Free cholesterol-loaded macrophages are an abundant source of tumor necrosis factor-alpha and interleukin-6: model of NF-kappaB- and map kinase-dependent inflammation in advanced atherosclerosis.
Two key features of atherosclerotic plaques that precipitate acute atherothrombotic vascular occlusion ("vulnerable plaques") are abundant inflammatory mediators and macrophages with excess unesterified, or "free," cholesterol (FC). Herein we show that FC accumulation in macrophages leads to the induction and secretion of two inflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6). The increases in TNF-alpha and IL-6 mRNA and protein were mediated by FC-induced activation of the IkappaB kinase/NF-kappaB pathway as well as activation of MKK3/p38, Erk1/2, and JNK1/2 mitogen-activated protein kinases (MAPK). Activation of IkappaB kinase and JNK1/2 was needed for the induction of both cytokines. However, MKK3/p38 signaling was specifically involved in TNF-alpha induction, and Erk1/2 signaling was required for IL-6. Most interestingly, activation of all of the signaling pathways and induction of both cytokines required cholesterol trafficking to the endoplasmic reticulum (ER). The CHOP branch of the unfolded protein response, an ER stress pathway, was required for Erk1/2 activation and IL-6 induction. In contrast, one or more other ER-related pathways were responsible for activation of p38, JNK1/2, and IkappaB kinase/NF-kappaB and for the induction of TNF-alpha. These data suggest a novel scenario in which cytokines are induced in macrophages by endogenous cellular events triggered by excess ER cholesterol rather than by exogenous immune cell mediators. Moreover, this model may help explain the relationship between FC accumulation and inflammation in vulnerable plaques.
Li
Yankun
Y
Department of Medicine, Columbia University, 630 West 168th Street, New York, NY 10032, USA.
Schwabe
Robert F
RF
DeVries-Seimon
Tracie
T
Yao
Pin Mei
PM
Gerbod-Giannone
Marie-Christine
MC
Tall
Alan R
AR
Davis
Roger J
RJ
Flavell
Richard
R
Brenner
David A
DA
Tabas
Ira
I
D000818:Animals; D001161:Arteriosclerosis; D001692:Biological Transport; D002467:Cell Nucleus / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism*; D016207:Cytokines / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004789:Enzyme Activation; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D015151:Immunoblotting; D007249:Inflammation; D015850:Interleukin-6 / Q000378:metabolism*; D020935:MAP Kinase Signaling System; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D008954:Models, Biological; D016328:NF-kappa B / Q000378:metabolism*; D017510:Protein Folding; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D016207:Cytokines; D015850:Interleukin-6; D016328:NF-kappa B; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D002784:Cholesterol; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases