Biology subjects

Lenzinger, D.

Publications and source records attributed to Lenzinger, D..

2 recordsLinked to original sources

bioRxiv2025

Stress-induced switch in small extracellular vesicle secretion: from constitutive 'torn bag mechanism' to exocytosis

The biogenesis of small extracellular vesicles (sEVs) is only partially understood. Our recent findings provide evidence that a newly described sEV secretion pathway, the amphiectosome release and the "torn bag mechanism", is present in all tested cell lines and in mouse liver and kidney. Surprisingly, in in situ fixed steady-state cells, transmission electron microscopy did not reveal the classical exosome secretion route, the sEV release via exocytosis of multivesicular endosomes (MVEs). In the current study, we investigated which parameters influence the activation of the two distinct sEV release mechanisms. Our results show that under stress conditions (such as Ca{superscript 2} ionophore-induced membrane stress or metabolic stress-induced by serum starvation), exocytosis of MVEs is activated, while this process is absent in steady-state conditions. By silencing ATG5 (a key regulator of autophagy) and RAB27a (essential small GTPase for MVE exocytosis), we selectively modulated these two mechanisms. Amphiectosome release depended on both autophagy and ATG5, while exocytosis of MVE was autophagy-independent but RAB27a-dependent. Our findings suggest that sEV release via the "torn bag mechanism" is a general and essential secretion pathway in non-stressed, steady-state mammalian cells, while stress conditions induce the sEV release via MVE exocytosis.

cell biology↗

bioRxiv2024

A "torn bag mechanism" of small extracellular vesicle release via limiting membrane rupture of en bloc released amphisomes (amphiectosomes)

Recent studies showed an unexpected complexity of extracellular vesicle (EV) biogenesis pathways. We previously found evidence that human colorectal cancer cells in vivo release large multivesicular body-like structures en bloc. Here, we tested whether this large extracellular vesicle type is unique to colorectal cancer cells. We found that all cell types we studied (including different cell lines and cells in their original tissue environment) released multivesicular large EVs (MV-lEVs). We also demonstrated that upon spontaneous rupture of the limiting membrane of the MV-lEVs, their intraluminal vesicles (ILVs) escaped to the extracellular environment by a "torn bag mechanism". We proved that the MV-lEVs were released by ectocytosis of amphisomes (hence, we termed them amphiectosomes). Both ILVs of amphiectosomes and small EVs separated from conditioned media were either exclusively CD63 or LC3B positive. According to our model, upon fusion of multivesicular bodies with autophagosomes, fragments of the autophagosomal inner membrane curl up to form LC3B positive ILVs of amphisomes, while CD63 positive small EVs are of multivesicular body origin. Our data suggest a novel common release mechanism for small EVs, distinct from the exocytosis of multivesicular bodies or amphisomes, as well as the small ectosome release pathway.

cell biology↗