Glucocorticoid-induced leucine zipper "quantifies" stressors and increases male susceptibility to PTSD

Application of methylation in the diagnosis of ankylosing spondylitis

Ankylosing spondylitis (AS) is a chronic inflammatory autoimmune disease, mainly characterized by perifibrocartilage osteitis of the sacroiliac joints and spinal enthesitis. To date, the exact pathogenesis of AS remains elusive. It is generally believed that AS is a multifactorial disease involving genetics, infection, environment, and immunity. Among them, genetic factors are the primary determinants of disease risk and severity. In recent years, epigenetic mechanisms such as DNA methylation have been extensively surveyed with respect to the pathogenesis of AS. This review summarizes the latest research progress of methylation in AS, from whole-genome sequencing to individual differentially methylated gene. And finally, the role of methylase in AS inflammation, autophagy, and osteogenic differentiation was explored. In summary, the results of this review attempt to explain the role of methylation in the occurrence and development of AS and point out the shortcomings of current methylation research, providing directions for subsequent methylation research in AS.

LAT1-dependent placental methionine uptake is a key player in fetal programming of metabolic disease

The Developmental Origins of Health and Disease hypothesis sustains that exposure to different stressors during prenatal development prepares the offspring for the challenges to be encountered after birth. We studied the gestational period as a particularly vulnerable window where different stressors can have strong implications for fetal programming of the offspring's life-long metabolic status via alterations of specific placentally expressed nutrient transporters. To study this mechanism, we used a murine prenatal stress model, human preeclampsia, early miscarriage, and healthy placental tissue samples, in addition to in vitro models of placental cells. In stressed mice, placental overexpression of L-type amino acid transporter 1 (Lat1) and subsequent global placental DNA hypermethylation was accompanied by fetal and adult hypothalamic dysregulation in global DNA methylation and gene expression as well as long-term metabolic abnormalities exclusively in female offspring. In human preeclampsia, early miscarriage, and under hypoxic conditions, placental LAT1 was significantly upregulated, leading to increased methionine uptake and global DNA hypermethylation. Remarkably, subgroups of healthy term placentas with high expression of stress-related genes presented increased levels of placental LAT1 mRNA and protein, DNA and RNA hypermethylation, increased methionine uptake capacity, one-carbon metabolic pathway disruption, higher methionine concentration in the placenta and transport to the fetus specifically in females. Since LAT1 mediates the intracellular accumulation of methionine, global DNA methylation, and one-carbon metabolism in the placenta, our findings hint at a major sex-specific global response to a variety of prenatal stressors affecting placental function, epigenetic programming, and life-long metabolic disease and provide a much-needed insight into early-life factors predisposing females/women to metabolic disorders.

Abnormal DNA methylation within HPA-axis genes years after paediatric critical illness

BACKGROUND

Critically ill children suffer from impaired physical/neurocognitive development 2 years later. Glucocorticoid treatment alters DNA methylation within the hypothalamus-pituitary-adrenal (HPA) axis which may impair normal brain development, cognition and behaviour. We tested the hypothesis that paediatric-intensive-care-unit (PICU) patients, sex- and age-dependently, show long-term abnormal DNA methylation within the HPA-axis layers, possibly aggravated by glucocorticoid treatment in the PICU, which may contribute to the long-term developmental impairments.

RESULTS

In a pre-planned secondary analysis of the multicentre PEPaNIC-RCT and its 2-year follow-up, we identified differentially methylated positions and differentially methylated regions within HPA-axis genes in buccal mucosa DNA from 818 former PICU patients 2 years after PICU admission (n = 608 no glucocorticoid treatment; n = 210 glucocorticoid treatment) versus 392 healthy children and assessed interaction with sex and age, role of glucocorticoid treatment in the PICU and associations with long-term developmental impairments. Adjusting for technical variation and baseline risk factors and correcting for multiple testing (false discovery rate < 0.05), former PICU patients showed abnormal DNA methylation of 26 CpG sites (within CRHR1, POMC, MC2R, NR3C1, FKBP5, HSD11B1, SRD5A1, AKR1D1, DUSP1, TSC22D3 and TNF) and three DNA regions (within AVP, TSC22D3 and TNF) that were mostly hypomethylated. These abnormalities were sex-independent and only partially age-dependent. Abnormal methylation of three CpG sites within FKBP5 and one CpG site within SRD5A1 and AKR1D1 was partly attributable to glucocorticoid treatment during PICU stay. Finally, abnormal methylation within FKBP5 and AKR1D1 was most robustly associated with long-term impaired development.

CONCLUSIONS

Two years after critical illness in children, abnormal methylation within HPA-axis genes was present, predominantly within FKBP5 and AKR1D1, partly attributable to glucocorticoid treatment in the PICU, and explaining part of the long-term developmental impairments. These data call for caution regarding liberal glucocorticoid use in the PICU.

Epigenetic Alterations in Post-Traumatic Stress Disorder: Comprehensive Review of Molecular Markers

Background

Post-traumatic stress disorder (PTSD) can occur after a traumatic event. PTSD is characterized by nightmares, flashbacks and avoidance of stressors. It currently affects 2-8% of the population, with military personnel particularly susceptible. Studies show that environmental stressors can induce various epigenetic changes that shape the PTSD phenotype. Despite the significant impact of epigenetic factors on PTSD symptoms and susceptibility, they have not been widely discussed in the literature. This review focuses on describing epigenetic mechanisms in PTSD, especially DNA methylation, chromatin regulation, and noncoding RNA.

Summary

The article includes relevant studies published from 2013 to 2023, excluding non-English-language studies or studies with insufficient data. This review investigated gene methylation changes in association with PTSD, including those related to the hypothalamic-pituitary-adrenal axis, brain-derived neurotrophic factor, neurotransmitters, and immune system functioning, as well as the role of histones and regulatory noncoding RNAs.

Key Messages

Epigenetic alterations play a crucial role in shaping PTSD susceptibility, symptomatology, and long-term outcomes, highlighting their potential as important markers and therapeutic targets. Understanding these alterations can aid in developing clinical strategies to better predict, prevent, and treat PTSD. However, further large-scale longitudinal studies are needed to establish the temporal relationship between epigenetic changes and the onset of PTSD, as well as to classify other potential epigenetic mechanisms.

Chronic adolescent stress alters GR-FKBP5 interactions in the hippocampus of adult female rats

Chronic stress exposure during development can have lasting behavioral consequences that differ in males and females. More specifically, increased depressive behaviors in females, but not males, are observed in both humans and rodent models of chronic stress. Despite these known stress-induced outcomes, the molecular consequences of chronic adolescent stress in the adult brain are less clear. The stress hormone corticosterone activates the glucocorticoid receptor, and activity of the receptor is regulated through interactions with co-chaperones-such as the immunophilin FK506 binding proteins 5 (FKBP5). Previously, it has been reported that the adult stress response is modified by a history of chronic stress; therefore, the current study assessed the impact of chronic adolescent stress on the interactions of the glucocorticoid receptor (GR) with its regulatory co-chaperone FKBP5 in response to acute stress in adulthood. Although protein presence for FKBP5 did not differ by group, assessment of GR-FKBP5 interactions demonstrated that adult females with a history of chronic adolescent stress had elevated GR-FKBP5 interactions in the hippocampus following an acute stress challenge which could potentially contribute to a reduced translocation pattern given previous literature describing the impact of FKBP5 on GR activity. Interestingly, the altered co-chaperone interactions of the GR in the stressed female hippocampus were not coupled to an observable difference in transcription of GR-regulated genes. Together, these studies show that chronic adolescent stress causes lasting changes to co-chaperone interactions with the glucocorticoid receptor following stress exposure in adulthood and highlight the potential role that FKBP5 plays in these modifications. Understanding the long-term implications of adolescent stress exposure will provide a mechanistic framework to guide the development of interventions for adult disorders related to early life stress exposures.

Modulation of recovery from neonatal hyperoxic lung injury by sex as a biological variable

Recovery from lung injury during the neonatal period requires the orchestration of many biological pathways. The modulation of such pathways can drive the developing lung towards proper repair or persistent maldevelopment that can lead to a disease phenotype. Sex as a biological variable can regulate these pathways differently in the male and female lung exposed to neonatal hyperoxia. In this study, we assessed the contribution of cellular diversity in the male and female neonatal lung following injury. Our objective was to investigate sex and cell-type specific transcriptional changes that drive repair or persistent injury in the neonatal lung and delineate the alterations in the immune-endothelial cell communication networks using single cell RNA sequencing (sc-RNAseq) in a murine model of hyperoxic injury. We generated transcriptional profiles of >55,000 cells isolated from the lungs of postnatal day 1 (PND 1; pre-exposure), PND 7, and PND 21neonatal male and female C57BL/6 mice exposed to 95 % FiO2 between PND 1-5 (saccular stage of lung development). We show the presence of sex-based differences in the transcriptional states of lung endothelial and immune cells at PND 1 and PND 21. Furthermore, we demonstrate that biological sex significantly influences the response to injury, with a greater number of differentially expressed genes showing sex-specific patterns than those shared between male and female lungs. Pseudotime trajectory analysis highlighted genes needed for lung development that were altered by hyperoxia. Finally, we show intercellular communication between endothelial and immune cells at saccular and alveolar stages of lung development with sex-based biases in the crosstalk and identify novel ligand-receptor pairs. Our findings provide valuable insights into the cell diversity, transcriptional state, developmental trajectory, and cell-cell communication underlying neonatal lung injury, with implications for understanding lung development and possible therapeutic interventions while highlighting the crucial role of sex as a biological variable.

Glucocorticoid receptor regulates protein chaperone, circadian clock and affective disorder genes in the zebrafish brain

Glucocorticoid resistance is commonly observed in depression, and has been linked to reduced expression and/or function of the glucocorticoid receptor (NR3C1 in human, hereafter referred to as GR). Previous studies have shown that GR-mutant zebrafish exhibit behavioural abnormalities that are indicative of an affective disorder, suggesting that GR plays a role in brain function. We compared the brain methylomes and brain transcriptomes of adult wild-type and GR-mutant zebrafish, and identified 249 differentially methylated regions (DMRs) that are regulated by GR. These include a cluster of CpG sites within the first intron of fkbp5, the gene encoding the glucocorticoid-inducible heat shock protein co-chaperone Fkbp5. RNA-sequencing analysis revealed that genes associated with chaperone-mediated protein folding, the regulation of circadian rhythm and the regulation of metabolism are particularly sensitive to loss of GR function. In addition, we identified subsets of genes exhibiting GR-regulated transcription that are known to regulate behaviour, and are linked to unipolar depression and anxiety. Taken together, our results identify key biological processes and novel molecular mechanisms through which the GR is likely to mediate responses to stress in the adult zebrafish brain, and they provide further support for the zebrafish GR mutant as a model for the study of affective disorders.

Modulation of Recovery from Neonatal Hyperoxic Lung Injury by Sex as a Biological Variable

Recovery from lung injury during the neonatal period requires the orchestration of many biological pathways. The modulation of such pathways can drive the developing lung towards proper repair or persistent maldevelopment that can lead to a disease phenotype. Sex as a biological variable can regulate these pathways differently in the male and female lung exposed to neonatal hyperoxia. In this study, we assessed the contribution of cellular diversity in the male and female neonatal lung following injury. Our objective was to investigate sex and cell-type specific transcriptional changes that drive repair or persistent injury in the neonatal lung and delineate the alterations in the immune-endothelial cell communication networks using single cell RNA sequencing (sc-RNAseq) in a murine model of hyperoxic injury. We generated transcriptional profiles of >55,000 cells isolated from the lungs of postnatal day 1 (PND 1) and postnatal day 21 (PND 21) neonatal male and female C57BL/6 mice exposed to 95% FiO 2 between PND 1-5 (saccular stage of lung development). We show the presence of sex-based differences in the transcriptional states of lung endothelial and immune cells at PND 1 and PND 21. Furthermore, we demonstrate that biological sex significantly influences the response to injury, with a greater number of differentially expressed genes showing sex-specific patterns than those shared between male and female lungs. Pseudotime trajectory analysis highlighted genes needed for lung development that were altered by hyperoxia. Finally, we show intercellular communication between endothelial and immune cells at saccular and alveolar stages of lung development with sex-based biases in the crosstalk and identify novel ligand-receptor pairs. Our findings provide valuable insights into the cell diversity, transcriptional state, developmental trajectory, and cell-cell communication underlying neonatal lung injury, with implications for understanding lung development and possible therapeutic interventions while highlighting the crucial role of sex as a biological variable.

Methyl-CpG binding protein 2 expression is associated with symptom severity in patients with PTSD in a sex-dependent manner

Traumatic events may lead to post-traumatic stress disorder (PTSD), with higher prevalence in women. Adverse childhood experiences (ACE) increase PTSD risk in adulthood. Epigenetic mechanisms play important roles in PTSD pathogenesis and a mutation in the methyl-CpG binding protein 2 (MECP2) in mice provide susceptibility to PTSD-like alterations, with sex-dependent biological signatures. The present study examined whether the increased risk of PTSD associated with ACE exposure is accompanied by reduced MECP2 blood levels in humans, with an influence of sex. MECP2 mRNA levels were analyzed in the blood of 132 subjects (58 women). Participants were interviewed to assess PTSD symptomatology, and asked to retrospectively report ACE. Among trauma-exposed women, MECP2 downregulation was associated with the intensification of PTSD symptoms linked to ACE exposure. MECP2 expression emerges as a potential contributor to post-trauma pathophysiology fostering novel studies on the molecular mechanisms underlying its potential sex-dependent role in PTSD onset and progression.

Low levels of Methyl-CpG binding protein 2 are accompanied by an increased vulnerability to the negative outcomes of stress exposure during childhood in healthy women

Numerous mental illnesses arise following stressful events in vulnerable individuals, with females being generally more affected than males. Adverse childhood experiences are known to increase the risk of developing psychopathologies and DNA methylation was demonstrated to drive the long-lasting effects of early life stress and promote stress susceptibility. Methyl-CpG binding protein 2 (MECP2), an X-linked reader of the DNA methylome, is altered in many mental disorders of stress origin, suggesting MECP2 as a marker of stress susceptibility; previous works also suggest a link between MECP2 and early stress experiences. The present work explored whether a reduced expression of MECP2 is paralleled by an increased vulnerability to the negative outcomes of stress exposure during childhood. To this aim, blood MECP2 mRNA levels were analyzed in 63 people without history of mental disorders and traits pertaining to depressive and anxiety symptom clusters were assessed as proxies of the vulnerability to develop stress-related disorders; stress exposure during childhood was also evaluated. Using structural equation modeling, we demonstrate that reduced MECP2 expression is accompanied by symptoms of anxiety/depression in association with exposure to stress in early life, selectively in healthy women. These results suggest a gender-specific involvement of MECP2 in the maladaptive outcomes of childhood adversities, and shed new light on the complex biology underlying gender bias in stress susceptibility.

Utility of 7,8-dihydroxyflavone in preventing astrocytic and synaptic deficits in the hippocampus elicited by PTSD

Astrocytic functions and brain-derived neurotrophic factor (BDNF)-tyrosine kinase receptor B (TrkB) signaling pathways are impaired in stress-related neuropsychiatric diseases. Previous studies have reported neuroprotective effects of 7,8-dihydroxyflavone (7,8-DHF), a TrkB activator. Here, we investigated the molecular mechanisms underlying pathogenesis of post-traumatic stress disorder (PTSD) using a modified single-prolonged stress (SPS&S) model and the potential beneficial effects of 7,8-DHF. SPS&S reduced the hippocampal expression of glial fibrillary acidic protein (GFAP), a marker of astrocytes, and induced morphological changes in astrocytes. From the perspective of synaptic function, the SPS&S model displayed reduced expression of BDNF, p-TrkB, postsynaptic density protein 95 (PSD95), AMPA receptor subunit GluR1 (GluA1), NMDA receptor subunit N2A/N2B ratio, calpain-1, phosphorylated protein kinase B (Akt) and phosphorylated mammalian target of rapamycin (mTOR) and conversely, higher phosphatase and tension homolog (PTEN) expression in the hippocampus. Acute or continuous intraperitoneal administration of 7,8-DHF (5 mg/kg) after SPS&S procedures prevented SPS&S-induced fear memory generalization and anxiety-like behaviors as well as abnormalities of hippocampal oscillations. Most importantly, 7,8-DHF attenuated SPS&S-induced abnormal BDNF-TrkB signaling and calpain-1-dependent cascade of synaptic deficits. Furthermore, treatment with a TrkB inhibitor completely blocked while an mTOR inhibitor partially blocked the effects of 7,8-DHF on behavioral changes of SPS&S model mice. Our collective findings suggest that 7,8-DHF effectively alleviates PTSD-like symptoms, including fear generalization and anxiety-like behavior, potentially by preventing astrocytic and synaptic deficits in the hippocampus through targeting of TrkB.

Amygdala DCX and blood Cdk14 are implicated as cross-species indicators of individual differences in fear, extinction, and resilience to trauma exposure

Doublecortin (DCX) has long been implicated in, and employed as a marker for, neurogenesis, yet little is known about its function in non-neurogenic brain regions, including the amygdala. This study sought first to explore, in rodents, whether fear learning and extinction modulate amygdala DCX expression and, second, to assess the utility of peripheral DCX correlates as predictive biomarkers of trauma response in rodents and humans. Pavlovian conditioning was found to alter DCX protein levels in mice 24 h later, resulting in higher DCX expression associated with enhanced learning in paradigms examining both the acquisition and extinction of fear (p < 0.001). This, in turn, is associated with differences in freezing on subsequent fear expression tests, and the same relationship between DCX and fear extinction was replicated in rats (p < 0.001), with higher amygdala DCX levels associated with more rapid extinction of fear. RNAseq of amygdala and blood from mice identified 388 amygdala genes that correlated with DCX (q < 0.001) and which gene ontology analyses revealed were significantly over-represented for neurodevelopmental processes. In blood, DCX-correlated genes included the Wnt signaling molecule Cdk14 which was found to predict freezing during both fear acquisition (p < 0.05) and brief extinction protocols (p < 0.001). High Cdk14 measured in blood immediately after testing was also associated with less freezing during fear expression testing (p < 0.01). Finally, in humans, Cdk14 expression in blood taken shortly after trauma was found to predict resilience in males for up to a year post-trauma (p < 0.0001). These data implicate amygdala DCX in fear learning and suggest that Cdk14 may serve as a predictive biomarker of trauma response.

Title: "Labels Matter: Is it stress or is it Trauma?"

In neuroscience, the term 'Stress' has a negative connotation because of its potential to trigger or exacerbate psychopathologies. Yet in the face of exposure to stress, the more common reaction to stress is resilience, indicating that resilience is the rule and stress-related pathology the exception. This is critical because neural mechanisms associated with stress-related psychopathology are expected to differ significantly from those associated with resilience.Research labels and terminology affect research directions, conclusions drawn from the results, and the way we think about a topic, while choice of labels is often influenced by biases and hidden assumptions. It is therefore important to adopt a terminology that differentiates between stress conditions, leading to different outcomes.Here, we propose to conceptually associate the term 'stress'/'stressful experience' with 'stress resilience', while restricting the use of the term 'trauma' only in reference to exposures that lead to pathology. We acknowledge that there are as yet no ideal ways for addressing the murkiness of the border between stressful and traumatic experiences. Yet ignoring these differences hampers our ability to elucidate the mechanisms of trauma-related pathologies on the one hand, and of stress resilience on the other. Accordingly, we discuss how to translate such conceptual terminology into research practice.

Sexual Dimorphism in Glucocorticoid Stress Response

Chronic stress is encountered in our everyday life and is thought to contribute to a number of diseases. Many of these stress-related disorders display a sex bias. Because glucocorticoid hormones are the main biological mediator of chronic stress, researchers have been interested in understanding the sexual dimorphism in glucocorticoid stress response to better explain the sex bias in stress-related diseases. Although not yet demonstrated for glucocorticoid regulation, sex chromosomes do influence sex-specific biology as soon as conception. Then a transient rise in testosterone start to shape the male brain during the prenatal period differently to the female brain. These organizational effects are completed just before puberty. The cerebral regions implicated in glucocorticoid regulation at rest and after stress are thereby impacted in a sex-specific manner. After puberty, the high levels of all gonadal hormones will interact with glucocorticoid hormones in specific crosstalk through their respective nuclear receptors. In addition, stress occurring early in life, in particular during the prenatal period and in adolescence will prime in the long-term glucocorticoid stress response through epigenetic mechanisms, again in a sex-specific manner. Altogether, various molecular mechanisms explain sex-specific glucocorticoid stress responses that do not exclude important gender effects in humans.

Knockdown of the astrocytic glucocorticoid receptor in the central nucleus of the amygdala diminishes conditioned fear expression and anxiety

The amygdala is a key structure involved in both physiological and behavioural effects of fearful and stressful stimuli. The central stress response is controlled by the activity of the hypothalamic-pituitary-adrenal (HPA) axis via glucocorticoid hormones, acting mainly through glucocorticoid receptors (GR), widely expressed among different brain regions, including the central nucleus of the amygdala (CeA). Although to date, neuronal GR was postulated to be involved in the mediating stress effects, increasing evidence points to the vital role of glial GR. Here, we aimed to evaluate the role of astrocytic GR in CeA in various aspects of the stress response. We used a lentiviral vector to disrupt an astrocytic GR in the CeA of Aldh1l1-Cre transgenic mice. Astrocytic GR knockdown mice (GR KD) exhibited an attenuated expression of fear-related memory in the fear conditioning paradigm. Interestingly, the consolidation of non-stressful memory in the novel object recognition test remained unchanged. Moreover, GR KD group presented reduced anxiety, measured in the open field test. However, knockdown of astrocytic GR in the CeA did not affect an acute response to stress in the tail suspension test. Taken together, obtained results suggest that astrocytic GR in the CeA promotes aversive memory consolidation and some aspects of anxiety behaviour.

The Pathways between Cortisol-Related Regulation Genes and PTSD Psychotherapy

Post-traumatic stress disorder (PTSD) only develops after exposure to a traumatic event in some individuals. PTSD can be chronic and debilitating, and is associated with co-morbidities such as depression, substance use, and cardiometabolic disorders. One of the most important pathophysiological mechanisms underlying the development of PTSD and its subsequent maintenance is a dysfunctional hypothalamic-pituitary-adrenal (HPA) axis. The corticotrophin-releasing hormone, cortisol, glucocorticoid receptor (GR), and their respective genes are some of the mediators of PTSD's pathophysiology. Several treatments are available, including medication and psychotherapies, although their success rate is limited. Some pharmacological therapies based on the HPA axis are currently being tested in clinical trials and changes in HPA axis biomarkers have been found to occur in response not only to pharmacological treatments, but also to psychotherapy-including the epigenetic modification of the GR gene. Psychotherapies are considered to be the first line treatments for PTSD in some guidelines, even though they are effective for some, but not for all patients with PTSD. This review aims to address how knowledge of the HPA axis-related genetic makeup can inform and predict the outcomes of psychotherapeutic treatments.

Glucocorticoids as Mediators of Adverse Outcomes of Prenatal Stress

A number of prenatal experiences are associated with adverse outcomes after birth, ranging from cardiovascular problems to psychiatric disease. Prenatal stress is associated with neurodevelopmental alterations that persist after birth and manifest at the behavioral level, for example, increased fearfulness, and at the physiological one, that is, brain structural and functional changes. Understanding the mechanisms that drive these lasting effects may help in preventing long-term negative outcomes of prenatal stress. Elevated glucocorticoid signaling in utero may be one of the key mediators of prenatal stress effects on the offspring. In this review, we summarize how prenatal glucocorticoids may impact the activity of the fetal hypothalamic-pituitary-adrenal (HPA) axis, disrupt neurodevelopmental processes and alter the epigenetic landscape of the fetus. We also discuss the need to take into consideration the interaction of these processes with the offspring's genetic landscape.

Nervous and Endocrine System Dysfunction in Posttraumatic Stress Disorder: An Overview and Consideration of Sex as a Biological Variable

Decades of research into the biological mechanisms of posttraumatic stress disorder (PTSD) suggests that chronic activation of the stress response leads to long-lasting changes in the structure and function of the nervous and endocrine systems. While the prevalence of PTSD is twice as high in females as males, little is known about how sex differences in neuroendocrine systems may contribute to PTSD. In response to the paucity of research on sex-related mechanisms, the National Institutes of Health created a policy that asks researchers to consider sex as a biological variable. This review provides an overview of the current understanding of nervous and endocrine dysfunction in PTSD (e.g., neural circuitry, autonomic arousal, hormonal response), highlighting areas where the influence of sex has been characterized and where further research is needed. We also provide recommendations for using the sex-as-a-biological-variable policy to address specific gaps in PTSD neuroscience research.

Traumatic Brain Injury and Posttraumatic Stress Disorder: Comorbid Consequences of War

Scientific literature is reviewed supporting a “consequence of war syndrome (CWS)” in Operation Enduring Freedom/Operation Iraqi Freedom/Operation New Dawn soldiers. CWS constituents include chronic pain and insomnia, other physical complaints, posttraumatic stress disorder (PTSD), anxiety, depression, and neuropsychological deficits. The foundation of CWS lies with the chronic stressors inherent to deployment and the cascade of biological events mediated and maintained by hypothalamic-pituitary-adrenal (HPA) axis dysregulation. Such dysregulation is modified by the individual’s specific experiences at war, difficulty reintegrating to post-deployment life, and the onset or exacerbation of the chronic and comorbid physical, emotional, and cognitive disorders. The circuit network between the prefrontal cortex (PFC), amygdala, and hippocampus is particularly sensitive to the consequences of war. The review’s specific conclusions are as follows: HPA axis dysregulation contributes to the chronic insomnia and hyperarousal seen in soldiers. There is considerable symptom overlap between PTSD and blast-related head injury, and it is difficult to determine the relative contributions of the two disorders to abnormal imaging studies. In some cases, traumatic brain injury (TBI) may directly precipitate PTSD symptoms. While not intuitive, the relationship between TBI and postconcussion syndrome appears indirect and mediated through PTSD. Blast-related or conventional head injury may have little long-term impact on neuropsychological functioning; contrarily, PTSD particularly accounts for current cognitive deficits. The psychological experience of CWS includes a “war-within” where soldiers continue to battle an internalized enemy. Successful treatment of CWS entails transdisciplinary care that addresses each of the constituent disorders.