The familial Alzheimer's disease APPV717I mutation alters APP processing and Tau expression in iPSC-derived neurons

Abstract

Alzheimer's disease (AD) is a complex neurodegenerative disorder characterized by extracellular plaques containing amyloid β (Aβ)-protein and intracellular tangles containing hyperphosphorylated Tau protein. Here, we describe the generation of inducible pluripotent stem cell lines from patients harboring the London familial AD (fAD) amyloid precursor protein (APP) mutation (V717I). We examine AD-relevant phenotypes following directed differentiation to forebrain neuronal fates vulnerable in AD. We observe that over differentiation time to mature neuronal fates, APP expression and levels of Aβ increase dramatically. In both immature and mature neuronal fates, the APPV717I mutation affects both β- and γ-secretase cleavage of APP. Although the mutation lies near the γ-secretase cleavage site in the transmembrane domain of APP, we find that β-secretase cleavage of APP is elevated leading to generation of increased levels of both APPsβ and Aβ. Furthermore, we find that this mutation alters the initial cleavage site of γ-secretase, resulting in an increased generation of both Aβ42 and Aβ38. In addition to altered APP processing, an increase in levels of total and phosphorylated Tau is observed in neurons with the APPV717I mutation. We show that treatment with Aβ-specific antibodies early in culture reverses the phenotype of increased total Tau levels, implicating altered Aβ production in fAD neurons in this phenotype. These studies use human neurons to reveal previously unrecognized effects of the most common fAD APP mutation and provide a model system for testing therapeutic strategies in the cell types most relevant to disease processes.

Modulatory Effects of Fingolimod (FTY720) on the Expression of Sphingolipid Metabolism-Related Genes in an Animal Model of Alzheimer’s Disease

“…The FAD/early-onset AD-linked V717I "London" AβPP mutation [2,3] increases AβPP cleavage into Aβ and shifts the proportions of the cleavage products in favor of the highly neurotoxic Aβ 42 [4]. Little is known on other aspects of the influence of the mutation on the (still elusive) functions of AβPP in neurons.…”

“…enhancing the pathology [4]. Synergy has also been reported between Aβ 42 toxicity and ApoE allele [6].…”

Modelling Neurodegenerative Diseases Using Human Pluripotent Stem Cells

“…One study also reported an increase in Aβ oligomers in the analysed neural cells and astrocytes [44], which again correlates well with the patient's phenotype [59]. Increased p-tau has been observed in patients from two different studies [43,58] and total tau has also been reported [58]. Increased αGSK-3β has also been reported [43].…”

“…These studies have conflicting results in relation to APP processing, likely related to diverse pathology dependent on the mutation. One study found elevated Aβ40 [43], another study found one patient had increased Aβ42 whilst a second patient had decreased Aβ40 [44], and a third study revealed a patient with both increased Aβ42 and Aβ38 [58]. Two of these studies showed good correlation with known patient pathology, whilst the study reporting increased Aβ42:Aβ40 levels cannot be validated to the patient pathology since this mutation has not been well characterized.…”

The Roles of Genetics in Aβ related Alzheimer's Diseases

“…Recently, Sieczkowski E found that I716F βAPP is a mutation associated with glutamate-Aβ, which increases the generation of senile plaques and nerve tangles [22]. The APP 717 mutation increases the production of the soluble βAPP, Aβ42 and Aβ38, which are associated with dementia [23][24][25]. The newly discovered K724 mutation in China (40-58 years old) has been shown to enhance the Aβ 1-42 / Aβ 1-40 ratio (over 2-fold).…”