Skeletal muscle phenotypic switching in heart failure with preserved ejection fraction

Dissecting the exercise pressor reflex in heart failure: A multi-step failure

The contribution of neural feedback originating from exercising limb muscles to the cardiovascular response to exercise was first recognized nearly 100 years ago. Today, it is well established that this influence is initiated by the activation of group III and IV sensory neurons with terminal endings located within contracting skeletal muscle. During exercise, these sensory neurons project feedback related to intramuscular mechanical and metabolic perturbations to medullary neural circuits which reflexively evoke decreases in parasympathetic and increases in sympathetic nervous system activity with the purpose of optimizing central and peripheral hemodynamics. Considerable evidence from animal and human studies suggests that the function of this regulatory control system, known as the exercise pressor reflex (EPR), is abnormal in heart failure and exaggerates sympatho-excitation which impairs the hemodynamic response to exercise and contributes to the functional limitations characterizing these patients. This review briefly introduces the key determinants of EPR control in health and covers the impact of heart failure on the integrity of each of its components and overall function. These include the sensitivity of group III/IV muscle afferents, afferent signal transmission in the spinal cord, and the central integration and processing of sensory feedback within the brainstem. Importantly, although most data relevant for this review come from studies in HFrEF, the limited HFpEF-specific insights are included when available. While arguably not part of the EPR, we also discuss the impact of heart failure on the exercise-induced increase of intramuscular stimuli of group III/IV muscle afferents and end-organ responsiveness to sympathetic/neurochemical stimulation.

Musclin Counteracts Skeletal Muscle Dysfunction and Exercise Intolerance in Heart Failure With Preserved Ejection Fraction

BACKGROUND

Exercise intolerance is a hallmark of heart failure with preserved ejection fraction (HFpEF) and is characterized by skeletal muscle (SkM) dysfunction with impaired oxidative capacity. To maintain oxidative capacity, the SkM secretes myokines such as musclin, which has been shown to potentiate NP (natriuretic peptide) signaling and induce PGC-1α (peroxisome proliferator-activated receptor-γ coactivator-1 alpha) signaling. We sought to investigate the role of musclin in SkM dysfunction in HFpEF. For this study, we selected the oxidative-predominant SkM soleus in HFpEF mice and vastus lateralis from patients with HFpEF.

METHODS

Using the SAUNA model, mice underwent HFpEF induction by uninephrectomy, d-aldosterone infusion, and 1% sodium chloride drinking water for 4 weeks. Exogenous musclin was given to HFpEF mice every 2 days during the last 2 weeks of HFpEF induction. Molecular analyses were conducted on blood samples and SkM from HFpEF mice and patients with HFpEF.

RESULTS

In HFpEF mice and patients with HFpEF, increased musclin expression was accompanied by decreased cyclic guanosine monophosphate levels and PGC-1α expression in SkM, suggesting impaired NP signaling. Exogenous administration of musclin in mice with HFpEF demonstrated augmented circulating musclin levels and potentiated NP signaling in SkM as shown by increased PKG1 (protein kinase G1) activity and PGC-1α expression. This was associated with a transition from type-2A to type-1 fiber (type-1 has more endurance) and increased succinate dehydrogenase activity, hindlimb blood flow, and capillary density in the soleus muscle. Exogenous musclin also mitigated cardiac hypertrophy without affecting blood pressure or diastolic function. Most importantly, HFpEF mice treated with musclin demonstrated improved functional and exercise capacity.

CONCLUSIONS

Musclin mediates beneficial effects in SkM and heart with improved exercise capacity likely by improving oxidative capacity in SkM. Future studies are warranted to address the therapeutic efficacy of exogenous musclin in humans with HFpEF.

Mechanisms of exercise intolerance in heart failure with preserved ejection fraction (HFpEF)

Exercise intolerance is a well-established symptom of heart failure with preserved ejection fraction (HFpEF) and is associated with impaired quality of life and worse clinical outcomes. Historically attributed to diastolic dysfunction of the left ventricle, exercise intolerance in HFpEF is now known to result not only from diastolic dysfunction, but also from impairments in left ventricular systolic function, left atrial pathology, right ventricular dysfunction, and valvular disease. Disorders of heart rate and rhythm such as chronotropic incompetence and atrial fibrillation have also been implicated in exercise intolerance in this population. Pathologic changes to extra-cardiac organ systems including the respiratory, vascular, hormonal, and skeletal muscle systems are also thought to play a role in exercise impairment. Finally, comorbidities such as obesity, inflammation, and anemia are common and likely contributory in many cases. The role of each of these factors is discussed in this review of exercise intolerance in patients with HFpEF.

Impact of Exercise on Physiological, Biochemical, and Analytical Parameters in Patients with Heart Failure with Reduced Ejection Fraction

Heart failure with reduced ejection fraction (HFrEF) is a condition marked by diminished cardiac output and impaired oxygen delivery to tissues. Exercise, once avoided in HFrEF patients due to safety concerns, is now recognized as an important therapeutic intervention. Structured exercise improves various physiological, biochemical, and analytical parameters, including cardiac output, endothelial function, skeletal muscle performance, and autonomic regulation. Biochemically, exercise induces favorable changes in inflammatory markers, lipid profiles, glucose metabolism, and renal function. This paper reviews these changes, highlighting how exercise can be safely incorporated into HFrEF management. Further research is needed to tailor exercise interventions for individual patients to optimize outcomes.

Histological changes in skeletal muscle induced by heart failure in human patients and animal models: A scoping review

OBJECTIVE

This scoping review aimed to characterize the histological changes in skeletal muscle after heart failure (HF) and to identify gaps in knowledge.

METHODS

On April 03, 2024, systematic searches were performed for papers in which histological analyses were conducted on skeletal muscle sampled from patients with HF or animal models of HF. Screening and data extraction were conducted by two independent authors.

RESULTS AND CONCLUSION

A total of 118 papers were selected, including 33 human and 85 animal studies. Despite some disagreements among studies, some trends were observed. These trends included a slow-to-fast transition, a decrease in muscle fiber size, capillary to muscle fiber ratio, and mitochondrial activity and content, and an increase in apoptosis. These changes may contribute to the fatigability and decrease in muscle strength observed after HF. Although there were some disagreements between the results of human and animal studies, the results were generally similar. Animal models of HF will therefore be useful in elucidating the histological changes in skeletal muscle that occur in human patients with HF. Because the muscles subjected to histological analysis were mostly thigh muscles in humans and mostly lower leg muscles in animals, it remains uncertain whether changes similar to those seen in lower limb (hindlimb) muscles after HF also occur in upper limb (forelimb) muscles. The results of this review will consolidate the current knowledge on HF-induced histological changes in skeletal muscle and consequently aid in the rehabilitation of patients with HF and future studies.

Native skeletal muscle T1-time on cardiac magnetic resonance: A predictor of outcome in patients with heart failure with preserved ejection fraction

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF) is associated with heart failure (HF) hospitalizations and death. Previous studies have shown that altered muscle composition is associated with higher risk of adverse outcome in HFpEF patients.

AIM

The purpose of our study was to investigate the association between skeletal muscle composition, as measured by skeletal muscle T1-times on cardiac magnetic resonance (CMR) imaging, and adverse outcome.

METHODS

We measured skeletal muscle T1-times of the back muscles on standard CMR images in a prospective cohort of HFpEF patients. Cox regression models were used to test the association of skeletal muscle T1-times and adverse outcome defined as hospitalization for HF and/or cardiovascular death.

RESULTS

We included 101 patients (mean age 72±7 years, 71 % female) in our study. The median skeletal muscle T1-times were 842 ms (IQR 806-881 ms). In univariate analysis high muscle T1-time was associated with adverse outcome (HR=1.96 [95 % CI, 1.31-2.94] per every 100 ms increase; p=.001). After adjustment for age, sex, body mass index, left- and right ventricular ejection fraction, N-terminal pro-brain natriuretic peptide and myocardial native T1-times, native skeletal muscle T1-time remained an independent predictor for adverse outcome (HR=1.94 [95 % CI, 1.24-3.03] per every 100 ms increase; p=.004).

CONCLUSION

In patients with HFpEF, high skeletal muscle T1-times on standard CMR scans are associated with higher rates of HF hospitalizations and cardiovascular death.

CONDENSED ABSTRACT

Skeletal muscle abnormalities are common in patients with heart failure with preserved ejection fraction (HFpEF). The present study evaluates skeletal muscle composition, as quantified by native skeletal muscle T1-times of the back muscles on standard cardiac magnetic resonance imaging, and assessed the association with adverse outcome, defined as hospitalization for heart failure and/or cardiovascular death. In a prospective cohort of 101 patients with HFpEF, we found that high native skeletal muscle T1-times are associated with an increased risk for adverse outcome. These findings suggest that native skeletal muscle T1-time may serve as marker for improved risk prediction.