Epigallocatechin-3-Gallate Reverses the Defects in Modulation of Ca2+-Sensitivity by Troponin I Phosphorylation Caused by Hypertrophic and Dilated Cardiomyopathy Mutations in Cardiac Muscle

Heart muscle contraction is regulated via the β-adrenergic response that leads to phosphorylation of Troponin I (TnI) at Ser 22/23, which changes the Ca2+-sensitivity of the cardiac myofilament. Previously it has been shown that mutations found in Dilated Cardiomyopathy (DCM) and Hypertrophic Cardiomyopathy (HCM) patients abolish the relationship between TnI phosphorylation and Ca2+-sensitivity (uncoupling).Ca2+-sensitisers and Ca2+-desensitisers that act upon troponin alter the Ca2+-sensitivity of the myofilament but their relationship with TnI phosphorylation has never been studied before.Epigallocatechin-3-gallate (EGCG) is a major extract of green tea and it also acts as a Ca2+-desensitiser by binding to Troponin C of the myofilament. 100 µM EGCG decreased Ca2+-sensitivity of phosphorylated and unphosphorylated wild-type thin filaments equally (by 2.15±0.45 and 2.80±0.48-fold respectively), retaining the coupling. In contrast, EGCG reduced Ca2+-sensitivity of phosphorylated but not unnphosphorylated thin filaments containing 8 DCM (TPM1 E54K and E40K, TNNC1 G159D, TNNI3 K36Q, ACTC E361G) and HCM (TPM1 E180G, TNNT2 K280N, ACTC E99K)-causing mutations. As a result the dependence of Ca2+-sensitivity upon TnI phosphorylation of uncoupled mutant thin filaments was restored in every case. In single myofibrils, EGCG reduced Ca2+-sensitivity of force and kACT and also preserved the coupling with wild type and restored coupling with ACTC E361G mutant myofibrils.The effect of EGCG demonstrates that it is possible to reverse the pathological defects in troponin caused by HCM mutations pharmacologically.