A new blood component
Mitochondria are able to float freely in human blood
A team of French scientists led by Alain R. Thierry from the Cancer Research Institute in Montpellier has discovered functional mitochondria in human blood. Scientists suggest that mitochondria freely moving through blood vessels may play an important role in intercellular communication.
As is known, mitochondria are present in eukaryotic cells and play an important role there – they synthesize ATP molecules, providing the cell with energy necessary for other vital processes. Mitochondria have their own genome and the ability to synthesize proteins independently, because once they were independent bacteria that entered into symbiosis with them at the dawn of eukaryotic evolution. But it has never been found before that mitochondria move in the body outside of cells.
However, in the course of previous studies, traces of mitochondrial DNA were found in human blood. Moreover, it turned out to be 50,000 times more than DNA from cell nuclei. They tried to explain this by the fact that mitochondrial DNA could get into the blood from collapsing cells and remain there for a relatively long time due to the stability of the molecule (the human mitochondrial DNA molecule has a ring, not a linear shape, therefore it is destroyed more slowly).
In a new study, Alain Thierry and his colleagues analyzed the blood plasma of a hundred people and found that the mitochondrial DNA in it is inside particles larger than 0.22 microns containing specific proteins of the mitochondrial membrane. Studying them under an electron microscope showed that they have other signs of mitochondria: the presence of external and internal membranes, a characteristic internal structure. As a result, scientists came to the conclusion that these particles are intact mitochondria existing outside the cells. Analysis of oxygen consumption showed that these mitochondria are able to perform their normal functions.
Cell-free mitochondria in the plasma of a healthy person (fluorescence microscopy). A snapshot from an article in FASEB.
According to the authors of the study, one milliliter of human blood plasma contains from 200,000 to 3.7 million mitochondria. The researchers suggest that these mitochondria circulating in the blood may be involved in many physiological or pathological processes that require communication between cells, for example, in the mechanisms of inflammation. It is quite possible that they may be an important sign for the early detection and prediction of various diseases.
The results of the study are published in the FASEB journal (Dache et al., Blood contains circulating cell‐free respiratory competitor mitochondria).
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