Skeletal muscle apoptosis in experimental heart failure: the only link between inflammation and skeletal muscle wastage?

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.

Sarcopenia and Cardiac Dysfunction

Although muscle loss is part of the natural course of human aging, sarcopenia has been associated with an increased risk of physical disability and mortality in older patients. Many heart failure patients concomitantly develop deficits in muscle mass and strength, resulting in decreased quality of life and exercise capacity. An underlying state of inflammation is central to the development of sarcopenia and muscle wasting in heart failure; however, additional research in human models is needed to further delineate the pathophysiology of muscle wasting in these patients. Previous studies have shed light on many of the potential targets for therapeutic intervention of sarcopenia in heart failure; however, physical exercise remains the prominent beneficial intervention. Future research must explore other therapeutic interventions in randomized, double-blind clinical trials, which may help to supplement exercise regimens. Sarcopenia shows promise as an easily measured predictor of outcomes after transcatheter aortic valve replacement.

Muscle Changes During Atrophy

Muscle atrophy typically is a direct effect of protein degradation induced by a diversity of pathophysiologic states such as disuse, immobilization, denervation, aging, sepsis, cachexia, glucocorticoid treatment, hereditary muscular disorders, cancer, diabetes and obesity, kidney and heart failure, and others. Muscle atrophy is defined by changes in the muscles, consisting in shrinkage of myofibers, changes in the types of fiber and myosin isoforms, and a net loss of cytoplasm, organelles and overall a protein loss. Although in the literature there are extensive studies in a range of animal models, the paucity of human data is a reality. This chapter is focused on various aspects of muscle wasting and describes the transitions of myofiber types during the progression of muscle atrophy in several pathological states. Clinical conditions associated with muscle atrophy have been grouped based on the fast-to-slow or slow-to-fast fiber-type shifts. We have also summarized the ultrastructural and histochemical features characteristic for muscle atrophy in clinical and experimental models for aging, cancer, diabetes and obesity, and heart failure and arrhythmia.

Muscle wasting and cachexia in heart failure: mechanisms and therapies

Body wasting is a serious complication that affects a large proportion of patients with heart failure. Muscle wasting, also known as sarcopenia, is the loss of muscle mass and strength, whereas cachexia describes loss of weight. After reaching guideline-recommended doses of heart failure therapies, the most promising approach to treating body wasting seems to be combined therapy that includes exercise, nutritional counselling, and drug treatment. Nutritional considerations include avoiding excessive salt and fluid intake, and replenishment of deficiencies in trace elements. Administration of omega-3 polyunsaturated fatty acids is beneficial in selected patients. High-calorific nutritional supplements can also be useful. The prescription of aerobic exercise training that provokes mild or moderate breathlessness has good scientific support. Drugs with potential benefit in the treatment of body wasting that have been tested in clinical studies in patients with heart failure include testosterone, ghrelin, recombinant human growth hormone, essential amino acids, and β₂-adrenergic receptor agonists. In this Review, we summarize the pathophysiological mechanisms of muscle wasting and cachexia in heart failure, and highlight the potential treatment strategies. We aim to provide clinicians with the relevant information on body wasting to understand and treat these conditions in patients with heart failure.

Skeletal muscle proteolysis is associated with sympathetic activation and TNF-α-ubiquitin-proteasome pathway in liver cirrhotic rats

BACKGROUND AND AIM

This study examined the effects of adrenergic blockade on muscle wasting and expression of the ubiquitin-proteasome system, tumor necrosis factor-α (TNF-α) and its signaling pathways in skeletal muscles of cirrhotic rats.

METHODS

Cirrhosis was induced by bile duct ligation in adult male Sprague-Dawley rats for 5 weeks. Oral administration of propranolol (75 mg/kg per day) and intraperitoneal administration of TNF-α receptor antagonist (100 µg/kg per day) were delivered for the last 7 and 14 days experimental periods, respectively.

RESULTS

Bile duct ligation caused a reduction of myosin heavy chain protein and muscle wasting. The release of free tyrosine and 3-methylhistidine, MAFbx and MuRF-1 ubiquitin ligase expression, myosin heavy chain protein ubiquitination, and 20S proteasome activity were higher in skeletal muscles of cirrhotic rats than in sham controls. In addition, circulating norepinephrine, protein levels of muscle TNF-α, TNF-α receptor-1, and TNF receptor-associated factor-2, phosphorylation of IKK-α/β, IκB-α, and p65, and NF-κB activity were also increased. Administration of propranolol and TNF-α receptor antagonist led to reduction of post-receptor actions of TNF-α and ubiquitin-proteasome activity in cirrhotic rats.

CONCLUSIONS

Our findings suggest a potential role of the sympathetic system, in association with pro-inflammatory responses, in the pathogenesis of muscle wasting in liver cirrhosis.

The wasting continuum in heart failure: from sarcopenia to cachexia

Sarcopenia (muscle wasting) and cachexia share some pathophysiological aspects. Sarcopenia affects approximately 20 %, cachexia <10 % of ambulatory patients with heart failure (HF). Whilst sarcopenia means loss of skeletal muscle mass and strength that predominantly affects postural rather than non-postural muscles, cachexia means loss of muscle and fat tissue that leads to weight loss. The wasting continuum in HF implies that skeletal muscle is lost earlier than fat tissue and may lead from sarcopenia to cachexia. Both tissues require conservation, and therapies that stop the wasting process have tremendous therapeutic appeal. The present paper reviews the pathophysiology of muscle and fat wasting in HF and discusses potential treatments, including exercise training, appetite stimulants, essential amino acids, growth hormone, testosterone, electrical muscle stimulation, ghrelin and its analogues, ghrelin receptor agonists and myostatin antibodies.

Skeletal myopathy in patients with chronic heart failure: significance of anabolic-androgenic hormones

In heart failure, impairment of cardiac muscle function leads to numerous neurohormonal and metabolic disorders, including an imbalance between anabolic and catabolic processes, in favour of the latter. These disorders cause loss of muscle mass with structural and functional changes within the skeletal muscles, known as skeletal myopathy. This phenomenon constitutes an important mechanism that participates in the pathogenesis of chronic heart failure. both its clinical symptoms and the progression of the disease. Attempts to reverse the above-mentioned pathologic processes by exploiting the anabolic action of androgenic hormones could provide a potentially attractive treatment option. The current concepts of anabolic androgen deficiency and resultant skeletal myopathy in patients with heart failure are reviewed, and the potential role of anabolic-androgenic hormones as an emerging therapeutic option for targeting heart failure is discussed.

Proteome Analysis of the Anti-inflammatory Response of Flavonoids Isolated from Korean Citrus aurantium L. in Lipopolysaccharide-Induced L6 Rat Skeletal Muscle Cells

Skeletal muscle is an important organ in our body and a dynamic composite of proteins. Citrus aurantium L. has been widely used in oriental medicine in Eastern Asia for a long time. It contains over 100 bioactive compounds and flavonoids that regulate the inflammatory response and tumorigenesis, through various mechanisms. In the present study, we investigated changes in the protein pattern using two-dimensional electrophoresis (2-DE) and matrix assisted laser desorption ionization time of flight mass spectroscopy (MALDI-TOF/MS) to assess the anti-inflammatory effect of flavonoids isolated from Korean C. aurantium L. in lipopolysaccharide (LPS)-induced L6 cells. L6 skeletal muscle cells were pretreated with flavonoids for 1 h and stimulated with LPS for 24 h. Proteins from the L6 cells of the control, LPS treated and flavonoid treated groups were extracted and resolved by 2-DE using pH 4–7 IPG strips loaded with 150 μg of protein. Forty-one differentially expressed protein spots were identified (more than two-fold was considered significant, p < 0.05), and 18 were detected by MALDI-TOF/MS. These results suggest that proteomics can be used to identify changes in the expression of marker proteins and the anti-inflammatory effect of flavonoids isolated from Korean C. aurantium L.

Cachexia in chronic heart failure: endocrine determinants and treatment perspectives

It is well documented in the current literature that chronic heart failure is often associated with cachexia, defined as involuntary weight loss of 5 % in 12 month or less. Clinical studies unraveled that the presence of cachexia decreases significantly mean survival of the patient. At the molecular level mainly myofibrillar proteins are degraded, although a reduced protein synthesis may also contribute to the loss of muscle mass. Endocrine factors clearly regulate muscle mass and function by influencing the normally precisely controlled balance between protein breakdown and protein synthesis The aim of the present article is to review the knowledge in the field with respect to the role of endocrine factors for the regulation of cachexia in patients with CHF and deduce treatment perspectives.

The contribution of stem cell therapy to skeletal muscle remodeling in heart failure

BACKGROUND

The aim of our study was to investigate whether stem cell (SC) therapy with human amniotic fluid stem cells (hAFS, fetal stem cells) and rat adipose tissue stromal vascular fraction cells-GFP positive cells (rSVC-GFP) was able to produce favorable effects on skeletal muscle (SM) remodeling in a well-established rat model of right heart failure (RHF).

METHODS

RHF was induced by monocrotaline (MCT) in Sprague-Dawley rats. Three weeks later, four millions of hAFS or rSVC-GFP cells were injected via tail vein. SM remodeling was assessed by Soleus muscle fiber cross sectional area (CSA), myocyte apoptosis, myosin heavy chain (MHC) composition, satellite cells pattern, and SC immunohistochemistry.

RESULTS

hAFS and rSVC-GFP injection produced significant SC homing in Soleus (0.68 ± 1.0 and 0.67 ± 0.75% respectively), with a 50% differentiation toward smooth muscle and endothelial cells. Pro-inflammatory cytokines were down regulated to levels similar to those of controls. SC-treated (SCT) rats showed increased CSA (p<0.004 vs MCT) similarly to controls with a reshift toward the slow MHC1 isoform. Apoptosis was significantly decreased (11.12.± 8.8 cells/mm(3) hAFS and 13.1+7.6 rSVC-GFP) (p<0.001 vs MCT) and similar to controls (5.38 ± 3.0 cells/mm(3)). RHF rats showed a dramatic reduction of satellite cells(MCT 0.2 ± 0.06% Pax7 native vs controls 2.60 ± 2.46%, p<0.001), while SCT induced a repopulation of both native and SC derived satellite cells (p<0.005).

CONCLUSIONS

SC treatment led to SM remodeling with satellite cell repopulation, decreased atrophy and apoptosis. Modulation of the cytokine milieu might play a crucial pathophysiological role with a possible scenario for autologous transplantation of SC in pts with CHF myopathy.

Molecular and cellular mechanisms of skeletal muscle atrophy: an update

Skeletal muscle atrophy is defined as a decrease in muscle mass and it occurs when protein degradation exceeds protein synthesis. Potential triggers of muscle wasting are long-term immobilization, malnutrition, severe burns, aging as well as various serious and often chronic diseases, such as chronic heart failure, obstructive lung disease, renal failure, AIDS, sepsis, immune disorders, cancer, and dystrophies. Interestingly, a cooperation between several pathophysiological factors, including inappropriately adapted anabolic (e.g., growth hormone, insulin-like growth factor 1) and catabolic proteins (e.g., tumor necrosis factor alpha, myostatin), may tip the balance towards muscle-specific protein degradation through activation of the proteasomal and autophagic systems or the apoptotic pathway. Based on the current literature, we present an overview of the molecular and cellular mechanisms that contribute to muscle wasting. We also focus on the multifacetted therapeutic approach that is currently employed to prevent the development of muscle wasting and to counteract its progression. This approach includes adequate nutritional support, implementation of exercise training, and possible pharmacological compounds.

Regional skeletal muscle remodeling and mitochondrial dysfunction in right ventricular heart failure

Exercise intolerance is a cardinal symptom of right ventricular heart failure (RV HF) and skeletal muscle adaptations play a role in this limitation. We determined regional remodeling of muscle structure and mitochondrial function in a rat model of RV HF induced by monocrotaline injection (MCT; 60 mg·kg(-1); n = 11). Serial sections of the plantaris were stained for fiber type, succinate dehydrogenase (SDH) activity and capillaries. Mitochondrial function was assessed in permeabilized fibers using respirometry, and isolated complex activity by blue native gel electrophoresis (BN PAGE). All measurements were compared with saline-injected control animals (CON; n = 12). Overall fiber cross-sectional area was smaller in MCT than CON: 1,843 ± 114 vs. 2,322 ± 120 μm(2) (P = 0.009). Capillary-to-fiber ratio was lower in MCT in the oxidative plantaris region (1.65 ± 0.09 vs. 1.93 ± 0.07; P = 0.03), but not in the glycolytic region. SDH activity (P = 0.048) and maximal respiratory rate (P = 0.012) were each ∼15% lower in all fibers in MCT. ADP sensitivity was reduced in both skeletal muscle regions in MCT (P = 0.032), but normalized by rotenone. A 20% lower complex I/IV activity in MCT was confirmed by BN PAGE. MCT-treatment was associated with lower mitochondrial volume density (lower SDH activity), quality (lower complex I activity), and fewer capillaries per fiber area in oxidative skeletal muscle. These features are consistent with structural and functional remodeling of the determinants of oxygen supply potential and utilization that may contribute to exercise intolerance and reduced quality of life in patients with RV HF.

The muscle fiber type-fiber size paradox: hypertrophy or oxidative metabolism?

An inverse relationship exists between striated muscle fiber size and its oxidative capacity. This relationship implies that muscle fibers, which are triggered to simultaneously increase their mass/strength (hypertrophy) and fatigue resistance (oxidative capacity), increase these properties (strength or fatigue resistance) to a lesser extent compared to fibers increasing either of these alone. Muscle fiber size and oxidative capacity are determined by the balance between myofibrillar protein synthesis, mitochondrial biosynthesis and degradation. New experimental data and an inventory of critical stimuli and state of activation of the signaling pathways involved in regulating contractile and metabolic protein turnover reveal: (1) higher capacity for protein synthesis in high compared to low oxidative fibers; (2) competition between signaling pathways for synthesis of myofibrillar proteins and proteins associated with oxidative metabolism; i.e., increased mitochondrial biogenesis via AMP-activated protein kinase attenuates the rate of protein synthesis; (3) relatively higher expression levels of E3-ligases and proteasome-mediated protein degradation in high oxidative fibers. These observations could explain the fiber type-fiber size paradox that despite the high capacity for protein synthesis in high oxidative fibers, these fibers remain relatively small. However, it remains challenging to understand the mechanisms by which contractile activity, mechanical loading, cellular energy status and cellular oxygen tension affect regulation of fiber size. Therefore, one needs to know the relative contribution of the signaling pathways to protein turnover in high and low oxidative fibers. The outcome and ideas presented are relevant to optimizing treatment and training in the fields of sports, cardiology, oncology, pulmonology and rehabilitation medicine.

Mechanisms to explain wasting of muscle and fat in cancer cachexia

PURPOSE OF REVIEW

To describe the most relevant recent findings concerning the molecular mechanisms involved in both fat and muscle tissues in cachectic cancer patients.

RECENT FINDINGS

Relevant progress has been made in the mechanism of signalling protein metabolism in skeletal muscle. PI3K has a dual role inhibiting protein degradation by inhibition of Atrogin-1 and MuRF1 gene expression and facilitating AKT phosphorylation, leading to increased protein synthesis. Interestingly, Caspase-3 activity is intimately associated with myofibrillar protein degradation in muscle tissue. With respect to fat metabolism, increased lipolysis in human cancer cachexia seems to be directly connected to increased hormone-sensitive lipase activity.

SUMMARY

The results and findings described in this review represent important progress in wasting disease mechanisms and may provide hints for future therapeutic approaches in cancer cachexia.

Skeletal muscle wastage in Crohn's disease: a pathway shared with heart failure?

BACKGROUND

Lean body mass wastage in active Crohn's disease is not only related to malnutrition, but also to local and systemic inflammation. Altered bowel permeability can represent a source of pro-inflammatory cytokines, that have been shown to produce muscle wastage by several mechanisms such as apoptosis. In our study we have evaluated the body composition and the pathological changes of skeletal muscle in patients with Crohn's disease to see whether a relationships between altered gut permeability, proinflammatory cytokines production and muscle wastage existed.

METHODS

Thirteen consecutive steroid-free patients with active Crohn's disease underwent evaluation of body composition, sugar test for intestinal permeability, determination of serum levels of TNF-alpha, sphingosine, bacterial lipopolysaccaride, and biopsy of gastrocnemius. In bioptic samples we determined fibres cross sectional area, distribution of myosin heavy chains and apoptosis. Twenty healthy subjects formed the control group.

RESULTS

In patients lean body mass was reduced and intestinal permeability increased (p<0.01 for both). TNFalpha, sphingosine and lipopolysaccaride were increased (p<0.01). Fibres size was reduced (p<0.01), with shift of Myosin Heavy Chains from the slow to the fast type. Apoptosis was found in 5 patients' biopsies, never in controls.

CONCLUSIONS

Crohn's patients have a myopathy characterized by myocyte apoptosis, modifications of myosin and muscle atrophy. TNF-alpha and sphingosine, that are increased because of the enhanced lipopolysaccaride concentration due to altered gut permeability, may play a pathophysiological role in the development of this myopathy.