Peripheral origin exosomal microRNAs aggravate glymphatic system dysfunction in diabetic cognitive impairment

Cognitive dysfunction is one of the common central nervous systems (CNS) complications of diabetes mellitus, which seriously affects the quality of life of patients and results in a huge economic burden. The glymphatic system dysfunction mediated by aquaporin-4 (AQP4) loss or redistribution in perivascular astrocyte endfeet plays a crucial role in diabetes-induced cognitive impairment (DCI). However, the mechanism of AQP4 loss or redistribution in the diabetic states remains unclear. Accumulating evidence suggests that peripheral insulin resistance target tissues and CNS communication affect brain homeostasis and that exosomal miRNAs are key mediators. Glucose and lipid metabolism disorder is an important pathological feature of diabetes mellitus, and skeletal muscle, liver and adipose tissue are the key target insulin resistance organs. In this review, the changes in exosomal miRNAs induced by peripheral metabolism disorders in diabetes mellitus were systematically reviewed. We focused on exosomal miRNAs that could induce low AQP4 expression and redistribution in perivascular astrocyte endfeet, which could provide an interorgan communication pathway to illustrate the pathogenesis of DCI. Furthermore, the mechanisms of exosome secretion from peripheral insulin resistance target tissue and absorption to the CNS were summarized, which will be beneficial for proposing novel and feasible strategies to optimize DCI prevention and/or treatment in diabetic patients.

The Exploration of Glymphatic System Alteration in Pediatric Acute Lymphoblastic Leukemia Using DTI-ALPS Method / 中山大学学报(医学科学版)

ObjectiveThe glymphatic system regulates cerebral spinal fluid and interstitial fluid transport which might be one of the pathways of central nervous system （CNS） leukemia at the early stage. This study aimed to investigate the alteration of glymphatic system based on diffusion tensor image-analysis along the perivascular space （DTI-ALPS） in pediatric acute lymphoblastic leukemia （ALL） without clinically diagnosed CNS infiltration. MethodsTwenty-five ALL and typically developing （TD） children were prospectively recruited， and all subjects underwent DTI. Group differences in brain water diffusivities and ALPS-index were evaluated using the analysis of covariance. The Spearman correlation analysis was used to evaluate the relationship between biological characteristics and significant parameters in pediatric ALL. ResultsCompared with TDs， decreased Dxassoc value （PFDR-corrected = 0.048） and increased Dzassoc value （PFDR-corrected = 0.033） were found in pediatric ALL. Hence， lower ALPS-index was found in children with ALL （PFDR-corrected < 0.001）. ALPS-index was negatively associated with the risk classification （rs = -0.47， P = 0.018） as well as immunophenotype （rs = -0.40， P = 0.046） in pediatric ALL. ConclusionsOur results show dysfunction of the glymphatic system is presented in pediatric ALL without clinically diagnosed CNS infiltration， which suggests that the glymphatic system might be one of pathway in the early-stage of ALL CNS infiltration. The DTI-ALPS method can be used to evaluate the change of glymphatic system， providing a new method for exploring the underlying mechanisms and early detection of pediatric ALL CNS infiltration.

Effect of sleep on brain clearing metabolites: thinking based on lymphoid system / 中华神经科杂志

Disruption of the structure of regular sleep is a common cause of neurodegenerative diseases such as Alzheimer′s disease and Parkinson′s disease, and its pathogenesis may be related to the deposition of waste products in the central nervous system. The glymphatic pathway, which is essentially a periarterial cerebrospinal fluid inflow pathway and peripheral venous clearance pathway, is functionally dependent on interstitial bulk flow coupling supported by aquaporin-4 on the astrocyte end-foot, also known as the lymphoid glial system. The glymphatic pathway, which removes waste proteins from the brain, is active primarily during sleep, and sleep quality declines with age, while the glymphatic pathway system also deteriorates with age, suggesting a relationship between sleep disturbances and symptom progression in neurodegeneration, and glymphatic system as a link closely links the two. The interaction of sleep, aging, metabolic waste and glymphatic pathway reticulation provides new clues to the pathogenesis of central nervous system degenerative diseases, and the glymphatic pathway may constitute a new target on treatment. The recent research progress on the effects of sleep and sleep disorders on the circulation of the glymphatic system, and proposes the possibility of sleep intervention to slow down the impairment of the lymphoid system function or even restore the function of the lymphoid system and thus improve the disease development process were reviewed in this paper.

Diffusion tensor imaging analysis along the perivascular space derived intracerebral glymphatic system circulatory function on neuromyelitis optica spectrum disorder: a follow-up study for curative effect / 中华放射学杂志

Objective:To evaluate the value of curative effect in neuromyelitis spectrum disease (NMOSD) based on circulatory function evaluation of intracerebral glymphatic system by using diffusion tensor imaging analysis along the perivascular space.Methods:The clinical and imaging data of 23 patients diagnosed with NMOSD at Tianjin Medical University General Hospital from March 2018 to December 2019 were retrospectively analyzed in this study. The clinical data included expanded disability status scale (EDSS), average relapse rate (ARR) and retinal nerve fiber layer (RNFL) thickness at baseline and 1 year follow-up after treatment. Among the 23 NMOSD patients, there were 22 females and 1 male, aged from 21 to 71 (45±13) years old. All the patients underwent MR scans at both baseline and 1 year after treatment, and the scanning sequences included cerebral 3D-T 1WI, T 2WI, diffusion tensor imaging and cervical spinal sagittal 3D-T 2WI, and the cervical spinal cord volume and bilateral diffusion tensor imaging analysis along the perivascular space index (ALPS index) were calculated. The partial correlation test was used to analyze the correlations between ALPS index and the clinical indicators such as EDSS, ARR, and bilateral RNFL, with the control variables as gender, age, years of education and course of disease. The multiple linear regression model was used to analyze the independent predictors for ALPS index and EDSS after treatment. Receiver operating characteristic curve (ROC) and area under the curve (AUC) were used to evaluate the diagnostic value of NMOSD treatment outcome by using ALPS index. Results:When controlling for gender, age, years of education and course of disease, there were significant negative correlations between right ALPS index and EDSS ( r=-0.50, P=0.048), bilateral average ALPS index and EDSS ( r=-0.53, P=0.034), left ALPS index and ARR ( r=-0.58, P=0.018), while there was significant positive correlations between right ALPS index and RNFL ( r=0.88, P=0.008) at 1 year follow-up after treatment. Multiple linear regression analysis showed that cervical spinal cord volume was an independent impact factor of bilateral average ALPS indexes (β=0.24, 95%CI 0.10-0.38, P=0.002), and bilateral average ALPS indexes (β=-3.22, 95%CI -5.97--0.48, P=0.024) and right RNFL (β=-0.05, 95%CI -0.08--0.02, P=0.002) at baseline were the independent impact factors of EDSS after treatment. ROC curve analysis showed that the bilateral average ALPS index at baseline had the best efficacy in predicting the curative effect of NMOSD patients with AUC=0.92. Conclusions:After treatment, NMOSD patients with severe clinical disability, high frequency of disease attack, poor visual performance, and severe cervical spinal cord atrophy have more serious impairment of intracerebral glymphatic system circulatory function. The ALPS index could help in predicting the clinical curative effect of NMOSD patients.

Updated Understanding of the Glial-Vascular Unit in Central Nervous System Disorders / 神经科学通报·英文版

The concept of the glial-vascular unit (GVU) was raised recently to emphasize the close associations between brain cells and cerebral vessels, and their coordinated reactions to diverse neurological insults from a "glio-centric" view. GVU is a multicellular structure composed of glial cells, perivascular cells, and perivascular space. Each component is closely linked, collectively forming the GVU. The central roles of glial and perivascular cells and their multi-level interconnections in the GVU under normal conditions and in central nervous system (CNS) disorders have not been elucidated in detail. Here, we comprehensively review the intensive interactions between glial cells and perivascular cells in the niche of perivascular space, which take part in the modulation of cerebral blood flow and angiogenesis, formation of the blood-brain barrier, and clearance of neurotoxic wastes. Next, we discuss dysfunctions of the GVU in various neurological diseases, including ischemic stroke, spinal cord injury, Alzheimer's disease, and major depression disorder. In addition, we highlight the possible therapies targeting the GVU, which may have potential clinical applications.

Avances recientes en el diagnóstico imagenológico de la hidrocefalia en niños. Revisión de la literatura de los últimos seis años / Recent advances of the imagological diagnosis of hydrocephalus in children. Review of the literature of the last six years

Resumen La hidrocefalia es un problema de salud frecuente en pediatría, en particular durante el primer mes de vida. La incidencia en América Latina es una de las más altas del mundo. En Colombia no existen datos representativos sobre la incidencia real de esta enfermedad. Recientes hallazgos relacionados con la dinámica del líquido cefalorraquídeo permitieron proponer nuevos modelos sobre la fisiopatología de la hidrocefalia que, junto con los hallazgos en la Resonancia Magnética, han llevado a tener una mejor comprensión de la enfermedad. El objetivo de este articulo es realizar una revisión de la información disponible en la literatura sobre los avances en la fisiopatología de la enfermedad y los hallazgos en neuroimágenes, además de realizar una breve revisión sobre el papel de estas en el diagnóstico y seguimiento de los pacientes. Se realizó una revisión bibliográfica con términos MeSH, en las bases de datos de PUBMED, OVID y SCOPUS con artículos publicados en los últimos 6 años, seleccionado un total de 30 artículos que abordaron el tema de forma integral. Los nuevos hallazgos descritos como lo son el sistema glinfático y el papel de las AQP4 y los avances en las neuroimágenes, sobre todo de la resonancia magnética, han ayudado a comprender mejor esta entidad, apoyando el desarrollo de un nuevo modelo de la dinámica del líquido cefalorraquídeo y a partir de él diferentes explicaciones sobre la fisiopatología. MÉD.UIS.2022;35(1): 17-29.

Abstract Hydrocephalus is a frequent health problem in pediatrics, particularly during the first month of life. The incidence in Latin America is one of the highest in the world. In Colombia there are no representative data. Recent findings related to the dynamics of cerebrospinal fluid allowed proposals of new models on the pathophysiology of hydrocephalus that, along with new findings on MRI, have led to a better understanding of the disease. The aim of this work is to review the information available in the literature about the progress in the pathophysiology of the disease and neuroimaging findings, in addition to conducting a brief review on the role of these in the diagnosis and follow-up of patients. A bibliographic review with MeSH terms was carried out in PUBMED, OVID and SCOPUS databases, with articles published in the last 6 years. 30 articles that dealt with the theme in a comprehensive way were included. New findings described as the glymphatic system and the role of AQP4, along with advances in neuroimaging, especially MRI, have helped to better understand hydrocephalus, supporting the development of a new model of cerebrospinal fluid dynamics, and based on it, different explanations regarding its pathophysiology. MÉD.UIS.2022;35(1): 17-29.

Glymphatic system and cerebral edema after ischemic stroke / 国际脑血管病杂志

Glymphatic system is a fluid transport and material clearance system found in recent years. It promotes the flow and exchange of cerebrospinal fluid and interstitial fluid, remove metabolic waste, and maintain the stability of the internal environment of the brain through the perivascular space and aquaporin 4 on astrocytes. Recent studies have shown that the glymphatic system plays an important role in the intake and discharge of the fluid in brain, and the changes of glymphatic system may be an important reason for brain edema after ischemic stroke. This article reviews the pathophysiological mechanism and related therapeutic targets of glymphatic system in the formation of cerebral edema after ischemic stroke, in order to provide new ideas for the treatment of cerebral edema after ischemic stroke.

Digoxin Ameliorates Glymphatic Transport and Cognitive Impairment in a Mouse Model of Chronic Cerebral Hypoperfusion / 神经科学通报·英文版

The glymphatic system plays a pivotal role in maintaining cerebral homeostasis. Chronic cerebral hypoperfusion, arising from small vessel disease or carotid stenosis, results in cerebrometabolic disturbances ultimately manifesting in white matter injury and cognitive dysfunction. However, whether the glymphatic system serves as a potential therapeutic target for white matter injury and cognitive decline during hypoperfusion remains unknown. Here, we established a mouse model of chronic cerebral hypoperfusion via bilateral common carotid artery stenosis. We found that the hypoperfusion model was associated with significant white matter injury and initial cognitive impairment in conjunction with impaired glymphatic system function. The glymphatic dysfunction was associated with altered cerebral perfusion and loss of aquaporin 4 polarization. Treatment of digoxin rescued changes in glymphatic transport, white matter structure, and cognitive function. Suppression of glymphatic functions by treatment with the AQP4 inhibitor TGN-020 abolished this protective effect of digoxin from hypoperfusion injury. Our research yields new insight into the relationship between hemodynamics, glymphatic transport, white matter injury, and cognitive changes after chronic cerebral hypoperfusion.

The process in research of anatomy of brain lymphatic system and the relationship between it and Alzheimer's disease / 中华显微外科杂志

Conventional wisdom holds that the central nervous system (CNS) does not have lymphatic vessels or lymphatic circulation, and it lacks lymphatic pathways to clear brain metabolites. However, with the development of study in intracranial clearance, it has been discovered that there are lymphatic systems in CNS, including glymphatic pathway and it meningeal lymphatic vessels. It further reveals the exchange system between cerebrospinal fluid (CSF) and interstitial fluid (ISF). It also closely relates to the development of neurodegenerative diseases, age-related changes of brain, traumatic brain injury, circulatory diseases and tumors. In the past 10 years, the research in CNS has been a hot spot in life sciences. This article aims to explain the research progress from the aspects of the discovery of glymphatic system, anatomical structure and function, and relationship with Alzheimer's disease (AD).

Glymphatic system in Parkinson′s disease / 中华神经科杂志

Parkinson′s disease is a degenerative disease of the central nervous system with abnormal protein deposition in the brain as the main pathological changes. The onset of Parkinson′s disease is related to abnormal deposition protein removal disorders, and the relevant mechanisms are still unclear. The glymphatic system is a metabolic waste and abnormal protein deposition removal system in the brain. In recent years, studies have shown that the changes of aquaporin 4, perivascular space and dural lymphatic vessels in Parkinson′s disease are closely related to the level of relevant pathological proteins in cerebrospinal fluid, leading to the occurrence and development of Parkinson′s disease. The researches on structure and biomarkers of the glymphatic system in Parkinson′s disease in recent years are reviewed in this article.

Recent advance of aquaporin-4 in neurodegenerative diseases / 中华神经科杂志

Neurodegenerative disease is a type of disease characterized by the progressive loss of neurons, the cause of which is not clear. Aquaporin-4 (AQP4) is a member of the aquaporin family, which plays an important role in maintaining water homeostasis in the brain. In recent years, researchers found that AQP4 has the functions of draining brain metabolic wastes and participating in material exchange through the glmphatic system. This review aims to summarize the current researches of AQP4 in the pathogenesis and progression of neurodegenerative diseases such as Parkinson′s disease and Alzheimer′s disease, and to propose future research directions.

The glymphatic system: a new exploration of the clearance of alpha-synuclein in Parkinson′s disease / 中华神经科杂志

Parkinson′s disease (PD) is a common neurodegenerative disease. Impaired balance between deposition and clearance of α-synuclein lies at the core of PD pathogenesis. The glymphatic system is a highly organized fluid transport system that is capable of removing brain waste. Emerging evidence revealed that glymphatic dysfunction plays a critical role in the pathogenesis of neurodegenerative diseases, yet study on its implication in PD is at its early stage. An in-depth study of the relationship between the function of the glymphatic system and α-synuclein clearance in PD may shed light on the pathogenesis and therapeutics of the disease.

Unveiling sleep mysteries: functions / Revelando mistérios do sono: funções

Sleep occupies roughly one-third of human lives, yet it is still not entirely scientifically clear about its purpose or function. However, the latest research achievement concluded that sleeping has much more effect on the brain than formerly believed. Much of these studies are about the effects of sleep deprivation, and the glymphatic pathway initially identified in the rodent brain. In this paper, it is presented some of the theories about sleep functions, besides a review of some physiologic function of sleep. Now, it is accepted that sleep is involved with cleaning the brain toxins, physical restoration, information processing and recall, regulation, besides strengthening the immune system. Sleep implies in a neuronal activity markedly different along with its phases. It is regulated by two parallel mechanisms, homeostatic and circadian. Besides, the sleep-waking cycle involves diverse brain circuits and neurotransmitters and their interaction is explained using a flip-flop model. Several theories may help clarify the reasons human beings spend an important part of their lives sleeping such as those of Inactivity, Energy Conservation, Restorative, and Brain Plasticity. Recently, it was emphasized the importance of the glymphatic system that is a waste clearence system that acts mainly during sleep support efficient removal of soluble proteins and metabolites from the central nervous system. Indeed, sleep meet the needs of higher brain functions along with basic vital processes.

O sono ocupa cerca de um terço da vida humana, mas ainda não é totalmente claro cientificamente o seu propósito ou função. No entanto, a mais recente pesquisa concluiu que dormir tem muito mais efeito no cérebro do que se pensava anteriormente. Muitos desses estudos são sobre os efeitos da privação do sono e o sistema glinfático inicialmente identificada no cérebro de roedores. Neste artigo, são apresentadas algumas das teorias sobre as funções do sono, além de uma revisão de algumas funções fisiológicas do sono. Agora, aceita-se que o sono esteja envolvido com a limpeza de toxinas cerebrais, restauração física, processamento e memorização de informações, regulação do humor, além de fortalecer o sistema imunológico. O sono implica em uma atividade neuronal marcadamente diferente ao longo de suas fases. É regulado por dois mecanismos paralelos, homeostático e circadiano. Além disso, o ciclo de vigília envolve diversos circuitos cerebrais e neurotransmissores e sua interação é explicada por meio de um modelo de flip-flop. Várias teorias podem ajudar a esclarecer as razões pelas quais o ser humano passa uma parte importante de suas vidas dormindo, como as de inatividade, conservação de energia, restauração e plasticidade cerebral. Recentemente, enfatizou-se a importância do sistema glinfático agir principalmente durante o sono, que é um sistema de eliminação de resíduos para apoiar a remoção eficiente de proteínas e metabólitos solúveis do sistema nervoso central. De fato, o sono atende às necessidades de funções cerebrais superiores, juntamente com processos vitais básicos.

Correlation Analysis of " Toxin Damaging Brain Collaterals" from Glymphatic System / 中国实验方剂学杂志

The collaterals are branches of the meridians and vessels system, and have the roles of connecting upper-lower and interior-exterior portions of the body, the characteristics of two-way flow in supporting the operation of Qi and blood, and the functions of material exchange and metabolism. The brain is the intersection of the Yang meridians. Crisscross brain collaterals permeate Qi and blood to enrich the brain, and spread Yang Qi, in order to warm the brain-mind, and provide material basis and source power to the " brain governing mind" . Under pathological conditions, cerebral collaterals are blocked, and toxic pathogens are endogenous, resulting in " toxin damaging brain collaterals" . This theory is not only applied to the study of stroke pathogenesis, but also extended to other encephalopathy, such as dementia, which promoted the development of the theory of pathogenesis in traditional Chinese medicine. Recently, a " glymphatic system" was discovered in the brain, which is an exchange flow system of cerebrospinal fluid-brain interstitial fluid mediated by astrocyte. The glymphatic system transports nutrients and neuroactive substances, such as glucose, lipids, electrolytes and apolipoprotein E in the cerebrospinal fluid, to brain tissue, and also removes metabolic products (such as lactic acid), soluble proteins (such as β-amyloid protein and Tau protein) from the brain and foreign bodies, which are important liquid flow systems that maintain the homeostasis of the brain. The discovery of the glymphatic system provides a new perspective for the study of pathological mechanism of neurological diseases, and may become a new target for interventions in neurological diseases, such as cerebrovascular diseases and neurodegenerative diseases. As a widely distributed cerebral metabolic waste removal way and material delivery system, the lymphatic system may be the biological foundation of " brain collateral" disease, and a cross point of understanding on " toxin impairing brain collaterals" by Western and traditional Chinese medicine. The study based on the glymphatic system will give a more rational explanation on " toxic damage to brain collaterals" .

Persistent Malfunction of Glymphatic and Meningeal Lymphatic Drainage in a Mouse Model of Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is a devastating cerebrovascular event that often is followed by permanent brain impairments. It is necessary to explore the pathogenesis of secondary pathological damages in order to find effective interventions for improving the prognosis of SAH. Blockage of brain lymphatic drainage has been shown to worsen cerebral ischemia and edema after acute SAH. However, whether or not there is persistent dysfunction of cerebral lymphatic drainage following SAH remains unclear. In this study, autologous blood was injected into the cisterna magna of mice to establish SAH model. One week after surgery, SAH mice showed decreases in fluorescent tracer drainage to the deep cervical lymph nodes (dcLNs) and influx into the brain parenchyma after injection into the cisterna magna. Moreover, SAH impaired polarization of astrocyte aquaporin-4 (AQP4) that is a functional marker of glymphatic clearance and resulted in accumulations of Tau proteins as well as CD3⁺, CD4⁺, and CD8⁺ cells in the brain. In addition, pathological changes, including microvascular spasm, activation of glial cells, neuroinflammation, and neuronal apoptosis were observed in the hippocampus of SAH mice. Present results demonstrate persistent malfunction of glymphatic and meningeal lymphatic drainage and related neuropathological damages after SAH. Targeting improvement of brain lymphatic clearance potentially serves as a new strategy for the treatment of SAH.

The Glymphatic System: A Review

The brain represents 2% of the adult body mass; conversely, it is responsible for 20% to 25% of the glucose and 20% of the oxygen consumption, receiving 15% of the cardiac output. This substantial metabolic rate is associated with a significant production of biological debris, which is potentially toxic. Therefore, a complex and efficient clearance system is required to prevent the accumulation of byproducts and ensure optimal function. However, until today, there is little knowledge about this topic. The glymphatic system, also known as perivascular pathway, is a recently described glialdependent network that is responsible for the clearance of metabolites from the central nervous system (CNS), playing a role equivalent to the one played by the lymphatic vessels present in other organs. Studies have demonstrated that the glymphatic pathway has a paramount role in protein homeostasis, and that the malfunction of this system may be related to the development of neurodegenerative disorders such as Alzheimer disease and normal pressure hydrocephalus. They also showed that body posture, exercise and the state of consciousness influence the glymphatic transport. In this context, the understanding of this clearance system could not only clarify the pathophysiology of several diseases, but also contribute to future therapeutic interventions. In the present article, we will evaluate the glymphatic pathway, focusing on the factors that regulate its flow, as well as on its role in CNS physiology and in disease initiation and progression, including dementia, hydrocephalus, glaucoma and traumatic brain injury. Ultimately, this review also aims to encourage further research on novel therapeutic targets.

Current understanding of neuroinflammation after traumatic brain injury and cell-based therapeutic opportunities / 中华创伤杂志(英文版)

Traumatic brain injury (TBI) remains a major cause of death and disability worldwide. Increasing evidence indicates that TBI is an important risk factor for neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and chronic traumatic encephalopathy. Despite improved supportive and rehabilitative care of TBI patients, unfortunately, all late phase clinical trials in TBI have yet to yield a safe and effective neuroprotective treatment. The disappointing clinical trials may be attributed to variability in treatment approaches and heterogeneity of the population of TBI patients as well as a race against time to prevent or reduce inexorable cell death. TBI is not just an acute event but a chronic disease. Among many mechanisms involved in secondary injury after TBI, emerging preclinical studies indicate that posttraumatic prolonged and progressive neuroinflammation is associated with neurodegeneration which may be treatable long after the initiating brain injury. This review provides an overview of recent understanding of neuroinflammation in TBI and preclinical cell-based therapies that target neuroinflammation and promote functional recovery after TBI.