Abnormal accumulation of the presynaptic protein alpha-synuclein has recently been implicated in the pathogenesis of Alzheimer's and Parkinson's diseases. Because neurodegeneration in these conditions might be associated with mitochondrial dysfunction and oxidative stress, the effects of alpha-synuclein were investigated in a hypothalamic neuronal cell line (GT1-7). alpha-Synuclein overexpression in these cells resulted in formation of alpha-synuclein-immunopositive inclusion-like structures and mitochondrial alterations accompanied by increased levels of free radicals and decreased secretion of gonadotropin-releasing hormone. These alterations were ameliorated by pretreatment with anti-oxidants such as vitamin E. Taken together these results suggest that abnormal accumulation of alpha-synuclein could lead to mitochondrial alterations that may result in oxidative stress and, eventually, cell death.

The precursor of non-amyloid beta protein component of Alzheimer's disease amyloid (NACP/alpha-synuclein), found in Lewy bodies of Parkinson's disease (PD), is a presynaptic protein genetically linked to some familial types PD. Mechanisms of abnormal NACP/alpha-synuclein aggregation in neurodegenerative diseases are unclear. Since oxidative stress might play a role in PD pathogenesis, we investigated the role of iron and peroxide in NACP/alpha-synuclein aggregation. Immunoblot analysis showed that human NACP/alpha-synuclein (but not beta-synuclein) aggregated in the presence of ferric ion and was inhibited by the iron chelator deferoxamine. Ferrous ion was not effective by itself, but it potentially aggregated NACP/alpha-synuclein in the presence of hydrogen peroxide. NACP/ alpha-synuclein aggregates displayed strong thioflavine-S and congo-red reactivity, reminiscent of amyloid. This study suggests that NACP/alpha-synuclein aggregation might be closely related to oxidative reactions which may play a critical role in neurodegeneration in disorders with Lewy bodies.

No abstract

␣-Synuclein is a major component of aggregates forming amyloid-like fibrils in diseases with Lewy bodies and other neurodegenerative disorders, yet the mechanism by which ␣-synuclein is intracellularly aggregated during neurodegeneration is poorly understood. Recent studies suggest that oxidative stress reactions might contribute to abnormal aggregation of this molecule. In this context, the main objective of the present study was to determine the potential role of the heme protein cytochrome c in ␣-synuclein aggregation. When recombinant ␣-synuclein was coincubated with cytochrome c/hydrogen peroxide, ␣-synuclein was concomitantly induced to be aggregated. This process was blocked by antioxidant agents such as N-acetyl-L-cysteine. Hemin/ hydrogen peroxide similarly induced aggregation of ␣-synuclein, and both cytochrome c/hydrogen peroxideand hemin/hydrogen peroxide-induced aggregation of ␣-synuclein was partially inhibited by treatment with iron chelator deferoxisamine. This indicates that ironcatalyzed oxidative reaction mediated by cytochrome c/hydrogen peroxide might be critically involved in promoting ␣-synuclein aggregation. Furthermore, double labeling studies for cytochrome c/␣-synuclein showed that they were colocalized in Lewy bodies of patients with Parkinson's disease.Taken together, these results suggest that cytochrome c, a well known electron transfer, and mediator of apoptotic cell death may be involved in the oxidative stressinduced aggregation of ␣-synuclein in Parkinson's disease and related disorders.

The expression of ␣-synuclein, a synaptic molecule implicated in the pathogenesis of neurodegenerative disorders such as Parkinson's disease and Lewy body disease is increased upon injury to the nervous system, indicating that it might play a role in regeneration and plasticity; however, the mechanisms are unclear. Because c-Jun N-terminal kinase (JNK), a member of the mitogen-activated protein kinase family, plays an important role in stress response, the main objective of the present study was to better understand the involvement of this pathway in the signaling responses associated with resistance to injury in cells expressing ␣-synuclein. Neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease (PD) 1 are characterized by selective neuronal and synaptic damage in cortical and subcortical regions resulting in cognitive and motor impairment (1). The mechanisms leading to neurodegeneration in these disorders are unclear; however, recent studies suggest that abnormal aggregation of misfolded neuronal proteins might play a central role (2, 3). Although in Alzheimer's disease intracellular (4, 5) and extracellular aggregation of amyloid ␤-protein (5) has been implicated in PD, intraneuronal aggregation of misfolded ␣-synuclein (6 -8) has been suggested to be involved in the pathogenesis of the neurodegenerative process. In supporting a role of misfolded ␣-synuclein in the pathogenesis of PD, previous studies show that missense mutations that accelerates ␣-synuclein aggregation (9) are associated with familial PD (10, 11). Furthermore, Lewy bodies that are intraneuronal inclusions found in patients with parkinsonism are primarily composed of misfolded ␣-synuclein (6 -8), and overexpression of ␣-synuclein in transgenic mice (12) and Drosophila (13) resulted in Lewy body-like formation associated with degeneration of dopaminergic neurons. ␣-Synuclein is an abundant synaptic protein that is a member of the synuclein family of peptides that includes ␣-, ␤-, and ␥-synuclein as well as synoretin (14,15). The physiological roles of these proteins are unclear, although they might play an important role in neuroplasticity and in response to neuronal cell damage (14, 16). In support of this possibility, recent studies show that ␣-synuclein expression is increased in models of developmental-targeted injury (17,18). In this model, up-regulation of ␣-synuclein at the mRNA level is associated with an increase number of neurons expressing ␣-synuclein, and at the cellular level, ␣-synuclein is almost exclusively expressed in normal neurons rather than in apoptotic cells (18). Moreover, during development, ␣-synuclein expression is up-regulated (19), and the expression of this synaptic molecule is not further up-regulated during the period of natural cell death (17,18). In neuronal cell lines, overexpression of wild type ␣-synuclein protects against oxidative stress (20). In contrast, neuronal cell lines expressing ␣-synuclein that contains mutations (A30P and A53T) associated with familial Parkinsonism and...