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Front. Physiol. | doi: 10.3389/fphys.2018.00243

Molecular defects in cardiac myofilament Ca2+- regulation due to cardiomyopathy-linked mutations can be reversed by small molecules binding to troponin

 Alice Sheehan1,  Andrew E. Messer1,  Maria Papadaki1, Afnan Choudhry1,  Vladimir Kren2, David Biedermann2, Brian Blagg3, Anuj Khandelwahl3 and  Steven B. Marston1*
  • 1Imperial College London, United Kingdom
  • 2Laboratory of Biotransformation, Institute of Microbiology, Czech Academy of Sciences, Czechia
  • 3University of Kansas, United States

The inherited cardiomyopathies, hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) are relatively common, potentially life-threatening and currently untreatable. Mutations are often in the contractile proteins of cardiac muscle and cause abnormal Ca2+ regulation via troponin. HCM is usually linked to higher myofilament Ca2+-sensitivity whilst in both HCM and DCM mutant tissue there is often an uncoupling of the relationship between troponin I (TnI) phosphorylation by PKA and modulation of myofilament Ca2+-sensitivity, essential for normal responses to adrenaline. The adrenergic response is blunted, and this may predispose the heart to failure under stress.
At present there are no compounds or interventions that can prevent or treat sarcomeric cardiomyopathies. There is a need for novel therapies that act at a more fundamental level to affect the disease process. We demonstrated that epigallocatechin-3 gallate (EGCG) was found to be capable of restoring the coupled relationship between Ca2+-sensitivity and TnI phosphorylation in mutant thin filaments to normal in vitro, independent of the mutation (15 mutations tested). We have labelled this property “re-coupling”. The action of EGCG in vitro to reverse the abnormality caused by myopathic mutations would appear to be an ideal pharmaceutical profile for treatment of inherited HCM and DCM but EGCG is known to be promiscuous in vivo and is thus unsuitable as therapeutic drug. We therefore investigated whether other structurally related compounds can re-couple myofilaments without these off-target effects.
We used the quantitative in vitro motility assay to screen 40 compounds, related to C-terminal Hsp90 inhibitors, and found 23 that can re-couple mutant myofilaments. There is no correlation between re-couplers and Hsp90 inhibitors. The Ca2+-sensitivity shift due to TnI phosphorylation was restored to 2.2±0.01 –fold (n=19) compared to 2.0±.24 fold (n=7) in wild-type thin filaments. Many of these compounds were either pure re-couplers or pure desensitisers, indicating these properties are independent; moreover, re-coupling ability could be lost with small changes of compound structure, indicating the possibility of specificity. Small molecules that can re-couple may have therapeutic potential.

Keywords: cardiomyopathy, sarcomeric protein mutations, Troponin I phosphorylation, PKA, Adrenergic beta-Agonists, ca2+ regulation, contractility, small molecule pharmacology, EGCG, silybin, Lusitropy, Structure Activity Relationships

Received: 04 Jan 2018; Accepted: 06 Mar 2018.

Edited by:

J-P Jin, Wayne State University School of Medicine, United States

Reviewed by:

Douglas Root, University of North Texas, United States
Aldrin V. Gomes, University of California, Davis, United States
Yi Yang, Guangzhou University of Chinese Medicine, China  

Copyright: © 2018 Sheehan, Messer, Papadaki, Choudhry, Kren, Biedermann, Blagg, Khandelwahl and Marston. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Steven B. Marston, Imperial College London, London, United Kingdom,