The microRNA (abbreviated miRNA) has been widely studied in recent years with a focus on understanding the mechanisms of communication between eukaryotic cells and tissues. After being first described in 1993, these small non-coding RNAs are increasingly recognized with multiple roles in the organism, although the main biological function of microRNAs is to regulate protein expression in the post-transcriptional phase. Researchers have found that various miRNAs are playing vital roles in regulating diverse physiological processes, such as cell proliferation, differentiation, development, signal transduction, metabolism, apoptosis, and immune responses. As a result, the abnormal expression of microRNAs is believed to be related to the development of many diseases. Recent studies have demonstrated that miRNAs circulate in a highly stable cell-free form in various body fluids, for example, plasma, serum, tears, saliva, and urine, and have been investigated as promising targets in biomarker discovery that help diagnose, predict disease prognosis, and monitor treatment response in different diseases.
A study recently published in Nature described that microRNAs related to the production of melanin pigments (or called melanogenesis) may work as biomarkers for vitiligo, a condition in which the skin loses its pigment cells. Researchers used the quantitative real-time PCR technique to assess 20 melanogenesis pathway-related microRNAs (miRNAs) selected by online bioinformatics tools in 85 non-segmental vitiligo (NSV) patients compared to 85 normal controls and then analyzed functions and pathway enrichment for the miRNAs with significant results. The result showed that 12 circulating miRNAs have a higher expression level in vitiligo patients compared with the control group. Based on the result of this study, researchers suggest that some circulating miRNAs signature might involve in the immune response associated with vitiligo pathogenesis, and specific miRNAs have the potential to be used as biomarkers for skin pigmentation disorders, including vitiligo.
Another research published in the journal of ACS Nano shared the advancement of identifying molecular markers, such as proteins and genes, in vesicular structures, exosomes, in particular, to improve the accuracy of disease diagnosis. In the study, researchers collected tear samples from patients with dry eye and type 2 diabetes and then exosomes and their contents were isolated and purified using a rapid isolation system. The team also performed nanoparticle tracking analysis, western blot analysis, on-device exosome detection, proteomic analysis, and exosome miRNA sequencing. Through these analytical methods, researchers were able to observe microRNAs differences in patients with diabetic retinopathy and without eye conditions, meaning that microRNAs might be used as biomarkers in tear exosomes to diagnose and track eye disorders and other diseases, such as neurodegenerative diseases and cancer, in a more sensitive, faster, and less invasive manner.
As a matter of fact, there are a variety of non-coding RNA types, while miRNAs receive the most research attention due to their powerful features, including less evolutionary complexity, a relatively small number with a large dynamic expression range, availability in all biological fluids, tissue- and cell-specific expression profiles, and high stability in clinical samples. Most importantly, miRNAs play a crucial role in pathway regulation, given that a single miRNA can target many genes while a single gene can be regulated by many different miRNAs.
In conclusion, leveraging the next generation sequencing techniques for the detection of RNA molecules in biological samples, microRNAs, the best known small type of non-coding RNAs, have been proposed as potential molecular biomarkers in cancer, liver and cardiovascular disease, central nervous system disorders, and skin pigmentation disorders, among many other diseases.
