Biochemistry and Immune Biomarkers Indicate Interacting Effects of Pre- and Postnatal Stressors in Pigs across Sexes

Immune and metabolic challenges induce changes in pain sensation and related pathways in the hypothalamus

The hypothalamic molecular processes participate in the regulation of the neuro-immune-endocrine system, including hormone, metabolite, chemokine circulation, and corresponding physiological and behavioral responses. RNA-sequencing profiles were analyzed to understand the effect of juvenile immune and metabolic distress 100 days after virally elicited maternal immune activation during gestation in pigs. Over 1,300 genes exhibited significant additive or interacting effects of gestational immune activation, juvenile distress, and sex. One-third of these genes presented multiple effects, emphasizing the complex interplay of these factors. Key functional categories enriched among affected genes included sensory perception of pain, steroidogenesis, prolactin, neuropeptide, and inflammatory signaling. These categories underscore the intricate relationship between gestational immune activation during gestation, distress, and the response of hypothalamic pathways to insults. These effects were sex-dependent for many genes, such as Prdm12, Oprd1, Isg20, Prl, Oxt, and Vip. The prevalence of differentially expressed genes annotated to proinflammatory and cell cycle processes suggests potential implications for synaptic plasticity and neuronal survival. The gene profiles affected by immune activation, distress, and sex pointed to the action of transcription factors SHOX2, STAT1, and REST. These findings underscore the importance of considering sex and postnatal challenges when studying causes of neurodevelopmental disorders and highlight the complexity of the "two-hit" hypothesis in understanding their etiology. Our study furthers the understanding of the intricate molecular responses in the hypothalamus to gestational immune activation and subsequent distress, shedding light on the sex-specific effects and the potential long-lasting consequences on pain perception, neuroendocrine regulation, and inflammatory processes.NEW & NOTEWORTHY The interaction of infection during gestation and insults later in life influences the molecular mechanisms in the hypothalamus that participate in pain sensation. The response of the hypothalamic transcriptome varies between sexes and can also affect synapses and immune signals. The findings from this study assist in the identification of agonists or antagonists that can guide pretranslational studies to ameliorate the effects of gestational insults interacting with postnatal challenges on physiological or behavioral disorders.

Prenatal and postnatal challenges affect the hypothalamic molecular pathways that regulate hormonal levels

This study aimed to improve our understanding of how the hypothalamus mediates the effects of prenatal and postnatal challenges on behavior and sensitivity to stimuli. A pig model of virally initiated maternal immune activation (MIA) was used to investigate potential interactions of the prenatal challenge both with sex and with postnatal nursing withdrawal. The hypothalami of 72 females and males were profiled for the effects of MIA and nursing withdrawal using RNA-sequencing. Significant differential expression (FDR-adjusted p value < 0.05) was detected in the profile of 222 genes. Genes involved in the Gene Ontology biological process of regulation of hormone levels tended to be over-expressed in individuals exposed to both challenges relative to individuals exposed to either one challenge, and most of these genes were over-expressed in MIA females relative to males across nursing levels. Differentially expressed genes included Fshb, Ttr, Agrp, Gata3, Foxa2, Tfap2b, Gh1, En2, Cga, Msx1, and Npy. The study also found that prenatal and postnatal challenges, as well as sex, impacted the regulation of neurotransmitter activity and immune effector processes in the hypothalamus. In particular, the olfactory transduction pathway genes were over-expressed in weaned MIA males, and several transcription factors were potentially found to target the differentially expressed genes. Overall, these results highlight how multiple environmental challenges can interact and affect the molecular mechanisms of the hypothalamus, including hormonal, immune response, and neurotransmitter processes.

Influence of Maternal Immune Activation and Stressors on the Hippocampal Metabolome

Prenatal stress often results in maternal immune activation (MIA) that can impact prenatal brain development, molecular processes, and substrates and products of metabolism that participate in physiological processes at later stages of life. Postnatal metabolic and immunological stressors can affect brain metabolites later in life, independently or in combination with prenatal stressors. The effects of prenatal and postnatal stressors on hippocampal metabolites were studied using a pig model of viral MIA exposed to immunological and metabolic stressors at 60 days of age using gas chromatography mass spectrometry. Postnatal stress and MIA elicited effects (FDR-adjusted p-value < 0.1) on fifty-nine metabolites, while eight metabolites exhibited an interaction effect. The hippocampal metabolites impacted by MIA or postnatal stress include 4-aminobutanoate (GABA), adenine, fumarate, glutamate, guanine, inosine, ornithine, putrescine, pyruvate, and xanthine. Metabolites affected by MIA or postnatal stress encompassed eight significantly (FDR-adjusted p-value < 0.1) enriched Kyoto Encyclopedia of Genes and Genomes Database (KEGG) pathways. The enriched arginine biosynthesis and glutathione metabolism pathways included metabolites that are also annotated for the urea cycle and polyamine biosynthesis pathways. Notably, the prenatal and postnatal challenges were associated with disruption of the glutathione metabolism pathway and changes in the levels of glutamic acid, glutamate, and purine nucleotide metabolites that resemble patterns elicited by drugs of abuse and may underlie neuroinflammatory processes. The combination of MIA and postnatal stressors also supported the double-hit hypothesis, where MIA amplifies the impact of stressors later in life, sensitizing the hippocampus of the offspring to future challenges. The metabolites and pathways characterized in this study offer evidence of the role of immunometabolism in understanding the impact of MIA and stressors later in life on memory, spatial navigation, neuropsychiatric disorders, and behavioral disorders influenced by the hippocampus.

Genes Participating in the Ensheathment of Neurons Are Affected by Postnatal Stress and Maternal Immune Activation in the Pituitary Gland

Immune challenges during gestation are associated with neurodevelopmental disorders and can interact with stress later in life. The pituitary gland participates in endocrine- and immune-related processes that influence development, growth, and reproduction and can modulate physiological and behavioral responses to challenges. The objective of this study was to investigate the effect of stressors at different time points on the molecular mechanisms of the pituitary gland and detect sex differences. RNA sequencing was used to profile the pituitary glands of female and male pigs exposed to weaning stress and virally induced maternal immune activation (MIA), relative to unchallenged groups. Significant effects (FDR-adjusted p-value < 0.05) of MIA and weaning stress were detected in 1829 and 1014 genes, respectively. Of these, 1090 genes presented significant interactions between stressors and sex. The gene ontology biological process of the ensheathment of neurons (GO:0007272), substance abuse, and immuno-related pathways, including the measles disease (ssc05162), encompasses many genes with profiles impacted by MIA and weaning stress. A gene network analysis highlighted the under-expression of myelin protein zero (Mpz) and inhibitors of DNA binding 4 (Id4) among the non-stressed males exposed to MIA, relative to the control and non-MIA males exposed to weaning stress, relative to non-stressed pigs. The detection of changes in the molecular mechanisms of the pituitary gland could advance our understanding of disruptions in the formation of the myelin sheath and the transmission of neuron-to-neuron signals in behavioral disorders associated with maternal immune activation and stress.

Hippocampal Changes Elicited by Metabolic and Inflammatory Stressors following Prenatal Maternal Infection

The hippocampus participates in spatial navigation and behavioral processes, displays molecular plasticity in response to environmental challenges, and can play a role in neuropsychiatric diseases. The combined effects of inflammatory prenatal and postnatal challenges can disrupt the hippocampal gene networks and regulatory mechanisms. Using a proven pig model of viral maternal immune activation (MIA) matched to controls and an RNA-sequencing approach, the hippocampal transcriptome was profiled on two-month-old female and male offspring assigned to fasting, mimetic viral, or saline treatments. More than 2600 genes presented single or combined effects (FDR-adjusted p-value < 0.05) of MIA, postnatal stress, or sex. Biological processes and pathways encompassing messenger cyclic adenosine 3',5'-monophosphate (cAMP) signaling were enriched with genes including gastric inhibitory polypeptide receptor (GIPR) predominantly over-expressed in the MIA-exposed fasting males relative to groups that differed in sex, prenatal or postnatal challenge. While this pattern was amplified in fasting offspring, the postnatal inflammatory challenge appeared to cancel out the effects of the prenatal challenge. The transcription factors C-terminal binding protein 2 (CTBP2), RE1 silencing transcription factor (REST), signal transducer and activator of transcription 1 (STAT1), and SUZ12 polycomb repressive complex 2 subunit were over-represented among the genes impacted by the prenatal and postnatal factors studied. Our results indicate that one environmental challenge can influence the effect of another challenge on the hippocampal transcriptome. These findings can assist in the identification of molecular targets to ameliorate the effects of pre-and post-natal stressors on hippocampal-associated physiology and behavior.

Prefrontal Cortex Response to Prenatal Insult and Postnatal Opioid Exposure

The influence of proinflammatory challenges, such as maternal immune activation (MIA) or postnatal exposure to drugs of abuse, on brain molecular pathways has been reported. On the other hand, the simultaneous effects of MIA and drugs of abuse have been less studied and sometimes offered inconsistent results. The effects of morphine exposure on a pig model of viral-elicited MIA were characterized in the prefrontal cortex of males and females using RNA-sequencing and gene network analysis. Interacting and main effects of morphine, MIA, and sex were detected in approximately 2000 genes (false discovery rate-adjusted p-value < 0.05). Among the enriched molecular categories (false discovery rate-adjusted p-value < 0.05 and −1.5 > normalized enrichment score > 1.5) were the cell adhesion molecule pathways associated with inflammation and neuronal development and the long-term depression pathway associated with synaptic strength. Gene networks that integrate gene connectivity and expression profiles displayed the impact of morphine-by-MIA interaction effects on the pathways. The cell adhesion molecules and long-term depression networks presented an antagonistic effect between morphine and MIA. The differential expression between the double-challenged group and the baseline saline-treated Controls was less extreme than the individual challenges. The previous findings advance the knowledge about the effects of prenatal MIA and postnatal morphine exposure on the prefrontal cortex pathways.

Terpenoid Backbone Biosynthesis among Pig Hippocampal Pathways Impacted by Stressors

Neurogenomic changes induced by maternal immune activation (MIA) during gestation and the social stress of weaning can alter brain plasticity in the hippocampus of offspring. The present study furthers the understanding of how these stressors impact hippocampus gene networks. The hippocampus transcriptome was profiled in pigs that were either exposed to MIA or not and were weaned or nursed. Overall, 1576 genes were differentially expressed (FDR-adjusted p-value < 0.05 and |log2 (fold change between pig groups)| > 1.2) in response to the main and interacting effects of MIA, weaning, and sex. Functional analysis identified 17 enriched immunological and neurological pathways in the Kyoto Encyclopedia of Genes and Genomes database. The enrichment of the terpenoid backbone biosynthesis pathway was characterized by genes under-expressed in MIA relative to non-MIA exposed, males relative to females, and weaned relative to nursed pigs. On the other hand, the enrichment of drug addiction pathways was characterized by gene over-expression in MIA relative to non-exposed pigs. Our results indicate that weaning and sex can modify the effects of MIA on the offspring hippocampus. This knowledge can aid in precise identification of molecular targets to reduce the prolonged effects of pre- and postnatal stressors.

Maternal Immune Activation and Dietary Soy Isoflavone Supplementation Influence Pig Immune Function but not Muscle Fiber Formation

The goals of this study were to determine the impact of maternal PRRSV infection on offspring muscle and immune development and the potential of dietary soy isoflavones to mitigate those effects. Thirteen first-parity gilts (“gilts”) were randomly allotted into one of three treatments: not infected and fed a diet devoid of isoflavones (CON), infected with porcine reproductive and respiratory syndrome virus (PRRSV) and fed the control diet (POS) or that supplemented with 1,500 mg/kg soy-derived isoflavones (ISF). Gilts were inoculated with PRRSV intranasally on gestational day (GD) 70. After farrowing (GD 114 ± 2), 1-2 offspring (“pigs”) closest to the average litter weight were selected either at birth (3 ± 2 d of age) or weaning (21 ±2 d of age) to determine body, muscle, and organ weights as well as muscle cell number and size. Four weaned pigs of average body weight within each litter were selected for postnatal immune challenge. At PND 52, pigs were injected with 5 µg/kg BW lipopolysaccharide (LPS) intraperitoneally. Serum was collected at 0, 4, and 8 h following LPS administration to analyze tumor necrosis factor alpha (TNF-α). At PND 59, pigs were administered a novel vaccine to elicit an adaptive immune response. At PND 59, 66, and 73, peripheral blood mononuclear cells were isolated and T-cell populations determined by flow cytometry. Both POS and ISF pigs exhibited persistent PRRSV infections throughout the study (PND 1-73). At PND 3, whole body, muscle, and organ weights were not different (P &gt; 0.22) between groups, with the exception of relative liver weight, which was increased (P &lt; 0.05) in POS compared with CON pigs. At PND 21, ISF pigs had reduced (P ≤ 0.05) whole body and muscle weights, but greater (P &lt; 0.05) kidney weight compared with CON, and greater (P &lt; 0.05) relative liver weight compared with CON and POS. Muscle fiber number and size were not different (P &gt; 0.39) between groups at birth or weaning. After LPS administration, TNF-α was greatest in ISF pigs (P &lt; 0.05) at both 0 and 8 h post-challenge. At the peak time-point of 4 h post-challenge, ISF pigs had the greatest concentration of TNF-α and CON pigs had the lowest, with POS pigs being intermediate (P = 0.01). After vaccination, ISF offspring had shifts in T-cell populations indicating an impaired immune response. These data indicate that maternal PRRSV infection may impact offspring organ growth and immune function, particularly when the dam is supplemented with isoflavones.

Disruption of Alternative Splicing in the Amygdala of Pigs Exposed to Maternal Immune Activation

The inflammatory response of gestating females to infection or stress can disrupt gene expression in the offspring’s amygdala, resulting in lasting neurodevelopmental, physiological, and behavioral disorders. The effects of maternal immune activation (MIA) can be impacted by the offspring’s sex and exposure to additional stressors later in life. The objectives of this study were to investigate the disruption of alternative splicing patterns associated with MIA in the offspring’s amygdala and characterize this disruption in the context of the second stress of weaning and sex. Differential alternative splicing was tested on the RNA-seq profiles of a pig model of viral-induced MIA. Compared to controls, MIA was associated with the differential alternative splicing (FDR-adjusted p-value < 0.1) of 292 and 240 genes in weaned females and males, respectively, whereas 132 and 176 genes were differentially spliced in control nursed female and male, respectively. The majority of the differentially spliced (FDR-adjusted p-value < 0.001) genes (e.g., SHANK1, ZNF672, KCNA6) and many associated enriched pathways (e.g., Fc gamma R-mediated phagocytosis, non-alcoholic fatty liver disease, and cGMP-PKG signaling) have been reported in MIA-related disorders including autism and schizophrenia in humans. Differential alternative splicing associated with MIA was detected in the gene MAG across all sex-stress groups except for unstressed males and SLC2A11 across all groups except unstressed females. Precise understanding of the effect of MIA across second stressors and sexes necessitates the consideration of splicing isoform profiles.

The Combined Effect of Weaning Stress and Immune Activation during Pig Gestation on Serum Cytokine and Analyte Concentrations

Weaning stress can elicit changes in the metabolic, hormone and immune systems of pigs and interact with prolonged disruptions stemming from maternal immune activation (MIA) during gestation. The present study advances the characterization of the combined effects of weaning stress and MIA on blood chemistry, immune and hormone indicators that inform on the health of pigs. Three-week-old female and male offspring of control gilts or gilts infected with the porcine reproductive and respiratory syndrome virus were allocated to weaned or nursed groups. The anion gap and bilirubin profiles suggest that MIA enhances tolerance to the effects of weaning stress. Interleukin 1 beta and interleukin 2 were highest among weaned MIA females, and cortisol was higher among weaned relative to nursed pigs across sexes. Canonical discriminant analysis demonstrated that weaned and nursed pigs have distinct chemistry profiles, whereas MIA and control pigs have distinct cytokine profiles. The results from this study can guide management practices that recognize the effects of the interaction between MIA and weaning stress on the performance and health of pigs.