Figure 4.
CSF exosomal α-synuclein from patients with dementia with Lewy bodies and Parkinson’s disease induces the oligomerization of soluble α-synuclein. (A) Illustration of the assay: human neuroglioma H4 cells are co-transfected with α-synuclein fused to split luciferase constructs (S1: N-terminal part of luciferase, S2: C-terminal part of luciferase). A luminescence signal is measured only after complementation of both split luciferase fragments (e.g. during dimerization and oligomerization of α-synuclein) and indicates the induction of α-synuclein aggregation. (B) Luminescence increase in reporter cells upon treatment with exosomes prepared from equal volumes of CSF. CSF was derived from the ‘Kassel cohort’ [dementia with Lewy bodies (DLB) patients: green bar, n = 9; Parkinson’s disease (PD) patients: red bar, n = 10 and neurological controls (Neurol. Ctr.), blue bar, n = 7]. All measurements were performed in duplicates (*P < 0.05, two-sided Student’s t-test, one-way ANOVA P = 0.000513). (C) Ratio of luminescence increase in reporter cells to CSF exosomal α-synuclein protein levels (patients with dementia with Lewy bodies: green bar, n = 8; Parkinson’s disease patients: red bar n = 9; neurological controls: blue bar, n = 6). All measurements were performed in duplicates. [(*)P < 0.10, *P < 0.05, two-tailed Mann-Whitney U-test, one-way ANOVA P = 0.00698]. (D) Correlation of luminescence increase indicative of α-synuclein oligomerization in the reporter cells with exosomal α-synuclein levels (prepared from 1 ml CSF) (dementia with Lewy bodies: green diamonds, n = 8, Parkinson’s disease: red rectangles, n = 9; neurological controls: blue triangles, n = 6). Pearson correlation coefficient: dementia with Lewy bodies and Parkinson’s disease r = 0.85, P = 1.6 × 10−5; neurological controls r = −0.25, P = 0.64. (E) Model (left) and summary table (right) of exosomal α-synuclein in different diseases (left). Exosomal α-synuclein in dementia with Lewy bodies: green diamonds, in Parkinson’s disease: red rectangles, in neurological controls: blue triangles. Depicting α-synuclein symbols as dimers in dementia with Lewy bodies and Parkinson’s disease exosomes indicates their potential to act as a seed to induce aggregate formation.