Extracellular microRNAs in follicular fluids: implication for reproductive diseases

MicroRNAs (miRNAs), a class of small non-coding RNAs, are important regulators on a post-transcriptional level. As a classical non-coding RNA, miRNAs are expressed in various tissue and are involved in many biological processes. More recently, increasing evidence has confirmed the existence of the secreted miRNAs in follicular fluid, which shed a light on the local intercellular communication. Interestingly, the miRNA profile of follicular fluids is different temporally, suggesting that miRNA secretion is finely controlled during times of development and aging. The secretion of miRNAs by somatic cells in the ovary follicle is an important resource of follicular fluid miRNAs. Comparing the miRNAs profile between follicular fluid and plasma could reveal critical miRNAs that come from circulation. The physiological functions of miRNAs in follicular fluid are believed to be a versatile message carrier for cell communications, however, due to the lack of cell-type-specific labeling methods, the route of information transmission remains elusive. It is well known that miRNA expression changes in different disease state, so it might be suitable as a biomarker. Further investigating the regulatory mechanisms mediated by these secreted miRNAs can help to understand the molecular mechanisms of oocyte maturation, early embryo development, and implantation. Therefore, this review summarizes the functions of extracellular follicular fluid miRNAs, and discusses recent progress on the potential of secreted miRNA as a biomarker in reproductive diseases.