Role of the JAKs/STATs pathway in the intracellular calcium changes induced by interleukin-6 in hippocampal neurons

JAK-STAT signaling in inflammation and stress-related diseases: implications for therapeutic interventions

The Janus kinase-signal transducer and transcription activator pathway (JAK-STAT) serves as a cornerstone in cellular signaling, regulating physiological and pathological processes such as inflammation and stress. Dysregulation in this pathway can lead to severe immunodeficiencies and malignancies, and its role extends to neurotransduction and pro-inflammatory signaling mechanisms. Although JAK inhibitors (Jakinibs) have successfully treated immunological and inflammatory disorders, their application has generally been limited to diseases with similar pathogenic features. Despite the modest expression of JAK-STAT in the CNS, it is crucial for functions in the cortex, hippocampus, and cerebellum, making it relevant in conditions like Parkinson's disease and other neuroinflammatory disorders. Furthermore, the influence of the pathway on serotonin receptors and phospholipase C has implications for stress and mood disorders. This review expands the understanding of JAK-STAT, moving beyond traditional immunological contexts to explore its role in stress-related disorders and CNS function. Recent findings, such as the effectiveness of Jakinibs in chronic conditions such as rheumatoid arthritis, expand their therapeutic applicability. Advances in isoform-specific inhibitors, including filgotinib and upadacitinib, promise greater specificity with fewer off-target effects. Combination therapies, involving Jakinibs and monoclonal antibodies, aiming to enhance therapeutic specificity and efficacy also give great hope. Overall, this review bridges the gap between basic science and clinical application, elucidating the complex influence of the JAK-STAT pathway on human health and guiding future interventions.

Janus kinase inhibitors are potential therapeutics for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a poorly treated multifactorial neurodegenerative disease associated with multiple cell types and subcellular organelles. As with other multifactorial diseases, it is likely that drugs will need to target multiple disease processes and cell types to be effective. We review here the role of Janus kinase (JAK)/Signal transducer and activator of transcription (STAT) signalling in ALS, confirm the association of this signalling with fundamental ALS disease processes using the BenevolentAI Knowledge Graph, and demonstrate that inhibitors of this pathway could reduce the ALS pathophysiology in neurons, glia, muscle fibres, and blood cells. Specifically, we suggest that inhibition of the JAK enzymes by approved inhibitors known as Jakinibs could reduce STAT3 activation and modify the progress of this disease. Analysis of the Jakinibs highlights baricitinib as a suitable candidate due to its ability to penetrate the central nervous system and exert beneficial effects on the immune system. Therefore, we recommend that this drug be tested in appropriately designed clinical trials for ALS.

Prolonged STAT1 activation in neurons drives a pathological transcriptional response

Neurons require physiological IFN-γ signaling to maintain central nervous system (CNS) homeostasis, however, pathological IFN-γ signaling can cause CNS pathologies. The downstream signaling mechanisms that cause these drastically different outcomes in neurons has not been well studied. We hypothesized that different levels of IFN-γ signaling in neurons results in differential activation of its downstream transcription factor, signal transducer and activator of transduction 1 (STAT1), causing varying outcomes. Using primary cortical neurons, we showed that physiological IFN-γ elicited brief and transient STAT1 activation, whereas pathological IFN-γ induced prolonged STAT1 activation, which primed the pathway to be more responsive to a subsequent IFN-γ challenge. This is an IFN-γ specific response, as other IFNs and cytokines did not elicit such STAT1 activation nor priming in neurons. Additionally, we did not see the same effect in microglia or astrocytes, suggesting this non-canonical IFN-γ/STAT1 signaling is unique to neurons. Prolonged STAT1 activation was facilitated by continuous janus kinase (JAK) activity, even in the absence of IFN-γ. Finally, although IFN-γ initially induced a canonical IFN-γ transcriptional response in neurons, pathological levels of IFN-γ caused long-term changes in synaptic pathway transcripts. Overall, these findings suggest that IFN-γ signaling occurs via non-canonical mechanisms in neurons, and differential STAT1 activation may explain how neurons have both homeostatic and pathological responses to IFN-γ signaling.

Neuroprotective compounds from marine invertebrates

Background

Neuroinflammation is a key pathological feature of a wide variety of neurological disorders, including Parkinson’s, multiple sclerosis, Alzheimer’s, and Huntington’s disease. While current treatments for these disorders are primarily symptomatic, there is a growing interest in developing new therapeutics that target the underlying neuroinflammatory processes.

Main body

Marine invertebrates, such as coral, sea urchins, starfish, sponges, and sea cucumbers, have been found to contain a wide variety of biologically active compounds that have demonstrated potential therapeutic properties. These compounds are known to target various key proteins and pathways in neuroinflammation, including 6-hydroxydopamine (OHDH), caspase-3 and caspase-9, p-Akt, p-ERK, p-P38, acetylcholinesterase (AChE), amyloid-β (Aβ), HSF-1, α-synuclein, cellular prion protein, advanced glycation end products (AGEs), paraquat (PQ), and mitochondria DJ-1.

Short conclusion

This review focuses on the current state of research on the neuroprotective effects of compounds found in marine invertebrates and the potential therapeutic implications of these findings for treating neuroinflammatory disorders. We also discussed the challenges and limitations of using marine-based compounds as therapeutics, such as sourcing and sustainability concerns, and the need for more preclinical and clinical studies to establish their efficacy and safety.

Graphical abstract

Interleukin-6 in retinal diseases: From pathogenesis to therapy

Interleukin-6 (IL-6) is a pleiotropic cytokine that participates in immunomodulation, inflammation, increases vascular permeability, hematopoiesis, and stimulates cell proliferation, among other biological processes. It exerts effects primarily through the classic and trans-signaling pathways. Many studies have demonstrated that IL-6 plays a critical role in the development of retinal diseases including diabetic retinopathy, uveitis, age-related macular degeneration, glaucoma, retinal vein occlusion, central serous chorioretinopathy and proliferative vitreoretinopathy. Thus, the progressive development of drugs targeting IL-6 and IL-6 receptor may play a role in the treatment of multiple retinal diseases. In this article, we comprehensively review the IL-6's biological functions of and its mechanisms in the pathogenesis of various retinal diseases. Furthermore, we summarize the drugs targeting IL-6 and its receptor and prospect their potential application in retinal diseases, hoping to provide new ideas for the treatment of retinal diseases.

Extracellular CIRP Induces Calpain Activation in Neurons via PLC-IP3-Dependent Calcium Pathway

Abnormal calcium homeostasis, activation of protease calpain, generation of p25 and hyperactivation of cyclin-dependent kinase 5 (Cdk5) have all been implicated in the pathogenesis of neurogenerative diseases including Alzheimer's disease. We have recently shown that extracellular cold-inducible RNA-binding protein (eCIRP) induces Cdk5 activation via p25. However, the precise molecular mechanism by which eCIRP regulates calcium signaling and calpain remains to be addressed. We hypothesized that eCIRP regulates p25 via Ca2+-dependent calpain activation. eCIRP increased calpain activity and decreased the endogenous calpain inhibitor calpastatin in Neuro 2a (N2a) cells. Calpain inhibition with calpeptin attenuated eCIRP-induced calpain activity and p25. eCIRP specifically upregulated cytosolic calpain 1, and calpain 1 silencing attenuated the eCIRP-induced increase in p25. eCIRP stimulation increased cytosolic free Ca2+, especially in hippocampal neuronal HT22 cells, which was attenuated by the eCIRP inhibitor Compound 23 (C23). Endoplasmic reticulum (ER) inositol 1,4,5-trisphosphate receptor (IP3R) inhibition using 2-aminoethoxy-diphenyl-borate or xestospongin-C (X-C), interleukin-6 receptor alpha (IL-6Rα)-neutralization, and phospholipase C (PLC) inhibition with U73122 attenuated eCIRP-induced Ca2+ increase, while Ca2+ influx across the plasma membrane remained unaffected by eCIRP. Finally, C23, IL-6Rα antibody, U73122 and X-C attenuated eCIRP-induced p25 in HT-22 cells. In conclusion, the current study uncovers eCIRP-triggered Ca2+ release from ER stores in an IL-6Rα/PLC/IP3-dependent manner as a novel molecular mechanism underlying eCIRP's induction of Cdk5 activity and potential involvement in neurodegeneration.

Paths to hippocampal damage in neuromyelitis optica spectrum disorders

AIMS

Many patients with neuromyelitis optica spectrum disorders (NMOSD) suffer from cognitive impairment affecting memory, processing speed and attention and suffer from depressive symptoms. Because some of these manifestations could trace back to the hippocampus, several magnetic resonance imaging (MRI) studies have been performed in the past, with a number of groups describing volume loss of the hippocampus in NMOSD patients, whereas others did not observe such changes. Here, we addressed these discrepancies.

METHODS

We performed pathological and MRI studies on the hippocampi of NMOSD patients, combined with detailed immunohistochemical analysis of hippocampi from experimental models of NMOSD.

RESULTS

We identified different pathological scenarios for hippocampal damage in NMOSD and its experimental models. In the first case, the hippocampus was compromised by the initiation of astrocyte injury in this brain region and subsequent local effects of microglial activation and neuronal damage. In the second case, loss of hippocampal volume was seen by MRI in patients with large tissue-destructive lesions in the optic nerves or the spinal cord, and the pathological work-up of tissue derived from a patient with such lesions revealed subsequent retrograde neuronal degeneration affecting different axonal tracts and neuronal networks. It remains to be seen whether remote lesions and associated retrograde neuronal degeneration on their own are sufficient to cause extensive volume loss of the hippocampus, or whether they act in concert with small astrocyte-destructive, microglia-activating lesions in the hippocampus that escape detection by MRI, either due to their small size or due to the chosen time window for examination.

CONCLUSIONS

Different pathological scenarios can culminate in hippocampal volume loss in NMOSD patients.

Role of JAK-STAT and PPAR-Gamma Signalling Modulators in the Prevention of Autism and Neurological Dysfunctions

The Janus-kinase (JAK) and signal transducer activator of transcription (STAT) signalling pathways regulate gene expression and control various factors involved in normal physiological functions such as cell proliferation, neuronal development, and cell survival. JAK activation phosphorylates STAT3 in astrocytes and microglia, and this phosphorylation has been linked to mitochondrial damage, apoptosis, neuroinflammation, reactive astrogliosis, and genetic mutations. As a regulator, peroxisome proliferator-activated receptor gamma (PPAR-gamma), in relation to JAK-STAT signalling, prevents this phosphorylation and aids in the treatment of the above-mentioned neurocomplications. Changes in cellular signalling may also contribute to the onset and progression of autism. Thus, PPAR-gamma agonist upregulation may be associated with JAK-STAT signal transduction downregulation. It may also be responsible for attenuating neuropathological changes by stimulating SOCS3 or involving RXR or SMRT, thereby reducing transcription of the various cytokine proteins and genes involved in neuronal damage. Along with JAK-STAT inhibitors, PPAR-gamma agonists could be used as target therapeutic interventions for autism. This research-based review explores the potential involvement and mutual regulation of JAK-STAT and PPAR-gamma signalling in controlling multiple pathological factors associated with autism.

Is the JAK-STAT Signaling Pathway Involved in the Pathogenesis of Depression?

(1) Background: Only 60–70% of depressed patients respond to standard antidepressant treatments. Hence, it is essential to search for new, effective and safe therapies for unmet clinical needs of treatment-resistant depression (TRD). Agents targeting the components of the JAK-STAT signaling pathway have been shown to be relevant in immunology and are commonly used in the treatment of many hematological, rheumatological and dermatological diseases. The aim of this study was to investigate the role of elements of the JAK-STAT signaling pathway in the etiopathogenesis of depressive disorders. (2) Methods: A total of 290 subjects took part in the study (190 depressed patients, 100 healthy controls). Sociodemographic data were collected. The severity of depressive symptoms was assessed using the Hamilton Depression Rating Scale (HDRS). The gene expression at the mRNA protein levels of JAK (JAK1-JAK3) and STAT (STAT1-STAT5) was assessed by using RT-PCR and ELISA. (3) Results: Increased expression of JAK3 and decreased expression of STAT1 were observed in the group of depressed patients. (4) Conclusions: Further studies are necessary to determine whether moderation of the JAK-STAT signaling pathways is involved in the treatment of depression.

Calcium Ions Aggravate Alzheimer's Disease Through the Aberrant Activation of Neuronal Networks, Leading to Synaptic and Cognitive Deficits

Alzheimer’s disease (AD) is a neurodegenerative disease that is characterized by the production and deposition of β-amyloid protein (Aβ) and hyperphosphorylated tau, leading to the formation of β-amyloid plaques (APs) and neurofibrillary tangles (NFTs). Although calcium ions (Ca²⁺) promote the formation of APs and NFTs, no systematic review of the mechanisms by which Ca²⁺ affects the development and progression of AD has been published. Therefore, the current review aimed to fill the gaps between elevated Ca²⁺ levels and the pathogenesis of AD. Specifically, we mainly focus on the molecular mechanisms by which Ca²⁺ affects the neuronal networks of neuroinflammation, neuronal injury, neurogenesis, neurotoxicity, neuroprotection, and autophagy. Furthermore, the roles of Ca²⁺ transporters located in the cell membrane, endoplasmic reticulum (ER), mitochondria and lysosome in mediating the effects of Ca²⁺ on activating neuronal networks that ultimately contribute to the development and progression of AD are discussed. Finally, the drug candidates derived from herbs used as food or seasoning in Chinese daily life are summarized to provide a theoretical basis for improving the clinical treatment of AD.

Extracellular CIRP Activates the IL-6Rα/STAT3/Cdk5 Pathway in Neurons

Extracellular cold-inducible RNA-binding protein (eCIRP) stimulates microglial inflammation causing neuronal damage during ischemic stroke and is a critical mediator of alcohol-induced cognitive impairment. However, the precise role of eCIRP in mediating neuroinflammation remains unknown. In this study, we report that eCIRP activates neurotoxic cyclin-dependent kinase-5 (Cdk5)/p25 through the induction of IL-6Rα/STAT3 pathway in neurons. Amyloid β (Aβ)-mediated neuronal stress, which is associated with Alzheimer's disease, increased the levels of eCIRP released from BV2 microglial cells. The released eCIRP levels from BV2 cells increased 3.2-fold upon stimulation with conditioned medium from Neuro-2a (N2a) cells containing Aβ compared to control N2a supernatant in a time-dependent manner. Stimulation of N2a cells and primary neurons with eCIRP upregulated the neuronal Cdk5 activator p25 expression in a dose- and time-dependent manner. eCIRP directly induced neuronal STAT3 phosphorylation and p25 increase via its novel receptor IL-6Rα. Next, we showed using surface plasmon resonance that eCIRP-derived peptide C23 inhibited the binding of eCIRP to IL-6Rα at 25 μM, with a 40-fold increase in equilibrium dissociation constant (K_d) value (from 8.08 × 10^-8 M to 3.43 × 10^-6 M), and completely abrogated the binding at 50 μM. Finally, C23 reversed the eCIRP-induced increase in neuronal STAT3 phosphorylation and p25 levels. In conclusion, the current study demonstrates that the upregulation of neuronal IL-6Rα/STAT3/Cdk5 pathway is a key mechanism of eCIRP's role in neuroinflammation and that C23 as a potent inhibitor of this pathway has translational potential in neurodegenerative pathologies controlled by eCIRP.

Potential Role of Extracellular CIRP in Alcohol-Induced Alzheimer's Disease

Alzheimer's disease (AD) is the sixth leading cause of death in the USA and the most common form of neurodegenerative dementia. In AD, microtubule-associated protein tau becomes pathologically phosphorylated and aggregated, leading to neurodegeneration and the cognitive deficits that characterize the disease. Prospective studies have shown that frequent and heavy alcohol drinking is linked to early onset and increased severity of AD. The precise mechanisms of how alcohol leads to AD, however, remain poorly understood. We have shown that extracellular cold-inducible RNA-binding protein (eCIRP) is a critical mediator of memory impairment induced by exposure to binge-drinking levels of alcohol, leading us to reason that eCIRP may be a key player in the relationship between alcohol and AD. In this review, we first discuss the mechanisms by which alcohol promotes AD. We then review eCIRP's role as a critical mediator of acute alcohol intoxication-induced neuroinflammation and cognitive impairment. Next, we explore the potential contribution of eCIRP to the development of alcohol-induced AD by targeting tau phosphorylation. We also consider the effects of eCIRP on neuronal death and neurogenesis linking alcohol with AD. Finally, we highlight the importance of further studying eCIRP as a critical molecular mechanism connecting acute alcohol intoxication, neuroinflammation, and tau phosphorylation in AD along with the potential of therapeutically targeting eCIRP as a new strategy to attenuate alcohol-induced AD.

Defective interaction of mutant calreticulin and SOCE in megakaryocytes from patients with myeloproliferative neoplasms

Approximately one-fourth of patients with essential thrombocythemia or primary myelofibrosis carry a somatic mutation of the calreticulin gene (CALR), the gene encoding for calreticulin. A 52-bp deletion (type I mutation) and a 5-bp insertion (type II mutation) are the most frequent genetic lesions. The mechanism(s) by which a CALR mutation leads to a myeloproliferative phenotype has been clarified only in part. We studied the interaction between calreticulin and store-operated calcium (Ca2+) entry (SOCE) machinery in megakaryocytes (Mks) from healthy individuals and from patients with CALR-mutated myeloproliferative neoplasms (MPNs). In Mks from healthy subjects, binding of recombinant human thrombopoietin to c-Mpl induced the activation of signal transducer and activator of transcription 5, AKT, and extracellular signal-regulated kinase 1/2, determining inositol triphosphate-dependent Ca2+ release from the endoplasmic reticulum (ER). This resulted in the dissociation of the ER protein 57 (ERp57)-mediated complex between calreticulin and stromal interaction molecule 1 (STIM1), a protein of the SOCE machinery that leads to Ca2+ mobilization. In Mks from patients with CALR-mutated MPNs, defective interactions between mutant calreticulin, ERp57, and STIM1 activated SOCE and generated spontaneous cytosolic Ca2+ flows. In turn, this resulted in abnormal Mk proliferation that was reverted using a specific SOCE inhibitor. In summary, the abnormal SOCE regulation of Ca2+ flows in Mks contributes to the pathophysiology of CALR-mutated MPNs. In perspective, SOCE may represent a new therapeutic target to counteract Mk proliferation and its clinical consequences in MPNs.

Attenuation of diabetic retinopathy and neuropathy by resveratrol: Review on its molecular mechanisms of action

Resveratrol is an important phenolic phytochemical from the therapeutic perspective. It has therapeutic impacts over wide range of diseases, especially the ones related to oxidative stress. Resveratrol, being primarily a potent anti-oxidant phytochemical, has significant impact against major diseases as inflammatory disorders, diabetes, and cancer. In the current review article, we intend to highlight the molecular aspects of the mechanism of action of resveratrol against major diabetic implications, namely, retinopathy and neuropathy. Both these diabetic implications are among the first fallouts of chronic hyperglycaemia. Resveratrol, via multiple molecular pathways, tend to attenuate and reverse these deformity and other disease-causing implications.

Postoperative 24-h Acute Sleep Deprivation Improves Learning and Memory Through Inhibition of Tau Phosphorylation in the Hippocampal Neurons of Splenectomized Rats

PURPOSE

As tau pathology is involved in impaired postoperative learning and memory in rats, we attempted to identify the possible mechanisms by which tau pathology affects postoperative sleep deprivation.

METHODS

Adult male Sprague-Dawley rats were randomly assigned into six groups as follows: the Control group, Anaesthesia group, Surgery group, Sleep deprivation (SD) group: 24-h SD with the modified multiple platform method (MMPM), Anaesthesia and SD (ASD) group, and Surgery and SD (SSD) group. Tau396 and FOXQ1 protein expression levels in the hippocampal neurons of all groups were analysed. Changes following co-culture of hippocampal neurons with IL-6 were detected by flow cytometry.

RESULTS

Twenty-four hours of acute SD decreased the error scores on postoperative day 5 in the ASD and SSD groups compared with the Anaesthesia and Surgery groups. Compared with the tau levels in the Control group, tau levels in the Anaesthesia and Surgery groups were increased, but SD decreased the expression of tau in the ASD and SSD groups. The expression levels of tau and FOXQ1 were inversely regulated. When hippocampal neurons were co-cultured with IL-6, the same changes were observed.

CONCLUSION

Postoperative 24-h acute SD improves learning and memory through inhibition of tau phosphorylation and increases IL-6-induced expression of FOXQ1 in the hippocampal neurons of splenectomized rats.

Ciliary neurotrophic factor signaling in the rat orbitofrontal cortex ameliorates stress-induced deficits in reversal learning

Deficits in cognitive flexibility, i.e. the ability to modify behavior in response to changes in the environment, are present in several psychiatric disorders and are often refractory to treatment. However, improving treatment response has been hindered by a lack of understanding of the neurobiology of cognitive flexibility. Using a rat model of chronic stress (chronic intermittent cold stress, CIC) that produces selective deficits in reversal learning, a form of cognitive flexibility dependent on orbitofrontal cortex (OFC) function, we have previously shown that JAK2 signaling is required for optimal reversal learning. In this study we explore the molecular basis of those effects. We show that, within the OFC, CIC stress reduces the levels of phosphorylated JAK2 and of ciliary neurotrophic factor (CNTF), a promoter of neuronal survival and an activator of JAK2 signaling, and that neutralizing endogenous CNTF with an intra-OFC microinjection of a specific antibody is sufficient to produce reversal-learning deficits similar to stress. Intra-OFC delivery of recombinant CNTF to CIC-stressed rats, at a dose that induces JAK2 and Akt but not STAT3 or ERK, ameliorates reversal-learning deficits, and Akt blockade prevents the positive effects of CNTF. Further analysis revealed that CNTF may exert its beneficial effects by inhibiting GSK3β, a substrate of Akt and a regulator of protein degradation. We also revealed a novel mechanism of CNTF action through modulation of p38/Mnk1/eIF4E signaling. This cascade controls translation of select mRNAs, including those encoding several plasticity-related proteins. Thus, we suggest that CNTF-driven JAK2 signaling corrects stress-induced reversal learning deficits by modulating the steady-state levels of plasticity-related proteins in the OFC.

Ethanol and Cytokines in the Central Nervous System

The innate immune system plays a critical role in the ethanol-induced neuroimmune response in the brain. Ethanol initiates the innate immune response via activation of the innate immune receptors Toll-like receptors (TLRs, e.g., TLR4, TLR3, TLR7) and NOD-like receptors (inflammasome NLRs) leading to a release of a plethora of chemokines and cytokines and development of the innate immune response. Cytokines and chemokines can have pro- or anti-inflammatory properties through which they regulate the immune response. In this chapter, we will focus on key cytokines (e.g., IL-1, IL-6, TNF-α) and chemokines (e.g., MCP-1/CCL2) that mediate the ethanol-induced neuroimmune responses. In this regard, we will use IL-1β, as an example cytokine, to discuss the neuromodulatory properties of cytokines on cellular properties and synaptic transmission. We will discuss their involvement through a set of evidence: (1) changes in gene and protein expression following ethanol exposure, (2) association of gene polymorphisms (humans) and alterations in gene expression (animal models) with increased alcohol intake, and (3) modulation of alcohol-related behaviors by transgenic or pharmacological manipulations of chemokine and cytokine systems. Over the last years, our understanding of the molecular mechanisms mediating cytokine- and chemokine-dependent regulation of immune responses has advanced tremendously, and we review evidence pointing to cytokines and chemokines serving as neuromodulators and regulators of neurotransmission.

Mechanism of the JAK2/STAT3-CAV-1-NR2B signaling pathway in painful diabetic neuropathy

PURPOSE

The aim of the present study was to further elucidate the role of JAK2/STAT3-CAV-1-NR2B on painful diabetic neuropathy.

METHODS

In vivo, the mechanical withdrawal threshold and thermal withdrawal latency were measured to evaluate neuropathic pain behaviors (n= 8), while western blot (n= 5) and an immunofluorescence double staining experiment (n= 6) were performed to understand the molecular mechanism. In vitro, the individual culture of BV2 mouse microglia cell lines, the co-culture of BV2 mouse microglia cell lines and PC12 rat neuron cell lines, and western blot analysis were performed to understand the molecular mechanism between microglia and neurons.

RESULTS

The expression of p-JAK2, p-STAT3, t-CAV-1, and p-NR2B was upregulated in the dorsal horn of DNP rats throughout the experiment. Through the immunofluorescence double staining experiment, it was found that p-STAT3 was mainly expressed in activated microglia, and this condition can be stably maintained for approximately 2 weeks after the establishment of the DNP model. The intrathecal injection of JAK2 inhibitor AG490 can relieve the abnormal expression of p-JAK2, p-STAT3, t-CAV-1, and p-NR2B, and relieve pain. The remission of AG490 began on the third day, and it could be stably sustained for 14 days. In vitro high-glucose induced the activation of p-STAT3 in microglia, thereby upregulating the expression of p-CAV-1 and p-NR2B in neurons in the co-culture system. JAK2 inhibitor AG490 can alleviate the abnormal expression of these proteins in the JAK2/STAT3-CAV-1-NR2B signaling pathway in vitro.

CONCLUSIONS

Microglial JAK2/STAT3 signaling probably contributes to neuropathic pain by activating the CAV-1-NR2B pathway.

Glucagon-Like Peptide-1-, but not Growth and Differentiation Factor 15-, Receptor Activation Increases the Number of Interleukin-6-Expressing Cells in the External Lateral Parabrachial Nucleus

Interleukin (IL)-6 in the hypothalamus and hindbrain is an important downstream mediator of suppression of body weight and food intake by glucagon-like peptide-1 (GLP-1) receptor stimulation. CNS GLP-1 is produced almost exclusively in prepro-glucagon neurons in the nucleus of the solitary tract. These neurons innervate energy balance-regulating areas, such as the external lateral parabrachial nucleus (PBNel); essential for induction of anorexia. Using a validated novel IL-6-reporter mouse strain, we investigated the interactions in PBNel between GLP-1, IL-6, and calcitonin gene-related peptide (CGRP, a well-known mediator of anorexia). We show that PBNel GLP-1R-containing cells highly (to about 80%) overlap with IL-6-containing cells on both protein and mRNA level. Intraperitoneal administration of a GLP-1 analogue exendin-4 to mice increased the proportion of IL-6-containing cells in PBNel 3-fold, while there was no effect in the rest of the lateral parabrachial nucleus. In contrast, injections of an anorexigenic peptide growth and differentiation factor 15 (GDF15) markedly increased the proportion of CGRP-containing cells, while IL-6-containing cells were not affected. In summary, GLP-1R are found on IL-6-producing cells in PBNel, and GLP-1R stimulation leads to an increase in the proportion of cells with IL-6-reporter fluorescence, supporting IL-6 mediation of GLP-1 effects on energy balance.

TRIM8-driven transcriptomic profile of neural stem cells identified glioma-related nodal genes and pathways

BACKGROUND

We recently reported TRIM8, encoding an E3 ubiquitin ligase, as a gene aberrantly expressed in glioblastoma whose expression suppresses cell growth and induces a significant reduction of clonogenic potential in glioblastoma cell lines.

METHODS

we provided novel insights on TRIM8 functions by profiling the transcriptome of TRIM8-expressing primary mouse embryonal neural stem cells by RNA-sequencing and bioinformatic analysis. Functional analysis including luciferase assay, western blot, PCR arrays, Real time quantitative PCR were performed to validate the transcriptomic data.

RESULTS

Our study identified enriched pathways related to the neurotransmission and to the central nervous system (CNS) functions, including axonal guidance, GABA receptor, Ephrin B, synaptic long-term potentiation/depression, and glutamate receptor signalling pathways. Finally, we provided additional evidence about the existence of a functional interactive crosstalk between TRIM8 and STAT3.

CONCLUSIONS

Our results substantiate the role of TRIM8 in the brain functions through the dysregulation of genes involved in different CNS-related pathways, including JAK-STAT.

GENERAL SIGNIFICANCE

This study provides novel insights on the physiological TRIM8 function by profiling for the first time the primary Neural Stem Cell over-expressing TRIM8 by using RNA-Sequencing methodology.

Glial contributions to neurodegeneration in tauopathies

Tauopathies are a broad set of neurodegenerative dementias characterized by aggregation of the tau protein into filamentous inclusions that can be found in neurons and glial cells. Activated microglia, astrocytes and elevated levels of proinflammatory molecules are also pathological hallmarks that are found in brain regions affected by tau pathology. There has been abundant research in recent years to understand the role of gliosis and neuroinflammation in neurodegenerative diseases, particularly in Alzheimer's disease (AD) which is the most common form of dementia. AD is a tauopathy characterized by both extracellular amyloid-β plaques in addition to intracellular neurofibrillary tangles and neuropil threads containing aggregated tau protein. Accumulating evidence suggests that neuroinflammation offers a possible mechanistic link between these pathologies. Additionally, there appears to be a role for neuroinflammation in aggravating tau pathology and neurodegeneration in tauopathies featuring tau deposits as the predominant pathological signature. In this review, we survey the literature regarding inflammatory mechanisms that may impact neurodegeneration in AD and related tauopathies. We consider a physical role for microglia in the spread of tau pathology as well as the non-cell autonomous effects of secreted proinflammatory cytokines, specifically interleukin 1 beta, interleukin 6, tumor necrosis factor alpha and complement proteins. These molecules appear to have direct effects on tau pathophysiology and overall neuronal health. They also indirectly impact neuronal homeostasis by altering glial function. We conclude by proposing a complex role for gliosis and neuroinflammation in accelerating the progression of AD and other tauopathies.

A Gap Junction Protein, Inx2, Modulates Calcium Flux to Specify Border Cell Fate during Drosophila oogenesis

Intercellular communication mediated by gap junction (GJ) proteins is indispensable during embryogenesis, tissue regeneration and wound healing. Here we report functional analysis of a gap junction protein, Innexin 2 (Inx2), in cell type specification during Drosophila oogenesis. Our data reveal a novel involvement of Inx2 in the specification of Border Cells (BCs), a migratory cell type, whose identity is determined by the cell autonomous STAT activity. We show that Inx2 influences BC fate specification by modulating STAT activity via Domeless receptor endocytosis. Furthermore, detailed experimental analysis has uncovered that Inx2 also regulates a calcium flux that transmits across the follicle cells. We propose that Inx2 mediated calcium flux in the follicle cells stimulates endocytosis by altering Dynamin (Shibire) distribution which is in turn critical for careful calibration of STAT activation and, thus for BC specification. Together our data provide unprecedented molecular insights into how gap junction proteins can regulate cell-type specification.

Gap junction mediated intercellular communication modulates several processes during development, morphogenesis and normal tissue homeostasis. While gap junction proteins play an important role during intercellular communication, the underlying molecular mechanism(s) as to how they regulate diverse signaling cascades are unclear. By employing the Drosophila melanogaster oogenesis model we have characterized the role of gap junction protein, Innexin 2 (Inx2), in cell fate specification during Drosophila oogenesis. Our data demonstrate that loss of inx2 affects border cell specification. Border cells are a small group of 6–8 follicle cells that acquire migratory fate in response to the activation of JAK-STAT signaling. We show that perturbing Inx2 levels in the follicle cells inhibits JAK-STAT signaling thereby adversely influencing border cell fate specification. Using live cell imaging and molecular genetic analysis, we have elucidated the molecular mechanism underlying Inx2 function in this process. We show that Inx2 mediates inter-follicular calcium flux that is critical for border cell fate determination. Furthermore, our observations indicate that Inx2 regulates Domeless receptor internalization possibly via influencing distribution of Drosophila Dynamin, Shibire in the follicle cells. Taken together these results suggest a functional link between Inx2, calcium flux and receptor endocytosis during border cell fate specification in Drosophila oogenesis.

Preproglucagon neurons in the hindbrain have IL-6 receptor-α and show Ca2+ influx in response to IL-6

Neuronal circuits in the hypothalamus and hindbrain are of importance for control of food intake, energy expenditure, and fat mass. We have recently shown that treatment with exendin-4 (Ex-4), an analog of the proglucagon-derived molecule glucagon-like peptide 1 (GLP-1), markedly increases mRNA expression of the cytokine interleukin-6 (IL-6) in the hypothalamus and hindbrain and that this increase partly mediates the suppression of food intake and body weight by Ex-4. Endogenous GLP-1 in the central nervous system (CNS) is produced by preproglucagon (PPG) neurons of the nucleus of the solitary tract (NTS) in the hindbrain. These neurons project to various parts of the brain, including the hypothalamus. Outside the brain, IL-6 stimulates GLP-1 secretion from the gut and pancreas. In this study, we aim to investigate whether IL-6 can affect GLP-1-producing PPG neurons in the nucleus of the solitary tract (NTS) in mouse hindbrain via the ligand binding part of the IL-6 receptor, IL-6 receptor-α (IL-6Rα). Using immunohistochemistry, we found that IL-6Rα was localized on PPG neurons of the NTS. Recordings of these neurons in GCaMP3/GLP-1 reporter mice showed that IL-6 enhances cytosolic Ca(2+) concentration in neurons capable of expressing PPG. We also show that the Ca(2+) increase originates from the extracellular space. Furthermore, we found that IL-6Rα was localized on cells in the caudal hindbrain expressing immunoreactive NeuN (a neuronal marker) or CNP:ase (an oligodendrocyte marker). In summary, IL-6Rα is present on PPG neurons in the NTS, and IL-6 can stimulate these cells by increasing influx of Ca(2+) to the cytosol from the extracellular space.

Trans-resveratrol attenuates high fatty acid-induced P2X7 receptor expression and IL-6 release in PC12 cells: possible role of P38 MAPK pathway

Diabetic neuropathy (DNP) is the most common chronic complication of diabetes. Elevated free fatty acids (FFAs) have been recently recognized as major causes of inflammation and are relevant to the functional changes of nerve system in diabetes. Trans-resveratrol (RESV), a polyphenolic natural compound, has long been acknowledged to have anti-inflammation properties and may exert a neuroprotective effect on neuronal damage in diabetes, while the mechanisms underlying are largely unknown. Our previous study on differential PC12 cells cultured with high FFAs has shown chronic FFAs overload increased PC12 interleukin (IL)-6 release mediated by P2X7 receptor, a ligand-gated cation channel activated by extracellular adenosine triphosphate (ATP); a high FFA-induced activation of P38 mitogen-activated protein kinase (MAPK) pathway was pointed to be a potential underlying mechanism. Data from this study indicated that RESV, in a dose-dependent manner, reduced high FFA-induced IL-6 release by impeding the activation of P2X7 receptor, as shown by the results that both high FFA-elevated P2X7 receptor messenger RNA (mRNA) and protein expression as well as high FFA-evoked [Ca(2+)]i in response to 3'-O-(4-benzoyl) benzoyl-ATP (a selective P2X7 receptor agonist) were significantly attenuated. Meanwhile, high FFA-induced activation of P38 MAPK, an essential prerequisite for high FFA-activated P2X7 receptor and subsequent IL-6 release, was also dose-dependently abrogated by RESV. Furthermore, RESV may hamper the activation of P38a MAPK (one paramount P38 isoform) via forming hydrogen bonding with Thr175 residue, surrounding the two residues (Thy180 and Tyr182) essential for canonical activation of P38a MAPK. Taken together, RESV could inhibit high FFA-induced inflammatory IL-6 release mediated by P2X7 receptor through deactivation of P38 MAPK signaling pathway. All these results outline the potential mechanisms involved in the neuroprotective roles of RESV and highlight the clinical application of RESV in treatment of inflammation in relation to DNP.

Calcium dysregulation via L-type voltage-dependent calcium channels and ryanodine receptors underlies memory deficits and synaptic dysfunction during chronic neuroinflammation

Background

Chronic neuroinflammation and calcium (Ca⁺²) dysregulation are both components of Alzheimer’s disease. Prolonged neuroinflammation produces elevation of pro-inflammatory cytokines and reactive oxygen species which can alter neuronal Ca⁺² homeostasis via L-type voltage-dependent Ca⁺² channels (L-VDCCs) and ryanodine receptors (RyRs). Chronic neuroinflammation also leads to deficits in spatial memory, which may be related to Ca⁺² dysregulation.

Methods

The studies herein use an in vivo model of chronic neuroinflammation: rats were infused intraventricularly with a continuous small dose of lipopolysaccharide (LPS) or artificial cerebrospinal fluid (aCSF) for 28 days. The rats were treated with the L-VDCC antagonist nimodipine or the RyR antagonist dantrolene.

Results

LPS-infused rats had significant memory deficits in the Morris water maze, and this deficit was ameliorated by treatment with nimodipine. Synaptosomes from LPS-infused rats had increased Ca⁺² uptake, which was reduced by a blockade of L-VDCCs either in vivo or ex vivo.

Conclusions

Taken together, these data indicate that Ca⁺² dysregulation during chronic neuroinflammation is partially dependent on increases in L-VDCC function. However, blockade of the RyRs also slightly improved spatial memory of the LPS-infused rats, demonstrating that other Ca⁺² channels are dysregulated during chronic neuroinflammation. Ca⁺²-dependent immediate early gene expression was reduced in LPS-infused rats treated with dantrolene or nimodipine, indicating normalized synaptic function that may underlie improvements in spatial memory. Pro-inflammatory markers are also reduced in LPS-infused rats treated with either drug. Overall, these data suggest that Ca⁺² dysregulation via L-VDCCs and RyRs play a crucial role in memory deficits resulting from chronic neuroinflammation.

Neuromodulatory properties of inflammatory cytokines and their impact on neuronal excitability

Increasing evidence underlines that prototypical inflammatory cytokines (IL-1β, TNF-α and IL-6) either synthesized in the central (CNS) or peripheral nervous system (PNS) by resident cells, or imported by immune blood cells, are involved in several pathophysiological functions, including an unexpected impact on synaptic transmission and neuronal excitability. This review describes these unconventional neuromodulatory properties of cytokines, that are distinct from their classical action as effector molecules of the immune system. In addition to the role of cytokines in brain physiology, we report evidence that dysregulation of their biosynthesis and cellular release, or alterations in receptor-mediated intracellular pathways in target cells, leads to neuronal cell dysfunction and modifications in neuronal network excitability. As a consequence, targeting of these cytokines, and related signalling molecules, is considered a novel option for the development of therapies in various CNS or PNS disorders associated with an inflammatory component. This article is part of a Special Issue entitled 'Neuroimmunology and Synaptic Function'.

The phosphorylation of STAT6 during ischemic reperfusion in rat cerebral cortex

For many years, brain ischemia has been known to be a leading cause of adult neurological disorder. In particular, many reports have shown that hyperexcitability of neurons and inflammatory response of the glia induced by ischemic reperfusion (I/R) determine the fate of cells in the ischemic core and the penumbra region. Although there are many reports on the activation and roles of signal transducer and activator of transcription (STAT) proteins (STAT1, STAT3, and STAT5) during hyperexcitation in the neuron and inflammation occurring following I/R, the temporal and spatial activation of STAT6 protein in the ischemic cortex still remain elusive. In this study, using a transient rat middle cerebral artery occlusion model, we primarily investigated the time-course expression of the phosphorylated STAT6 (pSTAT6) in the ischemic core region following I/R, which was compared with that of pSTAT3. We found that pSTAT6 significantly decreases at 1 and 12 h following I/R, whereas pSTAT3 markedly increases at each follow-up time point. In addition, the level of pSTAT6 is reduced in the ischemic core in comparison with the penumbra region at 12 h following I/R. However, there is no significant difference in pSTAT3 expression between the ischemic core and the penumbra. Taken together, our data suggest that pSTAT6 and pSTAT3 are modulated differently following I/R during ischemic stroke.

The role of JAK-STAT signaling within the CNS

JAK-STAT is an efficient and highly regulated system mainly dedicated to the regulation of gene expression. Primarily identified as functioning in hematopoietic cells, its role has been found critical in all cell types, including neurons. This review will focus on JAK-STAT functions in the mature central nervous system. Our recent research suggests the intriguing possibility of a non-nuclear role of STAT3 during synaptic plasticity. Dysregulation of the JAK-STAT pathway in inflammation, cancer and neurodegenerative diseases positions it at the heart of most brain disorders, highlighting the importance to understand how it can influence the fate and functions of brain cells.

Upregulation of excitatory amino acid transporters by coexpression of Janus kinase 3

Janus kinase 3 (JAK3) contributes to cytokine receptor signaling, confers cell survival and stimulates cell proliferation. The gain of function mutation JAK3(A572V) is found in acute megakaryoplastic leukemia. Replacement of ATP coordinating lysine by alanine yields inactive JAK3(K855A). Most recent observations revealed the capacity of JAK3 to regulate ion transport. This study thus explored whether JAK3 regulates glutamate transporters EAAT1-4, carriers accomplishing transport of glutamate and aspartate in a variety of cells including intestinal cells, renal cells, glial cells, and neurons. To this end, EAAT1, 2, 3, or 4 were expressed in Xenopus oocytes with or without additional expression of mouse wild-type JAK3, constitutively active JAK3(A568V) or inactive JAK3(K851A), and electrogenic glutamate transport was determined by dual electrode voltage clamp. Moreover, Ussing chamber was employed to determine electrogenic glutamate transport in intestine from mice lacking functional JAK3 (jak3(-/-)) and from corresponding wild-type mice (jak3(+/+)). As a result, in EAAT1, 2, 3, or 4 expressing oocytes, but not in oocytes injected with water, addition of glutamate to extracellular bath generated an inward current (Ig), which was significantly increased following coexpression of JAK3. Ig in oocytes expressing EAAT3 was further increased by JAK3(A568V) but not by JAK3(K851A). Ig in EAAT3 + JAK3 expressing oocytes was significantly decreased by JAK3 inhibitor WHI-P154 (22 µM). Kinetic analysis revealed that JAK3 increased maximal Ig and significantly reduced the glutamate concentration required for half maximal Ig (Km). Intestinal electrogenic glutamate transport was significantly lower in jak3(-/-) than in jak3(+/+) mice. In conclusion, JAK3 is a powerful regulator of excitatory amino acid transporter isoforms.

GBE50 Attenuates Inflammatory Response by Inhibiting the p38 MAPK and NF- κ B Pathways in LPS-Stimulated Microglial Cells

Overactivated microglia contribute to a variety of pathological conditions in the central nervous system. The major goal of the present study is to evaluate the potential suppressing effects of a new type of Ginko biloba extract, GBE50, on activated microglia which causes proinflammatory responses and to explore the underlying molecular mechanisms. Murine BV2 microglia cells, with or without pretreatmentof GBE50 at various concentrations, were activated by incubation with lipopolysaccharide (LPS). A series of biochemical and microscopic assays were performed to measure cell viability, cell morphology, release of tumor necrosis factor- α (TNF- α ) and interleukin-1 β (IL-1 β ), and signal transduction via the p38 MAPK and nuclear factor-kappa B (NF- κ B) p65 pathways. We found that GBE50 pretreatment suppressed LPS-induced morphological changes in BV2 cells. Moreover, GBE50 treatment significantly reduced the release of proinflammatory cytokines, TNF- α and IL-1 β , and inhibited the associated signal transduction through the p38 MAPK and NF- κ B p65 pathways. These results demonstrated the anti-inflammatory effect of GBE50 on LPS-activated BV2 microglia cells, and indicated that GBE50 reduced the LPS-induced proinflammatory TNF- α and IL-1 β release by inhibiting signal transduction through the NF- κ B p65 and p38 MAPK pathways. Our findings reveal, at least in part, the molecular basis underlying the anti-inflammatory effects of GBE50.

Calcium dysregulation and neuroinflammation: discrete and integrated mechanisms for age-related synaptic dysfunction

Some of the best biomarkers of age-related cognitive decline are closely linked to synaptic function and plasticity. This review highlights several age-related synaptic alterations as they relate to Ca(2+) dyshomeostasis, through elevation of intracellular Ca(2+), and neuroinflammation, through production of pro-inflammatory cytokines including interleukin-1 beta (IL-1β) and tumor necrosis factor-alpha (TNF-α). Though distinct in many ways, Ca(2+) and neuroinflammatory signaling mechanisms exhibit extensive cross-talk and bidirectional interactions. For instance, cytokine production in glial cells is strongly dependent on the Ca(2+) dependent protein phosphatase calcineurin, which shows elevated activity in animal models of aging and disease. In turn, pro-inflammatory cytokines, such as TNF, can augment the expression/activity of L-type voltage sensitive Ca(2+) channels in neurons, leading to Ca(2+) dysregulation, hyperactive calcineurin activity, and synaptic depression. Thus, in addition to discussing unique contributions of Ca(2+) dyshomeostasis and neuroinflammation, this review emphasizes how these processes interact to hasten age-related synaptic changes.

Inactivation of JAK2/STAT3 signaling axis and downregulation of M1 mAChR cause cognitive impairment in klotho mutant mice, a genetic model of aging

We previously reported cognitive dysfunction in klotho mutant mice. In the present study, we further examined novel mechanisms involved in cognitive impairment in these mice. Significantly decreased janus kinase 2 (JAK2) and signal transducer and activator of transcription3 (STAT3) phosphorylation were observed in the hippocampus of klotho mutant mice. A selective decrease in protein expression and binding density of the M1 muscarinic cholinergic receptor (M1 mAChR) was observed in these mice. Cholinergic parameters (ie, acetylcholine (ACh), choline acetyltransferase (ChAT), and acetylcholinesterase (AChE)) and NMDAR-dependent long-term potentiation (LTP) were significantly impaired in klotho mutant mice. McN-A-343 (McN), an M1 mAChR agonist, significantly attenuated these impairments. AG490 (AG), a JAK2 inhibitor, counteracted the attenuating effects of McN, although AG did not significantly alter the McN-induced effect on AChE. Furthermore, AG significantly inhibited the attenuating effects of McN on decreased NMDAR-dependent LTP, protein kinase C βII, p-ERK, p-CREB, BDNF, and p-JAK2/p-STAT3-expression in klotho mutant mice. In addition, k252a, a BDNF receptor tyrosine kinase B (TrkB) inhibitor, significantly counteracted McN effects on decreased ChAT, ACh, and M1 mAChR and p-JAK2/p-STAT3 expression. McN-induced effects on cognitive impairment in klotho mutant mice were consistently counteracted by either AG or k252a. Our results suggest that inactivation of the JAK2/STAT3 signaling axis and M1 mAChR downregulation play a critical role in cognitive impairment observed in klotho mutant mice.

Growth hormone and cognitive function

Emerging data indicate that growth hormone (GH) therapy could have a role in improving cognitive function. GH replacement therapy in experimental animals and human patients counteracts the dysfunction of many behaviours related to the central nervous system (CNS). Various behaviours, such as cognitive behaviours related to learning and memory, are known to be induced by GH; the hormone might interact with specific receptors located in areas of the CNS that are associated with the functional anatomy of these behaviours. GH is believed to affect excitatory circuits involved in synaptic plasticity, which alters cognitive capacity. GH also has a protective effect on the CNS, as indicated by its beneficial effects in patients with spinal cord injury. Data collected from animal models indicates that GH might also stimulate neurogenesis. This Review discusses the mechanisms underlying the interactions between GH and the CNS, and the data emerging from animal and human studies on the relationship between GH and cognitive function. In this article, particular emphasis is given to the role of GH as a treatment for patients with cognitive impairment resulting from deficiency of the hormone.

High fatty acids modulate P2X(7) expression and IL-6 release via the p38 MAPK pathway in PC12 cells

Diabetic neuropathy (DNP) is the most common chronic complication of diabetes. Elevated free fatty acids (FFAs) have been recently recognized as a major cause of nervous system damage in diabetes. P2X receptors play a primary role in regulation of neuronal interleukin (IL)-6 release, which is of paramount relevance to the functional changes of nerve system. The present study aimed to investigate the effects of high FFAs on the P2X7 expression and IL-6 release in PC12 cells. High FFAs induced P2X7 expression and IL-6 release significantly in PC12 cells. Moreover, high FFAs enhanced ATP or BzATP-induced Ca(2+) signals in PC12 cells. Inhibition of P2X7 by transfection with P2X7-siRNA or co-culture with BBG (a specific P2X7 inhibitor) at high concentrations of FFAs decreased ATP or BzATP-promoted Ca(2+) signals and IL-6 release in PC12 cells. High FFAs induced the phosphorylation of p38 in PC12 cells. Blockade of p38 pathways by SB-203580 inhibited P2X7 up-expression, ATP or BzATP-evoked [Ca(2+)]i rises as well as IL-6 release in PC12 cells exposed to high FFAs. Therefore, high concentrations of FFAs increased the expression of P2X7 in PC12 cells via activation of p38 mitogen-activated protein kinase (MAPK) signaling pathway, which contributed to P2X7-mediated IL-6 release from PC12 cells.

The Jak/STAT pathway is involved in synaptic plasticity

The Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway is involved in many cellular processes, including cell growth and differentiation, immune functions and cancer. It is activated by various cytokines, growth factors, and protein tyrosine kinases (PTKs) and regulates the transcription of many genes. Of the four JAK isoforms and seven STAT isoforms known, JAK2 and STAT3 are highly expressed in the brain where they are present in the postsynaptic density (PSD). Here, we demonstrate a new neuronal function for the JAK/STAT pathway. Using a variety of complementary approaches, we show that the JAK/STAT pathway plays an essential role in the induction of NMDA-receptor dependent long-term depression (NMDAR-LTD) in the hippocampus. Therefore, in addition to established roles in cytokine signaling, the JAK/STAT pathway is involved in synaptic plasticity in the brain.

Inhibitory effect of 4-O-methylhonokiol on lipopolysaccharide-induced neuroinflammation, amyloidogenesis and memory impairment via inhibition of nuclear factor-kappaB in vitro and in vivo models

Background

Neuroinflammation is important in the pathogenesis and progression of Alzheimer disease (AD). Previously, we demonstrated that lipopolysaccharide (LPS)-induced neuroinflammation caused memory impairments. In the present study, we investigated the possible preventive effects of 4-O-methylhonokiol, a constituent of Magnolia officinalis, on memory deficiency caused by LPS, along with the underlying mechanisms.

Methods

We investigated whether 4-O-methylhonokiol (0.5 and 1 mg/kg in 0.05% ethanol) prevents memory dysfunction and amyloidogenesis on AD model mice by intraperitoneal LPS (250 μg/kg daily 7 times) injection. In addition, LPS-treated cultured astrocytes and microglial BV-2 cells were investigated for anti-neuroinflammatory and anti-amyloidogenic effect of 4-O-methylhonkiol (0.5, 1 and 2 μM).

Results

Oral administration of 4-O-methylhonokiol ameliorated LPS-induced memory impairment in a dose-dependent manner. In addition, 4-O-methylhonokiol prevented the LPS-induced expression of inflammatory proteins; inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) as well as activation of astrocytes (expression of glial fibrillary acidic protein; GFAP) in the brain. In in vitro study, we also found that 4-O-methylhonokiol suppressed the expression of iNOS and COX-2 as well as the production of reactive oxygen species, nitric oxide, prostaglandin E₂, tumor necrosis factor-α, and interleukin-1β in the LPS-stimulated cultured astrocytes. 4-O-methylhonokiol also inhibited transcriptional and DNA binding activity of NF-κB via inhibition of IκB degradation as well as p50 and p65 translocation into nucleus of the brain and cultured astrocytes. Consistent with the inhibitory effect on neuroinflammation, 4-O-methylhonokiol inhibited LPS-induced Aβ_1-42 generation, β- and γ-secretase activities, and expression of amyloid precursor protein (APP), BACE1 and C99 as well as activation of astrocytes and neuronal cell death in the brain, in cultured astrocytes and in microglial BV-2 cells.

Conclusion

These results suggest that 4-O-methylhonokiol inhibits LPS-induced amyloidogenesis via anti-inflammatory mechanisms. Thus, 4-O-methylhonokiol can be a useful agent against neuroinflammation-associated development or the progression of AD.

Microarray analysis of the global gene expression profile following hypothermia and transient focal cerebral ischemia

BACKGROUND

Hypothermia is one of the most robust experimental neuroprotective interventions against cerebral ischemia. Identification of molecular pathways and gene networks together with single genes or gene families that are significantly associated with neuroprotection might help unravel the mechanisms of therapeutic hypothermia.

MATERIAL AND METHODS

We performed a microarray analysis of ischemic rat brains that underwent 90 min of middle cerebral artery occlusion (MCAO) and 48 h of reperfusion. Hypothermia was induced for 4 h, starting 1 h after MCAO in male Wistar rats. At 48 h, magnetic resonance imaging (MRI) was performed for infarct volumetry, and functional outcome was determined by a neuroscore. The brain gene expression profile of sham (S), ischemia (I), and ischemia plus hypothermia (HI) treatment were compared by analyzing changes of individual genes, pathways, and networks. Real-time reverse-transcribed polymerase chain reaction (RT-PCR) was performed on selected genes to validate the data.

RESULTS

Rats treated with HI had significantly reduced infarct volumes and improved neuroscores at 48 h compared with I. Of 4067 genes present on the array chip, HI compared with I upregulated 50 (1.23%) genes and downregulated 103 (3.20%) genes equal or greater than twofold. New genes potentially mediating neuroprotection by hypothermia were HNRNPAB, HIG-1, and JAK3. On the pathway level, HI globally suppressed the ischemia-driven gene response. Twelve gene networks were identified to be significantly altered by HI compared with I. The most significantly altered network contained genes participating in apoptosis suppression.

CONCLUSIONS

Our data suggest that although hypothermia at the pathway level restored gene expression to sham levels, it selectively regulated the expression of several genes implicated in protein synthesis and folding, calcium homeostasis, cellular and synaptic integrity, inflammation, cell death, and apoptosis.

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.

Neuroglobin overexpression in cultured human neuronal cells protects against hydrogen peroxide insult via activating phosphoinositide-3 kinase and opening the mitochondrial K(ATP) channel

Cultured neurons tolerate low H(2)O(2) concentrations (< or =50 microM) through the activity of constitutive antioxidant response elements (ARE). At H(2)O(2) levels (> or =100 microM), neurons increase expression of the gene encoding for inducible hemoxygenase-1 while superoxide dismutase-2 and catalase remain unchanged. Despite this adaptive response, the endogenous antioxidant systems are overwhelmed, leading to decreased viability. Elevating the neuronal cell content of human neuroglobin (Ngb) prior to insult with 100 or 200 microM H(2)O(2) enhanced cell viability and this resulted in a significant decrease in oxidative stress and an increase in the intracellular ATP concentration, whereas in parental cells exposed to the same H(2)O(2)-insult, oxidative stress and ATP increased and decreased, respectively. The mechanism for this increase in ATP involves sustained activation of the mito-K(ATP) channel and an increase in phosphoinositide-3 kinase (PI3K)-mediated phosphorylation of Akt. Pharmacological inhibitors directed toward PI3K (wortmannin and LY294002), or the mito-K(ATP) channel (glybenclamide) inhibited the H(2)O(2)-mediated increase in ATP in cells overexpressing human Ngb and consequently cell viability decreased. Neuroglobin's ability to bolster the intracellular pool of ATP in response to added H(2)O(2) is central to the preservation of cytoskeletal integrity and cell viability.

Neuroprotection of interleukin-6 against NMDA-induced apoptosis and its signal-transduction mechanisms

We have previously shown that interleukin-6 (IL-6)-protected neurons against the suppression of neuronal vitality and overload of intracellular Ca(2+) induced by glutamate or N-methyl-D: -aspartate (NMDA). Herein we provide further evidence for IL-6 neuroprotection against NMDA-induced apoptosis and explore the signal-transduction mechanisms underlying the anti-apoptotic action of IL-6. Cerebellar granule neurons (CGNs) from postnatal 8-day infant rats were chronically exposed to IL-6 (40 or 120 ng/ml) for 8 days, and stimulated with NMDA (100 μM) for 30 min. To observe the signaling pathways, we employed AG490 (5 or 10 μM), an inhibitor of Janus kinases (JAKs), or LY294002 (5 or 10 μM), an inhibitor of phosphatidylinositol 3-kinase (PI3K), to pretreat the CGNS together with IL-6. The levels of phosphorylation for the downstream effectors of JAKs and PI3K, i.e., phosphorylated STAT3 and Akt, were quantified by Western blot assay. In the cultured CGNs with various drug exposures, the expressions of Bcl-2, Bax, and caspase-3 were measured by real-time PCR and Western blot, and the percentage of apoptotic nuclei was tested by Hoechst 33342 staining. After the CGNs were chronically exposed to IL-6, NMDA stimulation led to an increase in the expression of Bcl-2 mRNA and a decrease in the expression of Bax and caspase-3 mRNAs and proteins when compared with those neurons lacking IL-6 exposure. IL-6 pretreatment of the neurons without NMDA stimulation concentration-dependently enhanced the expressions of Bcl-2 mRNA and protein while attenuating the expressions of Bax and caspase-3 mRNAs and proteins in comparison with control lacking any treatment. Furthermore, IL-6 prevented the increase in the percentage of apoptotic neurons induced by NMDA. The combined pretreatment of the CGNs with AG490 and IL-6 or with LY294002 and IL-6 reduced these anti-apoptotic effects of IL-6. Neither AG490 nor LY294002 exposure alone altered the expressions of Bcl-2, Bax, and cleaved caspase-3 proteins. IL-6 up-regulated the levels of phosphorylated STAT3 and Akt, and this was blocked by AG490 and LY294002, respectively. These results suggest that IL-6 protects neurons against NMDA-induced apoptosis, and that the IL-6 neuroprotection is jointly mediated by JAK-STAT3 and PI3K-Akt signaling pathways.

Roles of cholesterol and lipids in the etiopathogenesis of Alzheimer's disease

Alzheimer's disease is the principal cause of dementia throughout the world and the fourth cause of death in developed economies.This brain disorder is characterized by the formation of brain protein aggregates, namely, the paired helical filaments and senile plaques. Oxidative stress during life, neuroinflamamtion, and alterations in neuron-glia interaction patterns have been also involved in the etiopathogenesis of this disease. In recent years, cumulative evidence has been gained on the involvement of alteration in neuronal lipoproteins activity, as well as on the role of cholesterol and other lipids in the pathogenesis of this neurodegenerative disorder. In this review, we analyze the links between changes in cholesterol homeostasis, and the changes of lipids of major importance for neuronal activity and Alheimer's disease. The investigation on the fine molecular mechanisms underlying the lipids influence in the etiopathogenesis of Alzheimer's disease may shed light into its treatment and medical management.

Selective interaction of lansoprazole and astemizole with tau polymers: potential new clinical use in diagnosis of Alzheimer's disease

We describe the interactions of two benzimidazole derivatives, astemizole (AST) and lansoprazole (LNS), with anomalous aggregates of tau protein (neurofibrillary tangles). Interestingly, these compounds, with important medical applications in the treatment of allergies and gastrointestinal disorders respectively, specifically bind to aggregated variants of tau protein and to paired helical filaments isolated from brains of Alzheimer's disease (AD) patients. These ligands appear to be a powerful tool to tag brain-isolated tau-aggregates and heparin-induced polymers of recombinant tau. The interactions of AST and LNS with tau aggregates were assessed by classical radioligand assays, surface plasmon resonance, and bioinformatic approaches. The affinity of AST and LNS for tau aggregates was comparatively higher than that for amyloid-beta polymers according to our data. This is relevant since senile plaques are also abundant but are not pathognomonic in AD patients. Immunochemical studies on paired helical filaments from brains of AD patients and surface plasmon resonance studies confirm these findings. The capacity of these drugs to penetrate the blood-brain barrier was evaluated: i) in vitro by parallel artificial membrane permeability assay followed by experimental Log P determinations; and ii) in vivo by pharmacokinetic studies comparing distribution profiles in blood and brain of mice using HPLC/UV. Importantly, our studies indicate that the brain/blood concentration ratios for these compounds were suitable for their use as PET radiotracers. Since neurofibrillary tangles are positively correlated with cognitive impairment, we concluded that LNS and AST have a great potential in PET neuroimaing for in vivo early detection of AD and in reducing the formation of neurofibrillary tangles.

The role of the somatotrophic axis in neuroprotection and neuroregeneration of the addictive brain

Early studies have shown that the abuse of alcohol, central stimulants, and opiates such as heroin destroys brain cells, reducing attention span and memory. However, new research has suggested that there may be a way to regain some of the lost attention and recall. It has recently been shown that brain cells targeted for early death by continued opiate use can be salvaged by injections of synthetic human growth hormone (GH). GH is a polypeptide hormone, normally secreted by the anterior pituitary gland, which stimulates cell growth and controls body metabolism. Recombinant human GH is currently used in replacement therapy to alleviate the symptoms of adults and children with GH deficiency syndrome. The recent observation that GH can reverse morphine-induced cell damage could open the door to new ways of treating and preventing damage from the abuse of opiates in addicts and also of treating cell damage induced by alcohol and central stimulants. This article reviews current knowledge of the somatotrophic axis, including GH and insulin-like growth factor-1 (IGF-1), in the brain and also discusses the potential use of GH/IGF-1 as agents for treatment of brain pathology in addictive diseases.

Neuroprotection of interleukin-6 against NMDA attack and its signal transduction by JAK and MAPK

Cytokine interleukin-6 (IL-6) has been well shown to be elevated in brain injury and diseases. However, the significance of IL-6 production in such neuropathologic states remains controversial, and the intracellular signal-transduction pathways involved in the brain IL-6 action are primarily unclear. We previously indicated that exogenous IL-6 protected neurons against glutamate and N-methyl-d-aspartate (NMDA) attacks and the effects of IL-6 was blocked by anti-gp130 antibody. Here, we provide further evidence for the IL-6 neuroprotection and show signal molecules transducing the IL-6 message. The cerebellar granule neurons from postnatal 8-day infant rats were exposed to IL-6 for 8 days, and also pretreated chronically with Janus kinase (JAK) inhibitor AG490 and mitogen-activated protein kinase (MAPK) inhibitor PD98059. NMDA stimulated the cultured neurons for 30 min to induce neuronal injury and death. Cell counting kit-8 assay and Western blot were employed to measure neuronal vitality and cleaved caspase-3 expression, respectively. The chronic IL-6 exposure prevented the suppression of the neuronal vitality and the enhancement of the cleaved caspase-3 level induced by NMDA. The neuroprotective effect of IL-6 depended on IL-6 concentration and neuronal damaged degree. IL-6-induced STAT3 phosphorylation was inhibited by AG490 but not by PD98059; and IL-6-induced ERK1/2 activation was blocked by PD98059 but not by AG490. Either AG490 or PD98059 blocked the IL-6 protection against the NMDA-elicited neuronal vitality decrease and caspase-3 activation increase. These findings suggest that IL-6 protects neurons from NMDA-induced excitoxicity and the IL-6 neuroprotection may be transduced by both JAK/STAT3 and RAS/MAPK pathways.

Cytokines disrupt intracellular patterns of Parkinson's disease-associated proteins alpha-synuclein, tau and ubiquitin in cultured glial cells

The purpose of this study was to determine the effects of specific proinflammatory cytokines interleukin-6 (Il-6), interleukin-1beta (Il-1beta), interferon-gamma (IFN), and tumor necrosis factor-alpha (TNFalpha), on content and distribution of alpha-synuclein (alpha-synuclein), tau and ubiquitin in human derived cultured glial cells. Exposure paradigms mimicked acute (2 h), intermediate (18 h) and prolonged time frames (96 h); consisting of single or repeated low doses (10 ng/ml) or high doses (50 ng/ml), consistent with either mild or serious systemic infectious/inflammatory responses. Images of intracellular protein content and distribution were reconstructed from emission patterns generated by fluorescence deconvolution microscopy. Minor alterations were seen in protein content with IFN; Il-1beta decreased alpha-synuclein and tau at 18 and 96 h; TNFalpha inversely reduced alpha-synuclein and increased ubiquitin content. Combinations of Il-1beta and IFN produced a robust increase of alpha-synuclein and tau at 2 h. Consecutive low doses of Il-6 produced only minor increases in alpha-synuclein and ubiquitin after 4 h, whereas a single high dose resulted in major increases for all three proteins over the first 18 h. Protein localization patterns were distinctly different and were altered dependent upon cytokine treatment. A high dose exposure (2 x 50 ng/ml) with Il-6 and IFN demonstrated that protein increases and dispersals could be sustained and that the normal perinuclear tau and peripheral alpha-synuclein patterns were disrupted. These results support the postulate that specific cytokines affect temporal protein changes with concomitant pattern disruptions, possibly reflecting a mechanism of cell dysfunction in Parkinson's degeneration.

Neuroprotection: VEGF, IL-6, and clusterin: the dark side of the moon

Growth factors and their respective receptors are key regulators in development and homeostasis of the nervous system, and changes in the function, expression, or downstream signaling of growth factors are involved in many neuropathological disorders. Recently, research has yielded a rich harvest of information about molecules and gene, and currently the assumption "a gene-a protein", where each gene encodes the structure of a single protein, is becoming a paradox. In the past years, the discovery of synergic or antagonistic proteins deriving from the same gene is a novelty upsetting. In some way, the conventional function of proteins involved in DNA repair, cell death/growth induction, vascularization, and metabolism is inhibited or shifted toward other pathways by soluble mediators that orchestrate such change depending on the microenvironment conditions. In this chapter, we focus on the antithetic properties that proteins could exert, depending on the microenvironment that orchestrates the complex networks among proteins and their respective partners.