Herpes-simplex virus encephalitis is characterized by an early MMP-9 increase and collagen type IV degradation

Vulnerability of the Hippocampus to Insults: Links to Blood-Brain Barrier Dysfunction

The hippocampus is a critical brain substrate for learning and memory; events that harm the hippocampus can seriously impair mental and behavioral functioning. Hippocampal pathophysiologies have been identified as potential causes and effects of a remarkably diverse array of medical diseases, psychological disorders, and environmental sources of damage. It may be that the hippocampus is more vulnerable than other brain areas to insults that are related to these conditions. One purpose of this review is to assess the vulnerability of the hippocampus to the most prevalent types of insults in multiple biomedical domains (i.e., neuroactive pathogens, neurotoxins, neurological conditions, trauma, aging, neurodegenerative disease, acquired brain injury, mental health conditions, endocrine disorders, developmental disabilities, nutrition) and to evaluate whether these insults affect the hippocampus first and more prominently compared to other brain loci. A second purpose is to consider the role of hippocampal blood-brain barrier (BBB) breakdown in either causing or worsening the harmful effects of each insult. Recent research suggests that the hippocampal BBB is more fragile compared to other brain areas and may also be more prone to the disruption of the transport mechanisms that act to maintain the internal milieu. Moreover, a compromised BBB could be a factor that is common to many different types of insults. Our analysis indicates that the hippocampus is more vulnerable to insults compared to other parts of the brain, and that developing interventions that protect the hippocampal BBB may help to prevent or ameliorate the harmful effects of many insults on memory and cognition.

Transcription factor CEBPB mediates intracranial aneurysm rupture by inflammatory and immune response

INTRODUCTION

Genetic factors play a major part in mediating intracranial aneurysm (IA) rupture. However, research on the role of transcription factors (TFs) in IA rupture is rare.

AIMS

Bioinformatics analysis was performed to explore the TFs and related functional pathways involved in IA rupture.

RESULTS

A total of 63 differentially expressed transcription factors (DETFs) were obtained. Significantly enriched biological processes of these DETFs were related to regulation of myeloid leukocyte differentiation. The top 10 DETFs were screened based on the MCC algorithm from the protein-protein interaction network. After screening and validation, it was finally determined that CEBPB may be the hub gene for aneurysm rupture. The GSEA results of CEBPB were mainly associated with the inflammatory response, which was also verified by the experimental model of cellular inflammation in vitro.

CONCLUSION

The inflammatory and immune response may be closely associated with aneurysm rupture. CEBPB may be the hub gene for aneurysm rupture and may have diagnostic value. Therefore, CEBPB may serve as the diagnostic signature for RIAs and a potential target for intervention.

The Pathobiology of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: The Case for Neuroglial Failure

Although myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) has a specific and distinctive profile of clinical features, the disease remains an enigma because causal explanation of the pathobiological matrix is lacking. Several potential disease mechanisms have been identified, including immune abnormalities, inflammatory activation, mitochondrial alterations, endothelial and muscular disturbances, cardiovascular anomalies, and dysfunction of the peripheral and central nervous systems. Yet, it remains unclear whether and how these pathways may be related and orchestrated. Here we explore the hypothesis that a common denominator of the pathobiological processes in ME/CFS may be central nervous system dysfunction due to impaired or pathologically reactive neuroglia (astrocytes, microglia and oligodendrocytes). We will test this hypothesis by reviewing, in reference to the current literature, the two most salient and widely accepted features of ME/CFS, and by investigating how these might be linked to dysfunctional neuroglia. From this review we conclude that the multifaceted pathobiology of ME/CFS may be attributable in a unifying manner to neuroglial dysfunction. Because the two key features - post exertional malaise and decreased cerebral blood flow - are also recognized in a subset of patients with post-acute sequelae COVID, we suggest that our findings may also be pertinent to this entity.

Long COVID or Post-acute Sequelae of COVID-19 (PASC): An Overview of Biological Factors That May Contribute to Persistent Symptoms

The novel virus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused a pandemic of coronavirus disease 2019 (COVID-19). Across the globe, a subset of patients who sustain an acute SARS-CoV-2 infection are developing a wide range of persistent symptoms that do not resolve over the course of many months. These patients are being given the diagnosis Long COVID or Post-acute sequelae of COVID-19 (PASC). It is likely that individual patients with a PASC diagnosis have different underlying biological factors driving their symptoms, none of which are mutually exclusive. This paper details mechanisms by which RNA viruses beyond just SARS-CoV-2 have be connected to long-term health consequences. It also reviews literature on acute COVID-19 and other virus-initiated chronic syndromes such as post-Ebola syndrome or myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) to discuss different scenarios for PASC symptom development. Potential contributors to PASC symptoms include consequences from acute SARS-CoV-2 injury to one or multiple organs, persistent reservoirs of SARS-CoV-2 in certain tissues, re-activation of neurotrophic pathogens such as herpesviruses under conditions of COVID-19 immune dysregulation, SARS-CoV-2 interactions with host microbiome/virome communities, clotting/coagulation issues, dysfunctional brainstem/vagus nerve signaling, ongoing activity of primed immune cells, and autoimmunity due to molecular mimicry between pathogen and host proteins. The individualized nature of PASC symptoms suggests that different therapeutic approaches may be required to best manage care for specific patients with the diagnosis.

Age influences susceptibility of brain capillary endothelial cells to La Crosse virus infection and cell death

Background

A key factor in the development of viral encephalitis is a virus crossing the blood-brain barrier (BBB). We have previously shown that age-related susceptibility of mice to the La Crosse virus (LACV), the leading cause of pediatric arbovirus encephalitis in the USA, was associated with the ability of the virus to cross the BBB. LACV infection in weanling mice (aged around 3 weeks) results in vascular leakage in the olfactory bulb/tract (OB/OT) region of the brain, which is not observed in adult mice aged > 6–8 weeks. Thus, we studied age-specific differences in the response of brain capillary endothelial cells (BCECs) to LACV infection.

Methods

To examine mechanisms of LACV-induced BBB breakdown and infection of the CNS, we analyzed BCECs directly isolated from weanling and adult mice as well as established a model where these cells were infected in vitro and cultured for a short period to determine susceptibility to virus infection and cell death. Additionally, we utilized correlative light electron microscopy (CLEM) to examine whether changes in cell morphology and function were also observed in BCECs in vivo.

Results

BCECs from weanling, but not adult mice, had detectable infection after several days in culture when taken ex vivo from infected mice suggesting that these cells could be infected in vitro. Further analysis of BCECs from uninfected mice, infected in vitro, showed that weanling BCECs were more susceptible to virus infection than adult BCECs, with higher levels of infected cells, released virus as well as cytopathic effects (CPE) and cell death. Although direct LACV infection is not detected in the weanling BCECs, CLEM analysis of brain tissue from weanling mice indicated that LACV infection induced significant cerebrovascular damage which allowed virus-sized particles to enter the brain parenchyma.

Conclusions

These findings indicate that BCECs isolated from adult and weanling mice have differential viral load, infectivity, and susceptibility to LACV. These age-related differences in susceptibility may strongly influence LACV-induced BBB leakage and neurovascular damage allowing virus invasion of the CNS and the development of neurological disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02173-4.

Immunomodulatory Strategies in Herpes Simplex Virus Encephalitis

Herpes simplex virus 1 (HSV-1) can be responsible for life-threatening HSV encephalitis (HSE). The mortality rate of patients with HSE who do not receive antiviral treatment is 70%, with most survivors suffering from permanent neurological sequelae. The use of intravenous acyclovir together with improved diagnostic technologies such as PCR and magnetic resonance imaging has resulted in a reduction in the mortality rate to close to 20%. However, 70% of surviving patients still do not recover complete neurological functions. Thus, there is an urgent need to develop more effective treatments for a better clinical outcome. It is well recognized that cerebral damage resulting from HSE is caused by viral replication together with an overzealous inflammatory response. Both of these processes constitute potential targets for the development of innovative therapies against HSE. In this review, we discuss recent progress in therapy that may be used to ameliorate the outcome of patients with HSE, with a particular emphasis on immunomodulatory agents. Ideally, the administration of adjunctive immunomodulatory drugs should be initiated during the rise of the inflammatory response, and its duration should be limited in time to reduce undesired effects. This critical time frame should be optimized by the identification of reliable biomarkers of inflammation.

Human Coronaviruses and Other Respiratory Viruses: Underestimated Opportunistic Pathogens of the Central Nervous System?

Respiratory viruses infect the human upper respiratory tract, mostly causing mild diseases. However, in vulnerable populations, such as newborns, infants, the elderly and immune-compromised individuals, these opportunistic pathogens can also affect the lower respiratory tract, causing a more severe disease (e.g., pneumonia). Respiratory viruses can also exacerbate asthma and lead to various types of respiratory distress syndromes. Furthermore, as they can adapt fast and cross the species barrier, some of these pathogens, like influenza A and SARS-CoV, have occasionally caused epidemics or pandemics, and were associated with more serious clinical diseases and even mortality. For a few decades now, data reported in the scientific literature has also demonstrated that several respiratory viruses have neuroinvasive capacities, since they can spread from the respiratory tract to the central nervous system (CNS). Viruses infecting human CNS cells could then cause different types of encephalopathy, including encephalitis, and long-term neurological diseases. Like other well-recognized neuroinvasive human viruses, respiratory viruses may damage the CNS as a result of misdirected host immune responses that could be associated with autoimmunity in susceptible individuals (virus-induced neuro-immunopathology) and/or viral replication, which directly causes damage to CNS cells (virus-induced neuropathology). The etiological agent of several neurological disorders remains unidentified. Opportunistic human respiratory pathogens could be associated with the triggering or the exacerbation of these disorders whose etiology remains poorly understood. Herein, we present a global portrait of some of the most prevalent or emerging human respiratory viruses that have been associated with possible pathogenic processes in CNS infection, with a special emphasis on human coronaviruses.

β-Arrestin 2 protects against neurological function defects in HSV-1-induced encephalitis mice

The pathogenesis of herpes simplex encephalitis (HSE) needs to be fully explored. β-Arrestin 2 (Arrb2) is highly expressed in brain tissues and plays a key role in the regulation of systemic immune reactions by modulating various signaling pathways. However, the expression of Arrb2 in microglial cells and its influence on HSE prognosis is still undefined. We explore the pathophysiological effect of Arrb2 in the brain using experimental HSE mice. The expression of Arrb2 in microglia was decreased significantly 48 hours following HSV-1 infection. Arrb2 overexpression transgenic (TG) mice had a significantly lower mortality and survival rate was improved by 40% compared to wild-type mice. Arrb2 suppressed the generation of proinflammatory cytokines TNF-α and IL-6 and increased anti-inflammatory cytokines IL-10 and IL-4 expression. Arrb2 also inhibited the activation of the transcription factor NF-κB in microglial cells. Arrb2 TG mice attenuated the blood-brain barrier breakdown and relieved cerebral edema, meanwhile, Arrb2 improved mice neurological function compared with wild-type mice. Overall, Arrb2 favored microglia of the M2 phenotype, attenuated brain proinflammatory responses, protected the blood vessel wall integrity, reduced HSV-1-induced neurological impairment, and improved the survival rate in HSE mice.

MMPs and ADAMs in neurological infectious diseases and multiple sclerosis

Metalloproteinases-such as matrix metalloproteinases (MMPs) and a disintegrin and metalloproteinases (ADAMs)-are involved in various diseases of the nervous system but also contribute to nervous system development, synaptic plasticity and neuroregeneration upon injury. MMPs and ADAMs proteolytically cleave many substrates including extracellular matrix components but also signaling molecules and receptors. During neuroinfectious disease with associated neuroinflammation, MMPs and ADAMs regulate blood-brain barrier breakdown, bacterial invasion, neutrophil infiltration and cytokine signaling. Specific and broad-spectrum inhibitors for MMPs and ADAMs have experimentally been shown to decrease neuroinflammation and brain damage in diseases with excessive neuroinflammation as a common denominator, such as pneumococcal meningitis and multiple sclerosis, thereby improving the disease outcome. Timing of metalloproteinase inhibition appears to be critical to effectively target the cascade of pathophysiological processes leading to brain damage without inhibiting the neuroregenerative effects of metalloproteinases. As the critical role of metalloproteinases in neuronal repair mechanisms and regeneration was only lately recognized, the original idea of chronic MMP inhibition needs to be conceptually revised. Recently accumulated research urges for a second chance of metalloproteinase inhibitors, which-when correctly applied and dosed-harbor the potential to improve the outcome of different neuroinflammatory diseases.

Proteomics analysis of HSV-1-induced alterations in mouse brain microvascular endothelial cells

Herpes simplex virus 1 (HSV-1) is a predominant cause of herpes simplex encephalitis (HSE), leading to a high mortality rate and severe neurological sequelae worldwide. HSE is typically accompanied by the blood-brain barrier (BBB) disruption, but the underlying mechanisms are unclear. To explore the disruption mechanisms of the BBB, quantitative analysis of the cellular proteome was carried out to investigate the proteomic changes that occur after infection. In this study, bEnd.3 cells were infected with HSV-1, followed by liquid chromatography-tandem mass spectrometry. A total of 6761 proteins were identified in three independent mass spectrometry analyses. Compared to the uninfected cells, 386 and 293 differentially expressed proteins were markedly upregulated or downregulated, respectively. Bioinformatic analysis showed that the activator protein-1 factor, including Fos, Jun, and ATF family proteins and cell adhesion molecules were significantly changed. Further validation of the changes observed for these proteins was carried out by western blotting and quantitative real-time PCR. Transendothelial electrical resistance (TEER) studies were performed to explore the effects of ATF3, Fra1, or JunB overexpression on the function of bEnd.3 cells. Characterization of the differential expression of these proteins in bEnd.3 cells will facilitate further exploration of BBB disruption upon HSV-1 infection.

Chemokines and matrix metalloproteinases in cerebrospinal fluid of patients with central nervous system complications caused by varicella-zoster virus

BACKGROUND

Varicella-zoster virus (VZV) is a common viral agent causing central nervous system (CNS) infections including encephalitis, meningitis, and Ramsay Hunt syndrome. Neurological complications occur frequently despite antiviral treatment. Matrix metalloproteinases (MMPs) and cytokines are involved in the neuroinflammatory response during CNS infection. Their role in VZV CNS infections and how they differ between different CNS entities caused by VZV are poorly investigated.

METHODS

We analyzed the levels of 30 chemokines and 9 MMPs in cerebrospinal fluid (CSF) and serum from 66 patients with VZV CNS infections diagnosed by detection of VZV DNA in CSF and concomitant neurological symptoms and compared with a control group (n = 24).

RESULTS

Levels of CCL19, CXCL8, CXCL9, and CXCL10 were significantly increased and surpassing the levels in serum when analyzing all patients with VZV CNS infections whereas CXCL11 was only increased in CSF of patients with VZV meningitis. MMP-2-levels were highly elevated in CSF of all 66 VZV patients. The patients with encephalitis had the most significantly increased levels of MMPs in CSF, and MMP-3, MMP-8, and MMP-12 were exclusively increased in this group, whereas MMP-9 in CSF was increased in the patients with VZV meningitis.

CONCLUSIONS

We show that both chemokines and MMPs are elevated in the CSF of patients with VZV CNS infections. Encephalitis and meningitis patients differed with respect to other chemokines (CXCL11) and MMPs (MMP-3, MMP-8, MMP-9, and MMP-12), indicating that different location of the virus gives rise to qualitative differences in the ensuing inflammatory response. In addition, the pronounced increase of MMPs in CSF of the patients with encephalitis suggests an association to the severity of this manifestation, compared to VZV meningitis and Ramsay Hunt syndrome. The role of MMPs in association to chemokines should be further investigated to evaluate their significance in the neuropathogenesis of VZV CNS infections and as a potential target for new treatment alternatives.

Cerebrovascular manifestations of herpes simplex virus infection of the central nervous system: a systematic review

BACKGROUND

Intracerebral hemorrhage and ischemic stroke are increasingly recognized complications of central nervous system (CNS) infection by herpes simplex virus (HSV).

AIM OF THE STUDY

To analyze clinical, imaging, and laboratory findings and outcomes of cerebrovascular manifestations of HSV infection.

METHODS

Systematic literature review from January 2000 to July 2018.

RESULTS

We identified 38 patients (median age 45 years, range 1-73) comprising 27 cases of intracerebral hemorrhage, 10 of ischemic stroke, and 1 with cerebral venous sinus thrombosis. Intracerebral hemorrhage was predominantly (89%) a complication of HSV encephalitis located in the temporal lobe. Hematoma was present on the first brain imaging in 32%, and hematoma evacuation was performed in 30% of these cases. Infarction was frequently multifocal, and at times preceded by hemorrhage (20%). Both a stroke-like presentation and presence of HSV encephalitis in a typical location were rare (25% and 10%, respectively). There was evidence of cerebral vasculitis in 63%, which was exclusively located in large-sized vessels. Overall mortality was 21% for hemorrhage and 0% for infarction. HSV-1 was a major cause of hemorrhagic complications, whereas HSV-2 was the most prevalent agent in the ischemic manifestations.

CONCLUSION

We found a distinct pathogenesis, cause, and outcome for HSV-related cerebral hemorrhage and infarction. Vessel disruption within a temporal lobe lesion caused by HSV-1 is the presumed mechanism for hemorrhage, which may potentially have a fatal outcome. Brain ischemia is mostly related to multifocal cerebral large vessel vasculitis associated with HSV-2, where the outcome is more favorable.

Mechanisms of Blood-Brain Barrier Disruption in Herpes Simplex Encephalitis

Herpes simplex encephalitis (HSE) is often caused by infection with herpes simplex virus 1 (HSV-1), a neurotropic double-stranded DNA virus. HSE infection always impacts the temporal and frontal lobes or limbic system, leading to edema, hemorrhage, and necrotic changes in the brain parenchyma. Additionally, patients often exhibit severe complications following antiviral treatment, including dementia and epilepsy. HSE is further associated with disruptions to the blood-brain barrier (BBB), which consists of microvascular endothelial cells, tight junctions, astrocytes, pericytes, and basement membranes. Following an HSV-1 infection, changes in BBB integrity and permeability can result in increased movement of viruses, immune cells, and/or cytokines into the brain parenchyma. This leads to an enhanced inflammatory response in the central nervous system and further damage to the brain. Thus, it is important to protect the BBB from pathogens to reduce brain damage from HSE. Here, we discuss HSE and the normal structure and function of the BBB. We also discuss growing evidence indicating an association between BBB breakdown and the pathogenesis of HSE, as well as future research directions and potential new therapeutic targets. Graphical Abstract During herpes simplex encephalitis, the functions and structures of each composition of BBB have been altered by different factors, thus the permeability and integrity of BBB have been broken. The review aim to explore the potential mechanisms and factors in the process, probe the next research targets and new therapeutic targets.

Insights into the pathogenesis of herpes simplex encephalitis from mouse models

A majority of the world population is infected with herpes simplex viruses (HSV; human herpesvirus types 1 and 2). These viruses, perhaps best known for their manifestation in the genital or oral mucosa, can also cause herpes simplex encephalitis, a severe and often fatal disease of the central nervous system. Antiviral therapies for HSV are only partially effective since the virus can establish latent infections in neurons, and severe pathological sequelae in the brain are common. A better understanding of disease pathogenesis is required to develop new strategies against herpes simplex encephalitis, including the precise viral and host genetic determinants that promote virus invasion into the central nervous system and its associated immunopathology. Here we review the current understanding of herpes simplex encephalitis from the host genome perspective, which has been illuminated by groundbreaking work on rare herpes simplex encephalitis patients together with mechanistic insight from single-gene mouse models of disease. A complex picture has emerged, whereby innate type I interferon-mediated antiviral signaling is a central pathway to control viral replication, and the regulation of immunopathology and the balance between apoptosis and autophagy are critical to disease severity in the central nervous system. The lessons learned from mouse studies inform us on fundamental defense mechanisms at the interface of host–pathogen interactions within the central nervous system, as well as possible rationales for intervention against infections from severe neuropathogenic viruses.

Protective role of CX3CR1 signalling in resident cells of the central nervous system during experimental herpes simplex virus encephalitis

CX3CR1 is an important chemokine receptor expressed on the surface of microglia and blood leukocytes, including monocytes. Signalling through this receptor influences the immune activity of microglia and monocyte trafficking into the central nervous system (CNS) in several neurological diseases. During experimental herpes simplex virus 1 (HSV-1) encephalitis (HSE), CX3CR1 deficiency has been reported to exacerbate the outcome of the disease. However, the precise contribution of CX3CR1 expressed in resident cells of the CNS or peripheral monocytes in protection against HSE remains unclear. To dissect the role of CX3CR1 during HSE, we reconstituted irradiated C57BL/6 WT and CX3CR1-/- mice with CX3CR1-/- (CX3CR1-/-→WT) and WT (WT→CX3CR1-/-) bone marrow cells, respectively. Our results showed that following intranasal infection with 1.2×106 p.f.u. of HSV-1, mortality rates were significantly higher in CX3CR1-/- (61.7 %) and WT→CX3CR1-/- (66.2 %) compared to WT (16.6 %; P=0.012 and P=0.016, respectively) and CX3CR1-/-→WT animals (20 %; P=0.013 and P=0.011, respectively). Higher mortality rates in CX3CR1-/- and WT→CX3CR1-/- mice were associated with increased infectious viral titres and wider HSV dissemination in brains, as well as an overproduction of inflammatory cytokines and chemokines including IL-1β, IL-6, IFN-γ, C-C motif ligand 2 and C-C motif ligand 5. Furthermore, CX3CR1 deficiency in resident cells of the CNS resulted in excessive and sustained Ly6Chi inflammatory monocyte and neutrophil infiltration into the brain. These data suggest that CX3CR1 deficiency in resident cells of the CNS affects mouse survival, HSV-1 replication control and cerebral inflammatory response whereas its deficiency in the haematopoietic system does not appear to influence the outcome of HSE.

The effect of captopril on the expression of MMP-9 and the prognosis of neurological function in herpes simplex encephalitis mice

BACKGROUND AND PURPOSE

Early increased matrix metalloproteinase-9 (MMP-9) expression is involved in the evolution of herpes simplex encephalitis (HSE) by facilitating the development of cerebrovascular complications. However, the molecular mechanism underlying the detrimental effects of MMP-9 in HSE has not been elucidated. Recent research finds angiotensin II plays an important role in regulation of MMP-9 activity. The aim of this work was to identify the influence of angiotensin-converting enzyme inhibitor (ACEI) captopril on MMP-9 activation after herpes simplex virus 1 (HSV-1) infection.

METHODS

Animal models of HSE were established by intracerebral inoculation of HSV-1 into mice. Brain tissue ROS levels were measured by staining with dihydroethidium. MMP-9 protein expression was detected by immunofluorescence and brain water content was measured with dry-wet weight method. Neurological function score was quantified 5 d after HSV-1 infection. Microglial cells were treated with various concentrations of captopril. MMP-9 gelatinolytic activity in the supematant of the cell cultures was assessed by zymography. RT-PCR was used to detect the mRNA expressions of p47phox and MMP-9.

RESULTS

Immunofluorescence showed that expression of MMP-9 in brain tissue was mainly presented in OX-42 positive microglia. Quantification of gelatinolytic activity by densitometry showed that expression of MMP-9 in microglia was significantly increased after HSV-1 infection and inhibited by captopril treatment. NADPH oxidase subunit p47phox and MMP-9 mRNA expression were significantly increased 6 h after HSV-1 infection, and were seen reduced after captopril treatment in dose dependence. Captopril also downregulated ROS and MMP-9 protein expression following encephalitis in vivo, and attenuated brain edema, and improved neurological function.

DISCUSSION

This compelling evidence suggests that MMP-9 is a key pathogenic factor within HSE. ACEI captopril could reduce the expression of MMP-9 mediated by ROS, then relieve cerebral edema and improve neurological function, which may lay a foundation for further basic research and clinical application.

Neuroinvasion and Inflammation in Viral Central Nervous System Infections

Neurotropic viruses can cause devastating central nervous system (CNS) infections, especially in young children and the elderly. The blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB) have been described as relevant sites of entry for specific viruses as well as for leukocytes, which are recruited during the proinflammatory response in the course of CNS infection. In this review, we illustrate examples of established brain barrier models, in which the specific reaction patterns of different viral families can be analyzed. Furthermore, we highlight the pathogen specific array of cytokines and chemokines involved in immunological responses in viral CNS infections. We discuss in detail the link between specific cytokines and chemokines and leukocyte migration profiles. The thorough understanding of the complex and interrelated inflammatory mechanisms as well as identifying universal mediators promoting CNS inflammation is essential for the development of new diagnostic and treatment strategies.

Mouse Adenovirus Type 1 Early Region 1A Effects on the Blood-Brain Barrier

Encephalitis can be caused by viruses, and it is potentially life-threatening because of the vital nature of the brain and the lack of treatment options. MAV-1 produces viral encephalitis in its natural host, providing a model for investigating factors involved in development of encephalitis. MAV-1 infection disrupts the BBB and increases activity of matrix metalloproteinases in brains of infected mice. We investigated whether the major transcriptional regulator of adenoviruses, E1A protein, is responsible for any of the specific phenotypes that result from MAV-1 infection. For some of the functions assayed, an E1A mutant virus behaved like wild-type virus. However, expression of mRNA for one matrix metalloproteinase was higher in the virus lacking E1A protein production. This highlights the complex nature of encephalitis and suggests that E1A may have transcriptional effects on host genes important for the development of encephalitis.

Mouse adenovirus type 1 (MAV-1) infects endothelial cells and disrupts the blood-brain barrier (BBB), causing encephalitis in inbred and outbred mice. Using a virus mutant that does not produce the early region 1A protein E1A, we investigated whether the activity of this known viral transcriptional regulator is needed for BBB disruption and other phenotypes associated with encephalitis. The wild-type (wt) virus and E1A mutant virus caused similar levels of permeability of sodium fluorescein in brains of infected mice. In an in vitro assay of BBB integrity, wt and mutant virus caused similar decreases in transendothelial electrical resistance in primary mouse brain endothelial cell monolayers. These results indicate that E1A protein does not contribute to disruption of BBB integrity in animals or cultured cells. Both wt and E1A mutant virus infection of mice led to similar increases in the activity of two matrix metalloproteinases known to correlate with BBB disruption, MMP2 and MMP9, while causing no increase in the steady-state expression of MMP2 or MMP9 mRNA. In contrast, the amount of MMP3 transcripts increased upon infection by both viruses and to a higher level in infections by the mutant virus lacking E1A protein production. There was no difference in the levels of steady-state expression of mRNA for tight junction proteins among mock virus, wt virus, and mutant virus infections. Thus, the MAV-1 E1A protein does not measurably affect BBB integrity in the parameters assayed, although it reduces the amount of MMP3 mRNA steady-state expression induced in brains upon infection.

IMPORTANCE Encephalitis can be caused by viruses, and it is potentially life-threatening because of the vital nature of the brain and the lack of treatment options. MAV-1 produces viral encephalitis in its natural host, providing a model for investigating factors involved in development of encephalitis. MAV-1 infection disrupts the BBB and increases activity of matrix metalloproteinases in brains of infected mice. We investigated whether the major transcriptional regulator of adenoviruses, E1A protein, is responsible for any of the specific phenotypes that result from MAV-1 infection. For some of the functions assayed, an E1A mutant virus behaved like wild-type virus. However, expression of mRNA for one matrix metalloproteinase was higher in the virus lacking E1A protein production. This highlights the complex nature of encephalitis and suggests that E1A may have transcriptional effects on host genes important for the development of encephalitis.

MMP-9 in translation: from molecule to brain physiology, pathology, and therapy

Matrix metalloproteinase-9 (MMP-9) is a member of the metzincin family of mostly extracellularly operating proteases. Despite the fact that all of these enzymes might be target promiscuous, with largely overlapping catalogs of potential substrates, MMP-9 has recently emerged as a major and apparently unique player in brain physiology and pathology. The specificity of MMP-9 may arise from its very local and time-restricted actions, even when released in the brain from cells of various types, including neurons, glia, and leukocytes. In fact, the quantity of MMP-9 is very low in the naive brain, but it is markedly activated at the levels of enzymatic activity, protein abundance, and gene expression following various physiological stimuli and pathological insults. Neuronal MMP-9 participates in synaptic plasticity by controlling the shape of dendritic spines and function of excitatory synapses, thus playing a pivotal role in learning, memory, and cortical plasticity. When improperly unleashed, MMP-9 contributes to a large variety of brain disorders, including epilepsy, schizophrenia, autism spectrum disorder, brain injury, stroke, neurodegeneration, pain, brain tumors, etc. The foremost mechanism of action of MMP-9 in brain disorders appears to be its involvement in immune/inflammation responses that are related to the enzyme's ability to process and activate various cytokines and chemokines, as well as its contribution to blood-brain barrier disruption, facilitating the extravasation of leukocytes into brain parenchyma. However, another emerging possibility (i.e., the control of MMP-9 over synaptic plasticity) should not be neglected. The translational potential of MMP-9 has already been recognized in both the diagnosis and treatment domains. The most striking translational aspect may be the discovery of MMP-9 up-regulation in a mouse model of Fragile X syndrome, quickly followed by human studies and promising clinical trials that have sought to inhibit MMP-9. With regard to diagnosis, suggestions have been made to use MMP-9 alone or combined with tissue inhibitor of matrix metalloproteinase-1 or brain-derived neurotrophic factor as disease biomarkers. MMP-9, through cleavage of specific target proteins, plays a major role in synaptic plasticity and neuroinflammation, and by those virtues contributes to brain physiology and a host of neurological and psychiatric disorders. This article is part of the 60th Anniversary special issue.

Infiltration Pattern of Blood Monocytes into the Central Nervous System during Experimental Herpes Simplex Virus Encephalitis

The kinetics and distribution of infiltrating blood monocytes into the central nervous system and their involvement in the cerebral immune response together with resident macrophages, namely microglia, were evaluated in experimental herpes simplex virus 1 (HSV-1) encephalitis (HSE). To distinguish microglia from blood monocyte-derived macrophages, chimeras were generated by conditioning C57BL/6 recipient mice with chemotherapy regimen followed by transplantation of bone morrow-derived cells that expressed the green fluorescent protein. Mice were infected intranasally with a sub-lethal dose of HSV-1 (1.2x10⁶ plaque forming units). Brains were harvested prior to and on days 4, 6, 8 and 10 post-infection for flow cytometry and immunohistochemistry analysis. The amounts of neutrophils (P<0.05) and «Ly6C^hi» inflammatory monocytes (P<0.001) significantly increased in the CNS compared to non-infected controls on day 6 post-infection, which corresponded to more severe clinical signs of HSE. Levels decreased on day 8 for both leukocytes subpopulations (P<0.05 for inflammatory monocytes compared to non-infected controls) to reach baseline levels on day 10 following infection. The percentage of «Ly6C^low» patrolling monocytes significantly increased (P<0.01) at a later time point (day 8), which correlated with the resolution phase of HSE. Histological analysis demonstrated that blood leukocytes colonized mostly the olfactory bulb and the brainstem, which corresponded to regions where HSV-1 particles were detected. Furthermore, infiltrating cells from the monocytic lineage could differentiate into activated local tissue macrophages that express the microglia marker, ionized calcium-binding adaptor molecule 1. The lack of albumin detection in the brain parenchyma of infected mice showed that the infiltration of blood leukocytes was not necessarily related to a breakdown of the blood-brain barrier but could be the result of a functional recruitment. Thus, our findings suggest that blood monocyte-derived macrophages infiltrate the central nervous system and may contribute, with resident microglia, to the innate immune response seen during experimental HSE.

Leptomeningeal contrast enhancement and blood-CSF barrier dysfunction in aseptic meningitis

Objective:

To investigate the blood-CSF barrier (BCSFB) dysfunction in aseptic meningitis.

Methods:

In our case series of 14 patients with acute aseptic meningitis, we compared MRI characteristics with CSF findings.

Results:

Contrast enhancement in the sulcal space in a leptomeningeal pattern was visualized in 7 patients with BCSFB dysfunction categorized as moderate to severe as evidenced by the CSF/serum albumin ratio (Q_alb) but was not present in those with mild or no barrier disturbance (p = 0.001). The Q_alb as a marker for the leakiness of the BCSFB and, more indirectly, of the blood-brain barrier (BBB) was positively correlated with the incidence of leptomeningeal contrast enhancement seen on postcontrast fluid-attenuated inversion recovery (FLAIR) MRI (p = 0.003). Patients with a more pronounced brain barrier dysfunction recovered more slowly and stayed longer in the hospital.

Conclusions:

The severity of meningeal BBB disturbance can be estimated on postcontrast FLAIR MRI, which may be of diagnostic value in patients with aseptic meningitis.

Viral sensing at the blood-brain barrier: new roles for innate immunity at the CNS vasculature

Neurotropic viral infections are a major source of disease worldwide and represent a growing burden to public health. While the central nervous system (CNS) is normally protected from viral infection by the blood-brain barrier (BBB), many viruses are able to cross the BBB and establish CNS infection through processes that largely remain poorly understood. A growing body of recent research has begun to shed light on the viral and host factors that modulate BBB function, contributing to both protective and pathological disease processes. Central to these studies have been the actions of host cytokines and chemokines, which have increasingly been shown to be key regulators of BBB physiology. This review summarizes recent advances in understanding how BBB function governs both viral pathogenesis and host immune responses during neurotropic viral infections.

Matrix metalloproteinase-9 leads to blood-brain barrier leakage in mice with eosinophilic meningoencephalitis caused by Angiostrongylus cantonensis

Blood-brain barrier (BBB) disruption is associated with tight junction protein degradation, basal membrane disruption, and astrocyte damage. This study aims to investigate the role of matrix metalloproteinase (MMP)-9 in BBB disruption during Angiostrongylus cantonensis infection. We used mice infected with A. cantonensis, in which parasite-induced eosinophilia and inflammation might induce MMP-9 elevation. MMP-9 could cause claudin-5 degradation in endothelium tight junction, collagen type IV degradation in basal membranes, and S100B degradation in astrocytes of wild-type mice. BBB permeability was significantly attenuated in MMP-9 knockout mice than in wild-type mice in angiostrongyliasis meningoencephalitis. Immune cell aggregates were also more attenuated in the brains of MMP-9 knockout mice than in the brains of wild-type mice. Results suggest that MMP-9 activities are significant in BBB disruption in angiostrongyliasis meningoencephalitis. This study improves understanding of molecular mechanisms that underlie brain invasion by A. cantonensis, which is a key step in the pathogenesis of meningoencephalitis, and can offer a new strategy to reduce mortality.

Enhanced resistance of CXCR3 deficient mice to ocular HSV-1 infection is due to control of replication in the brain ependyma

CXCR3 deficient (CXCR3(-/-)) mice are resistant to ocular HSV-1 infection in that less mice develop encephalitis and succumb to infection in comparison to wild type (WT) animals. A region of the brain previously identified to be crucial for development of encephalitis was evaluated in HSV-1-infected CXCR3(-/-) and WT mice. In this region, known as the ependyma, viral titer, infiltrating leukocyte populations, and key anti-viral cytokine message levels were evaluated. We found that CXCR3(-/-) mice possessed significantly less HSV-1 and expressed significantly more IFN-β mRNA in the brain ependyma compared to WT animals during the development of encephalitis.

Neurofilament heavy chain as a marker of neuroaxonal pathology and prognosis in acute encephalitis

BACKGROUND AND PURPOSE

The neurological outcome of acute encephalitis can be devastating and early prognosis remains difficult. Biomarkers that quantify the extent of early brain injury are needed to improve the prognostic accuracy and aid patient management. Our objective was to assess whether cerebrospinal fluid (CSF) protein biomarkers of neuroaxonal and glial cell injury are elevated in distinct forms of acute encephalitis and predictive of poor outcome.

METHODS

This was a prospective study of patients presenting with acute encephalitis to three teaching hospitals in London, UK. Levels of neurofilament heavy chain (NfH, SMI35) and S100B were quantified in CSF using enzyme-linked immunosorbent assay. The outcome was assessed by the Glasgow Outcome Scale (GOS).

RESULTS

Fifty-six patients with acute encephalitis were recruited and classified into the following diagnostic categories: infectious (n = 20), inflammatory (n = 14) and unknown etiology (n = 22). Pathological levels of NfH and S100B were observed in 24/56 (43%) and 54/56 (96%), respectively. Patients with infectious encephalitis had significantly higher NfH levels compared with the other two groups (P < 0.05). A poor outcome (GOS < 5) was associated with significantly higher CSF NfH levels within samples taken 2 weeks after symptom onset.

CONCLUSIONS

This study suggests that longitudinal CSF NfH levels are of superior prognostic value compared with CSF S100B levels. Prolonged release of NfH, a marker of neuroaxonal damage, was associated with poor outcome. Potentially there is a window of opportunity for future neuroprotective treatment strategies in encephalitis.

Whole brain radiation-induced cognitive impairment: pathophysiological mechanisms and therapeutic targets

Radiation therapy, the most commonly used for the treatment of brain tumors, has been shown to be of major significance in tu-mor control and survival rate of brain tumor patients. About 200,000 patients with brain tumor are treated with either partial large field or whole brain radiation every year in the United States. The use of radiation therapy for treatment of brain tumors, however, may lead to devastating functional deficits in brain several months to years after treatment. In particular, whole brain radiation therapy results in a significant reduction in learning and memory in brain tumor patients as long-term consequences of treatment. Although a number of in vitro and in vivo studies have demonstrated the pathogenesis of radiation-mediated brain injury, the cel-lular and molecular mechanisms by which radiation induces damage to normal tissue in brain remain largely unknown. Therefore, this review focuses on the pathophysiological mechanisms of whole brain radiation-induced cognitive impairment and the iden-tification of novel therapeutic targets. Specifically, we review the current knowledge about the effects of whole brain radiation on pro-oxidative and pro-inflammatory pathways, matrix metalloproteinases (MMPs)/tissue inhibitors of metalloproteinases (TIMPs) system and extracellular matrix (ECM), and physiological angiogenesis in brain. These studies may provide a foundation for defin-ing a new cellular and molecular basis related to the etiology of cognitive impairment that occurs among patients in response to whole brain radiation therapy. It may also lead to new opportunities for therapeutic interventions for brain tumor patients who are undergoing whole brain radiation therapy.

Inhibitory effect of matrine on blood-brain barrier disruption for the treatment of experimental autoimmune encephalomyelitis

Dysfunction of the blood-brain barrier (BBB) is a primary characteristic of experimental autoimmune encephalomyelitis (EAE), an experimental model of multiple sclerosis (MS). Matrine (MAT), a quinolizidine alkaloid derived from the herb Radix Sophorae Flave, has been recently found to suppress clinical EAE and CNS inflammation. However, whether this effect of MAT is through protecting the integrity and function of the BBB is not known. In the present study, we show that MAT treatment had a therapeutic effect comparable to dexamethasone (DEX) in EAE rats, with reduced Evans Blue extravasation, increased expression of collagen IV, the major component of the basement membrane, and the structure of tight junction (TJ) adaptor protein Zonula occludens-1 (ZO-1). Furthermore, MAT treatment attenuated expression of matrix metalloproteinase-9 and -2 (MMP-9/-2), while it increased the expression of tissue inhibitors of metalloproteinase-1 and -2 (TIMP-1/-2). Our findings demonstrate that MAT reduces BBB leakage by strengthening basement membrane, inhibiting activities of MMP-2 and -9, and upregulating their inhibitors. Taken together, our results identify a novel mechanism underlying the effect of MAT, a natural compound that could be a novel therapy for MS.

Matrix metalloproteinases and their tissue inhibitors in serum and cerebrospinal fluid of children with Japanese encephalitis virus infection

The expression of matrix metalloproteinases (MMPs) is tightly regulated at the level of gene transcription, conversion of pro-enzyme to active MMPs, and the action of tissue inhibitors of metalloproteinases (TIMPs). The present study aimed to investigate the expression of some specific MMPs (2, 7, 9) and TIMPs (1, 2, 3) in serum and cerebrospinal fluid (CSF) of children with Japanese encephalitis virus (JEV) infection. Serum and CSF levels of MMPs and TIMPs in children with JEV infection and disease control (DC) were compared. The CSF and serum concentrations of MMP-2, TIMP-2 and TIMP-3 were significantly higher in children with JEV infection compared to DC. The concentration of MMP-9 in serum was significantly higher in children with JEV infection than in the DC and healthy control (HC), while in the CSF, no significant difference was observed compared to DC. The MMP-7 serum concentration was significantly higher in children with JEV infection compared to HC, but no significant difference was observed compared to DC. MMP-7 concentration was undetectable in CSF in both groups. The TIMP-1 CSF concentration was significantly higher, while the serum concentration was significantly lower, in children with JEV infection compared to DC. No correlation was found between the levels of each biomolecule measured in CSF and serum, suggesting that the levels in CSF represent local production within the CNS rather than production in the periphery. We also observed leucocytosis, mononuclear pleocytosis and elevated protein concentrations in the CSF of children with JEV infection compared to DC.

The alterations of matrix metalloproteinase-9 in mouse brainstem during herpes simplex virus type 1-induced facial palsy

The aim of this study is to explore the changes of matrix metalloproteinase-9 (MMP9) in the mouse brainstem during the development of facial paralysis induced by herpes simplex virus type 1 (HSV-1) and the inhibitory effect of methylprednisolone sodium succinate (MPSS) on MMP9 expression. HSV-1 was inoculated into the surface of posterior auricle of mouse to establish a paralyzed animal model. The paralyzed mice were divided randomly into three groups. In one group without any treatment, mice were killed at different time points of 6 h, 1, 2, 3, and 7 days post-induction of facial paralysis; in the other two groups, mice were injected daily with MPSS and a combination of MPSS and glucocorticoid receptor blocker (RU486) for 2 days, respectively. The expression of MMP9 in the facial nucleus of brainstem was detected by Western blot, quantitative real-time polymerase chain reaction, and immunofluorescence technique. A total of 52.07 % of mice developed unilateral facial paralysis after inoculated with HSV-1. Both mRNA and protein expression of MMP9 were present at low levels in normal facial nucleus of brainstem and were increased significantly after facial paralysis with its peak time at 2 days post-induction of facial paralysis. Expression of MMP9 of paralyzed mice was inhibited by MPSS, and the inhibition could be blocked by RU486. Our findings suggest that MMP9 in mouse brainstem is involved in the evolution of facial palsy induced by HSV-1 and may play an important role in the pathogenesis of this disease. MPSS might effectively relieve HSV-1-mediated damages by inhibitory effect on expression of MMP9 in HSV-1-induced facial paralysis.

Microglia and a functional type I IFN pathway are required to counter HSV-1-driven brain lateral ventricle enlargement and encephalitis

HSV-1 is the leading cause of sporadic viral encephalitis, with mortality rates approaching 30% despite treatment with the antiviral drug of choice, acyclovir. Permanent neurologic deficits are common in patients that survive, but the mechanism leading to this pathology is poorly understood, impeding clinical advancements in treatment to reduce CNS morbidity. Using magnetic resonance imaging and type I IFN receptor-deficient mouse chimeras, we demonstrate HSV-1 gains access to the murine brain stem and subsequently brain ependymal cells, leading to enlargement of the cerebral lateral ventricle and infection of the brain parenchyma. A similar enlargement in the lateral ventricles is found in a subpopulation of herpes simplex encephalitic patients. Associated with encephalitis is an increase in CXCL1 and CXCL10 levels in the cerebral spinal fluid, TNF-α expression in the ependymal region, and the influx of neutrophils of encephalitic mouse brains. Reduction in lateral ventricle enlargement using anti-secretory factor peptide 16 reduces mortality significantly in HSV-1-infected mice without any effect on expression of inflammatory mediators, infiltration of leukocytes, or changes in viral titer. Microglial cells but not infiltrating leukocytes or other resident glial cells or neurons are the principal source of resistance in the CNS during the first 5 d postinfection through a Toll/IL-1R domain-containing adapter inducing IFN-β-dependent, type I IFN pathway. Our results implicate lateral ventricle enlargement as a major cause of mortality in mice and speculate such an event transpires in a subpopulation of human HSV encephalitic patients.

Irradiation alters MMP-2/TIMP-2 system and collagen type IV degradation in brain

PURPOSE

Blood-brain barrier (BBB) disruption is one of the major consequences of radiation-induced normal tissue injury in the central nervous system. We examined the effects of whole-brain irradiation on matrix metalloproteinases (MMPs)/tissue inhibitors of metalloproteinases (TIMPs) and extracellular matrix (ECM) degradation in the brain.

METHODS AND MATERIALS

Animals received either whole-brain irradiation (a single dose of 10 Gy γ-rays or a fractionated dose of 40 Gy γ-rays, total) or sham-irradiation and were maintained for 4, 8, and 24 h following irradiation. mRNA expression levels of MMPs and TIMPs in the brain were analyzed by real-time reverse transcriptase-polymerase chain reaction (PCR). The functional activity of MMPs was measured by in situ zymography, and degradation of ECM was visualized by collagen type IV immunofluorescent staining.

RESULTS

A significant increase in mRNA expression levels of MMP-2, MMP-9, and TIMP-1 was observed in irradiated brains compared to that in sham-irradiated controls. In situ zymography revealed a strong gelatinolytic activity in the brain 24 h postirradiation, and the enhanced gelatinolytic activity mediated by irradiation was significantly attenuated in the presence of anti-MMP-2 antibody. A significant reduction in collagen type IV immunoreactivity was also detected in the brain at 24 h after irradiation. In contrast, the levels of collagen type IV were not significantly changed at 4 and 8 h after irradiation compared with the sham-irradiated controls.

CONCLUSIONS

The present study demonstrates for the first time that radiation induces an imbalance between MMP-2 and TIMP-2 levels and suggests that degradation of collagen type IV, a major ECM component of BBB basement membrane, may have a role in the pathogenesis of brain injury.

Viral disruption of the blood-brain barrier

The blood-brain barrier (BBB) provides significant protection against microbial invasion of the brain. However, the BBB is not impenetrable, and mechanisms by which viruses breach it are becoming clearer. In vivo and in vitro model systems are enabling identification of host and viral factors contributing to breakdown of the unique BBB tight junctions. Key mechanisms of tight junction damage from inside and outside cells are disruption of the actin cytoskeleton and matrix metalloproteinase activity, respectively. Viral proteins acting in BBB disruption are described for HIV-1, currently the most studied encephalitic virus; other viruses are also discussed.

A trypsin-like serine protease is involved in pseudorabies virus invasion through the basement membrane barrier of porcine nasal respiratory mucosa

Several alphaherpesviruses breach the basement membrane during mucosal invasion. In the present study, the role of proteases in this process was examined. The serine protease-specific inhibitor AEBSF inhibited penetration of the basement membrane by the porcine alphaherpesvirus pseudorabies virus (PRV) by 88.1% without affecting lateral spread. Inhibitors of aspartic-, cysteine-, and metalloproteases did not inhibit viral penetration of the basement membrane. Further analysis using the Soybean Type I-S trypsin inhibitor for the serine protease subcategory of trypsin-like serine proteases resulted in a 96.9% reduction in plaque depth underneath the basement membrane. These data reveal a role of a trypsin-like serine protease in PRV penetration of the basement membrane.

Intracerebral infection with dengue-3 virus induces meningoencephalitis and behavioral changes that precede lethality in mice

BACKGROUND

Dengue, one of the most important arboviral diseases of humans, may cause severe systemic disease. Although dengue virus (DENV) has been considered to be a non-neurotropic virus, dengue infection has been associated recently with a series of neurological syndromes, including encephalitis. In this work, we evaluated behavioral changes and inflammatory parameters in C57BL/6 mice infected with non-adapted dengue virus 3 (DENV-3) genotype I.

METHODS

C57BL/6 mice received 4×10(3) PFU of DENV-3 by an intracranial route. We evaluated the trafficking of leukocytes in brain microvasculature using intravital microscopy, and evaluated chemokine and cytokine profiling by an ELISA test at 3 and 6 days post infection (p.i.). Furthermore, we determined myeloperoxidase activity and immune cell populations, and also performed histopathological analysis and immunostaining for the virus in brain tissue.

RESULTS

All animals developed signs of encephalitis and died by day 8 p.i. Motor behavior and muscle tone and strength parameters declined at day 7 p.i. We observed increased leukocyte rolling and adhesion in brain microvasculature of infected mice at days 3 and 6 p.i. The infection was followed by significant increases in IFN-γ, TNF-α, CCL2, CCL5, CXCL1, and CXCL2. Histological analysis showed evidence of meningoencephalitis and reactive gliosis. Increased numbers of neutrophils, CD4+ and CD8+ T cells were detected in brain of infected animals, notably at day 6 p.i. Cells immunoreactive for anti-NS-3 were visualized throughout the brain.

CONCLUSION

Intracerebral infection with non-adapted DENV-3 induces encephalitis and behavioral changes that precede lethality in mice.

The combination of interferon-beta and HMG-CoA reductase inhibition in multiple sclerosis: enthusiasm lost too soon?

Recent studies support the notion that statins, widely prescribed cholesterol-lowering agents, may target key elements in the immunological cascade leading to inflammation and tissue damage in the pathogenesis of multiple sclerosis (MS). Compelling experimental and observational clinical studies highlighted the possibility that statins may also exert immunomodulatory synergy with approved MS drugs, resulting in several randomized clinical trials testing statins in combination with interferon-beta (IFN-β). Some data, however, suggest that this particular combination may not be clinically beneficial, and might actually have a negative effect on the disease course in some patients with MS. In this regard, a small North American trial indicated that atorvastatin administered in combination with IFN-β may increase disease activity in relapsing-remitting MS. Although other trials did not confirm this finding, the enthusiasm for studies with statins dwindled. This review aims to provide a comprehensive overview of the completed clinical trials and reports of the interim analyses evaluating the combination of IFN-β and statins in MS. Moreover, we try to address the evident question whether usage of this combination routinely requires caution, since the number of IFN-β-treated MS patients receiving statins for lowering of cholesterol is expected to grow.

Inflammation in neuroviral diseases

During any viral infection of the central nervous system (CNS), the extent and nature of neural cell alterations are dictated by the localization of virus replication and, possibly, persistence. However, one additional source of CNS damage comes from the immune response that develops following CNS viral infection. Indeed, despite of its major role in controlling virus spread in the infected CNS, the immune system is equipped with numerous molecular effectors shared with the nervous system that may greatly alter the homeostasis and function of neural cells. Proinflammatory cytokines and metalloproteases belong to this inflammatory cascade. Besides neurovirulence, the crosstalk engaged between neural and immune cells is a major factor determining the outcome of neuroviral infections.

Cyclooxygenase-2 inhibitor blocks the production of West Nile virus-induced neuroinflammatory markers in astrocytes

Inflammatory immune responses triggered initially to clear West Nile virus (WNV) infection later become detrimental and contribute to the pathological processes such as blood–brain barrier (BBB) disruption and neuronal death, thus complicating WNV-associated encephalitis (WNVE). It has been demonstrated previously that WNV infection in astrocytes results in induction of multiple matrix metalloproteinases (MMPs), which mediate BBB disruption. Cyclooxygenase (COX) enzymes and their product, prostaglandin E2 (PGE2), modulate neuroinflammation and regulate the production of multiple inflammatory molecules including MMPs. Therefore, this study determined and characterized the pathophysiological consequences of the expression of COX enzymes in human brain cortical astrocytes (HBCAs) following WNV infection. Whilst COX-1 mRNA expression did not change, WNV infection significantly induced RNA and protein expression of COX-2 in HBCAs. Similarly, PGE2 production was also enhanced significantly in infected HBCAs and was blocked in the presence of the COX-2-specific inhibitor NS-398, thus suggesting that COX-2, and not COX-1, was the source of the increased PGE2. Treatment of infected HBCAs with NS-398 attenuated the expression of MMP-1, -3 and -9 in a dose-dependent manner. Similarly, expression of interleukin-1β, -6 and -8, which were markedly elevated in infected HBCAs, exhibited a significant reduction in their levels in the presence of NS-398. These results provide direct evidence that WNV-induced COX-2/PGE2 is involved in modulating the expression of multiple neuroinflammatory mediators, thereby directly linking COX-2 with WNV disease pathogenesis. The ability of COX-2 inhibitors to modulate WNV-induced COX-2 and PGE2 signalling warrants further investigation in an animal model as a potential approach for clinical management of neuroinflammation associated with WNVE.

Favorable effects of MMP-9 knockdown in murine herpes simplex encephalitis using small interfering RNA

BACKGROUND AND PURPOSE

The prognosis of herpes simplex encephalitis (HSE) remains poor despite available antiviral treatment. Matrix metalloproteinase-9 (MMP-9) is currently considered to play a major role in promoting cerebrovascular complications which contribute to the high mortality and morbidity of HSE. We hypothesize that temporally knockdown MMP-9 expression in early phase of HSE might be an effective treatment strategy.

METHODS

The animal models of herpes simplex encephalitis were established by intracerebrally inoculated herpes simplex virus type 1 (HSV-1) in mice. Mice were inoculated intracerebrally with MMP-9 targeting siRNA (MMP-9 siRNA). MMP-9 expression was assessed by RT-PCR and western blot analysis at 3 and 7 days after HSV-1 infected. The blood-brain barrier (BBB) permeability was quantitated by Evans blue dye extravasations and brain water content. Immunohistochemistry method was adopted to analyse the expression of AQP4 protein. Quantitative real-time PCR analysis was used to detect cytokines expression. Neurological score was quantified using an established neurological scale at 7 days after HSE.

RESULTS

Using synthetic small interfering RNA, we found a single intracerebral injection of siRNA targeting murine MMP-9 mRNA (MMP-9 siRNA) silenced MMP-9 expression and reduced it to normal level at day 7 post-infection. The improvement in neurological function and increased cumulative survival reflected the functional consequence of this therapy. MMP-9 knockdown mice also displayed less uptake of Evans blue and reduced brain water content compared with control siRNA-treated group. Also the HSV-1-induced upregulation of proinflammatory cytokines was significantly diminished in MMP-9 siRNA-treated mice. In addition, aquaporin-4 expression in perivascular decreased in MMP-9 siRNA-treated mice and might contribute to the protection of blood-brain barrier.

DISCUSSION

This compelling evidence suggests that MMP-9 is a key pathogenic factor within HSE, and local injection of synthetic siRNA in the brain could knock down MMP-9 expression in acute phase of HSE, reduce brain edema and improves mice neurological function and increase cumulative survival.

[Acute viral and emerging viral CNS infections]

The morbidity and mortality of viral CNS infections can be reduced through early initiation of therapy, which could be specific or in most cases symptomatic. This in turn requires the physician to consider meningoencephalitis as a differential diagnosis.Increasing climate changes, global air travel and changing immune responses contribute to the emergence of rather rare viral pathogens on our continent. Thus, neurologists in Europe are facing an enormous challenge due to lacking knowledge and experience of these new germs, which needs to be taken care of.Novel therapeutic approaches with e.g. monoclonal antibodies awaken the hope of mitigating the partially lethal courses of these diseases.

Reversal of West Nile virus-induced blood-brain barrier disruption and tight junction proteins degradation by matrix metalloproteinases inhibitor

Though compromised blood-brain barrier (BBB) is a pathological hallmark of WNV-associated neurological sequelae, underlying mechanisms are unclear. We characterized the expression of matrix metalloproteinases (MMP) in WNV-infected human brain microvascular endothelial cells (HBMVE) and human brain cortical astrocytes (HBCA), components of BBB and their role in BBB disruption. Expression of multiple MMPs was significantly induced in WNV-infected HBCA cells. Naïve HBMVE cells incubated with the supernatant from WNV-infected HBCA cells demonstrated loss of tight junction proteins, which were rescued in the presence of MMP inhibitor, GM6001. Further, supernatant from WNV-infected HBCA cells compromised the in vitro BBB model integrity. Our data suggest astrocytes as one of the sources of MMP in the brain, which mediates BBB disruption allowing unrestricted entry of immune cells into the brain, thereby contributing to WNV neuropathogenesis. Because of the unavailability of WNV antivirals and vaccines, use of MMP inhibitors as an adjunct therapy to ameliorate WNV disease progression is warranted.

Matrix metalloproteinase 9 facilitates West Nile virus entry into the brain

West Nile virus (WNV) is the most-common cause of mosquito-borne encephalitis in the United States. Invasion of the brain by WNV is influenced by viral and host factors, and the molecular mechanism underlying disruption of the blood-brain barrier is likely multifactorial. Here we show that matrix metalloproteinase 9 (MMP9) is involved in WNV entry into the brain by enhancing blood-brain barrier permeability. Murine MMP9 expression was induced in the circulation shortly after WNV infection, and the protein levels remained high even when viremia subsided. In the murine brain, MMP9 expression and its enzymatic activity were upregulated and MMP9 was shown to partly localize to the blood vessels. Interestingly, we also found that cerebrospinal fluid from patients suffering from WNV contained increased MMP9 levels. The peripheral viremia and expression of host cytokines were not altered in MMP9(-/-) mice; however, these animals were protected from lethal WNV challenge. The resistance of MMP9(-/-) mice to WNV infection correlated with an intact blood-brain barrier since immunoglobulin G, Evans blue leakage into brain, and type IV collagen degradation were markedly reduced in the MMP9(-/-) mice compared with their levels in controls. Consistent with this, the brain viral loads, selected inflammatory cytokines, and leukocyte infiltrates were significantly reduced in the MMP9(-/-) mice compared to their levels in wild-type mice. These data suggest that MMP9 plays a role in mediating WNV entry into the central nervous system and that strategies to interrupt this process may influence the course of West Nile encephalitis.

Herpes Simplex Virus Type 1 infection: overview on relevant clinico-pathological features

Herpes Simplex Virus Type 1 (HSV-1) is a nuclear replicating enveloped virus, usually acquired through direct contact with infected lesions or body fluids (typically saliva). The prevalence of HSV-1 infection increases progressively from childhood, the seroprevalence being inversely related to socioeconomic background. Primary HSV-1 infections in children are either asymptomatic or following an incubation period of about 1 week gives rise to mucocutaneous vesicular eruptions. Herpetic gingivostomatitis typically affects the tongue, lips, gingival, buccal mucosa and the hard and soft palate. Most primary oro-facial HSV infection is caused by HSV-1, infection by HSV-2 is increasingly common. Recurrent infections, which occur at variable intervals, typically give rise to vesiculo-ulcerative lesions at mucocutaneous junctions particularly the lips (herpes labialis). Recurrent HSV-1 infection within the mouth is uncommon in otherwise healthy patients, although in immunocompromised patients, recurrent infection can be more extensive and/or aggressive. The diagnosis of common herpetic infection can usually be based upon the clinical history and presenting features. Confirmatory laboratory diagnosis is, however, required when patients are, or may be, immunocompromised.