The in vitro response of human retinal endothelial cells to cytokines and other chemically active agents is altered by coculture with vitreous-derived hyalocytes

Effects of tumor necrosis factor-α and interleukin-1β on human retinal endothelial cells

Uveitis, or intraocular inflammation, is a potentially blinding condition that mostly affects the working-age population. The cytokines, tumor necrosis factor (TNF)-α and interleukin (IL)-1β, play a role in the pathogenesis of non-infectious uveitis and have been linked to the breakdown of the inner blood-retinal barrier, composed mainly of retinal endothelial cells, leading to macular oedema and vascular leakage. However, the effects of TNF-α and IL-1β on human retinal endothelial function are not fully understood. In this work, we investigated the impact of TNF-α and IL-1β on several aspects of human retinal endothelial cell biology. Through a real-time biosensor, the impact of TNF-α and IL-1β on formation of a retinal endothelial cell barrier was analyzed. Changes in junctional components were assessed via RT-qPCR and immunolabelling. Cell survival, necrosis and apoptosis were appraised via cell proliferation and flow cytometric studies. Tumor necrosis factor-α and IL-1β impaired the electrical resistance of the retinal endothelial cell barrier, while the addition of a potentially barrier-impairing cytokine, IL-6, did not enhance the effect of TNF-α and IL-1β. Level of the gene transcript encoding zonula occludens (ZO)-1 was diminished, while ZO-1 protein configuration was changed by TNF-α and IL-1β. Both cytokines affected human retinal endothelial cell proliferation and viability, while only TNF-α increased rates of necrosis. These results indicate that TNF-α and IL-1β are important drivers of retinal endothelial dysfunction in non-infectious uveitis, suggesting that targeting these cytokines is critical when treating complications of uveitis, such as macular oedema and vascular leakage.

Inflammatory cytokines as mediators of retinal endothelial barrier dysfunction in non-infectious uveitis

Characterised by intraocular inflammation, non-infectious uveitis includes a large group of autoimmune and autoinflammatory diseases that either involve the eye alone or have both ocular and systemic manifestations. When non-infectious uveitis involves the posterior segment of the eye, specifically the retina, there is substantial risk of vision loss, often linked to breakdown of the inner blood-retinal barrier. This barrier is formed by non-fenestrated retinal vascular endothelial cells, reinforced by supporting cells that include pericytes, Müller cells and astrocytes. Across the published literature, a group of inflammatory cytokines stand out as prominent mediators of intraocular inflammation, with effects on the retinal endothelium that may contribute to breakdown of the inner blood-retinal barrier, namely tumour necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, IL-8, IL-17 and chemokine C-C motif ligand (CCL)2. This article reviews the function of each cytokine and discusses the evidence for their involvement in retinal endothelial barrier dysfunction in non-infectious uveitis, including basic laboratory investigations, studies of ocular fluids collected from patients with non-infectious uveitis, and results of clinical treatment trials. The review also outlines gaps in knowledge in this area. Understanding the disease processes at a molecular level can suggest treatment alternatives that are directed against appropriate biological targets to protect the posterior segment of eye and preserve vision in non-infectious uveitis.

Deciphering the Molecular Signature of Human Hyalocytes in Relation to Other Innate Immune Cell Populations

Purpose

Hyalocytes are the tissue-resident innate immune cell population of the vitreous body with important functions in health and vitreoretinal disease. The purpose of this study is to gain new insights into the biology and function of human hyalocytes in comparison to other innate immune cells.

Methods

The present study applies fluorescence-activated cell sorting and RNA sequencing to compare the transcriptional profiles of human hyalocytes, retinal microglia (rMG) and classical, intermediate, and non-classical monocytes isolated from the same patients. Immunohistochemistry was applied for morphological characterization of human hyalocytes.

Results

Pairwise analysis indicates distinct differences between hyalocytes and monocytes, whereas a high degree of similarity to rMG is apparent, with comparable expression levels of established microglia markers, such as TREM2, P2RY12, and TMEM119. Among the top expressed genes in hyalocytes, SPP1, CD74, and C3, were significantly upregulated when compared with monocytes. Despite the high level of similarity of hyalocytes and rMG, ten highly expressed genes in hyalocytes compared to microglia were identified, among them FOS, DUSP1, and EGR2.

Conclusions

This study reveals a high degree of similarity between hyalocytes and retinal microglia. Nevertheless, hyalocytes exhibit some expression differences that may adapt them to the specific needs of the vitreous and provide the basis for deciphering the multiple roles of this fascinating cell population in health and vitreoretinal diseases.

Antiangiogenic Effect of (±)-Haloperidol Metabolite II Valproate Ester [(±)-MRJF22] in Human Microvascular Retinal Endothelial Cells

(±)-MRJF22 [(±)-2], a novel prodrug of haloperidol metabolite II (sigma-1 receptor antagonist/sigma-2 receptor agonist ligand) obtained by conjugation to valproic acid (histone deacetylase inhibitor) via an ester bond, exhibits antiangiogenic activity, being able to reduce human retinal endothelial cell (HREC) viability in a comparable manner to bevacizumab. Moreover, (±)-2 was able to significantly reduce viable cells count, endothelial cell migration, and tube formation in vascular endothelial growth factor A (VEGF-A) stimulated HREC cultures.

Pharmacokinetics, pharmacodynamics and pre-clinical characteristics of ophthalmic drugs that bind VEGF

Drugs that prevent the binding of VEGF to its trans-membrane cognate receptors have revolutionized the treatment of the most important chorioretinal vascular disorders: exudative age-related macular degeneration, diabetic macular edema, and retinal vein occlusions. Pegaptanib, which binds to VEGF165 and longer isoforms, ranibizumab and bevacizumab, which bind all VEGF-A isoforms, and aflibercept, which binds VEGF-A, VEGF-B, and placental growth factor, all bind VEGF165 with high affinity. The drugs have relatively long half-lives (7 to 10 days) after intravitreal depot injections and clinical durations of action that usually exceed 4 weeks. Plasma VEGF concentrations decrease after intravitreal injections of bevacizumab and aflibercept because their systemic half-lives are extended by their Fc fragments. Extensive in vitro and in vivo testing shows that the drugs prevent VEGF-mediated activation of endothelial cells while exhibiting little evidence of toxicity. Further anti-VEGF drug development is on-going.

Modulation of retinal Müller cells by complement receptor C5aR

PURPOSE

Müller cells, a major type of glial cell found in the eye, are postulated to play an important role in many retinal diseases, including diabetic retinopathy (DR). Complement is an integral part of innate immunity, and the activation of complement has been associated with retinal diseases. However, the role of complement in the regulation of Müller cell function remains unclear. We were trying to address these issues in this study.

METHODS

Using primary human Müller cells and a spontaneously immortalized human Müller cell line, we examined the expression of complement receptor C5aR both at mRNA and protein levels. Regulation of C5aR expression on Müller cells by prostaglandin E2 and by hyperglycemia, both of which are integrally involved in DR, were studied. Significance of C5aR on Müller cells was also investigated by examining relevant cytokine productions and their impacts on retinal endothelial cell proliferation/permeability after ligating the receptor using its ligand, C5a.

RESULTS

C5aR is constitutively expressed in human Müller cells. Prostaglandin E2 and hyperglycemia individually and synergistically upregulate C5aR expression in Müller cells. Signaling through C5aR on Müller cells upregulates production of IL-6 and VEGF, which promotes the proliferation of human retinal endothelial cells and increases their permeability.

CONCLUSIONS

These results indicate that complement can regulate Müller cells through C5aR, which may contribute to the pathogenesis of retinal diseases, including DR.