Kim D, Yoo JM, Hwang H, Lee J, Lee SH, Yun SP, Park MJ, Lee M, Choi S, Kwon SH, Lee S, Kwon SH, Kim S, Park YJ, Kinoshita M, Lee YH, Shin S, Paik SR, Lee SJ, Lee S, Hong BH, Ko HS. Graphene quantum dots prevent α-synucleinopathy in Parkinson's disease. Nat Nanotechnol. 2018 Jul 9; PubMed.
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Brigham and Women's Hospital, Harvard Medical School
Through this study, Ko and his colleagues are helping to shed light on the critical role of graphene quantum dots on disaggregation of α-synuclein fibrils (which are one of the hallmarks of Parkinson disease). The excellent in vivo outcomes of these graphene quantum dots extend researchers’ commitment to applying this new finding to improve health care and reduce the huge social and clinically deteriorating effects of neurodegenerative diseases such as Parkinson’s and Alzheimer’s. The role of these graphene quantum dots should be tested in amyloid-β fibrils in Alzheimer’s disease. However, the scientific community should carefully monitor the possible side effects of such an approach, as it might cause complications. Disaggregation of Aβ fibrils may create highly-toxic Aβ oligomers.
View all comments by Morteza MahmoudiEPFL/ND BioSciences
This is a very interesting study that shows the potential of using quantum dots to modulate α-synuclein aggregation and protect against α-synuclein-induced toxicity and pathology spreading. However, the data presented do not support the proposed mechanism of action, i.e., that graphene quantum dots (GQD) inhibit and induce “complete disassociation of the fibrils” into monomers.
The proposed mode of action of GQDs can only be evaluated and commented on here on the basis of the in vitro aggregation data, because the assays used to assess the relationship between GQD modulation of α-synuclein fibril formation, pathology spreading, and toxicity do not allow for direct and quantitative assessment of the different aggregation states of α-synuclein.
GQDs treatment inhibits α-synuclein fibrillization
The thioflavin T and turbidity data shown in Figure 1b-d demonstrate that coincubation with GQDs completely blocked α-synuclein fibrillization. The absence of oligomers in the transmission electron microscopy images after seven days would argue for a mode of action where the GQDs act by stabilizing the monomeric state of α-synuclein. If true, this would be very exciting as it is rare to find molecules that stabilize the large and disordered conformation of the α-synuclein monomers.
Given this striking effect, it is not clear why the authors did not investigate the mechanism of inhibiting monomer aggregation and focused mainly on the interaction of the GQDs with the fibrils and their effect on fibril disassembly. It would have been nice to see circular dichroism/NMR data and solution measurements (light scattering, sedimentation velocity, or size-exclusion chromatography) on the conformation and distribution of α-synuclein species in the presence of GQDs at different time points and after seven days in particular. Do the GQDs stabilize a non-amyloidogenic monomeric conformation of α-synuclein?
“GQDs treatment inhibits a-synuclein fibrillization and disaggregates mature fibrils to monomers”
Although the data presented in Figures 1 and supplementary Figures 3 and 4 show that GQDs alter the aggregation and length of α-synuclein fibrils, they do not provide any direct evidence for disaggregation and/or disassembly of the fibrils into monomers. This can only be established using quantitative solution-based measurements such as light scattering, sedimentation velocity, or size-exclusion chromatography.
Fibril disaggregation
The BN-PAGE gels show a time-dependent increase in α-synuclein monomers. However, one could still detect a substantial amount of α-synuclein aggregates in the stacking gel. This is not consistent with the claim that GQDs induce complete disaggregation of preformed fibrils into monomers after seven days. This is also evident in the CD spectrum of the α-synuclein fibrils after one week of treatment with GQDs, which shows a spectrum that is consistent with a structure that is rich in β-sheet and β-turns. Given that monomeric α-synuclein exists predominantly in a disordered conformation, one would have expected to see a shift to a random coli (disordered) spectrum. The CD spectra and BN-PAGE results (Figure 1K and Supplementary Figure 4C) are not consistent with the EM data shown in Figures 1d, supporting figures and 1g, which were used to support disaggregation to monomers and show complete disappearance of fibrils and the absence of substantial amount of oligomers after seven days of treatment with GQDs.
The reported effects of GQDs on preformed fibrils by TEM (supplementary Figure 4) are also not consistent with the data reported by atomic force microscopy (AFM). The AFM data show that the α-synuclein fibrils prior to treatment with GQDs exhibit a length distribution from 600–1200 nm and that the addition of GQDs induce their disassociation leading to the population of short fibrils of less than 200 nm and 100 nm after 12 and 24 hours, respectively. However, the TEM data of the preformed fibrils before treatment with QGDs for one hour (Supplementary Figure 4) show a distribution of fibril length similar to that observed in previous experiments only in the presence of GQDs. Furthermore, the fibril length distribution of the preformed fibrils before and after treatment with QGDs for one hour was virtually identical and ranged from ~ 20–100 nm, with only a minor population of fibrils (six–10 fibrils) ranging in length from 180–200 nm.
Together, these discrepancies underscore the critical importance of using solution-based methods, combined with imaging techniques, to quantitatively assess the distribution of α-synuclein species (monomers, oligomers, and fibrils) and to achieve a more accurate understanding of the mechanisms of action of anti-amyloidgenic agents.
On fibril-seeding assays
It would be nice to know if the authors assessed whether the GQDs influence the extent of uptake/internalization of the preformed α-synuclein fibrils in their neuronal assays.
Since the authors suggest that they plan to start clinical trials in people within the next two years, it is crucial that there is a collaborative effort to replicate and validate these findings and test the proposed model. We will be happy to offer our expertise and contribute to this effort.
View all comments by Hilal LashuelMake a Comment
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