Elucidating the Role of Myosin Pseudo-Phosphorylation in a Novel Rescue Mouse Model of Cardiomyopathy

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This study focuses on a novel rescue mouse model generated to test the effect of regulatory light chain (RLC) phosphorylation on a diseased cardiac phenotype. Pseudo-phosphorylation of the D166V (aspartic acid to valine) mutation shown to be associated with a malignant phenotype of familial hypertrophic cardiomyopathy (FHC) was examined. Transgenic (Tg) mice carrying the D166V mutation demonstrated severe functional and physiological abnormalities and a significant decrease in endogenous RLC phosphorylation compared with Tg-WT mice. These detrimental phenotypes were partially rescued by either myosin light chain kinase-induced phosphorylation or by using phosphomimic (S15D) D166V-RLC exchanged in porcine cardiac muscle preparations. Transgenic rescue mice carrying the S15D-D166V mutation have been generated and subjected to functional measurements. Myofibrillar ATPase assays performed on Tg-S15D-D166V vs. Tg-D166V and Tg-WT mice cardiac samples showed a pseudo-phosphorylation rescue of an abnormal increase in calcium sensitivity (hallmark of FHC) caused by the D166V mutation. A D166V-induced decrease in maximal ATPase activity was also reversed in Tg-S15D-D166V mice. Similarly, maximal force and myofilament Ca2+-sensitivity, that were largely compromised in Tg-D166V skinned muscle fibers, were improved in the rescue mice and brought to the level observed in Tg-WT. Histopathological analyses of heart sections from age and gender matched mice from all groups demonstrated an approximately four-fold decrease in the extent of fibrosis in the rescue mice compared to Tg-D166V. The beneficial effects of S15D on the function of the D166V hearts were confirmed in vivo by invasive hemodynamics. Results from this study emphasize the significance of RLC phosphorylation in alleviating an FHC induced phenotype and could be used in the development of therapeutic interventions to restore the normal cardiac function.Supported by NIH-HL108343 and HL071778.