In vivo evidence for a role of toll-like receptor 4 in the development of intimal lesions.
BACKGROUND
Inflammation plays an important role in atherogenesis. The toll-like receptor 4 (TLR4) is the receptor for bacterial lipopolysaccharides and also recognizes cellular fibronectin and heat shock protein 60, endogenous peptides that are produced in response to tissue injury. To explore a possible role for this receptor in arterial obstructive disease, we determined the expression of TLR4 in the atherosclerotic arterial wall, including adventitia, and studied the effect of adventitial TLR4 activation on neointima formation in a mouse model.


RESULTS
Localization of TLR4 was studied in human atherosclerotic coronary arteries by immunohistochemistry and detected in plaque and adventitia. In the adventitia, not all TLR4-positive cells colocalized with macrophages. In primary human adventitial fibroblasts, expression of TLR4 was demonstrated by immunofluorescence, Western blot, and reverse transcriptase-polymerase chain reaction. Adding lipopolysaccharide to these fibroblasts induced activation of NF-kappaB and an increase of mRNAs of various cytokines. The effect of adventitial stimulation of TLR4 was studied in a mouse model. A peri-adventitial cuff was placed around the femoral artery. Application of lipopolysaccharide between cuff and artery augmented neointima formation induced by the cuff (intimal area+/-SEM, 9134+/-1714 versus 2353+/-1076 microm(2), P<0.01). In TLR4-defective mice, application of cuff and lipopolysaccharide resulted in a smaller neointima than in wild-type mice (intimal area, 3859+/-904 microm(2), P=0.02 versus wild type).


CONCLUSIONS
A functional TLR4 is expressed in human adventitial fibroblasts and macrophages. Adventitial TLR4 activation augmented neointima formation in a mouse model. These results provide evidence for a link between the immune receptor TLR4 and intimal lesion formation.
Vink
Aryan
A
Experimental Cardiology Laboratory, Heart Lung Center Utrecht, University Medical Center Utrecht, The Netherlands.
Schoneveld
Arjan H
AH
van der Meer
Jelger J
JJ
van Middelaar
Ben J
BJ
Sluijter
Joost P G
JP
Smeets
Mirjam B
MB
Quax
Paul H A
PH
Lim
Sai Kiang
SK
Borst
Cornelius
C
Pasterkamp
Gerard
G
de Kleijn
Dominique P V
DP
D000818:Animals; D001161:Arteriosclerosis / Q000209:etiology* / Q000378:metabolism / Q000473:pathology; D002478:Cells, Cultured; D003324:Coronary Artery Disease / Q000209:etiology / Q000378:metabolism; D003331:Coronary Vessels / Q000166:cytology / Q000378:metabolism; D016207:Cytokines / Q000096:biosynthesis / Q000235:genetics; D029721:Drosophila Proteins; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D008562:Membrane Glycoproteins / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D016328:NF-kappa B / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis; D011956:Receptors, Cell Surface / Q000235:genetics / Q000502:physiology*; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D017539:Tunica Intima / Q000166:cytology / Q000378:metabolism* / Q000473:pathology
D016207:Cytokines; D029721:Drosophila Proteins; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors