Glymphatic dysfunction in patients with early-stage amyotrophic lateral sclerosis

Tissue-to-fluid water-exchange imaging using T2-selective saturation labeling

PURPOSE

To propose and implement a new method to study water exchange between brain tissue and fluids.

METHODS

An MLEV T2-preparation combined with a cerebrospinal fluid (CSF) nulling inversion recovery was implemented in combination with an ultralong-echo time (TE) three-dimensional fast spin-echo readout. To handle systematic imperfections and isolate the exchange signal, T2-prepared images were subtracted from one of two control images. The first control turned off the T2 preparation and adjusted inversion timing to correct for relaxation. The second control used the same T2 preparation but shifted in time. Preparations were implemented on a 3T scanner and tested in 14 healthy volunteers. We evaluated the exchange signal magnitude and distribution, as well as robustness against B1 imperfection and intrasession reproducibility. We also compared the signal to that measured with ultralong-TE arterial spin labeling, another suggested marker of water exchange.

RESULTS

Initial experiments using the T2-preparation off control demonstrated a detectable exchange signal especially in the choroid plexus, but with substantial residual signal in CSF spaces, suggesting imperfect subtraction of non-exchanging spins. When using the time shifted control, we greatly reduced subtraction errors. Signal was consistently measured in the choroid plexus and at the boundaries between cortex and CSF with much higher signal-to-noise ratio and spatial resolution than ultralong-TE arterial spin labeling.

CONCLUSIONS

The measured water exchange distribution appears consistent with the localization of aquaporin channels at the CSF boundary. Because aquaporin activity may reflect CSF production and glymphatic clearance, our method may provide a noninvasive marker of these functions.

Exosomes in Regulating miRNAs for Biomarkers of Neurodegenerative Disorders

Exosomal proteins and miRNAs, including α-synuclein, Aβ, tau, CXCL12, miR-24, and miR-23b-3p, are emerging as valuable biomarkers for Parkinson's disease and prenatal diagnostics, with significant potential for personalized therapies. Advances in MRI and chitosan-based drug delivery systems are creating new opportunities for diagnosing and treating neurodegenerative disorders. Exosomes regulate miRNAs and proteins, presenting theranostic potential for Alzheimer's and Huntington's diseases, yet facing delivery and targeting challenges. Exosomal miRNAs, such as miR-1234, miR-5678, and miR-29a, are crucial for the early detection and monitoring of the progression of neurodegenerative diseases. Additionally, novel biomarkers such as SCA27B and FGF14 gene mutations and serum miR-455-3p offer promising noninvasive diagnostic methods for Alzheimer's disease. The expanding role of exosome-derived miRNAs in targeting oncogenes and regulating the cell cycle enhances therapeutic strategies for neurological disorders, opening doors to more personalized and effective disease management.

Selective removal of astrocytic PERK protects against glymphatic impairment and decreases toxic aggregation of β-amyloid and tau

Dysfunction of the glymphatic system, a brain-wide waste clearance network, is strongly linked to Alzheimer's disease (AD) and the accumulation of β-amyloid (Aβ) and tau proteins. Here, we identify an astrocytic signaling pathway that can be targeted to preserve glymphatic function and mitigate neurotoxic protein buildup. Analysis of astrocytes from both human AD brains and two transgenic mouse models (5XFAD and PS19) reveals robust activation of the protein kinase RNA-like endoplasmic reticulum (ER) kinase (PERK)-α subunit of eukaryotic initiation factor 2 (eIF2α) branch of the unfolded protein response. Chronic PERK activation suppresses astrocytic protein synthesis and, through casein kinase 2 (CK2)-dependent mechanisms, disrupts the perivascular localization of aquaporin-4 (AQP4), a water channel essential for glymphatic flow. Importantly, astrocyte-specific PERK deletion or pharmacological inhibition restores AQP4 localization, enhances glymphatic clearance, reduces Aβ and tau pathology, and improves cognitive performance in mice. These findings highlight the critical role of the astrocytic PERK-CK2-AQP4 axis in glymphatic dysfunction and AD pathogenesis, positioning this pathway as a promising therapeutic target.

Glymphatic dysfunction in relapsing-remitting multiple sclerosis and its association with brain structural damage and cognitive impairment

OBJECTIVE

To explore the glymphatic dysfunction in relapsing-remitting multiple sclerosis (RRMS) and its potential associations with brain structural damage, clinical disability, and cognitive impairment (Co-I).

METHODS

The study involved 70 patients with RRMS and 44 healthy controls. Neurological and MRI assessments were performed, and cognitive performance was assessed via the Brief Repeatable Battery of Neuropsychological Tests (BRB-N). To assess the glymphatic function, we calculated the choroid plexus volume (CPV) and diffusion tensor imaging along perivascular spaces (DTI-ALPS) index. Multivariable linear regression analyses were used to examine correlations between glymphatic dysfunction and MRI-derived brain damage metrics. Additionally, we utilised random forest analysis to identify predictors of Co-I and assessed the mediating role of DTI-ALPS.

RESULTS

Patients with RRMS, particularly those with Co-I, exhibited a low DTI-ALPS index and large CPV. A lower DTI-ALPS index was associated with longer disease duration, greater disability, larger lesion volume (LV), mean diffusivity (MD), and CPV, as well as lower fractional anisotropy (FA) (all FDR-p < 0.05). Moreover, DTI-ALPS mediated 27.21 % and 43.75 % of CPV effects on information processing speed and visuospatial memory, respectively. Random forest analysis indicated that lower education (relative importance [RI] = 100 %), higher CPV (RI = 95.8 %), lower DTI-ALPS index (RI = 80.7 %), higher MD (RI = 61.3 %), lower FA (RI = 60.5 %), older age (RI = 54.6 %), and higher EDSS score (RI = 45.4 %) are predictors of Co-I.

CONCLUSION

The study implied that glymphatic dysfunction may contribute to brain structural damage, clinical disability, and cognitive impairment in RRMS, indicating that glymphatic dysfunction may play a key role in the pathogenesis of RRMS.

Assessment of the glymphatic dysfunction in amyotrophic lateral sclerosis using the diffusion tensor imaging along the perivascular spaces index: a pilot study

Background

The glymphatic system plays a critical role in clearing interstitial waste from the brain. Dysfunction of this system has been linked to various neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). The diffusion tensor imaging-along the perivascular space (DTI-ALPS) index has emerged as a potential neuroimaging biomarker for evaluating glymphatic function. This study investigates whether glymphatic function differs in individuals with ALS compared to those with Parkinson's disease (PD) and normal controls (NCs), using the DTI-ALPS index.

Methods

This study included 35 ALS patients, 35 age- and sex-matched PD patients, and 13 NCs. Diffusion tensor imaging (DTI) was conducted, and the DTI-ALPS index was calculated. Clinical assessments included demographic data, disease duration, cognitive status, and functional scales. Group comparisons and correlation analyses were performed to assess the relationship between the DTI-ALPS index and clinical parameters.

Results

The ALS group exhibited a significantly lower right-side DTI-ALPS index than the NC group (p = 0.037), while no differences were observed between the ALS and PD groups. The DTI-ALPS index was negatively correlated with age in ALS and PD groups but showed no correlation with clinical measures in the ALS group. Women in the ALS group had a significantly higher DTI-ALPS index than in men.

Conclusion

Glymphatic dysfunction may contribute to the pathogenesis of ALS, as evidenced by a reduced DTI-ALPS index compared to NCs. However, its clinical relevance and specificity for ALS remain uncertain. Further studies with larger cohorts are warranted to validate these findings.

Sleep disturbances are related to glymphatic dysfunction in blepharospasm

Research has shown a close relationship between sleep and glymphatic function, with impaired glymphatic function potentially contributing to sleep problems in a bidirectional way. However, its role in sleep disturbances associated with dystonia remains unknown. This cross-sectional study aimed to investigate whether glymphatic function is impaired in dystonia and to explore its relationship with sleep disturbances. We conducted structural magnetic resonance imaging and diffusion tensor imaging (DTI) on two large cohorts: patients with blepharospasm (BSP, n = 45) and cervical dystonia (CD, n = 43), alongside age- and sex-matched healthy controls (HCs). Anxiety, depression, and sleep quality were evaluated using the Hamilton Anxiety Scale (HAMA), Hamilton Depression Scale (HAMD), and Pittsburgh Sleep Quality Index (PSQI), respectively. Analysis along the perivascular space (DTI-ALPS) index and choroid plexus volume (CPV) was used to assess glymphatic function in these participants. Patients with BSP and CD had higher HAMA, HAMD, and PSQI scores than those of HCs. Patients with BSP exhibited a lower DTI-ALPS index and larger CPV than those of HCs, while no significant differences were found between CD and HCs. In BSP and CD, PSQI scores positively correlated with HAMA and HAMD scores and negatively with the DTI-ALPS index in BSP. Multivariate analysis identified the DTI-ALPS index as a dependent predictive factor of the PSQI in patients with BSP. Our findings suggest that glymphatic function varies across types of focal dystonia, with glymphatic dysfunction potentially playing an important role in the pathogenesis of sleep disturbances in BSP.

Atrial fibrillation catheter ablation, brain glymphatic function, and cognitive performance

BACKGROUND AND AIMS

It remains unknown whether the brain glymphatic system, which is driven by the heartbeat-driven pulsation of arteries and is responsible for cerebral waste clearance, is impaired in atrial fibrillation (AF) and mediates cognitive dysfunction related to AF. The aim of this study was to assess brain glymphatic alterations in AF, their role in cognitive function, and whether catheter ablation can improve glymphatic activity.

METHODS

In this case-control and prospective before-and-after study, patients with AF and healthy controls (HCs) were enrolled. Participants underwent brain magnetic resonance imaging and a comprehensive neuropsychological battery. Glymphatic activity was quantified by diffusion tensor image analysis along the perivascular space (DTI-ALPS) index. Magnetic resonance imaging was repeated after surgery in patients who underwent ablation.

RESULTS

Overall, 87 patients with AF and 44 HCs were enrolled. Compared with HCs, patients with AF had a lower ALPS index (P = .016). Nonparoxysmal AF patients showed lower ALPS index than both HCs (P = .002) and paroxysmal AF patients (P = .044). A lower ALPS index was associated with worse scores of Trail Making Test, Digit Symbol Substitution Test, Digit Span Test, and Stroop Colour and Word Test (all P < .05). Mediation analyses revealed that glymphatic activity was a mediator between AF and cognitive decline. Among the 50 patients who underwent ablation therapy, DTI-ALPS index was improved after surgery (P = .015).

CONCLUSIONS

Brain glymphatic function measured by DTI-ALPS index was impaired in patients with AF, mediates the association between AF and cognitive decline, and was improved after ablation therapy.

Meningeal lymphatic drainage: novel insights into central nervous system disease

In recent years, increasing evidence has suggested that meningeal lymphatic drainage plays a significant role in central nervous system (CNS) diseases. Studies have indicated that CNS diseases and conditions associated with meningeal lymphatic drainage dysfunction include neurodegenerative diseases, stroke, infections, traumatic brain injury, tumors, functional cranial disorders, and hydrocephalus. However, the understanding of the regulatory and damage mechanisms of meningeal lymphatics under physiological and pathological conditions is currently limited. Given the importance of a profound understanding of the interplay between meningeal lymphatic drainage and CNS diseases, this review covers seven key aspects: the development and structure of meningeal lymphatic vessels, methods for observing meningeal lymphatics, the function of meningeal lymphatics, the molecular mechanisms of meningeal lymphatic injury, the relationships between meningeal lymphatic vessels and CNS diseases, potential regulatory mechanisms of meningeal lymphatics, and conclusions and outstanding questions. We will explore the relationship between the development, structure, and function of meningeal lymphatics, review current methods for observing meningeal lymphatic vessels in both animal models and humans, and identify unresolved key points in meningeal lymphatic research. The aim of this review is to provide new directions for future research and therapeutic strategies targeting meningeal lymphatics by critically analyzing recent advancements in the field, identifying gaps in current knowledge, and proposing innovative approaches to address these gaps.

Diffusion along Perivascular Spaces as a Marker for Glymphatic System Impairment in Huntington's Disease

BACKGROUND

The aim was to investigate if glymphatic function is impaired in patients with Huntington's disease (HD) and its clinical relevance.

METHODS

Forty-nine subjects carrying mutant Huntingtin (mHTT), comprising 35 manifest (mHD) and 14 pre-manifest (PreHD), and 35 healthy controls (HC) were recruited in this study. The diffusion along perivascular spaces (ALPS) index and the percentage of perivascular space in the basal ganglia (pPVS_BG) were obtained in different groups. The discrimination effects of ALPS index were detected using receiver operating characteristic (ROC) analysis, and the correlations of ALPS index with clinical features of HD were further analyzed.

RESULTS

ALPS index was decreased in mHTT carriers compared to HCs, and it was lower in mHD compared to PreHD patients. ROC analysis showed that the ALPS index could discriminate mHTT from HC (AUC [area under the curve] = 0.903), mHD from PreHD (AUC = 0.886), and PreHD from controls (AUC = 0.755). Lower ALPS index correlated with greater disease burden, severity of the disease, lager pPVS_BG, and lower brain volume and thickness of cortices. Regression analysis showed that ALPS index could predict the performance of motor and cognitive functions. Mediation analysis revealed that ALPS partially mediated the effects of CAG repeat and age on the cognitive decline in HD.

CONCLUSIONS

This study demonstrated that the impairment of the glymphatic system, especially in the paraventricular white matter and BG, was correlated with the clinical manifestations, disease burden, and brain structural changes in mHTT carriers. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Association between sleep and ALS-FTSD: A Prospective Cohort Study based on 396,918 UK biobank participants

Amyotrophic lateral sclerosis-frontotemporal spectrum disorder (ALS-FTSD) is a fatal neurodegenerative condition, and identifying its modifiable risk factors is a critical public health issue. This large-scale prospective cohort study investigated the role of sleep-related factors in ALS-FTSD risk using data from 396,918 UK Biobank participants. Eight sleep-related exposures were assessed, and Cox proportional hazards regression was employed to evaluate their associations with ALS-FTSD incidence. Subgroup and sensitivity analyses were conducted to validate the robustness of our findings. At baseline, participants had a mean age of 56.31 ± 8.12 years, with 47.5% being male. In the fully adjusted Cox model, organic sleep disorders (G47) (HR: 1.81, 95% CI: 1.21, 2.72, P = 0.004), hypersomnia (G47.1) (HR: 36.53, 95% CI: 9.04, 147.55, P < 0.001), and extreme short sleep (<5 h per day) (HR: 2.09, 95% CI: 1.09, 3.99, P = 0.046) were significantly associated with increased ALS-FTSD risk. In conclusions, these findings revealed the relationship between sleep and the risk of ALS-FTSD, identifying new modifiable risk factors and potential preventive possibilities for ALS-FTSD. Further research is warranted to elucidate the mechanistic links between sleep disturbances and ALS-FTSD pathogenesis.

A comprehensive update on neuroimaging endpoints in amyotrophic lateral sclerosis

INTRODUCTION

There are currently few treatments approved for amyotrophic lateral sclerosis (ALS). Additionally, there remains a significant unmet need for reliable, standardized biomarkers to assess endpoints in clinical trials. Magnetic resonance imaging (MRI)- and positron emission tomography (PET)-derived metrics could help in patient selection and stratification, shortening trial duration and reducing costs.

AREAS COVERED

This review focuses on the potential use of neuroimaging endpoints in the context of ALS therapeutic trials, providing insights on structural and functional neuroimaging, plexus and muscle alterations, glial involvement and neuroinflammation, envisioning how these surrogates of disease progression could be implemented in clinical trials. A PubMed search covering the past 15 years was performed.

EXPERT OPINION

Neuroimaging is essential in understanding ALS pathophysiology, aiding in disease progression tracking and evaluating therapeutic interventions. High costs, limited accessibility, lack of standardization, and patient tolerability limit their use in routine ALS care. Addressing these obstacles is essential for fully harnessing neuroimaging potential in improving diagnostics and treatment in ALS.

Perivascular space and white matter hyperintensities in Alzheimer's disease: associations with disease progression and cognitive function

BACKGROUND

Alzheimer's disease (AD) is the leading cause of dementia, characterized by the accumulation of amyloid-beta (Aβ) and neurofibrillary tangles. Recent studies emphasize the role of vascular factors, including the glymphatic system, in AD pathogenesis, particularly in Aβ clearance. The diffusion tensor image analysis along the perivascular space (DTI-ALPS; ALPS-Index) has emerged as a novel, non-invasive method to evaluate the glymphatic system in vivo, showing glymphatic insufficiency in AD. This study aimed to investigate alterations in the function of the glymphatic system in individuals with AD versus healthy controls (HC), and to explore its association with Aβ, cerebrovascular disease (CVD), white matter hyperintensities (WMH), and cognitive function.

METHODS

DTI MRI data from three independent study cohorts (ActiGliA: AD n = 16, Controls n = 18; DELCODE: AD n = 54, Controls n = 67; ADNI: AD n = 43, Controls n = 49) were used to evaluate the perivascular space (PVS) integrity; a potential biomarker for glymphatic activity. The DTI-Along the Perivascular Space technique was used to measure water diffusion along PVS providing an index to assess the efficiency of the glymphatic system's waste clearance function. WMH load was quantified in FLAIR MRI using the lesion segmentation tool. We quantified WMHs volume within our defined region of interest (ROI) and excluded participants with any WMHs to avoid confounding the ALPS-Index. Associations with cerebrospinal fluid (CSF) AD hallmark biomarkers, cognitive performance (MMSE) and clinical severity (CDR) were assessed.

RESULTS

AD patients had a significantly lower ALPS-Index vs. healthy controls (ActiGliA: AD: mean = 1.22, SD = 0.12; Controls: mean = 1.36, SD = 0.14, p = 0.004; DELCODE: AD: mean = 1.26, SD = 0.18; Controls: mean = 1.34, SD = 0.2, p = 0.035; ADNI: AD: mean = 1.08, SD = 0.24; Controls: mean = 1.19, SD = 0.13, p = 0.008). The ALPS-Index was associated with CSF Aβ concentration, WMH number and MMSE and CDR. WMH, found in the ROIs correlated negatively with the ALPS-Index.

CONCLUSIONS

This study highlights the potential of the DTI-ALPS-Index as a biomarker for glymphatic dysfunction in AD. It underscores the importance of considering vascular factors and the glymphatic system in the pathogenesis and diagnosis of AD as WMHs in the ROI could cause disturbances and inaccurate indices.

Advancements in PROTAC-based therapies for neurodegenerative diseases

Neurodegenerative diseases are characterized by impairments in movement and cognitive functions. These disorders are frequently associated with the accumulation of misfolded protein aggregates, which present significant challenges for treatment with conventional small-molecule inhibitors. While FDA-approved amyloid-beta-directed antibodies, such as Lecanemab, have recently shown clinical success in modifying disease progression, there are currently no treatments capable of curing neurodegenerative diseases. Emerging technologies like proteolysis-targeting chimeras (PROTACs) offer additional promise by targeting disease-causing proteins for degradation, potentially opening new therapeutic avenues. Recent experiments have demonstrated that PROTACs can specifically target and degrade pathogenic proteins associated with neurodegenerative diseases, thereby offering potential therapeutic avenues. This review discusses the latest advances in employing PROTACs for treating neurodegenerative diseases and delves into the associated challenges and opportunities. Our goal is to provide researchers in drug development with new insights on creating novel PROTACs for therapeutic applications.

In vivo imaging markers of glymphatic dysfunction in amyotrophic lateral sclerosis: Analysis of ALPS index and choroid plexus volume

BACKGROUND

The glymphatic system, essential for brain waste clearance, has been implicated in neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). Emerging imaging markers, such as the analysis along the perivascular space (ALPS) index and choroid plexus volume (CPV), may provide insights into glymphatic function, but their relevance to ALS remains unclear.

OBJECTIVE

To assess glymphatic dysfunction in ALS patients using the ALPS index and CPV.

METHODS

In this prospective single-center study, we analyzed 51 ALS patients and 51 age- and sex-matched healthy controls (HC). The ALPS index was calculated using diffusion tensor imaging, and 3D T1-weighted MRI was used for automated estimation of CPV and its fraction (CPV/total intracranial volume). Diagnostic performance was assessed using area under the receiver operating curve (AUC). Correlations between imaging markers and clinical parameters were also examined.

RESULTS

ALS patients had a significantly lower ALPS index (ALS: 1.45 ± 0.15; HC: 1.55 ± 0.16; p = 0.002) and higher CPV fraction (ALS: 0.12 ± 0.04 %; HC: 0.10 ± 0.02 %; p < 0.001). The ALPS index and CPV fraction had AUCs of 0.70 and 0.72, respectively. A significant inverse correlation was observed between the ALPS index and CPV fraction (r = -0.31, p = 0.002). Both markers correlated with aging but not with clinical disability or progression rate.

CONCLUSION

This study identifies glymphatic dysfunction in ALS, as evidenced by changes in the ALPS index and CPV. Larger studies are warranted to validate these findings and assess their potential as biomarkers for ALS.

MR Imaging Indices for Brain Interstitial Fluid Dynamics and the Effects of Orexin Antagonists on Sleep

PURPOSE

The purpose of this study was to assess the extent to which improvement in sleep with lemborexant contributed to changes in interstitial fluid dynamics.

METHODS

The 3 methods including diffusion tensor image analysis along the perivascular space (DTI-ALPS), dynamic contrast-enhanced method to assess tissue vascular permeability (Ktrans), and choroid plexus volume (CPV) were used. Correlations between these imaging indices and sleep parameters (latency to persistent sleep [LPS], wake after sleep onset [WASO], total sleep time [TST], and sleep efficiency [SE]) were evaluated using Pearson correlation analysis. Additionally, multiple regression analysis and linear mixed model analysis were employed to assess the relationship between baseline sleep status and imaging parameter changes. MRI and sleep assessments were performed before treatment initiation (week 0, w0) and at 12 weeks after lemborexant administration (week 12, w12).

RESULTS

The ALPS-index was inversely correlated with LPS and positively correlated with TST and SE at w0. In multiple regression analysis, ALPS-index was lower when sleep parameters other than LPS were poor at w0. A linear mixed model analysis suggested that poor sleep status in LPS and SE at w0 may have an effect on greater ALPS-index. In the evaluation of Ktrans measurement, the single regression analysis showed a statistically significant correlation between the reduction in Ktrans and the shortening in LPS. Examination of CPV and sleep parameters showed a significant negative correlation between TST and CPV at w0 and w12. Multiple regression analysis also showed that TST of w12 had a significant effect on CPV at w12.

CONCLUSION

Our results suggested that poor sleep status is related to the greater change of ALPS-index and CPV improvement after lemborexant administration may be related to in part to sleep parameter improvement.

Early-onset sleep alterations found in patients with amyotrophic lateral sclerosis are ameliorated by orexin antagonist in mouse models

Sleep alterations have been described in several neurodegenerative diseases yet are currently poorly characterized in amyotrophic lateral sclerosis (ALS). This study investigates sleep macroarchitecture and related hypothalamic signaling disruptions in ALS. Using polysomnography, we found that both patients with ALS as well as asymptomatic C9ORF72 and SOD1 mutation carriers exhibited increased wakefulness and reduced non-rapid eye movement sleep. Increased wakefulness correlated with diminished cognitive performance in both clinical cohorts. Similar changes in sleep macroarchitecture were observed in three ALS mouse models (Sod1G86R, FusΔNLS/+, and TDP43Q331K). A single oral administration of a dual-orexin receptor antagonist or intracerebroventricular delivery of melanin-concentrating hormone (MCH) through an osmotic pump over 15 days partially normalized sleep patterns in mouse models. MCH treatment did not extend the survival of Sod1G86R mice but did decrease the loss of lumbar motor neurons. These findings suggest MCH and orexin signaling as potential targets to treat sleep alterations that arise in early stages of the disease.

Association of Glymphatic Function With Clinical Characteristics in Patients With Clinical and Asymptomatic Creutzfeldt-Jakob Disease

BACKGROUND AND OBJECTIVES

Abnormal glymphatic system-related proteins have been identified in a small-scale pathologic study of patients with Creutzfeldt-Jakob disease (CJD). However, it remains unclear whether glymphatic dysfunction occurs in vivo in patients with CJD and whether this decline begins during the preclinical stage. This study aimed to investigate the relationship between glymphatic dysfunction and clinical characteristics in patients with CJD, as well as potential glymphatic impairment in preclinical CJD.

METHODS

This prospective cohort study recruited patients with CJD and healthy controls (HCs) from the Department of Neurology at Xuanwu Hospital, Capital Medical University, Beijing, China, from 2018 to 2022. In addition, a family with preclinical genetic CJD carrying the G114V pathogenic variant was followed over 6 years with 3 evaluations. All participants underwent diffusion tensor imaging along the perivascular space (DTI-ALPS) to measure glymphatic function in vivo and 18F-fludeoxyglucose-PET to identify CJD-related metabolic patterns. Associations between the DTI-ALPS index and Medical Research Council Prion Disease Rating Scale (MRC-PDRS) score were evaluated using multiple linear regression.

RESULTS

We enrolled 35 patients with CJD (mean age 59.6 ± 10.7 years, 40% female, with the time from onset to glymphatic dysfunction assessment averaging 39% of the total disease course), 28 age-matched and sex-matched HCs, and a family with preclinical genetic CJD consisting of 7 carriers and 7 noncarriers. Patients with CJD exhibited lower DTI-ALPS values compared with HCs (p < 0.001). Partial correlation analyses revealed significant correlations between the DTI-ALPS index and MRC-PDRS score (r = 0.346, p = 0.049) and disease progression (r = -0.468, p = 0.006), but not with disease duration or cognitive severity after adjusting for age and sex. Multivariate linear analysis demonstrated that poorer MRC-PDRS scores (β = 0.702, p = 0.014) were associated with a lower DTI-ALPS index. The DTI-ALPS index of asymptomatic G114V carriers showed no significant difference compared with noncarriers. However, a preclinical CJD case exhibited an 8.2% decrease in the DTI-ALPS index 3.3 years before onset. No significant correlation was found between regional metabolic standardized uptake value ratios and DTI-ALPS index.

DISCUSSION

Our study indicates that glymphatic dysfunction is associated with CJD severity and disease progression. Glymphatic dysfunction may occur in the preclinical stage, but these findings should be interpreted with caution because they are based on individual findings.

Longitudinal analysis of glymphatic function in amyotrophic lateral sclerosis and primary lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder of motor neurons in the brain and spinal cord. Accumulation of misfolded proteins is central to the pathogenesis of ALS and the glymphatic system is emerging as a potential therapeutic target to reduce proteinopathy. Using diffusion tensor imaging analysis along the perivascular spaces (DTI-ALPS) to assess glymphatic function, we performed a longitudinal analysis of glymphatic function in ALS and compared it to a disorder in the motor neuron disease spectrum, primary lateral sclerosis (PLS). From a cohort of 45 participants from the Calgary site in the CALSNIC study (Canadian ALS Neuroimaging Consortium), including 18 ALS, 5 PLS and 22 control participants, DTI-ALPS was analysed and correlated to clinical features (age, sex, disease presentation, disease severity and progression rate) and white matter hyperintensity burden. This included longitudinal measurements at three time points, 4 months apart. The DTI-ALPS index was reduced in ALS participants compared with PLS and control participants across all three time points. There was no association with clinical factors; however, the index tended to decline with advancing age. Our study suggests heterogeneity in glymphatic dysfunction in motor neuron diseases that may be related to the underlying pathogenesis.

Glymphatic system dysfunction and risk of clinical milestones in patients with Parkinson disease

BACKGROUND AND PURPOSE

Glymphatic dysfunction may play a significant role in the development of neurodegenerative diseases. We aimed to evaluate the association between glymphatic dysfunction and the risk of malignant event/clinical milestones in Parkinson disease (PD).

METHODS

This study included 236 patients from August 2014 to December 2020. Diffusion tensor imaging analysis along the perivascular space (DTI-ALPS) index was calculated as an approximate measure of glymphatic function. The primary outcomes were four clinical milestones including recurrent falls, wheelchair dependence, dementia, and placement in residential or nursing home care. The associations of DTI-ALPS with the risk of clinical milestones were examined using multivariate Cox proportional hazards regression models. Then, logistic regression was repeated using clinical variables and DTI-ALPS index individually and in combination of the two to explore the ability to distinguish patients who reached clinical milestones within a 5-year period.

RESULTS

A total of 175 PD patients with baseline DTI-ALPS index and follow-up clinical assessments were included. A lower DTI-ALPS was independently associated with increased risk of recurrent falls, wheelchair dependence, and dementia. Additionally, in 103 patients monitored over 5 years, a logistic regression model combining clinical variables and DTI-ALPS index showed better performance for predicting wheelchair dependence within 5 years than a model using clinical variables or DTI-ALPS index alone.

CONCLUSIONS

Glymphatic dysfunction, as measured by the DTI-ALPS index, was associated with increased risk of clinical milestones in patients with PD. This finding implies that therapy targeting the glymphatic system may serve as a viable strategy for slowing down the progression of PD.

Evaluating the robustness of DTI-ALPS in clinical context: a meta-analytic parallel on Alzheimer's and Parkinson's diseases

In recent years, the glymphatic system has received increasing attention due to its possible implications in biological mechanisms associated with neurodegeneration. In the field of human brain mapping, this led to the development of diffusion tensor image analysis along the perivascular space (DTI-ALPS) index. While this index has been repeatedly used to investigate possible differences between neurodegenerative disorders and healthy controls, a comprehensive evaluation of its stability across multiple measurements and different disorders is still missing. In this study, we perform a Bayesian meta-analysis aiming to assess the consistency of the DTI-ALPS results previously reported for 12 studies on Parkinson's disease and 11 studies on Alzheimer's disease. We also evaluated if the measured value of the DTI-ALPS index can quantitatively inform the diagnostic process, allowing disambiguation between these two disorders. Our results, expressed in terms of Bayes' Factor values, confirmed that the DTI-ALPS index is consistent in measuring the different functioning of the glymphatic system between healthy subjects and patients for both Parkinson's disease (Log10(BF10) = 30) and Alzheimer's disease (Log10(BF10) = 10). Moreover, we showed that the DTI-ALPS can be used to compare these two disorders directly, therefore providing a first proof of concept supporting the reliability of taking into consideration this neuroimaging measurement in the diagnostic process. Our study underscores the potential of the DTI-ALPS index in advancing our understanding of neurodegenerative pathologies and enhancing clinical diagnostics.

Therapeutic approaches to CNS diseases via the meningeal lymphatic and glymphatic system: prospects and challenges

The brain has traditionally been considered an "immune-privileged" organ lacking a lymphatic system. However, recent studies have challenged this view by identifying the presence of the glymphatic system and meningeal lymphatic vessels (MLVs). These discoveries offer new opportunities for waste clearance and treatment of central nervous system (CNS) diseases. Various strategies have been developed based on these pathways, including modulation of glymphatic system function, enhancement of meningeal lymphatic drainage, and utilization of these routes for drug delivery. Consequently, this review explores the developmental features and physiological roles of the cerebral lymphatic system as well as its significance in various CNS disorders. Notably, strategies for ameliorating CNS diseases have been discussed with a focus on enhancing glymphatic system and MLVs functionality through modulation of physiological factors along with implementing pharmacological and physical treatments. Additionally, emphasis is placed on the potential use of the CNS lymphatic system in drug delivery while envisioning future directions in terms of mechanisms, applications, and translational research.

Liquiritin ameliorates painful diabetic neuropathy in SD rats by inhibiting NLRP3-MMP-9-mediated reversal of aquaporin-4 polarity in the glymphatic system

Background

Despite advancements in diabetes treatment, the management of Painful Diabetic Neuropathy (PDN) remains challenging. Our previous research indicated a significant correlation between the expression and distribution of Aquaporin-4 (AQP4) in the spinal glymphatic system and PDN. However, the potential role and mechanism of liquiritin in PDN treatment remain uncertain.

Methods

This study established a rat model of PDN using a combination of low-dose Streptozotocin (STZ) and a high-fat, high-sugar diet. Rats were treated with liquiritin and MCC950 (an NLRP3 inhibitor). We monitored fasting blood glucose, body weight, and mechanical allodynia periodically. The glymphatic system's clearance function was evaluated using Magnetic Resonance Imaging (MRI), and changes in proteins including NLRP3, MMP-9, and AQP4 were detected through immunofluorescence and Western blot techniques.

Results

The rats with painful diabetic neuropathy (PDN) demonstrated several physiological changes, including heightened mechanical allodynia, compromised clearance function within the spinal glymphatic system, altered distribution of AQP4, increased count of activated astrocytes, elevated expression levels of NLRP3 and MMP-9, and decreased expression of AQP4. However, following treatment with liquiritin and MCC950, these rats exhibited notable improvements.

Conclusion

Liquiritin may promote the restoration of AQP4 polarity by inhibiting NLRP3 and MMP-9, thereby enhancing the clearance functions of the spinal cord glymphatic system in PDN rats, alleviating the progression of PDN.

Brain-body mechanisms contribute to sexual dimorphism in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is the most common form of human motor neuron disease. It is characterized by the progressive degeneration of upper and lower motor neurons, leading to generalized motor weakness and, ultimately, respiratory paralysis and death within 3-5 years. The disease is shaped by genetics, age, sex and environmental stressors, but no cure or routine biomarkers exist for the disease. Male individuals have a higher propensity to develop ALS, and a different manifestation of the disease phenotype, than female individuals. However, the mechanisms underlying these sex differences remain a mystery. In this Review, we summarize the epidemiology of ALS, examine the sexually dimorphic presentation of the disease and highlight the genetic variants and molecular pathways that might contribute to sex differences in humans and animal models of ALS. We advance the idea that sexual dimorphism in ALS arises from the interactions between the CNS and peripheral organs, involving vascular, metabolic, endocrine, musculoskeletal and immune systems, which are strikingly different between male and female individuals. Finally, we review the response to treatments in ALS and discuss the potential to implement future personalized therapeutic strategies for the disease.

Diffusion Tensor Image Analysis ALong the Perivascular Space (DTI-ALPS): Revisiting the Meaning and Significance of the Method

More than 5 years have passed since the Diffusion Tensor Image Analysis ALong the Perivascular Space (DTI-ALPS) method was proposed with the intention of evaluating the glymphatic system. This method is handy due to its noninvasiveness, provision of a simple index in a straightforward formula, and the possibility of retrospective analysis. Therefore, the ALPS method was adopted to evaluate the glymphatic system for many disorders in many studies. The purpose of this review is to look back and discuss the ALPS method at this moment.The ALPS-index was found to be an indicator of a number of conditions related to the glymphatic system. Thus, although this was expected in the original report, the results of the ALPS method are often interpreted as uniquely corresponding to the function of the glymphatic system. However, a number of subsequent studies have pointed out the problems on the data interpretation. As they rightly point out, a higher ALPS-index indicates predominant Brownian motion of water molecules in the radial direction at the lateral ventricular body level, no more and no less. Fortunately, the term "ALPS-index" has become common and is now known as a common term by many researchers. Therefore, the ALPS-index should simply be expressed as high or low, and whether it reflects a glymphatic system is better to be discussed carefully. In other words, when a decreased ALPS-index is observed, it should be expressed as "decreased ALPS-index" and not directly as "glymphatic dysfunction". Recently, various methods have been proposed to evaluate the glymphatic system. It has become clear that these methods also do not seem to reflect the entirety of the extremely complex glymphatic system. This means that it would be desirable to use various methods in combination to evaluate the glymphatic system in a comprehensive manner.

Ginkgolide B can alleviate spinal cord glymphatic system dysfunction and provide neuroprotection in painful diabetic neuropathy rats by inhibiting matrix metalloproteinase-9

The glymphatic system plays a crucial role in maintaining optimal central nervous system (CNS) function by facilitating the removal of metabolic wastes. Aquaporin-4 (AQP4) protein, predominantly located on astrocyte end-feet, is a key pathway for metabolic waste excretion. β-Dystroglycan (β-DG) can anchor AQP4 protein to the end-feet membrane of astrocytes and can be cleaved by matrix metalloproteinase (MMP)-9 protein. Studies have demonstrated that hyperglycemia upregulates MMP-9 expression in the nervous system, leading to neuropathic pain. Ginkgolide B (GB) exerts an inhibitory effect on the MMP-9 protein. In this study, we investigated whether inhibition of MMP-9-mediated β-DG cleavage by GB is involved in the regulation of AQP4 polarity within the glymphatic system in painful diabetic neuropathy (PDN) and exerts neuroprotective effects. The PDN model was established by injecting streptozotocin (STZ). Functional changes in the glymphatic system were observed using magnetic resonance imaging (MRI). The paw withdrawal threshold (PWT) was measured to assess mechanical allodynia. The protein expressions of MMP-9, β-DG, and AQP4 were detected by Western blotting and immunofluorescence. Our findings revealed significant decreases in the efficiency of contrast agent clearance within the spinal glymphatic system of the rats, accompanied by decreased PWT, increased MMP-9 protein expression, decreased β-DG protein expression, and loss of AQP4 polarity. Notably, GB treatment demonstrated the capacity to ameliorate spinal cord glymphatic function by modulating AQP4 polarity through MMP-9 inhibition, offering a promising therapeutic avenue for PDN.

Nanoplastics and Neurodegeneration in ALS

Plastic production, which exceeds one million tons per year, is of global concern. The constituent low-density polymers enable spread over large distances and micro/nano particles (MNPLs) induce organ toxicity via digestion, inhalation, and skin contact. Particles have been documented in all human tissues including breast milk. MNPLs, especially weathered particles, can breach the blood-brain barrier, inducing neurotoxicity. This has been documented in non-human species, and in human-induced pluripotent stem cell lines. Within the brain, MNPLs initiate an inflammatory response with pro-inflammatory cytokine production, oxidative stress with generation of reactive oxygen species, and mitochondrial dysfunction. Glutamate and GABA neurotransmitter dysfunction also ensues with alteration of excitatory/inhibitory balance in favor of reduced inhibition and resultant neuro-excitation. Inflammation and cortical hyperexcitability are key abnormalities involved in the pathogenic cascade of amyotrophic lateral sclerosis (ALS) and are intricately related to the mislocalization and aggregation of TDP-43, a hallmark of ALS. Water and many foods contain MNPLs and in humans, ingestion is the main form of exposure. Digestion of plastics within the gut can alter their properties, rendering them more toxic, and they cause gut microbiome dysbiosis and a dysfunctional gut-brain axis. This is recognized as a trigger and/or aggravating factor for ALS. ALS is associated with a long (years or decades) preclinical period and neonates and infants are exposed to MNPLs through breast milk, milk substitutes, and toys. This endangers a time of intense neurogenesis and establishment of neuronal circuitry, setting the stage for development of neurodegeneration in later life. MNPL neurotoxicity should be considered as a yet unrecognized risk factor for ALS and related diseases.

Choroid plexus enlargement in amyotrophic lateral sclerosis patients and its correlation with clinical disability and blood-CSF barrier permeability

BACKGROUND

Using in vivo neuroimaging techniques, growing evidence has demonstrated that the choroid plexus (CP) volume is enlarged in patients with several neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. However, although animal and postmortem findings suggest that CP abnormalities are likely important pathological mechanisms underlying amyotrophic lateral sclerosis (ALS), the third most common neurodegenerative disease, no available study has been conducted to thoroughly assess CP abnormalities and their clinical relevance in vivo in ALS patients to date. Thus, we aimed to determine whether in vivo CP enlargement may occur in ALS patients. We also aimed to identify the relationships of CP volume with clinical disabilities and blood-CSF barrier (BCSFB) permeability in ALS patients.

METHODS

In this retrospective study, based on structural MRI data, CP volume was assessed using a Gaussian mixture model and underwent further manual correction in 155 ALS patients and 105 age- and sex-matched HCs from October 2021 to April 2023. The ALS Functional Rating Scale-Revised (ALSFRS-R) was used to assess clinical disability. The CSF/serum albumin quotient (Qalb) was used to assess BCSFB permeability. Moreover, all the ALS patients completed genetic testing, and according to genetic testing, the ALS patients were further divided into genetic ALS subgroup and sporadic ALS subgroup.

RESULTS

We found that compared with HCs, ALS patients had a significantly higher CP volume (p < 0.001). Moreover, compared with HCs, CP volume was significantly increased in both ALS patients with and without known genetic mutations after family-wise error correction (p = 0.006 and p < 0.001, respectively), while there were no significant differences between the two ALS groups. Furthermore, the CP volume was significantly correlated with the ALSFRS-r score (r = -0.226; p = 0.005) and the Qalb (r = 0.479; p < 0.001) in ALS patients.

CONCLUSION

Our study first demonstrates CP enlargement in vivo in ALS patients, and continues to suggest an important pathogenetic role for CP abnormalities in ALS. Moreover, assessing CP volume is likely a noninvasive and easy-to-implement approach for screening BCSFB dysfunction in ALS patients.

Glymphatic system dysfunction in middle-aged and elderly chronic insomnia patients with cognitive impairment evidenced by diffusion tensor imaging along the perivascular space (DTI-ALPS)

BACKGROUND

Chronic insomnia impairs the glymphatic system and may lead to cognitive impairment and dementia in elderly population. The diffusion tensor image analysis along the perivascular space (DTI-ALPS) has been proposed as a non-invasive method to measure the activity of human brain glymphatic. We aim to explore whether glymphatic function is impaired in middle-aged and elderly chronic insomnia individuals and to identify the relationships between glymphatic dysfunction and cognitive impairment.

METHODS

A total of 33 chronic insomnia patients (57.36 ± 5.44 years, 30 females) and 20 age- and sex-matched healthy controls (57.95 ± 5.78 years, 16 females) were prospectively enrolled between May 2022 and January 2023. All participants completed MRI screening, cognition and sleep assessments, and DTI-ALPS index analysis.

RESULTS

Our findings revealed that the DTI-ALPS index was significantly difference among the chronic insomnia patients with impaired cognition group (1.32 ± 0.14), with normal cognition group (1.46 ± 0.09), and healthy controls (1.61 ± 0.16) (p = 0.0012, p < 0.0001, p = 0.0008, respectively). Mini-Mental State Examination (MMSE) scores of chronic insomnia patients with cognitive impairment were positively correlated with the DTI-ALPS index (Partial correlation analyses after correction for age, sex, education level and duration of chronic insomnia: r = 0.78, p = 0.002). DTI-ALPS had moderate accuracy in distinguishing chronic insomnia patients with cognitive impairment from those with normal cognition.

DATA CONCLUSION

The glymphatic system dysfunction is involved in chronic insomnia among middle-aged and elderly individuals, and it has been found to be correlated with cognitive decline.

Dynamic changes in glymphatic function in reversible cerebral vasoconstriction syndrome

BACKGROUND

The pathophysiology of the reversible cerebral vasoconstriction syndrome (RCVS) remains enigmatic and the role of glymphatics in RCVS pathophysiology has not been evaluated. We aimed to investigate RCVS glymphatic dynamics and its clinical correlates.

METHODS

We prospectively evaluated the glymphatic function in RCVS patients, with RCVS subjects and healthy controls (HCs) recruited between August 2020 and November 2023, by calculating diffusion-tensor imaging along the perivascular space (DTI-ALPS) index under a 3-T MRI. Clinical and vascular (transcranial color-coded duplex sonography) investigations were conducted in RCVS subjects. RCVS participants were separated into acute (≤ 30 days) and remission (≥ 90 days) groups by disease onset to MRI interval. The time-trend, acute stage and longitudinal analyses of the DTI-ALPS index were conducted. Correlations between DTI-ALPS index and vascular and clinical parameters were performed. Bonferroni correction was applied to vascular investigations (q = 0.05/11).

RESULTS

A total of 138 RCVS patients (mean age, 46.8 years ± 11.8; 128 women) and 42 HCs (mean age, 46.0 years ± 4.5; 35 women) were evaluated. Acute RCVS demonstrated lower DTI-ALPS index than HCs (p < 0.001) and remission RCVS (p < 0.001). A continuously increasing DTI-ALPS trend after disease onset was demonstrated. The DTI-ALPS was lower when the internal carotid arteries resistance index and six-item Headache Impact test scores were higher. In contrast, during 50-100 days after disease onset, the DTI-ALPS index was higher when the middle cerebral artery flow velocity was higher.

CONCLUSIONS

Glymphatic function in patients with RCVS exhibited a unique dynamic evolution that was temporally coupled to different vascular indices and headache-related disabilities along the disease course. These findings may provide novel insights into the complex interactions between glymphatic transport, vasomotor control and pain modulation.

Exploring Astrocyte-Mediated Mechanisms in Sleep Disorders and Comorbidity

Astrocytes, the most abundant cells in the brain, are integral to sleep regulation. In the context of a healthy neural environment, these glial cells exert a profound influence on the sleep-wake cycle, modulating both rapid eye movement (REM) and non-REM sleep phases. However, emerging literature underscores perturbations in astrocytic function as potential etiological factors in sleep disorders, either as protopathy or comorbidity. As known, sleep disorders significantly increase the risk of neurodegenerative, cardiovascular, metabolic, or psychiatric diseases. Meanwhile, sleep disorders are commonly screened as comorbidities in various neurodegenerative diseases, epilepsy, and others. Building on existing research that examines the role of astrocytes in sleep disorders, this review aims to elucidate the potential mechanisms by which astrocytes influence sleep regulation and contribute to sleep disorders in the varied settings of brain diseases. The review emphasizes the significance of astrocyte-mediated mechanisms in sleep disorders and their associated comorbidities, highlighting the need for further research.