Nuber S, Rajsombath M, Minakaki G, Winkler J, Müller CP, Ericsson M, Caldarone B, Dettmer U, Selkoe DJ. Abrogating Native α-Synuclein Tetramers in Mice Causes a L-DOPA-Responsive Motor Syndrome Closely Resembling Parkinson's Disease. Neuron. 2018 Oct 10;100(1):75-90.e5. PubMed.
Recommends
Please login to recommend the paper.
Comments
Indiana University School of Medicine
The mouse model presented by Nuber et al. is remarkable in that the patho-histology and the motor phenotypes closely resemble all the major hallmarks of Parkinson’s disease. Thus, it appears to be a good animal model for the disease. More broadly, their findings strongly support that the dynamic interconversion between monomeric and tetrameric α-synuclein is important for its function and that losing this ability results in aggregation and toxicity in mice.
Studying the tetrameric form of α-synuclein has been difficult due to its dynamic and transient nature, which is commonly observed in small proteins that are highly charged and mostly helical (such as osteocalcin for example, Hoang et al., 2003); however, this mouse model might enable investigations of α-synuclein-associated toxic mechanisms and the monomer-tetramer dynamics without the need to isolate the tetramers.
Given the results, I wonder what happens when a persistently tetrameric form of α-synuclein is expressed in mice and whether it could rescue the effects observed in the 3K mice.
References:
Hoang QQ, Sicheri F, Howard AJ, Yang DS. Bone recognition mechanism of porcine osteocalcin from crystal structure. Nature. 2003 Oct 30;425(6961):977-80. PubMed.
View all comments by Quyen HoangMedical Research Council Protein Phophorylation and Ubiquitylation Unit
I think that this is an extremely elegant study in which the authors rigorously assess the phenotype of transgenic mouse model in which the synuclein tetrameric form is destabilized. The phenotype seems more striking than observed in other mouse synuclein models and partial response to L-DOPA treatment also suggests that this model may mimic human disease. There has been a lot of discussion about the interplay of LRRK2 and synuclein biology. It would be fascinating to cross the new synuclein transgenic mouse model with LRRK2 pathogenic knock-in mutations or VPS35[D620N] mice that also display high LRRK2 pathway activity, to see if these exacerbates the phenotype or time that phenotype emerges.
It would also be fascinating to treat the new synuclein mouse model with LRRK2 inhibitors both before and after the phenotypes are observed to see if there is any delay and/or amelioration in phenotype. It would also be intriguing to test whether LRRK2 pathway is activated in brain tissues of the new synuclein transgenic mice, which could be achieved by studying Rab protein phosphorylation by immunofluorescence. Such studies would help provide further insight into whether LRRK2 contributes to disease effects of synuclein aggregation. I hope that these mice will be easy for researchers to access!
View all comments by Dario AlessiUniversity of California, San Diego
This study by Silke Nuber, Ulf Dettmer, Dennis Selkoe and colleagues explores a key idea that they have championed—that α-syn normally exists as a multimer/tetramer, but abrogation of these physiologic conformations leads to an increase in monomers, aggregation of these free monomers, and subsequent pathology. Here they generated a new mouse model (“3K line”) where they added three E->K mutations in the protein (the human E46K mutation, and two other E->K mutations that decrease α-syn multimers/tetramers—based on their own previous studies). The authors convincingly show that addition of these three mutants—and consequent decrease in α-syn multimers—leads to an increase in monomers as well as an increase in insoluble α-syn fractions; increase in pathologic signatures like α-syn phosphorylation at defined residues (Serine 129); motor deficits; and degeneration of nigral neurons. Though the 3K mutations are not disease-related, they are an elegant tool to explore the authors’ hypothesis in a true in vivo setting.
A few things were unclear. Since the E46K mutation is associated with human disease and is itself pathologic, it is important to show that pathology—and associated motor deficits—in the 3K mice is more pronounced than the E46K mutation alone. Though the authors did use mice expressing only the E46K mutation (“1K”) for some experiments, it was not clear if these were used to examine three key features: α-syn insolubility, dopaminergic degeneration, and motor deficits. Regarding the immuno-EM studies, the conclusion is that in the 3K mice, α-syn monomers are preferentially associated with synaptic vesicles. However, a large number of the α-syn gold particles are not on synaptic vesicles (for example, there is only ~ 1 immunogold particle per vesicle in the 3K boutons, whereas a visual inspection suggests that there are numerous scattered particles throughout). So it may be best to interpret these data cautiously. Also, the number of gold particles is higher in 3K to begin with—compared to WT—so it is not clear if the increase in vesicle association is specifically due to an increase in α-syn monomers (following a loss of tetramers). The 1K control is also missing here.
Finally, it is unclear if tetramers are the only higher-order α-syn species, as advocated by the authors. Though tetramers are certainly the predominant species in the M17D cells, a glance at the literature suggests that the conformations are cell-type dependent and not necessarily tetrameric. Thus, “multimers” might be a better usage until this issue is completely nailed down in neurons and synapses. Despite these comments, the studies by Nuber et al. are very exciting, and the authors need to be commended for their relentless pursuit of this unconventional (and once-unpopular) idea. Further studies may further clarify some of the mechanistic steps involved.
View all comments by Subhojit RoyJohns Hopkins University
This model, which recapitulates more cardinal features of PD than published PD models, supports the novel mechanistic insight that interfering with physiological α-synuclein tetramers can lead to PD. This mechanism is not widely recognized in the PD field, and should be confirmed in sporadic PD brain. Some issues including artificial effects and less degeneration of dopaminergic neurons than expected (30 percent) remain to be resolved. The new model would be an important step toward better animal models of PD and can be used for future mechanistic and therapeutic studies by PD and related α-synucleinopathy researchers.
View all comments by Hanseok KoThe University of Exeter
This is a fascinating finding which builds on the authors’ previous work highlighting the importance of an increase in the ratio of -synuclein monomers to tetramers as a key mechanism accelerating progressive changes.
They show in these very careful studies with their mouse model that the ratio of monomer to tetramer is significantly altered and that this is associated with clear toxic effects and leads to a behavioral phenotype—abnormal motor movements that are L-dopa responsive.
This is impressive work, but I don't think yet the model has been phenotyped sufficiently to recommend it as the PD animal model everyone should be using. I think we need more information re. transcriptional changes and the long-term progression of pathology and behavioral changes. We also need more understanding of how this impacts on other aspects of the disease that may be important—mitochondrial dysfunction, clearance of synuclein, neuroinflammation, etc., and the pros and cons compared to other emerging PD models, such as GBA mutations, which may be different for different types of studies.
Whilst this may become a key PD model—particularly for specific therapy development re. stabilizing tetramers and probably synuclein immunotherapy—I don't think we're quite there yet.
View all comments by Clive BallardMake a Comment
To make a comment you must login or register.