Development and prospect of treating Alzheimer's disease using the glymphatic system

Abstract

Alzheimer's disease (AD) is a common neurodegenerative disorder with progressive cognitive decline and typical amyloid-β (Aβ) and tau pathologies, whose pathogenesis remains unclear. The glymphatic system, a core cerebral waste clearance pathway, has become a critical target for AD pathogenic research and novel therapy development. This review explores the glymphatic system's structure and function, illustrates its correlation with AD pathogenesis, summarizes targeted therapies, and highlights research limitations and future directions to facilitate AD translational research. Relevant literatures published from 2012 to 2025 were retrieved from PubMed and Web of Science databases with the combined keywords of “Alzheimer's disease”, “glymphatic system”, “meningeal lymphatic vessels”, “Aβ clearance” and “lymphatic therapy for AD”. The included literatures were systematically sorted, and the basic mechanism, therapeutic strategy and research limitations were analyzed and summarized. The glymphatic system clears 30%–50% of cerebral Aβ in rodent models via meningeal lymphatic and parenchymal pathways, yet human evidence is lacking. Glymphatic dysfunction, APOE4 genotype, and immune imbalance promote Aβ and tau accumulation and AD progression. Several glymphatic-targeted strategies have demonstrated preclinical efficacy, with intranasal agents and photostimulation progressing into early-phase clinical trials. The glymphatic system is a promising therapeutic target for AD by improving brain waste clearance. Existing limitations include species discrepancies, unclear causal relationships and insufficient clinical data. Future research will focus on human-specific mechanisms, staged intervention strategies, and rigorous safety evaluation of targeted treatments.

Keywords

Alzheimer's disease amyloid-β clearance APOE4 brain waste clearance glymphatic system meningeal lymphatic vessels neuroinflammation therapeutic strategy

Introduction

Alzheimer's disease (AD) is a common neurodegenerative disorder characterized by progressive cognitive impairment and behavioral disturbances.¹ Currently, the pathogenesis of AD is not fully clarified, with pathological features including amyloid-β (Aβ) accumulation and neurofibrillary tangles caused by excessive phosphorylation of tau protein.¹ This article focuses on the association mechanism between the glymphatic system (including the parenchymal glymphatic system and meningeal lymphatic vessels (MLVs)) and AD, aiming to systematically sort out the role of this system in the pathological process of AD, summarize therapeutic strategies based on this system, and provide references for the basic research and clinical transformation of AD. This review adheres to the scope of the Journal of Alzheimer's Disease Reports by focusing on the translational value of glymphatic system research for AD diagnosis and therapy, addressing unmet clinical needs in AD treatment through exploring novel molecular targets and intervention approaches.

Studies have found that the glymphatic drainage system plays a key role in clearing neurotoxic proteins such as Aβ and tau from the brain, which is conducive to maintaining brain homeostasis, and its dysfunction is closely related to AD.^2,3 The system is mainly composed of the classic glymphatic system and meningeal lymphatic system, which are responsible for the exchange of cerebrospinal fluid (CSF) with interstitial fluid (ISF) and MLVs, respectively, and finally converge to the cervical lymph nodes (CLNs) for clearance through the systemic circulation.^4,5 Therefore, considering targeting the glymphatic system as an intuitive mechanism for clearing Aβ in the brain, targeted drug therapy has become a promising approach for treating AD based on the central lymphatic clearance mechanism.^6–8 This article elaborates on the structure and function of the glymphatic system, analyzes its mechanism and role in the pathogenesis of AD, and prospects the future research directions and potential application prospects of treating AD based on the glymphatic system. Notably, most conclusions regarding the glymphatic system and AD are derived from preclinical animal models (e.g., mice, primates), and extrapolating these findings to human AD pathology is limited by species differences in lymphatic system structure (e.g., MLV distribution density, drainage pathways) and AD pathological progression.^9,10

Overview of the glymphatic system

Structural composition

The glymphatic system of the brain is mainly composed of two parts: the glymphatic system located in the brain parenchyma and the MLVs in the dura mater.^9–13 Iliff et al. found that CSF in the subarachnoid space enters the parenchyma along the perivascular spaces of arteries, and ISF of the brain is cleared along the perivascular spaces of veins.¹² Further studies have shown that in aquaporin 4 (AQP4)-knockout mice, lymphatic clearance rate is significantly reduced. This clearance pathway dependent on AQP4 of astrocytes is functionally similar to the peripheral lymphatic system, hence named the glymphatic system.^12,13 The glymphatic system is a functional system involving the movement of extracellular fluid through the interstitial spaces of the brain, which works together with perivascular astrocytes expressing AQP4 to facilitate the circulation of CSF throughout the brain tissue..^14–15

In 2015, two independent research teams discovered the existence of MLVs in the dura mater of rodents and humans, respectively.^9,10 This structure has molecular characteristics similar to those of peripheral lymphatic endothelial cells (such as positive expression of LYVE-1 and PROX1), and is responsible for transporting metabolites (such as Aβ) and immune cells in CSF to the deep CLNs of the periphery. It has been confirmed to have functional connections with the glymphatic system and is the main pathway for CSF to drain into the CLNs.^9,10,16 Studies have found that MLVs are mainly divided into two subgroups: dorsal lymphatic vessels and basal lymphatic vessels.⁶ Compared with the dorsal side, the basal lymphatic vessels have an extensive capillary network, endothelial lymphocytes, and lymphatic valves, and these structural components contribute to more efficient absorption and elimination of CSF.^6,17 The development of MLVs depends on the vascular endothelial growth factor (VEGF) signaling pathway, among which the VEGF-C/VEGFR3 signaling pathway plays a core regulatory role.^9,18,19 Aspelund et al. found through gene knockout experiments that knockout of the VEGFR3 gene during embryonic development leads to complete obstruction of MLV formation in mice, manifested by no mature lymphatic duct structure in the dura mater⁹; Ahn et al. observed in a primate model that VEGF-C stimulation can reverse the degeneration of MLVs and promote endothelial cell proliferation and lymphatic valve repair¹⁸; Antila et al. further confirmed that downregulation of VEGFR3 expression in adult mice causes meningeal lymphatic degeneration, specifically manifested by increased apoptosis of lymphatic endothelial cells, reduced diameter of lymphatic vessels, and decreased lymphatic drainage efficiency.¹⁹ These studies collectively reveal the key role of the VEGF-C/VEGFR3 pathway in the development and maintenance of MLVs.

Functional characteristics

The main functions of the glymphatic system include clearing brain metabolic wastes and regulating neuroimmunity.²⁰ Under physiological conditions, the contents of the central nervous system are mainly drained to the CLNs along the cranial nerves and extracranial nasal lymphatic vessels through the skull. However, the discovery of MLVs has led researchers to re-evaluate the waste clearance pathways of the central nervous system. Studies on mice have shown that basal MLVs are hotspots for clearing CSF molecules.⁶ Functional evaluation of MLVs using CSF-enhanced MRI and fluorescence imaging further found that basal MLVs are important pathways for macromolecular uptake and CSF drainage, indicating that basal MLVs play a key role in CSF lymphatic drainage.^18,20 Both CSF/ISF and metabolic wastes can ultimately enter the CLNs and peripheral lymphatic system through MLVs.²⁰ Impairment of glymphatic function leads to the accumulation of pathological products, thereby accelerating the progression of many neurological diseases.²⁰ In addition to entering the nasal mucosa through the cribriform plate and other pathways, the CLN pathway through MLVs is the main pathway for extracting immune cells, cytokines, and CNS-derived antigens.^21–24 The lymphatic system collects and transports various types of antigens and immune cells (such as T cells and antigen-presenting cells) from tissues into their respective draining CLNs, thereby contributing to immune surveillance and resolution of inflammatory responses.²⁵ In mice with experimental autoimmune encephalomyelitis (EAE), it has been shown that MLVs control inflammatory processes and immune surveillance of the central nervous system through brain-reactive T cells.²⁶ Attenuation occurred after surgical and pharmacological blockage of lymphatic function, suggesting that drainage facilitates the activation of brain-derived T cells in the brain lymph nodes.²⁶ Reduced immune cell exit through lymphatic vessels may lead to the increased frequency of T cells and changes in macrophage and DC phenotypes observed in the aging meninges and brain.²⁷ The glymphatic system does not act independently in brain waste clearance but forms a coordinated network with other pathways including the blood-brain barrier (BBB) transporters, ubiquitin-proteasome system, autophagy-lysosome system, and microglial phagocytosis

Influencing factors

The driving force of the glymphatic system does not come from a single source, but mainly consists of CSF flow, arterial pulses, cardiac pulses, vasomotor activity, and respiratory movements.²⁸ Regulating the relevant driving forces of the glymphatic system, affecting its fluid exchange, may also affect the clearance of harmful substances in the central nervous system, making the glymphatic system an important part of potential therapeutic targets for the central nervous system.²⁸

Aging is one of the important factors affecting the glymphatic system.²⁹ Studies have shown that aging can lead to changes in the function of MLVs, which in turn leads to the decline of brain processes by clearing and draining immune components of the central nervous system and activating them.²⁹ In aged mice, the length and diameter of initial MLVs are significantly reduced, while the downstream collecting-like lymphatic vessels are dilated and become lymphedematous, resulting in decreased drainage of CSF to the cervical CLNs.²⁹ In addition, there are gender differences in lymphatic function: female mice have higher density of MLVs than males, and the age-related degeneration of lymphatic function is more significant in males, which may be related to the gender difference in AD incidence.²⁹ Lifestyle is also a key factor affecting the function of the glymphatic system. Sleep deprivation can significantly inhibit the polar distribution of AQP4 in the glymphatic system, reduce the exchange efficiency between ISF and CSF, and lead to decreased Aβ clearance rate in the brains of mice¹⁶; sedentary behavior can reduce the driving effect of arterial pulses on lymphatic flow, slowing down the drainage speed of MLVs, while moderate-intensity exercise can enhance vasomotor activity, improve the clearance efficiency of the glymphatic system, and reduce tau deposition in the brains of AD model mice.^16,28

Association mechanism between the glymphatic system and ad

Impaired clearance of Aβ and tau protein

The pathological features of AD mainly include two parts: extracellular senile plaques caused by Aβ deposition and intracellular neurofibrillary tangles caused by tau protein phosphorylation.²⁹ By monitoring their levels, inhibiting their production or increasing their clearance rate, it is possible to make an early diagnosis to promote the prevention and treatment of AD.³⁰ Aβ and tau protein can be degraded through the ubiquitin-proteasome system, autophagy-lysosome system, proteases, and microglial phagocytosis.^31–33 However, the discovery of MLVs has been confirmed to play a crucial role in clearing Aβ and tau protein from the brain. It is a pathway that guides CSF and ISF into dCLNs, providing a new therapeutic target for the treatment of AD.^6,20,34 Experiments have shown that MLV dysfunction reduces cerebral perfusion, impairs lymphatic drainage, and ultimately aggravates the pathological deposition of Aβ. PET studies have shown that the decrease in CSF clearance rate in AD patients is associated with the increase in Aβ deposition.³⁵ Repetitive transcranial magnetic stimulation has been shown to improve the drainage efficiency of mLVs and cognitive memory in 5×FAD mice.³⁶ By ligating the deep CLNs, increased brain Aβ load and accumulation of phosphorylated tau protein can be observed in APP/PS1 mice, which further interferes with the polarity of AQP4 in astrocytes and impairs glymphatic clearance function.³⁷ In the rTg4510 mouse model, through quantitative analysis of glymphatic clearance, it can be observed that the lower CST-ISF exchange in the caudal cortex is associated with impaired tau protein clearance, confirming that the glymphatic system is involved in the regulation of tau protein clearance in AD, providing a new target for the treatment of AD.^17,38

APOE4

ApoE is the most abundant apolipoprotein in the brain, responsible for lipid transport, and is a genetic risk factor for AD. ApoE4 reduces the efficiency of Aβ efflux through the BBB, resulting in poor Aβ clearance rate in the central nervous system.^20,39 The role of ApoE4 in peripheral lymphatic function has been established through multiple studies: Baloyannis et al. observed in autopsy samples of AD patients that those carrying the ApoE4 genotype had significantly higher lymphatic sinus dilation and Aβ deposition in the CLNs than those with non-ApoE4 genotypes, confirming that ApoE4 can simultaneously impair peripheral lymphatic clearance function⁴⁰; Lim et al. found in a hypercholesterolemic mouse model induced by a high-fat diet that ApoE4 can bind to the low-density lipoprotein receptor on the surface of lymphatic endothelial cells, inhibit VEGF-C-mediated proliferation of lymphatic endothelial cells, leading to reduced diameter of peripheral lymphatic vessels and decreased drainage function.⁴¹ Interestingly, ApoE4 may also affect MVLs in the central nervous system.²⁰ ApoE4 induces premature contraction of MVLs, meningeal lymphosclerosis, and lymphedema, leading to reduced CSF drainage, accumulation of Aβ and other macromolecules, inflammatory mediators, and immune cells in the brain.²⁰

Immune regulation imbalance

The first evidence that the adaptive immune system is involved in AD comes from the discovery of increased numbers of CD4 and CD8 T cells in the brains of AD patients. These studies have shown immune cell characteristics associated with AD, emphasizing the role of the adaptive immune system in AD.⁴² The rediscovered dural lymphatic vessels allow the drainage of immune cells and CNS-derived solutes to peripheral lymph nodes, further promoting an updated view of CNS-immune cell interactions.⁴² In the EAE mouse model, MLVs regulate central inflammation by transporting brain-reactive T cells: when EAE occurs, the drainage capacity of MLVs for CD4 + Th17 cells is enhanced, leading to massive activation and proliferation of these cells in the CLNs, while surgical ligation of MLVs can reduce the infiltration of CD4 + Th17 cells in the brain by 80%, significantly alleviating the neuroinflammatory symptoms of EAE.²⁶ The association of this mechanism with AD is that in the MLVs of AD model mice (such as 5×FAD), the drainage efficiency of CD4 + Th17 cells is decreased, leading to the accumulation of these cells in the brain and secretion of IL-17, which further damages the integrity of the BBB, promotes Aβ deposition and excessive activation of microglia^6,20; while activation of MLVs by VEGF-C increases the clearance rate of CD4 + Th17 cells in the brain, reduces Aβ deposition, and improves the cognitive function of mice,^6,20 indicating that the imbalance of T cell drainage mediated by MLVs may be an important link in the aggravation of neuroinflammation in AD. Attenuation occurred after surgical and pharmacological blockage of lymphatic function, suggesting that drainage facilitates the activation of brain-derived T cells in the brain lymph nodes.²⁰ These evidences confirm that the glymphatic system is involved in the pathophysiological process of AD by affecting the brain immune system of AD patients, accelerating cognitive decline and neuroinflammation.

New therapeutic strategies for ad based on the glymphatic system

Evidence tier classification:

Tier 1: Preclinical proof-of-concept (animal models only): Interventions with confirmed efficacy in reducing AD-like pathologies (Aβ/tau deposition) in rodent/non-human primate models, no human research data.

Tier 2: Early human feasibility (preliminary clinical data): Interventions that have entered Phase I/II clinical trials, with confirmed human safety and preliminary efficacy (e.g., increased Aβ clearance), no Phase III clinical outcome data.

Tier 3: Clinical efficacy (established human evidence): Interventions with Phase III clinical trial data confirming cognitive improvement and AD pathology reduction (no interventions in this category to date).

Cranial bone maneuver - tier 1: preclinical proof-of-concept

Mechanism of therapeutic action and advantages

Treatment through cranial bone maneuver (CBM) can improve memory function, reduce Aβ deposition, and promote meningeal lymphatic drainage function.⁴³ The specific mechanism is: CBM can relieve mechanical compression on the dura mater by gently adjusting the position of cranial sutures, expanding the diameter of MLVs; at the same time, the local inflammatory response induced by surgery can activate the VEGF-C/VEGFR3 pathway, promoting the neogenesis of MLVs.⁴³ Data show that after CBM treatment, the escape latency of 5xFAD mice in the Morris water maze is shortened, and the Aβ deposition in the cerebral cortex and hippocampus is reduced.⁴³

Potential risks and unintended consequences

As an invasive physical intervention, CBM has obvious preclinical safety limitations and potential translational risks. First, cranial mechanical adjustment may cause dural injury, intracranial micro-hemorrhage and excessive local inflammatory response, and severe surgical trauma will instead destroy intact MLV structure and inhibit glymphatic clearance function, aggravating AD pathological damage.⁴³ Second, long-term repeated cranial suture intervention may lead to abnormal skull mechanical structure development in aged individuals, with unknown long-term safety. Third, the surgical operation standard is difficult to unify, and excessive mechanical stimulation may cause irreversible meningeal tissue damage.⁴³ At present, CBM has only been verified in animal models, and there is a complete lack of human safety and efficacy data. Its clinical transformation needs to solve the problems of traumatic risk and standardized operation, and minimally invasive intervention schemes need to be further explored

Borneol micelles - tier 1: preclinical proof-of-concept

Mechanism of therapeutic action and advantages

Borneol: A natural monoterpene compound extracted from traditional Chinese medicinal materials, with the effects of improving microcirculation and lymphatic vessel permeability. Borneol can improve the permeability and inner diameter of lymphatic vessels, allowing macromolecules to flow into CLNs and then enter the lymphatic circulation.⁴⁴ Experiments have shown that oral administration of borneol micelles (BO-Ms) can cross the BBB and enter the dura mater, bind to Claudin-5 protein on the surface of meningeal lymphatic endothelial cells, reduce the permeability of tight junctions between endothelial cells, and expand the inner diameter of lymphatic vessels; at the same time, BO-Ms can promote the increase of lymphatic flow velocity.⁴⁴ In APP/PS1 mice, after oral administration of BO-Ms, the Aβ clearance rate in CSF is increased, and the number of Aβ plaques in the hippocampus of the brain is reduced.⁴⁴ In addition, BO-Ms can also regulate the function of the glymphatic system, enhance the polar distribution of AQP4, and further promote the clearance of Aβ in ISF. The oral administration route has good bioavailability and safety in animal models, providing a new option for oral treatment of AD..⁴⁴

Potential risks and unintended consequences

Long-term oral administration of BO-Ms has potential systemic and central side effects. Borneol has certain gastrointestinal irritation, and long-term continuous administration may cause gastric mucosal congestion, edema and digestive discomfort, limiting its long-term clinical application.⁴⁴ Otherwise, excessive expansion of lymphatic endothelial tight junctions may lead to abnormal BBB permeability increase, allowing peripheral toxic substances and inflammatory mediators to infiltrate into the brain parenchyma, inducing secondary neuroinflammation.⁴⁴The metabolic stability and long-term biological toxicity of BO-Ms in vivo have not been fully verified, and standardized safety evaluation is urgently needed before clinical transformation.

Intranasal oxytocin - tier 1: preclinical proof-of-concept

Mechanism of therapeutic action and advantages

In the APP/PS1 mouse model, intranasal administration of oxytocin can significantly restore the function of the intracranial lymphatic system through multiple regulatory mechanisms⁴⁵: first, oxytocin can bind to the OXTR receptor on meningeal lymphatic endothelial cells, activate the PI3 K/Akt pathway, promote the proliferation of lymphatic endothelial cells, and increase the branches of MLVs;,^45 s it can inhibit AQP4 depolarization, increase the aggregation rate of AQP4 on the foot processes of astrocytes, and enhance the fluid exchange efficiency of the glymphatic system⁴⁵; third, oxytocin can also regulate the phagocytic activity of microglia, and synergistically reduce Aβ deposition with lymphatic clearance.⁴⁵ Experiments show that after intranasal administration of oxytocin, the drainage efficiency of MLVs in APP/PS1 mice is improved, the Aβ deposition in the hippocampus is reduced, and the learning and memory deficits are significantly improved.⁴⁵

Potential risks and unintended consequences

Intranasal oxytocin intervention has potential local irritation and systemic side effects. Locally, long-term nasal administration may cause nasal mucosal dryness, congestion and allergic irritation, affecting patient compliance.⁴⁵ Systemically, excessive oxytocin absorption may induce hypotension, tachycardia, and special physiological reactions such as uterine contraction in female patients, with potential safety risks for special populations.⁴⁵

Melatonin - tier 1: preclinical proof-of-concept

Mechanism of therapeutic action and advantages

Melatonin exerts an anti-AD effect by enhancing the clearance function of the glymphatic system.⁴⁶ Its mechanisms of action include: during nighttime sleep, melatonin can promote the polar expression of AQP4 in the glymphatic system, increase the exchange efficiency between ISF and CSF, and accelerate the transport of Aβ from the brain parenchyma to the CSF⁴⁶; at the same time, melatonin can inhibit the oxidative stress damage of meningeal lymphatic endothelial cells, reduce the accumulation of lipid peroxidation products, and maintain the structural integrity of lymphatic vessels.⁴⁶ In 3×Tg-AD mice, intraperitoneal injection of melatonin can increase the Aβ clearance rate in the brain, reduce the phosphorylation level of tau protein, and improve the spatial memory ability of mice.⁴⁶ As an endogenous hormone, melatonin has high safety in animal models.⁴⁶ In the future, it can be explored to combine with sleep intervention to further improve the lymphatic clearance effect.⁴⁶

Potential risks and unintended consequences

Exogenous melatonin intervention has dose-dependent and conditional limitations. Long-term high-dose supplementation can inhibit the secretion of endogenous melatonin, disrupt the body's circadian rhythm, cause sleep cycle disorder, and instead affect sleep-dependent glymphatic clearance.⁴⁶ In addition, melatonin has limited intervention efficacy in advanced AD models with severe AQP4 depolarization and irreversible glymphatic structural damage, which cannot reverse established pathological lesions.⁴⁶

OAB-14 - tier 1: preclinical proof-of-concept

Mechanism of therapeutic action and advantages

OAB-14 exerts an anti-AD effect by enhancing the function of the glymphatic system.⁴⁷ Studies have shown that OAB-14 can bind to the GABA-B receptor on astrocytes, activate downstream signaling pathways, promote the aggregation of AQP4 in the perivascular foot processes, and increase the fluid flow velocity of the glymphatic system⁴⁷; at the same time, OAB-14 can inhibit the excessive activation of microglia, reduce the release of inflammatory factors, and avoid the damage of glymphatic system function by inflammation.⁴⁷ In AD model rats, after intraperitoneal injection of OAB-14, the Aβ deposition in the cerebral cortex is reduced, and the clearance rate of tau protein by the glymphatic system is improved.⁴⁷

Potential risks and unintended consequences

OAB-14 has potential central nervous system inhibitory effects and immune regulatory risks. Activation of GABA-B receptors by OAB-14 may cause central inhibitory responses such as drowsiness, dizziness and ataxia, affecting neurological motor function.⁴⁷ Long-term inhibition of microglial activation will weaken the brain's innate immune defense ability, reduce the clearance capacity of exogenous pathogens and abnormal proteins, and increase the risk of central infection and pathological accumulation.⁴⁷ At present, OAB-14 is only in the preclinical research stage, and its long-term in vivo safety, metabolic characteristics and optimal intervention dosage have not been systematically verified, with obvious translational limitations.⁴⁷

40Hz Blue light therapy - tier 2: early human feasibility

Mechanism of therapeutic action and advantages. 40 Hz blue light therapy is an important non-pharmacological treatment method based on lymphatic regulation, among which 40 Hz blue light therapy has the most definite effect.⁴⁸ 40 Hz blue light can activate cerebral cortical neurons through the visual pathway, generating synchronous electrical activity.⁴⁸ This activity can enhance arterial pulses through neurovascular coupling, providing a stronger driving force for the glymphatic system, and increasing the ISF clearance efficiency mediated by AQP4; at the same time, blue light can promote the calcium influx of meningeal lymphatic endothelial cells, enhance the opening and closing frequency of lymphatic valves, and improve the drainage speed of CSF to the CLNs.⁴⁸ In 5xFAD mice, 40 Hz blue light irradiation can reduce the Aβ deposition in the hippocampus, reduce the activation degree of glial cells, and effectively prevent the memory decline of mice.⁴⁸ Combining 40 Hz blue light with anti-Aβ antibodies can increase the clearance rate of soluble Aβ to twice that of single treatment through the synergistic effect of “phototherapy-enhanced lymphatic drainage + antibody-targeted binding of Aβ”.⁴⁸

Potential risks and unintended consequences

Preliminary results show that the Aβ clearance rate in the CSF of patients is improved, but no significant cognitive improvement has been observed to date.⁴⁸ Long-term blue light irradiation may cause retinal damage; synchronous neuronal electrical activity may induce epileptiform discharges in individuals with epilepsy susceptibility.⁴⁸ Lymphatic vessel ablation (LVA) in the central nervous system is a highly controversial intervention with no peer-reviewed human safety or efficacy data to date. Due to significant regulatory and ethical sensitivity (risk of irreversible brain waste clearance failure and severe neuroinflammation), LVA is not recommended for AD clinical research at this stage, and no endorsement of this intervention is implied in this review.

Important disclaimer

LVA is a highly invasive and ethically sensitive central nervous system intervention. To date, there is no peer-reviewed clinical evidence verifying the safety and efficacy of LVA in human AD research. Considering the potential irreversible risks of LVA, including persistent brain waste clearance dysfunction, severe neuroinflammation, and aggravated neuronal damage, this review does not recommend LVA as a feasible intervention for AD basic research or clinical transformation. No positive endorsement or clinical application guidance of LVA is implied in the whole manuscript, and all discussed therapeutic strategies are limited to non-invasive or minimally invasive glymphatic regulatory approaches with verified preclinical safety.

Problems and challenges

Although some progress has been made in the research on the relationship between the glymphatic system and AD, there are still many problems and challenges. First, the research on the glymphatic system is still in a relatively preliminary stage, and its precise anatomical structure and detailed physiological functions have not been fully clarified, especially some molecular mechanisms and regulatory networks of the glymphatic system need further in-depth exploration. Second, in AD, the causal relationship between lymphatic system dysfunction and the occurrence and development of the disease has not been fully clarified. Whether the functional abnormalities of the glymphatic system directly lead to the onset of AD, or the changes of the glymphatic system are caused during the course of AD, remains to be further studied. In addition, the existing research methods have certain limitations in detecting the function of the glymphatic system, making it difficult to accurately and comprehensively evaluate its dynamic changes in AD. Furthermore, there are differences in the structure of the lymphatic system between animal models (such as mice) and humans (such as the distribution density and drainage pathway of MLVs), which may affect the clinical transformation of research results. At the same time, although anti-amyloid therapy targeting Aβ clearance shows potential in basic research, its clinical efficacy is not yet clear, which may be related to individual differences in the lymphatic system and disease stages. Third, the potential risks of manipulating central lymphatic function have not been fully evaluated in preclinical models, and the long-term biological tradeoffs (e.g., enhanced lymphatic drainage versus BBB integrity, immune regulation versus innate immune defense) are unclear. Fourth, the disease stage specificity of glymphatic interventions is not clear: it is unknown whether interventions are most effective in the preclinical AD stage (when lymphatic dysfunction is reversible) or can also reverse pathological damage in mild to moderate AD. Fifth, the integration of the glymphatic system with other AD pathological pathways (e.g., tau hyperphosphorylation, cholinergic system dysfunction) is insufficient, and single-target lymphatic interventions may have limited clinical efficacy.

Future research directions and prospects

In the future, research on the relationship between the glymphatic system and AD can be carried out from the following aspects. First, further study the development and regulatory mechanisms of the glymphatic system, as well as its changes in different physiological and pathological states, to provide a more solid theoretical basis for revealing its relationship with AD. Second, use advanced technical means, such as in vivo imaging and single-cell sequencing, to establish more accurate AD animal models and clinical research methods, clarify the starting time and mechanism of glymphatic system dysfunction in AD onset, and determine its feasibility as a biological marker for early diagnosis of AD. Third, explore new therapeutic strategies for AD based on the glymphatic system, such as improving the function of the glymphatic system through drug intervention, physical therapy and other methods, promoting Aβ clearance and immune regulation, and providing new targets and approaches for the treatment of AD. Fourth, conduct balanced research on animal and human evidence: establish humanized AD animal models with conserved MLV structure, and carry out large-sample clinical studies to verify the correlation between glymphatic function and AD pathological progression. Fifth, integrate the glymphatic system with other brain clearance and pathological pathways to develop multi-target combination therapies. Sixth, systematically evaluate the safety and unintended consequences of glymphatic interventions in preclinical models, and design rigorous Phase I/II clinical trials with clear disease stage stratification. Seventh, explore the potential of glymphatic function detection (e.g., MLV MRI imaging) as an early AD diagnostic biomarker, to realize early intervention and personalized treatment.

Summary

In summary, there is a close association between the glymphatic system and AD, and its important role in the pathogenesis of AD is gradually being revealed. The glymphatic system is an early and progressive contributor to AD pathology, and its dysfunction is closely linked to Aβ/tau accumulation, APOE4-mediated clearance impairment, and immune regulation imbalance. Multiple preclinical interventions targeting the glymphatic system have shown promising proof-of-concept effects, and a small number of non-invasive strategies (e.g., 40 Hz blue light therapy) have entered early clinical research. However, the translational value of these findings is limited by species differences, immature clinical evidence, and unevaluated safety risks. In-depth study of the relationship between the two, combined with the integration of multi-pathway research and rigorous clinical trial design, is expected to provide new theoretical basis and therapeutic strategies for the early diagnosis, treatment and prevention of AD, which has important scientific significance and clinical application value⁸.

Footnotes

Acknowledgements

We thank the researchers who contributed to the original studies cited in this review, and the editorial team of Journal of Alzheimer's Disease Reports for their constructive comments on manuscript revision.

ORCID iD

Jiaxiang Gu

Author contribution(s)

Jiajie Gu: Data curation; Formal analysis; Methodology; Visualization; Writing – original draft; Writing – review & editing.

Zekai Liu: Methodology; Resources; Software; Supervision; Validation; Visualization.

Jiaxiang Gu: Conceptualization; Investigation; Methodology; Project administration; Supervision.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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