Endothelial cell migration assays and cell tube formation indication PX-478 attenuate cell migration and significantly weakened the cell cavity formation under the condition of hypoxia.

CONCLUSION

HIF-1α plays a main role in OIR and can be considered a therapeutic target in OIR by suppressing downstream angiogenic factors, PX-478 decreasing the retinal avascular area and NV.

Protective Efficacy of a Dietary Supplement Based on Forskolin, Homotaurine, Spearmint Extract, and Group B Vitamins in a Mouse Model of Optic Nerve Injury

Glaucoma is a multifactorial blinding disease with a major inflammatory component ultimately leading to apoptotic retinal ganglion cell (RGC) death. Pharmacological treatments lowering intraocular pressure can help slow or prevent vision loss although the damage caused by glaucoma cannot be reversed. Recently, nutritional approaches have been evaluated for their efficacy in preventing degenerative events in the retina although mechanisms underlying their effectiveness remain to be elucidated. Here, we evaluated the efficacy of a diet supplement consisting of forskolin, homotaurine, spearmint extract, and vitamins of the B group in counteracting retinal dysfunction in a mouse model of optic nerve crush (ONC) used as an in vivo model of glaucoma. After demonstrating that ONC did not affect retinal vasculature by fluorescein angiography, we determined the effect of the diet supplement on the photopic negative response (PhNR) whose amplitude is strictly related to RGC integrity and is therefore drastically reduced in concomitance with RGC death. We found that the diet supplementation prevents the reduction of PhNR amplitude (p < 0.001) and concomitantly counteracts RGC death, as in supplemented mice, RGC number assessed immunohistochemically is significantly higher than that in non-supplemented animals (p < 0.01). Major determinants of the protective efficacy of the compound are due to a reduction of ONC-associated cytokine secretion leading to decreased levels of apoptotic markers that in supplemented mice are significantly lower than in non-supplemented animals (p < 0.001), ultimately causing RGC survival and ameliorated visual dysfunction. Overall, our data suggest that the above association of compounds plays a neuroprotective role in this mouse model of glaucoma thus offering a new perspective in inflammation-associated neurodegenerative diseases of the inner retina.

HIF inhibitor topotecan has a neuroprotective effect in a murine retinal ischemia-reperfusion model

Purpose

The therapeutic approach for retinal ganglion cell (RGC) degeneration has not been fully established. Recently, it has been reported that hypoxia-inducible factor (HIF) may be involved with retinal neurodegeneration. In this study, we investigated neuroprotective effects of a HIF inhibitor against RGC degeneration induced in a murine model of retinal ischemia-reperfusion (I/R).

Methods

Eight-weeks-old male C57/BL6J mice were treated with intraperitoneal injection of a HIF inhibitor topotecan (1.25 mg/kg) for 14 days followed by a retinal I/R procedure. Seven days after the I/R injury, the therapeutic effect was evaluated histologically and electrophysiologically.

Results

The increase of HIF-1α expression and the decrease of retinal thickness and RGC number in I/R were significantly suppressed by administration of topotecan. Impaired visual function in I/R was improved by topotecan evaluated with electroretinogram and visual evoked potentials.

Conclusions

Topotecan administration suppressed HIF-1a expression and improved RGC survival resulting in a functional protection against retinal I/R. These data indicated that the HIF inhibitor topotecan may have therapeutic potentials for RGC degeneration induced with retinal ischemia or high intraocular pressure.

Roles of Drug Transporters in Blood-Retinal Barrier

Blood-retinal barrier (BRB) includes inner BRB (iBRB) and outer BRB (oBRB), which are formed by retinal capillary endothelial (RCEC) cells and by retinal pigment epithelial (RPE) cells in collaboration with Bruch's membrane and the choriocapillaris, respectively. Functions of the BRB are to regulate fluids and molecular movement between the ocular vascular beds and retinal tissues and to prevent leakage of macromolecules and other potentially harmful agents into the retina, keeping the microenvironment of the retina and retinal neurons. These functions are mainly attributed to absent fenestrations of RCECs, tight junctions, expression of a great diversity of transporters, and coverage of pericytes and glial cells. BRB existence also becomes a reason that systemic administration for some drugs is not suitable for the treatment of retinal diseases. Some diseases (such as diabetes and ischemia-reperfusion) impair BRB function via altering tight junctions, RCEC death, and transporter expression. This chapter will illustrate function of BRB, expressions and functions of these transporters, and their clinical significances.

Enhanced ROBO4 is mediated by up-regulation of HIF-1α/SP1 or reduction in miR-125b-5p/miR-146a-5p in diabetic retinopathy

Retinal cell damage caused by diabetes leads to retinal microvascular injury. Roundabout 4 (ROBO4) is involved in angiogenesis, which varies with the development of diabetic retinopathy (DR). Here, we explored the transcriptional regulation and microRNA‐mediated modulation of ROBO4 expression and related retinal cell function in DR. A streptozotocin‐induced type I diabetic animal model was established to detect the expression of hypoxia inducible factor‐1α (HIF‐1α), specificity protein 1 (SP1) and ROBO4. Retinal pigment epithelium (RPE) cells were cultured under hyperglycaemia or hypoxia and used for mechanistic analysis. Furthermore, roles of miR‐125b‐5p and miR‐146a‐5p were evaluated, and their targets were identified using luciferase assays. The cell functions were evaluated by MTS assays, permeability analysis and migration assays. The development of DR increased the levels of HIF‐1α, SP1 and ROBO4 both in the DR model and in hyperglycaemic/hypoxic RPE cells. They were co‐expressed and up‐regulated in diabetic retinas and in RPE cells under hyperglycaemia/hypoxia. Knockdown of HIF‐1α significantly inhibited SP1 and ROBO4, whereas SP1 down‐regulation abolished ROBO4 expression in RPE cells under hyperglycaemia/hypoxia. miR‐125b‐5p and miR‐146a‐5p were down‐regulated by hyperglycaemia and/or hypoxia. Up‐regulation of miRNAs reversed these changes and resulted in recovery of target gene expression. Moreover, luciferase assays confirmed miR‐125b‐5p targeted SP1 and ROBO4, and miR‐146a‐5p targeted HIF‐1α and ROBO4 directly. The decreased cell viability, enhanced permeability, and increased cell migration under DR conditions were mitigated by knockdown of HIF‐1α/SP1/ROBO4 or up‐regulation of miR‐125b‐5p/miR‐146a‐5p. In general, our results identified a novel mechanism that miR‐125b‐5p/miR‐146a‐5p targeting HIF‐1α/SP1‐dependent ROBO4 expression could retard DR progression.