PhD Scientific Days 2024

Theoretical and Translational Medicine I.

Release of Secreted Amphiectosome-Derived Small Extracellular Vesicles by a “Torn Bag Mechanism”

Text of the abstract

Extracellular vesicles (EVs) are membrane enclosed particles in the extracellular environment. They play an important role in cell-cell communication and have homeostatic functions. Recent studies suggest an unexpected complexity of EV biogenesis.
We focused on a recently observed EV secretion pathway, the release of large EVs with small intraluminal vesicles. We aimed to investigate the origin of these multivesicular large EVs (MV-lEVs), to define whether the release of this EV subtype was a unique or general process and to characterize its specific protein markers.
Confocal microscopy, transmission electron microscopy, super-resolution imaging and Western blot analysis were used. The detection of the MV-lEVs was made possible by our novel in situ fixation method. We characterized the MV-lEVs through classical and non-conventional protein markers and investigated the effects of inhibitors targeting cytoskeleton, endo-lysosomal system and autophagy on MV-lEV secretion.
MV-lEVs were present in all tested experimental systems. The EV production was sensitive to our treatments. The studied MV-lEVs were different from migrasomes based on their morphology and protein markers. Upon spontaneous rupture of the MV-lEVs limiting membrane, the intraluminal small EVs (sEVs) escaped to the extracellular environment by a ”torn bag mechanism”. Based on their intracellular origin and release mechanism, we designated them “amphiectosomes”.
Our model suggests that during amphisome formation, the inner LC3 positive membrane of autophagosomes fragments and forms vesicles. The intraluminal sEVs are secreted by the ”torn bag mechanism” into the extracellular space. This sEV formation is different from the previously described secretion pathways (exocytosis or plasma membrane budding). The discovered previously unknown EV secretion pathway expands our understanding on the biogenesis and roles of the EVs.

Fundings: NVKP_16-1-2016-0004; ÚNKP-23-3-I-SE-2; OTKA K120237; FK 138851; VEKOP-2.3.2-16-2016-00002; VEKOP-2.3.3-15-2017-00016; Higher Education Excellence Program (FIKP); Therapeutic Thematic Programme TKP2021-EGA-23; RRF-2.3.1-21-2022-00003 (National Cardiovascular Laboratory Program); 2019-2.1.7-ERA-NET-2021-00015; EU’s Horizon 2020 Research and Innovation Programme No. 739593

e-mail: lenzi.dorcsi@gmail.com
University: Semmelweis University
Supervisor: Dr. Tamás Visnovitz