In apicomplexan parasites, the macroautophagy/autophagy machinery is repurposed to maintain the plastid-like organelle apicoplast. Previously, we showed that in Toxoplasma and Plasmodium, ATG12 interacts with ATG5 in a non-covalent manner, in contrast to the covalent interaction in most organisms. However, it remained unknown whether apicomplexan parasites have functional orthologs of ATG16L1, a protein that is essential for the function of the covalent ATG12–ATG5 complex in vivo in other organisms. Furthermore, the mechanism used by the autophagy machinery to maintain the apicoplast is unclear. We report that the ATG12–ATG5-ATG16L complex exists in Toxoplasma gondii (Tg). This complex is localized on isolated structures at the periphery of the apicoplast dependent on TgATG16L. Inducible depletion of TgATG12, TgATG5, or TgATG16L caused loss of the apicoplast and affected parasite growth. We found that a putative soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) protein, synaptosomal-associated protein 29 (TgSNAP29, Qbc SNARE), is required to maintain the apicoplast in T. gondii. TgSNAP29 depletion disrupted TgATG8 localization at the apicoplast. Additionally, we identified a putative ubiquitin-interacting motif-docking site (UDS) of TgATG8. Mutation of the UDS site abolished TgATG8 localization on the apicoplast but not lipidation. These findings suggest that the TgATG12–TgATG5-TgATG16L complex is required for biogenesis of the apicoplast, in which TgATG8 is translocated to the apicoplast via vesicles in a SNARE -dependent manner in T. gondii.Abbreviations: AID: auxin-inducible degron; CCD: coiled-coil domain; HFF: human foreskin fibroblast; IAA: indole-3-acetic acid; LAP: LC3-associated phagocytosis; NAA: 1-naphthaleneacetic acid; PtdIns3P: phosphatidylinositol-3-phosphate; SNARE: soluble N-ethylmaleimide sensitive factor attachment protein receptor; UDS: ubiquitin-interacting motif-docking site; UIM: ubiquitin-interacting motif.
Emerging evidence implicates premature placental senescence as a central driver of pregnancy complications, though its underlying mechanisms remain elusive. Here, we report marked downregulation of IL33 (interleukin 33) in villi from unexplained recurrent pregnancy loss (URPL) patients, concomitant with elevated trophoblast senescence. More importantly, il33 knockout mice exhibited placental senescence and impaired trophoblast invasion. Mechanistically, senescent trophoblasts displayed metabolic dysregulation – including enhanced glycolysis and lactate accumulation – which disrupted macroautophagic/autophagic flux and mitochondrial function. Lactate-induced lysine lactylation at residue K169 of SNAP29 (synaptosome associated protein 29) promoted its degradation, impairing macroautophagy/autophagy and trophoblast function, ultimately driving pregnancy loss. In interventional studies, senotherapies with metformin or dasatinib plus quercetin restored placental development and improved pregnancy outcomes in both IL33-deficient and inflammation-induced miscarriage models. Our findings establish the IL33-senescence-lactate axis as a critical pathway in URPL pathogenesis and support senomodulation as a therapeutic strategy.Abbreviations: 2-DG: 2-deoxy-D-glucose; BafA1: bafilomycin A1; CHX: cycloheximide; CTB: cytotrophoblasts; D-gal: D-galactose; EVT: extravillous trophoblasts; HDAC: histone deacetylase; H2O2: hydrogen peroxide; IL33: Interleukin 33; LPS: lipopolysaccharide; SA-GLB1/β-gal: senescence-associated galactosidase beta 1; SASP: senescence-associated secretory phenotype; SNAP29: synaptosome associated protein 29; STB: syncytiotrophoblasts; UMAP: uniform manifold approximation and projection; URPL: unexplained recurrent pregnancy loss; VP: etoposide
Autophagosome–lysosome fusion mediated by SNARE complexes is an essential step in autophagy. Two SNAP29-containing SNARE complexes have been extensively studied in starvation-induced bulk autophagy, while the relevant SNARE complexes in other types of autophagy occurring under non-starvation conditions have been overlooked. Here, we found that autophagosome–lysosome fusion in selective autophagy under non-starvation conditions does not require SNAP29-containing SNARE complexes, but requires the STX17-SNAP47-VAMP7/VAMP8 SNARE complex. Further, the STX17-SNAP47-VAMP7/VAMP8 SNARE complex also functions in starvation-induced autophagy. SNAP47 is recruited to autophagosomes following concurrent detection of ATG8s and PI(4,5)P 2 via its Pleckstrin homology domain. By contrast, SNAP29-containing SNAREs are excluded from selective autophagy due to inactivation by O-GlcNAcylation under non-starvation conditions. These findings depict a previously unknown, default SNARE complex responsible for autophagosome–lysosome fusion in both selective and bulk autophagy, which could guide research and therapeutic development in autophagy-related diseases.
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