Deactivation of AMPKa/GSK-3B Leads to High-Level Glycogen Synthase in Poor Pork Meat Quality

We investigated glycogen synthase and upstream regulatory proteins determining meat quality in porcine longissimus dorsi at 24 h post-mortem. The general meat quality traits of 300 muscle samples were estimated. Muscle samples were classified into two groups based on ultimate pH of meat 24 h post-mortem (pH24h). Muscle glycogen synthase belonging to the low pH24h group showed remarkably higher expression than that in the high pH24h group. AMP activated protein kinase (AMPK) and glycogen synthase kinase 3 (GSK-3) as negative regulators of glycogen synthase deactivated the suppression of glycogen synthase by phosphorylating Ser485 of AMPK and Ser9 of GSK-3B. These inhibitory kinases lead to high glycogen synthase expression. These results suggest that the accumulation of glycogen by up-regulating glycogen synthase and inhibiting AMPKa and GSK-3B was rapidly converted to lactate resulting in acidic meat. This molecular clue representing acidic meat based on post-mortem muscular pH can be used to estimate meat quality via Akt-AMPK?/GSK-3?-mediated up-regulation of glycogen synthase.