Fluids and Barriers of the CNS

BackgroundP-glycoprotein (P-gp/ABCB1) is a key efflux transporter that maintains barrier integrity by clearing xenobiotics and toxic metabolites. At the feto-maternal interface, trophoblast-derived extracellular vesicles (CTC-EVs) naturally and transiently transfer functional P-gp to maternal decidual cells, restoring lost and or reduced P-gp function (exofection) to sustain pregnancy homeostasis. A similar loss of P-gp at the blood brain barrier (BBB) contributes to impaired amyloid-{beta} (A{beta}) clearance and neuroinflammation in Alzheimers disease. We investigated whether CTC-EV-mediated exofection could restore P-gp function in human brain endothelial cells (hBECs) and enhance A{beta} clearance under inflammatory and neurodegenerative conditions. MethodsCTC-EVs were isolated and characterized by nanoparticle tracking analysis and western blotting for P-gp and EV markers. Transcriptomic profiling of CTC-EVs identified enrichment of transporter-related genes, including solute carriers and ABC transporters, along with inflammatory mediators. Network analysis revealed coordinated modules linking EV cargo to transporter regulation, endocytosis/trafficking pathways, and inflammatory remodeling processes converging on BBB efflux activity. hBECs were exposed to LPS (500 ng/mL, 48 h) with or without CTC-EVs. P-gp expression was assessed by immunofluorescence (mean fluorescence intensity, MFI) and western blotting, while functional efflux was measured using Calcein-AM assays. A{beta} oligomer transport was evaluated using a transwell hBEC model. In vivo, 3xTg-AD mice received intravenous CTC-EVs (1x10L/day for 5 days), followed by assessment of P-gp expression, A{beta} burden, and neuroinflammatory markers. Pharmacokinetic studies in P-gp knockout mice were conducted to confirm functional transporter recovery. ResultsLPS exposure significantly reduced P-gp expression in hBECs (41.3% decrease in MFI, p=0.0084), which was restored by CTC-EVs (46.7% increase vs. LPS, p=0.0121). Exofection increased P-gp by a 2.1-fold following EV treatment as determined by western blot. Functional assays demonstrated enhanced efflux, with a 38.5% reduction in intracellular Calcein fluorescence (p<0.001). Network-informed mechanisms supported coordinated regulation of transporter and trafficking pathways. CTC-EVs improved A{beta} transport across inflamed hBEC monolayers. In vivo, EV-treated 3xTg-AD mice exhibited increased P-gp expression in the frontal cortex (38.6%) and hippocampus (42.1%), reduced A{beta} plaque burden (27.9%), and decreased inflammatory markers (IL-1{beta} and TNF-, p<0.05). In P-gp knockout mice, EVs reduced brain drug accumulation by 22.4% (p=0.032), confirming restoration of transporter function. ConclusionCTC derived EVs are natural carriers of functional transporter proteins and restore efflux capacity in compromised endothelial barriers. Integration of transcriptomic and network analyses highlights coordinated regulation of transporter, trafficking, and inflammatory pathways underlying exofection. This reproductive biology inspired strategy offers a promising therapeutic approach for enhancing A{beta} clearance and mitigating neuroinflammation in Alzheimers disease.

Extracellular vesicles (EVs) mediate cell-to-cell communication and are considered potential drug delivery vehicles. Nevertheless, whether EV-embedded cargo can be efficiently delivered into the cytosol of recipient cells remains debated. Here, we investigated the fate of syntenin, a well-established internal cargo of small EVs (sEVs). Using quantitative assays, we show that [~]85% of internalized sEV-embedded syntenin can be delivered to the cytosol of recipient cells within short periods of time. Yet, even at low dose, we find that the internalization of sEVs carrying syntenin is rather inefficient ([~]0.03% of the administered dose). Moreover, we observe that the capture of sEVs by recipient cells is non-saturable over time and largely more efficient than their internalization. Finally, we identify the N-terminal domain of syntenin and the phosphorylation state of a Src-targeted tyrosine residue in this domain, as key determinants for its incorporation into sEVs that support cytosolic delivery. These findings challenge, current views in the field by indicating that sEV internalization may be a marginal process (on the contrary to capture) and that cytosolic delivery can be highly efficient. Moreover, our study identifies molecular determinants governing cytosolic delivery of sEV-embedded syntenin.

BackgroundMachado-Joseph disease (MJD), or Spinocerebellar Ataxia type 3 (SCA3), is a neurodegenerative disorder caused by an expansion of the CAG repeat in the MJD1/ATXN3 gene, which encodes for a polyglutamine-expansion in Ataxin-3. Similar to what occurs in other neurodegenerative disorders, the cerebrovascular system, particularly the blood-brain barrier (BBB), is impaired in MJD. BBB is an important cellular barrier that controls homeostasis of the central nervous system, and its disruption compromises neuronal function. To date, there is no disease-modifying therapy for MJD. Our group previously demonstrated that MSC administration can ameliorate the phenotype of MJD transgenic mice. However, the effect of MSC on the neurovascular unit and BBB integrity remains unexplored in the context of MJD. In the present work, we aimed to evaluate the therapeutic potential of MSC in mitigating vascular abnormalities and BBB disruption in MJD. MethodsEight-month-old MJD transgenic mice were treated with two consecutive bone marrow-MSC intravenous injections (1 week apart). Behavioral tests to assess motor coordination were conducted before and after treatment. Vascular structure, function, and BBB disruption were evaluated by immunohistochemistry and western blot. ResultsMSC administration partially restored vascular impairment in MJD transgenic mice. Treated mice exhibited improved gait and motor performance footprint and beam walking tests) and concurrently attenuated vascular dysfunction. Specifically, MSC-treated mice exhibited a decrease in collagen IV surface area and stabilized cerebellar blood supply. Additionally, MSC treatment diminished BBB permeability to the Evans blue (EB) dye in MJD mice and restored the levels of important adherent and tight junction-associated proteins in the cellular membrane, including vascular endothelial cadherin (VE-cadherin), claudin-5, and occludin, in a sex-specific manner. Conclusionsour results highlight significant cerebrovascular dysregulations in MJD, which are sex-dependent and progress with the disease stage. Moreover, our findings suggest that MSC administration partially reverted vascular impairments, providing valuable insights into the mechanisms underlying the therapeutic potential of MSC in MJD. Graphical AbstractMSC treatment partially reverts neurovascular dysregulation in MJD. MJD mice exhibit increased vessel coverage, increased BBB permeability, and altered TJ and AJ expression and subcellular localization. MSC administration modulates vessel coverage, reduces BBB leakage, and partially normalizes TJ/AJ subcellular localization. List of abbreviations: AJ - Adherent junction; BBB - Blood-Brain barrier; MJD- Machado-Joseph disease; MSC - mesenchymal stromal cell; TJ - thigh junction. Created with BioRender.com O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=103 SRC="FIGDIR/small/703043v1_ufig1.gif" ALT="Figure 1"> View larger version (55K): org.highwire.dtl.DTLVardef@8fa0a2org.highwire.dtl.DTLVardef@17b13f9org.highwire.dtl.DTLVardef@15c5ce3org.highwire.dtl.DTLVardef@d67539_HPS_FORMAT_FIGEXP M_FIG C_FIG

Brain microvascular endothelial cells (BMECs) forming the blood-brain barrier (BBB) maintain brain homeostasis through specialized properties such as tight junctions, efflux transporters, and low levels of transcytosis. However, mechanisms governing induction of BBB properties during development remain poorly understood. We mined single-cell RNA sequencing datasets to identify transcription factors (TFs) critical for BBB development. Forty-four TFs were overexpressed in human pluripotent stem cell-derived endothelial cells cultured in the presence of the Wnt pathway agonist CHIR99021 to identify TFs capable of directing acquisition of BBB properties via forward programming. Individual TFs, including KLF2, KLF4, FOXF1, FOXF2, ZIC2, ZIC3, NR4A1, NR4A2, FOXC1, and FOXQ1, induced distinct BBB-like gene expression patterns. Combinations of these TFs induced many canonical BBB genes, yielding ECs with reduced endocytosis, increased efflux activity, and improved barrier function. The resultant forward programmed CNS-like ECs (fpCECs) offer promising tools for modeling human BBB development and neurovascular disease and for drug screening.

BackgroundChoroid plexus (ChP) produces cerebrospinal fluid (CSF), and regulates brain development and adult subventricular zone (SVZ) neurogenesis, but its role in hippocampal subgranular zone (SGZ) neurogenesis in adulthood and early postnatal stages is not well understood. Current tools to directly manipulate neonatal ChP/CSF volume are very limited, representing an urgent need in the field. MethodsWe first discovered the specific "leaky" expression of DTR gene in the ChP of adult ROSA26-iDTR mice which can be used to specifically ablate ChP in adult brain that generated robust and long-lasting ablation of ChP and reduction of CSF volume. In this study, we the effectiveness of ROSA26-iDTR allele in ablating neonatal ChP. We also developed a novel AAV2/5-CMV-DTR vector with validated ChP tropism in both neonatal and adult mice, which induces substantial CSF loss in both neonates and adult mice. With both the ROSA26-iDTR genetic and AAV2/5-DTR viral-mediated ChP ablation in young adults and at defined postnatal ages, we quantified ventricular CSF volume by MRI and characterized postnatal neurogenesis. Doublecortin-positive (DCX+) neuroblasts, Ki67+ proliferating cells, and TUNEL+ apoptotic cells were quantified in SVZ and SGZ using confocal microscopy and machine learning-assisted cell counting. ResultsWe show that ROSA26-iDTR-mediated ChP ablation is inefficient before postnatal day 10, suggesting that this line may be of limited utility for CSF reduction in the early neonatal period before P10. P3-5 Dtx treatment of a previously used dosage of 20ng/g dosage did not lead to a reduction in CSF volume. Higher dosage of 40ng/gX3 Dtx dosage at p3-5 generated only moderate partial reduction of CSF in third ventricle and total CSF volume, with indication of toxicity associated with high Dtx dosage in general. In contrast, p10-12 injection of 20ng/gX3 Dtx led to robust CSF reduction. To target early neonatal days, AAV2/5 CMV-DTR virus shows high tropism for ChP epithelial cells and leads to near-complete ablation of CSF in neonatal brains. ChP/CSF loss in neonates or young adult mice leads to a substantial reduction of DCX+ cells at the SVZ but a moderate but significant reduction of SGZ DCX+ neuroblasts, without changes in Ki67+ or TUNEL+ cells. ConclusionsThis study reports a novel role of the ChP/CSF in maintaining the neuroblast pool in the neurogenic niches in both early postnatal and adult stages. Moreover, we expand the available tools to target the ChP and CSF production in the neonate, with potential uses in treating conditions such as neonatal hydrocephalus.

The role of the choroid plexus (CP) as the primary source of cerebrospinal fluid (CSF) remains controversial. Here, we used dynamic indirect D2O magnetic resonance imaging (MRI) at 9.4T to investigate whole-brain CSF dynamics in rats. Spin-echo echo-planar imaging (SE-EPI) was performed during intravenous D2O infusion with a temporal resolution of 10.69 s and an in-plane resolution of 150 x 150 {micro}m. An echo time of 150.0 ms was employed to effectively suppress signals from brain parenchyma, blood, and interstitial fluid, resulting in preferential visualization of CSF. The ambient and supracerebellar cisterns (AC+SC) exhibited the greatest signal attenuation, reaching 47.32 {+/-} 15.70% of baseline, whereas the lateral ventricles (LV1, LV2) showed smaller reductions (68.73 {+/-} 18.72%-72.64 {+/-} 15.07% of baseline). CSF production rates were quantified using a one-compartment perfusion model. Estimated secretion rates were 0.11 and 0.13 {micro}L/min in the lateral ventricles and 1.30 {micro}L/min in the AC+SC region, indicating a 5.42-fold higher CSF production outside the ventricles. These findings provide direct in vivo evidence that the lateral ventricles are not the primary site of CSF production. The proposed D2O-based dynamic SE-EPI approach is safe, non-invasive, cost-effective, and suitable for widespread application.

During development, the size of the neuroepithelial cell pool plays a key role in establishing brain size, determining the numbers of derived progenitors and subsequent neuronal cell types. While early histogenesis is well modelled in brain organoids, the organ-scale geometry of the telencephalon is not accurately recapitulated. Herein, we present a new approach for generating ventral and dorsal forebrain organoids which develop a large ventricular neuroepithelium, characteristic of the closed telencephalic vesicle. Using a growth medium that supports aerobic glycolysis and is typically used for endothelial cells, we modulate neuroepithelial expansion to induce a more anatomically accurate neuroepithelial layer which, upon maturation, thickens physiologically to generate the typical neurogenic layered architecture. In addition, we present a new method for embedding organoids in miniature collagen spheres which mimics native extracellular matrix, stabilizes the ventricular geometry for dynamic culture conditions, and provides a means for incorporating vascular cells for neurovascular development. Finally, we demonstrate that human organoids grown under these conditions exhibit dramatically enlarged ventricles and delayed maturation compared to mouse. Together, this approach provides a model of the forebrain neuroepithelium with morphogenetic macroscale geometry and tissue architecture, suitable for investigating neurodevelopment and disease.

The extracellular matrix (ECM) plays a pivotal role in lymphatic vasculature physiology, yet the specific contribution of individual ECM components to lymphatic endothelial permeability remains poorly understood, limiting the development of physiologically relevant in vitro models for lymphatic disease research and therapeutic development. Here, we used an in vitro transwell platform to systematically investigate how four clinically relevant ECM proteins, collagen I, fibronectin, fibrin, and laminin, regulate human lymphatic endothelial cell (LEC) barrier function and junctional integrity. Fibrin and collagen I substrates enhanced barrier integrity, demonstrating 80% and 67% increases in transendothelial electrical resistance (TEER), respectively, compared to uncoated controls. FITC-dextran transport assays confirmed these findings, with fibrin and collagen I reducing permeability by 20% and 10%, respectively. Immunofluorescence analysis revealed elevated ZO-1 expression on fibrin, fibronectin, and laminin matrices, while VE-cadherin levels remained unchanged across conditions. Quantitative junctional analysis demonstrated that fibrin increased ZO-1 junction continuity by [~]35%, while collagen I and fibronectin enhanced continuity by [~]22%, with all ECM coatings reducing discontinuous junctions by 60-80%. Mechanistically, RhoA expression was reduced in LECs cultured on fibrin, suggesting decreased stress fiber formation contributes to enhanced barrier function, though overall actin cytoskeletal anisotropy remained unchanged. These findings demonstrate that ECM composition modulates LEC junctional organization and barrier integrity, with fibrin and collagen I exerting the most pronounced barrier-enhancing effects. This engineered platform provides a foundation for developing next-generation in vitro models of lymphatic vasculature that more accurately recapitulate physiological conditions, with applications in lymphedema research, cancer metastasis studies, and immune cell trafficking investigations.

Extracellular vesicles (EVs) are small lipid structures secreted by cells that originate from the cell surface (typically enriched in the tetraspanin (tspan) CD9) or from multivesicular bodies (typically enriched in the tspan CD63). Current methods for studying EVs involve concentrating and purifying EVs, without providing information about the distance or amount of EVs that may transfer from one cell to another. Here, we developed a coculture assay of human mammary MCF-7 cells to study the transfer of mCherry-CD81 or mCherry-CD9 from "donor" cells to a lawn of "acceptor" cells stained with cell tracker blue or green (CTB/CTG), non-transferrable fluorescent dyes. Using confocal fluorescence microscopy, we observed the presence of spots containing mCherry-CD81 or mCherry-CD9 outside donor cells, concentrated at short distance from donor cells and that overlapped with CTB signal, suggestive of their internalization in acceptor cells. Endogenous CD63, CD81 and CD9 also transferred more efficiently at short distances, even in the presence of a flow, as shown by immunostaining cocultures of wild type and KO CD-63, or -9, or -81 cells with antibodies directed against these tspans. Computation of the (x,y,z) coordinates of tspans-containing spots revealed a double polarized transfer: in (x,y), it distributed along a gradient that started from donor cells and decreased with the distance, and in (z), it was stronger in basal compared to upper planes, a (z) polarization that was affected by syntenin-1 depletion in donor cells. Simultaneous monitoring of CD9/CD81 transfer from into double CD81/CD9 KO cells showed that cells transferred more CD81 spots than of CD9. At the basal level, CD63 and CD81 spots were plasma membrane derived as they almost always contained CD9+, and resembled membranous remnants of migration. However, live cell imaging showed migration independent secretion of EVs in the extracellular space, in upper planes. Altogether, not only is our coculture assay suitable for the direct qualitative and quantitative study of EV-transfer, but it highlighted shared three-dimensional features of EV markers transfer between cells.

Extracellular vesicles (EVs) are key mediators of intercellular communication, yet their molecular profiles across tissues and species remain poorly characterized, particularly due to currently available methods requiring a large amount of biological material (tissue or biofluids). Here, we established a workflow allowing the deep phenotyping of EV cargos starting from single samples of human and mouse origin. We took advantage of standardised EV isolation procedures and multi-omic techniques for the isolation and analysis of EVs from brain and plasma of human and mouse, integrating flow cytometric profiling, proteomics, miRNA sequencing, and fatty acid profiling. Here we report specific brain-derived EVs proteome, enriched in neuronal and glial proteins, polyunsaturated fatty acids profiles, and distinct miRNAs. At the periphery, we also report plasma-derived EVs signatures reflecting immune, metabolic, and systemic transport functions. Despite these expected material-specific differences, EVs from the same source displayed greater similarity across species than EVs from different material, supporting the translational relevance of mouse models. Importantly, using state-of-the-art miRNA profiling approach, we identified novel EV-specific miRNAs in human and mouse brain EVs, potentially allowing the exploration of new roles in neuronal signalling. Overall, we report here a method enabling deep multi-omic characterization from minimal starting material, offering a practical approach for studies with limited biological samples. These findings also demonstrate that the origin strongly shapes EV composition, highlighting conserved and species-specific molecular features, and provide a scalable framework for multi-omic investigations of EV biology. Summary StatementWe present a standardised workflow allowing multi-omic profiling of brain and plasma-derived EVs from minimal human and mouse material. Our findings reveal both tissue-specific and species specific EV molecular signatures.

BackgroundExtracellular vesicles (EVs) are nano and macro-sized, lipid-bound particles, involved in cellular communication. Interestingly, cancer-derived EVs show a heterologous and cross-species tumour tropism which makes them a potential tool for efficient delivery of therapeutic small interfering RNA (siRNA) to the tumour cells. MethodsEVs derived from glioblastoma cells (U373P and U373vIII) were loaded with EGFRvIII siRNA to develop a targeted therapeutic strategy against glioblastoma. EV biodistribution was evaluated using fluorescent indocyanine green (ICG) staining followed by ex vivo imaging. Different loading strategies, including passive loading, sonication, saponin-mediated membrane permeabilization, electroporation, and transfection were assessed for their efficiency in loading siRNA into EVs. The efficiency of each method was evaluated by nano flowcytometry, in vitro uptake assay followed by immunoblot (western blot) analysis. Eventually, the most effective formulation was tested for the systemic siRNA administration and selective tumour delivery in vivo, followed by evaluation of tumour size and EGFRvIII expression. ResultsHere, we showed that siRNA transfection into EVs was the most effective loading strategy, as confirmed by nano-flow cytometry, uptake assays, and western blot analysis, achieving over 90% knockdown efficiency in vitro for EVs carrying EGFRvIII siRNA. In vivo, EGFRvIII siRNA-loaded EVs homed to the tumour site and downregulated EGFRvIII expression compared with the PBS-siRNA control group; however, no significant tumour shrinkage was observed. ConclusionEGFRvIII-targeting, glioblastoma cell-derived EVs can be used as siRNA delivery carriers for targeted gene therapy in glioblastoma. However, further optimization of siRNA delivery and treatment duration is required.

Pathogenic bacterial extracellular vesicles (BEVs) can disrupt the blood-brain barrier (BBB), leading to neuroinflammation. Prior in vitro studies of this process were performed in simple models that may have lacked important physiological factors. We sought to determine if treatment with Escherichia coli-derived BEVs could directly compromise the integrity of a BBB lab-on-chip model or if an immune component was required. Our device featured isogenic human induced pluripotent stem cell-derived brain microvascular endothelial-like cells (BMECs) and pericytes separated by an ultrathin, porous silicon nitride membrane. BEVs and free lipopolysaccharide (LPS) were capable of causing upregulation of intercellular adhesion molecule-1 on the BMEC surfaces, which is important for immune cell recruitment. However, neither BEVs nor LPS at physiological doses caused pronounced loss of BMEC tight junction proteins, nor did they increase barrier permeability to small dye molecules. In contrast, stimulating THP-1 macrophages with BEVs led to increased production of pro-inflammatory cytokines, and conditioned media from the stimulated macrophages disrupted BMEC tight junctions and increased barrier permeability. Our work demonstrates the importance of incorporating an immune component in studies of BEV-mediated disruption of BBB models.

IntroductionCurrent workflows for studying hydrocephalus in rodent models rely on manual segmentation or qualitative assessment of ventricular size on small animal magnetic resonance imaging, which are both inefficient and prone to variability. Atlas-based methods enable more streamlined segmentation, but their analysis is limited to morphologically normal samples. ObjectiveThis study aimed to develop and internally validate a deep learning model that performs automated segmentation of lateral ventricles in rodent brain MRIs, allowing for 3D ventricle reconstruction, morphological analysis, and ventriculomegaly detection. MethodsFour U-Net++ neural networks, each with different encoder backbones, were trained using 307 rodent brain MRIs (262 rats, 45 mice), each with manually segmented lateral ventricles serving as the ground truth. Model performance was evaluated using the Dice coefficient, intersection over union (IoU), and Hausdorff index. The most optimal model was evaluated further for its ability to quantify ventricle volume, convexity, surface area, and symmetry. ResultsThe U-Net++ model with an EfficientNet-B1 encoder achieved high accuracy (Dice: 0.823 {+/-} 0.136; IoU: 0.721 {+/-} 0.85). Further assessment of its morphological predictions found strong correlations with manual measurements of ventricular morphology, with Pearson and interclass correlation coefficients exceeding 0.96 across all metrics. The full validated pipeline was packaged into a publicly available application, hosted at https://ava-tar.org. ConclusionThis study introduces a deep learning tool for automated segmentation and morphological analysis of lateral ventricles in rodent MRIs. The tools efficiency and accuracy in quantifying ventricle morphology offers significant utility in preclinical hydrocephalus research with potential future application in the clinical setting.

Alzheimers disease (AD) is categorized as a neurodegenerative disease, but there is a growing recognition of the vascular components in AD pathophysiology. Reduction in cerebral perfusion is routinely observed in AD patients and preclinical models prior to overt clinical symptoms. However, there is a limited mechanistic understanding of the early neurovascular deficits in AD, and how these may ultimately contribute to pathology. Here, we investigated the mechanisms of early neurovascular dysfunction in AD by using 3-month-old 5xFAD mice, a familial mouse model of AD. Functional hyperemia--the increase in cerebral blood flow (CBF) in response to neuronal activity--is driven by inward rectifier K+ (Kir2.1)-mediated hyperpolarizing (electrical) signals and Ca2+-dependent nitric oxide production within the capillary endothelial cells (cECs). Electrical and Ca2+ signals are tightly coupled through cECs membrane potential, referred to as Electro-Calcium (E-Ca) coupling. We hypothesize that E-Ca uncoupling contributes to impaired functional hyperemia in 5xFAD mice and that these neurovascular deficits precede the neurodegeneration and cognitive decline. At three months of age, 5xFAD mice did not exhibit any impairment in spatial learning and memory, or neuronal density. However, whisker stimulation-induced functional hyperemia was significantly reduced in 5xFAD mice compared to controls. Functional hyperemia exhibited a bimodal response in controls--consisting of fast and slow phases--with the slow phase being significantly reduced in 5xFAD mice. To identify mechanisms underlying these deficits, we measured cortical neuronal and endothelial Ca2+ activity using in-vivo imaging. Neuronal Ca2+ activity was comparable between controls and 5xFAD mice, while cECs Ca2+ activity was significantly reduced in 5xFAD mice. Moreover, Kir2.1 channel blocker, barium (100 M) significantly suppressed cECs Ca2+ activity in controls, but not in 5xFAD mice, consistent with crippled E-Ca coupling. Despite these vascular functional impairments, capillary density was preserved in 5xFAD mice. TRPV4 channels are one of the major Ca2+ entry pathways in cECs and potentiate E-Ca coupling. cECs TRPV4 current density was significantly reduced in 5xFAD mice while Kir2.1 current density was unchanged, indicating that impaired TRPV4 function underlies the E-Ca uncoupling. In summary, early E-Ca uncoupling leads to impaired functional hyperemia in 5xFAD mice and may contribute to later neuronal and cognitive decline.

Dysfunctional lymphangiogenesis is a component of several diseases with hypoxic microenvironments, including secondary lymphedema and solid malignancies. These vessels are ineffective at draining interstitial fluid, resulting in complications such as increased inflammation, slowed wound healing, and, for cancer patients, increased risk of metastasis. Current treatments to normalize vasculature have negative effects on healthy vessels and do not specifically target lymphatic endothelial cells (LECs). As hypoxia is known to change endothelial cell metabolism, exploiting LEC-specific metabolic pathways may provide a focused approach to restoring lymphatic function in patients. However, outside of glycolysis, changes to LEC metabolism in hypoxic conditions are understudied. To address this gap in knowledge, we examined the impact of glutamine availability on factors critical to lymphangiogenesis, including glycolysis, cell proliferation, and migration. We found that increasing glutamine availability results in increased lactate production as well as a hypoxia-specific increase in glycolytic genes HK2, GLUT1, and GLUT3. The presence of glutamine also encouraged LEC proliferation, while blocking glutamine transport reduced lactate production, HK2 expression, and slowed collective LEC migration. In a vessel formation assay, we found that glutamine increased vessel formation in normoxic conditions, but lowered vessel connectivity in hypoxic conditions, reflecting the dysfunction seen in hypoxic diseases. However, attenuating glycolysis by blocking glutamine transport caused LECs to form longer, interconnected vascular networks. This study reveals that glutamine availability can modulate LEC glycolysis, and therefore lymphangiogenesis, in a hypoxia-dependent manner. Collectively, our study identifies glutamine availability as a potential target for lymphatic vessel normalization in chronic and hypoxic diseases.

Newborns are especially susceptible to bacterial meningitis, primarily caused by Group B Streptococcus (GBS), due to incomplete maturation of immune and barrier systems. While meningitis is well known to break down the blood-brain barrier (BBB), how the meningeal arachnoid barrier, a critical component of the blood-cerebrospinal fluid barrier (B-CSFB), responds to infection is poorly understood. Using a neonatal mouse model of bacterial meningitis, we demonstrate that GBS infection significantly increases arachnoid barrier permeability, coinciding with alterations in Claudin-11 tight junction distribution and elevated meningeal production of proinflammatory cytokines (IL-6, TNF-, CXCL1). CD206+/Lyve1+ border-associated macrophages (BAMs) undergo significant morphological and molecular activation post-infection, but their depletion prior to GBS infection did not attenuate arachnoid barrier leakage or inflammatory cytokine levels during infection. We show that meningeal fibroblasts are a main source of proinflammatory cytokines in response to GBS infection and that exposure to the inflammatory cytokine TNF- alone is sufficient to induce neonatal arachnoid barrier breakdown. These results support neonatal arachnoid barrier is vulnerable to cytokine-induced breakdown in bacterial infection and highlight the role of non-immune meningeal cells like fibroblasts during bacterial infection.

The glymphatic system is a macroscopic waste clearance pathway in the central nervous system (CNS), crucial to maintaining neural homeostasis through the exchange of cerebrospinal fluid (CSF) and interstitial fluid (ISF). Impairments in this system have been associated with neurodegenerative diseases such as Alzheimers and Parkinsons, emphasizing the need to understand and potentially improve glymphatic clearance. We investigate tracer diffusion and transport in the glymphatic system by combining optical imaging in rats and mathematical modeling using a partial differential equation of advection-diffusion type. The experimental conditions differ in the levels of isoflurane-induced anesthesia (1.5, 2 and 3%) and the molecular weight of the tracer compounds (1 and 160 kDa). The optimal parameters show a close clustering of the diffusion coefficients and a wider spread of the flow velocities of the cerebrospinal fluid. Our work contributes to a better understanding of flow processes in the brain parenchyma during sleep.

Intracerebral haemorrhage (ICH) is a severe form of stroke with high morbidity and mortality rates. For survivors, acute haematoma expansion strongly determines neurological outcome. Although blood pressure reduction is widely investigated as a strategy to limit haematoma growth, the haemodynamic mechanisms regulating haemorrhage development remain poorly understood. Zebrafish provide a tractable in vivo model to study cerebrovascular biology and spontaneous ICH, yet the contribution of vascular regulation to haemorrhage onset and expansion has not been explored in this species. Here, we investigated whether pharmacological modulation of vascular dilation influences ICH development in zebrafish larvae. We first characterised vascular changes during the developmental window in which spontaneous ICH occurs and observed increased heart rate and progressive reductions in arterial diameter between 2 and 3 days post-fertilisation, suggesting increased vascular resistance. We then tested whether vasoconstriction promotes haemorrhage using angiotensin II, which induced systemic and cerebrovascular vasoconstriction but did not increase ICH incidence or haematoma size in two independent ICH models. In contrast, pharmacological vasodilation using sodium nitroprusside or isoproterenol significantly reduced haematoma size in a high-incidence model of atorvastatin-induced ICH. Live imaging of cerebral blood flow revealed that vasodilation was associated with the confinement of red blood cells around affected vessels rather than dispersing into the brain ventricles. Together, these findings indicate that vascular dilation modulates haemorrhage progression in zebrafish ICH and establish this model as a platform to investigate haemodynamic mechanisms regulating haematoma expansion.

Caveolae, flask-shaped membrane invaginations highly enriched in endothelial cells, play a central role in buffering membrane tension, yet the principles governing their spatial organization remain elusive. This investigation sought to generate the most comprehensive and systematic analysis of blood vessel caveolar spatial organization. To do so, our group leveraged micropatterning technologies to impose precise biophysical constraints on endothelial cell geometry to probe how caveolae are organized under defined tensional and polarity environments. These experiments were integrated with a high-throughput spatial cell mapping computational pipeline for analyzing thousands of caveolae, providing an extremely high-fidelity analysis. Our results provide a governing framework of how total cellular caveolae are spatially organized during random and directional migration, non-motile polarized, nascent and stable monolayers with differing confinement levels as well as in angiogenic vasculature in vivo. Broadly, our results demonstrated caveolae preferentially organized in the rear of migrating and polarized endothelial cells. In differing monolayer configurations, caveolae default to a peri-junctional spatial organization. Lastly, in mouse retinal blood vessels caveolae are most prominent in the vascular front due to their responsiveness to vascular endothelial growth factor signaling. Overall, these results strongly suggest that caveolae cellular arrangement and number are highly predictive of vascular stability and remodeling states.

Steady-state volume of distribution (Vss) can be predicted using tissue-to-plasma partition coefficients (Kp) and tissue volumes. Kp values are important components of physiologically based pharmacokinetic (PBPK) models, allowing for estimation of distribution kinetics and simulation of concentration-time profiles. Many in silico approaches have been developed to predict tissue Kp values based on physicochemical processes that govern drug distribution. However, these methods frequently over- or under-predict tissue Kp values, highlighting the need to consider additional mechanisms that can impact drug distribution kinetics. Many drugs have been shown to bind to rat and human fatty acid binding proteins (FABPs) in vitro but the impact of this binding to drug distribution has not been incorporated into Kp predictions. We hypothesized that incorporating intracellular protein binding into tissue Kp predictions will improve Kp prediction accuracy. Using liver as a model organ, four physiologically based dynamic liver distribution models (LDMs) were developed to assess the role of distribution processes in Kp predictions. The developed LDMs incorporated known distribution mechanisms and intracellular drug binding to liver FABP (FABP1). The liver Kp values for drugs that bind to FABP1 were accurately predicted using the LDM that incorporates lipid partitioning, albumin distribution, and FABP1 binding but not using LDMs without FABP1 binding. Human FABP1 expression was quantified in 61 human livers and the interindividual variability in tissue FABP1 binding was incorporated into tissue Kp predictions. These simulations showed that intracellular FABP1 binding can cause interindividual variability in Kp values and result in concentration dependent tissue distribution. Significance StatementThis study shows that incorporating intracellular protein binding such as binding to FABP1 into tissue Kp predictions improves accuracy of the predictions. The novel dynamic LDM can be extrapolated to other organs of interest and integrated into full-body PBPK models to predict drug distribution kinetics. With dynamic and saturable distribution mechanisms incorporated into a PBPK model, nonlinear distribution kinetics can be simulated for various drugs.