Electronegative LDL induces priming and inflammasome activation leading to IL-1β release in human monocytes and macrophages.
BACKGROUND
Electronegative LDL (LDL(−)), a modified LDL fraction found in blood, induces the release of inflammatory mediators in endothelial cells and leukocytes. However, the inflammatory pathways activated by LDL(−) have not been fully defined. We aim to study whether LDL(−) induced release of the first-wave proinflammatory IL-1β in monocytes and monocyte-derived macrophages (MDM) and the mechanisms involved.


METHODS
LDL(−) was isolated from total LDL by anion exchange chromatography. Monocytes and MDM were isolated from healthy donors and stimulated with LDL(+) and LDL(−) (100 mg apoB/L).


RESULTS
In monocytes, LDL(−) promoted IL-1β release in a time-dependent manner, obtaining at 20 h-incubation the double of IL-1β release induced by LDL(−) than by native LDL. LDL(−)-induced IL-1β release involved activation of the CD14-TLR4 receptor complex. LDL(−) induced priming, the first step of IL-1β release, since it increased the transcription of pro-IL-1β (8-fold) and NLRP3 (3-fold) compared to native LDL. Several findings show that LDL(−) induced inflammasome activation, the second step necessary for IL-1β release. Preincubation of monocytes with K+ channel inhibitors decreased LDL(−)-induced IL-1β release. LDL(−) induced formation of the NLRP3-ASC complex. LDL(−) triggered 2-fold caspase-1 activation compared to native LDL and IL-1β release was strongly diminished in the presence of the caspase-1 inhibitor Z-YVAD. In MDM, LDL(−) promoted IL-1β release, which was also associated with caspase-1 activation.


CONCLUSIONS
LDL(−) promotes release of biologically active IL-1β in monocytes and MDM by induction of the two steps involved: priming and NLRP3 inflammasome activation.


CONCLUSIONS
By IL-1β release, LDL(−) could regulate inflammation in atherosclerosis.
Biomedical Research Institute Sant Pau (IIB-Sant Pau), Barcelona (Spain). C/Sant Antoni M. Claret, 167 08025 Barcelona, Spain. Electronic address: mestruch@santpau.cat.
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Estruch
Wihuri Research Institute (WRI). Haartmaninkatu, 8 FI-00290 Helsinki, Finland. Electronic address: kristiina.rajamaki@helsinki.fi.
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Rajamäki
Biomedical Research Institute Sant Pau (IIB-Sant Pau), Barcelona (Spain). C/Sant Antoni M. Claret, 167 08025 Barcelona, Spain; Molecular Biology and Biochemistry Department, Universitat Autònoma de Barcelona (UAB) Faculty of Medicine, Building M. Cerdanyola del Vallès, Spain. Electronic address: jsanchezq@santpau.cat.
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Sanchez-Quesada
Wihuri Research Institute (WRI). Haartmaninkatu, 8 FI-00290 Helsinki, Finland. Electronic address: petri.kovanen@wri.fi.
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PT
Kovanen
Wihuri Research Institute (WRI). Haartmaninkatu, 8 FI-00290 Helsinki, Finland. Electronic address: kati.oorni@wri.fi.
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K
Öörni
Biomedical Research Institute Sant Pau (IIB-Sant Pau), Barcelona (Spain). C/Sant Antoni M. Claret, 167 08025 Barcelona, Spain; Molecular Biology and Biochemistry Department, Universitat Autònoma de Barcelona (UAB) Faculty of Medicine, Building M. Cerdanyola del Vallès, Spain. Electronic address: sbenitez@santpau.cat.
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Benitez
Molecular Biology and Biochemistry Department, Universitat Autònoma de Barcelona (UAB) Faculty of Medicine, Building M. Cerdanyola del Vallès, Spain; Biochemistry Department. Hospital de la Santa Creu i Sant Pau Barcelona. C/Sant Quintí, 89 08026, Barcelona, Spain. Electronic address: jordonez@santpau.cat.
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Ordoñez-Llanos
D000075944:Apolipoprotein L1; D001053:Apolipoproteins / Q000494:pharmacology; D001055:Apolipoproteins B / Q000494:pharmacology; D053468:CARD Signaling Adaptor Proteins; D002352:Carrier Proteins / Q000235:genetics / Q000276:immunology; D020170:Caspase 1 / Q000235:genetics / Q000276:immunology; D002460:Cell Line; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000276:immunology; D005786:Gene Expression Regulation; D006801:Humans; D058847:Inflammasomes / Q000187:drug effects* / Q000276:immunology; D053583:Interleukin-1beta / Q000276:immunology / Q000378:metabolism*; D018950:Lipopolysaccharide Receptors / Q000235:genetics / Q000276:immunology; D008075:Lipoproteins, HDL / Q000494:pharmacology; D008077:Lipoproteins, LDL / Q000494:pharmacology*; D008262:Macrophage Activation / Q000187:drug effects; D008264:Macrophages / Q000166:cytology / Q000187:drug effects* / Q000276:immunology; D009000:Monocytes / Q000166:cytology / Q000187:drug effects* / Q000276:immunology; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D015221:Potassium Channels / Q000235:genetics / Q000276:immunology; D061251:Primary Cell Culture; D015398:Signal Transduction; D055672:Static Electricity; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000276:immunology; D014158:Transcription, Genetic
C108666:APOL1 protein, human; D000075944:Apolipoprotein L1; D001053:Apolipoproteins; D001055:Apolipoproteins B; D053468:CARD Signaling Adaptor Proteins; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D058847:Inflammasomes; D053583:Interleukin-1beta; D018950:Lipopolysaccharide Receptors; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; C453881:NLRP3 protein, human; C402202:PYCARD protein, human; D015221:Potassium Channels; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; C099252:oxidized low density lipoprotein; D020170:Caspase 1
Caspase-1; Electronegative LDL; Inflammasome; Interleukin-1β; Macrophages; Monocytes