588-P: Probing the Role of Muscle Glycogen Resynthesis on Postexercise AMPK Activation and Metabolic Protein Abundance Using a Novel Genetic Model

Acute exercise can alter the abundance of key metabolic proteins in skeletal muscle. These effects are influenced by postexercise (PEX) refeeding. Muscle glycogen resynthesis is a putative mediator of these refeeding effects. However, it is challenging to test this idea, because glycogen resynthesis is only one of many outcomes with refeeding. Therefore, we devised a novel genetic model to modify muscle expression of glycogen synthase 1 (GS1) using injection of rat skeletal muscle with adeno-associated viral (AAV) vectors for short hairpin RNA targeting GS1 (shRNA-GS1). Contralateral muscles were injected with scrambled shRNA (shRNA-Scr). Rats were sedentary (SED) or exercised (120min swim-exercise). Muscles were collected immediately postexercise (IPEX) and 9-hours PEX (9hPEX), along with time-matched SED controls. The 9hPEX and their SED-control rats were either refed (RF) or not-refed (NRF). Muscles were analyzed for glycogen and phosphorylation and abundance of key metabolic proteins. Muscles injected with shRNA-GS1 vs shRNA-Scr had lower GS1 abundance in all groups. Regardless of genotype, in IPEX vs SED rats: glycogen fell to similarly low values and phosphorylation of AMPK Thr172 (pAMPK) and its substrate ACC Ser79 (pACC) were comparably increased. Muscle glycogen was increased in all groups of 9h-RF rats, but it was lower for shRNA-GS1 vs shRNA-Scr from RF-9hPEX rats. In the NRF-9hPEX rats, pAMPK and pACC were greater for shRNA-GS1 vs shRNA-Scr muscles. Muscle pyruvate dehydrogenase kinase-4 abundance from 9hPEX rats (both NRF and RF) was greater for shRNA-GS1 vs shRNA-Scr. Hexokinase II (HKII) abundance was greater for 9hPEX vs SED in NRF rats regardless of genotype. In RF-9hPEX rats, HKII abundance was greater for shRNA-GS1 vs shRNA-Scr. These results support the idea that some PEX effects on metabolic protein abundance are influenced by muscle GS1 abundance and the extent of glycogen resynthesis