Epigenetic regulation of muscle phenotype and adaptation: a potential role in COPD muscle dysfunction

Decoding LncRNA in COPD: Unveiling Prognostic and Diagnostic Power and Their Driving Role in Lung Cancer Progression

Chronic obstructive pulmonary disease (COPD) and lung cancer represent formidable challenges in global health, characterized by intricate pathophysiological mechanisms and multifaceted disease progression. This comprehensive review integrates insights from diverse perspectives to elucidate the intricate roles of long non-coding RNAs (lncRNAs) in the pathogenesis of COPD and lung cancer, focusing on their diagnostic, prognostic, and therapeutic implications. In the context of COPD, dysregulated lncRNAs, such as NEAT1, TUG1, MALAT1, HOTAIR, and GAS5, emerge as pivotal regulators of genes involved in the disease pathogenesis and progression. Their identification, profiling, and correlation with the disease severity present promising avenues for prognostic and diagnostic applications, thereby shaping personalized disease interventions. These lncRNAs are also implicated in lung cancer, underscoring their multifaceted roles and therapeutic potential across both diseases. In the domain of lung cancer, lncRNAs play intricate modulatory roles in disease progression, offering avenues for innovative therapeutic approaches and prognostic indicators. LncRNA-mediated immune responses have been shown to drive lung cancer progression by modulating the tumor microenvironment, influencing immune cell infiltration, and altering cytokine production. Their dysregulation significantly contributes to tumor growth, metastasis, and chemo-resistance, thereby emphasizing their significance as therapeutic targets and prognostic markers. This review summarizes the transformative potential of lncRNA-based diagnostics and therapeutics for COPD and lung cancer, offering valuable insights into future research directions for clinical translation and therapeutic development.

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.

The role of muscle-specific MicroRNAs in patients with chronic obstructive pulmonary disease and skeletal muscle dysfunction

Skeletal muscle dysfunction is a systematic manifestation of chronic obstructive pulmonary disease (COPD), which is manifested through the changes in the respiratory and peripheral muscle fiber types, reducing muscle strength and endurance, and muscle atrophy. Muscle dysfunction limits the daily mobility, negatively affects the quality of life, and may increase the patient’s risk of mortality. MicroRNAs (miRNAs) as the regulators of gene expression, plays an important role in modulating skeletal muscle dysfunction in COPD by regulating skeletal muscle development (proliferation, differentiation), protein synthesis and degradation, inflammatory response, and metabolism. In particular, muscle-specific miRNAs (myomiRs) may play an important role in this process, although the different expression levels of myomiRs in COPD and skeletal muscle dysfunction and the mechanisms underlying their role remain unclear. In this paper, we review the differential expression of the myomiRs in COPD to identify myomiRs that play a role in skeletal muscle dysfunction in COPD. We further explore their possible mechanisms and action in order to provide new ideas for the prevention and treatment of the skeletal muscle dysfunction in COPD.

Impaired regenerative capacity contributes to skeletal muscle dysfunction in chronic obstructive pulmonary disease

Locomotor skeletal muscle dysfunction is a relevant comorbidity of chronic obstructive pulmonary disease (COPD) and is strongly associated with worse clinical outcomes including higher mortality. Over the last decades, a large body of literature helped characterize the process, defining the disruptive muscle phenotype caused by COPD that involves reduction in muscle mass, force-generation capacity, fatigue-tolerance, and regenerative potential following injury. A major limitation in the field has been the scarcity of well-calibrated animal models to conduct mechanistic research based on loss- and gain-of-function studies. This article provides an overall description of the process, the tools available to mechanistically investigate it, and the potential role of mitochondrially driven metabolic signals on the regulation muscle regeneration after injury in COPD. Finally, a description of future avenues to further expand on the area is proposed based on very recent evidence involving mitochondrial metabolic cues affecting myogenesis.

Impact of Physical Activity and Exercise on the Epigenome in Skeletal Muscle and Effects on Systemic Metabolism

Exercise and physical activity induces physiological responses in organisms, and adaptations in skeletal muscle, which is beneficial for maintaining health and preventing and/or treating most chronic diseases. These adaptations are mainly instigated by transcriptional responses that ensue in reaction to each individual exercise, either resistance or endurance. Consequently, changes in key metabolic, regulatory, and myogenic genes in skeletal muscle occur as both an early and late response to exercise, and these epigenetic modifications, which are influenced by environmental and genetic factors, trigger those alterations in the transcriptional responses. DNA methylation and histone modifications are the most significant epigenetic changes described in gene transcription, linked to the skeletal muscle transcriptional response to exercise, and mediating the exercise adaptations. Nevertheless, other alterations in the epigenetics markers, such as epitranscriptomics, modifications mediated by miRNAs, and lactylation as a novel epigenetic modification, are emerging as key events for gene transcription. Here, we provide an overview and update of the impact of exercise on epigenetic modifications, including the well-described DNA methylations and histone modifications, and the emerging modifications in the skeletal muscle. In addition, we describe the effects of exercise on epigenetic markers in other metabolic tissues; also, we provide information about how systemic metabolism or its metabolites influence epigenetic modifications in the skeletal muscle.

Hypercapnic Respiratory Failure-Driven Skeletal Muscle Dysfunction: It Is Time for Animal Model-Based Mechanistic Research

Dysfunction of locomotor muscles is frequent in chronic pulmonary diseases and strongly associated with worse outcomes including higher mortality. Although these associations have been corroborated over the last decades, there is poor mechanistic understanding of the process, in part due to the lack of adequate animal models to investigate this process. Most of the mechanistic research has so far been accomplished using relevant individual stimuli such as low oxygen or high CO₂ delivered to otherwise healthy animals as surrogates of the phenomena occurring in the clinical setting. This review advocates for the development of a syndromic model in which skeletal muscle dysfunction is investigated as a comorbidity of a well-validated pulmonary disease model, which could potentially allow discovering meaningful mechanisms and pathways and lead to more substantial progress to treat this devastating condition.

High CO2 Downregulates Skeletal Muscle Protein Anabolism via AMP-activated Protein Kinase α2-mediated Depressed Ribosomal Biogenesis

High CO₂ retention, or hypercapnia, is associated with worse outcomes in patients with chronic pulmonary diseases. Skeletal muscle wasting is also an independent predictor of poor outcomes in patients with acute and chronic pulmonary diseases. Although previous evidence indicates that high CO₂ accelerates skeletal muscle catabolism via AMPK (AMP-activated protein kinase)-FoxO3a-MuRF1 (E3-ubiquitin ligase muscle RING finger protein 1), little is known about the role of high CO₂ in regulating skeletal muscle anabolism. In the present study, we investigated the potential role of high CO₂ in attenuating skeletal muscle protein synthesis. We found that locomotor muscles from patients with chronic CO₂ retention demonstrated depressed ribosomal gene expression in comparison with locomotor muscles from non-CO₂-retaining individuals, and analysis of the muscle proteome of normo- and hypercapnic mice indicates reduction of important components of ribosomal structure and function. Indeed, mice chronically kept under a high-CO₂ environment show evidence of skeletal muscle downregulation of ribosomal biogenesis and decreased protein synthesis as measured by the incorporation of puromycin into skeletal muscle. Hypercapnia did not regulate the mTOR pathway, and rapamycin-induced deactivation of mTOR did not cause a decrease in ribosomal gene expression. Loss-of-function studies in cultured myotubes showed that AMPKα2 regulates CO₂-mediated reductions in ribosomal gene expression and protein synthesis. Although previous evidence has implicated TIF1A (transcription initiation factor-1α) and KDM2A (lysine-specific demethylase 2A) in AMPK-driven regulation of ribosomal gene expression, we found that these mediators were not required in the high CO₂-induced depressed protein anabolism. Our research supports future studies targeting ribosomal biogenesis and protein synthesis to alleviate the effects of high CO₂ on skeletal muscle turnover.

Physical Exercise and Epigenetic Modifications in Skeletal Muscle

Physical activity and sports play major roles in the overall health status of humans. It is well known that regular exercise helps to lower the risk for a broad variety of health problems, such as cardiovascular disease, type 2 diabetes, and cancer. Being physically active induces a wide variety of molecular adaptations, for example fiber type switches or other metabolic alterations, in skeletal muscle tissue. These adaptations are based on exercise-induced changes to the skeletal muscle transcriptome. Understanding their nature is crucial to improve the development of exercise-based therapeutic strategies. Recent research indicates that specifically epigenetic mechanisms, i.e., pathways that induce changes in gene expression patterns without altering the DNA base sequence, might play a major role in controlling skeletal muscle transcriptional patterns. Epigenetic mechanisms include DNA and histone modifications, as well as expression of specific microRNAs. They can be modulated by environmental factors or external stimuli, such as exercise, and eventually induce specific and fine-tuned changes to the transcriptional response. In this review, we highlight current knowledge on epigenetic changes induced in exercising skeletal muscle, their target genes, and resulting phenotypic changes. In addition, we raise the question of whether epigenetic modifications might serve as markers for the design and management of optimized and individualized training protocols, as prognostic tools to predict training adaptation, or even as targets for the design of "exercise mimics".

Differences in micro-RNA expression profile between vastus lateralis samples and myotubes in COPD cachexia

Quadriceps muscle weakness and wasting are common comorbidities in chronic obstructive pulmonary disease (COPD). Micro-RNA expression upregulation may favor muscle mass growth and differentiation. We hypothesized that the profile of muscle-enriched micro-RNAs in cultured myotubes differs between patients with COPD of a wide range of body composition and healthy controls and that expression levels of those micro-RNAs from patients with COPD and controls differ between in vivo and in vitro conditions. Twenty-nine patients with COPD [ n = 15 with muscle wasting and fat-free mass index (FFMI) 15 kg/m² and n = 14 with normal body composition and FFMI 18 kg/m²] and 10 healthy controls (FFMI 19 kg/m²) were consecutively recruited. Biopsies from the vastus lateralis muscle were obtained in all study subjects. A fragment of each biopsy was used to obtain primary cultures, in which muscle cells were first proliferated to be then differentiated into actual myotubes. In both sets of experiments (in vivo biopsies and in vitro myotubes) the following muscle-enriched micro-RNAs from all the study subjects were analyzed using quantitative real-time PCR amplification: micro-RNA (miR)-1, miR-133a, miR-206, miR-486, miR-29b, miR-27a, and miR-181a. Whereas the expression of miR-1, miR-206, miR-486, and miR-29b was upregulated in the muscle biopsies of patients with COPD compared with those of healthy controls, levels of none of the studied micro-RNAs in the myotubes (primary cultured cells) significantly differed between patients with COPD and the controls. We conclude from these findings that environmental factors (blood flow, muscle metabolism, and inflammation) taking place in vivo (biopsies) in muscles may account for the differences observed in micro-RNA expression between patients with COPD and controls. In the myotubes, however, the expression of the same micro-RNAs did not differ between the study subjects as such environmental factors were not present. These findings suggest that therapeutic strategies should rather target environmental factors in COPD muscle wasting as the profile of micro-RNA expression in myotubes was similar in patients to that observed in the healthy controls. NEW & NOTEWORTHY Environmental factors taking place in vivo (biopsies) in the muscles may explain differences observed in micro-RNA expression between patients with chronic obstructive pulmonary disease (COPD) and controls. In the myotubes, however, the expression of the same micro-RNAs did not differ between the study subjects as such environmental factors were not present. These findings suggest that therapeutic strategies should rather target environmental factors in COPD muscle wasting and cachexia as micro-RNA expression profile in myotubes was similar between patients and controls.

Epigenetic changes due to physical activity

One of the epigenetic-modifying factors is regular and continuous physical activity. This article attempts to investigate the effects of physical activity and exercise on changes in histone proteins and gene expression, as well as the effect of these exercises on the prevention of certain cancers and the ejection of age-related illnesses and cellular oxidation interactions. All of this is due to epigenetic changes and gene expression. Most studies have reported the positive effects of regular exercises on the expression of histone proteins. DNA methylation and the prevention of certain diseases such as cancer and respiratory diseases, caused by antioxidative interactions that occur more often in the elderly, have been studied.

Muscle atrophy in chronic obstructive pulmonary disease: molecular basis and potential therapeutic targets

Patients with chronic obstructive pulmonary disease (COPD) experience several systemic manifestations such skeletal muscle dysfunction with and without muscle mass loss. Moreover, frequent comorbidities such as nutritional abnormalities, heart failure, and pulmonary hypertension, which are frequently associated with COPD may further contribute to skeletal muscle mass loss and dysfunction. Muscle dysfunction impairs the patients' exercise capacity and quality of life as daily life activities may be hampered by this problem. Importantly, impaired muscle function and mass loss have been shown to impact negatively on the patients' prognosis and survival in several studies. Thus, this is a major clinical problem that deserves special attention in clinical settings. During the course of exacerbations muscle mass loss takes place, hence aggravating muscle status and performance even after hospital discharge, especially in the frequently exacerbator patients. Several factors and biological mechanisms are involved in the etiology of COPD muscle dysfunction. The biological mechanisms identified so far offer a niche for therapeutic interventions in the patients. In the current review, a general overview of the most relevant etiologic factors and their target biological mechanisms through which muscle mass loss and dysfunction take place in both the respiratory and lower limb muscles in COPD patients is provided. We conclude that more clinical research is still needed targeted to test several therapeutic interventions. Given its prognostic value, the assessment of skeletal muscle dysfunction should be included in the routine evaluation of patients with chronic respiratory disorders and in critical care settings.

Influence of dietary nitrate supplementation on lung function and exercise gas exchange in COPD patients

BACKGROUND

During exercise as pulmonary blood flow rises, pulmonary capillary blood volume increases and gas exchange surface area expands through distention and recruitment. We have previously demonstrated that pulmonary capillary recruitment is limited in COPD patients with poorer exercise tolerance. Hypoxia and endothelial dysfunction lead to pulmonary vascular dysregulation possibly in part related to nitric oxide related pathways.

PURPOSE

To determine if increasing dietary nitrate might influence lung surface area for gas exchange and subsequently impact exercise performance.

METHODS

Subjects had stable, medically treated COPD (n = 25), gave informed consent, filled out the St George Respiratory Questionnaire (SGRQ), had a baseline blood draw for Hgb, performed spirometry, and had exhaled nitric oxide (exNO) measured. Then they performed the intra-breath (IB) technique for lung diffusing capacity for carbon monoxide (DLCO) as well as pulmonary blood flow (Qc). Subsequently they completed a progressive semi-recumbent cycle ergometry test to exhaustion with measures of oxygen saturation (SpO₂) and expired gases along with DLCO and Qc measured during the 1st work load only. Subjects were randomized to nitrate supplement group (beetroot juice) or placebo group (black currant juice) for 8 days and returned for repeat of the above protocol.

RESULTS

Exhaled nitric oxide levels rose >200% in the nitrate group (p < 0.05) with minimal change in placebo group. The SGRQ suggested a small fall in perceived symptom limitation in the nitrate group, but no measure of resting pulmonary function differed post nitrate supplementation. With exercise, there was no influence of nitrate supplementation on peak VO₂ or other measures of respiratory gas exchange. There was a tendency for the exercise DLCO to increase slightly in the nitrate group with a trend towards a rise in the DLCO/Qc relationship (p = 0.08) but not in the placebo group. The only other significant finding was a fall in the exercise blood pressure in the nitrate group, but not placebo group (p < 0.05).

CONCLUSION

Despite evidence of a rise in exhaled nitric oxide levels with nitrate supplementation, there was minimal evidence for improvement in exercise performance or pulmonary gas exchange surface area in a stable medically treated COPD population.

Exosomes as Mediators of the Systemic Adaptations to Endurance Exercise

Habitual endurance exercise training is associated with multisystemic metabolic adaptations that lower the risk of inactivity-associated disorders such as obesity and type 2 diabetes mellitus (T2DM). Identification of complex systemic signaling networks responsible for these benefits are of great interest because of their therapeutic potential in metabolic diseases; however, specific signals that modulate the multisystemic benefits of exercise in multiple tissues and organs are only recently being discovered. Accumulated evidence suggests that muscle and other tissues have an endocrine function and release peptides and nucleic acids into the circulation in response to acute endurance exercise to mediate the multisystemic adaptations. Factors released from skeletal muscle have been termed myokines and we propose that the total of all factors released in response to endurance exercise (including peptides, nucleic acids, and metabolites) be termed, "exerkines." We propose that many of the exerkines are released within extracellular vesicles called exosomes, which regulate peripheral organ cross talk. Exosomes (30-140 nm) and larger microvesicles [MVs] (100-1000 nm) are subcategories of extracellular vesicles that are released into the circulation. Exosomes contain peptides and several nucleic acids (microRNA [miRNA], messenger RNA [mRNA], mitochondrial DNA [mtDNA]) and are involved in intercellular/tissue exchange of their contents. An acute bout of endurance exercise increases circulating exosomes that are hypothesized to mediate organ cross talk to promote systemic adaptation to endurance exercise. Further support for the role of exosomes (and possibly MVs) in mediating the systemic benefits of exercise comes from the fact that the majority of the previously reported myokines/exerkines are found in extracellular vesicles databases (Vesiclepedia and ExoCarta). We propose that exosomes isolated from athletes following exercise or exosomes bioengineered to incorporate one or many of known exerkines will be therapeutically useful in the treatment of obesity, T2DM, and other aging-associated metabolic disorders.

Muscle hypertrophy in hypoxia with inflammation is controlled by bromodomain and extra-terminal domain proteins

Some of the Chronic Obstructive Pulmonary Disease (COPD) patients engaged in exercise-based muscle rehabilitation programs are unresponsive. To unravel the respective role of chronic hypoxia and pulmonary inflammation on soleus muscle hypertrophic capacities, we challenged male Wistar rats to repeated lipopolysaccharide instillations, associated or not with a chronic hypoxia exposure. Muscle hypertrophy was initiated by bilateral ablation of soleus agonists 1 week before sacrifice. To understand the role played by the histone acetylation, we also treated our animals with an inhibitor of bromodomains and extra terminal proteins (I-BET) during the week after surgery. Pulmonary inflammation totally inhibited this hypertrophy response under both normoxic and hypoxic conditions (26% lower than control surgery, p < 0.05), consistent with the S6K1 and myogenin measurements. Changes in histone acetylation and class IIa histone deacetylases expression, following pulmonary inflammation, suggested a putative role for histone acetylation signaling in the altered hypertrophy response. The I-BET drug restored the hypertrophy response suggesting that the non-response of muscle to a hypertrophic stimulus could be modulated by epigenetic mechanisms, including histone-acetylation dependant pathways. Drugs targeting such epigenetic mechanisms may open therapeutic perspectives for COPD patients with systemic inflammation who are unresponsive to rehabilitation.

Metabolism and Skeletal Muscle Homeostasis in Lung Disease

There is increased awareness that patients with lung diseases develop muscle dysfunction. Muscle dysfunction is a major contributor to a decreased quality of life in patients with chronic pulmonary diseases. Furthermore, muscle dysfunction exacerbates lung disease outcome, as a decrease in muscle mass and function are associated with increased morbidity, often long after critical illness or lung disease has been resolved. As we are learning more about the role of metabolism in health and disease, we are appreciating more the direct role of metabolism in skeletal muscle homeostasis. Altered metabolism is associated with numerous skeletal muscle pathologies and, conversely, skeletal muscle diseases are associated with significant changes in metabolic pathways. In this review, we highlight the role of metabolism in the regulation of skeletal muscle homeostasis. Understanding the metabolic pathways that underlie skeletal muscle wasting is of significant clinical interest for critically ill patients as well as patients with chronic lung disease, in which proper skeletal muscle function is essential to disease outcome.

The potential of endurance exercise-derived exosomes to treat metabolic diseases

Endurance exercise-mediated multisystemic adaptations are known to mitigate metabolism-related disorders such as obesity and type 2 diabetes mellitus (T2DM). However, the underlying molecular mechanisms that promote crosstalk between organs and orchestrate the pro-metabolic effects of endurance exercise remain unclear. Exercise-induced release of peptides and nucleic acids from skeletal muscle and other organs (collectively termed 'exerkines') has been implicated in mediating these systemic adaptations. Given that the extracellular milieu is probably not a hospitable environment for labile exerkines, a lipid vehicle-based mode of delivery has originated over the course of evolution. Two types of extracellular vesicles, exosomes and microvesicles, have been shown to contain proteins and nucleic acids that participate in a variety of physiological and pathological processes. Exosomes, in particular, have been shown to facilitate the exchange of peptides, microRNA, mRNA and mitochondrial DNA between cells and tissues. Intriguingly, circulatory extracellular vesicle content increases in an intensity-dependant manner in response to endurance exercise. We propose that the systemic benefits of exercise are modulated by exosomes and/or microvesicles functioning in an autocrine, paracrine and/or endocrine manner. Furthermore, we posit that native or modified exosomes, and/or microvesicles enriched with exerkines will have therapeutic utility in the treatment of obesity and T2DM.

The role of MicroRNAs in COPD muscle dysfunction and mass loss: implications on the clinic

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) is a common preventable and treatable disease and a leading cause of morbidity and mortality worldwide. In COPD, comorbidities, acute exacerbations, and systemic manifestations negatively influence disease severity, prognosis, and progression regardless of the respiratory condition.

AREAS COVERED

Several factors and biological mechanisms are involved in the pathophysiology of COPD muscle dysfunction. The non-coding microRNAs were shown to be differentially expressed in the respiratory and limb muscles of patients with COPD. Moreover, a differential expression profile of muscle-specific microRNAs has also been demonstrated in the lower limb muscles of COPD patients with and without muscle mass loss and weakness. All these features are reviewed herein. The most relevant articles on the topic in question were selected from PubMed to write this review. Expert commentary: MicroRNAs are excellent targets for the design of specific therapeutic interventions in patients with muscle weakness. Selective enhancers of microRNAs that promote myogenesis (proliferation and differentiation of satellite cells) should be designed to alleviate the negative impact of skeletal muscle dysfunction and mass loss in COPD regardless of the degree of the airway obstruction.

Molecular and biological pathways of skeletal muscle dysfunction in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) will be a major leading cause of death worldwide in the near future. Weakness and atrophy of the quadriceps are associated with a significantly poorer prognosis and increased mortality in COPD. Despite that skeletal muscle dysfunction may affect both respiratory and limb muscle groups in COPD, the latter are frequently more severely affected. Therefore, muscle dysfunction in COPD is a common systemic manifestation that should be evaluated on routine basis in clinical settings. In the present review, several aspects of COPD muscle dysfunction are being reviewed, with special emphasis on the underlying biological mechanisms. Figures on the prevalence of COPD muscle dysfunction and the most relevant etiologic contributors are also provided. Despite that ongoing research will shed light into the contribution of additional mechanisms to COPD muscle dysfunction, current knowledge points toward the involvement of a wide spectrum of cellular and molecular events that are differentially expressed in respiratory and limb muscles. Such mechanisms are thoroughly described in the article. The contribution of epigenetic events on COPD muscle dysfunction is also reviewed. We conclude that in view of the latest discoveries, from now, on new avenues of research should be designed to specifically target cellular mechanisms and pathways that impair muscle mass and function in COPD using pharmacological strategies and/or exercise training modalities.

Electrical Stimulation Improves Rat Muscle Dysfunction Caused by Chronic Intermittent Hypoxia-Hypercapnia via Regulation of miRNA-Related Signaling Pathways

Skeletal muscle dysfunction in chronic obstructive pulmonary disease (COPD) patients is common. Neuromuscular Electrical Stimulation (NMES) is a powerful exercise training that may relieve muscle dysfunction in COPD. This study investigated whether electrical stimulation may have atypical adaptations via activation of miRNA related pathways in counteracting COPD muscle dysfunction. Forty-eight male Sprague-Dawley rats were randomly assigned to 3 groups. With the exception of the rats in the control group, the experimental rats were exposed to chronic intermittent hypoxia-hypercapnia (CIHH) (9∼11%O₂,5.5∼6.5%CO₂) for 2 or 4 weeks. Electrical stimulation was performed immediately after each CIHH session. Following assessment of the running capacity, biopsy samples were obtained from the gastrocnemius of the rats. The miR-1, miR-133a and miR-133b levels were measured, as well as their related proteins: phosphorylation of Akt (p-AKT), PGC-1alpha (PGC-1α), histone deacetylase 4 (HDAC4) and serum response factor (SRF). Myosin heavy chainⅡa (MHCⅡa) and myosin heavy chainⅡb (MHCⅡb) were also measured to assess fiber type changes. After 2 weeks, compared with the controls, only miR-1 and miR-133a were significantly increased (p<0.05) in the exposure group. After 4 weeks, the exposure group exhibited a decreased running distance (p = 0.054) and MHCⅡa-to-MHCⅡb shift (p<0.05). PGC-1α (p = 0.051), nuclear HDAC4 (p = 0.058), HDAC4, p-AKT, PGC-1α and SRF was also significantly decreased (p<0.05). In contrast, miR-1 and miR-133a were significantly increased (p<0.05). Four weeks of electrical stimulation can partly reversed those changes, and miR-133b exhibited a transient increase after 2 weeks electrical stimulation. Our study indicate miRNAs may have roles in the response of CIHH-impaired muscle to changes during electrical stimulation.

Quadriceps muscle weakness and atrophy are associated with a differential epigenetic profile in advanced COPD

Epigenetic mechanisms regulate muscle mass and function in models of muscle dysfunction and atrophy. We assessed whether quadriceps muscle weakness and atrophy are associated with a differential expression profile of epigenetic events in patients with advanced COPD (chronic obstructive pulmonary disease). In vastus lateralis (VL) of sedentary severe COPD patients (n=41), who were further subdivided into those with (n=25) and without (n=16) muscle weakness and healthy controls (n=19), expression of muscle-enriched miRNAs, histone acetyltransferases (HATs) and deacetylases (HDACs), growth and atrophy signalling markers, total protein and histone acetylation, transcription factors, small ubiquitin-related modifier (SUMO) ligases and muscle structure were explored. All subjects were clinically evaluated. Compared with controls, in VL of all COPD together and in muscle-weakness patients, expression of miR-1, miR-206 and miR-27a, levels of lysine-acetylated proteins and histones and acetylated histone 3 were increased, whereas expression of HDAC3, HDAC4, sirtuin-1 (SIRT-1), IGF-1 (insulin-like growth factor-1) were decreased, Akt (v-akt murine thymoma viral oncogene homologue 1) expression did not differ, follistatin expression was greater, whereas myostatin expression was lower, serum reponse factor (SRF) expression was increased and fibre size of fast-twitch fibres was significantly reduced. In VL of severe COPD patients with muscle weakness and atrophy, epigenetic events regulate muscle differentiation rather than proliferation and muscle growth and atrophy signalling, probably as feedback mechanisms to prevent those muscles from undergoing further atrophy. Lysine-hyperacetylation of histones may drive enhanced protein catabolism in those muscles. These findings may help design novel therapeutic strategies (enhancers of miRNAs promoting myogenesis and acetylation inhibitors) to selectively target muscle weakness and atrophy in severe COPD.

A double blind randomized placebo control crossover trial on the effect of dietary nitrate supplementation on exercise tolerance in stable moderate chronic obstructive pulmonary disease

BACKGROUND

Dietary nitrate supplementation has been shown to decrease the oxygen cost of exercise and prolong exercise tolerance, as measured by sub-maximal exercise endurance distance and time at 85% V̇O2max, in both elite athletes and normal healthy subjects. Patients with chronic obstructive pulmonary disease (COPD) have reduced quality of life and ability to perform activities of daily living attributable to diminished exercise tolerance, and dietary nitrate may be able to ameliorate this.

METHODS

We performed a double-blind, computer-randomized placebo control crossover trial at a tertiary Australian hospital to investigate whether dietary nitrate supplementation as beetroot juice (BR) would augment submaximal exercise endurance in individuals with spirometrically confirmed stable moderate COPD. Volunteers underwent an incremental shuttle walk test to determine V̇O2max followed by a test dose of BR to establish safety in the study population. Participants performed an endurance shuttle walk test (ESWT) at 85% V̇O2max after randomization to either a 3 day wash-in of BR (4.8 mmol twice a day) or placebo (nitrate deplete BR), with a final dose on the morning of testing. They then crossed over after 4 day washout. Repeated measures two sided paired t-tests were employed.

RESULTS

35 participants were recruited with 19 completing the trial. In the initial safety phase, we measured systolic blood pressure over four hours post first dose of BR, and found a mean 10 mmHg decrement maximal at 1 hour. One individual developed symptomatic postural hypotension and was excluded. The primary outcomes of ESWT distance and time to fatigue improved by 11% and 6% respectively; however these differences did not achieve statistical significance (p = 0.494 and 0.693 respectively).

CONCLUSIONS

Our study does not support a role for routine dietary nitrate supplementation for enhancement of exercise endurance in COPD.

TRIAL REGISTRATION

Australia and New Zealand Clinical Trial Register: ACTRN12611001088932.

Beyond the genome: epigenetic mechanisms in lung remodeling

The lung develops from a very simple outpouching of the foregut into a highly complex, finely structured organ with multiple specialized cell types that are required for its normal physiological function. During both the development of the lung and its remodeling in the context of disease or response to injury, gene expression must be activated and silenced in a coordinated manner to achieve the tremendous phenotypic heterogeneity of cell types required for homeostasis and pathogenesis. Epigenetic mechanisms, consisting of DNA base modifications such as methylation, alteration of histones resulting in chromatin modification, and the action of noncoding RNA, control the regulation of information "beyond the genome" required for both lung modeling and remodeling. Epigenetic regulation is subject to modification by environmental stimuli, such as oxidative stress, infection, and aging, and is thus critically important in chronic remodeling disorders such as idiopathic pulmonary fibrosis (IPF), chronic obstructive pulmonary disease (COPD), bronchopulmonary dysplasia (BPD), and pulmonary hypertension (PH). Technological advances have made it possible to evaluate genome-wide epigenetic changes (epigenomics) in diseases of lung remodeling, clarifying existing pathophysiological paradigms and uncovering novel mechanisms of disease. Many of these represent new therapeutic targets. Advances in epigenomic technology will accelerate our understanding of lung development and remodeling, and lead to novel treatments for chronic lung diseases.

Epigenetics and muscle dysfunction in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a common, preventable, and treatable disease and a major leading cause of morbidity and mortality worldwide. In COPD, comorbidities, acute exacerbations, and systemic manifestations negatively influence disease severity and progression regardless of the respiratory condition. Skeletal muscle dysfunction, which is one of the commonest systemic manifestations in patients with COPD, has a tremendous impact on their exercise capacity and quality of life. Several pathophysiological and molecular underlying mechanisms including epigenetics (the process whereby gene expression is regulated by heritable mechanisms that do not affect DNA sequence) have been shown to participate in the etiology of COPD muscle dysfunction. The epigenetic modifications identified so far in cells include DNA methylation, histone acetylation and methylation, and noncoding RNAs such as microRNAs. Herein, we first review the role of epigenetic mechanisms in muscle development and adaptation to environmental factors in several models. Moreover, the epigenetic events reported so far to be potentially involved in muscle dysfunction and mass loss of patients with COPD are also discussed. Furthermore, the different expression profile of several muscle-enriched microRNAs in the diaphragm and vastus lateralis muscles of patients with COPD are also reviewed from results recently obtained in our group. The role of protein hyperacetylation in enhanced muscle protein catabolism of limb muscles is also discussed. Future research should focus on the full elucidation of the triggers of epigenetic mechanisms and their specific downstream biological pathways in COPD muscle dysfunction and wasting.

Exercise training and DNA methylation in humans

The response to exercise training (trainability) has been shown to have a strong heritable component. There is growing evidence suggesting that traits such as trainability do not only depend on the genetic code, but also on epigenetic signals. Epigenetic signals play an important role in the modulation of gene expression, through mechanisms such as DNA methylation and histone modifications. There is an emerging evidence to show that physical activity influences DNA methylation in humans. The present review aims to summarize current knowledge on the link between DNA methylation and physical activity in humans. We have critically reviewed the literature and only papers focused on physical activity and its influence on DNA methylation status were included; a total of 25 papers were selected. We concluded that both acute and chronic exercises significantly impact DNA methylation, in a highly tissue- and gene-specific manner. This review also provides insights into the molecular mechanisms of exercise-induced DNA methylation changes, and recommendations for future research.

The COPD Knowledge Base: enabling data analysis and computational simulation in translational COPD research

Background

Previously we generated a chronic obstructive pulmonary disease (COPD) specific knowledge base (http://www.copdknowledgebase.eu) from clinical and experimental data, text-mining results and public databases. This knowledge base allowed the retrieval of specific molecular networks together with integrated clinical and experimental data.

Results

The COPDKB has now been extended to integrate over 40 public data sources on functional interaction (e.g. signal transduction, transcriptional regulation, protein-protein interaction, gene-disease association). In addition we integrated COPD-specific expression and co-morbidity networks connecting over 6 000 genes/proteins with physiological parameters and disease states. Three mathematical models describing different aspects of systemic effects of COPD were connected to clinical and experimental data. We have completely redesigned the technical architecture of the user interface and now provide html and web browser-based access and form-based searches. A network search enables the use of interconnecting information and the generation of disease-specific sub-networks from general knowledge. Integration with the Synergy-COPD Simulation Environment enables multi-scale integrated simulation of individual computational models while integration with a Clinical Decision Support System allows delivery into clinical practice.

Conclusions

The COPD Knowledge Base is the only publicly available knowledge resource dedicated to COPD and combining genetic information with molecular, physiological and clinical data as well as mathematical modelling. Its integrated analysis functions provide overviews about clinical trends and connections while its semantically mapped content enables complex analysis approaches. We plan to further extend the COPDKB by offering it as a repository to publish and semantically integrate data from relevant clinical trials. The COPDKB is freely available after registration at http://www.copdknowledgebase.eu.

Epigenetic mechanisms in respiratory muscle dysfunction of patients with chronic obstructive pulmonary disease

Epigenetic events are differentially expressed in the lungs and airways of patients with chronic obstructive pulmonary disease (COPD). Moreover, epigenetic mechanisms are involved in the skeletal (peripheral) muscle dysfunction of COPD patients. Whether epigenetic events may also regulate respiratory muscle dysfunction in COPD remains unknown. We hypothesized that epigenetic mechanisms would be differentially expressed in the main inspiratory muscle (diaphragm) of patients with COPD of a wide range of disease severity compared to healthy controls. In diaphragm muscle specimens (thoracotomy due to lung localized neoplasms) of sedentary patients with mild-to-moderate and severe COPD, with preserved body composition, and sedentary healthy controls, expression of muscle-enriched microRNAs, histone acetyltransferases (HATs) and deacetylases (HDACs), total DNA methylation and protein acetylation, small ubiquitin-related modifier (SUMO) ligases, muscle-specific transcription factors, and muscle structure were explored. All subjects were also clinically evaluated: lung and muscle functions and exercise capacity. Compared to healthy controls, patients exhibited moderate airflow limitation and diffusion capacity, and reduced exercise tolerance and transdiaphragmatic strength. Moreover, in the diaphragm of the COPD patients, muscle-specific microRNA expression was downregulated, while HDAC4 and myocyte enhancer factor (MEF)2C protein levels were higher, and DNA methylation levels, muscle fiber types and sizes did not differ between patients and controls. In the main respiratory muscle of COPD patients with a wide range of disease severity and normal body composition, muscle-specific microRNAs were downregulated, while HDAC4 and MEF2C levels were upregulated. It is likely that these epigenetic events act as biological adaptive mechanisms to better overcome the continuous inspiratory loads of the respiratory system in COPD. These findings may offer novel therapeutic strategies to specifically target respiratory muscle dysfunction in patients with COPD.

Do epigenetic events take place in the vastus lateralis of patients with mild chronic obstructive pulmonary disease?

Muscle dysfunction is a major comorbidity in Chronic Obstructive Pulmonary Disease (COPD). Several biological mechanisms including epigenetic events regulate muscle mass and function in models of muscle atrophy. Investigations conducted so far have focused on the elucidation of biological mechanisms involved in muscle dysfunction in advanced COPD. We assessed whether the epigenetic profile may be altered in the vastus lateralis of patients with mild COPD, normal body composition, and mildly impaired muscle function and exercise capacity. In vastus lateralis (VL) of mild COPD patients with well-preserved body composition and in healthy age-matched controls, expression of DNA methylation, muscle-enriched microRNAs, histone acetyltransferases (HTAs) and deacetylases (HDACs), protein acetylation, small ubiquitin-related modifier (SUMO) ligases, and muscle structure were explored. All subjects were clinically evaluated. Compared to healthy controls, in the VL of mild COPD patients, muscle function and exercise capacity were moderately reduced, DNA methylation levels did not differ, miR-1 expression levels were increased and positively correlated with both forced expiratory volume in one second (FEV₁) and quadriceps force, HDAC4 protein levels were increased, and muscle fiber types and sizes were not different. Moderate skeletal muscle dysfunction is a relevant feature in patients with mild COPD and preserved body composition. Several epigenetic events are differentially expressed in the limb muscles of these patients, probably as an attempt to counterbalance the underlying mechanisms that alter muscle function and mass. The study of patients at early stages of their disease is of interest as they are a target for timely therapeutic interventions that may slow down the course of the disease and prevent the deleterious effects of major comorbidities.

Moving towards patient-centered medicine for COPD management: multidimensional approaches versus phenotype-based medicine--a critical view

For decades, chronic obstructive pulmonary disease (COPD) has been considered a relentlessly progressive disease in which the deterioration of lung function is associated with an increase in symptoms, interrupted only by periods of exacerbation. However, this paradigm of COPD severity based on FEV1 has been challenged by currently available evidence. So far, three main approaches, though with contradictory aspects, have been proposed in order to address the complexity of COPD as well as to develop appropriate diagnostic, prognostic and therapeutic strategies for the disease: 1) the use of independent, clinically relevant variables, 2) the use of multidimensional indices, and 3) disease approaches based on clinical phenotypes. Multivariable systems seem superior to FEV1 in predicting prognosis and defining disease severity. However, selection of variables available from current literature must be confronted with issues of medical practice. Future evidence will be needed to reveal their effective relationship with disease long-term prognosis and to demonstrate the most adequate cutoff values to be used in clinical settings. Multidimensional scores provide a good prognostic instrument for the identification of patients with a particular degree of disease severity. Clinical phenotyping can help clinicians identify the patients who respond to specific pharmacological interventions; however, there is some controversy about the phenotypes to select and their long-term implications. Although these approaches are not perfect, they represent the first step towards patient-centered medicine for COPD. In the near-future, these different approaches should converge towards one new field to focus on the better management of COPD patients.

Molecular and physiological events in respiratory muscles and blood of rats exposed to inspiratory threshold loading

High-intensity exercise induces oxidative stress and inflammatory events in muscles. Tumor necrosis factor (TNF)-α may alter muscle protein metabolism or promote muscle regeneration. We hypothesized that a program of noninvasive chronic inspiratory loading of different intensities induces a differential pattern of physiological, molecular, and cellular events within rat diaphragms. Antioxidants and TNF-α blockade may influence those events. In the diaphragm, gastrocnemius, and blood of rats exposed to high-intensity inspiratory threshold loads (2 hour every 24 hours for 14 days), with and without treatment with N-acetyl cysteine or infliximab (anti-TNF-α antibody), inflammatory cells and cytokines, superoxide anion production, myogenesis markers, and muscle structure were explored. In all animals, maximum inspiratory pressure (MIP) and body weight were determined. High-intensity inspiratory loading for 2 weeks caused a decline in MIP and body weight, and in the diaphragm induced a reduction in fast-twitch fiber proportions and sizes, whereas inflammatory cells and cytokine levels, including TNF-α immunohistochemical expression, superoxide anion, internal nuclei counts, and markers of myogenesis were increased. Blockade of TNF-α improved respiratory muscle function and structure, and animal weight, and, in the diaphragm, reduced inflammatory cell numbers and superoxide anion production drastically while inducing larger increases in protein and messenger RNA levels and immunohistochemical expression of TNF-α, internal nuclei, and markers of muscle regeneration. Blunting of TNF-α also induced a reduction in blood inflammatory cytokines and superoxide anion production. We conclude that TNF-α synthesized by inflammatory cells or myofibers could have differential effects on muscle structure and function in response to chronic, noninvasive, high-intensity inspiratory threshold loading.

Protein carbonylation and muscle function in COPD and other conditions

Skeletal muscle, the most abundant tissue in mammals, is essential for any activity in life. Muscle dysfunction is a common systemic manifestation in highly prevalent conditions such as chronic obstructive pulmonary disease (COPD), cancer cachexia, and sepsis. It has a significant impact on exercise tolerance, thus worsening the patients' quality of life and survival. Among several factors, oxidative stress is a major player in the etiology of skeletal muscle dysfunction associated with those conditions. Whereas low levels of oxidants are absolutely required for normal cell adaptation, high levels of reactive oxygen species (ROS) alter the function and structure of molecules such as proteins, DNA, and lipids. Specifically, protein carbonylation, a common variety of protein oxidation, was shown to alter the function of key enzymes and structural proteins involved in muscle contractile performance. Moreover, increased levels of ROS may also activate proteolytic systems, thus leading to enhanced protein breakdown in several models. In the current review, the specific modifications induced by carbonylation in protein structure and function in muscles have been described. Furthermore, the potential role of ROS in the activation of proteolytic systems in skeletal muscles is also discussed. The review summarizes the effects of protein carbonylation on muscles in several models and conditions such as COPD, disuse muscle atrophy, cancer cachexia, sepsis, and aging. Future research should focus on the elucidation of the specific protein sites modified by ROS in these muscles using redox proteomics analyses and on the assessment of the consequent alterations in protein function and stability.