Inflammation kinase PKR phosphorylates α-synuclein and causes α-synuclein-dependent cell death.

Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy comprise a group of neurodegenerative diseases termed synucleinopathies. Synucleinopathie are, characterized by presence of inclusion bodies in degenerating brain cells which contain aggregated α-synuclein phosphorylated on Ser129. Although the inflammation-associated serine-threonine kinase, PKR (EIF2AK2), promotes cellular protection against infection, we demonstrate a pro-degenerative role of activated PKR in an α-synuclein-dependent cell model of multiple system atrophy, where inhibition and silencing of PKR decrease cellular degeneration. In vitro phosphorylation demonstrates that PKR can directly bind and phosphorylate monomeric and filamenteous α-synuclein on Ser129. Inhibition and knockdown of PKR reduce Ser129 phosphorylation in different models (SH-SY5Y ASYN cells, OLN-AS7 cells, primary mouse hippocampal neurons, and acute brain slices), while overexpression of constitutively active PKR increases Ser129 α-syn phosphorylation. Treatment with pre-formed α-synuclein fibrils, proteostatic stress-promoting MG-132 and known PKR activators, herpes simplex virus-1-∆ICP34.5 and LPS, as well as PKR inducer, IFN-ß-1b, lead to increased levels of phosphorylated Ser129 α-synuclein that is completely blocked by simultaneous PKR inhibition. These results reveal a direct link between PKR and the phosphorylation and toxicity of α-synuclein, and they support that neuroinflammatory processes play a role in modulating the pathogenicity of α-synuclein.

Loss of DJ-1 protein stability and cytoprotective function by Parkinson's disease-associated proline-158 deletion.

DJ-1 is a ubiquitous protein regulating cellular viability. Recessive mutations in the PARK7/DJ-1 gene are linked to Parkinson's disease (PD). Although the most dramatic L166P point mutation practically eliminates DJ-1 protein and function, the effects of other PD-linked mutations are subtler. Here, we investigated two recently described PD-associated DJ-1 point mutations, the A179T substitution and the P158Δ in-frame deletion. [A179T]DJ-1 protein was as stable as wild-type [wt]DJ-1, but the P158Δ mutant protein was less stable. In accord with the notion that dimer formation is essential for DJ-1 protein stability, [P158Δ]DJ-1 was impaired in dimer formation. Similar to our previous findings for [M26I]DJ-1, [P158Δ]DJ-1 bound aberrantly to apoptosis signal-regulating kinase 1. Thus, the PD-associated P158Δ mutation destabilizes DJ-1 protein and function. As there is also evidence for an involvement of DJ-1 in multiple system atrophy, a PD-related α-synucleinopathy characterized by oligodendroglial cytoplasmic inclusions, we studied an oligodendroglial cell line stably expressing α-synuclein. α-Synuclein aggregate dependent microtubule retraction upon co-transfection with tubulin polymerization-promoting protein p25α was ameliorated by [wt]DJ-1. In contrast, DJ-1 mutants including P158Δ failed to protect in this system, where we found evidence of apoptosis signal-regulating kinase 1 (ASK1) involvement. In conclusion, the P158Δ point mutation may contribute to neurodegeneration by protein destabilization and hence loss of DJ-1 function.

Antibodies against the C-terminus of α-synuclein modulate its fibrillation.

The 140-residue natively disordered protein α-synuclein (aSN) is a central component in the development of a family of neurodegenerative diseases termed synucleinopathies. This is attributed to its ability to form cytotoxic aggregates such as oligomers and amyloid fibrils. Consequently there have been intense efforts to avoid aggregation or reroute the aggregation pathway using pharmaceutical agents such as small molecules, chaperones and antibodies. aSN's lack of persistent structure in the monomeric state, as well as the multitude of different oligomeric and even different fibrillar states, makes it difficult to raise antibodies that would be efficacious in neutralizing all conformations of aSN. However, the C-terminal 20-40 residues of aSN are a promising epitope for antibody development. It is primarily disordered in both monomeric and aggregated forms, and an anti-C-terminal antibody will therefore be able to bind all forms. Furthermore, it might not interfere with the folding of aSN into membranes, which could be important for its physiological role. Here we report a screen of a series of monoclonal antibodies, which all target the C-terminal of aSN. According to dot blot analyses, different antibodies bound different forms of aSN with different preferences and showed reduced binding to monomeric compared to aggregated (oligomeric and fibrillary) aSN. Consequently they have different effects on aSN's ability to fibrillate and permeabilize membranes. Generally, the antibodies with strongest binding to aggregated aSN in dot blot, also inhibited fibrillation and membrane permeabilization the most, and promoted formation of amorphous aggregates surrounded by small and thin fibers. This suggests that the development of antibodies that targets the C-terminus, exposed in the aggregated forms of aSN, may be beneficial for improved immunotherapy against PD.