Ubiquitin is a common factor in intermediate filament inclusion bodies of diverse type in man, including those of Parkinson's disease, Pick's disease, and Alzheimer's disease, as well as Rosenthal fibres in cerebellar astrocytomas, cytoplasmic bodies in muscle, and mallory bodies in alcoholic liver disease

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.

Regulation of endothelial barrier function by TGF-β type I receptor ALK5: potential role of contractile mechanisms and heat shock protein 90

Multifunctional cytokine transforming growth factor-beta (TGF-β1) plays a critical role in the pathogenesis of acute lung inflammation by controlling endothelial monolayer permeability. TGF-β1 regulates endothelial cell (EC) functions via two distinct receptors, activin receptor-like kinase 1 (ALK1) and activin receptor-like kinase 5 (ALK5). The precise roles of ALK1 and ALK5 in the regulation of TGF-β1-induced lung endothelium dysfunction remain mostly unknown. We now report that adenoviral infection with constitutively active ALK5 (caALK5), but not caALK1, induces EC retraction and that this receptor predominantly controls EC permeability. We demonstrate that ubiquitinated ALK5 and phosphorylated heat shock protein 27 (phospho-Hsp27) specifically accumulate in the cytoskeleton fraction, which parallels with microtubule collapse, cortical actin disassembly and increased EC permeability. We have found that ALK1 and ALK5 interact with heat shock protein 90 (Hsp90). Moreover, the Hsp90 inhibitor radicicol (RA) prevents accumulation of ubiquitinated caALK5 and phospho-Hsp27 in the cytoskeletal fraction and restore the decreased EC permeability induced by caALK5. We hypothesize that specific translocation of ubiquitinated ALK5 receptor into the cytoskeleton compartment due to its lack of degradation is the mechanism that causes the divergence of caALK1 and caALK5 signaling.

Widespread neuronal and glial hyperphosphorylated tau deposition in ALS with cognitive impairment

Although the biological basis of frontotemporal syndromes associated with amyotrophic lateral sclerosis (ALS) is considered to be altered metabolism of TDP-43, in ALS with cognitive impairment (ALSci) the metabolism of tau protein is also altered. This includes neuronal hyperphosphorylation (pThr(175)). Using novel polyclonal phospho-tau antibodies (pSer(208, 210), pThr(217) and pThr(175)) and antibodies directed against PHF tau (pSer(202)), TDP-43 or ubiquitin, we characterized tau deposition in ALS and ALSci. In ALS, we observed pThr(175) tau immunoreactive intraneuronal and neuritic aggregates throughout the amygdala and entorhinal cortex. In ALSci, this extended to the anterior cingulate gyrus, superior frontal cortex and substantia nigra. The pThr(217) antibody detected widespread astrocytic tau deposition, including punctuate or fibrillary aggregates, or intensely immunoreactive tufted astrocytes in the superior frontal cortex, anterior cingulate gyrus, entorhinal cortex, amygdala and basal ganglia of ALS. In ALSci, a similar but more widely distributed pThr(217) pathology was observed. There was no correlation between the extent of pathological tau deposition and TDP-43 pathology, although nuclear TDP-43 immunoreactivity was absent in neurons with tau pathology. In conclusion, ALSci is unique in possessing both tau and TDP-43 pathology. The presence of widespread astrocytic tau pathology suggests that ALSci may initially be characterized by astrocytic pathology.

Balancing act: deubiquitinating enzymes in the nervous system

Many pathways important to the nervous system are regulated by the post-translational conjugation of ubiquitin to target proteins. The reversal of ubiquitination, or deubiquitination, is equally critical to neuronal function. By countering protein ubiquitination, deubiquitinating enzymes (DUBs) help control neuronal fate determination, axonal pathfinding and synaptic communication and plasticity. The significance of DUBs to the nervous system is underscored by links to various neurological diseases. Owing to cell type or substrate specificity, certain DUBs might also represent therapeutic targets for neurodegeneration. Here, we review recent findings that have shaped our current understanding of emerging functions for DUBs in the nervous system.

Biomarker-based dissection of neurodegenerative diseases

The diagnosis of neurodegenerative diseases within neurology and psychiatry are hampered by the difficulty in getting biopsies and thereby validating the diagnosis by pathological findings. Biomarkers for other types of disease have been readily adopted into the clinical practice where for instance troponins are standard tests when myocardial infarction is suspected. However, the use of biomarkers for neurodegeneration has not been fully incorporated into the clinical routine. With the development of cerebrospinal fluid (CSF) biomarkers that reflect pathological events within the central nervous system (CNS), important clinical diagnostic tools are becoming available. This review summarizes the most promising biomarker candidates that may be used to monitor different types of neurodegeneration and protein inclusions, as well as different types of metabolic changes, in living patients in relation to the clinical phenotype and disease progression over time. Our aim is to provide the reader with an updated lexicon on currently available biomarker candidates, how far they have come in development and how well they reflect pathogenic processes in different neurodegenerative diseases. Biomarkers for specific pathogenetic processes would also be valuable tools both to study disease pathogenesis directly in patients and to identify and monitor the effect of novel treatment strategies.

Ubiquitin/proteasome pathway impairment in neurodegeneration: therapeutic implications

The ubiquitin/proteasome pathway is the major proteolytic quality control system in cells. In this review we discuss the impact of a deregulation of this pathway on neuronal function and its causal relationship to the intracellular deposition of ubiquitin protein conjugates in pathological inclusion bodies in all the major chronic neurodegenerative disorders, such as Alzheimer's, Parkinson's and Huntington's diseases as well as amyotrophic lateral sclerosis. We describe the intricate nature of the ubiquitin/proteasome pathway and discuss the paradox of protein aggregation, i.e. its potential toxic/protective effect in neurodegeneration. The relations between some of the dysfunctional components of the pathway and neurodegeneration are presented. We highlight possible ubiquitin/proteasome pathway-targeting therapeutic approaches, such as activating the proteasome, enhancing ubiquitination and promoting SUMOylation that might be important to slow/treat the progression of neurodegeneration. Finally, a model time line is presented for neurodegeneration starting at the initial injurious events up to protein aggregation and cell death, with potential time points for therapeutic intervention.

Cytosolic aggregates perturb the degradation of nontranslocated secretory and membrane proteins

Protein aggregates are a common feature of numerous diseases and may have various detrimental effects that remain poorly understood. Here the authors show that one consequence of cytosolic aggregates is to selectively delay degradation of mislocalized secretory and membrane proteins, leading to their aberrant accumulation over time.

A wide range of diseases are associated with the accumulation of cytosolic protein aggregates. The effects of these aggregates on various aspects of normal cellular protein homeostasis remain to be determined. Here we find that cytosolic aggregates, without necessarily disrupting proteasome function, can markedly delay the normally rapid degradation of nontranslocated secretory and membrane protein precursors. In the case of mammalian prion protein (PrP), the nontranslocated fraction is recruited into preexisting aggregates before its triage for degradation. This recruitment permits the growth and persistence of cytosolic PrP aggregates, explaining their apparent “self-conversion” seen in earlier studies of transient proteasome inhibition. For other proteins, the aggregate-mediated delay in precursor degradation led to aggregation and/or soluble residence in the cytosol, often causing aberrant cellular morphology. Remarkably, improving signal sequence efficiency mitigated these effects of aggregates. These observations identify a previously unappreciated consequence of cytosolic aggregates for nontranslocated secretory and membrane proteins, a minor but potentially disruptive population the rapid disposal of which is critical to maintaining cellular homeostasis.

Proteomic analysis of rat hypothalamus revealed the role of ubiquitin-proteasome system in the genesis of DR or DIO

Obesity has become a global epidemic, contributing to the increasing burdens of cardiovascular disease and type 2 diabetes. However, the precise molecular mechanisms of obesity remain poorly elucidated. The hypothalamus plays a major part in regulating energy homeostasis by integrating all kinds of nutritional signals. This study investigated the hypothalamus protein profile in diet-induced obese (DIO) and diet-resistant (DR) rats using two dimensional gel electrophoresis (2-DE) combined with MALDI-TOF/TOF–MS analysis. Twenty-two proteins were identified in the hypothalamus of DIO or DR rats. These include metabolic enzymes, antioxidant proteins, proteasome related proteins, and signaling proteins, some of which are related to AMP-activated protein kinase (AMPK) signaling or mitochondrial respiration. Among these proteins, in comparison with the normal-diet group, Ubiquitin was significantly decreased in DR rats but not changed in DIO rats, while Ubiquitin carboxyl-terminal esterase L1 (UCHL-1) was decreased in DIO rats but not changed in DR rats. The expression level of Ubiquitin and UCHL-1 were further validated using Western blot analysis. Our study reveals that Ubiquitin and UCHL-1 are obesity-related factors in the hypothalamus that may play an important role in the genesis of DR or DIO by interfering with the integrated signaling network that control energy balance and feeding.

Proteomic characterization of aggregating proteins after the inhibition of the ubiquitin proteasome system

Protein aggregation, which is associated with the impairment of the ubiquitin proteasome system, is a hallmark of many neurodegenerative diseases. To better understand the contribution of proteasome inhibition in aggregation, we analyzed which proteins may potentially localize in chemically induced aggregates in human neuroblastoma tissue culture cells. We enriched for proteins in high-density structures by using a sucrose gradient in combination with stable isotope labeling with amino acids in cell culture (SILAC). The quantitative analysis allowed us to distinguish which proteins were specifically affected by the proteasome inhibition. We identified 642 potentially aggregating proteins, including the p62/sequestosome 1 and NBR1 ubiquitin-binding proteins involved in aggregation. We also identified the ubiquitin-associated protein 2 like (UBAP2L). We verified that it cofractionated with ubiquitin in the high-density fraction and that it was colocalized in the ubiquitin-containing aggregates after proteasome inhibition. In addition, we identified several chaperone proteins and used data from protein interaction networks to show that they potentially interact with distinct subgroups of proteins within the aggregating structures. Several other proteins associated with neurodegenerative diseases, like UCHL1, were identified, further underlining the potential of our analysis to better understand the aggregation process and proteotoxic stress caused by proteasome inhibition.

The role of DYRK1A in neurodegenerative diseases

Recent studies indicate that the dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) gene, which is located on chromosome 21q22.2 and is overexpressed in Down syndrome (DS), may play a significant role in developmental brain defects and in early onset neurodegeneration, neuronal loss and dementia in DS. The identification of hundreds of genes deregulated by DYRK1A overexpression and numerous cytosolic, cytoskeletal and nuclear proteins, including transcription factors, phosphorylated by DYRK1A, indicates that DYRK1A overexpression is central for the deregulation of multiple pathways in the developing and aging DS brain, with structural and functional alterations including mental retardation and dementia. DYRK1A overexpression in DS brains may contribute to early onset neurofibrillary degeneration directly through hyperphosphorylation of tau and indirectly through phosphorylation of alternative splicing factor, leading to an imbalance between 3R-tau and 4R-tau. The several-fold increases in the number of DYRK1A-positive and 3R-tau-positive neurofibrillary tangles in DS support this hypothesis. Moreover, the enhanced phosphorylation of amyloid precursor protein by overexpressed DYRK1A facilitates amyloidogenic amyloid precursor protein cleavage elevating Aβ40 and 42 levels, and leading to brain β-amyloidosis. Therefore, inhibiting DYRK1A activity in DS may serve to counteract the phenotypic effects of its overexpression and is a potential method of treatment of developmental defects and the prevention of age-associated neurodegeneration, including Alzheimer-type pathology.

Formation of distinct inclusion bodies by inhibition of ubiquitin-proteasome and autophagy-lysosome pathways

Accumulation of misfolded proteins is caused by the impairment of protein quality control systems, such as ubiquitin-proteasome pathway (UPP) and autophagy-lysosome pathway (ALP). In this study, the formation of inclusion bodies was examined after the blockade of UPP and/or ALP in A549 cells. UPP inhibition induced a single and large inclusion body localized in microtubule-organizing center. Interestingly, however, ALP inhibition generated dispersed small inclusion bodies in the cytoplasm. Tuberous sclerosis complex 2 was selectively accumulated in the inclusion bodies of UPP-inhibited cells, but not those of ALP-inhibited cells. Blockade of transcription and translation entirely inhibited the formation of inclusion body induced by UPP inhibition, but partially by ALP inhibition. Moreover, the simultaneous inhibition of two protein catabolic pathways independently developed two distinct inclusion bodies within a single cell. These findings clearly demonstrated that dysfunction of each catabolic pathway induced formation and accumulation of unique inclusion bodies on the basis of morphology, localization and formation process in A549 cells.

Steatohepatitic hepatocellular carcinoma (SH-HCC): a distinctive histological variant of HCC in hepatitis C virus-related cirrhosis with associated NAFLD/NASH

In explant livers with chronic hepatitis C (HCV-C) we have noted a distinctive histologic variant that we have termed steatohepatitic hepatocellular carcinoma (SH-HCC) with features resembling non-neoplastic steatohepatitis, including large droplet steatosis, ballooning of malignant hepatocytes, Mallory-Denk bodies, inflammation, and pericellular fibrosis. This study was undertaken to further describe the characteristics and prevalence of this histologic variant in HCV-C and any possible association with underlying risk factors for nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH). We selected two 2-year periods (mid-2003 to mid-2005 and 2007 to 2008), from which selected explant livers with HCV-C and HCC were examined to determine the characteristics and frequency of SH-HCC. The underlying cirrhotic liver was also reassessed for steatosis and evidence of steatohepatitis. Clinical records were consulted for concomitant NAFLD and NASH risk factors. The SH-HCC variant was found in a total of 22 of 62 HCC cases (35.5%). Fourteen of the 22 patients with SH-HCC (63.6%) had at least one known risk factor for NAFLD/NASH including diabetes (6 of 22, 27.3%), obesity (6 of 22, 27.3%), hypertension (11 of 22, 50%), and hyperlipidemia (5 of 22, 27.8%). In 14 of the 22 cases (63.6%) of SH-HCC, the non-neoplastic liver showed changes of NAFLD/NASH superimposed on otherwise typical features of HCV-C. In conclusion, in our series of HCV-C explants, approximately one-third of HCCs show a distinctive histological variant termed SH-HCC. Underlying risk factors for NAFLD and for NASH were identified in 63.6% of our cases. Moreover, non-neoplastic tissue in HCV-C explants showed changes of NAFLD/NASH in 63.6% of cases. These results suggest a possible NAFLD/NASH pathway leading to SH-HCC in the setting of HCV-C which requires further investigation in the future.

Enhanced expression of the ubiquitin-proteasome system in the myocardium from patients with dilated cardiomyopathy referred for left ventriculoplasty: an immunohistochemical study with special reference to oxidative stress

The ubiquitin (Ub)-proteasome system (UPS) is an important proteolytic mechanism for selecting and digesting cytotoxic proteins. The aim of this study is to elucidate expression and in situ localization of the UPS in the myocardium from patients with dilated cardiomyopathy (DCM) with refractory heart failure. The expression profile of the oxidative stress-induced cytotoxic proteins was also examined. Myocardium was obtained from 26 patients with DCM at the left ventriculoplasty. Ten normal autopsied hearts served as controls. Myocardial expressions of Ub and proteasomes were studied immunohistochemically. Oxidative stresses were examined in point of localization of the oxidation-induced modifier molecules (OMM). The relationship between immunohistochemical results and clinical parameters was also evaluated. Both Ub and proteasomes were stained positive in granular structures accumulating between the myofibrils and adjacent to nuclei in cardiomyocytes. The OMMs were also positive in the same Ub-positive granular structures. The area fraction of Ub, proteasomes and OMM was significantly higher in DCM hearts than in normal controls. Significant positive correlation was observed between the area fractions of Ub and plasma levels of brain natriuretic peptide (p = 0.046) in DCM hearts. In conclusion, enhanced expression of the UPS colocalized with OMM in cardiomyocytes may be involved in the pathophysiology of DCM hearts.

Role of ubiquitin-proteasome-mediated proteolysis in nervous system disease

Proteolysis by the ubiquitin-proteasome pathway (UPP) is now widely recognized as a molecular mechanism controlling myriad normal functions in the nervous system. Also, this pathway is intimately linked to many diseases and disorders of the brain. Among the diseases connected to the UPP are neurodegenerative disorders such as Alzheimer's, Parkinson's and Huntington's diseases. Perturbation in the UPP is also believed to play a causative role in mental disorders such as Angelman syndrome. The pathology of neurodegenerative diseases is characterized by abnormal deposition of insoluble protein aggregates or inclusion bodies within neurons. The ubiquitinated protein aggregates are believed to result from dysfunction of the UPP or from structural changes in the protein substrates which prevent their recognition and degradation by the UPP. An early effect of abnormal UPP in diseases of the nervous system is likely to be impairment of synaptic function. Here we discuss the UPP and its physiological roles in the nervous system and how alterations in the UPP relate to development of nervous system diseases. This article is part of a Special Issue entitled The 26S Proteasome: When degradation is just not enough!

The ubiquitin-proteasome pathway and synaptic plasticity

Proteolysis by the ubiquitin-proteasome pathway (UPP) has emerged as a new molecular mechanism that controls wide-ranging functions in the nervous system, including fine-tuning of synaptic connections during development and synaptic plasticity in the adult organism. In the UPP, attachment of a small protein, ubiquitin, tags the substrates for degradation by a multisubunit complex called the proteasome. Linkage of ubiquitin to protein substrates is highly specific and occurs through a series of well-orchestrated enzymatic steps. The UPP regulates neurotransmitter receptors, protein kinases, synaptic proteins, transcription factors, and other molecules critical for synaptic plasticity. Accumulating evidence indicates that the operation of the UPP in neurons is not homogeneous and is subject to tightly managed local regulation in different neuronal subcompartments. Investigations on both invertebrate and vertebrate model systems have revealed local roles for enzymes that attach ubiquitin to substrate proteins, as well as for enzymes that remove ubiquitin from substrates. The proteasome also has been shown to possess disparate functions in different parts of the neuron. Here I give a broad overview of the role of the UPP in synaptic plasticity and highlight the local roles and regulation of the proteolytic pathway in neurons.

The role of the ubiquitin proteasome pathway in keratin intermediate filament protein degradation

Lung injury, whether caused by hypoxic or mechanical stresses, elicits a variety of responses at the cellular level. Alveolar epithelial cells respond and adapt to such injurious stimuli by reorganizing the cellular cytoskeleton, mainly accomplished through modification of the intermediate filament (IF) network. The structural and mechanical integrity in epithelial cells is maintained through this adaptive reorganization response. Keratin, the predominant IF expressed in epithelial cells, displays highly dynamic properties in response to injury, sometimes in the form of degradation of the keratin IF network. Post-translational modification, such as phosphorylation, targets keratin proteins for degradation in these circumstances. As with other structural and regulatory proteins, turnover of keratin is regulated by the ubiquitin (Ub)-proteasome pathway. The degradation process begins with activation of Ub by the Ub-activating enzyme (E1), followed by the exchange of Ub to the Ub-conjugating enzyme (E2). E2 shuttles the Ub molecule to the substrate-specific Ub ligase (E3), which then delivers the Ub to the substrate protein, thereby targeting it for degradation. In some cases of injury and IF-related disease, aggresomes form in epithelial cells. The mechanisms that regulate aggresome formation are currently unknown, although proteasome overload may play a role. Therefore, a more complete understanding of keratin degradation--causes, mechanisms, and consequences--will allow for a greater understanding of epithelial cell biology and lung pathology alike.

Role of post-translational modifications in modulating the structure, function and toxicity of alpha-synuclein: implications for Parkinson's disease pathogenesis and therapies

A better understanding of the molecular and cellular determinants that influence the pathology of Parkinson's disease (PD) is essential for developing effective diagnostic, preventative and therapeutic strategies to treat this devastating disease. A number of post-translational modifications to alpha-syn are present within the Lewy bodies in the brains of affected patients and transgenic models of PD and related disorders. However, whether disease-associated alpha-syn post-translational modifications promote or inhibit alpha-syn aggregation and neurotoxicity in vivo remains unknown. Herein, we summarize and discuss the major disease-associated post-translational modifications (phosphorylation, truncation and ubiquitination) and present our current understanding of the effect of these modifications on alpha-syn aggregation and toxicity. Elucidating the molecular mechanisms underlying post-translation modifications of alpha-syn and the consequences of such modifications on the biochemical, structural, aggregation and toxic properties of the protein is essential for unravelling the molecular basis of its function(s) in health and disease. Furthermore, the identification of the natural enzymes involved in regulating the post-translational modifications of alpha-synuclein will yield novel and more tractable therapeutic targets to treat PD and related synucleinopathies.

Overexpression of the wild-type SPT1 subunit lowers desoxysphingolipid levels and rescues the phenotype of HSAN1

Mutations in the SPTLC1 subunit of serine palmitoyltransferase (SPT) cause an adult-onset, hereditary sensory, and autonomic neuropathy type I (HSAN1). We previously reported that mice bearing a transgene-expressing mutant SPTLC1 (tgSPTLC1(C133W)) show a reduction in SPT activity and hyperpathia at 10 months of age. Now analyzed at a later age, we find these mice develop sensory loss with a distal small fiber neuropathy and peripheral myelinopathy. This phenotype is largely reversed when these mice are crossed with transgenic mice overexpressing wild-type SPTLC1 showing that the mutant SPTLC1 protein is not inherently toxic. Simple loss of SPT activity also cannot account for the HSAN1 phenotype, since heterozygous SPTLC1 knock-out mice have reduced SPT activity but are otherwise normal. Rather, the presence of two newly identified, potentially deleterious deoxysphingoid bases in the tgSPTLC1(C133W), but not in the wild-type, double-transgenic tgSPTLC1(WT + C133W) or SPTLC1(+/-) mice, suggests that the HSAN1 mutations alter amino acid selectivity of the SPT enzyme such that palmitate is condensed with alanine and glycine, in addition to serine. This observation is consistent with the hypothesis that HSAN1 is the result of a gain-of-function mutation in SPTLC1 that leads to accumulation of a toxic metabolite.

The morbid anatomy of dementia in Parkinson's disease

Dementia in Parkinson's disease (PD/PDD) is a common complication with a prevalence of up to 50%, but the specific changes underlying the cognitive decline remain undefined. Neuronal degeneration resulting in the dysfunction of multiple subcortical neurochemical projection systems has been described along with Lewy body-type pathology in cortical and limbic regions. Advanced alpha-synuclein (alphaSyn) pathology is not necessarily sufficient for producing dementia and concomitant Alzheimer's disease (AD) change has also been proposed as a possible substrate of PDD. A lack of consensus in the extant literature likely stems from clinical heterogeneity and variable reliability in clinical characterisation as well as other historical and methodological issues. The concurrent presence of abnormally deposited alphaSyn, amyloid-beta and tau proteins in the PDD brain and the interaction of these molecules in a linked pathological cascade of AD and PD-related mechanisms may prove important in determining the underlying pathological process for the development of dementia in PD and this concept of combined pathologies awaits further investigation.

Copper-triggered aggregation of ubiquitin

Neurodegenerative disorders share common features comprising aggregation of misfolded proteins, failure of the ubiquitin-proteasome system, and increased levels of metal ions in the brain. Protein aggregates within affected cells often contain ubiquitin, however no report has focused on the aggregation propensity of this protein. Recently it was shown that copper, differently from zinc, nickel, aluminum, or cadmium, compromises ubiquitin stability and binds to the N-terminus with 0.1 micromolar affinity. This paper addresses the role of copper upon ubiquitin aggregation. In water, incubation with Cu(II) leads to formation of spherical particles that can progress from dimers to larger conglomerates. These spherical oligomers are SDS-resistant and are destroyed upon Cu(II) chelation or reduction to Cu(I). In water/trifluoroethanol (80∶20, v/v), a mimic of the local decrease in dielectric constant experienced in proximity to a membrane surface, ubiquitin incubation with Cu(II) causes time-dependent changes in circular dichroism and Fourier-transform infrared spectra, indicative of increasing β-sheet content. Analysis by atomic force and transmission electron microscopy reveals, in the given order, formation of spherical particles consistent with the size of early oligomers detected by gel electrophoresis, clustering of these particles in straight and curved chains, formation of ring structures, growth of trigonal branches from the rings, coalescence of the trigonal branched structures in a network. Notably, none of these ubiquitin aggregates was positive to tests for amyloid and Cu(II) chelation or reduction produced aggregate disassembly. The early formed Cu(II)-stabilized spherical oligomers, when reconstituted in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) liposomes and in POPC planar bilayers, form annular and pore-like structures, respectively, which are common to several neurodegenerative disorders including Parkinson's, Alzheimer's, amyotrophic lateral sclerosis, and prion diseases, and have been proposed to be the primary toxic species. Susceptibility to aggregation of ubiquitin, as it emerges from the present study, may represent a potential risk factor for disease onset or progression while cells attempt to tag and process toxic substrates.

Immunoreactivity to Lys63-linked polyubiquitin is a feature of neurodegeneration

The major human neurodegenerative diseases are characterised by ubiquitin-positive intraneuronal inclusions, however the precise nature of the ubiquitin modifications in these structures is unclear. Using a monoclonal antibody specific for Lys63-linked polyubiquitin we have performed the first immunohistochemical analysis of linkage-specific ubiquitination in vivo associated with neurodegeneration. Immunoreactivity was detected within the pathological lesions of Alzheimer's, Huntington's and Parkinson's disease brains, although staining of Lewy bodies in the substantia nigra in Parkinson's disease was rare, indicating a selective involvement of Lys63-linked polyubiquitin in inclusion biogenesis in this disorder. Immunoreactivity was also a feature in neurons of proteasome-depleted mice, suggesting a proteasomal contribution to the degradation of Lys63-linked polyubiquitinated proteins in vivo.

Hippocampal sclerosis with four-repeat tau-positive round inclusions in the dentate gyrus: a new type of four-repeat tauopathy

Hippocampal sclerosis is defined as selective neuronal loss and gliosis of the hippocampus with heterogeneous etiologies, including neurodegenerative tauopathies. We report a 78-year-old woman who presented with depression, in whom postmortem examination revealed almost complete loss of neurons with gliosis in the subiculum and CA1-3 regions of the hippocampus and abundant neuronal cytoplasmic inclusions in the dentate gyrus. The inclusions were round, slightly basophilic and argyrophilic, resembling Pick bodies. However, they were Gallyas- and 4-repeat tau-positive, and 3-repeat tau- and ubiquitin-negative. To our knowledge, the histopathological features in this case were different from those in hippocampal sclerosis or 4-repeat tauopathies reported previously. It is likely that this case is a new variant of 4-repeat tauopathy presenting with hippocampal sclerosis.

Intermediate filament transcription in astrocytes is repressed by proteasome inhibition

Increased expression of the astrocytic intermediate filament protein glial fibrillary acidic protein (GFAP) is a characteristic of astrogliosis. This process occurs in the brain during aging and neurodegeneration and coincides with impairment of the ubiquitin proteasome system. Inhibition of the proteasome impairs protein degradation; therefore, we hypothesized that the increase in GFAP may be the result of impaired proteasomal activity in astrocytes. We investigated the effect of proteasome inhibitors on GFAP expression and other intermediate filament proteins in human astrocytoma cells and in a rat brain model for astrogliosis. Extensive quantitative RT-PCR, immunocytochemistry, and Western blot analysis resulted unexpectedly in a strong decrease of GFAP mRNA to <4% of control levels [Control (DMSO) 100+/-19.2%; proteasome inhibitor (epoxomicin) 3.5+/-1.3%, n=8; P < or = 0.001] and a loss of GFAP protein in astrocytes in vitro. We show that the proteasome alters GFAP promoter activity, possibly mediated by transcription factors as demonstrated by a GFAP promoter-luciferase assay and RT(2) Profiler PCR array for human transcription factors. Most important, we demonstrate that proteasome inhibitors also reduce GFAP and vimentin expression in a rat model for induced astrogliosis in vivo. Therefore, proteasome inhibitors could serve as a potential therapy to modulate astrogliosis associated with CNS injuries and disease.

[Immunohistochemical study of nonspecific interstitial pneumonia and ubiquitin-positive pneumocytes in elderly patients]

AIM

The Ubiquitin (Ub)-proteasome system maintains cellular homeostasis through proteolysis, and Ub appears in the damaged cells of many organs. Nonspecific interstitial pneumonia (NSIP)in elderly patients was studied to clarify the relationship between Ub-positive cells, cellular damage, and resistance to therapy.

METHODS

Specimens of surgical lung biopsy with the NSIP pattern (NSIP/P) from 13 patients (mean age, 68 years old) were examined histologically and immunohistochemically. Pneumocytes examined under high-power microscopy were counted for eosinophilic inclusion bodies and Ub-positive cells. NSIP/P was histologically evaluated and cases were scored for erosion and intraluminal granulation tissue subtypes (polypoid, mural, or occluded) as lung injury markers. NSIP/P was subdivided into cellular NSIP and fibrosing NSIP according to the proportions of interstitial inflammation and fibrosis.

RESULTS

1) Six of 13 patients with NSIP/P had Ub-positive cells (Ub+ group), and all inclusions identified by light-microscope were positive for Ub. A greater number of Ub+ pneumocytes were found compared with the inclusions by light-microscope, and Ub immunostaining was useful for the detection of the inclusions. 2) Granulation tissue scores in the Ub+ group were significantly greater than in the Ub- group (p<0.05); there was no difference in granulation tissue subtypes between the groups. 3) Granulation tissue scores in fibrosing NSIP/P (including each subtype) were significantly greater than in cellular NSIP/P. 4) After a follow-up period, there was no correlation between Ub+ group and NSIP therapy resistance or between the granulation tissue subtypes and therapy resistance.

CONCLUSION

Some elderly patients with NSIP had inclusions, and these inclusions were Ub+. Pneumocyte injury might occur via the Ub-proteasome system pathway in elderly patients with NSIP/P, although there was no correlation between Ub+ pneumocytes and therapy resistance.

The role of the ubiquitin proteasome system in synapse remodeling and neurodegenerative diseases

The ubiquitin proteasome system is a potent regulatory mechanism used to control protein stability in numerous cellular processes, including neural development. Many neurodegenerative diseases are featured by the accumulation of UPS-associated proteins, suggesting the UPS dysfunction may be crucial for pathogenesis. Recent experiments have highlighted the UPS as a key player during synaptic development. Here we summarize recent discoveries centered on the role of the UPS in synapse remodeling and draw attention to the potential link between the synaptic UPS dysfunction and the pathology of neurodegenerative diseases.

Disruption of ubiquitin-mediated processes in diseases of the brain and bone

A role for ubiquitin in the pathogenesis of human diseases was first suggested some two decades ago, from studies that localized the protein to intracellular protein aggregates, which are a feature of the major human neurodegenerative disorders. Although several different mechanisms have been proposed to connect impairment of the UPS (ubiquitin-proteasome system) to the presence of these 'ubiquitin inclusions' within diseased neurones, their significance in the disease process remains to be fully clarified. Ubiquitin inclusions also contain ubiquitin-binding proteins, such as the p62 protein [also known as SQSTM1 (sequestosome 1)], which non-covalently interacts with the ubiquitinated protein aggregates and may serve to mediate their autophagic clearance. p62 is a multifunctional protein and, in the context of bone-resorbing osteoclasts, is an important scaffold in the RANK [receptor activator of NF-kappaB (nuclear factor kappaB)]-NF-kappaB signalling pathway. Further, mutations affecting the UBA domain (ubiquitin-associated domain) of p62 are commonly found in patients with the skeletal disorder PDB (Paget's disease of bone). These mutations impair the ability of p62 to bind to ubiquitin and result in disordered osteoclast NF-kappaB signalling that may underlie the disease aetiology. Recent structural insights into the unusual mechanism of ubiquitin recognition by the p62 UBA domain have helped rationalize the mechanisms by which different PDB mutations exert their negative effects on ubiquitin binding by p62, as well as providing an indication of the ubiquitin-binding selectivity of p62 and, by extension, its normal biological functions.

The Roc domain of leucine-rich repeat kinase 2 is sufficient for interaction with microtubules

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the leading cause of genetically inherited Parkinson's disease (PD). Although this multidomain protein has been shown to have both GTPase and kinase activities through the Roc and MAPKKK domains, respectively, the protein-protein interactions and pathways involved in LRRK2-mediated signaling remain elusive. Utilizing a combination of protein pull-down assays, mass spectrometry, Western blotting, and immunofluorescence microscopy, this study identifies and describes the interaction between LRRK2 and microtubules. The Roc or GTPase-like domain of LRRK2 is sufficient for interaction with alpha/beta-tubulin heterodimers. This interaction occurs in a guanine nucleotide-independent manner, suggesting that tubulin might not be an effector of the LRRK2 GTPase domain. The R1441C pathogenic mutation, located within the Roc domain, retains interaction with alpha/beta-tubulin heterodimers, suggesting that disruption of this interaction likely is not the mechanism whereby the R1441C mutation leads to disease. At a subcellular level, endogenous LRRK2 protein was found to colocalize with alpha/beta-tubulin in primary hippocampal neurons. These findings are significant in that they link LRRK2 with microtubules, a structural component of the cell that is critically involved in the pathogenesis of several neurodegenerative diseases, including PD.

Is malfunction of the ubiquitin proteasome system the primary cause of alpha-synucleinopathies and other chronic human neurodegenerative disease?

Neuropathological investigations have identified major hallmarks of chronic neurodegenerative disease. These include protein aggregates called Lewy bodies in dementia with Lewy bodies and Parkinson's disease. Mutations in the alpha-synuclein gene have been found in familial disease and this has led to intense focused research in vitro and in transgenic animals to mimic and understand Parkinson's disease. A decade of transgenesis has lead to overexpression of wild type and mutated alpha-synuclein, but without faithful reproduction of human neuropathology and movement disorder. In particular, widespread regional neuronal cell death in the substantia nigra associated with human disease has not been described. The intraneuronal protein aggregates (inclusions) in all of the human chronic neurodegenerative diseases contain ubiquitylated proteins. There could be several reasons for the accumulation of ubiquitylated proteins, including malfunction of the ubiquitin proteasome system (UPS). This hypothesis has been genetically tested in mice by conditional deletion of a proteasomal regulatory ATPase gene. The consequences of gene ablation in the forebrain include extensive neuronal death and the production of Lewy-like bodies containing ubiquitylated proteins as in dementia with Lewy bodies. Gene deletion in catecholaminergic neurons, including in the substantia nigra, recapitulates the neuropathology of Parkinson's disease.

Depletion of 26S proteasomes in mouse brain neurons causes neurodegeneration and Lewy-like inclusions resembling human pale bodies

Ubiquitin-positive intraneuronal inclusions are a consistent feature of the major human neurodegenerative diseases, suggesting that dysfunction of the ubiquitin proteasome system is central to disease etiology. Research using inhibitors of the 20S proteasome to model Parkinson's disease is controversial. We report for the first time that specifically 26S proteasomal dysfunction is sufficient to trigger neurodegenerative disease. Here, we describe novel conditional genetic mouse models using the Cre/loxP system to spatially restrict inactivation of Psmc1 (Rpt2/S4) to neurons of either the substantia nigra or forebrain (e.g., cortex, hippocampus, and striatum). PSMC1 is an essential subunit of the 26S proteasome and Psmc1 conditional knock-out mice display 26S proteasome depletion in targeted neurons, in which the 20S proteasome is not affected. Impairment of specifically ubiquitin-mediated protein degradation caused intraneuronal Lewy-like inclusions and extensive neurodegeneration in the nigrostriatal pathway and forebrain regions. Ubiquitin and alpha-synuclein neuropathology was evident, similar to human Lewy bodies, but interestingly, inclusion bodies contained mitochondria. We support this observation by demonstrating mitochondria in an early form of Lewy body (pale body) from Parkinson's disease patients. The results directly confirm that 26S dysfunction in neurons is involved in the pathology of neurodegenerative disease. The model demonstrates that 26S proteasomes are necessary for normal neuronal homeostasis and that 20S proteasome activity is insufficient for neuronal survival. Finally, we are providing the first reproducible genetic platform for identifying new therapeutic targets to slow or prevent neurodegeneration.

Ubiquitin-proteasome-mediated degradation of keratin intermediate filaments in mechanically stimulated A549 cells

We previously reported that shear stress induces phosphorylation and disassembly of keratin intermediate filaments (IFs). Shear stress also induces a time- and strain-dependent degradation of keratin IFs, and the current study examines the mechanisms involved in degradation of keratin proteins in human A549 cells exposed to 0-24 h of shear stress (7.5-30 dynes/cm(2)). Ubiquitin was found to be covalently associated with keratin proteins immunoprecipitated from shear-stressed cells, and pretreatment with the proteasomal inhibitor MG132 prevented the degradation of the keratin IF network. Importantly, phosphorylation of K8 Ser-73 is required for the shear stress-mediated ubiquitination, disassembly, and degradation of the keratin IF network. Immunofluorescence microscopy revealed that shear stress caused the thin array of keratin fibrils observed in control cells to be reorganized into a perinuclear aggregate, known as an aggresome, and that ubiquitin was also associated with this structure. Finally, the E2 enzymes, UbcH5b, -c, and Ubc3, but not E2-25K are required for the shear stress-mediated ubiquitin-proteasomal degradation of keratin proteins. These data suggest that shear stress promotes the disassembly and degradation of the keratin IF network via phosphorylation and the ubiquitin-proteasome pathway.

Neuronal cell death in neurodegenerative diseases: recurring themes around protein handling

Neuronal cell death plays a role in many chronic neurodegenerative diseases with the loss of particular subsets of neurons. The loss of the neurons occurs during a period of many years, which can make the mode(s) of cell death and the initiating factors difficult to determine. In vitro and in vivo models have proved invaluable in this regard, yielding insight into cell death pathways. This review describes the main mechanisms of neuronal cell death, particularly apoptosis, necrosis, excitotoxicity and autophagic cell death, and their role in neurodegenerative diseases such as ischaemia, Alzheimer's, Parkinson's and Huntington's diseases. Crosstalk between these death mechanisms is also discussed. The link between cell death and protein mishandling, including misfolded proteins, impairment of protein degradation, protein aggregation is described and finally, some pro-survival strategies are discussed.

TDP-43 immunoreactivity in anoxic, ischemic and neoplastic lesions of the central nervous system

TDP-43 proteinopathies are a newly categorized group of neurodegenerative diseases characterized by progressive cognitive and motor impairments associated with the abnormal accumulation and mislocalization of the nuclear TAR-DNA-binding protein-43 (TDP-43) in neurons and glia. Little is known about the expression and distribution of TDP-43 in normal and pathologic states. To determine whether TDP-43 inclusions arise in response to metabolic insults such as anoxia or ischemia, a panel of anoxic, ischemic and neoplastic lesions was examined for TDP-43 expression by immunohistochemistry. These lesions did not exhibit TDP-43 inclusions like those seen in neurodegenerative frontotemporal dementia and motor neuron disease. However, TDP-43 was found in Rosenthal fibers and eosinophilic granular bodies associated with low-grade tumors and reactive brain tissue. Furthermore, cytoplasmic TDP-43 was seen in M-phase tumor cells, but not in mitotic spindles. These findings expand our knowledge of the distribution and localization of TDP-43, and indicate that the TDP-43 inclusions seen in frontotemporal dementias and motor neuron diseases are specific to a neurodegenerative process.

Hypothalamic neurodegeneration and adult-onset obesity in mice lacking the Ubb polyubiquitin gene

Nearly all neurodegenerative diseases are associated with abnormal accumulation of ubiquitin (Ub) conjugates within neuronal inclusion bodies. To directly test the hypothesis that depletion of cellular Ub is sufficient to cause neurodegeneration, we have disrupted Ubb, one of four genes that supply Ub in the mouse. Here, we report that loss of Ubb led to a progressive degenerative disorder affecting neurons within the arcuate nucleus of the hypothalamus. This neurodegenerative cytopathology was accompanied by impaired hypothalamic control of energy balance and adult-onset obesity. Ubb was highly expressed in vulnerable hypothalamic neurons and total Ub levels were selectively reduced in the hypothalamus of Ubb-null mice. These findings demonstrate that maintenance of adequate supplies of cellular Ub is essential for neuronal survival and establish that decreased Ub availability is sufficient to cause neuronal dysfunction and death.

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.

Neuropathology for the neuroradiologist: plaques and tangles

Histologically identified intracellular and extracellular inclusions and structures often provide a tissue diagnosis of a specific disease process. Moreover, these deposits may provide clues about the pathogenesis of the disease in which they are found. Two distinctive structures seen within the brains of patients clinically diagnosed with dementia of the Alzheimer type are extracellular plaques and intracellular neurofibrillary tangles. The purpose of this report is to review the significance of plaques and neurofibrillary tangles in the context of Alzheimer disease.

Role of the ubiquitin proteasome system in Alzheimer's disease

Though Alzheimer's disease (AD) is a syndrome with well-defined clinical and neuropathological manifestations, an array of molecular defects underlies its pathology. A role for the ubiquitin proteasome system (UPS) was suspected in the pathogenesis of AD since the presence of ubiquitin immunoreactivity in AD-related neuronal inclusions, such as neurofibrillary tangles, is seen in all AD cases. Recent studies have indicated that components of the UPS could be linked to the early phase of AD, which is marked by synaptic dysfunction, as well as to the late stages of the disease, characterized by neurodegeneration. Insoluble protein aggregates in the brain of AD patients could result from malfunction or overload of the UPS, or from structural changes in the protein substrates, which prevent their recognition and degradation by the UPS. Defective proteolysis could cause the synaptic dysfunction observed early in AD since the UPS is known to play a role in the normal functioning of synapses. In this review, we discuss recent observations on possible links between the UPS and AD, and the potential for utilizing UPS components as targets for treatment of this disease.

Publication history: Republished from Current BioData's Targeted Proteins database (TPdb; ).

Role of the proteasome in ethanol-induced liver pathology

The ubiquitin-proteasome system has come to be known as a vital constituent of mammalian cells. The proteasome is a large nonlysosomal enzyme that acts in concert with an 8.5 kDa polypeptide called ubiquitin and a series of conjugating enzymes, known as E1, E2 and E3, that covalently bind multiple ubiquitin moieties in a polyubiquitin chain to protein substrates in a process called ubiquitylation. The latter process targets protein substrates for unfolding and degradation by the 26S proteasome. This enzyme system specifically recognizes and degrades polyubiquitylated proteins, many of which are key proteins involved in cell cycle regulation, apoptosis, signal transduction, and antigen presentation. The 26S proteasome contains a cylinder-shaped 20S catalytic core that, itself, degrades proteins in an ATP- and ubiquitin-independent manner. The 20S form is actually the predominant enzyme form in mammalian cells. Proteolysis by the constitutive 20S proteasome is vital in removing oxidized, misfolded and otherwise modified proteins. Such degradation is critical as a means of cellular detoxification, as intracellular accumulation of damaged and misfolded proteins is potentially lethal. Studies have shown that inhibition of proteasome activity can lead to cell death. Ethanol and its metabolism cause partial inhibition of the proteasome. This leads to a number of pleiotropic effects that can affect a variety of cellular processes. This critical review describes important aspects of ethanol metabolism and its influence on the proteasome. The review will summarize recent findings on: (1) the interactions between the proteasome and the ethanol metabolizing enzyme, CYP2E1; (2) the dynamics of proteasome inhibition by ethanol in animal models and cultured cells; (3) ethanol-elicited suppression of proteasome activity and its effect on signal transduction; (4) The role of proteasome inhibition in cytokine production by liver cells; and (5) ethanol elicited suppression of peptide hydrolysis and the potential effects on antigen presentation. While the principal focus is on alcohol-induced liver injury, the authors foresee that the findings presented in this review will prompt further research on the role of this proteolytic system in other tissues injured by excessive alcohol consumption.

Global changes to the ubiquitin system in Huntington's disease

Huntington's disease (HD) is a dominantly inherited neurodegenerative disorder caused by expansion of CAG triplet repeats in the huntingtin (HTT) gene (also called HD) and characterized by accumulation of aggregated fragments of polyglutamine-expanded HTT protein in affected neurons. Abnormal enrichment of HD inclusion bodies with ubiquitin, a diagnostic characteristic of HD and many other neurodegenerative disorders including Alzheimer's and Parkinson's diseases, has suggested that dysfunction in ubiquitin metabolism may contribute to the pathogenesis of these diseases. Because modification of proteins with polyubiquitin chains regulates many essential cellular processes including protein degradation, cell cycle, transcription, DNA repair and membrane trafficking, disrupted ubiquitin signalling is likely to have broad consequences for neuronal function and survival. Although ubiquitin-dependent protein degradation is impaired in cell-culture models of HD and of other neurodegenerative diseases, it has not been possible to evaluate the function of the ubiquitin-proteasome system (UPS) in HD patients or in animal models of the disease, and a functional role for UPS impairment in neurodegenerative disease pathogenesis remains controversial. Here we exploit a mass-spectrometry-based method to quantify polyubiquitin chains and demonstrate that the abundance of these chains is a faithful endogenous biomarker of UPS function. Lys 48-linked polyubiquitin chains accumulate early in pathogenesis in brains from the R6/2 transgenic mouse model of HD, from a knock-in model of HD and from human HD patients, establishing that UPS dysfunction is a consistent feature of HD pathology. Lys 63- and Lys 11-linked polyubiquitin chains, which are not typically associated with proteasomal targeting, also accumulate in the R6/2 mouse brain. Thus, HD is linked to global changes in the ubiquitin system to a much greater extent than previously recognized.

Oxidative stress induces the endoplasmic reticulum stress and facilitates inclusion formation in cultured cells

BACKGROUND/AIMS

The precise mechanism of formation and significance of Mallory bodies (MBs) are poorly understood. The endoplasmic reticulum (ER) is the organelle responsible for proper folding and elimination of unfolded proteins. Therefore, failure of this function increases defective proteins in the cell.

METHODS

We examined the effects of oxidative stress on induction of ER stress and keratin 8 and 18 (K8/18)-containing inclusion formation in cultured human hepatoma cells and hepatocytes by immunofluorescence and immunoblot analyses.

RESULTS

Generation of H(2)O(2) was detected in glucose oxidase (GO)-treated cells by 2',7'-dichlorodihydrofluorescein diacetate and co-treatment with GO and acetyl-leucyl-leucyl-norleucinal (ALLN), a proteasome inhibitor, induced formation of extensive keratin inclusions that were inhibited by pre-treatment with N-acetyl-cysteine. These inclusions shared similar features with MBs by immunofluorescence analysis. Electron microscopy showed that these structures appeared near the nuclei, surrounded by filamentous structures. GO and ALLN upregulated the expression of ER stress markers, however, 4-phenylbutyrate, a chemical chaperone, reduced formation of inclusions and expression of the ER stress markers.

CONCLUSIONS

The oxidative stress coupled with limited inhibition of the proteasome induces dysfunction of the ER and results in inclusion formation in cultured cells. This suggests that ER stress plays a role in MB formation in liver disease.

From Mallory to Mallory–Denk bodies: What, how and why?

Frank B. Mallory described cytoplasmic hyaline inclusions in hepatocytes of patients with alcoholic hepatitis in 1911. These inclusions became known as Mallory bodies (MBs) and have since been associated with a variety of other liver diseases including non-alcoholic fatty liver disease. Helmut Denk and colleagues described the first animal model of MBs in 1975 that involves feeding mice griseofulvin. Since then, mouse models have been instrumental in helping understand the pathogenesis of MBs. Given the tremendous contributions made by Denk to the field, we propose renaming MBs as Mallory-Denk bodies (MDBs). The major constituents of MDBs include keratins 8 and 18 (K8/18), ubiquitin, and p62. The relevant proteins and cellular processes that contribute to MDB formation and accumulation include the type of chronic stress, the extent of stress-induced protein misfolding and consequent proteasome overload, a K8-greater-than-K18 ratio, transamidation of K8 and other proteins, presence of p62 and autophagy. Although it remains unclear whether MDBs serve a bystander, protective or injury promoting function, they do serve an important role as histological and potential progression markers in several liver diseases.

Assembly of lysine 63-linked ubiquitin conjugates by phosphorylated alpha-synuclein implies Lewy body biogenesis

alpha-Synuclein (alpha-syn) and ubiquitin (Ub) are major protein components deposited in Lewy bodies (LBs) and Lewy neurites, which are pathologic hallmarks of idiopathic Parkinson disease (PD). Almost 90% of alpha-syn in LBs is phosphorylated at serine 129 (Ser(129)). However, the role of Ser(129)-phosphorylated alpha-syn in the biogenesis of LBs remains unclear. Here, we show that compared with coexpression of wild type (WT)alpha-syn and Ub, coexpression of phospho-mimic mutant alpha-syn (S129D) and Ub in neuro2a cells results in an increase of Ub-conjugates and the formation of ubiquitinated inclusions. Furthermore, S129D alpha-syn fails to increase the Ub-conjugates and form ubiquitinated inclusions in the presence of a K63R mutant Ub. In addition, as compared with WT alpha-syn, S129D alpha-syn increased cytoplasmic and neuritic aggregates of itself in neuro2a cells treated with H(2)O(2) and serum deprivation. These results suggest that the contribution of Ser(129)-phosphorylated alpha-syn to the Lys(63)-linked Ub-conjugates and aggregation of itself may be involved in the biogenesis of LBs in Parkinson disease and other related synucleinopathies.

Aging perturbs 26S proteasome assembly in Drosophila melanogaster

Aging is associated with loss of quality control in protein turnover. The ubiquitin-proteasome pathway is critical to this quality control process as it degrades mutated and damaged proteins. We identified a unique aging-dependent mechanism that contributes to proteasome dysfunction in Drosophila melanogaster. Our studies are the first to show that the major proteasome form in old (43-47 days old) female and male flies is the weakly active 20S core particle, while in younger (1-32 days old) flies highly active 26S proteasomes are preponderant. Old (43-47 days) flies of both genders also exhibit a decline (approximately 50%) in ATP levels, which is relevant to 26S proteasomes, as their assembly is ATP-dependent. The steep declines in 26S proteasome and ATP levels were observed at an age (43-47 days) when the flies exhibited a marked drop in locomotor performance, attesting that these are "old age" events. Remarkably, treatment with a proteasome inhibitor increases ubiquitinated protein levels and shortens the life span of old but not young flies. In conclusion, our data reveal a previously unknown mechanism that perturbs proteasome activity in "old-age" female and male Drosophila most likely depriving them of the ability to effectively cope with proteotoxic damages caused by environmental and/or genetic factors.