MNSF beta regulates placental development by conjugating IGF2BP2 to enhance trophoblast cell invasiveness

Objectives: Success in pregnancy in mammals predominantly depends on a well-developed placenta. The differentiation of invasive trophoblasts is a fundamental process of placentation, the abnormalities of which are tightly associated with pregnancy disorders including preeclampsia (PE). Monoclonal nonspecific suppressor factor beta (MNSF beta) is an immunosuppressive factor. Its conventional knockout in mice induced embryonic lethality, whereas the underlying mechanism of MNSF beta in regulating placentation and pregnancy maintenance remains to be elucidated. Methods: Trophoblast-specific knockout of MNSF beta was generated using Cyp19-Cre mice. In situ hybridization (ISH), haematoxylin and eosin (HE), immunohistochemistry (IHC) and immunofluorescence (IF) were performed to examine the distribution of MNSF beta and insulin-like growth factor 2 mRNA-binding protein 2 (IGF2BP2) at the foeto-maternal interface. The interaction and expression of MNSF beta, IGF2BP2 and invasion-related molecules were detected by immunoprecipitation (IP), immunoblotting and quantitative real-time polymerase chain reaction (qRT-PCR). The cell invasion ability was measured by the Transwell insert assay. Results: We found that deficiency of MNSF beta in trophoblasts led to embryonic growth retardation by mid-gestation and subsequent foetal loss, primarily shown as apparently limited trophoblast invasion. In vitro experiments in human trophoblasts demonstrated that the conjugation of MNSF beta with IGF2BP2 and thus the stabilization of IGF2BP2 essentially mediated the invasion-promoting effect of MNSF beta. In the placentas from MNSF beta-deficient mice and severe preeclamptic (PE) patients, downregulation of MNSF beta was evidently associated with the repressed IGF2BP2 expression. Conclusions: The findings reveal the crucial role of MNSF beta in governing the trophoblast invasion and therefore foetal development, and add novel hints to reveal the placental pathology of PE.