Protein content and lipid profiling of isolated native autophagosomes
Autophagy is a central eukaryotic catabolic pathway responsible for clearance and recycling of an extensive portfolio of cargoes, which are packed in vesicles, called autophagosomes, and are delivered to lysosomes for degradation. Besides basal autophagy, which constantly degrades cellular material, the pathway is highly responsive to several stress conditions. However, the exact protein content and phospholipid composition of autophagosomes under changing autophagy conditions remain elusive so far. Here, we introduce a FACS-based approach for isolation of native unmanipulated autophagosomes and ensure the quality of the preparations. Employing quantitative proteomics and phospholipidomics, we obtained a profound cargo and lipid profile of autophagosomes purified upon basal autophagy conditions, nutrient deprivation, and proteasome inhibition. Indeed, starvation only mildly affected the content profile, while interference with proteasome activity showed stronger effects and specifically altered autophagosome cargoes. Interestingly, the phospholipid composition of autophagosomes was unaffected by the different treatments. Thus, the novel isolation method enables purification of intact autophagosomes in large quantities and allows protein content and phospholipid profiling without the requirement of exhaustive cellular fractionation or genetic manipulation.