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  1. Paraoan L, Sharif U, Carlsson E, Supharattanasitthi W, Mahmud NM, Kamalden TA, et al.
    Prog Retin Eye Res, 2020 11;79:100859.
    PMID: 32278708 DOI: 10.1016/j.preteyeres.2020.100859
    Secretory proteostasis integrates protein synthesis, processing, folding and trafficking pathways that are essential for efficient cellular secretion. For the retinal pigment epithelium (RPE), secretory proteostasis is of vital importance for the maintenance of the structural and functional integrity of apical (photoreceptors) and basal (Bruch's membrane/choroidal blood supply) sides of the environment it resides in. This integrity is achieved through functions governed by RPE secreted proteins, which include extracellular matrix modelling/remodelling, angiogenesis and immune response modulation. Impaired RPE secretory proteostasis affects not only the extracellular environment, but leads to intracellular protein aggregation and ER-stress with subsequent cell death. Ample recent evidence implicates dysregulated proteostasis as a key factor in the development of age-related macular degeneration (AMD), the leading cause of blindness in the developed world, and research aiming to characterise the roles of various proteins implicated in AMD-associated dysregulated proteostasis unveiled unexpected facets of the mechanisms involved in degenerative pathogenesis. This review analyses cellular processes unveiled by the study of the top 200 transcripts most abundantly expressed by the RPE/choroid in the light of the specialised secretory nature of the RPE. Functional roles of these proteins and the mechanisms of their impaired secretion, due to age and genetic-related causes, are analysed in relation to AMD development. Understanding the importance of RPE secretory proteostasis in relation to maintaining retinal health and how it becomes impaired in disease is of paramount importance for the development and assessment of future therapeutic advancements involving gene and cell therapies.
    Matched MeSH terms: Retinal Pigment Epithelium/metabolism*; Retinal Pigment Epithelium/pathology
  2. Mahendra CK, Tan LTH, Pusparajah P, Htar TT, Chuah LH, Lee VS, et al.
    Oxid Med Cell Longev, 2020;2020:1904178.
    PMID: 32855763 DOI: 10.1155/2020/1904178
    Retinal pigment epithelial (RPE) cells are an essential part of the human eye because they not only mediate and control the transfer of fluids and solutes but also protect the retina against photooxidative damage and renew photoreceptor cells through phagocytosis. However, their function necessitates cumulative exposure to the sun resulting in UV damage, which may lead to the development of age-related macular degeneration (AMD). Several studies have shown that UVB induces direct DNA damage and oxidative stress in RPE cells by increasing ROS and dysregulating endogenous antioxidants. Activation of different signaling pathways connected to inflammation, cell cycle arrest, and intrinsic apoptosis was reported as well. Besides that, essential functions like phagocytosis, osmoregulation, and water permeability of RPE cells were also affected. Although the melanin within RPE cells can act as a photoprotectant, this photoprotection decreases with age. Nevertheless, the changes in lens epithelium-derived growth factor (LEDGF) and autophagic activity or application of bioactive compounds from natural products can reverse the detrimental effect of UVB. Additionally, in vivo studies on the whole retina demonstrated that UVB irradiation induces gene and protein level dysregulation, indicating cellular stress and aberrations in the chromosome level. Morphological changes like retinal depigmentation and drusen formation were noted as well which is similar to the etiology of AMD, suggesting the connection of UVB damage with AMD. Therefore, future studies, which include mechanism studies via in vitro or in vivo and other potential bioactive compounds, should be pursued for a better understanding of the involvement of UVB in AMD.
    Matched MeSH terms: Retinal Pigment Epithelium/pathology; Retinal Pigment Epithelium/radiation effects*
  3. Wong JG, Lai XJ, Sarafian RY, Wong HS, Smith JB
    Retin Cases Brief Rep, 2016;10(3):221-4.
    PMID: 26509999 DOI: 10.1097/ICB.0000000000000233
    PURPOSE: Choroidal nevus is the most common ocular fundus tumor in adults. Previous studies have widely discussed the features of choroidal neovascularization secondary to nevus and its treatment options. Polypoidal choroidal vasculopathy (PCV) is an exudative chorioretinopathy that is often underdiagnosed. Clinical features, natural history, and treatment response of PCV are distinct from occult choroidal neovascularization. Polypoidal choroidal vasculopathy secondary to choroidal nevus has not been previously documented. We report a patient with a history of stable choroidal nevus who developed a polypoidal lesion at the edge of the nevus lesion.

    METHODS: A white woman who presented with a choroidal nevus and clinical features of PCV was examined using fundoscopy, optical coherence tomography, fluorescein angiography, and indocyanine green angiography.

    RESULTS: A polypoidal lesion with an associated branching vascular network adjacent to the nevus was demonstrated by optical coherence tomography, fluorescein angiography, and indocyanine green angiography. The patient was asymptomatic and was managed conservatively.

    CONCLUSION: Our case showed that PCV developing in association with a stable choroidal nevus. Pathogenic mechanisms of this condition may include chronic degenerative or inflammatory changes at the level of the retinal pigment epithelium resulting in vascular changes. Unlike treatment of occult choroidal neovascularization secondary to nevus, optimal management of PCV secondary to nevus may vary. Indocyanine green angiography is the gold standard for the diagnosis of PCV and is a useful investigation in atypical choroidal neovascularization.

    Matched MeSH terms: Retinal Pigment Epithelium/pathology
  4. Sharif U, Mahmud NM, Kay P, Yang YC, Harding SP, Grierson I, et al.
    J Cell Mol Med, 2019 01;23(1):405-416.
    PMID: 30338926 DOI: 10.1111/jcmm.13944
    The retinal pigment epithelium (RPE) plays a central role in neuroretinal homoeostasis throughout life. Altered proteolysis and inflammatory processes involving RPE contribute to the pathophysiology of age-related macular degeneration (AMD), but the link between these remains elusive. We report for the first time the effect of advanced glycation end products (AGE)-known to accumulate on the ageing RPE's underlying Bruch's membrane in situ-on both key lysosomal cathepsins and NF-κB signalling in RPE. Cathepsin L activity and NF-κB effector levels decreased significantly following 2-week AGE exposure. Chemical cathepsin L inhibition also decreased total p65 protein levels, indicating that AGE-related change of NF-κB effectors in RPE cells may be modulated by cathepsin L. However, upon TNFα stimulation, AGE-exposed cells had significantly higher ratio of phospho-p65(Ser536)/total p65 compared to non-AGEd controls, with an even higher fold increase than in the presence of cathepsin L inhibition alone. Increased proportion of active p65 indicates an AGE-related activation of NF-κB signalling in a higher proportion of cells and/or an enhanced response to TNFα. Thus, NF-κB signalling modulation in the AGEd environment, partially regulated via cathepsin L, is employed by RPE cells as a protective (para-inflammatory) mechanism but renders them more responsive to pro-inflammatory stimuli.
    Matched MeSH terms: Retinal Pigment Epithelium/metabolism*
  5. Alsaeedi HA, Koh AE, Lam C, Rashid MBA, Harun MHN, Saleh MFBM, et al.
    J. Photochem. Photobiol. B, Biol., 2019 Sep;198:111561.
    PMID: 31352000 DOI: 10.1016/j.jphotobiol.2019.111561
    Blindness and vision loss contribute to irreversible retinal degeneration, and cellular therapy for retinal cell replacement has the potential to treat individuals who have lost light sensitive photoreceptors in the retina. Retinal cells are well characterized in function, and are a subject of interest in cellular replacement therapy of photoreceptors and the retinal pigment epithelium. However, retinal cell transplantation is limited by various factors, including the choice of potential stem cell source that can show variability in plasticity as well as host tissue integration. Dental pulp is one such source that contains an abundance of stem cells. In this study we used dental pulp-derived mesenchymal stem cells (DPSCs) to mitigate sodium iodate (NaIO3) insult in a rat model of retinal degeneration. Sprague-Dawley rats were first given an intravitreal injection of 3 × 105 DPSCs as well as a single systemic administration of NaIO3 (40 mg/kg). Electroretinography (ERG) was performed for the next two months and was followed-up by histological analysis. The ERG recordings showed protection of DPSC-treated retinas within 4 weeks, which was statistically significant (* P ≤ .05) compared to the control. Retinal thickness of the control was also found to be thinner (*** P ≤ .001). The DPSCs were found integrated in the photoreceptor layer through immunohistochemical staining. Our findings showed that DPSCs have the potential to moderate retinal degeneration. In conclusion, DPSCs are a potential source of stem cells in the field of eye stem cell therapy due to its protective effects against retinal degeneration.
    Matched MeSH terms: Retinal Pigment Epithelium/drug effects*; Retinal Pigment Epithelium/pathology
  6. Nur Aqilah, S., Wong, H.S., Syed Zulkifli, S.Z., Mushawiahti, M.
    Medicine & Health, 2018;13(1):88-96.
    MyJurnal
    Anti-vascular endothelial growth factor (VEGF) reduces choroidal thickness by choroidal hypoperfusion in diabetic macula oedema (DME) patients. Indirect effect of anti-VEGF towards outer retinal layers (ORL) which supplied by choroidal circulation has not been well described. We evaluate the ORL thickness between retinal pigment epithelium (RPE) with inner-segment-outer-segment photoreceptor junction (IS/OS) and RPE with external limiting membrane (ELM) in pre- and postintravitreal Ranibizumab (IVR) treated eyes with central foveal diabetic macula edema. A total of 60 eyes (40 patients) were analysed. ORL thickness measured with optical coherence tomography at pre- and post-injection day 1, week 4 and week 6. Mean thickness of RPE-IS/OS was statistically significant over time (p=0.023) but not for RPE-ELM (p=0.216). Thickness ratio between RPE-IS/OS and RPE-ELM and central subfoveal thickness (CST) both showed statistically significant result over time with p=0.038 and p=0.000, respectively. We observed an initial reduction of ORL thickness at day 1 followed by increased in thickness at week 4 with subsequent reduction at week 6 was observed. ORL is an aspect that can be explore and emphasized further in patients considered for IVR injections. The long-term effects of IVR to the ORL however could not be concluded due to short follow up period.
    Matched MeSH terms: Retinal Pigment Epithelium
  7. Han H, Chen N, Huang X, Liu B, Tian J, Lei H
    J Biol Chem, 2019 10 18;294(42):15408-15417.
    PMID: 31467081 DOI: 10.1074/jbc.RA119.010130
    Phosphoinositide 3-kinases (PI3Ks) are a family of lipid kinases that play a critical role in transmitting signals from cell-surface molecules to intracellular protein effectors. Key PI3Ks include PI3Kα, PI3Kβ, and PI3Kδ, which are regulated by receptors. The signaling pathway comprising the PI3Ks, along with a Ser/Thr kinase (AKT), a proto-oncogene product (mouse double minute (MDM)2), and a tumor suppressor protein (p53), plays an essential role in experimental proliferative vitreoretinopathy (PVR), which is a fibrotic blinding eye disorder. However, which PI3K isoforms are involved in PVR is unknown. A major characteristic of PVR is the formation of epi (or sub)-retinal membranes that consist of extracellular matrix and cells, including retinal pigment epithelium (RPE) cells, glial cells, and macrophages. RPE cells are considered key players in PVR pathogenesis. Using immunoblotting and immunofluorescence analyses, we herein provide the evidence that PI3Kδ is highly expressed in human RPEs when it is primarily expressed in leukocytes. We also found that PI3Kδ inactivation through two approaches, CRISPR/Cas9-mediated depletion and a PI3Kδ-specific inhibitor (idelalisib), not only blocks vitreous-induced activation of AKT and MDM2 but also abrogates a vitreous-stimulated decrease in p53. Furthermore, we demonstrate that PI3Kδ inactivation prevents vitreous-induced proliferation, migration, and contraction of human RPEs. These results suggest that PI3Kδ may represent a potential therapeutic target for RPE-related eye diseases, including PVR.
    Matched MeSH terms: Retinal Pigment Epithelium/cytology; Retinal Pigment Epithelium/enzymology; Retinal Pigment Epithelium/metabolism*
  8. Kumar Dubey S, Pradhan R, Hejmady S, Singhvi G, Choudhury H, Gorain B, et al.
    Int J Pharm, 2021 May 01;600:120499.
    PMID: 33753164 DOI: 10.1016/j.ijpharm.2021.120499
    Age-related macular degeneration (AMD), a degenerative eye disease, is the major cause of irreversible loss of vision among individuals aged 50 and older. Both genetic and environmental factors are responsible for the progressive damage to central vision. It is a multifactorial retinal disease with features such as drusen, hypopigmentation and/or hyperpigmentation of the retinal pigment epithelium, and even choroidal neovascularization in certain patients. AMD is of two major forms: exudative (wet) and atrophic (dry) with changes affecting the macula leading to impaired vision. Although the retina remains an accessible portion for delivering drugs, there are no current options to cure or treat AMD. The existing expensive therapeutics are unable to treat the underlying pathology but display several side effects. However, recent innovations in nanotherapeutics provide an optimal alternative of drug delivery to treat the neovascular condition. These new-age technologies in the nanometer scale would enhance bioactivity and improve the bioavailability of drugs at the site of action to treat AMD. The nanomedicine also provides sustained release of the drug with prolonged retention after penetrating across the ocular tissues. In this review, the insights into the cellular and molecular mechanisms associated with the pathophysiology of AMD are provided. It also serves to review the current progress in nanoparticle-based drug delivery systems that offer feasible treatments in AMD.
    Matched MeSH terms: Retinal Pigment Epithelium
  9. Chong YS, Mai CW, Leong CO, Wong LC
    Cutan Ocul Toxicol, 2018 Mar;37(1):52-60.
    PMID: 28554225 DOI: 10.1080/15569527.2017.1335748
    PURPOSE: Dysfunction of the microRNA (miRNA)-processing enzyme DICER1 and Alu RNA accumulation are linked to the pathogenesis of age-related macular degeneration (AMD). This study determined the optimal dose of lutein (LUT) and zeaxanthin (ZEA) to protect human retinal pigment epithelium (RPE) cells against hydrogen peroxide (H2O2). The effect of the optimal dose of LUT and ZEA as DICER1 and Alu RNA modulators in cultured human RPE cells challenged with H2O2 was investigated.

    MATERIALS AND METHODS: ARPE-19 cells were pre-treated with LUT, ZEA, or both for 24 h before 200 μM H2O2 challenge. Cell viability was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. DICER1 and Alu RNA were quantified by western blotting and real-time polymerase chain reaction, respectively.

    RESULTS: H2O2 increased cell Alu RNA expression and decreased cell viability of ARPE-19, but had no significant impact on the DICER1 protein level. LUT, alone and in combination with ZEA pre-treatment, prior to H2O2 challenge significantly improved cell viability of ARPE-19 and reduced the level of Alu RNA compared to the negative control.

    CONCLUSIONS: These results support the use of LUT alone, and in combination with ZEA, in AMD prevention and treatment. This study is also the first to report LUT modulating effects on Alu RNA.

    Matched MeSH terms: Retinal Pigment Epithelium/cytology*
  10. Mohd Fauzi Yap MFB, Mohd Zain A, Tumain NR, Palaniappan S, Nasaruddin RA, Md Din N
    Ocul Immunol Inflamm, 2020 Sep 24.
    PMID: 32967510 DOI: 10.1080/09273948.2020.1800050
    A 45-year-old man was diagnosed with diffuse large B-cell lymphoma stage IV which was confirmed by celiac lymph node biopsy. He subsequently completed six cycles of R-CHOP chemotherapy. Six months later, he presented with panuveitis OU with positive relative afferent pupillary defect OD. OCT revealed hyper-reflective lesions and irregularity of the retinal pigment epithelium OU. Fundus fluorescein angiogram shows hyper-auto fluorescence and granular changes on the retina. A month later, he developed swollen optic disc OD and hemorrhagic retinitis OU and treated as presumed CMV retinitis. Anti-TB was started after a positive Mantoux test. He finally consented for a vitreous biopsy which showed atypical lymphoid cells highly suggestive for vitreoretinal lymphoma and subsequently received intravitreal methotrexate OU.

    CONCLUSION: Optic nerve infiltration in systemic metastatic retinal lymphoma may have initial occult signs but with profound visual loss. Ocular infections like CMV retinitis and tuberculosis may mask and delay the diagnosis in immunocompromised patients.

    Matched MeSH terms: Retinal Pigment Epithelium
  11. Arumugam B, Palanisamy UD, Chua KH, Kuppusamy UR
    Mol Vis, 2019;25:47-59.
    PMID: 30820141
    Purpose: Oxidative stress is implicated in the etiology of diabetes and its debilitating complications, such as diabetic retinopathy (DR). Various flavonoids have been reported to be useful in reducing DR progression. Myricetin derivatives (F2) isolated from leaf extract of Syzygium malaccense have the potential to serve as functional food as reported previously. The present study was performed with the aim of determining the antioxidant potential and protective effect of myricetin derivatives (F2) isolated from leaf extract of S. malaccense against glucose oxidase (GO)-induced hydrogen peroxide (H2O2) production that causes oxidative stress in ARPE-19 (RPE) cells.

    Methods: Antioxidant properties were assessed through various radical (DPPH, ABTS, and nitric oxide) scavenging assays and determination of total phenolic content and ferric reducing antioxidant power level. ARPE-19 cells were preincubated with samples before the addition of GO (to generate H2O2). Cell viability, change in intracellular reactive oxygen species (ROS), H2O2 levels in cell culture supernatant, and gene expression were assessed.

    Results: F2 showed higher antioxidant levels than the extract when assessed for radical scavenging activities and ferric reducing antioxidant power. F2 protected the ARPE-19 cells against GO-H2O2-induced oxidative stress by reducing the production of H2O2 and intracellular reactive oxygen species. This was achieved by the activation of nuclear factor erythroid 2-related factor 2 (Nrf2/NFE2L2) and superoxide dismutase (SOD2), as well as downregulation of nitric oxide producer (NOS2) at the transcriptional level.

    Conclusions: The results showed that myricetin derivatives from S. malaccense have the capacity to exert considerable exogenous antioxidant activities and stimulate endogenous antioxidant activities. Therefore, these derivatives have excellent potential to be developed as therapeutic agents for managing DR.

    Matched MeSH terms: Retinal Pigment Epithelium/cytology; Retinal Pigment Epithelium/metabolism
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