Circulating microRNAs as clinical biomarkers in the predictions of pregnancy complications

Abstract

Predicting pregnancy complications is a major topic for clinicians and biologists for maternal and fetal monitoring. Noninvasive biomarkers in maternal blood such as circulating microRNAs (miRNAs) are promising molecules to predict pregnancy disorders. miRNAs are noncoding short RNAs that regulate mRNA expression by repressing the translation or cleaving the transcript. miRNAs are released to the extracellular systemic circulation via exosomes. The discovery of plasma- or serum-derived miRNAs and of free-circulating exosomes that contain miRNAs provides useful information about the physiological or pathophysiological roles of the miRNAs. Specific placental miRNAs are present in maternal plasma in different ways depending on whether the pregnancy is normal or pathological or if there is no pregnancy. This paper focuses on placental miRNAs and extracellular miRNAs to the placenta whose misregulation could lead to pregnancy complications.

Figure 1

miRNA biogenesis. miRNA gene is transcribed by RNA pol II to form a hairpin loop primary transcript, pri-miRNA, which is processed by Drosha/DCGR8 to form pre-miRNA. Pre-miRNA is exported to the cytoplasm by exportin 5 where Dicer cleaves off the hairpin loop to form a duplex that contains the mature miRNA. The mature miRNA is then incorporated into the RNA-induced silencing complex RISC to target the 3′ untranslated region of the target mRNA to silence expression by repression or cleavage.

Figure 2

Isolated exosomes analyzed on electron microscopy.