T. The microRNA miR-696 regulates PGC-1␣ in mouse skeletal muscle in response to physical activity. Am J Physiol Endocrinol Metab 298: E799 -E806, 2010. First published January 19, 2010 doi:10.1152/ajpendo.00448.2009 are small noncoding RNAs involved in posttranscriptional gene regulation that have been shown to be involved in growth, development, function, and stress responses of various organs. The purpose of this study was to identify the miRNA response to physical activity, which was related to functions such as nutrient metabolism, although the miRNAs involved are currently unknown. C57BL/6 mice were divided into exercise and control groups. The exercise group performed running exercise, with a gradual increase of the load over 4 wk. On the other hand, to examine the effect of muscle inactivity, the unilateral hindlimbs of other mice were fixed in a cast for 5 days. Microarray analysis for miRNA in gastrocnemius revealed that miR-696 was markedly affected by both exercise and immobilization, showing opposite responses to these two interventions. Peroxisome proliferator-activated receptor-␥ coactivator-1␣ (PGC-1␣), which was increased by exercise and decreased by immobilization in the protein level, was predicted as a target regulated by miR-696. In cultured myocytes, intracellular miR-696 variation led to negative regulation of PGC-1␣ protein along with the expression of mRNAs for downstream genes. In addition, we found decreases in the biogenesis of mitochondria and fatty acid oxidation in miR-696-overexpressing myocytes compared with normal control myocytes. These observations demonstrate that miR-696 is a physical activity-dependent miRNA involved in the translational regulation of PGC-1␣ and skeletal muscle metabolism in mice.peroxisome proliferator-activated receptor-␥ coactivator-1␣; exercise; immobilization; muscle metabolism; mitochondria biogenesis; microarray PHYSICAL ACTIVITY IMPROVES VARIOUS BODILY FUNCTIONS, including metabolism, cardiovascular function, and immune function. The skeletal muscles comprise the major organ supporting physical activity, and muscle function is altered dramatically by contractile activity. Numerous studies have shown that daily exercise improves muscle energy metabolism and strength (9, 21, 23), along with changes of the expression or activity of muscle enzymes and proteins, as well as alterations of their mRNA transcription. Conversely, low levels of physical activity and immobilization induce the atrophy of skeletal muscle and decrease its metabolic capacity (9,15,20,52), with the expression/activity of many proteins and mRNAs being negatively regulated by inactivity compared with the effect of exercise. Although considerable progress has been made in understanding the functions of muscles that are associated with physical activity, the underlying molecular pathways remain obscure, especially those related to translational regulation. In fact, the level of expression of a particular mRNA does not necessarily reflect the abundance of the corresponding protein becau...
