The role of AQP4 in the pathogenesis of depression, and possible related mechanisms

Targeting the brain's glymphatic pathway: A novel therapeutic approach for cerebral small vessel disease

Cerebral small vessel disease encompasses a group of neurological disorders characterized by injury to small blood vessels, often leading to stroke and dementia. Due to its diverse etiologies and complex pathological mechanisms, preventing and treating cerebral small vessel vasculopathy is challenging. Recent studies have shown that the glymphatic system plays a crucial role in interstitial solute clearance and the maintenance of brain homeostasis. Increasing evidence also suggests that dysfunction in glymphatic clearance is a key factor in the progression of cerebral small vessel disease. This review begins with a comprehensive introduction to the structure, function, and driving factors of the glymphatic system, highlighting its essential role in brain waste clearance. Afterwards, cerebral small vessel disease was reviewed from the perspective of the glymphatic system, after which the mechanisms underlying their correlation were summarized. Glymphatic dysfunction may lead to the accumulation of metabolic waste in the brain, thereby exacerbating the pathological processes associated with cerebral small vessel disease. The review also discussed the direct evidence of glymphatic dysfunction in patients and animal models exhibiting two subtypes of cerebral small vessel disease: arteriolosclerosis-related cerebral small vessel disease and amyloid-related cerebral small vessel disease. Diffusion tensor image analysis along the perivascular space is an important non-invasive tool for assessing the clearance function of the glymphatic system. However, the effectiveness of its parameters needs to be enhanced. Among various nervous system diseases, including cerebral small vessel disease, glymphatic failure may be a common final pathway toward dementia. Overall, this review summarizes prevention and treatment strategies that target glymphatic drainage and will offer valuable insight for developing novel treatments for cerebral small vessel disease.

Reduced glymphatic clearance in early psychosis

Psychosis involves neuroinflammation and oxidative stress, both affecting the glymphatic system, the lymphatic-like, fluid-transport system in the brain. However, it is unclear whether early psychosis is related to impairments in glymphatic functions. In resting-state fMRI, it has been recently established in a number of neurodegenerative diseases that the coupling relationship between cortical blood-oxygen-level-dependent (BOLD) signal and ventricular cerebrospinal fluid (CSF) flow is associated with brain waste clearance, a key glymphatic function that has not been examined in psychosis or any other psychiatric populations. In a large dataset (total n = 137, age = 23.86 ± 4.16), we demonstrated that glymphatic clearance marked by BOLD-CSF coupling was weaker and more delayed in patients with early psychosis compared to healthy controls. BOLD-CSF coupling also varied between the non-affective and affective psychosis groups with group differences most prominent in high-order but not low-order cortical regions. Finally, reduced global BOLD-CSF coupling was associated with cognitive decline and more severe psychotic symptoms. We provided novel evidence highlighting dysregulated coupling between cortical activity and macroscopic CSF flow as a biomarker for early psychosis. Similar to recent observations in neurodegenerative disorders, the association between reduced BOLD-CSF coupling and psychotic symptoms suggested that waste clearance is disrupted in psychosis which shed light on the pathophysiology of this disease from a glymphatic point of view.

Aquaporin 4 modulation drives amyloid burden and cognitive abilities in an APPPS1 mouse model of Alzheimer's disease

INTRODUCTION

Deficiency in the aquaporin-4 (AQP4) water channel has been linked to impaired amyloid beta (Aβ) clearance. However, a detailed morphopathological analysis of amyloid deposition following AQP4 therapeutic modulation remains unexplored.

METHODS

Two-month-old amyloid precursor protein presenilin 1 (APPPS1) mice were treated daily for 28 days with either the AQP4 facilitator N-(3-(Benzyloxy)pyridin-2-yl) benzene-sulfonamide (TGN-073) or the AQP4 inhibitor N-(1,3,4-thiadiazol-2-yl)pyridine-3-carboxamide dihydrochloride (TGN-020) (both at 200 mg/kg). Controls included vehicle-treated APPPS1 and WT C57BL/6J mice. Comprehensive histopathological, biochemical, and behavioral analyses were conducted.

RESULTS

Mice treated with AQP4 facilitator showed a significant reduction in total Aβ, fibrillar deposits, and soluble Aβ, while the AQP4 inhibitor caused a substantial increase in brain Aβ. AQP4-facilitator treatment also reduced Aβ40 levels and Aβ40/Aβ42 ratio, whereas the inhibitor treatment increased both Aβ40 and Aβ42. Additionally, facilitator-treated mice demonstrated reduced anxiety and improved memory performance.

DISCUSSION

These findings suggest that AQP4 modulation is a promising strategy to enhance Aβ clearance and a potential therapeutic target in Alzheimer's disease.

HIGHLIGHTS

Intramural periarterial drainage of the interstitial fluid mediated by aquaporin-4 (AQP4) is a key element that ensures clearance of catabolites/Aβ peptide from within the brain parenchyma. Inhibition of AQP4 in an APPPS1 mouse model of AD leads to increased amyloid deposition and deficient behavior compared to untreated transgenic animals. Pharmaceutical facilitation of AQP4 in the same APPPS1 mouse model leads to a massive decrease in amyloid burden and improves the behavioral performance of the animals compared to untreated control APPPS1 mice.

Melatonin Mitigates Sleep Restriction-Induced Cognitive and Glymphatic Dysfunction Via Aquaporin-4 Polarization

Chronic sleep restriction (SR) impairs the glymphatic clearance of macromolecular toxic metabolites, which is associated with the loss of perivascular polarization of aquaporin-4 (AQP4). Melatonin (Mel) has been shown to maintain the circadian rhythm of AQP4 polarization. However, the role of AQP4 polarization in Mel's protective effects against SR-induced brain dysfunction remains unclear. In the present study, using a modified rotating rod SR mouse model, we demonstrated the time-dependent effect of SR on short-term memory deficits and AQP4 mislocalization in the hippocampus. Subsequent experiments characterized the dose-dependent pattern of Mel ameliorating SR-induced impairments of cognitive function and AQP4 polarity. Mel's treatment enhanced glymphatic transport in SR mice, as revealed by cerebrospinal tracer experiments, and reduced hippocampal amyloid-beta and phosphorylated tau levels. Additionally, Mel significantly decreased glial cell activation, pro-inflammatory cytokine production, and synaptic protein loss in the hippocampus of SR mice. However, in AQP4 knockout mice, Mel's protective effects against SR-induced pathophysiological alterations described above were largely abolished. Mechanistically, Mel activated the vitamin D receptor and then upregulated expression of DTNA (Dystrobrevin Alpha), a key component of the dystrophin-associated complex, which in turn restored AQP4 polarization during chronic SR conditions. This finding indicates that AQP4-mediated lymphatic clearance is necessary for Mel to combat chronic SR-induced brain impairment.

Astrocytic cannabinoid receptor 1 promotes resilience by dampening stress-induced blood-brain barrier alterations

Blood-brain barrier (BBB) alterations contribute to stress vulnerability and the development of depressive behaviors. In contrast, neurovascular adaptations underlying stress resilience remain unclear. Here we report that high expression of astrocytic cannabinoid receptor 1 (CB1) in the nucleus accumbens (NAc) shell, particularly in the end-feet ensheathing blood vessels, is associated with resilience during chronic social stress in adult male mice. Viral-mediated overexpression of Cnr1 in astrocytes of the NAc shell results in baseline anxiolytic effects and dampens stress-induced anxiety- and depression-like behaviors in male mice. It promotes the expression of vascular-related genes and reduces astrocyte inflammatory response and morphological changes following an immune challenge with the cytokine interleukin-6, linked to stress susceptibility and mood disorders. Physical exercise and antidepressant treatment increase the expression of astrocytic Cnr1 in the perivascular region in male mice. In human tissue from male donors with major depressive disorder, we observe loss of CNR1 in the NAc astrocytes. Our findings suggest a role for the astrocytic endocannabinoid system in stress responses via modulation of the BBB.

Perivascular glial reactivity is a feature of phosphorylated tau lesions in chronic traumatic encephalopathy

Chronic traumatic encephalopathy (CTE), a neurodegenerative disease associated with repetitive head injuries, is characterised by perivascular hyperphosphorylated tau (p-tau) accumulations within the depths of cortical sulci. Although the majority of CTE literature focuses on p-tau pathology, other pathological features such as glial reactivity, vascular damage, and axonal damage are relatively unexplored. In this study, we aimed to characterise these other pathological features, specifically in CTE p-tau lesion areas, to better understand the microenvironment surrounding the lesion. We utilised multiplex immunohistochemistry to investigate the distribution of 32 different markers of cytoarchitecture and pathology that are relevant to both traumatic brain injury and neurodegeneration. We qualitatively assessed the multiplex images and measured the percentage area of labelling for each marker in the lesion and non-lesion areas of CTE cases. We identified perivascular glial reactivity as a prominent feature of CTE p-tau lesions, largely driven by increases in astrocyte reactivity compared to non-lesion areas. Furthermore, we identified astrocytes labelled for both NAD(P)H quinone dehydrogenase 1 (NQO1) and L-ferritin, indicating that lesion-associated glial reactivity may be a compensatory response to iron-induced oxidative stress. Our findings demonstrate that perivascular inflammation is a consistent feature of the CTE pathognomonic lesion and may contribute to the pathogenesis of brain injury-related neurodegeneration.

AQP4 is upregulated in schizophrenia and Its inhibition attenuates MK-801-induced schizophrenia-like behaviors in mice

BACKGROUND

The pathophysiology and molecular mechanisms of schizophrenia (SCZ) remain unclear, and the effective treatment resources are still limited. The goal of this study is to identify the expression of AQP4 in SCZ patients and explore whether AQP4 inhibition could ameliorate schizophrenia-like behaviors and its mechanisms.

METHODS

Microarray datasets of PFC compared with healthy control were searched in the Gene Expression Omnibus (GEO) database, and differentially expressed genes (DEGs) were analyzed with the GEO2R online tool. The Venny online tool and metascape online software were used to identify common abnormally expressed genes and conduct cell type signature enrichment analysis. SCZ mouse models were induced with MK-801, an NMDA receptor antagonist (intraperitoneal injection, 0.1 mg/kg/day for 7 days), and C6 cell models were treated with 100 μM MK-801. RT-qPCR, Western Blotting, and immunofluorescence were employed to determine the expression of AQP4, proinflammatory cytokines, and GFAP. Open field tests and social interaction tests were performed to evaluate the schizophrenia-like behaviors.

RESULTS

Bioinformatics analysis identified upregulation of AQP4 in the PFC of SCZ patients compared with healthy controls. Cell type signature enrichment analysis showed that all three DEGs lists were strongly enriched in the FAN EMBRYONIC CTX ASTROCYTE 2 category. Upregulation of AQP4 was also observed in MK-801-treated C6 cells and the PFC of MK-801-induced SCZ mouse model. Moreover, AQP4 inhibition with TGN-020 (an inhibitor of AQP4) improved anxiety-like behavior and social novelty preference defects in MK-801-treated mice. AQP4 inhibition also reduced the expression of IL-1β, IL-6, and TNF-α in MK-801-treated C6 cells and mouse model.

CONCLUSIONS

AQP4 is upregulated in the PFC of SCZ patients compared with healthy controls. AQP4 inhibition could alleviate the anxiety-like behavior and social novelty defects in MK-801-treated mice, this may be due to the role of AQP4 in the regulation of the expression of proinflammatory cytokines.

Glymphatic System and Psychiatric Disorders: A Rapid Comprehensive Scoping Review

BACKGROUND

Since discovering the glymphatic system, there has been a looming interest in exploring its relationship with psychiatric disorders. Recently, increasing evidence suggests an involvement of the glymphatic system in the pathophysiology of psychiatric disorders. However, clear data are still lacking. In this context, this rapid comprehensive PRISMA-ScR (Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews) scoping review aims to identify and analyze current evidence about the relation between the glymphatic system and psychiatric disorders.

METHODS

We conducted a comprehensive review of the literature and then proceeded to discuss the findings narratively. Tables were then constructed and articles were sorted according to authors, year, title, location of study, sample size, psychiatric disorder, the aim of the study, principal findings, implications.

RESULTS

Twenty papers were identified as eligible, among which 2 articles on Schizophrenia, 1 on Autism Spectrum Disorders, 2 on Depression, 1 on Depression and Trauma-related Disorders, 1 on Depression and Anxiety, 2 on Anxiety and Sleep Disorders, 8 on Sleep Disorders, 2 on Alcohol use disorder and 1 on Cocaine Use Disorder.

CONCLUSION

This review suggests a correlation between the glymphatic system and several psychiatric disorders: Schizophrenia, Depression, Anxiety Disorders, Sleep Disorders, Alcohol Use Disorder, Cocaine Use Disorder, Trauma-Related Disorders, and Autism Spectrum Disorders. Impairment of the glymphatic system could play a role in Trauma-Related Disorders, Alcohol Use Disorders, Cocaine Use Disorders, Sleep Disorders, Depression, and Autism Spectrum Disorders. It is important to implement research on this topic and adopt standardized markers and radio diagnostic tools.

Astrocytes in Post-Stroke Depression: Roles in Inflammation, Neurotransmission, and Neurotrophin Signaling

Post-stroke depression (PSD) is a frequent and disabling complication of stroke that affects up to one-third of stroke survivors. The pathophysiology of PSD involves multiple mechanisms, including neurochemical, neuroinflammatory, neurotrophic, and neuroplastic changes. Astrocytes are a type of glial cell that is plentiful and adaptable in the central nervous system. They play key roles in various mechanisms by modulating neurotransmission, inflammation, neurogenesis, and synaptic plasticity. This review summarizes the latest evidence of astrocyte involvement in PSD from human and animal studies, focusing on the alterations of astrocyte markers and functions in relation to monoamine neurotransmitters, inflammatory cytokines, brain-derived neurotrophic factor, and glutamate excitotoxicity. We also discuss the potential therapeutic implications of targeting astrocytes for PSD prevention and treatment. Astrocytes could be new candidates for antidepressant medications and other interventions that aim to restore astrocyte homeostasis and function in PSD. Astrocytes could be new candidates for antidepressant medications and other interventions that aim to restore astrocyte homeostasis and function in PSD.

Recent Developments in Protein Lactylation in PTSD and CVD: Novel Strategies and Targets

In 1938, Corneille Heymans received the Nobel Prize in physiology for discovering that oxygen sensing in the aortic arch and carotid sinus was mediated by the nervous system. The genetics of this process remained unclear until 1991 when Gregg Semenza while studying erythropoietin, came upon hypoxia-inducible factor 1, for which he obtained the Nobel Prize in 2019. The same year, Yingming Zhao found protein lactylation, a posttranslational modification that can alter the function of hypoxia-inducible factor 1, the master regulator of cellular senescence, a pathology implicated in both post-traumatic stress disorder (PTSD) and cardiovascular disease (CVD). The genetic correlation between PTSD and CVD has been demonstrated by many studies, of which the most recent one utilizes large-scale genetics to estimate the risk factors for these conditions. This study focuses on the role of hypertension and dysfunctional interleukin 7 in PTSD and CVD, the former caused by stress-induced sympathetic arousal and elevated angiotensin II, while the latter links stress to premature endothelial cell senescence and early vascular aging. This review summarizes the recent developments and highlights several novel PTSD and CVD pharmacological targets. They include lactylation of histone and non-histone proteins, along with the related biomolecular actors such as hypoxia-inducible factor 1α, erythropoietin, acid-sensing ion channels, basigin, and Interleukin 7, as well as strategies to delay premature cellular senescence by telomere lengthening and resetting the epigenetic clock.

Choroid Plexus Aquaporins in CSF Homeostasis and the Glymphatic System: Their Relevance for Alzheimer's Disease

The glymphatic system, a fluid-clearance pathway involved in brain waste clearance, is known to be impaired in neurological disorders, including Alzheimer's disease (AD). For this reason, it is important to understand the specific mechanisms and factors controlling glymphatic function. This pathway enables the flow of cerebrospinal fluid (CSF) into the brain and subsequently the brain interstitium, supported by aquaporins (AQPs). Continuous CSF transport through the brain parenchyma is critical for the effective transport and drainage of waste solutes, such as toxic proteins, through the glymphatic system. However, a balance between CSF production and secretion from the choroid plexus, through AQP regulation, is also needed. Thus, any condition that affects CSF homeostasis will also interfere with effective waste removal through the clearance glymphatic pathway and the subsequent processes of neurodegeneration. In this review, we highlight the role of AQPs in the choroid plexus in the modulation of CSF homeostasis and, consequently, the glymphatic clearance pathway, with a special focus on AD.

Aquaporins in Nervous System

Aquaporins (AQPs) mediate water flux between the four distinct water compartments in the central nervous system (CNS). In the present chapter, we mainly focus on the expression and function of the nine AQPs expressed in the CNS, which include five members of aquaporin subfamily: AQP1, AQP4, AQP5, AQP6, and AQP8; three members of aquaglyceroporin subfamily: AQP3, AQP7, and AQP9; and one member of superaquaporin subfamily: AQP11. In addition, AQP1, AQP2, and AQP4 expressed in the peripheral nervous system are also reviewed. AQP4, the predominant water channel in the CNS, is involved both in the astrocyte swelling of cytotoxic edema and the resolution of vasogenic edema and is of pivotal importance in the pathology of brain disorders such as neuromyelitis optica, brain tumors, and neurodegenerative disorders. Moreover, AQP4 has been demonstrated as a functional regulator of recently discovered glymphatic system that is a main contributor to clearance of toxic macromolecule from the brain. Other AQPs are also involved in a variety of important physiological and pathological process in the brain. It has been suggested that AQPs could represent an important target in treatment of brain disorders like cerebral edema. Future investigations are necessary to elucidate the pathological significance of AQPs in the CNS.

AQP4 Attenuated TRAF6/NFκB Activation in Acrylamide-Induced Neurotoxicity

Acrylamide (ACR) is present in high-temperature-processed high-carbohydrate foods, cigarette smoke, and industrial pollution. Chronic exposure to ACR may induce neurotoxicity from reactive oxygen species (ROS); however, the mechanisms underlying ACR-induced neurotoxicity remain unclear. We studied 28-day subacute ACR toxicity by repeatedly feeding ACR (0, 15, or 30 mg/kg) to rats. We conducted RNA sequencing and Western blot analyses to identify differences in mRNA expression in the blood and in protein expression in the brain tissues, respectively, of the rats. AQP4 transient transfection was performed to identify potential associations with protein regulation. The rats treated with 30 mg/kg ACR exhibited hind-limb muscle weakness. Matrix metalloproteinase (MMP9) expression was higher in the ACR-treated group than in the control group. ACR induced MMP-9 and AQP4 protein expression in the brain tissues of the rats, which subsequently presented with neurotoxicity. In the in vitro study, Neuro-2a cells were transiently transfected with AQP4, which inhibited MMP-9 and TNF receptor-associated factor 6 (TRAF6) expression, and inhibited ACR induced expression of TRAF6, IκBα, and nuclear factor κB (NFκB). Using a combination of in vivo and in vitro experiments, this study revealed that depressive symptoms associated with ACR-induced neurotoxicity are associated with downregulation of AQP4 and induction of the TRAF6 pathway.