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

Perturbations in skeletal muscle sarcomere structure in patients with heart failure and Type 2 diabetes: restorative effects of (−)-epicatechinrich cocoa

HF (heart failure) and T2D (Type 2 diabetes) associate with detrimental alterations in SkM (skeletal muscle) structure/function. We have demonstrated recently that (−)-ERC (epicatechin-rich cocoa) improves SkM mitochondrial structure [Taub, Ramirez-Sanchez, Ciaraldi, Perkins, Murphy, Naviaux, Hogan, Ceballos, Maisel, Henry et al. (2012) Clin. Trans. Sci. 5, 43–47]. We hypothesized that an improved mitochondrial structure may facilitate the reversal of detrimental alterations in sarcomeric microstructure. In a pilot study, five patients with HF and T2D consumed ERC for 3 months; treadmill testing [V̇O2max (maximum oxygen consumption)] and SkM biopsies were performed. Western blot analysis, immunohistochemistry and electron microscopy were used. We report severe perturbations in components of the DAPC (dystrophin-associated protein complex) as well as sarcomeric microstructure at baseline. ERC induced recovery/enhancement of DAPC protein levels, sarcomeric microstructure and, in a co-ordinated fashion, alterations in markers of SkM growth/differentiation consistent with myofibre regeneration. V̇O2max increased (~24%) but did not reach statistical significance. These initial results warrant further rigorous investigation, since the use of ERC (or pure epicatechin) may represent a safe and novel means of improving muscle function.

Intrinsic skeletal muscle alterations in chronic heart failure patients: a disease-specific myopathy or a result of deconditioning?

Chronic heart failure (CHF) patients frequently experience impaired exercise tolerance due to skeletal muscle fatigue. Studies suggest that this in part is due to intrinsic alterations in skeletal muscle of CHF patients, often interpreted as a disease-specific myopathy. Knowledge about the mechanisms underlying these skeletal muscle alterations is of importance for the pathophysiological understanding of CHF, therapeutic approach and rehabilitation strategies. We here critically review the evidence for skeletal muscle alterations in CHF, the underlying mechanisms of such alterations and how skeletal muscle responds to training in this patient group. Skeletal muscle characteristics in CHF patients are very similar to what is reported in response to chronic obstructive pulmonary disease (COPD), detraining and deconditioning. Furthermore, skeletal muscle alterations observed in CHF patients are reversible by training, and skeletal muscle of CHF patients seems to be at least as trainable as that of matched controls. We argue that deconditioning is a major contributor to the skeletal muscle dysfunction in CHF patients and that further research is needed to determine whether, and to what extent, the intrinsic skeletal muscle alterations in CHF represent an integral part of the pathophysiology in this disease.

Molecular mechanisms underlying skeletal muscle weakness in human cancer: reduced myosin-actin cross-bridge formation and kinetics

Many patients with cancer experience physical disability following diagnosis, although little is known about the mechanisms underlying these functional deficits. To characterize skeletal muscle adaptations to cancer in humans, we evaluated skeletal muscle structure and contractile function at the molecular, cellular, whole-muscle, and whole-body level in 11 patients with cancer (5 cachectic, 6 noncachectic) and 6 controls without disease. Patients with cancer showed a 25% reduction in knee extensor isometric torque after adjustment for muscle mass (P < 0.05), which was strongly related to diminished power output during a walking endurance test (r = 0.889; P < 0.01). At the cellular level, single fiber isometric tension was reduced in myosin heavy chain (MHC) IIA fibers (P = 0.05) in patients with cancer, which was explained by a reduction (P < 0.05) in the number of strongly bound cross-bridges. In MHC I fibers, myosin-actin cross-bridge kinetics were reduced in patients, as evidenced by an increase in myosin attachment time (P < 0.01); and reductions in another kinetic parameter, myosin rate of force production, predicted reduced knee extensor isometric torque (r = 0.689; P < 0.05). Patients with cancer also exhibited reduced mitochondrial density (-50%; P < 0.001), which was related to increased myosin attachment time in MHC I fibers (r = -0.754; P < 0.01). Finally, no group differences in myofilament protein content or ultrastructure were noted that explained the observed functional alterations. Collectively, our results suggest reductions in myofilament protein function as a potential molecular mechanism contributing to muscle weakness and physical disability in human cancer.

Skeletal muscle protein metabolism in human heart failure

PURPOSE OF REVIEW

This review considers evidence that the clinical condition of heart failure alters skeletal muscle protein synthesis and/or breakdown to promote skeletal muscle wasting and functional decrements that ultimately contribute to the symptomology of the disease.

RECENT FINDINGS

Advanced HF is frequently accompanied by muscle atrophy and a cachectic phenotype. Protein metabolic derangements that promote this phenotype are understudied and poorly understood. Instead, most investigations have evaluated regulatory hormones/signaling pathways thought to be reflective of protein synthesis and breakdown. Several of these recent studies have provided exciting data suggesting that the dysfunctional myocardium releases catabolic agents that could promote the skeletal muscle myopathic phenotype either directly or through modulation of other regulatory systems (e.g., energy balance).

SUMMARY

Although our understanding of skeletal muscle atrophy and dysfunction in heart failure is limited, recent studies have provided clues about the nature and timing of protein metabolic dysfunction. More specifically, skeletal muscle protein metabolic derangements likely evolve during periods of disease-related stress (i.e., acute disease exacerbation and hospitalization) and potentially derive in part, from signals promoted in the damaged/dysfunctional myocardium. Despite these compelling studies, there is a surprising lack of data regarding the nature or timing of specific protein metabolic defects in heart failure.

Central and peripheral quadriceps fatigue in congestive heart failure

AIMS

The clinical syndrome of heart failure includes exercise limitation that is not directly linked to measures of cardiac function. Quadriceps fatigability may be an important component of this and this may arise from peripheral or central factors.

METHODS AND RESULTS

We studied 10 men with CHF and 10 healthy age-matched controls. Compared with a rest condition, 10 min after incremental maximal cycle exercise, twitch quadriceps force in response to supramaximal magnetic femoral nerve stimulation fell in both groups (CHF 14.1% ± 18.1%, p=0.037;

CONTROL

20.8 ± 11.0%, p<0.001; no significant difference between groups). There was no significant change in quadriceps maximum voluntary contraction voluntary force. The difference in the motor evoked potential (MEP) response to transcranial magnetic stimulation of the motor cortex between rest and exercise conditions at 10 min, normalised to the peripheral action potential, also fell significantly in both groups (CHF: 27.3 ± 38.7%, p=0.037;

CONTROL

41.1 ± 47.7%, p=0.024). However, the fall in MEP was sustained for a longer period in controls than in patients (p=0.048).

CONCLUSIONS

The quadriceps is more susceptible to fatigue, with a similar fall in TwQ occurring in CHF patients at lower levels of exercise. This is associated with no change in voluntary activation but a lesser degree of depression of quadriceps motor evoked potential.

Skeletal muscle mitochondrial density, gene expression, and enzyme activities in human heart failure: minimal effects of the disease and resistance training

Impaired skeletal muscle energetics could adversely affect physical and metabolic function in patients with heart failure (HF). The effect of HF on aspects of mitochondrial structure and function, independent of muscle disuse and other disease-related confounding factors, however, is unclear. Moreover, no study has evaluated whether resistance exercise training, a modality that increases functional capacity, might derive its benefits through modulation of mitochondrial structure and function. Thirteen HF patients and 14 age- and physical activity-matched controls were evaluated for skeletal muscle mitochondrial size/content, gene expression, and enzyme activity before and after an 18-wk resistance exercise-training program. At baseline, HF patients and controls had similar mitochondrial fractional areas, although HF patients had larger average mitochondrion size (P < 0.05) and a trend toward a reduced number of mitochondria (P ≤ 0.10). No differences in the expression of transcriptional regulators or cytochrome oxidase subunits or the activity of mitochondrial and cytosolic enzymes were noted. Relationships among transcriptional regulators suggested that networks controlling mitochondrial content and gene expression are intact. Resistance training increased (P < 0.01) mitochondrial transcription factor A expression in patients and controls, and this increase was related to improvements in muscle strength (P = 0.05). Training did not, however, alter mitochondrial size/content, enzyme activities, or expression of other transcriptional regulators. In conclusion, our results suggest that the HF syndrome has minimal effects on skeletal muscle mitochondrial biology when the confounding effects of muscle disuse and other disease-related factors are removed. Moreover, the beneficial effects of resistance training on physical function in HF patients and controls are likely not related to alterations in mitochondrial biology.

Resistance training alters skeletal muscle structure and function in human heart failure: effects at the tissue, cellular and molecular levels

Reduced skeletal muscle function in heart failure (HF) patients may be partially explained by altered myofilament protein content and function. Resistance training increases muscle function, although whether these improvements are achieved by correction of myofilament deficits is not known. To address this question, we examined 10 HF patients and 14 controls prior to and following an 18 week high-intensity resistance training programme. Evaluations of whole muscle size and strength, single muscle fibre size, ultrastructure and tension and myosin-actin cross-bridge mechanics and kinetics were performed. Training improved whole muscle isometric torque in both groups, although there were no alterations in whole muscle size or single fibre cross-sectional area or isometric tension.Unexpectedly, training reduced the myofibril fractional area of muscle fibres in both groups. This structural change manifested functionally as a reduction in the number of strongly bound myosin-actin cross-bridges during Ca²⁺ activation. When post-training single fibre tension data were corrected for the loss of myofibril fractional area, we observed an increase in tension with resistance training. Additionally, training corrected alterations in cross-bridge kinetics (e.g. myosin attachment time) in HF patients back to levels observed in untrained controls. Collectively, our results indicate that improvements in myofilament function in sedentary elderly with and without HF may contribute to increased whole muscle function with resistance training. More broadly, these data highlight novel cellular and molecular adaptations in muscle structure and function that contribute to the resistance-trained phenotype.

Effect of resistance training on physical disability in chronic heart failure

PURPOSE

Patients with chronic heart failure (CHF) report difficulty performing activities of daily living. To our knowledge, however, no study has directly measured performance in activities of daily living in these patients to systematically assess their level of physical disability. Moreover, the contribution of skeletal muscle weakness to physical disability in CHF remains unclear. Thus, we measured performance in activities of daily living in CHF patients and controls, its relationship to aerobic capacity and muscle strength, and the effect of resistance exercise training to improve muscle strength and physical disability.

METHODS

Patients and controls were assessed for performance in activities of daily living, self-reported physical function, peak aerobic capacity, body composition, and muscle strength before and after an 18-wk resistance training program. To remove the confounding effects of several disease-related factors (muscle disuse, hospitalization, acute illness), we recruited controls with similar activity levels as CHF patients and tested patients >6 months after any disease exacerbation/hospitalization.

RESULTS

Performance in activities of daily living was 30% lower (P < 0.05) in CHF patients versus controls and was related to both reduced aerobic capacity (P < 0.001) and muscle strength (P < 0.01). Moreover, resistance training improved (P < 0.05 to P < 0.001) physical function and muscle strength in patients and controls similarly, without altering aerobic capacity.

CONCLUSIONS

CHF patients are characterized by marked physical disability compared with age- and physical activity-matched controls, which is related to reduced aerobic capacity and muscle strength. CHF patients respond to resistance training with normal strength/functional adaptations. Our results support muscle weakness as a determinant of physical disability in CHF and show that interventions that increase muscle strength (resistance training) reduce physical disability.

Biphasic response of skeletal muscle mitochondria to chronic cardiac pressure overload - role of respiratory chain complex activity

Pressure overload induced heart failure affects cardiac mitochondrial function and leads to decreased respiratory capacity during contractile dysfunction. A similar cardiac mitochondrial dysfunction has been demonstrated by studies which induce heart failure through myocardial infarction or pacing. These heart failure models differ in their loading conditions to the heart and show nevertheless the same cardiac mitochondrial changes. Based on these observations we speculated that a workload independent mechanism may be responsible for the impairment in mitochondrial function after pressure overload, which may then also affect the skeletal muscle. We aimed to characterize changes in mitochondrial function of skeletal muscle during the transition from pressure overload (PO) induced cardiac hypertrophy to chronic heart failure. PO by transverse aortic constriction caused compensated hypertrophy at 2 weeks, HF with normal ejection fraction (EF) at 6 and 10 weeks, and hypertrophy with reduced EF at 20 weeks. Cardiac output was normal at all investigated time points. PO did not cause skeletal muscle atrophy. Mitochondrial respiratory capacity in soleus and gastrocnemius muscles showed an early increase (up to 6 weeks) and a later decline (significant at 20 weeks). Respiratory chain complex activities responded to PO in a biphasic manner. At 2 weeks, activity of complexes I and II was increased. These changes pseudo-normalized within the 6-10 week interval. At 20 weeks, all complexes showed reduced activities which coincided with clinical heart failure symptoms. However, both protein expression and supercomplex assembly (Blue-Native gel) remained normal. There were also no relevant changes in mRNA expression of genes involved in mitochondrial biogenesis. This temporal analysis reveals that mitochondrial function of skeletal muscle is changed early in the development of pressure overload induced heart failure without being directly influenced by an increased loading condition. The observed early increase and the later decline in respiratory capacity can be explained by concomitant activity changes of complex I and complex II and is not due to differences in gene expression or supercomplex assembly.

Metabolomic distinction and insights into the pathogenesis of human primary dilated cardiomyopathy

BACKGROUND

Metabolomics, the comprehensive profile of small-molecule metabolites found in biological specimens, has the potential to provide insights into the pathogenesis of disease states and lead to the identification of new biomarkers.

METHODS AND RESULTS

We analysed 451 plasma metabolites by liquid chromatography/mass spectroscopy and gas chromatography/mass spectroscopy in 39 patients with primary dilated cardiomyopathy (DCM) and 31 age-, sex- and body mass index-matched controls. Sixty-one metabolites were significantly different between primary DCM and control individuals [false discovery rate (FDR) < 0·05]. Plasma levels of steroid metabolites, glutamine, threonine and histidine were reduced while levels of citric acid cycle intermediates and lipid β-oxidation products were increased in patients with primary DCM when compared to controls. Medications, particularly furosemide and angiotensin-1 converting enzyme-1 inhibitors, had significant effects on the plasma metabolites. Reduced levels of glutamine in conjunction with increased 3-methyhistidine and prolylhydroxyproline levels suggested enhanced myofibrillar and collagen degradation in DCM patients. Likewise, increased stachydrine and reduced indole-3-propionate implicated a role for intestinal-derived antioxidant molecules. Changes in steroid metabolites were notable for the loss of metabolic distinction between men and women in patients with primary DCM. Cortisol and cortisone levels were increased while androgen metabolites were decreased significantly, implying metabolic 'feminization' of men with primary DCM.

CONCLUSIONS

Metabolomic profiling identifies biologically active metabolites that could serve as markers of primary DCM and impart protective or harmful effects on cardiac structure and function.

Chronic heart failure reduces Akt phosphorylation in human skeletal muscle: relationship to muscle size and function

Patients with chronic heart failure (HF) frequently lose muscle mass and function during the course of the disease. A reduction in anabolic stimuli to the muscle has been put forth as a potential mechanism underlying these alterations. The present study examined the hypothesis that skeletal muscle tissue from HF patients would show reduced IGF-1 expression and phosphorylation of signaling molecules downstream of receptor activation. To isolate the unique effect of HF on these variables, we limited the confounding effects of muscle disuse and/or acute disease exacerbation by recruiting controls (n = 11) with similar physical activity levels as HF patients (n = 11) and by testing patients at least 6 mo following any bouts of disease exacerbation/hospitalization. IGF-1 expression in skeletal muscle was similar between patients and controls. Despite this, HF patients were characterized by reduced levels of phospho-Akt/Akt (S473; -43%; P < 0.05), whereas no differences were found in total Akt protein content or phospho- or total protein content of mammalian target of rapamycin (mTOR; S2448), glycogen synthase kinase-3β (GSK-3β; S9), eukaryotic translation initiation factor 4E binding protein-1 (eIF4E-BP; T37/46), p70 ribosomal S6 kinase (p70 S6K; T389), or eIF2Bε (S540). Reduced phospho-Akt/Akt levels and phospho-mTOR/mTOR were related to decreased skeletal muscle myosin protein content (r = 0.602; P < 0.02) and knee extensor isometric torque (r = 0.550; P < 0.05), respectively. Because patients and controls were similar for age, muscle mass, and physical activity, we ascribe the observed alterations in Akt phosphorylation and its relationship to myosin protein content to the unique effects of the HF syndrome.

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.

Impaired muscle protein anabolic response to insulin and amino acids in heart failure patients: relationship with markers of immune activation

Patients with chronic HF (heart failure) experience muscle atrophy during the course of the disease. The mechanisms underlying muscle atrophy in HF, however, are not understood. Thus we evaluated leg phenylalanine balance and kinetics in HF patients and controls following a brief fast (24 h) and under euglycaemic-hyperinsulinaemic-hyperaminoacidaemic conditions to determine whether HF increases muscle protein catabolism in response to nutritional deprivation and/or diminishes the anabolic response to meal-related stimuli (insulin and amino acids) and whether alterations in protein metabolism correlate to circulating cytokine levels. No differences in phenylalanine balance, rate of appearance or rate of disappearance were found between patients and controls under fasting conditions. However, the anabolic response to hyperinsulinaemia-hyperaminoacidaemia was reduced by more than 50% in patients compared with controls. The diminished anabolic response was due to reduced suppression of the leg phenylalanine appearance rate, an index of protein breakdown, in HF patients; whereas no group difference was found in the increase in the leg phenylalanine disappearance rate, an index of protein synthesis. The diminished responses of both phenylalanine balance and appearance rate to hyperinsulinaemia-hyperaminoacidaemia were related to greater circulating IL-6 (interleukin-6) levels. Our results suggest that, following a brief period of nutritional deprivation, HF patients demonstrate an impaired muscle protein anabolic response to meal-related stimuli, due to an inability to suppress muscle proteolysis, and that this diminished protein anabolic response correlates with markers of immune activation. The inability to stimulate muscle protein anabolism following periods of nutritional deficiency may contribute to muscle wasting in HF patients.

Comparative biomechanics of thick filaments and thin filaments with functional consequences for muscle contraction

The scaffold of striated muscle is predominantly comprised of myosin and actin polymers known as thick filaments and thin filaments, respectively. The roles these filaments play in muscle contraction are well known, but the extent to which variations in filament mechanical properties influence muscle function is not fully understood. Here we review information on the material properties of thick filaments, thin filaments, and their primary constituents; we also discuss ways in which mechanical properties of filaments impact muscle performance.