Mitochondria are one of the specialized structures or organelles that can be found in eukaryotic cells, and are known as energy-generating powerhouses that serve critical biological functions. These ancient organelles are also the only ones that carry their own genome. New research has shown that mitochondria can also be found free-floating in the bloodstream, functioning outside of the cell. (Learn more about the other components of blood from the video below.) The findings have been reported in the FASEB Journal.
Previous work has indicated that in healthy people, the plasma contains as much as 50,000 times more mitochondrial DNA compared to nuclear DNA. In this study, the researchers identified structures in the blood that carried mitochondrial genomes. Using electron and fluorescence microscopy, they learned that these structures were mitochondria.
This research was conducted over seven years by a team led by INSERM researcher Alain R. Thierry at the Montpellier Cancer Research Institute (Inserm/Université de Montpellier/Montpellier Cancer Institute). Many approaches were used to validate the findings.
"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," said Thierry. "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."
The exact role of these mitochondria is still unknown. They are not surrounded by any kind of membrane, the investigators found. However, the researchers have suggested that they are performing critical signaling functions. They noted that mitochondria have been shown to move from one cell to another under various conditions, including during cancer and tissue injury. They may also play a role in inflammatory states.
"The extracellular mitochondria could perform various tasks as messengers for the entire body," noted Thierry.
Researchers have known about the presence of mitochondrial cell‐free DNA (McfDNA) in the blood for many years, but McfDNA is now gaining attention as a potential biomarker of several diseases. The researchers are now interested in investigating whether it could be useful in oncology or non-invasive prenatal diagnosis.