Pattern of maternal circulating CRH in laboratory-housed squirrel and owl monkeys

Anthropoid primate-specific retroviral element THE1B controls expression of CRH in placenta and alters gestation length

Pregnancy and parturition are intricately regulated to ensure successful reproductive outcomes. However, the factors that control gestational length in humans and other anthropoid primates remain poorly defined. Here, we show the endogenous retroviral long terminal repeat transposon-like human element 1B (THE1B) selectively controls placental expression of corticotropin-releasing hormone (CRH) that, in turn, influences gestational length and birth timing. Placental expression of CRH and subsequently prolonged gestational length were found in two independent strains of transgenic mice carrying a 180-kb human bacterial artificial chromosome (BAC) DNA that contained the full length of CRH and extended flanking regions, including THE1B. Restricted deletion of THE1B silenced placental CRH expression and normalized birth timing in these transgenic lines. Furthermore, we revealed an interaction at the 5′ insertion site of THE1B with distal-less homeobox 3 (DLX3), a transcription factor expressed in placenta. Together, these findings suggest that retroviral insertion of THE1B into the anthropoid primate genome may have initiated expression of CRH in placental syncytiotrophoblasts via DLX3 and that this placental CRH is sufficient to alter the timing of birth.

The proper timing of delivery is critical during pregnancy; if too early or too late, the baby will be at risk of serious health problems and even death. Corticotropin-releasing hormone (CRH) is a protein that can be detected in maternal blood, and its concentration correlates with the timing of birth. In humans and other anthropoid primates, CRH is made by the placenta, whereas in other mammals, it is produced in a specialized region of the brain. To understand the regulation and evolution of this key protein, we inserted the human CRH gene and nearby regions into the mouse genome, which resulted in human CRH expression in the mouse placenta. Mouse litters that make CRH in their placentas are born later than control mice, showing that CRH can directly affect birth timing. Using our mouse model, we then selectively deleted a remnant of an ancient retrovirus that is normally found in the DNA of anthropoid primates and demonstrated that this specific region controls expression of CRH in the placenta. Deletion of this region also restored normal birth timing in the mice by eliminating CRH production from the placenta. We propose that retroviral regulation of CRH in the placenta may be a mechanism of controlling birth timing in humans and other anthropoid primates.

Measuring stress responses in female Geoffroy's spider monkeys: Validation and the influence of reproductive state

Fecal glucocorticoid metabolites are increasingly used to investigate physiological stress. However, it is crucial for researchers to simultaneously investigate the effects of reproductive state because estradiol and placental hormones can affect circulating glucocorticoid concentrations. Reports on the relationships between glucocorticoids and reproductive state are inconsistent among females. Unlike several primate species that have heightened glucocorticoid activity during lactation, humans experience reduced glucocorticoid activity during lactation. Rather than a taxonomic difference, we hypothesize that this is a result of different environmental stressors, particularly the threat of infanticide. Here, we expand the number of wild primate species tested by validating a glucocorticoid assay for female Geoffroy's spider monkeys. We investigate the effects of reproductive state on their glucocorticoid concentrations. Utilizing a routine veterinary exam on a captive population, we determined that fecal glucocorticoid metabolites increase in response to a stressor (anesthesia), and this rise is detected approximately 24 hr later. Additionally, we found that extracted hormone patterns in a wild population reflected basic reproductive biology-estradiol concentrations were higher in cycling than lactating females, and in lactating females with older offspring who were presumably resuming their cycle. However, we found that estradiol and glucocorticoid concentrations were significantly correlated in lactating but not cycling females. Similarly, we found that reproductive state and estradiol concentration, but not stage of lactation, predicted glucocorticoid concentrations. Unlike patterns in several other primate species that face a relatively strong threat of infanticide, lactating spider monkeys experience reduced glucocorticoid activity, possibly due to attenuating effects of oxytocin and lower male-initiated aggression than directed at cycling females. More broadly, we conclude that future studies using fecal glucocorticoid metabolites to index stress should consider that reproductive state might confound glucocorticoid measurements. Am. J. Primatol. 77:925-935, 2015. © 2015 Wiley Periodicals, Inc.

Comparative Immunohistochemistry of Placental Corticotropin-Releasing Hormone and the Transcription Factor RelB-NFκB2 Between Humans and Nonhuman Primates

The transcription factor RelB-NFκB2, activated by the noncanonical NFκB pathway, positively regulates corticotropin-releasing hormone (CRH) and prostaglandin production in the term human placenta and may play an important role in the timing of human parturition. Here we explored whether RelB-NFκB2 signaling plays a role in parturition in nonhuman anthropoid primates. We performed immunohistochemical staining to assess the correlation between CRH and nuclear activity of RelB-NFκB2 heterodimers in term placentas from humans, 3 catarrhine primate species, and a single platyrrhine primate species. Consistent with our previous studies, the human placenta showed cytoplasmic staining for CRH and nuclear staining for RelB-NFκB2. Similar staining patterns were noted in the 3 catarrhine primates (chimpanzee, baboon, and rhesus macaque). The platyrrhine (marmoset) placentas stained positively for CRH and RelB but not for NFκB2. Catarrhine (but not platyrrhine) nonhuman primate term placentas demonstrate the same CRH staining and nuclear localization patterns of RelB and NFκB2 as does human placenta. These results suggest that catarrhine primates, particularly rhesus macaques, may serve as useful animal models to study the biologic significance of the noncanonical NFκB pathway in human pregnancy.

Regulation of progesterone signaling during pregnancy: implications for the use of progestins for the prevention of preterm birth

Preterm birth is a major cause of neonatal morbidity and mortality. Progesterone plays a critical role in suppressing the inflammatory signals that would induce parturition prior to term. Progesterone signaling is regulated in a variety of ways during pregnancy. Endocrine production of high levels of progesterone by the placenta ensures the availability of high levels of progesterone throughout pregnancy. Paracrine regulation of progesterone metabolism in target tissues, particularly the myometrium and cervix, also determines the amount of progesterone ligand available. Progesterone metabolism can also lead to the formation of metabolites that contribute to its effects. In particular, 5β-dihydroprogesterone formation by aldo-keto reductase 1D1 appears to play an important role in maintaining uterine quiescence. Progesterone signaling can also be regulated at the receptor level through changes in the relative expression of the nuclear progesterone receptor isoforms, reduced expression of membrane receptors, and changes in the expression levels of coactivators and/or corepressors, including nuclear factor κB. Progesterone and 17α-hydroxyprogesterone caproate (17OH-PC) have recently been shown to reduce preterm births in women with previous preterm birth or shortened cervix. It is important to realize that these two progestins are likely to act in significantly different ways, which will likely influence their efficacy. The structural differences and resistance to metabolism exhibited by 17OH-PC means that it will be unable to activate some of the pathways that progesterone activates, but that it also will not be subject to paracrine inactivation. The fact that progesterone therapy works for maintaining pregnancy in some women, indicates that for those women insufficient levels of progesterone ligand in target tissues is a determining factor in early parturition, despite high levels of circulating progesterone. This article is part of a Special Issue entitled 'Pregnancy and Steroids'.

The physiological roles of placental corticotropin releasing hormone in pregnancy and childbirth

In response to stress, the hypothalamus releases cortiticotropin releasing hormone (CRH) that travels to the anterior pituitary, where it stimulates the release of adrenocorticotropic hormone (ACTH). ACTH travels to the adrenal cortex, where it stimulates the release of cortisol and other steroids that liberate energy stores to cope with the stress. During pregnancy, the placenta synthesises CRH and releases it into the bloodstream at increasing levels to reach concentrations 1,000 to 10, 000 times of that found in the non-pregnant individual. Urocortins, which are CRH analogues are also secreted by the placenta. Desensitisation of the maternal pituitary to CRH and resetting after birth may be a factor in post-partum depression. Recently, CRH has been found to modulate glucose transporter (GLUT) proteins in placental tissue, and therefore there may be a link between CRH levels and foetal growth. Evidence suggests CRH is involved in the timing of birth by modulating signalling systems that control the contractile properties of the myometrium. In the placenta, cortisol stimulates CRH synthesis via activation of nuclear factor kappa B (NF-κB), a component in a cellular messenger system that may also be triggered by stressors such as hypoxia and infection, indicating that intrauterine stress could bring forward childbirth and cause low birth weight infants. Such infants could suffer health issues into their adult life as a result of foetal programming. Future treatment of these problems with CRH antagonists is an exciting possibility.

On the function of placental corticotropin-releasing hormone: a role in maternal-fetal conflicts over blood glucose concentrations

Throughout the second and third trimesters, the human placenta (and the placenta in other anthropoid primates) produces substantial quantities of corticotropin-releasing hormone (placental CRH), most of which is secreted into the maternal bloodstream. During pregnancy, CRH concentrations rise over 1000-fold. The advantages that led selection to favour placental CRH production and secretion are not yet fully understood. Placental CRH stimulates the production of maternal adrenocorticotropin hormone (ACTH) and cortisol, leading to substantial increases in maternal serum cortisol levels during the third trimester. These effects are puzzling in light of widespread theory that cortisol has harmful effects on the fetus. The maternal hypothalamic-pituitary-adrenal (HPA) axis becomes less sensitive to cortisol during pregnancy, purportedly to protect the fetus from cortisol exposure. Researchers, then, have often looked for beneficial effects of placental CRH that involve receptors outside the HPA system, such as the uterine myometrium (e.g. the placental clock hypothesis). An alternative view is proposed here: the beneficial effect of placental CRH to the fetus lies in the fact that it does stimulate the production of cortisol, which, in turn, leads to greater concentrations of glucose in the maternal bloodstream available for fetal consumption. In this view, maternal HPA insensitivity to placental CRH likely reflects counter-adaptation, as the optimal rate of cortisol production for the fetus exceeds that for the mother. Evidence pertaining to this proposal is reviewed.