Mouse Brain Research Articles

Mitochondrial Treatment Improves Cognitive Impairment Induced by Lipopolysaccharide in Mice.

Neuroinflammation has been proven to drive cognitive impairment associated with neurodegenerative diseases. It has been demonstrated that mitochondrial dysfunction is associated with cognitive impairment caused by neuroinflammation. We hypothesized that the transfer of exogenous mitochondria may be beneficial to the therapy of cognitive impairment induced by neuroinflammation. In the study, the effect of exogenous mitochondria on cognitive impairment induced by neuroinflammation was investigated. The results showed that mitochondrial treatment ameliorated the cognitive performance of lipopolysaccharide (LPS)-treated mice. Additionally, mitochondrial therapy attenuated neuronal injury and down-regulated the expression of proinflammatory cytokines, including TNF-α and pro- and cleaved IL-1β, and the expression of Iba-1 and GFAP in the hippocampus and cortex of LPS-treated mice. Additionally, mitochondrial treatment increased mitochondrial ΔΨm, ATP level, and SOD activity and attenuated MDA level and ROS production in the brains of LPS-treated mice. The study reports the beneficial effect of mitochondrial treatment against cognitive impairment of LPS-treated mice, thereby providing a potential strategy for the treatment of cognitive impairment caused by neuroinflammation.

OsO2as the Contrast-Generating Chemical Species of Osmium-Stained Biological Tissues in Electron Microscopy.

Electron imaging of biological samples stained with heavy metals has enabled visualization of subcellular structures critical in chemical-, structural-, and neuro-biology. In particular, osmium tetroxide OsO4 has been widely adopted for selective lipid imaging. Despite the ubiquity of its use, the osmium speciation in lipid membranes and the process for contrast generation in electron microscopy (EM) have continued to be open questions, limiting efforts to improve staining protocols and therefore high-resolution nanoscale imaging of biological samples. Following our recent success using photoemission electron microscopy (PEEM) to image mouse brain tissues with synaptic resolution, we have used PEEM to determine the nanoscale electronic structure of Os-stained biological samples. Os(IV), in the form of OsO2, generates nanoaggregates in lipid membranes, leading to a strong spatial variation in the electronic structure and electron density of states. OsO2has a metallic electronic structure that drastically increases the electron density of states near the Fermi level. Depositing metallic OsO2 in lipid membranes allows for strongly enhanced EM signals and conductivity of biological materials. The identification of the chemical species and understanding of the membrane contrast mechanism of Os-stained biological specimens provides a new opportunity for the development of staining protocols for high-resolution, high-contrast EM imaging.

Effects of gestational hypothyroidism on mouse brain development: Gabaergic systems and oxidative stress

Hormonal imbalance during pregnancy is a risk factor for neuropsychiatric impairment in the offspring. It has been suggested that hypothyroidism leads to dysfunction of cortical GABAergic interneurons and inhibitory system development that in turn underlies impairment of the central nervous system. Here we investigated how gestational hypothyroidism affected offspring GABAergic system development as well as redox regulation parameters, because of previous links identified between the two. Experimental Gestational Hypothyroidism (EGH) was induced in CD-1 mice with 0.02% methimazole (MMI) in drinking water from embryonic day 9 (E9) until tissue collection at embryonic day 14 (E14) or E18. We examined GABAergic cell distribution and inhibitory system development gene expression as well as redox relevant gene expression and direct measures across all embryos regardless of sex. Intrauterine restriction of maternal thyroid hormones significantly impacted both of these outcomes in brain, as well as altering redox regulation in the placenta. GAD67+ neuronal migration was reduced, accompanied by a disruption in gene expression influencing GABAergic cell migration and cortical inhibitory neural system development. EGH also altered embryonic brain gene expression of Gpx1, Nfe2l2, Cat levels in the dorsal E14 brains. Additionally, EGH resulted in elevated TBARS, Gpx1 and Nfe2l2 in the ventral E18 brains. Furthermore, EGH downregulated placental Gpx1 gene expression at E14 and increased protein oxidation at E18. These findings support the hypothesis that sufficient maternal thyroid hormone supply to the fetus influences central nervous system development, including processes of GABAergic system development and redox equilibrium.

Multiple Administration of Dexamethasone Possesses a Deferred Long-Term Effect to Glycosylated Components of Mouse Brain.

Glucocorticoids are used during glioblastoma treatment to prevent the cerebral edema effect surrounding normal brain tissue. The aim of our study was to investigate the long-term effects of multiple administrations of glucocorticoids onto the glycosylated components (proteoglycans and glycosaminoglycans) of normal brain extracellular matrix and the glucocorticoid receptor (GR, Nr3c1) in an experimental model in vivo. Two-month-old male C57Bl/6 mice (n = 90) were injected intraperitoneally with various doses of dexamethasone (DXM) (1; 2.5 mg/kg) for 10 days. The mRNA levels of the GR, proteoglycans core proteins, and heparan sulfate metabolism-involved genes were determined at the 15th, 30th, 60th, and 90th days by a real-time RT-PCR. The glycosaminoglycans content was studied using dot blot and staining with Alcian blue. A DXM treatment increased total GAG content (2-fold), whereas the content of highly sulfated glycosaminoglycans decreased (1.5-2-fold). The mRNA level of the heparan sulfate metabolism-involved gene Hs3St2 increased 5-fold, the mRNA level of Hs6St2 increased6-7-fold, and the mRNA level of proteoglycan aggrecan increased 2-fold. A correlation analysis revealed an association between the mRNA level of the GR and the mRNA level of 8 of the 14 proteoglycans-coding and 4 of the 13 heparan sulfate metabolism-involved genes supporting GR involvement in the DXM regulation of the expression of these genes. In summary, multiple DXM administrations led to an increase in the total GAG content and reorganized the brain extracellular matrix in terms of its glycosylation pattern.

Mass Spectrometry Imaging Combined with Sparse Autoencoder Method Reveals Altered Phosphorylcholine Distribution in Imipramine Treated Wild-Type Mice Brains.

Mass spectrometry imaging (MSI) is essential for visualizing drug distribution, metabolites, and significant biomolecules in pharmacokinetic studies. This study mainly focuses on imipramine, a tricyclic antidepressant that affects endogenous metabolite concentrations. The aim was to use atmospheric pressure matrix-assisted laser desorption/ionization (AP-MALDI)-MSI combined with different dimensionality reduction methods to examine the distribution and impact of imipramine on endogenous metabolites in the brains of treated wild-type mice. Brain sections from both control and imipramine-treated mice underwent AP-MALDI-MSI. Dimensionality reduction methods, including principal component analysis, multivariate curve resolution, and sparse autoencoder (SAE), were employed to extract valuable information from the MSI data. Only the SAE method identified phosphorylcholine (ChoP) as a potential marker distinguishing between the control and treated mice brains. Additionally, a significant decrease in ChoP accumulation was observed in the cerebellum, hypothalamus, thalamus, midbrain, caudate putamen, and striatum ventral regions of the treated mice brains. The application of dimensionality reduction methods, particularly the SAE method, to the AP-MALDI-MSI data is a novel approach for peak selection in AP-MALDI-MSI data analysis. This study revealed a significant decrease in ChoP in imipramine-treated mice brains.

Mice deficient in the phosphatase activity of sEH show decreased levels of the endocannabinoid 2-AG in the olfactory bulb and depressive-like behavior.

Soluble epoxide hydrolase (sEH) is a bifunctional enzyme that has epoxide hydrolase activity and phosphatase activity. Our earlier study revealed that lysophosphatidic acids are a substrate of the phosphatase activity of sEH invitro, but its physiological function remained unknown. Herein, we used the CRISPR/Cas9 system and i-GONAD method to generate mice that are deficient in sEH phosphatase activity. In the mouse brain, sEH was highly expressed in the olfactory bulb. Deletion of the sEH phosphatase activity resulted in decreased levels of the endocannabinoid 2-arachidonoyl glycerol (2-AG), which is a dephosphorylated form of 2-arachidonoyl-lysophosphatidic acid in the olfactory bulb. The sEH-deficient mice showed depressive-like behavior. These results indicate that sEH can regulate the production of 2-AG and brain function in vivo.

High-resolution diffusion magnetic resonance imaging and spatial-transcriptomic in developing mouse brain

Brain development is a highly complex process regulated by numerous genes at the molecular and cellular levels. Brain tissue exhibits serial microstructural changes during the development process. High-resolution diffusion magnetic resonance imaging (dMRI) affords a unique opportunity to probe these changes in the developing brain non-destructively. In this study, we acquired multi-shell dMRI datasets at 32 µm isotropic resolution to investigate the tissue microstructure alterations, which we believe to be the highest spatial resolution dMRI datasets obtained for postnatal mouse brains. We adapted the Allen Developing Mouse Brain Atlas (ADMBA) to integrate quantitative MRI metrics and spatial transcriptomics. Diffusion tensor imaging (DTI), diffusion kurtosis imaging (DKI), and neurite orientation dispersion and density imaging (NODDI) metrics were used to quantify brain development at different postnatal days. We demonstrated that the differential evolutions of fiber orientation distributions contribute to the distinct development patterns in white matter (WM) and gray matter (GM). Furthermore, the genes enriched in the nervous system that regulate brain structure and function were expressed in spatial correlation with age-matched dMRI. This study is the first one providing high-resolution dMRI, including DTI, DKI, and NODDI models, to trace mouse brain microstructural changes in WM and GM during postnatal development. This study also highlighted the genotype-phenotype correlation of spatial transcriptomics and dMRI, which may improve our understanding of brain microstructure changes at the molecular level.

Benzoxazole-derivatives enhance progranulin expression and reverse the aberrant lysosomal proteome caused by GRN haploinsufficiency

Heterozygous loss-of-function mutations in the GRN gene are a major cause of hereditary frontotemporal dementia. The mechanisms linking frontotemporal dementia pathogenesis to progranulin deficiency are not well understood, and there is currently no treatment. Our strategy to prevent the onset and progression of frontotemporal dementia in patients with GRN mutations is to utilize small molecule positive regulators of GRN expression to boost progranulin levels from the remaining functional GRN allele, thus restoring progranulin levels back to normal within the brain. This work describes a series of blood-brain-barrier-penetrant small molecules which significantly increase progranulin protein levels in human cellular models, correct progranulin protein deficiency in Grn+/− mouse brains, and reverse lysosomal proteome aberrations, a phenotypic hallmark of frontotemporal dementia, more efficiently than the previously described small molecule suberoylanilide hydroxamic acid. These molecules will allow further elucidation of the cellular functions of progranulin and its role in frontotemporal dementia and will also serve as lead structures for further drug development.

Adult-onset deletion of ATP13A2 in mice induces progressive nigrostriatal pathway dopaminergic degeneration and lysosomal abnormalities

Although most cases of Parkinson’s disease (PD) are sporadic, mutations in over 20 genes are known to cause heritable forms of the disease. Recessive loss-of-function mutations in ATP13A2, a lysosomal transmembrane P5B-type ATPase and polyamine exporter, can cause early-onset familial PD. Familial ATP13A2 mutations are also linked to related neurodegenerative diseases, including Kufor-Rakeb syndrome, hereditary spastic paraplegias, neuronal ceroid lipofuscinosis, and amyotrophic lateral sclerosis. Despite the severe effects of ATP13A2 mutations in humans, ATP13A2 knockout (KO) mice fail to exhibit neurodegeneration even at advanced ages, making it challenging to study the neuropathological effects of ATP13A2 loss in vivo. Germline deletion of ATP13A2 in rodents may trigger the upregulation of compensatory pathways during embryonic development that mask the full neurotoxic effects of ATP13A2 loss in the brain. To explore this idea, we selectively deleted ATP13A2 in the adult mouse brain by the unilateral delivery of an AAV-Cre vector into the substantia nigra of young adult mice carrying conditional loxP-flanked ATP13A2 KO alleles. We observe a progressive loss of striatal dopaminergic nerve terminals at 3 and 10 months after AAV-Cre delivery. Cre-injected mice also exhibit robust dopaminergic neuronal degeneration in the substantia nigra at 10 months. Adult-onset ATP13A2 KO also recreates many of the phenotypes observed in aged germline ATP13A2 KO mice, including lysosomal abnormalities, p62-positive inclusions, and neuroinflammation. Our study demonstrates that the adult-onset homozygous deletion of ATP13A2 in the nigrostriatal pathway produces robust and progressive dopaminergic neurodegeneration that serves as a useful in vivo model of ATP13A2-related neurodegenerative diseases.

Ex vivo liquid core fiber photometry with high-resolution 3D printing

High resolution 3D printing emerges as an alternative to microfabrication due to its fine resolution along with one-step manufacturing. Thus, it is broadly used in many fields, such as biological and chemical applications. We introduce such a technique to the design of the optofluidic probe by integrating optics and microfluidics as an ex vivo liquid core fiber photometry. We build the optofluidic probes with various T-shapes and conduct the transmission measurements and the ray tracing simulations, where the results are comparable. Through the transmission and fluorescence measurements, we obtain optimized curl T-shape dimensions of 524 µm wide, ∼50 µm thick, and 350 µm long with longitudinal spaces between them of 260 um. Furthermore, a heightened level of complexity in structure, characterized by a feature size of 25 µm, is attained through the improvement process. We conclude the feasibility of this optofluidic system with two applications: the in vivo-like setting consisting of thyroid biopsy training phantom and human plasma and the ex vivo-like setting consisting of the mice brain slices stained with wheat germ agglutinin (WGA). This prototype is an important step of establishing a 3D printing optofluidic applications for various in vivo research.

Spatiotemporal transcriptomic profiling and modeling of mouse brain at single-cell resolution reveals cell proximity effects of aging and rejuvenation.

Old age is associated with a decline in cognitive function and an increase in neurodegenerative disease risk 1 . Brain aging is complex and accompanied by many cellular changes 2-20 . However, the influence that aged cells have on neighboring cells and how this contributes to tissue decline is unknown. More generally, the tools to systematically address this question in aging tissues have not yet been developed. Here, we generate spatiotemporal data at single-cell resolution for the mouse brain across lifespan, and we develop the first machine learning models based on spatial transcriptomics ('spatial aging clocks') to reveal cell proximity effects during brain aging and rejuvenation. We collect a single-cell spatial transcriptomics brain atlas of 4.2 million cells from 20 distinct ages and across two rejuvenating interventions-exercise and partial reprogramming. We identify spatial and cell type-specific transcriptomic fingerprints of aging, rejuvenation, and disease, including for rare cell types. Using spatial aging clocks and deep learning models, we find that T cells, which infiltrate the brain with age, have a striking pro-aging proximity effect on neighboring cells. Surprisingly, neural stem cells have a strong pro-rejuvenating effect on neighboring cells. By developing computational tools to identify mediators of these proximity effects, we find that pro-aging T cells trigger a local inflammatory response likely via interferon-γ whereas pro-rejuvenating neural stem cells impact the metabolism of neighboring cells possibly via growth factors (e.g. vascular endothelial growth factor) and extracellular vesicles, and we experimentally validate some of these predictions. These results suggest that rare cells can have a drastic influence on their neighbors and could be targeted to counter tissue aging. We anticipate that these spatial aging clocks will not only allow scalable assessment of the efficacy of interventions for aging and disease but also represent a new tool for studying cell-cell interactions in many spatial contexts.

Expansion-assisted selective plane illumination microscopy for nanoscale imaging of centimeter-scale tissues.

Recent advances in tissue processing, labeling, and fluorescence microscopy are providing unprecedented views of the structure of cells and tissues at sub-diffraction resolutions and near single molecule sensitivity, driving discoveries in diverse fields of biology, including neuroscience. Biological tissue is organized over scales of nanometers to centimeters. Harnessing molecular imaging across intact, three-dimensional samples on this scale requires new types of microscopes with larger fields of view and working distance, as well as higher throughput. We present a new expansion-assisted selective plane illumination microscope (ExA-SPIM) with aberration-free 1×1×3 μm optical resolution over a large field of view (10.6×8.0 mm 2 ) and working distance (35 mm) at speeds up to 946 megavoxels/sec. Combined with new tissue clearing and expansion methods, the microscope allows imaging centimeter-scale samples with 250×250×750 nm optical resolution (4× expansion), including entire mouse brains, with high contrast and without sectioning. We illustrate ExA-SPIM by reconstructing individual neurons across the mouse brain, imaging cortico-spinal neurons in the macaque motor cortex, and visualizing axons in human white matter.

RAB12-LRRK2 Complex Suppresses Primary Ciliogenesis and Regulates Centrosome Homeostasis in Astrocytes.

Leucine-rich repeat kinase 2 (LRRK2) phosphorylates a subset of RAB GTPases, and the phosphorylation levels are elevated by Parkinson's disease (PD)-linked mutations of LRRK2. However, the precise function of the specific RAB GTPase targeted by LRRK2 signaling in the brain remains to be elucidated. Here, we identify RAB12 as a robust LRRK2 substrate in the mouse brains through phosphoproteomics profiling and solve the structure of RAB12-LRRK2 protein complex through Cryo-EM analysis. Mechanistically, RAB12 cooperates with LRRK2 to inhibit primary ciliogenesis and regulate centrosome homeostasis in astrocytes through enhancing the phosphorylation of RAB10 and recruiting Rab interacting lysosomal protein like 1 (RILPL1), while the functions of RAB12 require a direct interaction with LRRK2 and LRRK2 kinase activity. Furthermore, the ciliary deficits and centrosome alteration caused by the PD-linked LRRK2-G2019S mutation are prevented by the deletion of Rab12 in astrocytes. Thus, our study reveals a physiological function of the RAB12-LRRK2 complex in regulating ciliogenesis and centrosome homeostasis. The RAB12-LRRK2 structure offers a guidance in the therapeutic development of PD by targeting the RAB12-LRRK2 interaction.

CCN1 Is a Therapeutic Target for Reperfused Ischemic Brain Injury.

Ischemic stroke can lead to systemic inflammation, which can activate peripheral immune cells, causing neuroinflammation and brain injury. Meningeal lymphatics play a crucial role in transporting solutes and immune cells out of the brain and draining them into cervical lymph nodes (CLNs). However, the role of meningeal lymphatics in regulating systemic inflammation during the reperfusion stage after ischemia is not well understood. In this study, we demonstrated that brain infarct size, neuronal loss, and the effector function of inflammatory macrophage subsets were reduced after ischemia-reperfusion and disruption of meningeal lymphatics. Spatial memory function was improved in the late stage of ischemic stroke following meningeal lymphatic disruption. Brain-infiltrating immune cells, including neutrophils, monocytes, and T and natural killer cells, were reduced after cerebral ischemia-reperfusion and meningeal lymphatic disruption. Single-cell RNA sequencing analysis revealed that meningeal lymphatic disruption reprogrammed the transcriptome profile related to chemotaxis and leukocyte migration in CLN lymphatic endothelial cells (LECs), and it also decreased chemotactic CCN1 expression in floor LECs. Replenishment of CCN1 through intraventricular injection increased brain infarct size and neuronal loss, while restoring numbers of macrophages/microglia in the brains of meningeal lymphatic-disrupted mice after ischemic stroke. Blocking CCN1 in cerebrospinal fluid reduced brain infarcts and improves spatial memory function after ischemia-reperfusion injury. In summary, this study indicates that CCN1-mediated detrimental inflammation was alleviated after cerebral ischemia-reperfusion injury and meningeal lymphatic disruption. CCN1 represents a novel therapeutic target for inhibiting systemic inflammation in the brain-CLN axis after ischemia-reperfusion injury.

Exploring the complexity of amyloid-beta fibrils: structural polymorphisms and molecular interactions.

The aggregation of amyloid-beta (Aβ) peptides into cross-β structures forms a variety of distinct fibril conformations, potentially correlating with variations in neurodegenerative disease progression. Recent advances in techniques such as X-ray crystallography, solid-state NMR, and cryo-electron microscopy have enabled the development of high-resolution molecular structures of these polymorphic amyloid fibrils, which are either grown in vitro or isolated from human and transgenic mouse brain tissues. This article reviews our current understanding of the structural polymorphisms in amyloid fibrils formed by Aβ40 and Aβ42, as well as disease-associated mutants of Aβ peptides. The aim is to enhance our understanding of various molecular interactions, including hydrophobic and ionic interactions, within and among cross-β structures.

In vivo mapping of cellular resolution neuropathology in brain ischemia with diffusion MRI.

Noninvasive mapping of cellular pathology can provide critical diagnostic and prognostic information. Recent advances in diffusion magnetic resonance imaging enabled in vivo examination of tissue microstructures well beyond the imaging resolution. Here, we proposed to use diffusion time-dependent diffusion kurtosis imaging (tDKI) to simultaneously assess cellular morphology and transmembrane permeability in hypoxic-ischemic (HI) brain injury. Through numerical simulations and organoid imaging, we demonstrated the feasibility of capturing effective size and permeability changes using tDKI. In vivo MRI of HI-injured mouse brains detected a shift of the tDKI peak to longer diffusion times, suggesting swelling of the cellular processes. Furthermore, we observed a faster decrease of the tDKI tail, reflecting increased transmembrane permeability associated with up-regulated water exchange or necrosis. Such information, unavailable from a single diffusion time, can predict salvageable tissues. Preliminary applications of tDKI in patients with ischemic stroke suggested increased transmembrane permeability in stroke regions, illustrating tDKI's potential for detecting pathological changes in the clinics.

Caspase-12 is Expressed in Purkinje Neurons and Prevents Psychiatric-Like Behavior in Mice.

Caspase-12 is a caspase family member for which functions in regulating cell death and inflammation have previously been suggested. In this study, we used caspase-12 lacZ reporter mice to elucidate the expression pattern of caspase-12 in order to obtain an idea about its possible in vivo function. Strikingly, these reporter mice showed that caspase-12 is expressed explicitly in Purkinje neurons of the cerebellum. As this observation suggested a function for caspase-12 in Purkinje neurons, we analyzed the brain and behavior of caspase-12 deficient mice in detail. Extensive histological analyses showed that caspase-12 was not crucial for establishing cerebellum structure or for maintaining Purkinje cell numbers. We then performed behavioral tests to investigate whether caspase-12 deficiency affects memory, motor, and psychiatric functions in mice. Interestingly, while the absence of caspase-12 did not affect memory and motor function, caspase-12 deficient mice showed depression and hyperactivity tendencies, together resembling manic behavior. Next, suggesting a possible molecular mechanistic explanation, we showed that caspase-12 deficient cerebella harbored diminished signaling through the brain-derived neurotrophic factor/tyrosine kinase receptor B/cyclic-AMP response binding protein axis, as well as strongly enhanced expression of the neuronal activity marker c-Fos. Thus, our study establishes caspase-12 expression in mouse Purkinje neurons and opens novel avenues of research to investigate the role of caspase-12 in regulating psychiatric behavior.

Herpes simplex virus 1 accelerates the progression of Alzheimer’s disease by modulating microglial phagocytosis and activating NLRP3 pathway

Accumulating evidence implicates that herpes simplex virus type 1 (HSV-1) has been linked to the development and progression of Alzheimer’s disease (AD). HSV-1 infection induces β-amyloid (Aβ) deposition in vitro and in vivo, but the effect and precise mechanism remain elusive. Here, we show that HSV-1 infection of the brains of transgenic 5xFAD mice resulted in accelerated Aβ deposition, gliosis, and cognitive dysfunction. We demonstrate that HSV-1 infection induced the recruitment of microglia to the viral core to trigger microglial phagocytosis of HSV-GFP-positive neuronal cells. In addition, we reveal that the NLRP3 inflammasome pathway induced by HSV-1 infection played a crucial role in Aβ deposition and the progression of AD caused by HSV-1 infection. Blockade of the NLRP3 inflammasome signaling reduces Aβ deposition and alleviates cognitive decline in 5xFAD mice after HSV-1 infection. Our findings support the notion that HSV-1 infection is a key factor in the etiology of AD, demonstrating that NLRP3 inflammasome activation functions in the interface of HSV-1 infection and Aβ deposition in AD.

MRNA Nuclear Clustering Leads to a Difference in Mutant Huntingtin mRNA and Protein Silencing by siRNAs In Vivo.

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease caused by CAG repeat expansion in the first exon of the huntingtin gene (HTT). Oligonucleotide therapeutics, such as short interfering RNA (siRNA), reduce levels of huntingtin mRNA and protein invivo and are considered a viable therapeutic strategy. However, the extent to which they silence huntingtin mRNA in the nucleus is not established. We synthesized siRNA cross-reactive to mouse (wild-type) Htt and human (mutant) HTT in a divalent scaffold and delivered to two mouse models of HD. In both models, divalent siRNA sustained lowering of wild-type Htt, but not mutant HTT mRNA expression in striatum and cortex. Near-complete silencing of both mutant HTT protein and wild-type HTT protein was observed in both models. Subsequent fluorescent in situ hybridization analysis shows that divalent siRNA acts predominantly on cytoplasmic mutant HTT transcripts, leaving clustered mutant HTT transcripts in the nucleus largely intact in treated HD mouse brains. The observed differences between mRNA and protein levels, exaggerated in the case of extended repeats, might apply to other repeat-associated neurological disorders.

18F]Flotaza for Aβ Plaque Diagnostic Imaging: Evaluation in Postmortem Human Alzheimer's Disease Brain Hippocampus and PET/CT Imaging in 5xFAD Transgenic Mice.

The diagnostic value of imaging Aβ plaques in Alzheimer's disease (AD) has accelerated the development of fluorine-18 labeled radiotracers with a longer half-life for easier translation to clinical use. We have developed [18F]flotaza, which shows high binding to Aβ plaques in postmortem human AD brain slices with low white matter binding. We report the binding of [18F]flotaza in postmortem AD hippocampus compared to cognitively normal (CN) brains and the evaluation of [18F]flotaza in transgenic 5xFAD mice expressing Aβ plaques. [18F]Flotaza binding was assessed in well-characterized human postmortem brain tissue sections consisting of HP CA1-subiculum (HP CA1-SUB) regions in AD (n = 28; 13 male and 15 female) and CN subjects (n = 32; 16 male and 16 female). Adjacent slices were immunostained with anti-Aβ and analyzed using QuPath. In vitro and in vivo [18F]flotaza PET/CT studies were carried out in 5xFAD mice. Post-mortem human brain slices from all AD subjects were positively IHC stained with anti-Aβ. High [18F]flotaza binding was measured in the HP CA1-SUB grey matter (GM) regions compared to white matter (WM) of AD subjects with GM/WM > 100 in some subjects. The majority of CN subjects had no decipherable binding. Male AD exhibited greater WM than AD females (AD WM♂/WM♀ > 5; p < 0.001) but no difference amongst CN WM. In vitro studies in 5xFAD mice brain slices exhibited high binding [18F]flotaza ratios (>50 versus cerebellum) in the cortex, HP, and thalamus. In vivo, PET [18F]flotaza exhibited binding to Aβ plaques in 5xFAD mice with SUVR~1.4. [18F]Flotaza is a new Aβ plaque PET imaging agent that exhibited high binding to Aβ plaques in postmortem human AD. Along with the promising results in 5xFAD mice, the translation of [18F]flotaza to human PET studies may be worthwhile.