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Comparison of the effects of mutaions modelling early-onset familial Alzheimer's disease and Sanfilippo syndrome childhood dementia in zebrafish larvae

ABSTRACT: Neural cells are under immense pressure to maintain proper degradation of molecules using their endo-lysosomal pathway (ELP). In Alzheimer’s disease (AD), the gradual cognitive worsening of this age-related disorder is partially due to dysfunction of the ELP. However, AD is a complex disorder and how the genetic landscape eventually leads to AD is unclear. Sanfilippo syndrome childhood dementia (mucopolysaccharidosis type III, MPSIII) is an extreme consequence of ELP dysfunction, where inherited recessive mutations result in the inability to properly catabolise a particular polysaccharide, which ultimately accumulates and interferes with the function of the ELP. Unlike AD, Sanfilippo is genetically simple (all causative genes are identified). The primary biochemical consequences are understood and animal models of Sanfilippo are considered excellent models of the human disease. Since Sanfilippo and AD show similar pathological changes, they likely share disease-associated mechanisms. Here, we dissect the similarity between AD and Sanfilippo using RNA-seq. We have generated zebrafish knock-in models of both diseases: the early-onset familial AD-like (EOfAD-like) mutation psen1 Q96_K97del and the MPSIII-like mutation naglu A603fs. We generated a family of zebrafish containing wild type, heterozygous EOfAD-like and homozygous MPSIII-like genotypes. We raised the family until 7 days post fertilisation and performed mRNA-seq on n = 8 induvial larvae per genotype. A power calculation revealed that this experiment was only contained ~50% power to detect differentially expressed genes. Nevertheless, changes to the expression of genes encoding proteins involved in lysosomal function could be detected in the MPS-III mutant larvae, suggesting a homeostatic response as the cells which make up the larval RNA-seq samples respond to dysfunctional lysosomes.

ORGANISM(S): Danio rerio

PROVIDER: GSE217196 | GEO | 2022/11/08

REPOSITORIES: GEO

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Project description:Early-onset familial Alzheimer’s disease (EOfAD) is promoted by dominant mutations, enabling the study of Alzheimer’s disease (AD) pathogenic mechanisms through generation of EOfAD-like mutations in animal models. In a previous study, we generated an EOfAD-like mutation, psen1Q96_K97del, in zebrafish and performed a transcriptome analysis comparing entire brains from 6-month-old wild type and heterozygous mutant fish. We identified predicted effects on mitochondrial function and endolysosomal acidification. Here we aimed to determine whether similar effects occur in 7 day post fertilization (dpf) zebrafish larvae that might be exploited in screening of chemical libraries to find ameliorative drugs. We generated clutches of wild type and heterozygous psen1Q96_K97del 7 dpf larvae using a paired-mating strategy to reduce extraneous genetic variation before performing a comparative transcriptome analysis. We identified 228 differentially expressed genes and performed Goseq analysis and gene set enrichment analysis (GSEA). This predicted a significant effect on oxidative phosphorylation, consistent with our earlier observations of predicted effects on ATP synthesis in adult heterozygous psen1Q96_K97del brains. The dysregulation of minichromosome maintenance protein complex (MCM) genes strongly contributed to predicted effects on DNA replication and the cell cycle and may explain earlier observations of genome instability due to PSEN1 mutation. The upregulation of crystallin gene expression may be a response to defective activity of mutant Psen1 protein in endolysosomal acidification. Extracellular matrix (ECM) related genes were downregulated, consistent with previous studies of EOfAD mutant iPSC neurons and postmortem late onset AD brains. Also, changes in expression of genes controlling iron ion transport were observed without identifiable changes in the prevalence of transcripts containing iron responsive elements (IREs) in their 3’ untranslated regions. These changes may, therefore, predispose to the apparent iron dyshomeostasis previously observed in 6-month-old heterozygous psen1Q96_K97del EOfAD-like mutant brains.

Project description:To prevent or delay the onset of Alzheimer’s disease (AD), we must understand its molecular basis. The great majority of AD cases arise sporadically with a late onset after 65 years of age (LOAD). However, rare familial cases of AD can occur due to dominant mutations in a small number of genes that cause an early onset prior to 65 years of age (EOfAD). As EOfAD and LOAD share similar pathologies and disease progression, analysis of EOfAD genetic models may give insight into both subtypes of AD. Sortilin-related receptor 1 (SORL1) is genetically associated with both EOfAD and LOAD and provides a unique opportunity to investigate the relationships between both forms of AD. Currently, the role of SORL1 mutations in AD pathogenesis is unclear. To understand the molecular consequences of SORL1 mutation, we performed targeted mutagenesis of the orthologous gene in zebrafish. We generated an EOfAD-like mutation, V1482Afs, and a putatively null mutation, to investigate whether EOfAD-like mutations in sorl1 display haploinsufficiency by acting through loss-of-function mechanisms. We performed mRNA-sequencing on whole brains, comparing wild type fish with their siblings heterozygous for EOfAD-like or putatively loss-of-function mutations in sorl1, or transheterozygous for these mutations. Differential gene expression analysis identified a small number of differentially expressed genes due to the sorl1 genotypes. We also performed enrichment analysis on all detectable genes to obtain a more complete view on changes to gene expression by performing three methods of gene set enrichment analysis, then calculated an overall significance value using the harmonic mean p-value. This identified subtle effects on expression of genes involved in energy production, mRNA translation and mTORC1 signalling in both the EOfAD-like and null mutant brains, implying that these effects are due to sorl1 haploinsufficiency. Surprisingly, we also observed changes to expression of genes occurring only in the EOfAD-mutation carrier brains, suggesting gain-of-function effects. Transheterozygosity for the EOfAD-like and null mutations (i.e. lacking wild type sorl1), caused apparent effects on iron homeostasis and other transcriptome changes distinct from the single-mutation heterozygous fish. Our results provide insight into the possible early brain molecular effects of an EOfAD mutation in human SORL1. Differential effects of heterozygosity and complete loss of normal SORL1 expression are revealed.

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Comparison of the effects of mutaions modelling early-onset familial Alzheimer's disease and Sanfilippo syndrome childhood dementia in zebrafish larvae

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