Evidence of adaptation of maternofetal transport of glutamine relative to placental size in normal mice, and in those with fetal growth restriction

Placental adaptations supporting fetal growth during normal and adverse gestational environments

NEW FINDINGS

What is the topic of this review? How the placenta, which transports nutrients and oxygen to the fetus, may alter its support of fetal growth developmentally and with adverse gestational conditions. What advances does it highlight? Placental formation and function alter with the needs of the fetus for substrates for growth during normal gestation and when there is enhanced competition for substrates in species with multiple gestations or adverse gestational environments, and this is mediated by imprinted genes, signalling pathways, mitochondria and fetal sexomes.

ABSTRACT

The placenta is vital for mammalian development and a key determinant of life-long health. It is the interface between the mother and fetus and is responsible for transporting the nutrients and oxygen a fetus needs to develop and grow. Alterations in placental formation and function, therefore, have consequences for fetal growth and birthweight, which in turn determine perinatal survival and risk of non-communicable diseases for the offspring in later postnatal life. However, the placenta is not a static organ. As this review summarizes, research from multiple species has demonstrated that placental formation and function alter developmentally to the needs of the fetus for substrates for growth during normal gestation, as well as when there is greater competition for substrates in polytocous species and monotocous species with multiple gestations. The placenta also adapts in response to the gestational environment, integrating information about the ability of the mother to provide nutrients and oxygen with the needs of the fetus in that prevailing environment. In particular, placental structure (e.g. vascularity, surface area, blood flow, diffusion distance) and transport capacity (e.g. nutrient transporter levels and activity) respond to suboptimal gestational environments, namely malnutrition, obesity, hypoxia and maternal ageing. Mechanisms mediating developmentally and environmentally induced homeostatic responses of the placenta that help support normal fetal growth include imprinted genes, signalling pathways, subcellular constituents and fetal sexomes. Identification of these placental strategies may inform the development of therapies for complicated human pregnancies and advance understanding of the pathways underlying poor fetal outcomes and their consequences for health and disease risk.

Alteration of LncRNA expression in mice placentae after frozen embryo transfer is associated with increased fetal weight

The birthweight after frozen embryo transfer (FET) was significantly higher compared with fresh embryo transfer (fresh ET), while the mechanism remains unclear. In this study, we transferred vitrified-warmed or fresh mice blastocysts into pseudopregnant recipients (n = 11 each group) produced by natural mating to avoid the influence of superovulation. The fetal weight, placental weight, placental efficiency and placental architecture were studied at E18.5. Placental RNA-Seq analysis was used to identify candidate different lncRNAs and mRNAs between the FET group and the fresh ET group. We found that the fetal weight was increased in the FET group, with increased placental efficiency and the proportion of placental function related labyrinth zone area. 554 lncRNAs and 1012 mRNAs were differentially expressed. KEGG and GO enrichment analyses showed these differentially expressed lncRNAs and their targeted mRNAs might be related to placental morphogenesis. Furthermore, the most differentially expressed 15 lncRNAs and 15 mRNAs were validated by qRT-PCR, we found the LncRNA embryonic stem cells expressed 1 (Lncenc1) was significantly decreased, and Gjb5, which played an important role in labyrinth zone development, was increased. Gjb5 protein increase was further confirmed by Western blot. Lncenc1 and Gjb5 had 48 predicted co-targeted miRNAs, while the correlation analysis of Lncenc1 and Gjb5 mRNA showed a significant inverse correlation. The results showed that FET treatment might enhance the placental function to increase mouse fetal weight via the network diagram of Lncenc1-miRNA-Gjb5.

Exposure to two-dimensional ultrathin Ti3C2 (MXene) nanosheets during early pregnancy impairs neurodevelopment of offspring in mice

Background

Two-dimensional ultrathin Ti₃C₂ (MXene) nanosheets have been extensively explored for various biomedical applications. However, safety issues and the effects of Ti₃C₂ on human health remain poorly understood.

Results

To explore the influence on foetal or offspring after exposure to Ti₃C₂ nanosheets, we established a mouse model exposed to different doses of Ti₃C₂ nanosheets during early pregnancy in this study. We found that Ti₃C₂ nanosheets had negligible effect on the reproductive ability of maternal mice, including average pregnancy days, number of new-borns, and neonatal weight, etc. Unexpectedly, abnormal neurobehavior and pathological changes in the cerebral hippocampus and cortex in adult offspring were observed following Ti₃C₂ nanosheet treatment. In further studies, it was found that Ti₃C₂ exposure led to developmental and functional defects in the placenta, including reduced area of labyrinth, disordered secretion of placental hormones, and metabolic function derailment. The long-chain unsaturated fatty acids were significantly higher in the placenta after Ti₃C₂ exposure, especially docosahexaenoic acid (DHA) and linoleic acid. The metabolic pathway analysis showed that biosynthesis of unsaturated fatty acids was upregulated while linoleic acid metabolism was downregulated.

Conclusions

These developmental and functional defects, particularly metabolic function derailment in placenta may be the cause for the neuropathology in the offspring. This is the first report about the effects of Ti₃C₂ nanosheet exposure on pregnancy and offspring. The data provides a better understanding of Ti₃C₂ nanosheets safety. It is suggested that future studies should pay more attention to the long-term effects of nanomaterials exposure, including the health of offspring in adulthood, rather than only focus on short-term effects, such as pregnancy outcomes. Metabolomics could provide clues for finding the prevention targets of the biological negative effect of Ti₃C₂ nanosheets.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01313-z.

Placental Angiogenesis in Mammals: A Review of the Regulatory Effects of Signaling Pathways and Functional Nutrients

Normal placental development and proper angiogenesis are essential for fetal growth during pregnancy. Angiogenesis involves the regulatory action of many angiogenic factors and a series of signal transduction processes inside and outside the cell. The obstruction of placental angiogenesis causes fetal growth restriction and serious pregnancy complications, even leading to fetal loss and pregnancy cessation. In this review, the effects of placental angiogenesis on fetal development are described, and several signaling pathways related to placental angiogenesis and their key regulatory mediators are summarized. These factors, which include vascular endothelial growth factor (VEGF)-VEGF receptor, delta-like ligand 4 (DLL-4)-Notch, Wnt, and Hedgehog, may affect the placental angiogenesis process. Moreover, the degree of vascularization depends on cell proliferation, migration, and differentiation, which is affected by the synthesis and secretion of metabolites or intermediates and mutual coordination or inhibition in these pathways. Furthermore, we discuss recent advances regarding the role of functional nutrients (including amino acids and fatty acids) in regulating placental angiogenesis. Understanding the specific mechanism of placental angiogenesis and its influence on fetal development may facilitate the establishment of new therapeutic strategies for the treatment of preterm birth, pre-eclampsia, or intrauterine growth restriction, and provide a theoretical basis for formulating nutritional regulation strategies during pregnancy.

Dexamethasone-induced intrauterine growth restriction modulates expression of placental vascular growth factors and fetal and placental growth

Prenatal exposure to glucocorticoids (GC) is a central topic of interest in medicine since GCs are essential for the maturation of fetal organs and intrauterine growth. Synthetic glucocorticoids, which are used in obstetric practice, exert beneficial effects on the fetus, but have also been reported to lead to intrauterine growth retardation (IUGR). In this study, a model of growth restriction in mice was established through maternal administration of dexamethasone during late gestation. We hypothesised that GC overexposure may adversely affect placental angiogenesis and fetal and placental growth. Female BALB/c mice were randomly assigned to control or dexamethasone treatment, either left to give birth or euthanised on days 15, 16, 17 and 18 of gestation followed by collection of maternal and fetal tissue. The IUGR rate increased to 100% in the dexamethasone group (8 mg/kg body weight on gestational days 14 and 15) and pups had clinical features of symmetrical IUGR at birth. Dexamethasone administration significantly decreased maternal body weight gain and serum corticosterone levels. Moreover, prenatal dexamethasone treatment not only induced fetal growth retardation but also decreased placental weight. In IUGR placentas, VEGFA protein levels and mRNA expression of VEGF receptors were reduced and NOS activity was lower. Maternal dexamethasone administration also reduced placental expression of the GC receptor, αGR. We demonstrated that maternal dexamethasone administration causes fetal and placental growth restriction. Furthermore, we propose that the growth retardation induced by prenatal GC overexposure may be caused, at least partially, by an altered placental angiogenic profile.

mTORC1 Transcriptional Regulation of Ribosome Subunits, Protein Synthesis, and Molecular Transport in Primary Human Trophoblast Cells

Mechanistic Target of Rapamycin Complex 1 (mTORC1) serves as positive regulator of placental nutrient transport and mitochondrial respiration. The role of mTORC1 signaling in modulating other placental functions is largely unexplored. We used gene array following silencing of raptor to identify genes regulated by mTORC1 in primary human trophoblast (PHT) cells. Seven hundred and thirty-nine genes were differentially expressed; 487 genes were down-regulated and 252 up-regulated. Bioinformatic analyses demonstrated that inhibition of mTORC1 resulted in decreased expression of genes encoding ribosomal proteins in the 60S and 40S ribosome subunits. Furthermore, down-regulated genes were functionally enriched in genes involved in eIF2, sirtuin and mTOR signaling, mitochondrial function, and glutamine and zinc transport. Stress response genes were enriched among up-regulated genes following mTORC1 inhibition. The protein expression of ribosomal proteins RPL26 (RPL26) and Ribosomal Protein S10 (RPS10) was decreased and positively correlated to mTORC1 signaling and System A amino acid transport in human placentas collected from pregnancies complicated by intrauterine growth restriction (IUGR). In conclusion, mTORC1 signaling regulates the expression of trophoblast genes involved in ribosome and protein synthesis, mitochondrial function, lipid metabolism, nutrient transport, and angiogenesis, representing novel links between mTOR signaling and multiple placental functions critical for normal fetal growth and development.

Human placental uptake of glutamine and glutamate is reduced in fetal growth restriction

Fetal growth restriction (FGR) is a significant risk factor for stillbirth, neonatal complications and adulthood morbidity. Compared with those of appropriate weight for gestational age (AGA), FGR babies have smaller placentas with reduced activity of amino acid transporter systems A and L, thought to contribute to poor fetal growth. The amino acids glutamine and glutamate are essential for normal placental function and fetal development; whether transport of these is altered in FGR is unknown. We hypothesised that FGR is associated with reduced placental glutamine and glutamate transporter activity and expression, and propose the mammalian target of rapamycin (mTOR) signaling pathway as a candidate mechanism. FGR infants [individualised birth weight ratio (IBR) < 5th centile] had lighter placentas, reduced initial rate uptake of ¹⁴C-glutamine and ¹⁴C-glutamate (per mg placental protein) but higher expression of key transporter proteins (glutamine: LAT1, LAT2, SNAT5, glutamate: EAAT1) versus AGA [IBR 20th-80th]. In further experiments, in vitro exposure to rapamycin inhibited placental glutamine and glutamate uptake (24 h, uncomplicated pregnancies) indicating a role of mTOR in regulating placental transport of these amino acids. These data support our hypothesis and suggest that abnormal glutamine and glutamate transporter activity is part of the spectrum of placental dysfunction in FGR.