Molecular anatomy and functions of the choroidal blood-cerebrospinal fluid barrier in health and disease

Choroid plexus enlargement in idiopathic normal pressure hydrocephalus and concept proposal for noninvasive volume-reductive therapies

BACKGROUND

Aberrant CSF dynamics in idiopathic normal pressure hydrocephalus (iNPH) are associated with excessive CSF volume and impaired resorption. Yet, the role of choroid plexus (CP) size in development and progression of iNPH remains unknown. Moreover, newer noninvasive CP-targeted volume-reductive treatments for iNPH might benefit selected vulnerable patients to avoid problematic long-term ventricular shunting. However, there are no studies to date that describe CP size in iNPH patients.

METHODS

We retrospectively studied brain 3T MRIs for 50 iNPH patients and 50 age and sex-matched healthy controls (HCs). We delineated areas and volumes of lateral ventricular CPs, then statistically compared both cohorts, with significance set at p < 0.05.

RESULTS

In iNPH patients, CP volume (1.58-fold) alone, CP volume normalized to total intracranial volume (1.75-fold), and CP areas at four different locations and their combined values (1.24-fold) were highly significantly larger (p < 0.000) in iNPH patients.

CONCLUSION

The novel finding of CP enlargement in iNPH should guide and support future investigations into potentially interrelated pathogenetic mechanisms. It also benefits considerations of new noninvasive targeted therapies (such as MR-guided high intensity focused ultrasound, and radiosurgery) to partially ablate CP and reduce its CSF secretion as a conceivable alternative to conventional ventricular shunting.

Glymphatic system dysfunction in adult ADHD: Relationship to cognitive performance

OBJECTIVES

While attention-deficit/hyperactivity disorder (ADHD) persists into adulthood, the relationship between glymphatic system function and cognitive performance in adult ADHD remains unclear. This study investigated the association between glymphatic system markers and cognitive outcomes in adults with ADHD.

METHODS

This case-control study includes 41 adults with ADHD and 108 age-matched healthy controls (HCs). Glymphatic function was evaluated using choroid plexus volume (CPV), diffusion tensor imaging along the perivascular space (DTI-ALPS) index and coupling between blood‑oxygen-level-dependent signals and cerebrospinal fluid signals (BOLD-CSF coupling). Cognitive performance was measured using standardized neuropsychological tests.

RESULTS

Compared with HCs, adults with ADHD exhibited significantly lower bilateral and whole-brain ALPS indices (P < 0.05). Although CPV was increased in the ADHD group, this difference did not reach statistical significance, and no significant differences were observed in BOLD-CSF coupling between the two groups. Furthermore, whole-brain ALPS indices were positively associated with visual memory performance (r = 0.422, P = 0.005), an effect that was more pronounced in the right hemisphere (r = 0.458, P = 0.002).

LIMITATIONS

The cross-sectional design limits causal inferences, and the effects of medication were not fully accounted for.

CONCLUSIONS

These findings identify an association between glymphatic dysfunction and cognitive impairment in adults with ADHD. The observed correlation suggests that alterations in glymphatic function may underlie ADHD-related cognitive deficits. Targeting these pathways could provide novel therapeutic opportunities in the management of adult ADHD.

Complex neural-immune interactions shape glioma immunotherapy

Rich neural-immune interactions in the central nervous system (CNS) shape its function and create a unique immunological microenvironment for immunotherapy in CNS malignancies. Far from the now-debunked concept of CNS "immune privilege," it is now understood that unique immunological niches and constant immune surveillance of the brain contribute in multifaceted ways to brain health and robustly influence immunotherapy approaches for CNS cancers. Challenges include immune-suppressive and neurotoxicity-promoting crosstalk between brain, immune, and tumor cells. Developing effective immunotherapies for cancers of the nervous system will require a deeper understanding of these neural-immune-malignant cell interactions. Here, we review progress and challenges in immunotherapy for gliomas of the brain and spinal cord in light of these unique neural-immune interactions and highlight future work needed to optimize promising immunotherapies for gliomas.

Choroid plexus: Insights from distinct epithelial cellular components

The choroid plexus (ChP) serves as a vital interface between blood and cerebrospinal fluid (CSF), playing a pivotal role in central nervous system (CNS) development and communication with the body. This review mainly summarizes how the ChP epithelial cells respond to physiological and pathological stimuli, emphasizing the role of distinct organelles and key molecular signaling pathways. Additionally, we discuss the roles of ChP cilia, an evolutionary conserved organelle whose function is still under investigation. Understanding these processes is essential for elucidating how ChP function modulates intrinsic and extrinsic stimuli, which are crucial for maintaining CNS and body homeostasis.

Dynamics of choroid plexus volume is associated with the presence and development of fatigue in multiple sclerosis

BACKGROUND

Immune-mediated processes are implicated in the pathogenesis of fatigue, a common symptom in multiple sclerosis (MS). The choroid plexus (CP) regulates central nervous system (CNS) immune homeostasis and undergoes volumetric modifications possibly contributing to MS-related fatigue. We explored the association between MS-related CP volume changes and fatigue dynamics.

METHOD

Eighty-five patients with MS and 68 healthy controls (HC) underwent brain 3T MRI, neurological evaluation and Modified Fatigue Impact Scale (MFIS) at two timepoints (median follow-up=1.4 years). Normalised brain and regional grey matter (GM) volumes were obtained using FSL-SIENAx, FIRST, SIENA and tensor-based morphometry. CP volumes were quantified with in-house methods, and longitudinal changes were analysed using linear mixed models.

RESULTS

At baseline, 25 (29%) patients with MS had fatigue (f-MS) (MFIS ≥38). Compared with HC, patients with MS had significantly higher brain T2-lesion volume, lower brain, deep GM, cortical volumes and higher CP volume (false discovery rate (FDR)-p ≤0.024). Compared with non-fatigued (nf-MS) patients, f-MS were older, more disabled (FDR-p ≤0.002) and showed numerically higher CP volume (FDR-p=0.076). At follow-up, 41 (68%) nf-MS remained non-fatigued (nf-FU-MS) and 19 (32%) developed fatigue (f-FU-MS). Patients with MS showed higher brain and deep GM atrophy rates versus HC (FDR-p ≤0.048), whereas clinical, lesional and brain volumetric changes were not significantly different among MS groups (FDR-p ≥0.287). CP volume significantly increased in all MS groups compared with HC (FDR-p ≤0.043), with greater enlargement in f-FU-MS versus nf-FU-MS (FDR-p=0.048).

CONCLUSIONS

Larger CP and greater enlargement are associated with the presence and development of fatigue in MS, likely reflecting dynamic inflammatory states within the CNS, supporting the immunological contribution to MS-related fatigue.

Macrophage-derived CTSS drives the age-dependent disruption of the blood-CSF barrier

The choroid plexus (CP) serves as the primary source of cerebrospinal fluid (CSF). The blood-CSF barrier, composed of tight junctions among the epithelial cells in the CP, safeguards CSF from unrestricted exposure to bloodborne factors. This barrier is thus indispensable to brain homeostasis and is associated with age-related neural disorders. Nevertheless, its aging is poorly understood. Here, we report that cathepsin S (CTSS), a protease secreted from the CP macrophages, is upregulated in aged CP due to increased cell senescence. CTSS cleaves the essential tight junction component, claudin 1 (CLDN1), and, in turn, impairs the blood-CSF barrier. Notably, inhibiting CTSS or upregulating CLDN1 in aged CP rejuvenates the blood-CSF barrier and brain functions. Our findings uncover a vital interplay between immune and barrier cells that accelerates CP and brain aging, identify CTSS as a potential target to improve brain homeostasis in aged animals, and underscore the critical role of circulating proteinases in aging.

Pathogenic Mechanisms of Immune Checkpoint Inhibitor (ICI)-Associated Retinal and Choroidal Adverse Reactions

PURPOSE

To summarize and categorize postulated mechanisms of immune checkpoint inhibitor (ICI)-mediated retinal and choroidal inflammation and discuss resulting implications for evaluation and management of these adverse reactions.

DESIGN

Targeted literature review with interpretation and perspective METHODS: We performed a review of selected literature describing immune-mediated retinal and choroidal adverse reactions associated with ICI therapy, synthesizing and categorizing the likely underlying pathogenic mechanisms. Based on these mechanistic categories, we provide perspective on a rational approach to the evaluation of patients with ICI-associated inflammatory disorders of the retina and choroid.

RESULTS

ICI-induced posterior segment adverse reactions can be categorized into 3 major mechanisms of unintended, targeted inflammation that share similarities to immunotherapy-related adverse events (irAEs) seen in other organ systems. In Type 1 reactions, T cell activation by ICIs can result in cross-reactivity of anti-tumor T cells with ocular tissues (Type 1a) or expansion of eye-specific T cells in predisposed individuals (Type 1b), leading to ocular inflammation that mimics known uveitic conditions. In Type 2 reactions, nonspecific ocular or systemic inflammation exacerbated by ICI use can cause retinal vasculitis through a "bystander" mechanism, potentially resulting in vision-threatening vascular occlusions. Finally, in Type 3 reactions, ICI use can prompt autoantibody-mediated inflammation and/or exacerbation of paraneoplastic processes likely related to T cell driven expansion of B cell populations.

CONCLUSIONS

Although relatively uncommon, posterior segment inflammatory disorders associated with systemic ICI therapy may be vision-threatening if not identified and treated appropriately. We propose that the pathogenic mechanisms underlying these chorioretinopathies falls into 3 major categories involving inadvertent T cell mediated inflammation. Visual prognosis with appropriate treatment is generally favorable, but some reactions, such as longstanding exudative retinal detachments and ICI-induced occlusive retinal vasculitis, can result in permanent visual defects.

The Role of Choroid Plexus in Hydrocephalus from the Perspective of Structure and Function: a Therapeutic Target

Hydrocephalus is one of the most common neurological diseases, characterized by abnormal excessive accumulation of cerebrospinal fluid (CSF) in the ventricular system. Its pathophysiological mechanism is believed to be related to the imbalance of CSF circulation and homeostasis. As the main source of CSF secretion, the choroid plexus is closely related to hydrocephalus. The choroid plexus is a specialized vascularized tissue located within the cerebral ventricles. It has multiple physiological functions including regulating CSF, immune response, endocrine metabolism, etc. Strategies that reduce choroid plexus CSF secretion have been shown to be effective in the treatment of hydrocephalus. However, the role of other physiological functions of the choroid plexus in hydrocephalus is still unclear. Recent studies on the choroid plexus and the blood-CSF barrier have deepened our understanding of the structure and function of the choroid plexus. The idea of targeting the choroid plexus to treat hydrocephalus has spawned many branches: choroid plexus epithelial cells, choroid plexus immune cells, choroid plexus peptides, and choroid plexus cilia, etc. This review introduces the basic structure and function of the choroid plexus, summarizes their changes in hydrocephalus, and analyzes the possibility of the choroid plexus as a therapeutic target for hydrocephalus.

Research priorities for non-invasive therapies to improve hydrocephalus outcomes

The Hydrocephalus Association organized two workshops with the support of the Rudi Schulte Research Institute and Cincinnati Children's Hospital Medical Center entitled "Developing Non-Invasive Hydrocephalus Therapies: Molecular and Cellular Targets", held September 27-29, 2023, in Dallas, TX, and "Developing Non-Invasive Hydrocephalus Therapies: Advancing Towards Clinical Trials", held April 12-13, 2024, in Cincinnati, OH. The goal of these workshops was to explore the frontiers of ongoing research for non-invasive therapies for the treatment of hydrocephalus across all etiologies and to improve patient outcomes at all stages of diagnosis and management. During the consensus-building discussions throughout the research workshops, basic, translational, and clinical scientists aimed to identify the next steps to develop novel treatments for hydrocephalus. This detailed report discusses the research priorities that emerged from these workshops to inspire researchers and guide studies towards better treatment for people living with hydrocephalus.

The research progress on meningeal metastasis in solid tumors

Meningeal metastasis (MM), particularly Leptomeningeal metastases (LM), represents the advanced stage of solid tumors and poses a significant threat to patients' lives. Moreover, it imposes a substantial burden on society. LM represents the ultimate and most fatal stage of solid tumors, inflicting devastating consequences on patients and imposing a substantial burden on society. The incidence of LM continues to rise annually, emphasizing the urgent need for early recognition and treatment initiation in individuals with LM to significantly extend overall patient survival. Despite rapid advancements in current LM detection and treatment methods, the diagnosis of LM remains constrained by several limitations such as low diagnostic efficiency, the therapeutic outcomes remain suboptimal. Furthermore, there is currently no universally recognized industry standard for LM treatment, further underscoring its status as an unresolved challenge in tumor management. Additionally, progress towards elucidating the mechanisms underlying MM has stagnated. Therefore, this review aims to comprehensively summarize recent research advances pertaining to MM in solid tumors by elucidating its underlying mechanisms, exploring diagnostic and prognostic biomarkers while addressing existing research challenges.

The glutathione-dependent neuroprotective activity of the blood-CSF barrier is inducible through the Nrf2 signaling pathway during postnatal development

BACKGROUND

Choroid plexuses regulate the exchanges between the blood and the CSF, and provide trophic factors necessary to brain development. They also express detoxifying enzymes that protect the developing brain from harmful substances. Targeting the Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) signaling pathway may enhance the detoxification capabilities of choroid plexuses that are linked to glutathione conjugation, but little is known about mechanisms of enzyme induction in this tissue.

METHODS

Rat pups were treated with dimethylfumarate and the subcellular localization of Nrf2 was analyzed in the choroidal tissue by confocal imaging. Glutathione-S-transferase (GST) activity was assessed ex vivo in the choroidal tissue, and 1-chloro-2,4-dinitrobenzene, a toxicant and prototypic GST substrate, was used to evaluate in vivo the efficiency of the glutathione-dependent enzymatic barrier function of choroid plexuses. Nrf2 knockout rat pups were used to establish the Nrf2 dependency of GST induction in this tissue.

RESULTS

We show an early postnatal expression of Nrf2 in the rat choroidal tissue. Treatment of rat pups with dimethylfumarate triggers Nrf2 nuclear translocation in choroidal epithelial cells. This treatment increases GST activity in choroid plexus, and reduces the blood-to-CSF permeation of 1-chloro-2,4-dinitrobenzene. In Nrf2 knockout rats, the constitutive activity of the choroidal glutathione-dependent detoxifying machinery is maintained, but the efficacy of dimethylfumarate to induce glutathione conjugation in the choroid plexuses is strongly reduced, indicating that dimethylfumarate acts mainly through the Nrf2 signaling pathway.

CONCLUSIONS

This work shows that the glutathione-dependent detoxifying function of the blood-CSF barrier can be pharmacologically enhanced through the Nrf2 signaling pathway to better protect the neural fluid environment from drug and toxic accumulation during the neonatal period.

Trojan Horse Delivery Strategies of Natural Medicine Monomers: Challenges and Limitations in Improving Brain Targeting

Central nervous system (CNS) diseases, such as brain tumors, Alzheimer's disease, and Parkinson's disease, significantly impact patients' quality of life and impose substantial economic burdens on society. The blood-brain barrier (BBB) limits the effective delivery of most therapeutic drugs, especially natural products, despite their potential therapeutic effects. The Trojan Horse strategy, using nanotechnology to disguise drugs as "cargo", enables them to bypass the BBB, enhancing targeting and therapeutic efficacy. This review explores the applications of natural products in the treatment of CNS diseases, discusses the challenges posed by the BBB, and analyzes the advantages and limitations of the Trojan Horse strategy. Despite the existing technical challenges, future research is expected to enhance the application of natural drugs in CNS treatment by integrating nanotechnology, improving delivery mechanisms, and optimizing targeting characteristics.

Blood-CSF barrier clearance of ABC transporter substrates is suppressed by interleukin-6 in lupus choroid plexus spheroids

BACKGROUND

The choroid plexus (CP) has been recently implicated in the pathogenesis of the neuropsychiatric manifestations of systemic lupus erythematosus (NPSLE). Lupus patients demonstrate increased serum and cerebrospinal fluid (CSF) concentrations of interleukin-6 (IL-6), which can disrupt vital blood-CSF barrier (B-CSFB) functions performed by the CP. However, difficulty accessing this tissue has largely precluded dynamic imaging or evaluation of CP barrier function in vivo.

METHODS

In this study, explant CP spheroids which replicate the functional and structural properties of the B-CSFB were generated from 12 + week old female MRL/lpr (IL-6 wildtype; IL-6 WT) lupus mice, IL-6 knockout (IL-6 KO) MRL/lpr mice, and congenic control MRL/mpj mice. CP spheroids derived from IL-6 WT MRL/lpr mice were found to synthesize and secrete IL-6, similar to the CP in vivo, whereas the IL-6 KO spheroids did not produce IL-6. Accumulation of different fluorescent tracers within the central CSF-like fluid vacuole of spheroids, modeling brain ventricles, was measured to probe transcellular permeability, paracellular diffusion, and clearance functions of the CP.

RESULTS

As shown by blocking the IL-6 receptor in IL-6 WT spheroids or comparing them to IL-6 KO spheroids, IL-6 signaling decreased spheroid clearance of methotrexate, a chemotherapeutic drug employed in the therapy of lupus, and lucifer yellow. This suppression occurred without altering CP epithelial morphology and ultrastructure. Methotrexate and lucifer yellow efflux can occur through ATP-binding cassette (ABC) transporters, including BCRP and MRP1. Cytoplasmic accumulation of the ABC-specific dye fluorescein diacetate was also increased by IL-6. Pharmacologic inhibition of either BCRP or MRP1 in IL-6 KO spheroids was sufficient to recreate the clearance deficits observed in IL-6 WT spheroids. Moreover, CP expression of BCRP was significantly lower in IL-6 WT mice.

CONCLUSIONS

In this study, we establish, validate, and apply a CP spheroid model to the study of B-CSFB function in lupus. Our results show that IL-6, a key cytokine increased in NPSLE, can potentially suppress the CP-specific function and expression of BCRP and MRP1. Therefore, IL-6 could affect the CSF clearance of inflammatory substrates (e.g., leukotrienes), the accumulation of which would incite neurotoxicity and promote progression of NPSLE.

The essential role of cerebrospinal fluid in the brain; a comprehensive review

There has been a significant amount of attention directed towards understanding brain development, shedding light on the underlying mechanisms. The proliferation and differentiation of brain stem cells have been a key focus. The process of neurolation occurs during the early stages of embryonic development, leading to the formation of the neural tube, a hollow nerve cord that gives rise to the central nervous system (CNS). There is a growing emphasis on the fluid-filled space inside the developing CNS and the potential role of cerebrospinal fluid (CSF) in brain development. The flow of CSF near the germinal epithelium significantly impacts the proliferation of cells in the cerebral cortex. CSF provides crucial support to the germinal epithelium, influencing the growth and differentiation of neural stem cells. It achieves this by releasing growth factors, cytokines, and morphogens that control the proliferation, survival, and migration of neuroepithelium. During development, the concentration of proteins in the CSF is notably higher compared to that in adults. Studies have indicated that removing CSF from the brain's ventricles during development causes an increase in neural cell deaths and a reduction in neural cell proliferation, ultimately leading to a thinner cerebral cortex. Additionally, many researches demonstrate that the composition of the CSF is essential for maintaining germinal matrix function and output, highlighting the critical role of CSF in brain development. It is concluded that CSF impacts the proliferation and differentiation of neural stem cells, which in turn plays a pivotal role in brain development.

Implications of the choroid plexus in Niemann-Pick disease Type C neuropathogenesis

BACKGROUND

Niemann-Pick Disease Type C (NPC) is an ultra-rare disorder characterized by progressive psychiatric and neurologic manifestations, with late infantile, juvenile, and adolescent/adult presentations. We examined morphological properties of the choroid plexus, a protective blood-cerebrospinal fluid barrier, in NPC, and their relationship with neurodegeneration, clinical status, and circulatory markers. This study also determined whether choroid plexus morphology differentiates between NPC and more prevalent illnesses, schizophrenia (SZ) and bipolar disorder (BD), which have overlapping psychiatric symptoms with adolescent and adult-onset NPC and are associated with misdiagnosis.

METHODS

Patients with NPC were assessed using neuroimaging, clinical instruments, and plasma protein quantification focusing on inflammatory markers. Morphological properties (i.e., choroid plexus volumes) were compared between patients with NPC (n = 17), SZ (n = 20), BD (n = 24), and healthy controls (HCs, n = 106).

RESULTS

Choroid plexus enlargement (p < 0.05) and reduced thalamic volumes (p < 0.05) were observed in NPC patients versus HCs and SZ or BD patients. A logistic regression model with choroid plexus and thalamic volumes as predictors yielded high prediction accuracy for NPC vs. HCs, NPC vs. SZ, and NPC vs. BD (area under the receiver operating characteristics curve [AUROC] of 1). Choroid plexus volumes were negatively correlated with left (p = 0.009-0.012) and right (p = 0.007-0.025) thalamic volumes, left (r = -0.69, p = 0.003) and right (r = -0.71, p = 0.002) crus I of the cerebellum, and greater severity on the NPC-Suspicion Index psychiatric subscale (ρ = 0.72, p = 0.042). Targeted protein expression quantification revealed differential expression of TGFA, HLA-DRA, TNFSF12, EGF, INFG, and IL-18 in NPC patients vs. HCs (p < 0.05), with higher choroid plexus volumes correlating with IL-18 levels (ρ = 0.71, p = 0.047).

CONCLUSION

The choroid plexus may play a critical role in NPC neuropathogenesis and serve as a novel biomarker for monitoring neurodegenerative and inflammatory processes in NPC.

Immune control of brain physiology

The peripheral immune system communicates with the brain through complex anatomical routes involving the skull, the brain borders, circumventricular organs and peripheral nerves. These immune-brain communication pathways were classically considered to be dormant under physiological conditions and active only in cases of infection or damage. Yet, peripheral immune cells and signals are key in brain development, function and maintenance. In this Perspective, we propose an alternative framework for understanding the mechanisms of immune-brain communication. During brain development and in homeostasis, these anatomical structures allow selected elements of the peripheral immune system to affect the brain directly or indirectly, within physiological limits. By contrast, in ageing and pathological settings, detrimental peripheral immune signals hijack the existing communication routes or alter their structure. We discuss why a diversity of communication channels is needed and how they work in relation to one another to maintain homeostasis of the brain.

Transcriptome analysis of novel B16 melanoma metastatic variants generated by serial intracarotid artery injection

The incidence of brain metastases (BrM) in patients with metastatic melanoma is reported to be 30-50% and constitutes the third most frequent BrM after breast and renal cancers. Treatment strategies including surgical resection, stereotactic radiation, and immunotherapy have improved clinical response rates and overall survival, but the changes that occur in circulating melanoma cells to promote invasion of the brain are not fully understood. To investigate brain tropism, we generated new variants of the B16 mouse melanoma model by serially passaging B16 cells through the brain of immune competent syngeneic C57BL/6 mice. Cells were injected into the right carotid artery and recovered from the brain after the mice had reached the study endpoint due to tumor burden, then expanded in vitro and reinjected. We compared the transcriptomes of 4th generation B16 cell populations from separate lineages with the founder B16-F0 cells. Gene set enrichment analysis (GSEA) of differentially expressed protein coding genes revealed that cells isolated from the brain as well as from the lung and meninges expressed higher levels of genes associated with an epithelial to mesenchymal transition (EMT), upregulation of the KRAS signaling pathway, and a metastasis aggressiveness gene signature associated with poor survival in melanoma patients. Principal component analysis of differentially expressed genes showed that 4th generation melanoma cells isolated from the brain, lung and meninges from one lineage were distinct from those of the other three lineages. Among the differentially expressed genes, transcript levels of several genes, including Itgb2, Rftn2, and Kcnn4, were significantly higher in all cell populations that comprised this lineage compared with all cell populations from the other three lineages. In conclusion, we have derived an aggressive, highly brain metastatic B16 variant associated with leptomeningeal disease by serially passaging cells in vivo.

Choroid plexus volume is enlarged in long COVID and associated with cognitive and brain changes

Patients with post-COVID condition (PCC) present with diverse symptoms which persist at long-term after SARS-CoV-2 infection. Among these symptoms, cognitive impairment is one of the most prevalent and has been related to brain structural and functional changes. The underlying mechanisms of these cognitive and brain alterations remain elusive but neuroinflammation and immune mechanisms have been majorly considered. In this sense, the choroid plexus (ChP) volume has been proposed as a marker of neuroinflammation in immune-mediated conditions and the ChP epithelium has been found particularly susceptible to the effects of SARS-CoV-2. The objective was to investigate the ChP in PCC and evaluate its relationships with cognition, brain, and immunological alterations. One-hundred and twenty-nine patients with PCC after a mean of 14.79 ± 7.17 months of evolution since the infection and 36 healthy controls were recruited. Participants underwent a neuropsychological, and neuroimaging assessment and immunological markers evaluation. Results revealed ChP volume enlargement in PCC compared to healthy controls. The ChP enlargement was associated with cognitive dysfunction, grey matter volume reduction in frontal and subcortical areas, white matter integrity and diffusivity changes and functional connectivity changes. These ChP changes were also related to intermediate monocytes levels. Findings suggest that the ChP integrity may play a relevant role in the pathophysiology of cognitive deficits and the observed brain changes in PCC. The previously documented function of the ChP in maintaining brain homeostasis and regulating the entry of immune cells into the brain supports the presence of neuroinflammatory mechanisms in this disorder.

Immune cell-enriched single-cell RNA sequencing unveils the interplay between infiltrated CD8+ T resident memory cells and choroid plexus epithelial cells in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurological disorder and the leading cause of dementia. Despite significant efforts, treatment strategies targeting amyloid-β have been less successful than anticipated. Recently, the role of neuroinflammation and adaptive immune response in AD pathogenesis has gained attention. Here, we performed immune cell-enriched single-cell RNA sequencing of brain parenchymal cells from 12-month-old 5xFAD, an AD mouse model. We analyzed 11,587 single cells and found distinct differences in T cell and choroid plexus cell populations between 5xFAD mouse and littermate control. Subsequent sub-clustering of T cells in the 5xFAD mouse revealed distinct subtypes, with CD8+ resident memory T cells (TRM) being the most prevalent T cell type. In addition, we observed an increase in T cell exhaustion markers, including Pdcd1, Ctla4, and Havcr2, with a particularly significant elevation of PD-1 and TIM-3 in CD8+ TRM in 5xFAD mouse. Furthermore, choroid plexus (ChP) epithelial cells showed altered gene expression patterns, with higher expression of MHC class I and Type I IFN-stimulated genes in 5xFAD mouse compared to the control mouse, suggesting an association with clonal expansion of AD-specific T cells in the brain. Through single-cell RNA sequencing (scRNA-seq) analysis, our study highlights the potential role of resident memory CD8+ T cell and their possible interactions with ChP epithelial cells. This study provides an exploration of the brain microenvironment landscape in AD, revealing critical insights into its underlying mechanisms.

Breaking boundaries: role of the brain barriers in metastatic process

Brain metastases (BMs) are the most common intracranial tumors in adults and occur 3-10 times more frequently than primary brain tumors. Despite intensive multimodal therapies, including resection, radiotherapy, and chemotherapy, BMs are associated with poor prognosis and remain challenging to treat. BMs predominantly originate from primary lung (20-56%), breast (5-20%), and melanoma (7-16%) tumors, although they can arise from other cancer types less frequently. The metastatic cascade is a multistep process involving local invasion, intravasation into the bloodstream or lymphatic system, extravasation into normal tissue, and colonization of the distal site. After reaching the brain, circulating tumor cells (CTCs) breach the blood-brain barrier (BBB).The selective permeability of the BBB poses a significant challenge for therapeutic compounds, limiting the treatment efficacy of BMs. Understanding the mechanisms of tumor cell interactions with the BBB is crucial for the development of effective treatments. This review provides an in-depth analysis of the brain barriers, including the BBB, blood-spinal cord barrier, blood-meningeal barrier, blood-arachnoid barrier, and blood-cerebrospinal fluid barrier. It explores the molecular and cellular components of these barriers and their roles in brain metastasis, highlighting the importance of this knowledge for identifying druggable targets to prevent or limit BM formation.

Frontiers of Neurodegenerative Disease Treatment: Targeting Immune Cells in Brain Border Regions

Neurodegenerative diseases (NDs) demonstrate a complex interaction with the immune system, challenging the traditional view of the brain as an "immune-privileged" organ. Microglia were once considered the sole guardians of the brain's immune response. However, recent research has revealed the critical role of peripheral immune cells located in key brain regions like the meninges, choroid plexus, and perivascular spaces. These previously overlooked cells are now recognized as contributors to the development and progression of NDs. This newfound understanding opens doors for pioneering therapeutic strategies. By targeting these peripheral immune cells, we may be able to modulate the brain's immune environment, offering an alternative approach to treat NDs and circumvent the challenges posed by the blood-brain barrier. This comprehensive review will scrutinize the latest findings on the complex interactions between these peripheral immune cells and NDs. It will also critically assess the prospects of targeting these cells as a ground-breaking therapeutic avenue for these debilitating disorders.

Mechanisms of cerebrospinal fluid secretion by the choroid plexus epithelium: Application to various intracranial pathologies

The choroid plexus (CP) is a small yet highly active epithelial tissue located in the ventricles of the brain. It secretes most of the CSF that envelops the brain and spinal cord. The epithelial cells of the CP have a high fluid secretion rate and differ from many other secretory epithelia in the organization of several key ion transporters. One striking difference is the luminal location of, for example, the vital Na+-K+-ATPase. In recent years, there has been a renewed focus on the role of ion transporters in CP secretion. Several studies have indicated that increased membrane transport activity is implicated in disorders such as hydrocephalus, idiopathic intracranial hypertension, and posthemorrhagic sequelae. The importance of the CP membrane transporters in regulating the composition of the CSF has also been a focus in research in recent years, particularly as a regulator of breathing and hemodynamic parameters such as blood pressure. This review focuses on the role of the fundamental ion transporters involved in CSF secretion and its ion composition. It gives a brief overview of the established factors and controversies concerning ion transporters, and finally discusses future perspectives related to the role of these transporters in the CP epithelium.

Choroid Plexus Pathophysiology

This review examines the roles of the choroid plexus (ChP) in central nervous system (CNS) pathology, emphasizing its involvement in disease mechanisms and therapeutic potential. Structural changes in the human ChP have been reported across various diseases in case reports and descriptive work, but studies have yet to pin down the physiological relevance of these changes. We highlight primary pathologies of the ChP, as well as their significance in neurologic disorders, including stroke, hydrocephalus, infectious diseases, and neurodegeneration. Synthesizing recent research, this review positions the ChP as a critical player in CNS homeostasis and pathology, advocating for enhanced focus on its mechanisms to unlock new diagnostic and treatment strategies and ultimately improve patient outcomes in CNS diseases. Whether acting as a principal driver of disease, a gateway for pathogens into the CNS, or an orchestrator of neuroimmune processes, the ChP holds tremendous promise as a therapeutic target to attenuate a multitude of CNS conditions.

Association between choroid plexus volume and cognitive function in community-dwelling older adults without dementia: a population-based cross-sectional analysis

BACKGROUND

An increase in choroid plexus (CP) volume may be associated with cognitive decline in older individuals without dementia. In this study, we aimed to clarify whether CP volume can serve as an imaging marker of cognitive decline, determine how strongly CP volume is associated with cognitive decline, and explore factors associated with CP volume in older adults.

METHODS

We measured CP volume, brain parenchyma, and cerebrospinal fluid (CSF) spaces associated with disproportionately enlarged subarachnoid space hydrocephalus (DESH), an imaging feature of normal-pressure hydrocephalus, in community-dwelling older adults aged ≥ 65 years without dementia.

RESULTS

In 1,370 participants, lower Mini-Mental State Examination (MMSE) scores were significantly associated with higher CP volume, even after adjusting for DESH-related CSF space and brain parenchymal volume. CP volume was more strongly associated with MMSE scores than DESH-related CSF space and brain parenchymal volume. History of smoking, white matter hyperintensity, enlarged perivascular spaces, age, body mass index, and diabetes mellitus were also associated with increased CP volume.

CONCLUSIONS

CP volume may be a highly sensitive imaging marker of cognitive decline in community-dwelling older adults without dementia, as it is linked to cognitive decline independently of brain parenchyma and CSF volumes. Our findings emphasize the importance of investigating CP volume increase to maintain cognitive function in older individuals. Accordingly, further longitudinal studies are required.

Choroidal vascularity index in health and systemic diseases: a systematic review

BACKGROUND

The choroid, a highly vascular structure within the eye, is significantly influenced by various systemic conditions. The advent of enhanced depth optical coherence tomography has improved our ability to evaluate choroidal pathophysiology. The choroidal vascularity index (CVI), a noninvasive and reliable tool, serves as an effective means of assessing the choroidal vascular structure. Recent studies have increasingly focused on exploring CVI alterations under different systemic conditions. This study aims to provide a comprehensive summary of the latest research findings in this area.

METHODS

A systematic literature review was conducted on October 1, 2023, using two databases, MEDLINE (via PubMed) and Scopus. Search terms were tailored specifically for each database to ensure a thorough exploration of relevant literature. The studies identified were qualitatively assessed, with particular emphasis on outcomes related to CVI and choroidal thickness.

RESULTS

A total of 48 studies were included in the review, encompassing a diverse range of systemic conditions such as diabetes, central nervous system disorders, cardiovascular diseases, autoimmune disorders, and infectious diseases. Notable reductions in CVI were observed in diabetic retinopathy, autoimmune diseases, and neurodegenerative disorders. Additionally, the review highlighted variations in CVI values related to the severity of systemic diseases, indicating its potential use as a biomarker for disease progression.

CONCLUSION

This review highlights the significant correlation between variations in the choroidal vascularity index and diverse systemic conditions affecting hemodynamics. An enhanced understanding of CVI provides deeper insights into the pathophysiological mechanisms underlying these disorders and positions CVI as a promising biomarker for early detection and monitoring. Nevertheless, its clinical utility warrants careful assessment. Future research should address the potential limitations of CVI to fully capitalize on its diagnostic and prognostic potential.

Endothelial pyroptosis-driven microglial activation in choroid plexus mediates neuronal apoptosis in hemorrhagic stroke rats

BACKGROUND

Spontaneous intracerebral hemorrhage (ICH) is associated with alarmingly high rates of disability and mortality, and current therapeutic options are suboptimal. A critical component of ICH pathology is the initiation of a robust inflammatory response, often termed "cytokine storm," which amplifies the secondary brain injury following the initial hemorrhagic insult. The precise sources and consequences of this cytokine-driven inflammation are not fully elucidated, necessitating further investigation.

METHODS

To address this knowledge gap, our study conducted a comprehensive cytokine profiling using Luminex® assays, assessing 23 key cytokines. We then employed single-cell RNA sequencing and spatial transcriptomics at three critical time points post-ICH: the hyperacute, acute, and subacute phases. Integrating these multimodal analyses allowed us to identify the cellular origins of cytokines and elucidate their mechanisms of action.

RESULTS

Luminex® cytokine assays revealed a significant upregulation of IL-6 and IL-1β levels at the 24-h post-ICH time point. Through the integration of scRNA-seq and spatial transcriptomics in the hemorrhagic hemisphere of rats, we observed a pronounced activation of cytokine-related signaling pathways within the choroid plexus. Initially, immune cell presence was sparse, but it surged 24 h post-ICH, particularly in the choroid plexus, indicating a substantial shift in the immune microenvironment. We traced the source of IL-1β and IL-6 to endothelial cells, establishing a link to pyroptosis. Endothelial pyroptosis post-ICH induced the production of IL-1β and IL-6, which activated microglial polarization characterized by elevated expression of Msr1, Lcn2, and Spp1 via the NF-κB pathway in the choroid plexus. Furthermore, we identified neuronal populations undergoing apoptosis, mediated by the Lcn2-SLC22A17 pathway in response to IL-1β and IL-6 signaling. Notably, the inhibition of pyroptosis using VX-765 significantly mitigated neurological impairments.

CONCLUSIONS

Our study provides evidence that endothelial pyroptosis, characterized by the release of IL-1β and IL-6, triggers microglial polarization through NF-κB pathway activation, ultimately leading to microglia-mediated neuronal apoptosis in the choroid plexus post-ICH. These findings suggest that targeted therapeutic strategies aimed at mitigating endothelial cell pyroptosis and neutralizing inflammatory cytokines may offer neuroprotection for both microglia and neurons, presenting a promising avenue for ICH treatment.

Melatonin and brain barriers: The protection conferred by melatonin to the blood-brain barrier and blood-cerebrospinal fluid barrier

The blood-brain barrier and the blood-cerebrospinal fluid barrier separate the blood from brain tissue and cerebrospinal fluid. These brain barriers are important to maintain homeostasis and complex functions by protecting the brain from xenobiotics and harmful endogenous compounds. The disruption of brain barriers is a characteristic of neurologic diseases. Melatonin is a lipophilic hormone that is mainly produced by the pineal gland. The blood-brain barrier and the blood-cerebrospinal fluid barriers are melatonin-binding sites. Among the several melatonin actions, the most characteristic one is the regulation of sleep-wake cycles, melatonin has anti-inflammatory and antioxidant properties. Since brain barriers disruption can arise from inflammation and oxidative stress, knowing the influence of melatonin on the integrity of brain barriers is extremely important. Therefore, the objective of this review is to gather and discuss the available literature about the regulation of brain barriers by melatonin.

Inflammation-Triggered Enlargement of Choroid Plexus in Subacute COVID-19 Patients with Neurological Symptoms

OBJECTIVE

To investigate whether choroid plexus volumes in subacute coronavirus disease 2019 (COVID-19) patients with neurological symptoms could indicate inflammatory activation or barrier dysfunction and assess their association with clinical data.

METHODS

Choroid plexus volumes were measured in 28 subacute COVID-19 patients via cerebral magnetic resonance imaging (MRI), compared with those in infection-triggered non-COVID-19 encephalopathy patients (n = 25), asymptomatic individuals after COVID-19 (n = 21), and healthy controls (n = 21). Associations with inflammatory serum markers (peak counts of leukocytes, C-reactive protein [CRP], interleukin 6), an MRI-based marker of barrier dysfunction (CSF volume fraction [V-CSF]), and clinical parameters like olfactory performance and cognitive scores (Montreal Cognitive Assessment) were investigated.

RESULTS

COVID-19 patients showed significantly larger choroid plexus volumes than control groups (p < 0.001, η2 = 0.172). These volumes correlated significantly with peak leukocyte levels (p = 0.001, Pearson's r = 0.621) and V-CSF (p = 0.009, Spearman's rho = 0.534), but neither with CRP nor interleukin 6. No significant correlations were found with clinical parameters.

INTERPRETATION

In patients with subacute COVID-19, choroid plexus volume is a marker of central nervous system inflammation and barrier dysfunction in the presence of neurologic symptoms. The absence of plexus enlargement in infection-triggered non-COVID-19 encephalopathy suggests a specific severe acute respiratory syndrome coronavirus 2 effect. This study also documents an increase in choroid plexus volume for the first time as a parainfectious event. ANN NEUROL 2024;96:715-725.

The Blood-Cerebrospinal Fluid Barrier Dysfunction in Brain Disorders and Stroke: Why, How, What For?

Ischemic stroke (IS) results in the interruption of blood flow to the brain, which can cause significant damage. The pathophysiological mechanisms of IS include ionic imbalances, oxidative stress, neuroinflammation, and impairment of brain barriers. Brain barriers, such as the blood-brain barrier (BBB) and the blood-cerebrospinal fluid (CSF) barrier (B-CSF), protect the brain from harmful substances by regulating the neurochemical environment. Although the BBB is widely recognized for its crucial role in protecting the brain and its involvement in conditions such as stroke, the B-CSF requires further study. The B-CSF plays a fundamental role in regulating the CSF environment and maintaining the homeostasis of the central nervous system (CNS). However, the impact of B-CSF impairment during pathological events such as IS is not yet fully understood. In conditions like IS and other neurological disorders, the B-CSF can become compromised, allowing the entry of inflammatory substances and increasing neuronal damage. Understanding and preserving the integrity of the B-CSF are crucial for mitigating damage and facilitating recovery after ischemic stroke, highlighting its fundamental role in regulating the CNS during adverse neurological conditions.

Influencing factors of glymphatic system during perioperative period

The glymphatic system is a functional cerebrospinal fluid circulatory system that uses peri-arterial space for inflow of cerebrospinal fluid and peri-venous space for efflux of cerebrospinal fluid from brain parenchyma. This brain-wide fluid transport pathway facilitates the exchange between cerebrospinal fluid and interstitial fluid and clears metabolic waste from the metabolically active brain. Multiple lines of work show that the glymphatic system is crucial to normal brain functions, and the dysfunction of the glymphatic system is closely associated with various neurological disorders, including aging, neurodegeneration, and acute brain injury. Currently, it is common to explore the functional and molecular mechanisms of the glymphatic system based on animal models. The function of glymphatic system during perioperative period is affected by many factors such as physiological, pathological, anesthetic and operative methods. To provide a reference for the interpretation of the results of glymphatic system studies during perioperative period, this article comprehensively reviews the physiological and pathological factors that interfere with the function of the glymphatic system during perioperative period, investigates the effects of anesthetic drugs on glymphatic system function and the potential underlying mechanisms, describes operative methods that interfere with the function of the glymphatic system, and potential intervention strategies based on the glymphatic system. Future, these variables should be taken into account as critical covariates in the design of functional studies on the glymphatic system.

Nanotechnology-driven Microemulsion Based Intranasal Delivery to Neurotechnology-driven Neuralink: Strategies to Improve Management of Neurodegenerative Disorders

Neurodegenerative disorder refers to malfunctioning of neurons their degradation leading to death of neurons. Among various neurodegenerative disorders APHD (Alzheimer's, Parkinson's, and Huntington's Disease) are particularly concerning due to their progressive and debilitating nature. The therapeutic agent used for treatment and management of APHD often show unsatisfactory clinical outcome owing to poor solubility and limited permeability across blood brain barrier (BBB). The nose-to brain delivery can overcome this BBB challenge as it can transport drug directly to brain though olfactory pathways bypassing BBB. Additionally, the nanotechnology has emerged as a cutting-edge methodology to address this issue and specifically mucoadhesive micro/nanoemulsion can improve the overall performance of the drug when administered intranasally. Beyond the therapy neurotechnology has emerged as are revolutionary AI-driven BCI (Brain computer interface) aimed to restore independence in patients with function loss due to neuron degeneration/death. A promising BCI Neuralink has been recently explored for clinical trials and results revealed that a quadriplegia bearing person with implanted Neuralink chip was able to perform few normal functions of daily routine such as playing online games, text messaging, reading, and learning foreign languages online through accessing the particular websites. This review will discuss the fundamental concepts of neurodegeneration, application of micro/nanoemulsion through intranasal route and integration of neurotechnology for the management and treatment of APHD.

The choroid plexus synergizes with immune cells during neuroinflammation

The choroid plexus (ChP) is a vital brain barrier and source of cerebrospinal fluid (CSF). Here, we use longitudinal two-photon imaging in awake mice and single-cell transcriptomics to elucidate the mechanisms of ChP regulation of brain inflammation. We used intracerebroventricular injections of lipopolysaccharides (LPS) to model meningitis in mice and observed that neutrophils and monocytes accumulated in the ChP stroma and surged across the epithelial barrier into the CSF. Bi-directional recruitment of monocytes from the periphery and, unexpectedly, macrophages from the CSF to the ChP helped eliminate neutrophils and repair the barrier. Transcriptomic analyses detailed the molecular steps accompanying this process and revealed that ChP epithelial cells transiently specialize to nurture immune cells, coordinating their recruitment, survival, and differentiation as well as regulation of the tight junctions that control the permeability of the ChP brain barrier. Collectively, we provide a mechanistic understanding and a comprehensive roadmap of neuroinflammation at the ChP brain barrier.

Choroid plexus enlargement in patients with obstructive sleep apnea

OBJECTIVES

The function of choroid plexus is to produce cerebrospinal fluid, which is critical for the glymphatic system function. In this study, we aimed to analyze the differences in choroid plexus volume between patients with obstructive sleep apnea (OSA) and healthy controls, with the goal of discovering the glymphatic system dysfunction in patients with OSA.

METHODS

We prospectively enrolled 40 patients with OSA confirmed by polysomnography and 38 age- and sex-matched healthy controls. All participants underwent three-dimensional T1-weighted brain imaging, which was suitable for volumetric analysis. We compared choroid plexus volumes between patients with OSA and healthy controls, and analyzed the association between choroid plexus volume and polysomnographic findings in patients with OSA.

RESULTS

Choroid plexus volumes were significantly larger in patients with OSA than in healthy controls (2.311 % vs. 2.096 %, p = 0.005). However, no significant association was detected between choroid plexus volume and polysomnographic findings.

CONCLUSION

This study demonstrated enlargement of the choroid plexus in patients with OSA compared with healthy controls. This finding could be related with glymphatic system dysfunction in patients with OSA.

In vitro models of the choroid plexus and the blood-cerebrospinal fluid barrier: advances, applications, and perspectives

The choroid plexus (CP), a highly vascularized endothelial-epithelial convolute, is placed in the ventricular system of the brain and produces a large part of the cerebrospinal fluid (CSF). Additionally, the CP is the location of a blood-CSF barrier (BCSFB) that separates the CSF from the blood stream in the CP endothelium. In vitro models of the CP and the BCSFB are of high importance to investigate the biological functions of the CP and the BCSFB. Since the CP is involved in several serious diseases, these in vitro models promise help in researching the processes contributing to the diseases and during the development of treatment options. In this review, we provide an overview on the available models and the advances that have been made toward more sophisticated and "in vivo near" systems as organoids and microfluidic lab-on-a-chip approaches. We go into the applications and research objectives for which the various modeling systems can be used and discuss the possible future prospects and perspectives.

Choroid plexus enlargement correlates with periventricular pathology but not with disease activity in radiologically isolated syndrome

BACKGROUND

Choroid plexus (ChP) enlargement is an emerging radiological biomarker in multiple sclerosis (MS).

OBJECTIVES

This study aims to assess ChP volume in a large cohort of patients with radiologically isolated syndrome (RIS) versus healthy controls (HC) and explore its relationship with other brain volumes, disease activity, and biological markers.

METHODS

RIS individuals were included retrospectively and compared with HC. ChPs were automatically segmented using an in-house automated algorithm and manually corrected.

RESULTS

A total of 124 patients fulfilled the 2023 RIS criteria, and 55 HCs were included. We confirmed that ChPs are enlarged in RIS versus HC (mean (±SD) normalized ChP volume: 17.24 (±4.95) and 11.61 (±3.58), respectively, p < 0.001). Larger ChPs were associated with more periventricular lesions (ρ = 0.26; r2 = 0.27; p = 0.005 for the correlation with lesion volume, and ρ = 0.2; r2 = 0.21; p = 0.002 for the correlation with lesion number) and lower thalamic volume (ρ = -0.38; r2 = 0.44; p < 0.001), but not with lesions in other brain regions. Conversely, ChP volume did not correlate with biological markers. No significant difference in ChP volume was observed between subjects who presented or did not have a clinical event or between those with or without imaging disease activity.

CONCLUSIONS

This study provides evidence that ChP volume is higher in RIS and is associated with measures reflecting periventricular pathology but does not correlate with biological, radiological, or clinical markers of disease activity.

The hypervirulent Group B Streptococcus HvgA adhesin promotes central nervous system invasion through transcellular crossing of the choroid plexus

BACKGROUND

Group B Streptococcus (GBS) is the leading cause of neonatal meningitis responsible for a substantial cause of death and disability worldwide. The vast majority of GBS neonatal meningitis cases are due to the CC17 hypervirulent clone. However, the cellular and molecular pathways involved in brain invasion by GBS CC17 isolates remain largely elusive. Here, we studied the specific interaction of the CC17 clone with the choroid plexus, the main component of the blood-cerebrospinal fluid (CSF) barrier.

METHODS

The interaction of GBS CC17 or non-CC17 strains with choroid plexus cells was studied using an in vivo mouse model of meningitis and in vitro models of primary and transformed rodent choroid plexus epithelial cells (CPEC and Z310). In vivo interaction of GBS with the choroid plexus was assessed by microscopy. Bacterial invasion and cell barrier penetration were examined in vitro, as well as chemokines and cytokines in response to infection.

RESULTS

GBS CC17 was found associated with the choroid plexus of the lateral, 3rd and 4th ventricles. Infection of choroid plexus epithelial cells revealed an efficient internalization of the bacteria into the cells with GBS CC17 displaying a greater ability to invade these cells than a non-CC17 strain. Internalization of the GBS CC17 strain involved the CC17-specific HvgA adhesin and occurred via a clathrin-dependent mechanism leading to transcellular transcytosis across the choroid plexus epithelial monolayer. CPEC infection resulted in the secretion of several chemokines, including CCL2, CCL3, CCL20, CX3CL1, and the matrix metalloproteinase MMP3, as well as immune cell infiltration.

CONCLUSION

Our findings reveal a GBS strain-specific ability to infect the blood-CSF barrier, which appears to be an important site of bacterial entry and an active site of immune cell trafficking in response to infection.

The Networking Brain: How Extracellular Matrix, Cellular Networks, and Vasculature Shape the In Vivo Mechanical Properties of the Brain

Mechanically, the brain is characterized by both solid and fluid properties. The resulting unique material behavior fosters proliferation, differentiation, and repair of cellular and vascular networks, and optimally protects them from damaging shear forces. Magnetic resonance elastography (MRE) is a noninvasive imaging technique that maps the mechanical properties of the brain in vivo. MRE studies have shown that abnormal processes such as neuronal degeneration, demyelination, inflammation, and vascular leakage lead to tissue softening. In contrast, neuronal proliferation, cellular network formation, and higher vascular pressure result in brain stiffening. In addition, brain viscosity has been reported to change with normal blood perfusion variability and brain maturation as well as disease conditions such as tumor invasion. In this article, the contributions of the neuronal, glial, extracellular, and vascular networks are discussed to the coarse-grained parameters determined by MRE. This reductionist multi-network model of brain mechanics helps to explain many MRE observations in terms of microanatomical changes and suggests that cerebral viscoelasticity is a suitable imaging marker for brain disease.

The immune and metabolic milieu of the choroid plexus as a potential target in brain protection

The brain's choroid plexus (CP), which operates as an anatomical and functional 'checkpoint', regulates the communication between brain and periphery and contributes to the maintenance of healthy brain homeostasis throughout life. Evidence from mouse models and humans reveals a link between loss of CP checkpoint properties and dysregulation of the CP immune milieu as a conserved feature across diverse neurological conditions. In particular, we suggest that an imbalance between different immune signals at the CP, including CD4+ T cell-derived cytokines, type-I interferon, and complement components, can perpetuate brain inflammation and cognitive deterioration in aging and neurodegeneration. Furthermore, we highlight the role of CP metabolism in controlling CP inflammation, and propose that targeting molecules that regulate CP metabolism could be effective in safeguarding brain function.

Blood-brain barrier injury and neuroinflammation induced by SARS-CoV-2 in a lung-brain microphysiological system

In some patients, COVID-19 can trigger neurological symptoms with unclear pathogenesis. Here we describe a microphysiological system integrating alveolus and blood-brain barrier (BBB) tissue chips that recapitulates neuropathogenesis associated with infection by SARS-CoV-2. Direct exposure of the BBB chip to SARS-CoV-2 caused mild changes to the BBB, and infusion of medium from the infected alveolus chip led to more severe injuries on the BBB chip, including endothelial dysfunction, pericyte detachment and neuroinflammation. Transcriptomic analyses indicated downregulated expression of the actin cytoskeleton in brain endothelium and upregulated expression of inflammatory genes in glial cells. We also observed early cerebral microvascular damage following lung infection with a low viral load in the brains of transgenic mice expressing human angiotensin-converting enzyme 2. Our findings suggest that systemic inflammation is probably contributing to neuropathogenesis following SARS-CoV-2 infection, and that direct viral neural invasion might not be a prerequisite for this neuropathogenesis. Lung-brain microphysiological systems should aid the further understanding of the systemic effects and neurological complications of viral infection.

Involvement of the choroid plexus in Alzheimer's disease pathophysiology: findings from mouse and human proteomic studies

BACKGROUND

Structural and functional changes of the choroid plexus (ChP) have been reported in Alzheimer's disease (AD). Nonetheless, the role of the ChP in the pathogenesis of AD remains largely unknown. We aim to unravel the relation between ChP functioning and core AD pathogenesis using a unique proteomic approach in mice and humans.

METHODS

We used an APP knock-in mouse model, APPNL-G-F, exhibiting amyloid pathology, to study the association between AD brain pathology and protein changes in mouse ChP tissue and CSF using liquid chromatography mass spectrometry. Mouse proteomes were investigated at the age of 7 weeks (n = 5) and 40 weeks (n = 5). Results were compared with previously published human AD CSF proteomic data (n = 496) to identify key proteins and pathways associated with ChP changes in AD.

RESULTS

ChP tissue proteome was dysregulated in APPNL-G-F mice relative to wild-type mice at both 7 and 40 weeks. At both ages, ChP tissue proteomic changes were associated with epithelial cells, mitochondria, protein modification, extracellular matrix and lipids. Nonetheless, some ChP tissue proteomic changes were different across the disease trajectory; pathways related to lysosomal function, endocytosis, protein formation, actin and complement were uniquely dysregulated at 7 weeks, while pathways associated with nervous system, immune system, protein degradation and vascular system were uniquely dysregulated at 40 weeks. CSF proteomics in both mice and humans showed similar ChP-related dysregulated pathways.

CONCLUSIONS

Together, our findings support the hypothesis of ChP dysfunction in AD. These ChP changes were related to amyloid pathology. Therefore, the ChP could become a novel promising therapeutic target for AD.

Regulation of brain fluid volumes and pressures: basic principles, intracranial hypertension, ventriculomegaly and hydrocephalus

The principles of cerebrospinal fluid (CSF) production, circulation and outflow and regulation of fluid volumes and pressures in the normal brain are summarised. Abnormalities in these aspects in intracranial hypertension, ventriculomegaly and hydrocephalus are discussed. The brain parenchyma has a cellular framework with interstitial fluid (ISF) in the intervening spaces. Framework stress and interstitial fluid pressure (ISFP) combined provide the total stress which, after allowing for gravity, normally equals intracerebral pressure (ICP) with gradients of total stress too small to measure. Fluid pressure may differ from ICP in the parenchyma and collapsed subarachnoid spaces when the parenchyma presses against the meninges. Fluid pressure gradients determine fluid movements. In adults, restricting CSF outflow from subarachnoid spaces produces intracranial hypertension which, when CSF volumes change very little, is called idiopathic intracranial hypertension (iIH). Raised ICP in iIH is accompanied by increased venous sinus pressure, though which is cause and which effect is unclear. In infants with growing skulls, restriction in outflow leads to increased head and CSF volumes. In adults, ventriculomegaly can arise due to cerebral atrophy or, in hydrocephalus, to obstructions to intracranial CSF flow. In non-communicating hydrocephalus, flow through or out of the ventricles is somehow obstructed, whereas in communicating hydrocephalus, the obstruction is somewhere between the cisterna magna and cranial sites of outflow. When normal outflow routes are obstructed, continued CSF production in the ventricles may be partially balanced by outflow through the parenchyma via an oedematous periventricular layer and perivascular spaces. In adults, secondary hydrocephalus with raised ICP results from obvious obstructions to flow. By contrast, with the more subtly obstructed flow seen in normal pressure hydrocephalus (NPH), fluid pressure must be reduced elsewhere, e.g. in some subarachnoid spaces. In idiopathic NPH, where ventriculomegaly is accompanied by gait disturbance, dementia and/or urinary incontinence, the functional deficits can sometimes be reversed by shunting or third ventriculostomy. Parenchymal shrinkage is irreversible in late stage hydrocephalus with cellular framework loss but may not occur in early stages, whether by exclusion of fluid or otherwise. Further studies that are needed to explain the development of hydrocephalus are outlined.

Shifting from ependyma to choroid plexus epithelium and the changing expressions of aquaporin-1 and aquaporin-4

The cells of the choroid plexus (CP) epithelium are specialized ependymal cells (ECs) but have distinct properties. The CP cells and ECs form single-cell sheets contiguous to each other at a transitional zone. The CP is underlined by a basal lamina and has barrier properties, whereas the ECs do not. The basal lamina of the CP is continuous with the glia limitans superficialis and, consequently, the CP stroma is continuous with the meninges along entering blood vessels. The CP has previously been reported to express aquaporin-1 (AQP1) mostly apically, and ECs show mostly basolateral aquaporin-4 (AQP4) expression. Recent evidence in various systems has shown that in changing conditions the expression and distribution of AQP4 can be modified, involving phosphorylation and calmodulin-triggered translocation. Studies on the human CP revealed that AQP4 is also expressed in some CP cells, which is likely to be increased during ageing based on mouse data. Moreover, subependymal astrocytic processes in the ependyma-CP transition, forming a glial plate around blood vessels and facing the CP stroma, were strongly positive for AQP4. We propose that the increased AQP4 expression might be a compensatory mechanism for the observed reduction in CSF production in the ageing human brain. The high AQP4 density in the transition zone might facilitate the transport of water into and out of the CP stroma and serve as a drainage and clearing pathway for metabolites in the CNS.

Serum and CSF metabolomics analysis shows Mediterranean Ketogenic Diet mitigates risk factors of Alzheimer's disease

Alzheimer's disease (AD) is influenced by a variety of modifiable risk factors, including a person's dietary habits. While the ketogenic diet (KD) holds promise in reducing metabolic risks and potentially affecting AD progression, only a few studies have explored KD's metabolic impact, especially on blood and cerebrospinal fluid (CSF). Our study involved participants at risk for AD, either cognitively normal or with mild cognitive impairment. The participants consumed both a modified Mediterranean Ketogenic Diet (MMKD) and the American Heart Association diet (AHAD) for 6 weeks each, separated by a 6-week washout period. We employed nuclear magnetic resonance (NMR)-based metabolomics to profile serum and CSF and metagenomics profiling on fecal samples. While the AHAD induced no notable metabolic changes, MMKD led to significant alterations in both serum and CSF. These changes included improved modifiable risk factors, like increased HDL-C and reduced BMI, reversed serum metabolic disturbances linked to AD such as a microbiome-mediated increase in valine levels, and a reduction in systemic inflammation. Additionally, the MMKD was linked to increased amino acid levels in the CSF, a breakdown of branched-chain amino acids (BCAAs), and decreased valine levels. Importantly, we observed a strong correlation between metabolic changes in the CSF and serum, suggesting a systemic regulation of metabolism. Our findings highlight that MMKD can improve AD-related risk factors, reverse some metabolic disturbances associated with AD, and align metabolic changes across the blood-CSF barrier.

JCPyV infection of primary choroid plexus epithelial cells reduces expression of critical junctional proteins and increases expression of barrier disrupting inflammatory cytokines

The human polyomavirus, JCPyV, establishes a lifelong persistent infection in the peripheral organs of a majority of the human population worldwide. Patients who are immunocompromised due to underlying infections, cancer, or to immunomodulatory treatments for autoimmune disease are at risk for developing progressive multifocal leukoencephalopathy (PML) when the virus invades the CNS and infects macroglial cells in the brain parenchyma. It is not yet known how the virus enters the CNS to cause disease. The blood-choroid plexus barrier is a potential site of virus invasion as the cells that make up this barrier are known to be infected with virus both in vivo and in vitro. To understand the effects of virus infection on these cells we challenged primary human choroid plexus epithelial cells with JCPyV and profiled changes in host gene expression. We found that viral infection induced the expression of proinflammatory chemokines and downregulated junctional proteins essential for maintaining blood-CSF and blood-brain barrier function. These data contribute to our understanding of how JCPyV infection of the choroid plexus can modulate the host cell response to neuroinvasive pathogens.

IMPORTANCE

The human polyomavirus, JCPyV, causes a rapidly progressing demyelinating disease in the CNS of patients whose immune systems are compromised. JCPyV infection has been demonstrated in the choroid plexus both in vivo and in vitro and this highly vascularized organ may be important in viral invasion of brain parenchyma. Our data show that infection of primary choroid plexus epithelial cells results in increased expression of pro-inflammatory chemokines and downregulation of critical junctional proteins that maintain the blood-CSF barrier. These data have direct implications for mechanisms used by JCPyV to invade the CNS and cause neurological disease.

Effect of Different Staining Methods on Brain Cryosections

Staining frozen sections is often required to distinguish cell types for spatial transcriptomic studies of the brain. The impact of the staining methods on the RNA integrity of the cells becomes one of the limitations of spatial transcriptome technology with microdissection. However, there is a lack of systematic comparisons of different staining modalities for the pretreatment of frozen sections of brain tissue as well as their effects on transcriptome sequencing results. In this study, four different staining methods were analyzed for their effect on RNA integrity in frozen sections of brain tissue. Subsequently, differences in RNA quality in frozen sections under different staining conditions and their impact on transcriptome sequencing results were assessed by RNA-seq. As one of the most commonly used methods for staining pathological sections, HE staining seriously affects the RNA quality of frozen sections of brain tissue. In contrast, the homemade cresyl violet staining method developed in this study has the advantages of short staining time, low cost, and less RNA degradation. The homemade cresyl violet staining proposed in this study can be applied instead of HE staining as an advance staining step for transcriptome studies in frozen sections of brain tissue. In the future, this staining method may be suitable for wide application in brain-related studies of frozen tissue sections. Moreover, it is expected to become a routine step for staining cells before sampling in brain science.

Choroid plexus calcifications are not associated with putative markers of glymphatic dysfunction: A population study in middle-aged and older adults

BACKGROUND AND PURPOSE

Recent studies have suggested an association between dysfunction of the choroid plexus and the glymphatic system. However, information is inconclusive. Following a population-based study design, we aimed to assess the association between choroid plexus calcifications (CPCs)-as a surrogate of choroid plexus dysfunction-and severity and progression of putative markers of glymphatic dysfunction, including white matter hyperintensities (WMH) of presumed vascular origin and abnormally enlarged basal ganglia perivascular spaces (BG-PVS).

METHODS

This study recruited community-dwellers aged ≥40 years living in neighboring Ecuadorian villages. Participants who had baseline head CTs and brain MRIs were included in cross-sectional analyses and those who additional had follow-up MRIs (after a mean of 6.4 ± 1.5 years) were included in longitudinal analyses. Logistic and Poisson regression models, adjusted for demographics and cardiovascular risk factors, were fitted to assess associations between CPCs and WMH and enlarged BG-PVS severity and progression.

RESULTS

A total of 590 individuals were included in the cross-sectional component of the study, and 215 in the longitudinal component. At baseline, 25% of participants had moderate-to-severe WMH and 27% had abnormally enlarged BG-PVS. At follow-up, 36% and 20% of participants had WMH and enlarged BG-PVS progression, respectively. Logistic regression models showed no significant differences between CPCs volumes stratified in quartiles and severity of WMH and enlarged BG-PVS. Poisson regression models showed no association between the exposure and WMH and enlarged BG-PVS progression. Baseline age remained significant in these models.

CONCLUSIONS

Choroid plexus calcifications are not associated with putative markers of glymphatic system dysfunction.

Current status and advances to improving drug delivery in diffuse intrinsic pontine glioma

Diffuse midline glioma (DMG), including tumors diagnosed in the brainstem (diffuse intrinsic pontine glioma - DIPG), is the primary cause of brain tumor-related death in pediatric patients. DIPG is characterized by a median survival of <12 months from diagnosis, harboring the worst 5-year survival rate of any cancer. Corticosteroids and radiation are the mainstay of therapy; however, they only provide transient relief from the devastating neurological symptoms. Numerous therapies have been investigated for DIPG, but the majority have been unsuccessful in demonstrating a survival benefit beyond radiation alone. Although many barriers hinder brain drug delivery in DIPG, one of the most significant challenges is the blood-brain barrier (BBB). Therapeutic compounds must possess specific properties to enable efficient passage across the BBB. In brain cancer, the BBB is referred to as the blood-brain tumor barrier (BBTB), where tumors disrupt the structure and function of the BBB, which may provide opportunities for drug delivery. However, the biological characteristics of the brainstem's BBB/BBTB, both under normal physiological conditions and in response to DIPG, are poorly understood, which further complicates treatment. Better characterization of the changes that occur in the BBB/BBTB of DIPG patients is essential, as this informs future treatment strategies. Many novel drug delivery technologies have been investigated to bypass or disrupt the BBB/BBTB, including convection enhanced delivery, focused ultrasound, nanoparticle-mediated delivery, and intranasal delivery, all of which are yet to be clinically established for the treatment of DIPG. Herein, we review what is known about the BBB/BBTB and discuss the current status, limitations, and advances of conventional and novel treatments to improving brain drug delivery in DIPG.

The circadian clock in the choroid plexus drives rhythms in multiple cellular processes under the control of the suprachiasmatic nucleus

Choroid plexus (ChP), the brain structure primarily responsible for cerebrospinal fluid production, contains a robust circadian clock, whose role remains to be elucidated. The aim of our study was to [1] identify rhythmically controlled cellular processes in the mouse ChP and [2] assess the role and nature of signals derived from the master clock in the suprachiasmatic nuclei (SCN) that control ChP rhythms. To accomplish this goal, we used various mouse models (WT, mPer2Luc, ChP-specific Bmal1 knockout) and combined multiple experimental approaches, including surgical lesion of the SCN (SCNx), time-resolved transcriptomics, and single cell luminescence microscopy. In ChP of control (Ctrl) mice collected every 4 h over 2 circadian cycles in darkness, we found that the ChP clock regulates many processes, including the cerebrospinal fluid circadian secretome, precisely times endoplasmic reticulum stress response, and controls genes involved in neurodegenerative diseases (Alzheimer's disease, Huntington's disease, and frontotemporal dementia). In ChP of SCNx mice, the rhythmicity detected in vivo and ex vivo was severely dampened to a comparable extent as in mice with ChP-specific Bmal1 knockout, and the dampened cellular rhythms were restored by daily injections of dexamethasone in mice. Our data demonstrate that the ChP clock controls tissue-specific gene expression and is strongly dependent on the presence of a functional connection with the SCN. The results may contribute to the search for a novel link between ChP clock disruption and impaired brain health.

Advancements in Cerebrospinal Fluid Biosensors: Bridging the Gap from Early Diagnosis to the Detection of Rare Diseases

Cerebrospinal fluid (CSF) is a body fluid that can be used for the diagnosis of various diseases. However, CSF collection requires an invasive and painful procedure called a lumbar puncture (LP). This procedure is applied to any patient with a known risk of central nervous system (CNS) damage or neurodegenerative disease, regardless of their age range. Hence, this can be a very painful procedure, especially in infants and elderly patients. On the other hand, the detection of disease biomarkers in CSF makes diagnoses as accurate as possible. This review aims to explore novel electrochemical biosensing platforms that have impacted biomedical science. Biosensors have emerged as techniques to accelerate the detection of known biomarkers in body fluids such as CSF. Biosensors can be designed and modified in various ways and shapes according to their ultimate applications to detect and quantify biomarkers of interest. This process can also significantly influence the detection and diagnosis of CSF. Hence, it is important to understand the role of this technology in the rapidly progressing field of biomedical science.

Breakthroughs in choroid plexus and CSF biology from the first European Choroid plexus Scientific Forum (ECSF)

The European Choroid plexus Scientific Forum (ECSF), held in Heidelberg, Germany between the 7th and 9th of November 2023, involved 21 speakers from eight countries. ECSF focused on discussing cutting-edge fundamental and medical research related to the development and functions of the choroid plexus and its implications for health, aging, and disease, including choroid plexus tumors. In addition to new findings in this expanding field, innovative approaches, animal models and 3D in vitro models were showcased to encourage further investigation into choroid plexus and cerebrospinal fluid roles.