Apoptosomes and Proteasomes from Exosomes Generated by Human Hematopoietic Stem Cells

Abstract

The activities of two classes of neutral proteases were studied: caspases and proteasomes, which could be contained in vesicles generated by human stem cells. The formation of apoptosomes could not be induced in human mesenchymal and hematopoietic stem cells (hereinafter—MSCs and HSCs, respectively) with the participation of cytochrome C. Caspase activity was found in the culture medium and in exosomes after the tumor necrosis factor α (TNFα) supplementation only. This activity is completely inhibited by a non-substrate caspase inhibitor emricane, and is not sensitive to proteasome inhibitors. It is assumed that this activity has a membrane and intracellular location. Supplementing of TNFα cell culture leads to the generation of neutrophils and other leukocytes and the formation of apoptosomes in them, which are secreted with the exosomes and remain circulating outside the cells. Extracellular activity pertains to protein complexes of molecular weight similar to 20S proteasomes and is probably represented by apoptosomes. It is suggested that TNFα induces in HSC culture the appearance of neutrophils or the generation of other differentiated cells that are capable of apoptosis, in contrast to HSCs or MSCs.

A guide to the expanding field of extracellular vesicles and their release in regulated cell death programs

“…During apoptosis, specific cargos are loaded into these vesicles during their biogenesis. Among them, cytokines, DAMPS, proteasome, apoptosome, and active caspases are often found in apoptotic bodies and microvesicles particularly [113,116,127,130,131]. The presence of active caspase-3 leads to intravesicular cargos cleavage, suggesting its role in amplifying the presence and release of DAMPs [113].…”