LPS-Induced TNF-αRelease from and Apoptosis in Rat Cardiomyocytes: Obligatory Role for CD14 in Mediating the LPS Response

The bacterial endotoxin lipopolysaccharide (LPS) contributes to the cardiovascular collapse and death observed in patients with sepsis. Because LPS has such profound effects on cardiac performance, we speculate that direct effects of LPS could be demonstrated on cardiomyocytes in culture, and that these direct effects are mediated by the LPS receptor, CD14. Accordingly, in this study, we provide evidence for CD14-dependent cardiotoxic effects of LPS including the LPS-stimulated secretion of tumor necrosis factor alpha (TNF-α) from cardiomyocytes. TNF-αis an inflammatory cytokine which is known for its negative inotropic effects on cardiac performance, but has not until recently been shown to be produced by cardiac cells. In this study, LPS was found to stimulate strongly in a dose-dependent manner the secretion of TNF-αfrom cultured adult rat cardiomyocytes. Further, LPS-induced TNF-αsecretion was blocked by an inhibitor of TNF-αprocessing, metallomatrix protease inhibitor (TAPI). Molecular and immunological evidence demonstrated the presence of LPS receptors (CD14) on cardiomyocytes. Attenuated TNF-αsecretion following PI-PLC treatment confirmed the functional importance of CD14 for LPS-mediated myocardial effects. Importantly, LPS also triggered apoptosis in cultured cardiomyocytes as quantified by single-cell gel electrophoresis of nuclei exhibiting DNA fragmentation patterns characteristic of apoptosis (i.e. cardiac comets). Apoptotic cell death was blocked by pre-incubation with the soluble TNF-αreceptor fragment (TNFRII:Fc), suggesting that LPS-induced apoptosis was TNF-α-dependent and probably involved an autocrine function for the TNF-αwhose secretion was under LPS control. The results of this study suggest that the cardiodepressant effects of LPS are dependent on CD14 signaling and may not only be due to acute negative inotropic effects of TNF-αbut also may be complicated by TNF-α-induced apoptotic cell death which effectively reduces the number of working myocardial cells.