Mechanisms Underlying Rare Inherited Pediatric Retinal Vascular Diseases: FEVR, Norrie Disease, Persistent Fetal Vascular Syndrome

Familial Exudative Vitreoretinopathy (FEVR), Norrie disease, and persistent fetal vascular syndrome (PFVS) are extremely rare retinopathies that are clinically distinct but are unified by abnormal retinal endothelial cell function, and subsequent irregular retinal vascular development and/or aberrant inner blood-retinal-barrier (iBRB) function. The early angiogenesis of the retina and its iBRB is a delicate process that is mediated by the canonical Norrin Wnt-signaling pathway in retinal endothelial cells. Pathogenic variants in genes that play key roles within this pathway, such as NDP, FZD4, TSPAN12, and LRP5, have been associated with the incidence of these retinal diseases. Recent efforts to further elucidate the etiology of these conditions have not only highlighted their multigenic nature but have also resulted in the discovery of pathological variants in additional genes such as CTNNB1, KIF11, and ZNF408, some of which operate outside of the Norrin Wnt-signaling pathway. Recent discoveries of FEVR-linked variants in two other Catenin genes (CTNND1, CTNNA1) and the Endoplasmic Reticulum Membrane Complex Subunit-1 gene (EMC1) suggest that we will continue to find additional genes that impact the neural retinal vasculature, especially in multi-syndromic conditions. The goal of this review is to briefly highlight the current understanding of the roles of their encoded proteins in retinal endothelial cells to understand the essential functional mechanisms that can be altered to cause these very rare pediatric retinal vascular diseases.

Overexpression of miR-181a-5p inhibits retinal neovascularization through endocan and the ERK1/2 signaling pathway

Retinal neovascularization (RNV) is a common pathological feature of angiogenesis‐related retinopathy. Endocan inhibition has previously been reported to suppress RNV in oxygen‐induced retinopathy (OIR); however, its molecular mechanisms remain to be elucidated. Here, we investigated the role and mechanism of endocan in OIR. We established an OIR mouse model and detected aberrant endocan overexpression in OIR mouse retinas. Endocan inhibition through small interfering RNA or a neutralizing antibody inhibited vascular endothelial growth factor‐induced cell survival, cell proliferation, and tube formation in human retinal endothelial cells in vitro and reduced the RNV area in vivo. Using RNA sequencing, a luciferase reporter assay, and bioinformatics analyses, we identified endocan as a microRNA‐181a‐5p target gene. The antiangiogenic effect of miR‐181a‐5p on RNV was verified by intravitreal injection, and we showed that this involved the extracellular signal‐regulated protein kinases 1 and 2 (ERK1/2) signaling pathway. Collectively, our data demonstrate that miR‐181a‐5p/endocan regulates retinal angiogenesis through the ERK1/2 signaling pathway and might represent an attractive therapeutic strategy for RNV.

The Impact of Hyperglycemia on VEGF Secretion in Retinal Endothelial Cells

BACKGROUND

Diabetic retinopathy is a serious sight-threatening complication which is manifested by excessive angiogenesis in diabetic patients.

AIM

We hypothesize that cultured Rhesus monkey retinal endothelial cells (RhRECs) respond to high glucose with a change in cell proliferation and vascular endothelial growth factor (VEGF) secretion.

MATERIALS AND METHODS

In our study, 20 000 cells per well were treated without glucose or with 5.5 mM, 18.5 mM and 30 mM glucose for 24 hours. Viable cells were counted using trypan blue dye exclusion method. VEGF concentrations were measured in cell media by ELISA method.

RESULTS

The number of viable cells incubated with 5.5 mM glucose increased significantly by 53.7% after 24 hours. In comparison, the number of viable cells decreased by 2.8% at 18.5 mM of glucose and by 20.4% at 30 mM of glucose after 24 hours of incubation. In contrast to this effect of glucose on the number of viable cells, a significant increase in VEGF levels (pg/mL) in the cell media with a glucose concentration of 0 mM compared to 5.5 mM of glucose was found. VEGF secretion in cell medium with 18.5 and 30 mM of glucose increased non-significantly in comparison with euglycemic levels.

CONCLUSION

Our results show that viability of retinal endothelial cells and VEGF release are highly responsive to changes in glucose concentration. Such glucose-induced changes in retinal endothelial cells may negatively impact the integrity of the microvasculature in the diabetic retina leading to angiogenesis and microaneursym.

Effects of LY294002 on the function of retinal endothelial cell in vitro

AIM

To study the effects of LY294002 [phosphatidylinositol 3-kinase (PI3K) inhibitor] on the function and mechanisms of retinal endothelial cells (RECs) in vitro.

METHODS

RECs were randomly divided into control group and LY294002 treatment group. RECs in the control group were placed the incubator for hypoxic exposure in vitro. RECs in the LY294002 treatment group were pretreated with LY294002 (40 µmol/L) under hypoxic condition. The expression of matrix metalloproteinase (MMP)-2, MMP-9, vascular endothelial growth factor (VEGF), and apoptosis and proliferation of RECs were evaluated with Western blot, real-time reverse transcription-polymerase chain reaction (RT-PCR), and flow cytometric analysis, correspondently.

RESULTS

Compared with the control group, treating the RECs with LY294002 was able to remarkably inhibit cell proliferation rates (t_1d=2.13, t_2d=2.65, t_3d=2.36, t_4d=2.06, all P<0.05). Flow cytometric analysis indicated that a moderate increase in apoptosis in the LY294002 treatment group compared to the control group (t=2.51, P<0.05). The expression of MMP-2, MMP-9 and VEGF were downregulated in the LY294002 treatment group by Western blot and real-time RT-PCR (all P<0.05).

CONCLUSION

LY294002 regulates the function of RECs by reducing the expression of MMP-2, MMP-9, and VEGF in vitro. LY294002 may provide an effective method for preventing pathological angiogenesis.

Time-lapse microscopy of oxidative stress demonstrates metabolic sensitivity of retinal pericytes under high glucose condition

Hyperglycemia affects retinal vascular cell function, promotes the development and progression of diabetic retinopathy and ultimately causes vision loss. Oxidative stress, reactive oxygen species (ROS) in excess, is a key biomarker for diabetic retinopathy. Using time-lapse fluorescence microscopy, ROS dynamics was monitored and the metabolic resistivity of retinal endothelial cells (REC) and pericytes (RPC) was compared under metabolic stress conditions including high glucose (HG). In the presence of a mitochondrial stressor, REC exhibited a significant increase in the rate of ROS production compared with RPC. Thus, under normal glucose (NG), REC may utilize oxidative metabolism as the bioenergetic source, while RPC metabolic activity is independent of mitochondrial respiration. In HG condition, the rate of ROS production in RPC was significantly higher, whereas this rate remained unchanged in REC. Thus, under HG condition RPC may preferentially utilize oxidative metabolism, which results in increased rate of ROS production. In contrast, REC use glycolysis as their major bioenergetic source for ATP production, and consequently HG minimally affects their ROS levels. These observations are consistent with our previous studies where we showed HG condition has minimal effect on apoptosis of REC, but results in increased rate of apoptosis in RPC. Collectively, our results suggest that REC and RPC exhibit different metabolic activity preferences under different glucose conditions. Thus, protection of RPC from oxidative stress may provide an early point of intervention in development and progression of diabetic retinopathy.

Pterostilbene impact on retinal endothelial cells under high glucose environment

Diabetic retinopathy (DR) has complicated pathogenic factors. Studies showed that DR belongs to chronic inflammatory disease, and retinal endothelial cells oxidation by free radicals is one of its mechanisms. Pterostilbene, as the homologous derivative of resveratrol, has obvious antioxidant effect. Its influence on the DR has not been studied. This study intended to investigate the effect and mechanism of pterostilbene on human retinal endothelial cells (hRECs) under high glucose environment to illustrate pterostilbene impact on DR and provide basis for DR clinical treatment. hRECs cultured in high glucose environment were treated by 1.0 mmol/L pterostilbene. MTT assay was applied to test cell proliferation. ELISA was used to detect inflammatory factor TNF-α and IL-1β content. Real time PCR and Western blot were performed to examine NF-κB mRNA and protein expression. ROS and SOD activities were analyzed. Under high glucose environment, hRECs proliferation increased, TNF-α and IL-1β expression elevated, and NF-κB protein level upregulated significantly. On the other side, ROS production increased and SOD activity decreased obviously (P < 0.05). Pterostilbene can suppress hRECs over proliferation, decrease TNF-α and IL-1β, inhibit NF-κB protein expression, reduce ROS production, and increase SOD activity markedly compared with high glucose group (P < 0.05). Pterostilbene may delay DR progress through alleviating inflammation and antioxidation to suppress hRECs over proliferation.

Negatively charged silver nanoparticles cause retinal vascular permeability by activating plasma contact system and disrupting adherens junction

Silver nanoparticles (AgNPs) have been extensively used as antibacterial component in numerous healthcare, biomedical and consumer products. Therefore, their adverse effects to biological systems have become a major concern. AgNPs have been shown to be absorbed into circulation and redistributed into various organs. It is thus of great importance to understand how these nanoparticles affect vascular permeability and uncover the underlying molecular mechanisms. A negatively charged mecaptoundeonic acid-capped silver nanoparticle (MUA@AgNP) was investigated in this work. Ex vivo experiments in mouse plasma revealed that MUA@AgNPs caused plasma prekallikrein cleavage, while positively charged or neutral AgNPs, as well as Ag ions had no effect. In vitro tests revealed that MUA@AgNPs activated the plasma kallikrein-kinin system (KKS) by triggering Hageman factor autoactivation. By using specific inhibitors aprotinin and HOE 140, we demonstrated that KKS activation caused the release of bradykinin, which activated B2 receptors and induced the shedding of adherens junction protein, VE-cadherin. These biological perturbations eventually resulted in endothelial paracellular permeability in mouse retina after intravitreal injection of MUA@AgNPs. The findings from this work provided key insights for toxicity modulation and biomedical applications of AgNPs.

Effect of miR-200b on retinal endothelial cell function under high glucose environment

As one of the important complications of diabetes, diabetic retinopathy (DR) presented high incidence worldwide. Hyperglycemia is an important promoting factor for DR occurrence and development. It can damage retinal endothelial cell, resulting in retinal structure and function disorder. Studies have shown that miR-200b may involve in regulating DR occurrence and development, but its specific function and mechanism have not been elucidated. This study aimed to investigate miR-200b effect and mechanism on human retinal endothelial cells (hRECs) under high glucose environment. hRECs were cultured under high glucose or normal environment. Real time PCR was applied to detect miR-200b expression. MiR-200b was transfected to hRECs and MTT was used to detect its effect on hRECs proliferation under high glucose environment. Real time PCR and Western blot were performed to determine VEGF and TGFβ1 expression in the retina endothelial cells. MiR-200b expression decreased significantly under high glucose environment, whereas hRECs proliferated obviously. Compared with normal control, VEGF and TGFβ1 mRNA and protein expression increased markedly (P < 0.05). After miR-200b transfection, miR-200b expression increased, while VEGF and TGFβ1 mRNA and protein expression decreased obviously. Compared with high glucose group, hRECs proliferation was inhibited (P < 0.05). MiR-200b can regulate RECs growth and proliferation by changing VEGF and TGFβ1 expression to delay DR.

Novel quinic acid derivative KZ-41 prevents retinal endothelial cell apoptosis without inhibiting retinoblastoma cell death through p38 signaling

PURPOSE

To determine whether a novel NF-κB inhibitor, KZ-41, can inhibit melphalan's actions on retinal endothelial cell (REC) inflammation and apoptosis, without eliminating the chemotherapeutic efficacy of melphalan on cell death of retinoblastoma cells (Y79).

METHODS

RECs were cultured in M131 medium supplemented with growth factors and antibiotics. Once cells reached confluence, they were treated with or without 10 μM KZ-41, following treatment with 4 μg/mL melphalan. Cell proteins were extracted and analyzed for intracellular adhesion molecule 1 (ICAM-1) levels and Cell Death ELISA. RECs were also transfected with or without NF-κB siRNA or treated with SB202190 (p38 [mitogen activated protein kinase] MAPK inhibitor) before melphalan treatment to determine the involvement of NF-κB and p38 MAPK in REC apoptosis and ICAM-1 levels. We also cultured retinoblastoma cells (Y79) in RMPI-1640 medium supplemented with 20% fetal bovine serum and performed a Cell Death ELISA after melphalan + KZ-41 treatment to determine if the treatments altered melphalan's ability to promote cell death of Y79 cells.

RESULTS

KZ-41 inhibited melphalan-stimulation of ICAM-1 levels and REC apoptosis, whereas KZ-41 did not alter melphalan's effects on Y79 cells. KZ-41's protective effects on REC were mediated through p38 MAPK activation. Although KZ-41 blocked both NF-κB- and p38 MAPK-dependent ICAM-1 stimulation; the p38 MAPK/ICAM-1 pathway appears to be the primary pathway involved in melphalan-induced REC apoptosis.

CONCLUSIONS

KZ-41 protects REC against melphalan-induced upregulation of ICAM-1 and apoptosis through p38 MAPK-dependent pathways.