A review of the amino acid metabolism in placental function response to fetal loss and low birth weight in pigs

Maternal Supplementation with Ornithine Promotes Placental Angiogenesis and Improves Intestinal Development of Suckling Piglets

The blood vessels of the placenta are crucial for fetal growth. Here, lower vessel density and ornithine (Orn) content were observed in placentae for low-birth-weight fetuses versus normal-birth-weight fetuses at day 75 of gestation. Furthermore, the Orn content in placentae decreased from day 75 to 110 of gestation. To investigate the role of Orn in placental angiogenesis, 48 gilts (Bama pig) were allocated into four groups. The gilts in the control group were fed a basal diet (CON group), while those in the experimental groups were fed a basal diet supplemented with 0.05% Orn (0.05% Orn group), 0.10% Orn (0.10% Orn group), and 0.15% Orn (0.15% Orn group), respectively. The results showed that 0.15% Orn and 0.10% Orn groups exhibited increased birth weight of piglets compared with the CON group. Moreover, the 0.15% Orn group was higher than the CON group in the blood vessel densities of placenta. Mechanistically, Orn facilitated placental angiogenesis by regulating vascular endothelial growth factor-A (VEGF-A). Furthermore, maternal supplementation with 0.15% Orn during gestation increased the jejunal and ileal villi height and the concentrations of colonic propionate and butyrate in suckling piglets. Collectively, these results showed that maternal supplementation with Orn promotes placental angiogenesis and improves intestinal development of suckling piglets.

KLF4 down-regulation underlies placental angiogenesis impairment induced by maternal glucose intolerance in late pregnancy

Maternal glucose intolerance in late pregnancy can easily impair pregnancy outcomes and placental development. The impairment of placental angiogenesis is closely related to the occurrence of glucose intolerance during pregnancy, but the mechanism remains largely unknown. In this study, the pregnant mouse model of maternal high-fat diet and endothelial injury model of porcine vascular endothelial cells (PVECs) was used to investigate the effect of glucose intolerance on pregnancy outcomes and placental development. Feeding pregnant mice, a high-fat diet was shown to induce glucose intolerance in late pregnancy, and significantly increase the incidence of resorbed fetuses. Moreover, a decrease was observed in the proportion of blood sinusoids area and the expression level of CD31 in placenta, indicating that placental vascular development was impaired by high-fat diet. Considering that hyperglycemia is an important symptom of glucose intolerance, we exposed PVECs to high glucose (50 mM), which verified the negative effects of high glucose on endothelial function. Bioinformatics analysis further emphasized that high glucose exposure could significantly affect the angiogenesis-related functions of PVECs and predicted that Krüppel-like factor 4 (KLF4) may be a key mediator of these functional changes. The subsequent regulation of KLF4 expression confirmed that the inhibition of KLF4 expression was an important reason why high glucose impaired the endothelial function and angiogenesis of PVECs. These results indicate that high-fat diet can aggravate maternal glucose intolerance and damage pregnancy outcome and placental angiogenesis, and that regulating the expression of KLF4 may be a potential therapeutic strategy for maintaining normal placental angiogenesis.

Retinoic Acid-PPARα Mediates β-Carotene Resistance to Placental Dysfunction Induced by Deoxynivalenol

Deoxynivalenol (DON), one of the most polluted mycotoxins in the environment and food, has been proven to have strong embryonic and reproductive toxicities. However, the effects of DON on placental impairment and effective interventions are still unclear. This study investigated the effect of β-carotene on placental functional impairment and its underlying molecular mechanism under DON exposure. Adverse pregnancy outcomes were caused by intraperitoneal injection of DON from 13.5 to 15.5 days of gestation in mice, resulting in higher enrichment of DON in placenta than in other tissue samples. Interestingly, 0.1% β-carotene dietary supplementation could significantly alleviate DON-induced pregnancy outcomes. Additionally, in vivo and in vitro placental barrier models demonstrated the association of DON-induced placental function impairment with placental permeability barrier disruption, angiogenesis impairment, and oxidative stress induction. Moreover, β-carotene regulated DON-induced placental toxicity by activating the expressions of claudin 1, zonula occludens-1, and vascular endothelial growth factor-A through retinoic acid-peroxisome proliferator-activated receptor α signaling.

Evaluating the Effect of Gestational Exposure to Perfluorohexane Sulfonate on Placental Development in Mice Combining Alternative Splicing and Gene Expression Analyses

BACKGROUND

Perfluorohexane sulfonate (PFHxS) is a frequently detected per- and polyfluoroalkyl substance in most populations, including in individuals who are pregnant, a period critical for early life development. Despite epidemiological evidence of exposure, developmental toxicity, particularly at realistic human exposures, remains understudied.

OBJECTIVES

We evaluated the effect of gestational exposure to human-relevant body burden of PFHxS on fetal and placental development and explored mechanisms of action combining alternative splicing (AS) and gene expression (GE) analyses.

METHODS

Pregnant ICR mice were exposed to 0, 0.03, and 0.3 μ g / kg / day  from gestational day 7 to day 17 via oral gavage. Upon euthanasia, PFHxS distribution was measured using liquid chromatography-tandem mass spectrometry. Maternal and fetal phenotypes were recorded, and histopathology was examined for placenta impairment. Multiomics was adopted by combining AS and GE analyses to unveil disruptions in mRNA quality and quantity. The key metabolite transporters were validated by quantitative real-time PCR (qRT-PCR) for quantification and three-dimensional (3D) structural simulation by AlphaFold2. Targeted metabolomics based on liquid chromatography-tandem mass spectrometry was used to detect amino acid and amides levels in the placenta.

RESULTS

Pups developmentally exposed to PFHxS exhibited signs of intrauterine growth restriction (IUGR), characterized by smaller fetal weight and body length (p < 0.01 ) compared to control mice. PFHxS concentration in maternal plasma was 5.01 ± 0.54  ng / mL . PFHxS trans-placenta distribution suggested dose-dependent transfer through placental barrier. Histopathology of placenta of exposed dams showed placental dysplasia, manifested with an attenuated labyrinthine layer area and deescalated blood sinus counts and placental vascular development index marker CD34. Combined GE and AS analyses pinpointed differences in genes associated with key biological processes of placental development, proliferation, metabolism, and transport in placenta of exposed dams compared to that of control dams. Further detection of placental key transporter gene expression, protein structure simulation, and amino acid and amide metabolites levels suggested that PFHxS exposure during pregnancy led to impairment of placental amino acid transportation.

DISCUSSION

The findings from this study suggest that exposure to human-relevant very-low-dose PFHxS during pregnancy in mice caused IUGR, likely via downregulating of placental amino acid transporters, thereby impairing placental amino acid transportation, resulting in impairment of placental development. Our findings confirm epidemiological findings and call for future attention on the health risk of this persistent yet ubiquitous chemical in the early developmental stage and provide a new approach for understanding gene expression from both quantitative and qualitative omics approaches in toxicological studies. https://doi.org/10.1289/EHP13217.

Exploring characteristics of placental transcriptome and cord serum metabolome associated with low birth weight in Kele pigs

The neonate with low birth weight (LBW) resulted from intrauterine growth retardation (IUGR) exists a substantial risk of postpartum death. Placental insufficiency is responsible for inadequate fetal growth; however, the pathological mechanisms of placental dysfunction-induced IUGR in pigs remain unclear. In this study, the characteristics of placental morphology, placental transcriptome, and cord serum metabolome were explored between the Kele piglets with LBW and the ones with normal birth weight (NBW). Results showed that LBW was a common occurrence in Kele piglets. The LBW placentas showed inferior villus development and lower villi density compared to NBW placentas. There were 1024 differentially expressed genes (DEGs) identified by transcriptome analysis between the LBW and NBW placentas, of which 218 and 806 genes were up- and down-regulated in the LBW placentas, respectively. PPI network analysis showed that ITGB2, CD4, IL6, ITGB3, LCK, RAC2, CD8A, JAK3, TYROBP, and CXCR4 were hub genes in all DEGs. From GO and KEGG enrichment analysis, DEGs were primarily enriched in immunological response, cell adhesion, immune response, cytokine-cytokine receptor interaction, and PI3K-Akt signaling pathway. By using metabolomic analysis, a total of 115 differential metabolites in the cord serum of LBW and NBW piglets were found, mostly linked to amino acid metabolism and sphingolipid metabolism. In comparison to NBW piglets, LBW piglets had lower levels of arginine, isoleucine, and aspartic acid in the cord. Taken together, these data revealed dysplasia of the placental villus, insufficient supply of nutrients, and abnormal immune function of the placenta may be associated with the occurrence and development of LBW in Kele pigs.

Embryonic signals mediate extracellular vesicle biogenesis and trafficking at the embryo-maternal interface

BACKGROUND

Extracellular vesicles (EVs) are membrane-coated nanoparticles secreted by almost all cell types in living organisms. EVs, as paracrine mediators, are involved in intercellular communication, immune response, and several reproductive events, including the maintenance of pregnancy. Using a domestic animal model (Sus scrofa) with an epitheliochorial, superficial type of placentation, we focused on EV biogenesis pathway at the embryo-maternal interface, when the embryonic signaling occurs for maternal recognition and the maintenance of pregnancy.

RESULTS

Transmission electron microscopy was used during early pregnancy to visualize EVs and apocrine and/or merocrine pathways of secretion. Immunofluorescent staining localized proteins responsible for EV biogenesis and cell polarization at the embryo-maternal interface. The expression profiles of genes involved in biogenesis and the secretion of EVs pointed to the possible modulation of endometrial expression by embryonic signals. Further in vitro studies showed that factors of embryonic origin can regulate the expression of the ESCRT-II complex and EV trafficking within endometrial luminal epithelial cells. Moreover, miRNA-mediated rapid negative regulation of gene expression was abolished by delivered embryonic signals.

CONCLUSIONS

Our findings demonstrated that embryonic signals are potent modulators of ESCRT-dependent EV-mediated secretory activity of the endometrium during the critical stages of early pregnancy. Video Abstract.

Placental Malfunction, Fetal Survival and Development Caused by Sow Metabolic Disorder: The Impact of Maternal Oxidative Stress

The energy and metabolic state of sows will alter considerably over different phases of gestation. Maternal metabolism increases dramatically, particularly in late pregnancy. This is accompanied by the development of an increase in oxidative stress, which has a considerable negative effect on the maternal and the placenta. As the only link between the maternal and the fetus, the placenta is critical for the maternal to deliver nutrients to the fetus and for the fetus' survival and development. This review aimed to clarify the changes in energy and metabolism in sows during different pregnancy periods, as well as the impact of maternal oxidative stress on the placenta, which affects the fetus' survival and development.

Dietary adenosine supplementation improves placental angiogenesis in IUGR piglets by up-regulating adenosine A2a receptor

Abnormal placental angiogenesis is associated with the occurrence of intrauterine growth restriction (IUGR) in piglets, and effective treatment strategies against this occurrence remain to be explored. Adenosine has been reported to play an important role in angiogenesis, but its role in placental angiogenesis is still unknown. Here, we investigated the effect of dietary adenosine supplementation on IUGR occurrence in piglets by analyzing the role of adenosine in placental angiogenesis for Normal and IUGR piglets. Specifically, 88 sows were allotted to 2 treatments (n = 44) and fed a basal diet supplemented with 0% or 0.1% of adenosine from day 65 of gestation until farrowing, followed by collecting the placental samples of Normal and IUGR piglets, and recording their characteristics. The results showed that adenosine supplementation increased the mean birth weight of piglets (P < 0.05) and placental efficiency (P < 0.05), while decreasing the IUGR piglet rate (P < 0.05). Expectedly, the placenta for IUGR neonates showed a down-regulated vascular density (P < 0.05) and angiogenesis as evidenced by the expression level of vascular cell adhesion molecule-1 (VCAM1) (P < 0.05). Notably, dietary adenosine supplementation promoted angiogenesis (P < 0.05) both in the Normal and IUGR placenta. More importantly, the expression level of adenosine A2a receptor (ADORA2A) was lower (P < 0.05) in the IUGR placenta than in Normal placenta, whereas adenosine treatment could significantly increase ADORA2A expression, and also had an interaction effect between factors IUGR and Ado. Collectively, placentae for IUGR piglets showed impaired angiogenesis and down-regulated expression level of ADORA2A, while dietary adenosine supplementation could activate ADORA2A expression, improve the placental angiogenesis, and ultimately decrease the occurrence of IUGR in piglets.

Effects of dietary supplementation of gestating sows with adenosine 5 '-monophosphate or adenosine on placental angiogenesis and vitality of their offspring

Our previous study found that dietary nucleotide supplementation, including adenosine 5 '-monophosphate (AMP), could increase AMP content in sow milk and promote piglet growth, but its effects on placental efficiency and piglet vitality remains unknown. This experiment aimed to investigate the effects of dietary AMP or its metabolite adenosine (ADO) supplementation on sow reproductive performance and placental angiogenesis. A total of 135 sows with a similar farrowing time were blocked by backfat and body weight (BW) at day 65 of gestation, and assigned to 1 of 3 dietary treatment groups (n = 45 per treatment): basal diet, basal diet supplemented with 0.1% AMP, or 0.1% ADO, respectively. Placental analysis and the characteristics of sows and piglets unveiled that compared with control (CON) group, AMP or ADO supplementation could improve sow placental efficiency (P<0.05) and newborn piglet vitality (P<0.05), increase piglet birth weight (P<0.05), and reduce stillbirth rate (P<0.05). More importantly, AMP or ADO supplementation could increase the contents of AMP, ADO, and their metabolites in placentae (P<0.05). Meanwhile, AMP or ADO supplementation could also increase placental vascular density (P<0.05) and the expression of vascular endothelial growth factor A (P<0.05), as well as promote the migration and tube formation of porcine iliac artery endothelial cells (P<0.05). Overall, maternal dietary AMP or ADO supplementation could increase their contents in the placenta, thereby improving placental angiogenesis and neonatal piglet vitality.

Gut microbiome-produced metabolites in pigs: a review on their biological functions and the influence of probiotics

The gastrointestinal tract is a complex ecosystem that contains a large number of microorganisms with different metabolic capacities. Modulation of the gut microbiome can improve the growth and promote health in pigs. Crosstalk between the host, diet, and the gut microbiome can influence the health of the host, potentially through the production of several metabolites with various functions. Short-chain and branched-chain fatty acids, secondary bile acids, polyamines, indoles, and phenolic compounds are metabolites produced by the gut microbiome. The gut microbiome can also produce neurotransmitters (such as γ-aminobutyric acid, catecholamines, and serotonin), their precursors, and vitamins. Several studies in pigs have demonstrated the importance of the gut microbiome and its metabolites in improving growth performance and feed efficiency, alleviating stress, and providing protection from pathogens. The use of probiotics is one of the strategies employed to target the gut microbiome of pigs. Promising results have been published on the use of probiotics in optimizing pig production. This review focuses on the role of gut microbiome-derived metabolites in the performance of pigs and the effects of probiotics on altering the levels of these metabolites.