Acidic Nanoparticles Are Trafficked to Lysosomes and Restore an Acidic Lysosomal pH and Degradative Function to Compromised ARPE-19 Cells

Baltazar, Gabriel C.; Guha, Sonia; Lu, Wennan; Lim, Jason; Boesze‐Battaglia, Kathleen; Laties, Alan M.; Tyagi, Puneet; Kompella, Uday B.; Mitchell, Claire H.

doi:10.1371/journal.pone.0049635

Cited by 108 publications

(119 citation statements)

References 30 publications

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“…Both, Boulton and Sparrow's laboratories have reported a phototoxic effect of A2E upon exposure to blue light (15,36). Accumulation of A2E leads to plasma membrane destabilization (17,19,37), increased lysosomal pH (38)(39)(40), decreased lysosomal enzyme activity (39), and derailing of cholesterol trafficking with the consequent buildup of free cholesterol in lysosomes (41). Moreover, accumulation of LBs in RPE is known to induce complement activation (42,43) and secretion of proinflammatory cytokines, including IL-1β, IL-8, IL-6, VEGFα, TNFa, and chemokines (44)(45)(46) responsible, at least in part, for the perpetuation of the chronic inflammatory milieu linked with AMD (47,48).…”

Section: Discussionmentioning

confidence: 99%

Beta cyclodextrins bind, stabilize, and remove lipofuscin bisretinoids from retinal pigment epithelium

Nociari

Lehmann

Bay

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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Accumulation of lipofuscin bisretinoids (LBs) in the retinal pigment epithelium (RPE) is the alleged cause of retinal degeneration in genetic blinding diseases (e.g., Stargardt) and a possible etiological agent for age-related macular degeneration. Currently, there are no approved treatments for these diseases; hence, agents that efficiently remove LBs from RPE would be valuable therapeutic candidates. Here, we show that beta cyclodextrins (β-CDs) bind LBs and protect them against oxidation. Computer modeling and biochemical data are consistent with the encapsulation of the retinoid arms of LBs within the hydrophobic cavity of β-CD. Importantly, β-CD treatment reduced by 73% and 48% the LB content of RPE cell cultures and of eyecups obtained from Abca4-Rdh8 double knock-out (DKO) mice, respectively. Furthermore, intravitreal administration of β-CDs reduced significantly the content of bisretinoids in the RPE of DKO animals. Thus, our results demonstrate the effectiveness of β-CDs to complex and remove LB deposits from RPE cells and provide crucial data to develop novel prophylactic approaches for retinal disorders elicited by LBs.aging | retinopathy | lipofuscinosis | residual bodies T he retinal pigment epithelium (RPE), strategically situated between the neural retina and the choroid blood vessels, is essential for photoreceptor (PR) function. It recycles vitamin A, which is required for the visual cycle and clears debris generated by the circadian shedding of PR outer segments (1, 2). Each RPE cell phagocytoses and digests the material produced by 30-50 overlying PRs, which shed 10% of their mass daily. The intense and continual phagocytic activity of RPE cells results in the progressive accumulation of indigestible products or "lipofuscin" in their lysosomal compartment (3, 4). Unlike lipofuscins found in other body tissues, which are composed mainly of protein, RPE lipofuscin consists predominantly of lipid-bisretinoids and only 2% protein (5). Lipofuscin bisretinoids (LBs) are vitamin A-derived side products of the visual cycle. Light converts 11-cis-retinal (11CR), the visual pigment chromophore, into all-trans-retinal (ATR), which is immediately flipped by the ATP-binding cassette transporter 4 (Abca4) transporter from the lumen of the outer segment discs to the cytoplasm, where it is reduced to inert all-trans-retinol by retinol dehydrogenase 8 (Rdh8), in mice (6, 7). Small fractions of 11CR and ATR are converted into N-retinylidine-N-ethanolamine (A2E) and other less abundant bisretinoids, which once accumulated in the lysosomes of RPE cells are refractory to all known lysosomal hydrolases (8, 9). The concept that LB accumulation causes retinal degeneration is supported by in vitro and in vivo data that show that excessive LBs are toxic for cultured RPE cells (10,11), that photoreceptors overlying A2E-laden RPE are more prone to degeneration (12) and that excessive accumulation of LBs in Stargardt's disease precedes macular degeneration (13). Mice carrying null mutations in Abca4 and Rdh8 develop blin...

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Section: Discussionmentioning

confidence: 99%

Beta cyclodextrins bind, stabilize, and remove lipofuscin bisretinoids from retinal pigment epithelium

Nociari

Lehmann

Bay

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…This sharp pH dependence of enzyme activity implies that alkalinizing lysosomes of RPE cells will lower the activity of multiple enzymes and interfere with the degradation of internalized outer segments. Autofluorescence associated with photoreceptor outer segments was increased in RPE cells exposed to cholorquine [15]. Lysosomal alkalinization decreased staining of Bodipy-pepstatin–A, suggesting the lysosomal enzyme cathepsin D was less effective in RPE cells with perturbed lysosomes [15, 16].…”

Section: 3 Consequences Of Lysosomal Alkalinization On Degradationmentioning

confidence: 99%

“…Autofluorescence associated with photoreceptor outer segments was increased in RPE cells exposed to cholorquine [15]. Lysosomal alkalinization decreased staining of Bodipy-pepstatin–A, suggesting the lysosomal enzyme cathepsin D was less effective in RPE cells with perturbed lysosomes [15, 16]. The clearance of outer segments is also decreased when the lysosomal pH is elevated with tamoxifen [17].…”

Section: 3 Consequences Of Lysosomal Alkalinization On Degradationmentioning

confidence: 99%

Rescue of Compromised Lysosomes Enhances Degradation of Photoreceptor Outer Segments and Reduces Lipofuscin-Like Autofluorescence in Retinal Pigmented Epithelial Cells

Guha

Baltazar

et al. 2014

Advances in Experimental Medicine and Biology

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Healthful cell maintenance requires the efficient degradative processing and removal of waste material. Retinal pigmented epithelial (RPE) cells have the onerous task of degrading both internal cellular debris generated through autophagy as well as phagocytosed photoreceptor outer segments. We propose that the inadequate processing material with the resulting accumulation of cellular waste contributes to the downstream pathologies characterized as age-related macular degeneration (AMD). The lysosomal enzymes responsible for clearance function optimally over a narrow range of acidic pH values; elevation of lysosomal pH by compounds like chloroquine or A2E can impair degradative enzyme activity and lead to a lipofuscin-like autofluorescence. Restoring acidity to the lysosomes of RPE cells can enhance activity of multiple degradative enzymes and is therefore a logical target in early AMD. We have identified several approaches to reacidify lysosomes of compromised RPE cells; stimulation of beta-adrenergic, A2A adenosine and D5 dopamine receptors each lowers lysosomal pH and improves degradation of photoreceptor outer segments. Activation of the CFTR chloride channel also reacidifies lysosomes and increases degradation. These approaches also restore the lysosomal pH of RPE cells from aged ABCA4−/− mice with chronically high levels of A2E, suggesting that functional signaling pathways to reacidify lysosomes are retained in aged cells like those in patients with AMD. Acidic nanoparticles transported to RPE lysosomes also lower pH and improve degradation of outer segments. In summary, the ability of diverse approaches to lower lysosomal pH and enhance outer segment degradation support the proposal that lysosomal acidification can prevent the accumulation of lipofuscin-like material in RPE cells.

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“…16 Interestingly, acidic nanoparticles (aNP) of poly(DL-lactide-co-glycolide) PLGA, which are approved by the US FDA, 17 have been reported to (i) traffic to lysosomes and (ii) act on the lysosomal pH. 18 However, whether PLGA-aNP can acidify sick lysosomes and restore lysosomal/autophagic function in pathological contexts remains to be determined. In addition, it is unknown whether such nanotechnology-based strategy can be translated to an in vivo situation.…”

Section: Introductionmentioning

confidence: 99%

Nanoparticles restore lysosomal acidification defects: Implications for Parkinson and other lysosomal-related diseases

et al. 2016

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Lysosomal impairment causes lysosomal storage disorders (LSD) and is involved in pathogenesis of neurodegenerative diseases, notably Parkinson disease (PD). Strategies enhancing or restoring lysosomalmediated degradation thus appear as tantalizing disease-modifying therapeutics. Here we demonstrate that poly(DL-lactide-co-glycolide) (PLGA) acidic nanoparticles (aNP) restore impaired lysosomal function in a series of toxin and genetic cellular models of PD, i.e. ATP13A2-mutant or depleted cells or glucocerebrosidase (GBA)-mutant cells, as well as in a genetic model of lysosomal-related myopathy. We show that PLGA-aNP are transported to the lysosome within 24 h, lower lysosomal pH and rescue chloroquine (CQ)-induced toxicity. Re-acidification of defective lysosomes following PLGA-aNP treatment restores lysosomal function in different pathological contexts. Finally, our results show that PLGA-aNP may be detected after intracerebral injection in neurons and attenuate PD-related neurodegeneration in vivo by mechanisms involving a rescue of compromised lysosomes.

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Acidic Nanoparticles Are Trafficked to Lysosomes and Restore an Acidic Lysosomal pH and Degradative Function to Compromised ARPE-19 Cells

Cited by 108 publications

References 30 publications

Beta cyclodextrins bind, stabilize, and remove lipofuscin bisretinoids from retinal pigment epithelium

Beta cyclodextrins bind, stabilize, and remove lipofuscin bisretinoids from retinal pigment epithelium

Rescue of Compromised Lysosomes Enhances Degradation of Photoreceptor Outer Segments and Reduces Lipofuscin-Like Autofluorescence in Retinal Pigmented Epithelial Cells

Nanoparticles restore lysosomal acidification defects: Implications for Parkinson and other lysosomal-related diseases

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