The Effect of Donepezil Hydrochloride in the Twitcher Mouse Model of Krabbe Disease

Krabbe disease (KD) is a rare demyelinating disorder characterized by demyelination caused by mutations in the GALC gene, resulting in toxic accumulation of psychosine. Psychosine has been identified as detrimental to oligodendrocytes, leading to demyelination through diverse hypothesized pathways. Reducing demyelination is essential to maintain neurological function in KD; however, therapeutic interventions are currently limited. Acetylcholinesterase inhibitors (AChEi) are commonly used for symptomatic management of Alzheimer's Disease and are suggested to have potential disease-modifying effects, including regulating myelin state. In particular, donepezil, an AChEi, has demonstrated promising effects in cellular and animal models, including promotion of the expression of myelin-related genes and reduction of glial cell reactivity. This drug also acts as an agonist for sigma-1 receptors (Sig-1R), which are implicated in demyelination diseases. In the context of drug repurposing, here, we demonstrate that administration of donepezil has protective effects in the twitcher mouse model of KD. We provide data showing that donepezil preserves myelin and reduces glial cell reactivity in the brains of twitcher mice. Moreover, donepezil also improves behavioral phenotypes and increases lifespan in twitcher animals. These findings suggest that donepezil, with its dual activity as an AChE inhibitor and Sig-1R agonist, may hold promise as a therapeutic candidate for demyelinating diseases, including KD.

The Effects of Antipsychotics in Experimental Models of Krabbe Disease

The role of altered myelin in the onset and development of schizophrenia and changes in myelin due to antipsychotics remains unclear. Antipsychotics are D₂ receptor antagonists, yet D₂ receptor agonists increase oligodendrocyte progenitor numbers and limit oligodendrocyte injury. Conflicting studies suggest these drugs promote the differentiation of neural progenitors to oligodendrocyte lineage, while others report antipsychotics inhibit the proliferation and differentiation of oligodendrocyte precursors. Here, we utilised in-vitro (human astrocytes), ex-vivo (organotypic slice cultures) and in-vivo (twitcher mouse model) experimental study designs of psychosine-induced demyelination, a toxin that accumulates in Krabbe disease (KD), to investigate direct effects of antipsychotics on glial cell dysfunction and demyelination. Typical and atypical antipsychotics, and selective D₂ and 5HT_2A receptor antagonists, attenuated psychosine-induced cell viability, toxicity, and morphological aberrations in human astrocyte cultures. Haloperidol and clozapine reduced psychosine-induced demyelination in mouse organotypic cerebellar slices. These drugs also attenuated the effects of psychosine on astrocytes and microglia and restored non-phosphorylated neurofilament levels, indicating neuroprotective effects. In the demyelinating twitcher mouse model of KD, haloperidol improved mobility and significantly increased the survival of these animals. Overall, this study suggests that antipsychotics directly regulate glial cell dysfunction and exert a protective effect on myelin loss. This work also points toward the potential use of these pharmacological agents in KD.

Hybrid Nanoparticles as a Novel Tool for Regulating Psychosine-Induced Neuroinflammation and Demyelination In Vitro and Ex vivo

Polymeric nanoparticles are being extensively investigated as an approach for brain delivery of drugs, especially for their controlled release and targeting capacity. Nose-to-brain administration of nanoparticles, bypassing the blood brain barrier, offers a promising strategy to deliver drugs to the central nervous system. Here, we investigated the potential of hybrid nanoparticles as a therapeutic approach for demyelinating diseases, more specifically for Krabbe's disease. This rare leukodystrophy is characterized by the lack of enzyme galactosylceramidase, leading to the accumulation of toxic psychosine in glial cells causing neuroinflammation, extensive demyelination and death. We present evidence that lecithin/chitosan nanoparticles prevent damage associated with psychosine by sequestering the neurotoxic sphingolipid via physicochemical hydrophobic interactions. We showed how nanoparticles prevented the cytotoxicity caused by psychosine in cultured human astrocytes in vitro, and how the nanoparticle size and PDI augmented while the electrostatic charges of the surface decreased, suggesting a direct interaction between psychosine and the nanoparticles. Moreover, we studied the effects of nanoparticles ex vivo using mouse cerebellar organotypic cultures, observing that nanoparticles prevented the demyelination and axonal damage caused by psychosine, as well as a moderate prevention of the astrocytic death. Taken together, these results suggest that lecithin-chitosan nanoparticles are a potential novel delivery system for drugs for certain demyelinating conditions such as Krabbe's disease, due to their dual effect: not only are they an efficient platform for drug delivery, but they exert a protective effect themselves in tampering the levels of psychosine accumulation.

EBI2 Is Temporarily Upregulated in MO3.13 Oligodendrocytes during Maturation and Regulates Remyelination in the Organotypic Cerebellar Slice Model

The EBI2 receptor regulates the immune system and is expressed in various immune cells including B and T lymphocytes. It is also expressed in astrocytes in the central nervous system (CNS) where it regulates pro-inflammatory cytokine release, cell migration and protects from chemically induced demyelination. Its signaling and expression are implicated in various diseases including multiple sclerosis, where its expression is increased in infiltrating immune cells in the white matter lesions. Here, for the first time, the EBI2 protein in the CNS cells in the human brain was examined. The function of the receptor in MO3.13 oligodendrocytes, as well as its role in remyelination in organotypic cerebellar slices, were investigated. Human brain sections were co-stained for EBI2 receptor and various markers of CNS-specific cells and the human oligodendrocyte cell line MO3.13 was used to investigate changes in EBI2 expression and cellular migration. Organotypic cerebellar slices prepared from wild-type and cholesterol 25-hydroxylase knock-out mice were used to study remyelination following lysophosphatidylcholine (LPC)-induced demyelination. The data showed that EBI2 receptor is present in OPCs but not in myelinating oligodendrocytes in the human brain and that EBI2 expression is temporarily upregulated in maturing MO3.13 oligodendrocytes. Moreover, we show that migration of MO3.13 cells is directly regulated by EBI2 and that its signaling is necessary for remyelination in cerebellar slices post-LPC-induced demyelination. The work reported here provides new information on the expression and role of EBI2 in oligodendrocytes and myelination and provides new tools for modulation of oligodendrocyte biology and therapeutic approaches for demyelinating diseases.

Spatiotemporal immunolocalisation of REST in the brain of healthy ageing and Alzheimer's disease rats

In the brain, REST (Repressor Element‐1 Silencing Transcription factor) is a key regulator of neuron cell‐specific gene expression. Nuclear translocation of neuronal REST has been shown to be neuroprotective in a healthy ageing context. In contrast, inability to upregulate nuclear REST is thought to leave ageing neurons vulnerable to neurodegenerative stimuli, such as Alzheimer’s disease (AD) pathology. Hippocampal and cortical neurons are known to be particularly susceptible to AD‐associated neurodegeneration. However, REST expression has not been extensively characterised in the healthy ageing brain. Here, we examined the spatiotemporal immunolocalisation of REST in the brains of healthy ageing wild‐type Fischer‐344 and transgenic Alzheimer’s disease rats (TgF344‐AD). Nuclear expression of REST increased from 6 months to 18 months of age in the hippocampus, frontal cortex and subiculum of wild‐type rats, but not in TgF344‐AD rats. No changes in REST were measured in more posterior cortical regions or in the thalamus. Interestingly, levels of the presynaptic marker synaptophysin, a known gene target of REST, were lower in CA1 hippocampal neurons of 18‐month TgF344‐AD rats compared to 18‐month wild‐types, suggesting that elevated nuclear REST may protect against synapse loss in the CA1 of 18‐month wild‐type rats. High REST expression in ageing wild‐type rats did not, however, protect against axonal loss nor against astroglial reactivity in the hippocampus. Taken together, our data confirm that changes in nuclear REST expression are context‐, age‐ and brain region‐specific. Moreover, key brain structures involved in learning and memory display elevated REST expression in healthy ageing wild‐type rats but not TgF344‐AD rats.

Inhibition of Piezo1 attenuates demyelination in the central nervous system

Piezo1 is a mechanosensitive ion channel that facilitates the translation of extracellular mechanical cues to intracellular molecular signaling cascades through a process termed, mechanotransduction. In the central nervous system (CNS), mechanically gated ion channels are important regulators of neurodevelopmental processes such as axon guidance, neural stem cell differentiation, and myelination of axons by oligodendrocytes. Here, we present evidence that pharmacologically mediated overactivation of Piezo1 channels negatively regulates CNS myelination. Moreover, we found that the peptide GsMTx4, an antagonist of mechanosensitive cation channels such as Piezo1, is neuroprotective and prevents chemically induced demyelination. In contrast, the positive modulator of Piezo1 channel opening, Yoda-1, induces demyelination and neuronal damage. Using an ex vivo murine-derived organotypic cerebellar slice culture model, we demonstrate that GsMTx4 attenuates demyelination induced by the cytotoxic lipid, psychosine. Importantly, we confirmed the potential therapeutic effects of GsMTx4 peptide in vivo by co-administering it with lysophosphatidylcholine (LPC), via stereotactic injection, into the cerebral cortex of adult mice. GsMTx4 prevented both demyelination and neuronal damage usually caused by the intracortical injection of LPC in vivo; a well-characterized model of focal demyelination. GsMTx4 also attenuated both LPC-induced astrocyte toxicity and microglial reactivity within the lesion core. Overall, our data suggest that pharmacological activation of Piezo1 channels induces demyelination and that inhibition of mechanosensitive channels, using GsMTx4, may alleviate the secondary progressive neurodegeneration often present in the latter stages of demyelinating diseases.

Piezo1 regulates calcium oscillations and cytokine release from astrocytes

Astrocytes are important for information processing in the brain and they achieve this by fine-tuning neuronal communication via continuous uptake and release of biochemical modulators of neurotransmission and synaptic plasticity. Often overlooked are their important functions in mechanosensation. Indeed, astrocytes can detect pathophysiological changes in the mechanical properties of injured, ageing, or degenerating brain tissue. We have recently shown that astrocytes surrounding mechanically-stiff amyloid plaques upregulate the mechanosensitive ion channel, Piezo1. Moreover, ageing transgenic Alzheimer's rats harboring a chronic peripheral bacterial infection displayed enhanced Piezo1 expression in amyloid plaque-reactive astrocytes of the hippocampus and cerebral cortex. Here, we have shown that the bacterial endotoxin, lipopolysaccharide (LPS), also upregulates Piezo1 in primary mouse cortical astrocyte cultures in vitro. Activation of Piezo1, via the small molecule agonist Yoda1, enhanced Ca²⁺ influx in both control and LPS-stimulated astrocytes. Moreover, Yoda1 augmented intracellular Ca²⁺ oscillations but decreased subsequent Ca²⁺ influx in response to adenosine triphosphate (ATP) stimulation. Neither blocking nor activating Piezo1 affected cell viability. However, LPS-stimulated astrocyte cultures exposed to the Piezo1 activator, Yoda1, migrated significantly slower than reactive astrocytes treated with the mechanosensitive channel-blocking peptide, GsMTx4. Furthermore, our data show that activating Piezo1 channels inhibits the release of cytokines and chemokines, such as IL-1β, TNFα, and fractalkine (CX₃ CL1), from LPS-stimulated astrocyte cultures. Taken together, our results suggest that astrocytic Piezo1 upregulation may act to dampen neuroinflammation and could be a useful drug target for neuroinflammatory disorders of the brain.

Inhibition of the Interaction Between Group I Metabotropic Glutamate Receptors and PDZ-Domain Proteins Prevents Hippocampal Long-Term Depression, but Not Long-Term Potentiation

The group I metabotropic glutamate (mGlu) receptor subtypes, mGlu1 and mGlu5, strongly regulate hippocampal synaptic plasticity. Both harbor PSD-95/discs-large/ZO-1 (PDZ) motifs at their extreme carboxyl terminals, which allow interaction with the PDZ domain of Tamalin, regulate the cell surface expression of group I mGlu receptors, and may modulate their coupling to signaling proteins. We investigated the functional role of this interaction in hippocampal long-term depression (LTD). Acute intracerebral treatment of adult rats with a cell-permeable PDZ-blocking peptide (pep-mGluR-STL), designed to competitively inhibit the interaction between Tamalin and group 1 mGlu receptors, prevented expression of LTD in the hippocampal CA1 region without affecting long-term potentiation (LTP) or basal synaptic transmission. Pep-mGluR-STL prevented facilitation by the group I mGlu receptor agonist, (S)-3,5-Dihydroxyphenylglycine (DHPG), and the mGlu5 agonist, (R,S)-2-chloro-5-Hydroxyphenylglycine (CHPG), of short-term depression (STD) into LTD, suggesting that Tamalin preferentially acts by mediating signaling through mGlu5. These data support that Tamalin is essential for the persistent expression of LTD and that it subserves the effective signaling of group 1 mGlu receptors.

Infection Augments Expression of Mechanosensing Piezo1 Channels in Amyloid Plaque-Reactive Astrocytes

A defining pathophysiological hallmark of Alzheimer's disease (AD) is the amyloid plaque; an extracellular deposit of aggregated fibrillar Aβ1-42 peptides. Amyloid plaques are hard, brittle structures scattered throughout the hippocampus and cerebral cortex and are thought to cause hyperphosphorylation of tau, neurofibrillary tangles, and progressive neurodegeneration. Reactive astrocytes and microglia envelop the exterior of amyloid plaques and infiltrate their inner core. Glia are highly mechanosensitive cells and can almost certainly sense the mismatch between the normally soft mechanical environment of the brain and very stiff amyloid plaques via mechanosensing ion channels. Piezo1, a non-selective cation channel, can translate extracellular mechanical forces to intracellular molecular signaling cascades through a process known as mechanotransduction. Here, we utilized an aging transgenic rat model of AD (TgF344-AD) to study expression of mechanosensing Piezo1 ion channels in amyloid plaque-reactive astrocytes. We found that Piezo1 is upregulated with age in the hippocampus and cortex of 18-month old wild-type rats. However, more striking increases in Piezo1 were measured in the hippocampus of TgF344-AD rats compared to age-matched wild-type controls. Interestingly, repeated urinary tract infections with Escherichia coli bacteria, a common comorbidity in elderly people with dementia, caused further elevations in Piezo1 channel expression in the hippocampus and cortex of TgF344-AD rats. Taken together, we report that aging and peripheral infection augment amyloid plaque-induced upregulation of mechanoresponsive ion channels, such as Piezo1, in astrocytes. Further research is required to investigate the role of astrocytic Piezo1 in the Alzheimer's brain, whether modulating channel opening will protect or exacerbate the disease state, and most importantly, if Piezo1 could prove to be a novel drug target for age-related dementia.

A novel modelling mechanism of PAEL receptor and GABARAPL2 interaction involved in Parkinson's disease

Parkin associated endothelin like receptor (PAELR) is G-protein coupled and ubiquitinated by parkin, promoting its degradation. In autosomal recessive Parkinson's disease, mutations in parkin lead to PAELR aggregation in the endoplasmic reticulum (ER), ER stress, neurotoxicity and cell death. We have identified previously that the protein kinase C interacting protein (PICK1) interacts with and regulates the expression and cell toxicity of PAELR. Here, we experimentally identify and provide in-silico modelling of a novel interaction between PAELR and GABARAPL2 (γ-aminobutyrate type A receptor associated protein like 2), which is an autophagosome-specific Ub-like protein implicated in vesicle trafficking and autophagy. We show that the family of GABARAPs interact with the carboxy terminal (ct) of PAELR and find the cysteine rich region (-CCCCCC-EEC) of ct-PAELR interacts with the GABA_A binding site of GABARAPL2. This interaction is modelled by in-slico analysis and confirmed using affinity chromatography, showing Myc-tagged GABARAPL2 is retained by a GST fusion of the ct-PAELR. We also demonstrate that transient transfection of GABARAPL2 in HEK293 cells reduces PAELR expression. This study supports the idea that protein levels of PAELR are likely regulated by a multitude of proteins including parkin, PICK1 and GABARAPL2 via mechanisms that include ubiquitination, proteasomal degradagtion and autophagy.

Sphingosine 1-phosphate receptors regulate TLR4-induced CXCL5 release from astrocytes and microglia

Sphingosine 1-phosphate receptors (S1PR) are G protein-coupled and compose a family with five subtypes, S1P1R-S1P5R. The drug Gilenya^® (Novartis, Basel, Switzerland) (Fingolimod; FTY720) targets S1PRs and was the first oral therapy for patients with relapsing-remitting multiple sclerosis (MS). The phosphorylated form of FTY720 (pFTY720) binds S1PRs causing initial agonism, then subsequent receptor internalization and functional antagonism. Internalization of S1P1R attenuates sphingosine 1-phosphate (S1P)-mediated egress of lymphocytes from lymph nodes, limiting aberrant immune function in MS. pFTY720 also exerts direct actions on neurons and glial cells which express S1PRs. In this study, we investigated the regulation of pro-inflammatory chemokine release by S1PRs in enriched astrocytes and microglial cultures. Astrocytes and microglia were stimulated with lipopolysaccharide (LPS) and increases in C-X-C motif chemokine 5 (CXCL5), also known as LIX (lipopolysaccharide-induced CXC chemokine) expression were quantified. Results showed that pFTY720 attenuated LPS-induced CXCL5 (LIX) protein release from astrocytes, as did the S1P1R selective agonist, SEW2871. In addition, pFTY720 blocked messenger ribonucleic acid (mRNA) transcription of the chemokines, (i) CXCL5/LIX, (ii) C-X-C motif chemokine 10 (CXCL10) also known as interferon gamma-induced protein 10 (IP10) and (iii) chemokine (C-C motif) ligand 2 (CCL2) also known as monocyte chemoattractant protein 1 (MCP1). Interestingly, inhibition of sphingosine kinase attenuated LPS-induced increases in mRNA levels of all three chemokines, suggesting that LPS-TLR4 (Toll-like receptor 4) signalling may enhance chemokine expression via S1P-S1PR transactivation. Lastly, these observations were not limited to astrocytes since we also found that pFTY720 attenuated LPS-induced release of CXCL5 from microglia. These data highlight a role for S1PR signalling in regulating the levels of chemokines in glial cells and support the notion that pFTY720 efficacy in multiple sclerosis may involve the direct modulation of astrocytes and microglia.

EBI2 regulates pro-inflammatory signalling and cytokine release in astrocytes

The endogenous oxysterol 7α, 25-dihydroxycholesterol (7α25HC) ligand activates the G protein-coupled receptor EBI2 to regulate T cell-dependant antibody response and B cell migration. We have demonstrated that EBI2 is expressed in human and mouse astrocytes, that 7α25HC induces intracellular signalling and astrocyte migration, and that EBI2 plays a role in the crosstalk between astrocytes and macrophages. Recently, we demonstrate that EBI2 regulates myelin development and inhibits LPC-induced demyelination. Here, we show that 7α25HC inhibits LPS- and IL17/TNF-induced pro-inflammatory cytokine release in astrocytes. We observe the following: 1. Human astrocytes treated with IL17/TNF increases the nuclear translocation of NFκB, which is attenuated by pre-treatment with 7α25HC; 2. IL17/TNF increases cell impedance in human astrocytes, which is also attenuated by pre-treatment with 7α25HC; 3. The EBI2 antagonist NIBR189 inhibits these effects of 7α25HC, supporting the role of EBI2; 4. in vivo data corroborate these in vitro findings, showing that EBI2 knock-out (KO) animals display enhanced pro-inflammatory cytokine in response to LPS challenge, in the brain. These results demonstrate a role for oxysterol/EBI2 signalling in attenuating the response of astrocytes to pro-inflammatory signals as well as limiting the levels of pro-inflammatory cytokines in the brain.

EBI2 receptor regulates myelin development and inhibits LPC-induced demyelination

BACKGROUND

The G protein-coupled receptor EBI2 (Epstein-Barr virus-induced gene 2) is activated by 7α, 25-dihydroxycholesterol (7α25HC) and plays a role in T cell-dependant antibody response and B cell migration. Abnormal EBI2 signaling is implicated in a range of autoimmune disorders; however, its role in the CNS remains poorly understood.

METHODS

Here we characterize the role of EBI2 in myelination under normal and pathophysiological conditions using organotypic cerebellar slice cultures and EBI2 knock-out (KO) animals.

RESULTS

We find that MBP expression in brains taken from EBI2 KO mice is delayed compared to those taken from wild type (WT) mice. In agreement with these in vivo findings, we show that antagonism of EBI2 reduces MBP expression in vitro. Importantly, we demonstrate that EBI2 activation attenuates lysolecithin (LPC)-induced demyelination in mouse organotypic slice cultures. Moreover, EBI2 activation also inhibits LPC-mediated release of pro-inflammatory cytokines such as IL6 and IL1β in cerebellar slices.

CONCLUSIONS

These results, for the first time, display a role for EBI2 in myelin development and protection from demyelination under pathophysiological conditions and suggest that modulation of this receptor may be beneficial in neuroinflammatory and demyelinating disorders such as multiple sclerosis.

Phospholipase A2 is involved in galactosylsphingosine-induced astrocyte toxicity, neuronal damage and demyelination

Krabbe disease is a fatal rare inherited lipid storage disorder affecting 1:100,000 births. This illness is caused by mutations in the galc gene encoding for the enzyme galactosylceramidase (GALC). Dysfunction of GALC has been linked to the toxic build-up of the galactolipid, galactosylsphingosine (psychosine), which induces cell death of oligodendrocytes. Previous studies show that phospholipase A2 (PLA2) may play a role in psychosine induce cell death. Here, we demonstrate that non-selective inhibition of cPLA2/sPLA2 and selective inhibition of cPLA2, but not sPLA2, also attenuates psychosine-induced cell death of human astrocytes. This study shows that extracellular calcium is required for psychosine induced cell death, but intracellular calcium release, reactive oxygen species or release of soluble factors are not involved. These findings suggest a cell autonomous effect, at least in human astrocytes. Supporting a role for PLA2 in psychosine-induced cell death of oligodendrocytes and astrocytes, the results show inhibition of PLA2 attenuates psychosine-induced decrease in the expression of astrocyte marker vimentin as well as myelin basic protein (MBP), myelin oligodendrocyte glycoprotein (MOG) and the neuronal marker SMI-32 in organotypic slice cultures. These findings provide further mechanistic details of psychosine-induced death of glia and suggest a role for PLA2 in the process. This work also supports the proposal that novel drugs for Krabbe disease may require testing on astrocytes as well as oligodendrocytes for more holistic prediction of pre-clinical and clinical efficacy.

The Role of the Oxysterol/EBI2 Pathway in the Immune and Central Nervous Systems

Oxysterols are pleiotropic messengers interacting with multiple receptor systems. One of the cognate receptors for oxysterols is EBI2, a G protein-coupled receptor highly expressed in the cells of the immune system. Here we discuss the receptor's role in the adapted immunity and inflammation as well as the receptor's expression and function in the CNS with the focus on astrocytes. We also discuss expression and signalling of oxysterol-producing enzymes such as CH25H and CYP7B1 in the CNS and the immune system. These steps will help to elucidate a possible role for this pathway in the physiology of the central and peripheral nervous system and its possible link to human disease.

The chemokine fractalkine (CX3CL1) attenuates H2O2-induced demyelination in cerebellar slices

Background

Fractalkine/CX3CR1 signalling has been implicated in many neurodegenerative and neurological diseases of the central nervous system (CNS). This signalling pathway plays an important role in regulating reactive oxygen species (ROS), as well as itself being altered in conditions of oxidative stress. Here, we investigated the effects of recombinant fractalkine (rCX3CL1) in models of hydrogen peroxide (H₂O₂)-induced demyelination and astrocyte toxicity, within organotypic cerebellar slice cultures.

Methods

Organotypic cerebellar slice cultures were generated from postnatal day 10 C57BL/6J mice to assess myelination. Immunohistochemistry was used to measure the degree of myelination. Fluorescent images were obtained using a leica SP8 confocal microscope and data analysed using ImageJ software.

Results

We show here, for the first time, that rCX3CL1 significantly attenuated bolus H₂O₂-induced demyelination as measured by expression of myelin basic protein (MBP) and attenuated reduced vimentin expression. Using the GOX-CAT system to continuously generate low levels of H₂O₂ and induce demyelination, we observed similar protective effects of rCX3CL1 on MBP and MOG fluorescence, although in this model, the decrease in vimentin expression was not altered.

Conclusions

This data indicates possible protective effects of fractalkine signalling in oxidative stress-induced demyelination in the central nervous system. This opens up the possibility of fractalkine receptor (CX3CR1) modulation as a potential new target for protecting against oxidative stress-induced demyelination in both inflammatory and non-inflammatory nervous system disorders.

Demyelination induced by oxidative stress is regulated by sphingosine 1-phosphate receptors

Oxidative stress is a pathological condition defined as an imbalance between production and removal of reactive oxygen species. This process causes structural cell damage, disrupts DNA repair and induces mitochondrial dysfunction. Many in vitro studies have used direct bolus application of H₂ O₂ to investigate the role of oxidative stress in cell culture. In this study, using mouse organotypic cerebellar slice cultures, the effects of H₂ O₂ -induced oxidative stress on myelination state were examined, using bolus concentrations of H₂ O₂ (0.1-1 mM) and low-continuous H₂ O₂ (∼20 μM) generated from glucose oxidase and catalase (GOX-CAT). Using these models, the potential therapeutic effects of pFTY720, an oral therapy used in multiple sclerosis, was also examined. We found bolus treatment of H₂ O₂ (0.5 mM) and, for the first time, low-continuous H₂ O₂ (GOX-CAT) to induce demyelination in organotypic slices. Both bolus H₂ O₂ and GOX-CAT treatments significantly decreased vimentin expression in these slice cultures as well as increased cell death in isolated astrocyte cultures. Importantly, pre-treatment with pFTY720 significantly attenuated both bolus H₂ O₂ and GOX-CAT-induced demyelination and the GOX-CAT-induced decrease in vimentin in cerebellar slices, without altering levels of the proinflammatory cytokines such as IL-6 and CX3CL1. We also observed increased SMI-32 immunoreactivity in the white matter tract induced by GOX-CAT indicating axonal damage, which was remarkably attenuated by pFTY720. Taken together, this data establishes a novel GOX-CAT model of demyelination and demonstrates that pFTY720 can act independently of inflammatory cytokines to attenuate decreases in vimentin, as well as axonal damage and demyelination induced by oxidative stress.

Fractalkine shedding is mediated by p38 and the ADAM10 protease under pro-inflammatory conditions in human astrocytes

Background

The fractalkine (CX3CR1) ligand is expressed in astrocytes and reported to be neuroprotective. When cleaved from the membrane, soluble fractalkine (sCX3CL1) activates the receptor CX3CR1. Although somewhat controversial, CX3CR1 is reported to be expressed in neurons and microglia. The membrane-bound form of CX3CL1 additionally acts as an adhesion molecule for microglia and infiltrating white blood cells. Much research has been done on the role of fractalkine in neuronal cells; however, little is known about the regulation of the CX3CL1 ligand in astrocytes.

Methods

The mechanisms involved in the up-regulation and cleavage of CX3CL1 from human astrocytes were investigated using immunocytochemistry, Q-PCR and ELISA. All statistical analysis was performed using GraphPad Prism 5.

Results

A combination of ADAM17 (TACE) and ADAM10 protease inhibitors was found to attenuate IL-1β-, TNF-α- and IFN-γ-induced sCX3CL1 levels in astrocytes. A specific ADAM10 (but not ADAM17) inhibitor also attenuated these effects, suggesting ADAM10 proteases induce release of sCX3CL1 from stimulated human astrocytes. A p38 MAPK inhibitor also attenuated the levels of sCX3CL1 upon treatment with IL-1β, TNF-α or IFN-γ. In addition, an IKKβ inhibitor significantly reduced the levels of sCX3CL1 induced by IL-1β or TNF-α in a concentration-dependent manner, suggesting a role for the NF-kB pathway.

Conclusions

In conclusion, this study shows that the release of soluble astrocytic fractalkine is regulated by ADAM10 proteases with p38 MAPK also playing a role in the fractalkine shedding event. These findings are important for understanding the role of CX3CL1 in healthy and stimulated astrocytes and may benefit our understanding of this pathway in neuro-inflammatory and neurodegenerative diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0659-7) contains supplementary material, which is available to authorized users.

In vitro and ex vivo models of multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disorder of the central nervous system (CNS). Current therapies suppress a misdirected myelin-destructive immune response. To combat the progressive, neurodestructive phase of MS, the therapeutic research focus is currently on compounds that might boost the endogenous potential of the brain to remyelinate axons, thereby achieving lesion repair. Here, we describe the testing of fingolimod on cultures of oligodendrocytes (OLs) and organotypic brain slices. We detail the protocols, pros, and cons of these in vitro and ex vivo approaches, along with the potential benefit of exploiting skin-punch biopsies from patients with MS, before concluding with a summary of future developments.

The EBI2 signalling pathway plays a role in cellular crosstalk between astrocytes and macrophages

EBI2 is a G protein-coupled receptor activated by oxysterol 7α, 25-dihydroxycholesterol (7α25HC) and regulates T cell-dependant antibody response and B cell migration. We recently found EBI2 is expressed in human astrocytes, regulates intracellular signalling and modulates astrocyte migration. Here, we report that LPS treatment of mouse astrocytes alters mRNA levels of EBI2 and oxysterols suggesting that the EBI2 signalling pathway is sensitive to LPS-mediated immune challenge. We also find that conditioned media obtained from LPS-stimulated mouse astrocytes induces macrophage migration, which is inhibited by the EBI2 antagonist NIBR189. These results demonstrate a role for the EBI2 signalling pathway in astrocytes as a sensor for immune challenge and for communication with innate immune cells such as macrophages.

The dual S1PR1/S1PR5 drug BAF312 (Siponimod) attenuates demyelination in organotypic slice cultures

Background

BAF312 (Siponimod) is a dual agonist at the sphingosine-1 phosphate receptors, S1PR1 and S1PR5. This drug is currently undergoing clinical trials for the treatment of secondary progressive multiple sclerosis (MS). Here, we investigated the effects of BAF312 on isolated astrocyte and microglia cultures as well as in slice culture models of demyelination.

Methods

Mouse and human astrocytes were treated with S1PR modulators and changes in the levels of pERK, pAkt, and calcium signalling as well as S1PR1 internalization and cytokine levels was investigated using Western blotting, immunochemistry, ELISA and confocal microscopy. Organotypic slice cultures were prepared from the cerebellum of 10-day-old mice and treated with lysophosphatidylcholine (LPC), psychosine and/or S1PR modulators, and changes in myelination states were measured by fluorescence of myelin basic protein and neurofilament H.

Results

BAF312 treatment of human and mouse astrocytes activated pERK, pAKT and Ca²⁺ signalling as well as inducing S1PR1 internalization. Notably, activation of S1PR1 increased pERK and pAKT in mouse astrocytes while both S1PR1 and S1PR3 equally increased pERK and pAKT in human astrocytes, suggesting that the coupling of S1PR1 and S1PR3 to pERK and pAKT differ in mouse and human astrocytes. We also observed that BAF312 moderately attenuated lipopolysaccharide (LPS)- or TNFα/IL17-induced levels of IL6 in both astrocyte and microglia cell cultures. In organotypic slice cultures, BAF312 reduced LPC-induced levels of IL6 and attenuated LPC-mediated demyelination. We have shown previously that the toxic lipid metabolite psychosine induces demyelination in organotypic slice cultures, without altering the levels of cytokines, such as IL6. Importantly, psychosine-induced demyelination was also attenuated by BAF312.

Conclusions

Overall, this study suggests that BAF312 can modulate glial cell function and attenuate demyelination, highlighting this drug as a further potential therapy in demyelinating disorders, beyond MS.

Pathway specific modulation of S1P1 receptor signalling in rat and human astrocytes

BACKGROUND AND PURPOSE

The sphingosine 1-phosphate receptor subtype 1 (S1P1R) is modulated by phosphorylated FTY720 (pFTY720), which causes S1P1R internalization preventing lymphocyte migration thus limiting autoimmune response. Studies indicate that internalized S1P1Rs continue to signal, maintaining an inhibition of cAMP, thus raising question whether the effects of pFTY720 are due to transient initial agonism, functional antagonism and/or continued signalling. To further investigate this, the current study first determined if continued S1P1R activation is pathway specific.

EXPERIMENTAL APPROACH

Using human and rat astrocyte cultures, the effects of S1P1R activation on cAMP, pERK and Ca(2+) signalling was investigated. In addition, to examine the role of S1P1R redistribution on these events, a novel biologic (MNP301) that prevented pFTY720-mediated S1P1R redistribution was engineered.

KEY RESULTS

The data showed that pFTY720 induced long-lasting S1P1R redistribution and continued cAMP signalling in rat astrocytes. In contrast, pFTY720 induced a transient increase of Ca(2+) in astrocytes and subsequent antagonism of Ca(2+) signalling. Notably, while leaving pFTY720-induced cAMP signalling intact, the novel MNP301 peptide attenuated S1P1R-mediated Ca(2+) and pERK signalling in cultured rat astrocytes.

CONCLUSIONS AND IMPLICATIONS

These findings suggested that pFTY720 causes continued cAMP signalling that is not dependent on S1P1R redistribution and induces functional antagonism of Ca(2+) signalling after transient stimulation. To our knowledge, this is the first report demonstrating that pFTY720 causes continued signalling in one pathway (cAMP) versus functional antagonism of another pathway (Ca(2+)) and which also suggests that redistributed S1P1Rs may have differing signalling properties from those expressed at the surface.

Increased interleukin 23 (IL23) levels in schizophrenia patients treated with depot antipsychotic medication

BACKGROUND

Schizophrenia is a mental disorder, where genetic and environmental factors contribute to disease onset and progression. The immune system appears to play a role in schizophrenia, where altered cytokines levels and autoantibodies have been described. Notably however, to our knowledge, IL23 levels have not before been measured in schizophrenia patients treated with depot medication.

METHODS

We examined IL23 levels in serum samples obtained from patients with schizophrenia, treated with depot medication (n=35) compared with healthy controls (n=38) and correlated these levels with treatment time, patient age and illness severity.

RESULTS

IL23 levels were raised in depot treated groups compared with healthy controls. No correlation was observed, however, between IL23 levels and treatment time, patient age or illness severity.

CONCLUSIONS

IL23 levels are raised in schizophrenia patients prescribed with depot medication, supporting the role of aberrant cytokine signalling in schizophrenia.

Galactosylsphingosine (psychosine) induced demyelination is attenuated by sphingosine 1-phosphate signalling

Globoid cell leukodystrophy (Krabbe disease, KD) is a rare infantile neurodegenerative disorder. KD is caused by deficiency in the lysosomal enzyme galactocerebrosidase (GALC) resulting in brain accumulation, in the micromolar range, of the toxic metabolite galactosylsphingosine (psychosine). Here we find psychosine induces human astrocyte cell death likely via an apoptotic process in a concentration- and time-dependent manner (EC50 ∼15 µM at 4h). We show these effects of psychosine are attenuated by pre-treatment with the sphingosine 1-phosphate receptor agonist pFTY720 (Fingolimod) (IC50 ∼100nM). Psychosine (1 µM, 10 µM) also potentiates LPS-induced (EC50 ∼100ng/ml) production of pro-inflammatory cytokines in mouse astrocytes, which is also attenuated by pFTY720 (1 µM). Most notably, for the first time, we show that psychosine, at a concentration found in the brains of patients with KD (EC50 ∼100nM) directly induces demyelination in mouse organotypic cerebellar slices in a manner that is independent of proinflammatory cytokine response and that pFTY720 (0.1nM) significantly inhibits. These results support the idea that psychosine is a pathogenic agent in KD and suggest that sphingosine 1-phosphate signalling could be a potential drug target for this illness.

The selective anti-IL17A monoclonal antibody secukinumab (AIN457) attenuates IL17A-induced levels of IL6 in human astrocytes

The family of interleukin 17 receptors (IL17Rs), subtypes IL17RA-IL17RE, is targeted by the group of pro-inflammatory IL17 cytokines (IL17A-F) and moreover the newly developed anti-IL17A antibody secukinumab (AIN457) has shown promise in Phase II trials in multiple sclerosis. Here, we show that human astrocytes, isolated from a fetal cerebral cortex, express IL17RA and IL17RC and in vitro treatment with IL17A increases protein levels of IL6 in human astrocytes, which is enhanced in the presence of TNFα, as determined by homogeneous time resolved fluorescence. Studies on acutely isolated mouse astrocytes are comparable to human astrocytes although the protein levels of IL6 are lower in mouse astrocytes, which also show a lower response to IL17F and IL1β in promoting IL6 levels. In human astrocytes, IL17A and TNFα also induce mRNA expression of IL6, IL8 and the Th17 cytokines CXCL1, CXCL2, and CCL20, with little effect on Th1 cytokines CXCL9, CXCL10, and CXCL11. The effects of IL17A are associated with nuclear translocation of the NF-κB transcription factor, as determined by immunocytochemistry, where treatment of human astrocytes with the inhibitors of the NF-κB pathway and with secukinumab inhibits the IL17A and IL17A/TNFα-induced increase in nuclear translocation of NF-κB and levels of IL6. Taken together the data shows that IL17A signaling plays a key role in regulating the levels of cytokines, such as IL6, in human astrocytes via a mechanism that involves NF-κB signaling and that selective inhibition of IL17A signaling attenuates levels of pro-inflammatory molecules in astrocytes.

EBI2 regulates intracellular signaling and migration in human astrocyte

The G protein-coupled receptor EBI2 (Epstein-Barr virus-induced gene 2) is activated by 7α, 25-dihydroxycholesterol (7α25HC) and plays a role in T cell-dependant antibody response and B cell migration. Aberrant EBI2 signaling is implicated in a range of autoimmune disorders however its role in the CNS remains unknown. Here we characterize the functional role of EBI2 in GLIA cells using primary human astrocytes and EBI2 knockout animals. We find human and mouse astrocytes express EBI2 and the enzymes necessary for synthesis and degradation of 7α25HC. In astrocytes, EBI2 activation stimulates ERK phosphorylation, Ca(2+) signaling and induces cellular migration. These results, for the first time, demonstrate a role for EBI2 in astrocyte function and suggest that modulation of this receptor may be beneficial in neuroinflammatory disorders.

The use of cytokine signature patterns: separating drug naïve, interferon and natalizumab-treated multiple sclerosis patients

Multiple sclerosis (MS) is an inflammatory illness characterized by demyelination and axonal neurodegeneration. Here, we used serum samples from MS patients to demonstrate if "cytokine signature" patterns can separate different patient groups better than using single cytokines. In this case, we used cytokine profiling to demonstrate if "cytokine signature" patterns can separate MS patients treated with interferon or natalizumab from drug naïve patients. Serum levels of eight individual cytokines (TNFα, IFNγ, S100B, IL-1β, IL-6, IL-8, IL-17 and IL-23) in MS patients treated with interferons (n = 11) and natalizumab (n = 14) were measured and, in general, showed reduced levels compared to drug naïve MS patients (n = 12). More evident changes were seen when analyzing "cytokine signatures" (i.e. summed value of all eight cytokines), which showed that patients treated with natalizumab and interferons showed significantly reduced cytokine signature levels than drug naïve MS patients. Moreover, patients treated with natalizumab were separated from drug naïve patients by almost 100% fidelity and that patients treated with natalizumab also had reduced levels of pro-inflammatory cytokines compared to patients treated with interferon. Overall, this study provides an example showing that the use of "cytokine signatures" may provide benefits over the analysis of single cytokines for the development of potential biomarkers.

Pro-inflammatory cytokine levels are raised in female schizophrenia patients treated with clozapine

BACKGROUND

We have previously shown that the neurotrophic factor, S100B, is raised in serum samples of female patients with schizophrenia, but not male patients, compared to controls, and this may be associated with raised BMI. Here we analysed the levels of additional proinflammatory cytokines in patients with schizophrenia to further investigate these gender differences.

METHODS

The levels of six cytokines (IL1β, IL6, IL8, IL17, IL23, TNFα) were measured in serum samples obtained from patients with schizophrenia, treated with clozapine (n=91) and compared with healthy controls (n=50). Individual cytokine levels were measured using dot-immunoblotting methods and a 'cytokine signature' was also generated by summing all 6 cytokines. Treatment time, patient age, gender, illness severity and metabolic parameters were also measured.

RESULTS

The levels of proinflammatory cytokines and BMI were significantly raised in female, but not male, patients treated with clozapine compared to healthy controls. Compared to individual cytokines, the 'cytokine signature' analysis showed less scatter of data although this 'cytokine signature' method did not improve separation of individual patients and controls.

CONCLUSIONS

This study supports previous findings that raised BMI, which is likely associated with increased number of adipocytes, may contribute to increased cytokine serum concentrations in females.

Targeting S1P receptors in experimental autoimmune encephalomyelitis in mice improves early deficits in locomotor activity and increases ultrasonic vocalisations

Fingolimod (FTY720) is an oral therapy for relapsing remitting multiple sclerosis (MS) and targets sphingosine 1-phosphate receptors (S1PRs). FTY720 also rescues animals from experimental autoimmune encephalomyelitis (EAE), an animal model of MS. The protective effects of FTY720 in EAE are primarily scored manually by examining weight loss and limb paralysis that begins around 10-12 days after immunisation. To our knowledge, pre-clinical effects of FTY720 on animal behaviour early in EAE have not been explored. Here, we developed an automated behaviour monitoring system to examine the early effects of FTY720 on subtle pre-symptomatic behaviour of mice induced with EAE. Our automated home-cage monitoring system (AHC-MS) enabled non-contact detection of movement and ultrasonic vocalisations (USVs) of mice induced with EAE, thus allowing detection of subtle changes in mouse behaviour before paralysis occurs. Mice receiving FTY720 emit longer USVs and display higher levels of motor activity than vehicle-treated EAE mice before clinical symptoms become apparent. Importantly, this study promotes the 3Rs ethics (replacement, reduction and refinement) in the EAE animal model and may also improve pre-screening of potentially novel MS therapies. In addition, this is the first report showing the early effects of FTY720 in EAE which underscores its protective effects.

The protein interacting with C-kinase (PICK1) interacts with and attenuates parkin-associated endothelial-like (PAEL) receptor-mediated cell death

The parkin-associated endothelial-like receptor (PAELR, GPR37) is an orphan G protein-coupled receptor that interacts with and is degraded by parkin-mediated ubiquitination. Mutations in parkin are thought to result in PAELR accumulation and increase neuronal cell death in Parkinson's disease. In this study, we find that the protein interacting with C-kinase (PICK1) interacts with PAELR. Specifically, the Postsynaptic density protein-95/Discs large/ZO-1 (PDZ) domain of PICK1 interacted with the last three residues of the c-terminal (ct) located PDZ motif of PAELR. Pull-down assays indicated that recombinant and native PICK1, obtained from heterologous cells and rat brain tissue, respectively, were retained by a glutathione S-transferase fusion of ct-PAELR. Furthermore, coimmunoprecipitation studies isolated a PAELR-PICK1 complex from transiently transfected cells. PICK1 interacts with parkin and our data showed that PICK1 reduces PAELR expression levels in transiently transfected heterologous cells compared to a PICK1 mutant that does not interact with PAELR. Finally, PICK1 over-expression in HEK293 cells reduced cell death induced by PAEALR over-expression during rotenone treatment and these effects of PICK1 were attenuated during inhibition of the proteasome. These results suggest a role for PICK1 in preventing PAELR-induced cell toxicity.

The expression of neuronal sorting nexin 8 (SNX8) exacerbates abnormal cholesterol levels

SNX8 is a PX-BAR domain sub-family of sorting nexins (SNXs), which is reported as a β-amyloid (Aβ) toxicity enhancer and associated with Alzheimer's disease. We have also described SNX8 as a novel activator of the sterol regulatory element binding protein (SREBP) transcription factor, a major regulator of cholesterol homeostasis. In that study, we have showed that SNX8 reduced an insulin-induced gene (INSIG)-dependent block of SREBP-mediated transcription. Here, for the first time, we investigated the expression and function of SNX8 within the CNS. We found that SNX8 was expressed within neurons, but not astrocytes or microglia, with neuronal localisation primarily in the soma. The protein levels of neuronal SNX8 were unchanged in the presence of moderately high cholesterol but were decreased by mevinolin (a cholesterol-lowering statin) and U18666a (which causes cholesterol to accumulate within the lysosome). To determine if SNX8 overexpression alters the levels of cholesterol, we engineered a GFP-SNX8 lentivirus. The overexpression of GFP-SNX8 had no effect on cholesterol in neurons under control conditions or in already strongly altered cholesterol conditions of mevinolin or U18666a. In contrast, in moderately high cholesterol, the overexpression of GFP-SNX8 caused redistribution of cholesterol within neurons creating a phenotype similar to U18666a treatment. Taken together, these data suggest that extreme changes in cholesterol reduce SNX8 expression and that overexpression of SNX8 exacerbates aberrant handling of neuronal cholesterol. This work further supports the role for SNX8 in regulating cholesterol levels, which could be important in understanding its role as an Aβ toxicity enhancer and its association with Alzheimer's disease.

The role of sphingosine 1-phosphate receptors in the treatment of demyelinating diseases

Sphingosine 1-phosphate receptors (S1PRs) are a family of G-protein coupled receptors composed of subtypes S1PR1–5 and activated by the endogenous ligand sphingosine 1-phosphate. S1PRs are modulated by the recently approved oral therapy for relapsing–remitting multiple sclerosis, called fingolimod (FTY720). The phosphorylated version of FTY720 (pFTY720) is a pan-S1PR agonist, with the exception of S1PR2. This drug promotes the internalization of S1PR1s in T cells and is said to act as a ‘functional antagonist’ making lymphocytes ‘blind’ to sphingosine 1-phosphate gradients and limiting cell egress from lymph nodes. This immunomodulatory effect of pFTY720 is proposed to be the prime mechanism by which this compound is efficacious in the treatment of multiple sclerosis. Importantly, however, S1PRs are also expressed in many other cell types, for example, cells of the cardiovascular system and the CNS. Studies have shown that pFTY720 enters the CNS and that modulation of S1PRs can alter the cellular physiology of neurons, astrocytes, microglia and oligodendrocytes. These works are suggestive of a potential role for S1PRs expressed in brain cells as targets for pFTY720. This article reviews the role of S1PRs in oligodendrocytes. The authors start by first debating whether pFTY720-mediated internalization of S1PRs causes ‘functional antagonism’ and/or ‘pathway-specific continued signaling’. The authors then describe the signaling pathways that are modulated by S1PRs expressed in oligodendrocytes and also outline the role of S1PRs in oligodendrocyte differentiation, process extension, survival and migration. Finally, the authors discuss the in vitro studies that suggest pFTY720 promotes myelination state versus the in vivo studies that suggest pFTY720 may not alter myelination. The authors conclude by suggesting that S1PRs in the CNS may be of potential use as drug targets not only for multiple sclerosis, but possibly for a number of other demyelinating disorders.

Small-molecule inhibitors at the PSD-95/nNOS interface have antidepressant-like properties in mice

Previous studies have demonstrated that nitric oxide (NO) synthase inhibitors are as efficacious as tricyclic antidepressants in preclinical antidepressant screening procedures and in attenuating behavioural deficits associated with animal models of depression. The N-methyl-D-aspartate receptor (NMDA-R) complex gates Ca(2+), which interacts with calmodulin to subsequently activate NO synthase. We hypothesised that uncoupling neuronal nitric oxide synthase (nNOS) from the NMDA-R through the scaffolding protein postsynaptic density protein 95 (PSD-95) would produce behavioural antidepressant effects similar to NO synthase inhibitors. Small-molecule inhibitors of the PSD-95/nNOS interaction, IC87201 (0.01-2 mg/kg) and ZL006 (10 mg/kg) were tested for antidepressant properties in tests of antidepressant activity namely the tail suspension and forced swim tests in mice. We now report that IC87201 and ZL006 produce antidepressant-like responses in the forced swimming test (FST) and tail suspension test (TST) following a single administration in mice. By contrast to the tricyclic antidepressant imipramine (25 mg/kg), the effects are not observed 1 h following drug administration but are apparent 24 and 72 h later. Furthermore prior exposure to the TST or FST is required in order to observe the antidepressant-related activity. Similar delayed and sustained antidepressant-like effects were observed following TRIM (50 mg/kg) and ketamine (30 mg/kg) in the TST. The antidepressant-like effects of ZL006 also generalise to IC87201 in the TST. IC87201 was devoid of effects on locomotor activity and step-through latency in the passive avoidance cognition test. These data support the hypothesis that targeting the PSD-95/nNOS interaction downstream of NMDA-R produces antidepressant effects and may represent a novel class of therapeutics for major depressive disorders.

The structure and function of the S1P1 receptor

Sphingosine 1-phosphate (S1P) receptors (S1PRs) belong to the class A family of G protein-coupled receptors (GPCRs). S1PRs are widely expressed on many cell types, including those of the immune, cardiovascular, and central nervous systems. The S1PR family is rapidly gaining attention as an important mediator of many cellular processes, including cell differentiation, migration, survival, angiogenesis, calcium homeostasis, inflammation and immunity. Importantly, S1PRs are known drug targets for multiple sclerosis (MS), for which the newly developed oral therapy fingolimod, an S1PR modulator, has recently been approved for clinical use. Much progress has also recently been made in the field of structural biology and in the modeling of heterotrimeric GPCRs allowing the crystal structure of the S1PR1 subtype to be elucidated and key interactions defined. Here, we outline the structure and function of S1PR1, highlighting the key residues involved in receptor activation, signaling, transmembrane interactions, ligand binding, post-translational modification, and protein-protein interactions.

Levels of S100B are raised in female patients with schizophrenia

BACKGROUND

The neurotrophic factor, S100B, is released primarily from astrocytes, with serum and CSF levels of S100B reported as altered in schizophrenia. However, many of these reports are contradictory. Here, serum levels of S100B in schizophrenia and influence of age, gender, medication and illness severity were examined.

METHODS

Serum S100B levels were measured in patients with schizophrenia treated with clozapine. Lifestyle, metabolic and illness severity parameters were correlated with S100B concentrations.

RESULTS

Data showed raised serum levels of S100B in schizophrenia female patients, but not male patients, compared to controls. Correlation analysis demonstrated a positive association between S100B serum concentrations and BMI.

CONCLUSIONS

This study supports previous findings that adipocytes may contribute to S100B serum concentrations in females, in addition to astrocytes. This study also supports the hypothesis that metabolic effects of medication, lifestyle choices and the illness itself, may be contributing factors to altered levels of S100B.

The binding affinities of proteins interacting with the PDZ domain of PICK1

Protein interacting with C kinase (PICK1) is well conserved throughout evolution and plays a critical role in synaptic plasticity by regulating the trafficking and posttranslational modification of its interacting proteins. PICK1 contains a single PSD95/DlgA/Zo-1 (PDZ) protein-protein interaction domain, which is promiscuous and shown to interact with over 60 proteins, most of which play roles in neuronal function. Several reports have suggested the role of PICK1 in disorders such as epilepsy, pain, brain trauma and stroke, drug abuse and dependence, schizophrenia and psychosis. Importantly, lead compounds that block PICK1 interactions are also now becoming available. Here, a new modeling approach was developed to investigate binding affinities of PDZ interactions. Using these methods, the binding affinities of all major PICK1 interacting proteins are reported and the effects of PICK1 mutations on these interactions are described. These modeling methods have important implications in defining the binding properties of proteins interacting with PICK1 as well as the general structural requirements of PDZ interactions. The study also provides modeling methods to support in the drug design of ligands for PDZ domains, which may further aid in development of the family of PDZ domains as a drug target.

The PSD-95/nNOS complex: new drugs for depression?

Drug treatment of major depressive disorder is currently limited to the use of agents which influence monoaminergic neuronal transmission including inhibitors of presynaptic transporters and monoamine oxidase. Typically improvement in depressive symptoms only emerges after several weeks of treatment, suggesting that downstream neuronal adaptations rather than the elevation in synaptic monoamine levels are responsible for antidepressant effects. In recent years, the NMDA receptor has emerged as a promising target for treating CNS disorders including stroke, pain and depression. In this review, we outline the molecular mechanisms underlying NMDA receptor signalling in neurons and in particular provide an overview of the role of the NMDAR/PSD-95/nNOS complex in CNS disorders. We discuss novel drug developments made that suggest the NMDAR/PSD-95/nNOS complex as a potential target for the treatment of depression. The review also provides examples of how PDZ-based protein-protein interactions can be exploited as novel drug targets for disease.

Neuropathology in mice expressing mouse alpha-synuclein

α-Synuclein (αSN) in human is tightly linked both neuropathologically and genetically to Parkinson's disease (PD) and related disorders. Disease-causing properties in vivo of the wildtype mouse ortholog (mαSN), which carries a threonine at position 53 like the A53T human mutant version that is genetically linked to PD, were never reported. To this end we generated mouse lines that express mαSN in central neurons at levels reaching up to six-fold compared to endogenous mαSN. Unlike transgenic mice expressing human wildtype or mutant forms of αSN, these mαSN transgenic mice showed pronounced ubiquitin immunopathology in spinal cord and brainstem. Isoelectric separation of mαSN species revealed multiple isoforms including two Ser129-phosphorylated species in the most severely affected brain regions. Neuronal Ser129-phosphorylated αSN occured in granular and small fibrillar aggregates and pathological staining patterns in neurites occasionally revealed a striking ladder of small alternating segments staining either for Ser129-phosphorylated αSN or ubiquitin but not both. Axonal degeneration in long white matter tracts of the spinal cord, with breakdown of myelin sheaths and degeneration of neuromuscular junctions with loss of integrity of the presynaptic neurofilament network in mαSN transgenic mice, was similar to what we have reported for mice expressing human αSN wildtype or mutant forms. In hippocampal neurons, the mαSN protein accumulated and was phosphorylated but these neurons showed no ubiquitin immunopathology. In contrast to the early-onset motor abnormalities and muscle weakness observed in mice expressing human αSN, mαSN transgenic mice displayed only end-stage phenotypic alterations that manifested alongside with neuropathology. Altogether these findings show that increased levels of wildtype mαSN does not induce early-onset behavior changes, but drives end-stage pathophysiological changes in murine neurons that are strikingly similar to those evoked by expression of human wildtype or mutant forms.

Identification of novel genes and pathways regulating SREBP transcriptional activity

BACKGROUND

Lipid metabolism in mammals is orchestrated by a family of transcription factors called sterol regulatory element-binding proteins (SREBPs) that control the expression of genes required for the uptake and synthesis of cholesterol, fatty acids, and triglycerides. SREBPs are thus essential for insulin-induced lipogenesis and for cellular membrane homeostasis and biogenesis. Although multiple players have been identified that control the expression and activation of SREBPs, gaps remain in our understanding of how SREBPs are coordinated with other physiological pathways.

METHODOLOGY

To identify novel regulators of SREBPs, we performed a genome-wide cDNA over-expression screen to identify proteins that might modulate the transcription of a luciferase gene driven from an SREBP-specific promoter. The results were verified through secondary biological assays and expression data were analyzed by a novel application of the Gene Set Enrichment Analysis (GSEA) method.

CONCLUSIONS/SIGNIFICANCE

We screened 10,000 different cDNAs and identified a number of genes and pathways that have previously not been implicated in SREBP control and cellular cholesterol homeostasis. These findings further our understanding of lipid biology and should lead to new insights into lipid associated disorders.

Lentivirus Tau (P301S) expression in adult amyloid precursor protein (APP)-transgenic mice leads to tangle formation

AIMS

In this study, we aimed to investigate the interaction between amyloid- and Tau-associated pathologies to gain further insights into the development of Alzheimer's disease. We examined the formation of neurofibrillary tangles (NFT) in adult mouse brain without the prior overexpression of Tau at embryonic or early post-natal stages to dissociate any developmental mechanisms.

METHODS

Lentivirus technology was used to examine the effects of overexpressing mutant Tau-P301S in the adult mouse brains of both wild-type and amyloid precursor protein (APP)-transgenic mice.

RESULTS

We find that injection of lentivirus Tau-P301S into the hippocampus of adult wild-type mice increases levels of hyperphosphorylated Tau, as early as 3 months post injection. However, no NFT are found even after 13 months of Tau expression. In contrast, the overexpression of Tau-P301S in adult APP-transgenic animals results in the formation of Gallyas-stained NFT.

CONCLUSIONS

Our current findings are the first to show that overexpression of Tau-P301S in adult mice overexpressing APP, but not wild-type mice, leads to enhanced Tau-related pathology.

SCFCdc4 acts antagonistically to the PGC-1alpha transcriptional coactivator by targeting it for ubiquitin-mediated proteolysis

Peroxisome proliferator-activated receptor gamma (PPARgamma) coactivator-1alpha (PGC-1alpha) is a highly regulated transcriptional coactivator that coordinates energy metabolism in mammals. Misregulation of PGC-1alpha has been implicated in the pathogenesis of several human diseases, including diabetes, obesity, and neurological disorders. We identified SCF(Cdc4) as an E3 ubiquitin ligase that regulates PGC-1alpha through ubiquitin-mediated proteolysis. PGC-1alpha contains two Cdc4 phosphodegrons that bind Cdc4 when phosphorylated by Glycogen Synthase Kinase 3beta (GSK3beta) and p38 MAPK, leading to SCF(Cdc4)-dependent ubiquitylation and proteasomal degradation of PGC-1alpha. Furthermore, SCF(Cdc4) negatively regulates PGC-1alpha-dependent transcription. We demonstrate that RNAi-mediated reduction of Cdc4 in primary neurons results in an increase of endogenous PGC-1alpha protein, while ectopic expression of Cdc4 leads to a reduction of endogenous PGC-1alpha protein. Finally, under conditions of oxidative stress in neurons, Cdc4 levels are decreased, leading to an increase in PGC-1alpha protein and PGC-1alpha-dependent transcription. These results suggest that attenuation of SCF(Cdc4)-dependent proteasomal degradation of PGC-1alpha has a role in mediating the PGC-1alpha-dependent transcriptional response to oxidative stress.

Amyloid precursor protein knockout mice show age-dependent deficits in passive avoidance learning

Amyloid precursor protein (APP) is involved in the pathogenesis of Alzheimer's disease (AD), but its role in cognition has been relatively little studied. APP knockout (KO) animals have been described previously and show deficits in grip strength, reduced locomotor activity and impaired learning and memory in a conditioned avoidance test and the Morris water-maze. In order to further investigate the in vivo function of APP and its proteolytic derivatives, we tested APP KO mice and age-matched wild type controls at two different ages, 3 and 8 months, in a range of behavioural tests measuring neuromuscular, locomotor and cognitive functions. These tests included the acquisition of a passive avoidance response as a measure of long-term memory of an aversive experience, and spontaneous alternation in a Y-maze, regarded as a measure of spatial short-term memory. The absence of APP expression in APP KO mice was confirmed at the protein level using hippocampal tissue in Western blotting. APP KO mice displayed deficits in forelimb grip strength and locomotor activity in agreement with previous studies. In the Y-maze test used for spontaneous alternation behaviour, APP KO animals did not exhibit reduced alternation rates. On the other hand, in the passive avoidance test, APP KO mice showed an age-related deficit in retention of memory for an aversive experience. The results suggest that APP and/or its proteolytic derivatives may play a role in long-term memory in adult brain and/or may be required during the development and maintenance of neuronal networks involved in this type of memory.

Phosphorylated FTY720 promotes astrocyte migration through sphingosine-1-phosphate receptors

Sphingosine-1-phosphate (S1P) receptors are widely expressed in the central nervous system where they are thought to regulate glia cell function. The phosphorylated version of fingolimod/FTY720 (FTY720P) is active on a broad spectrum of S1P receptors and the parent compound is currently in phase III clinical trials for the treatment of multiple sclerosis. Here, we aimed to identify which cell type(s) and S1P receptor(s) of the central nervous system are targeted by FTY720P. Using calcium imaging in mixed cultures from embryonic rat cortex we show that astrocytes are the major cell type responsive to FTY720P in this assay. In enriched astrocyte cultures, we detect expression of S1P1 and S1P3 receptors and demonstrate that FTY720P activates Gi protein-mediated signaling cascades. We also show that FTY720P as well as the S1P1-selective agonist SEW2871 stimulate astrocyte migration. The data indicate that FTY720P exerts its effects on astrocytes predominantly via the activation of S1P1 receptors, whereas S1P signals through both S1P1 and S1P3 receptors. We suggest that this distinct pharmacological profile of FTY720P, compared with S1P, could play a role in the therapeutic effects of FTY720 in multiple sclerosis.

Brain sphingosine-1-phosphate receptors: implication for FTY720 in the treatment of multiple sclerosis

Multiple sclerosis (MS) is an autoimmune, neurological disability with unknown etiology. The current therapies available for MS work by an immunomodulatory action, preventing T-cell- and macrophage-mediated destruction of brain-resident oligodendrocytes and axonal loss. Recently, FTY720 (fingolimod) was shown to significantly reduce relapse rates in MS patients and is currently in Phase III clinical trials. This drug attenuates trafficking of harmful T cells entering the brain by regulating sphingosine-1-phosphate (S1P) receptors. Here, we outline the direct roles that S1P receptors play in the central nervous system (CNS) and discuss additional modalities by which FTY720 may provide direct neuroprotection in MS.

Amyloid precursor protein knockdown by siRNA impairs spontaneous alternation in adult mice

The cleavage-product of amyloid precursor protein (APP) constitutes the core component of plaques found in the brains of Alzheimer's disease (AD) patients. APP is ubiquitously expressed and its precise physiological functions remain unclear. This protein has been proposed to regulate synaptic function and processes underlying learning and memory. While APP knockout mice show behavioral impairments, these may occur due to early changes during development and/or due to abolition of APP function in adult. To investigate the acute effects of APP knockdown without involving developmental processes, APP expression was reduced using RNA interference in adult mouse brain. Small interfering RNAs (siRNAs) that down-regulated mouse APP protein levels (APP-siRNA) were identified using an APP plasmid-siRNA co-transfection assay in mouse NIH/3T3 fibroblast cells. Infusion of APP-siRNAs into the ventricular system for 2 weeks also down-regulated APP mRNA in mouse brain. Highest knockdown of APP mRNA levels was found in the CA2-CA3 regions of the hippocampus. Mice treated with the most active APP-siRNA showed a significant reduction in spontaneous alternation rate in the Y-maze, without effects on forelimb grip strength or locomotor activity. These data suggest that acute knockdown of APP in adult mouse brain impairs hippocampus-dependent spatial working memory.