Palmitate Enhances Protein Tyrosine Phosphatase 1B (PTP1B) Gene Expression at Transcriptional Level in C2C12 Skeletal Muscle Cells

The factors responsible for regulating PTP1B expression in certain metabolic states have been unclear. We investigated the effects of palmitate on PTP1B gene transcription in C2C12 myotubes and myotubes co-cultured with J774A.1 macrophages. PTP1B mRNA and promoter activity levels were measured in C2C12 myotubes and direct or indirect co-culture of myotubes with macrophages using real time PCR and luciferase activity, respectively. Palmitate significantly induced PTP1B mRNA and promoter activity levels 1.36- and 1.32-fold, respectively, in C2C12 cells compared with the untreated myotubes. Palmitate showed a 2.3-fold increase in PTP1B mRNA level in myotubes co-cultured indirectly with macrophages. PTP1B promoter activity was also significantly induced by palmitate in direct (1.8-fold) and indirect (1.48-fold) co-culture of myotubes with macrophages. These data suggest that while palmitate treatment significantly induced PTP1B expression at the transcriptional level, the presence of an inflammatory process exerted by macrophages can augment this effect in the muscle cells.