Circulating cell wall components derived from gram-negative, not gram-positive, bacteria cause a profound induction of the gene-encoding Toll-like receptor 2 in the CNS

Raspberry Ketone Prevents LPS-Induced Depression-Like Behaviors in Mice by Inhibiting TLR-4/NF-κB Signaling Pathway via the Gut-Brain Axis

SCOPE

Depression, a prevalent mental disorder, has significantly impacted the lives of 350 million people, yet it holds promise for amelioration through food-derived phenolics. Raspberries, renowned globally for their delectable flavor, harbor a phenolic compound known as raspberry ketone (RK). However, the impact of RK on depressive symptoms remains ambiguous. This study aims to investigate the impact of RK on lipopolysaccharide (LPS)-induced depressed mice and elucidates its potential mechanisms, focusing on the gut-brain axis.

METHODS AND RESULTS

Through behavioral tests, RK exerts a notable preventive effect on LPS-induced depression-like behaviors in mice. RK proves capable of attenuating gut inflammation, repairing gut barrier impairment, modulating the composition of the gut microbiome (Muribaculaceae, Streptococcus, Lachnospiraceae, and Akkermansia), and promoting the production of short-chain fatty acids. Furthermore, RK alleviates neuroinflammation by suppressing the TLR-4/NF-κB pathway and bolsters synaptic function by elevating levels of neurotrophic factors and synapse-associated proteins.

CONCLUSION

The current study provides compelling evidence that RK effectively inhibits the TLR-4/NF-κB pathway via the gut-brain axis, leading to the improvement of LPS-induced depression-like behaviors in mice. This study addresses the research gap in understanding the antidepressant effects of RK and illuminates the potential of utilizing RK as a functional food for preventing depression.

Chlamydia pneumoniae in Alzheimer's disease pathology

While recent advances in diagnostics and therapeutics offer promising new approaches for Alzheimer's disease (AD) diagnosis and treatment, there is still an unmet need for an effective remedy, suggesting new avenues of research are required. Besides many plausible etiologies for AD pathogenesis, mounting evidence supports a possible role for microbial infections. Various microbes have been identified in the postmortem brain tissues of human AD patients. Among bacterial pathogens in AD, Chlamydia pneumoniae (Cp) has been well characterized in human AD brains and is a leading candidate for an infectious involvement. However, no definitive studies have been performed proving or disproving Cp's role as a causative or accelerating agent in AD pathology and cognitive decline. In this review, we discuss recent updates for the role of Cp in human AD brains as well as experimental models of AD. Furthermore, based on the current literature, we have compiled a list of potential mechanistic pathways which may connect Cp with AD pathology.

A Promising Drug Candidate as Potent Therapeutic Approach for Neuroinflammation and Its In Silico Justification of Chalcone Congeners: a Comprehensive Review

Multiple genetic, environmental, and immunological variables cause neuropsychiatric disorders (NPDs). The induced inflammatory immune response is also connected to the severity and treatment outcomes of various NPDs. These reactions also significantly impact numerous brain functions such as GABAergic signaling and neurotransmitter synthesis through inflammatory cytokines and chemokines. Chalcones (1,3-diaryl-2-propen-1-ones) and their heterocyclic counterparts are flavonoids with various biological characteristics including anti-inflammatory activity. Several pure chalcones have been clinically authorized or studied in humans. Chalcones are favored for their diagnostic and therapeutic efficacy in neuroinflammation due to their tiny molecular size, easy manufacturing, and flexibility for changes to adjust lipophilicity ideal for BBB penetrability. These compounds reached an acceptable plasma concentration and were well-tolerated in clinical testing. As a result, they are attracting increasing attention from scientists. However, chalcones' therapeutic potential remains largely untapped. This paper is aimed at highlighting the causes of neuroinflammation, more potent chalcone congeners, their mechanisms of action, and relevant structure-activity relationships.

Brain-Gut-Microbiota Axis in Amyotrophic Lateral Sclerosis: A Historical Overview and Future Directions

Amyotrophic Lateral Sclerosis (ALS) is a devastating neurodegenerative disease which is strongly associated with age. The incidence of ALS increases from the age of 40 and peaks between the ages of 65 and 70. Most patients die of respiratory muscle paralysis or lung infections within three to five years of the appearance of symptoms, dealing a huge blow to patients and their families. With aging populations, improved diagnostic methods and changes in reporting criteria, the incidence of ALS is likely to show an upward trend in the coming decades. Despite extensive researches have been done, the cause and pathogenesis of ALS remains unclear. In recent decades, large quantities of studies focusing on gut microbiota have shown that gut microbiota and its metabolites seem to change the evolvement of ALS through the brain-gut-microbiota axis, and in turn, the progression of ALS will exacerbate the imbalance of gut microbiota, thereby forming a vicious cycle. This suggests that further exploration and identification of the function of gut microbiota in ALS may be crucial to break the bottleneck in the diagnosis and treatment of this disease. Hence, the current review summarizes and discusses the latest research advancement and future directions of ALS and brain-gut-microbiota axis, so as to help relevant researchers gain correlative information instantly.

Microglia in epilepsy

Epilepsy is one of most common chronic neurological disorders, and the antiseizure medications developed by targeting neurocentric mechanisms have not effectively reduced the proportion of patients with drug-resistant epilepsy. Further exploration of the cellular or molecular mechanism of epilepsy is expected to provide new options for treatment. Recently, more and more researches focus on brain network components other than neurons, among which microglia have attracted much attention for their diverse biological functions. As the resident immune cells of the central nervous system, microglia have highly plastic transcription, morphology and functional characteristics, which can change dynamically in a context-dependent manner during the progression of epilepsy. In the pathogenesis of epilepsy, highly reactive microglia interact with other components in the epileptogenic network by performing crucial functions such as secretion of soluble factors and phagocytosis, thus continuously reshaping the landscape of the epileptic brain microenvironment. Indeed, microglia appear to be both pro-epileptic and anti-epileptic under the different spatiotemporal contexts of disease, rendering interventions targeting microglia biologically complex and challenging. This comprehensive review critically summarizes the pathophysiological role of microglia in epileptic brain homeostasis alterations and explores potential therapeutic or modulatory targets for epilepsy targeting microglia.

Glial functions in the blood-brain communication at the circumventricular organs

The circumventricular organs (CVOs) are located around the brain ventricles, lack a blood-brain barrier (BBB) and sense blood-derived molecules. This review discusses recent advances in the importance of CVO functions, especially glial cells transferring periphery inflammation signals to the brain. The CVOs show size-limited vascular permeability, allowing the passage of molecules with molecular weight <10,000. This indicates that the lack of an endothelial cell barrier does not mean the free movement of blood-derived molecules into the CVO parenchyma. Astrocytes and tanycytes constitute a dense barrier at the distal CVO subdivision, preventing the free diffusion of blood-derived molecules into neighboring brain regions. Tanycytes in the CVOs mediate communication between cerebrospinal fluid and brain parenchyma via transcytosis. Microglia and macrophages of the CVOs are essential for transmitting peripheral information to other brain regions via toll-like receptor 2 (TLR2). Inhibition of TLR2 signaling or depletion of microglia and macrophages in the brain eliminates TLR2-dependent inflammatory responses. In contrast to TLR2, astrocytes and tanycytes in the CVOs of the brain are crucial for initiating lipopolysaccharide (LPS)-induced inflammatory responses via TLR4. Depletion of microglia and macrophages augments LPS-induced fever and chronic sickness responses. Microglia and macrophages in the CVOs are continuously activated, even under normal physiological conditions, as they exhibit activated morphology and express the M1/M2 marker proteins. Moreover, the microglial proliferation occurs in various regions, such as the hypothalamus, medulla oblongata, and telencephalon, with a marked increase in the CVOs, due to low-dose LPS administration, and after high-dose LPS administration, proliferation is seen in most brain regions, except for the cerebral cortex and hippocampus. A transient increase in the microglial population is beneficial during LPS-induced inflammation for attenuating sickness response. Transient receptor potential receptor vanilloid 1 expressed in astrocytes and tanycytes of the CVOs is responsible for thermoregulation upon exposure to a warm environment less than 37°C. Alternatively, Nax expressed in astrocytes and tanycytes of the CVOs is crucial for maintaining body fluid homeostasis. Thus, recent findings indicate that glial cells in the brain CVOs are essential for initiating neuroinflammatory responses and maintaining body fluid and thermal homeostasis.

Microbiota and Microglia Interactions in ASD

Autism spectrum disorders (ASD) are serious, highly variable neurodevelopmental disorders, commonly characterized by the manifestation of specific behavioral abnormalities, such as stereotypic behaviors and deficits in social skills, including communication. Although the neurobiological basis for ASD has attracted attention in recent decades, the role of microglial cells, which are the main resident myeloid cell population in the brain, is still controversial and underexplored. Microglia play several fundamental roles in orchestrating brain development and homeostasis. As such, alterations in the intrinsic functions of these cells could be one of the driving forces responsible for the development of various neurodevelopmental disorders, including ASD. Microglia are highly sensitive to environmental cues. Amongst the environmental factors known to influence their intrinsic functions, the gut microbiota has emerged as a central player, controlling both microglial maturation and activation. Strikingly, there is now compelling data suggesting that the intestinal microbiota can play a causative role in driving the behavioural changes associated with ASD. Not only is intestinal dysbiosis commonly reported in ASD patients, but therapies targeting the microbiome can markedly alleviate behavioral symptoms. Here we explore the emerging mechanisms by which altered microglial functions could contribute to several major etiological factors of ASD. We then demonstrate how pre- and postnatal environmental stimuli can modulate microglial cell phenotype and function, underpinning the notion that reciprocal interactions between microglia and intestinal microbes could play a crucial role in ASD aetiology.

IL-6 Regulates Hepcidin Expression Via the BMP/SMAD Pathway by Altering BMP6, TMPRSS6 and TfR2 Expressions at Normal and Inflammatory Conditions in BV2 Microglia

The hormone hepcidin plays a central role in controlling iron homeostasis. Iron-mediated hepcidin synthesis is triggered via the BMP/SMAD pathway. At inflammation, mainly IL-6 pro-inflammatory cytokine mediates the regulation of hepcidin via the JAK/STAT signalling pathway. Microglial cells of the central nervous system are able to recognize a broad spectrum of pathogens via toll-like receptors and initiate inflammatory response. Although the regulation of hepcidin synthesis is well described in many tissues, little is known about the inflammation mediated hepcidin regulation in microglia. In this study, we investigated the pathways, which are involved in HAMP regulation in BV2 microglia due to inflammatory mediators and the possible relationships between the iron regulatory pathways. Our results showed that IL-6 produced by resting BV2 cells was crucial in maintaining the basal HAMP expression and hepcidin secretion. It was revealed that IL-6 neutralization decreased both STAT3 and SMAD1/5/9 phosphorylation suggesting that IL-6 proinflammatory cytokine is necessary to maintain SMAD1/5/9 activation. We revealed that IL-6 influences BMP6 and TMPRSS6 protein levels, moreover it modified TfR2 expression, as well. In this study, we revealed that BV2 microglia increased their hepcidin secretion upon IL-6 neutralization although the major regulatory pathways were inhibited. Based on our results it seems that both at inflammation and at normal condition the absence of IL-6 triggered HAMP transcription and hepcidin secretion via the NFκB pathway and possibly by the autocrine effect of TNFα cytokine on BV2 microglia.

Lipoteichoic acid, a cell wall component of Gram-positive bacteria, induces sleep and fever and suppresses feeding

Fragments of the bacterial cell wall are bioactive microbial molecules that have profound effects on the function of the brain. Some of the cell wall constituents are common to both Gram-positive and Gram-negative bacteria, e.g., peptidoglycans, while other cell wall components are specific to either Gram-positive or Gram-negative microbes. Lipopolysaccharide (LPS), also called endotoxin, is found exclusively in Gram-negative bacteria, while lipoteichoic acid (LTA) is specific to Gram-positive bacteria. The effects of peptidoglycans, their fragments, and LPS are well characterized, they induce sleep, fever and anorexia. In the present study, we investigated the sleep, body temperature and food intake modulating effects of LTA. We found that intraperitoneal injection of 100 and 250 μg LTA from B. subtilis and S. aureus increases non-rapid-eye movement sleep (NREMS) in mice. The effects were dose-dependent, and the changes were accompanied by decreased motor activity and feeding as well as febrile responses. Intraperitoneal injection of 10 μg LTA induced monophasic increases in body temperature, while 100 and 250 μg LTA from B. subtilis induced initial hypothermia followed by fever. Treatment with 250 μg LTA from S. aureus elicited monophasic hypothermia. Administration of 300 μg/kg LTA from S. aureus directly into the portal vein elicited similar sleep responses in rats but did not affect body temperature. The sleep-modulating effects of LTA were similar to that of LPS in mice, although LTA appears to be less potent. These findings suggest that the role of LTA in signaling by Gram-positive bacteria in the host body is analogous to the role of LPS/endotoxin in signaling by Gram-negative microbes. LTA may play a role in the development of sickness response in clinically manifest Gram-positive bacterial infections and may contribute to sleep signaling by the commensal intestinal microbiota.

Aging and Microglial Response following Systemic Stimulation with Escherichia coli in Mice

Systemic infection is an important risk factor for the development cognitive impairment and neurodegeneration in older people. Animal experiments show that systemic challenges with live bacteria cause a neuro-inflammatory response, but the effect of age on this response in these models is unknown. Young (2 months) and middle-aged mice (13-14 months) were intraperitoneally challenged with live Escherichia coli (E. coli) or saline. The mice were sacrificed at 2, 3 and 7 days after inoculation; for all time points, the mice were treated with ceftriaxone (an antimicrobial drug) at 12 and 24 h after inoculation. Microglial response was monitored by immunohistochemical staining with an ionized calcium-binding adaptor molecule 1 (Iba-1) antibody and flow cytometry, and inflammatory response by mRNA expression of pro- and anti-inflammatory mediators. We observed an increased microglial cell number and moderate morphologically activated microglial cells in middle-aged mice, as compared to young mice, after intraperitoneal challenge with live E. coli. Flow cytometry of microglial cells showed higher CD45 and CD11b expressions in middle-aged infected mice compared to young infected mice. The brain expression levels of pro-inflammatory genes were higher in middle-aged than in young infected mice, while middle-aged infected mice had similar expression levels of these genes in the systemic compartment. We conclude that systemic challenge with live bacteria causes an age-dependent neuro-inflammatory and microglial response. Our data show signs of an age-dependent disconnection of the inflammatory transcriptional signature between the brain and the systemic compartment.

Interactions and Signal Transduction Pathways Involved during Central Nervous System Entry by Neisseria meningitidis across the Blood-Brain Barriers

The Gram-negative diplococcus Neisseria meningitidis, also called meningococcus, exclusively infects humans and can cause meningitis, a severe disease that can lead to the death of the afflicted individuals. To cause meningitis, the bacteria have to enter the central nervous system (CNS) by crossing one of the barriers protecting the CNS from entry by pathogens. These barriers are represented by the blood–brain barrier separating the blood from the brain parenchyma and the blood–cerebrospinal fluid (CSF) barriers at the choroid plexus and the meninges. During the course of meningococcal disease resulting in meningitis, the bacteria undergo several interactions with host cells, including the pharyngeal epithelium and the cells constituting the barriers between the blood and the CSF. These interactions are required to initiate signal transduction pathways that are involved during the crossing of the meningococci into the blood stream and CNS entry, as well as in the host cell response to infection. In this review we summarize the interactions and pathways involved in these processes, whose understanding could help to better understand the pathogenesis of meningococcal meningitis.

Co-ultraPEALut: Role in Preclinical and Clinical Delirium Manifestations

BACKGROUND

Delirium is a disorder in awareness, attention and cognition. Pathophysiologically it is a response to stress. Postoperative delirium (POD) is a usual complication in aged patients following hip fracture surgery. Neuroinflammation is an important factor linked with the progress of POD. Though there are no efficient cures for delirium the endocannabinoid system may have a role in neuropsychiatric disorders.

OBJECTIVE

Therefore, we examined the effects of co-ultramicronized PEALut (co-ultraPEALut) in the LPS murine model of delirium and in elderly hip fractured patients.

METHODS

In the preclinical study, mice were injected intraperitoneally (i.p.) with Escherichia coli LPS (10 mg/kg). Co-ultraPEALut (1 mg/kg o.s.) was administered 1h before LPS injection or 1h and 6h after LPS injection or 1h before LPS injection and 1h and 6h after LPS. In the clinical study, the effects of Glialia® (co-ultramicronized 700 mg PEA + 70 mg luteolin) administration was evaluated in elderly hip fractured patients with an interventional, randomized, single-blind, monocentric study.

RESULTS

Administration of co-ultraPEALut to LPS-challenged mice ameliorated cognitive dysfunctions and locomotor activity; moreover, it reduced inflammation and apoptosis, while stimulating antioxidant response and limiting the loss of neurotrophins. In the clinical study, the results obtained demonstrated that administration of Glialia® to these surgical patients prevented the onset of POD and attenuated symptom intensity and their duration.

CONCLUSION

Therefore, the results obtained enhanced the idea that co-ultraPEALut may be a potential treatment to control cognitive impairment and the inflammatory and oxidative processes associated with delirium.

Solar inactivated Vibrio cholerae induces maturation of JAWS II dendritic cell line in vitro

Solar disinfection (SODIS) has been shown to reduce the risk associated with the contraction of water borne diseases such as cholera. However, little or no research has been undertaken in exploring the role played by the immune system following the consumption of solar inactivated water pathogens. This study investigated the potential for solar inactivated Vibrio cholerae to induce the maturation of dendritic cells in vitro. Dendritic cells are professional antigen presenting cells found in mammals. However, only in their mature form are dendritic cells able to play their role towards a long lasting immune response. Three strains of V. cholerae were solar irradiated for 7 hours. Thereafter, the solar irradiated, non-solar irradiated, phosphate buffered saline prepared and heat/chemically inactivated cultures of V. cholerae as well as lipopolysaccharide and cholerae toxin-β subunit were used to stimulate immature dendritic cells. After 48 hours, the dendritic cells were assessed for the expression of CD54, CD80, CD83, CD86, MHC-I and MHC-II cell surface markers. Results show that solar inactivated V. cholerae was able to induce maturation of the dendritic cells in vitro. These findings suggest that there may be an immunological benefit in consuming SODIS treated water.

The interaction between microbiome and host central nervous system: the gut-brain axis as a potential new therapeutic target in the treatment of obesity and cardiometabolic disease

INTRODUCTION

The role of the intestinal microbiota in host cardiometabolic health and disease has gained significant attention over recent decades. Previous studies have shown effects on metabolic health through gut microbiota modulation; this suggests diverse interaction pathways that constitute the communication between gut microbiota and host central nervous system, the so-called gut-brain axis.

AREAS COVERED

This article provides an overview of the various mechanisms that may mediate the gut-brain axis. It places an emphasis on cardiometabolic health, including effects of short-chain fatty acids (SCFA), alterations in neurotransmitters and gut peptides and microbial effects on chronic inflammation and immune function. Moreover, this paper sheds light on whether these mechanisms afford therapeutic targets to promote metabolic health. To this end, a PubMed search with the terms 'gut microbiota,' 'obesity' and 'insulin sensitivity' was performed.

EXPERT OPINION

Many properties of the human gut microbiome are associated with the central regulation of appetite and metabolic status. Some of these relationships are causal and there are positive effects from certain intervention methods. Microbial manipulation may offer a means to prevent or treat obesity and associated co-morbidities. However, to establish direct causal relations between altered gut microbiota and metabolic disease, clinical intervention studies are necessary.

Microglial activation and responses to vasculature that result from an acute LPS exposure

Bacterial cell wall endotoxins, i.e. lipopolysaccharides (LPS), are some of the original compounds shown to evoke the classic signs of systemic inflammation/innate immune response and neuroinflammation. The term neuroinflammation often is used to infer the elaboration of proinflammatory mediators by microglia elicited by neuronal targeted activity. However, it also is possible that the microglia are responding to vasculature through several signaling mechanisms. Microglial activation relative to the vasculature in the hippocampus and parietal cortex was determined after an acute exposure of a single subcutaneous injection of 2 mg/kg LPS. Antibodies to allograft inflammatory factor (Aif1, a.k.a. Iba1) were used to track and quantify morphological changes in microglia. Immunostaining of platelet/endothelial cell adhesion molecule 1 (Pecam1, a.k.a. Cd31) was used to visualize vasculature in the forebrain and glial acidic fibrillary protein (GFAP) to visualize astrocytes. Neuroinflammation and other aspects of neurotoxicity were evaluated histologically at 3 h, 6 h, 12 h, 24 h, 3 d and 14 d following LPS exposure. LPS did not cause neurodegeneration as determined by Fluoro Jade C labeling. Also, there were no signs of mouse IgG leakage from brain vasculature due to LPS. Some changes in microglia size occurred at 6 h, but by 12 h microglial activation had begun with the combined soma and proximal processes size increasing significantly (1.5-fold). At 24 h, almost all the microglia soma and proximal processes in the hippocampus, parietal cortex, and thalamus were closely associated with the vasculature and had increased almost 2.0-fold in size. In many areas where microglia were juxtaposed to vasculature, astrocytic endfeet appeared to be displaced. The microglial activation had subsided slightly by 3 d with microglial size 1.6-fold that of control. We hypothesize that acute LPS activation can result in vascular mediated microglial responses through several mechanisms: 1) binding to Cd14 and Tlr4 receptors on microglia processes residing on vasculature; 2) damaging vasculature and causing the release of cytokines; and 3) possibly astrocytic endfeet damage resulting in cytokine release. These acute responses may serve as an adaptive mechanism to exposure to circulating LPS where the microglia surround the vasculature. This could further prevent the pathogen(s) circulating in blood from entering the brain. However, diverting microglial interactions away from synaptic remodeling and other types of microglial interactions with neurons may have adverse effects on neuronal function.

Activation of microglia and macrophages in the circumventricular organs of the mouse brain during TLR2-induced fever and sickness responses

Toll-like receptor 2 (TLR2) recognizes cell wall components from Gram-positive bacteria. Until now, however, little has been known about the significance of brain TLR2 in controlling inflammation and thermoregulatory responses during systemic Gram-positive bacterial infection. In the present study, the TLR2 immunoreactivity was seen to be prominent in the microglia/macrophages of the circumventricular organs (CVOs) of the mouse brain. The intraperitoneal injection of Pam3CSK4, a TLR2 agonist, induced nuclear factor-κ B activation in the microglia/macrophages of the CVOs. The injection of Pam3CSK4 also produced the expression of Fos at astrocytes and neurons in the CVOs and the regions neighboring the CVOs. The Pam3CSK4 injection induced fever and sickness responses. Pretreatment with lipopolysaccharide, a TLR4 agonist, augmented the Pam3CSK4-induced fever together with the increased TLR2 immunoreactivity. These results indicate that the TLR2 in microglia/macrophages of the CVOs are possibly associated with initiating and transmitting inflammatory responses in the brain.

Innate Immunity in the Central Nervous System: A Missing Piece of the Autoimmune Encephalitis Puzzle?

The autoimmune encephalitides are a group of autoimmune conditions targeting the central nervous system and causing severe clinical symptoms including drug-resistant seizures, cognitive dysfunction and psychiatric disturbance. Although these disorders appear to be antibody mediated, the role of innate immune responses needs further clarification. Infiltrating monocytes and microglial proliferation at the site of pathology could contribute to the pathogenesis of the disease with resultant blood brain barrier dysfunction, and subsequent activation of adaptive immune response. Both innate and adaptive immune cells can produce pro-inflammatory molecules which can perpetuate ongoing neuroinflammation and drive ongoing seizure activity. Ultimately neurodegenerative changes can ensue with resultant long-term neurological sequelae that can impact on ongoing patient morbidity and quality of life, providing a potential target for future translational research.

Different Approaches to Modulation of Microglia Phenotypes After Spinal Cord Injury

Microglial cells, which are highly plastic, immediately respond to any change in the microenvironment by becoming activated and shifting the phenotype toward neurotoxicity or neuroprotection. The polarization of microglia/macrophages after spinal cord injury (SCI) seems to be a dynamic process and can change depending on the microenvironment, stage, course, and severity of the posttraumatic process. Effective methods to modulate microglia toward a neuroprotective phenotype in order to stimulate neuroregeneration are actively sought for. In this context, available approaches that can selectively impact the polarization of microglia/macrophages regulate synthesis of trophic factors and cytokines/chemokines in them, and their phagocytic function and effects on the course and outcome of SCI are discussed in this review.

Microglial Drug Targets in AD: Opportunities and Challenges in Drug Discovery and Development

Alzheimer’s disease (AD) is a large and increasing unmet medical need with no disease-modifying treatment currently available. Genetic evidence from genome-wide association studies (GWASs) and gene network analysis has clearly revealed a key role of the innate immune system in the brain, of which microglia are the most important element. Single-nucleotide polymorphisms (SNPs) in genes predominantly expressed in microglia have been associated with altered risk of developing AD. Furthermore, microglia-specific pathways are affected on the messenger RNA (mRNA) expression level in post-mortem AD tissue and in mouse models of AD. Together these findings have increased the interest in microglia biology, and numerous scientific reports have proposed microglial molecules and pathways as drug targets for AD. Target identification and validation are generally the first steps in drug discovery. Both target validation and drug lead identification for central nervous system (CNS) targets and diseases entail additional significant obstacles compared to peripheral targets and diseases. This makes CNS drug discovery, even with well-validated targets, challenging. In this article, we will illustrate the special challenges of AD drug discovery by discussing the viability/practicality of possible microglia drug targets including cluster of differentiation 33 (CD33), K_Ca3.1, kynurenines, ionotropic P2 receptor 7 (P2X7), programmed death-1 (PD-1), Toll-like receptors (TLRs), and triggering receptor expressed in myeloid cells 2 (TREM2).

Understanding the Role of Innate Immunity in the Response to Intracortical Microelectrodes

Intracortical microelectrodes exhibit enormous potential for researching the nervous system, steering assistive devices and functional electrode stimulation systems for severely paralyzed individuals, and augmenting the brain with computing power. Unfortunately, intracortical microelectrodes often fail to consistently record signals over clinically useful periods. Biological mechanisms, such as the foreign body response to intracortical microelectrodes and self-perpetuating neuroinflammatory cascades, contribute to the inconsistencies and decline in recording performance. Unfortunately, few studies have directly correlated microelectrode performance with the neuroinflammatory response to the implanted devices. However, of those select studies that have, the role of the innate immune system remains among the most likely links capable of corroborating the results of different studies, across laboratories. Therefore, the overall goal of this review is to highlight the role of innate immunity signaling in the foreign body response to intracortical microelectrodes and hypothesize as to appropriate strategies that may become the most relevant in enabling brain-dwelling electrodes of any geometry, or location, for a range of clinical applications.

Chondroitin sulfate proteoglycans as novel drivers of leucocyte infiltration in multiple sclerosis

Multiple sclerosis presents with profound changes in the network of molecules involved in maintaining central nervous system architecture, the extracellular matrix. The extracellular matrix components, particularly the chondroitin sulfate proteoglycans, have functions beyond structural support including their potential interaction with, and regulation of, inflammatory molecules. To investigate the roles of chondroitin sulfate proteoglycans in multiple sclerosis, we used the experimental autoimmune encephalomyelitis model in a time course study. We found that the 4-sulfated glycosaminoglycan side chains of chondroitin sulfate proteoglycans, and the core protein of a particular family member, versican V1, were upregulated in the spinal cord of mice at peak clinical severity, correspondent with areas of inflammation. Versican V1 expression in the spinal cord rose progressively over the course of experimental autoimmune encephalomyelitis. A particular structure in the spinal cord and cerebellum that presented with intense upregulation of chondroitin sulfate proteoglycans is the leucocyte-containing perivascular cuff, an important portal of entry of immune cells into the central nervous system parenchyma. In these inflammatory perivascular cuffs, versican V1 and the glycosaminoglycan side chains of chondroitin sulfate proteoglycans were observed by immunohistochemistry within and in proximity to lymphocytes and macrophages as they migrated across the basement membrane into the central nervous system. Expression of versican V1 transcript was also documented in infiltrating CD45+ leucocytes and F4/80+ macrophages by in situ hybridization. To test the hypothesis that the chondroitin sulfate proteoglycans regulate leucocyte mobility, we used macrophages in tissue culture studies. Chondroitin sulfate proteoglycans significantly upregulated pro-inflammatory cytokines and chemokines in macrophages. Strikingly, and more potently than the toll-like receptor-4 ligand lipopolysaccharide, chondroitin sulfate proteoglycans increased the levels of several members of the matrix metalloproteinase family, which are implicated in the capacity of leucocytes to cross barriers. In support, the migratory capacity of macrophages in vitro in a Boyden chamber transwell assay was enhanced by chondroitin sulfate proteoglycans. Finally, using brain specimens from four subjects with multiple sclerosis with active lesions, we found chondroitin sulfate proteoglycans to be associated with leucocytes in inflammatory perivascular cuffs in all four patients. We conclude that the accumulation of chondroitin sulfate proteoglycans in the perivascular cuff in multiple sclerosis and experimental autoimmune encephalomyelitis boosts the activity and migration of leucocytes across the glia limitans into the central nervous system parenchyma. Thus, chondroitin sulfate proteoglycans represent a new class of molecules to overcome in order to reduce the inflammatory cascades and clinical severity of multiple sclerosis.

Effect of Ascophyllan from Brown Algae Padina tetrastromatica on Cell Migration and Extracellular Matrix Stabilisation in Burn Wounds

Background:

Burn injuries are the most common injuries and a major health problem affecting communities worldwide. Many alternative therapies are used as treatment for burns. The healing efficacy of sulphated polysaccharide ascophyllan was evaluated and studied its mechanism of action on experimental burn wounds in rats.

Methods:

Ascophyllan fractions were extracted from marine brown algae Padina tetrastromatica (Dictyotaceae) and evaluated its burn wound healing potential. Full thickness burn wounds induced in male albino rats were used for in vivo study and evaluated wound healing parameters.

Results:

The results showed that Ascophyllan Fraction 3 (AF3) had no cytotoxic effect and it increases cell migration and production of VEGF in fibroblasts. AF3 significantly reduced in vitro secretion of cytokines in blood mononuclear cells treated with Lipopolysaccharide (LPS). In vivo study showed that AF3 (5%) has significant wound healing activity in albino rats and this dose was used for studying the healing mechanism. The reference control used for the study was povidone-iodine ointment. Wound area contraction and reepithelialisation was faster in AF3 (5%) administered group. When applied topically, AF3 (5%) increased hydroxyproline and hexosamine content at the wound site. Uronic acid, DNA and proteins levels were also increased. Compared to the control groups, AF3 (5%) treatment showed an increase in neovascularization and fibroblast proliferation as evidenced by histopathology of granulation tissue.

Conclusion:

Sulphated polysaccharide ascophyllan is beneficial for the wound environment as it enhances the healing process and suggested the safe usage of this algal polysaccharide as an alternative for replacing current synthetic wound healing agents in medicine.

Role of Microglia TLRs in Neurodegeneration

Toll-like receptors (TLRs) are a group of receptors widely distributed in the organism. In the central nervous system, they are expressed in neurons, astrocytes and microglia. Although their involvement in immunity is notorious, different articles have demonstrated their roles in physiological and pathological conditions, including neurodegeneration. There is increasing evidence of an involvement of TLRs, especially TLR2, 4 and 9 in neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), and amyotrophic lateral sclerosis (ALS). In this sense, their expression in microglia might modulate the activity of these cells, which in turn, lead to protective or deleterious effects over neurons and other cells. Therefore, TLRs might mediate the link between inflammation and neurodegenerative diseases. However, further studies have to be performed to elucidate the role of the other TLRs in these diseases and to further prove and confirm the pathophysiological role of all TLRs in neurodegeneration. In this article, we revise and summarize the current knowledge regarding the role of TLRs in neurodegeneration with the focus on the possible functions of these receptors in microglia.

Diverging mRNA and Protein Networks in Activated Microglia Reveal SRSF3 Suppresses Translation of Highly Upregulated Innate Immune Transcripts

Uncontrolled microglial activation may lead to the development of inflammation-induced brain damage. Here, we uncover a ribosome-based mechanism/checkpoint involved in control of the innate immune response and microglial activation. Using an in vivo model system for analysis of the dynamic translational state of microglial ribosomes, with mRNAs as input and newly synthesized peptides as an output, we find a marked dissociation of microglia mRNA and protein networks following innate immune challenge. Highly upregulated and ribosome-associated mRNAs were not translated, resulting in two distinct microglial molecular signatures, a highly specialized pro-inflammatory mRNA signature and an immunomodulatory/homeostatic protein signature. We find that this is due to specific translational suppression of highly expressed mRNAs through a 3' UTR-mediated mechanism involving the RNA-binding protein SRSF3. This discovery suggests avenues for therapeutic modulation of innate immune response in resident microglia.

mCSF-Induced Microglial Activation Prevents Myelin Loss and Promotes Its Repair in a Mouse Model of Multiple Sclerosis

A pathological hallmark of multiple sclerosis (MS) is myelin loss in brain white matter accompanied by compromised remyelination. Demyelinated lesions are deeply associated with oligodendrocyte apoptosis and a robust inflammatory response. Although various studies point towards a noxious role of inflammation in MS, others emphasize a positive role for the innate immune cells in disease progression. A cytokine well-known to stimulate cell survival, proliferation and differentiation of myeloid cells, macrophage colony-stimulating factor (mCSF), was administered to mice during a 5 week-long cuprizone diet. Treated mice exhibited reduced myelin loss during the demyelination phase, together with an increased number of microglia and oligodendrocyte precursor cells in lesion sites. Tamoxifen-induced conditional deletion of the mCSF receptor in microglia from cuprizone-fed mice caused aberrant myelin debris accumulation in the corpus callosum and reduced microglial phagocytic response. mCSF therefore plays a key role in stimulating myelin clearance by the brain innate immune cells, which is a prerequisite for proper remyelination and myelin repair processes.

Ouabain Protects Mice Against Lipopolysaccharide-Induced Acute Lung Injury

Background

Ouabain, an inhibitor of Na⁺/K⁺-ATPase, is a type of endogenous hormone synthesized in the adrenal cortex and hypothalamus. Previous studies found that ouabain potently inhibited inflammatory reactions and regulated immunological processes. Our present study aimed to investigate the therapeutic role of ouabain on lipopolysaccharide (LPS)-induced acute lung injury (ALI) in mice.

Material/Methods

Ouabain (0.1 mg/kg) or vehicles were intraperitoneally injected into male C57BL/6J mice once a day for 3 consecutive days. One hour after the last injection of ouabain, LPS (5 mg/kg) was administrated through intranasal instillation to induce ALI. 6 hours and 24 hours later, bronchoalveolar lavage fluid (BALF) and lung tissues were harvested to detect the protective effects of ouabain, including protein concentration, inflammation cell counts, lung wet-to-dry ratio, and lung damage.

Results

The results showed that ouabain attenuated LPS-induced ALI in mice, which was indicated by alleviated pathological changes, downregulated TNF-α, IL-1β, and IL-6 production, inhibited neutrophils infiltration and macrophages, and ameliorated pulmonary edema and permeability. Further results found the activation of nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways were suppressed by ouabain in LPS-induced ALI.

Conclusions

These results suggest that ouabain negatively modulates the severity of LPS-induced ALI.

Influence of Artemisia annua L. on toll-like receptor expression in brain of mice infected with Acanthamoeba sp

The treatment of acanthamoebiasis is a still a problem. Our previous studies showed that the application of extracts from Artemisia annua L. significantly prolonged the survival of mice infected by Acanthamoeba. This plant has medicinal properties in the treatment of human parasitic diseases. The aim of this study was to evaluate the effects of A. annua on expression of Toll-like receptors (TLRs) 2 and 4 in brain of mice with Acanthamoeba infection. Mice were infected with Acanthamoeba sp. strain Ac309 (KY203908) by intranasal inoculation without and after application of A. annua extract. The administration of extract from A. annua significantly reduced the level of expression of TLR2 and modified the level of expression of TLR4. A. annua extract is a natural substance that is well tolerated in animals and may be considered as a combination therapy in treatment of acanthamoebiasis. Our study suggested that A. annua extract may be used as an alternative therapeutic tool.

The diverse cellular responses of the choroid plexus during infection of the central nervous system

The choroid plexus (CP) is responsible for the production of a large amount of the cerebrospinal fluid (CSF). As a highly vascularized structure, the CP also presents a significant frontier between the blood and the central nervous system (CNS). To seal this border, the epithelium of the CP forms the blood-CSF barrier, one of the most important barriers separating the CNS from the blood. During the course of infectious disease, cells of the CP can experience interactions with intruding pathogens, especially when the CP is used as gateway for entry into the CNS. In return, the CP answers to these encounters with diverse measures. Here, we will review the distinct responses of the CP during infection of the CNS, which include engaging of signal transduction pathways, the regulation of gene expression in the host cells, inflammatory cell response, alterations of the barrier, and, under certain circumstances, cell death. Many of these actions may contribute to stage an immunological response against the pathogen and subsequently help in the clearance of the infection.

Live imaging of the innate immune response in neonates reveals differential TLR2 dependent activation patterns in sterile inflammation and infection

Activation of microglial cells in response to brain injury and/or immune stimuli is associated with a marked induction of Toll-like receptors (TLRs). While in adult brain, the contribution of individual TLRs, including TLR2, in pathophysiological cascades has been well established, their role and spatial and temporal induction patterns in immature brain are far less understood. To examine whether infectious stimuli and sterile inflammatory stimuli trigger distinct TLR2-mediated innate immune responses, we used three models in postnatal day 9 (P9) mice, a model of infection induced by systemic endotoxin injection and two models of sterile inflammation, intra-cortical IL-1β injection and transient middle cerebral artery occlusion (tMCAO). We took advantage of a transgenic mouse model bearing the dual reporter system luciferase/GFP under transcriptional control of a murine TLR2 promoter (TLR2-luc-GFP) to visualize the TLR2 response in the living neonatal brain and then determined neuroinflammation, microglial activation and leukocyte infiltration. We show that in physiological postnatal brain development the in vivo TLR2-luc signal undergoes a marked ∼30-fold decline and temporal-spatial changes during the second and third postnatal weeks. We then show that while endotoxin robustly induces the in vivo TLR2-luc signal in the living brain and increases levels of several inflammatory cytokines and chemokines, the in vivo TLR2-luc signal is reduced after both IL-1β and tMCAO and the inflammatory response is muted. Immunofluorescence revealed that microglial cells are the predominant source of TLR2 production during postnatal brain development and in all three neonatal models studied. Flow cytometry revealed developmental changes in CD11b+/CD45+ and CD11b+/Ly6C+ cell populations, involvement of cells of the monocyte lineage, but lack of Ly6G+ neutrophils or CD3+ cells in acutely injured neonatal brains. Cumulatively, our results suggest distinct TLR2 induction patterns following PAMP and DAMP - mediated inflammation in immature brain.

Systemic Inflammation as a Driver of Brain Injury: the Astrocyte as an Emerging Player

Severe systemic inflammation has strong effects on brain functions, promoting permanent neurocognitive dysfunction and high mortality rates. Additionally, hippocampal damage seems to be directly involved in this process and astrocytes play an important role in neuroinflammation and in the neuroimmune response. However, the contribution of the astrocytes to the pathology of acute brain dysfunction is not well understood. Recently, our group established a protocol for obtaining astrocyte cultures from mature brain to allow the characterization of these cells and their functions under pathologic conditions. The present study was designed to characterize astrocyte function after acute systemic inflammation induced by cecal ligation and perforation (CLP). Hippocampal astrocyte cultures from CLP animals presented increased levels of tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6, IL-18, and cyclooxygenase-2 and decreased levels of IL-10. This proinflammatory profile was accompanied by an increase in Toll-like receptor (TLR)2 mRNA expression levels and no change either in TLR4 or in vascular endothelial growth factor (VEGF) gene expression. These alterations were associated with increased expressions of p21, nuclear factor kappa B (NFκB), and inducible nitric oxide synthase (iNOS) in astrocytes from CLP animals. The same parameters were also evaluated in whole hippocampal tissue, but differences in this profile were found compared to hippocampal astrocyte cultures from CLP, reflecting an interaction between other central nervous system cell types, which may mask specific astrocytic changes. These results improve our understanding of the mechanisms by which astrocytes react against systemic inflammation, and suggest these cells to be potential targets for therapeutic modulation.

Toll-like receptors in the brain of mice following infection with Acanthamoeba spp

The Toll-like receptors (TLRs) of the innate immune system play an important role in the recognition of pathogens such as bacteria, viruses, fungi, and parasites. In this study, we examined the changes in the level of expression of TLR2 and TLR4 mRNA and protein in the brains of mice infected with Acanthamoeba spp. The Acanthamoeba strains were isolated from a patient with Acanthamoeba keratitis (AK) (Ac55) and Malta Lake (Ac43). In the brain isolated from mice at 2 days post-infection (dpi) with Acanthamoeba strains Ac55 and Ac43, mRNAs for TLR2 and TLR4 were significantly more strongly expressed in comparison with the uninfected mice. In Acanthamoeba-infected mice, TLR2 and TLR4 expression was detected in neurons, glial cells, and endothelial cells within the neocortex. These receptors showed more intense expression in ependymocytes of the choroid plexus of infected mice at 2 dpi. Increased levels of TLR2 and TLR4 mRNA expression in infected mice suggest the involvement of these TLRs in the recognition of Acanthamoeba spp. pathogen-associated molecular patterns (PAMPs).

Glucocorticoids: Protectors of the Brain during Innate Immune Responses

The innate immune response is a coordinated set of reactions involving cells of myeloid lineage and a network of signaling molecules. Such a response takes place in the CNS during trauma, stroke, spinal cord injury, and neurodegenerative diseases, suggesting that macrophages/microglia are the cells that perpetuate the progressive neuronal damage. However, there is accumulating evidence that these cells and their secreted proinflammatory molecules have more beneficial effects than detrimental consequences for the neuronal elements. Indeed, a timely controlled innate immune response may limit toxicity in swiftly eliminating foreign materials and debris that are known to interfere with recovery and regeneration. Each step of the immune cascade is under the tight control of stimulatory and inhibitory signals. Glucocorticoids (GCs) act as the critical negative feedback on all myeloid cells, including those present within the brain parenchyma. Because too little is like too much, both an inappropriate feedback of GCs on microglia and high circulating GC levels in stressed individuals have been associated with deleterious consequences for the brain. In this review, the authors discuss both sides of the story with a particular emphasis on the neuro-protective role of endogenous GCs during immune challenges and the problems in determining whether GCs can be a good therapy for the treatment of neuropathological conditions.

Inflammatory transcription factors as activation markers and functional readouts in immune-to-brain communication

Immune-to-brain communication pathways involve humoral mediators, including cytokines, central modulation by neuronal afferents and immune cell trafficking to the brain. During systemic inflammation these pathways contribute to mediating brain-controlled sickness symptoms including fever. Experimentally, activation of these signaling pathways can be mimicked and studied when injecting animals with pathogen associated molecular patterns (PAMPS). One central component of the brain inflammatory response, which leads, for example, to fever induction, is transcriptional activation of brain cells via cytokines and PAMPS. We and others have studied the spatiotemporal activation and the physiological significance of transcription factors for the induction of inflammation within the brain and the manifestation of fever. Evidence has revealed a role of nuclear factor (NF)κB in the initiation, signal transducer and activator of transcription (STAT)3 in the maintenance and NF-interleukin (IL)6 in the maintenance or even termination of brain-inflammation and fever. Moreover, psychological stressors, such as exposure to a novel environment, leads to increased body core temperature and genomic NF-IL6-activation, suggesting a potential use of NF-IL6-immunohistochemistry as a multimodal brain cell activation marker and a role for NF-IL6 for differential brain activity. In addition, the nutritional status, as reflected by circulating levels of the cytokine-like hormone leptin, influence immune-to-brain communication and age-dependent changes in LPS-induced fever. Overall, transcription factors remain therapeutically important targets for the treatment of brain-inflammation and fever induction during infectious/non-infectious inflammatory and psychological stress. However, the exact physiological role and significance of these transcription factors requires to be further investigated.

Toll-like receptor expression and function in type I bipolar disorder

Bipolar disorder (BD) has been associated with immune imbalance and low-grade inflammation. The underlying mechanisms remain largely obscure but may involve changes in cell signaling. Toll-like receptors (TLRs) are widely expressed by immune cells. Specific binding of TLRs to pathogen- or danger-associated signals leads to inflammatory responses. Here, we analyzed the frequencies of TLR-1, TLR-2, TLR-4, TLR-5 and TLR-6 in monocytes, regulatory T cells (Tregs) and activated T cells from type I BD euthymic patients and healthy controls (HCs). Monocytes were stimulated in vitro with specific TLR agonists (flagellin, LPS, LTA, BLP and PGN) and immunophenotyped. Cytokines (IL-8, IL-1beta, IL-6, IL-10, TNF-alpha and IL-12p70) were assessed with cytometric bead arrays. At baseline, increased percentages of TLR-1+ and TLR-2+ monocytes and reduced expression of TLR-5 were observed in BD. Following stimulation, the percentage of TLR-1+, TLR-2+, and TLR-6+ monocytes was higher in BD subjects than in HCs. Increased levels of IL-8, IL-12p70 and TNF were observed following stimulation with TLR-1, TLR-2 and TLR-6 agonists, suggesting increased signaling via these receptors in BD. In contrast to HCs, BD patients exhibited no changes in TLR-5 expression following stimulation. The percentage of TLR-2+ Treg cells as well as activated T cells expressing both TLR-2 and TLR-5 increased in BD patients. Given the importance of TLRs in triggering immune responses, our data indicate a role for these receptors in the low-grade inflammatory profile documented in BD.

The relation of saturated fatty acids with low-grade inflammation and cardiovascular disease

The mantra that dietary (saturated) fat must be minimized to reduce cardiovascular disease (CVD) risk has dominated nutritional guidelines for decades. Parallel to decreasing intakes of fat and saturated fatty acids (SFA), there have been increases in carbohydrate and sugar intakes, overweight, obesity and type 2 diabetes mellitus. The "lipid hypothesis" coined the concept that fat, especially SFA, raises blood low-density lipoprotein-cholesterol and thereby CVD risk. In view of current controversies regarding their adequate intakes and effects, this review aims to summarize research regarding this heterogenic group of fatty acids and the mechanisms relating them to (chronic) systemic low-grade inflammation, insulin resistance, metabolic syndrome and notably CVD. The intimate relationship between inflammation and metabolism, including glucose, fat and cholesterol metabolism, revealed that the dyslipidemia in Western societies, notably increased triglycerides, "small dense" low-density lipoprotein and "dysfunctional" high-density lipoprotein, is influenced by many unfavorable lifestyle factors. Dietary SFA is only one of these, not necessarily the most important, in healthy, insulin-sensitive people. The environment provides us not only with many other proinflammatory stimuli than SFA but also with many antiinflammatory counterparts. Resolution of the conflict between our self-designed environment and ancient genome may rather rely on returning to the proinflammatory/antiinflammatory balance of the Paleolithic era in consonance with the 21st century culture. Accordingly, dietary guidelines might reconsider recommendations for SFA replacement and investigate diet in a broader context, together with nondietary lifestyle factors. This should be a clear priority, opposed to the reductionist approach of studying the effects of single nutrients, such as SFA.

Ligand engagement of Toll-like receptors regulates their expression in cortical microglia and astrocytes

Background

Toll-like receptor (TLR) activation on microglia and astrocytes are key elements in neuroinflammation which accompanies a number of neurological disorders. While TLR activation on glia is well-established to up-regulate pro-inflammatory mediator expression, much less is known about how ligand engagement of one TLR may affect expression of other TLRs on microglia and astrocytes.

Methods

In the present study, we evaluated the effects of agonists for TLR2 (zymosan), TLR3 (polyinosinic-polycytidylic acid (poly(I:C)), a synthetic analogue of double-stranded RNA) and TLR4 (lipopolysaccaride (LPS)) in influencing expression of their cognate receptor as well as that of the other TLRs in cultures of rat cortical purified microglia (>99.5 %) and nominally microglia-free astrocytes. Elimination of residual microglia (a common contaminant of astrocyte cultures) was achieved by incubation with the lysosomotropic agent l-leucyl-l-leucine methyl ester (L-LME).

Results

Flow cytometric analysis confirmed the purity (essentially 100 %) of the obtained microglia, and up to 5 % microglia contamination of astrocytes. L-LME treatment effectively removed microglia from the latter (real-time polymerase chain reaction). The three TLR ligands robustly up-regulated gene expression for pro-inflammatory markers (interleukin-1 and interleukin-6, tumor necrosis factor) in microglia and enriched, but not purified, astrocytes, confirming cellular functionality. LPS, zymosan and poly(I:C) all down-regulated TLR4 messenger RNA (mRNA) and up-regulated TLR2 mRNA at 6 and 24 h. In spite of their inability to elaborate pro-inflammatory mediator output, the nominally microglia-free astrocytes (>99 % purity) also showed similar behaviours to those of microglia, as well as changes in TLR3 gene expression. LPS interaction with TLR4 activates downstream mitogen-activated protein kinase and nuclear factor-κB signalling pathways and subsequently causes inflammatory mediator production. The effects of LPS on TLR2 mRNA in both cell populations were antagonized by a nuclear factor-κB inhibitor.

Conclusions

TLR2 and TLR4 activation in particular, in concert with microglia and astrocytes, comprise key elements in the initiation and maintenance of neuropathic pain. The finding that both homologous (zymosan) and heterologous (LPS, poly(I:C)) TLR ligands are capable of regulating TLR2 gene expression, in particular, may have important implications in understanding the relative contributions of different TLRs in neurological disorders associated with neuroinflammation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0458-6) contains supplementary material, which is available to authorized users.

Neuron-astrocyte interactions in neurodegenerative diseases: Role of neuroinflammation

Selective neuron loss in discrete brain regions is a hallmark of various neurodegenerative disorders, although the mechanisms responsible for this regional vulnerability of neurons remain largely unknown. Earlier studies attributed neuron dysfunction and eventual loss during neurodegenerative diseases as exclusively cell autonomous. Although cell-intrinsic factors are one critical aspect in dictating neuron death, recent evidence also supports the involvement of other central nervous system cell types in propagating non-cell autonomous neuronal injury during neurodegenerative diseases. One such example is astrocytes, which support neuronal and synaptic function, but can also contribute to neuroinflammatory processes through robust chemokine secretion. Indeed, aberrations in astrocyte function have been shown to negatively impact neuronal integrity in several neurological diseases. The present review focuses on neuroinflammatory paradigms influenced by neuron-astrocyte cross-talk in the context of select neurodegenerative diseases.

Systemic inflammation and microglial activation: systematic review of animal experiments

Background

Animal studies show that peripheral inflammatory stimuli may activate microglial cells in the brain implicating an important role for microglia in sepsis-associated delirium. We systematically reviewed animal experiments related to the effects of systemic inflammation on the microglial and inflammatory response in the brain.

Methods

We searched PubMed between January 1, 1950 and December 1, 2013 and Embase between January 1, 1988 and December 1, 2013 for animal studies on the influence of peripheral inflammatory stimuli on microglia and the brain. Identified studies were systematically scored on methodological quality. Two investigators extracted independently data on animal species, gender, age, and genetic background; number of animals; infectious stimulus; microglial cells; and other inflammatory parameters in the brain, including methods, time points after inoculation, and brain regions.

Results

Fifty-one studies were identified of which the majority was performed in mice (n = 30) or in rats (n = 19). Lipopolysaccharide (LPS) (dose ranging between 0.33 and 200 mg/kg) was used as a peripheral infectious stimulus in 39 studies (76 %), and live or heat-killed pathogens were used in 12 studies (24 %). Information about animal characteristics such as species, strain, sex, age, and weight were defined in 41 studies (80 %), and complete methods of the disease model were described in 35 studies (68 %). Studies were also heterogeneous with respect to methods used to assess microglial activation; markers used mostly were the ionized calcium binding adaptor molecule-1 (Iba-1), cluster of differentiation 68 (CD68), and CD11b. After LPS challenge microglial activation was seen 6 h after challenge and remained present for at least 3 days. Live Escherichia coli resulted in microglial activation after 2 days, and heat-killed bacteria after 2 weeks. Concomitant with microglial response, inflammatory parameters in the brain were reviewed in 23 of 51 studies (45 %). Microglial activation was associated with an increase in Toll-like receptor (TLR-2 and TLR-4), tumor necrosis factor alpha (TNF-α), and interleukin 1 beta (IL-1β) messenger ribonucleic acid (mRNA) expression or protein levels.

Interpretation

Animal experiments robustly showed that peripheral inflammatory stimuli cause microglial activation. We observed distinct differences in microglial activation between systemic stimulation with (supranatural doses) LPS and live or heat-killed bacteria.

Selective Impairment of Spatial Cognition Caused by Autoantibodies to the N-Methyl-D-Aspartate Receptor

Patients with systemic lupus erythematosus (SLE) experience cognitive abnormalities in multiple domains including processing speed, executive function, and memory. Here we show that SLE patients carrying antibodies that bind DNA and the GluN2A and GluN2B subunits of the N-methyl-d-aspartate receptor (NMDAR), termed DNRAbs, displayed a selective impairment in spatial recall. Neural recordings in a mouse model of SLE, in which circulating DNRAbs penetrate the hippocampus, revealed that CA1 place cells exhibited a significant expansion in place field size. Structural analysis showed that hippocampal pyramidal cells had substantial reductions in their dendritic processes and spines. Strikingly, these abnormalities became evident at a time when DNRAbs were no longer detectable in the hippocampus. These results suggest that antibody-mediated neurocognitive impairments may be highly specific, and that spatial cognition may be particularly vulnerable to DNRAb-mediated structural and functional injury to hippocampal cells that evolves after the triggering insult is no longer present.

Stimulation of monocytes, macrophages, and microglia by amphotericin B and macrophage colony-stimulating factor promotes remyelination

Approaches to stimulate remyelination may lead to recovery from demyelinating injuries and protect axons. One such strategy is the activation of immune cells with clinically used medications, since a properly directed inflammatory response can have healing properties through mechanisms such as the provision of growth factors and the removal of cellular debris. We previously reported that the antifungal medication amphotericin B is an activator of circulating monocytes, and their tissue-infiltrated counterparts and macrophages, and of microglia within the CNS. Here, we describe that amphotericin B activates these cells through engaging MyD88/TRIF signaling. When mice were subjected to lysolecithin-induced demyelination of the spinal cord, systemic injections of nontoxic doses of amphotericin B and another activator, macrophage colony-stimulating factor (MCSF), further elevated the representation of microglia/macrophages at the site of injury. Treatment with amphotericin B, particularly in combination with MCSF, increased the number of oligodendrocyte precursor cells and promoted remyelination within lesions; these pro-regenerative effects were mitigated in mice treated with clodronate liposomes to reduce circulating monocytes and tissue-infiltrated macrophages. Our results have identified candidates among currently used medications as potential therapies for the repair of myelin.

Profile of toll-like receptor mRNA expression in the choroid plexus in adult ewes

The blood-cerebrospinal fluid barrier (BCSFB) located in the epithelial cells of the choroid plexus (CP) forms the interface between the cerebrospinal fluid (CSF) and pathogen components circulating in the blood. The CP is also implicated in the passage of peripheral immune signals and circulation of immune cells into the central nervous system. Toll-like receptors (TLRs) are patternrecognition receptors that play a crucial role in the recognition of pathogens and triggering of the innate immune response. In sheep, ten members of the TLR family have been identified and cloned. We used real-time PCR analyses to examine the profiles of TLR mRNA expression in the CP of cerebral ventricles in healthy adult ewes. The transcripts for all ten TLRs except TLR8 were present; however, we observed a high variation in the degree of expression of the TLR5 and TLR1 genes (coefficient of variation: 61% and 46%, respectively) as well as a moderate variation in the expression of the TLR4 (34%), TLR2 (27%) and TLR6 (26%) genes. The TLR9, TLR7, TLR3 and TLR10 genes were the four receptors with relatively invariable expression levels (coefficient of variation: 7%, 8%, 16% and 17%, respectively) across the six adult ewes. The concentration of cortisol in blood collected prior to sacrificing the ewes ranged from 0.18 to 78.9 ng/ml. There was no correlation between cortisol concentration and mRNA expression of any of the examined TLRs. These data suggest that the CP has the potential to sense the presence of many bacterial and viral components and mediate responses for the elimination of invading microorganisms, thereby protecting the brain.

Signaling function of Na,K-ATPase induced by ouabain against LPS as an inflammation model in hippocampus

BACKGROUND

Ouabain (OUA) is a newly recognized hormone that is synthesized in the adrenal cortex and hypothalamus. Low doses of OUA can activate a signaling pathway by interaction with Na,K-ATPase, which is protective against a number of insults. OUA has central and peripheral anti-inflammatory effects. Lipopolysaccharide (LPS), via toll-like receptor 4 activation, is a widely used model to induce systemic inflammation. This study used a low OUA dose to evaluate its effects on inflammation induced by LPS injection in rats.

METHODS

Adult male Wistar rats received acute intraperitoneal (ip) OUA (1.8 μg/kg) or saline 20 minutes before LPS (200 μg/kg, ip) or saline injection. Some of the animals had their femoral artery catheterized in order to assess arterial blood pressure values before and after OUA administration. Na,K-ATPase activity, cytokine mRNA levels, apoptosis-related proteins, NF-κB activation brain-derived neurotrophic factor BDNF, corticosterone and TNF-α levels were measured.

RESULTS

OUA pretreatment decreased mRNA levels of the pro-inflammatory cytokines, inducible nitric oxide synthase (iNOS) and IL-1β, which are activated by LPS in the hippocampus, but with no effect on serum measures of these factors. None of these OUA effects were linked to Na,K-ATPase activity. The involvement of the inflammatory transcription factor NF-κB in the OUA effect was indicated by its prevention of LPS-induced nuclear translocation of the NF-κB subunit, RELA (p65), as well as the decreased cytosol levels of the NF-κB inhibitor, IKB, in the hippocampus. OUA pretreatment reversed the LPS-induced glial fibrillary acidic protein (GFAP) activation and associated inflammation in the dentate gyrus. OUA also prevented LPS-induced increases in the hippocampal Bax/Bcl2 ratio suggesting an anti-apoptotic action in the brain.

CONCLUSION

Our results suggest that a low dose of OUA has an important anti-inflammatory effect in the rat hippocampus. This effect was associated with decreased GFAP induction by LPS in the dentate gyrus, a brain area linked to adult neurogenesis.

Toll-like receptors in central nervous system injury and disease: a focus on the spinal cord

Toll-like receptors (TLRs) are best known for recognizing pathogens and initiating an innate immune response to protect the host. However, they also detect tissue damage and induce sterile inflammation upon the binding of endogenous ligands released by stressed or injured cells. In addition to immune system-related cells, TLRs have been identified in central nervous system (CNS) neurons and glial subtypes including microglia, astrocytes and oligodendrocytes. Direct and indirect effects of TLR ligands on neurons and glial subtypes have been documented in vitro. Likewise, the effects of TLR ligands have been demonstrated in vivo using animal models of CNS trauma and disease including spinal cord injury (SCI), amyotrophic lateral sclerosis (ALS) and neuropathic pain. The indirect effects are most likely mediated via microglia or immune system cells that infiltrate the diseased or injured CNS. Despite considerable progress over the past decade, the role of TLRs in the physiological and pathological function of the spinal cord remains inadequately defined. Published reports collectively highlight TLRs as promising targets for therapeutic interventions in spinal cord pathology. The findings also underscore the complexity of TLR-mediated mechanisms and the necessity for further research in this field. The goals of the current review are to recapitulate the studies that investigated the role of TLRs in the spinal cord, to discuss potential future research directions, and to examine some of the challenges associated with pre-clinical studies pertinent to TLRs in the injured or diseased spinal cord.

Regional brain metabolism in a murine systemic lupus erythematosus model

Systemic lupus erythematosus (SLE) is characterized by multiorgan inflammation, neuropsychiatric disorders (NPSLE), and anti-nuclear antibodies. We previously identified a subset of anti-DNA antibodies (DNRAb) cross-reactive with the N-methyl-D-aspartate receptor, present in 30% to 40% of patients, able to enhance excitatory post-synaptic potentials and trigger neuronal apoptosis. DNRAb+ mice exhibit memory impairment or altered fear response, depending on whether the antibody penetrates the hippocampus or amygdala. Here, we used 18F-fluorodeoxyglucose (FDG) microPET to plot changes in brain metabolism after regional blood-brain barrier (BBB) breach. In DNRAb+ mice, metabolism declined at the site of BBB breach in the first 2 weeks and increased over the next 2 weeks. In contrast, DNRAb- mice exhibited metabolic increases in these regions over the 4 weeks after the insult. Memory impairment was present in DNRAb+ animals with hippocampal BBB breach and altered fear conditioning in DNRAb+ mice with amygdala BBB breach. In DNRAb+ mice, we observed an inverse relationship between neuron number and regional metabolism, while a positive correlation was observed in DNRAb- mice. These findings suggest that local metabolic alterations in this model take place through different mechanisms with distinct time courses, with important implications for the interpretation of imaging data in SLE subjects.

TRIL is involved in cytokine production in the brain following Escherichia coli infection

TLR4 interactor with leucine-rich repeats (TRIL) is a brain-enriched accessory protein that is important in TLR3 and TLR4 signaling. In this study, we generated Tril(-/-) mice and examined TLR responses in vitro and in vivo. We found a role for TRIL in both TLR4 and TLR3 signaling in mixed glial cells, consistent with the high level of expression of TRIL in these cells. We also found that TRIL is a modulator of the innate immune response to LPS challenge and Escherichia coli infection in vivo. Tril(-/-) mice produce lower levels of multiple proinflammatory cytokines and chemokines specifically within the brain after E. coli and LPS challenge. Collectively, these data uncover TRIL as a mediator of innate immune responses within the brain, where it enhances neuronal cytokine responses to infection.

A Decade of Research on TLR2 Discovering Its Pivotal Role in Glial Activation and Neuroinflammation in Neurodegenerative Diseases

Toll-like receptors (TLRs) belong to a class of pattern recognition receptors that play an important role in host defense against pathogens. TLRs on innate immune cells recognize a wide variety of pathogen-associated molecular patterns (PAMPs) and trigger innate immune responses. Later, it was revealed that the same receptors are also utilized to detect tissue damage to trigger inflammatory responses in the context of non-infectious inflammation. In the nervous system, different members of the TLR family are expressed on glial cells including astrocytes, microglia, oligodendrocytes, and Schwann cells, implicating their putative role in innate/inflammatory responses in the nervous system. In this regard, we have investigated the function of TLRs in neuroinflammation. We discovered that a specific member of the TLR family, namely TLR2, functions as a master sentry receptor to detect neuronal cell death and tissue damage in many different neurological conditions including nerve transection injury, intracerebral hemorrhage, traumatic brain injury, and hippocampal excitotoxicity. In this review, we have summarized our research for the last decade on the role of TLR2 in neuroinflammation in the above neurological disorders. Our data suggest that TLR2 can be an efficient target to regulate unwanted inflammatory response in these neurological conditions.

Infection-induced inflammation and cerebral injury in preterm infants

Preterm birth and infectious diseases are the most common causes of neonatal and early childhood deaths worldwide. The rates of preterm birth have increased over recent decades and account for 11% of all births worldwide. Preterm infants are at significant risk of severe infection in early life and throughout childhood. Bacteraemia, inflammation, or both during the neonatal period in preterm infants is associated with adverse outcomes, including death, chronic lung disease, and neurodevelopmental impairment. Recent studies suggest that bacteraemia could trigger cerebral injury even without penetration of viable bacteria into the CNS. Here we review available evidence that supports the concept of a strong association between bacteraemia, inflammation, and cerebral injury in preterm infants, with an emphasis on the underlying biological mechanisms, clinical correlates, and translational opportunities.