Pivotal role of phospholipase C in cardiac TNF‐α expression during endotoxemia

Abstract

Myocardial dysfunction is a common complication of sepsis. Lipopolysaccharides (LPS) of Gram-negative bacteria are important pathogens responsible for myocardial depression during sepsis. LPS-induced TNF-α is one of the main factors for cardiac dysfunction. The purpose of this study was to investigate the role of phospholipase C (PLC) in cardiac TNF-α expression during LPS stimulation. In cultured neonatal cardiomyocytes, U73122 treatment abrogated TNF-α expression induced by LPS, suggesting an essential role of PLC in LPS-induced TNF-α expression. To clarify which isozyme of three classes of PLC isozymes (β, γ, δ) is important in LPS-induced TNF-α expression, cardiomyocytes were co-incubated with LPS and a protein tyrosine kinase inhibitor genestein. Genestein blocked LPS-induced TNF-α expression, suggesting that PLCγ may play an important role in TNF-α expression since only PLCγ is activated through tyrosine kinase. This was confirmed by the following experimental results. First, LPS increased PLCγ1 phosphorylation in cardiomyocytes. Second, knockdown of PLCγ1 using specific siRNA decreased LPS-induced TNF-α expression by 55% in cardiomyocytes. To investigate the role of PLC in endotoxemia, adult mice were treated with LPS (4 mg/kg, i.p.) in the presence of vehicle or U73122 for 2 hours. U73122 treatment decreased cardiac TNF-α mRNA by 60% and significantly attenuated LPS-induced myocardial depression. In conclusion, our data demonstrated an important role of PLCγ1 in cardiac TNF-α expression and myocardial dysfunction during endotoxemia.