Rationale:
Hyperexcitability is Alzheimer’s disease (AD) has captured attention because it appears to occur early in the disease and contribute to cognitive impairment and increased amyloid b (Ab). In our prior work with AD mouse models, we found hyperexcitability extremely early in life, just 1 month of age. In vivo, aberrant activity emerged mainly as interictal spikes (IIS) in sleep, with later onset of rarer seizure events. Silicon probe recordings suggested IIS were generated in the dentate gyrus (DG). In vitro patch-clamp studies identified that there was increased activity in some of the cell types in the DG at the 1 month age, but why this elevated activity occurred was not clear.
Methods:
To gain insight, we examined DG gene expression in wild type (WT) vs. Tg2576 mice, which overexpress a mutant form of the precursor to Ab (APPSwe). Single-nucleus RNA sequencing (snRNA-seq) was performed using DG from slices of 1 month-old WT and Tg2576 mice (n=3/group). We used Particle-templated Instant Partition Sequencing (PIP-seq) from the NYU Genome Technology Center, which also processed and sequenced the isolated DG nuclei. High quality nuclei were then selected and annotated using validated marker genes that identify 9 major DG cell types.
Results:
We found similar proportions of the 9 cell types in both Tg2576 and WT mice at nuclei yields consistent with prior studies. Notably, differentially expressed gene (DEG) analysis identified thousands of DEGs, many of which may be involved in regulation of excitability, including known risk genes for AD and epilepsy. Surprisingly, a set of shared genes that can regulate excitability were altered across all 9 major cell types.
Conclusions:
We have identified gene regulatory programs and gene expression alterations that may promote or inhibit early-disease hyperexcitability in the dentate gyrus in the context of AD. Many of these genes across cell types match those that show altered expression in AD and epilepsy patient hippocampal proteomics studies. These findings will help develop hypotheses for drivers of DG hyperexcitability and could provide new insights into hyperexcitability in clinical AD.
Funding:
This project was supported by NIH T32 AG052909 (GS), NIH R01 109305 (HES), NIH R37 126529 (HES), Alz Association AARFD-22-926807 (DAG), NYS Dept of Health (HES), and many thanks to the NYU Genome Technology Center.