Dopamine Affects the Stability, Hydration, and Packing of Protofibrils and Fibrils of the Wild Type and Variants of α-Synuclein

Abstract

Parkinson's disease (PD) is characterized by the presence of cytoplasmic inclusions composed of R-synuclein (R-syn) in dopaminergic neurons. This suggests a pivotal role of dopamine (DA) on PD development. Here, we show that DA modulates differently the stability of protofibrils (PF) and fibrils (F) composed of wild type or variants of R-syn (A30P and A53T) as probed by high hydrostatic pressure (HHP). While in the absence of DA, all R-syn PF exhibited identical stability, in its presence, the variantcomposed PF acquired a greater stability (DAPF wt < DAPF A30P ) DAPF A53T ), implying that they would last longer, which could shed light onto why these mutations are so aggressive. When R-syn was incubated for long times (18 days) in the presence of DA, we observed the formation of F by electronic microscopy, suggesting that the PF trapped in the presence of DA in short times can evolve into F. The stability of F was also altered by DA. DAF wt was more labile than F wt , indicating that the former would be more susceptible to breakage. PF A30P and DAPF A30P , when added to mesencephalic and cortical neurons in culture, decreased the number and length of neurites and increased the number of apoptotic cells. Surprisingly, these toxic effects of PF A30P and DAPF A30P were practically abolished with HHP treatment, which was able to break the PF into smaller aggregates, as seen by atomic force microscopy. These results suggest that strategies aimed at breaking and/or clearing these aggregates is promising in alleviating the symptoms of PD.Parkinson's disease (PD) 1 is the second most common neurodegenerative brain disorder, after Alzheimer's disease, affecting ∼1% of the population over 65 years of age (1). The symptoms of PD include difficulty in initiating movements, resting tremor, muscular rigidity, impaired postural reflexes, and bradykinesia, resulting from the loss of dopaminergic neurons and depletion of dopamine (DA) in the regions of the brain involved in motor functions [the substantia nigra (SN)] (2). The remaining neurons of the SN are characterized by the presence of an intracellular inclusion, known as Lewy bodies (LB), composed primarily of fibrillar R-synuclein (R-syn) (3-6).

Oligomerization and Membrane-binding Properties of Covalent Adducts Formed by the Interaction of α-Synuclein with the Toxic Dopamine Metabolite 3,4-Dihydroxyphenylacetaldehyde (DOPAL)

“…1D). Although it has been suggested that DA specifically stabilizes aS oligomers, the presence of fibrils can be observed after long term incubation with DA (30). This misleading conclusion might be attributed to the fact that the effect of DA oxidation products on ThT fluorescence has been neglected.…”

Direct Observation of Amyloid Nucleation under Nanomechanical Stretching

“…The image reveals the ribbon structure with a width 8.7±2.7nm and 25±5nm and height 4.5±1.3nm. The cross section of the smaller width fiber seems to follow Gaussian distribution while cross section of the larger width fiber is square, with a little bump in the center [48] of the fiber. This implied that the fiber that has smaller width have one unit while the wider fibers originated from two fibers running parallel to each other.…”

Fármacos multifuncionais: monoamina oxidase e &#945;-sinucleína como alvos terapêuticos na doença de Parkinson

“…64 Follmer e colaboradores mostraram que DA interage com a-sinucleína e modula diferentemente a estabilidade de agregados gerados a partir das formas selvagem ou mutantes da proteína. 65 Na ausência de DA, protofibras de a-sinucleína exibem estabilidades semelhantes quando submetidas à dissociação por pressão hidrostática. Entretanto, protofibras geradas a partir das variantes da a-sinucleína (Ala30Pro ou Ala53Thr), quando em presença de DA, apresentaram uma maior estabilidade quando comparadas às protofibras geradas a partir da forma selvagem da proteína.…”

“…66 Visto que selegilina previne (ou retarda) o processo de oxidação da DA, uma importante questão é de que forma este fármaco influenciaria no sistema a-sinucleína-DA, quando estes dois fármacos são combinados na terapia da DP. Diante dos dados mostrando o efeito da DA sobre a agregação da a-sinucleína previamente discutidos, 65 uma abordagem de tratamento racional para DP deverá considerar a ação combinada destes fármacos na doença.…”

“…68 Selegilina estaria assim interferindo com a formação do núcleo envolvido na fase lenta da cinética de fibrilação. Quando combinada com DA, que promove a formação de protofibras tóxicas, 65 selegilina previne a formação dos agregados tóxicos, o que pode representar um importante efeito quando o IMAO e L-dopa (que será convertida em DA) são coadministradas. No conjunto, estes dados sugerem que selegilina possa ser um fármaco multifuncional sob o ponto de vista da inibição da MAO e da inibição da formação de agregados tóxicos de a-sinucleína.…”