Rexach, Jessica E.

Abstract The Tau Global Conference 2025, hosted by the Alzheimer's Association, CurePSP, and the Rainwater Charitable Foundation, convened international experts from academia, industry, government, and philanthropy to explore advances and challenges in tauopathy research. The meeting highlighted progress across tau biology, including emerging models of tau regulation, degradation, and propagation; advances in biomarker development for the diagnosis and staging of tauopathies; and evolving therapeutic strategies targeting diverse aspects of tau pathophysiology. Discussions also emphasized the importance of cross‐sector collaboration, and global initiatives to address disparities in tau research. This report synthesizes key insights from the conference and underscores the critical role of interdisciplinary, biomarker‐driven, and globally inclusive approaches in accelerating the translation of tau research into effective clinical applications.

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 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.

AbstractBackgroundAs new anti‐amyloid immunotherapies emerge for Alzheimer’s disease (AD), it is clear that early diagnosis of AD pathology is crucial for treatment success. This can be challenging in atypical presentations of AD and, together with our reliance on CSF or PET scans, can, at times, lead to delayed diagnosis. Here, we further explore the possible role of plasma tau phosphorylated at threonine 217 (P‐tau217) for the detection of primary AD or AD co‐pathology when frontotemporal dementia spectrum disorders are the main clinical presentation.MethodParticipants were recruited through ALLFTD, a North American multisite research consortium for the longitudinal assessment of frontotemporal lobar degeneration. After excluding cases with known FTD‐causing mutations, 573 participants with sporadic disease, mild cognitive/behavioral impairment, or healthy familial controls evaluated between 2014 and 2023 were included in this analysis (45.8% female, median age 66 years). 39 of those cases underwent neuropathological evaluation. Plasma P‐tau217 was measured with the Eli Lilly electrochemiluminescence‐based assay. P‐tau217 concentrations were compared by phenotype, disease severity, genotype, and, when available, neuropathological diagnosis with non‐parametric tests. Its diagnostic performance was tested with ROC curves. Associations between plasma P‐tau217 concentrations and clinical scales of global cognition, memory, executive function, motor function, and social cognition with linear regressions and non‐parametric tests.ResultPlasma P‐tau217 concentrations were higher in logopenic variant primary progressive aphasia (lvPPA) and amnestic dementia (AmDem), compared to participants with normal cognition or other FTD phenotypes. P‐tau217 concentrations were higher in APOE e4 carriers, compared to non‐carriers, regardless of phenotype, but were not affected by disease severity. P‐tau217 concentrations showed associations with clinical measures of global cognition, memory, and executive function, but had no associations with measures of motor function or social cognition. Plasma P‐tau217 concentrations were elevated in high and intermediate ADNC scoring, or more advanced Braak stages, even when AD was not the primary pathology.ConclusionEven when FTD is suspected, high plasma p‐tau 217 concentrations are strongly associated with underlying AD as primary pathology or contributing co‐pathology. Plasma P‐tau217 could be a tool to support the development of disease‐modifying therapies for atypical Alzheimer’s disease presentations or for FTD cases with Alzheimer’s disease co‐pathology.

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.

Abstract The immune system is a key player in the onset and progression of neurodegenerative disorders. While brain resident immune cell‐mediated neuroinflammation and peripheral immune cell (eg, T cell) infiltration into the brain have been shown to significantly contribute to Alzheimer's disease (AD) pathology, the nature and extent of immune responses in the brain in the context of AD and related dementias (ADRD) remain unclear. Furthermore, the roles of the peripheral immune system in driving ADRD pathology remain incompletely elucidated. In March of 2023, the Alzheimer's Association convened the Alzheimer's Association International Conference (AAIC), Advancements: Immunity, to discuss the roles of the immune system in ADRD. A wide range of topics were discussed, such as animal models that replicate human pathology, immune‐related biomarkers and clinical trials, and lessons from other fields describing immune responses in neurodegeneration. This manuscript presents highlights from the conference and outlines avenues for future research on the roles of immunity in neurodegenerative disorders. Highlights The immune system plays a central role in the pathogenesis of Alzheimer's disease. The immune system exerts numerous effects throughout the brain on amyloid‐beta, tau, and other pathways. The 2023 AAIC, Advancements: Immunity, encouraged discussions and collaborations on understanding the role of the immune system.

ImportanceFrontotemporal lobar degeneration (FTLD) is relatively rare, behavioral and motor symptoms increase travel burden, and standard neuropsychological tests are not sensitive to early-stage disease. Remote smartphone-based cognitive assessments could mitigate these barriers to trial recruitment and success, but no such tools are validated for FTLD.ObjectiveTo evaluate the reliability and validity of smartphone-based cognitive measures for remote FTLD evaluations.Design, Setting, and ParticipantsIn this cohort study conducted from January 10, 2019, to July 31, 2023, controls and participants with FTLD performed smartphone application (app)–based executive functioning tasks and an associative memory task 3 times over 2 weeks. Observational research participants were enrolled through 18 centers of a North American FTLD research consortium (ALLFTD) and were asked to complete the tests remotely using their own smartphones. Of 1163 eligible individuals (enrolled in parent studies), 360 were enrolled in the present study; 364 refused and 439 were excluded. Participants were divided into discovery (n = 258) and validation (n = 102) cohorts. Among 329 participants with data available on disease stage, 195 were asymptomatic or had preclinical FTLD (59.3%), 66 had prodromal FTLD (20.1%), and 68 had symptomatic FTLD (20.7%) with a range of clinical syndromes.ExposureParticipants completed standard in-clinic measures and remotely administered ALLFTD mobile app (app) smartphone tests.Main Outcomes and MeasuresInternal consistency, test-retest reliability, association of smartphone tests with criterion standard clinical measures, and diagnostic accuracy.ResultsIn the 360 participants (mean [SD] age, 54.0 [15.4] years; 209 [58.1%] women), smartphone tests showed moderate-to-excellent reliability (intraclass correlation coefficients, 0.77-0.95). Validity was supported by association of smartphones tests with disease severity (r range, 0.38-0.59), criterion-standard neuropsychological tests (r range, 0.40-0.66), and brain volume (standardized β range, 0.34-0.50). Smartphone tests accurately differentiated individuals with dementia from controls (area under the curve [AUC], 0.93 [95% CI, 0.90-0.96]) and were more sensitive to early symptoms (AUC, 0.82 [95% CI, 0.76-0.88]) than the Montreal Cognitive Assessment (AUC, 0.68 [95% CI, 0.59-0.78]) (z of comparison, −2.49 [95% CI, −0.19 to −0.02]; P = .01). Reliability and validity findings were highly similar in the discovery and validation cohorts. Preclinical participants who carried pathogenic variants performed significantly worse than noncarrier family controls on 3 app tasks (eg, 2-back β = −0.49 [95% CI, −0.72 to −0.25]; P &amp;lt; .001) but not a composite of traditional neuropsychological measures (β = −0.14 [95% CI, −0.42 to 0.14]; P = .32).Conclusions and RelevanceThe findings of this cohort study suggest that smartphones could offer a feasible, reliable, valid, and scalable solution for remote evaluations of FTLD and may improve early detection. Smartphone assessments should be considered as a complementary approach to traditional in-person trial designs. Future research should validate these results in diverse populations and evaluate the utility of these tests for longitudinal monitoring.

AbstractBackgroundFrontotemporal dementia spectrum disorders (FTD) display complex neuropathological substrates and poor clinicopathological correlations, which hinders therapy development. Plasma P‐tau217 is an emerging tool to screen for Alzheimer’s disease (AD) pathology and may have diagnostic value in FTD.MethodPlasma P‐tau217 was measured cross‐sectionally by electrochemiluminescence in FTD patients referred to ALLFTD from ARTFL (n = 628, 45.7% female, median age 66 ± 12 years). P‐tau217 differences by baseline phenotype, disease severity and genotype were determined with non‐parametric tests and general linear models. Associations between P‐tau217 and measures of disease severity and neuropsychological performance were determined with linear regressions corrected for age, sex, phenotype and APOE.ResultThe sample included 33% behavioral variant FTD, 23.6% primary progressive aphasia (PPA), 28.5% atypical parkinsonism, 1.6% amnestic dementia (AmDem), 2.8% FTD/motoneuron disease, 3% mild cognitive/behavioral impairment and 7.5% healthy controls. Only 1.6% carried FTD‐causing mutations. P‐tau217 was not related to age (r = 0.034, 95%CI ‐0.03 – 0.12, p = 0.4). Compared to controls (0.18 ± 0.07 pg/mL), P‐tau217 was elevated only in AmDem (0.58 ± 0.9 pg/mL, p = 0.001) and logopenic PPA (lvPPA, 0.71 ± 0.62 pg/mL p < 0.001). P‐tau217 ≥ 0.42 pg/mL effectively discriminated AmDem and lvPPA from all other phenotypes (AUC 0.87, 95%CI 0.77 – 0.96, p = 0.001, 77% sensitivity, 92% specificity). AmDem (60%) and lvPPA (91.7%) had the highest prevalence of high (≥ 0.42 pg/mL) P‐tau217, and the highest prevalence of APOE4 (AmDem 40%, lvPPA 63.6%). APOE4 carriers (0.23 ± 0.22 pg/mL) had higher P‐tau217, than non‐carriers (0.19 ± 0.09 pg/mL), regardless of phenotype (APOE effect p = .002, APOE x phenotype, p = 0.44). P‐tau217 was associated with worse clinical severity, mood, memory and executive function, but not with worse motor symptoms or social cognition.ConclusionWhen FTD is suspected, high plasma P‐tau217 is strongly associated with amnestic dementia and logopenic PPA phenotypes. Pending completion of ongoing neuropathological, CSF and molecular neuroimaging analyses, the data support the use of plasma P‐tau217 to identify atypical AD as a cause or AD as a co‐pathology contributing to FTD clinical presentation.