FCSM · Human myosins

Human myosins

In utero development is critical for normal skeletal and cardiac muscle function throughout life. Many diseases, such as distal arthrogryposis (affecting 1/3000 live births) and clubfoot (1/1000) in skeletal muscle and arrhythmias in cardiac muscle (1/4000), manifest in the embryonic and foetal period. They permanently affect longevity and quality of life. Because the effects of these diseases are present at birth, the study of in utero samples is essential to understanding the diseases’ properties and effects on the developing muscle tissues. Additionally, many of these afflictions are caused by mutations in the isoforms of troponin or myosin II that are predominantly expressed during human development. Studying the native muscle is all the more important as a control in furthering research on the effects of mutations in troponin and myosin. In particular, human foetal-specific isoforms of myosin II expressed in these muscle are poorly understood and very little has been published about these isoforms. We do know from the literature that myosin’s use of its substrate, ATP, varies widely between isoforms and that the myosin expression changes during times of physiological distress, such as heart failure. Because congenital abnormalities of the heart and skeletal muscle both can originate in the foetal muscle, further investigation is needed into the myosins’ biophysical and biomechanical mechanisms. The overarching goal of this project was to improve understanding of how foetal forms of skeletal and cardiac myosins work and are regulated, using biophysical-biochemical, molecular biology and computational modelling techniques. This was accomplished by experimentally determining the kinetics of myosin-ATP and myosin-actin interactions using stopped-flow kinetic analysis, experimentally determining the rates of force development and relaxation as well as the quantity of force developed using single myofibrils, and experimentally determining a qualitative and quantitative analysis of myosin composition using mass spectrometry. Overall we have concluded that the change in force development and rates of force development and relaxation in skeletal muscle are significantly contributed to by changes in the myosin isoform in skeletal foetal development. We have found that these changes in the performance of myosin are slightly different than the changes seen in cardiac myosin isoforms, although the overall effect on the force development appears similar. However, the rates of force development and parts of the relaxation process do seem to have slight differences in the way they change between skeletal and cardiac isoforms. These changes, and the specific of how the myosins change their interaction with both their substrate ATP and actin, help us in better understanding how mutations that appear in similar locations on the myosin molecule lead to different outcomes in the growth and performance of the muscle as it matures, and will help with developing targeted therapeutics in the future.

Data: CORDIS, © European Union