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Uptake of Oxidized LDL by Macrophages Results in Partial Lysosomal Enzyme Inactivation and Relocation
Linköping University, Department of Neuroscience and Locomotion, Pathology. Linköping University, Department of Medicine and Care, Internal Medicine. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Neuroscience and Locomotion, Pathology. Linköping University, Department of Medicine and Care, Internal Medicine. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Medical and Health Sciences, Internal Medicine. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Neuroscience and Locomotion, Pathology. Linköping University, Faculty of Health Sciences.
1998 (English)In: Arteriosclerosis, Thrombosis and Vascular Biology, ISSN 1079-5642, E-ISSN 1524-4636, Vol. 18, no 2, 177-84 p.Article in journal (Refereed) Published
Abstract [en]

The cytotoxicity of oxidized LDL (oxLDL) to several types of artery wall cells might contribute to atherosclerosis by causing cell death, presumably by both apoptosis and necrosis. After its uptake into macrophage lysosomes by receptor-mediated endocytosis, oxLDL is poorly degraded, resulting in ceroid-containing foam cells. We studied the influence of oxLDL on lysosomal enzyme activity and, in particular, on lysosomal membrane stability and the modulation of these cellular characteristics by HDL and vitamin E (vit-E). Unexposed cells and cells exposed to acetylated LDL (AcLDL) were used as controls. The lysosomal marker enzymes cathepsin L and N-acetyl-β-glucosaminidase (NAβGase) were biochemically assayed in J-774 cells after fractionation. Lysosomal integrity in living cells was assayed by the acridine orange (AO) relocation test. Cathepsin D was immunocytochemically demonstrated in J-774 cells and human monocyte-derived macrophages. We found that the total activities of NAβGase and cathepsin L were significantly decreased, whereas their relative cytosolic activities were enhanced, after oxLDL exposure. Labilization of the lysosomal membranes was further proven by decreased lysosomal AO uptake and relocation to the cytosol of cathepsin D, as estimated by light and electron microscopic immunocytochemistry. HDL and vit-E diminished the cytotoxicity of oxLDL by decreasing the lysosomal damage. The results indicate that endocytosed oxLDL not only partially inactivates lysosomal enzymes but also destabilizes the acidic vacuolar compartment, causing relocation of lysosomal enzymes to the cytosol. Exposure to AcLDL resulted in its uptake with enlargement of the lysosomal apparatus, but the stability of the lysosomal membranes was not changed.

Place, publisher, year, edition, pages
1998. Vol. 18, no 2, 177-84 p.
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-65822DOI: 10.1161/​01.ATV.18.2.177PubMedID: 9484981OAI: oai:DiVA.org:liu-65822DiVA: diva2:399249
Available from: 2011-02-21 Created: 2011-02-21 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Oxidized Lipids and Lysosomal Pathology in Atherogenesis
Open this publication in new window or tab >>Oxidized Lipids and Lysosomal Pathology in Atherogenesis
2000 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Macrophages take up large amount of exogenous materials such as oxidatively modified low-density lipoproteins (oxLDL) and lysosomotropic agents. OxLDL is taken up into macrophage lysosomes through receptor-mediated endocytosis, but poorly degraded, resulting in foam cell formation. Cholesterol oxidation products, major toxic components of oxLDL, are involved in foam cell formation and the initiation of atherosclerosis. The production of ROS/RNS, cytokines, and matrix proteases by macrophages and the apoptosis of arterial cells may contribute to atherosclerotic plaque development and destabilization.

We had four objectives in this study, first we study the influence of oxLDL on lysosomal membrane stability, location and activity of lysosomal enzymes, macrophage cell death, and the modulation of these cellular characteristics by high-density lipoprotein (HDL), vitantin E (vit E), and the iron chelator desferrioximine (DFO) or iron complex. Second, we examined the role of lysosomal enzymes in macrophage apoptosis induced by oxysterols, the major cytotoxic components of oxLDL. Third, we analyzed the expression of cysteine protease cathepsins B and L and studied their relationship to macrophage apoptosis in human atherosclerotic lesions. And fourth, we investigated whether lysosomal rupture and release of lysosomal enzymes could initiate apoptosis using the lysosomotropic detergent MSDH.

The results suggest that oxLDL causes lysosomal destabilization and relocation of lysos'omal enzymes as indicated by increased cytosolic NABGase, cathepsin-L, and cathepsin D, and decreased lysosomal acridine orange (AO)-induced red fluorescence. AcLDL had no cytotoxic effects on the cells and their lysosomes. HDL, vit E, and the iron chelator DFO diminished the cytotoxicity of oxLDL by decreasing lysosomal damage, while the iron complex enhanced oxLDL cytotoxicity. Macrophage apoptosis induced by ChOx and 7-oxysterols (7B-OH and 7- keto) is associated with lysosomal rupture and release of lysosomal enzymes to the cytosol. The lysosomal punctuated immune-granularity of cathepsins B and L was decreased in 7 -oxysteroltreated cells compared to control cells. Moreover, there is enhancement and dispersion of cathepsins B and L immunoreactivity throughout 7-oxysterols-treated cells and an extensive immunoreaction in the nuclei and around nuclear areas of apoptotic cells. Using MSDH, a lysosomotropic detergent, we further demonstrated that lysosomal rupture and release of lytic enzymes indeed play an initial role in macrophage apoptosis.

There is a lesion dependent eo-expression of cathepsins B and Land caspase-3 in early and advanced human atherosclerotic lesions, which is associated with macrophage apoptosis.

We conclude that macrophage cell death including apoptosis induced by oxLDL and oxysterols is associated with lysosomal rupture and relocation of lysosomal hydrolytic enzymes to the cytosol. The released enzymes may initiate ceU death by activating the caspase cascade, attacking mitochondria, or directly attacking the nuclear of the cells. The high eo-expression of cathepsins B and L with caspase-3 in apoptotic macrophages in human atheroma lesions suggests that macrophage apoptosis and related hydrolytic enzymes may play an important role in lesion development and plaque instability.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2000. 56 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 652
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-28056 (URN)12819 (Local ID)91-7219-753-6 (ISBN)12819 (Archive number)12819 (OAI)
Public defence
2000-12-01, Berzeliussalen, Universitetssjukhuset, Linköping, 13:00 (Swedish)
Opponent
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2012-08-16Bibliographically approved

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Li, WeiYuan, Xi MingOlsson, AndersBrunk, Ulf

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