Abstract：
Small extracellular vesicles (sEVs) contain abundant circular RNAs (circRNAs) and are involved in cellular processes, particularly hypoxia. However, the process that packaging of circRNAs into neuronal sEVs under hypoxia is unclear. This study revealed the spatial mechanism of the Fused in Sarcoma protein (FUS) that facilitates the loading of functional circRNAs into sEVs in hypoxia neurons. It is found that FUS translocated from the nucleus to the cytoplasm and is more enriched in hypoxic neuronal sEVs than in normal sEVs. Cytoplasmic FUS formed aggregates with the sEVs marker protein CD63 in cytoplasmic stress granules (SGs) under hypoxic stress. Meanwhile, cytoplasmic FUS recruited of functional cytoplasmic circRNAs to SGs. Upon relief of hypoxic stress and degradation of SGs, cytoplasmic FUS is transported with those circRNAs from SGs to sEVs. Validation of FUS knockout dramatically reduced the recruitment of circRNAs from SGs and led to low circRNA loading in sEVs, which is also confirmed by the accumulation of circRNAs in the cytoplasm. Furthermore, it is showed that the FUS Zf_RanBP domain regulates the transport of circRNAs to sEVs by interacting with hypoxic circRNAs in SGs. Overall, these findings have revealed a FUS-mediated transport mechanism of hypoxia-related cytoplasmic circRNAs loaded into sEVs under hypoxic conditions.
摘要：
小细胞外囊泡（sEV）含有丰富的环状RNA（circRNAs），并参与细胞过程，尤其是缺氧。然而,缺氧下circRNAs包装成神经元sEV的过程尚不清楚.这项研究揭示了Fusedin肉瘤蛋白（FUS）的空间机制，该机制有助于将功能性circRNAs加载到缺氧神经元的sEV中。发现FUS从细胞核转移到细胞质，并且在缺氧神经元sEV中比在正常sEV中更富集。在低氧应激下，细胞质FUS与sEV标记蛋白CD63在细胞质应激颗粒（SGs）中形成聚集体。同时,细胞质FUS将功能性细胞质circRNAs募集到SGs。在缓解低氧应激和SGs降解后，细胞质FUS与那些circRNA一起从SGs转运到sEV。FUS敲除的验证显着减少了来自SGs的circRNAs的募集，并导致sEV中circRNA负载低，circRNAs在细胞质中的积累也证实了这一点。此外，结果表明，FUSZf_RanBP结构域通过与SGs中的缺氧circRNAs相互作用来调节circRNAs向sEV的转运。总的来说,这些发现揭示了FUS介导的缺氧相关细胞质circRNAs在缺氧条件下的转运机制.
