Purinergic Signaling Controls Fibroblast Growth Factor‐21 Expression in Skeletal Muscle through Akt/mTOR Pathway.

Fibroblast Growth Factor‐21 (FGF‐21) is a myokine which induce fiber type transformation and metabolic adaptations in muscle. However, little is known about the molecular mechanisms involved in the regulation of FGF‐21 expression in skeletal muscle in non‐pathological conditions. We have previously described that purinergic signaling is related with muscle adaptations and IL6‐myokine production through the “excitation‐transcription coupling” (ETC) mechanism, in which extracellular ATP (eATP) promotes gene expression in skeletal muscle. We have also demonstrated that eATP activates the PI3K/Akt signaling pathway in myotubes. Considering that Akt has been proposed as a master regulator for FGF‐21 expression control, the aim of this work is to determine the role of extracellular ATP over the FGF‐21 production in adult mouse skeletal muscle, and their dependence on the Akt/mTOR signaling pathway . Mice FDB‐ isolated fibers or whole‐muscle were used in this study. The mRNA levels of FGF‐21 after electrical (20 Hz, 270 pulses, 0.3 msec each) or exogenous ATP (100 μM) stimulation were assessed by qPCR. FGF‐21 protein levels were assessed by immunoblot. We used pharmacological inhibitors of purinergic receptors (100 μM Suramin) and Akt/mTOR pathway inhibitors (50 μM LY294002; 1 μM Akt inhibitor VIII; 100 nM rapamycin), to turn off different interactors of the putative signaling pathway. ATP stimulation (100 μM) evoked an 8‐fold increase in FGF‐21 mRNA levels in isolated FDB fibers at 30 min post stimulation. The increase in FGF‐21 mRNA levels evoked by eATP was inhibited by suramin, a general antagonist of P2Y/P2X nucleotide receptors. Electrical stimulation also evokes an increase in FGF‐21 mRNA levels, which was inhibited by both nifedipine (a DHPR blocker) and suramin. Exogenous ATP increased protein levels of FGF‐21 in whole FDB‐muscles at 120 min, in a concentration‐dependent manner, with a maximal increase of 3.5 folds with 3 μM ATP. The increase in FGF‐21 protein level evoked by ATP, was abolished by LY294002 (a PI3K inhibitor), Akt inhibitor VIII, and rapamycin (mTOR inhibitor). In this work, we demonstrated for the first time that extracellular ATP evokes an increase in the mRNA and protein levels of FGF‐21 in skeletal muscle. The increase on FGF‐21 levels evoked by ATP is dependent on Akt/mTOR pathway activation. These results suggest that ETC mechanism could be involved in regulation of FGF‐21 expression in skeletal muscle. Support or Funding Information Funded by CONICYT PCHA 21151035(MA‐C), 63140009(CM) and Fondecyt 1151353(SB), 1151293(EJ) This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .