Inhibition of integrin α5β1 ameliorates VEGF-induced retinal neovascularization and leakage by suppressing NLRP3 inflammasome signaling in a mouse model

Classical and Innovative Evidence for Therapeutic Strategies in Retinal Dysfunctions

The human retina is a complex anatomical structure that has no regenerative capacity. The pathogenesis of most retinopathies can be attributed to inflammation, with the activation of the inflammasome protein platform, and to the impact of oxidative stress on the regulation of apoptosis and autophagy/mitophagy in retinal cells. In recent years, new therapeutic approaches to treat retinopathies have been investigated. Experimental data suggest that the secretome of mesenchymal cells could reduce oxidative stress, autophagy, and the apoptosis of retinal cells, and in turn, the secretome of the latter could induce changes in mesenchymal cells. Other studies have evidenced that noncoding (nc)RNAs might be new targets for retinopathy treatment and novel disease biomarkers since a correlation has been found between ncRNA levels and retinopathies. A new field to explore is the interaction observed between the ocular and intestinal microbiota; indeed, recent findings have shown that the alteration of gut microbiota seems to be linked to ocular diseases, suggesting a gut-eye axis. To explore new therapeutical strategies for retinopathies, it is important to use proper models that can mimic the complexity of the retina. In this context, retinal organoids represent a good model for the study of the pathophysiology of the retina.

ATN-161 Ameliorates Ischemia/Reperfusion-induced Oxidative Stress, Fibro-inflammation, Mitochondrial damage, and Apoptosis-mediated Tight Junction Disruption in bEnd.3 Cells

We have previously demonstrated the significance of endothelial cell-expressed α5β1 integrin in ischemic stroke, having shown that α5β1 integrin endothelial cell-selective knockout mice are significantly resistance to ischemic stroke injury via preservation of the tight junction protein claudin-5 and subsequent stabilization of the blood–brain barrier (BBB). In addition, inhibition of α5β1 by the small peptide noncompetitive integrin α5 inhibitor, ATN-161, is beneficial in a mouse model of ischemic stroke through reduction of infarct volume, edema, stabilization of the BBB, and reduced inflammation and immune cell infiltration into the brain. In continuation with our previous findings, we have further evaluated the mechanistic role of ATN-161 in vitro and found that oxygen and glucose deprivation and reperfusion (OGD/R)-induced inflammation, oxidative stress, apoptosis, mitochondrial depolarization, and fibrosis attenuate tight junction integrity via induction of α5, NLRP3, p-FAK, and p-AKT signaling in mouse brain endothelial cells. ATN-161 treatment (10 µM) effectively inhibited OGD/R-induced extracellular matrix (ECM) deposition by reducing integrin α5, MMP-9, and fibronectin expression, as well as reducing oxidative stress by reducing mitochondrial superoxide radicals, intracellular ROS, inflammation by reducing NLRP3 inflammasome, tight junction loss by reducing claudin-5 and ZO-1 expression levels, mitochondrial damage by inhibiting mitochondrial depolarization, and apoptosis via regulation of p-FAK and p-AKT levels. Taken together, our results further support therapeutically targeting α5 integrin with ATN-161, a safe, well-tolerated, and clinically validated peptide, in ischemic stroke.

The IL-23/IL-17 axis promotes the formation of retinal neovascularization by activating the NLRP3 inflammasome in macrophages in an experimental retinopathy mouse model

Retinal neovascularization (RNV), a pathological process shared among diabetic retinopathy, retinopathy of prematurity and other retinopathies, has been widely studied, but the mechanism remains unclear. In this study, the mechanism by which the interleukin (IL)-23/IL-17 axis regulates RNV in oxygen-induced retinopathy (OIR) model mice and in cell experiments in vitro was characterized. In the retinas of OIR mice, IL-23/IL-17 axis activation was increased and regulated RNV formation, and this effect was accompanied by increased macrophage recruitment and nucleotide-binding domain leucine-rich repeat and pyrin domain containing receptor 3 (NLRP3) inflammasome activation. Moreover, inhibiting the IL-23/IL-17 axis reduced the number of macrophage and the expression and activation of NLRP3 inflammasome. On the other hand, recombinant (r) IL-23p19 and rIL-17A promoted the expression and activation of NLRP3 inflammasome, and the proliferation and migration of macrophages. Furthermore, macrophage elimination decreased the activation of IL-23/IL-17 axis and the expression and activation of NLRP3 inflammasome. In summary, our experiments showed that the IL-23/IL-17 axis promoted the formation of RNV by activating the NLRP3 inflammasome in retinal macrophages of an OIR mouse model.

Targeting RGD-binding integrins as an integrative therapy for diabetic retinopathy and neovascular age-related macular degeneration

Integrins are a class of transmembrane receptors that are involved in a wide range of biological functions. Dysregulation of integrins has been implicated in many pathological processes and consequently, they are attractive therapeutic targets. In the ophthalmology arena, there is extensive evidence suggesting that integrins play an important role in diabetic retinopathy (DR), age-related macular degeneration (AMD), glaucoma, dry eye disease and retinal vein occlusion. For example, there is extensive evidence that arginyl-glycyl-aspartic acid (Arg-Gly-Asp; RGD)-binding integrins are involved in key disease hallmarks of DR and neovascular AMD (nvAMD), specifically inflammation, vascular leakage, angiogenesis and fibrosis. Based on such evidence, drugs that engage integrin-linked pathways have received attention for their potential to block all these vision-threatening pathways. This review focuses on the pathophysiological role that RGD-binding integrins can have in complex multifactorial retinal disorders like DR, diabetic macular edema (DME) and nvAMD, which are leading causes of blindness in developed countries. Special emphasis will be given on how RGD-binding integrins can modulate the intricate molecular pathways and regulate the underlying pathological mechanisms. For instance, the interplay between integrins and key molecular players such as growth factors, cytokines and enzymes will be summarized. In addition, recent clinical advances linked to targeting RGD-binding integrins in the context of DME and nvAMD will be discussed alongside future potential for limiting progression of these diseases.

RGD-binding integrins and TGF-β in SARS-CoV-2 infections - novel targets to treat COVID-19 patients?

The new coronavirus SARS-CoV-2 is a global pandemic and a severe public health crisis. SARS-CoV-2 is highly contagious and shows high mortality rates, especially in elderly and patients with pre-existing medical conditions. At the current stage, no effective drugs are available to treat these patients. In this review, we analyse the rationale of targeting RGD-binding integrins to potentially inhibit viral cell infection and to block TGF-β activation, which is involved in the severity of several human pathologies, including the complications of severe COVID-19 cases. Furthermore, we demonstrate the correlation between ACE2 and TGF-β expression and the possible consequences for severe COVID-19 infections. Finally, we list approved drugs or drugs in clinical trials for other diseases that also target the RGD-binding integrins or TGF-β. These drugs have already shown a good safety profile and, therefore, can be faster brought into a trial to treat COVID-19 patients.

Experimental models and examination methods of retinal detachment

Retinal detachment refers to the separation of the retinal neuroepithelium and pigment epithelium, usually involving the death of photoreceptor cells. Severe detachment may lead to permanent visual impairment if not treated properly and promptly. According to the underlying causes, retinal detachment falls into one of three categories: exudative retinal detachment, traction detachment, and rhegmatogenous retinal detachment. Like many other diseases, it is difficult to study the pathophysiology of retinal detachment directly in humans, because the human retinal tissues are precious, scarce and non-regenerative; thus, establishing experimental models that better mimic the disease is necessary. In this review, we summarize the existing models of the three categories of retinal detachment both in vivo and in vitro, along with an overview of their examination methods and the major strengths and weaknesses of each model.

Inhibiting the NLRP3 inflammasome with MCC950 ameliorates retinal neovascularization and leakage by reversing the IL-1β/IL-18 activation pattern in an oxygen-induced ischemic retinopathy mouse model

Activation of the nucleotide-binding domain leucine-rich repeat and pyrin domain containing receptor 3 (NLRP3) inflammasome plays an important role in ocular neovascularization. In our study, we found that the expression and activation levels of NLRP3 inflammasome components, including NLRP3, an apoptosis-associated speck-like protein (ASC) containing caspase activation and recruitment domain (CARD) and caspase-1 (CAS1), were significantly upregulated. In addition, we found interleukin (IL)-1β activity increased while IL-18 activity decreased in the retinas of oxygen-induced ischemic retinopathy (OIR) mice. MCC950, an inhibitor of NLRP3, reversed the IL-1β/IL-18 activation pattern, inhibited the formation of retinal neovascularization (RNV), decreased the number of acellular capillaries and reduced leakage of retinal vessels. Moreover, MCC950 could regulate the expression of endothelial cell- and pericyte function-associated molecules, such as vascular endothelial growth factor (VEGF), VEGF receptor (VEGFR)1, VEGFR2, matrix metalloproteinase (MMP)2, MMP9, tissue inhibitor of metalloproteinases (TIMP)1, TIMP2, platelet-derived growth factor receptor-β (PDGFR-β), platelet-derived growth factor-B (PDGF-B), and angiopoietin2 (Ang2). In vitro, recombinant human (r)IL-18 and rIL-1β regulated the expression of endothelial cell- and pericyte function-associated molecules and the proliferation and migration of endothelial cells and pericytes. We therefore determined that inhibiting the NLRP3 inflammasome with MCC950 can regulate the function of endothelial cells and pericytes by reversing the IL-1β/IL-18 activation pattern to ameliorate RNV and leakage; thereby opening new avenues to treat RNV-associated ocular diseases.

Anti-integrin therapy for retinovascular diseases

INTRODUCTION

Integrins are a family of multi-functional cell-adhesion molecules, heterodimeric receptors that connect extracellular matrix (ECM) to actin cytoskeleton in the cell cortex, thus regulating cellular adhesion, migration, proliferation, invasion, survival, and apoptosis. Consequently, integrins play a role in inflammation, angiogenesis and fibrosis.

AREAS COVERED

This review examines individual anti-integrin agents in terms of their chemical nature, route of administration, and anti-integrin action. It also provides a summary of preclinical and clinical studies. Current clinical candidates include risuteganib, THR-687, and SF-0166, which have shown promise in treating diabetic macular edema (DME) and/or age-related macular degeneration (AMD) in early clinical studies. Preclinical candidates include SB-267268, AXT-107, JNJ-26076713, Cilengitide and Lebecetin, which exhibit a decrease in retinal permeability, angiogenesis and/or choroidal neovascularization (CNV).

EXPERT OPINION

Anti-integrin therapies show potential in treating retinal diseases. Anti-integrin agents tackle the multi-factorial nature of diabetic retinopathy (DR) and AMD and show promise as injectable and topical agents in preclinical and early clinical studies. Integrin inhibition has potential to serve as primary therapy, adjunctive therapy to anti-vascular endothelial growth factor agents, or secondary therapy in refractory cases.

Integrin α5β1 promotes BMCs mobilization and differentiation to exacerbate choroidal neovascularization

Choroidal neovascularization (CNV) is an acknowledged pathogenic mechanism of various ocular diseases, and in situ cells and mobilized bone marrow-derived cells (BMCs) are thought to participate in this process. We aimed to evaluate the roles of integrin α5 in BMCs and vascular endothelial cells (VECs) in the CNV process mediated by SDF-1/CXCR4 signaling. Adult wild-type mice were engrafted with whole BMCs obtained from GFP transgenic mice and then laser injured to induce CNV. BMCs and RF/6A cells were cultured to discover the mechanism of CNV in vitro. BMCs were mobilized to CNV areas, which expressed elevated SDF-1 and CXCR4. When SDF-1 was intravitreally injected, the number of BMCs was profoundly increased. In the SDF-1-treated group, the levels of integrin α5 expressed on BMCs and VECs were significantly higher than those on the cells in the control group. SDF-1 significantly increased the expression and positive ratio of integrin α5, which was involved in the recruitment and differentiation of BMCs into BMC-derived VECs, and these effects were suppressed by the CXCR4 inhibitor AMD3100. The PI3K/AKT pathway rather than the ERK pathway mediated SDF-1/CXCR4 induction of integrin α5. Integrin α5 suppression efficiently prevented the production of TGF-β and bFGF but not VEGF. Inhibiting the SDF-1/CXCR4-PI3K/AKT-integrin α5 axis reduced CNV severity. Integrin α5 participates in BMC recruitment and differentiation in SDF-1/CXCR4-induced CNV and inhibition of this pathway may be a new approach to inhibit CNV.

Toxicity of cooking oil fume derived particulate matter: Vitamin D3 protects tubule formation activation in human umbilical vein endothelial cells

Cooking oil fumes-derived PM_2.5 (COFs-derived PM_2.5) is the main source of indoor pollution. Exposure to COFs-derived PM_2.5 can cause oxidative stress and affect angiogenesis. Here we investigated the roles of vitamin D₃ (VD₃) in protecting tubule formation injury induced by COFs-derived PM_2.5, and the roles of ROS/NLRP3/VEGF signaling pathway in the effects. Human umbilical vein endothelial cells (HUVECs) were exposed to 0 (1‰ DMSO), 1000 nmol/l VD₃, 100 μg/ml PM_2.5, and 1000 nmol/l VD₃ + 100 μg/ml PM_2.5, respectively. Cell viability and tube formation, as well as protein and mRNA levels were measured. The results showed that exposure of COFs-derived PM_2.5 dose-and time-dependently reduced the viability of HUVECs, increased the levels of mitochondrial and intracellular ROS, and changed the mitochondrial membrane potential level. While co-incubation with VD₃ rescued these adverse effects. Both Western blot and real-time PCR (RT-PCR) showed that the expressions of NLRP3, caspase-1, Interleukin (IL)-1β, and IL-18 in COFs-derived PM_2.5 exposure group increased significantly, which could be effectively decreased by co-incubation with VD₃. COFs-derived PM_2.5 exposure could also reduce the expression of VEGF, while co-incubating HUVECs with VD₃ evidently up-regulated the protein level of VEGF in HUVECs. In addition, COFs-derived PM_2.5 could also inhibit the tube formation of HUVECs in vitro, which could be effectively rescued by the co-incubation of VD₃. Our study proved that COFs-derived PM_2.5 could damage the tubule formation of HUVECs in vitro, which could be effectively rescue by co-incubation with VD₃, in which processes the ROS/NLRP3/VEGF signaling pathway played a crucial role. It provides a new theoretical basis for further study on the toxicity of PM_2.5 to umbilical cord blood vessels.

NLRP3 Blockade Suppresses Pro-Inflammatory and Pro-Angiogenic Cytokine Secretion in Diabetic Retinopathy

BACKGROUND

Inflammation and angiogenesis are the two dominant mechanisms of diabetic retinopathy (DR), which act more as mutual pathways rather than individual processes. However, the underlying mechanism of their interactions is still unclear. Here, we explored the potential crossing points between these pathways and the targeted therapeutic method in rats with DR.

MATERIALS AND METHODS

Sprague-Dawley rats were randomly assigned to four groups: normal control group, streptozocin (STZ)-induced diabetes mellitus (DM) group, DM+shNC (non-specific negative control shRNA) group, and DM+shNLRP3 group. Silencing the NLR family pyrin domain containing 3 (NLRP3) protein was performed by intravitreal injections of NLRP3-targeted shRNA (shNLRP3) for rats in the DM+shNLRP3 group. All the rats' retinas were collected for further morphological examination and pro-inflammatory and pro-angiogenic cytokine detection. Human retinal endothelial cells (HRECs) were also employed to explore the underlying mechanism.

RESULTS

NLRP3-targeted shRNA given by intravitreal injection effectively alleviated the retinal histopathological changes in STZ-induced diabetic rats, which reduced the activation of the NLRP3 inflammasome and suppressed the expressions of hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF), and inflammatory cytokines in diabetic rats' retinas. In HRECs, NLRP3 over-expressing plasmid evoked an increase in pro-inflammatory cytokines and VEGF. In addition, YC-1, a HIF-1α inhibitor, could reverse the NLRP3 over-expression-induced VEGF production but not the pro-inflammatory cytokine expressions.

CONCLUSION

Our results suggest NLRP3 inflammasome as the potential cross-point between inflammation and pro-angiogenesis in DR and support the effectiveness of NLRP3-targeted shRNA administrated by intravitreal injection in animal models of DR. The protective effect of NLRP3-targeted shRNA may stem from the inhibition of both pro-inflammatory cytokines and HIF-1α/VEGF axis.

Extracellular Vesicles as a Neprilysin Delivery System Memory Improvement in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative brain disorder which has no effective treatment yet due to the blood barrier in the brain that limits the drugs with the potential of disease improvement. Extracellular vesicles (EVs) are biocompatible nanoparticles with a lipid membrane. These vesicles are secreted from various cells such as mesenchymal stem cells (MSCs) and can pass through biological barriers for transfer of information such as signals or be used as carriers for various proteins like Neprilysin (NEP). NEP is an active enzyme in the clearance of abnormal aggregated beta-amyloid sheets in the brain. In the present study, we used EVs to carry NEP for memory improvement in Alzheimer's disease. For this purpose, bone marrow MSCs were isolated from rat femur. Stemness evaluation of established cells was characterized by differentiation potency and specific markers with flowcytometry. EVs were isolated from MSCs supernatant by ultracentrifugation and analyzed by scanning electron microscopy (SEM), dynamic light scattering (DLS) and western blotting. EVs were loaded with NEP by freeze-thaw cycle and then administrated intranasally in a rat model of the AD for 14 days. Our findings showed EV-loaded NEP caused a decrease in IL-1beta and also BAX but an increase in BCL2 expression level in the rat brain. Altogether, these data showed that EV-loaded NEP can improve brain-related behavioural function which may be mediated through the regulation of inflammation and apoptosis. These findings suggest that EV-loaded NEP can be considered as a potential drug delivery system for the improvement of AD.

ATN-161 reduces virus proliferation in PHEV-infected mice by inhibiting the integrin α5β1-FAK signaling pathway

Porcine hemagglutinating encephalomyelitis virus (PHEV) is a typical neurotropic virus that can cause obvious nerve damage. Integrin α5β1 is a transmembrane macromolecular that closely related to neurological function. We recently demonstrated that integrin α5β1 plays a critical role in PHEV invasion in vitro. To determine the function and mechanism of integrin α5β1 in virus proliferation in vivo, we established a mouse model of PHEV infection. Integrin α5β1-FAK signaling pathway was activated in PHEV-infected mice by qPCR, Western blotting, and GST pull-down assays. Viral proliferation and integrin α5β1-FAK signaling pathway were significantly inhibited after intravenous injection of ATN-161, an integrin α5β1 inhibitor. Through a histological analysis, we found that ATN-161-treated mice only showed pathological changes in neuronal cytoplasmic swelling at 5 day post-infection. In summary, our results provide the first evidence that ATN-161 inhibits the proliferation of PHEV in mice and explores its underlying mechanisms of action.

β‑elemene inhibits oxygen‑induced retinal neovascularization via promoting miR‑27a and reducing VEGF expression

The present study aimed to investigate the significant role of β-elemene in mouse models of oxygen-induced retinopathy (OIR). C57BL/6J neonatal mice were used to establish OIR models. They were divided into four groups: Normoxia, OIR, OIR control and OIR‑treated. Mice in the OIR group were exposed to 75±5% oxygen for 5 days and returned to a normal oxygen environment on postnatal day 12 (P12). The OIR treated group was intravitreally injected with 1 µl β‑elemene on P12 and subsequently returned to a normal oxygen environment for 5 days (P12‑P17). Retinas were obtained on P17. Retinal neovascularization (RNV) was detected using adenosine diphosphatase staining and analyzed by counting the nuclei of neovascular endothelial cells. Vascular endothelial growth factor (VEGF) expression was determined by reverse transcription‑quantitative polymerase chain reaction, immunohistochemistry and western blot analysis. MicroRNA (miRNA/miR) microarrays were used to screen out differentially expressed miRNAs between the OIR and β‑elemene‑treated groups. Binding the 3'‑untranslated region (UTR) of VEGF and miR‑27a was confirmed using luciferase assays. It was found that high oxygen concentrations accelerated RNV and increased the number of preretinal neovascular cells; β‑elemene treatment reduced these effects. VEGF mRNA and protein expression was higher in the OIR and OIR control groups, compared with the normoxia and OIR‑treated groups. Further, it was shown that miR‑22, miR‑181a‑1, miR‑335‑5p, miR‑669n, miR‑190b, miR‑27a and miR‑93 were upregulated in the OIR‑treated group, and downregulated in the OIR group. The prediction websites TargetScan and miRanda revealed that VEGF contained a potential miR‑27a binding site in its 3'‑untranslated region (UTR). Luciferase assays demonstrated that miR‑27a directly bound to the 3'‑UTR of VEGF. In vitro experiments demonstrated that miR‑27a inhibited VEGF expression. In addition, β‑elemene treatment upregulate miR‑27a expression in vivo and in vitro. When miR‑27a expression was depleted by miR‑27a inhibitor, the protective effect of β‑elemene on RNV was eliminated. The present study demonstrated that β‑elemene reduced RNV in mouse OIR models via miR‑27a upregulation, leading to reduced VEGF expression. This finding may contribute to the development of novel therapeutic strategies for human retinopathy.