We previously observed that mild exercise causes structural and functional modifications in fasted skeletal muscle, both in rodents and humans. Wistar rats, housed at thermoneutrality, were submitted to mild exercise during a 66h-period of fasting by five 30-min-treadmill runs at 15 m/min without inclination. To gain deeper insight in the underlying mechanisms/factors we studied alterations in the proteome, lipidome, and cellular signaling/metabolic pathways comparing the combined intervention to each separate intervention. Untargeted proteome analysis of gastrocnemius muscle revealed that exercise with fasting inversely modulated proteome networks involved in the proteasome, cellular respiration and muscle development with respect to fasting alone. Targeted lipidomic analysis revealed palmitoleic acid (P) to be increased by exercise in fasted muscle, an observation that adds to the previously observed increase in muscle beta-hydroxybutyrate (BHB). In muscle L6 myoblasts, cultured under conditions that mimicked fasting, we studied P vs BHB-induced alterations in Akt, AMPK, and mTOR signaling, crucial for glucose metabolism and myogenesis. We observed that P counteracted the repressing effect of BHB in L6 muscle cells on Akt Ser 473 phosphorylation and did not induce AMPK Thr172 phosphorylation, as opposed to BHB. These observations reflect the response to exercise we previously observed in fasting muscle. Both compounds increased sarcolemmal GLUT4 levels. BHB normalized P-induced inhibition of mTOR signaling. Finally, the myogenic factors Myogenin and MyoD expression were inversely regulated by BHB and P. In conclusion, we identify P and BHB as important players in the response to exercise during fasting regarding glucose sensitivity and muscle maintenance.
Castillo et al. (Wed,) studied this question.