Skeletal muscle contractile protein function is preserved in human heart failure

Heart Failure-Induced Skeletal Muscle Wasting

PURPOSE OF REVIEW

Heart failure (HF) is a structural or functional cardiac abnormality which leads to failure of the heart to deliver oxygen commensurately with the requirements of the tissues and it may progress to a generalized wasting of skeletal muscle, fat tissue, and bone tissue (cardiac cachexia). Clinically, dyspnea, fatigue, and exercise intolerance are some typical signs and symptoms that characterize HF patients. This review focused on the phenotypic characteristics of HF-induced skeletal myopathy as well as the mechanisms of muscle wasting due to HF and highlighted possible therapeutic strategies for skeletal muscle wasting in HF.

RECENT FINDINGS

The impaired exercise capacity of those patients is not attributed to the reduced blood flow in the exercising muscles, but rather to abnormal metabolic responses, myocyte apoptosis and atrophy of skeletal muscle. Specifically, the development of skeletal muscle wasting in chronic HF is characterized by structural, metabolic, and functional abnormalities in skeletal muscle and may be a result not only of reduced physical activity, but also of metabolic or hormonal derangements that favour catabolism over anabolism. In particular, abnormal energy metabolism, mitochondrial dysfunction, transition of myofibers from type I to type II, muscle atrophy, and reduction in muscular strength are included in skeletal muscle abnormalities which play a central role in the decreased exercise capacity of HF patients. Skeletal muscle alterations and exercise intolerance observed in HF are reversible by exercise training, since it is the only demonstrated intervention able to improve skeletal muscle metabolism, growth factor activity, and functional capacity and to reverse peripheral abnormalities.

Dilated cardiomyopathy-mediated heart failure induces a unique skeletal muscle myopathy with inflammation

Background

Skeletal muscle myopathy and exercise intolerance are diagnostic hallmarks of heart failure (HF). However, the molecular adaptations of skeletal muscles during dilated cardiomyopathy (DCM)-mediated HF are not completely understood.

Methods

Skeletal muscle structure and function were compared in wild-type (WT) and cardiac myosin binding protein-C null mice (t/t), which develop DCM-induced HF. Cardiac function was examined by echocardiography. Exercise tolerance was measured using a graded maximum treadmill running test. Hindlimb muscle function was assessed in vivo from measurements of plantar flexor strength. Inflammatory status was evaluated from the expression of inflammatory markers and the presence of specific immune cell types in gastrocnemius muscles. Muscle regenerative capacityat days 3, 7, and 14 after eccentric contraction-induced injury was determined from the number of phenotypically new and adult fibers in the gastrocnemius, and functional recovery of plantar flexion torque.

Results

t/t mice developed DCM-induced HF in association with profound exercise intolerance, consistent with previous reports. Compared to WT, t/t mouse hearts show significant hypertrophy of the atria and ventricles and reduced fractional shortening, both systolic and diastolic. In parallel, the skeletal muscles of t/t mice exhibit weakness and myopathy. Compared to WT, plantar flexor muscles of t/t null mice produce less peak isometric plantar torque (Po), develop torque more slowly (+ dF/dt), and relax more slowly (− dF/dt, longer half-relaxation times,1/2RT). Gastrocnemius muscles of t/t mice have a greater number of fibers with smaller diameters and central nuclei. Oxidative fibers, both type I and type IIa, show significantly smaller cross-sectional areas and more central nuclei. These fiber phenotypes suggest ongoing repair and regeneration under homeostatic conditions. In addition, the ability of muscles to recover and regenerate after acute injury is impaired in t/t mice.

Conclusions

Our studies concluded that DCM-induced HF induces a unique skeletal myopathy characterized by decreased muscle strength, atrophy of oxidative fiber types, ongoing inflammation and damage under homeostasis, and impaired regeneration after acute muscle injury. Furthermore, this unique myopathy in DCM-induced HF likely contributes to and exacerbates exercise intolerance. Therefore, efforts to develop therapeutic interventions to treat skeletal myopathy during DCM-induced HF should be considered.

Electronic supplementary material

The online version of this article (10.1186/s13395-019-0189-y) contains supplementary material, which is available to authorized users.

Skeletal Muscle Changes in Chronic Cardiac Disease and Failure

Peak exercise performance in healthy man is limited not only by pulmonary or skeletal muscle function but also by cardiac function. Thus, abnormalities in cardiac function will have a major impact on exercise performance. Many cardiac diseases affect exercise performance and indeed for some cardiac conditions such as atherosclerotic heart disease, exercise testing is frequently used not only to measure functional capacity but also to make a diagnosis of heart disease, evaluate the efficacy of treatment, and predict prognosis. Early in the course of cardiac diseases, exercise performance will be minimally affected but with disease progression impairment in exercise capacity will become apparent. Ejection fraction, that is, the percent of blood volume ejected with each cardiac cycle is often used as a measure of cardiac performance but frequently there is a dissociation between the ejection fraction and exercise capacity in patients with heart disease. How abnormalities in cardiac function impacts the muscles, vasculature, and lungs to impact exercise performance will here be reviewed. The focus of this work will be on patients with systolic heart failure as the incidence and prevalence of heart failure is reaching epidemic proportions and heart failure is the end result of many other chronic cardiac diseases. The prognostic role of exercise and benefits of exercise training will also be discussed.

Skeletal muscle myofilament adaptations to aging, disease, and disuse and their effects on whole muscle performance in older adult humans

Skeletal muscle contractile function declines with aging, disease, and disuse. In vivo muscle contractile function depends on a variety of factors, but force, contractile velocity and power generating capacity ultimately derive from the summed contribution of single muscle fibers. The contractile performance of these fibers are, in turn, dependent upon the isoform and function of myofilament proteins they express, with myosin protein expression and its mechanical and kinetic characteristics playing a predominant role. Alterations in myofilament protein biology, therefore, may contribute to the development of functional limitations and disability in these conditions. Recent studies suggest that these conditions are associated with altered single fiber performance due to decreased expression of myofilament proteins and/or changes in myosin-actin cross-bridge interactions. Furthermore, cellular and myofilament-level adaptations are related to diminished whole muscle and whole body performance. Notably, the effect of these various conditions on myofilament and single fiber function tends to be larger in older women compared to older men, which may partially contribute to their higher rates of disability. To maintain functionality and provide the most appropriate and effective countermeasures to aging, disease, and disuse in both sexes, a more thorough understanding is needed of the contribution of myofilament adaptations to functional disability in older men and women and their contribution to tissue level function and mobility impairment.

Metabolic and structural impairment of skeletal muscle in heart failure

Physiologic endurance exercise performance is primarily limited by cardiac function. In patients with heart failure, there is dissociation between cardiac performance and exercise capacity, suggesting a distinct role of abnormal peripheral organ function, including skeletal muscle function. The impact of heart failure upon skeletal muscle and exercise performance will be discussed with a focus on molecular, structural, and functional derangements in skeletal muscle of patients with heart failure.

Cardiac myosin binding protein-C plays no regulatory role in skeletal muscle structure and function

Myosin binding protein-C (MyBP-C) exists in three major isoforms: slow skeletal, fast skeletal, and cardiac. While cardiac MyBP-C (cMyBP-C) expression is restricted to the heart in the adult, it is transiently expressed in neonatal stages of some skeletal muscles. However, it is unclear whether this expression is necessary for the proper development and function of skeletal muscle. Our aim was to determine whether the absence of cMyBP-C alters the structure, function, or MyBP-C isoform expression in adult skeletal muscle using a cMyBP-C null mouse model (cMyBP-C((t/t))). Slow MyBP-C was expressed in both slow and fast skeletal muscles, whereas fast MyBP-C was mostly restricted to fast skeletal muscles. Expression of these isoforms was unaffected in skeletal muscle from cMyBP-C((t/t)) mice. Slow and fast skeletal muscles in cMyBP-C((t/t)) mice showed no histological or ultrastructural changes in comparison to the wild-type control. In addition, slow muscle twitch, tetanus tension, and susceptibility to injury were all similar to the wild-type controls. Interestingly, fMyBP-C expression was significantly increased in the cMyBP-C((t/t)) hearts undergoing severe dilated cardiomyopathy, though this does not seem to prevent dysfunction. Additionally, expression of both slow and fast isoforms was increased in myopathic skeletal muscles. Our data demonstrate that i) MyBP-C isoforms are differentially regulated in both cardiac and skeletal muscles, ii) cMyBP-C is dispensable for the development of skeletal muscle with no functional or structural consequences in the adult myocyte, and iii) skeletal isoforms can transcomplement in the heart in the absence of cMyBP-C.

Exercício resistido no cardiopata: revisão sistemática

INTRODUÇÃO: A perda de massa muscular secundária à idade e à inatividade física é clinicamente relevante na população cardíaca; contudo, a prescrição do exercício resistido dinâmico para esses pacientes apresenta-se inconclusiva na literatura. OBJETIVOS: Reunir informações e apresentar as principais diretrizes relacionadas à prescrição de exercícios resistidos em cardiopatas. MATERIAIS E MÉTODOS: Foi realizada busca sistemática de literatura, a partir das bases de dados LILACS, SciELO e MEDLINE, utilizando os seguintes descritores na língua portuguesa: força muscular, exercício isométrico, esforço físico, cardiopatia e coronariopatia, e seus correspondentes na língua inglesa (muscle strength, isometric exercise, physical effort, heart disease e artery coronary disease), os quais foram pesquisados separadamente e em cruzamentos, sendo considerados para esta revisão apenas artigos publicados entre 2005 e 2010. RESULTADOS E DISCUSSÃO: De um total de 806 artigos foram selecionados 22 para integrar a revisão, sendo 14 estudos classificados como artigos originais, 2 artigos de atualização da literatura e 6 artigos de revisão, além do capítulo 8 do livro intitulado Diretrizes do ACSM (American College of Sports Medicine) para os testes de esforço e sua prescrição, publicado em 2007. CONCLUSÃO: O exercício resistido, independente da variada metodologia utilizada na prescrição dos componentes específicos do treinamento, mostrou-se eficiente para aumentar a força muscular de membros superiores e inferiores em cardiopatas e sua aplicação pode ser considerada segura para esses pacientes, desde que prescrito corretamente.

Chronic heart failure decreases cross-bridge kinetics in single skeletal muscle fibres from humans

Skeletal muscle function is impaired in heart failure patients due, in part, to loss of myofibrillar protein content, in particular myosin. In the present study, we utilized small-amplitude sinusoidal analysis for the first time in single human skeletal muscle fibres to measure muscle mechanics, including cross-bridge kinetics, to determine if heart failure further impairs contractile performance by altering myofibrillar protein function. Patients with chronic heart failure (n = 9) and controls (n = 6) were recruited of similar age and physical activity to diminish the potentially confounding effects of ageing and muscle disuse. Patients showed decreased cross-bridge kinetics in myosin heavy chain (MHC) I and IIA fibres, partially due to increased myosin attachment time (t(on)). The increased t(on) compensated for myosin protein loss previously found in heart failure patients by increasing the fraction of the total cycle time myosin is bound to actin, resulting in a similar number of strongly bound cross-bridges in patients and controls. Accordingly, isometric tension did not differ between patients and controls in MHC I or IIA fibres. Patients also had decreased calcium sensitivity in MHC IIA fibres and alterations in the viscoelastic properties of the lattice structure of MHC I and IIA fibres. Collectively, these results show that heart failure alters skeletal muscle contraction at the level of the myosin-actin cross-bridge, leading to changes in muscle mechanics which could contribute to impaired muscle function. Additionally, we uncovered a unique kinetic property of MHC I fibres, a potential indication of two distinct populations of cross-bridges, which may have important physiological consequences.

The molecular basis of frictional loads in the in vitro motility assay with applications to the study of the loaded mechanochemistry of molecular motors

Molecular motors convert chemical energy into mechanical movement, generating forces necessary to accomplish an array of cellular functions. Since molecular motors generate force, they typically work under loaded conditions where the motor mechanochemistry is altered by the presence of a load. Several biophysical techniques have been developed to study the loaded behavior and force generating capabilities of molecular motors yet most of these techniques require specialized equipment. The frictional loading assay is a modification to the in vitro motility assay that can be performed on a standard epifluorescence microscope, permitting the high-throughput measurement of the loaded mechanochemistry of molecular motors. Here, we describe a model for the molecular basis of the frictional loading assay by modeling the load as a series of either elastic or viscoelastic elements. The model, which calculates the frictional loads imposed by different binding proteins, permits the measurement of isotonic kinetics, force-velocity relationships, and power curves in the motility assay. We show computationally and experimentally that the frictional load imposed by alpha-actinin, the most widely employed actin binding protein in frictional loading experiments, behaves as a viscoelastic rather than purely elastic load. As a test of the model, we examined the frictional loading behavior of rabbit skeletal muscle myosin under normal and fatigue-like conditions using alpha-actinin as a load. We found that, consistent with fiber studies, fatigue-like conditions cause reductions in myosin isometric force, unloaded sliding velocity, maximal power output, and shift the load at which peak power output occurs.

Mechanisms underlying skeletal muscle weakness in human heart failure: alterations in single fiber myosin protein content and function

BACKGROUND

Patients with chronic heart failure (HF) frequently experience skeletal muscle weakness that limits physical function. The mechanisms underlying muscle weakness, however, have not been clearly defined.

METHODS AND RESULTS

This study examined the hypothesis that HF promotes a loss of myosin protein from single skeletal muscle fibers, which in turn reduces contractile performance. Ten patients with chronic HF and 10 controls were studied. Muscle atrophy was not evident in patients, and groups displayed similar physical activity levels, suggesting that observed differences reflect the effects of HF and not muscle atrophy or disuse. In single muscle fibers, patients with HF showed reduced myosin heavy chain protein content (P<0.05) that manifested as a reduction in functional myosin-actin cross-bridges (P<0.05). No evidence was found for a generalized loss of myofilament protein, suggesting a selective loss of myosin. Accordingly, single muscle fiber maximal Ca(2+)-activated tension was reduced in myosin heavy chain I fibers in patients (P<0.05). However, tension was maintained in myosin heavy chain IIA fibers in patients because a greater proportion of available myosin heads were bound to actin during Ca(2+) activation (P<0.01).

CONCLUSIONS

Collectively, our results show that HF alters the quantity and functionality of the myosin molecule in skeletal muscle, leading to reduced tension in myosin heavy chain I fibers. Loss of single fiber myosin protein content represents a potential molecular mechanism underlying muscle weakness and exercise limitation in patients with HF.

Comparison of skeletal muscle strength between cardiac patients and age-matched healthy controls

The purpose of the present study was to compare muscular strength of knee extensors and arm flexor muscles of cardiac patients (n = 638) and healthy controls (n = 961) in different age groups. Isometric torques were measured in a sitting position with the elbow, hip, and knee flexed to 90(0). For statistical analysis, age groups were pooled in decades from the age of 30 to 90 years. Additionally, the influence of physical lifestyle prior to disease on muscular strength was obtained in the patients. For statistical analysis three-way ANOVA (factors age, gender, and physical activity level) was used.Both in patients and in controls a significant age-dependent decline in maximal torque could be observed for arm flexors and knee extensors. Maximal leg extensor muscle showed statistically significant differences between healthy controls and cardiac patients as well as between subgroups of patients: Physically inactive patients showed lowest torques (male: 148 +/- 18 Nm; female: 82 +/- 25 Nm) while highest values were measured in control subjects (male: 167 +/- 16 Nm; female: 93 +/- 17 Nm). In contrast, arm flexor muscles did not show any significant influence of health status or sports history.This qualitative difference between weight-bearing leg muscles and the muscle group of the upper extremity suggest that lower skeletal muscle strength in heart patients is mainly a consequence of selective disuse of leg muscles rather than any pathological skeletal muscle metabolism. Since a certain level of skeletal muscle strength is a prerequisite to cope with everyday activities, strength training is recommended as an important part of cardiac rehabilitation.