The majority of microRNAs detectable in serum and saliva is concentrated in exosomes

There is an increasing interest in using microRNAs (miRNA) as biomarkers in autoimmune diseases. They are easily accessible in many body fluids but it is controversial if they are circulating freely or are encapsulated in microvesicles, particularly exosomes. We investigated if the majority of miRNa...

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Bibliographic Details
Published in:PloS one 2012-03, Vol.7 (3), p.e30679-e30679
Main Authors: Gallo, Alessia, Tandon, Mayank, Alevizos, Ilias, Illei, Gabor G
Format: Article
Language:English
Subjects:
Autoimmune diseases
B cells
Biology
Biomarkers
Biomarkers - analysis
Biomarkers - blood
Biosynthesis
Blotting, Western
Body fluids
Cancer
Depletion
Exosomes
Exosomes - chemistry
Humans
Medicine
MicroRNA
MicroRNAs
MicroRNAs - analysis
MicroRNAs - blood
Microscopy, Electron
miRNA
Physiology
Polymerase chain reaction
Reverse Transcriptase Polymerase Chain Reaction
Ribonucleic acid
RNA
Saliva
Saliva - chemistry
Studies
Trends
Ultracentrifugation
Urine
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Summary:There is an increasing interest in using microRNAs (miRNA) as biomarkers in autoimmune diseases. They are easily accessible in many body fluids but it is controversial if they are circulating freely or are encapsulated in microvesicles, particularly exosomes. We investigated if the majority of miRNas in serum and saliva are free-circulating or concentrated in exosomes. Exosomes were isolated by ultracentrifugation from fresh and frozen human serum and saliva. The amount of selected miRNAs extracted from the exosomal pellet and the exosome-depleted serum and saliva was compared by quantitative RT-PCR. Some miRNAs tested are ubiquitously expressed, others were previously reported as biomarkers. We included miRNAs previously reported to be free circulating and some thought to be exosome specific. The purity of exosome fraction was confirmed by electronmicroscopy and western blot. The concentration of miRNAs was consistently higher in the exosome pellet compared to the exosome-depleted supernatant. We obtained the same results using an equal volume or equal amount of total RNA as input of the RT-qPCR. The concentration of miRNA in whole, unfractionated serum, was between the exosomal pellet and the exosome-depleted supernatant. Selected miRNAs, which were detectable in exosomes, were undetectable in whole serum and the exosome-depleted supernantant. Exosome isolation improves the sensitivity of miRNA amplification from human biologic fluids. Exosomal miRNA should be the starting point for early biomarker studies to reduce the probability of false negative results involving low abundance miRNAs that may be missed by using unfractionated serum or saliva.
ISSN:1932-6203
1932-6203
DOI:10.1371/journal.pone.0030679