Faculty Bibliography

Individuals with Down syndrome (DS) are at risk for early-onset Alzheimer's disease (AD), marked by neurodegeneration in hippocampal and basal forebrain circuits. Early-life interventions offer therapeutic potential, including maternal choline supplementation (MCS). MCS improves cognitive outcomes and neuroplasticity in rodent models of neurodevelopmental and neurodegenerative disorders, yet cell-type specific molecular effects remain unknown. We investigated the effect of MCS upon the onset of septohippocampal degeneration at 6 months of age in the Ts65Dn mouse model of DS/AD. Using laser capture microdissection and single population RNA-sequencing, transcriptomic changes were profiled within hippocampal CA1 and CA3 pyramidal neurons and dentate gyrus granule cells comparing trisomic and disomic offspring. Bioinformatic analysis revealed MCS-mediated downregulation of apoptotic pathways and upregulation of cognition-related functions across all populations, alongside cell-specific responses. These findings highlight MCS as a promising strategy for modulating disease-relevant pathways in a hippocampal cell-type-specific manner during early neurodegeneration in DS/AD.

INTRODUCTION/BACKGROUND:The long-standing cholinergic hypothesis posits that cholinergic signaling is uniformly deficient in Alzheimer's disease (AD) and Down syndrome (DS). We tested the hypothesis that this deficiency occurs primarily late in disease, while early stages involve excessive cholinergic signaling, with distinct implications for memory. METHODS:Tg2576 (AD model; n = 38), Ts65Dn (DS model; n = 14), and wild-type (WT; n = 17) mice at young (3 to 4 months) and old (>14 months) ages received treatments to reduce cholinergic signaling (medial septum chemogenetic inhibition, muscarinic antagonist scopolamine) or enhance it (acetylcholinesterase inhibitor donepezil). Memory assessments used novel object recognition. RESULTS:Anticholinergic manipulations restored memory in young Tg2576 and Ts65Dn mice but impaired age-matched WT mice. Conversely, donepezil improved the memory of old Tg2576, Ts65Dn, and WT but not young Tg2576 and Ts65Dn animals. DISCUSSION/CONCLUSIONS:These findings refine and challenge the cholinergic hypothesis, revealing for the first time a functional shift from cholinergic hyperactivity driving early cognitive impairment to late-stage degeneration requiring enhancement.

Pyramidal cells (PCs) of hippocampal area CA2 exhibit increased excitability in temporal lobe epilepsy (TLE) and in mouse models of TLE. In epileptic mice, selective inhibition of CA2 PCs reduces chronic seizures. Here we asked if activating CA2 PCs increases seizures. Mice expressing Cre recombinase in CA2 PCs (Amigo2-Cre mice) were injected with the convulsant pilocarpine to induce a period of severe seizures (status epilepticus, SE), which leads to chronic seizures after 3-4 weeks (epilepsy). Epileptic mice were injected with a Cre-dependent adeno-associated virus (AAV) to express an excitatory designer receptor exclusively activated by designer drug (eDREADD; hM3Dq) in dorsal CA2 bilaterally and implanted with subdural EEG electrodes. After recovery, mice were recorded continuously using video and EEG for 6 weeks, 3 weeks with drinking water containing the eDREADD activator clozapine-N-oxide (CNO) and 3 weeks without CNO. CA2 activation with CNO caused a significant increase in seizure frequency and duration. Seizures occurred in clusters (many seizures per day over several consecutive days) and mice given water with CNO had a greater maximum number of seizures per day during a cluster compared to water without CNO. CNO had no significant effect in control mice. In naïve Amigo2-Cre mice expressing hM3Dq, pre-treatment with CNO before pilocarpine administration shortened the latency to SE and increased EEG power at the start of SE. Taken together with prior findings, the results suggest that CA2 is a control point for regulating seizures in the pilocarpine mouse model of TLE.

Individuals with Alzheimer's disease (AD) have an increased incidence of seizures, which worsen cognitive decline. Using a transgenic mouse model of AD neuropathology that exhibits spontaneous seizures, we previously found that seizure activity stimulates and accelerates depletion of the hippocampal neural stem cell (NSC) pool, which was associated with deficits in neurogenesis-dependent spatial discrimination. However, the precise molecular mechanisms that drive seizure-induced activation and depletion of NSCs are unclear. Here, using mice of both sexes, we performed RNA-sequencing on the hippocampal dentate gyrus and identified differentially-expressed regulators of neurogenesis in the Wnt signaling pathway that regulates many aspects of cell proliferation. We found that the expression of sFRP3, a Wnt signaling inhibitor, is altered in a seizure-dependent manner and might be regulated by ΔFosB, a seizure-induced transcription factor. Increasing sFRP3 expression prevented NSC depletion and improved spatial discrimination, suggesting that the loss of sFRP3 might mediate seizure-driven impairment in cognition in AD model mice, and perhaps also in AD.Significance statement There is increased incidence of seizures in individuals with Alzheimer's disease (AD), but it is unclear how seizures contribute to cognitive decline. Here, we uncover a molecular mechanism by which seizures in AD induce expression of a long-lasting transcription factor in the hippocampal dentate gyrus that suppresses expression of sFRP3, an inhibitor of neural stem cell division, accelerating the depletion of a finite pool of neural stem cells and dysregulating adult hippocampal neurogenesis. We found that restoring sFRP3 expression prevents accelerated use and depletion of neural stem cells and improves performance in an adult neurogenesis-dependent cognitive task. Our findings have implications for AD, epilepsy, and other neurological disorders that are accompanied by seizures.

BACKGROUND:Accumulated levels of mutant huntingtin protein (mHTT) and its fragments are considered contributors to the pathogenesis of Huntington's disease (HD). Stimulating autophagy may enhance clearance of mHTT and its aggregates which has been considered as a possible therapeutic strategy. However, the role and competence of the autophagy-lysosomal pathway (ALP) during HD progression in the human disease remains largely unknown. METHODS:Here, we used multiplex confocal and ultrastructural immunocytochemical analyses of ALP functional markers in relation to mHTT aggresome pathology in striatum and the less affected cortex or cerebellum of HD brains staged from Grade HD2 to HD4 by Vonsattel neuropathological criteria compared to controls. RESULTS:Immunolabeling revealed the localization of HTT/mHTT in ALP vesicular compartments labeled by autophagy-related adaptor proteins sequestosome 1 (p62/SQSTM1) and ubiquitin, and cathepsin D (CTSD) as well as HTT-positive inclusions. Although comparatively normal at HD2, neurons at later HD stages exhibited progressive enlargement and clustering of CTSD-immunoreactive autolysosomes/lysosomes and, ultrastructurally, autophagic vacuole/lipofuscin granules accumulated progressively, more prominently in striatum than cortex. These changes were accompanied by rises in levels of HTT/mHTT and p62/SQSTM1, particularly their fragments, in striatum but not in the cortex, and by increases of LAMP1 and LAMP2 RNA and LAMP1 protein. In addition, cargo-loaded autophagosomes and cathepsin-positive autolysosomes were readily observed, implying a lack of significant blockage in autophagosome formation and autophagosome-lysosome fusion. CONCLUSIONS:The findings collectively suggest that upregulated lysosomal biogenesis and preserved proteolysis maintain autophagic clearance in early-stage HD, but the observed progressive HTT build-up and AL accumulation at advanced disease stages may signify a failure in autophagy substrate clearance. These findings support the prospect that ALP stimulation applied at early disease stages, when clearance machinery is fully competent, could lead to therapeutic benefits in HD patients.

Advanced EEG technology has revealed that epileptiform activity occurs more frequently in Alzheimer's disease (AD) than previously recognized, prompting debate over the utility of EEG in AD diagnostics. Yet, unlike epilepsy, epileptiform activity is not always observed in AD, leading to skepticism. Historically, this absence has been attributed to limited recording depth or insufficient recording duration. We tested an alternative hypothesis that certain types of epileptiform activity, specifically high-frequency oscillations (HFOs, defined as 250-500Hz fast ripples), inhibit interictal spikes (IIS), which are currently used to assess hyperexcitability clinically. We recorded wideband (0.1-500Hz) hippocampal local field potentials in three AD (Tg2576, Presenilin 2^-/-, Ts65Dn Down syndrome model) and two epilepsy (intrahippocampal kainic acid, pilocarpine) mouse models during wakefulness and sleep. In both AD and epilepsy, HFOs consistently outnumbered IIS across behavioral states, age and recording contact. However, IIS and HFOs showed divergent relationships: a negative correlation between their rates was observed only in AD, in contrast to a positive correlation in epilepsy. HFOs preceded IIS at much shorter intervals in epilepsy than in AD. Co-occurrence of IIS with ripples did not differ between AD and epilepsy. These findings reveal a novel dissociation between clinically-relevant EEG biomarkers in AD and epilepsy. In AD, HFOs may inhibit IIS, which could lead to underestimation of hyperexcitability and hinder patient stratification for anti-seizure therapies. While non-invasive HFO detection remains challenging, we stress the need for wideband EEG/MEG, particularly in AD, to assess the full extent of hyperexcitability and biomarker interactions that would otherwise remain undetected.

Solid tissue-derived extracellular vesicles (ST-EVs) are extracellular vesicles (EVs) separated directly from solid tissues of both vertebrates and invertebrates. ST-EVs provide a physiologically relevant snapshot of tissue-specific molecular dynamics and can be enriched directly in situ, from tissues in their natural state, preserving the native characteristics of ST-EVs. However, their enrichment presents unique technical challenges compared to EVs derived from biofluids or cell culture media. The need for transparent reporting in ST-EV research is crucial to enhance the reproducibility, comparability, and reliability of research findings. The Solid Tissue Task Force, part of the Scientific Reproducibility Subcommittee of International Society for Extracellular Vesicles, aims to recommend reporting parameters and identify outstanding questions related to the pre-analytical and analytical handling of solid tissues, as well as ST-EV separation and characterization. These steps are essential for advancing the understanding of the biological roles of ST-EVs and their potential clinical applications.