Maternal predator odour exposure programs metabolic responses in adult offspring

Exogenous corticosterone administration during pregnancy in mice alters placental and fetal thyroid hormone availability in females

INTRODUCTION

Maternal prenatal psychological stress is associated with adverse pregnancy outcomes and increased risk of adverse health outcomes in children. While the molecular mechanisms that govern these associations has not been fully teased apart, stress-induced changes in placental function can drive sex-specific phenotypes in offspring. We sought to identify and examine molecular pathways in the placenta that are altered in response to maternal prenatal stress.

METHODS

We previously employed a mouse model of maternal prenatal stress where pregnant dams were treated with stress hormone (CORT) beginning in mid-gestation. Using this model, we conducted RNAseq analysis of whole placenta at E18.5. We used qRT-PCR to validate gene expression changes in the placenta and in a trophoblast cell line. ELISAs were used to measure the abundance of thyroid hormones in maternal and fetal serum and in the placenta.

RESULTS

Dio2 was amongst the top differentially expressed genes in response to exogenous stress hormone. Dio2 expression was more downregulated in placenta of female fetuses from CORT-treated dams than both control placenta from females and placenta from male fetuses. Consistent with Dio2's role in production of bioactive thyroid hormone (T3), we found that there was a reduction of T3 in placenta and serum of female embryos from CORT-treated dams at E18.5. Both T3 and T4 were reduced in the fetal compartment of the placenta of female fetuses from CORT-treated dams at E16.5. Exogenous stress hormone induced reduction in thyroid hormone in females was independent of circulating levels of TH in the dams.

DISCUSSION

The placental thyroid hormone synthesis pathway may be a target of elevated maternal stress hormone and modulate fetal programming of health and disease of offspring in a sex-specific fashion.

Exogenous corticosterone administration during pregnancy alters placental and fetal thyroid hormone availability in females

Introduction

Maternal prenatal stress is associated with adverse pregnancy outcomes and predisposition to long-term adverse health outcomes in children. While the molecular mechanisms that govern these associations has not been fully teased apart, stress-induced changes in placental function can drive sex-specific phenotypes in offspring. We sought to identify and examine molecular pathways in the placenta that are altered in response to maternal prenatal stress.

Methods

Using a mouse model of maternal prenatal stress, we conducted RNA-seq analysis of whole placenta at E18.5. We used qRT-PCR to validate gene expression changes in the placenta and in a trophoblast cell line. ELISAs were used to measure the abundance of thyroid hormones in maternal and fetal serum and in the placenta.

Results

Dio2 was amongst the top differentially expressed genes in response to elevated maternal stress hormone. Dio2 expression was more downregulated in female placenta from stressed dams than both female control and male placenta. Consistent with Dio2's role in production of bioactive thyroid hormone (T3), we found that there was a reduction of T3 in placenta and serum of female embryos from stressed dams at E18.5. Both T3 and T4 were reduced in the fetal compartment of the female placenta from stressed dams at E16.5. Stress hormone induced reduction in thyroid hormone in females was independent of circulating levels of TH in the dams.

Discussion

The placental thyroid hormone synthesis pathway may be a target of maternal stress and modulate fetal programming of health and disease of offspring in a sex-specific fashion.

Sex-specific maternal programming of corticosteroid-binding globulin by predator odour

Predation is a key organizing force in ecosystems. The threat of predation may act to programme the endocrine hypothalamic-pituitary-adrenal axis during development to prepare offspring for the environment they are likely to encounter. Such effects are typically investigated through the measurement of corticosteroids (Cort). Corticosteroid-binding globulin (CBG) plays a key role in regulating the bioavailability of Cort, with only free unbound Cort being biologically active. We investigated the effects of prenatal predator odour exposure (POE) in mice on offspring CBG and its impact on Cort dynamics before, during and after restraint stress in adulthood. POE males, but not females, had significantly higher serum CBG at baseline and during restraint and lower circulating levels of Free Cort. Restraint stress was associated with reduced liver transcript abundance of SerpinA6 (CBG-encoding gene) only in control males. POE did not affect SerpinA6 promoter DNA methylation. Our results indicate that prenatal exposure to a natural stressor led to increased CBG levels, decreased per cent of Free Cort relative to total and inhibited restraint stress-induced downregulation of CBG transcription. These changes suggest an adaptive response to a high predator risk environment in males but not females that could buffer male offspring from chronic Cort exposure.

Intergenerational trauma transmission is associated with brain metabotranscriptome remodeling and mitochondrial dysfunction

Intergenerational trauma increases lifetime susceptibility to depression and other psychiatric disorders. Whether intergenerational trauma transmission is a consequence of in-utero neurodevelopmental disruptions versus early-life mother–infant interaction is unknown. Here, we demonstrate that trauma exposure during pregnancy induces in mouse offspring social deficits and depressive-like behavior. Normal pups raised by traumatized mothers exhibited similar behavioral deficits to those induced in pups raised by their biological traumatized mothers. Good caregiving by normal mothers did not reverse prenatal trauma-induced behaviors, indicating a two-hit stress mechanism comprising both in-utero abnormalities and early-life poor parenting. The behavioral deficits were associated with profound changes in the brain metabotranscriptome. Striking increases in the mitochondrial hypoxia marker and epigenetic modifier 2-hydroxyglutaric acid in the brains of neonates and adults exposed prenatally to trauma indicated mitochondrial dysfunction and epigenetic mechanisms. Bioinformatic analyses revealed stress- and hypoxia-response metabolic pathways in the neonates, which produced long-lasting alterations in mitochondrial energy metabolism and epigenetic processes (DNA and chromatin modifications). Most strikingly, early pharmacological interventions with acetyl-L-carnitine (ALCAR) supplementation produced long-lasting protection against intergenerational trauma-induced depression.

Sammy Alhassen, Siwei Chen, et al. use mouse models to examine the effects of prenatal and postnatal stress on metabolomic and transcriptomic pathways in the brain. Their results suggest that altered mitochondrial metabolism may underlie trauma-induced behavioral deficits, and that correcting metabolism with ALCAR supplementation may protect against intergenerational transmission of traumatic stress.

Early life variations in temperature exposure affect the epigenetic regulation of the paraventricular nucleus in female rat pups

Early life maternal care received has a profound effect on later-life behaviour in adult offspring, and previous studies have suggested epigenetic mechanisms are involved. Changes in thyroid hormone receptor signalling may be related to differences in maternal care received and DNA methylation modifications. We investigated the effects of variations in temperature exposure (a proxy of maternal contact) and licking-like tactile stimulation on these processes in week-old female rat pups. We assessed thyroid hormone receptor signalling by measuring circulating triiodothyronine and transcript abundance of thyroid hormone receptors and the thyroid hormone-responsive genes DNA methyltransferase 3a and oxytocin in the paraventricular nucleus of the hypothalamus. DNA methylation of the oxytocin promoter was assessed in relation to changes in thyroid hormone receptor binding. Repeated room temperature exposure was associated with a decrease in thyroid hormone receptor signalling measures relative to nest temperature exposure, while acute room temperature exposure was associated with an increase. Repeated room temperature exposure also increased thyroid hormone receptor binding and DNA methylation at the oxytocin promoter. These findings suggest that repeated room temperature exposure may affect DNA methylation levels as a consequence of alterations in thyroid hormone receptor signalling.

Sensitive phases in the development of rodent social behavior

Here, we summarize recent advances on how environmental influences during sensitive phases alter the social behavioral phenotype of rodents later in life. Current studies support the view that the prenatal, early postnatal and adolescent periods of life can be regarded as sensitive phases. Environmental cues acting on the organism during these phases have a wide variety of effects on adult social behavior. One pattern that emerges across species and sensitive phases is that adversity tends to reduce social interactions and particularly affiliative social behavior. Concerning underlying mechanisms, various hormones can be involved; however, glucocorticoids frequently serve as the signal instigating plasticity. There is also increasing appreciation of non-endocrine mechanisms, specifically epigenetics and the microbiome. Concerning function, some evidence exists that sensitive phase outcomes adjust the individual's social phenotype to the nature of the social environment to be present during adulthood and breeding, though additional empirical support is still needed.

Perinatal high-fat diet impairs pup retrieval and induces sex-specific changes in ultrasonic vocalization characteristics of rat pups

Rodent pups emit ultrasonic vocalizations (USVs) to solicit maternal behavior, promoting their survival. Conversely, maternal behaviors affect the expression of pup USVs. We previously demonstrated that a maternal diet high in saturated fat (HFD) alters maternal behavior and is associated with early maturation of pups and their stress physiology. Here, we assessed the developmental profiles of pup USVs using quantitative and qualitative measures on postnatal days (PND)7 and 13. Quantitative measures included call counts, duration, and frequency, while qualitative measures examined calls' sonographic structures. HFD offspring lacked the typical decrease in USV numbers with age observed among control offspring. They also had shorter calls at PND7 compared to control and HFD offspring at PND13. HFD female offspring showed a greater number of one-frequency-sweep calls, while male pups showed a greater number of two-frequency-sweep calls compared to control offspring. Concomitantly, HFD dams showed impaired pup retrieval on PND7. The data suggest that fewer USVs of shorter duration in HFD offspring may alter dam solicitation and thus impair maternal pup retrieval. This study highlights the impacts of perinatal HFD exposure on the dyadic reciprocal interaction between dam and pups, which may set the stage for long-lasting effects on offspring physiology and behavior.

Developmental programming of the HPA axis and related behaviours: epigenetic mechanisms

It has been approximately 30 years since the seminal discoveries of David Barker and his colleagues, and research is beginning to unravel the mechanisms that underlie developmental programming. The early environment of the embryo, foetus and newborn have been clearly linked to altered hypothalamic-pituitary-adrenal (HPA) function and related behaviours through the juvenile period and into adulthood. A number of recent studies have shown that these effects can pass across multiple generations. The HPA axis is highly responsive to the environment, impacts both central and peripheral systems and is critical to health in a wide variety of contexts. Mechanistic studies in animals are linking early exposures to adversity with changes in gene regulatory mechanisms, including modifications of DNA methylation and altered levels of miRNA. Similar associations are emerging from recent human studies. These findings suggest that epigenetic mechanisms represent a fundamental link between adverse early environments and developmental programming of later disease. The underlying biological mechanisms that connect the perinatal environment with modified long-term health outcomes represent an intensive area of research. Indeed, opportunities for early interventions must identify the relevant environmental factors and their molecular targets. This new knowledge will likely assist in the identification of individuals who are at risk of developing poor outcomes and for whom early intervention is most effective.

Predator species related adaptive changes in larval growth and digestive physiology

Prey species are often non-randomly distributed along predator gradients but according to how they trade off growth against predation risk. The foraging-mediated growth/predation risk trade-off is well established, with increased foraging accelerating growth but also increasing predator induced mortality. While adaptations in digestive physiology may partly modify the relationship between foraging and growth in response to predation risk, studies exploring the impact of digestive physiology on growth in prey subjected to predation risk are still scarce. Larvae of the dragonfly genus Leucorrhinia segregate at the species level between lakes either being dominated by predatory fish (fish-lakes) or predatory invertebrates (dragonfly-lakes). Predators of these two lake types differ dramatically in their hunting style like searching and pursuing mode causing different selection pressure on prey traits including foraging. In a laboratory experiment we estimated growth rate, digestive physiology (ingested food, growth efficiency, assimilation efficiency, conversion efficiency) and metabolic rate (oxygen consumption) in the presence and absence of predator cues. Whereas fish-lake and dragonfly-lake Leucorrhinia species did not differ in growth rate, they evolved different pathways of digestive physiology to achieve similar growth rate. Because fish-lake species expressed a higher metabolic rate than dragonfly-lake species, we assume energy to be differently allocated and used for metabolic demands between species of both predator environments. Further, growth rate, but not digestive physiology was plastic in response to the presence of predator cues. Our results highlight the impact of digestive physiology in shaping the foraging-mediated growth/predation risk trade-off, with digestive physiology contributing to species distribution patterns along predator gradients.

Maternal Predator Odor Exposure in Mice Programs Adult Offspring Social Behavior and Increases Stress-Induced Behaviors in Semi-Naturalistic and Commonly-Used Laboratory Tasks

Maternal stress has a profound impact on the long-term behavioral phenotype of offspring, including behavioral responses to stressful and social situations. In this study, we examined the effects of maternal exposure to predator odor, an ethologically relevant psychogenic stressor, on stress-induced behaviors in both semi-naturalistic and laboratory-based situations. Adult C57BL/6 mice offspring of dams exposed to predator odor during the last half of pregnancy showed increased anti-predatory behavior, more cautious foraging behavior and, in the elevated plus maze, avoidance of elevated open areas and elevated open areas following restraint stress challenge. These offspring also exhibited alterations in social behavior including reduced free interaction and increased initial investigation despite normal social recognition. These changes in behavior were associated with increased transcript abundance of corticotropin-releasing factor, mineralocorticoid receptor and oxytocin (Oxt) in the periventricular nucleus of the hypothalamus. Taken together, the findings are consistent with a long-term increase in ethologically-relevant behavioral and neural responses to stress in male and female offspring as a function of maternal predator odor exposure.