Uncoupling protein 3 (UCP3) 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 WT myoblasts. Both whole-body UCP3 knockout (wKO) and conditional UCP3 knockout (cKO) myoblasts displayed increased activation of AMPK (pAMPK) and elevated levels of PPARδ/β and GLUT4 proteins compared to wild type (WT) myoblasts. This altered energy signaling was further associated with UCP3 KO myoblasts exhibiting impaired insulin-stimulated glucose uptake, while WT cells and UCP3 KO cells expressing WT UCP3 were sensitive to insulin stimulation. Moroever, UCP3 KO myoblasts had an accumulation of fatty acids and upregulation of downstream PPARδ target genes in UCP3 KO cells. Lastly, UCP3 KO myoblasts were found to be more sensitive to oxidative stress and hypoxia, due in part to a decrease in the GSH/GSSG ratio compared to WT myoblasts. Collectively, these findings demonstrate that UCP3 is a key modulator of energy sensing and oxidative stress in undifferentiated skeletal muscle myoblasts.