Placental growth factor stabilizes VEGF receptor-2 protein in retinal pigment epithelial cells by downregulating glycogen synthase kinase 3 activity.

Placental growth factor (PlGF) belongs to the vascular endothelial growth factor (VEGF) family of proteins that participate in angiogenesis and vasculogenesis. Anti-VEGF therapy has become the standard treatment for ocular angiogenic disorders in ophthalmological practice. However, there is emerging evidence that anti-VEGF treatment may increase the risk of atrophy of the retinal pigment epithelium (RPE), which is important for the homeostasis of retinal tissue. Whereas the cytoprotective role of VEGF family molecules, particularly that of VEGF A (VEGFA) through its receptor VEGF receptor-2 (VEGFR-2), has been recognized, the physiological role of PlGF in the retina is still unknown. In this study, we explored the role of PlGF in the RPE using PlGF-knockdown RPE cells generated by retrovirus-based PlGF-shRNA transduction. We show that VEGFA reduced apoptosis induced by serum starvation in RPE cells, whereas the antiapoptotic effect of VEGFA was abrogated by VEGFR-2 knockdown. Furthermore, PlGF knockdown increased serum starvation-induced cell apoptosis and unexpectedly reduced the protein level of VEGFR-2 in the RPE. The antiapoptotic effect of VEGFA was also diminished in PlGF-knockdown RPE cells. In addition, we found that glycogen synthase kinase 3 activity was involved in proteasomal degradation of VEGFR-2 in RPE cells and inactivated by PlGF via AKT phosphorylation. Overall, the present data demonstrate that PlGF is crucial for RPE cell viability and that PlGF supports VEGFA/VEGFR-2 signaling by stabilizing the VEGFR-2 protein levels through glycogen synthase kinase 3 inactivation.

Accessory structures that originate from photoreceptor bundles in the retina of the teleost Notopterus notopterus (Pallas).

The teleost species Notopterus notopterus (Pallas) possess bundled photoreceptors in their retina. It was found that the margin of the inner portion (the vitreal half) of photoreceptor bundles emits thin processes. Each process terminates on the contralateral photoreceptor bundle, or the processes from adjacent photoreceptor bundle may fuse. The site of the inner half of the photoreceptor bundles from where they arise shows minimal support of the photoreceptor bundles by retinal pigment epithelium, and so it is likely that those accessory structures may aid to hold the photoreceptor bundles in correct orientation.

Phenotypic heterogeneity of human retinal pigment epithelial cells in passaged cell populations.

Human retinal pigment epithelial (RPE) cells at different population doublings (PDs) were cultured for 28 days to examine their phenotypic heterogeneity in a confluent state. In an early population (PD = 2.8), cells showed a cobblestone-like appearance (type I), which gradually became small and tight, and eventually exhibited dark pigmentation. Some cells showed a dome-like structure (type II), which detached from the culture surface during culture. With increasing PD, the cells showed active migration that caused a shift in phenotype from a single layer of large, flattened cells (type III) to a multiple cell layers (stratified) with flattened, irregularly shaped cells (type IV). Immunostaining of specific RPE markers, ZO-1 and Na+/K+-ATPase revealed that cells have markedly decreased expressions in a late population (PD = 10.1). RPE phenotypes were classified into four types by measuring the nuclear size and local density. The frequencies of type I cells decreased with increasing PD value, while the frequencies of type III and IV cells increased along with the decrease in type I. The frequencies of type IV cells at PD = 10.1 had increased by 10.3-fold compared with PD = 2.8. From these results, the nuclear size and local density were proposed as indicators for understanding phenotypic heterogeneity of RPE cells in the passaged cell population during cell expansion. It is concluded that the population doubling level is an important factor to affect the transition of RPE phenotype and thereby to modulate the quality of cultured cells.

Differentially cleaving peptides as a strategy for controlled drug release in human retinal pigment epithelial cells.

Currently, drug delivery to the posterior eye segment relies on intravitreal injections of therapeutics. This approach requires frequent injections and does not guarantee drug delivery to intracellular targets. Controlled release systems and nanoparticles are being investigated to mitigate these challenges but most of these approaches lack translational success to the clinics. In our present study, we report a peptide-based delivery system that utilizes enzyme assisted cleavable linkers to release conjugated cargo within the retinal pigment epithelial (RPE) cells. Peptide linkers with differential cleavage rates were developed and tested in the vitreous humor, RPE cell homogenates and intact RPE cells. Selected peptide linkers were conjugated to cell penetrating peptides and d-peptide cargoes. The peptide-based delivery systems were non-toxic to the RPE cells, chemically stable in porcine vitreous and delivered cargo prototypes (hydrophobic & hydrophilic) to the RPE cells. Importantly, we show quantitatively with LC/MS analytics that the intracellular cargo release is controlled by the sequence of the peptide linker. The controlled cleavage of the peptide linkers is not only a useful strategy for intracellular drug delivery to the RPE targets but might also be useful in utilizing the RPE cells as mediators of drug delivery to intracellular targets and surrounding tissues (such as neural retina and choroid).

Subretinal Pigment Epithelial Deposition of Drusen Components Including Hydroxyapatite in a Primary Cell Culture Model.

Purpose: Extracellular deposits containing hydroxyapatite, lipids, proteins, and trace metals that form between the basal lamina of the RPE and the inner collagenous layer of Bruch's membrane are hallmarks of early AMD. We examined whether cultured RPE cells could produce extracellular deposits containing all of these molecular components. Methods: Retinal pigment epithelium cells isolated from freshly enucleated porcine eyes were cultured on Transwell membranes for up to 6 months. Deposit composition and structure were characterized using light, fluorescence, and electron microscopy; synchrotron x-ray diffraction and x-ray fluorescence; secondary ion mass spectroscopy; and immunohistochemistry. Results: Apparently functional primary RPE cells, when cultured on 10-µm-thick inserts with 0.4-µm-diameter pores, can produce sub-RPE deposits that contain hydroxyapatite, lipids, proteins, and trace elements, without outer segment supplementation, by 12 weeks. Conclusions: The data suggest that sub-RPE deposit formation is initiated, and probably regulated, by the RPE, as well as the loss of permeability of the Bruch's membrane and choriocapillaris complex associated with age and early AMD. This cell culture model of early AMD lesions provides a novel system for testing new therapeutic interventions against sub-RPE deposit formation, an event occurring well in advance of the onset of vision loss.

Facilitation of uniform maturation of human retinal pigment epithelial cells through collective movement in culture.

Understanding of the fundamental mechanisms that govern tight junction formation of retinal pigment epithelial (RPE) cells provides surface design strategies for promoting their maturation in culture. RPE cells were cultured to investigate their migratory behavior and the expression of tight junction protein ZO-1 in the central and peripheral regions of a culture vessel. Regardless of locational differences in the culture vessel, the cells at day 1 were elongated in shape, did not form tight junctions, and migrated actively. As the culture progressed, the cells in the central region slowly moved with morphological change of a cobblestone-like shape via interaction between contact cells and exhibiting the shift from random migration to collective movement toward the center, accompanied by tight junction formation. On the other hand, the cells in the peripheral region maintained the random migration at day 5, meaning spatial heterogeneity in maturation in the vessel. At day 5, RPE cells were incubated in medium with Rac1 inhibitor and the exposure to the Rac1 inhibitor triggered the rapid conversion of migratory behavior from random migration to collective movement toward the center of the vessel, resulting in uniform maturation. These findings indicate that the change in migratory patterns is an important cues and the collective movement toward the center causes the facilitation of uniform maturation in the vessel.

Efficiency of Membrane Protein Expression Following Infection with Recombinant Adenovirus of Polarized Non-Transformed Human Retinal Pigment Epithelial Cells.

Transient expression of exogenous proteins facilitates studies of molecular mechanisms and utility for transplantation of retinal pigment epithelial (RPE) cells in culture. Here, we compared expression of the membrane protein ß5 integrin-GFP (ß5-GFP) in two recently established models of differentiated human RPE, adult RPE stem cell-derived RPE and primary fetal RPE, upon infection with recombinant adenovirus or transfection with DNA in liposomes. We varied viral titer and duration of virus incubation and examined ß5-GFP and the tight junction marker ZO-1 in manipulated cells by confocal microscopy. Fewer than 5 % of cells expressed ß5-GFP after liposome-mediated transfection. The percentage of cells with detectable ß5-GFP exceeded 90 % after adenovirus infection for as little as 1 h. Decreasing virus titer two-fold did not alter the fraction of cells expressing ß5-GFP but increased variability of ß5-GFP level among cells. In cells with low expression levels, ß5-GFP localized mostly to the apical plasma membrane like endogenous αvß5 integrin. In cells with high expression levels, ß5-GFP localized to the cytoplasm in addition to the apical surface suggesting accumulation in trafficking compartments. Altogether, adenovirus delivery yields efficient exogenous membrane protein expression of correct polarity in differentiated human RPE cells in culture.

Systems Analysis of Protein Fatty Acylation in Herpes Simplex Virus-Infected Cells Using Chemical Proteomics.

Protein fatty acylation regulates diverse aspects of cellular function and organization and plays a key role in host immune responses to infection. Acylation also modulates the function and localization of virus-encoded proteins. Here, we employ chemical proteomics tools, bio-orthogonal probes, and capture reagents to study myristoylation and palmitoylation during infection with herpes simplex virus (HSV). Using in-gel fluorescence imaging and quantitative mass spectrometry, we demonstrate a generalized reduction in myristoylation of host proteins, whereas palmitoylation of host proteins, including regulators of interferon and tetraspanin family proteins, was selectively repressed. Furthermore, we found that a significant fraction of the viral proteome undergoes palmitoylation; we identified a number of virus membrane glycoproteins, structural proteins, and kinases. Taken together, our results provide broad oversight of protein acylation during HSV infection, a roadmap for similar analysis in other systems, and a resource with which to pursue specific analysis of systems and functions.

[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.

Locational heterogeneity of maturation by changes in migratory behaviors of human retinal pigment epithelial cells in culture.

To better characterize human retinal pigment epithelial (RPE) cells, their maturation was studied by time-lapse observation and immunostaining of the tight junction protein ZO-1. During subconfluency with active migration, the cells had an elongated shape. During cell division to reach confluency, RPE cells became small and tight, exhibiting cobblestone-like morphology. In addition, RPE maturation at the peripheral region of the culture vessel was delayed when compared with the central region, demonstrating local heterogeneity during maturation. To correlate cellular migration and maturation, we compared frequencies of migration rate and number of ZO-1-positive cells at the central and peripheral regions. Cells having migration rates less than 5.0 µm/h in the central region were 1.4-fold higher than in the peripheral region at day 5. Regardless of locational differences in the culture vessel, the frequency of cells having migration rates less than 5.0 µm/h showed 90% agreement with the frequency of ZO-1-positive cells. To inhibit cell migration, RPE cells were exposed to medium containing 50 µg/ml Rac1 inhibitor at day 5. Frequencies of ZO-1-positive cells and cells having migration rates less than 5.0 µm/h at the peripheral region were similar to those at the central region. The results show that migration is an important factor affecting maturation, and demonstrate that location heterogeneity during maturation is caused by different migratory behaviors in the culture vessel.

The influence of substrate elastic modulus on retinal pigment epithelial cell phagocytosis.

To better understand if a complex process such as phagocytosis is influenced by substrate stiffness, we investigated the influence of substrate elastic modulus on phagocytosis in the retinal pigment epithelial (RPE) cell line ARPE-19. RPE cells lie on Bruch's membrane, directly under the retina, and phagocytose the shed photoreceptor outer segments. Bruch's membrane is known to increase in stiffness by an order of magnitude with age and thus, this study has potential relevance in explaining retinal changes in age-related macular degeneration. ARPE-19 cells were plated on laminin-coated polyacrylamide substrates of varying elastic modulus. After 14 days in culture, a solution of latex fluorescent beads suspended in PBS was placed in each well. After an incubation time of 4h, flow cytometry was performed to determine the number of cells that phagocytosed a bead. The number of ARPE-19 cells that phagocytosed a bead decreased continuously as a function of increasing substrate elastic modulus (p=0.0135), and this was found to be a linear relationship (slope=-0.03305 ± 0.01104, R2=0.4726 per 10,000 cells). Our results suggest that RPE cells display decreased phagocytosis when grown on firmer substrates, and thus, RPE cells in older eyes, in which Bruch's membrane is stiffer, may demonstrate decreased phagocytosis. Impaired phagocytosis by RPE cells may contribute to impaired metabolism of photoreceptor outer segments and to development of macular degeneration. Material stiffness may be a critical parameter in the development of neural therapies, including retinal prosthetics and stem cell therapies.

Orientation of actin filaments in teleost retinal pigment epithelial cells, and the effect of the lectin, Concanavalin A, on melanosome motility.

Retinal pigment epithelial cells of teleosts contain numerous melanosomes (pigment granules) that exhibit light-dependent motility. In light, melanosomes disperse out of the retinal pigment epithelium (RPE) cell body (CB) into long apical projections that interdigitate with rod photoreceptors, thus shielding the photoreceptors from bleaching. In darkness, melanosomes aggregate through the apical projections back into the CB. Previous research has demonstrated that melanosome motility in the RPE CB requires microtubules, but in the RPE apical projections, actin filaments are necessary and sufficient for motility. We used myosin S1 labeling and platinum replica shadowing of dissociated RPE cells to determine actin filament polarity in apical projections. Actin filament bundles within RPE apical projections are uniformly oriented with barbed ends toward the distal tips. Treatment of RPE cells with the tetravalent lectin, Concanavalin A, which has been shown to suppress cortical actin flow by crosslinking of cell-surface proteins, inhibited melanosome aggregation and stimulated ectopic filopodia formation but did not block melanosome dispersion. The polarity orientation of F-actin in apical projections suggests that a barbed-end directed myosin motor could effect dispersion of melanosomes from the CB into apical projections. Inhibition of aggregation, but not dispersion, by ConA confirms that different actin-dependent mechanisms control these two processes and suggests that melanosome aggregation is sensitive to treatments previously shown to disrupt actin cortical flow.

Immediate differentiation of neuronal cells from stem/progenitor-like cells in the avian iris tissues.

A simple culture method that was recently developed in our laboratory was applied to the chick iris tissues to characterize neural stem/progenitor-like cells. Iris tissue is a non-neuronal tissue and does not contain any neuronal cells. In the present study we isolated iris tissues from chick embryos just prior to hatching. The isolated iris pigmented epithelium (IPE) or the stroma was embedded in Matrigel and cultured in Dulbecco's MEM supplemented with either fetal bovine serum or the synthetic serum replacement solution B27. Within 24 h of culture, elongated cells with long processes extended out from the explants of both tissues and were positively stained for various neuronal markers such as transitin, Tuj-1 and acetylated tubulin. After a longer culture period, cells positive for photoreceptor markers like rhodopsin, iodopsin and visinin were found, suggesting that the iris tissues contain retinal stem/progenitor-like cells. Several growth factors were examined to determine their effects on neuronal differentiation. EGF was shown to dramatically enhance neuronal cell differentiation, particularly the elongation of neuronal fibers. The addition of exogenous FGF2, however, did not show any positive effects on neuronal differentiation, although FGF signaling inhibitor, SU5402, suppressed neuronal differentiation. The results show that neuronal stem/progenitor-like cells can differentiate into neuronal cells immediately after they are transferred into an appropriate environment. This process did not require any exogenous factors, suggesting that neural stem/progenitor-like cells are simply suppressed from neuronal differentiation within the tissue, and isolation from the tissue releases the cells from the suppression mechanism.

Multiple A2E treatments lead to melanization of rod outer segment-challenged ARPE-19 cells.

PURPOSE: Daily phagocytosis of outer segments (OSs) and retinoid recycling by the RPE lead to the accumulation of storage bodies in the RPE containing autofluorescent lipofuscin, which consists of lipids and bisretinoids such as A2E and its oxidation products. Accumulation of A2E and its oxidation products is implicated in the pathogenesis of several retinal degenerative diseases. However, A2E accumulates in the RPE during normal aging. In this study, we used a cell model to determine the homeostatic mechanisms of RPE cells in response to A2E accumulation. METHODS: To distinguish between pathologic and normal responses of the RPE to A2E accumulation, we treated established ARPE-19 cells (cultured for 3 weeks after reaching confluence) with low micromolar amounts of A2E for several weeks. We compared the lysosomal function, lysosomal pH, degree of OS digestion, and melanization of the treated cells to untreated control cells in response to a challenge of purified rod OSs (ROSs). A2E was analyzed with high-performance liquid chromatography (HPLC); and A2E and melanin were identified with mass spectrometry. RESULTS: We found that post-confluent ARPE-19 cells took up and accumulated A2E under dim light conditions. Spectral analysis of the HPLC separations and mass spectrometry showed that A2E-fed cells contained A2E and oxidized A2E (furan-A2E). A2E accumulation led to a modest increase (up to 0.25 unit) in lysosomal pH in these cells. The specific activity of cathepsin D and lysosomal acid phosphatase was reduced in the A2E-treated cells, but ROS degradation was not impaired. We found that, upon challenge with ROSs, melanin pigment was induced in the lysosomal fraction of the A2E-treated ARPE-19 cells. Thus, the ARPE-19 cells responded to the A2E treatment and ROS challenge by producing a melanin-containing lysosome fraction. We speculate that this prevents them from becoming impaired in OS processing. CONCLUSIONS: We used a modified ARPE-19 cell model in which melanization was elicited as a response to chronic accumulation of A2E. We found that although A2E treatment led, as has been previously reported, to modest lysosomal alkalinization and lysosomal impairment of ARPE-19 cells, a potential homeostatic mechanism may involve production of a special type of lysosomes containing melanin.

Notch signaling in the pigmented epithelium of the anterior eye segment promotes ciliary body development at the expense of iris formation.

The ciliary body and iris are pigmented epithelial structures in the anterior eye segment that function to maintain correct intra-ocular pressure and regulate exposure of the internal eye structures to light, respectively. The cellular and molecular factors that mediate the development of the ciliary body and iris from the ocular pigmented epithelium remain to be fully elucidated. Here, we have investigated the role of Notch signaling during the development of the anterior pigmented epithelium by using genetic loss- and gain-of-function approaches. Loss of canonical Notch signaling results in normal iris development but absence of the ciliary body. This causes progressive hypotony and over time leads to phthisis bulbi, a condition characterized by shrinkage of the eye and loss of structure/function. Conversely, Notch gain-of-function results in aniridia and profound ciliary body hyperplasia, which causes ocular hypertension and glaucoma-like disease. Collectively, these data indicate that Notch signaling promotes ciliary body development at the expense of iris formation and reveals novel animal models of human ocular pathologies.

Intrinsic lens forming potential of mouse lens epithelial versus newt iris pigment epithelial cells in three-dimensional culture.

Adult newts (Notophthalmus viridescens) are capable of complete lens regeneration that is mediated through dorsal iris pigment epithelial (IPE) cells transdifferentiation. In contrast, higher vertebrates such as mice demonstrate only limited lens regeneration in the presence of an intact lens capsule with remaining lens epithelial cells. To compare the intrinsic lens regeneration potential of newt IPE versus mouse lens epithelial cells (MLE), we have established a novel culture method that uses cell aggregation before culture in growth factor-reduced Matrigel. Dorsal newt IPE aggregates demonstrated complete lens formation within 1 to 2 weeks of Matrigel culture without basic fibroblast growth factor (bFGF) supplementation, including the establishment of a peripheral cuboidal epithelial cell layer, and the appearance of central lens fibers that were positive for αA-crystallin. In contrast, the lens-forming potential of MLE cell aggregates cultured in Matrigel was incomplete and resulted in the formation of defined-size lentoids with partial optical transparency. While the peripheral cell layers of MLE aggregates were nucleated, cells in the center of aggregates demonstrated a nonapoptotic nuclear loss over a time period of 3 weeks that was representative of lens fiber formation. Matrigel culture supplementation with bFGF resulted in higher transparent bigger-size MLE aggregates that demonstrated increased appearance of ßB1-crystallin expression. Our study demonstrates that bFGF is not required for induction of newt IPE aggregate-dependent lens formation in Matrigel, while the addition of bFGF seems to be beneficial for the formation of MLE aggregate-derived lens-like structures. In conclusion, the three-dimensional aggregate culture of IPE and MLE in Matrigel allows to a higher extent than older models the indepth study of the intrinsic lens-forming potential and the corresponding identification of lentogenic factors.

Apelin-13 induces proliferation, migration, and collagen I mRNA expression in human RPE cells via PI3K/Akt and MEK/Erk signaling pathways.

PURPOSE: Our previous study showed that apelin was increased in the vitreous and fibrotic membranes of patients with proliferative diabetic retinopathy (PDR) in vivo, which suggested that apelin may be involved in the development of PDR. In this study, we investigated whether the expression of apelin was upregulated in human retinal pigment epithelial (RPE) cells in vitro under high glucose conditions. Furthermore, to explore the role of apelin in RPE cells, we investigated the effect of exogenous recombinant apelin on proliferation, migration, and collagen I (a major component of extracellular matrix molecules, associated with PDR) expression and investigated the signaling pathways involved in these processes. METHODS: Real-time PCR and western blot were performed to determine the apelin expression in ARPE-19 cells under high glucose conditions. Exogenous recombinant apelin was used to study the effect of apelin on ARPE-19 cells in vitro. Cell proliferation, migration, and collagen I expression were assessed using an MTT assay, a transwell assay, and real-time PCR analysis. LY294002 (an inhibitor of phosphatidylinositol 3-kinase) and PD98059 (an inhibitor of mitogen-activated protein kinase) were used to help to determine the apelin signaling mechanism. RESULTS: High glucose upregulated apelin expression in RPE cells. Exogenous recombinant apelin activated protein kinase B (Akt) and extracellular signal-regulated kinase (Erk) phosphorylation and promoted proliferation, migration, and collagen I expression in RPE cells. Pretreatment with LY294002 and PD98059 abolished apelin-induced activation of Akt and Erk, proliferation, and collagen I expression. Apelin-induced migration was partially blocked by pretreatment with LY294002 and PD98059. CONCLUSIONS: The expression of apelin was upregulated under high glucose conditions in RPE cells in vitro. Exogenous recombinant apelin increased the biologic activity of RPE cells, as well as the expression of collagen I. Apelin promoted proliferation, migration, and collagen I expression through the PI3K/Akt and MEK/Erk signaling pathways in RPE cells. From these results, we revealed the role of apelin in regulating proliferation, migration, and collagen I expression in RPE cells and the signaling mechanism under these processes, which suggested that apelin may play a profibrotic role in the development of PDR.

Fibrotic remodeling of the extracellular matrix through a novel (engineered, dual-function) antibody reactive to a cryptic epitope on the N-terminal 30 kDa fragment of fibronectin.

Fibrosis is characterized by excessive accumulation of scar tissue as a result of exaggerated deposition of extracellular matrix (ECM), leading to tissue contraction and impaired function of the organ. Fibronectin (Fn) is an essential component of the ECM, and plays an important role in fibrosis. One such fibrotic pathology is that of proliferative vitreoretinopathy (PVR), a sight-threatening complication which develops as a consequence of failure of surgical repair of retinal detachment. Such patients often require repeated surgeries for retinal re-attachment; therefore, a preventive measure for PVR is of utmost importance. The contractile membranes formed in PVR, are composed of various cell types including the retinal pigment epithelial cells (RPE); fibronectin is an important constituent of the ECM surrounding these cells. Together with the vitreous, fibronectin creates microenvironments in which RPE cells proliferate. We have successfully developed a dual-action, fully human, fibronectin-specific single chain variable fragment antibody (scFv) termed Fn52RGDS, which acts in two ways: i) binds to cryptic sites in fibronectin, and thereby prevents its self polymerization/fibrillogenesis, and ii) interacts with the cell surface receptors, ie., integrins (through an attached "RGD" sequence tag), and thereby blocks the downstream cell signaling events. We demonstrate the ability of this antibody to effectively reduce some of the hallmark features of fibrosis--migration, adhesion, fibronectin polymerization, matrix metalloprotease (MMP) expression, as well as reduction of collagen gel contraction (a model of fibrotic tissue remodeling). The data suggests that the antibody can be used as a rational, novel anti-fibrotic candidate.

A microarray analysis of gene expression patterns during early phases of newt lens regeneration.

PURPOSE: Notophthalmus viridescens, the red-spotted newt, possesses tremendous regenerative capabilities. Among the tissues and organs newts can regenerate, the lens is regenerated via transdifferentiation of the pigment epithelial cells of the dorsal iris, following complete removal (lentectomy). Under normal conditions, the same cells from the ventral iris are not capable of regenerating. This study aims to further understand the initial signals of lens regeneration. METHODS: We performed microarray analysis using RNA from a dorsal or ventral iris isolated 1, 3, and 5 days after lentectomy and compared to RNA isolated from an intact iris. This analysis was supported with quantitative real-time polymerase chain reaction (qRT-PCR) of selected genes. RESULTS: Microarrays showed 804 spots were differentially regulated 1, 3, and 5 days post-lentectomy in the dorsal and ventral iris. Functional annotation using Gene Ontology revealed interesting terms. Among them, factors related to cell cycle and DNA repair were mostly upregulated, in the microarray, 3 and 5 days post-lentectomy. qRT-PCR for rad1 and vascular endothelial growth factor receptor 1 showed upregulation for the dorsal iris 3 and 5 days post- lentectomy and for the ventral iris 5 days post-lentectomy. Rad1 was also upregulated twofold more in the dorsal iris than in the ventral iris 5 days post-lentectomy (p<0.001). Factors related to redox homeostasis were mostly upregulated in the microarray in all time points and samples. qRT-PCR for glutathione peroxidase 1 also showed upregulation in all time points for the ventral and dorsal iris. For the most part, mitochondrial enzymes were downregulated with the notable exception of cytochrome c-related oxidases that were mostly upregulated at all time points. qRT-PCR for cytochrome c oxidase subunit 2 showed upregulation especially 3 days post-lentectomy for the dorsal and ventral iris (p<0.001). Factors related to extracellular matrix and tissue remodeling showed mostly upregulation (except collagen I) for all time points and samples. qRT-PCR for stromelysin 1/2 alpha and avidin showed upregulation in all the time points for the dorsal and ventral iris. CONCLUSIONS: The results show that the dorsal iris and the ventral iris follow the same general pattern with some distinct differences especially 5 days after lentectomy. In addition, while the expression of genes involved in DNA repair, redox homeostasis, and tissue remodeling in preparation for proliferation and transdifferentiation is altered in the entire iris, the response is more prominent in the dorsal iris following lentectomy.