Phospholipase C Modulates -Adrenergic Receptor– Dependent Cardiac Contraction and Inhibits Cardiac Hypertrophy

Phospholipase C (PLC) is a recently identified enzyme regulated by a wide range of molecules including Ras family small GTPases, Rho A, G 12/13, and G with primary sites of expression in the heart and lung. In a screen for human signal transduction genes altered during heart failure, we found that PLC mRNA is upregulated. Two murine models of cardiac hypertrophy confirmed upregulation of PLC protein expression or PLC RNA. To identify a role for PLC in cardiac function and pathology, a PLC -deficient mouse strain was created. Echocardiography indicated PLC / mice had decreased cardiac function, and direct measurements of left ventricular contraction demonstrated that PLC / mice had a decreased contractile response to acute isoproterenol administration. Cardiac myocytes isolated from PLC / mice had decreased -adrenergic receptor ( AR)-dependent increases in Ca transient amplitudes, likely accounting for the contractile deficiency in vivo. This defect appears to be independent from the ability of the AR system to produce cAMP and regulation of sarcoplasmic reticulum Ca pool size. To address the significance of these functional deficits to cardiac pathology, PLC / mice were subjected to a chronic isoproterenol model of hypertrophic stress. PLC / mice were more susceptible than wild-type littermates to development of hypertrophy than wild-type littermates. Together, these data suggest a novel PLC-dependent component of AR signaling in cardiac myocytes responsible for maintenance of maximal contractile reserve and loss of PLC signaling sensitizes the heart to development of hypertrophy in response to chronic cardiac stress. (Circ Res. 2005;97:1305-1313.)