Aquaporin 4 is differentially increased and dislocated in association with tau and amyloid-beta

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.

Dual orexin receptor antagonists as promising therapeutics for Alzheimer's disease

We examine the relationship between sleep, glymphatics and Alzheimer's disease (AD), and recent work questioning glymphatic clearance during sleep. We highlight a need for understanding glymphatic and/or other mechanism of clearance during sleep, and review glymphatic flow measurement methods. Further, we explore dual orexin receptor antagonists (DORAs) potential to mitigate AD sleep disturbances and enhance clearance. Further research could elucidate a linkage between DORAs, improved sleep and reducing AD pathophysiology.

Regional Alterations in Müller Cell Protein Expression in Human and a Rat Model of Geographic Atrophy

Purpose

Despite being crucial to neuronal survival, the role Müller cells play in geographic atrophy (GA) has only recently been considered. We investigated whether Müller cells retain their normal functional profile or form a fibrotic scar when remodeling in human GA eyes and our subretinal sodium iodate (NaIO3) model.

Methods

Sprague Dawley rats given subretinal injections of NaIO3 (5 mg/mL) were sacrificed at 3 and 12 weeks. Cryosections and retinal flatmounts from rats and cryosections from human GA eyes were stained with antibodies against the Müller cell proteins glutamine synthetase (GS), inwardly rectifying potassium channel 4.1 (Kir4.1), aquaporin 4 (AQP4), cellular retinaldehyde-binding protein 1 (CRALBP), and glial fibrillary acidic protein (GFAP), as well as alpha smooth muscle actin (α-SMA), fibronectin, and collagens I and IV. The immunofluorescence intensity of AQP4 and Kir4.1 was quantified using Image J, and Kir4.1 protein levels were verified by western blot.

Results

In both human GA eyes and NaIO3-injected rats, Müller cell processes at the external limiting membrane (ELM) descent and in the subretinal membrane exhibited increased GS expression. GFAP was elevated throughout the Müller cells. AQP4 staining at the ELM descent was particularly pronounced throughout the radial processes, including those extending into the subretinal space. In NaIO3-injected rats, perivascular Kir4.1 expression significantly decreased in the atrophic retina, but expression increased in the subretinal glial membrane. α-SMA and extracellular matrix proteins were not detected in the subretinal membrane.

Conclusions

Our findings underscore the persistence of homeostatic proteins, albeit altered, in Müller cells as they remodel and extend into the subretinal space.

Spiral volumetric optoacoustic tomography of reduced oxygen saturation in the spinal cord of M83 mouse model of Parkinson's disease

PURPOSE

Metabolism and bioenergetics in the central nervous system play important roles in the pathophysiology of Parkinson's disease (PD). Here, we employed a multimodal imaging approach to assess oxygenation changes in the spinal cord of the transgenic M83 murine model of PD overexpressing the mutated A53T alpha-synuclein form in comparison with non-transgenic littermates.

METHODS

In vivo spiral volumetric optoacoustic tomography (SVOT) was performed to assess oxygen saturation (sO2) in the spinal cords of M83 mice and non-transgenic littermates. Ex vivo high-field T1-weighted (T1w) magnetic resonance imaging (MRI) at 9.4T was used to assess volumetric alterations in the spinal cord. 3D SVOT analysis and deep learning-based automatic segmentation of T1w MRI data for the mouse spinal cord were developed for quantification. Immunostaining for phosphorylated alpha-synuclein (pS129 α-syn), as well as vascular organization (CD31 and GLUT1), was performed after MRI scan.

RESULTS

In vivo SVOT imaging revealed a lower sO2SVOT in the spinal cord of M83 mice compared to non-transgenic littermates at sub-100 μm spatial resolution. Ex vivo MRI-assisted by in-house developed deep learning-based automatic segmentation (validated by manual analysis) revealed no volumetric atrophy in the spinal cord of M83 mice compared to non-transgenic littermates at 50 μm spatial resolution. The vascular network was not impaired in the spinal cord of M83 mice in the presence of pS129 α-syn accumulation.

CONCLUSION

We developed tools for deep-learning-based analysis for the segmentation of mouse spinal cord structural MRI data, and volumetric analysis of sO2SVOT data. We demonstrated non-invasive high-resolution imaging of reduced sO2SVOT in the absence of volumetric structural changes in the spinal cord of PD M83 mouse model.

Astrocytic proteins involved in regulation of the extracellular environment are increased in the Alzheimer's disease middle temporal gyrus

Alzheimer's disease (AD) has complex pathophysiology involving numerous cell types and brain processes. Astrocyte involvement in AD is gaining increased attention, however a complete characterisation of astrocytic changes in the AD human brain is warranted. Astrocytes perform important homeostatic functions including regulation of the extracellular microenvironment, critical for the health of all brain cells. We have investigated changes to key astrocyte proteins involved in the regulation of CNS extracellular environment in the human AD middle temporal gyrus (MTG): aquaporin-4 (AQP-4), glutamate transporter-1 (GLT-1) and inwardly-rectifying potassium channel 4.1 (Kir4.1). We have used a high-throughput human brain tissue microarray platform with automated quantitative image analysis to measure protein changes in a large cohort of neurological control and AD cases. We found increased astrocytic glial acidic fibrillary protein (GFAP), AQP-4, GLT-1 and Kir4.1 expression that correlates with advancing Braak stage, increasing amyloid pathology and, to a greater extent, the degree of tau pathology. We confirmed that Kir4.1 immunostaining is predominantly found in astrocytes and revealed a novel redistribution of Kir4.1 protein expression into astrocytic processes in the AD MTG. Our study presents novel and potentially modifiable glial changes in the AD human brain that are critical to our understanding of disease pathogenesis.

Visualizing alpha-synuclein and iron deposition in M83 mouse model of Parkinson's disease in vivo

Abnormal alpha-synuclein (αSyn) and iron accumulation in the brain play an important role in Parkinson's disease (PD). Herein, we aim to visualize αSyn inclusions and iron deposition in the brains of M83 (A53T) mouse models of PD in vivo. The fluorescent pyrimidoindole derivative THK-565 probe was characterized by means of recombinant fibrils and brains from 10- to 11-month-old M83 mice. Concurrent wide-field fluorescence and volumetric multispectral optoacoustic tomography (vMSOT) imaging were subsequently performed in vivo. Structural and susceptibility weighted imaging (SWI) magnetic resonance imaging (MRI) at 9.4 T as well as scanning transmission x-ray microscopy (STXM) were performed to characterize the iron deposits in the perfused brains. Immunofluorescence and Prussian blue staining were further performed on brain slices to validate the detection of αSyn inclusions and iron deposition. THK-565 showed increased fluorescence upon binding to recombinant αSyn fibrils and αSyn inclusions in post-mortem brain slices from patients with PD and M83 mice. Administration of THK-565 in M83 mice showed higher cerebral retention at 20 and 40 min post-intravenous injection by wide-field fluorescence compared to nontransgenic littermate mice, in congruence with the vMSOT findings. SWI/phase images and Prussian blue indicated the accumulation of iron deposits in the brains of M83 mice, presumably in the Fe3+ form, as evinced by the STXM results. In conclusion, we demonstrated in vivo mapping of αSyn by means of noninvasive epifluorescence and vMSOT imaging and validated the results by targeting the THK-565 label and SWI/STXM identification of iron deposits in M83 mouse brains ex vivo.

Relationship Between Reactive Astrocytes, by [18F]SMBT-1 Imaging, with Amyloid-Beta, Tau, Glucose Metabolism, and TSPO in Mouse Models of Alzheimer's Disease

Reactive astrocytes play an important role in the development of Alzheimer's disease (AD). Here, we aimed to investigate the temporospatial relationships among monoamine oxidase-B, tau and amyloid-β (Aβ), translocator protein, and glucose metabolism by using multitracer imaging in AD transgenic mouse models. Positron emission tomography (PET) imaging with [18F]SMBT-1 (monoamine oxidase-B), [18F]florbetapir (Aβ), [18F]PM-PBB3 (tau), [18F]fluorodeoxyglucose (FDG), and [18F]DPA-714 (translocator protein) was carried out in 5- and 10-month-old APP/PS1, 11-month-old 3×Tg mice, and aged-matched wild-type mice. The brain regional referenced standard uptake value (SUVR) was computed with the cerebellum as the reference region. Immunofluorescence staining was performed on mouse brain tissue slices. [18F]SMBT-1 and [18F]florbetapir SUVRs were greater in the cortex and hippocampus of 10-month-old APP/PS1 mice than in those of 5-month-old APP/PS1 mice and wild-type mice. No significant difference in the regional [18F]FDG or [18F]DPA-714 SUVRs was observed in the brains of 5- or 10-month-old APP/PS1 mice or wild-type mice. No significant difference in the SUVRs of any tracer was observed between 11-month-old 3×Tg mice and age-matched wild-type mice. A positive correlation between the SUVRs of [18F]florbetapir and [18F]DPA-714 in the cortex and hippocampus was observed among the transgenic mice. Immunostaining validated the distribution of MAO-B and limited Aβ and tau pathology in 11-month-old 3×Tg mice; and Aβ deposits in brain tissue from 10-month-old APP/PS1 mice. In summary, these findings provide in vivo evidence that an increase in astrocyte [18F]SMBT-1 accompanies Aβ accumulation in APP/PS1 models of AD amyloidosis.

Non-coding RNAs and Aquaporin 4: Their Role in the Pathogenesis of Neurological Disorders

Neurological disorders are a major group of non-communicable diseases affecting quality of life. Non-Coding RNAs (ncRNAs) have an important role in the etiology of neurological disorders. In studies on the genesis of neurological diseases, aquaporin 4 (AQP4) expression and activity have both been linked to ncRNAs. The upregulation or downregulation of several ncRNAs leads to neurological disorder progression by targeting AQP4. The role of ncRNAs and AQP4 in neurological disorders is discussed in this review.

Reduced SV2A and GABAA receptor levels in the brains of type 2 diabetic rats revealed by [18F]SDM-8 and [18F]flumazenil PET

PURPOSE

Type 2 diabetes mellitus (T2DM) is associated with a greater risk of Alzheimer's disease. Synaptic impairment and protein aggregates have been reported in the brains of T2DM models. Here, we assessed whether neurodegenerative changes in synaptic vesicle 2 A (SV2A), γ-aminobutyric acid type A (GABAA) receptor, amyloid-β, tau and receptor for advanced glycosylation end product (RAGE) can be detected in vivo in T2DM rats.

METHODS

Positron emission tomography (PET) using [18F]SDM-8 (SV2A), [18F]flumazenil (GABAA receptor), [18F]florbetapir (amyloid-β), [18F]PM-PBB3 (tau), and [18F]FPS-ZM1 (RAGE) was carried out in 12-month-old diabetic Zucker diabetic fatty (ZDF) and SpragueDawley (SD) rats. Immunofluorescence staining, Thioflavin S staining, proteomic profiling and pathway analysis were performed on the brain tissues of ZDF and SD rats.

RESULTS

Reduced cortical [18F]SDM-8 uptake and cortical and hippocampal [18F]flumazenil uptake were observed in 12-month-old ZDF rats compared to SD rats. The regional uptake of [18F]florbetapir and [18F]PM-PBB3 was comparable in the brains of 12-month-old ZDF and SD rats. Immunofluorescence staining revealed Thioflavin S-negative, phospho-tau-positive inclusions in the cortex and hypothalamus in the brains of ZDF rats and the absence of amyloid-beta deposits. The level of GABAA receptors was lower in the cortex of ZDF rats than SD rats. Proteomic analysis further demonstrated that, compared with SD rats, synaptic-related proteins and pathways were downregulated in the hippocampus of ZDF rats.

CONCLUSION

These findings provide in vivo evidence for regional reductions in SV2A and GABAA receptor levels in the brains of aged T2DM ZDF rats.

Glymphatic System Pathology and Neuroinflammation as Two Risk Factors of Neurodegeneration

The key to the effective treatment of neurodegenerative disorders is a thorough understanding of their pathomechanism. Neurodegeneration and neuroinflammation are mutually propelling brain processes. An impairment of glymphatic system function in neurodegeneration contributes to the progression of pathological processes. The question arises as to how neuroinflammation and the glymphatic system are related. This review highlights the direct and indirect influence of these two seemingly independent processes. Protein aggregates, a characteristic feature of neurodegeneration, are correlated with glymphatic clearance and neuroinflammation. Glial cells cannot be overlooked when considering the neuroinflammatory processes. Astrocytes are essential for the effective functioning of the glymphatic system and play a crucial role in the inflammatory responses in the central nervous system. It is imperative to acknowledge the significance of AQP4, a protein that exhibits a high degree of polarization in astrocytes and is crucial for the functioning of the glymphatic system. AQP4 influences inflammatory processes that have not yet been clearly delineated. Another interesting issue is the gut-brain axis and microbiome, which potentially impact the discussed processes. A discussion of the correlation between the functioning of the glymphatic system and neuroinflammation may contribute to exploring the pathomechanism of neurodegeneration.

Circadian therapy interventions for glymphatic dysfunction in concussions injuries: A narrative review

There are two primary threats to the brain after concussion. The first is a buildup of neurotoxic proteins in the brain. The second, a partial consequence of the first, is a sustained neuroinflammatory response that may lead to central sensitization and the development of persistent post-concussive symptoms. These threats make neurotoxin clearance a high clinical priority in the acute period after injury. The glymphatic system is the brain's primary mechanism for clearing neurotoxic waste. The glymphatic system is intimately tied to the sleep cycle and circadian dynamics. However, glymphatic dysfunction and sleep disturbances are nearly ubiquitous in the acute period after concussion injury. Because of this, sleep optimization via circadian therapy is a time-sensitive and critical tool in acute concussion management.

Visualizing alpha-synuclein and iron deposition in M83 mouse model of Parkinson's disease in vivo

Background

Abnormal alpha-synuclein and iron accumulation in the brain play an important role in Parkinson's disease (PD). Herein, we aim at visualizing alpha-synuclein inclusions and iron deposition in the brains of M83 (A53T) mouse models of PD in vivo.

Methods

Fluorescently labelled pyrimidoindole-derivative THK-565 was characterized by using recombinant fibrils and brains from 10-11 months old M83 mice, which subsequently underwent in vivo concurrent wide-field fluorescence and volumetric multispectral optoacoustic tomography (vMSOT) imaging. The in vivo results were verified against structural and susceptibility weighted imaging (SWI) magnetic resonance imaging (MRI) at 9.4 Tesla and scanning transmission X-ray microscopy (STXM) of perfused brains. Brain slice immunofluorescence and Prussian blue staining were further performed to validate the detection of alpha-synuclein inclusions and iron deposition in the brain, respectively.

Results

THK-565 showed increased fluorescence upon binding to recombinant alpha-synuclein fibrils and alpha-synuclein inclusions in post-mortem brain slices from patients with Parkinson's disease and M83 mice. i.v. administration of THK-565 in M83 mice showed higher cerebral retention at 20 and 40 minutes post-injection by wide-field fluorescence compared to non-transgenic littermate mice, in congruence with the vMSOT findings. SWI/phase images and Prussian blue indicated the accumulation of iron deposits in the brains of M83 mice, presumably in the Fe3+ form, as evinced by the STXM results.

Conclusion

We demonstrated in vivo mapping of alpha-synuclein by means of non-invasive epifluorescence and vMSOT imaging assisted with a targeted THK-565 label and SWI/STXM identification of iron deposits in M83 mouse brains ex vivo.