The choroid plexus as a site of damage in hemorrhagic and ischemic stroke and its role in responding to injury

The choroid plexus maintains adult brain ventricles and subventricular zone neuroblast pool, which facilitates poststroke neurogenesis

The brain's neuroreparative capacity after injuries such as ischemic stroke is partly contained in the brain's neurogenic niches, primarily the subventricular zone (SVZ), which lies in close contact with the cerebrospinal fluid (CSF) produced by the choroid plexus (ChP). Despite the wide range of their proposed functions, the ChP/CSF remain among the most understudied compartments of the central nervous system (CNS). Here, we report a mouse genetic tool (the ROSA26iDTR mouse line) for noninvasive, specific, and temporally controllable ablation of CSF-producing ChP epithelial cells to assess the roles of the ChP and CSF in brain homeostasis and injury. Using this model, we demonstrate that ChP ablation causes rapid and permanent CSF volume loss in both aged and young adult brains, accompanied by disruption of ependymal cilia bundles. Surprisingly, ChP ablation did not result in overt neurological deficits at 1 mo postablation. However, we observed a pronounced decrease in the pool of SVZ neuroblasts (NBs) following ChP ablation, which occurs due to their enhanced migration into the olfactory bulb. In the middle cerebral artery occlusion model of ischemic stroke, NB migration into the lesion site was also reduced in the CSF-depleted mice. Thus, our study establishes an important role of ChP/CSF in regulating the regenerative capacity of the adult brain under normal conditions and after ischemic stroke.

The choroid plexus maintains ventricle volume and adult subventricular zone neuroblast pool, which facilitates post-stroke neurogenesis

The brain's neuroreparative capacity after injuries such as ischemic stroke is contained in the brain's neurogenic niches, primarily the subventricular zone (SVZ), which lies in close contact with the cerebrospinal fluid (CSF) produced by the choroid plexus (ChP). Despite the wide range of their proposed functions, the ChP/CSF remain among the most understudied compartments of the central nervous system (CNS). Here we report a mouse genetic tool (the ROSA26iDTR mouse line) for non-invasive, specific, and temporally controllable ablation of CSF-producing ChP epithelial cells to assess the roles of the ChP and CSF in brain homeostasis and injury. Using this model, we demonstrate that ChP ablation causes rapid and permanent CSF volume loss accompanied by disruption of ependymal cilia bundles. Surprisingly, ChP ablation did not result in overt neurological deficits at one-month post-ablation. However, we observed a pronounced decrease in the pool of SVZ neuroblasts following ChP ablation, which occurs due to their enhanced migration into the olfactory bulb. In the MCAo model of ischemic stroke, neuroblast migration into the lesion site was also reduced in the CSF-depleted mice. Thus, our study establishes an important and novel role of ChP/CSF in regulating the regenerative capacity of the adult brain under normal conditions and after ischemic stroke.

Optical Coherence Tomography Angiography: Revolutionizing Clinical Diagnostics and Treatment in Central Nervous System Disease

Optical coherence tomography angiography (OCTA), as a new generation of non-invasive and efficient fundus imaging technology, can provide non-invasive assessment of vascular lesions in the retina and choroid. In terms of anatomy and development, the retina is referred to as an extension of the central nervous system (CNS). CNS diseases are closely related to changes in fundus structure and blood vessels, and direct visualization of fundus structure and blood vessels provides an effective "window" for CNS research. This has important practical significance for identifying the characteristic changes of various CNS diseases on OCTA in the future, and plays a key role in promoting early screening, diagnosis, and monitoring of disease progression in CNS diseases. This article reviews relevant fundus studies by comparing and summarizing the unique advantages and existing limitations of OCTA in various CNS disease patients, in order to demonstrate the clinical significance of OCTA in the diagnosis and treatment of CNS diseases.

Immune compartments at the brain's borders in health and neurovascular diseases

Recent evidence implicates cranial border immune compartments in the meninges, choroid plexus, circumventricular organs, and skull bone marrow in several neuroinflammatory and neoplastic diseases. Their pathogenic importance has also been described for cardiovascular diseases such as hypertension and stroke. In this review, we will examine the cellular composition of these cranial border immune niches, the potential pathways through which they might interact, and the evidence linking them to cardiovascular disease.

Inflammatory Response and Exosome Biogenesis of Choroid Plexus Organoids Derived from Human Pluripotent Stem Cells

The choroid plexus (ChP) is a complex structure in the human brain that is responsible for the secretion of cerebrospinal fluid (CSF) and forming the blood-CSF barrier (B-CSF-B). Human-induced pluripotent stem cells (hiPSCs) have shown promising results in the formation of brain organoids in vitro; however, very few studies to date have generated ChP organoids. In particular, no study has assessed the inflammatory response and the extracellular vesicle (EV) biogenesis of hiPSC-derived ChP organoids. In this study, the impacts of Wnt signaling on the inflammatory response and EV biogenesis of ChP organoids derived from hiPSCs was investigated. During days 10-15, bone morphogenetic protein 4 was added along with (+/-) CHIR99021 (CHIR, a small molecule GSK-3β inhibitor that acts as a Wnt agonist). At day 30, the ChP organoids were characterized by immunocytochemistry and flow cytometry for TTR (~72%) and CLIC6 (~20%) expression. Compared to the -CHIR group, the +CHIR group showed an upregulation of 6 out of 10 tested ChP genes, including CLIC6 (2-fold), PLEC (4-fold), PLTP (2-4-fold), DCN (~7-fold), DLK1 (2-4-fold), and AQP1 (1.4-fold), and a downregulation of TTR (0.1-fold), IGFBP7 (0.8-fold), MSX1 (0.4-fold), and LUM (0.2-0.4-fold). When exposed to amyloid beta 42 oligomers, the +CHIR group had a more sensitive response as evidenced by the upregulation of inflammation-related genes such as TNFα, IL-6, and MMP2/9 when compared to the -CHIR group. Developmentally, the EV biogenesis markers of ChP organoids showed an increase over time from day 19 to day 38. This study is significant in that it provides a model of the human B-CSF-B and ChP tissue for the purpose of drug screening and designing drug delivery systems to treat neurological disorders such as Alzheimer's disease and ischemic stroke.

NLRP3-dependent lipid droplet formation contributes to posthemorrhagic hydrocephalus by increasing the permeability of the blood-cerebrospinal fluid barrier in the choroid plexus

Hydrocephalus is a severe complication that can result from intracerebral hemorrhage, especially if this hemorrhage extends into the ventricles. Our previous study indicated that the NLRP3 inflammasome mediates cerebrospinal fluid hypersecretion in the choroid plexus epithelium. However, the pathogenesis of posthemorrhagic hydrocephalus remains unclear, and therapeutic strategies for prevention and treatment are lacking. In this study, an Nlrp3^-/- rat model of intracerebral hemorrhage with ventricular extension and primary choroid plexus epithelial cell culture were used to investigate the potential effects of NLRP3-dependent lipid droplet formation and its role in the pathogenesis of posthemorrhagic hydrocephalus. The data indicated that NLRP3-mediated dysfunction of the blood-cerebrospinal fluid barrier (B-CSFB) accelerated neurological deficits and hydrocephalus, at least in part, through the formation of lipid droplets in the choroid plexus; these lipid droplets interacted with mitochondria and increased the release of mitochondrial reactive oxygen species that destroyed tight junctions in the choroid plexus after intracerebral hemorrhage with ventricular extension. This study broadens the current understanding of the relationship among NLRP3, lipid droplets and the B-CSFB and provides a new therapeutic target for the treatment of posthemorrhagic hydrocephalus. Strategies to protect the B-CSFB may be effective therapeutic approaches for posthemorrhagic hydrocephalus.

Altered endocannabinoid metabolism compromises the brain-CSF barrier and exacerbates chronic deficits after traumatic brain injury in mice

Endocannabinoids [2-arachidonoylglycerol (2-AG) and N-arachidonoylethanolamine (AEA)], endogenously produced arachidonate-based lipids, are anti-inflammatory physiological ligands for two known cannabinoid receptors, CB1 and CB2, yet the molecular and cellular mechanisms underlying their effects after brain injury are poorly defined. In the present study, we hypothesize that traumatic brain injury (TBI)-induced loss of endocannabinoids exaggerates neurovascular injury, compromises brain-cerebrospinal fluid (CSF) barriers (BCB) and causes behavioral dysfunction. Preliminary analysis in human CSF and plasma indicates changes in endocannabinoid levels. This encouraged us to investigate the levels of endocannabinoid-metabolizing enzymes in a mouse model of controlled cortical impact (CCI). Reductions in endocannabinoid (2-AG and AEA) levels in plasma were supported by higher expression of their respective metabolizing enzymes, monoacylglycerol lipase (MAGL), fatty acid amide hydrolase (FAAH), and cyclooxygenase 2 (Cox-2) in the post-TBI mouse brain. Following increased metabolism of endocannabinoids post-TBI, we observed increased expression of CB2, non-cannabinoid receptor Transient receptor potential vanilloid-1 (TRPV1), aquaporin 4 (AQP4), ionized calcium binding adaptor molecule 1 (IBA1), glial fibrillary acidic protein (GFAP), and acute reduction in cerebral blood flow (CBF). The BCB and pericontusional cortex showed altered endocannabinoid expressions and reduction in ventricular volume. Finally, loss of motor functions and induced anxiety behaviors were observed in these TBI mice. Taken together, our findings suggest endocannabinoids and their metabolizing enzymes play an important role in the brain and BCB integrity and highlight the need for more extensive studies on these mechanisms.

Inhibition of interaction between ROCK1 and Rubicon restores autophagy in endothelial cells and attenuates brain injury after prolonged ischemia

Acute ischemic stroke (AIS) induces cerebral endothelial cell death resulting in the breakdown of the blood-brain barrier (BBB). Endothelial cell autophagy acts as a protective mechanism against cell death. Autophagy is activated in the very early stages of ischemic stroke and declines after prolonged ischemia. Previous studies have shown that Rubicon can inhibit autophagy. The current study aimed to investigate whether continuous long-term ischemia can inhibit autophagy in endothelial cells after ischemic stroke by regulating the function of Rubicon and its underlying mechanism. Wild-type male C57BL/6J mice were subjected to transient middle cerebral artery occlusion (tMCAO). ROCK1, ROCK2, and NOX2 inhibitors were injected into male mice 1 h before the onset of tMCAO. Disease severity and BBB permeability were evaluated. bEnd.3 cells were cultured in vitro and subjected to oxygen-glucose deprivation (OGD). bEnd.3 cells were pretreated with or without ROCK1, ROCK2, or NOX2 inhibitors overnight and then subjected to OGD. Cell viability and permeability were also evaluated. The expression of Rubicon, ROCK1, and autophagy-related proteins were analyzed. Increased BBB permeability was correlated with Rubicon expression in tMCAO mice and Rubicon was upregulated in endothelial cells subjected to OGD. Autophagy was inhibited in endothelial cells after long-term OGD treatment and knockdown of Rubicon expression restored autophagy and viability in endothelial cells subjected to 6-h OGD. ROCK1 inhibition decreased the interaction between Beclin1 and Rubicon and restored cell viability and autophagy suppressed by 6-h OGD treatment in endothelial cells. Additionally, ROCK1 inhibition suppressed Rubicon, attenuated BBB disruption, and brain injury induced by prolonged ischemia in 6-h tMCAO mice. Prolonged ischemia induced the death of brain endothelial cells and the breakdown of the BBB, thus aggravating brain injury by increasing the interaction of ROCK1 and Rubicon with Beclin1 while inhibiting canonical autophagy. Inhibition of ROCK1 signaling in endothelial cells could be a promising therapeutic strategy to prolong the therapeutic time window in AIS.

D* from diffusion MRI reveals a correspondence between ventricular cerebrospinal fluid volume and flow in the ischemic rodent model

Quantitative measurement of cerebrospinal fluid (CSF) flow and volume and longitudinal monitoring of CSF dynamics provide insights into the compensatory characteristics of post-stroke CSF. In this study, we compared the MRI pseudo-diffusion index (D*) of live and sacrificed rat brains to confirm the effect of ventricular CSF flow on diffusion signals. We observed the relationship between the CSF peak velocities and D* through Monte Carlo (MC) simulations to further understand the source of D* contrast. We also determined the dominant CSF flow using D* in three directions. Finally, we investigated the dynamic evolutions of ventricular CSF flow and volume in a stroke rat model (n = 8) from preoperative to up to 45 days after surgery and determined the correlation between ventricular CSF volume and flow. MC simulations showed a strong positive correlation between the CSF peak velocity and D* (r = 0.99). The dominant CSF flow variations in the 3D ventricle could be measured using the maximum D* map. A longitudinal positive correlation between ventricular CSF volume and D* was observed in the lateral (r = 0.74) and ventral-third (r = 0.81) ventricles, respectively. The directional D* measurements provide quantitative CSF volume and flow information, which would provide useful insights into ischemic stroke with diffusion MRI.

A new perspective on cerebrospinal fluid dynamics after subarachnoid hemorrhage: From normal physiology to pathophysiological changes

Knowledge about the dynamic metabolism and function of cerebrospinal fluid (CSF) physiology has rapidly progressed in recent decades. It has traditionally been suggested that CSF is produced by the choroid plexus and drains to the arachnoid villi. However, recent findings have revealed that the brain parenchyma produces a large portion of CSF and drains through the perivascular glymphatic system and meningeal lymphatic vessels into the blood. The primary function of CSF is not limited to maintaining physiological CNS homeostasis but also participates in clearing waste products resulting from neurodegenerative diseases and acute brain injury. Aneurysmal subarachnoid hemorrhage (SAH), a disastrous subtype of acute brain injury, is associated with high mortality and morbidity. Post-SAH complications contribute to the poor outcomes associated with SAH. Recently, abnormal CSF flow was suggested to play an essential role in the post-SAH pathophysiological changes, such as increased intracerebral pressure, brain edema formation, hydrocephalus, and delayed blood clearance. An in-depth understanding of CSF dynamics in post-SAH events would shed light on potential development of SAH treatment options. This review summarizes and updates the latest physiological characteristics of CSF dynamics and discusses potential pathophysiological changes and therapeutic targets after SAH.

Macular Microvasculature Is Associated With Total Cerebral Small Vessel Disease Burden in Recent Single Subcortical Infarction

Purpose

To assess the retinal microvasculature, choriocapillaris, and choroidal thickness in recent single subcortical infarction (RSSI) patients compared with healthy controls. We also assessed the correlation between the macular microvascular changes and choroidal changes with their clinical implications in RSSI patients.

Methods

Forty-six RSSI patients and 39 healthy controls (HC) were enrolled in our study. Magnetic resonance imaging (MRI) was done for all RSSI patients, and a total cerebral small vessel disease (CSVD) score was assessed for all patients. Swept-source optical coherence tomography (SS-OCT) was used to image and assess the choroidal thickness and SS-OCT angiography (SS-OCTA) was used to image and assess the macular microvasculature and choriocapillaris in all participants. Clinical information was collected for all participants.

Results

RSSI patients showed significantly sparser inner retinal microvasculature (P = 0.003) when compared with healthy controls. RSSI patients showed significantly thinner choroidal thickness (P < 0.001) when compared with HC. No significant difference (P = 0.247) was seen when the choriocapillaris was compared between the two groups. CSVD burden (P = 0.014) and NIHSS score (P = 0.010) showed significant correlation with the inner retinal microvasculature of RSSI patients. The inner retinal microvasculature (P = 0.016) and choroidal thickness (P = 0.018) showed a significant correlation with the MoCA scores in RSSI patients.

Conclusions

Our report suggests that retinal and choroidal imaging may serve as useful indicators to expand our understanding of RSSI and its clinical validity.

Post-injury ventricular enlargement associates with iron in choroid plexus but not with seizure susceptibility nor lesion atrophy-6-month MRI follow-up after experimental traumatic brain injury

Ventricular enlargement is one long-term consequence of a traumatic brain injury, and a risk factor for memory disorders and epilepsy. One underlying mechanisms of the chronic ventricular enlargement is disturbed cerebrospinal-fluid secretion or absorption by choroid plexus. We set out to characterize the different aspects of ventricular enlargement in lateral fluid percussion injury (FPI) rat model by magnetic resonance imaging (MRI) and discovered choroid plexus injury in rats that later developed hydrocephalus. We followed the brain pathology progression for 6 months and studied how the ventricular growth was associated with the choroid plexus injury, cortical lesion expansion, hemorrhagic load or blood perfusion deficits. We correlated MRI findings with the seizure susceptibility in pentylenetetrazol challenge and memory function in Morris water-maze. Choroid plexus injury was validated by ferric iron (Prussian blue) and cytoarchitecture (Nissl) stainings. We discovered choroid plexus injury that accumulates iron in 90% of FPI rats by MRI. The amount of the choroid plexus iron remained unaltered 1-, 3- and 6-month post-injury. During this time, the ventricles kept on growing bilaterally. Ventricular growth did not depend on the cortical lesion severity or the cortical hemorrhagic load suggesting a separate pathology. Instead, the results indicate choroidal injury as one driver of the post-traumatic hydrocephalus, since the higher the choroid plexus iron load the larger were the ventricles at 6 months. The ventricle size or the choroid plexus iron load did not associate with seizure susceptibility. Cortical hypoperfusion and memory deficits were worse in rats with greater ventricular growth.

Functional and structural alternations in the choroid plexus upon methamphetamine exposure

Choroid plexus (CP) is the principal source of cerebrospinal fluid. CP can produce and release a wide range of materials including growth factors, neurotrophic factors, etc. all of which play an important role in the maintenance and proper functioning of the brain. Methamphetamine (METH) is a CNS neurostimulant that causes brain dysfunction. Herein, we investigated the potential effects of METH exposure on CP structure and function. Stereological analysis revealed a significant alteration in CP volume, epithelial cells and capillary number upon METH treatment. Electron microscopy exhibited changes in ultrastructure. Moreover, the upregulation of neurotrophic factors such as BDNF and VEGF as well as autophagy and apoptosis gene following METH administration were observed. We also identified several signaling cascades related to autophagy. In conclusion, gene expression changes coupled with structural alterations of the CP in response to METH suggested METH-induced autophagy in CP.

Bidirectional Enhancement of Cell Proliferation Between Iron Oxide Nanoparticle-Labeled Mesenchymal Stem Cells and Choroid Plexus in a Cell-Based Therapy Model of Ischemic Stroke

PURPOSE

Stem cell therapy for ischemic stroke has shown success in experimental settings, but its translation into clinical practice is challenging. The choroid plexus (CP) plays a regulatory role in neural regeneration. Mesenchymal stem cells (MSCs) promote neurogenesis in the ventricular-subventricular zone. However, it is unclear whether MSCs interact with the CP in brain tissue repair.

METHODS

Rat (r)MSCs were labeled with iron oxide nanoparticles (IONs) and transduced with red fluorescent protein, and then injected into the brain of rats with ischemic stroke and monitored over time by magnetic resonance imaging. The functional recovery of rats was determined by the corner test score, Modified Neurological Severity score, and stroke volume. MSCs and CP were also co-cultured for 14 days, and the medium was analyzed with a cytokine array.

RESULTS

In vivo imaging and histologic analysis revealed that ION-labeled MSCs were mainly located at the injection site and migrated to the infarct area and to the CP. Functional recovery was greater in rats treated with MSCs as compared to those that received mock treatment. Bidirectional enhancement of proliferation in MSCs and CP was observed in the co-culture; moreover, MSCs migrated to the CP. Cytokine analysis revealed elevated levels of proliferation- and adhesion-related cytokines and chemokines in the culture medium. Wikipathway predictions indicated that insulin-like growth factor 1/Akt signaling (WP3675), chemokine signaling pathway (WP2292), and spinal cord injury (WP2432) are involved in the increased proliferation and migration of MSCs co-cultured with the CP.

CONCLUSION

Crosstalk with the CP enhances MSC proliferation and migration in a transwell assay. Moreover, MRI reveals MSC migration towards the CP in an ischemic stroke model. The secreted factors resulting from this interaction have therapeutic potential for promoting functional recovery in the brain after ischemic stroke.

Elevated Pro-Inflammatory Cell-Free MicroRNA Levels in Cerebrospinal Fluid of Premature Infants after Intraventricular Hemorrhage

Intraventricular hemorrhage (IVH) represents a high risk of neonatal mortality and later neurodevelopmental impairment in prematurity. IVH is accompanied with inflammation, hemolysis, and extracellular hemoglobin (Hb) oxidation. However, microRNA (miRNA) expression in cerebrospinal fluid (CSF) of preterm infants with IVH has been unknown. Therefore, in the present study, candidate pro-inflammatory cell-free miRNAs were analyzed in CSF samples from 47 preterm infants with grade III or IV IVH vs. clinical controls (n = 14). miRNAs were quantified by RT-qPCR, normalized to “spike-in” cel-miR-39. Oxidized Hb and total heme levels were determined by spectrophotometry as well as IL-8, VCAM-1, ICAM-1, and E-selectin concentrations by ELISA. To reveal the origin of the investigated miRNAs, controlled hemolysis experiments were performed in vitro; in addition, human choroid plexus epithelial cell (HCPEpiC) cultures were treated with metHb, ferrylHb, heme, or TNF-α to replicate IVH-triggered cellular conditions. Levels of miR-223, miR-155, miR-181b, and miR-126 as well as Hb metabolites along with IL-8 were elevated in CSF after the onset of IVH vs. controls. Significant correlations were observed among the miRNAs, oxidized Hb forms, and the soluble adhesion molecules. During the post-IVH follow-up, attenuated expression of miRNAs and protein biomarkers in CSF was observed upon elimination of Hb metabolites. These miRNAs remained unaffected by a series of artificially induced hemolysis, which excluded red blood cells as their origin, while stimulation of HCPEpiCs with oxidized Hb fractions and heme resulted in increased extracellular miRNA levels in the cell culture supernatant. Overall, the hemorrhage-induced CSF miRNAs reflected inflammatory conditions as potential biomarkers in preterm IVH.

Choroid Plexus Enlargement and Allostatic Load in Schizophrenia

Although schizophrenia is a brain disorder, increasing evidence suggests that there may be body-wide involvement in this illness. However, direct evidence of brain structures involved in the presumed peripheral-central interaction in schizophrenia is still unclear. Seventy-nine previously treatment-naïve first-episode schizophrenia patients who were within 2-week antipsychotics initial stabilization, and 41 age- and sex-matched healthy controls were enrolled in the study. Group differences in subcortical brain regional structures measured by MRI and the subclinical cardiovascular, metabolic, immune, and neuroendocrine biomarkers as indexed by allostatic load, and their associations were explored. Compared with controls, patients with schizophrenia had significantly higher allostatic load (P = .001). Lateral ventricle (P < .001), choroid plexus (P < .001), and thalamus volumes (P < .001) were significantly larger, whereas amygdala volume (P = .001) was significantly smaller in patients. The choroid plexus alone was significantly correlated with higher allostatic load after age, sex, education level, and the total intracranial volume were taken into account (t = 3.60, P < .001). Allostatic load was also significantly correlated with PANSS positive (r = 0.28, P = .016) and negative (r = -0.31, P = .008) symptoms, but in opposite directions. The peripheral multisystemic and central nervous system abnormalities in schizophrenia may interact through the choroid plexus during the early stage of the illness. The choroid plexus might provide a sensitive structural biomarker to study the treatment and prevention of brain-periphery interaction abnormalities in schizophrenia.

Autophagy-mediated occludin degradation contributes to blood-brain barrier disruption during ischemia in bEnd.3 brain endothelial cells and rat ischemic stroke models

Background

The blood–brain barrier (BBB) maintains homeostasis of the brain environment by tightly regulating the entry of substances from systemic circulation. A breach in the BBB results in increased permeability to potentially toxic substances and is an important contributor to amplification of ischemic brain damage. The precise molecular pathways that result in impairment of BBB integrity remain to be elucidated. Autophagy is a degradation pathway that clears damaged or unnecessary proteins from cells. However, excessive autophagy can lead to cellular dysfunction and death under pathological conditions.

Methods

In this study, we investigated whether autophagy is involved in BBB disruption in ischemia, using in vitro cells and in vivo rat models. We used brain endothelial bEnd.3 cells and oxygen glucose deprivation (OGD) to simulate ischemia in culture, along with a rat ischemic stroke model to evaluate the role of autophagy in BBB disruption during cerebral ischemia.

Results

OGD 18 h induced cellular dysfunction, and increased permeability with degradation of occludin and activation of autophagy pathways in brain endothelial cells. Immunostaining revealed that occludin degradation is co-localized with ischemic autophagosomes. OGD-induced occludin degradation and permeability changes were significantly decreased by inhibition of autophagy using 3-methyladenine (3-MA). Enhanced autophagic activity and loss of occludin were also observed in brain capillaries isolated from rats with middle cerebral artery occlusion (MCAO). Intravenous administration of 3-MA inhibited these molecular changes in brain capillaries, and recovered the increased permeability as determined using Evans blue.

Conclusions

Our findings provide evidence that autophagy plays an important role in ischemia-induced occludin degradation and loss of BBB integrity.

Subarachnoid Hemorrhage Induces Dynamic Immune Cell Reactions in the Choroid Plexus

Subarachnoid hemorrhage (SAH) is a specific form of hemorrhagic stroke that frequently causes intracranial hypertension. The choroid plexus (CP) of the brain ventricles is responsible for producing cerebrospinal fluid and forms the blood - cerebrospinal fluid barrier. The aim of the current study was to determine whether SAH induces an immune cell reaction in the CP and whether the resulting increase in intracranial pressure (ICP) itself can lead to cellular changes in the CP. SAH was induced by injecting non-heparinized autologous blood to the cisterna magna. Artificial cerebrospinal fluid (ACSF) instead of blood was used to assess influence of increased ICP alone. SAH and ACSF animals were left to survive for 1, 3, and 7 days. SAH induced significantly increased numbers of M1 (ED1+, CCR7+) and M2 (ED2+, CD206+) macrophages as well as MHC-II+ antigen presenting cells (APC) compared to naïve and ACSF animals. Increased numbers of ED1+ macrophages and APC were found in the CP only 3 and 7 days after ACSF injection, while ED2+ macrophage number did not increase. CD3+ T cells were not found in any of the animals. Following SAH, proliferation activity in the CP gradually increased over time while ACSF application induced higher cellular proliferation only 1 and 3 days after injection. Our results show that SAH induces an immune reaction in the CP resulting in an increase in the number of several macrophage types in the epiplexus position. Moreover, we also found that increased ICP due to ACSF application induced both an immune reaction and increased proliferation of epiplexus cells in the CP. These findings indicate that increased ICP, and not just blood, contributes to cellular changes in the CP following SAH.

Effects of minocycline on epiplexus macrophage activation, choroid plexus injury and hydrocephalus development in spontaneous hypertensive rats

Hydrocephalus has been reported to occur in spontaneous hypertensive rats (SHRs). The purposes of this study were (1) to use T2 magnetic resonance imaging to examine time of onset, (2) to elucidate potential underlying mechanisms and (3) to determine whether minocycline could prevent hydrocephalus development. Ventriculomegaly was evaluated by T2 imaging in SHRs and Wistar-Kyoto rats from weeks 4 to 7 after birth. Brain histology and transmission electron microscopy were used to assess the periventricular and choroid plexus damage. SHRs were also treated with either vehicle or minocycline. We found that hydrocephalus was observed in SHRs but not in Wistar-Kyoto rats. It occurred at seven weeks of age but was not present at four and five weeks. The hydrocephalus was associated with epiplexus cell (macrophage) activation, choroid plexus cell death and damage to the ventricle wall. Treatment with minocycline from week 5 attenuated hydrocephalus development and pathological changes in choroid plexus and ventricular wall at week 7. The current study found that spontaneous hydrocephalus arises at ∼7 weeks in male SHRs. The early development of hydrocephalus (persistent ventricular dilatation) may result from epiplexus cell activation, choroid plexus cell death and periventricular damage, which can be ameliorated by treatment with minocycline.

Culture Model for Non-human Primate Choroid Plexus

While there are murine and rat choroid plexus epithelial cell cultures, a translationally relevant model for choroid plexus activation and function is still lacking. The rhesus macaque is the gold standard for modeling viral infection and activation of CNS, including HIV-associated neurocognitive disorders. We have developed a rhesus macaque choroid plexus epithelial cell culture model which we believe to be suitable for studies of inflammation associated with viral infection of the CNS. Epithelial morphology and function were assessed using vimentin, phalloidin, the tight junction protein zonula-occludens-1 (ZO-1), and focal adhesion kinase (FAK). Choroid plexus epithelial cell type was confirmed using immunofluorescence with two proteins highly expressed in the choroid plexus: transthyretin and α-klotho. Finally, barrier properties of the model were monitored using pro- and anti-inflammatory mediators (TNF-α, the TLR2 agonist PamCys3K, and dexamethasone). When pro-inflammatory TNF-α was added to the xCelligence wells, there was a decrease in barrier function, which decreased in a step-wise fashion with each additional administration. This barrier function was repaired upon addition of the steroid dexamethasone. The TLR2 agonist PAM3CysK increased barrier functions in TNF-α treated wells. We have presented a model of the blood-CSF barrier that will allow study into pro- and anti-inflammatory conditions in the brain, while simultaneously measuring real time changes to epithelial cells.

Oxygen-Glucose Deprivation/Reoxygenation Induces Human Brain Microvascular Endothelial Cell Hyperpermeability Via VE-Cadherin Internalization: Roles of RhoA/ROCK2

The destruction of the blood-brain barrier (BBB) contributes to a spectrum of neurological diseases such as stroke, and the hyperpermeability of endothelial cells is one of the characters of stroke, which is possibly exacerbated after reperfusion. However, the underlying mechanisms involving hyperpermeability after reperfusion between the endothelial cells remain poorly understood. Therefore, in the present study, the human microvascular endothelial cells (HBMECs) were exposed to oxygen-glucose deprivation/reperfusion (OGD/R) to mimic ischemic stroke condition in vitro with the aim to investigate the potential mechanisms induced by OGD/R. The permeability of cultured HBMECs was measured using FITC-labeled dextran in a Transwell system and transendothelial electrical resistance (TEER), while the RhoA activity was detected by pull-down assay. In addition, the phosphorylation of MYPT1, which reflects the activation of ROCK and the internalization of VE-cadherin, was detected by Western blot. It showed that OGD/R treatment significantly increased the permeability of HBMEC monolayers and facilitated the internalization of VE-cadherin in HBMEC monolayers. Pull-down assay showed that RhoA activation was obviously enhanced after OGD/R treatment, while RhoA and ROCK inhibitor significantly reversed OGD/R-induced HBMEC monolayers hyperpermeability and the internalization of VE-cadherin. Meanwhile, the knockdown assay showed that RhoA small interfering RNA (siRNA) led to similar effects. The inactivation of the downstream effector protein ROCK was also examined. Intriguingly, ROCK2 rather than ROCK1 exerted its adverse effects on HBMEC monolayer integrity, since ROCK2 knockdown markedly reverses the injury of OGD/R in HBMEC monolayers. In conclusion, the present study provides evidence that OGD/R may induce HBMEC monolayer hyperpermeability via RhoA/ROCK2-mediated VE-cadherin internalization, which may provide an impetus for the development of therapeutics targeting BBB damage in ischemic stroke.

Choroid plexus volume after stroke

BACKGROUND

Cerebrospinal fluid circulation is crucial for the functioning of the brain. Aging and brain pathologies such as Alzheimer's disease have been associated with a change in the morphology of the ventricles and the choroid plexus. Despite the evidence from animal models that the cerebrospinal fluid system plays an important role in neuroinflammation and the restoration of the brain after ischemic brain injury, little is known about changes to the choroid plexus after stroke in humans.

AIMS

Our goal was to characterize structural choroid plexus changes poststroke.

METHODS

We used an automatic segmentation tool to estimate the volumes of choroid plexus and lateral ventricles in stroke and control participants at three time points (at baseline, 3 and 12 months) over the first year after stroke. We assessed group differences cross-sectionally at each time point and longitudinally. For stroke participants, we specifically differentiated between ipsi- and contra-lesional volumes. Statistical analyses were conducted for each region separately and included covariates such as age, sex, total intracranial volume, and years of education.

RESULTS

We observed significantly larger choroid plexus volumes in stroke participants compared to controls in both cross-sectional and longitudinal analyses. Choroid plexus volumes did not exhibit any change over the first year after stroke, with no difference between ipsi- and contra-lesional volumes. This was in contrast to the volume of lateral ventricles that we found to enlarge over time in all participants, with more accelerated expansion in stroke survivors ipsi-lesionally.

CONCLUSIONS

Our results suggest that chronic stages of stroke are characterized by larger choroid plexus volumes, but the enlargement likely takes place prior to or very early after the stroke incident.

Thrombin disrupts vascular endothelial-cadherin and leads to hydrocephalus via protease-activated receptors-1 pathway

AIMS

Previous studies indicated that intraventricular injection of thrombin would induce hydrocephalus. But how thrombin works in this process remains unclear. Since cadherin plays a critical role in hydrocephalus, we aimed to explore the mechanisms of how thrombin acted on choroid plexus vascular endothelium and how thrombin interacted with vascular endothelial-cadherin (VE-cadherin) during hydrocephalus.

METHODS

There were two parts in this study. Firstly, rats received an injection of saline or thrombin into the right lateral ventricle. Magnetic resonance imaging was applied to measure the lateral ventricle volumes. Albumin leakage and Evans blue content were assessed to test the blood-brain barrier function. Immunofluorescence and Western blot were applied to detect the location and the expression of VE-cadherin. Secondly, we observed the roles of protease-activated receptors-1 (PAR1) inhibitor (SCH79797), Src inhibitor (PP2), p21-activated kinase-1 (PAK1) inhibitor (IPA3) in the thrombin-induced hydrocephalus, and their effects on the regulation of VE-cadherin.

RESULTS

Our study demonstrated that intraventricular injection of thrombin caused significant downregulation of VE-cadherin in choroid plexus and dilation of ventricles. In addition, the inhibition of PAR1/p-Src/p-PAK1 pathway reversed the decrease of VE-cadherin and attenuated thrombin-induced hydrocephalus.

CONCLUSIONS

Our results suggested that the thrombin-induced hydrocephalus was associated with the inhibition of VE-cadherin via the PAR1/p-Src/p-PAK1 pathway.

AQP1 and AQP4 Contribution to Cerebrospinal Fluid Homeostasis

Aquaporin 1 (AQP1), expressed in epithelial cells of the choroid plexus, and aquaporin 4 (AQP4) present in ependymal cells and glia limitants have been proposed to play a significant role in cerebrospinal fluid (CSF) production and homeostasis. However, the specific contribution of each water channel to these functions remains unknown, being a subject of debate during the last years. Here, we analyzed in detail how AQP1 and AQP4 participate in different aspects of the CSF homeostasis such as the load and drainage of ventricles, and further explored if these proteins play a role in the ventricular compliance. To do that, we carried out records of intraventricular pressure and CSF outflow, and evaluated ventricular volume by magnetic resonance imaging in AQP1^−/−, AQP4^−/−, double AQP1^−/−-AQP4^−/− knock out and wild type mice controls. The analysis performed clearly showed that both AQPs have a significant participation in the CSF production, and additionally revealed that the double AQP1-AQP4 mutation alters the CSF drainage and the ventricular compliance. The data reported here indicate a significant extra-choroidal CSF formation mediated by AQP4, supporting the idea of an important and constant CSF production/absorption process, sustained by efflux/influx of water between brain capillaries and interstitial fluid. Moreover, our results suggest the participation of AQPs in structural functions also related with CSF homeostasis such as the distensibility capacity of the ventricular system.

Brain endothelial cell junctions after cerebral hemorrhage: Changes, mechanisms and therapeutic targets

Vascular disruption is the underlying cause of cerebral hemorrhage, including intracerebral, subarachnoid and intraventricular hemorrhage. The disease etiology also involves cerebral hemorrhage-induced blood-brain barrier (BBB) disruption, which contributes an important component to brain injury after the initial cerebral hemorrhage. BBB loss drives vasogenic edema, allows leukocyte extravasation and may lead to the entry of potentially neurotoxic and vasoactive compounds into brain. This review summarizes current information on changes in brain endothelial junction proteins in response to cerebral hemorrhage (and clot-related factors), the mechanisms underlying junction modification and potential therapeutic targets to limit BBB disruption and, potentially, hemorrhage occurrence. It also addresses advances in the tools that are now available for assessing changes in junctions after cerebral hemorrhage and the potential importance of such junction changes. Recent studies suggest post-translational modification, conformational change and intracellular trafficking of junctional proteins may alter barrier properties. Understanding how cerebral hemorrhage alters BBB properties beyond changes in tight junction protein loss may provide important therapeutic insights to prevent BBB dysfunction and restore normal function.

Opportunities in posthemorrhagic hydrocephalus research: outcomes of the Hydrocephalus Association Posthemorrhagic Hydrocephalus Workshop

The Hydrocephalus Association Posthemorrhagic Hydrocephalus Workshop was held on July 25 and 26, 2016 at the National Institutes of Health. The workshop brought together a diverse group of researchers including pediatric neurosurgeons, neurologists, and neuropsychologists with scientists in the fields of brain injury and development, cerebrospinal and interstitial fluid dynamics, and the blood-brain and blood-CSF barriers. The goals of the workshop were to identify areas of opportunity in posthemorrhagic hydrocephalus research and encourage scientific collaboration across a diverse set of fields. This report details the major themes discussed during the workshop and research opportunities identified for posthemorrhagic hydrocephalus. The primary areas include (1) preventing intraventricular hemorrhage, (2) stopping primary and secondary brain damage, (3) preventing hydrocephalus, (4) repairing brain damage, and (5) improving neurodevelopment outcomes in posthemorrhagic hydrocephalus.

Progress in brain barriers and brain fluid research in 2017

The past year, 2017, has seen many important papers published in the fields covered by Fluids and Barriers of the CNS. This article from the Editors highlights some.

Cell-free DNA as a biomarker in stroke: Current status, problems and perspectives

There is currently no proposed stroke biomarker with consistent application in clinical practice. A number of studies have examined cell-free DNA (cfDNA), which circulates in biological fluids during stroke, as a potential biomarker of this disease. The data available suggest that dynamically-determined levels of blood cfDNA may provide new prognostic information for assessment of stroke severity and outcome. However, such an approach has its own difficulties and limitations. This review covers the potential role of cfDNA as a biomarker in stroke, and includes evidence from both animal models and clinical studies, protocols used to analyze cfDNA, and hypotheses on the origin of cfDNA.

Release of interleukin-10 and neurotrophic factors in the choroid plexus: possible inductors of neurogenesis following copolymer-1 immunization after cerebral ischemia

Copolymer-1 (Cop-1) is a peptide with immunomodulatory properties, approved by the Food and Drug Administration of United States in the treatment of multiple sclerosis. Cop-1 has been shown to exert neuroprotective effects and induce neurogenesis in cerebral ischemia models. Nevertheless, the mechanism involved in the neurogenic action of this compound remains unknown. The choroid plexus (CP) is a network of cells that constitute the interphase between the immune and central nervous systems, with the ability to mediate neurogenesis through the release of cytokines and growth factors. Therefore, the CP could play a role in Cop-1-induced neurogenesis. In order to determine the participation of the CP in the induction of neurogenesis after Cop-1 immunization, we evaluated the gene expression of various growth factors (brain-derived neurotrophic factor, insulin-like growth factor 1, neurotrophin-3) and cytokines (tumor necrosis factor alpha, interferon-gamma, interleukin-4 (IL-4), IL-10 and IL-17), in the CP at 14 days after ischemia. Furthermore, we analyzed the correlation between the expression of these genes and neurogenesis. Our results showed that Cop-1 was capable of stimulating an upregulation in the expression of the genes encoding for brain-derived neurotrophic factor, insulin-like growth factor 1, neurotrophin-3 and IL-10 in the CP, which correlated with an increase in neurogenesis in the subventricular and subgranular zone. As well, we observed a downregulation of IL-17 gene expression. This study demonstrates the effect of Cop-1 on the expression of growth factors and IL-10 in the CP, in the same way, presents a possible mechanism involved in the neurogenic effect of Cop-1.

Challenges for intraventricular hemorrhage research and emerging therapeutic targets

INTRODUCTION

Intraventricular hemorrhage (IVH) affects both premature infants and adults. In both demographics, it has high mortality and morbidity. There is no FDA approved therapy that improves neurological outcome in either population highlighting the need for additional focus on therapeutic targets and treatments emerging from preclinical studies. Areas covered: IVH induces both initial injury linked to the physical effects of the blood (mass effect) and secondary injury linked to the brain response to the hemorrhage. Preclinical studies have identified multiple secondary injury mechanisms following IVH, and particularly the role of blood components (e.g. hemoglobin, iron, thrombin). This review, with an emphasis on pre-clinical IVH research, highlights therapeutic targets and treatments that may be of use in prevention, acute care, or repair of damage. Expert opinion: An IVH is a potentially devastating event. Progress has been made in elucidating injury mechanisms, but this has still to translate to the clinic. Some pathways involved in injury also have beneficial effects (coagulation cascade/inflammation). A greater understanding of the downstream pathways involved in those pathways may allow therapeutic development. Iron chelation (deferoxamine) is in clinical trial for intracerebral hemorrhage and preclinical data suggest it may be a potential treatment for IVH.