Letter to the Editor
Egr-1, a Major Link Between Infection
and Atherosclerosis?
Downloaded from http://circres.ahajournals.org/ by guest on June 18, 2017
p38 kinase pathway with SB203580 (Calbiochem) but not to the
same extent as blocking of the ERK1/2 kinase pathway. Whereas
enhanced expression of VEGF in response to the stimulation with
LPS via the p38 kinase pathway has been described previously,7 our
results newly depict the enhanced VEGF expression via ERK1/2
kinase and Egr-1 activation to be dependent on the presence of viable
pathogen.
Taken together, the recent article by Bea et al1 convincingly
describes the central role of Egr-1 activation in the induction of
tissue factor expression in mouse macrophages via the MEKERK1/2 pathway linking infection and procoagulatory activity.
Platelet-derived growth factor (PDGF) could be another candidate,
as it was previously shown that Egr-1 binds to the proximal PDGF-A
and PDGF-B promoter regions.8 Our findings on C pneumoniae–
infected human blood monocytes expand this view and indicate that
enhanced Egr-1 expression may be a common step in the regulation
of proatherosclerotic factors involved in the pathogenesis of atherosclerosis not limited to promoting procoagulatory activity. Detection
of C pneumoniae in blood monocytes within the circulation of
humans9 favors this pathogen as a causative agent for enhanced
Egr-1 activation in blood monocytes among others.
To the Editor:
The study of Bea et al,1 recently published in Circulation
Research, investigated the role of Chlamydia pneumoniae infection
in mouse macrophages on the induction of tissue factor (TF) via
activation of Egr-1. Chlamydial infection of RAW mouse macrophages clearly resulted in enhanced Egr-1 protein expression and a
subsequent time-dependent increase in TF mRNA expression and
procoagulatory activity. We can confirm the postinfectious Egr-1
induction described by Bea et al. In addition, we can expand their
findings and demonstrate a broader regulatory influence of Egr-1 on
proatherosclerotic factors in C pneumoniae–infected mononuclear
cells that is not limited to prothrombotic molecules and not restricted
to mouse macrophages.
We performed similar experiments as Bea et al1 but used blood
monocytes from healthy blood donors and found that infection with
the cardiovascular chlamydial strain CV-6 (isolated from a 68-yearold man with coronary restenosis2) significantly induced Egr-1
mRNA expression (15.8-fold⫾4.7, n⫽5; P⬍0.01; RT-PCR, LightCycler, Roche Molecular Biochemicals) after 1 hour. This is in line
with the results of Bea et al, who observed maximum Egr-1 protein
levels in the nuclei of infected RAW cells at 1 to 2 hours after
infection. In contrast to Bea et al who focused on TF expression in
mouse macrophages, we were interested whether Egr-1 is involved
in the regulation of C pneumoniae–induced expression of the
vascular endothelial growth factor (VEGF), which has been recently
incriminated to promote atherosclerotic lesion formation and thus
might also link infection and atherosclerosis.3 Enhanced VEGF
immunoreactivity within the vessel wall was associated with increased recruitment of mononuclear cells and with the development
of intimal thickening in a rat cardiac allograft model.
Infection of human blood monocytes with C pneumoniae significantly enhanced VEGF mRNA expression (9.4-fold⫾5.0, n⫽5;
P⬍0.05; RT-PCR, LightCycler) compared with noninfected cells. In
accordance with Bea et al,1 C pneumoniae–induced activation of
Egr-1 and subsequent upregulation of VEGF in human blood
monocytes was not abolished by heat treatment of the chlamydiae.
Compared with Guha et al,4 who showed that lipopolysaccharide
(LPS) from Escherichia coli is a potent stimulus of Egr-1 in human
monocytic cells, our results indicate that Egr-1 induction in human
blood monocytes requires viable chlamydiae and is not mediated by
the heat-stable chlamydial LPS alone. Furthermore, we could show
that Egr-1 induction in human monocytic cells is not specific for C
pneumoniae, as coincubation of blood monocytes with Salmonella
enterica enteritidis and Staphylococcus aureus also resulted in a
rapid and distinct enhancement of Egr-1 mRNA expression. However, these pathogens are not chronically present in the circulation.
Although C pneumoniae is the pathogen best described in relation to
atherosclerosis so far, our findings encourage the hypothesis that the
“pathogen burden,”5 used as a paraphrase for infections with
multiple pathogens (eg, C pneumoniae, Helicobacter pylori, herpes
simplex virus), may predispose to the development of atherosclerosis
in humans.6
Our investigation supports the results from Bea et al1 that the
MEK-ERK1/2 MAP kinase pathway plays a superior role in the
regulation of Egr-1 in C pneumoniae–infected mononuclear cells, as
coincubation with the ERK1/2 inhibitor UO126 (Calbiochem) completely blocked postinfectious Egr-1 mRNA expression. Interestingly, the C pneumoniae–induced expression of VEGF mRNA in
human monocytes was partially inhibited through blocking of the
Jan Rupp
Matthias Maass
Institute of Medical Microbiology
and Hygiene
University of Lübeck
Lübeck, Germany
[email protected]
1. Bea F, Puolakkainen MH, McMillen T, Hudson FN, Mackman N, Kuo
CC, Campbell LE, Rosenfeld ME. Chlamydia pneumoniae induces tissue
factor expression in mouse macrophages via activation of Egr-1 and the
MEK-ERK1/2 pathway. Circ Res. 2003;92:394 – 401.
2. Maass M, Bartels C, Engel PM, Mamat U, Sievers HH. Endovascular
presence of viable Chlamydia pneumoniae is a common phenomenon in
coronary artery disease. J Am Coll Cardiol. 1998;31:823– 827.
3. Lemström KB, Krebs R, Nykänen AI, Tikkanen JM, Sihvola RK, Aaltola
EM, Häyry PJ, Wood J, Alitalo K, Ylä-Herttuala S, Koskinen PK.
Vascular endothelial growth factor enhances cardiac allograft arteriosclerosis. Circulation. 2002;105:2524 –2530.
4. Guha M, O’Connel MA, Pawlinski R, Hollis A, McGovern P, Yan SF,
Stern D, Mackman N. Lipopolysaccharide activation of the MEKERK1/2 pathway in human monocytic cells mediates tissue factor and
tumor necrosis factor ␣ expression by inducing Elk-1 phosphorylation
and Egr-1 expression. Blood. 2001;98:1429 –1439.
5. Prasad A, Zhu J, Halcox JPJ, Waclawiw MA, Epstein SE, Quyyumi AA.
Predisposition to atherosclerosis by infections. Circulation. 2002;106:
184 –190.
6. Espinola-Klein C, Rupprecht HJ, Blankenberg S, Bickel C, Kopp H,
Rippin G, Victor A, Hafner G, Schlumberger W, Meyer J, AtheroGene
investigators. Impact of infectious burden on extent and long-term
prognosis of atherosclerosis. Circulation. 2002;105:15–21.
7. Itaya H, Imaizumi T, Yoshida H, Koyama M, Suzuki S, Satoh K.
Expression of vascular endothelial growth factor in human monocytes/
macrophages stimulated with lipopolysaccharide. Thromb Haemost.
2001;85:171–176.
8. Khachigian LM, Lindner V, Williams AJ, Collins T. Egr-1 induced
endothelial gene expression: a common theme in vascular injury. Science.
1996;271:1427–1431.
9. Gieffers J, Füllgraf H, Klinger M, Dalhoff K, Katus HA, Solbach W,
Maass M. Chlamydia pneumoniae infection in circulating human
monocytes is refractory to antibiotic treatment. Circulation. 2001;103:
351–356.
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Egr-1, a Major Link Between Infection and Atherosclerosis?
Jan Rupp and Matthias Maass
Downloaded from http://circres.ahajournals.org/ by guest on June 18, 2017
Circ Res. 2003;92:e78
doi: 10.1161/01.RES.0000072823.84611.9B
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