PGC-1α and PGC-1β increase CrT expression and creatine uptake in myotubes via ERRα

Intramuscular creatine plays a crucial role in maintaining skeletal muscle energy homeostasis, and its entry into the cell is dependent upon the sodium chloride dependent Creatine Transporter (CrT; Slc6a8). CrT activity is regulated by a number of factors including extra- and intracellular creatine concentrations, hormones, changes in sodium concentration, and kinase activity, however very little is known about the regulation of CrT gene expression. The present study aimed to investigate how Creatine Transporter (CrT) gene expression is regulated in skeletal muscle. Within the first intron of the CrT gene, we identified a conserved sequence that includes the motif recognized by the Estrogen-related receptor alpha (ERR alpha), also known as an Estrogen-related receptor response element (ERRE). Additional ERREs confirming to the known consensus sequence were also identified in the region upstream of the promoter. When partnered with peroxisome proliferator-activated receptorgamma co-activator-lalpha (PGC-1 alpha) or beta (PGC-1 beta), ERR alpha induces the expression of many genes important for cellular bioenergetics. We therefore hypothesized that PGC-1 and ERR alpha could also regulate CrT gene expression and creatine uptake in skeletal muscle. Here we show that adenoviral overexpression of PGC-1 alpha or PGC-1 beta in L6 myotubes increased CrT mRNA (2.1 and 1.7-fold, P < 0.0125) and creatine uptake (1.8 and 1.6-fold, P < 0.0125), and this effect was inhibited with co-expression of shRNA for ERR alpha. Overexpression of a constitutively active ERR alpha (VP16-ERR alpha) increased CrT mRNA approximately 8-fold (P < 0.05), resulting in a 2.2-fold (P < 0.05) increase in creatine uptake. Lastly, chromatin immunoprecipitation assays revealed that PGC-1 alpha and ERRa directly interact with the CrT gene and increase CrT gene expression. (C) 2014 Elsevier B.V. All rights reserved.