alpha-synuclein and Down-Syndrome

Neurodegenerative diseases constitute a set of pathological conditions originating from the slow, irreversible and systematic cell loss within the various regions of the brain and/or the spinal cord. Neurodegenerative diseases are proteinopathies associated with misbehavior and disarrangement of a specific protein, affecting its processing, functioning, and/or folding. Many proteins associated with human neurodegenerative diseases are intrinsically disordered; i.e., they lack stable tertiary and/or secondary structure under physiological conditions in vitro. Intrinsically disordered proteins (IDPs) have broad presentation in nature. Functionally, they complement ordered proteins, being typically involved in regulation, signaling and control. Structures and functions of IDPs are intensively modulated by alternative splicing and posttranslational modifications. It is recognized now that nanoimaging offers a set of tools to analyze protein misfolding and self-assembly via monitoring the aggregation process, to visualize protein aggregates, and to analyze properties of these aggregates. The major goals of this review are to show the interconnections between intrinsic disorder and human neurodegenerative diseases and to overview a recent progress in development of novel nanoimaging tools to follow protein aggregation.

Topics: alpha-Synuclein; Alzheimer Disease; Amino Acid Sequence; Amyloid; Amyloidosis; Computational Biology; Down Syndrome; Humans; Lewy Body Disease; Models, Molecular; Nerve Tissue Proteins; Neurodegenerative Diseases; Parkinson Disease; Prion Diseases; Protein Conformation

Recently, mutations of the alpha-synuclein gene were found to cause dominantly inherited Lewy-body Parkinson's disease (PD) and alpha-synuclein was identified as a major component of the Lewy body. However, the cause of the common form of PD, with a multifactorial rather than autosomal dominant inheritance pattern, remains unknown. Alpha-synuclein precipitates slowly and apparently spontaneously at high concentration in solution and the mutations that cause PD accelerate precipitation. Other dominantly inherited late-onset or adult-onset dominantly inherited neurodegenerative diseases are associated with precipitation of proteins. In Alzheimer disease, beta-amyloid and tau abnormalities are present and in prion disorders, prion proteins are found. In Huntington disease, a disorder with expanded CAG repeats, huntingtin precipitates occur. In dominantly inherited spinocerebellar ataxias, also expanded CAG repeat disorders, the corresponding ataxin protein precipitates are found. In multiple system atrophy, alpha-synuclein precipitates are encountered and in progressive supranuclear palsy, tau precipitates occur. In familial amyotrophic lateral sclerosis, a group of dominantly inherited disorders, SOD1 precipitates are found. Most of these disorders can involve the basal ganglia in some way. Since similar processes seem to affect neurons of adults or older individuals and since a relatively limited group of proteins seems to be involved, each producing a form of neurodegeneration, it is possible that certain common features are present that affect this group of proteins. Candidates include a conformational shift, as in prions, an abnormality of the ubiquitin-proteosome pathway, as seen in PD, an abnormality of a pathway preventing precipitation (e.g. chaperonins), or potentiation of a pathway promoting precipitation (e.g. gamma-glutamyl-transpeptidase) or apoptosis. Elucidation of the pathways causing this protein insolubilisation is the first step towards approaching prevention and reversal in these late-onset neurodegenerative diseases.

Topics: Adult; Aged; alpha-Synuclein; Alzheimer Disease; Amyloid; Basal Ganglia; Chemical Precipitation; Down Syndrome; Heredodegenerative Disorders, Nervous System; Humans; Middle Aged; Multiple System Atrophy; Mutation; Nerve Tissue Proteins; Parkinson Disease; Solubility; Synucleins; tau Proteins

Alpha-synuclein (SNCA), a presynaptic protein, is significantly reduced in individuals with Down syndrome (DS) and Ts65Dn mice, a mouse model of DS. Methylation analyses of promoter proximal CpG sites indicate similar reduction in Ts65Dn mice compared to control mice. Epigallocatechin-3-gallate (EGCG), a polyphenolic catechin present in green tea extract, increases methylation of SNCA promoter proximal CpG sites and expression in Ts65Dn mice. These results suggest a positive link between CpG methylation and SNCA expression in Down syndrome.

Topics: alpha-Synuclein; Animals; Catechin; Disease Models, Animal; DNA Methylation; Down Syndrome; Epigenesis, Genetic; Mice; Promoter Regions, Genetic

We reported that iron influx drives the translational expression of the neuronal amyloid precursor protein (APP), which has a role in iron efflux. This is via a classic release of repressor interaction of APP mRNA with iron-regulatory protein-1 (IRP1) whereas IRP2 controls the mRNAs encoding the L- and H-subunits of the iron storage protein, ferritin. Here, we identified thirteen potent APP translation blockers that acted selectively towards the uniquely configured iron-responsive element (IRE) RNA stem loop in the 5' untranslated region (UTR) of APP mRNA. These agents were 10-fold less inhibitory of 5'UTR sequences of the related prion protein (PrP) mRNA. Western blotting confirmed that the 'ninth' small molecule in the series selectively reduced neural APP production in SH-SY5Y cells at picomolar concentrations without affecting viability or the expression of α-synuclein and ferritin. APP blocker-9 (JTR-009), a benzimidazole, reduced the production of toxic Aβ in SH-SY5Y neuronal cells to a greater extent than other well tolerated APP 5'UTR-directed translation blockers, including posiphen, that were shown to limit amyloid burden in mouse models of Alzheimer's disease (AD). RNA binding assays demonstrated that JTR-009 operated by preventing IRP1 from binding to the IRE in APP mRNA, while maintaining IRP1 interaction with the H-ferritin IRE RNA stem loop. Thus, JTR-009 constitutively repressed translation driven by APP 5'UTR sequences. Calcein staining showed that JTR-009 did not indirectly change iron uptake in neuronal cells suggesting a direct interaction with the APP 5'UTR. These studies provide key data to develop small molecules that selectively reduce neural APP and Aβ production at 10-fold lower concentrations than related previously characterized translation blockers. Our data evidenced a novel therapeutic strategy of potential impact for people with trisomy of the APP gene on chromosome 21, which is a phenotype long associated with Down syndrome (DS) that can also cause familial Alzheimer's disease.

Topics: 5' Untranslated Regions; alpha-Synuclein; Alzheimer Disease; Amyloid beta-Protein Precursor; Aniline Compounds; Animals; Base Sequence; Benzimidazoles; Blotting, Western; Cell Line, Tumor; Cell Survival; Cells, Cultured; Down Syndrome; Humans; Iron; Iron Regulatory Protein 1; Mice; Mice, Transgenic; Molecular Sequence Data; Neurons; Physostigmine; Protein Binding; Protein Biosynthesis; Response Elements; RNA, Messenger; Sequence Homology, Nucleic Acid

The triplication of genes located on chromosome 21 is known to cause a wide spectrum of pathology seen in Down syndrome (DS), including leukemia, seizures, stroke, and mental retardation. Studies on RNA and protein expression of genes in DS brain have demonstrated the role of triplicated genes in several DS phenotypes. Significant changes in the expression of nontriplicated genes have also been observed. However, little information is available regarding the role of nonchromosome 21 genes in DS pathology. We have found that α-synuclein (SNCA), a presynaptic protein whose gene is located on chromosome 6 in the Ts65Dn mouse model for DS, is significantly reduced in the cortex and other brain regions. We hypothesize that this alteration may play a critical role in the reduced synaptic function observed in DS. We have found an increase in the level of neurosin, a key negative regulator of SNCA in Ts65Dn cortex. We have also found increased levels of protein phosphatase 2A, a negative regulator of the activation of tyrosine hydroxylase and a key enzyme in the biosynthetic pathway for dopamine in Ts65Dn cortex. These findings reveal potential target sites for intervention in the treatment of DS pathology.

Topics: Adolescent; Adult; Aged; alpha-Synuclein; Animals; Blotting, Western; Brain; Disease Models, Animal; Down Syndrome; Humans; Immunohistochemistry; Kallikreins; Mice; Middle Aged; Protein Phosphatase 2; Reverse Transcriptase Polymerase Chain Reaction; Synaptic Transmission; Young Adult

We examined alpha-synuclein immunoreactivity in the brains from 23 patients with Alzheimer's disease (AD) and two patients with Down's syndrome. In ten of the 23 AD cases and both the two Down's syndrome cases, alpha-synuclein immunoreactivities were observed in the neurons of the limbic areas, predominantly of the amygdala. Nearly all alpha-synuclein-positive neurons had tau-positive neurofibrillary tangles (NFT) in the same neurons, and these consisted of intermingled-type and superimposed-type. By immunoelectron microscopy, the intermingled-type revealed aggregations of alpha-synuclein-positive filamentous components, which were in continuity with paired helical filaments (PHF), while the superimposed-type revealed accumulations of alpha-synuclein-positive non-filamentous components in PHF bundles. These findings suggest that alpha-synuclein can accumulate in PHF and form filamentous aggregations in neurons of the limbic areas in AD cases.

Topics: Actin Cytoskeleton; Age of Onset; Aged; alpha-Synuclein; Alzheimer Disease; Amygdala; Down Syndrome; Humans; Limbic System; Microscopy, Immunoelectron; Middle Aged; Nerve Tissue Proteins; Neurofibrillary Tangles; Neurons; Synucleins

Immunohistochemical examination of 20 Down's syndrome brains, using antibodies to alpha-, beta-, and gamma-synuclein, demonstrated many alpha-synuclein-positive Lewy bodies and dystrophic neurites in 50% of amygdala samples from Down's syndrome brains with Alzheimer's disease. Similar lesions were less common in other regions of these brains, none of which contained beta-synuclein or gamma-synuclein abnormalities. Thus, alpha-synuclein-positive Lewy bodies and neuritic processes frequently occur with Alzheimer's disease in Down's syndrome brains.

Topics: Aged; alpha-Synuclein; Alzheimer Disease; Antibodies; beta-Synuclein; Brain; Child, Preschool; Down Syndrome; Female; gamma-Synuclein; Humans; Immunohistochemistry; Infant; Lewy Bodies; Male; Middle Aged; Nerve Tissue Proteins; Synucleins

Alpha-synuclein is a predominantly neuronal presynaptic protein that may play an important role during synaptogenesis and CNS development. In order to elucidate the human developmental expression profile, we used a polyclonal antiserum against the NAC domain of alpha-synuclein. In normal fetal cortex neuroectodermal precursor cells elicited staining in the soma, whereas, in adult cortex, we observed a staining pattern compatible with synaptic function. The same developmental intraneuronal redistribution was found in neurodegenerative disorders, i.e. somatic staining in neuroectodermal precursors in fetal (trisomy 21) and a synaptic pattern in adult (Down's syndrome, Alzheimer's disease) brains. RT-PCR and Western blot analysis revealed expression at all time points studied (4-7.5 months) during human brain development.

Topics: Adult; Aging; alpha-Synuclein; Alzheimer Disease; Blotting, Western; Brain; Cerebral Cortex; Down Syndrome; Embryonic and Fetal Development; Fetus; Humans; Immunohistochemistry; Nerve Tissue Proteins; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Synucleins