Long-term hyperglycemia aggravatesα-synuclein aggregation and dopaminergic neuronal loss in a Parkinson’s disease mouse model

Background:Growing evidence suggests an association between Parkinson’s disease(PD)and diabetes mellitus(DM).At the cellular level,long-term elevated levels of glucose have been shown to lead to nigrostriatal degeneration in PD models.However,the underlying mechanism is still unclear.Previously,we have elucidated the potential of type 2 diabetes mellitus(T2DM)in facilitating PD progression,involving aggregation of both alpha-synuclein(α-syn)and islet amyloid polypeptide in the pancreatic and brain tissues.However,due to the complicated effect of insulin resistance on PD onset,the actual mechanism of hyperglycemia-induced dopaminergic degeneration remains unknown.Methods:We employed the type 1 diabetes mellitus(T1DM)model induced by streptozotocin(STZ)injection in a transgenic mouse line(BAC-α-syn-GFP)overexpressing humanα-syn,to investigate the direct effect of elevated blood glucose on nigrostriatal degeneration.Results:STZ treatment induced more severe pathological alterations in the pancreatic islets and T1DM symptoms inα-syn-overexpressing mice than in wild-type mice,at one month and three months after STZ injections.Behavioral tests evaluating motor performance confirmed the nigrostriatal degeneration.Furthermore,there was a marked decrease in dopaminergic profiles and an increase ofα-syn accumulation and Serine 129(S129)phosphorylation in STZ-treatedα-syn mice compared with the vehicle-treated mice.In addition,more severe neuroinflammation was observed in the brains of the STZ-treatedα-syn mice.Conclusion:Our results solidify the potential link between DM and PD,providing insights into how hyperglycemia induces nigrostriatal degeneration and contributes to pathogenic mechanisms in PD.

Differential seeding and propagating efficiency ofα-synuclein strains generated in different conditions

Background:Accumulation of alpha-synuclein(α-syn)is a main pathological hallmark of Parkinson’s and related diseases,which are collectively known as synucleinopathies.Growing evidence has supported that the same protein can induce remarkably distinct pathological progresses and disease phenotypes,suggesting the existence of strain difference amongα-syn fibrils.Previous studies have shown thatα-syn pathology can propagate from the peripheral nervous system(PNS)to the central nervous system(CNS)in a“prion-like”manner.However,the difference of the propagation potency from the periphery to CNS among differentα-syn strains remains unknown and the effect of different generation processes of these strains on the potency of seeding and propagation remains to be revealed in more detail.Methods:Three strains of preformedα-syn fibrils(PFFs)were generated in different buffer conditions which varied in pH and ionic concentrations.Theα-syn PFFs were intramuscularly(IM)injected into a novel bacterial artificial chromosome(BAC)transgenic mouse line that expresses wild-type humanα-syn,and the efficiency of seeding and propagation of these PFFs from the PNS to the CNS was evaluated.Results:The three strains ofα-syn PFFs triggered distinct propagation patterns.The fibrils generated in mildly acidic buffer led to the most severeα-syn pathology,degeneration of motor neurons and microgliosis in the spinal cord.Conclusions:The differentα-syn conformers generated in different conditions exhibited strain-specific pathology and propagation patterns from the periphery to the CNS,which further supports the view thatα-syn strains may be responsible for the heterogeneity of pathological features and disease progresses among synucleinopathies.