Mitochondria are organelles that are found in the eukaryotic cells. A place of cellular respiration, they are the cells'"batteries" and play a major role in energy metabolism and intercellular communication. Their particularity is to possess their own genome, transmitted solely by the mother and separate from the DNA contained in the nucleus. The mitochondria can sometimes be observed outside the cells in the form of fragments encapsulated within microvesicles. Under certain very specific conditions the platelets are also capable of releasing intact mitochondria into the extracellular space.
The work of a team led by Inserm researcher Alain R. Thierry at the Montpellier Cancer Research Institute (Inserm/Université de Montpellier/Montpellier Cancer Institute) has now revolutionized knowledge of this organelle by revealing that whole functioning extracellular mitochondria are in fact found in the bloodstream.
The researchers used previous findings which showed that the plasma of a healthy individual contains up to 50,000 times more mitochondrial DNA than nuclear DNA. They hypothesized that for it to be detectable and quantifiable in the blood in this manner, the mitochondrial DNA had to be protected by a structure of sufficient stability. In order to identify such a structure, plasma samples from around 100 individuals were analyzed.
This analysis revealed the presence in the blood circulation of highly stable structures containing whole mitochondrial genomes. Following examination of their size and density, as well as the integrity of their mitochondrial DNA, these structures observed using electron microscopy (up to 3.7 million per ml of plasma) were revealed to be intact and functional mitochondria.
Throughout the seven-year research period, the scientists used as many technical and methodological approaches as possible to validate this presence of circulating extracellular mitochondria in the blood.
When we consider the sheer number of extracellular mitochondria found in the blood, we have to ask why such a discovery had not been made before. Our team has built up expertise in the specific and sensitive detection of DNA in the blood, by working on the fragmentation of extracellular DNA derived from the mitochondria in particular." Alain R. Thierry, Inserm researcher Related Stories
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