The NLRP3 inflammasome is essential for IL-18 production in a murine model of macrophage activation syndrome

Hyperinflammatory disease is associated with an aberrant immune response resulting in cytokine storm. One such instance of hyperinflammatory disease is known as macrophage activation syndrome (MAS). The pathology of MAS can be characterised by significantly elevated serum levels of interleukin (IL)-18 and interferon (IFN)-γ. Given the role for IL-18 in MAS, we sought to establish the role of inflammasomes in the disease process. Using a murine model of CpG-DNA induced MAS, we discovered that the expression of the NLRP3 inflammasome was increased and correlated with IL-18 production. Inhibition of the NLRP3 inflammasome, or downstream caspase-1, prevented MAS-mediated upregulation of plasma IL-18 but interestingly did not alleviate key features of hyperinflammatory disease including hyperferritinaemia and splenomegaly. Furthermore IL-1 receptor blockade with IL-1Ra did not prevent the development of CpG-induced MAS, despite being clinically effective in the treatment of MAS. These data demonstrate that in the development of MAS, the NLRP3 inflammasome was essential for the elevation in plasma IL-18, a key cytokine in clinical cases of MAS, but was not a driving factor in the pathogenesis of CpG-induced MAS.

Brazilin is a natural product inhibitor of the NLRP3 inflammasome

Excessive or aberrant NLRP3 inflammasome activation has been implicated in the progression and initiation of many inflammatory conditions; however, currently no NLRP3 inflammasome inhibitors have been approved for therapeutic use in the clinic. Here we have identified that the natural product brazilin effectively inhibits both priming and activation of the NLRP3 inflammasome in cultured murine macrophages, a human iPSC microglial cell line and in a mouse model of acute peritoneal inflammation. Through computational modeling, we predict that brazilin can adopt a favorable binding pose within a site of the NLRP3 protein which is essential for its conformational activation. Our results not only encourage further evaluation of brazilin as a therapeutic agent for NLRP3-related inflammatory diseases, but also introduce this small-molecule as a promising scaffold structure for the development of derivative NLRP3 inhibitor compounds.

Intracerebral Administration of a Novel Self-Assembling Peptide Hydrogel Is Safe and Supports Cell Proliferation in Experimental Intracerebral Haemorrhage

Intracerebral haemorrhage (ICH) is the deadliest form of stroke, but current treatment options are limited, meaning ICH survivors are often left with life-changing disabilities. The significant unmet clinical need and socioeconomic burden of ICH mean novel regenerative medicine approaches are gaining interest. To facilitate the regeneration of the ICH lesion, injectable biomimetic hydrogels are proposed as both scaffolds for endogenous repair and delivery platforms for pro-regenerative therapies. In this paper, the objective was to explore whether injection of a novel self-assembling peptide hydrogel (SAPH) Alpha2 was feasible, safe and could stimulate brain tissue regeneration, in a collagenase-induced ICH model in rats. Alpha2 was administered intracerebrally at 7 days post ICH and functional outcome measures, histological markers of damage and repair and RNA-sequencing were investigated for up to 8 weeks. The hydrogel Alpha2 was safe, well-tolerated and was retained in the lesion for several weeks, where it allowed infiltration of host cells. The hydrogel had a largely neutral effect on functional outcomes and expression of angiogenic and neurogenic markers but led to increased numbers of proliferating cells. RNAseq and pathway analysis showed that ICH altered genes related to inflammatory and phagocytic pathways, and these changes were also observed after administration of hydrogel. Overall, the results show that the novel hydrogel was safe when injected intracerebrally and had no negative effects on functional outcomes but increased cell proliferation. To elicit a regenerative effect, future studies could use a functionalised hydrogel or combine it with an adjunct therapy.

A multi-disciplinary commentary on preclinical research to investigate vascular contributions to dementia

Although dementia research has been dominated by Alzheimer's disease (AD), most dementia in older people is now recognised to be due to mixed pathologies, usually combining vascular and AD brain pathology. Vascular cognitive impairment (VCI), which encompasses vascular dementia (VaD) is the second most common type of dementia. Models of VCI have been delayed by limited understanding of the underlying aetiology and pathogenesis. This review by a multidisciplinary, diverse (in terms of sex, geography and career stage), cross-institute team provides a perspective on limitations to current VCI models and recommendations for improving translation and reproducibility. We discuss reproducibility, clinical features of VCI and corresponding assessments in models, human pathology, bioinformatics approaches, and data sharing. We offer recommendations for future research, particularly focusing on small vessel disease as a main underpinning disorder.

Filter exchange imaging with crusher gradient modelling detects increased blood-brain barrier water permeability in response to mild lung infection

Blood-brain barrier (BBB) dysfunction occurs in many brain diseases, and there is increasing evidence to suggest that it is an early process in dementia which may be exacerbated by peripheral infection. Filter-exchange imaging (FEXI) is an MRI technique for measuring trans-membrane water exchange. FEXI data is typically analysed using the apparent exchange rate (AXR) model, yielding estimates of the AXR. Crusher gradients are commonly used to remove unwanted coherence pathways arising from longitudinal storage pulses during the mixing period. We first demonstrate that when using thin slices, as is needed for imaging the rodent brain, crusher gradients result in underestimation of the AXR. To address this, we propose an extended crusher-compensated exchange rate (CCXR) model to account for diffusion-weighting introduced by the crusher gradients, which is able to recover ground truth values of BBB water exchange (k_in) in simulated data. When applied to the rat brain, k_in estimates obtained using the CCXR model were 3.10 s^-1 and 3.49 s^-1 compared to AXR estimates of 1.24 s^-1 and 0.49 s^-1 for slice thicknesses of 4.0 mm and 2.5 mm respectively. We then validated our approach using a clinically relevant Streptococcus pneumoniae lung infection. We observed a significant 70 ± 10% increase in BBB water exchange in rats during active infection (k_in = 3.78 ± 0.42 s^-1) compared to before infection (k_in = 2.72 ± 0.30 s^-1; p = 0.02). The BBB water exchange rate during infection was associated with higher levels of plasma von Willebrand factor (VWF), a marker of acute vascular inflammation. We also observed 42% higher expression of perivascular aquaporin-4 (AQP4) in infected animals compared to non-infected controls, while levels of tight junction proteins remain consistent between groups. In summary, we propose a modelling approach for FEXI data which removes the bias in estimated water-exchange rates associated with the use of crusher gradients. Using this approach, we demonstrate the impact of peripheral infection on BBB water exchange, which appears to be mediated by endothelial dysfunction and associated with an increase in perivascular AQP4.

Characterisation of C101248: A novel selective THIK-1 channel inhibitor for the modulation of microglial NLRP3-inflammasome

Neuroinflammation, specifically the NLRP3 inflammasome cascade, is a common underlying pathological feature of many neurodegenerative diseases. Evidence suggests that NLRP3 activation involves changes in intracellular K+. Nuclear Enriched Transcript Sort Sequencing (NETSseq), which allows for deep sequencing of purified cell types from human post-mortem brain tissue, demonstrated a highly specific expression of the tandem pore domain halothane-inhibited K+ channel 1 (THIK-1) in microglia compared to other glial and neuronal cell types in the human brain. NETSseq also showed a significant increase of THIK-1 in microglia isolated from cortical regions of brains with Alzheimer's disease (AD) relative to control donors. Herein, we report the discovery and pharmacological characterisation of C101248, the first selective small-molecule inhibitor of THIK-1. C101248 showed a concentration-dependent inhibition of both mouse and human THIK-1 (IC50: ∼50 nM) and was inactive against K2P family members TREK-1 and TWIK-2, and Kv2.1. Whole-cell patch-clamp recordings of microglia from mouse hippocampal slices showed that C101248 potently blocked both tonic and ATP-evoked THIK-1 K+ currents. Notably, C101248 had no effect on other constitutively active resting conductance in slices from THIK-1-depleted mice. In isolated microglia, C101248 prevented NLRP3-dependent release of IL-1β, an effect not seen in THIK-1-depleted microglia. In conclusion, we demonstrated that inhibiting THIK-1 (a microglia specific gene that is upregulated in brains from donors with AD) using a novel selective modulator attenuates the NLRP3-dependent release of IL-1β from microglia, which suggests that this channel may be a potential therapeutic target for the modulation of neuroinflammation in AD.

Looking into the IL-1 of the storm: are inflammasomes the link between immunothrombosis and hyperinflammation in cytokine storm syndromes?

Inflammasomes and the interleukin (IL)-1 family of cytokines are key mediators of both inflammation and immunothrombosis. Inflammasomes are responsible for the release of the pro-inflammatory cytokines IL-1β and IL-18, as well as releasing tissue factor (TF), a pivotal initiator of the extrinsic coagulation cascade. Uncontrolled production of inflammatory cytokines results in what is known as a "cytokine storm" leading to hyperinflammatory disease. Cytokine storms can complicate a variety of diseases and results in hypercytokinemia, coagulopathies, tissue damage, multiorgan failure, and death. Patients presenting with cytokine storm syndromes have a high mortality rate, driven in part by disseminated intravascular coagulation (DIC). While our knowledge on the factors propagating cytokine storms is increasing, how cytokine storm influences DIC remains unknown, and therefore treatments for diseases, where these aspects are a key feature are limited, with most targeting specific cytokines. Currently, no therapies target the immunothrombosis aspect of hyperinflammatory syndromes. Here we discuss how targeting the inflammasome and pyroptosis may be a novel therapeutic strategy for the treatment of hyperinflammation and its associated pathologies.

The two pore potassium channel THIK-1 regulates NLRP3 inflammasome activation

The NLRP3 (NLR family, pyrin domain containing 3) inflammasome is a multi-protein complex responsible for the activation of caspase-1 and the subsequent cleavage and activation of the potent proinflammatory cytokines IL-1β and IL-18, and pyroptotic cell death. NLRP3 is implicated as a driver of inflammation in a range of disorders including neurodegenerative diseases, type 2 diabetes, and atherosclerosis. A commonly reported mechanism contributing to NLRP3 inflammasome activation is potassium ion (K⁺ ) efflux across the plasma membrane. Identification of K⁺ channels involved in NLRP3 activation remains incomplete. Here, we investigated the role of the K⁺ channel THIK-1 in NLRP3 activation. Both pharmacological inhibitors and cells from THIK-1 knockout (KO) mice were used to assess THIK-1 contribution to macrophage NLRP3 activation in vitro. Pharmacological inhibition of THIK-1 inhibited caspase-1 activation and IL-1β release from mouse bone-marrow-derived macrophages (BMDMs), mixed glia, and microglia in response to NLRP3 agonists. Similarly, BMDMs and microglia from THIK-1 KO mice had reduced NLRP3-dependent IL-1β release in response to P2X7 receptor activation with ATP. Overall, these data suggest that THIK-1 is a regulator of NLRP3 inflammasome activation in response to ATP and identify THIK-1 as a potential therapeutic target for inflammatory disease.

LRRC8A is dispensable for a variety of microglial functions and response to acute stroke

Microglia, resident brain immune cells, are critical in orchestrating responses to central nervous system (CNS) injury. Many microglial functions, such as phagocytosis, motility and chemotaxis, are suggested to rely on chloride channels, including the volume‐regulated anion channel (VRAC), but studies to date have relied on the use of pharmacological tools with limited specificity. VRAC has also been proposed as a drug target for acute CNS injury, and its role in microglial function is of considerable interest for developing CNS therapeutics. This study aimed to definitively confirm the contribution of VRAC in microglia function by using conditional LRRC8A‐knockout mice, which lacked the essential VRAC subunit LRRC8A in microglia. We demonstrated that while VRAC contributed to cell volume regulation, it had no effect on phagocytic activity, cell migration or P2YR12‐dependent chemotaxis. Moreover, loss of microglial VRAC did not affect microglial morphology or the extent of ischemic damage following stroke. We conclude that VRAC does not critically regulate microglial responses to brain injury and could be targetable in other CNS cell types (e.g., astrocytes) without impeding microglial function. Our results also demonstrate a role for VRAC in cell volume regulation but show that VRAC is not involved in several major cellular functions that it was previously thought to regulate, and point to other, alternative mechanisms of chloride transport in innate immunity.

Regenerative Potential of Hydrogels for Intracerebral Hemorrhage: Lessons from Ischemic Stroke and Traumatic Brain Injury Research

Intracerebral hemorrhage (ICH) is a deadly and debilitating type of stroke, caused by the rupture of cerebral blood vessels. To date, there are no restorative interventions approved for use in ICH patients, highlighting a critical unmet need. ICH shares some pathological features with other acute brain injuries such as ischemic stroke (IS) and traumatic brain injury (TBI), including the loss of brain tissue, disruption of the blood-brain barrier, and activation of a potent inflammatory response. New biomaterials such as hydrogels have been recently investigated for their therapeutic benefit in both experimental IS and TBI, owing to their provision of architectural support for damaged brain tissue and ability to deliver cellular and molecular therapies. Conversely, research on the use of hydrogels for ICH therapy is still in its infancy, with very few published reports investigating their therapeutic potential. Here, the published use of hydrogels in experimental ICH is commented upon and how approaches reported in the IS and TBI fields may be applied to ICH research to inform the design of future therapies is described. Unique aspects of ICH that are distinct from IS and TBI that should be considered when translating biomaterial-based therapies between disease models are also highlighted.

Nanoparticle-Enabled Enrichment of Longitudinal Blood Proteomic Fingerprints in Alzheimer's Disease

Blood-circulating biomarkers have the potential to detect Alzheimer's disease (AD) pathology before clinical symptoms emerge and to improve the outcomes of clinical trials for disease-modifying therapies. Despite recent advances in understanding concomitant systemic abnormalities, there are currently no validated or clinically used blood-based biomarkers for AD. The extremely low concentration of neurodegeneration-associated proteins in blood necessitates the development of analytical platforms to address the "signal-to-noise" issue and to allow an in-depth analysis of the plasma proteome. Here, we aimed to discover and longitudinally track alterations of the blood proteome in a transgenic mouse model of AD, using a nanoparticle-based proteomics enrichment approach. We employed blood-circulating, lipid-based nanoparticles to extract, analyze and monitor AD-specific protein signatures and to systemically uncover molecular pathways associated with AD progression. Our data revealed the existence of multiple proteomic signals in blood, indicative of the asymptomatic stages of AD. Comprehensive analysis of the nanoparticle-recovered blood proteome by label-free liquid chromatography-tandem mass spectrometry resulted in the discovery of AD-monitoring signatures that could discriminate the asymptomatic phase from amyloidopathy and cognitive deterioration. While the majority of differentially abundant plasma proteins were found to be upregulated at the initial asymptomatic stages, the abundance of these molecules was significantly reduced as a result of amyloidosis, suggesting a disease-stage-dependent fluctuation of the AD-specific blood proteome. The potential use of the proposed nano-omics approach to uncover information in the blood that is directly associated with brain neurodegeneration was further exemplified by the recovery of focal adhesion cascade proteins. We herein propose the integration of nanotechnology with already existing proteomic analytical tools in order to enrich the identification of blood-circulating signals of neurodegeneration, reinvigorating the potential clinical utility of the blood proteome at predicting the onset and kinetics of the AD progression trajectory.

Inhibition of the NLRP3 inflammasome by HSP90 inhibitors

Excessive and dysregulated inflammation is known to contribute to disease progression. HSP90 is an intracellular chaperone known to regulate inflammatory processes including the NLRP3 inflammasome and secretion of the pro‐inflammatory cytokine interleukin(IL)‐1β. Here, primarily using an in vitro inflammasome ASC speck assay, and an in vivo model of murine peritonitis, we tested the utility of HSP90 inhibitors as anti‐inflammatory molecules. We report that the HSP90 inhibitor EC144 effectively inhibited inflammatory processes including priming and activation of NLRP3 in vitro and in vivo. A specific inhibitor of the β HSP90 isoform was ineffective suggesting the importance of the α isoform in inflammatory signalling. EC144 inhibited IL‐1β and IL‐6 in vivo when administered orally, and was brain‐penetrant. These data suggest that HSP90 inhibitors may be useful for targeting inflammation in diverse diseases that are worsened by the presence of inflammation.

Selective inhibition of the K+ efflux sensitive NLRP3 pathway by Cl- channel modulation

The NLRP3 inflammasome regulates production of the pro-inflammatory cytokines interleukin-1β (IL-1β) and IL-18, and contributes to inflammation exacerbating disease. Fenamate non-steroidal anti-inflammatory drugs (NSAIDs) were recently described as NLRP3 inflammasome inhibitors via chloride channel inhibition. Fenamate NSAIDs inhibit cyclooxygenase (COX) enzymes, limiting their potential as therapeutics for NLRP3-associated diseases due to established side effects. The aim here was to develop properties of the fenamates that inhibit NLRP3, and at the same time to reduce COX inhibition. We synthesised a library of analogues, with feedback from in silico COX docking potential, and IL-1β release inhibitory activity. Through iterative screening and rational chemical design, we established a collection of chloride channel inhibiting active lead molecules with potent activity at the canonical NLRP3 inflammasome and no activity at COX enzymes, but only in response to stimuli that activated NLRP3 by a K⁺ efflux-dependent mechanism. This study identifies a model for the isolation and removal of unwanted off-target effects, with the enhancement of desired activity, and establishes a new chemical motif for the further development of NLRP3 inflammasome inhibitors.

The NLRP3 inflammasome regulates production of the pro-inflammatory cytokines interleukin-1β (IL-1β) and IL-18, and contributes to inflammation exacerbating disease.

Anti-inflammatories in Alzheimer's disease-potential therapy or spurious correlate?

Epidemiological evidence suggests non-steroidal anti-inflammatory drugs reduce the risk of Alzheimer’s disease. However, clinical trials have found no evidence of non-steroidal anti-inflammatory drug efficacy. This incongruence may be due to the wrong non-steroidal anti-inflammatory drugs being tested in robust clinical trials or the epidemiological findings being caused by confounding factors. Therefore, this study used logistic regression and the innovative approach of negative binomial generalized linear mixed modelling to investigate both prevalence and cognitive decline, respectively, in the Alzheimer’s Disease Neuroimaging dataset for each commonly used non-steroidal anti-inflammatory drug and paracetamol. Use of most non-steroidal anti-inflammatories was associated with reduced Alzheimer’s disease prevalence yet no effect on cognitive decline was observed. Paracetamol had a similar effect on prevalence to these non-steroidal anti-inflammatory drugs suggesting this association is independent of the anti-inflammatory effects and that previous results may be due to spurious associations. Interestingly, diclofenac use was significantly associated with both reduce incidence and slower cognitive decline warranting further research into the potential therapeutic effects of diclofenac in Alzheimer’s disease.

Therapeutic potential of extracellular vesicles in preclinical stroke models: a systematic review and meta-analysis

Objectives

Currently there is a paucity of clinically available regenerative therapies for stroke. Extracellular vesicles (EV) have been investigated for their potential as modulators of regeneration in the poststroke brain. This systematic review and meta-analysis aims to provide a summary of the efficacy of therapeutic EVs in preclinical stroke models, to inform future research in this emerging field.

Methods

Studies were identified by a comprehensive literature search of two online sources and subsequent screening. Studies using lesion volume or neurological score as outcome measures were included. Standardised mean difference (SMD) and 95% CIs were calculated using a restricted maximum likelihood random effects model. Publication bias was assessed with Egger’s regression and presented as funnel plots with trim and fill analysis. Subgroup analysis was performed to assess the effects of different study variables. Study quality and risk of bias were assessed using the CAMARADES checklist.

Results

A total of 20 publications were included in the systematic review, of which 19 were assessed in the meta-analysis (43 comparisons). Overall, EV interventions improved lesion volume (SMD: −1.95, 95% CI −2.72 to 1.18) and neurological scores (SMD: −1.26, 95% CI −1.64 to 0.87) compared with control groups. Funnel plots were asymmetrical suggesting publication bias, and trim and fill analysis predicted seven missing studies for lesion volume. Subgroup analysis suggested administration at 0–23 hours after stroke was the most effective timepoint for EV treatment. The median score on the CAMARADES checklist was 7 (IQR: 5–8).

Conclusions

EVs may offer a promising new avenue for stroke therapies, as EV-based interventions had positive impacts on lesion volume and neurological score in preclinical stroke models.

PROSPERO registration number

CRD42019134925.

Comorbidity and age in the modelling of stroke: are we still failing to consider the characteristics of stroke patients?

Stroke is a significant cause of mortality and morbidity for which there are limited treatment options. Virtually all drug interventions that have been successful preclinically in experimental stroke have failed to translate to an effective treatment in the clinical setting. In this review, we examine one of the factors likely contributing to this lack of translation, the failure of preclinical studies to consider fully the advanced age and comorbidities (eg, hypertension or diabetes) present in most patients with stroke. Age and comorbidities affect the likelihood of suffering a stroke, disease progression and the response to treatment. Analysing data from preclinical systematic reviews of interventions for ischaemic stroke we show that only 11.4% of studies included an aged or comorbid model, with hypertension being the most frequent. The degree of protection (% reduction in infarct volume) varied depending on the comorbidity and the type of intervention. We consider reasons for the lack of attention to comorbid and aged animals in stroke research and discuss the value of testing a potential therapy in models representing a range of comorbidities that affect patients with stroke. These models can help establish any limits to a treatment's efficacy and inform the design of clinical trials in appropriate patient populations.

Stroke Induces Prolonged Changes in Lipid Metabolism, the Liver and Body Composition in Mice

During recovery, stroke patients are at risk of developing long-term complications that impact quality of life, including changes in body weight and composition, depression and anxiety, as well as an increased risk of subsequent vascular events. The aetiologies and time-course of these post-stroke complications have not been extensively studied and are poorly understood. Therefore, we assessed long-term changes in body composition, metabolic markers and behaviour after middle cerebral artery occlusion in mice. These outcomes were also studied in the context of obesity, a common stroke co-morbidity proposed to protect against post-stroke weight loss in patients. We found that stroke induced long-term changes in body composition, characterised by a sustained loss of fat mass with a recovery of lean weight loss. These global changes in response to stroke were accompanied by an altered lipid profile (increased plasma free fatty acids and triglycerides) and increased adipokine release at 60 days. After stroke, the liver also showed histological changes indicative of liver damage and a decrease in plasma alanine aminotransferase (ALT) was observed. Stroke induced depression and anxiety-like behaviours in mice, illustrated by deficits in exploration, nest building and burrowing behaviours. When initial infarct volumes were matched between mice with and without comorbid obesity, these outcomes were not drastically altered. Overall, we found that stroke induced long-term changes in depressive/anxiety-like behaviours, and changes in plasma lipids, adipokines and the liver that may impact negatively on future vascular health.

Reproducibility of CRISPR-Cas9 methods for generation of conditional mouse alleles: a multi-center evaluation

BACKGROUND

CRISPR-Cas9 gene-editing technology has facilitated the generation of knockout mice, providing an alternative to cumbersome and time-consuming traditional embryonic stem cell-based methods. An earlier study reported up to 16% efficiency in generating conditional knockout (cKO or floxed) alleles by microinjection of 2 single guide RNAs (sgRNA) and 2 single-stranded oligonucleotides as donors (referred herein as "two-donor floxing" method).

RESULTS

We re-evaluate the two-donor method from a consortium of 20 laboratories across the world. The dataset constitutes 56 genetic loci, 17,887 zygotes, and 1718 live-born mice, of which only 15 (0.87%) mice contain cKO alleles. We subject the dataset to statistical analyses and a machine learning algorithm, which reveals that none of the factors analyzed was predictive for the success of this method. We test some of the newer methods that use one-donor DNA on 18 loci for which the two-donor approach failed to produce cKO alleles. We find that the one-donor methods are 10- to 20-fold more efficient than the two-donor approach.

CONCLUSION

We propose that the two-donor method lacks efficiency because it relies on two simultaneous recombination events in cis, an outcome that is dwarfed by pervasive accompanying undesired editing events. The methods that use one-donor DNA are fairly efficient as they rely on only one recombination event, and the probability of correct insertion of the donor cassette without unanticipated mutational events is much higher. Therefore, one-donor methods offer higher efficiencies for the routine generation of cKO animal models.

Proteolysis of the low density lipoprotein receptor by bone morphogenetic protein-1 regulates cellular cholesterol uptake

The development of cardiovascular disease is intimately linked to elevated levels of low-density lipoprotein (LDL) cholesterol in the blood. Hepatic LDL receptor (LDLR) levels regulate the amount of plasma LDL. We identified the secreted zinc metalloproteinase, bone morphogenetic protein 1 (BMP1), as responsible for the cleavage of human LDLR within its extracellular ligand-binding repeats at Gly₁₇₁↓Asp₁₇₂. The resulting 120 kDa membrane-bound C-terminal fragment (CTF) of LDLR had reduced capacity to bind LDL and when expressed in LDLR null cells had compromised LDL uptake as compared to the full length receptor. Pharmacological inhibition of BMP1 or siRNA-mediated knockdown prevented the generation of the 120 kDa CTF and resulted in an increase in LDL uptake into cells. The 120 kDa CTF was detected in the livers from humans and mice expressing human LDLR. Collectively, these results identify that BMP1 regulates cellular LDL uptake and may provide a target to modulate plasma LDL cholesterol.

Old Dog New Tricks; Revisiting How Stroke Modulates the Systemic Immune Landscape

Infections in the post-acute phase of cerebral ischaemia impede optimal recovery by exacerbating morbidity and mortality. Our review aims to reconcile the increased infection susceptibility of patients post-stroke by consolidating our understanding of compartmentalised alterations to systemic immunity. Mounting evidence has catalogued alterations to numerous immune cell populations but an understanding of the mechanisms of long-range communication between the immune system, nervous system and other organs beyond the involvement of autonomic signalling is lacking. By taking our cues from established and emerging concepts of neuro-immune interactions, immune-mediated inter-organ cross-talk, innate immune training and the role of microbiota-derived signals in central nervous system (CNS) function we will explore mechanisms of how cerebral ischaemia could shape systemic immune function. In this context, we will also discuss a key question: how are immune requirements critical for mediating repair of the ischaemic insult balanced by the need for anti-microbial immunity post-stroke, given that they are mediated by mutually exclusive immune networks? Our reformed understanding of the immune landscape post-stroke and novel mechanisms at play could guide targeted therapeutic interventions and initiate a step-change in the clinical management of these infectious complications post-stroke.

Acute high-fat feeding leads to disruptions in glucose homeostasis and worsens stroke outcome

Chronic consumption of diets high in fat leads to obesity and can negatively affect brain function. Rodents made obese by long-term maintenance on a high-fat diet have worse outcome after experimental stroke. High-fat consumption for only three days does not induce obesity but has rapid effects on the brain including memory impairment. However, the effect of brief periods of high-fat feeding or high-fat consumption in the absence of obesity on stroke is unknown. We therefore tested the effect of an acute period of high-fat feeding (three days) in C57B/6 mice on outcome after middle cerebral artery occlusion (MCAo). In contrast to a chronic high-fat diet (7.5 months), an acute high-fat diet had no effect on body weight, adipose tissue, lipid profile or inflammatory markers (in periphery and the brain). Three days of high-fat feeding impaired glucose tolerance, increased plasma glucose and insulin and brain expression of the glucose transporter GLUT-1. Ischaemic damage was increased (48%) in mice fed an acute high-fat diet, and was associated with a further reduction in GLUT-1 in the ischaemic hemisphere. These data demonstrate that only a brief period of high-fat consumption has a negative effect on glucose homeostasis and worsens outcome after ischaemic stroke.

Ligature-induced periodontitis induces systemic inflammation but does not alter acute outcome after stroke in mice

Background

Stroke is a major cause of disability and mortality. Poorer outcome after stroke is associated with concomitant inflammatory and infectious disease. Periodontitis is a chronic inflammatory disease of the dental supporting structures and is a prominent risk factor for many systemic disorders, including cardiovascular disease and stroke. While epidemiological studies suggest that periodontitis increases the likelihood of stroke, its impact on stroke severity is poorly understood. Here, we sought to determine the contribution of periodontitis to acute stroke pathology.

Methods

We characterized a murine ligature model of periodontitis for inflammatory responses that could potentially impact stroke outcome. We applied this model and then subjected mice to either transient or permanent middle cerebral artery occlusion. We also enhanced the periodontitis model with repeated intravenous administration of a periodontal-specific lipopolysaccharide to better mimic the clinical condition.

Results

Ligature-induced periodontitis caused bone loss, bacterial growth, and increased local inflammatory cell trafficking. Systemically, periodontitis increased circulating levels of pro-inflammatory cytokines, and primed bone marrow monocytes to produce elevated tumour necrosis factor-alpha (TNFα). Despite these changes, periodontitis alone or in tandem with repeated lipopolysaccharide challenge did not alter infarct volume, blood–brain barrier breakdown, or systemic inflammation after experimental stroke.

Conclusions

Our data show that despite elevated systemic inflammation in periodontitis, oral inflammatory disease does not impact acute stroke pathology in terms of severity, determined primarily by infarct volume. This indicates that, at least in this experimental paradigm, periodontitis alone does not alter acute outcome after cerebral ischemia.

Is Targeting the Inflammasome a Way Forward for Neuroscience Drug Discovery?

Neuroinflammation is becoming increasingly recognized as a critical factor in the pathology of both acute and chronic neurological conditions. Inflammasomes such as the one formed by NACHT, LRR, and PYD domains containing protein 3 (NLRP3) are key regulators of inflammation due to their ability to induce the processing and secretion of interleukin 1β (IL-1β). IL-1β has previously been identified as a potential therapeutic target in a variety of conditions due to its ability to promote neuronal damage under conditions of injury. Thus, inflammasome inhibition has the potential to curtail inflammatory signaling, which could prove beneficial in certain diseases. In this review, we discuss the evidence for inflammasome contributions to the pathology of neurodegenerative conditions such as Alzheimer's disease and Parkinson's disease, epilepsy, and acute degeneration following brain trauma or stroke. In addition, we review the current landscape of drug development targeting the NLRP3 inflammasome.

Small vessels, dementia and chronic diseases - molecular mechanisms and pathophysiology

Cerebral small vessel disease (SVD) is a major contributor to stroke, cognitive impairment and dementia with limited therapeutic interventions. There is a critical need to provide mechanistic insight and improve translation between pre-clinical research and the clinic. A 2-day workshop was held which brought together experts from several disciplines in cerebrovascular disease, dementia and cardiovascular biology, to highlight current advances in these fields, explore synergies and scope for development. These proceedings provide a summary of key talks at the workshop with a particular focus on animal models of cerebral vascular disease and dementia, mechanisms and approaches to improve translation. The outcomes of discussion groups on related themes to identify the gaps in knowledge and requirements to advance knowledge are summarized.

Inflammasomes as therapeutic targets for Alzheimer's disease

Alzheimer's disease is the most common form of progressive dementia, typified initially by short term memory deficits which develop into a dramatic global cognitive decline. The classical hall marks of Alzheimer's disease include the accumulation of amyloid oligomers and fibrils, and the intracellular formation of neurofibrillary tangles of hyperphosphorylated tau. It is now clear that inflammation also plays a central role in the pathogenesis of the disease through a number of neurotoxic mechanisms. Microglia are the key immune regulators of the CNS which detect amyloidopathy through cell surface and cytosolic pattern recognition receptors (PRRs) and respond by initiating inflammation through the secretion of cytokines such as interleukin-1β (IL-1β). Inflammasomes, which regulate IL-1β release, are formed following activation of cytosolic PRRs, and using genetic and pharmacological approaches, NLRP3 and NLRP1 inflammasomes have been found to be integral in pathogenic neuroinflammation in animal models of Alzheimer's disease. Therefore, the inflammasomes are very promising novel pharmacological targets which merit further research in the continued endeavor for efficacious therapeutics for Alzheimer's disease.

Mitochondrial Abnormalities and Synaptic Loss Underlie Memory Deficits Seen in Mouse Models of Obesity and Alzheimer's Disease

Obesity is associated with impaired memory in humans, and obesity induced by high-fat diets leads to cognitive deficits in rodents and in mouse models of Alzheimer's disease (AD). However, it remains unclear how high-fat diets contribute to memory impairment. Therefore, we tested the effect of a high-fat diet on memory in male and female control non-transgenic (Non-Tg) and triple-transgenic AD (3xTgAD) mice and determined if a high-fat diet caused similar ultrastructural abnormalities to those observed in AD. Behavior was assessed in mice on control or high-fat diet at 4, 8, or 14 months of age and ultrastructural analysis at 8 months of age. A high-fat diet increased body weight, fat weight, and insulin levels with some differences in these metabolic responses observed between Non-Tg and 3xTgAD mice. In both sexes, high-fat feeding caused memory impairments in Non-Tg mice and accelerated memory deficits in 3xTgAD mice. In 3xTgAD mice, changes in hippocampal mitochondrial morphology were observed in capillaries and brain neuropil that were accompanied by a reduction in synapse number. A high-fat diet also caused mitochondria abnormalities and a reduction in synapse number in Non-Tg mice, but did not exacerbate the changes seen in 3xTgAD mice. Our data demonstrate that a high-fat diet affected memory in Non-Tg mice and produced similar impairments in mitochondrial morphology and synapse number comparable to those seen in AD mice, suggesting that the detrimental effects of a high-fat diet on memory might be due to changes in mitochondrial morphology leading to a reduction in synaptic number.

Adipose tissue and metabolic and inflammatory responses to stroke are altered in obese mice

Obesity is an independent risk factor for stroke, although several clinical studies have reported that obesity improves stroke outcome. Obesity is hypothesised to aid recovery by protecting against post-stroke catabolism. We therefore assessed whether obese mice had an altered metabolic and inflammatory response to stroke. Obese ob/ob mice underwent a 20-min middle cerebral artery occlusion and 24-h reperfusion. Lipid metabolism and expression of inflammatory cytokines were assessed in the plasma, liver and adipose tissue. The obese-specific metabolic response to stroke was assessed in plasma using non-targeted ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS) metabolomics coupled with univariate and multivariate analysis. Obesity had no effect on the extent of weight loss 24 h after stroke but affected the metabolic and inflammatory responses to stroke, predominantly affecting lipid metabolism. Specifically, obese mice had increases in plasma free fatty acids and expression of adipose lipolytic enzymes. Metabolomics identified several classes of metabolites affected by stroke in obese mice, including fatty acids and membrane lipids (glycerophospholipids, lysophospholipids and sphingolipids). Obesity also featured increases in inflammatory cytokines in the plasma and adipose tissue. Overall, these results demonstrate that obesity affected the acute metabolic and inflammatory response to stroke and suggest a potential role for adipose tissue in this effect. These findings could have implications for longer-term recovery and also further highlight the importance of considering comorbidities in preclinical stroke research, especially when identifying biomarkers for stroke. However, further work is required to assess whether these changes translate into long-term effects on recovery.

Summary: Obesity, a co-morbidity for stroke, affected the acute metabolic and inflammatory response to stroke, highlighting the importance of considering comorbidities in preclinical stroke research, especially when identifying biomarkers.

The blood-brain barrier after stroke: Structural studies and the role of transcytotic vesicles

Blood-brain barrier breakdown worsens ischaemic damage, but it is unclear how molecules breach the blood-brain barrier in vivo. Using the obese ob/ob mouse as a model of enhanced blood-brain barrier breakdown, we investigated how stroke-induced structural changes to the microvasculature related to blood-brain barrier permeability. Ob/ob mice underwent middle cerebral artery occlusion, followed by 4 or 24 h reperfusion. Blood-brain barrier integrity was assessed using IgG and horseradish peroxidase staining, and blood-brain barrier structure by two-dimensional and three-dimensional electron microscopy. At 4 and 24 h post-stroke, ob/ob mice had increased ischaemic damage and blood-brain barrier breakdown compared to ob/- controls, and vessels from both genotypes showed astrocyte end-foot swelling and increased endothelial vesicles. Ob/ob mice had significantly more endothelial vesicles at 4 h in the striatum, where blood-brain barrier breakdown was most severe. Both stroke and genotype had no effect on tight junction structure visualised by electron microscopy, or protein expression in isolated microvessels. Astrocyte swelling severity did not correlate with tissue outcome, being unaffected by genotype or reperfusion times. However, the rare instances of vessel lumen collapse were always associated with severe astrocyte swelling in two-dimensional and three-dimensional electron microscopy. Endothelial vesicles were therefore the best spatial and temporal indicators of blood-brain barrier breakdown after cerebral ischaemia.

Obesity and stroke: Can we translate from rodents to patients?

Obesity is a risk factor for stroke and is consequently one of the most common co-morbidities found in patients. There is therefore an identified need to model co-morbidities preclinically to allow better translation from bench to bedside. In preclinical studies, both diet-induced and genetically obese rodents have worse stroke outcome, characterised by increased ischaemic damage and an altered inflammatory response. However, clinical studies have reported an 'obesity paradox' in stroke, characterised by reduced mortality and morbidity in obese patients. We discuss the potential reasons why the preclinical and clinical studies may not agree, and review the mechanisms identified in preclinical studies through which obesity may affects stroke outcome. We suggest inflammation plays a central role in this relationship, as obesity features increases in inflammatory mediators such as C-reactive protein and interleukin-6, and chronic inflammation has been linked to worse stroke risk and outcome.

Elevated Hypothalamic Glucocorticoid Levels Are Associated With Obesity and Hyperphagia in Male Mice

Glucocorticoid (Gc) excess, from endogenous overproduction in disorders of the hypothalamic-pituitary-adrenal axis or exogenous medical therapy, is recognized to cause adverse metabolic side effects. The Gc receptor (GR) is widely expressed throughout the body, including brain regions such as the hypothalamus. However, the extent to which chronic Gcs affect Gc concentrations in the hypothalamus and impact on GR and target genes is unknown. To investigate this, we used a murine model of corticosterone (Cort)-induced obesity and analyzed Cort levels in the hypothalamus and expression of genes relevant to Gc action. Mice were administered Cort (75 μg/mL) or ethanol (1%, vehicle) in drinking water for 4 weeks. Cort-treated mice had increased body weight, food intake, and adiposity. As expected, Cort increased plasma Cort levels at both zeitgeber time 1 and zeitgeber time 13, ablating the diurnal rhythm. Liquid chromatography dual tandem mass spectrometry revealed a 4-fold increase in hypothalamic Cort, which correlated with circulating levels and concentrations of Cort in other brain regions. This occurred despite decreased 11β-hydroxysteroid dehydrogenase (Hsd11b1) expression, the gene encoding the enzyme that regenerates active Gcs, whereas efflux transporter Abcb1 mRNA was unaltered. In addition, although Cort decreased hypothalamic GR (Nr3c1) expression 2-fold, the Gc-induced leucine zipper (Tsc22d3) mRNA increased, which indicated elevated GR activation. In keeping with the development of hyperphagia and obesity, Cort increased Agrp, but there were no changes in Pomc, Npy, or Cart mRNA in the hypothalamus. In summary, chronic Cort treatment causes chronic increases in hypothalamic Cort levels and a persistent elevation in Agrp, a mediator in the development of metabolic disturbances.

Fenamate NSAIDs inhibit the NLRP3 inflammasome and protect against Alzheimer's disease in rodent models

Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit cyclooxygenase-1 (COX-1) and COX-2 enzymes. The NLRP3 inflammasome is a multi-protein complex responsible for the processing of the proinflammatory cytokine interleukin-1β and is implicated in many inflammatory diseases. Here we show that several clinically approved and widely used NSAIDs of the fenamate class are effective and selective inhibitors of the NLRP3 inflammasome via inhibition of the volume-regulated anion channel in macrophages, independently of COX enzymes. Flufenamic acid and mefenamic acid are efficacious in NLRP3-dependent rodent models of inflammation in air pouch and peritoneum. We also show therapeutic effects of fenamates using a model of amyloid beta induced memory loss and a transgenic mouse model of Alzheimer's disease. These data suggest that fenamate NSAIDs could be repurposed as NLRP3 inflammasome inhibitors and Alzheimer's disease therapeutics.

Elevation of brain glucose and polyol-pathway intermediates with accompanying brain-copper deficiency in patients with Alzheimer's disease: metabolic basis for dementia

Impairment of brain-glucose uptake and brain-copper regulation occurs in Alzheimer's disease (AD). Here we sought to further elucidate the processes that cause neurodegeneration in AD by measuring levels of metabolites and metals in brain regions that undergo different degrees of damage. We employed mass spectrometry (MS) to measure metabolites and metals in seven post-mortem brain regions of nine AD patients and nine controls, and plasma-glucose and plasma-copper levels in an ante-mortem case-control study. Glucose, sorbitol and fructose were markedly elevated in all AD brain regions, whereas copper was correspondingly deficient throughout (all P < 0.0001). In the ante-mortem case-control study, by contrast, plasma-glucose and plasma-copper levels did not differ between patients and controls. There were pervasive defects in regulation of glucose and copper in AD brain but no evidence for corresponding systemic abnormalities in plasma. Elevation of brain glucose and deficient brain copper potentially contribute to the pathogenesis of neurodegeneration in AD.

Systemic inflammation affects reperfusion following transient cerebral ischaemia

Reperfusion after stroke is critical for improved patient survival and recovery and can be achieved clinically through pharmacological (recombinant tissue plasminogen activator) or physical (endovascular intervention) means. Yet these approaches remain confined to a small percentage of stroke patients, often with incomplete reperfusion, and therefore there is an urgent need to learn more about the mechanisms underlying the no-reflow phenomenon that prevents restoration of adequate microvascular perfusion. Recent evidence suggests systemic inflammation as an important contributor to no-reflow and to further investigate this here we inject interleukin 1 (IL-1) i.p. 30 min prior to an ischaemic challenge using a remote filament to occlude the middle cerebral artery (MCA) in mice. Before, during and after the injection of IL-1 and occlusion we use two-dimensional optical imaging spectroscopy to record the spatial and temporal dynamics of oxyhaemoglobin concentration in the cortical areas supplied by the MCA. Our results reveal that systemic inflammation significantly reduces oxyhaemoglobin reperfusion as early as 3h after filament removal compared to vehicle injected animals. CD41 immunohistochemistry shows a significant increase of hyper-coagulated platelets within the microvessels in the stroked cortex of the IL-1 group compared to vehicle. We also observed an increase of pathophysiological biomarkers of ischaemic damage including elevated microglial activation co-localized with interleukin 1α (IL-1α), increased blood brain barrier breakdown as shown by IgG infiltration and increased pyknotic morphological changes of cresyl violet stained neurons. These data confirm systemic inflammation as an underlying cause of no-reflow in the post-ischaemic brain and that appropriate anti-inflammatory approaches could be beneficial in treating ischaemic stroke.

Prolonged diet-induced obesity in mice modifies the inflammatory response and leads to worse outcome after stroke

Background

Obesity increases the risk for ischaemic stroke and is associated with worse outcome clinically and experimentally. Most experimental studies have used genetic models of obesity. Here, a more clinically relevant model, diet-induced obesity, was used to study the impact of obesity over time on the outcome and inflammatory response after stroke.

Methods

Male C57BL/6 mice were maintained on a high-fat (60 % fat) or control (12 % fat) diet for 2, 3, 4 and 6 months when experimental stroke was induced by transient occlusion of the middle cerebral artery (MCAo) for either 20 (6-month diet) or 30 min (2-, 3-, 4- and 6-month diet). Ischaemic damage, blood–brain barrier (BBB) integrity, neutrophil number and chemokine expression in the brain were assessed at 24 h. Plasma chemokine levels (at 4 and 24 h) and neutrophil number in the liver (at 24 h) were measured. Physiological parameters (body weight and blood glucose) were measured in naïve control- and high-fat-fed mice at all time points and blood pressure at 3 and 6 months. Blood cell counts were also assessed in naïve 6-month control- and high-fat-fed mice.

Results

Mice fed a high-fat diet for 6 months had greater body weight, blood glucose and white and red blood cell count but no change in systolic blood pressure. After 4 and 6 months of high-fat feeding, and in the latter group with a 30-min (but not 20-min) occlusion of the MCA, obese mice had greater ischaemic brain damage. An increase in blood–brain barrier permeability, chemokine expression (CXCL-1 and CCL3), neutrophil number and microglia/macrophage cells was observed in the brains of 6-month high-fat-fed mice after 30-min MCAo. In response to stroke, chemokine (CXCL-1) expression in the plasma and liver was significantly different in obese mice (6-month high-fat fed), and a greater number of neutrophils were detected in the liver of control but not obese mice.

Conclusions

The detrimental effects of diet-induced obesity on stroke were therefore dependent on the severity of obesity and length of ischaemic challenge. The altered inflammatory response in obese mice may play a key role in its negative impact on stroke.

Maternal high-fat diet worsens memory deficits in the triple-transgenic (3xTgAD) mouse model of Alzheimer's disease

Alzheimer’s disease (AD) is not normally diagnosed until later in life, although evidence suggests that the disease starts at a much earlier age. Risk factors for AD, such as diabetes, hypertension and obesity, are known to have their affects during mid-life, though events very early in life, including maternal over-nutrition, can predispose offspring to develop these conditions. This study tested whether over-nutrition during pregnancy and lactation affected the development of AD in offspring, using a transgenic AD mouse model. Female triple-transgenic AD dam mice (3xTgAD) were exposed to a high-fat (60% energy from fat) or control diet during pregnancy and lactation. After weaning (at 3 weeks of age), female offspring were placed on a control diet and monitored up until 12 months of age during which time behavioural tests were performed. A transient increase in body weight was observed in 4-week-old offspring 3xTgAD mice from dams fed a high-fat diet. However, by 5 weeks of age the body weight of 3xTgAD mice from the maternal high-fat fed group was no different when compared to control-fed mice. A maternal high-fat diet led to a significant impairment in memory in 2- and 12-month-old 3xTgAD offspring mice when compared to offspring from control fed dams. These effects of a maternal high-fat diet on memory were accompanied by a significant increase (50%) in the number of tau positive neurones in the hippocampus. These data demonstrate that a high-fat diet during pregnancy and lactation increases memory impairments in female 3xTgAD mice and suggest that early life events during development might influence the onset and progression of AD later in life.

High-fat diet-induced memory impairment in triple-transgenic Alzheimer's disease (3xTgAD) mice is independent of changes in amyloid and tau pathology

Obesity and consumption of a high-fat diet are known to increase the risk of Alzheimer's disease (AD). Diets high in fat also increase disease neuropathology and/or cognitive deficits in AD mouse models. However, the effect of a high-fat diet on both the neuropathology and memory impairments in the triple-transgenic mouse model of AD (3xTgAD) is unknown. Therefore, groups of 2-month-old male 3xTgAD and control (non-Tg) mice were maintained on a high-fat or control diet and memory was assessed at the age of 3-4, 7-8, 11-12, and 15-16 months using a series of behavioral tests. A comparable increase in body weight was observed in non-Tg and 3xTgAD mice after high-fat feeding at all ages tested but a significantly greater increase in epididymal adipose tissue was observed in 3xTgAD mice at the age of 7-8, 11-12, and 15-16 months. A high-fat diet caused memory impairments in non-Tg control mice as early as the age of 3-4 months. In 3xTgAD mice, high-fat consumption led to a reduction in the age of onset and an increase in the extent of memory impairments. Some of these effects of high-fat diet on cognition in non-Tg and 3xTgAD mice were transient, and the age at which cognitive impairment was detected depended on the behavioral test. The effect of high-fat diet on memory in the 3xTgAD mice was independent of changes in AD neuropathology as no significant differences in (plaques, oligomers) or tau neuropathology were observed. An acute increase in microglial activation was seen in high-fat fed 3xTgAD mice at the age of 3-4 months but in non-Tg control mice microglial activation was not observed until the age of 15-16 months. These data indicate therefore that a high-fat diet has rapid and long-lasting negative effects on memory in both control and AD mice that are associated with neuroinflammation, but independent of changes in beta amyloid and tau neuropathology in the AD mice.

Zinc depletion regulates the processing and secretion of IL-1β

Sterile inflammation contributes to many common and serious human diseases. The pro-inflammatory cytokine interleukin-1β (IL-1β) drives sterile inflammatory responses and is thus a very attractive therapeutic target. Activation of IL-1β in sterile diseases commonly requires an intracellular multi-protein complex called the NLRP3 (NACHT, LRR, and PYD domains-containing protein 3) inflammasome. A number of disease-associated danger molecules are known to activate the NLRP3 inflammasome. We show here that depletion of zinc from macrophages, a paradigm for zinc deficiency, also activates the NLRP3 inflammasome and induces IL-1β secretion. Our data suggest that zinc depletion damages the integrity of lysosomes and that this event is important for NLRP3 activation. These data provide new mechanistic insight to how zinc deficiency contributes to inflammation and further unravel the mechanisms of NLRP3 inflammasome activation.

Analysis of global gene expression changes in human bronchial epithelial cells exposed to spores of the allergenic fungus, Alternaria alternata

Exposure and sensitivity to ubiquitous airborne fungi such as Alternaria alternata have long been implicated in the development, onset, and exacerbation of chronic allergic airway disorders. This present study is the first to investigate global changes in host gene expression during the interaction of cultured human bronchial epithelial cells and live Alternaria spores. In in vitro experiments human bronchial epithelial cells (BEAS-2B) were exposed to spores or media alone for 24 h. RNA was collected from three biological replicates per treatment and was used to assess changes in gene expression patterns using Affymetrix Human Genome U133 Plus 2.0 Arrays. In cells treated with Alternaria spores compared to controls, 613 probe sets representing 460 individual genes were found differentially expressed (p ≤ 0.05). In this set of 460 statistically significant, differentially expressed genes, 397 genes were found to be up-regulated and 63 were down-regulated. Of these 397 up-regulated genes, 156 genes were found to be up-regulated ≥2 fold. Interestingly, none of the 63 down-regulated genes were found differentially expressed at ≤−2 fold. Differentially expressed genes were identified following statistical analysis and subsequently used for pathway and network evaluation. Interestingly, many cytokine and chemokine immune response genes were up-regulated with a particular emphasis on interferon-inducible genes. Genes involved in cell death, retinoic acid signaling, and TLR3 response pathways were also significantly up-regulated. Many of the differentially up-regulated genes have been shown in other systems to be associated with innate immunity, inflammation and/or allergic airway diseases. This study now provides substantial information for further investigating specific genes and innate immune system pathways activated by Alternaria in the context of allergic airway diseases.

The immune system in stroke: clinical challenges and their translation to experimental research

Stroke represents an unresolved challenge for both developed and developing countries and has a huge socio-economic impact. Although considerable effort has been made to limit stroke incidence and improve outcome, strategies aimed at protecting injured neurons in the brain have all failed. This failure is likely to be due to both the incompleteness of modelling the disease and its causes in experimental research, and also the lack of understanding of how systemic mechanisms lead to an acute cerebrovascular event or contribute to outcome. Inflammation has been implicated in all forms of brain injury and it is now clear that immune mechanisms profoundly influence (and are responsible for the development of) risk and causation of stroke, and the outcome following the onset of cerebral ischemia. Until very recently, systemic inflammatory mechanisms, with respect to common comorbidities in stroke, have largely been ignored in experimental studies. The main aim is therefore to understand interactions between the immune system and brain injury in order to develop novel therapeutic approaches. Recent data from clinical and experimental research clearly show that systemic inflammatory diseases -such as atherosclerosis, obesity, diabetes or infection - similar to stress and advanced age, are associated with dysregulated immune responses which can profoundly contribute to cerebrovascular inflammation and injury in the central nervous system. In this review, we summarize recent advances in the field of inflammation and stroke, focusing on the challenges of translation between pre-clinical and clinical studies, and potential anti-inflammatory/immunomodulatory therapeutic approaches.

Impaired satiation and increased feeding behaviour in the triple-transgenic Alzheimer's disease mouse model

Alzheimer's disease (AD) is associated with non-cognitive symptoms such as changes in feeding behaviour that are often characterised by an increase in appetite. Increased food intake is observed in several mouse models of AD including the triple transgenic (3×TgAD) mouse, but the mechanisms underlying this hyperphagia are unknown. We therefore examined feeding behaviour in 3×TgAD mice and tested their sensitivity to exogenous and endogenous satiety factors by assessing food intake and activation of key brain regions. In the behavioural satiety sequence (BSS), 3×TgAD mice consumed more food after a fast compared to Non-Tg controls. Feeding and drinking behaviours were increased and rest decreased in 3×TgAD mice, but the overall sequence of behaviours in the BSS was maintained. Exogenous administration of the satiety factor cholecystokinin (CCK; 8–30 µg/kg, i.p.) dose-dependently reduced food intake in Non-Tg controls and increased inactive behaviour, but had no effect on food intake or behaviour in 3×TgAD mice. CCK (15 µg/kg, i.p.) increased c-Fos protein expression in the supraoptic nucleus of the hypothalamus, and the nucleus tractus solitarius (NTS) and area postrema of the brainstem to the same extent in Non-Tg and 3×TgAD mice, but less c-Fos positive cells were detected in the paraventricular hypothalamic nucleus of CCK-treated 3×TgAD compared to Non-Tg mice. In response to a fast or a period of re-feeding, there was no difference in the number of c-Fos-positive cells detected in the arcuate nucleus of the hypothalamus, NTS and area postrema of 3×TgAD compared to Non-Tg mice. The degree of c-Fos expression in the NTS was positively correlated to food intake in Non-Tg mice, however, this relationship was absent in 3×TgAD mice. These data demonstrate that 3×TgAD mice show increased feeding behaviour and insensitivity to satiation, which is possibly due to defective gut-brain signalling in response to endogenous satiety factors released by food ingestion.

Age-related changes in core body temperature and activity in triple-transgenic Alzheimer's disease (3xTgAD) mice

Alzheimer’s disease (AD) is characterised, not only by cognitive deficits and neuropathological changes, but also by several non-cognitive behavioural symptoms that can lead to a poorer quality of life. Circadian disturbances in core body temperature and physical activity are reported in AD patients, although the cause and consequences of these changes are unknown. We therefore characterised circadian patterns of body temperature and activity in male triple transgenic AD mice (3xTgAD) and non-transgenic (Non-Tg) control mice by remote radiotelemetry. At 4 months of age, daily temperature rhythms were phase advanced and by 6 months of age an increase in mean core body temperature and amplitude of temperature rhythms were observed in 3xTgAD mice. No differences in daily activity rhythms were seen in 4- to 9-month-old 3xTgAD mice, but by 10 months of age an increase in mean daily activity and the amplitude of activity profiles for 3xTgAD mice were detected. At all ages (4–10 months), 3xTgAD mice exhibited greater food intake compared with Non-Tg mice. The changes in temperature did not appear to be solely due to increased food intake and were not cyclooxygenase dependent because the temperature rise was not abolished by chronic ibuprofen treatment. No β-amyloid (Aβ) plaques or neurofibrillary tangles were noted in the hypothalamus of 3xTgAD mice, a key area involved in temperature regulation, although these pathological features were observed in the hippocampus and amygdala of 3xTgAD mice from 10 months of age. These data demonstrate age-dependent changes in core body temperature and activity in 3xTgAD mice that are present before significant AD-related neuropathology and are analogous to those observed in AD patients. The 3xTgAD mouse might therefore be an appropriate model for studying the underlying mechanisms involved in non-cognitive behavioural changes in AD.

Obese mice exhibit an altered behavioural and inflammatory response to lipopolysaccharide

Obesity is associated with an increase in the prevalence and severity of infections. Genetic animal models of obesity (ob/ob and db/db mice) display altered centrally-mediated sickness behaviour in response to acute inflammatory stimuli such as lipopolysaccharide (LPS). However, the effect of diet-induced obesity (DIO) on the anorectic and febrile response to LPS in mice is unknown. This study therefore determined how DIO and ob/ob mice respond to a systemic inflammatory challenge. C57BL/6 DIO and ob/ob mice, and their respective controls, were given an intraperitoneal (i.p.) injection of LPS. Compared with controls, DIO and ob/ob mice exhibited an altered febrile response to LPS (100 μg/kg) over 8 hours. LPS caused a greater and more prolonged anorexic effect in DIO compared with control mice and, in ob/ob mice, LPS induced a reduction in food intake and body weight earlier than it did in controls. These effects of LPS in obese mice were also seen after a fixed dose of LPS (5 μg). LPS (100 μg/kg) induced Fos protein expression in several brain nuclei of control mice, with fewer Fos-positive cells observed in the brains of obese mice. An altered inflammatory response to LPS was also observed in obese mice compared with controls: changes in cytokine expression and release were detected in the plasma, spleen, liver and peritoneal macrophages in obese mice. In summary, DIO and ob/ob mice displayed an altered behavioural response and cytokine release to systemic inflammatory challenge. These findings could help explain why obese humans show increased sensitivity to infections.

Hypermetabolism in a triple-transgenic mouse model of Alzheimer's disease

A common feature of Alzheimer's disease (AD) is weight loss, even though there is often an increase in food intake in AD patients. The reasons for this weight loss are unknown, but may be due to increased energy expenditure (metabolic rate) or a reduction in energy intake. This was investigated in the present study, using a triple-transgenic (3xTgAD) mouse model of AD. Two-month-old 3xTgAD mice displayed greater food intake (17%) and body weight (34%) but no difference in metabolic rate, as compared with nontransgenic controls (non-Tg). At 12 months of age, 3xTgAD mice still consumed more food (30%), but their body weight was significantly lower (15%) than non-Tg controls. This reduction in body weight was accompanied by a significant rise in metabolic rate, indicated by greater oxygen consumption (24%) and carbon dioxide production (29%); the effects were also observed in 18-month-old 3xTgAD mice. These data demonstrate for the first time the existence of a hypermetabolic state in an experimental model of AD, but whether this can explain the weight loss observed in AD patients remains to be determined.

Interleukin-1 mediates the anorexic and febrile actions of galanin-like Peptide

Galanin-like peptide (GALP) is a neuropeptide that has complex actions on energy balance, producing orexigenic effects in the short term in rats but anorexigenic and febrile effects over the longer term in rats and mice. GALP is thought to promote feeding via neuropeptide Y and orexin neurons, but the mediators of the anorexia are unknown. However, the anorexic and febrile actions of GALP are similar in magnitude and profile to those seen after central injections of the cytokine IL-1. Thus, the aim of this study was to test the hypothesis that IL-1 mediates the effects of GALP on energy balance. Intracerebroventricular injection of GALP (1.5 nmol) in male Sprague-Dawley rats stimulated production of IL-1alpha and IL-1beta protein in macrophages and/or microglia in selected brain areas, including the meninges, and periventricular brain regions. Intracerebroventricular injection of GALP in rats stimulated food intake over 1 h but decreased feeding and body weight at 24 h and caused a rise in core body temperature over 8 h. Coinfusion of the IL-1 receptor antagonist had no effect on the GALP-induced orexigenic response but significantly reduced the longer-term actions of GALP observed at 24 h and its effect on body temperature. Furthermore, the actions of GALP on feeding, body weight, and body temperature were significantly reduced in IL-1alpha/beta-, IL-1beta-, or IL-1 type I receptor (IL-1RI)-deficient mice. These data suggest that GALP induces expression of IL-1 in the brain, and its anorexic and febrile actions are mediated by this cytokine acting via IL-1 type I receptor.

Galanin-like peptide: a role in the homeostatic regulation of energy balance?

Galanin-like peptide (GALP) is a neuropeptide that has been proposed to play a role in the regulation of food intake behaviour and body weight. However, the actions of GALP on energy balance are complex. In rats, it appears to impel both appetite stimulating and suppressing effects, whereas in mice, the only effect is a reduction in food intake. Thus, it is currently unclear whether GALP is important in the homeostatic regulation of energy balance, or if it produces effects on appetite and body weight by non-specific actions. This review discusses current evidence of the role of GALP with respect to energy balance, and the mechanisms involved in its regulation. We describe recent evidence that suggests that GALP may elicit differential effects in different rodent species. Furthermore, we provide an insight into a potential novel role for GALP in inflammation, and discuss how this may relate to the non-homeostatic regulation of energy balance.