Toll-like receptor 2 activation by bacterial peptidoglycan-associated lipoprotein activates cardiomyocyte inflammation and contractile dysfunction.
OBJECTIVE
Although cardiac dysfunction plays an important role in the pathogenesis of sepsis, the mechanisms that underlie cardiac dysfunction in sepsis remain poorly understood. Bacterial peptidoglycan-associated lipoprotein (PAL), an outer-membrane protein of Gram-negative bacteria, was recently found to be released into the bloodstream in sepsis and to cause inflammation and death in mice. The present studies assessed the effects of PAL on cardiomyocyte function and its signal transduction in cardiomyocytes.


METHODS
Randomized prospective animal study.


METHODS
Research laboratory.


METHODS
Male C57BL/6 mice, B6;129S-Tnfrsf1a(tm1Imx) Tnfrsf1b(tm1Imx)/J knockout mice, Toll-like receptor 2 (TLR2) knockout mice, and myeloid differentiation factor 88 (MyD88) knockout mice.


METHODS
None.


RESULTS
Immunohistochemical staining and immunoblot analysis indicated that intravenously injected PAL bound to myocardium. Injection of PAL decreased cardiac function in vivo. Challenge with PAL altered cell shortening and Ca2+ transients in isolated mouse cardiomyocytes but not in cardiomyocytes isolated from TLR2 -/- and MyD88 -/- mice. Cytokine profiling arrays demonstrated that tumor necrosis factor-alpha (TNFalpha), granulocyte colony-stimulating factor, and interferon-gamma-production were elevated in PAL-treated cardiomyocytes. Increased TNFalpha production was abolished in MyD88 -/- cardiomyocytes but restored by adenovirally mediated expression of MyD88. PAL did not affect cell shortening and Ca2+ cycling in cardiomyocytes obtained from mice deficient for TNFalpha receptor (TNFR) 1 and TNFR2 (TNFR1/2 -/-).


CONCLUSIONS
Our data reveal that PAL uses the TLR2/MyD88 signaling cascade to induce cardiomyocyte dysfunction and inflammatory responses and that TNFalpha is a major mediator of PAL-induced dysfunction in cardiomyocytes. These studies suggest that circulating PAL and other TLR2 agonists may contribute to cardiac dysfunction in sepsis.
Zhu
Xinsheng
X
Department of Anesthesia and Critical Care, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
Bagchi
Aranya
A
Zhao
Huailong
H
Kirschning
Carsten J
CJ
Hajjar
Roger J
RJ
Chao
Wei
W
Hellman
Judith
J
Schmidt
Ulrich
U
D000818:Animals; D001425:Bacterial Outer Membrane Proteins / Q000276:immunology*; D002118:Calcium / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000276:immunology*; D008074:Lipoproteins / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D053594:Myeloid Differentiation Factor 88 / Q000235:genetics / Q000502:physiology*; D009200:Myocardial Contraction / Q000276:immunology*; D009205:Myocarditis / Q000276:immunology*; D032383:Myocytes, Cardiac / Q000276:immunology; D010457:Peptidoglycan / Q000276:immunology*; D047888:Receptors, Tumor Necrosis Factor, Type I / Q000235:genetics / Q000502:physiology*; D047889:Receptors, Tumor Necrosis Factor, Type II / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D018746:Systemic Inflammatory Response Syndrome / Q000276:immunology; D051195:Toll-Like Receptor 2 / Q000235:genetics / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology; D018487:Ventricular Dysfunction, Left / Q000276:immunology*
D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; C031163:ExcC protein, E coli; D008074:Lipoproteins; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; D010457:Peptidoglycan; D047888:Receptors, Tumor Necrosis Factor, Type I; D047889:Receptors, Tumor Necrosis Factor, Type II; C493486:Tlr2 protein, mouse; D051195:Toll-Like Receptor 2; D014409:Tumor Necrosis Factor-alpha; D002118:Calcium