Investigation into transcriptomic control of dentate granule cell maturation and hyperexcitability in the apoE4 Alzheimer's Disease model - PROJECT SUMMARY Alzheimer’s disease (AD) is a pervasive neurodegenerative disease that remains largely intractable. Apolipoprotein E4 (apoE4) is the strongest genetic risk factor for late-onset AD, increasing its incidence and reducing the age of onset. Hippocampal network hyperactivity, specifically in the CA3 and dentate gyrus (DG) regions critical for memory, occurs early in prodromal AD, is aggravated by apoE4, and is predictive of future cognitive decline. CA3/DG hippocampal hyperactivity also occurs in young non-demented apoE4 carriers as well as in human apoE4 knock-in (hE4-KI) mice where apoE4 has been shown to disrupt adult-born dentate granule cell (DGCs) neurogenesis and network integration. Preliminary data from our lab revealed that DGCs in hE4-KI mice are intrinsically hyperexcitable and exhibit a progressive excitation-inhibition imbalance compared to those from hE3-KI mice. We also found two electrophysiologically distinct DGC classes: adapting DGCs (aDGCs) which possess electrophysiological characteristics of immature neurons and are hyperexcitable compared to neighboring mature non-adapting DGCs (nDGCs). aDGCs’ population increases in an age- and apoE4- dependent manner. The two DGC functional subtypes are paralleled by two DGC transcriptomic clusters uncovered by single-nucleus RNA sequencing (snRNA-seq) analysis of hippocampal neurons from hE3-KI and hE4-KI mice. Motivated by these findings and published data, I will test the central hypothesis in this proposal: aDGCs are adult-born neurons that fail to reach functional maturity. ApoE4 expression modifies adult-born DGC’s transcriptome, leading to disrupted maturation and integration process, and consequently in the increase of hyperexcitable aDGC population with aging, resulting in hippocampal hyperactivity. I will also explore potential genetic modification strategies to restore normal DGC and network physiology in hE4-KI mice for potential therapeutic development. The proposed work will harness the combinatorial electrophysiological, transcriptomic, and morphological analyses from individual cells to interrogate apoE4-related pathophysiology in DGC maturation, circuit integration, and network dysfunction (Aim 1). In addition, I will use the multimodal high- resolution data to generate and validate potential therapeutic gene targets to ameliorate apoE4-induced pathology and provide new avenues of research into the underlying pathophysiology and treatment of AD (Aim 2). The fellowship program will provide intensive training in cutting-edge technical skills such as patch clamp electrophysiology, scRNA sequencing, and CRISPRa/i methodology, as well as career development. My sponsors, Drs. Zilberter and Huang at the Gladstone Institute for Neurological Disease (GIND), will guide me through this training. With state-of-the-art facilities and equipment and comprehensive support for career development, Gladstone Institutes is an ideal place to conduct the proposed research. This rigorous and well- rounded training will enable me to attain research independence in the future.
