Mechanisms of protein aggregation in the retinal pigment epithelial cells

Kaarniranta, Kai; Hyttinen, Juha M. T.; Ryhänen, Tuomas; Viiri, Johanna; Paimela, Tuomas; Toropainen, Elisa; Sorri, Iiris; Salminen, Antero

doi:10.2741/e198

Cited by 75 publications

(64 citation statements)

References 84 publications

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“…In proteasome inhibitortreated RPE cells, the perinuclear protein aggregates undergo effective autophagic clearance. These findings open new avenues for understanding the mechanisms of proteolytic processes in retinal cells, and could be useful in the development of novel therapies targeting p62 and HSP70 [50][51][52], or the proteins that regulate lysosomal-mediated proteolysis [52,53], with the aim of preventing retinal cell deterioration during aging such as that occurring in AMD [1].…”

Section: Discussionmentioning

confidence: 99%

p62/sequestosome 1 as a regulator of proteasome inhibitor‐induced autophagy in human retinal pigment epithelial cells

KAARNIRANTA

2010

Acta Ophthalmologica

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Purpose:The pathogenesis of age-related macular degeneration involves impaired protein degradation in retinal pigment epithelial (RPE) cells. The ubiquitin-proteasome pathway and the lysosomal pathway including autophagy are the major proteolytic systems in eukaryotic cells. Prior to proteolysis, heat shock proteins (HSPs) attempt to refold stress-induced misfolded proteins and thus prevent the accumulation of cytoplasmic protein aggregates. Recently, p62/sequestosome 1 (p62) has been shown to be a key player linking the proteasomal and lysosomal clearance systems. In the present study, the functional roles of p62 and HSP70 were evaluated in conjunction with proteasome inhibitor-induced autophagy in human RPE cells . Methods: The p62, HSP70, and ubiquitin protein levels and localization were analyzed by western blotting and immunofluorescense. Confocal and transmission electron microscopy were used to detect cellular organelles and to evaluate the morphological changes. The p62 and HSP70 levels were modulated using RNA interference and overexpression techniques. Cell viability was measured by colorimetric assay. Results: Proteasome inhibition evoked the accumulation of perinuclear aggregates that strongly colocalized with p62 and HSP70. The p62 perinuclear accumulation was time-and concentration-dependent after MG-132 proteasome inhibitor loading. The silencing of p62, rather than Hsp70, evoked suppression of autophagy, when related to decreased LC3-II levels after bafilomycin treatment. In addition, the p62 silencing decreased the ubiquitination level of the perinuclear aggregates. Recently, we showed that hsp70 mRNA depletion increased cell death in ARPE-19 cells. Here, we demonstrate that p62 mRNA silencing has similar effects on cellular viability. Conclusions:Our findings open new avenues for understanding the mechanisms of proteolytic processes in retinal cells, and could be useful in the development of novel therapies targeting p62 and HSP70.Age-related macular degeneration (AMD) is the leading cause of blindness of elderly people in the developed countries. The disease affects the macula, which is located in the central area of the retina. Primarily, AMD is characterized by degeneration of the macular retinal pigment epithelial (RPE) cells [1]. The RPE cells take care of the health of rods and cones. Therefore, the degeneration and cell death of RPE cells cause secondary adverse effects on the neural cells, ultimately leading to visual loss. Chronic oxidative stress and inflammation are key factors evoking RPE degeneration and promoting the AMD process [2,3]. One hallmark of AMD is the accumulation of lysosomal lipofuscins, and extracellular drusens between RPE cells and Bruch's membrane. This cargo is a clear evidence of a disturbance in the cellular protein Correspondence to: Kai Kaarniranta, Department of Ophthalmology, University of Kuopio, P.O. Box 1627, 70211 Kuopio, Finland; Phone.: +358-17-162015; FAX: +358-17-162048; email: Kai.Kaarniranta@uef.fi clearance system in aged RPE cells [1]. Recently,...

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Section: Discussionmentioning

confidence: 99%

p62/sequestosome 1 as a regulator of proteasome inhibitor‐induced autophagy in human retinal pigment epithelial cells

KAARNIRANTA

2010

Acta Ophthalmologica

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“…AMD is divided into early and late diseases, as well as the atrophic and exudative degeneration categories. Both forms of AMD involve the appearance of local inflammation but the neovascularisation through Bruch's membrane and the RPE layer is a diagnostic marker for exudative AMD (Kaarniranta et al, 2010). Primarily AMD is characterized by degeneration of the macular retinal pigment epithelial (RPE) cells.…”

Section: Introductionmentioning

confidence: 99%

“…RPE cells are exposed to chronic oxidative stress; they are constantly absorbing light energy and undergoing phagocytization of the lipid rich shed tips of photoreceptor outer segments involved in physiological visual cycle. Oxidative stress refers to progressive cellular damage and chronic inflammation that contributes to protein misfolding and functional abnormalities in the RPE cells during cellular senescence (Kaarniranta & Salminen, 2009;Kaarniranta et al, 2010). Degeneration and cell death of RPE cells cause secondary adverse effects on neural retina leading to visual loss.…”

Section: Introductionmentioning

confidence: 99%

Plant flavonol quercetin and isoflavone biochanin A differentially induce protection against oxidative stress and inflammation in ARPE-19 cells

Saviranta

Veeroos

Granlund

et al. 2011

Food Research International

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“…Furthermore, the disease can be subdivided into early and late stage disease . Dry AMD can gradually progress over a period of months or even years to geographic atrophy; it is particularly treacherous because it may not display any symptoms in its early stages (Sunness et al 1997;AREDS 2000;Kaarniranta et al 2010). Dry AMD may take even years to develop whereas wet AMD may progress rapidly within a few weeks.…”

Section: Introductionmentioning

confidence: 98%

Absence of collagen XVIII in mice causes age-related insufficiency in retinal pigment epithelium proteostasis

et al. 2016

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Collagen XVIII has the structural properties of both collagen and proteoglycan. It has been found at the basement membrane/stromal interface where it is thought to mediate their attachment. Endostatin, a proteolytic fragment from collagen XVIII C-terminal end has been reported to possess anti-angiogenic properties. Age-related vision loss in collagen XVIII mutant mice has been accompanied with a pathological accumulation of deposits under the retinal pigment epithelium (RPE). We have recently demonstrated that impaired proteasomal and autophagy clearance are associated with the pathogenesis of age-related macular degeneration. This study examined the staining levels of proteasomal and autophagy markers in the RPE of different ages of the Col18a1 (-/-) mice. Eyes from 3, 6-7, 10-13 and 18 months old mice were enucleated and embedded in paraffin according to the routine protocol. Sequential 5 μm-thick parasagittal samples were immunostained for proteasome and autophagy markers ubiquitin (ub), SQSTM1/p62 and beclin-1. The levels of immunopositivity in the RPE cells were evaluated by confocal microscopy. Collagen XVIII knock-out mice had undergone age-related RPE degeneration accompanied by an accumulation of drusen-like deposits. Ub protein conjugate staining was prominent in both RPE cytoplasm and extracellular space whereas SQSTM1/p62 and beclin-1 stainings were clearly present in the basal part of RPE cell cytoplasm in the Col18a1 (-/-) mice. SQSTM1/p62 displayed mild extracellular space staining. Disturbed proteostasis regulated by collagen XVIII might be responsible for the RPE degeneration, increased protein aggregation, ultimately leading to choroidal neovascularization.

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Mechanisms of protein aggregation in the retinal pigment epithelial cells

Cited by 75 publications

References 84 publications

p62/sequestosome 1 as a regulator of proteasome inhibitor‐induced autophagy in human retinal pigment epithelial cells

p62/sequestosome 1 as a regulator of proteasome inhibitor‐induced autophagy in human retinal pigment epithelial cells

Plant flavonol quercetin and isoflavone biochanin A differentially induce protection against oxidative stress and inflammation in ARPE-19 cells

Absence of collagen XVIII in mice causes age-related insufficiency in retinal pigment epithelium proteostasis

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