Effects of neonatal progestin exposure on female reproductive tract structure and function in the adult ewe

The IGF system in the neonatal ovine uterus

Postnatal development of the ovine uterus primarily involves uterine gland morphogenesis or adenogenesis. Adenogenesis involves the budding differentiation of the glandular epithelium (GE) from the luminal epithelium (LE) and then GE proliferation and coiling/branching morphogenetic development within the stroma between birth (postnatal day or PND 0) and PND 56. Insulin-like growth factor (IGF)-I and IGF-II mRNAs were previously found to be expressed only in the endometrial stroma, whereas the IGF receptor (IGF-1R) mRNA was most abundant in epithelia and in stroma, suggesting that an intrinsic IGF system regulates postnatal development of the uterus. Given that the biological activities of IGFs are modulated by a family of six IGF binding proteins (IGFBPs) and specific proteases, the objective was to determine the effects of age and estrogen disruption on expression of IGFs, IGFBPs and pregnancy-associated plasma protein A (PAPP-A or IGFBP-4 protease) in the ovine uterus. In Study One, circulating levels of IGF-I and IGF-II in the serum of neonatal ewes did not change between PND 0 and PND 56. Levels of immunoreactive IGF-I, IGF-II and IGF-1R protein were most abundant on the apical surface of the endometrial LE and GE. RT-PCR analyses detected expression of IGFBPs (3, 4, 5 and 6) as well as PAPP-A mRNAs in the uterus, but not IGFBP-1 and IGFBP-2 mRNAs. IGFBP-3 and IGFBP-4 mRNAs were expressed specifically in the endometrial stroma and myometrium and increased after birth. PAPP-A mRNA was expressed specifically in the endometrial stroma and increased after birth. In Study Two, ewes were treated from birth with estradiol-17beta valerate (EV), which reduces uterine growth and inhibits endometrial adenogenesis. On PNDs 14 and 56, IGFBP-3 mRNA was decreased in the uterus of EV-treated ewes, but IGF-1R and IGFBP-4 mRNAs were not affected. PAPP-A mRNA was increased by EV treatment on PND 14, but decreased on PND 56. These results support the hypothesis that an intrinsic IGF system in the uterus regulates epithelial-stromal interactions important for postnatal uterine growth and endometrial gland morphogenesis in the sheep.

Actions of progesterone on uterine immunosuppression and endometrial gland development in the uterine gland knockout (UGKO) ewe

In ewes, the uterine gland knockout (UGKO) phenotype is caused by neonatal exposure to norgestomet to arrest uterine gland development and produce an adult which has a uterus characterized by the lack of endometrial glands. Since endometrial glands in the sheep produce the lymphocyte-inhibitory protein, ovine uterine serpin (OvUS), an experiment was conducted with ewes of the UGKO phenotype to evaluate whether the inhibitory actions of progesterone on tissue rejection responses in utero are dependent upon the presence of endometrial glands. Control and UGKO ewes were ovariectomized and subsequently treated with either 100 mg/day progesterone or corn oil vehicle for 30 days. An autograft and allograft of skin were then placed in each uterine lumen and treatments were continued for an additional 30 days before grafts were examined for survival. All autografts survived and had a healthy appearance after histological analysis. Allografts were generally rejected in ewes treated with vehicle but were present for hormone-treated ewes, regardless of uterine phenotype. Analysis of the histoarchitecture and protein synthetic capacity of the uterus revealed that progesterone induced differentiation of endometrial glands and synthesis and secretion of OvUS in UGKO ewes. The UGKO ewes had reduced density of CD45R+ lymphocytes in the endometrial epithelium and there was a tendency for progesterone to reduce this effect in luminal epithelium. Taken together, results confirm the actions of progesterone to inhibit graft rejection response in utero. Responses of UGKO ewes to progesterone indicate that the hormone can induce de novo development and differentiation of endometrial glands, at least when skin grafts are in the uterus.

Comparative developmental biology of the mammalian uterus

The uterus is an essential organ for reproduction in mammals. Despite the importance of the uterus for the fertility and health of women and their offspring, relatively little is known about the hormonal, cellular, and molecular mechanisms that regulate development of the uterus in either the fetus or neonate. Disruption of uterine development in the fetus and neonate by genetic defects or exposure to endocrine disruptors can program the function of the uterus in the adult and lead to infertility, cancer, and even death. The intent of this chapter is to review the current knowledge of regulatory factors and pathways governing prenatal organogenesis and postnatal morphogenesis of the uterus in mammals, with a particular focus on laboratory and domestic animals. Prenatal organogenesis, postnatal morphogenesis, and adult functional differentiation of the uterus are complex, multifactorial processes. Although conservation of some factors and pathways are observed between species, it is clear that mutation of candidate genes in the mouse does not always recapitulate the same defects observed in the human. Therefore, comparative biology of the mechanisms regulating uterine development in other species may be useful to identify candidate genes and pathways to understand congenital abnormalities in humans. This knowledge is necessary to develop rational therapies to prevent and treat infertility and to enhance fertility in humans and domestic animals.

Implantation mechanisms: insights from the sheep

Implantation in all mammals involves shedding of the zona pellucida, followed by orientation, apposition, attachment and adhesion of the blastocyst to the endometrium. Endometrial invasion does not occur in domestic ruminants; thus, definitive implantation is achieved by adhesion of the mononuclear trophoblast cells to the endometrial lumenal epithelium (LE) and formation of syncytia by the fusion of trophoblast binucleate cells with the LE. This review highlights new information on mechanisms regulating the implantation cascade in sheep. The embryo enters the uterus on day 4 at the morula stage of development and then develops into a blastocyst by day 6. The blastocyst sheds the zona pellucida (day 8), elongates to a filamentous form (days 11–16), and adheres to the endometrial LE (day 16). Between days 14 and 16, the binucleate cells begin to differentiate in the trophoblast and subsequently migrate and fuse with the endometrial LE to form syncytia. Continuous exposure of the endometrium to progesterone in early pregnancy downregulates the progesterone receptors in the epithelia, a process which is associated with loss of the cell-surface mucin MUC1 and induction of several secreted adhesion proteins. Recurrent early pregnancy loss in the uterine gland knockout ewe model indicates that secretions of the endometrial epithelia have a physiologic role in blastocyst elongation and implantation. A number of endometrial proteins have been identified as potential regulators of blastocyst development and implantation in sheep, including glycosylated cell adhesion molecule 1 (GlyCAM-1), galectin-15, integrins and osteopontin. The epithelial derived secreted adhesion proteins (GlyCAM-1, galectin-15 and osteopontin) are expressed in a dynamic temporal and spatial manner and regulated by progesterone and/or interferon tau, which is the pregnancy recognition signal produced by the trophoblast during blastocyst elongation. The noninvasive and protracted nature of implantation in domestic animals provides valuable opportunities to investigate fundamental processes of implantation that are shared among all mammals. Understanding of the cellular and molecular signals that regulate uterine receptivity and implantation can be used to diagnose and identify causes of recurrent pregnancy loss and to improve pregnancy outcome in domestic animals and humans.

Neonatal estrogen exposure disrupts uterine development in the postnatal sheep

Postnatal development of the ovine uterus between birth and postnatal day (PND) 56 involves budding differentiation of the endometrial glandular epithelium from the luminal epithelium (LE) followed by extensive coiling and branching morphogenesis of the tubular glands. To determine the short- and long-term effects of estrogen on neonatal ovine uterine development after PND 14, neonatal sheep were randomly assigned at birth (PND 0) to be treated daily with estradiol-17beta benzoate (EB; 0, 0.01, 0.1, 1, or 10 microg/kg body weight.d) during one of two developmental periods (PND 14-27 or 42-55). All ewes were hemiovariohysterectomized at the end of EB treatment on either PND 28 or 56, and the remaining uterine horn and ovary removed on PND 112. Immediate responses to EB treatment included dose- and age-dependent increases in uterine wet weight, thickness of the endometrium, myometrium, and LE, but decreases in endometrial glands on PND 28 and 56. Transient exposure to EB decreased gland number and thickness of the endometrium and LE on PND 112 but did not affect extrauterine reproductive tract structures. The mechanism of estrogen inhibition of uterine development did not involve effects on cell proliferation. Real-time PCR analyses found that EB exposure disrupted normal patterns of growth factor (IGF-I, IGF-II, fibroblast growth factor-7, fibroblast growth factor-10, and hepatocyte growth factor) and receptor mRNA expression in the uterus. Transient exposure of the neonatal ewe to estrogens during critical periods specifically alters growth factor networks that perturb normal development of the uterus, leading to permanent alterations in uterine structure and function.

Osteopontin: roles in implantation and placentation

Osteopontin (OPN) is an acidic member of the small integrin-binding ligand N-linked glycoprotein (SIBLING) family of extracellular matrix proteins/cytokines that undergoes extensive posttranslational modification, including phosphorylation, glycosylation, and cleavage, yielding molecular mass variants ranging in size from 25 to 75 kDa. The result is a versatile protein(s) with multiple functions arising from its role as a mediator of cell-cell and cell-extracellular matrix (ECM) communication that encompass both normal and tumorigenic developmental processes, immunological responses during inflammation and wound healing, and biomineralization. Studies in primates, pigs, sheep, and rodents have revealed that OPN is a major constituent of the uterine-placental microenvironment with influence as 1) a component of histotroph required for adhesion and signal transduction at the uterine-placental interface throughout pregnancy, 2) a gene product expressed by uterine stroma contributing to a decidualization-like transformation that correlates with the degree of conceptus invasiveness, and 3) a product of resident uterine and placental immune cells that may regulate their behavior and cytokine production. This minireview summarizes information regarding uterine and placental expression of OPN that has accumulated over the past 15 yr, and we briefly describe structural/functional properties of this protein that are likely relevant to its role(s) during pregnancy. Comparative studies have offered insights into the potential hormonal/cytokine, cellular, and molecular mechanisms underlying OPN-mediated adhesion, remodeling, and cell-cell/cell-ECM communication within the uterus and placenta. OPN has the potential to profoundly impact pregnancy, and investigators are now challenged to focus on the mechanistic nature of the functions of this multifaceted and major component of the uterine-placental microenvironment.

Estrogen-induced disruption of neonatal porcine uterine development alters adult uterine function

In the pig, estradiol-17beta valerate (EV) exposure from birth (Postnatal Day [PND] 0) disrupts estrogen receptor-alpha (ER)-dependent uterine development and increases embryo mortality in adults. To determine effects of neonatal EV exposure on adult uterine morphology and function, 36 gilts received corn oil (CO) or EV from PND 0 to PND 13. Cyclic and pregnant (PX) adults from each treatment group were hysterectomized on Day 12 after estrus/mating. Treatment and pregnancy effects were determined for uterine weight and horn volume, uterine luminal fluid (ULF) protein and estradiol content, endometrial incorporation of 3H-leucine (3H-Leu) into nondialyzable product, and endometrial mRNA levels for ER, progesterone receptor (PR), uteroferrin (UF), retinol-binding protein (RBP), and keratinocyte growth factor (KGF). Adults cycled normally and had similar numbers of corpora lutea. Uteri of PX gilts contained tubular/filamentous conceptuses, and ULF estradiol content was unaffected by treatment. However, pregnancy increased uterine weight and size only in CO gilts (Treatment x Status, P < 0.01). Treatment reduced ULF protein content (P < 0.01), endometrial 3H-Leu incorporation (P < 0.05), and the pregnancy-associated increase in ULF protein (Treatment x Status, P < 0.01). Treatment did not affect endometrial ER or PR mRNA levels but attenuated the pregnancy-associated increase in UF mRNA (Treatment x Status; P < 0.01), increased RBP (P < 0.10), and decreased KGF mRNA levels (P < 0.05). These results establish that transient postnatal estrogen exposure affects porcine uterine responsiveness to potentially embryotrophic signals and that estrogen-sensitive postnatal uterine organizational events are determinants of uterine size and functionality.

Prolactin regulation of neonatal ovine uterine gland morphogenesis

Uterine gland development or adenogenesis in the neonatal ovine uterus involves budding, proliferation, and branching morphogenesis of the glandular epithelium (GE) from the luminal epithelium (LE) between birth (postnatal day or PND 0) and PND 56. This critical developmental event is coincident with increases in serum PRL and expression of long and short PRL receptors specifically in the nascent and proliferating GE. In study one, ewes were treated with a placebo pellet as a control (CX) or a bromocryptine mesylate pellet from PNDs 0-56. On PND 56, the endometrium of bromocryptine mesylate ewes contained fewer glands, particularly in the stratum spongiosum that contained numerous coiled and branched glands in CX uteri. In study two, ewes were treated with saline as a CX or recombinant ovine PRL from PNDs 0-56. Treatment with PRL increased gland number and density on PND 14 and PND 56. In study three, expression of signal transducers and activators of transcription (STAT) 1, 3, and 5 proteins was detected in the developing glands from PNDs 7-56. In study four, Western blot analyses indicated that PRL increased levels of phosphorylated STATs 1 and 5, but not STAT 3, and phosphorylated ERK 1 and 2 MAPKs and c-Jun N-terminal kinase/stress-activated protein kinase proteins in explanted PND 28 ovine uteri. Collectively, results indicate that PRL regulates endometrial adenogenesis in the neonatal ovine uterus.

Morphometric analysis of the uterine endometrium of swine on days 12 and 16 postestrus

The uterine endometrium of swine is comprised of luminal epithelial, glandular epithelial, and stromal cells that secrete the luteolysin, prostaglandin F(2alpha) (PGF(2alpha)), during late diestrus. However, which of these cells contribute the most to luteolytic PGF(2alpha) secretion is unknown because the cellular composition of the endometrium has not been quantified. Therefore, this study quantified the cellular composition of the endometrium on days 12 and 16 postestrus by histologic and morphometric analyses. On day 12, the endometrium consisted predominantly of stromal cells (47% of total cell quantity) and glandular epithelial cells (37%), whereas luminal epithelial cells represented only 16% of the total of the three cell types. The number of glandular epithelial cells tended to increase (P < 0.10) between days 12 and 16, such that they comprised 45% of the endometrium by day 16, while the number of stromal and luminal cells did not change and accounted for 45% and 10% of the cells, respectively. Luminal epithelial cells had a 58% greater cross-sectional area (P < 0.001) than glandular epithelial cells, whereas glandular epithelial cells had a 22% greater area (P < 0.001) than stromal cells. Glandular epithelial cells decreased (P < 0.001) in cross-sectional area between days 12 and 16, whereas the area of luminal epithelial and stromal cells remained unchanged. These results indicate that the porcine endometrium is comprised predominantly of stromal and glandular epithelial cells that are likely to contribute substantially to endometrial PGF(2alpha) secretion during luteolysis. The contribution of glandular epithelium to luteolytic PGF(2alpha) secretion probably increases during diestrus as the number of these cells increases.

Expression of endogenous betaretroviruses in the ovine uterus: effects of neonatal age, estrous cycle, pregnancy, and progesterone

The ovine genome contains 15 to 20 copies of endogenous retroviruses (enJSRVs) highly related to the oncogenic jaagsiekte sheep retrovirus (JSRV) and enzootic nasal tumor virus. enJSRVs are highly expressed in the endometrial lumenal epithelia (LE) and glandular epithelia (GE) of the ovine uterus. The effects of neonatal age, estrous cycle, pregnancy, and progesterone on expression of enJSRVs in the ovine uterus were determined. Expression of enJSRV RNAs was absent from the uterus of ewes at birth, but enJSRV RNAs were expressed specifically in the LE and developing GE from postnatal day (PND) 7 to PND 56. In adult ewes, enJSRV RNAs were detected only in the epithelia of the uterine endometrium, as well as epithelia of the oviduct, cervix, and vagina. In cyclic ewes, endometrial enJSRV RNA abundance was lowest on day 1, increased 12-fold between days 1 and 13, and then decreased to day 15. In pregnant ewes, levels of endometrial enJSRV RNAs were high on day 11, increased to day 13, and then decreased to day 19. In day 17 and 19 conceptuses, enJSRV RNAs were also detected in binucleate cells of the trophectoderm. Immunoreactive JSRV capsid and envelope proteins were detected in the endometrial LE and GE, as well as in the binucleate cells of the conceptus. In transfection assays utilizing ovine endometrial LE cells, progesterone increased transcriptional activity of several enJSRV long terminal repeats. Collectively, these results indicate that transcription of enJSRVs in the endometrial epithelia of the ovine uterus is increased by progesterone and might support a role for enJSRVs in conceptus-endometrium interactions during the peri-implantation period and early placental morphogenesis.

Developmental biology of uterine glands

All mammalian uteri contain endometrial glands that synthesize or transport and secrete substances essential for survival and development of the conceptus (embryo/fetus and associated extraembryonic membranes). In rodents, uterine secretory products of the endometrial glands are unequivocally required for establishment of uterine receptivity and conceptus implantation. Analyses of the ovine uterine gland knockout model support a primary role for endometrial glands and, by default, their secretions in peri-implantation conceptus survival and development. Uterine adenogenesis is the process whereby endometrial glands develop. In humans, this process begins in the fetus, continues postnatally, and is completed during puberty. In contrast, endometrial adenogenesis is primarily a postnatal event in sheep, pigs, and rodents. Typically, endometrial adenogenesis involves differentiation and budding of glandular epithelium from luminal epithelium, followed by invagination and extensive tubular coiling and branching morphogenesis throughout the uterine stroma to the myometrium. This process requires site-specific alterations in cell proliferation and extracellular matrix (ECM) remodeling as well as paracrine cell-cell and cell-ECM interactions that support the actions of specific hormones and growth factors. Studies of uterine development in neonatal ungulates implicate prolactin, estradiol-17 beta, and their receptors in mechanisms regulating endometrial adenogenesis. These same hormones appear to regulate endometrial gland morphogenesis in menstruating primates and humans during reconstruction of the functionalis from the basalis endometrium after menses. In sheep and pigs, extensive endometrial gland hyperplasia and hypertrophy occur during gestation, presumably to provide increasing histotrophic support for conceptus growth and development. In the rabbit, sheep, and pig, a servomechanism is proposed to regulate endometrial gland development and differentiated function during pregnancy that involves sequential actions of ovarian steroid hormones, pregnancy recognition signals, and lactogenic hormones from the pituitary or placenta. That disruption of uterine development during critical organizational periods can alter the functional capacity and embryotrophic potential of the adult uterus reinforces the importance of understanding the developmental biology of uterine glands. Unexplained high rates of peri-implantation embryonic loss in humans and livestock may reflect defects in endometrial gland morphogenesis due to genetic errors, epigenetic influences of endocrine disruptors, and pathological lesions.

Neonatal estradiol exposure alters uterine morphology and endometrial transcriptional activity in prepubertal gilts

Porcine endometrial development between birth (postnatal day = PND 0) and PND 56 involves differentiation of glandular epithelium (GE) from luminal epithelium (LE) and estrogen receptor-alpha (ER) expression. Juvenile ER architecture evolves after birth, as stroma and nascent GE first express ER. Mature ER architecture is evident after PND 30, when stroma, GE and LE are ER-positive. When administered during discrete periods between PND 0 and 56, effects of estradiol-17beta valerate (EV) on the neonatal porcine uterus relate to endometrial ER architecture. Transient EV exposure from birth reduces embryo survival in pregnant adult gilts. Effects of EV, administered as juvenile endometrial ER architecture develops (P1, PND 0-13), or after mature ER architecture is established (P2, PND 42-55), were evaluated in uteri from gilts treated with corn oil or EV in P1 or P2 and hysterectomized on PND 100 without additional steroids (NSt), on PND 102 after EV on PND100-101 (EV2), or on PND 117 after EV2 followed by progesterone on PND 102-116 (EP). Neonatal EV reduced uterine weight (P < 0.02), size (P < 0.01), luminal protein content (P < 0.07), and percent incorporation of 3H-leucine into nondialyzable endometrial products in vitro (P < 0.01). Group (NSt, EV2, EP) -specific treatment effects detected for endometrial ER, progesterone receptor, uteroferrin, and/or retinol binding protein mRNA levels were frequently related to period (P1,P2). Results support the idea that estrogen-sensitive postnatal organizational events, including those defined, in part, by endometrial ER architecture, are likely components of genetic and epigenetic programs governing uterine morphogenesis and ontogeny of endometrial function in the pig.