Molecular basis of force-pCa relation in MYL2 cardiomyopathy mice: Role of the super-relaxed state of myosin

• Published in: Proceedings of the National Academy of Sciences - PNAS 2022-02, Vol.119 (8), p.1-10
• Main Authors: Yuan, Chen-Ching, Kazmierczak, Katarzyna, Liang, Jingsheng, Ma, Weikang, Irving, Thomas C., Szczesna-Cordary, Danuta
• Format: Article
• Language: English
• Subjects: Actin; Actins - metabolism; Animal models; Animals; BASIC BIOLOGICAL SCIENCES; Biological Sciences; Calcium; Calcium ions; Cardiac Myosins - genetics; Cardiac Myosins - metabolism; Cardiomyopathies - genetics; Cardiomyopathies - metabolism; Cardiomyopathy; Cardiomyopathy, Hypertrophic - genetics; Disease Models, Animal; Energy conservation; equatorial intensity ratio; Female; Filaments; Force measurement; Humans; Hypertrophy - metabolism; interfilament lattice spacing; Isometric; isometric force; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Muscles; Mutation; Myl2 gene; Myocardial Contraction - genetics; Myosin; Myosin Light Chains - genetics; Myosin Light Chains - metabolism; Myosins - metabolism; Myosins - physiology; Phenotype; Phenotypes; Phosphorylation; Sarcomeres; Sarcomeres - metabolism; Structure-Activity Relationship; Structure-function relationships; super-relaxed state of myosin; transgenic RLC mice; Ventricle; X-ray diffraction; X-Ray Diffraction - methods
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2110328119

In this study, we investigated the role of the super-relaxed (SRX) state of myosin in the structure–function relationship of sarcomeres in the hearts of mouse models of cardiomyopathy-bearing mutations in the human ventricular regulatory light chain (RLC, MYL2 gene). Skinned papillary muscles from hypertrophic (HCM–D166V) and dilated (DCM–D94A) cardiomyopathy models were subjected to small-angle X-ray diffraction simultaneously with isometric force measurements to obtain the interfilament lattice spacing and equatorial intensity ratios (I11/I10) together with the force-pCa relationship over a full range of [Ca2+] and at a sarcomere length of 2.1 μm. In parallel, we studied the effect of mutations on the ATP-dependent myosin energetic states. Compared with wild-type (WT) and DCM–D94A mice, HCM–D166V significantly increased the Ca2+ sensitivity of force and left shifted the I11/I10-pCa relationship, indicating an apparent movement of HCM–D166V cross-bridges closer to actin-containing thin filaments, thereby allowing for their premature Ca2+ activation. The HCM–D166V model also disrupted the SRX state and promoted an SRX-to-DRX (super-relaxed to disordered relaxed) transition that correlated with an HCM-linked phenotype of hypercontractility. While this dysregulation of SRX ↔ DRX equilibrium was consistent with repositioning of myosin motors closer to the thin filaments and with increased force-pCa dependence for HCM–D166V, the DCM–D94A model favored the energy-conserving SRX state, but the structure/function–pCa data were similar to WT. Our results suggest that the mutation-induced redistribution of myosin energetic states is one of the key mechanisms contributing to the development of complex clinical phenotypes associated with human HCM–D166V and DCM–D94A mutations.