The IL-6/sIL-6R fusion protein hyper-IL-6 promotes neurite outgrowth and neuron survival in cultured enteric neurons

Microglia modulate proliferation, neurite generation and differentiation of human neural progenitor cells

Microglia, the primary immune cells of the brain, significantly influence the fate of neurons after neural damage. Depending on the local environment, they exhibit a wide range of phenotypes, including patrolling (naïve), proinflammatory, and anti-inflammatory characteristics, which greatly affects neurotoxicity. Despite the fact that neural progenitor cells (NPCs) and hippocampal neurons represent cell populations, which play pivotal role in neural regeneration, interaction between microglia and these cell types is poorly studied. In the present work, we investigated how microglial cells affect the proliferation and neurite outgrowth of human stem cell-derived NPCs, and how microglia stimulation with proinflammatory or anti-inflammatory agents modulates this interaction. We found that naïve microglia slightly diminish NPC proliferation and have no effect on neurite outgrowth. In contrast, proinflammatory stimulated microglia promote both proliferation and neurite generation, whereas microglia stimulated with anti-inflammatory cytokines augment neurite outgrowth leaving NPC proliferation unaffected. We also studied how microglia influence neurite development and differentiation of hippocampal dentate gyrus granule cells differentiated from NPCs. We found that proinflammatory stimulated microglia inhibit axonal development but facilitate dendrite generation in these differentiating neurons. Our results elucidate a fine-tuned modulatory effect of microglial cells on cell types crucial for neural regeneration, opening perspectives for novel regenerative therapeutic interventions.

Dual Effects: Intrastriatal Injection of α-syn N103/tau N368 Preformed Fibrils Promotes Endogenous α-synuclein Aggregates in the Proximal Colon

BACKGROUND

Pathological changes in the brain can affect the gastrointestinal tract, whereas there is less evidence regarding the brain-gut axis.

OBJECTIVE

To identify whether cerebral endogenous phosphorylated α-synuclein induces gastrointestinal dysfunction via the brain-gut axis, mediated by the vagus nerve.

METHODS

α-syn N103/tau N368 preformed fibrils were injected into the dorsal lateral striatum of rodents, and the cerebral and colonic synucleinopathies and changes in the enteric nervous system were analyzed. Moreover, subdiaphragmatic vagotomy was conducted to confirm the role of the vagus nerve in brain-gut propagation.

RESULTS

An anterograde propagation of phosphorylated α-synuclein from the brain to the proximal colon mainly via the vagus nerve was observed at one month. The accumulation of phosphorylated α-synuclein was detected in the proximal colon over time, accompanied by infiltration of macrophages and eosinophils in the mucosa and submucosa. Upon injection with lower doses of preformed fibrils, the accumulation of phosphorylated α-synuclein and dopaminergic neuron loss was reduced to levels consistent with control at six months, while the expression levels of GFAP, Iba-1, and IL-6 increased. Under high preformed fibrils dose conditions, fecal traits and gastrointestinal motility were significantly reduced at six months, and aggregations of phosphorylated α-synuclein and an increasing level of IL-1β appeared.

CONCLUSION

Induced endogenous α-synuclein can quickly propagate into the proximal colon mainly via the vagus nerve. Injections of low doses of preformed fibrils can elicit recovery of the enteric nervous system and degradation of α-synuclein aggregates whereas high doses cause accumulation of pathological α-synuclein, enteric inflammation, and prominent gastrointestinal dysfunction.

Mechanistic Insights Into Gut Microbiome Dysbiosis-Mediated Neuroimmune Dysregulation and Protein Misfolding and Clearance in the Pathogenesis of Chronic Neurodegenerative Disorders

The human gut microbiota is a complex, dynamic, and highly diverse community of microorganisms. Beginning as early as in utero fetal development and continuing through birth to late-stage adulthood, the crosstalk between the gut microbiome and brain is essential for modulating various metabolic, neurodevelopmental, and immune-related pathways. Conversely, microbial dysbiosis – defined as alterations in richness and relative abundances – of the gut is implicated in the pathogenesis of several chronic neurological and neurodegenerative disorders. Evidence from large-population cohort studies suggests that individuals with neurodegenerative conditions have an altered gut microbial composition as well as microbial and serum metabolomic profiles distinct from those in the healthy population. Dysbiosis is also linked to psychiatric and gastrointestinal complications – comorbidities often associated with the prodromal phase of Parkinson’s disease (PD) and Alzheimer’s disease (AD). Studies have identified potential mediators that link gut dysbiosis and neurological disorders. Recent findings have also elucidated the potential mechanisms of disease pathology in the enteric nervous system prior to the onset of neurodegeneration. This review highlights the functional pathways and mechanisms, particularly gut microbe-induced chronic inflammation, protein misfolding, propagation of disease-specific pathology, defective protein clearance, and autoimmune dysregulation, linking gut microbial dysbiosis and neurodegeneration. In addition, we also discuss how pathogenic transformation of microbial composition leads to increased endotoxin production and fewer beneficial metabolites, both of which could trigger immune cell activation and enteric neuronal dysfunction. These can further disrupt intestinal barrier permeability, aggravate the systemic pro-inflammatory state, impair blood–brain barrier permeability and recruit immune mediators leading to neuroinflammation and neurodegeneration. Continued biomedical advances in understanding the microbiota-gut-brain axis will extend the frontier of neurodegenerative disorders and enable the utilization of novel diagnostic and therapeutic strategies to mitigate the pathological burden of these diseases.

Interleukin-6 promotes microtubule stability in axons via Stat3 protein-protein interactions

The interleukin-6 (IL-6) family of cytokines and its downstream effector, STAT3, are important mediators of neuronal health, repair, and disease throughout the CNS, including the visual system. Here, we elucidate a transcription-independent mechanism for the neuropoietic activities of IL-6 related to axon development, regeneration, and repair. We examined the outcome of IL-6 deficiency on structure and function of retinal ganglion cell (RGC) axons, which form the optic projection. We found that IL-6 deficiency substantially delays anterograde axon transport in vivo. The reduced rate of axon transport is accompanied by changes in morphology, structure, and post-translational modification of microtubules. In vivo and in vitro studies in mice and swine revealed that IL-6-dependent microtubule phenotypes arise from protein-protein interactions between STAT3 and stathmin. As in tumor cells and T cells, this STAT3-stathmin interaction stabilizes microtubules in RGCs. Thus, this IL-6-STAT3-dependent mechanism for axon architecture is likely a fundamental mechanism for microtubule stability systemically.

Role of IL-6 in the regulation of neuronal development, survival and function

The pleiotropic cytokine interleukin-6 (IL-6) is emerging as a molecule with both beneficial and destructive potentials. It can exert opposing actions triggering either neuron survival after injury or causing neurodegeneration and cell death in neurodegenerative or neuropathic disorders. Importantly, neurons respond differently to IL-6 and this critically depends on their environment and whether they are located in the peripheral or the central nervous system. In addition to its hub regulator role in inflammation, IL-6 is recently emerging as an important regulator of neuron function in health and disease, offering exciting possibilities for more mechanistic insight into the pathogenesis of mental, neurodegenerative and pain disorders and for developing novel therapies for diseases with neuroimmune and neurogenic pathogenic components.

Biological characteristics of IL-6 and related intestinal diseases

The intestine serves as an important digestive and the largest immune organ in the body. Interleukin-6(IL-6), an important mediator of various pathways, participates in the interactions between different kinds of cells and closely correlates with intestinal physiological and pathological condition. In this review we summarize the signaling pathways of IL-6 and its functions in maintaining intestinal homeostasis. We also explored its relation with nervous system and highlight its potential role in Parkinson's disease. Based on its specialty of the double-side influences on intestinal tumors and inflammation, we summarize how they are done through distinctive process.

Molecular Mechanisms Involved in Neural Substructure Development during Phosphodiesterase Inhibitor Treatment of Mesenchymal Stem Cells

Stem cells are highly important in biology due to their unique innate ability to self-renew and differentiate into other specialised cells. In a neurological context, treating major injuries such as traumatic brain injury, spinal cord injury and stroke is a strong basis for research in this area. Mesenchymal stem cells (MSC) are a strong candidate because of their accessibility, compatibility if autologous, high yield and multipotency with a potential to generate neural cells. With the use of small-molecule chemicals, the neural induction of stem cells may occur within minutes or hours. Isobutylmethyl xanthine (IBMX) has been widely used in cocktails to induce neural differentiation. However, the key molecular mechanisms it instigates in the process are largely unknown. In this study we showed that IBMX-treated mesenchymal stem cells induced differentiation within 24 h with the unique expression of several key proteins such as Adapter protein crk, hypoxanthine-guanine phosphoribosyltransferase, DNA topoisomerase 2-beta and Cell division protein kinase 5 (CDK5), vital in linking signalling pathways. Furthermore, the increased expression of basic fibroblast growth factor in treated cells promotes phosphatidylinositol 3-kinase (PI3K), mitogen-activated protein kinase (MAPK) cascades and GTPase–Hras interactions. Bioinformatic and pathway analyses revealed upregulation in expression and an increase in the number of proteins with biological ontologies related to neural development and substructure formation. These findings enhance the understanding of the utility of IBMX in MSC neural differentiation and its involvement in neurite substructure development.

Gut-seeded α-synuclein fibrils promote gut dysfunction and brain pathology specifically in aged mice

Parkinson's disease is a synucleinopathy that is characterized by motor dysfunction, death of midbrain dopaminergic neurons and accumulation of α-synuclein (α-Syn) aggregates. Evidence suggests that α-Syn aggregation can originate in peripheral tissues and progress to the brain via autonomic fibers. We tested this by inoculating the duodenal wall of mice with α-Syn preformed fibrils. Following inoculation, we observed gastrointestinal deficits and physiological changes to the enteric nervous system. Using the AAV-PHP.S capsid to target the lysosomal enzyme glucocerebrosidase for peripheral gene transfer, we found that α-Syn pathology is reduced due to the increased expression of this protein. Lastly, inoculation of α-Syn fibrils in aged mice, but not younger mice, resulted in progression of α-Syn histopathology to the midbrain and subsequent motor defects. Our results characterize peripheral synucleinopathy in prodromal Parkinson's disease and explore cellular mechanisms for the gut-to-brain progression of α-Syn pathology.

Postinfection Irritable Bowel Syndrome: The Links Between Gastroenteritis, Inflammation, the Microbiome, and Functional Disease

Postinfection irritable bowel syndrome (PI-IBS) is a diarrheal disease that develops after infectious gastroenteritis (IGE). Profound alterations in the microbiota accompany IGE yet only 10% of IGE patients progress to PI-IBS. This review explores research linking IGE severity, psychological comorbidity, PI-IBS, and the microbiome in various patient populations. Selective pressures caused by inflammation and increased gastrointestinal motility during gastroenteritis can alter intestinal bacterial phyla including Bacteroidetes, Firmicutes, and Proteobacteria. More specifically, classes such as Bacteroides and Clostridia are differentially abundant in many PI-IBS patients. Altered microbiota may perpetuate a cycle of enteric and systemic inflammation, potently activating neural afferent signaling in the enteric nervous system and causing pain and diarrhea in PI-IBS patients. Altered production of microbial metabolites, for example short chain fatty acids, may have enteric and systemic effects on the host. Longitudinal sampling to characterize changes in the microbiota's genetic, metabolic, and transcriptional activities over time from IGE to PI-IBS may enable improved diagnosis and classification of PI-IBS cases into subtypes, allowing for targeted antibiotic, probiotic, and prebiotic treatments. PI-IBS is a heterogenous and largely organic disease marked by specific alterations in functions of the microbiota and is an important model for studying microbial influences on intestinal, neurological, and psychological host functions.

Peripheral Inflammation and Demyelinating Diseases

In recent decades, several neurodegenerative diseases have been shown to be exacerbated by systemic inflammatory processes. There is a wide range of literature that demonstrates a clear but complex relationship between the central nervous system (CNS) and the immunological system, both under naïve or pathological conditions. In diseased brains, peripheral inflammation can transform "primed" microglia into an "active" state, which can trigger stronger pathological responses. Demyelinating diseases are a group of neurodegenerative diseases characterized by inflammatory lesions associated with demyelination, which in turn induces axonal damage, neurodegeneration, and progressive loss of function. Among them, the most important are multiple sclerosis (MS) and neuromyelitis optica (NMO). In this review, we will analyze the effect of specific peripheral inflammatory stimuli in the progression of demyelinating diseases and discuss their animal models. In most cases, peripheral immune stimuli are exacerbating.

The Enteric Network: Interactions between the Immune and Nervous Systems of the Gut

Interactions between the nervous and immune systems enable the gut to respond to the variety of dietary products that it absorbs, the broad spectrum of pathogens that it encounters, and the diverse microbiome that it harbors. The enteric nervous system (ENS) senses and reacts to the dynamic ecosystem of the gastrointestinal (GI) tract by translating chemical cues from the environment into neuronal impulses that propagate throughout the gut and into other organs in the body, including the central nervous system (CNS). This review will describe the current understanding of the anatomy and physiology of the GI tract by focusing on the ENS and the mucosal immune system. We highlight emerging literature that the ENS is essential for important aspects of microbe-induced immune responses in the gut. Although most basic and applied research in neuroscience has focused on the brain, the proximity of the ENS to the immune system and its interface with the external environment suggest that novel paradigms for nervous system function await discovery.

Cyclosporine A-Mediated IL-6 Expression Promotes Neural Induction in Pluripotent Stem Cells

Differentiation of pluripotent stem cells (PSCs) to neural lineages has gathered huge attention in both basic research and regenerative medicine. The major hurdle lies in the efficiency of differentiation and identification of small molecules that facilitate neurogenesis would partly circumvent this limitation. The small molecule Cyclosporine A (CsA), a commonly used immunosuppressive drug, has been shown to enhance in vivo neurogenesis. To extend the information to in vitro neurogenesis, we examined the effect of CsA on neural differentiation of PSCs. We found CsA to increase the expression of neural progenitor genes during early neural differentiation. Gene silencing approach revealed CsA-mediated neural induction to be dependent on blocking the Ca²⁺-activated phosphatase calcineurin (Cn) signaling. Similar observation with FK506, an independent inhibitor of Cn, further strengthened the necessity of blocking Cn for enhanced neurogenesis. Surprisingly, mechanistic insight revealed Cn-inhibition dependent upregulation of IL-6 protein to be necessary for CsA-mediated neurogenesis. Together, these findings provide a comprehensive understanding of the role of CsA in neurogenesis, thus suggesting a method for obtaining large numbers of neural progenitors from PSCs for possible transplantation.

Interleukin-6-Mediated Induced Pluripotent Stem Cell (iPSC)-Derived Neural Differentiation

In an aging society with an increasing threat to higher brain cognitive functions due to dementia, it becomes imperative to identify new molecular remedies for supporting adult neurogenesis. Interleukin-6 (IL-6) is a promising cytokine that can support neurogenesis under conditions of neurodegeneration, and neuron replacement is eventually possible due to its agonistic acting soluble receptor sIL-6R. Here, we report that activation of the IL-6-signal transducer and activator of transcription 3 (STAT3) axis is neurogenic and has potential therapeutic applications for the treatment of neurodegenerative diseases such as Parkinson's disease (PD).

Infections and Brain Development

Several different bodies of evidence support a link between infection and altered brain development. Maternal infections, such as influenza and human immunodeficiency virus, have been linked to the development of autism spectrum disorders, differences in cognitive test scores, and bipolar disorder; an association that has been shown in both epidemiologic and retrospective studies. Several viral, bacterial, and parasitic illnesses are associated with alterations in fetal brain structural anomalies including brain calcifications and hydrocephalus. The process of infection can activate inflammatory pathways causing the release of various proinflammatory biomarkers and histological changes consistent with an infectious intrauterine environment (chorioamnionitis) or umbilical cord (funisitis). Elevations in inflammatory cytokines are correlated with cerebral palsy, schizophrenias, and autism. Animal studies indicate that the balance of proinflammatory and anti-inflammatory cytokines is critical to the effect prenatal inflammation plays in neurodevelopment. Finally, chorioamnionitis is associated with cerebral palsy and other abnormal neurodevelopmental outcomes. In conclusion, a plethora of evidence supports, albeit with various degrees of certainty, the theory that maternal infection and inflammation that occur during critical periods of fetal development could theoretically alter brain structure and function in a time-sensitive manner.

Boosting Central Nervous System Axon Regeneration by Circumventing Limitations of Natural Cytokine Signaling

Retinal ganglion cells (RGCs) do not normally regenerate injured axons, but die upon axotomy. Although IL-6-like cytokines are reportedly neuroprotective and promote optic nerve regeneration, their overall regenerative effects remain rather moderate. Here, we hypothesized that direct activation of the gp130 receptor by the designer cytokine hyper-IL-6 (hIL-6) might induce stronger RGC regeneration than natural cytokines. Indeed, hIL-6 stimulated neurite growth of adult cultured RGCs with significantly higher efficacy than CNTF or IL-6. This neurite growth promoting effect could be attributed to stronger activation of the JAK/STAT3 and PI3K/AKT/mTOR signaling pathways and was also observed in peripheral dorsal root ganglion neurons. Moreover, hIL-6 abrogated axon growth inhibition by central nervous system (CNS) myelin. Remarkably, continuous hIL-6 expression upon RGC-specific AAV transduction after optic nerve crush exerted stronger axon regeneration than other known regeneration promoting treatments such as lens injury and PTEN knockout, with some axons growing through the optic chiasm 6 weeks after optic nerve injury. Combination of hIL-6 with RGC-specific PTEN knockout further enhanced optic nerve regeneration. Therefore, direct activation of gp130 signaling might be a novel, clinically applicable approach for robust CNS repair.

Fas and TRAIL 'death receptors' as initiators of inflammation: Implications for cancer

Fas (CD95/APO-1) and TRAIL (CD253, TNFSF10, APO2) are members of a subset of the TNF receptor superfamily known as 'death receptors'. To date, the overwhelming majority of studies on Fas and TRAIL (TNF-related apoptosis-inducing ligand) have explored the role of these receptors as initiators of apoptosis. However, sporadic reports also suggest that engagement of the Fas and TRAIL receptors can lead to other outcomes such as cytokine and chemokine production, cell proliferation, cell migration and differentiation. Indeed, although transformed cells frequently express Fas and TRAIL, most do not undergo apoptosis upon engagement of these receptors and significant effort has been devoted toward exploring how to sensitize such cells to the pro-apoptotic effects of 'death receptor' stimulation. Moreover, the expression of Fas and TRAIL receptors is greatly elevated in many cancer types such as hepatocellular carcinoma, renal carcinoma and ovarian cancer, suggesting that such tumors benefit from the expression of these receptors. Furthermore, several studies have shown that tumor proliferation, progression and invasion can be impaired through blocking or downregulation of Fas expression, but the mechanistic basis for these effects is largely unknown. Thus, the characterization of Fas and TRAIL as 'death receptors' is a gross oversimplification, especially in the context of cancer. It is becoming increasingly clear that 'death receptor' engagement can lead to outcomes, other than apoptosis, that become subverted by certain tumors to their benefit. Here we will discuss death-independent outcomes of Fas and TRAIL signaling and their implications for cancer.

Peripheral nerve regeneration and NGF-dependent neurite outgrowth of adult sensory neurons converge on STAT3 phosphorylation downstream of neuropoietic cytokine receptor gp130

After nerve injury, adult sensory neurons can regenerate peripheral axons and reconnect with their target tissue. Initiation of outgrowth, as well as elongation of neurites over long distances, depends on the signaling of receptors for neurotrophic growth factors. Here, we investigated the importance of gp130, the signaling subunit of neuropoietic cytokine receptors in peripheral nerve regeneration. After sciatic nerve crush, functional recovery in vivo was retarded in SNS-gp130(-/-) mice, which specifically lack gp130 in sensory neurons. Correspondingly, a significantly reduced number of free nerve endings was detected in glabrous skin from SNS-gp130(-/-) compared with control mice after nerve crush. Neurite outgrowth and STAT3 activation in vitro were severely reduced in cultures in gp130-deficient cultured neurons. Surprisingly, in neurons obtained from SNS-gp130(-/-) mice the increase in neurite length was reduced not only in response to neuropoietic cytokine ligands of gp130 but also to nerve growth factor (NGF), which does not bind to gp130-containing receptors. Neurite outgrowth in the absence of neurotrophic factors was partially rescued in gp130-deficient neurons by leptin, which activates STAT3 downstream of leptic receptor and independent of gp130. The neurite outgrowth response of gp130-deficient neurons to NGF was fully restored in the presence of leptin. Based on these findings, gp130 signaling via STAT3 activation is suggested not only to be an important regulator of peripheral nerve regeneration in vitro and in vivo, but as determining factor for the growth promoting action of NGF in adult sensory neurons.

Maintenance of the enteric stem cell niche by bacterial lipopolysaccharides? Evidence and perspectives

The enteric nervous system (ENS) has to respond to continuously changing microenvironmental challenges within the gut and is therefore dependent on a neural stem cell niche to keep the ENS functional throughout life. In this study, we hypothesize that this stem cell niche is also affected during inflammation and therefore investigated lipopolysaccharides (LPS) effects on enteric neural stem/progenitor cells (NSPCs). NSPCs were derived from the ENS and cultured under the influence of different LPS concentrations. LPS effects upon proliferation and differentiation of enteric NSPC cultures were assessed using immunochemistry, flow cytometry, western blot, Multiplex ELISA and real-time PCR. LPS enhances the proliferation of enteric NSPCs in a dose-dependent manner. It delays and modifies the differentiation of these cells. The expression of the LPS receptor toll-like receptor 4 on NSPCs could be demonstrated. Moreover, LPS induces the secretion of several cytokines. Flow cytometry data gives evidence for individual subgroups within the NSPC population. ENS-derived NSPCs respond to LPS in maintaining at least partially their stem cell character. In the case of inflammatory disease or trauma where the liberation and exposure to LPS will be increased, the expansion of NSPCs could be a first step towards regeneration of the ENS. The reduced and altered differentiation, as well as the induction of cytokine signalling, demonstrates that the stem cell niche may take part in the LPS-transmitted inflammatory processes in a direct and defined way.

A novel role for brain interleukin-6: facilitation of cognitive flexibility in rat orbitofrontal cortex

Cytokines, small proteins released by the immune system to combat infection, are typically studied under inflammatory conditions. However, these molecules are also expressed in the brain in basal, nonpathological states, where they can regulate neuronal processes, such as learning and memory. However, little is known about how cytokine signaling in the brain may influence higher-order cognitive functions. Cognitive flexibility is one such executive process, mediated by the prefrontal cortex, which requires an adaptive modification of learned behaviors in response to environmental change. We explored the role of basal IL-6 signaling in the orbitofrontal cortex (OFC) in reversal learning, a form of cognitive flexibility that can be measured in the rat using the attentional set-shifting test. We found that inhibiting IL-6 or its downstream JAK/STAT signaling pathway in the OFC impaired reversal learning, suggesting that basal IL-6 and JAK/STAT signaling facilitate cognitive flexibility. Further, we demonstrated that elevating IL-6 in the OFC by adeno-associated virus-mediated gene delivery reversed a cognitive deficit induced by chronic stress, thus identifying IL-6 and the downstream JAK/STAT signaling pathway as potentially novel therapeutic targets for the treatment of stress-related psychiatric diseases associated with cognitive dysfunction.

The GDNF System Is Altered in Diverticular Disease - Implications for Pathogenesis

Background & Aims

Absence of glial cell line-derived neurotrophic factor (GDNF) leads to intestinal aganglionosis. We recently demonstrated that patients with diverticular disease (DD) exhibit hypoganglionosis suggesting neurotrophic factor deprivation. Thus, we screened mRNA expression pattern of the GDNF system in DD and examined the effects of GDNF on cultured enteric neurons.

Methods

Colonic specimens obtained from patients with DD (n = 21) and controls (n = 20) were assessed for mRNA expression levels of the GDNF system (GDNF, GDNF receptors GFRα1 and RET). To identify the tissue source of GDNF and its receptors, laser-microdissected (LMD) samples of human myenteric ganglia and intestinal muscle layers were analyzed separately by qPCR. Furthermore, the effects of GDNF treatment on cultured enteric neurons (receptor expression, neuronal differentiation and plasticity) were monitored.

Results

mRNA expression of GDNF and its receptors was significantly down-regulated in the muscularis propria of patients with DD. LMD samples revealed high expression of GDNF in circular and longitudinal muscle layers, whereas GDNF receptors were also expressed in myenteric ganglia. GDNF treatment of cultured enteric neurons increased mRNA expression of its receptors and promoted neuronal differentiation and plasticity revealed by synaptophysin mRNA and protein expression.

Conclusions

Our results suggest that the GDNF system is compromised in DD. In vitro studies demonstrate that GDNF enhances expression of its receptors and promotes enteric neuronal differentiation and plasticity. Since patients with DD exhibit hypoganglionosis, we propose that the observed enteric neuronal loss in DD may be due to lacking neurotrophic support mediated by the GDNF system.

IL-6 attenuates trimethyltin-induced cognitive dysfunction via activation of JAK2/STAT3, M1 mAChR and ERK signaling network

We previously reported that interleukin (IL)-6 deficiency potentiates trimethyltin (TMT)-induced convulsive neurotoxicity. The purpose in this study was to investigate the molecular mechanism by which cytokines affect TMT-induced cognitive impairment. To accomplish this, we examined hippocampal changes in Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling in relation to cholinergic parameters after TMT treatment in mice genetically deficient in IL-6 (IL-6(-/-)), tumor necrosis factor-α (TNF-α(-/-)), or interferon-γ (IFN-γ(-/-)). The IL-6(-/-) mice were the most susceptible to TMT-induced cognitive dysfunction and exhibited significant decreases in JAK2/STAT3 signaling and M1 muscarinic acetylcholine receptor (mAChR) expression, as well as other cholinergic parameters, compared with wild-type (WT) animals. Recombinant IL-6 protein (rIL-6) significantly attenuated these impairments in TMT-treated IL-6(-/-) mice, whereas an IL-6 receptor antibody potentiated these impairments in TMT-treated WT animals. Inhibition of JAK2 with AG490 or inhibition of cholinergic signaling with the M1 mAChR antagonist dicyclomine counteracted the attenuating effects of rIL-6 on phosphorylated extracellular signal-regulated kinase (ERK) expression, or on cognitive impairment in TMT-treated IL-6(-/-) mice. However, neither AG490 nor dicyclomine significantly attenuated effects of rIL-6 on acetylcholinesterase values. Our results suggest that activation of JAK2/STAT3 signaling and upregulation of the M1 mAChR are essential components of IL-6-mediated memory improvement against TMT toxicity.

Interleukin-6 (IL-6) receptor/IL-6 fusion protein (Hyper IL-6) effects on the neonatal mouse brain: possible role for IL-6 trans-signaling in brain development and functional neurobehavioral outcomes

Adverse neurodevelopmental outcomes are linked to perinatal production of inflammatory mediators, including interleukin 6 (IL-6). While a pivotal role for maternal elevation in IL-6 has been established in determining neurobehavioral outcomes in the offspring and considered the primary target mediating the fetal inflammatory response, questions remain as to the specific actions of IL-6 on the developing brain. CD-1 male mice received a subdural injection of the bioactive fusion protein, hyper IL-6 (HIL-6) on postnatal-day (PND)4 and assessed from preweaning until adulthood. Immunohistochemical evaluation of astrocytes and microglia and mRNA levels for pro-inflammatory cytokines and host response genes indicated no evidence of an acute neuroinflammatory injury response. HIL-6 accelerated motor development and increased reactivity to stimulation and number of entries in a light/dark chamber, decreased ability to learn to withhold a response in passive avoidance, and effected deficits in social novelty behavior. No changes were observed in motor activity, pre-pulse startle inhibition, or learning and memory in the Morris water maze or radial arm maze, as have been reported for models of more severe developmental neuroinflammation. In young animals, mRNA levels for MBP and PLP/DM20 decreased and less complexity of MBP processes in the cortex was evident by immunohistochemistry. The non-hydroxy cerebroside fraction of cerebral lipids was increased. These results provide evidence for selective effects of IL-6 signaling, particularly trans-signaling, in the developing brain in the absence of a general neuroinflammatory response. These data contribute to our further understanding of the multiple aspects of IL-6 signaling in the developing brain.

Tissue-protective cytokines: structure and evolution

Cytokines are important mediators of host defense and immunity, and were first identified for their role in immunity to infections. It was then found that some of them are pathogenic mediators in inflammatory diseases and much of the emphasis is now on pro-inflammatory cytokines, also in consideration of the fact that TNF inhibitors became effective drugs in chronic inflammatory diseases. The recent studies on the tissue-protective activities of erythropoietin (EPO) led to the term "tissue-protective cytokine." We discuss here how tissue-protective actions might be common to other cytokines, particularly those of the 4-alpha helical structural superfamily.

Neural transmembrane protease and endothelial Gs protein activation in cell contact-dependent signaling between neural stem/progenitor cells and brain endothelial cells

Vasculature is an important component of the neural stem cell niche in brain. It regulates neural stem/progenitor (NS/P) cell self-renewal, differentiation, and migration. In the neurogenic niches of adult brain, NS/P cells lie close to blood vessels, and proliferating NS/P cells frequently contact the vasculature. In the present study we showed that NS/P cells in co-culture with brain endothelial (bEND) cells activated endothelial G proteins and p38 mitogen-activated protein kinase (p38 MAPK) and stimulated cytokine/chemokine expression. These NS/P cell-induced endothelial responses took place during NS/P cell and bEND cell direct contact and were critically dependent on the expression of the type II transmembrane serine protease matriptase (MTP) by NS/P cells, because knocking down of MTP in NS/P cells impaired and re-expression of MTP restored their ability to induce endothelial cytokine/chemokine expression, p38 MAPK, or G protein activation. Cholera toxin blocked NS/P cell-induced endothelial responses, suggesting that the endothelial G protein activated by NS/P MTP is in the G(s) subfamily. The addition of p38 MAPK inhibitor impaired NS/P cell-induced endothelial cytokine/chemokine expression. The known G protein-coupled receptor substrate of MTP, protease-activated receptor 2, was not involved in this system. These results revealed a novel signaling pathway in neural stem cell vascular niches that is mediated by neural MTP and endothelial G(s) protein signaling at the cell-cell interface. This is the first report of direct cell-cell signaling between NS/P and bEND cells.

Protective potential of IL-6 against trimethyltin-induced neurotoxicity in vivo

We investigated the role of cytokines in trimethyltin (TMT)-induced convulsive neurotoxicity. Evaluation of TNF-α, interferon-γ, and interleukin (IL)-6 knockout (-/-) mice showed that the IL-6(-/-) mice had the greatest susceptibility to TMT-induced seizures. In both wild-type and IL-6(-/-) mice, TMT treatment increased glutathione oxidation, lipid peroxidation, protein oxidation, and levels of reactive oxygen species in the hippocampus. These effects were more pronounced in the IL-6(-/-) mice than in wild-type controls. In addition, the ability of TMT to induce nuclear translocation of Nrf2 and upregulation of heme oxygenase-1 and γ-glutamylcysteine ligase was significantly decreased in IL-6(-/-) mice. Treatment of IL-6(-/-) mice with recombinant IL-6 protein (rIL-6) restored these effects of TMT. Treatment with rIL-6 also significantly attenuated the TMT-induced inhibition of phosphoinositol 3-kinase (PI3K)/Akt signaling, thereby increasing phosphorylation of Bad (Bcl-xL/Bcl-2-associated death promoter protein), expression of Bcl-xL and Bcl-2, and the interaction between p-Bad and 14-3-3 protein and decreasing Bax expression and caspase-3 cleavage. Furthermore, in IL-6(-/-) mice, rIL-6 provided significant protection against TMT-induced neuronal degeneration; this effect of rIL-6 was counteracted by the PI3K inhibitor LY294002. These results suggest that activation of Nrf2-dependent glutathione homeostasis and PI3K/Akt signaling is required for the neuroprotective effects of IL-6 against TMT.

Genetic evidence for an essential role of neuronally expressed IL-6 signal transducer gp130 in the induction and maintenance of experimentally induced mechanical hypersensitivity in vivo and in vitro

Tenderness and mechanical allodynia are key symptoms of malignant tumor, inflammation and neuropathy. The proinflammatory cytokine interleukin-6 (IL-6) is causally involved in all three pathologies. IL-6 not only regulates innate immunity and inflammation but also causes nociceptor sensitization and hyperalgesia. In general and in most cell types including immune cells and sensory neurons, IL-6 binds soluble μ receptor subunits which heteromerizes with membrane bound IL-6 signal transducer gp130. In the present study, we used a conditional knock-out strategy to investigate the importance of signal transducer gp130 expressed in C nociceptors for the generation and maintenance of mechanical hypersensitivity. Nociceptors were sensitized to mechanical stimuli by experimental tumor and this nociceptor sensitization was preserved at later stages of the pathology in control mice. However, in mice with a conditional deletion of gp130 in Nav1.8 expressing nociceptors mechanical hypersensitivity by experimental tumor, nerve injury or inflammation recovery was not preserved in the maintenance phase and nociceptors exhibited normal mechanical thresholds comparable to untreated mice. Together, the results argue for IL-6 signal transducer gp130 as an essential prerequisite in nociceptors for long-term mechanical hypersensitivity associated with cancer, inflammation and nerve injury.

Breast milk contains relevant neurotrophic factors and cytokines for enteric nervous system development

Breast-feeding plays an important role for the development of the newborn. Non-breast fed premature born infants show a significantly higher risk of developing diseases like infantile diarrhoea and necrotizing enterocolitis. In this study, the content of neurotrophic factors and cytokines, which might influence the postnatal development of the enteric nervous system (ENS), was determined in human breast milk. Glial cell-line-derived neurotrophic factor (GDNF), ciliary neurotrophic factor (CNTF) as well as a panel of cytokines were analyzed using single factor or multiplex ELISA. In order to link their presence in milk with possible effects on the development of the ENS, rat myenteric neurons were cultured in protein extracts from breast milk. Neurite outgrowth, neuron survival and nestin expression in glial cells were measured. Growth factors and cytokines were found in all breast milk samples at varying concentrations. It could be demonstrated that protein extracts of breast milk increased the amount of surviving enteric neurones as well as neurite outgrowth. Additionally it was shown, that the number of nestin and S100-expressing glial cells increased significantly after incubating in breast milk protein extracts. The data suggest that milk-born proteins support the development of the enteric nervous system.

Interleukin-6, a mental cytokine

Almost a quarter of a century ago, interleukin-6 (IL-6) was discovered as an inflammatory cytokine involved in B cell differentiation. Today, IL-6 is recognized to be a highly versatile cytokine, with pleiotropic actions not only in immune cells, but also in other cell types, such as cells of the central nervous system (CNS). The first evidence implicating IL-6 in brain-related processes originated from its dysregulated expression in several neurological disorders such as multiple sclerosis, Alzheimer's disease and Parkinson's disease. In addition, IL-6 was shown to be involved in multiple physiological CNS processes such as neuron homeostasis, astrogliogenesis and neuronal differentiation. The molecular mechanisms underlying IL-6 functions in the brain have only recently started to emerge. In this review, an overview of the latest discoveries concerning the actions of IL-6 in the nervous system is provided. The central position of IL-6 in the neuroinflammatory reaction pattern, and more specifically, the role of IL-6 in specific neurodegenerative processes, which accompany Alzheimer's disease, multiple sclerosis and excitotoxicity, are discussed. It is evident that IL-6 has a dichotomic action in the CNS, displaying neurotrophic properties on the one hand, and detrimental actions on the other. This is in agreement with its central role in neuroinflammation, which evolved as a beneficial process, aimed at maintaining tissue homeostasis, but which can become malignant when exaggerated. In this perspective, it is not surprising that 'well-meant' actions of IL-6 are often causing harm instead of leading to recovery.

Plasticity and neural stem cells in the enteric nervous system

The enteric nervous system (ENS) is a highly organized part of the autonomic nervous system, which innervates the whole gastrointestinal tract by several interconnected neuronal networks. The ENS changes during development and keeps throughout its lifespan a significant capacity to adapt to microenvironmental influences, be it in inflammatory bowel diseases or changing dietary habits. The presence of neural stem cells in the pre-, postnatal, and adult gut might be one of the prerequisites to adapt to changing conditions. During the last decade, the ENS has increasingly come into the focus of clinical neural stem cell research, forming a considerable pool of neural crest derived stem cells, which could be used for cell therapy of dysganglionosis, that is, diseases based on the deficient or insufficient colonization of the gut by neural crest derived stem cells; in addition, the ENS could be an easily accessible neural stem cell source for cell replacement therapies for neurodegenerative disorders or traumatic lesions of the central nervous system.

A key role for gp130 expressed on peripheral sensory nerves in pathological pain

Interleukin-6 (IL-6) is a key mediator of inflammation. Inhibitors of IL-6 or of its signal transducing receptor gp130 constitute a novel class of anti-inflammatory drugs, which raise great hopes for improved treatments of painful inflammatory diseases such as rheumatoid arthritis. IL-6 and gp130 may enhance pain not only indirectly through their proinflammatory actions but also through a direct action on nociceptors (i.e., on neurons activated by painful stimuli). We found indeed that the IL-6/gp130 ligand-receptor complex induced heat hypersensitivity both in vitro and in vivo. This process was mediated by activation of PKC-delta via Gab1/2/PI(3)K and subsequent regulation of TRPV1, a member of the transient receptor potential (TRP) family of ion channels. To assess the relevance of this direct pain promoting effect of IL-6, we generated conditional knock-out mice, which lack gp130 specifically in nociceptors, and tested them in models of inflammatory and tumor-induced pain. These mice showed significantly reduced levels of inflammatory and tumor-induced pain but no changes in immune reactions or tumor growth. Our results uncover the significance of gp130 expressed in peripheral pain sensing neurons in the pathophysiology of major clinical pain disorders and suggest their use as novel pain relieving agents in inflammatory and tumor pain.

IL-6-trans-signalling increases rapid-eye-movement sleep in rats

Interleukin 6 (IL-6), a cytokine of the gp130-signalling-family, plays an important role in immediate immunological functions, in metabolism and in the central nervous system. IL-6-signalling is mediated by classic-signalling via the membrane bound IL-6 receptor or by IL-6-trans-signalling via the soluble IL-6 receptor. Whereas the receptor subunit gp130 is ubiquitously expressed within the body, IL-6 receptor expression is restricted to distinct cell populations. Within the brain parenchyma the IL-6 receptor is sparsely expressed, and therefore the brain is mostly dependent on IL-6-trans-signalling in its response to IL-6. Recently we have shown that IL-6-trans-signalling but not classic-signalling plays a pivotal role in the establishment and maintenance of chronic inflammation and cancer, whereas its role in sleep regulation has not been studied so far. We reasoned that the IL-6-trans-signalling mimetic Hyper-IL-6 which in contrast to IL-6 alone can activate almost all cells of the brain might have a profound effect on sleep regulation and performed sleep recordings with rats injected with recombinant Hyper-IL-6. In the present study, the i.c.v. administration of the designer cytokine Hyper-IL-6 into rats at dark onset increased the amount of rapid-eye-movement sleep (REM sleep) but did not affect non-rapid-eye-movement sleep (non-REM sleep). Our data define a new role of IL-6-trans-signalling in sleep regulation.

Interleukin-6 and neural stem cells: more than gliogenesis

Besides its wide range of action as a proinflammatory cytokine in the immune system, interleukin-6 (IL-6) has also attracted much attention due to its influence on the nervous system. In the present study we show that the designer fusion protein H-IL-6, consisting of IL-6 and its specific receptor IL-6R-alpha, but not IL-6 alone, mediates both neuro- as well as gliogenesis. Using immunocytochemistry, Western blot, and patch-clamp recording, we demonstrate that H-IL-6 induces the differentiation of neural stem cells (NSCs) specifically into glutamate-responsive neurons and two morphological distinctive astroglia cell types. H-IL-6-activated neurogenesis seems to be induced by the MAPK/CREB (mitogen-activated protein kinase/cAMP response element-binding protein) cascade, whereas gliogenesis is mediated via the STAT-3 (signal transducers and activators of transcription protein-3) signaling pathway. Our finding that IL-6 mediates both processes depending on its specific soluble receptor sIL-6R-alpha has implications for the potential treatment of neurodegenerative diseases.

The autonomic nervous system and inflammatory bowel disease

Crohn's disease and ulcerative colitis, collectively known as inflammatory bowel disease (IBD), are chronic, recurring, inflammatory conditions of the intestine. The precise mechanisms underlying the pathogenesis of IBD are not yet clear but they are believed to involve a number of precipitating factors, most notably genetic susceptibility and environmental influences. The autonomic nervous system (ANS) has long been known as a critical regulator of intestinal function and much evidence now exists to suggest that it also plays an important role in the development of IBD. Dramatic changes in the ANS in IBD are apparent from the cellular to the molecular level ultimately leading to altered communication between the ANS and effector cells of the intestine. This review aims to synthesize the current understanding of the pathogenesis of IBD with a particular emphasis on the role that the ANS plays in the progression of these diseases.

Interleukin-6 and its receptor: from bench to bedside

Interleukin-6 (IL-6) is an inflammatory cytokine with a well-documented role in inflammation and cancer. The cytokine binds to a membrane bound IL-6 receptor (IL-6R) and this complex associates with two molecules of the signal transducing protein gp130 thereby initiating intracellular signaling. While gp130 is present on most if not all cells of the body, the IL-6R is only present on some cells, mainly hepatocytes and several leukocytes. Cells, which only express gp130 and no IL-6R are refractory to IL-6 signals. We have shown earlier that the IL-6R can exist as a soluble protein generated by limited proteolysis of the membrane bound receptor or by translation from an alternatively spliced mRNA. This soluble IL-6R (sIL-6R) can bind the ligand IL-6 and the soluble complex of sIL-6R and IL-6 can bind to gp130 on cells which lack the membrane bound IL-6R and trigger gp130 signaling. We have named this process 'trans-signaling'. We will review data, which clearly show that IL-6 uses classical signaling via the membrane bound receptor and trans-signaling via the soluble receptor in various physiological and pathophysiological situations. Furthermore, we have developed designer cytokines, which can specifically enhance or inhibit IL-6 trans-signaling. These designer cytokines have been shown to be extremely useful to in therapeutic applications ranging from the long-term culture of stem cells and enhancing liver regeneration up to the blockade of chronic inflammation and cancer.

Fast modulation of heat-activated ionic current by proinflammatory interleukin 6 in rat sensory neurons

The pro-inflammatory cytokine interleukin-6 (IL-6) together with its soluble receptor (sIL-6R) induces and maintains thermal hyperalgesia. It facilitates the heat-induced release of calcitonin gene-related peptide from rat cutaneous nociceptors in vivo and in vitro. Here we report that exposure of nociceptive neurons to the IL-6-sIL-6R complex or the gp130-stimulating designer IL-6-sIL-6R fusion protein Hyper-IL-6 (HIL-6) resulted in a potentiation of heat-activated inward currents (I(heat)) and a shift of activation thresholds towards lower temperatures without affecting intracellular calcium levels. The Janus tyrosine kinase inhibitor AG490, the selective protein kinase C (PKC) inhibitor, bisindolylmaleimide 1 (BIM1), as well as rottlerin, a selective blocker of the PKCdelta isoform, but not the cyclooxygenase inhibitor indomethacin, effectively reduced the effect. Reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization revealed expression of mRNA for the signal-transducing beta subunit of the receptor gp130 in neuronal somata, rather than satellite cells in rat dorsal root ganglia. Together, the results suggest that IL-6-sIL-6R acts directly on sensory neurons. It increases their susceptibility to noxious heat via the gp130/Jak/PKCdelta signalling pathway.

Differential expression of suppressors of cytokine signaling-1, -2, and -3 in the rat hippocampus after seizure: implications for neuromodulation by gp130 cytokines

Numerous studies have investigated the expression of various cytokine families in the CNS after brain injury. The gp130 or interleukin (IL)-6-type cytokines have received a great deal of focus, and it is clear that they exhibit an acute and robust upregulation in various brain injury models. We are interested to determine, however, whether endogenously expressed cytokines in the CNS act in a direct neuromodulatory manner. In an accompanying study, we examined the expression of five gp130 cytokines and their receptors in the lithium-pilocarpine model of status epilepticus. We follow up that study here by trying to determine if gp130 signal transduction occurs in hippocampal principal neurons after seizure. Therefore, using the expression of suppressors of cytokine signaling (SOCS)-1 and -3 as indices of gp130 signal transduction, we performed a detailed in situ hybridization seizure time-course study in the adult rat hippocampus. For comparison, we also examined SOCS-2, which is involved in insulin-like growth factor signaling. We found that while SOCS-1 and -3 were faintly expressed under basal conditions, only SOCS-3 exhibited a rapid, robust, and transient induction. This occurred first in non-principal cells, which appeared to be glial, peaking at approximately 12 h post-seizure. Subsequently, a robust induction of SOCS-3 occurred in pyramidal and granule neurons, peaking at approximately 24 h. SOCS-2 displayed a relatively higher level of basal expression, particularly in CA3, and a mild and transient downregulation by 24 h. These findings corroborate the hypothesis that seizure-induced gp130 cytokines play a direct neuromodulatory role in the hippocampus. Since in our previous study we did not detect cytokine receptor expression in non-principal cells, it is unclear what elicits SOCS-3 expression in this population.

Association between -174 G/C polymorphism of interleukin-6 gene and alcoholism

OBJECTIVES

IL-6 plays the role as a physiological neuromodulator involved in dopaminergic, serotonergic and other neurotransmissions. The aim of the present association study was to examine the effect of the G/C -174 polymorphism of the IL-6 gene on disposition to alcoholism.

METHODS

We investigated the relationship between the G/C -174 polymorphism of the IL-6 gene and alcohol dependence in 281 alcoholics and 242 control subjects.

RESULTS

The significant difference in G allele frequency between alcoholic group (0.52) and control group (0.59) was found (P < 0.03).

CONCLUSION

To our knowledge, this is the first finding providing evidence for an association between alcoholism and the polymorphism of the IL-6 gene. The background of the relationship between the IL-6 gene and alcoholism is discussed.

Rapid method for culturing embryonic neuron-glial cell cocultures

A streamlined, simple technique for primary cell culture from E17 rat tissue is presented. In an attempt to standardize culturing methods for all neuronal cell types in the embryo, we evaluated a commercial medium without serum and used similar times for trypsinization and tested different surfaces for plating. In 1 day, using one method and a single medium, it is possible to produce robust E17 cultures of dorsal root ganglia (DRG), cerebellum, and enteric plexi. Allowing the endogenous glial cells to repopulate the cultures saves time compared with existing techniques, in which glial cells are added to cultures first treated with antimitotic agents. It also ensures that all the cells present in vivo will be present in the culture. Myelination commences after approximately 2 weeks in culture for dissociated DRG and 3-4 weeks in cerebellar cultures. In enteric cultures, glial wrapping of the enteric neurons is seen after 3 weeks (2 weeks in ascorbic acid), suggesting that basal lamina production is important even for glial ensheathment in the enteric nervous system. No overgrowth of fibroblasts or other nonneuronal cells was noted in any cultures, and myelination of the peripheral nervous system and central nervous system cultures was very robust.

The role of interleukin-6 in nociception and pain

IMPLICATIONS

That IL-6 is an interesting target in the study of pain is underscored by its biomolecular properties, its localization after experimental pain, and its modulating effect on pain after administration.

Neuroprotective effects of interleukin-6 on NMDA-induced rat retinal damage

This study shows that interleukin-6 (IL-6) combined with soluble interleukin-6 receptors (sIL-6R) modulates N-methyl-D-aspartate (NMDA)-induced retinal damage. Eyes pretreated with a combined injection of IL-6 and sIL-6R had NMDA administered into the vitreous cavity. Morphometric analysis and retrograde labeling analysis found that pretreatment with either IL-6 or sIL-6R alone did not bring about any neuroprotective effect. However, pretreatment with a combined administration of IL-6 and sIL-6R induced a significant neuroprotective effect against NMDA-induced retinal damage. Apoptotic changes in the retina were assessed by the TUNEL method. The results indicated that pretreatment with IL-6 combined with sIL-6R prevents NMDA-induced apoptosis. Western blotting studies demonstrated upregulation of gp130 expression in the NMDA-injected retina. Present studies suggest that IL-6 combined with sIL-6R provides a neuroprotective effect on NMDA-induced retinal damage.

Interleukin-6 protects anterior horn neurons from lethal virus-induced injury

We evaluated the role of interleukin-6 (IL-6) in neuronal injury after CNS infection. IL-6-/- and IL-6+/+ mice of resistant major histocompatibility complex (MHC) H-2b haplotype intracerebrally infected with Theiler's virus cleared the infection normally without development of viral persistence, lethal neuronal infection, or late phase demyelination. In contrast, infection of IL-6-/- mice on a susceptible H-2q haplotype resulted in frequent deaths and severe neurologic deficits within 2 weeks of infection as compared with infected IL-6+/+ H-2q littermate controls. Morphologic analysis demonstrated dramatic injury to anterior horn neurons of IL-6-/- H-2q mice at 12 d after infection. Infectious viral titers in the CNS (brain and spinal cord combined) were equivalent between IL-6-/- H-2q and IL-6+/+ H-2q mice. In contrast, more viral RNA was detected in the spinal cord of IL-6-/- mice compared with IL-6+/+ H-2q mice. Virus antigen was localized predominantly to anterior horn cells in infected IL-6-/- H-2q mice. IL-6 deletion did not affect the humoral response directed against virus, nor did it affect the expression of CD4, CD8, MHC class I, or MHC class II in the CNS. Importantly, IL-6 was expressed by astrocytes of infected IL-6+/+ mice but not in astrocytes of IL-6-/- mice or uninfected IL-6+/+ mice. Furthermore, expression of various chemokines was robust at 12 d after infection in both H-2b and H-2q IL-6-/- mice, indicating that intrinsic CNS inflammatory responses did not depend on the presence of IL-6. Finally, in vitro analysis of virus-induced death in neuroblastoma-spinal cord-34 motor neurons and primary anterior horn cell neurons showed that IL-6 exerted a neuroprotective effect. These data support the hypothesis that IL-6 plays a critical role in protecting specific populations of neurons from irreversible injury.

Delivery of hyper-interleukin-6 to the injured spinal cord increases neutrophil and macrophage infiltration and inhibits axonal growth

Cytokine growth factors of the interleukin (IL)-6 family have recently been shown to play an important role in central nervous system (CNS) development, repair, and inflammation. These cytokines, which interact via specific membrane receptors, share a signal-transducing receptor subunit, glycoprotein 130 (gp130). Gp130 is expressed by motoneurons in the gray matter of the rat spinal cord and by several brainstem nuclei that project to the spinal cord including the red, reticular, and vestibular nuclei. In this study, we examined whether stimulation of gp130 signaling, with the use of grafts of fibroblasts genetically modified to deliver the fusion protein, hyper-IL-6 (H-IL-6), which consists of the cytokine growth factor, IL-6, and its alpha receptor, would elicit growth of injured spinal cord axons. Particular emphasis was placed on examining the potentially competing effects of growth factor versus proinflammatory influences of H-IL-6 in the context of spinal cord injury. Our results demonstrated that grafts delivering H-IL-6 induce a sixfold increase in the number of neutrophils (P < 0.05) and a twofold increase in the areas of spinal tissue occupied by macrophages and activated microglia (P < 0.01) at the site of the spinal cord injury when compared with control grafts. Of note, this augmentation in inflammatory cell infiltration correlated with a significant twofold increase in lesion size (P < 0.05) and a fourfold reduction in axonal growth (P < 0.01) at the lesion site. Thus, potential neurotrophic properties of this cytokine family of growth factors must be balanced against their inflammatory properties when considering therapeutic application to CNS injury.

The effect of gp130 stimulation on glutamate-induced excitotoxicity in primary hippocampal neurons

Primary hippocampal neurons from newborn rats treated with glutamate showed clear excitotoxicity. This excitotoxicity could be reversed by treatment of the cells with cytokines of the interleukin-6 family. Stimulation of gp130 on hippocampal neurons resulted in tyrosine phosphorylation of STAT3 and activation of p42 and p44 MAP kinases. Receptors for the interleukin-6 type cytokines are active in membrane bound and soluble form. To address the question whether the neurotrophic effect of interleukin-6 type cytokines requires soluble cytokine receptors we used fusion proteins of interleukin-6 coupled to the soluble interleukin-6 receptor and ciliary neurotrophic factor coupled to the soluble ciliary neurotrophic factor receptor. Ciliary neurotrophic factor was as active as the cytokine-receptor fusion protein, indicating that hippocampal neurons express ciliary neurotrophic factor receptor on the cell surface. In contrast, interleukin-6 was only active at very high concentrations whereas the fusion protein of interleukin-6 coupled to the soluble interleukin-6 receptor (Hyper-IL-6) exhibited high neurotrophic activity at the same concentrations as ciliary neurotrophic factor. These data indicate that interleukin-6 receptor expression is very low on hippocampal neurons and that gp130 stimulation can be used to rescue hippocampal neurons from excitotoxicity.

Differential response of neuronal cells to a fusion protein of ciliary neurotrophic factor/soluble CNTF-receptor and leukemia inhibitory factor

Ciliary neurotrophic factor (CNTF) displays neurotrophic activities on motor neurons and neural cell populations both in vivo and in vitro. On target cells lacking intrinsic expression of specific receptor alpha subunits cytokines of the IL-6 family only act in the presence of their specific agonistic soluble receptors. Here, we report the construction and expression of a CNTF/soluble CNTF-receptor (sCNTF-R) fusion protein (Hyper-CNTF) with enhanced biological activity on cells expressing gp130 and leukemia inhibitory factor receptor (LIF-R), but not membrane-bound CNTF-R. At the cDNA level, the C-terminus of the extracellular domain of human CNTF-R (amino acids 1-346) was linked via a single glycine residue to the N-terminus of human CNTF (amino acids 1-186). Recombinant Hyper-CNTF protein was expressed in COS-7 cells. Hyper-CNTF efficiently induced dose-dependent STAT3 phosphorylation and proliferation of BAF-3 cells stably transfected with gp130 and LIF-R cDNAs. While on BAF3/gp130/LIF-R cells, Hyper-CNTF and LIF exhibited similar biological responses, the activity of Hyper-CNTF on pheochromocytoma cells (PC12 cells) was quite distinct from that of LIF. In contrast to LIF, Hyper-CNTF stimulated neurite outgrowth of PC12 cells in a time- and dose-dependent manner correlating with the ability to phosphorylate MAP kinases. These data indicate that although LIF and Hyper-CNTF use the same heterodimeric receptor complex of gp130 and LIFR, only Hyper-CNTF induces neuronal differentiation. The therapeutic potential of Hyper-CNTF as a superagonistic neurotrophin is discussed.

Effects of IL-1beta, IL-6 or LIF on rat sensory neurons co-cultured with fibroblast-like cells

Inflammation may affect the local presence of sensory nerve fibers in situ and inflammatory mediators influence sensory neurons in vitro. In the present study we have investigated effects of the cytokines interleukin-1beta (IL-1beta, interleukin-6 (IL-6), and leukemia inhibitory factor (LIF) on survival of and neurite growth from neonatal rat sensory neurons co-cultured with fibroblast-like cells prepared from neonatal rat skin (sFLCs) or perichondrium (pFLCs). The results showed that both FLC types expressed receptors for all three cytokines. Five ng/ml of either cytokine, but not lower or higher concentrations, supported survival of DRG neurons co-cultured with sFLCs. Neuronal survival was also enhanced by addition of the soluble IL-6 receptor (rsIL-6R) with or without IL-6. In co-cultures with pFLCs neuronal survival was promoted by IL-6, increasing with cytokine concentration. Addition of rsIL-6R without IL-6 did also stimulate neuronal survival. The growth of neurites from DRG neurons co-cultured with sFLCs was stimulated by 0.5 ng/ml LIF, unaffected by 5 ng/ml LIF and inhibited by 50 ng/ml LIF. Considering DRG neurons co-cultured with pFLCs, 50 ng/ml of either of the three cytokines, as well as rsIL-6R conditioned medium, stimulated neurite outgrowth. Some of the cytokine effects observed were reduced by application of antibodies against nerve growth factor (NGF). We conclude that that the cytokines examined affect DRG neurons in terms of survival or neuritogenesis, that the effects are influenced by cytokine concentration and the origin of the FLCs and that some of the effects are indirect, probably being mediated by factors released from FLCs.

Neuroprotective effect of interleukin-6 and IL6/IL6R chimera in the quinolinic acid rat model of Huntington's syndrome

Ciliary neurotrophic factor prevents behavioural deficits and striatal degeneration in rat and primate models of Huntington's disease. Interleukin-6, another member of the cytokine family, and the chimeric molecule (IL6/IL6R) in which interleukin-6 and its soluble receptor are fused, have been shown to exert trophic action on various neuronal populations in the central nervous system. Therefore, we investigated the neuroprotective effect of these two molecules in the quinolinic acid model of Huntington's disease. LacZ-, interleukin-6- and IL6/IL6R-expressing lentiviral vectors were stereotaxically injected into the striatum of Wistar rats. Three weeks later the animals were lesioned through the intrastriatal injection of 180 nmol of quinolinic acid. The extent of the striatal damage was significantly diminished in the rats that had been treated with interleukin-6 or IL6/IL6R. The neuroprotective effect was, however, more pronounced with the IL6/IL6R chimera than with interleukin-6 as indicated by the volume of the lesions (38.6 +/- 10% in the IL6/IL6R group, 63.3 +/- 3.6% in the IL-6 group and 84.3 +/-2.9% in the control group). Quantitative analysis of striatal interneurons further demonstrated that the IL6/IL6R chimera is more neuroprotective than IL-6 on ChAT- and NADPH-d-immunoreactive neurons. These results suggest that the IL6/IL6R chimera is a potential treatment for Huntington's disease.

Factors controlling axonal and dendritic arbors

The sculpting and maintenance of axonal and dendritic arbors is largely under the control of molecules external to the cell. These factors include both substratum-associated and soluble factors that can enhance or inhibit the outgrowth of axons and dendrites. A large number of factors that modulate axonal outgrowth have been identified, and the first stages of the intracellular signaling pathways by which they modify process outgrowth have been characterized. Relatively fewer factors and pathways that affect dendritic outgrowth have been described. The factors that affect axonal arbors form an incompletely overlapping set with those that affect dendritic arbors, allowing selective control of the development and maintenance of these critical aspects of neuronal morphology.

Continuous interleukin-6 application in vivo via macroencapsulation of interleukin-6-expressing COS-7 cells induces massive gliosis

The inflammatory cytokine interleukin-6 (IL-6) was found in senile plaques of Alzheimer's patients and might be involved in the pathology of Parkinson's disease and multiple sclerosis. Interestingly, an astocytosis is also found in these neurodegenerative disorders. To evaluate the direct effects of IL-6 in vivo on glial cells, we created a new in vivo model. IL-6 and mock-transfected (control group) COS-7 cells were encapsulated in a poly-acryl-nitril membrane for implantation into the rat striatum. Afterward, the host immune reaction to the membrane without encapsulated cells and the biological action of IL-6-producing capsules was evaluated. Animals with an implanted membrane without cells showed a moderate astrocytosis 5 days after the operation. Furthermore, microglia and T-cells could be detected and after 30 days the astrocytosis decreased to a small layer around the membrane. In comparison to the control group, which received a sham operation, our results demonstrate that the response of glial cells is caused by the mechanical damage of the surgical procedure itself rather than due to the introduced membrane material. In contrast, we found a massive proliferation and activation of astrocytes and microglia after 10 days by IL-6-secreting capsules, indicating that IL-6 is involved in the induction of gliosis. Control animals that received encapsulated mock-transfected COS-7 cells showed only a weak response. These data point to an involvement of IL-6 in the proliferation and activation of glial cells as seen in neurodegenerative disorders.