Soluble interleukin-6 receptor induces motor stereotypies and co-localizes with gp130 in regions linked to cortico-striato-thalamo-cortical circuits

Cytokine expression profiles in children and adolescents with tic disorders

The etiology of tic disorders (TDs) is not precisely known, although several lines of evidence suggest involvement of the immune system in pathogenesis. Here, we aimed to determine the expression levels of pro-inflammatory and anti-inflammatory cytokines in children with TD and compare them with those of healthy controls. Furthermore, we also evaluated their association with clinical variables in the TD group. Within the study period, 88 children with tic disorders and 111 healthy control children were enrolled. Most children with tic disorders were diagnosed with Tourette's disorder (n = 47, 53.4%) or persistent motor tic disorder (n = 39, 44.3%), while the remainder (n = 2, 2.3%) were diagnosed with persistent vocal tic disorder. We found that children with tic disorders had significantly elevated levels of IL-1β, TNF-α, IL-6 and IL-4 expression, while we detected lower expression levels of IL-17 in children with tic disorders. Our findings provide a molecular landscape of cytokine expression in children with TD, which may suggest a proinflammatory state not affected by the presence of comorbidity and symptom severity. Delineating the contribution of alterations in the immune system to the pathogenesis of tic disorders may pave the way for better therapeutic interventions.

Brain uptake pharmacokinetics of albiglutide, dulaglutide, tirzepatide, and DA5-CH in the search for new treatments of Alzheimer's and Parkinson's diseases

BACKGROUND

A number of peptide incretin receptor agonists (IRAs) show promise as therapeutics for Alzheimer's disease (AD) and Parkinson's disease (PD). Transport across the blood-brain barrier (BBB) is one way for IRAs to act directly within the brain. To determine which IRAs are high priority candidates for treating these disorders, we have studied their brain uptake pharmacokinetics.

METHODS

We quantitatively measure the ability of four IRAs to cross the BBB. We injected adult male CD-1 mice intravenously with 125I- or 14C-labeled albiglutide, dulaglutide, DA5-CH, or tirzepatide and used multiple-time regression analyses to measure brain kinetics up to 1 hour. For those IRAs failing to enter the brain 1 h after intravenous injection, we also investigated their ability to enter over a longer time frame (i.e., 6 h).

RESULTS

Albiglutide and dulaglutide had the fastest brain uptake rates within 1 hour. DA5-CH appears to enter the brain rapidly, reaching equilibrium quickly. Tirzepatide does not appear to cross the BBB within 1 h after iv injection but like albumin, did so slowly over 6 h, presumably via the extracellular pathways.

CONCLUSIONS

We find that IRAs can cross the BBB by two separate processes; one that is fast and one that is slow. Three of the four IRAs investigated here have fast rates of transport and should be taken into consideration for testing as AD and PD therapeutics as they would have the ability to act quickly and directly on the brain as a whole.

Comparison of predictive effect of the dietary inflammatory index and empirically derived food-based dietary inflammatory index on the menopause-specific quality of life and its complications

INTRODUCTION

Menopause, defined as the cessation of menstruation for at least 12 months, is one of the important stages of a woman's life cycle. Some hormonal variations occur during the transition to menopause, which affects women's quality of life. Recently, the role of dietary factors in alleviating symptoms has been investigated.

AIM OF THIS STUDY

We tried to investigate the relationship between dietary inflammatory index (DII), food-based dietary inflammatory index (FDII) and quality of life, and menopausal symptoms, comparing their predictive power and suggesting the best cut-off point.

METHODOLOGY

One hundred forty-nine postmenopausal women were included in the cross-sectional study. After collecting data by interview, the desired variables were calculated. Logistic regression and ROC curves were used to investigate the relationship and predictive power of DII and FDII with menopausal symptoms.

FINDINGS

We observed that both DII and FDII were significantly associated with the severity of sexual symptoms. The first tertile of DII (OR = 0.252, P-value = 0.002) and FDII (OR = 0.316, P-value = 0.014) had a significantly lower odds ratio for severe to moderate symptoms compared to the third tertile. Both inflammatory indices had significant predictive power in predicting the probability of having severe to moderate poor quality of life (FDII (p-value = 0.004) > DII (p-value = 0.006)) and sexual symptoms (DII (p-value = 0.002) > FDII (p-value = 0.003)). Also, regarding the physical subtype, only FDII (p-value = 0.002) results were significant.

CONCLUSION

Both dietary inflammatory indices appear to be suitable for predicting quality of life, but FDII had slightly more predictive power. It seems that the quality of life and severity of menopausal symptoms may be improved, particularly with regard to sexual symptoms, by following an anti-inflammatory diet.

Comparison of predictive effect of the dietary inflammatory index and empirically derived food-based dietary inflammatory index on the menopause-specific quality of life and its complications

INTRODUCTION

Menopause, defined as the cessation of menstruation for at least 12 months, is one of the important stages of a woman's life cycle. Some hormonal variations occur during the transition to menopause, which affects women's quality of life. Recently, the role of dietary factors in alleviating symptoms has been investigated.

AIM OF THIS STUDY

We tried to investigate the relationship between dietary inflammatory index (DII), food-based dietary inflammatory index (FDII) and quality of life, and menopausal symptoms, comparing their predictive power and suggesting the best cut-off point.

METHODOLOGY

One hundred forty-nine postmenopausal women were included in the cross-sectional study. After collecting data by interview, the desired variables were calculated. Logistic regression and ROC curves were used to investigate the relationship and predictive power of DII and FDII with menopausal symptoms.

FINDINGS

We observed that both DII and FDII were significantly associated with the severity of sexual symptoms. The first tertile of DII (OR = 0.252, P-value = 0.002) and FDII (OR = 0.316, P-value = 0.014) had a significantly lower odds ratio for severe to moderate symptoms compared to the third tertile. Both inflammatory indices had significant predictive power in predicting the probability of having severe to moderate poor quality of life (FDII (p-value = 0.004) > DII (p-value = 0.006)) and sexual symptoms (DII (p-value = 0.002) > FDII (p-value = 0.003)). Also, regarding the physical subtype, only FDII (p-value = 0.002) results were significant.

CONCLUSION

Both dietary inflammatory indices appear to be suitable for predicting quality of life, but FDII had slightly more predictive power. It seems that the quality of life and severity of menopausal symptoms may be improved, particularly with regard to sexual symptoms, by following an anti-inflammatory diet.

Modulating neuroinflammation in COVID-19 patients with obsessive-compulsive disorder

Exacerbation of symptoms of obsessive-compulsive disorder (OCD) during COVID-19 or new onset of the OCD symptoms resulting from COVID-19 infection is an understudied area of research. It is possible that increased proinflammatory immune status is associated with the onset of obsessive-compulsive symptoms in patients with COVID-19 and that targeted anti-inflammatory treatments for COVID-19 infection can mitigate the new onset of Obsessive-Compulsive (OC) spectrum symptoms. In this review, we cover OCD pathogenesis as related to COVID-19, summarize the impact of cytokines on behavior, and suggest that anti-cytokine treatments can help mitigate post-COVID-19 and new onset of the OC symptoms.

Inflammation, hippocampal volume, and cognition in schizophrenia: results from the Northern Finland Birth Cohort 1966

Increased blood interleukin-6 (IL-6) levels are a replicated abnormality in schizophrenia, and may be associated with smaller hippocampal volumes and greater cognitive impairment. These findings have not been investigated in a population-based birth cohort. The general population Northern Finland Birth Cohort 1966 was followed until age 43. Subjects with schizophrenia were identified through the national Finnish Care Register. Blood IL-6 levels were measured in n = 82 subjects with schizophrenia and n = 5373 controls at age 31. Additionally, 31 patients with schizophrenia and 63 healthy controls underwent brain structural MRI at age 34, and cognitive testing at ages 34 and 43. Patients with schizophrenia had significantly higher median (interquartile range) blood IL-6 levels than controls (5.31, 0.85-17.20, versus 2.42, 0.54-9.36, p = 0.02) after controlling for potential confounding factors. In both schizophrenia and controls, higher blood IL-6 levels were predictors of smaller hippocampal volumes, but not cognitive performance at age 34. We found evidence for increased IL-6 levels in patients with midlife schizophrenia from a population-based birth cohort, and replicated associations between IL-6 levels and hippocampal volumes. Our results complement and extend the previous findings, providing additional evidence that IL-6 may play a role in the pathophysiology of schizophrenia and associated brain alterations.

Analyses of peripheral blood dendritic cells and magnetic resonance spectroscopy support dysfunctional neuro-immune crosstalk in Tourette syndrome

BACKGROUND

Evidence supports that neurodevelopmental diseases, such as Tourette syndrome (TS), may involve dysfunctional neural-immune crosstalk. This could lead to altered brain maturation and differences in immune and stress responses. Dendritic cells (DCs) play a major role in immunity as professional antigen-presenting cells; changes in their frequency have been observed in several autoimmune conditions.

METHODS

In 18 TS patients (15 on stable pharmacological treatment, three unmedicated) and 18 age-matched healthy volunteers (HVs), we explored circulating blood-derived DCs and their relationship with clinical variables and brain metabolites, measured via proton magnetic resonance spectroscopy (1H-MRS). DC subsets, including plasmacytoid and myeloid type 1 and 2 dendritic cells (MDC1, MDC2), were studied with flow cytometry. 1H-MRS was used to measure total choline, glutamate plus glutamine, total creatine (tCr), and total N-acetylaspartate and N-acetylaspartyl-glutamate levels in frontal white matter (FWM) and the putamen.

RESULTS

We did not observe differences in absolute concentrations of DC subsets or brain inflammatory metabolites between patients and HVs. However, TS patients manifesting anxiety showed a significant increase in MDC1s compared to TS patients without anxiety (p = 0.01). We also found a strong negative correlation between MDC1 frequency and tCr in the FWM of patients with TS (p = 0.0015), but not of HVs.

CONCLUSION

Elevated frequencies of the MDC1 subset in TS patients manifesting anxiety may reflect a proinflammatory status, potentially facilitating altered neuro-immune crosstalk. Furthermore, the strong inverse correlation between brain tCr levels and MDC1 subset frequency in TS patients suggests a potential association between proinflammatory status and metabolic changes in sensitive brain regions.

Dysregulation of the gut-brain-skin axis and key overlapping inflammatory and immune mechanisms of psoriasis and depression

The occurrence, progression and recurrence of psoriasis are thought to be related to mood and psychological disorders such as depression. Psoriasis can lead to depression, and depression, in turn, exacerbates psoriasis. No specific mechanism can explain the association between psoriasis and depression. The gut-brain-skin axis has been used to explain correlations among the gut microbiota, emotional states and systemic and skin inflammation, and this axis may be associated with overlapping mechanisms between psoriasis and depression. Therefore, in the context of the gut-brain-skin axis, we systematically summarized and comparatively analysed the inflammatory and immune mechanisms of psoriasis and depression and illustrated the dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis and the gut microbiota. This review provides a theoretical basis and new targets for the treatment of psoriasis and depression.

Immunological Dysfunction in Tourette Syndrome and Related Disorders

Chronic tic disorder and Tourette syndrome are common childhood-onset neurological diseases. However, the pathophysiology underlying these disorders is unclear, and most studies have focused on the disinhibition of the corticostriatal–thalamocortical circuit. An autoimmune dysfunction has been proposed in the pathogenetic mechanism of Tourette syndrome and related neuropsychiatric disorders such as obsessive–compulsive disorder, autism, and attention-deficit/hyperactivity disorder. This is based on evidence from animal model studies and clinical findings. Herein, we review and give an update on the clinical characteristics, clinical evidence, and genetic studies in vitro as well as animal studies regarding immune dysfunction in Tourette syndrome.

Ningdong Granule Upregulates the Striatal DA Transporter and Attenuates Stereotyped Behavior of Tourette Syndrome in Rats

This study aimed to evaluate the possible mechanism of Ningdong granule (NDG) for the treatment of Tourette syndrome (TS). The rats with stereotyped behavior were established by microinjection with TS patients' sera; then, the model rats were divided into NDG and haloperidol (Hal) group, and the nonmedication model rats were regarded as treatment control (TS group). The stereotyped behavior of the rats was recorded, the level of dopamine (DA) in striatum, and the content of homovanillic acid (HVA) in sera were tested, and dopamine transporter (DAT) expression was measured in the study. The experimental results showed that NDG effectively inhibited the stereotyped behavior (P < 0.01), decreased the levels of DA in the striatum (P < 0.05), increased the content of sera HVA (P < 0.01), and enhanced the protein and mRNA expression of DAT in the striatum (P < 0.01). Additionally, the results also revealed Hal could improve the stereotyped behavior as well but had no remarkable influence on DAT expression and DA metabolism. In conclusion, NDG attenuates stereotyped behavior, and its mechanism of action might be associated with the upregulation of DAT expression to regulate DA metabolism in the brain.

Molecular basis of mood and cognitive adverse events elucidated via a combination of pharmacovigilance data mining and functional enrichment analysis

Drug-induced Mood- and Cognition-related adverse events (MCAEs) are often only detected during the clinical trial phases of drug development, or even after marketing, thus posing a major safety concern and a challenge for both pharmaceutical companies and clinicians. To fill some gaps in the understanding and elucidate potential biological mechanisms of action frequently associated with MCAEs, we present a unique workflow linking observational population data with the available knowledge at molecular, cellular, and psychopharmacology levels. It is based on statistical analysis of pharmacovigilance reports and subsequent signaling pathway analyses, followed by evidence-based expert manual curation of the outcomes. Our analysis: (a) ranked pharmaceuticals with high occurrence of such adverse events (AEs), based on disproportionality analysis of the FDA Adverse Event Reporting System (FAERS) database, and (b) identified 120 associated genes and common pathway nodes possibly underlying MCAEs. Nearly two-thirds of the identified genes were related to immune modulation, which supports the critical involvement of immune cells and their responses in the regulation of the central nervous system function. This finding also means that pharmaceuticals with a negligible central nervous system exposure may induce MCAEs through dysregulation of the peripheral immune system. Knowledge gained through this workflow unravels putative hallmark biological targets and mediators of drug-induced mood and cognitive disorders that need to be further assessed and validated in experimental models. Thereafter, they can be used to substantially improve in silico/in vitro/in vivo tools for predicting these adversities at a preclinical stage.

Interactions between inflammation and female sexual desire and arousal function

PURPOSE OF REVIEW

To describe the current state of research on interactions between inflammation and female sexual function.

RECENT FINDINGS

Inflammation may interfere with female sexual desire and arousal via direct (neural) and indirect (endocrine, vascular, social/behavioral) pathways. There are significant sex differences in the effect of inflammation on sexual function, arising from different evolutionary selection pressures on regulation of reproduction. A variety of inflammation-related conditions are associated with risk of female sexual dysfunction, including cardiovascular disease, metabolic syndrome, and chronic pain.

SUMMARY

Clinical implications include the need for routine assessment for sexual dysfunction in patients with inflammation-related conditions, the potential for anti-inflammatory diets to improve sexual desire and arousal function, and consideration of chronic inflammation as moderator of sexual effects of hormonal treatments. Although the evidence points to a role for inflammation in the development and maintenance of female sexual dysfunction, the precise nature of these associations remains unclear.

Novel Treatment Targets Based on Insights in the Etiology of Depression: Role of IL-6 Trans-Signaling and Stress-Induced Elevation of Glutamate and ATP

Inflammation and psychological stress are risk factors for major depression and suicide. Both increase central glutamate levels and activate the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system. Both factors also affect the function of the chloride transporters, Na-K-Cl-cotransporter-1 (NKCC1) and K-Cl-cotransporter-2 (KCC2), and provoke interleukin-6 (IL-6) trans-signaling. This leads to measurable increases in circulating corticosteroids, catecholamines, anxiety, somatic and psychological symptoms, and a decline in cognitive functions. Recognition of the sequence of pathological events allows the prediction of novel targets for therapeutic intervention. Amongst others, these include blockade of the big-K potassium channel, blockade of the P2X4 channel, TYK2-kinase inhibition, noradrenaline α2B-receptor antagonism, nicotinic α7-receptor stimulation, and the Sgp130Fc antibody. A better understanding of downstream processes evoked by inflammation and stress also allows suggestions for tentatively better biomarkers (e.g., SERPINA3N, MARCKS, or ¹³C-tryptophan metabolism).

A Randomized, Double-Blind, Placebo-Controlled Clinical Trial of Tocilizumab, An Interleukin-6 Receptor Antibody, For Residual Symptoms in Schizophrenia

Evidence from preclinical, epidemiological, and human studies indicates that inflammation, and in particular elevated interleukin-6 (IL-6) activity, may be related to clinical manifestations and pathophysiology of schizophrenia. Furthermore, studies in preclinical models suggest that decreasing IL-6 activity may mitigate or reverse some of these deficits. The purpose of this trial was to test whether an IL-6 receptor antibody, tocilizumab, would improve residual positive and negative symptoms and cognitive deficits in schizophrenia. We randomized 36 clinically stable, moderately symptomatic (i.e., Positive and Negative Syndrome Scale (PANSS) >60) individuals with schizophrenia to 3 monthly infusions of 8 mg/kg tocilizumab or placebo (normal saline). The primary outcome was effect at week 12 on the PANSS Total Score. Effects on the MATRICS, other PANSS subscales, Clinical Global Impression, and Global Assessment of Functioning were secondary outcomes. There were no observed treatment effects on any behavioral outcome measure. Baseline C-reactive protein (CRP) or cytokine levels did not predict treatment outcome, nor were there correlations between changes in these inflammatory markers and the measured outcomes. As expected, IL-6 and IL-8 increased, while CRP decreased, in the tocilizumab group compared with the placebo group. This study did not reveal any evidence that an IL-6 receptor antibody affects behavioral outcomes in schizophrenia. One potential explanation is the lack of capacity of this agent to penetrate the central nervous system. Additional trials of medications aimed at targeting cytokine overactivity that act directly on brain function and/or treatment in early-stage psychosis populations are needed.

Neuroimmune Axes of the Blood-Brain Barriers and Blood-Brain Interfaces: Bases for Physiological Regulation, Disease States, and Pharmacological Interventions

Central nervous system (CNS) barriers predominantly mediate the immune-privileged status of the brain, and are also important regulators of neuroimmune communication. It is increasingly appreciated that communication between the brain and immune system contributes to physiologic processes, adaptive responses, and disease states. In this review, we discuss the highly specialized features of brain barriers that regulate neuroimmune communication in health and disease. In section I, we discuss the concept of immune privilege, provide working definitions of brain barriers, and outline the historical work that contributed to the understanding of CNS barrier functions. In section II, we discuss the unique anatomic, cellular, and molecular characteristics of the vascular blood-brain barrier (BBB), blood-cerebrospinal fluid barrier, and tanycytic barriers that confer their functions as neuroimmune interfaces. In section III, we consider BBB-mediated neuroimmune functions and interactions categorized as five neuroimmune axes: disruption, responses to immune stimuli, uptake and transport of immunoactive substances, immune cell trafficking, and secretions of immunoactive substances. In section IV, we discuss neuroimmune functions of CNS barriers in physiologic and disease states, as well as pharmacological interventions for CNS diseases. Throughout this review, we highlight many recent advances that have contributed to the modern understanding of CNS barriers and their interface functions.

Beneficial potential of intravenously administered IL-6 in improving outcome after murine experimental stroke

Interleukin-6 (IL-6) is a pleiotropic cytokine with neuroprotective properties. Still, the therapeutic potential of IL-6 after experimental stroke has not yet been investigated in a clinically relevant way. Here, we investigated the therapeutic use of intravenously administered IL-6 and the soluble IL-6 receptor (sIL-6R) alone or in combination, early after permanent middle cerebral artery occlusion (pMCAo) in mice. IL-6 did not affect the infarct volume in C57BL/6 mice, at neither 24 nor 72h after pMCAo but reduced the infarct volume in IL-6 knockout mice at 24h after pMCAo. Assessment of post-stroke behavior showed an improved grip strength after a single IL-6 injection and also improved rotarod endurance after two injections, in C57BL/6 mice at 24h. An improved grip strength and a better preservation of sensory functions was also observed in IL-6 treated IL-6 knockout mice 24h after pMCAo. Co-administration of IL-6 and sIL-6R increased the infarct volume, the number of infiltrating polymorphonuclear leukocytes and impaired the rotarod endurance of C57BL/6 mice 24h after pMCAo. IL-6 administration to naïve C57BL/6 mice lead after 45min to increased plasma-levels of CXCL1 and IL-10, whereas IL-6 administration to C57BL/6 mice lead to a reduction in the ischemia-induced increase in IL-6 and CXCL1 at both mRNA and protein level in brain, and of IL-6 and CXCL1 in serum. We also investigated the expression of IL-6 and IL-6R after pMCAo and found that cortical neurons upregulated IL-6 mRNA and protein, and upregulated IL-6R after pMCAo. In conclusion, the results show a complex but potentially beneficial effect of intravenously administered IL-6 in experimental stroke.

Addressing the Complexity of Tourette's Syndrome through the Use of Animal Models

Tourette's syndrome (TS) is a neurodevelopmental disorder characterized by fluctuating motor and vocal tics, usually preceded by sensory premonitions, called premonitory urges. Besides tics, the vast majority—up to 90%—of TS patients suffer from psychiatric comorbidities, mainly attention deficit/hyperactivity disorder (ADHD) and obsessive-compulsive disorder (OCD). The etiology of TS remains elusive. Genetics is believed to play an important role, but it is clear that other factors contribute to TS, possibly altering brain functioning and architecture during a sensitive phase of neural development. Clinical brain imaging and genetic studies have contributed to elucidate TS pathophysiology and disease mechanisms; however, TS disease etiology still is poorly understood. Findings from genetic studies led to the development of genetic animal models, but they poorly reflect the pathophysiology of TS. Addressing the role of neurotransmission, brain regions, and brain circuits in TS disease pathomechanisms is another focus area for preclinical TS model development. We are now in an interesting moment in time when numerous innovative animal models are continuously brought to the attention of the public. Due to the diverse and largely unknown etiology of TS, there is no single preclinical model featuring all different aspects of TS symptomatology. TS has been dissected into its key symptomst hat have been investigated separately, in line with the Research Domain Criteria concept. The different rationales used to develop the respective animal models are critically reviewed, to discuss the potential of the contribution of animal models to elucidate TS disease mechanisms.

From blood-brain barrier to blood-brain interface: new opportunities for CNS drug delivery

One of the biggest challenges in the development of therapeutics for central nervous system (CNS) disorders is achieving sufficient blood-brain barrier (BBB) penetration. Research in the past few decades has revealed that the BBB is not only a substantial barrier for drug delivery to the CNS but also a complex, dynamic interface that adapts to the needs of the CNS, responds to physiological changes, and is affected by and can even promote disease. This complexity confounds simple strategies for drug delivery to the CNS, but provides a wealth of opportunities and approaches for drug development. Here, I review some of the most important areas that have recently redefined the BBB and discuss how they can be applied to the development of CNS therapeutics.

Genetic and environmental determinants of population variation in interleukin-6, its soluble receptor and C-reactive protein: insights from identical and fraternal twins

Interleukin-6 and C-reactive protein are commonly assessed biomarkers linked to illness, obesity, and stressful life events. However, relatively little is known about their heritability. By comparing Caucasian twins from the Midlife in the US project (MIDUS), we estimated the heritability of IL-6, its soluble receptor, and CRP. Based on the hypothesis that adiposity might contribute more to IL-6 than to sIL-6r, we fit heritability models quantifying the extent to which each reflected genetic and environmental factors shared with obesity. Genetic influences on IL-6 and its receptor proved to be distinct. Further, the appearance of a heritable basis for IL-6 was mediated largely via shared paths with obesity. Supporting this conclusion, we confirmed that when unrelated adult controls are carefully matched to twin participants on BMI, age, gender and socioeconomic indices, their IL-6 is similar to the corresponding twins. In contrast, the effect of BMI on CRP was split between shared genetics and environmental influences. In conclusion, IL-6 is strongly affected by factors associated with obesity accounting for its lability and responsiveness to diet, life style and contemporaneous events.

Animal models of tic disorders: a translational perspective

Tics are repetitive, sudden movements and/or vocalizations, typically enacted as maladaptive responses to intrusive premonitory urges. The most severe tic disorder, Tourette syndrome (TS), is a childhood-onset condition featuring multiple motor and at least one phonic tic for a duration longer than 1 year. The pharmacological treatment of TS is mainly based on antipsychotic agents; while these drugs are often effective in reducing tic severity and frequency, their therapeutic compliance is limited by serious motor and cognitive side effects. The identification of novel therapeutic targets and development of better treatments for tic disorders is conditional on the development of animal models with high translational validity. In addition, these experimental tools can prove extremely useful to test hypotheses on the etiology and neurobiological bases of TS and related conditions. In recent years, the translational value of these animal models has been enhanced, thanks to a significant re-organization of our conceptual framework of neuropsychiatric disorders, with a greater focus on endophenotypes and quantitative indices, rather than qualitative descriptors. Given the complex and multifactorial nature of TS and other tic disorders, the selection of animal models that can appropriately capture specific symptomatic aspects of these conditions can pose significant theoretical and methodological challenges. In this article, we will review the state of the art on the available animal models of tic disorders, based on genetic mutations, environmental interventions as well as pharmacological manipulations. Furthermore, we will outline emerging lines of translational research showing how some of these experimental preparations have led to significant progress in the identification of novel therapeutic targets for tic disorders.

The role of immune mechanisms in Tourette syndrome

Tourette syndrome (TS) is a childhood-onset tic disorder associated with abnormal development of brain networks involved in the sensory and motor processing. An involvement of immune mechanisms in its pathophysiology has been proposed. Animal models based on active immunization with bacterial or viral mimics, direct injection of cytokines or patients' serum anti-neuronal antibodies, and transgenic approaches replicated stereotyped behaviors observed in human TS. A crucial role of microglia in the neural-immune crosstalk within TS and related disorders has been proposed by animal models and confirmed by recent post mortem studies. With analogy to autism, genetic and early life environmental factors could foster the involvement of immune mechanisms to the abnormal developmental trajectories postulated in TS, as well as lead to systemic immune dysregulation in this condition. Clinical studies demonstrate an association between TS and immune responses to pathogens like group A Streptococcus (GAS), although their role as risk-modifiers is still undefined. Overactivity of immune responses at a systemic level is suggested by clinical studies exploring cytokine and immunoglobulin levels, immune cell subpopulations, and gene expression profiling of peripheral lymphocytes. The involvement of autoantibodies, on the other hand, remains uncertain and warrants more work using live cell-based approaches. Overall, a body of evidence supports the hypothesis that disease mechanisms in TS, like other neurodevelopmental illnesses (e.g. autism), may involve dysfunctional neural-immune cross-talk, ultimately leading to altered maturation of brain pathways controlling different behavioral domains and, possibly, differences in organising immune and stress responses. This article is part of a Special Issue entitled SI: Neuroimmunology in Health And Disease.

Targeting classical IL-6 signalling or IL-6 trans-signalling in depression?

INTRODUCTION

Increased IL-6 and soluble IL-6 receptor (sIL-6R) levels in depressed patients was first shown over 20 years ago. The pro-inflammatory effects of IL-6 are predominantly mediated by IL-6 trans-signalling via the sIL-6R, whereas IL-6R membrane signalling has anti-inflammatory effects.

AREAS COVERED

We review data on IL-6 and sIL-6R in inflammation, depression, animal models of depression and the effects of different classes of antidepressants. The biological context for IL-6 trans-signalling as a pathogenic factor in depression involves its role in the acute phase response, disorders in zinc and the erythron, hypothalamic-pituitary-adrenal axis activation, induction of the tryptophan catabolite pathway, oxidative stress, bacterial translocation, transition towards sensitisation, autoimmune processes and neuroprogression and the multicausal aetiology of depression, considering that psychosocial stressors and comorbid immune-inflammatory diseases are associated with the onset of depression.

EXPERT OPINION

The homeostatic functions of IL-6 imply that ubiquitous IL-6 inhibitors, for example, tocilizumab, may not be the optimal treatment target in depression. A more promising target may be to increase soluble glycoprotein 130 (sgp130) inhibition of IL-6 trans-signalling, while allowing the maintenance of IL-6R membrane signalling. Future research should delineate the effects of treatments with sgp130Fc in combination with antidepressants in various animal models of chronic depression.

Long-term behavioral effects of neonatal blockade of gastrin-releasing peptide receptors in rats: similarities to autism spectrum disorders

Gastrin releasing peptide, the mammalian counterpart of the amphibian peptide, bombesin, has been increasingly implicated in regulating normal brain function as well as in the pathogenesis of psychiatric and/or neurodevelopmental disorders. We have previously shown that the neonatal blockade of the gastrin-releasing peptide receptor (GRPr) in rats produces long-lasting consequences during central nervous system development that are commonly observed in neurodevelopmental disorders such as autism spectrum disorders. The present investigation assessed in further detail, long-term behavioral effects of neonatal GRPr blockade. During postnatal days 1-10, male Wistar rat pups (n=5-10/litter) were injected (subcutaneously) with the GRPr antagonist, RC-3095 (1 mg/kg), or a vehicle (control), twice daily. Following the drug treatment regimen, several behaviors were assessed (starting on postnatal day 14) including specific social behaviors (namely, group huddling characteristics, social interaction, and social approach), restrictive/repetitive and stereotyped behaviors (y-maze, repetitive novel object contact task, observation for stereotypies) and anxiety/fear-related responses (open field, elevated plus maze and contextual fear conditioning). Rats treated neonatally with RC-3095 showed reduced sociability, restrictive interests, motor stereotypies and enhanced learned fear response compared to the controls (vehicle-treated rats). These behavioral abnormalities are consistent with those observed in autism spectrum disorders and provide further evidence that neonatal blockade of GRPr could potentially serve as a useful model to gain a better understanding of the underlying neurodevelopmental disruptions contributing to the expression of autism-relevant phenotypes.

The soluble form of the EIAV receptor encoded by an alternative splicing variant inhibits EIAV infection of target cells

Equine lentivirus receptor 1 (ELR1) has been identified as the sole receptor for equine infectious anemia virus (EIAV) and is a member of the tumor necrosis factor receptor (TNFR) superfamily. In addition to the previously described membrane-associated form of ELR1, two other major alternative splicing variant mRNAs were identified in equine monocyte-derived macrophages (eMDMs). One major spliced species (ELR1-IN) contained an insertion of 153 nt, which resulted in a premature stop codon situated 561 nt upstream of the predicted membrane spanning domain. The other major species (ELR1-DE) has a deletion of 109 nt that causes a shift of the open reading frame and generates a stop codon 312 nt downstream. Because ELR1-DE presumably encodes a peptide of a mere 23 residues, only ELR1-IN was further analyzed. The expression of a soluble form of ELR1 (sELR1) by ELR1-IN was confirmed by Western blot and immunofluorescence analyses. Similar to ELR1, the transcription level of ELR1-IN varied among individual horses and at different time points in the same individuals. The ratio of ELR1-IN mRNA species to ELR1 mRNA was approximately 1∶2.5. Pre-incubation of the recombinant sELR1 with EIAV significantly inhibited EIAV infection in equine macrophages, the primary in vivo target cell of the virus. Fetal equine dermal (FED) cells are susceptible to EIAV in vitro, and the replication of EIAV in FED cells transiently transfected with ELR1-IN was markedly reduced when compared with replication in cells transfected with the empty vector. Finally, the expression levels of both forms of the EIAV receptor were significantly regulated by infection with this virus. Taken together, our data indicate that sELR1 acts as a secreted cellular factor that inhibits EIAV infection in host cells.

Brain pericytes increase the lipopolysaccharide-enhanced transcytosis of HIV-1 free virus across the in vitro blood-brain barrier: evidence for cytokine-mediated pericyte-endothelial cell crosstalk

Background

Human immunodeficiency virus-1 (HIV-1) enters the brain by crossing the blood–brain barrier (BBB) as both free virus and within infected immune cells. Previous work showed that activation of the innate immune system with lipopolysaccharide (LPS) enhances free virus transport both in vivo and across monolayer monocultures of brain microvascular endothelial cells (BMECs) in vitro.

Methods

Here, we used monocultures and co-cultures of brain pericytes and brain endothelial cells to examine the crosstalk between these cell types in mediating the LPS-enhanced permeation of radioactively-labeled HIV-1 (I-HIV) across BMEC monolayers.

Results

We found that brain pericytes when co-cultured with BMEC monolayers magnified the LPS-enhanced transport of I-HIV without altering transendothelial electrical resistance, indicating that pericytes affected the transcytotic component of HIV-1 permeation. As LPS crosses the BBB poorly if at all, and since pericytes are on the abluminal side of the BBB, we postulated that luminal LPS acts indirectly on pericytes through abluminal secretions from BMECs. Consistent with this, we found that the pattern of secretion of cytokines by pericytes directly exposed to LPS was different than when the pericytes were exposed to the abluminal fluid from LPS-treated BMEC monolayers.

Conclusion

These results are evidence for a cellular crosstalk in which LPS acts at the luminal surface of the brain endothelial cell, inducing abluminal secretions that stimulate pericytes to release substances that enhance the permeability of the BMEC monolayer to HIV.

Immune-mediated animal models of Tourette syndrome

An autoimmune diathesis has been proposed in Tourette syndrome (TS) and related neuropsychiatric disorders such as obsessive-compulsive disorder, attention-deficit/hyperactivity disorder, autism and anorexia nervosa. Environmental triggers including infection and xenobiotics are hypothesized to lead to the production of brain-directed autoantibodies in a subset of genetically susceptible individuals. Although much work has focused on Group A Streptococcus (GAS), the role of this common childhood infection remains controversial. Animal model studies based on immune and autoantibody findings in TS have demonstrated immunoglobulin (Ig) deposits and stereotypic movements and related behavioral disturbances reminiscent of TS following exposure to GAS, other activators of host anti-microbial responses, soluble immune mediators and anti-GAS or anti-neuronal antibodies. Demonstration of the ability to recreate these abnormalities through passive transfer of serum IgG from GAS-immunized mice into naïve mice and abrogation of this activity through depletion of IgG has provided compelling evidence in support of the autoimmune hypothesis. Immunologically-based animal models of TS are a potent tool for dissecting the pathogenesis of this serious neuropsychiatric syndrome.