Aug 2026· Acta Neuropathologica· Vol 152· 0 citations· 92 references
Medicine
TL;DR
The data show that activated microglial phenotypes in the CA2 of LBD patients are associated with worse clinical outcomes and retrograde n-asyn transmission, and suggest that measures of microglial states can refine LBD histopathological progression models.
Abstract
Histopathologic staging models of neuronal α-synuclein pathology (n-asyn) in Lewy body disease (LBD) seldom evaluate brain regions with direct synaptic connectivity to model the role of microglial processes. We address this gap by testing the hypothesis that, within the well-defined synaptic connectivity of the intrahippocampal circuit, n-asyn is associated with activated microglial phenotypes. We selected a cohort of autopsy-confirmed LBD patients and minimal age-related copathologies (n = 62) and a control cohort of cognitively healthy patients with isolated hippocampal tau accumulation (i.e., primary age-related tauopathy, PART; n = 12), to control for neurodegenerative pathology without amyloid plaques. We immunostained consecutive hippocampal sections for n-asyn and established markers of activated microglial phenotypes, Iba1, HLA-DR, and CD68. With validated digital histology methods, we measured percent area occupied (%AO) of each marker in 6 hippocampal subfields to compare and correlate microglial morphologic and proteomic activation phenotypes between cohorts and used linear mixed effects models to compare the %AO between subfields while covariying for demographics. We also constructed groups of n-asyn restricted to the cornu ammonis (CA) 2–3 subfields (Focal Subtype) or widespread n-asyn within additional subfields (Widespread Subtype) to model hypothesized n-asyn spread within the intrahippocampal circuit. LBD patients exhibited increased HLA-DR and CD68%AO in most hippocampal subfields compared with PART. In LBD patients, all microglial markers were the highest in the CA2. CA2 n-asyn correlated with HLA-DR and CD68 but not Iba1%AO. Patients classified as Widespread Subtype had worse cognitive impairment and increased CA2 HLA-DR and CD68%AO. CA2 HLA-DR and CD68%AO correlated with distal n-asyn in retrograde, but not anterograde connected subfields. Our data show that activated microglial phenotypes in the CA2 of LBD patients are associated with worse clinical outcomes and retrograde n-asyn transmission. These data suggest that measures of microglial states can refine LBD histopathological progression models.
BACKGROUND Accumulations of AD and LATE-NC both contribute to changes in hippocampal volume, possibly via distinct and/or overlapping mechanisms. Microglia-driven inflammation is a shared pathway associated with both AD and LATE-NC. However, the extent to which microglia inflammation is associated with hippocampal volume is less understood. OBJECTIVE Examine the relationship between AD and LATE-NC with hippocampal volume in persons with differing levels of microglia inflammation. METHODS Cerebral hemispheres from 441 older adults who came to autopsy were studied. All hemispheres underwent ex-vivo MRI and detailed neuropathologic examination for neurodegenerative and cerebrovascular pathologies. Microglia were quantified in the hippocampal CA1/subiculum region using machine learning-based classifiers trained on digitized CR3-43-stained images via the HALO digital pathology platform. First, linear regression models examined the association of microglia with hippocampal volume, adjusting for demographics, postmortem interval (PMI), and common age-related pathologies. Second, linear regression models were employed to examine whether microglia density modified associations of β-amyloid, tangle, or LATE-NC on hippocampal volume. RESULTS Participants had a mean age of 90 years at death with 75% being women. Intermediate or high likelihood ADNC was present in 64% and LATE-NC (stage 2/3) was present in 52%. In linear regression models, adjusting for demographics and PMI, higher microglia density was associated with a lower hippocampal volume to hemisphere ratio (estimate = −0.021 SE=0.01, p=0.002); however, after adjusting for common age-related pathologies the association was attenuated (p=0.70). β-amyloid, tangles, and LATE-NC remained independently associated with a lower hippocampal volume. The association of LATE-NC with hippocampal volume was stronger in brains with greater microglia burden (estimate for the interaction term = −0.016; SE=0.01, p=0.002). No interactions were seen between β-amyloid or tangles with microglia on hippocampal volume. In stratified analyses, microglial density modified the association between LATE-NC and hippocampal volume, independent of AD neuropathologic status. CONCLUSION Microglia-driven inflammation strengthens the association of LATE-NC, but not AD pathology, on hippocampal volume loss. These findings emphasize the importance of inflammatory pathways [when interpreting MRI-based neurodegeneration markers] in aging and mixed pathology.
A. Kapasi, L. Yu, SE Leurgans et al.· bioRxiv· 0 citations
Variation in the microtubule-binding protein tau is causally implicated in numerous neurodegenerative diseases, including Alzheimer’s disease. However, the mechanisms by which such variation results in disease are not well understood. The JNPL3(P301L) mouse model mimics the effects of the P301L mutation on human tau associated with frontotemporal dementia. As previously reported, phospho-tau aggregates immunolabeled with AT8 increase with age in a rostral progression from the brainstem; however, there is relatively limited forebrain pathology by the time these animals die prematurely at approximately 1 year of age. In this study, we investigated the functional effects of P301L tau expression on electrophysiological signatures as a function of age in mice expressing P301L tau from 3 to 10 months. The P301L mice had a distinct electrophysiological phenotype of increased power in higher EEG frequency bands detected with a depth electrode in the hippocampus and, to a lesser extent, with dural surface electrodes over the frontal and parietal cortices. Significantly, this electrophysiological phenotype was present at the first recording at 3 months of age and did not differ over monthly recordings up to 9 months of age, after which point animals became moribund and were euthanized. P301L mice at 10 months of age also showed electrical synchronization to a 40 Hz tone (ASSR) that was not observed in WT mice and an increase in inter-trial coherence compared with WT mice. We confirmed that AT8, as well as markers of neuroinflammation, increased progressively with age from the hindbrain to the forebrain, as previously reported. Together, these data suggest an increase in neuronal excitability in P301L mice compared with WT, but that this phenotype is not correlated with the age-dependent accumulation of AT8-labeled tau aggregates and the accompanying neuroinflammation. We hypothesize that the expression of P301L mutant tau disrupted the physiological functions of tau, resulting in the functional electrophysiological phenotype. Whether this functional effect drives neurodegeneration or is a separable phenomenon has implications for understanding the mechanisms underlying the role of tau variation in neurodegenerative conditions.
K. Dunton, Hugo Monchal, Brie E Achorn et al.· Frontiers in Neuroscience· 0 citations
Alzheimer’s disease (AD) is characterised by the intraneuronal aggregation of phosphorylated Tau (pTau) into neurofibrillary tangles and by the extracellular deposition of β-amyloid (Aβ). Tau pathology restricted to the hippocampal formation is frequently observed in the elderly brain in the absence of any Aβ deposition and considered as “primary age-related tauopathy” (PART). Here, we applied an unbiased proteomic approach to determine how concomitant Aβ pathology modifies the neurofibrillary tangle proteome. Neurofibrillary tangles were isolated by dissecting Tau pSer202/pThr205 “AT8” immunopositive neuronal profiles, combining chromogenic immunohistochemistry with laser capture microdissection, from hippocampal sections of 17 post-mortem brains spanning three groups: PART (n = 5; A0, B1–2, C0 scores), intermediate AD (n = 6; A1–2, B2–3, C1–2 scores) and advanced AD (n = 6; A3, B3, C3 scores). A label-free quantitative liquid chromatography–mass spectrometry based proteomic analysis, using data independent acquisition (DIA) on a Bruker timsTOF, was performed. A conserved core of 63 proteins was identified as enriched in tangles across all groups, mostly associated with “RNA binding” and “regulation of mRNA metabolic process”, based on the Gene Ontology database. Group-specific signatures were also observed: 33 proteins were significantly enriched only in tangles collected from PART cases and were predominantly linked to “structural molecule activity”, whereas Aβ-positive cases showed specific enrichment of “RNA binding” and “cytoplasmic translation” pathways—with intermediate AD cases displaying a transitional profile. Our findings are consistent with PART having distinct tangle proteomic features; however, the majority of its proteomic signature is in common with tangles within the AD continuum. By addressing how Aβ accumulation alters the tangle proteome, this study provides mechanistic insights into the expansion of Tau pathology, paving the way towards the identification of biomarkers and therapeutic strategies that would allow for stabilisation of Tau pathology in the elderly.
Manon Thierry, D. Leitner, Kaleah Balcomb et al.· Acta Neuropathologica· 0 citations
Higher plasma YKL‐40 was associated with greater white matter hyperintensity (WMH), whereas higher plasma GFAP was related to increased 18F‐florbetapir (FBP) standardized uptake value ratio (SUVR) and higher plasma p‐tau217 was associated with reduced MTL cortical thickness and hippocampal volume.
Batool Rizvi, Jenna N. Adams, Alison R. Bamford et al.· Alzheimer's & Dementia· 1 citation
A “cellular state–pathological network–therapeutic window” framework is proposed and the roles of microglia in amyloid-β plaque seeding and compaction, NLRP3 inflammasome activation, mitochondrial DNA–cGAS–STING signaling, complement-mediated synaptic engulfment, and bidirectional microglia–tau feedback are systematically discussed.
Lian-Jing Xu, Ying Zhang, Li Jiang et al.· Frontiers in Cellular Neuros...· 0 citations
INTRODUCTION Microglia regulate amyloid plaque-associated microenvironments that contribute to downstream tau pathology in Alzheimer’s disease (AD). Variants within the MS4A locus are strongly associated with AD risk and resilience and are linked to microglial biology; however, the functional role of MS4A4A in plaque-associated tau pathology remains poorly understood. METHODS Single-nucleus RNA sequencing (snRNA-seq) was performed on hippocampi from non-transgenic, Ms4a4a knockout (4A-KO), 5xFAD, and 5xFAD 4A-KO mice at 6 months of age. To assess plaque-associated tau pathology, AD-derived tau aggregates were injected into the hippocampus of 5xFAD and 5xFAD 4A-KO mice at 6 months, and histological analyses were performed 3 months later. RESULTS Amyloid pathology was the dominant driver of microglial state transitions, while Ms4a4a loss selectively remodeled activated microglial transcriptional programs enriched for interferon, lysosomal, autophagic, and proteostatic pathways. Activated microglia from 5xFAD 4A-KO mice exhibited altered expression of genes linked to immune signaling and protein handling. Following AD-tau inoculation, Ms4a4a loss did not significantly alter overall phospho-tau burden but selectively reduced dense-core plaque-associated neuritic plaque tau (NP-tau), particularly in the contralateral hemisphere. This phenotype was strongest surrounding X-34-positive fibrillar plaques and occurred without major changes in plaque-associated microgliosis. DISCUSSION These findings identify Ms4a4a as a regulator of plaque-associated microglial programs linked to NP-tau accumulation in the amyloid-bearing brain. More broadly, this work supports a model in which AD resilience-associated microglial pathways selectively shape plaque-associated microenvironments that promote downstream tau pathology.
E. Danhash, Shao-Yu Fang, Jacob A. Marsh et al.· bioRxiv· 0 citations
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