Macroautophagy, commonly referred to as autophagy, is a highly conserved cellular degradation pathway that involves the sequestration of targeted materials within double-membrane autophagosomes and transports them to lysosomes for degradation and recycling. Autophagy not only serves as a pivotal quality control mechanism for cells to eliminate unwanted components, but also acts as a vital survival strategy during stress conditions, such as nutrient deprivation. Dysregulation of autophagy has been linked to the development and progression of various diseases, especially neurological disorders. Neurons, as post-mitotic cells incapable of division, heavily rely on autophagy to remove damaged organelles and protein aggregates, thereby preserving their normal function. Given their highly polarized structures, neurons exhibit a distinctive autophagic process: autophagosomes are primarily generated at synapses located at axonal terminals. They subsequently undergo retrograde transport to cell bodies for fusion with lysosomes. Thus, neural autophagy requires specialized factors and steps, the molecular mechanisms of which remain unclear.

Associate Professor Yan Zhao’s research team from the School of Life Sciences at the Southern University of Science and Technology (SUSTech) has revealed that ATG2A orchestrates autophagosome-lysosome fusion in nerve cells by interacting with the SNARE membrane fusion complex and other associated molecules.

These findings, entitled “ATG2A acts as a tether to regulate autophagosome-lysosome fusion in neural cells”, have been published in Autophagy.

Previous studies in yeast and mammals have established ATG2’s role in early autophagosome formation through its lipid transfer activity, which aids in shuttling phospholipids from the endoplasmic reticulum (ER) to isolation membranes for expansion. ATG2 forms stable complexes with autophagy proteins WDR45 and WDR45B. The research team’s earlier investigations have uncovered the crucial functions of WDR45 and WDR45B in mediating autophagy within the central nervous system of mice by facilitating autophagosome-lysosome fusion. These findings prompted them to explore the potential involvement of ATG2 in the later stages of autophagy within neural cells.

Mammals possess two homologs of yeast Atg2—ATG2A and ATG2B—which exhibit functional redundancy. Depletion of either ATG2A or ATG2B alone in non-neuronal cells showed negligible effects on autophagy, whereas the simultaneous deficiency of both genes impeded the early autophagic pathway. When the researchers selectively knocked down Atg2a or Atg2b using siRNA in Neuro-2a (N2a) cells—a mouse neuroblastoma cell line—the results demonstrated that siAtg2a, but not siAtg2b, led to a marked accumulation of the autophagy substrate SQSTM1/p62 and lipidated LC3-II (Figure 1). This observation was further validated in primary cultured neurons, suggesting a distinct role for ATG2A in neuronal autophagy.

Figure 1. Immunoblot analysis demonstrates SQSTM1/p62 and LC3-II accumulation in siAtg2a and Atg2a/2b DKD N2a cells, but not in siAtg2b cells

Electron microscopy analysis revealed that cells deficient in Atg2a/2b accumulated unclosed cup-shaped isolation membrane structures, while siAtg2a cells exhibited closed autophagosome (Figure 2). Additional experiments utilizing Halo-LC3 and other methods confirmed the presence of numerous closed autophagosomes in Atg2a-deficient cells.

Subsequent investigation through RFP-GFP-LC3 reporter systems and LC3-Rab7 colocalization demonstrated impaired autophagosome-late endosome/lysosome fusion upon ATG2A depletion. Mechanistic studies unveiled that ATG2A, acting as a tether protein, interacts with WDR45 on autophagosomes and WDR45B on late endosomes/lysosomes, along with the membrane fusion protein SNARE and another tether protein EPG5. These interactions promoted the assembly of the fusion complex, facilitating the fusion process between autophagosomes and lysosomes. Additionally, the interplay between ATG2A and WDR45/45B was shown to enhance the stability of these proteins.

Figure 2. Electron micrographs of starved N2a cells showing closed autophagosomes in siAtg2a cells versus immature structures in siAtg2a/2b cells

This study elucidates the pivotal role of ATG2A in autophagosome maturation within neural cells. Unlike ATG2B, ATG2A serves as a tether protein that mediates the fusion of autophagosomes with late endosomes/lysosomes (Figure 3). This research not only advances our understanding of the molecular mechanisms underpinning autophagosome maturation in neural cells, but also provides significant implications for the prevention and treatment of neurodegenerative disorders associated with autophagy-related anomalies.

Figure 3. Schematic illustration of ATG2A-mediated autophagosome maturation in neural cells

Ph.D. student Ze Zheng from SUSTech is the first author of this paper. Associate Professor Yan Zhao is the corresponding author. Drs. Cuicui Ji and Hongyu Zhao from the Institute of Biophysics at the Chinese Academy of Sciences are co-authors of the study.

Paper link: https://www.tandfonline.com/doi/10.1080/15548627.2025.2479427?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%20%200pubmed

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