Published online before print October 29, 2009, doi: 10.1161/CIRCRESAHA.109.209643
Submitted on May 8, 2009
Revised on October 15, 2009
Accepted on October 19, 2009
Extracellular Heat Shock Protein 60, Cardiac Myocytes, and Apoptosis
Se-Chan Kim ;
From Molecular & Cellular Cardiology (S.-C.K., J.P.S., L.C., J.S.J., S.G., Y.W., A.A.K.), University of California, Davis; Department of Anesthesiology and Intensive Care Medicine (S.-C.K., G.B.), University of Bonn, Germany; Veterans Affairs Medical Center (L.C., A.A.K.), Sacramento, Calif; Base College, Ningxia Medical University, Yinchuan, People's Republic of China; and Baylor College of Medicine (J.T.), Houston, Tex.
* To whom correspondence should be addressed. E-mail: aaknowlton{at}ucdavis.edu.
Rationale: 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 TLR-4.
Methods and 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 TLR-4 and by nuclear factor 
B 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 TLR-4 may be a mechanism of myocyte loss in heart failure, where HSP60 has been detected in the plasma.
Key words: Toll-like receptor-4 • apoptosis • heat shock protein 60 • cardiac myocytes • tumor necrosis factor