• Amy Lewis, Joanna Riddoch-Contreras, Samantha A Natanek, Anna Donaldson, William D-C Man, John Moxham, Nicholas S Hopkinson, Michael I Polkey, and Paul R Kemp.
• Section of Molecular Medicine, National Heart and Lung Institute, Imperial College London, SAF Building South Kensington Campus, London SW7 2AZ, UK.
• Thorax. 2012 Jan 1; 67 (1): 26-34.

RationaleMuscle 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.Methods31 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.ResultsA 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.ConclusionsDownregulation 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.

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