Functional assessment of atrial myosin mutations in familial atrial arrhythmia

PROJECT SUMMARY Atrial fibrillation (afib) is a very common arrhythmia that affects up to 1 in 4 people over the age of 40 in their lifetime, leading to major complications such as stroke and heart failure. There is growing evidence that a proportion of afib cases result from an atrial cardiomyopathic process in which the fundamental contractile function of the myocytes is altered, yet the fundamental mechanism is not well understood. Therapeutic approaches to treating afib have largely focused on electrical modulation and structurally isolating the abnormal rhythm, but this approach does not address the underlying pathology of the atria, and, unsurprisingly, many patients have recurrence due to further progression of atrial remodeling. Therefore, it is critical to study the fundamental contractile function in atrial cardiomyocytes to gain further insights into the mechanism of afib. Here, we propose to study known genetic causes of afib in atrial cardiac myosin using the human recombinant α-cardiac myosin system and state-of-the-art biochemical and biophysical assays we have developed with the β-cardiac myosin platform. In Aim 1, we will construct the α-cardiac myosin heavy chain (MYH6), essential light chain (MYL4), and regulatory light chain (MYL7), and compare their function with the β-cardiac myosin. We will make several structural variations of the wildtype α-cardiac myosin using the heavy chain and light chains above to perform a comprehensive analysis. In Aim 2, we will produce mutant α-cardiac myosin found in familial afib cases with mutations in MYH6 (R721W, E933Δ). Some of these mutations (MYH6 R721W and E933Δ) are seen in patients with hypertrophic cardiomyopathy when the same location in β-cardiac myosin is mutated. We will determine their effect on myosin activity and overall sarcomere function. Our experimental platform will be the first to comprehensively study the human α-cardiac myosin with various mutations using the recombinant protein to carry out sophisticated biochemical and biophysical analysis. The results from this study will lead to critical preliminary data for an R01 grant to further study the mechanism of afib and will help develop novel therapies for this very common cardiovascular disease.