Thy-1 Regulates VEGF-Mediated Choroidal Endothelial Cell Activation and Migration: Implications in Neovascular Age-Related Macular Degeneration

Cholesterol metabolism: physiological regulation and diseases

Cholesterol homeostasis is crucial for cellular and systemic function. The disorder of cholesterol metabolism not only accelerates the onset of cardiovascular disease (CVD) but is also the fundamental cause of other ailments. The regulation of cholesterol metabolism in the human is an extremely complex process. Due to the dynamic balance between cholesterol synthesis, intake, efflux and storage, cholesterol metabolism generally remains secure. Disruption of any of these links is likely to have adverse effects on the body. At present, increasing evidence suggests that abnormal cholesterol metabolism is closely related to various systemic diseases. However, the exact mechanism by which cholesterol metabolism contributes to disease pathogenesis remains unclear, and there are still unknown factors. In this review, we outline the metabolic process of cholesterol in the human body, especially reverse cholesterol transport (RCT). Then, we discuss separately the impact of abnormal cholesterol metabolism on common diseases and potential therapeutic targets for each disease, including CVD, tumors, neurological diseases, and immune system diseases. At the end of this review, we focus on the effect of cholesterol metabolism on eye diseases. In short, we hope to provide more new ideas for the pathogenesis and treatment of diseases from the perspective of cholesterol.

Cholesterol Oxidation Products: Potential Adverse Effect and Prevention of Their Production in Foods

Cholesterol oxidation products (COPs) are a group of substances formed during food processing. COPs in diet is a health concern because they may affect human health in association with the risk of various diseases including atherosclerosis, Alzheimer's disease, age-related macular degeneration, diabetes, and chronic gastrointestinal inflammatory colitis. Production of COPs in foods can be affected by many factors such as temperature, pH, light, oxygen, water, carbohydrates, fatty acids, proteins, and metal cations. The key issue is preventing its generation in foods. Some COPs can also be produced in vivo by both nonenzymatic and enzymatic-catalyzed oxidation reactions. Currently, a number of natural antioxidants such as catechins, flavonoids, and other polyphenols have been proven to inhibit the generation of COPs. In addition, measures taken during food processing can also minimize the production of COPs, such as the Maillard reaction and marinating food with plant polyphenol-rich seasonings. In conclusion, a comprehensive approach encompassing the suppression on COPs generation and implementation of processing measures is imperative to safeguard human health against the production of COPs in the food chain.

7-Ketocholesterol Promotes Retinal Pigment Epithelium Senescence and Fibrosis of Choroidal Neovascularization via IQGAP1 Phosphorylation-Dependent Signaling

Accumulation of 7-ketocholesterol (7KC) occurs in age-related macular degeneration (AMD) and was found previously to promote fibrosis, an untreatable cause of vision loss, partly through induction of endothelial-mesenchymal transition. To address the hypothesis that 7KC causes mesenchymal transition of retinal pigment epithelial cells (RPE), we exposed human primary RPE (hRPE) to 7KC or a control. 7KC-treated hRPE did not manifest increased mesenchymal markers, but instead maintained RPE-specific proteins and exhibited signs of senescence with increased serine phosphorylation of histone H3, serine/threonine phosphorylation of mammalian target of rapamycin (p-mTOR), p16 and p21, β-galactosidase labeling, and reduced LaminB1, suggesting senescence. The cells also developed senescence-associated secretory phenotype (SASP) determined by increased IL-1β, IL-6, and VEGF through mTOR-mediated NF-κB signaling, and reduced barrier integrity that was restored by the mTOR inhibitor, rapamycin. 7KC-induced p21, VEGF, and IL-1β were inhibited by an inhibitor of protein kinase C. The kinase regulates IQGAP1 serine phosphorylation. Furthermore, after 7KC injection and laser-induced injury, mice with an IQGAP1 serine 1441-point mutation had significantly reduced fibrosis compared to littermate control mice. Our results provide evidence that age-related accumulation of 7KC in drusen mediates senescence and SASP in RPE, and IQGAP1 serine phosphorylation is important in causing fibrosis in AMD.

Inhibition of AIF-1 alleviates laser-induced macular neovascularization by inhibiting endothelial cell proliferation via restrained p44/42 MAPK signaling pathway

Age-related macular degeneration (AMD) is a leading blinding disease worldwide, and macular neovascularization (MNV) is a common complication encountered in the advanced stages of AMD. While the underlying causes of MNV remain elusive, aberrant multiplication of choroidal endothelial cells (CECs) and increased vascular endothelial growth factor (VEGF) are thought to play significant roles in the occurrence and development of MNV. Allograft inflammatory factor-1(AIF-1) is a crucial regulatory factor of vascular tubular structure formation and growth, involving the proliferation and migration of vascular endothelial cells and various tumor cells. This study aimed to understand how AIF-1 effects the proliferation of CECs and the subsequent progression of MNV. To study this, a mouse MNV model was established through laser injury, and the AIF-1 expression levels were then measured using western blot and immunohistochemistry. AIF-1 siRNA was intravitreally injected to silence AIF-1 gene expression. Western blot and choroidal flat mount were performed to measure the progression of MNV and proliferation of the CECs. These results showed that the protein expression of AIF-1 was significantly elevated in the laser-induced mouse MNV model, and the expression trend was consistent with VEGF. The protein level of AIF-1 was significantly decreased after the intravitreal injection of AIF-1 siRNA, the damage range of laser lesions was significantly reduced, and the proliferation of endothelial cells was inhibited. Knockdown of the AIF-1 gene significantly inhibited the expression of mitogen-activated protein kinase p44/42 in MNV lesions. In summary, this research demonstrates that AIF-1 promoted MNV progression by promoting the proliferation of CECs and that silencing AIF-1 significantly ameliorates MNV progression in mouse models, which may act through the p44/42 MAPK signaling pathway. AIF-1 could be a new potential molecular target for MNV.

An innovative immunotherapeutic strategy for rheumatoid arthritis: Selectively suppressing angiogenesis and osteoclast differentiation by fully human antibody targeting thymocyte antigen-1

Thymocyte antigen-1 (THY-1)is a potential target for rheumatoid arthritis (RA) treatment, and THY-1 positive fibroblast-like synoviocytes (FLS) are enriched in the synovium of RA patients and participate in angiogenesis to accelerate RA progression. In this study, we screened an antibody targeting THY-1 (THY-1 Ab) and explored its mechanism in alleviating RA progression. THY-1 Ab was screened from ScFv phage antibody library by phage display technology (PDT). THY-1 Ab-treated collagen induced arthritis (CIA) mice had lower degree of arthritis scores. We explore the mechanism of THY-1 Ab in alleviating RA progression. THY-1 Ab can remarkably inhibit the secretion of pro-inflammatory factors and promote the secretion of anti-inflammatory factors. Further experiments showed that THY1 Ab downregulated the expression of JUNB by the hsa_circ_0094342/miRNA-155-5P/SPI1 axis, inhibited RA angiogenesis and osteoclast differentiation, and relieved RA progression. These findings support that THY-1 Ab is a promising therapeutic antibody for RA treatment.

Thy-1 (CD90), Integrins and Syndecan 4 are Key Regulators of Skin Wound Healing

Acute skin wound healing is a multistage process consisting of a plethora of tightly regulated signaling events in specialized cells. The Thy-1 (CD90) glycoprotein interacts with integrins and the heparan sulfate proteoglycan syndecan 4, generating a trimolecular complex that triggers bi-directional signaling to regulate diverse aspects of the wound healing process. These proteins can act either as ligands or receptors, and they are critical for the successful progression of wound healing. The expression of Thy-1, integrins, and syndecan 4 is controlled during the healing process, and the lack of expression of any of these proteins results in delayed wound healing. Here, we review and discuss the roles and regulatory events along the stages of wound healing that support the relevance of Thy-1, integrins, and syndecan 4 as crucial regulators of skin wound healing.

Regulation of Rac1 Activation in Choroidal Endothelial Cells: Insights into Mechanisms in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is one of the leading causes of blindness worldwide. Vision loss from the neovascular form is associated with the invasion of choroidal endothelial cells into the neural retina to form vision-threatening macular neovascularization (MNV). Anti-angiogenic agents are the current standard of care but are effective in only ~50% of AMD cases. The molecular mechanisms involved in invasive MNV point to the importance of regulating signaling pathways that lead to pathologic biologic outcomes. In studies testing the effects of AMD-related stresses, activation of the Rho GTPase, Rac1, was found to be important for the choroidal endothelial cell invasion into the neural retina. However, current approaches to prevent Rac1 activation are inefficient and less effective. We summarize active Rac1-mediated mechanisms that regulate choroidal endothelial cell migration. Specifically, we discuss our work regarding the role of a multidomain protein, IQ motif containing GTPase activating protein 1 (IQGAP1), in sustaining pathologic Rac1 activation and a mechanism by which active Rap1, a Ras-like GTPase, may prevent active Rac1-mediated choroidal endothelial cell migration.

Memantine, Simvastatin, and Epicatechin Inhibit 7-Ketocholesterol-induced Apoptosis in Retinal Pigment Epithelial Cells But Not Neurosensory Retinal Cells In Vitro

Purpose

7-ketocholesterol (7kCh), a natural byproduct of oxidation in lipoprotein deposits is implicated in the pathogenesis of diabetic retinopathy and age-related macular degeneration (AMD). This study was performed to investigate whether several clinical drugs can inhibit 7kCh-induced caspase activation and mitigate its apoptotic effects on retinal cells in vitro.

Methods

Two populations of retinal cells, human retinal pigment epithelial cells (ARPE-19) and rat neuroretinal cells (R28) were exposed to 7kCh in the presence of the following inhibitors: Z-VAD-FMK (pan-caspase inhibitor), simvastatin, memantine, epicatechin, and Z-IETD-FMK (caspase-8 inhibitor) or Z-ATAD-FMK (caspase-12 inhibitor). Caspase-3/7, -8, and -12 activity levels were measured by fluorochrome caspase assays to quantify cell death. IncuCyte live-cell microscopic images were obtained to quantify cell counts.

Results

Exposure to 7kCh for 24 hours significantly increased caspase activities for both ARPE-19 and R28 cells (P< 0.05). In ARPE cells, pretreatment with various drugs had significantly lower caspase-3/7, -8, and -12 activities, reported in % change in mean signal intensity (msi): Z-VAD-FMK (48% decrease, P< 0.01), memantine (decreased 47.8% at 1 µM, P = 0.0039 and 81.9% at 1 mM, P< 0.001), simvastatin (decreased 85.3% at 0.01 µM, P< 0.001 and 84.8% at 0.05 µM, P< 0.001) or epicatechin (83.6% decrease, P< 0.05), Z-IETD-FMK (68.1% decrease, P< 0.01), and Z-ATAD-FMK (47.7% decrease, P = 0.0017). In contrast, R28 cells exposed to 7kCh continued to have elevated caspase-3/7, -8, and -12 activities (between 25.7% decrease and 17.5% increase in msi, P> 0.05) regardless of the pretreatment.

Conclusion

Several current drugs protect ARPE-19 cells but not R28 cells from 7kCh-induced apoptosis, suggesting that a multiple-drug approach is needed to protect both cells types in various retinal diseases.

Computational Approach to Investigating Key GO Terms and KEGG Pathways Associated with CNV

Choroidal neovascularization (CNV) is a severe eye disease that leads to blindness, especially in the elderly population. Various endogenous and exogenous regulatory factors promote its pathogenesis. However, the detailed molecular biological mechanisms of CNV have not been fully revealed. In this study, by using advanced computational tools, a number of key gene ontology (GO) terms and KEGG pathways were selected for CNV. A total of 29 validated genes associated with CNV and 17,639 nonvalidated genes were encoded based on the features derived from the GO terms and KEGG pathways by using the enrichment theory. The widely accepted feature selection method-maximum relevance and minimum redundancy (mRMR)-was applied to analyze and rank the features. An extensive literature review for the top 45 ranking features was conducted to confirm their close associations with CNV. Identifying the molecular biological mechanisms of CNV as described by the GO terms and KEGG pathways may contribute to improving the understanding of the pathogenesis of CNV.

Inhibition of YAP ameliorates choroidal neovascularization via inhibiting endothelial cell proliferation

Purpose

Age-related macular degeneration (AMD) is the leading cause of central visual loss among patients over the age of 55 years worldwide. Neovascular-type AMD (nAMD) accounts for approximately 10% of patients with AMD and is characterized by choroidal neovascularization (CNV). The proliferation of choroidal endothelial cells (CECs) is one important step in the formation of new vessels. Transcriptional coactivator Yes-associated protein (YAP) can promote the proliferation of multiple cancer cells, corneal endothelial cells, and vascular smooth muscle cells, which participate in angiogenesis. This study intends to reveal the expression and functions of YAP during the CNV process.

Methods

In the study, a mouse CNV model was generated by laser photocoagulation. YAP expression was detected with western blotting and immunohistochemistry. YAP siRNA and ranibizumab, a VEGF monoclonal antibody, were injected intravitreally in CNV mice. The YAP and VEGF expression levels after injection were detected with western blotting. The incidence and leakage area of CNV were measured with fundus fluorescein angiography, choroidal flat mounting, and hematoxylin and eosin (HE) staining. Immunofluorescent double staining was used to detect YAP cellular localization with CD31 (an endothelial cell marker) antibody. Proliferating cell nuclear antigen (PCNA) expression in CNV mice without or with YAP siRNA intravitreal injection and the colocalization of PCNA and CD31 were measured with western blotting and immunofluorescent double staining, respectively.

Results

YAP expression increased following laser exposure, in accordance with vascular endothelial growth factor (VEGF) expression. YAP siRNA and ranibizumab decreased VEGF expression and the incidence and leakage area of CNV. YAP was localized in the vascular endothelium within the CNV site. Additionally, after laser exposure, YAP siRNA inhibited the increased expression of PCNA, which was colocalized with endothelial cells.

Conclusions

This study showed that YAP upregulation promoted CNV formation by upregulating the proliferation of endothelial cells, providing evidence for the molecular mechanisms of CNV and suggesting a novel molecular target for nAMD treatment.

Serine racemase deficiency attenuates choroidal neovascularization and reduces nitric oxide and VEGF levels by retinal pigment epithelial cells

Choroidal neovascularization (CNV) is a leading cause of blindness in age-related macular degeneration. Production of vascular endothelial growth factor (VEGF) and macrophage recruitment by retinal pigment epithelial cells (RPE) significantly contributes to the process of CNV in an experimental CNV model. Serine racemase (SR) is expressed in retinal neurons and glial cells, and its product, d-serine, is an endogenous co-agonist of N-methyl-d-aspartate receptor. Activation of the receptor results in production of nitric oxide (^. NO), a molecule that promotes retinal and choroidal neovascularization. These observations suggest possible roles of SR in CNV. With laser-injured CNV mice, we found that inactivation of SR-coding gene (Srr_null ) significantly reduced CNV volume, neovascular density, and invading macrophages. We exploited the underlying mechanism in vivo and ex vivo. RPE from wild-type (WT) mice expressed SR. To explore the possible downstream target of SR inactivation, we showed that choroid/RPE homogenates extracted from laser-injured Srr_null mice contained less inducible nitric oxide synthase and decreased phospho-VEGFR2 compared to amounts in WT mice. In vitro, inflammation-primed WT RPEs expressed more inducible NOS, produced more^. NO and VEGF than did inflammation-primed Srr_null RPEs. When co-cultured with inflammation-primed Srr_null RPE, significantly fewer RF/6A-a cell line of choroidal endothelial cell, migrated to the opposite side of the insert membrane than did cells co-cultured with pre-treated WT RPE. Altogether, SR deficiency reduces RPE response to laser-induced inflammatory stimuli, resulting in decreased production of a cascade of pro-angiogenic cytokines, including^. NO and VEGF, and reduced macrophage recruitment, which contribute synergistically to attenuated angiogenesis.