The human periconceptional maternal-embryonic space in health and disease.

Pregnancy is established during the periconceptional period as a continuum beginning with blastocyst attachment to the endometrial epithelial surface followed by embryo invasion and placenta formation. This period sets the foundation for the child and mother's health during pregnancy. Emerging evidence indicates that prevention of downstream pathologies in both the embryo/newborn and pregnant mother may be possible at this stage. In this review, we discuss current advances in the periconceptional space, including the preimplantation human embryo and maternal endometrium. We also discuss the role of the maternal decidua, the periconceptional maternal-embryonic interface, the dialogue between these elements, and the importance of the endometrial microbiome in the implantation process and pregnancy. Finally, we discuss the myometrium in the periconceptional space and review its role in determining pregnancy health.

Differentiation of bone marrow derived mesenchymal stem cells into male germ-like cells in co-culture with testicular cells.

OBJECTIVE: Stem cell therapy, specifically, pre-induction of mesenchymal stem cells toward male germ-like cells may be useful in patients with azoospermia. The aim of this study was to evaluate in vitro differentiation of mouse bone marrow-derived mesenchymal stem cells (BMSCs) into male germ-like cells by indirect co-culture with testicular cells in the presence of bone morphogenetic protein 4 (BMP4). METHODS: Experimental groups included: control (mouse BMSCs), treatment group-1 (BMSCs treated with BMP4), treatment group-2 (indirect co-culture of BMSCs with mouse testicular cells in the presence of BMP4) and treatment group-3 (indirect co-culture of BMSCs with testicular cells). BMSCs-derived male germ-like cells were evaluated by the expression of Dazl, and Stra8 using RT-qPCR. RESULTS: Stra8 gene expression was significantly increased in the treatment group-2 and Dazl gene was significantly increased in the treatment group-1 compared to other groups. In conclusion, indirect co-culturing of BMSCs with testicular cells and BMP4 leads to the differentiation of BMSCs into male germ-like cells which express specific male germ-like genes. Testicular cells released factors that contributed to the differentiation of BMSCs into male germ progenitor cells. CONCLUSION: This study suggests that mesenchymal stem cells may be differentiated into male germ-like cells and therefore, may be a novel treatment option for men with azoospermia.

DNA methylation mediated up-regulation of TERRA non-coding RNA is coincident with elongated telomeres in the human placenta.

STUDY QUESTION: What factors regulate elongated telomere length in the human placenta? SUMMARY ANSWER: Hypomethylation of TERRA promoters in the human placenta is associated with high TERRA expression, however, no clear mechanistic link between these phenomena and elongated telomere length in the human placenta was found. WHAT IS KNOWN ALREADY: Human placenta tissue and trophoblasts show longer telomere lengths compared to gestational age-matched somatic cells. However, telomerase (hTERT) expression and activity in the placenta is low, suggesting a role for an alternative lengthening of telomeres (ALT). While ALT is observed in 10-15% of human cancers and in some mouse stem cells, ALT has never been reported in non-cancerous human tissues. STUDY DESIGN, SAMPLES/MATERIALS, METHODS: Human term placental tissue and matched cord blood mononuclear cells (CBMCs) were collected as part of the Peri/Postnatal Epigenetic Twins study (PETS). In addition, first trimester placental villi, purified cytotrophoblasts, choriocarcinoma cell lines and a panel of ALT-positive cancer cell lines were tested. Telomere length was determined using the Terminal Restriction Fragment (TRF) assay and a relative quantitative PCR method. DNA methylation levels at several CpG rich subtelomeric TERRA promoters were determined using bisulfite conversion and the SEQUENOM EpiTYPER platform. Expression of TERRA and hTERT was determined using quantitative RT-PCR. ALT was assessed using the C-circle assay (CCA). MAIN RESULTS AND THE ROLE OF CHANCE: The human placenta tissue and purified first trimester trophoblasts showed low subtelomeric (TERRA) DNA methylation compared to matched CBMCs and other somatic cells. Interestingly placental TERRA methylation was lower than ALT-cancer cell lines, previously reported to be hypomethylated at these loci. Low TERRA methylation was associated with higher expression of TERRA RNA in placenta compared to matched CBMCs. Detectable levels of C-circles were observed in first trimester placental villi, but not term placenta, suggesting that the ALT mechanism may be active in specific placental cells in early gestation. C-circle analysis of purified first trimester trophoblasts and ALT-associated PML bodies (APB) staining of first trimester villi cross-sections failed to identify this specific cell type population. LIMITATIONS, REASONS FOR CAUTION: While first trimester villi showed detectable levels of C-circles, these levels were very low compared with those observed in ALT-positive tumours and cell lines. This is consistent with a small sub-population of ALT-positive cells but this requires further investigation. Finally, no mechanistic link was established between TERRA DNA methylation, the presence of C-circles and longer telomere length. WIDER IMPLICATIONS OF THE FINDINGS: Given the previously described role of TERRA ncRNA as a negative regulator of telomerase, the finding of elevated TERRA and long telomeres is counterintutive. ALT as a mechanism for telomere length maintenance has only been reported in certain human cancers, and recently in mouse embryonic stem cells and embryos. As with many aspects of cancer, it appears that ALT activity in tumours may be the inappropriate activation of a pathway found in very specific cell types in human development. Our data are the first supportive evidence for ALT in a non-cancerous human tissue, a result that requires further investigation and replication. The level of TERRA methylation in the human placenta is significantly lower than found in ALT cancer cell lines and somatic cells, raising the possibility of a novel mechanism in maintaining low methylation at subtelomeric regions. LARGE SCALE DATA: Not applicable. STUDY FUNDING AND COMPETING INTERESTS: This study was supported by NHMRC early career fellowship (B.N.), NHMRC Senior Research Fellowship (R.S.) and the Victoria Government Infrastructure Grant. R.R. holds a patent for the C-circle assay. No other conflicts declared.

IL-11 is a parietal cell cytokine that induces atrophic gastritis.

BACKGROUND AND AIMS: IL-is important in gastric damage, mucosal repair and gastric cancer progression. We analysed IL-11 expression in H.pylori infected mouse stomach, the site of gastric IL-11 expression in mice and humans, and the effect of exogenous IL-11 on gastric mucosal homeostasis. METHODS: IL-11 protein was localised in mouse and human stomach. The impact of chronic, exogenous IL-11 on normal mouse stomach was examined histologically and transcriptionally by microarray, confirmed by mRNA and protein analysis. Functional impact of IL-11 on gastric acid secretion was determined. RESULTS: In mice infected with H.pylori, IL-11 was increased in fundic mucosa with temporal expression similar to IL-1b. IL-11 protein was localised predominantly to parietal cells in mouse and human stomach. Application of exogenous IL-11 to resulted in fundic parietal and chief cell loss, hyperplasia, mucous cell metaplasia and inflammation. Coincident with cellular changes were an increased gastric pH, altered parietal cell ultrastructure and altered gene expression, particularly genes involved in immune response and ion transport which could result in compromised acid secretion. We confirmed that a single dose of IL-11 effectively ablated the gastric response to histamine. CONCLUSIONS: IL-11 is a parietal cell cytokine that blocks gastric acid secretion, likely via reducing expression of parietal cell ion transport genes, CCKb and histamine H2 receptors. IL-11 expression is increased in H. pylori infected mouse stomach and treatment of wild type mice with IL-11 induced changes in the gastric fundic mucosa reminiscent of chronic atrophic gastritis, a precursor to gastric cancer.

Subcellular localization of L-selectin ligand in the endometrium implies a novel function for pinopodes in endometrial receptivity.

BACKGROUND: Apical surfaces of human endometrial epithelium and endothelium are key elements for the initiation of molecular interactions to capture the blastocyst or leukocyte, respectively. The L-selectin adhesion system has been strongly proposed to play an important role in the initial steps of trophoblast adhesion and promotion of integrin-dependent processes, ultimately culminating in the establishment of the embryo-maternal interface. On the basis of these facts, we hypothesized a novel role for pinopodes as the first embryo-fetal contact sites to contain the highest subcellular expression of L-selectin ligand suggesting its role in early adhesion as predicted. Thus, the objective of this study was therefore to determine the subcellular pattern of distribution of the L-selectin ligand (MECA-79) in human endometrial apical membrane region during the window of implantation. METHODS: Endometrial biopsies of secretory phases from fertile females ranging in age between 25 and 42 years were studied using several approaches, including scanning electron microscopy (SEM), immunostaining for light microscopy and transmission electron microscopy (TEM), and immunoblotting as well as statistical analysis of the area-related numerical densities of immunoreactive MECA-79-bound nanogolds to detect the expression pattern and the subcellular distribution pattern of L-selectin ligand (MECA-79) in human endometrium during the window of implantation. RESULTS: The endometrial biopsies were scored according the dating criteria of Noyes et al. by an experienced histologist. The SEM images of the midluteal phase specimens revealed that fully developed pinopodes were abundant in our samples. HRP-immunostaining and immunofluorescent staining as well as immunoblotting revealed that MECA-79 was expressed in the midluteal phase specimens. The results of immunogold TEM illustrated the expression of MECA-79 in human pinopodes in the midluteal phase and a higher area-relate numerical density in pinopodes compared to that of the uterodome-free areas. CONCLUSIONS: This is the first demonstration of the subcellular localization of MECA-79 in the human pinopodes which may indicate a novel role for pinopodes to be capable of shear-stress-dependent tethering-type adhesion in the initial phases of human embryo implantation.

Cyclic adenosine monophosphate (cAMP) analog and phosphodiesterase inhibitor (IBMX) ameliorate human sperm capacitation and motility.

OBJECTIVES: Human sperm quality is decreasing progressively. One of the foremost reasons for infertility is the failure in sperm capacitation. We examined the influence of a cAMP (cyclic-adenosine mono phosphate analog)+IBMX (3-isobutyl-1-methylxanthine) on the motility and capacitation rate of human sperm over time. MATERIAL AND METHODS: Samples were gotten from 20 asthenozoospermic infertile patients referring to the Academic Center for Education, Culture and Research unit of the infertility research center, Qom, Iran. Samples were processed with a Density Gradient Centrifuging. Spermatozoa were divided into 4 groups: control, experimental 1, 2 and 3 (E1, E2, E3) based on the dose/time schedules (cAMP 5mmol+IBMX 0.2mmol/2, 4, and 6h, respectively). The computer-assisted sperm analysis and chlortetracycline assays were used to measure sperm motility and capacitation. RESULTS: After incubation with a cAMP analog and IBMX, the levels of progressive motile sperms considerably improved in all experimental groups compared to the control group (E1=18.89±7.1, E2=30±9.7, E3=26.3±9.6 vs Control=10.28±6.2, P<0.05) especially in E2 group (P<0.05), indicating a greater effect of db cAMP (5mmol) and IBMX (0.2mmol) for 4h compared to the same doses at 2 and 6h. Also, non-progressive motile sperms significantly decreased in E2 group compared to the other groups (P<0.05). Moreover, both patterns C and B were substantially improved in all experimental groups especially in E2 group (P<0.05). CONCLUSION: Our findings support that the supplementation of sperm with db cAMP+IBMX specially for 4h, could be useful for men with asthenozoospermia to improve the success of assisted reproductive technology.

Galectin-7 Impairs Placentation and Causes Preeclampsia Features in Mice.

Preeclampsia is a serious pregnancy-induced disorder unique to humans. The etiology of preeclampsia is poorly understood; however, poor placental formation is thought causal. Galectin-7 is produced by trophoblast and is elevated in first-trimester serum of women who subsequently develop preeclampsia. We hypothesized that elevated placental galectin-7 may be causative of preeclampsia. Here, we demonstrated increased galectin-7 production in chorionic villous samples from women who subsequently develop preterm preeclampsia compared with uncomplicated pregnancies. In vitro, galectin-7 impaired human first-trimester trophoblast outgrowth, increased placental production of the antiangiogenic sFlt-1 splice variant, sFlt-1-e15a, and reduced placental production and secretion of ADAM12 (a disintegrin and metalloproteinase12) and angiotensinogen. In vivo, galectin-7 administration (E8-E12) to pregnant mice caused elevated systolic blood pressure, albuminuria, impaired placentation (reduced labyrinth vascular branching, impaired decidual spiral artery remodeling, and a proinflammatory placental state demonstrated by elevated IL1ß, IL6 and reduced IL10), and dysregulated expression of renin-angiotensin system components in the placenta, decidua, and kidney, including angiotensinogen, prorenin, and the angiotensin II type 1 receptor. Collectively, this study demonstrates that elevated galectin-7 during placental formation contributes to abnormal placentation and suggests that it leads to the development of preeclampsia via altering placental production of sFlt-1 and renin-angiotensin system components. Targeting galectin-7 may be a new treatment option for preeclampsia.

Interleukin 11 is upregulated in preeclampsia and leads to inflammation and preeclampsia features in mice.

Preeclampsia is a dangerous pregnancy complication, which is often associated with fetal growth restriction and can have serious life-long effects for both mother and baby. While the establishment of the placenta in the first trimester is the sentinel event in the development of preeclampsia little is known of the critical mechanisms of placentation that lead to the syndrome. Locally produced inflammatory cytokines are thought to play a role in the development of preeclampsia. This review summarizes the evidence that interleukin 11 is dysregulated in preeclampsia and contributes to the initiation of preeclampsia via effects on placentation. It discusses the benefits and drawbacks of targeting IL11 as a novel treatment option for preeclampsia.

Chondroitin sulfate proteoglycan protein is stimulated by interleukin 11 and promotes endometrial epithelial cancer cell proliferation and migration.

Endometrial cancer is the most common gynecological cancer. We identified interleukin 11 (IL11) as a critical mediator of endometrial tumourigenesis and demonstrated that IL11 regulates chondroitin sulfate proteoglycan (CSPG4) in human placental trophoblasts. CSPG4 is a cell membrane protein overexpressed in numerous human cancers, although its role in endometrial cancer has not been investigated. We examined CSPG4 expression and localization in primary human type I endometrioid grade (G) 1-3 tumours by qPCR and immunohistochemistry and determined whether IL11 stimulated CSPG4. IL11 upregulated CSPG4 mRNA in HEC1A (G2-derived endometrial epithelial cancer cell line) cells. IL11 administration to BALB/c nude mice enhanced HEC1A xenograft tumour growth and increased CSPG4 protein in tumours. CSPG4 mRNA was unchanged between human G1-3 endometrial cancer and control tissues. CSPG4 protein levels were elevated in the epithelium of G2 and G3 endometrial cancer and in the tumour-associated stroma of G3 tumour tissues compared to proliferative phase or post-menopausal endometrium. CSPG4 knockdown by siRNA reduced HEC1A proliferation and migration in vitro and reduced gene expression of the key epithelial-to-mesenchymal transition (EMT) regulator SNAIL. Our data suggest that CSPG4 inhibition may impair endometrial cancer progression by reducing cancer cell proliferation, migration and potentially EMT.

Fibulin-5 localisation in human endometrial cancer shifts from epithelial to stromal with increasing tumour grade, and silencing promotes endometrial epithelial cancer cell proliferation.

Endometrial cancer is the most common invasive gynaecological malignancy. While endocrine, genetic and inflammatory factors are thought to contribute to its pathogenesis, its precise etiology and molecular regulators remain poorly understood. Fibulin-5 is an extracellular matrix (ECM) protein that inhibits cell growth and invasion in several cancer cell types and is downregulated in a number of types of human cancer. However, it is unknown whether fibulin-5 plays a role in endometrial tumourigenesis. In the current report, the expression and localisation of fibulin-5 in type I endometrioid human endometrial cancers of grades (G) 1-3 was investigated using reverse transcription-quantitative polymerase chain reaction and immunohistochemistry. Fibulin-5 mRNA was found to be significantly reduced in whole tumour tissues from women across G1-3 compared with benign endometrium (P<0.0001). Consistently, fibulin-5 protein was also reduced in the tumour epithelial compartment across increasing tumour grades. By contrast, increased protein localisation to the tumour stroma was observed with increasing grade. Knockdown by small interfering RNA in Ishikawa endometrial epithelial cancer cells expressing fibulin-5 stimulated cell adhesion and proliferation in vitro. Fibulin-5 mRNA expression in Ishikawa cells was induced by transforming growth factor-ß and fibulin-5 in turn activated extracellular signal-regulated kinases (ERK1/2), suggesting that it may act via the mitogen-activated protein kinase pathway. In summary, the present study identified fibulin-5 as a downregulated ECM gene in human endometrial cancer and observed a shift from epithelial to stromal protein localisation with increasing tumour grade in women. These data suggest that loss of fibulin-5 function may promote endometrial cancer progression by enhancing epithelial cell adhesion and proliferation.

Fertile ground: human endometrial programming and lessons in health and disease.

The human endometrium is a highly dynamic tissue that is cyclically shed, repaired, regenerated and remodelled, primarily under the orchestration of oestrogen and progesterone, in preparation for embryo implantation. Humans are among the very few species that menstruate and that, consequently, are equipped with unique cellular and molecular mechanisms controlling these cyclic processes. Many reproductive pathologies are specific to menstruating species, and studies in animal models rarely translate to humans. Abnormal remodelling and regeneration of the human endometrium leads to a range of reproductive complications. Furthermore, the processes regulating endometrial remodelling and implantation, including those controlling hormonal impact, breakdown and repair, stem/progenitor cell activation, inflammation and cell invasion have broad applications to other fields. This Review presents current knowledge regarding the normal and abnormal function of the human endometrium. The development of biomarkers for prediction of uterine diseases and pregnancy disorders and future avenues of investigation to improve fertility and enhance endometrial function are also discussed.

Transcytosis of IL-11 and Apical Redirection of gp130 Is Mediated by IL-11α Receptor.

Interleukin (IL)-11 signaling is involved in various processes, including epithelial intestinal cell regeneration and embryo implantation. IL-11 signaling is initiated upon binding of IL-11 to IL-11R1 or IL-11R2, two IL-11α-receptor splice variants, and gp130. Here, we show that IL-11 signaling via IL-11R1/2:gp130 complexes occurs on both the apical and basolateral sides of polarized cells, whereas IL-6 signaling via IL-6R:gp130 complexes is restricted to the basolateral side. We show that basolaterally supplied IL-11 is transported and released to the apical extracellular space via transcytosis in an IL-11R1-dependent manner. By contrast, IL-6R and IL-11R2 do not promote transcytosis. In addition, we show that transcytosis of IL-11 is dependent on the intracellular domain of IL-11R1 and that synthetic transfer of the intracellular domain of IL-11R1 to IL-6R promotes transcytosis of IL-6. Our data define IL-11R as a cytokine receptor with transcytotic activity by which IL-11 and IL-6:soluble IL-6R complexes are transported across cellular barriers.

Leukemia inhibitory factor and interleukin-11: cytokines with key roles in implantation.

Members of the interleukin-6 family of cytokines include leukaemia inhibitory factor (LIF), interleukin-6, interleukin-11, cardiotrophin, ciliary neurotropic growth factor, oncostatin M and the recently discovered cardiotropin-like cytokine (NNT-1). These ligands signal via heterodimeric receptors composed of ligand-specific alpha chains and the common signal-transducing subunit gp130. Gene targeting in mice provided the first indication of a role for interleukin 6 family cytokines in implantation with the generation of mice with a null mutation of the gene encoding LIF. LIF null female mice were infertile because of failure of blastocyst implantation. More recently, interleukin-11 signalling has been shown to be required for the uterine decidualization response. This review describes the insights into the role of interleukin-6 family cytokines in female fertility that have come from gene targeting experiments in mice.

Effects of gefitinib, an epidermal growth factor receptor inhibitor, on human placental cell growth.

OBJECTIVE: Placenta has the highest expression of epidermal growth factor (EGF) receptor of all tissues, a cell signaling pathway promoting survival and growth. Therefore, EGF receptor inhibition could potentially treat ectopic pregnancy. We undertook preclinical studies to examine whether gefitinib (orally available EGF receptor inhibitor) with or without methotrexate inhibits placental cell growth. METHODS: Gefitinib and methotrexate were added to placental cells and their ability inhibit cell growth, block EGF receptor signaling, and induce apoptosis (programmed cell death) was examined. They were also administered to two animal mouse models to examine their effects on placental tissue in vivo. RESULTS: Epidermal growth factor receptor was highly expressed in placental tissue from ectopic pregnancies. Combining gefitinib with methotrexate potently inhibited growth of placental cells, including placental cell lines (JEG3, BeWo cells) and cells isolated from first-trimester placenta. These drugs were additive in blocking EGF receptor signaling and inducing apoptosis. Gefitinib and methotrexate administered together were more potent in decreasing the volume of human placental cells xenografted subcutaneously onto mice compared with either alone. By day 19 after xenografting, mean (± standard error of the mean), xenograft volumes were: 821 (± 68) mm after gefitinib treatment, 901 (± 204) mm after methotrexate treatment, and 345 (±137) mm after both drugs were given (P<.01 for both comparisons of single therapy compared with combination therapy). Combining these agents doubled rates of fetal resorption in pregnant mice compared with each drug alone. CONCLUSION: Combining gefitinib with methotrexate potently inhibits placental cell growth in vitro and in mouse models. The combination may have potential in treating ectopic pregnancies.

IL-11/IL11RA receptor mediated signaling: a web accessible knowledgebase.

Abstract Interleukin-11 (IL-11) is a pleiotropic cytokine that belongs to gp130 family. It plays a significant role in the synthesis and maturation of hematopoietic cells, inhibition of adipogenesis, regulation of embryo implantation, and trophoblasts invasion. Although IL-11 signaling has been described in several biological processes, a centralized resource documenting these molecular reactions induced by IL-11 is not publicly available. In the current study, we have manually annotated the molecular reactions and interactions induced by IL-11 from literature available. We have documented 40 unique molecules involved in 18 protein-protein interactions, 26 enzyme-substrate reactions, 7 translocation events, and 4 activation/ inhibition reactions. We have also annotated 23 genes reported to be differentially regulated under IL-11 stimulation. We have enabled the data availability in standard exchange formats from 'NetPath', a repository for signaling pathways. We believe that this will help in the identification of potential therapeutic targets in IL-11-associated disorders.

Dilated thin-walled blood and lymphatic vessels in human endometrium: a potential role for VEGF-D in progestin-induced break-through bleeding.

Progestins provide safe, effective and cheap options for contraception as well as the treatment of a variety of gynaecological disorders. Episodes of irregular endometrial bleeding or breakthrough bleeding (BTB) are a major unwanted side effect of progestin treatment, such that BTB is the leading cause for discontinued use of an otherwise effective and popular medication. The cellular mechanisms leading to BTB are poorly understood. In this study, we make the novel finding that the large, dilated, thin walled vessels characteristic of human progestin-treated endometrium include both blood and lymphatic vessels. Increased blood and lymphatic vessel diameter are features of VEGF-D action in other tissues and we show by immunolocalisation and Western blotting that stromal cell decidualisation results in a significant increase in VEGF-D protein production, particularly of the proteolytically processed 21 kD form. Using a NOD/scid mouse model with xenografted human endometrium we were able to show that progestin treatment causes decidualisation, VEGF-D production and endometrial vessel dilation. Our results lead to a novel hypothesis to explain BTB, with stromal cell decidualisation rather than progestin treatment per se being the proposed causative event, and VEGF-D being the proposed effector agent.

Placenta-specific methylation of the vitamin D 24-hydroxylase gene: implications for feedback autoregulation of active vitamin D levels at the fetomaternal interface.

Plasma concentrations of biologically active vitamin D (1,25-(OH)(2)D) are tightly controlled via feedback regulation of renal 1alpha-hydroxylase (CYP27B1; positive) and 24-hydroxylase (CYP24A1; catabolic) enzymes. In pregnancy, this regulation is uncoupled, and 1,25-(OH)(2)D levels are significantly elevated, suggesting a role in pregnancy progression. Epigenetic regulation of CYP27B1 and CYP24A1 has previously been described in cell and animal models, and despite emerging evidence for a critical role of epigenetics in placentation generally, little is known about the regulation of enzymes modulating vitamin D homeostasis at the fetomaternal interface. In this study, we investigated the methylation status of genes regulating vitamin D bioavailability and activity in the placenta. No methylation of the VDR (vitamin D receptor) and CYP27B1 genes was found in any placental tissues. In contrast, the CYP24A1 gene is methylated in human placenta, purified cytotrophoblasts, and primary and cultured chorionic villus sampling tissue. No methylation was detected in any somatic human tissue tested. Methylation was also evident in marmoset and mouse placental tissue. All three genes were hypermethylated in choriocarcinoma cell lines, highlighting the role of vitamin D deregulation in this cancer. Gene expression analysis confirmed a reduced capacity for CYP24A1 induction with promoter methylation in primary cells and in vitro reporter analysis demonstrated that promoter methylation directly down-regulates basal promoter activity and abolishes vitamin D-mediated feedback activation. This study strongly suggests that epigenetic decoupling of vitamin D feedback catabolism plays an important role in maximizing active vitamin D bioavailability at the fetomaternal interface.