Jin, Yunjung

AbstractBackgroundThe aggregation of α‐synuclein protein, encoded by the SNCA gene, forms Lewy bodies (LBs) in neurons and is a key pathological feature of Lewy body dementia (LBD). Interestingly, the apolipoprotein E gene (APOE), primarily expressed in glial cells, is the strongest genetic modifier for LBD. The ε4 allele of this gene (APOE4) notably increases the risk of LBD. However, the specific mechanisms through which APOE‐regulated glial cells affect α‐synuclein aggregation in neurons are not yet fully understood.MethodTo explore this, we conducted spatial transcriptomics using the 10X Genomics Visium CytAssist platform on Formalin‐Fixed Paraffin‐Embedded tissue slides from the temporal cortex of human LBD brains (N = 4 brains in controls and N = 6 brains in LBD group, with an equal ratio of APOE3/3 and APOE3/4 genotypes). We defined the neuronal layers of the gray matter (Layers 1 to 6, L1‐6) and white matter in each brain based on the gene signature of each spot. We also identified LBs from hematoxylin and eosin (H&E) staining on the same slides, and annotated LB‐positive (LB+), LB‐surrounding and LB‐negative (LB‐) spots in each brain using Loupe Browser. We evaluated SNCA and APOE gene expression in each layer and analyzed cell‐cell communication using the CellChat tool across the layers.ResultWe observed that the SNCA gene was highly expressed in L5, which corresponded to the areas where most LBs were found. Notably, within LB+ spots across all layers, both SNCA and APOE gene expression levels were elevated in APOE3/4 cases compared to APOE3/3 cases. Furthermore, we identified cell‐cell communication networks between LB+ and LB‐surrounding spots, particularly in L4 and L5. These networks were enriched by microglia‐related signaling pathways, including APOE signaling, migration inhibitory factor (MIF) signaling, and colony stimulating factor 1 (CSF1) signaling. Interestingly, APOE3/4 brains exhibited significantly reduced interactions and lower interaction strength in these networks compared to APOE3/3 samples.ConclusionOur findings indicate that impaired cell‐cell communication, such as microglia‐mediated immune responses around LB regions, may be associated with the increased risk presented by the APOE4 allele in LBD brains.

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.

AbstractBackgroundAccumulating evidence demonstrates that 40‐50% of Alzheimer’s disease (AD) brains present with concomitant Lewy pathologies at autopsy, suggesting that α‐synuclein (α‐SYN) aggregation is likely involved in the pathogenesis of AD. Interestingly, the genome‐wide association study (GWAS) revealed that the ε4 allele of APOE (APOE4) gene, the strongest genetic risk factor for AD, is also the most replicated genetic risk factor for Lewy body dementia (LBD), signifying the important role of APOE4 in both amyloid β (Aβ) and α‐SYN pathogenesis. However, how APOE4 modulates the α‐SYN aggregation in AD is still unclear.MethodWe performed biochemical analyses measuring α‐SYN levels on a pathologically confirmed human AD cohort (N = 469) obtained from the Mayo Clinic Brain Bank, wherein 54.4% of our cohort presented with co‐morbid α‐SYN pathology upon diagnosis of AD with Lewy Body pathology (hereinafter referred to as AD+LB), which was subdivided into APOE4 non‐carriers (APOE4−) and carriers (APOE4+). To determine the seeding activity of α‐SYN, we performed Real‐time quaking‐induced conversion (RT‐QuIC) assays with the soluble TBS protein fractions of the brain lysates. The cytotoxicities of the amplified α‐SYN seeds were tested with MTT assay for cell viability and neuronal outgrowth measurement by immunofluorescence staining with human induced pluripotent stem cells (iPSC)‐derived neurons.ResultWe found that AD+LB cases showed the significantly higher seeding activity of α‐SYN compared to AD cases without LB pathologies. Furthermore, APOE4+ AD+LB brains had the highest α‐SYN seeding activity compared to AD+LB APOE4− cases. The α‐SYN seeding activity was associated with the level of α‐SYN, tau, or APOE aggregates, but not Aβ. Finally, we showed that the amplified α‐SYN aggregates derived from AD+LB APOE4+ had highest protease resistance and cytotoxicities in iPSC‐derived neurons.ConclusionThese findings suggest that APOE4 modulates the conformation of α‐SYN seeds which leads to high seeding activity and toxicity of α‐SYN in AD.

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.