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Galectins have the potential to interact with transmembrane glycoproteins to modulate their functions. Since galectin-1 interacts with PDGF-Rβ, we analyzed the effect of galectin-1 on PDGF-BB-mediated AKT signaling in primary human retinal pigment epithelial (RPE) cells and galectin-1-deficient immortalized human RPE cells (LGALS1−/−/ARPE-19) following incubation with PDGF-BB and galectin-1. Expression and localization of galectin-1, PDGF-Rβ and pAKT were investigated using western blot analysis and immunohistochemical staining. Cell proliferation of RPE cells was analyzed using BrdU ELISA. Following treatment of human RPE cells with human recombinant (hr)-galectin-1 and PDGF-BB, an intense clustering of PDGF-Rβ and colocalization with galectin-1 were detected. By Western blot analysis and immunocytochemistry of human RPE cells, an enhanced PDGF-BB-mediated expression of pAKT was observed, which was substantially reduced by additional incubation with hr-galectin-1. Vice versa, in LGALS1−/−/ARPE-19 cells, the PDGF-BB-induced pAKT signal was enhanced compared to wild-type cells. Furthermore, a decreased expression of PDGF-Rβ in human RPE cells was observed after treatment with PDGF-BB and hr-galectin-1, while in untreated LGALS1−/−/ARPE-19 cells, its constitutive expression was increased. In addition, after treatment of RPE cells with hr-galectin-1, the PDGF-BB-induced proliferation was markedly reduced. In summary, galectin-1 has the distinct potential to reduce PDGF-mediated pAKT signaling and proliferation in human RPE cells—an effect that is most likely facilitated via a decreased expression of PDGF-Rβ. [ABSTRACT FROM AUTHOR]

Retinal detachment (RD) is the most serious problem of modern ophthalmology, often leading to a decrease or irreversible loss of visual functions. The literature review is devoted to the latest trends in the study of the mechanisms of development and course of rhegmatogenous retinal detachment (RRD) against the background of proliferative vitreoretinopathy. In the pathogenesis of RD, there are five theories, as well as nine main risk factors for development. It is known that the contact between the retinal neuroepithelium and the retinal pigment epithelium is maintained by physical and metabolic forces, as well as by the friction force of the outer segments of photoreceptors and RPE cells. With synchisis and simultaneous syneresis, vitreous detachment develops, with increased traction forces and the possible development of RRD. Retinal detachment is the most serious problem of modern ophthalmology, often leading to a decrease or irreversible loss of visual functions. The review of the literature is devoted to the latest trends in the study of the mechanisms of development and course of rhegmatogenous retinal detachment against the background of proliferative vitreoretinopathy. In the pathogenesis of RD, there are five theories, as well as nine main risk factors for development. It is known that the contact between the retinal neuroepithelium and the retinal pigment epithelium is maintained by physical and metabolic forces, as well as by the friction force of the outer segments of photoreceptors and RPE cells. With synchisis and simultaneous syneresis, vitreous detachment develops, with an increase in traction forces and the possible development of RRD. The presence of a retinal tear rarely leads to RRD. It has been established that a pronounced traction effect, rather than a through rupture of the retina, is a key factor in the development and progression of RRD. Traction occurs in the course of proliferative vitreoretinopathy and the epiretinal layer of the vitreum remaining in the posterior vitreous detachment. With the development of detachment, damage to the hematoophthalmic barrier occurs, leading to the release of cells into the vitreous cavity that affect the development of PVR (epi-, sub- and intraretinally) with the formation of an epiretinal membrane. At the same time, communication with the choroid is lost, hypoxia and acidosis develop. ERMs formed during retinal detachment include glial cells and their subtypes — fibrous astrocytes, Muller cells, microglia, hyalocytes, RPE cells, fibroblasts and myofibroblasts. However, the leading role in the formation and development of ERM belongs to Muller cells and astrocytes. Also involved in the pathological process of ERM formation are: transforming growth factor β2, fibroblast growth factor, nerve growth factor, vascular endothelial growth factor, platelet growth factor, laminin, fibronectin, thrombospondin-1, osteonectin, transcription factor. Against the background of ROS, one should not forget about the change in the chemical composition of the vitreous body (increased content): serum albumin, transferrin, antithrombin III, α1-antichymotrypsin, α1-antitrypsin, α2-HS-glycoprotein, hemopexin, transthyretin, apolipoprotein A1, and fibrinogen

Retinal degeneration (RD), a group of diseases leading to irreversible vision loss, is characterised by retinal pigment epithelium (RPE) or retinal neuron damage and loss. With fewer risks of immune rejection and tumorigenesis, stem cell‐secreted extracellular vesicles (EVs) offer a new cell‐free therapeutic paradigm for RD, which remains to be investigated. Human retinal organoid‐derived retinal progenitor cells (hERO‐RPCs) are an easily accessible and advanced cell source for RD treatment. However, hERO‐RPCs‐derived EVs require further characterisation. Here, we compared the characteristics of EVs from hERO‐RPCs (hRPC‐EVs) with those of human embryonic stem cell (hESC)‐derived EVs (hESC‐EVs) as controls. Based on in‐depth proteomic analysis, we revealed remarkable differences between hRPC‐EVs and hESC‐EVs. A comparison between EVs and their respective cells of origin demonstrated that the protein loading of hRPC‐EVs was more selective than that of hESC‐EVs. In particular, hESC‐EVs were enriched with proteins related to angiogenesis and cell cycle, whereas hRPC‐EVs were enriched with proteins associated with immune modulation and retinal development. More importantly, compared with that of hESC‐EVs, hRPC‐EVs exhibited a lower correlation with cell proliferation and a unique capacity to regulate lipid metabolism. It was further confirmed that hRPC‐EVs potentially eliminated lipid deposits, inhibited lipotoxicity and oxidative stress, and enhanced phagocytosis and survival of oleic acid‐treated ARPE‐19 cells. Mechanistically, hRPC‐EVs are integrated into the mitochondrial network of oleic acid‐treated ARPE‐19 cells, and increased the level of mitochondrial fatty acid β‐oxidation‐related proteins. Thus, organoid‐derived hRPC‐EVs represent a promising source of cell‐free therapy for RD, especially for blinding diseases related to abnormal lipid metabolism in RPE cells. [ABSTRACT FROM AUTHOR]

Age-related macular degeneration (AMD) is the leading cause of blindness in the elderly, with the non-neovascular or atrophic form being the most common. Current treatment options are limited, emphasizing the urgent need for new therapeutic strategies. Our key finding is that increased levels of AKT2 in the RPE cells impair lysosomal function and trigger secretory autophagy; a non-canonical macroautophagy/autophagy pathway where cellular materials are released via the plasma membrane rather than being degraded by lysosomes. We showed that this process involves a protein complex, AKT2-SYTL1-TRIM16-SNAP23, releasing factors contributing to drusen biogenesis, a clinical hallmark of AMD development. Importantly, SIRT5 can inhibit this pathway, potentially offering a protective effect. Understanding mechanisms by which this non-canonical autophagy pathway promotes extracellular waste accumulation could provide new insights into drusen biogenesis. Future therapies for atrophic AMD could focus on regulating secretory autophagy or manipulating proteins involved in this process. [ABSTRACT FROM AUTHOR]

AIM: To investigate the occurrence and possible mechanism of blue light-induced ferroptosis in retinal pigment epithelial cells.METHODS: ARPE-19 cells cultured in vitro were irradiated by 405 nm blue light at 50 mW/cm2 irradiance with different duration and were divided into control, 16.3J/cm2, 32.6J/cm2, and 65.2J/cm2 groups; the 65.2J/cm2 group was defined as the high-level blue light irradiation group and cells were further divided into control, high-level blue light irradiation group and high-level blue light irradiation + ferroptosis inhibitor group. CCK-8 assay was used to detect cell viability, commercial kits were used to detect intracellular glutathione(GSH), ferrous iron and malondialdehyde(MDA)concentration, and Western blot was used to detect the relative expression of glutathione peroxidase 4(GPX4)and xCT proteins in cells.RESULTS: The decrease of ARPE-19 cell viability caused by blue light irradiation was dose-dependent, and the reduction of intracellular GSH concentration, the increase of ferrous iron concentration and MDA concentration were all caused by high-level blue light irradiation(all P

Myopia is currently one of the eye diseases that seriously threaten patients' vision worldwide, and its occurrence and development is a complex mechanism. It has been found that retinal pigment epithelium(RPE)cells play a key role in the progression of myopia. RPE cells mainly regulate cell function by regulating the expression of intracellular growth factor and matrix metalloproteinase-2(MMP-2)through the signal pathway of mammalian target of rapamycin(mTOR). At the same time, RPE cells can also be regulated by dopamine receptor agonists, so that cell function changes. When dopamine receptor activation weakened, RPE cell function will be impaired, thus promoting the development of myopia. Studies have shown that the expression of acetylcholine and all-trans retinoic acid in RPE cells can regulate the secretion of growth factors by RPE cells, and the growth factors act on scleral fibroblasts, thus indirectly regulating the course of myopia. Additionally, some studies have shown that RPE cells can coordinate the regulation of γ-aminobutyric acid on scleral cells and indirectly regulate the course of myopia. Besides, the expression of microRNA(microRNA)in RPE cells, such as microRNA-328 and microRNA-29a, was found through previous studies that they can affect the content and composition of extracellular matrix by regulating the expression of MMP-2 in RPE cells, thus leading to the occurrence and development of myopia. Therefore, the expression of multiple signaling pathways and miRNA in RPE cells are closely related to the occurrence and development of myopia. This article reviews the research progress of the molecular mechanism of RPE in the development of myopia, with a view to provide some theoretical basis for the specific molecular mechanism in the development of myopia.

Phagocytosis is one of the key functions of retinal pigment epithelium (RPE) cells, which maintain photoreceptor health by removing photoreceptor outer segments (POSs) that are regularly shed. A deficiency in RPE function to phagocytose POSs may lead to vision loss in inherited retinal diseases and eventually to age-related macular degeneration (AMD) with geographic atrophy. Significant progress has been made in the field of cell replacement therapy for AMD using stem-cell-derived RPE. To test their function, RPE cells are incubated with purified bovine POSs for the demonstration of efficient binding, internalization, and digestion of POSs. Here, we present an image-based method to measure phagocytosis activity by using POSs labeled with a pH-sensitive fluorescent dye, which has low fluorescence at neutral pH outside of the cell and high fluorescence at low pH inside the phagosome. Further, we introduce a unique flow-cytometry-based method for the characterization of POSs by measuring specific markers for POSs such as rhodopsin and opsin. Using this method, we demonstrated a comparable quality of several bovine POS isolation batches and a reliable assessment of POS quality on RPE phagocytosis assay performance when subjected to different stress conditions. This work provides new tools to characterize POSs and insight into RPE phagocytosis assay development for the functional evaluation of RPE cells in the field of cell replacement therapy. [ABSTRACT FROM AUTHOR]

In the eye, an increase in galectin-1 is associated with various chorioretinal diseases, in which retinal pigment epithelium (RPE) cells play a crucial role in disease development and progression. Since little is known about the function of endogenous galectin-1 in these cells, we developed a galectin-1-deficient immortalized RPE cell line (ARPE-19-LGALS1−/−) using a sgRNA/Cas9 all-in-one expression vector and investigated its cell biological properties. Galectin-1 deficiency was confirmed by Western blot analysis and immunocytochemistry. Cell viability and proliferation were significantly decreased in ARPE-19-LGALS1−/− cells when compared to wild-type controls. Further on, an increased attachment of galectin-1-deficient RPE cells was observed by cell adhesion assay when compared to control cells. The diminished viability and proliferation, as well as the enhanced adhesion of galectin-1-deficient ARPE-19 cells, could be blocked, at least in part, by the additional treatment with human recombinant galectin-1. In addition, a significantly reduced migration was detected in ARPE-19-LGALS1−/− cells. In comparison to control cells, galectin-1-deficient RPE cells had enhanced expression of sm-α-actin and N-cadherin, whereas expression of E-cadherin showed no significant alteration. Finally, a compensatory expression of galectin-8 mRNA was observed in ARPE-19-LGALS1−/− cells. In conclusion, in RPE cells, endogenous galectin-1 has crucial functions for various cell biological processes, including viability, proliferation, migration, adherence, and retaining the epithelial phenotype. [ABSTRACT FROM AUTHOR]

Age-related macular degeneration (AMD) is one of an increasing number of diseases that causes irreversible impairment and loss of vision in the elderly. AMD occurs by oxidative stress-mediated apoptosis of retinal pigment epithelium cells. The onset of AMD may be positively correlated with the exposure to blue light. We screened food-derived carotenoids for cytoprotective action against blue light irradiation using human ARPE-19 retinal pigment epithelium cells. This study revealed that blue light irradiation triggered apoptosis and oxidative stress in all-trans-retinal (atRAL)-exposed ARPE-19 cells by generating singlet oxygen (¹O2), leading to significant cell death. We found that astaxanthin, a potent anti-oxidative xanthophyll abundant in several marine organisms including microalgae, salmon, and shrimp, significantly suppresses blue lightinduced apoptotic cell death of atRAL-exposed ARPE-19 cells by scavenging ¹O2. Mechanistic studies using the blue-light irradiated cells also demonstrated that the cytoprotective effects of astaxanthin can be attributed to scavenging of ¹O2 directly. Our results suggest the potential value of astaxanthin as a dietary strategy to prevent blue light-induced retinal degeneration including AMD. [ABSTRACT FROM AUTHOR]

CLCN2 encodes a two-pore homodimeric chloride channel protein (CLC-2) that is widely expressed in human tissues. The association between Clcn2 and the retina is well-established in mice, as loss-of-function of CLC-2 can cause retinopathy in mice; however, the ocular phenotypes caused by CLCN2 mutations in humans and the underlying mechanisms remain unclear. The present study aimed to define the ocular features and reveal the pathogenic mechanisms of CLCN2 variants associated with retinal degeneration in humans using an in vitro overexpression system, as well as patient-induced pluripotent stem cell (iPSC)-derived retinal pigment epithelium (RPE) cells and retinal organoids (ROs). A patient carrying the homozygous c.2257C > T (p.R753X) nonsense CLCN2 mutation was followed up for > 6 years. Ocular features were comprehensively characterized with multimodality imaging and functional examination. The patient presented with severe bilateral retinal degeneration with loss of photoreceptor and RPE. In vitro, mutant CLC-2 maintained the correct subcellular localization, but with reduced channel function compared to wild-type CLC-2 in HEK293T cells. Additionally, patient iPSC-derived RPE cells carrying the CLCN2 mutation exhibited dysfunctional ClC-2 chloride channels and outer segment phagocytosis. Notably, these functions were rescued following the repair of the CLCN2 mutation using the CRISPR-Cas9 system. However, this variant did not cause significant photoreceptor degeneration in patient-derived ROs, indicating that dysfunctional RPE is likely the primary cause of biallelic CLCN2 variant-mediated retinopathy. This study is the first to establish the confirmatory ocular features of human CLCN2-related retinal degeneration, and reveal a pathogenic mechanism associated with biallelic CLCN2 variants, providing new insights into the cause of inherited retinal dystrophies. [ABSTRACT FROM AUTHOR]

Proliferative vitreoretinopathy(PVR)is a serious complication that occurs in the natural history of rhegmatogenous retinal detachment(RRD)or after retinal detachment surgery, often resulting in vision loss. Currently, there has no effective treatment. The pathological characteristics of PVR are the excessive inflammatory response and abnormal proliferation of various cells under the action of cytokines, which eventually form a layer of proliferative membrane around the retinal surface, and further lead to traction retinal detachment(TRD). In-depth studies on the pathogenesis of PVR will help to find promising molecular targets for its treatment. Recent studies have found that vascular endothelial growth factor(VEGF)and the epithelial-mesenchymal transition(EMT)of retinal pigment epithelium(RPE)cells play an important role in the pathogenesis of PVR. This article summarizes the roles of VEGF and RPE cell EMT in the pathogenesis of PVR and the interaction mechanism between them, with the aim to provide new ideas for the treatment and clinical research of PVR.

• Salidroside reduces ferroptosis-induced damage in dry age-related macular degeneration. • FAC-treated ARPE-19 cells show increased lipid peroxidation and iron accumulation. • Salidroside ameliorates outer nuclear layer thinning and RPE tight junction disruption in mouse retinal degeneration. • Nrf2/SLC7A11/GPX4 signaling pathway mediates Salidroside's protective effects. • Nrf2 knockdown attenuates the protective effects of Salidroside on RPE cells. Age-related macular degeneration (AMD) is a significant contributor to irreversible impairment in visual capability, particularly in its non-neovascular (dry) form. Ferroptosis, an emerging form of programmed necrosis, involves generating lipid peroxidation (LOS) through free iron and reactive oxygen species (ROS). Salidroside, a glycoside from Rhodiola rosea, known for anti-inflammatory and antioxidant properties. The research aim was exploring whether ferroptosis exists in dry AMD pathogenesis and elucidate salidroside's protective mechanisms against ferroptosis in AMD murine models and ARPE-19 cells. ARPE-19 cells were treated with varying concentrations of ferrous ammonium citrate (FAC) and salidroside. In an in vivo model, C57BL/6 mice were administered intraperitoneal injections of salidroside for 7 consecutive days, followed by an intravitreal injection (IVT) of FAC. After 7 days, the eyeballs were harvested for subsequent analyses. Ferroptosis markers were assessed using western blotting, immunofluorescence staining, and flow cytometry. To further elucidate the modulatory role of Nrf2 in ferroptosis, ARPE-19 cells were transfected with si-Nrf2. In vitro, FAC-treated ARPE-19 cells exhibited reduced viability, decreased mitochondrial membrane potential (MMP), and accumulation of iron and lipid peroxidation (LOS) products. In vivo, FAC administration by IVT led to outer nuclear layer thinning and compromised tight junctions in RPE cells. The GPX4, Nrf2, and SLC7A11 expressions were downregulated both in vitro and in vivo. Salidroside upregulated Nrf2 and ameliorated these outcomes, but its effects were attenuated in ARPE-19 cells transfected with si-Nrf2. Our study establishes that FAC induces RPE cell ferroptosis within dry AMD, and salidroside exerts therapeutic effects by triggering Nrf2/SLC7A11/GPX4 signaling axis. [ABSTRACT FROM AUTHOR]

Age-related macular degeneration(ARMD)is a main cause of irreversible visual impairment in the elderly. The major pathological features are drusen formation, macular pigment disorder, geographic atrophy and abnormal neovascularization. Retinal pigment epithelium(RPE)function is impaired in ARMD. Endoplasmic reticulum(ER)is an organelle in eukaryotes responsible for protein synthesis, modification, integration and quality control. ER also participates in the maintenance of calcium homeostasis and lipid biosynthesis. Stimuli from the external and internal environment may trigger ER stress and therefore activate the intracellular signal transduction pathway-the unfolded protein response(UPR), to restore cell homeostasis. However, prolonged ER stress may lead to apoptosis. The pathogenesis of ARMD has not been fully elucidated, nevertheless, compelling evidence demonstrates that ER stress is involved. In this article, we summarize recent advances in UPR pathways, as well as the role of ER stress in the physiological function of RPE and in the pathogenesis of ARMD.

AIM: To explore the temporal mitochondrial characteristics of retinal pigment epithelium (RPE) cells obtained from human embryonic stem cells (hESC)-derived retinal organoids (hEROs-RPE), to verify the optimal period for using hEROs-RPE as donor cells from the aspect of mitochondria and to optimize RPE cell-based therapeutic strategies for age-related macular degeneration (AMD). METHODS: RPE cells were obtained from hEROs and from spontaneous differentiation (SD-RPE). The mitochondrial characteristics were analyzed every 20d from day 60 to 160. Mitochondrial quantity was measured by MitoTracker Green staining. Transmission electron microscopy (TEM) was adopted to assess the morphological features of the mitochondria, including their distribution, length, and cristae. Mitochondrial membrane potentials (MMPs) were determined by JC-1 staining and evaluated by flow cytometry, reactive oxygen species (ROS) levels were evaluated by flow cytometry, and adenosine triphosphate (ATP) levels were measured by a luminometer. Differences between two groups were analyzed by the independent-samples t-test, and comparisons among multiple groups were made using one-way ANOVA or Kruskal-Wallis H test when equal variance was not assumed. RESULTS: hEROs-RPE and SD-RPE cells from day 60 to 160 were successfully differentiated from hESCs and expressed RPE markers (Pax6, MITF, Bestrophin-1, RPE65, Cralbp). RPE features, including a cobblestone-like morphology with tight junctions (ZO-1), pigments and microvilli, were also observed in both hEROs-RPE and SD-RPE cells. The mitochondrial quantities of hEROs-RPE and SD-RPE cells both peaked at day 80. However, the cristae of hEROs-RPE mitochondria were less mature and abundant than those of SD-RPE mitochondria at day 80, with hEROs-RPE mitochondria becoming mature at day 100. Both hEROs-RPE and SD-RPE cells showed low ROS levels from day 100 to 140 and maintained a normal MMP during this period. However, hEROs-RPE mitochondria maintained a longer time to produce high levels of ATP (from day 120 to 140) than SD-RPE cells (only day 120). CONCLUSION: hEROs-RPE mitochondria develop more slowly and maintain a longer time to supply high-level energy than SD-RPE mitochondria. From the mitochondrial perspective, hEROs-RPE cells from day 100 to 140 are an optimal cell source for treating AMD.

AIM: To investigate the effect of leucine-rich-alpha-2-glycoprotein 1 (LRG1) on epithelial-mesenchymal transition (EMT) in retinal pigment epithelium (RPE) cells, and to explore the role of NADPH oxidase 4 (NOX4). METHODS: RPE cells (ARPE-19 cell line) were treated with transforming growth factor-β1 (TGF-β1) to induce EMT. Changes of the mRNA and protein expression levels of LRG1 were tested in the TGF-β1 treated cells. The recombinant human LRG1 protein (rLRG1) and siRNA of LRG1 were used to establish accumulation of exogenous LRG1 model and the down-regulation of LRG1 model in ARPE-19 cells respectively, and to detect EMT-related markers including fibronectin, α-smooth muscle actin (α-SMA) and zonula occludens-1 (ZO-1). The mRNA and protein expression level of NOX4 were measured according to the above treatments. VAS2870 was used as a NOX4 inhibitor in rLRG1-treated cells. EMT-related markers were detected to verify the effect of NOX4 in the process of EMT. RESULTS: TGF-β1 promoted the expression of LRG1 at both the mRNA and protein levels during the process of EMT which showed the up-regulation of fibronectin and α-SMA, as well as the down-regulation of ZO-1. Furthermore, the rLRG1 promoted EMT of ARPE-19 cells, which manifested high levels of fibronectin and α-SMA and low level of ZO-1, whereas knockdown of LRG1 prevented EMT by decreasing the expressions of fibronectin and α-SMA and increasing the expression of ZO-1 in ARPE-19 cells. Besides, the rLRG1 activated and LRG1 siRNA suppressed NOX4 expression. EMT was inhibited when VAS2870 was used in the rLRG1-treated cells. CONCLUSION: These results for the first time demonstrate that LRG1 promotes EMT of RPE cells by activating NOX4, which may provide a novel direction to explore the mechanisms of subretinal fibrosis.

Abstract Background Age-related macular degeneration (AMD) is the primary cause of blindness and severe vision loss in developed countries and is responsible for 8.7% of blindness globally. Ultraviolet radiation can induce DNA breakdown, produce reactive oxygen species, and has been implicated as a risk factor for AMD. This study investigated the effects of UVA radiation on Human retinal pigment epithelial cell (ARPE-19) growth and protein expression. Methods ARPE-19 cells were irradiated with a UVA lamp at different doses (5, 10, 20, 30 and 40 J/cm2) from 10 cm. Cell viability was determined by MTT assay. Visual inspection was first achieved with inverted light microscopy and then the DeadEnd™ Fluorometric TUNEL System was used to observe nuclear DNA fragmentation. Flow cytometry based-Annexin V-FITC/PI double-staining was used to further quantify cellular viability. Mitochondrial membrane potential was assessed with JC-1 staining. 2D electrophoresis maps of exposed cells were compared to nonexposed cells and gel images analyzed with PDQuest 2-D Analysis Software. Spots with greater than a 1.5-fold difference were selected for LC-MS/MS analysis and some confirmed by western blot. We further investigated whether caspase activation, apoptotic-related mitochondrial proteins, and regulators of ER stress sensors were involved in UVA-induced apoptosis. Results We detected 29 differentially expressed proteins (9 up-regulated and 20 down-regulated) in the exposed cells. Some of these proteins such as CALR, GRP78, NPM, Hsp27, PDI, ATP synthase subunit alpha, PRDX1, and GAPDH are associated with anti-proliferation, induction of apoptosis, and oxidative-stress protection. We also detected altered protein expression levels among caspases (caspase 3 and 9) and in the mitochondrial (cytosolic cytochrome C, AIF, Mcl-1, Bcl-2, Bcl-xl, Bax, Bad, and p-Bad) and ER stress-related (p-PERK, p-eIF2α, ATF4 and CHOP) apoptotic pathways. Conclusions UVA irradiation suppressed the proliferation of ARPE-19 cells in a dose-dependent manner, caused quantitative loses in transmembrane potential (ΔΨm), and induced both early and late apoptosis.

AIM: To evaluate the expression of uncoupling protein 2 (UCP2) in a retinal pigment epithelium cell line (ARPE-19), under oxidative stress (OS). METHODS: ARPE-19 cells were divided into groups treated with various concentrations of hydrogen peroxide (H2O2; 0, 150, 300, 500, 700, and 900 µmol/L) for 24h, to induce oxidative damage and cell viability was assessed by MTT assay. UCP2 mRNA expression in cells treated with H2O2 was investigated by reverse transcription-polymerase chain reaction (RT-PCR). UCP2 protein expression was assessed by Western blotting and ROS levels analyzed by flow cytometry (FCM). Further, UCP2-siRNA treated cultures were exposed to H2O2 (0, 75, 150, and 300 µmol/L) for 2h and cell viability determined by MTT assay. RESULTS: Cells treated with higher concentrations of H2O2 appeared shrunken; their adhesion to adjacent cells was disrupted, and the number of dead cells increased. The results of cell viability assays demonstrated that the numbers of cells were decreased in a dose-dependent manner following treatment with H2O2. Compared with untreated controls, cell viability was significantly reduced after treatment with >300 µmol/L H2O2 (P

AIM: To investigate the regulation of vascular endothelial growth factors (VEGF) and pigment epithelium-derived factor (PEDF) expression by autophagy in retinal pigment epithelium (RPE) cells on exposure to hypoxia. METHODS: ARPE-19, an RPE cell line, was treated as following: the control group was kept in a normoxic incubator; the hypoxia group was incubated in a hypoxic incubator with 1% O2/5% CO2/94% N2 for 24h; the hypoxia + 3-methyladenine (3-MA) group was pretreated with 10 mmol/L 3-MA for 1h and then in the hypoxic incubator for 24h; and the hypoxia + chloroquine (CQ) group was pretreated with 50 μmol/L CQ for 1h and then in the hypoxic incubator for 24h. The morphology and ultrastructure of the cells was observed by an inverted microscope or a transmission electronic microscope (TEM). Western blot was performed to assay the expression of autophagy-associated markers, including microtubule associated protein 1 light chain 3 B (LC3B), Beclin-1, Atg5 and p62. The concentration of VEGF and PEDF in the culture supernatant was determined by ELISA, and the ratio of VEGF/PEDF was calculated. RESULTS: There were no obvious differences in cell morphology among different groups and autolysosomes could be observed in the cytoplasm in all groups. Compared to the control cells, the LC3B-II/I ratio and levels of Beclin-1 and Atg5 were significantly increased and p62 level was significantly decreased in the hypoxia group. With the increase of VEGF and decrease of PEDF concentration, the VEGF/PEDF ratio was significantly increased in the hypoxia group compared to the control cells. The LC3B-II/I ratio was significantly reduced by 3-MA treatment and increased by CQ treatment. The expressions of Beclin-1 and Atg5 were significantly reduced by 3-MA or CQ treatment, while expression of p62 was increased in the 3-MA or CQ treated cells. The concentration of VEGF was significantly decreased and PEDF increased, thereby the VEGF/PEDF ratio was decreased in the hypoxia + 3-MA group and hypoxia + CQ group compared with that in the hypoxia group. CONCLUSION: Hypoxia leads to elevated autophagy in RPE cells, and expression of VEGF and PEDF might be regulated by autophagy on exposure to hypoxia to further participate in regulating the formation of retinal neovascularization.

AIM: To analyze the expression of uncoupling protein 2 (UCP2) in retinal pigment epithelium (RPE) cells at the different human age, further explore the possible new target of RPE cells protection. METHODS: Adult retinal pigment epithelial-19 (ARPE-19) cells and the primary RPE cells at the different age (9-20y, RESULTS: Cells from the donors more than 60y are larger and more fibroblastic in appearance compared to ARPE-19 cells and those primary cultures obtained from the younger individuals by using phase-contrast micrographs. Results of RT-PCR, Western blot and confocal microscopy all showed that UCP2 was highly expressed in ARPE-19 cells and in the younger primary cultured human RPE cells at the age of 9-20y and 50-55y, whereas lower expression of UCP2 was measured in the older primary cultured human RPE cells at the age more than 60y. CONCLUSION: Expression of UCP2 gene is decreased in aged RPE cells, promoting the lower ability of anti-oxidation in these cells. It is indicated that UCP2 gene might be a new target for protecting the cells from oxidative stress damage.

Age-related macular degeneration (AMD) is a complex multifactorial degenerative disease that leads to irreversible blindness. AMD affects the macula, the central part of the retina responsible for sharp central vision. Retinal pigment epithelium (RPE) is the main cellular type affected in dry AMD. RPE cells form a monolayer between the choroid and the neuroretina and are in close functional relationship with photoreceptors; moreover, RPE cells are part of the blood retina barrier that is disrupted in ocular diseases such as AMD. During ocular inflammation lymphocytes and macrophages are recruited, contact RPE and produce pro-inflammatory cytokines, which play an important role in AMD pathogenesis. The interaction between RPE and immune cells is mediated by leukocyte integrins, heterodimeric transmembrane receptors, and adhesion molecules, including VCAM-1 and ICAM-1. Within this frame, this study aimed to characterize RPE-leukocytes interaction and to investigate any potentially beneficial effects induced by integrin antagonists (DS-70, MN27 and SR714), developed in previous studies. ARPE-19 cells were co-cultured for different incubation times with Jurkat cells and apoptosis and necrosis levels were analyzed by flow cytometry. Moreover, we measured the mRNA levels of the pro-inflammatory cytokine IL-1β and the expression of adhesion molecules VCAM-1 and ICAM-1. We found that RPE-lymphocyte interaction increased apoptosis and necrosis levels in RPE cells and the expression of IL-1β. This interaction was mediated by the binding of α4β1 and αLβ2 integrins to VCAM-1 and ICAM-1, respectively. The blockade of RPE-lymphocyte interaction with blocking antibodies highlighted the pivotal role played by integrins. Therefore, α4β1 and αLβ2 integrin antagonists were employed to disrupt RPE-lymphocyte crosstalk. Small molecule integrin antagonists proved to be effective in reducing RPE cell death and expression of IL-1β, demonstrating that integrin antagonists could protect RPE cells from detrimental effects induced by the interaction with immune cells recruited to the retina. Overall, the leukocyte integrin antagonists employed in the present study may represent a novel opportunity to develop new drugs to fight dry AMD.

Abstract Background By investigating that (i) all-trans retinoic acid (ATRA) affects human retinal pigment epithelium (RPE) in expressing and secreting transforming growth factor (TGF)-β2 and (ii) U73122 (phospholipase C inhibitor) and SQ22536 (adenylyl cyclase inhibitor) regulate the ATRA-induced secretion of TGF-β2 in human RPE, we sought to interpret the signaling pathway of ATRA in promoting the development of myopia. Methods The RPE cell line (D407) was treated with (i) ATRA (10 μM), (ii) U73122 (5–40 μM) and ATRA (10 μM), or (iii) SQ22536 (5–40 μM) and ATRA (10 μM). The control group was no-treated. After stimulated at 2, 4, 8, 16, 24, and 48 h, The expression and secretion of TGF-β2 was detected. Results TGF-β2 in the cytoplasm was time-dependent increased by ATRA (p 0.05). Conclusions In RPE cells, ATRA stimulates the secretion of TGF-β2 via the phospholipase C signaling pathway but not the adenylyl cyclase signaling pathway. U73122 may inhibit the promotion of ATRA in the development of myopia.

AIM: To observe the effects of pyridoxamine(PM)on RAGE, ROS and apoptosis in RPE cells treated with advanced glycation end products(AGEs), and to investigate the protective effect of PM on RPE cells in diabetic retinopathy. METHODS:Primary cultured human RPE cells, the third generation of cells were synchronized with serum-free Dulbecco-modified Eagle medium for 24h, and then grouped: 1)Control group: cultured with 100mg/L BSA for 48h; 2)AGEs-treated group: cultured with 200mg/L AGEs for 48h; 3)PM group: PM1 group: cultured with 16mg/L PM+200mg/L AGEs for 48h; PM2 group: cultured with 32mg/L PM+200mg/L AGEs for 48h. The expression of RAGE protein was detected by immunohistochemistry. The formation of ROS was observed by fluorescence microscopy. The apoptosis of cells was detected by TUNEL. RESULTS:The expression of RAGE protein, ROS and apoptosis of RPE cells in PM group were significantly lower than those in AGEs-treated group, and decreased with the increase of PM concentration. CONCLUSION:Pyridoxamine can inhibit the expression of RAGE and the production of ROS, reduce apoptosis, and have a protective effect on RPE cells.

AIM: To invesitigate the effect of invigorating blood and dissipating masses traditional Chinese medicine compound drug-containing plasma on the proliferation of rabbit retinal pigment epithelium(RPE)cells treated with platelet derived growth factor(PDGF). METHODS: Primary cells of RPE cells were obtained by enzymatic digestion, and the primitive culture and subculture of RPE cells were proceeded; prepared blood plasma-contained traditional Chinese medicine compound drug-containing plasma; the fourth genertation rabbit RPE cells were selected as the experimental cells by PDGF of low, medium and high doses(5μg/L, 10μg/L, 20μg/L)for 48h. Suitable concentration was detected and selected in cells experiment by using CCK-8 method. Establishing rabbit model of RPE cell proliferation treated with PDGF. The experimental groups were blank control group(DMEM), normal plasma group, PDGF(10 μg/L)group, PDGF(10 μg/L)+ AG1296(10 μmol/L)group, PDGF(10 μg/L)+ 10% drug-containing plasma, PDGF(10 μg/L)+ 20% drug-containing plasma. Respectively, transwell method was used to determine the migration of rabbit RPE cells after 24h intervention in each group; CCK-8 was used to determine the cell viability OD value of rabbit RPE cells after 48h of intervention in each group.RESULTS: The plasma containing 10% and 20% concentration of invigorating blood and dissipating masses traditional Chinese medicine compound drug can effectively inhibit cell viability and cell migration of RPE cells treated with PDGF. CONCLUSION: We found the certain concentration of invigorating blood and dissipating masses traditional Chinese medicine compound drug can effectively inhibit cell viability and cell migration of RPE cells treated with PDGF, which may be an effective treatment for proliferative vitreoretinopathy and provide a new way to study the mechanism of proliferative vitreoretinopathy.

AIM: To identify the pathological role of amyloid beta (Aβ) deposition in retinal degeneration, and explore Aβ deposition on the retinal pigment epithelium cells (RPE) layer and the associated structural and functional changes in Alzheimer’s disease transgenic mice. METHODS: RPE changes in the eyes of APPswe/PS1 transgenic and none transgenic (NTG) mice over 20 months old were examined. Histological changes were investigated via hematoxylin and eosin (H&E) staining and transmission electron microscopy (TEM) examination, whereas the expression of amyloid precursor protein (APP), Aβ, Zonula occludens-1 (ZO-1) and Ionized calcium binding adaptor molecule-1 (IBA-1) were investigated using immunohistochemistry and immunofluorescence techniques. All of the obtained results were quantitatively and statistically analyzed. RESULTS: In aged transgenic mice, an APP-positive immunoreaction and Aβ deposition were detected on the RPE layer but were undetectable in NTG mice. The RPE demonstrated some vacuole changes, shortened basal infoldings and basal deposition in histopathological examination and TEM tests, wherein irregular shapes were indicated by ZO-1 disorganization through fluorescence. Furthermore, IBA-1 positive cells were observed to have accumulated and infiltrated into the RPE layer and localized beneath the RPE/Bruch’s membrane (BrM) complex, which was accompanied by an increase in BrM thickness in aged transgenic mice in comparison to NTG mice. The IBA-1 positive cells were found to be co-stained with Aβ deposition on the RPE flat mounts. CONCLUSION: The observed Aβ deposition in the RPE layer may cause RPE dysfunction, which is associated with microglia cells infiltration into the retina of aged transgenic mice, suggesting that Aβ deposition probably plays a significant role in RPE-related degenerative disease.

Oxidation of docosahexaenoate (DHA)-containing phospholipids in the cell plasma membrane leads to release of the α,β-unsaturated aldehyde 4-hydroxy-7-oxo-5-heptenoic acid (HOHA) lactone which is capable of inducing retinal pigmented epithelial (RPE) cell dysfunction. Previously, HOHA lactone was shown to induce apoptosis and angiogenesis, and to activate the alternative complement pathway. RPE cells metabolize HOHA lactone through enzymatic conjugation with glutathione (GSH). Competing with this process is the adduction of HOHA lactone to protein lysyl residues generating 2-(ω-carboxyethyl)pyrrole (CEP) derivatives that have pathological relevance to age-related macular degeneration (AMD). We now find that HOHA lactone induces mitochondrial dysfunction. It decreases ATP levels, mitochondrial membrane potentials, enzymatic activities of mitochondrial complexes, depletes GSH and induces oxidative stress in RPE cells. The present study confirmed that pyridoxamine and other primary amines, which have been shown to scavenge γ-ketoaldehydes formed by carbohydrate or lipid peroxidation, are ineffective for scavenging the α,β-unsaturated aldehydes. Histidyl hydrazide (HH), that has both hydrazide and imidazole nucleophile functionalities, is an effective scavenger of HOHA lactone and it protects ARPE-19 cells against HOHA lactone-induced cytotoxicity. The HH α-amino group is not essential for this electrophile trapping activity. The Nα-acyl L-histidyl hydrazide derivatives with 2- to 7-carbon acyl groups with increasing lipophilicities are capable of maintaining the effectiveness of HH in protecting ARPE-19 cells against HOHA lactone toxicity, which potentially has therapeutic utility for treatment of age related eye diseases. Image 1 • HOHA lactone is toxic to mitochondrial complexes I, II and IV in RPE cells. • HOHA lactone causes loss of mitochondrial membrane potential in RPE cells. • Histidyl hydrazide traps HOHA lactone preventing mitochondrial dysfunction. • Histidyl hydrazide traps HOHA lactone preventing GSH depletion and oxidative stress. [ABSTRACT FROM AUTHOR]

• Macrophage functions in CNV are regulated partly by the mTORC1 pathway. • mTORC1 pathway promotes M1 activation and inhibits M2 activation in macrophages. • mTORC1 activity of macrophages influences cytokine expression of RPE cells. Macrophages are involved in choroidal neovascularization (CNV). The mechanistic target of rapamycin complex 1 (mTORC1) is a central cell regulator, but mTORC1 function in macrophages in CNV is not fully understood. We explored the effect of mTORC1 pathway regulation on macrophages in CNV. A laser-induced murine CNV model was performed. Expression of phospho-S6 and F4/80 in CNV lesions was analyzed by immunofluorescence. Macrophages in CNV lesions were found at 1 day after laser treatment, reached a peak at 5 days, and decreased at 7 and 14 days. mTORC1 activity of cells in CNV lesions was increased from 3 to 7 days, and deceased at 14 days. Most infiltrating macrophages in CNV lesions had strong mTORC1 activity at 3 and 5 days that subsequently decreased. In vitro , THP-1 macrophages were polarized to M1 or M2 with rapamycin or siRNA treatment. The human retinal pigment epithelium (RPE) cell line ARPE-19 was co-cultured with macrophages. Cytokine expression of macrophages and ARPE-19 cells was detected by quantitative PCR. Inhibiting mTORC1 activity of macrophages reduced M1 and strengthened M2, which was reversed by mTORC1 hyperactivation. Both M1 and M2 macrophages induced RPE cells to express less PEDF and more MMP9, IL-1β and MCP-1. Inhibiting or enhancing mTORC1 activity of macrophages changed cytokine expression of RPE cells. Together, we demonstrated that macrophage functions in CNV were regulated partly by the mTORC1 pathway, and mTORC1 activity of macrophages influenced the expression of cytokines that are associated with CNV development in RPE cells. This study provides more understanding about the regulatory mechanism of macrophages in CNV. [ABSTRACT FROM AUTHOR]

Increasing evidence suggests that general control nonderepressible 2 (GCN2) is a critical regulator of oxidative stress and cell apoptosis in response to various stimuli. However, the role of GCN2 in diabetic retinopathy remains unclear. The aim of the present study was to investigate the effects of GCN2 on oxidative stress and apoptosis in ARPE‐19 cells exposed to high glucose. The results showed that GCN2 was highly expressed in high glucose‐induced ARPE‐19 cells. Moreover, knockdown of GCN2 greatly improved ARPE‐19 cell viability in response to high glucose. In addition, GCN2 knockdown significantly suppressed the production of reactive oxygen species (ROS) and malondialdehyde (MDA), as well as increased superoxide dismutase (SOD) activity in high glucose‐stimulated ARPE‐19 cells. Furthermore, GCN2 knockdown reduced cell apoptosis and enhanced the activation of nuclear factor E2‐related factor 2/heme oxygenase‐1 (Nrf2/HO‐1) pathway in high glucose‐stimulated ARPE‐19 cells. However, knockdown of Nrf2 reversed the effects of GCN2 on oxidative stress and cell apoptosis. Taken together, our findings suggest that knockdown of GCN2 inhibits high glucose‐induced oxidative stress and apoptosis in ARPE‐19 cells through activation of the Nrf2/HO‐1 pathway. [ABSTRACT FROM AUTHOR]

Activation of the NF-E2-related factor 2 (Nrf2) cascade can offer significant protection against oxidative stress in retinal pigment epithelium (RPE) cells. Here, we identified a novel kelch-like ECH-associated protein 1 (Keap1)-targeting microRNA, microRNA-626 (miR-626) that activates Nrf2 signaling. In ARPE-19 cells and primary human RPE cells, ectopic overexpression of miR-626 targeting the 3′-UTR (3′-untranslated region) of Keap1 downregulated its expression, promoting Nrf2 protein stabilization and nuclear translocation, leading to expression of ARE-dependent genes (HO1 , NOQ1 and GCLC). Functional studies showed that miR-626 protected RPE cells from hydrogen peroxide (H 2 O 2)-induced oxidative injury. Conversely, miR-626 inhibition induced Keap1 upregulation and Nrf2 cascade inhibition, exacerbating oxidative injury in RPE cells. Further studies demonstrated that miR-626 was ineffective in Keap1-knockout or Nrf2-knockout RPE cells. Importantly, miR-626 also activated Keap1-Nrf2 signaling cascade in human lens epithelial cells (HLECs) and primary human retinal ganglion cells (RGCs), providing protection from H 2 O 2. At last, we show that plasma miR-626 levels are significantly downregulated in age-related macular degeneration (AMD) patients than those in the healthy donors. We conclude that targeting Keap1 by miR-626 protects RPE cells and other ophthalmic cells from oxidative injury via activation of Nrf2 signaling cascade. Image 1 • miR-626 downregulates Keap1 and activates Nrf2 signaling in human RPE cells. • miR-626 overexpression protects RPE cells from oxidative stress. • miR-626 inhibition induced Keap1 upregulation and Nrf2 cascade inhibition. [ABSTRACT FROM AUTHOR]

Inhibitor of growth 4 (ING4), a potential tumor suppressor, is implicated in cell migration and angiogenesis. However, its effects on diabetic retinopathy (DR) have not been elucidated. In this study, we aimed to evaluate ING4 expression in normal and diabetic rats and clarify its effects on hypoxia‐induced dysfunction in human retinal pigment epithelial (ARPE‐19) cells. A Type 1 diabetic model was generated by injecting rats intraperitoneally with streptozotocin and then killed them 4, 8, or 12 weeks later. ING4 expression in retinal tissue was detected using western blot analysis, reverse transcription quantitative real‐time polymerase chain reaction (RT‐qPCR), and immunohistochemistry assays. After transfection with an ING4 overexpression lentiviral vector or small interfering RNA (siRNA), ARPE‐19 migration under hypoxia was tested using wound healing and transwell assays. The angiogenic effect of conditioned medium (CM) from ARPE‐19 cells was examined by assessing human retinal endothelial cell (HREC) capillary tube formation. Additionally, western blot analysis and RT‐qPCR were performed to investigate the signaling pathways in which ING4, specificity protein 1 (Sp1), matrix metalloproteinase 2 (MMP‐2), MMP‐9, and vascular endothelial growth factor A (VEGF‐A) were involved. Here, we found that ING4 expression was significantly reduced in the diabetic rats' retinal tissue. Silencing ING4 aggravated hypoxia‐induced ARPE‐19 cell migration. CM collected from ING4 siRNA‐transfected ARPE‐19 cells under hypoxia promoted HREC angiogenesis. These effects were reversed by ING4 overexpression. Furthermore, ING4 suppressed MMP‐2, MMP‐9, and VEGF‐A expression in an Sp1‐dependent manner in hypoxia‐conditioned ARPE‐19 cells. Overall, our results provide valuable mechanistic insights into the protective effects of ING4 on hypoxia‐induced migration and angiogenesis regulation in ARPE‐19 cells. Restoring ING4 may be a novel strategy for treating DR. [ABSTRACT FROM AUTHOR]

Activation of Nrf2 cascade can protect retinal pigment epithelium (RPE) cells from hydrogen peroxide (H 2 O 2) and other oxidative injury. The current study identified microRNA-601 (miR-601) as a novel cullin 3 (Cul3)-targeting miRNA that activates Nrf2 cascade. In ARPE-19 cells and primary human RPE cells, forced overexpression of miR-601 significantly inhibited Cul3 3′-UTR activity and downregulated Cul3 mRNA /protein expression, leading to Nrf2 protein stabilization and its nuclear translocation as well as expression of anti-oxidant response elements (ARE)-dependent genes (HO1 , NQO1 and GCLC). H 2 O 2 treatment increased miR-601 levels in RPE cells. Significantly, ectopic miR-601 overexpression attenuated H 2 O 2 -induced oxidative injury and apoptosis in RPE cells. In contrast, miR-601 inhibition promoted Cul3 expression, lowered basal Nrf2 activation, and enhanced H 2 O 2 -induced oxidative stress and apoptosis in RPE cells. In ARPE-19 cells, CRISPC/Cas9-mediated knockout (KO) of Cul3 or Keap1 not only mimicked, but also nullified, miR-601-inudced anti-H 2 O 2 actions. Furthermore, Nrf2 silencing by targeted shRNAs abolished miR-601-inudced cytoprotection in H 2 O 2 -treated ARPE-19 cells. Taken together, we show that miR-601 activates Nrf2 signaling to protect RPE cells from H 2 O 2 by targeting Cul3. • miR-601 selectively targets cullin 3 (Cul3) and activates Nrf2 signaling in RPE cells. • miR-601 overexpression inhibits H 2 O 2 -induced oxidative injury in RPE cells • miR-601 inhibition suppresses Nrf2 signaling and enhances H 2 O 2 -induced cytotoxicity in RPE cells • Cul3-Keap1-Nrf2 cascade activation is required for miR-601-induced RPE cell protection against H 2 O 2 [ABSTRACT FROM AUTHOR]

Abstract Dysfunction of retinal pigment epithelial (RPE) cells has been associated with the pathogenesis of age-related macular degeneration in relation to increased oxidative stress, subsequent mitochondrial dysfunction and cell death. Permeability-glycoprotein (P-gp), encoded by the multidrug resistance 1 gene (MDR1), is an active efflux pump involved in cell homeostasis and nuclear factor κB (NF-κB) shows potential involvement in P-gp regulation due to its binding to the promoter domains of MDR1 gene. This study sought to determine the role of P-gp expression regulated by NF-κB in RPE cells during oxidative stress. The human RPE D407 cells were exposed to increasing concentrations of hydrogen peroxide (H 2 O 2) for 24 h. The small-interfering RNA (siRNA) transfection was used to down-regulate P-gp and NF-κB, and the expressions of P-gp and NF-κB p65 were determined by quantitative real-time PCR, western blot and immunofluorescence. The activity of NF-κB was detected by luciferase reporter assay. Mitochondrial membrane potential and cell death rate were detected by flow cytometry. We found that H 2 O 2 exposure caused increasing rate of cell death and induced an elevated expression of P-gp as well as NF-κB activation and nucleus translocation in D407 cells. Inhibiting or silencing NF-κB led to a decrease in the oxidative-induced expression of P-gp. Down-regulation of P-gp by siRNA transfection further impaired the mitochondrial membrane potential and cell death rate in oxidative cells. Moreover, inhibition/knockdown of NF-κB decreased the high rate of cell death caused by H 2 O 2. In conclusion, P-gp can provide moderate cytoprotection for the human RPE cells by ameliorating the mitochondrial dysfunction and NF-κB activation may be a potential regulator of P-gp expression response to oxidative stress. Highlights • Oxidative stress facilitates the expression of permeability-glycoprotein in human retinal pigment epithelium cells in vitro. • The over-expression of permeability-glycoprotein confers a limited cytoprotection against oxidative damage. • The NF-κB signaling pathway is involved in the oxidatively-induced up-regulation of permeability-glycoprotein. [ABSTRACT FROM AUTHOR]

Background/Aims: Microgravity (µg) has adverse effects on the eye of humans in space. The risk of visual impairment is therefore one of the leading health concerns for NASA. The impact of µg on human adult retinal epithelium (ARPE-19) cells is unknown. Methods: In this study we investigated the influence of simulated µg (s-µg; 5 and 10 days (d)), using a Random Positioning Machine (RPM), on ARPE-19 cells. We performed phase-contrast/fluorescent microscopy, qRT-PCR, Western blotting and pathway analysis. Results: Following RPM-exposure a subset of ARPE-19 cells formed multicellular spheroids (MCS), whereas the majority of the cells remained adherent (AD). After 5d, alterations of F-actin and fibronectin were observed which reverted after 10d-exposure, suggesting a time-dependent adaptation to s-µg. Gene expression analysis of 12 genes involved in cell structure, shape, adhesion, migration, and angiogenesis suggested significant changes after a 10d-RPM-exposure. 11 genes were down-regulated in AD and MCS 10d-RPM-samples compared to 1g, whereas FLK1 was up-regulated in 5d- and 10d-RPM-MCS-samples. Similarly, TIMP1 was up-regulated in 5d-RPM-samples, whereas the remaining genes were down-regulated in 5d-RPM-samples. Western blotting revealed similar changes in VEGF, β-actin, laminin and fibronectin of 5d-RPM-samples compared to 10d, whereas different alterations of β-tubulin and vimentin were observed. The pathway analysis showed complementing effects of VEGF and integrin β-1. Conclusions: These findings clearly show that s-µg induces significant alterations in the F-actin-cytoskeleton and cytoskeleton-related proteins of ARPE-19, in addition to changes in cell growth behavior and gene expression patterns involved in cell structure, growth, shape, migration, adhesion and angiogenesis.

Katarzyna Michalska-Małecka,1,2 Agnieszka Regucka,2 Dorota Śpiewak,2 Magdalena Sosnowska-Pońska,2 Alfred Niewiem2 1Department of Ophthalmology, School of Medicine in Katowice, Medical University of Silesia, Katowice, Poland; 2University Clinical Center, University Hospital Medical University of Silesia, Katowice, Poland Purpose: Acetylsalicylic acid (ASA) is one of the most commonly used drugs in the world due to its anti-inflammatory, analgesic, and antipyretic properties. This review aims to describe the relationship between acetylsalicylic acid and age-related macular degeneration (AMD) – a chronic disease that causes deterioration of visual acuity and is one of the most common ophthalmological diseases these days. Methods: Data presented in this review were collected from both research and review articles concerning ophthalmology and pharmacology. Results: The results of the studies analyzed in this review are not unambiguous. Moreover, the studies are not homogenous. They differed from one another in terms of the number of patients, the age criteria, the ASA dose, and the duration of control period. The reviewed studies revealed that ASA therapy, which is applied as a protection in cardiovascular diseases in patients with early forms of AMD and geographic atrophy, should not be discontinued. Conclusion: On the basis of the present studies, it cannot be unequivocally said whether ASA influences people’s vision and if people endangered with AMD progression or who are diagnosed with AMD should use this drug. It may increase the risk of AMD, but it can also reduce the risk of life-threatening conditions. The authors suggest that in order to avoid possible risks of AMD development, people who frequently take ASA should have their vision checked regularly. Keywords: acetylsalicylic acid, AMD, lipofuscin genesis, drusen genesis, retinal pigment epithelium cells, geographic atrophy

Age-related macular degeneration (AMD) is a progressive eye disease that causes irreversible impairment of central vision, and effective treatment is not yet available. Extracellular accumulation of amyloid-beta (Aβ) in drusen that lie under the retinal pigment epithelium (RPE) has been reported as one of the early signs of AMD and was found in more than 60% of Alzheimer’s disease (AD) patients. Extracellular deposition of Aβ can induce the expression of inflammatory cytokines such as IL-1β, TNF-α, COX-2, and iNOS in RPE cells. Thus, finding a compound that can effectively reduce the inflammatory response may help the treatment of AMD. In this research, we investigated the anti-inflammatory effect of the coral-derived compound 4-(phenylsulfanyl) butan-2-one (4-PSB-2) on Aβ1-42 oligomer (oAβ1-42) added to the human adult retinal pigment epithelial cell line (ARPE-19). Our results demonstrated that 4-PSB-2 can decrease the elevated expressions of TNF-α, COX-2, and iNOS via NF-κB signaling in ARPE-19 cells treated with oAβ1-42 without causing any cytotoxicity or notable side effects. This study suggests that 4-PSB-2 is a promising drug candidate for attenuation of AMD.

Purpose: Age-related macular degeneration (AMD) is a major cause of blindness in the elderly, and the activation of the NACHT, LRR, and PYD domain-containing protein 3 (NLRP3) inflammasome is involved in AMD pathogenesis. We investigated whether photooxidative blue-light stimulation in retinal pigment epithelium (RPE) cells promotes exosome secretion and modulates the activity of the NLRP3 inflammasome in vitro. Methods: Exosomes were isolated from ARPE-19 cultures stimulated or not with blue-light photostimulation (488 nm). Isolated exosomes were characterized by transmission electron microscope and Western blot analyses. The contents of the NLRP3 inflammasome (IL-1β, IL-18, and caspase-1 as markers of the inflammasome) in exosomes were analyzed by Western blotting. After culture, IL-1β, IL-18, and caspase-1 in RPE cells were analyzed by both immunofluorescence and Western blotting. RT-PCR and Western blotting were conducted to assess the contents of NLRP3 in RPE cells. Results: Exosomes exhibited a typical characteristic morphology (cup-shaped) and size (diameter between 50 and 150 nm) in both groups. The exosome markers CD9, CD63, and CD81 were strongly present. After blue-light photostimulation, ARPE-19 cells were noted to release exosomes with higher levels of IL-1β, IL-18, and caspase-1 than those in the control group. The levels of IL-1β, IL-18, and caspase-1 in ARPE-19 cells were significantly enhanced when treated with stressed RPE exosomes. Additionally, the NLRP3 mRNA and protein levels were found to be markedly higher in the treated group than in the control group. Conclusions: Under photooxidative blue-light stimulation, RPE-derived exosomes may aggravate a potentially harmful oxidative response through the upregulation of the NLRP3 inflammasome. [ABSTRACT FROM AUTHOR]

Abstract AMP-activated protein kinase (AMPK) signaling activation can inhibit Ultra-violet (UV) radiation (UVR)-induced retinal pigment epithelium (RPE) cell injuries. LB-100 is a novel inhibitor of protein phosphatase 2A (PP2A), the AMPKα1 phosphatase. Here, our results demonstrated that LB-100 significantly inhibited UVR-induced viability reduction, cell death and apoptosis in established ARPE-19 cells and primary murine RPE cells. LB-100 activated AMPK, nicotinamide adenine dinucleotide phosphate (NADPH) and Nrf2 (NF-E2-related factor 2) signalings, inhibiting UVR-induced oxidative injuries and DNA damage in RPE cells. Conversely, AMPK inhibition, by AMPKα1-shRNA, -CRISPR/Cas9 knockout or -T172A mutation, almost blocked LB-100-induced RPE cytoprotection against UVR. Importantly, CRISPR/Cas9-mediated PP2A knockout mimicked and nullified LB-100-induced anti-UVR activity in RPE cells. Collectively, these results show that PP2A inhibition by LB-100 protects RPE cells from UVR via activation of AMPK signaling. Highlights • LB-100, the PP2A inhibitor, protects retinal pigment epithelium (RPE) cells from UVR. • LB-100 activates AMPK signaling, inhibiting UVR-induced oxidative injuries in RPE cells. • LB-100-induced RPE cytoprotection against UVR requires AMPK activation. • PP2A knockout mimics and nullifies LB-100-induced RPE cytoprotection against UVR. [ABSTRACT FROM AUTHOR]

Oxidative stress has been implicated in the progression of age-related macular degeneration (AMD). Treatment with antioxidants seems to delay progression of AMD. In this study, we suggested an antioxidant delivery system based on redox-sensitive liposome composed of phospholipids and a diselenide centered alkyl chain. Dynamic light scattering assessment indicated that the liposomes had an average size of 140 nm with a polydispersity index below 0.2. The percentage of encapsulation efficiency of the liposomes was calculated by high-performance liquid chromatography. The carriers were loaded with N-acetyl cysteine as a model antioxidant drug. We demonstrated responsiveness of the nanocarrier and its efficiency in drug delivery in an oxidative stress model of human embryonic stem cell-derived retinal pigment epithelial (hESC-RPE) cells. The modeled cells treated with diselenide containing liposomes loaded with 10 mM NAC, showed a better therapeutic effect with a cell metabolic activity of 90%, which was significantly higher compared to insensitive liposomes or NAC treated groups (P < 0.05). In addition, the expression of oxidative-sensitive gene markers in diselenide containing liposomes groups were improved. Our results demonstrated fabricated smart liposomes opens new opportunity for targeted treatment of retinal degeneration. [ABSTRACT FROM AUTHOR]

Ultra-violet (UV) radiation (UVR) to human retinas induces oxidative injury to the resident retinal pigment epithelium (RPE) cells. PF-06409577 a novel, potent and direct AMP-activated protein kinase (AMPK) activator. In ARPE-19 cells and primary murine RPE cells, PF-06409577 significantly inhibited UVR-induced viability reduction, cell death and apoptosis. PF-06409577 activated AMPK signaling in RPE cells by increasing AMPKα1-acetyl-CoA carboxylase phosphorylation and AMPK activity. AMPK inhibition, by AMPKα1-shRNA, -CRISPR/Cas9 knockout or -T172A dominant negative mutation, almost abolished PF-06409577-induced RPE cytoprotection against UVR. PF-06409577 enhanced nicotinamide adenine dinucleotide phosphate (NADPH) activity and expression levels of Nrf2-dependent genes in RPE cells. Furthermore, UVR-induced reactive oxygen species (ROS) production, lipid peroxidation and DNA damage were largely inhibited by the AMPK activator. In summary, PF-06409577 inhibits UVR-induced oxidative stress and RPE cell death by activating AMPK signaling. [ABSTRACT FROM AUTHOR]

Abstract: Nobiletin (3′,4′,5,6,7,8‐hexamethoxyflavone), a dietary polymethoxylated flavonoid found in Citrus fruits, has been reported to have antioxidant effect. However, the effect of nobiletin on human retinal pigment epithelium (RPE) cells induced by hydrogen peroxide (H2O2) is still unclear. Therefore, we investigated the protective effect of nobiletin against H2O2‐induced cell death in RPE cells. Our results demonstrated that nobiletin significantly increased cell viability from oxidative stress. Nobiletin inhibited H2O2‐induced ROS production and caspase‐3/7 activity in ARPE‐19 cells. Furthermore, nobiletin significantly increased Akt phosphorylation in ARPE‐19 cells exposed to H2O2. Meanwhile, LY294002, an inhibitor of PI3K/Akt, abolished the protective effect of nobiletin against H2O2‐induced decreased cell viability and increased caspase‐3/7 activity in ARPE‐19 cells. In summary, these data show that nobiletin protects RPE cells against oxidative stress through activation of the Akt‐signaling pathway. Thus, nobiletin should be an oxidant that attenuates the development of age‐related macular degeneration. [ABSTRACT FROM AUTHOR]

Hypoxia has been demonstrated to be a proangiogenic factor that induces vascular endothelial growth factor (VEGF) in retinal pigment epithelial (RPE) cells. Dickkopf2 (DKK2), originally known as Wnt antagonist, has recently been demonstrated to have an important regulatory role in angiogenesis; however, the specific role of DKK2 in RPE cells is not known. In the present study, the effects of DKK2 on VEGF expression under hypoxic conditions were investigated, as well as the molecular mechanisms involved. The results demonstrated that the expression of DKK2 was markedly increased under hypoxic conditions compared with normoxic conditions. Knockdown of DKK2 markedly attenuated the CoCl2‑induced expression of hypoxia‑inducible factor (HIF)‑1α and VEGF in RPE cells. Furthermore, knockdown of DKK2 markedly inhibited the expression of β‑catenin induced by hypoxia. In conclusion, the findings of the present study demonstrate that knockdown of DKK2 inhibits the hypoxia‑induced production of VEGF by suppressing the activation of the Wnt/β‑catenin signaling pathway. [ABSTRACT FROM AUTHOR]

Transforming growth factor (TGF)‑β2‑induced epithelial‑mesenchymal transition (EMT) in human retinal pigment epithelium (RPE) cells has an important role in the pathophysiology of intraocular fibrotic disorders, which may cause vision impairment and blindness. Autophagy, an intracellular homeostatic pathway, contributes to the physiological and pathological processes of RPE. Furthermore, autophagy has previously been reported to function in the EMT process in numerous tissue and cell types. However, the association between autophagy and the EMT process in RPE cells has not yet been fully determined. The present study demonstrated that TGF‑β2‑treated human RPE cells (ARPE‑19 cell line) exhibited a significantly increased autophagic flux compared with control cells, as determined by western blot analysis of the protein levels of microtubule‑associated protein 1 light chain 3‑II and p62 (also termed sequestosome 1). Furthermore, it was demonstrated that autophagy activation enhanced the TGF‑β2‑induced EMT process in ARPE‑19 cells, and inhibition of autophagy by chloroquine administration attenuated TGF‑β2‑induced EMT, which was determined by analyzing the expression of mesenchymal and epithelial markers by reverse transcription‑quantitative polymerase chain reaction and/or western blotting. A transwell migration and invasion assays was also performed that demonstrated that autophagy activation by rapamycin enhanced TGF‑β2‑stimulated RPE cell migration and invasion, and inhibition of autophagy reduced TGF‑β2‑stimulated RPE cell migration and invasion. These results also demonstrated that autophagy activation enhanced the TGF‑β2‑induced EMT process in ARPE‑19 cells, and inhibition of autophagy attenuated TGF‑β2‑induced EMT. Overall, the results of the present study demonstrated that TGF‑β2‑induced EMT may be regulated by autophagy, thus indicating that autophagy may serve as a potential therapeutic target for the attenuation of EMT in intraocular fibrotic disorders. [ABSTRACT FROM AUTHOR]

Pyroptosis of retinal pigment epithelium (RPE) cells is associated with the etiology of diabetic retinopathy (DR). In this study, we investigated the effect of DNMT1 on RPE cell pyroptosis by regulating miR-20a/TXNIP expression through DNA methylation. High glucose (HG)-induced ARPE-19 cells and mice were injected with streptozotocin (STZ) to generate DR cells and animal models. RT‒qPCR was used to detect the expression of miR-20a, and methylation-specific PCR (MS-PCR) was used to determine the occurrence of methylation of miR-20a. The expression of pyroptosis-related proteins (caspase-1 and NLRP3) and DNA methyltransferase (DNMT1) was detected by western blotting, and the expression of inflammatory factors (IL-1β and IL-18) was detected by ELISA. Apoptosis was detected by flow cytometry and TUNEL. HE staining was used to observe the pathological changes in retinal tissue in mice. In HG-induced DR cell models, the expression of miR-20a was significantly downregulated, while the expression of inflammatory factors (IL-1β, IL-18) and pyroptosis-associated proteins (caspase-1, NLRP3) was significantly upregulated. Transfection of miR-20a mimic can effectively reverse HG-induced pyroptosis and release of inflammatory factors. DNMT1 promotes miR-20a methylation and inhibits the expression of miR-20a. DNMT1-mediated methylation is involved in the pyroptosis process of high glucose-induced RPE cells, and silencing DNMT1 can promote the expression of miR-20a, thereby inhibiting the release of IL-1β and IL-18 and reducing the occurrence of cell pyroptosis. miR-20a targets negative regulation of TXNIP expression, and overexpression of TXNIP can effectively reverse the inhibitory effect of miR-20a on pyroptosis. The methylation inhibitor 5-AZ can inhibit the occurrence of pyroptosis and DR processes, while treatment with a miR-20a inhibitor or OE-TXNIP can reverse the effect of 5-AZ. DNMT1 promotes DNA methylation, decreases the expression of miR-20a and increases the expression of TXNIP, which ultimately leads to the occurrence of pyroptosis in RPE cells. • miR-20a inhibits hyperglycemia-induced pyrosis of retinal pigment epithelial cells. • DNMT1-mediated methylation is involved in the pyroptosis process of RPE cells. • DNMT1 promotes pyroptosis by mediating methylation of miR-20a. • miR-20a targets TXNIP to mediate pyroptosis in RPE cells. • DNMT1 affects the progression of diabetic retinopathy through miR-20a/TXNIP. [ABSTRACT FROM AUTHOR]

AIM: To investigate the effect of 17-allylamio-17-demethoxygeldanamycin(17-AAG), an heat shock protein 90(Hsp90)inhibitor, on the expression of integrin- linked kinase(ILK)induced by hypoxia in retinal pigment epithelium(RPE)cells.METHODS: RPE cells were cultured with 200μmol/L cobalt chloride(CoCl2)for 12 hours to imitate chemical hypoxia. Pretreatment of 17-AAG was 1 hour prior to hypoxic insult. Experiment was divided into hypoxic control group, Dimethyl sulfoxide(DMSO)control group and 17-AAG pretreatment group(0.01, 0.10, 0.50, 1.00, 5.00 and 10.00μmol/L). RT-PCR and Western blot analysis were used to examine the expression of ILK in cultured RPE cells.RESULTS: The density ratios of ILK mRNA and β-actin mRNA of hypoxic control group, DMSO control group and 17-AAG pretreatment groups were 1.32±0.04,1.29±0.03,0.93±0.06,0.70±0.05,0.53±0.03,0.44±0.04,0.32±0.04,0.30±0.03; and the density ratios of ILK protein and β-actin protein were 2.16±0.04, 2.13±0.04, 1.65±0.04, 1.13±0.05, 0.74±0.03, 0.41±0.06, 0.35±0.04, 0.35±0.03. The ILK expression in 17-AAG pretreated groups were inhibited compared to hypoxic control group(P < 0.05), and the decrease was in concentration-dependent manner.CONCLUSION: Hsp90 inhibitor 17-AAG was effective to inhibit the expression of ILK induced by hypoxia in RPE cells.

Isorhamnetin, a 3-O-methylated metabolite of quercetin, exhibits antioxidant effects. However, to the best of our knowledge, no study to date has focused on the effects of isorhamnetin on retinal pigment epithelium (RPE) cells, and its underlying molecular mechanisms. Therefore, the present study aimed to examine the potential protective effect of isorhamnetin against oxidative stress in human RPE cells. The results demonstrated that pretreatment of RPE cells with isorhamnetin significantly protected cell viability against oxidative stress. In addition, isorhamnetin pretreatment inhibited hydrogen peroxide (H2O2)-induced reactive oxygen species (ROS) production and caspase-3 activation in RPE cells. Furthermore, isorhamnetin pretreatment significantly increased the phosphorylation of phosphoinositide 3-kinase (PI3K) and AKT serine/threonine kinase 1 (Akt) in RPE cells exposed to H2O2, compared with cells treated with H2O2 alone. Taken together, the present results demonstrated that isorhamnetin protected human RPE cells from oxidative stress-induced cell death, and this effect was associated with activation of the PI3K/Akt signaling pathway. Thus, isorhamnetin may be considered as a potential antioxidant useful for the prevention of age-related macular degeneration. [ABSTRACT FROM AUTHOR]

Acrylamide is a substance that can be neurotoxic in humans and experimental animals. It is formed at different rates in starchy foods cooked at temperatures above 120 °C as a result of interaction between monosaccharides and the amino acid asparagine. Carnosic acid accounts for over 90% of the antioxidant properties of rosemary extract and is a powerful inhibitor of lipid peroxidation in microsomal and liposomal systems. Carnosic acid has been shown to protect against oxidative and inflammatory effects. In order to investigate the protective properties of carnosic acid against acrylamide-induced toxicity in human retinal pigment epithelium (RPE) cells, ARPE-19 cells were pre-treated with 10 μM carnosic acid for 24 h followed by treatment with acrylamide (0.7 or 1 mM) for 24 h. ARPE-19 cells pre-treated with 10 μM carnosic acid showed significantly increased cell viability and decreased cell death rate when compared to ARPE-19 cells treated with acrylamide alone. Activities of SOD and catalase and the level of GSH and expression of NRF2 and a number of anti-oxidant genes were significantly decreased in ARPE-19 cells, while there were significant increases in ROS and MDA; pre-treatment with carnosic acid significantly counteracted these changes. Our results suggest that carnosic acid protected RPE cells from acrylamide-induced toxicity. [ABSTRACT FROM AUTHOR]

AIM: To study the effect of platelet derived growth factor ɑ receptor(PDGFR-ɑ)antibody on the rust-induced human retinal pigment epithelial cell(hRPE)proliferation. METHODS: In vitro rust hRPE cells proliferation differentiation model was established. Blank control group, rust group, PDGFR-ɑ antibody(1, 10, 50, and 100μg/mL)treatment group were established. The effect of anti-PDGFR-ɑ antibody on the growth of RPE was determined by MTT colorimetric assay after 0, 12, 24, 48h,and the inhibition rates were calculated accordingly. RESULTS: After adding the anti-PDGFR-ɑ antibody, hRPE cells proliferation activity was decreased at certain concentration as the antibody concentration increased, and 50μg/mL anti-PDGFR-ɑ antibody was the optimum concentration to inhibit hRPE cells proliferation, the inhibitory rate of hRPE was 42.44%.CONCLUSION: The anti-PDGFR-ɑ antibody shows strong inhibitory effect on the growth of cultured hRPE.