Human muscle miRNA sequencing at rest and after protein feeding and the relationship with muscle phenotype. Homo sapiens

The loss of muscle size, strength and quality with ageing, is a major determinant of morbidity and mortality in the elderly. The regulatory pathways that impact on the muscle phenotype include the translational regulation maintained by microRNAs (miRNA). Yet the miRNAs that are expressed in human skeletal muscle and whose expression levels correlate to muscle size, strength and quality are unknown. Here we used next-generation sequencing to characterise the expression profile of miRNAs in the m. vastus lateralis obtained by biopsy from middle-aged males (n=48; 50.0±4.3 years). Isokinetic strength testing and mid-thigh computed tomography was undertaken for muscle phenotype analysis. miR-486-5p accounted for 21% of the total miR sequence reads, with miR-10b-5p, miR-133a-3p, and miR-22-3p accounting for a further 15%, 12% and 10% respectively. Isokinetic knee extension strength and muscle cross-sectional area were positively correlated with miR-100-5p, miR-99b-5p and miR-191-5p expression. Whilst muscle attenuation, reflective of myofiber lipid content was negatively correlated to let-7f-5p, miR-30d-5p and miR-125b-5p expression. In-silico analysis implicates miRNAs related to strength and muscle size in the regulation of mammalian target of rapamycin, whist miRNAs related to muscle attenuation may have potential roles controlling the transforming growth factor- β/SMAD3 pathway which regulated fibrosis, adipogenesis and lipid accumulation. Overall design: Fasted muscle biopsies were collected from 49 healthy middle aged men from the vastus lateralis muscle. The men also underwent an isokinetic strength test of knee extension as 60degrees/s. Computed tomography imaging was also performed at 50% of femur length to identify muscle cross sectional area and attenuation. A subset of men ingested 20g of dairy protein and an additional biopsy was collected at 90 minutes (n=9) or 210 minutes afterwards (n=16).Musclel mRNA profiles were generated by next generation sequencing using Illumina HiSeq 2500.