Rizzi, Liara

Introduction Blood-based biomarkers offer a promising, minimally invasive approach to Alzheimer’s disease (AD) diagnosis, yet validation in admixed populations remains limited. We investigated whether plasma biomarkers predict CSF-defined AD pathology in a Brazilian cohort. Methods Seventy-eight older adults [including individuals with mild cognitive impairment (MCI), subjective cognitive decline (SCD), and cognitively unimpaired controls] underwent cognitive testing, neuroimaging, and plasma biomarker assessment. CSF data were available for symptomatic participants (MCI and SCD; n = 61), and regression and ROC analyses were performed in the subset with both CSF and APOE genotyping data ( n = 53). Plasma Aβ42, p-Tau181, p-Tau217, t-Tau, and derived ratios were quantified. Multivariable logistic regression and ROC analyses evaluated prediction of abnormal CSF p-Tau181/Aβ42 and t-Tau/Aβ42, adjusting for age, sex, and APOE ε4 status. Results Approximately 25% of individuals with MCI exhibited abnormal CSF p-Tau181/Aβ42 and t-Tau/Aβ42 ratios. Moderate correlations were observed between plasma and CSF biomarkers (r > 0.4), particularly for Aβ42/p-Tau217 and p-Tau217. In adjusted models, plasma p-Tau217 and the Aβ42/p-Tau217 ratio independently predicted abnormal CSF pathology. Each one standard deviation increase in p-Tau217 was associated with 3.53–4.83-fold higher odds of abnormal CSF ( p ≤ 0.003). In contrast, higher Aβ42/p-Tau217 ratios were associated with substantially lower odds of pathology, with each one standard deviation increase corresponding to a 91%–93% reduction in risk ( p ≤ 0.002). The ratio showed stronger associations than p-Tau217 alone. ROC analyses demonstrated good discrimination. For CSF p-Tau181/Aβ42, Aβ42/p-Tau217 achieved an AUC of 0.88 (83% sensitivity, 85% specificity), compared with 0.83 for p-Tau217. For CSF t-Tau/Aβ42, both biomarkers yielded AUCs of 0.89. Discussion Plasma Aβ42/p-Tau217 and p-Tau217 effectively identify CSF-defined AD pathology in an admixed cohort. While higher p-Tau217 levels were associated with increased odds of pathology, higher Aβ42/p-Tau217 ratios were associated with lower pathological burden and demonstrated stronger effect sizes, supporting the added value of combining amyloid and tau biomarkers. These findings provide initial evidence for local validation of blood-based AD biomarkers in Brazil.

A bstract Alzheimer’s disease (AD) presents with substantial clinical and anatomical heterogeneity, including both typical amnestic and atypical variants such as posterior cortical atrophy and logopenic primary progressive aphasia. Although neurofibrillary tangle (NFT) burden is a defining pathological feature of AD, its regional distribution varies across clinical phenotypes, suggesting that selective neuronal vulnerability may shape disease presentation. However, the cellular and molecular determinants underlying this vulnerability remain incompletely understood. Here, we profiled single-nucleus transcriptomes across multiple brain regions, including hippocampal (CA1) and neocortical (superior temporal gyrus and occipital cortex) regions, from individuals with typical and atypical AD and healthy controls. Integrative analysis identified major cell classes and resolved diverse excitatory and inhibitory neuronal subpopulations that were reproducibly observed across regions and individuals. Using quasi-binomial regression models to assess compositional changes, we quantified subtype-specific vulnerability associated with AD pathology. We identified a distinct excitatory neuronal subpopulation characterized by NRGN and BEX1 expression, which showed reproducible depletion across multiple regions, with the strongest evidence in amnestic AD and in neocortical regions in lvPPA. This vulnerable population showed concordance with previously reported AD-associated excitatory neuron signatures, supporting a conserved transcriptional program of susceptibility. Genes enriched in this population were associated with chemical synaptic transmission and regulation of synaptic plasticity and formed interconnected networks in protein-protein interaction analyses. These findings suggest that intrinsic properties related to synaptic function may predispose specific neuronal populations to degeneration in AD. Together, our results define a conserved, transcriptionally distinct excitatory neuron subpopulation that is selectively vulnerable across AD phenotypes and brain regions. This work provides a framework for linking regional pathology to cell-type-specific susceptibility and highlights synaptic regulatory pathways as potential contributors to neuronal degeneration in Alzheimer’s disease.

Abstract The diagnosis of predementia stages indicates an increased risk of progression to dementia. The Amyloid, Tau, and Neurodegeneration AT(N) classification considers measurements of altered proteins and the presence of neurodegeneration to classify the risk groups regarding the pathophysiology of Alzheimer's disease (AD). The cognitive and anatomical characteristics of the patients in the predementia stage according to the AT(N) classification are not fully understood. To investigate whether there are differences in the clinical and anatomical profiles among older adults in the predementia stage according to the ATN classification, and to investigate the associations involving cognition and cortical thickness and subcortical volume in the AT(N) groups. In total, 72 older adults with subjective cognitive decline and mild cognitive impairment were allocated to groups according to the AT(N) classification (AD continuum: n = 37; suspected non-AD pathophysiology: n = 8; normal biomarkers: n = 27). The participants were investigated through cognitive tests, magnetic resonance imaging scans, and cerebrospinal fluid analyses. We used multivariate and univariate analyses with post-hoc testing to verify differences among groups. In addition, linear regressions were performed to verify the interactions involving cognition and gray matter metrics. The suspected non-AD pathophysiology group showed worse performance in attention/executive function than the AD continuum and normal biomarkers groups (p = 0.04). However, the ATN classification groups did not differ in terms of cortical thickness (p > 0.05). In addition, in the AD continuum group, memory was associated with left fusiform gyrus thickness (p = 0.000 uncorrected; r = 0.238). Cognition, but not gray matter metrics, differs among AT(N) classification groups. Memory is associated with cortical thickness in patients with positive amyloid Beta (AD continuum).

Abstract Background Individuals meeting neuropathological criteria for Alzheimer's disease (AD) can exhibit distinct clinical syndromes, suggesting region‐specific neuronal susceptibilities to tau pathology. Amnestic AD cases show greater tau burden in CA1, logopenic variant primary progressive aphasia (lvPPA) in the superior temporal gyrus (STG), and posterior cortical atrophy (PCA) in the occipital cortex. We hypothesize that by contrasting these AD variants and examining their respective pathological hotspots, we can identify the most vulnerable neuronal subpopulations ‐ those that exhibit the greatest reduction in their specific hotspot area compared to other regions. Using single‐nucleus RNA sequencing (snRNA‐seq), we investigate the molecular mechanisms driving this selective neuronal vulnerability. Methods We performed snRNA‐seq using the Chromium Single Cell 3′ (10X Genomics, USA) platform on nuclei extracted from the CA1 hippocampal sector, posterior STG, and occipital cortex of postmortem brain tissue from 68 individuals. The cohort included 24 amnestic AD cases, 11 lvPPA cases, and 6 PCA cases (all meeting A3B3C3 pathological criteria), along with 27 healthy controls (A≤1B≤1C≤1). Bioinformatics analysis was conducted using the Seurat library in R. Cell subpopulation comparisons were performed using the Wald statistical test, with p ‐values < .05 considered significant. Results Following quality control, we recovered over 1.58 million nuclei, with an average of 2,129 genes detected per nucleus. UMAP clustering identified 17 inhibitory and 16 excitatory neuronal subpopulations across all three regions. Among these, one excitatory subpopulation was highly enriched in CA1. We identified six excitatory subpopulations (Exc‐subs) exhibiting region‐specific vulnerability. Notably, the Ex L2/3 IT RORB GRIN1 subpopulation showed pronounced vulnerability in CA1 among amnestic cases, in STG among amnestic and lvPPA cases, and displayed a vulnerability trend in the occipital cortex among PCA cases, though not statistically significant. Conclusion Our findings suggest that a specific excitatory neuron subpopulation exhibits heightened susceptibility across highly tau‐affected regions in amnestic and atypical AD syndromes, including PCA. Ongoing validation using quantitative pathology aims to confirm these findings, and further case analyses will refine our understanding of the molecular drivers of neuronal vulnerability in AD.

AbstractBackgroundIndividuals meeting neuropathological criteria for Alzheimer’s disease (AD) may manifest with atypical clinical syndromes. Past work showed that the neurobiological basis for these differences is related to specific neuronal vulnerabilities for tau pathology. For instance, amnestic cases have a higher burden of neurofibrillary changes in CA1. In contrast, logopenic variant primary progressive aphasia (lvPPA) cases have a higher tau burden in the superior temporal gyrus (STG). Single‐cell technology enables investigations on the molecular basis of differential neuronal vulnerability in AD. Consequently, we delved into the factors that underlie this selective vulnerability by analyzing brain samples from individuals exclusively afflicted with AD but exhibiting diverse clinical manifestations.MethodsnRNA Sequencing using the Chromium Single Cell 3′ (10X Genomics, USA) on nuclei cells extracted from the CA1 sector and posterior STG of postmortem brain tissue of 48 individuals either meeting pathological criteria for AD (A3B3C3; 24 amnestic and eleven lvPPA) and healthy controls (A≤1B≤1C≤1; n = 13) (Table 1, Fig. 1A/B). Bioinformatics analyses were conducted using Cell Ranger and R software. Comparisons between cell subpopulations were conducted with the Wald statistical test, and p‐values < .05 were considered significant.ResultAfter quality control, we recovered more than 250k nuclei with a mean of 2,130 genes per nuclei. Upon cross‐sample alignment and t‐stochastic neighborhood embedding clustering (Fig. 1C), we found 21 excitatory neuronal subpopulations (Exc‐sub) in CA1 and 26 in STG, and 22 and 25 inhibitory neuronal subpopulations (Inh‐sub) in CA1 and STG, respectively; 16 astrocytes subpopulations in both areas and 20 microglia subpopulations in CA1 and 17 in STG (Fig. 2). One STG Exc‐sub, expressing CUX2 and LAMP5 genes showed vulnerability in lvPPA patients. Also, one STG Inh‐sub, expressing the ADARB2 gene, showed vulnerability for all AD patients.ConclusionOur preliminary study identified a vulnerable population of excitatory neurons related to lvPPA. We are conducting validation studies using quantitative pathology to confirm these results. Furthermore, analysis of a higher number of cases is ongoing and will continue to inform on factors associated with neuronal vulnerability.