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

TLR2 regulates Moraxella catarrhalis adhesion to and invasion into alveolar epithelial cells and mediates inflammatory responses

Moraxella catarrhalis is a major cause of chronic obstructive pulmonary disease. Toll-like receptor 2 (TLR2) plays an important role in the inflammatory response in host respiratory epithelial cells. M. catarrhalis induces an inflammatory immune response in respiratory epithelial cells that is mostly dependent on TLR2. However, the mechanisms by which this pathogen adheres to and invades the respiratory epithelium are not well understood. The present study aimed to reveal the role of TLR2 in M. catarrhalis adhesion to and invasion into alveolar epithelial cells, using molecular techniques. Pretreatment with the TLR2 inhibitor TLR2-IN-C29 enhanced M. catarrhalis adhesion to A549 cells but reduced its invasion, whereas the agonist Pam3CSK4 reduced both M. catarrhalis adhesion and invasion into A549 cells. Similarly, M. catarrhalis 73-OR strain adhesion and invasion were significantly reduced in TLR2-/- A549 cells. Moreover, the lung clearance rate of the 73-OR strain was significantly higher in TLR2-/- C57/BL6J mice than in wild-type (WT) mice. Histological analysis showed that inflammatory responses were milder in TLR2-/- C57/BL6J mice than in WT mice, which was confirmed by a decrease in cytokine levels in TLR2-/- C57/BL6J mice. Overall, these results indicate that TLR2 promoted M. catarrhalis adhesion and invasion of A549 cells and lung tissues and mediated inflammatory responses in infected lungs. This study provides important insights into the development of potential therapeutic strategies against M. catarrhalis and TLR2-induced inflammatory responses.

Factor XI as a therapeutic target in neuroinflammatory disease

PURPOSE OF REVIEW

This review summarizes the pathophysiology and potential therapeutic options for treatment of multiple sclerosis, a common neuronal demyelinating disorder affecting 2.2 million people worldwide. As an autoimmune disorder, multiple sclerosis is associated with neuroinflammation and increased permeability of the blood-brain barrier (BBB), although the cause linking multiple sclerosis with compromised barrier function remains ill-defined. It has been previously shown that coagulation factors, including thrombin and fibrin, exacerbate the inflammatory processes and permeability of the BBB.

RECENT FINDINGS

Increased levels of the coagulation factor (F) XII have been found in patients presenting with relapsing-remitting multiple sclerosis, with a deleterious role for FXII being validated in murine model of multiple sclerosis, experimental autoimmune encephalitis (EAE). Recent work has uncovered a role for the major substrate activated by FXII and thrombin, FXI, in the disorder of EAE. The study found that pharmacological targeting of FXI decreased clinical symptoms, lymphocyte invasion, and white matter destruction in a multiple sclerosis model.

SUMMARY

This review emphasizes the role of FXII and FXI in regulating barrier function and the immune response in neuroinflammation. These new findings broaden the potential for therapeutic utility of FXI inhibitors beyond thrombosis to include neuroinflammatory diseases associated with compromised BBB function, including multiple sclerosis.

Innovative and potential treatments for fungal central nervous system infections

Fungal infections of the central nervous system (FI-CNS) are a problematic and important medical challenge considering that those most affected are immunocompromised. Individuals with systemic cryptococcosis (67-84%), candidiasis (3-64%), blastomycosis (40%), coccidioidomycosis (25%), histoplasmosis (5-20%), mucormycosis (12%), and aspergillosis (4-6%) are highly susceptible to develop CNS involvement, which often results in high mortality (15-100%) depending on the mycosis and the affected immunosuppressed population. Current antifungal drugs are limited, prone to resistance, present host toxicity, and show reduced brain penetration, making FI-CNS very difficult to treat. Given these limitations and the rise in FI-CNS, there is a need for innovative strategies for therapeutic development and treatments to manage FI-CNS in at-risk populations. Here, we discuss standards of care, antifungal drug candidates, and novel molecular targets in the blood-brain barrier, which is a protective structure that regulates movement of particles in and out of the brain, to prevent and combat FI-CNS.

Universal method for the isolation of microvessels from frozen brain tissue: A proof-of-concept multiomic investigation of the neurovasculature

The neurovascular unit, comprised of vascular cell types that collectively regulate cerebral blood flow to meet the needs of coupled neurons, is paramount for the proper function of the central nervous system. The neurovascular unit gatekeeps blood-brain barrier properties, which experiences impairment in several central nervous system diseases associated with neuroinflammation and contributes to pathogenesis. To better understand function and dysfunction at the neurovascular unit and how it may confer inflammatory processes within the brain, isolation and characterization of the neurovascular unit is needed. Here, we describe a singular, standardized protocol to enrich and isolate microvessels from archived snap-frozen human and frozen mouse cerebral cortex using mechanical homogenization and centrifugation-separation that preserves the structural integrity and multicellular composition of microvessel fragments. For the first time, microvessels are isolated from postmortem ventromedial prefrontal cortex tissue and are comprehensively investigated as a structural unit using both RNA sequencing and Liquid Chromatography with tandem mass spectrometry (LC-MS/MS). Both the transcriptome and proteome are obtained and compared, demonstrating that the isolated brain microvessel is a robust model for the NVU and can be used to generate highly informative datasets in both physiological and disease contexts.

Shedding light on the molecular and regulatory mechanisms of TLR4 signaling in endothelial cells under physiological and inflamed conditions

Toll-like receptor 4 (TLR4) are part of the innate immune system. They are capable of recognizing pathogen-associated molecular patterns (PAMPS) of microbes, and damage-associated molecular patterns (DAMPs) of damaged tissues. Activation of TLR4 initiates downstream signaling pathways that trigger the secretion of cytokines, type I interferons, and other pro-inflammatory mediators that are necessary for an immediate immune response. However, the systemic release of pro-inflammatory proteins is a powerful driver of acute and chronic inflammatory responses. Over the past decades, immense progress has been made in clarifying the molecular and regulatory mechanisms of TLR4 signaling in inflammation. However, the most common strategies used to study TLR4 signaling rely on genetic manipulation of the TLR4 or the treatment with agonists such as lipopolysaccharide (LPS) derived from the outer membrane of Gram-negative bacteria, which are often associated with the generation of irreversible phenotypes in the target cells or unintended cytotoxicity and signaling crosstalk due to off-target or pleiotropic effects. Here, optogenetics offers an alternative strategy to control and monitor cellular signaling in an unprecedented spatiotemporally precise, dose-dependent, and non-invasive manner. This review provides an overview of the structure, function and signaling pathways of the TLR4 and its fundamental role in endothelial cells under physiological and inflammatory conditions, as well as the advances in TLR4 modulation strategies.

Novel Therapeutic Opportunities for Neurodegenerative Diseases with Mesenchymal Stem Cells: The Focus on Modulating the Blood-Brain Barrier

Neurodegenerative disorders encompass a broad spectrum of profoundly disabling situations that impact millions of individuals globally. While their underlying causes and pathophysiology display considerable diversity and remain incompletely understood, a mounting body of evidence indicates that the disruption of blood-brain barrier (BBB) permeability, resulting in brain damage and neuroinflammation, is a common feature among them. Consequently, targeting the BBB has emerged as an innovative therapeutic strategy for addressing neurological disorders. Within this review, we not only explore the neuroprotective, neurotrophic, and immunomodulatory benefits of mesenchymal stem cells (MSCs) in combating neurodegeneration but also delve into their recent role in modulating the BBB. We will investigate the cellular and molecular mechanisms through which MSC treatment impacts primary age-related neurological conditions like Alzheimer's disease, Parkinson's disease, and stroke, as well as immune-mediated diseases such as multiple sclerosis. Our focus will center on how MSCs participate in the modulation of cell transporters, matrix remodeling, stabilization of cell-junction components, and restoration of BBB network integrity in these pathological contexts.

Orthohantavirus Replication in the Context of Innate Immunity

Orthohantaviruses are rodent-borne, negative-sense RNA viruses that are capable of causing severe vascular disease in humans. Over the course of viral evolution, these viruses have tailored their replication cycles in such a way as to avoid and/or antagonize host innate immune responses. In the rodent reservoir, this results in life long asymptomatic infections. However, in hosts other than its co-evolved reservoir, the mechanisms for subduing the innate immune response may be less efficient or absent, potentially leading to disease and/or viral clearance. In the case of human orthohantavirus infection, the interaction of the innate immune response with viral replication is thought to give rise to severe vascular disease. The orthohantavirus field has made significant advancements in understanding how these viruses replicate and interact with host innate immune responses since their identification by Dr. Ho Wang Lee and colleagues in 1976. Therefore, the purpose of this review, as part of this special issue dedicated to Dr. Lee, was to summarize the current knowledge of orthohantavirus replication, how viral replication activates innate immunity, and how the host antiviral response, in turn, impacts viral replication.

Neurochemical effects of sepsis on the brain

Sepsis is a life-threatening organ dysfunction triggered by a dysregulated host immune response to eliminate an infection. After the host immune response is activated, a complex, dynamic, and time-dependent process is triggered. This process promotes the production of inflammatory mediators, including acute-phase proteins, complement system proteins, cytokines, chemokines, and antimicrobial peptides, which are required to initiate an inflammatory environment for eliminating the invading pathogen. The physiological response of this sepsis-induced systemic inflammation can affect blood-brain barrier (BBB) function; subsequently, endothelial cells produce inflammatory mediators, including cytokines, chemokines, and matrix metalloproteinases (MMPs) that degrade tight junction (TJ) proteins and decrease BBB function. The resulting BBB permeability allows peripheral immune cells from the bloodstream to enter the brain, which then release a range of inflammatory mediators and activate glial cells. The activated microglia and astrocytes release reactive oxygen species (ROS), cytokines, chemokines, and neurochemicals, initiate mitochondrial dysfunction and neuronal damage, and exacerbate the inflammatory milieu in the brain. These changes trigger sepsis-associated encephalopathy (SAE), which has the potential to increase cognitive deterioration and susceptibility to cognitive decline later in life.

Cerebral Malaria Model Applying Human Brain Organoids

Neural injuries in cerebral malaria patients are a significant cause of morbidity and mortality. Nevertheless, a comprehensive research approach to study this issue is lacking, so herein we propose an in vitro system to study human cerebral malaria using cellular approaches. Our first goal was to establish a cellular system to identify the molecular alterations in human brain vasculature cells that resemble the blood-brain barrier (BBB) in cerebral malaria (CM). Through transcriptomic analysis, we characterized specific gene expression profiles in human brain microvascular endothelial cells (HBMEC) activated by the Plasmodium falciparum parasites. We also suggest potential new genes related to parasitic activation. Then, we studied its impact at brain level after Plasmodium falciparum endothelial activation to gain a deeper understanding of the physiological mechanisms underlying CM. For that, the impact of HBMEC-P. falciparum-activated secretomes was evaluated in human brain organoids. Our results support the reliability of in vitro cellular models developed to mimic CM in several aspects. These systems can be of extreme importance to investigate the factors (parasitological and host) influencing CM, contributing to a molecular understanding of pathogenesis, brain injury, and dysfunction.

The Active Role of Pericytes During Neuroinflammation in the Adult Brain

Microvessels in the central nervous system (CNS) have one of the highest populations of pericytes, indicating their crucial role in maintaining homeostasis. Pericytes are heterogeneous cells located around brain microvessels; they present three different morphologies along the CNS vascular tree: ensheathing, mesh, and thin-strand pericytes. At the arteriole-capillary transition ensheathing pericytes are found, while mesh and thin-strand pericytes are located at capillary beds. Brain pericytes are essential for the establishment and maintenance of the blood-brain barrier, which restricts the passage of soluble and potentially toxic molecules from the circulatory system to the brain parenchyma. Pericytes play a key role in regulating local inflammation at the CNS. Pericytes can respond differentially, depending on the degree of inflammation, by secreting a set of neurotrophic factors to promote cell survival and regeneration, or by potentiating inflammation through the release of inflammatory mediators (e.g., cytokines and chemokines), and the overexpression of cell adhesion molecules. Under inflammatory conditions, pericytes may regulate immune cell trafficking to the CNS and play a role in perpetuating local inflammation. In this review, we describe pericyte responses during acute and chronic neuroinflammation.

Neuroprotection by Preconditioning in Mice is Dependent on MyD88-Mediated CXCL10 Expression in Endothelial Cells

The central nervous system (CNS) can be preconditioned to resist damage by peripheral pretreatment with low-dose gram-negative bacterial endotoxin lipopolysaccharide (LPS). Underlying mechanisms associated with transient protection of the cerebral cortex against traumatic brain injury include increased neuronal production of antiapoptotic and neurotrophic molecules, microglial-mediated displacement of inhibitory presynaptic terminals innervating the soma of cortical projection neurons, and synchronized firing of cortical projection neurons. However, the cell types and signaling responsible for these neuronal and microglial changes are unknown. A fundamental question is whether LPS penetrates the CNS or acts on the luminal surface of brain endothelial cells, thereby triggering an indirect parenchymal neuroprotective response. The present study shows that a low-dose intraperitoneal LPS treatment increases brain endothelial cell activation markers CD54, but does not open the blood-brain barrier or alter brain endothelial cell tight junctions as assessed by electron microscopy. NanoString nCounter transcript analyses of CD31-positive brain endothelial cells further revealed significant upregulation of Cxcl10, C3, Ccl2, Il1β, Cxcl2, and Cxcl1, consistent with identification of myeloid differentiation primary response 88 (MyD88) as a regulator of these transcripts by pathway analysis. Conditional genetic endothelial cell gene ablation approaches demonstrated that both MyD88-dependent Toll-like receptor 4 (TLR4) signaling and Cxcl10 expression are essential for LPS-induced neuroprotection and microglial activation. These results suggest that C-X-C motif chemokine ligand 10 (CXCL10) production by endothelial cells in response to circulating TLR ligands may directly or indirectly signal to CXCR3 on neurons and/or microglia. Targeted activation of brain endothelial receptors may thus provide an attractive approach for inducing transient neuroprotection.

The Dectin-1 Receptor Signaling Pathway Mediates the Remyelination Effect of Lentinan through Suppression of Neuroinflammation and Conversion of Microglia

Demyelinating diseases such as multiple sclerosis (MS) are chronic inflammatory autoimmune diseases and involve demyelination and axonal degeneration. Microglia rapidly respond to changes in the environment by altering morphotype and function during the progressive disease stage. Although substantial progress has been made in the drug development for MS, treatment of the progressive forms of the disease remains unsatisfactory. There is great interest in identifying novel agents for treating MS. Lentinus edodes is a traditional food, which can improve physiological function. Lentinan (LNT), a type of polysaccharide extracted from mushroom Lentinus edodes, is an anti-inflammatory and immunomodulatory agent. Here, we studied the remyelination effects of LNT and its therapeutic target in regulating the functions of neuroinflammation. We found that LNT enhanced remyelination and rescued motor deficiency by regulating dectin-1 receptor to inhibit neuroinflammation and microglial cell transformation. LNT promoted the conversion of microglial cells from the M1 status induced by LPS to the M2 status, enhanced the anti-inflammatory markers IL-10 and BDNF, inhibited inflammatory markers TNF-α and IL-1β, and downregulated the microglia activation and oligodendrocyte and astrocyte proliferation by modulating dectin-1. If we injected the dectin-1-specific inhibitor laminarin (Lam), the remyelination effects induced by LNT were completely abolished. Thus, these results suggest that LNT is a novel and potential therapeutic agent that can rescue MS neuroimmune imbalance and remyelination through a dectin-1 receptor-dependent mechanism.

Advances in NURR1-Regulated Neuroinflammation Associated with Parkinson's Disease

Neuroinflammation plays a crucial role in the progression of neurodegenerative disorders, particularly Parkinson's disease (PD). Glial cell activation and subsequent adaptive immune involvement are neuroinflammatory features in familial and idiopathic PD, resulting in the death of dopaminergic neuron cells. An oxidative stress response, inflammatory mediator production, and immune cell recruitment and activation are all hallmarks of this activation, leading to chronic neuroinflammation and progressive neurodegeneration. Several studies in PD patients' cerebrospinal fluid and peripheral blood revealed alterations in inflammatory markers and immune cell populations that may lead to or exacerbate neuroinflammation and perpetuate the neurodegenerative process. Most of the genes causing PD are also expressed in astrocytes and microglia, converting their neuroprotective role into a pathogenic one and contributing to disease onset and progression. Nuclear receptor-related transcription factor 1 (NURR1) regulates gene expression linked to dopaminergic neuron genesis and functional maintenance. In addition to playing a key role in developing and maintaining neurotransmitter phenotypes in dopaminergic neurons, NURR1 agonists have been shown to reverse behavioral and histological abnormalities in animal PD models. NURR1 protects dopaminergic neurons from inflammation-induced degeneration, specifically attenuating neuronal death by suppressing the expression of inflammatory genes in microglia and astrocytes. This narrative review highlights the inflammatory changes in PD and the advances in NURR1-regulated neuroinflammation associated with PD. Further, we present new evidence that targeting this inflammation with a variety of potential NURR1 target therapy medications can effectively slow the progression of chronic neuroinflammation-induced PD.

Antimicrobial peptides could antagonize uncontrolled inflammation via Toll-like 4 receptor

Antimicrobial peptides are part of the organism's defense system. They are multifunctional molecules capable of modulating the host's immune system and recognizing molecules present in pathogens such as lipopolysaccharides (LPSs). LPSs are recognized by molecular patterns associated with pathogens known as Toll-like receptors (TLRs) that protect the organism from pathological microorganisms. TLR4 is responsible for LPS recognition, thus inducing an innate immune response. TLR4 hyperstimulation induces the uncontrolled inflammatory process that is observed in many illnesses, including neurodegenerative, autoimmune and psoriasis). Molecules that act on TLR4 can antagonize the exacerbated inflammatory process. In this context, antimicrobial peptides (AMPs) are promising molecules capable of mediating toll-like receptor signaling. Therefore, here we address the AMPs studied so far with the aim of inhibiting the intense inflammatory process. In addition, we aim to explore some of the interactions between exogenous AMPs and TLR4.

Research progress of mechanisms for tight junction damage on blood-brain barrier inflammation

Inflammation in the central nervous system (CNS) contributes to disease pathologies by disrupting the integrity of the blood-brain barrier (BBB). Tight junctions (TJ) are a key component of the BBB. Following hypoxic-ischaemic or mechanical injury to the brain, inflammatory mediators are released such as cytokines, chemokines, and growth factors. Simultaneously, matrix metalloproteinases (MMPs) are released which can degrade TJ proteins. Subsequently, the function and morphology of the BBB are disrupted, which allows immune cells an opportunity to enter into the brain parenchyma. This review summarises the information on the role of TJ protein families in the BBB and provides a comprehensive summary of the mechanisms whereby inflammation breaks down the BBB by increasing degradation of TJ proteins.

Upregulation of TLR4/MyD88 pathway in alcohol-induced Wernicke’s encephalopathy: Findings in preclinical models and in a postmortem human case

Wernicke’s encephalopathy (WE) is a neurologic disease caused by vitamin B1 or thiamine deficiency (TD), being the alcohol use disorder its main risk factor. WE patients present limiting motor, cognitive, and emotional alterations related to a selective cerebral vulnerability. Neuroinflammation has been proposed to be one of the phenomena that contribute to brain damage. Our previous studies provide evidence for the involvement of the innate immune receptor Toll-like (TLR)4 in the inflammatory response induced in the frontal cortex and cerebellum in TD animal models (animals fed with TD diet [TDD] and receiving pyrithiamine). Nevertheless, the effects of the combination of chronic alcohol consumption and TD on TLR4 and their specific contribution to the pathogenesis of WE are currently unknown. In addition, no studies on TLR4 have been conducted on WE patients since brains from these patients are difficult to achieve. Here, we used rat models of chronic alcohol (CA; 9 months of forced consumption of 20% (w/v) alcohol), TD hit (TDD + daily 0.25 mg/kg i.p. pyrithiamine during 12 days), or combined treatment (CA + TDD) to check the activation of the proinflammatory TLR4/MyD88 pathway and related markers in the frontal cortex and the cerebellum. In addition, we characterized for the first time the TLR4 and its coreceptor MyD88 signature, along with other markers of this proinflammatory signaling such as phospo-NFκB p65 and IκBα, in the postmortem human frontal cortex and cerebellum (gray and white matter) of an alcohol-induced WE patient, comparing it with negative (no disease) and positive (aged brain with Alzheimer’s disease) control subjects for neuroinflammation. We found an increase in the cortical TLR4 and its adaptor molecule MyD88, together with an upregulation of the proinflammatory signaling molecules p-NF-ĸB and IĸBα in the CA + TDD animal model. In the patient diagnosed with alcohol-induced WE, we observed cortical and cerebellar upregulation of the TLR4/MyD88 pathway. Hence, our findings provide evidence, both in the animal model and the human postmortem brain, of the upregulation of the TLR4/MyD88 proinflammatory pathway in alcohol consumption–related WE.

Pericyte derived chemokines amplify neutrophil recruitment across the cerebrovascular endothelial barrier

Excessive neutrophil extravasation can drive immunopathology, exemplified in pyogenic meningitis caused by Streptococcus pneumoniae infection. Insufficient knowledge of the mechanisms that amplify neutrophil extravasation has limited innovation in therapeutic targeting of neutrophil mediated pathology. Attention has focussed on neutrophil interactions with endothelia, but data from mouse models also point to a role for the underlying pericyte layer, as well as perivascular macrophages, the only other cell type found within the perivascular space in the cerebral microvasculature. We tested the hypothesis that human brain vascular pericytes (HBVP) contribute to neutrophil extravasation in a transwell model of the cerebral post-capillary venule. We show that pericytes augment endothelial barrier formation. In response to inflammatory cues, they significantly enhance neutrophil transmigration across the endothelial barrier, without increasing the permeability to small molecules. In our model, neither pericytes nor endothelia responded directly to bacterial stimulation. Instead, we show that paracrine signalling by multiple cytokines from monocyte derived macrophages drives transcriptional upregulation of multiple neutrophil chemokines by pericytes. Pericyte mediated amplification of neutrophil transmigration was independent of transcriptional responses by endothelia, but could be mediated by direct chemokine translocation across the endothelial barrier. Our data support a model in which microbial sensing by perivascular macrophages generates an inflammatory cascade where pericytes serve to amplify production of neutrophil chemokines that are translocated across the endothelial barrier to act directly on circulating neutrophils. In view of the striking redundancy in inflammatory cytokines that stimulate pericytes and in the neutrophil chemokines they produce, we propose that the mechanism of chemokine translocation may offer the most effective therapeutic target to reduce neutrophil mediated pathology in pyogenic meningitis.

The Pathological Mechanism Between the Intestine and Brain in the Early Stage of Parkinson's Disease

Parkinson's disease (PD) is the second most common chronic progressive neurodegenerative disease. The main pathological features are progressive degeneration of neurons and abnormal accumulation of α-synuclein. At present, the pathogenesis of PD is not completely clear, and many changes in the intestinal tract may be the early pathogenic factors of PD. These changes affect the central nervous system (CNS) through both nervous and humoral pathways. α-Synuclein deposited in the intestinal nerve migrates upward along the vagus nerve to the brain. Inflammation and immune regulation mediated by intestinal immune cells may be involved, affecting the CNS through local blood circulation. In addition, microorganisms and their metabolites may also affect the progression of PD. Therefore, paying attention to the multiple changes in the intestinal tract may provide new insight for the early diagnosis and treatment of PD.

Opioid Use, Gut Dysbiosis, Inflammation, and the Nervous System

Opioid use disorder (OUD) is defined as the chronic use or misuse of prescribed or illicitly obtained opioids and is characterized by clinically significant impairment. The etiology of OUD is multifactorial as it is influenced by genetics, environmental factors, stress response and behavior. Given the profound role of the gut microbiome in health and disease states, in recent years there has been a growing interest to explore interactions between the gut microbiome and the central nervous system as a causal link and potential therapeutic source for OUD. This review describes the role of the gut microbiome and opioid-induced immunopathological disturbances at the gut epithelial surface, which collectively contribute to OUD and perpetuate the vicious cycle of addiction and relapse.

Immunological defense of CNS barriers against infections

Neuroanatomical barriers with physical, chemical, and immunological properties play an essential role in preventing the spread of peripheral infections into the CNS. A failure to contain pathogens within these barriers can result in very serious CNS diseases. CNS barriers are inhabited by an elaborate conglomerate of innate and adaptive immune cells that are highly responsive to environmental challenges. The CNS and its barriers can also be protected by memory T and B cells elicited by prior infection or vaccination. Here, we discuss the different CNS barriers from a developmental, anatomical, and immunological standpoint and summarize our current understanding of how memory cells protect the CNS compartment. We then discuss a contemporary challenge to CNS-barrier system (SARS-CoV-2 infection) and highlight approaches to promote immunological protection of the CNS via vaccination.

Gut Microbiota Interact With the Brain Through Systemic Chronic Inflammation: Implications on Neuroinflammation, Neurodegeneration, and Aging

It has been noticed in recent years that the unfavorable effects of the gut microbiota could exhaust host vigor and life, yet knowledge and theory are just beginning to be established. Increasing documentation suggests that the microbiota-gut-brain axis not only impacts brain cognition and psychiatric symptoms but also precipitates neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS). How the blood-brain barrier (BBB), a machinery protecting the central nervous system (CNS) from the systemic circulation, allows the risky factors derived from the gut to be translocated into the brain seems paradoxical. For the unique anatomical, histological, and immunological properties underpinning its permeable dynamics, the BBB has been regarded as a biomarker associated with neural pathogenesis. The BBB permeability of mice and rats caused by GM dysbiosis raises the question of how the GM and its metabolites change BBB permeability and causes the brain pathophysiology of neuroinflammation and neurodegeneration (NF&ND) and brain aging, a pivotal multidisciplinary field tightly associated with immune and chronic systemic inflammation. If not all, gut microbiota-induced systemic chronic inflammation (GM-SCI) mainly refers to excessive gut inflammation caused by gut mucosal immunity dysregulation, which is often influenced by dietary components and age, is produced at the interface of the intestinal barrier (IB) or exacerbated after IB disruption, initiates various common chronic diseases along its dispersal routes, and eventually impairs BBB integrity to cause NF&ND and brain aging. To illustrate the immune roles of the BBB in pathophysiology affected by inflammatory or "leaky" IB resulting from GM and their metabolites, we reviewed the selected publications, including the role of the BBB as the immune barrier, systemic chronic inflammation and inflammation influences on BBB permeability, NF&ND, and brain aging. To add depth to the bridging role of systemic chronic inflammation, a plausible mechanism indispensable for BBB corruption was highlighted; namely, BBB maintenance cues are affected by inflammatory cytokines, which may help to understand how GM and its metabolites play a major role in NF&ND and aging.

Midazolam Ameliorates Impairment of the Blood-Brain Barrier (BBB) Against LPS

Central nervous system (CNS) dysfunction induced by sepsis and pathogenic microbial infections is reported to be closely associated with increased permeability of the blood-brain barrier (BBB), which is mainly mediated by the stimulation of lipopolysaccharide (LPS) on inflammatory signaling. Midazolam is a novel sedative acting on the benzodiazepine receptor, which is recently reported to exert a neuroprotective effect by inhibiting inflammation. The present study will explore the potential repair capacity of Midazolam on LPS-induced damage to the BBB. The in vivo mice model was established by intraperitoneal injection of LPS, while the in vitro model was constructed by stimulating endothelial cells utilizing LPS. We found that the increased malondialdehyde (MDA) level and reduced superoxide dismutase (SOD) activity in the brain cortices, promoted serum concentration of inflammatory factors, and elevated BBB permeability were found in the LPS group, all of which were dramatically reversed by 1 mg/kg and 2 mg/kg Midazolam. Interestingly, Midazolam increased the expression of the tight junction protein zonula occludens-1 (ZO-1). In LPS-challenged in vitro human brain microvascular endothelial cells (HBMECs), the increased concentration of inflammatory factors, reduced trans-endothelial electrical resistance (TEER) level, elevated relative value of trans-endothelial permeability, and downregulated ZO-1 were observed, all of which were pronouncedly alleviated by Midazolam, accompanied by the inhibition on the Ras homolog family member A/ Rho-kinase 2 (RhoA/ROCK-2) pathway. Furthermore, the regulatory effects of Midazolam on ZO-1 expression and the endothelial monolayer permeability in LPS-challenged HBMECs were abolished by the overexpression of RhoA. Collectively, our data imply that Midazolam ameliorated the impairment of the BBB against LPS by regulating the RhoA/ROCK2 pathway.

The Blood–Brain Barrier—A Key Player in Multiple Sclerosis Disease Mechanisms

Over the past decade, multiple sclerosis (MS), a chronic neuroinflammatory disease with severe personal and social consequences, has undergone a steady increase in incidence and prevalence rates worldwide. Despite ongoing research and the development of several novel therapies, MS pathology remains incompletely understood, and the prospect for a curative treatment continues to be unpromising in the near future. A sustained research effort, however, should contribute to a deeper understanding of underlying disease mechanisms, which will undoubtedly yield improved results in drug development. In recent years, the blood–brain barrier (BBB) has increasingly become the focus of many studies as it appears to be involved in both MS disease onset and progression. More specifically, neurovascular unit damage is believed to be involved in the critical process of CNS immune cell penetration, which subsequently favors the development of a CNS-specific immune response, leading to the classical pathological and clinical hallmarks of MS. The aim of the current narrative review is to merge the relevant evidence on the role of the BBB in MS pathology in a comprehensive and succinct manner. Firstly, the physiological structure and functions of the BBB as a component of the more complex neurovascular unit are presented. Subsequently, the authors review the specific alteration of the BBB encountered in different stages of MS, focusing on both the modifications of BBB cells in neuroinflammation and the CNS penetration of immune cells. Finally, the currently accepted theories on neurodegeneration in MS are summarized.

Lysophosphatidic Acid Receptor 5 (LPA5) Knockout Ameliorates the Neuroinflammatory Response In Vivo and Modifies the Inflammatory and Metabolic Landscape of Primary Microglia In Vitro

Systemic inflammation induces alterations in the finely tuned micromilieu of the brain that is continuously monitored by microglia. In the CNS, these changes include increased synthesis of the bioactive lipid lysophosphatidic acid (LPA), a ligand for the six members of the LPA receptor family (LPA_1-6). In mouse and human microglia, LPA₅ belongs to a set of receptors that cooperatively detect danger signals in the brain. Engagement of LPA₅ by LPA polarizes microglia toward a pro-inflammatory phenotype. Therefore, we studied the consequences of global LPA₅ knockout (^-/-) on neuroinflammatory parameters in a mouse endotoxemia model and in primary microglia exposed to LPA in vitro. A single endotoxin injection (5 mg/kg body weight) resulted in lower circulating concentrations of TNFα and IL-1β and significantly reduced gene expression of IL-6 and CXCL2 in the brain of LPS-injected LPA₅^-/- mice. LPA₅ deficiency improved sickness behavior and energy deficits produced by low-dose (1.4 mg LPS/kg body weight) chronic LPS treatment. LPA₅^-/- microglia secreted lower concentrations of pro-inflammatory cyto-/chemokines in response to LPA and showed higher maximal mitochondrial respiration under basal and LPA-activated conditions, further accompanied by lower lactate release, decreased NADPH and GSH synthesis, and inhibited NO production. Collectively, our data suggest that LPA₅ promotes neuroinflammation by transmiting pro-inflammatory signals during endotoxemia through microglial activation induced by LPA.

Enhanced Antioxidant Effects of the Anti-Inflammatory Compound Probucol when Released from Mesoporous Silica Particles

Brain endothelial cells mediate the function and integrity of the blood brain barrier (BBB) by restricting its permeability and exposure to potential toxins. However, these cells are highly susceptible to cellular damage caused by oxidative stress and inflammation. Consequent disruption to the integrity of the BBB can lead to the pathogenesis of neurodegenerative diseases. Drug compounds with antioxidant and/or anti-inflammatory properties therefore have the potential to preserve the structure and function of the BBB. In this work, we demonstrate the enhanced antioxidative effects of the compound probucol when loaded within mesoporous silica particles (MSP) in vitro and in vivo zebrafish models. The dissolution kinetics were significantly enhanced when released from MSPs. An increased reduction in lipopolysaccharide (LPS)-induced reactive oxygen species (ROS), cyclooxygenase (COX) enzyme activity and prostaglandin E₂ production was measured in human brain endothelial cells treated with probucol-loaded MSPs. Furthermore, the LPS-induced permeability across an endothelial cell monolayer by paracellular and transcytotic mechanisms was also reduced at lower concentrations compared to the antioxidant ascorbic acid. Zebrafish pre-treated with probucol-loaded MSPs reduced hydrogen peroxide-induced ROS to control levels after 24-h incubation, at significantly lower concentrations than ascorbic acid. We provide compelling evidence that the encapsulation of antioxidant and anti-inflammatory compounds within MSPs can enhance their release, enhance their antioxidant effects properties, and open new avenues for the accelerated suppression of neuroinflammation.

Effects of Natural Polyphenols on Oxidative Stress-Mediated Blood–Brain Barrier Dysfunction

The blood-brain barrier (BBB), which consists mainly of brain microvascular endothelial cells and astrocytes connected by tight junctions (TJs) and adhesion molecules (AMs), maintains the homeostatic balance between brain parenchyma and extracellular fluid. Accumulating evidence shows that BBB dysfunction is a common feature of neurodegenerative diseases, including stroke, traumatic brain injury, and Alzheimer’s disease. Among the various pathological pathways of BBB dysfunction, reactive oxygen species (ROS) are known to play a key role in inducing BBB disruption mediated via TJ modification, AM induction, cytoskeletal reorganization, and matrix metalloproteinase activation. Thus, antioxidants have been suggested to exert beneficial effects on BBB dysfunction-associated brain diseases. In this review, we summarized the sources of ROS production in multiple cells that constitute or surround the BBB, such as BBB endothelial cells, astrocytes, microglia, and neutrophils. We also reviewed various pathological mechanisms by which BBB disruption is caused by ROS in these cells. Finally, we summarized the effects of various natural polyphenols on BBB dysfunction to suggest a therapeutic strategy for BBB disruption-related brain diseases.

Toll-Like Receptor 4 in Pain: Bridging Molecules-to-Cells-to-Systems

Pain impacts the lives of billions of people around the world - both directly and indirectly. It is complex and transcends beyond an unpleasant sensory experience to encompass emotional experiences. To date, there are no successful treatments for sufferers of chronic pain. Although opioids do not provide any benefit to chronic pain sufferers, they are still prescribed, often resulting in more complications such as hyperalgesia and dependence. In order to develop effective and safe medications to manage, and perhaps even treat pain, it is important to evaluate novel contributors to pain pathologies. As such, in this chapter we review the role of Toll-like receptor 4, a receptor of the innate immune system, that continues to gain substantial attention in the field of pain research. Positioned in the nexus of the neuro and immune systems, TLR4 may provide one of the missing pieces in understanding the complexities of pain. Here we consider how TLR4 enables a mechanistical understanding of pain as a multidimensional biopsychosocial state from molecules to cells to systems and back again.

Acute Effect of Caffeine on the Synthesis of Pro-Inflammatory Cytokines in the Hypothalamus and Choroid Plexus during Endotoxin-Induced Inflammation in a Female Sheep Model

This study was designed to determine the effect of acute caffeine (CAF) administration, which exerts a broad spectrum of anti-inflammatory activity, on the synthesis of pro-inflammatory cytokines and their receptors in the hypothalamus and choroid plexus (ChP) during acute inflammation caused by the injection of bacterial endotoxin—lipopolysaccharide (LPS). The experiment was performed on 24 female sheep randomly divided into four groups: control; LPS treated (iv.; 400 ng/kg of body mass (bm.)); CAF treated (iv.; 30 mg/kg of bm.); and LPS and CAF treated. The animals were euthanized 3 h after the treatment. It was found that acute administration of CAF suppressed the synthesis of interleukin (IL-1β) and tumor necrosis factor (TNF)α, but did not influence IL-6, in the hypothalamus during LPS-induced inflammation. The injection of CAF reduced the LPS-induced expression of TNF mRNA in the ChP. CAF lowered the gene expression of IL-6 cytokine family signal transducer (IL6ST) and TNF receptor superfamily member 1A (TNFRSF1) in the hypothalamus and IL-1 type II receptor (IL1R2) in the ChP. Our study on the sheep model suggests that CAF may attenuate the inflammatory response at the hypothalamic level and partly influence the inflammatory signal generated by the ChP cells. This suggests the potential of CAF to suppress neuroinflammatory processes induced by peripheral immune/inflammatory challenges.

The blood-brain barrier in systemic infection and inflammation

The vascular blood-brain barrier is a highly regulated interface between the blood and brain. Its primary function is to protect central neurons while signaling the presence of systemic inflammation and infection to the brain to enable a protective sickness behavior response. With increasing degrees and duration of systemic inflammation, the vascular blood-brain barrier becomes more permeable to solutes, undergoes an increase in lymphocyte trafficking, and is infiltrated by innate immune cells; endothelial cell damage may occasionally occur. Perturbation of neuronal function results in the clinical features of encephalopathy. Here, the molecular and cellular anatomy of the vascular blood-brain barrier is reviewed, first in a healthy context and second in a systemic inflammatory context. Distinct from the molecular and cellular mediators of the blood-brain barrier's response to inflammation, several moderators influence the direction and magnitude at genetic, system, cellular and molecular levels. These include sex, genetic background, age, pre-existing brain pathology, systemic comorbidity, and gut dysbiosis. Further progress is required to define and measure mediators and moderators of the blood-brain barrier's response to systemic inflammation in order to explain the heterogeneity observed in animal and human studies.

The Blood-Brain Barrier, Oxidative Stress, and Insulin Resistance

The blood–brain barrier (BBB) is a network of specialized endothelial cells that regulates substrate entry into the central nervous system (CNS). Acting as the interface between the periphery and the CNS, the BBB must be equipped to defend against oxidative stress and other free radicals generated in the periphery to protect the CNS. There are unique features of brain endothelial cells that increase the susceptibility of these cells to oxidative stress. Insulin signaling can be impacted by varying levels of oxidative stress, with low levels of oxidative stress being necessary for signaling and higher levels being detrimental. Insulin must cross the BBB in order to access the CNS, levels of which are important in peripheral metabolism as well as cognition. Any alterations in BBB transport due to oxidative stress at the BBB could have downstream disease implications. In this review, we cover the interactions of oxidative stress at the BBB, how insulin signaling is related to oxidative stress, and the impact of the BBB in two diseases greatly affected by oxidative stress and insulin resistance: diabetes mellitus and Alzheimer’s disease.

Combination of Probiotics and Natural Compounds to Treat Multiple Sclerosis via Warburg Effect

Multiple sclerosis (MS) is a chronic demyelinating disease of the central nervous system (CNS). It is an auto-immune disorder. Its usual symptoms are unique to each person. In MS lesions vast fractions of pyruvate molecules are instantly transformed into lactate. This reprogramming mechanism of glycolysis is known as the Warburg effect. MS has no efficient treatment yet. Hence, there is a requirement for profitable immunomodulatory agents in MS. Probiotics perform as an immunomodulator because they regulate the host’s immune responses. Its efficacy gets enhanced for an extended period when it combines with prebiotics. In this review, we focus on the metabolic alterations behind the MS lesions via the Warburg effect, and also suggesting, the combined efficacy of prebiotics and probiotics for the effective treatment of MS without side effects. The Warburg effect mechanism intensifies the infiltration of activated T-cells and B-cells into the CNS. It provokes the inflammation process on the myelin sheath. The infiltration of immune cells can be inhibited by the combination therapy of probiotics and prebiotics. By this review, we can recommend that the idea of this combinational therapy can do miracles in the treatment of MS in the future.

Autocrine Effects of Brain Endothelial Cell-Produced Human Apolipoprotein E on Metabolism and Inflammation in vitro

Reports of APOE4-associated neurovascular dysfunction during aging and in neurodegenerative disorders has led to ongoing research to identify underlying mechanisms. In this study, we focused on whether the APOE genotype of brain endothelial cells modulates their own phenotype. We utilized a modified primary mouse brain endothelial cell isolation protocol that enabled us to perform experiments without subculture. Through initial characterization we found, that compared to APOE3, APOE4 brain endothelial cells produce less apolipoprotein E (apoE) and have altered metabolic and inflammatory gene expression profiles. Further analysis revealed APOE4 brain endothelial cultures have higher preference for oxidative phosphorylation over glycolysis and, accordingly, higher markers of mitochondrial activity. Mitochondrial activity generates reactive oxygen species, and, with APOE4, there were higher mitochondrial superoxide levels, lower levels of antioxidants related to heme and glutathione and higher markers/outcomes of oxidative damage to proteins and lipids. In parallel, or resulting from reactive oxygen species, there was greater inflammation in APOE4 brain endothelial cells including higher chemokine levels and immune cell adhesion under basal conditions and after low-dose lipopolysaccharide (LPS) treatment. In addition, paracellular permeability was higher in APOE4 brain endothelial cells in basal conditions and after high-dose LPS treatment. Finally, we found that a nuclear receptor Rev-Erb agonist, SR9009, improved functional metabolic markers, lowered inflammation and modulated paracellular permeability at baseline and following LPS treatment in APOE4 brain endothelial cells. Together, our data suggest that autocrine signaling of apoE in brain endothelial cells represents a novel cellular mechanism for how APOE regulates neurovascular function.

Cerebral Pericytes and Endothelial Cells Communicate through Inflammasome-Dependent Signals

By upregulation of cell adhesion molecules and secretion of proinflammatory cytokines, cells of the neurovascular unit, including pericytes and endothelial cells, actively participate in neuroinflammatory reactions. As previously shown, both cell types can activate inflammasomes, cerebral endothelial cells (CECs) through the canonical pathway, while pericytes only through the noncanonical pathway. Using complex in vitro models, we demonstrate here that the noncanonical inflammasome pathway can be induced in CECs as well, leading to a further increase in the secretion of active interleukin-1β over that observed in response to activation of the canonical pathway. In parallel, a more pronounced disruption of tight junctions takes place. We also show that CECs respond to inflammatory stimuli coming from both the apical/blood and the basolateral/brain directions. As a result, CECs can detect factors secreted by pericytes in which the noncanonical inflammasome pathway is activated and respond with inflammatory activation and impairment of the barrier properties. In addition, upon sensing inflammatory signals, CECs release inflammatory factors toward both the blood and the brain sides. Consequently, CECs activate pericytes by upregulating their expression of NLRP3 (NOD-, LRR-, and pyrin domain-containing protein 3), an inflammasome-forming pattern recognition receptor. In conclusion, cerebral pericytes and endothelial cells mutually activate each other in inflammation.

TLR4 pathway impairs synaptic number and cerebrovascular functions through astrocyte activation following traumatic brain injury

Background and Purpose

Activation of astrocytes contributes to synaptic remodelling, tissue repair and neuronal survival following traumatic brain injury (TBI). The mechanisms by which these cells interact to resident/infiltrated inflammatory cells to rewire neuronal networks and repair brain functions remain poorly understood. Here, we explored how TLR4‐induced astrocyte activation modified synapses and cerebrovascular integrity following TBI.

Experimental Approach

To determine how functional astrocyte alterations induced by activation of TLR4 pathway in inflammatory cells regulate synapses and neurovascular integrity after TBI, we used pharmacology, genetic approaches, live calcium imaging, immunofluorescence, flow cytometry, blood–brain barrier (BBB) integrity assessment and molecular and behavioural methods.

Key Results

Shortly after a TBI, there is a recruitment of excitable and reactive astrocytes mediated by TLR4 pathway activation with detrimental effects on post‐synaptic density‐95 (PSD‐95)/vesicular glutamate transporter 1 (VGLUT1) synaptic puncta, BBB integrity and neurological outcome. Pharmacological blockage of the TLR4 pathway with resatorvid (TAK‐242) partially reversed many of the observed effects. Synapses and BBB recovery after resatorvid administration were not observed in IP₃R2^−/− mice, indicating that effects of TLR4 inhibition depend on the subsequent astrocyte activation. In addition, TBI increased the astrocytic‐protein thrombospondin‐1 necessary to induce a synaptic recovery in a sub‐acute phase.

Conclusions and Implications

Our data demonstrate that TLR4‐mediated signalling, most probably through microglia and/or infiltrated monocyte–astrocyte communication, plays a crucial role in the TBI pathophysiology and that its inhibition prevents synaptic loss and BBB damage accelerating tissue recovery/repair, which might represent a therapeutic potential in CNS injuries and disorders.

The taste of neuroinflammation: Molecular mechanisms linking taste sensing to neuroinflammatory responses

Evidence indicates a critical role of neuroinflammatory response as an underlying pathophysiological process in several central nervous system disorders, including neurodegenerative diseases. However, the molecular mechanisms that trigger neuroinflammatory processes are not fully known. The discovery of bitter taste receptors in regions other than the oral cavity substantially increased research interests on their functional roles in extra-oral tissues. It is now widely accepted that bitter taste receptors, for instance, in the respiratory, intestinal, reproductive and urinary tracts, are crucial not only for sensing poisonous substances, but also, act as immune sentinels, mobilizing defense mechanisms against pathogenic aggression. The relatively recent discovery of bitter taste receptors in the brain has intensified research investigation on the functional implication of cerebral bitter taste receptor expression. Very recent data suggest that responses of bitter taste receptors to neurotoxins and microbial molecules, under normal condition, are necessary to prevent neuroinflammatory reactions. Furthermore, emerging data have revealed that downregulation of key components of the taste receptor signaling cascade leads to increased oxidative stress and inflammasome signaling in neurons that ultimately culminate in neuroinflammation. Nevertheless, the mechanisms that link taste receptor mediated surveillance of the extracellular milieu to neuroinflammatory responses are not completely understood. This review integrates new data on the molecular mechanisms that link bitter taste receptor sensing to neuroinflammatory responses. The role of bitter taste receptor-mediated sensing of toxigenic substances in brain disorders is also discussed. The therapeutic significance of targeting these receptors for potential treatment of neurodegenerative diseases is also highlighted.

Ganoderma lucidum polysaccharides ameliorated depression-like behaviors in the chronic social defeat stress depression model via modulation of Dectin-1 and the innate immune system

Major depressive disorder (MDD) is a prevalent, chronic, and recurrent disease. At least one-third of patients have treatment-resistant depression; therefore, there is an urgent need for novel drug development. Cumulative studies have suggested an inflammatory mechanism for the pathophysiology of MDD. Ganoderma lucidum polysaccharides (GLP) is an anti-inflammatory and immunomodulatory agent. Here, we found that an injection of GLP led to a rapid and robust antidepressant effect after 60 min in the tail suspension test. This antidepressant effect remained after 5 days of treatment with GLP in the forced swim test. Unlike psychostimulants, GLP did not show a hyperactive effect in the open field test. After 60 min or 5 days of treatment, GLP exhibited an antidepressant effect in a chronic social defeat stress (CSDS) depression animal model. Moreover, after 5 days of treatment, GLP attenuated the expression of the proinflammatory cytokines IL-1β and TNF-α, enhanced the expression of the anti-inflammatory cytokine IL-10 and the neurotrophic factor BDNF, and inhibited the activation of microglia and proliferation of astrocytes in the hippocampus of CSDS mice. In addition, after 5 days of treatment, GLP significantly enhanced GluA1 S845 phosphorylation as well as GluA1 and GluA2 expression levels in the hippocampus of CSDS mice. To determine whether the antidepressant effect was mediated by Dectin-1, we found that GLP treatment enhanced Dectin-1 expression in the hippocampus in CSDS mice, and the Dectin-1-specific inhibitor laminarin almost completely blocked the antidepressant effect of GLP. This study identified GLP, an agonist of Dectin-1, as a novel and rapid antidepressant with clinical potential and multiple beneficial mechanisms, particularly in regulating the neuroimmune system and, subsequently, AMPA receptor function.

Lipopolysaccharide influences the plasma and brain pharmacokinetics of subcutaneously-administered HsTX1[R14A], a KV1.3-blocking peptide

K_V1.3 is a voltage-gated potassium channel that is upregulated in neuroinflammatory conditions, such as Alzheimer's disease and Parkinson's disease. HsTX1[R14A] is a potent and selective peptide blocker of K_V1.3 with the potential to block microglial K_V1.3, but its brain uptake is expected to be limited owing to the restrictive nature of the blood-brain barrier. To assess its peripheral and brain exposure, a LC-MS/MS assay was developed to quantify HsTX1[R14A] concentrations in mouse plasma and brain homogenate that was reliable and reproducible in the range of 6.7-66.7 nM (r² = 0.9765) and 15-150 pmol/g (r² = 0.9984), respectively. To assess if neuroinflammation affected HsTX1[R14A] disposition, C57BL/6 mice were administered HsTX1[R14A] subcutaneously (2 mg/kg) 24 h after an intraperitoneal dose of Escherichia coli lipopolysaccharide (LPS), which is commonly used to induce neuroinflammation; brain and plasma concentrations of HsTX1[R14A] were then quantified over 120 min. LPS treatment significantly retarded the decline in HsTX1[R14A] plasma concentrations, presumably as a result of reducing renal clearance, and led to substantial brain uptake of HsTX1[R14A], presumably through disruption of brain inter-endothelial tight junctions. This study suggests that HsTX1[R14A] may reach microglia in sufficient concentrations to block K_V1.3 in neuroinflammatory conditions, and therefore has the potential to reduce neurodegenerative diseases.

Function of Multidrug Resistance Transporters is Disrupted by Infection Mimics in Human Brain Endothelial Cells

P-glycoprotein (P-gp/ABCB1) and breast cancer resistance protein (BCRP/ABCG2) modulate the distribution of drugs and toxins across the blood-brain barrier (BBB). Animal studies reported that infection-induced disruption of these transporters in the developing BBB impairs fetal brain protection. However, the impact of infection mimics on P-gp/BCRP function in human brain endothelium is less well understood. We hypothesized that Toll-like receptor ligands mimicking bacterial and viral infection would modify the expression and function of P-gp and BCRP in human brain endothelial cells (BECs). Human cerebral microvascular endothelial cells (hCMEC/D3) were challenged with bacterial [Lipopolysaccharide (LPS)] and viral-mimics [polyinosinic:polycytidylic acid (PolyI:C) or single-stranded RNA (ssRNA)], or pro-inflammatory cytokines interleukin (IL)-6, tumor necrosis factor (TNF)-α and interferon gamma (IFN)-ɣ. P-gp and BCRP function was assessed after 4 or 24 h, using Calcein-AM and Chlorin-6 assays, respectively. Western blot and qPCR quantified P-gp/ABCB1 and BCRP/ABCG2 expression following treatments. Infection mimics are potent modulators of drug transporters in human BECs in vitro. LPS and PolyI:C increased, while ssRNA exposure reduced P-gp activity. In contrast, LPS and PolyI:C decreased, while ssRNA increased BCRP activity (P < .05). There was little correlation between drug transporter function, gene expression and total protein level. Altered plasma membrane BCRP may suggest modified intracellular trafficking induced by infection in human BECs. Bacterial and viral infection mimics modify P-gp and BCRP transport function in human BECs, in vitro. This knowledge may contribute and have important implications for human brain protection and possible altered biodistribution of drugs and xenobiotics in the brain following exposure to TLR agonists.

Cerebrospinal Fluid and Plasma Lipopolysaccharide Levels in Human Immunodeficiency Virus Type 1 Infection and Associations With Inflammation, Blood-Brain Barrier Permeability, and Neuronal Injury

Human immunodeficiency virus (HIV) infection is associated with increased systemic microbial translocation, neuroinflammation, and occasionally, neuronal injury. Whether systemic lipopolysaccharide (LPS) penetrates into the brain and contributes to neuroinflammation remain unknown in HIV. Here, we measured plasma and cerebrospinal fluid (CSF) LPS levels along with biomarkers of neuroinflammation (white blood cell counts and 40 soluble markers) and neurofilament light chain (NfL). Notably, CSF LPS was undetectable in all samples, including 3 HIV-infected individuals with dementia. Increased plasma LPS, neuroinflammation, and blood-brain barrier (BBB) dysfunction were found in untreated HIV-infected individuals, but not in healthy or treated HIV-infected individuals. Plasma LPS levels were directly correlated with various markers of inflammation in both plasma and CSF, as well as with degree of BBB permeability but not with CSF NfL in HIV-infected subjects. These results suggest that the magnitude of microbial translocation associates with neuroinflammation and BBB permeability in HIV without direct penetration into the central nervous system.

Analysis of Melanoma Secretome for Factors That Directly Disrupt the Barrier Integrity of Brain Endothelial Cells

We have recently demonstrated that invasive melanoma cells are capable of disrupting the brain endothelial barrier integrity. This was shown using ECIS biosensor technology, which revealed rapid disruption via the paracellular junctions. In this paper, we demonstrate that melanoma cells secrete factors (e.g., cytokines) that weaken the endothelial barrier integrity. Through proteome profiling, we attempt to identify the barrier-disrupting cytokines. Melanoma conditioned media were collected from three New Zealand melanoma lines. ECIS technology was used to assess if the conditioned media disrupted the endothelial barrier independent of the melanoma cells. The melanoma cell secretome was assessed using cytometric bead array (CBA), Luminex immunoassay and multiplex Proteome Profilers, to detect the expression of secretory proteins, which may facilitate metastasis. Finally, ECIS technology was used to assess the direct effects of secreted proteins identified as candidates from the proteome screens. We show that melanoma-conditioned media significantly disrupted the brain endothelial barrier, however, to a much lesser extent than the cells from which they were collected. Cytokine and proteome profiling of the conditioned media showed evidence of high concentrations of approximately 15 secreted proteins (including osteopontin, IL-8, GDF-15, MIF and VEGF). These 15 secreted proteins were expressed variably across the melanoma lines. Surprisingly, the addition of these individually to the brain endothelial cells did not substantially affect the barrier integrity. ANGPTL-4 and TGFβ were also produced by the melanoma cells. Whilst TGFβ-1 had a pronounced effect on the barrier integrity, surprisingly ANGPTL-4 did not. However, its C-terminal fragment did and within a very similar period to the conditioned media, albeit not to the same extent. Herein we show that melanoma cells produce a wide-range of soluble factors at high concentrations, which most likely favour support or survival of the cancer cells. Most of these, except for TGFβ-1 and the C-terminal fragment of ANGPTL-4, did not have an impact on the integrity of the brain endothelial cells.

TLR4-mediated hippocampal MMP/TIMP imbalance contributes to the aggravation of perioperative neurocognitive disorder in db/db mice

Although type 2 diabetes is an important predictor of perioperative neurocognitive disorder (PND), little is currently known about its mechanism of action. Adult male db/db and db/m mice were subjected to four different treatments, including either sham or tibial fracture surgery as well as intraperitoneal injection of vehicle or TAK-242 (the selective inhibitor of TLR4) at 1, 24, and 48 h after surgery. The fear conditioning test was performed to detect cognitive impairment on post-operative day (POD) 3. The hippocampus was collected on POD 1 for western-blots and on POD 3 for western-blots, transmission electron microscopy, and electrophysiological experiments. Toll-like receptor 4 (TLR4) inhibition reversed more profound decline in the freezing behavior of db/db mice on POD 3. The surgery reduced the slope of hippocampal field excitatory postsynaptic potentials, and induced blood-brain barrier (BBB) damage in db/db mice on POD 3. The surgery also increased protein levels of TLR4, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, albumin, matrix metalloproteinase (MMP)-2, and MMP-9, and decreased protein levels of claudin-5, occludin, tissue inhibitor of matrix metalloproteinase (TIMP)-1, and TIMP-2 in the hippocampus of db/db and db/m mice. These changes were all reversed by TAK-242 treatment. At last, compared with those in post-operative db/m mice, the surgery increased protein levels of TLR4, TNF-α, and IL-1β, decreased protein levels of claudin-5 and occludin, and sustained the MMP/TIMP imbalance in the hippocampus of db/db mice on POD 3. Our results suggest that TLR4-mediated aggravated hippocampal MMP/TIMP imbalance, BBB disruption, sustained inflammatory cytokine release, and impairment of long-term potentiation play a key role in tibial fracture surgery-induced persistent PND in db/db mice.

Focal TLR4 activation mediates disturbed flow-induced endothelial inflammation

AIMS

Disturbed blood flow at arterial branches and curvatures modulates endothelial function and predisposes the region to endothelial inflammation and subsequent development of atherosclerotic lesions. Activation of the endothelial Toll-like receptors (TLRs), in particular TLR4, contributes to vascular inflammation. Therefore, we investigate whether TLR4 can sense disturbed flow (DF) to mediate the subsequent endothelial inflammation.

METHODS AND RESULTS

En face staining of endothelium revealed that TLR4 expression, activation, and its downstream inflammatory markers were elevated in mouse aortic arch compared with thoracic aorta, which were absent in Tlr4mut mice. Similar results were observed in the partial carotid ligation model where TLR4 signalling was activated in response to ligation-induced flow disturbance in mouse carotid arteries, and such effect was attenuated in Tlr4mut mice. DF in vitro increased TLR4 expression and activation in human endothelial cells (ECs) and promoted monocyte-EC adhesion, which were inhibited in TLR4-knockdown ECs. Among endogenous TLR4 ligands examined as candidate mediators of DF-induced TLR4 activation, fibronectin containing the extra domain A (FN-EDA) expressed by ECs was increased by DF and was revealed to directly interact with and activate TLR4.

CONCLUSION

Our findings demonstrate the indispensable role of TLR4 in DF-induced endothelial inflammation and pinpoint FN-EDA as the endogenous TLR4 activator in this scenario. This novel mechanism of vascular inflammation under DF condition may serve as a critical initiating step in atherogenesis.

Potential Roles of Myeloid Differentiation Factor 2 on Neuroinflammation and Its Possible Interventions

Neuroinflammation is the primary response by immune cells in the nervous system to protect against infection. Chronic and uncontrolled neuroinflammation triggers neuronal injury and neuronal death resulting in a variety of neurodegenerative disorders. Therefore, fine tuning of the immune response in the nervous system is now extensively considered as a potential therapeutic intervention for those diseases. The immune cells of the nervous system express Toll-like receptor 4 (TLR4) together with myeloid differentiation factor 2 (MD-2) to protect against the pathogens. Over the last 10 years, antagonists targeting the functional domains of MD-2 have become attractive pharmacological intervention strategies in pre-clinical studies into neuroinflammation and its associated brain pathologies. This review aims to summarize and discuss the roles of TLR4-MD-2 signaling pathway activation in various models of neuroinflammation. This review article also highlights the studies reporting the effect of MD-2 antagonists on neuroinflammation in in vitro and in vivo studies.

When Innate Immunity Meets Angiogenesis-The Role of Toll-Like Receptors in Endothelial Cells and Pulmonary Hypertension

Toll-like receptors serve a central role in innate immunity, but they can also modulate cell function in various non-immune cell types including endothelial cells. Endothelial cells are necessary for the organized function of the vascular system, and part of their fundamental role is also the regulation of immune function and inflammation. In this review, we summarize the current knowledge of how Toll-like receptors contribute to the immune and non-immune functions of the endothelial cells.

Inflammation in Parkinson's Disease: Mechanisms and Therapeutic Implications

Parkinson's disease (PD) is a common neurodegenerative disorder primarily characterized by the death of dopaminergic neurons that project from the substantia nigra pars compacta. Although the molecular bases for PD development are still little defined, extensive evidence from human samples and animal models support the involvement of inflammation in onset or progression. However, the exact trigger for this response remains unclear. Here, we provide a systematic review of the cellular mediators, i.e., microglia, astroglia and endothelial cells. We also discuss the genetic and transcriptional control of inflammation in PD and the immunomodulatory role of dopamine and reactive oxygen species. Finally, we summarize the preclinical and clinical approaches targeting neuroinflammation in PD.

Neurovascular Inflammaging in Health and Disease

Aging is characterized by a chronic low-grade sterile inflammation dubbed as inflammaging, which in part originates from accumulating cellular debris. These, acting as danger signals with many intrinsic factors such as cytokines, are sensed by a network of pattern recognition receptors and other cognate receptors, leading to the activation of inflammasomes. Due to the inflammasome activity-dependent increase in the levels of pro-inflammatory interleukins (IL-1β, IL-18), inflammation is initiated, resulting in tissue injury in various organs, the brain and the spinal cord included. Similarly, in age-related diseases of the central nervous system (CNS), inflammasome activation is a prominent moment, in which cells of the neurovascular unit occupy a significant position. In this review, we discuss the inflammatory changes in normal aging and summarize the current knowledge on the role of inflammasomes and contributing mechanisms in common CNS diseases, namely Alzheimer’s disease, Parkinson’s disease, amyotrophic lateral sclerosis and stroke, all of which occur more frequently with aging.

TLR-4 Signaling vs. Immune Checkpoints, miRNAs Molecules, Cancer Stem Cells, and Wingless-Signaling Interplay in Glioblastoma Multiforme-Future Perspectives

Toll-like-receptor (TLR) family members were detected in the central nervous system (CNS). TLR occurrence was noticed and widely described in glioblastomamultiforme (GBM) cells. After ligand attachment, TLR-4 reorients domains and dimerizes, activates an intracellular cascade, and promotes further cytoplasmatic signaling. There is evidence pointing at a strong relation between TLR-4 signaling and micro ribonucleic acid (miRNA) expression. The TLR-4/miRNA interplay changes typical signaling and encourages them to be a target for modern immunotherapy. TLR-4 agonists initiate signaling and promote programmed death ligand-1 (PD-1L) expression. Most of those molecules are intensively expressed in the GBM microenvironment, resulting in the autocrine induction of regional immunosuppression. Another potential target for immunotreatment is connected with limited TLR-4 signaling that promotes Wnt/DKK-3/claudine-5 signaling, resulting in a limitation of GBM invasiveness. Interestingly, TLR-4 expression results in bordering proliferative trends in cancer stem cells (CSC) and GBM. All of these potential targets could bring new hope for patients suffering from this incurable disease. Clinical trials concerning TLR-4 signaling inhibition/promotion in many cancers are recruiting patients. There is still a lot to do in the field of GBM immunotherapy.

MicroRNA Let-7i Is a Promising Serum Biomarker for Post-stroke Cognitive Impairment and Alleviated OGD-Induced Cell Damage in vitro by Regulating Bcl-2

Background

The mechanism of post-stroke cognitive impairment (PSCI) has not been explained. We aimed to investigate whether miR-let-7i participates in the PSCI and illuminates its underlying role in oxygen–glucose deprivation (OGD)-induced cell apoptosis.

Methods

Blood samples from 36 subjects with PSCI and 38 with post-stroke cognitive normality (Non-PSCI) were collected to evaluate the differential expression of miR-let-7 family members, using qRT-PCT analysis. Spearman correlation was performed to estimate the correlation between the miR-1et-7i level and Montreal Cognitive Assessment (MoCA) score. Treatment of SH-SY5Y cells with OGD was used to induce cell apoptosis in vitro. Effects of miR-let-7i on OGD-induced cell apoptosis was estimated after transfection. The target gene of miR-let-7i was analyzed by dual luciferase reporter gene assay.

Results

The expression of miR-let-7i was up-regulated in PSCI patients compared with Non-PSCI (p < 0.001) and negatively correlated with MoCA score (r = −0.643, p < 0.001). When exposed to OGD, SH-SY5Y cells showed significant apoptosis accompanied by miR-let-7i up-regulation. In OGD-treated cells, miR-let-7i up-regulation was accompanied by cell apoptosis, while down-regulation showed the opposite effect. Luciferase reporter assay showed that Bcl-2 was a target gene of miR-let-7i. Western blot showed that miR-let-7i up-regulation promoted Bcl-2 expression, while qRT-PCR showed that miR-let-7i had no effect on Bcl-2 expression.

Conclusion

miR-let-7i was overexpressed in PSCI patients and it could be used as a diagnostic biomarker for PSCI. We illuminated the potential mechanism that miR-let-7i alleviated OGD-induced cell damage by targeting Bcl-2 at the post-transcriptional level.

Systemic microbial TLR2 agonists induce neurodegeneration in Alzheimer's disease mice

BACKGROUND

Accumulating data suggest a central role for brain microglia in mediating cortical neuronal death in Alzheimer's disease (AD), and for Toll-like receptor 2 (TLR2) in their toxic activation. Amyloid deposition in preclinical AD is associated with microglial activation but not directly with neurodegeneration. We examined in transgenic 5xFAD mice the hypothesis that systemic TLR2 agonists, derived from common infectious agents, may accelerate neurodegeneration in AD.

METHODS

Microbial wall-derived TLR2 agonists zymosan and lipoteichoic acid were administered intraperitoneally or intracerebroventricularly to 7-month-old wild-type or 5xFAD mice. Immunofluorescent stainings were used to quantify cortical neurons and evaluate tissue reaction. Microglial activation was assessed using functional assays, RNA expression, and FACS analysis.

RESULTS

Repeated low-dose systemic administration of zymosan or lipoteichoic acid killed cortical neurons in 5xFAD mice but not in wild-type mice. Direct CNS delivery of a selective TLR2 antagonist blocked the neurotoxicity of systemically administered zymosan, indicating that CNS TLR2 mediates this effect. Systemically administered zymosan crossed the disrupted blood-brain barrier in 5xFAD mice and entered brain parenchyma. By intracerebroventricular delivery, we found a dose- and exposure time-dependent acute neurotoxic effect of the microbial TLR2 agonist, killing cortical neurons. 5xFAD mice exhibited significantly increased vulnerability to TLR2 agonist-induced neuronal loss as compared to wild-type mice. Microbial TLR2-induced neurodegeneration was abolished by inhibiting microglia. The vulnerability of 5xFAD mice brains was mediated by an increase in number and neurotoxic phenotype of TLR2-expressing microglia.

CONCLUSIONS

We suggest that repeated exposure to microbial TLR2 agonists may facilitate neurodegeneration in AD by their microglial-mediated toxicity to the hyper-vulnerable environment of the AD brain.

Polyinosinic-Polycytidylic Acid Induces CXCL1 Expression in Cultured hCMEC/D3 Human Cerebral Microvascular Endothelial Cells

OBJECTIVE

Brain microvascular endothelial cells are integral components of the blood-brain barrier and play a role in protecting the brain from invading microbes. CXC motif chemokine ligand 1 (CXCL1) induces the chemotaxis of neutrophils, and neutrophils are important in host defense in the brain. However, dysregulated neutrophil infiltration leads to brain diseases. Toll-like receptor 3 (TLR3) is a pattern recognition receptor that recognizes viral double-stranded RNA (dsRNA). The aim of this study was to investigate the effect of an TLR3 agonist on the expression of CXCL1 in brain vascular endothelial cells.

METHODS

hCMEC/D3 human cerebral microvascular endothelial cells were cultured and treated with polyinosinic-polycytidylic acid (poly IC), a potent synthetic dsRNA agonist for TLR3. The production of CXCL1 mRNA and protein was assessed by real-time RT-PCR and ELISA. The expression of CXCL1 was compared with that of CXCL8. The effect of pretreatment of cells with a NF-κB inhibitor (SN50), a p38 mitogen-activated protein kinase (MAPK) inhibitor (SB203580), a c-Jun N-terminal kinase (JNK) inhibitor (SP600125), an interferon (IFN) regulatory factor 3 inhibitor (MRT67307), and an anti-type I IFN-neutralizing antibody mixture was examined. Phosphorylation of p38 was examined using Western blotting.

RESULTS

Treating cultured hCMEC/D3 human cells with poly IC induced the expression of CXCL1 as well as another chemokine CXCL8. Pretreatment of cells with SN50, SB203580, and SP600125 decreased the induction of CXCL1 by poly IC. However, it was not affected by MRT67307 or by an anti-type I IFN-neutralizing antibody mixture. Pretreatment of cells with SN50 decreased the poly IC-induced phosphorylation of p38.

CONCLUSIONS

Poly IC induces the expression of CXCL1 in hCMEC/D3 cells. NF-κB, p38 MAPK, and JNK are involved in this reaction. There is a cross-talk between NF-κB and p38, and NF-κB partially regulates phosphorylation of p38. CXCL1 produced by brain microvascular endothelial cells may contribute to the brain's defense against viral infection and various neurological diseases associated with neutrophil accumulation.