Article

Toll-like receptor 4 is involved in outward arterial remodeling

Leiden University, Leyden, South Holland, Netherlands
Circulation (Impact Factor: 14.95). 02/2004; 109(3):393-8. DOI: 10.1161/01.CIR.0000109140.51366.72
Source: PubMed

ABSTRACT Toll-like receptor 4 (Tlr4) is the receptor for exogenous lipopolysaccharides (LPS). Expression of endogenous Tlr4 ligands, heat shock protein 60 (Hsp60) and extra domain A of fibronectin, has been observed in arthritic and oncological specimens in which matrix turnover is an important feature. In atherosclerosis, outward remodeling is characterized by matrix turnover and a structural change in arterial circumference and is associated with a vulnerable plaque phenotype. Since Tlr4 ligands are expressed during matrix turnover, we hypothesized that Tlr4 is involved in arterial remodeling.
In a femoral artery cuff model in the atherosclerotic ApoE3 (Leiden) transgenic mouse, Tlr4 activation by LPS stimulated plaque formation and subsequent outward arterial remodeling. With the use of the same model in wild-type mice, neointima formation and outward remodeling occurred. In Tlr4-deficient mice, however, no outward arterial remodeling was observed independent of neointima formation. Carotid artery ligation in wild-type mice resulted in outward remodeling without neointima formation in the contralateral artery. This was associated with an increase in Tlr4 expression and EDA and Hsp60 mRNA levels. In contrast, outward remodeling was not observed after carotid ligation in Tlr4-deficient mice.
These findings provide genetic evidence that Tlr4 is involved in outward arterial remodeling, probably through upregulation of Tlr4 and Tlr4 ligands.

Download full-text

Full-text

Available from: Aryan Vink, Jun 30, 2015
0 Followers
 · 
113 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Activation of toll-like receptors (TLR) in articular chondrocytes has been reported to increase the catabolic compartment, leading to matrix degradation, while the main consequence of TLR activation in monocytic cells is the expression and secretion of components of the innate immune response, particularly that of inflammatory cytokines. The objective of the work reported here was to obtain a more complete picture of the response repertoire of articular chondrocytes to TLR activation. Mass spectrometry was used to analyse the secretome of stimulated and unstimulated cells. Characterization of TLR expression in rat articular chondrocytes by RT/PCR indicated that TLR4 was the major receptor form. Exposure of these cells to lipopolysaccharide (LPS), the well-characterized TLR4 ligand, induced production not only of the matrix metalloproteinases MMP3 and 13, but also of components traditionally associated with the innate immune response, such as the complement components C1r, C3 and complement factor B, long pentraxin-3 and osteoglycin. Neither TNF-alpha nor IL-1 was detectable in culture media following exposure to LPS. One of the most prominently-induced proteins was the chitinase-like protein, Chi3L1, linking its expression to the innate immune response repertoire of articular chondrocytes. In intact femoral heads, LPS induced expression of Chi3L1 in chondrocytes close to the articular surface, suggesting that only these cells mount a stress response to LPS. Thus articular chondrocytes have a capacity to respond to TLR activation, which results in the expression of matrix metalloproteases as well as subsets of components of the innate immune response without significant increases in the production of inflammatory cytokines. This could influence the erosive processes leading to cartilage degeneration as well as the repair of damaged matrix.
    Matrix Biology 04/2008; 27(2):107-18. DOI:10.1016/j.matbio.2007.09.009 · 3.65 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have previously demonstrated that nuclear factor kappa B (NFkappaB) activation is needed for the development of cardiac hypertrophy in vivo. NFkappaB is a downstream transcription factor in the Toll-like receptor (TLR)-mediated signaling pathway; therefore, we investigated a role of TLR4 in cardiac hypertrophy in vivo. TLR4-deficient mice (C.C3H-Tlr4(lps-d), n = 6), wild-type (WT) genetic background mice (BALB/c, n = 6), TLR4-deleted strain (C57BL/10ScCr, n = 8), and WT controls (C57BL/10ScSn, n = 8) were subjected to aortic banding for 2 weeks. Age-matched surgically operated mice served as controls. In a separate experiment, rapamycin (2 mg/kg, daily) was administered to TLR4-deficient mice and WT mice immediately following aortic banding. The ratio of heart weight/body weight (HW/BW) was calculated, and cardiac myocyte size was examined by FITC-labeled wheat germ agglutinin staining of membranes. NFkappaB binding activity and the levels of phospho-p70S6K in the myocardium were also examined. Aortic banding significantly increased the ratio of HW/BW by 33.9% (0.601 +/- 0.026 vs. 0.449 +/- 0.004) and cell size by 68.4% in WT mice and by 10.00% (0.543 +/- 0.011 vs. 0.495 +/- 0.005) and by 11.8% in TLR4-deficient mice, respectively, compared with respective sham controls. NFkappaB binding activity and phospho-p70S6K levels were increased by 182.6% and 115.2% in aortic-banded WT mice and by 78.0% and 162.0% in aortic-banded TLR4-deficient mice compared with respective sham controls. In rapamycin-treated aortic-banded mice, the ratio of HW/BW was increased by 18.0% in WT mice and by 3.5% in TLR4-deficient mice compared with respective sham controls. Our results demonstrate that TLR4 is a novel receptor contributing to the development of cardiac hypertrophy in vivo and that both the TLR4-mediated pathway and PI3K/Akt/mTOR signaling are involved in the development of cardiac hypertrophy in vivo.
    Cardiovascular Research 12/2005; 68(2):224-34. DOI:10.1016/j.cardiores.2005.05.025 · 5.81 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The studies described in this thesis suggest that peptidoglycan (PG) is involved in initiation and progression of atherosclerosis. PG is an antigen that can be found in large amounts in the Gram-positive bacterial wall and only in small amounts in the Gram-negative bacterial wall. PG is able to stimulate the Toll-like receptor 2 (TLR2), a receptor that plays an important role in the innate immune system. In the normal situation PG is present in the intestinal mucosal flora, but under certain pathological circumstances PG is able to promote chronic inflammation at non-mucosal sites in the body. IgM, IgG and IgA antibodies against PG are present in serum of healthy subjects. However, in atherosclerotic patients the IgM antibody levels against PG are lower compared to control subjects. Furthermore, IgM antibody levels against PG are negatively associated with intima-media thickness in coronary arteries and therefore with more pronounced human atherosclerotic disease. We found these associations in a cross-sectional study, but these IgM antibody levels against PG are not prognostic markers for development of adverse cardiovascular events after elective coronary angioplasty. We also showed that adventitial fibroblasts and human coronary arteries express TLR2 and that TLR2 stimulation of adventitial fibroblasts increases expression of pro-inflammatory cytokines and chemokines, like IL-1β, IL-6, IL-8 and MCP-1. In addition, in wild-type mice Pam3Cys-SK4 stimulation promotes intimal lesion formation, which is clearly TLR2-mediated since TLR2-/- mice show no significant increase in intimal hyperplasia. In ApoE-/- mice TLR2 stimulation increases development of atherosclerotic plaques. In addition to recognition by TLR2, degradation products of PG can also be recognized by intracellular NOD and Nalp proteins. We found that NOD1 and NOD2 protein expression is significantly increased in human atherosclerotic lesions and in those lesions NOD2 protein is present in macrophages within inflammatory areas and in endothelial cells lining the vessel wall. NOD1 protein expression is associated with the presence of smooth muscle cells (SMC) and collagen, but also with macrophages when SMC are absent. Furthermore, both NOD1 and NOD2 protein levels are inversely associated with matrix metalloproteinase (MMP)-2 levels and positively with MMP-8 and MMP-9 levels. Previous studies from our group showed that PG is present in human atherosclerotic plaques that reveal an inflammatory, vulnerable phenotype and that PG is present in the macrophage-rich regions of those plaques. In this thesis we extend this finding by showing that peripheral blood monocytes that are stimulated with PG increase expression and functionality of integrins on their surface, thereby promoting firm adhesion of the monocytes to endothelial cells and migratory properties. Furthermore, peritoneal macrophages stimulated with PG in vitro show increased homing into atherosclerotic plaques in vivo. These studies not only suggest that PG promotes atherosclerotic lesion development and progression; they also show that PG enhances accumulation of monocytes and/or macrophages at sites of inflammation thereby promoting the formation of vulnerable plaques. These vulnerable plaques are prone to rupture and thereby promote the formation of a thrombus. Such a thrombus eventually might cause a myocardial infarction or stroke.