Downregulation of the serum response factor/miR-1 axis in the quadriceps of patients with COPD

Increased skeletal muscle-specific microRNA in the blood of patients with COPD

BACKGROUND

Skeletal muscle weakness in chronic obstructive pulmonary disease (COPD) carries a poor prognosis, therefore a non-invasive marker of this process could be useful. Reduced expression of muscle-specific microRNA (myomiRs) in quadriceps muscle in patients with COPD is associated with skeletal muscle weakness and changes in muscle fibre composition. Circulating exosomal miRNAs can be measured in blood, making them candidate biomarkers of biopsy phenotype. To determine whether plasma myomiR levels were associated with fibre size or fibre proportion, we measured myomiRs in plasma from patients with COPD and healthy controls.

METHODS AND RESULTS

103 patients with COPD and 25 age-matched controls were studied. Muscle-specific miRNA was elevated in the plasma of patients with COPD and showed distinct patterns. Specifically, miR-1 was inversely associated with fat-free mass in the cohort, whereas levels of miR-499 were more directly associated with strength and quadriceps type I fibre proportion. Two miRs not restricted to muscle in origin (miR-16 and miR-122) did not differ between patients and controls. Plasma miR-499 was also associated with muscle nuclear factor κB p50 but not p65 in patients with early COPD whereas plasma inflammatory cytokines were associated with miR-206 in patients with more advanced disease.

CONCLUSIONS

Plasma levels of individual myomiRs are altered in patients with COPD but alone do not predict muscle fibre size or proportion. Our findings are consistent with an increase in muscle wasting and turnover associated with the development of skeletal muscle dysfunction and fibre-type shift in patients with stable COPD.

Downregulation of miR-133 via MAPK/ERK signaling pathway involved in nicotine-induced cardiomyocyte apoptosis

Tobacco smoking is a risk factor for many diseases, and nicotine is a major component of tobacco. Our previous work revealed that nicotine can induce myocardial fibrosis. This study aimed to investigate whether nicotine can induce cardiomyocyte apoptosis and to explore the mechanisms involved. Cardiomyocytes were exposed to different nicotine concentrations for 48 h. MTT assay showed that the viability of cardiomyocytes was significantly inhibited by nicotine in a dose- and time-dependent manner. Loss of mitochondrial membrane potential, nuclear and DNA defragmentation determined by TUNEL and ELISA assays, and morphological alterations all revealed the pro-apoptotic property of nicotine. Meanwhile, miR-133, a muscle-specific microRNA, was markedly downregulated by nicotine. Consistently, caspase-9, a target gene for miR-133, was significantly upregulated, leading to an increase in caspase-3, in nicotine-treated cardiomyocytes compared to non-treated cells. Furthermore, ERK1/2 protein levels were considerably downregulated, along with reduction of serum response factor (SRF), which is a downstream target protein of ERK1/2 and an upstream transactivator of miR-133 as well. Our findings therefore revealed that inhibition of the ERK1/2-SRF-miR-133 signaling pathway to increase caspases-9 and -3 is a novel mechanism for nicotine to induce cardiomyocyte apoptosis and these tobacco smokers.

MuRF-1 and atrogin-1 protein expression and quadriceps fiber size and muscle mass in stable patients with COPD

INTRODUCTION

Animal studies demonstrate the importance of the E3 ubiquitin ligases, Muscle RING-Finger Protein 1 (MuRF-1) and atrogin-1, in muscle protein degradation during acute muscle atrophy. Small clinical studies suggest MuRF-1 and atrogin-1 expression in the quadriceps muscle is also increased in stable patients with Chronic Obstructive Pulmonary Disease compared to controls. However, it remains unclear whether these ligases have a role in maintaining a muscle-wasted state in COPD patients.

METHODS

32 stable COPD patients (16 with a low fat-free mass index (FFMI), 16 with a normal FFMI) and 15 controls underwent lung function and quadriceps strength tests and a percutaneous quadriceps biopsy. Quadriceps MuRF-1 and atrogin-1 protein were quantified with western blotting. Quadriceps fiber cross-sectional area (CSA) and fiber proportions were determined by immunohistochemistry on muscle sections. MuRF-1 and atrogin-1 levels were compared between COPD patients with and without a low FFMI, and between patients and controls, and correlations between MuRF-1 and atrogin-1 levels and quadriceps fiber CSA in the patients were investigated.

RESULTS

Atrogin-1 protein levels were lower in patients than controls, but similar in patients with a low and normal FFMI. MuRF-1 levels did not differ between any groups. MuRF-1 and atrogin-1 levels were not associated with quadriceps fiber CSA or quadriceps strength in patients.

CONCLUSIONS

Chronic upregulation of ubiquitin ligases was not evident in the quadriceps muscle of stable COPD patients with a low muscle mass. This does not exclude the possibility of transient increases in ubiquitin ligases during acute catabolic episodes.

MicroRNAs in skeletal muscle and their regulation with exercise, ageing, and disease

Skeletal muscle makes up approximately 40% of the total body mass, providing structural support and enabling the body to maintain posture, to control motor movements and to store energy. It therefore plays a vital role in whole body metabolism. Skeletal muscle displays remarkable plasticity and is able to alter its size, structure and function in response to various stimuli; an essential quality for healthy living across the lifespan. Exercise is an important stimulator of extracellular and intracellular stress signals that promote positive adaptations in skeletal muscle. These adaptations are controlled by changes in gene transcription and protein translation, with many of these molecules identified as potential therapeutic targets to pharmacologically improve muscle quality in patient groups too ill to exercise. MicroRNAs (miRNAs) are recently identified regulators of numerous gene networks and pathways and mainly exert their effect by binding to their target messenger RNAs (mRNAs), resulting in mRNA degradation or preventing protein translation. The role of exercise as a regulatory stimulus of skeletal muscle miRNAs is now starting to be investigated. This review highlights our current understanding of the regulation of skeletal muscle miRNAs with exercise and disease as well as how they may control skeletal muscle health.

Reduction of microRNA-206 contributes to the development of bronchopulmonary dysplasia through up-regulation of fibronectin 1

OBJECTIVE

To characterize microRNA-206 (miR-206) in the development of bronchopulmonary dysplasia (BPD).

DESIGN/METHODS

We assessed the expression of miR-206 in BPD mouse lung tissues and blood samples of BPD patients by quantitative real-time PCR. Then, the role of miR-206 in regulating cell biology were examined by XTT assay, flow cytometry, transwell invasion assay, wound healing assay and adhesion assay in vitro. Furthermore, luciferase reporter assay, real-time PCR, western blot and Immunofluorescence staining were performed to figure out the target gene of miR-206.

RESULTS

A reduction in expression of miR-206 was observed in BPD mice compared with controls and in BPD patients compared with controls. miR-206 overexpression significantly induced cell apoptosis, reduced cell proliferation, migration and adhesion abilities, whereas the inhibition of miR-206 expression had the opposite effect. Fibronectin 1 (FN1) is a direct target of miR-206, and fn 1 can be transcriptionally and translationally regulated by miR-206. Down-regulation of miR-206 modulates biological functions of the cells, at least in part, by increasing the level of fn 1. Furthermore, fn 1 expression levels were increased in the BPD mice and BPD patients.

CONCLUSIONS

The expression of miR-206 and its target gene, fn 1, may contribute to the progression of BPD.

Regulation of miRNAs in human skeletal muscle following acute endurance exercise and short-term endurance training

  The identification of microRNAs (miRNAs) has established new mechanisms that control skeletal muscle adaptation to exercise. The present study investigated the mRNA regulation of components of the miRNA biogenesis pathway (Drosha, Dicer and Exportin-5), muscle enriched miRNAs, (miR-1, -133a, -133b and -206), and several miRNAs dysregulated in muscle myopathies (miR-9, -23, -29, -31 and -181). Measurements were made in muscle biopsies from nine healthy untrained males at rest, 3 h following an acute bout of moderate-intensity endurance cycling and following 10 days of endurance training. Bioinformatics analysis was used to predict potential miRNA targets. In the 3 h period following the acute exercise bout, Drosha, Dicer and Exportin-5, as well as miR-1, -133a, -133-b and -181a were all increased. In contrast miR-9, -23a, -23b and -31 were decreased. Short-term training increased miR-1 and -29b, while miR-31 remained decreased. Negative correlations were observed between miR-9 and HDAC4 protein (r=-0.71; P=0.04), miR-31 and HDAC4 protein (r=-0.87; P=0.026) and miR-31 and NRF1 protein (r=-0.77; P=0.01) 3 h following exercise. miR-31 binding to the HDAC4 and NRF1 3 untranslated region (UTR) reduced luciferase reporter activity. Exercise rapidly and transiently regulates several miRNA species in muscle. Several of these miRNAs may be involved in the regulation of skeletal muscle regeneration, gene transcription and mitochondrial biogenesis. Identifying endurance exercise-mediated stress signals regulating skeletal muscle miRNAs, as well as validating their targets and regulatory pathways post exercise, will advance our understanding of their potential role/s in human health.

Pathophysiology of muscle dysfunction in COPD

Muscle dysfunction often occurs in patients with chronic obstructive pulmonary disease (COPD) and may involve both respiratory and locomotor (peripheral) muscles. The loss of strength and/or endurance in the former can lead to ventilatory insufficiency, whereas in the latter it limits exercise capacity and activities of daily life. Muscle dysfunction is the consequence of complex interactions between local and systemic factors, frequently coexisting in COPD patients. Pulmonary hyperinflation along with the increase in work of breathing that occur in COPD appear as the main contributing factors to respiratory muscle dysfunction. By contrast, deconditioning seems to play a key role in peripheral muscle dysfunction. However, additional systemic factors, including tobacco smoking, systemic inflammation, exercise, exacerbations, nutritional and gas exchange abnormalities, anabolic insufficiency, comorbidities and drugs, can also influence the function of both respiratory and peripheral muscles, by inducing modifications in their local microenvironment. Under all these circumstances, protein metabolism imbalance, oxidative stress, inflammatory events, as well as muscle injury may occur, determining the final structure and modulating the function of different muscle groups. Respiratory muscles show signs of injury as well as an increase in several elements involved in aerobic metabolism (proportion of type I fibers, capillary density, and aerobic enzyme activity) whereas limb muscles exhibit a loss of the same elements, injury, and a reduction in fiber size. In the present review we examine the current state of the art of the pathophysiology of muscle dysfunction in COPD.

MicroRNA in myogenesis and muscle atrophy

PURPOSE OF REVIEW

To understand the impact of microRNA on myogenesis and muscle wasting in order to provide valuable information for clinical investigation.

RECENT FINDINGS

Muscle wasting increases the risk of morbidity/mortality in primary muscle diseases, secondary muscle disorders and elderly population. Muscle mass is controlled by several different signalling pathways. Insulin-like growth factor/PI3K/Akt is a positive signalling pathway, as it increases muscle mass by increasing protein synthesis and decreasing protein degradation. This pathway is directly and/or indirectly downregulated by miR-1, miR-133, miR-206 or miR-125b, and upregulated by miR-23a or miR-486. Myostatin and the transforming growth factor-β signalling pathway are negative regulators that cause muscle wasting. An increase of miR-27 reduces myostatin and increases muscle cell proliferation. Muscle regeneration capacity also plays a significant role in the regulation of muscle mass. This review comprehensively describes the effect of microRNA on myoblasts proliferation and differentiation, and summarizes the varied influences of microRNA on different muscle atrophy.

SUMMARY

Growing evidence indicates that microRNAs significantly impact muscle growth, regeneration and metabolism. MicroRNAs have a great potential to become diagnostic and/or prognostic markers, therapeutic agents and therapeutic targets.

The mechanisms of cachexia underlying muscle dysfunction in COPD

Pulmonary cachexia is a prevalent, debilitating, and well-recognized feature of COPD associated with increased mortality and loss of peripheral and respiratory muscle function. The exact cause and underlying mechanisms of cachexia in COPD are still poorly understood. Increasing evidence, however, shows that pathological changes in intracellular mechanisms of muscle mass maintenance (i.e., protein turnover and myonuclear turnover) are likely involved. Potential factors triggering alterations in these mechanisms in COPD include oxidative stress, myostatin, and inflammation. In addition to muscle wasting, peripheral muscle in COPD is characterized by a fiber-type shift toward a more type II, glycolytic phenotype and an impaired oxidative capacity (collectively referred to as an impaired oxidative phenotype). Atrophied diaphragm muscle in COPD, however, displays an enhanced oxidative phenotype. Interestingly, intrinsic abnormalities in (lower limb) peripheral muscle seem more pronounced in either cachectic patients or weight loss-susceptible emphysema patients, suggesting that muscle wasting and intrinsic changes in peripheral muscle's oxidative phenotype are somehow intertwined. In this manuscript, we will review alterations in mechanisms of muscle mass maintenance in COPD and discuss the involvement of oxidative stress, inflammation, and myostatin as potential triggers of cachexia. Moreover, we postulate that an impaired muscle oxidative phenotype in COPD can accelerate the process of cachexia, as it renders muscle in COPD less energy efficient, thereby contributing to an energy deficit and weight loss when not dietary compensated. Furthermore, loss of peripheral muscle oxidative phenotype may increase the muscle's susceptibility to inflammation- and oxidative stress-induced muscle damage and wasting.

RNAi Therapeutic Platforms for Lung Diseases

RNA interference (RNAi) is rapidly becoming an important method for analyzing gene functions in many eukaryotes and holds promise for the development of therapeutic gene silencing. The induction of RNAi relies on small silencing RNAs, which affect specific messenger RNA (mRNA) degradation. Two types of small RNA molecules, i.e. small interfering RNAs (siRNAs) and microRNAs (miRNAs), are central to RNAi. Drug discovery studies and novel treatments of siRNAs are currently targeting a wide range of diseases, including various viral infections and cancers. Lung diseases in general are attractive targets for siRNA therapeutics because of their lethality and prevalence. In addition, the lung is anatomically accessible to therapeutic agents via the intrapulmonary route. Recently, increasing evidence indicates that miRNAs play an important role in lung abnormalities, such as inflammation and oncogenesis. Therefore, miRNAs are being targeted for therapeutic purposes. In this review, we present strategies for RNAi delivery and discuss the current state-of-the-art RNAi-based therapeutics for various lung diseases.

Clinical relevance of plasma miR-106b levels in patients with chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is characterized by both chronic inflammation in the airway and systemic inflammation; however, the molecular mechanism of COPD has not been fully elucidated. By measuring microRNA (miRNA) expression in the plasma of COPD subjects, we aimed to identify the clinical relevance of plasma miRNA levels in these patients. Blood samples were obtained from COPD patients and age-matched normal controls. We initially produced plasma miRNA expression profiles using TaqMan low-density array screening. For further validation, individual qRT-PCRs were performed in 40 COPD patients and 20 healthy subjects. TaqMan low-density array screening showed that 9 miRNAs (miR-29b, miR-483-5p, miR-152, miR-629, miR-26b, miR-101, miR-106b, miR-532-5p and miR-133b) were significantly downregulated in the plasma from COPD patients when compared with normal smokers. Among these miRNAs, we focused on miR-106b. A reduction in the plasma miR-106b levels was evident in COPD ex-smokers and COPD current smokers compared with levels in smokers. There was a negative correlation between the plasma miR-106b level and the duration of disease since diagnosis in COPD ex-smokers and the duration of smoking in COPD current smokers. These findings support the concept that progressive reduction in the plasma miR-106b level may reflect persistent and systemic changes even after the discontinuation of smoking in COPD patients. miR-106b may therefore play an important role in the pathogenesis of COPD.

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

Quadriceps muscle dysfunction occurs in one-third of patients with chronic obstructive pulmonary disease (COPD) in very early stages of their condition, even prior to the development of airway obstruction. Among several factors, deconditioning and muscle mass loss are the most relevant contributing factors leading to this dysfunction. Moreover, epigenetics, defined as the process whereby gene expression is regulated by heritable mechanisms that do not affect DNA sequence, could be involved in the susceptibility to muscle dysfunction, pathogenesis, and progression. Herein, we review the role of epigenetic mechanisms in muscle development and adaptation to environmental factors such as immobilization and exercise, and their implications in the pathophysiology and susceptibility to muscle dysfunction in COPD. The epigenetic modifications identified so far include DNA methylation, histone acetylation and methylation, and non-coding RNAs such as microRNAs (miRNAs). In the present review, we describe the specific contribution of epigenetic mechanisms to the regulation of embryonic myogenesis, muscle structure and metabolism, immobilization, and exercise, and in muscles of COPD patients. Events related to muscle development and regeneration and the response to exercise and immobilization are tightly regulated by epigenetic mechanisms. These environmental factors play a key role in the outcome of muscle mass and function as well as in the susceptibility to muscle dysfunction in COPD. Future research remains to be done to shed light on the specific target pathways of miRNA function and other epigenetic mechanisms in the susceptibility, pathogenesis, and progression of COPD muscle dysfunction.

Renin-angiotensin system blockade: a novel therapeutic approach in chronic obstructive pulmonary disease

ACE (angiotensin-converting enzyme) inhibitors and ARBs (angiotensin II receptor blockers) are already widely used for the treatment and prevention of cardiovascular disease and their potential role in other disease states has become increasingly recognized. COPD (chronic obstructive pulmonary disease) is characterized by pathological inflammatory processes involving the lung parenchyma, airways and vascular bed. The aim of the present review is to outline the role of the RAS (renin-angiotensin system) in the pathogenesis of COPD, including reference to results from fibrotic lung conditions and pulmonary hypertension. The review will, in particular, address the emerging evidence that ACE inhibition could have a beneficial effect on skeletal muscle function and cardiovascular co-morbidity in COPD patients. The evidence to support the effect of RAS blockade as a novel therapeutic approach in COPD will be discussed.

Muscle function in COPD: a complex interplay

The skeletal muscles play an essential role in life, providing the mechanical basis for respiration and movement. Skeletal muscle dysfunction is prevalent in all stages of chronic obstructive pulmonary disease (COPD), and significantly influences symptoms, functional capacity, health related quality of life, health resource usage and even mortality. Furthermore, in contrast to the lungs, the skeletal muscles are potentially remedial with existing therapy, namely exercise-training. This review summarizes clinical and laboratory observations of the respiratory and peripheral skeletal muscles (in particular the diaphragm and quadriceps), and current understanding of the underlying etiological processes. As further progress is made in the elucidation of the molecular mechanisms of skeletal muscle dysfunction, new pharmacological therapies are likely to emerge to treat this important extra-pulmonary manifestation of COPD.

Epigenetics in asthma and COPD

Epigenetic mechanisms are likely to play a role in many complex diseases, the extent of which we only beginning to understand. COPD and asthma are two respiratory diseases subject to strong environmental influences depending on underlying genetic susceptibility. Epigenetic mechanisms such as DNA methylation, histone modification and microRNA may be involved in these processes by modulating environmental effects to influence disease development. Given their demonstrated modifiable nature, epigenetic mechanisms may open new possibilities for therapeutic intervention. Here we give an overview of recent developments in the field of respiratory epigenetics in relation to asthma and COPD in the context of our current understanding of mechanisms leading to such diseases.

Analysis of serum micro-RNAs as potential biomarker in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) as a complex disease with genetic and environmental compound is one of the leading causes of death in worldwide. This disease is characterized by lower airway inflammation, and increases risk of lung cancer in smokers. Micro-RNA (miRNA) molecules are key regulators in gene expression that have been widely associated with a several diseases. Differential expression of miRNAs is involved in lung tissue of COPD, but there is no information about biomarker potential of circulating miRNAs in patients. To analyze the miRNA expression profile in COPD, levels of serum miRNAs were profiled by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) array system. The authors examined 72 miRNAs by qRT-PCR array, in 20 COPD patients and 12 control subjects. U6snRNA was used for normalization of the expression of miRNAs for each sample. According to the results, 5 miRNAs were found to be significantly dysregulated. There was down-regulation of miR-20a, miR-28-3p, miR-34c-5p, and miR-100, and up-regulation of miR-7, compared with the controls. This was the first study in COPD for screening of serum miRNAs for searching for biomarker. These results are preliminary screening data and should be confirmed with large patient groups. If so, these miRNAs are likely being involved in pathogenesis of COPD and may give clues for designing therapeutic strategy.

Role of MicroRNAs in lung disease

MicroRNAs (miRNAs) are small non-coding RNA molecules that negatively regulate gene expression. They actively participate in the modulation of important cell physiological processes and are involved in the pathogenesis of lung diseases such as lung cancer, pulmonary fibrosis, asthma and chronic obstructive pulmonary disease. A better understanding of the role that miRNAs play in these diseases could lead to the development of new diagnostic and therapeutic tools. In this review, we discuss the role of some miRNAs in different lung diseases as well as the possible future of these discoveries in clinical applications.

Role of MicroRNAs in lung disease

MicroRNAs (miRNAs) are small non-coding RNA molecules that negatively regulate gene expression. They actively participate in the modulation of important cell physiological processes and are involved in the pathogenesis of lung diseases such as lung cancer, pulmonary fibrosis, asthma and chronic obstructive pulmonary disease. A better understanding of the role that miRNAs play in these diseases could lead to the development of new diagnostic and therapeutic tools. In this review, we discuss the role of some miRNAs in different lung diseases as well as the possible future of these discoveries in clinical applications.