Long term rescue of Alzheimer's deficits in vivo by one-time gene-editing of App C-terminus

Gene-editing technologies promise to create a new class of therapeutics that can achieve permanent correction with a single intervention. Besides eliminating mutant alleles in familial disease, gene-editing can also be used to favorably manipulate upstream pathophysiologic events and alter disease-course in wider patient populations, but few such feasible therapeutic avenues have been reported. Here we use CRISPR-Cas9 to edit the last exon of amyloid precursor protein ( App ), relevant for Alzheimer's disease (AD). Our strategy effectively eliminates an endocytic (YENPTY) motif at APP C-terminus, while preserving the N-terminus and compensatory APP-homologues. This manipulation favorably alters events along the amyloid-pathway - inhibiting toxic APP-β-cleavage fragments (including Aβ) and upregulating neuroprotective APP-α-cleavage products. AAV-driven editing ameliorates neuropathologic, electrophysiologic, and behavioral deficits in an AD knockin mouse model. Effects persist for many months, and no abnormalities are seen in WT mice even after germline App -editing; underlining overall efficacy and safety. Pathologic alterations in the glial-transcriptome of App -KI mice, as seen by single nuclei RNA-sequencing (sNuc-Seq), are also normalized by App C-terminus editing. Our strategy takes advantage of innate transcriptional rules that render terminal exons insensitive to nonsense-decay, and the upstream manipulation is expected to be effective for all forms of AD. These studies offer a path for a one-time disease-modifying treatment for AD.

The Intellectual Disability Risk Gene Kdm5b Regulates Long-Term Memory Consolidation in the Hippocampus

The histone lysine demethylase KDM5B is implicated in recessive intellectual disability disorders, and heterozygous, protein-truncating variants in KDM5B are associated with reduced cognitive function in the population. The KDM5 family of lysine demethylases has developmental and homeostatic functions in the brain, some of which appear to be independent of lysine demethylase activity. To determine the functions of KDM5B in hippocampus-dependent learning and memory, we first studied male and female mice homozygous for a Kdm5b Δ ARID allele that lacks demethylase activity. Kdm5b Δ ARID/ Δ ARID mice exhibited hyperactivity and long-term memory deficits in hippocampus-dependent learning tasks. The expression of immediate early, activity-dependent genes was downregulated in these mice and hyperactivated upon a learning stimulus compared with wild-type (WT) mice. A number of other learning-associated genes were also significantly dysregulated in the Kdm5b Δ ARID/ Δ ARID hippocampus. Next, we knocked down Kdm5b specifically in the adult, WT mouse hippocampus with shRNA. Kdm5b knockdown resulted in spontaneous seizures, hyperactivity, and hippocampus-dependent long-term memory and long-term potentiation deficits. These findings identify KDM5B as a critical regulator of gene expression and synaptic plasticity in the adult hippocampus and suggest that at least some of the cognitive phenotypes associated with KDM5B gene variants are caused by direct effects on memory consolidation mechanisms.

Specific exercise patterns generate an epigenetic molecular memory window that drives long-term memory formation and identifies ACVR1C as a bidirectional regulator of memory in mice

Exercise has beneficial effects on cognition throughout the lifespan. Here, we demonstrate that specific exercise patterns transform insufficient, subthreshold training into long-term memory in mice. Our findings reveal a potential molecular memory window such that subthreshold training within this window enables long-term memory formation. We performed RNA-seq on dorsal hippocampus and identify genes whose expression correlate with conditions in which exercise enables long-term memory formation. Among these genes we found Acvr1c, a member of the TGF ß family. We find that exercise, in any amount, alleviates epigenetic repression at the Acvr1c promoter during consolidation. Additionally, we find that ACVR1C can bidirectionally regulate synaptic plasticity and long-term memory in mice. Furthermore, Acvr1c expression is impaired in the aging human and mouse brain, as well as in the 5xFAD mouse model, and over-expression of Acvr1c enables learning and facilitates plasticity in mice. These data suggest that promoting ACVR1C may protect against cognitive impairment.

BIN1K358R suppresses glial response to plaques in mouse model of Alzheimer's disease

INTRODUCTION

The BIN1 coding variant rs138047593 (K358R) is linked to Late-Onset Alzheimer's Disease (LOAD) via targeted exome sequencing.

METHODS

To elucidate the functional consequences of this rare coding variant on brain amyloidosis and neuroinflammation, we generated BIN1K358R knock-in mice using CRISPR/Cas9 technology. These mice were subsequently bred with 5xFAD transgenic mice, which serve as a model for Alzheimer's pathology.

RESULTS

The presence of the BIN1K358R variant leads to increased cerebral amyloid deposition, with a dampened response of astrocytes and oligodendrocytes, but not microglia, at both the cellular and transcriptional levels. This correlates with decreased neurofilament light chain in both plasma and brain tissue. Synaptic densities are significantly increased in both wild-type and 5xFAD backgrounds homozygous for the BIN1K358R variant.

DISCUSSION

The BIN1 K358R variant modulates amyloid pathology in 5xFAD mice, attenuates the astrocytic and oligodendrocytic responses to amyloid plaques, decreases damage markers, and elevates synaptic densities.

HIGHLIGHTS

BIN1 rs138047593 (K358R) coding variant is associated with increased risk of LOAD. BIN1 K358R variant increases amyloid plaque load in 12-month-old 5xFAD mice. BIN1 K358R variant dampens astrocytic and oligodendrocytic response to plaques. BIN1 K358R variant decreases neuronal damage in 5xFAD mice. BIN1 K358R upregulates synaptic densities and modulates synaptic transmission.

Genetic diversity promotes resilience in a mouse model of Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD) is a neurodegenerative disorder with multifactorial etiology, including genetic factors that play a significant role in disease risk and resilience. However, the role of genetic diversity in preclinical AD studies has received limited attention.

METHODS

We crossed five Collaborative Cross strains with 5xFAD C57BL/6J female mice to generate F1 mice with and without the 5xFAD transgene. Amyloid plaque pathology, microglial and astrocytic responses, neurofilament light chain levels, and gene expression were assessed at various ages.

RESULTS

Genetic diversity significantly impacts AD-related pathology. Hybrid strains showed resistance to amyloid plaque formation and neuronal damage. Transcriptome diversity was maintained across ages and sexes, with observable strain-specific variations in AD-related phenotypes. Comparative gene expression analysis indicated correlations between mouse strains and human AD.

DISCUSSION

Increasing genetic diversity promotes resilience to AD-related pathogenesis, relative to an inbred C57BL/6J background, reinforcing the importance of genetic diversity in uncovering resilience in the development of AD.

HIGHLIGHTS

Genetic diversity's impact on AD in mice was explored. Diverse F1 mouse strains were used for AD study, via the Collaborative Cross. Strain-specific variations in AD pathology, glia, and transcription were found. Strains resilient to plaque formation and plasma neurofilament light chain (NfL) increases were identified. Correlations with human AD transcriptomics were observed.

Relapse to cocaine seeking is regulated by medial habenula NR4A2/NURR1 in mice

Drugs of abuse can persistently change the reward circuit in ways that contribute to relapse behavior, partly via mechanisms that regulate chromatin structure and function. Nuclear orphan receptor subfamily4 groupA member2 (NR4A2, also known as NURR1) is an important effector of histone deacetylase 3 (HDAC3)-dependent mechanisms in persistent memory processes and is highly expressed in the medial habenula (MHb), a region that regulates nicotine-associated behaviors. Here, expressing the Nr4a2 dominant negative (Nurr2c) in the MHb blocks reinstatement of cocaine seeking in mice. We use single-nucleus transcriptomics to characterize the molecular cascade following Nr4a2 manipulation, revealing changes in transcriptional networks related to addiction, neuroplasticity, and GABAergic and glutamatergic signaling. The network controlled by NR4A2 is characterized using a transcription factor regulatory network inference algorithm. These results identify the MHb as a pivotal regulator of relapse behavior and demonstrate the importance of NR4A2 as a key mechanism driving the MHb component of relapse.

C5aR1 signaling promotes region- and age-dependent synaptic pruning in models of Alzheimer's disease

INTRODUCTION

Synaptic loss is a hallmark of Alzheimer's disease (AD) that correlates with cognitive decline in AD patients. Complement-mediated synaptic pruning has been associated with this excessive loss of synapses in AD. Here, we investigated the effect of C5aR1 inhibition on microglial and astroglial synaptic pruning in two mouse models of AD.

METHODS

A combination of super-resolution and confocal and tridimensional image reconstruction was used to assess the effect of genetic ablation or pharmacological inhibition of C5aR1 on the Arctic48 and Tg2576 models of AD.

RESULTS

Genetic ablation or pharmacological inhibition of C5aR1 partially rescues excessive pre-synaptic pruning and synaptic loss in an age and region-dependent fashion in two mouse models of AD, which correlates with improved long-term potentiation (LTP).

DISCUSSION

Reduction of excessive synaptic pruning is an additional beneficial outcome of the suppression of C5a-C5aR1 signaling, further supporting its potential as an effective targeted therapy to treat AD.

HIGHLIGHTS

C5aR1 ablation restores long-term potentiation in the Arctic model of AD. C5aR1 ablation rescues region specific excessive pre-synaptic loss. C5aR1 antagonist, PMX205, rescues VGlut1 loss in the Tg2576 model of AD. C1q tagging is not sufficient to induce VGlut1 microglial ingestion. Astrocytes contribute to excessive pre-synaptic loss at late stages of the disease.

Inhibition of Cpeb3 ribozyme elevates CPEB3 protein expression and polyadenylation of its target mRNAs and enhances object location memory

A self-cleaving ribozyme that maps to an intron of the cytoplasmic polyadenylation element-binding protein 3 (Cpeb3) gene is thought to play a role in human episodic memory, but the underlying mechanisms mediating this effect are not known. We tested the activity of the murine sequence and found that the ribozyme's self-scission half-life matches the time it takes an RNA polymerase to reach the immediate downstream exon, suggesting that the ribozyme-dependent intron cleavage is tuned to co-transcriptional splicing of the Cpeb3 mRNA. Our studies also reveal that the murine ribozyme modulates maturation of its harboring mRNA in both cultured cortical neurons and the hippocampus: inhibition of the ribozyme using an antisense oligonucleotide leads to increased CPEB3 protein expression, which enhances polyadenylation and translation of localized plasticity-related target mRNAs, and subsequently strengthens hippocampal-dependent long-term memory. These findings reveal a previously unknown role for self-cleaving ribozyme activity in regulating experience-induced co-transcriptional and local translational processes required for learning and memory.

C5aR1 signaling promotes region and age dependent synaptic pruning in models of Alzheimer's Disease

INTRODUCTION

Synaptic loss is a hallmark of Alzheimer's disease (AD) that correlates with cognitive decline in AD patients. Complement-mediated synaptic pruning has been associated with this excessive loss of synapses in AD. Here, we investigated the effect of C5aR1 inhibition on microglial and astroglial synaptic pruning in two mouse models of AD.

METHODS

A combination of super-resolution and confocal and tridimensional image reconstruction was used to assess the effect of genetic ablation or pharmacological inhibition of C5aR1 on the Arctic48 and Tg2576 models of AD.

RESULTS

Genetic ablation or pharmacological inhibition of C5aR1 rescues the excessive pre-synaptic pruning and synaptic loss in an age and region dependent fashion in two mouse models of AD, which correlates with improved long-term potentiation (LTP).

DISCUSSION

Reduction of excessive synaptic pruning is an additional beneficial outcome of the suppression of C5a-C5aR1 signaling, further supporting its potential as an effective targeted therapy to treat AD.

The sparing effect of FLASH-RT on synaptic plasticity is maintained in mice with standard fractionation

Long-term potentiation (LTP) was used to gauge the impact of conventional and FLASH dose rates on synaptic transmission. Data collected from the hippocampus and medial prefrontal cortex confirmed significant inhibition of LTP after 10 fractions of 3 Gy (30 Gy total) conventional radiotherapy. Remarkably, 10x3Gy FLASH radiotherapy and unirradiated controls were identical and exhibited normal LTP.

Inhibition of CPEB3 ribozyme elevates CPEB3 protein expression and polyadenylation of its target mRNAs, and enhances object location memory

A self-cleaving ribozyme that maps to an intron of the cytoplasmic polyadenylation element binding protein 3 (CPEB3) gene is thought to play a role in human episodic memory, but the underlying mechanisms mediating this effect are not known. We tested the activity of the murine sequence and found that the ribozyme's self-scission half-life matches the time it takes an RNA polymerase to reach the immediate downstream exon, suggesting that the ribozyme-dependent intron cleavage is tuned to co-transcriptional splicing of the CPEB3 mRNA. Our studies also reveal that the murine ribozyme modulates maturation of its harboring mRNA in both cultured cortical neurons and the hippocampus: inhibition of the ribozyme using an antisense oligonucleotide leads to increased CPEB3 protein expression, which enhances polyadenylation and translation of localized plasticity-related target mRNAs, and subsequently strengthens hippocampal-dependent long-term memory. These findings reveal a previously unknown role for self-cleaving ribozyme activity in regulating experience-induced co-transcriptional and local translational processes required for learning and memory.

Elucidating the neurological mechanism of the FLASH effect in juvenile mice exposed to hypofractionated radiotherapy

BACKGROUND

Ultrahigh dose-rate radiotherapy (FLASH-RT) affords improvements in the therapeutic index by minimizing normal tissue toxicities without compromising antitumor efficacy compared to conventional dose-rate radiotherapy (CONV-RT). To investigate the translational potential of FLASH-RT to a human pediatric medulloblastoma brain tumor, we used a radiosensitive juvenile mouse model to assess adverse long-term neurological outcomes.

METHODS

Cohorts of 3-week-old male and female C57Bl/6 mice exposed to hypofractionated (2 × 10 Gy, FLASH-RT or CONV-RT) whole brain irradiation and unirradiated controls underwent behavioral testing to ascertain cognitive status four months posttreatment. Animals were sacrificed 6 months post-irradiation and tissues were analyzed for neurological and cerebrovascular decrements.

RESULTS

The neurological impact of FLASH-RT was analyzed over a 6-month follow-up. FLASH-RT ameliorated neurocognitive decrements induced by CONV-RT and preserved synaptic plasticity and integrity at the electrophysiological (long-term potentiation), molecular (synaptophysin), and structural (Bassoon/Homer-1 bouton) levels in multiple brain regions. The benefits of FLASH-RT were also linked to reduced neuroinflammation (activated microglia) and the preservation of the cerebrovascular structure, by maintaining aquaporin-4 levels and minimizing microglia colocalized to vessels.

CONCLUSIONS

Hypofractionated FLASH-RT affords significant and long-term normal tissue protection in the radiosensitive juvenile mouse brain when compared to CONV-RT. The capability of FLASH-RT to preserve critical cognitive outcomes and electrophysiological properties over 6-months is noteworthy and highlights its potential for resolving long-standing complications faced by pediatric brain tumor survivors. While care must be exercised before clinical translation is realized, present findings document the marked benefits of FLASH-RT that extend from synapse to cognition and the microvasculature.

Uncovering the Protective Neurologic Mechanisms of Hypofractionated FLASH Radiotherapy

Implementation of ultra-high dose-rate FLASH radiotherapy (FLASH-RT) is rapidly gaining traction as a unique cancer treatment modality able to dramatically minimize normal tissue toxicity while maintaining antitumor efficacy compared with standard-of-care radiotherapy at conventional dose rate (CONV-RT). The resultant improvements in the therapeutic index have sparked intense investigations in pursuit of the underlying mechanisms. As a preamble to clinical translation, we exposed non-tumor-bearing male and female mice to hypofractionated (3 × 10 Gy) whole brain FLASH- and CONV-RT to evaluate differential neurologic responses using a comprehensive panel of functional and molecular outcomes over a 6-month follow-up. In each instance, extensive and rigorous behavioral testing showed FLASH-RT to preserve cognitive indices of learning and memory that corresponded to a similar protection of synaptic plasticity as measured by long-term potentiation (LTP). These beneficial functional outcomes were not found after CONV-RT and were linked to a preservation of synaptic integrity at the molecular (synaptophysin) level and to reductions in neuroinflammation (CD68+ microglia) throughout specific brain regions known to be engaged by our selected cognitive tasks (hippocampus, medial prefrontal cortex). Ultrastructural changes in presynaptic/postsynaptic bouton (Bassoon/Homer-1 puncta) within these same regions of the brain were not found to differ in response to dose rate. With this clinically relevant dosing regimen, we provide a mechanistic blueprint from synapse to cognition detailing how FLASH-RT reduces normal tissue complications in the irradiated brain.

Significance

Functional preservation of cognition and LTP after hypofractionated FLASH-RT are linked to a protection of synaptic integrity and a reduction in neuroinflammation over protracted after irradiation times.

Machine learned interatomic potential for dispersion strengthened plasma facing components

Tungsten (W) is a material of choice for the divertor material due to its high melting temperature, thermal conductivity, and sputtering threshold. However, W has a very high brittle-to-ductile transition temperature, and at fusion reactor temperatures (≥1000 K), it may undergo recrystallization and grain growth. Dispersion-strengthening W with zirconium carbide (ZrC) can improve ductility and limit grain growth, but much of the effects of the dispersoids on microstructural evolution and thermomechanical properties at high temperatures are still unknown. We present a machine learned Spectral Neighbor Analysis Potential for W-ZrC that can now be used to study these materials. In order to construct a potential suitable for large-scale atomistic simulations at fusion reactor temperatures, it is necessary to train on ab initio data generated for a diverse set of structures, chemical environments, and temperatures. Further accuracy and stability tests of the potential were achieved using objective functions for both material properties and high temperature stability. Validation of lattice parameters, surface energies, bulk moduli, and thermal expansion is confirmed on the optimized potential. Tensile tests of W/ZrC bicrystals show that although the W(110)-ZrC(111) C-terminated bicrystal has the highest ultimate tensile strength (UTS) at room temperature, observed strength decreases with increasing temperature. At 2500 K, the terminating C layer diffuses into the W, resulting in a weaker W-Zr interface. Meanwhile, the W(110)-ZrC(111) Zr-terminated bicrystal has the highest UTS at 2500 K.

A Trem2R47H mouse model without cryptic splicing drives age- and disease-dependent tissue damage and synaptic loss in response to plaques

BACKGROUND

The TREM2 R47H variant is one of the strongest genetic risk factors for late-onset Alzheimer's Disease (AD). Unfortunately, many current Trem2 R47H mouse models are associated with cryptic mRNA splicing of the mutant allele that produces a confounding reduction in protein product. To overcome this issue, we developed the Trem2R47H NSS (Normal Splice Site) mouse model in which the Trem2 allele is expressed at a similar level to the wild-type Trem2 allele without evidence of cryptic splicing products.

METHODS

Trem2R47H NSS mice were treated with the demyelinating agent cuprizone, or crossed with the 5xFAD mouse model of amyloidosis, to explore the impact of the TREM2 R47H variant on inflammatory responses to demyelination, plaque development, and the brain's response to plaques.

RESULTS

Trem2R47H NSS mice display an appropriate inflammatory response to cuprizone challenge, and do not recapitulate the null allele in terms of impeded inflammatory responses to demyelination. Utilizing the 5xFAD mouse model, we report age- and disease-dependent changes in Trem2R47H NSS mice in response to development of AD-like pathology. At an early (4-month-old) disease stage, hemizygous 5xFAD/homozygous Trem2R47H NSS (5xFAD/Trem2R47H NSS) mice have reduced size and number of microglia that display impaired interaction with plaques compared to microglia in age-matched 5xFAD hemizygous controls. This is associated with a suppressed inflammatory response but increased dystrophic neurites and axonal damage as measured by plasma neurofilament light chain (NfL) level. Homozygosity for Trem2R47H NSS suppressed LTP deficits and loss of presynaptic puncta caused by the 5xFAD transgene array in 4-month-old mice. At a more advanced (12-month-old) disease stage 5xFAD/Trem2R47H NSS mice no longer display impaired plaque-microglia interaction or suppressed inflammatory gene expression, although NfL levels remain elevated, and a unique interferon-related gene expression signature is seen. Twelve-month old Trem2R47H NSS mice also display LTP deficits and postsynaptic loss.

CONCLUSIONS

The Trem2R47H NSS mouse is a valuable model that can be used to investigate age-dependent effects of the AD-risk R47H mutation on TREM2 and microglial function including its effects on plaque development, microglial-plaque interaction, production of a unique interferon signature and associated tissue damage.

Galactic cosmic radiation exposure causes multifaceted neurocognitive impairments

Technological advancements have facilitated the implementation of realistic, terrestrial-based complex 33-beam galactic cosmic radiation simulations (GCR Sim) to now probe central nervous system functionality. This work expands considerably on prior, simplified GCR simulations, yielding new insights into responses of male and female mice exposed to 40-50 cGy acute or chronic radiations relevant to deep space travel. Results of the object in updated location task suggested that exposure to acute or chronic GCR Sim induced persistent impairments in hippocampus-dependent memory formation and reconsolidation in female mice that did not manifest robustly in irradiated male mice. Interestingly, irradiated male mice, but not females, were impaired in novel object recognition and chronically irradiated males exhibited increased aggressive behavior on the tube dominance test. Electrophysiology studies used to evaluate synaptic plasticity in the hippocampal CA1 region revealed significant reductions in long-term potentiation after each irradiation paradigm in both sexes. Interestingly, network-level disruptions did not translate to altered intrinsic electrophysiological properties of CA1 pyramidal cells, whereas acute exposures caused modest drops in excitatory synaptic signaling in males. Ultrastructural analyses of CA1 synapses found smaller postsynaptic densities in larger spines of chronically exposed mice compared to controls and acutely exposed mice. Myelination was also affected by GCR Sim with acutely exposed mice exhibiting an increase in the percent of myelinated axons; however, the myelin sheathes on small calibur (< 0.3 mm) and larger (> 0.5 mm) axons were thinner when compared to controls. Present findings might have been predicted based on previous studies using single and mixed beam exposures and provide further evidence that space-relevant radiation exposures disrupt critical cognitive processes and underlying neuronal network-level plasticity, albeit not to the extent that might have been previously predicted.

Temporal endurance of exercise-induced benefits on hippocampus-dependent memory and synaptic plasticity in female mice

Exercise facilitates hippocampal neurogenesis and neuroplasticity that in turn, promotes cognitive function. Our previous studies have demonstrated that in male mice, voluntary exercise enables hippocampus-dependent learning in conditions that are normally subthreshold for long-term memory formation in sedentary animals. Such cognitive enhancement can be maintained long after exercise has ceased and can be re-engaged by a subsequent subthreshold exercise session, suggesting exercise-induced benefits are temporally dynamic. In females, the extent to which the benefits of exercise can be maintained and the mechanisms underlying this maintenance have yet to be defined. Here, we examined the exercise parameters required to initiate and maintain the benefits of exercise in female C57BL/6J mice. Using a subthreshold version of the hippocampus-dependent task called object-location memory (OLM) task, we show that 14d of voluntary exercise enables learning under subthreshold acquisition conditions in female mice. Following the initial exercise, a 7d sedentary delay results in diminished performance, which can be re-facilitated when animals receive 2d of reactivating exercise following the sedentary delay. Assessment of estrous cycle reveals enhanced wheel running activity during the estrus phase relative to the diestrus phase, whereas estrous phase on training or test had no effect on OLM performance. Utilizing the same exercise parameters, we demonstrate that 14d of exercise enhances long-term potentiation (LTP) in the CA1 region of the hippocampus, an effect that persists throughout the sedentary delay and following the reactivating exercise session. Previous studies have proposed exercise-induced BDNF upregulation as the mechanism underlying exercise-mediated benefits on synaptic plasticity and cognition. However, our assessment of hippocampal Bdnf mRNA expression following memory retrieval reveals no difference between exercise conditions and control, suggesting that persistent Bdnf upregulation may not be required for maintenance of exercise-induced benefits. Together, our data indicate that 14d of voluntary exercise can initiate long-lasting benefits on neuroplasticity and cognitive function in female mice, establishing the first evidence on the temporal endurance of exercise-induced benefits in females.

Targeting acetyl-CoA metabolism attenuates the formation of fear memories through reduced activity-dependent histone acetylation

Histone acetylation is a key component in the consolidation of long-term fear memories. Histone acetylation is fueled by acetyl-coenzyme A (acetyl-CoA), and recently, nuclear-localized metabolic enzymes that produce this metabolite have emerged as direct and local regulators of chromatin. In particular, acetyl-CoA synthetase 2 (ACSS2) mediates histone acetylation in the mouse hippocampus. However, whether ACSS2 regulates long-term fear memory remains to be determined. Here, we show that Acss2 knockout is well tolerated in mice, yet the Acss2-null mouse exhibits reduced acquisition of long-term fear memory. Loss of Acss2 leads to reductions in both histone acetylation and expression of critical learning and memory-related genes in the dorsal hippocampus, specifically following fear conditioning. Furthermore, systemic administration of blood-brain barrier-permeable Acss2 inhibitors during the consolidation window reduces fear-memory formation in mice and rats and reduces anxiety in a predator-scent stress paradigm. Our findings suggest that nuclear acetyl-CoA metabolism via ACSS2 plays a critical, previously unappreciated, role in the formation of fear memories.

Systematic Phenotyping and Characterization of the 3xTg-AD Mouse Model of Alzheimer’s Disease

Animal models of disease are valuable resources for investigating pathogenic mechanisms and potential therapeutic interventions. However, for complex disorders such as Alzheimer’s disease (AD), the generation and availability of innumerous distinct animal models present unique challenges to AD researchers and hinder the success of useful therapies. Here, we conducted an in-depth analysis of the 3xTg-AD mouse model of AD across its lifespan to better inform the field of the various pathologies that appear at specific ages, and comment on drift that has occurred in the development of pathology in this line since its development 20 years ago. This modern characterization of the 3xTg-AD model includes an assessment of impairments in long-term potentiation followed by quantification of amyloid beta (Aβ) plaque burden and neurofibrillary tau tangles, biochemical levels of Aβ and tau protein, and neuropathological markers such as gliosis and accumulation of dystrophic neurites. We also present a novel comparison of the 3xTg-AD model with the 5xFAD model using the same deep-phenotyping characterization pipeline and show plasma NfL is strongly driven by plaque burden. The results from these analyses are freely available via the AD Knowledge Portal (https://modeladexplorer.org/). Our work demonstrates the utility of a characterization pipeline that generates robust and standardized information relevant to investigating and comparing disease etiologies of current and future models of AD.

Exercise Reduces H3K9me3 and Regulates Brain Derived Neurotrophic Factor and GABRA2 in an Age Dependent Manner

Exercise improves cognition in the aging brain and is a key regulator of neuronal plasticity genes such as BDNF. However, the mechanism by which exercise modifies gene expression continues to be explored. The repressive histone modification H3K9me3 has been shown to impair cognition, reduce synaptic density and decrease BDNF in aged but not young mice. Treatment with ETP69, a selective inhibitor of H3K9me3's catalyzing enzyme (SUV39H1), restores synapses, BDNF and cognitive performance. GABA receptor expression, which modulates BDNF secretion, is also modulated by exercise and H3K9me3. In this study, we examined if exercise and ETP69 regulated neuronal plasticity genes by reducing H3K9me3 at their promoter regions. We further determined the effect of age on H3K9me3 promoter binding and neuronal plasticity gene expression. Exercise and ETP69 decreased H3K9me3 at BDNF promoter VI in aged mice, corresponding with an increase in BDNF VI expression with ETP69. Exercise increased GABRA2 in aged mice while increasing BDNF 1 in young mice, and both exercise and ETP69 reduced GABRA2 in young mice. Overall, H3K9me3 repression at BDNF and GABA receptor promoters decreased with age. Our findings suggest that exercise and SUV39H1 inhibition differentially modulate BDNF and GABRA2 expression in an age dependent manner.

Examining age-dependent DNA methylation patterns and gene expression in the male and female mouse hippocampus

DNA methylation is a well-characterized epigenetic modification involved in numerous molecular and cellular functions. Methylation patterns have also been associated with aging mechanisms. However, how DNA methylation patterns change within key brain regions involved in memory formation in an age- and sex-specific manner remains unclear. Here, we performed reduced representation bisulfite sequencing (RRBS) from mouse dorsal hippocampus - which is necessary for the formation and consolidation of specific types of memories - in young and aging mice of both sexes. Overall, our findings demonstrate that methylation levels within the dorsal hippocampus are divergent between sexes during aging in genomic features correlating to mRNA functionality, transcription factor binding sites, and gene regulatory elements. These results define age-related changes in the methylome across genomic features and build a foundation for investigating potential target genes regulated by DNA methylation in an age- and sex-specific manner.

Systematic phenotyping and characterization of the 5xFAD mouse model of Alzheimer's disease

Mouse models of human diseases are invaluable tools for studying pathogenic mechanisms and testing interventions and therapeutics. For disorders such as Alzheimer's disease in which numerous models are being generated, a challenging first step is to identify the most appropriate model and age to effectively evaluate new therapeutic approaches. Here we conducted a detailed phenotypic characterization of the 5xFAD model on a congenic C57BL/6 J strain background, across its lifespan - including a seldomly analyzed 18-month old time point to provide temporally correlated phenotyping of this model and a template for characterization of new models of LOAD as they are generated. This comprehensive analysis included quantification of plaque burden, Aβ biochemical levels, and neuropathology, neurophysiological measurements and behavioral and cognitive assessments, and evaluation of microglia, astrocytes, and neurons. Analysis of transcriptional changes was conducted using bulk-tissue generated RNA-seq data from microdissected cortices and hippocampi as a function of aging, which can be explored at the MODEL-AD Explorer and AD Knowledge Portal. This deep-phenotyping pipeline identified novel aspects of age-related pathology in the 5xFAD model.

Cocaine induces paradigm-specific changes to the transcriptome within the ventral tegmental area

During the initial stages of drug use, cocaine-induced neuroadaptations within the ventral tegmental area (VTA) are critical for drug-associated cue learning and drug reinforcement processes. These neuroadaptations occur, in part, from alterations to the transcriptome. Although cocaine-induced transcriptional mechanisms within the VTA have been examined, various regimens and paradigms have been employed to examine candidate target genes. In order to identify key genes and biological processes regulating cocaine-induced processes, we employed genome-wide RNA-sequencing to analyze transcriptional profiles within the VTA from male mice that underwent one of four commonly used paradigms: acute home cage injections of cocaine, chronic home cage injections of cocaine, cocaine-conditioning, or intravenous-self administration of cocaine. We found that cocaine alters distinct sets of VTA genes within each exposure paradigm. Using behavioral measures from cocaine self-administering mice, we also found several genes whose expression patterns corelate with cocaine intake. In addition to overall gene expression levels, we identified several predicted upstream regulators of cocaine-induced transcription shared across all paradigms. Although distinct gene sets were altered across cocaine exposure paradigms, we found, from Gene Ontology (GO) term analysis, that biological processes important for energy regulation and synaptic plasticity were affected across all cocaine paradigms. Coexpression analysis also identified gene networks that are altered by cocaine. These data indicate that cocaine alters networks enriched with glial cell markers of the VTA that are involved in gene regulation and synaptic processes. Our analyses demonstrate that transcriptional changes within the VTA depend on the route, dose and context of cocaine exposure, and highlight several biological processes affected by cocaine. Overall, these findings provide a unique resource of gene expression data for future studies examining novel cocaine gene targets that regulate drug-associated behaviors.

Acute, Low-Dose Neutron Exposures Adversely Impact Central Nervous System Function

A recognized risk of long-duration space travel arises from the elevated exposure astronauts face from galactic cosmic radiation (GCR), which is composed of a diverse array of energetic particles. There is now abundant evidence that exposures to many different charged particle GCR components within acute time frames are sufficient to induce central nervous system deficits that span from the molecular to the whole animal behavioral scale. Enhanced spacecraft shielding can lessen exposures to charged particle GCR components, but may conversely elevate neutron radiation levels. We previously observed that space-relevant neutron radiation doses, chronically delivered at dose-rates expected during planned human exploratory missions, can disrupt hippocampal neuronal excitability, perturb network long-term potentiation and negatively impact cognitive behavior. We have now determined that acute exposures to similar low doses (18 cGy) of neutron radiation can also lead to suppressed hippocampal synaptic signaling, as well as decreased learning and memory performance in male mice. Our results demonstrate that similar nervous system hazards arise from neutron irradiation regardless of the exposure time course. While not always in an identical manner, neutron irradiation disrupts many of the same central nervous system elements as acute charged particle GCR exposures. The risks arising from neutron irradiation are therefore important to consider when determining the overall hazards astronauts will face from the space radiation environment.