Toll-like recepetors play a major role in the myocardial pro-inflammatory and anti-inflammatory responses

Acute cardiac dysfunction due to myocardial infarction and septic shock may contribute to hypotension, low cardiac output, or death. A common outcome of these disease states is the induction of inflammation, a major contributor to acute cardiac dysfunction. Acute inflammatory reactions often involve the Toll-Like receptor/NFκB pathway. Toll-Like receptors (TLRs) are members of the innate immune system and are responsible for recognizing foreign Pathogen Associated Molecular Patterns (PAMPs) expressed by infecting organisms. Ligation of cardiomyocyte TLRs by PAMPs initiates an inflammatory response and can reduce cardiomyocyte contractility. Recently, endogenous molecules known as Damage Associated Molecular Patterns (DAMPs) which are released during myocardial infarctions have proven to initiate an inflammatory response similar to PAMPs in inflammatory cells. We hypothesize that DAMPs ligate to TLRs causing a pro-inflammatory response by cardiomyocytes whilst reducing cardiac contractility. Additionally, this pro-inflammatory response can be attenuated by using TLR9 ligand, CpG, in a pre-treatment model. Our first objective was to assay a variety of DAMPs for an effect on the inflammatory and functional responses of cardiomyocytes, and determine which TLRs are involved. We found that the DAMP, HSP70, induces an inflammatory response via TLR2 and the NFkB signalling pathway. Our second objective was to determine if a TLR ligand was capable of activating NFκB signalling inducing a tolerant state without affecting cardiac contractility. We found that pre-treatment with TLR9 ligand (CpG) induced tolerance and down-regulated NFkB signalling and expression of inflammatory markers. In accord with these observations, we found CpG pre-treatment attenuated decreases in cardiomyocyte contractility in an LPS model and coronary artery ligation model of ischemia reperfusion. Microarray analysis identified a group of NFkB pathway inhibitors induced by CpG that may be responsible for the diminished inflammatory response. TNFAIP3 (A20) was identified as a highly regulated suppressor of NFkB in cardiomyocytes. In conclusion, a discrete set of TLRs play a major role in myocardial pro-inflammatory responses caused by DAMPs, PAMPs and ischemic injury that lead to decreased contractility and inflammation. However, using TLR9 ligand CpG pre-emptively has shown to reduce the inflammatory response while maintaining proper cardiac function.Medicine, Faculty ofMedicine, Department ofExperimental Medicine, Division ofGraduat