The cKit Inhibitor, Masitinib, Prevents Diabetes-Induced Retinal Vascular Leakage.

To investigate the mechanisms underlying 15(S)-HETE-induced angiogenesis, we have studied the role of the small GTPase, Rac1. We find that 15(S)-HETE activated Rac1 in human retinal microvascular endothelial cells (HRMVEC) in a time-dependent manner. Blockade of Rac1 by adenovirus-mediated expression of its dominant negative mutant suppressed HRMVEC migration as well as tube formation and Matrigel plug angiogenesis. 15(S)-HETE stimulated Src in HRMVEC in a time-dependent manner and blockade of its activation inhibited 15(S)-HETE-induced Rac1 stimulation in HRMVEC and the migration and tube formation of these cells as well as Matrigel plug angiogenesis. 15(S)-HETE stimulated JNK1 in Src-Rac1-dependent manner in HRMVEC and adenovirus-mediated expression of its dominant negative mutant suppressed the migration and tube formation of these cells and Matrigel plug angiogenesis. 15(S)-HETE activated ATF-2 in HRMVEC in Src-Rac1-JNK1-dependent manner and interference with its activation via adenovirus-mediated expression of its dominant negative mutant abrogated migration and tube formation of HRMVEC and Matrigel plug angiogenesis. In addition, 15(S)-HETE-induced MEK1 stimulation was found to be dependent on Src-Rac1 activation. Blockade of MEK1 activation inhibited 15(S)-HETE-induced JNK1 activity and ATF-2 phosphorylation. Together, these findings show that 15(S)-HETE activates ATF-2 via the Src-Rac1-MEK1-JNK1 signaling axis in HRMVEC leading to their angiogenic differentiation.

Pathological angiogenesis leads to the development of retinal vasculopathies and causes severe vision impairment. Increased understanding of the mechanisms underlying the angiogenic behavior of retinal endothelial cells helps provide new insights for developing treatment of retinal vasculopathies. Pro-angiogenic function of miR-210 has previously been identified. However, the functional implication of miR-210 in retinal endothelial cells remains unknown. Human retinal microvascular endothelial cells (HRECs) were employed to investigate the impact of miR-210 on the angiogenic capacity of retinal endothelial cells. It was observed that without affecting the viability of HRECs, miR-210 significantly suppressed the migration and capillary-like tube formation in HRECs. Moreover, pro-angiogenic insulin growth factor 2 (IGF2) was newly identified as a direct target of miR-210 in HRECs. MiR-210 decreased the expression of IGF2 at both mRNA and protein levels in HRECs. IGF2-simulated activation of p38 MAPK was attenuated by miR-210 in HRECs. Recombinant IGF2 protein rescued miR-210-induced impairment of tube formation in HRECs. Therefore, in contrast to the previously reported pro-angiogenic function of miR-210, the current work reveals novel anti-angiogenic activity of miR-210 in HRECs. Furthermore, IGF2 is identified for the first time as a direct target of miR-210 in HRECs, adding new mechanistic insights into the expression regulation of pro-angiogenic IGF2 in human retinal endothelial cells. The current work helps increase the understanding of regulatory mechanisms underlying retinal endothelial cell physiology, justifying further evaluation for the therapeutic implications of miR-210/IGF2 interaction in the treatment of related retinal vasculopathies.

Aryl hydrocarbon receptor deficiency augments dysregulated microangiogenesis and diabetic retinopathy

To provide the direct evidence for the crucial role of trimethylamine N-oxide (TMAO) in vascular permeability and endothelial cell dysfunction under diabetic condition. The role of TMAO on the in vitro biological effect of human retinal microvascular endothelial cells (HRMEC) under high glucose conditions was tested by a cell counting kit, wound healing, a transwell and a tube formation assay. The inflammation-related gene expression affected by TMAO was tested by real-time polymerase chain reaction (RT-PCR). The expression of the cell junction was measured by Western blotting (WB) and immunofluorescence staining. In addition, two groups of rat models, diabetic and non-diabetic, were fed with normal or 0.1% TMAO for 16wk, and their plasma levels of TMAO, vascular endothelial growth factor (VEGF), interleukin (IL)-6 and tumor necrosis factor (TNF)-α were tested. The vascular permeability of rat retinas was measured using FITC-Dextran, and the expression of zonula occludens (ZO)-1 and claudin-5 in rat retinas was detected by WB or immunofluorescence staining. TMAO administration significantly increased the cell proliferation, migration, and tube formation of primary HRMEC either in normal or high-glucose conditions. RT-PCR showed elevated inflammation-related gene expression of HRMEC under TMAO stimulation, while WB or immunofluorescence staining indicated decreased cell junction ZO-1 and occludin expression after high-glucose and TMAO treatment. Diabetic rats showed higher plasma levels of TMAO as well as retinal vascular leakage, which were even higher in TMAO-feeding diabetic rats. Furthermore, TMAO administration increased the rat plasma levels of VEGF, IL-6 and TNF-α while decreasing the retinal expression levels of ZO-1 and claudin-5. TMAO enhances the proliferation, migration, and tube formation of HRMEC, as well as destroys their vascular integrity and tight connection. It also regulates the expression of VEGF, IL-6, and TNF-α.

A transcriptomics and molecular biology based investigation reveals the protective effect and mechanism of carnosol on t-BHP induced HRMECs via Nrf2 signaling pathway

Diabetic retinopathy (DR) is a leading cause of vision loss and is primarily driven by chronic hyperglycemia, which induces retinal vascular damage through mechanisms involving vascular endothelial growth factor (VEGF) and the renin-angiotensin system (RAS). This study investigated the effects of hyperglycemia and different insulin formulations-regular, glulisine, and aspart-on VEGF-A and angiotensinogen (AGT) gene expression in two human retinal cell types: retinal pigment epithelial (RPE) cells and human retinal microvascular endothelial cells (HRECs). Cells were cultured from donor tissue and exposed to physiologic and hyperglycemic glucose concentrations, with or without insulin treatment. Gene expression levels were quantified using real-time PCR. Hyperglycemia significantly upregulated VEGF-A and AGT in both RPE and HREC cells (e.g., VEGF-A in RPE: 2.62-fold, P = 0.001; AGT in RPE: 3.32-fold, P = 0.093), supporting a role for both osmotic and glucose-specific pathways. Among insulin treatments, regular insulin significantly reduced VEGF-A expression in both RPE (0.72-fold, P = 0.033) and HRECs (0.57-fold, P = 0.009). In contrast, aspart and glulisine had modest effects on VEGF-A in HRECs (0.82-fold each; P = 0.035 and P = 0.060, respectively) and no significant impact in RPE cells. Regarding AGT, aspart insulin showed the most consistent suppressive effect, reducing expression in both RPE (0.15-fold, P < 0.001) and HRECs (0.22-fold, P = 0.004). Glulisine significantly increased AGT in RPE (1.56-fold, P = 0.009) but reduced it in HRECs (0.58-fold, P = 0.074). Regular insulin showed no effect on AGT in RPE (P = 0.680) and a non-significant increase in HRECs (1.36-fold, P = 0.097). These findings highlight the differential biological effects of insulin analogues and suggest that aspart insulin, in particular, may offer therapeutic benefits beyond glycemic control by modulating both VEGF-A and RAS-related pathways. Tailored insulin therapies could represent innovative strategies for managing or slowing the progression of diabetic retinopathy.

Dysfunction of the blood-retinal barrier (BRB) contributes to the pathophysiology of several vascular eye diseases, often resulting in retinal edema and subsequent vision loss. The inner blood-retinal barrier (iBRB) is mainly composed of retinal vascular endothelium with low permeability under physiological conditions. This feature of low permeability is tightly regulated and maintained by low rates of paracellular transport between adjacent retinal microvascular endothelial cells, as well as transcellular transport (transcytosis) through them. The assessment of retinal transcellular barrier permeability may provide fundamental insights into iBRB integrity in health and disease. In this study, we describe an endothelial cell (EC) transcytosis assay, as an in vitro model for evaluating iBRB permeability, using human retinal microvascular endothelial cells (HRMECs). This assay assesses the ability of HRMECs to transport transferrin and horseradish peroxidase (HRP) in receptor- and caveolae-mediated transcellular transport processes, respectively. Fully confluent HRMECs cultured on porous membrane were incubated with fluorescent-tagged transferrin (clathrin-dependent transcytosis) or HRP (caveolae-mediated transcytosis) to measure the levels of transferrin or HRP transferred to the bottom chamber, indicative of transcytosis levels across the EC monolayer. Wnt signaling, a known pathway regulating iBRB, was modulated to demonstrate the caveolae-mediated HRP-based transcytosis assay method. The EC transcytosis assay described here may provide a useful tool for investigating the molecular regulators of EC permeability and iBRB integrity in vascular pathologies and for screening drug delivery systems.

Physiological shear stress is higher in the retinal microcirculatory network than in other organs. The effects of laminar shear stress on gene expression in human retinal microvascular endothelial cells (HRMECs) was investigated. Cultured HRMECs on glass plates were exposed to a laminar shear stress of 0, 1.5, 6, 15, 30, 60, or 100 dyne/cm(2) for 24 hours and to 60 dyne/cm(2) for 0, 1, 3, 6, 12, 24, or 48 hours. The mRNA expressions of endothelial nitric oxide synthase (eNOS), endothelin-1 (ET-1), and thrombomodulin (TM) in the HRMECs were evaluated using real-time reverse transcription polymerase chain reaction. The HRMECs elongated and aligned parallel with the flow direction based on the shear stress and exposure times. The expression of eNOS mRNA gradually increased and became saturated at 60 dyne/cm(2); ET-1 mRNA expression increased at 1.5 dyne/cm(2) but decreased below that of the static control at shear stresses of 30 dyne/cm(2) or more. TM mRNA expression in response to shear stress increased linearly from 0 to 100 dyne/cm(2). A shear stress of 60 dyne/cm(2) for 6 hours or more promoted eNOS and TM mRNA expression but suppressed ET-1 mRNA expression in HRMECs. Long-term exposure to a physiological shear stress in the retinal arterioles up-regulated eNOS and TM mRNA expressions and downregulated ET-1 mRNA expression in HRMECs. These results suggest that shear stress may be associated with the vasoregulatory and antithrombotic properties of retinal vessels under physiological conditions present during retinal circulation.

The purpose of our study was to investigate the role of TGF-β1 in the endothelial-to-mesenchymal transition (EndoMT) and fibrosis in high glucose (HG)-treated human retinal microvascular endothelial cells (HRMECs). HRMECs were cultured not only under normal glucose (NG) conditions with or without TGF-β1, but also under HG conditions with or without the TGF-β1 inhibitor SB431542. The expression of TGF-β1 was detected by real time-PCR and enzyme-linked immunosorbent assay. Morphological changes and migration of the HRMECs were observed using electron microscopy and scratch-wound assay. Endothelial markers, such as CD31 and vascular endothelial (VE)-cadherin, and the acquisition of fibrotic markers, such as alpha smooth muscle actin (α-SMA) and fibroblast-specific protein-1 (FSP-1), were determined by immunofluorescent staining and western blot. The level of TGF-β1 was significantly upregulated in HG-treated HRMECs. And HG stimulation promoted obvious morphological changes and the migration ability in HRMECs. Our results also demonstrated increased expression of α-SMA and FSP-1, and decreased expression of CD31 and VE-cadherin, in HG-treated HRMECs. These EndoMT-related changes were promoted by TGF-β1 and abrogated by SB431542. The results of this study demonstrated the important role of TGF-β1 in HG-induced vitreoretinal fibrosis. EndoMT is likely to be involved in the associated effects.

Retinal heparanase expression in streptozotocin-induced diabetic rats

Pathological retinal angiogenesis is a typical manifestation of vision-threatening ocular diseases. Many patients exhibit poor response or resistance to anti-vascular endothelial growth factor (VEGF) agents. Bruton's tyrosine kinase (BTK) controls the proliferation and function of immune cells. Therefore, we examined the anti-inflammatory and anti-angiogenic effects of BTK inhibition on retinal angiogenesis. Retinal neovascularisation and vascular leakage in oxygen-induced retinopathy in C57/BL6J mice were assessed by whole-mount retinal immunofluorescence. PLX5622 was used to deplete microglia and Rag1-knockout mice were used to test the contribution of lymphocytes to the effects of BTK inhibition. The cytokines, activation markers, inflammatory and immune-regulatory activities of retinal microglia/macrophages were detected using qRT-PCR and immunofluorescence. NLRP3 was detected by western blotting, and the effects of BTK inhibition on the co-culture of microglia and human retinal microvascular endothelial cells (HRMECs) were examined. BTK inhibition suppressed pathological angiogenesis and vascular leakage, and significantly reduced retinal inflammation, which involved microglia/macrophages but not lymphocytes. BTK inhibition increased anti-inflammatory factors and reduced pro-inflammatory cytokines that resulted from NLRP3 inflammasome activation. BTK inhibition suppressed the inflammatory activity of microglia/macrophages, and acted synergistically with anti-VEGF without retinal toxicity. Moreover, the supernatant of microglia incubated with BTK-inhibitor reduced the proliferation, tube formation and sprouting of HRMECs. BTK inhibition suppressed retinal neovascularisation and vascular leakage by modulating the inflammatory activity of microglia and macrophages. Our study suggests BTK inhibition as a novel and promising approach for alleviating pathological retinal angiogenesis. This article is part of a themed issue Drugs and Drug Targets in Metabolic and Chronic Inflammatory Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v182.20/issuetoc.

Objective To detect the protein expression change in the proliferation of human retinal microvascular endothelial cells (hRMECs) stimulated with 4-Hydroxynonenal (4-HNE). Methods hRMECs were in a logarithmic growth phase, and then were separated into 4-HNE-stimulated group and negative control group. The concentration of 4-HNE included 5, 10, 20 and 50 μmol/L in 4-HNE-stimulated group, while the negative control group was added in the same volume of ethanol (the solvent of 4-HNE). Then the cells were stimulated with 4-HNE for 24 hours following by CCK-8 kits incubating for 4 hours to detect absorbance. It was found that 10 μmol/L 4-HNE had the most obvious effect on the proliferation of hRMECs. Therefore, the cellular proteins from 10 μmol/L 4-HNE-stimulated group and negative control group were acquired and prepared by FASP sample preparation method. Data independent acquisition was used for data acquisition, and the GO analysis and pathway enrichment were performed for analysis of differentially expressed proteins. Results CCK-8 kits detection results showed that the A value of the 10 and 20 μmol/L 4-HNE-stimulated groups were significantly higher than negative control group and 5 μmol/L 4-HNE-stimulated group (F=25.42, P 1.5, P<0.05). Seventy-two proteins were up-regulated after 4-HNE stimulation, whereas 46 proteins were down-regulated. Particularly, the expressions of Heme oxygenase-1, Sulfoxdoxin-1, Heat shock protein A1B, Thioredoxin reductase-1, Glutathione reductase, ATPase and prothrombin were increased when cells were added in 4-HNE, whereas the expressions of apolipoprotein A1 and programmed cell death protein 4 were decreased. These differentially expressed proteins were mainly involved in the biological processes such as oxidative stress, cell detoxification, and ATPase-coupled membrane transport. Conclusion After stimulated with 4-HNE, the oxidative stress, cell detoxification, and ATPase-coupled membrane transport protein expression may change in hRMECs in order to regulate oxidative stress and growth situation. Key words: Reitinal vessels/cytology; Endothelial; Cell cultured; Proteomics; 4- Hydroxynonenal

To determine the impact of sodium butyrate on the activation of the reactive oxygen species (ROS)/nuclear factor kappa B (NF-κB)/NLR family pyrin domain containing 3 (NLRP3) signaling pathway and angiogenesis in human retinal microvascular endothelial cells (HRMECs) caused by high glucose (HG). HRMECs were grown for 24h or 72h in HG solution (30mmol/L D-glucose) with 5mM NaB. Using Cell Counting Kit-8, the effects of HG and NaB levels on the viability of HRMECs were examined. Using various kits, intracellular ROS levels, lactate dehydrogenase (LDH), and Malondialdehyde (MDA) in cell supernatants were measured. Western blot, Immunofluorescence, and Real-time quantitative polymerase chain reaction were employed to quantify protein and messenger RNA expression. Using wound-healing and tube formation tests, the migratory proficiency and angiogenesis of HRMECs were evaluated. NaB demonstrated a reduction in ROS production, as well as the release of LDH and MDA in HG-induced HRMECs. Additionally, NaB led to a decrease in protein expression of phosphorylation of NF-κB, NLRP3, Caspase 1, interleukin, vascular cell adhesion molecule-1 and intercellular adhesion molecule-1. The impact of HG on zonula occluden-1, a tight junction protein, was attenuated by NaB. Furthermore, NaB inhibited the migration and tube formation of HRMECs partly by ROS/NF-κB/NLRP3 pathway. NaB suppresses the activation of ROS/NF-κB/NLRP3 signaling pathway and angiogenesis in HRMECs induced by HG.

To determine and interrelate the levels of heparanase, syndecan-1, and VEGF in proliferative diabetic retinopathy (PDR), and to study the production of heparanase by human retinal microvascular endothelial cells (HRMEC) and its effect on HRMEC barrier function. Vitreous samples from 33 PDR and 27 nondiabetic patients, epiretinal membranes from 16 patients with PDR and HRMEC were studied by enzyme-linked immunosorbent assay, immunohistochemistry, and Western blot analysis. The effect of heparanase on HRMEC barrier function was evaluated by transendothelial electrical resistance. We showed a significant increase in the expression of heparanase, syndecan-1, and VEGF in vitreous samples from PDR patients compared with nondiabetic controls (P < 0.0001 for all comparisons). Significant positive correlations were found between the levels of heparanase and the levels of syndecan-1 (r = 0.75, P < 0.0001) and VEGF (r = 0.91, P < 0.0001) and between the levels of syndecan-1 and the levels of VEGF (r = 0.78, P < 0.0001). In epiretinal membranes, heparanase was expressed in vascular endothelial cells and CD45-expressing leukocytes. High-glucose, tumor necrosis factor alpha (TNF-α), and the combination of TNF-α and interleukin (IL)-1β, but not cobalt chloride induced upregulation of heparanase in HRMEC. Heparanase-reduced transendothelial electrical resistance of HRMEC. Our findings suggest a link between heparanase, syndecan-1, and VEGF in the progression of PDR and that heparanase is a potential target for therapy of diabetic retinopathy.

Low shear stress up-regulation of proinflammatory gene expression in human retinal microvascular endothelial cells