Evidence and potential in vivo functions for biofluid miRNAs: From expression profiling to functional testing

Abstract

A controversial hypothesis in RNA biology is that extracellular microRNAs (miRNAs), including those in biofluids, have non-cell-autonomous activities. Several studies have characterized biofluid miRNA profiles in healthy or diseased individuals but generally have failed to identify distinct disease signatures. It remains unclear whether alterations in fluid miRNA levels are simply indicators of physiological change or whether miRNAs are taken up by new cells at concentrations sufficient to affect gene expression. There are limitations to biofluid miRNA studies performed to date: methodology for isolating and quantifying biofluid miRNAs is not standardized across studies; mechanistic details of miRNA release and uptake are incomplete; and efforts to assess non-cell-autonomous effects of extracellular miRNAs have employed predominantly in vitro strategies. We describe controversies and questions that need to be addressed to test possible in vivo roles of extracellular miRNAs and propose model organisms with rich genetic toolkits for carrying out in vivo functional analyses.

MicroRNA exocytosis by large dense-core vesicle fusion

“…Extracellular circulating miRNAs have been detected in serum, so they might be biomarkers of diseases103031. Most studies have proposed that extracellular miRNAs can be packaged into membrane-associated organelles such as exosomes, microvesicles, and extracellular vesicles1032, but the mechanisms and origins of vesicle-free extracellular miRNAs remain unclear.…”

“…Most studies have proposed that extracellular miRNAs can be packaged into membrane-associated organelles such as exosomes, microvesicles, and extracellular vesicles1032, but the mechanisms and origins of vesicle-free extracellular miRNAs remain unclear. To our knowledge, our data are the first to identify miRNA exocytosis by LDCV fusion.…”

“…They participate in cell-to-cell communication9. Extracellular miRNAs have been hypothesized to be incorporated in secretory vesicles such as exosomes, microvesicles, and apoptotic bodies10, although the copy number is <111. Vesicle-free extracellular miRNAs are also detected in complexes with high-density lipoproteins (HDL)12 or Argonaute 213.…”

Molecular mechanisms of Dicer: endonuclease and enzymatic activity

“…miRNAs transported via exosomes could function as gene expression regulators in recipient cells, and growing evidence from exosomes in cancer and other processes has expanded the known subsets of exosome functions [121,125–128]. The discovery of miRNAs in exosomes also suggests a mechanism through which dysregulation of endogenous miRNAs may affect disease pathogenesis.…”

Dysregulated MicroRNA Expression Profiles and Potential Cellular, Circulating and Polymorphic Biomarkers in Non-Hodgkin Lymphoma

“…According to Mestdagh et al [89], it is possible that mean miRNA expression levels can reduce variation between samples and more accurately detect aberrant expression profiles rather than using ECs. Although NGS is more specific and able to detect novel mature miRNA isoforms (isomiRs), it may not detect lower levels of miRNAs in biofluids, and so qRT-PCR or Nanostring nCounter assays are perhaps more feasible for serum and plasma profiling [90]. …”