Sarcomere Neutralization Therapy in HCM/RCM: Therapeutic Application of the Calcium Desensitizer W7 to Remediate Hyper-Calcium Sensitive Disease States

Abstract

The sarcomere is the functional unit of the heart. Alterations in sarcomere activation lead to disease states such as hypertrophic and restrictive cardiomyopathy (HCM/RCM). HCM is the most common monogenic cardiovascular disease, affecting 1:500 and is the leading cause of death in young athletes. Mutations in many of the sarcomeric genes are causal for HCM. In most cases, these mutations result in increased calcium sensitivity of the sarcomere giving rise to altered systolic and diastolic function. We show here that sarcomere neutralization therapy, with the calcium desensitizer W7, is a potential therapeutic strategy for HCM/RCM. W7 has previously been shown to decrease calcium sensitivity of the sarcomere through binding to cTnC and altering cTnI-cTnC interactions. Acute treatment of adult cardiac myocytes with W7 caused a dose-dependent (1-10 μM) decrease in contractility, independent of calcium transient changes. Alkalosis was used as an acute model of heightened calcium sensitivity, resulting in increased contractility and decreased baseline sarcomere length. Treatment with W7 in alkalosis remediated both phenotypes. R193H cTnI transgenic (Tg) myocytes were used as a model of RCM. R193H cTnI Tg myocytes display significant decreased baseline sarcomere length and slowed relaxation. Acute treatment with W7 dose-dependently increased baseline sarcomere length and remediated the slowed relaxation. Langendorff perfused whole heart pacing stress was used to study W7 effects at the organ level. R193H cTnI transgenic hearts had elevated end diastolic pressures at all stimulation frequencies compared to nontransgenic mice. Acute treatment with W7 restored normal end diastolic pressures throughout pacing in R193H cTnI transgenic mice. These results provide evidence that drug-based sarcomere neutralization therapy is a potential new approach to remediate hyper-calcium sensitive sarcomere function evident in acquired (respiratory alkalosis) and inherited (HCM/RCM) cardiac diseases.