Silybin B, resveratrol and epigallocatechin-3 gallate (EGCG) bind to troponin to restore the loss of lusitropy caused by cardiomyopathy mutations in vitro, in vivo, and in silico
Adrenergic activation of protein kinase A (PKA) targets the thin filaments of the cardiac muscle, specifically phosphorylating cTroponin I Ser22 and Ser23, causing a higher rate of Ca2+ dissociation from cTnC leading to a faster relaxation rate (lusitropy). This modulation is often suppressed by mutations that cause cardiomyopathy (uncoupling) and this could be sufficient to induce cardiomyopathy. A drug that could restore the phosphorylation-dependent modulation of relaxation rate could have the potential for treatment of these pathologies. We found, using single thin filament in vitro motility assays that the small molecules including silybin B, resveratrol, and epigallocatechin-3 gallate (EGCG) can restore coupling. We performed molecular dynamics simulations of the unphosphorylated and phosphorylated cardiac Troponin core with the TNNC1 G159D mutation. We found that silybin B, EGCG, and resveratrol restored the phosphorylation-induced change in the TnC helix A/B angle and the interdomain angle to wild-type values, whilst silybin A and epicatechin gallate (ECG) did not. In unphosphorylated G159D the recoupling molecules were observed to be frequently intercalated between The N terminal peptide of Troponin I and troponin C. In contrast, the controls, silybin A, and ECG bound to the surface. All of the interactions were diminished when troponin I was phosphorylated. We also performed studies with intact transgenic ACTC E99K mouse cells and TNNT2 R92Q-transfected guinea pig cardiomyocytes. The mutations blunt the increase in relaxation speed due to dobutamine; resveratrol, EGCG, and silybin B could restore the dobutamine response whilst silybin A did not. Thus recoupling by small molecules is demonstrated in vitro, in vivo, and in silico.