Meningeal Lymphatics Research Articles

RADT-16. ADJUVANT CHEMO-RADIATION THERAPY AS A RISK FACTOR FOR POSTOPERATIVE HYDROCEPHALUS FOLLOWING RESECTION OF HIGH-GRADE GLIOMA: A PROPENSITY-MATCHED CASE SERIES

Abstract The discovery of the neural glymphatic network in the past decade has significant implications for clinical investigations on hydrocephalus. With emerging understanding of how meningeal lymphatics and perivascular pathways impact cerebrospinal fluid dynamics, it is conceivable that inflammatory and fibrotic changes induced by radiation and chemotherapy may contribute to the pathogenesis of postoperative hydrocephalus, a well-documented sequela of resective neurosurgery. This study investigates differences in adjuvant chemo-radiation therapy patterns between patients who develop hydrocephalus following high-grade glioma resection and those who do not experience this postoperative complication. A retrospective chart review identified 328 adult patients who underwent tumor resection at our institution between 2010-2020, of which 257 had high-grade gliomas. Demographic and clinical data were collected, including resection history and adjuvant chemotherapy and radiation history. Propensity Score Matching generated comparative cohorts (n=27) using covariates sex, age at first surgery, surgery type, tumor location, extent of first resection, tumor-associated seizures, ventricular opening, number of additional resective surgeries, and pre-surgical Karnofsky Performance Scale score. Independent t-tests assessed differences in adjunctive chemo-radiation trends between patients who developed hydrocephalus within 3 years postoperatively and those who did not. 27 of 257 patients (10.5%) who underwent resection for high-grade glioma developed hydrocephalus within 3 years of their first surgery. Patients who developed hydrocephalus were more likely to have initiated the Stupp protocol(P=0.004), completed the Stupp protocol(P=0.02), and undertaken multiple cycles of the Stupp protocol(P=0.0004). Additionally, these patients had a smaller time window between surgery and adjuvant chemo-radiotherapy initiation than patients who did not develop hydrocephalus (P=0.02). Importantly, engagement in other clinical trial regimens with chemotherapy or radiation therapy did not differ significantly between groups(P=0.08, P=0.49, respectively). Shortened time to initiation of chemo-radiation therapy postoperatively and increased number of chemo-radiation cycles may increase a patient’s susceptibility to develop postoperative hydrocephalus following resection of high-grade glioma.

Expanding Applications and Future of Robotic Microsurgery.

Robotic-assisted microsurgery has emerged as a transformative technology, offering enhanced precision for complex procedures across various fields, including lymphatic surgery, breast reconstruction, trauma, and neurosurgery. This paper reviews current advancements, applications, and potential future directions for robotic-assisted microsurgery. In lymphatic surgery, robotic systems such as Symani have improved precision in thoracic duct reconstruction and lymphatic vessel anastomoses, reducing morbidity despite longer surgery times. In breast reconstruction, robotic systems are being used to refine techniques like the miraDIEP approach, minimizing tissue damage and enhancing precision in individualized treatments. Trauma reconstruction, particularly for extremities, has also benefited from robotic assistance, enabling successful sutures in small vessels and nerves. Emerging applications in meningeal lymphatics show potential for treating neurodegenerative diseases through improved drainage. In neurosurgery, robots enhance precision in deep and narrow anatomic spaces, although advancements in specialized instruments are needed for full implementation. Future development of robotic microsurgery systems will focus on improved maneuverability, miniaturization, and integration of tools like augmented reality and haptic feedback. The goal is to combine robotic precision, data storage, and processing with human skills such as judgment and flexibility. Although robots are unlikely to replace surgeons, they are poised to play an increasingly significant role in enhancing surgical outcomes. As the technology evolves, further research and clinical trials are needed to refine robotic systems and validate their expanding applications in clinical practice.

Enhancing Th17 cells drainage through meningeal lymphatic vessels alleviate neuroinflammation after subarachnoid hemorrhage

BackgroundSubarachnoid hemorrhage (SAH) is a severe cerebrovascular disorder primarily caused by the rupture of aneurysm, which results in a high mortality rate and consequently imposes a significant burden on society. The occurrence of SAH initiates an immune response that further exacerbates brain damage. The acute inflammatory reaction subsequent to SAH plays a crucial role in determining the prognosis. Th17 cells, a subset of T cells, are related to the brain injury following SAH, and it is unclear how Th17 cells are cleared in the brain. Meningeal lymphatic vessels are a newly discovered intracranial fluid transport system that has been shown to drain large molecules and immune cells to deep cervical lymph nodes. There is limited understanding of the role of the meningeal lymphatic system in SAH. The objective of this research is to explore the impact and underlying mechanism of drainage Th17 cells by meningeal lymphatics on SAH.MethodsTreatments to manipulate meningeal lymphatic function and the CCR7-CCL21 pathway were administered, including laser ablation, injection of VEGF-C geneknockout, and protein injection. Mouse behavior was assessed using the balance beam experiment and the modified Garcia scoring system. Flow cytometry, enzyme-linked immunosorbent assays (ELISA), and immunofluorescence staining were used to study the impact of meningeal lymphatic on SAH drainage. Select patients with unruptured and ruptured aneurysms in our hospital as the control group and the SAH group, with 7 cases in each group. Peripheral blood and cerebrospinal fluid (CSF) samples were assessed by ELISA and flow cytometry.ResultsMice with SAH showed substantial behavioral abnormalities and brain damage in which immune cells accumulated in the brain. Laser ablation of the meningeal lymphatic system or knockout of the CCR7 gene leads to Th17 cell aggregation in the meninges, resulting in a decreased neurological function score and increased levels of inflammatory factors. Injection of VEGF-C or CCL21 protein promotes Th17 cell drainage to lymph nodes, an increased neurological function score, and decreased levels of inflammatory factors. Clinical blood and CSF results showed that inflammatory factors in SAH group were significantly increased. The number of Th17 cells in the SAH group was significantly higher than the control group. Clinical results confirmed Th17 cells aggravated the level of neuroinflammation after SAH.ConclusionThis study shows that improving the drainage of Th17 cells by meningeal lymphatics via the CCR7-CCL21 pathway can reduce brain damage and improve behavior in the SAH mouse model. This could lead to new treatment options for SAH.

Symposium Highlight: BRAIN LYMPHATICS: REDISCOVERY AND NEW INSIGHTS INTO LYMPHATIC INVOLVEMENT IN DISEASES OF HUMAN BRAINS

The brain’s lymphatic system is comprised of a glymphatic—meningeal—cervical lymphatic vessel pathway. The study of its mechanism and pathophysiology in neurodegenerative disease has been one of the most exciting topics in basic and translational neuroscience of the last decade. However, while there has been some debate about when the meningeal lymphatics were discovered, it cannot be denied that studies in preclinical models and humans in this century represent a monumental step forward in our understanding of how the brain removes metabolic waste, the role this system plays in neurodegenerative disease, and, most importantly, its potential as a novel therapeutic target. This is a summary of the history, functional anatomy, and role of the brain’s lymphatics in neurodegenerative disease.

Oligodendrocytes go with the flow: Meningeal lymphatics promote myelin integrity

The meningeal lymphatics system plays diverse roles in facilitating neuroimmune function at brain borders, yet its specific contribution toward glial function and homeostasis is not known. In this issue of Immunity, Das Neves etal. (2024) describe a novel role for the meningeal lymphatics in maintaining oligodendrocyte survival and myelination.

Photodynamic opening of the blood-brain barrier affects meningeal lymphatics and the brain's drainage in healthy male mice.

Here, we present the new vascular effects of photodynamic therapy (PDT) with 5-aminolevulinic acid (5-ALA). PDT with 5-ALA induces a leakage of both the meningeal and cerebral blood vessels. The extravasation of photo-excited 5-ALA from the leaky blood vessels into the meninges causes photo-damage of the meningeal lymphatics (MLVs) leading to a dramatic reducing the MLV network and brain's drainage. The PDT-induced impairment of lymphatic regulation of brain's drainage can lead to excessive accumulation of fluids in brain tissues, which is important to consider in the PDT therapy for brain diseases as s possible side effect of PDT with 5-ALA.

Abstract P346: Expansion of meningeal lymphatic vessels in DOCA-salt hypertension

The meningeal lymphatic system is critical for proper brain waste clearance and maintenance of the local meningeal neuroimmune niche. Meningeal lymphatic function is impaired during aging and neurodegenerative diseases and is associated with the development of cognitive impairment. There is a bidirectional communication between meningeal lymphatic function and dural T cells, whereby the drainage of T cells into the deep cervical lymph nodes depends on functional lymphatic vessels, and meningeal lymphatic function is itself modulated by T cell derived cytokines. We have previously shown that IL-17A producing T cells accumulate in the dura during deoxycorticosterone acetate (DOCA)-salt hypertension and contribute to the impairment of neurovascular coupling and cognitive function. However, the mechanisms by which these T cells accumulate in the dura remain to be determined. Here, we tested the hypothesis that the meningeal lymphatic vessels are impaired during DOCA-salt hypertension, thus contributing to dural T cell accumulation. 12-week old C57BL6 male mice were implanted with a s.c. DOCA pellet and received 0.9% NaCl in the drinking water for 21 days (n=4). Control mice underwent a sham surgery (n=4). Blood pressure was monitored by tail-cuff plethysmography. Meningeal lymphatic vessels were assessed by immunohistochemistry using the lymphatic vessel marker LYVE1. In a separate group of mice, we assessed meningeal lymphatic function by delivering Alexa647-Ovalbumin or IgG-RPE into the cisterna magna and measuring fluorescence in the deep cervical lymph nodes one hour after injection. DOCA-salt mice developed increased systolic blood pressure (control: 117.7 ± 4.9 vs DOCA: 141.5 ± 2.9mmHg). We observed no difference in the CD31+ dural sinus area between control and DOCA-salt (control: 11.482 ± 0.718 vs DOCA: 11.816 ± 0.662 mm 2 ). We found a significant increase in LYVE1+ area surrounding the dural sinuses in DOCA-salt (control: 0.508 ± 0.039 vs DOCA: 0.816 ± 0.105 mm 2 ; p=0.0329 by unpaired two-tailed t-test) and an increase in LYVE1+/CD31+ % area (control: 4.476 ± 0.462 vs DOCA: 6.840 ± 0.609 %; p=0.0213 by unpaired two-tailed t-test) which was not different between the sagittal sinus or the transverse sinus. Contrary to our hypothesis, our data suggests that the meningeal lymphatic vessels are expanded, not retracted, during DOCA-salt hypertension. The interaction between meningeal lymphatics and dura immunity in hypertension remains to be determined.

Comparative study of 3D-T2WI vs. 3D-T2-FLAIR MRI in displaying human meningeal lymphatics vessels

Comparative study of 3D-T2WI vs. 3D-T2-FLAIR MRI in displaying human meningeal lymphatics vessels

Meningeal lymphatic function promotes oligodendrocyte survival and brain myelination

The precise neurophysiological changes prompted by meningeal lymphatic dysfunction remain unclear. Here, we showed that inducing meningeal lymphatic vessel ablation in adult mice led to gene expression changes in glial cells, followed by reductions in mature oligodendrocyte numbers and specific lipid species in the brain. These phenomena were accompanied by altered meningeal adaptive immunity and brain myeloid cell activation. During brain remyelination, meningeal lymphatic dysfunction provoked a state of immunosuppression that contributed to delayed spontaneous oligodendrocyte replenishment and axonal loss. The deficiencies in mature oligodendrocytes and neuroinflammation due to impaired meningeal lymphatic function were solely recapitulated in immunocompetent mice. Patients diagnosed with multiple sclerosis presented reduced vascular endothelial growth factor C in the cerebrospinal fluid, particularly shortly after clinical relapses, possibly indicative of poor meningeal lymphatic function. These data demonstrate that meningeal lymphatics regulate oligodendrocyte function and brain myelination, which might have implications for human demyelinating diseases.

Cellular Contributions to Glymphatic and Lymphatic Waste Clearance in the Brain.

Cerebrospinal fluid (CSF) bathes and cushions the brain; however, it also serves a major role in the clearance of metabolic wastes and in the distribution of glucose, lipids, and amino acids. Unlike every other organ in the body, the brain parenchyma lacks a traditional lymphatic system to drain fluids and central nervous system (CNS) antigens. It was historically assumed that all brain wastes were removed by endogenous processing, such as phagocytosis and autophagy, while excess fluids drained directly into the blood. However, the twin discoveries of the glial-lymphatic (glymphatic) system and meningeal lymphatics have transformed our understanding of brain waste clearance. The glymphatic system describes the movement of fluids through the subarachnoid space (SAS), the influx along periarterial spaces into the brain parenchyma, and the ultimate efflux back into the SAS along perivenous spaces where it comes into direct contact with the meningeal lymphatics. The dura mater of the meninges contains a bona fide lymphatic network that can drain CSF that has entered the dura. Together, these pathways provide insights into the clearance of molecules and fluids from the brain, and show that the CNS is physically connected to the adaptive immune system. Here, we outline the glymphatic and lymphatic systems, and describe the cellular components that are important to their function.

Meningeal Lymphatics in Central Nervous System Diseases.

Since its recent discovery, the meningeal lymphatic system has reshaped our understanding of central nervous system (CNS) fluid exchange, waste clearance, immune cell trafficking, and immune privilege. Meningeal lymphatics have also been demonstrated to functionally modify the outcome of neurological disorders and their responses to treatment, including brain tumors, inflammatory diseases such as multiple sclerosis, CNS injuries, and neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. In this review, we discuss recent evidence of the contribution of meningeal lymphatics to neurological diseases, as well as the available experimental methods for manipulating meningeal lymphatics in these conditions. Finally, we also provide a discussion of the pressing questions and challenges in utilizing meningeal lymphatics as a prime target for CNS therapeutic intervention and possibly drug delivery for brain disorders.

Deep cervical lymph nodes in Parkinson's disease and atypical Parkinson's disease: A potential ultrasound biomarker for differential diagnosis.

Parkinson's disease (PD) is a common degenerative disease caused by abnormal accumulation of α-synuclein. The glymphatic pathway is essential for removing macromolecular proteins including α-synuclein from the brain, which flows into deep cervical lymph nodes (DCLNs) through meningeal lymphatics. As a terminal station for the cerebral lymphatic system drainage, DCLNs can be easily assessed clinically. Although the drainage function of the cerebral lymphatic system is impaired in PD, the correlation between DCLNs and PD remains unknown. Single-center retrospective cross-sectional study. The size of the DCLNs were measured using ultrasound. The Movement Disorder Society Sponsored Revision Unified Parkinson's Disease Rating Scale and other scales were used to assess PD motor and non-motor symptoms. Compared with the healthy control (HC) and the atypical Parkinson's disease (AP) groups, the size of the second and third DCLNs in the Parkinson's disease (PD) group was significantly smaller (P < .05). The width diameter of the third DCLN (DCLN3(y)) was significantly smaller in the PD group than in the AP group (P = .014). DCLN3(y) combined with a variety of clinical features improved the sensitivity of AP identification (sensitivity = .813). DCLNs were able to distinguish HC, PD and AP and were mainly located in Robbins ΙΙA level. PD and AP were associated with different factors that influenced the size of the DCLNs. DCLN3(y) plays an important role in differentiating PD from AP, which, combined with other clinical features, has the ability to distinguish PD from AP; in particular, the sensitivity of AP diagnosis was improved.

CCN1 Is a Therapeutic Target for Reperfused Ischemic Brain Injury.

Ischemic stroke can lead to systemic inflammation, which can activate peripheral immune cells, causing neuroinflammation and brain injury. Meningeal lymphatics play a crucial role in transporting solutes and immune cells out of the brain and draining them into cervical lymph nodes (CLNs). However, the role of meningeal lymphatics in regulating systemic inflammation during the reperfusion stage after ischemia is not well understood. In this study, we demonstrated that brain infarct size, neuronal loss, and the effector function of inflammatory macrophage subsets were reduced after ischemia-reperfusion and disruption of meningeal lymphatics. Spatial memory function was improved in the late stage of ischemic stroke following meningeal lymphatic disruption. Brain-infiltrating immune cells, including neutrophils, monocytes, and T and natural killer cells, were reduced after cerebral ischemia-reperfusion and meningeal lymphatic disruption. Single-cell RNA sequencing analysis revealed that meningeal lymphatic disruption reprogrammed the transcriptome profile related to chemotaxis and leukocyte migration in CLN lymphatic endothelial cells (LECs), and it also decreased chemotactic CCN1 expression in floor LECs. Replenishment of CCN1 through intraventricular injection increased brain infarct size and neuronal loss, while restoring numbers of macrophages/microglia in the brains of meningeal lymphatic-disrupted mice after ischemic stroke. Blocking CCN1 in cerebrospinal fluid reduced brain infarcts and improves spatial memory function after ischemia-reperfusion injury. In summary, this study indicates that CCN1-mediated detrimental inflammation was alleviated after cerebral ischemia-reperfusion injury and meningeal lymphatic disruption. CCN1 represents a novel therapeutic target for inhibiting systemic inflammation in the brain-CLN axis after ischemia-reperfusion injury.

Ultrasonic cerebrospinal fluid clearance improves outcomes in hemorrhagic brain injury models.

Impaired clearance of the byproducts of aging and neurologic disease from the brain exacerbates disease progression and severity. We have developed a noninvasive, low intensity transcranial focused ultrasound protocol that facilitates the removal of pathogenic substances from the cerebrospinal fluid (CSF) and the brain interstitium. This protocol clears neurofilament light chain (NfL) - an aging byproduct - in aged mice and clears red blood cells (RBCs) from the central nervous system in two mouse models of hemorrhagic brain injury. Cleared RBCs accumulate in the cervical lymph nodes from both the CSF and interstitial compartments, indicating clearance through meningeal lymphatics. Treating these hemorrhagic brain injury models with this ultrasound protocol reduced neuroinflammatory and neurocytotoxic profiles, improved behavioral outcomes, decreased morbidity and, importantly, increased survival. RBC clearance efficacy was blocked by mechanosensitive channel antagonism and was effective when applied in anesthetized subjects, indicating a mechanosensitive channel mediated mechanism that does not depend on sensory stimulation or a specific neural activity pattern. Notably, this protocol qualifies for an FDA non-significant risk designation given its low intensity, making it readily clinically translatable. Overall, our results demonstrate that this low-intensity transcranial focused ultrasound protocol clears hemorrhage and other harmful substances from the brain via the meningeal lymphatic system, potentially offering a novel therapeutic tool for varied neurologic disorders.

Impaired Meningeal Lymphatics and Glymphatic Pathway in Patients with White Matter Hyperintensity.

White matter hyperintensity (WMH) represents a critical global medical concern linked to cognitive decline and dementia, yet its underlying mechanisms remain poorly understood. Here, humans are directly demonstrated that high WMH burden correlates with delayed drainage of meningeal lymphatic vessels (mLVs) and glymphatic pathway. Additionally, a longitudinal cohort study reveals that glymphatic dysfunction predicts WMH progression. Next, in a rat model of WMH, the presence of impaired lymphangiogenesis and glymphatic drainage is confirmed, followed by elevated microglial activation and white matter demyelination. Notably, enhancing meningeal lymphangiogenesis through adeno-associated virus delivery of vascular endothelial growth factor-C (VEGF-C) mitigates microglial gliosis and white matter demyelination. Conversely, blocking the growth of mLVs with a VEGF-C trap strategy exacerbates these changes. The findings highlight the role of mLVs and glymphatic pathway dysfunction in aggravating brain white matter injury, providing a potential novel strategy for WMH prevention and treatment.

Skull bone marrow serves as a niche of adaptive immunity for CNS immunosurveillance

Abstract The central nervous system (CNS) has been considered as an ‘immune-privileged’ organ owing to limited graft- and cancer-rejection, as well as the absence of lymphocytes and lymphatics. However, recent findings unveiled that the immune system actively discerns the status of the CNS through the glymphatic system and meningeal lymphatics. There is a diverse immune repertoire in the CNS borders presenting antigen, affecting behaviors, and defending CNS tissues. Recent studies discovered the channels in the skull bone marrow (SBM), exchanging immune cells and cerebrospinal fluid (CSF). Consequently, molecular exchange and immune cell activation occur in the CNS border, including SBM, like mucosal tissues. Nevertheless, the mechanism responding to CNS antigens and the maintenance of tolerance is unclear. In this study, we noted greater activation and differentiation of T/ B cells in the SBM than dura mater and other BMs. SBM displayed premature features of lymphoid structures, encompassing Tfh, activated B cells, and antibody-secreting cells. We also observed that Tfh cells directly interacted with B cells and induced differentiation. Moreover, our observations indicated that skull T/B cells respond to CNS antigens, but not microbial/food antigen. Thus, our study suggests that the SBM is a niche for adaptive immune cells in response to CNS antigens. The SBM may sustain heightened inflammatory states to promptly counteract tumorigenesis and pathogen invasion, protecting CNS.

Cervical lymphatic vessel dysfunction induced by amyloid-β and in the 5x-FAD mouse model of Alzheimer’s disease

Alzheimer’s dementia is a multifactorial disease characterized by amyloid-β (Aβ) accumulation in the brain. Aβ clearance occurs partially via meningeal lymphatics into cervical lymph nodes through superficial cervical lymphatic vessels (sCLV), which relies on intrinsic contractions of sCLV. Previous studies showed increased Aβ build up in the brain following ablation of meningeal lymphatics; however, whether Aβ alters sCLV function remains unclear. We hypothesize that sCLV contractile function will be reduced by acute Aβ exposure and in the 5x-FAD mouse model of Alzheimer’s disease. Contractile function of freshly isolated sCLV was assessed using pressure myography. Acute Aβ exposure was achieved by intraluminal incubation of pressurized sCLV with Aβ(1-40) (5 μM) or vehicle for 15 minutes prior to the start of the experiment. Repeated end-diastolic (EDD) and end-systolic (ESD) measurements were used to calculate fractional pump flow (FPF), the product of contractile frequency (FREQ) measured as contractions per minute (Hz), and ejection fraction (EF) calculated as (EDD2-ESD2)/EDD2, at incremental intraluminal pressures ranging from 2 to 10 cmH2O. Statistical differences were determined by two-way ANOVA followed by Sidak correction for multiple comparisons. All data are means ± SEM. In sCLV isolated from 5 months-old males and females C57bl/6J mice, acute Aβ exposure significantly decreased FREQ (Vehicle vs Aβ, n=4 / n=7, p&lt;0.01), without changes in EF (Vehicle vs Aβ, n=4 / n=7, p=0.115) or FPF (Vehicle vs Aβ, n=4 / n=7, p= 0.536). In pressurized sCLV isolated from 5x-FAD mice, when compared to wild-type littermates, we observed a significant reduction in FREQ (Wild-type vs 5x-FAD, n=4 / n=5, p&lt;0.01). No differences were observed in EF (Wild-type vs 5x-FAD, n=4 / n=5, p=0.1224) or FPF (Wild-type vs 5x-FAD, n=4 / n=5, p=0.193). Together, these preliminary data suggest that acute exposure to Aβ(1-40) decreases FREQ of isolated sCLV, a similar effect observed in sCLV isolated from 5x-FAD mice, albeit not reaching statistical power for multiple comparison significance. Consequently, a decrease contractile frequency can contribute to impairments in lymphatic pumping, which to some extent, can be compensated by prolonged filling times, thus leading to increased ejection fraction. In conclusion, we predict that in vivo sCLV contractile function is maintained via compensatory increases in ejection fraction in conditions of exacerbated Aβ production and deposition. Funding: National Institutes of Health (R01 AG073230) and the Alzheimer’s Association (AARGD-21-850835). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

300 Intracranial Tumors Hijack the Meningeal Venolymphatic Network Through VEGFR-2 Signaling

INTRODUCTION: Glioblastoma and other intracranial neoplasms have been associated with breakdown of the blood brain barrier. Other protective CNS barriers have sparsely been studied in brain tumors. Here, we identify the ability of intracranial neoplasms to hijack the meningeal venolymphatic network, which is driven through VEGFR-2/VEGF-A signaling. METHODS: C57BL/6J mice were stereotactically injected with syngeneic SB28 (glioblastoma) cell lines. Mice were treated with either isotype control or a VEGFR-2 inhibitor. Two-photon microscopy was used to visualize vascular cytoarchitecture and dynamics in vivo. Meningeal whole mounts, brains and spleens were also collected and analyzed by confocal microscopy and high parameter flow cytometry. Human dura mater from glioblastoma patients underwent multiplex immunohistochemistry to confirm the translatability of our findings. RESULTS: Our imaging studies revealed that glioblastomas can generate an extensive de novo network of meningeal blood vessels and lymphatics both in mice and humans. Lymphatic vessels were often observed developing in parallel to the newly formed vasculature. Intravital two-photon microscopy further revealed that the peritumoral vascular bed in the meninges of mice was leaky, dysfunctional, and generated a hypoxic microenvironment. Importantly, inhibition of VEGFR signaling impeded formation of this faulty venolymphatic network, which slowed tumor growth, reduced peritumoral hypoxia, enhanced immune infiltration, and increased survival. CONCLUSIONS: Our results demonstrate that glioblastomas can invade the meninges and hijack the venolymphatic network through VEGFR-2 and PECAM-1 signaling. While VEGFR-2 is associated with angiogenesis, our data suggest that it may also have an important role in regulating the simultaneous development of de novo meningeal venous and lymphatic drainage during glioblastoma.

Piezo1 regulates meningeal lymphatic vessel drainage and alleviates excessive CSF accumulation

Piezo1 regulates multiple aspects of the vascular system by converting mechanical signals generated by fluid flow into biological processes. Here, we find that Piezo1 is necessary for the proper development and function of meningeal lymphatic vessels and that activating Piezo1 through transgenic overexpression or treatment with the chemical agonist Yoda1 is sufficient to increase cerebrospinal fluid (CSF) outflow by improving lymphatic absorption and transport. The abnormal accumulation of CSF, which often leads to hydrocephalus and ventriculomegaly, currently lacks effective treatments. We discovered that meningeal lymphatics in mouse models of Down syndrome were incompletely developed and abnormally formed. Selective overexpression of Piezo1 in lymphatics or systemic administration of Yoda1 in mice with hydrocephalus or Down syndrome resulted in a notable decrease in pathological CSF accumulation, ventricular enlargement and other associated disease symptoms. Together, our study highlights the importance of Piezo1-mediated lymphatic mechanotransduction in maintaining brain fluid drainage and identifies Piezo1 as a promising therapeutic target for treating excessive CSF accumulation and ventricular enlargement.

Meningeal lymphatics can influence stroke outcome.

Meningeal lymphatics are conduits for cerebrospinal fluid drainage to lymphatics and lymph nodes in the neck. In this issue of JEM, Boisserand et al. (https://doi.org/10.1084/jem.20221983) provide evidence that expansion of meningeal lymphatics protects against ischemic stroke.