Loss of class I MHC function alters behavior and stress reactivity

Microbe-Immune Crosstalk: Evidence That T Cells Influence the Development of the Brain Metabolome

Cross-talk between the immune system and the brain is essential to neuronal development, neuronal excitability, neuroplasticity, and neurotransmission. Gut microbiota are essential to immune system development and immune function; hence, it is essential to consider more broadly the microbiota-immune-brain axis in neurodevelopment. The gut, brain, and microbial metabolomes obtained from C57Bl/6 and T-cell-deficient mice across four developmental timepoints (postnatal day 17, 24, 28, and 84) were studied by 1H NMR spectroscopy. 16S rRNA gene sequencing was performed on cecal and fecal samples. In the absence of T-cells, the developmental trajectory of the gut microbiota and of the host's metabolic profile was altered. The novel insights from this work include (1) the requirement of functional T-cells for the normal trajectory of microbiotal development and the metabolic maturation of the supra-organism, (2) the potential role for Muribaculaceae taxa in modulating the cecal availability of metabolites previously implicated with a role in the gut-brain axis in T-cell deficient mice, and (3) the impact of T-cell-deficiency on central levels of neuroactive metabolites.

Mouse models of immune dysfunction: their neuroanatomical differences reflect their anxiety-behavioural phenotype

Extensive evidence supports the role of the immune system in modulating brain function and behaviour. However, past studies have revealed striking heterogeneity in behavioural phenotypes produced from immune system dysfunction. Using magnetic resonance imaging, we studied the neuroanatomical differences among 11 distinct genetically modified mouse lines (n = 371), each deficient in a different element of the immune system. We found a significant and heterogeneous effect of immune dysfunction on the brains of both male and female mice. However, by imaging the whole brain and using Bayesian hierarchical modelling, we were able to identify patterns within the heterogeneous phenotype. Certain structures-such as the corpus callosum, midbrain, and thalamus-were more likely to be affected by immune dysfunction. A notable brain-behaviour relationship was identified with neuroanatomy endophenotypes across mouse models clustering according to anxiety-like behaviour phenotypes reported in literature, such as altered volume in brains regions associated with promoting fear response (e.g., the lateral septum and cerebellum). Interestingly, genes with preferential spatial expression in the most commonly affected regions are also associated with multiple sclerosis and other immune-mediated diseases. In total, our data suggest that the immune system modulates anxiety behaviour through well-established brain networks.

Functional MHCI deficiency induces ADHD-like symptoms with increased dopamine D1 receptor expression

Inappropriate synaptic development has been proposed as a potential mechanism of neurodevelopmental disorders, including attention-deficit hyperactivity disorder (ADHD). Major histocompatibility complex class I (MHCI), an immunity-associated molecule expressed by neurons in the brain, regulates synaptic development; however, the involvement of MHCI in these disorders remains elusive. We evaluated whether functional MHCI deficiency induced by β2m^-/-Tap1^-/- double-knockout in mice leads to abnormalities akin to those seen in neurodevelopmental disorders. We found that functional MHCI deficiency induced locomotor hyperactivity, motor impulsivity, and attention deficits, three major symptoms of ADHD. In contrast, these mice showed normal spatial learning, behavioral flexibility, social behavior, and sensorimotor integration. In the analysis of the dopamine system, upregulation of dopamine D1 receptor (D1R) expression in the nucleus accumbens and a greater locomotor response to D1R agonist SKF 81297 were found in the functional MHCI-deficient mice. Low-dose methylphenidate, used for the treatment of ADHD patients, alleviated the three behavioral symptoms and suppressed c-Fos expression in the D1R-expressing medium spiny neurons of the mice. These findings reveal an unexpected role of MHCI in three major symptoms of ADHD and may provide a novel landmark in the pathogenesis of ADHD.

Coping Strategies and Stress Related Disorders in Patients with COVID-19

Patients with severe COVID-19 experience high-stress levels and thus are at risk for developing acute stress disorder (ASD) and/or post-traumatic stress disorder (PTSD). The present study aims to search for correlations between psychiatric response to stress and coping strategies among individuals with acute vs. remitted COVID-19. Ninety subjects with COVID-19 were included in the study, divided into two samples by disease category. Our focus was analysing the perceived stress intensity according to NSESSS and PCL-C-17 scales, and coping strategies with COPE-60. High NSESSS scores were found in 40% of acute patients, and 15.6% of remitted patients had high PCL-C-17 scores fulfilling the criteria for PTSD. We found a negative correlation between stress level and disease category. Acute patients used significantly more engagement and emotion-focused coping methods, but less disengagement types of coping than patients in the remitted phase. Remitted patients under high stress levels are prone to use disengagement and emotion-focused coping strategies. In conclusion, remitted COVID-19 patients experience lower levels of stress and use less emotion-focused strategies, except among those who developed PTSD post-COVID-19 infection, presenting with high-stress levels and using more disengagement and emotion-focused types of coping strategies.

Immune system regulation and role of the human leukocyte antigen in posttraumatic stress disorder

Posttraumatic stress disorder (PTSD) is a debilitating condition that adversely affect mental and physical health. Recent studies have increasingly explored the role of the immune system in risk for PTSD and its related symptoms. Dysregulation of the immune system may lead to central nervous system tissue damage and impair learning and memory processes. Individuals with PTSD often have comorbid inflammatory or auto-immune disorders. Evidence shows associations between PTSD and multiple genes that are involved in immune-related or inflammatory pathways. In this review, we will summarize the evidence of immune dysregulation in PTSD, outlining the contributions of distinct cell types, genes, and biological pathways. We use the Human Leukocyte Antigen (HLA) locus to illustrate the contribution of genetic variation to function in different tissues that contribute to PTSD etiology, severity, and comorbidities.

Loss of T cells influences sex differences in stress-related gene expression

Deficiencies in the adaptive immune system have been linked to anxiety-like behaviours and stress reactivity. Mice lacking T lymphocytes through knockout of the T cell receptor (TCR) β and δ chains were compared to wild type C57Bl/6 mice. Central stress circuitry gene expression was assessed following repeated restraint stress. TCRβ-/-δ-/- mice showed an increased baseline plasma corticosterone and exaggerated changes in stress-related gene expression after repeated restraint stress. Sexual dimorphic stress responses were observed in wild-type C57Bl/6 mice but not in TCRβ-/-δ-/- mice. These data suggest that T cell-brain interactions influence sex-differences in CNS stress circuitry and stress reactivity.

Longitudinal epigenome-wide association studies of three male military cohorts reveal multiple CpG sites associated with post-traumatic stress disorder

BACKGROUND

Epigenetic mechanisms have been suggested to play a role in the development of post-traumatic stress disorder (PTSD). Here, blood-derived DNA methylation data (HumanMethylation450 BeadChip) collected prior to and following combat exposure in three cohorts of male military members were analyzed to assess whether DNA methylation profiles are associated with the development of PTSD. A total of 123 PTSD cases and 143 trauma-exposed controls were included in the analyses. The Psychiatric Genomics Consortium (PGC) PTSD EWAS QC pipeline was used on all cohorts, and results were combined using a sample size weighted meta-analysis in a two-stage design. In stage one, we jointly analyzed data of two new cohorts (N = 126 and 78) for gene discovery, and sought to replicate significant findings in a third, previously published cohort (N = 62) to assess the robustness of our results. In stage 2, we aimed at maximizing power for gene discovery by combining all three cohorts in a meta-analysis.

RESULTS

Stage 1 analyses identified four CpG sites in which, conditional on pre-deployment DNA methylation, post-deployment DNA methylation was significantly associated with PTSD status after epigenome-wide adjustment for multiple comparisons. The most significant (intergenic) CpG cg05656210 (p = 1.0 × 10-08) was located on 5q31 and significantly replicated in the third cohort. In addition, 19 differentially methylated regions (DMRs) were identified, but failed replication. Stage 2 analyses identified three epigenome-wide significant CpGs, the intergenic CpG cg05656210 and two additional CpGs located in MAD1L1 (cg12169700) and HEXDC (cg20756026). Interestingly, cg12169700 had an underlying single nucleotide polymorphism (SNP) which was located within the same LD block as a recently identified PTSD-associated SNP in MAD1L1. Stage 2 analyses further identified 12 significant differential methylated regions (DMRs), 1 of which was located in MAD1L1 and 4 were situated in the human leukocyte antigen (HLA) region.

CONCLUSIONS

This study suggests that the development of combat-related PTSD is associated with distinct methylation patterns in several genomic positions and regions. Our most prominent findings suggest the involvement of the immune system through the HLA region and HEXDC, and MAD1L1 which was previously associated with PTSD.

Gut Microbiota and Brain Function: An Evolving Field in Neuroscience

There is a growing appreciation of the importance of gut microbiota to health and disease. This has been driven by advances in sequencing technology and recent findings demonstrating the important role of microbiota in common health disorders such as obesity. Moreover, the potential role of gut microbiota in influencing brain function, behavior, and mental health has attracted the attention of neuroscientists and psychiatrists. At the 29(th) International College of Neuropsychopharmacology (CINP) World Congress held in Vancouver, Canada, in June 2014, a group of experts presented the symposium, "Gut microbiota and brain function: Relevance to psychiatric disorders" to review the latest findings in how gut microbiota may play a role in brain function, behavior, and disease. The symposium covered a broad range of topics, including gut microbiota and neuroendocrine function, the influence of gut microbiota on behavior, probiotics as regulators of brain and behavior, and imaging the gut-brain axis in humans. This report provides an overview of these presentations.

Loss of T cells influences sex differences in behavior and brain structure

Clinical and animal studies demonstrate that immune-brain communication influences behavior and brain function. Mice lacking T cell receptor β and δ chains were tested in the elevated plus maze, open field, and light-dark test and showed reduced anxiety-like behavior compared to wild type. Interestingly sex differences were observed in the behavioural phenotype of TCRβ-/-δ- mice. Specifically, female TCRβ-/-δ- mice spent more time in the light chamber compared to wild type females, whereas male TCRβ-/-δ- spent more time in the center of the open field compared to wild type males. In addition, TCRβ-/-δ- mice did not show sex differences in activity-related behaviors observed in WT mice. Ex vivo brain imaging (7 Tesla MRI) revealed volume changes in hippocampus, hypothalamus, amygdala, periaqueductal gray, and dorsal raphe and other brain regions between wild type and T cell receptor knockout mice. There was also a loss of sexual dimorphism in brain volume in the bed nucleus of the stria terminalis, normally the most sexually dimorphic region in the brain, in immune compromised mice. These data demonstrate the presence of T cells is important in the development of sex differences in CNS circuitry and behavior.

Genetic association of impulsivity in young adults: a multivariate study

Impulsivity is a heritable, multifaceted construct with clinically relevant links to multiple psychopathologies. We assessed impulsivity in young adult (N~2100) participants in a longitudinal study, using self-report questionnaires and computer-based behavioral tasks. Analysis was restricted to the subset (N=426) who underwent genotyping. Multivariate association between impulsivity measures and single-nucleotide polymorphism data was implemented using parallel independent component analysis (Para-ICA). Pathways associated with multiple genes in components that correlated significantly with impulsivity phenotypes were then identified using a pathway enrichment analysis. Para-ICA revealed two significantly correlated genotype-phenotype component pairs. One impulsivity component included the reward responsiveness subscale and behavioral inhibition scale of the Behavioral-Inhibition System/Behavioral-Activation System scale, and the second impulsivity component included the non-planning subscale of the Barratt Impulsiveness Scale and the Experiential Discounting Task. Pathway analysis identified processes related to neurogenesis, nervous system signal generation/amplification, neurotransmission and immune response. We identified various genes and gene regulatory pathways associated with empirically derived impulsivity components. Our study suggests that gene networks implicated previously in brain development, neurotransmission and immune response are related to impulsive tendencies and behaviors.

The spatio-temporal expression of MHC class I molecules during human hippocampal formation development

In the immune system, the major histocompatibility complex (MHC) class I molecules mediate both the innate and adaptive immune responses in vertebrates. There has been a dogma that the central nervous system (CNS) is immune privileged and healthy neurons do not express MHC class I molecules. However, recent studies have indicated that the expression and non-immunobiologic roles of MHC class I in mammalian CNS. But data referring to humans are scarce. In this study we report the expression and cellular localization of MHC class I in the human fetal, early postnatal and adult hippocampal formation. The expression of MHC class I was very low in the hippocampus at 20 (gestational weeks) GW and slowly increased at 27-33 GW. The gradually increased expression in the somata of some granular cells in dentate gyrus (DG) was observed at 30-33 GW. Whereas, a rapid increase in MHC class I molecules expression was found in the subiculum and it reached high levels at 31-33 GW and maintained at postnatal 55 days. No expression of MHC class I was found in hippocampal formation in adult. MHC class I heavy chain and β2 microglobulin (β2M) showed similar expression in some cells of the hippocampal formation at 30-33 GW. Moreover, MHC class I molecules were mainly expressed in neurons and most MHC class I-expressing neurons were glutamatergic. The temporal and spatial patterns of MHC class I expression appeared to follow gradients of pyramidal neurons maturation in the subiculum at prenatal stages and suggested that MHC class I molecules are likely to regulate neuron maturation. This article is part of a Special Issue entitled Priority to Publish.

Variation in the major histocompatibility complex [MHC] gene family in schizophrenia: associations and functional implications

Schizophrenia is a chronic debilitating neuropsychiatric disorder with a complex genetic contribution. Although multiple genetic, immunological and environmental factors are known to contribute to schizophrenia susceptibility, the underlying neurobiological mechanism(s) is yet to be established. The immune system dysfunction theory of schizophrenia is experiencing a period of renewal due to a growth in evidence implicating components of the immune system in brain function and human behavior. Current evidence indicates that certain immune molecules such as Major Histocompatibility Complex (MHC) and cytokines, the key regulators of immunity and inflammation are directly involved in the neurobiological processes related to neurodevelopment, neuronal plasticity, learning, memory and behavior. However, the strongest support in favor of the immune hypothesis has recently emerged from on-going genome wide association studies advocating MHC region variants as major determinants of one's risk for developing schizophrenia. Further identification of the interacting partners and receptors of MHC molecules in the brain and their role in down-stream signaling pathways of neurotransmission have implicated these molecules as potential schizophrenia risk factors. More recently, combined brain imaging and genetic studies have revealed a relationship between genetic variations within the MHC region and neuromorphometric changes during schizophrenia. Furthermore, MHC molecules play a significant role in the immune-infective and neurodevelopmental pathogenetic pathways, currently hypothesized to contribute to the pathophysiology of schizophrenia. Herein, we review the immunological, genetic and expression studies assessing the role of the MHC in conferring risk for developing schizophrenia, we summarize and discuss the possible mechanisms involved, making note of the challenges to, and future directions of, immunogenetic research in schizophrenia.