Absence of Depressive and Anxious Behavior with Genetic Dysregulation in Adult C57Bl/6J Mice after Prenatal Exposure to Ionizing Radiation.

The exposure of ionizing radiation during early gestation often leads to deleterious and even lethal effects; however, few extensive studies have been conducted on late gestational exposures. This research examined the behavior al effects of C57Bl/6J mouse offspring exposed to low dose ionizing gamma irradiation during the equivalent third trimester. Pregnant dams were randomly assigned to sham or exposed groups to either low dose or sublethal dose radiation (50, 300, or 1000 mGy) at gestational day 15. Adult offspring underwent a behavioral and genetic analysis after being raised under normal murine housing conditions. Our results indicate very little change in the behavioral tasks measuring general anxiety, social anxiety, and stress-management in animals exposed prenatally across the low dose radiation conditions. Quantitative real-time polymerase chain reactions were conducted on the cerebral cortex, hippocampus, and cerebellum of each animal; results indicate some dysregulation in markers of DNA damage, synaptic activity, reactive oxygen species (ROS) regulation, and methylation pathways in the offspring. Together, our results provide evidence in the C57Bl/6J strain, that exposure to sublethal dose radiation (<1000 mGy) during the last period of gestation leads to no observable changes in behaviour when assessed as adults, although some changes in gene expression were observed for specific brain regions. These results indicate that the level of oxidative stress occurring during late gestation for this mouse strain is not sufficient for a change in the assessed behavioral phenotype, but results in some modest dysregulation of the genetic profile of the brain.

The role of sexual isolation during rapid ecological divergence: Evidence for a new dimension of isolation in Rhagoletis pomonella.

The pace of divergence and likelihood of speciation often depends on how and when different types of reproductive barriers evolve. Questions remain about how reproductive isolation evolves after initial divergence. We tested for the presence of sexual isolation (reduced mating between populations due to divergent mating preferences and traits) in Rhagoletis pomonella flies, a model system for incipient ecological speciation. We measured the strength of sexual isolation between two very recently diverged (~170 generations) sympatric populations, adapted to different host fruits (hawthorn and apple). We found that flies from both populations were more likely to mate within than between populations. Thus, sexual isolation may play an important role in reducing gene flow allowed by early-acting ecological barriers. We also tested how warmer temperatures predicted under climate change could alter sexual isolation and found that sexual isolation was markedly asymmetric under warmer temperatures - apple males and hawthorn females mated randomly while apple females and hawthorn males mated more within populations than between. Our findings provide a window into the early speciation process and the role of sexual isolation after initial ecological divergence, in addition to examining how environmental conditions could shape the likelihood of further divergence.

Effect of Prenatal Glucocorticoid Exposure on Circadian Rhythm Gene Expression in the Brains of Adult Rat Offspring.

Circadian clocks control many vital aspects of physiology from the sleep-wake cycle to metabolism. The circadian clock operates through transcriptional-translational feedback loops. The normal circadian signaling relies on a 'master clock', located in the suprachiasmatic nucleus (SCN), which synchronizes peripheral oscillators. Glucocorticoid receptor (GR) signaling has the ability to reset the phase of peripheral clocks. It has been shown that maternal exposure to glucocorticoids (GCs) can lead to modification of hypothalamic-pituitary-adrenal (HPA) function, impact stress-related behaviors, and result in a hypertensive state via GR activation. We previously demonstrated altered circadian rhythm signaling in the adrenal glands of offspring exposed to the synthetic GC, dexamethasone (Dex). Results from the current study show that prenatal exposure to Dex affects circadian rhythm gene expression in a brain region-specific and a sex-specific manner within molecular oscillators of the amygdala, hippocampus, paraventricular nucleus, and prefrontal cortex, as well as the main oscillator in the SCN. Results also show that spontaneously hypertensive rats (SHR) exhibited dysregulated circadian rhythm gene expression in these same brain regions compared with normotensive Wistar-Kyoto rats (WKY), although the pattern of dysregulation was markedly different from that seen in adult offspring prenatally exposed to GCs.

Untargeted metabolomics reveals sex-specific differences in lipid metabolism of adult rats exposed to dexamethasone in utero.

Prenatal stress through glucocorticoid (GC) exposure leads to an increased risk of developing diseases such as cardiovascular disease, metabolic syndrome and hypertension in adulthood. We have previously shown that administration of the synthetic glucocorticoid, dexamethasone (Dex), to pregnant Wistar-Kyoto dams produces offspring with elevated blood pressures and disrupted circadian rhythm signaling. Given the link between stress, circadian rhythms and metabolism, we performed an untargeted metabolomic screen on the livers of offspring to assess potential changes induced by prenatal Dex exposure. This metabolomic analysis highlighted 18 significantly dysregulated metabolites in females and 12 in males. Pathway analysis using MetaboAnalyst 4.0 highlighted key pathway-level metabolic differences: glycerophospholipid metabolism, purine metabolism and glutathione metabolism. Gene expression analysis revealed significant upregulation of several lipid metabolism genes in females while males showed no dysregulation. Triglyceride concentrations were also found to be significantly elevated in female offspring exposed to Dex in utero, which may contribute to lipid metabolism activation. This study is the first to conduct an untargeted metabolic profile of liver from GC exposed offspring. Corroborating metabolic, gene expression and lipid profiling results demonstrates significant sex-specific lipid metabolic differences underlying the programming of hepatic metabolism.

Late gestational exposure to dexamethasone and fetal programming of abnormal behavior in Wistar Kyoto rats.

INTRODUCTION: Fetal programming was characterized a few decades ago, explaining the correlation of physiological phenotypes of offspring exposed to early-life stress. High acute or chronic prenatal stress can overwhelm the enzymatic placental barrier, inducing transcriptional changes in the fetus that can result in different adverse behavioral and physiological phenotypes. The current study investigates the impact of exposure to the synthetic glucocorticoid, dexamethasone, during late gestation on behavioral outcomes. METHODS: Pregnant Wistar Kyoto rats were given daily subcutaneous injections from gestational days 15-21 of either dexamethasone (0.9% NaCl, 4% EtOH, 100 µg kg-1  day-1 ) or were physically manipulated as naïve controls. Pups were raised normally until 17 weeks of age and underwent the Porsolt swim task and elevated plus maze for depressive and anxiety-like behaviors, respectively. Neural tissue was preserved for genetic analysis using quantitative real-time polymerase chain reaction. RESULTS: Statistical analyses show significant disruption of behavior and genetic profiles of offspring exposed to dexamethasone in-utero. Exposed animals spent more time immobile on the swim task and entered open arms of the elevated plus maze more often than their naïve counterparts. In the prefrontal cortex, there was a sex by treatment interaction on gene expression relevant to neural transmission in ryanodine receptor 2, as well as increased gene expression in SNAP25, COMT, and LSAMP in males prenatally exposed to dexamethasone compared with controls. Both dysregulated genes and behavior are linked to decreased anxiety and fear inhibition. CONCLUSION: Our results indicate adult offspring exposed to dexamethasone in-utero have a tendency toward passive stress-coping strategies and an inhibition of anxiety on behavioral tasks. Methyltransferase activity, synaptic activity, and cellular processes were disrupted in the prefrontal cortices of these animals. Specifically, genes involved in emotional response pathways were overexpressed, supporting the link between the behavioral and genetic profiles. Combined, we determine that dexamethasone offspring have adaptive predispositions when faced with novel situations, with increased immobility in the swim task and increased exploration on the elevated plus maze.

Whole transcriptome analysis of adrenal glands from prenatal glucocorticoid programmed hypertensive rodents.

Prenatal glucocorticoid exposure is associated with the development of hypertension in adults. We have previously demonstrated that antenatal dexamethosone (DEX) administration in Wistar-Kyoto dams results in offspring with increased blood pressure coupled with elevated plasma epinephrine levels. In order to elucidate the molecular mechanisms responsible for prenatal DEX-mediated programming of hypertension, a whole-transcriptome analysis was performed on DEX programmed WKY male adrenal glands using the Rat Gene 2.0 microarray. Differential gene expression (DEG) analysis of DEX-exposed offspring compared with saline-treated controls revealed 142 significant DEGs (109 upregulated and 33 downregulated genes). DEG pathway enrichment analysis demonstrated that genes involved in circadian rhythm signaling were most robustly dysregulated. RT-qPCR analysis confirmed the increased expression of circadian genes Bmal1 and Npas2, while Per2, Per3, Cry2 and Bhlhe41 were significantly downregulated. In contrast, gene expression profiling of Spontaneously Hypertensive (SHR) rats, a genetic model of hypertension, demonstrated decreased expression of Bmal1 and Npas2, while Per1, Per2, Per3, Cry1, Cry2, Bhlhe41 and Csnk1D were all upregulated compared to naïve WKY controls. Taken together, this study establishes that glucocorticoid programmed adrenals have impaired circadian signaling and that changes in adrenal circadian rhythm may be an underlying molecular mechanism responsible for the development of hypertension.

Dose threshold for radiation induced fetal programming in a mouse model at 4 months of age: Hepatic expression of genes and proteins involved in glucose metabolism and glucose uptake in brown adipose tissue.

Exposure to ionizing radiation contributing to negative health outcomes is a widespread concern. However, the impact of low dose and sub-lethal dose radiation (SLDR) exposures remain contentious, particularly in pregnant women who represent a vulnerable group. The fetal programming hypothesis states that an adverse in utero environment or stress during development of an embryo or fetus can result in permanent physiologic changes often resulting in progressive metabolic dysfunction with age. To assess changes in gene expression profiles of glucose/insulin signaling and lipid metabolism caused by radiation exposure in utero, pregnant C57Bl/6J mice were irradiated using a dose response ranging from low dose to SLDR and compared to a Sham-irradiated group. mRNA expression analysis in 16 week old offspring (n = 84) revealed that genes involved in metabolic function including glucose metabolism, insulin signaling and lipid metabolism were unaffected by prenatal radiation exposures up to 300 mGy. However, female offspring of dams exposed to 1000 mGy had upregulated expression of genes contributing to insulin resistance and gluconeogenesis. In a second cohort of mice, the effects of SLDR on fetal programming of hepatic SOCS3 and PEPCK protein expression were assessed. 4 month old female offspring of dams irradiated at 1000 mGy had: 1) increased liver weights, 2) increased hepatic expression of proteins involved in glucose metabolism and 3) increased 18F-fluorodeoxyglucose (FDG) uptake in interscapular brown adipose tissue (IBAT) measured by positron emission tomography (PET) (n = 25). The results of this study indicate that prenatal radiation exposure does not affect metabolic function up to 300 mGy and 1000 mGy may be a threshold dose for sex-specific alterations in glucose uptake and hepatic gene and protein expression of SOCS3, PEPCK, PPARGC1A and PPARGC1B. These findings suggest that SLDR doses alter glucose uptake in IBAT and hepatic gene and protein expression of offspring and these changes may progress with age.

Fetal programming of adrenal PNMT and hypertension by glucocorticoids in WKY rats is dose and sex-dependent.

Biochemical changes in utero may alter normal fetal development, resulting in disease later in life, a phenomenon known as fetal programming. Recent epidemiological studies link fetal programming to negative health outcomes, such as low birth weight and hypertension in adulthood. Here, we used a WKY rat model and studied the molecular changes triggered by prenatal glucocorticoid (GC) exposure on the development of hypertension, and on the regulation of phenylethanolamine N-methyl transferase (PNMT), the enzyme responsible for biosynthesis of epinephrine, and a candidate gene linked to hypertension. Clinically, high doses of the synthetic GC dexamethasone (DEX) are used to treat infant respiratory distress syndrome. Elevated maternal GCs have been correlated with fetal programming of hypertension. The aim of this study was to determine if lower doses of DEX would not lead to detrimental fetal programming effects such as hypertension. Our data suggests that prenatal stress programs for increased expression of PNMT and altered regulation of PNMT in males and females. Importantly, we identified that DEX mediated programming was more apparent in the male rats, and the lower dose 10µg/kg/day of DEX did not lead to changes in blood pressure (BP) in female rats suggesting that this dose is below the threshold for programming of hypertension. Furthermore, sex-specific differences were observed in regards to programming mechanisms that may account for hypertension in males.