Quantitative Neuropathological Assessment to Investigate Cerebral Multi-Morbidity

The aging brain is characterized by the simultaneous presence of multiple pathologies, and the prevalence of cerebral multi-morbidity increases with age. To understand the impact of each subtype of pathology and the combined effects of cerebral multi-morbidity on clinical signs and symptoms, large clinico-pathological correlative studies have been performed. However, such studies are often based on semi-quantitative assessment of neuropathological hallmark lesions. Here, we discuss some of the new methods for high-throughput quantitative neuropathological assessment. These methods combine increased quantitative rigor with the added technical capacity of computers and networked analyses. There are abundant new opportunities - with specific techniques that include slide scanners, automated microscopes, and tissue microarrays - and also potential pitfalls. We conclude that quantitative and digital neuropathologic approaches will be key resources to further elucidate cerebral multi-morbidity in the aged brain and also hold the potential for changing routine neuropathologic diagnoses

Rod-Shaped Microglia Morphology Is Associated with Aging in 2 Human Autopsy Series

A subtype of microglia is defined by the morphological appearance of the cells as rod-shaped. Little is known about this intriguing cell type, as there are only a few case reports describing rod-shaped microglia in the neuropathological literature. Rod-shaped microglia were shown recently to account for a substantial proportion of the microglia cells in the hippocampus of both demented and cognitively intact aged individuals. We hypothesized that aging could be a defining feature in the occurrence of rod-shaped microglia. To test this hypothesis, two independent series of autopsy cases (total n=168 cases), which covered the adult lifespan from 20 – 100+ years old, were included in the study. The presence or absence of rod-shaped microglia was scored on IBA1 immunohistochemically stained slides for the hippocampus and cortex. We found that age was one of the strongest determinants for the presence of rod-shaped microglia in the hippocampus and the cortex. We found no association with the presence of rod-shaped microglia and a self-reported history of a TBI. Alzheimer’s disease related pathology was found to influence the presence of rod-shaped microglia, but only in the parietal cortex and not in the hippocampus or temporal cortex. Future studies are warranted to determine the functional relevance of rod-shaped microglia in supporting the health of neurons in the aged brain, and the signaling processes that regulate the formation of rod-shaped microglia

Dystrophic Microglia Are Associated with Neurodegenerative Disease and not Healthy Aging in the Human Brain

Loss of physiological microglial function may increase the propagation of neurodegenerative diseases. Cellular senescence is a hallmark of aging; thus, we hypothesized age could be a cause of dystrophic microglia. Stereological counts were performed for total microglia, 2 microglia morphologies (hypertrophic and dystrophic) across the human lifespan. An age-associated increase in the number of dystrophic microglia was found in the hippocampus and frontal cortex. However, the increase in dystrophic microglia was proportional to the age-related increase in the total number of microglia. Thus, aging alone does not explain the presence of dystrophic microglia. We next tested if dystrophic microglia could be a disease-associated microglia morphology. Compared with controls, the number of dystrophic microglia was greater in cases with either Alzheimer\u27s disease, dementia with Lewy bodies, or limbic-predominant age-related TDP-43 encephalopathy. These results demonstrate that microglia dystrophy, and not hypertrophic microglia, are the disease-associated microglia morphology. Finally, we found strong evidence for iron homeostasis changes in dystrophic microglia, providing a possible molecular mechanism driving the degeneration of microglia in neurodegenerative disease

Disease-Related Microglia Heterogeneity in the Hippocampus of Alzheimer\u27s Disease, Dementia with Lewy Bodies, and Hippocampal Sclerosis of Aging

Introduction: Neuropathological, genetic, and biochemical studies have provided support for the hypothesis that microglia participate in Alzheimer\u27s disease (AD) pathogenesis. Despite the extensive characterization of AD microglia, there are still many unanswered questions, and little is known about microglial morphology in other common forms of age-related dementia: particularly, dementia with Lewy bodies (DLB) and hippocampal sclerosis of aging (HS-Aging). In addition, no prior studies have attempted to compare and contrast the microglia morphology in the hippocampus of various neurodegenerative conditions. Results: Here we studied cases with pathologically-confirmed AD (n = 7), HS-Aging (n = 7), AD + HS-aging (n = 4), DLB (n = 12), and normal (cognitively intact) controls (NC) (n = 9) from the University of Kentucky Alzheimer\u27s Disease Center autopsy cohort. We defined five microglia morphological phenotypes in the autopsy samples: ramified, hypertrophic, dystrophic, rod-shaped, and amoeboid. The Aperio ScanScope digital neuropathological tool was used along with two well-known microglial markers: IBA1 (a marker for both resting and activated microglia) and CD68 (a lysosomal marker in macrophages/microglia associated with phagocytic cells). Hippocampal staining analyses included studies of subregions within the hippocampal formation and nearby white matter. Using these tools and methods, we describe variation in microglial characteristics that show some degree of disease specificity, including, (1) increased microglia density and number in HS-aging and AD + HS-aging; (2) low microglia density in DLB; (3) increased number of dystrophic microglia in HS-aging; and (4) increased proportion of dystrophic to all microglia in DLB. Conclusions: We conclude that variations in morphologies among microglial cells, and cells of macrophage lineage, can help guide future work connecting neuroinflammatory mechanisms with specific neurodegenerative disease subtypes

Expression of miR-15/107 Family MicroRNAs in Human Tissues and Cultured Rat Brain Cells

The miR-15/107 family comprises a group of 10 paralogous microRNAs (miRNAs), sharing a 5\u27 AGCAGC sequence. These miRNAs have overlapping targets. In order to characterize the expression of miR-15/107 family miRNAs, we employed customized TaqMan Low-Density micro-fluid PCR-array to investigate the expression of miR-15/107 family members, and other selected miRNAs, in 11 human tissues obtained at autopsy including the cerebral cortex, frontal cortex, primary visual cortex, thalamus, heart, lung, liver, kidney, spleen, stomach and skeletal muscle. miR-103, miR-195 and miR-497 were expressed at similar levels across various tissues, whereas miR-107 is enriched in brain samples. We also examined the expression patterns of evolutionarily conserved miR-15/107 miRNAs in three distinct primary rat brain cell preparations (enriched for cortical neurons, astrocytes and microglia, respectively). In primary cultures of rat brain cells, several members of the miR-15/107 family are enriched in neurons compared to other cell types in the central nervous system (CNS). In addition to mature miRNAs, we also examined the expression of precursors (pri-miRNAs). Our data suggested a generally poor correlation between the expression of mature miRNAs and their precursors. In summary, we provide a detailed study of the tissue and cell type-specific expression profile of this highly expressed and phylogenetically conserved family of miRNA genes

Hippocampal Sclerosis of Aging, a Prevalent and High-Morbidity Brain Disease

Hippocampal sclerosis of aging (HS-Aging) is a causative factor in a large proportion of elderly dementia cases. The current definition of HS-Aging rests on pathologic criteria: neuronal loss and gliosis in the hippocampal formation that is out of proportion to AD-type pathology. HS-Aging is also strongly associated with TDP-43 pathology. HS-Aging pathology appears to be most prevalent in the oldest-old: autopsy series indicate that 5-30 % of nonagenarians have HS-Aging pathology. Among prior studies, differences in study design have contributed to the study-to-study variability in reported disease prevalence. The presence of HS-Aging pathology correlates with significant cognitive impairment which is often misdiagnosed as AD clinically. The antemortem diagnosis is further confounded by other diseases linked to hippocampal atrophy including frontotemporal lobar degeneration and cerebrovascular pathologies. Recent advances characterizing the neurocognitive profile of HS-Aging patients have begun to provide clues that may help identify living individuals with HS-Aging pathology. Structural brain imaging studies of research subjects followed to autopsy reveal hippocampal atrophy that is substantially greater in people with eventual HS-Aging pathology, compared to those with AD pathology alone. Data are presented from individuals who were followed with neurocognitive and neuroradiologic measurements, followed by neuropathologic evaluation at the University of Kentucky. Finally, we discuss factors that are hypothesized to cause or modify the disease. We conclude that the published literature on HS-Aging provides strong evidence of an important and under-appreciated brain disease of aging. Unfortunately, there is no therapy or preventive strategy currently available

Arteriolosclerosis that affects multiple brain regions is linked to hippocampal sclerosis of ageing

Hippocampal sclerosis of ageing is a prevalent brain disease that afflicts older persons and has been linked with cerebrovascular pathology. Arteriolosclerosis is a subtype of cerebrovascular pathology characterized by concentrically thickened arterioles. Here we report data from multiple large autopsy series (University of Kentucky Alzheimer's Disease Centre, Nun Study, and National Alzheimer's Coordinating Centre) showing a specific association between hippocampal sclerosis of ageing pathology and arteriolosclerosis. The present analyses incorporate 226 cases of autopsy-proven hippocampal sclerosis of ageing and 1792 controls. Case-control comparisons were performed including digital pathological assessments for detailed analyses of blood vessel morphology. We found no evidence of associations between hippocampal sclerosis of ageing pathology and lacunar infarcts, large infarcts, Circle of Willis atherosclerosis, or cerebral amyloid angiopathy. Individuals with hippocampal sclerosis of ageing pathology did not show increased rates of clinically documented hypertension, diabetes, or other cardiac risk factors. The correlation between arteriolosclerosis and hippocampal sclerosis of ageing pathology was strong in multiple brain regions outside of the hippocampus. For example, the presence of arteriolosclerosis in the frontal cortex (Brodmann area 9) was strongly associated with hippocampal sclerosis of ageing pathology (P 5 0.001). This enables informative evaluation of anatomical regions outside of the hippocampus. To assess the morphology of brain microvasculature far more rigorously than what is possible using semi-quantitative pathological scoring, we applied digital pathological (Aperio ScanScope) methods on a subsample of frontal cortex sections from hippocampal sclerosis of ageing (n = 15) and control (n = 42) cases. Following technical studies to optimize immunostaining methods for small blood vessel visualization, our analyses focused on sections immunostained for smooth muscle actin (a marker of arterioles) and CD34 (an endothelial marker), with separate analyses on grey and white matter. A total of 43 834 smooth muscle actin-positive vascular profiles and 603 798 CD34-positive vascular profiles were evaluated. In frontal cortex of cases with hippocampal sclerosis of ageing, smooth muscle actin-immunoreactive arterioles had thicker walls (P 5 0.05), larger perimeters (P 5 0.03), and larger vessel areas (P 5 0.03) than controls. Unlike the arterioles, CD34-immunoreactive capillaries had dimensions that were unchanged in cases with hippocampal sclerosis of ageing versus controls. Arteriolosclerosis appears specific to hippocampal sclerosis of ageing brains, because brains with Alzheimer's disease pathology did not show the same morphological alterations. We conclude that there may be a pathogenetic change in aged human brain arterioles that impacts multiple brain areas and contributes to hippocampal sclerosis of ageing

Frequency of LATE neuropathologic change across the spectrum of Alzheimer’s disease neuropathology: combined data from 13 community-based or population-based autopsy cohorts

Limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC) and Alzheimer’s disease neuropathologic change (ADNC) are each associated with substantial cognitive impairment in aging populations. However, the prevalence of LATE-NC across the full range of ADNC remains uncertain. To address this knowledge gap, neuropathologic, genetic, and clinical data were compiled from 13 high-quality community- and population-based longitudinal studies. Participants were recruited from United States (8 cohorts, including one focusing on Japanese–American men), United Kingdom (2 cohorts), Brazil, Austria, and Finland. The total number of participants included was 6196, and the average age of death was 88.1 years. Not all data were available on each individual and there were differences between the cohorts in study designs and the amount of missing data. Among those with known cognitive status before death (n = 5665), 43.0% were cognitively normal, 14.9% had MCI, and 42.4% had dementia—broadly consistent with epidemiologic data in this age group. Approximately 99% of participants (n = 6125) had available CERAD neuritic amyloid plaque score data. In this subsample, 39.4% had autopsy-confirmed LATE-NC of any stage. Among brains with “frequent” neuritic amyloid plaques, 54.9% had comorbid LATE-NC, whereas in brains with no detected neuritic amyloid plaques, 27.0% had LATE-NC. Data on LATE-NC stages were available for 3803 participants, of which 25% had LATE-NC stage > 1 (associated with cognitive impairment). In the subset of individuals with Thal Aβ phase = 0 (lacking detectable Aβ plaques), the brains with LATE-NC had relatively more severe primary age-related tauopathy (PART). A total of 3267 participants had available clinical data relevant to frontotemporal dementia (FTD), and none were given the clinical diagnosis of definite FTD nor the pathological diagnosis of frontotemporal lobar degeneration with TDP-43 inclusions (FTLD-TDP). In the 10 cohorts with detailed neurocognitive assessments proximal to death, cognition tended to be worse with LATE-NC across the full spectrum of ADNC severity. This study provided a credible estimate of the current prevalence of LATE-NC in advanced age. LATE-NC was seen in almost 40% of participants and often, but not always, coexisted with Alzheimer’s disease neuropathology

LATE-NC staging in routine neuropathologic diagnosis : an update

An international consensus report in 2019 recommended a classification system for limbic-predominant age-related TDP-43 encephalopathy neuropathologic changes (LATE-NC). The suggested neuropathologic staging system and nomenclature have proven useful for autopsy practice and dementia research. However, some issues remain unresolved, such as cases with unusual features that do not fit with current diagnostic categories. The goal of this report is to update the neuropathologic criteria for the diagnosis and staging of LATE-NC, based primarily on published data. We provide practical suggestions about how to integrate available genetic information and comorbid pathologies [e.g., Alzheimer's disease neuropathologic changes (ADNC) and Lewy body disease]. We also describe recent research findings that have enabled more precise guidance on how to differentiate LATE-NC from other subtypes of TDP-43 pathology [e.g., frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS)], and how to render diagnoses in unusual situations in which TDP-43 pathology does not follow the staging scheme proposed in 2019. Specific recommendations are also made on when not to apply this diagnostic term based on current knowledge. Neuroanatomical regions of interest in LATE-NC are described in detail and the implications for TDP-43 immunohistochemical results are specified more precisely. We also highlight questions that remain unresolved and areas needing additional study. In summary, the current work lays out a number of recommendations to improve the precision of LATE-NC staging based on published reports and diagnostic experience.Peer reviewe