Jenzer, Celine et al. (2015) International Worm Meeting "Determination of functional specificity of autophagic proteins during phagocytosis of apoptotic cells in embryo."

Largeau, Celine, Legouis, Renaud, Yao, Tianyou, Jenzer, Celine, Liu, Xianghua, Simionato, Elena, Zhou, Zheng

[International Worm Meeting, 2015]

Phagocytosis and autophagy are two lysosome-mediated processes involved in the clearance of extracellular and intracellular components, respectively. These two processes are involved in various human diseases such as cancers. Previously, the laboratory has shown a sequential and specific involvement of autophagic proteins in the autophagic cascade [1,2]. Recent studies have identified the recruitment of autophagic proteins during phagocytosis of apoptotic corpses in the so called LC3-associated phagocytosis (LAP) [3]. LAP is a distinct process from autophagy but it relies on some members of autophagy pathway to allow an efficient degradation of the phagocytosed cargo. The objective of this study is to elucidate the physiological and pathological roles of autophagy in the phagocytosis of apoptotic corpses in Caenorhabditis elegans. Using time-lapse microscopy, electron microscopy and genetic approaches, we analyzed the function of the LC3 homologues, LGG-1 and LGG-2, during this process. In this study, we showed that these proteins are involved in the phagocytosis of apoptotic cells. Indeed, lgg-1 and lgg-2 mutants present an enhanced number of apoptotic cells compared to wild type embryos. Moreover, differences in LGG-1 and LGG-2 expression profile in apoptototic corpses and phagocytic cells demonstrated differential participation of the two proteins. Finally, we characterized the interaction between these autophagic proteins and the machinery of phagosome maturation (HOPS, Rab, ...). Our results suggest complex roles of the C. elegans LC3 homologs in the clearance of apoptotic cells.[1] Manil-Segalen, M. et al. The C. elegans LC3 Acts Downstream of GABARAP to Degrade Autophagosomes by Interacting with the HOPS Subunit VPS39. Dev. Cell 28. 43-55 (2014).[2] Jenzer, C. et al. Human GABARAP can restore autophagosome biogenesis in C. elegans lgg 1 mutant. Autophagy 10. 1868-1872 (2014).[3] Martinez, J. et al. Microtubule-associated protein 1 light chain 3 alpha (LC3)-associated phagocytosis is required for the efficient clearance of dead cells. Proc. Natl. Acad. Sci. U. S. A. 108. 17396-17401 (2011).

Pena-Ramos, Omar et al. (2021) International Worm Meeting "Autophagy and the degradation of apoptotic cells"

Chiao, Lucia, Wang, Ying, Gao, Lidan, Liu, Xianghua, He, Henry, Yao, Tianyou, Zhou, Zheng, Pena-Ramos, Omar

[International Worm Meeting, 2021]

The autophagy pathway generates autophagosomes, double-membrane structures responsible for degrading protein aggregates, intracellular organelles, and other cellular components. This intracellular trafficking process is essential for the cell stress response, recycling the degraded material for use in different cellular processes. During C. elegans embryonic development, 113 somatic cells undergo apoptosis; these cells are then swiftly internalized by neighboring engulfing cells through phagocytosis, generating phagosomes. The newly formed phagosome then enters a maturation process during which acidic vesicles are fused to the phagosome promoting its degradation. Components of the autophagy pathway have previously been linked to phagosome maturation in mammalian cells in a process called LC3-associated phagocytosis (LAP). The autophagy machinery generates a single membrane-vesicle to conjugate LC3 directly onto the phagosome membrane promoting phagosome-lysosome fusion. Using live imaging on developing C. elegans embryos, we discovered that LC3-labeled puncta generated in engulfing cells are recruited to the surface of phagosomes and subsequently fuse to them, depositing their content into the phagosomal lumen. The observed fusion pattern suggests that the puncta are of a double-membrane nature, indicative of double-membranous autophagosomes and not single-membrane LAP vesicles. We also observed that these autophagosomes form two distinct populations, those that are labeled with LGG-1 and those marked with LGG-2, both homologs of yeast Atg8 and mammalian LC3. Lacking either group of autophagosomes significantly delay the degradation of apoptotic cells, indicating that both LGG-1 and LGG-2 function in the clearance of apoptotic cells. Finally, we identified that a signaling pathway with a previously known role in phagosome-lysosome fusion also facilitates the integration of autophagosomes to phagosomes. Our findings have collectively added autophagosomes to the list of intracellular organelles involved in phagosome maturation. Furthermore, we have demonstrated that in C. elegans, it is autophagosomes, not LAP vesicles, that facilitate phagosome maturation, and we have revealed a novel function of the autophagy pathway in the clearance of apoptotic cells.