A number of studies have shown that rodents submitted to a mild whole body heat shock become resistant to a subsequent lethal dose of lipopolysaccharides (LPS). It is still unclear how a pre-heat treatment protects against endotoxins but one of the main results of a heat shock is the increased synthesis of a group of proteins known as the heat shock proteins (hsp). The hsp70 is the most abundant of these hsps and has been postulated to be the principal mediator of the observed protection against LPS. Since one of the majors consequences of endotoxemia is the induction of myocardial contractile dysfunction and hsp70 has been previously shown to protect against myocardial dysfunction due to infarction. We therefore propose to investigate the mechanism by which the hsp70 protects the myocardium during endotoxemia. Our preliminary results show that heat shocked isolated rat neonatal cardiomyocytes are tolerant to a subsequent exposure to LPS. In addition, cardiomyocytes infected with adenoviral vectors containing the hsp70 gene are also tolerant to endotoxin exposure in vitro. We also find that a transgenic mouse line overexpressing a hsp70 gene is more tolerant to endotoxemia than littermates that do not express the hsp70 transgene. The mechanism in which hsp70 renders the cardiomyocyte both in vitro and in vivo tolerant to endotoxemic injury would seem to involve a reduction in inducible nitric oxide synthase expression according to our preliminary results. We therefore propose to study in both isolated cardiomyocytes and the heart tissue of transgenic mice, the level of the mediators of endotoxin-induced cell injury: TNF-alpha, IL-1, nitric oxide (NO), inducible NO synthase and the transcription factor NFkB and how they are affected by the increased presence of hsp70. The proposed research project should clearly demonstrate if the sole presence of increased levels of hsp70 is protective against endotoxemia. This proposed study may open the way to harness the endogenous protective mechanisms in cardiomyocytes and to new innovative and effective therapies against the myocardial depression caused by endotoxins. ? ?
