Morphological and behavioral changes induced by transgenic overexpression of interleukin-1ra in the brain

Tryptophan metabolism as a 'reflex' feature of neuroimmune communication: Sensor and effector functions for the indoleamine-2, 3-dioxygenase kynurenine pathway

Although the central nervous system (CNS) and immune system were regarded as independent entities, it is now clear that immune system cells can influence the CNS, and neuroglial activity influences the immune system. Despite the many clinical implications for this 'neuroimmune interface', its detailed operation at the molecular level remains unclear. This narrative review focuses on the metabolism of tryptophan along the kynurenine pathway, since its products have critical actions in both the nervous and immune systems, placing it in a unique position to influence neuroimmune communication. In particular, since the kynurenine pathway is activated by pro-inflammatory mediators, it is proposed that physical and psychological stressors are the stimuli of an organismal protective reflex, with kynurenine metabolites as the effector arm co-ordinating protective neural and immune system responses. After a brief review of the neuroimmune interface, the general perception of tryptophan metabolism along the kynurenine pathway is expanded to emphasize this environmentally driven perspective. The initial enzymes in the kynurenine pathway include indoleamine-2,3-dioxygenase (IDO1), which is induced by tissue damage, inflammatory mediators or microbial products, and tryptophan-2,3-dioxygenase (TDO), which is induced by stress-induced glucocorticoids. In the immune system, kynurenic acid modulates leucocyte differentiation, inflammatory balance and immune tolerance by activating aryl hydrocarbon receptors and modulates pain via the GPR35 protein. In the CNS, quinolinic acid activates N-methyl-D-aspartate (NMDA)-sensitive glutamate receptors, whereas kynurenic acid is an antagonist: the balance between glutamate, quinolinic acid and kynurenic acid is a significant regulator of CNS function and plasticity. The concept of kynurenine and its metabolites as mediators of a reflex coordinated protection against stress helps to understand the variety and breadth of their activity. It should also help to understand the pathological origin of some psychiatric and neurodegenerative diseases involving the immune system and CNS, facilitating the development of new pharmacological strategies for treatment.

Loss of interleukin 1 signaling causes impairment of microglia- mediated synapse elimination and autistic-like behaviour in mice

In the last years, the hypothesis that elevated levels of proinflammatory cytokines contribute to the pathogenesis of neurodevelopmental diseases has gained popularity. IL-1 is one of the main cytokines found to be elevated in Autism spectrum disorder (ASD), a complex neurodevelopmental condition characterized by defects in social communication and cognitive impairments. In this study, we demonstrate that mice lacking IL-1 signaling display autistic-like defects associated with an excessive number of synapses. We also show that microglia lacking IL-1 signaling at early neurodevelopmental stages are unable to properly perform the process of synapse engulfment and display excessive activation of mammalian target of rapamycin (mTOR) signaling. Notably, even the acute inhibition of IL-1R1 by IL-1Ra is sufficient to enhance mTOR signaling and reduce synaptosome phagocytosis in WT microglia. Finally, we demonstrate that rapamycin treatment rescues the defects in IL-1R deficient mice. These data unveil an exclusive role of microglial IL-1 in synapse refinement via mTOR signaling and indicate a novel mechanism possibly involved in neurodevelopmental disorders associated with defects in the IL-1 pathway.

The Role of the Interleukin-1 Family in Complications of Prematurity

Preterm birth is a major contributor to neonatal morbidity and mortality. Complications of prematurity such as bronchopulmonary dysplasia (BPD, affecting the lung), pulmonary hypertension associated with BPD (BPD-PH, heart), white matter injury (WMI, brain), retinopathy of prematurity (ROP, eyes), necrotizing enterocolitis (NEC, gut) and sepsis are among the major causes of long-term morbidity in infants born prematurely. Though the origins are multifactorial, inflammation and in particular the imbalance of pro- and anti-inflammatory mediators is now recognized as a key driver of the pathophysiology underlying these illnesses. Here, we review the involvement of the interleukin (IL)-1 family in perinatal inflammation and its clinical implications, with a focus on the potential of these cytokines as therapeutic targets for the development of safe and effective treatments for early life inflammatory diseases.

An integrated cytokine and kynurenine network as the basis of neuroimmune communication

Two of the molecular families closely associated with mediating communication between the brain and immune system are cytokines and the kynurenine metabolites of tryptophan. Both groups regulate neuron and glial activity in the central nervous system (CNS) and leukocyte function in the immune system, although neither group alone completely explains neuroimmune function, disease occurrence or severity. This essay suggests that the two families perform complementary functions generating an integrated network. The kynurenine pathway determines overall neuronal excitability and plasticity by modulating glutamate receptors and GPR35 activity across the CNS, and regulates general features of immune cell status, surveillance and tolerance which often involves the Aryl Hydrocarbon Receptor (AHR). Equally, cytokines and chemokines define and regulate specific populations of neurons, glia or immune system leukocytes, generating more specific responses within restricted CNS regions or leukocyte populations. In addition, as there is a much larger variety of these compounds, their homing properties enable the superimposition of dynamic variations of cell activity upon local, spatially limited, cell populations. This would in principle allow the targeting of potential treatments to restricted regions of the CNS. The proposed synergistic interface of 'tonic' kynurenine pathway affecting baseline activity and the superimposed 'phasic' cytokine system would constitute an integrated network explaining some features of neuroimmune communication. The concept would broaden the scope for the development of new treatments for disorders involving both the CNS and immune systems, with safer and more effective agents targeted to specific CNS regions.

Polymorphism of interleukin-1β and interleukin-1 receptor antagonist genes in children with autism spectrum disorders

In this study, we first investigated interleukin-1 beta (IL-1β) and IL-1 receptor antagonist (IL-1RA) levels in a cohort of Egyptian children with autism spectrum disorder (ASD) and in healthy controls. Second, we examined the single-nucleotide polymorphisms (SNPs) at positions -31 and - 511 of the IL-1β gene promoter and IL1RA and assessed the association between IL1B and IL1RA polymorphisms with ASD. We examined IL1β promoter polymorphism at -511 (IL-1β-511) and - 31 (IL-1β-31) and IL1RA gene polymorphism in 80 children with ASD and 60 healthy children. The children with ASD had significantly higher levels of IL-1β and IL-1RA than the controls. The children with ASD also had significantly higher frequencies of homozygous (CC) and heterozygous (TC) genotype variants of IL-1β-511, and IL-1RA than the controls. Moreover, the frequency of the IL-1β-511 allele (C) was higher in the ASD group than in the controls (p = .001). The homozygous and heterozygous variants of IL-1RA allele II were also significantly higher in the ASD group than in the control group. There was no significant association between the IL-1β-31 genotype and autism classes. However, there were significant differences in the distribution of the IL-1RA heterogeneous genotype and allele II among children with severe autism. The inflammatory role of cytokines has been implicated in a variety of neuropsychiatric pathologies, including autism. Our data show alterations in the IL-1β system, with abnormally increased serum levels of IL-1β and IL-1RA in the children with ASD. Further, polymorphisms in the IL-1β-511 and IL-1RA genotype variants correlated positively with autism severity and behavioral abnormalities. IL-1β-511 and IL-1RA gene polymorphisms could impact ASD risk and may be used as potential biomarkers of ASD. Variations in the IL-1β and IL-1RA systems may have a role in the pathophysiology of ASD.

Refining anti-inflammatory therapy strategies for bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a severe lung disease of preterm infants, which is characterized by fewer, enlarged alveoli and increased inflammation. BPD has grave consequences for affected infants, but no effective and safe therapy exists. We previously showed that prophylactic treatment with interleukin-1 receptor antagonist (IL-1Ra) prevents murine BPD induced by perinatal inflammation and hyperoxia. Here, we used the same BPD model to assess whether an alternative anti-inflammatory agent, protein C (PC), is as effective as IL-1Ra against BPD. We also tested whether delayed administration or a higher dose of IL-1Ra affects its ability to ameliorate BPD and investigated aspects of drug safety. Pups were reared in room air (21% O2 ) or hyperoxia (65% or 85% O2 ) and received daily injections with vehicle, 1200 IU/kg PC, 10 mg/kg IL-1Ra (early or late onset) or 100 mg/kg IL-1Ra. After 3 or 28 days, lung and brain histology were assessed and pulmonary cytokines were analysed using ELISA and cytokine arrays. We found that PC only moderately reduced the severe impact of BPD on lung structure (e.g. 18% increased alveolar number by PC versus 34% by IL-1Ra); however, PC significantly reduced IL-1β, IL-1Ra, IL-6 and macrophage inflammatory protein (MIP)-2 by up to 89%. IL-1Ra at 10 mg/kg prevented BPD more effectively than 100 mg/kg IL-1Ra, but only if treatment commenced at day 1 of life. We conclude that prophylactic low-dose IL-1Ra and PC ameliorate BPD and have potential as the first remedy for one of the most devastating diseases preterm babies face.

PFOS induces behavioral alterations, including spontaneous hyperactivity that is corrected by dexamfetamine in zebrafish larvae

Perfluorooctane sulfonate (PFOS) is a widely spread environmental contaminant. It accumulates in the brain and has potential neurotoxic effects. The exposure to PFOS has been associated with higher impulsivity and increased ADHD prevalence. We investigated the effects of developmental exposure to PFOS in zebrafish larvae, focusing on the modulation of activity by the dopaminergic system. We exposed zebrafish embryos to 0.1 or 1 mg/L PFOS (0.186 or 1.858 µM, respectively) and assessed swimming activity at 6 dpf. We analyzed the structure of spontaneous activity, the hyperactivity and the habituation during a brief dark period (visual motor response), and the vibrational startle response. The findings in zebrafish larvae were compared with historical data from 3 months old male mice exposed to 0.3 or 3 mg/kg/day PFOS throughout gestation. Finally, we investigated the effects of dexamfetamine on the alterations in spontaneous activity and startle response in zebrafish larvae. We found that zebrafish larvae exposed to 0.1 mg/L PFOS habituate faster than controls during a dark pulse, while the larvae exposed to 1 mg/L PFOS display a disorganized pattern of spontaneous activity and persistent hyperactivity. Similarly, mice exposed to 0.3 mg/kg/day PFOS habituated faster than controls to a new environment, while mice exposed to 3 mg/kg/day PFOS displayed more intense and disorganized spontaneous activity. Dexamfetamine partly corrected the hyperactive phenotype in zebrafish larvae. In conclusion, developmental exposure to PFOS in zebrafish induces spontaneous hyperactivity mediated by a dopaminergic deficit, which can be partially reversed by dexamfetamine in zebrafish larvae.

Cytokine dysregulation in autism spectrum disorders (ASD): possible role of the environment

Autism spectrum disorders (ASD) are neurodevelopmental diseases that affect an alarming number of individuals. The etiological basis of ASD is unclear, and evidence suggests it involves both genetic and environmental factors. There are many reports of cytokine imbalances in ASD. These imbalances could have a pathogenic role, or they may be markers of underlying genetic and environmental influences. Cytokines act primarily as mediators of immunological activity but they also have significant interactions with the nervous system. They participate in normal neural development and function, and inappropriate activity can have a variety of neurological implications. It is therefore possible that cytokine dysregulation contributes directly to neural dysfunction in ASD. Further, cytokine profiles change dramatically in the face of infection, disease, and toxic exposures. Imbalances in cytokines may represent an immune response to environmental contributors to ASD. The following review is presented in two main parts. First, we discuss select cytokines implicated in ASD, including IL-1Β, IL-6, IL-4, IFN-γ, and TGF-Β, and focus on their role in the nervous system. Second, we explore several neurotoxic environmental factors that may be involved in the disorders, and focus on their immunological impacts. This review represents an emerging model that recognizes the importance of both genetic and environmental factors in ASD etiology. We propose that the immune system provides critical clues regarding the nature of the gene by environment interactions that underlie ASD pathophysiology.

Claudin expression profile separates Alzheimer's disease cases from normal aging and from vascular dementia cases

We have reported earlier that tight-junction proteins are detectable by standard immunohistochemistry in the brain parenchyma, namely in the cell bodies of neurons, astrocytes, and oligodendrocytes. Here we show, by projection to latent structures - discriminate analysis (PLS-DA), that the immunohistochemical detection profile of tight junction proteins clearly distinguishes the AD cases from healthy aging controls and from the cases of dementia with a predominantly vascular pathology underlying the symptoms (vascular dementia, VaD; cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, CADASIL; and cerebral amyloid angiopathy, CAA). Our findings might be valuable in the perspective of developing biomarkers for AD.

Epilepsy and brain inflammation

During the last decade, experimental research has demonstrated a prominent role of glial cells, activated in brain by various injuries, in the mechanisms of seizure precipitation and recurrence. In particular, alterations in the phenotype and function of activated astrocytes and microglial cells have been described in experimental and human epileptic tissue, including modifications in potassium and water channels, alterations of glutamine/glutamate cycle, changes in glutamate receptor expression and transporters, release of neuromodulatory molecules (e.g. gliotransmitters, neurotrophic factors), and induction of molecules involved in inflammatory processes (e.g. cytokines, chemokines, prostaglandins, complement factors, cell adhesion molecules) (Seifert et al., 2006; Vezzani et al., 2011; Wetherington et al., 2008). In particular, brain injury or proconvulsant events can activate microglia and astrocytes to release a number of proinflammatory mediators, thus initiating a cascade of inflammatory processes in brain tissue. Proinflammatory molecules can alter neuronal excitability and affect the physiological functions of glia by paracrine or autocrine actions, thus perturbing the glioneuronal communications. In experimental models, these changes contribute to decreasing the threshold to seizures and may compromise neuronal survival (Riazi et al., 2010; Vezzani et al., 2008). In this context, understanding which are the soluble mediators and the molecular mechanisms crucially involved in glio-neuronal interactions is instrumental to shed light on how brain inflammation may contribute to neuronal hyperexcitability in epilepsy. This review will report the clinical observations in drug-resistant human epilepsies and the experimental findings in adult and immature rodents linking brain inflammation to the epileptic process in a causal and reciprocal manner. By confronting the clinical evidence with the experimental findings, we will discuss the role of specific soluble inflammatory mediators in the etiopathogenesis of seizures, reporting evidence for both their acute and long term effects on seizure threshold. The possible contribution of these mediators to co-morbidities often described in epilepsy patients will be also discussed. Finally, we will report on the anti-inflammatory treatments with anticonvulsant actions in experimental models highlighting possible therapeutic options for treating drug-resistant seizures and for prevention of epileptogenesis.