Placental, renal, and ileal sulfate transporter gene expression in mouse gestation

Obesogenic Diet in Mice Leads to Inflammation and Oxidative Stress in the Mother in Association with Sex-Specific Changes in Fetal Development, Inflammatory Markers and Placental Transcriptome

BACKGROUND

Obesity during pregnancy is related to adverse maternal and neonatal outcomes. Factors involved in these outcomes may include increased maternal insulin resistance, inflammation, oxidative stress, and nutrient mishandling. The placenta is the primary determinant of fetal outcomes, and its function can be impacted by maternal obesity. The aim of this study on mice was to determine the effect of obesity on maternal lipid handling, inflammatory and redox state, and placental oxidative stress, inflammatory signaling, and gene expression relative to female and male fetal growth.

METHODS

Female mice were fed control or obesogenic high-fat/high-sugar diet (HFHS) from 9 weeks prior to, and during, pregnancy. On day 18.5 of pregnancy, maternal plasma, and liver, placenta, and fetal serum were collected to examine the immune and redox states. The placental labyrinth zone (Lz) was dissected for RNA-sequencing analysis of gene expression changes.

RESULTS

the HFHS diet induced, in the dams, hepatic steatosis, oxidative stress (reduced catalase, elevated protein oxidation) and the activation of pro-inflammatory pathways (p38-MAPK), along with imbalanced circulating cytokine concentrations (increased IL-6 and decreased IL-5 and IL-17A). HFHS fetuses were asymmetrically growth-restricted, showing sex-specific changes in circulating cytokines (GM-CSF, TNF-α, IL-6 and IFN-γ). The morphology of the placenta Lz was modified by an HFHS diet, in association with sex-specific alterations in the expression of genes and proteins implicated in oxidative stress, inflammation, and stress signaling. Placental gene expression changes were comparable to that seen in models of intrauterine inflammation and were related to a transcriptional network involving transcription factors, LYL1 and PLAG1.

CONCLUSION

This study shows that fetal growth restriction with maternal obesity is related to elevated oxidative stress, inflammatory pathways, and sex-specific placental changes. Our data are important, given the marked consequences and the rising rates of obesity worldwide.

Sulfur-Containing Amino Acids, Hydrogen Sulfide, and Sulfur Compounds on Kidney Health and Disease

Hydrogen sulfide (H₂S) plays a decisive role in kidney health and disease. H₂S can ben synthesized via enzymatic and non-enzymatic pathways, as well as gut microbial origins. Kidney disease can originate in early life induced by various maternal insults throughout the process, namely renal programming. Sulfur-containing amino acids and sulfate are essential in normal pregnancy and fetal development. Dysregulated H₂S signaling behind renal programming is linked to deficient nitric oxide, oxidative stress, the aberrant renin-angiotensin-aldosterone system, and gut microbiota dysbiosis. In animal models of renal programming, treatment with sulfur-containing amino acids, N-acetylcysteine, H₂S donors, and organosulfur compounds during gestation and lactation could improve offspring's renal outcomes. In this review, we summarize current knowledge regarding sulfide/sulfate implicated in pregnancy and kidney development, current evidence supporting the interactions between H₂S signaling and underlying mechanisms of renal programming, and recent advances in the beneficial actions of sulfide-related interventions on the prevention of kidney disease. Modifying H₂S signaling is the novel therapeutic and preventive approach to reduce the global burden of kidney disease; however, more work is required to translate this into clinical practice.

Serum sulfate level and Slc13a1 mRNA expression remain unaltered in a mouse model of moderate vitamin D deficiency

Sulfate is essential for healthy foetal growth and neurodevelopment. The SLC13A1 sulfate transporter is primarily expressed in the kidney where it mediates sulfate reabsorption and maintains circulating sulfate levels. To meet foetal demands, maternal sulfate levels increase by twofold in pregnancy via upregulated SLC13A1 expression. Previous studies found hyposulfataemia and reduced renal Slc13a1 mRNA expression in rodent models with either severe vitamin D deficiency or perturbed vitamin D signalling. Here we investigated a mouse model of moderate vitamin D deficiency. However, serum sulfate level and renal Slc13a1 mRNA expression was not decreased by a moderate reduction in circulating vitamin D level. We confirmed that the mouse Slc13a1 5'-flanking region was upregulated by 1,25(OH)₂D₃ using luciferase assays in a cultured renal OK cell line. These results support the presence of a functional VDRE in the mouse Slc13a1 but suggests that moderate vitamin D deficiency does not impact on sulfate homeostasis. As sulfate biology is highly conserved between rodents and humans, we proposed that human SLC13A1 would be under similar transcriptional regulation by 1,25(OH)₂D₃. Using an online prediction tool we identified a putative VDRE in the SLC13A1 5'-flanking region but unlike the mouse Slc13a1 sequence, the human sequence did not confer a significant response to 1,25(OH)₂D₃ in vitro. Overall, this study suggests that moderate vitamin D deficiency may not alter sulfate homeostasis. This needs to be confirmed in humans, particularly during pregnancy when vitamin D and sulfate levels need to be maintained at high levels for healthy maternal and child outcomes.

Oxalate Flux Across the Intestine: Contributions from Membrane Transporters

Epithelial oxalate transport is fundamental to the role occupied by the gastrointestinal (GI) tract in oxalate homeostasis. The absorption of dietary oxalate, together with its secretion into the intestine, and degradation by the gut microbiota, can all influence the excretion of this nonfunctional terminal metabolite in the urine. Knowledge of the transport mechanisms is relevant to understanding the pathophysiology of hyperoxaluria, a risk factor in kidney stone formation, for which the intestine also offers a potential means of treatment. The following discussion presents an expansive review of intestinal oxalate transport. We begin with an overview of the fate of oxalate, focusing on the sources, rates, and locations of absorption and secretion along the GI tract. We then consider the mechanisms and pathways of transport across the epithelial barrier, discussing the transcellular, and paracellular components. There is an emphasis on the membrane-bound anion transporters, in particular, those belonging to the large multifunctional Slc26 gene family, many of which are expressed throughout the GI tract, and we summarize what is currently known about their participation in oxalate transport. In the final section, we examine the physiological stimuli proposed to be involved in regulating some of these pathways, encompassing intestinal adaptations in response to chronic kidney disease, metabolic acid-base disorders, obesity, and following gastric bypass surgery. There is also an update on research into the probiotic, Oxalobacter formigenes, and the basis of its unique interaction with the gut epithelium. © 2021 American Physiological Society. Compr Physiol 11:1-41, 2021.

The Placental Ferroxidase Zyklopen Is Not Essential for Iron Transport to the Fetus in Mice

BACKGROUND

The ferroxidase zyklopen (Zp) has been implicated in the placental transfer of iron to the fetus. However, the evidence for this is largely circumstantial.

OBJECTIVES

This study aimed to determine whether Zp is essential for placental iron transfer.

METHODS

A model was established using 8- to 12-wk-old pregnant C57BL/6 mice on standard rodent chow in which Zp was knocked out in the fetus and fetal components of the placenta. Zp was also disrupted in the entire placenta using global Zp knockout mice. Inductively coupled plasma MS was used to measure total fetal iron, an indicator of the amount of iron transferred by the placenta to the fetus, at embryonic day 18.5 of gestation. Iron transporter expression in the placenta was measured by Western blotting, and the expression of Hamp1, the gene encoding the iron regulatory hormone hepcidin, was determined in fetal liver by real-time PCR.

RESULTS

There was no change in the amount of iron transferred to the fetus when Zp was disrupted in either the fetal component of the placenta or the entire placenta. No compensatory changes in the expression of the iron transport proteins transferrin receptor 1 or ferroportin were observed, nor was there any change in fetal liver Hamp1 mRNA. Hephl1, the gene encoding Zp, was expressed mainly in the maternal decidua of the placenta and not in the nutrient-transporting syncytiotrophoblast. Disruption of Zp in the whole placenta resulted in a 26% increase in placental size (P < 0.01).

CONCLUSIONS

Our data indicate that Zp is not essential for the efficient transfer of iron to the fetus in mice and is localized predominantly in the maternal decidua. The increase in placental size observed when Zp is knocked out in the entire placenta suggests that this protein may play a role in placental development.

Physiological and Pathological Functions of SLC26A6

Solute Carrier Family 26 (SLC26) is a conserved anion transporter family with 10 members in human (SLC26A1-A11, A10 being a pseudogene). All SLC26 genes except for SLC26A5 (prestin) are versatile anion exchangers with notable ability to transport a variety of anions. SLC26A6 has the most extensive exchange functions in the SLC26 family and is widely expressed in various organs and tissues of mammals. SLC26A6 has some special properties that make it play a particularly important role in ion homeostasis and acid-base balance. In the past few years, the function of SLC26A6 in the diseases has received increasing attention. SLC26A6 not only participates in the development of intestinal and pancreatic diseases but also serves a significant role in mediating nephrolithiasis, fetal skeletal dysplasia and arrhythmia. This review aims to explore the role of SLC26A6 in physiology and pathophysiology of relative mammalian organs to guide in-depth studies about related diseases of human.

Molecular analysis of the human placental cysteine dioxygenase type 1 gene

Sulfate is essential for healthy fetal growth and development. Cysteine dioxygenase type 1 (CDO1) plays an important role in the catabolism of cysteine to sulfate. Cdo1 knockout mice exhibit severe and lethal fetal phenotypes but the involvement of CDO1 gene variants in human development is unknown. We searched the NCBI and Ensembl gene databases and identified four alternatively spliced CDO1 coding mRNA transcripts, as well as 148 validated CDO1 gene variants, including 138 missense, 6 nonsense, 1 frameshift, 1 in-frame deletion, and 2 splice site variants. In silico analyses predicted 68 of the missense variants to be deleterious to CDO1 protein structure and function. We examined the relative abundance of the four CDO1 coding mRNA transcripts in human term placentas using qRT-PCR. CDO1 mRNA variant 2 was the most abundant transcript, with intermediate levels of variant 4 and lower levels of variants 1 and 3. Using in situ hybridization, we localised CDO1 mRNA expression to the syncytiotrophoblast layer of human term placenta. To investigate the regulation of CDO1 gene expression, we analysed the transcriptional activity of the human CDO1 5'-flanking region in the JEG-3 placental cell line using luciferase reporter assays. Transcriptional activities were identified in the regions -5 to -269 and - 269 to -1200 nucleotides upstream of the CDO1 transcription initiation site. Mutational analyses of a single nucleotide polymorphism -289C > G that is common in the general population (allele frequency = 0.37) and a putative transcription factor binding motif (CCAAT enhancer binding protein beta) did not alter transcriptional activity of the CDO1 5'-flanking region. Collectively, this study provides an overview and analysis of human CDO1 for future investigations of this gene in human health.

Kidney microRNA profile in pregnant mice reveals molecular insights into kidney adaptation to pregnancy: A pilot study

The maternal kidneys undergo numerous physiological changes during pregnancy to maintain a healthy pregnancy for mother and child. Over the past decade, interest in microRNAs (miRNAs) for regulating gene expression during pregnancy has expanded. However, the role of miRNAs in modulating kidney physiology during pregnancy has not been extensively investigated. In this study, miRNome profiling suggested differential expression of 163 miRNAs (of 887 miRNAs detected) in the kidneys from pregnant mice at 6.5 days gestation when compared to non-pregnant female mice, of which 35 and 128 miRNAs were potentially down- and up-regulated, respectively. We performed network and pathway analyses of the >1700 potential mRNA targets of the differentially expressed miRNAs using MiRNet, Gene Ontology, Reactome and KEGG analyses. The mRNA targets were over-represented in numerous cellular signalling pathways, including cellular protective responses. In addition, we explored 13 and 29 potential differentially expressed miRNAs to have putative binding sites in the Slc13a1 and Slc26a1 sulfate transporter mRNAs, respectively, and that decreased levels of mir-466k may potentially explain the increased expression of these sulfate transporters in early mouse gestation. Collectively, this study suggests altered expression levels of miRNAs during mouse gestation, which provides pilot data for future investigations into the molecular events that modulate kidney adaptsation to pregnancy.

Postnatal N-acetylcysteine administration rescues impaired social behaviors and neurogenesis in Slc13a4 haploinsufficient mice

Background

Sulfate availability is crucial for the sulfonation of brain extracellular matrix constituents, membrane phospholipids, neurosteroids, and neurotransmitters. Observations from humans and mouse models suggest dysregulated sulfate levels may be associated with neurodevelopmental disorders, such as autism. However, the cellular mechanisms governing sulfate homeostasis within the developing or adult brain are not fully understood.

Methods

We utilized a mouse model with a conditional allele for the sulfate transporter Slc13a4, and a battery of behavioral tests, to assess the effects of disrupted sulfate transport on maternal behaviors, social interactions, memory, olfaction, exploratory behavior, anxiety, stress, and metabolism. Immunohistochemistry examined neurogenesis within the stem cells niches.

Findings

The sulfate transporter Slc13a4 plays a critical role in postnatal brain development. Slc13a4 haploinsufficiency results in significant behavioral phenotypes in adult mice, notably impairments in social interaction and long-term memory, as well as increased neurogenesis in the subventricular stem cell niche. Conditional gene deletion shows these phenotypes have a developmental origin, and that full biallelic expression of Slc13a4 is required only in postnatal development. Furthermore, administration of N-acetylcysteine (NAC) within postnatal window P14-P30 prevents the onset of phenotypes in adult Slc13a4^+/− mice.

Interpretation

Slc13a4 haploinsufficient mice highlight a requirement for adequate sulfate supply in postnatal development for the maturation of important social interaction and memory pathways. With evidence suggesting dysregulated sulfate biology may be a feature of some neurodevelopmental disorders, the utility of sulfate levels as a biomarker of disease and NAC administration as an early preventative measure should be further explored.

Suppressing UPR-dependent overactivation of FGFR3 signaling ameliorates SLC26A2-deficient chondrodysplasias

Background

Mutations in the SLC26A2 gene cause a spectrum of currently incurable human chondrodysplasias. However, genotype-phenotype relationships of SLC26A2-deficient chondrodysplasias are still perplexing and thus stunt therapeutic development.

Methods

To investigate the causative role of SLC26A2 deficiency in chondrodysplasias and confirm its skeleton-specific pathology, we generated and analyzed slc26a2^−/− and Col2a1-Cre; slc26a2^fl/fl mice. The therapeutic effect of NVP-BGJ398, an FGFR inhibitor, was tested with both explant cultures and timed pregnant females.

Findings

Two lethal forms of human SLC26A2-related chondrodysplasias, achondrogenesis type IB (ACG1B) and atelosteogenesis type II (AO2), are phenocopied by slc26a2^−/− mice. Unexpectedly, slc26a2^−/− chondrocytes are defective for collagen secretion, exhibiting intracellular retention and compromised extracellular deposition of ColII and ColIX. As a consequence, the ATF6 arm of the unfolded protein response (UPR) is preferentially triggered to overactivate FGFR3 signaling by inducing excessive FGFR3 in slc26a2^−/− chondrocytes. Consistently, suppressing FGFR3 signaling by blocking either FGFR3 or phosphorylation of the downstream effector favors the recovery of slc26a2^−/− cartilage cultures from impaired growth and unbalanced cell proliferation and apoptosis. Moreover, administration of an FGFR inhibitor to pregnant females shows therapeutic effects on pathological features in slc26a2^−/− newborns. Finally, we confirm the skeleton-specific lethality and pathology of global SLC26A2 deletion through analyzing the Col2a1-Cre; slc26a2^fl/fl mouse line.

Interpretation

Our study unveils a previously unrecognized pathogenic mechanism underlying ACG1B and AO2, and supports suppression of FGFR3 signaling as a promising therapeutic approach for SLC26A2-related chondrodysplasias.

Fund

This work was supported by National Natural Science Foundation of China (81871743, 81730065 and 81772377).

Identification of placental nutrient transporters associated with intrauterine growth restriction and pre-eclampsia

Background

Gestational disorders such as intrauterine growth restriction (IUGR) and pre-eclampsia (PE) are main causes of poor perinatal outcomes worldwide. Both diseases are related with impaired materno-fetal nutrient transfer, but the crucial transport mechanisms underlying IUGR and PE are not fully elucidated. In this study, we aimed to identify membrane transporters highly associated with transplacental nutrient deficiencies in IUGR/PE.

Results

In silico analyses on the identification of differentially expressed nutrient transporters were conducted using seven eligible microarray datasets (from Gene Expression Omnibus), encompassing control and IUGR/PE placental samples. Thereby 46 out of 434 genes were identified as potentially interesting targets. They are involved in the fetal provision with amino acids, carbohydrates, lipids, vitamins and microelements. Targets of interest were clustered into a substrate-specific interaction network by using Search Tool for the Retrieval of Interacting Genes. The subsequent wet-lab validation was performed using quantitative RT-PCR on placentas from clinically well-characterized IUGR/PE patients (IUGR, n = 8; PE, n = 5; PE+IUGR, n = 10) and controls (term, n = 13; preterm, n = 7), followed by 2D-hierarchical heatmap generation. Statistical evaluation using Kruskal-Wallis tests was then applied to detect significantly different expression patterns, while scatter plot analysis indicated which transporters were predominantly influenced by IUGR or PE, or equally affected by both diseases. Identified by both methods, three overlapping targets, SLC7A7, SLC38A5 (amino acid transporters), and ABCA1 (cholesterol transporter), were further investigated at the protein level by western blotting. Protein analyses in total placental tissue lysates and membrane fractions isolated from disease and control placentas indicated an altered functional activity of those three nutrient transporters in IUGR/PE.

Conclusions

Combining bioinformatic analysis, molecular biological experiments and mathematical diagramming, this study has demonstrated systematic alterations of nutrient transporter expressions in IUGR/PE. Among 46 initially targeted transporters, three significantly regulated genes were further investigated based on the severity and the disease specificity for IUGR and PE. Confirmed by mRNA and protein expression, the amino acid transporters SLC7A7 and SLC38A5 showed marked differences between controls and IUGR/PE and were regulated by both diseases. In contrast, ABCA1 may play an exclusive role in the development of PE.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4518-z) contains supplementary material, which is available to authorized users.

Deletion of the Syncytin A receptor Ly6e impairs syncytiotrophoblast fusion and placental morphogenesis causing embryonic lethality in mice

Fetal growth and survival is dependent on the elaboration and propinquity of the fetal and maternal circulations within the placenta. Central to this is the formation of the interhaemal membrane, a multi-cellular lamina facilitating exchange of oxygen, nutrients and metabolic waste products between the mother and fetus. In rodents, this cellular barrier contains two transporting layers of syncytiotrophoblast, which are multinucleated cells that form by cell-cell fusion. Previously, we reported the expression of the GPI-linked cell surface protein LY6E by the syncytial layer closest to the maternal sinusoids of the mouse placenta (syncytiotrophoblast layer I). LY6E has since been shown to be a putative receptor for the fusogenic protein responsible for fusion of syncytiotrophoblast layer I, Syncytin A. In this report, we demonstrate that LY6E is essential for the normal fusion of syncytiotrophoblast layer I, and for the proper morphogenesis of both fetal and maternal vasculatures within the placenta. Furthermore, specific inactivation of Ly6e in the epiblast, but not in placenta, is compatible with embryonic development, indicating the embryonic lethality reported for Ly6e^−/− embryos is most likely placental in origin.

Perinatal exposure to high dietary advanced glycation end products in transgenic NOD8.3 mice leads to pancreatic beta cell dysfunction

The contribution of environmental factors to pancreatic islet damage in type 1 diabetes remains poorly understood. In this study, we crossed mice susceptible to type 1 diabetes, where parental male (CD8+ T cells specific for IGRP206-214; NOD8.3) and female (NOD/ShiLt) mice were randomized to a diet either low or high in AGE content and maintained on this diet throughout pregnancy and lactation. After weaning, NOD8.3+ female offspring were identified and maintained on the same parental feeding regimen for until day 28 of life. A low AGE diet, from conception to early postnatal life, decreased circulating AGE concentrations in the female offspring when compared to a high AGE diet. Insulin, proinsulin and glucagon secretion were greater in islets isolated from offspring in the low AGE diet group, which was akin to age matched non-diabetic C57BL/6 mice. Pancreatic islet expression of Ins2 gene was also higher in offspring from the low AGE diet group. Islet expression of glucagon, AGEs and the AGE receptor RAGE, were each reduced in low AGE fed offspring. Islet immune cell infiltration was also decreased in offspring exposed to a low AGE diet. Within pancreatic lymph nodes and spleen, the proportions of CD4+ and CD8+ T cells did not differ between groups. There were no significant changes in body weight, fasting glucose or glycemic hormones. This study demonstrates that reducing exposure to dietary AGEs throughout gestation, lactation and early postnatal life may benefit pancreatic islet secretion and immune infiltration in the type 1 diabetic susceptible mouse strain, NOD8.3.

Molecular analysis of sequence and splice variants of the human SLC13A4 sulfate transporter

The solute linked carrier 13A4 gene (SLC13A4) is abundantly expressed in the human and mouse placenta where it is proposed to transport nutrient sulfate to the fetus. In mice, targeted disruption of placental Slc13a4 leads to severe and lethal fetal phenotypes, however the involvement of SLC13A4 in human development is unknown. A search of the NCBI and Ensembl gene databases identified two alternatively spliced SLC13A4 mRNA transcripts and 98 SLC13A4 gene variants, including 85 missense, 4 splice site, 5 frameshift and 2 nonsense variants, as well as 2 in-frame deletions. We examined the relative abundance of the two SLC13A4 mRNA transcripts and then compared the sulfate transport function and plasma membrane expression of both isoforms as well as 6 sequence variants that predict disrupted SLC13A4 protein structure and function. SLC13A4 mRNA variant 1 has three additional nucleotides CAG compared to SLC13A4 mRNA variant 2 as a result of alternative splicing at the 5'-end of exon 6. Using qRT-PCR, we show a 4-fold higher abundance of SLC13A4 mRNA variant 1 compared to variant 2 in term human placentas and cultured BeWo and JEG-3 cell lines. The corresponding SLC13A4 protein isoforms 1 and 2 were found to have similar sulfate uptake activity and apical membrane expression in cultured MDCK cells. In addition, sulfate uptake into MDCK cells was similar between SLC13A4 isoform 1 and four missense variants N300S, F310C, E360Q and I570V, whereas V513M and frameshift variant L72Sfs led to partial (≈75% decrease) and complete loss-of-function, respectively. Localisation of these variants in MDCK cells showed N300S, E360Q, V513M and I570V expression on the apical plasma membrane, L72Sfs intracellularly and F310C on both apical and basolateral membranes. Our finding of partial and complete loss-of-function variants warrants further studies of the potential involvement of SLC13A4 in fetal pathophysiology.

Structure, organization and tissue expression of the pig SLC13A1 and SLC13A4 sulfate transporter genes

Sulfate is an obligate nutrient for fetal growth and development. In mice, the renal Slc13a1 sulfate transporter maintains high maternal circulating levels of sulfate in pregnancy, and the placental Slc13a4 sulfate transporter mediates sulfate supply to the fetus. Both of these genes have been linked to severe embryonal defects and fetal loss in mice. However, the clinical significance of SLC13A1 and SLC13A4 in human gestation is unknown. One approach towards understanding the potential involvement of these genes in human fetal pathologies is to use an animal model, such as the pig, which mimics the developmental trajectory of the human fetus more closely than the previously studied mouse models. In this study, we determined the tissue distribution of pig SLC13A1 and SLC13A4 mRNA, and compared the gene, cDNA and protein sequences of the pig, human and mouse homologues. Pig SLC13A1 mRNA was expressed in the ileum and kidney, whereas pig SLC13A4 mRNA was expressed in the placenta, choroid plexus and eye, which is similar to the tissue distribution in human and mouse. The pig SLC13A1 gene contains 15 exons spread over 76 kb on chromosome 8, and encodes a protein of 594 amino acids that shares 90% and 85% identity with the human and mouse homologues, respectively. The pig SLC13A4 gene is located approximately 11 Mb from SLC13A1 on chromosome 8, and contains 16 exons spanning approximately 70 kb. The pig SLC13A4 protein contains 626 amino acids that share 91% and 90% identity with human and mouse homologues, respectively. The 5’-flanking region of SLC13A1 contains several putative transcription factor binding sites, including GATA-1, GATA-3, Oct1 and TATA-box consensus sequences, which are conserved in the homologous human and mouse sequences. The 5’-flanking sequence of SLC13A4 contains multiple putative transcription factor consensus sites, including GATA-1, TATA-box and Vitamin D responsive elements. This is the first report to define the tissue distribution of pig SLC13A1 and SLC13A4 mRNAs, and compare the gene, cDNA, 5’-flanking region and protein sequences to human and mouse.

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Pig SLC13A1 and SLC13A4 are highly conserved with human and mouse homologues.

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Pig SLC13A1 and SLC13A4 proteins share high identity with human and mouse sequences.

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Tissue distribution of pig SLC13A1 and SLC26A1 mRNA is similar to human and mouse.

Epithelial magnesium transport by TRPM6 is essential for prenatal development and adult survival

Mg²⁺ regulates many physiological processes and signalling pathways. However, little is known about the mechanisms underlying the organismal balance of Mg²⁺. Capitalizing on a set of newly generated mouse models, we provide an integrated mechanistic model of the regulation of organismal Mg²⁺ balance during prenatal development and in adult mice by the ion channel TRPM6. We show that TRPM6 activity in the placenta and yolk sac is essential for embryonic development. In adult mice, TRPM6 is required in the intestine to maintain organismal Mg²⁺ balance, but is dispensable in the kidney. Trpm6 inactivation in adult mice leads to a shortened lifespan, growth deficit and metabolic alterations indicative of impaired energy balance. Dietary Mg²⁺ supplementation not only rescues all phenotypes displayed by Trpm6-deficient adult mice, but also may extend the lifespan of wildtype mice. Hence, maintenance of organismal Mg²⁺ balance by TRPM6 is crucial for prenatal development and survival to adulthood.

The role of intestinal oxalate transport in hyperoxaluria and the formation of kidney stones in animals and man

The intestine exerts a considerable influence over urinary oxalate in two ways, through the absorption of dietary oxalate and by serving as an adaptive extra-renal pathway for elimination of this waste metabolite. Knowledge of the mechanisms responsible for oxalate absorption and secretion by the intestine therefore have significant implications for understanding the etiology of hyperoxaluria, as well as offering potential targets for future treatment strategies for calcium oxalate kidney stone disease. In this review, we present the recent developments and advances in this area over the past 10 years, and put to the test some of the new ideas that have emerged during this time, using human and mouse models. A key focus for our discussion are the membrane-bound anion exchangers, belonging to the SLC26 gene family, some of which have been shown to participate in transcellular oxalate absorption and secretion. This has offered the opportunity to not only examine the roles of these specific transporters, revealing their importance to oxalate homeostasis, but to also probe the relative contributions made by the active transcellular and passive paracellular components of oxalate transport across the intestine. We also discuss some of the various physiological stimuli and signaling pathways which have been suggested to participate in the adaptation and regulation of intestinal oxalate transport. Finally, we offer an update on research into Oxalobacter formigenes, alongside recent investigations of other oxalate-degrading gut bacteria, in both laboratory animals and humans.

Involvement of Cl(-)/HCO3(-) exchanger SLC26A3 and SLC26A6 in preimplantation embryo cleavage

Bicarbonate (HCO3(-)) is essential for preimplantation embryo development. However, the mechanism underlying the HCO3(-) transport into the embryo remains elusive. In the present study, we examined the possible involvement of Cl(-)/HCO3(-) exchanger in mediating HCO3(-) transport into the embryo. Our results showed that depletion of extracellular Cl(-), even in the presence of HCO3(-), suppressed embryo cleavage in a concentration-dependent manner. Cleavage-associated HCO3(-)-dependent events, including increase of intracellular pH, upregulation of miR-125b and downregulation of p53, also required Cl(-). We further showed that Cl(-)/HCO3(-) exchanger solute carrier family 26 (SLC26) A3 and A6 were expressed at 2-cell through blastocyst stage. Blocking individual exchanger's activity by inhibitors or gene knockdown differentially decreased embryo cleavage and inhibited HCO3(-)-dependent events, while inhibiting/knocking down both produced an additive effect to an extent similar to that observed when CFTR was inhibited. These results indicate the involvement of SLC26A3 and A6 in transporting HCO3(-) essential for embryo cleavage, possibly working in concert with CFTR through a Cl(-) recycling pathway. The present study sheds light into our understanding of molecular mechanisms regulating embryo cleavage by the female reproductive tract.

Placental and fetal cysteine dioxygenase gene expression in mouse gestation

Nutrient sulfate is important for fetal development. The fetus has a limited capacity to generate sulfate and relies on maternal sulfate supplied via the placenta. The gestational age when fetal sulfate generation begins is unknown but would require cysteine dioxygenase (CDO1) which mediates a major step of sulfate production from cysteine. We investigated the ontogeny of Cdo1 mRNA expression in mouse fetal and placental tissues, which showed increasing levels from embryonic day 10.5 and was localised to the decidua and several fetal tissues including nasal cavities and brain. These findings suggest a role for Cdo1 in sulfate generation from mid-gestation.

Genetic ablation of placental sinusoidal trophoblast giant cells causes fetal growth restriction and embryonic lethality

A specialized subtype of trophoblast giant cells (TGCs) line the torturous sinusoids of the murine placental labyrinth, and can be distinguished from most other TGCs by the expression of Ctsq. We generated a transgenic mouse line expressing Cre recombinase from the Ctsq promoter. Crosses with Cre-inducible tdTomato reporter mice indicated Cre activity was restricted to the sinusoidal TGCs of the labyrinth, as well as the recently characterized channel TGCs. When crossed with Cre-inducible DTA transgenic mice, ablation of sinusoidal TGCs was achieved in double transgenic embryos, resulting in fetal growth restriction by E16.5, and embryonic lethality by term.

Transcriptome of early embryonic invasion at implantation sites in a murine model

Successful implantation relies on the interaction between a competent embryo and a receptive endometrium. The aim of the present study was to investigate genes differentially expressed in early invasive embryonic tissue versus decidual tissue in mice. Samples were obtained from the ectoplacental cone, the immediately surrounding deciduas and from deciduas from interimplantation sites. Microarray analysis showed that 817 genes were differentially expressed between extra-embryonic tissue and the surrounding decidua and that 360 genes were differentially expressed between the different deciduas, with a high representation of developmental processes. Genes differentially expressed in the maternal compartment included chemokines, lipoproteins, growth factors and transcription factors, whereas the embryonic invasive tissue expressed genes commonly observed in invasive tumour-like processes. These results provide information about genes involved in early embryonic invasion and the control exerted by the surrounding decidua. This information may be useful to find targets involved in pathologies associated with implantation failure and early pregnancy loss.

Reference intervals for plasma sulfate and urinary sulfate excretion in pregnancy

Background

Sulfate is important for fetal growth and development. During pregnancy, the fetus relies on sulfate from the maternal circulation. We report reference intervals for maternal plasma sulfate levels and fractional excretion index (FEI) for sulfate in pregnancy, as well as sulfate levels in cord blood from term pregnancies.

Methods

Plasma and urine were collected from 103 pregnant women of 10-20 weeks gestation and 106 pregnant women of 30-37 weeks gestation. Venous cord plasma was collected from 80 healthy term babies. Sulfate levels were measured by ion chromatography. Plasma and urinary creatinine levels were used to calculate FEI sulfate in pregnant women. Analyses provide reference intervals, and explored the relationship between maternal sulfate data with several prenatal factors.

Results

Median maternal plasma sulfate levels were 452 μmol/L and 502 μmol/L at 10-20 and 30-37 weeks gestation, respectively, and inversely correlated with FEI sulfate median values of 0.15 and 0.11. Overall reference intervals were 305-710 and 335-701 μmol/L (2.5th; 97.5th percentile; for 10-20 and 30-37 weeks gestation, respectively) for maternal plasma sulfate, and 0.06-0.31 and 0.05-0.28 for maternal FEI sulfate. Term venous cord plasma sulfate median levels were significantly (p = 0.038) higher in female babies (375 μmol/L) when compared to male babies (342 μmol/L), with an overall reference interval of 175-603 μmol/L.

Conclusions

We provide the first reference intervals for maternal plasma sulfate levels and FEI sulfate, as well as cord plasma sulfate levels. These findings provide reference data for further studies of sulfate levels in both mother and child.

Electronic supplementary material

The online version of this article (doi:10.1186/s12884-015-0526-z) contains supplementary material, which is available to authorized users.

The Role of C5a Receptor Signaling in Endotoxin-Induced Miscarriage and Preterm Birth

PROBLEM

Complement factor 5a (C5a), a potent pro-inflammatory mediator of the complement system, has been implicated in fetal rejection throughout gestation, from miscarriage to preterm birth. This study aimed to investigate the role of the principal C5a receptor, C5aR1 (CD88), in both miscarriage and preterm birth, in a bacterial endotoxin (lipopolysaccharide; LPS) murine model.

METHOD OF STUDY

Wild-type and C5ar1 knockout mice were administered LPS at 9.5 or 15.5 days post-conception to induce miscarriage or preterm birth, respectively.

RESULTS

C5ar1 knockout mice were protected against miscarriage in response to administration of LPS in early gestation. However, the absence of C5aR1 had no effect on the rates of preterm birth when LPS was administered in late gestation.

CONCLUSION

There may be a gestational window in which excessive activation of C5a can exert deleterious effects in pregnancy. Future strategies targeting the C5a-C5aR1 signaling axis should be considered to ameliorate miscarriages in patients with recurrent pregnancy loss.

Sulphate in pregnancy

Sulphate is an obligate nutrient for healthy growth and development. Sulphate conjugation (sulphonation) of proteoglycans maintains the structure and function of tissues. Sulphonation also regulates the bioactivity of steroids, thyroid hormone, bile acids, catecholamines and cholecystokinin, and detoxifies certain xenobiotics and pharmacological drugs. In adults and children, sulphate is obtained from the diet and from the intracellular metabolism of sulphur-containing amino acids. Dietary sulphate intake can vary greatly and is dependent on the type of food consumed and source of drinking water. Once ingested, sulphate is absorbed into circulation where its level is maintained at approximately 300 μmol/L, making sulphate the fourth most abundant anion in plasma. In pregnant women, circulating sulphate concentrations increase by twofold with levels peaking in late gestation. This increased sulphataemia, which is mediated by up-regulation of sulphate reabsorption in the maternal kidneys, provides a reservoir of sulphate to meet the gestational needs of the developing foetus. The foetus has negligible capacity to generate sulphate and thereby, is completely reliant on sulphate supply from the maternal circulation. Maternal hyposulphataemia leads to foetal sulphate deficiency and late gestational foetal death in mice. In humans, reduced sulphonation capacity has been linked to skeletal dysplasias, ranging from the mildest form, multiple epiphyseal dysplasia, to achondrogenesis Type IB, which results in severe skeletal underdevelopment and death in utero or shortly after birth. Despite being essential for numerous cellular and metabolic functions, the nutrient sulphate is largely unappreciated in clinical settings. This article will review the physiological roles and regulation of sulphate during pregnancy, with a particular focus on animal models of disturbed sulphate homeostasis and links to human pathophysiology.

Expression of aldehyde dehydrogenase family 1, member A3 in glycogen trophoblast cells of the murine placenta

INTRODUCTION

Retinoic acid (RA) signaling is a well known regulator of trophoblast differentiation and placental development, and maternal decidual cells are recognized as the source of much of this RA. We explored possible trophoblast-derived sources of RA by examining the expression of RA synthesis enzymes in the developing mouse placenta, as well as addressed potential sites of RA action by examining the ontogeny of gene expression for other RA metabolizing and receptor genes. Furthermore, we investigated the effects of endogenous RA production on trophoblast differentiation.

METHODS

Placental tissues were examined by in situ hybridization and assayed for RARE-LacZ transgene activity to locate sites of RAR signaling. Trophoblast stem cell cultures were differentiated in the presence of ALDH1 inhibitors (DEAB and citral), and expression of labyrinth (Syna, Ctsq) and junctional zone (Tpbpa, Prl7b1, Prl7a2) marker genes were analyzed by qRT-PCR.

RESULTS

We show Aldh1a3 is strongly expressed in a subset of ectoplacental cone cells and in glycogen trophoblast cells of the definitive murine placenta. Most trophoblast subtypes of the placenta express RA receptor combinations that would enable them to respond to RA signaling. Furthermore, expression of junctional zone markers decrease in differentiating trophoblast cultures when endogenous ALDH1 enzymes are inhibited.

DISCUSSION

Aldh1a3 is a novel marker for glycogen trophoblast cells and their precursors and may play a role in the differentiation of junctional zone cell types via production of a local source of RA.

Sulfate secretion and chloride absorption are mediated by the anion exchanger DRA (Slc26a3) in the mouse cecum

Inorganic sulfate (SO₄²⁻) is essential for a multitude of physiological processes. The specific molecular pathway has been identified for uptake from the small intestine but is virtually unknown for the large bowel, although there is evidence for absorption involving Na⁺-independent anion exchange. A leading candidate is the apical chloride/bicarbonate (Cl⁻/HCO₃⁻) exchanger DRA (down-regulated in adenoma; Slc26a3), primarily linked to the Cl⁻ transporting defect in congenital chloride diarrhea. The present study set out to characterize transepithelial ³⁵SO₄²⁻ and ³⁶Cl⁻ fluxes across the isolated, short-circuited cecum from wild-type (WT) and knockout (KO) mice and subsequently to define the contribution of DRA. The cecum demonstrated simultaneous net SO₄²⁻ secretion (-8.39 ± 0.88 nmol·cm⁻²·h⁻¹) and Cl⁻ absorption (10.85 ± 1.41 μmol·cm⁻²·h⁻¹). In DRA-KO mice, SO₄²⁻ secretion was reversed to net absorption via a 60% reduction in serosal to mucosal SO₄²⁻ flux. Similarly, net Cl⁻ absorption was abolished and replaced by secretion, indicating that DRA represents a major pathway for transcellular SO₄²⁻ secretion and Cl⁻ absorption. Further experiments including the application of DIDS (500 μM), bumetanide (100 μM), and substitutions of extracellular Cl⁻ or HCO₃⁻/CO₂ helped to identify specific ion dependencies and driving forces and suggested that additional anion exchangers were operating at both apical and basolateral membranes supporting SO₄²⁻ transport. In conclusion, DRA contributes to SO₄²⁻ secretion via DIDS-sensitive HCO₃⁻/SO₄²⁻ exchange, in addition to being the principal DIDS-resistant Cl⁻/HCO₃⁻ exchanger. With DRA linked to the pathogenesis of other gastrointestinal diseases extending its functional characterization offers a more complete picture of its role in the intestine.

Human placental sulfate transporter mRNA profiling from term pregnancies identifies abundant SLC13A4 in syncytiotrophoblasts and SLC26A2 in cytotrophoblasts

Sulfate is an important nutrient for fetal growth and development. The fetus has no mechanism for producing its own sulfate and is therefore totally reliant on sulfate from the maternal circulation via placental sulfate transport. To build a model of directional sulfate transport in the placenta, we investigated the relative abundance of the 10 known sulfate transporter mRNAs in human placenta from uncomplicated term pregnancies. SLC13A4 and SLC26A2 were the most abundant sulfate transporter mRNAs, which localized to syncytiotrophoblast and cytotrophoblast cells, respectively. These findings indicate important physiological roles for SLC13A4 and SLC26A2 in human placental sulfate transport.

Molecular analysis of the human SLC13A4 sulfate transporter gene promoter

The human solute linked carrier (SLC) 13A4 gene is primarily expressed in the placenta where it is proposed to mediate the transport of nutrient sulfate from mother to fetus. The molecular mechanisms involved in the regulation of SLC13A4 expression remain unknown. To investigate the regulation of SLC13A4 gene expression, we analysed the transcriptional activity of the human SLC13A4 5'-flanking region in the JEG-3 placental cell line using luciferase reporter assays. Basal transcriptional activity was identified in the region -57 to -192 nucleotides upstream of the SLC13A4 transcription initiation site. Mutational analysis of the minimal promoter region identified Nuclear factor Y (NFY), Specificity protein 1 (SP1) and Krüppel like factor 7 (KLF7) motifs which conferred positive transcriptional activity, as well as Zinc finger protein of the cerebellum 2 (ZIC2) and helix-loop-helix protein 1 (HEN1) motifs that repressed transcription. The conserved NFY, SP1, KLF7, ZIC2 and HEN1 motifs in the SLC13A4 promoter of placental species but not in non-placental species, suggests a potential role for these putative transcriptional factor binding motifs in the physiological control of SLC13A4 mRNA expression.