Increased Expression of Tight Junctions in ARPE-19 Cells Under Endoplasmic Reticulum Stress

Molecular mechanism of ATF6 in unfolded protein response and its role in disease

Activating transcription factor 6 (ATF6), an important signaling molecule in unfolded protein response (UPR), plays a role in the pathogenesis of several diseases, including diseases such as congenital retinal disease, liver fibrosis and ankylosing spondylitis. After endoplasmic reticulum stress (ERS), ATF6 is activated after separation from binding immunoglobulin protein (GRP78/BiP) in the endoplasmic reticulum (ER) and transported to the Golgi apparatus to be hydrolyzed by site 1 and site 2 proteases into ATF6 fragments, which localize to the nucleus and regulate the transcription and expression of ERS-related genes. In these diseases, ERS leads to the activation of UPR, which ultimately lead to the occurrence and development of diseases by regulating the physiological state of cells through the ATF6 signaling pathway. Here, we discuss the evidence for the pathogenic importance of ATF6 signaling in different diseases and discuss preclinical results.

Baicalein, Baicalin, and Wogonin: Protective Effects against Ischemia-Induced Neurodegeneration in the Brain and Retina

Ischemia is a common pathological condition present in many neurodegenerative diseases, including ischemic stroke, retinal vascular occlusion, diabetic retinopathy, and glaucoma, threatening the sight and lives of millions of people globally. Ischemia can trigger excessive oxidative stress, inflammation, and vascular dysfunction, leading to the disruption of tissue homeostasis and, ultimately, cell death. Current therapies are very limited and have a narrow time window for effective treatment. Thus, there is an urgent need to develop more effective therapeutic options for ischemia-induced neural injuries. With emerging reports on the pharmacological properties of natural flavonoids, these compounds present potent antioxidative, anti-inflammatory, and antiapoptotic agents for the treatment of ischemic insults. Three major active flavonoids, baicalein, baicalin, and wogonin, have been extracted from Scutellaria baicalensis Georgi (S. baicalensis); all of which are reported to have low cytotoxicity. They have been demonstrated to exert promising pharmacological capabilities in preventing cell and tissue damage. This review focuses on the therapeutic potentials of these flavonoids against ischemia-induced neurotoxicity and damage in the brain and retina. The bioactivity and bioavailability of baicalein, baicalin, and wogonin are also discussed. It is with hope that the therapeutic potential of these flavonoids can be utilized and developed as natural treatments for ischemia-induced injuries of the central nervous system (CNS).

Multiexon deletion alleles of ATF6 linked to achromatopsia

Achromatopsia (ACHM) is an autosomal recessive disease that results in severe visual loss. Symptoms of ACHM include impaired visual acuity, nystagmus, and photoaversion starting from infancy; furthermore, ACHM is associated with bilateral foveal hypoplasia and absent or severely reduced cone photoreceptor function on electroretinography. Here, we performed genetic sequencing in 3 patients from 2 families with ACHM, identifying and functionally characterizing 2 mutations in the activating transcription factor 6 (ATF6) gene. We identified a homozygous deletion covering exons 8-14 of the ATF6 gene from 2 siblings from the same family. In another patient from a different family, we identified a heterozygous deletion covering exons 2 and 3 of the ATF6 gene found in trans with a previously identified ATF6 c.970C>T (p.Arg324Cys) ACHM disease allele. Recombinant ATF6 proteins bearing these exon deletions showed markedly impaired transcriptional activity by qPCR and RNA-Seq analysis compared with WT-ATF6. Finally, RNAscope revealed that ATF6 and the related ATF6B transcripts were expressed in cones as well as in all retinal layers in normal human retina. Overall, our data identify loss-of-function ATF6 disease alleles that cause human foveal disease.

ER stress induced by ER calcium depletion and UVB irradiation regulates tight junction barrier integrity in human keratinocytes

BACKGROUND

Endoplasmic reticulum (ER) calcium depletion-induced ER stress is a crucial signal for keratinocyte differentiation and barrier homeostasis, but its effects on the epidermal tight junction (TJ) have not been characterized. Ultraviolet B (UVB) causes ER calcium release in keratinocytes and disrupts epidermal TJ, however, the involvement of ER stress in the UVB-induced TJ alterations remains unknown.

OBJECTIVES

To investigate the effect of ER stress by pharmacological ER calcium depletion or UVB on the TJ integrity in normal human epidermal keratinocytes (NHEK).

METHODS

NHEK were exposed to ER calcium pump inhibitor thapsigargin (Tg) or UVB. ER stress markers and TJ molecules expression, TJ and F-actin structures, and TJ barrier function were analyzed.

RESULTS

Tg or UVB exposure dose-dependently triggered unfolded protein response (UPR) in NHEK. Low dose Tg induced the IRE1α-XBP1 pathway and strengthened TJ barrier. Contrary, high dose Tg activated PERK phosphorylation and disrupted TJ by F-actin disorganization. UVB disrupted TJ and F-actin structures dose dependently. IRE1α RNase inhibition induced or exacerbated TJ and F-actin disruption in the presence of low dose Tg or UVB. High dose Tg increased RhoA activity. 4-PBA or Rho kinase (ROCK) inhibitor partially prevented the disruption of TJ and F-actin following high dose Tg or UVB.

CONCLUSIONS

ER stress has bimodal effects on the epidermal TJ depending on its intensity. The IRE1α pathway is critical for the maintenance of TJ integrity during mild ER stress. Severe ER stress-induced UPR or ROCK signalling mediates the disruption of TJ through cytoskeletal disorganization during severe ER stress.

Genome-wide mRNA profiling identifies RCAN1 and GADD45A as regulators of the transitional switch from survival to apoptosis during ER stress

Endoplasmic reticulum (ER) stress conditions promote a cellular adaptive mechanism called the unfolded protein response (UPR) that utilizes three stress sensors, inositol-requiring protein 1, protein kinase RNA-like ER kinase, and activating transcription factor 6. These sensors activate a number of pathways to reduce the stress and facilitate cell survival. While much is known about the mechanisms involved that modulate apoptosis during chronic stress, less is known about the transition between the prosurvival and proapoptotic factors that determine cell fate. Here, we employed a genetic screen that utilized three different pharmacological stressors to induce ER stress in a human-immortalized airway epithelial cell line, immortalized human bronchial epithelial cells. We followed the stress responses over an 18-h time course and utilized real-time monitoring of cell survival, next-generation sequencing, and quantitative real-time PCR to identify and validate genes that were upregulated with all three commonly employed ER stressors, inhibitor of calpain 1, tunicamycin, and thapsigargin. growth arrest and DNA damage-inducible alpha (GADD45A), a proapoptotic factor, and regulator of calcineurin 1 (RCAN1) mRNAs were identified and verified by showing that small interfering RNA (siRNA) knockdown of GADD45A decreased CCAAT-enhancer-binding protein homologous protein (a.k.a DDIT3), BCL2-binding component 3 (a.k.a. BBC3), and phorbol-12-myristate-13-acetate-induced protein 1 expression, 3 proapoptotic factors, and increased cell viability during ER stress conditions, whereas siRNA knockdown of RCAN1 dramatically decreased cell viability. These results suggest that the relative levels of these two genes regulate cell fate decisions during ER stress independent of the type of ER stressor.

δ Opioid Receptor Agonism Preserves the Retinal Pigmented Epithelial Cell Tight Junctions and Ameliorates the Retinopathy in Experimental Diabetes

Purpose

Outer blood retinal barrier breakdown is a neglected feature of diabetic retinopathy (DR). We demonstrated that the agonism of the δ opioid receptor (DOR) by epicatechin preserves the tight junction proteins in ARPE-19 cells under diabetic conditions. Presently, we aimed to evaluate the possible role of the DOR on the maintenance of tight junction of RPE layer and on the early markers of experimental DR.

Methods

DR markers and external retinal tight junction proteins were evaluated in CL57B diabetic mice submitted to intravitreous injection of short hairpin RNA (shRNA)-DOR (108 transducing units [TU]/mL) treated or not with DOR agonist (0.05 g/animal/d of epicatechin in drinking water) for 16 weeks. The presence of DOR in human retina from postmortem eyes from diabetic and nondiabetic donors were also performed.

Results

DOR is present in RPE layer and in neuro retina. The treatment with DOR agonist prevented the upregulation of the early markers of retinopathy (glial fibrillary acidic protein, VEGF) and the downregulation of pigment epithelium-derived factor, occludin, claudin-1, and zonula occludens-1 tight junction expressions. The silencing of DOR in retina of diabetic mice partially abolished the protective effects of epicatechin. In human retina specimens, DOR is present throughout the retina, similarly in nondiabetic and diabetic donors.

Conclusions

This set of experiments strongly indicates that the DOR agonism preserves RPE tight junctions and reduces the early markers of retinopathy in model of diabetes. These novel findings designate DOR as a potential therapeutic tool to treat DR with preservation of the RPE tight junction proteins.

Effects of concentration of amyloid β (Aβ) on viability of cultured retinal pigment epithelial cells

Background

Amyloid beta (Aβ) is a constituent of drusen that is a common sign of age-related macular degeneration (AMD). The purpose of this study was to investigate the effect of Aβ on human retinal pigment epithelial (RPE) cells in culture.

Methods

Cells from a human RPE cell line (ARPE-19) were exposed to 0 to 25 μM of Aβ 1–40 for 48 h, and the number of living cells was determined by WST-8 cleavage. Replicative DNA synthesis was measured by the incorporation of 5′-bromo-2′-deoxyuridine. The cell death pathway was investigated by the WST-8 cleavage assay after the addition of caspase-9 inhibitor, an anti-apoptotic factor. Real-time qRT-PCR was performed using Aβ-exposed cellular RNA to determine the level of vascular endothelial growth factor (VEGF)-A and pigment epithelium derived factor (PEDF). To determine the effect of receptor-for-advanced glycation end products (RAGE), the siRNA for RAGE was inserted into ARPE-19 treated with Aβ, and the levels of expression of VEGF-A and PEDF were determined.

Results

The number of living ARPE-19 cells was increased by exposure to 5 μM Aβ but was decreased by exposure to 25 μM of Aβ. Replicative DNA synthesis by ARPE-19 cells exposed to 25 μM of Aβ was significantly decreased indicating that 25 μM of Aβ inhibited cell proliferation. Real-time RT-PCR showed that the level of the mRNA of PEDF was increased by exposure to 5 μM Aβ, and the levels of the mRNAs of PEDF and VEGF-A were also increased by exposure to 25 μM Aβ. The addition of an inhibitor of caspase-9 blocked the decrease the number of ARPE-19 cells exposed to 25 μM Aβ. Exposure to si-RAGE attenuated the increase of VEGF-A and PEDF mRNA expression in ARPE-19 exposed to Aβ.

Conclusions

Exposure of ARPE-19 cells to low concentrations of Aβ increases the level of PEDF which then inhibits the apoptosis of ARPE-19 cells leading to RPE cell proliferation. Exposure to high concentrations of Aβ induces RPE cell death and enhances the expression of the mRNA of VEGF-A in RPE cells. The Aβ-RAGE pathway may lead to the expression VEGF-A and PEDF in RPE cells. These results suggest that Aβ is strongly related to the pathogenesis of choroidal neovascularization.

Role of oxidative stress in Retinitis pigmentosa: new involved pathways by an RNA-Seq analysis

Retinitis pigmentosa (RP) is a very heterogeneous inherited ocular disorder group characterized by progressive retinal disruption. Retinal pigment epithelium (RPE) degeneration, due to oxidative stress which arrests the metabolic support to photoreceptors, represents one of the principal causes of RP. Here, the role of oxidative stress in RP onset and progression was analyzed by a comparative whole transcriptome analysis of human RPE cells, treated with 100 µg/ml of oxLDL and untreated, at different time points. Experiment was thrice repeated and performed on Ion Proton^TM sequencing system. Data analysis, including low quality reads trimming and gene expression quantification, was realized by CLC Genomics Workbench software. The whole analysis highlighted 14 clustered "macro-pathways" and many sub-pathways, classified by selection of 5271 genes showing the highest alteration of expression. Among them, 23 genes were already known to be RP causative ones (15 over-expressed and 8 down-expressed), and their enrichment and intersection analyses highlighted new 77 candidate related genes (49 over-expressed and 28 down-expressed). A final filtering analysis then highlighted 29 proposed candidate genes. This data suggests that many new genes, not yet associated with RP, could influence its etiopathogenesis.

The cross-talk between autophagy and endoplasmic reticulum stress in blood-spinal cord barrier disruption after spinal cord injury

Spinal cord injury induces the disruption of blood-spinal cord barrier and triggers a complex array of tissue responses, including endoplasmic reticulum (ER) stress and autophagy. However, the roles of ER stress and autophagy in blood-spinal cord barrier disruption have not been discussed in acute spinal cord trauma. In the present study, we respectively detected the roles of ER stress and autophagy in blood-spinal cord barrier disruption after spinal cord injury. Besides, we also detected the cross-talking between autophagy and ER stress both in vivo and in vitro. ER stress inhibitor, 4-phenylbutyric acid, and autophagy inhibitor, chloroquine, were respectively or combinedly administrated in the model of acute spinal cord injury rats. At day 1 after spinal cord injury, blood-spinal cord barrier was disrupted and activation of ER stress and autophagy were involved in the rat model of trauma. Inhibition of ER stress by treating with 4-phenylbutyric acid decreased blood-spinal cord barrier permeability, prevented the loss of tight junction (TJ) proteins and reduced autophagy activation after spinal cord injury. On the contrary, inhibition of autophagy by treating with chloroquine exacerbated blood-spinal cord barrier permeability, promoted the loss of TJ proteins and enhanced ER stress after spinal cord injury. When 4-phenylbutyric acid and chloroquine were combinedly administrated in spinal cord injury rats, chloroquine abolished the blood-spinal cord barrier protective effect of 4-phenylbutyric acid by exacerbating ER stress after spinal cord injury, indicating that the cross-talking between autophagy and ER stress may play a central role on blood-spinal cord barrier integrity in acute spinal cord injury. The present study illustrates that ER stress induced by spinal cord injury plays a detrimental role on blood-spinal cord barrier integrity, on the contrary, autophagy induced by spinal cord injury plays a furthersome role in blood-spinal cord barrier integrity in acute spinal cord injury.

A compartmentalized microfluidic chip with crisscross microgrooves and electrophysiological electrodes for modeling the blood-retinal barrier

The interconnection of different tissue-tissue interfaces may extend organ-on-chips to a new generation of sophisticated models capable of recapitulating more complex organ-level functions. Single interfaces are largely recreated in organ-on-chips by culturing the cells on opposite sides of a porous membrane that splits a chamber in two or by connecting the cells of two adjacent compartments through microchannels. However, it is difficult to interconnect more than one interface using these approaches. To address this challenge, we present a novel microfluidic device where cells are arranged in parallel compartments and are highly interconnected through a grid of microgrooves, which facilitates paracrine signaling and heterotypic cell-cell contact between multiple tissues. In addition, the device includes electrodes on the substrate for the measurement of transepithelial electrical resistance (TEER). Unlike conventional methods for measuring the TEER where electrodes are on each side of the cell barrier, a method with only electrodes on the substrate has been validated. As a proof-of-concept, we have used the device to mimic the structure of the blood-retinal barrier by co-culturing primary human retinal endothelial cells (HREC), a human neuroblastoma cell line (SH-SY5Y), and a human retinal pigment epithelial cell line (ARPE-19). Cell barrier formations were assessed by a permeability assay, TEER measurements, and ZO-1 expression. These results validate the proposed microfluidic device with microgrooves as a promising in vitro tool for the compartmentalization and monitoring of barrier tissues.

The Role of IRE-XBP1 Pathway in Regulation of Retinal Pigment Epithelium Tight Junctions

Purpose

The retinal pigment epithelium (RPE) tight junctions play a pivotal role in maintaining the homeostatic environment of the neural retina. Herein, we investigated the role of X-box binding protein 1 (XBP1), an endoplasmic reticulum (ER) stress-responsive transcription factor, in regulation of RPE tight junctions.

Methods

Human RPE cell line (ARPE-19) and primary primate RPE cells were used for in vitro experiments and RPE-specific XBP1 knockout (KO) mice were used for in vivo study. Endoplasmic reticulum stress was induced by a sublethal dose of thapsigargin or tunicamycin. XBP1 activation was manipulated by IRE inhibitor 4μ8C, which suppresses XBP1 mRNA splicing. The integrity of tight junctions and the involvement of calcium-dependent RhoA/Rho kinase pathway were examined.

Results

Induction of ER stress by thapsigargin, but not tunicamycin, disrupted RPE tight junctions in ARPE-19 cells. Inhibition of XBP1 activation by 4μ8C resulted in a remarkable downregulation of tight junction proteins (ZO-1 and occludin) and defects in tight junction formation in the presence or absence of ER stress inducers. Overexpression of active XBP1 partially reversed 4μ8C-induced anomalies in tight junctions. Mechanistically, XBP1 inhibition resulted in increased intracellular Ca2+ concentration, upregulation of RhoA expression, redistribution of F-actin, and tight junction damage, which was attenuated by Rho kinase inhibitor Y27632. In vivo, deletion of XBP1 in the RPE resulted in defective RPE tight junctions accompanied by increased VEGF expression.

Conclusions

Taken together, these results suggest a protective role of XBP1 in maintaining RPE tight junctions possibly through regulation of calcium-dependent RhoA/Rho kinase signaling and actin cytoskeletal reorganization.

Hydroxychloroquine for treatment of rheumatoid arthritis: multifocal electroretinogram and laser flare-cell photometry study

Purpose

To evaluate early changes in multifocal electroretinogram (mfERG) and subclinical aqueous humor flare and cellularity in patients receiving hydroxychloroquine (HCQ) as treatment for rheumatoid arthritis.

Methods

Ten patients receiving treatment with HCQ and no ophthalmic symptoms were enrolled. After complete ocular examination, mfERG and laser flare-cell photometry were performed. Patients were also divided into two subgroups with HCQ cumulative dose (CD) higher or lower than 500 g. Results obtained were compared with a control group of ten healthy subjects and statistical analysis was performed.

Results

In patients receiving HCQ treatment, mfERG P1-wave in ring 2 showed a significant reduction in amplitude and a significant increase in latency compared to healthy control subjects, respectively resulting in 1.143 μV vs 1.316 μV (P=0.040) and 38.611 ms vs 36.334 ms (P=0.024). These changes are highly related to CD. Furthermore, when using the laser flare-cell photometry, a significant increase in aqueous humor flare and cellularity was shown in patients with CD higher than 500 g, resulting in a mean value of 14.4 ph/ms compared to 8.1 ph/ms in patients with CD lower than 500 g (P=0.0029). These reports appear highly related to CD (P=0.001). Receiver operating characteristic curve analysis showed mfERG P1-wave amplitude in ring 2 as the most sensitive value in detecting early HCQ-related retinopathy.

Conclusion

MfERG was shown to be a very sensitive test in detecting early retinal toxicity and should be used for the screening of patients receiving HCQ treatment. Although less sensitive, laser flare-cell photometry can provide further information to evaluate early toxic retinal cell damage.

Wogonin protects human retinal pigment epithelium cells from LPS-induced barrier dysfunction and inflammatory responses by regulating the TLR4/NF-κB signaling pathway

Inflammation in the retinal pigment epithelium is an important contributor to the pathogenesis of age-related macular degeneration. Wogonin is a flavonoid isolated from the root of Scutellaria baicalensis and has multiple pharmacological effects, including anti‑inflammatory effects. The present study sought to determine if the pharmacological effects of wogonin were relevant to the treatment of AMD. ARPE‑19 cells were pre‑conditioned with different concentrations of wogonin (0‑50 µM) prior to induction of inflammation with LPS (2 µg/ml). Transepithelial electrical resistance analysis demonstrated that 24 h treatment with 10 and 50 µM wogonin ameliorated LPS‑induced changes. Reverse transcription-quantitative polymerase chain reaction (RT‑qPCR) and immunofluorescence analyses revealed that wogonin restrained LPS-induced tight junction proteins, claudin‑1 and ZO‑1. LPS‑induced upregulation of inflammatory mediators in ARPE‑19 cells, including IL‑1β, IL‑6, IL‑8, cyclooxygenase‑2 (COX‑2), inducible nitric oxide synthase (iNOS) and TNF‑α was reduced after pre-treatment with wogonin. In addition, RT‑qPCR and western blotting demonstrated that wogonin inhibited the expression of TLR4 in LPS‑stimulated ARPE‑19 cells. This is a novel mechanism indicating that pre‑treatment with wogonin could attenuate the TLR4/NF‑κB‑mediated inflammatory response in LPS‑stimulated ARPE‑19 cells, and thus could be a potential therapy for the treatment of AMD.

Proteomic Analysis Revealed the Important Role of Vimentin in Human Cervical Carcinoma HeLa Cells Treated With Gambogic Acid

Gambogic acid (GA) is an anticancer agent in phase IIb clinical trial in China. In HeLa cells, GA inhibited cell proliferation, induced cell cycle arrest at G2/M phase and apoptosis, as showed by results of MTT assay and flow cytometric analysis. Possible target-related proteins of GA were searched using comparative proteomic analysis (2-DE) and nine proteins at early (3 h) stage together with nine proteins at late (24 h) stage were found. Vimentin was the only target-related protein found at both early and late stage. Results of both 2-DE analysis and Western blotting assay suggested cleavage of vimentin induced by GA. MS/MS analysis of cleaved vimentin peptides indicated possible cleavage sites of vimentin at or near ser51 and glu425. Results of targeted proteomic analysis showed that GA induced change in phosphorylation state of the vimentin head domain (aa51-64). Caspase inhibitors could not abrogate GA-induced cleavage of vimentin. Over-expression of vimentin ameliorated cytotoxicity of GA in HeLa cells. The GA-activated signal transduction, from p38 MAPK, heat shock protein 27 (HSP27), vimentin, dysfunction of cytoskeleton, to cell death, was predicted and then confirmed. Results of animal study showed that GA treatment inhibited tumor growth in HeLa tumor-bearing mice and cleavage of vimentin could be observed in tumor xenografts of GA-treated animals. Results of immunohistochemical staining also showed down-regulated vimentin level in tumor xenografts of GA-treated animals. Furthermore, compared with cytotoxicity of GA in HeLa cells, cytotoxicity of GA in MCF-7 cells with low level of vimentin was weaker whereas cytotoxicity of GA in MG-63 cells with high level of vimentin was stronger. These results indicated the important role of vimentin in the cytotoxicity of GA. The effects of GA on vimentin and other epithelial-to-mesenchymal transition (EMT) markers provided suggestion for better usage of GA in clinic.

Involvement of endoplasmic reticulum stress in optic nerve degeneration after chronic high intraocular pressure in DBA/2J mice

DBA/2J mice are one of several animal strains used for experimental models of both intraocular hypertension and glaucoma. This study investigates the relationship between endoplasmic reticulum (ER) stress and optic nerve degeneration in DBA/2J mice. Intraocular pressure (IOP) was measured in DBA/2J mice between the ages of 6 and 15 months. Optic nerve damage was assessed at 15 months of age. The nerve was immunostained with antibodies to either neurofilament heavy chain (NFH) or phosphorylated NFH (pNFH), and optic nerve damage was assessed by performing NFH- and pNFH-positive axon counts. Expression levels of the ER stress proteins 78-kDa glucose-regulated protein, also known as binding immunoglobulin protein, and C/EBP homologous protein were assayed with Western blotting. We also investigated ER stress localization in the optic nerve by double immunostaining with antibodies to ionized calcium-binding adaptor molecule 1, myelin basic protein, and glial fibrillary acidic protein (GFAP). In DBA/2J mice, IOP began to rise at 8 months of age, and retinal degeneration was detected at 15 months of age. DBA/2J mice had fewer axons than controls at 15 months of age. ER stress-related protein levels were higher in the optic nerves of DBA/2J mice and were colocalized with GFAP-positive astrocytes. Our findings suggest that ER stress plays a role in optic nerve degeneration during chronic ocular hypertension. Furthermore, ER stress may be related in some way to astrocyte activation.

Human retinal pigment epithelial cell proliferation by the combined stimulation of hydroquinone and advanced glycation end-products via up-regulation of VEGF gene

Although recent research showed that advanced glycation endproduct (AGE) and hydroquinone (HQ) are related to the pathogenesis of age-related macular degeneration (AMD), the mechanism how AGE and HQ induce or accelerate AMD remains elusive. In the present study, we examined the effects of AGE and HQ on changes of human retinal pigment epithelial (RPE) cell numbers and found that the viable cell numbers were markedly reduced by HQ by apoptosis and that AGE prevented the decreases of HQ-treated cell numbers by increased replicative DNA synthesis of RPE cells without changing apoptosis. Real-time RT-PCR revealed that vascular endothelial growth factor (VEGF)-A mRNA was increased by HQ treatment and the addition of HQ+AGE resulted in a further increment. The increase of VEGF secretion was confirmed by ELISA, and inhibition of VEGF signaling by chemical inhibitors and small interfering RNA decreased the HQ+AGE-induced increases in RPE cell numbers. The deletion analysis demonstrated that -102 to -43 region was essential for the VEGF-A promoter activation. Site-directed mutaions of specificity protein 1 (SP1) binding sequences in the VEGF-A promoter and RNA interference of SP1 revealed that SP1 is an essential transcription factor for VEGF-A expression. These results indicate that HQ induces RPE cell apoptosis, leading to dry AMD, and suggest that AGE stimulation in addition to HQ enhances VEGF-A transcription via the AGE-receptor for AGE pathway in HQ-damaged cells. As a result, the secreted VEGF acts as an autocrine/paracrine growth factor for RPE and/or adjacent vascular cells, causing wet AMD.

Mutation of ATF6 causes autosomal recessive achromatopsia

Achromatopsia (ACHM) is an early-onset retinal dystrophy characterized by photophobia, nystagmus, color blindness and severely reduced visual acuity. Currently mutations in five genes CNGA3, CNGB3, GNAT2, PDE6C and PDE6H have been implicated in ACHM. We performed homozygosity mapping and linkage analysis in a consanguineous Pakistani ACHM family and mapped the locus to a 15.12-Mb region on chromosome 1q23.1-q24.3 with a maximum LOD score of 3.6. A DNA sample from an affected family member underwent exome sequencing. Within the ATF6 gene, a single-base insertion variant c.355_356dupG (p.Glu119Glyfs*8) was identified, which completely segregates with the ACHM phenotype within the family. The frameshift variant was absent in public variant databases, in 130 exomes from unrelated Pakistani individuals, and in 235 ethnically matched controls. The variant is predicted to result in a truncated protein that lacks the DNA binding and transmembrane domains and therefore affects the function of ATF6 as a transcription factor that initiates the unfolded protein response during endoplasmic reticulum (ER) stress. Immunolabeling with anti-ATF6 antibodies showed localization throughout the mouse neuronal retina, including retinal pigment epithelium, photoreceptor cells, inner nuclear layer, inner and outer plexiform layers, with a more prominent signal in retinal ganglion cells. In contrast to cytoplasmic expression of wild-type protein, in heterologous cells ATF6 protein with the p.Glu119Glyfs*8 variant is mainly confined to the nucleus. Our results imply that response to ER stress as mediated by the ATF6 pathway is essential for color vision in humans.

MicroRNAs are essential for differentiation of the retinal pigmented epithelium and maturation of adjacent photoreceptors

Dysfunction of the retinal pigmented epithelium (RPE) results in degeneration of photoreceptors and vision loss and is correlated with common blinding disorders in humans. Although many protein-coding genes are known to be expressed in RPE and are important for its development and maintenance, virtually nothing is known about the in vivo roles of non-coding transcripts. The expression patterns of microRNAs (miRNAs) have been analyzed in a variety of ocular tissues, and a few were implicated to play role in RPE based on studies in cell lines. Here, through RPE-specific conditional mutagenesis of Dicer1 or Dgcr8 in mice, the importance of miRNAs for RPE differentiation was uncovered. miRNAs were found to be dispensable for maintaining RPE fate and survival, and yet they are essential for the acquisition of important RPE properties such as the expression of genes involved in the visual cycle pathway, pigmentation and cell adhesion. Importantly, miRNAs of the RPE are required for maturation of adjacent photoreceptors, specifically for the morphogenesis of the outer segments. The alterations in the miRNA and mRNA profiles in the Dicer1-deficient RPE point to a key role of miR-204 in regulation of the RPE differentiation program in vivo and uncover the importance of additional novel RPE miRNAs. This study reveals the combined regulatory activity of miRNAs that is required for RPE differentiation and for the development of the adjacent neuroretina.

Neutral sphingomyelinase inhibition decreases ER stress-mediated apoptosis and inducible nitric oxide synthase in retinal pigment epithelial cells

Endoplasmic reticulum (ER) stress and excessive nitric oxide production via the induction of inducible nitric oxide synthase (NOS2) have been implicated in the pathogenesis of ocular diseases characterized by retinal degeneration. Previous studies have revealed the sphingomyelinase/ceramide pathway in the regulation of NOS2 induction. Thus, the objective of this study was to determine the activity of the sphingomyelinase/ceramide pathway, assess nitric oxide production, and examine apoptosis in human retinal pigment epithelial (RPE) cells undergoing ER stress. Sphingomyelinase (SMase) activity; nuclear factor κB (NF-κB) activation; NOS2, nitrite/nitrate, and nitrotyrosine levels; and apoptosis were determined in cultured human RPE cell lines subjected to ER stress via exposure to tunicamycin. Induction of ER stress was confirmed by increased intracellular levels of ER stress markers including phosphorylated PKR-like ER kinase, C/EBP-homologous protein, and 78-kDa glucose-regulated protein. ER stress increased nuclear translocation of NF-κB, NOS2 expression, nitrite/nitrate levels, and nitrotyrosine formation and caused apoptosis in RPE cell lines. Inhibition of neutral SMase (N-SMase) activity via GW 4869 treatment caused a significant reduction in nuclear translocation of NF-κB, NOS2 expression, nitrite/nitrate levels, nitrotyrosine formation, and apoptosis in ER-stressed RPE cells. In conclusion, N-SMase inhibition reduced nitrative stress and apoptosis in RPE cells undergoing ER stress. Obtained data suggest that NOS2 can be regulated by N-SMase in RPE cells experiencing ER stress.

Ocular inflammation and endoplasmic reticulum stress are attenuated by supplementation with grape polyphenols in human retinal pigmented epithelium cells and in C57BL/6 mice

Inflammation and endoplasmic reticulum (ER) stress are common denominators for vision-threatening diseases such as diabetic retinopathy and age-related macular degeneration. Based on our previous study, supplementation with muscadine grape polyphenols (MGPs) alleviated systemic insulin resistance and proinflammatory responses. In this study, we hypothesized that MGPs would also be effective in attenuating ocular inflammation and ER stress. We tested this hypothesis using the human retinal pigmented epithelium (ARPE-19) cells and C57BL/6 mice. In ARPE-19 cells, tumor necrosis factor-α-induced proinflammatory gene expression of interleukin (IL)-1β, IL-6, and monocyte chemotactic protein-1 was decreased by 35.0%, 68.8%, and 62.5%, respectively, with MGP pretreatment, which was primarily due to the diminished mitogen-activated protein kinase activation and subsequent reduction of nuclear factor κ-B activation. Consistently, acute ocular inflammation and leukocyte infiltration were almost completely dampened (>95%) by MGP supplementation (100-200 mg/kg body weight) in C57BL/6 mice. Moreover, MGPs reduced inflammation-mediated loss of tight junctions and retinal permeability. To further investigate the protective roles of MGPs against ER stress, ARPE-19 cells were stimulated with thapsigargin. Pretreatment with MGPs significantly decreased the following: 1) ER stress-mediated vascular endothelial growth factor secretion (3.47 ± 0.06 vs. 1.58 ± 0.02 μg/L, P < 0.0001), 2) unfolded protein response, and 3) early apoptotic cell death (64.4 ± 6.85 vs. 33.7 ± 4.32%, P = 0.0003). Collectively, we have demonstrated that MGP is effective in attenuating ocular inflammation and ER stress. Our work also suggests that MGP may provide a novel dietary strategy to prevent vision-threatening retinal diseases.

Regulation of claudins in blood-tissue barriers under physiological and pathological states

Claudins are pivotal building blocks of tight junctions that form the paracellular barrier in epithelia and endothelia. In mammals, claudins are a 27-gene family that encodes tetraspan membrane proteins, playing a crucial role in the formation and integrity of tight junctions and regulate the barrier function. Claudin isoforms are expressed in a tissue- and/or developmental stage-dependent manner. A growing body of evidence indicates that pathological states characterized by neuroinflammation, such as Alzheimer disease, multiple sclerosis, diabetic retinopathy and retinopathy of prematurity share a common feature: the barrier breakdown. This review aims integrating and summarizing the most relevant and recent work developed in the field of claudins, with particular attention to their role in blood-brain and blood-retinal barriers, as well as describing their regulation in the aforementioned human diseases.

The vasculome of the mouse brain

The blood vessel is no longer viewed as passive plumbing for the brain. Increasingly, experimental and clinical findings suggest that cerebral endothelium may possess endocrine and paracrine properties – actively releasing signals into and receiving signals from the neuronal parenchyma. Hence, metabolically perturbed microvessels may contribute to central nervous system (CNS) injury and disease. Furthermore, cerebral endothelium can serve as sensors and integrators of CNS dysfunction, releasing measurable biomarkers into the circulating bloodstream. Here, we define and analyze the concept of a brain vasculome, i.e. a database of gene expression patterns in cerebral endothelium that can be linked to other databases and systems of CNS mediators and markers. Endothelial cells were purified from mouse brain, heart and kidney glomeruli. Total RNA were extracted and profiled on Affymetrix mouse 430 2.0 micro-arrays. Gene expression analysis confirmed that these brain, heart and glomerular preparations were not contaminated by brain cells (astrocytes, oligodendrocytes, or neurons), cardiomyocytes or kidney tubular cells respectively. Comparison of the vasculome between brain, heart and kidney glomeruli showed that endothelial gene expression patterns were highly organ-dependent. Analysis of the brain vasculome demonstrated that many functionally active networks were present, including cell adhesion, transporter activity, plasma membrane, leukocyte transmigration, Wnt signaling pathways and angiogenesis. Analysis of representative genome-wide-association-studies showed that genes linked with Alzheimer’s disease, Parkinson’s disease and stroke were detected in the brain vasculome. Finally, comparison of our mouse brain vasculome with representative plasma protein databases demonstrated significant overlap, suggesting that the vasculome may be an important source of circulating signals in blood. Perturbations in cerebral endothelial function may profoundly affect CNS homeostasis. Mapping and dissecting the vasculome of the brain in health and disease may provide a novel database for investigating disease mechanisms, assessing therapeutic targets and exploring new biomarkers for the CNS.