Alzheimer's disease is neuropathologically characterized by the deposition of the amyloid β-peptide (Aβ) as amyloid plaques. Aβ plaque pathology starts in the neocortex before it propagates into further brain regions. Moreover, Aβ aggregates undergo maturation indicated by the occurrence of post-translational modifications. Here, we show that propagation of Aβ plaques is led by presumably non-modified Aβ followed by Aβ aggregate maturation. This sequence was seen neuropathologically in human brains and in amyloid precursor protein transgenic mice receiving intracerebral injections of human brain homogenates from cases varying in Aβ phase, Aβ load and Aβ maturation stage. The speed of propagation after seeding in mice was best related to the Aβ phase of the donor, the progression speed of maturation to the stage of Aβ aggregate maturation. Thus, different forms of Aβ can trigger propagation/maturation of Aβ aggregates, which may explain the lack of success when therapeutically targeting only specific forms of Aβ.
Keywords:
Alzheimer’s disease; amyloid β protein; human brain; maturation and propagation; mouse model; seeding.
C.A.F.v.A. received honoraria from serving on the scientific advisory board of Biogen, Roche and Dr Willmar Schwabe GmbH & Co. KG, has received funding for travel and speaker honoraria from Biogen, Roche Diagnostics AG and Dr Willmar Schwabe GmbH & Co. KG and has received research support from Roche Diagnostics AG. D.R.T. received speaker honoraria from Novartis Pharma Basel (Switzerland) and Biogen (USA), travel reimbursement from GE-Healthcare (UK) and UCB (Belgium), and collaborated with GE-Healthcare (UK), Novartis Pharma Basel (Switzerland), Probiodrug (Germany) and Janssen Pharmaceutical Companies (Belgium). D.R.T. received additional funding from Stichting Alzheimer Onderzoek (Belgium) in the context of another project and serves in the editorial board of Brain but was not involved in the handling of this manuscript at any stage.
Figures
Figure 1
Aβ, Aβ N3pE and Aβp …
Figure 1
Aβ, Aβ N3pE and Aβp Ser8 loads in the human brain among different…
Figure 1
Aβ, AβN3pE and AβpSer8 loads in the human brain among different Aβ phases. (A–D) Box plot diagrams comparing Aβ loads in the human brain among Aβ phases 0–5. Aβ, AβN3pE and AβpSer8 loads were obtained immunohistochemically in the temporal neocortex (Brodmann area 36) (A), the cingulate gyrus (Brodmann area 24) (B), the putamen (C) and the cerebellar cortex (D) (n = 44). All Aβ, AβN3pE and AβpSer8 loads increased with advancing Aβ phase as dependent variable (linear regression analysis with age and sex as additional covariates: P < 0.05; β: 0.289–0.731), except for the cerebellar AβpSer8 load (linear regression analysis with age and sex as additional covariates: P = 0.233). Presumably non-modified Aβ prevailed over AβN3pE and AβpSer8 in the temporal cortex, cingulate gyrus and putamen [Friedman test corrected for multiple testing (two-sided): P < 0.05]. AβN3pE was here more abundant than AβpSer8 [Friedman test corrected for multiple testing (two-sided): P < 0.05]. In the cerebellar cortex, which was only involved in Aβ pathology in 10 out of 11 Aβ phase 5 cases, presumably non-modified Aβ was more abundant than AβpSer8 [Friedman test corrected for multiple testing (two-sided): P < 0.001] and a trend was observed for more abundant AβN3pE than AβpSer8 [Friedman test corrected for multiple testing (two-sided): P = 0.059; non-corrected P = 0.019]. Box elements: centre line = median; box limits = upper and lower quartiles; whiskers = 1.5× interquartile range; dots/stars = outliers.
Figure 2
Propagation and maturation of Aβ…
Figure 2
Propagation and maturation of Aβ pathology in the mouse brain after seed injection.…
Figure 2
Propagation and maturation of Aβ pathology in the mouse brain after seed injection. Schematic representation of the experimental design. (A) Production of nonAD, p-preAD and Alzheimer’s disease brain homogenates for inoculation in the mouse brain. For this purpose, a slightly modified centrifugation protocol according to Meyer-Luehmann et al. was used to generate the ‘total supernatant’ fractions, which was in a second step divided into soluble and insoluble but dispersible material. In short, after homogenization of occipital cortex (Brodmann area 17) samples and addition of a proteinase inhibitor cocktail, the lysates were centrifuged at 3000g. The pellet was discarded. The supernatant was considered as the total supernatant fraction. Part of the total supernatant fraction were ultracentrifuged and concentrated 10 times to separate the soluble (supernatant) and dispersible (resuspended pellet) fractions (Supplementary material). (B) Induction of Aβ seeding in the mouse left mouse hippocampal formation by brain homogenates of nonAD, p-preAD and symAD cases by soluble, dispersible and total supernatant fractions. To carry out this experiment, 2-month-old APP23 mice received injections of soluble, dispersible or total supernatant fractions from human brain homogenates from one sympAD and one p-preAD case. Likewise, additional mice received the dispersible fraction of two controls or two additional p-preAD cases.
Figure 3
Relationship between ‘donor’ Aβ pathology…
Figure 3
Relationship between ‘donor’ Aβ pathology and propagation and maturation in the ‘host’ brain …
Figure 3
Relationship between ‘donor’ Aβ pathology and propagation and maturation in the ‘host’ brain. Box plot diagrams of the induced Aβ loads (A–C) and hAP scores (D–F) with the Aβ phases (A and D), B-Aβ stages (B and E) and temporal cortex Aβ loads (C and F), of the respective cases used for the generation of the brain lysates. ANOVA indicated an increasing tendency of the induced hAP scores for all three Aβ species with increasing Aβ phase of the injected ‘donor’ brains (ANOVA: P ≤ 0.023, n = 38 mice) and Aβ load (ANOVA: P < 0.001, n = 38 mice). AβN3pE and AβpSer8 loads did not increase continuously with Aβ phase although ANOVA indicated differences among the groups (ANOVA: P ≤ 0.005, n = 38 mice). Increasing B-Aβ stages and temporal cortex Aβ loads of the ‘donor’ brains did not go along with a continuous increase of the induced Aβ and AβN3pE loads and hAP scores and the AβpSer8 load, whereas the AβpSer8 hAP score continuously rose. Note that the Aβ loads and hAP scores for Aβ detectable with antibodies raised against non-modified forms of Aβ were higher than those for AβN3pE and AβpSer8 in mice with Aβ pathology [Friedman test corrected for multiple testing (two-sided): P < 0.01, n = 24 mice; see also Supplementary Table 2B]. Box elements: centre line = median; box limits = upper and lower quartiles; whiskers = 1.5× interquartile range; dots/stars = outliers.
Figure 4
Seeded Aβ in mice receiving…
Figure 4
Seeded Aβ in mice receiving the dispersible fraction from p-preAD case 14. ( …
Figure 4
Seeded Aβ in mice receiving the dispersible fraction from p-preAD case 14. (A) Seeded plaques stained with a non-C terminus-specific polyclonal antibody raised against Aβ1−40. The Aβ deposits were easily detectable even at low magnification level. (B and C) At low magnification level AβN3pE- and AβpSer8-positive plaques were less widespread and less visible. Calibration bar in C is valid for A–C. (D and E) At high power magnification both AβN3pE and AβpSer8 was seen at the white matter next to the hippocampal sector CA1. Note that AβN3pE-positive material was more widely distributed compared to AβpSer8. Calibration bar in E is valid for D and E.
Figure 5
Schematic representation of Aβ protein…
Figure 5
Schematic representation of Aβ protein deposition, propagation, maturation and its acceleration by seeds …
Figure 5
Schematic representation of Aβ protein deposition, propagation, maturation and its acceleration by seeds. Although Aβ propagation and maturation correlate with one another acceleration of these two aspects in the pathogenesis of Alzheimer’s disease is modified in a differential manner: propagation of Aβ deposition is accelerated by any kind of Aβ seeds whereas maturation increase depends on the presence of AβN3pE and AβpSer8 in the seeds in a biochemically detectable concentration. Note that AβpSer8-positive plaques are mainly cored plaques.
Alzheimer's Association . 2016Alzheimer's disease facts and figures. Alzheimers Dement. 2016;12: 459–509.
-
PubMed
Alzheimer A. Über eine eigenartige Erkrankung der Hirnrinde. Allg Zschr Psych. 1907;64:146–148.
Masters CL, Simms G, Weinman NA, Multhaup G, McDonald BL, Beyreuther K. Amyloid plaque core protein in Alzheimer disease and Down syndrome. Proc Natl Acad Sci USA. 1985;82:4245–4249.
-
PMC
-
PubMed
Grundke-Iqbal I, Iqbal K, Quinlan M, Tung YC, Zaidi MS, Wisniewski HM. Microtubule-associated protein tau. A component of Alzheimer paired helical filaments. J Biol Chem 1986;261: 6084–6089.
-
PubMed
Braak H, Braak E. Neuropathological stageing of Alzheimer-related changes. Acta Neuropathol. 1991;82:239–259.
-
PubMed
