Extracellular heat shock protein 60, cardiac myocytes, and apoptosis.
BACKGROUND
Previously, we have found that changes in the location of intracellular heat shock protein (HSP)60 are associated with apoptosis. HSP60 has been reported to be a ligand of toll-like receptor (TLR)-4.


OBJECTIVE
We hypothesized that extracellular HSP60 (exHSP60) would mediate apoptosis via TLR4.


RESULTS
Adult rat cardiac myocytes were treated with HSP60, either recombinant human or with HSP60 purified from the media of injured rat cardiac myocytes. ExHSP60 induced apoptosis in cardiac myocytes, as detected by increased caspase 3 activity and increased DNA fragmentation. Apoptosis could be reduced by blocking antibodies to TLR4 and by nuclear factor kappaB binding decoys, but not completely inhibited, even though similar treatment blocked lipopolysaccharide-induced apoptosis. Three distinct controls showed no evidence for involvement of a ligand other than exHSP60 in the mediation of apoptosis.


CONCLUSIONS
This is the first report of HSP60-induced apoptosis via the TLRs. HSP60-mediated activation of TLR4 may be a mechanism of myocyte loss in heart failure, where HSP60 has been detected in the plasma.
Kim
Se-Chan
SC
Molecular & Cellular Cardiology, University of California-Davis, One Shields Ave, Davis, CA 95616, USA.
Stice
James P
JP
Chen
Le
L
Jung
James S
JS
Gupta
Sanjiv
S
Wang
Yin
Y
Baumgarten
Georg
G
Trial
Joann
J
Knowlton
Anne A
AA
D000818:Animals; D000906:Antibodies; D017209:Apoptosis; D053148:Caspase 3 / Q000378:metabolism; D018834:Chaperonin 60 / Q000378:metabolism*; D053938:DNA Fragmentation; D004731:Endotoxins / Q000378:metabolism; D055551:HSP27 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D053583:Interleukin-1beta / Q000235:genetics; D015850:Interleukin-6 / Q000235:genetics; D008024:Ligands; D018950:Lipopolysaccharide Receptors / Q000378:metabolism; D008297:Male; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D016328:NF-kappa B / Q000378:metabolism; D010766:Phosphorylation; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D051195:Toll-Like Receptor 2 / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000276:immunology / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D000906:Antibodies; D018834:Chaperonin 60; D004731:Endotoxins; D055551:HSP27 Heat-Shock Proteins; C486114:Hspb1 protein, rat; D053583:Interleukin-1beta; D015850:Interleukin-6; D008024:Ligands; D018950:Lipopolysaccharide Receptors; D016328:NF-kappa B; D012333:RNA, Messenger; D011994:Recombinant Proteins; C495343:Tlr2 protein, rat; C495347:Tlr4 protein, rat; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; D048051:p38 Mitogen-Activated Protein Kinases; C505410:Casp3 protein, rat; D053148:Caspase 3