Toll4 (TLR4) expression in cardiac myocytes in normal and failing myocardium.
Expression of innate immune response proteins, including IL-1beta, TNF, and the cytokine-inducible isoform of nitric oxide synthase (iNOS), have been documented in the hearts of humans and experimental animals with heart failure regardless of etiology, although the proximal events leading to their expression are unknown. Noting that expression of a human homologue of Drosophila Toll, a proximal innate immunity transmembrane signaling protein in the fly, now termed human Toll-like receptor 4 (hTLR4), appeared to be relatively high in the heart, we examined TLR4 mRNA and protein abundance in isolated cellular constituents of cardiac muscle and in normal and abnormal murine, rat, and human myocardium. TLR4 expression levels in cardiac myocytes and in coronary microvascular endothelial cells could be enhanced by either LPS or IL-1beta, an effect inhibited by the oxygen radical scavenger PDTC. Transfection of a constitutively active TLR4 construct, CD4/hTLR4, resulted in activation of a nuclear factor-kappaB reporter construct, but not of an AP-1 or an iNOS reporter construct, in cardiac myocytes. In normal murine, rat, and human myocardium, TLR4 expression was diffuse, and presumably cytoplasmic, in cardiac myocytes. However, in remodeling murine myocardium remote from sites of ischemic injury and in heart tissue from patients with idiopathic dilated cardiomyopathy, focal areas of intense TLR4 staining were observed in juxtaposed regions of 2 or more adjacent myocytes; this staining was not observed in control myocardium. Increased expression and signaling by TLR4, and perhaps other Toll homologues, may contribute to the activation of innate immunity in injured myocardium.
Frantz
S
S
Cardiovascular Division, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA.
Kobzik
L
L
Kim
Y D
YD
Fukazawa
R
R
Medzhitov
R
R
Lee
R T
RT
Kelly
R A
RA
D000595:Amino Acid Sequence; D000818:Animals; D015704:CD4 Antigens / Q000235:genetics; D002478:Cells, Cultured; D003001:Cloning, Molecular; D003331:Coronary Vessels / Q000166:cytology; D018076:DNA, Complementary / Q000302:isolation & purification; D029721:Drosophila Proteins; D005786:Gene Expression Regulation / Q000276:immunology; D006333:Heart Failure / Q000378:metabolism* / Q000473:pathology; D006352:Heart Ventricles / Q000166:cytology; D006801:Humans; D007150:Immunohistochemistry; D007371:Interferon-gamma / Q000494:pharmacology; D007375:Interleukin-1 / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D008297:Male; D008562:Membrane Glycoproteins / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D009203:Myocardial Infarction / Q000378:metabolism / Q000473:pathology; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D016328:NF-kappa B / Q000378:metabolism / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D009928:Organ Specificity / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D011956:Receptors, Cell Surface / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D018808:Transcription Factor AP-1 / Q000378:metabolism
D015704:CD4 Antigens; D018076:DNA, Complementary; D029721:Drosophila Proteins; D007375:Interleukin-1; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; C495345:TLR4 protein, human; C495347:Tlr4 protein, rat; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D018808:Transcription Factor AP-1; D007371:Interferon-gamma; C496319:NOS2 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; C496318:Nos2 protein, rat