The alpha-synuclein gene and Parkinson disease in a Chinese population

OBJECTIVE: To study the Ala53Thr and Ala30Pro mutations of the alpha-synuclein gene in a large number of Chinese patients with Parkinson disease (PD) as well as controls. METHODS: We recruited 183 Chinese patients with sporadic PD, 17 with younger-onset PD (onset age <50 years), and 7 with PD and a positive family history as well as 227 unaffected Chinese control subjects from the outpatient departments of 2 major hospitals in Hong Kong. All subjects were assessed for the the diagnosis of PD by a consultant neurologist or geriatrician. Subjects were interviewed with a standard questionnaire that also questioned for family history. Venous blood samples were obtained from the subjects and genomic DNA was extracted and studied for the presence of Ala53Thr mutation in exon 4 and Ala30Pro mutation in exon 3 of the alpha-synuclein gene using a polymerase chain reaction restriction fragment length polymorphism method. RESULTS: None of the Chinese PD patients or controls had either the Ala53Thr (exon 4) or Ala30Pro (exon 3) mutation of the alpha-synuclein gene. CONCLUSION: We failed to discover Ala53Thr or Ala30Pro mutations in a large number of Chinese patients with PD and control subjects, adding to the emerging consensus that variations in the alpha-synuclein gene are associated with PD in few families worldwide.     

Levels of alpha-synuclein mRNA in sporadic Parkinson disease patients.

Lewy bodies, the pathological hallmark of Parkinson's disease (PD), consist largely of alpha-synuclein, a 14.5-kDa presynaptic neuronal protein implicated in familial PD. An increased copy number and elevated expression of wild-type alpha-synuclein (SNCA) has been shown to cause early-onset familial PD. However, it is not clear whether increased alpha-synuclein expression also plays a role in the pathogenesis of sporadic disease. In the current study, we analyzed the levels of SNCA-mRNA in affected brains of sporadic PD patients. We compared the levels of steady state SNCA-mRNA in 7 sporadic PD brain samples and 7 normal controls using real-time polymerase chain reaction of RNA extracted from mid-brain tissue, including the substantia nigra. Despite that there is neuronal loss in the substantia nigra of PD brains, overall the SNCA-mRNA levels were increased in PD brains an average of nearly fourfold over normal control mid-brain, although there was much greater variability in samples from PD patients compared to controls. Frontal cortex samples from selected individuals were also analyzed. SNCA-mRNA levels were not significantly changed in PD frontal cortex compared to controls. These results suggest that elevated expression levels of SNCA-mRNA are found in the affected regions of PD brain and support the hypothesis that increases in alpha-synuclein expression is associated, among other factors, with the development of sporadic PD.     

Nitration and increased alpha-synuclein expression associated with dopaminergic neurodegeneration in equine pituitary pars intermedia dysfunction

Equine pituitary pars intermedia dysfunction (PPID) is a spontaneously occurring progressive disease affecting aged horses and ponies. The pathogenesis of PPID is poorly understood, but the available evidence supports a loss of dopaminergic inhibition of the melanotropes of the pars intermedia. Horses with PPID have increased plasma concentrations of pars intermedia pro-opiomelanocortin-derived peptides that decrease in response to dopamine or dopamine agonist administration. Dopamine and dopamine metabolite concentrations are decreased in the pars intermedia of affected horses compared to age-matched control horses. Horses with disease that are treated with the dopamine agonist pergolide show improvement in clinical signs and normalisation of diagnostic test results. In the present study, immunohistochemical evaluation of pituitary and hypothalamic tissue demonstrated reduced tyrosine hydroxylase immunoreactivity in affected horses compared to age-matched and young controls, supporting the role of dopaminergic neurodegeneration in PPID. In addition, immunohistochemical evaluation revealed an increase in the oxidative stress marker, 3-nitrotyrosine and in nerve terminal protein, alpha-synuclein that colocalised in the pars intermedia of horses with disease. These findings suggest a role for nitration of overexpressed alpha-synuclein in the pathogenesis of neurodegeneration in PPID.     

Staging of sporadic Parkinson disease-related alpha-synuclein pathology: inter- and intra-rater reliability

Sporadic Parkinson disease (sPD) is characterized by alpha-synuclein (alpha-syn) inclusions. The distribution of such inclusions appears to relate to disease progression and severity. We propose and test a simple staging protocol based on the presence of alpha-syn immunoreactivity in 5 paraffin sections that, taken together, contain up to 8 vulnerable brain regions. Six stages of alpha-syn pathology reminiscent for sPD are defined based on the presence or absence of inclusions in the assessed sections. Six observers from 5 different institutions rated 21 cases on the basis of written instructions only. The agreement of the raters was highly significant with a mean error below one stage. Both inter- and intra-rater reliability were also substantial to almost perfect as analyzed by paired comparison between all raters. We propose that the staging procedure for alpha-syn pathology is suitable for application in routine neuropathology and brain banking. Clearly defined stages of alpha-synpathology might aid the comparability between studies and also help to distinguish sPD from other synucleinopathies.     

Oxidative-stress-induced apoptosis in PBLs of two patients with Parkinson disease secondary to alpha-synuclein mutation

Alpha-synuclein has been implicated in the pathology of certain neurodegenerative diseases, including Parkinson disease (PD). Although the precise physiological and pathological role of alpha-synuclein is unclear, overexpression of the protein or its mutants may reduce cell viability. In this study we evaluated the apoptotic response to oxidative stress induced by 2-deoxy-d-ribose (dRib) in peripheral blood lymphocytes (PBLs) of two siblings with Parkinson disease secondary to A53T alpha-synuclein mutation. PBLs exposed to oxidative stress showed a higher percentage of apoptotic cells in PD patients than in controls. However in cells of PD patients, the increase of apoptotic response was lower than in controls, suggesting that cells of PD patients have greater "resistance" to oxidative stress. We conclude that other environmental agents could play a key role in inducing programmed cell death in cells of PD patients with mutant alpha-synuclein.     

Failure to find alpha-synuclein gene dosage changes in 190 patients with familial Parkinson disease

BACKGROUND: Recently, a triplication of the alpha-synuclein locus was found associated with autosomal dominant Parkinson disease in a large family. OBJECTIVE: To determine whether a triplication or some other dosage alteration in the alpha-synuclein gene is present in one or more patients with familial PD in a large multinational collective. DESIGN: Retrospective recruitment of the largest families who were willing to cooperate with the study. SETTING: Centers with specialization in movement disorders genetics. PATIENTS: One hundred ninety unrelated patients with familial PD from Germany, Portugal, and Yugoslavia. MAIN OUTCOME MEASURES: Alpha-synuclein gene dosage values measured with real-time polymerase chain reaction. RESULTS: None of the samples showed alpha-synuclein triplication, duplication, or deletion. CONCLUSION: Alterations in alpha-synuclein gene dosage are rare in familial PD.     

Relationship among alpha-synuclein accumulation, dopamine synthesis, and neurodegeneration in Parkinson disease substantia nigra

The histologic hallmark of Parkinson disease (PD) is loss of pigmented neurons in the substantia nigra (SN) and locus ceruleus (LC) with accumulation of alpha-synuclein (alphaS). It has been reported that tyrosine hydroxylase (TH)-negative pigmented neurons are present in these nuclei of patients with PD. However, the relationship between TH immunoreactivity and alphaS accumulation remains uncertain. We immunohistochemically examined the SN and LC from patients with PD (n = 10) and control subjects (n = 7). A correlation study indicated a close relationship among decreased TH immunoreactivity, alphaS accumulation, and neuronal loss. In addition, 10% of pigmented neurons in the SN and 54.9% of those in the LC contained abnormal alphaS aggregates. Moreover, 82.3% of pigmented neurons bearing alphaS aggregates in the SN and 39.2% of those in the LC lacked TH immunoreactivity, suggesting that pigmented neurons in the SN have a greater tendency to lack TH activity than those in the LC. Recent studies have shown that this decrease of TH activity leads to a decrease of cytotoxic substances and that decreased dopamine synthesis leads to a reduction of cytotoxic alphaS oligomers. Therefore, the decrease of TH immunoreactivity in pigmented neurons demonstrated here can be considered to represent a cytoprotective mechanism in PD.     

Reelin-deficient mice show impaired neurogenesis and increased stroke size

Reelin (Reln) is a protein involved in migration of newborn neurons during development. Reln mutations produce the reeler phenotype in mice, which is characterized by a defect in brain lamination, and autosomal recessive lissencephaly in humans. Reln expression persists in adult brain, but little is known about its function. We used reeler mice to investigate the effects of Reln deficiency on neurogenesis and the response to injury in the adult brain. Newborn neurons were decreased in number in the dentate gyrus and rostral migratory stream of reeler, compared to wild-type, mice. This was due, at least in part, to impaired cell migration. In addition, reeler mice showed increased susceptibility to ischemic brain injury. Cerebral infarcts from middle cerebral artery occlusion were larger in reeler than in wild-type mice, and associated neurobehavioral abnormalities were more severe. The brains of reeler mice also showed larger excitotoxic lesions after the intracerebral injection of N-methyl-D-aspartate. Finally, despite the fact that reeler mice had larger cerebral infarcts, the ischemia-induced enhancement of neurogenesis observed in wild-type mice was attenuated. These findings suggest that, in addition to its neurodevelopmental effects, Reln deficiency continues to influence neurogenesis and ischemic neuronal injury in the adult brain.     

Mice lacking neuropeptide Y show increased sensitivity to cocaine

There is increasing data implicating neuropeptide Y (NPY) in the neurobiology of addiction. This study explored the possible role of NPY in cocaine-induced behavior using NPY knockout mice. The transgenic mice showed a hypersensitive response to cocaine in three animal models of cocaine addiction. Whether this is due to an observed compensatory increase in striatal dopamine transporter binding or an anxiogenic phenotype of the transgenic mice remains to be determined.     

Occurrence of neuronal inclusions combined with increased nigral expression of alpha-synuclein within dopaminergic neurons following treatment with amphetamine derivatives in mice

In recent years several clinical and research findings have demonstrated the involvement of the presynaptic protein alpha-synuclein in a variety of neurodegenerative disorders which are known as synucleinopathies. Although the function of this protein in the physiology of the cell remains unknown, it is evident that both genetic alterations or a mere overexpression of the native molecule produces a degeneration of nigral dopamine-containing neurons leading to movement disorders, as demonstrated in inherited Parkinson's disease. In the present study, we investigated whether widely abused drugs such as methamphetamine and methylenedioxymethamphetamine (ecstasy), which are known to damage the nigrostriatal dopamine pathway of mice, increase the expression of alpha-synuclein within dopamine neurons of the substantia nigra pars compacta. The results of this study demonstrate that nigrostriatal dopamine denervation and occurrence of intracellular inclusions in nigral neurons produced by amphetamine derivatives are related to increased expression of alpha-synuclein within dopamine neurons of the substantia nigra. This lends substance to the hypothesis that increased amounts of native alpha-synuclein may be per se a detrimental factor for the dopamine neurons.     

Alteration in alpha-synuclein mRNA expression in Parkinson's disease.

The presynaptic protein alpha-synuclein is considered to play an important role in the pathophysiology of Parkinson's disease (PD). Point mutations in the alpha-synuclein gene have been demonstrated in familial PD and alpha-synuclein is a major component of Lewy bodies, the pathological hallmark of the sporadic disease. It is not clear whether abnormal accumulation of alpha-synuclein is the result of abnormal levels of expression of the gene in neurodegenerative conditions. Expression of alpha-synuclein mRNA was therefore studied in control and PD brain using semiquantitative in situ hybridization. alpha-synuclein was expressed widely and hybridization signal was seen in most cortical regions, hippocampus, cerebellum, and brain stem. There was little mRNA in the striatum and no hybridization signal was detected in glia. High levels of alpha-synuclein mRNA expression in neurons did not seem to be a marker for Lewy body formation. Abundant signal was seen both in regions in which Lewy body deposition occurs commonly in idiopathic PD (PD), such as substantia nigra and frontal and temporal cortex, as well as in less susceptible regions, e.g. visual cortex. Quantitative comparison of mRNA expression in regions of predilection for Lewy body formation showed that mRNA expression was reduced significantly in melanized substantia nigra neurons and frontal cortex neurons in Parkinson's disease. In substantia nigra neurons there seemed to be a negative correlation between cellular mRNA expression and disease duration. These findings are in broad agreement with other studies of the expression of alpha-synuclein mRNA in human brain and suggest that Lewy body formation is unlikely to be the result of overexpression of alpha-synuclein.     

The new mutation, E46K, of alpha-synuclein causes Parkinson and Lewy body dementia

Familial parkinsonism and dementia with cortical and subcortical Lewy bodies is uncommon, and no genetic defect has been reported in the previously described sibships. We present a Spanish family with autosomal dominant parkinsonism, dementia, and visual hallucinations of variable severity. The postmortem examination showed atrophy of the substantia nigra, lack of Alzheimer pathology, and numerous Lewy bodies which were immunoreactive to alpha-synuclein and ubiquitin in cortical and subcortical areas. Sequencing of the alpha-synuclein gene showed a novel, nonconservative E46K mutation in heterozygosis. The E46K mutation was present in all affected family members and in three young asymptomatic subjects, but it was absent in healthy and pathological controls. The novel mutation, that substitutes a dicarboxylic amino acid, glutamic acid, with a basic amino acid such as lysine in a much conserved area of the protein, is likely to produce severe disturbance of protein function. Our data show that, in addition to the previously described hereditary alpha-synucleinopathies, dementia with Lewy bodies is related to mutation of alpha-synuclein.