Anna V. Donaldson

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

Rationale Muscle atrophy confers a poor prognosis in patients with chronic obstructive pulmonary disease (COPD), yet the molecular pathways responsible are poorly characterised. Muscle-specific microRNAs and serum response factor (SRF) are important regulators of muscle phenotype that contribute to a feedback system to regulate muscle gene expression. The role of these factors in the skeletal muscle dysfunction that accompanies COPD is unknown. Methods 31 patients with COPD and 14 healthy age-matched controls underwent lung and quadriceps function assessments, measurement of daily activity and a percutaneous quadriceps muscle biopsy. The expression of muscle-specific microRNAs, myosin heavy chains and components of the serum response factor signalling pathway were determined by qPCR. Results A reduction in expression of miR-1 (2.5-fold, p=0.01) and the myocardin-related transcription factors (MRTFs) A and B was observed in patients compared with controls (MRTF-A mRNA: twofold, p=0.028; MRTF-B mRNA: fourfold, p=0.011). miR-1 expression was associated with smoking history, lung function, fat-free mass index, 6 min walk distance and percentage of type 1 fibres. miR-133 and miR-206 were negatively correlated with daily physical activity. Insulin-like growth factor 1 mRNA was increased in the patients and miR-1 was negatively correlated with phosphorylation of the kinase Akt. Furthermore, the protein levels of histone deacetylase 4, another miR-1 target, were increased in the patients. Conclusions Downregulation of the activity of the MRTF-SRF axis and the expression of muscle-specific microRNAs, particularly miR-1, may contribute to COPD-associated skeletal muscle dysfunction.

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.

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.

Increased expression of H19/miR-675 is associated with a low fat-free mass index in patients with COPD

Loss of muscle mass and strength is a significant comorbidity in patients with chronic obstructive pulmonary disease (COPD) that limits their quality of life and has prognostic implications but does not affect everyone equally. To identify mechanisms that may contribute to the susceptibility to a low muscle mass, we investigated microRNA (miRNA) expression, methylation status, and regeneration in quadriceps muscle from COPD patients and the effect of miRNAs on myoblast proliferation in vitro. The relationships of miRNA expression with muscle mass and strength was also determined in a group of healthy older men.

Growth differentiation factor-15 is associated with muscle mass in chronic obstructive pulmonary disease and promotes muscle wasting in vivo.

Loss of muscle mass is a co‐morbidity common to a range of chronic diseases including chronic obstructive pulmonary disease (COPD). Several systemic features of COPD including increased inflammatory signalling, oxidative stress, and hypoxia are known to increase the expression of growth differentiation factor‐15 (GDF‐15), a protein associated with muscle wasting in other diseases. We therefore hypothesized that GDF‐15 may contribute to muscle wasting in COPD.

Circulating miRNAs from imprinted genomic regions are associated with peripheral muscle strength in COPD patients

Reduced muscle mass and strength are common comorbidities of COPD that lead to a poorer quality of life and are associated with increased mortality. Whilst the presence of disease may be viewed as a ‘necessary’ factor for the loss of muscle mass and strength, disease severity itself is not tightly linked to muscle loss, as some patients with mild disease have a significant loss of muscle mass and strength, whereas others with severe disease appear to maintain a normal muscle mass and strength [1]. These differences in susceptibility to changes in muscle are likely to be caused by the interplay between genetic, epigenetic and environmental factors. Circulating levels of miR-485-3p, a maternally expressed miRNA, are associated with muscle strength in COPD patients http://ow.ly/Wq51309fQtK

miR-422a suppresses SMAD4 protein expression and promotes resistance to muscle loss

Loss of muscle mass and strength are important sequelae of chronic disease, but the response of individuals is remarkably variable, suggesting important genetic and epigenetic modulators of muscle homeostasis. Such factors are likely to modify the activity of pathways that regulate wasting, but to date, few such factors have been identified.

S73 4-Metre gait speed as a functional outcome measure in patients with Chronic Obstructive Pulmonary Disease (COPD)

Introduction Well-established functional outcome measures in COPD include the 6-min walk test (6MW) and incremental shuttle walk test (ISW). However, these tests require space, repetition, and can be time-consuming. In the elderly population, gait speed alone has been shown to be a significant predictor of disability and mortality. We hypothesised that the 4-m gait speed in COPD patients would correlate well with the 6MW and ISW, and with validated COPD mortality composite scores such as BODE and ADO. Methods 26 well-characterised COPD patients were studied. Each underwent 6MW test as per ATS guidelines, ISW test and completed a 4-m walk in random order. For the 4-m walk, participants were instructed to walk at their usual speed along a marked, flat unobstructed course. Timing was stopped when the first foot completely crossed the 4-m mark. The faster of two timed walks was used for scoring purposes, and a gait speed was calculated in m/s. Data were analysed using Spearmans rank correlation to assess association between 4-m gait speed and 6MW, ISW, BODE score and ADO index. Results Baseline characteristics are presented as mean (SD) or median (25th, 75th percentile): 11M: 15 F; age=69 (8); FEV1% predicted=43 (20); 6MW=330 (83); ISW=291 (122.5); MRC dyspnoea 3 (2, 4); St Georges Respiratory Questionnaire (SGRQ)=49.6 (21.0); BMI=25.9 (4.9); BODE=4.5 (1.75, 6.0), ADO=5 (4, 6). Mean (SD) 4-m gait speed was 0.96 (0.20) m/s. There was a significant correlation between 4-m gait speed and 6MW (r=0.62, p=<0.001), ISW (r=0.80, p=<0.0001)—see Abstract S73 Figure 1, BODE score (r=−0.56, p=0.003) and ADO index (r=−0.43, p=0.03).Abstract S73 Figure 1 Conclusions 4-m gait speed correlates well with existing functional outcome measures and validated mortality composite scores used in COPD. It is an easy and quick to perform field test, and does not require specialist training or equipment. Further longitudinal and intervention studies are required to validate the 4-m gait speed as an assessment tool.