The expression of miRNA encoded by C19MC and miR-371-3 strongly varies among individual placentas but does not differ between spontaneous and induced abortions

Abstract

miRNAs of the largest human miRNA gene cluster at all, i.e., C19MC, are almost exclusively expressed in the placenta. Nevertheless, only little is known about the interindividual variation of their expression and even about possible influence of gestational age, conflicting data is reported as well as for miRNAs of the much smaller miR-371-3 cluster. Our present study aims at the analyses of the expression of miRNAs from both clusters at different times of pregnancy, possible differences between placenta samples obtained from spontaneous or induced abortions in the first trimester, and the possible variation of miRNA expression at different sites within same placentas. miR-371a-3p, miR-372-3p, miR-373-3p, miR-517a-3p, and miR-520c-3p were quantified in 85 samples and miR-371a-3p was quantified in maternal serum samples taken immediately before delivery. While for miRNA-517a-3p and miR-520c-3p the expression increased with increasing gestational age, the present study revealed strong interindividual differences in the expression of miR-371-3 in full-term placental tissue as well as for miRNAs of the C19MC cluster, where the levels differed to a much lesser extent than for the former microRNAs. Also, strong interindividual differences were noted between the serum samples but differences related to the site of the placenta where the sample has been taken from were excluded. For neither of the data from placental tissue, the study revealed differences between the spontaneous and induced abortion group. Thus, the differences do not in general seem to be related to first trimester abortion. It remains to be elucidated whether or not they affect other prenatal processes.

Keywords: Abortion; C19MC; Placenta; Sampling site; miR-371-3; microRNA.

Fig. 1

Boxplots showing miRNA expression in six sampling sites of three placentas. A = chorion plate, near umbilical cord; B = chorion plate, middle distance between umbilical cord and marginal sinus; C = chorion plate, near marginal sinus; D = 2 cm closer to basal plate, near umbilical cord; E = 2 cm closer to basal plate, middle distance between umbilical cord and marginal sinus; F = 2 cm closer to basal plate, near marginal sinus. The Kruskal-Wallis analysis of variance showed no significant differences in expression between six sampling sites (miR-371a-3p: p = 0.9369, miR-372-3p: p = 0.6265, miR-373-3p: p = 0.6788, miR-517a-3p: p = 0.6159, miR-520c-3p: p = 0.8767). Boxes contain the central 50% of values, lines inside boxes denote the median, whiskers extend to the extreme values or to 1.5* box height, whatever is smaller

Fig. 2

Differences in the expression of placental tissue throughout pregnancy. Linear regression line with 95% confidence range. Red dots, induced abortions; green dots, spontaneous abortions; blue dots, full-term placentas