Dorfin localizes to the ubiquitylated inclusions in Parkinson's disease, dementia with Lewy bodies, multiple system atrophy, and amyotrophic lateral sclerosis

Proteostasis in neurodegenerative diseases

Proteostasis is essential for normal function of proteins and vital for cellular health and survival. Proteostasis encompasses all stages in the "life" of a protein, that is, from translation to functional performance and, ultimately, to degradation. Proteins need native conformations for function and in the presence of multiple types of stress, their misfolding and aggregation can occur. A coordinated network of proteins is at the core of proteostasis in cells. Among these, chaperones are required for maintaining the integrity of protein conformations by preventing misfolding and aggregation and guide those with abnormal conformation to degradation. The ubiquitin-proteasome system (UPS) and autophagy are major cellular pathways for degrading proteins. Although failure or decreased functioning of components of this network can lead to proteotoxicity and disease, like neuron degenerative diseases, underlying factors are not completely understood. Accumulating misfolded and aggregated proteins are considered major pathomechanisms of neurodegeneration. In this chapter, we have described the components of three major branches required for proteostasis-chaperones, UPS and autophagy, the mechanistic basis of their function, and their potential for protection against various neurodegenerative conditions, like Alzheimer's, Parkinson's, and Huntington's disease. The modulation of various proteostasis network proteins, like chaperones, E3 ubiquitin ligases, proteasome, and autophagy-associated proteins as therapeutic targets by small molecules as well as new and unconventional approaches, shows promise.

RNF19a inhibits antiviral immune response to RNA viruses through degradation of TBK1

TANK-binding kinase 1 (TBK1) plays a pivotal role in antiviral innate immunity. TBK1 mediates the activation of interferon regulatory factor (IRF) 3, leading to the induction of type I IFNs (IFN-α/β) and of NF-κB signal transduction following viral infections. TBK1 must be tightly regulated to effectively control viral infections and maintain immune homeostasis. Here, we found that E3 ubiquitin ligase RNF19a mediated K48-linked ubiquitination and proteasomal degradation of TBK1. Specifically, the silence of RNF19a enhanced the production of type I interferons and suppressed RNA viral replication. Our results uncover that RNF19a acts as a negative mediator in the RIG-I signaling pathway to attenuate antiviral immune responses and suggest RNF19a as a potential therapy target in clinical infectious and inflammatory diseases.

Association of low-frequency and rare coding variants with information processing speed

Measures of information processing speed vary between individuals and decline with age. Studies of aging twins suggest heritability may be as high as 67%. The Illumina HumanExome Bead Chip genotyping array was used to examine the association of rare coding variants with performance on the Digit-Symbol Substitution Test (DSST) in community-dwelling adults participating in the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) Consortium. DSST scores were available for 30,576 individuals of European ancestry from nine cohorts and for 5758 individuals of African ancestry from four cohorts who were older than 45 years and free of dementia and clinical stroke. Linear regression models adjusted for age and gender were used for analysis of single genetic variants, and the T5, T1, and T01 burden tests that aggregate the number of rare alleles by gene were also applied. Secondary analyses included further adjustment for education. Meta-analyses to combine cohort-specific results were carried out separately for each ancestry group. Variants in RNF19A reached the threshold for statistical significance (p = 2.01 × 10^-6) using the T01 test in individuals of European descent. RNF19A belongs to the class of E3 ubiquitin ligases that confer substrate specificity when proteins are ubiquitinated and targeted for degradation through the 26S proteasome. Variants in SLC22A7 and OR51A7 were suggestively associated with DSST scores after adjustment for education for African-American participants and in the European cohorts, respectively. Further functional characterization of its substrates will be required to confirm the role of RNF19A in cognitive function.

SAK3 Administration Improves Spine Abnormalities and Cognitive Deficits in AppNL-G-F/NL-G-F Knock-in Mice by Increasing Proteasome Activity through CaMKII/Rpt6 Signaling

Alzheimer's disease (AD) is the most common form of dementia and is characterized by neuropathological hallmarks consisting of accumulation of extracellular amyloid-β (Aβ) plaques and intracellular neurofibrillary tangles (NFT). Recently, we have identified a new AD therapeutic candidate, ethyl-8'-methyl-2',4-dioxo-2-(piperidin-1-yl)-2'H-spiro[cyclopentane-1,3'-imidazo [1,2-a] pyridin]-2-ene-3-carboxylate (SAK3), which ameliorates the AD-like pathology in AppNL-F/NL-F knock-in mice. However, the detailed mechanism underlying the therapeutic effects of SAK3 remains unclear. In this study, we found that SAK3 administration improved the reduced proteasome activity through the activation of CaMKII/Rpt6 signaling in AppNL-F/NL-F knock-in (NL-G-F) mice. Moreover, spine abnormalities observed in NL-G-F mice were significantly reversed by SAK3 administration. Along with this, cognitive impairments found in NL-G-F mice were markedly ameliorated by SAK3. In summary, our data suggest that SAK3 administration increases the activity of the proteasome via activation of the CaMKII/Rpt6 signaling pathway, contributing to improvements in spine abnormalities and cognitive deficits in NL-G-F mice. Overall, our findings suggest that SAK3 might be a new attractive drug candidate, representing a new mechanism for the treatment of AD pathology.

Insights into the pathogenesis of multiple system atrophy: focus on glial cytoplasmic inclusions

Multiple system atrophy (MSA) is a debilitating and fatal neurodegenerative disorder. The disease severity warrants urgent development of disease-modifying therapy, but the disease pathogenesis is still enigmatic. Neurodegeneration in MSA brains is preceded by the emergence of glial cytoplasmic inclusions (GCIs), which are insoluble α-synuclein accumulations within oligodendrocytes (OLGs). Thus, preventive strategies against GCI formation may suppress disease progression. However, although numerous studies have tried to elucidate the molecular pathogenesis of GCI formation, difficulty remains in understanding the pathological interaction between the two pivotal aspects of GCIs; α-synuclein and OLGs. The difficulty originates from several enigmas: 1) what triggers the initial generation and possible propagation of pathogenic α-synuclein species? 2) what contributes to OLG-specific accumulation of α-synuclein, which is abundantly expressed in neurons but not in OLGs? and 3) how are OLGs and other glial cells affected and contribute to neurodegeneration? The primary pathogenesis of GCIs may involve myelin dysfunction and dyshomeostasis of the oligodendroglial cellular environment such as autophagy and iron metabolism. We have previously reported that oligodendrocyte precursor cells are more prone to develop intracellular inclusions in the presence of extracellular fibrillary α-synuclein. This finding implies a possibility that the propagation of GCI pathology in MSA brains is mediated through the internalization of pathological α-synuclein into oligodendrocyte precursor cells. In this review, in order to discuss the pathogenesis of GCIs, we will focus on the composition of neuronal and oligodendroglial inclusions in synucleinopathies. Furthermore, we will introduce some hypotheses on how α-synuclein pathology spreads among OLGs in MSA brains, in the light of our data from the experiments with primary oligodendrocyte lineage cell culture. While various reports have focused on the mysterious source of α-synuclein in GCIs, insights into the mechanism which regulates the uptake of pathological α-synuclein into oligodendroglial cells may yield the development of the disease-modifying therapy for MSA. The interaction between glial cells and α-synuclein is also highlighted with previous studies of post-mortem human brains, cultured cells, and animal models, which provide comprehensive insight into GCIs and the MSA pathomechanisms.

Multiple System Atrophy: An Oligodendroglioneural Synucleinopathy1

Multiple system atrophy (MSA) is an orphan, fatal, adult-onset neurodegenerative disorder of uncertain etiology that is clinically characterized by various combinations of parkinsonism, cerebellar, autonomic, and motor dysfunction. MSA is an α-synucleinopathy with specific glioneuronal degeneration involving striatonigral, olivopontocerebellar, and autonomic nervous systems but also other parts of the central and peripheral nervous systems. The major clinical variants correlate with the morphologic phenotypes of striatonigral degeneration (MSA-P) and olivopontocerebellar atrophy (MSA-C). While our knowledge of the molecular pathogenesis of this devastating disease is still incomplete, updated consensus criteria and combined fluid and imaging biomarkers have increased its diagnostic accuracy. The neuropathologic hallmark of this unique proteinopathy is the deposition of aberrant α-synuclein in both glia (mainly oligodendroglia) and neurons forming glial and neuronal cytoplasmic inclusions that cause cell dysfunction and demise. In addition, there is widespread demyelination, the pathogenesis of which is not fully understood. The pathogenesis of MSA is characterized by propagation of misfolded α-synuclein from neurons to oligodendroglia and cell-to-cell spreading in a "prion-like" manner, oxidative stress, proteasomal and mitochondrial dysfunction, dysregulation of myelin lipids, decreased neurotrophic factors, neuroinflammation, and energy failure. The combination of these mechanisms finally results in a system-specific pattern of neurodegeneration and a multisystem involvement that are specific for MSA. Despite several pharmacological approaches in MSA models, addressing these pathogenic mechanisms, no effective neuroprotective nor disease-modifying therapeutic strategies are currently available. Multidisciplinary research to elucidate the genetic and molecular background of the deleterious cycle of noxious processes, to develop reliable biomarkers and targets for effective treatment of this hitherto incurable disorder is urgently needed.

Inside out: the role of nucleocytoplasmic transport in ALS and FTLD

Neurodegenerative diseases are characterized by the presence of protein inclusions with a different protein content depending on the type of disease. Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are no exceptions to this common theme. In most ALS and FTLD cases, the predominant pathological species are RNA-binding proteins. Interestingly, these proteins are both depleted from their normal nuclear localization and aggregated in the cytoplasm. This key pathological feature has suggested a potential dual mechanism with both nuclear loss of function and cytoplasmic gain of function being at play. Yet, why and how this pathological cascade is initiated in most patients, and especially sporadic cases, is currently unresolved. Recent breakthroughs in C9orf72 ALS/FTLD disease models point at a pivotal role for the nuclear transport system in toxicity. To address whether defects in nuclear transport are indeed implicated in the disease, we reviewed two decades of ALS/FTLD literature and combined this with bioinformatic analyses. We find that both RNA-binding proteins and nuclear transport factors are key players in ALS/FTLD pathology. Moreover, our analyses suggest that disturbances in nucleocytoplasmic transport play a crucial initiating role in the disease, by bridging both nuclear loss and cytoplasmic gain of functions. These findings highlight this process as a novel and promising therapeutic target for ALS and FTLD.

Mice lacking the PSD-95-interacting E3 ligase, Dorfin/Rnf19a, display reduced adult neurogenesis, enhanced long-term potentiation, and impaired contextual fear conditioning

Protein ubiquitination has a significant influence on diverse aspects of neuronal development and function. Dorfin, also known as Rnf19a, is a RING finger E3 ubiquitin ligase implicated in amyotrophic lateral sclerosis and Parkinson's disease, but its in vivo functions have not been explored. We report here that Dorfin is a novel binding partner of the excitatory postsynaptic scaffolding protein PSD-95. Dorfin-mutant (Dorfin(-/-)) mice show reduced adult neurogenesis and enhanced long-term potentiation in the hippocampal dentate gyrus, but normal long-term potentiation in the CA1 region. Behaviorally, Dorfin(-/-) mice show impaired contextual fear conditioning, but normal levels of cued fear conditioning, fear extinction, spatial learning and memory, object recognition memory, spatial working memory, and pattern separation. Using a proteomic approach, we also identify a number of proteins whose ubiquitination levels are decreased in the Dorfin(-/-) brain. These results suggest that Dorfin may regulate adult neurogenesis, synaptic plasticity, and contextual fear memory.

Oligodendroglia and Myelin in Neurodegenerative Diseases: More Than Just Bystanders?

Oligodendrocytes, the myelinating cells of the central nervous system, mediate rapid action potential conduction and provide trophic support for axonal as well as neuronal maintenance. Their progenitor cell population is widely distributed in the adult brain and represents a permanent cellular reservoir for oligodendrocyte replacement and myelin plasticity. The recognition of oligodendrocytes, their progeny, and myelin as contributing factors for the pathogenesis and the progression of neurodegenerative disease has recently evolved shaping our understanding of these disorders. In the present review, we aim to highlight studies on oligodendrocytes and their progenitors in neurodegenerative diseases. We dissect oligodendroglial biology and illustrate evolutionary aspects in regard to their importance for neuronal functionality and maintenance of neuronal circuitries. After covering recent studies on oligodendroglia in different neurodegenerative diseases mainly in view of their function as myelinating cells, we focus on the alpha-synucleinopathy multiple system atrophy, a prototypical disorder with a well-defined oligodendroglial pathology.

Multiple system atrophy: a prototypical synucleinopathy for disease-modifying therapeutic strategies

Despite active fundamental, translational and clinical research, no therapeutic intervention has yet shown convincing effects on disease progression in Parkinson's disease (PD) patients. Indeed, several disease-modification trials failed or proved to be inconclusive due to lack of consistency between clinical rating scales and putative surrogate markers of disease progression, or confounding symptomatic effects of the tested compound. Multiple system atrophy (MSA) is a rapidly progressing orphan disorder leading to severe motor disability within a few years. Together with PD and dementia with Lewy bodies (DLB), MSA belongs to the synucleinopathies, a group of neurodegenerative disorders characterized by the abnormal accumulation of alpha-synuclein. Crucial milestones have been reached for successfully conducting clinical intervention trials in a large number of patients with MSA. In this personal view, we will review evidence, and discuss why MSA could prove the most relevant clinical model for assessing treatments that target mechanisms operating in all synucleinopathies.

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.

E3 ubiquitin ligases in protein quality control mechanism

In living cells, polypeptide chains emerging from ribosomes and preexisting polypeptide chains face constant threat of misfolding and aggregation. To prevent protein aggregation and to fulfill their biological activity, generally, protein must fold into its proper three-dimensional structure throughout their lifetimes. Eukaryotic cell possesses a quality control (QC) system to contend the problem of protein misfolding and aggregation. Cells achieve this functional QC system with the help of molecular chaperones and ubiquitin-proteasome system (UPS). The well-conserved UPS regulates the stability of various proteins and maintains all essential cellular function through intracellular protein degradation. E3 ubiquitin ligase enzyme determines specificity for degradation of certain substrates via UPS. New emerging evidences have provided considerable information that various E3 ubiquitin ligases play a major role in cellular QC mechanism and principally designated as QC E3 ubiquitin ligases. Nevertheless, very little is known about how E3 ubiquitin ligase maintains QC mechanism against abnormal proteins under various stress conditions. Here in this review, we highlight and discuss the functions of various E3 ubiquitin ligases implicated in protein QC mechanism. Improving our knowledge about such processes may provide opportunities to modulate protein QC mechanism in age-of-onset diseases that are caused by protein aggregation.

Averaged differential expression for the discovery of biomarkers in the blood of patients with prostate cancer

BACKGROUND

The identification of a blood-based diagnostic marker is a goal in many areas of medicine, including the early diagnosis of prostate cancer. We describe the use of averaged differential display as an efficient mechanism for biomarker discovery in whole blood RNA. The process of averaging reduces the problem of clinical heterogeneity while simultaneously minimizing sample handling.

METHODOLOGY/PRINCIPAL FINDINGS

RNA was isolated from the blood of prostate cancer patients and healthy controls. Samples were pooled and subjected to the averaged differential display process. Transcripts present at different levels between patients and controls were purified and sequenced for identification. Transcript levels in the blood of prostate cancer patients and controls were verified by quantitative RT-PCR. Means were compared using a t-test and a receiver-operating curve was generated. The Ring finger protein 19A (RNF19A) transcript was identified as having higher levels in prostate cancer patients compared to healthy men through the averaged differential display process. Quantitative RT-PCR analysis confirmed a more than 2-fold higher level of RNF19A mRNA levels in the blood of patients with prostate cancer than in healthy controls (p = 0.0066). The accuracy of distinguishing cancer patients from healthy men using RNF19A mRNA levels in blood as determined by the area under the receiving operator curve was 0.727.

CONCLUSIONS/SIGNIFICANCE

Averaged differential display offers a simplified approach for the comprehensive screening of body fluids, such as blood, to identify biomarkers in patients with prostate cancer. Furthermore, this proof-of-concept study warrants further analysis of RNF19A as a clinically relevant biomarker for prostate cancer detection.

Dysfunction of constitutive and inducible ubiquitin-proteasome system in amyotrophic lateral sclerosis: implication for protein aggregation and immune response

The ubiquitin-proteasome system (UPS) is the major intracellular proteolytic mechanism controlling the degradation of misfolded/abnormal proteins. A common hallmark in amyotrophic lateral sclerosis (ALS) and in other neurodegenerative disorders is the accumulation of misfolded/abnormal proteins into the damaged neurons, leading to the formation of cellular inclusions that are mostly ubiquitin-positive. Although proteolysis is a complex mechanism requiring the participation of different pathways, the abundant accumulation of ubiquitinated proteins strongly suggests an important contribution of UPS to these neuropathological features. The use of cellular and animal models of ALS, particularly those expressing mutant SOD1, the gene mutation most represented in familiar ALS, has provided significant evidence for a role of UPS in protein inclusions formation and motor neuron death. This review will specifically discuss this piece of evidence and provide suggestions of potential strategies for therapeutic intervention. We will also discuss the finding that, unlike the constitutive proteasome subunits, the inducible subunits are overexpressed early during disease progression in SOD1 mice models of ALS. These subunits form the immunoproteasome and generate peptides for the major histocompatibility complex class I molecules, suggesting a role of this system in the immune responses associated with the pathological features of ALS. Since recent discoveries indicate that innate and adaptive immunity may influence the disease process, in this review we will also provide evidence of a possible connection between immune-inflammatory reactions and UPS function, in the attempt to better understand the etiopathology of ALS and to identify appropriate targets for novel treatment strategies of this devastating disease.

Synphilin-1 inhibits alpha-synuclein degradation by the proteasome

Intracellular deposits of aggregated alpha-synuclein are a hallmark of Parkinson's disease. Protein-protein interactions are critical in the regulation of cell proteostasis. Synphilin-1 interacts both in vitro and in vivo with alpha-synuclein promoting its aggregation. We report here that synphilin-1 specifically inhibits the degradation of alpha-synuclein wild-type and its missense mutants by the 20S proteasome due at least in part by the interaction of the ankyrin and coiled-coil domains of synphilin-1 (amino acids 331-555) with the N-terminal region (amino acids 1-60) of alpha-synuclein. Co-expression of synphilin-1 and alpha-synuclein wild-type in HeLa and N2A cells produces a specific increase in the half-life of alpha-synuclein, as degradation of unstable fluorescent reporters is not affected. Synphilin-1 inhibition can be relieved by co-expression of Siah-1 that targets synphilin-1 to degradation. Synphilin-1 inhibition of the proteasomal pathway of degradation of alpha-synuclein may help to understand the pathophysiological changes occurring in PD and other synucleinopathies.

Dorfin ameliorates phenotypes in a transgenic mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that is characterized by progressive motor neuron degeneration and leads to death within a few years of diagnosis. One of the pathogenic mechanisms of ALS is proposed to be a dysfunction in the protein quality-control machinery. Dorfin has been identified as a ubiquitin ligase (E3) that recognizes and ubiquitinates mutant SOD1 proteins, thereby accelerating their degradation and reducing their cellular toxicity. We examined the effects of human Dorfin overexpression in G93A mutant SOD1 transgenic mice, a mouse model of familial ALS. In addition to causing a decrease in the amount of mutant SOD1 protein in the spinal cord, Dorfin overexpression ameliorated neurological phenotypes and motor neuron degeneration. Our results indicate that Dorfin overexpression or the activation or induction of E3 may be a therapeutic avenue for mutant SOD1-associated ALS.

[Exploration of pathogenesis-associated molecules and development of disease models for sporadic ALS]

The mechanism underlying the characteristic selective motor neuron degeneration in amyotrophic lateral sclerosis (ALS) has remained elusive. Modest advances in this research field have been achieved by the identification of copper/zinc superoxide dismutase 1 (SOD1) as one of the causative genes for rare familial ALS and by the development and analysis of mutant SOD1 transgenic animal models. However, in sporadic ALS (SALS) with many more patients, causative or critical genes situated upstream of the disease pathway have not yet been elucidated and no available disease models have been established. We have been working on screening these genes employing and combining several new technologies such as cDNA microarray, molecular indexing, and laser capture microdissection. Many of the resultant genes are of intense interest and may provide a powerful tool for determining the molecular mechanisms of SALS. Of these, in this paper, we will focus on Dorfin, a RING finger-type E3 ubiquitin ligase and dynactin1, a major component of dynein/dynactin complex that is important for retrograde axonal transport. We are now challenging creation of the disease models by simulating the gene expression changes specifically observed in SALS patients.

A strategy for developing effective amyotropic lateral sclerosis pharmacotherapy: from clinical trials to novel pharmacotherapeutic strategies

BACKGROUND

The pathomechanism of sporadic amyotropic lateral sclerosis is not clearly understood, although a proportion of familial amyotropic lateral sclerosis is caused by superoxide dismutase 1 mutations. Theories based on studies of human post-mortem tissue, research on animal models and in vitro work have been proposed for the pathogenesis of amyotropic lateral sclerosis, but the pathogenesis is not the same between sporadic and familial amyotropic lateral sclerosis.

OBJECTIVE/METHODS

Drug candidates were tested using superoxide dismutase 1 mutant mice. Although the candidates were shown to be effective in mice, clinical trials in humans have failed to identify any truly effective pharmacotherapies in sporadic amyotropic lateral sclerosis, with only riluzole providing a modest improvement in survival. Ongoing or planned trials are exploring the value of antiglutamatergic drugs, antioxidants, neurotrophic factors, anti-inflammatory drugs and anti-aggregation drugs.

RESULTS/CONCLUSIONS

A combination of drugs acting on different mechanisms is needed for effective therapy. Moreover, gene expression profiling and genome-wide association studies, together with inhibitory RNA techniques, are helpful for developing new pharmacotherapeutic strategies including gene therapy. It is also likely that the recently advanced generation of induced pluripotent stem cells will lead to the development of cell therapy for amyotropic lateral sclerosis. In addition to finding effective therapies, research is also needed in order to detect early disease markers since pharmacotherapy is most beneficial when given early in the course of sporadic amyotropic lateral sclerosis.

Cooperative exonization of MaLR and AluJo elements contributed an alternative promoter and novel splice variants of RNF19

The RNF19 protein, which contains RING-finger and IBR motifs, acts as an E3 ubiquitin ligase localized to Lewy bodies. RNF19 is located on human chromosome 8q22.2, has a 4.4-kb transcript, and is ubiquitously expressed in various tissues. Here, we identified an alternative RNF19 promoter region and alternative RNF19 transcripts derived from MaLR (mammalian apparent LTR-retrotransposon) and AluJo elements. Comparative analyses indicated human-specific expression of the MaLR- and AluJo-related transcripts. From the expression analysis of 72 tissue samples including human normal, tumor, and primate tissues, three different isoforms (V1, V2, and V3) of MaLR-derived transcripts were identified. Quantitative RT-PCR analysis showed a dominant expression pattern of the V2 MaLR-derived transcript. A reporter gene assay for MaLR element promoter activity indicated that pGL2-RNF19/MaLR in the forward orientation is capable of driving luciferase gene expression in Cos7 and HCT116 cells. These findings suggest that RNF19 has acquired a new promoter and alternative exons via continuous retrotransposition events of MaLR and AluJo elements during mammalian and primate evolution, respectively.

Amyotrophic lateral sclerosis: from current developments in the laboratory to clinical implications

Amyotrophic lateral sclerosis (ALS) is a late-onset progressive degeneration of motor neurons occurring both as a sporadic and a familial disease. The etiology of ALS remains unknown, but one fifth of instances are due to specific gene defects, the best characterized of which is point mutations in the gene coding for Cu/Zn superoxide dismutase (SOD1). Because sporadic and familial ALS affect the same neurons with similar pathology, it is hoped that understanding these gene defects will help in devising therapies effective in both forms. A wealth of evidence has been collected in rodents made transgenic for mutant SOD1, which represent the best available models for familial ALS. Mutant SOD1 likely induces selective vulnerability of motor neurons through a combination of several mechanisms, including protein misfolding, mitochondrial dysfunction, oxidative damage, cytoskeletal abnormalities and defective axonal transport, excitotoxicity, inadequate growth factor signaling, and inflammation. Damage within motor neurons is enhanced by noxious signals originating from nonneuronal neighboring cells, where mutant SOD1 induces an inflammatory response that accelerates disease progression. The clinical implication of these findings is that promising therapeutic approaches can be derived from multidrug treatments aimed at the simultaneous interception of damage in both motor neurons and nonmotor neuronal cells.

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.

Gene expressions specifically detected in motor neurons (dynactin 1, early growth response 3, acetyl-CoA transporter, death receptor 5, and cyclin C) differentially correlate to pathologic markers in sporadic amyotrophic lateral sclerosis

In a differential gene expression profile, we showed previously that dynactin 1 (DCTN1), early growth response 3 (EGR3), acetyl-CoA transporter (ACATN), death receptor 5 (DR5), and cyclin C (CCNC) were prominently up- or downregulated in motor neurons of sporadic amyotrophic lateral sclerosis (ALS). In the present study, we examined the correlation between the expression levels of these genes and the levels of pathologic markers for motor neuron degeneration (i.e. cytoplasmic accumulation of phosphorylated neurofilament H [pNF-H] and ubiquitylated protein) and the numbers of residual motor neurons in 20 autopsies of patients with sporadic ALS. DCTN1 and EGR3 were widely downregulated, and the changes in gene expression were correlated to the number of residual motor neurons. In particular, DCTN1 was markedly downregulated in most residual motor neurons before the accumulation of pNF-H, even in cases with well-preserved motor neuron populations. ACATN, DR5, and CCNC were upregulated in subpopulations of residual motor neurons, and their expression levels were well correlated with the levels of pNF-H accumulation and the number of residual motor neurons. The expressions of DCTN1, EGR3, ACATN, and DR5 were all markedly altered before ubiquitylated protein accumulation. DCTN1 downregulation appears to be an early event before the appearance of neurodegeneration markers, whereas upregulations of DR5 and CCNC are relatively later phenomena associated with pathologic markers and leading to neuronal death. The sequence of motor neuron-specific gene expression changes in sporadic ALS can be beneficial information in developing appropriate therapeutic strategies for neurodegeneration.

The ring between ring fingers (RBR) protein family

An overview of the large and functionally diverse RBR protein family that mediates protein-protein interactions of various kinds in development and disease.

Summary

Proteins of the ring between ring fingers (RBR)-domain family are characterized by three groups of specifically clustered (typically eight) cysteine and histidine residues. Whereas the amino-terminal ring domain (N-RING) binds two zinc ions and folds into a classical cross-brace ring finger, the carboxy-terminal ring domain (C-RING) involves only one zinc ion. The three-dimensional structure of the central ring domain, the IBR domain, is still unsolved. About 400 genes coding for RBR proteins have been identified in the genomes of uni- and multicellular eukaryotes and some of their viruses, but the family has not been found in archaea or bacteria. The RBR proteins are classified into 15 major subfamilies (besides some orphan cases) by the phylogenetic relationships of the RBR segments and the conservation of their sequence architecture. The RBR domain mediates protein-protein interactions and a subset of RBR proteins has been shown to function as E3 ubiquitin ligases. RBR proteins have attracted interest because of their involvement in diseases such as parkinsonism, dementia with Lewy bodies, and Alzheimer's disease, and in susceptibility to some intracellular bacterial pathogens. Here, we present an overview of the RBR-domain containing proteins and their subcellular localization, additional domains, function, specificity, and regulation.

Dorfin-CHIP chimeric proteins potently ubiquitylate and degrade familial ALS-related mutant SOD1 proteins and reduce their cellular toxicity

The ubiquitin-proteasome system (UPS) is involved in the pathogenetic mechanisms of neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS). Dorfin is a ubiquitin ligase (E3) that degrades mutant SOD1 proteins, which are responsible for familial ALS. Although Dorfin has potential as an anti-ALS molecule, its life in cells is short. To improve its stability and enhance its E3 activity, we developed chimeric proteins containing the substrate-binding hydrophobic portion of Dorfin and the U-box domain of the carboxyl terminus of Hsc70-interacting protein (CHIP), which has strong E3 activity through the U-box domain. All the Dorfin-CHIP chimeric proteins were more stable in cells than was wild-type Dorfin (Dorfin(WT)). One of the Dorfin-CHIP chimeric proteins, Dorfin-CHIP(L), ubiquitylated mutant SOD1 more effectively than did Dorfin(WT) and CHIP in vivo, and degraded mutant SOD1 protein more rapidly than Dorfin(WT) does. Furthermore, Dorfin-CHIP(L) rescued neuronal cells from mutant SOD1-associated toxicity and reduced the aggresome formation induced by mutant SOD1 more effectively than did Dorfin(WT).

The role of ubiquitin-protein ligases in neurodegenerative disease

Alzheimer's disease and Parkinson's disease are the most common neurodegenerative conditions associated with the ageing process. The pathology of these and other neurodegenerative disorders, including polyglutamine diseases, is characterised by the presence of inclusion bodies in brain tissue of affected patients. In general, these inclusion bodies consist of insoluble, unfolded proteins that are commonly tagged with the small protein, ubiquitin. Covalent tagging of proteins with chains of ubiquitin generally targets them for degradation. Indeed, the ubiquitin/proteasome system (UPS) is the major route through which intracellular proteolysis is regulated. This strongly implicates the UPS in these disease-associated inclusions, either due to malfunction (of specific UPS components) or overload of the system (due to aggregation of unfolded/mutant proteins), resulting in subsequent cellular toxicity. Protein targeting for degradation is a highly regulated process. It relies on transfer of ubiquitin molecules to the target protein via an enzyme cascade and specific recognition of a substrate protein by ubiquitin-protein ligases (E3s). Recent advances in our knowledge gained from the Human Genome Mapping Project have revealed the presence of potentially hundreds of E3s within the human genome. The discovery that parkin, mutations in which are found in at least 50% of patients with autosomal recessive juvenile parkinsonism, is an E3 further highlights the importance of the UPS in neurological disease. To date, parkin is the only E3 confirmed to have a direct causal role in neurodegenerative disorders. However, a number of other (putative) E3s have now been identified that may cause disease directly or interact with neurological disease-associated proteins. Many of these are either lost or mutated in a given disease or fail to process disease-associated mutant proteins correctly. In this review, we will discuss the role(s) of E3s in neurodegenerative disorders.

NK Lytic-Associated Molecule, Involved in NK Cytotoxic Function, Is an E3 Ligase

NK lytic-associated molecule (NKLAM) is a protein involved in the cytolytic function of NK cells and CTLs. It has been localized to the cytolytic granules in NK cells and is up-regulated when cells are exposed to cytokines IL-2 or IFN-beta. We report in this study that NKLAM contains a cysteine-rich really interesting new gene (RING) in between RING-RING domain, and that this domain possesses strong homology to the RING domain of the known E3 ubiquitin ligase, Dorfin. To determine whether NKLAM functions as an E3 ligase, we performed coimmunoprecipitation binding assays with ubiquitin conjugates (Ubcs) UbcH7, UbcH8, and UbcH10. We demonstrated that both UbcH7 and UbcH8 bind to full-length NKLAM. We then performed a similar binding assay using endogenous NKLAM and UbcH8 expressed by human NK clone NK3.3 to show that the protein interaction occurs in vivo. Using the yeast two-hybrid system, we identified uridine kinase like-1 (URKL-1) protein as a substrate for NKLAM. We confirmed that NKLAM and URKL-1 interact in mammalian cells by using both immunoprecipitation and confocal microscopy. We demonstrated decreased protein expression and enhanced ubiquitination of URKL-1 in the presence of NKLAM. These data indicate that NKLAM is a RING finger protein that binds Ubcs and has as one of its substrates, URKL-1, thus defining this cytolytic protein as an E3 ubiquitin ligase.

Calcium-sensing Receptor Ubiquitination and Degradation Mediated by the E3 Ubiquitin Ligase Dorfin

Calcium-sensing receptors (CaR) contribute to regulation of systemic calcium homeostasis by activation of G(q)- and G(i)-linked signaling pathways in the parathyroids, kidney, and intestine. Little is known about the mechanisms regulating CaR synthesis and degradation. Screening of a human kidney yeast two-hybrid library identified the E3 ubiquitin ligase dorfin as a binding partner for the intracellular carboxyl terminus of CaR. Interaction between CaR and dorfin was confirmed by coimmunoprecipitation from HEK293 cells. Ubiquitination of CaR was observed in the presence of the proteasomal inhibitor MG132; mutation of all putative intracellular loop and carboxyl-terminal lysine residues abolished ubiquitination of CaR. Coexpression with dorfin decreased the amount of total CaR protein and increased CaR ubiquitination, whereas a dominant negative fragment of dorfin had opposite effects. The AAA-ATPase p97/valosin-containing protein associates with both CaR and dorfin in HEK293 cells. Treatment with tunicamycin, an inhibitor of N-linked glycosylation, induced the appearance of the unglycosylated 115-kDa CaR form, which was further increased by exposure to MG132, or upon transfection with a dorfin dominant negative construct, suggesting that dorfin-mediated proteasomal degradation of immature CaR occurs from the endoplasmic reticulum. Because endogenous CaR in Madin-Darby canine kidney cells is also subject to degradation from the endoplasmic reticulum, dorfin-mediated ubiquitination may contribute to a general mechanism for CaR quality control during biosynthesis.

In vivo models of multiple system atrophy

Multiple system atrophy (MSA) is a sporadic adult-onset neurodegenerative disorder of unknown etiology clinically characterized by a combination of parkinsonian, pyramidal, and cerebellar signs. Levodopa-unresponsive parkinsonism is present in 80% of MSA cases, and this dominant clinical presentation (MSA-P) is associated with a combined degeneration of the substantia nigra pars compacta and the striatum in anatomically related areas. The limited knowledge of the pathophysiology of MSA and the lack of therapeutic strategies prompted the development of lesion models reproducing striatonigral degeneration, the substrate of levodopa-unresponsive parkinsonism in MSA-P. This method was carried out first in rats with two different stereotaxic strategies using either two neurotoxins ("double toxin-double lesion") or a single neurotoxin ("single toxin-double lesion"). Double-lesioned rat models showed severe motor impairment compared to those with a single nigral or striatal lesion and helped to mimic different stages of the disease. Systemic models were also developed in mice and primates using the nigral toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and the striatal toxin 3-nitropropionic (3-NP). In mice, although MPTP reduced the subsequent sensitivity to 3-NP in a sequential lesion, simultaneous nigral and striatal insults were shown to exacerbate striatal damage. MPTP-treated monkeys displayed a significant worsening of parkinsonism and a loss of levodopa-responsiveness after the appearance of hindlimb dystonia and striatal lesion formation induced by subsequent 3-NP intoxication. The different species and intoxication paradigms used will be useful to investigate functional changes in substantia nigra and striatum and to define neuroprotective, neurorestorative, or symptomatic therapeutic strategies.

Microarray Analysis of VEGF-C Responsive Genes in Human Lymphatic Endothelial Cells

Vascular endothelial growth factor-C (VEGF-C) is considered one of the most important factors influencing lymphatic endothelial cell biology. The goal of this work was to characterize the gene expression response by lymphatic endothelial cells (LECs) to VEGF-C. Primary cultures of human microvascular LECs were exposed to 100 ng/mL VEGF-C for 30 minutes and 6 hours, and their lysates were evaluated by microarray analysis to determine changes in mRNA expression induced by VEGF-C. Characteristic of a response to a growth factor stimulus, the largest number of differentially expressed genes were transcription factors and cell cycle related. A number of genes known to be important in angiogenesis, tumorigenesis and tumor invasion, and the transport of proteins, solutes, and lipids were also affected. Interestingly, a number of genes related to lipid metabolism as well as neurogenesis and neurodegeneration were also responsive to VEGF-C stimulation. Further analysis of these genes may not only provide insight into the molecular mechanisms underlying lymphangiogenesis and associated pathogenesis, but may also identify other important roles of VEGF-C.

Tuft-shaped astrocytes in Lewy body disease

We investigated the occurrence and distribution of tuft-shaped astrocytes (TuSAs) in 60 brains from patients with Lewy body disease (LBD), which were clinically diagnosed as Parkinson's disease (PD) or dementia with Lewy bodies (DLB), and 85 brains from control subjects. TuSAs have been documented as a neuropathological hallmark of progressive supranuclear palsy (PSP). We found phosphorylated tau (p-tau)-positive and alpha-synuclein-negative TuSAs in 10 of 60 patients with LBD and 3 of 85 control cases. TuSAs were mainly located within the precentral and premotor gyri of the frontal lobe cortex. There were only few TuSAs, but the distribution pattern and morphological and immunohistological features were similar to that in PSP. Furthermore, other p-tau positive structures, including aggregates in neurons, coiled-like glial cells and threads showed a similar distribution to those in PSP; mainly in the hippocampus, striatum, subthalamic nucleus, precentral and premotor gyri, brainstem nucleus, and dentate nucleus. In these cases, however, neuronal loss and gliosis were not seen in the regions involved in PSP, such as the subthalamic nucleus, pallidum, inferior olivary, cerebellar dentate nuclei, and periaqueductal gray matter. Clinical features were indistinguishable between the LBD with and without TuSAs. The appearance of TuSAs was not related to the frequency of Lewy bodies, neurofibrillary tangles, and senile plaques, but was significantly more pronounced with advancing age in both LBD and controls. These findings suggest that in a subgroup of elderly individual cases, especially associated with LB pathology, the glial and neuronal p-tau accumulation is increased and has a distributional pattern similar to PSP.

Gene expression profile of spinal motor neurons in sporadic amyotrophic lateral sclerosis

The causative pathomechanism of sporadic amyotrophic lateral sclerosis (ALS) is not clearly understood. Using microarray technology combined with laser-captured microdissection, gene expression profiles of degenerating spinal motor neurons isolated from autopsied patients with sporadic ALS were examined. Gene expression was quantitatively assessed by real-time reverse transcription polymerase chain reaction and in situ hybridization. Spinal motor neurons showed a distinct gene expression profile from the whole spinal ventral horn. Three percent of genes examined were downregulated, and 1% were upregulated in motor neurons. Downregulated genes included those associated with cytoskeleton/axonal transport, transcription, and cell surface antigens/receptors, such as dynactin, microtubule-associated proteins, and early growth response 3 (EGR3). In contrast, cell death-associated genes were mostly upregulated. Promoters for cell death pathway, death receptor 5, cyclins A1 and C, and caspases-1, -3, and -9, were upregulated, whereas cell death inhibitors, acetyl-CoA transporter, and NF-kappaB were also upregulated. Moreover, neuroprotective neurotrophic factors such as ciliary neurotrophic factor (CNTF), Hepatocyte growth factor (HGF), and glial cell line-derived neurotrophic factor were upregulated. Inflammation-related genes, such as those belonging to the cytokine family, were not, however, significantly upregulated in either motor neurons or ventral horns. The motor neuron-specific gene expression profile in sporadic ALS can provide direct information on the genes leading to neurodegeneration and neuronal death and are helpful for developing new therapeutic strategies.

Alpha-synuclein and transgenic mouse models

Identified as the cause of some familial forms of Parkinson disease (PD) and as one of the major component of Lewy bodies, alpha-synuclein (alpha-syn) became the molecular hallmark of several neurodegenerative conditions now designated as synucleinopathies. Transgenic models have been generated to elucidate its physiological and pathologic roles. Although none of the lines created display dopaminergic neuronal death in the substantia nigra, the models recapitulate some features of synucleinopathies and are useful to study the potential pathogenic role of alpha-synuclein and its molecular partners. This review describes the different alpha-synuclein transgenic models, their clinical relevance to synucleinopathies, and their further utilization to understand the disease process.

Physical and Functional Interaction between Dorfin and Valosin-containing Protein That Are Colocalized in Ubiquitylated Inclusions in Neurodegenerative Disorders

Dorfin, a RING-IBR type ubiquitin ligase (E3), can ubiquitylate mutant superoxide dismutase 1, the causative gene of familial amyotrophic lateral sclerosis (ALS). Dorfin is located in ubiquitylated inclusions (UBIs) in various neurodegenerative disorders, such as ALS and Parkinson's disease (PD). Here we report that Valosin-containing protein (VCP) directly binds to Dorfin and that VCP ATPase activity profoundly contributes to the E3 activity of Dorfin. High through-put analysis using mass spectrometry identified VCP as a candidate of Dorfin-associated protein. Glycerol gradient centrifugation analysis showed that endogenous Dorfin consisted of a 400-600-kDa complex and was co-immunoprecipitated with endogenous VCP. In vitro experiments showed that Dorfin interacted directly with VCP through its C-terminal region. These two proteins were colocalized in aggresomes in HEK293 cells and UBIs in the affected neurons of ALS and PD. VCP(K524A), a dominant negative form of VCP, reduced the E3 activity of Dorfin against mutant superoxide dismutase 1, whereas it had no effect on the autoubiquitylation of Parkin. Our results indicate that VCPs functionally regulate Dorfin through direct interaction and that their functional interplay may be related to the process of UBI formation in neurodegenerative disorders, such as ALS or PD.

Genes, proteins, and neurotoxins involved in Parkinson’s disease

Parkinson's disease (PD) is a common neurodegenerative disorder. The etiology of PD is likely due to combinations of environmental and genetic factors. In addition to the loss of neurons, including dopaminergic neurons in the substantia nigra pars compacta, a further morphologic hallmark of PD is the presence of Lewy bodies and Lewy neurites. The formation of these proteinaceous inclusions involves interaction of several proteins, including alpha-synuclein, synphilin-1, parkin and UCH-L1. Animal models allow to get insight into the mechanisms of several symptoms of PD, allow investigating new therapeutic strategies and, in addition, provide an indispensable tool for basic research. In animals PD does not arise spontaneously, thus, characteristic and specific functional changes have to be mimicked by application of neurotoxic agents or by genetic manipulations. In this review we will focus on genes and gene loci involved in PD, the functions of proteins involved in the formation of cytoplasmatic inclusions, their interactions, and their possible role in PD. In addition, we will review the current animal models of PD.

Parkin and relatives: the RBR family of ubiquitin ligases

Mutations in the parkin gene cause autosomal-recessive juvenile parkinsonism. Parkin encodes a ubiquitin-protein ligase characterized by having the RBR domain, composed of two RING fingers plus an IBR/DRIL domain. The RBR family is defined as the group of genes whose products contain an RBR domain. RBR family members exist in all eukaryotic species for which significant sequence data is available, including animals, plants, fungi, and several protists. The integration of comparative genomics with structural and functional data allows us to conclude that RBR proteins have multiple roles, not only in protein quality control mechanisms, but also as indirect regulators of transcription. A recently formulated hypothesis, based on a case of gene fusion, suggested that RBR proteins may be often part of cullin-containing ubiquitin ligase complexes. Recent data on Parkin protein agrees with that hypothesis. We discuss the involvement of RBR proteins in several neurodegenerative diseases and cancer.

Activated p38MAPK Is a Novel Component of the Intracellular Inclusions Found in Human Amyotrophic Lateral Sclerosis and Mutant SOD1 Transgenic Mice

Cytoskeletal abnormalities with accumulation of ubiquilated inclusions in the anterior horn cells are a pathological hallmark of both familial and sporadic amyotrophic lateral sclerosis (ALS) and of mouse models for ALS. Phosphorylated neurofilaments besides ubiquitin and dorfin have been identified as one of the major components of the abnormal intracellular perikaryal aggregates. As we recently found that p38 mitogen-activated protein kinase (p38MAPK) colocalized with phosphorylated neurofilaments in spinal motor neurons of SOD1 mutant mice, a model of familial ALS, we investigated whether this kinase also contributed to the inclusions found in ALS patients and SOD1 mutant mice. Intense immunoreactivity for activated p38MAPK was observed in degenerating motor neurons and reactive astrocytes in ALS cases. The intracellular immunostaining for activated p38MAPK appeared in some neurons as filamentous skein-like and ball-like inclusions, with an immunohistochemical pattern identical to that of ubiquitin. Intracellular p38MAPK-positive aggregates containing ubiquitin and neurofilaments were also found in the spinal motor neurons of SOD1 mutant mice. Our observations indicate that activation of p38MAPK might contribute significantly to the pathology of motor neurons in ALS.

The Ubiquitin Proteasome System in Neurodegenerative Diseases

The ubiquitin-proteasome system targets numerous cellular proteins for degradation. In addition, modifications by ubiquitin-like proteins as well as proteins containing ubiquitin-interacting and -associated motifs modulate many others. This tightly controlled process involves multiple specific and general enzymes of the system as well as many modifying and ancillary proteins. Thus, it is not surprising that ubiquitin-mediated degradation/processing/modification regulates a broad array of basic cellular processes. Moreover, aberrations in the system have been implicated, either as a primary cause or secondary consequence, in the pathogenesis of both inherited and acquired neurodegenerative diseases. Recent findings indicate that the system is involved in the pathogenesis of Parkinson's, Alzheimer's, Huntington's, and Prion diseases as well as amyotrophic lateral sclerosis. This raises hopes for a better understanding of the pathogenetic mechanisms involved in these diseases and for the development of novel, mechanism-based therapeutic modalities.