Aggrephagy is a selective autophagy pathway that ensures the targeted degradation and clearance of protein aggregates from the cell. Although compromised aggrephagy has been associated with neurodegenerative disorders, little is known about the spatiotemporal functioning of the pathway. In previous work, the group of Lukas Kapitein developed the ‘particles induced by multimerization’ (PIM) assay, which allows the tracking of aggregate clearance by the lysosome-autophagy system. In this study (Janssen et al., 2021), they now describe the mKeima-PIM assay, in which a single-color pH-sensitive fluorophore enables the live-cell imaging of the degradation of inducible protein aggregates while also visualising autophagy. The authors show that the isolation membrane begins forming from the omegasome at the site of the aggregate itself. Interestingly, fully formed autophagosomes are relatively short-lived and persist for only a few minutes. Furthermore, maturation into autolysosomes and the corresponding acidification of cargo is facilitated by multiple ‘kiss-and-run’ events with endosomes and lysosomes. The finding that core autophagy components are recruited to the largely immobile aggregates reveals that this pathway is different from the mechanism underlying bulk autophagy, thus providing new insights into the spatiotemporal regulation of aggrephagy. Future studies employing the two PIM assays may help to better understand the aggrephagy pathway, with possible clinical applications.
