Comparative Analysis of Methodological Aspects of the Study of Extracellular Vesicles and Extracellular Mitochondria: From Isolation to Internalization

Mitochondrial transfer in mammals has been proven to occur both under physiological conditions and during pathological conditions. It has been shown that neighboring cells can exchange mitochondria via nanotunnel tubes. However, there is evidence that free mitochondria, as well as whole mitochondria and individual mitochondrial fragments, can be transported between cells within extracellular vesicles (EVs). This review discusses the methodological aspects of isolation and a minimal set of methods for characterizing mitochondria-rich EVs (mitoEVs), as well as methodological approaches for studying the nucleic acid, protein, and lipid composition. It has been shown that mitoEVs, as well as extracellular mitochondria, contain a characteristic set of nucleic acids of mitochondrial origin. First and foremost, the dominant fraction of mitochondrial nucleic acids is mitochondrial DNA (mtDNA), a circular double-stranded molecule approximately 16.6 thousand base pairs in length. The mechanisms involved in EV internalization include clathrin-dependent endocytosis, caveolin-dependent endocytosis, raft-mediated endocytosis, and macropinocytosis. Mitochondrial-enriched autologous and xenogeneic EVs are thought to be internalized by similar mechanisms. The review also presents the main sources (stem cells, platelet concentrate, peripheral blood mononuclear cells) for obtaining mitochondria-rich EVs for therapeutic purposes.