To observe the ameliorative effects of exogenous miR-146a-5p on lipopolysaccharide (LPS)-induced embryonic resorption and fetal mouse dysplasiamice, and to preliminarily investigate its mechanism of action.

1) After 36 healthy adult female mice were mated with male mice, uterine tissues were collected from females on day (D) 0 (D0/not pregnant), D0.5 (the day of embryo observed), D4.5, D7.5, D9.5 and D13.5 of gestation, and the expression levels of miR-146a-5p and its target gene TRAF6 protein in uterine tissues of mice at different gestation periods were detected by real-time fluorescent quantitative PCR (qPCR) and Western blotting. 2) The mice on D7.5 of pregnancy were treated with intraperitoneal injection of saline (control, COL group), intraperitoneal injection of 250 μg/kg LPS (named LPS250 group), LPS combined with tail vein injection of 10 nmol miR-146a-5p unrelated sequence (negative control, NC, named LPS250+NC group), or LPS combined with tail vein injection of 10 nmol miR-146a-5p agonist (miR-146a-5p agomir, named LPS250+miR-146a-5p agomir group). The total number of embryos and the number of absorbed embryos in the uterus of pregnant mice were measured and statistically analyzed on D8.5, and the expression levels of TNFα mRNA and TRAF6 protein in uterine tissues were detected by qPCR and Western blotting. 3) Then we reduced the dosage of LPS to 50 μg/kg and treated the same groups, named LPS50+NC group, LPS50+miR-146a-5p agomir group, respectively. The total number of fetal mice/embryos, the number of absorbed embryos, the number of surviving fetal mice, the weight of surviving fetal mice and the weight of the placenta were measured and statistically analyzed on D16.5. 4) Primary mouse bone marrow-derived macrophages (BMDM) were isolated and cultured. Mouse BMDM was inducted to M1 polarization by LPS stimulation, and then was transient transfected miR-146a-5p mimics or their NC fragments. The expression levels of TNFα mRNA and pSTAT1 protein were detected by qPCR and Western blotting.

The expression level of miR-146a-5p was significantly higher in the implantation sites of D7.5, D9.5 and D13.5 pregnant mice than in the non-implantation sites (P=0.013, P=0.012, P=0.003), and the protein expression level of TRAF6 was significantly lower in the implantation site of D13.5 pregnant mice than in the non-implantation site (P=0.012). After intraperitoneal injection of 250 μg/kg of LPS into D7.5 pregnant mice, the embryo absorption rate of the LPS group on D8.5 was 43.13%±3.31%, which was significantly higher than that of COL group (0%, P=0.002), while the embryo absorption rate of the LPS250+miR-146a-5p agomir group (13.50%±0.87%) was significantly lower than that of the LPS250+NC group (59.33%±4.04%, P=0.001). After intraperitoneal injection of 50 μg/kg of LPS combined with tail vein injection of NC or miR-146a-5p agomir to D7.5 pregnant mice, the fetal mouse weight [(0.29±0.09) g] and placental weight [(0.06±0.02) g] of surviving fetal mice in the LPS50+NC group on D16.5 and the LPS50+miR-146a-5p agomir group were statistically significant [(0.46±0.06) g, P<0.001; (0.07±0.02) g, P=0.021], and the differences in the number of absorbed embryos and embryo uptake rate between the two groups were not statistically significant (all P>0.05). The expression levels of both pSTAT1 protein and TNFα mRNA were significantly downregulated in BMDM transfected with miR-146a-5p mimics compared with those transfected with NC (P=0.012, P=0.039).

miR-146a-5p expression levels were significantly increased at the maternal-fetal interface during the late stage of mouse embryo implantation and placental development. Exogenous miR-146a-5p could effectively improve LPS-induced mouse embryo resorption and fetal mouse dysplasia. miR-146a-5p could inhibit the M1 polarization activity of mouse macrophages, suggesting that miR-146a-5p may inhibit the M1 polarization activity of mouse macrophages by suppressing M1 polarization of mouse maternal-fetal interface macrophages to safeguard the normal establishment and maintenance of pregnancy.

Macrophages; Lipopolysaccharide; miR-146a-5p; Embryo absorption; Abnormal fetal development