The endosomal pathway in Parkinson's disease.

Parkinson's disease is primarily a movement disorder with predilection for the nigral dopaminergic neurons and is often associated with widespread neurodegeneration and diffuse Lewy body deposition. Recent advances in molecular genetics and studies in model organisms have transformed our understanding of Parkinson's pathogenesis and suggested unifying biochemical pathways despite the clinical heterogeneity of the disease. In this review, we summarized the evidence that a number of Parkinson's associated genetic mutations or polymorphisms (LRRK2, VPS35, GBA, ATP13A2, ATP6AP2, DNAJC13/RME-8, RAB7L1, GAK) disrupt protein trafficking and degradation via the endosomal pathway and discussed how such defects could arise from or contribute to the accumulation and misfolding of α-synuclein in Lewy bodies. We propose that an age-related pathological depletion of functional endolysosomes due to neuromelanin deposition in dopaminergic neurons may increase their susceptibility to stochastic molecular defects in this pathway and we discuss how enzymes that regulate ubiquitin signaling, as exemplified by the ubiquitin ligase Nedd4, could provide the missing link between genetic and acquired defects in endosomal trafficking. This article is part of a Special Issue entitled 'Neuronal Protein'.

Perrett RM ，Alexopoulou Z ，Tofaris GK 《-》

Lysosome-dependent pathways as a unifying theme in Parkinson's disease.

Although the pathogenesis of Parkinson's disease (PD) is considered multifactorial, evidence from genetics and cell biology has implicated specific molecular pathways. This article summarizes evidence that suggests that the level of intracellular alpha-synuclein is critical for the onset of neurodegeneration with Lewy bodies and dependent, to a large extent, on lysosomal degradation. The function of other key proteins that emerged from genetics is discussed: Pink1 and Parkin regulate the degradation of damaged mitochondria by the lysosome (mitophagy). Glucocerebrosidase and ATP13A2 are important components of this degradative organelle. VPS35 and LRRK2 may regulate trafficking within lysosome-dependent pathways, such as autophagy and endosomal vesicle recycling. Clinically, diffuse alpha-synucleinopathy or dementia seems to correlate with mutations which interfere with the broader function of lysosomal pathways, whereas a predominantly motor syndrome and nigrostriatal degeneration is associated with specific defects in mitophagy. Based on these studies, it is proposed that a protein network involved in trafficking to, or degradation by, lysosomes could be sufficient to explain the phenotypic spectrum within PD in a unifying biochemical pathway.

Tofaris GK 《-》

Alpha-synuclein redistributes to neuromelanin lipid in the substantia nigra early in Parkinson's disease.

Halliday GM ，Ophof A ，Broe M ，Jensen PH ，Kettle E ，Fedorow H ，Cartwright MI ，Griffiths FM ，Shepherd CE ，Double KL ... -  《-》

Parkinson's disease and alpha synuclein: is Parkinson's disease a prion-like disorder?

Altered protein handling is thought to play a key role in the etiopathogenesis of Parkinson's disease (PD), as the disorder is characterized neuropathologically by the accumulation of intraneuronal protein aggregates (Lewy bodies and Lewy neurites). Attention has particularly focused on the α-synuclein protein, as it is the principal component of Lewy pathology. Moreover, point mutations in the α-synuclein gene cause rare familial forms of PD. Importantly, duplication/triplication of the wild type α-synuclein gene also cause a form of PD, indicating that increased levels of the normal α-synuclein protein is sufficient to cause the disease. Further, single nucleotide polymorphisms in the α-synuclein gene are associated with an increased risk of developing sporadic PD. Recent evidence now suggests the possibility that α-synuclein is a prion-like protein and that PD is a prion-like disease. Within cells, α-synuclein normally adopts an α-helical conformation. However, under certain circumstances, the protein can undergo a profound conformational transition to a β-sheet-rich structure that polymerizes to form toxic oligomers and amyloid plaques. Recent autopsy studies of patients with advanced PD who received transplantation of fetal nigral mesencephalic cells more than a decade earlier demonstrated that typical Lewy pathology had developed within grafted neurons. This suggests that α-synuclein in an aberrantly folded, β-sheet-rich form had migrated from affected to unaffected neurons. Laboratory studies confirm that α-synuclein can transfer from affected to unaffected nerve cells, where it appears that the misfolded protein can act as a template to promote misfolding of host α-synuclein. This leads to the formation of larger aggregates, neuronal dysfunction, and neurodegeneration. Indeed, recent reports demonstrate that a single intracerebral inoculation of misfolded α-synuclein can induce Lewy-like pathology in cells that can spread from affected to unaffected regions and can induce neurodegeneration with motor disturbances in both transgenic and normal mice. Further, inoculates derived from the brains of elderly α-synuclein-overexpressing transgenic mice have now been shown to accelerate the disease process when injected into the brains of young transgenic animals. Collectively, these findings support the hypothesis that α-synuclein is a prion-like protein that can adopt a self-propagating conformation that causes neurodegeneration. We propose that this mechanism plays an important role in the development of PD and provides novel targets for candidate neuroprotective therapies.

Olanow CW ，Brundin P 《-》

Parkinson's disease-linked DNAJC13 mutation aggravates alpha-synuclein-induced neurotoxicity through perturbation of endosomal trafficking.

Yoshida S ，Hasegawa T ，Suzuki M ，Sugeno N ，Kobayashi J ，Ueyama M ，Fukuda M ，Ido-Fujibayashi A ，Sekiguchi K ，Ezura M ，Kikuchi A ，Baba T ，Takeda A ，Mochizuki H ，Nagai Y ，Aoki M ... -  《-》