Fig. 3.

Regulation of glycogen synthesis and degradation in the heart. Akt signaling promotes glycogen synthesis via relieving the GSK3β-mediated inhibition of glycogen synthase. PKA signaling promotes glycogen degradation via activation of glycogen phosphorylase kinase and subsequent activation of glycogen phosphorylase. Phosphorylase removes a glycosyl residue from the glycogen strand to release glucose-1-phosphate. STBD1 tags glycogen for degradation via glycophagy. Glycogen is engulfed by the glycophagosome, which may involve STBD1 binding to GABARAPL1 in the forming glycophagosome membrane. The glycophagosome fuses with a lysosome, and the glycogen is degraded to free glucose by acid α-glucosidase (black dots).