The protein α-synuclein has a central role in Parkinson disease, but the mechanism by which it contributes to neural degeneration remains unknown. We now show that the expression of α-synuclein in mammalian cells, including neurons in vitro and in vivo, causes the fragmentation of mitochondria. The effect is specific for synuclein, with more fragmentation by α- than β- or γ-isoforms, and it is not accompanied by changes in the morphology of other organelles or in mitochondrial membrane potential. However, mitochondrial fragmentation is eventually followed by a decline in respiration and neuronal death. The fragmentation does not require the mitochondrial fission protein Drp1 and involves a direct interaction of synuclein with mitochondrial membranes. In vitro, synuclein fragments artificial membranes containing the mitochondrial lipid cardiolipin, and this effect is specific for the small oligomeric forms of synuclein. α-Synuclein thus exerts a primary and direct effect on the morphology of an organelle long implicated in the pathogenesis of Parkinson disease.
"Of importance, α-syn seems to induce cell toxicity through its different pathological α-syn species, which include post-translationally modified, mutant, oligomeric and aggregated forms. These can (i) disrupt its typical function in neurotransmission release (Abeliovich et al., 2000; Jenco et al., 1998); (ii) impair mitochondrial dynamics, structure and function (Martin et al., 2006; Nakamura et al., 2011; Stefanovic et al., 2014); and (iii) disrupt ER-Golgi vesicle trafficking (Cooper et al., 2006; Gitler et al., 2008) and mitochondria-associated ER membrane (Mercado et al., 2013; Guardia-Laguarta et al., 2014), which results in ER stress. Further supporting the α-syn species toxicity, CMA inhibition by either PD-linked α-syn mutants or dopamine-modified wild-type α-syn results in an accumulation of α-syn, but also of undegraded CMA-substrates, involved for instance in the regulation of neuronal survival through the degradation of the neuronal survival factor myocyte enhancer factor 2D (MEF2D; Yang et al., 2009). "
[Show abstract][Hide abstract] ABSTRACT: Neurodegenerative diseases are (i) characterized by a selective neuronal vulnerability to degeneration in specific brain regions; and (ii) likely to be caused by disease-specific protein misfolding. Parkinson's disease (PD) is characterized by the presence of intraneuronal proteinacious cytoplasmic inclusions, called Lewy Bodies (LB). α-Synuclein, an aggregation prone protein, has been identified as a major protein component of LB and the causative for autosomal dominant PD. Lysosomes are responsible for the clearance of long-lived proteins, such as α-synuclein, and for the removal of old or damaged organelles, such as mitochondria. Interestingly, PD-linked α-synuclein mutants and dopamine-modified wild-type α-synuclein block its own degradation, which result in insufficient clearance, leading to its aggregation and cell toxicity. Moreover, both lysosomes and lysosomal proteases have been found to be involved in the activation of certain cell death pathways. Interestingly, lysosomal alterations are observed in the brains of patients suffering from sporadic PD and also in toxic and genetic rodent models of PD-related neurodegeneration. All these events have unraveled a causal link between lysosomal impairment, α-synuclein accumulation, and neurotoxicity. In this review, we emphasize the pathophysiological mechanisms connecting α-synuclein and lysosomal dysfunction in neuronal cell death.
Frontiers in Neuroanatomy 08/2014; 8(83). DOI:10.3389/fnana.2014.00083 · 3.54 Impact Factor
"These mitochondria often presented with a swollen pathological morphology, although this was not always the case. Indeed, mitochondrial dysfunction has been identified as one of the hallmarks of α-synuclein toxicity and is thought to play a major role in neuronal degeneration , . "
[Show abstract][Hide abstract] ABSTRACT: Synucleinopathies, characterized by intracellular aggregation of α-synuclein protein, share a number of features in pathology and disease progression. However, the vulnerable cell population differs significantly between the disorders, despite being caused by the same protein. While the vulnerability of dopamine cells in the substantia nigra to α-synuclein over-expression, and its link to Parkinson's disease, is well studied, animal models recapitulating the cortical degeneration in dementia with Lewy-bodies (DLB) are much less mature. The aim of this study was to develop a first rat model of widespread progressive synucleinopathy throughout the forebrain using adeno-associated viral (AAV) vector mediated gene delivery. Through bilateral injection of an AAV6 vector expressing human wild-type α-synuclein into the forebrain of neonatal rats, we were able to achieve widespread, robust α-synuclein expression with preferential expression in the frontal cortex. These animals displayed a progressive emergence of hyper-locomotion and dysregulated response to the dopaminergic agonist apomorphine. The animals receiving the α-synuclein vector displayed significant α-synuclein pathology including intra-cellular inclusion bodies, axonal pathology and elevated levels of phosphorylated α-synuclein, accompanied by significant loss of cortical neurons and a progressive reduction in both cortical and striatal ChAT positive interneurons. Furthermore, we found evidence of α-synuclein sequestered by IBA-1 positive microglia, which was coupled with a distinct change in morphology. In areas of most prominent pathology, the total α-synuclein levels were increased to, on average, two-fold, which is similar to the levels observed in patients with SNCA gene triplication, associated with cortical Lewy body pathology. This study provides a novel rat model of progressive cortical synucleinopathy, showing for the first time that cholinergic interneurons are vulnerable to α-synuclein over-expression. This animal model provides a powerful new tool for studies of neuronal degeneration in conditions of widespread cortical α-synuclein pathology, such as DLB, as well an attractive model for the exploration of novel biomarkers.
PLoS ONE 07/2014; 9(7):e100869. DOI:10.1371/journal.pone.0100869 · 3.23 Impact Factor
"Moreover , αsyn can translocate to mitochondria and accumulate, causing complex I impairment  . Our results, showing mitochondrial fragmentation, are in agreement with the literature     , excluding Zhu et al. (2012) . Moreover, our data suggest that there is a relationship between the presence of αsyn oligomers in the cytoplasm and variations in mitochondria morphology, while others could only establish a link between αsyn overexpression and mitochondria conditions. "
[Show abstract][Hide abstract] ABSTRACT: Background
Alpha-synuclein oligomerization is associated to Parkinson's disease etiopathogenesis. The study of alpha-synuclein oligomerization properties in live cell and the definition of their effects on cellular viability are among fields expected to provide the knowledge required to unravel the mechanism(s) of toxicity that lead to the disease.
We used Number and Brightness method, which is a method based on fluorescence fluctuation analysis, to monitor alpha-synuclein tagged with EGFP aggregation in living SH-SY5Y cells. The presence of alpha-synuclein oligomers detected with this method was associated with intracellular structure conditions, evaluated by fluorescence confocal imaging.
Cells overexpressing alpha-synuclein-EGFP present a heterogeneous ensemble of oligomers constituted by less than 10 monomers, when the protein approaches a threshold concentration value of about 90 nM in the cell cytoplasm. We show that the oligomeric species are partially sequestered by lysosomes and that the mitochondria morphology is altered in cells presenting oligomers, suggesting that these mitochondria may be dysfunctional.
We showed that alpha-synuclein overexpression in SH-SY5Y causes the formation of alpha-synuclein oligomeric species, whose presence is associated with mitochondrial fragmentation and autophagic-lysosomal pathway activation in live cells.
The unique capability provided by the Number and Brightness analysis to study alpha-synuclein oligomers distribution and properties, and the study their association to intracellular components in single live cells is important to forward our understanding of the molecular mechanisms Parkinson’s disease and it may be of general significance when applied to the study of other aggregating proteins in cellular models.
Biochimica et Biophysica Acta (BBA) - General Subjects 06/2014; 1840(6). DOI:10.1016/j.bbagen.2014.02.013 · 4.38 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.