Uncoupling protein 3 regulates energy and stress-related pathways in undifferentiated skeletal muscle myoblasts.

Uncoupling protein 3 (UCP3), a member of the mitochondrial solute carrier family, shares high homology with both UCP1 and UCP2. Its exact functional role has been elusive since its discovery, with previous studies primarily focusing on studying UCP3 function in differentiated skeletal muscle myotubes or whole animal models because basal levels of UCP3 protein are low in undifferentiated myoblasts. In the present study, we demonstrate that UCP3 plays a role in modulating energy and redox stress-related pathways in undifferentiated muscle myoblasts. Although low, UCP3 mRNA and protein levels were detectable in wild-type (WT) myoblasts. Both whole body UCP3 knockout (wKO) and conditional UCP3 knockout (cKO) myoblasts displayed increased activation of AMP-activated protein kinase (phosphorylation of AMPK) and elevated levels of peroxisome proliferator-activated receptor delta/beta (PPARδ/β) and glucose transporter 4 (GLUT4) proteins compared with WT myoblasts. This altered energy signaling was further associated with UCP3 KO myoblasts exhibiting impaired insulin-stimulated glucose uptake, whereas WT cells and UCP3 KO cells expressing WT UCP3 were sensitive to insulin stimulation. Moreover, UCP3 KO myoblasts had an accumulation of fatty acids and upregulation of downstream PPARδ target genes in UCP3 KO cells. Finally, UCP3 KO myoblasts were found to be more sensitive to oxidative stress and hypoxia, due in part to a decrease in the reduced glutathione (GSH)/oxidized glutathione (GSSG) ratio compared with WT myoblasts. Collectively, these findings demonstrate that UCP3 is a key modulator of energy sensing and oxidative stress in undifferentiated skeletal muscle myoblasts.NEW & NOTEWORTHY This article provides new information demonstrating that UCP3 plays a role in modulating energy and redox stress-related signaling pathways in proliferative muscle myoblasts. The studies used both UCP3 whole body knockout (KO) myoblasts as well as a novel UCP3 conditional KO mouse generated as part of the current study. Collectively, these findings show that, despite low levels, UCP3 is a key modulator of energy metabolism and oxidative stress in undifferentiated muscle myoblasts.