Stress and depression-associated shifts in gut microbiota: A pilot study of human pregnancy.

Background: Psychosocial stress and mood-related disorders, such as depression, are prevalent and vulnerability to these conditions is heightened during pregnancy. Psychosocial stress induces consequences via several mechanisms including the gut microbiota-brain axis and associated signaling pathways. Previous preclinical work indicates that prenatal stress alters maternal gut microbial composition and impairs offspring development. Importantly, although the fecal and vaginal microenvironments undergo alterations across pregnancy, we lack consensus regarding which shifts are adaptive or maladaptive in the presence of prenatal stress and depression. Clinical studies interrogating these relationships have identified unique taxa but have been limited in study design. Methods: We conducted a prospective cohort study of pregnant individuals consisting of repeated administration of psychometrics (Perceived Stress Scale (PSS) and Center for Epidemiological Studies Depression Scale (CES-D)) and collection of fecal and vaginal microbiome samples. Fecal and vaginal microbial community composition across psychometric responses were interrogated using full-length 16S rRNA sequencing followed by α and ß-diversity metrics and taxonomic abundance. Results: Early pregnancy stress was associated with increased abundance of fecal taxa not previously identified in related studies, and stress from late pregnancy through postpartum was associated with increased abundance of typical vaginal taxa and opportunistic pathogens in the fecal microenvironment. Additionally, in late pregnancy, maternal stress and depression scores were associated with each other and with elevated maternal C-C motif chemokine ligand 2 (CCL2) concentrations. At delivery, concordant with previous literature, umbilical CCL2 concentration was negatively correlated with relative abundance of maternal fecal Lactobacilli. Lastly, participants with more severe depressive symptoms experienced steeper decreases in prenatal vaginal α-diversity. Conclusion: These findings a) underscore previous preclinical and clinical research demonstrating the effects of prenatal stress on maternal microbiome composition, b) suggest distinct biological pathways for the consequences of stress versus depression and c) extend the literature by identifying several taxa which may serve critical roles in mediating this relationship. Thus, further interrogation of the role of specific maternal microbial taxa in relation to psychosocial stress and its sequelae is warranted.

The Maternal Microbiome as a Map to Understanding the Impact of Prenatal Stress on Offspring Psychiatric Health.

Stress and psychiatric disorders have been independently associated with disruption of the maternal and offspring microbiome and with increased risk of the offspring developing psychiatric disorders, both in clinical studies and in preclinical studies. However, the role of the microbiome in mediating the effect of prenatal stress on offspring behavior is unclear. While preclinical studies have identified several key mechanisms, clinical studies focusing on mechanisms are limited. In this review, we discuss 3 specific mechanisms by which the microbiome could mediate the effects of prenatal stress: 1) altered production of short-chain fatty acids; 2) disruptions in TH17 (T helper 17) cell differentiation, leading to maternal and fetal immune activation; and 3) perturbation of intestinal and microbial tryptophan metabolism and serotonergic signaling. Finally, we review the existing clinical literature focusing on these mechanisms and highlight the need for additional mechanistic clinical research to better understand the role of the microbiome in the context of prenatal stress.

Fetal CCL2 signaling mediates offspring social behavior and recapitulates effects of prenatal stress.

Maternal stress during pregnancy is prevalent and associated with increased risk of neurodevelopmental disorders in the offspring. Maternal and offspring immune dysfunction has been implicated as a potential mechanism by which prenatal stress shapes offspring neurodevelopment; however, the impact of prenatal stress on the developing immune system has yet to be elucidated. Furthermore, there is evidence that the chemokine C-C motif chemokine ligand 2 (CCL2) plays a key role in mediating the behavioral sequelae of prenatal stress. Here, we use an established model of prenatal restraint stress in mice to investigate alterations in the fetal immune system, with a focus on CCL2. In the placenta, stress led to a reduction in CCL2 and Ccr2 expression with a concomitant decrease in leukocyte number. However, the fetal liver exhibited an inflammatory phenotype, with upregulation of Ccl2, Il6, and Lbp expression, along with an increase in pro-inflammatory Ly6CHi monocytes. Prenatal stress also disrupted chemokine signaling and increased the number of monocytes and microglia in the fetal brain. Furthermore, stress increased Il1b expression by fetal brain CD11b+ microglia and monocytes. Finally, intra-amniotic injections of recombinant mouse CCL2 partially recapitulated the social behavioral deficits in the adult offspring previously observed in the prenatal restraint stress model. Altogether, these data suggest that prenatal stress led to fetal inflammation, and that fetal CCL2 plays a role in shaping offspring social behavior.

Maternal anxiety, depression and stress affects offspring gut microbiome diversity and bifidobacterial abundances.

Uncovering mechanisms underlying fetal programming during pregnancy is of critical importance. Atypical neurodevelopment during the pre- and immediate postnatal period has been associated with long-term adverse health outcomes, including mood disorders and aberrant cognitive ability in offspring. Maternal factors that have been implicated in anomalous offspring development include maternal inflammation and tress, anxiety, and depression. One potential mechanism through which these factors perturb normal offspring postnatal development is through microbiome disruption. The mother is a primary source of early postnatal microbiome seeding for the offspring, and the transference of a healthy microbiome is key in normal neurodevelopment. Since psychological stress, mood disorders, and inflammation have all been implicated in altering maternal microbiome community structure, passing on aberrant microbial communities to the offspring that may then affect developmental outcomes. Therefore, we examined how maternal stress, anxiety and depression assessed with standardized instruments, and maternal inflammatory cytokine levels in the pre- and postnatal period are associated with the offspring microbiome within the first 13 months of life, utilizing full length 16S sequencing on infant stool samples, that allowed for species-level resolution. Results revealed that infants of mothers who reported higher anxiety and perceived stress had reduced alpha diversity. Additionally, the relative taxonomic quantitative abundances of Bifidobacterium dentium and other species that have been associated with either modulation of the gut-brain axis, or other beneficial health outcomes, were reduced in the offspring of mothers with higher anxiety, perceived stress, and depression. We also found associations between bifidobacteria and prenatal maternal pro-inflammatory cytokines IL-6, IL-8, and IL-10. In summary, specific microbial taxa involved in maintaining proper brain and immune function are lower in offspring born to mothers with anxiety, depression, or stress, providing strong evidence for a mechanism by which maternal factors may affect offspring health through microbiota dysregulation.

Discrete role for maternal stress and gut microbes in shaping maternal and offspring immunity.

Psychosocial stress is prevalent during pregnancy, and is associated with immune dysfunction, both for the mother and the child. The gut microbiome has been implicated as a potential mechanism by which stress during pregnancy can impact both maternal and offspring immune function; however, the complex interplay between the gut microbiome and the immune system is not well-understood. Here, we leverage a model of antimicrobial-mediated gut microbiome reduction, in combination with a well-established model of maternal restraint stress, to investigate the independent effects of and interaction between maternal stress and the gut microbiome in shaping maternal and offspring immunity. First, we confirmed that the antimicrobial treatment reduced maternal gut bacterial load and altered fecal alpha and beta diversity, with a reduction in commensal microbes and an increase in the relative abundance of rare taxa. Prenatal stress also disrupted the gut microbiome, according to measures of both alpha and beta diversity. Furthermore, prenatal stress and antimicrobials independently induced systemic and gastrointestinal immune suppression in the dam with a concomitant increase in circulating corticosterone. While stress increased neutrophils in the maternal circulation, lymphoid cells and monocytes were not impacted by either stress or antimicrobial treatment. Although the fetal immune compartment was largely spared, stress increased circulating neutrophils and CD8 T cells, and antibiotics increased neutrophils and reduced T cells in the adult offspring. Altogether, these data indicate similar, but discrete, roles for maternal stress and gut microbes in influencing maternal and offspring immune function.

Stressor-Induced Reduction in Cognitive Behavior is Associated with Impaired Colonic Mucus Layer Integrity and is Dependent Upon the LPS-Binding Protein Receptor CD14.

Purpose: Commensal microbes are impacted by stressor exposure and are known contributors to cognitive and social behaviors, but the pathways through which gut microbes influence stressor-induced behavioral changes are mostly unknown. A murine social stressor was used to determine whether host-microbe interactions are necessary for stressor-induced inflammation, including neuroinflammation, that leads to reduced cognitive and social behavior. Methods: C57BL/6 male mice were exposed to a paired fighting social stressor over a 1 hr period for 6 consecutive days. Y-maze and social interaction behaviors were tested following the last day of the stressor. Serum cytokines and lipopolysaccharide binding protein (LBP) were measured and the number and morphology of hippocampal microglia determined via immunohistochemistry. Intestinal mucous thickness and antimicrobial peptide expression were determined via fluorescent staining and real-time PCR (respectively) and microbial community composition was assessed using 16S rRNA gene amplicon sequencing. To determine whether the microbiota or the LBP receptor (CD14) are necessary for stressor-induced behavioral changes, experiments were performed in mice treated with a broad-spectrum antibiotic cocktail or in CD14-/- mice. Results: The stressor reduced Y-maze spontaneous alternations, which was accompanied by increased microglia in the hippocampus, increased circulating cytokines (eg, IL-6, TNF-α) and LBP, and reduced intestinal mucus thickness while increasing antimicrobial peptides and cytokines. These stressor-induced changes were largely prevented in mice given broad-spectrum antibiotics and in CD14-/- mice. In contrast, social stressor-induced alterations of social behavior were not microbe-dependent. Conclusion: Stressor-induced cognitive deficits involve enhanced bacterial interaction with the intestine, leading to low-grade, CD14-dependent, inflammation.

Stressor-Induced Increases in Circulating, but Not Colonic, Cytokines Are Related to Anxiety-like Behavior and Hippocampal Inflammation in a Murine Colitis Model.

Stressor exposure increases colonic inflammation. Because inflammation leads to anxiety-like behavior, we tested whether stressor exposure in mice recovering from dextran-sulfate-sodium (DSS)-induced colitis enhances anxiety-like behavior. Mice received 2% DSS for five consecutive days prior to being exposed to a social-disruption (SDR) stressor (or being left undisturbed). After stressor exposure, their behavior was tested and colitis was assessed via histopathology and via inflammatory-cytokine measurement in the serum and colon. Cytokine and chemokine mRNA levels in the colon, mesenteric lymph nodes (MLNs), hippocampus, and amygdala were measured with RT-PCR. SDR increased anxiety-like behaviors, which correlated with serum and hippocampal IL-17A. The stressor also reduced IL-1ß, CCL2, and iNOS in the colonic tissue, but increased iNOS, IFNγ, IL-17A, and TNFα in the MLNs. A network analysis indicated that reductions in colonic iNOS were related to elevated MLN iNOS and IFNγ. These inflammatory markers were related to serum and hippocampal IL-17A and associated with anxiety-like behavior. Our data suggest that iNOS may protect against extra-colonic inflammation, and when suppressed during stress it is associated with elevated MLN IFNγ, which may coordinate gut-to-brain inflammation. Our data point to hippocampal IL-17A as a key correlate of anxiety-like behavior.

Prenatal stress-induced disruptions in microbial and host tryptophan metabolism and transport.

The aromatic amino acid tryptophan (Trp) is a precursor for multiple metabolites that can steer proper immune and neurodevelopment as well as social behavior in later life. Dysregulation in the Trp metabolic pathways and abundance of Trp or its derivatives, including indoles, kynurenine (Kyn), and particularly serotonin, has been associated with behavioral deficits and neuropsychiatric disorders including autism spectrum disorders (ASD) and schizophrenia. Previously, we have shown that prenatal stress (PNS) alters placental Trp and serotonin, and reduces Trp-metabolizing members of the maternal colonic microbiota. Given that PNS also results in alterations in offspring neurodevelopment, behavior and immune function, we hypothesized that PNS affects Trp metabolism and transport in both the maternal and fetal compartments, and that these alterations continue into adolescence. We surmised that this is due to reductions in Trp-metabolizing microbes that would otherwise reduce the Trp pool under normal metabolic conditions. To test this, pregnant mice were exposed to a restraint stressor and gene expression of enzymes involved in Trp and serotonin metabolism were measured. Specifically, tryptophan 2,3-dioxygenase, aryl hydrocarbon receptor, and solute carrier proteins, were altered due to PNS both prenatally and postnatally. Additionally, Parasutterella and Bifidobacterium, which metabolize Trp in the gut, were reduced in both the dam and the offspring. Together, the reductions of Trp-associated microbes and concomitant dysregulation in Trp metabolic machinery in dam and offspring suggest that PNS-induced Trp metabolic dysfunction may mediate aberrant fetal neurodevelopment.

Moderately pathogenic maternal influenza A virus infection disrupts placental integrity but spares the fetal brain.

Maternal infection during pregnancy is a known risk factor for offspring mental health disorders. Animal models of maternal immune activation (MIA) have implicated specific cellular and molecular etiologies of psychiatric illness, but most rely on pathogen mimetics. Here, we developed a mouse model of live H3N2 influenza A virus (IAV) infection during pregnancy that induces a robust inflammatory response but is sublethal to both dams and offspring. We observed classic indicators of lung inflammation and severely diminished weight gain in IAV-infected dams. This was accompanied by immune cell infiltration in the placenta and partial breakdown of placental integrity. However, indications of fetal neuroinflammation were absent. Further hallmarks of mimetic-induced MIA, including enhanced circulating maternal IL-17A, were also absent. Respiratory IAV infection did result in an upregulation in intestinal expression of transcription factor RORγt, master regulator of a subset of T lymphocytes, TH17 cells, which are heavily implicated in MIA-induced etiologies. Nonetheless, subsequent augmentation in IL-17A production and concomitant overt intestinal injury was not evident. Our results suggest that mild or moderately pathogenic IAV infection during pregnancy does not inflame the developing fetal brain, and highlight the importance of live pathogen infection models for the study of MIA.

Maternal Exposure to Adversity: Impact on the Microbiota-Gut-Brain Axis, Inflammation and Offspring Psychiatric Outcomes.

Psychosocial stress, driven by a variety of sources and influences, can be ubiquitous in our modern society. Prolonged exposure to these stressors can have detrimental biological and psychological effects; extant findings in childhood adversity indicate that the cumulative effects of exposure to childhood adversity increase risk for developmental delays, altered immune responses, and psychopathology later in life. The pathways by which these effects are conferred continue to be studied. Given that pregnancy is a critical period during which susceptibility to lifetime health and illness are programmed, this chapter will focus on the impacts of maternal history of childhood adversity on offspring mental health, including the role of the microbiota-gut-brain axis. One of the most commonly used frameworks of the last several decades for measuring childhood adversity is the Adverse Childhood Experiences (ACEs) psychometric. We provide an overview of the possible mechanisms through which maternal stress, including the cumulative effects of maternal ACEs, may increase susceptibility to disease in offspring. These include altered epigenetic regulation, hypothalamic-pituitary-adrenal axis function and peripheral inflammation, and gut microbial composition. Finally, we conclude with clinical considerations, including possible future therapeutic interventions.

Unique maternal immune and functional microbial profiles during prenatal stress.

Maternal stress during pregnancy is widespread and is associated with poor offspring outcomes, including long-term mental health issues. Prenatal stress-induced fetal neuroinflammation is thought to underlie aberrant neurodevelopment and to derive from a disruption in intrauterine immune homeostasis, though the exact origins are incompletely defined. We aimed to identify divergent immune and microbial metagenome profiles of stressed gestating mice that may trigger detrimental inflammatory signaling at the maternal-fetal interface. In response to stress, maternal glucocorticoid circuit activation corresponded with indicators of systemic immunosuppression. At the maternal-fetal interface, density of placental mononuclear leukocytes decreased with stress, yet maternal whole blood leukocyte analysis indicated monocytosis and classical M1 phenotypic shifts. Genome-resolved microbial metagenomic analyses revealed reductions in genes, microbial strains, and metabolic pathways in stressed dams that are primarily associated with pro-inflammatory function. In particular, disrupted Parasutterella excrementihominis appears to be integral to inflammatory and metabolic dysregulation during prenatal stress. Overall, these perturbations in maternal immunological and microbial regulation during pregnancy may displace immune equilibrium at the maternal-fetal interface. Notably, the absence of and reduction in overt maternal inflammation during stress indicates that the signaling patterns driving fetal outcomes in this context are more nuanced and complex than originally anticipated.

Prenatal stress causes intrauterine inflammation and serotonergic dysfunction, and long-term behavioral deficits through microbe- and CCL2-dependent mechanisms.

Prenatal stress (PNS) is associated with neuropsychiatric disorders in offspring, including anxiety, depression, and autism spectrum disorders. There is mounting evidence that these behavioral phenotypes have origins in utero. Maternal microbes, inflammation, and serotonergic dysfunction have been implicated as potential mediators of the behavioral consequences of PNS; whether and how these systems interact is unclear. Here, we examine the effects of PNS in utero using late-gestation maternal restraint stress in wild-type (WT), germ-free (GF), and CCL2-/- genetic knock-out (KO) mice. In WT mice, PNS leads to placental and fetal brain inflammation, including an elevation in the chemokine CCL2. This inflammation is largely absent in GF mice, indicating the critical role of maternal microbes in mediating immune processes in utero. Furthermore, PNS in the absence of CCL2 failed to increase pro-inflammatory cytokine IL-6 in the fetal brain. PNS offspring also exhibited deficits in sociability and anxiety-like behavior that were absent in CCL2-/- PNS offspring. Tryptophan and serotonin (5-HT) were elevated in the WT PNS placenta, but not in CCL2-/- and GF animals. Altogether, these findings suggest that a complex interaction between maternal microbes, inflammation, and serotonin metabolism regulates the emergence of behavioral abnormalities following PNS.

Intrauterine Microbiota: Missing, or the Missing Link?

The intrauterine environment provides a key interface between the mother and the developing fetus during pregnancy, and is a target for investigating mechanisms of fetal programming. Studies have demonstrated an association between prenatal stress and neurodevelopmental disorders. The role of the intrauterine environment in mediating this effect is still being elucidated. In this review, we discuss emerging preclinical and clinical evidence suggesting the existence of microbial communities in utero. We also outline possible mechanisms of bacterial translocation to the intrauterine environment and immune responses to the presence of microbes or microbial components. Lastly, we overview the effects of intrauterine inflammation on neurodevelopment. We hypothesize that maternal gestational stress leads to disruptions in the maternal oral, gut, and vaginal microbiome that may lead to the translocation of bacteria to the intrauterine environment, eliciting an inflammatory response and resulting in deficits in neurodevelopment.

Prenatal stress disrupts social behavior, cortical neurobiology and commensal microbes in adult male offspring.

In utero and early neonatal exposure to maternal stress is linked with psychiatric disorders, and the underlying mechanisms are currently being elucidated. We used a prenatal stressor in pregnant mice to examine novel relationships between prenatal stress exposure, changes in the gut microbiome, and social behavior. Here, we show that males exposed to prenatal stress had a significant reduction in social behavior in adulthood, with increased corticosterone release following social interaction. Male offspring exposed to prenatal stress also had neuroinflammation, decreased oxytocin receptor, and decreased serotonin metabolism in their cortex in adulthood, which are linked to decreased social behavior. Finally, we found a significant difference in commensal microbes, including decreases in Bacteroides and Parabacteroides, in adult male offspring exposed to prenatal stress when compared to non-stressed controls. Our findings indicate that gestation is a critical window where maternal stress contributes to the development of aberrant social behaviors and alterations in cortical neurobiology, and that prenatal stress is sufficient to disrupt the male gut-brain axis into adulthood.

The relationship between progestin hormonal contraception and depression: a systematic review.

OBJECTIVE: We performed a systematic review to look for an association between progestin-only contraception and depression. METHODS: We searched PubMed, Ovid and Web of Science for English-language articles including progestin-only contraception and depression from database inception to September 2016. We evaluated study quality with the procedures guiding reviews for the United States Preventive Services Task Force and the Cochrane Risk of Bias Tools. We included studies that evaluated progestin-only contraception and depression, focusing on externally validated depression measures. We excluded case studies, review articles and other psychiatric disorders. RESULTS: We identified 26 studies that met the inclusion criteria, including 5 randomized controlled trials, 11 cohort studies and 10 cross-sectional studies. We found minimal association between progestin-only methods and depression. No correlation with depression was found in five low-quality, high-risk-of-bias progestin subdermal implant studies and four out of five varying-quality and medium-risk-of-bias levonorgestrel intrauterine device studies. Three medroxyprogesterone acetate intramuscular injection trials with varying levels of quality and bias show no difference in depression. Two progestin-only contraceptive pill studies with varying levels of quality and bias indicate no increase in depression scores, while one good-quality, medium-bias study shows an association between progestin-only pills, the intrauterine device and depression. CONCLUSION: Despite perceptions in the community of increased depression following the initiation of progestin contraceptives, the preponderance of evidence does not support an association based on validated measures (mostly level II-1 evidence, moderate quality, low risk of bias).

Prenatal stress affects placental cytokines and neurotrophins, commensal microbes, and anxiety-like behavior in adult female offspring.

Recent studies demonstrate that exposure to stress changes the composition of the intestinal microbiota, which is associated with development of stress-induced changes to social behavior, anxiety, and depression. Stress during pregnancy has also been related to the emergence of these disorders; whether commensal microbes are part of a maternal intrauterine environment during prenatal stress is not known. Here, we demonstrate that microbiome changes are manifested in the mother, and also found in female offspring in adulthood, with a correlation between stressed mothers and female offspring. Alterations in the microbiome have been shown to alter immune responses, thus we examined cytokines in utero. IL-1ß was increased in placenta and fetal brain from offspring exposed to the prenatal stressor. Because IL-1ß has been shown to prevent induction of brain derived neurotrophic factor (BDNF), we examined BDNF and found a reduction in female placenta and adult amygdala, suggesting in utero impact on neurodevelopment extending into adulthood. Furthermore, gastrointestinal microbial communities were different in adult females born from stressed vs. non-stressed pregnancies. Adult female offspring also demonstrated increased anxiety-like behavior and alterations in cognition, suggesting a critical window where stress is able to influence the microbiome and the intrauterine environment in a deleterious manner with lasting behavioral consequences. The microbiome may be a key link between the intrauterine environment and adult behavioral changes.

Combined hormonal contraception and its effects on mood: a critical review.

OBJECTIVES: Adverse mood changes are sometimes cited as a reason for discontinuing combined hormonal contraception (CHC). A systematic review of recent literature was undertaken to characterise the nature of these side effects and identify characteristics that might predispose women to such effects. METHODS: A MEDLINE review of studies from the past 30 years that focused on CHC and mood was performed. Database search was supplemented with studies found through citations and references. RESULTS: The research literature on this topic is limited by a lack of prospective studies, a variety of measurements of mood, and a consolidation of many disparate types of contraceptives studied together in a single cohort. Common themes that emerge from review of these papers include (1) most women using CHC demonstrate no effect or a beneficial effect on mood, with a low incidence of adverse effects; (2) contraceptives containing less androgenic progestins may have fewer adverse effects on mood; (3) continuous and perhaps non-oral dosing of CHC has the fewest mood effects; (4) women with underlying mood disorders may be predisposed to mood effects, but this may reflect factors related to choice of contraception rather than the mood disorder itself. CONCLUSION: Inconsistent research methods and lack of uniform assessments make it difficult to make strong conclusions about which CHC users are at risk for adverse mood effects. Until more prospective data is available, clinicians should recognise that such effects are infrequent and CHC may be prescribed with confidence.

Effects of Stress on Commensal Microbes and Immune System Activity.

The body harbors a vast array of microbes that are collectively known as the microbiota. Increasing attention is being paid to the role of the gut microbiota in the health of the host. Gut microbial communities are relatively resistant to change, though alterations in homeostasis can also significantly change gut microbial community structure. An important factor that has been demonstrated to alter the composition of the gut microbiota is exposure to psychological stressors. And, evidence indicates that the commensal microbiota are involved in stressor-induced immunomodulation. This chapter will discuss the impact of psychosocial stress on immunity, and present evidence that stressor-induced alterations in the composition of gut microbial communities contributes to stressor-induced immunomodulation and neurobiological sequelae. Finally, the role of the microbiota in the perinatal time period will be explored, and an integrative hypothesis of the role of the microbiome in health and stress response will be proposed.