Sheep models of Alzheimer's Disease
Year: 2023
Type: article
Abstract: Alzheimer’s disease (AD) is a devastating neurodegenerative disease. The prevalence is rapidly increasing due to an ageing population worldwide, creating a looming population health crisis. Many rodent models of AD have been created, but none capture the full symptomatology without massively overexpressing multiple human mutations in transgenes. The aim of this project was to create large animal models of AD with single mutations in native genes. Sheep have larger bodies and a gyrencephalic brain similar to human. Importantly, they naturally develop plaques and tangles as they age. Major AD-related genes, such as APP, PSEN1 and PSEN2, and the APP cleavage sites which produce the Aβ peptide, are highly conserved between human and sheep. Also and importantly, sheep are naturally fixed for the APOE4 allele associated with late onset AD in humans. They can also be efficiently bred in large numbers and simply maintained in a normal farming situation. Two gene edited sheep lines were produced by injection of CRISPR-Cas9 RNP complexes, including a single strand donor DNA carrying the PSEN1 E280A or APP Swedish mutation, into single cell zygotes, which were then implanted. Five founder animals were born carrying the PSEN1 E280A mutation. One ewe is homozygous, two ewes are heterozygous, and two rams are hemizygous with frameshift mutations on their non-E280A allele. Two rams were heterozygous for the APP Swedish mutation. The founder lambs were genotyped by PCR and whole genome sequenced to confirm zygosity. No off-target editing was detected. All animals are outwardly healthy and growing normally. Repeated plasma biomarker analysis of the PSEN1 E280A animals revealed that Aβ1-42:Aβ1-40 peptide ratios are increased in the mutation carriers. The APP Swedish lambs had greatly enhanced Aβ1-40 and Aβ1- 42 concentrations. Both of these phenotypes correspond with human mutation carriers. For the PSEN1 E280A founders, one heterozygous ewe and one ram have been used to create F1 lines carrying the mutation. The mutation carrying offspring from the ewe lamb have inherited the Aβ biomarker phenotype, as expected. The offspring from the ram have just been born and will be part of a life history study. For the APP Swedish founders, one ram has been used to create an F1 line, which will also be part of a natural history study. If these animals can recapitulate the entire disease from a single gene cause, they will likely shed light on the underlying mechanisms of AD that have proven elusive with small animal models. These animals are also likely to be useful for preclinical pharmaceutical testing.
Subfield: Physiology
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W7135332299
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