The chemokine CXCL1 and its receptor CXCR2 contribute to chronic stress-induced depression in mice

Chronic stress induces depression-like behavior in rats through affecting brain mitochondrial function and inflammation

Chronic stress is involved in pathophysiology of depression, and causes some neurochemical alterations in brain. Both mitochondrial dysfunction and neuroinflammation are implicated in mediating the depression-like behavior. The objectives of present study were, at first, to confirm that chronic unpredictable mild stress (CUMS) induces depression-like behavior and alters mitochondrial function and inflammatory responses within the brain, and then to explore the role of mitochondria in the development of this depression-like behavior. It has been found that CUMS exposure induced depression-like behavior, mitochondrial dysfunction, increased IL-1, IL-6, IFN-γ and TNF-α levels in hippocampus and PFC. Moreover, the level of ATP, the key index of mitochondrial function, was inversely correlated with the levels of proinflammatory cytokine. Intracerebroventricular (ICV) injection of the mitochondrial targeted antioxidant MnTBAP significantly alleviated depression-like behavior in CUMS group. These findings suggested that CUMS results in depression-like behavior, mitochondrial dysfunction as well as neuroinflammation, and mitochondria dysfunction contributes to depression-like behavior caused by CUMS.

Dynamic human gut microbiome and immune shifts during an immersive psychosocial intervention program

BACKGROUND

Although depression is a leading cause of disability worldwide, the pathophysiological mechanisms underlying this disorder-particularly those involving the gut microbiome-are poorly understood.

METHOD

To investigate, we conducted a community-based observational study to explore complex associations between changes in the gut microbiome, cytokine levels, and depression symptoms in 52 participants (Mage = 49.56, SD = 13.31) receiving an immersive psychosocial intervention. A total of 142 multi-omics samples were collected from participants before, during, and three months after the nine-day inquiry-based stress reduction program.

RESULTS

Results revealed that depression was associated with both an increased presence of putatively pathogenic bacteria and reduced microbial beta-diversity. Following the intervention, we observed reductions in neuroinflammatory cytokines and improvements in several mental health indicators. Interestingly, participants with a Prevotella-dominant microbiome showed milder symptoms when depressed, along with a more resilient microbiome and more favorable inflammatory cytokine profile, including reduced levels of CXCL-1.

CONCLUSIONS

These findings reveal a potentially protective link between the Prevotella-dominant microbiome and depression, as evidenced by a reduced pro-inflammatory environment and fewer depressive symptoms. These insights, coupled with observed improvements in neuroinflammatory markers and mental health from the intervention, may highlight potential avenues for microbiome-targeted therapies for managing depression.

A Prospective Cohort Study on the Effects of Repeated Acute Stress on Cortisol Awakening Response and Immune Function in Military Medical Students

Background: The cortisol awakening response (CAR) is a pivotal component of the body's stress response, yet its dynamics under repeated acute stress and its interplay with immune biomarkers remain inadequately understood. Methods: This study examined 80 second-year military medical students undergoing a 5-day intensive surgical simulation designed to elicit stress responses. Salivary samples were collected daily upon waking and 30 min thereafter to measure cortisol and a panel of cytokines using bead-based multiplex ELISA. Results: Analysis revealed a significant blunting of the CAR on the third day of training (p = 0.00006), followed by a recovery on the fourth day (p = 0.0005). Concurrently, specific cytokines such as CXCL1 (r = 0.2, p = 0.0005), IL-6 (r = 0.13, p = 0.02), IL-10 (r = 0.14, p = 0.02), and VEGF-A (r = 0.17, p = 0.003) displayed patterns correlating with the CAR, with increased strength of associations observed when assessing cytokine levels against the CAR of the preceding day (CXCL1 r = 0.41, p = 0.0002. IL-6 r = 0.38, p = 0.0006. IL-10 r = 0.3, p = 0.008. VEGF-A r = 0.41, p = 0.0002). Conclusions: These results suggest a temporal relationship between stress-induced cortisol dynamics and immune regulation. The CAR pattern demonstrated in this study may represent induction of and recovery from psychological burnout. Moreover, the observed cytokine associations provide insight into the mechanisms by which stress can influence immune function. The results may have broader implications for managing stress in high-performance environments, such as military and medical professions, and for identifying individuals at risk of stress-related immune suppression.

Keratinocyte-Derived Cytokine in the Hippocampus Disrupts Extinction of Conditioned Fear Memory in Tumor-Bearing Mice

While patients with cancer show a higher prevalence of psychiatric disorders than the general population, the mechanism underlying this interaction remains unclear. The present study examined whether tumor-bearing (TB) mice show psychological changes using the conditioned fear paradigm and the role of cytokines in these changes. TB mice were established by transplantation with mouse osteosarcoma AXT cells. These TB mice were then found to exhibit disruption in extinction of conditioned fear memory. Eighteen cytokines in serum were increased in TB mice, among which i.c.v. injection of interleukin (IL)-1β and IL-6 strengthened fear memory in normal mice. Contents of IL-17 and keratinocyte-derived cytokine (KC) in the amygdala and KC in the hippocampus were increased in TB mice. KC mRNA in both the amygdala and hippocampus was also increased in TB mice, and i.c.v. injection of KC dose-dependently strengthened fear memory in normal mice. In addition, injection of IL-1β, but not IL-6, increased KC mRNA in the amygdala and hippocampus. In TB mice KC mRNA was increased in both astrocytes and microglia of the amygdala and hippocampus. The microglia inhibitor minocycline, but not the astrocyte inhibitor fluorocitrate, alleviated disruption in extinction of conditioned fear memory in TB mice. Microinjection of KC into the hippocampus, but not into the amygdala, increased fear memory in normal mice. These findings indicate that TB mice show an increase in serum cytokines, including IL-1β, that increases KC production in microglia of the hippocampus, which then disrupts extinction of fear memory.

Dynamic Human Gut Microbiome and Immune Shifts During an Immersive Psychosocial Therapeutic Program

Background

Depression is a leading cause of disability worldwide yet its underlying factors, particularly microbial associations, are poorly understood.

Methods

We examined the longitudinal interplay between the microbiome and immune system in the context of depression during an immersive psychosocial intervention. 142 multi-omics samples were collected from 52 well-characterized participants before, during, and three months after a nine-day inquiry-based stress reduction program.

Results

We found that depression was associated with both an increased presence of putatively pathogenic bacteria and reduced microbial beta-diversity. Following the intervention, we observed reductions in neuroinflammatory cytokines and improvements in several mental health indicators. Interestingly, participants with a Prevotella-dominant microbiome showed milder symptoms when depressed, along with a more resilient microbiome and more favorable inflammatory cytokine profile, including reduced levels of CXCL-1.

Conclusions

Our findings reveal a protective link between the Prevotella-dominant microbiome and depression, associated with a less inflammatory environment and moderated symptoms. These insights, coupled with observed improvements in neuroinflammatory markers and mental health from the intervention, highlight potential avenues for microbiome-targeted therapies in depression management.

CXCR4/CXCL12 axis: "old" pathway as "novel" target for anti-inflammatory drug discovery

Inflammation is the body's defense response to exogenous or endogenous stimuli, involving complex regulatory mechanisms. Discovering anti-inflammatory drugs with both effectiveness and long-term use safety is still the direction of researchers' efforts. The inflammatory pathway was initially identified to be involved in tumor metastasis and HIV infection. However, research in recent years has proved that the CXC chemokine receptor type 4 (CXCR4)/CXC motif chemokine ligand 12 (CXCL12) axis plays a critical role in the upstream of the inflammatory pathway due to its chemotaxis to inflammatory cells. Blocking the chemotaxis of inflammatory cells by CXCL12 at the inflammatory site may block and alleviate the inflammatory response. Therefore, developing CXCR4 antagonists has become a novel strategy for anti-inflammatory therapy. This review aimed to systematically summarize and analyze the mechanisms of action of the CXCR4/CXCL12 axis in more than 20 inflammatory diseases, highlighting its crucial role in inflammation. Additionally, the anti-inflammatory activities of CXCR4 antagonists were discussed. The findings might help generate new perspectives for developing anti-inflammatory drugs targeting the CXCR4/CXCL12 axis.

Protective Effects of Long-Term Escitalopram Administration on Memory and Hippocampal BDNF and BCL-2 Gene Expressions in Rats Exposed to Predictable and Unpredictable Chronic Mild Stress

Stress and escitalopram (an anti-stress medication) can affect brain functions and related gene expression. This study investigated the protective effects of long-term escitalopram administration on memory, as well as on hippocampal BDNF and BCL-2 gene expressions in rats exposed to predictable and unpredictable chronic mild stress (PCMS and UCMS, respectively). Male rats were randomly assigned to different groups: control (Co), sham (Sh), predictable and unpredictable stress (PSt and USt, respectively; 2 h/day for 21 consecutive days), escitalopram (Esc; 10 mg/kg for 21 days), and predictable and unpredictable stress with escitalopram (PSt-Esc and USt-Esc, respectively). The passive avoidance test was used to assess behavioral variables. The expressions of the BDNF and BCL-2 genes were assessed using real-time quantitative PCR. Latency significantly decreased in the PSt and USt groups. Additionally, latency showed significant improvement in the PSt-Esc group compared to the PSt group. The expression of the BDNF gene significantly decreased only in the USt group. BDNF gene expression significantly increased in the PSt-Esc and USt-Esc groups compared to their respective stress-related groups, whereas the expression of the BCL-2 gene did not change significantly in both PSt-Esc and USt-Esc groups. PCMS and UCMS had devastating effects on memory. Escitalopram improved memory only under PCMS conditions. PCMS and UCMS exhibited fundamental differences in hippocampal BDNF and BCL-2 gene expressions. Furthermore, escitalopram increased hippocampal BDNF gene expression in the PCMS and UCMS subjects. Hence, neurogenesis occurred more significantly than anti-apoptosis under both PCMS and UCMS conditions with escitalopram.

Correlation analysis of salivary cytokines and hormones with resiliency

BACKGROUND

Frequent exposure to acute stress increases risk of suicide, posttraumatic stress disorder, and other stress-related disorders. Neuroendocrine and immunologic dysregulation associated with stress may underlie predispositions to psychological disorders and inflammatory disease processes in individuals, such as first-responders and other healthcare professionals, who function in high stress situations. The Hardiness Resilience Gauge (HRG) can be used to psychometrically measure resilience, a psychological modifier of the stress response. Using the HRG alongside salivary biomarker profiling, may help to identify low resilience phenotypes and allow mitigation and early therapeutic interventions. There is a paucity of knowledge regarding biomarkers of resilience. This study aims to evaluate the relationship between factors of resilience with salivary biomarker levels and fluctuations during and following acute stress.

METHODS

Sixty-three first responders underwent a standardized stress-inducing training exercise, providing salivary samples before (prestress), immediately after (post-stress), and 1 hour after the event (recovery). The HRG was administered before (initial) and after (final) the event. Multiplex ELISA panels quantified 42 cytokines and 6 hormones from the samples, which were analyzed for relationships to psychometric factors of resilience measured by the HRG.

RESULTS

Several biomarkers correlated with psychological resilience following the acute stress event. The HRG scores correlated ( p < 0.05) with a select set of biomarkers with moderate-to-strong correlations (|r| > 0.3). These included EGF, GROα, PDGFAA, TGFα, VEGFA, interleukin (IL)1Ra, TNFα, IL18, cortisol, FGF2, IL13, IL15, and IL6. Interestingly, fluctuations of EGF, GROα, and PDGFAA in post-stress compared with recovery were positively correlated with factors of resilience, which were negatively correlated from the pre-stress to post-stress period.

CONCLUSION

This exploratory analysis discovered a small subset of salivary biomarkers that are significantly correlated with acute stress and resilience. Further investigation of their specific roles in acute stress and associations with resiliency phenotypes is warranted.

Chemokine (C-X-C motif) ligand 1 maintains the immune surveillance function of natural killer cells via the PDK2/mTOR signaling pathway

Chemokine (C-X-C motif) ligand 1 (CXCL1) is mainly expressed on neutrophils and macrophages and has neutrophil chemoattractant activity. However, natural killer (NK) cells also express CXCL1. We were curious about the role played by CXCL1 in NK cells. Knocking out CXCL1 in hematopoietic cells does not affect the occurrence of NK cells; however, it does hinder NK cell maturity. CXCL1 deletion enhances the expression of immature markers and decreases the expression of functional markers in NK cells, which may explain why it hinders the maturation of NK cells. Specific knockout of CXCL1 in NK cells (CXCL1flox/flox Ncr1-cre) leads to impaired IFN-γ production and degranulation of NK cells. The lack of CXCL1 may prevent IFN-γ production and degranulation of NK cells by inhibiting the phosphorylation of AKTS473 and S6. Therefore, we have discovered a new role for CXCL1 in regulating NK cell development and immune surveillance, providing a novel theoretical basis for immunotherapy based on NK cells and potential therapeutic targets for the clinical use of NK cells. 1. Knockout of CXCL1 in hematopoietic cells inhibits the maturation of NK cells. 2. Knockout of CXCL1 in NK cells inhibits the clearance of lymphoma by NK cells and reduces IFN-γ production and CD107 expression in NK cells. 3. CXCL1 activates the PKD2/mTOR signaling pathway, and promotes the production of IFN-γ and the expression of CD107a in NK cells.

Central regulation of stress-evoked peripheral immune responses

Stress-linked psychiatric disorders, including anxiety and major depressive disorder, are associated with systemic inflammation. Recent studies have reported stress-induced alterations in haematopoiesis that result in monocytosis, neutrophilia, lymphocytopenia and, consequently, in the upregulation of pro-inflammatory processes in immunologically relevant peripheral tissues. There is now evidence that this peripheral inflammation contributes to the development of psychiatric symptoms as well as to common co-morbidities of psychiatric disorders such as metabolic syndrome and immunosuppression. Here, we review the specific brain and spinal regions, and the neuronal populations within them, that respond to stress and transmit signals to peripheral tissues via the autonomic nervous system or neuroendocrine pathways to influence immunological function. We comprehensively summarize studies that have employed retrograde tracing to define neurocircuits linking the brain to the bone marrow, spleen, gut, adipose tissue and liver. Moreover, we highlight studies that have used chemogenetic or optogenetic manipulation or intracerebroventricular administration of peptide hormones to control somatic immune responses. Collectively, this growing body of literature illustrates potential mechanisms through which stress signals are conveyed from the CNS to immune cells to regulate stress-relevant behaviours and comorbid pathophysiology.

The role of CXCL1/CXCR2 axis in neurological diseases

The C-X-C chemokine ligand (CXCL) 1 and its receptor C-X-C chemokine receptor (CXCR) 2 are widely expressed in the peripheral nervous systems (PNS) and central nervous systems (CNS) and are involved in the development of inflammation and pain after various nerve injuries. Once a nerve is damaged, it affects not only the neuron itself but also lesions elsewhere in its dominant site. After the CXCL1/CXCR2 axis is activated, multiple downstream pathways can be activated, such as c-Raf/MAPK/AP-1, p-PKC-μ/p-ILK/NLRP3, JAK2/STAT3, TAK1/NF-κB, etc. These pathways in turn mediate cellular motility state or cell migration. CXCR2 is expressed on the surface of neutrophils and monocytes/macrophages. These cells can be recruited to the lesion through the CXCL1/CXCR2 axis to participate in the inflammatory response. The expression of CXCR2 in neurons can activate some pathways in neurons through the CXCL1/CXCR2 axis, thereby causing damage to neurons. CXCR2 is also expressed in astrocytes, and when CXCR2 activated, it increases the number of astrocytes but impairs their function. Since inflammation can occur at almost any site of injury, elucidating the mechanism of CXCL1/CXCR2 axis' influence on inflammation may provide a favorable target for clinical treatment. Therefore, this article reviews the research progress of the CXCL1/CXCR2 axis in neurological diseases, aiming to provide a more meaningful theoretical basis for the treatment of neurological diseases.

Microglial Cytokines Mediate Plasticity Induced by 10 Hz Repetitive Magnetic Stimulation

Microglia, the resident immune cells of the CNS, sense the activity of neurons and regulate physiological brain functions. They have been implicated in the pathology of brain diseases associated with alterations in neural excitability and plasticity. However, experimental and therapeutic approaches that modulate microglia function in a brain region-specific manner have not been established. In this study, we tested for the effects of repetitive transcranial magnetic stimulation (rTMS), a clinically used noninvasive brain stimulation technique, on microglia-mediated synaptic plasticity; 10 Hz electromagnetic stimulation triggered a release of plasticity-promoting cytokines from microglia in mouse organotypic brain tissue cultures of both sexes, while no significant changes in microglial morphology or microglia dynamics were observed. Indeed, substitution of tumor necrosis factor α (TNFα) and interleukin 6 (IL6) preserved synaptic plasticity induced by 10 Hz stimulation in the absence of microglia. Consistent with these findings, in vivo depletion of microglia abolished rTMS-induced changes in neurotransmission in the mPFC of anesthetized mice of both sexes. We conclude that rTMS affects neural excitability and plasticity by modulating the release of cytokines from microglia.SIGNIFICANCE STATEMENT Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive brain stimulation technique that induces cortical plasticity. Despite its wide use in neuroscience and clinical practice (e.g., depression treatment), the cellular and molecular mechanisms of rTMS-mediated plasticity remain not well understood. Herein, we report an important role of microglia and plasticity-promoting cytokines in synaptic plasticity induced by 10 Hz rTMS in organotypic slice cultures and anesthetized mice, thereby identifying microglia-mediated synaptic adaptation as a target of rTMS-based interventions.

Depressive-like Behavior Is Accompanied by Prefrontal Cortical Innate Immune Fatigue and Dendritic Spine Losses after HIV-1 Tat and Morphine Exposure

Opioid use disorder (OUD) and HIV are comorbid epidemics that can increase depression. HIV and the viral protein Tat can directly induce neuronal injury within reward and emotionality brain circuitry, including the prefrontal cortex (PFC). Such damage involves both excitotoxic mechanisms and more indirect pathways through neuroinflammation, both of which can be worsened by opioid co-exposure. To assess whether excitotoxicity and/or neuroinflammation might drive depressive behaviors in persons infected with HIV (PWH) and those who use opioids, male mice were exposed to HIV-1 Tat for eight weeks, given escalating doses of morphine during the last two weeks, and assessed for depressive-like behavior. Tat expression decreased sucrose consumption and adaptability, whereas morphine administration increased chow consumption and exacerbated Tat-induced decreases in nesting and burrowing-activities associated with well-being. Across all treatment groups, depressive-like behavior correlated with increased proinflammatory cytokines in the PFC. Nevertheless, supporting the theory that innate immune responses adapt to chronic Tat exposure, most proinflammatory cytokines were unaffected by Tat or morphine. Further, Tat increased PFC levels of the anti-inflammatory cytokine IL-10, which were exacerbated by morphine administration. Tat, but not morphine, decreased dendritic spine density on layer V pyramidal neurons in the anterior cingulate. Together, our findings suggest that HIV-1 Tat and morphine differentially induce depressive-like behaviors associated with increased neuroinflammation, synaptic losses, and immune fatigue within the PFC.

Inflammatory Markers of Geriatric Depression Response to Tai Chi or Health Education Adjunct Interventions

BACKGROUND

Underlying inflammation is associated with an increased risk of depression in older adults. In this study, we examined the role of inflammatory biomarkers in antidepressant response in depressed older adults undergoing adjunct Tai Chi Chih (TCC) or Health education interventions.

METHODS

Older adults aged 60 years and above with a diagnosis of major depression were randomized to 12 weeks of TCC versus Health and Wellness Education (HEW) as an adjunct therapy to their stable antidepressant treatment regimen. A panel of 19 cytokine/chemokines was measured at baseline and 12 weeks. Five factors were derived using factor analysis. General linear models were estimated to examine the change in factor scores and the association of these changes on depression remission rates, controlling for age, sex, and body mass index.

RESULTS

Of the 170 randomized participants (TCC: n = 85 and HEW: n = 85), 55 TCC and 58 HEW completed the 3-month assessment. The groups did not differ at baseline in any measure. At follow-up, neither the changes in cytokine/chemokines scores nor the depression remission rate differed significantly between TCC and HEW. However, remitters and non-remitters differed significantly in changes in a factor composed of growth-regulated oncogene protein-alpha (GRO-alpha), epidermal growth factor (EGF), and soluble CD40 ligand (sCD40L). GRO-alpha and EGF levels (in both groups) were significantly increased in remitters compared to non-remitters.

CONCLUSION

Changes in certain cytokines/chemokines may accompany improvement in depressive symptoms in older adults. Future studies will need to explore the role of these molecules in remission of late-life depression.

Identification of key genes in late-onset major depressive disorder through a co-expression network module

Late-onset major depressive disorder (LOD) increases the risk of disability and suicide in elderly patients. However, the complex pathological mechanism of LOD still remains unclear. We selected 10 LOD patients and 12 healthy control samples from the GSE76826 dataset for statistical analysis. Under the screening criteria, 811 differentially expressed genes (DEGs) were screened. We obtained a total of two most clinically significant modules through the weighted gene co-expression network analysis (WGCNA). Functional analysis of the genes in the most clinically significant modules was performed to explore the potential mechanism of LOD, followed by protein-protein interaction (PPI) analysis and hub gene identification in the core area of the PPI network. Furthermore, we identified immune infiltrating cells using the cell-type identification by estimating relative subsets of RNA transcripts (CIBERSORT) algorithm between healthy subjects and LOD patients with the GSE98793 dataset. Next, six hub genes (CD27, IL7R, CXCL1, CCR7, IGLL5, and CD79A) were obtained by intersecting hub genes with DEGs, followed by verifying the diagnostic accuracy with the receiver operating characteristic curve (ROC). In addition, we constructed the least absolute shrinkage and selection operator (LASSO) regression model for hub gene cross-validation. Finally, we found that CD27 and IGLL5 were good diagnostic indicators of LOD, and CD27 may be the key gene of immune function change in LOD. In conclusion, our research shows that the changes in the immune function may be an important mechanism in the development of LOD, which can provide some guidance for the related research of LOD in the future.

Inflammatory pathophysiological mechanisms implicated in postpartum depression

Postpartum Depression (PPD) is a serious psychiatric disorder of women within the first year after delivery. It grievously damages women's physical and mental health. Inflammatory reaction theory is well-established in depression, and also has been reported associated with PPD. This review summarized the inflammatory pathophysiological mechanisms implicated in PPD, including decreased T cell activation, increased proinflammatory cytokines secretion, active kynurenine pathway, and initiated NLRP3 inflammasome. Clinical and preclinical research are both gathered. Potential therapeutical alternatives targeting the inflammatory mechanisms of PPD were introduced. In addition, this review briefly discussed the differences of inflammatory mechanisms between PPD and depression. The research of inflammation in PPD is limited and seems just embarking, which indicates the direction we can further study. As a variety of risky factors contribute to PPD collectively, therapy for women with PPD should be comprehensive, and clinical heterogeneity should be taken into consideration. As PPD has a predictability, early clinical screening and interventions are also needed. This review aims to help readers better understand the inflammatory pathological mechanisms in PPD, so as to identify biomarkers and potential therapeutic targets in the future.

Sex differences in inflammation in the hippocampus and amygdala across the lifespan in rats: associations with cognitive bias

Background

Cognitive symptoms of major depressive disorder, such as negative cognitive bias, are more prevalent in women than in men. Cognitive bias involves pattern separation which requires hippocampal neurogenesis and is modulated by inflammation in the brain. Previously, we found sex differences in the activation of the amygdala and the hippocampus in response to negative cognitive bias in rats that varied with age. Given the association of cognitive bias to neurogenesis and inflammation, we examined associations between cognitive bias, neurogenesis in the hippocampus, and cytokine and chemokine levels in the ventral hippocampus (HPC) and basolateral amygdala (BLA) of male and female rats across the lifespan.

Results

After cognitive bias testing, males had more IFN-γ, IL-1β, IL-4, IL-5, and IL-10 in the ventral HPC than females in adolescence. In young adulthood, females had more IFN-γ, IL-1β, IL-6, and IL-10 in the BLA than males. Middle-aged rats had more IL-13, TNF-α, and CXCL1 in both regions than younger groups. Adolescent male rats had higher hippocampal neurogenesis than adolescent females after cognitive bias testing and young rats that underwent cognitive bias testing had higher levels of hippocampal neurogenesis than controls. Neurogenesis in the dorsal hippocampus was negatively associated with negative cognitive bias in young adult males.

Conclusions

Overall, the association between negative cognitive bias, hippocampal neurogenesis, and inflammation in the brain differs by age and sex. Hippocampal neurogenesis and inflammation may play greater role in the cognitive bias of young males compared to a greater role of BLA inflammation in adult females. These findings lay the groundwork for the discovery of sex-specific novel therapeutics that target region-specific inflammation in the brain and hippocampal neurogenesis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12979-022-00299-4.

• Adolescent male rats had more hippocampal inflammation than females after cognitive bias testing.

• Adult female rats had more basolateral amygdalar inflammation than males after cognitive bias testing.

• HPC neurogenesis was negatively associated to cognitive bias in young adult male rats.

Aging Promotes Chronic Stress-Induced Depressive-Like Behavior by Activating NLRP1 Inflammasome-Driven Inflammatory Signaling in Mice

NLRP1 inflammasome has been reported to participate in many neurological disorders. Our previous study has demonstrated that NLRP1 inflammasome is implicated in chronic stress-induced depressive-like behaviors in mice. Age has been reported to be related to depression. Here we examine whether NLRP1 inflammasome is involved in the effect of age on depressive disorder. Two chronic stress stimuli, chronic social defeat stress (CSDS) and repeat social defeat stress (RSDS), were used to establish a depression model in mice of different ages. We found that aged mice exhibited worse depressive-like behaviors and locomotor activity compared to young mice. Interestingly, the expression of hippocampal NLRP1 inflammasome complexes and the levels of the inflammatory cytokines were increased in an age-dependent manner. Also, chronic stress-induced increase in the expression of the hippocampal chemokine C-X-C motif ligand 1 (CXCL1), and its cognate receptor, CXC-motif receptor 2 (CXCR2), was more remarkable in aged mice than that in young mice. Moreover, aged mice exhibited lower hippocampal BDNF levels compared to young mice. Hippocampal Nlrp1a knockdown reduced the levels of pro-inflammatory cytokines and the expression of CXCL1/CXCR2, restored BDNF levels, and alleviated chronic stress-induced depressive-like behaviors in aged mice. Our results suggest that NLRP1 inflammasome-CXCL1/CXCR2-BDNF signaling contributes to the effect of age on chronic stress-induced depressive-like behavior in mice.

Identifying Antidepressant Effects of Brain-Derived Neurotrophic Factor and IDO1 in the Mouse Model Based on RNA-Seq Data

Deletion of brain-derived neurotrophic factor (BDNF) and upregulation of indoleamine 2,3-dioxygenase 1 (IDO1) are associated with depression severity in animals. The neurotransmitter hypothesis of depression at the transcriptomic level can be tested using BDNF- and IDO1-knockout mouse models and RNA-seq. In this study, BDNF^+/−, IDO1^−/−, and chronic ultra-mild stress (CUMS)-induced depression mouse models and controls were developed, and the differentially expressed genes were analyzed. Furthermore, the ceRNA package was used to search the lncRNA2Target database for potential lncRNAs. Finally, a protein–protein interaction (PPI) network was constructed using STRINGdb. By comparing the control and CUMS model groups, it was found that pathway enrichment analysis and ceRNA network analysis revealed that most differentially expressed genes (DEGs) were associated with protection of vulnerable neuronal circuits. In addition, we found the enriched pathways were associated with nervous system development and synapse organization when comparing the control and BDNF^+/−model groups. When replicating the neurotransmitter disruption features of clinical patients, such comparisons revealed the considerable differences between CUMS and knockdown BDNF models, and the BDNF^+/−model may be superior to the classic CUMS model. The data obtained in the present study implicated the potential DEGs and their enriched pathway in three mouse models related to depression and the regulation of the ceRNA network-mediated gene in the progression of depression. Together, our findings may be crucial for uncovering the mechanisms underlying the neurotransmitter hypothesis of depression in animals.

Interactions Among Brain-Derived Neurotrophic Factor and Neuroimmune Pathways Are Key Components of the Major Psychiatric Disorders

The purpose of this review is to summarize the current knowledge regarding the reciprocal associations between brain-derived neurotrophic factor (BDNF) and immune-inflammatory pathways and how these links may explain the involvement of this neurotrophin in the immune pathophysiology of mood disorders and schizophrenia. Toward this end, we delineated the protein-protein interaction (PPI) network centered around BDNF and searched PubMed, Scopus, Google Scholar, and Science Direct for papers dealing with the involvement of BDNF in the major psychosis, neurodevelopment, neuronal functions, and immune-inflammatory and related pathways. The PPI network was built based on the significant interactions of BDNF with neurotrophic (NTRK2, NTF4, and NGFR), immune (cytokines, STAT3, TRAF6), and cell-cell junction (CTNNB, CDH1) DEPs (differentially expressed proteins). Enrichment analysis shows that the most significant terms associated with this PPI network are the tyrosine kinase receptor (TRKR) and Src homology region two domain-containing phosphatase-2 (SHP2) pathways, tyrosine kinase receptor signaling pathways, positive regulation of kinase and transferase activity, cytokine signaling, and negative regulation of the immune response. The participation of BDNF in the immune response and its interactions with neuroprotective and cell-cell adhesion DEPs is probably a conserved regulatory process which protects against the many detrimental effects of immune activation and hyperinflammation including neurotoxicity. Lowered BDNF levels in mood disorders and schizophrenia (a) are associated with disruptions in neurotrophic signaling and activated immune-inflammatory pathways leading to neurotoxicity and (b) may interact with the reduced expression of other DEPs (CTNNB1, CDH1, or DISC1) leading to multiple aberrations in synapse and axonal functions.

Differences in Circulating Extracellular Vesicle and Soluble Cytokines in Older Versus Younger Breast Cancer Patients With Distinct Symptom Profiles

Because extracellular vesicle (EV)-associated cytokines, both encapsulated and surface bound, have been associated with symptom severity, and may vary over the lifespan, they may be potential biomarkers to uncover underlying mechanisms of various conditions. This study evaluated the associations of soluble and EV-associated cytokine concentrations with distinct symptom profiles reported by 290 women with breast cancer prior to surgery. Patients were classified into older (≥60 years, n = 93) and younger (< 60 years, n = 197) cohorts within two previously identified distinct symptom severity profiles, that included pain, depressive symptoms, sleep disturbance, and fatigue (i.e., High Fatigue Low Pain and All Low). EVs were extracted using ExoQuick. Cytokine concentrations were determined using Luminex multiplex assay. Mann Whitney U test evaluated the differences in EV and soluble cytokine levels between symptom classes and between and within the older and younger cohorts adjusting for Karnofsky Performance Status (KPS) score, body mass index (BMI), and stage of disease. Partial correlation analyses were run between symptom severity scores and cytokine concentrations. Results of this study suggest that levels of cytokine concentrations differ between EV and soluble fractions. Several EV and soluble pro-inflammatory cytokines had positive associations with depressive symptoms and fatigue within both age cohorts and symptom profiles. In addition, in the older cohort with High Fatigue Low Pain symptom profile, EV GM-CSF concentrations were higher compared to the All Low symptom profile (p < 0.05). Albeit limited by a small sample size, these exploratory analyses provide new information on the association between cytokines and symptom profiles of older and younger cohorts. Of note, unique EV-associated cytokines were found in older patients and in specific symptom classes. These results suggest that EVs may be potential biomarker discovery tools. Understanding the mechanisms that underlie distinct symptom class profiles categorized by age may inform intervention trials and offer precision medicine approaches.

Association between increased inflammatory cytokine expression in the lateral habenular nucleus and depressive-like behavior induced by unpredictable chronic stress in rats

Depression induced by unpredictable chronic stress (UCS) has been widely studied using animal models. However, its underlying pathological mechanisms remain unclear. Increased inflammatory cytokines (ICs) in the central nervous system (CNS) are closely related to depressive disorder. UCS was used as an animal model in this study to investigate how UCS-induced changes in cytokine signaling lead to depression. We found that UCS could increase ICs in the CNS, especially in the habenular nucleus (Hb). UCS resulted in decreased expression of Menin in Hb and increased the activation of the NF-κB signaling pathway. Local administration of tumor necrosis factor-α in the lateral Hb (LHb) could induce depressive-like behavior in rats. The anti-inflammatory drug aspirin and the NF-κB inhibitor pyrrolidine dithiocarbamate could alleviate depressive-like behavior. This phenomenon was not observed for local administration in the dorsal raphe nucleus and paraventricular nucleus. These results indicate that LHb is the main central target for ICs to regulate depressive-like behaviors. We also found that LHb lesions could improve the inflammatory response in the hippocampus, reduce the activation of the NF-κB signaling pathway and the expression of ICs, and increase the expression of brain-derived neurotrophic factor and its receptor tropomyosin receptor kinase B, collectively improving the neuroinflammation caused by UCS. Moreover, LHb lesions improve not only hippocampal neurogenesis damage caused by UCS by activating the PI3K/mTOR signaling pathway but also hippocampal function by reducing the expression of apoptosis-related proteins, including phosphorylated p53, Bax, Bcl2, and cleaved-caspase3. In conclusion, our study sheds light on the pathogenesis of ICs-induced depression. Anti-inflammation in the CNS could be a new strategy in the treatment of depression.

Analysis of Differentially Expressed Genes That Aggravate Metabolic Diseases in Depression

Depression is considered the second leading cause of the global health burden after cancer. It is recognized as the most common physiological disorder. It affects about 350 million people worldwide to a serious degree. The onset of depression, inadequate food intake, abnormal glycemic control and cognitive impairment have strong associations with various metabolic disorders which are mediated through alterations in diet and physical activities. The regulatory key factors among metabolic diseases and depression are poorly understood. To understand the molecular mechanisms of the dysregulation of genes affected in depressive disorder, we employed an analytical, quantitative framework for depression and related metabolic diseases. In this study, we examined datasets containing patients with depression, obesity, diabetes and NASH. After normalizing batch effects to minimize the heterogeneity of all the datasets, we found differentially expressed genes (DEGs) common to all the datasets. We identified significantly associated enrichment pathways, ontology pathways, protein–protein cluster networks and gene–disease associations among the co-expressed genes co-expressed in depression and the metabolic disorders. Our study suggested potentially active signaling pathways and co-expressed gene sets which may play key roles in crosstalk between metabolic diseases and depression.

Activation of the adipocyte CREB/CRTC pathway in obesity

Obesity is a major risk factor for the development of type II diabetes. Increases in adipose tissue mass trigger insulin resistance via the release of pro-inflammatory cytokines from adipocytes and macrophages. CREB and the CRTC coactivators have been found to promote insulin resistance in obesity, although the mechanism is unclear. Here we show that high fat diet feeding activates the CREB/CRTC pathway in adipocytes by decreasing the expression of SIK2, a Ser/Thr kinase that phosphorylates and inhibits CRTCs. SIK2 levels are regulated by the adipogenic factor C/EBPα, whose expression is reduced in obesity. Exposure to PPARγ agonist rescues C/EBPα expression and restores SIK2 levels. CRTC2/3 promote insulin resistance via induction of the chemokines CXCL1/2. Knockout of CRTC2/3 in adipocytes reduces CXCL1/2 expression and improves insulin sensitivity. As administration of CXCL1/2 reverses salutary effects of CRTC2/3 depletion, our results demonstrate the importance of the CREB/CRTC pathway in modulating adipose tissue function.

Blood Serum Cytokines in Patients with Subacute Spinal Cord Injury: A Pilot Study to Search for Biomarkers of Injury Severity

Background. Despite considerable interest in the search for a spinal cord injury (SCI) therapy, there is a critical need to develop a panel of diagnostic biomarkers to determine injury severity. In this regard, there is a requirement for continuing research into the fundamental processes of neuroinflammatory and autoimmune reactions in SCI, identifying changes in the expression of cytokines. Methods. In this pilot study, an extended multiplex analysis of the cytokine profiles in the serum of patients at 2 weeks post-SCI (n = 28) was carried out, together with an additional assessment of neuron-specific enolase (NSE) and vascular endothelial growth factor (VEGF) levels by enzyme-linked immunosorbent assay. A total of 16 uninjured subjects were enrolled as controls. Results. The data obtained showed a large elevation of IFNγ (>52 fold), CCL27 (>13 fold), and CCL26 (>8 fold) 2 weeks after SCI. The levels of cytokines CXCL5, CCL11, CXCL11, IL10, TNFα, and MIF were different between patients with baseline American Spinal Injury Association Impairment Scale (AIS) grades of A or B, whilst IL2 (>2 fold) and MIP-3a (>6 fold) were significantly expressed in the cervical and thoracic regions. There was a trend towards increasing levels of NSE. However, the difference in NSE was lost when the patient set was segregated based on AIS group. Conclusions. Our pilot research demonstrates that serum concentrations of cytokines can be used as an affordable and rapid detection tool to accurately stratify SCI severity in patients.

Role of inflammatory chemokines in hypertension

Hypertension is associated with immune cells activation and their migration into the kidney, vasculature, heart and brain. These inflammatory mechanisms are critical for blood pressure regulation and mediate target organ damage, creating unique novel targets for pharmacological modulation. In response to angiotensin II and other pro-hypertensive stimuli, the expression of several inflammatory chemokines and their receptors is increased in the target organs, mediating homing of immune cells. In this review, we summarize the contribution of key inflammatory chemokines and their receptors to increased accumulation of immune cells in target organs and effects on vascular dysfunction, remodeling, oxidative stress and fibrosis, all of which contribute to blood pressure elevation. In particular, the role of CCL2, CCL5, CXCL8, CXCL9, CXCL10, CXCL11, CXCL16, CXCL1, CX3CL1, XCL1 and their receptors in the context of hypertension is discussed. Recent studies have tested the efficacy of pharmacological or genetic targeting of chemokines and their receptors on the development of hypertension. Promising results indicate that some of these pathways may serve as future therapeutic targets to improve blood pressure control and prevent target organ consequences including kidney failure, heart failure, atherosclerosis or cognitive impairment.

Upregulation of Chemokines in the Paraventricular Nucleus of the Hypothalamus in Rats with Stress-Induced Hypertension

Background

The neuroinflammation of paraventricular nucleus (PVN) of the hypothalamus has been implicated in the development of hypertension. The promoted invasion of peripheral immune cells into PVN may be attributed to the upregulation of chemokines, then exacerbating neuroinflammation. We studied the expressions of chemokines, activation of microglial cells, and inflammatory mediators in PVN of rats with stress-induced hypertension (SIH).

Material/Methods

SIH was induced by electrical foot shock combined with noise for 2 h twice a day, at an interval of 4 h for 14 consecutive days. At the end of the 14th day, fresh PVN tissues were collected to measure the expressions of chemokines using the RayBiotech antibody array.

Results

We are the first to report that the expression of CXCL7 was extremely high in PVN of control rats, and was significantly lower in SIH rats. The expressions of CCL2 and CX3CL1 in PVN of SIH rats significantly exceeded those of control rats. The numbers of CX3CR1 (receptor of CX3CL1)-immunostained cells and oxycocin-42 (OX-42, marker of microglia)-positive cells increased in PVN of the SIH rats. The stress enhanced the protein expressions of proinflammatory cytokines IL-6 and IL-17 and reduced those of anti-inflammatory cytokines TGF-β and IL-10 in PVN.

Conclusions

In PVN of SIH rats, chronic stress induced neuroinflammation characterized by the activated microglia and upregulated proinflammatory cytokines. Expressions of chemokines CXCL7, CX3CL1, and CCL2 were altered. The causal link of chemokines to PVN neuroinflammation and hypertension remain to be determined.

Associations among serum markers of inflammation, life stress and suicide risk in patients with major depressive disorder

BACKGROUND

Patients with major depressive disorder (MDD) are at high risk for suicide. As the worst outcome of MDD and common self-concealment in patients with suicide risk, studies of biomarkers may provide useful tools for suicide prevention and treatment.

METHODS

This study recruited 168 patients with MDD from the Objective Diagnostic Markers and Personalized Intervention in MDD patients (ODMPIM), including 50 patients with suicide risk. Based on previous evidence and hypothesis, 23 targeted serum biomarkers involving immune-inflammation, neurotrophins, hypothalamic-pituitary-adrenal (HPA) axis and metabolism, were measured. We used path analysis and principal components analysis (PCA) to clarify the associations among serum biomarkers, childhood adversities, adulthood life events, severity of depression and suicide risk.

RESULTS

We identified that patients with suicide risk had a higher level of inflammatory markers in serum than patients without suicide risk (P < 0.001), especially chemokine (C-X-C motif) ligand 1 (CXCL-1). After using the Bonferroni correction, there were no differences in biomarkers related to neurotrophins, HPA-axis and metabolism. In addition, a higher proportion of patients with suicide risk had adulthood adversity (assessed by Life Events Scale) (P = 0.003). Intriguingly, path analysis demonstrated that the association between adulthood adversity and suicide risk mainly depended on severity of depression and inflammatory index.

CONCLUSION

This study highlights the possible role of inflammation involved in suicide risk of MDD patients. Inflammatory markers have the potential for early identification and then reducing suicidal behaviors or becoming novel treatment targets in suicide risk management.

NLRP1 inflammasome contributes to chronic stress-induced depressive-like behaviors in mice

BACKGROUND

Major depressive disorder (MDD) is a highly prevalent psychiatric disorder, and inflammation has been considered crucial components of the pathogenesis of depression. NLRP1 inflammasome-driven inflammatory response is believed to participate in many neurological disorders. However, it is unclear whether NLRP1 inflammasome is implicated in the development of depression.

METHODS

Animal models of depression were established by four different chronic stress stimuli including chronic unpredictable mild stress (CUMS), chronic restrain stress (CRS), chronic social defeat stress (CSDS), and repeat social defeat stress (RSDS). Depressive-like behaviors were determined by sucrose preference test (SPT), forced swim test (FST), tail-suspension test (TST), open-field test (OFT), social interaction test (SIT), and light-dark test (LDT). The expression of NLRP1 inflammasome complexes, BDNF, and CXCL1/CXCR2 were tested by western blot and quantitative real-time PCR. The levels of inflammatory cytokines were tested by enzyme-linked immunosorbent assay (ELISA) kits. Nlrp1a knockdown was performed by an adeno-associated virus (AAV) vector containing Nlrp1a-shRNA-eGFP infusion.

RESULTS

Chronic stress stimuli activated hippocampal NLRP1 inflammasome and promoted the release of pro-inflammatory cytokines IL-1β, IL-18, IL-6, and TNF-α in mice. Hippocampal Nlrp1a knockdown prevented NLRP1 inflammasome-driven inflammatory response and ameliorated stress-induced depressive-like behaviors. Also, chronic stress stimuli caused the increase in hippocampal CXCL1/CXCR2 expression and low BDNF levels in mice. Interestingly, Nlrp1a knockdown inhibited the up-regulation of CXCL1/CXCR2 expression and restored BDNF levels in the hippocampus.

CONCLUSIONS

NLRP1 inflammasome-driven inflammatory response contributes to chronic stress induced depressive-like behaviors and the mechanism may be related to CXCL1/CXCR2/BDNF signaling pathway. Thus, NLRP1 inflammasome could become a potential antidepressant target.

Polyinosinic-Polycytidylic Acid Induces CXCL1 Expression in Cultured hCMEC/D3 Human Cerebral Microvascular Endothelial Cells

OBJECTIVE

Brain microvascular endothelial cells are integral components of the blood-brain barrier and play a role in protecting the brain from invading microbes. CXC motif chemokine ligand 1 (CXCL1) induces the chemotaxis of neutrophils, and neutrophils are important in host defense in the brain. However, dysregulated neutrophil infiltration leads to brain diseases. Toll-like receptor 3 (TLR3) is a pattern recognition receptor that recognizes viral double-stranded RNA (dsRNA). The aim of this study was to investigate the effect of an TLR3 agonist on the expression of CXCL1 in brain vascular endothelial cells.

METHODS

hCMEC/D3 human cerebral microvascular endothelial cells were cultured and treated with polyinosinic-polycytidylic acid (poly IC), a potent synthetic dsRNA agonist for TLR3. The production of CXCL1 mRNA and protein was assessed by real-time RT-PCR and ELISA. The expression of CXCL1 was compared with that of CXCL8. The effect of pretreatment of cells with a NF-κB inhibitor (SN50), a p38 mitogen-activated protein kinase (MAPK) inhibitor (SB203580), a c-Jun N-terminal kinase (JNK) inhibitor (SP600125), an interferon (IFN) regulatory factor 3 inhibitor (MRT67307), and an anti-type I IFN-neutralizing antibody mixture was examined. Phosphorylation of p38 was examined using Western blotting.

RESULTS

Treating cultured hCMEC/D3 human cells with poly IC induced the expression of CXCL1 as well as another chemokine CXCL8. Pretreatment of cells with SN50, SB203580, and SP600125 decreased the induction of CXCL1 by poly IC. However, it was not affected by MRT67307 or by an anti-type I IFN-neutralizing antibody mixture. Pretreatment of cells with SN50 decreased the poly IC-induced phosphorylation of p38.

CONCLUSIONS

Poly IC induces the expression of CXCL1 in hCMEC/D3 cells. NF-κB, p38 MAPK, and JNK are involved in this reaction. There is a cross-talk between NF-κB and p38, and NF-κB partially regulates phosphorylation of p38. CXCL1 produced by brain microvascular endothelial cells may contribute to the brain's defense against viral infection and various neurological diseases associated with neutrophil accumulation.