Disruption of phospholipase Cgamma1 signalling attenuates cardiac tumor necrosis factor-alpha expression and improves myocardial function during endotoxemia.

AIMS: Lipopolysaccharide (LPS) induces tumor necrosis factor-alpha (TNF-alpha) expression in cardiomyocytes, which contributes to myocardial dysfunction during sepsis. The purpose of this study was to investigate the role of phosphatidylinositol (PI) phospholipase Cgamma1 (PLCgamma1) in cardiac TNF-alpha expression, and myocardial dysfunction during endotoxemia. METHODS AND
RESULTS: In cultured mouse neonatal cardiomyocytes, LPS increased PLCgamma1 phosphorylation. Knockdown of PLCgamma1 with specific siRNA or inhibition of PLCgamma1 with U73122 attenuated TNF-alpha expression induced by LPS. This action of PLCgamma1 was mediated through inositol-1,4,5-trisphosphate (IP3)/IP3 receptor (IP3R) pathways since blocking either IP3 or IP3R decreased LPS-induced TNF-alpha expression. In contrast, neither diacylglycerol agonist nor antagonist had any evident effect on LPS-induced TNF-alpha expression in cardiomyocytes. To investigate the role of PLCgamma1 in endotoxemia in vivo, wild-type and heterozygous PLCgamma1 knockout (PLCgamma1(+/-)) mice were pre-treated with either U73122, or its inactive analog U73343, or vehicle for 15 min, followed by LPS for 4 h. Inhibition of PLCgamma1 by U73122 or by heterozygous deletion of the PLCgamma1 gene decreased cardiac TNF-alpha expression. More importantly, LPS-induced myocardial dysfunction was also attenuated in PLCgamma1(+/-) mice or by U73122 treatment.
CONCLUSION: PLCgamma1 signalling induces cardiac TNF-alpha expression and myocardial dysfunction during LPS stimulation. The action of PLCgamma1 on TNF-alpha expression is mediated through IP3/IP3R pathways. The present results suggest that PLCgamma1 may be a potential therapeutic target for myocardial dysfunction in sepsis.