Chlamydia pneumoniae-induced foam cell formation requires MyD88-dependent and -independent signaling and is reciprocally modulated by liver X receptor activation - PubMed (original) (raw)

Chlamydia pneumoniae-induced foam cell formation requires MyD88-dependent and -independent signaling and is reciprocally modulated by liver X receptor activation

Shuang Chen et al. J Immunol. 2008.

Abstract

Chlamydia pneumoniae is detected by macrophages and other APCs via TLRs and can exacerbate developing atherosclerotic lesions, but how that occurs is not known. Liver X receptors (LXRs) centrally control reverse cholesterol transport, but also negatively modulate TLR-mediated inflammatory pathways. We isolated peritoneal macrophages from wild-type, TLR2, TLR3, TLR4, TLR2/4, MyD88, TRIF, MyD88/TRIF, and IFN regulatory factor 3 (IRF3) KO mice, treated them with live or UV-killed C. pneumoniae in the presence or absence of oxidized LDL, then measured foam cell formation. In some experiments, the synthetic LXR agonist GW3965 was added to macrophages infected with C. pneumoniae in the presence of oxidized LDL. Both live and UV-killed C. pneumoniae induced IRF3 activation and promoted foam cell formation in wild-type macrophages, whereas the genetic absence of TLR2, TLR4, MyD88, TRIF, or IRF3, but not TLR3, significantly reduced foam cell formation. C. pneumoniae-induced foam cell formation was significantly reduced by the LXR agonist GW3965, which in turn inhibited C. pneumoniae-induced IRF3 activation, suggesting a bidirectional cross-talk. We conclude that C. pneumoniae facilitates foam cell formation via activation of both MyD88-dependent and MyD88-independent (i.e., TRIF-dependent and IRF3-dependent) pathways downstream of TLR2 and TLR4 signaling and that TLR3 is not involved in this process. This mechanism could at least partly explain why infection with C. pneumoniae accelerates the development of atherosclerotic plaque and lends support to the proposal that LXR agonists might prove clinically useful in suppressing atherogenesis.

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Figures

Fig. 1

Fig. 1. C. pneumoniae promotes the formation of foam cells in the presence of ox-LDL from wild type-derived macrophages

A Representative formation of foam cells following C. pneumoniae (MOI=5) or ox-LDL (100 μg/ml) alone or in combination. B. The amount of foam cells was significantly increased following live (p<0.05) or UV-killed (p<0.05) C. pneumoniae and ox-LDL administration. C. The treatment with GW3965 (2 μM) significantly reduced foam cell formation induced by the addition of ox-LDL and live (p<0.01) or UV-killed (p<0.01) C. pneumoniae. Foam cells are expressed as percentage of positive Oil Red O cells compared with total macrophages (MΦ). Data represent mean±SEM, experiments were repeated in four times in triplicates. Statistical difference was evaluated by means of Students’ t test.

Fig. 2

Fig. 2. Live- or UV-killed _C. pneumoniae-_induced foam cell formation is TLR2- TLR4-, MyD88- and TRIF-dependent

Peritoneal macrophages of wild type (WT), TLR2−/−, TLR4−/− and TLR2−/−:TLR4−/− mice were treated with live (A) or UV killed (B) C. pneumoniae (MOI=5) with or without ox-LDL (100 μg/ml). The same experimental protocol was applied to macrophages derived from MyD88−/−, TRIF−/− and MyD88−/−:TRIF−/− mice (C and D). Foam cells are expressed as percentage of positive Oil Red O cells compared with total M. Data represent mean±SEM, experiments were repeated three times in triplicate. Statistical difference, denoted as * for p<0.05, was evaluated by means of Students’ t test.

Fig. 3

Fig. 3. C. pneumoniae induced NF-κB and IRF3 activation and modulation by the LXR agonist GW3965

NF-kB activation with live (A) or UV-killed (B) C. pneumoniae in the presence of ox-LDL. The treatment with GW3965 further reduced NF-κB activation (A and B). Panel C and D represent the detection of IRF3 activation following live (C) or UV-killed (D) C. pneumoniae and ox-LDL. GW 3965 significantly reduced the formation of foam cells (C and D; p<0.001 and p<0.001, respectively). Data represent mean±SEM, experiments were repeated three times in triplicate. Statistical difference, denoted as * for p<0.05 and ** for p<0.01 as evaluated by means of Students’ t test.

Fig. 4

Fig. 4. _C. pneumoniae_-mediated foam cell formation requires IRF3 activation as IRF3−/− macrophages are resistant to infection-mediated foam cell production

Peritoneal macrophages from IRF3−/− mice and wt mice were stimulated with live (A) or UV-killed (B) C. pneumoniae and ox-LDL. Panel C is a representative picture of foam cells induced in peritoneal macrophages obtained in wild type mice compared with those obtained from IRF3 −/− mice in the presence of live C. pneumoniae and ox-LDL. Data represent mean±SEM, experiments were repeated three time in triplicate. Statistical difference, denoted as * for p<0.05, was evaluated by means of Students’ t test.

Fig. 5

Fig. 5. _C. pneumoniae_-mediated foam cell production does not involve TLR3 signaling

Peritoneal macrophages derived from wild type or TLR3−/− mice were stimulated with live (A) or UV-killed (B) C. pneumoniae and ox-LDL and Oil Red O positive stained cells were calculated to measure foam cell formation. Data represent mean±SEM, experiments were repeated three times in triplicate. Statistical difference, denoted as ** for p<0.01 was evaluated by means of Students’ t test.

Fig. 6

Fig. 6. Schematic representation of _C. pneumoniae_- mediated foam cell formation

C. pneumoniae infection mediates foam cell formation through at least two signalling pathways: TLR2 and TLR4-dependent signaling through MyD88, and TLR4-TRIF-dependent signalling. The MyD88 pathway leads to activation of NF-κB, and the TRIF pathway leads to activation of IRF3. The addition of ox-LDL increases _C. pneumoniae_-promoted foam cell formation and activates NF-κB and IRF3 signalling pathways. LXR agonists like GW3965 reverse _C. pneumoniae_-induced foam cell formation by increasing cholesterol efflux via ABCA1 expression. Others have shown that TLRs that can activate TRIF and IRF3 inhibit LXR responses (35) and we show that the LXR agonist GW3965, in turn, can inhibit _C. pneumoniae_-induced IRF3 activation, suggesting a bi-directional cross-talk. Thus, LXR activation can negatively modulate both TLR/MyD88 and TLR/TRIF-dependent innate immune signaling networks. Abbreviations: LXR= liver-X-receptor; ABCA1= ATP-binding cassette transporter.

References

    1. Saikku P, Leinonen M, Mattila K, Ekman MR, Nieminen MS, Makela PH, Huttunen JK, Valtonen V. Serological evidence of an association of a novel Chlamydia, TWAR, with chronic coronary heart disease and acute myocardial infarction. Lancet. 1988;2:983–986. -PubMed
    1. Kaukoranta-Tolvanen SS, Ronni T, Leinonen M, Saikku P, Laitinen K. Expression of adhesion molecules on endothelial cells stimulated by Chlamydia pneumoniae. Microb Pathog. 1996;21:407–411. -PubMed
    1. Kalayoglu MV, Byrne GI. A Chlamydia pneumoniae component that induces macrophage foam cell formation is chlamydial lipopolysaccharide. Infect Immun. 1998;66:5067–5072. -PMC -PubMed
    1. Kiechl S, Lorenz E, Reindl M, Wiedermann CJ, Oberhollenzer F, Bonora E, Willeit J, Schwartz DA. Toll-like receptor 4 polymorphisms and atherogenesis. N Engl J Med. 2002;347:185–192. -PubMed
    1. Molestina RE, Miller RD, Ramirez JA, Summersgill JT. Infection of human endothelial cells with Chlamydia pneumoniae stimulates transendothelial migration of neutrophils and monocytes. Infect Immun. 1999;67:1323–1330. -PMC -PubMed

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