Glycation potentiates α-synuclein-associated neurodegeneration in synucleinopathies.

α-Synuclein misfolding and aggregation is a hallmark in Parkinson's disease and in several other neurodegenerative diseases known as synucleinopathies. The toxic properties of α-synuclein are conserved from yeast to man, but the precise underpinnings of the cellular pathologies associated are still elusive, complicating the development of effective therapeutic strategies. Combining molecular genetics with target-based approaches, we established that glycation, an unavoidable age-associated post-translational modification, enhanced α-synuclein toxicity in vitro and in vivo, in Drosophila and in mice. Glycation affected primarily the N-terminal region of α-synuclein, reducing membrane binding, impaired the clearance of α-synuclein, and promoted the accumulation of toxic oligomers that impaired neuronal synaptic transmission. Strikingly, using glycation inhibitors, we demonstrated that normal clearance of α-synuclein was re-established, aggregation was reduced, and motor phenotypes in Drosophila were alleviated. Altogether, our study demonstrates glycation constitutes a novel drug target that can be explored in synucleinopathies as well as in other neurodegenerative conditions.

Overexpression of synphilin-1 promotes clearance of soluble and misfolded alpha-synuclein without restoring the motor phenotype in aged A30P transgenic mice.

Lewy bodies and neurites are the pathological hallmark of Parkinson's disease. These structures are composed of fibrillized and ubiquitinated alpha-synuclein suggesting that impaired protein clearance is an important event in aggregate formation. The A30P mutation is known for its fast oligomerization, but slow fibrillization rate. Despite its toxicity to neurons, mechanisms involved in either clearance or conversion of A30P alpha-synuclein from its soluble state into insoluble fibrils and their effects in vivo are poorly understood. Synphilin-1 is present in Lewy bodies, interacting with alpha-synuclein in vivo and in vitro and promotes its sequestration into aggresomes, which are thought to act as cytoprotective agents facilitating protein degradation. We therefore crossed animals overexpressing A30P alpha-synuclein with synphilin-1 transgenic mice to analyze its impact on aggregation, protein clearance and phenotype progression. We observed that co-expression of synphilin-1 mildly delayed the motor phenotype caused by A30P alpha-synuclein. Additionally, the presence of N- and C-terminal truncated alpha-synuclein species and fibrils were strongly reduced in double-transgenic mice when compared with single-transgenic A30P mice. Insolubility of mutant A30P and formation of aggresomes was still detectable in aged double-transgenic mice, paralleled by an increase of ubiquitinated proteins and high autophagic activity. Hence, this study supports the notion that co-expression of synphilin-1 promotes formation of autophagic-susceptible aggresomes and consecutively the degradation of human A30P alpha-synuclein. Notably, although synphilin-1 overexpression significantly reduced formation of fibrils and astrogliosis in aged animals, a similar phenotype is present in single- and double-transgenic mice suggesting additional neurotoxic processes in disease progression.