The retinal pigment epithelium in visual function

Mechanisms for countering oxidative stress and damage in retinal pigment epithelium

Clinical and experimental evidence supports that chronic oxidative stress is a primary contributing factor to numerous retinal degenerative diseases, such as age-related macular degeneration (AMD). Eyes obtained postmortem from AMD patients have extensive free radical damage to the proteins, lipids, DNA, and mitochondria of their retinal pigment epithelial (RPE) cells. In addition, several mouse models of chronic oxidative stress develop many of the pathological hallmarks of AMD. However, the extent to which oxidative stress is an etiologic component versus its involvement in disease progression remains a major unanswered question. Further, whether the primary target of oxidative stress and damage is photoreceptors or RPE cells, or both, is still unclear. In this review, we discuss the major functions of RPE cells with an emphasis on the oxidative challenges these cells encounter and the endogenous antioxidant mechanisms employed to neutralize the deleterious effects that such stresses can elicit if left unchecked.

The SLC16A family of monocarboxylate transporters (MCTs)--physiology and function in cellular metabolism, pH homeostasis, and fluid transport

The SLC16A family of monocarboxylate transporters (MCTs) is composed of 14 members. MCT1 through MCT4 (MCTs 1-4) are H(+)-coupled monocarboxylate transporters, MCT8 and MCT10 transport thyroid hormone and aromatic amino acids, while the substrate specificity and function of other MCTs have yet to be determined. The focus of this review is on MCTs 1-4 because their role in lactate transport is intrinsically linked to cellular metabolism in various biological systems, including skeletal muscle, brain, retina, and testis. Although MCTs 1-4 all transport lactate, they differ in their transport kinetics and vary in tissue and subcellular distribution, where they facilitate "lactate-shuttling" between glycolytic and oxidative cells within tissues and across blood-tissue barriers. However, the role of MCTs 1-4 is not confined to cellular metabolism. By interacting with bicarbonate transport proteins and carbonic anhydrases, MCTs participate in the regulation of pH homeostasis and fluid transport in renal proximal tubule and corneal endothelium, respectively. Here, we provide a comprehensive review of MCTs 1-4, linking their cellular distribution to their functions in various parts of the human body, so that we can better understand the physiological roles of MCTs at the systemic level.

New insights into the regulation of myosin light chain phosphorylation in retinal pigment epithelial cells

The retinal pigment epithelium (RPE) plays an essential role in the function of the neural retina and the maintenance of vision. Most of the functions displayed by RPE require a dynamic organization of the acto-myosin cytoskeleton. Myosin II, a main cytoskeletal component in muscle and non-muscle cells, is directly involved in force generation required for organelle movement, selective molecule transport within cell compartments, exocytosis, endocytosis, phagocytosis, and cell division, among others. Contractile processes are triggered by the phosphorylation of myosin II light chains (MLCs), which promotes actin-myosin interaction and the assembly of contractile fibers. Considerable evidence indicates that non-muscle myosin II activation is critically involved in various pathological states, increasing the interest in studying the signaling pathways controlling MLC phosphorylation. Particularly, recent findings suggest a role for non-muscle myosin II-induced contraction in RPE cell transformation involved in the establishment of numerous retinal diseases. This review summarizes the current knowledge regarding myosin function in RPE cells, as well as the signaling networks leading to MLC phosphorylation under pathological conditions. Understanding the molecular mechanisms underlying RPE dysfunction would improve the development of new therapies for the treatment or prevention of different ocular disorders leading to blindness.

Electrical signaling in control of ocular cell behaviors

Epithelia of the cornea, lens and retina contain a vast array of ion channels and pumps. Together they produce a polarized flow of ions in and out of cells, as well as across the epithelia. These naturally occurring ion fluxes are essential to the hydration and metabolism of the ocular tissues, especially for the avascular cornea and lens. The directional transport of ions generates electric fields and currents in those tissues. Applied electric fields affect migration, division and proliferation of ocular cells which are important in homeostasis and healing of the ocular tissues. Abnormalities in any of those aspects may underlie many ocular diseases, for example chronic corneal ulcers, posterior capsule opacity after cataract surgery, and retinopathies. Electric field-inducing cellular responses, termed electrical signaling here, therefore may be an unexpected yet powerful mechanism in regulating ocular cell behavior. Both endogenous electric fields and applied electric fields could be exploited to regulate ocular cells. We aim to briefly describe the physiology of the naturally occurring electrical activities in the corneal, lens, and retinal epithelia, to provide experimental evidence of the effects of electric fields on ocular cell behaviors, and to suggest possible clinical implications.

Subretinal transplantation of putative retinal pigment epithelial cells derived from human embryonic stem cells in rat retinal degeneration model

OBJECTIVE

To differentiate the human embryonic stem cells (hESCs) into the retinal pigment epithelium (RPE) in the defined culture condition and determine its therapeutic potential for the treatment of retinal degenerative diseases.

METHODS

The embryoid bodies were formed from hESCs and attached on the matrigel coated culture dishes. The neural structures consisting neural precursors were selected and expanded to form rosette structures. The mechanically isolated neural rosettes were differentiated into pigmented cells in the media comprised of N2 and B27. Expression profiles of markers related to RPE development were analyzed by reverse transcription-polymerase chain reaction and immunostaining. Dissociated putative RPE cells (10(5) cells/5 µL) were transplanted into the subretinal space of rat retinal degeneration model induced by intravenous sodium iodate injection. Animals were sacrificed at 1, 2, and 4 weeks after transplantation, and immnohistochemistry study was performed to verify the survival of the transplanted cells.

RESULTS

The putative RPE cells derived from hESC showed characteristics of the human RPE cells morphologically and expressed molecular markers and associated with RPE fate. Grafted RPE cells were found to survive in the subretinal space up to 4 weeks after transplantation, and the expression of RPE markers was confirmed with immunohistochemistry.

CONCLUSION

Transplanted RPE cells derived from hESC in the defined culture condition successfully survived and migrated within subretinal space of rat retinal degeneration model. These results support the feasibility of the hESC derived RPE cells for cell-based therapies for retinal degenerative disease.

WITHDRAWN: Ultrastructure of the human retina in aging and various pathological states

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Electric impedance of human embryonic stem cell-derived retinal pigment epithelium

The barrier properties of epithelium are conventionally defined by transepithelial resistance (TER). TER provides information about the tightness of the epithelium. Electrical impedance spectroscopy (EIS) provides additional information regarding cell membrane properties, such as changes in electric capacitance and possible parallel or serial pathways that may correlate with the morphology of the cell layer. This study presents EIS of retinal pigment epithelial (RPE) cell model of the putative RPE differentiated from human embryonic stem cells (hESC-RPE). The generally utilized RPE cell model, ARPE-19, was used as immature control. The measured EIS was analyzed by fitting an equivalent electrical circuit model describing the resistive and capacitive properties of the RPE. Our results indicated that TER of hESC-RPE cells was close to the values of human RPE presented in the literature. This provides evidence that the stem cell-derived RPE in vitro can reach high-barrier function. Furthermore, hESC-RPE cells produced impedance spectra that can be modeled by the equivalent circuit of one time constant. ARPE-19 cells produced low-barrier properties, that is, an impedance spectra that suggested poor maturation of ARPE-19 cells. To conclude, EIS could give us means for non-invasively estimating the functionality and maturation of differentiated-RPE cells.

Expression pattern of Kv11 (Ether à-go-go-related gene; erg) K+ channels in the mouse retina

In response to light, most retinal neurons exhibit gradual changes in membrane potential. Therefore K+ channels that mediate threshold currents are well-suited for the fine-tuning of signal transduction. In the present study we demonstrate the expression of the different Kv11 (ether-à-go-go related gene; erg) channel subunits in the human and mouse retina by RT PCR and quantitative PCR, respectively. Immunofluorescence analysis with cryosections of mouse retinae revealed the following local distribution of the three Kv11 subunits: Kv11.1 (m-erg1) displayed the most abundant expression with the strongest immunoreactivity in rod bipolar cells. In addition, immunoreactivity was found in the inner part of the outer plexiform layer (OPL), in the inner plexiform layer (IPL) and in the inner segments of photoreceptors. Immunoreactivity for Kv11.2 (m-erg2) was observed in the outer part of the OPL and throughout the IPL. Double-labeling for vGluT1 or synaptophysin indicated a mainly presynaptic localization of Kv11.2. While no significant staining for Kv11.3 (m-erg3) was detected in the neuronal retina, strong Kv11.3 immunoreactivity was present in the apical membrane of the retinal pigment epithelium. The different expression levels were confirmed by real-time PCR showing almost equal levels of Kv11.1 and Kv11.2, while Kv11.3 mRNA expression was significantly lower. The two main splice variants of Kv11.1, isoforms a and b were detected in comparable levels suggesting a possible formation of cGMP/cGK-sensitive Kv11.1 channels in photoreceptors and rod bipolar cells. Taken together, the immunohistological results revealed different expression patterns of the three Kv11 channels in the mouse retina supposing distinct physiological roles.

Regulation of VEGF expression in human retinal cells by cytokines: implications for the role of inflammation in age-related macular degeneration

Chronic inflammation is implicated in the pathogenesis of age-related macular degeneration (AMD). Choroidal neovascularization (CNV) observed in exudative form of AMD results in vision loss. Human retinal pigment epithelial cell (HRPE) layer and choroidal tissue are the primary pathological sites in AMD. Pathological and therapeutic evidences have strongly indicated the vascular endothelial growth factor (VEGF) molecules as critical components in CNV pathogenesis. In these studies, we used human primary HRPE and choroidal fibroblast cells (HCHF) prepared from adult donor eyes. The effects of inflammatory cytokine (IFN-γ+ TNF-α+IL-1β) mix (ICM) on global gene expression profiles in HRPE cells, revealed 10- and 9-fold increase in VEGF-A and VEGF-C expression, respectively. The microarray results were validated by quantitative RT-PCR and secretion of VEGFs proteins. IL-1β is the most potent in inducing VEGFs secretion followed by IFN-γ and TNF-α, and the secretion was more effective in the presence of 2 and 3 cytokines. NF-κB and JAK-STAT pathway, but not HIF-1α, Sp-1, Sp-3, and STAT-3, transcription factors were upregulated and translocated to nucleus by ICM treatment. The mRNA levels of VEGF-A and VEGF-C and secretion of these proteins were also significantly enhanced by ICM in HCHF cells. The secretion of other angiogenic molecules, PEDF, SDF-1α, endostatin, and angiopoietins was not affected by ICM. Our results show that the inflammatory cytokines enhance secretion of VEGF-A and VEGF-C by HRPE and HCHF cells. These studies indicate that VEGFs secreted by these cells initiate and promote pathological choroidal and retinal noevascularization processes in AMD.

A novel melano-lysosome in the retinal epithelium of rhesus monkeys

The large phagocytic load that confronts the retinal pigment epithelium (RPE) is thought to play a possible role in the pathogenesis of age related macular degeneration (AMD) that afflicts both humans and monkeys. Our knowledge of how RPE degrades phagosomes and other intra-cellular material by lysosomal action is still rudimentary. In this paper we examine organelles that play a role in this process, melanosome, lysosomes and phagosomes, in the RPE of young and old rhesus monkeys in order to better understand lysosomal autophagy and heterophagy in the RPE and its possible role in AMD. We used electron microscopy to detect and describe the characteristics of melanosomes and lysosome-like organelles in the macular RPE of rhesus monkeys (Macaca mulatta) that were 1, 6, 24, 24, 26 and 35 years of age. The measurements include the number, shape and size of these organelles located in the basal, middle and apical regions of RPE cells. Phaagosomes were also examined but not counted or measured for size or shape because of their rarity. Melanosomes were homogeneously dark with a circular or elliptical shape and decreased in number with age. Smaller melanosomes were more common at the basal side of the RPE. Among the small melanosomes, we found an organelle that was losing melanin in varying degrees; in some cases was nearly devoid of melanin. Because of the melanin loss, we considered this organelle to be a unique type of autophagic melano-lysosome, which we called a Type 1 lysosome. We found another organelle, more canonically lysosomal, which we called a Type 2 lysosome. This organelle was composed of a light matrix containing melanosomes in various stages of degradation. Type 2 lysosomes without melanosomes were rare. Type 2 lysosomes increased while Type 1 decreased in number with age. Phagosomes were rare in both young and old monkeys. They made close contact with Type 2 lysosomes which we considered responsible for their degradation. Melanosomes are being lost from monkey RPE with age. Much of this loss is carried out by two types of lysosomes. One, not defined as unique before, appears to be autophagic in digesting its own melanin; it has been called a Type 1 lysosome. The other, a more canonical lysosome, is both heterophagic in digesting phagosomes and autophagic in digesting local melanosomes; it has been called a Type 2 lysosome. Type 1 lysosomes decrease while type 2 lysosomes increase with age. The loss of melanin is considered to be detrimental to the RPE since it reduces melanin's protective action against light toxicity and oxidative stress. Phagosomes appear to be degraded by membrane contacts with Type 2 lysosomes. The loss of melanin and the buildup of Type 2 lysosomes occur at an earlier age in monkeys than humans implying that a greater vulnerability to senescence accelerates the rate of AMD in monkeys.

Enhanced retinal pigment epithelium regeneration after injury in MRL/MpJ mice

Regenerative medicine holds the promise of restoring cells and tissues that are destroyed in human disease, including degenerative eye disorders. However, development of this approach in the eye has been limited by a lack of animal models that show robust regeneration of ocular tissue. Here, we test whether MRL/MpJ mice, which exhibit enhanced wound healing, can efficiently regenerate the retinal pigment epithelium (RPE) after an injury that mimics the loss of this tissue in age-related macular degeneration. The RPE of MRL/MpJ and control AKR/J mice was injured by retro-orbital injection of sodium iodate at 20 mg/kg body weight, which titration studies indicated was optimal for highlighting strain differences in the response to injury. Five days after sodium iodate injection at this dose, electroretinography of both strains revealed equivalent retinal responses that were significantly reduced compared to untreated mice. At one and two months post-injection, retinal responses were restored in MRL/MpJ but not AKR/J mice. Bright field and fluorescence microscopy of eyecup cryosections indicated an initial central loss of RPE cells and RPE65 immunostaining in MRL/MpJ and AKR/J mice, with preservation of peripheral RPE. Phalloidin staining of posterior eye whole mounts confirmed this pattern of RPE loss, and revealed a transition region characterized by RPE cell shedding and restructuring in both strains, suggesting a similar initial response to injury. At one month post-injection, central RPE cells, RPE65 immunostaining and phalloidin staining were restored in MRL/MpJ but not AKR/J mice. BrdU incorporation was observed throughout the RPE of MRL/MpJ but not AKR/J mice after one month of administration following sodium iodate treatment, consistent with RPE proliferation. These findings provide evidence for a dramatic regeneration of the RPE after injury in MRL/MpJ mice that supports full recovery of retinal function, which has not been observed previously in mammalian eyes. This model should prove useful for understanding molecular mechanisms that underlie regeneration, and for identifying factors that promote RPE regeneration in age-related macular degeneration and related diseases.

Effects of KCNQ channel modulators on the M-type potassium current in primate retinal pigment epithelium

Recently, we demonstrated the expression of KCNQ1, KCNQ4, and KCNQ5 transcripts in monkey retinal pigment epithelium (RPE) and showed that the M-type current in RPE cells is blocked by the specific KCNQ channel blocker XE991. Using patch-clamp electrophysiology, we investigated the pharmacological sensitivity of the M-type current in isolated monkey RPE cells to elucidate the subunit composition of the channel. Most RPE cells exhibited an M-type current with a voltage for half-maximal activation of approximately -35 mV. The M-type current activation followed a double-exponential time course and was essentially complete within 1 s. The M-type current was inhibited by micromolar concentrations of the nonselective KCNQ channel blockers linopirdine and XE991 but was relatively insensitive to block by 10 μM chromanol 293B or 135 mM tetraethylammonium (TEA), two KCNQ1 channel blockers. The M-type current was activated by 1) 10 μM retigabine, an opener of all KCNQ channels except KCNQ1, 2) 10 μM zinc pyrithione, which augments all KCNQ channels except KCNQ3, and 3) 50 μM N-ethylmaleimide, which activates KCNQ2, KCNQ4, and KCNQ5, but not KCNQ1 or KCNQ3, channels. Application of cAMP, which activates KCNQ1 and KCNQ4 channels, had no significant effect on the M-type current. Finally, diclofenac, which activates KCNQ2/3 and KCNQ4 channels but inhibits KCNQ5 channels, inhibited the M-type current in the majority of RPE cells but activated it in others. The results indicate that the M-type current in monkey RPE is likely mediated by channels encoded by KCNQ4 and KCNQ5 subunits.

Dynamic colocalization microscopy to characterize intracellular trafficking of nanomedicines

To gain a better understanding of intracellular processing of nanomedicines, we employed quantitative live-cell fluorescence colocalization microscopy to study endosomal trafficking of polyplexes in retinal pigment epithelium cells. A new, dynamic colocalization algorithm was developed, based on particle tracking and trajectory correlation, allowing for spatiotemporal characterization of internalized polyplexes in comparison with endosomal compartments labeled with EGFP constructs. This revealed early trafficking of the polyplexes specifically to Rab5- and flotillin-2-positive vesicles and subsequent delivery to Rab7 and LAMP1-labeled late endolysosomes where the major fraction of the polyplexes remains entrapped for days, suggesting the functional loss of these nanomedicines. Colocalization of polyplexes with the autophagy marker LC3 suggests for the first time that the process of xenophagy could play an important role in the persistent endosomal entrapment of nanomedicines.

Inhibition of RPE cell sterile inflammatory responses and endotoxin-induced uveitis by a cell-impermeable HSP90 inhibitor

Dying cells release pro-inflammatory molecules, functioning as cytokines to trigger cell/tissue inflammation that is relevant to disease pathology. Heat-shock protein 90 (HSP90) is believed to act as a danger signal for tissue damage once released extracellularly. Potential roles of HSP90 were explored in retinal pigment epithelial (RPE) inflammatory responses to necrosis. Cellular extracts can trigger ARPE-19 cell inflammatory responses, producing cytokines that lead to an increase in ARPE-19 cell monolayer permeability. Addition of recombinant HSP90β mimics the induction of chemokines IL-8 and MCP-1 in cultured RPE cells, suggesting that released HSP90 can incite RPE cell sterile inflammatory responses. Consistent with this, classical HSP90 inhibitors were shown to substantially reduce necrosis-induced cytokine production and permeability increases in ARPE-19 cells. Moreover, a cell-impermeable inhibitor, 17-N,N-dimethylaminoethylamino-17-demethoxy-geldanamycin-N-oxide, also efficiently inhibited necrosis-induced cytokine production and TNF-α/IL-1β-induced increase in ARPE-19 cell permeability in vitro and endotoxin-induced development of uveitis in vivo, suggesting that HSP90 can contribute to necrosis-induced RPE inflammatory responses. Collectively, our data identify HSP90 as a pro-inflammatory molecule in RPE cell sterile inflammatory responses.

Human induced pluripotent stem-derived retinal pigment epithelium (RPE) cells exhibit ion transport, membrane potential, polarized vascular endothelial growth factor secretion, and gene expression pattern similar to native RPE

Age-related macular degeneration (AMD) is one of the major causes of blindness in aging population that progresses with death of retinal pigment epithelium (RPE) and photoreceptor degeneration inducing impairment of central vision. Discovery of human induced pluripotent stem (hiPS) cells has opened new avenues for the treatment of degenerative diseases using patient-specific stem cells to generate tissues and cells for autologous cell-based therapy. Recently, RPE cells were generated from hiPS cells. However, there is no evidence that those hiPS-derived RPE possess specific RPE functions that fully distinguish them from other types of cells. Here, we show for the first time that RPE generated from hiPS cells under defined conditions exhibit ion transport, membrane potential, polarized vascular endothelial growth factor secretion, and gene expression profile similar to those of native RPE. The hiPS-RPE could therefore be a very good candidate for RPE replacement therapy in AMD. However, these cells show rapid telomere shortening, DNA chromosomal damage, and increased p21 expression that cause cell growth arrest. This rapid senescence might affect the survival of the transplanted cells in vivo and therefore, only the very early passages should be used for regeneration therapies. Future research needs to focus on the generation of "safe" as well as viable hiPS-derived somatic cells.

Müller glial cells in retinal disease

Virtually all pathogenic stimuli activate Müller cells. Reactive Müller cells exert protective and toxic effects on photoreceptors and neurons. They contribute to oxidative stress and glutamate toxicity due to malfunctions of glutamate uptake and glutathione synthesis. Downregulation of potassium conductance disrupts transcellular potassium and water transport, resulting in neuronal hyperexcitability and edema. Protective effects of reactive Müller cells include upregulation of adenosine 5'-triphosphate (ATP)-degrading ectoenzymes, which enhances the extracellular availability of the neuroprotectant adenosine, abrogation of the osmotic release of ATP, which might protect retinal ganglion cells from apoptosis, and the release of antioxidants and neurotrophic factors. The dedifferentiation of reactive Müller cells to progenitor-like cells might have an impact on future therapeutic approaches. A better understanding of the gliotic mechanisms will be helpful in developing efficient therapeutic strategies aiming at increased protective and regenerative properties and decreased toxicity of reactive Müller cells.

LEDGF(1-326) decreases P23H and wild type rhodopsin aggregates and P23H rhodopsin mediated cell damage in human retinal pigment epithelial cells

Background

P23H rhodopsin, a mutant rhodopsin, is known to aggregate and cause retinal degeneration. However, its effects on retinal pigment epithelial (RPE) cells are unknown. The purpose of this study was to determine the effect of P23H rhodopsin in RPE cells and further assess whether LEDGF_1-326, a protein devoid of heat shock elements of LEDGF, a cell survival factor, reduces P23H rhodopsin aggregates and any associated cellular damage.

Methods

ARPE-19 cells were transiently transfected/cotransfected with pLEDGF_1-326 and/or pWT-Rho (wild type)/pP23H-Rho. Rhodopsin mediated cellular damage and rescue by LEDGF_1-326 was assessed using cell viability, cell proliferation, and confocal microscopy assays. Rhodopsin monomers, oligomers, and their reduction in the presence of LEDGF_1-326 were quantified by western blot analysis. P23H rhodopsin mRNA levels in the presence and absence of LEDGF_1-326 was determined by real time quantitative PCR.

Principal Findings

P23H rhodopsin reduced RPE cell viability and cell proliferation in a dose dependent manner, and disrupted the nuclear material. LEDGF_1-326 did not alter P23H rhodopsin mRNA levels, reduced its oligomers, and significantly increased RPE cell viability as well as proliferation, while reducing nuclear damage. WT rhodopsin formed oligomers, although to a smaller extent than P23H rhodopsin. Further, LEDGF_1-326 decreased WT rhodopsin aggregates.

Conclusions

P23H rhodopsin as well as WT rhodopsin form aggregates in RPE cells and LEDGF_1-326 decreases these aggregates. Further, LEDGF_1-326 reduces the RPE cell damage caused by P23H rhodopsin. LEDGF_1-326 might be useful in treating cellular damage associated with protein aggregation diseases such as retinitis pigmentosa.

Evaluation of status of zinc, copper, and iron levels in biological samples of normal children and children with night blindness with age groups of 3-7 and 8-12 years

The causes of night blindness in children are multifactorial, and particular consideration has been given to childhood nutritional deficiency, which is the most common problem found in underdeveloped countries. Such deficiency can result in physiological and pathological processes that in turn influence hair composition. This study was designed to compare the levels of zinc (Zn), copper (Cu), and iron (Fe) in scalp hair, blood, and urine of both genders of children with night blindness with age range of 3-7 and 8-12 years, comparing them to sex- and age-matched controls. A microwave-assisted wet acid digestion procedure was developed as a sample pretreatment, for the determination of zinc, copper, and iron in biological samples of children with night blindness. The proposed method was validated by using conventional wet digestion and certified reference samples of hair, blood, and urine. The digests of all biological samples were analyzed for Cu, Fe, and Zn by flame atomic absorption spectrometry using an air/acetylene flame. The results indicated significantly lower levels of Fe, Cu, and Zn in the biological samples (blood and scalp hair) of male and female children with night blindness, compared with control subjects of both genders. These data present guidance to clinicians and other professionals investigating the deficiency of essential trace metals in biological samples (scalp hair and blood) of children with night blindness.

Nanoparticle-mediated gene transfer specific to retinal pigment epithelial cells

Previously, we demonstrated that CK30PEG10k-compacted DNA nanoparticles (NPs) efficiently target photoreceptor cells and improve visual function in a retinitis pigmentosa model. Here, we test the ability of these NPs in driving transgene expression in the retinal pigment epithelium (RPE), using an RPE-specific reporter vector (VMD2-eGFP). NPs, uncompacted plasmid, or saline were subretinally delivered to adult BALB/c mice. NP-based expression was specific to RPE cells and caused no deleterious effects on retinal structure and function. eGFP expression levels in NP-injected eyes peaked at post-injection day 2 (PI-2), stabilized at levels ~3-fold higher than in naked DNA-injected eyes, and remained elevated at the latest time-point examined (PI-30). Unlike naked DNA, which only transfected cells at the site of injection, NPs were able to transfect cells throughout the RPE. Subretinal injections of rhodamine labeled NPs and naked DNA showed comparable initial uptake into RPE cells. However, at PI-7 and -30 days significantly more fluorescence was detected inside the RPE of NP-injected eyes compared to naked DNA, suggesting NPs are stable inside the cell which could possibly lead to higher and sustained expression. Overall, our results demonstrate that NPs can efficiently deliver genes to the RPE and hold great potential for the treatment of RPE-associated diseases.

Moderate light-induced degeneration of rod photoreceptors with delayed transducin translocation in shaker1 mice

PURPOSE. Usher syndrome is characterized by congenital deafness associated with retinitis pigmentosa (RP). Mutations in the myosin VIIa gene (MYO7A) cause a common and severe subtype of Usher syndrome (USH1B). Shaker1 mice have mutant MYO7A. They are deaf and have vestibular dysfunction but do not develop photoreceptor degeneration. The goal of this study was to investigate abnormalities of photoreceptors in shaker1 mice. METHODS. Immunocytochemistry and hydroethidine-based detection of intracellular superoxide production were used. Photoreceptor cell densities under various conditions of light/dark exposures were evaluated. RESULTS. In shaker1 mice, the rod transducin translocation is delayed because of a shift of its light activation threshold to a higher level. Even moderate light exposure can induce oxidative damage and significant rod degeneration in shaker1 mice. Shaker1 mice reared under a moderate light/dark cycle develop severe retinal degeneration in less than 6 months. CONCLUSIONS. These findings show that, contrary to earlier studies, shaker1 mice possess a robust retinal phenotype that may link to defective rod protein translocation. Importantly, USH1B animal models are likely vulnerable to light-induced photoreceptor damage, even under moderate light.

dlx and sp6-9 Control optic cup regeneration in a prototypic eye

Optic cups are a structural feature of diverse eyes, from simple pit eyes to camera eyes of vertebrates and cephalopods. We used the planarian prototypic eye as a model to study the genetic control of optic cup formation and regeneration. We identified two genes encoding transcription factors, sp6-9 and dlx, that were expressed in the eye specifically in the optic cup and not the photoreceptor neurons. RNAi of these genes prevented formation of visible optic cups during regeneration. Planarian regeneration requires an adult proliferative cell population with stem cell-like properties called the neoblasts. We found that optic cup formation occurred only after migration of progressively differentiating progenitor cells from the neoblast population. The eye regeneration defect caused by dlx and sp6-9 RNAi can be explained by a failure to generate these early optic cup progenitors. Dlx and Sp6-9 genes function as a module during the development of diverse animal appendages, including vertebrate and insect limbs. Our work reveals a novel function for this gene pair in the development of a fundamental eye component, and it utilizes these genes to demonstrate a mechanism for total organ regeneration in which extensive cell movement separates new cell specification from organ morphogenesis.

Some invertebrates, such as planarians and Hydra, can regenerate fully after amputations that remove large parts of the body. We investigated how cells in the body of planarians provide new cells for eye regeneration after complete head removal. Planarians possess highly potent regenerative cells (neoblasts) in a compartment inside the worm, and these cells must be present in a body fragment for it to regenerate. We identify a pair of transcription factors, sp6-9 and dlx, that are expressed in the optic cup, and use expression of these genes as markers to demonstrate that lineage restriction of eye cells during regeneration begins within the neoblast compartment. dlx and sp6-9 are essential for formation of optic cup progenitors, and inhibition of these genes with RNA interference results in eyes that lack optic cups after regeneration. During eye development in both flies and vertebrates, progenitors form within a patterned epithelium. Interestingly, planarian eye precursors only aggregate once they have stopped cycling and undergone extensive migration. At this stage they already express markers of the terminally differentiated state. Therefore, we identify a mechanism for eye formation during regeneration and a novel function for a conserved gene pair in eye regeneration.

Phagocytic clearance in neurodegeneration

The cellular and molecular mechanisms of phagocytic clearance of apoptotic cells and debris have been intensely studied in invertebrate model organisms and in the mammalian immune system. This evolutionarily conserved process serves multiple purposes. Uncleared debris from dying cells or aggregated proteins can be toxic and may trigger exaggerated inflammatory responses. Even though apoptotic cell death and debris accumulation are key features of neurodegenerative diseases, relatively little attention has been paid to this important homeostatic function in the central nervous system (CNS). This review attempts to summarize our knowledge of phagocytic clearance in the CNS, with a focus on retinal degeneration, forms of which are caused by mutations in genes within known phagocytic pathways, and on Alzheimer's disease (AD). Interest in phagocytic clearance mechanisms in AD was stimulated by the discovery that immunization could promote phagocytic clearance of amyloid-β; however, much less is known about clearance of neuronal and synaptic corpses in AD and other neurodegenerative diseases. Because the regulation of phagocytic activity is intertwined with cytokine signaling, this review also addresses the relationships among CNS inflammation, glial responses, and phagocytic clearance.

Polyurethanes as supports for human retinal pigment epithelium cell growth

PURPOSE

The transplant of retinal pigment epithelium (RPE) cells on supports may well be an effective therapeutic approach to improve the visual results of patients with age-related macular degeneration. In this study, two biodegradable polyurethanes were investigated as supports for human RPE cells (ARPE-19).

METHODS

Polyurethane aqueous dispersions based on poly(caprolactone) and/or poly(ethylene glycol) as soft segments, and isophorone diisocyanate and hydrazine as hard segments were prepared. Polyurethane films were produced by casting the dispersions and allowing them to dry at room temperature for one week. The ARPE-19 cells were seeded onto the polyurethane films and they were investigated as supports for in vitro adhesion, proliferation, and uniform distribution of differentiated ARPE-19 cells. Additionally, the in vivo ocular biocompatibility of the polyurethane films was evaluated.

RESULTS

The RPE adhered to and proliferated onto the polyurethane supports, thus establishing cell-PUD surface interactions. Upon confluence, the cells formed an organized monolayer, exhibited a polygonal appearance, and displayed actin filaments which ran along the upper cytoplasm. At 15 days of seeding, the occluding expression was confirmed between adjacent cells, representing the barrier functionality of epithelial cells on polymeric surfaces and the establishment of cell-cell interactions. Results from the in vivo study indicated that polyurethanes exhibited a high degree of short-term intraocular biocompatibility.

CONCLUSIONS

Biodegradable polyurethane films display the proper mechanical properties for an easy transscleral-driven subretinal implantation and can be considered as biocompatible supports for a functional ARPE-19 monolayer.

Knock-down of cathepsin D affects the retinal pigment epithelium, impairs swim-bladder ontogenesis and causes premature death in zebrafish

The lysosomal aspartic protease Cathepsin D (CD) is ubiquitously expressed in eukaryotic organisms. CD activity is essential to accomplish the acid-dependent extensive or partial proteolysis of protein substrates within endosomal and lysosomal compartments therein delivered via endocytosis, phagocytosis or autophagocytosis. CD may also act at physiological pH on small-size substrates in the cytosol and in the extracellular milieu. Mouse and fruit fly CD knock-out models have highlighted the multi-pathophysiological roles of CD in tissue homeostasis and organ development. Here we report the first phenotypic description of the lack of CD expression during zebrafish (Danio rerio) development obtained by morpholino-mediated knock-down of CD mRNA. Since the un-fertilized eggs were shown to be supplied with maternal CD mRNA, only a morpholino targeting a sequence containing the starting ATG codon was effective. The main phenotypic alterations produced by CD knock-down in zebrafish were: 1. abnormal development of the eye and of retinal pigment epithelium; 2. absence of the swim-bladder; 3. skin hyper-pigmentation; 4. reduced growth and premature death. Rescue experiments confirmed the involvement of CD in the developmental processes leading to these phenotypic alterations. Our findings add to the list of CD functions in organ development and patho-physiology in vertebrates.

The Ran importin system in cilia trafficking

Cilia are microtubule-based organelles that arise from the centrosome and project from the surface of many cells. Defects in cilia-localized proteins are felt to lead to polycystic kidney disease as well as ciliopathies with multiple organ involvement. Movement of proteins along mammalian cilia is a specialized process that is highly related to the intraflagellar movement of proteins in lower organisms. Entry of proteins into the cilia appears to be a tightly regulated process. Several cilia-targeting sequences have been identified that appear to mediate the movement of proteins into cilia, although the molecular basis through which these sequences operate is still being elucidated. Entry of proteins into cilia appears to be regulated at the base of the cilia at a region known as the transition zone. It has been proposed that a ciliary pore exists in this zone that controls entry of proteins into the cilia, similar to the nuclear pore that controls entry of proteins into the nucleus. Our group at the University of Michigan has found that proteins important in nuclear import appear to function similarly in cilia entry. In particular, we have identified roles for the small GTPase, Ran and its binding partners, the importins, in regulating cilia entry of specific proteins.

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.

Integration of tight junctions and claudins with the barrier functions of the retinal pigment epithelium

The retinal pigment epithelium (RPE) forms the outer blood-retinal barrier by regulating the movement of solutes between the fenestrated capillaries of the choroid and the photoreceptor layer of the retina. Blood-tissue barriers use various mechanisms to accomplish their tasks including membrane pumps, transporters, and channels, transcytosis, metabolic alteration of solutes in transit, and passive but selective diffusion. The last category includes tight junctions, which regulate transepithelial diffusion through the spaces between neighboring cells of the monolayer. Tight junctions are extraordinarily complex structures that are dynamically regulated. Claudins are a family of tight junctional proteins that lend tissue specificity and selectivity to tight junctions. This review discusses how the claudins and tight junctions of the RPE differ from other epithelia and how its functions are modulated by the neural retina. Studies of RPE-retinal interactions during development lend insight into this modulation. Notably, the characteristics of RPE junctions, such as claudin composition, vary among species, which suggests the physiology of the outer retina may also vary. Comparative studies of barrier functions among species should deepen our understanding of how homeostasis is maintained in the outer retina. Stem cells provide a way to extend these studies of RPE-retinal interactions to human RPE.

Alterations of retinal pigment epithelium cause AMD-like retinopathy in senescence-accelerated OXYS rats

Pathogenesis of age-related macular degeneration (AMD), the leading cause of blindness in the world, remains poorly understood. This makes it necessary to create animal models for studying AMD pathogenesis and to design new therapeutic approaches. Here we showed that retinopathy in OXYS rats is similar to human AMD according to clinical signs, morphology, and vascular endothelium growth factor (VEGF) and pigment epithelium-derived factor (PEDF) genes expression. Clinical signs of retinopathy OXYS rats manifest by the age 3 months against the background of significantly reduced expression level of VEGF and PEDF genes due to the decline of the amount of retinal pigment epithelium (RPE) cells and alteration of choroidal microcirculation. The disruption in OXYS rats' retina starts at the age of 20 days and appears as reduce the area of RPE cells but does not affect their ultrastructure. Ultrastructural pathological alterations of RPE as well as develop forms of retinopathy are observed in OXYS rats from age 12 months and manifested as excessive accumulation of lipofuscin in RPE regions adjacent to the rod cells, whirling extentions of the basement membrane into the cytoplasm. These data suggest that primary cellular degenerative alterations in the RPE cells secondarily lead to choriocapillaris atrophy and results in complete loss of photoreceptor cells in the OXYS rats' retina by the age of 24 months.

Retinal pigment epithelial expression of complement regulator CD46 is altered early in the course of geographic atrophy

In geographic atrophy (GA), the non-neovascular end stage of age-related macular degeneration (AMD), the macular retinal pigment epithelium (RPE) progressively degenerates. Membrane cofactor protein (MCP, CD46) is the only membrane-bound regulator of complement expressed on the human RPE basolateral surface. Based on evidence of the role of complement in AMD, we hypothesized that altered CD46 expression on the RPE would be associated with GA development and/or progression. Here we report the timeline of CD46 protein expression changes across the GA transition zone, relative to control eyes, and relative to events in other chorioretinal layers. Eleven donor eyes (mean age 87.0 ± 4.1 yr) with GA and 5 control eyes (mean age 84.0 ± 8.9 yr) without GA were evaluated. Macular cryosections were stained with PASH for basal deposits, von Kossa for calcium, and for CD46 immunoreactivity. Internal controls for protein expression were provided by an independent basolateral protein, monocarboxylate transporter 3 (MCT3) and an apical protein, ezrin. Within zones defined by 8 different semi-quantitative grades of RPE morphology, we determined the location and intensity of immunoreactivity, outer segment length, and Bruch's membrane calcification. Differences between GA and control eyes and between milder and more severe RPE stages in GA eyes were assessed statistically. Increasing grades of RPE degeneration were associated with progressive loss of polarity and loss of intensity of staining of CD46, beginning with the stages that are considered normal aging (grades 0-1). Those GA stages with affected CD46 immunoreactivity exhibited basal laminar deposit, still-normal photoreceptors, and concomitant changes in control protein expression. Activated or anteriorly migrated RPE (grades 2-3) exhibited greatly diminished CD46. Changes in RPE CD46 expression thus occur early in GA, before there is evidence of morphological RPE change. At later stages of degeneration, CD46 alterations occur within a context of altered RPE polarity. These changes precede degeneration of the overlying retina and suggest that therapeutic interventions be targeted to the RPE.

Fenofibric acid prevents retinal pigment epithelium disruption induced by interleukin-1β by suppressing AMP-activated protein kinase (AMPK) activation

AIMS/HYPOTHESIS

The mechanisms involved in the beneficial effects of fenofibrate on the development and progression of diabetic macular oedema (DMO) remain to be elucidated. To shed light on this issue we have explored the effect of fenofibric acid on the barrier function of human retinal pigment epithelium (RPE) cells.

METHODS

ARPE-19 cells (a human RPE line) were cultured for 18 days under standard conditions and under conditions leading to the disruption of the monolayer (D-glucose, 25 mmol/l, with IL-1β, 10 ng/ml, added at days 16 and 17). Fenofibric acid, 25 μmol/l and 100 μmol/l, was added on the last 3 days of the experiment (one application/day). RPE cell permeability was evaluated by measuring apical-basolateral movements of FITC-dextran (40 kDa). The production of tight junction proteins and AMP-activated protein kinase (AMPK) phosphorylation was assessed by western blot. Immunohistochemical studies of tight junction proteins and small interfering RNA transfection to AMPK were also performed in ARPE-19 monolayers.

RESULTS

Treatment of ARPE-19 cells with fenofibric acid significantly reduced the increment of permeability and the breakdown of the ARPE-19 cell monolayer induced by D-glucose, 25 mmol/l, and IL-1β, 10 ng/ml, in a dose-dependent manner. This effect was unrelated to changes in the content of tight junction proteins. Fenofibric acid prevented the activation of AMPK induced by IL-1β and the hyperpermeability induced by IL-1β was blocked by silencing AMPK.

CONCLUSIONS/INTERPRETATION

Disruption of RPE induced by IL-1β is prevented by fenofibric acid through its ability to suppress AMPK activation. This mechanism could be involved in the beneficial effects of fenofibrate on DMO development.

Ciliary neurotrophic factor induces genes associated with inflammation and gliosis in the retina: a gene profiling study of flow-sorted, Müller cells

Background

Ciliary neurotrophic factor (CNTF), a member of the interleukin-6 cytokine family, has been implicated in the development, differentiation and survival of retinal neurons. The mechanisms of CNTF action as well as its cellular targets in the retina are poorly understood. It has been postulated that some of the biological effects of CNTF are mediated through its action via retinal glial cells; however, molecular changes in retinal glia induced by CNTF have not been elucidated. We have, therefore, examined gene expression dynamics of purified Müller (glial) cells exposed to CNTF in vivo.

Methodology/Principal Findings

Müller cells were flow-sorted from mgfap-egfp transgenic mice one or three days after intravitreal injection of CNTF. Microarray analysis using RNA from purified Müller cells showed differential expression of almost 1,000 transcripts with two- to seventeen-fold change in response to CNTF. A comparison of transcriptional profiles from Müller cells at one or three days after CNTF treatment showed an increase in the number of transcribed genes as well as a change in the expression pattern. Ingenuity Pathway Analysis showed that the differentially regulated genes belong to distinct functional types such as cytokines, growth factors, G-protein coupled receptors, transporters and ion channels. Interestingly, many genes induced by CNTF were also highly expressed in reactive Müller cells from mice with inherited or experimentally induced retinal degeneration. Further analysis of gene profiles revealed 20–30% overlap in the transcription pattern among Müller cells, astrocytes and the RPE.

Conclusions/Significance

Our studies provide novel molecular insights into biological functions of Müller glial cells in mediating cytokine response. We suggest that CNTF remodels the gene expression profile of Müller cells leading to induction of networks associated with transcription, cell cycle regulation and inflammatory response. CNTF also appears to function as an inducer of gliosis in the retina.

The loss of vacuolar protein sorting 11 (vps11) causes retinal pathogenesis in a vertebrate model of syndromic albinism

PURPOSE

To establish the zebrafish platinum mutant as a model for studying vision defects caused by syndromic albinism diseases such as Chediak-Higashi syndrome, Griscelli syndrome, and Hermansky-Pudlak syndrome (HPS).

METHODS

Bulked segregant analysis and candidate gene sequencing revealed that the zebrafish platinum mutation is a single-nucleotide insertion in the vps11 (vacuolar protein sorting 11) gene. Expression of vps11 was determined by RT-PCR and in situ hybridization. Mutants were analyzed for pigmentation defects and retinal disease by histology, immunohistochemistry, and transmission electron microscopy.

RESULTS

Phenocopy and rescue experiments determined that a loss of Vps11 results in the platinum phenotype. Expression of vps11 appeared ubiquitous during zebrafish development, with stronger expression in the developing retina and retinal pigmented epithelium (RPE). Zebrafish platinum mutants exhibited reduced pigmentation in the body and RPE; however, melanophore development, migration, and dispersion occurred normally. RPE, photoreceptors, and inner retinal neurons formed normally in zebrafish platinum mutants. However, a gradual loss of RPE, an absence of mature melanosomes, and the subsequent degradation of RPE/photoreceptor interdigitation was observed.

CONCLUSIONS

These data show that Vps11 is not necessary for normal retinal development or initiation of melanin biosynthesis, but is essential for melanosome maturation and healthy maintenance of the RPE and photoreceptors.

Inhibition of Mdm2 sensitizes human retinal pigment epithelial cells to apoptosis

PURPOSE

Because recent studies indicate that blocking the interaction between p53 and Mdm2 results in the nongenotoxic activation of p53, the authors sought to investigate whether the inhibition of p53-Mdm2 binding activates p53 and sensitizes human retinal epithelial cells to apoptosis.

METHODS

Apoptosis was evaluated by the activation of caspases and DNA fragmentation assays. The Mdm2 antagonist Nutlin-3 was used to dissociate p53 from Mdm2 and, thus, to increase p53 activity. Knockdown of p53 expression was accomplished by using p53 siRNA.

RESULTS

ARPE-19 and primary RPE cells expressed high levels of the antiapoptotic proteins Bcl-2 and Bcl-xL. Exposure of these cells to camptothecin (CPT) or TNF-α/ cycloheximide (CHX) failed to induce apoptosis. In contrast, treatment with the Mdm2 antagonist Nutlin-3 in the absence of CPT or TNF-α/CHX increased apoptosis. Activation of p53 in response to Nutlin-3 also increased levels of Noxa, p53-upregulated modulator of apoptosis (PUMA), and Siva-1, decreased expression of Bcl-2 and Bcl-xL, and simultaneously increased caspases-9 and -3 activities and DNA fragmentation. Knockdown of p53 decreased the basal expression of p21Cip1 and Bcl-2, inhibited the Nutlin-3-induced upregulation of Siva-1 and PUMA expression, and consequently inhibited caspase-3 activation.

CONCLUSIONS

These results indicate that the normally available pool of intracellular p53 is predominantly engaged in the regulation of cell cycle checkpoints by p21Cip1 and does not trigger apoptosis in response to DNA-damaging agents. However, the blockage of p53 binding to Mdm2 frees a pool of p53 that is sufficient, even in the absence of DNA-damaging agents, to increase the expression of proapoptotic targets and to override the resistance of RPE cells to apoptosis.

Interaction of bestrophin-1 and Ca2+ channel β-subunits: identification of new binding domains on the bestrophin-1 C-terminus

Bestrophin-1 modulates currents through voltage-dependent L-type Ca²⁺ channels by physically interacting with the β-subunits of Ca²⁺ channels. The main function of β-subunits is to regulate the number of pore-forming Ca_V-subunits in the cell membrane and modulate Ca²⁺ channel currents. To understand the influence of full-length bestrophin-1 on β-subunit function, we studied binding and localization of bestrophin-1 and Ca²⁺ channel subunits, together with modulation of Ca_V1.3 Ca²⁺ channels currents. In heterologeous expression, bestrophin-1 showed co-immunoprecipitation with either, β3-, or β4-subunits. We identified a new highly conserved cluster of proline-rich motifs on the bestrophin-1 C-terminus between amino acid position 468 and 486, which enables possible binding to SH3-domains of β-subunits. A bestrophin-1 that lacks these proline-rich motifs (ΔCT-PxxP bestrophin-1) showed reduced efficiency to co-immunoprecipitate with β3 and β4-subunits. In the presence of ΔCT-PxxP bestrophin-1, β4-subunits and Ca_V1.3 subunits partly lost membrane localization. Currents from Ca_V1.3 subunits were modified in the presence of β4-subunit and wild-type bestrophin-1: accelerated time-dependent activation and reduced current density. With ΔCTPxxP bestrophin-1, currents showed the same time-dependent activation as with wild-type bestrophin-1, but the current density was further reduced due to decreased number of Ca²⁺ channels proteins in the cell membrane. In summary, we described new proline-rich motifs on bestrophin-1 C-terminus, which help to maintain the ability of β-subunits to regulate surface expression of pore-forming Ca_V Ca²⁺-channel subunits.

Early visual impacts of optical coherence tomographic parameters in patients with age-related macular degeneration following the first versus repeated ranibizumab injection

BACKGROUND

The aim of this study is to evaluate the early visual impacts of various optical coherence tomographic (OCT) parameters after the first versus repeated intravitreal ranibizumab injection in patients with exudative age-related macular degeneration (AMD).

METHODS

A retrospective comparative case series study was conducted on 20 eyes of 18 consecutive patients who received intravitreal ranibizumab injection for exudative AMD either for the first time (group 1; n = 8) with no prior anti-vascular endothelial growth factor (anti-VEGF) injection in the same or fellow eye, or for repeated times during the course of monthly injected ranibizumab (group 2; n = 12 eyes). The following baseline and 1 month post-injection data was collected for both groups and compared: best-corrected visual acuity (BCVA), qualitative and quantitative OCT parameters including: foveal thickness, foveal volume (central 1-mm circle), retinal volume at 3- and 5-mm central circles, retinal pigment epithelium (RPE) elevation, type of fluid collections, and type of AMD lesion. The size of the fluid and fibrovascular lesion (FVL) areas were measured using manual delineation and automatic calculation of the device. We made correlations between the post-injection visual acuity (VA) and each of post-injection OCT parameters in both groups and these were the main outcome measures.

RESULTS

In group 1, there was a strong correlation between post-injection logarithm of minimum angle of resolution (logMAR) BCVA and each of the following: FVL size, foveal thickness, retinal volume at 3- and 5-mm central circles, RPE elevation, the size of the fluid area, and age of the patient (r > 0.70, p < 0.05), whereas in group 2; logMAR BCVA was strongly correlated only with foveal volume (r = 0.74, p = 0.01). Multivariate analysis showed that post-injection FVL size (r (2) = 0.69) and foveal volume (r (2) = 0.55) were the most important factors for VA 1 month following the initial and repeated ranibizumab injection, respectively.

CONCLUSIONS

The size of FVL and foveal volume showed a significant correlation with VA in AMD patients shortly after the first and repeated ranibizumab injection, respectively. Further studies with larger sample sizes are needed in order to support these results.

Antiapoptotic properties of erythropoietin: novel strategies for protection of retinal pigment epithelial cells

INTRODUCTION

Oxidative damage of the retinal pigment epithelium (RPE) may play a role in the development and progression of age-related macula degeneration (ARMD). Therapeutic reduction of oxidative stress failed or had only slight effects in ARMD patients. This study evaluates antiapoptotic properties of erythropoietin (epo) at the RPE as a novel approach to protect RPE cells against oxidative damage.

MATERIALS AND METHODS

Cultured ARPE-19 cells were exposed to hydroxyl (OH) radicals generated from H(2)O(2) under catalysis of Fe(3+) (Fenton reaction) for 5 min. Apoptosis rate was determined by Annexin V labelling and terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling assay. Epo was added in concentrations from 0 to 100 U/ml to the media 24 and 1 h before radical exposure as well as shortly after radical exposure. Expression of epo receptor was determined by western blotting.

RESULTS

Hydroxyl radical exposure induced an increase of apoptosis rate from virtually 0 to 11.8+/-1.7%. Apoptosis was detectable up to 24 h after radical exposure and reached its maximum after 6 h. Epo reduced apoptosis rate by up to 88% even if applied after the radical exposure. Best protection was achieved at 5 U/ml epo. Western blot confirmed presence of epo receptor independent of a pre-incubation of the cells with epo.

DISCUSSION

Epo exerts antiapoptotic effects on cultured RPE cells even if applied after the radical exposure. This might qualify epo as future candidate for therapy and prevention of dry ARMD.