Plasma metabolites are altered before and after diagnosis of preeclampsia or fetal growth restriction.

Metabolomics is the study of small molecules (metabolites), within cells, tissues and biofluids. Maternal metabolites can provide important insight into the health and development of both mother and fetus throughout pregnancy. This study assessed metabolic profiles in the maternal circulation prior to and at the time of diagnosis of preeclampsia and fetal growth restriction. Maternal plasma samples were collected from two independent cohorts: (1) Established disease cohort: 50 participants diagnosed with early-onset preeclampsia (< 34 weeks' gestation), 14 with early-onset fetal growth restriction, and 25 gestation-matched controls. (2) Prospective cohort, collected at 36 weeks' gestation before diagnosis: 17 participants later developed preeclampsia, 49 delivered infants with fetal growth restriction (birthweight < 5th centile), and 72 randomly selected controls. Metabolic evaluation was performed by Metabolomics Australia on the Agilent 6545 QTOF Mass Spectrometer. In the established disease cohort, 77 metabolites were altered in circulation from participants with preeclampsia - increased L-cysteine (3.73-fold), L-cystine (3.28-fold), L-acetylcarnitine (2.57-fold), and carnitine (1.53-fold) (p < 0.05). There were 53 metabolites dysregulated in participants who delivered a fetal growth restriction infant-including increased levulinic acid, citric acid (1.93-fold), and creatine (1.14-fold) (p < 0.05). In the prospective cohort, 30 metabolites were altered in participants who later developed preeclampsia at term - reduced glutaric acid (0.85-fold), porphobilinogen (0.77-fold) and amininohippuric acid (0.82-fold) (p < 0.05) was observed. There were 5 metabolites altered in participants who later delivered a fetal growth restriction infant - including reduced 3-methoxybenzenepropanoic acid (p < 0.05). Downstream pathway analysis revealed aminoacyl-tRNA biosynthesis to be most significantly altered in the established cohort in preeclampsia (13/48 hits, p < 0.001) and fetal growth restriction (7/48 hits, p < 0.001). The predictive cohort showed no significant pathway alterations. This study observed altered metabolites in maternal plasma collected before and after diagnosis of a preeclampsia or fetal growth restriction. While a significant number of metabolites were altered with established disease, few changes were observed in the predictive cohort. Thus, metabolites measured in this study may not be useful as predictors of preeclampsia or fetal growth restriction.

Trophoblast Side-Population Markers are Dysregulated in Preeclampsia and Fetal Growth Restriction.

Dysregulated progenitor cell populations may contribute to poor placental development and placental insufficiency pathogenesis. Side-population cells possess progenitor properties. Recent human trophoblast side-population isolation identified enrichment of 8 specific genes (CXCL8, ELL2, GATA6, HK2, HLA-DPB1, INTS6, SERPINE3 and UPP1) (Gamage et al. 2020, Stem Cell Rev Rep). We characterised these trophoblast side-population markers in human placenta and in placental insufficiency disorders: preeclampsia and fetal growth restriction (FGR). Trophoblast side-population markers localised to mononuclear trophoblasts lining the placental villous basement membrane in preterm control, preeclamptic and FGR placental sections (n = 3, panel of 3 markers/serial section). Analysis of single-cell transcriptomics of an organoid human trophoblast stem cell (hTSC) to extravillous trophoblast (EVT) differentiation model (Shannon et al. 2022, Development) identified that all side-population genes were enriched in mononuclear trophoblast and trophoblasts committed to differentiation under hTSC culture conditions. In vitro validation via 96 h time course hTSC differentiation to EVTs or syncytiotrophoblasts (n = 5) demonstrated ELL2 and HK2 increased with differentiation (p < 0.0024, p < 0.0039 respectively). CXCL8 and HLA-DPB1 were downregulated (p < 0.030, p < 0.011 respectively). GATA6 and INTS6 increased with EVT differentiation only, and UPP1 reduced with syncytialisation. SERPINE3 was undetectable. Trophoblast side-population marker mRNA was measured in human placentas (< 34-weeks' gestation; n = 78 preeclampsia, n = 30 FGR, and n = 18 gestation-matched controls). ELL2, HK2 and CXCL8 were elevated in preeclamptic (p = 0.0006, p < 0.0001, p = 0.0335 respectively) and FGR placentas (p = 0.0065, p < 0.0001, p = 0.0001 respectively) versus controls. Placental GATA6 was reduced in pregnancies with preeclampsia and FGR (p = 0.0014, p = 0.0146 respectively). Placental INTS6 was reduced with FGR only (p < 0.0001). This study identified the localisation of a unique trophoblast subset enriched for side-population markers. Aberrant expression of some side-population markers may indicate disruptions to unique trophoblast subtypes in placental insufficiency.

Cell surface associated protein mucin 15 (MUC15) is elevated in preeclampsia.

BACKGROUND: Mucins are a family of proteins that protect the epithelium. A particular type of mucin, MUC15 is highly expressed in the placenta. This study aimed to characterise MUC15 in preeclampsia and investigate its role in placental stem cell biology. METHODS: MUC15 mRNA and protein were measured in placentas from patients with early onset (<34 weeks' gestation) preeclampsia. Circulating serum MUC15 was measured via ELISA. MUC15 was localised in the placenta using in situ hybridisation. MUC15 mRNA expression was measured across differentiation of human trophoblast stem cells (hTSCs) to syncytiotrophoblast and extravillous trophoblasts. MUC15 was measured after syncytialised hTSCs were cultured in hypoxic (1% O2) and proinflammatory (TNF α, IL-6) conditions. MUC15 secretion was assessed when syncytialised hTSCs were treated with brefeldin A (impairs protein trafficking) and batimastat (inhibits matrix metalloproteinases). RESULTS: MUC15 protein was significantly increased in the placenta (P = 0.0003, n = 32 vs n = 20 controls) and serum (P = 0.016, n = 32 vs n = 22 controls) of patients with preeclampsia, whilst MUC15 mRNA remained unchanged (n = 61 vs n = 18 controls). MUC15 mRNA (P = 0.005) and protein secretion (P = 0.006) increased following differentiation to syncytiotrophoblast cells. In situ hybridisation confirmed MUC15 localised to the syncytiotrophoblast cell within the placenta. Neither hypoxic or inflammatory conditions changed MUC15 mRNA expression or secretion. Brefeldin A treated hTSCs did not alter MUC15 secretion, whilst batimastat reduced MUC15 secretion (P = 0.044). CONCLUSIONS: MUC15 is increased in early onset preeclampsia and is cleaved by matrix metalloproteinases. Increased MUC15 may reflect a protective mechanism associated with placental dysfunction. Further research will aid in confirming this.

Paternal Expressed Gene 10 (PEG10) is decreased in early-onset preeclampsia.

BACKGROUND: Preeclampsia is a severe complication of pregnancy which is attributed to placental dysfunction. The retrotransposon, Paternal Expressed Gene 10 (PEG10) harbours critical placental functions pertaining to placental trophoblast cells. Limited evidence exists on whether PEG10 is involved in preeclampsia pathogenesis. This study characterised the expression and regulation of PEG10 in placentas from patients with early-onset preeclampsia compared to gestation-matched controls. METHODS: PEG10 expression was measured in plasma and placentas collected from patients with early-onset preeclampsia (< 34 weeks') and gestation-matched controls using ELISA (protein) and RT-qPCR (mRNA). First-trimester human trophoblast stem cells (hTSCs) were used for in vitro studies. PEG10 expression was measured during hTSC differentiation and hTSC exposure to hypoxia (1% O2) and inflammatory cytokines (IL-6 and TNFα) using RT-qPCR. Functional studies used PEG10 siRNA to measure the effect of reduced PEG10 on canonical TGF-[Formula: see text] signalling and proliferation using luciferase and xCELLigence assays, respectively. RESULTS: PEG10 mRNA expression was significantly reduced in placentas from patients with early-onset preeclampsia (< 34 weeks' gestation) relative to controls (p = 0.04, n = 78 vs n = 18 controls). PEG10 protein expression was also reduced in preeclamptic placentas (p = 0.03, n = 5 vs n = 5 controls, blinded assessment of immunohistochemical staining), but neither PEG10 mRNA nor protein could be detected in maternal circulation. PEG10 was most highly expressed in hTSCs, and its expression was reduced as hTSCs differentiated into syncytiotrophoblasts (p < 0.0001) and extravillous trophoblasts (p < 0.001). Trophoblast differentiation was not altered when hTSCs were treated with PEG10 siRNA (n = 5 vs n = 5 controls). PEG10 was significantly reduced in hTSCs exposed to hypoxia (p < 0.01). PEG10 was also reduced in hTSCs treated with the inflammatory cytokine TNF [Formula: see text] (p < 0.01), but not IL-6. PEG10 knocked down (siRNA) in hTSCs showed reduced activation of the canonical TGF-ß signalling effector, the SMAD binding element (p < 0.05) relative to controls. PEG10 knockdown in hTSCs however was not associated with any significant alterations in proliferation. CONCLUSIONS: Placental PEG10 is reduced in patients with early-onset preeclampsia. In vitro studies suggest that hypoxia and inflammation may contribute to PEG10 downregulation. Reduced PEG10 alters canonical TGF-[Formula: see text] signalling, and thus may be involved in trophoblast dysfunction associated with this pathway.

Plasma lipids are dysregulated preceding diagnosis of preeclampsia or delivery of a growth restricted infant.

BACKGROUND: Lipids serve as multifunctional metabolites that have important implications for the pregnant mother and developing fetus. Abnormalities in lipids have emerged as potential risk factors for pregnancy diseases, such as preeclampsia and fetal growth restriction. The aim of this study was to assess the potential of lipid metabolites for detection of late-onset preeclampsia and fetal growth restriction. METHODS: We used a case-cohort of 144 maternal plasma samples at 36 weeks' gestation from patients before the diagnosis of late-onset preeclampsia (n = 22), delivery of a fetal growth restricted infant (n = 55, defined as <5th birthweight centile), gestation-matched controls (n = 72). We performed liquid chromatography-tandem mass spectrometry (LC-QQQ) -based targeted lipidomics to identify 421 lipids, and fitted logistic regression models for each lipid, correcting for maternal age, BMI, smoking, and gestational diabetes. FINDINGS: Phosphatidylinositol 32:1 (AUC = 0.81) and cholesterol ester 17:1 (AUC = 0.71) best predicted the risk of developing preeclampsia or delivering a fetal growth restricted infant, respectively. Five times repeated five-fold cross validation demonstrated the lipids alone did not out-perform existing protein biomarkers, soluble tyrosine kinase-1 (sFlt-1) and placental growth factor (PlGF) for the prediction of preeclampsia or fetal growth restriction. However, lipids combined with sFlt-1 and PlGF measurements improved disease prediction. INTERPRETATION: This study successfully identified 421 lipids in maternal plasma collected at 36 weeks' gestation from participants who later developed preeclampsia or delivered a fetal growth restricted infant. Our results suggest the predictive capacity of lipid measurements for gestational disorders holds the potential to improve non-invasive assessment of maternal and fetal health. FUNDING: This study was funded by a grant from National Health and Medical Research Council.

Circulating Chemerin Is Elevated in Women With Preeclampsia.

BACKGROUND: Preeclampsia is a severe complication of pregnancy. Chemerin is an adipokine secreted from adipose tissue and highly expressed in placenta. This study evaluated the biomarker potential of circulating chemerin to predict preeclampsia. METHODS: Maternal plasma and placenta were collected from women with early-onset preeclampsia (<34 weeks), with preeclampsia and eclampsia, or before preeclampsia diagnosis (36 weeks). Human trophoblast stem cells were differentiated into syncytiotrophoblast or extravillous trophoblasts across 96 hours. Cells were cultured in 1% O2 (hypoxia) or 5% O2 (normoxia). Chemerin was measured by enzyme-linked immunosorbent assay (ELISA) and RARRES2 (gene coding chemerin) by reverse transcription-quantitative polymerase chain reaction. RESULTS: Circulating chemerin was increased in 46 women with early-onset preeclampsia (<34 weeks) compared to 17 controls (P < .0006). Chemerin was increased in placenta from 43 women with early-onset preeclampsia compared to 24 controls (P < .0001). RARRES2 was reduced in placenta from 43 women with early-onset preeclampsia vs 24 controls (P < .0001). Chemerin was increased in plasma from 26 women with established preeclampsia (P = .006), vs 15 controls. Circulating chemerin was increased in 23 women who later developed preeclampsia vs 182 who did not (P = 3.23 × 10-6). RARRES2 was reduced in syncytiotrophoblast (P = .005) or extravillous trophoblasts (P < .0001). Hypoxia increased RARRES2 expression in syncytiotrophoblast (P = .01) but not cytotrophoblast cells. CONCLUSIONS: Circulating chemerin was elevated in women with early-onset preeclampsia, established preeclampsia, and preceding preeclampsia diagnosis of preeclampsia. RARRES2 was dysregulated in placenta complicated by preeclampsia and may be regulated through hypoxia. Chemerin may have potential as a biomarker for preeclampsia but would need to be combined with other biomarkers.

Placental galectin-3 is reduced in early-onset preeclampsia.

Preeclampsia is a disease of pregnancy responsible for significant maternal and neonatal mortality. Galectin-3 is a ß-Galactoside binding protein. This study aimed to characterise galectin-3 in women with preeclampsia and human trophoblast stem cells (hTSCs). Galectin-3 was measured in placental lysates and plasma collected from patients with early-onset preeclampsia (delivered <34 weeks' gestation) and gestation matched controls. Placental galectin-3 protein was significantly reduced in 43 women with early-onset preeclampsia compared to 21 controls. mRNA expression of LGALS3 (galectin-3 encoding gene) was reduced in 29 women with early-onset preeclampsia, compared to 18 controls (p = 0.009). There was no significant difference in plasma galectin-3 protein in 46 women with early-onset preeclampsia compared to 20 controls. In a separate cohort of samples collected at 36 weeks' gestation, circulating galectin-3 was not altered in 23 women who later developed preeclampsia, versus 182 who did not. In syncytialised hTSCs, hypoxia increased mRNA expression of LGALS3 (p = 0.01). Treatment with inflammatory cytokines (TNF-α and IL-6) had no effect on LGALS3 mRNA expression. However, TNF-α treatment caused an increase in mRNA expression of LGALS3BP (galectin-3 binding protein encoding gene) in hTSCs (p = 0.03). This study showed a reduction of galectin-3 in placenta from pregnancies complicated by early-onset preeclampsia. LGALS3 mRNA expression was dysregulated by hypoxia exposure in placental stem cells.

Transcriptional profiles of genes related to mitochondrial aging in placental pathologies.

As the placenta develops across gestation, the mitochondria and other organelles like the endoplasmic reticulum (ER) must continue to adapt to stressors such as oxidative stress. As pregnancy approaches term, these stressors may contribute to placental aging, including mitochondrial changes leading to cellular senescence. When these processes are exacerbated, pregnancy pathologies arise. This study aimed to identify correlations between genes related to mitochondria, ER and cellular senescence in placentae complicated by pregnancy complications. Placental samples from pregnancies classified as preterm, term, post-term, preterm with foetal growth restriction (FGR), preterm with preeclampsia (PE) and preterm with PE and FGR were used to measure gene expression of TOMM20, MFN1, TFAM, MFN2, PARK2, PINK1, EIF2AK3, TP53 and ERN1. MetaboAnalyst 5.0 was used to generate heatmaps, principal component analysis plots, correlation graphs and receiver operating characteristic analysis. This study found that genes-related mitochondrial dynamics and aging undergo changes in placentae affected by pregnancy pathologies. The TOMM20/PARK2 ratio may be a promising marker to discriminate between healthy and unhealthy placental tissue. Future studies should explore circulating biomarkers of mitochondrial aging and dysfunction as indicators of placental health.

The effect of gestational age on mitochondrial properties of the mouse placenta.

Mitochondria are organelles within the cell that generate energy, which is essential to the developing placenta. As the placenta approaches term, organelles such as mitochondria and the endoplasmic reticulum adapt to cellular stressors (e.g. oxidative stress and fluctuations in oxygen concentration) which are likely to result in the progressive decline of tissue function, known as placental ageing. This ageing phenotype may induce cellular senescence, a process whereby the cell is no longer proliferating, yet remains metabolically active. Mitochondria, endoplasmic reticulum and senescent processes are still poorly understood in the developing placenta. Therefore, a rodent ontogeny model was used to measure genes and proteins involved in mitochondrial biogenesis, antioxidant function, electron transport chain, mitophagy, dynamics and unfolded protein response in the placenta. CD-1 mouse placental samples were collected at embryonic day (E)12.5, E14.5, E16.5 and E18.5 of pregnancy for gene and protein analysis via qPCR, protein assays and Western blotting. Mitochondrial content, SDHB (complex II) and MFN2 (mitochondrial fusion) proteins were all increased throughout pregnancy, while citrate synthase activity/mitochondrial content, Tfam, Sirt3, Mfn1, TOMM20 (mitochondrial biogenesis and dynamics); Tp53(senescence); Eif2ak3, Eif4g1(endoplasmic reticulum stress);NDUFB8, UQCRC2, ATP5A (electron transport chain sub-complexes) were decreased at E18.5, compared to E12.5. Overall, mitochondria undergo changes in response to gestational progression and pathways associated with cellular ageing to facilitate adaptions in a healthy pregnancy. This data holds great promise that mitochondrial markers across pregnancy may help to establish when a placenta is ageing inappropriately. Lay summary: Human pregnancy lasts approximately 266 days. If a baby is born early, organs may be poorly formed but if pregnancy continues past this time, stillbirth risk is increased. Gestational duration is regulated by the placenta. As the placenta approaches the end of pregnancy, it displays properties similar to tissues from aged individuals. However, it is unknown how this placental ageing contributes to pregnancy duration. This study characterised normal placental ageing by measuring properties of mitochondria in healthy placentas collected at four different gestational ages ranging from 7 days before birth to 1 day before birth of the 19-day mouse pregnancy. We found that mitochondrial number increased per cell but that a marker of mitochondrial function was reduced. Proteins that control mitochondrial number, morphology and function also changed over time. This work lays the platform to understand how placental ageing contributes to adverse pregnancy outcomes related to altered pregnancy duration.

Analysis of mitochondrial regulatory transcripts in publicly available datasets with validation in placentae from pre-term, post-term and fetal growth restriction pregnancies.

INTRODUCTION: The human placenta has a defined lifespan and placental aging is a key feature as pregnancy progresses. Placental aging and mitochondrial dysfunction are known to play a key role in pregnancy pathophysiology. Premature aging of the placenta has also been linked with placental dysfunction resulting in poor fetal development and premature birth. METHODS: The expression of key mitochondrial-related genes were analysed in a series of publicly available databases then expression changes were validated in placental samples collected from term, pre-term, post-term pregnancies and pregnancies complicated by fetal growth restriction (FGR). Gene and protein expression levels of MFN1, MFN2, TFAM, TOMM20, OPA3 and SIRT4 were measured in placental tissues via qPCR and western blotting. RESULTS: Initial analysis found that key mitochondrial transcripts related to biogenesis, bioenergetics and mitophagy clustered by pregnancy trimester. A refined list of 13 mitochondrial-related genes were investigated in additional external datasets of pregnancy complications. In the new cohort, protein expression of MFN1 was decreased in FGR and MFN2 is decreased in post-term placenta. Analysis of placental tissues revealed that TOMM20 gene and protein expression was altered in FGR and post-term placenta. DISCUSSION: MFN1 and MFN2 play a major role in mitochondrial dynamics, and alterations in these markers have been highlighted in early unexplained miscarriage. TOMM20 is an importer protein that plays a major role in mitophagy and changes have also been identified in age-related diseases. Significant changes in MFN1, MFN2 and TOMM20 indicate that mitochondrial regulators play a critical role in placental aging and placental pathophysiology.

Maternal selenium deficiency in mice promotes sex-specific changes to urine flow and renal expression of mitochondrial proteins in adult offspring.

Selenium deficiency during pregnancy can impair fetal development and predispose offspring to thyroid dysfunction. Given that key selenoproteins are highly expressed in the kidney and that poor thyroid health can lead to kidney disease, it is likely that kidney function may be impaired in offspring of selenium-deficient mothers. This study utilized a mouse model of maternal selenium deficiency to investigate kidney protein glycation, mitochondrial adaptations, and urinary excretion in offspring. Female C57BL/6 mice were fed control (>190 µg selenium/kg) or low selenium (<50 µg selenium/kg) diets four weeks prior to mating, throughout gestation, and lactation. At postnatal day (PN) 170, offspring were placed in metabolic cages for 24 hr prior to tissue collection at PN180. Maternal selenium deficiency did not impact selenoprotein antioxidant activity, but increased advanced glycation end products in female kidneys. Male offspring had reduced renal Complex II and Complex IV protein levels and lower 24 hr urine flow. Although renal aquaporin 2 (Aqp2) and arginine vasopressin receptor 2 (Avpr2) mRNA were not altered by maternal selenium deficiency, a correlation between urine flow and plasma free T4 concentrations in male but not female offspring suggests that programed thyroid dysfunction may be mediating impaired urine flow. This study demonstrates that maternal selenium deficiency can lead to long-term deficits in kidney parameters that may be secondary to impaired thyroid dysfunction. Considering the significant burden of renal dysfunction as a comorbidity to metabolic diseases, improving maternal selenium intake in pregnancy may be one simple measure to prevent lifelong disease.

Mitochondrial dysfunction in placental trophoblast cells experiencing gestational diabetes mellitus.

KEY POINTS: Mitochondrial dysfunction is known to occur in diabetic phenotypes including type 1 and 2 diabetes mellitus. The incidence of gestational diabetes mellitus (GDM) is increasing and defined as the onset of a diabetic phenotype during pregnancy. The role of placental mitochondria in the aetiology of GDM remains unclear and is an emerging area of research. Differing mitochondrial morphologies within the placenta may influence the pathogenesis of the disorder. This study observed mitochondrial dysfunction in GDM placenta when assessing whole tissue. Upon further investigation into mitochondrial isolates from the cytotrophoblast and syncytiotrophoblast, mitochondrial dysfunction appears exaggerated in syncytiotrophoblast. Assessing mitochondrial populations individually enabled the determination of differences between cell lineages of the placenta and established varying levels of mitochondrial dysfunction in GDM, in some instances establishing significance in pathways previously inconclusive or confounded when assessing whole tissue. This research lays the foundation for future work into mitochondrial dysfunction in the placenta and the role it may play in the aetiology of GDM. ABSTRACT: Mitochondrial dysfunction has been associated with diabetic phenotypes, yet the involvement of placental mitochondria in gestational diabetes mellitus (GDM) remains inconclusive. This is in part complicated by the different mitochondrial subpopulations present in the two major trophoblast cell lineages of the placenta. To better elucidate the role of mitochondria in this pathology, this study examined key aspects of mitochondrial function in placentas from healthy pregnancies and those complicated by GDM in both whole tissue and isolated mitochondria. Mitochondrial content, citrate synthase activity, reactive oxygen species production and gene expression regulating metabolic, hormonal and antioxidant control was examined in placental tissue, before examining functional differences between mitochondrial isolates from cytotrophoblast (Cyto-Mito) and syncytiotrophoblast (Syncytio-Mito). Our study observed evidence of mitochondrial dysfunction across multiple pathways when assessing whole placental tissue from GDM pregnancies compared with healthy controls. Furthermore, by examining isolated mitochondria from the cytotrophoblast and syncytiotrophoblast cell lineages of the placenta we established that although both mitochondrial populations were dysfunctional, they were differentially impacted. These data highlight the need to consider changes in mitochondrial subpopulations at the feto-maternal interface when studying pregnancy pathologies.

Mitochondrial transformations in the aging human placenta.

Mitochondria play a key role in homeostasis and are central to one of the leading hypotheses of aging, the free radical theory. Mitochondria function as a reticulated network, constantly adapting to the cellular environment through fusion (joining), biogenesis (formation of new mitochondria), and fission (separation). This adaptive response is particularly important in response to oxidative stress, cellular damage, and aging, when mitochondria are selectively removed through mitophagy, a mitochondrial equivalent of autophagy. During this complex process, mitochondria influence surrounding cell biology and organelles through the release of signaling molecules. Given that the human placenta is a unique organ having a transient and somewhat defined life span of ∼280 days, any adaption or dysfunction associated with mitochondrial physiology as a result of aging will have a dramatic impact on the health and function of both the placenta and the fetus. Additionally, a defective placenta during gestation, resulting in reduced fetal growth, has been shown to influence the development of chronic disease in later life. In this review we focus on the mitochondrial adaptions and transformations that accompany gestational length and share similarities with age-related diseases. In addition, we discuss the role of such changes in regulating placental function throughout gestation, the etiology of gestational complications, and the development of chronic diseases later in life.

Maternal Selenium Deficiency in Mice Alters Offspring Glucose Metabolism and Thyroid Status in a Sexually Dimorphic Manner.

Selenium is an essential micronutrient commonly deficient in human populations. Selenium deficiency increases the risks of pregnancy complications; however, the long-term impact of selenium deficiency on offspring disease remains unclear. This study investigates the effects of selenium deficiency during pregnancy on offspring metabolic function. Female C57BL/6 mice were allocated to control (>190 µg selenium/kg, n = 8) or low selenium (<50 µg selenium/kg, n = 8) diets prior to mating and throughout gestation. At postnatal day (PN) 170, mice underwent an intraperitoneal glucose tolerance test and were culled at PN180 for biochemical analysis. Mice exposed to selenium deficiency in utero had reduced fasting blood glucose but increased postprandial blood glucose concentrations. Male offspring from selenium-deficient litters had increased plasma insulin levels in conjunction with reduced plasma thyroxine (tetraiodothyronine or T4) concentrations. Conversely, females exposed to selenium deficiency in utero exhibited increased plasma thyroxine levels with no change in plasma insulin. This study demonstrates the importance of adequate selenium intake around pregnancy for offspring metabolic health. Given the increasing prevalence of metabolic disease, this study highlights the need for appropriate micronutrient intake during pregnancy to ensure a healthy start to life.

Placental mitochondria and reactive oxygen species in the physiology and pathophysiology of pregnancy.

Mitochondria are central to cell function. The placenta forms the interface between maternal and fetal systems, and placental mitochondria have critical roles in maintaining pregnancy. The placenta is unusual in having two adjacent cell layers (cytotrophoblasts and the syncytiotrophoblast) with vastly different mitochondria that have distinct functions in health and disease. Mitochondria both produce the majority of reactive oxygen species (ROS), and are sensitive to ROS. ROS are important in allowing cells to sense their environment through mitochondrial-centred signalling, and this signalling also helps cells/tissues adapt to changing environments. However, excessive ROS are damaging, and increased ROS levels are associated with pregnancy complications, including the important disorders preeclampsia and gestational diabetes mellitus. Here we review the function of placental mitochondria in healthy pregnancy, and also in pregnancy complications. Placental mitochondria are critical to cell function, and mitochondrial damage is a feature of pregnancy complications. However, the responsiveness of mitochondria to ROS signalling may be central to placental adaptations that mitigate damage, and placental mitochondria are an attractive target for the development of therapeutics to improve pregnancy outcomes.

Maternal selenium deficiency during pregnancy in mice increases thyroid hormone concentrations, alters placental function and reduces fetal growth.

KEY POINTS: Inappropriate intake of key micronutrients in pregnancy is known to alter maternal endocrine status, impair placental development and induce fetal growth restriction. Selenium is an essential micronutrient required for the function of approximately 25 important proteins. However, the specific effects of selenium deficiency during pregnancy on maternal, placental and fetal outcomes are poorly understood. The present study demonstrates that maternal selenium deficiency increases maternal triiodothyronine and tetraiodothyronine concentrations, reduces fetal blood glucose concentrations, and induces fetal growth restriction. Placental expression of key selenium-dependent thyroid hormone converting enzymes were reduced, whereas the expression of key placental nutrient transporters was dysregulated. Selenium deficiency had minimal impact on selenium-dependent anti-oxidants but increased placental copper concentrations and expression of superoxide dismutase 1. These results highlight the idea that selenium deficiency during pregnancy may contribute to thyroid dysfunction, causing reduced fetal growth, that may precede programmed disease outcomes in offspring. ABSTRACT: Selenium is a trace element fundamental to diverse homeostatic processes, including anti-oxidant regulation and thyroid hormone metabolism. Selenium deficiency in pregnancy is common and increases the risk of pregnancy complications including fetal growth restriction. Although altered placental formation may contribute to these poor outcomes, the mechanism by which selenium deficiency contributes to complications in pregnancy is poorly understood. Female C57BL/6 mice were randomly allocated to control (>190 µg kg-1 , n = 8) or low selenium (<50 µg kg-1 , n = 8) diets 4 weeks prior to mating and throughout gestation. Pregnant mice were killed at embryonic day 18.5 followed by collection of maternal and fetal tissue. Maternal and fetal plasma thyroid hormone concentrations were analysed, as was placental expression of key selenoproteins involved in thyroid metabolism and anti-oxidant defences. Selenium deficiency increased plasma tetraiodothyronine and triiodothyronine concentrations. This was associated with a reduction in placental expression of key selenodependent deiodinases, DIO2 and DIO3. Placental expression of selenium-dependent anti-oxidants was unaffected by selenium deficiency. Selenium deficiency reduced fetal glucose concentrations, leading to reduced fetal weight. Placental glycogen content was increased within the placenta, as was Slc2a3 mRNA expression. This is the first study to demonstrate that selenium deficiency may reduce fetal weight through increased maternal thyroid hormone concentrations, impaired placental thyroid hormone metabolism and dysregulated placental nutrient transporter expression. The study suggests that the magnitude of selenium deficiency commonly reported in pregnant women may be sufficient to impair thyroid metabolism but not placental anti-oxidant concentrations.

Maternal corticosterone in the mouse alters oxidative stress markers, antioxidant function and mitochondrial content in placentas of female fetuses.

KEY POINTS: Maternal exposure to the stress hormone corticosterone is known to programme a range of sex specific disease outcomes in offspring. Sex differences in placental adaptations are thought to mediate these processes. Placental oxidative stress is implicated in a range of pregnancy disorders but the role of placental oxidative stress in sex specific disease outcomes following prenatal corticosterone exposure is unknown. This study demonstrates that maternal corticosterone reduced placental hydrogen peroxide and 8-hydroxy-2'-deoxyguanosine concentrations but increased protein carbonyl content and advanced glycation end product concentrations in placentas of female fetuses but not male fetuses. These results highlight that placentas of female fetuses respond differently to maternal corticosterone exposure, with oxidative stress a major finding in placentas of female fetuses. ABSTRACT: Maternal exposure to glucocorticoids during pregnancy increases offspring risk of developing a range of sex specific disease phenotypes. These sex specific disease outcomes are thought to be in part mediated by different placental adaptations in males and females. The placenta is a highly metabolic organ which is vulnerable to the effects of oxidative stress. In other tissues, males and females have been shown to respond differently to the pro-oxidant effects of glucocorticoids. This study therefore used a well characterized animal model of maternal corticosterone exposure to investigate sex specific alterations in reactive oxygen species production, antioxidant concentrations and mitochondrial properties that might contribute to sex differences in placental outcomes. C57BL/6 mice were implanted with osmotic minipumps containing corticosterone (33 µg kg-1  h-1 ) at embryonic day (E) 12.5 and placentas collected at E14.5 for analysis. Corticosterone exposure reduced placental hydrogen peroxide (H2 O2 ) and 8-hydroxy-2'-deoxyguanosine concentrations but increased protein carbonyl content and advanced glycation end product concentrations in placentas of female fetuses but not male fetuses. This dysregulation of different markers of oxidative stress may be due to increased placental activity of thioredoxin reductase in female but not male fetuses. Corticosterone reduced placental mitochondrial content but increased protein expression of the autophagosome cargo protein p62. This study demonstrates that placentas of female fetuses respond differently to maternal corticosterone exposure and highlights an important role of reactive oxygen species, mitochondrial adaptations and antioxidant responses in glucocorticoid induced programmed disease.