In a partnership thought to originate in ancient times the presence of mitochondria in human cells originates from a symbiotic relationship between primitive eukaryotic cells and prokaryotes. Mitochondria are responsible for producing more than 90% of the energy needed by the body to sustain life and support organ function. It does this via the conversion of food molecules into the ATP within the cell body.
Mitochondrial components have also been found in the extracellular space, as fragments or encapsulated in vesicles, these components also include mitochondrial cell‐free DNA (McfDNA). However, little is known about the purpose or structure of these mitochondrial elements.
A new constituent of blood
Now, a study from researchers at INSERM shows whole functioning extracellular mitochondria is a newly discovered component of the bloodstream. The team states they observed these structurally intact cell‐free mitochondria can consume oxygen, with normal and tumor cultured cells able to secrete their mitochondria into blood circulation. The opensource study is published in the journal FASEB Journal.
Previous studies show cell‐derived mitochondrial components, including mitochondrial DNA, have been found in the extracellular space, circulating in the blood of healthy subjects and patients with various diseases.
Recently, McfDNA has emerged as a circulating biomarker due to its potential role in diagnostic applications in multiple diseases such as diabetes or cancer. Despite the sound hypothesis involving McfDNA in clinical applications, knowledge regarding its origin, composition, structure, and function is still unclear. The current study investigates structures containing mitochondrial DNA in human blood.
The current study took seven years to reveal, analyze and observe the presence of highly stable structures containing whole mitochondrial genomes in the blood circulation. Results show, using electron microscopy, these structures are whole, intact and functional mitochondria. Data findings estimate there are between 200 000 and 3.7 million of these cell‐free intact mitochondria per ml of plasma.
Cell-free mitochondria DNA
Results show human blood contains intact cell‐free full‐length mitochondrial DNA in dense and biologically stable structures over 0.22 µm in diameter. The group states these structures have mitochondrial proteins, double membranes, and a morphology specific to mitochondria. They go on to explain recent studies have demonstrated the ability of certain cells to transfer mitochondria between themselves, such as the stem cells with damaged cells, proffering therapeutic solutions.
The team surmises they have identified whole functional extracellular mitochondria in the blood circulation. For the future, the researchers state therapeutic transplantation of mitochondria between cells is an active area of research, with the hope natural mitochondria can be transferred between the donor cells and recipient cells.
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