Molecular mechanisms of cerebrospinal fluid production

Genome wide analysis of novel copy number variations duplications/deletions of different epileptic patients in Saudi Arabia

Background

Epilepsy is genetically complex neurological disorder affecting millions of people of different age groups varying in its type and severity. Copy number variants (CNVs) are key players in the genetic etiology of numerous neurodevelopmental disorders and prior findings also revealed that chromosomal aberrations are more susceptible against the pathogenesis of epilepsy. Novel technologies, such as array comparative genomic hybridization (array-CGH), may help to uncover the pathogenic CNVs in patients with epilepsy.

Results

This study was carried out by high density whole genome array-CGH analysis with blood DNA samples from a cohort of 22 epilepsy patients to search for CNVs associated with epilepsy. Pathogenic rearrangements which include 6p12.1 microduplications in 5 patients covering a total region of 99.9kb and 7q32.3 microdeletions in 3 patients covering a total region of 63.9kb were detected. Two genes BMP5 and PODXL were located in the predicted duplicated and deleted regions respectively. Furthermore, these CNV findings were confirmed by qPCR.

Conclusion

We have described, for the first time, several novel CNVs/genes implicated in epilepsy in the Saudi population. These findings enable us to better describe the genetic variations in epilepsy, and could provide a foundation for understanding the critical regions of the genome which might be involved in the development of epilepsy.

Spontaneous intracranial hypotension syndrome treated with fludrocortisone

Spontaneous intracranial hypotension is a rare syndrome characterized by orthostatic headache not associated with trauma or dural puncture. In most cases, it is caused by a spontaneous spinal cerebrospinal fluid leakage as demonstrated by neuroradiological studies. The standard of care consists of conservative treatment including bed rest, hydration, and administration of caffeine or glucocorticoids. When such conservative therapy fails, an epidural blood patch is recommended. In this report, we describe the treatment of 2 patients with spontaneous intracranial hypotension who failed conservative treatment and went on to have complete and sustained resolution of their symptoms after the administration of oral fludrocortisone.

Choroid plexus in the eye: a case study

PURPOSE

The purpose of this report is to describe a pediatric case of total retinal detachment (RD) with secondary glaucoma in the setting of posterior coloboma with the metaplastic retinal pigment epithelium showing abrupt transition to choroid plexus tissue.

METHODS

Retrospective case report.

RESULTS

A 3-month-old patient presented with leukocoria and enlarged right eye. She was found to have a funnel RD with anterior displacement of lens-iris diaphragm and secondary glaucoma. Orbital imaging ruled out retinoblastoma, and posterior coloboma was identified. Intraocular pressures remained significantly elevated despite maximal medical therapy on glaucoma drops and transscleral cycloablation, and the eye was enucleated for comfort. Histologic analysis confirmed neovascularization of the iris, total RD, and posterior coloboma with the associated metaplastic retinal pigment epithelium showing abrupt transition to choroid plexus tissue.

CONCLUSION

This is the first reported case of choroid plexus in the human eye. A close association of choroid plexus with coloboma and RD raises possibility that this tissue may have functionally contributed to pathogenesis of RD by secreting cerebrospinal fluid within subretinal space.

Altered expression of aquaporin 1 and 5 in the choroid plexus following preterm intraventricular hemorrhage

Intraventricular hemorrhage (IVH) with posthemorrhagic ventricular dilatation (PHVD) is a common cause of hydrocephalus in infants. Dysregulation of cerebrospinal fluid (CSF) production by the choroid plexus may contribute to the development of PHVD. The aquaporins (AQPs), transmural water transporting proteins, are believed to contribute to CSF production. The aim of the study was to characterize the expression and localization of AQP1, 4 and 5 in the choroid plexus following preterm IVH. Using a preterm rabbit pup model, the mRNA expression, protein level and localization of AQP1, 4 and 5 were investigated in the choroid plexus at 24 and 72 h following IVH with PHVD. Further, AQP1, 4 and 5 expression were characterized in primary human plexus epithelial cells exposed to CSF from preterm human infants with IVH and to hemoglobin metabolites. IVH with PHVD in the immature brain caused a downregulation of AQP1 mRNA, the key AQP in CSF production, but an upregulation of AQP1 protein level with apical epithelial cell localization. Notably, AQP5 was expressed in the choroid plexus with upregulated mRNA expression and protein levels during PHVD with apical epithelial cell localization. Analysis of human choroid plexus epithelial cells in vitro, following exposure to posthemorrhagic CSF and to hemin, displayed results concordant with those observed in vivo, i.e. downregulation of AQP1 mRNA and upregulation of AQP5 mRNA expression. AQP4 was neither detectable in vivo nor in vitro. The changes observed in AQP1 and AQP5 expression in the choroid plexus suggest an adaptive response following IVH with possible functional implications for the development of PHVD.

Plasminogen in cerebrospinal fluid originates from circulating blood

Background

Plasminogen activation is a ubiquitous source of fibrinolytic and proteolytic activity. Besides its role in prevention of thrombosis, plasminogen is involved in inflammatory reactions in the central nervous system. Plasminogen has been detected in the cerebrospinal fluid (CSF) of patients with inflammatory diseases; however, its origin remains controversial, as the blood–CSF barrier may restrict its diffusion from blood.

Methods

We investigated the origin of plasminogen in CSF using Alexa Fluor 488–labelled rat plasminogen injected into rats with systemic inflammation and blood–CSF barrier dysfunction provoked by lipopolysaccharide (LPS). Near-infrared fluorescence imaging and immunohistochemistry fluorescence microscopy were used to identify plasminogen in brain structures, its concentration and functionality were determined by Western blotting and a chromogenic substrate assay, respectively. In parallel, plasminogen was investigated in CSF from patients with Guillain-Barré syndrome (n = 15), multiple sclerosis (n = 19) and noninflammatory neurological diseases (n = 8).

Results

Endogenous rat plasminogen was detected in higher amounts in the CSF and urine of LPS-treated animals as compared to controls. In LPS-primed rats, circulating Alexa Fluor 488–labelled rat plasminogen was abundantly localized in the choroid plexus, CSF and urine. Plasminogen in human CSF was higher in Guillain-Barré syndrome (median = 1.28 ng/μl (interquartile range (IQR) = 0.66 to 1.59)) as compared to multiple sclerosis (median = 0.3 ng/μl (IQR = 0.16 to 0.61)) and to noninflammatory neurological diseases (median = 0.27 ng/μl (IQR = 0.18 to 0.35)).

Conclusions

Our findings demonstrate that plasminogen is transported from circulating blood into the CSF of rats via the choroid plexus during inflammation. Our data suggest that a similar mechanism may explain the high CSF concentrations of plasminogen detected in patients with inflammation-derived CSF barrier impairment.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-014-0154-y) contains supplementary material, which is available to authorized users.

Idiopathic cerebrospinal fluid overproduction: case-based review of the pathophysiological mechanism implied in the cerebrospinal fluid production

Cerebrospinal fluid (CSF) overproduction results from either CSF infection or choroid plexus hypertrophy or tumor, with only a single idiopathic case described so far. We report a unique case of a male infant with Crouzon syndrome who presented with intracranial hypertension, caused by up to 4-fold increase in CSF daily production. Conditions related to CSF overproduction, namely central nervous system infections and choroid plexus hypertrophy or tumor, were ruled out by repeated magnetic resonance imaging and CSF samples. Medical therapy failed to reduce CSF production and the patient underwent several shunting procedures, cranial expansion, and endoscopic coagulation of the choroid plexus. This article thoroughly reviews pertinent literature on CSF production mechanisms and possible therapeutic implications.

Brain disposition of α-Synuclein: roles of brain barrier systems and implications for Parkinson's disease

Parkinson’s disease (PD) is a neurodegenerative disorder characterized by the accumulation of α-Synuclein (a-Syn) into Lewy body inclusions and the loss of dopaminergic neurons in the substantia nigra (SN). Accumulation of a-Syn can induce a progressive, cyclical pathology that results in the transmission of toxic, aggregated a-Syn species to healthy neurons, leading to further neurodegeneration such as occurs in PD. The blood–brain barrier (BBB) and blood-cerebrospinal fluid (CSF) barriers (BCSFB) are responsible for regulating the access of nutrients and other molecules to the brain, but very little is known about their regulatory roles in maintaining the homeostasis of a-Syn in the CSF and brain parenchyma. This review analyzes the current literature reports on the transport of a-Syn by various brain cell types with a particular focus on the potential transport mechanisms of a-Syn at the BBB and BCSFB. The indication of altered a-Syn transport by brain barriers in PD pathoetiology and the perspectives in this research area are also discussed.

Role of oligomeric proanthocyanidins derived from an extract of persimmon fruits in the oxidative stress-related aging process

Many researchers have focused on the oligomeric form of proanthocyanidins with a lower level of polymerization found in foodstuffs such as grape seeds and blackberries. The present study indicated that the oral administration of oligomers isolated from persimmon fruits extended the lifespan of senescence-accelerated mouse prone/8 (SAMP8), a murine model of accelerated senescence. On the other hand, oligomer-treated SAMP8 did not show stereotypical behavior. We also revealed that the oral administration of oligomers improved spatial and object recognition memory in SAMP8. The density of axons in the hippocampal CA1 was significantly increased by oligomer administration. Moreover, the administration of oligomers increased the phosphorylation of vascular endothelial growth factor receptor (VEGFR)-2 in the hippocampal CA3, hypothalamus, and choroid plexus. We speculate that memory improvement accompanied by histological changes may be induced directly in the hippocampus and indirectly in the hypothalamus and choroid plexus through VEGFR-2 signaling. In the present study, we elucidated the protective effect of oligomers against memory impairment with aging. VEGFR-2 signaling may provide a new insight into ways to protect against memory deficit in the aging brain.

A new look at cerebrospinal fluid circulation

According to the traditional understanding of cerebrospinal fluid (CSF) physiology, the majority of CSF is produced by the choroid plexus, circulates through the ventricles, the cisterns, and the subarachnoid space to be absorbed into the blood by the arachnoid villi. This review surveys key developments leading to the traditional concept. Challenging this concept are novel insights utilizing molecular and cellular biology as well as neuroimaging, which indicate that CSF physiology may be much more complex than previously believed. The CSF circulation comprises not only a directed flow of CSF, but in addition a pulsatile to and fro movement throughout the entire brain with local fluid exchange between blood, interstitial fluid, and CSF. Astrocytes, aquaporins, and other membrane transporters are key elements in brain water and CSF homeostasis. A continuous bidirectional fluid exchange at the blood brain barrier produces flow rates, which exceed the choroidal CSF production rate by far. The CSF circulation around blood vessels penetrating from the subarachnoid space into the Virchow Robin spaces provides both a drainage pathway for the clearance of waste molecules from the brain and a site for the interaction of the systemic immune system with that of the brain. Important physiological functions, for example the regeneration of the brain during sleep, may depend on CSF circulation.

Aquaporin and brain diseases

BACKGROUND

The presence of water channel proteins, aquaporins (AQPs), in the brain led to intense research in understanding the underlying roles of each of them under normal conditions and pathological conditions.

SCOPE OF REVIEW

In this review, we summarize some of the recent knowledge on the 3 main AQPs (AQP1, AQP4 and AQP9), with a special focus on AQP4, the most abundant AQP in the central nervous system.

MAJOR CONCLUSIONS

AQP4 was most studied in several brain pathological conditions ranging from acute brain injuries (stroke, traumatic brain injury) to the chronic brain disease with autoimmune neurodegenerative diseases. To date, no specific therapeutic agents have been developed to either inhibit or enhance water flux through these channels. However, experimental results strongly underline the importance of this topic for future investigation. Early inhibition of water channels may have positive effects in prevention of edema formation in brain injuries but at later time points during the course of a disease, AQP is critical for clearance of water from the brain into blood vessels.

GENERAL SIGNIFICANCE

Thus, AQPs, and in particular AQP4, have important roles both in the formation and resolution of edema after brain injury. The dual, complex function of these water channel proteins makes them an excellent therapeutic target. This article is part of a Special Issue entitled Aquaporins.

The role of choroid plexus in IVIG-induced beta-amyloid clearance

We have shown that intravenous immunoglobulin (IVIG) contains anti-Aβ autoantibodies and IVIG could induce beta amyloid (Aβ) efflux from cerebrospinal fluid (CSF) to blood in both Multiple Sclerosis (MS) and Alzheimer disease (AD) patients. However, the molecular mechanism underlying IVIG-induced Aβ efflux remains unclear. In this study, we used amyloid precursor protein (AβPP) transgenic mice to investigate if the IVIG could induce efflux of Aβ from the brain and whether low-density lipoprotein receptor-related protein-1 (LRP1), a hypothetic Aβ transporter in blood-CSF barrier (BCB); could mediate this clearance process. We currently provide strong evidence to demonstrate that IVIG could reduce brain Aβ levels by pulling Aβ into the blood system in AβPP transgenic mice. In the mechanistic study, IVIG could induce Aβ efflux through the in vitro BCB membrane formed by cultured BCB epithelial cells. Both receptor-associated protein (RAP; a functional inhibitor of LRP1), and LRP1 siRNA were able to significantly inhibit the Aβ efflux. Should Aβ prove to be the underlying cause of AD, our results strongly suggest that IVIG could be beneficial in the therapy for AD by inducing efflux of Aβ from the brain through the LRP1 in the BCB.

Blood pressure regulation via the epithelial sodium channel: from gene to kidney and beyond

The epithelial sodium channel (ENaC) has long been recognized as playing a vital role in blood pressure (BP) regulation due to its involvement in fluid balance. The genes encoding the three ENaC subunits are likewise important contributors to hypertension, both in rare monogenic diseases and in the general population. The unusually high numbers of genetic variants associated with complex traits, including BP, that are located in non-coding areas suggest an involvement of these variants in regulatory functions. This may involve differential regulation of expression in different tissues. Emerging evidence indicates that the ENaC plays an important role in BP determination not only via its actions in the kidney, but also in other tissues commonly involved in BP regulation. The ENaC in the central nervous system is proposed to regulate BP via sympathetic nervous system activity. Recent evidence suggests that the ENaC contributes to vascular function and the myogenic response. Additional roles potentially include initiation of the baroreceptor reflex via ENaC in the baroreceptors and driving high salt intake with a 'taste for salt' via ENaC in the tongue. The present review describes the involvement of the ENaC in the determination of BP at a genetic and physiological level, detailing recent evidence for its role in the kidney and in other pertinent tissues.

Enhanced activity of an angiotensin-(1-7) neuropeptidase in glucocorticoid-induced fetal programming

We previously identified angiotensin converting enzyme (ACE) and an endopeptidase activity that degraded angiotensin-(1-7) [Ang-(1-7)] to Ang-(1-5) and Ang-(1-4), respectively, in the cerebrospinal fluid (CSF) of 6-month old male sheep. The present study undertook a more comprehensive analysis of the CSF peptidase that converts Ang-(1-7) to Ang-(1-4) in control and in utero betamethasone-exposed sheep (BMX). Characterization of the Ang-(1-7) peptidase revealed that the thiol agents 4-aminophenylmercuric acetate (APMA) and p-chloromercuribenzoic acid (PCMB), as well as the metallo-chelators o-phenanthroline and EDTA essentially abolished the enzyme activity. Additional inhibitors for serine, aspartyl, and cysteine proteases, as well as selective inhibitors against the endopeptidases neprilysin, neurolysin, prolyl and thimet oligopeptidases did not attenuate enzymatic activity. Competition studies against the peptidase revealed similar IC50s for Ang-(1-7) (5μM) and Ang II (3μM), but lower values for Ala(1)-Ang-(1-7) and Ang-(2-7) of 1.8 and 2.0μM, respectively. In contrast, bradykinin exhibited a 6-fold higher IC50 (32μM) than Ang-(1-7) while neurotensin was a poor competitor. Mean arterial pressure (78±1 vs. 94±2mmHg, N=4-5, P<0.01) and Ang-(1-7) peptidase activity (14.2±1 vs 32±1.5fmol/min/ml CSF, N=5, P<0.01) were higher in the BMX group, and enzyme activity inversely correlated with Ang-(1-7) content in CSF. Lower Ang-(1-7) expression in brain is linked to baroreflex impairment in hypertension and aging, thus, increased activity of an Ang-(1-7) peptidase may contribute to lower CSF Ang-(1-7) levels, elevated blood pressure and impaired reflex function in this model of fetal programming.

The choroid plexus: a comprehensive review of its history, anatomy, function, histology, embryology, and surgical considerations

INTRODUCTION

The role of the choroid plexus in cerebrospinal fluid production has been identified for more than a century. Over the years, more intensive studies of this structure has lead to a better understanding of the functions, including brain immunity, protection, absorption, and many others. Here, we review the macro- and microanatomical structure of the choroid plexus in addition to its function and embryology.

METHOD

The literature was searched for articles and textbooks for data related to the history, anatomy, physiology, histology, embryology, potential functions, and surgical implications of the choroid plexus. All were gathered and summarized comprehensively.

CONCLUSION

We summarize the literature regarding the choroid plexus and its surgical implications.

Gene expression-based comparison of the human secretory neuroepithelia of the brain choroid plexus and the ocular ciliary body: potential implications for glaucoma

Background

The neuroepithelia of the choroid plexus (CP) in the brain and the ciliary body (CB) of the eye have common embryological origins and share similar micro-structure and functions. The CP epithelium (CPE) and the non-pigmented epithelium (NPE) of the CB produce the cerebrospinal fluid (CSF) and the aqueous humor (AH) respectively. Production and outflow of the CSF determine the intracranial pressure (ICP); production and outflow of the AH determine the intraocular pressure (IOP). Together, the IOP and ICP determine the translaminar pressure on the optic disc which may be involved in the pathophysiology of primary open angle glaucoma (POAG). The aim of this study was to compare the molecular machinery of the secretory neuroepithelia of the CP and CB (CPE versus NPE) and to determine their potential role in POAG.

Methods

We compared the transcriptomes and functional annotations of healthy human CPE and NPE. Microarray and bioinformatic studies were performed using an Agilent platform and the Ingenuity Knowledge Database (IPA).

Results

Based on gene expression profiles, we found many similar functions for the CPE and NPE including molecular transport, neurological disease processes, and immunological functions. With commonly-used selection criteria (fold-change > 2.5, p-value < 0.05), 14% of the genes were expressed significantly differently between CPE and NPE. When we used stricter selection criteria (fold-change > 5, p-value < 0.001), still 4.5% of the genes were expressed differently, which yielded specific functions for the CPE (ciliary movement and angiogenesis/hematopoiesis) and for the NPE (neurodevelopmental properties). Apart from a few exceptions (e.g. SLC12A2, SLC4A4, SLC4A10, KCNA5, and SCN4B), all ion transport protein coding genes involved in CSF and AH production had similar expression profiles in CPE and NPE. Three POAG disease genes were expressed significantly higher in the CPE than the NPE, namely CDH1, CDKN2B and SIX1.

Conclusions

The transcriptomes of the CPE and NPE were less similar than we previously anticipated. High expression of CSF/AH production genes and candidate POAG disease genes in the CPE and NPE suggest that both might be involved in POAG.

The presence of oligoclonal IgG bands in human CSF during the course of neurological diseases

The analysis of cerebrospinal fluid (CSF) is an important tool for the diagnosis of neurological diseases. However, there is limited knowledge about the representativity of a single oligoclonal band (OCB) analysis for a neurological disease during its clinical course. In this study, we analyzed the presence of OCB in the CSF of patients who underwent lumbar puncture more than once. We retrospectively analyzed anonymized data from serial 17,002 CSF analyses done in the CSF laboratory of the Department of Neurology, University Hospital Zurich. We included cases with documented diagnosis in whom OCB were determined more than once. We included 144 patients. The median time span between the first and second OCB analysis was 274 days (range, 1-3,533 days). The result of the second OCB analysis was identical in 109 cases, and different in 35 (24 %). Twenty-five patients acquired and ten patients lost OCB over time. Three of 24 MS patients did not show OCB at the first CSF analysis, but in the second. In the entire group, newly occurring OCB were often associated with new symptoms or occurred after the acute phase of CNS infectious diseases, supposedly as a consequence of the immune reaction. A loss of OCB was often associated with remissions from diseases, e.g., during effective treatment. In patients with neurological diseases, both initially positive and negative OCB results may change over time, which often parallels the clinical condition. Such variability must be taken into account for the interpretation of OCB results.

Clinical pharmacokinetics of antibacterials in cerebrospinal fluid

In the past 20 years, an increased discrepancy between new available antibacterials and the emergence of multidrug-resistant strains has been observed. This condition concerns physicians involved in the treatment of central nervous system (CNS) infections, for which clinical and microbiological success depends on the rapid achievement of bactericidal concentrations. In order to accomplish this aim, the choice of drugs is based on their disposition toward the cerebrospinal fluid (CSF), which is influenced by the physicochemical characteristics of antibacterials. A reduced distribution into CSF has been documented for beta-lactams, especially cephalosporins and carbapenems, on the basis of their hydrophilic nature. However, they represent a cornerstone of the majority of combined therapeutic schemes for their ability to achieve bactericidal concentrations, especially in the presence of inflamed meninges. The good tolerability of beta-lactams makes possible high daily dose intensities, which may be associated with increased probability of cure. Furthermore, the adoption of continuous infusion seems to be a fruitful option. Fluoroquinolones, namely moxifloxacin, and antituberculosis drugs, together with the agents such as linezolid, reach the highest CSF/plasma concentration ratio, which is greater than 0.8, and for most of these drugs it is near 1. For all drugs that are currently used for the treatment of CNS infections, the evaluation of pharmacokinetic/pharmacodynamic parameters, on the basis of dosing regimens and their time-dependent or concentration-dependent pattern of bacterial killing, remains an important aspect of clinical investigation and medical practice.

Gene expression and functional annotation of the human and mouse choroid plexus epithelium

BACKGROUND

The choroid plexus epithelium (CPE) is a lobed neuro-epithelial structure that forms the outer blood-brain barrier. The CPE protrudes into the brain ventricles and produces the cerebrospinal fluid (CSF), which is crucial for brain homeostasis. Malfunction of the CPE is possibly implicated in disorders like Alzheimer disease, hydrocephalus or glaucoma. To study human genetic diseases and potential new therapies, mouse models are widely used. This requires a detailed knowledge of similarities and differences in gene expression and functional annotation between the species. The aim of this study is to analyze and compare gene expression and functional annotation of healthy human and mouse CPE.

METHODS

We performed 44k Agilent microarray hybridizations with RNA derived from laser dissected healthy human and mouse CPE cells. We functionally annotated and compared the gene expression data of human and mouse CPE using the knowledge database Ingenuity. We searched for common and species specific gene expression patterns and function between human and mouse CPE. We also made a comparison with previously published CPE human and mouse gene expression data.

RESULTS

Overall, the human and mouse CPE transcriptomes are very similar. Their major functionalities included epithelial junctions, transport, energy production, neuro-endocrine signaling, as well as immunological, neurological and hematological functions and disorders. The mouse CPE presented two additional functions not found in the human CPE: carbohydrate metabolism and a more extensive list of (neural) developmental functions. We found three genes specifically expressed in the mouse CPE compared to human CPE, being ACE, PON1 and TRIM3 and no human specifically expressed CPE genes compared to mouse CPE.

CONCLUSION

Human and mouse CPE transcriptomes are very similar, and display many common functionalities. Nonetheless, we also identified a few genes and pathways which suggest that the CPE between mouse and man differ with respect to transport and metabolic functions.

Neuropsychiatric Lupus, the Blood Brain Barrier, and the TWEAK/Fn14 Pathway

Patients with systemic lupus erythematosus (SLE) can experience acute neurological events such as seizures, cerebrovascular accidents, and delirium, psychiatric conditions including depression, anxiety, and psychosis, as well as memory loss and general cognitive decline. Neuropsychiatric SLE (NPSLE) occurs in between 30 and 40% of SLE patients, can constitute the initial patient presentation, and may occur outside the greater context of an SLE flare. Current efforts to elucidate the mechanistic underpinnings of NPSLE are focused on several different and potentially complementary pathways, including thrombosis, brain autoreactive antibodies, and complement deposition. Furthermore, significant effort is dedicated to understanding the contribution of neuroinflammation induced by TNF, IL-1, IL-6, and IFN-γ. More recent studies have pointed to a possible role for the TNF family ligand TWEAK in the pathogenesis of neuropsychiatric disease in human lupus patients, and in a murine model of this disease. The blood brain barrier (BBB) consists of tight junctions between endothelial cells (ECs) and astrocytic projections which regulate paracellular and transcellular flow into the central nervous system (CNS), respectively. Given the privileged environment of the CNS, an important question is whether and how the integrity of the BBB is compromised in NPSLE, and its potential pathogenic role. Evidence of BBB violation in NPSLE includes changes in the albumin quotient (Q_alb) between plasma and cerebrospinal fluid, activation of brain ECs, and magnetic resonance imaging. This review summarizes the evidence implicating BBB damage as an important component in NPSLE development, occurring via damage to barrier integrity by environmental triggers such as infection and stress; cerebrovascular ischemia as result of a generally prothrombotic state; and immune mediated EC activation, mediated by antibodies and/or inflammatory cytokines. Additionally, new evidence supporting the role of TWEAK/Fn14 signaling in compromising the integrity of the BBB in lupus will be presented.

Updated physiology and pathophysiology of CSF circulation--the pulsatile vector theory

INTRODUCTION

Hydrocephalus is still a not well-understood diagnostic and a therapeutic dilemma because of the lack of sufficient and comprehensive model of cerebrospinal fluid circulation and pathological alterations.

CONCLUSIONS

Based on current studies, reviews, and knowledge of cerebrospinal fluid dynamics, brain water dynamics, intracranial pressure, and cerebral perfusion physiology, a new concept is deducted that can describe normal and pathological changes of cerebrospinal fluid circulation and pathophysiology of idiopathic intracranial hypertension.

Cerebrospinal Fluid Secretion by the Choroid Plexus

The choroid plexus epithelium is a cuboidal cell monolayer, which produces the majority of the cerebrospinal fluid. The concerted action of a variety of integral membrane proteins mediates the transepithelial movement of solutes and water across the epithelium. Secretion by the choroid plexus is characterized by an extremely high rate and by the unusual cellular polarization of well-known epithelial transport proteins. This review focuses on the specific ion and water transport by the choroid plexus cells, and then attempts to integrate the action of specific transport proteins to formulate a model of cerebrospinal fluid secretion. Significant emphasis is placed on the concept of isotonic fluid transport across epithelia, as there is still surprisingly little consensus on the basic biophysics of this phenomenon. The role of the choroid plexus in the regulation of fluid and electrolyte balance in the central nervous system is discussed, and choroid plexus dysfunctions are described in a very diverse set of clinical conditions such as aging, Alzheimer's disease, brain edema, neoplasms, and hydrocephalus. Although the choroid plexus may only have an indirect influence on the pathogenesis of these conditions, the ability to modify epithelial function may be an important component of future therapies.

Ciliogenesis and cerebrospinal fluid flow in the developing Xenopus brain are regulated by foxj1

Background

Circulation of cerebrospinal fluid (CSF) through the ventricular system is driven by motile cilia on ependymal cells of the brain. Disturbed ciliary motility induces the formation of hydrocephalus, a pathological accumulation of CSF resulting in ventricle dilatation and increased intracranial pressure. The mechanism by which loss of motile cilia causes hydrocephalus has not been elucidated. The aim of this study was: (1) to provide a detailed account of the development of ciliation in the brain of the African clawed frog Xenopus laevis; and (2) to analyze the relevance of ependymal cilia motility for CSF circulation and brain ventricle morphogenesis in Xenopus.

Methods

Gene expression analysis of foxj1, the bona fide marker for motile cilia, was used to identify potentially ciliated regions in the developing central nervous system (CNS) of the tadpole. Scanning electron microscopy (SEM) was used to reveal the distribution of mono- and multiciliated cells during successive stages of brain morphogenesis, which was functionally assessed by bead injection and video microscopy of ventricular CSF flow. An antisense morpholino oligonucleotide (MO)-mediated gene knock-down that targeted foxj1 in the CNS was applied to assess the role of motile cilia in the ventricles.

Results

RNA transcripts of foxj1 in the CNS were found from neurula stages onwards. Following neural tube closure, foxj1 expression was seen in distinct ventricular regions such as the zona limitans intrathalamica (ZLI), subcommissural organ (SCO), floor plate, choroid plexus (CP), and rhombomere boundaries. In all areas, expression of foxj1 preceded the outgrowth of monocilia and the subsequent switch to multiciliated ependymal cells. Cilia were absent in foxj1 morphants, causing impaired CSF flow and fourth ventricle hydrocephalus in tadpole-stage embryos.

Conclusions

Motile ependymal cilia are important organelles in the Xenopus CNS, as they are essential for the circulation of CSF and maintenance of homeostatic fluid pressure. The Xenopus CNS ventricles might serve as a novel model system for the analysis of human ciliary genes whose deficiency cause hydrocephalus.

Mechanisms that determine the internal environment of the developing brain: a transcriptomic, functional and ultrastructural approach

We provide comprehensive identification of embryonic (E15) and adult rat lateral ventricular choroid plexus transcriptome, with focus on junction-associated proteins, ionic influx transporters and channels. Additionally, these data are related to new structural and previously published permeability studies. Results reveal that most genes associated with intercellular junctions are expressed at similar levels at both ages. In total, 32 molecules known to be associated with brain barrier interfaces were identified. Nine claudins showed unaltered expression, while two claudins (6 and 8) were expressed at higher levels in the embryo. Expression levels for most cytoplasmic/regulatory adaptors (10 of 12) were similar at the two ages. A few junctional genes displayed lower expression in embryos, including 5 claudins, occludin and one junctional adhesion molecule. Three gap junction genes were enriched in the embryo. The functional effectiveness of these junctions was assessed using blood-delivered water-soluble tracers at both the light and electron microscopic level: embryo and adult junctions halted movement of both 286Da and 3kDa molecules into the cerebrospinal fluid (CSF). The molecular identities of many ion channel and transporter genes previously reported as important for CSF formation and secretion in the adult were demonstrated in the embryonic choroid plexus (and validated with immunohistochemistry of protein products), but with some major age-related differences in expression. In addition, a large number of previously unidentified ion channel and transporter genes were identified for the first time in plexus epithelium. These results, in addition to data obtained from electron microscopical and physiological permeability experiments in immature brains, indicate that exchange between blood and CSF is mainly transcellular, as well-formed tight junctions restrict movement of small water-soluble molecules from early in development. These data strongly indicate the brain develops within a well-protected internal environment and the exchange between the blood, brain and CSF is transcellular and not through incomplete barriers.

Senescent changes in cerebrospinal fluid circulatory physiology and their role in the pathogenesis of normal-tension glaucoma

PURPOSE

To evaluate the evidence supporting a role for senescent changes in cerebrospinal fluid (CSF) circulatory physiology in the pathogenesis of normal-tension glaucoma (NTG).

DESIGN

Literature review and personal perspective of the authors.

METHODS

Analysis of selected articles in the peer-reviewed literature with interpretation and perspective.

RESULTS

Recent studies have reported that intracranial pressure is lower in patients with NTG when compared with patients with primary open-angle glaucoma and nonglaucomatous control subjects. It has been suggested that a low intracranial pressure in patients with normal intraocular pressure could lead to glaucomatous damage. This low intracranial pressure, leading to an abnormally high trans-lamina cribrosa pressure difference, could result in barotraumatically induced optic nerve damage at the lamina cribrosa. However, several experimental studies do not support the speculation that low intracranial pressure and the resulting pressure-dependent effects cause bowing back of the lamina cribrosa and optic disc cupping. On the other hand, CSF production and turnover have been shown to be decreased in aging and in pathologic conditions, such as Alzheimer disease and normal pressure hydrocephalus. Interestingly, recent studies have revealed that both Alzheimer disease patients and patients with normal pressure hydrocephalus may have a higher risk of developing glaucoma. Therefore, we believe that CSF circulatory failure, ultimately resulting in reduced neurotoxin clearance along the optic nerves, could be an alternative explanation as to why glaucoma develops in patients with low intracranial pressure.

CONCLUSIONS

On the basis of the evidence available from the peer-reviewed literature, our tentative conclusion is that age-related changes in CSF circulatory physiology and the subsequent decrease in CSF turnover, with diminished clearance of toxic substances, can account for, at least in part, the pathogenesis of NTG. It should be stressed that for the moment at least, the present hypothesis remains unproven. Further research will be necessary to determine the possible role of CSF circulatory dysfunction in NTG. If confirmed, this hypothesis could provide new, important insights into the pathogenesis of NTG.

"Compensated hyperosmolarity" of cerebrospinal fluid and the development of hydrocephalus

Acute osmolar loading of cerebrospinal fluid within one lateral ventricle of dogs was examined as a cause of water extraction from the bloodstream and an increase in intracranial pressure. We have shown that a certain amount of (3)H₂O from the bloodstream enters osmotically loaded cerebrospinal fluid significantly faster, hence causing a significant increase in intracranial pressure. The noted phenomenon in which intracranial pressure still significantly increases, but in which the hyperosmolarity of the cerebrospinal fluid is no longer present, was named "compensated hyperosmolarity". In the case of the sub-chronic application of hyperosmolar solutions into cat ventricles, we observed an increase in cerebrospinal fluid volume and a more pronounced development of hydrocephalus in the area of application, but without significant increase in intracranial pressure and without blockage of cerebrospinal fluid pathways. These results support the newly proposed hypothesis of cerebrospinal fluid hydrodynamics and the ability to develop new strategies for the treatment of cerebrospinal fluid-related diseases.

Riding the wave of ependymal cilia: genetic susceptibility to hydrocephalus in primary ciliary dyskinesia

Congenital hydrocephalus is a relatively common and debilitating birth defect with several known physiological causes. Dysfunction of motile cilia on the ependymal cells that line the ventricular surface of the brain can result in hydrocephalus by hindering the proper flow of cerebrospinal fluid. As a result, hydrocephalus can be associated with primary ciliary dyskinesia, a rare pediatric syndrome resulting from defects in ciliary and flagellar motility. Although the prevalence of hydrocephalus in primary ciliary dyskinesia patients is low, it is a common hallmark of the disease in mouse models, suggesting that distinct genetic mechanisms underlie the differences in the development and physiology of human and mouse brains. Mouse models of primary ciliary dyskinesia reveal strain-specific differences in the appearance and severity of hydrocephalus, indicating the presence of genetic modifiers segregating in inbred strains. These models may provide valuable insight into the genetic mechanisms that regulate susceptibility to hydrocephalus under the conditions of ependymal ciliary dysfunction.

3β-hydroxysteroid dehydrogenase in the brain ependymocytes

We studied activity of 3β-hydroxysteroid dehydrogenase in rat brain ependymocytes. Enzyme activity was found in the cytoplasm of cells lining the villi in the vascular plexuses in the lateral ventricles and cells lining the ventricles. These data suggest that ependymocyte can synthesize neurosteroids.

Reassessing cerebrospinal fluid (CSF) hydrodynamics: a literature review presenting a novel hypothesis for CSF physiology

The traditional model of cerebrospinal fluid (CSF) hydrodynamics is being increasingly challenged in view of recent scientific evidences. The established model presumes that CSF is primarily produced in the choroid plexuses (CP), then flows from the ventricles to the subarachnoid spaces, and is mainly reabsorbed into arachnoid villi (AV). This model is seemingly based on faulty research and misinterpretations. This literature review presents numerous evidence for a new hypothesis of CSF physiology, namely, CSF is produced and reabsorbed throughout the entire CSF-Interstitial fluid (IF) functional unit. IF and CSF are mainly formed and reabsorbed across the walls of CNS blood capillaries. CP, AV and lymphatics become minor sites for CSF hydrodynamics. The lymphatics may play a more significant role in CSF absorption when CSF-IF pressure increases. The consequences of this complete reformulation of CSF hydrodynamics may influence applications in research, publications, including osteopathic manual treatments.

The impact of P-gp functionality on non-steady state relationships between CSF and brain extracellular fluid

In the development of central nervous system (CNS)-targeted drugs, the prediction of human CNS target exposure is a big challenge. Cerebrospinal fluid (CSF) concentrations have often been suggested as a ‘good enough’ surrogate for brain extracellular fluid (brain_ECF, brain target site) concentrations in humans. However, brain anatomy and physiology indicates prudence. We have applied a multiple microdialysis probe approach in rats, for continuous measurement and direct comparison of quinidine kinetics in brain_ECF, CSF, and plasma. The data obtained indicated important differences between brain_ECF and CSF kinetics, with brain_ECF kinetics being most sensitive to P-gp inhibition. To describe the data we developed a systems-based pharmacokinetic model. Our findings indicated that: (1) brain_ECF- and CSF-to-unbound plasma AUC_0–360 ratios were all over 100 %; (2) P-gp also restricts brain intracellular exposure; (3) a direct transport route of quinidine from plasma to brain cells exists; (4) P-gp-mediated efflux of quinidine at the blood–brain barrier seems to result of combined efflux enhancement and influx hindrance; (5) P-gp at the blood–CSF barrier either functions as an efflux transporter or is not functioning at all. It is concluded that in parallel obtained data on unbound brain_ECF, CSF and plasma concentrations, under dynamic conditions, is a complex but most valid approach to reveal the mechanisms underlying the relationship between brain_ECF and CSF concentrations. This relationship is significantly influenced by activity of P-gp. Therefore, information on functionality of P-gp is required for the prediction of human brain target site concentrations of P-gp substrates on the basis of human CSF concentrations.

The mastermind approach to CNS drug therapy: translational prediction of human brain distribution, target site kinetics, and therapeutic effects

Despite enormous advances in CNS research, CNS disorders remain the world's leading cause of disability. This accounts for more hospitalizations and prolonged care than almost all other diseases combined, and indicates a high unmet need for good CNS drugs and drug therapies.Following dosing, not only the chemical properties of the drug and blood-brain barrier (BBB) transport, but also many other processes will ultimately determine brain target site kinetics and consequently the CNS effects. The rate and extent of all these processes are regulated dynamically, and thus condition dependent. Therefore, heterogenious conditions such as species, gender, genetic background, tissue, age, diet, disease, drug treatment etc., result in considerable inter-individual and intra-individual variation, often encountered in CNS drug therapy.For effective therapy, drugs should access the CNS "at the right place, at the right time, and at the right concentration". To improve CNS therapies and drug development, details of inter-species and inter-condition variations are needed to enable target site pharmacokinetics and associated CNS effects to be translated between species and between disease states. Specifically, such studies need to include information about unbound drug concentrations which drive the effects. To date the only technique that can obtain unbound drug concentrations in brain is microdialysis. This (minimally) invasive technique cannot be readily applied to humans, and we need to rely on translational approaches to predict human brain distribution, target site kinetics, and therapeutic effects of CNS drugs.In this review the term "Mastermind approach" is introduced, for strategic and systematic CNS drug research using advanced preclinical experimental designs and mathematical modeling. In this way, knowledge can be obtained about the contributions and variability of individual processes on the causal path between drug dosing and CNS effect in animals that can be translated to the human situation. On the basis of a few advanced preclinical microdialysis based investigations it will be shown that the "Mastermind approach" has a high potential for the prediction of human CNS drug effects.

Brain-wide pathway for waste clearance captured by contrast-enhanced MRI

The glymphatic system is a recently defined brain-wide paravascular pathway for cerebrospinal fluid (CSF) and interstitial fluid (ISF) exchange that facilitates efficient clearance of solutes and waste from the brain. CSF enters the brain along para-arterial channels to exchange with ISF, which is in turn cleared from the brain along para-venous pathways. Because soluble amyloid β clearance depends on glymphatic pathway function, we proposed that failure of this clearance system contributes to amyloid plaque deposition and Alzheimer's disease progression. Here we provide proof of concept that glymphatic pathway function can be measured using a clinically relevant imaging technique. Dynamic contrast-enhanced MRI was used to visualize CSF-ISF exchange across the rat brain following intrathecal paramagnetic contrast agent administration. Key features of glymphatic pathway function were confirmed, including visualization of para-arterial CSF influx and molecular size-dependent CSF-ISF exchange. Whole-brain imaging allowed the identification of two key influx nodes at the pituitary and pineal gland recesses, while dynamic MRI permitted the definition of simple kinetic parameters to characterize glymphatic CSF-ISF exchange and solute clearance from the brain. We propose that this MRI approach may provide the basis for a wholly new strategy to evaluate Alzheimer's disease susceptibility and progression in the live human brain.

Utility of CSF in translational neuroscience

Human cerebrospinal fluid (CSF) sampling is of high value as the only general applicable methodology to obtain information on free drug concentrations in individual human brain. As the ultimate interest is in the free drug concentration at the CNS target site, the question is what CSF concentrations may tell us in that respect. Studies have been performed in rats and other animals for which concentrations in brain extracellular fluid (brain ECF) as a target site for many drugs, have been compared to (cisterna magna) CSF concentrations, at presumed steady state conditions,. The data indicated that CSF drug concentrations provided a rather good indication of, but not a reliable measure for predicting brain ECF concentrations. Furthermore, comparing rat with human CSF concentrations, human CSF concentrations tend to be higher and display much more variability. However, this comparison of CSF concentrations cannot be a direct one, as humans probably had a disease for which CSF was collected in the first place, while the rats were healthy. In order to be able to more accurately predict human brain ECF concentrations, understanding of the complexity of the CNS in terms of intrabrain pharmacokinetic relationships and the influence of CNS disorders on brain pharmacokinetics needs to be increased. This can be achieved by expanding a currently existing preclinically derived physiologically based pharmacokinetic model for brain distribution. This model has been shown to successfully predict data obtained for human lumbar CSF concentrations of acetaminophen which renders trust in the model prediction of human brain ECF concentrations. This model should further evolute by inclusion of influences of drug properties, fluid flows, transporter functionalities and different disease conditions. Finally the model should include measures of target site engagement and CNS effects, to ultimately learn about concentrations that best predict particular target site concentrations, via human CSF concentrations.

Manual drainage of the zebrafish embryonic brain ventricles

Cerebrospinal fluid (CSF) is a protein rich fluid contained within the brain ventricles. It is present during early vertebrate embryonic development and persists throughout life. Adult CSF is thought to cushion the brain, remove waste, and carry secreted molecules(1,2). In the adult and older embryo, the majority of CSF is made by the choroid plexus, a series of highly vascularized secretory regions located adjacent to the brain ventricles(3-5). In zebrafish, the choroid plexus is fully formed at 144 hours post fertilization (hpf)(6). Prior to this, in both zebrafish and other vertebrate embryos including mouse, a significant amount of embryonic CSF (eCSF) is present . These data and studies in chick suggest that the neuroepithelium is secretory early in development and may be the major source of eCSF prior to choroid plexus development(7). eCSF contains about three times more protein than adult CSF, suggesting that it may have an important role during development(8,9). Studies in chick and mouse demonstrate that secreted factors in the eCSF, fluid pressure, or a combination of these, are important for neurogenesis, gene expression, cell proliferation, and cell survival in the neuroepithelium(10-20). Proteomic analyses of human, rat, mouse, and chick eCSF have identified many proteins that may be necessary for CSF function. These include extracellular matrix components, apolipoproteins, osmotic pressure regulating proteins, and proteins involved in cell death and proliferation(21-24). However, the complex functions of the eCSF are largely unknown. We have developed a method for removing eCSF from zebrafish brain ventricles, thus allowing for identification of eCSF components and for analysis of the eCSF requirement during development. Although more eCSF can be collected from other vertebrate systems with larger embryos, eCSF can be collected from the earliest stages of zebrafish development, and under genetic or environmental conditions that lead to abnormal brain ventricle volume or morphology. Removal and collection of eCSF allows for mass spectrometric analysis, investigation of eCSF function, and reintroduction of select factors into the ventricles to assay their function. Thus the accessibility of the early zebrafish embryo allows for detailed analysis of eCSF function during development.

Is higher choroid plexus ‘load’ an aetiologic factor in idiopathic intracranial hypertension? A clinico-imaging morphometric correlative study

Background

Idiopathic intracranial hypertension (IIH) is a condition of raised cerebrospinal fluid (CSF) pressure with normal ventricular size. Although the pathogenesis of IIH remains controversial, increased CSF formation may be important. We hypothesised that if increased CSF formation was an aetiologic factor, it might result in a macroscopic increase in size of the choroid plexus (CP).

Method

We retrospectively studied 50 patients with IIH. Total size of the CP was estimated on computed tomography (CT) venograms from the sum of axial areas measured at three locations. Results were compared with the CP load of 50 matched controls on post-contrast head CTs. Evans Index was measured to exclude ventriculomegaly. Results were analysed using a Student’s t test for independent samples ( p < 0.05), and the effect of ICP was tested on the dependent variable (area of CP) using regression analysis.

Results

There was no significant difference in the size of the CP glomus, total axial areas of the CP between IIH patients (183 mm2) and controls (178 mm2) and no correlation between the ‘load’ of CP and the degree of intracranial pressure (ICP) ( R2 < 0.02).

Conclusion

If increased CSF formation is an aetiologic factor in IIH, this is not reflected in a corresponding raised ‘load’ of CP.

The pressure distribution of cerebrospinal fluid responds to residual compression and decompression in an animal model of acute spinal cord injury

STUDY DESIGN

In vivo large animal (pig) model study of cerebrospinal fluid (CSF) pressures after acute experimental spinal cord injury (SCI).

OBJECTIVE

To determine how the CSF pressure (CSFP) and CSF pulse pressure amplitude (CSFPPA) cranial and caudal to the injury site change after an acute SCI with subsequent thecal occlusion and decompression.

SUMMARY OF BACKGROUND DATA

Lowering intrathecal pressure via CSF drainage is currently instituted to prevent ischemia-induced SCI during thoracoabdominal aortic aneurysm surgery and was recently investigated as a potential intervention for acute traumatic SCI. However, in SCI patients, persistent extradural compression commonly occludes the subarachnoid space. This may generate a CSFP differential across the injury site, which cannot be appreciated with lumbar catheter pressure measurements.

METHODS

Anesthetized pigs were subjected to an acute contusive SCI at T11 and 8 hours of sustained compression (n = 12), or sham surgery (n = 2). CSFP was measured cranial and caudal to the injury site, using miniature pressure transducers, during compression and for 6 hours after decompression.

RESULTS

The cranial-caudal CSFP differential increased (mean, 0.39 mm Hg/h), predominantly due to increased cranial pressure. On decompression, cranial CSFP decreased (mean, -1.16 mm Hg) and caudal CSFP increased (mean, 0.65 mm Hg). The CSFP differential did not change significantly after decompression. Cranial CSFPPA was greater than caudal CSFPPA, but this differential did not change during compression. On decompression, the caudal CSFPPA increased in some but not all animals.

CONCLUSION

Although extradural compression exists at the site of injury, lumbar CSFP may not accurately indicate CSFP cranial to the injury. Decompression may provide immediate, though perhaps partial, resolution of the pressure differential. CSFPPA was not a consistent indicator of decompression in this animal model. These findings may have implications for the design of future clinical protocols in which CSFP is monitored after acute SCI.

Different routes of administration of human umbilical tissue-derived cells improve functional recovery in the rat after focal cerebral ischemia

Human umbilical tissue-derived cells (hUTC) are a potential neurorestorative candidate for stroke treatment. Here, we test the effects of hUTC treatment in a rat model of stroke via various routes of administration. Rats were treated with hUTC or phosphate-buffered saline (PBS) via different routes including intraarterial (IA), intravenous (IV), intra-cisterna magna (ICM), lumber intrathecal (IT), or intracerebral injection (IC) at 24h after stroke onset. Treatment with hUTC via IV and IC route led to significant functional improvements starting at day 14, which persisted to day 60 compared with respective PBS-treated rats. HUTC administered via IA, ICM, and IT significantly improved neurological functional recovery starting at day 14 and persisted up to day 49 compared with PBS-treated rats. Although IA administration resulted in the highest donor cell number detected within the ischemic brain compared to the other routes, hUTC treatments significantly increased ipsilateral bromodeoxyuridine incorporating subventricular zone (SVZ) cells and vascular density in the ischemic boundary compared with PBS-treated rats regardless of the route of administration. While rats received hUTC treatment via IA, IV, IC, and ICM routes showed greater synaptophysin immunoreactivity, significant reductions in TUNEL-positive cells in the ipsilateral hemisphere were observed in IA, IV, and IC routes compared with PBS-treated rats. hUTC treatments did not reduce infarct volume when compared to the PBS groups. Our data indicate that hUTC administered via multiple routes provide therapeutic benefit after stroke. The enhancement of neurorestorative events in the host brain may contribute to the therapeutic benefits of hUTC in the treatment of stroke.

Structural defects in cilia of the choroid plexus, subfornical organ and ventricular ependyma are associated with ventriculomegaly

Background

Hydrocephalus is a heterogeneous disorder with multiple etiologies that are not yet fully understood. Animal models have implicated dysfunctional cilia of the ependyma and choroid plexus in the development of the disorder. In this report, we sought to determine the origin of the ventriculomegaly in four Bardet Biedl syndrome (BBS) mutant mouse strains as models of a ciliopathy.

Methods

Evans Blue dye was injected into the lateral ventricle of wild- type and BBS mutant mice to determine whether obstruction of intra- or extra-ventricular CSF flow contributed to ventriculomegaly. Transmission electron microscopy (TEM) was used to examine the ultrastructure of the choroid plexus, subfornical organ (SFO), subcommisural organ (SCO), and ventricular ependyma to evaluate their ultrastructure and the morphology of their primary and motile cilia.

Results and discussion

No obstruction of intra- or extra-ventricular CSF flow was observed, implying a communicating form of hydrocephalus in BBS mutant mice. TEM analyses of the mutants showed no evidence of choroidal papillomas or breakdown of the blood:CSF barrier. In contrast, structural defects were observed in a subpopulation of cilia lining the choroid plexus, SFO, and ventricular ependyma. These included disruptions of the microtubular structure of the axoneme and the presence of electron-dense vesicular-like material along the ciliary shaft and at the tips of cilia.

Conclusions

Abnormalities in cilia structure and function have the potential to influence ciliary intraflagellar transport (IFT), cilia maintenance, protein trafficking, and regulation of CSF production. Ciliary structural defects are the only consistent pathological features associated with CSF-related structures in BBS mutant mice. These defects are observed from an early age, and may contribute to the underlying pathophysiology of ventriculomegaly.

Expression Profiling of Solute Carrier Gene Families at the Blood-CSF Barrier

The choroid plexus (CP) is a highly vascularized tissue in the brain ventricles and acts as the blood-cerebrospinal fluid (CSF) barrier (BCSFB). A main function of the CP is to secrete CSF, which is accomplished by active transport of small ions and water from the blood side to the CSF side. The CP also supplies the brain with certain nutrients, hormones, and metal ions, while removing metabolites and xenobiotics from the CSF. Numerous membrane transporters are expressed in the CP in order to facilitate the solute exchange between the blood and the CSF. The solute carrier (SLC) superfamily represents a major class of transporters in the CP that constitutes the molecular mechanisms for CP function. Recently, we systematically and quantitatively examined Slc gene expression in 20 anatomically comprehensive brain areas in the adult mouse brain using high-quality in situ hybridization data generated by the Allen Brain Atlas. Here we focus our analysis on Slc gene expression at the BCSFB using previously obtained data. Of the 252 Slc genes present in the mouse brain, 202 Slc genes were found at detectable levels in the CP. Unsupervised hierarchical cluster analysis showed that the CP Slc gene expression pattern is substantially different from the other 19 analyzed brain regions. The majority of the Slc genes in the CP are expressed at low to moderate levels, whereas 28 Slc genes are present in the CP at the highest levels. These highly expressed Slc genes encode transporters involved in CSF secretion, energy production, and transport of nutrients, hormones, neurotransmitters, sulfate, and metal ions. In this review, the functional characteristics and potential importance of these Slc transporters in the CP are discussed, with particular emphasis on their localization and physiological functions at the BCSFB.

Cell trafficking through the choroid plexus

The choroid plexus is a multifunctional organ that sits at the interface between the blood and cerebrospinal fluid (CSF). It serves as a gateway for immune cell trafficking into the CSF and is in an excellent position to provide continuous immune surveillance by CD4 (+) T cells, macrophages and dendritic cells and to regulate immune cell trafficking in response to disease and trauma. However, little is known about the mechanisms that control trafficking through this structure. Three cell types within the choroid plexus, in particular, may play prominent roles in controlling the development of immune responses within the nervous system: the epithelial cells, which form the blood-CSF barrier, and resident macrophages and dendritic cells in the stromal matrix. Adhesion molecule and chemokine expression by the epithelial cells allows substantial control over the selection of cells that transmigrate. Macrophages and dendritic cells can present antigen within the choroid plexus and/or transmigrate into the cerebral ventricles to serve a variety of possible immune functions. Studies to better understand the diverse functions of these cells are likely to reveal new insights that foster the development of novel pharmacological and macrophage-based interventions for the control of CNS immune responses.

Do genes and environment meet to regulate cerebrospinal fluid dynamics? Relevance for schizophrenia

Schizophrenia is a neurodevelopment disorder in which the interplay of genes and environment contributes to disease onset and establishment. The most consistent pathological feature in schizophrenic patients is an enlargement of the brain ventricles. Yet, so far, no study has related this finding with dysfunction of the choroid plexus (CP), the epithelial cell monolayer located within the brain ventricles that is responsible for the production of most of the cerebrospinal fluid (CSF). Enlarged brain ventricles are already present at the time of disease onset (young adulthood) and, of notice, isolated mild ventriculomegaly detected in utero is associated with subsequent mild neurodevelopmental abnormalities similar to those observed in children at high risk of developing schizophrenia. Here we propose that altered CP/CSF dynamics during neurodevelopment may be considered a risk, causative and/or participating factor for development of schizophrenia.

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

BACKGROUND

There is increasing awareness that, aside from producing cerebrospinal fluid, the choroid plexus (CP) might be a key regulator of immune activity in the central nervous system (CNS) during neuroinflammation. Specifically, the CP has recently been posited to control entry of sentinel T cells into the uninflamed CNS during the early stages of neuroinflammatory diseases, like multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE). As the CP is compartmentalized into a stromal core containing fenestrated capillaries devoid of typical blood-brain barrier properties, surrounded by a tight junction-expressing choroidal epithelium, each of these compartments might mount unique responses that instigate the neuroinflammatory process.

METHODS

To discern responses of the respective CP stromal capillary and choroidal epithelial tissues during evolving neuroinflammation, we investigated morphology and in situ expression of 93 immune-related genes during early stages of EAE induced by immunization with myelin oligodendrocyte glycoprotein peptide (MOG35-55). Specifically, 3-D immunofluorescent imaging was employed to gauge morphological changes, and laser capture microdissection was coupled to an Immune Panel TaqMan Low Density Array to detail alterations in gene expression patterns at these separate CP sites on days 9 and 15 post-immunization (p.i.). To resolve CP effects due to autoimmunity against MOG peptide, from those due to complete Freund's adjuvant (CFA) and pertussis toxin (PTX) included in the immunization, analysis was performed on MOG-CFA/PTX-treated, CFA/PTX-treated, and naïve cohorts.

RESULTS

The CP became swollen and displayed significant molecular changes in response to MOG-CFA/PTX immunization. Both stromal capillary and choroidal epithelial tissues mounted vigorous, yet different, changes in expression of numerous genes over the time course analyzed - including those encoding adhesion molecules, cytokines, chemokines, statins, interleukins, T cell activation markers, costimulatory molecules, cyclooxygenase, pro-inflammatory transcription factors and pro-apoptotic markers. Moreover, CFA/PTX-treatment, alone, resulted in extensive, though less robust, alterations in both CP compartments.

CONCLUSIONS

MOG-CFA/PTX immunization significantly affects CP morphology and stimulates distinct expression patterns of immune-related genes in CP stromal capillary and epithelial tissues during evolving EAE. CFA/PTX treatment, alone, causes widespread gene alterations that could prime the CP to unlock the CNS to T cell infiltration during neuroinflammatory disease.

Multiple roles for the Na,K-ATPase subunits, Atp1a1 and Fxyd1, during brain ventricle development

Formation of the vertebrate brain ventricles requires both production of cerebrospinal fluid (CSF), and its retention in the ventricles. The Na,K-ATPase is required for brain ventricle development, and we show here that this protein complex impacts three associated processes. The first requires both the alpha subunit (Atp1a1) and the regulatory subunit, Fxyd1, and leads to formation of a cohesive neuroepithelium, with continuous apical junctions. The second process leads to modulation of neuroepithelial permeability, and requires Atp1a1, which increases permeability with partial loss of function and decreases it with overexpression. In contrast, fxyd1 overexpression does not alter neuroepithelial permeability, suggesting that its activity is limited to neuroepithelium formation. RhoA regulates both neuroepithelium formation and permeability, downstream of the Na,K-ATPase. A third process, likely to be CSF production, is RhoA-independent, requiring Atp1a1, but not Fxyd1. Consistent with a role for Na,K-ATPase pump function, the inhibitor ouabain prevents neuroepithelium formation, while intracellular Na(+) increases after Atp1a1 and Fxyd1 loss of function. These data include the first reported role for Fxyd1 in the developing brain, and indicate that the Na,K-ATPase regulates three aspects of brain ventricle development essential for normal function: formation of a cohesive neuroepithelium, restriction of neuroepithelial permeability, and production of CSF.

A novel look at astrocytes: aquaporins, ionic homeostasis, and the role of the microenvironment for regeneration in the CNS

Aquaporin-4 (AQP4) water channels are located at the basolateral membrane domain of many epithelial cells involved in ion transport and secretion. These epithelial cells separate fluid compartments by forming apical tight junctions. In the brain, AQP4 is located on astrocytes in a polarized distribution: At the border to blood vessels or the pial surface, its density is very high. During ontogeny and phylogeny, astroglial cells go through a stage of expressing tight junctions, separating fluid compartments differently than in adult mammals. In adult mammals, this barrier is formed by arachnoid, choroid plexus, and endothelial cells. The ontogenetic and phylogenetic barrier transition from glial to endothelial cells correlates with the regenerative capacity of neuronal structures: Glial cells forming tight junctions, and expressing no or unpolarized AQP4 are found in the fish optic nerve and the olfactory nerve in mammals both known for their regenerative ability. It is hypothesized that highly polarized AQP4 expression and the lack of tight junctions on astrocytes increase ionic homeostasis, thus improving neuronal performance possibly at the expense of restraining neurogenesis and regeneration.

Aquaporin-4 expression is not elevated in mild hydrocephalus

BACKGROUND

Aquaporin-4 (aqp-4) is a member of water channel family proteins primarily expressed in the central nervous system. Physiologically it is the main channel providing water transport into the nervous system water compartments and across the blood-brain barrier. Several studies demonstrated its compensatory role in severe hydrocephalus. However, its role is not clear during the initial stages of hydrocephalus.

OBJECTIVE

This study was designed to investigate aqp-4 expression in less severe forms of hydrocephalus and to determine its role in disease progression.

METHODS

Twenty-five male Wistar-Hannover rats, were distributed into experimental (n = 20) and control (n = 5) groups. Hydrocephalus was induced in the experimental group by injection of 5 μl 25% kaolin suspension into the cisterna magna. Control animals received an injection of 5 μl normal saline. Eight weeks later, the animals were killed by the perfusion-fixation method. Immunohistochemical and Western blot analysis were performed.

RESULTS

Ventricular dilatations were noted in all experimental animals. Both groups demonstrated positive immunoreactive signals to aqp-4. Immunohistochemically there were no changes in aqp-4 pattern and expression intensity between experimental and control animals. Similarly, Western blot analysis revealed mean aqp-4 values in experimental and control groups as 0.3436 and 0.3917, respectively, and the difference did not reach statistical significance (p > 0.05).

CONCLUSION

Our results indicate that aqp-4 is not up-regulated during the initial stages of hydrocephalus. This implies that aqp-4 may not play a significant role in hydrocephalus compensation until severe ventricular dilatation occurs.

Mechanisms of dendritic cell trafficking across the blood-brain barrier

Although the central nervous system (CNS) is considered to be an immunoprivileged site, it is susceptible to a host of autoimmune as well as neuroinflammatory disorders owing to recruitment of immune cells across the blood-brain barrier into perivascular and parenchymal spaces. Dendritic cells (DCs), which are involved in both primary and secondary immune responses, are the most potent immune cells in terms of antigen uptake and processing as well as presentation to T cells. In light of the emerging importance of DC traficking into the CNS, these cells represent good candidates for targeted immunotherapy against various neuroinflammatory diseases. This review focuses on potential physiological events and receptor interactions between DCs and the microvascular endothelial cells of the brain as they transmigrate into the CNS during degeneration and injury. A clear understanding of the underlying mechanisms involved in DC migration may advance the development of new therapies that manipulate these mechanistic properties via pharmacologic intervention. Furthermore, therapeutic validation should be in concurrence with the molecular imaging techniques that can detect migration of these cells in vivo. Since the use of noninvasive methods to image migration of DCs into CNS has barely been explored, we highlighted potential molecular imaging techniques to achieve this goal. Overall, information provided will bring this important leukocyte population to the forefront as key players in the immune cascade in the light of the emerging contribution of DCs to CNS health and disease.