Mavacamten, a precision medicine for hypertrophic cardiomyopathy: From a motor protein to patients

Mavacamten in hypertrophic obstructive cardiomyopathy: Prospects for AI integration and mitigating healthcare disparities

Hypertrophic obstructive cardiomyopathy (HOCM) is an autosomal dominant condition that still remains significantly under-diagnosed worldwide. Early detection through clinical evaluation, imaging, and familial history is crucial to prevent severe complications such as heart failure and sudden cardiac death. While cuddsnt management strategies primarily offer symptomatic relief through pharmacotherapy or invasive procedures, their effectiveness and accessibility are limited, revealing substantial gaps in care. The emergence of Mavacamten, a recently FDA-approved drug, could potentially revolutionize HOCM management as it addresses the underlying pathophysiology by inhibiting cardiac myosin ATPase, showing promise in reducing obstruction and improving cardiac function. Our review aims to assess mavacamten's efficacy, emphasizing the pivotal role of genetic testing in identifying at-risk individuals and guiding precise diagnoses for personalized treatments. Additionally, we aim to highlight disparities in access to advanced diagnostics and therapies, particularly affecting underserved populations globally and within communities, as well as explore the potential of artificial intelligence (AI) in enhancing early detection and monitoring treatment responses in HOCM. This review thus offers valuable insights to inform future research directions and clinical practices aimed at optimizing outcomes for individuals with HOCM.

Sleep duration and heart failure risk: Insights from a Mendelian Randomization Study

To investigate the causal relationship between sleep duration and heart failure (HF) in a European population. We focused on the continuous sleep duration of 460,099 European individuals as our primary exposure. Genome-wide significant single nucleotide polymorphisms (SNPs, n = 9851,867) linked to continuous sleep duration were adopted as instrumental variables. The outcome of interest was based on HF events in a European cohort (n = 977,323; with 930,014 controls and 47,309 cases). We employed a two-sample Mendelian randomization (MR) approach to infer causality between sleep duration and the incidence of HF. For validation purposes, an additional cohort of 336,965 European individuals diagnosed with insomnia was selected as a secondary exposure group. Using its SNPs, a subsequent two-sample MR analysis was conducted with the HF cohort to further corroborate our initial findings. Employing the MR methodology, we selected 57 SNPs that are associated with sleep duration, and 24 SNPs that are associated with insomnia as instrumental variables. We discerned a substantial association between genetically inferred sleep duration and HF risk (odds ratio: 0.61; 95% confidence interval: 0.47-0.78, P < .0001). Our subsequent analysis highlighted a pronounced increased HF risk associated with insomnia (odds ratio: 1.54; 95% confidence interval: 1.08-2.17, P < .02). These conclusions were further bolstered by consistent results from sensitivity analyses. Our study suggests a causal linkage between sleep duration and the onset risk of HF in the European population. Notably, shorter sleep durations were associated with a heightened risk of HF.

Functional control of myosin motors in the cardiac cycle

Contraction of the heart is driven by cyclical interactions between myosin and actin filaments powered by ATP hydrolysis. The modular structure of heart muscle and the organ-level synchrony of the heartbeat ensure tight reciprocal coupling between this myosin ATPase cycle and the macroscopic cardiac cycle. The myosin motors respond to the cyclical activation of the actin and myosin filaments to drive the pressure changes that control the inflow and outflow valves of the heart chambers. Opening and closing of the valves in turn switches the myosin motors between roughly isometric and roughly isotonic contraction modes. Peak filament stress in the heart is much smaller than in fully activated skeletal muscle, although the myosin filaments in the two muscle types have the same number of myosin motors. Calculations indicate that only ~5% of the myosin motors in the heart are needed to generate peak systolic pressure, although many more motors are needed to drive ejection. Tight regulation of the number of active motors is essential for the efficient functioning of the healthy heart - this control is commonly disrupted by gene variants associated with inherited heart disease, and its restoration might be a useful end point in the development of novel therapies.

An overview of the treatments for hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a very prevalent inherited disease with a wide global distribution and a prevalence rate of approximately 0.2% in the general population. Left ventricular hypertrophy (LVH) caused by sarcomere mutation is the primary reason of HCM. The histopathology feature is that cardiomyocyte hypertrophy, myocyte disorder and myocardial fibrosis lead to diminished diastolic function, left ventricular outflow tract obstruction (LVOTO) and arrhythmia, all of which result in serious cardiac complications. Previously, HCM was considered a malignant disease that was almost untreatable. With the improvement of medical standards and increasing awareness of HCM, it has become a highly treatable disease in contemporary times, with a significant decrease in mortality rates. However, there are still significant unmet requirements in the therapy of HCM. This paper draws on more than 100 references from the past four decades and summarizes current advances in the treatment of HCM. The article will review the pathogenesis and types, recent development in pharmacotherapy, invasive treatments and gene therapies, as well as dilemma and future development of HCM.

Genetic Mutations and Mitochondrial Redox Signaling as Modulating Factors in Hypertrophic Cardiomyopathy: A Scoping Review

Hypertrophic cardiomyopathy (HCM) is a heart condition characterized by cellular and metabolic dysfunction, with mitochondrial dysfunction playing a crucial role. Although the direct relationship between genetic mutations and mitochondrial dysfunction remains unclear, targeting mitochondrial dysfunction presents promising opportunities for treatment, as there are currently no effective treatments available for HCM. This review adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Extension for Scoping Reviews guidelines. Searches were conducted in databases such as PubMed, Embase, and Scopus up to September 2023 using "MESH terms". Bibliographic references from pertinent articles were also included. Hypertrophic cardiomyopathy (HCM) is influenced by ionic homeostasis, cardiac tissue remodeling, metabolic balance, genetic mutations, reactive oxygen species regulation, and mitochondrial dysfunction. The latter is a common factor regardless of the cause and is linked to intracellular calcium handling, energetic and oxidative stress, and HCM-induced hypertrophy. Hypertrophic cardiomyopathy treatments focus on symptom management and complication prevention. Targeted therapeutic approaches, such as improving mitochondrial bioenergetics, are being explored. This includes coenzyme Q and elamipretide therapies and metabolic strategies like therapeutic ketosis. Understanding the biomolecular, genetic, and mitochondrial mechanisms underlying HCM is crucial for developing new therapeutic modalities.

Myosin-Catalyzed ATP Hydrolysis in the Presence of Disease-Causing Mutations: Mavacamten as a Way to Repair Mechanism

Hypertrophic cardiomyopathy is one of the most common forms of genetic cardiomyopathy. Mavacamten is a first-in-class myosin modulator that was identified via activity screening on the wild type, and it is FDA-approved for the treatment of obstructive hypertrophic cardiomyopathy (HCM). The drug selectively binds to the cardiac β-myosin, inhibiting myosin function to decrease cardiac contractility. Though the drug is thought to affect multiple steps of the myosin cross-bridge cycle, its detailed mechanism of action is still under investigation. Individual steps in the overall cross-bridge cycle must be queried to elucidate the full mechanism of action. In this study, we utilize the rare-event method of transition path sampling to generate reactive trajectories to gain insights into the action of the drug on the dynamics and rate of the ATP hydrolysis step for human cardiac β-myosin. We study three known HCM causative myosin mutations: R453C, P710R, and R712L to observe the effect of the drug on the alterations caused by these mutations in the chemical step. Since the crystal structure of the drug-bound myosin was not available at the time of this work, we created a model of the drug-bound system utilizing a molecular docking approach. We find a significant effect of the drug in one case, where the actual mechanism of the reaction is altered from the wild type by mutation. The drug restores both the rate of hydrolysis to the wildtype level and the mechanism of the reaction. This is a way to check the effect of the drug on untested mutations.

Emerging Concepts of Mechanisms Controlling Cardiac Tension: Focus on Familial Dilated Cardiomyopathy (DCM) and Sarcomere-Directed Therapies

Novel therapies for the treatment of familial dilated cardiomyopathy (DCM) are lacking. Shaping research directions to clinical needs is critical. Triggers for the progression of the disorder commonly occur due to specific gene variants that affect the production of sarcomeric/cytoskeletal proteins. Generally, these variants cause a decrease in tension by the myofilaments, resulting in signaling abnormalities within the micro-environment, which over time result in structural and functional maladaptations, leading to heart failure (HF). Current concepts support the hypothesis that the mutant sarcomere proteins induce a causal depression in the tension-time integral (TTI) of linear preparations of cardiac muscle. However, molecular mechanisms underlying tension generation particularly concerning mutant proteins and their impact on sarcomere molecular signaling are currently controversial. Thus, there is a need for clarification as to how mutant proteins affect sarcomere molecular signaling in the etiology and progression of DCM. A main topic in this controversy is the control of the number of tension-generating myosin heads reacting with the thin filament. One line of investigation proposes that this number is determined by changes in the ratio of myosin heads in a sequestered super-relaxed state (SRX) or in a disordered relaxed state (DRX) poised for force generation upon the Ca2+ activation of the thin filament. Contrasting evidence from nanometer-micrometer-scale X-ray diffraction in intact trabeculae indicates that the SRX/DRX states may have a lesser role. Instead, the proposal is that myosin heads are in a basal OFF state in relaxation then transfer to an ON state through a mechano-sensing mechanism induced during early thin filament activation and increasing thick filament strain. Recent evidence about the modulation of these mechanisms by protein phosphorylation has also introduced a need for reconsidering the control of tension. We discuss these mechanisms that lead to different ideas related to how tension is disturbed by levels of mutant sarcomere proteins linked to the expression of gene variants in the complex landscape of DCM. Resolving the various mechanisms and incorporating them into a unified concept is crucial for gaining a comprehensive understanding of DCM. This deeper understanding is not only important for diagnosis and treatment strategies with small molecules, but also for understanding the reciprocal signaling processes that occur between cardiac myocytes and their micro-environment. By unraveling these complexities, we can pave the way for improved therapeutic interventions for managing DCM.

A therapeutic leap: how myosin inhibitors moved from cardiac interventions to skeletal muscle myopathy solutions

The myosin inhibitor mavacamten has transformed the management of obstructive hypertrophic cardiomyopathy (HCM) by targeting myosin ATPase activity to mitigate cardiac hypercontractility. This therapeutic mechanism has proven effective for patients with HCM independent of having a primary gene mutation in myosin. In this issue of the JCI, Buvoli et al. report that muscle hypercontractility is a mechanism of pathogenesis underlying muscle dysfunction in Laing distal myopathy, a disorder characterized by mutations altering the rod domain of β myosin heavy chain. The authors performed detailed physiological, molecular, and biomechanical analyses and demonstrated that myosin ATPase inhibition can correct a large extent of muscle abnormalities. The findings offer a therapeutic avenue for Laing distal myopathy and potentially other myopathies. This Commentary underscores the importance of reevaluating myosin activity's role across myopathies in general for the potential development of targeted myosin inhibitors to treat skeletal muscle disorders.

Complex architecture of cardiac muscle thick filaments revealed

Muscle contraction is orchestrated by the well-understood thin filaments and the markedly complex thick filaments. Studies by Dutta et al. and Tamborrini et al., discussed here, have unravelled the structure of the mammalian heart thick filament in exquisite near-atomic detail and pave the way for understanding physiological modulation pathways and mutation-induced dysfunction and for designing potential drugs to modify defects.

Myosin in autoinhibited off state(s), stabilized by mavacamten, can be recruited in response to inotropic interventions

Mavacamten is a FDA-approved small-molecule therapeutic designed to regulate cardiac function at the sarcomere level by selectively but reversibly inhibiting the enzymatic activity of myosin. It shifts myosin toward ordered off states close to the thick filament backbone. It remains elusive whether these myosin heads in the off state(s) can be recruited in response to physiological stimuli when required to boost cardiac output. We show that cardiac myosins stabilized in these off state(s) by mavacamten are recruitable by 1) Ca2+, 2) increased chronotropy [heart rate (HR)], 3) stretch, and 4) β-adrenergic (β-AR) stimulation, all known physiological inotropic interventions. At the molecular level, we show that Ca2+ increases myosin ATPase activity by shifting mavacamten-stabilized myosin heads from the inactive super-relaxed state to the active disordered relaxed state. At the myofilament level, both Ca2+ and passive lengthening can shift mavacamten-ordered off myosin heads from positions close to the thick filament backbone to disordered on states closer to the thin filaments. In isolated rat cardiomyocytes, increased stimulation rates enhanced shortening fraction in mavacamten-treated cells. This observation was confirmed in vivo in telemetered rats, where left-ventricular dP/dtmax, an index of inotropy, increased with HR in mavacamten-treated animals. Finally, we show that β-AR stimulation in vivo increases left-ventricular function and stroke volume in the setting of mavacamten. Our data demonstrate that the mavacamten-promoted off states of myosin in the thick filament are at least partially activable, thus preserving cardiac reserve mechanisms.