Abstract
Background
Cortical superficial siderosis (cSS) has recently emerged as one of the most important predictors of symptomatic intracerebral hemorrhage and is a risk factor for post-stroke ...dementia in cerebral amyloid angiopathy (CAA). However, it remains unknown whether cSS is just a marker of severe CAA pathology or may itself contribute to intracerebral hemorrhage risk and cognitive decline. cSS is a chronic manifestation of convexal subarachnoid hemorrhage and is neuropathologically characterized by iron deposits in the superficial cortical layers. We hypothesized that these iron deposits lead to local neuroinflammation, a potentially contributory pathway towards secondary tissue injury.
Methods
Accordingly, we assessed the distribution of inflammatory markers in relation to cortical iron deposits in post-mortem tissue from CAA cases. Serial sections from the frontal, parietal, temporal, and occipital lobes of nineteen autopsy cases with CAA were stained with Perls’ Prussian blue (iron) and underwent immunohistochemistry against glial fibrillary acidic protein (GFAP, reactive astrocytes) and cluster of differentiation 68 (CD68, activated microglia/macrophages). Digitized sections were uploaded to the cloud-based Aiforia
®
platform, where deep-learning algorithms were utilized to detect tissue, iron deposits, and GFAP-positive and CD68-positive cells.
Results
We observed a strong local relationship between cortical iron deposits and reactive astrocytes. Like cSS-related iron, reactive astrocytes were mainly found in the most superficial layers of the cortex. Although we observed iron within both astrocytes and activated microglia/macrophages on co-stains, there was no clear local relationship between the density of microglia/macrophages and the density of iron deposits.
Conclusion
Iron deposition resulting from cSS is associated with local reactive astrogliosis.
Perivascular spaces (PVS) are compartments surrounding cerebral blood vessels that become visible on MRI when enlarged. Enlarged PVS (EPVS) are commonly seen in patients with cerebral small vessel ...disease (CSVD) and have been suggested to reflect dysfunctional perivascular clearance of soluble waste products from the brain. In this study, we investigated histopathological correlates of EPVS and how they relate to vascular amyloid-β (Aβ) in cerebral amyloid angiopathy (CAA), a form of CSVD that commonly co-exists with Alzheimer’s disease (AD) pathology. We used ex vivo MRI, semi-automatic segmentation and validated deep-learning-based models to quantify EPVS and associated histopathological abnormalities. Severity of MRI-visible PVS during life was significantly associated with severity of MRI-visible PVS on ex vivo MRI in formalin fixed intact hemispheres and corresponded with PVS enlargement on histopathology in the same areas. EPVS were located mainly around the white matter portion of perforating cortical arterioles and their burden was associated with CAA severity in the overlying cortex. Furthermore, we observed markedly reduced smooth muscle cells and increased vascular Aβ accumulation, extending into the WM, in individually affected vessels with an EPVS. Overall, these findings are consistent with the notion that EPVS reflect impaired outward flow along arterioles and have implications for our understanding of perivascular clearance mechanisms, which play an important role in the pathophysiology of CAA and AD.
Sensory stimulation evokes a local, vasodilation-mediated blood flow increase to the activated brain region, which is referred to as functional hyperemia. Spontaneous vasomotion is a change in ...arteriolar diameter that occurs without sensory stimulation, at low frequency (∼0.1 Hz). These vessel diameter changes are a driving force for perivascular soluble waste clearance, the failure of which has been implicated in neurodegenerative disease. Stimulus-evoked vascular reactivity is known to propagate along penetrating arterioles to pial arterioles, but it is unclear whether spontaneous vasomotion propagates similarly. We therefore imaged both stimulus-evoked and spontaneous changes in pial arteriole diameter in awake, head-fixed mice with 2-photon microscopy. By cross-correlating different regions of interest (ROIs) along the length of imaged arterioles, we assessed vasomotion propagation. We found that both during rest and during visual stimulation, one-third of the arterioles showed significant propagation (i.e., a wave), with a median (interquartile range) wave speed of 405 (323) µm/s at rest and 345 (177) µm/s during stimulation. In a second group of mice, with GCaMP expression in their vascular smooth muscle cells, we also found spontaneous propagation of calcium signaling along pial arterioles. In summary, we demonstrate that spontaneous vasomotion propagates along pial arterioles like stimulus-evoked vascular reactivity.
Objective
A definite diagnosis of cerebral amyloid angiopathy (CAA), characterized by the accumulation of amyloid β in walls of cerebral small vessels, can only be obtained through pathological ...examination. A diagnosis of probable CAA during life relies on the presence of hemorrhagic markers, including lobar cerebral microbleeds (CMBs). The aim of this project was to study the histopathological correlates of lobar CMBs in false‐positive CAA cases.
Methods
In 3 patients who met criteria for probable CAA during life, but showed no CAA upon neuropathological examination, lobar CMBs were counted on ex vivo 3T magnetic resonance imaging (MRI) and on ex vivo 7T MRI. Areas with lobar CMBs were next sampled and cut into serial sections, on which the CMBs were then identified.
Results
Collectively, there were 25 lobar CMBs on in vivo MRI and 22 on ex vivo 3T MRI of the analyzed hemispheres. On ex vivo MRI, we targeted 12 CMBs for sampling, and definite histopathological correlates were retrieved for 9 of them, of which 7 were true CMBs. No CAA was found on any of the serial sections. The “culprit vessels” associated with the true CMBs instead showed moderate to severe arteriolosclerosis. Furthermore, CMBs in false‐positive CAA cases tended to be located more often in the juxtacortical or subcortical white matter than in the cortical ribbon.
Interpretation
These findings suggest that arteriolosclerosis can generate lobar CMBs and that more detailed investigations into the exact localization of CMBs with respect to the cortical ribbon could potentially aid the diagnosis of CAA during life. ANN NEUROL 2023;94:856–870
Traditionally, analysis of neuropathological markers in neurodegenerative diseases has relied on visual assessments of stained sections. Resulting semiquantitative scores often vary between ...individual raters and research centers, limiting statistical approaches. To overcome these issues, we have developed six deep learning-based models, that identify some of the most characteristic markers of Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA). The deep learning-based models are trained to differentially detect parenchymal amyloid β (Aβ)-plaques, vascular Aβ-deposition, iron and calcium deposition, reactive astrocytes, microglia, as well as fibrin extravasation. The models were trained on digitized histopathological slides from brains of patients with AD and CAA, using a workflow that allows neuropathology experts to train convolutional neural networks (CNNs) on a cloud-based graphical interface. Validation of all models indicated a very good to excellent performance compared to three independent expert human raters. Furthermore, the Aβ and iron models were consistent with previously acquired semiquantitative scores in the same dataset and allowed the use of more complex statistical approaches. For example, linear mixed effects models could be used to confirm the previously described relationship between leptomeningeal CAA severity and cortical iron accumulation. A similar approach enabled us to explore the association between neuroinflammation and disparate Aβ pathologies. The presented workflow is easy for researchers with pathological expertise to implement and is customizable for additional histopathological markers. The implementation of deep learning-assisted analyses of histopathological slides is likely to promote standardization of the assessment of neuropathological markers across research centers, which will allow specific pathophysiological questions in neurodegenerative disease to be addressed in a harmonized way and on a larger scale.
Abstract
Cerebral amyloid angiopathy is a small vessel disease associated with cortical microbleeds and lobar intracerebral haemorrhage due to amyloid-β deposition in the walls of leptomeningeal and ...cortical arterioles. The mechanisms of cerebral amyloid angiopathy–related haemorrhage remain largely unknown. Recent work has demonstrated that ruptured blood vessels have limited (or no) amyloid-β at the site of bleeding and evidence of local vascular remodelling. We hypothesized that blood–brain barrier leakage and perivascular inflammation may be involved in this remodelling process. This study examined cortical arterioles at various stages of cerebral amyloid angiopathy–related vascular pathology (without evidence of microhaemorrhage) in autopsy tissue from seven cases with definite cerebral amyloid angiopathy. We included temporo-occipital sections with microbleeds guided by ex vivo MRI from two cases with severe cerebral amyloid angiopathy and systematically sampled occipital sections from five consecutive cases with varying cerebral amyloid angiopathy severity. Haematoxylin and eosin stains and immunohistochemistry against amyloid-β, fibrin(ogen), smooth muscle actin, reactive astrocytes (glial fibrillary acidic protein) and activated microglia (cluster of differentiation 68) were performed. Arterioles were graded using a previously proposed scale of individual vessel cerebral amyloid angiopathy severity, and a blinded assessment for blood–brain barrier leakage, smooth muscle actin and perivascular inflammation was performed. Blood–brain barrier leakage and smooth muscle actin loss were observed in significantly more vessels with mild amyloid-β deposition (Grade 1 vessels; P = 0.044 and P = 0.012, respectively) as compared to vessels with no amyloid-β (Grade 0), and blood–brain barrier leakage was observed in 100% of vessels with evidence of vessel remodelling (Grades 3 and 4). Perivascular inflammation in the form of reactive astrocytes and activated microglia was observed predominantly surrounding arterioles at later stages of vessel pathology (Grades 2–4) and consistently around vessels with the same morphological features as ruptured vessel segments (Grade 4). These findings suggest a role for blood–brain barrier leakage and perivascular inflammation leading to arteriolar remodelling and haemorrhage in cerebral amyloid angiopathy, with early blood–brain barrier leakage as a potential trigger for subsequent perivascular inflammation.
To date, it is still controversial whether tau phosphorylation plays a role in Huntington's disease (HD), as previous studies demonstrated either no alterations or increases in phosphorylated tau ...(pTau) in HD postmortem brain and mouse models.
The goal of this study was to determine whether total tau and pTau levels are altered in HD.
Immunohistochemistry, cellular fractionations, and western blots were used to measure total tau and pTau levels in a large cohort of HD and control postmortem prefrontal cortex (PFC). Furthermore, western blots were performed to assess tau, and pTau levels in HD and control isogenic embryonic stem cell (ESC)-derived cortical neurons and neuronal stem cells (NSCs). Similarly, western blots were used to assess tau and pTau levels in HttQ111 and transgenic R6/2 mice. Lastly, total tau levels were assessed in HD and healthy control plasma using Quanterix Simoa assay.
Our results revealed that, while there was no difference in total tau or pTau levels in HD PFC compared to controls, the levels of tau phosphorylated at S396 were increased in PFC samples from HD patients 60 years or older at time of death. Additionally, tau and pTau levels were not changed in HD ESC-derived cortical neurons and NSCs. Similarly, total tau or pTau levels were not altered in HttQ111 and transgenic R6/2 mice compared to wild-type littermates. Lastly, tau levels were not changed in plasma from a small cohort of HD patients compared to controls.
Together these findings demonstrate that pTau-S396 levels increase significantly with age in HD PFC.
Abstract
The impact of vascular lesions on cognition is location dependent. Here, we assessed the contribution of small vessel disease lesions in the corpus callosum to vascular cognitive impairment ...in cerebral amyloid angiopathy, as a model for cerebral small vessel disease. Sixty-five patients with probable cerebral amyloid angiopathy underwent 3T magnetic resonance imaging, including a diffusion tensor imaging scan, and neuropsychological testing. Microstructural white-matter integrity was quantified by fractional anisotropy and mean diffusivity. Z-scores on individual neuropsychological tests were averaged into five cognitive domains: information processing speed, executive functioning, memory, language and visuospatial ability. Corpus callosum lesions were defined as haemorrhagic (microbleeds or larger bleeds) or ischaemic (microinfarcts, larger infarcts and diffuse fluid-attenuated inversion recovery hyperintensities). Associations between corpus callosum lesion presence, microstructural white-matter integrity and cognitive performance were examined with multiple regression models. The prevalence of corpus callosum lesions was confirmed in an independent cohort of memory clinic patients with and without cerebral amyloid angiopathy (n = 82). In parallel, we assessed corpus callosum lesions on ex vivo magnetic resonance imaging in cerebral amyloid angiopathy patients (n = 19) and controls (n = 5) and determined associated tissue abnormalities with histopathology. A total number of 21 corpus callosum lesions was found in 19/65 (29%) cerebral amyloid angiopathy patients. Corpus callosum lesion presence was associated with reduced microstructural white-matter integrity within the corpus callosum and in the whole-brain white matter. Patients with corpus callosum lesions performed significantly worse on all cognitive domains except language, compared with those without corpus callosum lesions after correcting for age, sex, education and time between magnetic resonance imaging and neuropsychological assessment. This association was independent of the presence of intracerebral haemorrhage, whole-brain fractional anisotropy and mean diffusivity, and white-matter hyperintensity volume and brain volume for the domains of information processing speed and executive functioning. In the memory clinic patient cohort, corpus callosum lesions were present in 14/54 (26%) patients with probable and 2/8 (25%) patients with possible cerebral amyloid angiopathy, and in 3/20 (15%) patients without cerebral amyloid angiopathy. In the ex vivo cohort, corpus callosum lesions were present in 10/19 (53%) patients and 2/5 (40%) controls. On histopathology, ischaemic corpus callosum lesions were associated with tissue loss and demyelination, which extended beyond the lesion core. Together, these data suggest that corpus callosum lesions are a frequent finding in cerebral amyloid angiopathy, and that they independently contribute to cognitive impairment through strategic microstructural disruption of white-matter tracts.
Freeze et al. report that corpus callosum lesions are a frequent finding in cerebral amyloid angiopathy, and that they independently contribute to cognitive impairment through strategic microstructural disruption of white-matter tracts.
Graphical Abstract
Graphical Abstract
We assessed the prevalence and impact of corpus callosum lesions on whole brain microstructural white matter integrity and cognitive performance in patients with cerebral amyloid angiopathy (CAA). Corpus callosum lesions were prevalent in patients with CAA (29%) and their presence was significantly associated with reduced whole-brain microstructural white matter integrity and reduced cognitive performance in the domains of executive functioning and information processing speed.
Background
Cerebral amyloid angiopathy (CAA) is a common cause of intracerebral hemorrhage and cognitive impairment in older individuals. Hallmark manifestations of CAA on MRI include cortical ...hemorrhages, as well as perivascular spaces (PVS) in the white matter centrum semiovale and white matter hyperintensities (WMH) in a subcortical multi‐spot pattern. We performed an ex vivo MRI‐neuropathological study to: 1) determine the relationship between WMH volume and CAA severity, and 2) assess the histopathological substrate of confluent WMH, WMH in a multi‐spot pattern (WM_MS), and normal‐appearing white matter (NAWM).
Method
Nineteen autopsy cases with pathologically confirmed CAA (age 75±8y; 7F) and five non‐CAA controls (age 88±5y; 3F) were included. Formalin‐fixed hemispheres underwent 3T MRI, including a T2‐weighted (500µm isotropic resolution, to obtain manual WMH segmentations) and a T2*‐weighted sequence (1mm isotropic resolution, to automatically segment hemisphere volume using SynthSeg). After scanning, five pre‐defined standard areas were sampled from each brain, then processed to obtain manually assessed arteriolosclerosis scores and AI‐derived cortical and leptomeningeal CAA area measurements. In the CAA cases, specific areas with ex vivo MRI‐observed WM_MS (n = 7), confluent WMH (n = 9), and NAWM (n = 9) were sampled. Sections were stained with LH&E (to determine WM rarefaction, % PVS area, and degree of arteriolosclerosis), and CD68 (a marker of activated microglia, to assess density of CD68‐positive cells).
Result
Total normalized WMH volume did not differ between CAA cases (0.037±0.024) and non‐CAA controls (0.027±0.026) (Mann‐Whitney U test 36, p = 0.31). Within the CAA cases, a multivariable regression model corrected for age at death revealed that normalized WMH volume was associated with cortical CAA area (p = 0.010) and arteriolosclerosis (p = 0.066), but not leptomeningeal CAA area (p = 0.94). Targeted neuropathological assessment revealed that WM rarefaction, arteriolosclerosis score, and density of CD68‐positive cells were higher in areas with WMH compared to WM_MS and NAWM. In contrast, % PVS area was higher in WM_MS compared to WMH and NAWM.
Conclusion
The observed differences in neuropathological correlates between WMH in a multi‐spot pattern and confluent WMH in CAA suggest different pathophysiological mechanisms. Future studies are needed to determine these mechanisms as well as the causal relationship between cortical CAA severity and WMH burden.
Perivascular spaces (PVS) are compartments surrounding cerebral blood vessels that become visible on MRI when enlarged. Enlarged PVS (EPVS) are commonly seen in patients with cerebral small vessel ...disease (CSVD) and have been suggested to reflect dysfunctional perivascular clearance of soluble waste products from the brain. In this study, we investigated histopathological correlates of EPVS and how they relate to vascular amyloid-beta (Abeta) in cerebral amyloid angiopathy (CAA), a form of CSVD that commonly co-exists with Alzheimer's disease (AD) pathology. We used ex vivo MRI, semi-automatic segmentation and validated deep-learning-based models to quantify EPVS and associated histopathological abnormalities. Severity of MRI-visible PVS during life was significantly associated with severity of MRI-visible PVS on ex vivo MRI in formalin fixed intact hemispheres and corresponded with PVS enlargement on histopathology in the same areas. EPVS were located mainly around the white matter portion of perforating cortical arterioles and their burden was associated with CAA severity in the overlying cortex. Furthermore, we observed markedly reduced smooth muscle cells and increased vascular Abeta accumulation, extending into the WM, in individually affected vessels with an EPVS. Overall, these findings are consistent with the notion that EPVS reflect impaired outward flow along arterioles and have implications for our understanding of perivascular clearance mechanisms, which play an important role in the pathophysiology of CAA and AD.
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