Abstract 123: Study Of The Role Of Myosin-binding Protein C In The Structure-function Of Intact Cardiac Muscles Through The Use Of A Sarcomere Activation Biosensor

Cardiomyopathies affect as many as 1 in 500 adults, with hypertrophic cardiomyopathy (HCM) being the most commonly inherited heart disease. Although there are various genetic mutations which cause HCM, 40-50% of mutations identified in patients with this disease are found in the cardiac myosin-binding protein C (MyBP-C) gene. Thus, understanding this protein's role in sarcomere activation is critical for the development of effective therapeutic strategies. Previous work has identified MyBP-C as a key modulator of the sarcomere through inter-myofilament signaling. Although these studies have provided valuable information on the function of MyBP-C protein, the bulk of this work has been done with either in vitro protein recombination or permeabilized muscle. Unfortunately, these systems lack significant physiological features of muscle, such as load and intact excitation-contraction coupling mechanisms. Therefore, a large gap exists in the ability to monitor muscle sarcomere activation in an intact system in real time. In order to further advance the study of sarcomere activation in HCM disease models, specifically those targeting MyBP-C, a cardiac specific myofilament-targeted FRET based biosensor has been designed and validated. This new sarcomere activation biosensor reports real-time myofilament dynamics during physiological twitch contractions in live cardiac muscle. This allows for the in vivo biophysical tracking of FRET-detected conformation changes in TnC, which reflect the ensemble of regulatory events which lead to sarcomere activation. Currently, the biosensor is being utilized to investigate changes in sarcomere activation in MyBP-C knockout mice. We find that intact cardiac muscle under load shows slowed isometric twitch relaxation kinetics in MyBP-C knockout mice versus controls. In concert with thin and thick filament modifying small molecules, this biosensor system will be used to investigate sarcomere-based mechanisms of intact cardiac muscle performance in health and disease.