Mouse retinal pigmented epithelial cell lines retain their phenotypic characteristics after transfection with human papilloma virus: a new tool to further the study of RPE biology

The unanticipated contribution of Zap70 in retinal degeneration: Implications for microglial inflammatory activation

Inflammation is a major mechanism of photoreceptor cell death in the retina during macular degeneration leading to the blindness. In this study, we investigated the role of the kinase molecule Zap70, which is an inflammatory regulator of the systemic immune system, to elucidate the control mechanism of inflammation in the retina. We observed activated microglial cells migrated and populated the retinal layer following blue LED-induced photoreceptor degeneration and activated microglial cells in the LED-injured retina expressed Zap70, unlike the inactive microglial cells in the normal retina. Visual function was considerably decreased in blue-LED light-exposed mice, and animals with Zap70 mutations were adversely affected. Furthermore, extensive photoreceptor cell death was observed in the SKG mice, bearing a Zap70 mutation that induces autoimmune disease. In the blue-LED light-exposed groups, SKG retinas had significantly higher levels of inflammatory cytokines than those in wild-type mice. Furthermore, regulating Zap70 activity has a significant influence on microglial inflammatory state. We discovered that active microglial cells expressing Zap70 could modify vascular endothelial growth factor A (Vegfa) signaling in primary retinal pigment epithelial (RPE) cells. Our novel study revealed that the production of Zap70 by retinal microglial cells is responsible for inflammatory signals that promote apoptosis in photoreceptor cells. Furthermore, Zap70-positive microglial cells were capable of regulating Vegfa signaling in RPE cells, which matches the hallmark of macular degeneration. Overall, we discovered Zap70's inflammatory activity in the retina, which is necessary for upregulating multiple inflammatory cytokines and cell death. Zap70 represents a novel therapeutic target for treating retinal degeneration.

Looking into the Eyes—In Vitro Models for Ocular Research

Animal research undoubtedly provides scientists with virtually unlimited data but inflicts pain and suffering on animals. Currently, legislators and scientists alike are promoting alternative in vitro approaches allowing for an accurate evaluation of processes occurring in the body without animal sacrifice. Historically, one of the most infamous animal tests is the Draize test, mainly performed on rabbits. Even though this test was considered the gold standard for around 50 years, the Draize test fails to mimic human response mainly due to human and rabbit eye physiological differences. Therefore, many alternative assays were developed to evaluate ocular toxicity and drug effectiveness accurately. Here we review recent achievements in tissue engineering of in vitro 2D, 2.5D, 3D, organoid and organ-on-chip ocular models, as well as in vivo and ex vivo models in terms of their advantages and limitations.

Uncontrolled Oxygen Levels in Cultures of Retinal Pigment Epithelium: Have We Missed the Obvious?

Retinal pigment epithelium (RPE) is the outermost layer of retina located between the photoreceptor cells and the choroid. This highly-polarized monolayer provides critical support for the functioning of the other parts of the retina, especially photoreceptors. Methods of culturing RPE have been under development since its establishment in 1920s. Despite considering various factors, oxygen (O₂) levels in RPE microenvironments during culture preparation and experimental procedure have been overlooked. O₂ is a crucial parameter in the cultures, and therefore, maintaining RPE cells at O₂ levels different from their native environment (70-90 mm Hg of O₂) could have unintended consequences. Owing to the importance of the topic, lack of sufficient discussion in the literature and to encourage future research, this paper will focus on uncontrolled O₂ level in cultures of RPE cells.

Role of Nuclear Factor of Activated T Cells (NFAT) Pathway in Regulating Autophagy and Inflammation in Retinal Pigment Epithelial Cells

Nuclear factor of activated T cells (NFAT) family of transcription factors are substrates of calcineurin and play an important role in integrating Ca²⁺ signaling with a variety of cellular functions. Of the five NFAT proteins (NFAT1-5), NFAT1-4 are subject to dephosphorylation and activation by calcineurin, a Ca²⁺-calmodulin-dependent phosphatase. Increased levels of intracellular Ca²⁺ activates calcineurin, which in turn dephosphorylates and promotes nuclear translocation of NFAT. We investigated the functions of NFAT proteins in the retinal pigment epithelial cells (RPE). Our results show that NFAT-mediated luciferase activity was induced upon treatment with the bacterial endotoxin, lipopolysaccharide (LPS) and treatment with the NFAT peptide inhibitor, MAGPHPVIVITGPHEE (VIVIT) decreased LPS-induced NFAT luciferase activity. LPS-induced activation of NFAT-regulated cytokines (IL-6 and IL-8) is inhibited by treatment of cells with VIVIT. We also investigated the effects of NFAT signaling on the autophagy pathway. Our results show that inhibition of NFAT with VIVIT in cells deprived of nutrients resulted in cytosolic retention of transcription Factor EB (TFEB), decreased expression of TFEB-regulated coordinated Lysosomal Expression and Regulation CLEAR network genes and decreased starvation-induced autophagy flux in the RPE cells. In summary, these studies suggest that the NFAT pathway plays an important role in the regulation of autophagy and inflammation in the RPE.

The Pharmacological Effects of Lutein and Zeaxanthin on Visual Disorders and Cognition Diseases

Lutein (L) and zeaxanthin (Z) are dietary carotenoids derived from dark green leafy vegetables, orange and yellow fruits that form the macular pigment of the human eyes. It was hypothesized that they protect against visual disorders and cognition diseases, such as age-related macular degeneration (AMD), age-related cataract (ARC), cognition diseases, ischemic/hypoxia induced retinopathy, light damage of the retina, retinitis pigmentosa, retinal detachment, uveitis and diabetic retinopathy. The mechanism by which they are involved in the prevention of eye diseases may be due their physical blue light filtration properties and local antioxidant activity. In addition to their protective roles against light-induced oxidative damage, there are increasing evidences that L and Z may also improve normal ocular function by enhancing contrast sensitivity and by reducing glare disability. Surveys about L and Z supplementation have indicated that moderate intakes of L and Z are associated with decreased AMD risk and less visual impairment. Furthermore, this review discusses the appropriate consumption quantities, the consumption safety of L, side effects and future research directions.

The COX-2-Selective Antagonist (NS-398) Inhibits Choroidal Neovascularization and Subretinal Fibrosis

Choroidal neovascularization (CNV) is an important pathologic component of neovascular age-related macular degeneration (AMD), and CNV lesions later develop into fibrous scars, which contribute to the loss of central vision. Nowadays, the precise molecular and cellular mechanisms underlying CNV and subretinal fibrosis have yet to be fully elucidated. Cyclooxygenase-2 (COX-2) has previously been implicated in angiogenesis and fibrosis. However, the role of COX-2 in the pathogenesis of CNV and subretinal fibrosis is poorly understood. The present study reveals several important findings concerning the relationship of COX-2 signaling with CNV and subretinal fibrosis. Experimental CNV lesions were attenuated by the administration of NS-398, a COX-2-selective antagonist. NS-398-induced CNV suppression was found to be mediated by the attenuation of macrophage infiltration and down-regulation of VEGF in the retinal pigment epithelium-choroid complex. Additionally, NS-398 attenuated subretinal fibrosis, in an experimental model of subretinal scarring observed in neovascular AMD, by down-regulation of TGF-β2 in the retinal pigment epithelium-choroid complex. Moreover, we cultured mouse RPE cells and found that NS-398 decreased the secretion of VEGF and TGF-β2 in mouse RPE cells. The results of the present study provide new findings regarding the molecular basis of CNV and subretinal fibrosis, and provide a proof-of-concept approach for the efficacy of COX-2 inhibition in treating subretinal fibrosis.

Barrier properties of cultured retinal pigment epithelium

The principal function of an epithelium is to form a dynamic barrier that regulates movement between body compartments. Each epithelium is specialized with barrier functions that are specific for the tissues it serves. The apical surface commonly faces a lumen, but the retinal pigment epithelium (RPE) appears to be unique by a facing solid tissue, the sensory retina. Nonetheless, there exists a thin (subretinal) space that can become fluid filled during pathology. RPE separates the subretinal space from the blood supply of the outer retina, thereby forming the outer blood-retinal barrier. The intricate interaction between the RPE and sensory retina presents challenges for learning how accurately culture models reflect native behavior. The challenge is heightened by findings that detail the variation of RPE barrier proteins both among species and at different stages of the life cycle. Among the striking differences is the expression of claudin family members. Claudins are the tight junction proteins that regulate ion diffusion across the spaces that lie between the cells of a monolayer. Claudin expression by RPE varies with species and life-stage, which implies functional differences among commonly used animal models. Investigators have turned to transcriptomics to supplement functional studies when comparing native and cultured tissue. The most detailed studies of the outer blood-retinal barrier have focused on human RPE with transcriptome and functional studies reported for human fetal, adult, and stem-cell derived RPE.

Efficacy of Ethanol Extract of Fructus lycii and Its Constituents Lutein/Zeaxanthin in Protecting Retinal Pigment Epithelium Cells against Oxidative Stress: In Vivo and In Vitro Models of Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a major cause of blindness worldwide. Oxidative stress plays a large role in the pathogenesis of AMD. The present study was to evaluate the effects of Fructus lycii ethanol extract on AMD in mice and to investigate whether combination of lutein and zeaxanthin, two carotenoid pigments in Fructus lycii, could protect human retinal pigment epithelial ARPE-19 cells treated with hydrogen peroxide (H₂O₂) in vitro. We found that severe sediment beneath retinal pigment epithelium and thickened Bruch membrane occurred in AMD mice. However, Fructus lycii ethanol extract improved the histopathologic changes and decreased the thickness of Bruch membrane. Furthermore, the gene and protein expression of cathepsin B and cystatin C was upregulated in AMD mice but was eliminated by Fructus lycii ethanol extract. Investigations in vitro showed that ARPE-19 cell proliferation was suppressed by H₂O₂. However, lutein/zeaxanthin not only stimulated cell proliferation but also abrogated the enhanced expression of MMP-2 and TIMP-1 in H₂O₂-treated ARPE-19 cells. These data collectively suggested that Fructus lycii ethanol extract and its active components lutein/zeaxanthin had protective effects on AMD in vivo and in vitro, providing novel insights into the beneficial role of Fructus lycii for AMD therapy.

Impacts of hypoxia-inducible factor-1 knockout in the retinal pigment epithelium on choroidal neovascularization

PURPOSE

Hypoxia-inducible factor (HIF)-1 is a key oxygen sensor and is believed to play an important role in neovascularization (NV). The purpose of this study is to determine the role of retinal pigment epithelium (RPE)-derived HIF-1α on ocular NV.

METHODS

Conditional HIF-1α knockout (KO) mice were generated by crossing transgenic mice expressing Cre in the RPE with HIF-1α floxed mice, confirmed by immunohistochemistry, Western blot analysis, and fundus fluorescein angiography. The mice were used for the oxygen-induced retinopathy (OIR) and laser-induced choroidal neovascularization (CNV) models.

RESULTS

HIF-1α levels were significantly decreased in the RPE layer of ocular sections and in primary RPE cells from the HIF-1α KO mice. Under normal conditions, the HIF-1α KO mice exhibited no apparent abnormalities in retinal histology or visual function as shown by light microscopy and electroretinogram recording, respectively. The HIF-1α KO mice with OIR showed no significant difference from the wild-type (WT) mice in retinal levels of HIF-1α and VEGF as well as in the number of preretinal neovascular cells. In the laser-induced CNV model, however, the disruption of HIF-1α in the RPE attenuated the over expression of VEGF and the intercellular adhesion molecule 1 (ICAM-1), and reduced vascular leakage and CNV area.

CONCLUSIONS

RPE-derived HIF-1α plays a key role in CNV, but not in ischemia-induced retinal NV.

Preparation of pre-confluent retinal cells increases graft viability in vitro and in vivo: a mouse model

PURPOSE

Graft failure remains an obstacle to experimental subretinal cell transplantation. A key step is preparing a viable graft, as high levels of necrosis and apoptosis increase the risk of graft failure. Retinal grafts are commonly harvested from cell cultures. We termed the graft preparation procedure "transplant conditions" (TC). We hypothesized that culture conditions influenced graft viability, and investigated whether viability decreased following TC using a mouse retinal pigment epithelial (RPE) cell line, DH01.

METHODS

Cell viability was assessed by trypan blue exclusion. Levels of apoptosis and necrosis in vitro were determined by flow cytometry for annexin V and propidium iodide and Western blot analysis for the pro- and cleaved forms of caspases 3 and 7. Graft viability in vivo was established by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and cleaved caspase 3 immunolabeling of subretinal allografts.

RESULTS

Pre-confluent cultures had significantly less nonviable cells than post-confluent cultures (6.6%±0.8% vs. 13.1%±0.9%, p<0.01). Cell viability in either group was not altered significantly following TC. Caspases 3 and 7 were not altered by levels of confluence or following TC. Pre-confluent cultures had low levels of apoptosis/necrosis (5.6%±1.1%) that did not increase following TC (4.8%±0.5%). However, culturing beyond confluence led to progressively increasing levels of apoptosis and necrosis (up to 16.5%±0.9%). Allografts prepared from post-confluent cultures had significantly more TUNEL-positive cells 3 hours post-operatively than grafts of pre-confluent cells (12.7%±3.1% vs. 4.5%±1.4%, p<0.001). Subretinal grafts of post-confluent cells also had significantly higher rates of cleaved caspase 3 than pre-confluent grafts (20.2%±4.3% vs. 7.8%±1.8%, p<0.001).

CONCLUSION

Pre-confluent cells should be used to maximize graft cell viability.

Estrogen receptor beta protects against in vivo injury in RPE cells

Epidemiological data suggest that estrogen deficiency in postmenopausal women may contribute to the severity of AMD. We discovered that 17beta-estradiol (E2) was a crucial regulator of the severity of extracellular matrix turnover (ECM) dysregulation both in vivo and in vitro. We also found in vitro that the presence of estrogen receptor (ER)beta regulates MMP-2 activity. Therefore in an attempt to delineate the role of the ER subtypes, female estrogen receptor knockout (ERKO) mice were fed a high-fat diet, and the eyes were exposed to seven 5-second doses of nonphototoxic levels of blue-green light over 2 weeks. Three months after cessation of blue light treatment, transmission electron microscopy was performed to assess severity of deposits, Bruchs membrane changes, and choriocapillaris endothelial morphology. We found that changes in the trimolecular complex of pro-MMP-2, MMP-14 and TIMP-2 correlated with increased Bruch's membrane thickening or sub-retinal deposit formation (basal laminar deposits) in ERKObeta mice. In addition RPE isolated from ERKObeta mice had an increase in expression of total collagen and a decrease in MMP-2 activity. Finally we found that ERK an intermediate signaling molecule in the MMP pathway was activated in RPE isolated from ERKObeta mice. These data suggest that mice which lack ERbeta are more susceptible to in vivo injury associated with environmental light and high fat diet.