Sarcopenia in pulmonary diseases is associated with elevated sarcoplasmic reticulum stress and myonuclear disorganization

Mechanisms and Countermeasures for Muscle Atrophy in Microgravity

Previous studies have revealed that muscle atrophy emerges as a significant challenge faced by astronauts during prolonged missions in space. A loss in muscle mass results in a weakening of skeletal muscle strength and function, which will not only contribute to a decline in overall physical performance but also elevate the risk of various age-related diseases. Skeletal muscle atrophy in the microgravity environment is thought to be associated with changes in energy metabolism, protein metabolism, calcium ion homeostasis, myostatin levels, and apoptosis. Modulating some pathways could be a promising approach to mitigating muscle atrophy in the microgravity environment. This review serves as a comprehensive summary of research on the impact of microgravity on skeletal muscle, with the aim of providing insights into its pathogenesis and the development of effective treatments.

Muscle contractile properties and perceived fatigue in the general and diseased population

Knowledge of muscle contractile properties, physical fitness, and their associations with perceived fatigue may provide insights into mechanisms inducing fatigue and treatment targets. We aimed to identify differences in contractile properties and physical fitness between populations, and examine associations with perceived fatigue. We pooled data on perceived fatigue, physical fitness, and contractile properties from six studies, including a control group (n = 90), cancer survivors (n = 27), patients with chronic obstructive pulmonary disease (COPD; n = 16), chronic myeloid leukemia (CML; n = 20), and statin users (n = 64). We evaluated differences between populations, and associations of contractile properties and physical fitness with perceived fatigue. Compared with the control group, we found differences in contractile properties of patients with COPD (larger muscle force decline: β = -10.5%, 95% CI = -16.7; -4.2, increase in early relaxation time (Rt): β = 84.4%, 95% CI = 51.7; 117.0, increase in half Rt: β = 83.1%, 95% CI = 45.5; 120.7, muscle force rise (MFR): β = 0.2%/ms, 95% CI = 0.1; 0.3, and decrease in MFR: β = -24.3%, 95% CI = -35.7; -13.0) and statin users (early Rt: β = -5.4 ms, 95% CI = -10.0; -0.8, increase in early Rt: β = 19.8%, 95% CI = 2.5; 37.1). Associations between contractile properties and perceived fatigue varied across populations. Longer relaxation times were associated with higher perceived fatigue in hemato-oncological populations. To conclude, contractile properties were impaired in patients with COPD and statin users. Associations between contractile properties and perceived fatigue varied across populations. In hemato-oncological populations, impaired muscle relaxation was associated with higher perceived fatigue.

Plasma levels of Neurofilament light chain correlate with handgrip strength and sarcopenia in patients with chronic obstructive pulmonary disease

BACKGROUND

Age-associated muscle decline, termed sarcopenia, is a common systemic effect of chronic obstructive pulmonary disease (COPD). Circulating Neurofilament light chain (NfL) levels reflect neuronal degradation and may be relevant to sarcopenia phenotype. However, such an association in COPD patients remains elusive.

METHODS

We investigated male, 60-76 years old controls (n = 50) and COPD patients (n = 139) for plasma NfL levels in relation to sarcopenia and physical capacity markers. We measured handgrip strength (HGS), body composition, and short physical performance battery (SPPB) to evaluate sarcopenia and physical capacity.

RESULTS

COPD patients had higher plasma NfL and lower HGS and SPPB performance than controls. Plasma NfL levels demonstrated negative associations with HGS and gait speed in COPD patients (all p < 0.05). Further, NfL levels were negatively associated with total SPPB scores in controls and patients with advanced COPD (p < 0.05). Plasma NfL also demonstrated an acceptable accuracy in diagnosing sarcopenia in controls (AUC = 0.757, p < 0.05) and COPD (AUC = 0.806, p < 0.05) patients.

CONCLUSION

Collectively, plasma NfL may be helpful in evaluating sarcopenia phenotype and physical capacity in geriatric patients with COPD.

Musculoskeletal crosstalk in chronic obstructive pulmonary disease and comorbidities: Emerging roles and therapeutic potentials

Chronic Obstructive Pulmonary Disease (COPD) is a multifaceted respiratory disorder characterized by progressive airflow limitation and systemic implications. It has become increasingly apparent that COPD exerts its influence far beyond the respiratory system, extending its impact to various organ systems. Among these, the musculoskeletal system emerges as a central player in both the pathogenesis and management of COPD and its associated comorbidities. Muscle dysfunction and osteoporosis are prevalent musculoskeletal disorders in COPD patients, leading to a substantial decline in exercise capacity and overall health. These manifestations are influenced by systemic inflammation, oxidative stress, and hormonal imbalances, all hallmarks of COPD. Recent research has uncovered an intricate interplay between COPD and musculoskeletal comorbidities, suggesting that muscle and bone tissues may cross-communicate through the release of signalling molecules, known as "myokines" and "osteokines". We explored this dynamic relationship, with a particular focus on the role of the immune system in mediating the cross-communication between muscle and bone in COPD. Moreover, we delved into existing and emerging therapeutic strategies for managing musculoskeletal disorders in COPD. It underscores the development of personalized treatment approaches that target both the respiratory and musculoskeletal aspects of COPD, offering the promise of improved well-being and quality of life for individuals grappling with this complex condition. This comprehensive review underscores the significance of recognizing the profound impact of COPD on the musculoskeletal system and its comorbidities. By unravelling the intricate connections between these systems and exploring innovative treatment avenues, we can aspire to enhance the overall care and outcomes for COPD patients, ultimately offering hope for improved health and well-being.

Role of nutrition in patients with coexisting chronic obstructive pulmonary disease and sarcopenia

Chronic obstructive pulmonary disease (COPD) is one of the most common chronic diseases in the elderly population and is characterized by persistent respiratory symptoms and airflow obstruction. During COPD progression, a variety of pulmonary and extrapulmonary complications develop, with sarcopenia being one of the most common extrapulmonary complications. Factors that contribute to the pathogenesis of coexisting COPD and sarcopenia include systemic inflammation, hypoxia, hypercapnia, oxidative stress, protein metabolic imbalance, and myocyte mitochondrial dysfunction. These factors, individually or in concert, affect muscle function, resulting in decreased muscle mass and strength. The occurrence of sarcopenia severely affects the quality of life of patients with COPD, resulting in increased readmission rates, longer hospital admission, and higher mortality. In recent years, studies have found that oral supplementation with protein, micronutrients, fat, or a combination of nutritional supplements can improve the muscle strength and physical performance of these patients; some studies have also elucidated the possible underlying mechanisms. This review aimed to elucidate the role of nutrition among patients with coexisting COPD and sarcopenia.

Suppression of endoplasmic reticulum stress reverses hindlimb unloading-induced hepatic cellular processes in mice

BACKGROUND

The Hindlimb unloaded mouse, an animal model of simulated microgravity demonstrates significant metabolic and hepatic derangements. However, cellular and molecular mechanisms driving liver dysfunction in Hindlimb unloaded mice are poorly characterized.

METHODS

We investigated the possible contribution of dysregulated protein homeostasis by endoplasmic reticulum, endoplasmic reticulum stress, to liver dysfunction during HU. C57BL/6j male mice were grouped into ground-based controls or Hindlimb unloaded groups treated daily with vehicle or 4-phenylbutyrate (4-PBA), a potent inhibitor of endoplasmic reticulum stress. Following three weeks of HU, mice were sacrificed, and liver tissues were dissected for further analysis.

RESULTS

Hindlimb unloaded was associated with hepatic atrophy and elevated endoplasmic reticulum stress, which was restored by 4-PBA treatment. The Gene Ontology analysis revealed the downregulation of genes primarily involved in liver metabolic and Wingless-related integration site (WNT) signaling pathways, while those related to cytochrome P450, and liver fibrosis were upregulated. The Kyoto Encyclopedia of Genes and Genomes pathway analysis revealed downregulation of several genes involved in metabolic pathways following treatment with 4-PBA, induced by HU.

CONCLUSIONS

We report several differential and uniquely expressed genes associated with microgravity-induced elevated ER stress and liver injury. Our data has translational potential in unraveling novel molecular targets for pharmaceutical therapies of liver diseases.

GENERAL SIGNIFICANCE

Our novel findings show a pathogenic role for elevated ER stress in liver injury in microgravity conditions.

Main Pathogenic Mechanisms and Recent Advances in COPD Peripheral Skeletal Muscle Wasting

Chronic obstructive pulmonary disease (COPD) is a worldwide prevalent respiratory disease mainly caused by tobacco smoke exposure. COPD is now considered as a systemic disease with several comorbidities. Among them, skeletal muscle dysfunction affects around 20% of COPD patients and is associated with higher morbidity and mortality. Although the histological alterations are well characterized, including myofiber atrophy, a decreased proportion of slow-twitch myofibers, and a decreased capillarization and oxidative phosphorylation capacity, the molecular basis for muscle atrophy is complex and remains partly unknown. Major difficulties lie in patient heterogeneity, accessing patients' samples, and complex multifactorial process including extrinsic mechanisms, such as tobacco smoke or disuse, and intrinsic mechanisms, such as oxidative stress, hypoxia, or systemic inflammation. Muscle wasting is also a highly dynamic process whose investigation is hampered by the differential protein regulation according to the stage of atrophy. In this review, we report and discuss recent data regarding the molecular alterations in COPD leading to impaired muscle mass, including inflammation, hypoxia and hypercapnia, mitochondrial dysfunction, diverse metabolic changes such as oxidative and nitrosative stress and genetic and epigenetic modifications, all leading to an impaired anabolic/catabolic balance in the myocyte. We recapitulate data concerning skeletal muscle dysfunction obtained in the different rodent models of COPD. Finally, we propose several pathways that should be investigated in COPD skeletal muscle dysfunction in the future.

Suppression of endoplasmic reticulum stress prevents disuse muscle atrophy in a mouse model of microgravity

BACKGROUND

Hind-limb unloaded (HLU) mouse model exhibits skeletal muscle atrophy and weakness mimicking the conditions such as prolonged spaceflight. However, the molecular mechanisms and interventions of muscle loss during muscle unloading remain elusive. Dysfunction of protein folding by ednoplasmic reticulum (ER), a condition called ER stress, is implicated in diseases of various cell types, but its contribution to skeletal muscle detriment remains elusive. In this study, we investigated the contribution of ER stress to muscle atrophy.

METHODS

Sixteen-week-old c57BL/6j male mice were grouped into ground-based controls and HLU group, which was subsequently injected with injected saline (HLU-sal.) or pan-ER stress inhibitor 4-PBA (100mg/kg/d; HLU- 4PBA) via intraperitoneal injections for three weeks.

RESULTS

Three weeks of HLU resulted in reduction in muscle mass and strength, which were restored with 4PBA injections. We also report myofibers atrophy, myonuclear apoptosis, and aterations in the expressions of genes associated with ER stress, apoptosis, and calcium dysregulation. These findings were reversed by 4-PBA treatment.

CONCLUSION

Altogether, our results indicate that ER stress contributes to muscle atrophy in HLU conditions. We suggest that blocking ER stress may be an effective pharmacological therapy to prevent muscle weakness and atrophy during prolonged muscle unloading.

Mitigating sarcoplasmic reticulum stress limits disuse-induced muscle loss in hindlimb unloaded mice

Muscle disuse in the hindlimb unloaded (HU) mice causes significant atrophy and weakness. However, the cellular and molecular mechanisms driving disuse-muscle atrophy remain elusive. We investigated the potential contribution of proteins dysregulation by sarcoplasmic reticulum (SR), a condition called SR stress, to muscle loss during HU. Male, c57BL/6j mice were assigned to ground-based controls or HU groups treated with vehicle or 4-phenylbutyrate (4-PBA), a potent inhibitor of SR stress, once a day for three weeks. We report that the 4-PBA reduced the SR stress and partly reversed the muscle atrophy and weakness in the HU mice. Transcriptome analysis revealed that several genes were switched on (n = 3688) or differentially expressed (n = 1184) due to HU. GO, and KEGG term analysis revealed alterations in pathways associated with the assembly of cilia and microtubules, extracellular matrix proteins regulation, calcium homeostasis, and immune modulation during HU. The muscle restoration with 4-PBA partly reversed these changes along with differential and unique expression of several genes. The analysis of genes among the two comparisons (HU-v vs. control and HU-t vs. HU-v.) shows 841 genes were overlapped between the two comparisons and they may be regulated by 4-PBA. Altogether, our findings suggest that the pharmacological suppression of SR stress may be an effective strategy to prevent disuse-induced muscle weakness and atrophy.

Relationship of Haptoglobin Phenotypes With Sarcopaenia in Patients With Congestive Heart Failure

BACKGROUND

Systemic inflammation in patients with chronic heart failure (CHF) contributes to age-related muscle loss or sarcopaenia. However, the relationship of plasma haptoglobin (Hp), an acute-phase reactant, with muscle and physical health in CHF is unknown.

METHODS

This study investigated the associations of plasma haptoglobin levels and phenotypes with handgrip strength (HGS), appendicular skeletal muscle index (ASMI) and physical capacity in healthy controls (n=67) and CHF patients (n=61) aged 55-73 years.

RESULTS

Patients with CHF had higher plasma Hp levels and higher proportions of Hp2-2 phenotype when compared with healthy controls. Plasma Hp2-1 and Hp2-2 levels were negatively associated with HGS and ASMI in healthy controls and CHF (both p<0.05). A negative association of plasma Hp2-2 with gait speed and plasma Hp2-1 with daily steps count was also found in CHF (p<0.05). Patients with Hp2 phenotype showed higher expressions of inflammation and oxidative stress markers, as well as low scores on quality of life parameters.

CONCLUSIONS

Circulating Hp may be a valuable biomarker for assessing muscle health and physical capacity in CHF.