Zhao, Na

Abstract In Alzheimer’s disease (AD), tau pathology arises in entorhinal cortex layer II (ECII) and advances through defined hippocampal circuits to CA1 and connected neocortical regions, yet the determinants of this hierarchical spread remain unclear. We previously established a circuit-defined propagation model by expressing Cre-inducible human P301L 2N4R tau selectively in Wolframin-1 (Wfs1) + ECII neurons using AAV-FLEX-Tau P301L in Wfs1-Cre mice. Here, to test how amyloid-β (Aβ) and human tau background shape propagation, we generated human MAPT knock-in Wfs1 mice and APP NL-G-F / MAPT double knock-in Wfs1 mice (T-Wfs1 and AT-Wfs1) and induced ECII-restricted Tau P301L expression. Three months after injection, phosphorylated or misfolded tau-positive neurons were enriched in proximal CA1 in Wfs1 and T-Wfs1 mice, resembling primary age-related tauopathy, whereas AT-Wfs1 mice showed preferential accumulation near the CA1/subiculum (Sub) boundary, consistent with an AD-like pattern. In T-Wfs1 and AT-Wfs1 mice, tau spread extended through Sub to neocortical regions, and phosphorylated tau accumulated predominantly in excitatory rather than inhibitory neurons. Electrophysiological analyses revealed increased spontaneous neuronal firing and impaired GABAergic transmission in the CA1/Sub boundary and neocortical areas in T-Wfs1 and AT-Wfs1 mice, indicative of impaired GABAergic input and enhanced neuronal excitability in these regions. Together, these data indicate that human MAPT and Aβ pathology shift the circuit topography of tau propagation and are associated with early network dysfunction, supporting a synergistic interaction that promotes AD-like spread and synaptic imbalance.

Abstract Alzheimer’s disease (AD) risk and progression are significantly influenced by APOE genotype with APOE4 increasing and APOE2 decreasing susceptibility compared to APOE3. While the effect of those genotypes was extensively studied on blood metabolome, less is known about their impact in the brain. Here we investigated the impacts of APOE genotypes and aging on brain metabolic profiles across the lifespan, using human APOE-targeted replacement mice. Biocrates P180 targeted metabolomics platform was used to measure a broad range of metabolites probing various metabolic processes. In all genotypes investigated we report changes in acylcarnitines, biogenic amines, amino acids, phospholipids and sphingomyelins during aging. The decreased ratio of medium to long-chain acylcarnitine suggests a reduced level of fatty acid β-oxidation and thus the possibility of mitochondrial dysfunction as these animals age. Additionally, aging APOE2/2 mice had altered branch-chain amino acids (BCAA) profile and increased their downstream metabolite C5 acylcarnitine, indicating increased branched-chain amino acid utilization in TCA cycle and better energetic profile endowed by this protective genotype. We compared these results with human dorsolateral prefrontal cortex metabolomic data from the Religious Orders Study/Memory and Aging Project, and we found that the carriers of APOE2/3 genotype had lower markers of impaired BCAA katabolism, including tiglyl carnitine, methylmalonate and 3-methylglutaconate. In summary, these results suggest a potential involvement of the APOE2 genotype in BCAA utilization in the TCA cycle and nominate these humanized APOE mouse models for further study of APOE in AD, brain aging, and brain BCAA utilization for energy. We have previously shown lower plasma BCAA to be associated with incident dementia, and their higher levels in brain with AD pathology and cognitive impairment. Those findings together with our current results could potentially explain the AD-protective effect of APOE2 genotype by enabling higher utilization of BCAA for energy during the decline of fatty acid β-oxidation.

Aggregated α-synuclein (α-SYN) proteins, encoded by the SNCA gene, are hallmarks of Lewy body disease (LBD), affecting multiple brain regions. However, the specific mechanisms underlying α-SYN pathology in cortical neurons, crucial for LBD-associated dementia, remain unclear. Here, we recapitulated α-SYN pathologies in human induced pluripotent stem cells (iPSCs)–derived cortical organoids generated from patients with LBD with SNCA gene triplication. Single-cell RNA sequencing, combined with functional and molecular validation, identified synaptic and mitochondrial dysfunction in excitatory neurons exhibiting high expression of the SNCA gene, aligning with observations in the cortex of autopsy-confirmed LBD human brains. Furthermore, we screened 1280 Food and Drug Administration–approved drugs and identified four candidates (entacapone, tolcapone, phenazopyridine hydrochloride, and zalcitabine) that inhibited α-SYN seeding activity in real-time quaking-induced conversion assays with human brains, reduced α-SYN aggregation, and alleviated mitochondrial dysfunction in SNCA triplication organoids and excitatory neurons. Our findings establish human cortical LBD models and suggest potential therapeutic drugs targeting α-SYN aggregation for LBD.

AbstractINTRODUCTIONThe apolipoprotein E gene (APOE) is an established central player in the pathogenesis of Alzheimer's disease (AD), with distinct apoE isoforms exerting diverse effects. apoE influences not only amyloid‐beta and tau pathologies but also lipid and energy metabolism, neuroinflammation, cerebral vascular health, and sex‐dependent disease manifestations. Furthermore, ancestral background may significantly impact the link between APOE and AD, underscoring the need for more inclusive research.METHODSIn 2023, the Alzheimer's Association convened multidisciplinary researchers at the “AAIC Advancements: APOE” conference to discuss various topics, including apoE isoforms and their roles in AD pathogenesis, progress in apoE‐targeted therapeutic strategies, updates on disease models and interventions that modulate apoE expression and function.RESULTSThis manuscript presents highlights from the conference and provides an overview of opportunities for further research in the field.DISCUSSIONUnderstanding apoE's multifaceted roles in AD pathogenesis will help develop targeted interventions for AD and advance the field of AD precision medicine.Highlights APOE is a central player in the pathogenesis of Alzheimer's disease. APOE exerts a numerous effects throughout the brain on amyloid‐beta, tau, and other pathways. The AAIC Advancements: APOE conference encouraged discussions and collaborations on understanding the role of APOE.

ObjectiveRecent evidence supports a link between increased TDP‐43 burden and the presence of an APOE4 gene allele in Alzheimer's disease (AD); however, it is difficult to conclude the direct effect of APOE on TDP‐43 pathology due to the presence of mixed AD pathologies. The goal of this study is to address how APOE isoforms impact TDP‐43 pathology and related neurodegeneration in the absence of typical AD pathologies.MethodsWe overexpressed human TDP‐43 via viral transduction in humanized APOE2, APOE3, APOE4 mice, and murine Apoe‐knockout (Apoe‐KO) mice. Behavior tests were performed across ages. Animals were harvested at 11 months of age and TDP‐43 overexpression‐related neurodegeneration and gliosis were assessed. To further address the human relevance, we analyzed the association of APOE with TDP‐43 pathology in 160 postmortem brains from autopsy‐confirmed amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with motor neuron disease (FTLD‐MND) in the Mayo Clinic Brain Bank.ResultsWe found that TDP‐43 overexpression induced motor function deficits, neuronal loss, and gliosis in the motor cortex, especially in APOE2 mice, with much milder or absent effects in APOE3, APOE4, or Apoe‐KO mice. In the motor cortex of the ALS and FTLD‐MND postmortem human brains, we found that the APOE2 allele was associated with more severe TDP‐43‐positive dystrophic neurites.InterpretationOur data suggest a genotype‐specific effect of APOE on TDP‐43 proteinopathy and neurodegeneration in the absence of AD pathology, with the strongest association seen with APOE2. ANN NEUROL 2023;93:830–843

TREM2 is exclusively expressed by microglia in the brain and is strongly linked to the risk for Alzheimer’s disease (AD). As microglial responses modulated by TREM2 are central to AD pathogenesis, enhancing TREM2 signaling has been explored as an AD therapeutic strategy. However, the effective therapeutic window targeting TREM2 is unclear. Here, by using microglia-specific inducible mouse models overexpressing human wild-type TREM2 (TREM2-WT) or R47H risk variant (TREM2-R47H), we show that TREM2-WT expression reduces amyloid deposition and neuritic dystrophy only during the early amyloid seeding stage, whereas TREM2-R47H exacerbates amyloid burden during the middle amyloid rapid growth stage. Single-cell RNA sequencing reveals suppressed disease-associated microglia (DAM) signature and reduced DAM population upon TREM2-WT expression in the early stage, whereas upregulated antigen presentation pathway is detected with TREM2-R47H expression in the middle stage. Together, our findings highlight the dynamic effects of TREM2 in modulating AD pathogenesis and emphasize the beneficial effect of enhancing TREM2 function in the early stage of AD development.

A rare APOE variant APOE3 -Jac reduces self-aggregation and promotes healthy brain aging.

Abstract Triggering receptor expressed on myeloid cell 2 (TREM2) is a surface receptor that, in the central nervous system, is exclusively expressed on microglia. TREM2 variants have been linked to increased risk for neurodegenerative diseases, but the functional effects of microglial TREM2 remain largely unknown. To this end, we investigated TAR-DNA binding protein 43 kDa (TDP-43)-related neurodegenerative disease via viral-mediated expression of human TDP-43 protein (hTDP-43) in mice or inducible expression of hTDP43 with defective nuclear localization signals in transgenic mice. We found that TREM2 deficiency impaired microglia phagocytic clearance of pathological TDP-43, and enhanced neuronal damage and motor function impairments. Mass cytometry analysis revealed that hTDP-43 induced a TREM2-dependent subpopulation of microglia with high CD11c expression and higher phagocytic ability. Using mass spectrometry, we further demonstrated an interaction between TDP-43 and TREM2, in vitro and in vivo, in hTDP-43-expressing transgenic mouse brains. We computationally identified the region within hTDP-43 that interacts with TREM2 and observed the potential interaction in ALS patient tissues. Our data reveal the novel interaction between TREM2 and TDP-43, highlighting that TDP-43 is a potential ligand for microglial TREM2 and the interaction mediates neuroprotection of microglial TREM2 in TDP-43-related neurodegeneration.

AbstractIntroductionCerebrovascular pathologies including cerebral amyloid angiopathy (CAA) and blood‐brain barrier (BBB) dysregulation are prominent features in the majority of Alzheimer's disease (AD) cases.MethodsWe performed neuropathologic and biochemical studies on a large, neuropathologically confirmed human AD cohort (N = 469). Amounts of endothelial tight junction proteins claudin‐5 (CLDN5) and occludin (OCLN), and major AD‐related molecules (amyloid beta [Aβ40], Aβ42, tau, p‐tau, and apolipoprotein E) in the temporal cortex were assessed by ELISA.ResultsHigher levels of soluble tau, insoluble p‐tau, and apolipoprotein E (apoE) were independently correlated with lower levels of endothelial tight junction proteins CLDN5 and OCLN in AD brains. Although high Aβ40 levels, APOE ε4, and male sex were predominantly associated with exacerbated CAA severity, those factors did not influence tight junction protein levels.DiscussionRefining the molecular mechanisms connecting tau, Aβ, and apoE with cerebrovascular pathologies is critical for greater understanding of AD pathogenesis and establishing effective therapeutic interventions for the disease.