Accelerated brain aging towards transcriptional inversion in a zebrafish model of the K115fs mutation of human PSEN2

BACKGROUND:The molecular changes involved in Alzheimer's disease (AD) progression remain unclear since we cannot easily access antemortem human brains. Some non-mammalian vertebrates such as the zebrafish preserve AD-relevant transcript isoforms of the PRESENILIN genes lost from mice and rats. One example is PS2V, the alternative transcript isoform of the PSEN2 gene. PS2V is induced by hypoxia/oxidative stress and shows increased expression in late onset, sporadic AD brains. A unique, early onset familial AD mutation of PSEN2, K115fs, mimics the PS2V coding sequence suggesting that forced, early expression of PS2V-like isoforms may contribute to AD pathogenesis. Here we use zebrafish to model the K115fs mutation to investigate the effects of forced PS2V-like expression on the transcriptomes of young adult and aged adult brains. METHODS:We edited the zebrafish genome to model the K115fs mutation. To explore its effects at the molecular level, we analysed the brain transcriptome and proteome of young (6-month-old) and aged (24-month-old) wild type and heterozygous mutant female sibling zebrafish. Finally, we used gene co-expression network analysis (WGCNA) to compare molecular changes in the brains of these fish to human AD. RESULTS:Young heterozygous mutant fish show transcriptional changes suggesting accelerated brain aging and increased glucocorticoid signalling. These early changes precede a transcriptional 'inversion' that leads to glucocorticoid resistance and other likely pathological changes in aged heterozygous mutant fish. Notably, microglia-associated immune responses regulated by the ETS transcription factor family are altered in both our zebrafish mutant model and in human AD. The molecular changes we observe in aged heterozygous mutant fish occur without obvious histopathology and possibly in the absence of Aβ. CONCLUSIONS:Our results suggest that forced expression of a PS2V-like isoform contributes to immune and stress responses favouring AD pathogenesis. This highlights the value of our zebrafish genetic model for exploring molecular mechanisms involved in AD pathogenesis.Nhi Hin, Morgan Newman, Jan Kaslin, Alon M. Douek, Amanda Lumsden, Seyed Hani Moussavi Nik ... et al

The impact of cholesterol intake on expression of Alzheimer's disease–related genes in the guinea pig brain

Poster presentationGiuseppe Verdile, Matthew Sharman, Mengqi Chen, Seyed Moussavi Nik, Daniel Ong, Linda Wijaya, Newman Morgan, Michael Lardelli, Ralph Martin

Accelerated loss of hypoxia response in zebrafish with familial Alzheimer's disease-like mutation of Presenilin 1

Ageing is the major risk factor for Alzheimer's disease (ad), a condition involving brain hypoxia. The majority of early onset familial ad (EOfAD) cases involve dominant mutations in the gene PSEN1. PSEN1 null mutations do not cause EOfAD. We exploited putative hypomorphic and EOfAD-like mutations in the zebrafish psen1 gene to explore the effects of age and genotype on brain responses to acute hypoxia. Both mutations accelerate age-dependent changes in hypoxia-sensitive gene expression supporting that ageing is necessary, but insufficient, for ad occurrence. Curiously, the responses to acute hypoxia become inverted in extremely aged fish. This is associated with an apparent inability to upregulate glycolysis. Wild type PSEN1 allele expression is reduced in post-mortem brains of human EOfAD mutation carriers (and extremely aged fish), possibly contributing to EOfad pathogenesis. We also observed that age-dependent loss of HIF1 stabilisation under hypoxia is a phenomenon conserved across vertebrate classes.Morgan Newman, Hani Moussavi Nik, Greg T Sutherland, Nhi Hin, Woojin S Kim, Glenda M Halliday ... et al