Identification of Exosomal Muscle-Specific miRNAs in Serum

Myotonic dystrophy type 1 (DM1) is the most common form of adult-onset muscular dystrophy, which is characterised by progressive muscle wasting and the discovery of reliable blood-based biomarkers could be useful for the disease progress monitoring. There have been some reports showing that the presence of specific miRNAs in blood correlate with DM1. In one of these, a group from Cyprus Institute of Neurology & Genetics identified four muscle-specific miRNAs, miR-1, miR-133a, miR-133b and miR-206, which correlated with the progression of muscle wasting observed in DM1 patients. The levels of the four muscle-specific miRNAs were elevated in the serum of DM1 patients compared to healthy participants and were also elevated in the serum of progressive muscle wasting DM1 patients compared to disease-stable DM1 patients.

The aim of this work was to characterise the ontology of these four muscle-specific miRNAs in the blood circulation of DM1 patients. Here the researchers show that the four muscle-specific miRNAs are encapsulated within exosomes isolated from DM1 patients. These results show for the first time, the presence of miRNAs encapsulated within exosomes in blood circulation of DM1 patients. More interestingly, the levels of the four exosomal muscle-specific miRNAs are associated with the progression of muscle wasting in DM1 patients. They propose that exosomal muscle-specific miRNAs may be useful molecular biomarkers for monitoring the progress of muscle wasting in DM1 patients. There has been a growing interest regarding the clinical applications of exosomes and their role in prognosis and therapy of various diseases and the above results contribute towards this way.

Exosomes are present in serum of DM1 patients

Exosomes were isolated from serum samples of DM1 patients and healthy participants. The isolated exosomes were initially characterized by SEM, TRPS and western blot analysis. (A) SEM micrographs of round exosomes at 60,000x magnification, (B) SEM micrograph and anaglyph analysis shown statistical information of the maximum mean diameter (100 nm) of the exosomes and their roundness level (0.701), (C) Advance surface analysis of specific exosomes e.g. #16 of mean diameter 0.105μm, (D) Quantification and size analysis of exosomes using TRPS. Replicates of patient exosomes compared to known size and concentration of polysterine beads. Once the exosomes sample is calibrated to the reference beads, the recorded blockades in nA, can be calculated to absolute sizes in nm. The particles rates are used to calculate the concentration of exosomes. (E) Exosomes were immunogold labeled with anti-CD63 and anti-CD81. (F) Western blot analysis of the exosomal markers CD63, CD81 and TSG101 of the exosomal lysates isolated from serum samples of DM1 patients confirmed the successful isolation of the exosomes. Calnexin, Cytochrome C, GM130 and Nucleoporin were also analysed as negative controls. Lysates from human muscle cell lines were served as controls.