Cerebral microbleeds in early Alzheimer's disease

Influence of Tau on Neurotoxicity and Cerebral Vasculature Impairment Associated with Alzheimer's Disease

Alzheimer's disease is a fatal chronic neurodegenerative condition marked by a gradual decline in cognitive abilities and impaired vascular function within the central nervous system. This affliction initiates its insidious progression with the accumulation of two aberrant protein entities including Aβ plaques and neurofibrillary tangles. These chronic elements target distinct brain regions, steadily erasing the functionality of the hippocampus and triggering the erosion of memory and neuronal integrity. Several assumptions are anticipated for AD as genetic alterations, the occurrence of Aβ plaques, altered processing of amyloid precursor protein, mitochondrial damage, and discrepancy of neurotropic factors. In addition to Aβ oligomers, the deposition of tau hyper-phosphorylates also plays an indispensable part in AD etiology. The brain comprises a complex network of capillaries that is crucial for maintaining proper function. Tau is expressed in cerebral blood vessels, where it helps to regulate blood flow and sustain the blood-brain barrier's integrity. In AD, tau pathology can disrupt cerebral blood supply and deteriorate the BBB, leading to neuronal neurodegeneration. Neuroinflammation, deficits in the microvasculature and endothelial functions, and Aβ deposition are characteristically detected in the initial phases of AD. These variations trigger neuronal malfunction and cognitive impairment. Intracellular tau accumulation in microglia and astrocytes triggers deleterious effects on the integrity of endothelium and cerebral blood supply resulting in further advancement of the ailment and cerebral instability. In this review, we will discuss the impact of tau on neurovascular impairment, mitochondrial dysfunction, oxidative stress, and the role of hyperphosphorylated tau in neuron excitotoxicity and inflammation.

Cerebral Microbleeds in Different Brain Regions and Their Associations With the Digital Clock-Drawing Test: Secondary Analysis of the Framingham Heart Study

BACKGROUND

Cerebral microbleeds (CMB) increase the risk for Alzheimer disease. Current neuroimaging methods that are used to detect CMB are costly and not always accessible.

OBJECTIVE

This study aimed to explore whether the digital clock-drawing test (DCT) may provide a behavioral indicator of CMB.

METHODS

In this study, we analyzed data from participants in the Framingham Heart Study offspring cohort who underwent both brain magnetic resonance imaging scans (Siemens 1.5T, Siemens Healthcare Private Limited; T2*-GRE weighted sequences) for CMB diagnosis and the DCT as a predictor. Additionally, paper-based clock-drawing tests were also collected during the DCT. Individuals with a history of dementia or stroke were excluded. Robust multivariable linear regression models were used to examine the association between DCT facet scores with CMB prevalence, adjusting for relevant covariates. Receiver operating characteristic (ROC) curve analyses were used to evaluate DCT facet scores as predictors of CMB prevalence. Sensitivity analyses were conducted by further including participants with stroke and dementia.

RESULTS

The study sample consisted of 1020 (n=585, 57.35% female) individuals aged 45 years and older (mean 72, SD 7.9 years). Among them, 64 (6.27%) participants exhibited CMB, comprising 46 with lobar-only, 11 with deep-only, and 7 with mixed (lobar+deep) CMB. Individuals with CMB tended to be older and had a higher prevalence of mild cognitive impairment and higher white matter hyperintensities compared to those without CMB (P<.05). While CMB were not associated with the paper-based clock-drawing test, participants with CMB had a lower overall DCT score (CMB: mean 68, SD 23 vs non-CMB: mean 76, SD 20; P=.009) in the univariate comparison. In the robust multiple regression model adjusted for covariates, deep CMB were significantly associated with lower scores on the drawing efficiency (β=-0.65, 95% CI -1.15 to -0.15; P=.01) and simple motor (β=-0.86, 95% CI -1.43 to -0.30; P=.003) domains of the command DCT. In the ROC curve analysis, DCT facets discriminated between no CMB and the CMB subtypes. The area under the ROC curve was 0.76 (95% CI 0.69-0.83) for lobar CMB, 0.88 (95% CI 0.78-0.98) for deep CMB, and 0.98 (95% CI 0.96-1.00) for mixed CMB, where the area under the ROC curve value nearing 1 indicated an accurate model.

CONCLUSIONS

The study indicates a significant association between CMB, especially deep and mixed types, and reduced performance in drawing efficiency and motor skills as assessed by the DCT. This highlights the potential of the DCT for early detection of CMB and their subtypes, providing a reliable alternative for cognitive assessment and making it a valuable tool for primary care screening before neuroimaging referral.

Blood-brain barrier disruption in dementia: Nano-solutions as new treatment options

Candidate drugs targeting the central nervous system (CNS) demonstrate extremely low clinical success rates, with more than 98% of potential treatments being discontinued due to poor blood-brain barrier (BBB) permeability. Neurological conditions were shown to be the second leading cause of death globally in 2016, with the number of people currently affected by neurological disorders increasing rapidly. This increasing trend, along with an inability to develop BBB permeating drugs, is presenting a major hurdle in the treatment of CNS-related disorders, like dementia. To overcome this, it is necessary to understand the structure and function of the BBB, including the transport of molecules across its interface in both healthy and pathological conditions. The use of CNS drug carriers is rapidly gaining popularity in CNS research due to their ability to target BBB transport systems. Further research and development of drug delivery vehicles could provide essential information that can be used to develop novel treatments for neurological conditions. This review discusses the BBB and its transport systems and evaluates the potential of using nanoparticle-based delivery systems as drug carriers for CNS disease with a focus on dementia.

An arrayed CRISPR knockout screen identifies genetic regulators of GLUT1 expression

Glucose, a primary fuel source under homeostatic conditions, is transported into cells by membrane transporters such as glucose transporter 1 (GLUT1). Due to its essential role in maintaining energy homeostasis, dysregulation of GLUT1 expression and function can adversely affect many physiological processes in the body. This has implications in a wide range of disorders such as Alzheimer's disease (AD) and several types of cancers. However, the regulatory pathways that govern GLUT1 expression, which may be altered in these diseases, are poorly characterized. To gain insight into GLUT1 regulation, we performed an arrayed CRISPR knockout screen using Caco-2 cells as a model cell line. Using an automated high content immunostaining approach to quantify GLUT1 expression, we identified more than 300 genes whose removal led to GLUT1 downregulation. Many of these genes were enriched along signaling pathways associated with G-protein coupled receptors, particularly the rhodopsin-like family. Secondary hit validation confirmed that removal of select genes, or modulation of the activity of a corresponding protein, yielded changes in GLUT1 expression. Overall, this work provides a resource and framework for understanding GLUT1 regulation in health and disease.

Analysis of Risk Factors for Cerebral Microbleeds and the Relationship between Cerebral Microbleeds and Cognitive Impairment

(1) Background: Cerebral microbleeds (CMBs) are attracting increasing attention. Nevertheless, the risk factors for CMBs remain poorly identified, and the relationship between CMBs and cognitive impairment is still up for debate; (2) Objective: The present study analyzed the risk factors for CMBs and probed into the potential correlations between the presence, number, and location of CMBs and cognition; (3) Methods: This study enrolled 406 subjects who underwent both brain 3.0-T magnetic resonance imaging scans and cognitive testing. Spearman correlation was used to assess the relationship between the number of CMBs and cognition. Multiple linear regression was utilized to analyze the relationship between the regions of CMBs and each cognitive domain; (4) Results: Multivariate logistic regression analysis results showed that age (odds ratio (OR) = 1.045, 95% confidence interval (95%CI; 1.009, 1.082)), smoking (OR = 3.604, 95%CI (1.995, 6.509)), hypertension (OR = 3.607, 95%CI (2.204, 5.901)), total cholesterol (OR = 0.611, 95%CI (0.467, 0.799)), and Amyloid-β1-42 (Aβ1-42) (OR = 1.028, 95%CI (1.018, 1.037)) were the influencing factors of CMBs. Education years (OR = 0.959, 95%CI (0.930, 0.988)), white matter lesions (OR = 2.687, 95%CI (1.782, 4.051)), and CMBs (OR = 21.246, 95%CI (5.728, 21.576)) were the risk factors for cognitive impairment. Hypertension increased the probability of deep CMBs (OR = 12.54, 95%CI (2.21, 71.28)), while Aβ1-42 elevated the probability of lobar CMBs (OR = 1.02, 95%CI (1.00, 1.03)). There was a linear correlation between the number of CMBs and Montreal Cognitive Assessment scores (r = −0.756, p < 0.001). However, CMBs in each region were not related to specific cognitive domains (p > 0.05), except CMBs in the mixed group that were negatively correlated with attention (OR = −0.669, 95%CI (−0.034, −5.270)); (5) Conclusions: Taken together, serum Aβ1-42 levels are related to the presence of CMBs. Cognitive impairment is correlated with the number of CMBs rather than their region. These findings suggest that CMBs play a role in cognitive impairment and that CMBs mark the presence of diffuse vascular injury and neurodegenerative brain damage.

Clinical impact of microbleeds in patients with Alzheimer's disease

Introduction

Cerebral microbleeds (CMBs) are more frequent in patients with Alzheimer’s disease (AD) than in the general population. However, their clinical significance remains poorly understood. We carried out a multimodal approach to evaluate the impact of CMBs at a clinical, neuropsychological, and survival level, as well as on core AD biomarkers in the cerebrospinal fluid (CSF) in AD patients.

Methods

We prospectively recruited 98 patients with mild-moderate AD. At baseline, they underwent brain MRI, and AD CSF biomarkers and APOE genotypes were analysed. An extensive neuropsychological battery was performed at baseline and after 1 year of follow-up. We analysed the stroke incidence and mortality with survival analyses.

Results

Forty-eight (48.5%) patients had at least one CMBs. Eight (8.2%) patients had strictly nonlobar CMBs, 39 (40.2%) had any lobar CMB locations. The incidence of stroke was higher in AD patients with lobar CMBs than in those without CMBs (p < 0.05). Mortality did not differ among groups (p > 0.05). At the cognitive level, CMBs patients deteriorated more rapidly at 12 months according to MMSE scores, with no differences observed at 24 months. We did not observe differences in the other tests, except for an increase in caregiver burden in the CMBs group. The presence of cerebral amyloidosis and APOE ε4 were associated with a greater presence of CMBs.

Conclusion

CMBs are associated with an increased risk of ischemic stroke in AD patients without differences in mortality. Patients with CMBs did not seem to have different consequences associated with cognitive decline except for an increase in caregiver overload.

Biomarkers involved in the pathogenesis of cerebral small-vessel disease

Cerebral small-vessel disease (CSVD) has been found to have a strong association with vascular cognitive impairment (VCI) and functional loss in elderly patients. At present, the diagnosis of CSVD mainly relies on brain neuroimaging markers, but they cannot fully reflect the overall picture of the disease. Currently, some biomarkers were found to be related to CSVD, but the underlying mechanisms remain unclear. We aimed to systematically review and summarize studies on the progress of biomarkers related to the pathogenesis of CSVD, which is mainly the relationship between these indicators and neuroimaging markers of CSVD. Concerning the pathophysiological mechanism of CSVD, the biomarkers of CSVD have been described as several categories related to sporadic and genetic factors. Monitoring of biomarkers might contribute to the early diagnosis and progression prediction of CSVD, thus providing ideas for better diagnosis and treatment of CSVD.

Neurovascular Dysfunction in Diverse Communities With Health Disparities-Contributions to Dementia and Alzheimer's Disease

Alzheimer's disease and related dementias (ADRD) are an expanding worldwide crisis. In the absence of scientific breakthroughs, the global prevalence of ADRD will continue to increase as more people are living longer. Racial or ethnic minority groups have an increased risk and incidence of ADRD and have often been neglected by the scientific research community. There is mounting evidence that vascular insults in the brain can initiate a series of biological events leading to neurodegeneration, cognitive impairment, and ADRD. We are a group of researchers interested in developing and expanding ADRD research, with an emphasis on vascular contributions to dementia, to serve our local diverse community. Toward this goal, the primary objective of this review was to investigate and better understand health disparities in Alabama and the contributions of the social determinants of health to those disparities, particularly in the context of vascular dysfunction in ADRD. Here, we explain the neurovascular dysfunction associated with Alzheimer's disease (AD) as well as the intrinsic and extrinsic risk factors contributing to dysfunction of the neurovascular unit (NVU). Next, we ascertain ethnoregional health disparities of individuals living in Alabama, as well as relevant vascular risk factors linked to AD. We also discuss current pharmaceutical and non-pharmaceutical treatment options for neurovascular dysfunction, mild cognitive impairment (MCI) and AD, including relevant studies and ongoing clinical trials. Overall, individuals in Alabama are adversely affected by social and structural determinants of health leading to health disparities, driven by rurality, ethnic minority status, and lower socioeconomic status (SES). In general, these communities have limited access to healthcare and healthy food and other amenities resulting in decreased opportunities for early diagnosis of and pharmaceutical treatments for ADRD. Although this review is focused on the current state of health disparities of ADRD patients in Alabama, future studies must include diversity of race, ethnicity, and region to best be able to treat all individuals affected by ADRD.

GLP-1 Receptor Agonists in Neurodegeneration: Neurovascular Unit in the Spotlight

Defects in brain energy metabolism and proteopathic stress are implicated in age-related degenerative neuronopathies, exemplified by Alzheimer’s disease (AD) and Parkinson’s disease (PD). As the currently available drug regimens largely aim to mitigate cognitive decline and/or motor symptoms, there is a dire need for mechanism-based therapies that can be used to improve neuronal function and potentially slow down the underlying disease processes. In this context, a new class of pharmacological agents that achieve improved glycaemic control via the glucagon-like peptide 1 (GLP-1) receptor has attracted significant attention as putative neuroprotective agents. The experimental evidence supporting their potential therapeutic value, mainly derived from cellular and animal models of AD and PD, has been discussed in several research reports and review opinions recently. In this review article, we discuss the pathological relevance of derangements in the neurovascular unit and the significance of neuron–glia metabolic coupling in AD and PD. With this context, we also discuss some unresolved questions with regard to the potential benefits of GLP-1 agonists on the neurovascular unit (NVU), and provide examples of novel experimental paradigms that could be useful in improving our understanding regarding the neuroprotective mode of action associated with these agents.

Blood-brain barrier leakage in Alzheimer's disease: From discovery to clinical relevance

Alzheimer's disease (AD) is the most common form of dementia. AD brain pathology starts decades before the onset of clinical symptoms. One early pathological hallmark is blood-brain barrier dysfunction characterized by barrier leakage and associated with cognitive decline. In this review, we summarize the existing literature on the extent and clinical relevance of barrier leakage in AD. First, we focus on AD animal models and their susceptibility to barrier leakage based on age and genetic background. Second, we re-examine barrier dysfunction in clinical and postmortem studies, summarize changes that lead to barrier leakage in patients and highlight the clinical relevance of barrier leakage in AD. Third, we summarize signaling mechanisms that link barrier leakage to neurodegeneration and cognitive decline in AD. Finally, we discuss clinical relevance and potential therapeutic strategies and provide future perspectives on investigating barrier leakage in AD. Identifying mechanistic steps underlying barrier leakage has the potential to unravel new targets that can be used to develop novel therapeutic strategies to repair barrier leakage and slow cognitive decline in AD and AD-related dementias.

Peripheral Pathways to Neurovascular Unit Dysfunction, Cognitive Impairment, and Alzheimer’s Disease

Alzheimer’s disease (AD) is the most common form of dementia. It was first described more than a century ago, and scientists are acquiring new data and learning novel information about the disease every day. Although there are nuances and details continuously being unraveled, many key players were identified in the early 1900’s by Dr. Oskar Fischer and Dr. Alois Alzheimer, including amyloid-beta (Aβ), tau, vascular abnormalities, gliosis, and a possible role of infections. More recently, there has been growing interest in and appreciation for neurovascular unit dysfunction that occurs early in mild cognitive impairment (MCI) before and independent of Aβ and tau brain accumulation. In the last decade, evidence that Aβ and tau oligomers are antimicrobial peptides generated in response to infection has expanded our knowledge and challenged preconceived notions. The concept that pathogenic germs cause infections generating an innate immune response (e.g., Aβ and tau produced by peripheral organs) that is associated with incident dementia is worthwhile considering in the context of sporadic AD with an unknown root cause. Therefore, the peripheral amyloid hypothesis to cognitive impairment and AD is proposed and remains to be vetted by future research. Meanwhile, humans remain complex variable organisms with individual risk factors that define their immune status, neurovascular function, and neuronal plasticity. In this focused review, the idea that infections and organ dysfunction contribute to Alzheimer’s disease, through the generation of peripheral amyloids and/or neurovascular unit dysfunction will be explored and discussed. Ultimately, many questions remain to be answered and critical areas of future exploration are highlighted.

Blood-brain barrier link to human cognitive impairment and Alzheimer's Disease

Vascular dysfunction is frequently seen in disorders associated with cognitive impairment, dementia and Alzheimer's disease (AD). Recent advances in neuroimaging and fluid biomarkers suggest that vascular dysfunction is not an innocent bystander only accompanying neuronal dysfunction. Loss of cerebrovascular integrity, often referred to as breakdown in the blood-brain barrier (BBB), has recently shown to be an early biomarker of human cognitive dysfunction and possibly underlying mechanism of age-related cognitive decline. Damage to the BBB may initiate or further invoke a range of tissue injuries causing synaptic and neuronal dysfunction and cognitive impairment that may contribute to AD. Therefore, better understanding of how vascular dysfunction caused by BBB breakdown interacts with amyloid-β and tau AD biomarkers to confer cognitive impairment may lead to new ways of thinking about pathogenesis, and possibly treatment and prevention of early cognitive impairment, dementia and AD, for which we still do not have effective therapies.

Basal lamina changes in neurodegenerative disorders

BACKGROUND

Neurodegenerative disorders are a group of age-associated diseases characterized by progressive degeneration of the structure and function of the CNS. Two key pathological features of these disorders are blood-brain barrier (BBB) breakdown and protein aggregation.

MAIN BODY

The BBB is composed of various cell types and a non-cellular component---the basal lamina (BL). Although how different cells affect the BBB is well studied, the roles of the BL in BBB maintenance and function remain largely unknown. In addition, located in the perivascular space, the BL is also speculated to regulate protein clearance via the meningeal lymphatic/glymphatic system. Recent studies from our laboratory and others have shown that the BL actively regulates BBB integrity and meningeal lymphatic/glymphatic function in both physiological and pathological conditions, suggesting that it may play an important role in the pathogenesis and/or progression of neurodegenerative disorders. In this review, we focus on changes of the BL and its major components during aging and in neurodegenerative disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). First, we introduce the vascular and lymphatic systems in the CNS. Next, we discuss the BL and its major components under homeostatic conditions, and summarize their changes during aging and in AD, PD, and ALS in both rodents and humans. The functional significance of these alterations and potential therapeutic targets are also reviewed. Finally, key challenges in the field and future directions are discussed.

CONCLUSIONS

Understanding BL changes and the functional significance of these changes in neurodegenerative disorders will fill the gap of knowledge in the field. Our goal is to provide a clear and concise review of the complex relationship between the BL and neurodegenerative disorders to stimulate new hypotheses and further research in this field.

Novel MRI Techniques Identifying Vascular Leak and Paravascular Flow Reduction in Early Alzheimer Disease

With beta amyloid and tau antibody treatment trial failures, avenues directed to other facets of the disease pathophysiology are being explored to treat in the preclinical or early clinical state. Clear evidence of blood–brain barrier (BBB) breakdown occurring early in the AD process has recently been established. Likewise, the glymphatic system regulating water and solute inflow and outflow in parallel with the vascular system is affected causing delayed clearance of fluid waste. Its dysfunction as a component of AD along with BBB leak are reasonable candidates to explore for future treatments. Ideally, human medication trials require a minimally invasive method of quantifying both improvements in BBB integrity and glymphatic fluid clearance correlated with clinical outcomes. We will review the known physiology and anatomy of the BBB system, and its relationship to the glymphatic system and the microglial surveillance system. Dysfunction of this tripart system occurring in preclinical Alzheimer disease (AD) will be reviewed along with existing MRI tools for identifying altered flow dynamics useful for monitoring improved functionality with future treatments. High-resolution dynamic contrast enhanced MRI imaging demonstrating BBB leak and the recently reported non-invasive 3D PASL MRI pilot study demonstrating significant delay in glymphatic clearance in AD subjects appear to be the best candidates.

Cerebral Amyloid Angiopathy and Neuritic Plaque Pathology Correlate with Cognitive Decline in Elderly Non-Demented Individuals

BACKGROUND

Cerebral amyloid angiopathy (CAA) is a vascular neuropathology commonly reported in non-cognitively impaired (NCI), mild cognitive impairment, and Alzheimer's disease (AD) brains. However, it is unknown whether similar findings are present in non-demented elderly subjects.

OBJECTIVE

This study determined the association between CAA and cognition among elderly NCI subjects with varying levels of AD pathology.

METHODS

Data from 182 cases that received a diagnosis of NCI at their first clinical assessment were obtained from the Rush Religious Orders study (RROS). A cognitive composite score was used to measure cognitive decline. CAA was dichotomized as present or absent. Cases were also dichotomized according to CERAD neuropathological diagnosis and Braak staging. A mixed model-repeated measures analysis assessed decline on the cognitive composite score.

RESULTS

CAA, alone, was not associated with cognitive decline [-0.87 (95% CI: -3.33, 1.58), p = 0.49]. However, among those with CAA, the High CERAD group had significantly greater decline relative to the Low CERAD group [-4.08 (95% CI: -7.10, -1.06), p = 0.008]. The High and Low CERAD groups were not significantly different [-1.77 (95% CI: -6.14, 2.60), p = 0.43] in those without CAA. Composite score decline in the High and Low Braak groups with [-1.32 (95% CI: -4.40, 1.75), p = 0.40] or without [0.27 (95% CI: -4.01, 4.56), p = 0.90] CAA was not significantly different.

CONCLUSION

The current data shows that an interaction between CAA and plaque load is associated with greater decline on a cognitive composite score used to test non-cognitively impaired elderly participants in AD prevention trials.

Increased prevalence of cerebral microbleeds in patients with low left ventricular systolic function

Gradient-echo T2-star (T2*)-weighted magnetic resonance imaging (MRI) is a sensitive method to detect cerebral microbleeds (CMBs). The presence of CMBs was reported to be a marker of future cardiovascular mortality and is associated with various cardiovascular risk factors, use of antithrombotic drugs, and cognitive dysfunction. However, the relationship between cardiac function and CMBs remains unclear. We investigated the association between cardiac function and presence of CMBs in patients with cardiovascular diseases. This single-center retrospective study included a total of 424 participants (mean age 70 ± 12 years; men 286 (67%); mean left ventricular ejection fraction (LVEF) 61% ± 12%] who underwent echocardiography and brain T2*-weighted MRI within 1 month without neurologic abnormality. CMBs were found in 118 (28%) patients. There was no significant relationship between CMBs and anticoagulant or antiplatelet therapy. LVEF was significantly lower in patients with CMBs than in those without CMBs (59% ± 13% vs. 62% ± 11%, P < 0.05). On multivariate logistic analysis, lower LVEF [odds ratio (OR) 0.98, 95% confidence interval (CI) 0.96-1.00; P < 0.05] and age (OR 1.02, 95% CI 1.00-1.05; P < 0.05) were significantly associated with CMBs. The presence of CMBs was frequently observed in the patients with cardiovascular disease and was significantly associated with age and LVEF.

Current and emerging avenues for Alzheimer's disease drug targets

Alzheimer's disease (AD), the most frequent cause of dementia, is escalating as a global epidemic, and so far, there is neither cure nor treatment to alter its progression. The most important feature of the disease is neuronal death and loss of cognitive functions, caused probably from several pathological processes in the brain. The main neuropathological features of AD are widely described as amyloid beta (Aβ) plaques and neurofibrillary tangles of the aggregated protein tau, which contribute to the disease. Nevertheless, AD brains suffer from a variety of alterations in function, such as energy metabolism, inflammation and synaptic activity. The latest decades have seen an explosion of genes and molecules that can be employed as targets aiming to improve brain physiology, which can result in preventive strategies for AD. Moreover, therapeutics using these targets can help AD brains to sustain function during the development of AD pathology. Here, we review broadly recent information for potential targets that can modify AD through diverse pharmacological and nonpharmacological approaches including gene therapy. We propose that AD could be tackled not only using combination therapies including Aβ and tau, but also considering insulin and cholesterol metabolism, vascular function, synaptic plasticity, epigenetics, neurovascular junction and blood-brain barrier targets that have been studied recently. We also make a case for the role of gut microbiota in AD. Our hope is to promote the continuing research of diverse targets affecting AD and promote diverse targeting as a near-future strategy.

Human Bone Marrow Endothelial Progenitor Cell Transplantation into Symptomatic ALS Mice Delays Disease Progression and Increases Motor Neuron Survival by Repairing Blood-Spinal Cord Barrier

Convincing evidence demonstrated impairment of the blood-spinal cord barrier (BSCB) in Amyotrophic Lateral Sclerosis (ALS), mainly by endothelial cell (EC) alterations. Replacing damaged ECs by cell transplantation is a potential barrier repair strategy. Recently, we showed that intravenous (iv) administration of human bone marrow CD34⁺ (hBM34⁺) cells into symptomatic ALS mice benefits BSCB restoration and postpones disease progression. However, delayed effect on motor function and some severely damaged capillaries were noted. We hypothesized that hematopoietic cells from a restricted lineage would be more effective. This study aimed to establish the effects of human bone marrow-derived endothelial progenitor cells (hBMEPCs) systemically transplanted into G93A mice at symptomatic disease stage. Results showed that transplanted hBMEPCs significantly improved behavioral disease outcomes, engrafted widely into capillaries of the gray/white matter spinal cord and brain motor cortex/brainstem, substantially restored capillary ultrastructure, significantly decreased EB extravasation into spinal cord parenchyma, meaningfully re-established perivascular astrocyte end-feet, and enhanced spinal cord motor neuron survival. These results provide novel evidence that transplantation of hBMEPCs effectively repairs the BSCB, potentially preventing entry of detrimental peripheral factors, including immune/inflammatory cells, which contribute to motor neuron dysfunction. Transplanting EC progenitor cells may be a promising strategy for barrier repair therapy in this disease.

The Full Spectrum of Alzheimer's Disease Is Rooted in Metabolic Derangements That Drive Type 3 Diabetes

The standard practice in neuropathology is to diagnose Alzheimer's disease (AD) based on the distribution and abundance of neurofibrillary tangles and Aβ deposits. However, other significant abnormalities including neuroinflammation, gliosis, white matter degeneration, non-Aβ microvascular disease, and insulin-related metabolic dysfunction require further study to understand how they could be targeted to more effectively remediate AD. This review addresses non-Aβ and non-pTau AD-associated pathologies, highlighting their major features, roles in neurodegeneration, and etiopathic links to deficits in brain insulin and insulin-like growth factor signaling and cognitive impairment. The discussion delineates why AD with its most characteristic clinical and pathological phenotypic profiles should be regarded as a brain form of diabetes, i.e., type 3 diabetes, and entertains the hypothesis that type 3 diabetes is just one of the categories of insulin resistance diseases that can occur independently or overlap with one or more of the others, including type 2 diabetes, metabolic syndrome, and nonalcoholic fatty liver disease.

Vascular dysfunction-The disregarded partner of Alzheimer's disease

Increasing evidence recognizes Alzheimer's disease (AD) as a multifactorial and heterogeneous disease with multiple contributors to its pathophysiology, including vascular dysfunction. The recently updated AD Research Framework put forth by the National Institute on Aging-Alzheimer's Association describes a biomarker-based pathologic definition of AD focused on amyloid, tau, and neuronal injury. In response to this article, here we first discussed evidence that vascular dysfunction is an important early event in AD pathophysiology. Next, we examined various imaging sequences that could be easily implemented to evaluate different types of vascular dysfunction associated with, and/or contributing to, AD pathophysiology, including changes in blood-brain barrier integrity and cerebral blood flow. Vascular imaging biomarkers of small vessel disease of the brain, which is responsible for >50% of dementia worldwide, including AD, are already established, well characterized, and easy to recognize. We suggest that these vascular biomarkers should be incorporated into the AD Research Framework to gain a better understanding of AD pathophysiology and aid in treatment efforts.

Blood-Brain Barrier: From Physiology to Disease and Back

The blood-brain barrier (BBB) prevents neurotoxic plasma components, blood cells, and pathogens from entering the brain. At the same time, the BBB regulates transport of molecules into and out of the central nervous system (CNS), which maintains tightly controlled chemical composition of the neuronal milieu that is required for proper neuronal functioning. In this review, we first examine molecular and cellular mechanisms underlying the establishment of the BBB. Then, we focus on BBB transport physiology, endothelial and pericyte transporters, and perivascular and paravascular transport. Next, we discuss rare human monogenic neurological disorders with the primary genetic defect in BBB-associated cells demonstrating the link between BBB breakdown and neurodegeneration. Then, we review the effects of genes underlying inheritance and/or increased susceptibility for Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease, and amyotrophic lateral sclerosis (ALS) on BBB in relation to other pathologies and neurological deficits. We next examine how BBB dysfunction relates to neurological deficits and other pathologies in the majority of sporadic AD, PD, and ALS cases, multiple sclerosis, other neurodegenerative disorders, and acute CNS disorders such as stroke, traumatic brain injury, spinal cord injury, and epilepsy. Lastly, we discuss BBB-based therapeutic opportunities. We conclude with lessons learned and future directions, with emphasis on technological advances to investigate the BBB functions in the living human brain, and at the molecular and cellular level, and address key unanswered questions.

Blood-Brain Barrier Dysfunction in Small Vessel Disease Related Intracerebral Hemorrhage

Background and Purpose: Hypertensive vasculopathy and cerebral amyloid angiopathy are the two most common forms of cerebral small vessel disease. Both forms are associated with the development of primary intracerebral hemorrhage, but the pathophysiological mechanisms underlying spontaneous vessel rupture remain unknown. This work constitutes a systematic review on blood-brain barrier dysfunction in the etiology of spontaneous intracerebral hemorrhage due to cerebral small vessel disease.

Methods: We searched Medline (1946–2018) and Embase (1974–2018) for animal and human studies reporting on blood-brain barrier dysfunction associated with intracerebral hemorrhage or cerebral microbleeds.

Results: Of 26 eligible studies, 10 were animal studies and 16 were in humans. The authors found indications for blood-brain barrier dysfunction in all four animal studies addressing hypertensive vasculopathy-related intracerebral hemorrhage (n = 32 hypertensive animals included in all four studies combined), and in four of six studies on cerebral amyloid angiopathy-related intracerebral hemorrhage (n = 47). Of the studies in humans, five of six studies in patients with cerebral amyloid angiopathy-related intracerebral hemorrhage (n = 117) and seven out of nine studies examining intracerebral hemorrhage with mixed or unspecified underlying etiology (n = 489) found indications for blood-brain barrier dysfunction. One post-mortem study in hypertensive vasculopathy-related intracerebral hemorrhage (n = 82) found no evidence for blood-brain barrier abnormalities.

Conclusions: Signs of blood-brain barrier dysfunction were found in 20 out of 26 studies. Blood-brain barrier integrity deserves further investigation with a view to identification of potential treatment targets for spontaneous intracerebral hemorrhage.

High serum sICAM-1 is correlated with cerebral microbleeds and hemorrhagic transformation in ischemic stroke patients

Object: Intercellular adhesion molecule 1 (ICAM-1) is an adhesive protein involved in inflammatory responses and endothelial dysfunction. ICAM-1 expression is upregulated in cerebrovascular tissue affected by stroke. We investigated whether serum soluble ICAM-1 (sICAM-1) levels are associated with cerebral microbleeds (CMBs) and risk of hemorrhagic transformation (HT).Methods: 148 patients with acute ischemic stroke were enrolled. Serum sICAM-1 levels were measured and compared between patients and healthy controls. Multivariate logistic regression analysis was performed to estimate the relationship between serum sICAM-1 levels and the HT risk.Results: Serum sICAM-1 levels were significantly higher in ischemic stroke patients compared with healthy controls (p < .001), and higher in patients with CMBs (n = 81) compared with patients without CMBs (n = 67) (p < .001). Patients with high sICAM-1 levels (≥250.5 ng/mL) were more likely to have hypertension, diabetes mellitus, previous stroke, and CMBs compared with patients with low sICAM-1 levels. In stroke patients with CMBs, higher serum sICAM-1 levels were independently associated with increased HT risk.Conclusion: Serum sICAM-1 levels are associated with presence of CMBs and increased risk of HT in ischemic stroke patients.

Cerebral small vessel disease and the risk of Alzheimer's disease: A systematic review

BACKGROUND

Cerebral small vessel disease (CSVD) comprises a variety of disorders affecting small arteries and microvessels of the brain, manifesting as white matter hyperintensities (WMHs), cerebral microbleeds (CMBs), and deep brain infarcts. In addition to its contribution to vascular dementia (VaD), it has also been suggested to contribute to the pathogenesis of Alzheimer's disease (AD).

METHOD

A systematic review of the literature available on Medline, Embase and Pubmed was undertaken, whereby CSVD was divided into WMHs, CMBs and deep brain infarcts. Biomarkers of AD pathology in the cerebrospinal fluid or plasma, or positron emission tomographic imaging for amyloid and/or tau deposition were used for AD pathology.

RESULTS

A total of 4117 articles were identified and 41 articles met criteria for inclusion. These consisted of 17 articles on vascular risk factors for clinical AD, 21 articles on Aβ pathology and 15 articles on tau pathology, permitting ten meta-analyses. CMBs or lobar CMBs were associated with pooled relative risk (RR) of AD at 1.546, (95%CI 0.842-2.838, z = 1.41 p = 0.160) and 1.526(95%CI 0.760-3.063, z = 1.19, p = 0.235) respectively, both non-significant. Microinfarcts were associated with significantly increased AD risk, with pooled odds ratio OR at 1.203(95%CI 1.014-1.428, 2.12 p = 0.034). Aβ pathology was significantly associated with WMHs in AD patients but not in normal age-matched controls. The pooled β (linear regression) for total WMHs with CSF Aβ42 in AD patients was -0.19(95%CI -0.26-0.11, z = 4.83 p = 0.000) and the pooled r (correlation coefficient) for WMHs and PiB in the normal population was -0.10 (95%CI -0.11-0.30, 0.93 p = 0.351). CMBs were significantly associated with Aβ pathology in AD patients. The pooled standardized mean difference (SMD) was -0.453, 95%CI -0.697- -0.208, z = 3.63 p = 0.000. There was no significant relationship between the incidence of lacunes and levels of CSFAβ, with a pooled β of 0.057 (95%CI -0.050-0.163, z = 1.05 p = 0.295). No significant relationship was found between CMBs and the levels of CSFt-tau/CSFp-tau in AD patients (-0.014, 95%CI -0.556-0.529, z = 0.05 p = 0.960; -0.058, 95%CI -0.630-0.515, z = 0.20 p = 0.844) and cortical CMBs and CSF p-tau in the normal population (0.000, 95%CI -0.706-0.706, z = 0.00 p = 0.999).

CONCLUSIONS

Some CSVD markers were significantly associated with clinical AD pathology and may be associated with Aβ/tau pathology. WMHs and microinfarcts were associated with increased risk of AD. It remains unclear whether they precede or follow AD pathology.

The role of brain vasculature in neurodegenerative disorders

Adequate supply of blood and structural and functional integrity of blood vessels are key to normal brain functioning. On the other hand, cerebral blood flow shortfalls and blood-brain barrier dysfunction are early findings in neurodegenerative disorders in humans and animal models. Here we first examine molecular definition of cerebral blood vessels, as well as pathways regulating cerebral blood flow and blood-brain barrier integrity. Then we examine the role of cerebral blood flow and blood-brain barrier in the pathogenesis of Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, and multiple sclerosis. We focus on Alzheimer's disease as a platform of our analysis because more is known about neurovascular dysfunction in this disease than in other neurodegenerative disorders. Finally, we propose a hypothetical model of Alzheimer's disease biomarkers to include brain vasculature as a factor contributing to the disease onset and progression, and we suggest a common pathway linking brain vascular contributions to neurodegeneration in multiple neurodegenerative disorders.

In vivo imaging and analysis of cerebrovascular hemodynamic responses and tissue oxygenation in the mouse brain

Cerebrovascular dysfunction has an important role in the pathogenesis of multiple brain disorders. Measurement of hemodynamic responses in vivo can be challenging, particularly as techniques are often not described in sufficient detail and vary between laboratories. We present a set of standardized in vivo protocols that describe high-resolution two-photon microscopy and intrinsic optical signal (IOS) imaging to evaluate capillary and arteriolar responses to a stimulus, regional hemodynamic responses, and oxygen delivery to the brain. The protocol also describes how to measure intrinsic NADH fluorescence to understand how blood O2 supply meets the metabolic demands of activated brain tissue, and to perform resting-state absolute oxygen partial pressure (pO2) measurements of brain tissue. These methods can detect cerebrovascular changes at far higher resolution than MRI techniques, although the optical nature of these techniques limits their achievable imaging depths. Each individual procedure requires 1-2 h to complete, with two to three procedures typically performed per animal at a time. These protocols are broadly applicable in studies of cerebrovascular function in healthy and diseased brain in any of the existing mouse models of neurological and vascular disorders. All these procedures can be accomplished by a competent graduate student or experienced technician, except the two-photon measurement of absolute pO2 level, which is better suited to a more experienced, postdoctoral-level researcher.

Are the brain's vascular and Alzheimer pathologies additive or interactive?

PURPOSE OF REVIEW

Alzheimer's disease and cerebrovascular disease (CVD) commonly co-occur. Whether CVD promotes the progression of Alzheimer's disease pathology remains a source of great interest. Recent technological developments have enabled us to examine their inter-relationship using quantifiable, biomarker-based approaches. We provide an overview of advances in understanding the relationship between vascular and Alzheimer's disease pathologies, with particular emphasis on β-amyloid and tau as measured by positron emission tomography and cerebrospinal fluid (CSF) concentration, and magnetic resonance imaging markers of small vessel disease (SVD).

RECENT FINDINGS

The relationship between cerebral β-amyloid and various markers of SVD has been widely studied, albeit with somewhat mixed results. Significant associations have been elucidated, particularly between β-amyloid burden and white matter hyperintensities (WMH), as well as lobar cerebral microbleeds (CMB), with additive effects on cognition. There is preliminary evidence for an association between SVD and tau burden in vivo, although compared with β-amyloid, fewer studies have examined this relationship.

SUMMARY

The overlap between Alzheimer's disease and cerebrovascular pathologies is now being increasingly supported by imaging and CSF biomarkers, indicating a synergistic effect of these co-pathologies on cognition. The association of WMH and CMB with Alzheimer's disease pathology does not establish direction of causality, for which long-term longitudinal studies are needed.

Blood-brain barrier breakdown in Alzheimer disease and other neurodegenerative disorders

The blood-brain barrier (BBB) is a continuous endothelial membrane within brain microvessels that has sealed cell-to-cell contacts and is sheathed by mural vascular cells and perivascular astrocyte end-feet. The BBB protects neurons from factors present in the systemic circulation and maintains the highly regulated CNS internal milieu, which is required for proper synaptic and neuronal functioning. BBB disruption allows influx into the brain of neurotoxic blood-derived debris, cells and microbial pathogens and is associated with inflammatory and immune responses, which can initiate multiple pathways of neurodegeneration. This Review discusses neuroimaging studies in the living human brain and post-mortem tissue as well as biomarker studies demonstrating BBB breakdown in Alzheimer disease, Parkinson disease, Huntington disease, amyotrophic lateral sclerosis, multiple sclerosis, HIV-1-associated dementia and chronic traumatic encephalopathy. The pathogenic mechanisms by which BBB breakdown leads to neuronal injury, synaptic dysfunction, loss of neuronal connectivity and neurodegeneration are described. The importance of a healthy BBB for therapeutic drug delivery and the adverse effects of disease-initiated, pathological BBB breakdown in relation to brain delivery of neuropharmaceuticals are briefly discussed. Finally, future directions, gaps in the field and opportunities to control the course of neurological diseases by targeting the BBB are presented.

Assessment of cerebral microbleeds by susceptibility-weighted imaging at 3T in patients with end-stage organ failure

PURPOSE

Cerebral microbleeds (CMBs) are small rounded lesions representing cerebral hemosiderin deposits surrounded by macrophages that results from previous microhemorrhages. The aim of this study was to review the distribution of cerebral microbleeds in patients with end-stage organ failure and their association with specific end-stage organ failure risk factors.

MATERIALS AND METHODS

Between August 2015 and June 2017, we evaluated 15 patients, 9 males, and 6 females, (mean age 65.5 years). Patients population was subdivided into three groups according to the organ failure: (a) chronic kidney failure (n = 8), (b) restrictive cardiomyopathy undergoing heart transplantation (n = 1), and (c) end-stage liver failure undergoing liver transplantation (n = 6). The MR exams were performed on a 3T MR unit and the SWI sequence was used for the detection of CMBs. CMBs were subdivided in supratentorial lobar distributed, supratentorial non-lobar distributed, and infratentorial distributed.

RESULTS

A total of 91 microbleeds were observed in 15 patients. Fifty-nine CMBs lesions (64.8%) had supratentorial lobar distribution, 17 CMBs lesions (18.8%) had supratentorial non-lobar distribution and the remaining 15 CMBs lesions (16.4%) were infratentorial distributed. An overall predominance of supratentorial multiple lobar localizations was found in all types of end-stage organ failure. The presence of CMBs was significantly correlated with age, hypertension, and specific end-stage organ failure risk factors (p < 0.001).

CONCLUSIONS

CMBs are mostly founded in supratentorial lobar localization in end-stage organ failure. The improved detection of CMBs with SWI sequences may contribute to a more accurate identification of patients with cerebral risk factors to prevent complications during or after the organ transplantation.

Metabolic Risk Factors of Alzheimer's Disease, Dementia with Lewy Bodies, and Normal Elderly: A Population-Based Study

BACKGROUND

Alzheimer's disease (AD) and dementia with Lewy bodies (DLB) share many risk factors. Evidence suggests that metabolic risk factors are important to AD; however, their association with DLB is unclear. The risk of cardiovascular diseases (CVD) associated with AD and DLB is also uncertain. Thus, this nationwide, population-based study was designed to evaluate the metabolic and CVD risks in AD and DLB.

MATERIALS AND METHODS

Data were obtained from the Taiwan National Health Insurance Research Database. AD patients, DLB patients, and normal control (NC) individuals from 1996 to 2013 were enrolled for risk assessment.

RESULTS

In total, 7544 NC individuals, 1324 AD patients, and 562 DLB patients were enrolled. Participants with one or more metabolic risk factors had significantly higher odds of AD or DLB. No significant differences in metabolic risk factors were observed between DLB and AD patients. AD patients had a lower risk of CVD (aHR = 0.67, 95% CI = 0.59-0.76, p value < 0.001) and coronary artery disease (CAD) (aHR = 0.59, 95% CI = 0.51-0.69, p value < 0.001) than NC. DLB patients had a higher risk of ischemic stroke (aHR = 2.27, 95% CI = 1.68-3.06, p value < 0.001) than NC.

CONCLUSION

Metabolic risk factors are important in AD and DLB. Patients with AD might have a lower risk of CAD and ischemic strokes. Patients with DLB might have a higher risk of ischemic stroke.

Alzheimer's disease: A matter of blood-brain barrier dysfunction?

Montagne et al. examine the role of blood–brain barrier (BBB) dysfunction in Alzheimer’s neurodegeneration and how targeting the BBB can influence the course of neurological disorder in transgenic models with human APP, PSEN1 and TAU mutations, APOE4 (major genetic risk), and pericyte degeneration causing loss of BBB integrity.

The blood–brain barrier (BBB) keeps neurotoxic plasma-derived components, cells, and pathogens out of the brain. An early BBB breakdown and/or dysfunction have been shown in Alzheimer’s disease (AD) before dementia, neurodegeneration and/or brain atrophy occur. However, the role of BBB breakdown in neurodegenerative disorders is still not fully understood. Here, we examine BBB breakdown in animal models frequently used to study the pathophysiology of AD, including transgenic mice expressing human amyloid-β precursor protein, presenilin 1, and tau mutations, and apolipoprotein E, the strongest genetic risk factor for AD. We discuss the role of BBB breakdown and dysfunction in neurodegenerative process, pitfalls in BBB measurements, and how targeting the BBB can influence the course of neurological disorder. Finally, we comment on future approaches and models to better define, at the cellular and molecular level, the underlying mechanisms between BBB breakdown and neurodegeneration as a basis for developing new therapies for BBB repair to control neurodegeneration.