Glial Cell-Elicited Activation of Brain Microvasculature in Response to Brucella abortus Infection Requires ASC Inflammasome-Dependent IL-1β Production

NLRP3 activation induces BBB disruption and neutrophil infiltration via CXCR2 signaling in the mouse brain

NLRP3 is an intracellular sensor molecule that affects neutrophil functionality and infiltration in brain disorders such as experimental autoimmune encephalomyelitis (EAE). However, the detailed molecular mechanisms underlying the role of NLRP3 in these processes remain unknown. We found that NLRP3 is crucial for neutrophil infiltration, whereas dispensable for neutrophil priming. Notably, NLRP3 activation in neutrophils induced blood-brain barrier (BBB) disruption and neutrophil infiltration into the brain via CXCL1/2 secretion and subsequent activation of the CXCL1/2-CXCR2 signaling axis. Moreover, CXCL1 and CXCL2 in the inflamed brain directly reduced Claudin-5 expression, which regulates BBB permeability in brain endothelial cells. Furthermore, neutrophil-specific NLRP3 activation aggravated EAE pathogenesis by promoting CXCR2-mediated infiltration of both neutrophils and CD4+ T cells into the central nervous system at disease onset. Thus, the CXCL1/2-CXCR2 axis plays a role in EAE progression. Therefore, this chemokine axis could be a potential therapeutic target for attenuating neuroinflammatory diseases through modulating of neutrophil and CD4+ T cell infiltration and BBB disruption.

Neurobrucellosis (Brucella ceti) in striped dolphins (Stenella coeruleoalba): Immunohistochemical studies on immune response and neuroinflammation

Neurobrucellosis is a shared condition of cetaceans and humans. However, the pathogenesis and immune response in cetacean neurobrucellosis has not been extensively studied. In this multicentric investigation, 21 striped dolphin (Stenella coeruleoalba) neurobrucellosis (Brucella ceti) cases diagnosed over a 10-year period (2012-2022) were retrospectively evaluated. For each case, morphological changes were assessed by evaluating 21 histological parameters. Furthermore, the immunohistochemical expression of Brucella antigen, glial fibrillary acid protein (GFAP), and a selection of inflammatory cell (IBA-1, CD3, and CD20) and cytokine (tumor necrosis factor-alpha [TNF-α], interferon-gamma [IFN-γ], interleukin [IL]-1β, IL-2, and IL-6) markers were investigated. Inflammation of the leptomeninges, ependyma, and/or choroid plexus was lymphohistiocytic, containing macrophages/microglia (IBA-1+), T-cells (CD3+), and B-cells (CD20+) in equal proportion. B-cells occasionally formed tertiary follicles. GFAP expression showed astrocytosis in most cases. Expression of TNF-α, IFN-γ, and IL-2 indicated an intense proinflammatory response, stimulating both macrophages and T-cells. Our results showed that the inflammation and neuroinflammation in neurobrucellosis of striped dolphins mimic human neurobrucellosis and in vitro and in vivo studies in laboratory animals. Cetacean disease surveillance can be exploited to expand the knowledge of the pathogenesis and immunology of infectious diseases, particularly brucellosis, under a One Health approach.

The intricate interactions between inflammasomes and bacterial pathogens: Roles, mechanisms, and therapeutic potentials

Inflammasomes are intracellular multiprotein complexes that consist of a sensor, an adaptor, and a caspase enzyme to cleave interleukin (IL)-1β and IL-18 into their mature forms. In addition, caspase-1 and -11 activation results in the cleavage of gasdermin D to form pores, thereby inducing pyroptosis. Activation of the inflammasome and pyroptosis promotes host defense against pathogens, whereas dysregulation of the inflammasome can result in various pathologies. Inflammasomes exhibit versatile microbial signal detection, directly or indirectly, through cellular processes, such as ion fluctuations, reactive oxygen species generation, and the disruption of intracellular organelle function; however, bacteria have adaptive strategies to manipulate the inflammasome by altering microbe-associated molecular patterns, intercepting innate pathways with secreted effectors, and attenuating inflammatory and cell death responses. In this review, we summarize recent advances in the diverse roles of the inflammasome during bacterial infections and discuss how bacteria exploit inflammasome pathways to establish infections or persistence. In addition, we highlight the therapeutic potential of harnessing bacterial immune subversion strategies against acute and chronic bacterial infections. A more comprehensive understanding of the significance of inflammasomes in immunity and their intricate roles in the battle between bacterial pathogens and hosts will lead to the development of innovative strategies to address emerging threats posed by the expansion of drug-resistant bacterial infections.

The effect of Brucella abortus on glial activation and cell death in adult male rat's hippocampus

A zoonotic disease called brucellosis can cause flu-like symptoms and heart inflammation. The bacteria responsible for this disease can also enter the brain, causing a condition called neurobrucellosis that can result in long-term neurological problems. In this study, researchers aimed to determine the changes in the hippocampal cells of rats infected with Brucella. For the study, 24 adult male albino rats were inoculated with 1 × 106 CFU Brucella abortus 544. The rats were then deeply anesthetized, and their hippocampus samples were taken for stereological, histological, and molecular studies. The results showed that the infected rats had increased microgliosis and astrogliosis. Furthermore, a high level of caspase-3 in their hippocampal tissue indicated their susceptibility to apoptosis. Additionally, there was a decrease in expression of Ki67, which further supported this. Sholl's analysis confirmed a significant failure in glial morphology. The study demonstrated that the pathogen has the ability to destroy the hippocampus and potentially affect its normal physiology. However, more research is needed to clarify various aspects of neurobrucellosis.

Manifestations, complications, and treatment of neurobrucellosis: a systematic review and meta-analysis

PURPOSE

Central nervous system involvement by Brucella species is the most morbid form of brucellosis disease. Studies on neurobrucellosis are scarce and limited to case reports and series. Brucella is unable to infect or harm neurons without the assistance of monocytes. This raises the question of whether ceftriaxone-based regimens are effective.

METHODS

The primary aim of this study was to identify, evaluate, and summarize the findings of all relevant individual studies in the past 30 years to help better understand the disease. To achieve this, a broad systematic search was undertaken to identify all relevant records. Epidemiological and clinical features of the disease were assessed by the pooled analysis of descriptive studies. Through a meta-analysis, the treatment period duration was compared between the ceftriaxone-based and oral regimens using Standardized mean differences to measure effect size.

RESULTS

448 patients were included in the Meta-analyses from 5 studies. A moderate positive effect was found for ceftriaxone-based regimens over oral treatments, and there was a significant difference between these two groups (SMD 0.428, 95% CI -0.63 to -0.22, I 2 = 37.64). Neurobrucellosis has a different clinical picture in pediatric patients. The disease is less chronic in children. Fever, nausea and vomiting, fatigue, and abdominal pain were significantly more prevalent symptoms in children, and Convulsions, ascites, sensorineural hearing loss, and papilledema were significantly more prevalent signs in children than adults.

CONCLUSION

It is recommended to initiate the treatment of neurobrucellosis with IV ceftriaxone therapy in combination with oral therapy.

Bystander activation of microglia by Brucella abortus-infected astrocytes induces neuronal death via IL-6 trans-signaling

Inflammation plays a key role in the pathogenesis of neurobrucellosis where glial cell interactions are at the root of this pathological condition. In this study, we present evidence indicating that soluble factors secreted by Brucella abortus-infected astrocytes activate microglia to induce neuronal death. Culture supernatants (SN) from B. abortus-infected astrocytes induce the release of pro-inflammatory mediators and the increase of the microglial phagocytic capacity, which are two key features in the execution of live neurons by primary phagocytosis, a recently described mechanism whereby B. abortus-activated microglia kills neurons by phagocytosing them. IL-6 neutralization completely abrogates neuronal loss. IL-6 is solely involved in increasing the phagocytic capacity of activated microglia as induced by SN from B. abortus-infected astrocytes and does not participate in their inflammatory activation. Both autocrine microglia-derived and paracrine astrocyte-secreted IL-6 endow microglial cells with up-regulated phagocytic capacity that allows them to phagocytose neurons. Blocking of IL-6 signaling by soluble gp130 abrogates microglial phagocytosis and concomitant neuronal death, indicating that IL-6 activates microglia via trans-signaling. Altogether, these results demonstrate that soluble factors secreted by B. abortus-infected astrocytes activate microglia to induce, via IL-6 trans-signaling, the death of neurons. IL-6 signaling inhibition may thus be considered a strategy to control inflammation and CNS damage in neurobrucellosis.

Intrahippocampal injection of IL-1β upregulates Siah1-mediated degradation of synaptophysin by activation of the ERK signaling in male rat

Interleukin-1β (IL-1β) has been described to exert important effect on synapses in the brain. Here, we explored if the synapses in the hippocampus would be adversely affected following intracerebral IL-1β injection and, if so, to clarify the underlying molecular mechanisms. Adult male Sprague-Dawley rats were divided into control, IL-1β, IL-1β + PD98059, and IL-1β + MG132 groups and then sacrificed for detection of synaptophysin (syn) protein level, synaptosome glutamate release, and synapse ultrastructure by western blotting, glutamate kit and electron microscopy, respectively. These rats were tested by Morris water maze for learning and memory ability. It was determined by western blotting whether IL-1β exerted the effect of on syn and siah1 expression in primary neurons via extracellular regulated protein kinases (ERK) signaling pathway. Intrahippocampal injection of IL-1β in male rats and sacrificed at 8d resulted in a significant decrease in syn protein, damage of synapse structure, and abnormal release of neurotransmitters glutamate. ERK inhibitor and proteosome inhibitor treatment reversed the above changes induced by IL-1β both in vivo and in vitro. In primary cultured neurons incubated with IL-1β, the expression level of synaptophysin was significantly downregulated coupled with abnormal glutamate release. Furthermore, use of PD98059 had confirmed that ERK signaling pathway was implicated in synaptic disorders caused by IL-1β treatment. The present results suggest that exogenous IL-1β can suppress syn protein level and glutamate release. A possible mechanism for this is that IL-1β induces syn degradation that is regulated by the E3 ligase siah1 via the ERK signaling pathway.

Expression of NLRP3 and AIM2 inflammasome in Peripheral blood in Chinese patients with acute and chronic brucellosis

Brucellosis is a zoonotic disease caused by Brucella abortus. An efficient immune response is crucial for curing brucellosis. The inflammasome plays a significant role in the immune response. It is unclear which inflammasome is active in acute and chronic brucellosis and how its levels relate to inflammatory cytokines. A total of 40 patients with acute or chronic brucellosis and 20 healthy volunteers had peripheral blood samples collected. The expression levels of AIM2, NLRP3, ASC, and Caspase-1 were determined by a real-time polymerase chain reaction from RNA and serum samples, and IL-1β, IL-18, and IFN-γ were measured by enzyme-linked immunosorbent assay. In the acute brucellosis group, AIM2 expression was significantly higher, while ACS expression was significantly lower than that of healthy volunteers. In patients with chronic brucellosis, AIM2 expression was significantly lower, while Caspase-1 expression was significantly higher than that of healthy volunteers. Serum IL-18 and IFN-γ levels were significantly higher in patients with acute brucellosis than in healthy controls. The IFN-γ level was also significantly higher in patients with chronic brucellosis than in healthy controls. The inflammasome responds differently in different stages of brucellosis. The inflammasome may be the site of action of immune escape in brucellosis.

Microglia at the Crossroads of Pathogen-Induced Neuroinflammation

Microglia are the resident tissue macrophages of the central nervous system (CNS). Recent findings point out that in the steady state the major role of microglia, is to instruct and regulate the correct function of the neuronal networks and different components of the neurovascular unit in the adult CNS, while providing immune surveillance. Paradoxically, during CNS infection immune activation of microglia generates an inflammatory milieu that contributes to the clearance of the pathogen but can, in the process, harm nearby cells of CNS. Most of the knowledge about the harmful effects of activated microglia on CNS has arisen from studies on neurodegenerative diseases. In this review we will focus on the beneficial role and detrimental functions of microglial cells on the neighboring cells of the CNS upon infection.

Neurobrucellosis: Brief Review

BACKGROUND

Brucella are small, nonmotile, intracellular, and aerobic gram-negative bacteria. Of the 10 species that currently form the genus Brucella, 5 were shown to be pathogenic in humans.

REVIEW SUMMARY

The epidemiology, clinical manifestations, diagnosis and imaging, and treatment of neurobrucellosis will be reviewed.Brucellosis's transmission to humans occurs by direct contact with contaminated animals. Older patients are at increased risk of nervous system involvement in brucellosis. Brucella spp. can lead to central nervous system involvement through direct damage via invasion of neural tissue or indirect damage caused by endotoxins or immune inflammatory reactions elicited by the presence of the bacteria in the body. Patients can have general nonspecific symptoms in addition to neurological and psychiatric symptoms. There are 4 diagnostic criteria for the diagnosis of neurobrucellosis, which include signs and symptoms suggestive of neurobrucellosis, a positive finding of Brucella spp. in the cerebrospinal fluid (CSF), and/or a positive titer of antibodies targeting brucella in the CSF, lymphocytosis with high protein levels and low glucose levels in CSF, and imaging findings (either cranial magnetic resonance imaging or computed tomography) peculiar to neurobrucellosis. For the treatment, a combined therapy is favored over monotherapy for the eradication of Brucella. Moreover, a multirouted therapy has been associated with increased treatment efficacy. The prognosis of neurobrucellosis is dependent on patients' clinical presentation: brucellar meningitis is associated with a good prognosis, whereas diffuse central nervous system involvement is associated with the development of long-term sequelae.

CONCLUSIONS

Neurobrucellosis affects patients globally and in endemic areas. Neurologists should familiarize themselves with its clinical presentation, diagnosis, and treatment to provide optimal care for their patients.

Transcriptomic analysis of human brain microvascular endothelial cells exposed to laminin binding protein (adhesion lipoprotein) and Streptococcus pneumoniae

Streptococcus pneumoniae invades the CNS and triggers a strong cellular response. To date, signaling events that occur in the human brain microvascular endothelial cells (hBMECs), in response to pneumococci or its surface adhesins are not mapped comprehensively. We evaluated the response of hBMECs to the adhesion lipoprotein (a laminin binding protein—Lbp) or live pneumococci. Lbp is a surface adhesin recently identified as a potential ligand, which binds to the hBMECs. Transcriptomic analysis was performed by RNA-seq of three independent biological replicates and validated with qRT-PCR using 11 genes. In total 350 differentially expressed genes (DEGs) were identified after infection with S. pneumoniae, whereas 443 DEGs when challenged with Lbp. Total 231 DEGs were common in both treatments. Integrative functional analysis revealed participation of DEGs in cytokine, chemokine, TNF signaling pathways and phagosome formation. Moreover, Lbp induced cell senescence and breakdown, and remodeling of ECM. This is the first report which maps complete picture of cell signaling events in the hBMECs triggered against S. pneumoniae and Lbp. The data obtained here could contribute in a better understanding of the invasion of pneumococci across BBB and underscores role of Lbp adhesin in evoking the gene expression in neurovascular unit.

Brucella abortus-Stimulated Platelets Activate Brain Microvascular Endothelial Cells Increasing Cell Transmigration through the Erk1/2 Pathway

Central nervous system invasion by bacteria of the genus Brucella results in an inflammatory disorder called neurobrucellosis. A common feature associated with this pathology is blood-brain barrier (BBB) activation. However, the underlying mechanisms involved with such BBB activation remain unknown. The aim of this work was to investigate the role of Brucella abortus-stimulated platelets on human brain microvascular endothelial cell (HBMEC) activation. Platelets enhanced HBMEC activation in response to B. abortus infection. Furthermore, supernatants from B. abortus-stimulated platelets also activated brain endothelial cells, inducing increased secretion of IL-6, IL-8, CCL-2 as well as ICAM-1 and CD40 upregulation on HBMEC compared with supernatants from unstimulated platelets. Outer membrane protein 19, a B. abortus lipoprotein, recapitulated B. abortus-mediated activation of HBMECs by platelets. In addition, supernatants from B. abortus-activated platelets promoted transendothelial migration of neutrophils and monocytes. Finally, using a pharmacological inhibitor, we demonstrated that the Erk1/2 pathway is involved in the endothelial activation induced by B. abortus-stimulated platelets and also in transendothelial migration of neutrophils. These results describe a mechanism whereby B. abortus-stimulated platelets induce endothelial cell activation, promoting neutrophils and monocytes to traverse the BBB probably contributing to the inflammatory pathology of neurobrucellosis.

Brucella abortus Infection Elicited Hepatic Stellate Cell-Mediated Fibrosis Through Inflammasome-Dependent IL-1β Production

In human brucellosis, the liver is frequently affected. Brucella abortus triggers a profibrotic response on hepatic stellate cells (HSCs) characterized by inhibition of MMP-9 with concomitant collagen deposition and TGF-β1 secretion through type 4 secretion system (T4SS). Taking into account that it has been reported that the inflammasome is necessary to induce a fibrotic phenotype in HSC, we hypothesized that Brucella infection might create a microenvironment that would promote inflammasome activation with concomitant profibrogenic phenotype in HSCs. B. abortus infection induces IL-1β secretion in HSCs in a T4SS-dependent manner. The expression of caspase-1 (Casp-1), absent in melanoma 2 (AIM2), Nod-like receptor (NLR) containing a pyrin domain 3 (NLRP3), and apoptosis-associated speck-like protein containing a CARD (ASC) was increased in B. abortus-infected HSC. When infection experiments were performed in the presence of glyburide, a compound that inhibits NLRP3 inflammasome, or A151, a specific AIM2 inhibitor, the secretion of IL-1β was significantly inhibited with respect to uninfected controls. The role of inflammasome activation in the induction of a fibrogenic phenotype in HSCs was determined by performing B. abortus infection experiments in the presence of the inhibitors Ac-YVAD-cmk and glyburide. Both inhibitors were able to reverse the effect of B. abortus infection on the fibrotic phenotype in HSCs. Finally, the role of inflammasome in fibrosis was corroborated in vivo by the reduction of fibrotic patches in liver from B. abortus-infected ASC, NLRP, AIM2, and cCasp-1/11 knock-out (KO) mice with respect to infected wild-type mice.

Brucella abortus Infection of Placental Trophoblasts Triggers Endoplasmic Reticulum Stress-Mediated Cell Death and Fetal Loss via Type IV Secretion System-Dependent Activation of CHOP

Subversion of endoplasmic reticulum (ER) function is a feature shared by multiple intracellular bacteria and viruses, and in many cases this disruption of cellular function activates pathways of the unfolded protein response (UPR). In the case of infection with Brucella abortus, the etiologic agent of brucellosis, the unfolded protein response in the infected placenta contributes to placentitis and abortion, leading to pathogen transmission. Here we show that B. abortus infection of pregnant mice led to death of infected placental trophoblasts in a manner that depended on the VirB type IV secretion system (T4SS) and its effector VceC. The trophoblast death program required the ER stress-induced transcription factor CHOP. While NOD1/NOD2 expression in macrophages contributed to ER stress-induced inflammation, these receptors did not play a role in trophoblast death. Both placentitis and abortion were independent of apoptosis-associated Speck-like protein containing a caspase activation and recruitment domain (ASC). These studies show that B. abortus uses its T4SS to induce cell-type-specific responses to ER stress in trophoblasts that trigger placental inflammation and abortion. Our results suggest further that in B. abortus the T4SS and its effectors are under selection as bacterial transmission factors.IMPORTANCEBrucella abortus infects the placenta of pregnant cows, where it replicates to high levels and triggers abortion of the calf. The aborted material is highly infectious and transmits infection to both cows and humans, but very little is known about how B. abortus causes abortion. By studying this infection in pregnant mice, we discovered that B. abortus kills trophoblasts, which are important cells for maintaining pregnancy. This killing required an injected bacterial protein (VceC) that triggered an endoplasmic reticulum (ER) stress response in the trophoblast. By inhibiting ER stress or infecting mice that lack CHOP, a protein induced by ER stress, we could prevent death of trophoblasts, reduce inflammation, and increase the viability of the pups. Our results suggest that B. abortus injects VceC into placental trophoblasts to promote its transmission by abortion.

Immune Mediators of Pathology in Neurobrucellosis: From Blood to Central Nervous System

Neurobrucellosis, which is the most morbid form of brucellosis disease, presents with inflammatory signs and symptoms. Recent experimental evidence clearly indicates that deregulation of astrocytes and microglia caused by Brucella infection creates a microenvironment in the central nervous system (CNS) in which secretion of pro-inflammatory mediators lead to destabilization of the glial structure, the damage of the blood brain barrier (BBB) and neuronal demise. This review of Brucella interactions with cells of the CNS and the BBB is intended to present recent immunological findings that can explain, at least in part, the basis for the inflammatory pathogenesis of the nervous system that takes place upon Brucella infection.

Common Differences: The Ability of Inflammasomes to Distinguish Between Self and Pathogen Nucleic Acids During Infection

The innate immune system detects the presence of pathogens based on detection of non-self. In other words, most pathogens possess intrinsic differences that can distinguish them from host cells. For example, bacteria and fungi have cell walls comprised of peptidoglycan and carbohydrates (like mannans), respectively. Germline encoded pattern recognition receptors (PRRs) of the Toll-like receptor (TLR) and C-type lectin receptor (CLR) family have the ability to detect such unique pathogen associated features. However, some TLRs and members of the RIG-I-like receptor (RLR), NOD-like receptor (NLR), or AIM2-like receptor (ALR) family can sense pathogen invasion based on pathogen nucleic acids. Nucleic acids are not unique to pathogens, thus raising the question of how such PRRs evolved to detect pathogens but not self. In this chapter, we will examine the PRRs that sense pathogen nucleic acids and subsequently activate the inflammasome signaling pathway. We will examine the selective mechanisms by which these receptors distinguish pathogens from "self" and discuss the importance of such pathways in disease development in animal models and human patients.

Cytosolic Recognition of Microbes and Pathogens: Inflammasomes in Action

Infection is a dynamic biological process underpinned by a complex interplay between the pathogen and the host. Microbes from all domains of life, including bacteria, viruses, fungi, and protozoan parasites, have the capacity to cause infection. Infection is sensed by the host, which often leads to activation of the inflammasome, a cytosolic macromolecular signaling platform that mediates the release of the proinflammatory cytokines interleukin-1β (IL-1β) and IL-18 and cleavage of the pore-forming protein gasdermin D, leading to pyroptosis. Host-mediated sensing of the infection occurs when pathogens inject or carry pathogen-associated molecular patterns (PAMPs) into the cytoplasm or induce damage that causes cytosolic liberation of danger-associated molecular patterns (DAMPs) in the host cell. Recognition of PAMPs and DAMPs by inflammasome sensors, including NLRP1, NLRP3, NLRC4, NAIP, AIM2, and Pyrin, initiates a cascade of events that culminate in inflammation and cell death. However, pathogens can deploy virulence factors capable of minimizing or evading host detection. This review presents a comprehensive overview of the mechanisms of microbe-induced activation of the inflammasome and the functional consequences of inflammasome activation in infectious diseases. We also explore the microbial strategies used in the evasion of inflammasome sensing at the host-microbe interaction interface.

Electroacupuncture Could Influence the Expression of IL-1β and NLRP3 Inflammasome in Hippocampus of Alzheimer's Disease Animal Model

Background

Effective therapies for Alzheimer's disease (AD) are still being explored. Electroacupuncture with traditional Chinese medicine theory may improve spatial learning and memory abilities and glucose metabolism rates in an animal model of AD. However, the mechanism of electroacupuncture in intervention of AD is still unclear. According to recent studies of AD mechanisms, the NLRP3 inflammasome regulated the expression of IL-1β in the brain which may mediate AD related processes. Therefore, in our study, we intend to explore the possible relation between electroacupuncture and the expression of NLRP 3 inflammasome in the hippocampus of an AD animal model.

Method

In this study, 7.5-month-old male senescence-accelerated mouse prone 8 (SAMP8) mice were used as an AD animal model, which were randomly divided into two groups: Alzheimer's disease model group (AD group) and electroacupuncture group (EA group). In the control paradigm, 7.5-month-old male SAMR1 mice were used as the normal control group (N group). DU20, DU26, and EX-HN3 were selected as the acupuncture points, and after a 15-day treatment of electroacupuncture, we used immunohistochemistry and Western blotting to examine the expression of IL-1β and NLRP3, ASC, and Caspase-1 in the hippocampus of the AD animal model.

Results

Compared with N group, IL-1β, NLRP3, ASC, and Caspase-1 positive cells in AD group were increased, and the relative expression of all above proteins significantly increased (P < 0.01). Compared with AD group, the expression of IL-1β, NLRP3, ASC, and Caspase-1 in EA group was significantly decreased (P < 0.01).

Conclusion

Electroacupuncture treatment could inhibit the inflammation reaction in the hippocampus of SAMP8 mice. What is more, the possible mechanism of electroacupuncture reduced the expression of IL-1β and NLRP3 inflammasome relative protein.

Brucella abortus Traverses Brain Microvascular Endothelial Cells Using Infected Monocytes as a Trojan Horse

Neurobrucellosis is an inflammatory disease caused by the invasion of Brucella spp. to the central nervous system (CNS). The pathogenesis of the disease is not well characterized; however, for Brucella to gain access to the brain parenchyma, traversing of the blood-brain barrier (BBB) must take place. To understand the CNS determinants of the pathogenesis of B. abortus, we have used the in vitro BBB model of human brain microvascular endothelial cells (HBMEC) to study the interactions between B. abortus and brain endothelial cells. In this study, we showed that B. abortus is able to adhere and invade HBMEC which was dependent on microtubules, microfilaments, endosome acidification and de novo protein synthesis. After infection, B. abortus rapidly escapes the endosomal compartment of HBMEC and forms a replicative Brucella-containing vacuole that involves interactions with the endoplasmic reticulum. Despite the ability of B. abortus to invade and replicate in HBMEC, the bacterium was unable by itself to traverse HBMEC, but could traverse polarized HBMEC monolayers within infected monocytes. Importantly, infected monocytes that traversed the HBMEC monolayer were a bacterial source for de novo infection of glial cells. This is the first demonstration of the mechanism whereby B. abortus is able to traverse the BBB and infect cells of the CNS. These results may have important implications in our understanding of the pathogenesis of neurobrucellosis.

Role of pattern recognition receptors of the neurovascular unit in inflamm-aging

Aging is associated with chronic inflammation partly mediated by increased levels of damage-associated molecular patterns, which activate pattern recognition receptors (PRRs) of the innate immune system. Furthermore, many aging-related disorders are associated with inflammation. PRRs, such as Toll-like receptors (TLRs) and nucleotide-binding oligomerization domain-like receptors (NLRs), are expressed not only in cells of the innate immune system but also in other cells, including cells of the neurovascular unit and cerebral vasculature forming the blood-brain barrier. In this review, we summarize our present knowledge about the relationship between activation of PRRs expressed by cells of the neurovascular unit-blood-brain barrier, chronic inflammation, and aging-related pathologies of the brain. The most important damage-associated molecular pattern-sensing PRRs in the brain are TLR2, TLR4, and NLR family pyrin domain-containing protein-1 and pyrin domain-containing protein-3, which are activated during physiological and pathological aging in microglia, neurons, astrocytes, and possibly endothelial cells and pericytes.

Brucella abortus-activated microglia induce neuronal death through primary phagocytosis

Inflammation has long been implicated as a contributor to pathogenesis in neurobrucellosis. Many of the associated neurocognitive symptoms of neurobrucellosis may be the result of neuronal dysfunction resulting from the inflammatory response induced by Brucella abortus infection in the central nervous system. In this manuscript, we describe an immune mechanism for inflammatory activation of microglia that leads to neuronal death upon B. abortus infection. B. abortus was unable to infect or harm primary cultures of mouse neurons. However, when neurons were co-cultured with microglia and infected with B. abortus significant neuronal loss occurred. This phenomenon was dependent on TLR2 activation by Brucella lipoproteins. Neuronal death was not due to apoptosis, but it was dependent on the microglial release of nitric oxide (NO). B. abortus infection stimulated microglial proliferation, phagocytic activity and engulfment of neurons. NO secreted by B. abortus-activated microglia induced neuronal exposure of the "eat-me" signal phosphatidylserine (PS). Blocking of PS-binding to protein milk fat globule epidermal growth factor-8 (MFG-E8) or microglial vitronectin receptor-MFG-E8 interaction was sufficient to prevent neuronal loss by inhibiting microglial phagocytosis without affecting their activation. Taken together, our results indicate that B. abortus is not directly toxic to neurons; rather, these cells become distressed and are killed by phagocytosis in the inflammatory surroundings generated by infected microglia. Neuronal loss induced by B. abortus-activated microglia may explain, in part, the neurological deficits observed during neurobrucellosis.

Brucella Melitensis 16M Regulates the Effect of AIR Domain on Inflammatory Factors, Autophagy, and Apoptosis in Mouse Macrophage through the ROS Signaling Pathway

Brucellosis is a highly contagious zoonosis caused by Brucella. Brucella can invade and persist inside host cells, which results in chronic infection. We constructed AIR interference and overexpression lentiviruses to acquire AIR interference, overexpression, and rescue stable expression cell lines. We also established a Brucella melitensis 16M-infected macrophage model, which was treated with either the vehicle control or NAC (ROS scavenger N-acetylcysteine (NAC) for 0, 3, 6, 12, and 24 h. Confocal laser microscopy, transmission electron microscopy, fluorescence quantitative PCR, flow cytometry, ELISA, and Western blot were used to detect inflammation, cell autophagy and apoptosis-related protein expression levels, ROS levels, and the distribution of mitochondria. It was found that after interference and overexpression of AIR, ROS release was significantly changed, and mitochondria became abnormally aggregated. B. melitensis 16M activated the NLRP3/AIM2 inflammatory complex, and induced RAW264.7 cells to secrete IL-1β and IL-18 through the ROS pathway. B. melitensis 16M also altered autophagy-related gene expression, increased autophagy activity, and induced cell apoptosis through the ROS pathway. The results showed that after B. melitensis 16M infection, ROS induced apoptosis, inflammation, and autophagy while AIR inhibited autophagosome maturation and autophagy initiation. Autophagy negatively regulated the activation of inflammasomes and prevented inflammation from occurring. In addition, mitophagy could promote cell apoptosis.

The role of NLRP3 and AIM2 in inflammasome activation during Brucella abortus infection

The innate immune system is essential for the detection and elimination of bacterial pathogens. Upon inflammasome activation, caspase-1 cleaves pro-IL-1β and pro-IL-18 to their mature forms IL-1β and IL-18, respectively, and the cell undergoes inflammatory death termed pyroptosis. Here, we reviewed recent findings demonstrating that Brucella abortus ligands activate NLRP3 and AIM2 inflammasomes which lead to control of infection. This protective effect is due to the inflammatory response caused by IL-1β and IL-18 rather than cell death. Brucella DNA is sensed by AIM2 and bacteria-induced mitochondrial reactive oxygen species is detected by NLRP3. However, deregulation of pro-inflammatory cytokine production can lead to immunopathology. Nervous system invasion by bacteria of the genus Brucella results in an inflammatory disorder termed neurobrucellosis. Herein, we discuss the mechanism of caspase-1 activation and IL-1β secretion in glial cells infected with B. abortus. Our results demonstrate that the ASC inflammasome is indispensable for inducing the activation of caspase-1 and secretion of IL-1β upon infection of astrocytes and microglia with Brucella. Moreover, our results demonstrate that secretion of IL-1β by Brucella-infected glial cells depends on NLRP3 and AIM2 and leads to neurobrucellosis. Further, the inhibition of the host cell inflammasome as an immune evasion strategy has been described for bacterial pathogens. We discuss here that the bacterial type IV secretion system VirB is required for inflammasome activation in host cells during infection. Taken together, our results indicate that Brucella is sensed by ASC inflammasomes mainly NLRP3 and AIM2 that collectively orchestrate a robust caspase-1 activation and pro-inflammatory response.