To elucidate the role of the synaptic protein alpha-synuclein in neurodegenerative disorders, transgenic mice expressing wild-type human alpha-synuclein were generated. Neuronal expression of human alpha-synuclein resulted in progressive accumulation of alpha-synuclein-and ubiquitin-immunoreactive inclusions in neurons in the neocortex, hippocampus, and substantia nigra. Ultrastructural analysis revealed both electron-dense intranuclear deposits and cytoplasmic inclusions. These alterations were associated with loss of dopaminergic terminals in the basal ganglia and with motor impairments. These results suggest that accumulation of wild-type alpha-synuclein may play a causal role in Parkinson's disease and related conditions.

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.

Overexpression of mutated human amyloid precursor protein (hAPP717V-->F) under control of platelet-derived growth factor promoter (PDAPP minigene) in transgenic (tg) mice results in neurodegenerative changes similar to Alzheimer's disease (AD). To clarify the pathology of these mice, we studied images derived from laser scanning confocal and electron microscopy and performed comparisons between PDAPP tg mice and AD. Similar to AD, neuritic plaques in PDAPP tg mouse contained a dense amyloid core surrounded by anti-hAPP- and antineurofilament-immunoreactive dystrophic neurites and astroglial cells. Neurons were found in close proximity to plaques in PDAPP tg mice and, to a lesser extent, in AD. In PDAPP tg mice, and occasionally in AD, neuronal processes contained fine intracellular amyloid fibrils in close proximity to the rough endoplasmic reticulum, coated vesicles, and electron-dense material. Extracellular amyloid fibrils (9-11 nm in diameter) were abundant in PDAPP tg and were strikingly similar to those observed in AD. Dystrophic neurites in plaques of PDAPP tg mouse and AD formed synapses and contained many dense multilaminar bodies and neurofilaments (10 nm). Apoptotic-like figures were present in the tg mice. No paired helical filaments have yet been observed in the heterozygote PDAPP tg mice. In summary, this study shows that PDAPP tg mice develop massive neuritic plaque formation and neuronal degeneration similar to AD. These findings show that overproduction of hAPP717V-->F in tg mice is sufficient to cause not only amyloid deposition, but also many of the complex subcellular degenerative changes associated with AD.

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