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Kathleen Boesze-Battaglia, Alan Laties, Laura Frost; Induction Of Lysosome Dependent Pathways In RPE Cells In Response To Oxidative Stressors. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3344.
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RPE cells take up lipids originating from spent photoreceptor outer segments (POS) a portion of which exocytose through the base of the RPE to be eliminated via the choroid. In addition, these cells ingest oxidized lipids from their cell base in an effort to clear the sub-retinal space from deposits. In age-related degenerative changes there is an accumulation of lipoprotein and lipid-containing sub-RPE and Bruch’s membrane (BM) debris, implying imbalance in the accumulation/clearance of these products. The purpose of this study was to determine which lysosome dependent pathways are stimulated in response to challenge with oxidative stressor; Ox LDL and/or oxidized POS in an effort to understand how and why certain lipid components appear to evade the degradative process.
Human RPE cells were challenged with LDL, OxLDL, photoreceptor outer segments (POS) or oxidized OS alone or in various combinations for 30 min, 4 hrs or 8hrs. Lysosomogenesis was followed at mRNA and protein level by qPCR and immunoblotting, respectively. Distribution profile of autophagic markers was followed using qPCR and immunoblotting. Lastly, the role of melanoregulin in these processes was examined using an RPE cell line devoid of MREG expression.
Upon OxLDL challenge Cathepsin D and LAMP1 levels were upregulated at both mRNA and protein levels. Furthermore, immature Cathepsin D was secreted into the media. Several autophagy markers were also upregulated in response to challenge with OxLDL versus LDL. Consistent with this, RPE cells pretreated with OxLDL showed a marked increase in LC3B expression as well as Cathepsin-D and VEGF secretion upon subsequent ingestion of OS.
Collectively, our results suggest that lysosome maturation is enhanced upon RPE cell challenge with OxLDL however this pool of lysosomes may be used in the formation of autophagolysosomes
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