Extracellular Heat Shock Protein 70 Induces Cardiomyocyte Inflammation and Contractile Dysfunction via TLR2

Background: Toll-like receptors (TLRs) are expressed on cardiomyocytes and recognize pathogen-associated molecular patterns. Whether endogenous molecules produced by tissue injury (damage associated molecular patterns, DAMPs) can induce cardiomyocyte inflammation via TLR signalling pathways and/or reduce cardiomyocyte contractility is unknown. Methods and Results: Primary cardiomyocytes isolated from nuclear factor kappa B (NF kappa B)-luciferase knock-in mice were used to assess NF kappa B signalling. DAMPs, HSP60, HSP70 and HMGB1, increased NF kappa B transcriptional activity compared to controls. HSP70 stood out compared to other DAMPs and even lipopolysaccharide (LPS). Subsequent experiments focused on HSP70. Cardiomyocytes exposed to HSP70 had a 58% decrease in contractility without a decrease in calcium flux. Exposure of cultured HL-1 cardiomyocytes to HSP70 resulted in increased expression of intercellular adhesion molecule 1 (ICAM-1), interleukin 6 (IL-6) and keratinocyte-derived chemokine (KC) compared to controls. Knock-out mice for TLR2, TLR4 and MyD88, plus background strain controls (C57BL/6) were used to assess induction of cardiomyocyte inflammation by HSP70. The cardiomyocyte expression of ICAM-1 induced by HSP70 was significantly reduced in TLR2 and MyD88 knock-out mice but not TLR4 knock-out mice; implicating the TLR2 signalling pathway. Furthermore, blocking antibodies to TLR2 were able to abrogate HSP70-induced contractile dysfunction and cell death. Conclusions: Extracellular HSP70 acting via TLR2 and its obligate downstream adaptor molecule, MyD88, activate NF kappa B. This causes cardiomyocyte inflammation and decreased contractility. (Circ J 2011; 75: 2445-2452)