Aggregation of alpha-synuclein (ASYN) in Lewy bodies and Lewy neurites is the typical pathological hallmark of Parkinson's disease (PD) and other synucleinopathies. Furthermore, mutations in the gene ...encoding for ASYN are associated with familial and sporadic forms of PD, suggesting this protein plays a central role in the disease. However, the precise contribution of ASYN to neuronal dysfunction and death is unclear. There is intense debate about the nature of the toxic species of ASYN and little is known about the molecular determinants of oligomerization and aggregation of ASYN in the cell. In order to clarify the effects of different mutations on the propensity of ASYN to oligomerize and aggregate, we assembled a panel of 19 ASYN variants and compared their behaviour. We found that familial mutants linked to PD (A30P, E46K, H50Q, G51D and A53T) exhibited identical propensities to oligomerize in living cells, but had distinct abilities to form inclusions. While the A30P mutant reduced the percentage of cells with inclusions, the E46K mutant had the opposite effect. Interestingly, artificial proline mutants designed to interfere with the helical structure of the N-terminal domain, showed increased propensity to form oligomeric species rather than inclusions. Moreover, lysine substitution mutants increased oligomerization and altered the pattern of aggregation. Altogether, our data shed light into the molecular effects of ASYN mutations in a cellular context, and established a common ground for the study of genetic and pharmacological modulators of the aggregation process, opening new perspectives for therapeutic intervention in PD and other synucleinopathies.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Parkinson disease is associated with the progressive loss of dopaminergic neurons from the substantia nigra. The pathological hallmark of the disease is the accumulation of intracytoplasmic ...inclusions known as Lewy bodies that consist mainly of post-translationally modified forms of α-synuclein. Whereas phosphorylation is one of the major modifications of α-synuclein in Lewy bodies, sumoylation has recently been described. The interplay between α-synuclein phosphorylation and sumoylation is poorly understood. Here, we examined the interplay between these modifications as well as their impact on cell growth and inclusion formation in yeast. We found that α-synuclein is sumoylated in vivo at the same sites in yeast as in human cells. Impaired sumoylation resulted in reduced yeast growth combined with an increased number of cells with inclusions, suggesting that this modification plays a protective role. In addition, inhibition of sumoylation prevented autophagy-mediated aggregate clearance. A defect in α-synuclein sumoylation could be suppressed by serine 129 phosphorylation by the human G protein-coupled receptor kinase 5 (GRK5) in yeast. Phosphorylation reduced foci formation, alleviated yeast growth inhibition, and partially rescued autophagic α-synuclein degradation along with the promotion of proteasomal degradation, resulting in aggregate clearance in the absence of a small ubiquitin-like modifier. These findings suggest a complex interplay between sumoylation and phosphorylation in α-synuclein aggregate clearance, which may open new horizons for the development of therapeutic strategies for Parkinson disease.
Parkinson disease is the second most common neurodegenerative disease. The molecular hallmark is the accumulation of proteinaceous inclusions termed Lewy bodies containing misfolded and aggregated ...α-synuclein. The molecular mechanism of clearance of α-synuclein aggregates was addressed using the bakers' yeast Saccharomyces cerevisiae as the model. Overexpression of wild type α-synuclein or the genetic variant A53T integrated into one genomic locus resulted in a gene copy-dependent manner in cytoplasmic proteinaceous inclusions reminiscent of the pathogenesis of the disease. In contrast, overexpression of the genetic variant A30P resulted only in transient aggregation, whereas the designer mutant A30P/A36P/A76P neither caused aggregation nor impaired yeast growth. The α-synuclein accumulation can be cleared after promoter shut-off by a combination of autophagy and vacuolar protein degradation. Whereas the proteasomal inhibitor MG-132 did not significantly inhibit aggregate clearance, treatment with phenylmethylsulfonyl fluoride, an inhibitor of vacuolar proteases, resulted in significant reduction in clearance. Consistently, a cim3-1 yeast mutant restricted in the 19 S proteasome regulatory subunit was unaffected in clearance, whereas an Δatg1 yeast mutant deficient in autophagy showed a delayed aggregate clearance response. A cim3-1Δatg1 double mutant was still able to clear aggregates, suggesting additional cellular mechanisms for α-synuclein clearance. Our data provide insight into the mechanisms yeast cells use for clearing different species of α-synuclein and demonstrate a higher contribution of the autophagy/vacuole than the proteasome system. This contributes to the understanding of how cells can cope with toxic and/or aggregated proteins and may ultimately enable the development of novel strategies for therapeutic intervention.
Background: The hallmark of Parkinson disease is α-synuclein aggregation, whose cytotoxic effects are reproducible in yeast.
Results: α-Synuclein aggregate clearance is impaired by vacuolar protease inhibitor PMSF but not by proteasome inhibitor MG132.
Conclusion: Yeast recovers from α-synuclein-induced toxicity by clearing aggregates via autophagy and vacuolar pathways.
Significance: The data provide insight into the mechanisms used by yeast cells to clear toxic aggregated proteins.
Aggregation of alpha-synuclein (ASYN) in Lewy bodies and Lewy neurites is the typical pathological hallmark of Parkinson's disease (PD) and other synucleinopathies. Furthermore, mutations in the gene ...encoding for ASYN are associated with familial and sporadic forms of PD, suggesting this protein plays a central role in the disease. However, the precise contribution of ASYN to neuronal dysfunction and death is unclear. There is intense debate about the nature of the toxic species of ASYN and little is known about the molecular determinants of oligomerization and aggregation of ASYN in the cell. In order to clarify the effects of different mutations on the propensity of ASYN to oligomerize and aggregate, we assembled a panel of 19 ASYN variants and compared their behaviour. We found that familial mutants linked to PD (A30P, E46K, H50Q, G51D and A53T) exhibited identical propensities to oligomerize in living cells, but had distinct abilities to form inclusions. While the A30P mutant reduced the percentage of cells with inclusions, the E46K mutant had the opposite effect. Interestingly, artificial proline mutants designed to interfere with the helical structure of the N-terminal domain, showed increased propensity to form oligomeric species rather than inclusions. Moreover, lysine substitution mutants increased oligomerization and altered the pattern of aggregation. Altogether, our data shed light into the molecular effects of ASYN mutations in a cellular context, and established a common ground for the study of genetic and pharmacological modulators of the aggregation process, opening new perspectives for therapeutic intervention in PD and other synucleinopathies.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Posttranslationale Modifikationen modulieren verschiedene Charakteristika von Proteinen. Sie können die Aktivität, Lokalisierung und Stabilität ihrer Substrate regulieren, verändern aber auch ...Eigenschaften und Strukturvon Proteinen, die mit Krankheiten assoziiert sind. Ein wichtiges Kennzeichen der Parkinson-Krankheit ist die Akkumulation von Proteinaggregaten (Lewy Körperchen). Dies führt zu neuronalem Zelltod durch verschiedene, bisher oft unbekannte Mechanismen. α-Synuclein, ein präsynaptisches, neuronales Protein, ist der Hauptbestandteil der Lewy-Körperchen und spielt eine wichtige Rolle in der Pathogenese der Parkinson-Krankheit. Es unterliegt verschiedenen posttranslationalen Modifikationen unter pathologischen Bedingungen. Die Zytotoxizität und Aggregation von α-Synuclein kann in Hefe imitiert werden. In dieser Studie werden zwei wichtigen posttranslationalen Modifikationen von α-Synuclein, Sumoylierung und Phosphorylierung von Serin 129 (S129), untersucht. Heterolog exprimertes Wildtyp-α-Synuclein und die A30P Mutante sind in Hefe an den gleichen Resten, Lysin 96 (K96) und Lysin 102 (K102), sumoyliert wie im Menschen. Eine Absenkung des zellulären Pools des Ubiquitin-ähnlichen Proteins SUMO führte zu einer starken Wachstumsreduktion von Zellen, welche α-Synuclein exprimieren. Dies korrelierte mit einer erhöhten Zahl an Zellen, die Einschlüsse bildeten. Dies legt nahe, dass Sumoylierung die Hefen vor α-Synuclein vermittelter Toxizität und Einschlussbildung schützt. Die Expression von sumoylierungsdefizienten α-Synuclein verursachte die gleiche Wachstumsrate, was die protektive Rolle der α-Synuclein Sumoylierung in cis bestätigt. Eine Überexpression der humanen Kinasen GRK5 und PLK2 erhöhten den Anteil an S129 phosphoryierten α-Synuclein. Interessanterweise wurde die α-Synuclein–vermittelte Zytotoxizität in Zusammenhang mit einer beeinträchtigten Sumoylierung durch eine höhere Kinase-abhängige S129 α-Synuclein Phosphorylierungsrate kompensiert. Phosphorylierung reduzierte die Einschlussbildung und verminderte die Wachstumshemmung. Um mehr Einblicke in eine plausible wechselseitige Beeinflussung zwischen α-Synuclein Sumoylierung und S129 Phosphorylierung zu erhalten, wurde die Beseitigung der α-Synuclein Aggregate beobachtet. Promotor „shut-off“ Studien wurden parallel mit chemischer Inhibition der zellulären Abbauwege durchgeführt. In der Abwesenheit von SUMO wurden α-Synuclein-Aggregate hauptsächlich durch das Ubiquitin-Proteasom-System abgebaut. Dies legt nahe, dass Sumoylierung den Abbau der α-Synuclein-Aggregate durch Autophagie unterstützt. In Anwesenheit der humanen Kinasen GRK5 oder PLK2, wurden die sumoylierungsdefizienten α-Synuclein-Aggregate Kinasen abhängig sowohl dem Ubiquitin-Proteasom als auch dem Autophagie-System zugeführt. Dies ging einher mit einem veränderten Ubiquitinierungs-Profil von α-Synuclein. GRK5 war in der Lage den Abbau von sumoylierungsdefizienten α-Synuclein-Aggregaten durch Autophagie partiell zu retten und außerdem das Proteasom-System zu unterstützen. In Abwesenheit von SUMO, wenn PLK2 überexprimiert wird, trugen beide Abbauwege gleich stark zur Beseitigung der α-Synuclein-Aggregate bei. Diese wechselseitige Beeinflussung zwischen α-Synuclein Phosphorylierung und Sumoylierung könnte neue Wege für eine therapeutische Intervention in der Parkinsonkrankheit und anderen Synucleinopathien eröffnen.
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