The response of neonatal rat ventricular myocytes to lipopolysaccharide-induced stress

Sepsis induced by exposure to lipopolysaccharide (LPS) can be life-threatening and lead to multiple-organ dysfunction. Sepsis-associated cardiac dysfunction is a primary cause of mortality. The response of isolated cardiac myocytes to LPS exposure is poorly understood. Cultured neonatal rat ventricular cardiomyocytes were used to evaluate the response to LPS exposure. Other authors have reported that LPS exposure at doses sufficient to induce tumor necrosis factor alpha (TNF-alpha) production and apoptosis in adult cardiomyocytes do not induce apoptosis in neonatal cardiomyocytes. We therefore hypothesized that neonatal cardiomyocytes have innate protective mechanisms that protect from septic damage. Cultured neonatal rat ventricular cardiomyocytes were stimulated by exposure to LPS for varying lengths of time. NFkappaB signaling pathways, TNF-alpha production, and Akt activation were monitored. We also assessed the induction of apoptosis in these cells by monitoring caspase-3 activity. LPS rapidly stimulates nuclear translocation of NFkappaB and Akt activation. TNF-alpha production is also stimulated. However, high doses of LPS are unable to induce apoptosis in these cells, and protection is not a function of Akt activation. LPS treatment also stimulated the levels of cyclooxygenase-2 and the production of downstream metabolites, specifically PGE2 and 15deoxyDelta12-14PGJ2 (15dPGJ2). Specific inhibition of cyclooxygenase-2 activity induced apoptosis in the presence of LPS, whereas direct exposure to 15dPGJ2 at pharmacological levels induced apoptosis. Neonatal rat ventricular cardiomyocytes have innate protective mechanisms that prevent apoptotic cell death after LPS exposure. Metabolic products of arachidonic acid metabolized by the cyclooxygenase pathway can be potentially apoptotic or antiapoptotic. The balance of these products within these cells may define the cellular response to LPS exposure.