sox1a:eGFP transgenic line and single-cell transcriptomics reveal the origin of zebrafish intraspinal serotonergic neurons

Sox transcription factors are crucial for vertebrate nervous system development. In zebrafish embryo, sox1 genes are expressed in neural progenitor cells and neurons of ventral spinal cord. Our recent study revealed that the loss of sox1a and sox1b function results in a significant decline of V2 subtype neurons (V2s). Using single-cell RNA sequencing, we analyzed the transcriptome of sox1a lineage progenitors and neurons in the zebrafish spinal cord at four time points during embryonic development, employing the Tg(sox1a:eGFP) line. In addition to previously characterized sox1a-expressing neurons, we discovered the expression of sox1a in late-developing intraspinal serotonergic neurons (ISNs). Developmental trajectory analysis suggests that ISNs arise from lateral floor plate (LFP) progenitor cells. Pharmacological inhibition of the Notch signaling pathway revealed its role in negatively regulating LFP progenitor cell differentiation into ISNs. Our findings highlight the zebrafish LFP as a progenitor domain for ISNs, alongside known Kolmer-Agduhr (KA) and V3 interneurons

RNA methyltransferase NSun2 deficiency promotes neurodegeneration through epitranscriptomic regulation of tau phosphorylation.

Epitranscriptomic regulation adds a layer of post-transcriptional control to brain function during development and adulthood. The identification of RNA-modifying enzymes has opened the possibility of investigating the role epitranscriptomic changes play in the disease process. NOP2/Sun RNA methyltransferase 2 (NSun2) is one of the few known brain-enriched methyltransferases able to methylate mammalian non-coding RNAs. NSun2 loss of function due to autosomal-recessive mutations has been associated with neurological abnormalities in humans. Here, we show NSun2 is expressed in adult human neurons in the hippocampal formation and prefrontal cortex. Strikingly, we unravel decreased NSun2 protein expression and an increased ratio of pTau/NSun2 in the brains of patients with Alzheimer’s disease (AD) as demonstrated by Western blotting and immunostaining, respectively. In a well-established Drosophila melanogaster model of tau-induced toxicity, reduction of NSun2 exacerbated tau toxicity, while overexpression of NSun2 partially abrogated the toxic effects. Conditional ablation of NSun2 in the mouse brain promoted a decrease in the miR-125b m6A levels and tau hyperphosphorylation. Utilizing human induced pluripotent stem cell (iPSC)-derived neuronal cultures, we confirmed NSun2 deficiency results in tau hyperphosphorylation. We also found that neuronal NSun2 levels decrease in response to amyloid-beta oligomers (AβO). Notably, AβO-induced tau phosphorylation and cell toxicity in human neurons could be rescued by overexpression of NSun2. Altogether, these results indicate that neuronal NSun2 deficiency promotes dysregulation of miR-125b and tau phosphorylation in AD and highlights a novel avenue for therapeutic targeting.post-print10112 K

Modeling of Alzheimer’s disease in adult zebrafish brain and characterization of pathology-induced neural stem cell plasticity

Die Alzheimer-Krankheit ist eine gewaltige Bedrohung für eine alternde Gesellschaft. Millionen von Menschen leben weltweit mit der Alzheimer-Krankheit, für die es keine aktuelle Behandlung gibt. Die Amyloidkaskaden-Hypothese (AKH) ist die aktuell am meisten akzeptierte Hypothese zur Ursache der Alzheimer-Krankheit. Die AKH bietet eine mechanistische Sicht auf die pathologische Kaskade, ausgehend von der Amyloid-Aggregation über die chronische Entzündung bis hin zur TAU-Pathologie. Die Medikamente, die auf der Grundlage der AKH entwickelt wurden, konnten Amyloid-Plaques bei Alzheimer-Patienten entfernen, brachten aber keine Verbesserung der kognitiven Fähigkeiten. Diese Misserfolge legen nahe, dass die Alzheimer-Krankheit nicht nur theoretisch im Rahmen der AKH betrachtet werden kann. Neuere Hypothesen kulminieren die Auswirkungen verschiedener Zelltypen (z.B. neurale Stammzellen, Astrozyten, Oligodendrozyten) auf den Ausbruch der Alzheimer-Erkrankung. Komplexe Rückkopplungs- und Feed-Forward-Mechanismen sind in der Pathophysiologie der Alzheimer-Demenz wahrscheinlich. Das Zusammenspiel zwischen der Pathologie und der Beteiligung anderer Zelltypen macht diese Krankheit multifaktoriell und komplex. Kürzlich zeigten zwei Studien (Moreno-Jimenez et al., 2019; Tobin et al., 2019), dass die Produktion neuer Neuronen im menschlichen Gehirn bei der Alzheimer-Erkrankung dramatisch abnimmt. Eine interessante Hypothese wurde durch diese Studien gestützt: Die pathologisch induzierte Erzeugung neuer Neuronen (regenerative Neurogenese) bei Alzheimer-Patienten könnte helfen, die Pathologie der Alzheimer-Erkrankung rückgängig zu machen. Da die Regenerationsfähigkeit bei Säugetieren entwicklungsmäßig wenig ausgeprägt ist (Tanaka und Ferretti, 2009), kann uns die Untersuchung der Neurodegeneration in einem Modellorganismus mit Regenerationsfähigkeit daher lehren, wie man die Proliferation und Neurogenese neuraler Stammzellen unter pathologischen Bedingungen induzieren kann. Für diese spezielle Frage können uns Modellorganismen mit natürlicher Regenerationsfähigkeit zeigen, wie man Proliferation und Neurogenese unter den pathologischen Bedingungen der Alzheimer-Erkrankung induzieren kann. Der Zebrafisch bietet eine beispiellose Möglichkeit, die Neurodegeneration und Regeneration zu modellieren, um die molekularen Mechanismen zu untersuchen, wie anhand der Neurogenese in Wirbeltiergehirnen die Alzheimer-Krankheit verbessert werden kann. Dies wurde in unserem Labor bereits in mehreren Publikationen gezeigt. Aus diesem Grund habe ich in meiner Doktorarbeit Zebrafische verwendet, um die Plastizität neuraler Stammzellen (NSZ) zu untersuchen. Besonders interessierte mich die Heterogenität von NSZ-Populationen in Bezug auf ihre molekularen Programme und die molekulare Grundlage der regenerativen Neurogenese von NSZ auf das Amyloid-β-42 (Aβ42) und TAU-Pathologien

Single Cell/Nucleus Transcriptomics Comparison in Zebrafish and Humans Reveals Common and Distinct Molecular Responses to Alzheimer’s Disease

Neurogenesis is significantly reduced in Alzheimer’s disease (AD) and is a potential therapeutic target. Contrary to humans, a zebrafish can regenerate its diseased brain, and thus is ideal for studying neurogenesis. To compare the AD-related molecular pathways between humans and zebrafish, we compared single cell or nuclear transcriptomic data from a zebrafish amyloid toxicity model and its controls (N = 12) with the datasets of two human adult brains (N = 10 and N = 48 (Microglia)), and one fetal brain (N = 10). Approximately 95.4% of the human and zebrafish cells co-clustered. Within each cell type, we identified differentially expressed genes (DEGs), enriched KEGG pathways, and gene ontology terms. We studied synergistic and non-synergistic DEGs to point at either common or uniquely altered mechanisms across species. Using the top DEGs, a high concordance in gene expression changes between species was observed in neuronal clusters. On the other hand, the molecular pathways affected by AD in zebrafish astroglia differed from humans in favor of the neurogenic pathways. The integration of zebrafish and human transcriptomes shows that the zebrafish can be used as a tool to study the cellular response to amyloid proteinopathies. Uniquely altered pathways in zebrafish could highlight the specific mechanisms underlying neurogenesis, which are absent in humans, and could serve as potential candidates for therapeutic developments

Modeling of Alzheimer’s disease in adult zebrafish brain and characterization of pathology-induced neural stem cell plasticity

Die Alzheimer-Krankheit ist eine gewaltige Bedrohung für eine alternde Gesellschaft. Millionen von Menschen leben weltweit mit der Alzheimer-Krankheit, für die es keine aktuelle Behandlung gibt. Die Amyloidkaskaden-Hypothese (AKH) ist die aktuell am meisten akzeptierte Hypothese zur Ursache der Alzheimer-Krankheit. Die AKH bietet eine mechanistische Sicht auf die pathologische Kaskade, ausgehend von der Amyloid-Aggregation über die chronische Entzündung bis hin zur TAU-Pathologie. Die Medikamente, die auf der Grundlage der AKH entwickelt wurden, konnten Amyloid-Plaques bei Alzheimer-Patienten entfernen, brachten aber keine Verbesserung der kognitiven Fähigkeiten. Diese Misserfolge legen nahe, dass die Alzheimer-Krankheit nicht nur theoretisch im Rahmen der AKH betrachtet werden kann. Neuere Hypothesen kulminieren die Auswirkungen verschiedener Zelltypen (z.B. neurale Stammzellen, Astrozyten, Oligodendrozyten) auf den Ausbruch der Alzheimer-Erkrankung. Komplexe Rückkopplungs- und Feed-Forward-Mechanismen sind in der Pathophysiologie der Alzheimer-Demenz wahrscheinlich. Das Zusammenspiel zwischen der Pathologie und der Beteiligung anderer Zelltypen macht diese Krankheit multifaktoriell und komplex. Kürzlich zeigten zwei Studien (Moreno-Jimenez et al., 2019; Tobin et al., 2019), dass die Produktion neuer Neuronen im menschlichen Gehirn bei der Alzheimer-Erkrankung dramatisch abnimmt. Eine interessante Hypothese wurde durch diese Studien gestützt: Die pathologisch induzierte Erzeugung neuer Neuronen (regenerative Neurogenese) bei Alzheimer-Patienten könnte helfen, die Pathologie der Alzheimer-Erkrankung rückgängig zu machen. Da die Regenerationsfähigkeit bei Säugetieren entwicklungsmäßig wenig ausgeprägt ist (Tanaka und Ferretti, 2009), kann uns die Untersuchung der Neurodegeneration in einem Modellorganismus mit Regenerationsfähigkeit daher lehren, wie man die Proliferation und Neurogenese neuraler Stammzellen unter pathologischen Bedingungen induzieren kann. Für diese spezielle Frage können uns Modellorganismen mit natürlicher Regenerationsfähigkeit zeigen, wie man Proliferation und Neurogenese unter den pathologischen Bedingungen der Alzheimer-Erkrankung induzieren kann. Der Zebrafisch bietet eine beispiellose Möglichkeit, die Neurodegeneration und Regeneration zu modellieren, um die molekularen Mechanismen zu untersuchen, wie anhand der Neurogenese in Wirbeltiergehirnen die Alzheimer-Krankheit verbessert werden kann. Dies wurde in unserem Labor bereits in mehreren Publikationen gezeigt. Aus diesem Grund habe ich in meiner Doktorarbeit Zebrafische verwendet, um die Plastizität neuraler Stammzellen (NSZ) zu untersuchen. Besonders interessierte mich die Heterogenität von NSZ-Populationen in Bezug auf ihre molekularen Programme und die molekulare Grundlage der regenerativen Neurogenese von NSZ auf das Amyloid-β-42 (Aβ42) und TAU-Pathologien

Single Cell/Nucleus Transcriptomics Comparison in Zebrafish and Humans Reveals Common and Distinct Molecular Responses to Alzheimer’s Disease

Neurogenesis is significantly reduced in Alzheimer’s disease (AD) and is a potential therapeutic target. Contrary to humans, a zebrafish can regenerate its diseased brain, and thus is ideal for studying neurogenesis. To compare the AD-related molecular pathways between humans and zebrafish, we compared single cell or nuclear transcriptomic data from a zebrafish amyloid toxicity model and its controls (N = 12) with the datasets of two human adult brains (N = 10 and N = 48 (Microglia)), and one fetal brain (N = 10). Approximately 95.4% of the human and zebrafish cells co-clustered. Within each cell type, we identified differentially expressed genes (DEGs), enriched KEGG pathways, and gene ontology terms. We studied synergistic and non-synergistic DEGs to point at either common or uniquely altered mechanisms across species. Using the top DEGs, a high concordance in gene expression changes between species was observed in neuronal clusters. On the other hand, the molecular pathways affected by AD in zebrafish astroglia differed from humans in favor of the neurogenic pathways. The integration of zebrafish and human transcriptomes shows that the zebrafish can be used as a tool to study the cellular response to amyloid proteinopathies. Uniquely altered pathways in zebrafish could highlight the specific mechanisms underlying neurogenesis, which are absent in humans, and could serve as potential candidates for therapeutic developments

KYNA/Ahr Signaling Suppresses Neural Stem Cell Plasticity and Neurogenesis in Adult Zebrafish Model of Alzheimer’s Disease

Neurogenesis decreases in Alzheimer’s disease (AD) patients, suggesting that restoring the normal neurogenic response could be a disease modifying intervention. To study the mechanisms of pathology-induced neuro-regeneration in vertebrate brains, zebrafish is an excellent model due to its extensive neural regeneration capacity. Here, we report that Kynurenic acid (KYNA), a metabolite of the amino acid tryptophan, negatively regulates neural stem cell (NSC) plasticity in adult zebrafish brain through its receptor, aryl hydrocarbon receptor 2 (Ahr2). The production of KYNA is suppressed after amyloid-toxicity through reduction of the levels of Kynurenine amino transferase 2 (KAT2), the key enzyme producing KYNA. NSC proliferation is enhanced by an antagonist for Ahr2 and is reduced with Ahr2 agonists or KYNA. A subset of Ahr2-expressing zebrafish NSCs do not express other regulatory receptors such as il4r or ngfra, indicating that ahr2-positive NSCs constitute a new subset of neural progenitors that are responsive to amyloid-toxicity. By performing transcriptome-wide association studies (TWAS) in three late onset Alzheimer disease (LOAD) brain autopsy cohorts, we also found that several genes that are components of KYNA metabolism or AHR signaling are differentially expressed in LOAD, suggesting a strong link between KYNA/Ahr2 signaling axis to neurogenesis in LOAD

IL4/STAT6 Signaling Activates Neural Stem Cell Proliferation and Neurogenesis upon Amyloid-β42 Aggregation in Adult Zebrafish Brain

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

Neuron-glia interaction through Serotonin-BDNF-NGFR axis enables regenerative neurogenesis in Alzheimer's model of adult zebrafish brain.

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

Glia-neuron interactions underlie state transitions to generalized seizures

Brain activity and connectivity alter drastically during epileptic seizures. The brain networks shift from a balanced resting state to a hyperactive and hypersynchronous state. It is, however, less clear which mechanisms underlie the state transitions. By studying neural and glial activity in zebrafish models of epileptic seizures, we observe striking differences between these networks. During the preictal period, neurons display a small increase in synchronous activity only locally, while the gap-junction-coupled glial network was highly active and strongly synchronized across large distances. The transition from a preictal state to a generalized seizure leads to an abrupt increase in neural activity and connectivity, which is accompanied by a strong alteration in glia-neuron interactions and a massive increase in extracellular glutamate. Optogenetic activation of glia excites nearby neurons through the action of glutamate and gap junctions, emphasizing a potential role for glia-glia and glia-neuron connections in the generation of epileptic seizures.status: publishe