Abstract
The R47H variant of the Triggering-Receptor-Expressed on Myeloid cells 2 (TREM2) increases the risk of Alzheimer’s disease (AD). Mutagenesis of exon 2 in Knock-in (KI) mouse models of the R47H variant introduced a cryptic splice site, leading to nonsense mediated decay. Since haploinsufficiency does not model Trem2-R47H function, a new rat KI model, the Trem2R47H KI rat was created. Human Aβ has higher propensity to form toxic Aβ species, which are considered the main pathogenic entity in AD, as compared to rodent Aβ, the rat Amyloid Precursor Protein (App) gene was mutated to produce human Aβ. Trem2 splicing and expression was measured in Trem2R47H KI rat brains and microglia by qualitative and quantitative RT-PCR. Trem2 levels and Trem2 processing was assessed by Western analysis. APP metabolite levels were determined by enzyme-linked immunosorbent assay (ELISA), for Human Aβ and soluble APP, and Western analysis, for full length APP, βCTF and αCTF. Trem2 expression and Trem2 levels are unchanged in Trem2R47H KI rats. The artifactual splicing seen in KI mouse models is not present; additionally, two novel isoforms of rat Trem2 are described. Trem2R47H rat brains have lower human Aβ38, sAPPα and sAPPβ levels. Thus, Trem2R47H KI rats may prove valuable to define pathogenic mechanisms triggered by the Trem2 R47H variant, including those mediated by toxic species of human Aβ peptides.
Highlights
Alzheimer’s disease (AD) is a progressive neurodegenerative disorder and the most common form of dementia in the elderly[1]
Because Aβ and Aβ-plaques are believed central to the pathogenesis of AD, it is postulated that Triggering-Receptor-Expressed on Myeloid cells 2 (TREM2) mutations reduce TREM2 function and increase dementia risk by hampering the anti-amyloidogenic activity of Department of Pharmacology, Physiology & Neuroscience New Jersey Medical School, Brain Health Institute, Jacqueline Krieger Klein Center in Alzheimer’s Disease and Neurodegeneration Research, Rutgers, The State University of New Jersey, 185 South Orange Ave, Newark, NJ, 07103, USA. *email: luciano.dadamio@rutgers.edu www.nature.com/scientificreports/
Rat Amyloid Precursor Protein (App) was humanized for the following reasons: 1) aggregated or oligomeric forms of Aβ are by and large considered the main pathogenic entity in AD; 2) human Aβ has higher propensity to form toxic Aβ species as compared to rodent Aβ; 3) as discussed above, TREM2 pathogenic variants may facilitate neurodegeneration by increasing human Aβ-mediated neurotoxicity, Here, we characterize the effect of Trem2R47H on human Aβ levels and APP processing
Summary
Alzheimer’s disease (AD) is a progressive neurodegenerative disorder and the most common form of dementia in the elderly[1]. Because Aβ and Aβ-plaques are believed central to the pathogenesis of AD, it is postulated that TREM2 mutations reduce TREM2 function and increase dementia risk by hampering the anti-amyloidogenic activity of www.nature.com/scientificreports microglia. Analysis of Trem[2] expression in these models revealed a reduction in Trem[2] levels that resulted from the generation of a cryptic splice site which introduces a premature stop codon[14,16]. This splicing impairment was not seen in transcriptional analysis of a human TREM2-R47H minigene, TREM2-R47H iPSC-derived human microglia-like cells, or in brain from patients heterozygous for the mutation[14]. Our findings put forward a rat KI model of Trem[2] as a viable model for the investigation of p.R47H in animals producing human Aβ
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