Insulin-Like Growth Factor-1 Bioregulation System Abnormalities: Another Explanatory Mechanism of Exercise Intolerance in Heart Failure

Exercise Training Enhances Angiogenesis-Related Gene Responses in Skeletal Muscle of Patients with Chronic Heart Failure

Peripheral myopathy consists of a hallmark of heart failure (HF). Exercise enhanced skeletal muscle angiogenesis, and thus, it can be further beneficial towards the HF-induced myopathy. However, there is limited evidence regarding the exercise type that elicits optimum angiogenic responses of skeletal muscle in HF patients. This study aimed to (a) compare the effects of a high-intensity-interval-training (HIIT) or combined HIIT with strength training (COM) exercise protocol on the expression of angiogenesis-related factors in skeletal muscle of HF patients, and (b) examine the potential associations between the expression of those genes and capillarization in the trained muscles. Thirteen male patients with chronic HF (age: 51 ± 13 y; BMI: 27 ± 4 kg/m²) were randomly assigned to a 3-month exercise program that consisted of either HIIT (N = 6) or COM training (N = 7). Vastus lateralis muscle biopsies were performed pre- and post-training. RT-PCR was used to quantify the fold changes in mRNA expression of vascular endothelial growth factor (VEGF), vascular endothelial growth factor receptor 2 (VEGFR-2), hypoxia-inducible factor 1 alpha (HIF-1α), angiopoietin 1 (Ang-1), angiopoietin 2 (Ang-2), angiopoietin receptor (Tie2), and matrix metallopeptidase 9 (MMP-9), and immunohistochemistry to assess capillarization in skeletal muscle post-training. There was an overall increase in the expression levels of VEGF, VEGFR-2, HIF-1α, Ang2, and MMP9 post-training, while these changes were not different among groups. Changes in capillary-to-fibre ratio were found to be strongly associated with Tie2 and HIF-1α expression. This was the first study demonstrating that both HIIT and combined HIIT with strength training enhanced similarly the expression profile of angiogenic factors in skeletal muscle of HF patients, possibly driving the angiogenic program in the trained muscles, although those gene expression increases were found to be only partially related with muscle capillarization.

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.