Parkin and synphilin-1 isoform expression changes in Lewy body diseases

Alternative splicing gives rise to at least seven parkin and eight synphilin-1 isoforms. Since both parkin and synphilin-1 have been involved in Lewy body (LB) formation, we decided to explore whether their isoforms are differentially expressed in LB diseases. With this aim, we studied relative mRNA expression levels of parkin and synphilin-1 isoforms in the frontal cortices of patients with dementia with LBs, the LB variant of Alzheimer's disease and Parkinson's disease and compared the findings with those obtained from Alzheimer's disease patients and control individuals. Duplex real-time PCR reactions, with beta-actin as internal standard, were carried out in a LightCycler. mRNA expression levels of parkin and synphilin-1 isoforms were seen to be specifically altered in each of the LB diseases studied. These findings suggest that parkin and synphilin-1 isoform expression changes play a significant role in the pathogenesis of LB diseases.     

Parkin and defective ubiquitination in Parkinson's disease

Parkinson's Disease (PD) is a common neurodegenerative disorder that is characterized by the progressive loss of dopamine (DA) neurons. Accompanying the loss the of DA neurons is the accumulation of Lewy bodies and neurites, intracytoplasmic proteinaceous inclusions that contain alpha-synuclein, synphilin-1, components of the ubiquitin proteasomal pathway and parkin. Recent advances indicate that PD is due in some individuals to genetic mutations in alpha-synuclein, DJ-1, PINK-1, LRRK2, and parkin. Understanding the molecular mechanisms by which mutations in familial-linked genes cause PD holds great promise for unraveling the mechanisms by which DA neurons degenerate in PD. Parkin is E3-ubiquitin-protein ligase that ubiquitinates itself and promotes its own degradation. Familial associated mutations of parkin have impaired ubiquitin ligase function suggesting that this may be the cause of familial autosomal recessive PD. Parkin might be required for formation of Lewy bodies as Lewy bodies are absent in patients with parkin mutations. Parkin interacts with and ubiquitinates the alpha-synuclein interacting protein, synphilin-1. Formation of Lewy-body-like ubiquitin-positive cytosolic inclusions occurs upon coexpression of alpha-synuclein, synphilin-1 and parkin. Nitric oxide inhibits Parkin's E-3 ligase activity and its protective function by nitric oxide through S-nitrosylation both in vitro and in vivo. Nitrosative and oxidative stress link parkin function with the more common sporadic form of Parkinson's disease and the related alpha-synucleinopathy, DLBD. Development of new therapies for PD and other disorders associated with nitrosative and oxidative stress may follow the elucidation of the pathways by which NO S-nitrosylates and inhibits parkin. Moreover, parkin and alpha-synuclein are linked in common pathogenic mechanism through their interaction with synphilin-1 and parkin may be important for the formation of Lewy bodies.     

The role of synphilin-1 in the pathogenesis of Parkinson＇s disease

Parkinson＇s disease （PD） is one of the commonest neurodegenerative disorders characterized by the loss of dopaminergic （DAergic） neurons in the substantia nigra and the appearance of Lewy bodies （LBs）, whose cytoplasmic inclusions are highly enriched with ubiquitin, synphilin- 1, α-synuclein and park：in. Synphilin- 1 is an α-synuclein-binding protein and a major component of LBs, It is widely accepted that synphilin- 1 is involved in the pathogenic process of PD. This review will provide an overall view of the role of synphilin- 1 in the pathogenesis of Parkinson＇ s disease and the latest findings in this field.     

A putative polymorphic Val44Ala variation in the synphilin-1 gene is undetectable in Japanese sporadic Parkinson''s disease patients

Recently, a novel protein-interaction partner of alpha-synuclein, designated synphilin-1, is identified as a constituent of Lewy bodies (LB) in Parkinson's disease (PD) brains. To investigate an involvement of genetic variations of synphilin-1 in development of sporadic PD, a possible single nucleotide polymorphism (SNP) of T131C corresponding to a valine (Val) to alanine (Ala) substitution at codon 44 in exon 3 of the synphilin-1 gene was studied in a Japanese population of 55 patients with sporadic PD and 61 patients with non-PD by direct sequencing analysis. All 116 subjects showed a homozygosity of Val at codon 44 in the synphilin-1 gene, suggesting that this SNP is unlikely to affect genetic susceptibility to sporadic PD in the Japanese population.     

Immunocytochemical localization of synphilin-1, an α-synuclein-associated protein, in neurodegenerative disorders

Alpha-synuclein is a major component of Lewy bodies (LB) in Parkinson's disease (PD) and dementia with LB (DLB), as well as of glial cytoplasmic inclusions (GCI) in multiple system atrophy (MSA). Recently, a novel protein called synphilin-1 has been identified that associates with alpha-synuclein, and it has been reported that co-transfection of both alpha-synuclein and synphilin-1 in mammalian cells yielded eosinophilic cytoplasmic inclusions resembling LB. Immunocytochemical and ultrastructural investigations have now been performed on the brain of patients with various neurodegenerative disorders using anti-synphilin-1 antibodies. These antibodies immunostained the neuropil in a punctate pattern throughout the brain of control subjects. In PD, most LB observed in the brain stem were positive for synphilin-1. These LB showed intense staining in their central cores, but their peripheral portions were only weakly stained or unstained. Pale bodies and Lewy neurites, which were positive for alpha-synuclein, were synphilin-1 negative. In DLB, a small fraction of cortical LB were immunolabeled by anti-synphilin-1. In MSA, numerous GCI were positive for synphilin-1. Immunoelectron microscopy revealed that the reaction product was localized within filamentous and circular structures in LB. Various neuronal and glial inclusions in neurodegenerative disorders other than LB disease and MSA were synphilin-1 negative. These findings suggest that abnormal accumulation of synphilin-1 is specific for brain lesions in which alpha-synuclein is a major component.     

Differential expression of alpha-synuclein isoforms in dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is characterized by the widespread presence of Lewy bodies (LBs) in the brain. alpha-Synuclein, the main component of LBs, is expressed as two main isoforms (112 and 140), but little is known about their differential expression in the brain. We compared alpha-synuclein 112 and alpha-synuclein 140 expression levels in the prefrontal cortices of six DLB patients, eight Alzheimer disease (AD) patients, and six control subjects. Relative alpha-synuclein 112 and alpha-synuclein 140 expression levels were determined by real-time polymerase chain reaction with competimer technology using a LightCycler System. Whereas total alpha-synuclein levels were just marginally elevated in DLB in comparison with the other groups, alpha-synuclein 112 was seen to be markedly increased in DLB compared with AD cases and controls. In contrast, alpha-synuclein 140 levels were significantly diminished in both neurodegenerative disorders in comparison with controls. These results show differential overexpression of alpha-synuclein 112 in DLB, a finding that could be of importance in DLB pathogenesis.     

Neuropathological correlates to clinically defined dementia with Lewy bodies

OBJECTIVES: To analyse the neuropathological changes behind clinically defined dementia with Lewy bodies (clinDLB) compared with clinically diagnosed Alzheimer's disease (clinAD). METHODS: The prevalence of neuropathological findings in 48 clinDLB and 45 clinAD cases was compared. Sixteen clinDLB and 10 clinAD cases were reassessed with alpha-synuclein staining for Lewy bodies (LB). RESULTS: Alzheimer pathology was found in 81% of the clinDLB and 93% of the clinAD cases. The clinDLB group had a higher prevalence of frontal white matter pathology, mostly of ischemic type, and a more severe degeneration of the substantia nigra compared with the clinAD group. In hematoxylin-eosin staining, LBs were identified in seven (15%) of the clinDLB and in four (9%) of the clinAD group. In alpha-synuclein staining, 38% of the clinDLB and 40% of the clinAD cases exhibited LBs. The cases without LBs, in the clinDLB group, had AD pathology in combination with frontal white matter disease. Vascular pathology of significant degree was prevalent in more than 40% of all the cases with verified LBs regardless of clinical diagnosis. CONCLUSION: Consecutive dementia cases, fulfilling the clinical consensus criteria for DLB, may exhibit combinations of neuropathological changes which in themselves can explain the clinical picture of DLB even when LBs are absent.     

Synphilin-1 and parkin show overlapping expression patterns in human brain and form aggresomes in response to proteasomal inhibition

Lewy bodies (LBs) are the characteristic inclusions of Parkinson's disease brain but the mechanism responsible for their formation is obscure. Lewy bodies (LBs) are composed of a number of proteins of which alpha-synuclein (alpha-SYN) is a major constituent. In this study, we have investigated the distribution patterns of synphilin-1 and parkin proteins in control and sporadic PD brain tissue by immunohistochemistry (IH), immunoblotting, and immunoelectron microscopy (IEM). We demonstrate the presence of synphilin-1 and parkin in the central core of a majority of LBs using IH and IEM. Using IH, we show an overlapping distribution profile of the two proteins in central neurons. Additionally, we show sensitivity of both endogenous synphilin-1 and parkin to proteolytic dysfunction and their co-localization in aggresomes formed in response to the proteasome inhibitor MG-132. We confirm that synphilin-1 and parkin are components of majority of LBs in Parkinson's disease and that both proteins are susceptible to proteasomal degradation.     

Screening for mutations in synaptotagmin XI in Parkinson's disease

Parkinson's disease (PD) is characterized by selective degeneration of neurons in the substantia nigra and subsequent dysfunction of dopaminergic neurotransmission. Genes identified in familial forms of PD encode proteins that are linked to the ubiquitin-proteasome system indicating the pathogenic relevance of disturbed protein degradation in PD. Some of them, i.e. alpha-synuclein, parkin and synphilin-1, have been implicated in presynaptic neurotransmission based on their localization in synaptic vesicles. Synaptotagmin XI is linked to the pathogenesis of PD based on its identification as a substrate of the ubiquitin-E3-ligase parkin. Moreover synaptotagmin XI is involved in the maintainance of synaptic function and represents a component of Lewy bodies (LB) in brains of PD patients. Therefore, we performed a detailed mutation analysis of the synaptotagmin XI gene in a large sample of 393 familial and sporadic PD patients. We did not find any disease causing mutations arguing against a major role of mutations in the synaptotagmin XI gene in the pathogenesis of PD.