Presenilin-1 Targeted Morpholino Induces Cognitive Deficits, Increased Brain Aß1-42 and Decreased Synaptic Marker PSD-95 in Zebrafish Larvae.

Presenilins are transmembrane proteases required for the proteolytic cleavage of Notch and also act as the catalytic core of the γ-secretase complex, which is responsible for the final cleavage of the amyloid precursor protein into Amyloid-ß (Aß) peptides of varying lengths. Presenilin-1 gene (psen1) mutations are the main cause of early-onset autosomal-dominant Familial Alzheimer Disease. Elucidating the roles of Presenilin-1 and other hallmark proteins involved in Alzheimer's disease is crucial for understanding the disease etiology and underlying molecular mechanisms. In our study, we used a morpholino antisense nucleotide that targets exon 8 splicing site of psen1 resulting in a dominant negative protein previously validated to investigate behavioral and molecular effects in 5 days post fertilization (dpf) zebrafish larvae. Morphants showed specific cognitive deficits in two optomotor tasks and morphological phenotypes similar to those induced by suppression of Notch signaling pathway. They also had increased mRNA levels of neurog1 at 5 dpf, confirming the potential interaction of Presenilin-1 and Notch in our model. We also evaluated levels of apoptotic markers including p53, PAR-4, Caspase-8 and bax-alpha and found only bax-a decreased at 5dpf. Western Blot analysis showed an increase in Aß1-42 and a decrease in the selective post-synaptic marker PSD-95 at 5 dpf. Our data demonstrates that psen1 splicing interference induces phenotypes that resemble early-stage AD, including cognitive deficit, Aß1-42 accumulation and synaptic reduction, reinforcing the potential contribution of zebrafish larvae to studies of human brain diseases.

Brain intraventricular injection of amyloid-ß in zebrafish embryo impairs cognition and increases tau phosphorylation, effects reversed by lithium.

Alzheimer's disease (AD) is a devastating neurodegenerative disorder with no effective treatment and commonly diagnosed only on late stages. Amyloid-ß (Aß) accumulation and exacerbated tau phosphorylation are molecular hallmarks of AD implicated in cognitive deficits and synaptic and neuronal loss. The Aß and tau connection is beginning to be elucidated and attributed to interaction with different components of common signaling pathways. Recent evidences suggest that non-fibrillary Aß forms bind to membrane receptors and modulate GSK-3ß activity, which in turn phosphorylates the microtubule-associated tau protein leading to axonal disruption and toxic accumulation. Available AD animal models, ranging from rodent to invertebrates, significantly contributed to our current knowledge, but complementary platforms for mechanistic and candidate drug screenings remain critical for the identification of early stage biomarkers and potential disease-modifying therapies. Here we show that Aß1-42 injection in the hindbrain ventricle of 24 hpf zebrafish embryos results in specific cognitive deficits and increased tau phosphorylation in GSK-3ß target residues at 5dpf larvae. These effects are reversed by lithium incubation and not accompanied by apoptotic markers. We believe this may represent a straightforward platform useful to identification of cellular and molecular mechanisms of early stage AD-like symptoms and the effects of neuroactive molecules in pharmacological screenings.