Brain, Behavior, and Immunity

Microbes residing in the gastrointestinal tract exert immunomodulatory impacts on the brain through the gut-brain axis. Short-chain fatty acids (SCFAs) produced by bacterial fermentation of dietary fiber can enter the brain parenchyma and are implicated in microglia-mediated inflammation. While the gut microbiome is required to maintain microglial homeostasis, the mechanisms by which microbiota-derived metabolites affect microglia remains unknown. We examined the roles of SCFAs, specifically butyrate, propionate and acetate, on microglial function in response to SCFAs both in vitro using BV2 cells and in vivo in mice. We observed in vivo that SCFAs impact microglial transcriptional responses to LPS in a sex- and metabolite-specific manner with butyrate having the strongest effect. Enriched gene sets included signatures associated with LPS responsive microglia, Arg1 positive microglia, microglial cell cycle related genes and genes affiliated with changes in microglial morphology. We observed a similar effect in vitro, where metabolite administration enhanced phagocytosis, blunted proliferation and nitric oxide production. We then evaluated global histone modification levels following metabolite treatment and detected an enhancement of H3K9ac, H3K27ac, and H3K4me3 both in vivo and in BV2 cells treated with butyrate. Finally, we showed that butyrate is a potent HDAC inhibitor possibly contributing to enhanced acetylation. Hence, our findings suggest that SCFAs impact microglial function in a metabolite- and sex-specific manner, and that butyrate blunts inflammation by regulating microglial histone acetylation. Our results provide a more in-depth understanding of gut microbiome-microglia crosstalk, opening the door for new microbiome- and microglia-targeted therapies.

Ulcerative colitis (UC) is a chronic inflammatory disease characterized by colonic inflammation and bloody diarrhoea. Accumulating evidence suggests that UC not only affects the intestinal tract, but also distant organs including the brain. Environmental factors are key determinants of the disease course, yet the impact and potential disease modifying effects of living environment complexity on microbiota-gut-brain axis signalling during colitis remain unclear. To address this gap, we investigated how enhanced environmental complexity (EC) affects the disease course and gut-brain axis signalling during experimental colitis in mice. Our results show that EC exacerbates dextran sulphate sodium (DSS)-induced colitis in female mice, but not in male mice, as evidenced by greater weight loss and higher disease activity. Immune cell profiling across the gut-brain axis reveals strong effects of DSS treatment on colonic, circulating and brain immune cell populations and a restriction of central nervous system (CNS) T cell infiltration due to EC. In addition, female EC/DSS mice have higher circulating corticosterone levels than controls indicating chronic stress. Metabolomics across the gut-brain axis revealed that EC exacerbates colitis-induced metabolite perturbations in plasma, brain tissue, brain interstitial and cerebrospinal fluid. Notably, microbiota-derived metabolites, including deoxycholic acid and trimethylamine-N-oxide (TMAO), are increased in EC/DSS mice, concordant with EC-associated microbiome changes and anxiety-like behaviour. Overall, this study indicates that EC worsens experimental colitis in female mice and directs microbiota-gut-brain axis signalling during colitis towards a less favourable state. From a translational perspective, this study highlights the importance of environmental factors for a sex-specific disease course of UC and associated neurobehavioral comorbidities.

The SARS-CoV-2 S1 protein is associated with immune cell activation and persistent neurological symptoms, yet the underlying mechanisms remain unclear, posing a major challenge in elucidating Long COVID pathophysiology. To investigate how circulating S1 contributes to long-term neurological alterations, we intravenously injected hACE2 mice with varying doses of S1 (5, 10, and 20 {micro}g) and observed temporally dysregulated systemic inflammatory responses accompanied by sub-acute CD4+ T cell infiltration into central limbic regions. This immune response induced mild sustained increases in cFos+ cells in the amygdala and mild neuroinflammation in the hippocampal CA1 region, resulting in both acute and long-term anxiety-like behaviors, while working memory remained unaffected. Together, these findings suggest that systemic S1 protein induces a sustained proinflammatory response that promotes lasting neurological alterations through immune-to-brain signaling pathways. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=136 SRC="FIGDIR/small/733010v1_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@10982caorg.highwire.dtl.DTLVardef@169a275org.highwire.dtl.DTLVardef@28e66aorg.highwire.dtl.DTLVardef@12f6c85_HPS_FORMAT_FIGEXP M_FIG C_FIG

Cyclooxygenase-1 (COX-1) is classically regarded as a constitutive enzyme that produces eicosanoids with housekeeping functions, but recent evidence indicates that it may also be involved in the acute phase of severe systemic inflammation. There is evidence indicating that COX-1 is selectively activated in the spleen via post-translational mechanisms early the course of LPS-induced systemic inflammation. However, the mechanistic link between COX-1 and the spleen has not yet been demonstrated in direct experiments. The present study was conducted to fill this gap. The effects of the COX-1 inhibitor SC-560 on the LPS-induced severity triad (hypotension, hypothermia and acidosis) were evaluated in rats subjected to splenectomy or in sham-operated controls. In the sham-operated group, SC-560 significantly attenuated the severity triad independently of changes in plasma cytokines (TNF and IL-1{beta}). In the splenectomized rats, SC-560 completely lost its ability to attenuate the hypotension and the acidosis induced by LPS. The effect of SC-560 on LPS-induced hypothermia was also impaired by splenectomy, though not completely. We then conducted a lipidomic screening to identify which COX-1-derived eicosanoids might be responsible for mediating the severity triad. Based on spleen-blood correlations, the screening identified PGE2 and PGD2 as putative candidates. In conclusion, the present study provides direct evidence for a mechanistic link between the spleen and COX-1 in the mediation of severity in systemic inflammation, and identifies PGE2 and PGD2 as putative candidates involved.

Maternal sleep disturbance is an underrecognized risk factor for adverse offspring outcomes. Prolonged sleep disruption can elicit inflammation, an established risk factor for neuropsychiatric disorders in offspring. Sleep disruptions and inflammation elevate tryptophan degradation via the kynurenine pathway (KP), increasing kynurenic acid (KYNA), a metabolite that inhibits glutamatergic and cholinergic neurotransmission and may thereby affect neurodevelopment. Because KYNA is elevated in the brains of individuals with neurodevelopmental psychotic illnesses, we hypothesize that prenatal KYNA elevation may represent a mechanism link between disturbed maternal sleep, inflammation, and adverse offspring neurodevelopmental health. To test this hypothesis, we employed a novel maternal sleep fragmentation (SleepFrag) paradigm during the final week of gestation. We found that six days of SleepFrag increased maternal plasma inflammatory markers, placental KP metabolism, sex-specific placental inflammation, and fetal brain KP metabolism, including elevated KYNA, without altering KP metabolism in maternal plasma or brain. A parallel embryonic kynurenine (EKyn) model was tested to increase prenatal KP metabolism via a maternal kynurenine-supplemented diet. EKyn increased maternal plasma kynurenine and KYNA, and fetal brain KYNA, with a male-specific increase in fetal brain KYNAto-kynurenine ratio, despite minimal effects on maternal sleep-wake architecture or inflammation. Together, these findings identify elevated fetal brain KYNA as a convergent outcome through which maternal sleep disruption, inflammation, and KP activation may influence sex-specific neurodevelopment. They further support the EKyn model as a translational tool for isolating consequences of increased prenatal KP metabolism. Protecting maternal sleep and stabilizing fetal brain KYNA levels may promote long-term offspring brain health.

Background. Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and irritable bowel syndrome (IBS) frequently co-occur following infection, yet shared genetic architecture at the locus level has not been systematically characterised. Aims. To estimate global and local genetic correlations between ME/CFS (including infection-onset subgroup), IBS, major depressive disorder (MDD) and loneliness/isolation, and characterise ME/CFS cell-type heritability enrichment. Method. GWAS summary statistics: DecodeME (15,579 ME/CFS; 9,738 infection-onset), FinnGen R9 (9,296 IBS), PGC MDD Wave 2 (45,396) and UK Biobank loneliness (N=455,364). LDSC for global correlations; LAVA for local correlations across 2,495 loci; MAGMA for cell-type enrichment (Descartes Human atlas); coloc.abf for colocalisation. Results. All pairwise global correlations were significant after Bonferroni correction, including ME/CFS-all-MDD (rg=0.598, 95% CI 0.46-0.74) and ME/CFS-all-IBS (rg=0.573, 0.39-0.75). Of 4,232 local tests, 16 reached FDR<0.05; two lonelinessxMDD loci were Bonferroni-significant. ME/CFS-MDD showed three FDR-significant local correlations, but all were boundary-estimated and non-Bonferroni-significant. A borderline infection-onset ME/CFS-IBS signal occurred at chr12q24.22 ({rho}=1.000, FDR=0.046), but colocalisation did not support a shared causal variant (PP.H4=0.007). ME/CFS heritability was enriched in inhibitory neurons (P=1.210x-7) and enteric nervous system neurons (FDR=0.004), with no FDR-significant peripheral immune cell-type enrichment in the atlas used. Conclusions. High global ME/CFS-MDD correlation was accompanied by limited, boundary-estimated, non-Bonferroni-robust local sharing; the data do not support reducing ME/CFS to depression at the genetic-architecture level. Neural enrichment, including enteric nervous system neurons, supports involvement of neural components in ME/CFS susceptibility without excluding immune mechanisms. A borderline ME/CFS-IBS signal at a NOS1-containing region generated hypotheses requiring replication.

Sickness is an organismal response to inflammation, yet its immune, metabolic, neural, and behavioral components are often studied separately and predominantly in male C57BL/6 mice. In this study, we characterized these responses to systemic lipopolysaccharide (LPS) in female BALB/c mice. Mice received intraperitoneal LPS at moderate concentrations and outcomes were assessed during the acute and resolving phases of endotoxemia. LPS caused rapid disappearance of resident peritoneal macrophages, followed by neutrophil accumulation and increased circulating TNF- and IL-6. In the liver, LPS induced inflammatory, acute-phase, and anti-inflammatory transcripts while suppressing genes involved in lipid, cholesterol, and xenobiotic metabolism. Hepatic glutathione was reduced, whereas total superoxide dismutase activity was unchanged. These peripheral responses were followed by transient hypothermia, reduced food intake, and body weight loss. Regional brain mapping showed increased c-Fos labeling in the area postrema, nucleus of the solitary tract, external lateral parabrachial nucleus, paraventricular nucleus of the hypothalamus, and arcuate nucleus. In parallel, LPS selectively promoted IBA1-positive area in the median eminence and arcuate nucleus, whereas several other regions showed no changes, indicating that neuronal and microglial responses are regionally distinct. Behaviorally, LPS reduced locomotion and exploration, increased freezing, and increased forced-swim immobility. Changes in spatial exploration were most pronounced during the acute phase, whereas locomotor suppression and passive stress-coping persisted longer and varied in magnitude with the timing of inflammatory challenge. Together, these findings show that systemic LPS produces a coordinated sickness state in female BALB/c mice that links peripheral inflammation and hepatic metabolic and redox changes with region-specific neuronal and microglial responses, altered thermoregulation and feeding, and behavioral suppression.

Although cannabinoids such as delta-9-tetrahydrocannabinol (THC) are generally immunosuppressive in preclinical models, chronic cannabis use in humans is paradoxically associated with increased infection risk and systemic inflammation. In this study, we demonstrate that THC directly strengthens intestinal epithelial barrier function in vitro by increasing trans-epithelial electrical resistance in a concentration-dependent manner in Caco-2 monolayers. In a cross-sectional study of chronic cannabis users via smoking or snorting compared with non-using controls, plasma lipopolysaccharide (LPS), and microbial translocation-driven inflammatory cytokines (IL-23, MCP-1, IL-8) were significantly reduced, while some cytokines (IL-6, IL-1{beta}, TNF-, IL-10) remained unchanged. Concurrently, users exhibited elevated macrophage-derived chemokine (MDC) and homeostatic cytokines IL-15 and IL-21, markedly suppressed IL-7 and IL-4. Plasma IL-15 and MDC levels correlated with consumption intensity, and IL-23, IL-7, and IP-10 correlated with age of first use or during heaviest use. These findings suggest that habitual cannabis use may protect gut barrier integrity and reduce microbial translocation and associated inflammation, while simultaneously disrupting systemic immune homeostasis through selective cytokine dysregulation. This dual, dose-dependent immunomodulatory profile highlights the complex balance between potential benefits and risks in both recreational and therapeutic cannabis use.

Chronic cocaine use is associated with neuroinflammation and cognitive dysfunction, but the underlying mechanisms remain unclear. We previously identified oral enrichment of Streptococcus parasanguinis (SP) and other species in individuals with cocaine use disorder (CUD), and here demonstrate that cocaine selectively enhanced SP growth in vitro. To investigate causality, antibiotic-pretreated wild-type C57BL/6 mice received chronic oral inoculation of SP, S. salivarius, Neisseria flavescens, or vehicle. SP-treated mice exhibited spatial memory impairment, increased brain IL-1{beta}, and non-region-specific microglial activation, without detectable bacterial translocation into the brain. While amyloid-associated signaling changes were observed across all bacterial treatment groups, only SP induced cognitive deficits and neuroinflammation. Untargeted metabolomics identified distinct SP-associated oral-to-brain metabolite signatures, including cysteine S-sulfate (CSS) and altered histamine-associated metabolites. CSS and histamine induced neuroinflammatory and amyloid-associated responses in vitro. Together, these findings identify a cocaine-associated oral pathobiont that promotes neuroinflammation and neurodegeneration, suggesting a novel oral microbiome-brain axis in CUD.

Early life stress (ELS), modeled in rodents through neonatal maternal separation (NMS), induces lasting behavioral and molecular alterations including pain hypersensitivity, anxiety-like behaviors, and cognitive deficits. While NMS disrupts the oxytocinergic system, the specific contribution of oxytocin receptor (OTR) dysfunction during critical neurodevelopmental periods remains unclear. Here, we investigated whether neonatal OTR blockade alone could recapitulate key features of the NMS phenotype. Control rats received daily injections of the selective OTR antagonist d(CH2)5-Tyr(Me)-[Orn8]-vasotocin (dOVT) during postnatal days 2-12, matching the NMS period. At adulthood, behavioral assessments revealed that control+dOVT animals exhibited mechanical and cold thermal hypersensitivity similar to NMS rats, though hot thermal sensitivity was unaffected. Anxiety-like behaviors observed in NMS animals were not reproduced by dOVT treatment. Notably, sex-specific spatial memory deficits emerged: male NMS and female control+dOVT rats showed impaired object location recognition, while females and males in their respective opposite groups remained unaffected. Molecular analyses of spinal cord tissue revealed significant downregulation of GAD65, BDNF, and CD11b in control+dOVT animals. Chloride cotransporters NKCC1 and KCC2 exhibited sexual dimorphism with opposite changes in NMS males versus females and different responses to dOVT. These expressions yet converged on an elevated NKCC1/KCC2 ratio in both sexes, indicating compromised chloride homeostasis despite sex-divergent molecular pathways. These findings demonstrate that developmental OTR dysfunction likely contributes to nociceptive and cognitive consequences of ELS, while anxiety-like phenotypes probably involve additional mechanisms. This work highlights OTR as a critical mediator of neurodevelopmental programming and a potential therapeutic target for mitigating ELS-related disorders.

Psilocybin acutely alters neurotrophic, neurochemical, and immune markers, but the relationships between these responses and circulating microRNAs (miRNAs), i.e. non-coding RNAs that regulate post-transcriptional gene expression, remain unclear. In a randomized, double-blind, placebo-controlled study of 62 healthy adults who received psilocybin (0.17 mg/kg) or placebo, we previously demonstrated that let-7g-5p and miR-150-5p were transiently differentially expressed 360 minutes after psilocybin administration. Here, we examined whether changes in these miRNAs were associated with concurrent neurotrophic, inflammatory, pharmacokinetic, and glutamatergic measures. Expression changes from baseline to 360 min and 7 days were analysed using linear regression against changes in BDNF, TNF-, IL-6, C-reactive protein, cortisol, medial prefrontal cortex glutamate/total creatine, and psilocin concentrations. Psilocybin increased let-7g-5p and decreased miR-150-5p expression. Changes in let-7g-5p were positively associated with psilocin concentrations, suggesting sensitivity to inter-individual pharmacokinetic variability, whereas miR-150-5p showed no concentration-dependent association. In both groups, miRNA changes were negatively related to baseline expression: lower baseline let-7g-5p predicted larger increases, whereas higher baseline miR-150-5p predicted larger decreases. BDNF changes were associated with both miRNAs under placebo but not psilocybin, consistent with reduced between-subject variability and a flattened BDNF-miRNA relationship following treatment. Medial prefrontal glutamate was negatively associated with miR-150-5p change under psilocybin. No associations were found with immune biomarkers. Together, these findings support the predicted involvement of let-7g-5p and miR-150-5p in neuroplasticity and their potential as accessible blood-based biomarkers of individual neurobiological responsiveness to psilocybin and other psychedelics.

Brain development, especially developmental myelination, continues through young adulthood. Concordantly, children may be particularly vulnerable to neural-immune challenges. To investigate the consequences of major childhood immune challenges, juvenile mice were exposed to respiratory influenza (H1N1) infection. White matter-specific microglial reactivity accompanied by oligodendrocyte loss was evident until two months following infection. Mice exhibited hyperlocomotion and impaired attention, but not anxiety-like behavior, at one month following infection. Linking the oligodendroglial and behavioral deficits, genetic disruption of oligodendrocyte development at the same juvenile timepoint recapitulated this behavioral phenotype. Microglial reactivity and oligodendrocyte numbers normalized by young adulthood. However, myelin development was disrupted, with persistently decreased myelinated axon density and reduced myelin sheath thickness. Hyperlocomotion resolved, but anxiety-related behaviors emerged at two months after infection. At 6 months, anxiety resolved but cognitive deficits persisted. Elevated CSF chemokines and microglial chemokine expression prompted testing the role of the multi-chemokine receptor CCR3. CCR3 inhibition rescued these cellular and behavioral aberrations after juvenile H1N1 infection. Together, these findings underscore the potential for disruption of myelin development and lasting cognitive and neuropsychiatric sequelae following major immune challenges during the juvenile period and highlight chemokine signaling as an important therapeutic target.

Stress is a major risk factor for numerous neuropsychiatric disorders and induces enduring synaptic plasticity within the nucleus accumbens core (NAcore), a key brain region involved in reward and stress-related behaviors. Previous studies from our laboratory demonstrated that stress-induced plasticity depends on matrix metalloproteinase (MMP)-2/9-mediated extracellular matrix (ECM) remodeling; however, the upstream cellular mechanisms regulating MMP activation remain unclear. Because microglia regulate neuroimmune signaling, ECM dynamics, and synaptic plasticity, we tested the hypothesis that microglial colony-stimulating factor 1 receptor (CSF1R) signaling contributes to stress-induced MMP-2/9 activation within the NAcore. Male rats received the CSF1R inhibitor PLX3397 prior to acute restraint stress. In vivo fluorescent zymography, immunohistochemistry, and quantitative PCR were used to assess MMP activity, microglial signaling, and inflammatory gene expression. Acute stress increased MMP-2/9 activity enhanced microglial CD68-associated phagocytic signaling, and elevated expression of Csf1r, Tnfa, Cnr2, and Mmp16 within the NAcore. Importantly, CSF1R inhibition attenuated stress-induced increases in MMP-2/9 activity and CD68 immunoreactivity. Combined, these findings identify microglial CSF1R signaling as an upstream regulator of stress-induced ECM remodeling within the NAcore and provide mechanistic insight into how acute stress recruits neuroimmune pathways to remodel reward circuitry.

Friedreich Ataxia (FRDA) is an autosomal recessive neurodegenerative disorder characterized by progressive loss of cerebellar and proprioceptive neurons that control movement and coordination. In most patients, FRDA is caused by homozygous GAA trinucleotide repeat expansions in the first intron of the frataxin (FXN) gene, resulting in reduced expression of frataxin, a mitochondrial protein essential for biogenesis of iron-sulfur clusters and mitochondrial function. Although recent therapeutic advances have provided modest clinical benefit, effective disease-modifying treatments remain lacking. Increasing evidence indicates that microglial cell dysfunction contributes to FRDA pathogenesis, highlighting these cells as potential therapeutic targets. However, the molecular mechanisms underlying FXN-deficient microglial dysfunction remain poorly understood. Here, we show that microglia generated from FRDA patient-derived iPSCs exhibit a cell-autonomous pro-inflammatory phenotype in the absence of exogenous inflammatory stimuli. This phenotype is characterized by coordinated activation of immune transcriptional programs, dysregulated secretion of neuroinflammatory proteins, impaired autophagy-lysosomal function, and activation of inflammasomes pathways involving NLRP2 and NLRP3. These findings demonstrate that FXN deficiency is sufficient to induce intrinsic microglial activation and identify molecular pathways that may represent attractive targets for future FRDA therapies.

Social isolation is commonly used to model social stress and is a known risk factor for depression, with impacts on hippocampal function and postnatal neurogenesis. However, most studies focus on social isolation in juvenile mice isolation during adolescence, leaving the effects of prolonged adult isolation less understood. Post-transcriptional regulation of gene expression by microRNAs (miRNAs) plays a role in hippocampal function, and altered miRNA, as well as gene expression, has been reported in the hippocampus of mice exposed to social isolation. A single-nucleotide polymorphism in miR-30e in humans is associated with increased expression of the mature miRNA, impaired cognition, electroencephalogram waveform latency, depression, and schizophrenia. We investigated whether adult isolation in mice alters gene regulation via microRNAs, particularly miR-30e-5p, and affects hippocampal function. In adult BALB/c male mice, 10 weeks of isolation increased miR-30e-5p expression in the ventral hippocampus, reduced its target gene Neurod1, and impaired hippocampal-dependent cognition (object pattern separation), without clear anxiety- or depression-like behaviours. Isolated mice also showed a blunted response to acute stress. These findings suggest that adult social isolation affects hippocampal function through post-transcriptional gene regulation, highlighting a role for miR-30e-5p in neurogenesis and cognition in response to psychological stress.

IntroductionEnvironmental factors are increasingly implicated in the etiology of autism spectrum disorder (ASD). Polybrominated diphenyl ethers (PBDEs) are anthropogenic toxicants added as flame retardants to consumer products that have become ubiquitous environmental contaminants and disrupt thyroid hormone (TH) and neuroendocrine systems. We have previously shown that developmental PBDE exposure produces ASD-like traits with involvement of oxytocin (OXT)-thyroid hormone signaling. Limosilactobacillus reuteri (LR), a widely used probiotic bacterium, has been shown to improve social functioning and increase TH and OXT levels in murine models. Therefore, we tested the hypothesis that LR supplementation (LR) prevents PBDE-induced deficits in socioemotional behavior with concomitant modulation of TH signaling genes on hypothalamic OXT neurons. MethodsC57BL/6N mouse offspring were exposed to a commercial penta-mixture of PBDE congeners, DE-71, at an environmentally realistic concentration, 0.1 mg/kg/d (DE-71), or to corn oil vehicle (VEH/CON) via their mothers during gestation and lactation. Offspring received supplementation with LR ATCC PTA 6475 (107-108 CFU/mL, po) indirectly via the dam or continuation directly through adulthood. Unsupplemented controls were given saline. ResultsFecal microbiome analysis in offspring confirmed colonization of LR at postnatal day (P) 40 and depletion by P104. LR treatment increased plasma total thyroxine in DE-71 and plasma OXT in VEH/CON dams. In DE-71 offspring of both sexes, LR normalized deficient scores on social novelty preference and emotional recognition in adult females and males and deficient long-term social recognition memory (SRM) in adult DE-71 females; DE-71 males were normal. Reduced olfactory dishabituation between two social odors may partly explain the compromised socioemotional behavior produced by DE-71 in an LR-dependent manner. Multiplex RNA in situ hybridization performed on immunoreactive OXT-ergic neurons in the paraventricular hypothalamic nucleus (PVH) revealed significant upregulation of TH transporter monocarboxylate transporter 8 (Mct8) and downregulation of iodothyronine deiodinase 3 (Dio3) in DE-71 relative to VEH/CON females. This toxicant-induced reprogramming was prevented by probiotic treatment. DE-71 males expressed reduction in Mct8 and Dio3 transcripts on OXT-ergic neurons with minimal LR protection. In the female supraoptic nucleus (SON), Mct8 and Dio3 were downregulated by DE-71 and normalized in DE-71+LR; there were no group effects on transcript levels in male SON. Results of fecal 16S rRNA sequencing indicated reduced -diversity and altered {beta}-diversity in the gut bacterial community of female but not male DE-71 exposed offspring; most changes were correctable by LR. Alterations in taxa-level abundance caused by DE-71 and reversed by LR were observed in both sexes. These involved Bifidobacterium, Coprococcus, Desulfovibrio, Oscillospira, and Peptococcaceae in females and Desulfovibrionaceae, Rikenella, and Turicibacter in males. Exposed dams showed no detriment in - and {beta}-diversity while showing reduced abundance of several Firmicutes and Proteobacteria taxa that could be rescued by LR. The relative abundance of Lactobacillus was upregulated in DE-71 males and DE-71+LR males and dams. ConclusionsThese results indicate that developmental probiotic supplementation effectively mitigated organohalogen-induced ASD-like deficits in socioemotional behavior and partially corrected dysbiosis of gut bacterial communities in exposed offspring of both sexes. Concomitantly, PBDEs altered the expression of TH regulatory genes Mct8 and Dio3 in PVH OXT neurons in a sex-dependent manner, suggesting that TH regulation of OXT neuroendocrine cells may modulate the emergence of toxicant-induced ASD-relevant behavior. While LR reinstated normal behavioral outcomes in PBDE-exposed offspring of both sexes, coincident normalization of hypothalamic TH signaling transcripts occurred more broadly in females, indicating the existence of unique parallel processes influencing the preventive effects of LR on ASD-relevant behavioral deficits in both sexes.

RTL6 (also known as SIRH3) is a eutherian-specific metavirus-derived gene highly conserved among placental mammals. We previously demonstrated that RTL6 is expressed in microglia and secreted into the brain extracellular space, where it mediates the trapping and clearance of bacterial lipopolysaccharide (LPS). However, its role in microglial TLR4 signaling remained unclear. To investigate the earliest LPS response, we performed RNA-seq analysis of wild-type and Rtl6-deficient primary microglia following 10 min of LPS stimulation. Rtl6-deficient microglia exhibited compensatory upregulation of residual transcripts derived from the untranslated region of Rtl6, suggesting feedback regulation of Rtl6 expression. Loss of RTL6 attenuated the induction of immediate-early response genes, including Fos, Jun, Nr4a1, Nr4a2, Egr2, and Egr3, together with broad suppression of interferon-responsive and inflammatory transcriptional programs. Altered neuronal and oligodendrocyte/myelin interaction pathways indicated remodeling of microglial communication networks. Strikingly, genes involved in cell-cycle progression, DNA replication, chromatin assembly, DNA repair, and genome maintenance were coordinately upregulated, including multiple disease-associated microglia (DAM)-related genes. Collectively, these findings indicate that RTL6 couples extracellular LPS sensing to inflammatory transcriptional responses while regulating microglial functional state transitions. Our results identify RTL6 as a previously unrecognized component of the regulatory network governing microglial functional states in placental mammals.

Interleukin-17A (IL-17A) has been implicated in stress- and pain-related inflammation, yet evidence for acute IL-17A stress response in humans remains scarce. This study examined whether the Maastricht Acute Stress Test (MAST) induces changes in circulating IL-17A and how IL-17A dynamics relate to cortisol and subjective stress/pain. Forty-six healthy adults (mean age: 30.50, SD = 12.86 years; 54% female) completed the standardized MAST. Serum IL-17A and cortisol were assessed repeatedly across baseline and recovery. Stress- and pain-related ratings (VAS) and trait questionnaires (e.g., chronic stress, psychological distress, resilience) were completed. There was a significant increase over time in IL-17A and cortisol following the MAST, with an 36 % increase of IL-17A level measured at 105 min post-stressor and cortisol peaking at 10 min post-stressor. IL-17A indices (baseline and AUCi) showed no meaningful associations with cortisol, subjective stress/pain, or psychological traits, whereas cortisol response (AUCi) correlated positively with perceived acute stress and pain. Overall, the MAST produced clear IL-17A and cortisol responses that appeared dissociable in healthy individuals. Future studies should include broader inflammatory panels and clinical or high-stress samples to clarify conditions under which IL-17A covaries with HPA-axis activity and subjective experience.

Immune checkpoint inhibitor (ICI) combinations that block cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein 1 (PD-1) signaling have revolutionized cancer care but also exert a range of immune-related adverse events (irAE) in various tissues, including the brain. Our understanding of the mechanisms of irAE in the brain is still evolving, and we recently demonstrated that ICI (blockade of CTLA-4 and PD-1) perturbs hippocampal-dependent memory function by derailing neuro-immune homeostasis and compromising synaptic integrity. However, the spatial patterns and the cell-type-specific molecular mechanisms underlying ICI-related brain dysfunction remain not well-defined. To address this gap, we performed spatial transcriptomic profiling of the hippocampal region using multiplexed error-robust fluorescence in situ hybridization (MERFISH) to map gene expression at single-cell resolution. By integrating spatial single-cell data with bulk RNA-seq, we define the distribution of microglia, astrocytes, synaptic, and neuroinflammatory markers, and determine how ICI reshapes hippocampal cellular composition in a syngeneic murine melanoma model. MERFISH revealed upregulation of microglial, astrocytic, oligodendrocytic, and T cell markers post-ICI treatment, revealing unique pathways driving neuroinflammation, synaptic function, and cellular signaling. Furthermore, immunofluorescence analysis of postmortem brains from patients treated with ICI corroborates our findings of ICI-related immune activation of microglia. Finally, using a conditional deletion model, we show that T cells are indispensable for ICI-driven microglial activation. Altogether, our study provides a high-resolution spatial framework for understanding irAEs in brain function and a T cell-microglia crosstalk axis as a driving mechanism of dysregulated neuro-immune homeostasis during ICI.

Air pollution exposure has been associated with increased risk of developing mental health problems. It is possible that individuals at high genetic risk for psychopathology may be more vulnerable to these effects; however, this question remains to be investigated. We leveraged longitudinal data from n=10,620 participants from the Adolescent Brain Cognitive Development Study to first investigate sex-stratified associations of particulate matter (PM2.) exposure and genetic risk with mental health trajectories across 9-16 years including internalizing symptoms and psychotic like experiences (PLEs). Additionally, we tested whether genetic risk for schizophrenia (PRS-SCZ) and major depressive disorder (PRS-MDD) exacerbate the association with PM2. exposure and change in symptoms over time. PM2. exposure was associated with lower decreases in PLEs over time in females (p-FDR=0.005), with no effects on internalising symptom trajectories in either sex. Genetic influences were sex-specific, with higher PRS-SCZ and PRS-MDD linked to greater increases in internalising symptoms in females (p-FDR=0.009; p-FDR=0.022) and higher PRS-MDD associated with greater decreases in PLEs in males (p-FDR=0.001). In females we also observed an interaction between PM2. and PRS-MDD on PLEs trajectories (p-FDR=0.048) such that those with high genetic risk and high PM2.5 exposure demonstrated increases in PLEs over time. Our results suggest that PM2. exposure and polygenic risk for depression jointly shape mental health during adolescence. This underscores the potential of interventions aimed at lowering air pollution during sensitive periods of neurodevelopment in improving adolescent mental health.