Autophagy of Glycogen Is Non-Selective in Komagataella phaffii

Glycogen is an important reserve polysaccharide from bacteria to human. It is organized in glycogen granules that also contain several proteins involved in their metabolism. Glycogen granules can be mobilized in mammalian lysosomes and yeast vacuoles. They are delivered to these organelles by macroautophagy (hereafter autophagy). However, whether this is a selective or a non-selective process remains a matter of debate. It was proposed to be selective and called "glycophagy" (for selective autophagy of glycogen) in the mouse liver. However, the evidence of this selectivity is lacking in other glycogen-rich organs, such as the heart and skeletal muscle, which both are heavily impacted by the aberrant lysosomal accumulation of glycogen in Pompe disease. We recently developed the Komagataella phaffii yeast as a simple model to study the relationship of glycogen and autophagy. Using this model, we showed that cytosolic glycogen granules are delivered to the vacuole by non-selective autophagy, at least during nitrogen starvation. We speculate that this type of autophagy might be responsible for the lysosomal glycogen turnover in non-hepatic mammalian tissues.