STUDY QUESTION Is the protein L-arginine methyltransferase 3 (PRMT3)/asymmetrical dimethylarginine (ADMA)/nitric oxide (NO) pathway involved in the development of recurrent miscarriage (RM), and what is the potential mechanism? SUMMARY ANSWER Elevated levels of PRMT3 and ADMA inhibit NO formation in the decidua, thereby impairing the functions of trophoblast cells at the maternal–foetal interface. WHAT IS KNOWN ALREADY Decreased NO bioavailability is associated with RM. ADMA, an endogenous inhibitor of nitric oxide synthase (NOS), is derived from the methylation of protein arginine residues by PRMTs and serves as a predictor of mortality in critical illness. STUDY DESIGN, SIZE, DURATION A total of 145 women with RM and 149 healthy women undergoing elective termination of an early normal pregnancy were enrolled. Ninety-six female CBA/J, 24 male DBA/2 and 24 male BALB/c mice were included. CBA/J × DBA/2 matings represent the abortion group, while CBA/J × BALB/c matings represent the normal control group. The CBA/J pregnant mice were then categorised into four groups: (i) normal + vehicle group (n = 28), (ii) abortion + vehicle group (n = 28), (iii) normal + SGC707 (a PRMT3 inhibitor) group (n = 20) and (iv) abortion + SGC707 group (n = 20). All injections were made intraperitoneally on Days 0.5, 3.5 and 6.5 of pregnancy. Decidual tissues were collected on Days 8.5, 9.5 and 10.5 of gestation. The embryo resorption rates were calculated on Day 9.5 and Day 10.5 of gestation. PARTICIPANTS/MATERIALS, SETTING, METHODS NO concentration, ADMA content, NOS activity, expression levels of NOS and PRMTs in decidual tissues were determined using conventional assay kits or western blotting. PRMT3 expression was further analysed in decidual stromal cells, macrophages and natural killer cells. A co-culture system between decidual macrophages (DMs) and HTR-8/SVneo trophoblasts was constructed to study the roles of the PRMT3/ADMA/NO signalling pathway. Trophoblast apoptosis was analysed via Annexin V-fluorescein isothiocyanate/propidium iodide staining. CBA/J × DBA/2 mouse models were used to investigate the effects of SGC707 on embryo resorption rates. MAIN RESULTS AND THE ROLE OF CHANCE Our results show that NO concentration and NOS activity were decreased, but ADMA content and PRMT3 expression were increased in the decidua of RM patients. Moreover, compared with the normal control subjects, PRMT3 expression was significantly up-regulated in the macrophages but not in the natural killer cells or stromal cells of the decidua from RM patients. The inhibition of PRMT3 results in a significant decrease in ADMA accumulation and an increase in NO concentration in macrophages. When co-cultured with DMs, which were treated with SGC707 and ADMA, trophoblast apoptosis was suppressed and induced, respectively. In vivo experiments revealed that the administration of SGC707 reduced the embryo resorption rate of CBA/J × DBA/2 mice. LIMITATIONS, REASONS FOR CAUTION All sets of experiments were not performed with the same samples. The main reason is that each tissue needs to be reserved for clinical diagnosis and only a small piece of each tissue can be cut and collected for this study. WIDER IMPLICATIONS OF THE FINDINGS Our results indicate that the PRMT3/ADMA/NO pathway is a potential marker and target for the clinical diagnosis and therapy of RM. STUDY FUNDING/COMPETING INTEREST(S) This study was supported by the National Key Research and Development Program of China (2017YFC1001401), National Natural Science Foundation of China (81730039, 82071653, 81671460, 81971384 and 82171657) and Shanghai Municipal Medical and Health Discipline Construction Projects (2017ZZ02015). The authors have declared no conflict of interest. TRIAL REGISTRATION NUMBER N/A.

Abstract Recurrent spontaneous miscarriage (RSM) is a systemic disorder that has been defined as two or more pregnancies lost before the 20th week of gestation. Although the impaired function of macrophages at the maternal–fetal interface has been reported to be associated with RSM, the underlying mechanisms have not been fully elucidated. Here, we revealed that HDAC8 plays a critical role in RSM. Our results show that the mRNA and protein expression of HDAC8 was decreased in decidual macrophages from RSM patients. Moreover, the knockdown of HDAC8 resulted in a significant decrease in CD163 expression and an increase in apoptosis in dTHP-1 macrophages. Mechanistically, the ERK signaling pathway was activated in HDAC8-knockdown macrophages. When HDAC8-knockdown cells were pretreated with the ERK inhibitor U0126, expression levels of CD163, activated caspases 3, 7 and 9, and the apoptosis rate, were rescued. Taken together, our current results suggest that HDAC8 plays an important role in macrophage activation and apoptosis and may contribute to maintaining normal pregnancy by increasing the expression of M2 marker genes and inhibiting the apoptosis of macrophages at the maternal–fetal interface.

Objective: Preeclampsia is a pregnancy-specific disorder that is a major cause of maternal and foetal morbidity and mortality, with a prevalence of 6-8% of pregnancies. Although the downregulation of lysyl oxidase (LOX) and LOX-like protein 2 (LOXL2), which leads to reduced trophoblast cell migration and invasion through activation of the TGF-b1/Smad3/collagen pathway, is relevant to preeclampsia, the mechanisms regulating differences in the gene expression of LOX and LOXL2 in placentas are not yet understood. This study aimed to investigate the mechanisms regulating differences in the gene expression of LOX and LOXL2 in placentas. Methods:The expression of miRNAs, LOX and LOXL2 in preeclamptic placentas and control placentas was analysed by qPCR. Localisation of miR29a and LOXL2 in preeclamptic placentas was performed by RNA-Fluorescence in-situ hybridization assay. The direct regulation of LOXL2 by miR-29a was assessed by dualluciferase reporter assays in human extravillous trophoblast cells (HTR8/SVneo). Cell migration and invasion were evaluated by Transwell assays in HTR8/SVneo cells.Results: miR-29a expression was upregulated in preeclamptic placentas and negatively correlated with LOXL2 mRNA expression levels. RNA-Fluorescence in-situ hybridization assay revealed a clear overlap between miR-29a and LOXL2 in the placentas of preeclampic women. LOXL2 was a direct target gene of miR-29a, as confirmed by a dual-luciferase reporter assay in HTR8/SVneo trophoblast cells. miR-29a suppressed HTR8/SVneo trophoblast cell migration and invasion. LOXL2 overexpression reversed the inhibitory effects of miR-29a on HTR8/SVneo trophoblast cell migration and invasion. Conclusion:Our results suggest that the upregulation of miR-29a suppresses the migration and invasion of HTR8/ SVneo trophoblast cells by directly targeting LOXL2 in preeclampsia.

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