Central administration of murine interferon-α induces depressive-like behavioral, brain cytokine and neurochemical alterations in mice: a mini-review and original experiments

Lipopolysaccharide triggers exacerbated microglial activation, excessive cytokine release and behavioural disturbances in mice with truncated Fused-in-Sarcoma Protein (FUS)

CNS inflammation, including microglial activation, in response to peripheral infections are known to contribute to the pathology of both familial and sporadic neurodegenerative disease. The relationship between Fused-in-Sarcoma Protein (FUS)-mediated disease in the transgenic FUS[1-359] animals and the systemic inflammatory response have not been explored. Here, we investigated microglial activation, inflammatory gene expression and the behavioural responses to lipopolysaccharide-induced (LPS; 0.1 mg/kg) systemic inflammation in the FUS[1-359] transgenic mice. The pathology of these mice recapitulates the key features of mutant FUS-associated familial frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS). Here, pre-symptomatic 8-week-old mutant or wild type controls were challenged with LPS or with saline and sucrose intake, novel cage exploration, marble burying and swimming behaviours were analyzed. The level of pro-inflammatory gene expression was also determined, and microglial activation was evaluated. In chronic experiments, to discover whether the LPS challenge would affect the onset of ALS-like paralysis, animals were evaluated for clinical signs from 5 to 7 weeks post-injection. Compared to controls, acutely challenged FUS[1-359]-tg mice exhibited decreased sucrose intake and increased floating behaviours. The FUS[1-359]-tg mice exhibited an increase in immunoreactivity for Iba1-positive cells in the prefrontal cortex and ventral horn of the spinal cord, which was accompanied by increased expression of interleukin-1β, tumour necrosis factor, cyclooxygenase-(COX)-1 and COX-2. However, the single LPS challenge did not alter the time to development of paralysis in the FUS[1-359]-tg mice. Thus, while the acute inflammatory response was enhanced in the FUS mutant animals, it did not have a lasting impact on disease progression.

Mitochondrial dysfunction and type I interferon signaling induce anxiodepressive-like behaviors in mice with neuropathic pain

Clinical evidence indicates that major depression is a common comorbidity of chronic pain, including neuropathic pain; however, the cellular basis for chronic pain-mediated major depression remains unclear. Mitochondrial dysfunction induces neuroinflammation and has been implicated in various neurological diseases, including depression. Nevertheless, the relationship between mitochondrial dysfunction and anxiodepressive-like behaviors in the neuropathic pain state remains unclear. The current study examined whether hippocampal mitochondrial dysfunction and downstream neuroinflammation are involved in anxiodepressive-like behaviors in mice with neuropathic pain, which was induced by partial sciatic nerve ligation (PSNL). At 8 weeks after surgery, there was decreased levels of mitochondrial damage-associated molecular patterns, such as cytochrome c and mitochondrial transcription factor A, and increased level of cytosolic mitochondrial DNA in the contralateral hippocampus, suggesting the development of mitochondrial dysfunction. Type I interferon (IFN) mRNA expression in the hippocampus was also increased at 8 weeks after PSNL surgery. The restoration of mitochondrial function by curcumin blocked the increased cytosolic mitochondrial DNA and type I IFN expression in PSNL mice and improved anxiodepressive-like behaviors. Blockade of type I IFN signaling by anti-IFN alpha/beta receptor 1 antibody also improved anxiodepressive-like behaviors in PSNL mice. Together, these findings suggest that neuropathic pain induces hippocampal mitochondrial dysfunction followed by neuroinflammation, which may contribute to anxiodepressive-behaviors in the neuropathic pain state. Improving mitochondrial dysfunction and inhibiting type I IFN signaling in the hippocampus might be a novel approach to reducing comorbidities associated with neuropathic pain, such as depression and anxiety.

Targeting inflammatory pathways for treatment of the major depressive disorder

Current treatments modalities for major depressive disorder (MDD) mainly target the monoaminergic neurotransmission. However, the therapeutic inadequacy and adverse effects confine the use of these conventional antidepressants to a limited subset of MDD patients. The classical antidepressants are increasingly proving unsatisfactory in tackling the treatment-resistant depression (TRD). Hence, the focus of treatment is shifting to alternative pathogenic pathways involved in depression. Preclinical and clinical evidences accumulated across the last decades have unequivocally affirmed the causative role of immuno-inflammatory pathways in the progression of depression. There is an upsurge in the clinical evaluations of the drugs having anti-inflammatory effects as antidepressants. This review highlights the molecular mechanisms connecting the inflammatory pathways to the MDD and current clinical status of inflammation modulating drugs in the treatment of MDD.

Low-dose-rate ionizing radiation affects innate immunity protein IFITM3 in a mouse model of Alzheimer's disease

PURPOSE

Although the adverse health risks associated with low-dose radiation (LDR) are highly debated, relevant data on neuronal function following chronic LDR exposure are still lacking.

MATERIALS AND METHODS

To confirm the effect of chronic LDR on the progression of Alzheimer's disease (AD), we investigated changes in behavior and neuroinflammation after radiation exposure in wild-type (WT) and 5xFAD (TG) mice, an animal model of AD. WT and TG mice, classified by genotyping, were exposed to low-dose-rate radiation for 112 days, with cumulative doses of 0, 0.1, and 0.3 Gy, then evaluated using the open-field and Y-maze behavioral function tests. Changes in the levels of APP processing- and neuroinflammation-related genes were also investigated.

RESULTS

No apparent change was evident in either non-spatial memory function or locomotor activity, as examined by the Y-maze and open field tests, respectively. Although chronic LDR did not affect the levels of APP processing, gliosis (Iba1 and GFAP), or inflammatory cytokines (IL-1β, IL-6, and TNF-α), the levels of IFN-γ were significantly downregulated in TG mice following LDR exposure. In an additional analysis, we examined the genes related to IFN signaling and found that the levels of interferon induced transmembrane protein 3 (IFITM3) were decreased significantly in TG mice following LDR with 0.1 or 0.3 Gy.

CONCLUSIONS

Therefore, this study revealed the possibility that LDR could affect the progression of AD, which may be associated with decreased IFN-related signaling, especially IFITM3. Our findings suggest that further studies are required regarding the potential role of LDR in the progression of AD.

The Survival of Psychobiotics in Fermented Food and the Gastrointestinal Tract: A Review

In recent years, scientists have been particularly interested in the gut-brain axis, as well as the impact of probiotics on the nervous system. This has led to the creation of the concept of psychobiotics. The present review describes the mechanisms of action of psychobiotics, their use in food products, and their viability and survival during gastrointestinal passage. Fermented foods have a high potential of delivering probiotic strains, including psychobiotic ones. However, it is important that the micro-organisms remain viable in concentrations ranging from about 10⁶ to 10⁹ CFU/mL during processing, storage, and digestion. Reports indicate that a wide variety of dairy and plant-based products can be effective carriers for psychobiotics. Nonetheless, bacterial viability is closely related to the type of food matrix and the micro-organism strain. Studies conducted in laboratory conditions have shown promising results in terms of the therapeutic properties and viability of probiotics. Because human research in this field is still limited, it is necessary to broaden our understanding of the survival of probiotic strains in the human digestive tract, their resistance to gastric and pancreatic enzymes, and their ability to colonize the microbiota.

Concerted type I interferon signaling in microglia and neural cells promotes memory impairment associated with amyloid β plaques

The principal signals that drive memory and cognitive impairment in Alzheimer's disease (AD) remain elusive. Here, we revealed brain-wide cellular reactions to type I interferon (IFN-I), an innate immune cytokine aberrantly elicited by amyloid β plaques, and examined their role in cognition and neuropathology relevant to AD in a murine amyloidosis model. Using a fate-mapping reporter system to track cellular responses to IFN-I, we detected robust, Aβ-pathology-dependent IFN-I activation in microglia and other cell types. Long-term blockade of IFN-I receptor (IFNAR) rescued both memory and synaptic deficits and resulted in reduced microgliosis, inflammation, and neuritic pathology. Microglia-specific Ifnar1 deletion attenuated the loss of post-synaptic terminals by selective engulfment, whereas neural Ifnar1 deletion restored pre-synaptic terminals and decreased plaque accumulation. Overall, IFN-I signaling represents a critical module within the neuroinflammatory network of AD and prompts concerted cellular states that are detrimental to memory and cognition.

Type I interferon response drives neuroinflammation and synapse loss in Alzheimer disease

Type I interferon (IFN) is a key cytokine that curbs viral infection and cell malignancy. Previously, we demonstrated a potent IFN immunogenicity of nucleic acid-containing (NA-containing) amyloid fibrils in the periphery. Here, we investigated whether IFN is associated with β-amyloidosis inside the brain and contributes to neuropathology. An IFN-stimulated gene (ISG) signature was detected in the brains of multiple murine Alzheimer disease (AD) models, a phenomenon also observed in WT mouse brain challenged with generic NA-containing amyloid fibrils. In vitro, microglia innately responded to NA-containing amyloid fibrils. In AD models, activated ISG-expressing microglia exclusively surrounded NA+ amyloid β plaques, which accumulated in an age-dependent manner. Brain administration of rIFN-β resulted in microglial activation and complement C3-dependent synapse elimination in vivo. Conversely, selective IFN receptor blockade effectively diminished the ongoing microgliosis and synapse loss in AD models. Moreover, we detected activated ISG-expressing microglia enveloping NA-containing neuritic plaques in postmortem brains of patients with AD. Gene expression interrogation revealed that IFN pathway was grossly upregulated in clinical AD and significantly correlated with disease severity and complement activation. Therefore, IFN constitutes a pivotal element within the neuroinflammatory network of AD and critically contributes to neuropathogenic processes.

Antiviral Immune Response in Alzheimer's Disease: Connecting the Dots

Alzheimer’s disease (AD) represents an enormous public health challenge currently and with increasing urgency in the coming decades. Our understanding of the etiology and pathogenesis of AD is rather incomplete, which is manifested in stagnated therapeutic developments. Apart from the well-established Amyloid Hypothesis of AD, gaining traction in recent years is the Pathogen Hypothesis, which postulates a causal role of infectious agents in the development of AD. Particularly, infection by viruses, among a diverse range of microorganisms, has been implicated. Recently, we described a prominent antiviral immune response in human AD brains as well as murine amyloid beta models, which has consequential effects on neuropathology. Such findings expectedly allude to the question about viral infections and AD. In this Perspective, we would like to discuss the molecular mechanism underlying the antiviral immune response, highlight how such pathway directly promotes AD pathogenesis, and depict a multilayered connection between antiviral immune response and other agents and factors relevant to AD. By tying together these threads of evidence, we provide a cohesive perspective on the uprising of antiviral immune response in AD.

Decreased motor impulsivity following chronic lithium treatment in male rats is associated with reduced levels of pro-inflammatory cytokines in the orbitofrontal cortex

Lithium's efficacy in reducing both symptom severity in bipolar disorder (BD) and suicide risk across clinical populations may reflect its ability to reduce impulsivity. Changes in immune markers are associated with BD and suicidality yet their exact role in symptom expression remains unknown. Evidence also suggests that lithium may decrease levels of pro-inflammatory cytokines in the periphery and central nervous system, and that such changes are related to its therapeutic efficacy. However, issues of cause and effect are hard to infer from clinical data alone. Here, we investigated the effects of chronic dietary lithium treatment on rats' performance of the 5-Choice Serial Reaction Time Task (5CSRTT), a well-validated operant behavioural task measuring aspects of impulsivity, attention and motivation. Male Long-Evans rats received a diet supplemented with 0.3% LiCl (n = 13), or the equivalent control diet (n = 16), during behavioural testing. Blood and brain tissue samples were assayed for a wide range of cytokines once any changes in impulsivity became significant. After 12 weeks, chronic lithium treatment reduced levels of motor impulsivity, as indexed by premature responses in the 5CSRTT; measures of sustained attention and motivation were unaffected. Plasma levels of IL-1β, IL-10 and RANTES (CCL-5) were reduced in lithium-treated rats at this time point. IL-1β, IL-6 and RANTES were also reduced selectively within the orbitofrontal cortex of lithium-treated rats, whereas cytokine levels in the medial prefrontal cortex and nucleus accumbens were comparable with control subjects. These results are consistent with the hypothesis that lithium may improve impulse control deficits in clinical populations by minimising the effects of pro-inflammatory signalling on neuronal activity, particularly within the orbitofrontal cortex.

The molecular and cellular mechanisms of depression: a focus on reward circuitry

Depression is a complex disorder that takes an enormous toll on individual health. As affected individuals display a wide variation in their clinical symptoms, the precise neural mechanisms underlying the development of depression remain elusive. Although it is impossible to phenocopy every symptom of human depression in rodents, the preclinical field has had great success in modeling some of the core affective and neurovegetative depressive symptoms, including social withdrawal, anhedonia, and weight loss. Adaptations in select cell populations may underlie these individual depressive symptoms and new tools have expanded our ability to monitor and manipulate specific cell types. This review outlines some of the most recent preclinical discoveries on the molecular and neurophysiological mechanisms in reward circuitry that underlie the expression of behavioral constructs relevant to depressive symptoms.

Endocannabinoid modulation of inflammatory hyperalgesia in the IFN-α mouse model of depression

Depression is a well-recognised effect of long-term treatment with interferon-alpha (IFN-α), a widely used treatment for chronic viral hepatitis and malignancy. In addition to the emotional disturbances, high incidences of painful symptoms such as headache and joint pain have also been reported following IFN-α treatment. The endocannabinoid system plays an important role in emotional and nociceptive processing, however it is unknown whether repeated IFN-α administration induces alterations in this system. The present study investigated nociceptive responding in the IFN-α-induced mouse model of depression and associated changes in the endocannabinoid system. Furthermore, the effects of modulating peripheral endocannabinoid tone on inflammatory pain-related behaviour in the IFN-α model was examined. Repeated IFN-α administration (8000 IU/g/day) to male C57/Bl6 mice increased immobility in the forced swim test and reduced sucrose preference, without altering body weight gain or locomotor activity, confirming development of the depressive-like phenotype. There was no effect of repeated IFN-α administration on latency to respond in the hot plate test on day 4 or 7 of treatment, however, formalin-evoked nociceptive behaviour was significantly increased in IFN-α treated mice following 8 days of IFN-α administration. 2-Arachidonoyl glycerol (2-AG) levels in the periaqueductal grey (PAG) and rostroventromedial medulla (RVM), and anandamide (AEA) levels in the RVM, were significantly increased in IFN-α-, but not saline-, treated mice following formalin administration. There was no change in endocannabinoid levels in the prefrontal cortex, spinal cord or paw tissue between saline- or IFNα-treated mice in the presence or absence of formalin. Furthermore, repeated IFN-α and/or formalin administration did not alter mRNA expression of genes encoding the endocannabinoid catabolic enzymes (fatty acid amide hydrolase or monoacylglycerol lipase) or endocannabinoid receptor targets (CB_1, CB₂ or PPARs) in the brain, spinal cord or paw tissue. Intra plantar administration of PF3845 (1 μg/10 μl) or MJN110 (1 μg/10 μl), inhibitors of AEA and 2-AG catabolism respectively, attenuated formalin-evoked hyperalgesia in IFN-α, but not saline-, treated mice. In summary, increasing peripheral endocannabinoid tone attenuates inflammatory hyperalgesia induced following repeated IFN-α administration. These data provide support for the endocannabinoid system in mediating and modulating heightened pain responding associated with IFNα-induced depression.

A longitudinal study assessing depression in hepatitis C: Does gender play a role in the new-onset depression during interferon-alpha treatment?

In this prospective study conducted from October 2013 to June 2015 in Brighton, England, we examined differences between men and women in new-onset major depressive disorder (MDD) during interferon-alpha-based (IFN-α) therapy for hepatitis C virus (HCV). We included 155 HCV-infected patients (47 women), eligible to receive HCV therapy, including direct-acting antivirals. The Semi-Structured Clinical Interview was used to assess MDD. Severity of depressive symptoms was assessed using the Hamilton Depression Rating Scale. Patients were assessed at baseline, during treatment and 6 months after treatment completion. A significant increase in depressive symptoms was observed in the total sample from baseline to week 4, and a significant decrease was observed from end of treatment (week 24) to the sustained virological response (SVR) end point at 6 months posttreatment. Women were more likely to have a MDD at week 24. In both men and women, neurovegetative and mood-cognitive syndromes increased significantly at the early stage of treatment but remitted by the end of HCV therapy. Proportions with SVR were similar among females and males (91.5 percent vs. 87 percent). Under an inflammatory condition, boosted by interferon-based treatments, these results suggest that female gender is not associated with increased vulnerability for developing depression during IFN-α therapy.

cAMP/PKA-CREB-BDNF signaling pathway in hippocampus mediates cyclooxygenase 2-induced learning/memory deficits of rats subjected to chronic unpredictable mild stress

To investigate the mechanism of cyclooxygenase 2 (COX2) in learning and memory impairments in rats subjected to chronic unpredictable mild stress (CUMS), meloxicam was used intragastrically to inhibit the activity of cyclooxygenase 2. Moreover, cyclooxygenase 2 over-expressing or RNA interfere lentivirus was injected intraventricularly to increase or decrease the enzyme's expression, respectively. The body weights and sucrose consumption were used to analyze depressive behaviors, while the Morris water maze and step-down-type passive avoidance tests were carried out to evaluate the learning-memory functions. The levels of inflammatory cytokines were measured to estimate inflammation and the contents of cyclic adenosine monophosphate (cAMP) were used to measure the levels of the second messenger. Changes in cyclooxygenase 2 mRNA levels were analyzed using reverse transcription polymerase chain reaction. Moreover, the expression of cyclooxygenase 2, brain-derived neurotrophic factor (BDNF), prostaglandins receptor 3 (EP3), protein kinase A (PKA), cAMP response element binding protein (CREB), and phosphorylated CREB were estimated using immunohistochemical staining or western blotting. The results showed that CUMS led to significant depressive-like behaviors and learning and memory dysfunctions. Also, the cAMP levels decreased significantly, while levels of inflammatory cytokines and prostaglandins E2 increased significantly. The expressions of PKA, BDNF, phosphorylated CREB/CREB declined and cyclooxygenase 2 was increased. Meloxicam and cyclooxygenase 2 RNA interfere lentivirus reversed the changes caused by CUMS while cyclooxygenase 2-overexpressing lentivirus worsened these abnormalities. The findings also showed that CUMS increased cyclooxygenase 2 expression, which can cause learning and memory impairments, mainly through activating the hippocampal neuronal cAMP/PKA-CREB-BDNF signaling pathways.

Visceral Inflammation and Immune Activation Stress the Brain

Stress refers to a dynamic process in which the homeostasis of an organism is challenged, the outcome depending on the type, severity, and duration of stressors involved, the stress responses triggered, and the stress resilience of the organism. Importantly, the relationship between stress and the immune system is bidirectional, as not only stressors have an impact on immune function, but alterations in immune function themselves can elicit stress responses. Such bidirectional interactions have been prominently identified to occur in the gastrointestinal tract in which there is a close cross-talk between the gut microbiota and the local immune system, governed by the permeability of the intestinal mucosa. External stressors disturb the homeostasis between microbiota and gut, these disturbances being signaled to the brain via multiple communication pathways constituting the gut-brain axis, ultimately eliciting stress responses and perturbations of brain function. In view of these relationships, the present article sets out to highlight some of the interactions between peripheral immune activation, especially in the visceral system, and brain function, behavior, and stress coping. These issues are exemplified by the way through which the intestinal microbiota as well as microbe-associated molecular patterns including lipopolysaccharide communicate with the immune system and brain, and the mechanisms whereby overt inflammation in the GI tract impacts on emotional-affective behavior, pain sensitivity, and stress coping. The interactions between the peripheral immune system and the brain take place along the gut-brain axis, the major communication pathways of which comprise microbial metabolites, gut hormones, immune mediators, and sensory neurons. Through these signaling systems, several transmitter and neuropeptide systems within the brain are altered under conditions of peripheral immune stress, enabling adaptive processes related to stress coping and resilience to take place. These aspects of the impact of immune stress on molecular and behavioral processes in the brain have a bearing on several disturbances of mental health and highlight novel opportunities of therapeutic intervention.

Beneficial effect of aspirin against interferon-α-2b-induced depressive behavior in Sprague Dawley rats

Accumulating data advocates that inflammatory mediators may contribute to depression in experimental models as well as in humans. Nonetheless, whether anti-inflammatory treatments can prevent depression still remains controversial. To substantiate our hypothesis, we used an interferon-α-2b model of depression using Sprague Dawley rats. Interferon-α-2b is a cytokine which activates immune response and also produces depression. The animals were treated for 21 days with aspirin (10 mg/kg, per oral (p.o.)) dexamethasone (1 mg/kg p.o.) and amitriptyline (10 mg/kg p.o.). Amitriptyline was used as reference standard, and given concurrently with aspirin and dexamethasone to examine any synergy. Interferon-α-2b (6000 IU/kg, intraperitoneal (i.p.)) was administered in all the above groups daily, except normal control. Tests performed included sucrose preference test, behavioural tests like forced swim test, elevated plus maze, light dark box and locomotor activity along with biochemical estimations like serum cortisol and brain neurotransmitters. The rats in the group treated with Interferon-α-2b produced depressive behaviour in rats. We found that animals treated with aspirin decreased immobility time in forced swim test, increased sucrose preference, decreased serum cortisol and increased brain serotonin levels signifying antidepressant action. In contrast, there was no effect in groups treated with dexamethasone. Our results suggest that aspirin can serve as a potential antidepressant both individually and as adjuvant agent in the treatment of depression. Inhibition of the cyclo-oxygenase-2 levels and prostaglandins concentration or any other potential physiological and biochemical mechanisms may be involved in antidepressant effect.

Repeated daily administration of increasing doses of lipopolysaccharide provides a model of sustained inflammation-induced depressive-like behaviour in mice that is independent of the NLRP3 inflammasome

Mounting preclinical evidence has implicated the NLRP3 inflammasome in depression-related behaviours elicited by chronic stress or acute lipopolysaccharide (LPS) challenge. However, the relevance of acute LPS as a model of depression has been questioned and behavioural time-courses of its effects can be inconsistent. The aims of this study were (1) to develop a novel protocol for repeated daily LPS administration and (2) to use this model to assess the involvement of NLRP3 inflammasome signalling in sustained inflammation-induced depressive-like behaviour in adult C57BL/6J mice deficient in NLRP3. Acute LPS (0.83mg/kg; i.p.) induced sickness behaviour evident as hypolocomotor activity. However, there was no significant increase in depressive-like behaviour in the forced swim test 24h post-administration. Interestingly, depressive-like behaviours were observed in the female urine sniffing test and in the sucrose preference test at 24h, but not 48h, post-administration of acute LPS. To mimic a period of sustained inflammation, 3-day repeated increasing LPS doses (0.1, 0.42 and 0.83mg/kg; i.p.) was compared to constant LPS doses (0.83mg/kg; i.p.). Sickness behaviour was seen in response to increasing doses, but tolerance developed to repeated constant doses of LPS. Furthermore, 3-day increasing doses of LPS resulted in a significant increase in immobility time in the forced swim test, consistent with depressive-like behaviour. When NLRP3^-/- mice received this 3-day increasing dose regimen of LPS, sickness behaviours were attenuated compared to wild-type mice. The behaviour in the forced swim test was not significantly altered in NLRP3^-/- mice. We propose that this increasing repeated dosing LPS model of inflammation-induced depressive-like behaviour may better model the sustained inflammation observed in depression and may provide a more translationally relevant paradigm to study the inflammatory mechanisms that contribute to depression.

Brain and Peripheral Atypical Inflammatory Mediators Potentiate Neuroinflammation and Neurodegeneration

Neuroinflammatory response is primarily a protective mechanism in the brain. However, excessive and chronic inflammatory responses can lead to deleterious effects involving immune cells, brain cells and signaling molecules. Neuroinflammation induces and accelerates pathogenesis of Parkinson’s disease (PD), Alzheimer’s disease (AD) and Multiple sclerosis (MS). Neuroinflammatory pathways are indicated as novel therapeutic targets for these diseases. Mast cells are immune cells of hematopoietic origin that regulate inflammation and upon activation release many proinflammatory mediators in systemic and central nervous system (CNS) inflammatory conditions. In addition, inflammatory mediators released from activated glial cells induce neurodegeneration in the brain. Systemic inflammation-derived proinflammatory cytokines/chemokines and other factors cause a breach in the blood brain-barrier (BBB) thereby allowing for the entry of immune/inflammatory cells including mast cell progenitors, mast cells and proinflammatory cytokines and chemokines into the brain. These peripheral-derived factors and intrinsically generated cytokines/chemokines, α-synuclein, corticotropin-releasing hormone (CRH), substance P (SP), beta amyloid 1–42 (Aβ1–42) peptide and amyloid precursor proteins can activate glial cells, T-cells and mast cells in the brain can induce additional release of inflammatory and neurotoxic molecules contributing to chronic neuroinflammation and neuronal death. The glia maturation factor (GMF), a proinflammatory protein discovered in our laboratory released from glia, activates mast cells to release inflammatory cytokines and chemokines. Chronic increase in the proinflammatory mediators induces neurotoxic Aβ and plaque formation in AD brains and neurodegeneration in PD brains. Glial cells, mast cells and T-cells can reactivate each other in neuroinflammatory conditions in the brain and augment neuroinflammation. Further, inflammatory mediators from the brain can also enter into the peripheral system through defective BBB, recruit immune cells into the brain, and exacerbate neuroinflammation. We suggest that mast cell-associated inflammatory mediators from systemic inflammation and brain could augment neuroinflammation and neurodegeneration in the brain. This review article addresses the role of some atypical inflammatory mediators that are associated with mast cell inflammation and their activation of glial cells to induce neurodegeneration.

Biological mechanisms of depression following treatment with interferon for chronic hepatitis C: A critical systematic review

BACKGROUND

A significant subset of patients infected by the hepatitis C virus (HCV) develops a major depressive episode (MDE) during Interferon-alpha (IFN-α) based immunotherapy. We performed a systematic review of studies which examined biological mechanisms contributing to the onset of a MDE during IFN-α-based immunotherapy for HCV.

METHODS

Major electronic databases were searched from inception up until 15th February 2016 for peer-reviewed prospective studies that had enrolled HCV infected patients who received IFN-α treatment. A diagnosis of MDE had to be established by means of a standardized diagnostic interview at baseline and endpoint.

RESULTS

Eight unique references met inclusion criteria. A total of 826 participants with HCV (37.3% females, mean age 46.7 years) were included in this systematic review. The overall MDE incidence rate was 34.8%, with follow-up ranging between 4 and 48 weeks. The methodological quality varied across selected studies. It was observed that Interleukin-6, salivary cortisol, arachidonic acid / eicosapentaenoicacid plus docosahexaenoic acid ratio, and genetic polymorphisms may present variations which are linked to a predisposition to INF-α-induced depression.

LIMITATIONS

A meta-analysis could not be performed due to the diverse biological mechanisms investigated and the lack of replicated evidence.

CONCLUSIONS

This systematic review indicates that several potential mechanisms may be implicated in the onset of a MDE following IFN-α-based immunotherapy for chronic HCV. However, replicated evidence is lacking and therefore the mechanisms involved in IFN-α-induced depression in humans remain unclear.

Paeoniflorin ameliorates interferon-alpha-induced neuroinflammation and depressive-like behaviors in mice

Long-term treatment with high-dose Interferon-alpha (IFN-α) has resulted in depression in 30-50% of the patients. Paeoniflorin may ameliorate the IFN-α-induced depression; however, the underlying mechanism is less studied. Here, we investigated the prophylactic antidepressant and anti-neuroinflammatory effects of paeoniflorin on the behaviors and specific emotion-related regions of the brain in mice with IFN-α-induced depression. A series of behavior assessments were conducted to identify the depressive state after subcutaneously IFN-α injections and with or without intragastrically paeoniflorin administration in C57BL/6J mice. Levels of many inflammatory-related cytokines in serum, mPFC, vHi and amygdala were determined by cytokine array analysis. Furthermore, microglia and astrocyte activation in these three regions were evaluated by immunohistochemistry. We found that the mice which were subcutaneously injected IFN-α 15×106 IU/kg for 4 successive weeks to mimic an IFN-α-induced depression model had distinct inflammatory changes in the amygdala. Interestingly, 4-week 20 mg/kg or 40 mg/kg paeoniflorin pretreatments reversed the depressive-like behaviors and the abnormal inflammatory cytokine levels in the serum, mPFC, vHi and amygdala. These cytokines were not limited to the commonly reported IL-6, IL-1β and TNF-α, but also IL-9, IL-10, IL-12, and MCP-1. Besides, the increased density of microglia in IFN-α-treated mice was reversed by paeoniflorin in these three brain areas. Taken together, our data suggest that paeoniflorin can reverse the long-term, high-dose IFN-α-induced depressive-like behaviors that were associated with local distinct neuroinflammation in the mPFC, vHi and particularly the amygdala. Paeoniflorin might have a preventive therapeutic potential in IFN-α-induced depression.

Kynurenine metabolic balance is disrupted in the hippocampus following peripheral lipopolysaccharide challenge

Background

Inflammation increases the risk of developing depression-related symptoms, and tryptophan metabolism is an important mediator of these behavior changes. Peripheral immune activation results in central up-regulation of pro-inflammatory cytokine expression, microglia activation, and the production of neurotoxic kynurenine metabolites. The neuroinflammatory and kynurenine metabolic response to peripheral immune activation has been largely characterized at the whole brain level. It is unknown if this metabolic response exhibits regional specificity even though the unique indoleamine 2,3-dioxygenase (IDO)-dependent depressive-like behaviors are known to be controlled by discrete brain regions. Therefore, regional characterization of neuroinflammation and kynurenine metabolism might allow for better understanding of the potential mechanisms that mediate inflammation-associated behavior changes.

Methods

Following peripheral immune challenge with lipopolysaccharide (LPS), brain tissue from behaviorally relevant regions was analyzed for changes in mRNA of neuroinflammatory targets and kynurenine pathway enzymes. The metabolic balance of the kynurenine pathway was also determined in the peripheral circulation and these brain regions.

Results

Peripheral LPS treatment resulted in region-independent up-regulation of brain expression of pro-inflammatory cytokines and glial cellular markers indicative of a neuroinflammatory response. The expression of kynurenine pathway enzymes was also largely region-independent. While the kynurenine/tryptophan ratio was elevated significantly in both the plasma and in each brain regions evaluated, the balance of kynurenine metabolism was skewed toward production of neurotoxic metabolites in the hippocampus.

Conclusions

The upstream neuroinflammatory processes, such as pro-inflammatory cytokine production, glial cell activation, and kynurenine production, may be similar throughout the brain. However, it appears that the balance of downstream kynurenine metabolism is a tightly regulated brain region-dependent process.

Depression as sickness behavior? A test of the host defense hypothesis in a high pathogen population

Sadness is an emotion universally recognized across cultures, suggesting it plays an important functional role in regulating human behavior. Numerous adaptive explanations of persistent sadness interfering with daily functioning (hereafter "depression") have been proposed, but most do not explain frequent bidirectional associations between depression and greater immune activation. Here we test several predictions of the host defense hypothesis, which posits that depression is part of a broader coordinated evolved response to infection or tissue injury (i.e. "sickness behavior") that promotes energy conservation and reallocation to facilitate immune activation. In a high pathogen population of lean and relatively egalitarian Bolivian forager-horticulturalists, we test whether depression and its symptoms are associated with greater baseline concentration of immune biomarkers reliably associated with depression in Western populations (i.e. tumor necrosis factor alpha [TNF-α], interleukin-1 beta [IL-1β], interleukin-6 [IL-6], and C-reactive protein [CRP]). We also test whether greater pro-inflammatory cytokine responses to ex vivo antigen stimulation are associated with depression and its symptoms, which is expected if depression facilitates immune activation. These predictions are largely supported in a sample of older adult Tsimane (mean±SD age=53.2±11.0, range=34-85, n=649) after adjusting for potential confounders. Emotional, cognitive and somatic symptoms of depression are each associated with greater immune activation, both at baseline and in response to ex vivo stimulation. The association between depression and greater immune activation is therefore not unique to Western populations. While our findings are not predicted by other adaptive hypotheses of depression, they are not incompatible with those hypotheses and future research is necessary to isolate and test competing predictions.

Insights from interferon-α-related depression for the pathogenesis of depression associated with inflammation

Interferon-α (IFN-α) is a pleiotropic cytokine that is administered as a therapeutic in highly prevalent medical conditions such as chronic hepatitis C and B virus infection, melanoma and lymphoma. IFN-α induces, to a clinically relevant degree, concentration, memory, drive and mood disturbances in almost half of all patients. For this reason, IFN-α is increasingly being replaced by more specifically acting drugs. In the past decades, IFN-α has offered a valuable insight into the pathogenesis of major depression, particularly in settings associated with inflammation. IFN-α triggers immune responses, hypothalamo-pituitary-adrenal axis abnormalities and disturbances of brain metabolism resembling those in other depression states. IFN-α stimulates indoleamine-2,3 dioxygenase-1, activating the kynurenine pathway with reduced formation of the neurotransmitters serotonin and dopamine, excessive formation of the NMDA agonist quinolinic acid, and reduced formation of the NMDA antagonist kynurenic acid. In addition, IFN-α disturbs neurotrophic signaling and impedes neurite outgrowth, synaptic plasticity, endogenous neurogenesis and neuronal survival. Consequently, IFN-α-related depression may represent a model for the neurodegenerative changes that are noticed in late-life major depression. Indeed, the observation that brain responses in IFN-α-related depression resemble idiopathic depression is supported by the existence of common genetic signatures, among which of note, a number of neuronal survival and plasticity genes have been identified. In view of the high incidence of depressive symptoms, IFN-α-related depression is an attractive model for studying links between neuronal plasticity, neurodegeneration and depression. We predict that in the latter areas new targets for anti-depressant therapies could be identified, which may deepen our understanding of idiopathic major depression.

Rapid Regulation of Depression-Associated Genes in a New Mouse Model Mimicking Interferon-α-Related Depression in Hepatitis C Virus Infection

Major depression is a serious side effect of interferon-α (IFN-α), which is used in the therapy of hepatitis C virus (HCV) infection. Due to the lack of reproducible animal models, the mechanisms underlying IFN-α-related depression are largely unknown. We herein established a mouse model, in which murine IFN-α (250 IU/day) and polyinosinic/polycytidylic acid (poly(I:C); 1 μg/day), a toll-like receptor-3 (TLR3) agonist that mimics the effect of HCV double-strand RNA, were continuously infused into the lateral ventricle via miniosmotic pumps over up to 14 days. The delivery of IFN-α and poly(I:C), but not of IFN-α or poly(I:C) alone, resulted in a reproducible depression-like state that was characterized by reduced exploration behavior in open-field tests, increased immobility in tail suspension and forced swimming tests, and a moderate loss of body weight. In the hippocampus and prefrontal cortex, the pro-inflammatory genes TNF-α, IL-6, tissue inhibitor of metalloproteinases-1 (Timp-1), CXC motif ligand-1 (Cxcl1), Cxcl10, and CC motif ligand-5 (Ccl5) were synergistically induced by IFN-α and poly(I:C), most pronounced after 14-day exposure. In comparison, the interferon-inducible genes of signal transducer and activator of transcription-1 (Stat1), guanylate binding protein-1 (Gbp1), proteasome subunit-β type-9 (Psmb9), ubiquitin-conjugating enzyme E2L-6 (Ube2l6), receptor transporter protein-4 (Rtp4), and GTP cyclohydrolase-1 (Gch1), which had previously been elevated in the blood of IFN-α-treated patients developing depression, in the brains of suicidal individuals, and in primary neurons exposed to IFN-α and poly(I:C), were induced even earlier, reaching maximum levels mostly after 24 hours. We propose that interferon-inducible genes might be useful markers of imminent depression.

Dorsal raphe neuroinflammation promotes dramatic behavioral stress dysregulation

Impulsivity, risk-taking behavior, and elevated stress responsivity are prominent symptoms of mania, a behavioral state common to schizophrenia and bipolar disorder. Though inflammatory processes activated within the brain are involved in the pathophysiology of both disorders, the specific mechanisms by which neuroinflammation drives manic behavior are not well understood. Serotonin cell bodies originating within the dorsal raphe (DR) play a major role in the regulation of behavioral features characteristic of mania. Therefore, we hypothesized that the link between neuroinflammation and manic behavior may be mediated by actions on serotonergic neurocircuitry. To examine this, we induced local neuroinflammation in the DR by viral delivery of Cre recombinase into interleukin (IL)-1β(XAT) transgenic male and female mice, resulting in overexpressing of the proinflammatory cytokine, IL-1β. For assertion of brain-region specificity of these outcomes, the prefrontal cortex (PFC), as a downstream target of DR serotonergic projections, was also infused. Inflammation within the DR, but not the PFC, resulted in a profound display of manic-like behavior, characterized by increased stress-induced locomotion and responsivity, and reduced risk-aversion/fearfulness. Microarray analysis of the DR revealed a dramatic increase in immune-related genes, and dysregulation of genes important in GABAergic, glutamatergic, and serotonergic neurotransmission. Behavioral and physiological changes were driven by a loss of serotonergic neurons and reduced output as measured by high-performance liquid chromatography, demonstrating inflammation-induced serotonergic hypofunction. Behavioral changes were rescued by acute selective serotonin reuptake inhibitor treatment, supporting the hypothesis that serotonin dysregulation stemming from neuroinflammation in the DR underlies manic-like behaviors.

Mechanisms for interferon-α-induced depression and neural stem cell dysfunction

New neurons generated by the neural stem cells (NSCs) in the adult hippocampus play an important role in emotional regulation and respond to the action of antidepressants. Depression is a common and serious side effect of interferon-α (IFN-α), which limits its use as an antiviral and antitumor drug. However, the mechanism(s) underlying IFN-induced depression are largely unknown. Using a comprehensive battery of behavioral tests, we found that mice subjected to IFN-α treatment exhibited a depression-like phenotype. IFN-α directly suppressed NSC proliferation, resulting in the reduced generation of new neurons. Brain-specific mouse knockout of the IFN-α receptor prevented IFN-α-induced depressive behavioral phenotypes and the inhibition of neurogenesis, suggesting that IFN-α suppresses hippocampal neurogenesis and induces depression via its receptor in the brain. These findings provide insight for understanding the neuropathology underlying IFN-α-induced depression and for developing new strategies for the prevention and treatment of IFN-α-induced depressive effects.

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IFN-α-treated mice show a depression-like phenotype in a behavioral test battery

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IFN-α directly suppresses NSC proliferation in adult hippocampus

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IFN-α suppresses neurogenesis and induced depression via its receptor in the brain

The role of brain-derived neurotrophic factor in comorbid depression: possible linkage with steroid hormones, cytokines, and nutrition

Increasing evidence demonstrates a connection between growth factor function (including brain-derived neurotrophic factor, BDNF), glucocorticoid levels (one of the steroid hormones), and the pathophysiology of depressive disorders. Because both BDNF and glucocorticoids regulate synaptic function in the central nervous system, their functional interaction is of major concern. Interestingly, alterations in levels of estrogen, another steroid hormone, may play a role in depressive-like behavior in postpartum females with fluctuations of BDNF-related molecules in the brain. BDNF and cytokines, which are protein regulators of inflammation, stimulate multiple intracellular signaling cascades involved in neuropsychiatric illness. Pro-inflammatory cytokines may increase vulnerability to depressive symptoms, such as the increased risk observed in patients with cancer and/or autoimmune diseases. In this review, we discuss the possible relationship between inflammation and depression, in addition to the cross-talk among cytokines, BDNF, and steroids. Further, since nutritional status has been shown to affect critical pathways involved in depression through both BDNF function and the monoamine system, we also review current evidence surrounding diet and supplementation (e.g., flavonoids) on BDNF-mediated brain functions.

The neuro-immune axis: prospect for novel treatments for mental disorders

Disturbed bidirectional pathways between the (central) nervous system and immune system have been implicated in various mental disorders, including depressive and neurodevelopmental disorders. In this minireview, the role of the neuro-immune axis and its targetability in relation to major depression and autism spectrum disorder will be discussed. All together, the management of these and possibly other multi-factorial mental disorders needs a new and integrated therapeutic approach. Pharmacologically bioactive molecules as well as medical nutrition targeting the (gut)-immune-brain axis could be such an approach.

N-acetyl-cysteine prevents toxic oxidative effects induced by IFN-α in human neurons

Currently IFN-α is widely used for effective treatment of viral infections and several malignancies. However, IFN-α can cause neuropsychiatric disturbances and mental impairments, including fatigue, insomnia, depression, irritability and cognitive deficits. Molecular and cellular mechanisms leading to such side-effects are still poorly understood. Neurons seem to be an important target in mediating cellular effects induced by exposure to this cytokine, but so far little is known about IFN-α-induced effects on these cells. We have investigated the ability of IFN-α (2-100 ng/ml) to induce damage and toxicity to the human neuroblastoma SH-SY5Y cell line, commonly used for studying such phenomena, and the mechanisms underlying these effects. After 24 h treatment, IFN-α increased mitochondrial activity, whereas cell density was reduced in a dose- and time-dependent manner. This effect did not depend on reduced cell proliferation, but rather the activation of apoptosis, as revealed by an increased Bax:Bcl-2 mRNA ratio after 72-h IFN-α exposure. At this time-point, IFN-α also reduced the expression of the brain-derived neurotrophic factor gene, and induced an increase in reactive oxygen species (ROS). A co-treatment with N-acetyl-cysteine (NAC; 5 mm), a potent antioxidant and mitochondrial modulator, was able to counteract all of these IFN-α-induced effects. These findings demonstrated that IFN-α induces neurotoxicity and apoptosis that is, in part, very likely due to mitochondrial damages and production of ROS. We suggest that NAC, already tested for the treatment of psychiatric disorders, may be useful to prevent IFN-α-induced central side-effects in a safe and effective way.

The brain reward circuitry in mood disorders

Mood disorders are common and debilitating conditions characterized in part by profound deficits in reward-related behavioural domains. A recent literature has identified important structural and functional alterations within the brain's reward circuitry--particularly in the ventral tegmental area-nucleus accumbens pathway--that are associated with symptoms such as anhedonia and aberrant reward-associated perception and memory. This Review synthesizes recent data from human and rodent studies from which emerges a circuit-level framework for understanding reward deficits in depression. We also discuss some of the molecular and cellular underpinnings of this framework, ranging from adaptations in glutamatergic synapses and neurotrophic factors to transcriptional and epigenetic mechanisms.

Malaise, melancholia and madness: the evolutionary legacy of an inflammatory bias

Evolutionary imperatives bred a vigorous and highly orchestrated behavioral and immune response to the microbial world that served to promote species survival and propagation. The resultant legacy is an inflammatory bias which goes largely unchecked in the modern world and is provoked not only by pathogens but also now by people. In this commentary, the authors' contributions to the special issue on Inflammation and Mental Health are described, beginning with the origins of the inflammatory bias, its roots in genetic predispositions to behavioral adaptations and ultimately maladaptations, and its consequences on the developing brain. In addition, the mechanisms by which the immune system engages behavior are described including a central role for the inflammasome which may serve to link psychological stress with inflammatory and behavioral responses. Neurotransmitter systems that mediate effects of the immune system on behavior are also described along with interactions of the inflammatory bias with depression and their convergent impact on the response to stress and medical illness. Finally, translational implications are discussed including data from a clinical trial using a cytokine antagonist in depressed patients, which suggests an interaction of the inflammatory bias with other evolutionary legacies including those related to food consumption and their modern consequences of obesity and the metabolic syndrome. Taken together, the articles offer a sampling of the rich literature that has evolved regarding the role of the immune system in behavioral disorders. The grounding of this relationship in our evolutionary past may serve to inform future research both theoretically and therapeutically.

Evidence for a dysregulated immune system in the etiology of psychiatric disorders

There is extensive bi-directional communication between the brain and the immune system in both health and disease. In recent years, the role of an altered immune system in the etiology of major psychiatric disorders has become more apparent. Studies have demonstrated that some patients with major psychiatric disorders exhibit characteristic signs of immune dysregulation and that this may be a common pathophysiological mechanism that underlies the development and progression of these disorders. Furthermore, many psychiatric disorders are also often accompanied by chronic medical conditions related to immune dysfunction such as autoimmune diseases, diabetes and atherosclerosis. One of the major psychiatric disorders that has been associated with an altered immune system is schizophrenia, with approximately one third of patients with this disorder showing immunological abnormalities such as an altered cytokine profile in serum and cerebrospinal fluid. An altered cytokine profile is also found in a proportion of patients with major depressive disorder and is thought to be potentially related to the pathophysiology of this disorder. Emerging evidence suggests that altered immune parameters may also be implicated in the neurobiological etiology of autism spectrum disorders. Further support for a role of immune dysregulation in the pathophysiology of these psychiatric disorders comes from studies showing the immunomodulating effects of antipsychotics and antidepressants, and the mood altering effects of anti-inflammatory therapies. This review will not attempt to discuss all of the psychiatric disorders that have been associated with an augmented immune system, but will instead focus on several key disorders where dysregulation of this system has been implicated in their pathophysiology including depression, schizophrenia and autism spectrum disorder.

Increased IFNα activity and differential antibody response in patients with a history of Lyme disease and persistent cognitive deficits

Following antibiotic treatment for Lyme disease, some patients report persistent or relapsing symptoms of pain, fatigue, and/or cognitive deficits. Factors other than active infection, including immune abnormalities, have been suggested, but few clues regarding mechanism have emerged. Furthermore, the effect of antibiotic treatment on immune response in affected individuals remains unknown. In this study, a longitudinal analysis of specific immune markers of interest was carried out in patients with a history of Lyme disease and persistent objective memory impairment, prior to and following treatment with either ceftriaxone or placebo. IFNα activity was measured by detection of serum-induced changes in specific target genes, using a functional cell-based assay and quantitative real-time PCR. Level and pattern of antibody reactivity to brain antigens and to Borrelia burgdorferi proteins were analyzed by ELISA and immunoblotting. Sera from the patient cohort induced significantly higher expression of IFIT1 and IFI44 target genes than those from healthy controls, indicating increased IFNα activity. Antibody reactivity to specific brain and borrelial proteins was significantly elevated in affected patients. IFNα activity and antibody profile did not change significantly in response to ceftriaxone. The heightened antibody response implies enhanced immune stimulation, possibly due to prolonged exposure to the organism prior to the initial diagnosis and antibiotic treatment of Lyme disease. The increase in IFNα activity is suggestive of a mechanism contributing to the ongoing neuropsychiatric symptoms.