MicroRNAs (miRNAs) are evolutionarily conserved small non-coding RNA species 
involved in post-transcriptional gene regulation. In vitro studies have 
identified a small number of skeletal muscle-specific miRNAs which play a 
crucial role in myoblast proliferation and differentiation. In skeletal muscle, 
an acute bout of endurance exercise results in the up-regulation of 
transcriptional networks that regulate mitochondrial biogenesis, glucose and 
fatty acid metabolism, and skeletal muscle remodelling. The purpose of this 
study was to assess the expressional profile of targeted miRNA species following 
an acute bout of endurance exercise and to determine relationships with 
previously established endurance exercise responsive transcriptional networks. 
C57Bl/6J wild-type male mice (N = 7/group) were randomly assigned to either 
sedentary or forced-endurance exercise (treadmill run @ 15 m/min for 90 min) 
group. The endurance exercise group was sacrificed three hours following a 
single bout of exercise. The expression of miR- 181, 1, 133, 23, and 107, all of 
which have been predicted to regulate transcription factors and co-activators 
involved in the adaptive response to exercise, was measured in quadriceps 
femoris muscle. Endurance exercise significantly increased the expression of 
miR-181, miR-1, and miR-107 by 37%, 40%, and 56%, respectively, and reduced 
miR-23 expression by 84% (P<or=0.05 for all), with no change in miR-133. 
Importantly, decreased expression of miRNA-23, a putative negative regulator of 
PGC-1alpha was consistent with increased expression of PGC-1alpha mRNA and 
protein along with several downstream targets of PGC-1alpha including ALAS, CS, 
and cytochrome c mRNA. PDK4 protein content remains unaltered despite an 
increase in its putative negative regulator, miR-107, and PDK4 mRNA expression. 
mRNA expression of miRNA processing machinery (Drosha, Dicer, and DGCR8) 
remained unchanged. We conclude that miRNA-mediated post-transcriptional 
regulation is potentially involved in the complex regulatory networks that 
govern skeletal muscle adaptation to endurance exercise in C57Bl/6J male mice.