Expression and regulation of toll-like receptors in cerebral endothelial cells

Protection of Gastrointestinal Mucosa from Acute Heavy Alcohol Consumption: The Effect of Berberine and Its Correlation with TLR2, 4/IL1β-TNFα Signaling

The purpose of the present study is to confirm the protective effect of berberine (BBR) on gastrointestinal injury caused by acute heavy alcohol exposure, an effect that has not been reported previously. Our research details how BBR protects against gastrointestinal injuries from acute alcohol exposure using both in vivo and in vitro experiments. Acute high alcohol concentrations lead to obvious damage to the gastrointestinal mucosa, resulting in necrosis of the intestinal mucosa. Oral administration of BBR was able to significantly reduce this alcohol-induced damage, inhibit increases of alcohol-induced TNFα and IL-1β expression in gastrointestinal mucosa as well as their upstream signals TLR2 and TLR4, and regulate cytokines that modulate tight junctions. Alcohol consumption is a popular human social behavior worldwide, and the present study reports a comprehensive mechanism by which BBR protects against gastrointestinal injuries from alcohol stress, providing people with a novel application of BBR.

Brain Invasion by Mouse Hepatitis Virus Depends on Impairment of Tight Junctions and Beta Interferon Production in Brain Microvascular Endothelial Cells

Coronaviruses (CoVs) have shown neuroinvasive properties in humans and animals secondary to replication in peripheral organs, but the mechanism of neuroinvasion is unknown. The major aim of our work was to evaluate the ability of CoVs to enter the central nervous system (CNS) through the blood-brain barrier (BBB). Using the highly hepatotropic mouse hepatitis virus type 3 (MHV3), its attenuated variant, 51.6-MHV3, which shows low tropism for endothelial cells, and the weakly hepatotropic MHV-A59 strain from the murine coronavirus group, we investigated the virus-induced dysfunctions of BBB in vivo and in brain microvascular endothelial cells (BMECs) in vitro. We report here a MHV strain-specific ability to cross the BBB during acute infection according to their virulence for liver. Brain invasion was observed only in MHV3-infected mice and correlated with enhanced BBB permeability associated with decreased expression of zona occludens protein 1 (ZO-1), VE-cadherin, and occludin, but not claudin-5, in the brain or in cultured BMECs. BBB breakdown in MHV3 infection was not related to production of barrier-dysregulating inflammatory cytokines or chemokines by infected BMECs but rather to a downregulation of barrier protective beta interferon (IFN-β) production. Our findings highlight the importance of IFN-β production by infected BMECs in preserving BBB function and preventing access of blood-borne infectious viruses to the brain.

IMPORTANCE

Coronaviruses (CoVs) infect several mammals, including humans, and are associated with respiratory, gastrointestinal, and/or neurological diseases. There is some evidence that suggest that human respiratory CoVs may show neuroinvasive properties. Indeed, the severe acute respiratory syndrome coronavirus (SARS-CoV), causing severe acute respiratory syndrome, and the CoVs OC43 and 229E were found in the brains of SARS patients and multiple sclerosis patients, respectively. These findings suggest that hematogenously spread CoVs may gain access to the CNS at the BBB level. Herein we report for the first time that CoVs exhibit the ability to cross the BBB according to strain virulence. BBB invasion by CoVs correlates with virus-induced disruption of tight junctions on BMECs, leading to BBB dysfunction and enhanced permeability. We provide evidence that production of IFN-β by BMECs during CoV infection may prevent BBB breakdown and brain viral invasion.

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.

Central pathways causing fatigue in neuro-inflammatory and autoimmune illnesses

BACKGROUND

The genesis of severe fatigue and disability in people following acute pathogen invasion involves the activation of Toll-like receptors followed by the upregulation of proinflammatory cytokines and the activation of microglia and astrocytes. Many patients suffering from neuroinflammatory and autoimmune diseases, such as multiple sclerosis, Parkinson's disease and systemic lupus erythematosus, also commonly suffer from severe disabling fatigue. Such patients also present with chronic peripheral immune activation and systemic inflammation in the guise of elevated proinflammtory cytokines, oxidative stress and activated Toll-like receptors. This is also true of many patients presenting with severe, apparently idiopathic, fatigue accompanied by profound levels of physical and cognitive disability often afforded the non-specific diagnosis of chronic fatigue syndrome.

DISCUSSION

Multiple lines of evidence demonstrate a positive association between the degree of peripheral immune activation, inflammation and oxidative stress, gray matter atrophy, glucose hypometabolism and cerebral hypoperfusion in illness, such as multiple sclerosis, Parkinson's disease and chronic fatigue syndrome. Most, if not all, of these abnormalities can be explained by a reduction in the numbers and function of astrocytes secondary to peripheral immune activation and inflammation. This is also true of the widespread mitochondrial dysfunction seen in otherwise normal tissue in neuroinflammatory, neurodegenerative and autoimmune diseases and in many patients with disabling, apparently idiopathic, fatigue. Given the strong association between peripheral immune activation and neuroinflammation with the genesis of fatigue the latter group of patients should be examined using FLAIR magnetic resonance imaging (MRI) and tested for the presence of peripheral immune activation.

SUMMARY

It is concluded that peripheral inflammation and immune activation, together with the subsequent activation of glial cells and mitochondrial damage, likely account for the severe levels of intractable fatigue and disability seen in many patients with neuroimmune and autoimmune diseases.This would also appear to be the case for many patients afforded a diagnosis of Chronic Fatigue Syndrome.

The blood-brain barrier in neuroimmunology: Tales of separation and assimilation

Neuroimmunology is concerned with the relations between the central nervous and immune systems and with the mechanisms that drive those relations. The blood-brain barrier (BBB) employs mechanisms that both separate and connect these two systems. In fact, the relative immune privilege of the central nervous system (CNS) is largely attributable to the BBB's ability to prevent the unregulated exchange of immune cells and their secretions between the CNS and blood. Having separated the two systems, the BBB then participates in mechanisms that allow them to influence, communicate, and interact with one another. Likewise, the BBB itself is influenced by immune events that are occurring in the periphery and in the CNS so that these three components (the BBB, the immune system, and the CNS) form neuroimmune axes that adapt to physiological and pathological conditions. To date, four major themes have emerged by which the BBB participates in these neuroimmune axes. The first of these four, the formation of the barrier, acts to separate the immune and central nervous systems. The other three themes provide mechanisms for re-establishing communication: response of the BBB to immunomodulatory molecules (e.g., prostaglandins, cytokines, chemokines, nitric oxide) secreted by immune and CNS cells; the controlled, regulated exchange of chemokines, cytokines, and immune cells between the CNS and the blood (i.e., transport across the BBB); the secretion of immunomodulatory molecules by the BBB, often in a polarized fashion. Taken together, these mechanisms reveal the BBB to be a dynamic, interactive, and adaptable interface between the immune system and the CNS, separating them on the one hand and fostering their interactions on the other hand, adjusting to physiological changes, while being a target for disease processes. This review examines specific examples by which the BBB plays an interactive, defining role in neuroimmunology.

The Neuro-Immune Pathophysiology of Central and Peripheral Fatigue in Systemic Immune-Inflammatory and Neuro-Immune Diseases

Many patients with systemic immune-inflammatory and neuro-inflammatory disorders, including depression, rheumatoid arthritis, systemic lupus erythematosus, Sjögren's disease, cancer, cardiovascular disorder, Parkinson's disease, multiple sclerosis, stroke, and chronic fatigue syndrome/myalgic encephalomyelitis, endure pathological levels of fatigue. The aim of this narrative review is to delineate the wide array of pathways that may underpin the incapacitating fatigue occurring in systemic and neuro-inflammatory disorders. A wide array of immune, inflammatory, oxidative and nitrosative stress (O&NS), bioenergetic, and neurophysiological abnormalities are involved in the etiopathology of these disease states and may underpin the incapacitating fatigue that accompanies these disorders. This range of abnormalities comprises: increased levels of pro-inflammatory cytokines, e.g., interleukin-1 (IL-1), IL-6, tumor necrosis factor (TNF) α and interferon (IFN) α; O&NS-induced muscle fatigue; activation of the Toll-Like Receptor Cycle through pathogen-associated (PAMPs) and damage-associated (DAMPs) molecular patterns, including heat shock proteins; altered glutaminergic and dopaminergic neurotransmission; mitochondrial dysfunctions; and O&NS-induced defects in the sodium-potassium pump. Fatigue is also associated with altered activities in specific brain regions and muscle pathology, such as reductions in maximum voluntary muscle force, downregulation of the mitochondrial biogenesis master gene peroxisome proliferator-activated receptor gamma coactivator 1-alpha, a shift to glycolysis and buildup of toxic metabolites within myocytes. As such, both mental and physical fatigue, which frequently accompany immune-inflammatory and neuro-inflammatory disorders, are the consequence of interactions between multiple systemic and central pathways.

Activation of adult rat CNS endothelial cells by opioid-induced toll-like receptor 4 (TLR4) signaling induces proinflammatory, biochemical, morphological, and behavioral sequelae

CNS immune signaling contributes to deleterious opioid effects including hyperalgesia, tolerance, reward, and dependence/withdrawal. Such effects are mediated by opioid signaling at toll-like receptor 4 (TLR4), presumptively of glial origin. Whether CNS endothelial cells express TLR4 is controversial. If so, they would be well positioned for activation by blood-borne opioids, contributing to opioid-induced pro-inflammatory responses. These studies examined adult primary rat CNS endothelial cell responses to (-)-morphine or its mu opioid receptor (MOR)-inactive metabolite morphine-3-glucuronide (M3G), both known TLR4 agonists. We demonstrate that adult rat CNS endothelial cells express functional TLR4. M3G activated nuclear factor kappaB (NF-κB), increased tumor necrosis factor-α (TNFα) and cyclooxygenase-2 (COX2) mRNAs, and released prostaglandin E2 (PGE2) from these cells. (-)-Morphine-induced upregulation of TNFα mRNA and PGE2 release were unmasked by pre-treatment with nalmefene, a MOR antagonist without TLR4 activity (unlike CTAP, shown to have both MOR- and TLR4-activity), suggestive of an interplay between MOR and TLR4 co-activation by (-)-morphine. In support, MOR-dependent Protein Kinase A (PKA) opposed TLR4 signaling, as PKA inhibition (H-89) also unmasked (-)-morphine-induced TNFα and COX2 mRNA upregulation. Intrathecal injection of CNS endothelial cells, stimulated in vitro with M3G, produced TLR4-dependent tactile allodynia. Further, cortical suffusion with M3G in vivo induced TLR4-dependent vasodilation. Finally, endothelial cell TLR4 activation by lipopolysaccharide and/or M3G was blocked by the glial inhibitors AV1013 and propentofylline, demonstrating endothelial cells as a new target of such drugs. These data indicate that (-)-morphine and M3G can activate CNS endothelial cells via TLR4, inducing proinflammatory, biochemical, morphological, and behavioral sequelae. CNS endothelial cells may have previously unanticipated roles in opioid-induced effects, in phenomena blocked by presumptive glial inhibitors, as well as TLR4-mediated phenomena more broadly.

Neisseria meningitidis elicits a pro-inflammatory response involving IκBζ in a human blood-cerebrospinal fluid barrier model

BACKGROUND

The human-specific, Gram-negative bacterium Neisseria meningitidis (Nm) is a leading cause of bacterial meningitis worldwide. The blood-cerebrospinal fluid barrier (BCSFB), which is constituted by the epithelial cells of the choroid plexus (CP), has been suggested as one of the potential entry sites of Nm into the CSF and can contribute to the inflammatory response during infectious diseases of the brain. Toll-like receptors (TLRs) are involved in mediating signal transduction caused by the pathogens.

METHODS

Using a recently established in vitro model of the human BCSFB based on human malignant CP papilloma (HIBCPP) cells we investigated the cellular response of HIBCPP cells challenged with the meningitis-causing Nm strain, MC58, employing transcriptome and RT-PCR analysis, cytokine bead array, and enzyme-linked immunosorbent assay (ELISA). In comparison, we analyzed the answer to the closely related unencapsulated carrier isolate Nm α14. The presence of TLRs in HIBCPP and their role during signal transduction caused by Nm was studied by RT-PCR and the use of specific agonists and mutant bacteria.

RESULTS

We observed a stronger transcriptional response after infection with strain MC58, in particular with its capsule-deficient mutant MC58siaD-, which correlated with bacterial invasion levels. Expression evaluation and Gene Set Enrichment Analysis pointed to a NFκB-mediated pro-inflammatory immune response involving up-regulation of the transcription factor IκBζ. Infected cells secreted significant levels of pro-inflammatory chemokines and cytokines, including, among others, IL8, CXCL1-3, and the IκBζ target gene product IL6. The expression profile of pattern recognition receptors in HIBCPP cells and the response to specific agonists indicates that TLR2/TLR6, rather than TLR4 or TLR2/TLR1, is involved in the cellular reaction following Nm infection.

CONCLUSIONS

Our data show that Nm can initiate a pro-inflammatory response in human CP epithelial cells probably involving TLR2/TLR6 signaling and the transcriptional regulator IκBζ.

Neuroimmune regulation of microglial activity involved in neuroinflammation and neurodegenerative diseases

Neuroinflammation constitutes a fundamental process involved in the progression of several neurodegenerative disorders, such as Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis and multiple sclerosis. Microglial cells play a central role in neuroinflammation, promoting neuroprotective or neurotoxic microenvironments, thus controlling neuronal fate. Acquisition of different microglial functions is regulated by intercellular interactions with neurons, astrocytes, the blood-brain barrier, and T-cells infiltrating the central nervous system. In this study, an overview of the regulation of microglial function mediated by different intercellular communications is summarised and discussed. Afterward, we focus in T-cell-mediated regulation of neuroinflammation involved in neurodegenerative disorders.

Phosphoinositide 3-kinase γ affects LPS-induced disturbance of blood-brain barrier via lipid kinase-independent control of cAMP in microglial cells

The breakdown of the blood-brain barrier (BBB) is a key event in the development of sepsis-induced brain damage. BBB opening allows blood-born immune cells to enter the CNS to provoke a neuroinflammatory response. Abnormal expression and activation of matrix metalloproteinases (MMP) was shown to contribute to BBB opening. Using different mouse genotypes in a model of LPS-induced systemic inflammation, our present report reveals phosphoinositide 3-kinase γ (PI3Kγ) as a mediator of BBB deterioration and concomitant generation of MMP by microglia. Unexpectedly, microglia expressing lipid kinase-deficient mutant PI3Kγ exhibited similar MMP regulation as wild-type cells. Our data suggest kinase-independent control of cAMP phosphodiesterase activity by PI3Kγ as a crucial mediator of microglial cell activation, MMP expression and subsequent BBB deterioration. The results identify the suppressive effect of PI3Kγ on cAMP as a critical mediator of immune cell functions.

A comparative review of toll-like receptor 4 expression and functionality in different animal species

Toll-like receptors (TLRs) belong to the pattern recognition receptor (PRR) family, a key component of the innate immune system. TLRs detect invading pathogens and initiate an immediate immune response to them, followed by a long-lasting adaptive immune response. Activation of TLRs leads to the synthesis of pro-inflammatory cytokines and chemokines and the expression of co-stimulatory molecules. TLR4 specifically recognizes bacterial lipopolysaccharide, along with several other components of pathogens and endogenous molecules produced during abnormal situations, such as tissue damage. Evolution across species can lead to substantial diversity in the TLR4’s affinity and specificity to its ligands, the TLR4 gene and cellular expression patterns and tissue distribution. Consequently, TLR4 functions vary across different species. In recent years, the use of synthetic TLR agonists as adjuvants has emerged as a realistic therapeutic goal, notably for the development of vaccines against poorly immunogenic targets. Given that an adjuvanted vaccine must be assessed in pre-clinical animal models before being tested in humans, the extent to which an animal model represents and predicts the human condition is of particular importance. This review focuses on the current knowledge on the critical points of divergence between human and the mammalian species commonly used in vaccine research and development (non-human primate, mouse, rat, rabbit, swine, and dog), in terms of molecular, cellular, and functional properties of TLR4.

Toll-like receptor polymorphisms are associated with increased neurosyphilis risk

BACKGROUND

Single-nucleotide polymorphisms (SNPs) in toll-like receptors (TLR) 1, 2, and 6 impair cell signaling in response to spirochetal lipoproteins. We investigated whether common SNPs in TLR1, TLR2, or TLR6 were associated with laboratory- or clinically-defined neurosyphilis.

METHODS

Polymorphisms in the genes for TLR1 (a T→G mutation at position 1805), TLR2 (a G→A mutation at position 2258), and TLR6 (a C→T mutation at position 745) were sought in 456 white patients with syphilis. Laboratory-defined neurosyphilis included a reactive cerebrospinal fluid (CSF)-Venereal Disease Research Laboratory (VDRL) test. Clinically-defined neurosyphilis included new vision or hearing loss. Controls had CSF white blood cells of 5/μL or less, nonreactive CSF-Venereal Disease Research Laboratory, and no vision or hearing loss.

RESULTS

Overall, 26.2% of patients had laboratory-defined and 36.2% had clinically-defined neurosyphilis. Compared with controls, patients with any of the 3 SNPs were more likely to have laboratory-defined neurosyphilis. Those with TLR2 or TLR6 SNPs were more likely to have clinically-defined neurosyphilis. These associations were independent of serum rapid plasma reagin titer.

CONCLUSIONS

A common TLR1 polymorphism is associated with an increased risk of laboratory-defined neurosyphilis, and common TLR2 and TLR6 polymorphisms are associated with an increased risk of both laboratory- and clinically-defined neurosyphilis. These data suggest that host factors impact the natural history of syphilis.

Assessment of blood-brain barrier function and the neuroinflammatory response in the rat brain by using cerebral open flow microperfusion (cOFM)

Blood-brain barrier (BBB) impairment in systemic inflammation leads to neuroinflammation. Several factors including cytokines, chemokines and signal transduction molecules are implicated in BBB dysfunction in response to systemic inflammation. Here, we have adopted a novel in vivo technique; namely, cerebral open flow microperfusion (cOFM), to perform time-dependent cytokine analysis (TNF-alpha, IL-6 and IL-10) in the frontal cortex of the rat brain in response to a single peripheral administration of lipopolysaccharide (LPS). In parallel, we monitored BBB function using sodium fluorescein as low molecular weight reporter in the cOFM sample. In response to the systemic LPS administration, we observed a rapid increase of TNF-alpha in the serum and brain, which coincides with the BBB disruption. Brain IL-6 and IL-10 synthesis was delayed by approximately 1 h. Our data demonstrate that cOFM can be used to monitor changes in brain cytokine levels and BBB disruption in a rat sepsis model.

Involvement of brain cytokines in zymosan-induced febrile response

This study compared the involvement of interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α (TNF-α) within the central nervous system (CNS) in the febrile response induced by zymosan (zym) and lipopolysaccharide (LPS). In addition, we investigated whether zym could activate important regions related to fever; namely, the vascular organ of the laminae terminalis (OVLT) and the median preoptic nucleus (MnPO). Intraperitoneal injection of zym (1, 3, and 10 mg/kg) induced a dose-related increase in core temperature. Zym (3 mg/kg) also reduced tail skin temperature, suggesting the activation of heat conservation mechanisms, as expected, during fever. LPS increased plasma levels of TNF-α measured at 1 h, IL-1β measured at 2 h, and IL-6 measured at 3 h after injection. Zym increased circulating levels of IL-6 but not those of TNF-α or IL-1β at the same time points. In addition, an intracerebroventricular injection of antibodies against TNF-α (2.5 μg) and IL-6 (10 μg) or the IL-1 receptor antagonist (160 ng) reduced the febrile response induced by zym and LPS. Zym (100 μg/ml) also increased intracellular calcium concentration in the OVLT and MnPO from rat primary neuroglial cultures and increased release of TNF-α and IL-6 into the supernatants of these cultures. Together, these results suggest that TNF-α, IL-1β, and IL-6 within the CNS participate in the febrile response induced by zym. However, the time course of release of these cytokines may be different from that of LPS. In addition, zym can directly activate the brain areas related to fever.

Blood-brain barrier pathophysiology in traumatic brain injury

The blood-brain barrier (BBB) is formed by tightly connected cerebrovascular endothelial cells, but its normal function also depends on paracrine interactions between the brain endothelium and closely located glia. There is a growing consensus that brain injury, whether it is ischemic, hemorrhagic, or traumatic, leads to dysfunction of the BBB. Changes in BBB function observed after injury are thought to contribute to the loss of neural tissue and to affect the response to neuroprotective drugs. New discoveries suggest that considering the entire gliovascular unit, rather than the BBB alone, will expand our understanding of the cellular and molecular responses to traumatic brain injury (TBI). This review will address the BBB breakdown in TBI, the role of blood-borne factors in affecting the function of the gliovascular unit, changes in BBB permeability and post-traumatic edema formation, and the major pathophysiological factors associated with TBI that may contribute to post-traumatic dysfunction of the BBB. The key role of neuroinflammation and the possible effect of injury on transport mechanisms at the BBB will also be described. Finally, the potential role of the BBB as a target for therapeutic intervention through restoration of normal BBB function after injury and/or by harnessing the cerebrovascular endothelium to produce neurotrophic growth factors will be discussed.

TLR4 signaling is involved in brain vascular toxicity of PCB153 bound to nanoparticles

PCBs bind to environmental particles; however, potential toxicity exhibited by such complexes is not well understood. The aim of the present study is to study the hypothesis that assembling onto nanoparticles can influence the PCB153-induced brain endothelial toxicity via interaction with the toll-like receptor 4 (TLR4). To address this hypothesis, TLR4-deficient and wild type control mice (males, 10 week old) were exposed to PCB153 (5 ng/g body weight) bound to chemically inert silica nanoparticles (PCB153-NPs), PCB153 alone, silica nanoparticles (NPs; diameter, 20 nm), or vehicle. Selected animals were also subjected to 40 min ischemia, followed by a 24 h reperfusion. As compared to exposure to PCB153 alone, treatment with PCB153-NP potentiated the brain infarct volume in control mice. Importantly, this effect was attenuated in TLR4-deficient mice. Similarly, PCB153-NP-induced proinflammatory responses and disruption of tight junction integrity were less pronounced in TLR4-deficient mice as compared to control animals. Additional in vitro experiments revealed that TLR4 mediates toxicity of PCB153-NP via recruitment of tumor necrosis factor-associated factor 6 (TRAF6). The results of current study indicate that binding to seemingly inert nanoparticles increase cerebrovascular toxicity of PCBs and suggest that targeting the TLR4/TRAF6 signaling may protect against these effects.

Immune activation of human brain microvascular endothelial cells inhibits HIV replication in macrophages

There is limited information about the role of blood-brain barrier (BBB) endothelial cells (ECs) in the central nervous system (CNS) and their innate immunity against HIV. We examined whether brain ECs can be immunologically activated to produce antiviral factors that inhibit HIV replication in macrophages. Human brain microvascular ECs expressed functional toll-like receptor 3 (TLR3) that could be activated by polyinosinic-polycytidylic acid (PolyI:C), resulting in the induction of endogenous interferon-β (IFN-β) and IFN-λ. The TLR3 activation of ECs also induced the phosphorylation of interferon regulatory transcription factor 3 (IRF3) and IRF7, the key regulators of IFN signaling pathway. When supernatant (SN) of PolyI:C-activated EC cultures was applied to infected macrophage cultures, HIV replication was significantly suppressed. This SN action of ECs on HIV was mediated through both IFN-β and IFN-λ because antibodies to their receptors could neutralize the SN-mediated anti-HIV effect. The role of IFNs in EC-mediated anti-HIV activity is further supported by the observation that treatment with SN from EC cultures induced the expression of IFN-stimulated genes (ISGs: ISG56, OAS-1, and MxA) in macrophages. These observations indicate that brain microvascular ECs may be a key regulatory bystander, playing a crucial role in the BBB innate immunity against HIV infection.

Recognition of pathogen-associated nucleic acids by endosomal nucleic acid-sensing toll-like receptors

Foreign nucleic acids, the essential signature molecules of invading pathogens that act as danger signals for host cells, are detected by endosomal nucleic acid-sensing toll-like receptors (TLRs) 3, 7, 8, 9, and 13. These TLRs have evolved to recognize ‘non-self’ nucleic acids within endosomal compartments and rapidly initiate innate immune responses to ensure host protection through induction of type I interferons, inflammatory cytokines, chemokines, and co-stimulatory molecules and maturation of immune cells. In this review, we highlight our understanding of the recognition of pathogen-associated nucleic acids and activation of corresponding signaling pathways through endosomal nucleic acid-sensing TLRs 3, 7, 8, 9, and 13 for an enormous diversity of pathogens, with particular emphasis on their compartmentalization, intracellular trafficking, proteolytic cleavage, autophagy, and regulatory programs.

Innate immune regulation by toll-like receptors in the brain

The innate immune system plays an important role in cerebral health and disease. In recent years the role of innate immune regulation by toll-like receptors in the brain has been highlighted. In this paper the expression of toll-like receptors and endogenous toll-like receptor ligands in the brain and their role in cerebral ischemia will be discussed. Further, the ability of systemic toll-like receptor ligands to induce cerebral inflammation will be reviewed. Finally, the capacity of toll-like receptors to both increase (sensitization) and decrease (preconditioning/tolerance) the vulnerability of the brain to damage will be disclosed. Studies investigating the role of toll-like receptors in the developing brain will be emphasized.

Inflammation and neurodegeneration: the story 'retolled'

Toll-like receptors (TLRs) play a crucial role in innate immunity by recognizing conserved motifs predominantly found in microorganisms. Increasing evidence supports a role for TLRs in sterile inflammation as observed in neurodegenerative disorders. This includes work suggesting a contribution for these receptors to the pathophysiology of Alzheimer's disease (AD), Parkinson's disease (PD), and related disorders. In this review, the potential role of TLRs in the context of protein aggregation, neuronal degeneration, and genetic risk factors is addressed. In particular, we discuss the evidence derived from experimental models of both AD and PD which suggests that activation of TLRs can have beneficial and detrimental effects on pathological features such as protein aggregation and neuronal death. A deeper understanding of these dichotomous observations could be used for therapeutic benefit.

Lipopolysaccharide potentiates polychlorinated biphenyl-induced disruption of the blood-brain barrier via TLR4/IRF-3 signaling

Exposure to polychlorinated biphenyls (PCBs) is associated with numerous adverse health effects. Although the main route of exposure to PCBs is through the gastrointestinal tract, little is known about the contribution of the gut to the health effects of PCBs. We hypothesize that PCBs can disrupt intestinal integrity, causing lipopolysaccharide (LPS) translocation into the bloodstream and potentiation of the systemic toxicity of PCBs. C57BL/6 mice were exposed to individual PCB congeners by oral gavage, followed by the assessment of small intestine morphology and plasma levels of proinflammatory mediators. In addition, mice and human brain endothelial cells were exposed to PCB118 in the presence or absence of LPS to evaluate the contribution of LPS to PCB-induced toxicity at the blood-brain barrier (BBB) level. Oral administration of PCB153, PCB118, or PCB126 disrupted intestinal morphology and increased plasma levels of LPS and proinflammatory cytokines. Direct injection of LPS and PCB118 into the cerebral microvasculature resulted in synergistic disruption of BBB integrity and decreased expression of tight junction proteins in brain microvessels. In vitro experiments confirmed these effects and indicated that stimulation of the toll-like receptor 4 (TLR4) pathway can be responsible for these effects via activation of interferon regulatory factor-3 (IRF-3). These results indicate that LPS may be a contributing factor in PCB-induced dysfunction of the brain endothelium via stimulation of the TLR4/IRF-3 pathway.

Combination therapy with VELCADE and tissue plasminogen activator is neuroprotective in aged rats after stroke and targets microRNA-146a and the toll-like receptor signaling pathway

OBJECTIVE

Activation of the toll-like receptor (TLR) signaling pathway exacerbates ischemic brain damage. The present study tested the hypothesis that combination treatment with VELCADE and tissue plasminogen activator (tPA) modulates the TLR signaling pathway on cerebral vasculature, which leads to neuroprotection in aged rats after stroke.

METHODS AND RESULTS

Focal cerebral ischemia acutely increased TLR2, TLR4, and interleukin-1 receptor-activated kinases 1 immunoreactivity on fibrin/fibrinogen-positive vessels in aged rats. Monotherapy of tPA further amplified these signals. However, VELCADE in combination with tPA-blocked stroke- and tPA-potentiated vascular TLR signals, leading to robust reduction of infarct volume compared with respective monotherapies. Quantitative reverse transcription polymerase chain reaction analysis of cerebral endothelial cells isolated by laser capture microdissection revealed that the combination treatment increased miR-l46a levels, which was inversely associated with the reduction of vascular interleukin-1 receptor-activated kinases 1 immunoreactivity. In vitro, fibrin upregulated interleukin-1 receptor-activated kinases 1 and TLR4 expression and downregulated miR-146a on primary human cerebral endothelial cells. VELCADE elevated miR-146 levels and abolished fibrin-increased interleukin-1 receptor activated kinases 1 proteins.

CONCLUSIONS

Stroke acutely activates the TLR signaling pathway on cerebral vasculature. Upregulation of miR-146a and inactivation of ischemia and tPA-potentiated TLR signaling pathway by VELCADE may play an important role in the neuroprotective effect of the combination therapy of VELCADE and tPA for acute stroke.

Expression, regulation, and function of atypical chemerin receptor CCRL2 on endothelial cells

Chemokine (CC motif) receptor-like 2 (CCRL2) binds leukocyte chemoattractant chemerin and can regulate local levels of the attractant, but does not itself support cell migration. In this study, we show that CCRL2 and VCAM-1 are upregulated on cultured human and mouse vascular endothelial cells (EC) and cell lines by proinflammatory stimuli. CCRL2 induction is dependent on NF-κB and JAK/STAT signaling pathways, and activated endothelial cells specifically bind chemerin. In vivo, CCRL2 is constitutively expressed at high levels by lung endothelial cells and at lower levels by liver endothelium; and liver but not lung EC respond to systemic LPS injection by further upregulation of the receptor. Plasma levels of total chemerin are elevated in CCRL2(-/-) mice and are significantly enhanced after systemic LPS treatment in CCRL2(-/-) mice compared with wild-type mice. Following acute LPS-induced pulmonary inflammation in vivo, chemokine-like receptor 1 (CMKLR1)(+) NK cell recruitment to the airways is significantly impaired in CCRL2(-/-) mice compared with wild-type mice. In vitro, chemerin binding to CCRL2 on endothelial cells triggers robust adhesion of CMKLR1(+) lymphoid cells through an α(4)β(1) integrin/VCAM-1-dependent mechanism. In conclusion, CCRL2 is expressed by EC in a tissue- and activation-dependent fashion, regulates circulating chemerin levels and its bioactivity, and enhances chemerin- and CMKLR1-dependent lymphocyte/EC adhesion in vitro and recruitment to inflamed airways in vivo. Its expression and/or induction on EC by proinflammatory stimuli provide a novel and specific mechanism for the local enrichment of chemerin at inflammatory sites, regulating the recruitment of CMKLR1(+) cells.

Lipopolysaccharide appears to activate human endometrial endothelial cells through TLR-4-dependent and TLR-4-independent mechanisms

PROBLEM

Uterine innate immunity remains poorly characterized, and while endometrial endothelial cells are known to express Toll-like receptors (TLRs), little is known about their function in these cells. The present study evaluated the effect of Gram-negative bacterial lipopolysaccharide (LPS) on human endometrial endothelial cell (HEECs) cytokine secretion and tissue factor expression, and the role of TLR-4 in these responses.

METHODS

Human endometrial endothelial cells were treated with or without LPS ± LPS-RS, a TLR-4 antagonist, via the binding of MD-2. After 24 hr, cell-free supernatants were evaluated for cytokines by multiplex analysis and cell lysates were analyzed for tissue factor expression by Western blot.

RESULTS

Treatment of HEECs with LPS significantly upregulated the secretion of IL-6, IL-8, and G-CSF, and this was prevented by LPS-RS. LPS also induced tissue factor expression by the HEECs; however, this was unaffected by LPS-RS.

CONCLUSION

These findings suggest that TLR-4 is functional in HEECs and its activation by bacterial LPS induces a specific cytokine/chemokine response. However, bacterial LPS also induced tissue factor expression in what seemed to be a TLR-4-independent fashion, suggesting that this bacterial component can act on the HEECs through TLR-4-dependent and TLR-4-independent pathways. These findings indicate that endometrial endothelial cells may play an active role in uterine innate immunity.

The neurovascular unit and combination treatment strategies for stroke

Tissue plasminogen activator (tPA) administered within 4.5h of symptom onset restores cerebral blood flow (CBF) and promotes neurological recovery of stroke patients. However, the narrow therapeutic time window and the risk of intracerebral hemorrhage after tPA treatment pose major hurdles to its clinical usage. In light of the failures of neuroprotective therapies in clinical trials, emerging concepts suggest that neuroprotection alone without restoration of tissue perfusion and vascular integrity may not be adequate for treatment of acute stroke. Here we review evidence of the use of adjuvant pharmacological agents to extend the therapeutic window for tPA via targeting the neurovascular unit and the underlying mechanisms of the combination therapy in experimental stroke.

Exposure to lipopolysaccharide and/or unconjugated bilirubin impair the integrity and function of brain microvascular endothelial cells

Background

Sepsis and jaundice are common conditions in newborns that can lead to brain damage. Though lipopolysaccharide (LPS) is known to alter the integrity of the blood-brain barrier (BBB), little is known on the effects of unconjugated bilirubin (UCB) and even less on the joint effects of UCB and LPS on brain microvascular endothelial cells (BMEC).

Methodology/Principal Findings

Monolayers of primary rat BMEC were treated with 1 µg/ml LPS and/or 50 µM UCB, in the presence of 100 µM human serum albumin, for 4 or 24 h. Co-cultures of BMEC with astroglial cells, a more complex BBB model, were used in selected experiments. LPS led to apoptosis and UCB induced both apoptotic and necrotic-like cell death. LPS and UCB led to inhibition of P-glycoprotein and activation of matrix metalloproteinases-2 and -9 in mono-cultures. Transmission electron microscopy evidenced apoptotic bodies, as well as damaged mitochondria and rough endoplasmic reticulum in BMEC by either insult. Shorter cell contacts and increased caveolae-like invaginations were noticeable in LPS-treated cells and loss of intercellular junctions was observed upon treatment with UCB. Both compounds triggered impairment of endothelial permeability and transendothelial electrical resistance both in mono- and co-cultures. The functional changes were confirmed by alterations in immunostaining for junctional proteins β-catenin, ZO-1 and claudin-5. Enlargement of intercellular spaces, and redistribution of junctional proteins were found in BMEC after exposure to LPS and UCB.

Conclusions

LPS and/or UCB exert direct toxic effects on BMEC, with distinct temporal profiles and mechanisms of action. Therefore, the impairment of brain endothelial integrity upon exposure to these neurotoxins may favor their access to the brain, thus increasing the risk of injury and requiring adequate clinical management of sepsis and jaundice in the neonatal period.

Morphine activates neuroinflammation in a manner parallel to endotoxin

Opioids create a neuroinflammatory response within the CNS, compromising opioid-induced analgesia and contributing to various unwanted actions. How this occurs is unknown but has been assumed to be via classic opioid receptors. Herein, we provide direct evidence that morphine creates neuroinflammation via the activation of an innate immune receptor and not via classic opioid receptors. We demonstrate that morphine binds to an accessory protein of Toll-like receptor 4 (TLR4), myeloid differentiation protein 2 (MD-2), thereby inducing TLR4 oligomerization and triggering proinflammation. Small-molecule inhibitors, RNA interference, and genetic knockout validate the TLR4/MD-2 complex as a feasible target for beneficially modifying morphine actions. Disrupting TLR4/MD-2 protein-protein association potentiated morphine analgesia in vivo and abolished morphine-induced proinflammation in vitro, the latter demonstrating that morphine-induced proinflammation only depends on TLR4, despite the presence of opioid receptors. These results provide an exciting, nonconventional avenue to improving the clinical efficacy of opioids.

A novel pathway for human endothelial cell activation by antiphospholipid/anti-β2 glycoprotein I antibodies

Antiphospholipid Abs (APLAs) are associated with thrombosis and recurrent fetal loss. These Abs are primarily directed against phospholipid-binding proteins, particularly β(2)GPI, and activate endothelial cells (ECs) in a β(2)GPI-dependent manner after binding of β(2)GPI to EC annexin A2. Because annexin A2 is not a transmembrane protein, the mechanisms of APLA/anti-β(2)GPI Ab-mediated EC activation are uncertain, although a role for a TLR4/myeloid differentiation factor 88-dependent pathway leading to activation of NF-κB has been proposed. In the present study, we confirm a critical role for TLR4 in anti-β(2)GPI Ab-mediated EC activation and demonstrate that signaling through TLR4 is mediated through the assembly of a multiprotein signaling complex on the EC surface that includes annexin A2, TLR4, calreticulin, and nucleolin. An essential role for each of these proteins in cell activation is suggested by the fact that inhibiting the expression of each using specific siRNAs blocked EC activation mediated by APLAs/anti-β(2)GPI Abs. These results provide new evidence for novel protein-protein interactions on ECs that may contribute to EC activation and the pathogenesis of APLA/anti-β(2)GPI-associated thrombosis and suggest potential new targets for therapeutic intervention in antiphospholipid syndrome.

Simvastatin in traumatic brain injury: effect on brain edema mechanisms

OBJECTIVES

Traumatic brain injury causes deleterious brain edema, leading to high mortality and morbidity. Brain edema exacerbates neurologic deficits and may be attributable to the breakdown of endothelial cell junction protein, leukocyte infiltration, and matrix metalloproteinase activation. These all contribute to loss of blood-brain barrier integrity. The pleiotropic effects of statins, hydroxymethylglutaryl-coenzyme A reductase inhibitors, may inhibit posttraumatic brain edema. We therefore investigated the effect of acute simvastatin on neurologic deficits, cerebral edema, and its origins.

DESIGN

Randomized laboratory animal study.

SETTINGS

University-affiliated research laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Rats were subjected to lateral fluid percussion traumatic brain injury. Our preliminary dose-effect study indicated that 37.5 mg/kg simvastatin, administered orally 1 hr and 6 hrs after traumatic brain injury, has the greatest anti-edematous effect. This dose was used to study its effects on brain edema and on its mechanisms.

MEASUREMENTS AND MAIN RESULTS

We first assessed the effects of simvastatin 24 hrs after traumatic brain injury on brain edema, brain claudin-5 expression, and the vascular endothelial-cadherin (pTyr731)/total vascular endothelial-cadherin ratio, matrix metalloproteinase-9 activity, intercellular adhesion molecule-1 expression, and polymorphonuclear neutrophil infiltration. We also evaluated blood-brain barrier permeability by measuring Evans blue and fluorescein sodium salt extravasation into the cerebral parenchyma. We then investigated whether simvastatin reduces neurologic deficits, edema, and blood-brain barrier permeability earlier than 24 hrs; these effects were evaluated 6 hrs after traumatic brain injury. The anti-edematous effect of simvastatin 24 hrs after traumatic brain injury was associated with increased claudin-5 and decreased intercellular adhesion molecule-1, polymorphonuclear neutrophil infiltration, and blood-brain barrier permeability, with no effect on matrix metalloproteinase-9 activity or vascular endothelial-cadherin phosphorylation. Earlier, 6-hrs after traumatic brain injury, simvastatin reduced neurologic deficits, cerebral edema, and blood-brain barrier permeability.

CONCLUSIONS

Simvastatin could be a new therapy for reducing posttraumatic edema by preventing damage to tight junctions and neutrophil infiltration into the parenchyma, thus preserving blood-brain barrier integrity.

Oxidative stress and blood-brain barrier dysfunction under particular consideration of matrix metalloproteinases

A cell's "redox" (oxidation and reduction) state is determined by the sum of all redox processes yielding reactive oxygen species (ROS), reactive nitrogen species (RNS), and other reactive intermediates. Low amounts of ROS/RNS are generated by different mechanisms in every cell and are important regulatory mediators in many signaling processes (redox signaling). When the physiological balance between the generation and elimination of ROS/RNS is disrupted, oxidative/nitrosative stress with persistent oxidative damage of the organism occurs. Oxidative stress has been suggested to act as initiator and/or mediator of many human diseases. The cerebral vasculature is particularly susceptible to oxidative stress, which is critical since cerebral endothelial cells play a major role in the creation and maintenance of the blood-brain barrier (BBB). This article will only contain a focused introduction on the biochemical background of redox signaling, since this has been reported already in a series of excellent recent reviews. The goal of this work is to increase the understanding of basic mechanisms underlying ROS/RNS-induced BBB disruption, with a focus on the role of matrix metalloproteinases, which, after all, appear to be a key mediator in the initiation and progression of BBB damage elicited by oxidative stress.

Pathways underlying the gut-to-brain connection in autism spectrum disorders as future targets for disease management

Autism spectrum disorders (ASDs) are pervasive neurodevelopmental disorders, characterized by impairments in social interaction and communication and the presence of limited, repetitive and stereotyped interests and behavior. Bowel symptoms are frequently reported in children with ASD and a potential role for gastrointestinal disturbances in ASD has been suggested. This review focuses on the importance of (allergic) gastrointestinal problems in ASD. We provide an overview of the possible gut-to-brain pathways and discuss opportunities for pharmaceutical and/or nutritional approaches for therapy.

Neurotoxic effects of the HCV core protein are mediated by sustained activation of ERK via TLR2 signaling

Hepatitis C virus (HCV) infection is a serious problem among those co-infected with human immunodeficiency virus; however, its impact in the central nervous system (CNS) remains unclear. This study aimed to investigate the mechanisms underlying HCV core protein-mediated neurodegeneration. Analysis of human HCV seropositive cases demonstrated widespread damage to neuronal dendritic processes and sustained activation of extracellular signal-related kinase (ERK); analogous pathologies were observed in wild type injected with HCV core protein into the hippocampus. In vitro analysis in neuronal cells exposed to HCV core demonstrated retraction of the neuronal processes in an ERK/Signal Transducer and Activator of Transcription 3 (STAT3)-dependent manner dependent on toll-like receptor 2 (TLR2) signaling activation. These results indicate that HCV core protein neurotoxicity may be mediated by the sustained activation of ERK/STAT3 via TLR2-IRAK1 signaling pathway. These pathways provide novel targets for development of neuroprotective treatments for HCV involvement of the CNS.

How do immune cells overcome the blood-brain barrier in multiple sclerosis?

The presence of the blood-brain barrier (BBB) restricts the movement of soluble mediators and leukocytes from the periphery to the central nervous system (CNS). Leukocyte entry into the CNS is nonetheless an early event in multiple sclerosis (MS), an inflammatory disorder of the CNS. Whether BBB dysfunction precedes immune cell infiltration or is the consequence of perivascular leukocyte accumulation remains enigmatic, but leukocyte migration modifies BBB permeability. Immune cells of MS subjects express inflammatory cytokines, reactive oxygen species (ROS) and enzymes that can facilitate their migration to the CNS by influencing BBB function, either directly or indirectly. In this review, we describe how immune cells from the peripheral blood overcome the BBB and promote CNS inflammation in MS through BBB disruption.