microRNA concept: Frequently Asked Questions (FAQ)

microRNA concept: Frequently Asked Questions (FAQ).  In what form does free microRNA exist in the blood?

microRNA concept FAQ: 

Q1: What is Circulating microRNA?

A: Free microRNA refers to the microRNA that is free in the peripheral blood, circulating, and not contained in the complete cell structure.

Q2: What is the source of free miRNA?

A: There may be two sources of free miRNA, one is the microRNA in the original cell contained in the dead cell debris, and the other is the microRNA that is actively secreted and released by living cells.

Q3: In what form does free microRNA exist in the blood?

A: Free microRNA exists in various forms in the blood. If it is a miRNA encapsulated in dead cell debris, it is mainly nucleic acid in naked form; if it is actively secreted and released by living cells, it is mostly anchored to RNA binding. Proteins (such as Ago2) exist in the form of protein-nucleic acid complexes, or exist in vesicle structures called exosomes-these two specific binding methods determine the biological characteristics of free microRNAs that are not easily degraded.

Q4: What kind of cells secrete free microRNA?

A: Many cell types—including normal cells and malignant tumor cells—can secrete microRNA. Therefore, the cell source of microRNA cannot be determined based on the type of disease and the characteristics of microRNA expression alone. For example, even if we find that the amount of free microRNA detected in a certain blood is closely related to the occurrence or prognosis of tumors, it is impossible to judge from this basic fact that this free microRNA is secreted by tumor cells.

Q5: What are the biological functions of free microRNAs actively secreted by living cells?

A: Free microRNAs actively secreted by living cells (especially microRNAs encapsulated in exosomes) can be absorbed by other cells in the microenvironment (which can be cells of the same type or different types of cells) through endocytosis and are being absorbed The corresponding signal regulation function of the microRNA is exerted in the cell. This effect can even be extended to target cells that are far away from secretory cells by the blood circulatory system. Because this free microRNA is very special, similar to the mechanism of hormones, this microRNA is also called exsomalshuttle RNA.

Q6: Except for blood, do other body fluids contain free microRNA?

A: In addition to blood, free microRNA can be detected in common body fluid types, such as saliva, tears, urine, breast milk, semen, and cerebrospinal fluid.

Q7: Are there very few types and contents of free microRNA?

A: The types of free microRNA are relatively abundant, and the content is hundreds of nanograms/ml (depending on the type of health and disease). The following table is a list of the types and contents of free microRNA in 12 kinds of body fluids of healthy people.

(source:internet, reference only)

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