Active induction of experimental autoimmune encephalomyelitis by MOG35-55 peptide immunization is associated with differential responses in separate compartments of the choroid plexus

Choroid plexus enlargement is associated with future periventricular neurodegeneration in multiple sclerosis

BACKGROUND

The choroid plexus (CP), located within the ventricles of the brain and the primary producer of cerebrospinal fluid, has been shown to be enlarged in patients with multiple sclerosis (MS) and linked to periventricular remyelination failure. Atrophied T2-lesion volume (aT2-LV), a promising neurodegenerative imaging marker in progressive MS (PMS), reflects the volume of periventricular lesions subsumed into cerebrospinal fluid over the follow-up.

METHODS

In a cohort of 143 people with relapsing-remitting MS (RRMS) and 53 with PMS, we used 3T magnetic resonance imaging (MRI) to quantify CP volume (CPV) at baseline and aT2-LV over an average of 5.4 years of follow-up. Partial correlations, adjusting for age and sex, and linear regression analyses were used to assess the relationships between imaging measures.

RESULTS

In both cohorts, CPV was associated with aT2-LV in both the RRMS group (r = 0.329, p < 0.001) as well as the PMS group (r = 0.522, p < 0.001). In regression analyses predicting aT2-LV, ventricular volume (final adjusted R2 = 0.407, p < 0.001) explained additional variance beyond age, sex, and T2-lesion volume in the RRMS group while CPV (final adjusted R2 = 0.446, p = 0.009) was retained in the PMS group.

CONCLUSION

Findings from this study suggest that the CP enlargement is associated with future neurodegeneration, with a particularly relevant role in PMS.

Immune cells as messengers from the CNS to the periphery: the role of the meningeal lymphatic system in immune cell migration from the CNS

In recent decades there has been a large focus on understanding the mechanisms of peripheral immune cell infiltration into the central nervous system (CNS) in neuroinflammatory diseases. This intense research led to several immunomodulatory therapies to attempt to regulate immune cell infiltration at the blood brain barrier (BBB), the choroid plexus (ChP) epithelium, and the glial barrier. The fate of these infiltrating immune cells depends on both the neuroinflammatory environment and their type-specific interactions with innate cells of the CNS. Although the fate of the majority of tissue infiltrating immune cells is death, a percentage of these cells could become tissue resident immune cells. Additionally, key populations of immune cells can possess the ability to "drain" out of the CNS and act as messengers reporting signals from the CNS toward peripheral lymphatics. Recent data supports that the meningeal lymphatic system is involved not just in fluid homeostatic functions in the CNS but also in facilitating immune cell migration, most notably dendritic cell migration from the CNS to the meningeal borders and to the draining cervical lymph nodes. Similar to the peripheral sites, draining immune cells from the CNS during neuroinflammation have the potential to coordinate immunity in the lymph nodes and thus influence disease. Here in this review, we will evaluate evidence of immune cell drainage from the brain via the meningeal lymphatics and establish the importance of this in animal models and humans. We will discuss how targeting immune cells at sites like the meningeal lymphatics could provide a new mechanism to better provide treatment for a variety of neurological conditions.

The interplay between T helper cells and brain barriers in the pathogenesis of multiple sclerosis

The blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB) represent two complex structures protecting the central nervous system (CNS) against potentially harmful agents and circulating immune cells. The immunosurveillance of the CNS is governed by immune cells that constantly patrol the BCSFB, whereas during neuroinflammatory disorders, both BBB and BCSFB undergo morphological and functional alterations, promoting leukocyte intravascular adhesion and transmigration from the blood circulation into the CNS. Multiple sclerosis (MS) is the prototype of neuroinflammatory disorders in which peripheral T helper (Th) lymphocytes, particularly Th1 and Th17 cells, infiltrate the CNS and contribute to demyelination and neurodegeneration. Th1 and Th17 cells are considered key players in the pathogenesis of MS and its animal model, experimental autoimmune encephalomyelitis. They can actively interact with CNS borders by complex adhesion mechanisms and secretion of a variety of molecules contributing to barrier dysfunction. In this review, we describe the molecular basis involved in the interactions between Th cells and CNS barriers and discuss the emerging roles of dura mater and arachnoid layer as neuroimmune interfaces contributing to the development of CNS inflammatory diseases.

Advancing brain barriers RNA sequencing: guidelines from experimental design to publication

BACKGROUND

RNA sequencing (RNA-Seq) in its varied forms has become an indispensable tool for analyzing differential gene expression and thus characterization of specific tissues. Aiming to understand the brain barriers genetic signature, RNA seq has also been introduced in brain barriers research. This has led to availability of both, bulk and single-cell RNA-Seq datasets over the last few years. If appropriately performed, the RNA-Seq studies provide powerful datasets that allow for significant deepening of knowledge on the molecular mechanisms that establish the brain barriers. However, RNA-Seq studies comprise complex workflows that require to consider many options and variables before, during and after the proper sequencing process.

MAIN BODY

In the current manuscript, we build on the interdisciplinary experience of the European PhD Training Network BtRAIN ( https://www.btrain-2020.eu/ ) where bioinformaticians and brain barriers researchers collaborated to analyze and establish RNA-Seq datasets on vertebrate brain barriers. The obstacles BtRAIN has identified in this process have been integrated into the present manuscript. It provides guidelines along the entire workflow of brain barriers RNA-Seq studies starting from the overall experimental design to interpretation of results. Focusing on the vertebrate endothelial blood-brain barrier (BBB) and epithelial blood-cerebrospinal-fluid barrier (BCSFB) of the choroid plexus, we provide a step-by-step description of the workflow, highlighting the decisions to be made at each step of the workflow and explaining the strengths and weaknesses of individual choices made. Finally, we propose recommendations for accurate data interpretation and on the information to be included into a publication to ensure appropriate accessibility of the data and reproducibility of the observations by the scientific community.

CONCLUSION

Next generation transcriptomic profiling of the brain barriers provides a novel resource for understanding the development, function and pathology of these barrier cells, which is essential for understanding CNS homeostasis and disease. Continuous advancement and sophistication of RNA-Seq will require interdisciplinary approaches between brain barrier researchers and bioinformaticians as successfully performed in BtRAIN. The present guidelines are built on the BtRAIN interdisciplinary experience and aim to facilitate collaboration of brain barriers researchers with bioinformaticians to advance RNA-Seq study design in the brain barriers community.

Choroid plexus and the blood-cerebrospinal fluid barrier in disease

The choroid plexus (CP) forming the blood-cerebrospinal fluid (B-CSF) barrier is among the least studied structures of the central nervous system (CNS) despite its clinical importance. The CP is an epithelio-endothelial convolute comprising a highly vascularized stroma with fenestrated capillaries and a continuous lining of epithelial cells joined by apical tight junctions (TJs) that are crucial in forming the B-CSF barrier. Integrity of the CP is critical for maintaining brain homeostasis and B-CSF barrier permeability. Recent experimental and clinical research has uncovered the significance of the CP in the pathophysiology of various diseases affecting the CNS. The CP is involved in penetration of various pathogens into the CNS, as well as the development of neurodegenerative (e.g., Alzheimer´s disease) and autoimmune diseases (e.g., multiple sclerosis). Moreover, the CP was shown to be important for restoring brain homeostasis following stroke and trauma. In addition, new diagnostic methods and treatment of CP papilloma and carcinoma have recently been developed. This review describes and summarizes the current state of knowledge with regard to the roles of the CP and B-CSF barrier in the pathophysiology of various types of CNS diseases and sets up the foundation for further avenues of research.

Human CD4+ T cell subsets differ in their abilities to cross endothelial and epithelial brain barriers in vitro

Background

The brain barriers establish compartments in the central nervous system (CNS) that significantly differ in their communication with the peripheral immune system. In this function they strictly control T-cell entry into the CNS. T cells can reach the CNS by either crossing the endothelial blood–brain barrier (BBB) or the epithelial blood-cerebrospinal fluid barrier (BCSFB) of the choroid plexus (ChP).

Objective

Analysis of the cellular and molecular mechanisms involved in the migration of different human CD4⁺ T-cell subsets across the BBB versus the BCSFB.

Methods

Human in vitro models of the BBB and BCSFB were employed to study the migration of circulating and CNS-entry experienced CD4⁺ T helper cell subsets (Th1, Th1*, Th2, Th17) across the BBB and BCSFB under inflammatory and non-inflammatory conditions in vitro.

Results

While under non-inflammatory conditions Th1* and Th1 cells preferentially crossed the BBB, under inflammatory conditions the migration rate of all Th subsets across the BBB was comparable. The migration of all Th subsets across the BCSFB from the same donor was 10- to 20-fold lower when compared to their migration across the BBB. Interestingly, Th17 cells preferentially crossed the BCSFB under both, non-inflamed and inflamed conditions. Barrier-crossing experienced Th cells sorted from CSF of MS patients showed migratory characteristics indistinguishable from those of circulating Th cells of healthy donors. All Th cell subsets could additionally cross the BCSFB from the CSF to ChP stroma side. T-cell migration across the BCSFB involved epithelial ICAM-1 irrespective of the direction of migration.

Conclusions

Our observations underscore that different Th subsets may use different anatomical routes to enter the CNS during immune surveillance versus neuroinflammation with the BCSFB establishing a tighter barrier for T-cell entry into the CNS compared to the BBB. In addition, CNS-entry experienced Th cell subsets isolated from the CSF of MS patients do not show an increased ability to cross the brain barriers when compared to circulating Th cell subsets from healthy donors underscoring the active role of the brain barriers in controlling T-cell entry into the CNS. Also we identify ICAM-1 to mediate T cell migration across the BCSFB.

High Speed Ventral Plane Videography as a Convenient Tool to Quantify Motor Deficits during Pre-Clinical Experimental Autoimmune Encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is the most commonly used multiple sclerosis animal model. EAE mice typically develop motor deficits in a caudal-to-rostral pattern when inflammatory lesions have already developed. However, to monitor more subtle behavioral deficits during lesion development (i.e., pre-clinical phase), more sophisticated methods are needed. Here, we investigated whether high speed ventral plane videography can be applied to monitor early motor deficits during ‘pre-clinical’ EAE. For this purpose, EAE was induced in C57BL/6 mice and gait abnormalities were quantified using the DigiGait™ apparatus. Gait deficits were related to histopathological changes. 10 out of 10 control (100%), and 14 out of 18 (77.8%) pre-clinical EAE mice could be evaluated using DigiGait™. EAE severity was not influenced by DigiGait™-related mice handlings. Most gait parameters recorded from day 6 post-immunization until the end of the experiment were found to be stable in control mice. During the pre-clinical phase, when conventional EAE scorings failed to detect any functional impairment, EAE mice showed an increased Swing Time, increased %Swing Stride, decreased %Stance Stride, decreased Stance/Swing, and an increased Absolute Paw Angle. In summary, DigiGait™ is more sensitive than conventional scoring approaches to study motor deficits during the EAE pre-clinical phase.

Corticosteroid signaling at the brain-immune interface impedes coping with severe psychological stress

The immune system supports brain plasticity and homeostasis, yet it is prone to changes following psychological stress. Thus, it remains unclear whether and how stress-induced immune alterations contribute to the development of mental pathologies. Here, we show that following severe stress in mice, leukocyte trafficking through the choroid plexus (CP), a compartment that mediates physiological immune-brain communication, is impaired. Blocking glucocorticoid receptor signaling, either systemically or locally through its genetic knockdown at the CP, facilitated the recruitment of Gata3- and Foxp3-expressing T cells to the brain and attenuated post-traumatic behavioral deficits. These findings functionally link post-traumatic stress behavior with elevated stress-related corticosteroid signaling at the brain-immune interface and suggest a novel therapeutic target to attenuate the consequences of severe psychological stress.

Claudin-3-deficient C57BL/6J mice display intact brain barriers

The tight junction protein claudin-3 has been identified as a transcriptional target of the Wnt/β-catenin signaling pathway regulating blood-brain barrier (BBB) maturation. In neurological disorders loss of claudin-3 immunostaining is observed at the compromised BBB and blood-cerebrospinal fluid barrier (BCSFB). Although these observations support a central role of claudin-3 in regulating brain barriers’ tight junction integrity, expression of claudin-3 at the brain barriers has remained a matter of debate. This prompted us to establish claudin-3^−/− C57BL/6J mice to study the role of claudin-3 in brain barrier integrity in health and neuroinflammation. Bulk and single cell RNA sequencing and direct comparative qRT-PCR analysis of brain microvascular samples from WT and claudin-3^−/− mice show beyond doubt that brain endothelial cells do not express claudin-3 mRNA. Detection of claudin-3 protein at the BBB in vivo and in vitro is rather due to junctional reactivity of anti-claudin-3 antibodies to an unknown antigen still detected in claudin-3^−/− brain endothelium. We confirm expression and junctional localization of claudin-3 at the BCSFB of the choroid plexus. Our study clarifies that claudin-3 is not expressed at the BBB and shows that absence of claudin-3 does not impair brain barrier function during health and neuroinflammation in C57BL/6J mice.

Mechanism of Siponimod: Anti-Inflammatory and Neuroprotective Mode of Action

Multiple sclerosis (MS) is a neuroinflammatory disorder of the central nervous system (CNS), and represents one of the main causes of disability in young adults. On the histopathological level, the disease is characterized by inflammatory demyelination and diffuse neurodegeneration. Although on the surface the development of new inflammatory CNS lesions in MS may appear consistent with a primary recruitment of peripheral immune cells, questions have been raised as to whether lymphocyte and/or monocyte invasion into the brain are really at the root of inflammatory lesion development. In this review article, we discuss a less appreciated inflammation-neurodegeneration interplay, that is: Neurodegeneration can trigger the formation of new, focal inflammatory lesions. We summarize old and recent findings suggesting that new inflammatory lesions develop at sites of focal or diffuse degenerative processes within the CNS. Such a concept is discussed in the context of the EXPAND trial, showing that siponimod exerts anti-inflammatory and neuroprotective activities in secondary progressive MS patients. The verification or rejection of such a concept is vital for the development of new therapeutic strategies for progressive MS.

Spatiotemporal resolution of spinal meningeal and parenchymal inflammation during experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) induced by active immunization of C57BL/6 mice with peptide from myelin oligodendrocyte protein (MOG_35-55), is a neuroinflammatory, demyelinating disease widely recognized as an animal model of multiple sclerosis (MS). Typically, EAE presents with an ascending course of paralysis, and inflammation that is predominantly localized to the spinal cord. Recent studies have further indicated that inflammation - in both MS and EAE - might initiate within the meninges and propagate from there to the underlying parenchyma. However, the patterns of inflammation within the respective meningeal and parenchymal compartments along the length of the spinal cord, and the progression with which these patterns develop during EAE, have yet to be detailed. Such analysis could hold key to identifying factors critical for spreading, as well as constraining, inflammation along the neuraxis. To address this issue, high-resolution 3-dimensional (3D) confocal microscopy was performed to visualize, in detail, the sequence of leukocyte infiltration at distinct regions of the spinal cord. High quality virtual slide scanning for imaging the entire spinal cord using epifluorescence was further conducted to highlight the directionality and relative degree of inflammation. Meningeal inflammation was found to precede parenchymal inflammation at all levels of the spinal cord, but did not develop equally or simultaneously throughout the subarachnoid space (SAS) of the meninges. Instead, meningeal inflammation was initially most obvious in the caudal SAS, from which it progressed to the immediate underlying parenchyma, paralleling the first signs of clinical disease in the tail and hind limbs. Meningeal inflammation could then be seen to extend in the caudal-to-rostral direction, followed by a similar, but delayed, trajectory of parenchymal inflammation. To additionally determine whether the course of ascending paralysis and leukocyte infiltration during EAE is reflected in differences in inflammatory gene expression by meningeal and parenchymal microvessels along the spinal cord, laser capture microdissection (LCM) coupled with gene expression profiling was performed. Expression profiles varied between these respective vessel populations at both the cervical and caudal levels of the spinal cord during disease progression, and within each vessel population at different levels of the cord at a given time during disease. These results reinforce a significant role for the meninges in the development and propagation of central nervous system inflammation associated with MS and EAE.

Inflammatory demyelination induces ependymal modifications concomitant to activation of adult (SVZ) stem cell proliferation

Ependymal cells (E1/E2) and ciliated B1cells confer a unique pinwheel architecture to the ventricular surface of the subventricular zone (SVZ), and their cilia act as sensors to ventricular changes during development and aging. While several studies showed that forebrain demyelination reactivates the SVZ triggering proliferation, ectopic migration, and oligodendrogenesis for myelin repair, the potential role of ciliated cells in this process was not investigated. Using conventional and lateral wall whole mount preparation immunohistochemistry in addition to electron microscopy in a forebrain-targeted model of experimental autoimmune encephalomyelitis (tEAE), we show an early decrease in numbers of pinwheels, B1 cells, and E2 cells. These changes were transient and simultaneous to tEAE-induced SVZ stem cell proliferation. The early drop in B1/E2 cell numbers was followed by B1/E2 cell recovery. While E1 cell division and ependymal ribbon disruption were never observed, E1 cells showed important morphological modifications reflected by their enlargement, extended cytoskeleton, and reinforced cell-cell junction complexes overtime, possibly reflecting protective mechanisms against ventricular insults. Finally, tEAE disrupted motile cilia planar cell polarity and cilia orientation in ependymal cells. Therefore, significant ventricular modifications in ciliated cells occur early in response to tEAE suggesting a role for these cells in SVZ stem cell signalling not only during development/aging but also during inflammatory demyelination. These observations may have major implications for understanding pathophysiology of and designing therapeutic approaches for inflammatory demyelinating diseases such as MS.

Combined effect of BCG vaccination and enriched environment promote neurogenesis and spatial cognition via a shift in meningeal macrophage M2 polarization

Background

The spatial learning abilities of developing mice benefit from extrinsic cues, such as an enriched environment, with concomitant enhancement in cognitive functions. Interestingly, such enhancements can be further increased through intrinsic Bacillus Calmette-Guérin (BCG) vaccination.

Results

Here, we first report that combined neonatal BCG vaccination and exposure to an enriched environment (Enr) induced combined neurobeneficial effects, including hippocampal long-term potentiation, and increased neurogenesis and spatial learning and memory, in mice exposed to the Enr and vaccinated with BCG relative to those in the Enr that did not receive BCG vaccination. Neonatal BCG vaccination markedly induced anti-inflammatory meningeal macrophage polarization both in regular and Enr breeding mice. The meninges are composed of the pia mater, dura mater, and choroid plexus. Alternatively, this anti-inflammatory activity of the meninges occurred simultaneously with increased expression of the neurotrophic factors BDNF/IGF-1 and the M2 microglial phenotype in the hippocampus. Our results reveal a critical role for BCG vaccination in the regulation of neurogenesis and spatial cognition through meningeal macrophage M2 polarization and neurotrophic factor expression; these effects were completely or partially prevented by minocycline or anti-IL-10 antibody treatment, respectively.

Conclusions

Together, we first claim that immunological factor and environmental factor induce a combined effect on neurogenesis and cognition via a common pathway-meningeal macrophage M2 polarization. We also present a novel functional association between peripheral T lymphocytes and meningeal macrophages after evoking adaptive immune responses in the periphery whereby T lymphocytes are recruited to the meninges in response to systemic IFN-γ signaling. This leads to meningeal macrophage M2 polarization, subsequent to microglial M2 activation and neurotrophic factor expression, and eventually promotes a positive behavior.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-017-0808-7) contains supplementary material, which is available to authorized users.

The choroid plexus in health and in disease: dialogues into and out of the brain

This article brings the choroid plexus into the context of health and disease. It is remarkable that the choroid plexus, composed by a monolayer of epithelial cells that lie in a highly vascularized stroma, floating within the brain ventricles, gets so little attention in major physiology and medicine text books and in the scientific literature in general. Consider that it is responsible for producing most of the about 150mL of cerebrospinal fluid that fills the brain ventricles and the subarachnoid space and surrounds the spinal cord in the adult human central nervous system, which is renewed approximately 2-3 times daily. As such, its activity influences brain metabolism and function, which will be addressed. Reflect that it contains an impressive number of receptors and transporters, both in the apical and basolateral sides of the epithelial cells, and as such is a key structure for the communication between the brain and the periphery. This will be highlighted in the context of neonatal jaundice, multiple sclerosis and Alzheimer's disease. Realize that the capillaries that irrigate the choroid plexus stroma do not possess tight junctions and that the blood flow to the choroid plexus is five times higher than that in the brain parenchyma, allowing for a rapid sensing system and delivery of molecules such as nutrients and metals as will be revised. Recognize that certain drugs reach the brain parenchyma solely through the choroid plexus epithelia, which has potential to be manipulated in diseases such as neonatal jaundice and Alzheimer's disease as will be discussed. Without further notice, it must be now clear that understanding the choroid plexus is necessary for comprehending the brain and how the brain is modulated and modulates all other systems, in health and in disease. This review article intends to address current knowledge on the choroid plexus, and to motivate the scientific community to consider it when studying normal brain physiology and diseases of the central nervous system. It will guide the reader through several aspects of the choroid plexus in normal physiology, in diseases characteristic of various periods of life (newborns-kernicterus, young adults-multiple sclerosis and the elder-Alzheimer's disease), and how sex-differences may relate to disease susceptibility.

A(H1N1) vaccination recruits T lymphocytes to the choroid plexus for the promotion of hippocampal neurogenesis and working memory in pregnant mice

We previously demonstrated that A(H1N1) influenza vaccine (AIV) promoted hippocampal neurogenesis and working memory in pregnant mice. However, the underlying mechanism of flu vaccination in neurogenesis and memory has remained unclear. In this study, we found that T lymphocytes were recruited from the periphery to the choroid plexus (CP) of the lateral and third (3rd) ventricles in pregnant mice vaccinated with AIV (Pre+AIV). Intracerebroventricular delivery of anti-TCR antibodies markedly decreased neurogenesis and the working memory of the Pre+AIV mice. Similarly, intravenous delivery of anti-CD4 antibodies to the periphery also down-regulated neurogenesis. Furthermore, AIV vaccination caused microglia to skew toward an M2-like phenotype (increased Arginase-1 and Ym1 mRNA levels), and elevated levels of brain-derived growth factor (BDNF) and insulin-like growth factor-1 (IGF-1) were found in the hippocampus, whereas these effects were offset by anti-TCR antibody treatment. Additionally, in the CP, the expression level of adhesion molecules and chemokines, which assist leukocytes in permeating into the brain, were also elevated after AIV vaccination of pregnant mice. Collectively, the results suggested that the infiltrative T lymphocytes in the CP contribute to the increase in hippocampal neurogenesis and working memory caused by flu vaccination, involving activation of the brain's CP, M2 microglial polarization and neurotrophic factor expression.

Modeling immune functions of the mouse blood-cerebrospinal fluid barrier in vitro: primary rather than immortalized mouse choroid plexus epithelial cells are suited to study immune cell migration across this brain barrier

Background

The blood–cerebrospinal fluid barrier (BCSFB) established by the choroid plexus (CP) epithelium has been recognized as a potential entry site of immune cells into the central nervous system during immunosurveillance and neuroinflammation. The location of the choroid plexus impedes in vivo analysis of immune cell trafficking across the BCSFB. Thus, research on cellular and molecular mechanisms of immune cell migration across the BCSFB is largely limited to in vitro models. In addition to forming contact-inhibited epithelial monolayers that express adhesion molecules, the optimal in vitro model must establish a tight permeability barrier as this influences immune cell diapedesis.

Methods

We compared cell line models of the mouse BCSFB derived from the Immortomouse^® and the ECPC4 line to primary mouse choroid plexus epithelial cell (pmCPEC) cultures for their ability to establish differentiated and tight in vitro models of the BCSFB.

Results

We found that inducible cell line models established from the Immortomouse^® or the ECPC4 tumor cell line did not express characteristic epithelial proteins such as cytokeratin and E-cadherin and failed to reproducibly establish contact-inhibited epithelial monolayers that formed a tight permeability barrier. In contrast, cultures of highly-purified pmCPECs expressed cytokeratin and displayed mature BCSFB characteristic junctional complexes as visualized by the junctional localization of E-cadherin, β-catenin and claudins-1, -2, -3 and -11. pmCPECs formed a tight barrier with low permeability and high electrical resistance. When grown in inverted filter cultures, pmCPECs were suitable to study T cell migration from the basolateral to the apical side of the BCSFB, thus correctly modelling in vivo migration of immune cells from the blood to the CSF.

Conclusions

Our study excludes inducible and tumor cell line mouse models as suitable to study immune functions of the BCSFB in vitro. Rather, we introduce here an in vitro inverted filter model of the primary mouse BCSFB suited to study the cellular and molecular mechanisms mediating immune cell migration across the BCSFB during immunosurveillance and neuroinflammation.

Do not judge a cell by its cover--diversity of CNS resident, adjoining and infiltrating myeloid cells in inflammation

Specialized populations of tissue-resident myeloid cells inhabit every organ of the body. While many of these populations appear similar morphologically and phenotypically, they exhibit great functional diversity. The central nervous system (CNS), as an immune privileged organ, possesses a unique tissue-resident macrophage population, the microglia, as well as numerous myeloid cell subsets at its boarders and barriers in CNS-adjoining tissues, namely the meninges, the perivascular space, and the choroid plexus. Recent research has added much to our knowledge about microglia, whereas the populations of CNS-surrounding phagocytes are just starting to be appreciated. As guardians of CNS homeostasis, these myeloid cells perform immune surveillance and immune modulatory tasks in health and disease. As such, microglia and CNS-surrounding antigen-presenting cells have been shown to be crucially involved not only in the initiation and progression but also resolution of multiple sclerosis (MS). MS and its rodent model, experimental autoimmune encephalomyelitis, are autoimmune inflammatory demyelinating CNS pathologies. While some crucial aspects of the disease pathogenesis have been solved, much of the complex involvement and interplay of the innate immune compartment remains yet to be clarified. Here, we will discuss the current understanding of the scope of phenotypes and functions of myeloid cells involved in CNS neuroinflammation.

Brain barriers: Crosstalk between complex tight junctions and adherens junctions

Unique intercellular junctional complexes between the central nervous system (CNS) microvascular endothelial cells and the choroid plexus epithelial cells form the endothelial blood–brain barrier (BBB) and the epithelial blood–cerebrospinal fluid barrier (BCSFB), respectively. These barriers inhibit paracellular diffusion, thereby protecting the CNS from fluctuations in the blood. Studies of brain barrier integrity during development, normal physiology, and disease have focused on BBB and BCSFB tight junctions but not the corresponding endothelial and epithelial adherens junctions. The crosstalk between adherens junctions and tight junctions in maintaining barrier integrity is an understudied area that may represent a promising target for influencing brain barrier function.

Pathological differences between white and grey matter multiple sclerosis lesions

Multiple sclerosis (MS) is a debilitating disease characterized by demyelination of the central nervous system (CNS), resulting in widespread formation of white matter lesions (WMLs) and grey matter lesions (GMLs). WMLs are pathologically characterized by the presence of immune cells that infiltrate the CNS, whereas these immune cells are barely present in GMLs. This striking pathological difference between WMLs and GMLs raises questions about the underlying mechanism. It is known that infiltrating leukocytes contribute to the generation of WMLs; however, since GMLs show a paucity of infiltrating immune cells, their importance in GML formation remains to be determined. Here, we review pathological characteristics of WMLs and GMLs, and suggest some possible explanations for the observed pathological differences. In our view, cellular and molecular characteristics of WM and GM, and local differences within WMLs and GMLs (in particular, in glial cell populations and the molecules they express), determine the pathway to demyelination. Further understanding of GML pathogenesis, considered to contribute to chronic MS, may have a direct impact on the development of novel therapeutic targets to counteract this progressive neurological disorder.

Clinical implications of leukocyte infiltration at the choroid plexus in (neuro)inflammatory disorders

The choroid plexus (CP) is a highly vascularized organ located in the brain ventricles and contains a single epithelial cell layer forming the blood-cerebrospinal fluid barrier (BCSFB). This barrier is crucial for immune surveillance in health and is an underestimated gate for entry of immune cells during numerous inflammatory disorders. Several of these disorders are accompanied by disturbance of the BCSFB and increased leukocyte infiltration, which affects neuroinflammation. Understanding the mechanism of immune cell entry at the CP might lead to identification of new therapeutic targets. Here, we focus on current knowledge of leukocyte infiltration at the CP in inflammatory conditions and its therapeutic implications.

Disturbed function of the blood-cerebrospinal fluid barrier aggravates neuro-inflammation

Multiple sclerosis (MS) is a chronic neuro-inflammatory disorder, which is marked by the invasion of the central nervous system by monocyte-derived macrophages and autoreactive T cells across the brain vasculature. Data from experimental animal models recently implied that the passage of leukocytes across the brain vasculature is preceded by their traversal across the blood-cerebrospinal fluid barrier (BCSFB) of the choroid plexus. The correlation between the presence of leukocytes in the CSF of patients suffering from MS and the number of inflammatory lesions as detected by magnetic resonance imaging suggests that inflammation at the choroid plexus contributes to the disease, although in a yet unknown fashion. We here provide first insights into the involvement of the choroid plexus in the onset and severity of the disease and in particular address the role of the tight junction protein claudin-3 (CLDN3) in this process. Detailed analysis of human post-mortem brain tissue revealed a selective loss of CLDN3 at the choroid plexus in MS patients compared to control tissues. Importantly, mice that lack CLDN3 have an impaired BCSFB and experience a more rapid onset and exacerbated clinical signs of experimental autoimmune encephalomyelitis, which coincides with enhanced levels of infiltrated leukocytes in their CSF. Together, this study highlights a profound role for the choroid plexus in the pathogenesis of multiple sclerosis, and implies that CLDN3 may be regarded as a crucial and novel determinant of BCSFB integrity.

Resolution of central nervous system astrocytic and endothelial sources of CCL2 gene expression during evolving neuroinflammation

BACKGROUND

The chemokine CCL2 is a critical mediator of neuroinflammation in diseases such as multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). CCL2 drives mononuclear cell infiltration into the central nervous system (CNS), alters expression and distribution of microvascular endothelial tight junction proteins, and disrupts the blood-brain and blood-spinal cord barriers. Immunohistochemistry has consistently revealed astrocytes to be a source of this chemokine during neuroinflammation, while providing less uniform evidence that CNS endothelial cells may also express CCL2. Moreover, the relative contributions of these cell types to the CNS pool of CCL2 during MS/EAE are unclear and the aim of this study was to investigate this further.

METHODS

CCL2 gene expression was determined by qRT-PCR in different populations of CNS cells at different times following EAE induced by immunization with MOG35-55 peptide and adjuvants, or after injection with adjuvants alone. CNS cells types were isolated by two different protocols: bulk isolation to yield crude microvascular and parenchymal fractions (containing astrocytes, other glia, and neurons), or laser capture microdissection (LCM) to acquire more precisely microvascular endothelial cells, astrocytes or other parenchymal cells.

RESULTS

Both CNS microvessel and parenchymal populations prepared by crude bulk isolation showed up-regulation of CCL2 mRNA following MOG immunization or injection of adjuvants alone. More exact dissection by LCM revealed microvascular endothelial cells and astrocytes to be the specific sources of CCL2 gene induction following MOG immunization, while only astrocytes showed elevated CCL2 mRNA in response to just adjuvants. Astrocytes displayed the greatest degree of stimulation of CCL2 gene expression following EAE induction.

CONCLUSIONS

High-precision LCM affirmed both microvascular endothelial cells and astrocytes as the major CNS sources of CCL2 gene expression during EAE. Given the high accessibility of the CNS microvascular endothelium, endothelial-derived CCL2 could prove a viable target for therapeutic intervention in neuroinflammatory disease.

MOG extracellular domain (p1-125) triggers elevated frequency of CXCR3+ CD4+ Th1 cells in the CNS of mice and induces greater incidence of severe EAE

BACKGROUND

Myelin-specific T cells are implicated in multiple sclerosis (MS) and drive experimental autoimmune encephalomyelitis (EAE). EAE is commonly induced with short peptides, whereas in MS, whole myelin proteins are available for immune response. We asked whether immunization with the immunoglobulin-like domain of myelin oligodendrocyte glycoprotein (MOG(Igd), residues 1-125) might induce distinct CD4+ T-cell response and/or a stronger CD8+ T-cell response, compared to the 21 amino acid immunodominant MHC II-associating peptide (p35-55).

OBJECTIVES

Compare both EAE and T-cell responses in C57BL/6 mice immunized with MOG(Igd) and MOG p35-55.

METHODS

Cytokine production, and chemokine receptor expression by CD4+ and CD8+ T cells in the mouse central nervous system (CNS), were analyzed by flow cytometry.

RESULTS

MOG(Igd) triggered progression to more severe EAE than MOG p35-55, despite similar time of onset and overall incidence. EAE in MOG(Igd)-immunized mice was characterized by an increased percentage of CXCR3+ interferon-γ-producing CD4+ T cells in CNS. The CD8+ T-cell response to both immunogens was similar.

CONCLUSIONS

Increased incidence of severe disease following MOG(Igd) immunization, accompanied by an increased percentage of CD4+ T cells in the CNS expressing CXCR3 and producing interferon-γ, identifies a pathogenic role for interferon-γ that is not seen when disease is induced with a single Major Histocompatibility Complex (MHC) II-associating epitope.

Cell-selective knockout and 3D confocal image analysis reveals separate roles for astrocyte-and endothelial-derived CCL2 in neuroinflammation

Background

Expression of chemokine CCL2 in the normal central nervous system (CNS) is nearly undetectable, but is significantly upregulated and drives neuroinflammation during experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis which is considered a contributing factor in the human disease. As astrocytes and brain microvascular endothelial cells (BMEC) forming the blood–brain barrier (BBB) are sources of CCL2 in EAE and other neuroinflammatory conditions, it is unclear if one or both CCL2 pools are critical to disease and by what mechanism(s).

Methods

Mice with selective CCL2 gene knockout (KO) in astrocytes (Astro KO) or endothelial cells (Endo KO) were used to evaluate the respective contributions of these sources to neuroinflammation, i.e., clinical disease progression, BBB damage, and parenchymal leukocyte invasion in a myelin oligodendrocyte glycoprotein peptide (MOG_35-55)-induced EAE model. High-resolution 3-dimensional (3D) immunofluorescence confocal microscopy and colloidal gold immuno-electron microscopy were employed to confirm sites of CCL2 expression, and 3D immunofluorescence confocal microscopy utilized to assess inflammatory responses along the CNS microvasculature.

Results

Cell-selective loss of CCL2 immunoreactivity was demonstrated in the respective KO mice. Compared to wild-type (WT) mice, Astro KO mice showed reduced EAE severity but similar onset, while Endo KO mice displayed near normal severity but significantly delayed onset. Neither of the KO mice showed deficits in T cell proliferation, or IL-17 and IFN-γ production, following MOG_35-55 exposure in vitro, or altered MOG-major histocompatibility complex class II tetramer binding. 3D confocal imaging further revealed distinct actions of the two CCL2 pools in the CNS. Astro KOs lacked the CNS leukocyte penetration and disrupted immunostaining of CLN-5 at the BBB seen during early EAE in WT mice, while Endo KOs uniquely displayed leukocytes stalled in the microvascular lumen.

Conclusions

These results point to astrocyte and endothelial pools of CCL2 each regulating different stages of neuroinflammation in EAE, and carry implications for drug delivery in neuroinflammatory disease.

Interleukin-1β and interleukin-1 receptor antagonist appear in grey matter additionally to white matter lesions during experimental multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) has been mainly attributed to white matter (WM) pathology. However, recent evidence indicated the presence of grey matter (GM) lesions. One of the principal mediators of inflammatory processes is interleukin-1β (IL-1β), which is known to play a role in MS pathogenesis. It is unknown whether IL-1β is solely present in WM or also in GM lesions. Using an experimental MS model, we questioned whether IL-1β and the IL-1 receptor antagonist (IL-1ra) are present in GM in addition to affected WM regions.

METHODS

The expression of IL-1β and IL-1ra in chronic-relapsing EAE (cr-EAE) rats was examined using in situ hybridization, immunohistochemistry and real-time PCR. Rats were sacrificed at the peak of the first disease phase, the trough of the remission phase, and at the peak of the relapse. Histopathological characteristics of CNS lesions were studied using immunohistochemistry for PLP, CD68 and CD3 and Oil-Red O histochemistry.

RESULTS

IL-1β and IL-ra expression appears to a similar extent in affected GM and WM regions in the brain and spinal cord of cr-EAE rats, particularly in perivascular and periventricular locations. IL-1β and IL-1ra expression was dedicated to macrophages and/or activated microglial cells, at sites of starting demyelination. The time-dependent expression of IL-1β and IL-1ra revealed that within the spinal cord IL-1β and IL-1ra mRNA remained present throughout the disease, whereas in the brain their expression disappeared during the relapse.

CONCLUSIONS

The appearance of IL-1β expressing cells in GM within the CNS during cr-EAE may explain the occurrence of several clinical deficits present in EAE and MS which cannot be attributed solely to the presence of IL-1β in WM. Endogenously produced IL-1ra seems not capable to counteract IL-1β-induced effects. We put forward that IL-1β may behold promise as a target to address GM, in addition to WM, related pathology in MS.

IFN-γ-dependent activation of the brain's choroid plexus for CNS immune surveillance and repair

Infiltrating T cells and monocyte-derived macrophages support central nervous system repair. Although infiltration of leucocytes to the injured central nervous system has recently been shown to be orchestrated by the brain's choroid plexus, the immunological mechanism that maintains this barrier and regulates its activity as a selective gate is poorly understood. Here, we hypothesized that CD4(+) effector memory T cells, recently shown to reside at the choroid plexus stroma, regulate leucocyte trafficking through this portal through their interactions with the choroid plexus epithelium. We found that the naïve choroid plexus is populated by T helper 1, T helper 2 and regulatory T cells, but not by encephalitogenic T cells. In vitro findings revealed that the expression of immune cell trafficking determinants by the choroid plexus epithelium is specifically induced by interferon-γ. Tumour necrosis factor-α and interferon-γ reciprocally controlled the expression of their receptors by the choroid plexus epithelium, and had a synergistic effect in inducing the epithelial expression of trafficking molecules. In vivo, interferon-γ-dependent signalling controlled trafficking through the choroid plexus; interferon-γ receptor knockout mice exhibited reduced levels of T cells and monocyte entry to the cerebrospinal fluid and impaired recovery following spinal cord injury. Moreover, reduced expression of trafficking molecules by the choroid plexus was correlated with reduced CD4(+) T cells in the choroid plexus and cerebrospinal fluid of interferon-γ receptor knockout mice. Similar effect on the expression of trafficking molecules by the choroid plexus was found in bone-marrow chimeric mice lacking interferon-γ receptor in the central nervous system, or reciprocally, lacking interferon-γ in the circulation. Collectively, our findings attribute a novel immunological plasticity to the choroid plexus epithelium, allowing it to serve, through interferon-γ signalling, as a tightly regulated entry gate into the central nervous system for circulating leucocytes immune surveillance under physiological conditions, and for repair following acute injury.

Altered cognitive-emotional behavior in early experimental autoimmune encephalitis--cytokine and hormonal correlates

Multiple sclerosis (MS) is often associated with co-morbid behavioural and cognitive impairments; however the presence of these symptoms does not necessarily correlate with neurological damage. This suggests that an alternate mechanism may subserve these impairments relative to motor deficits. We investigated whether these abnormalities could be studied in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. In myelin oligodendrocyte glycoprotein peptide (MOG35-55)-induced EAE mice, no motor deficits were observed until d9 after immunization. This enabled us to carry out a series of neurobehavioral tests during the presymptomatic stage, between d6 and d8 post-immunization. EAE mice spent more time in the outer zone in an open field test and in the closed arms of an elevated plus maze and, showed decreased latency for immobility in the tail suspension and forced swim tests and reduced social interaction compared with controls. These results are indicative of anxiety- and depression- like behavior. In addition, EAE mice appeared to exhibit memory impairment compared to controls based on their reduced time spent in the target quadrant in the Morris water maze and their faster memory extinction in the fear conditioning test. No demyelination, microglial activation or astrogliosis was observed in the brain at this early stage. Transcript analysis by RT-PCR from d6 to d8 brain revealed elevated interleukin (IL)-1β and TNF-α in the hypothalamus but not in the amygdala or hippocampus of EAE mice. Lastly, plasma corticosterone levels increased in EAE mice compared to controls. In conclusion, emotional and cognitive deficits are observed in EAE prior to demyelination and are associated with elevated IL-1β and TNF-α in the hypothalamus and changes in the hypothalamic-pituitary-adrenal axis.

Innovations in studying in vivo cell behavior and pharmacology in complex tissues--microvascular endothelial cells in the spotlight

Many studies on the molecular control underlying normal cell behavior and cellular responses to disease stimuli and pharmacological intervention are conducted in single-cell culture systems, while the read-out of cellular engagement in disease and responsiveness to drugs in vivo is often based on overall tissue responses. As the majority of drugs under development aim to specifically interact with molecular targets in subsets of cells in complex tissues, this approach poses a major experimental discrepancy that prevents successful development of new therapeutics. In this review, we address the shortcomings of the use of artificial (single) cell systems and of whole tissue analyses in creating a better understanding of cell engagement in disease and of the true effects of drugs. We focus on microvascular endothelial cells that actively engage in a wide range of physiological and pathological processes. We propose a new strategy in which in vivo molecular control of cells is studied directly in the diseased endothelium instead of at a (far) distance from the site where drugs have to act, thereby accounting for tissue-controlled cell responses. The strategy uses laser microdissection-based enrichment of microvascular endothelium which, when combined with transcriptome and (phospho)proteome analyses, provides a factual view on their status in their complex microenvironment. Combining this with miniaturized sample handling using microfluidic devices enables handling the minute sample input that results from this strategy. The multidisciplinary approach proposed will enable compartmentalized analysis of cell behavior and drug effects in complex tissue to become widely implemented in daily biomedical research and drug development practice.

Iron oxide magnetic nanoparticles highlight early involvement of the choroid plexus in central nervous system inflammation

Neuroinflammation during multiple sclerosis involves immune cell infiltration and disruption of the BBB (blood–brain barrier). Both processes can be visualized by MRI (magnetic resonance imaging), in multiple sclerosis patients and in the animal model EAE (experimental autoimmune encephalomyelitis). We previously showed that VSOPs (very small superparamagnetic iron oxide particles) reveal CNS (central nervous system) lesions in EAE which are not detectable by conventional contrast agents in MRI. We hypothesized that VSOP may help detect early, subtle inflammatory events that would otherwise remain imperceptible. To investigate the capacity of VSOP to reveal early events in CNS inflammation, we induced EAE in SJL mice using encephalitogenic T-cells, and administered VSOP prior to onset of clinical symptoms. In parallel, we administered VSOP to mice at peak disease, and to unmanipulated controls. We examined the distribution of VSOP in the CNS by MRI and histology. Prior to disease onset, in asymptomatic mice, VSOP accumulated in the choroid plexus and in spinal cord meninges in the absence of overt inflammation. However, VSOP was undetectable in the CNS of non-immunized control mice. At peak disease, VSOP was broadly distributed; we observed particles in perivascular inflammatory lesions with apparently preserved glia limitans. Moreover, at peak disease, VSOP was prominent in the choroid plexus and was seen in elongated endothelial structures, co-localized with phagocytes, and diffusely disseminated in the parenchyma, suggesting multiple entry mechanisms of VSOP into the CNS. Thus, using VSOP we were able to discriminate between inflammatory events occurring in established EAE and, importantly, we identified CNS alterations that appear to precede immune cell infiltration and clinical onset.

Antenatal betamethasone exposure is associated with lower ANG-(1-7) and increased ACE in the CSF of adult sheep

Antenatal betamethasone (BM) therapy accelerates lung development in preterm infants but may induce early programming events with long-term cardiovascular consequences. To elucidate these events, we developed a model of programming whereby pregnant ewes are administered BM (2 doses of 0.17 mg/kg) or vehicle at the 80th day of gestation and offspring are delivered at term. BM-exposed (BMX) offspring develop elevated blood pressure; decreased baroreflex sensitivity; and alterations in the circulating, renal, and brain renin-angiotensin systems (RAS) by 6 mo of age. We compared components of the choroid plexus fourth ventricle (ChP4) and cerebral spinal fluid (CSF) RAS between control and BMX male offspring at 6 mo of age. In the choroid plexus, high-molecular-weight renin protein and ANG I-intact angiotensinogen were unchanged between BMX and control animals. Angiotensin-converting enzyme 2 (ACE2) activity was threefold higher than either neprilysin (NEP) or angiotensin 1-converting enzyme (ACE) in control and BMX animals. Moreover, all three enzymes were equally enriched by approximately 2.5-fold in ChP4 brush-border membrane preparations. CSF ANG-(1-7) levels were significantly lower in BMX animals (351.8 ± 76.8 vs. 77.5 ± 29.7 fmol/mg; P < 0.05) and ACE activity was significantly higher (6.6 ± 0.5 vs. 8.9 ± 0.5 fmol·min(-1)·ml(-1); P < 0.05), whereas ACE2 and NEP activities were below measurable limits. A thiol-sensitive peptidase contributed to the majority of ANG-(1-7) metabolism in the CSF, with higher activity in BMX animals. We conclude that in utero BM exposure alters CSF but not ChP RAS components, resulting in lower ANG-(1-7) levels in exposed animals.

Biomarkers in Multiple Sclerosis: An Up-to-Date Overview

During the last decades, the effort of establishing satisfactory biomarkers for multiple sclerosis has been proven to be very difficult, due to the clinical and pathophysiological complexities of the disease. Recent knowledge acquired in the domains of genomics-immunogenetics and neuroimmunology, as well as the evolution in neuroimaging, has provided a whole new list of biomarkers. This variety, though, leads inevitably to confusion in the effort of decision making concerning strategic and individualized therapeutics. In this paper, our primary goal is to provide the reader with a list of the most important characteristics that a biomarker must possess in order to be considered as reliable. Additionally, up-to-date biomarkers are further divided into three subgroups, genetic-immunogenetic, laboratorial, and imaging. The most important representatives of each category are presented in the text and for the first time in a summarizing workable table, in a critical way, estimating their diagnostic potential and their efficacy to correlate with phenotypical expression, neuroinflammation, neurodegeneration, disability, and therapeutical response. Special attention is given to the "gold standards" of each category, like HLA-DRB1∗ polymorphisms, oligoclonal bands, vitamin D, and conventional and nonconventional imaging techniques. Moreover, not adequately established but quite promising, recently characterized biomarkers, like TOB-1 polymorphisms, are further discussed.

Novel 3D analysis of Claudin-5 reveals significant endothelial heterogeneity among CNS microvessels

Tight junctions (TJs) feature critically in maintaining the integrity of the blood-brain barrier (BBB), and undergo significant disruption during neuroinflammatory diseases. Accordingly, the expression and distribution of CLN-5, a prominent TJ protein in central nervous system (CNS) microvessels and BBB determinant, has been shown to parallel physiological and pathophysiological changes in microvascular function. However, efforts to quantify CLN-5 within the CNS microvasculature in situ, by using conventional two-dimensional immunohistochemical analysis of thin sections, are encumbered by the tortuosity of capillaries and distorted diameters of inflamed venules. Herein, we describe a novel contour-based 3D image visualization and quantification method, employing high-resolution confocal z-stacks from thick immunofluorescently-stained thoraco-lumbar spinal cord cryosections, to analyze CLN-5 along the junctional regions of different-sized CNS microvascular segments. Analysis was performed on spinal cords of both healthy mice, and mice experiencing experimental autoimmune encephalomyelitis (EAE), an animal model of the neuroinflammatory disease multiple sclerosis. Results indicated that, under normal conditions, the density of CLN-5 staining (CLN-5 intensity/ endothelial surface area) was greatest in the capillaries and smaller venules, and least in the larger venules. This heterogeneity in junctional CLN-5 staining was exacerbated during EAE, as spinal venules revealed a significant loss of junctional CLN-5 staining that was associated with focal leukocyte extravasation, while adjacent capillaries exhibited neither CLN-5 loss nor infiltrating leukocytes. However, despite only venules displaying these behaviors, both capillaries and venules evidenced leakage of IgG during disease, further underscoring the heterogeneity of the inflammatory response in CNS microvessels. This method should be readily adaptable to analyzing other junctional proteins of the CNS and peripheral microvasculature, and serve to highlight their role(s) in health and disease.