Hippocampal neurobiology and function in an aged mouse model of TDP-43 proteinopathy in an APP/PSEN1 background

Single-Cell Transcriptomic Profiling Reveals Regional Differences in the Prefrontal and Entorhinal Cortex of Alzheimer's Disease Brain

Previous studies have largely overlooked cellular differential alterations across differentially affected brain regions in both disease mechanisms and therapeutic development of Alzheimer's disease (AD). This study aimed to compare the differential cellular and transcriptional changes in the prefrontal cortex (PFC) and entorhinal cortex (EC) of AD patients through an integrated single-cell transcriptomic analysis. We integrated three single-cell RNA sequencing (scRNA-seq) datasets comprising PFC and EC samples from AD patients and age-matched healthy controls. A total of 124,658 nuclei and 31 cell clusters were obtained and classified into eight major cell types, with EC exhibiting much more pronounced transcriptional alterations than PFC. Through network analysis, we pinpointed hub regulatory genes that form interconnected networks driving AD pathogenesis, findings validated by RT-qPCR showing more pronounced expression changes in EC versus PFC of AD mice. Moreover, dysregulation of the LINC01099-associated regulatory networks in the PFC and EC, showing correlation with AD progression, may present new therapeutic targets for AD. Together, these results suggest that effective AD biomarkers and therapeutic strategies may require simultaneous, precise targeting of specific cell populations across multiple brain regions.

Cytoplasmic expression of trans-active response DNA-binding protein-43 in aged mice display hippocampal sclerosis-like degeneration and neuronal loss with reduced lifespan

Trans-active response DNA-binding protein-43 (TDP-43) is the major pathological protein in motor neuron disease and TDP-43 pathology has been described in the brains of up to 50% of patients with Alzheimer disease (AD). Hippocampal sclerosis of aging (HS-A), an age-related neuropathology characterized by severe neuronal loss and gliosis in CA1 and/or subiculum, is found in ∼80% of cases that are positive for phosphorylated TDP-43. HS-A is seen as a co-pathology in cases with AD, limbic-predominant age-related TDP-43 encephalopathy neuropathologic changes (LATE-NC), and frontotemporal degeneration. To understand the pathogenetic relationships between HS-A and LATE-NC, mice that selectively express human TDP-43 and TDP-43 with a defective nuclear localization signal (ΔNLS) in the hippocampus, alone or in an APP/PSEN1 background, were evaluated using histology, HALO software's object recognition algorithms, and protein expression assays. Twenty-four-month-old mice expressing cytosolic TDP-43 displayed marked neuronal loss and atrophy in the hippocampus, decreased β-amyloid plaque deposition and modulation of microglia and intermediate filament activation. TDP-43ΔNLS-expressing mice survived to only ∼24 months of age whether or not they had an APP/PSEN1 background. This HS-A-like model may provide insights into the pathogenesis of neurodegeneration seen in HS-A and in other TDP-43 proteinopathies.

TDP43 is a newly identified substrate for PS1, enhancing the expression of APP following cleavage

Alzheimer's disease (AD) has been comprehensively studied; however, most research has focused on Aβ plaque deposition and Tau protein phosphorylation. Emerging evidence suggests that TDP43 may be significantly involved AD and potentially worsening its pathology. To investigate the role of TDP43 in the pathological development of AD, we employed the STRING protein network interaction tool to identify potential relationships between TDP43 and other proteins, including PS1 and APP. Subsequent co-immunoprecipitation experiments were conducted, and the results indicated that TDP43 could interact with PS1. Further studies have shown that the interaction between the two would also lead to the loss of nuclear localization of TDP43. We also found that overexpression or knockdown of PS1 in both primary cells, HeLa and NSC34 cells indicated that TDP43 is likely to be a substrate of PS1. Subsequent use of the L685,458 and z-VAD, the PS1 mutant plasmids D257A and D385A, and bioinformatics approaches demonstrated that PS1 is dependent on γ-secretase and caspase activity to cleave TDP43, and that the cleavage site is at amino acid 315 of TDP43. Besides, our study demonstrated that the interaction of TDP43 with PS1 in primary cells, HeLa and NSC34 cells can promote APP expression, resulting in elevated Aβ levels. Finally, we investigated whether the interaction between TDP43 and PS1 affects the expression of other PS1 substrates, Notch and E-cadherin. Our results demonstrated that TDP43 cleaved by PS1 only promoted APP expression and had no effect on other PS1 substrates. In conclusion, these results suggest that TDP43 is a new substrate of PS1 and that TDP43 cleaved by PS1 promotes APP expression, which leads to increased Aβ content, which may explain why TDP43 promotes AD development. These insights enhance our understanding of TDP43's role in AD development.