Neutralization of colony-stimulating factor 1 receptor prevents sickness behavior syndrome by reprogramming inflammatory monocytes to produce IL-10

Apoptosis-induced decline in hippocampal microglia mediates the development of depression-like behaviors in adult mice triggered by unpredictable stress during adolescence

Depression triggered by harmful stress during adolescence is a common problem that can affect mental health. To date, the mechanisms underlying this type of depression remain unclear. One mechanism for the promotion of depression by chronic stress in adulthood is the loss of hippocampal microglia. Since deleterious stress in adolescence also activates microglia, we investigated the dynamic changes of microglia in the hippocampus in mice exposed to chronic unpredictable stress (CUS) in adolescence. Our results showed that 12 days of CUS stimulation in adolescence induced typical depression-like behaviors in adult mice, which were accompanied by a significant decrease and dystrophy of microglia in the dentate gyrus of the hippocampus. Further analysis showed that this decrease in microglia was mediated by the initial response of microglia to unpredictable stress in the dentate gyrus of the hippocampus and their subsequent apoptosis. Blocking the initial response of microglia to unpredictable stress by pretreatment with minocycline was able to prevent apoptosis and microglial decline as well as the development of depression-like behaviors in adult mice induced by adolescent CUS. Moreover, administration of lipopolysaccharide (LPS) or macrophage-colony stimulatory factor (M-CSF), two drugs that reversed microglia decline in the dentate gyrus, ameliorated the depression-like behaviors induced by CUS stimulation in adolescence. These findings reveal a novel mechanism for the development of depression-like behaviors in animals triggered by deleterious stress in adolescence and suggest that reversing microglial decline in the hippocampus may be a hopeful strategy for the treatment of depression triggered by deleterious stress in adolescence.

Epigenetic Regulation of Inflammatory Mechanisms and a Psychological Symptom Cluster in Patients Receiving Chemotherapy

BACKGROUND

A psychological symptom cluster is the most common cluster identified in oncology patients. Although inflammatory mechanisms are hypothesized to underlie this cluster, epigenetic contributions are unknown.

OBJECTIVES

This study's purpose was to evaluate associations between the occurrence of a psychological symptom cluster and levels of DNA methylation for inflammatory genes in a heterogeneous sample of patients with cancer receiving chemotherapy.

METHODS

Prior to their second or third cycle of chemotherapy, 1,071 patients reported the occurrence of 38 symptoms using the Memorial Symptom Assessment Scale. A psychological cluster was identified using exploratory factor analysis. Differential methylation analyses were performed in two independent samples using Illumina Infinium 450K and EPIC microarrays. Expression-associated CpG (eCpG) loci in the promoter region of 114 inflammatory genes on the 450K and 112 genes on the EPIC microarray were evaluated for associations with the psychological cluster. Robust rank aggregation was used to identify differentially methylated genes across both samples. Significance was assessed using a false discovery rate of 0.05 under the Benjamini-Hochberg procedure.

RESULTS

Cluster of differentiation 40 ( CD40 ) was differentially methylated across both samples. All six promoter eCpGs for CD40 that were identified across both samples were hypomethylated in the psychological cluster group.

CONCLUSIONS

This study is the first to suggest associations between a psychological symptom cluster and differential DNA methylation of a gene involved in tissue inflammation and cell-mediated immunity. Our findings suggest that increased CD40 expression through hypomethylation of promoter eCpG loci is involved in the occurrence of a psychological symptom cluster in patients receiving chemotherapy. These findings suggest a direction for mechanistic studies.

CD40 Agonist Monoclonal Antibody-Mediated Hepatitis in TNF-Receptor 1 Gene Knockout Mice

Tumor necrosis factor-alpha (TNF-α) plays an important role in liver inflammation. CD40-CD40 ligand (CD40-CD40L) is a key receptor–ligand signaling pair involved in the adaptive immune response and pathogenesis of autoimmune diseases. In mice, CD40 activation leads to sickness behavior syndrome (SBS) comprising weight loss, sleep disruption and depression, which can be blocked by administration of the TNF-inhibitor etanercept. In the present study, we assessed the extent of hepatic inflammation in mice devoid of the TNF-receptor 1 (TNFR1)-mediated signaling pathway. The TNFR1-depleted (TNFR1−/−) adult mice and their wild type littermates were given a single intra-peritoneal injection of CD40 agonist monoclonal antibody (mAb) or rat IgG2a isotope control. As described previously, TNFR1−/− mice were protected from SBS upon CD40 mAb treatment. Cd40, tnf and tnfr1 mRNA and Tnf-α peptide were increased in the liver of CD40 mAb-stimulated wild type mice. Serum alanine aminotransferase was elevated in both CD40-activated wild type and TNFR1−/− mice. TNFR1−/− mice showed much less intra-parenchymal infiltrates, hepatocellular necrosis, and perivascular clusters upon CD40 mAb activation than their wild type littermates. A gene expression microarray detected increased activity of metabolic and detoxification pathways and decreased activity of inflammatory pathways. We conclude that immune activation and development of liver inflammation in CD40L interactions depend on TNFR1-mediated signaling pathways and are counteracted by alterations in metabolic pathways.

Microglia depletion fails to abrogate inflammation-induced sickness in mice and rats

Background

Production of inflammatory mediators by reactive microglial cells in the brain is generally considered the primary mechanism underlying the development of symptoms of sickness in response to systemic inflammation.

Methods

Depletion of microglia was achieved in C57BL/6 mice by chronic oral administration of PLX5622, a specific antagonist of colony stimulating factor-1 receptor, and in rats by a knock-in model in which the diphtheria toxin receptor was expressed under the control of the endogenous fractalkine receptor (CX3CR1) promoter sequence. After successful microglia depletion, mice and rats were injected with a sickness-inducing dose of lipopolysaccharide according to a 2 (depletion vs. control) × 2 (LPS vs. saline) factorial design. Sickness was measured by body weight loss and decreased locomotor activity in rats and mice, and reduced voluntary wheel running in mice.

Results

Chronic administration of PLX5622 in mice and administration of diphtheria toxin to knock-in rats depleted microglia and peripheral tissue macrophages. However, it did not abrogate the inducible expression of proinflammatory cytokines in the brain in response to LPS and even exacerbated it for some of the cytokines. In accordance with these neuroimmune effects, LPS-induced sickness was not abrogated, rather it was exacerbated when measured by running wheel activity in mice.

Conclusions

These findings reveal that the sickness-inducing effects of acute inflammation can develop independently of microglia activation.

Cytokine signatures in chronic fatigue syndrome patients: a Case Control Study and the effect of anakinra treatment

BACKGROUND

Cytokine disturbances have been suggested to be associated with the Chronic Fatigue Syndrome/Myalgic encephalomyelitis (CFS/ME) for decades.

METHODS

Fifty female CFS patients were included in a study on the effect of the interleukin-1-receptor antagonist anakinra or placebo during 4 weeks. EDTA plasma was collected from patients before and directly after treatment. At baseline, plasma samples were collected at the same time from 48 healthy, age-matched female neighborhood controls. A panel of 92 inflammatory markers was determined in parallel in 1 μL samples using a 'proximity extension assay' (PEA) based immunoassay. Since Transforming growth factor beta (TGF-β) and interleukin-1 receptor antagonist (IL-1Ra) were not included in this platform, these cytokines were measured with ELISA.

RESULTS

In CFS/ME patients, the 'normalized protein expression' value of IL-12p40 and CSF-1 was significantly higher (p value 0.0042 and 0.049, respectively). Furthermore, using LASSO regression, a combination of 47 markers yielded a prediction model with a corrected AUC of 0.73. After correction for multiple testing, anakinra had no effect on circulating cytokines. TGF-β did not differ between patients and controls.

CONCLUSIONS

In conclusion, this study demonstrated increased IL-12p40 and CSF-1 concentrations in CFS/ME patients in addition to a set of predictive biomarkers. There was no effect of anakinra on circulating cytokines other than IL-1Ra.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02108210 , Registered April 2014.

Differential effects of stress on microglial cell activation in male and female medial prefrontal cortex

Susceptibility to stress-linked psychological disorders, including post-traumatic stress disorder and depression, differs between men and women. Dysfunction of medial prefrontal cortex (mPFC) has been implicated in many of these disorders. Chronic stress affects mPFC in a sex-dependent manner, differentially remodeling dendritic morphology and disrupting prefrontally mediated behaviors in males and females. Chronic restraint stress induces microglial activation, reflected in altered microglial morphology and immune factor expression, in mPFC in male rats. Unstressed females exhibit increased microglial ramification in several brain regions compared to males, suggesting both heightened basal activation and a potential for sex-dependent effects of stress on microglial activation. Therefore, we assessed microglial density and ramification in the prelimbic region of mPFC, and immune-associated genes in dorsal mPFC in male and female rats following acute or chronic restraint stress. Control rats were left unstressed. On the final day of restraint, brains were collected for either qPCR or visualization of microglia using Iba-1 immunohistochemistry. Microglia in mPFC were classified as ramified, primed, reactive, or amoeboid, and counted stereologically. Expression of microglia-associated genes (MHCII, CD40, IL6, CX3CL1, and CX3CR1) was also assessed using qPCR. Unstressed females showed a greater proportion of primed to ramified microglia relative to males, alongside heightened CX3CL1-CX3CR1 expression. Acute and chronic restraint stress reduced the proportion of primed to ramified microglia and microglial CD40 expression in females, but did not significantly alter microglial activation in males. This sex difference in microglial activation could contribute to the differential effects of stress on mPFC structure and function in males versus females.

CD40-TNF activation in mice induces extended sickness behavior syndrome co-incident with but not dependent on activation of the kynurenine pathway

The similarity between sickness behavior syndrome (SBS) in infection and autoimmune disorders and certain symptoms in major depressive disorder (MDD), and the high co-morbidity of autoimmune disorders and MDD, constitutes some of the major evidence for the immune-inflammation hypothesis of MDD. CD40 ligand-CD40 immune-activation is important in host response to infection and in development of autoimmunity. Mice given a single intra-peritoneal injection of CD40 agonist antibody (CD40AB) develop SBS for 2-3days characterized by weight loss and increased sleep, effects that are dependent on the cytokine, tumor necrosis factor (TNF). Here we report that CD40AB also induces behavioral effects that extend beyond acute SBS and co-occur with but are not mediated by kynurenine pathway activation and recovery. CD40AB led to decreased saccharin drinking (days 1-7) and decreased Pavlovian fear conditioning (days 5-6), and was without effect on physical fatigue (day 5). These behavioral effects co-occurred with increased plasma and brain levels of kynurenine and its metabolites (days 1-7/8). Co-injection of TNF blocker etanercept with CD40AB prevented each of SBS, reduced saccharin drinking, and kynurenine pathway activation in plasma and brain. Repeated oral administration of a selective indoleamine 2,3-dioxygenase (IDO) inhibitor blocked activation of the kynurenine pathway but was without effect on SBS and saccharin drinking. This study provides novel evidence that CD40-TNF activation induces deficits in saccharin drinking and Pavlovian fear learning and activates the kynurenine pathway, and that CD40-TNF activation of the kynurenine pathway is not necessary for induction of the acute or extended SBS effects.