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

Abstract

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 κ B (NFκB)-luciferase knock-in mice were used to assess NFκB signalling. DAMPs, HSP60, HSP70 and HMGB1, increased NFκB 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 NFκB. This causes cardiomyocyte inflammation and decreased contractility. (Circ J 2011; 75: 2445 - 2452

Expression of heat shock protein 70 in transport-stressed broiler pectoralis major muscle and its relationship with meat quality

“…Furthermore, we found the distribution or migration of HSP70 from the cytoplasm to the extracellular matrix in the PSE-like muscle groups, as indicated in Figure 3. Previous study has shown that HSPs are located outside the cell, particularly after various pathological conditions such as inflammatory response syndrome, muscle contractile dysfunction and severe diseases (Mathur et al, 2011). Vega et al (2008) revealed that HSP70 translocates into membranes after stress and is released within membranous structures from intact HepG2 cells that activate the immune system to generate a systemic response to avoid the propagation of initial stress.…”

Genotoxic stress modulates the release of exosomes from multiple myeloma cells capable of activating NK cell cytokine production: Role of HSP70/TLR2/NF-kB axis

“…56,57 In general, these molecular chaperones are usually expressed intracellularly where they support the folding and the transport of a great variety of proteins. In contrast, membrane-bound and extracellular-located HSPs act as potent danger signals.…”

Isolated hearts treated with skeletal muscle homogenates exhibit altered function

“…The soleus and HSWG homogenates contained elevated levels of two known DAMPs (HSP60 and HSP72), suggesting that DAMPs released from specific skeletal muscle fibers may be capable of altering cardiac function. In support of this, eHSPs have been implicated as "alarm proteins" or "alarmins" (Manson et al 2012;Stoecklein et al 2012), and both HSP60 and HSP72 have been shown to interact with cardiac TLR4 and depress cardiomyocyte contractility (Kim et al 2009;Mathur et al 2011;Vabulas et al 2002). Therefore, the reduction in LVDP and +dP/dt observed in the hearts treated with soleus and HSWG muscle homogenates as well No significant differences were observed.…”

“…Interestingly, when HSP60, an HSP normally confined to mitochondria, was added to cultured cardiomyocytes, cell shortening was reduced (Kim et al 2009). Similarly, when HSP72, the stressinducible isoform of the HSP70 family, was added to cultured cardiomyocytes, it was shown to cause an inflammatory response and decrease contractility (Mathur et al 2011). Thus, when skeletal muscle fibers are damaged and their contents released into the extracellular environment, specific molecules such as HSP60 and HSP72 may act as DAMPs and initiate an immune and/or inflammatory response in other cells and tissues, including the heart.…”