Associations between fetal size, sex and placental angiogenesis in the pig

Morphologic development of the first-trimester utero-placental vasculature is positively associated with embryonic and fetal growth: the Rotterdam Periconception Cohort

STUDY QUESTION

Is morphologic development of the first-trimester utero-placental vasculature associated with embryonic growth and development, fetal growth, and birth weight percentiles?

SUMMARY ANSWER

Using the utero-placental vascular skeleton (uPVS) as a new imaging marker, this study reveals morphologic development of the first-trimester utero-placental vasculature is positively associated with embryonic growth and development, fetal growth, and birth weight percentiles.

WHAT IS KNOWN ALREADY

First-trimester development of the utero-placental vasculature is associated with placental function, which subsequently impacts embryonic and fetal ability to reach their full growth potential. The attribution of morphologic variations in the utero-placental vascular development, including the vascular structure and branching density, on prenatal growth remains unknown.

STUDY DESIGN, SIZE, DURATION

This study was conducted in the VIRTUAL Placental study, a subcohort of 214 ongoing pregnancies, embedded in the prospective observational Rotterdam Periconception Cohort (Predict study). Women were included before 10 weeks gestational age (GA) at a tertiary referral hospital in The Netherlands between January 2017 and March 2018.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We obtained three-dimensional power Doppler volumes of the gestational sac including the embryo and the placenta at 7, 9, and 11 weeks of gestation. Virtual Reality-based segmentation and a recently developed skeletonization algorithm were applied to the power Doppler volumes to generate the uPVS and to measure utero-placental vascular volume (uPVV). Absolute vascular morphology was quantified by assigning a morphologic characteristic to each voxel in the uPVS (i.e. end-, bifurcation-crossing-, or vessel point). Additionally, total vascular length (mm) was calculated. The ratios of the uPVS characteristics to the uPVV were calculated to determine the density of vascular branching. Embryonic growth was estimated by crown-rump length and embryonic volume. Embryonic development was estimated by Carnegie stages. Fetal growth was measured by estimated fetal weight in the second and third trimester and birth weight percentiles. Linear mixed models were used to estimate trajectories of longitudinal measurements. Linear regression analysis with adjustments for confounders was used to evaluate associations between trajectories of the uPVS and prenatal growth. Groups were stratified for conception method (natural/IVF-ICSI conceptions), fetal sex (male/female), and the occurrence of placenta-related complications (yes/no).

MAIN RESULTS AND THE ROLE OF CHANCE

Increased absolute vascular morphologic development, estimated by positive random intercepts of the uPVS characteristics, is associated with increased embryonic growth, reflected by crown-rump length (endpoints β = 0.017, 95% CI [0.009; 0.025], bifurcation points β = 0.012, 95% CI [0.006; 0.018], crossing points β = 0.017, 95% CI [0.008; 0.025], vessel points β = 0.01, 95% CI [0.002; 0.008], and total vascular length β = 0.007, 95% CI [0.003; 0.010], and similarly with embryonic volume and Carnegie stage, all P-values ≤ 0.01. Density of vascular branching was negatively associated with estimated fetal weight in the third trimester (endpoints: uPVV β = -94.972, 95% CI [-185.245; -3.698], bifurcation points: uPVV β = -192.601 95% CI [-360.532; -24.670]) and birth weight percentiles (endpoints: uPVV β = -20.727, 95% CI [-32.771; -8.683], bifurcation points: uPVV β -51.097 95% CI [-72.257; -29.937], and crossing points: uPVV β = -48.604 95% CI [-74.246; -22.961])), all P-values < 0.05. After stratification, the associations were observed in natural conceptions specifically.

LIMITATION, REASONS FOR CAUTION

Although the results of this prospective observational study clearly demonstrate associations between first-trimester utero-placental vascular morphologic development and prenatal growth, further research is required before we can draw firm conclusions about a causal relationship.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings support the hypothesis that morphologic variations in utero-placental vascular development play a role in the vascular mechanisms involved in embryonic and fetal growth and development. Application of the uPVS could benefit our understanding of the pathophysiology underlying placenta-related complications. Future research should focus on the clinical applicability of the uPVS as an imaging marker for the early detection of fetal growth restriction.

STUDY FUNDING/COMPETING INTEREST(S)

This research was funded by the Department of Obstetrics and Gynecology of the Erasmus MC, University Medical Centre, Rotterdam, The Netherlands. There are no conflicts of interest.

TRIAL REGISTRATION NUMBER

Registered at the Dutch Trial Register (NTR6854).

FGR-associated placental insufficiency and capillary angiogenesis involves disruptions in human placental miRNAs and mRNAs

Fetal growth restriction (FGR) is one of the most common pregnancy complications culminating in adverse fetal outcome, including preterm birth, neonatal mortality and stillbirth. Compromised placental development and function, especially disruption in angiogenesis and inadequate nutrient supply are contributing factors. Fetal sex also influences placental function. Knowledge of gene expression changes and epigenetic factors contributing to placental dysfunction in FGR pregnancies will help identify biomarkers and help target interventions. This study tested the hypothesis that FGR pregnancies are associated with disruptions in miRNA - an epigenetic factor and mRNAs involving key mediators of angiogenesis and microvessel development. Changes in expression of key genes/proteins involved in placental dysfunction by RT-PCR and immunohistochemistry and miRNA changes by RNA sequencing were undertaken with term placenta from 12 control and 20 FGR pregnancies. Findings showed changes in expression of genes involved in steroidogenesis, steroid action, IGF family members, inflammatory cytokines and angiogenic factors in FGR pregnancies. In addition, upregulation of MIR451A and downregulation of MIR543 in placentas from FGR group with female newborns and upregulation of MIR520G in placentas from FGR group with male newborns were also noted. MIR451A and MIR543 have been implicated in angiogenesis. Consistent with gene changes, CD34, the microvessel angiogenesis marker, also showed reduced staining only in female FGR group. These findings provide evidence that epigentically regulated gene expression changes in angiogenesis and capillary development influence placental impairment in FGR pregnancies. Our preliminary observations also support for these changes to be driven in a sex-specific manner.

Maternal GLP-1 receptor activation inhibits fetal growth

Glucagon-like peptide 1 (GLP-1) regulates food intake, insulin production, and metabolism. Our recent study demonstrated that pancreatic α-cells-secreted (intraislet) GLP-1 effectively promotes maternal insulin secretion and metabolic adaptation during pregnancy. However, the role of circulating GLP-1 in maternal energy metabolism remains largely unknown. Our study aims to investigate systemic GLP-1 response to pregnancy and its regulatory effect on fetal growth. Using C57BL/6 mice, we observed a gradual decline in maternal blood GLP-1 concentrations. Subsequent administration of the GLP-1 receptor agonist semaglutide (Sem) to dams in late pregnancy revealed a modest decrease in maternal food intake during initial treatment. At the same time, no significant alterations were observed in maternal body weight or fat mass. Notably, Sem-treated dams exhibited a significant decrease in fetal body weight, which persisted even following the restoration of maternal blood glucose levels. Despite no observable change in placental weight, a marked reduction in the placenta labyrinth area from Sem-treated dams was evident. Our investigation further demonstrated a substantial decrease in the expression levels of various pivotal nutrient transporters within the placenta, including glucose transporter one and sodium-neutral amino acid transporter one, after Sem treatment. In addition, Sem injection led to a notable reduction in the capillary area, number, and surface densities within the labyrinth. These findings underscore the crucial role of modulating circulating GLP-1 levels in maternal adaptation, emphasizing the inhibitory effects of excessive GLP-1 receptor activation on both placental development and fetal growth.NEW & NOTEWORTHY Our study reveals a progressive decline in maternal blood glucagon-like peptide 1 (GLP-1) concentration. GLP-1 receptor agonist injection in late pregnancy significantly reduced fetal body weight, even after restoration of maternal blood glucose concentration. GLP-1 receptor activation significantly reduced the placental labyrinth area, expression of some nutrient transporters, and capillary development. Our study indicates that reducing maternal blood GLP-1 levels is a physiological adaptation process that benefits placental development and fetal growth.

Preweaning performance in intrauterine growth-restricted piglets: Characteristics and interventions

Intrauterine growth restriction (IUGR) is frequently observed in pig production, especially when using highly prolific sows. IUGR piglets are born with low body weight and shape indicative of differences in organ growth. Insufficient uteroplacental nutrient transfer to the fetuses is the leading cause of growth restriction in the pig. Supplementing the sow's gestation diet with arginine and/or glutamine improves placenta growth and functionality and consequently is able to reduce IUGR incidence. IUGR piglets are at higher risk of dying preweaning and face higher morbidity than their normal-weight littermates. A high level of surveillance during farrowing and individual nutrient supplementation can reduce the mortality rates. Still, these do not reverse the long-term consequences of IUGR, which are induced by persistent structural deficits in different organs. Dietary interventions peri-weaning can optimize performance but these are less effective in combating the metabolic changes that occurred in IUGR, which affect reproductive performance later in life. IUGR piglets share many similarities with IUGR infants, such as a poorer outcome of males. Using the IUGR piglet as an animal model to further explore the structural and molecular basis of the long-term consequences of IUGR and the potential sex bias could aid in fully understanding the impact of prenatal undernutrition and finding solutions for both species and sexes.

Sexual dimorphism in placental development and function: Comparative physiology with an emphasis on the pig

Across mammalian species, it has been demonstrated that sex influences birth weight, with males being heavier than females; a characteristic that can be observed from early gestation. Male piglets are more likely to be stillborn and have greater preweaning mortality than their female littermates, despite the additional maternal investment into male fetal growth. Given the conserved nature of the genome between the sexes, it is hypothesized that these developmental differences between males and females are most likely orchestrated by differential placental adaptation. This review summarizes the current understanding of fetal sex-specific differences in placental and endometrial structure and function, with an emphasis on pathways found to be differentially regulated in the pig including angiogenesis, apoptosis, and proliferation. Given the importance of piglet sex in agricultural enterprises, and the potential for skewed litter sex ratios, it is imperative to improve understanding of the relationship between fetal sex and molecular signaling in both the placenta and endometria across gestation.

RACK1 may participate in placental development at mid-gestation via regulating trophoblast cell proliferation and migration in pigs

Intrauterine growth restriction (IUGR) is a severe complication in swine production. Placental insufficiency is responsible for inadequate fetal growth, but the specific etiology of placental dysfunction-induced IUGR in pigs remains poorly understood. In this work, placenta samples supplying the lightest weight (LW) and mean weight (MW) pig fetuses in the litter at Day 65 (D65) of gestation were collected, and the relationship between fetal growth and placental morphologies and functions was investigated using histomorphological analysis, RNA sequencing, quantitative polymerase chain reaction, and in vitro experiment in LW and MW placentas. Results showed that the folded structure of the epithelial bilayer of LW placentas followed a poor and incomplete development compared with that of MW placentas. A total of 654 differentially expressed genes (DEGs) were screened out between the LW and MW placentas, and the gene encodes receptor for activated C kinase 1 (RACK1) was found to be downregulated in LW placentas. The DEGs were mainly enriched in translation, ribosome, protein synthesis, and mammalian target of rapamycin (mTOR) signaling pathway according to gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses. In vitro experiments indicated that the decreased RACK1 in LW placentas may be involved in abnormal development of placental folds (PFs) by inhibiting the proliferation and migration of porcine trophoblast cells. Taken together, these results revealed that RACK1 may be a vital regulator in the development of PFs via regulating trophoblast cell proliferation and migration in pigs.

Integrins and ligands, are correlated at pig placental interface during pregnancy?

In the present work, we emphasize the studies about integrins and their receptors in pig placental interface at different times of gestation. Uterine placental interface (n=24) of 17-, 30-, 60- and 70-days gestation (dg) and non-pregnant uterus (n=4) of crossbred sows were used. The presence of αvβ3 and α5β1 integrins, and their ligands fibronectin (FN), and osteopontin (OPN) were detected by immunohistochemistry, and the immunolabelled area percentage (IAP) and the optical density (OD) were determined. The integrins and its ligands analyzed have presented peaks of expression in early and mid-gestation, both in IAP and the OD area decreasing at 70 dg. These temporal changes showed us that the molecules studied in this work participate in embryo/feto-maternal attachment, variably. Besides, we found a significant correlation both in the intensity and in the extension of immunostaining for trophoblastic FN and endometrial αvβ3, and trophoblastic OPN and endometrial α5β1, throughout the entire pig pregnancy. At late gestation, take place a notable placental remodelation with subsequent removal or renewal of folds at the uterine-placental interface that results in the loss of focal adhesions. The decrease of the expression of some integrins and their ligands in late gestation, particularly at 70 dg, would demonstrate that there would be other adhesion molecules and other ligands that could be participating in the establishment of the maternal-fetal interface.

IFN-γ and IL-10: seric and placental profile during pig gestation Seric and placental cytokines in pig gestation

Concentration of interferon-gamma and interleukin-10 in maternal serum and in maternal and fetal porcine placental extracts from different gestation periods was determined. Crossbred pigs' placental samples of 17, 30, 60, 70, and 114 days gestation and non-pregnant uteri were used. Interferon-gamma concentration was increased at the placental interface at 17 days, in maternal and fetal placenta, and decreased significantly in the remaining gestation periods. Interferon-gamma showed a peak in serum at 60 days. Regarding interleukin-10, placental tissue concentrations were unaltered, there were no significant differences with non-gestating uteri samples. In serum interleukin-10 increased at 17, 60, and 114 days gestation. At 17 days there are uterus structural and molecular changes that allow the embryos implantation and placenta development. The presence of interferon-gamma found at this moment in the interface would favor that placental growth. Moreover, its significant increase in serum at 60 days, would generate a proinflammatory cytokine pattern that facility the placental remodeling characteristic of this moment of porcine gestation. On the other hand, a significant interleukin-10 increase in serum at 17, 60 and 114 days could indicate its immunoregulatory role at a systemic level during pig gestation.

Associations between maternal vitamin D status and porcine litter characteristics throughout gestation

Emerging evidence suggests an important role of vitamin D in the establishment and maintenance of pregnancy, and the regulation of foetal growth across mammalian species. However, the temporal changes in maternal vitamin D status throughout gestation in the pig and the relationship between maternal vitamin D status and litter characteristics of interest across gestation remain poorly understood and under-investigated. The abundance of 25(OH)D in maternal plasma was quantified by HPLC–MS/MS at gestational days (GD) 18, 30, 45, 60 and 90 (n = 5–11 gilts/GD). Maternal plasma 25(OH)D concentrations significantly increased between GD18 and GD30 (P < 0.05). The relationship between maternal vitamin D metabolite concentrations and litter characteristics of interest including gilt weight, ovulation rate, mean litter weight, number of live foetuses, percentage prenatal survival, and sex ratio of the litter was assessed. Maternal 25(OH)D (P = 0.059) concentrations tended to be positively associated with percentage prenatal survival on GD60. On GD90, maternal 25(OH)D (P < 0.05) concentrations were inversely associated with gilt weight. Maternal plasma 25(OH)D concentrations were inversely associated with the percentage of male foetuses in the litter on GD90 (P < 0.05). This study has provided novel insights into temporal changes in maternal vitamin D status throughout gestation and the relationship between maternal vitamin D status and the economically important litter characteristics of gilt weight, percentage prenatal survival and percentage of male foetuses in the litter. Improving the understanding of the role of vitamin D across important developmental timepoints in relation to foetal growth is essential to improve reproductive success in livestock species.

Gestational heat stress alters skeletal muscle gene expression profiles and vascularity in fetal pigs in a sexually dimorphic manner

BACKGROUND

There is evidence that sow heat stress (HS) during gestation affects fetal development with implications for impaired muscle growth. We have previously demonstrated that maternal HS during early to mid-gestation compromised muscle fibre hyperplasia in developing fetal pigs. Thus, we hypothesised these phenotypic changes are associated with a change in expression of genes regulating fetal skeletal muscle development and metabolism. To test this, at d 60 of gestation, RNA sequencing and immunohistochemistry were performed on fetal longissimus dorsi (LD) muscle biopsies collected from pregnant gilts that had experienced either thermoneutral control (CON, 20 °C, n = 7 gilts, 18 LD samples) or controlled HS (cyclic 28 to 33 °C, n = 8 gilts, 23 LD samples) conditions for 3 weeks.

RESULTS

A total of 282 genes were differentially expressed between the HS and CON groups in female LD muscles (false discovery rate (FDR) ≤ 0.05), whereas no differentially expressed genes were detected in male LD muscles between the two groups (FDR > 0.05). Gestational HS increased the expression of genes associated with transcription corepressor activity, adipogenesis cascades, negative regulation of angiogenesis and pro-inflammatory signalling in female LD muscles. Immunohistochemical analyses revealed a decreased muscle vascularity density in fetuses from HS group for both sexes compared to those from the CON group (P = 0.004).

CONCLUSIONS

These results reveal gilt HS during early to mid-gestation altered gene expression profiles in fetal LD muscles in a sexually dimorphic manner. The molecular responses, including transcription and angiogenesis repressions and enhanced adipogenesis cascades, were exclusively observed in females. However, the associated reductions in muscle vascularity were observed independently of sexes. Collectively this may indicate female fetal pigs are more adaptive to gestational HS in terms of gene expression changes, and/or there may be sexually dimorphic differences with respect to the timing of muscle molecular responses to gestational HS.

Association of fetal sex with angiogenic factors in normotensive and hypertensive pregnancy states

OBJECTIVES

With the incorporation of angiogenic biomarkers into clinical practice, identification of potential modifiers of the angiogenic profile, including fetal sex, is essential.

STUDY DESIGN

In this retrospective cohort analysis, patients with hypertensive disorders of pregnancy (HDP) and normotensive pregnancies were enrolled upon admission to Labor and Delivery. Blood samples for angiogenic factors were assessed using an automated platform. Clinical and demographic information was abstracted from each patient's medical records.

MAIN OUTCOME MEASURES

Soluble fms-like tyrosine kinase-1 (sFlt1) and placental growth factor (PlGF) levels and their ratio in relation to fetal sex in patients with normotensive pregnancies compared to those with HDP were evaluated.

RESULTS

A total of 617 patients were analyzed (299 normotensive, 113 gestational hypertensive, 71 chronic hypertensive, and 134 preeclamptic patients). There was no difference between the number of patients who had a male fetus among preeclampsia and normotensive parturients (56.0 % vs 50.2 %, p = 0.26). Normotensive patients carrying a male fetus had significantly higher sFlt1 (pg/ml) (3168 [IQR: 2160-4945] vs 2678 [IQR: 1752-4271]; p = 0.01) and sFlt1/PlGF ratios (18 [IQR: 7-44] vs 12 [IQR: 5-30]; p = 0.01) in comparison to pregnant patients carrying a female fetus. This difference between fetal sexes was not observed in the angiogenic profile of patients with HDP.

CONCLUSIONS

Our study of primarily Black, obese patients demonstrates that normotensive patients carrying a male fetus have a significantly higher sFlt1 and sFlt1/PlGF ratio as compared to those carrying a female fetus at term gestation. Fetal sex should be considered as a covariate when studying angiogenic factors in normotensive pregnant patients.

Placental structure, function, and mitochondrial phenotype relate to fetal size in each fetal sex in mice†

Fetal growth depends on placental function, which requires energy from mitochondria. Here we investigated whether mitochondrial function in the placenta relates to the growth of the lightest and heaviest fetuses of each sex within the litter of mice. Placentas from the lightest and heaviest fetuses were taken to evaluate placenta morphology (stereology), mitochondrial energetics (high-resolution respirometry), mitochondrial regulators, nutrient transporters, hormone handling, and signaling pathways (qPCR and Western blotting). We found that mitochondrial complex I and II oxygen consumption rate was greater for placentas supporting the lightest female fetuses, although placental complex I abundance of the lightest females and complexes III and V of the lightest males were decreased compared to their heaviest counterparts. Expression of mitochondrial biogenesis (Nrf1) and fission (Drp1 and Fis1) genes was lower in the placenta from the lightest females, whilst biogenesis-related gene Tfam was greater in the placenta of the lightest male fetuses. In addition, placental morphology and steroidogenic gene (Cyp17a1 and Cyp11a1) expression were aberrant for the lightest females, but glucose transporter (Slc2a1) expression was lower in only the lightest males versus their heaviest counterparts. Differences in intra-litter placental phenotype were related to changes in the expression of hormone-responsive (androgen receptor) and metabolic signaling (AMPK, AKT, and PPARγ) pathways. Thus, in normal mouse pregnancy, placental structure, function, and mitochondrial phenotype are differentially responsive to the growth of the female and male fetus. This study may inform the design of sex-specific therapies for placental insufficiency and fetal growth abnormalities with life-long benefits for the offspring.

Associations between testicular development and fetal size in the pig

Background

Impaired reproductive performance is the largest contributing factor for the removal of boars from commercial systems. Intrauterine growth restricted piglets represent 25% of the total number of piglets born and have impaired reproductive performance. This study aimed to improve the understanding of temporal changes in testicular gene expression during testes development in fetuses of different size. The lightest and closest to mean litter weight (CTMLW) male Large White × Landrace littermates were collected at gestational days (GD) 45, 60 and 90 (n = 5–6 litters/GD).

Results

Testes weight and testes weight as a percentage of fetal weight were not associated with fetal size at GD60 or 90. Fetal plasma testosterone was not associated with fetal size at GD90. There was no association between fetal size and seminiferous tubule area and number, number of germ or Sertoli cells per tubule. The lightest fetuses tended to have wider seminiferous tubules compared to the CTMLW fetuses at GD90 (P = 0.077). The testicular expression of KI67 (P ≤ 0.01) and BAX:BCL2 ratio (P = 0.058) mRNAs decreased as gestation progressed. Greater SPP1 mRNA expression was observed at GD60 when compared with GD45 and 90 (P ≤ 0.05). Lower expression of DMRT1 and SPP1 (P < 0.01) mRNAs was observed in testes associated with the lightest fetuses compared to the CTMLW fetuses at GD90.

Conclusions

These findings provide novel insights into the expression profiles of genes associated with testicular development and function. Further, these data suggest that programming of reproductive potential in IUGR boars occurs late in gestation, providing a platform for further mechanistic investigation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-022-00678-3.

Effects of exogenous progesterone on expression of mineral regulatory molecules by ovine endometrium and placentomes

This study aimed to determine whether the acceleration of conceptus development induced by administration of exogenous progesterone (P4) during the pre-implantation period of pregnancy alters calcium, phosphate, and vitamin D signaling at the maternal-conceptus interface. Suffolk ewes (n = 48) were mated to fertile rams and received daily intramuscular injections of either corn oil vehicle (CO) or 25 mg progesterone in CO (P4) for the first 8 days of pregnancy and hysterectomized on either Day 9 (CO n = 5; P4 n = 6), 12 (CO n = 9; P4 n = 4) or 125 (CO n = 14; P4 n = 10) of gestation. Expression of S100A12 (P < 0.05) and FGFR2 (P < 0.01) mRNAs was lower in endometria from P4-treated ewes on Day 12. Expression of ADAM10 (P < 0.05) mRNA was greater in endometria from P4-treated ewes on Day 125. Expression of ADAM10 (P < 0.01), FGFR2 (P < 0.05), SLC20A1 (P < 0.05), TRPV5 (P < 0.05), and TRPV6 (P < 0.01) mRNAs was greater, but KL mRNA expression was lower (P < 0.05) in placentomes from P4-treated ewes at Day 125. There was lower endometrial and greater placentomal expression of mRNAs involved in mineral metabolism and transport in twin compared to singleton pregnancies. Further, expression of mRNAs involved in mineral metabolism and transport was greater in P4-treated twin placentomes. KL, FGF23, VDR, S100A9, S100A12, S100G, and CYP27B1 proteins were immunolocalized in endometria and placentomes. Exogenous P4 in early pregnancy altered expression of regulators of calcium, phosphate, and vitamin D on Day 125 of pregnancy indicating a novel effect of P4 on mineral transport at the maternal-conceptus interface.

Pregnancy in pigs: the journey of an early life

Embryo mortality is responsible for greater losses in litter size in pigs. It is well known that pregnancy establishment is a complex process, and important changes occur continuously in both the corpora lutea and the endometrium, which varies depending on the pre-natal development phase: embryonic, pre-implantation or fetal stages. The placenta is a key organ responsible for the exchange of nutrients, metabolites and respiratory gases between mother and fetuses. The porcine placenta is diffuse, epitheliochorial, and placentation begins with implantation, which involves specialized cell adhesion and cell migration, leading to the attachment of the trophectoderm to the uterine endometrial lumen epithelium. The efficiency with which the placenta provides adequate amounts of nutrients and oxygen to the fetus is crucial for proper fetal growth and development. In the last decades, emphasis on selection for sow prolificacy has resulted in a substantial increase in the number of piglets born per litter, which had a direct effect on piglet quality, compromising birth weight and litter uniformity. Placental insufficiency will lead to fetal intrauterine growth restriction. This review addresses the main events of early embryo development, including preimplantation and implantation periods. In addition, placentation and its role on fetal development are covered, as well as intrauterine growth restriction, as it is a natural condition in the pig, with long lasting detrimental effects to the production chain.

Neuronatin gene expression levels affect foetal growth and development by regulating glucose transport in porcine placenta

Imprinted genes play important regulatory roles in the growth and development of placentas and foetuses during pregnancy. In a previous study, we found that the imprinted gene Neuronatin (NNAT) is involved in foetal development; NNAT expression was significantly lower in the placentas of piglets that died neonatally compared to the placentas of surviving piglets. However, the function and mechanism of NNAT in regulating porcine placental development is still unknown. In this study, we collected the placentas of high- and low-weight foetuses at gestational day (GD 65, 90), (n = 4-5 litters/GD) to investigate the role of NNAT in regulating foetal growth and development. We found that the mRNA and protein levels of NNAT were significantly higher in the placentas of high-weight than low-weight foetuses. We then overexpressed NNAT in porcine placental trophoblast cell lines (pTr2) and demonstrated that NNAT activated the PI3K-AKT pathway, and further promoted the expression of glucose transporter 1 (GLUT1) and increased cellular calcium ion levels, which improved glucose transport in placental trophoblast cells in vitro. To conclude, our study suggests that NNAT expression impacts porcine foetal development by regulating placental glucose transport.

Sexually Dimorphic Transcriptomic Changes of Developing Fetal Brain Reveal Signaling Pathways and Marker Genes of Brain Cells in Domestic Pigs

In this study, transcriptomic changes of the developing brain of pig fetuses of both sexes were investigated on gestation days (GD) 45, 60 and 90. Pig fetal brain grows rapidly around GD60. Consequently, gene expression of the fetal brain was distinctly different on GD90 compared to that of GD45 and GD60. In addition, varying numbers of differentially expressed genes (DEGs) were identified in the male brain compared to the female brain during development. The sex of adjacent fetuses also influenced gene expression of the fetal brain. Extensive changes in gene expression at the exon-level were observed during brain development. Pathway enrichment analysis showed that the ionotropic glutamate receptor pathway and p53 pathway were enriched in the female brain, whereas specific receptor-mediated signaling pathways were enriched in the male brain. Marker genes of neurons and astrocytes were significantly differentially expressed between male and female brains during development. Furthermore, comparative analysis of gene expression patterns between fetal brain and placenta suggested that genes related to ion transportation may play a key role in the regulation of the brain-placental axis in pig. Collectively, the study suggests potential application of pig models to better understand influence of fetal sex on brain development.

Fetal Brain Elicits Sexually Conflicting Transcriptional Response to the Ablation of Uterine Forkhead Box A2 (Foxa2) in Mice

In this study, we investigated the effects of ablation of uterine Forkhead Box A2 (Foxa2) on gene expression of fetal brain relative to placenta. Using a conditional knockout mouse model for uterine Foxa2, here we show that the lack of uterine Foxa2 elicits a sexually-conflicting transcriptional response in the fetal brain relative to placenta. The ablation of Foxa2 in the uterus altered expression of genes related to growth, nutrient sensing, aging, longevity and angiogenesis among others. In the wildtype mice, these genes were expressed higher in the fetal brain and placenta of males compared to females. However, in mice lacking uterine Foxa2, the same genes showed the opposite pattern i.e., higher expression in the fetal brain and placenta of females compared to males. Based on the known marker genes of mice placenta and fetal brain cells, we further predicted that the genes exhibiting the sexually conflicting expression were associated with vascular endothelial cells. Overall, our study suggests that uterine Foxa2 plays a role in the regulation of the brain-placental axis by influencing the fetoplacental vascular changes during pregnancy.

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.

Novel mineral regulatory pathways in ovine pregnancy: II. Calcium-binding proteins, calcium transporters, and vitamin D signaling

Mineralization of the fetal mammalian skeleton requires a hypercalcemic gradient across the placenta from mother to fetus. However, the mechanisms responsible for maintaining the placental transport of calcium remain poorly understood. This study aimed to identify calcium and vitamin D regulatory pathway components in ovine endometria and placentae across gestation. Suffolk ewes were bred with fertile rams upon detection of estrus (Day 0). On Days 9, 12, 17, 30, 70, 90, 110, and 125 of pregnancy (n=3-14/Day), ewes were euthanized and hysterectomized. Calcium abundance was influenced by gestational day in uterine flushings and allantoic fluid (P<0.05). The expression of S100G, S100A9, S100A12, ATP2B3, ATP2B4, TRPV5, TRPV6, CYP11A1, CYP2R1, CYP24, and VDR mRNAs known to be involved in calcium binding, calcium transport, and vitamin D metabolism were quantified by qPCR. Mediators of calcium and vitamin D signaling were expressed by Day 17 conceptus tissue, and endometria and placentae across gestation. Gestational day influenced the expression of S100G, S100A9, S100A12, TRPV6, VDR, and CYP24 mRNAs in endometria and placentae (P<0.05). Gestational day influenced endometrial expression of ATP2B3, and placental expression of TRPV5, ATP2B4, and CYP11A1 (P<0.05). VDR protein localized to the endoderm and trophectoderm (Day 17 conceptus) and was expressed in endometria and placentae throughout gestation. The observed spatiotemporal profile suggests a potential role of calcium and vitamin D in the establishment of pregnancy and regulation of fetal and placental growth, providing a platform for further mechanistic investigation.

Novel mineral regulatory pathways in ovine pregnancy: I. phosphate, klotho signaling, and sodium-dependent phosphate transporters

Appropriate mineralization of the fetal skeleton requires an excess of phosphate in the fetus compared to the mother. However, mechanisms for placental phosphate transport are poorly understood. This study aimed to identify phosphate regulatory pathways in ovine endometria and placentae throughout gestation. Suffolk ewes were bred with fertile rams upon visual detection of estrus (Day 0). On Days 9, 12, 17, 30, 70, 90, 110, and 125 of pregnancy (n = 3-14/Day), ewes were euthanized and hysterectomized. Phosphate abundance varied across gestational days in uterine flushings, allantoic fluid, and homogenized endometria and placentae (P < 0.05). The expression of mRNAs for sodium-dependent phosphate transporters (SLC20A1 and SLC20A2) and klotho signaling mediators (FGF7, FGF21, FGF23, FGFR1-4, KL, KLB, ADAM10, and ADAM17) were quantified by qPCR. Day 17 conceptus tissue expressed SLC20A1, SLC20A2, KLB, FGF7, FGF21, FGF23, FGFR1, and FGFR2 mRNAs. Both sodium-dependent phosphate transporters and klotho signaling mediators were expressed in endometria and placentae throughout gestation. Gestational day influenced the expression of SLC20A1, ADAM10, ADAM17, FGF21, FGFR1, and FGFR3 mRNAs in both endometria and placentae (P < 0.05). Gestational day influenced endometrial expression of FGF7 (P < 0.001), and placental expression of FGF23 (P < 0.05). Immunohistochemistry confirmed that both FGF23 and KL proteins were expressed in endometria and placentae throughout gestation. The observed spatiotemporal profile of KL-FGF signaling suggests a potential role in the establishment of pregnancy and regulation of fetal growth. This study provides a platform for further mechanistic investigation into the role for KL-FGF signaling in the regulation of phosphate transport at the ovine maternal-conceptus interface.

Male fetal sex affects uteroplacental angiogenesis in growth restriction mouse model†

Abnormally increased angiotensin II activity related to maternal angiotensinogen (AGT) genetic variants, or aberrant receptor activation, is associated with small-for-gestational-age babies and abnormal uterine spiral artery remodeling in humans. Our group studies a murine AGT gene titration transgenic (TG; 3-copies of the AGT gene) model, which has a 20% increase in AGT expression mimicking a common human AGT genetic variant (A[-6]G) associated with intrauterine growth restriction (IUGR) and spiral artery pathology. We hypothesized that aberrant maternal AGT expression impacts pregnancy-induced uterine spiral artery angiogenesis in this mouse model leading to IUGR. We controlled for fetal sex and fetal genotype (e.g., only 2-copy wild-type [WT] progeny from WT and TG dams were included). Uteroplacental samples from WT and TG dams from early (days 6.5 and 8.5), mid (d12.5), and late (d16.5) gestation were studied to assess uterine natural killer (uNK) cell phenotypes, decidual metrial triangle angiogenic factors, placental growth and capillary density, placental transcriptomics, and placental nutrient transport. Spiral artery architecture was evaluated at day 16.5 by contrast-perfused three-dimensional microcomputed tomography (3D microCT). Our results suggest that uteroplacental angiogenesis is significantly reduced in TG dams at day 16.5. Males from TG dams are associated with significantly reduced uteroplacental angiogenesis from early to late gestation compared with their female littermates and WT controls. Angiogenesis was not different between fetal sexes from WT dams. We conclude that male fetal sex compounds the pathologic impact of maternal genotype in this mouse model of growth restriction.

Novel relationships between porcine fetal size, sex, and endometrial angiogenesis†

It is hypothesized that growth restriction occurs due to inadequate vascularization of the feto-maternal interface. Evidence exists for sexual dimorphism in placental function although associations between fetal sex and the endometrium remain poorly investigated. This study investigated the relationship between porcine fetal size, sex and endometrial angiogenesis at multiple gestational days (GD). Endometrial samples supplying the lightest and closest to mean litter weight (CTMLW), male and female Large White X Landrace conceptuses or fetuses were obtained at GD18, 30, 45, 60, and 90 (n = 5-9 litters/GD). Immunohistochemistry for CD31 revealed a greater number of blood vessels in endometrium supplying females compared to those supplying males at GD45. Endometrial samples supplying the lightest fetuses had fewer blood vessels (GD60) and uterine glands (GD90) compared to those supplying the CTMLW fetuses. Quantitative PCR revealed decreased CD31 (GD60), HPSE and VEGFA (GD90) expression, alongside increased HIF1A (GD45) expression in endometrial samples supplying the lightest compared to the CTMLW fetuses. At GD30, PTGFR, CD31, and VEGFA mRNA expression was increased in samples supplying female fetuses compared to those supplying male fetuses. Intriguingly, decreased expression of ACP5, CD31, HIF1A, and VEGFA mRNAs was observed at GD60 in endometrial samples supplying female fetuses compared to those supplying their male littermates. Endothelial cell branching assays demonstrated impaired endothelial cell branching in response to conditioned media from endometrial samples supplying the lightest and female fetuses compared with the CTMLW and male fetuses, respectively. This study has highlighted that endometrial tissues supplying the lightest and female fetuses have impaired angiogenesis when compared with the CTMLW and female fetuses respectively. Importantly, the relationship between fetal size, sex and endometrial vascularity is dynamic and dependent upon the GD investigated.

Associations between foetal size and ovarian development in the pig

It is estimated that intra-uterine growth restricted piglets represent 25 % of the total number of piglets born. Growth restricted female pigs have impaired reproductive performance postnatally. HHowever, when during gestation this phenotype arises is not known. With this study, the aim was to improve the understanding of foetal ovarian development in normal and small foetuses throughout gestation. Female Large White X Landrace foetuses were obtained at gestational day (GD) 45, 60 and 90 (n = 5-6 litters/GD). Histological analysis of GATA4 stained foetal ovaries at GD60 and 90 indicated there were fewer primary follicles (P ≤ 0.05) in the foetuses weighing the least compared to those with a weight similar to the mean for the litter (CTMLW) at GD90. Plasma oestradiol concentrations were less in the foetuses with lesser weights compared with greater weight foetuses at GD90 (P ≤ 0.05). The RNA was extracted from ovaries of the lesser weight and CTMLW foetuses at GD45, 60 and 90 and qPCR was performed to quantify relative abundance of 12 candidate mRNAs for which encoded proteins that modulate ovarian function and development. Gestational changes in relative abundances of CD31, PTGFR, SPP1 and VEGFA mRNA transcripts were observed. Relative abundance of KI67 (P = 0.066) and P53 (P ≤ 0.05) was less in ovaries of the lesser weight compared to CTMLW foetuses at GD60. There was a lesser relative abundance of PTGFR mRNA transcript in ovaries from the foetuses with lesser weight compared to CTMLW foetuses at GD45 and 60 (P ≤ 0.05). These findings indicate that postnatal differences in the reproductive potential of growth restricted females are programmed early in gestation. It is hoped that further investigation will improve the understanding of the relationship between prenatal reproductive development and postnatal reproductive performance.

Spatiotemporal heterogeneity of PPARγ expression in porcine uteroplacenta for regulating of placental angiogenesis through VEGF-mediated signalling

Non-infectious prenatal mortality severely affects the porcine industry, with pathological placentation as a likely key reason. Previous studies have demonstrated that peroxisome proliferator-activated receptor gamma (PPARγ) deficiency causes defects in the uteroplacental vasculature and induces embryonic losses in mice. However, its role in porcine placental angiogenesis remains unclear. In the present study, PPARγ expression was investigated in porcine uteroplacental tissues at gestational day (GD) 25, GD40 and GD70 via quantitative polymerase chain reaction (qPCR), Western blot and immunohistochemistry (IHC). Moreover, the roles of PPARγ in porcine placental angiogenesis were investigated using a cell model of porcine umbilical vein endothelial cells (PUVECs) to conduct proliferation, migration and tube formation assays in vitro and a mouse xenograft model to assess capillary formation in vivo. The results showed that PPARγ was mainly located in the glandular epithelium, trophoblast, amniotic chorion epithelium and vascular endothelium, as indicated by the higher expression levels at GD25 and GD40 than at GD70 in endometrium and by higher expression levels at GD40 and GD70 than at GD25 in placenta. Moreover, PPARγ expression was significantly downregulated in placenta with dead foetus. In PUVECs, knocking out PPARγ significantly inhibited proliferation, migration and tube formation in vitro and inhibited capillary formation in mouse xenografts in vivo by blocking S-phase, promoting apoptosis and downregulating the angiogenic factors of VEGF and its receptors. Overall, the spatiotemporal heterogeneity of PPARγ expression in porcine uteroplacental tissue suggests its vital role in endometrial remodelling and placental angiogenesis, and PPARγ regulates placental angiogenesis through VEGF-mediated signalling.

Identification of appropriate reference genes for qPCR analyses of porcine placentae and endometria, supplying foetuses of different size and sex, at multiple gestational days

Recent studies suggest associations exist between foetal size and sex, and gene expression at the porcine feto-maternal interface. It is essential to identify reference genes which have stable expression throughout gestation in feto-placental units associated with foetuses of different size and sex. qPCR was performed for 11 genes within porcine placentae and endometria at gestational days (GD) 30, 60 and 90. Several reference genes were found to have stable expression in these samples. The combination of B2m1 and Tbp1, and Hprt1 and Tbp1 had the most stable expression in endometria and placentae, respectively. Reference genes identified as having stable expression were utilized in a larger experiment with placentae and endometria associated with foetuses of different size and sex at four GD. The average expression of B2m1 and Tbp1 mRNAs was suitable for the normalization of temporal changes in endometria, and comparison between endometria supplying foetuses of different size throughout gestation. The average expression of Hprt1 and Tbp1 mRNAs was suitable for the normalization of placental mRNA expression for comparison of temporal changes and sex differences between placentae supplying foetuses of different sex throughout gestation. This combination was suitable for the normalization of mRNA expression in placentas supplying GD30, GD60 and GD90 foetuses of different size. This study has identified reference genes with stable expression in placentae and endometria across multiple gestational days, in tissues associated with foetuses of different size and sex. The results of these experiments highlight the importance of selecting appropriate reference genes for the biological comparison under investigation.

Outcomes of a low birth weight phenotype on piglet gut microbial composition and intestinal transcriptomic profile

Decades of selection for increased litter size has caused a proportion of sows to consistently produce low birth weight (LBW) litters resulting in economic loss for producers due to reduced piglet survivability and growth. We hypothesized that piglets from LBW litters would have altered gut microbial composition, intestinal architecture, and intestinal transcriptomic profiles compared with piglets from high birth weight (HBW) litters. Sows were designated LBW (n = 45) or HBW (n = 46) based on litter birth weights of three successive parities. LBW piglets were 22% lighter (P < 0.001) at birth; however, no longer differed (P > 0.05) in weight at weaning compared with HBW piglets. LBW piglets had reduced (P < 0.05) fecal microbial diversity with a 114% increase in fecal Enterobacteriaceae (P < 0.05), as well as reduced (P < 0.05) abundance of cecal Roseburia and Faecalibacterium, fiber-degrading butyrate producers. Several genes associated with metabolic (PER2, CES1, KLHL38, and HK2) and immune pathways (IL-1B, IRF8, and TNIP3) were differentially expressed, suggesting altered metabolic and immune function in LBW piglets. In conclusion, LBW piglets had potentially unfavorable shifts in microbial structure in comparison to HBW piglets accompanied with alterations in metabolic and immune gene expression. Results indicate some biological consequences linking LBW phenotype to changes in production efficiency later in life.

Association of foetal size and sex with porcine foeto-maternal interface integrin expression

Integrins regulate adhesion at the foeto-maternal interface by interacting with secreted phosphoprotein 1 (SPP1) and fibronectin (FN). It is hypothesised that impaired foetal growth of ‘runt’ piglets is linked to altered integrin signalling at the foeto-maternal interface. Placental and endometrial samples associated with the lightest and closest to mean litter weight (CTMLW) (gestational day (GD18, 30, 45, 60 and 90), of both sex (GD30, 45, 60 and 90) (n = 5–8 litters/GD), Large White × Landrace conceptuses or foetuses were obtained. The mRNA expression of the integrin subunits (ITG) ITGA2, ITGAV, ITGB1, ITGB3, ITGB5, ITGB6, ITGB8, SPP1 and FN was quantified by qPCR. Temporal changes in mRNA expression were observed, with different profiles in the two tissues. Endometrial ITGB1 (P ≤ 0.05, GD45) and SPP1 (P ≤ 0.05, all GD combined and GD60) expression was decreased in samples supplying the lightest compared to the CTMLW foetuses. Placentas supplying female foetuses had decreased expression of ITGB6 (GD45, P ≤ 0.05) and FN (GD90, P ≤ 0.05) compared to those supplying male foetuses. Endometrial samples supplying females had increased ITGB3 (P ≤ 0.05, GD60) and FN (P ≤ 0.05, GD30) expression and decreased SPP1 (P ≤ 0.05, GD60) expression compared to male foetuses. Correlations between mean within-gilt mRNA expression and percentage prenatal survival, number of live foetuses or conceptuses and percentage male foetuses were observed. This study has highlighted novel and dynamic associations between foetal size, sex and integrin subunit mRNA expression at the porcine foeto-maternal interface. Further studies should be performed to improve the understanding of the mechanisms behind these novel findings.