Cell cycle aberrations by alpha-synuclein over-expression and cyclin B immunoreactivity in Lewy bodies

α-synuclein regulates Cyclin D1 to promote abnormal initiation of the cell cycle and induce apoptosis in dopamine neurons

The etiology of Parkinson's disease (PD) is characterized by the death of dopamine neurons in the substantia nigra pars compacta, while misfolding and abnormal aggregation of α-synuclein (α-syn) are core pathological features. Previous studies have suggested that damage to dopamine neurons may be related to cell cycle dysregulation, but the specific mechanisms remain unclear. In this study, a PD mouse model was induced by stereotactic injection of α-syn into the nucleus, and treated with the cell cycle inhibitor, roscovitine (Rosc). The results demonstrated that Rosc improved behavioral disorders caused by α-syn, increased TH protein expression, inhibited α-syn and p-α-syn protein expression, and reduced the expression levels of G1/S phase cell cycle genes Cyclin D1, Cyclin E, CDK2, CDK4, E2F and pRB. Additionally, Rosc decreased Bax and Caspase-3 expression caused by α-syn, while increasing Bcl-2 protein expression. Meanwhile, we observed that α-syn can influence neuronal cell autophagy by decreasing the expression level of Beclin 1 and increasing the expression level of P62. However, Rosc can improve this phenomenon. In a cell model induced by α-syn in dopamine neuron injury cells, knockdown of Cyclin D1 led to similar results as those observed in animal experiments: Knocking down Cyclin D1 improved the abnormal initiation of the cell cycle caused by α-syn and regulated cellular autophagy, resulting in a reduction of apoptosis in dopamine neurons. In summary, exogenous α-syn can lead to the accumulation of α-syn and phosphorylated α-syn in dopamine neurons, increase key factors of the G1/S phase cell cycle such as Cyclin D1, and regulate downstream related indicators, causing the cell cycle to restart and leading to apoptosis of dopamine neurons. This exacerbates PD symptoms. However, knockdown of Cyclin D1 inhibits the progression of the cell cycle and can reverse this situation. These findings suggest that a Cyclin D inhibitor may be a novel therapeutic target for treating PD.

Uncovering Cell Cycle Dysregulations and Associated Mechanisms in Cancer and Neurodegenerative Disorders: A Glimpse of Hope for Repurposed Drugs

The cell cycle is the sequence of events orchestrated by a complex network of cell cycle proteins. Unlike normal cells, mature neurons subsist in a quiescent state of the cell cycle, and aberrant cell cycle activation triggers neuronal death accompanied by neurodegeneration. The periodicity of cell cycle events is choreographed by various mechanisms, including DNA damage repair, oxidative stress, neurotrophin activity, and ubiquitin-mediated degradation. Given the relevance of cell cycle processes in cancer and neurodegeneration, this review delineates the overlapping cell cycle events, signaling pathways, and mechanisms associated with cell cycle aberrations in cancer and the major neurodegenerative disorders. We suggest that dysregulation of some common fundamental signaling processes triggers anomalous cell cycle activation in cancer cells and neurons. We discussed the possible use of cell cycle inhibitors for neurodegenerative disorders and described the associated challenges. We propose that a greater understanding of the common mechanisms driving cell cycle aberrations in cancer and neurodegenerative disorders will open a new avenue for the development of repurposed drugs.

Extracellular vesicle microRNA-mediated transcriptional regulation may contribute to dementia with Lewy bodies molecular pathology

OBJECTIVE

Dementia with Lewy bodies (DLB) is the second most common dementia. Advancing our limited understanding of its molecular pathogenesis is essential for identifying novel biomarkers and therapeutic targets for DLB. DLB is an α-synucleinopathy, and small extracellular vesicles (SEV) from people with DLB can transmit α-synuclein oligomerisation between cells. Post-mortem DLB brains and serum SEV from those with DLB share common miRNA signatures, and their functional implications are uncertain. Hence, we aimed to investigate potential targets of DLB-associated SEV miRNA and to analyse their functional implications.

METHODS

We identified potential targets of six previously reported differentially expressed miRNA genes in serum SEV of people with DLB (MIR26A1, MIR320C2, MIR320D2, MIR548BA, MIR556, and MIR4722) using miRBase and miRDB databases. We analysed functional implications of these targets using EnrichR gene set enrichment analysis and analysed their protein interactions using Reactome pathway analysis.

RESULTS

These SEV miRNA may regulate 4278 genes that were significantly enriched among the genes involved in neuronal development, cell-to-cell communication, vesicle-mediated transport, apoptosis, regulation of cell cycle, post-translational protein modifications, and autophagy lysosomal pathway, after Benjamini-Hochberg false discovery rate correction at 5%. The miRNA target genes and their protein interactions were significantly associated with several neuropsychiatric disorders and with multiple signal transduction, transcriptional regulation, and cytokine signalling pathways.

CONCLUSION

Our findings provide in-silico evidence that potential targets of DLB-associated SEV miRNAs may contribute to Lewy pathology by transcriptional regulation. Experimental validation of these dysfunctional pathways is warranted and could lead to novel therapeutic avenues for DLB.

Synuclein Proteins in Cancer Development and Progression

Synucleins are a family of small, soluble proteins mainly expressed in neural tissue and in certain tumors. Since their discovery, tens of thousands of scientific reports have been published about this family of proteins as they are associated with severe human diseases. Although the physiological function of these proteins is still elusive, their relationship with neurodegeneration and cancer has been clearly described over the years. In this review, we summarize data connecting synucleins and cancer, going from the structural description of these molecules to their involvement in tumor-related processes, and discuss the putative use of these proteins as cancer molecular biomarkers.

Genetic modifiers of synucleinopathies-lessons from experimental models

α-Synuclein is a pleiotropic protein underlying a group of progressive neurodegenerative diseases, including Parkinson's disease and dementia with Lewy bodies. Together, these are known as synucleinopathies. Like all neurological diseases, understanding of disease mechanisms is hampered by the lack of access to biopsy tissues, precluding a real-time view of disease progression in the human body. This has driven researchers to devise various experimental models ranging from yeast to flies to human brain organoids, aiming to recapitulate aspects of synucleinopathies. Studies of these models have uncovered numerous genetic modifiers of α-synuclein, most of which are evolutionarily conserved. This review discusses what we have learned about disease mechanisms from these modifiers, and ways in which the study of modifiers have supported ongoing efforts to engineer disease-modifying interventions for synucleinopathies.

Gene Set Enrichment Analysis and Genetic Experiment Reveal Changes in Cell Signaling Pathways Induced by α-Synuclein Overexpression

Abnormal accumulation of alpha synuclein (α-Syn) in sporadic and familial Parkinson's disease (PD) may be a key step in its pathogenesis. In this study, the expression matrix of the GSE95427 dataset after α-Syn overexpression in human glioma cell line H4 was obtained from the GEO database. We used the Gene Set Enrichment Analysis (GSEA) method to reanalyze this dataset to evaluate the possible functions of α-Syn. The results showed that the tumor necrosis factor alpha (TNF-α) signal was significantly activated in α-Syn-overexpressing cells, and oxidative phosphorylation signal, extracellular matrix signal, cell cycle related signal and fatty acid metabolism signal were significantly inhibited. Moreover, we employed the α-Syn-expressing transgenic Drosophila model of Parkinson's disease and knocked-down eiger, a TNF superfamily ligand homologue, indicating that the TNF-α pathway plays a role in the common pathogenesis of synucleinopathies. Our analysis based on GSEA data provides more clues for a better understanding of α-Syn function.

Genetic Elements at the Alpha-Synuclein Locus

Genome-wide association studies have consistently shown that the alpha-synuclein locus is significantly associated with Parkinson's disease. The mechanism by which this locus modulates the disease pathology and etiology remains largely under-investigated. This is due to the assumption that SNCA is the only driver of the functional aspects of several single nucleotide polymorphism (SNP) risk-signals at this locus. Recent evidence has shown that the risk associated with the top GWAS-identified variant within this locus is independent of SNCA expression, calling into question the validity of assigning function to the nearest gene, SNCA. In this review, we examine additional genes and risk variants present at the SNCA locus and how they may contribute to Parkinson's disease. Using the SNCA locus as an example, we hope to demonstrate that deeper and detailed functional validations are required for high impact disease-linked variants.

In Pancreatic Adenocarcinoma Alpha-Synuclein Increases and Marks Peri-Neural Infiltration

α-Synuclein (α-syn) is a protein involved in neuronal degeneration. However, the family of synucleins has recently been demonstrated to be involved in the mechanisms of oncogenesis by selectively accelerating cellular processes leading to cancer. Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal human cancers, with a specifically high neurotropism. The molecular bases of this biological behavior are currently poorly understood. Here, α-synuclein was analyzed concerning the protein expression in PDAC and the potential association with PDAC neurotropism. Tumor (PDAC) and extra-tumor (extra-PDAC) samples from 20 patients affected by PDAC following pancreatic resections were collected at the General Surgery Unit, University of Pisa. All patients were affected by moderately or poorly differentiated PDAC. The amount of α-syn was compared between tumor and extra-tumor specimen (sampled from non-affected neighboring pancreatic areas) by using in situ immuno-staining with peroxidase anti-α-syn immunohistochemistry, α-syn detection by using Western blotting, and electron microscopy by using α-syn-conjugated immuno-gold particles. All the methods consistently indicate that each PDAC sample possesses a higher amount of α-syn compared with extra-PDAC tissue. Moreover, the expression of α-syn was much higher in those PDAC samples from tumors with perineural infiltration compared with tumors without perineural infiltration.

Oncogenic Pathways in Neurodegenerative Diseases

Cancer and neurodegenerative diseases are two of the leading causes of premature death in modern societies. Their incidence continues to increase, and in the near future, it is believed that cancer will kill more than 20 million people per year, and neurodegenerative diseases, due to the aging of the world population, will double their prevalence. The onset and the progression of both diseases are defined by dysregulation of the same molecular signaling pathways. However, whereas in cancer, these alterations lead to cell survival and proliferation, neurodegenerative diseases trigger cell death and apoptosis. The study of the mechanisms underlying these opposite final responses to the same molecular trigger is key to providing a better understanding of the diseases and finding more accurate treatments. Here, we review the ten most common signaling pathways altered in cancer and analyze them in the context of different neurodegenerative diseases such as Alzheimer's (AD), Parkinson's (PD), and Huntington's (HD) diseases.

Spreading of Alpha Synuclein from Glioblastoma Cells towards Astrocytes Correlates with Stem-like Properties

Simple Summary

The present study questions whether cells from glioblastoma multiforme (GBM), which overexpress α-synuclein (α-syn), may alter neighboring non-tumoral astrocyte cell lines. The occurrence of α-syn in GBM correlates with the expression of the stem cell marker nestin. When astrocytes are co-cultured with GBM cells in a trans-well apparatus the occurrence of α-syn and nestin rises remarkably. The increase in α-syn in co-cultured astrocytes is more pronounced at the plasma membrane, which mimics the placement of α-syn in GBM cells. When the mTOR inhibitor rapamycin is administered, GBM-induced expression of α-syn and nestin within co-cultured astrocytes is occluded, and morphological alterations are reverted. In the presence of rapamycin the sub-cellular placement of α-syn is modified being allocated within whorls and vacuoles instead of the plasma membrane. The effects induced by rapamycin occur both in baseline GBM cells and within astrocytes primed by co-cultured GBM cells.

Abstract

Evidence has been recently provided showing that, in baseline conditions, GBM cells feature high levels of α-syn which are way in excess compared with α-syn levels measured within control astrocytes. These findings are consistent along various techniques. In fact, they are replicated by using antibody-based protein detection, such as immuno-fluorescence, immuno-peroxidase, immunoblotting and ultrastructural stoichiometry as well as by measuring α-syn transcript levels at RT-PCR. The present manuscript further questions whether such a high amount of α-syn may be induced within astrocytes, which are co-cultured with GBM cells in a trans-well system. In astrocytes co-cultured with GBM cells, α-syn overexpression is documented. Such an increase is concomitant with increased expression of the stem cell marker nestin, along with GBM-like shifting in cell morphology. This concerns general cell morphology, subcellular compartments and profuse convolutions at the plasma membrane. Transmission electron microscopy (TEM) allows us to assess the authentic amount and sub-cellular compartmentalization of α-syn and nestin within baseline GBM cells and the amount, which is induced within co-cultured astrocytes, as well as the shifting of ultrastructure, which is reminiscent of GBM cells. These phenomena are mitigated by rapamycin administration, which reverts nestin- and α-syn-related overexpression and phenotypic shifting within co-cultured astrocytes towards baseline conditions of naïve astrocytes. The present study indicates that: (i) α-syn increases in astrocyte co-cultured with GBM cells; (ii) α-syn increases in astrocytes along with the stem cell marker nestin; (iii) α-syn increases along with a GBM-like shift of cell morphology; (iv) all these changes are replicated in different GBM cell lines and are reverted by the mTOR inhibitor rapamycin. The present findings indicate that α-syn does occur in high amount within GBM cells and may transmit to neighboring astrocytes as much as a stem cell phenotype. This suggests a mode of tumor progression for GBM cells, which may transform, rather than merely substitute, surrounding tissue; such a phenomenon is sensitive to mTOR inhibition.

Occurrence of Total and Proteinase K-Resistant Alpha-Synuclein in Glioblastoma Cells Depends on mTOR Activity

Simple Summary

The accumulation of alpha-synuclein (α-syn) is considered a pathological hallmark of the neurodegenerative disorders known as synucleinopathies. The clearance of α-syn depends on autophagy activity, which is inhibited by the mechanistic target of rapamycin (mTOR). Thus, it is likely that α-syn accumulation may occur whenever mTOR is overactive and autophagy is suppressed. In fact, the lack of effective autophagy increases the amount of α-syn and may produce protein aggregation. Therefore, in the present study, we questioned whether cells from glioblastoma multiforme (GBM), a lethal brain neoplasm, wherein mTOR is upregulated and autophagy is suppressed, may overexpress α-syn. In fact, a large quantity of α-syn is measured in GBM cells compared with astrocytes, which includes proteinase K-resistant α-syn. Rapamycin, while inhibiting mTOR activity, significantly reduces the amount of α-syn and allocates α-syn within autophagy-like vacuoles.

Abstract

Alpha-synuclein (α-syn) is a protein considered to be detrimental in a number of degenerative disorders (synucleinopathies) of which α-syn aggregates are considered a pathological hallmark. The clearance of α-syn strongly depends on autophagy, which can be stimulated by inhibiting the mechanistic target of rapamycin (mTOR). Thus, the overexpression of mTOR and severe autophagy suppression may produce α-syn accumulation, including the proteinase K-resistant protein isoform. Glioblastoma multiforme (GBM) is a lethal brain tumor that features mTOR overexpression and severe autophagy inhibition. Cell pathology in GBM is reminiscent of a fast, progressive degenerative disorder. Therefore, the present work questions whether, as is analogous to neurons during degenerative disorders, an overexpression of α-syn occurs within GBM cells. A high amount of α-syn was documented in GBM cells via real-time PCR (RT-PCR), Western blotting, immunohistochemistry, immuno-fluorescence, and ultrastructural stoichiometry, compared with the amount of β- and γ-synucleins and compared with the amount of α-syn counted within astrocytes. The present study indicates that (i) α-syn is overexpressed in GBM cells, (ii) α-syn expression includes a proteinase-K resistant isoform, (iii) α-syn is dispersed from autophagy-like vacuoles to the cytosol, (iv) α-syn overexpression and cytosol dispersion are mitigated by rapamycin, and (v) the α-syn-related GBM-like phenotype is mitigated by silencing the SNCA gene.

Alpha-synuclein negatively controls cell proliferation in dopaminergic neurons

As researchers grapple with the mechanisms and implications of alpha-synuclein (α-syn) in neuropathology, it is often forgotten that the function(s) of α-syn in healthy cells remain largely elusive. Previous work has relied on observing α-syn localization in the cell or using knockout mouse models. Here, we address the specific role of α-syn in human dopaminergic neurons by disrupting its gene (SNCA) in the human dopaminergic neuron cell line, LUHMES. SNCA-null cells were able to differentiate grossly normally and showed modest effects on gene expression. The effects on gene expression were monodirectional, resulting primarily in the significant decrease of expression for 401 genes, implicating them as direct, or indirect positive targets of α-syn. Gene ontological analysis of these genes showed enrichment in terms associated with proliferation, differentiation, and synapse activity. These results add to the tapestry of α-syn biological functions. SIGNIFICANCE STATEMENT: The normal functions of α-syn have remained controversial, despite its clear importance in Parkinson's Disease pathology, where it accumulates in Lewy bodies and contributes to neurodegeneration. Its name implies synaptic and nuclear functions, but how it participates at these locations has not been resolved. Via knock-out experiments in dopaminergic neurons, we implicate α-syn as a functional participant in synapse activity and in proliferation/differentiation, the latter being novel and provide insight into α-syn's role in neuronal development.

Transcriptome Analysis in a Mouse Model of Premature Aging of Dentate Gyrus: Rescue of Alpha-Synuclein Deficit by Virus-Driven Expression or by Running Restores the Defective Neurogenesis

The dentate gyrus of the hippocampus and the subventricular zone are neurogenic niches where neural stem and progenitor cells replicate throughout life to generate new neurons. The Btg1 gene maintains the stem cells of the neurogenic niches in quiescence. The deletion of Btg1 leads to an early transient increase of stem/progenitor cells division, followed, however, by a decrease during adulthood of their proliferative capability, accompanied by apoptosis. Since a physiological decrease of neurogenesis occurs during aging, the Btg1 knockout mouse may represent a model of neural aging. We have previously observed that the defective neurogenesis of the Btg1 knockout model is rescued by the powerful neurogenic stimulus of physical exercise (running). To identify genes responsible for stem and progenitor cells maintenance, we sought here to find genes underlying this premature neural aging, and whose deregulated expression could be rescued by running. Through RNA sequencing we analyzed the transcriptomic profiles of the dentate gyrus isolated from Btg1 wild-type or Btg1 knockout adult (2-month-old) mice submitted to physical exercise or sedentary. In Btg1 knockout mice, 545 genes were deregulated, relative to wild-type, while 2081 genes were deregulated by running. We identified 42 genes whose expression was not only down-regulated in the dentate gyrus of Btg1 knockout, but was also counter-regulated to control levels by running in Btg1 knockout mice, vs. sedentary. Among these 42 counter-regulated genes, alpha-synuclein (Snca), Fos, Arc and Npas4 showed significantly greater differential regulation. These genes control neural proliferation, apoptosis, plasticity and memory and are involved in aging. In particular, Snca expression decreases during aging. We tested, therefore, whether an Snca-expressing lentivirus, by rescuing the defective Snca levels in the dentate gyrus of Btg1 knockout mice, could also reverse the aging phenotype, in particular the defective neurogenesis. We found that the exogenous expression of Snca reversed the Btg1 knockout-dependent decrease of stem cell proliferation as well as the increase of progenitor cell apoptosis. This indicates that Snca has a functional role in the process of neural aging observed in this model, and also suggests that Snca acts as a positive regulator of stem cell maintenance.

Alpha-Synuclein Pathology Coincides With Increased Number of Early Stage Neural Progenitors in the Adult Hippocampus

Alpha-synuclein pathology driven impairment in adult neurogenesis was proposed as a potential cause of, or at least contributor to, memory impairment observed in both patients and animal models of Parkinson’s disease (PD) and Dementia with Lewy Bodies (DLB). Mice overexpressing wild-type alpha-synuclein under the Thy-1 promoter (Thy1-aSyn, line 61) uniquely replicate early cognitive deficits together with multiple other characteristic motor and non-motor symptoms, alpha-synuclein pathology and dopamine loss. Here we report overt intracellular accumulation of phosphorylated alpha-synuclein in the hippocampus of these transgenic mice. To test whether this alters adult neurogenesis and total number of mature neurons, we employed immunohistochemistry and an unbiased stereology approach to quantify the distinct neural progenitor cells and neurons in the hippocampal granule cell layer and subgranular zone of 6 (prodromal stage) and 16-month (dopamine loss) old Thy1-aSyn mice. Surprisingly, we observed an increase in the number of early stage, i.e., Pax6 expressing, progenitors whereas the numbers of late stage, i.e., Tbr2 expressing, progenitors and neurons were not altered. Astroglia marker was increased in the hippocampus of transgenic mice, but this was not specific to the regions where adult neurogenesis takes place, arguing against a commitment of additional early stage progenitors to the astroglia lineage. Together, this uncovers a novel aspect of alpha-synuclein pathology in adult neurogenesis. Studying its mechanisms in Thy1-aSyn mice could lead to discovery of effective therapeutic interventions for cognitive dysfunction in PD and DLB.

Next-Generation RNA-Sequencing of Serum Small Extracellular Vesicles Discovers Potential Diagnostic Biomarkers for Dementia With Lewy Bodies

OBJECTIVE

There is an urgent clinical need for identifying blood-based diagnostic biomarkers for Dementia with Lewy Bodies (DLB). Transcriptomic studies have reported unique RNA changes in postmortem DLB brains. Small extracellular vesicles (SEV) that transport RNA between brain and peripheral circulation enable identifying molecular changes in living human brain. Hence, we aimed to identify differentially expressed RNA in serum SEVs from people with DLB.

METHODS

We investigated serum SEV total RNA profiles in people with DLB (n = 10) and age and gender matched comparisons (n = 10) using next-generation RNA-sequencing. SEVs were separated by ultracentrifugation with density gradient and were characterized by nanoparticle analysis and western blotting. We verified the differential expression levels of identified differentially expressed genes (DEG) using high-throughput qPCR. Functional implications of identified DEG were evaluated using Ingenuity pathway analyses.

RESULTS

We identified 846 nominally significant DEG including 30 miRNAs in DLB serum SEVs. We identified significant downregulation of proinflammatory genes, IL1B, CXCL8, and IKBKB. Previously reported postmortem DLB brain DEGs were significantly enriched (χ²=4.99; df=1; p = 0.03) among the identified DEGs, and the differential expression of 40 postmortem DLB brain DEGs could be detected in serum SEVs of people living with DLB. Functional pathway and network analyses highlighted the importance of immunosenescence, ubiquitin proteasome system (UPS) dysfunction, DNA repair, and RNA post-transcriptional modification deficits in DLB pathology.

CONCLUSION

Identified DEGs, especially reduced expression levels of inflammation, and UPS-associated RNA, may aid diagnosing DLB, and their biomarker potential warrants further investigation in larger clinical cohorts. Our findings corroborate the absence of chronic neuroinflammation in DLB.

Comprehensive miRNome-Wide Profiling in a Neuronal Cell Model of Synucleinopathy Implies Involvement of Cell Cycle Genes

Growing evidence suggests that epigenetic mechanisms like microRNA-mediated transcriptional regulation contribute to the pathogenesis of parkinsonism. In order to study the influence of microRNAs (miRNAs), we analyzed the miRNome 2 days prior to major cell death in α-synuclein-overexpressing Lund human mesencephalic neurons, a well-established cell model of Parkinson’s disease (PD), by next-generation sequencing. The expression levels of 23 miRNAs were significantly altered in α-synuclein-overexpressing cells, 11 were down- and 12 upregulated (P < 0.01; non-adjusted). The in silico analysis of known target genes of these miRNAs was complemented by the inclusion of a transcriptome dataset (BeadChip) of the same cellular system, revealing the G0/G1 cell cycle transition to be markedly enriched. Out of 124 KEGG-annotated cell cycle genes, 15 were present in the miRNA target gene dataset and six G0/G1 cell cycle genes were found to be significantly altered upon α-synuclein overexpression, with five genes up- (CCND1, CCND2, and CDK4 at P < 0.01; E2F3, MYC at P < 0.05) and one gene downregulated (CDKN1C at P < 0.001). Additionally, several of these altered genes are targeted by miRNAs hsa-miR-34a-5p and hsa-miR-34c-5p, which also modulate α-synuclein expression levels. Functional intervention by siRNA-mediated knockdown of the cell cycle gene cyclin D1 (CCND1) confirmed that silencing of cell cycle initiation is able to substantially reduce α-synuclein-mediated cytotoxicity. The present findings suggest that α-synuclein accumulation induces microRNA-mediated aberrant cell cycle activation in post-mitotic dopaminergic neurons. Thus, the mitotic cell cycle pathway at the level of miRNAs might offer interesting novel therapeutic targets for PD.

Prolyl Oligopeptidase Regulates Dopamine Transporter Oligomerization and Phosphorylation in a PKC- and ERK-Independent Manner

Prolyl oligopeptidase (PREP) is a serine protease that binds to alpha-synuclein (aSyn) and induces its aggregation. PREP inhibitors have been shown to have beneficial effects in Parkinson's disease models by enhancing the clearance of aSyn aggregates and modulating striatal dopamine. Additionally, we have shown that PREP regulates phosphorylation and internalization of dopamine transporter (DAT) in mice. In this study, we clarified the mechanism behind this by using HEK-293 and PREP knock-out HEK-293 cells with DAT transfection. We tested the effects of PREP, PREP inhibition, and alpha-synuclein on PREP-related DAT regulation by using Western blot analysis and a dopamine uptake assay, and characterized the impact of PREP on protein kinase C (PKC) and extracellular signal-regulated kinase (ERK) by using PKC assay and Western blot, respectively, as these kinases regulate DAT phosphorylation. Our results confirmed our previous findings that a lack of PREP can increase phosphorylation and internalization of DAT and decrease uptake of dopamine. PREP inhibition had a variable impact on phosphorylation of ERK dependent on the metabolic state of cells, but did not have an effect on phosphorylation or function of DAT. PREP modifications did not affect PKC activity either. Additionally, a lack of PREP elevated a DAT oligomerization that is associated with intracellular trafficking of DAT. Our results suggest that PREP-mediated phosphorylation, oligomerization, and internalization of DAT is not dependent on PKC or ERK.

LncRNA-T199678 Mitigates α-Synuclein-Induced Dopaminergic Neuron Injury via miR-101-3p

Parkinson's disease (PD) is the second most common neurodegenerative disorder characterized by dopaminergic neuron death and the abnormal accumulation and aggregation of α-synuclein (α-Syn) in the substantia nigra (SN). Although the abnormal accumulation of α-Syn can solely promote and accelerate the progress of PD, the underlying molecular mechanisms remain unknown. Mounting evidence confirms that the abnormal expression of long non-coding RNA (lncRNA) plays an important role in PD. Our previous study found that exogenous α-Syn induced the downregulation of lncRNA-T199678 in SH-SY5Y cells via a gene microarray analysis. This finding suggested that lncRNA-T199678 might have a potential pathological role in the pathogenesis of PD. This study aimed to explore the influence of lncRNA-T199678 on α-Syn-induced dopaminergic neuron injury. Overexpression of lncRNA-T199678 ameliorated the neuron injury induced by α-Syn via regulating oxidative stress, cell cycle, and apoptosis. Studies indicate lncRNAs could regulate posttranscriptional gene expression via regulating the downstream microRNA (miRNA). To discover the downstream molecular target of lncRNA-T199678, the following experiment found out that miR-101-3p was a potential target for lncRNA-T199678. Further study showed that the upregulation of lncRNA-T199678 reduced α-Syn-induced neuronal damage through miR-101-3p in SH-SY5Y cells and lncRNA-T199678 was responsible for the α-Syn-induced intracellular oxidative stress, dysfunction of the cell cycle, and apoptosis. All in all, lncRNA-T199678 mitigated the α-Syn-induced dopaminergic neuron injury via targeting miR-101-3p, which contributed to promote PD. Our results highlighted the role of lncRNA-T199678 in mitigating dopaminergic neuron injury in PD and revealed a new molecular target for PD.

Cell Cycle Deficits in Neurodegenerative Disorders: Uncovering Molecular Mechanisms to Drive Innovative Therapeutic Development

Cell cycle dysregulation has been implicated in the pathogenesis of neurodegenerative disorders. Specialised function obligates neuronal cells to subsist in a quiescent state of cell cycle once differentiated and therefore the circumstances and mechanisms underlying aberrant cell cycle activation in post-mitotic neurons in physiological and disease conditions remains an intriguing area of research. There is a strict requirement of concurrence to cell cycle regulation for neurons to ensure intracellular biochemical conformity as well as interrelationship with other cells within neural tissues. This review deliberates on various mechanisms underlying cell cycle regulation in neuronal cells and underscores potential implications of their non-compliance in neural pathology. Recent research suggests that successful duplication of genetic material without subsequent induction of mitosis induces inherent molecular flaws that eventually assert as apoptotic changes. The consequences of anomalous cell cycle activation and subsequent apoptosis are demonstrated by the increased presence of molecular stress response and apoptotic markers. This review delineates cell cycle events under normal physiological conditions and deficits amalgamated by alterations in protein levels and signalling pathways associated with cell-division are analysed. Cell cycle regulators essentially, cyclins, CDKs, cip/kip family of inhibitors, caspases, bax and p53 have been identified to be involved in impaired cell cycle regulation and associated with neural pathology. The pharmacological modulators of cell cycle that are shown to impart protection in various animal models of neurological deficits are summarised. Greater understanding of the molecular mechanisms that are indispensable to cell cycle regulation in neurons in health and disease conditions will facilitate targeted drug development for neuroprotection.

α-Synuclein toxicity in yeast and human cells is caused by cell cycle re-entry and autophagy degradation of ribonucleotide reductase 1

α‐Synuclein (aSyn) toxicity is associated with cell cycle alterations, activation of DNA damage responses (DDR), and deregulation of autophagy. However, the relationships between these phenomena remain largely unknown. Here, we demonstrate that in a yeast model of aSyn toxicity and aging, aSyn expression induces Ras2‐dependent growth signaling, cell cycle re‐entry, DDR activation, autophagy, and autophagic degradation of ribonucleotide reductase 1 (Rnr1), a protein required for the activity of ribonucleotide reductase and dNTP synthesis. These events lead to cell death and aging, which are abrogated by deleting RAS2, inhibiting DDR or autophagy, or overexpressing RNR1. aSyn expression in human H4 neuroglioma cells also induces cell cycle re‐entry and S‐phase arrest, autophagy, and degradation of RRM1, the human homologue of RNR1, and inhibiting autophagic degradation of RRM1 rescues cells from cell death. Our findings represent a model for aSyn toxicity that has important implications for understanding synucleinopathies and other age‐related neurodegenerative diseases.

Region- and Cell-specific Aneuploidy in Brain Aging and Neurodegeneration

Variations in genomic DNA content, or aneuploidy, are a well-recognized feature of normal human brain development. Whether changes in the levels of aneuploidy are a factor in Alzheimer's disease (AD) is less clear, as the data reported to date vary substantially in the levels of aneuploidy detected (0.7-11.5%), possibly due to methodological limitations, but also influenced by individual, regional and cellular heterogeneity as well as variations in cell subtypes. These issues have not been adequately addressed to date. While it is known that the DNA damage response increases with age, the limited human studies investigating aneuploidy in normal aging also show variable results, potentially due to susceptibility to age-related neurodegenerative processes. Neuronal aneuploidy has recently been reported in multiple brain regions in Lewy body disease, but similar genomic changes are not a feature of all synucleinopathies and aneuploidy does not appear to be related to alpha-synuclein aggregation. Rather, aneuploidy was associated with Alzheimer's pathology in the hippocampus and anterior cingulate cortex and neuronal degeneration in the substantia nigra. The association between Alzheimer's pathology and aneuploidy in regions with limited neurodegeneration is supported by a growing body of in vitro and in vivo data on aneuploidy and beta-amyloid and tau abnormalities. Large-scale studies using high-resolution techniques alongside other sensitive and specific methodologies are now required to assess the true extent of cell- and region-specific aneuploidy in aging and neurodegeneration, and to determine any associations with pathologies.

Proteasome impairment by α-synuclein

Parkinson’s disease (PD) is the second most prevalent neurodegenerative disorder worldwide and characterized by the loss of dopaminergic neurons in the patients’ midbrains. Both the presence of the protein α-synuclein in intracellular protein aggregates in surviving neurons and the genetic linking of the α-synuclein encoding gene point towards a major role of α-synuclein in PD etiology. The exact pathogenic mechanisms of PD development are not entirely described to date, neither is the specific role of α-synuclein in this context. Previous studies indicate that one aspect of α-synuclein-related cellular toxicity might be direct proteasome impairment. The 20/26S proteasomal machinery is an important instrument of intracellular protein degradation. Thus, direct proteasome impairment by α-synuclein might explain or at least contribute to the formation of intracellular protein aggregates. Therefore this study investigates direct proteasomal impairment by α-synuclein both in vitro using recombinant α-synuclein and isolated proteasomes as well as in living cells. Our experiments demonstrate that the impairment of proteasome activity by α-synuclein is highly dependent upon the cellular background and origin. We show that recombinant α-synuclein oligomers and fibrils scarcely affect 20S proteasome function in vitro, neither does transient α-synuclein expression in U2OS ps 2042 (Ubi(G76V)-GFP) cells. However, stable expression of both wild-type and mutant α-synuclein in dopaminergic SH-SY5Y and PC12 cells results in a prominent impairment of the chymotrypsin-like 20S/26S proteasomal protein cleavage. Thus, our results support the idea that α-synuclein in a specific cellular environment, potentially present in dopaminergic cells, cannot be processed by the proteasome and thus contributes to a selective vulnerability of dopaminergic cells to α-synuclein pathology.

Metabotropic glutamate receptor 5 mediates the suppressive effect of 6-OHDA-induced model of Parkinson's disease on liver cancer

Numerous epidemiological studies suggested that there is a variable cancer risk in patients with Parkinson's disease (PD). However, the underlying mechanisms remain unclear. In the present study, the role of metabotropic glutamate receptor 5 (mGluR5) has been investigated in 6-hydroxydopamine (6-OHDA)-induced PD combined with liver cancer both in vitro and in vivo. We found that PD cellular model from 6-OHDA-lesioned MN9D cells suppressed the growth, migration, and invasion of Hepa1-6 cells via down-regulation of mGluR5-mediated ERK and Akt pathway. The application of 2-methyl-6-(phenylethyl)-pyridine and knockdown of mGluR5 further decreased the effect on Hepa-1-6 cells when co-cultured with conditioned media. The effect was increased by (S)-3,5-dihydroxyphenylglycine and overexpression of mGluR5. Moreover, more release of glutamate from 6-OHDA-lesioned MN9D cells suppressed mGluR5-mediated effect of Hepa1-6 cells. Application of riluzole eliminated the increased glutamate release induced by 6-OHDA in MN9D cells and aggravated the suppressive effect on Hepa-1-6 cells. In addition, the growth of implanted liver cancer was inhibited in 6-OHDA induced PD-like rats, and was associated with increased glutamate release in the serum and down-regulation of mGluR5 in tumor tissue. Collectively, these results indicate that selective antagonism of glutamate and mGluR5 has a potentially beneficial effect in both liver cancer and PD, and thus may provide more understanding for the clinical investigation and further an additional therapeutic target for these two diseases.

The yin and yang of α-synuclein-associated epigenetics in Parkinson's disease

Parkinson's disease is the second most prevalent neurodegenerative disorder. The main neuropathological hallmarks of the disease are the degeneration of dopaminergic neurons in the substantia nigra pars compacta and the accumulation of protein inclusions known as Lewy bodies. Recently, great attention has been given to the study of genes associated with both familial and sporadic forms of Parkinson's disease. Among them, the α-synuclein gene is believed to play a central role in the disease and is, therefore, one of the most studied genes. Parkinson's disease is a complex disorder and, as such, derives from the interaction between genetic and environmental factors. Here, we offer an update on the landscape of epigenetic-mediated regulation of gene expression that has been linked with α-synuclein and associated with Parkinson's disease. We also provide an overview of how epigenetic modifications can influence the transcription and/or translation of the α-synuclein gene and, on the other hand, how α-synuclein function/dysfunction can, per se, affect the epigenetic landscape. Finally, we discuss how a deeper understanding of the epigenetic profile of α-synuclein may enable the development of novel therapeutic approaches for Parkinson's disease and other synucleinopathies.

Aneuploidy in Lewy body diseases

An increase in DNA content is associated with neuronal degeneration in Alzheimer's disease but has not been evaluated in Lewy body diseases. Using stereological principles, flow cytometry, and standard histopathologic methods, we evaluated the number and DNA content of neurons and all cells and the severity of Lewy and Alzheimer pathologies, in brain regions affected at different stages in Lewy body diseases compared with controls. An increase in neuronal DNA content was observed in all the affected brain regions examined, although this change was related to different pathologies. In the substantia nigra, increased neuronal DNA content related to neuronal loss, whereas in the cortex and hippocampus, increased neuronal DNA content related to Alzheimer pathologies. Of note, increased neuronal DNA content did not relate to the deposition of Lewy bodies in any region examined. These data support the concept that increased DNA content increases neuronal susceptibility to degeneration and Alzheimer pathologies.

Apoptosis signal-regulating kinase 1 modulates the phenotype of α-synuclein transgenic mice

α-Synuclein is a key pathogenic protein in α-synucleinopathies including Parkinson's disease, and its overexpression and aggregation in model systems are associated with a neuroinflammatory response and increased oxidative stress. Apoptosis signal-regulating kinase 1 (ASK1) is activated upon stress signaling events such as oxidative stress and is a central player linking oxidative stress with neuroinflammation. Here, we demonstrate that overexpression of human α-synuclein activates ASK1 in both PC12 cells and in the brains of α-synuclein transgenic mice. Deleting ASK1 in mice mitigates the neuronal damage and neuroinflammation induced by α-synuclein and improves performance of the animals on the rotarod. ASK1 deletion does not impact the aggregation profile or phosphorylation state of α-synuclein in the mouse brain. These results collectively implicate ASK1 in the cascade of events triggered by α-synuclein overexpression, likely because of the inflammatory response and oxidative stress that lead to ASK1 activation. These conclusions raise the possibility that potent antioxidants and anti-inflammatory agents may ameliorate the phenotype of α-synucleinopathies.

Postmortem studies in Parkinson's disease

No animal model to date perfectly replicates Parkinson's disease (PD) etiopathogenesis, and the anatomical organization of the nigrostriatal system differs considerably between species. Human postmortem material therefore remains the gold standard for both formulating hypotheses for subsequent testing in in vitro and in vivo PD models and verifying hypotheses derived from experimental PD models with regard to their validity in the human disease. This article focuses on recent and relevant fields in which human postmortem work has generated significant impact in our understanding of PD. These fields include Lewy body formation, regional vulnerability of dopaminergic neurons, oxidative/nitrative cellular stress, inflammation, apoptosis, infectious and environmental agents, and nondopaminergic lesions.

The Lewy body in Parkinson's disease and related neurodegenerative disorders

The histopathological hallmark of Parkinson's disease (PD) is the presence of fibrillar aggregates referred to as Lewy bodies (LBs), in which α-synuclein is a major constituent. Pale bodies, the precursors of LBs, may serve the material for that LBs continue to expand. LBs consist of a heterogeneous mixture of more than 90 molecules, including PD-linked gene products (α-synuclein, DJ-1, LRRK2, parkin, and PINK-1), mitochondria-related proteins, and molecules implicated in the ubiquitin-proteasome system, autophagy, and aggresome formation. LB formation has been considered to be a marker for neuronal degeneration because neuronal loss is found in the predilection sites for LBs. However, recent studies have indicated that nonfibrillar α-synuclein is cytotoxic and that fibrillar aggregates of α-synuclein (LBs and pale bodies) may represent a cytoprotective mechanism in PD.

Functional characterization and expression profiling of human induced pluripotent stem cell- and embryonic stem cell-derived endothelial cells

With regard to human induced pluripotent stem cells (hiPSCs), in which adult cells are reprogrammed into embryonic-like cells using defined factors, their functional and transcriptional expression pattern during endothelial differentiation has yet to be characterized. In this study, hiPSCs and human embryonic stem cells (hESCs) were differentiated using the embryoid body method, and CD31(+) cells were sorted. Fluorescence activated cell sorting analysis of hiPSC-derived endothelial cells (hiPSC-ECs) and hESC-derived endothelial cells (hESC-ECs) demonstrated similar endothelial gene expression patterns. We showed functional vascular formation by hiPSC-ECs in a mouse Matrigel plug model. We compared the gene profiles of hiPSCs, hESCs, hiPSC-ECs, hESC-ECs, and human umbilical vein endothelial cells (HUVECs) using whole genome microarray. Our analysis demonstrates that gene expression variation of hiPSC-ECs and hESC-ECs contributes significantly to biological differences between hiPSC-ECs and hESC-ECs as well as to the "distances" among hiPSCs, hESCs, hiPSC-ECs, hESC-ECs, and HUVECs. We further conclude that hiPSCs can differentiate into functional endothelial cells, but with limited expansion potential compared with hESC-ECs; thus, extensive studies should be performed to explore the cause and extent of such differences before clinical application of hiPSC-ECs can begin.

G93A SOD1 alters cell cycle in a cellular model of Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative multifactorial disease characterized, like other diseases such as Alzheimer's disease (AD), Parkinson's disease (PD) or frontotemporal dementia (FTD), by the degeneration of specific neuronal cell populations. Motor neuron loss is distinctive of ALS. However, the causes of onset and progression of motor neuron death are still largely unknown. In about 2% of all cases, mutations in the gene encoding for the Cu/Zn superoxide dismutase (SOD1) are implicated in the disease. Several alterations in the expression or activation of cell cycle proteins have been described in the neurodegenerative diseases and related to cell death. In this work we show that mutant SOD1 can alter cell cycle in a cellular model of ALS. Our findings suggest that modifications in the cell cycle progression could be due to an increased interaction between mutant G93A SOD1 and Bcl-2 through the cyclins regulator p27. As previously described in post mitotic neurons, cell cycle alterations could fatally lead to cell death.

Expression and subcellular location of alpha-synuclein during mouse-embryonic development

Alpha-synuclein (alpha-SYN) is one of the major components of intracellular fibrillary aggregates in the brains of a subset of neurodegenerative disorders. Although alpha-SYN expression has been found in developing mouse brain, a detailed distribution during mouse-embryonic development has not been made. Here we describe the expression pattern of alpha-SYN during the development of mice from E9.5 to P0 by immunohistochemistry (IHC). As a result, alpha-SYN was detected as early as E9.5. During the embryonic stages, alpha-SYN was dynamically expressed in several regions of the brain. In the neocortex, expression was detected in the marginal zone (MZ) in the early stages and was later condensed in the MZ and in the subplate (SP); in the cerebellum, expression was initially detected in the deep cerebellar nuclei (DCN) and was later condensed in the Purkinje cells. These spatio-temporal expression patterns matched the neuronal migratory pathways and the formation of the synapse connections. Additionally, alpha-SYN was detected in the sensory systems, including the nasal mucosa, the optic cup, the sensory ganglia, and their dominating nerve fibers. Furthermore, the nuclear location of alpha-SYN protein was found in developing neurons in the early stages, and later it was mostly found in the non-nuclear compartments. This finding was further confirmed by Western blot analysis. These results suggest that alpha-SYN may be involved not only in the migration of neurons and in the synaptogenesis of the central nervous system (CNS) but also in the establishment of the sensory systems. The nuclear location of alpha-SYN may hint at an important function in these events.

Dopamine induces supernumerary centrosomes and subsequent cell death through Cdk2 up-regulation in dopaminergic neuronal cells

Aggregation of proteins in the centrosome is implicated in the pathophysiology of Parkinson's disease. However, the relevance of the centrosome in neurodegeneration is still obscure. Centrosome duplication is initiated by the cyclin E/cyclin-dependent kinase 2 (Cdk2) complex. The present study determined changes in cyclin E or Cdk2 expression and in the centrosomal structure in dopaminergic neuronal CATH.a cells exposed to 50, 100 and 150 micromolar dopamine (DA) for 24 h. DA induced significant increase in Cdk2 protein and cyclin E protein, but not cyclin e mRNA. In DA-treated cells, the intense cyclin E- and Cdk2-immunofluorescence signals were co-localized around large and supernumerary centrosomes, and these two parameters of centrosome amplification were significantly increased compared with the control. Simultaneous co-treatment with DA and a Cdk2 inhibitor blocked centrosome amplification and enhanced cell viability. Our results demonstrated that DA could lead to cyclin E accumulation and Cdk2 up-regulation triggering supernumerary centrosomes and apoptotic cell death.

Semi-quantitative analysis of alpha-synuclein in subcellular pools of rat brain neurons: an immunogold electron microscopic study using a C-terminal specific monoclonal antibody

Alpha-synuclein (alpha-Syn) is a brain-enriched protein of 140 amino acids. Despite of strong evidence showing the implication of the protein in the pathogenesis of several neurodegenerative diseases, its physiological function remains poorly understood. To study the physiological function of alpha-Syn, a depiction of its precise subcellular localization is necessary. Although alpha-Syn expression in the brain has been extensively investigated using several different antibodies, its precise subcellular localization in neurons remains elusive. In this study, immunogold electron microscopy with a newly produced 3D5 monoclonal antibody recognizing the C-terminal 115-121 amino acids of alpha-Syn was used to examine its subcellular localization in rat brain neurons. In addition, the relative amount of the protein in different subcellular pools of the neurons in several brain regions was evaluated and compared. The results showed that alpha-Syn-positive gold particles were unevenly distributed in axons, presynaptic terminals, cytoplasm and nucleus in the neuron, with the density of gold particles being greater in presynaptic terminals and nucleus than in other subcellular pools. In the cytoplasmic region, relatively dense gold particles were seen in some mitochondria. In the same subcellular pools, the density of gold particles was varied among the neurons from different brain regions. Although the cortical neurons showed much higher density of gold particles in the presynaptic terminals and nuclei than in striatal, hippocampal and substantia nigral neurons, the density of gold particles in their mitochondria was much lower compared with the mitochondria of striatal, hippocampal and substantia nigral neurons. The relative high level of mitochondrial alpha-Syn in hippocampus, striatum and substantia nigral neurons may have special pathophysiological significance, which deserves further investigation.

Parkinson's disease and the gut: a well known clinical association in need of an effective cure and explanation

Parkinson's disease (PD) is a neurodegenerative disorder which leads to severe movement impairment; however, Parkinsonian patients frequently suffer from gastrointestinal (GI) problems which at present are poorly understood, scarcely investigated, and lack an effective cure. Traditionally, PD is attributed to the loss of mesencephalic dopamine-containing neurons; nonetheless, additional nuclei, such as the dorsal motor nucleus of the vagus nerve and specific central noradrenergic nuclei, are now identified as targets of PD. While the effects of PD on the somatic motor systems are well characterized, the influence on the digestive system still needs to be clarified. Recent findings demonstrate the occurrence of pathological alterations within peripheral neuronal networks in the GI tract of Parkinsonian patients. However, it remains unclear whether a real cell loss occurs, and whether this happens specifically for a subclass of autonomic neurons or if it reflects the sole loss of autonomic nerves. This review summarizes the neurochemical and morphological changes which might be responsible for impaired GI motility. Moreover, we focus on the experimental models to reproduce the altered digestive system of Parkinsonian patients since an experimental model able to mimic such features of PD is required. In the last part of the manuscript, we suggest potential therapeutic targets.

The Lewy body in Parkinson's disease: molecules implicated in the formation and degradation of alpha-synuclein aggregates

The histological hallmark of Parkinson's disease (PD) is the presence of fibrillar aggregates called Lewy bodies (LBs). LB formation has been considered to be a marker for neuronal degeneration, because neuronal loss is found in the predilection sites for LBs. To date, more than 70 molecules have been identified in LBs, in which alpha-synuclein is a major constituent of LB fibrils. Alpha-synuclein immunohistochemistry reveals that diffuse cytoplasmic staining develops into pale bodies via compaction, and that LBs arise from the peripheral portion of pale bodies. This alpha-synuclein abnormality is found in 10% of pigmented neurons in the substantia nigra and more than 50% of those in the locus ceruleus in PD. Recent studies have suggested that oligomers and protofibrils of alpha-synuclein are cytotoxic, and that LBs may represent a cytoprotective mechanism in PD.

Human-based studies on α-synuclein deposition and relationship to Parkinson's disease symptoms

This article reviews the current knowledge on alpha-synuclein and its cellular locations in studies using human brain tissue. Alterations in the conformation and distribution of alpha-synuclein are examined in Parkinson's disease and the relationship between clinical symptoms and pathology explored. alpha-Synuclein as a molecular chaperone has several isoforms and is known to have different environment-dependent conformations. Processing methods for studying human brain tissue significantly impact on the conformational type of alpha-synuclein analysed, and antibody species used for the in situ detection of alpha-synuclein give variable results depending on the epitope visualised. Human studies show that alpha-synuclein is not isolated to neurons, but is also found in glia, making the interpretation of studies using brain tissue homogenates less clearly related to neurons. These methodological issues impact significantly on our understanding of the form, location, and therefore function of alpha-synuclein in normal human brain tissue. There are less methodological issues regarding highly aggregated alpha-synuclein found in the major hallmark of Parkinson's disease, the Lewy body. However, it remains unclear whether these alpha-synuclein inclusions are harmful to host neurons or provide protection. Several correlations exist between the clinical symptoms of Parkinson's disease and the distribution of Lewy pathology, the strongest being the association between limbic and cortical Lewy bodies and well-formed visual hallucinations. Further correlation studies in prospectively-followed patients and, perhaps more importantly, controls are required in order to determine normal versus pathologic alpha-synuclein and how to detect such differences in clinical situations.

Location, location, location: altered transcription factor trafficking in neurodegeneration

Neurons may be particularly sensitive to disruptions in transcription factor trafficking. Survival and injury signals must traverse dendrites or axons, in addition to soma, to affect nuclear transcriptional responses. Transcription factors exhibit continued nucleocytoplasmic shuttling; the predominant localization is regulated by binding to anchoring proteins that mask nuclear localization/export signals and/or target the factor for degradation. Two functional groups of karyopherins, importins and exportins, mediate RanGTPase-dependent transport through the nuclear pore. A growing number of recent studies, in Alzheimer, Parkinson, and Lewy body diseases, amyotrophic lateral sclerosis, and human immunodeficiency virus encephalitis, implicate aberrant cytoplasmic localization of transcription factors and their regulatory kinases in degenerating neurons. Potential mechanisms include impaired nuclear import, enhanced export, suppression of degradation, and sequestration in protein aggregates or organelles and may reflect unmasking of alternative cytoplasmic functions, both physiologic and pathologic. Some "nuclear" factors also function in mitochondria, and importins are also involved in axonal protein trafficking. Detrimental consequences of a decreased nuclear to cytoplasmic balance include suppression of neuroprotective transcription mediated by cAMP- and electrophile/antioxidant-response elements and gain of toxic cytoplasmic effects. Studying the pathophysiologic mechanisms regulating transcription factor localization should facilitate strategies to bypass deficits and restore adaptive neuroprotective transcriptional responses.

The nature of the cell cycle in neurons: Focus on a “non-canonical” pathway of DNA replication causally related to death

The mechanism whereby a reactivation of cell cycle in neurons causes cell death is beginning to be identified. In cellular models of Alzheimer's disease, activation of a non-canonical pathway of DNA replication contributes to neuronal death. This pathway involves the repair enzyme DNA polymerase-beta, which is highly expressed in neurons of the Alzheimer's brain at early stages of the disease. Loading of DNA polymerase-beta into the replication forks generates a death signal, which involves the tumor suppressor p53. The increasing knowledge of the main actors of the unscheduled DNA replication in neurons will pave the way for novel therapeutic interventions in Alzheimer's disease and other neurodegenerative disorders.

Extensive nuclear localization of alpha-synuclein in normal rat brain neurons revealed by a novel monoclonal antibody

Synuclein was initially named for its localization in both presynaptic nerve terminals and portions of nuclear envelope. However, subsequent studies only confirmed the presynaptic localization of this protein in the brain; its nuclear localization in the neurons remained elusive. Here, two new monoclonal antibodies against alpha-synuclein (alpha-SYN) were produced. Epitope mapping using phage peptide display showed that the epitopes of the two antibodies were localized in two distinct specific sequences of the C-terminal domain of alpha-SYN. One antibody named 3D5 recognized amino acids 115-121 of alpha-SYN and the other antibody named 2E3 identified the amino acids 134-138 of the protein. Western blot analysis demonstrated that both 2E3 and 3D5 detected a 19 kD protein from rat and human brain homogenates, which was identical to the molecular size of recombinant alpha-SYN. However, immunohistochemical staining on normal adult rat brain sections showed that the two antibodies revealed distinct patterns of subcellular localization of alpha-SYN immunoreactivity. Both 3D5 and 2E3 detected the presynaptic alpha-SYN but only 3D5 detected the nuclear alpha-SYN. The nuclear localization of alpha-SYN was further confirmed by Western blot analysis in isolated nuclear fraction where the same size of alpha-SYN was detected, and by immunoelectron microscopy using colloidal gold probes where gold particles were specifically localized in portions of peri- and intra-nucleus. The nuclear positive neurons were distributed extensively in almost all the brain regions. This is the first report well characterizing the extensive localization of alpha-SYN in the neuronal nuclei throughout the brain in normal conditions. This finding indicates an important physiological function of this molecule in the nuclei of brain neurons, which deserves further investigations.

Convergent roles of alpha-synuclein, DA metabolism, and the ubiquitin-proteasome system in nigrostriatal toxicity

Recent studies disclosed the relevance of specific molecules for the onset of Parkinson's disease (PD) and for the composition of neuronal inclusions. The scenario which is now emerging leads to identify a potential common pathway named the ubiquitin-proteasome (UP) system. In line with this, striatal or systemic inhibiton of the UP system causes experimental Parkinsonism characterized by the formation of neuronal inclusions. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which is also a complex I inhibitor, has been used for decades to produce experimental Parkinsonism with no evidence for neuronal inclusions in rodents. This leaves open the question whether neuronal inclusions need an alternative mechanism or the inhibition of complex I needs to be carried out continuously to build up inclusions. In the present article, we administered continuously MPTP. In these experimental conditions we compared the neurological consequence of intermittent versus continuous MPTP. In both cases we observed a severe dopamine (DA) denervation and cell loss. However, when MPTP was delivered continuously, spared DA nigral neurons develop ubiquitin, parkin, and alpha-synuclein positive inclusions, which are not detectable after intermittent dosing. The onset of Parkinsonism is associated with inhibition of the UP system. We compared these results with those obtained with amphetamine derivative in vivo and in vitro in which occurrence of neuronal inclusions was associated with inhibition of the UP system and we evaluated the role of DA metabolism in inducing these effects.

alpha-Synuclein stimulates differentiation of osteosarcoma cells: relevance to down-regulation of proteasome activity

Because a limited study previously showed that alpha-synuclein (alpha-syn), the major pathogenic protein for Parkinson disease, was expressed in differentiating brain tumors as well as various peripheral cancers, the main objective of the present study was to determine whether alpha-syn might be involved in the regulation of tumor differentiation. For this purpose, alpha-syn and its non-amyloidogenic homologue beta-syn were stably transfected to human osteosarcoma MG63 cell line. Compared with beta-syn-overexpressing and vector-transfected cells, alpha-syn-overexpressing cells exhibited distinct features of differentiated osteoblastic phenotype, as shown by up-regulation of alkaline phosphatase and osteocalcin as well as inductive matrix mineralization. Further studies revealed that proteasome activity was significantly decreased in alpha-syn-overexpressing cells compared with other cell types, consistent with the fact that proteasome inhibitors stimulate differentiation of various osteoblastic cells. In alpha-syn-overexpressing cells, protein kinase C (PKC) activity was significantly decreased, and reactivation of PKC by phorbol ester significantly restored the proteasome activity and abrogated cellular differentiation. Moreover, activity of lysosome was up-regulated in alpha-syn-overexpressing cells, and treatment of these cells with autophagy-lysosomal inhibitors resulted in a decrease of proteasome activity associated with up-regulation of alpha-syn expression, leading to enhance cellular differentiation. Taken together, these results suggest that the stimulatory effect of alpha-syn on tumor differentiation may be attributed to down-regulation of proteasome, which is further modulated by alterations of various factors, such as protein kinase C signaling pathway and a autophagy-lysosomal degradation system. Thus, the mechanism of alpha-syn regulation of tumor differentiation and neuropathological effects of alpha-syn may considerably overlap with each other.

Distinct destructive signal pathways of neuronal death in Alzheimer's disease

Abundant neuron loss is a major feature of Alzheimer's disease (AD). Hypotheses for this loss include abnormal amyloid precursor protein processing (i.e. excess Abeta production, protein aggregation or misfolding), oxidative stress, excitotoxicity and inflammation. Neuron loss is a major cause of dementia in AD; however, it seems that there is no definitive pathway that causes cell death in the AD brain. Here, we examine the hypotheses for neuron loss in AD and pose the argument that the means by which neurons degenerate is irrelevant for cognitive decline. The best treatment for cognitive decline is to prevent the toxicity that first sets the neuron on its path to destruction, which is the production of Abeta peptide.

Th1 Response and Cytotoxicity Genes Are Down-Regulated in Cutaneous T-Cell Lymphoma

PURPOSE

Increased production of Th2 cytokines characterizes Sezary syndrome, the leukemic form of cutaneous T-cell lymphomas (CTCL). To identify the molecular background and to study whether shared by the most common CTCL subtype, mycosis fungoides, we analyzed the gene expression profiles in both subtypes.

EXPERIMENTAL DESIGN

Freshly isolated cells from 30 samples, representing skin, blood, and enriched CD4(+) cell populations of mycosis fungoides and Sezary syndrome, were analyzed with Affymetrix (Santa Clara, CA) oligonucleotide microarrays, quantitative PCR, or immunohistochemistry. The gene expression profiles were combined with findings of comparative genomic hybridization of the same samples to identify chromosomal changes affecting the aberrant gene expression.

RESULTS

We identified a set of Th1-specific genes [e.g., TBX21 (T-bet), NKG7, and SCYA5 (RANTES)] to be down-regulated in Sezary syndrome as well as in a proportion of mycosis fungoides samples. In both Sezary syndrome and mycosis fungoides blood samples, the S100P and LIR9 gene expression was up-regulated. In lesional skin, IL7R and CD52 were up-regulated. Integration of comparative genomic hybridization and transcriptomic data identified chromosome arms 1q, 3p, 3q, 4q, 12q, 16p, and 16q as likely targets for new CTCL-associated gene aberrations.

CONCLUSIONS

Our findings revealed several new genes involved in CTCL pathogenesis and potential therapeutic targets. Down-regulation of a set of genes involved in Th1 polarization, including the major Th1-polarizing factor, TBX21, was for the first time associated with CTCL. In addition, a plausible explanation for the proliferative response of CTCL cells to locally produced interleukin-7 was revealed.