Dopamine induces the accumulation of insoluble prion protein and affects autophagic flux

Abstract

Accumulation of protein aggregates is a histopathological hallmark of several neurodegenerative diseases, but in most cases the aggregation occurs without defined mutations or clinical histories, suggesting that certain endogenous metabolites can promote aggregation of specific proteins. One example that supports this hypothesis is dopamine and its metabolites. Dopamine metabolism generates several oxidative metabolites that induce aggregation of α-synuclein, and represents the main etiology of Parkinson's diseases. Because dopamine and its metabolites are unstable and can be highly reactive, we investigated whether these molecules can also affect other proteins that are prone to aggregate, such as cellular prion protein (PrPC). In this study, we showed that dopamine treatment of neuronal cells reduced the number of viable cells and increased the production of reactive oxygen species (ROS) as demonstrated in previous studies. Overall PrPC expression level was not altered by dopamine treatment, but its unglycosylated form was consistently reduced at 100 μM of dopamine. At the same concentration, the level of phosphorylated mTOR and 4EBP1 was also reduced. Moreover, dopamine treatment decreased the solubility of PrPC, and increased its accumulation in autophagosomal compartments with concomitant induction of LC3-II and p62/SQSTM1 levels. In vitro oxidation of dopamine promoted formation of high-order oligomers of recombinant prion protein. These results suggest that dopamine metabolites alter the conformation of PrPC, which in turn is sorted to degradation pathway, causing autophagosome overload and attenuation of protein synthesis. Accumulation of PrPC aggregates is an important feature of prion diseases. Thus, this study brings new insight into the dopamine metabolism as a source of endogenous metabolites capable of altering PrPC solubility and its subcellular localization.

Merging the Multi-Target Effects of Phytochemicals in Neurodegeneration: From Oxidative Stress to Protein Aggregation and Inflammation

“…Also, in AMD, a neurodegenerative disorder of the macula, proteins such as α-syn and Aβ are detected in “drusen”, which are amorphous proteinaceous deposits occurring between the retinal pigment epithelium and the photoreceptors [ 7 ]. Finally, besides classic prion diseases, insoluble aggregates of PrP, are found in models of PD, which is bound to oxidative dopamine metabolism similar to what was reported for α-syn [ 194 , 195 ]. These pieces of evidence converge in that a generalized defect in proteostasis plays a leading role across different neurodegenerative disorders independently of nosography and symptomatology.…”

“…Remarkably, due to their bulky structure, insoluble molecules, including AGEs, large protein aggregates, and AGE-derived cross-linked proteins, cannot be digested by the proteasome [ 27 , 40 ]. This fuels an increase in the amount of oxidized/glycated and aggregates proteins, which, in turn, may contribute to engulfing the autophagy compartments [ 38 , 40 , 195 ]. In this way, AGEs coupled with autophagy failure make protein aggregates irreversible and protease-resistant meanwhile increasing their propensity to spread from cell to cell.…”

Iron-Restricted Diet Affects Brain Ferritin Levels, Dopamine Metabolism and Cellular Prion Protein in a Region-Specific Manner

“…Since both PrP C and α-synuclein play roles in iron and dopamine metabolism (Wong and Duce, 2014 ; Haldar et al, 2015 ; da Luz et al, 2015 , 2016 ; Benskey et al, 2016 ), we investigated how dietary iron restriction affected the expression level of these proteins in each region by Western Blots. For the quantification of PrP C , we measured the intensity of three bands that correspond to di-, mono-, and unglycosylated forms.…”

“…Oxidative dopamine metabolites are known to promote the aggregation of α-synuclein into non-ordered toxic oligomers, and these molecular alterations are closely associated with pathogenesis of Parkinson's disease (Lotharius and Brundin, 2002 ; Yamakawa et al, 2010 ). Dopamine can also induce the aggregation of PrP C , another aggregation-prone protein associated with transmissible spongiform encephalopathies, a fatal neurodegenerative disease (da Luz et al, 2015 ).…”

Autophagy-Based Hypothesis on the Role of Brain Catecholamine Response During Stress

“…This occurs in various brain regions including the LC itself, though the VTA remains to be examined. In this frame, it is likely that stress- and drug-induced catecholamine alterations may increase the susceptibility of LC and VTA to neuronal damage by increasing the formation of highly oxidative DA- and NE-derived metabolites, which are known to impair neuronal proteostasis ( 125 , 126 ). This would explain why catecholamine-containing neurons are particularly susceptible to degeneration associated with an autophagy failure ( 127 – 129 ).…”