The Meningeal Lymphatic System: A New Player in Neurophysiology

Meningeal lymphatic vessel crosstalk with central nervous system immune cells in aging and neurodegenerative diseases

Meningeal lymphatic vessels form a relationship between the nervous system and periphery, which is relevant in both health and disease. Meningeal lymphatic vessels not only play a key role in the drainage of brain metabolites but also contribute to antigen delivery and immune cell activation. The advent of novel genomic technologies has enabled rapid progress in the characterization of myeloid and lymphoid cells and their interactions with meningeal lymphatic vessels within the central nervous system. In this review, we provide an overview of the multifaceted roles of meningeal lymphatic vessels within the context of the central nervous system immune network, highlighting recent discoveries on the immunological niche provided by meningeal lymphatic vessels. Furthermore, we delve into the mechanisms of crosstalk between meningeal lymphatic vessels and immune cells in the central nervous system under both homeostatic conditions and neurodegenerative diseases, discussing how these interactions shape the pathological outcomes. Regulation of meningeal lymphatic vessel function and structure can influence lymphatic drainage, cerebrospinal fluid-borne immune modulators, and immune cell populations in aging and neurodegenerative disorders, thereby playing a key role in shaping meningeal and brain parenchyma immunity.

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 et al. (2024) describe a novel role for the meningeal lymphatics in maintaining oligodendrocyte survival and myelination.

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

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

Blockage of CSF Outflow in Rats after Deep Cervical Lymph Node Ligation Observed Using Gd-based MR Imaging

PURPOSE

To investigate whether deep cervical lymph node (DCLN) ligation alters intracranial cerebrospinal fluid (CSF) tracer dynamics and outflow using a rat model with intrathecal dynamic contrast-enhanced (DCE) MRI.

METHODS

Six bilateral DCLN-ligated and six sham-operated rats were subjected to DCE MRI with Gd-BTDO3A, and dynamic T1-weighted images were acquired. ROIs were collected from the CSF at the C1 level (CSF_C1), CSF between the olfactory bulbs (CSF_OB), CSF at the pituitary recess (CSF_PitR), and CSF at the pineal recess (CSF_PinR), upper nasal turbinate (UNT), olfactory bulbs, cerebrum, and the jugular region. Time-intensity curves were evaluated, and the maximum slope, peak timing, peak signal ratio, and elimination half-life for the four CSF ROIs and UNT were calculated and compared.

RESULTS

Delayed tracer arrival in the rostral CSF space and the nasal cavity with tracer retention in the ventral CSF space were observed in the ligation group. The maximum slopes were smaller in the ligation group at UNT (sham: 0.075 ± 0.0061, ligation: 0.044 ± 0.0086/min, P = 0.011). A significant difference was not detected in peak timings. The peak signal ratio values were lower in the ligation group at UNT (sham: 2.12 ± 0.19, ligation: 1.72 ± 0.11, P = 0.011). The elimination half-life was delayed in the ligation group at CSF_C1 (sham: 30.5 ± 2.70, ligation: 44.4 ± 12.6 min, P = 0.043), CSF_OB (sham: 30.2 ± 2.67, ligation: 44.8 ± 7.47 min, P = 0.021), and CSF_PitR (sham: 30.2 ± 2.49, ligation: 41.3 ± 7.57 min, P = 0.021).

CONCLUSION

The DCLN ligation in rats blocked CSF outflow into the nasal cavity and caused CSF retention.

Engineered 3D human neurovascular model of Alzheimer's disease to study vascular dysfunction

The blood-brain barrier (BBB) serves as a selective filter that prevents harmful substances from entering the healthy brain. Dysfunction of this barrier is implicated in several neurological diseases. In the context of Alzheimer's disease (AD), BBB breakdown plays a significant role in both the initiation and progression of the disease. This study introduces a three-dimensional (3D) self-assembled in vitro model of the human neurovascular unit to recapitulate some of the complex interactions between the BBB and AD pathologies. It incorporates primary human brain endothelial cells, pericytes and astrocytes, and stem cell-derived neurons and astrocytes harboring Familial AD (FAD) mutations. Over an extended co-culture period, the model demonstrates increased BBB permeability, dysregulation of key endothelial and pericyte markers, and morphological alterations mirroring AD pathologies. The model enables visualization of amyloid-beta (Aβ) accumulation in both neuronal and vascular compartments. This model may serve as a versatile tool for neuroscience research and drug development to provide insights into the dynamic relationship between vascular dysfunction and AD pathogenesis.

Simulating the impact of tumor mechanical forces on glymphatic networks in the brain parenchyma

The brain glymphatic system is currently being explored in the context of many neurological disorders and diseases, including traumatic brain injury, Alzheimer's disease, and ischemic stroke. However, little is known about the impact of brain tumors on glymphatic function. Mechanical forces generated during tumor development and growth may be responsible for compromised glymphatic transport pathways, reducing waste clearance and cerebrospinal fluid (CSF) transport in the brain parenchyma. One such force is solid stress, i.e., growth-induced forces from cell hyperproliferation and excess matrix deposition. Because there are no prior studies assessing the impact of tumor-derived solid stress on glymphatic system structure and performance in the brain parenchyma, this study serves to fill an important gap in the field. We adapted a previously developed Electrical Analog Model using MATLAB Simulink for glymphatic transport coupled with Finite Element Analysis for tumor mechanical stresses and strains in COMSOL. This allowed simulation of the impact of tumor mechanical force generation on fluid transport within brain parenchymal glymphatic units-which include perivascular spaces, astrocytic networks, interstitial spaces, and capillary basement membranes. We conducted a parametric analysis to compare the contributions of tumor size, tumor proximity, and ratio of glymphatic subunits to the stress and strain experienced by the glymphatic unit and corresponding reduction in flow rate of CSF. Mechanical stresses intensify with proximity to the tumor and increasing tumor size, highlighting the vulnerability of nearby glymphatic units to tumor-derived forces. Our stress and strain profiles reveal compressive deformation of these surrounding glymphatics and demonstrate that varying the relative contributions of astrocytes vs. interstitial spaces impact the resulting glymphatic structure significantly under tumor mechanical forces. Increased tumor size and proximity caused increased stress and strain across all glymphatic subunits, as does decreased astrocyte composition. Indeed, our model reveals an inverse correlation between extent of astrocyte contribution to the composition of the glymphatic unit and the resulting mechanical stress. This increased mechanical strain across the glymphatic unit decreases the venous efflux rate of CSF, dependent on the degree of strain and the specific glymphatic subunit of interest. For example, a 20% mechanical strain on capillary basement membranes does not significantly decrease venous efflux (2% decrease in flow rates), while the same magnitude of strain on astrocyte networks and interstitial spaces decreases efflux flow rates by 7% and 22%, respectively. Our simulations reveal that solid stress from growing brain tumors directly reduces glymphatic fluid transport, independently from biochemical effects from cancer cells. Understanding these pathophysiological implications is crucial for developing targeted interventions aimed at restoring effective waste clearance mechanisms in the brain. This study opens potential avenues for future experimental research in brain tumor-related glymphatic dysfunction.

Low-/Negative-Pressure Hydrocephalus: To Understand the Formation Mechanism from the Perspective of Clinicians

Low-/negative-pressure hydrocephalus (LPH/NePH) is uncommon in clinical practice, and doctors are unfamiliar with it. LPH/NePH is frequently caused by other central nervous system diseases, and patients are frequently misdiagnosed with other types of hydrocephalus, resulting in delayed treatment. LPH/NePH therapy evolved to therapeutic measures based on "external ventricular drainage below atmospheric pressure" as the number of patients with LPH/NePH described in the literature has increased. However, the mechanism of LPH/NePH formation is unknown. Thus, understanding the process of LPH/NePH development is the most important step in improving diagnosis and treatment capability. Based on case reports of LPH/NePH, we reviewed theories of transcortical pressure difference, excessive cerebral venous drainage, brain viscoelastic changes, and porous elastic sponges.

Emerging microglial biology highlights potential therapeutic targets for Alzheimer's disease

Alzheimer's disease is a chronic degenerative disease of the central nervous system, which primarily affects elderly people and accounts for 70-80 % of dementia cases. The current prevailing amyloid cascade hypothesis suggests that Alzheimer's disease begins with the deposition of amyloid β (Aβ) in the brain. Major therapeutic strategies target Aβ production, aggregation, and clearance, although many clinical trials have shown that these therapeutic strategies are not sufficient to completely improve cognitive deficits in AD patients. Recent genome-wide association studies have identified that multiple important regulators are the most significant genetic risk factors for Alzheimer's disease, especially in the innate immune pathways. These genetic risk factors suggest a critical role for microglia, highlighting their therapeutic potential in treating neurodegenerative diseases. In this review, we discuss how these recently documented AD risk genes affect microglial function and AD pathology and how they can be further targeted to regulate microglial states and slow AD progression, especially the highly anticipated APOE and TREM2 targets. We focused on recent findings that modulation of innate and adaptive neuroimmune microenvironment crosstalk reverses cognitive deficits in AD patients. We also considered novel strategies for microglia in AD patients.

Restoration of cervical lymphatic vessel function in aging rescues cerebrospinal fluid drainage

Cervical lymphatic vessels (cLVs) have been shown to drain solutes and cerebrospinal fluid (CSF) from the brain. However, their hydrodynamical properties have never been evaluated in vivo. Here, we developed two-photon optical imaging with particle tracking in vivo of CSF tracers (2P-OPTIC) in superficial and deep cLVs of mice, characterizing their flow and showing that the major driver is intrinsic pumping by contraction of the lymphatic vessel wall. Moreover, contraction frequency and flow velocity were reduced in aged mice, which coincided with a reduction in smooth muscle actin expression. Slowed flow in aged mice was rescued using topical application of prostaglandin F2α, a prostanoid that increases smooth muscle contractility, which restored lymphatic function in aged mice and enhanced central nervous system clearance. We show that cLVs are important regulators of CSF drainage and that restoring their function is an effective therapy for improving clearance in aging.

Ligation of cervical lymphatic vessels decelerates blood clearance and worsens outcomes after experimental subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is characterized by the extravasation of blood into the subarachnoid space, in which erythrocyte lysis is the primary contributor to cell death and brain injuries. New evidence has indicated that meningeal lymphatic vessels (mLVs) are essential in guiding fluid and macromolecular waste from cerebrospinal fluid (CSF) into deep cervical lymph nodes (dCLNs). However, the role of mLVs in clearing erythrocytes after SAH has not been completely elucidated. Hence, we conducted a cross-species study. Autologous blood was injected into the subarachnoid space of rabbits and rats to induce SAH. Erythrocytes in the CSF were measured with/without deep cervical lymph vessels (dCLVs) ligation. Additionally, prior to inducing SAH, we administered rats with vascular endothelial growth factor C (VEGF-C), which is essential for meningeal lymphangiogenesis and maintaining integrity and survival of lymphatic vessels. The results showed that the blood clearance rate was significantly lower after dCLVs ligation in both the rat and rabbit models. DCLVs ligation aggravated neuroinflammation, neuronal damage, brain edema, and behavioral impairment after SAH. Conversely, the treatment of VEGF-C enhanced meningeal lymphatic drainage of erythrocytes and improved outcomes in SAH. In summary, our research highlights the indispensable role of the meningeal lymphatic pathway in the clearance of blood and mediating consequences after SAH.

Cannabidiol Alleviates Neurological Deficits After Traumatic Brain Injury by Improving Intracranial Lymphatic Drainage

Traumatic brain injury (TBI) persists as a substantial clinical dilemma, largely because of the absence of effective treatments. This challenge is exacerbated by the hindered clearance of intracranial metabolic byproducts and the continual accrual of deleterious proteins. The glymphatic system (GS) and meningeal lymphatic vessels (MLVs), key elements of the intracranial lymphatic network, play critical roles in the clearance of harmful substances. Cannabidiol (CBD) has shown promise in reducing metabolite overload and bolstering cognitive performance in various neurodegenerative diseases. The precise mechanisms attributing to its beneficial effects in TBI scenarios, however, are yet to be distinctly understood. Utilizing a fluid percussion injury paradigm, our research adopted a multifaceted approach, encompassing behavioral testing, immunofluorescence and immunohistochemical analyses, laser speckle imaging, western blot techniques, and bilateral cervical efferent lymphatic ligation. This methodology aimed to discern the influence of CBD on both neurological outcomes and intracranial lymphatic clearance in a murine TBI model. We observed that CBD administration notably ameliorated motor, memory, and cognitive functions, concurrently with a significant reduction in the concentration of phosphorylated tau protein and amyloid-β. In addition, CBD expedited the turnover and elimination of intracranial tracers, increased cerebral blood flow, and enhanced the efficacy of fluorescent tracer migration from MLVs to deep cervical lymph nodes (dCLNs). Remarkably, CBD treatment also induced a reversion in aquaporin-4 (AQP-4) polarization and curtailed neuroinflammatory indices. A pivotal discovery was that the surgical interruption of efferent lymphatic conduits in the neck nullified CBD's positive contributions to intracranial waste disposal and cognitive improvement, yet the anti-neuroinflammatory actions remained unaffected. These insights suggest that CBD may enhance intracranial metabolite clearance, potentially via the regulation of the intracranial lymphatic system, thereby offering neurofunctional prognostic improvement in TBI models. Our findings underscore the potential therapeutic applicability of CBD in TBI interventions, necessitating further comprehensive investigations and clinical validations to substantiate these initial conclusions.

A Panel of miRNA Biomarkers Common to Serum and Brain-Derived Extracellular Vesicles Identified in Mouse Model of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive motor neuron disease characterised by the deposition of aggregated proteins including TAR DNA-binding protein 43 (TDP-43) in vulnerable motor neurons and the brain. Extracellular vesicles (EVs) facilitate the spread of neurodegenerative diseases and can be easily accessed in the bloodstream. This study aimed to identify a panel of EV miRNAs that can capture the pathology occurring in the brain and peripheral circulation. EVs were isolated from the cortex (BDEVs) and serum (serum EVs) of 3 month-old and 6-month-old TDP-43*Q331K and TDP-43*WT mice. Following characterisation and miRNA isolation, the EVs underwent next-generation sequencing where 24 differentially packaged miRNAs were identified in the TDP-43*Q331K BDEVs and 7 in the TDP-43*Q331K serum EVs. Several miRNAs, including miR-183-5p, were linked to ALS. Additionally, miR-122-5p and miR-486b-5p were identified in both panels, demonstrating the ability of the serum EVs to capture the dysregulation occurring in the brain. This is the first study to identify miRNAs common to both the serum EVs and BDEVs in a mouse model of ALS.

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.

Neuroimmune modulation in liver pathophysiology

The liver, the largest organ in the human body, plays a multifaceted role in digestion, coagulation, synthesis, metabolism, detoxification, and immune defense. Changes in liver function often coincide with disruptions in both the central and peripheral nervous systems. The intricate interplay between the nervous and immune systems is vital for maintaining tissue balance and combating diseases. Signaling molecules and pathways, including cytokines, inflammatory mediators, neuropeptides, neurotransmitters, chemoreceptors, and neural pathways, facilitate this complex communication. They establish feedback loops among diverse immune cell populations and the central, peripheral, sympathetic, parasympathetic, and enteric nervous systems within the liver. In this concise review, we provide an overview of the structural and compositional aspects of the hepatic neural and immune systems. We further explore the molecular mechanisms and pathways that govern neuroimmune communication, highlighting their significance in liver pathology. Finally, we summarize the current clinical implications of therapeutic approaches targeting neuroimmune interactions and present prospects for future research in this area.

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.

Changes in plasma concentrations of novel vascular and inflammatory biomarkers in obstructive sleep apnea patients pre- and post-stroke

BACKGROUND

Obstructive sleep apnea (OSA) is increasingly recognized as a common condition in the general population and causes significant OSA-associated morbidities including cardiovascular and cerebrovascular events such as cerebral small vessel disease (CSVD) and stroke.

METHODS

In this study, using sensitive ELISA immunoassays, we measured subset of endothelial/vascular and inflammatory biomarkers as well as neurofilament light chain (NfL), a sensitive marker for neuroaxonal injury, using plasma from OSA patients post-stroke (Acute Cerebral Infarction (ACI), N = 26) to determine their usefulness as potential prognostic markers in disease progression.

RESULTS

Our results showed significantly increased plasma TNFα and NfL concentrations and decreased concentrations of platelet derived growth factor (PDGF-AA) in post-stroke OSA patients with more severe white matter hyperintensities (WMHs). And after separating the patients based on sex, compared to females, male post-stroke OSA patients with severe WMHs have increased circulating levels of inflammatory chemokine CXCL10 and cytokine Interleukin-10 (IL-10) and significantly decreased levels of Angiopoietin-1 (Ang-1) an important protein responsible for endothelial/vascular integrity functions. Importantly, in a subset of newly diagnosed OSA patients (without prior history of stroke), significantly increased plasma CXCL10 levels and decreased plasma Ang-1 levels were also readily observed when compared to healthy controls, indicating possible altered endothelial integrity and ongoing vascular inflammation in these newly diagnosed OSA patients.

CONCLUSIONS

In summary, our study has identified a novel set of plasma biomarkers including PDGF-AA, CXCL10 and Ang-1 for their potential prognostic value for disease outcomes pre- and post-stroke in OSA patients and use as surrogate markers to measure efficacy of treatment modalities.

Dissolving microneedles loaded with nimodipine for prevention of sleep disorders at a high altitude

Sleep disorders are one of the most common acute reactions on the plateau, which can cause serious complications. However, there is no effective and safe treatment currently available. Nimodipine (NMD) is a dihydropyridine calcium channel blocker with neuroprotective and vasodilating activity, mainly used for the treatment of ischemic brain injury. Commercial oral or injectable NMD formulations are not a good option for central neuron diseases due to their poor brain delivery. In this study, nimodipine dissolving microneedles (NDMNs) were prepared for the prevention of sleep disorders caused by hypoxia. NDMNs were composed of NMD and polyvinyl pyrrolidone (PVP) K90 with a conical morphology and high rigidity. After administration of NDMNs on the back neck of mice, the concentration of NMD in the brain was significantly higher than that of oral medication as was confirmed by the fluorescent imaging on mouse models. NDMNs enhanced cognitive function, alleviated oxidative stress, and improved the sleep quality of mice with high-altitude sleep disorders. The blockage of calcium ion overloading may be an important modulation mechanism. NDMNs are a promising and user-friendly formulation for the prevention of high-altitude sleep disorders.

Neuroimmune modulation by tryptophan derivatives in neurological and inflammatory disorders

The nervous and immune systems are highly developed, and each performs specialized physiological functions. However, they work together, and their dysfunction is associated with various diseases. Specialized molecules, such as neurotransmitters, cytokines, and more general metabolites, are essential for the appropriate regulation of both systems. Tryptophan, an essential amino acid, is converted into functional molecules such as serotonin and kynurenine, both of which play important roles in the nervous and immune systems. The role of kynurenine metabolites in neurodegenerative and psychiatric diseases has recently received particular attention. Recently, we found that hyperactivity of the kynurenine pathway is a critical risk factor for septic shock. In this review, we first outline neuroimmune interactions and tryptophan derivatives and then summarized the changes in tryptophan metabolism in neurological disorders. Finally, we discuss the potential of tryptophan derivatives as therapeutic targets for neuroimmune disorders.

Glymphatic pathway: An emerging perspective in the pathophysiology of neurodegenerative diseases

The central nervous system (CNS) is widely recognized as the only organ system without lymphatic capillaries to promote the removal of interstitial metabolic by-products. Thus, the newly identified glymphatic system which provides a pseudolymphatic activity in the nervous system has been focus of latest research in neurosciences. Also, findings reported that, sleep stimulates the elimination actions of glymphatic system and is linked to normal brain homeostatis. The CNS is cleared of potentially hazardous compounds via the glymphatic system, particularly during sleep. Any age-related alterations in brain functioning and pathophysiology of various neurodegenerative illnesses indicates the disturbance of the brain's glymphatic system. In this context, β-amyloid as well as tau leaves the CNS through the glymphatic system, it's functioning and CSF discharge markedly altered in elderly brains as per many findings. Thus, glymphatic failure may have a potential mechanism which may be therapeutically targetable in several neurodegenerative and age-associated cognitive diseases. Therefore, there is an urge to focus for more research into the connection among glymphatic system and several potential brain related diseases. Here, in our current review paper, we reviewed current research on the glymphatic system's involvement in a number of prevalent neurodegenerative and neuropsychiatric diseases and, we also discussed several therapeutic approaches, diet and life style modifications which might be used to acquire a more thorough performance and purpose of the glymphatic system to decipher novel prospects for clinical applicability for the management of these diseases.

Alzheimer's disease and its treatment-yesterday, today, and tomorrow

Alois Alzheimer described the first patient with Alzheimer's disease (AD) in 1907 and today AD is the most frequently diagnosed of dementias. AD is a multi-factorial neurodegenerative disorder with familial, life style and comorbidity influences impacting a global population of more than 47 million with a projected escalation by 2050 to exceed 130 million. In the USA the AD demographic encompasses approximately six million individuals, expected to increase to surpass 13 million by 2050, and the antecedent phase of AD, recognized as mild cognitive impairment (MCI), involves nearly 12 million individuals. The economic outlay for the management of AD and AD-related cognitive decline is estimated at approximately 355 billion USD. In addition, the intensifying prevalence of AD cases in countries with modest to intermediate income countries further enhances the urgency for more therapeutically and cost-effective treatments and for improving the quality of life for patients and their families. This narrative review evaluates the pathophysiological basis of AD with an initial focus on the therapeutic efficacy and limitations of the existing drugs that provide symptomatic relief: acetylcholinesterase inhibitors (AChEI) donepezil, galantamine, rivastigmine, and the N-methyl-D-aspartate receptor (NMDA) receptor allosteric modulator, memantine. The hypothesis that amyloid-β (Aβ) and tau are appropriate targets for drugs and have the potential to halt the progress of AD is critically analyzed with a particular focus on clinical trial data with anti-Aβ monoclonal antibodies (MABs), namely, aducanumab, lecanemab and donanemab. This review challenges the dogma that targeting Aβ will benefit the majority of subjects with AD that the anti-Aβ MABs are unlikely to be the "magic bullet". A comparison of the benefits and disadvantages of the different classes of drugs forms the basis for determining new directions for research and alternative drug targets that are undergoing pre-clinical and clinical assessments. In addition, we discuss and stress the importance of the treatment of the co-morbidities, including hypertension, diabetes, obesity and depression that are known to increase the risk of developing AD.

Simulating the Impact of Tumor Mechanical Forces on Glymphatic Networks in the Brain Parenchyma

Background

The brain glymphatic system is currently being explored in the context of many neurological disorders and diseases, including traumatic brain injury, Alzheimer's disease, and ischemic stroke. However, little is known about the impact of brain tumors on glymphatic function. Mechanical forces generated during tumor development and growth may be responsible for compromised glymphatic transport pathways, reducing waste clearance and cerebrospinal fluid (CSF) transport in the brain parenchyma. One such force is solid stress, i.e., growth-induced forces from cell hyperproliferation and excess matrix deposition. Because there are no prior studies assessing the impact of tumor-derived solid stress on glymphatic system structure and performance in the brain parenchyma, this study serves to fill an important gap in the field.

Methods

We adapted a previously developed Electrical Analog Model using MATLAB Simulink for glymphatic transport coupled with Finite Element Analysis for tumor mechanical stresses and strains in COMSOL. This allowed simulation of the impact of tumor mechanical force generation on fluid transport within brain parenchymal glymphatic units - which include paravascular spaces, astrocytic networks, interstitial spaces, and capillary basement membranes. We conducted a parametric analysis to compare the contributions of tumor size, tumor proximity, and ratio of glymphatic subunits to the stress and strain experienced by the glymphatic unit and corresponding reduction in flow rate of CSF.

Results

Mechanical stresses intensify with proximity to the tumor and increasing tumor size, highlighting the vulnerability of nearby glymphatic units to tumor-derived forces. Our stress and strain profiles reveal compressive deformation of these surrounding glymphatics and demonstrate that varying the relative contributions of astrocytes vs. interstitial spaces impact the resulting glymphatic structure significantly under tumor mechanical forces. Increased tumor size and proximity caused increased stress and strain across all glymphatic subunits, as does decreased astrocyte composition. Indeed, our model reveals an inverse correlation between extent of astrocyte contribution to the composition of the glymphatic unit and the resulting mechanical stress. This increased mechanical strain across the glymphatic unit decreases the venous efflux rate of CSF, dependent on the degree of strain and the specific glymphatic subunit of interest. For example, a 20% mechanical strain on capillary basement membranes does not significantly decrease venous efflux (2% decrease in flow rates), while the same magnitude of strain on astrocyte networks and interstitial spaces decreases efflux flow rates by 7% and 22%, respectively.

Conclusion

Our simulations reveal that solid stress from brain tumors directly reduces glymphatic fluid transport, independently from biochemical effects from cancer cells. Understanding these pathophysiological implications is crucial for developing targeted interventions aimed at restoring effective waste clearance mechanisms in the brain.This study opens potential avenues for future experimental research in brain tumor-related glymphatic dysfunction.

Water channels in the brain and spinal cord-overview of the role of aquaporins in traumatic brain injury and traumatic spinal cord injury

Knowledge about the mechanisms underlying the fluid flow in the brain and spinal cord is essential for discovering the mechanisms implicated in the pathophysiology of central nervous system diseases. During recent years, research has highlighted the complexity of the fluid flow movement in the brain through a glymphatic system and a lymphatic network. Less is known about these pathways in the spinal cord. An important aspect of fluid flow movement through the glymphatic pathway is the role of water channels, especially aquaporin 1 and 4. This review provides an overview of the role of these aquaporins in brain and spinal cord, and give a short introduction to the fluid flow in brain and spinal cord during in the healthy brain and spinal cord as well as during traumatic brain and spinal cord injury. Finally, this review gives an overview of the current knowledge about the role of aquaporins in traumatic brain and spinal cord injury, highlighting some of the complexities and knowledge gaps in the field.

John Cunningham Virus and Progressive Multifocal Leukoencephalopathy: A Falsely Played Diagnosis

Progressive Multifocal Leukoencephalopathy (PML) is a possibly fatal demyelinating disease and John Cunningham Polyomavirus (JCPyV) is believed to cause this condition. The so-called JCPyV was initially reported in lymphoma and Human Immunodeficiency Virus (HIV) cases, whereas nowadays, its incidence is increasing in Multiple Sclerosis (MS) cases treated with natalizumab (Tysabri). However, there are conflicting literature data on its pathology and diagnosis, whereas some misdiagnosed reports exist, giving rise to further questions towards the topic. In reality, the so-called PML and the supposed JCPyV are not what they seem to be. In addition, novel and more frequent PML-like conditions may be reported, especially after the Coronavirus Disease 2019 (COVID-19) pandemic.

Mitochondrial dysfunction in chronic neuroinflammatory diseases (Review)

Chronic neuroinflammation serves a key role in the onset and progression of neurodegenerative disorders. Mitochondria serve as central regulators of neuroinflammation. In addition to providing energy to cells, mitochondria also participate in the immunoinflammatory response of neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, multiple sclerosis and epilepsy, by regulating processes such as cell death and inflammasome activation. Under inflammatory conditions, mitochondrial oxidative stress, epigenetics, mitochondrial dynamics and calcium homeostasis imbalance may serve as underlying regulatory mechanisms for these diseases. Therefore, investigating mechanisms related to mitochondrial dysfunction may result in therapeutic strategies against chronic neuroinflammation and neurodegeneration. The present review summarizes the mechanisms of mitochondria in chronic neuroinflammatory diseases and the current treatment approaches that target mitochondrial dysfunction in these diseases.

Same yet different - how lymph node heterogeneity affects immune responses

Lymph nodes are secondary lymphoid organs in which immune responses of the adaptive immune system are initiated and regulated. Distributed throughout the body and embedded in the lymphatic system, local lymph nodes are continuously informed about the state of the organs owing to a constant drainage of lymph. The tissue-derived lymph carries products of cell metabolism, proteins, carbohydrates, lipids, pathogens and circulating immune cells. Notably, there is a growing body of evidence that individual lymph nodes differ from each other in their capacity to generate immune responses. Here, we review the structure and function of the lymphatic system and then focus on the factors that lead to functional heterogeneity among different lymph nodes. We will discuss how lymph node heterogeneity impacts on cellular and humoral immune responses and the implications for vaccination, tumour development and tumour control by immunotherapy.

Transcranial direct current stimulation alters cerebrospinal fluid-interstitial fluid exchange in mouse brain

BACKGROUND

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that has gained prominence recently. Clinical studies have explored tDCS as an adjunct to neurologic disease rehabilitation, with evidence suggesting its potential in modulating brain clearance mechanisms. The glymphatic system, a proposed brain waste clearance system, posits that cerebrospinal fluid-interstitial fluid (CSF-ISF) exchange aids in efficient metabolic waste removal. While some studies have linked tDCS to astrocytic inositol trisphosphate (IP3)/Ca2+ signaling, the impact of tDCS on CSF-ISF exchange dynamics remains unclear.

HYPOTHESIS

tDCS influences the dynamics of CSF-ISF exchange through astrocytic IP3/Ca2+ signaling.

METHODS

In this study, we administered tDCS (0.1 mA for 10 min) to C57BL/6N mice anesthetized with ketamine-xylazine (KX). The anode was positioned on the cranial bone above the cortex, and the cathode was inserted into the neck. Following tDCS, we directly assessed brain fluid dynamics by injecting biotinylated dextran amine (BDA) as a CSF tracer into the cisterna magna (CM). The brain was then extracted after either 30 or 60 min and fixed. After 24 h, the sectioned brain slices were stained with Alexa 594-conjugated streptavidin (SA) to visualize BDA using immunohistochemistry. We conducted Electroencephalography (EEG) recordings and aquaporin 4 (AQP4)/CD31 immunostaining to investigate the underlying mechanisms of tDCS. Additionally, we monitored the efflux of Evans blue, injected into the cisterna magna, using cervical lymph node imaging. Some experiments were subsequently repeated with inositol trisphosphate receptor type 2 (IP3R2) knockout (KO) mice.

RESULTS

Post-tDCS, we observed an increased CSF tracer influx, indicating a modulation of CSF-ISF exchange by tDCS. Additionally, tDCS appeared to enhance the brain's metabolic waste efflux. EEG recordings showed an increase in delta wave post-tDCS. But no significant change in AQP4 expression was detected 30 min post-tDCS. Besides, we found no alteration in CSF-ISF exchange and delta wave activity in IP3R2 KO mice after tDCS.

CONCLUSION

Our findings suggest that tDCS augments the glymphatic system's influx and efflux. Through astrocytic IP3/Ca2+ signaling, tDCS was found to modify the delta wave, which correlates positively with brain clearance. This study underscores the potential of tDCS in modulating brain metabolic waste clearance.

Inferior Frontal Sulcal Hyperintensities on Brain MRI Are Associated with Amyloid Positivity beyond Age-Results from the Multicentre Observational DELCODE Study

Inferior frontal sulcal hyperintensities (IFSHs) on fluid-attenuated inversion recovery (FLAIR) sequences have been proposed to be indicative of glymphatic dysfunction. Replication studies in large and diverse samples are nonetheless needed to confirm them as an imaging biomarker. We investigated whether IFSHs were tied to Alzheimer's disease (AD) pathology and cognitive performance. We used data from 361 participants along the AD continuum, who were enrolled in the multicentre DELCODE study. The IFSHs were rated visually based on FLAIR magnetic resonance imaging. We performed ordinal regression to examine the relationship between the IFSHs and cerebrospinal fluid-derived amyloid positivity and tau positivity (Aβ42/40 ratio ≤ 0.08; pTau181 ≥ 73.65 pg/mL) and linear regression to examine the relationship between cognitive performance (i.e., Mini-Mental State Examination and global cognitive and domain-specific performance) and the IFSHs. We controlled the models for age, sex, years of education, and history of hypertension. The IFSH scores were higher in those participants with amyloid positivity (OR: 1.95, 95% CI: 1.05-3.59) but not tau positivity (OR: 1.12, 95% CI: 0.57-2.18). The IFSH scores were higher in older participants (OR: 1.05, 95% CI: 1.00-1.10) and lower in males compared to females (OR: 0.44, 95% CI: 0.26-0.76). We did not find sufficient evidence linking the IFSH scores with cognitive performance after correcting for demographics and AD biomarker positivity. IFSHs may reflect the aberrant accumulation of amyloid β beyond age.

CSF pulsations measured in Parkinson's disease patients using EPI-based fMRI data

Introduction

Cerebrospinal fluid (CSF) flow is involved in brain waste clearance and may be impaired in neurodegenerative diseases such as Parkinson's disease. This study aims to investigate the relationship between the CSF pulsation and the development of dementia in Parkinson's disease (PD) patients using EPI-based fMRI.

Methods

We measured CSF pulsation in the 4th ventricle of 17 healthy controls and 35 PD patients using a novel CSF pulsation index termed "CSFpulse" based on echo-planar imaging (EPI)-based fMRI. The PD patients were classified into a PD with dementia high-risk group (PDD-H, n = 19) and a low risk group (PDD-L, n = 16), depending on their development of dementia within 5 years after initial brain imaging. The size of the 4th ventricle was measured using intensity-based thresholding.

Results

We found that CSF pulsation was significantly higher in PD patients than in healthy controls, and that PD patients with high risk of dementia (PDD-H) had the highest CSF pulsation. We also observed an enlargement of the 4th ventricle in PD patients compared to healthy controls.

Conclusion

Our results suggest that CSF pulsation may be a potential biomarker for PD progression and cognitive decline, and that EPI-based fMRI can be a useful tool for studying CSF flow and brain function in PD.

A Long-Acting Lyotropic Liquid Crystalline Implant Promotes the Drainage of Macromolecules by Brain-Related Lymphatic System in Treating Aged Alzheimer's Disease

Numerous evidence has demonstrated that the brain is not an immune-privileged organ but possesses a whole set of lymphatic transport system, which facilitates the drainage of harmful waste from brains to maintain cerebral homeostasis. However, as individuals age, the shrinkage and dysfunction of meningeal and deep cervical lymphatic networks lead to reduced waste outflow and elevated neurotoxic molecules deposition, further inducing aging-associated cognitive decline, which act as one of the pathological mechanisms of Alzheimer's disease. Consequently, recovering the function of meningeal and deep cervical lymph node (dCLNs) networks (as an important part of the brain waste removal system (BWRS)) of aged brains might be a feasible strategy. Herein we showed that the drug brain-entering efficiency was highly related to administration routes (oral, subcutaneous, or dCLN delivery). Besides, by injecting a long-acting lyotropic liquid crystalline implant encapsulating cilostazol (an FDA-approved selective PDE-3 inhibitor) and donepezil hydrochloride (a commonly used symptomatic relief agent to inhibit acetylcholinesterase for Alzheimer's disease) near the deep cervical lymph nodes of aged mice (about 20 months), an increase of lymphatic vessel coverage in the nodes and meninges was observed, along with accelerated drainage of macromolecules from brains. Compared with daily oral delivery of cilostazol and donepezil hydrochloride, a single administered dual drugs-loaded long-acting implants releasing for more than one month not only elevated drug concentrations in brains, improved the clearing efficiency of brain macromolecules, reduced Aβ accumulation, enhanced cognitive functions of the aged mice, but improved patient compliance as well, which provided a clinically accessible therapeutic strategy toward aged Alzheimer's diseases.

The anatomic basis of leptomeningeal metastasis

Leptomeningeal metastasis (LM), or spread of cancer to the cerebrospinal fluid (CSF)-filled space surrounding the central nervous system, is a fatal complication of cancer. Entry into this space poses an anatomical challenge for cancer cells; movement of cells between the blood and CSF is tightly regulated by the blood-CSF barriers. Anatomical understanding of the leptomeninges provides a roadmap of corridors for cancer entry. This Review describes the anatomy of the leptomeninges and routes of cancer spread to the CSF. Granular understanding of LM by route of entry may inform strategies for novel diagnostic and preventive strategies as well as therapies.

Comparison of metabolic rates of ropivacaine in cerebrospinal fluid as inferred from plasma concentrations between elderly patients and young patients

BACKGROUND

With the aging of human society, more and more elderly patients have to undergo surgery and anesthesia. Clinical observations have indicated from time to time that spinal anesthesia in the elderly appears to last longer than in young people, although there is limited research in this area and the mechanism is unclear at present time. This research work is expected to help understand the decline of local anesthetic metabolism in cerebrospinal fluid of elderly patients so as to help them with precise anesthesia and rapid rehabilitation.

METHODS

Twenty patients with spinal anesthesia in orthopedic lower limb surgery were selected to study the rate of drug metabolism in cerebrospinal fluid in two age groups, i.e.,18-30 years old and 75-90 years old. Ropivacaine in peripheral blood is used as a probe to reflect the speed of drug metabolism in cerebrospinal fluid. The contents of total Aβ protein and hyaluronic acid in the cerebrospinal fluid were investigated as well.

RESULTS

The equivalent dose of ropivacaine anesthetizes the elderly group for a longer time. The metabolism rate of ropivacaine in an elderly patient was slower than that of a young patient. No significant difference in total Aβ protein between the two groups was observed while hyaluronic acid in the elderly group was significantly higher than that in the young group.

CONCLUSIONS

This study shows that the dose of ropivacaine should be reduced when used for anesthesia in elderly patients. The cumulation of ropivacaine and HA appears to imitate the degeneration of central lymphatic circulation metabolism in elderly people.

Myeloid cells in vascular dementia and Alzheimer's disease: Possible therapeutic targets?

Growing evidence supports the suggestion that the peripheral immune system plays a role in different pathologies associated with cognitive impairment, such as vascular dementia (VD) or Alzheimer's disease (AD). The aim of this review is to summarize, within the peripheral immune system, the implications of different types of myeloid cells in AD and VD, with a special focus on post-stroke cognitive impairment and dementia (PSCID). We will review the contributions of the myeloid lineage, from peripheral cells (neutrophils, platelets, monocytes and monocyte-derived macrophages) to central nervous system (CNS)-associated cells (perivascular macrophages and microglia). Finally, we will evaluate different potential strategies for pharmacological modulation of pathological processes mediated by myeloid cell subsets, with an emphasis on neutrophils, their interaction with platelets and the process of immunothrombosis that triggers neutrophil-dependent capillary stall and hypoperfusion, as possible effector mechanisms that may pave the way to novel therapeutic avenues to stop dementia, the epidemic of our time. LINKED ARTICLES: This article is part of a themed issue From Alzheimer's Disease to Vascular Dementia: Different Roads Leading to Cognitive Decline. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.6/issuetoc.

Dynamic Contrast-enhanced MRI Quantification of Altered Vascular Permeability in Autoimmune Encephalitis

Background Blood-brain barrier (BBB) permeability change is a possible pathologic mechanism of autoimmune encephalitis. Purpose To evaluate the change in BBB permeability in patients with autoimmune encephalitis as compared with healthy controls by using dynamic contrast-enhanced (DCE) MRI and to explore its predictive value for treatment response in patients. Materials and Methods This single-center retrospective study included consecutive patients with probable or possible autoimmune encephalitis and healthy controls who underwent DCE MRI between April 2020 and May 2021. Automatic volumetric segmentation was performed on three-dimensional T1-weighted images, and volume transfer constant (Ktrans) values were calculated at encephalitis-associated brain regions. Ktrans values were compared between the patients and controls, with adjustment for age and sex with use of a nonparametric approach. The Wilcoxon rank sum test was performed to compare Ktrans values of the good (improvement in modified Rankin Scale [mRS] score of at least two points or achievement of an mRS score of  ≤2) and poor (improvement in mRS score of less than two points and achievement of an mRS score >2) treatment response groups among the patients. Results Thirty-eight patients with autoimmune encephalitis (median age, 38 years [IQR, 29-59 years]; 20 [53%] female) and 17 controls (median age, 71 years [IQR, 63-77 years]; 12 [71%] female) were included. All brain regions showed higher Ktrans values in patients as compared with controls (P < .001). The median difference in Ktrans between the patients and controls was largest in the right parahippocampal gyrus (25.1 × 10-4 min-1 [95% CI: 17.6, 43.4]). Among patients, the poor treatment response group had higher baseline Ktrans values in both cerebellar cortices (P = .03), the left cerebellar cortex (P = .02), right cerebellar cortex (P = .045), left cerebral cortex (P = .045), and left postcentral gyrus (P = .03) than the good treatment response group. Conclusion DCE MRI demonstrated that BBB permeability was increased in all brain regions in patients with autoimmune encephalitis as compared with controls, and baseline Ktrans values were higher in patients with poor treatment response in the cerebellar cortex, left cerebral cortex, and left postcentral gyrus as compared with the good response group. © RSNA, 2024 Supplemental material is available for this article. See also the editorial by Filippi and Rocca in this issue.

Glymphatic and lymphatic communication with systemic responses during physiological and pathological conditions in the central nervous system

Crosstalk between central nervous system (CNS) and systemic responses is important in many pathological conditions, including stroke, neurodegeneration, schizophrenia, epilepsy, etc. Accumulating evidence suggest that signals for central-systemic crosstalk may utilize glymphatic and lymphatic pathways. The glymphatic system is functionally connected to the meningeal lymphatic system, and together these pathways may be involved in the distribution of soluble proteins and clearance of metabolites and waste products from the CNS. Lymphatic vessels in the dura and meninges transport cerebrospinal fluid, in part collected from the glymphatic system, to the cervical lymph nodes, where solutes coming from the brain (i.e., VEGFC, oligomeric α-syn, β-amyloid) might activate a systemic inflammatory response. There is also an element of time since the immune system is strongly regulated by circadian rhythms, and both glymphatic and lymphatic dynamics have been shown to change during the day and night. Understanding the mechanisms regulating the brain-cervical lymph node (CLN) signaling and how it might be affected by diurnal or circadian rhythms is fundamental to find specific targets and timing for therapeutic interventions.

Unraveling the mechanisms of NK cell dysfunction in aging and Alzheimer's disease: insights from GWAS and single-cell transcriptomics

Background

Aging is an important factor in the development of Alzheimer's disease (AD). The senescent cells can be recognized and removed by NK cells. However, NK cell function is gradually inactivated with age. Therefore, this study used senescence as an entry point to investigate how NK cells affect AD.

Methods

The study validated the correlation between cognition and aging through a prospective cohort of the National Health and Nutrition Examination Survey database. A cellular trajectory analysis of the aging population was performed using single-cell nuclear transcriptome sequencing data from patients with AD and different ages. The genome-wide association study (GWAS) cohort of AD patients was used as the outcome event, and the expression quantitative trait locus was used as an instrumental variable. Causal associations between genes and AD were analyzed by bidirectional Mendelian randomization (MR) and co-localization. Finally, clinical cohorts were constructed to validate the expression of key genes.

Results

A correlation between cognition and aging was demonstrated using 2,171 older adults over 60 years of age. Gene regulation analysis revealed that most of the highly active transcription factors were concentrated in the NK cell subpopulation of AD. NK cell trajectories were constructed for different age populations. MR and co-localization analyses revealed that CHD6 may be one of the factors influencing AD.

Conclusion

We explored different levels of AD and aging from population cohorts, single-cell data, and GWAS cohorts and found that there may be some correlations of NK cells between aging and AD. It also provides some basis for potential causation.

Granulocyte macrophage colony-stimulating factor-induced macrophages of individuals with autism spectrum disorder adversely affect neuronal dendrites through the secretion of pro-inflammatory cytokines

BACKGROUND

A growing body of evidence suggests that immune dysfunction and inflammation in the peripheral tissues as well as the central nervous system are associated with the neurodevelopmental deficits observed in autism spectrum disorder (ASD). Elevated expression of pro-inflammatory cytokines in the plasma, serum, and peripheral blood mononuclear cells of ASD has been reported. These cytokine expression levels are associated with the severity of behavioral impairments and symptoms in ASD. In a prior study, our group reported that tumor necrosis factor-α (TNF-α) expression in granulocyte-macrophage colony-stimulating factor-induced macrophages (GM-CSF MΦ) and the TNF-α expression ratio in GM-CSF MΦ/M-CSF MΦ (macrophage colony-stimulating factor-induced macrophages) was markedly higher in individuals with ASD than in typically developed (TD) individuals. However, the mechanisms of how the macrophages and the highly expressed cytokines affect neurons remain to be addressed.

METHODS

To elucidate the effect of macrophages on human neurons, we used a co-culture system of control human-induced pluripotent stem cell-derived neurons and differentiated macrophages obtained from the peripheral blood mononuclear cells of five TD individuals and five individuals with ASD. All participants were male and ethnically Japanese.

RESULTS

Our results of co-culture experiments showed that GM-CSF MΦ affect the dendritic outgrowth of neurons through the secretion of pro-inflammatory cytokines, interleukin-1α and TNF-α. Macrophages derived from individuals with ASD exerted more severe effects than those derived from TD individuals.

LIMITATIONS

The main limitations of our study were the small sample size with a gender bias toward males, the use of artificially polarized macrophages, and the inability to directly observe the interaction between neurons and macrophages from the same individuals.

CONCLUSIONS

Our co-culture system revealed the non-cell autonomous adverse effects of GM-CSF MΦ in individuals with ASD on neurons, mediated by interleukin-1α and TNF-α. These results may support the immune dysfunction hypothesis of ASD, providing new insights into its pathology.

Yoda1 opens the lymphatic path for craniosynostosis therapy

The rediscovery of meningeal lymphatic vessels (MLVs) has sparked research interest in their function in numerous neurological pathologies. Craniosynostosis (CS) is caused by a premature fusion of cranial sutures during development. In this issue of the JCI, Matrongolo and colleagues show that Twist1-haploinsufficient mice that develop CS exhibit raised intracranial pressure, diminished cerebrospinal fluid (CSF) outflow, and impaired paravascular CSF-brain flow; all features that were associated with MLV defects and exacerbated pathology in mouse models of Alzheimer's disease. Activation of the mechanosensor Piezo1 with Yoda1 restored MLV function and CSF perfusion in CS models and in aged mice, opening an avenue for further development of therapeutics.

Computational fluid dynamic modeling of the lymphatic system: a review of existing models and future directions

Historically, research into the lymphatic system has been overlooked due to both a lack of knowledge and limited recognition of its importance. In the last decade however, lymphatic research has gained substantial momentum and has included the development of a variety of computational models to aid understanding of this complex system. This article reviews existing computational fluid dynamic models of the lymphatics covering each structural component including the initial lymphatics, pre-collecting and collecting vessels, and lymph nodes. This is followed by a summary of limitations and gaps in existing computational models and reasons that development in this field has been hindered to date. Over the next decade, efforts to further characterize lymphatic anatomy and physiology are anticipated to provide key data to further inform and validate lymphatic fluid dynamic models. Development of more comprehensive multiscale- and multi-physics computational models has the potential to significantly enhance the understanding of lymphatic function in both health and disease.

The nasal lymphatic route of CSF outflow: implications for neurodegenerative disease diagnosis and monitoring

Cerebrospinal fluid (CSF) plays a crucial role in the brain's lymphatics as it traverses the central nervous system (CNS). Its primary function is to facilitate the outward transport of waste. Among the various CSF outflow pathways, the route through the cribriform plate along the olfactory nerves stands out as the most predominant. This review describes the outflow pathway of CSF into the nasal lymphatics. Additionally, we examine existing studies to describe mutual influences observed between the brain and extracranial regions due to this outflow pathway. Notably, pathological conditions in the CNS often influence CSF outflow, leading to observable changes in extracranial regions. The established connection between the brain and the nose is significant, and our review underscores its potential relevance in monitoring CNS ailments, including neurodegenerative diseases. Considering that aging - the most significant risk factor for the onset of neurodegeneration - is also a principal factor in CSF turnover alterations, we suggest a novel approach to studying neurodegenerative diseases in therapeutic terms.

Imaging of brain barrier inflammation and brain fluid drainage in human neurological diseases

The intricate relationship between the central nervous system (CNS) and the immune system plays a crucial role in the pathogenesis of various neurological diseases. Understanding the interactions among the immunopathological processes at the brain borders is essential for advancing our knowledge of disease mechanisms and developing novel diagnostic and therapeutic approaches. In this review, we explore the emerging role of neuroimaging in providing valuable insights into brain barrier inflammation and brain fluid drainage in human neurological diseases. Neuroimaging techniques have enabled us not only to visualize and assess brain structures, but also to study the dynamics of the CNS in health and disease in vivo. By analyzing imaging findings, we can gain a deeper understanding of the immunopathology observed at the brain-immune interface barriers, which serve as critical gatekeepers that regulate immune cell trafficking, cytokine release, and clearance of waste products from the brain. This review explores the integration of neuroimaging data with immunopathological findings, providing valuable insights into brain barrier integrity and immune responses in neurological diseases. Such integration may lead to the development of novel diagnostic markers and targeted therapeutic approaches that can benefit patients with neurological disorders.

Deregulation of the Glymphatic System in Alzheimer's Disease: Genetic and Non-Genetic Factors

Alzheimer's disease (AD) is the most prevalent form of dementia and is characterized by progressive degeneration of brain function. AD gradually affects the parts of the brain that control thoughts, language, behavior and mental function, severely impacting a person's ability to carry out daily activities and ultimately leading to death. The accumulation of extracellular amyloid-β peptide (Aβ) and the aggregation of intracellular hyperphosphorylated tau are the two key pathological hallmarks of AD. AD is a complex condition that involves both non-genetic risk factors (35%) and genetic risk factors (58-79%). The glymphatic system plays an essential role in clearing metabolic waste, transporting tissue fluid, and participating in the immune response. Both non-genetic and genetic risk factors affect the glymphatic system to varying degrees. The main purpose of this review is to summarize the underlying mechanisms involved in the deregulation of the glymphatic system during the progression of AD, especially concerning the diverse contributions of non-genetic and genetic risk factors. In the future, new targets and interventions that modulate these interrelated mechanisms will be beneficial for the prevention and treatment of AD.

Age-related Decline of Intrinsic Cerebrospinal Fluid Outflow in Healthy Humans Detected with Non-contrast Spin-labeling MR Imaging

PURPOSE

Clearance of cerebrospinal fluid (CSF) is important for the removal of toxins from the brain, with implications for neurodegenerative diseases. Imaging evaluation of CSF outflow in humans has been limited, relying on venous or invasive intrathecal injections of contrast agents. The objective of this study was to introduce a novel spin-labeling MRI technique to detect and quantify the movement of endogenously tagged CSF, and then apply it to evaluate CSF outflow in normal humans of varying ages.

METHODS

This study was performed on a clinical 3-Tesla MRI scanner in 16 healthy subjects with an age range of 19-71 years with informed consent. Our spin-labeling MRI technique applies a tag pulse on the brain hemisphere, and images the outflow of the tagged CSF into the superior sagittal sinus (SSS). We obtained 3D images in real time, which was analyzed to determine tagged-signal changes in different regions of the meninges involved in CSF outflow. Additionally, the signal changes over time were fit to a signal curve to determine quantitative flow metrics. These were correlated against subject age to determine aging effects.

RESULTS

We observed the signal of the tagged CSF moving from the dura mater and parasagittal dura, and finally draining into the SSS. In addition, we observed a possibility of another pathway which is seen in some young subjects. Furthermore, quantitative CSF outflow metrics were shown to decrease significantly with age.

CONCLUSION

We demonstrate a novel non-invasive MRI technique identifying two intrinsic CSF clearance pathways, and observe an age-related decline of CSF flow metrics in healthy subjects. Our work provides a new opportunity to better understand the relationships of these CSF clearance pathways during the aging process, which may ultimately provide insight into the age-related prevalence of neurodegenerative diseases.

The Interplay between Meningeal Lymphatic Vessels and Neuroinflammation in Neurodegenerative Diseases

Meningeal lymphatic vessels (MLVs) are essential for the drainage of cerebrospinal fluid, macromolecules, and immune cells in the central nervous system. They play critical roles in modulating neuroinflammation in neurodegenerative diseases. Dysfunctional MLVs have been demonstrated to increase neuroinflammation by horizontally blocking the drainage of neurotoxic proteins to the peripheral lymph nodes. Conversely, MLVs protect against neuroinflammation by preventing immune cells from becoming fully encephalitogenic. Furthermore, evidence suggests that neuroinflammation affects the structure and function of MLVs, causing vascular anomalies and angiogenesis. Although this field is still in its infancy, the strong link between MLVs and neuroinflammation has emerged as a potential target for slowing the progression of neurodegenerative diseases. This review provides a brief history of the discovery of MLVs, introduces in vivo and in vitro MLV models, highlights the molecular mechanisms through which MLVs contribute to and protect against neuroinflammation, and discusses the potential impact of neuroinflammation on MLVs, focusing on recent progress in neurodegenerative diseases.

Transcranial photobiomodulation for brain diseases: review of animal and human studies including mechanisms and emerging trends

The brain diseases account for 30% of all known diseases. Pharmacological treatment is hampered by the blood-brain barrier, limiting drug delivery to the central nervous system (CNS). Transcranial photobiomodulation (tPBM) is a promising technology for treating brain diseases, due to its effectiveness, non-invasiveness, and affordability. tPBM has been widely used in pre-clinical experiments and clinical trials for treating brain diseases, such as stroke and Alzheimer's disease. This review provides a comprehensive overview of tPBM. We summarize emerging trends and new discoveries in tPBM based on over one hundred references published in the past 20 years. We discuss the advantages and disadvantages of tPBM and highlight successful experimental and clinical protocols for treating various brain diseases. A better understanding of tPBM mechanisms, the development of guidelines for clinical practice, and the study of dose-dependent and personal effects hold great promise for progress in treating brain diseases.

CCBE1 regulates the development and prevents the age-dependent regression of meningeal lymphatics

Recent studies have described the importance of lymphatics in numerous organ-specific physiological and pathological processes. The role of meningeal lymphatics in various neurological and cerebrovascular diseases has been suggested. It has also been shown that these structures develop postnatally and are altered by aging and that the vascular endothelial growth factor C (VEGFC)/ vascular endothelial growth factor receptor 3 (VEGFR3) signaling plays an essential role in the development and maintenance of them. However, the molecular mechanisms governing the development and maintenance of meningeal lymphatics are still poorly characterized. Recent in vitro cell culture-based experiments, and in vivo studies in zebrafish and mouse skin suggest that collagen and calcium binding EGF domains 1 (CCBE1) is involved in the processing of VEGFC. However, the organ-specific role of CCBE1 in developmental lymphangiogenesis and maintenance of lymphatics remains unclear. Here, we aimed to investigate the organ-specific functions of CCBE1 in developmental lymphangiogenesis and maintenance of meningeal lymphatics during aging. We demonstrate that inducible deletion of CCBE1 leads to impaired postnatal development of the meningeal lymphatics and decreased macromolecule drainage to deep cervical lymph nodes. The structural integrity and density of meningeal lymphatics are gradually altered during aging. Furthermore, the meningeal lymphatic structures in adults showed regression after inducible CCBE1 deletion. Collectively, our results indicate the importance of CCBE1-dependent mechanisms not only in the development, but also in the prevention of the age-related regression of meningeal lymphatics. Therefore, targeting CCBE1 may be a good therapeutic strategy to prevent age-related degeneration of meningeal lymphatics.

Enhanced Brain Clearance of Tau and Amyloid-β in Alzheimer's Disease Patients by Transcranial Radiofrequency Wave Treatment: A Central Role of Vascular Endothelial Growth Factor (VEGF)

Background

While drainage/removal of fluid and toxins from the brain by cerebrospinal fluid (CSF) directly into venous blood is well-known, a second drainage route has recently been (re)discovered-meningeal lymphatic vessels (mLVs)-which are responsible for up to half of total brain fluid/toxin drainage. The cytokine vascular endothelial growth factor (VEGF) increases mLV diameter and numbers to increase mLV drainage, resulting in increased mLV drainage. Alzheimer's disease (AD) is characterized by low plasma and CSF levels of VEGF.

Objective

To determine if non-invasive transcranial radiofrequency wave treatment (TRFT), through modulation of VEGF levels in blood and CSF, can affect removal of toxins tau and amyloid-β (Aβ) from the brain.

Methods

Eight mild/moderate AD subjects were given twice-daily 1-hour TRFT sessions at home by their caregivers. Blood and CSF samples were taken at baseline and following completion of 2 months of TRFT.

Results

In plasma and/or CSF, strong baseline correlations between VEGF levels and AD markers (t-tau, p-tau, Aβ1-40, Aβ1-42) were eliminated by TRFT. This effect was primarily due to TRFT-induced increases in VEGF levels in AD subjects with low or unmeasurable "baseline" VEGF levels. These increased VEGF levels were associated with increased clearance/drainage of tau and Aβ from the brain, likely through VEGF's actions on mLVs.

Conclusions

A new mechanism of TRFT is identified (facilitation of brain tau and Aβ clearance via VEGF) that is likely contributory to TRFT's reversal of cognitive impairment in AD subjects. TRFT may be particularly effective for cognitive benefit in AD subjects who have low VEGF levels.

The Drainage Dysfunction of Meningeal Lymphatic Vessels Is Correlated with the Recurrence of Chronic Subdural Hematoma: a Prospective Study

Meningeal lymphatic vessels (mLVs) were recently discovered to be involved in the waste drainage process in the brain, which has also been associated with a variety of neurological diseases. This research paper hypothesizes that the drainage function of mLVs may be affected after chronic subdural hematoma (CSDH) and the alterations of mLVs' drainage may predict CSDH recurrence. In this prospective observational study, unenhanced 3D T2-fluid-attenuated inversion recovery (3D T2-FLAIR) MRI data were collected from CSDH patients and healthy participants for analysis. Patients with CSDH who underwent surgery received MRI scans before and after surgery, whereas healthy controls and patients with CSDH who received pharmaceutical treatment received only one MRI scan at enrollment. The signal unit ratio (SUR) of mLVs were then measured according to the MRI data and calculated to define mLVs' drainage function. Finally, the relationship between mLVs' drainage function and CSDH recurrence was analyzed accordingly. Thirty-four participants were enrolled in this study, including 27 CSDH patients and 7 controls. The SUR of mLVs in all CSDH patients changed significantly before and after surgery. Moreover, the drainage function of the mLVs ipsilateral to hematoma (mLVs-IH) in CSDH patients was significantly lower than that in the controls (p < 0.05). Last, a higher improvement rate of the drainage function of the mLVs-IH is correlated to a lower risk of recurrence (p < 0.05). This study revealed the mLVs' drainage dysfunction after CSDH through non-invasive MRI. Furthermore, the drainage function of mLVs is an independent predictive factor of CSDH recurrence.

Investigating the causal impact of gut microbiota on glioblastoma: a bidirectional Mendelian randomization study

BACKGROUND

Currently, the influence of microbiota on the occurrence, progression, and treatment of cancer is a topic of considerable research interest. Therefore, based on the theory of the gut-brain axis proved by previous studies, our objective was to uncover the causal relationship between glioblastoma and the gut microbiome using Mendelian randomization analysis.

METHODS

We conducted a bidirectional Mendelian randomization study using summary statistics of gut microbiota derived from the MiBioGen consortium, the largest database of gut microbiota. Summary statistics for glioblastoma were obtained from IEU OpenGWAS project, which included 91 cases and 218,701 controls. We assessed the presence of heterogeneity and horizontal pleiotropy in the analyzed data. We primarily employed the inverse variance weighting method to investigate the causal relationship between gut microbiota and glioblastoma after excluding cases of horizontal pleiotropy. Four other analysis methods were employed as supplementary. Excluding abnormal results based on leave-one-out sensitivity analysis. Finally, reverse Mendelian randomization analysis was performed.

RESULTS

Four genus-level taxa and one family-level taxa exhibited causal associations with glioblastoma. And these results of reverse Mendelian randomization analysis shown glioblastoma exhibited causal associations with three genus-level taxa and one family-level taxa. However, the Prevotella7(Forward, P=0.006, OR=0.34, 95%CI:0.158-0.732; Reverse, P=0.004, OR=0.972, 95%CI:0.953-0.991) shown the causal associations with glioblastoma in the bidirectional Mendelian randomization.

CONCLUSIONS

In this bidirectional Mendelian randomization study, we identified five gut microbiota species with causal associations to glioblastoma. However, additional randomized controlled trials are required to clarify the impact of gut microbiota on glioblastoma and to reveal its precise mechanisms.

Disturbed meningeal lymphatic function associated with malignancy and progression in patients with intracranial malignant tumors

BACKGROUND

Meningeal lymphatic vessels (mLVs) have proven to bear a relationship with tumor immunity and therapeutic efficacy of intracranial malignant tumors in pre-clinical animal studies. We aimed to explore the association between mLV function and intracranial malignant tumors in clinical participants.

METHODS

The participants were allocated to a control group or a group of patients with intracranial tumors. Dynamic enhanced magnetic resonance was used to evaluate the wash-in and wash-out functions of mLVs around the superior sagittal sinus and the sigmoid sinus.

FINDINGS

A total of 246 individuals were recruited for our study. The area under curve and wash-in rate of mLVs in the intracranial tumor group were higher than in the control group (2,749 vs. 2,110, p < 0.001 and 3.72 vs. 2.87, p < 0.001, respectively). The wash-out ratio of mLVs was lower in the intracranial tumor group than in the control group (0.65 vs. 0.73, p < 0.001). Decreased wash-out of mLVs was associated with tumor progression (β = -0.118; p < 0.001). High-grade glioma and isocitrate dehydrogenase wild type were associated with a lower mLV wash-out function (β = -0.057, p = 0.044 and β = -0.069, p = 0.047, respectively).

CONCLUSIONS

Intracranial malignant tumors were associated with elevated wash-in function and decreased wash-out function of mLVs. High-grade glioma and isocitrate dehydrogenase wild type were associated with low mLV wash-out function, and long-term decreased mLV wash-out function was a risk factor for tumor progression.

FUNDING

There was no funding.