Engineering a Biomimetic In Vitro Model of Bruch's Membrane Using Hagfish Slime Intermediate Filament Proteins

Bruch's membrane resides in the subretinal tissue and regulates the flow of nutrients and waste between the retinal pigment epithelial (RPE) and vascular layers of the eye. With age, Bruch's membrane becomes thicker, stiffer, and less permeable, which impedes its function as a boundary layer in the subretina. These changes contribute to pathologies such as age-related macular degeneration (AMD). To better understand how aging in Bruch's membrane affects surrounding tissues and to determine the relationship between aging and disease, an in vitro model of Bruch's membrane is needed. An accurate model of Bruch's membrane must be a proteinaceous, semipermeable, and nonporous biomaterial with similar mechanical properties to in vivo conditions. Additionally, this model must support RPE cell growth. While models of subretinal tissue exist, they typically differ from in vivo Bruch's membrane in one or more of these properties. This study evaluates the capability of membranes created from recombinant hagfish intermediate filament (rHIF) proteins to accurately replicate Bruch's membrane in an in vitro model of the subretinal tissue. The physical characteristics of these rHIF membranes were evaluated using mechanical testing, permeability assays, brightfield microscopy, and scanning electron microscopy. The capacity of the membranes to support RPE cell culture was determined using brightfield and fluorescent microscopy, as well as immunocytochemical staining. This study demonstrates that rHIF protein membranes are an appropriate biomaterial to accurately mimic both healthy and aged Bruch's membrane for in vitro modeling of the subretinal tissue.

Regulation of Aqueous Humor Secretion by Melatonin in Porcine Ciliary Epithelium

Secretion of melatonin, a natural hormone whose receptors are present in the ciliary epithelium, displays diurnal variation in the aqueous humor (AH), potentially contributing to the regulation of intraocular pressure. This study aimed to determine the effects of melatonin on AH secretion in porcine ciliary epithelium. The addition of 100 µM melatonin to both sides of the epithelium significantly increased the short-circuit current (Isc) by ~40%. Stromal administration alone had no effect on the Isc, but aqueous application triggered a 40% increase in Isc, similar to that of bilateral application without additive effect. Pre-treatment with niflumic acid abolished melatonin-induced Isc stimulation. More importantly, melatonin stimulated the fluid secretion across the intact ciliary epithelium by ~80% and elicited a sustained increase (~50-60%) in gap junctional permeability between pigmented ciliary epithelial (PE) cells and non-pigmented ciliary epithelial (NPE) cells. The expression of MT3 receptor was found to be >10-fold higher than that of MT1 and MT2 in porcine ciliary epithelium. Aqueous pre-treatment with MT1/MT2 antagonist luzindole failed to inhibit the melatonin-induced Isc response, while MT3 antagonist prazosin pre-treatment abolished the Isc stimulation. We conclude that melatonin facilitates Cl- and fluid movement from PE to NPE cells, thereby stimulating AH secretion via NPE-cell MT3 receptors.

Single-cell RNA-sequencing analysis of the ciliary epithelium and contiguous tissues in the mouse eye

The ciliary epithelium plays a central role in ocular homeostasis but cells of the pigmented and non-pigmented layers are difficult to isolate physically and study. Here we used single-cell RNA-sequencing (scRNA-seq) to analyze the transcriptional signatures of cells harvested from the ciliary body and contiguous tissues. Microdissected tissue was dissociated by collagenase digestion and the transcriptomes of individual cells were obtained using a droplet-based scRNA-seq approach. In situ hybridization was used to verify the expression patterns of selected differentially-expressed genes. High quality transcriptomes were obtained from 10,024 cells and unsupervised clustering distinguished 22 cell types. Although efforts were made to specifically isolate the ciliary body, approximately half of the sequenced cells were derived from the adjacent retina. Cluster identities were assigned using expression of canonical markers or cluster-specific genes. The transcriptional signature of cells in the PCE and NPCE were distinct from each other and from cells in contiguous tissues. PCE cell transcriptomes were characterized by genes involved in melanin synthesis and transport proteins such as Slc4a4. Among the most differentially expressed genes in NPCE cells were those encoding members of the Zic family of transcription factors (Zic1, 2, 4), collagen XVIII (Col18a1), and corticotrophin-releasing hormone-binding protein (Crhbp). The ocular melanocyte population was distinguished by expression of the gap junction genes Gjb2 and Gjb6. Two fibroblast signatures were detected in the ciliary body preparation and shown by in situ hybridization to correspond to uveal and scleral populations. This cell atlas for the ciliary body and contiguous layers represents a useful resource that may facilitate studies into the development of the ciliary epithelium, the production of the aqueous and vitreous humors, and the synthesis of the ciliary zonule.

Let-7, Lin28 and Hmga2 Expression in Ciliary Epithelium and Retinal Progenitor Cells

Purpose

Ciliary epithelium (CE) of adult mammalian eyes contains quiescent retinal progenitor/stem cells that generate neurospheres in vitro and differentiate into retinal neurons. This ability doesn't evolve efficiently probably because of regulatory mechanisms, such as microRNAs (miRNAs) that control pluripotent, progenitor, and differentiation genes. Here we investigate the presence of Let-7 miRNAs and its regulator and target, Lin28 and Hmga2, in CE cells from neurospheres, newborns, and adult tissues.

Methods

Newborn and adult rats CE cells were dissected into pigmented and nonpigmented epithelium (PE and NPE). Newborn PE cells were cultured with growth factors to form neurospheres and we analyzed Let-7, Lin28a, and Hmga2 expression. During the neurospheres formation, we added chemically modified single-stranded oligonucleotides designed to bind and inhibit or mimic endogenous mature Let-7b and Let-7c. After seven days in culture, we analyzed neurospheres size, number and expression of Let-7, Lin28, and Hmga2.

Results

Let-7 miRNAs were expressed at low rates in newborn CE cells with significant increase in adult tissues, with higher levels on NPE cells, that does not present the stem cells reprogramming ability. The Lin28a and Hmga2 protein and transcripts were more expressed in newborns than adults cells, opposed to Let-7. Neurospheres presented higher Lin28 and Hmga2 expression than newborn and adult, but similar Let-7 than newborns. Let-7b inhibitor upregulated Hmga2 expression, whereas Let-7c mimics upregulated Lin28 and downregulated Hmga2.

Conclusions

This study shows the dynamic of Lin28-Let-7-Hmga regulatory axis in CE cells. These components may develop different roles during neurospheres formation and postnatal CE cells.

Generation and Characterization of Anti-Glucosepane Antibodies Enabling Direct Detection of Glucosepane in Retinal Tissue

Although there is ample evidence that the advanced glycation end-product (AGE) glucosepane contributes to age-related morbidities and diabetic complications, the impact of glucosepane modifications on proteins has not been extensively explored due to the lack of sufficient analytical tools. Here, we report the development of the first polyclonal anti-glucosepane antibodies using a synthetic immunogen that contains the core bicyclic ring structure of glucosepane. We investigate the recognition properties of these antibodies through ELISAs involving an array of synthetic AGE derivatives and determine them to be both high-affinity and selective in binding glucosepane. We then employ these antibodies to image glucosepane in aging mouse retinae via immunohistochemistry. Our studies demonstrate for the first time accumulation of glucosepane within the retinal pigment epithelium, Bruch's membrane, and choroid: all regions of the eye impacted by age-related macular degeneration. Co-localization studies further suggest that glucosepane colocalizes with lipofuscin, which has previously been associated with lysosomal dysfunction and has been implicated in the development of age-related macular degeneration, among other diseases. We believe that the anti-glucosepane antibodies described in this study will prove highly useful for examining the role of glycation in human health and disease.

Calf melanin immunomodulates RPE cell attachment to extracellular matrix protein

PURPOSE

It is widely accepted that RPE melanin has a protective effect against oxidative damage in RPE cells. It is possible that an additional protective characteristic of melanin is the ability to modulate RPE cell immune response. In this study, in vitro modeling was used to probe the relationship between RPE pigmentation and immune response by monitoring IL-6 expression and secretion in calf melanin pigmented ARPE-19 cells seeded onto glycated extracellular matrix as a stressor.

METHODS

ARPE-19 cells were left unpigmented or were pigmented with either calf melanin or latex beads, and were then seeded onto RPE-derived extracellular matrix (ECM) or tissue culture-treated plates (no ECM). ECMs were modified by glycation. IL-6 expression was measured using qPCR and IL-6 secretion was determined using an ELISA, both at 30 min and 24 h after seeding. MTT assay was used to quantify cell attachment to glycated matrices 30 min after seeding. In unpigmented ARPE-19 cells, rate of cell attachment to substrate was monitored for 60 min after seeding using a hemacytometer to count unattached cells. Additionally, cell viability was evaluated using the Neutral Red assay 24 h after seeding.

RESULTS

A significant increase in IL-6 expression was observed in calf melanin pigmented cells versus latex bead and unpigmented controls (p < 0.0001) 30 min after seeding onto ECM. Twenty-four hours after seeding, a significant decrease in IL-6 expression was observed in calf melanin pigmented cells (p < 0.0001) versus controls, implicating down-regulation of the cytokine. Additionally, calf melanin pigmented cell populations showed significant increase in attachment compared to unpigmented controls on either no ECM or unmodified ECM.

CONCLUSIONS

Pigmentation of RPE cells with calf melanin resulted in significant changes in IL-6 expression regardless of ECM modification, in vitro. These findings suggest that melanin in the RPE may participate in immune response modulation in the retina with particular regard to cell attachment to protein substrates. The results of this study further implicate the role of chemical changes to melanin in regulating inflammation in retinal disease.

Ocular Pathology in Light Chain Deposition Disease

Light-chain deposition disease (LCDD), a rare form of monoclonal gammopathy, is characterized by deposits of amorphous light-chain material, mainly in the kidneys but also in various other organs. Here we present the first report of a light-, electron microscopic and immunohistochemical study of the globes of a patient suffering from LCDD secondary to multiple myeloma. Massive deposits of kappa light chains similar to those typically present in the kidneys were found beneath the basement membrane of the ciliary pigment epithelium, on vessels of the ciliary body, within the collagenous zones of Bruch's membrane, and in the innermost part of the choroid. The choriocapillaris in the macular area was partly obstructed by these deposits, and an exudative retinal detachment was present. Whether this detachment was the consequence of disturbed circulation of the choriocapillaris remains speculative.

Analysis of the Rhodopsin and Peripherin/Rds Gene in Two Families with Pattern Dystrophy of the Retinal Pigment Epithelium

Mutations of the peripherin/retinal degeneration slow (RDS) gene have been reported in autosomal dominant retinitis pigmentosa and variable forms of pattern dystrophy of the retinal pigment epithelium. We screened the rhodopsin and the peripherin/RDS gene in the members of two families who presented the clinical features of pattern dystrophy of the retinal pigment epithelium transmitted as an autosomal dominant trait. No migration patterns were detected in single strand conformation polymorphism or hydrolink gels. Both the rhodopsin and the peripherin/RDS gene were normal in one family. In the second, the proband had a normal rhodopsin gene and, although he passed a different haplotype to each of his affected daughters, there was no linkage with the peripherin/RDS gene. The origin of the retinal disturbance in our two pedigrees must therefore be sought, if indeed DNA is involved, elsewhere in the genome. Our findings provide additional evidence that pattern dystrophies of the retinal pigment epithelium may be pathogenically related in spite of different etiological origins. The genetic polymorphism can probably account for the wide range of phenotypes.

Autofluorescence in a Patient with Adult Vitelliform Degeneration

The case of an 83 year-old woman is presented in whom bilateral vitelliform macular cysts were observed to fluoresce during the pre-injection phase of intravenous fluorescein angiography. This suggests that the vitelliform response is a non-specific event occurring in retinal pigment epithelial disease in which lipofuscin may or may not be manufactured.

Age-Related Macular Degeneration: Review of Pathogenesis

Age-related macular degeneration is a condition (a) characterized by accumulation of membranous debris on both sides of the retinal pigment epithelium (RPE) basement membrane. Clinical manifestations of drusen, atrophy of the RPE/choriocapillaris, RPE detachment, and choroidal new vessel (CNV) formation occur after age 50 years. A hypothetical pathogenic sequence of events consistent with known data is: 1) RPE dysfunction (e.g., precipitated by an inherited susceptibility and/or environmental exposure); 2) accumulation of intracellular material in the RPE (e.g., accumulation of normal substrate material that is not enzymatically degraded properly vs. abnormal substrate material); 3) abnormal accumulation of extracellular material (basal laminar and basal linear deposit); 4) change in Bruch's membrane composition (e.g., increased lipid deposition and protein crosslinking); 5) change in Bruch's membrane parmeability to nutrients (e.g., impaired diffusion of water soluble plasma constituents across Bruch's membrane); and 6) response of the RPE to metabolic distress (i.e., atrophy vs. CNV growth). Histopathological and clinical studies indicate that areas of choroidal ischemia often are seen near CNVs in AMD patients. In response to decreased oxygen delivery/metabolic “distress”, the RPE may elaborate substances leading to CNV growth. Perhaps RPE atrophy, followed by choriocapillaris and photoreceptor atrophy, is a response to decreased nutrients/increasing metabolic abnormalities in areas of excessive accumulation of extracellular debris. Unanswered questions regarding AMD include: 1) is AMD an ocular manifestation of a systemic disease or purely an ocular disease?; 2) what determines whether CNVs vs.atrophy of the RPE-choriocapillaris-photoreceptors develops?; and 3) what induces the maturation of CNVs into an inactive scar, and what limits the growth of most CNVs to the area centralis?

Effect of berberine on lipopolysaccharide-induced monocyte chemotactic protein-1 and interleukin-8 expression in a human retinal pigment epithelial cell line

Purpose

In this study, we elucidated the effects of berberine, a major alkaloid component contained in medicinal herbs, such as Phellodendri Cortex and Coptidis Rhizoma, on expression of monocyte chemotactic protein-1 (MCP-1) and interleukin-8 (IL-8) in a human retinal pigment epithelial cell line (ARPE-19) caused by lipopolysaccharide (LPS) stimulation.

Methods

ARPE-19 cells were cultured to confluence. Berberine and LPS were added to the medium. MCP-1 and IL-8 mRNA were measured by real-time polymerase chain reaction. MCP-1 and IL-8 protein concentrations in the media were measured using enzyme-linked immunosorbent assay.

Results

After stimulation with LPS, MCP-1 and IL-8 mRNA in ARPE-19 cells reached maximum levels at 3 h, and MCP-1 and IL-8 protein in the culture media reached maximum levels at 24 h. Berberine dose-dependently inhibited MCP-1 and IL-8 mRNA expression of the cells and protein levels in the media stimulated with LPS.

Conclusions

These findings indicate that berberine inhibited the expression of MCP-1 and IL-8 induced by LPS.

Pigment epithelium-derived factor improves TNFα-induced hepatic steatosis in grass carp (Ctenopharyngodon idella)

Pro-inflammatory cytokines, such as tumor necrosis factor alpha (TNFα), may contribute to hepatic steatosis in the situation of excess lipid accumulation in farmed fish. Pigment epithelium-derived factor (PEDF) is an endogenous anti-inflammatory factor and promotes lipolysis. Accordingly, we isolated PEDF from grass carp and investigated its role in TNFα-induced hepatic steatosis. Sequence analysis showed that PEDF gene, which possesses 8 exons and 7 introns, encodes a protein with 409 amino acids. PEDF was a critical determinant of the transcriptional response to nutrient availability in grass carp. Endogenous PEDF was an intracellular protein with cytoplasmic distribution and directly interacts with adipose triglyceride lipase (ATGL), which might mediate PEDF-induced lipolysis. TNFα significantly promoted lipid accumulation in vivo and in vitro, accompanied with a decrease in mRNA levels of PEDF and peroxisome proliferator-activated receptor alpha (PPARα). Recombinant PEDF and PPARα agonist diminished the TNFα-induced hepatic steatosis. Meanwhile, PPARα agonist caused an increase in PEDF expression, suggesting that TNFα antagonizes the actions of PEDF possibly in a PPARα-dependent manner. These findings suggest that PEDF is an important protective factor against hepatic steatosis induced by TNFα, which provided a new therapeutic target for inflammation-associated hepatic steatosis.

[The correlation between the concentrations of VEGF and PEDF and Ca2+-PKC signaling pathways in human retinal pigment epithelial cells cultured in vitro after exposuring to blue light]

OBJECTIVE

To investigate the concentrations of vascular endothelial growth factor (VEGF), pigment epithelium-derived factor (PEDF), inositol triphosphate (IP3) and diacylglycerol (DAG) in human retinal pigment epithelium (RPE) cells after exposuring to blue light, and to explore the relationship with Ca2+-PKC signaling pathways, to evaluate the role of Ca2+-PKC signaling pathways of blue-light irradiation induced apoptosis in RPE cells.

METHODS

The fourth generation human RPE cells in vitro were exposured to blue light (2000±500 lux) for 6 hours, 24 hours prolongation of post-exposure culture. The concentrations of VEGF, PEDF, IP3 and DAG were assayed by enzyme linked immunosorbent assay (ELISA). Cells were randomly divided into 6 groups, group A (control), group B (exposure to blue light), group C (exposure to blue light+PMA), group D (exposure to blue light+Calphostin C), group E (exposure to blue light+Nifedipine), group F (exposure to blue light+Calphostin C+Nifedipine). Flow cytometry was used to detect the apoptosis rate of human RPE cells in A, B and F group.

RESULTS

Comparing with group A (584.38±10.66), the concentration of VEGF in group B (700.70±5.88), group C (698.21±6.66) and group E (648.30±4.91) was higher, the difference was statistically significant (P=0.002, 0.002, 0.016). Comparing with group B (700.70±5.88), the concentration of VEGF in Group D (623.87±3.12) and E (648.30±4.91) was lower (P=0.001, 0.002). Comparing with group A (75.96±1.70), the concentration of PEDF in Group B (71.82±1.67) and C (72.43±0.58) was lower (P=0.004, 0.011), but the concentration of PEDF in Group D (86.31±1.35) and E (93.72±1.24) was higher (P=0.000, 0.000). Comparing with group B (71.82±1.67), the concentration of PEDF in Group D (86.31±1.35) and E (93.72±1.24) was higher (P=0.000, 0.000). Comparing with group A (7.70±0.29), the ratio of VEGF to PEDF in Group B (9.85±0.34) and Croup C (9.64±0.02) was higher (P=0.008, 0.027) Comparing with group B, The ratio of VEGF to PEDF in Group D (7.23±0.08) and E (6.92±0.06) was lower (P=0.016, 0.015). Comparing with group A (108.42±0.75, 995.47± 13.61), the concentration of IP3 and DAG in Group B (117.24±1.06, 1070.10±10.07), C (137.12±2.71, 1046.40±7.90), D (139.17±1.40, 1041.13±9.76) and E (149.61±0.77, 1273.14±10.89) was higher, the difference was statistically significant (P=0.003, 0.007, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000). Comparing with group B, the concentration of IP3 in Group C, D and E was higher (P=0.011, 0.000, 0.000). Comparing with group B, the concentration of DAG in Group C and D was lower (P=0.021, 0.007). Comparing with group B, the concentration of DAG in Group E was higher (P=0.000). Comparing with group A (10.27±1.88), the apoptosis rate of RPE cells in Group B(25.07±2.66) and F(19.37±3.23) was higher, the difference was statistically significant (P=0.001, 0.009). Comparing with group B (25.07±2.66), the apoptosis rate of RPE cells in Group F (19.37±3.23) was lower (P=0.038).

CONCLUSIONS

(1) After exposuring to blue light, the concentrations of VEGF, IP3 and DAG are increased and the ratio of VEGF to PEDF is also increased and the concentration of PEDF is decreased in human RPE cells. (2) L-Type Calcium Channels and Ca2+-PKC signaling pathways may be regulate the concentrations of VEGF, PEDF, IP3 and DAG in RPE cells after exposuring to blue light by feedback regulation. (3) The application of Calphostin C combined with Nifedipine may be restrain the apoptosis of RPE cells after exposuring to blue light.

Collagen formation by periretinal cellular membranes

In eyes with experimental retinal detachment, pigment epithelial cells and glial cells may form membranes on all available surfaces. In the subretinal space -- where normally no vitreous collagen is found -- variable amounts of collagen were detected in the intercellular space of these membranes. It is therefore concluded that retinal pigment epithelial cells and retinal glial cells are both capable of producing collagen. The type of collagen produced is indistinguishable from vitreous collagen.

[Modern trends of basic research in pathogenesis of progressive myopia]

The growing prevalence of progressive myopia and its disabling consequences explains the elaboration of reliable diagnostic markers and new treatment strategies based on the research results of molecular mechanisms underlying the development of the condition. The paper reviews recent basic pathogenetic research studies which have greatly broadened the awareness of the deep causes of progressive myopia associated with the activity of certain growth factors, local and systemic protein metabolism, and regulation of hormonal and neural processes. Practical clinical guidelines for new criteria of diagnosis and control of myopia are published as they could be useful while selecting individual treatment plans including indications to sclera-strengthening therapy and its evaluation. The results may be promising in the elaboration of systemic and local medications for the prevention of myopia progression, which should address the regulation of connective tissue disorders, hormonal shifts, and imbalanced autonomic nervous system.

[FGF2 signaling pathway components in tissues of the posterior eye sector in the adult newt Pleurodeles waltl]

The FGF2 signaling pathway components in tissues of the posterior wall in the normal and regenerating eye of the adult Pleurodeles waltl newt were detected for the first time. The fgf2 gene expression was found in the retina, retinal pigment epithelium, and choroid using polymerase chain reaction (PCR). A high homology of the mRNA nucleotide sequence of the most conservative fgf2 gene region in the P. waltl with the fgf2 orthologs in other vertebrates was proved. The Fgf2 protein aminoacid sequence of the P. waltl newt demonstrates even more homology with this growth factor in other vertebrates. The Fgf2 protein with a molecular weight 35 kDa was found in the studied eye tissues using Western blot hybridization. Localization of the Fgf2 protein and its Fgfr receptors was immunohistochemically studied in the pigment epithelium, choroid, central and growth retina regions of the newt native eye, and in the connective cilium of photoreceptors. Using real-time PCR and immunohistochemistry methods, it was found that the fgf2 gene down-regulation and a decrease in the intensity of the immunochemical reaction of its protein product (Fgf2) occur in the early period after the retina removal (in 4-8 days) (as compared with those in the same department of the unoperated eye).

Loss of CD34 expression in aging human choriocapillaris endothelial cells

Structural and gene expression changes in the microvasculature of the human choroid occur during normal aging and age-related macular degeneration (AMD). In this study, we sought to determine the impact of aging and AMD on expression of the endothelial cell glycoprotein CD34. Sections from 58 human donor eyes were categorized as either young (under age 40), age-matched controls (> age 60 without AMD), or AMD affected (>age 60 with early AMD, geographic atrophy, or choroidal neovascularization). Dual labeling of sections with Ulex europaeus agglutinin-I lectin (UEA-I) and CD34 antibodies was performed, and the percentage of capillaries labeled with UEA-I but negative for anti-CD34 was determined. In addition, published databases of mouse and human retinal pigment epithelium-choroid were evaluated and CD34 expression compared between young and old eyes. Immunohistochemical studies revealed that while CD34 and UEA-I were colocalized in young eyes, there was variable loss of CD34 immunoreactivity in older donor eyes. While differences between normal aging and AMD were not significant, the percentage of CD34 negative capillaries in old eyes, compared to young eyes, was highly significant (p = 3.8×10(-6)). Endothelial cells in neovascular membranes were invariably CD34 positive. Published databases show either a significant decrease in Cd34 (mouse) or a trend toward decreased CD34 (human) in aging. These findings suggest that UEA-I and endogenous alkaline phosphatase activity are more consistent markers of aging endothelial cells in the choroid, and suggest a possible mechanism for the increased inflammatory milieu in the aging choroid.

[Determination of mRNA-transcripts and heat shock proteins HSP70 and HSP90 in retina of the adult Spanish Ribbed Newt Pleurodeles waltl]

Expression of genes and heat shock proteins in normal intact retina of the Spanish Ribbed Newt Pleurodeles waltl was studied using polymerase chain reaction, Western blot hybridization, and immunohistochemistry. It was shown that the proteins HSP70 and HSP90, as well as their encoding transcripts of relevant genes, are constitutively expressed in eye tissues. These proteins were distributed differentially, and they were characterized by expression of different levels in the retina: HSP70 dominated in the external retina, while HSP90 dominated in the internal one, in particular, in Muller glial cells and the optic nerve. Transcripts and heat shock proteins HSP70 and HSP90 were also found in the retinal pigment epithelium and eye growth zone.

Angiopoietin-like protein 4 (ANGPTL4) is induced by high glucose in retinal pigment epithelial cells and exhibits potent angiogenic activity on retinal endothelial cells

PURPOSE

Hyperglycaemia has been identified as major risk factor for diabetic retinopathy (DR). It is widely accepted that the progression of DR is mainly due to a local imbalance of pro- versus anti-angiogenic factors in the retina. In this study, we investigated whether retinal pigment epithelial (RPE) cells produced pro-angiogenic factors under high glucose (HG) conditions in vitro.

METHODS

Cultured human retinal endothelial (RE) cells were exposed to conditioned medium from retinal pigment epithelium cells (ARPE-19) grown in HG medium and assessed for tube formation. Based on the expression profiles of ARPE-19, we investigated whether ANGPTL4 was a major angiogenic factor released from ARPE-19 under HG conditions using cultured human RE cells as the test system for experiments with recombinant protein, conditioned medium from ARPE-19 and RNA interference (RNAi).

RESULTS

The conditioned medium from ARPE-19 cultured under HG conditions promoted tube formation of cultured human RE cells. GeneChip analysis showed that ANGPTL4 was one of the highest upregulated genes under HG conditions. In addition, recombinant ANGPTL4 promoted all of the elements of angiogenesis in human RE cells in vitro. The results of experiments using conditioned medium from ARPE-19 combined with RNAi demonstrated that ANGPTL4 was a major angiogenic factor released from ARPE-19 under HG conditions.

CONCLUSIONS

ANGPTL4 was induced by high glucose in RPE cells and exhibited potent angiogenic activity on RE cells. Our results are unique and may potentially add a new candidate to the long list of molecules involved in diabetic retinopathy.

[Prevention and treatment of age-related macular degeneration by extract of Fructus lycii and its constituents lutein/zeaxanthin: an in vive and in vitro experimental research]

OBJECTIVE

To investigate the in vivo inhibition of extract of Fructus lycii (FL) on the expressions of cathepsin B (Cat B) and cystatin C (Cys C) in high-fat diet and hydroquinone (HQ) induced model mice with age-related macular degeneration (AMD), and to explore the in vitro effects of lutein and zeaxanthin on hydrogen peroxide (H2O2,) induced expressions of matrix metalloproteinase 2 (MMP-2) and tissue inhibitor of metalloproteinase 2 (TIMP-2) on ARPE-19 cells.

METHODS

Fifty female 8-month-old C57BL/6 mice were recruited in this research. Ten mice fed with regular diet was taken as the age control group. The rest 40 mice were fed with high fat diet for 6 months, followed by adding HQ (0. 8%) in the drinking water for 3 consecutive months. Then the modeled mice were randomly divided into the model control group (n =10), the high (at the daily dose of 3.75 g/kg), middle (at the daily dose of 2.50 g/kg), and low dose (at the daily dose of 1.25 g/kg) FL groups, 10 in each group. The extract of FL at each dose was respectively administered to mice by gastrogavage for 3 successive months. By the end of the experiment, the mice were killed and their eyeballs were removed. The protein expressions of Cat B and Cys C were observed by immunohistochemical assay. The mRNA and protein expressions of Cat B and Cys C were detected by real-time PCR and Western blot respectively. The drug concentrations of H2O2, lutein, and zeaxanthin were screened and detected using the activity of cell proliferation. The protein expressions of MMP-2 and TIMP-2 were detected using Western blot.

RESULTS

Compared with the age control group, the mRNA and protein expressions of Cat B and Cys C were significantly higher in the in vivo model control group (P <0.05, P <0.01). The mRNA expressions of Cat B and Cys C were weaker in the middle and high dose FL groups than in the model control group (P <0. 05, P <0. 01). In in vitro cells, lutein and zeaxanthin could down-regulate the protein expressions of MMP-2 and TIMP-2 in H202 induced ARPE-19 cells (P <0. 05, P <0. 01).

CONCLUSIONS

Extract of FL could down-regulate the high protein expressions of Cat B and Cys C in high-fat diet and HQ induced model mice. Lutein and zeaxanthin could down-regulate the protein expressions of MMP-2 and TIMP-2 in H202 induced ARPE-19 cells.

Gene expression and functional annotation of the human ciliary body epithelia

Purpose

The ciliary body (CB) of the human eye consists of the non-pigmented (NPE) and pigmented (PE) neuro-epithelia. We investigated the gene expression of NPE and PE, to shed light on the molecular mechanisms underlying the most important functions of the CB. We also developed molecular signatures for the NPE and PE and studied possible new clues for glaucoma.

Methods

We isolated NPE and PE cells from seven healthy human donor eyes using laser dissection microscopy. Next, we performed RNA isolation, amplification, labeling and hybridization against 44×k Agilent microarrays. For microarray conformations, we used a literature study, RT-PCRs, and immunohistochemical stainings. We analyzed the gene expression data with R and with the knowledge database Ingenuity.

Results

The gene expression profiles and functional annotations of the NPE and PE were highly similar. We found that the most important functionalities of the NPE and PE were related to developmental processes, neural nature of the tissue, endocrine and metabolic signaling, and immunological functions. In total 1576 genes differed statistically significantly between NPE and PE. From these genes, at least 3 were cell-specific for the NPE and 143 for the PE. Finally, we observed high expression in the (N)PE of 35 genes previously implicated in molecular mechanisms related to glaucoma.

Conclusion

Our gene expression analysis suggested that the NPE and PE of the CB were quite similar. Nonetheless, cell-type specific differences were found. The molecular machineries of the human NPE and PE are involved in a range of neuro-endocrinological, developmental and immunological functions, and perhaps glaucoma.

Melanoregulin, product of the dsu locus, links the BLOC-pathway and OA1 in organelle biogenesis

Humans with Hermansky-Pudlak Syndrome (HPS) or ocular albinism (OA1) display abnormal aspects of organelle biogenesis. The multigenic disorder HPS displays broad defects in biogenesis of lysosome-related organelles including melanosomes, platelet dense granules, and lysosomes. A phenotype of ocular pigmentation in OA1 is a smaller number of macromelanosomes, in contrast to HPS, where in many cases the melanosomes are smaller than normal. In these studies we define the role of the Mreg^dsu gene, which suppresses the coat color dilution of Myo5a, melanophilin, and Rab27a mutant mice in maintaining melanosome size and distribution. We show that the product of the Mreg^dsu locus, melanoregulin (MREG), interacts both with members of the HPS BLOC-2 complex and with Oa1 in regulating melanosome size. Loss of MREG function facilitates increase in the size of micromelanosomes in the choroid of the HPS BLOC-2 mutants ruby, ruby2, and cocoa, while a transgenic mouse overexpressing melanoregulin corrects the size of retinal pigment epithelium (RPE) macromelanosomes in Oa1^ko/ko mice. Collectively, these results suggest that MREG levels regulate pigment incorporation into melanosomes. Immunohistochemical analysis localizes melanoregulin not to melanosomes, but to small vesicles in the cytoplasm of the RPE, consistent with a role for this protein in regulating membrane interactions during melanosome biogenesis. These results provide the first link between the BLOC pathway and Oa1 in melanosome biogenesis, thus supporting the hypothesis that intracellular G-protein coupled receptors may be involved in the biogenesis of other organelles. Furthermore these studies provide the foundation for therapeutic approaches to correct the pigment defects in the RPE of HPS and OA1.

Temporally controlled targeted somatic mutagenesis in mouse eye pigment epithelium

To generate temporally controlled site-specific somatic mutations in the mouse eye pigment epithelium, we generated a TRP1-Cre-ER(T2) transgenic mouse line that expresses the tamoxifen-dependent Cre-ER(T2) recombinase under the control of the tyrosinase-related protein 1 (TRP1) promoter. Cre-ER(T2) transcripts were readily detected in the retinal pigment epithelium (RPE), and tamoxifen treatment of adult TRP1-Cre-ER(T2) transgenic mice induced efficient excision of floxed DNA in patches of RPE cells, in numerous epithelial cells of the iris and ciliary body, and in very few cells of the neural retina. Importantly, no excision was detected in any cells in the absence of tamoxifen treatment. Thus, the TRP1-Cre-ER(T2) mouse line provides a powerful tool to study in vivo gene functions in the mouse eye pigment epithelium.

Axitinib modulates hypoxia-induced blood-retina barrier permeability and expression of growth factors

This study investigates the effects of the multikinase inhibitor axitinib on the expression of vascular endothelial growth factor (VEGF) receptors 1/2 (VEGFR-1/2) and platelet-derived growth factor (PDGF) receptor beta (PDGFR-β), hypoxia-induced increased tissue permeability, occludin, zonula occludens protein 1 (ZO-1), VEGF-A, and PDGF expression of human retinal pigment epithelial (RPE) cells and human umbilical vein endothelial cells (HUVECs). Primary human RPE cells and HUVECs were exposed to hypoxia and axitinib. Viability of cells, tissue permeability, and expression of occludin, ZO-1, VEGF, PDGF, VEGFR-1/2 and PDGFR-β, and their mRNAs, were investigated by reverse transcription-polymerase chain reaction, enzyme-linked immunosorbent assay, western blotting, and immunohistochemistry. Treatment with axitinib reduced expression of VEGFR-1/2 and PDGFR-β. Hypoxia decreased cell viability, occludin, and ZO-1 expression and increased tissue permeability, expression, and secretion of VEGF and PDGF. Axitinib significantly reduced hypoxia-induced effects on HUVEC and RPE cells. Our in vitro results suggest that axitinib may have promising properties as a potential treatment for diabetic macular edema.

[Genotyping in progressive age-related macular degeneration]

After presenting both the prevalence and the staging of the age-related macular degeneration (AMD), the disease progression is discussed; it is determined primarily by genetic factors but is also influenced by environmental, demographic and behavioral factors. The genes working by means of the high-density lipoprotein cholesterol (HDL) pathway have critical roles in the drusen initiation in the early AMD stages. After the drusen have accumulated between retinal pigment epithlium (RPE) and Bruch's membrane, the genes acting in the alternative complement pathway are activated so influencing in this way the progression from the intermediate and large drusen to the advanced AMD stages (e.g. the geographic atrophy of the RPE and neovascular stages).

Pigment epithelial cells isolated from human peripheral iridectomies have limited properties of retinal stem cells

PURPOSE

The identification of cells with properties of retinal progenitor cells (RPCs) in the adult human ciliary margin (CM) prompted a number of studies of their proliferative and differentiation potential. One of the remaining challenges is to find a feasible method of isolating RPCs from the patient's eye. In the human CM, only the iris pigment epithelium (IPE) is easily obtained by a minimally invasive procedure. In the light of recent studies questioning the existence of RPCs in the adult mammalian CM, we wanted to assess the potential of the adult human IPE as source of RPCs.

METHODS

The IPE were isolated from peripheral iridectomies during glaucoma surgery, and IPE and ciliary body (CB) epithelium were also isolated from post-mortem tissue. Cells were cultivated in sphere-promoting conditions or as monolayers. Whole-tissue samples, undifferentiated and differentiated cells were studied by immunocytochemistry, RT-PCR and transmission electron microscopy.

RESULTS

The adult human IPE, like the CB, expressed markers of RPCs such as Pax6, Sox2 and Nestin in vivo. Both sphere-promoting and monolayer cultures preserved this phenotype. However, both IPE/CB cultures expressed markers of differentiated epithelial cells such as Claudin, microphtalmia-associated transcription factor (MITF) and Cytokeratin-19. Ultrastructurally, IPE spheres displayed epithelial-like junctions and contained mature melanosomes. After induced differentiation, IPE-derived cells showed only partial neuronal differentiation expressing β-III-tubulin, Map-2 and Rhodopsin, whereas no mature glial markers were found.

CONCLUSION

Proliferative cells with some properties of RPCs can be isolated from the adult human IPE by peripheral iridectomies. Yet, many cells retain properties of differentiated epithelial cells and lack central properties of somatic stem cells.

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.

Epithelial membrane protein-2 (EMP2) and experimental proliferative vitreoretinopathy (PVR)

PURPOSE

Proliferative vitreoretinopathy (PVR) is believed to result in part from de-differentiation of retinal pigment epithelium (RPE) with cellular migration in the vitreous cavity, membrane formation, and contraction in an aberrant wound-healing strategy. In an in vitro collagen-gel contraction assay, epithelial membrane protein 2 (EMP2) controls contraction through activation of focal adhesion kinase (FAK) in a RPE cell line (ARPE-19). The purpose of this study was to investigate how blocking or altering the level of EMP2 expression changed clinical PVR in an in vivo model.

METHODS

Using the ARPE-19 cell line, the levels of EMP2 modulated through stable transfections of an EMP2 overexpressing construct, EMP2 ribozyme, or vector alone. These transfected cell lines were used in a rabbit model of PVR. The severity of PVR was classified by two masked observers. An EMP2 blocking antibody was also used to decrease functional EMP2 in the PVR model. Immunohistochemistry was used to evaluate EMP2 expression in vivo.

RESULTS

The transfectants with lower levels of EMP2 had significantly less PVR severity than the degree of PVR induced by wild-type cells (p = 0.05). Also, the transfectants with a low-level of EMP2 expression showed a strong trend of less PVR severity than the high-levels EMP2 transfectants (p = 0.06). Blocking EMP2 with a specific polyclonal antibody significantly decreased the level of PVR severity (p = 0.02). PVR membranes were found to be positive for EMP2 expression.

CONCLUSIONS

These in vivo studies support a direct correlation between EMP2 expression and severity of PVR. These results validate the potential for controlling RPE biology through a change in EMP2 expression, and provide a potential therapeutic target for this disease.

Influence of drug solubility and lipophilicity on transscleral retinal delivery of six corticosteroids

The influence of drug properties including solubility, lipophilicity, tissue partition coefficients, and in vitro transscleral permeability on ex vivo and in vivo transscleral delivery from corticosteroid suspensions was determined. Solubility, tissue/buffer partition coefficients for bovine sclera and choroid-retinal pigment epithelium (CRPE), and in vitro bovine sclera and sclera-choroid-retinal pigment epithelium (SCRPE) transscleral transport were determined at pH 7.4 for triamcinolone, prednisolone, dexamethasone, fluocinolone acetonide, triamcinolone acetonide, and budesonide in solution. Ex vivo and in vivo transscleral delivery was assessed in Brown Norway rats after posterior subconjunctival injection of a 1 mg/ml suspension of each corticosteroid. Corticosteroid solubility and partition coefficients ranged from ∼ 17 to 300 μg/ml and 3.0 to 11.4 for sclera and from 7.1 to 35.8 for CRPE, respectively, with the more lipophilic molecules partitioning more into both tissues. Transport across sclera and SCRPE was in the range of 3.9 to 10.7% and 0.3 to 1.8%, respectively, with the transport declining with an increase in lipophilicity. Ex vivo and in vivo transscleral delivery indicated tissue distribution in the order CRPE ≥ sclera > retina > vitreous. Tissue partitioning showed a positive correlation with drug lipophilicity (R(2) = 0.66-0.96). Ex vivo and in vivo sclera, CRPE, retina, and vitreous tissue levels of all corticosteroids showed strong positive correlation with drug solubility (R(2) = 0.91-1.0) but not lipophilicity (R(2) = 0.24-0.41) or tissue partitioning (R(2) = 0.24-0.46) when delivered as suspensions. In vivo delivery was lower in all eye tissues assessed than ex vivo delivery, with the in vivo/ex vivo ratios being the lowest in the vitreous (0.085-0.212). Upon exposure to corticosteroid suspensions ex vivo or in vivo, transscleral intraocular tissue distribution was primarily driven by the drug solubility.

[The effects of hyperosmotic stress on rabbit ocular surface and mucin 5AC expression]

OBJECTIVE

To investigate the effects of hyperosmotic stress on rabbit ocular surface and mucin 5AC (MUC5AC) expression.

METHODS

Experimental study. Eighteen New Zealand white rabbits were randomly divided into three groups with equal number as hyperosmolar saline solution (HOSS, 500 mmol/L) group, normal saline (NS, 308 mmol/L) group and blank control group respectively. In HOSS and NS groups, the HOSS and NS eye drops were instilled on bilateral eyes six times every day for 14 days. On day 0, 7 and 14, Schirmer I test and tear break-up time (BUT) were measured and conjunctival impression cytology specimens were collected. On day 7 and 14, cornea and conjunctiva were harvested for Hematoxylin and Eosin (HE) staining, scanning and transmission electron microscopy observation and conjunctival TUNEL examination. On day 14, the conjunctiva were also harvested for immunology histological staining and western blot to evaluate the expression of MUC5AC.

RESULTS

In HOSS group, the BUT on day 7 and 14 was (7.6 ± 2.5) and (7.0 ± 2.3) s respectively which was significantly shorter than the (10.3 ± 2.5) s on day 0(t = 5.800, 4.950; P < 0.01), and also significantly shorter than the BUT in NS and control groups (F = 8.030, P < 0.01). But the Schirmer I test value did not change obviously in and between all those three groups. The mean conjunctival goblet cell (GC) density in HOSS group on day 7 and 14 was (19.5 ± 16.6) and (32.3 ± 18.2) cells/mm(2) respectively which was also significantly lower than the (75.7 ± 43.4) cells/mm(2) on day 0 (t = 5.319, 2.970; P < 0.05). However the GC density did not change obviously in other two groups with time. After instillation of HOSS for 14 days, subepithelial inflammatory cell infiltration was showed on conjunctival tissue specimens and decreased epithelial layers and evident desquamation were found in the cornea specimens by the HE staining. Under the electron microscope, decreased microvilli and loosened intercellular junction in the superficial epithelium and increased autophagic vesicles in basal epithelium were observed in the cornea in HOSS group; and decreased microvilli and mucous granules were found in the conjunctiva in HOSS group. Obvious TUNEL positive staining was showed in the conjunctiva in the HOSS group. Also the MUC5AC immunology histological staining and western blot indicated decreased MUC5AC protein expression in HOSS group.

CONCLUSION

Hyperosmotic stress destroyed the structure of ocular surface epithelium, induced the decrease of conjunctival goblet cell density and MUC5AC expression, and led to the decreased tear film stability.

[Fundus autofluorescence in eyes with dry and wet form of age-related macular degeneration (AMD)--clinical implications]

PURPOSE

To evaluate retinal pigment epithelium (FIPE) and photoreceptors layer integrity in different stages of AMO based on fundus autofluorescence imaging and to correlate autofluorescence images with visual acuity.

MATERIAL AND METHODS

322 eyes of 200 patients with different forms and stages of AMD were studied. Mean age was 70 years (49-91 years). Apart from complete ophthalmologic examination patients were examined every 6 months by using a confocal scanning ophthalmoscope HRA2. Follow-up period ranged trom 1 to 40 months (mean--18 months).

RESULTS

In 116 eyes with early AMO punctuate changes in autofluorescence images were observed while in 22 eyes (16%) no distinct changes were present. In 52 eyes (62%) with wet AMD normal or near normal autotluorescence signal was present and 34 eyes (38%) with wet AMO had changes in autofluorescence signal corresponding with choroidal neovascularisation (WV) area. In the group of eyes with autofluorescence changes in the CNV area median BCVA was 0.1 and in the group without autofluorescence changes within the CNV area--0.4. All eyes with disciform scar were characterized by uneven autofluorescence signal decrease in scar area with increased signal in surroundig area. Eyes with geographic atrophy (GA) had lack of autofluorescence signal corresponding to RPE atrophy and in 40 cases (95%) increase autofluorescence signal junctional to GA was noted.

CONCLUSIONS

Fundus autofluorescence images of the AMO eyes varies greatly. Decrease of autofluorescence signal correlates with visual acuity decrease.

[The relationship between MERTK gene and protein kinase C in the phagocytic process of human retinal pigment epithelial cells]

OBJECTIVE

To investigate relationship of the expression of MERTK gene and the activity of protein kinase C (PKC) in the phagocytic process of human retinal pigment epithelial (hRPE) cells.

METHODS

Cultured hRPE cells were incubated with rod outer segments (ROS) suspension (containing ROS 1x10(10)/L) at 37 degrees C, then cells were rinsed at different times to terminate the phagocytosis. The kinetic of phagocytosis was measured by double-fluorescent labeling. The activity of PKC and the expression level of MERTK gene were measured by counting gamma-32P radio-activity with liquid scintillation and RT-PCR respectively. Change of MERTK gene expression was measured after hRPE was treated cells with stimulator or inhibitor of PKC. Statistical analysis was performed by SPSS 13.0 software.

RESULTS

The phagocytic assay showed that the quality of bound and ingested ROS by hRPE cells increased. The quality of ingested ROS by hRPE cells at 24 hours was (2.85+/-0.11)x10(6), which reached maximum contrast with control (0.00+/-0.00)x10(6) (t=47.64, P<0.05). The activity of PKC (both in cytoplasm and on membrane) decreased during all the incubation periods compared with control [cytoplasm: (329.63+/-14.26) nmolxg(-1)xmin(-1)and on membrane: (467.67+/-68.87) nmolxg(-1)xmin(-1)], and reached the minimum at 24 h[cytoplasm: (151.13+/-17.67) nmolxg(-1)xmin(-1) and on membrane: (152.45+/-64.83) nmolxg(-1)xmin(-1); cytoplasm t=89.66 and membrane t=10.31, P<0.05]. The level of MERTK mRNA increased in pulse-chase and long-time incubation test. The gray level for 90 min was 1.8853+/-0.0077, contrasted with control 0.7246+/-0.0062, F=16,060.2167 and P<0.05. The gray level for 24 h was 0.5946+/-0.0082, contrasted with control 0.3343+/-0.0064, F=919.8421 and P<0.05. When up-regulating the activity of PKC in hRPE cells, the level of MERTK mRNA was decreased in the proceeding incubating with ROS contrasted with control (pulse-chase group F=17,142.2331, long time group F=1886.4614; P<0.05). After down-regulating the activity of PKC in hRPE cells, the level of MERTK mRNA waved between 4.4670+/-0.0092 and 5.7034+/-0.0095 in the first 30 min of incubating with ROS, which lower than control 0.9117+/-0.0021 (F=199,012.9138, P<0.05).

CONCLUSIONS

The lower activity of PKC and the higher expression MERTK gene are very important for sustaining phagocytic process of ROS by hRPE cells. MERTK gene and PKC both as up-stream regulators are negative-correlated in the phagocytic process of hRPE.

Dynamics of H2O2 availability to ARPE-19 cultures in models of oxidative stress

Oxidative injury to cells such as the retinal pigment epithelium (RPE) is often modeled using H(2)O(2)-treated cultures, but H(2)O(2) concentrations are not sustained in culture medium. Here medium levels of H(2)O(2) and cytotoxicity were analyzed in ARPE-19 cultures after H(2)O(2) delivery as a single pulse or with continuous generation using glucose oxidase (GOx). When added as a pulse, H(2)O(2) is rapidly depleted (within 2 h); cytotoxicity at 24 h, determined by the MTT assay for mitochondrial function, is unaffected by medium replacement at 2 h. Continuous generation of H(2)O(2) produces complex outcomes. At low GOx concentrations, H(2)O(2) levels are sustained by conditions under which generation matches depletion, but when GOx concentrations produce cytotoxic levels of H(2)O(2), oxidant depletion accelerates. Acceleration results partly from the release of contents from oxidant-damaged cells as indicated by testing depletion after controlled membrane disruption with detergents. Cytotoxicity analyses show that cells can tolerate short exposure to high H(2)O(2) doses delivered as a pulse but are susceptible to lower chronic doses. The results provide broadly applicable guidance for using GOx to produce sustained H(2)O(2) levels in cultured cells. This approach will be specifically useful for modeling chronic stress relevant to RPE aging and have a wider value for studying cellular effects of sublethal oxidant injury and for evaluating antioxidants that may protect significantly against mild but not lethal stress.

Aging, age-related macular degeneration, and the response-to-retention of apolipoprotein B-containing lipoproteins

The largest risk factor for age-related macular degeneration (ARMD) is advanced age. A prominent age-related change in the human retina is the accumulation of histochemically detectable neutral lipid in normal Bruch's membrane (BrM) throughout adulthood. This change has the potential to have a major impact on physiology of the retinal pigment epithelium (RPE). It occurs in the same compartment as drusen and basal linear deposit, the pathognomonic extracellular, lipid-containing lesions of ARMD. Here we present evidence from light microscopic histochemistry, ultrastructure, lipid profiling of tissues and isolated lipoproteins, and gene expression analysis that this deposition can be accounted for by esterified cholesterol-rich, apolipoprotein B-containing lipoprotein particles constitutively produced by the RPE. This work collectively allows ARMD lesion formation and its aftermath to be conceptualized as a response to the retention of a sub-endothelial apolipoprotein B lipoprotein, similar to a widely accepted model of atherosclerotic coronary artery disease (CAD) (Tabas et al., 2007). This approach provides a wide knowledge base and sophisticated clinical armamentarium that can be readily exploited for the development of new model systems and the future benefit of ARMD patients.

Cellular and molecular events mediated by docosahexaenoic acid-derived neuroprotectin D1 signaling in photoreceptor cell survival and brain protection

Deficiency in docosahexaenoic acid (DHA) is associated with impaired visual and neurological postnatal development, cognitive decline, macular degeneration, and other neurodegenerative diseases. DHA is an omega-3 polyunsaturated fatty acyl chain concentrated in phospholipids of brain and retina, with photoreceptor cells displaying the highest content of DHA of all cell membranes. The identification and characterization of neuroprotectin D1 (NPD1, 10R, 17S-dihydroxy-docosa-4Z,7Z,11E,13E,15Z,19Z-hexaenoic acid) contributes in understanding the biological significance of DHA. In oxidative stress-challenged human retinal pigment epithelial (RPE) cells, human brain cells, or rat brains undergoing ischemia-reperfusion, NPD1 synthesis is enhanced as a response for sustaining homeostasis. Thus, neurotrophins, Abeta peptide 42 (Abeta42), calcium ionophore A23187, interleukin (IL)-1beta, or DHA supply enhances NPD1 synthesis. NPD1, in turn, up-regulates the antiapoptotic proteins of the Bcl-2 family and decreases the expression of proapoptotic Bcl-2 family members. Moreover, NPD1 inhibits IL-1beta-stimulated expression of cyclooxygenase-2 (COX-2). Because both RPE and photoreceptors are damaged and then die in retinal degenerations, elucidating how NPD1 signaling contributes to retinal cell survival may lead to a new understanding of disease mechanisms. In human neural cells, DHA attenuates amyloid-beta (Abeta) secretion, resulting in concomitant formation of NPD1. NPD1 was found to be reduced in the Alzheimer's disease (AD) cornu ammonis region 1 (CA1) hippocampal region, but not in other areas of the brain. The expression of key enzymes for NPD1 biosynthesis, cytosolic phospholipase A(2) (cPLA(2)), and 15-lipoxygenase (15-LOX) was found altered in the AD hippocampal CA1 region. NPD1 repressed Abeta42-triggered activation of pro-inflammatory genes and upregulated the antiapoptotic genes encoding Bcl-2, Bcl-xl, and Bfl-1(A1) in human brain cells in culture. Overall, these results support the concept that NPD1 promotes brain and retina cell survival via the induction of antiapoptotic and neuroprotective gene-expression programs that suppress Abeta42-induced neurotoxicity and other forms of cell injury, which in turn fosters homeostasis during development in aging, as well as during the initiation and progression of neurodegenerative diseases.

Contribution of Calpain to Cellular Damage in Human Retinal Pigment Epithelial Cells Cultured with Zinc Chelator

PURPOSE

We previously showed involvement of calpains in neural retina degeneration induced by hypoxia and ischemia-reperfusion. Age-related macular degeneration (AMD) is one of the leading causes for loss of vision. AMD showed degeneration of neural retina due to dysfunction and degeneration of the retinal pigment epithelium (RPE). RPE performs critical functions in neural retina, such as phagocytosis of shed rod outer segments. The purpose of the current study was to determine the contribution of calpain-induced proteolysis to damage in cultured human RPE cells. Zinc chelator TPEN was used to induce cellular damage as zinc deficiency is a suspected risk factor for AMD.

METHODS

In RPE/choroid preparations from normal and AMD patients, calpain mRNAs were measured by qPCR, and calpain activity was assessed by casein zymography. Third- to fifth-passage cells from human RPE cells were cultured with TPEN. Cell damage was morphologically assessed under the phase-contrast microscope, and TUNEL staining was performed to detect apoptosis. Leakage of lactate dehydrogenase (LDH) into the medium was measured as a marker of RPE cell damage. Activation of calpains and proteolysis of the known calpain substrate alpha -spectrin were assessed by immunoblotting. To further confirm calpain-induced proteolysis, calpain in homogenized RPE was also activated directly by addition of calcium.

RESULTS

RPE/choroid from normal patients expressed mRNAs for calpain 1, calpain 2, and calpastatin moderately, and calpain 2 activity tended to be lower in AMD patients. TPEN caused RPE cell damage with positive TUNEL staining. TPEN also caused leakage of LDH into the medium from RPE cells, and calpain inhibitor SJA6017 inhibited the leakage. Caspase-3 inhibitors z-VAD and z-DEVD also showed inhibitory effects. Immunoblotting for calpain and alpha -spectrin showed activation of calpain in RPE cells cultured with TPEN. Proteolysis by activated calpain was confirmed by addition of calcium to homogenized RPE.

CONCLUSIONS

These results suggested that activation of calpain contributed to cellular damage induced by TPEN in cultured human RPE cells.

Effect of Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) on IL-6, IL-8, and MCP-1 Expression in Human Retinal Pigment Epithelial Cell Line

PURPOSE

To examine pituitary adenylate cyclase-activating polypeptide (PACAP) receptors (PAC1, VPAC1, and VPAC2) mRNA and the effect of PACAP on interleukin-6 (IL-6), interleukin-8 (IL-8), and monocyte chemotactic protein-1 (MCP-1) expression in human retinal pigment epithelial cell line (ARPE-19) stimulated with interleukin-1beta (IL-1beta).

METHODS

Expression of PACAP receptor mRNA was examined by reverse transcription polymerase chain reaction (RT-PCR). PACAP and IL-1beta were added to serum-free medium. IL-6, IL-8, and MCP-1 mRNA were measured by real-time PCR. IL-6, IL-8, and MCP-1 protein concentrations were measured using enzyme-linked immunosorbent assay. Nuclear factor kappaB (NF-kappaB) translocation was examined by immunofluorescence.

RESULTS

PAC1 and VCAP1 receptors mRNA were expressed in unstimulated cells. VCAP2 mRNA was expressed in cells stimulated with IL-1beta. IL-1beta stimulated IL-6, IL-8, and MCP-1 mRNA expression and protein levels. PACAP (10(- 7) to 10(- 6) M) inhibited IL-1beta -stimulated IL-6, IL-8, and MCP-1 mRNA and protein levels. Immunofluorescence of NF-kappaB in the nucleus was dense 30 min after stimulation with IL-1beta, and it was decreased by PACAP.

CONCLUSIONS

ARPE-19 cells had PACAP receptors mRNA. PACAP inhibited IL-6, IL-8, and MCP-1 expression and protein secretion. Possibly, the effect on cytokines may be via suppression of NF-kappaB translocation.

A Novel Zinc Compound (Zinc Monocysteine) Enhances the Antioxidant Capacity of Human Retinal Pigment Epithelial Cells

PURPOSE

The aim of this study was to document the effect of a novel zinc amino acid combination on the concentrations of important antioxidants in cultured human retinal pigment epithelial (hRPE) cells.

METHODS

Primary confluent hRPE cells were treated with 30 microM of zinc acetate, zinc chloride, zinc cysteine, and zinc sulfate. The antioxidants catalase, glutathione, glutathione peroxidase, and metallothionein were measured. MTT assays were performed to determine the relative protection of the zinc compounds from the cytotoxic effects of H202 and t-butyl hydroperoxide.

RESULTS

Catalase and glutathione peroxidase activities were increased by the zinc formulations compared with the untreated control. Glutathione and metallothionein content were also increased. The greatest increases occurred with zinc conjugated to the amino acid cysteine. The MTT assays showed that zinc monocysteine protected cultured RPE cells from the toxicity of H2O2 and t-butyl hydroperoxide.

CONCLUSIONS

Our results demonstrate that zinc treatment of RPE cells increases antioxidants and protects cultured RPE cells from the cytotoxic effects of H2O2 and t-butyl hydroperoxide. The results show that zinc conjugated to cysteine offers greater benefits than either zinc salts or cysteine alone.

Expression of glutamate transporter subtypes in cultured retinal pigment epithelial and retinoblastoma cells

PURPOSE

Glutamate is the major excitatory neurotransmitter in the retina and glutamate uptake is essential for normal glutamate signalling. Retinal diseases may induce neurochemical changes which affect retinal cells including retinal pigment epithelium (RPE). The aim of the study was to investigate the expression of glutamate transporter subtypes in RPE and retinoblastoma cells and to clarify the effect of proliferation modulators on the levels of the expressed transporter in the RPE cell line.

METHODS

Cultured pig RPE cells and two human RPE cell lines, D407 and ARPE-19, as well as the human retinoblastoma cell line Y79 were used. Glutamate transporter expression was evaluated with Western blot analysis and immunocytochemistry.

RESULTS

The study revealed unexpected expression of neuronal glutamate transporter/chloride channel EAAT4 in these three cell lines, but not in cultured pig RPE cells, whereas another glutamate carrier, EAAC1, was present in all cell types utilized. Other transporter subtypes, GLT1, GLAST and EAAT5 were not found. Neither tamoxifen, known to inhibit both proliferation and glutamate uptake in RPE cells, nor retinoic acid nor insulin, also known to affect cell proliferation rates, were capable of changing the total levels of EAAT4 in APRE-19 cells.

CONCLUSIONS

Neuronal glutamate transporter EAAC1 is expressed in RPE cells. The robust expression of EAAT4 in cell lines may reflect a role of EAAT4 in cell proliferation and migration. Unaltered steady-state expression of this carrier and chloride-channel protein hints at posttranslational mechanisms of regulation of EAAT4.

Oxysterols Induced Inflammation and Oxidation in Primary Porcine Retinal Pigment Epithelial Cells

PURPOSE

Aging is associated with an accumulation of cholesterol esters in the Bruch membrane. Cholesterol esters are prone to undergo oxidation and generate oxysterols that have cytotoxic and proinflammatory properties. We investigated the effects of three oxysterols on mitochondrial dysfunctions, inflammation, and oxidative stress in primary cultures of porcine retinal pigment epithelial (RPE) cells.

METHODS

RPE cells were incubated with oxysterols (50 micro M of 24-hydroxycholesterol, 25-hydroxycholesterol, or 7-ketocholesterol) for 24 hr and 48 hr. Oxysterol content was determined in cells and in corresponding media by gas chromatography. Mitochondrial activity was measured by mitochondrial dehydrogenase activity. The intracellular formation of reactive oxygen species in RPE cells was detected by using the fluorescent probe DCFH-DA. IL-8 was assayed in the supernatants by ELISA, and the corresponding cellular transcripts were semiquantified by RT-PCR.

RESULTS

Analyses of the oxysterols content in the RPE cells and corresponding media suggested a high rate of cellular uptake, although some differences were observed between 7-ketocholesterol on the one hand and 24-hydroxycholesterol and 25-hydroxycholesterol on the other hand. All oxysterols induced slight mitochondrial dysfunctions but a significant 2- to 4-fold increase in reactive oxygen species (ROS) production compared with the control. They also enhanced IL-8 gene expression and IL-8 protein secretion in the following decreasing order: 25-hydroxycholesterol > 24-hydroxycholesterol > 7-ketocholesterol.

CONCLUSIONS

We conclude that in confluent primary porcine RPE cells, 24-hydroxycholesterol, 25-hydroxycholesterol, and 7-ketocholesterol are potent inducers of oxidation and inflammation.

Protective Effect of Hepatocyte Growth Factor Against Degeneration of the Retinal Pigment Epithelium and Photoreceptor in Sodium Iodate–Injected Rats

PURPOSE

To investigate the possible protective effect of hepatocyte growth factor (HGF) against degeneration of photoreceptors and retinal pigment epithelium (RPE) in vivo.

METHODS

Sprague-Dawley (SD) rats received an intravitreal injection of HGF in the right eye. The left eye was injected with vehicle as a control. Two days after the intravitreal injections, rats were administered 40 mg/kg of sodium iodate (NaIO3) intravenously. Scotopic ERGs were elicited by different stimulus intensities with a maximum luminance of 0.84 log cds/m2. To evaluate RPE function, the azide response was evoked by intravenous injection of 0.1 mg sodium azide. These electrophysiological measurements were conducted on days 4, 7, 14, and 28 after the NaIO3 injections. After recording ERGs or azide response, animals were sacrificed for quantification of the histological change and immunohistochemical analysis using antibodies against RPE 65.

RESULTS

The threshold for the scotopic b-wave was significantly lower in HGF-treated eyes than in untreated control eyes (p < 0.005), and maximum b-wave amplitudes (Vbmax) were significantly larger in HGF-treated eyes (p < 0.05) across all experimental time points after NaIO3 injection. Azide response amplitudes were significantly larger in the HGF-treated eyes than in the untreated eyes (p < 0.05). The structure of the outer retina was preserved to a greater degree in the HGF-treated eyes than in the untreated eyes (p < 0.05). Immunohistochemical analysis demonstrated that irregular alignment of the outer nuclear layer was confined to the retinal area that was not stained with RPE 65.

CONCLUSIONS

Our results indicated that an intravitreal injection of HGF provided significant protection against degeneration of the photoreceptor and RPE induced by systemic administration of NaIO3. This suggests that HGF could be used as a therapeutic agent for degeneration of photoreceptors as well as RPE.

Toxicity of Indocyanine Green (ICG) in Combination with Light on Retinal Pigment Epithelial Cells and Neurosensory Retinal Cells

PURPOSE

To evaluate the toxicity of indocyanine green (ICG) in combination with light.

METHODS

Human retinal pigment epithelial cells (ARPE-19) and rat neurosensory retinal cells (R28) were treated with four different concentrations of ICG in combination with light exposure. Cell viability, mitochondrial function, and DNA synthesis were measured.

RESULTS

All concentrations of ICG with 10 min of light exposure caused a significant decrease in mitochondrial dehydrogenase activity in R28 and ARPE-19 cells. ICG without light exposure did not decrease mitochondrial dehydrogenase activity. In both cell lines, [(3)H]thymidine incorporation was increased when treated with ICG with or without light. R28 cells did not show any significant decrease in cell viability.

CONCLUSIONS

The duration of light was a significant factor in ICG toxicity. ICG needs to be used with caution as it decreases the mitochondrial dehydrogenase activity and increases the DNA synthesis in retinal cells, markers for cell toxicity and dysfunction.

Contrary effects of cytokines on mRNAs of cell cycle- and ECM-related proteins in hRPE cells in vitro

PURPOSE

Retinal pigment epithelial (RPE) cells play a pivotal role in the pathogenesis of proliferative vitreoretinopathy (PVR). As a result of a breakdown of the blood-retina barrier, growth factors obtain access to the subretinal space and stimulate several retinal cell types. The aim of the present study was to analyze the effect of several growth factors on the proliferation of human (h)RPE cells, and on the mRNA expression of transcription factors, cell cycle proteins, and extracellular matrix (ECM) proteins.

METHODS

hRPE cells were incubated in the presence of TGF-beta1, TGF-beta2, PDGF, VEGF, or bFGF for 24-72 h. Cell proliferation was assessed by determinating BrdU incorporation. Changes in mRNA expression of c-fos, c-myc, PCNA, FEN1, Ki67, collagen III, and collagen IV were investigated by ribonuclease protection assay (RPA).

RESULTS

RPE cell proliferation was significantly increased by exposure to PDGF and bFGF for 48 h, and was decreased by application of TGF-beta1 and TGF-beta2 for 48 and 72 h. All the tested growth factors significantly elevated the amounts of c-fos mRNA (after 1 h) and of c-myc mRNA (after 24 h). PDGF and bFGF up-regulated the expression of Ki67 mRNA, and down-regulated that of collagen III and collagen IV mRNA after 24 h. TGF-beta1 and TGF-beta2 decreased the expression of Ki67 mRNA, and increased that of collagen III and collagen IV mRNA.

CONCLUSION

Our results show that distinct cytokines may induce contrary effects with respect to proliferation of, and ECM formation by, hRPE cells in vitro. This knowledge may be useful for the development of improved therapeutic approaches.