Molecular Mechanisms Involved in Cardioskeletal Dysfunction Caused by Mutations in Myosin RLC Linked to Hypertrophic Cardiomyopathy

Abstract

The MYL2 gene concurrently expresses the human myosin regulatory light chain (RLC) in the ventricles of the heart and in the slow-twitch skeletal muscle. Mutations in MYL2 are known to cause hypertrophic cardiomyopathy (HCM), but in some cases they also lead to cardioskeletal myopathy in humans. Using transgenic animal models of HCM, we studied the mutation-induced morphological, structural and functional changes and the signaling pathways that trigger pathological remodeling of the HCM heart and slow-twitch skeletal muscle. Electron microscopy data showed severe myofilament disarray, a hallmark of HCM, in the hearts and in the soleus muscle of RLC-mouse models of HCM. Likewise, functional measurements of contractile force in skinned papillary and soleus muscle fibers showed similar direction of changes in HCM mice. Mutation-induced structural abnormalities in papillary and soleus muscles from HCM-R58Q mice were confirmed by high resolution X-ray diffraction showing similar changes in d1,0 (interfilament lattice spacing) and in equatorial reflections’ intensity I1,1/I1,0 ratio in both papillary and soleus muscles. Quantitative proteomic analysis revealed that out of >1560 TMT-labeled proteins identified with high confidence, 372 were different in the hearts of R58Q vs. WT mice, while in the soleus skeletal muscle out of >1100 TMT-proteins, 255 were different in R58Q vs. WT. The two major biological processes affected in both types of muscles in R58Q were the metabolic and cellular processes, with a greater percentage of metabolic processes affected in cardiac muscle. Common metabolic proteins decreased in heart/soleus of R58Q vs. WT mice included the energy production proteins, while the cellular processes included the calcium handling proteins. Our comprehensive data clearly indicated adverse heart/soleus muscle remodeling in HCM mice making them an ideal model to study the molecular, energetic and cellular mechanisms of cardioskeletal myopathy associated with MYL2. Supported by NIH-HL123255 (DSC).