Oxidized LDL-induced JAB1 influences NF-κB independent inflammatory signaling in human macrophages during foam cell formation.
BACKGROUND
Oxidized low-density lipoprotein (oxLDL) mediates the transformation of macrophages (MΦ) to cholesterol-rich foam cells and the release of pro-inflammatory cytokines during atherogenesis. JAB1 (Jun activation domain binding protein-1) is present in all stages of human plaques, involved in the Toll-like receptor-mediated activation of p38 mitogen-activated protein kinase (MAPK) and controls nuclear factor-kappa B (NF-κB) activation. Thus, we were interested in the role of JAB1 during foam cell formation of MΦ after oxLDL exposition.


RESULTS
We found that JAB1 was present in CD68-immunoreactive (-ir) MΦ in atherosclerotic plaques of apolipoprotein E knockout (ApoE-/-) mice after a high cholesterol/fat diet. Furthermore, differentiated human U937 MΦ - incubated with oxLDL (4 h) to induce foam cell formation - showed a significant increase of JAB1 (50 μg/ml: 1.39 + 0.15-fold; 100 μg/ml: 1.80 + 0.26-fold; 200 μg/ml: 2.05 + 0.30-fold; p < 0.05) on the protein level compared to the control. Independent from JAB1 silencing, we found an increase of total cholesterol (TC), free cholesterol (FC) and cholesteryl ester (CE) after oxLDL exposition. However, siJAB1-MФ showed a reduction of tumor necrosis factor-alpha (TNF-α) (36%; p < 0.05 vs. non-transfected MФ) and interleukin (IL)-6 (30%; p < 0.05 vs. non-transfected MФ) mRNA expression, as well as TNF-α (46%; p < 0.05 vs. non-transfected MФ) and IL-6 (32%; p < 0.05 vs. non-transfected MФ) protein secretion after oxLDL exposition. In parallel with an upregulation of inflammatory cytokines (TNF-α, IL-6) after oxLDL exposition, we found a significant (p < 0.05) increase of 37% in p38 MAPK activation after 4 h oxLDL-treatment, independent from NF-kB signaling. In this context, we showed regional co-localization of JAB1 with p38 MAPK in atherosclerotic plaques of ApoE-/-mice. Moreover, we detected interaction of JAB1 with p38 MAPK in U937 cells.


CONCLUSIONS
We demonstrate that oxLDL induces JAB1 expression and influences its cellular localization, whereby the p38 MAPK signaling pathway is modified with consequences for inflammation of human MΦ in foam cells and atherosclerotic lesions.
Anatomy and Cell Biology, Department of Medical Cell Biology, University of Marburg, Robert-Koch-Straße 8, 35032, Marburg, Germany. anja.schwarz@staff.uni-marburg.de.
Anja
A
Schwarz
Anatomy and Cell Biology, Department of Medical Cell Biology, University of Marburg, Robert-Koch-Straße 8, 35032, Marburg, Germany.
Gabriel A
GA
Bonaterra
Anatomy and Cell Biology, Department of Medical Cell Biology, University of Marburg, Robert-Koch-Straße 8, 35032, Marburg, Germany.
Hans
H
Schwarzbach
Anatomy and Cell Biology, Department of Medical Cell Biology, University of Marburg, Robert-Koch-Straße 8, 35032, Marburg, Germany.
Ralf
R
Kinscherf
D000818:Animals; D000075686:COP9 Signalosome Complex; D005487:Foam Cells / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000096:biosynthesis* / Q000235:genetics; D008077:Lipoproteins, LDL / Q000494:pharmacology*; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D051379:Mice; D018345:Mice, Knockout; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000096:biosynthesis* / Q000235:genetics; D058226:Plaque, Atherosclerotic / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D020298:U937 Cells; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism
D047908:Intracellular Signaling Peptides and Proteins; D008077:Lipoproteins, LDL; D016328:NF-kappa B; C099252:oxidized low density lipoprotein; D048051:p38 Mitogen-Activated Protein Kinases; D010447:Peptide Hydrolases; C501488:COPS5 protein, human; D000075686:COP9 Signalosome Complex
Atherosclerosis; Foam cells; JAB1; Macrophages; oxLDL