The presenilin 1 mutation P436S causes familial Alzheimer's disease with elevated Aβ43 and atypical clinical manifestations

Abstract

Introduction: Familial Alzheimer's disease (fAD) is heterogeneous in terms of age at onset and clinical presentation. A greater understanding of the pathogenicity of fAD variants and how these contribute to heterogeneity will enhance our understanding of the mechanisms of AD more widely.

Methods: To determine the pathogenicity of the unclassified PSEN1 P436S mutation, we studied an expanded kindred of eight affected individuals, with magnetic resonance imaging (MRI) (two individuals), patient-derived induced pluripotent stem cell (iPSC) models (two donors), and post-mortem histology (one donor).

Results: An autosomal dominant pattern of inheritance of fAD was seen, with an average age at symptom onset of 46 years and atypical features. iPSC models and post-mortem tissue supported high production of amyloid beta 43 (Aβ43). PSEN1 peptide maturation was unimpaired.

Discussion: We confirm that the P436S mutation in PSEN1 causes atypical fAD. The location of the mutation in the critical PSEN1 proline-alanine-leucine-proline (PALP) motif may explain the early age at onset despite appropriate protein maturation.

Highlights: PSEN1 P436S mutations cause familial Alzheimer's disease. This mutation is associated with atypical clinical presentation. Induced pluripotent stem cells (iPSCs) and post-mortem studies support increased amyloid beta (Aβ43) production. Early age at onset highlights the importance of the PALP motif in PSEN1 function.

Keywords: AD; Aβ; PALP; PSEN1; familial Alzheimer's disease; iPSC.

FIGURE 1

PSEN1 P436S expanded family kindred and MRI findings support autosomal dominant fAD. (A) Updated kindred of family. II‐4 is the individual reported previously by Palmer et al. (B) Example MRI images from individual III‐5. T1 axial and coronal images are shown at age 48, demonstrating generalized atrophy and low‐volume hippocampi. (C) Example MRI images from individual III‐8. T1 axial and coronal images are shown at age 51, demonstrating posterior cerebral atrophy, widening of the left Sylvian fissure, and relatively preserved hippocampal volume.

FIGURE 2

PSEN1 P436S patient‐derived iPSC neuron models display fAD‐associated Aβ profiles. (A) Immunocytochemical analysis of iPSCs (top) confirming expression of pluripotency markers NANOG and SSEA4. Immunocytochemical analysis of iPSC‐derived neurons at day 50 of differentiation, bottom, displaying neuronal morphology, expression of deep layer cortical marker TBR1, and neuronal‐specific tubulin TUJ1. (B) Western blot analysis of PSEN1 maturation in neuronal lysates collected after 100 days of differentiation. Immature PSEN1 at 48 kDa (*) is cleaved to a mature N‐terminal fragment (NTF) at around 28 kDa. PSEN1 R278I is displayed as a mutation that causes maturation defects. Actin is used as a loading control. Two (of three) independent inductions are shown (all three replicates are shown in Figure S2A). (C–E) Aβ peptide analysis by electrochemiluminescence to depict the disease‐associated Aβ42:40 ratio, the Aβ43:40 ratio, and the processivity ratio Aβ42:38. Int4del and Y115H (green) display typical PSEN1 mutation‐associated ratio changes; R278I and E280G (yellow) are shown as high Aβ43 producing mutations, each serving as comparators to control (gray) and P436S (red) lines. P436S lines display significantly increased Aβ42:40 and Aβ43:40 ratios. Data represent three independent inductions for each line. Significance represents one‐way ANOVA and Dunnett's multiple comparisons test for each patient‐derived line versus pooled controls, ** = p < .01, *** = p < .001, **** = p < .0001. fAD, Familial Alzheimer's disease; iPSC, induced pluripotent stem cells.

FIGURE 3

Immunohistochemical staining of post‐mortem tissue displays Aβ43 deposition. (A–C) Total Aβ staining shows plaque pathology (A, B) and amyloid angiopathy (C). Cotton wool plaques (black single arrow), senile/cored plaques (black double arrow), and leptomeningeal cerebral amyloid angiopathy (CAA; red arrows) are depicted. (D–E) Aβ43‐specific staining demonstrates substantial Aβ43 deposition in both parenchymal plaques and in vessels as cerebral amyloid angiopathy. Senile cored plaques (black double arrows) and leptomeningeal CAA (red arrows) are depicted. (G–I) AT8 immunostaining for phosphorylated tau, demonstrating neuritic plaques (purple arrows) and neurofibrillary tangles (blue arrows). Scale bar represents 500 µm in A, D, and G; and 50 µm in B, C, E, F, H, and I.