The placenta is the organ that transports nutrients, respiratory gases, and wastes between the maternal and fetal systems.
Consequently, placental blood flow and vascular development are essential ...components of normal placental function and are
critical to fetal growth and development. Normal fetal growth and development are important to ensure optimum health of offspring
throughout their subsequent life course. In numerous sheep models of compromised pregnancy, in which fetal or placental growth,
or both, are impaired, utero-placental blood flows are reduced. In the models that have been evaluated, placental vascular
development also is altered. Recent studies found that treatments designed to increase placental blood flow can ârescueâ fetal
growth that was reduced due to low maternal dietary intake. Placental blood flow and vascular development are thus potential
therapeutic targets in compromised pregnancies.
Placental vascular development (angiogenesis) is critical for placental function and thus for normal embryonic/fetal growth and development. Specific environmental factors or use of assisted ...reproductive techniques may result in poor placental angiogenesis, which may contribute to embryonic losses and/or fetal growth retardation. Uterine tissues were collected on days 14, 16, 18, 20, 22, 24, 26, 28, and 30 after mating and on day 10 after estrus (nonpregnant controls) to determine vascular development and expression of several factors involved in the regulation of angiogenesis in the endometrium. Compared with controls, several measurements of endometrial vascularity increased (P<0.001) including vascular labeling index (LI; proportion of proliferating cells), the tissue area occupied by capillaries, area per capillary (capillary size), total capillary circumference per unit of tissue area, and expression of factor VIII (marker of endothelial cells), but capillary number decreased (P<0.001). Compared with controls, mRNA for placental growth factor, vascular endothelial growth factor receptors, angiopoietins (ANGPT) 1 and 2, ANGPT receptor TEK, endothelial nitric oxide synthase, and hypoxia-inducible factor 1α increased (P<0.05) during early pregnancy. Vascular LI was positively correlated (P<0.05) with several measurements of vascularity and with mRNA expression of angiogenic factors. These data indicate that endometrial angiogenesis, manifested by increased vascularity and increased expression of several factors involved in the regulation of angiogenesis, is initiated very early in pregnancy. This more complete description of early placental angiogenesis may provide the foundation for determining whether placental vascular development is altered in compromised pregnancies.
Functions of corpus luteum (CL) are influenced by numerous factors including hormones, growth and angiogenic factors, nutritional plane and dietary supplements such as arginine (Arg), a ...semi-essential amino acid and precursor for proteins, polyamines and nitric oxide (NO). The aim of this study was to determine if Arg supplementation to ewes fed different planes of nutrition influences: (1) progesterone (P4) concentrations in serum and luteal tissue, (2) luteal vascularity, cell proliferation, endothelial NO synthase (eNOS) and receptor (R) soluble guanylate cyclase β protein and mRNA expression and (3) luteal mRNA expression for selected angiogenic factors during the estrous cycle. Ewes (n = 111) were categorized by weight and randomly assigned to one of three nutritional planes: maintenance control (C), overfed (2× C) and underfed (0.6× C) beginning 60 days prior to onset of estrus. After estrus synchronization, ewes from each nutritional plane were assigned randomly to one of two treatments: Arg or saline. Serum and CL were collected at the early, mid and late luteal phases. The results demonstrated that: (1) nutritional plane affected ovulation rates, luteal vascularity, cell proliferation and NOS3, GUCY1B3, vascular endothelial growth factor (VEGF) and VEGFR2 mRNA expression, (2) Arg affected luteal vascularity, cell proliferation and NOS3, GUCY1B3, VEGF and VEGFR2 mRNA expression and (3) luteal vascularity, cell proliferation and the VEGF and NO systems depend on the stage of the estrous cycle. These data indicate that plane of nutrition and/or Arg supplementation can alter vascularization and expression of selected angiogenic factors in luteal tissue during the estrous cycle in sheep.
Morphometric methodologies were developed and applied to investigate the patterns of vascular development in maternal (caruncular; CAR) and fetal (cotyledonary; COT) sheep placentas throughout the ...last two thirds of gestation. We also examined the expression levels of the major angiogenic factors and their receptors in CAR and COT sheep placentas. Although the vascularity of the CAR tissues increased continuously from Day 50 through Day 140 of pregnancy, those of the COT tissues increased at about twice the instantaneous rate (i.e., the proportionate increase/day) of the CAR. For CAR, vascularity increased 2-fold from Day 50 through Day 140 via relatively small increases in capillary number and 2- to 3-fold increases in capillary diameter. For COT, the increased vascularity resulted from a 12-fold increase in capillary number associated with a concomitant 2-fold decrease in capillary diameter. This large increase in fetal placental capillary number, which was due to increased branching, resulted in 6-fold increases in total capillary cross-sectional area and total capillary surface, per unit of COT tissue. Different patterns of expression of the mRNAs for angiogenic factors and their receptors were observed for CAR and COT. The dilation-like angiogenesis of CAR was correlated with the expression of vascular endothelial growth factor receptor-1 (FLT1), angiopoietin-2 (ANGPT2), and soluble guanylate cyclase (GUCY1B3) mRNAs. The branching-like angiogenesis of COT was correlated with the expression of vascular endothelial growth factor (VEGF), FLT1, angiopoietin-1 (ANGPT1), ANGPT2, and FGF2 mRNAs. Monitoring the expression of angiogenic factors and correlating the levels with quantitative measures of vascularity enable one to model angiogenesis in a spatiotemporal fashion.
To evaluate expression of progesterone receptor (PGR) AB in follicle stimulating hormone (FSH)-treated or non-treated sheep administered with arginine (Arg) or saline (Sal) fed a control (C), excess ...(O) or restricted (U) diet, uterine tissues were collected at the early, mid and/or late luteal phases. In exp. 1, ewes from each diet were randomly assigned to one of two treatments, Arg or Sal administration three times daily from day 0 of the first estrous cycle until uterine tissue collection. In exp. 2, ewes were injected twice daily with FSH on days 13–15 of the first estrous cycle. Uterine tissues were immunostained to detect PGR followed by image analysis. PGR were detected in luminal epithelium (LE), endometrial glands (EG), endometrial stroma (ES), myometrium (Myo), and endometrial and myometrial blood vessels. The percentage of PR-positive cells and/or intensity of staining were affected by phase of the estrous cycle, plane of nutrition, and/or FSH but not by Arg. In exp. 1, percentage of PGR-positive cells in LE and EG but not in ES and Myo was greater at the early and mid than late luteal phase, was not affected by plane of nutrition, and was similar in LE and EG. Intensity of staining was affected by phase of the estrous cycle and plane of nutrition in LE, EG and Myo, and was the greatest in LE, less in EG, and least in ES and Myo. In exp. 2, percentage of PGR-positive cells in LE, EG, ES and Myo was affected by phase of the estrous cycle, but not by plane of nutrition; was greater at the early than mid luteal phase; and was greatest in LE and EG, less in luminal (superficial) ES and Myo and least in deep ES. Intensity of staining was affected by phase of the estrous cycle and plane of nutrition in all compartments but ES, and was the greatest in LE and luminal EG, less in deep EG, and least in ES and Myo. Comparison of data for FSH (superovulated) and Sal-treated (non-superovulated) ewes demonstrated that FSH affected PR expression in all evaluated uterine compartments depending on plane of nutrition and phase of the estrous cycle. Thus, PGR are differentially distributed in uterine compartments, and PGR expression is affected by nutritional plane and FSH, but not Arg depending on phase of the estrous cycle. Such changes in dynamics of PGR expression indicate that diet plays a regulatory role and that FSH-treatment may alter uterine functions.
•Progesterone receptors (PR) protein is differentially distributed in uterine compartments.•PR expression is affected by nutritional plane and FSH, but not Arg depending on phase of the estrous cycle.•Changes in dynamics of PR expression indicate that diet plays a regulatory role in uterine functions.•FSH-treatment may alter uterine functions in non-pregnant animals.
This review discusses the importance of placental vascular development, as reflected by placental angiogenesis and placental blood flow, to placental function in normal pregnancies. We then summarize ...our current understanding of how maternal stress, including inadequate maternal nutrition as well as the application of assisted reproductive technologies (ART), leads to compromised placental angiogenesis and function and the subsequent effects on fetal and neonatal growth and development. Finally, we discuss several promising therapeutic approaches to 'rescue' placental vascular development and function in compromised pregnancies, leading to improved pregnancy and postnatal outcomes.
The importance of the placenta and its vascular development to fetal growth and development has been appreciated since ancient times. Based on numerous studies in humans and animal model organisms in ...the last 2-3 decades, normal placental angiogenesis is critically important to ensure adequate blood flow to the placenta and therefore to provide the substrates that support normal fetal growth. Placental angiogenesis is abnormal at term in compromised pregnancies (those in which fetal growth is altered), including those resulting from maternal nutritional or environmental stress, maternal age, increased numbers of fetuses, maternal or fetal genotype, or the use of assisted reproductive technologies (e.g., cloning by somatic cell nuclear transfer). We and others have recently shown that these defects in placental vascular development occur quite early in pregnancy and may therefore presage compromised fetal growth and development. The challenges will be to find biomarkers of abnormal placental angiogenesis and to develop therapeutic strategies to "rescue" placental vascular development and thus fetal growth in compromised pregnancies. Animal models will be essential in meeting these challenges.
Utero-placental growth and vascular development are critical for pregnancy establishment that may be altered by various factors including assisted reproductive technologies (ART), nutrition, or ...others, leading to compromised pregnancy. We hypothesized that placental vascularization and expression of angiogenic factors are altered early in pregnancies after transfer of embryos created using selected ART methods. Pregnancies were achieved through natural mating (NAT), or transfer of embryos from NAT (NAT-ET), or IVF or in vitro activation (IVA). Placental tissues were collected on day 22 of pregnancy. In maternal caruncles (CAR), vascular cell proliferation was less (P<0.05) for IVA than other groups. Compared with NAT, density of blood vessels was less (P<0.05) for IVF and IVA in fetal membranes (FM) and for NAT-ET, IVF, and IVA in CAR. In FM, mRNA expression was decreased (P<0.01-0.08) in NAT-ET, IVF, and IVA compared with NAT for vascular endothelial growth factor (VEGF) and its receptor FLT1, placental growth factor (PGF), neuropilin 1 (NP1) and NP2, angiopoietin 1 (ANGPT1) and ANGPT2, endothelial nitric oxide synthase 3 (NOS3), hypoxia-inducible factor 1A (HIF1A), fibroblast growth factor 2 (FGF2), and its receptor FGFR2. In CAR, mRNA expression was decreased (P<0.01-0.05) in NAT-ET, IVF, and IVA compared with NAT for VEGF, FLT1, PGF, ANGPT1, and TEK. Decreased mRNA expression for 12 of 14 angiogenic factors across FM and CAR in NAT-ET, IVF, and IVA pregnancies was associated with reduced placental vascular development, which would lead to poor placental function and compromised fetal and placental growth and development.
To characterize early fetal placental development, gravid uterine tissues were collected from pregnant ewes every other day from day 16 to 30 after mating. Determination of 1) cell proliferation was ...based on Ki67 protein immunodetection; 2) global methylation was based on 5-methyl-cytosine (5mC) expression and mRNA expression for DNA methyltransferases (DNMTs) 1, 3a, and 3b; and 3) vascular development was based on smooth muscle cell actin immunolocalization and on mRNA expression of several factors involved in the regulation of angiogenesis in fetal membranes (FMs). Throughout early pregnancy, the labeling index (proportion of proliferating cells) was very high (21%) and did not change. Expression of 5mC and mRNA for DNMT3b decreased, but mRNA for DNMT1 and 3a increased. Blood vessels were detected in FM on days 18-30 of pregnancy, and their number per tissue area did not change. The patterns of mRNA expression for placental growth factor, vascular endothelial growth factor, and their receptors FLT1 and KDR; angiopoietins 1 and 2 and their receptor TEK; endothelial nitric oxide synthase and the NO receptor GUCY13B; and hypoxia inducing factor 1 α changed in FM during early pregnancy. These data demonstrate high cellular proliferation rates, and changes in global methylation and mRNA expression of factors involved in the regulation of DNA methylation and angiogenesis in FM during early pregnancy. This description of cellular and molecular changes in FM during early pregnancy will provide the foundation for determining the basis of altered placental development in pregnancies compromised by environmental, genetic, or other factors.
The aim of this study was to evaluate lipid droplet (LD) expression in uteri of FSH-treated or nontreated sheep administered with arginine (Arg) or vehicle (saline, Sal) and fed a control (C), excess ...(overfed, O) or restricted (underfed, U) diet. In experiment 1, ewes from each diet were randomly assigned to Arg or Sal treatments administered three times daily starting on Day 0 of the first estrous cycle until blood sample and uterine tissue collection at the early- or mid-luteal phase of the second estrous cycle or the late-luteal phase of the first estrous cycle. In experiment 2, ewes were injected twice daily with FSH on Days 13 to 15 of the first estrous cycle, and blood samples and uterine tissue were collected at the early- and mid-luteal phases of the second estrous cycle. Cryopreserved in optimum cutting temperature (OCT) compound, cross-sections of uterine horn were stained with boron-dipyrromethene (BODIPY; marker of LDs) followed by 4′,6-diamidino-2-phenylindole (DAPI) staining and image analysis to determine the proportion (%) of area occupied by LD in luminal epithelium (LE) and endometrial glands (EGs). Control ewes maintained, O ewes gained, and U ewes lost body weight during the experiments. Serum progesterone concentration was not affected by nutritional plane or Arg treatment and was 5.5-fold greater in FSH- than Sal-treated ewes. LDs were detected in LE and superficial EG (close to LE) but not deep EG, or other uterine compartments, and area occupied by LD was greater in LE than in EG. In experiment 1, in LE and EG, area occupied by LDs was greater in C than in O or U; greater in Arg than in Sal; and greater at the late-, less at mid-, and least at early-luteal phases. In experiment 2, in LE and EG, area occupied by LDs was greater at mid- than in early-luteal phase. Comparison of data from FSH-treated and nontreated ewes (e.g., experiment 1 vs. experiment 2) demonstrated that FSH increased the area occupied by LD in LE and EG regardless of diet. Interactions between FSH treatment, stage of the estrous cycle, and plane of nutrition demonstrated that FSH increased the area occupied by LD in LE and EG at the mid-luteal phase in O and U. Thus, LDs are differentially distributed in uterine compartments, and area occupied by LD in endometrium is affected by nutritional plane, Arg or FSH, and stage of the estrous cycle. Such changes in dynamics of LD in the endometrium during the estrous cycle indicate their specific role in uterine functions.
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