Alzheimer's disease-related peptide PS2V plays ancient, conserved roles in suppression of the unfolded protein response under hypoxia and stimulation of γ-secretase activity.

The PRESENILIN1 and PRESENILIN2 genes encode structurally related proteases essential for γ-secretase activity. Of nearly 200 PRESENILIN mutations causing early onset, familial Alzheimer's disease (FAD) only the K115Efx10 mutation of PSEN2 causes truncation of the open reading frame. If translated, the truncated product would resemble a naturally occurring isoform of PSEN2 named PS2V that is induced by hypoxia and found at elevated levels in late onset Alzheimer's disease (AD) brains. The function of PS2V is largely unexplored. We show that zebrafish possess a PS2V-like isoform, PS1IV, produced from the fish's PSEN1 rather than PSEN2 orthologous gene. The molecular mechanism controlling formation of PS2V/PS1IV was probably present in the ancient common ancestor of the PSEN1 and PSEN2 genes. Human PS2V and zebrafish PS1IV have highly divergent structures but conserved abilities to stimulate γ-secretase activity and to suppress the unfolded protein response (UPR) under hypoxia. The putative protein truncation caused by K115Efx10 resembles PS2V in its ability to increase γ-secretase activity and suppress the UPR. This supports increased Aß levels as a common link between K115Efx10 early onset AD and sporadic, late onset AD. The ability of mutant variants of PS2V to stimulate γ-secretase activity partially correlates with their ability to suppress the UPR. The cytosolic, transmembrane and luminal domains of PS2V are all critical to its γ-secretase and UPR-suppression activities. Our data support a model in which chronic hypoxia in aged brains promotes excessive Notch signalling and accumulation of Aß that contribute to AD pathogenesis.

Differential, dominant activation and inhibition of Notch signalling and APP cleavage by truncations of PSEN1 in human disease.

PRESENILIN1 (PSEN1) is the major locus for mutations causing familial Alzheimer's disease (FAD) and is also mutated in Pick disease of brain, familial acne inversa and dilated cardiomyopathy. It is a critical facilitator of Notch signalling and many other signalling pathways and protein cleavage events including production of the Amyloidß (Aß) peptide from the AMYLOID BETA A4 PRECURSOR PROTEIN (APP). We previously reported that interference with splicing of transcripts of the zebrafish orthologue of PSEN1 creates dominant negative effects on Notch signalling. Here, we extend this work to show that various truncations of human PSEN1 (or zebrafish Psen1) protein have starkly differential effects on Notch signalling and cleavage of zebrafish Appa (a paralogue of human APP). Different truncations can suppress or stimulate Notch signalling but not Appa cleavage and vice versa. The G183V mutation possibly causing Pick disease causes production of aberrant transcripts truncating the open reading frame after exon 5 sequence. We show that the truncated protein potentially translated from these transcripts avidly incorporates into very stable Psen1-dependent higher molecular weight complexes and suppresses cleavage of Appa but not Notch signalling. In contrast, the truncated protein potentially produced by the P242LfsX11 acne inversa mutation has no effect on Appa cleavage but, unexpectedly, enhances Notch signalling. Our results suggest novel hypotheses for the pathological mechanisms underlying these diseases and illustrate the importance of investigating the function of dominant mutations at physiologically relevant expression levels and in the normally heterozygous state in which they cause human disease rather than in isolation from healthy alleles.

The development of an in vivo γ-secretase assay using zebrafish embryos.

Aberrant proteolytic processing of amyloid-ß protein precursor by γ-secretase complexes may result in an imbalance between production and clearance of the Aß proteolytic product and promote neuronal dysfunction and death. Presenilin proteins form the catalytic core of γ-secretase complexes. The zebrafish, Danio rerio, is a versatile vertebrate model for investigating the molecular basis of Alzheimer's disease pathology. It possesses genes orthologous to human PSEN1 and PSEN2 (psen1 and psen2 respectively), and AßPP (appa and appb that are duplicates of an ancestral AßPP orthologue). Currently there is no in vivo assay appropriate for directly monitoring γ-secretase activity. Here, we describe such an assay in which the level of a γ-secretase substrate (a modified form of Appa protein) is observed in zebrafish embryos by western immunoblotting relative to a co-expressed protein not subject to γ-secretase activity. We have used the assay to analyze the effects on γ-secretase activity of blocking translation of transcripts of zebrafish psen1 and/or psen2.

Patents associated with high-cost drugs in Australia.

Australia, like most countries, faces high and rapidly-rising drug costs. There are longstanding concerns about pharmaceutical companies inappropriately extending their monopoly position by "evergreening" blockbuster drugs, through misuse of the patent system. There is, however, very little empirical information about this behaviour. We fill the gap by analysing all of the patents associated with 15 of the costliest drugs in Australia over the last 20 years. Specifically, we search the patent register to identify all the granted patents that cover the active pharmaceutical ingredient of the high-cost drugs. Then, we classify the patents by type, and identify their owners. We find a mean of 49 patents associated with each drug. Three-quarters of these patents are owned by companies other than the drug's originator. Surprisingly, the majority of all patents are owned by companies that do not have a record of developing top-selling drugs. Our findings show that a multitude of players seek monopoly control over innovations to blockbuster drugs. Consequently, attempts to control drug costs by mitigating misuse of the patent system are likely to miss the mark if they focus only on the patenting activities of originators.

The BACE1-PSEN-AßPP regulatory axis has an ancient role in response to low oxygen/oxidative stress.

Oxygen homeostasis is essential for the development and normal physiology of an organism. Hypoxia causes the mitochondrial electron transport chain to generate higher levels of reactive oxygen species resulting in oxidative stress. Hypoxia can be a direct consequence of hypoperfusion, a common vascular component among Alzheimer's disease (AD) risk factors, and may play an important role in AD pathogenesis. Beta-site amyloid-ß A4 precursor protein-cleaving enzyme 1 (BACE1) is responsible, with γ-secretase, for cleavage of the amyloid-ß protein precursor (AßPP) to produce amyloid-ß (Aß) peptide. A recent study observed that oxidative stress increases BACE1 expression via a regulatory pathway dependent on γ-secretase cleavage of AßPP and this increases Aß peptide production. Zebrafish embryos represent normal cells in which complex and subtle manipulations of gene activity can be performed to facilitate analysis of genes involved in human disease. Here we identify and describe the expression of bace1, the zebrafish ortholog of human BACE1. We observe that the zebrafish AD-related genes bace1, psen1, psen2, appa, and appb all show increased mRNA levels under hypoxia. A dominant negative form of psen1 putatively blocking γ-secretase activity blocks bace1 upregulation under hypoxia. Hypoxia increases catalase gene mRNA indicating increased oxidative stress but we did not observe increased levels of F2-isoprostanes that indicate peroxidation of arachidonic acid, possibly due to relatively low levels of arachidonic acid in zebrafish. Our results demonstrate that upregulation of PSEN1 & 2, AßPP and the γ-secretase-dependent upregulation of BACE1 is an ancient, conserved, and thus selectively advantageous response to hypoxia/oxidative stress.

A zebrafish melanophore model of amyloid beta toxicity.

Reliable animal models are required to facilitate the understanding of neurodegenerative pathways in Alzheimer's disease. Animal models can also be employed to search for disease-modifying drugs. The embryos and larvae of zebrafish are particularly advantageous for this purpose. For Alzheimer's disease, drugs that can ameliorate amyloid beta (A beta) toxicity have therapeutic and/or prophylactic potential. We attempted to generate a zebrafish model of A beta toxicity that would be viable and fertile but have a highly visible pigmentation phenotype in larvae. The larvae could then be arrayed in microtiter plates to screen compound libraries for drugs acting to reduce A beta toxicity. We used the promoter of the zebrafish mitfa (nacre) gene to drive expression of the pathological 42 amino acid species of human A beta, A beta(42), specifically in the highly visible melanophores (melanocytes) of transgenic zebrafish. However, the transgenic fish only showed an aberrant pigment phenotype in adults at the advanced age of 16 months. Nevertheless, our results show that alteration of zebrafish pigment pattern may be useful for analysis of toxic peptide action.