Inhibition of amyloid-β plaque formation by α-synuclein

Journal name:
Nature Medicine
Volume:
21,
Pages:
802–807
Year published:
DOI:
doi:10.1038/nm.3885
Received
Accepted
Published online

Amyloid-β (Aβ) plaques and α-synuclein (α-syn)-rich Lewy bodies are the major neuropathological hallmarks of Alzheimer's disease (AD) and Parkinson's disease, respectively. An overlap of pathologies is found in most individuals with dementia with Lewy bodies (DLB)1 and in more than 50% of AD cases2. Their brains display substantial α-syn accumulation not only in Lewy bodies, but also in dystrophic neurites decorating Aβ plaques2, 3, 4. Several studies report binding and coaggregation of Aβ and α-syn5, 6, 7, yet the precise role of α-syn in amyloid plaque formation remains elusive. Here we performed intracerebral injections of α-syn–containing preparations into amyloid precursor protein (APP) transgenic mice (expressing APP695KM670/671NL and PSEN1L166P under the control of the neuron-specific Thy-1 promoter; referred to here as 'APPPS1'). Unexpectedly, α-syn failed to cross-seed Aβ plaques in vivo, but rather it inhibited plaque formation in APPPS1 mice coexpressing SNCAA30P (referred to here as 'APPPS1 × [A30P]aSYN' double-transgenic mice). This was accompanied by increased Aβ levels in cerebrospinal fluid despite unchanged overall Aβ levels. Notably, the seeding activity of Aβ-containing brain homogenates was considerably reduced by α-syn, and Aβ deposition was suppressed in grafted tissue from [A30P]aSYN transgenic mice. Thus, we conclude that an interaction between Aβ and α-syn leads to inhibition of Aβ deposition and to reduced plaque formation.

At a glance

Figures

  1. [alpha]-syn-containing preparations do not induce A[beta] plaque formation in 6-week-old APPPS1 [times] Thy1-GFP transgenic mice.
    Figure 1: α-syn–containing preparations do not induce Aβ plaque formation in 6-week-old APPPS1 × Thy1-GFP transgenic mice.

    (a) Immunostaining against Aβ with antibody 3552 (red) of hippocampi from male APPPS1 × Thy1-GFP mice with neuronal Thy1-GFP expression (green) euthanized 10 weeks after injections. Representative images of Aβ and GFP immunoreactivity from uninjected mice (n = 4) and mice injected with WT brain homogenate (n = 4), APPPS1 brain homogenate (n = 4) or [A30P]aSYN brain homogenate (n = 4). White arrowheads and the inset indicate the presence of Aβ deposits. (b) Representative image of Aβ and GFP immunoreactivity in an APPPS1 brain homogenate–injected Thy1-GFP animal (n = 5). (c) Immunoblot analysis of brain homogenates from WT, APPPS1 and [A30P]aSYN mice that were used for injections. (d) Quantification of hippocampal Aβ load. Data are presented as mean ± s.e.m., *P < 0.05 by Kruskal-Wallis test. (e) Immunostaining against Aβ (red) from hippocampi of APPPS1 × Thy1-GFP transgenic animals injected with brainstem homogenate from a symptomatic 21-month-old [A30P]aSYN transgenic mouse (n = 5), brain homogenate from a DLB patient with confirmed LB pathology (n = 5), PFFs of NAC peptide (n = 5) and recombinant α-syn PFFs (n = 6). (f) Immunostaining of pathological α-syn inclusions with phospho-Ser129 antibody (red) in uninjected (n = 4) and α-syn PFF–injected (n = 6) APPPS1 × Thy1-GFP transgenic mice. Scale bars in a,b,e, 300 μm; in a (inset), 80 μm; lower magnification in f (left and second from right), 100 μm; higher magnification in f (right and second from left), 50 μm.

  2. Reduced hippocampal plaque load in APPPS1 [times] [A30P]aSYN transgenic mice.
    Figure 2: Reduced hippocampal plaque load in APPPS1 × [A30P]aSYN transgenic mice.

    (a) Representative images of immunofluorescence staining of Aβ plaques (red) and neuronal nuclei (NeuN, green) from 4-month-old female APPPS1 transgenic (n = 9) or APPPS1 × [A30P]aSYN transgenic littermates (n = 6). (b) Quantification of the hippocampal Aβ load as Aβ-positive area fraction. Data are presented as mean ± s.e.m., *P < 0.05 by two-tailed Mann-Whitney test. (c,d) Representative images (c) and quantification (d) of thiazin red (TR) staining of dense-core plaques in APPPS1 (n = 9) and APPPS1 × [A30P]aSYN (n = 6) transgenic animals. Data are presented as mean ± s.e.m., *P < 0.05 by two-tailed Mann-Whitney test. (e,f) Aβ immunoassay for Aβ-40 (e) and Aβ-42 (f) in CSF samples from 4-month-old female WT (n = 6), [A30P]aSYN (n = 8), APPPS1 (n = 10) and APPPS1 × [A30P]aSYN (n = 5) transgenic mice. Data are presented as mean ± s.e.m., *P < 0.05, **P < 0.01 by two-tailed Mann-Whitney test. Scale bars in a,c, 300 μm.

  3. A[beta] seeding is decreased by [alpha]-syn.
    Figure 3: Aβ seeding is decreased by α-syn.

    (a) Immunofluorescence staining of Aβ plaques (red) in hippocampi of male APPPS1 (left) or APPPS1 × [A30P]aSYN (right) transgenic host animals injected with brain homogenates from aged APPPS1 transgenic mice. (b) Quantification of Aβ load in APPPS1 and APPPS1 × [A30P]aSYN transgenic host animals from a (n = 4; data are presented as mean ± s.e.m., two-tailed Mann-Whitney test, *P < 0.05). (c) APPPS1 transgenic animals injected with APPPS1 transgenic brain homogenates mixed with either WT (left, n = 5), [A30P]aSYN transgenic (middle, n = 5) or α-syn–immunodepleted [A30P]aSYN (right, n = 4) brain homogenate. (d) Aβ load in hippocampi injected with brain homogenate mixture from APPPS1, [A30P]aSYN transgenic mice or α-syn–immunodepleted brain homogenate mixture from APPPS1 and [A30P]aSYN transgenic mice. Data are presented as mean ± s.e.m., N.S., not significant (P > 0.05), *P < 0.05 by Dunn's multiple comparisons test after Kruskal-Wallis test. (e) Immunoblot analysis of Aβ and α-syn from injected brain homogenates. (f) Representative images of APPPS1 transgenic animals injected with brain homogenates from the frontal association cortex of either an individual with AD (with no Lewy bodies or neurites; left) or an individual with DLB with mixed pathologies (amyloid plaques, Lewy bodies and neurites; right), n = 5 animals injected per group. (g) Quantification of hippocampal Aβ load in injected animals (n = 5; data are presented as mean ± s.e.m., two-tailed Mann-Whitney test, **P < 0.01). (h) Immunoblot analysis of Aβ in human brain homogenates used for injections. Scale bars in a,c,f, 350 μm. Ctrl, healthy control subject. White arrowheads indicate the presence of Aβ deposits.

  4. Suppressed A[beta] deposition and reduced A[beta]-42 fibril formation in the presence of [alpha]-syn.
    Figure 4: Suppressed Aβ deposition and reduced Aβ-42 fibril formation in the presence of α-syn.

    (a,b) Representative immunostaining images of WT (n = 20) (a) and [A30P]aSYN transgenic (n = 10) (b) cortical grafts in female APPPS1 × Thy1-GFP host tissue. Left, APP (red) and GFP (green) labeling of host and grafted tissue, respectively. Human α-syn (blue) in [A30P]aSYN transgenic graft. Middle, Aβ-specific immunostaining (red), DAPI (blue) and GFP (green). Right, Iba1 (red), NeuN (blue) and GFP (green). The dashed white lines mark the border of the graft and the white arrowheads indicate the presence of Aβ deposits. Scale bars, 100 μm. (c) Fraction of WT (n = 20) or [A30P]aSYN transgenic (n = 10) grafts positive or negative for amyloid plaques. ***P < 0.001 by two-tailed Fisher's exact test. (d) Number of plaques per graft within WT or [A30P]aSYN transgenic grafts. Data are presented as mean ± s.e.m., ***P < 0.001 by two-tailed Mann-Whitney test. (e,f) Analysis of Aβ fibril formation in vitro in the presence of WT α-syn or α-synA30P. (e) In vitro ThT assay of Aβ-42 fibril formation. Blank subtracted values were normalized against Aβ-42 ThT fluorescence after 24 h agitation of the respective aggregation experiment. Data points represent mean ± s.e.m. from three independent aggregation experiments. (f) As a control, α-syn was added at the end of the Aβ aggregation phase. (g) Ultrastructural analysis of in vitro Aβ-42 fibril formation in the presence of WT α-syn or α-synA30P. Scale bar, 100 nm.

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Author information

Affiliations

  1. Adolf Butenandt Institute, Department of Biochemistry, Ludwig-Maximilians University, Munich, Germany.

    • Teresa Bachhuber,
    • Joanna F McCarter,
    • Claudia Abou-Ajram &
    • Melanie Meyer-Luehmann
  2. Neurocenter, Department of Neurology, University of Freiburg, Freiburg, Germany.

    • Natalie Katzmarski,
    • Desiree Loreth &
    • Melanie Meyer-Luehmann
  3. Faculty of Biology, University of Freiburg, Freiburg, Germany.

    • Natalie Katzmarski
  4. German Center for Neurodegenerative Diseases (DZNE), Munich, Germany.

    • Sabina Tahirovic,
    • Harald Steiner &
    • Christian Haass
  5. Department of Metabolic Biochemistry, Ludwig-Maximilians University, Munich, Germany.

    • Frits Kamp,
    • Brigitte Nuscher,
    • Harald Steiner &
    • Christian Haass
  6. MassGeneral Institute for Neurodegenerative Disease, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts, USA.

    • Alberto Serrano-Pozo &
    • Bradley T Hyman
  7. Institute of Neuropathology, University of Freiburg, Freiburg, Germany.

    • Alexandra Müller &
    • Marco Prinz
  8. Centre for Biological Signalling Studies (BIOSS), University of Freiburg, Freiburg, Germany.

    • Marco Prinz
  9. Munich Cluster for Systems Neurology (SyNergy), Munich, Germany.

    • Christian Haass

Contributions

T.B., C.H. and M.M.-L. conceived the experiments. T.B., N.K., J.F.M., D.L., S.T., C.A.-A., B.N., F.K. and A.S.-P. performed experiments. B.T.H. provided human brain samples. A.M., D.L. and M.P. performed electron microscopy. H.S., S.T., F.K. and A.S.-P. provided important experimental guidance. T.B., J.F.M., H.S., B.T.H., C.H. and M.M.-L. discussed the results. T.B., J.F.M. and M.M.-L. wrote the manuscript. M.M.-L. supervised the project and coordinated the study. All authors edited the paper.

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The authors declare no competing financial interests.

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