scholarly journals Phosphoinositide Lipids in Ocular Tissues

Biology ◽  
2020 ◽  
Vol 9 (6) ◽  
pp. 125 ◽  
Author(s):  
Ammaji Rajala ◽  
Austin McCauley ◽  
Richard S. Brush ◽  
Khuong Nguyen ◽  
Raju V.S. Rajala
Keyword(s):  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Retinal Disease ◽  
Cell Physiology ◽  
Phosphoinositide Metabolism ◽  
Cellular Functions ◽  
Ocular Tissues ◽  
Head Groups ◽  
Inositol Phospholipids ◽  
Nuclear Events

Inositol phospholipids play an important role in cell physiology. The inositol head groups are reversibly phosphorylated to produce seven distinct phosphorylated inositides, commonly referred to as phosphoinositides (PIs). These seven PIs are dynamically interconverted from one PI to another by the action of PI kinases and PI phosphatases. The PI signals regulate a wide variety of cellular functions, including organelle distinction, vesicular transport, cytoskeletal organization, nuclear events, regulation of ion channels, cell signaling, and host–pathogen interactions. Most of the studies of PIs in ocular tissues are based on the PI enzymes and PI phosphatases. In this study, we examined the PI levels in the cornea, retinal pigment epithelium (RPE), and retina using PI-binding protein as probes. We have examined the lipids PI(3)P, PI(4)P, PI(3,4)P2, PI(4,5)P2, and PI(3,4,5)P3, and each is present in the cornea, RPE, and retina. Alterations in the levels of these PIs in mouse models of retinal disease and corneal infections have been reported, and the results of our study will help in the management of anomalous phosphoinositide metabolism in ocular tissues.

scholarly journals Loss of melanoregulin (MREG) enhances cathepsin-D secretion by the retinal pigment epithelium

2013 ◽  
Vol 30 (3) ◽  
pp. 55-64 ◽  
Author(s):  
LAURA S. FROST ◽  
VANDA S. LOPES ◽  
FRANK P. STEFANO ◽  
ALVINA BRAGIN ◽  
DAVID S. WILLIAMS ◽  
...  
Keyword(s):  
Retinal Pigment Epithelium ◽  
Cathepsin D ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Retinal Disease ◽  
Protective Role ◽  
Phagocytic Cells ◽  
Phagocytic Capacity ◽  
Photoreceptor Outer Segments ◽  
Age Dependent

AbstractCathepsin-D (Cat-D) is a major proteolytic enzyme in phagocytic cells. In the retinal pigment epithelium (RPE), it is responsible for the daily degradation of photoreceptor outer segments (POSs) to maintain retinal homeostasis. Melanoregulin (MREG)-mediated loss of phagocytic capacity has been linked to diminished intracellular Cat-D activity. Here, we demonstrate that loss of MREG enhances the secretion of intermediate Cat-D (48 kDa), resulting in a net enhancement of extracellular Cat-D activity. These results suggest that MREG is required to maintain Cat-D homeostasis in the RPE and likely plays a protective role in retinal health. In this regard, in the Mregdsu/dsu mouse, we observe increased basal laminin. Loss of the Mregdsu allele is not lethal and therefore leads to slow age-dependent changes in the RPE. Thus, we propose that this model will allow us to study potential dysregulatory functions of Cat-D in retinal disease.

scholarly journals PRDX6 Protects ARPE-19 Cells from Oxidative Damage via PI3K/AKT Signaling

2015 ◽  
Vol 36 (6) ◽  
pp. 2217-2228 ◽  
Author(s):  
Xu Zha ◽  
Guojiu Wu ◽  
Xueying Zhao ◽  
Liqiong Zhou ◽  
Hong Zhang ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Oxidative Damage ◽  
Blue Light ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Annexin V ◽  
Retinal Disease ◽  
Akt Signaling ◽  
The Body ◽  
H2o2 Treatment

Background/Aims: Oxidative stress that damages cells of the retinal pigment epithelium (RPE) can cause the development of hereditary retinal disease (HRD). PRDX6, which is a member of the PRDX family, is essential for removing metabolic free radicals from the body. However, the effect of PRDX6 on oxidative stress in HRD remains unknown. In this study, we sought to investigate the role of PRDX6 in oxidative stress-induced HRD in ARPE-19 cells and the molecular mechanism involved. Methods: ARPE-19 cells were used in the current study. Intracellular ROS levels were determined by flow cytometry. Lipid peroxidation was measured using a commercial MDA assay kit. Cellular variability was determined by MTT assay. Apoptosis was determined using an Annexin V-FITC Apoptosis Detection Kit. mRNA and protein expression levels were detected by real-time PCR and western blot analysis, respectively. Results: We found that H2O2 and blue light could induce significant oxidative stress damage and cell death in ARPE-19 cells. Furthermore, we found that PRDX6 levels significantly decreased after H2O2 treatment. PRDX6 overexpression protected ARPE-19 cells from H2O2- and blue light-induced oxidative damage, while PRDX6 knockdown enhanced oxidative damage in these cells. Mechanistically, we found that PRDX6 prevented oxidative damage and promoted ARPE-19 cell survival through the PI3K/AKT signaling pathway. Conclusions: Collectively, these results suggest that PRDX6 protects ARPE-19 cells from H2O2-induced oxidative stress and apoptosis and that this protection is mediated at least partially through the PI3K/AKT pathway.

scholarly journals Light-Evoked Responses of the Retinal Pigment Epithelium: Changes Accompanying Photoreceptor Loss in the Mouse

2010 ◽  
Vol 104 (1) ◽  
pp. 391-402 ◽  
Author(s):  
Ivy S. Samuels ◽  
Gwen M. Sturgill ◽  
Gregory H. Grossman ◽  
Mary E. Rayborn ◽  
Joe G. Hollyfield ◽  
...  
Keyword(s):  
Retinal Pigment Epithelium ◽  
Structural Changes ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Retinal Disease ◽  
Rod Photoreceptor ◽  
Evoked Responses ◽  
Photoreceptor Degeneration ◽  
Rod Photoreceptors ◽  
Slow Piii

Mutations in genes expressed in the retinal pigment epithelium (RPE) underlie a number of human inherited retinal disorders that manifest with photoreceptor degeneration. Because light-evoked responses of the RPE are generated secondary to rod photoreceptor activity, RPE response reductions observed in human patients or animal models may simply reflect decreased photoreceptor input. The purpose of this study was to define how the electrophysiological characteristics of the RPE change when the complement of rod photoreceptors is decreased. To measure RPE function, we used an electroretinogram (dc-ERG)-based technique. We studied a slowly progressive mouse model of photoreceptor degeneration ( Prph Rd2/+), which was crossed onto a Nyxnob background to eliminate the b-wave and most other postreceptoral ERG components. On this background, Prph Rd2/+ mice display characteristic reductions in a-wave amplitude, which parallel those in slow PIII amplitude and the loss of rod photoreceptors. At 2 and 4 mo of age, the amplitude of each dc-ERG component (c-wave, fast oscillation, light peak, and off response) was larger in Prph Rd2/+ mice than predicted by rod photoreceptor activity (RmP3) or anatomical analysis. At 4 mo of age, the RPE in Prph Rd2/+ mice showed several structural abnormalities including vacuoles and swollen, hypertrophic cells. These data demonstrate that insights into RPE function can be gained despite a loss of photoreceptors and structural changes in RPE cells and, moreover, that RPE function can be evaluated in a broader range of mouse models of human retinal disease.

scholarly journals Biochemical adaptations of the retina and retinal pigment epithelium support a metabolic ecosystem in the vertebrate eye

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Mark A Kanow ◽  
Michelle M Giarmarco ◽  
Connor SR Jankowski ◽  
Kristine Tsantilas ◽  
Abbi L Engel ◽  
...  
Keyword(s):  
Retinal Pigment Epithelium ◽  
Metabolic Flux ◽  
Vision Loss ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Retinal Disease ◽  
Glucose Consumption ◽  
Age Related ◽  
Underlying Causes ◽  
Vertebrate Eye

Here we report multiple lines of evidence for a comprehensive model of energy metabolism in the vertebrate eye. Metabolic flux, locations of key enzymes, and our finding that glucose enters mouse and zebrafish retinas mostly through photoreceptors support a conceptually new model for retinal metabolism. In this model, glucose from the choroidal blood passes through the retinal pigment epithelium to the retina where photoreceptors convert it to lactate. Photoreceptors then export the lactate as fuel for the retinal pigment epithelium and for neighboring Müller glial cells. We used human retinal epithelial cells to show that lactate can suppress consumption of glucose by the retinal pigment epithelium. Suppression of glucose consumption in the retinal pigment epithelium can increase the amount of glucose that reaches the retina. This framework for understanding metabolic relationships in the vertebrate retina provides new insights into the underlying causes of retinal disease and age-related vision loss.

scholarly journals Bestrophin 1 is indispensable for volume regulation in human retinal pigment epithelium cells

2015 ◽  
Vol 112 (20) ◽  
pp. E2630-E2639 ◽  
Author(s):  
Andrea Milenkovic ◽  
Caroline Brandl ◽  
Vladimir M. Milenkovic ◽  
Thomas Jendryke ◽  
Lalida Sirianant ◽  
...  
Keyword(s):  
Retinal Pigment Epithelium ◽  
Volume Regulation ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Cell Swelling ◽  
Macular Dystrophy ◽  
Cell Physiology ◽  
Rpe Cells ◽  
Human Retinal Pigment Epithelium ◽  
Molecular Identity

In response to cell swelling, volume-regulated anion channels (VRACs) participate in a process known as regulatory volume decrease (RVD). Only recently, first insight into the molecular identity of mammalian VRACs was obtained by the discovery of the leucine-rich repeats containing 8A (LRRC8A) gene. Here, we show that bestrophin 1 (BEST1) but not LRRC8A is crucial for volume regulation in human retinal pigment epithelium (RPE) cells. Whole-cell patch-clamp recordings in RPE derived from human-induced pluripotent stem cells (hiPSC) exhibit an outwardly rectifying chloride current with characteristic functional properties of VRACs. This current is severely reduced in hiPSC-RPE cells derived from macular dystrophy patients with pathologic BEST1 mutations. Disruption of the orthologous mouse gene (Best1−/−) does not result in obvious retinal pathology but leads to a severe subfertility phenotype in agreement with minor endogenous expression of Best1 in murine RPE but highly abundant expression in mouse testis. Sperm from Best1−/− mice showed reduced motility and abnormal sperm morphology, indicating an inability in RVD. Together, our data suggest that the molecular identity of VRACs is more complex—that is, instead of a single ubiquitous channel, VRACs could be formed by cell type- or tissue-specific subunit composition. Our findings provide the basis to further examine VRAC diversity in normal and diseased cell physiology, which is key to exploring novel therapeutic approaches in VRAC-associated pathologies.

scholarly journals Hydroquinone Induces NLRP3-Independent IL-18 Release from ARPE-19 Cells

Cells ◽  
2021 ◽  
Vol 10 (6) ◽  
pp. 1405
Author(s):  
Niina Bhattarai ◽  
Eveliina Korhonen ◽  
Yashavanthi Mysore ◽  
Kai Kaarniranta ◽  
Anu Kauppinen
Keyword(s):  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Retinal Disease ◽  
Oxidase Inhibitor ◽  
Age Related Macular Degeneration ◽  
Rpe Cells ◽  
Pyrin Domain ◽  
Age Related ◽  
Domain 3 ◽  
Human Rpe Cells

Age-related macular degeneration (AMD) is a retinal disease leading to impaired vision. Cigarette smoke increases the risk for developing AMD by causing increased reactive oxygen species (ROS) production and damage in the retinal pigment epithelium (RPE). We have previously shown that the cigarette tar component hydroquinone causes oxidative stress in human RPE cells. In the present study, we investigated the propensity of hydroquinone to induce the secretion of interleukin (IL)-1β and IL-18. The activation of these cytokines is usually regulated by the Nucleotide-binding domain, Leucine-rich repeat, and Pyrin domain 3 (NLRP3) inflammasome. ARPE-19 cells were exposed to hydroquinone, and cell viability was monitored using the lactate dehydrogenase (LDH) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide salt (MTT) assays. Enzyme-linked immunosorbent assays (ELISAs) were used to measure the levels of proinflammatory cytokines IL-1β and IL-18 as well as NLRP3, caspase-1, and poly (ADP-ribose) polymerase (PARP). Hydroquinone did not change IL-1β release but significantly increased the secretion of IL-18. Cytoplasmic NLRP3 levels increased after the hydroquinone treatment of IL-1α-primed RPE cells, but IL-18 was equally released from primed and nonprimed cells. Hydroquinone reduced the intracellular levels of PARP, which were restored by treatment with the ROS scavenger N-acetyl-cysteine (NAC). NAC concurrently reduced the NLRP3 levels but had no effect on IL-18 release. In contrast, the NADPH oxidase inhibitor ammonium pyrrolidinedithiocarbamate (APDC) reduced the release of IL-18 but had no effect on the NLRP3 levels. Collectively, hydroquinone caused DNA damage seen as reduced intracellular PARP levels and induced NLRP3-independent IL-18 secretion in human RPE cells.

scholarly journals Cathepsin A activity of normal bovine ocular tissues and pathological human intraocular fluids.

1996 ◽  
Vol 43 (4) ◽  
pp. 687-692 ◽  
Author(s):  
I Obuchowska ◽  
A Stankiewicz ◽  
Z Mariak
Keyword(s):  
Retinal Pigment Epithelium ◽  
Aqueous Humor ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Metastatic Tumor ◽  
Vitreous Humor ◽  
Ph Optimum ◽  
Ocular Tissues ◽  
Intraocular Tumors ◽  
Bovine Ocular Tissues

Cathepsin A activity assayed with N-Cbz-Phe-Ala, N-Cbz-Glu-Tyr and N-Cbz-Glu-Phe as substrates, was measured in fresh corneas, lenses, aqueous humor, vitreous humor and choroid plus retinal pigment epithelium taken from normal bovine eye balls and in human intraocular fluids from the eye balls in various ocular diseases (cataract, glaucoma, diabetes, intraocular tumors). Cathepsin A exhibited a pH optimum at 5.0 and showed the highest specificity towards N-Cbz-Phe-Ala as a substrate. In bovine ocular tissues high cathepsin A activity was found in the choroid plus retinal pigment epithelium and in cornea. The lens and the vitreous humor showed low enzyme activity and the aqueous humor none at all. In the human aqueous humor of the eye with cataract cathepsin A activity was more than three times higher then in the eye with choroid tumor. In human vitreous humor in absolute glaucoma the activity was twice as high as in melanoma and almost three times higher than in the case of lung metastatic tumor. Diabetes in glaucoma increased seven fold cathepsin A activity in the vitreous humor.

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