Glycophagy — the physiological perspective on a newly characterized glycogen-selective autophagy

Degradation of intracellular components through autophagy is a fundamental process to maintain cellular integrity and homeostasis. Recently, a glycogen-selective autophagy pathway has been described, termed ‘glycophagy’. Glycogen is a primary storage depot and regulator of glucose availability, and glycophagy is emerging as a critical physiological process involved in energy metabolism. Glycophagy-mediated degradation of glycogen appears to operate in parallel with the well-described canonical pathway of glycogenolysis involving glycogen phosphorylase. Evidence suggests that starch-binding domain protein 1 (Stbd1) is a key glycogen-binding protein involved in tagging glycogen for glycophagy, and that GABA Type A Receptor Protein Like 1 is primarily involved as the Atg8 family protein recruiting the Stbd1–glycogen complex into the forming glycophagosome. The nuances of glycophagy protein machinery, regulation, and lysosomal glucose release are yet to be fully elucidated. In this mini-review, we critically analyze the current evidence base for glycophagy as a selective-autophagy process of physiological importance and highlight areas where further investigation is warranted.