Neural stem cells (NSCs) constitute an endogenous reservoir for neurons that could potentially be harnessed for regenerative therapies in disease contexts such as neurodegeneration. However, in ...Alzheimer's disease (AD), NSCs lose plasticity and thus possible regenerative capacity. We investigate how NSCs lose their plasticity in AD by using starPEG-heparin-based hydrogels to establish a reductionist 3D cell-instructive neuro-microenvironment that promotes the proliferative and neurogenic ability of primary and induced human NSCs. We find that administration of AD-associated Amyloid-β42 causes classical neuropathology and hampers NSC plasticity by inducing kynurenic acid (KYNA) production. Interleukin-4 restores NSC proliferative and neurogenic ability by suppressing the KYNA-producing enzyme Kynurenine aminotransferase (KAT2), which is upregulated in APP/PS1dE9 mouse model of AD and in postmortem human AD brains. Thus, our culture system enables a reductionist investigation of regulation of human NSC plasticity for the identification of potential therapeutic targets for intervention in AD.
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•Human neural stem cell plasticity and AD are modeled in 3D culture•KAT2 enzyme, but not IL-4, increases in 3D culture and mouse and human brains with AD•Aβ42-induced production of KYNA suppresses plasticity of human neural stem cells•IL-4 antagonizes KYNA production and loss of human neural stem cell plasticity in AD
Papadimitriou et al. developed a starPEG-heparin-based hydrogel 3D neuro-microenvironment that promotes human neural stem cell proliferative and neurogenic capacity. Using the system to model Alzheimer's disease (AD) uncovered kynurenic acid/IL-4 interplay, which is also observed in AD mouse and human brains, suggesting its utility for reductionist investigation of AD therapeutic targets.
Abstract
Microtubule-associated TAU protein is a pathological hallmark in Alzheimer’s disease (AD), where hyperphosphorylation of TAU generates neurofibrillary tangles. To investigate the effects of ...TAU in a regenerative adult vertebrate brain system, we generated a cre/lox-based transgenic model of zebrafish that chronically expresses human TAU
P301L
, which is a variant of human TAU protein that forms neurofibrillary tangles in mouse models and humans. Interestingly, we found that although chronic and abundant expression of TAU
P301L
starting from early embryonic development led to hyperphosphorylation, TAU
P301L
did not form oligomers and neurofibrillary tangles, and did not cause elevated apoptosis and microglial activation, which are classical symptoms of tauopathies in mammals. Additionally, TAU
P301L
neither increased neural stem cell proliferation nor activated the expression of regenerative factor Interleukin-4, indicating that TAU
P301L
toxicity is prevented in the adult zebrafish brain. By combining TAU
P301L
expression with our established Aβ42 toxicity model, we found that Aβ42 ceases to initiate neurofibrillary tangle formation by TAU
P301L
, and TAU
P301L
does not exacerbate the toxicity of Aβ42. Therefore, our results propose a cellular mechanism that protects the adult zebrafish brain against tauopathies, and our model can be used to understand how TAU toxicity can be prevented in humans.
INTRODUCTION
Despite a two‐fold risk, individuals of African ancestry have been underrepresented in Alzheimer's disease (AD) genomics efforts.
METHODS
Genome‐wide association studies (GWAS) of 2,903 ...AD cases and 6,265 controls of African ancestry. Within‐dataset results were meta‐analyzed, followed by functional genomics analyses.
RESULTS
A novel AD‐risk locus was identified in MPDZ on chromosome (chr) 9p23 (rs141610415, MAF = 0.002, p = 3.68×10−9). Two additional novel common and nine rare loci were identified with suggestive associations (P < 9×10−7). Comparison of association and linkage disequilibrium (LD) patterns between datasets with higher and lower degrees of African ancestry showed differential association patterns at chr12q23.2 (ASCL1), suggesting that this association is modulated by regional origin of local African ancestry.
DISCUSSION
These analyses identified novel AD‐associated loci in individuals of African ancestry and suggest that degree of African ancestry modulates some associations. Increased sample sets covering as much African genetic diversity as possible will be critical to identify additional loci and deconvolute local genetic ancestry effects.
Highlights
Genetic ancestry significantly impacts risk of Alzheimer's Disease (AD). Although individuals of African ancestry are twice as likely to develop AD, they are vastly underrepresented in AD genomics studies.
The Alzheimer's Disease Genetics Consortium has previously identified 16 common and rare genetic loci associated with AD in African American individuals. The current analyses significantly expand this effort by increasing the sample size and extending ancestral diversity by including populations from continental Africa.
Single variant meta‐analysis identified a novel genome‐wide significant AD‐risk locus in individuals of African ancestry at the MPDZ gene, and 11 additional novel loci with suggestive genome‐wide significance at p < 9×10−7.
Comparison of African American datasets with samples of higher degree of African ancestry demonstrated differing patterns of association and linkage disequilibrium at one of these loci, suggesting that degree and/or geographic origin of African ancestry modulates the effect at this locus.
These findings illustrate the importance of increasing number and ancestral diversity of African ancestry samples in AD genomics studies to fully disentangle the genetic architecture underlying AD, and yield more effective ancestry‐informed genetic screening tools and therapeutic interventions.
Background
Recent studies increased the number of genes that are associated with the co‐existence of vascular pathologies and Alzheimer’s disease (AD). However, the biological functions and the ...mechanism of action by which they contribute to the disease pathology are still to be further elucidated. Therefore, animal models that allow streamlined large‐throughput functional screens in a biologically relevant manner are essential. Towards this goal, we generated adult zebrafish models of amyloid toxicity to functionally analyze candidate genes and how they relate to disease perturbations.
Method
Through cerebroventricular injection of human amyloid‐beta42 monomers into the cerebrospinal fluid of the adult zebrafish brain, we inflict acute amyloid toxicity. By performing immunohistological analyses, single cell transcriptomics, gene editing for generating gene variants or full knockouts, transient functional knockdown of candidate genes, pharmacological intervention of selected signalling pathways and comparing the findings to human AD brain transcriptomics datasets, we determined the similarities and differences of the effects of amyloid pathology on the vasculature in zebrafish in relation to the human conditions.
Results
We found that amyloid pathology in zebrafish brain shows histological and molecular similarities to human brains. Integration of single cell transcriptomics showed remarkable similarities in neurons to amyloid in humans and zebrafish. We identified several molecular mechanisms that underlie this pathology‐induced cellular response and translated to mammalian models including rodent brains. By performing genome‐wide association in AD patients, we identified that the FMNL2 links cerebrovascular disease and AD, by regulating the astroglial and blood vessel interactions and controlling the efficient clearance of toxic proteins from the brain. Our new single cell transcriptomics analyses of the gliovascular niche cells of the zebrafish brain revealed potential cellular interactions and the pathways perturbed in vascular disease and AD.
Conclusion
We propose zebrafish as a useful model for functional investigation of vascular pathology and AD‐related genes identified in clinical studies by providing in vivo biological knowledge on disease mechanisms, on which novel drug development strategies can be based.
Background
Although African Americans are twice as likely to develop Alzheimer’s Disease (AD), individuals with African ancestry are under‐represented in genetic research of the disease. In the ...largest AD genome‐wide association studies to date for African‐Americans (Reitz et al. JAMA 2013; Kunkle at al. JAMA Neurol 2021) we previously identified several novel susceptibility loci in addition to APOE, including ABCA7, API5, RBFOX1, and IGF1R.
Method
We performed a genome‐wide association meta‐analysis of 2,844 AD cases and 6,251 cognitively healthy controls of African ancestry (AA) assembled across 17 different cohorts. Single‐variant association analysis was conducted adjusting for age, sex, principal components, and subsequently APOE, applying logistic regression for case‐control and general estimating equations for family‐based datasets. Within‐study results were meta‐analyzed using METAL, and followed by gene‐based, pathway, scRNA‐seq, and colocalization analyses.
Result
Single variant meta‐analysis identified a novel genome‐wide significant AD risk locus in the MPDZ gene on chromosome 9p23 (rs141610415, MAF = .002, P = 3.68×10−9). MPDZ (MUPP1) is a vital component of the NMDAR signaling complex in excitatory synapses of hippocampal neurons critical for learning and memory. Two additional novel common loci and 9 novel rare loci approached genome‐wide significance at P<9×10−7. Genes at these loci are acting in biologically plausible pathways: signal transduction (PLEKHG1), synaptic transmission (CNTNAP4), synaptic connectivity (SDK1), neural development/function (SRGAP3, KIDINS220, UNC5C, TSSC1, TANC2), and neuronal differentiation (ASCL1). Single‐cell RNA‐sequence analysis shows that all genes are expressed in the brain, and that expression of the orthologs of SRGAP3, TANC2, and MMP16 is upregulated with amyloid toxicity in zebrafish. Pathway analyses support the notion that immune response, transcription/DNA repair, lipid processing, and intracellular trafficking are major AD‐associated pathways in African Americans. Except for SIPA1L2 and ACER3, all previously reported loci, including ABCA7, API5, RBFOX1 and IGF1R, remain genome‐wide or close to genome‐wide significant.
Conclusion
We identified several novel loci for AD in individuals with African ancestry with the strongest association observed for MPDZ involved in hippocampal synaptic signaling. Identification of a significant number of loci at suggestive significance indicates that future studies with further increased sample size will be critical to identify additional disease‐associated loci in individuals of African ancestry.
Background
Inter‐cellular communication within the gliovascular unit (GVU) is critical for cerebral blood flow regulation, and maintenance of the blood‐brain‐barrier (BBB) properties. The breakdown ...of BBB in Alzheimer’s disease (AD) is well‐established, but precise underlying molecular changes remain unclear. Additionally, whether GVU molecular alterations observed in AD brains are also detected in blood from living patients is unknown. Further, these GVU molecular perturbations require further investigation in different model systems to identify both human brain‐specific and cross‐species conserved alterations. In this study, we investigated prioritized GVU molecules altered in AD brains for their conservation in blood and cross‐species model systems.
Methods
We performed single nucleus RNA sequencing (snRNAseq) of temporal cortex tissue in AD and control brains. We analyzed this data to detect cell‐specific GVU molecular perturbations and their interactions. We investigated molecular interactions between vascular and astrocyte clusters, the major cell types of the GVU of the BBB. To determine whether GVU transcriptional alterations detected in the brain are preserved in the blood, existing blood expression, genetic, and neuroimaging data from two longitudinal antemortem cohorts were analyzed. Using model systems, including mouse, drosophila, and zebrafish, we evaluated the cross‐species conservation of the top GVU alterations detected in AD brains.
Results
Brain snRNAseq revealed transcriptional profiles of 6,541 astrocytes and 2,210 vascular cells. The latter formed three distinct vascular clusters characterized as pericytes, endothelia and perivascular fibroblasts. We identified differentially expressed genes and their enriched pathways within these clusters and observed the highest levels of transcriptional changes within pericytes. Vascular targets that interact with astrocytic ligands have biological functions in cell signaling, angiogenesis, amyloid ß metabolism, and cytoskeletal architecture. We discovered that genetic variants influencing blood expression levels of some of the prioritized GVU genes were associated with neuroimaging burden of cerebrovascular disease in living human cohorts. Our ongoing studies in model systems revealed conservation of some of the top prioritized molecular perturbations across species.
Conclusion
Our findings prioritized by multiscale, cross‐tissue human data revealed GVU perturbations within interacting pericyte and astrocyte molecules, which are conserved across multiple cross‐species models. These results nominate new molecular targets and mechanistic insights for BBB disruptions in AD.
Microtubule-associated TAU protein is a pathological hallmark in Alzheimer's disease (AD), where hyperphosphorylation of TAU generates neurofibrillary tangles. To investigate the effects of TAU in a ...regenerative adult vertebrate brain system, we generated a cre/lox-based transgenic model of zebrafish that chronically expresses human TAU
, which is a variant of human TAU protein that forms neurofibrillary tangles in mouse models and humans. Interestingly, we found that although chronic and abundant expression of TAU
starting from early embryonic development led to hyperphosphorylation, TAU
did not form oligomers and neurofibrillary tangles, and did not cause elevated apoptosis and microglial activation, which are classical symptoms of tauopathies in mammals. Additionally, TAU
neither increased neural stem cell proliferation nor activated the expression of regenerative factor Interleukin-4, indicating that TAU
toxicity is prevented in the adult zebrafish brain. By combining TAU
expression with our established Aβ42 toxicity model, we found that Aβ42 ceases to initiate neurofibrillary tangle formation by TAU
, and TAU
does not exacerbate the toxicity of Aβ42. Therefore, our results propose a cellular mechanism that protects the adult zebrafish brain against tauopathies, and our model can be used to understand how TAU toxicity can be prevented in humans.
It was recently suggested that supplying the brain with new neurons could counteract Alzheimer's disease (AD). This provocative idea requires further testing in experimental models in which the ...molecular basis of disease-induced neuronal regeneration could be investigated. We previously found that zebrafish stimulates neural stem cell (NSC) plasticity and neurogenesis in AD and could help to understand the mechanisms to be harnessed for developing new neurons in diseased mammalian brains. Here, by performing single-cell transcriptomics, we found that amyloid toxicity-induced interleukin-4 (IL4) promotes NSC proliferation and neurogenesis by suppressing the tryptophan metabolism and reducing the production of serotonin. NSC proliferation was suppressed by serotonin via down-regulation of brain-derived neurotrophic factor (BDNF)-expression in serotonin-responsive periventricular neurons. BDNF enhances NSC plasticity and neurogenesis via nerve growth factor receptor A (NGFRA)/ nuclear factor 'kappa-light-chain-enhancer' of activated B-cells (NFkB) signaling in zebrafish but not in rodents. Collectively, our results suggest a complex neuron-glia interaction that regulates regenerative neurogenesis after AD conditions in zebrafish.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Human brains are prone to neurodegeneration, given that endogenous neural stem/progenitor cells (NSPCs) fail to support neurogenesis. To investigate the molecular programs potentially mediating ...neurodegeneration-induced NSPC plasticity in regenerating organisms, we generated an Amyloid-β42 (Aβ42)-dependent neurotoxic model in adult zebrafish brain through cerebroventricular microinjection of cell-penetrating Aβ42 derivatives. Aβ42 deposits in neurons and causes phenotypes reminiscent of amyloid pathophysiology: apoptosis, microglial activation, synaptic degeneration, and learning deficits. Aβ42 also induces NSPC proliferation and enhanced neurogenesis. Interleukin-4 (IL4) is activated primarily in neurons and microglia/macrophages in response to Aβ42 and is sufficient to increase NSPC proliferation and neurogenesis via STAT6 phosphorylation through the IL4 receptor in NSPCs. Our results reveal a crosstalk between neurons and immune cells mediated by IL4/STAT6 signaling, which induces NSPC plasticity in zebrafish brains.
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•Amyloid-β42 (Aβ42) forms aggregates in neurons of adult zebrafish brain•Aβ42 causes apoptosis, inflammation, synaptic loss, and memory deficits in zebrafish•Aβ42 leads to interleukin-4 (IL4) upregulation in neurons and microglia•IL4/STAT6 signaling induces neural stem cell proliferation
Bhattarai et al. shows that adult zebrafish brain displays Alzheimer’s disease-like phenotypes after Amyloid-β42 (Aβ42) aggregation. Aβ42 can also activate neural stem cell proliferation and neurogenesis. Interleukin-4, which induces STAT6 phosphorylation, is a key factor for mediating the neuro-immune crosstalk between diseased neurons, immune cells, and stem cells.
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