White matter lesions in an unselected cohort of the elderly: astrocytic, microglial and oligodendrocyte precursor cell responses

Inhibition of ADORA3 promotes microglial phagocytosis and alleviates chronic ischemic white matter injury

BACKGROUND

Adenosine A3 receptor (ADORA3) belongs to the adenosine receptor families and the role of ADORA3 in vascular dementia (VaD) is largely unexplored. The present study sought to determine the therapeutic role of ADORA3 antagonist in a mouse model of VaD.

METHODS

The GSE122063 dataset was selected to screen the differential expression genes and pathways between VaD patients and controls. A mouse model of bilateral carotid artery stenosis (BCAS) was established. The cognitive functions were examined by the novel object recognition test, Y maze test, and fear of conditioning test. The white matter injury (WMI) was examined by 9.4 T MRI, western blot, and immunofluorescence staining. The mechanisms of ADORA3-regulated phagocytosis by microglia were examined using qPCR, western blot, dual immunofluorescence staining, and flow cytometry.

RESULTS

The expression of ADORA3 was elevated in brain tissues of VaD patients and ADORA3 was indicated as a key gene for VaD in the GSE122063. In BCAS mice, the expression of ADORA3 was predominantly elevated in microglia in the corpus callosum. ADORA3 antagonist promotes microglial phagocytosis to myelin debris by facilitating cAMP/PKA/p-CREB pathway and thereby ameliorates WMI and cognitive impairment in BCAS mice. The therapeutic effect of ADORA3 antagonist was partially reversed by the inhibition of the cAMP/PKA pathway.

CONCLUSIONS

ADORA3 antagonist alleviates chronic ischemic WMI by modulating myelin clearance of microglia, which may be a potential therapeutic target for the treatment of VaD.

Hepatopancreatic metabolic disorders and their implications in the development of Alzheimer's disease and vascular dementia

Dementia has been faced with significant public health challenges and economic burdens that urges the need to develop safe and effective interventions. In recent years, an increasing number of studies have focused on the relationship between dementia and liver and pancreatic metabolic disorders that result in diseases such as diabetes, obesity, hypertension and dyslipidemia. Previous reports have shown that there is a plausible correlation between pathologies caused by hepatopancreatic dysfunctions and dementia. Glucose, insulin and IGF-1 metabolized in the liver and pancreas probably have an important influence on the pathophysiology of the most common dementias: Alzheimer's and vascular dementia. This current review highlights recent studies aimed at identifying convergent mechanisms, such as insulin resistance and other diseases, linked to altered hepatic and pancreatic metabolism, which are capable of causing brain changes that ultimately lead to dementia.

Three-dimensional identification of microvascular pathology and neurovascular inflammation in severe white matter hyperintensity: a case report

White matter hyperintensities (WMH) are the most prevalent markers of cerebral small vessel disease (SVD), which is the major vascular risk factor for dementia. Microvascular pathology and neuroinflammation are suggested to drive the transition from normal-appearing white matter (NAWM) to WMH, particularly in individuals with hypertension. However, current imaging techniques cannot capture ongoing NAWM changes. The transition from NAWM into WMH is a continuous process, yet white matter lesions are often examined dichotomously, which may explain their underlying heterogeneity. Therefore, we examined microvascular and neurovascular inflammation pathology in NAWM and severe WMH three-dimensionally, along with gradual magnetic resonance imaging (MRI) fluid-attenuated inversion recovery (FLAIR) signal (sub-)segmentation. In WMH, the vascular network exhibited reduced length and complexity compared to NAWM. Neuroinflammation was more severe in WMH. Vascular inflammation was more pronounced in NAWM, suggesting its potential significance in converting NAWM into WMH. Moreover, the (sub-)segmentation of FLAIR signal displayed varying degrees of vascular pathology, particularly within WMH regions. These findings highlight the intricate interplay between microvascular pathology and neuroinflammation in the transition from NAWM to WMH. Further examination of neurovascular inflammation across MRI-visible alterations could aid deepening our understanding on WMH conversion, and therewith how to improve the prognosis of SVD.

Inhibiting CSF1R alleviates cerebrovascular white matter disease and cognitive impairment

White matter abnormalities, related to poor cerebral perfusion, are a core feature of small vessel cerebrovascular disease, and critical determinants of vascular cognitive impairment and dementia. Despite this importance there is a lack of treatment options. Proliferation of microglia producing an expanded, reactive population and associated neuroinflammatory alterations have been implicated in the onset and progression of cerebrovascular white matter disease, in patients and in animal models, suggesting that targeting microglial proliferation may exert protection. Colony-stimulating factor-1 receptor (CSF1R) is a key regulator of microglial proliferation. We found that the expression of CSF1R/Csf1r and other markers indicative of increased microglial abundance are significantly elevated in damaged white matter in human cerebrovascular disease and in a clinically relevant mouse model of chronic cerebral hypoperfusion and vascular cognitive impairment. Using the mouse model, we investigated long-term pharmacological CSF1R inhibition, via GW2580, and demonstrated that the expansion of microglial numbers in chronic hypoperfused white matter is prevented. Transcriptomic analysis of hypoperfused white matter tissue showed enrichment of microglial and inflammatory gene sets, including phagocytic genes that were the predominant expression modules modified by CSF1R inhibition. Further, CSF1R inhibition attenuated hypoperfusion-induced white matter pathology and rescued spatial learning impairments and to a lesser extent cognitive flexibility. Overall, this work suggests that inhibition of CSF1R and microglial proliferation mediates protection against chronic cerebrovascular white matter pathology and cognitive deficits. Our study nominates CSF1R as a target for the treatment of vascular cognitive disorders with broader implications for treatment of other chronic white matter diseases.

An Integrative Nomogram for Identifying Cognitive Impairment Using Seizure Type and Cerebral Small Vessel Disease Neuroimaging Markers in Patients with Late-Onset Epilepsy of Unknown Origin

INTRODUCTION

Cognitive impairment (CI) is a common comorbidity in patients with late-onset epilepsy of unknown origin (LOEU). However, limited data are available on effective screening methods for CI at an early stage. We aimed to develop and internally validate a nomogram for identifying patients with LOEU at risk of CI and investigate the potential moderating effect of education on the relationship between periventricular white matter hyperintensities (PVHs) and cognitive function.

METHODS

We retrospectively reviewed the clinical data of 61 patients aged ≥ 55 years diagnosed with LOEU. The main outcome was CI, reflected as an adjusted Montreal Cognition Assessment score of < 26 points. A nomogram based on a multivariable logistic regression model was constructed. Its discriminative ability, calibration, and clinical applicability were tested using calibration plots, the area under the curve (AUC), and decision curves. Internal model validation was conducted using the bootstrap method. The moderating effect of education on the relationship between PVH and cognitive function was examined using hierarchical linear regression.

RESULTS

Forty-four of 61 (72.1%) patients had CI. A nomogram incorporating seizure type, total cerebral small vessel disease burden score, and PVH score was built to identify the risk factors for CI. The AUC of the model was 0.881 (95% confidence interval: 0.771-0.994) and 0.78 (95% confidence interval: 0.75-0.8) after internal validation. Higher educational levels blunted the negative impact of PVH on cognitive function.

CONCLUSION

Our nomogram provides a convenient tool for identifying patients with LOEU who are at risk of CI. Moreover, our findings demonstrate the importance of education for these patients.

Human in vivo evidence of reduced astrocyte activation and neuroinflammation in patients with treatment-resistant depression following electroconvulsive therapy

AIM

The current study aimed to investigate the neuroinflammatory hypothesis of depression and the potential anti-inflammatory effect of electroconvulsive therapy (ECT) in vivo, utilizing astrocyte-derived extracellular vesicles (ADEVs) isolated from plasma.

METHODS

A total of 40 patients with treatment-resistant depression (TRD) and 35 matched healthy controls were recruited at baseline, and 34 patients with TRD completed the post-ECT visits. Blood samples were collected at baseline and post-ECT. Plasma ADEVs were isolated and confirmed, and the concentrations of two astrocyte markers (glial fibrillary acidic protein [GFAP] and S100β), an extracellular vesicle marker cluster of differentiation 81 (CD81), and nine inflammatory markers in ADEVs were measured as main analyses. In addition, correlation analysis was conducted between clinical features and ADEV protein levels as exploratory analysis.

RESULTS

At baseline, the TRD group exhibited significantly higher levels of two astrocyte markers GFAP and S100β, as well as CD81 compared with the healthy controls. Inflammatory markers interferon γ (IFN-γ), interleukin (IL) 1β, IL-4, IL-6, tumor necrosis factor α, IL-10, and IL-17A were also significantly higher in the TRD group. After ECT, there was a significant reduction in the levels of GFAP, S100β, and CD81, along with a significant decrease in the levels of IFN-γ and IL-4. Furthermore, higher levels of GFAP, S100β, CD81, and inflammatory cytokines were associated with more severe depressive symptoms and poorer cognitive function.

CONCLUSION

This study provides direct insight supporting the astrocyte activation and neuroinflammatory hypothesis of depression using ADEVs. ECT may exert an anti-inflammatory effect through inhibition of such activation of astrocytes.

DAP12 deficiency alters microglia-oligodendrocyte communication and enhances resilience against tau toxicity

Pathogenic tau accumulation fuels neurodegeneration in Alzheimer's disease (AD). Enhancing aging brain's resilience to tau pathology would lead to novel therapeutic strategies. DAP12 (DNAX-activation protein 12) is critically involved in microglial immune responses. Previous studies have showed that mice lacking DAP12 in tauopathy mice exhibit higher tau pathology but are protected from tau-induced cognitive deficits. However, the exact mechanism remains elusive. Our current study uncovers a novel resilience mechanism via microglial interaction with oligodendrocytes. Despite higher tau inclusions, Dap12 deletion curbs tau-induced brain inflammation and ameliorates myelin and synapse loss. Specifically, removal of Dap12 abolished tau-induced disease-associated clusters in microglia (MG) and intermediate oligodendrocytes (iOli), which are spatially correlated with tau pathology in AD brains. Our study highlights the critical role of interactions between microglia and oligodendrocytes in tau toxicity and DAP12 signaling as a promising target for enhancing resilience in AD.

Assessment of white matter hyperintensity severity using multimodal magnetic resonance imaging

White matter hyperintensities are radiological abnormalities reflecting cerebrovascular dysfunction detectable using MRI. White matter hyperintensities are often present in individuals at the later stages of the lifespan and in prodromal stages in the Alzheimer's disease spectrum. Tissue alterations underlying white matter hyperintensities may include demyelination, inflammation and oedema, but these are highly variable by neuroanatomical location and between individuals. There is a crucial need to characterize these white matter hyperintensity tissue alterations in vivo to improve prognosis and, potentially, treatment outcomes. How different MRI measure(s) of tissue microstructure capture clinically-relevant white matter hyperintensity tissue damage is currently unknown. Here, we compared six MRI signal measures sampled within white matter hyperintensities and their associations with multiple clinically-relevant outcomes, consisting of global and cortical brain morphometry, cognitive function, diagnostic and demographic differences and cardiovascular risk factors. We used cross-sectional data from 118 participants: healthy controls (n = 30), individuals at high risk for Alzheimer's disease due to familial history (n = 47), mild cognitive impairment (n = 32) and clinical Alzheimer's disease dementia (n = 9). We sampled the median signal within white matter hyperintensities on weighted MRI images [T1-weighted (T1w), T2-weighted (T2w), T1w/T2w ratio, fluid-attenuated inversion recovery (FLAIR)] as well as the relaxation times from quantitative T1 (qT1) and T2* (qT2*) images. qT2* and fluid-attenuated inversion recovery signals within white matter hyperintensities displayed different age- and disease-related trends compared to normal-appearing white matter signals, suggesting sensitivity to white matter hyperintensity-specific tissue deterioration. Further, white matter hyperintensity qT2*, particularly in periventricular and occipital white matter regions, was consistently associated with all types of clinically-relevant outcomes in both univariate and multivariate analyses and across two parcellation schemes. qT1 and fluid-attenuated inversion recovery measures showed consistent clinical relationships in multivariate but not univariate analyses, while T1w, T2w and T1w/T2w ratio measures were not consistently associated with clinical variables. We observed that the qT2* signal was sensitive to clinically-relevant microstructural tissue alterations specific to white matter hyperintensities. Our results suggest that combining volumetric and signal measures of white matter hyperintensity should be considered to fully characterize the severity of white matter hyperintensities in vivo. These findings may have implications in determining the reversibility of white matter hyperintensities and the potential efficacy of cardio- and cerebrovascular treatments.

RAGE acted as a new anti-inflammatory target for Icariin's treatment against vascular dementia based on network pharmacology-directed verification

Vascular dementia (VaD) ranks as the second most prevalent form of dementia and poses a considerable global health challenge. Icariin has been recognized for its robust neuroprotective effects in combating VaD. Nonetheless, the underlying mechanisms have not been fully elucidated. An integrated approach involving network pharmacology, molecular docking, and molecular dynamics simulations (MDS) was employed to systematically investigate the potential pharmacological actions of Icariin in counteracting VaD. The AGE/RAGE pathway was identified as a promising anti-inflammatory pathway. A chronic cerebral hypoperfusion mouse model was utilized to establish VaD. Both Icariin and FP S-ZM1 (a RAGE inhibitor) were administered through oral gavage and intraperitoneal injection, respectively. The Morris water maze (MWZ) was used to evaluate cognitive functions. Moreover, immunofluorescence, RT-qP CR, and Western blot analyses were carried out to evaluate the effects of FP S-ZM1 on neuroinflammation. Network analysis identified 14 crucial targets and highlighted the AGE-RAGE signaling cascade in diabetic complications as the foremost KEGG pathway with potential anti-neuroinflammatory property. MDS results suggested a stable binding of the RAGE-Icariin complex. Remarkably, Icariin was found to effectively mitigate cognitive deficits in VaD mice, which was correlated with the upregulation of the P I3K/AKT pathway and downregulation of the JNK/cJUN signaling cascade. Critically, co-administration of FP S-ZM1 enhanced Icariin's ameliorative effects on cognitive deficits, owing to bolstered anti-neuroinflammatory action. This study unveils the potential of Icariin in alleviating cognitive dysfunction and neuroinflammation in VaD, which may be attributed to the modulation of the AGE/RAGE pathway.Communicated by Ramaswamy H. Sarma.

Insights into the pathological basis of dementia from population-based neuropathology studies

The epidemiological neuropathology perspective of population and community-based studies allows unbiased assessment of the prevalence of various pathologies and their relationships to late-life dementia. In addition, this approach provides complementary insights to conventional case-control studies, which tend to be more representative of a younger clinical cohort. The Cognitive Function and Ageing Study (CFAS) is a longitudinal study of cognitive impairment and frailty in the general United Kingdom population. In this review, we provide an overview of the major findings from CFAS, alongside other studies, which have demonstrated a high prevalence of pathology in the ageing brain, particularly Alzheimer's disease neuropathological change and vascular pathology. Increasing burdens of these pathologies are the major correlates of dementia, especially neurofibrillary tangles, but there is substantial overlap in pathology between those with and without dementia, particularly at intermediate burdens of pathology and also at the oldest ages. Furthermore, additional pathologies such as limbic-predominant age-related TDP-43 encephalopathy, ageing-related tau astrogliopathy and primary age-related tauopathies contribute to late-life dementia. Findings from ageing population-representative studies have implications for the understanding of dementia pathology in the community. The high prevalence of pathology and variable relationship to dementia status has implications for disease definition and indicate a role for modulating factors on cognitive outcome. The complexity of late-life dementia, with mixed pathologies, indicates a need for a better understanding of these processes across the life-course to direct the best research for reducing risk in later life of avoidable clinical dementia syndromes.

Emerging Roles of Cells and Molecules of Innate Immunity in Alzheimer's Disease

The inflammatory response that marks Alzheimer's disease (neuroinflammation) is considered a double-edged sword. Microglia have been shown to play a protective role at the beginning of the disease. Still, persistent harmful stimuli further activate microglia, inducing an exacerbating inflammatory process which impairs β-amyloid peptide clearance capability and leads to neurotoxicity and neurodegeneration. Moreover, microglia also appear to be closely involved in the spread of tau pathology. Soluble TREM2 also represents a crucial player in the neuroinflammatory processes. Elevated levels of TREM2 in cerebrospinal fluid have been associated with increased amyloid plaque burden, neurodegeneration, and cognitive decline in individuals with Alzheimer's disease. Understanding the intricate relationship between innate immunity and Alzheimer's disease will be a promising strategy for future advancements in diagnosis and new therapeutic interventions targeting innate immunity, by modulating its activity. Still, additional and more robust studies are needed to translate these findings into effective treatments. In this review, we focus on the role of cells (microglia, astrocytes, and oligodendrocytes) and molecules (TREM2, tau, and β-amyloid) of the innate immune system in the pathogenesis of Alzheimer's disease and their possible exploitation as disease biomarkers and targets of therapeutical approaches.

The contribution of DNA methylation to the (dys)function of oligodendroglia in neurodegeneration

Neurodegenerative diseases encompass a heterogeneous group of conditions characterised by the progressive degeneration of the structure and function of the central or peripheral nervous systems. The pathogenic mechanisms underlying these diseases are not fully understood. However, a central feature consists of regional aggregation of proteins in the brain, such as the accumulation of β-amyloid plaques in Alzheimer's disease (AD), inclusions of hyperphosphorylated microtubule-binding tau in AD and other tauopathies, or inclusions containing α-synuclein in Parkinson's disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA). Various pathogenic mechanisms are thought to contribute to disease, and an increasing number of studies implicate dysfunction of oligodendrocytes (the myelin producing cells of the central nervous system) and myelin loss. Aberrant DNA methylation, the most widely studied epigenetic modification, has been associated with many neurodegenerative diseases, including AD, PD, DLB and MSA, and recent findings highlight aberrant DNA methylation in oligodendrocyte/myelin-related genes. Here we briefly review the evidence showing that changes to oligodendrocytes and myelin are key in neurodegeneration, and explore the relevance of DNA methylation in oligodendrocyte (dys)function. As DNA methylation is reversible, elucidating its involvement in pathogenic mechanisms of neurodegenerative diseases and in dysfunction of specific cell-types such as oligodendrocytes may bring opportunities for therapeutic interventions for these diseases.

Comparison of the clinical value of MRI and plasma markers for cognitive impairment in patients aged ≥75 years: a retrospective study

Background

Dementia has become the main cause of disability in older adults aged ≥75 years. Cerebral small vessel disease (CSVD) is involved in cognitive impairment (CI) and dementia and is a cause of vascular CI (VCI), which is manageable and its onset and progression can be delayed. Simple and effective markers will be beneficial to the early detection and intervention of CI. The aim of this study is to investigate the clinical application value of plasma amyloid β1-42 (Aβ42), phosphorylated tau 181 (p-tau181) and conventional structural magnetic resonance imaging (MRI) parameters for cognitive impairment (CI) in patients aged ≥75 years.

Methods

We retrospectively selected patients who visited the Affiliated Hospital of Xuzhou Medical University and were clinically diagnosed with or without cognitive dysfunction between May 2018 and November 2021. Plasma indicators (Aβ42 and p-tau181) and conventional structural MRI parameters were collected and analyzed. Multivariate logistic regression and receiver operator characteristic (ROC) curve were used to evaluate the diagnostic value.

Results

One hundred and eighty-four subjects were included, including 54 cases in CI group and 130 cases in noncognitive impairment (NCI) groups, respectively. Univariate logistic regression analysis revealed that the percentages of Aβ42+_, P-tau 181+, and Aβ42+/P-tau181+ showed no significant difference between the groups of CI and NCI (all P > 0.05). Multivariate logistic regression analysis showed that moderate/severe periventricular WMH (PVWMH) (OR 2.857, (1.365-5.983), P = 0.005), lateral ventricle body index (LVBI) (OR 0.413, (0.243-0.700), P = 0.001), and cortical atrophy (OR 1.304, (1.079-1.575), P = 0.006) were factors associated with CI. The combined model including PVWMH, LVBI, and cortical atrophy to detect CI and NCI showed an area under the ROC curve (AUROC) is 0.782, with the sensitivity and specificity 68.5% and 78.5%, respectively.

Conclusion

For individuals ≥75 years, plasma Aβ42 and P-tau181 might not be associated with cognitive impairment, and MRI parameters, including PVWMH, LVBI and cortical atrophy, are related to CI. The cognitive statuses of people over 75 years old were used as the endpoint event in this study. Therefore, it can be considered that these MRI markers might have more important clinical significance for early assessment and dynamic observation, but more studies are still needed to verify this hypothesis.

Regional contribution of vascular dysfunction in white matter dementia: clinical and neuropathological insights

The maintenance of adequate blood supply and vascular integrity is fundamental to ensure cerebral function. A wide range of studies report vascular dysfunction in white matter dementias, a group of cerebral disorders characterized by substantial white matter damage in the brain leading to cognitive impairment. Despite recent advances in imaging, the contribution of vascular-specific regional alterations in white matter dementia has been not extensively reviewed. First, we present an overview of the main components of the vascular system involved in the maintenance of brain function, modulation of cerebral blood flow and integrity of the blood-brain barrier in the healthy brain and during aging. Second, we review the regional contribution of cerebral blood flow and blood-brain barrier disturbances in the pathogenesis of three distinct conditions: the archetypal white matter predominant neurocognitive dementia that is vascular dementia, a neuroinflammatory predominant disease (multiple sclerosis) and a neurodegenerative predominant disease (Alzheimer's). Finally, we then examine the shared landscape of vascular dysfunction in white matter dementia. By emphasizing the involvement of vascular dysfunction in the white matter, we put forward a hypothetical map of vascular dysfunction during disease-specific progression to guide future research aimed to improve diagnostics and facilitate the development of tailored therapies.

Chronic cerebral hypoperfusion: a critical feature in unravelling the etiology of vascular cognitive impairment

Vascular cognitive impairment (VCI) describes a wide spectrum of cognitive deficits related to cerebrovascular diseases. Although the loss of blood flow to cortical regions critically involved in cognitive processes must feature as the main driver of VCI, the underlying mechanisms and interactions with related disease processes remain to be fully elucidated. Recent clinical studies of cerebral blood flow measurements have supported the role of chronic cerebral hypoperfusion (CCH) as a major driver of the vascular pathology and clinical manifestations of VCI. Here we review the pathophysiological mechanisms as well as neuropathological changes of CCH. Potential interventional strategies for VCI are also reviewed. A deeper understanding of how CCH can lead to accumulation of VCI-associated pathology could potentially pave the way for early detection and development of disease-modifying therapies, thus allowing preventive interventions instead of symptomatic treatments.

MYELIN, AGING, AND PHYSICAL EXERCISE

Myelin sheath is a structure in neurons fabricated by oligodendrocytes and Schwann cells responsible for increasing the efficiency of neural synapsis, impulse transmission, and providing metabolic support to the axon. They present morpho-functional changes during health aging as deformities of the sheath and its fragmentation, causing an increased load on microglial phagocytosis, with Alzheimer's disease aggravating. Physical exercise has been studied as a possible protective agent for the nervous system, offering benefits to neuroplasticity. In this regard, studies in animal models for Alzheimer's and depression reported the efficiency of physical exercise in protecting against myelin degeneration. A reduction of myelin damage during aging has also been observed in healthy humans. Physical activity promotes oligodendrocyte proliferation and myelin preservation during old age, although some controversies remain. In this review, we will address how effective physical exercise can be as a protective agent of the myelin sheath against the effects of aging in physiological and pathological conditions.

Roles of NG2 Glia in Cerebral Small Vessel Disease

Cerebral small vessel disease (CSVD) is one of the most prevalent pathologic processes affecting 5% of people over 50 years of age and contributing to 45% of dementia cases. Increasing evidence has demonstrated the pathological roles of chronic hypoperfusion, impaired cerebral vascular reactivity, and leakage of the blood-brain barrier in CSVD. However, the pathogenesis of CSVD remains elusive thus far, and no radical treatment has been developed. NG2 glia, also known as oligodendrocyte precursor cells, are the fourth type of glial cell in addition to astrocytes, microglia, and oligodendrocytes in the mammalian central nervous system. Many novel functions for NG2 glia in physiological and pathological states have recently been revealed. In this review, we discuss the role of NG2 glia in CSVD and the underlying mechanisms.

Neuroprotective effect of lipopolysaccharides in a dual-hit rat pup model of preterm hypoxia-ischemia

The combination of lipopolysaccharide (LPS) and hypoxia-ischemia (HI) has been used to model the brain injury sustained by sick pre-term infants in order to study the pathological conditions of diffuse white matter injury, which is a major cause of preterm morbidity. Prior studies have shown that the timing and dose of LPS administration will determine whether the injury is reduced or exacerbated. Here we show that administering a single injection of LPS (0.1 mg/kg) to postnatal-day-2 rat pups 14 h before inducing HI effectively protects the brain from HI-associated damage. We show that the LPS-treated HI rat pups have significantly less histopathology compared to the saline-treated HI rat pups. Apoptotic deaths were dramatically curtailed in both the neocortex and white matter when evaluated at 2 days of recovery. Microglial activation was reduced when the percentage of CD68+/Iba1+ cells was quantified in the neocortex of the LPS-treated vs the saline-treated HI rat pups. One mechanism through which LPS pre-treatment appears to be preventing injury is through the AKT-endothelial nitric oxide synthase (eNOS) pathway as LPS induced an increase in both the expression and phosphorylation of eNOS. Altogether these data show that the neocortex, as well as the white matter sustain damage after HI at this timepoint in forebrain development and that acutely activating the immune system can protect the brain from brain injury.

Amyloid-PET of the white matter: Relationship to free water, fiber integrity, and cognition in patients with dementia and small vessel disease

White matter (WM) injury is frequently observed along with dementia. Positron emission tomography with amyloid-ligands (Aβ-PET) recently gained interest for detecting WM injury. Yet, little is understood about the origin of the altered Aβ-PET signal in WM regions. Here, we investigated the relative contributions of diffusion MRI-based microstructural alterations, including free water and tissue-specific properties, to Aβ-PET in WM and to cognition. We included a unique cohort of 115 participants covering the spectrum of low-to-severe white matter hyperintensity (WMH) burden and cognitively normal to dementia. We applied a bi-tensor diffusion-MRI model that differentiates between (i) the extracellular WM compartment (represented via free water), and (ii) the fiber-specific compartment (via free water-adjusted fractional anisotropy [FA]). We observed that, in regions of WMH, a decrease in Aβ-PET related most closely to higher free water and higher WMH volume. In contrast, in normal-appearing WM, an increase in Aβ-PET related more closely to higher cortical Aβ (together with lower free water-adjusted FA). In relation to cognitive impairment, we observed a closer relationship with higher free water than with either free water-adjusted FA or WM PET. Our findings support free water and Aβ-PET as markers of WM abnormalities in patients with mixed dementia, and contribute to a better understanding of processes giving rise to the WM PET signal.

Chronic Neuroinflammation and Cognitive Decline in Patients with Cardiac Disease: Evidence, Relevance, and Therapeutic Implications

Acute and chronic cardiac disorders predispose to alterations in cognitive performance, ranging from mild cognitive impairment to overt dementia. Although this association is well-established, the factors inducing and accelerating cognitive decline beyond ageing and the intricate causal pathways and multilateral interdependencies involved remain poorly understood. Dysregulated and persistent inflammatory processes have been implicated as potentially causal mediators of the adverse consequences on brain function in patients with cardiac disease. Recent advances in positron emission tomography disclosed an enhanced level of neuroinflammation of cortical and subcortical brain regions as an important correlate of altered cognition in these patients. In preclinical and clinical investigations, the thereby involved domains and cell types of the brain are gradually better characterized. Microglia, resident myeloid cells of the central nervous system, appear to be of particular importance, as they are extremely sensitive to even subtle pathological alterations affecting their complex interplay with neighboring astrocytes, oligodendrocytes, infiltrating myeloid cells, and lymphocytes. Here, we review the current evidence linking cognitive impairment and chronic neuroinflammation in patients with various selected cardiac disorders including the aspect of chronic neuroinflammation as a potentially druggable target.

[A role of altered inflammation-related gene expression in cerebral small vessel disease with cognitive impairment]

OBJECTIVE

To identify the role of changes in the expression of inflammation-related genes in cerebral microangiopathy/cerebral small vessel disease (cSVD).

MATERIAL AND METHODS

Forty-four cSVD patients (mean age 61.4±9.2) and 11 controls (mean age 57.3±9.7) were studied. Gene expression was assessed on an individual NanoString nCounter panel of 58 inflammation-related genes and 4 reference genes. A set of genes was generated based on converging results of complete genome-wide association studies (GWAS) in cSVD and Alzheimer's disease (AD) and circulating markers associated with vascular wall and Brain lesions in cSVD. RNA was isolated from blood leukocytes and analyzed with the nCounter Analysis System, followed by analysis in nSolver 4.0. Results were verified by real-time PCR.

RESULTS

CSVD patients had a significant decrease in BIN1 (log2FC=-1.272; p=0.039) and VEGFA (log2FC=-1.441; p=0.038) expression compared to controls, which showed predictive ability for cSVD. The cut-off for BIN1 expression was 5.76 a.u. (sensitivity 73%; specificity 75%) and the cut-off for VEGFA expression was 9.27 a.u. (sensitivity 64%; specificity 86%). Reduced expression of VEGFA (p=0.011), VEGFC (p=0.017), CD2AP (p=0.044) was associated with cognitive impairment (CI). There was a significant direct correlation between VEGFC expression and the scores on the Montreal Cognitive Assessment test and between BIN1 and VEGFC expression and delayed memory.

CONCLUSION

The possible prediction of cSVD by reduced expression levels of BIN1, VEGFA and the association of clinically significant CI with reduced VEGFA and VEGFC expression indicate their importance in the development and progression of the disease. The established importance of these genes in the pathogenesis of AD suggests that similar changes in their expression profile in cSVD may be one of the conditions for the comorbidity of the two pathologies.

What type of cell death occurs in chronic cerebral hypoperfusion? A review focusing on pyroptosis and its potential therapeutic implications

Chronic cerebral hypoperfusion (CCH) is a major global disease with chronic cerebral blood flow reduction. It is also the main cause of cognitive impairment and neurodegenerative diseases. Pyroptosis, a novel form of cell death, is characterized by the rupture of the cell membrane and the release of pro-inflammatory mediators. In recent years, an increasing number of studies have identified the involvement of pyroptosis and its mediated inflammatory response in the pathological process of CCH. Therefore, preventing the activation of pyroptosis following CCH is beneficial to inhibit the inflammatory cascade and reduce brain injury. In this review, we discuss the research progress on the relationship between pyroptosis and CCH, in order to provide a reference for research in related fields.

Forgetful, sad and old: Do vascular cognitive impairment and depression share a common pre-disease network and how is it impacted by ageing?

Vascular cognitive impairment (VCI) and depression frequently coexist in geriatric populations and reciprocally increase disease risks. We assert that a shared pre-disease state of the psycho-immune-neuroendocrine (PINE) network model mechanistically explains bidirectional associations between VCI and depression. Five pathophysiological sub-networks are identified that are shared by VCI and depression: neuroinflammation, kynurenine pathway imbalance, hypothalamic-pituitary-adrenal (HPA) axis overactivity, impaired neurotrophic support and cerebrovascular dysfunction. These do not act independently, and their complex interactions necessitate a systems biology approach to better define disease pathogenesis. The PINE network is already established in the context of non-communicable diseases (NCDs) such as depression, hypertension, atherosclerosis, coronary heart disease and type 2 diabetes mellitus. We build on previous literature to specifically explore mechanistic links between MDD and VCI in the context of PINE pathways and discuss key mechanistic commonalities linking these comorbid conditions and identify a common pre-disease state which precedes transition to VCI and MDD. We expand the model to incorporate bidirectional interactions with biological ageing. Diathesis factors for both VCI and depression feed into this network and the culmination of shared mechanisms (on an ageing substrate) lead to a critical network transition to one or both disease states. A common pre-disease state underlying VCI and depression can provide clinicians a unique opportunity for early risk assessment and intervention in disease development. Establishing the mechanistic elements and systems biology of this network can reveal early warning or predictive biomarkers together with novel therapeutic targets. Integrative studies are recommended to elucidate the dynamic networked biology of VCI and depression over time.

Cerebral small vessel disease: Pathological mechanisms and potential therapeutic targets

Cerebral small vessel disease (CSVD) represents a diverse cluster of cerebrovascular diseases primarily affecting small arteries, capillaries, arterioles and venules. The diagnosis of CSVD relies on the identification of small subcortical infarcts, lacunes, white matter hyperintensities, perivascular spaces, and microbleeds using neuroimaging. CSVD is observed in 25% of strokes worldwide and is the most common pathology of cognitive decline and dementia in the elderly. Still, due to the poor understanding of pathophysiology in CSVD, there is not an effective preventative or therapeutic approach for CSVD. The most widely accepted approach to CSVD treatment is to mitigate vascular risk factors and adopt a healthier lifestyle. Thus, a deeper understanding of pathogenesis may foster more specific therapies. Here, we review the underlying mechanisms of pathological characteristics in CSVD development, with a focus on endothelial dysfunction, blood-brain barrier impairment and white matter change. We also describe inflammation in CSVD, whose role in contributing to CSVD pathology is gaining interest. Finally, we update the current treatments and preventative measures of CSVD, as well as discuss potential targets and novel strategies for CSVD treatment.

Association of Cerebral Small Vessel Disease With Gait and Balance Disorders

Cerebral small vessel disease (CSVD) is a common cerebrovascular disease and an important cause of gait and balance disorders. Gait and balance disorders can further lead to an increased risk of falls and a decreased quality of life. CSVD can damage gait and balance function by affecting cognitive function or directly disrupting motor pathways, and different CSVD imaging features have different characteristics of gait and balance impairment. In this article, the correlation between different imaging features of sporadic CSVD and gait and balance disorders has been reviewed as follows, which can provide beneficial help for standardized management of CSVD.

In vivo myelin imaging and tissue microstructure in white matter hyperintensities and perilesional white matter

White matter hyperintensities negatively impact white matter structure and relate to cognitive decline in aging. Diffusion tensor imaging detects changes to white matter microstructure, both within the white matter hyperintensity and extending into surrounding (perilesional) normal-appearing white matter. However, diffusion tensor imaging markers are not specific to tissue components, complicating the interpretation of previous microstructural findings. Myelin water imaging is a novel imaging technique that provides specific markers of myelin content (myelin water fraction) and interstitial fluid (geometric mean T₂). Here we combined diffusion tensor imaging and myelin water imaging to examine tissue characteristics in white matter hyperintensities and perilesional white matter in 80 individuals (47 older adults and 33 individuals with chronic stroke). To measure perilesional normal-appearing white matter, white matter hyperintensity masks were dilated in 2 mm segments up to 10 mm in distance from the white matter hyperintensity. Fractional anisotropy, mean diffusivity, myelin water fraction, and geometric mean T₂ were extracted from white matter hyperintensities and perilesional white matter. We observed a spatial gradient of higher mean diffusivity and geometric mean T₂, and lower fractional anisotropy, in the white matter hyperintensity and perilesional white matter. In the chronic stroke group, myelin water fraction was reduced in the white matter hyperintensity but did not show a spatial gradient in perilesional white matter. Across the entire sample, white matter metrics within the white matter hyperintensity related to whole-brain white matter hyperintensity volume; with increasing white matter hyperintensity volume there was increased mean diffusivity and geometric mean T₂, and decreased myelin water fraction in the white matter hyperintensity. Normal-appearing white matter adjacent to white matter hyperintensities exhibits characteristics of a transitional stage between healthy white matter and white matter hyperintensities. This effect was observed in markers sensitive to interstitial fluid, but not in myelin water fraction, the specific marker of myelin concentration. Within the white matter hyperintensity, interstitial fluid was higher and myelin concentration was lower in individuals with more severe cerebrovascular disease. Our data suggests white matter hyperintensities have penumbra-like effects in perilesional white matter that specifically reflect increased interstitial fluid, with no changes to myelin concentration. In contrast, within the white matter hyperintensity there are varying levels of demyelination, which vary based on the severity of cerebrovascular disease. Diffusion tensor imaging and myelin imaging may be useful clinical markers to predict white matter hyperintensity formation, and to stage neuronal damage within white matter hyperintensities.

Neuroinflammation in Vascular Cognitive Impairment and Dementia: Current Evidence, Advances, and Prospects

Vascular cognitive impairment and dementia (VCID) is a major heterogeneous brain disease caused by multiple factors, and it is the second most common type of dementia in the world. It is caused by long-term chronic low perfusion in the whole brain or local brain area, and it eventually develops into severe cognitive dysfunction syndrome. Because of the disease’s ambiguous classification and diagnostic criteria, there is no clear treatment strategy for VCID, and the association between cerebrovascular pathology and cognitive impairment is controversial. Neuroinflammation is an immunological cascade reaction mediated by glial cells in the central nervous system where innate immunity resides. Inflammatory reactions could be triggered by various damaging events, including hypoxia, ischemia, and infection. Long-term chronic hypoperfusion-induced ischemia and hypoxia can overactivate neuroinflammation, causing apoptosis, blood–brain barrier damage and other pathological changes, triggering or aggravating the occurrence and development of VCID. In this review, we will explore the mechanisms of neuroinflammation induced by ischemia and hypoxia caused by chronic hypoperfusion and emphasize the important role of neuroinflammation in the development of VCID from the perspective of immune cells, immune mediators and immune signaling pathways, so as to provide valuable ideas for the prevention and treatment of the disease.

Biological aging processes underlying cognitive decline and neurodegenerative disease

Alzheimer's disease and related dementias (ADRD) are among the top contributors to disability and mortality in later life. As with many chronic conditions, aging is the single most influential factor in the development of ADRD. Even among older adults who remain free of dementia throughout their lives, cognitive decline and neurodegenerative changes are appreciable with advancing age, suggesting shared pathophysiological mechanisms. In this Review, we provide an overview of changes in cognition, brain morphology, and neuropathological protein accumulation across the lifespan in humans, with complementary and mechanistic evidence from animal models. Next, we highlight selected aging processes that are differentially regulated in neurodegenerative disease, including aberrant autophagy, mitochondrial dysfunction, cellular senescence, epigenetic changes, cerebrovascular dysfunction, inflammation, and lipid dysregulation. We summarize research across clinical and translational studies to link biological aging processes to underlying ADRD pathogenesis. Targeting fundamental processes underlying biological aging may represent a yet relatively unexplored avenue to attenuate both age-related cognitive decline and ADRD. Collaboration across the fields of geroscience and neuroscience, coupled with the development of new translational animal models that more closely align with human disease processes, is necessary to advance novel therapeutic discovery in this realm.

Small Vessel Disease: Ancient Description, Novel Biomarkers

Small vessel disease (SVD) is one of the most frequent pathological conditions which lead to dementia. Biochemical and neuroimaging might help correctly identify the clinical diagnosis of this relevant brain disease. The microvascular alterations which underlie SVD have common origins, similar cognitive outcomes, and common vascular risk factors. Nevertheless, the arteriolosclerosis process, which underlines SVD development, is based on different mechanisms, not all completely understood, which start from a chronic hypoperfusion state and pass through a chronic brain inflammatory condition, inducing a significant endothelium activation and a consequent tissue remodeling action. In a recent review, we focused on the pathophysiology of SVD, which is complex, involving genetic conditions and different co-morbidities (i.e., diabetes, chronic hypoxia condition, and obesity). Currently, many points still remain unclear and discordant. In this paper, we wanted to focus on new biomarkers, which can be the expression of the endothelial dysfunction, or of the oxidative damage, which could be employed as markers of disease progression or for future targets of therapies. Therefore, we described the altered response to the endothelium-derived nitric oxide-vasodilators (ENOV), prostacyclin, C-reactive proteins, and endothelium-derived hyperpolarizing factors (EDHF). At the same time, due to the concomitant endothelial activation and chronic neuroinflammatory status, we described hypoxia-endothelial-related markers, such as HIF 1 alpha, VEGFR2, and neuroglobin, and MMPs. We also described blood–brain barrier disruption biomarkers and imaging techniques, which can also describe perivascular spaces enlargement and dysfunction. More studies should be necessary, in order to implement these results and give them a clinical benefit.

The role of inflammasomes in vascular cognitive impairment

There is an increasing prevalence of Vascular Cognitive Impairment (VCI) worldwide, and several studies have suggested that Chronic Cerebral Hypoperfusion (CCH) plays a critical role in disease onset and progression. However, there is a limited understanding of the underlying pathophysiology of VCI, especially in relation to CCH. Neuroinflammation is a significant contributor in the progression of VCI as increased systemic levels of the proinflammatory cytokine interleukin-1β (IL-1β) has been extensively reported in VCI patients. Recently it has been established that CCH can activate the inflammasome signaling pathways, involving NLRP3 and AIM2 inflammasomes that critically regulate IL-1β production. Given that neuroinflammation is an early event in VCI, it is important that we understand its molecular and cellular mechanisms to enable development of disease-modifying treatments to reduce the structural brain damage and cognitive deficits that are observed clinically in the elderly. Hence, this review aims to provide a comprehensive insight into the molecular and cellular mechanisms involved in the pathogenesis of CCH-induced inflammasome signaling in VCI.

Amide Proton Transfer MRI Could Be Used to Evaluate the Pathophysiological Status of White Matter Hyperintensities

BACKGROUND

The pathophysiology of white matter hyperintensities (WMH) remains unclear, investigations of amide proton transfer (APT) signals in WMH disease may provide relevant pathophysiological information.

PURPOSE

To evaluate the APT signals differences and heterogeneity of WMH and adjacent normal-appearing white matter (NAWM) at different Fazekas grades and different locations.

STUDY TYPE

Prospective.

POPULATION

In all, 180 WMH patients (age, 40-76; male/female, 77/103) and 59 healthy controls (age, 42-70; male/female, 23/36).

FIELD STRENGTH/SEQUENCE

A 3 T; 3D fluid-attenuated inversion recovery (FLAIR), 3D APT-weighted (APTw).

ASSESSMENT

The mean APTw values (APTw_mean ) and the APTw signals heterogeneity (APTw_max-min ) among different grades WMH and NAWM and the APTw_mean of the same grade deep WMH (DWMH) and paraventricular WMH (PWMH) were calculated and compared. Regions of interests were delineated on WMH lesions, NAWM and healthy white matter.

STATISTICAL TESTS

One-way analysis of variance (ANOVA); independent sample t test; Chi-square test. Significance level: P < 0.05.

RESULTS

APTw_mean among different grade WMH (from grade 0 to 3, 0.58 ± 0.14% vs. 0.29 ± 0.23% vs. 0.37 ± 0.24% vs. 0.61 ± 0.22%, respectively) were significantly different except between grade 1 and 2 (P = 0.27) and between grade 0 and 3 (P = 0.97). The differences in APTw_mean between WMH and NAWM were significant (WMH vs. NAWM from grade 1 to 3, 0.29% ± 0.23% vs. 0.55% ± 0.27%; 0.37% ± 0.24% vs. 0.59% ± 0.22%; 0.61% ± 0.22% vs. 0.42% ± 0.24%, respectively). Lower APTw_mean values were found only in grade 3 NAWM than other grades NAWM and controls. The APTw_max-min values of grade 1-3 WMH (0.38% ± 0.27% vs. 0.51% ± 0.31% vs. 0.67% ± 0.34%, respectively) were significantly different. Higher APT_mean values were found only in grade 2 PWMH (0.47% ± 0.22% vs. 0.32% ± 0.24%).

DATA CONCLUSION

Significant differences of APT signals were found in WMH of different Fazekas grades and different locations.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 3.

Peak ependymal cell stretch overlaps with the onset locations of periventricular white matter lesions

Deep and periventricular white matter hyperintensities (dWMH/pvWMH) are bright appearing white matter tissue lesions in T2-weighted fluid attenuated inversion recovery magnetic resonance images and are frequent observations in the aging human brain. While early stages of these white matter lesions are only weakly associated with cognitive impairment, their progressive growth is a strong indicator for long-term functional decline. DWMHs are typically associated with vascular degeneration in diffuse white matter locations; for pvWMHs, however, no unifying theory exists to explain their consistent onset around the horns of the lateral ventricles. We use patient imaging data to create anatomically accurate finite element models of the lateral ventricles, white and gray matter, and cerebrospinal fluid, as well as to reconstruct their WMH volumes. We simulated the mechanical loading of the ependymal cells forming the primary brain-fluid interface, the ventricular wall, and its surrounding tissues at peak ventricular pressure during the hemodynamic cycle. We observe that both the maximum principal tissue strain and the largest ependymal cell stretch consistently localize in the anterior and posterior horns. Our simulations show that ependymal cells experience a loading state that causes the ventricular wall to be stretched thin. Moreover, we show that maximum wall loading coincides with the pvWMH locations observed in our patient scans. These results warrant further analysis of white matter pathology in the periventricular zone that includes a mechanics-driven deterioration model for the ventricular wall.

Microvessel stenosis, enlarged perivascular spaces, and fibrinogen deposition are associated with ischemic periventricular white matter hyperintensities

Periventricular white matter hyperintensities (pvWMH) are neuroimaging abnormalities surrounding the lateral ventricles that are apparent on magnetic resonance imaging (MRI). They are associated with age, neurodegenerative disease, and cerebrovascular risk factors. While pvWMH ultimately represent a loss of white matter structural integrity, the pathological causes are heterogeneous in nature, and currently, cannot be distinguished using neuroimaging alone. pvWMH could occur because of a combination of small vessel disease (SVD), ependymal loss, blood–brain barrier dysfunction, and microgliosis. In this study we aimed to characterize microvascular stenosis, fibrinogen extravasation, and microgliosis within pvWMH with and without imaging evidence of periventricular infarction. Using postmortem neuroimaging of human brains (n = 20), we identified pvWMH with and without periventricular infarcts (PVI). We performed histological analysis of microvessel stenosis, perivascular spaces, microgliosis, and immunohistochemistry against fibrinogen as a measure of serum protein extravasation. Herein, we report distinctions between pvWMH with and without periventricular infarcts based on associations with microvessel stenosis, enlarged perivascular spaces, and fibrinogen IHC. Microvessel stenosis was significantly associated with PVI and with cellular deposition of fibrinogen in the white matter. The presence of fibrinogen was associated with PVI and increased number of microglia. These findings suggest that neuroimaging‐based detection of infarction within pvWMH may help distinguish more severe lesions, associated with underlying microvascular disease and BBB dysfunction, from milder pvWMH that are a highly frequent finding on MRI.

Cognitive Dysfunction after Heart Disease: A Manifestation of the Heart-Brain Axis

The functions of the brain and heart, which are the two main supporting organs of human life, are closely linked. Numerous studies have expounded the mechanisms of the brain-heart axis and its related clinical applications. However, the effect of heart disease on brain function, defined as the heart-brain axis, is less studied even though cognitive dysfunction after heart disease is one of its most frequently reported manifestations. Hypoperfusion caused by heart failure appears to be an important risk factor for cognitive decline. Blood perfusion, the immune response, and oxidative stress are the possible main mechanisms of cognitive dysfunction, indicating that the blood-brain barrier, glial cells, and amyloid-β may play active roles in these mechanisms. Clinicians should pay more attention to the cognitive function of patients with heart disease, especially those with heart failure. In addition, further research elucidating the associated mechanisms would help discover new therapeutic targets to intervene in the process of cognitive dysfunction after heart disease. This review discusses cognitive dysfunction in relation to heart disease and its potential mechanisms.

Glia and extracellular matrix molecules: What are their importance for the electrographic and MRI changes in the epileptogenic zone?

Glial cells and extracellular matrix (ECM) molecules are crucial for the maintenance of brain homeostasis. Especially because of their actions regarding neurotransmitter and ionic control, and synaptic function, these cells can potentially contribute to the hyperexcitability seen in the epileptogenic, while ECM changes are linked to synaptic reorganization. The present review will explore glial and ECM homeostatic roles and their potential contribution to tissue plasticity. Finally, we will address how glial, and ECM changes in the epileptogenic zone can be seen in magnetic resonance imaging (MRI), pointing out their importance as markers for the extension of the epileptogenic area. This article is part of the Special Issue "NEWroscience 2018".

The phenomenon of clasmatodendrosis

Clasmatodendrosis derives from the Greek for fragment (klasma), tree (dendron), and condition (- osis). Cajal first used the term in 1913: he observed disintegration of the distal cell processes of astrocytes, along with a fragmentation or beading of proximal processes closer to the astrocyte cell body. In contemporary clinical and experimental reports, clasmatodendrosis has been observed in models of cerebral ischemia and seizures (including status epilepticus), in elderly brains, in white matter disease, in hippocampal models and cell cultures associated with amyloid plaques, in head trauma, toxic exposures, demyelinating diseases, encephalitides and infection-associated encephalopathies, and in the treatment of cancer using immune effector cells. We examine evidence to support a claim that clasmatodendrotic astrocyte cell processes overtly bead (truncate) as a morphological sign of ongoing damage premortem. In grey and white matter and often in relationship to vascular lumina, beading becomes apparent with immunohistochemical staining of glial fibrillary acidic protein when specimens are examined at reasonably high magnification, but demonstration of distal astrocytic loss of processes may require additional marker study and imaging. Proposed mechanisms for clasmatodendrotic change have examined hypoxic-ischemic, osmotic-demyelinating, and autophagic models. In these models as well as in neuropathological reports, parenchymal swelling, vessel-wall leakage, or disturbed clearance of toxins can occur in association with clasmatodendrosis. Clasmatodendrotic features may serve as a marker for gliovascular dysregulation either acutely or chronically. We review correlative evidence for blood-brain barrier (BBB) dysfunction associated with astrocytic structural change, with attention to interactions between endothelial cells, pericytes, and astrocytic endfeet.

Anti-NR2 glutamate receptor antibodies as an early biomarker of cerebral small vessel disease

OBJECTIVES

Cerebral small vessel disease (SVD) associated with age and vascular risk factors is one of the leading causes of cognitive disorders as well as ischemic and hemorrhagic strokes. The pathogenesis of this disease has not been fully understood yet. The previously established association of the antibodies against the NR2 subunit of the NMDA receptor (NR2ab) with the mechanisms of SVD such as ischemia and blood-brain barrier (BBB) disruption, might suggest their importance in the brain damage.

DESIGN & METHODS

We studied the NR2ab serum level in 70 patients (45 females, 61.1 ± 6.3 y.o.) with different severity of cognitive impairment and MRI features of SVD and 20 healthy volunteers (12 females, 58.5 ± 6.4 y.o.).

RESULTS

The elevated level of NR2ab was associated with subjective cognitive impairment (SCI) (p = 0.028) and mild cognitive impairment (MCI) (p = 0.017), Fazekas grade (F) 2 (p = 0,002) and F3 (p = 0,009) of white matter hyperintensities (WMH) and the numbers of lacunes in the cerebral white matter (less than 5) (p = 0,039).

CONCLUSION

The detected increase in serum NR2ab level in patients with SCI, as well as the minimal amount of white matter lacunes, is most likely caused by hypoxia-induced endothelial damage in the early stage of SVD. Normal NR2ab values in patients with F1 WMH, the increased NR2ab level in patients with F2 and F3 WMH and those with the minimal number of lacunes can indicate that NR2bs are involved in diffuse brain damage due to hypoxia-induced loss of BBB integrity.

White matter hyperintensity volume in pre-diabetes, diabetes and normoglycemia

INTRODUCTION

As white matter hyperintensities (WMHs) of the brain are associated with an increased risk of stroke, cognitive decline, and depression, elucidating the associated risk factors is important. In addition to age and hypertension, pre-diabetes and diabetes may play important roles in the development of WMHs. Previous studies have, however, shown conflicting results. We aimed to investigate the effect of diabetes status and quantitative markers of glucose metabolism on WMH volume in a population-based cohort without prior cardiovascular disease.

RESEARCH DESIGN AND METHODS

400 participants underwent 3 T MRI. WMHs were manually segmented on 3D fluid-attenuated inversion recovery images. An oral glucose tolerance test (OGTT) was administered to all participants not previously diagnosed with diabetes to assess 2-hour serum glucose concentrations. Fasting glucose concentrations and glycated hemoglobin (HbA1c) levels were measured. Zero-inflated negative binomial regression analyses of WMH volume and measures of glycemic status were performed while controlling for cardiovascular risk factors and multiple testing.

RESULTS

The final study population comprised 388 participants (57% male; age 56.3±9.2 years; n=98 with pre-diabetes, n=51 with diabetes). Higher WMH volume was associated with pre-diabetes (p=0.001) and diabetes (p=0.026) compared with normoglycemic control participants after adjustment for cardiovascular risk factors. 2-hour serum glucose (p<0.001), but not fasting glucose (p=0.389) or HbA1c (p=0.050), showed a significant positive association with WMH volume after adjustment for cardiovascular risk factors.

CONCLUSION

Our results indicate that high 2-hour serum glucose concentration in OGTT, but not fasting glucose levels, may be an independent risk factor for the development of WMHs, with the potential to inform intensified prevention strategies in individuals at risk of WMH-associated morbidity.

Correlations in post-mortem imaging-histopathology studies of sporadic human cerebral small vessel disease: A systematic review

AIMS

Sporadic human cerebral small vessel disease (SVD) commonly causes stroke and dementia but its pathogenesis is poorly understood. There are recognised neuroimaging and histopathological features. However, relatively few studies have examined the relationship between the radiological and pathological correlates of SVD; better correlation would promote greater insight into the underlying biological changes.

METHODS

We performed a systematic review to collate and appraise the information derived from studies that correlated histological with neuroimaging-defined SVD lesions. We searched for studies describing post-mortem imaging and histological tissue examination in adults, extracted data from published studies, categorised the information and compiled this narrative.

RESULTS

We identified 38 relevant studies, including at least 1146 subjects, 342 of these with SVD: 29 studies focussed on neuroradiological white matter lesions (WML), six on microinfarcts and three on dilated perivascular spaces (PVS) and lacunes. The histopathology terminology was diverse with few robust definitions. Reporting and methodology varied widely between studies, precluding formal meta-analysis. PVS and 'oedema' were frequent findings in WML, being described in at least 94 and 18 radiological WML, respectively, in addition to myelin pallor. Histopathological changes extended beyond the radiological lesion margins in at least 33 radiological WML. At least 43 radiological lesions not seen pathologically and at least 178 histological lesions were not identified on imaging.

CONCLUSIONS

Histopathological assessment of human SVD is hindered by inconsistent methodological approaches and unstandardised definitions. The data from this systematic review will help to develop standardised definitions to promote consistency in human SVD research.

The association between white matter hyperintensity volume and gait performance under single and dual task conditions in older people with dementia: A cross-sectional study

BACKGROUND

Understanding the relationship between white matter hyperintensities (WMHs) and gait may assist in understanding the central control of gait and determining treatment modalities. These relationships are yet to be realized in older people with dementia.

OBJECTIVE

To examine the association between WMH volume and gait under single-task and dual task (DT) conditions in people with dementia.

METHODS

Twenty-eight community-dwelling older people with dementia (median age=83 years; [IQR=77-86]; 36% female) had timed gait speed assessed at usual pace. Gait (speed, stride length, cadence) was assessed using the GAITRite® mat under three conditions (n = 18/28): a) single-task, b) functional DT: carrying a glass of water and c) cognitive DT: counting backwards from 30. WMH volumes were quantified using a fully automated segmentation toolbox.

RESULTS

Total, temporal and parietal WMH volumes were negatively correlated with timed and functional DT gait speed, and with stride length under single-task, functional DT and cognitive DT conditions. Frontal WMH volumes were negatively correlated with timed gait speed and stride length under single-task and functional DT conditions. Participants with higher total WMH burden had significantly slower timed and functional DT gait speed and reduced stride length under single-task, functional DT and cognitive DT conditions compared to participants with lower WMH burden.

CONCLUSIONS

WMH volume was associated with slower gait speed and reduced stride length, but not cadence, under single-task and DT conditions in people with dementia. Further research is needed to confirm these findings and determine whether vascular risk management can improve gait in older people with dementia.

Diffusion tensor imaging revealed different pathological processes of white matter hyperintensities

Background

Although increasing evidence showed the correlations between white matter hyperintensities (WMHs) and cognitive impairment, the relationship between them is still modest. Many researchers began to focus on the variation caused by the heterogeneity of WMH. We tried to explore the pathological heterogeneity in WMH by using diffusion tensor imaging (DTI), so as to provide a new insight into the future research.

Methods

Diffusion weighted images (DWIs) of the brain were acquired from 73 patients with WMH and 18 healthy controls, which were then modeled by DTI. We measured fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) of white matter of the periventricular frontal lobe (pFL), periventricular occipital lobe (pOL), periventricular parietal lobe (pPL) and deep centrum ovales (dCO), and grouped these measures according to the Fazekas scale. Then we compared the DTI metrics of different regions with the same Fazekas scale grade.

Results

Significantly lower FA values (all p < 0.001), and higher MD (all p < 0.001) and RD values (all p < 0.001) were associated with WMH observed in the periventricular frontal lobe (pFL) compared to all other regions with the same Fazekas grades. The AD of WMH in the pFL was higher than that of pPL and dCO, but the differences between groups was not as high as of MD and RD, as indicated by the effect size. In the normal control group, DTI metrics between pFL and other regions were not significantly different or less significant different. The difference of DTI metrics of WMH between pPL, pOL and dCO was lower than that of normal white matter, as indicated by the effect size.

Conclusion

Distinct pathological processes can be revealed by DTI between frontal periventricular WMH and other regions. These processes may represent the effects of severe demyelination within the frontal periventricular WMH.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-021-02140-9.

Distinct Hippocampal Subfields Atrophy in Older People With Vascular Brain Injuries

BACKGROUND AND PURPOSE

Many neurological or psychiatric diseases affect the hippocampus during aging. The study of hippocampal regional vulnerability may provide important insights into the pathophysiological mechanisms underlying these processes; however, little is known about the specific impact of vascular brain damage on hippocampal subfields atrophy.

METHODS

To analyze the effect of vascular injuries independently of other pathological conditions, we studied a population-based cohort of nondemented older adults, after the exclusion of people who were diagnosed with neurodegenerative diseases during the 14-year clinical follow-up period. Using an automated segmentation pipeline, 1.5T-magnetic resonance imaging at inclusion and 4 years later were assessed to measure both white matter hyperintensities and hippocampal subfields volume. Annualized rates of white matter hyperintensity progression and annualized rates of hippocampal subfields atrophy were then estimated in each participant.

RESULTS

We included 249 participants in our analyses (58% women, mean age 71.8, median Mini-Mental State Evaluation 29). The volume of the subiculum at baseline was the only hippocampal subfield volume associated with total, deep/subcortical, and periventricular white matter hyperintensity volumes, independently of demographic variables and vascular risk factors (β=-0.17, P=0.011; β=-0.25, P=0.020 and β=-0.14, P=0.029, respectively). In longitudinal measures, the annualized rate of subiculum atrophy was significantly higher in people with the highest rate of deep/subcortical white matter hyperintensity progression, independently of confounding factors (β=-0.32, P=0.014).

CONCLUSIONS

These cross-sectional and longitudinal findings highlight the links between vascular brain injuries and a differential vulnerability of the subiculum within the hippocampal loop, unbiased of the effect of neurodegenerative diseases, and particularly when vascular injuries affect deep/subcortical structures.

CD36 - A novel molecular target in the neurovascular unit

CD36 is an integral membrane protein primarily known for its function as a fatty acid transporter, yet also playing other biological roles from lipid metabolism to inflammation modulation. These pleiotropic effects are explained by the existence of multiple different ligands and the extensive distribution in numerous cell types. Moreover, the receptor is related to various pathologies and it may prove to be a good target for prospective therapeutic strategies. In the neurovascular unit (NVU), CD36 is expressed in cells like microglia, microvascular endothelial cells, astrocytes and neurons. In the normal brain, CD36 was proven to be involved in phagocytosis of apoptotic cells, oro‐sensory detection of dietary lipids, and fatty acid transport across the blood brain barrier (BBB). CD36 was also acknowledged as a potentially important player in central nervous system (CNS) disorders, such as Alzheimer Disease‐associated vascular dysfunction and oxidative stress and the neuroinflammatory response in stroke. Despite continuous efforts, the therapeutic arsenal for such diseases is still scarce and there is an increasing interest in discovering new molecular targets for more specific therapeutic approaches. In this review, we summarize the role of CD36 in the normal function of the NVU and in several CNS disorders, focusing on the dysregulation of the NVU and the potential therapeutic modulation.

Heterogeneity of cellular inflammatory responses in ageing white matter and relationship to Alzheimer's and small vessel disease pathologies

White matter lesions (WML) are common in the ageing brain, often arising in a field effect of diffuse white matter abnormality. Although WML are associated with cerebral small vessel disease (SVD) and Alzheimer’s disease (AD), their cause and pathogenesis remain unclear. The current study tested the hypothesis that different patterns of neuroinflammation are associated with SVD compared to AD neuropathology by assessing the immunoreactive profile of the microglial (CD68, IBA1 and MHC‐II) and astrocyte (GFAP) markers in ageing parietal white matter (PARWM) obtained from the Cognitive Function and Ageing Study (CFAS), an ageing population‐representative neuropathology cohort. Glial responses varied extensively across the PARWM with microglial markers significantly higher in the subventricular region compared to either the middle‐zone (CD68 p = 0.028, IBA1 p < 0.001, MHC‐II p < 0.001) or subcortical region (CD68 p = 0.002, IBA1 p < 0.001, MHC‐II p < 0.001). Clasmatodendritic (CD) GFAP⁺ astrocytes significantly increased from the subcortical to the subventricular region (p < 0.001), whilst GFAP⁺ stellate astrocytes significantly decreased (p < 0.001). Cellular reactions could be grouped into two distinct patterns: an immune response associated with MHC‐II/IBA1 expression and CD astrocytes; and a more innate response characterised by CD68 expression associated with WML. White matter neuroinflammation showed weak relationships to the measures of SVD, but not to the measures of AD neuropathology. In conclusion, glial responses vary extensively across the PARWM with diverse patterns of white matter neuroinflammation. Although these findings support a role for vascular factors in the pathogenesis of age‐related white matter neuroinflammation, additional factors other than SVD and AD pathology may drive this. Understanding the heterogeneity in white matter neuroinflammation will be important for the therapeutic targeting of age‐associated white matter damage.

Associated factors of white matter hyperintensity volume: a machine-learning approach

To identify the most important parameters associated with cerebral white matter hyperintensities (WMH), in consideration of potential collinearity, we used a data-driven machine-learning approach. We analysed two independent cohorts (KORA and SHIP). WMH volumes were derived from cMRI-images (FLAIR). 90 (KORA) and 34 (SHIP) potential determinants of WMH including measures of diabetes, blood-pressure, medication-intake, sociodemographics, life-style factors, somatic/depressive-symptoms and sleep were collected. Elastic net regression was used to identify relevant predictor covariates associated with WMH volume. The ten most frequently selected variables in KORA were subsequently examined for robustness in SHIP. The final KORA sample consisted of 370 participants (58% male; age 55.7 ± 9.1 years), the SHIP sample comprised 854 participants (38% male; age 53.9 ± 9.3 years). The most often selected and highly replicable parameters associated with WMH volume were in descending order age, hypertension, components of the social environment (i.e. widowed, living alone) and prediabetes. A systematic machine-learning based analysis of two independent, population-based cohorts showed, that besides age and hypertension, prediabetes and components of the social environment might play important roles in the development of WMH. Our results enable personal risk assessment for the development of WMH and inform prevention strategies tailored to the individual patient.

Reduced [18F]flortaucipir retention in white matter hyperintensities compared to normal-appearing white matter

PURPOSE

Recent research has suggested the use of white matter (WM) reference regions for longitudinal tau-PET imaging. However, tau tracers display affinity for the β-sheet structure formed by myelin, and thus WM lesions might influence tracer retention. Here, we explored whether the tau-sensitive tracer [¹⁸F]flortaucipir shows reduced retention in WM hyperintensities (WMH) and how this retention changes over time.

METHODS

We included 707 participants from the Alzheimer's Disease Neuroimaging Initiative with available [¹⁸F]flortaucipir-PET and structural and FLAIR MRI scans. WM segments and WMH were automatically delineated in the structural MRI and FLAIR scans, respectively. [¹⁸F]flortaucipir standardized uptake value ratios (SUVR) of WMH and normal-appearing WM (NAWM) were calculated using the inferior cerebellar grey matter as reference region, and a 3-mm erosion was applied to the combined NAWM and WMH masks to avoid partial volume effects. Longitudinal [¹⁸F]flortaucipir SUVR changes in NAWM and WMH were estimated using linear mixed models. The percent variance of WM-referenced cortical [¹⁸F]flortaucipir SUVRs explained by longitudinal changes in the WM reference region was estimated with the R² coefficient.

RESULTS

Compared to NAWM, WMH areas displayed significantly reduced [¹⁸F]flortaucipir SUVR, independent of cognitive impairment or Aβ status (mean difference = 0.14 SUVR, p < 0.001). Older age was associated with lower [¹⁸F]flortaucipir SUVR in both NAWM (- 0.002 SUVR/year, p = 0.005) and WMH (- 0.004 SUVR/year, p < 0.001). Longitudinally, [¹⁸F]flortaucipir SUVR decreased in NAWM (- 0.008 SUVR/year, p = 0.03) and even more so in WMH (- 0.02 SUVR/year, p < 0.001). Between 17% and 66% of the variance of longitudinal changes in cortical WM-referenced [¹⁸F]flortaucipir SUVRs were explained by longitudinal changes in the reference region.

CONCLUSIONS

[¹⁸F]flortaucipir retention in the WM decreases over time and is influenced by the presence of WMH, supporting the hypothesis that [¹⁸F]flortaucipir retention in the WM is partially myelin-dependent. These findings have implications for the use of WM reference regions for [¹⁸F]flortaucipir-PET imaging.

Transcriptomic Analysis of Age-Associated Periventricular Lesions Reveals Dysregulation of the Immune Response

White matter lesions (WML) are a common feature of the ageing brain associated with cognitive impairment. The gene expression profiles of periventricular lesions (PVL, n = 7) and radiologically-normal-appearing (control) periventricular white matter cases (n = 11) obtained from the Cognitive Function and Ageing Study (CFAS) neuropathology cohort were interrogated using microarray analysis and NanoString to identify novel mechanisms potentially underlying their formation. Histological characterisation of control white matter cases identified a subgroup (n = 4) which contained high levels of MHC-II immunoreactive microglia, and were classified as “pre-lesional.” Microarray analysis identified 2256 significantly differentially-expressed genes (p ≤ 0.05, FC ≥ 1.2) in PVL compared to non-lesional control white matter (1378 upregulated and 878 downregulated); 2649 significantly differentially-expressed genes in “pre-lesional” cases compared to PVL (1390 upregulated and 1259 downregulated); and 2398 significantly differentially-expressed genes in “pre-lesional” versus non-lesional control cases (1527 upregulated and 871 downregulated). Whilst histological evaluation of a single marker (MHC-II) implicates immune-activated microglia in lesion pathology, transcriptomic analysis indicates significant downregulation of a number of activated microglial markers and suggests established PVL are part of a continuous spectrum of white matter injury. The gene expression profile of “pre-lesional” periventricular white matter suggests upregulation of several signalling pathways may be a neuroprotective response to prevent the pathogenesis of PVL.

Role of non-coding RNAs in age-related vascular cognitive impairment: An overview on diagnostic/prognostic value in Vascular Dementia and Vascular Parkinsonism

Age is the pivotal risk factor for different common medical conditions such as cardiovascular diseases, cancer and dementia. Among age-related disorders, cardiovascular and cerebrovascular diseases, represent the leading causes of premature mortality strictly related to vascular ageing, a pathological condition characterized by endothelial dysfunction, atherosclerosis, hypertension, heart disease and stroke. These features negatively impact on the brain, owing to altered cerebral blood flow, neurovascular coupling and impaired endothelial permeability leading to cerebrovascular diseases (CVDs) as Vascular Dementia (VD) and Parkinsonism (VP). It is an increasing opinion that neurodegenerative disorders and cerebrovascular diseases are associated from a pathogenetic point of view, and in this review, we discuss how cerebrovascular dysfunctions, due to epigenetic alterations, are linked with neuronal degeneration/dysfunction that lead to cognitive impairment. The relation between neurodegenerative and cerebrovascular diseases are reviewed with a focus on role of ncRNAs in age-related vascular diseases impairing the endothelium in the blood-brain barrier with consequent dysfunction of cerebral blood flow. In this review we dissert about different regulatory mechanisms of gene expression implemented by ncRNAs in the pathogenesis of age-related neurovascular impairment, aiming to highlight the potential use of ncRNAs as biomarkers for diagnostic/prognostic purposes as well as novel therapeutic targets.

Tissue microarray (TMA) use in post mortem neuropathology

BACKGROUND

Tissue microarrays (TMAs), where each block (and thus section) contains multiple tissue cores from multiple blocks potentially allow more efficient use of tissue, reagents and time in neuropathology.

NEW METHOD

The relationship between data from TMA cores and whole sections was investigated using 'virtual' TMA cores. This involved quantitative assessments of microglial pathology in white matter lesions and motor neuron disease, alongside qualitative TDP-43 inclusion status in motor neuron disease cases. Following this, a protocol was developed for TMA construction.

RESULTS

For microglial pathology we found good concordance between virtual cores and whole sections for volume density using one 1.75 mm core (equivalent to a 2 mm core after accounting for peripheral tissue loss). More sophisticated microglial cell size and measures required two cores. Qualitative results of pTDP-43 pathology showed use of one 1.75 mm core gave a 100 % sensitivity and specificity within grey matter, and 88.3 % sensitivity and 100 % specificity within white matter. A method of producing the TMAs was suitable for immunohistochemistry both manually and by autostainer, with the minimal core loss from the microscope slide.

COMPARISON WITH EXISTING METHODS

TMAs have been used infrequently in post mortem neuropathology research. However, we believe TMAs give comparable tissue assessment results and can be constructed, sectioned and stained with relative ease.

CONCLUSIONS

We found TMAs could be used to assess both quantitative (microglial pathology) and qualitative pathology (TDP-43 proteinopathy) with greatly reduced quantities of tissue, time and reagents. These could be used for further work to improve data acquisition efficiency.

Cardiorespiratory fitness diminishes the effects of age on white matter hyperintensity volume

White matter hyperintensities (WMHs) are among the most commonly observed marker of cerebrovascular disease. Age is a key risk factor for WMH development. Cardiorespiratory fitness (CRF) is associated with increased vessel compliance, but it remains unknown if high CRF affects WMH volume. This study explored the effects of CRF on WMH volume in community-dwelling older adults. We further tested the possibility of an interaction between CRF and age on WMH volume. Participants were 76 adults between the ages of 59 and 77 (mean age = 65.36 years, SD = 3.92) who underwent a maximal graded exercise test and structural brain imaging. Results indicated that age was a predictor of WMH volume (beta = .32, p = .015). However, an age-by-CRF interaction was observed such that higher CRF was associated with lower WMH volume in older participants (beta = -.25, p = .040). Our findings suggest that higher levels of aerobic fitness may protect cerebrovascular health in older adults.