gms | German Medical Science

Introduction: The release of different types of extracellular vesicles (EV) is observed after cellular activation or apoptosis induction. A role for EV in the pathogenesis of autoimmune diseases has been discussed. Microvesicles (MV) are a type of EV which are released from the outer cellular membrane (200-1,000nm diameter). MV are distinct from exosomes, which originate from multivesicular bodies (intracellular compartment). Exosomes are characterized by a diameter of 50-200nm. We investigated whether, besides their sizes, MV and exosomes, released from activated and apoptotic human lymphoblasts, can be distinguished by their morphology and protein content.

Methods: MV and exosomes from activated and apoptotic human lymphoblasts were isolated by filtration and ultracentrifugation (MV: 10,000g; exosomes: 100,000g). Isolated vesicles were analyzed by transmission electron microscopy (TEM). Further, proteins were analyzed by western blot analysis and 2D-gel electrophoresis.

Results: In TEM, preparations of MV showed them as membrane-coated vesicles (diameter: 200-550nm), and isolated exosomes also appeared as coated vesicles (diameter: 80-150nm). In 2D-gel electrophoresis around 7800 protein spots were detected, showing that activated and apoptotic MV/exosomes present a distinct protein expression pattern. We observed proteins which expression in MV was significantly different from exosomes. Furthermore, we observed that apoptosis led EV (both MV and exosomes) to express a significantly higher amount of particular proteins compared to activated ones. This differential regulation of protein expression within EV populations (depending on cellular activation or apoptosis induction) was also confirmed by western blot analysis. For example HMGB1 was exclusively found within MV isolated from apoptotic cells, while LAT and LCK were detected in MV isolated from activated and apoptotic cells. In contrast, actin or Hsp70 were detected within exosomes and MV.

Conclusion: We observed that MV and exosomes are membrane-coated vesicles with different sizes. Further, we identified a differential regulation of protein content within distinct vesicle preparations. The protein content of EV is tightly regulated depending on the stimuli causing EV release. Moreover, while activated cells mainly release exosomes, we observed a shift to the release of MV after induction of apoptosis. A dysregulation of EV might contribute to the emergence of autoimmune diseases.