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bioRxiv2022

Spatial proteomics and iPSC modeling uncover mechanisms of axonal pathology in Alzheimer's disease

Axonal spheroids (dystrophic neurites) are commonly found around amyloid deposits in Alzheimers disease (AD). They impair electrical conduction, disrupt neural circuits, and correlate with AD severity. Despite their significance, the mechanisms underlying spheroid formation remain unknown. To address this, we developed a proximity labeling proteomics approach to uncover the proteome of spheroids in human postmortem and mouse brains. Additionally, we established a human iPSC-derived AD model allowing mechanistic investigation of spheroid pathology and optical electrophysiology. This approach revealed the subcellular molecular architecture of spheroids and identified abnormalities in key biological processes, including protein turnover, cytoskeleton dynamics, and lipid transport. Notably, the PI3K/AKT/mTOR pathway, which regulates these processes, was activated within spheroids. Furthermore, phosphorylated mTOR levels in spheroids strongly correlated with AD severity in humans. Importantly, inhibition of mTOR in iPSC-derived neurons and in mice ameliorated spheroid pathology. Altogether, our study provides a multidisciplinary toolkit for investigating mechanisms and novel targets for axonal pathology in neurodegeneration.

neuroscience↗

bioRxiv2022

Targeting the pathological network: feasibility of network-based optimization of transcranial magnetic stimulation coil placement for treatment of psychiatric disorders

It has been recognized that the efficacy of TMS-based modulation may depend on the network profile of the stimulated regions throughout the brain. However, what profile of this stimulation network optimally benefits treatment outcomes is yet to be addressed. The answer to the question is crucial for informing network-based optimization of stimulation parameters, such as coil placement, in TMS treatments. In this study, we aimed to investigate the feasibility of taking a disease-specific network as the target of stimulation network for guiding individualized coil placement in TMS treatments. We present here a novel network-based model for TMS targeting of the pathological network. First, combining E-field modeling and resting-state functional connectivity, stimulation networks were modeled from locations and orientations of the TMS coil. Second, the spatial anti-correlation between the stimulation network and the pathological network of a given disease was hypothesized to predict the treatment outcome. The proposed model was validated to predict treatment efficacy from the position and orientation of TMS coils in two depression cohorts and one auditory verbal hallucinations cohort. We further demonstrate the utility of the proposed model in guiding individualized TMS treatment for psychiatric disorders. In this proof-of-concept study, we demonstrated the feasibility of the novel network-based targeting strategy that uses the whole-brain, system-level abnormity of a specific psychiatric disease as a target. Results based on empirical data suggest that the strategy may potentially be utilized to identify individualized coil parameters for maximal therapeutic effects. HighlightsO_LIProposed a model of targeting pathological brain networks for pre-treatment TMS coil placement planning in the treatment of psychiatric disorders; C_LIO_LIValidated the network targeting model in three cohorts of patients with depression or auditory verbal hallucinations, via prediction of individual TMS treatment efficacy from the parameters of coil placement; C_LIO_LIDemonstrated the utility of the network targeting model in guiding individualized TMS coil placement. C_LI

neuroscience↗

bioRxiv2022

A pan-cancer PDX histology image repository with genomic and pathological annotations for deep learning analysis

Patient-derived xenografts (PDXs) model human intra-tumoral heterogeneity in the context of the intact tissue of immunocompromised mice. Histological imaging via hematoxylin and eosin (H&E) staining is performed on PDX samples for routine assessment and, in principle, captures the complex interplay between tumor and stromal cells. Deep learning (DL)-based analysis of large human H&E image repositories has extracted inter-cellular and morphological signals correlated with disease phenotype and therapeutic response. Here, we present an extensive, pan-cancer repository of nearly 1,000 PDX and paired human progenitor H&E images. These images, curated from the PDXNet consortium, are associated with genomic and transcriptomic data, clinical metadata, pathological assessment of cell composition, and, in several cases, detailed pathological annotation of tumor, stroma, and necrotic regions. We demonstrate that DL can be applied to these images to classify tumor regions and to predict xenograft-transplant lymphoproliferative disorder, the unintended outgrowth of human lymphocytes at the transplantation site. This repository enables PDX-specific, investigations of cancer biology through histopathological analysis and contributes important model system data that expand on existing human histology repositories. We expect the PDXNet Image Repository to be valuable for controlled digital pathology analysis, both for the evaluation of technical issues such as stain normalization and for development of novel computational methods based on spatial behaviors within cancer tissues.

bioinformatics↗

bioRxiv2022

A Web/Cloud based Digital Pathology Platform Framework for AI Development and Deployment

Digitization of glass slides has brought several opportunities with it for computational pathology and artificial intelligence (AI). The application of AI in digital pathology slides shows potential for QA/QC, triaging cases, and assisting pathologists in clinical decision making. We present an extensible and modular web/cloud based digital pathology framework for AI development and deployment. The proposed platform supports collaborative multi-user and multi-device annotation, remote slide access, and remote telepathology or teleconsultation tasks.

bioinformatics↗

bioRxiv2022

Retinal microvascular and neuronal pathologies probed in vivo by adaptive optical two-photon fluorescence microscopy

The retina, behind the transparent optics of the eye, is the only neural tissue whose physiology and pathology can be non-invasively probed by optical microscopy. The aberrations intrinsic to the mouse eye, however, prevent high-resolution investigation of retinal structure and function in vivo. Optimizing the design of a two-photon fluorescence microscope (2PFM) and sample preparation procedure, we found that adaptive optics (AO), by measuring and correcting ocular aberrations, is essential for resolving synapses and achieving three-dimensional cellular resolution in the mouse retina in vivo. Applying AO-2PFM to longitudinal retinal imaging in transgenic models of retinal pathology, we characterized microvascular lesions and observed microglial migration in a proliferative vascular retinopathy model, and found Lidocaine to effectively suppress retinal ganglion cell hyperactivity in a retinal degeneration model. Tracking structural and functional changes at high resolution longitudinally, AO-2PFM enables microscopic investigations of retinal pathology and pharmacology for disease diagnosis and treatment in vivo.

neuroscience↗

bioRxiv2023

Early-life stress exposure impacts the hippocampal synaptic proteome in a mouse model of Alzheimer's disease: age- and pathology-dependent effects on mitochondrial proteins

Epidemiological evidence indicates that early life stress (ES) exposure increases the risk for later-life diseases, such as Alzheimers disease (AD). Accordingly, we and others have shown that ES aggravates the development of, and response to, amyloid-beta (A{beta}) pathology in animal models. Moreover, ES-exposed transgenic APP/PS1 mice display deficits in both cognitive flexibility and synaptic function. As the mechanisms behind these changes were unclear, we here investigated how exposure to ES, using the limited nesting and bedding model, affects the synaptic proteome across 2 different ages in both wildtype and APP/PS1 transgenic mice. We found that, compared to wildtype mice, the hippocampal synaptosomes of APP/PS1 mice at an early pathological stage (4 months) showed a higher abundance of mitochondrial proteins and lower levels of proteins involved in actin dynamics. Interestingly, ES exposure in wildtype mice had similar effects on the level of mitochondrial and actin-related synaptosomal proteins at this age, whereas ES exposure had no additional effect on the synaptosomal proteome of early-stage APP/PS1 mice. Accordingly, ultrastructural analysis of the synapse using electron microscopy in a follow-up cohort showed fewer mitochondria in pre- and post-synaptic compartments of APP/PS1 and ES-exposed mice, respectively. At a later pathological stage (10 months), the hippocampal synaptic proteome of APP/PS1 mice revealed an upregulation of proteins related to A{beta} processing, that was accompanied by a downregulation of proteins related to postsynaptic receptor endocytosis. ES exposure no longer affected the synaptic proteome of wildtype animals by this age, whereas it affected the expression of astrocytic proteins involved in lipid metabolism in APP/PS1 mice. We confirmed a dysregulation of astrocyte protein expression in a separate cohort of 12-month-old mice, by immunostaining for the alpha subunit of the mitochondrial trifunctional protein and fatty acid synthase in astrocytes. In conclusion, our data suggest that ES and amyloidosis share pathogenic pathways involving synaptic mitochondrial dysfunction and astrocytic lipid metabolism. These pathways might be underlying contributors to the long-term aggravation of the APP/PS1 phenotype by ES, as well as to the ES-associated risk for AD progression. These data are publicly accessible online as a web app via https://amsterdamstudygroup.shinyapps.io/ES_Synaptosome_Proteomics_Visualizer/.

neuroscience↗

bioRxiv2023

Endogenous pathology in tauopathy mice progresses via brain networks

Neurodegenerative tauopathies are hypothesized to propagate via brain networks. This is uncertain because we have lacked precise network resolution of pathology. We therefore developed whole-brain staining methods with anti-p-tau nanobodies and imaged in 3D PS19 tauopathy mice, which have pan-neuronal expression of full-length human tau containing the P301S mutation. We analyzed patterns of p-tau deposition across established brain networks at multiple ages, testing the relationship between structural connectivity and patterns of progressive pathology. We identified core regions with early tau deposition, and used network propagation modeling to determine the link between tau pathology and connectivity strength. We discovered a bias towards retrograde network-based propagation of tau. This novel approach establishes a fundamental role for brain networks in tau propagation, with implications for human disease. One-Sentence SummaryNovel whole brain imaging of p-tau deposition reveals retrograde-dominant network propagation in a tauopathy mouse model.

neuroscience↗

bioRxiv2023

Progressive excitability changes in the medial entorhinal cortex in the 3xTg mouse model of Alzheimer's disease pathology

Alzheimers disease (AD) is a chronic neurodegenerative disorder that is characterized by memory loss and progressive cognitive impairments. In mouse models of AD pathology, studies have found neuronal and synaptic deficits in the hippocampus, but less is known about what happens in the medial entorhinal cortex (MEC), which is the primary spatial input to the hippocampus and an early site of AD pathology. Here, we measured the neuronal intrinsic excitability and synaptic activity in MEC layer II (MECII) stellate cells, MECII pyramidal cells, and MEC layer III (MECIII) excitatory neurons at early (3 months) and late (10 months) time points in the 3xTg mouse model of AD pathology. At 3 months of age, prior to the onset of memory impairments, we found early hyperexcitability in MECII stellate and pyramidal cells intrinsic properties, but this was balanced by a relative reduction in synaptic excitation (E) compared to inhibition (I), suggesting intact homeostatic mechanisms regulating activity in MECII. Conversely, MECIII neurons had reduced intrinsic excitability at this early time point with no change in the synaptic E/I ratio. By 10 months of age, after the onset of memory deficits, neuronal excitability of MECII pyramidal cells and MECIII excitatory neurons was largely normalized in 3xTg mice. However, MECII stellate cells remained hyperexcitable and this was further exacerbated by an increased synaptic E/I ratio. This observed combination of increased intrinsically and synaptically generated excitability suggests a breakdown in homeostatic mechanisms specifically in MECII stellate cells at this post-symptomatic time point. Together, these data suggest that the breakdown in homeostatic excitability mechanisms in MECII stellate cells may contribute to the emergence of memory deficits in AD.

neuroscience↗

bioRxiv2023

Early Alzheimer's disease pathology in human cortex is associated with a transient phase of distinct cell states

Cellular perturbations underlying Alzheimers disease are primarily studied in human postmortem samples and model organisms. Here we generated a single-nucleus atlas from a rare cohort of cortical biopsies from living individuals with varying degrees of Alzheimers disease pathology. We next performed a systematic cross-disease and cross-species integrative analysis to identify a set of cell states that are specific to early AD pathology. These changes-which we refer to as the Early Cortical Amyloid Response--were prominent in neurons, wherein we identified a transient state of hyperactivity preceding loss of excitatory neurons, which correlated with the selective loss of layer 1 inhibitory neurons. Microglia overexpressing neuroinflammatory-related processes also expanded as AD pathological burden increased. Lastly, both oligodendrocytes and pyramidal neurons upregulated genes associated with amyloid beta production and processing during this early hyperactive phase. Our integrative analysis provides an organizing framework for targeting circuit dysfunction, neuroinflammation, and amyloid production early in AD pathogenesis.

genomics↗

bioRxiv2023

The Genetic Architecture of Dietary Iron Overload and Associated Pathology in Mice

Tissue iron overload is a frequent pathologic finding in multiple disease states including non-alcoholic fatty liver disease (NAFLD), neurodegenerative disorders, cardiomyopathy, diabetes, and some forms of cancer. The role of iron, as a cause or consequence of disease progression and observed phenotypic manifestations, remains controversial. In addition, the impact of genetic variation on iron overload related phenotypes is unclear, and the identification of genetic modifiers is incomplete. Here, we used the Hybrid Mouse Diversity Panel (HMDP), consisting of over 100 genetically distinct mouse strains optimized for genome-wide association studies and systems genetics, to characterize the genetic architecture of dietary iron overload and pathology. Dietary iron overload was induced by feeding male mice (114 strains, 6-7 mice per strain on average) a high iron diet for six weeks, and then tissues were collected at 10-11 weeks of age. Liver metal levels and gene expression were measured by ICP-MS/ICP-AES and RNASeq, and lipids were measured by colorimetric assays. FaST-LMM was used for genetic mapping, and Metascape, WGCNA, and Mergeomics were used for pathway, module, and key driver bioinformatics analyses. Mice on the high iron diet accumulated iron in the liver, with a 6.5 fold difference across strain means. The iron loaded diet also led to a spectrum of copper deficiency and anemia, with liver copper levels highly positively correlated with red blood cell count, hemoglobin, and hematocrit. Hepatic steatosis of various severity was observed histologically, with 52.5 fold variation in triglyceride levels across the strains. Liver triglyceride and iron mapped most significantly to an overlapping locus on chromosome 7 that has not been previously associated with either trait. Based on network modeling, significant key drivers for both iron and triglyceride accumulation are involved in cholesterol biosynthesis and oxidative stress management. To make the full data set accessible and useable by others, we have made our data and analyses available on a resource website. Author summaryThe response to a high iron diet is determined in part by genetic factors. We now report the responses to such a diet in a diverse set of inbred strains of mice, known as the Hybrid Mouse Diversity Panel, that enables high resolution genetic mapping and systems genetics analyses. The levels of iron in the liver varied about >5 fold across the strains, with genetic variation explaining up to 74% of the variation in liver iron. Pathologies included copper deficiency, anemia, and fatty liver, with liver triglycerides varying over 50 fold among the strains. Genetic mapping and network modeling identified significant genetic loci and pathways underlying the response to diet.

genetics↗

bioRxiv2023

A dual target molecular MRI probe for noninvasive profiling of pathologic alpha-synuclein and microgliosis in a mouse model of Parkinson's disease

Parkinsons disease is characterized progressive deposition of pathologic alpha-synuclein (-syn) aggregates, neuroinflammation, and death of dopaminergic neurons in the substantia nigra projecting to the striatum. Noninvasive in vivo profiling of -syn aggregate accumulation and microgliosis by molecular imaging can provide insights on the underlying mechanisms of disease progression, facilitating the development of effective treatment. However, no classical imaging methods have been successful, despite several attempts. We demonstrate a novel method to noninvasive in vivo profiling of pathologic -syn in combination with microgliosis using molecular magnetic resonance imaging (MRI), by targeting oligomeric -syn in cerebrospinal fluid with nano scavengers (T) bearing a T1-relaxive Gd(III) payload. In this proof-of-concept report we demonstrate, in vitro, that microglia and neuroblastoma cell lines internalize cross-linked T/oligomeric -syn agglomerates. Delayed in vivo T1-weighted MRI scans following intravenous administration in the M83 -syn transgenic mouse line show statistically significant T1 signal enhancement in test mice versus controls. The in vivo data was validated by ex-vivo immunohistochemical analysis which showed a strong correlation between in vivo MRI signal enhancement, Lewy pathology distribution, and microglia activity in the treated brain tissue. Furthermore, neuronal, and microglial cells in brain tissue from treated mice displayed strong cytosolic signal originating from T, confirming in vivo cell uptake of the nano scavengers.

neuroscience↗

bioRxiv2023

Phenotyping the virulence of SARS-CoV-2 variants in hamsters by digital pathology and machine learning

SARS-CoV-2 has continued to evolve throughout the COVID-19 pandemic, giving rise to multiple variants of concern (VOCs) with different biological properties. As the pandemic progresses, it will be essential to test in near real time the potential of any new emerging variant to cause severe disease. BA.1 (Omicron) was shown to be attenuated compared to the previous VOCs like Delta, but it is possible that newly emerging variants may regain a virulent phenotype. Hamsters have been proven to be an exceedingly good model for SARS-CoV-2 pathogenesis. Here, we aimed to develop robust quantitative pipelines to assess the virulence of SARS-CoV-2 variants in hamsters. We used various approaches including RNAseq, RNA in situ hybridization, immunohistochemistry, and digital pathology, including software assisted whole section imaging and downstream automatic analyses enhanced by machine learning, to develop methods to assess and quantify virus-induced pulmonary lesions in an unbiased manner. Initially, we used Delta and Omicron to develop our experimental pipelines. We then assessed the virulence of recent Omicron sub-lineages including BA.5, XBB, BQ.1.18, BA.2 and BA.2.75. We show that in experimentally infected hamsters, accurate quantification of alveolar epithelial hyperplasia and macrophage infiltrates represent robust markers for assessing the extent of virus-induced pulmonary pathology, and hence virus virulence. In addition, using these pipelines, we could reveal how some Omicron sub-lineages (e.g., BA.2.75) have regained virulence compared to the original BA.1. Finally, to maximise the utility of the digital pathology pipelines reported in our study, we developed an online repository containing representative whole organ histopathology sections that can be visualised at variable magnifications (https://covid-atlas.cvr.gla.ac.uk). Overall, this pipeline can provide unbiased and invaluable data for rapidly assessing newly emerging variants and their potential to cause severe disease.

microbiology↗

bioRxiv2023

Pathological brain states in Alzheimer's disease

Dynamic and rapid reconfigurations of neural activation patterns, known as brain states, support cognition. Recent analytic advances applied to functional magnetic resonance imaging now enable the quantification of brain states, which offers a substantial methodological improvement in characterizing spatiotemporal dynamics of activation over previous functional connectivity methods. Dysfunction to the persistence and temporal transitions between discrete brain states may be proximal factors reflecting neurophysiological disruptions in Alzheimers disease, although this has not yet been established. Here, we identified six distinct brain states, representing spatiotemporal trajectories of coactivation at single time points, in older adults across the Alzheimers disease continuum. Critically, we identified a pathological brain state that reflects coactivation within limbic regions. Higher persistence within and transitions to this limbic state, at the expense of other brain states, is associated with an increased likelihood of a clinically impaired diagnosis, worse cognitive performance, greater Alzheimers pathology, and neurodegeneration. Together, our results provide compelling evidence that neural activity settling into a pathological limbic state reflects the progression to Alzheimers disease. As brain states have recently been shown to be modifiable targets, this work may inform the development of novel neuromodulation techniques to reduce limbic state persistence. This application would be an innovative clinical approach to rescue cognitive decline in the early stages of Alzheimers disease.

neuroscience↗

bioRxiv2023

Differential reorganization of episodic and semantic memory systems in epilepsy-related mesiotemporal pathology

Declarative memory encompasses episodic and semantic divisions. Episodic memory captures singular events with specific spatiotemporal relationships, while semantic memory houses context-independent knowledge. Behavioural and functional neuroimaging studies have revealed common and distinct neural substrates of both memory systems, implicating mesiotemporal lobe (MTL) regions such as the hippocampus and distributed neocortices. Here, we explored declarative memory system reorganization in patients with unilateral temporal lobe epilepsy (TLE), as a human disease model to test the impact of variable degrees of MTL pathology on memory function. Our cohort included 31 patients with TLE as well as 60 age and sex-matched healthy controls and all participants underwent episodic and semantic retrieval tasks during a multimodal MRI session. The functional MRI tasks were closely matched in terms of stimuli and trial design. Capitalizing on non-linear connectome gradient mapping techniques, we derived task-based functional topographies during episodic and semantic memory states, both in the MTL and in neocortical networks. Comparing neocortical and hippocampal functional gradients between TLE patients and healthy controls, we observed a marked topographic reorganization of both neocortical and MTL systems during episodic memory states. In the neocortex, alterations were characterized by reduced functional differentiation in patients in lateral temporal and midline parietal cortices in both hemispheres. In the MTL, on the other hand, patients presented with a more marked functional differentiation of posterior and anterior hippocampal segments ipsilateral to the seizure focus and pathological core, indicating perturbed intrahippocampal connectivity. Semantic memory reorganization was also found in bilateral lateral temporal and ipsilateral angular regions, while hippocampal functional topographies were unaffected. Leveraging MRI proxies of MTL pathology, we furthermore observed alterations in hippocampal microstructure and morphology are associated with TLE-related functional reorganization during episodic memory. Moreover, correlation analysis and statistical mediation models revealed that these functional alterations contributed to behavioural deficits in episodic, but again not semantic memory in patients. Altogether, our findings suggest that semantic processes rely on distributed neocortical networks, while episodic processes are supported by a network involving both the hippocampus and neocortex. Alterations of such networks can provide a compact signature of state-dependent reorganization in conditions associated with MTL damage, such as TLE.

neuroscience↗

bioRxiv2023

Cognitive Reserve Against Alzheimer's Pathology Is Linked to Brain Activity During Memory Formation

The cognitive reserve (CR) hypothesis posits that individuals can differ in how their brain function is disrupted by pathology associated with aging and neurodegeneration. Here, we tested this hypothesis in the Alzheimers disease continuum using longitudinal data from 490 participants of the DELCODE multicentric observational study. Brain function was measured using task fMRI of visual memory encoding. Using a multivariate moderation analysis we identified a CR-related activity pattern underlying successful memory encoding that moderated the detrimental effect of AD pathological load on cognitive performance. CR was mainly represented by a more pronounced expression of the task-active network encompassing the default mode network (DMN), anterior cingulate cortex (ACC) and inferior temporal regions including the fusiform gyrus. We devised personalized fMRI-based CR scores that moderated the impact of AD pathology on cognitive performance and were positively associated with years of education. Furthermore, higher CR scores were associated with slower cognitive decline over time. Our findings suggest maintenance of core cognitive circuits including the DMN and ACC as the primary mechanism of CR. Individual brain activity levels of these areas during memory encoding have prognostic value for future cognitive decline.

neuroscience↗

bioRxiv2023

Regional interneuron transcriptional changes reveal pathologic markers of disease progression in a mouse model of Alzheimer's disease

Alzheimers disease (AD) is a progressive neurodegenerative disorder and leading cause of dementia, characterized by neuronal and synapse loss, amyloid-{beta} and tau protein aggregates, and a multifactorial pathology involving neuroinflammation, vascular dysfunction, and disrupted metabolism. Additionally, there is growing evidence of imbalance between neuronal excitation and inhibition in the AD brain secondary to dysfunction of parvalbumin (PV)- and somatostatin (SST)-positive interneurons, which differentially modulate neuronal activity. Importantly, impaired interneuron activity in AD may occur upstream of amyloid-{beta} pathology rendering it a potential therapeutic target. To determine the underlying pathologic processes involved in interneuron dysfunction, we spatially profiled the brain transcriptome of the 5XFAD AD mouse model versus controls, across four brain regions, dentate gyrus, hippocampal CA1 and CA3, and cortex, at early-stage (12 weeks-of-age) and late-stage (30 weeks-of-age) disease. Global comparison of differentially expressed genes (DEGs) followed by enrichment analysis of 5XFAD versus control highlighted various biological pathways related to RNA and protein processing, transport, and clearance in early-stage disease and neurodegeneration pathways at late-stage disease. Early-stage DEGs examination found shared, e.g., RNA and protein biology, and distinct, e.g., N-glycan biosynthesis, pathways enriched in PV-versus somatostatin SST-positive interneurons and in excitatory neurons, which expressed neurodegenerative and axon- and synapse-related pathways. At late-stage disease, PV-positive interneurons featured cancer and cancer signaling pathways along with neuronal and synapse pathways, whereas SST-positive interneurons showcased glycan biosynthesis and various infection pathways. Late-state excitatory neurons were primarily characterized by neurodegenerative pathways. These fine-grained transcriptomic profiles for PV- and SST-positive interneurons in a time- and spatial-dependent manner offer new insight into potential AD pathophysiology and therapeutic targets.

neuroscience↗

bioRxiv2023

Loss of TREM2 exacerbates parenchymal amyloid pathology but diminishes CAA in Tg-SwDI mice

Alzheimers disease (AD) is a progressive neurodegenerative disease, and it is the most common cause of dementia worldwide. Recent genome-wide association studies (GWAS) identified TREM2 (triggering receptor expressed on myeloid cells 2) as one of the major risk factors for AD. TREM2 is a surface receptor expressed on microglia and largely mediates microglial functions and immune homeostasis in the brain. The functions of TREM2 in AD pathogenesis, including in the formation of the key pathology parenchymal amyloid-{beta} (A{beta}) plaques, have been investigated by introducing Trem2 deficiency in AD mouse models. However, the role of TREM2 in cerebrovascular amyloidosis, in particular cerebral amyloid angiopathy (CAA) remains unexplored. CAA features A{beta} deposition along the cerebral vessels, signifying an intersection between AD and vascular dysfunction. Using a well-characterized CAA-prone, transgenic mouse model of AD, Tg-SwDI (SwDI), we found that loss of TREM2 led to a marked increase in overall A{beta} load in the brain, but a dramatic decrease in CAA in microvessel-rich regions, along with reduced microglial association with CAA. Transcriptomic analysis revealed that in the absence of Trem2, microglia were activated but trapped in transition to the fully reactive state. Like microglia, perivascular macrophages were activated with upregulation of cell junction related pathways in Trem2-deficient SwDI mice. In addition, vascular mural cells and astrocytes exhibited distinct responses to Trem2 deficiency, contributing to the pathological changes in the brain of Trem2-null SwDI mice. Our study provides the first evidence that TREM2 differentially modulates parenchymal and vascular A{beta} pathologies, which may have significant implications for both TREM2- and A{beta}-targeting therapies for AD.

neuroscience↗

bioRxiv2023

Fibroblast Nrf2 inhibits profibrotic transcription with Ddx54 and mitigates pathological fibrosis in the mouse heart and kidney

BackgroundTissue fibrosis is a common feature of many organ dysfunctions, such as heart failure and chronic kidney disease. However, no fundamental treatment has been developed. This study aims to identify novel molecular mechanisms for antifibrotic intervention, focusing on fibroblast activation. MethodsWe performed a forward genetic screen using a genome-wide CRISPR library in the context of transforming growth factor {beta} (TGF-{beta})-mediated connective tissue growth factor (CTGF) expression, and used unbiased techniques such as Cleavage Under Targets and Tagmentation (CUT&Tag) and proximity-dependent biotin labeling by TurboID to reveal the detailed molecular mechanisms. ResultsCRISPR library screening identified a number of players in both the canonical Smad pathway and the non-canonical pathway. In addition to the known factors, the Keap1-Nrf2 pathway was identified as a predominant regulator of TGF-{beta}-mediated CTGF expression. Keap1 deletion and consequent Nrf2 activation broadly suppressed profibrotic gene expression, independently of conventional antioxidant effects. CUT&Tag revealed that Nrf2 bound to the proximity of fibrosis-related genes including Ctgf and Fn1. Subsequent individual analysis revealed Smad3 and RNA polymerase II binding to the Nrf2 peak site, which was attenuated by Keap1 deletion. TurboID experiments further discovered that Nrf2 interacts with Ddx54, which acts as a corepressor. Consistently, Keap1 deletion-mediated repression of profibrotic gene expression was reversed by additional Ddx54 deletion. The impact of the Keap1-Nrf2 pathway on pathological fibrosis was examined using tamoxifen-inducible fibroblast-specific Keap1 knockout mice. Pressure overload for 4 weeks robustly induced cardiac hypertrophy, fibrosis and contractile dysfunction. However, deletion of Keap1 in the Postn lineage attenuated these cardiac pathologies. The anti-fibrotic effects of Keap1 deletion were also confirmed in renal fibrosis in the unilateral ureteral obstruction (UUO) model. ConclusionsFibroblast Nrf2 transcriptionally represses fibrosis-related genes in cooperation with the corepressor Ddx54. Fibroblast-specific deletion of Keap1 attenuated pathological fibrosis in pressure overload heart failure and renal fibrosis.

cell biology↗