Toll-like receptor 3 and 4 signalling through the TRIF and TRAM adaptors in haematopoietic cells promotes atherosclerosis

• AIMS: Members of the Toll-like receptor (TLR) family initiate innate immune responses and were recently shown to play a role in atherosclerosis. However, the mechanisms that link TLR ligation to vascular inflammation and atherogenesis remain unclear. To identify which signalling pathways downstream of TLRs in immune cells are pro-atherogenic, we analysed the role of the TLR-specific adaptors MyD88 adaptor-like (MAL), TRIF-related adaptor molecule (TRAM), and TIR-domain-containing adaptor-inducing interferon-beta (TRIF) in atherosclerosis. METHODS AND RESULTS: Using a bone-marrow transplantation strategy into low-density lipoprotein receptor-deficient (Ldlr-/-) mice, we could specifically study the absence of the TLR adaptors in immune cells. We showed that haematopoietic deficiency of TRAM and TRIF, but not MAL, reduces atherosclerosis without affecting cholesterol metabolism. This was mediated by decreased aortic inflammation, indicated by lower aortic levels of pro-inflammatory mediators, and reduced influx of macrophages and T cells. Furthermore, by studying Tlr3-/- chimeric Ldlr-/- mice, we found that deleting TLR3 in immune cells significantly reduced both aortic inflammation and atherosclerotic burden. CONCLUSIONS: By studying hypercholesterolaemic mice with defects in TLR-signalling adaptors, we demonstrated that deleting either TRAM or TRIF in immune cells is sufficient to attenuate vessel inflammation and protect against atherosclerosis. In addition, these adaptors elicit partly different sets of inflammatory mediators and can independently inhibit the disease process. Furthermore, we identify TLR3 as a pro-atherogenic receptor in haematopoietic immune cells. The identification of these pro-atherogenic pathways downstream of TLR3 and TLR4 contributes to a better understanding of TLRs and their signalling pathways in the pathogenesis of atherosclerosis.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Annan medicin och hälsovetenskap (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Other Medical and Health Sciences (hsv//eng)

MEDICIN OCH HÄLSOVETENSKAP  -- Medicinska och farmaceutiska grundvetenskaper -- Immunologi inom det medicinska området (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Basic Medicine -- Immunology in the medical area (hsv//eng)

MEDICIN OCH HÄLSOVETENSKAP  -- Medicinska och farmaceutiska grundvetenskaper -- Cell- och molekylärbiologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Basic Medicine -- Cell and Molecular Biology (hsv//eng)

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Kardiologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Cardiac and Cardiovascular Systems (hsv//eng)

Nyckelord

Atherosclerosis TRAM TRIF TLR3 Vascular inflammation

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