Research ArticleMitochondrial translocation of α-synuclein is promoted by intracellular acidification
Introduction
Oxidative stress and metabolic dysfunction appear to be important factors in a number of neurodegenerative diseases, including Parkinson's disease (PD), although the cellular pathways through which the various stresses converge are only slowly being uncovered [1], [2]. Many of the pathological features of PD, including the selective loss of dopaminergic neurons and α-synuclein aggregation can be reproduced by environmental toxins that principally target mitochondria [3], [4]. Impairments in the electron transport chain are associated with increased levels of reactive oxygen species and decreased energy production [4], [5], and can be amplified by proteasome inhibition [6], [7]. In addition to environmental factors, multiple genes mediating familial forms of PD or affecting PD risk have been identified, several of which encode proteins that localize to mitochondria and/or are associated with mitochondrial homeostasis. These include PINK1 [8], DJ-1 [9], [10], parkin [11], [12], and Omi/HtrA2 [13]. Since mitochondrial complex I deficiencies have been reported in patients with sporadic PD [14], [15], a common cellular network likely links familial and sporadic forms of the disease.
There is increasing evidence that the first familial PD gene to be identified, α-synuclein, also influences cellular responses to mitochondrial stress. Wild-type α-synuclein protects or sensitizes cells to apoptotic stimuli, depending on the cell type and insult examined [16], [17], whereas mutant α-synucleins (A30P or A53T) generally increase neuronal vulnerability to mitochondria-associated toxicity [16], [18], [19]. Conversely, α-synuclein knockout mice show marked resistance to several mitochondrial toxins [20]. Mitochondrial morphology or physiology may also be affected by α-synuclein overexpression [21], [22], and mitochondrial abnormalities are observed in α-synuclein-expressing mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) [23]. There is, however, little evidence that α-synuclein exerts these effects by a direct physical association with mitochondria.
We now report that, in response to reduced intracellular pH, α-synuclein translocates from the cytosol onto the surface of mitochondria. This occurs under a number of oxidative and/or metabolic stress conditions, and is likely mediated by pH-dependent exposure of mitochondria-specific lipids. Thus, α-synuclein may play a direct role in mitochondrial physiology, ostensibly establishing a link between mitochondrial dysfunction and α-synuclein-associated toxicity in PD pathogenesis.
Section snippets
Cell lines, plasmids, and antibodies
All cell lines were from the ATCC. Stable cells were selected in G418 (500 μg/ml for HEK293) and 200 μg/ml (for SK-N-SH). Primary rat hippocampal neurons were provided by C. Winters (NINDS). Plasmids for expression of various synucleins in eukaryotic and prokaryotic cells were as previously described [24], [25]. Antibodies to synucleins included 202 (1/100, for immunofluorescence and immunoelectron microscopy, from V. Lee, Univ. of Pennsylvania; this antibody recognizes α- and β-synuclein) and
Synuclein translocates to mitochondria in response to cellular stress
α-Synuclein is a presynaptic neuronal protein that, when expressed in most non-neuronal cells, is diffusely distributed throughout the cytosol with little accumulation at specific intracellular sites [24], [34], [35]. A number of reports have demonstrated an effect of α-synuclein expression on responses to various stress conditions. Alterations in the subcellular distribution of α-synuclein under these conditions, however, have not been carefully addressed. We therefore examined α-synuclein
Discussion
Oxidative stress and mitochondrial dysfunction are common features in virtually all neurodegenerative diseases, and there is increasing evidence for a causal role of these stresses in disease pathogenesis. In PD, identification of disease-specific genes that influence mitochondrial physiology, either directly or indirectly, have contributed greatly to our understanding of the role of mitochondrial impairment in the etiology of this disease [1], [2]. For example, mitochondrial pathology and
Acknowledgments
We thank the NINDS electron microscopy facility for sample preparation, C. Winters (NINDS) for providing rat primary hippocampal neurons, and C. Ellis (NHGRI) for purified mitochondria. We also thank John Church (Department of Physiology, Univ. of British Columbia) for advice on intracellular pH measurements, and Rod Levine (NHLBI) for many helpful discussions. Part of this work was funded by the NINDS intramural program (to N.B.C.).
While this manuscript was under revision, two papers [69], [70]
References (70)
- et al.
Proteasome inhibition alters neural mitochondrial homeostasis and mitochondria turnover
J. Biol. Chem.
(2004) - et al.
Mitochondrial dysfunction and oxidative damage in parkin-deficient mice
J. Biol. Chem.
(2004) - et al.
Mice lacking alpha-synuclein are resistant to mitochondrial toxins
Neurobiol. Dis.
(2006) - et al.
Alpha-synuclein promotes mitochondrial deficit and oxidative stress
Am. J. Pathol.
(2000) - et al.
Enhanced substantia nigra mitochondrial pathology in human alpha-synuclein transgenic mice after treatment with MPTP
Exp. Neurol.
(2004) - et al.
Lipid droplet binding and oligomerization properties of the Parkinson's disease protein alpha-synuclein
J. Biol. Chem.
(2002) - et al.
Metal-catalyzed oxidation of alpha-synuclein: helping to define the relationship between oligomers, protofibrils, and filaments
J. Biol. Chem.
(2005) - et al.
Lipid extraction of tissues with a low-toxicity solvent
Anal. Biochem.
(1978) - et al.
The biosynthesis and functional role of cardiolipin
Prog. Lipid Res.
(2000) - et al.
Molecular order and dynamics in bilayers consisting of highly polyunsaturated phospholipids
Biophys. J.
(1998)
Oxidative stress induces nuclear translocation of C-terminus of alpha-synuclein in dopaminergic cells
Biochem. Biophys. Res. Commun.
The lysosomal-mitochondrial axis theory of postmitotic aging and cell death
Chem. Biol. Interact.
A novel mechanism of interaction between alpha-synuclein and biological membranes
J. Mol. Biol.
Quantification of alpha-synuclein binding to lipid vesicles using fluorescence correlation spectroscopy
Biophys. J.
Lipids of mitochondria
Biochim. Biophys. Acta.
Binding of 10-N-nonyl acridine orange to cardiolipin-deficient yeast cells: implications for assay of cardiolipin
Anal. Biochem.
Alpha-Synuclein is degraded by both autophagy and the proteasome
J. Biol. Chem.
Mitochondrial import and accumulation of alpha -synuclein impairs complex I in human dopaminergic neuronal cultures and Parkinson's disease brain
J. Biol. Chem.
Expanding insights of mitochondrial dysfunction in Parkinson's disease
Nat. Rev. Neurosci.
Mitochondrial dysfunction and oxidative stress in neurodegenerative diseases
Nature
Mechanistic approaches to Parkinson's disease pathogenesis
Brain Pathol.
MPTP as a mitochondrial neurotoxic model of Parkinson's disease
J. Bioenerg. Biomembr.
Mechanism of toxicity of pesticides acting at complex I: relevance to environmental etiologies of Parkinson's disease
J. Neurochem.
Dysfunction of mitochondrial complex I and the proteasome: interactions between two biochemical deficits in a cellular model of Parkinson's disease
J. Neurochem.
Hereditary early-onset Parkinson's disease caused by mutations in PINK1
Science
The Parkinson's disease protein DJ-1 is neuroprotective due to cysteine-sulfinic acid-driven mitochondrial localization
Proc. Natl. Acad. Sci. U. S. A.
Hypersensitivity of DJ-1-deficient mice to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrindine (MPTP) and oxidative stress
Proc. Natl. Acad. Sci. U. S. A.
Mitochondrial pathology and apoptotic muscle degeneration in Drosophila parkin mutants
Proc. Natl. Acad. Sci. U. S. A.
Loss of function mutations in the gene encoding Omi/HtrA2 in Parkinson's disease
Hum. Mol. Genet.
Mitochondrial complex I deficiency in Parkinson's disease
J. Neurochem.
Mitochondrial dysfunction in Parkinson's disease
Ann. Neurol.
Effect of the overexpression of wild-type or mutant alpha-synuclein on cell susceptibility to insult
J. Neurochem.
Antiapoptotic property of human alpha-synuclein in neuronal cell lines is associated with the inhibition of caspase-3 but not caspase-9 activity
J. Neurochem.
Inducible expression of mutant alpha-synuclein decreases proteasome activity and increases sensitivity to mitochondria-dependent apoptosis
Hum. Mol. Genet.
Parkinson's disease genetic mutations increase cell susceptibility to stress: Mutant alpha-synuclein enhances H(2)O(2)- and Sin-1-induced cell death
Neurobiol. Aging.
Cited by (160)
A penetratin-derived peptide reduces the membrane permeabilization and cell toxicity of α-synuclein oligomers
2022, Journal of Biological ChemistryFatal attraction – The role of hypoxia when alpha-synuclein gets intimate with mitochondria
2021, Neurobiology of AgingExploring lipid-dependent conformations of membrane-bound α-synuclein with the VDAC nanopore
2021, Biochimica et Biophysica Acta - BiomembranesCitation Excerpt :The immediate question is what are the endogenous factors that regulate the discovered αSyn-VDAC interaction in vivo? One would expect that the αSyn expression level [45,56], its disease-related mutations [62], post-translational modifications (PTM) [63,64], and different cytosolic factors such as pH [65] could affect this process. Here we address the question of how αSyn-VDAC interaction could be regulated by mitochondria.
- 1
Current Address: Division of Medical Genetics, University of California, San Francisco School of Medicine, San Francisco, CA, USA.