Uncoupling of myofilament Ca2+ sensitivity from troponin I phosphorylation by mutations can be reversed by epigallocatechin-3-gallate

作者：Papadaki Maria; Vikhorev Petr G; Marston Steven B; Messer Andrew E^*

来源：Cardiovascular Research, 2015, 108(1): 99-110.

DOI：10.1093/cvr/cvv181

• Ca2+ sensitizers
• Epigallocatechin-3-gallate
• Ca2+ regulation of contractility
• Troponin phosphorylation
• Cardiomyopathies

Aims Heart muscle contraction is regulated via the b-adrenergic response that leads to phosphorylation of Troponin I (TnI) at Ser22/23, which changes the Ca2+ sensitivity of the cardiac myofilament. Mutations in thin filament proteins that cause dilated cardiomyopathy (DCM) and some mutations that cause hypertrophic cardiomyopathy (HCM) abolish the relationship between TnI phosphorylation and Ca2+ sensitivity (uncoupling). Small molecule Ca2+ sensitizers and Ca2+ desensitizers that act upon troponin alter the Ca2+ sensitivity of the thin filament, but their relationship with TnI phosphorylation has never been studied before.
Methods and results Quantitative in vitro motility assay showed that 30 mu M EMD57033 and 100 mu M Bepridil increase Ca2+ sensitivity of phosphorylated cardiac thin filaments by 3.1-and 2.8-fold, respectively. Additionally they uncoupled Ca2+ sensitivity from TnI phosphorylation, mimicking the effect of HCM mutations. Epigallocatechin-3-gallate (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. Moreover, EGCG also reduced Ca2+ sensitivity of phosphorylated but not unphosphorylated thin filaments containing DCM and HCM-causing mutations; thus, the dependence of Ca2+ sensitivity upon TnI phosphorylation of uncoupled mutant thin filaments was restored in every case. In single mouse heart myofibrils, EGCG reduced Ca2+ sensitivity of force and kACT and also preserved coupling. Myofibrils from the ACTC E361G (DCM) mouse were uncoupled; EGCG reduced Ca2+ sensitivity more for phosphorylated than for unphosphorylated myofibrils, thus restoring coupling.
Conclusion We conclude that it is possible to both mimic and reverse the pathological defects in troponin caused by cardiomyopathy mutations pharmacologically. Re-coupling by EGCG may be of potential therapeutic significance for treating cardiomyopathies.

• 出版日期2015-10-1