Modeling Amyloid-β42 Toxicity and Neurodegeneration in Adult Zebrafish Brain

Abstract

Alzheimer's disease (AD) is a debilitating neurodegenerative disease in which accumulation of toxic amyloid-β42 (Aβ42) peptides leads to synaptic degeneration, inflammation, neuronal death, and learning deficits. Humans cannot regenerate lost neurons in the case of AD in part due to impaired proliferative capacity of the neural stem/progenitor cells (NSPCs) and reduced neurogenesis. Therefore, efficient regenerative therapies should also enhance the proliferation and neurogenic capacity of NSPCs. Zebrafish (Danio rerio) is a regenerative organism, and we can learn the basic molecular programs with which we could design therapeutic approaches to tackle AD. For this reason, the generation of an AD-like model in zebrafish was necessary. Using our methodology, we can introduce synthetic derivatives of Aβ42 peptide with tissue penetrating capability into the adult zebrafish brain, and analyze the disease pathology and the regenerative response. The advantage over the existing methods or animal models is that zebrafish can teach us how a vertebrate brain can naturally regenerate, and thus help us to treat human neurodegenerative diseases better by targeting endogenous NSPCs. Therefore, the amyloid-toxicity model established in the adult zebrafish brain may open new avenues for research in the field of neuroscience and clinical medicine. Additionally, the simple execution of this method allows for cost-effective and efficient experimental assessment. This manuscript describes the synthesis and injection of Aβ42 peptides into zebrafish brain.

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

“…Since Aβ42/IL4 enhances neural stem cell (NSC) proliferation in adult zebrafish brain (Bhattarai et al, 2017a;Bhattarai et al, 2016;Bhattarai et al, 2017b;Kizil, 2018;Kizil and Bhattarai, 2018b) and they downregulate 5-HT ( Figure 1E,F), we hypothesized that 5-HT could be negatively affecting NSC plasticity. To test this, we injected 5-HT into adult zebrafish brain and analyzed the proliferation of NSCs (S100b/PCNA double positive cells) (Figure 2A-C).…”

“…Amyloid-β42 (Aβ42) synthesis was performed as described . Cerebroventricular microinjection in adult zebrafish brain were performed as previously described (Bhattarai et al, 2017a;Bhattarai et al, 2016;Bhattarai et al, 2017b). PBS (1μl), Aβ42 (1 μl, 20 μM), IL4 (1 μl, 10 μg/ml), BDNF (1 μl, 100ng/ml), 5-HT (1 μl, 100 μM), ngfra morpholino (1μl, 10uM) were injected.…”

“…Therefore, examining how NSCs could be made proliferative and neurogenic during the course of AD could provide important clinical ramifications towards the treatment of this disease (Kizil and Bhattarai, 2018a); however, little is known about the mechanisms by which neural stem cells would enhance their proliferative response (Dong et al, 2019;Kempermann et al, 2018;Morrens et al, 2012). Recently, we established a zebrafish model, which can recapitulate the symptoms of AD in humans such as neuronal death, synaptic degeneration, chronic inflammation and cognitive decline (Bhattarai et al, 2017a;Bhattarai et al, 2016). Interestingly, in contrast to humans, zebrafish brain could enhance NSC proliferation and neurogenesis through a previously unidentified neuro-immune regulation involving Interleukin-4 (IL4).…”

Single cell analyses of the effects of Amyloid-beta42 and Interleukin-4 on neural stem/progenitor cell plasticity in adult zebrafish brain

“…Its direct effect on neuronal integrity and stem cell plasticity, and whether it is the causative agent for Alzheimer’s pathology are still controversial. We previously showed that Aβ42 treatment causes phenotypes reminiscent of human AD conditions, namely, cell death, synaptic degeneration, inflammation and cognitive deficits (Bhattarai et al, 2017a; Bhattarai et al, 2016b; Bhattarai et al, 2017b). However, in contrast to mammals, zebrafish NSPCs increased their proliferation and neurogenic output indicating that adult zebrafish brain responds to Aβ42 toxicity by enhancing NSPC plasticity and neuroregeneration (Bhattarai et al, 2016b; Bhattarai et al, 2017b).…”

“…Central nervous system regeneration is catching particular attention because of robust neural regeneration ability in zebrafish and clinical ramifications it might bring, which could not be possible to elucidate with mammalian models. For instance, we have recently generated an Amyloid toxicity model in adult zebrafish brain and identified that zebrafish can effectively enhance its neural stem cell proliferation and neurogenesis with key activity of Interleukin-4 (IL4) that mediates the crosstalk between disease pathology in neurons and initiation of regenerative output in stem cells (Bhattarai et al, 2017a; Bhattarai et al, 2016b; Bhattarai et al, 2017b; Kizil, 2018). We also found that IL4 can directly affect the human neural stem cells in a similar fashion to induce the proliferative and neurogenic ability (Papadimitriou et al, 2018).…”