Brain diseases. Ubiquitous variations in nerves

Hydrogen-Deuterium Exchange Profiles of Polyubiquitin Fibrils

Ubiquitin and its polymeric forms are conjugated to intracellular proteins to regulate diverse intracellular processes. Intriguingly, polyubiquitin has also been identified as a component of pathological protein aggregates associated with Alzheimer's disease and other neurodegenerative disorders. We recently found that polyubiquitin can form amyloid-like fibrils, and that these fibrillar aggregates can be degraded by macroautophagy. Although the structural properties appear to function in recognition of the fibrils, no structural information on polyubiquitin fibrils has been reported so far. Here, we identify the core of M1-linked diubiquitin fibrils from hydrogen-deuterium exchange experiments using solution nuclear magnetic resonance (NMR) spectroscopy. Intriguingly, intrinsically flexible regions became highly solvent-protected in the fibril structure. These results indicate that polyubiquitin fibrils are formed by inter-molecular interactions between relatively flexible structural components, including the loops and edges of secondary structure elements.

Isolation and characterization of a minimal building block of polyubiquitin fibrils

As a posttranslational modifier, polyubiquitin is involved in the regulation of diverse intracellular processes; however, it is also found in pathological protein aggregates associated with Alzheimer's disease and other neurodegenerative disorders. We previously observed that various types of polyubiquitin can form amyloid-like fibrils; however, the structural properties of these polyubiquitin fibrils have not been examined at an atomic level. Here we demonstrate that a soluble intermediate species can be extracted from disulfide-conjugated diubiquitin fibrils after cleaving the disulfide bonds in the fibrils. This newly discovered molecule is structurally and physicochemically distinguishable from native ubiquitin. In addition, it is thermodynamically metastable, as demonstrated by real-time NMR measurements. Collectively, our results suggest that the fibril-derived molecule is a minimal building block of polyubiquitin fibrils that reflects their structural and physicochemical properties.

The evolving world of ubiquitin: transformed polyubiquitin chains

The regulation of diverse cellular events by proteins that have undergone post-translational modification with ubiquitin is well documented. Ubiquitin can be polymerized and eight types of polyubiquitin chain contribute to the complexity and specificity of the ubiquitin signal. Unexpectedly, recent studies have shown that ubiquitin itself undergoes post-translational modification by acetylation and phosphorylation; moreover, amyloid-like fibrils comprised of polyubiquitin chains have been discovered. Thus, ubiquitin is not only conjugated to substrate proteins, but also modified and transformed itself. Here, we review these novel forms of ubiquitin signal, with a focus on fibril formation of polyubiquitin chains and its underlying biological relevance.

The unexpected role of polyubiquitin chains in the formation of fibrillar aggregates

Ubiquitin is known to be one of the most soluble and stably folded intracellular proteins, but it is often found in inclusion bodies associated with various diseases including neurodegenerative disorders and cancer. To gain insight into this contradictory behaviour, we have examined the physicochemical properties of ubiquitin and its polymeric chains that lead to aggregate formation. We find that the folding stability of ubiquitin chains unexpectedly decreases with increasing chain length, resulting in the formation of amyloid-like fibrils. Furthermore, when expressed in cells, polyubiquitin chains covalently linked to EGFP also form aggregates depending on chain length. Notably, these aggregates are selectively degraded by autophagy. We propose a novel model in which the physical and chemical instability of polyubiquitin chains drives the formation of fibrils, which then serve as an initiation signal for autophagy.

The correlation between ubiquitin in the brainstem and sleep apnea in SIDS victims

BACKGROUND

The sudden infant death syndrome (SIDS) is still the main cause of postneonatal infant death and its etiology has stimulated many competing theories, among which is the role of hypoxia and brainstem abnormalities. One report claims an increased in ubiquitin in the liver of SIDS victims, ubiquitin being one of the heat-shock proteins. The correlation between ubiquitin in the brainstem and sleep apnea in SIDS was investigated here.

MATERIALS AND METHODS

Among 27,000 infants studied prospectively to characterize their sleep-wake behavior, 38 infants died under 6 months of age, including 26 cases of SIDS. All the infants had been recorded during one night in a pediatric sleep laboratory some 3-12 weeks before death. The frequency and duration of sleep apnea were analyzed. Brainstem material was collected at autopsy and examined immunohistochemically for ubiquitin. The density of ubiquitin-positive elements was measured semiquantitatively. Correlation analyses were carried out between the density of ubiquitin-positive elements and the data on sleep apnea.

RESULTS

In the victims of SIDS, a statistically significant positive correlation was found between the density of ubiquitin-positive neuronal factors in the pons and the frequency of obstructive apnea (p=0.001) and statistically significant negative correlations were seen between the density of ubiquitin-positive cells in the ependyma in the pons and the duration of obstructive apnea (p=0.044) and between the density of ubiquitin-positive cells in the subependyma in the medulla and the frequency of central apnea (p=0.024).

CONCLUSIONS

It was found that three significant associations existed between the pathological data referring to ubiquitin and physiological data in SIDS victims. These facts are in agreements with the association of sleep apnea in SIDS.

Kennedy's disease: a triplet repeat disorder or a motor neuron disease?

Two definite genetic causes of adult motor neuron degeneration have been identified to date: CAG repeat expansion in the androgen receptor gene in Kennedy's disease and point mutations in the SOD1 gene, encoding the enzyme, Cu/Zn superoxide dismutase, in some familial forms of amyotrophic lateral sclerosis. Although both have unrelated genetic causes, Kennedy's disease and SOD1-linked amyotrophic lateral sclerosis share several pathogenic features. First, expanded androgen receptor and mutant Cu/Zn superoxide dismutase have a propensity to aggregate into insoluble complexes and form inclusion bodies in affected neurons. Deposits of mutant proteins could be detrimental to neuronal viability by interfering with the normal housekeeping functions of chaperones and of the ubiquitin/proteasome system. Secondly, cytoskeletal function may be impaired in both diseases as decreased transactivational activity of expanded androgen receptor may cause an abnormal pattern of tubulin expression in motor neurons in Kennedy's disease and disruption of neurofilament organisation is a hallmark of amyotrophic lateral sclerosis. The concept of activation of overlapping cell death cascades by two distinct genetic defects could help elucidating downstream pathogenic processes and may provide novel targets for pharmacological intervention or gene therapy for the treatment of motor neuron disorders.

Structural and functional characterization of 20S and 26S proteasomes from bovine brain

Two proteins were isolated, in a stable form, from bovine brain by ion exchange chromatography, gel filtration and ultracentrifugation on glycerol gradient. They were identified as 20S and 26S proteasomes on the basis of molecular mass, migration velocity on non-denaturing gels, immunoreactivity, multipeptidase activity and the 26S proteasome also for dependence on ATP for the degradation of short peptides and ubiquitinylated proteins. However, the 26S proteasome has some properties not yet described for its counterpart of other tissues and from brain of this and other species. In particular, the ATP concentration required by the 26S proteasome to reach maximal peptidase activity was approximately 40-fold lower than the one required for maximal proteolytic activity on polyubiquitinylated substrates. Moreover, plots of substrate concentration vs. velocity gave a saturation curve for the 26S proteasome only, which, for the trypsin-like and post-glutamyl peptide hydrolase activities fitted the Michaelis-Menten equation, whereas for the chymotrypsin-like activity indicated multibinding site kinetics with positive cooperativity (n = 2.32+/-0.38). As concerns the 20S proteasome, its electrophoretic pattern on native gel revealed a single protein band, a feature, to our knowledge, not yet described for the brain particle of any species.

Unique characteristics of ubiquitin-bonded complex play a pathological role in dentatorubral-pallidoluysian atrophy

Abnormal complex formation of dentatorubral-pallidoluysian atrophy (DRPLA) protein and pathological ubiquitination of abnormal complex are two pathological processes involved in DRPLA neurodegeneration. Pathological ubiquitination and solubility in SDS and reducing agent are two unique characteristics of the DRPLA protein complex. Ubiquitination of abnormal DRPLA protein complex in DRPLA brain tissue is heat-resistant and stronger than that in control brain tissue. Pathological ubiquitination of DRPLA protein complex correlates with the onset of symptoms and the size of an expanded glutamine repeat in brain tissue of patients with DRPLA. Pathological ubiquitination plays an important role in DRPLA pathology. DRPLA protein complex is water-insoluble but soluble in SDS and reducing agent, and displays no difference in water insolubility between control and DRPLA brain tissue. Abnormal insoluble complex formation is not developed by a qualitative change in water insolubility of DRPLA protein complex but is developed by a spontaneous accumulation of an abnormally large amount of the DRPLA protein complex.

Abnormal dentatorubral-pallidoluysian atrophy (DRPLA) protein complex is pathologically ubiquitinated in DRPLA brains

Dentatorubral-pallidoluysian atrophy (DRPLA) is caused by expansion of a glutamine repeat in DRPLA protein. DRPLA protein undergoes greater complex formation in DRPLA brain tissue, and expanded glutamine repeat enhances complex formation of DRPLA protein. Immunoblots with and without reduction show that the DRPLA protein complex is ubiquitinated only in DRPLA brain tissue. Moreover, immunoblots of regional DRPLA brain tissues reveal that pathological ubiquitination of DRPLA protein complex is found selectively in affected lesions. Double-labeling immunohistochemical studies with antibodies against DRPLA protein and ubiquitin demonstrate that the DRPLA protein is co-localized with ubiquitin in DRPLA neurons and show characteristic neuronal cytoplasmic inclusions with ubiquitinated DRPLA protein complex in the center. Our findings suggest that DRPLA protein undergoes abnormal complex formation with expanded glutamine repeat, and then the complex is pathologically ubiquitinated in DRPLA brain tissue. Pathological ubiquitination of abnormal DRPLA protein complex plays a role in DRPLA pathology.

Cellular antioxidant properties of human natural killer enhancing factor B

The protein, NKEF (natural killer enhancing factor), has been identified as a member of an antioxidant family of proteins capable of protecting against protein oxidation in cell-free assay systems. The mechanism of action for this family of proteins appears to involve scavenging or suppressing formation of protein thiyl radicals. In the present study we investigated the antioxidant protective properties of the NKEF-B protein overexpressed in an endothelial cell line (ECV304). Nkef-B-transfected cells displayed significantly lower levels of reactive oxygen species (ROS) compared with control or vector-transfected cells. Tert-Butylhydroperoxide-induced ROS was 15% lower in nkef-B-transfected cells and cytotoxicity was slightly, though not significantly, lower. NKEF-B had no effect on ROS induced by menadione or xanthine plus xanthine oxidase. NKEF-B overexpression resulted in slightly (approximately 10%) lower levels of cellular glutathione (GSH) and had no effect on rate or extent of GSH depletion following either diethylmaleate (DEM) or buthionine sulfoximine (BSO) treatment. Lipid peroxidation, assessed as thiobarbituric acid-reactive substances, was 40% lower in nkef-B-transfected cells compared with vector-only-transfected cells. DEM-induced lipid peroxidation was suppressed by NKEF-B at DEM concentrations of 20 microM to 1 mM. At 10 mM DEM, lipid peroxidation was unaffected by NKEF-B. NKEF-B expression also protected cells against menadione-induced inhibition of [3H]-thymidine uptake. The NKEF-B protein appears most effective in suppressing basal low-level oxidative injury such as that produced during normal metabolism. These results indicate that overexpression of the NKEF-B protein promotes resistance to oxidative stress in this endothelial cell line.

Purification and properties of the 26S proteasome from the rat brain: evidence for its degradation of myelin basic protein in a ubiquitin-dependent manner

A ubiquitin(Ub)/ATP-dependent proteolytic complex (26S proteasome) was highly purified from the rat brain. The brain 26S proteasome consisted of 22-110 kDa subunits characteristic of the typical 26S proteasome on the basis of SDS-PAGE. The two-dimensional PAGE (NEPHGE and SDS-PAGE) pattern revealed that the pI values and molecular masses of the brain 26S proteasome subunits were similar to those of the subunits of 26S proteasomes purified from the rat liver and skeletal muscles. The enzymatic properties of the brain 26S proteasome were similar to those of the liver complex and also to the Ub-conjugate degrading activity in the cerebral cortex extract. Furthermore, it was found that the brain 26S proteasome was capable of degrading the myelin basic protein in a Ub-dependent manner. These results indicate that the brain contains the Ub-conjugate-degrading 26S proteasome, the subunit composition of which appears similar to those of the other tissues, and that the myelin basic protein may be a candidate physiological substrate for the brain 26S proteasome.

Correlation between anti-ubiquitin immunoreactivity and region-specific neuronal death in N-methyl-D-aspartate-treated rat hippocampal organotypic cultures

Neuronal degeneration appears to be associated with changes in anti-ubiquitin immunoreactivity (UIR). To elucidate the relationship between the two events, we examined the time course of changes in UIR in pyramidal neurons of hippocampal organotypic cultures following exposure to an excitotoxin, N-methyl-D-aspartate (NMDA). In nontreated cultures, weak UIR was confined to the nucleus. Exposure to 100 microM NMDA for 15 min induced degeneration of pyramidal neurons, within 24 h, in the CA1 and CA3c regions. In these neurons, the nuclear UIR was reduced, and instead, UIR developed in the cytoplasm. In response to the same procedure, CA3a,b pyramidal neurons showed slight shrinkage but otherwise virtually normal morphological features. Little perikaryal (cytoplasmic) UIR developed in CA3a,b neurons. Both degeneration and perikaryal UIR were observed in CA3a,b neurons, however, when the culture was exposed to 300 microM NMDA. Immunoblot analysis showed that changes in the amount of a ubiquitin protein conjugate (24 kDa), presumably ubiquitinated histone, are similar to those of nuclear UIR in the same time course. We propose that the changes in the expression of nuclear and perikaryal ubiquitinated proteins represent some process closely related to neuronal death.

Ubiquitin-protein conjugates in different structures of the central nervous system of the rat

The capacity to form ubiquitin (Ub)-protein conjugates was investigated in the cytosol of different structures of the rat central nervous system (CNS) in order to confirm the presence of this extralysosomal, adenosine triphosphate (ATP)-dependent, protein degradation system as well as its structural localization. Using 125I-Ub, we found that in the presence of ATP, the cytosol obtained from whole brains was able to form high molecular weight Ub-protein conjugates. These conjugates could be detected after sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and radioautography. The formation of these conjugates was much higher in the cerebral cortex than in the brain stem, which is mainly constituted by white matter, being intermediate in the cytosol isolated from whole brain total homogenates. These results suggested to us that under normal conditions the capacity to form Ub-protein conjugates was mainly located in structures containing neuronal cell bodies. Strong support for this contention was obtained when the cytosol isolated from rat optic nerves or from oligodendroglial cells isolated from whole brain was found to be totally unable to form Ub-protein conjugates. The inability of certain CNS structures to form conjugates with Ub could be attributed, among other reasons, to the lack of enzymes catalyzing the various steps of the Ub degradation system, to the absence of short half-life (target) proteins in those structures, or to the lack of activity of the enzymes catalyzing the reaction due to regulatory control mechanisms operating under normal conditions.

The soluble but not mitochondrially bound hexokinase is a substrate for the ATP- and ubiquitin-dependent proteolytic system

Intracellular protein degradation is highly selective, however, the mechanism(s) underlying this selectivity are not fully understood. We have previously shown that purified rabbit hexokinase type I, an enzyme present in mammalian brain both in soluble and mitochondrial bound form, is conjugate to ubiquitin and then degraded by a rabbit reticulocyte fraction II. In the present study we report that the mitochondrial bound hexokinase is stable for several hours in the same proteolytic system both in the presence or absence of ATP. E1, E2 and E3, the enzymes of the ubiquitin conjugating system, are able to incorporate 125I- or biotin-labelled ubiquitin in an ATP-dependent manner in soluble hexokinase as well as in a number of mitochondrial proteins. Furthermore, the mitochondria by themselves have a pronounced ATP-dependent ability to conjugate 125I-ubiquitin. However, Western blotting experiments, using a specific antibody against hexokinase, or against ubiquitin, showed that the mitochondrial bound enzyme is neither ubiquitinated nor degraded. This result has been confirmed by purification of bound hexokinase from the brain mitochondrial fraction or following the incubation of intact mitochondria with ATP, 125I-ubiquitin and E1, E2 and E3. Thus, mitochondrial bound hexokinase is not recognized by the ubiquitin conjugating system while the soluble enzyme is conjugate to ubiquitin and then degraded. Furthermore, the soluble hexokinase from rabbit brain was isolated by immunoaffinity chromatography and shown to be recognized by an anti-ubiquitin antibody. These results suggest that the intracellular distribution of protein is an important feature of a protein which determines its susceptibility to ubiquitin-dependent degradation.

Repetitious structure and transcription control of a polyubiquitin gene in Volvox carteri

Southern analysis indicated the presence of at least four ubiquitin gene loci in the Volvox carteri genome. Three of these, a polyubiquitin gene described here and a non-segregating ubiquitin gene pair, were assigned to two different linkage groups by RFLP mapping; the non-polymorphic fourth gene locus remained unassigned. The polyubiquitin gene was cloned and its 2,116-bp sequence determined. It contains six exons each interrupted by an intron at Gly35, and it encodes a pentameric polyubiquitin polypeptide consisting of five runs of 76 identical amino-acid residues and a C-terminal extension of one leucine. The five tandem repeats of coding units plus introns exhibit an unusually high degree of overall sequence identity indicating an efficient process of gene homogenization in this region of the V. carteri genome. S1 mapping revealed two closely-spaced transcription starts, 24 and 28 nucleotides downstream from a putative TATA sequence. Preceding the TATA box are two 14-bp conserved heat-shock elements (HSEs) and two octameric sequences closely resembling an yesat HSE. Consistent with a 1.6-kb transcript seen on Northern blots are two polyadenylation signals (TGTAA) located 99 bp and 169 bp downstream from the TGA translational stop. The polyubiquitin gene was transcribed throughout the Volvox life cycle with peaks in the 1.6-kb mRNA levels during pre-cleavage, cleavage, and post-inversion. In contrast, an 0.6-kb monoubiquitin transcript was abundant only at the pre-cleavage stage suggesting a different type of gene control. Heat shock increased the level of polyubiquitin mRNA, whereas the level of monoubiquitin mRNA was down-regulated.

The distribution of amyloid beta precursor protein in canine brain

The distribution of amyloid beta precursor protein (APP) in canine brain was investigated. By immunoblot analysis, APP-positive bands corresponding to proteins of 105-120 kilodalton were recognized in all canine brains regardless of the individual age of the dogs. Bands of similar molecular mass were also detected in the meninges, cerebrospinal fluid, and several visceral organs. Immunohistochemical studies were performed using cryostat and paraffin-embedded sections pretreated with formic acid or by the hydrated autoclave method. In the normal canine brain, APP was found to be distributed in the neurons and vascular system. In the brains with SP, obvious accumulation of APP was observed in swollen neurites within amyloid plaques, although the relationship between APP and diffuse plaques was unclear. APP accumulation in swollen axons was also seen around necrotic foci in the brain of one dog with necrotizing purulent encephalitis. These studies revealed that distribution of APP in canine tissues, especially in the brain, and the accumulation of APP in swollen neurites or axons.

Anti-ubiquitin immunoreactivity associates with pyramidal cell death induced by intraventricular infusion of leupeptin in rat hippocampus

Pathological studies on several neurodegenerative diseases including Alzheimer's disease have revealed common deposition of ubiquitin in many inclusion bodies. This implies a possible association of ubiquitin with neurodegeneration. To address this possibility, we examined histochemically the effect of intraventricular infusion of leupeptin, a thiol proteinase inhibitor, which is known to elevate anti-ubiquitin immunoreactivity in rat Purkinje cells. In the leupeptin-infused rat, an intense anti-ubiquitin immunoreactivity in the cytoplasm of neurons occurred not only in cerebellar Purkinje cells but also elsewhere in a wide area of the rat brain. The increase in the immunoreactivity was followed by a gradual depletion of pyramidal neurons in the hippocampal CA1 and CA3 subfields. The immunoreactive neurons disappeared concurrently. The number of anti-ubiquitin immunoreactive neurons was negatively correlated with that of surviving neurons when the duration of leupeptin infusion was varied. These results suggest that increased anti-ubiquitin immunoreactivity associates with neuronal death in leupeptin-treated rat brain.

Transfection-mediated expression of human Hsp70i protects rat dorsal root ganglian neurones and glia from severe heat stress

Considerable evidence suggests that the expression of heat shock proteins prior to a toxic insult (e.g. ischaemia, excitoxins, heat) can confer protection to neurones and glia. It is not certain which hsp(s) are involved in conveying these neuroprotective effects. Here we show that calcium phosphate-mediated transfection of dorsal root ganglia with an EF-1 alpha promoter-hsp70i expression vector significantly increased the survival of neurones and glia exposed to a severe heat stress. These data suggest that overexpression of hsp70i plays an important role in protecting neurones and glia from the denaturing effects of severe thermal stress. Inducing the expression of specific hsps may lead to the development of novel treatment strategies for CNS diseases.

Reduced numbers and intense anti-ubiquitin immunostaining of bovine motor neurons affected with spinal muscular atrophy

Motor neurons in the spinal cord affected with bovine spinal muscular atrophy (SMA) were investigated immunohistochemically using antibodies against bovine ubiquitin. Anti-ubiquitin immunostained many chromatolytic and swollen degenerating motor neurons in the ventral horn of the SMA-affected spinal cord. The most severely swollen cells showed a lightly-stained center and a strongly-stained periphery after immunostaining. However, there were many dark, shrunken neurons in a more advanced stage that showed a completely negative reaction when immunostained. Motor neuron counts differed significantly between SMA-affected and normal animals at the lumbar intumescence and at the fourth lumbar neuromere, but not at the brachial intumescence or the second cervical level.

Opposite effects of axon damage on heat shock proteins (hsp 70) and ubiquitin contents in motor neurons of neuropathic rats

Alteration in the motoneurone contents of heat shock protein (hsp 70) and ubiquitin were studied in rats which had been subject to loose ligation of one common sciatic nerve. This results in a unilateral peripheral neuropathy which peaks at 14 days following ligation and is characterized by transient degeneration of both myelinated and unmyelinated nerve fibres, abnormal motor behaviours (posture of the hind limb, walking patterns) and thermal and mechanical allodynia of the hind paw. Hsp 70 and ubiquitin are proteins involved in protein metabolism and their expression is regulated during cellular stress. The contralateral unlesioned side was used as control. Motoneurone staining for hsp 70 and ubiquitin were differentially altered at the peak of the neuropathy. Axon damage resulted in a decrease in hsp 70 labeling while ubiquitin staining increased. At the same time motoneurones undergoing axon damage overstained for the immediate early gene encoded protein c-JUN and for nerve growth factor receptor (rNGF). In contrast, no clear alteration was seen, at that time, in the intensity of labeling for calcitonin gene-related peptide (CGRP). This study demonstrates that peripheral neuropathy resulting from loose ligation of the common sciatic nerve not only produces sensory alterations as previously reported but also leads to pronounced alterations in motoneurone functioning that could partly explain the observed abnormal motor behaviours. Results are discussed in accordance with presumed roles for hsp 70 and ubiquitin in protein metabolism and in relationship with possible interaction with c-JUN and rNGF expressions.

Changes in heat shock protein 70 and ubiquitin mRNA levels in C1300 N2A mouse neuroblastoma cells following treatment with iron

We have shown that following heat shock (42.5 degree C for 30 min), mouse-derived C1300 N2A neuroblastoma cells contain increased levels of mRNA coding for the inducible form of heat shock protein 70 and for ubiquitin. Incubation of C1300 cells with iron also induces an elevation in content of mRNAs coding for the same two proteins that can be blocked by alpha-tocopherol and desferrioxamine. Iron was shown to increase mitochondrial and lysosomal activities in differentiated C1300 N2A cultures, as shown by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and neutral red cytotoxicity assays. These responses were not initially associated with any loss of viability, as assessed by the lactate dehydrogenase release assay. These results suggest that there is production of cytoprotective heat shock proteins in response to iron-mediated cell damage, probably involving free radical generation, in neural cells. The apparent stress response of vulnerable neurones in human neurodegenerative diseases, particularly Parkinson's disease, may be induced by iron-mediated free radical production in degenerating neurones, making investigation of the mechanism of free radical-induced responses in neuronal cells of special interest.

Immunocytochemical localization of ubiquitin at human neuromuscular junctions

Using several specific monoclonal and polyclonal antibodies, we found that ubiquitin is highly concentrated in the post-synaptic domain of human neuromuscular junctions. The distribution and pattern of ubiquitin immunoreactivity is identical to the localization of bound alpha-bungarotoxin, suggesting that ubiquitin may be involved in post-translational modification or turnover of the acetylcholine receptor or other junctional proteins of the muscle fibre.

Pathologic changes in olfactory neurons in Alzheimer's disease

Olfactory deficits and degenerative changes in central olfactory pathways are prominent in patients with Alzheimer's disease (AD). We hypothesized that peripheral olfactory neurons that reside in the nasal epithelium would show degenerative changes similar to the characteristic pathologic features of AD brain. Immunohistochemical studies of nasal tissue taken at autopsy reveal extensive degeneration in the sensory epithelium as well as abnormal neurites that share immunoreactive epitopes with dystrophic neurites and neurofibrillary tangles of the AD brain. The neuritic masses are stained with well-characterized monoclonal antibodies that do not normally stain olfactory neurons but which are very reactive with dystrophic neuritic structures and neurofibrillary tangles in AD brain. These include antibodies to phosphorylated and nonphosphorylated neurofilament subunits, tau, and also ALZ50, which is characteristically reactive with AD but not with normal brains. Such changes are present in 81% of AD patients. Similar accumulations of ectopic neurites are found in the olfactory epithelium of about 22% of non-demented patients. Preliminary statistical analysis fails to reveal any age-linked association. It has been proposed that the aged monkey is a good model for AD inasmuch as amyloid accumulations similar to those of humans are found in monkey brain. We examined a series of 13 rhesus monkeys, including aged animals with behavioral deficits. Although the olfactory epithelium was very similar to that of humans, no abnormal olfactory structures were observed. Aged rhesus monkeys do not appear to be a good model for the neuritic abnormalities of AD.

The gene for human neurone specific ubiquitin C-terminal hydrolase (UCHL1, PGP9.5) maps to chromosome 4p14

Ubiquitin carboxy terminal hydrolase 1, UCHL1, is a neurone-specific protein involved in the ubiquitin-mediated proteolytic pathway. The gene for human UCHL1 has been mapped to chromosome 4 using the polymerase chain reaction to amplify specifically the human UCHL1 sequences in rodent/human somatic cell hybrid DNA. A regional assignment of this locus to 4p14 has been made by in situ hybridization to metaphase chromosomes using both tritium and fluorescently labelled probes.

Immunolocalization of ubiquitin in muscle biopsies of patients with inclusion body myositis and oculopharyngeal muscular dystrophy

In 10/10 inclusion body myositis (IBM) patients and 2/2 oculopharyngeal muscular dystrophy (OPMD) patients, vacuolated muscle fibers contained darkly stained ubiquitin (Ub)-immunoreactive cytoplasmic inclusions. By electronmicroscopy, Ub-immunoreactive material was strictly localized to the 15-21 nm pathologic cytoplasmic tubulofilaments (CTFs). None of 18 control muscle biopsies contained the Ub-immunoreactive inclusions that are typical for IBM and OPMD. Thus, (a) finding that CTFs are ubiquitinated places their protein in the Ub-mediated turnover pathway and provides their first molecular marker; (b) easy accessibility, as compared to the central nervous system, of muscle tissue containing ubiquitinated inclusions should be advantageous for biochemical and molecular studies and may provide information important to both systems.

Identification of a ubiquitin- and ATP-dependent protein degradation pathway in rat cerebral cortex

To investigate the existence of a ubiquitin-dependent protein degradation system in the brain, the proteolytic activity of the cerebral cortex was examined. The soluble extract of rat cerebral cortex degraded 125I-radiolabeled lysozyme in an ATP-dependent manner. The ATP-dependent proteolysis was suppressed with iodoacetamide, which inhibits ubiquitin conjugation, and was abolished by blocking of the amino residues of lysozyme. These results suggest the participation of ubiquitination in the proteolytic activity. An ATP-dependent 125I-ubiquitin-conjugating activity was detected in fraction II from the cerebral cortex. The presence of ATP-dependent proteolytic activity which acted preferentially on ubiquitinated lysozyme was demonstrated, using ubiquitin-125I-lysozyme conjugates as a substrate. The proteinase had a molecular mass of 1500 kDa and displayed nucleotide dependence and sensitivity to various proteinase inhibitors similar to those of the 26S proteinase complex found in reticulocytes. Dialysis of the soluble fraction caused a decrease in the proteolytic activity of ATP-dependent and preferential for ubiquitin-lysozyme conjugates and a reciprocal increase in the ATP-independent free 125I-lysozyme-degrading activity which was scarcely detected before dialysis. The former ATP-dependent proteolytic activity may play a physiological role in the brain.

Dystrophic neurites around amyloid plaques of human patients with Gerstmann-Sträussler-Scheinker disease contain ubiquitinated inclusions

Dystrophic neurites have been previously observed around prionic protein-derived amyloid plaques of Gerstmann-Sträussler-Scheinker (GSS) disease. Ubiquitin (Ubq) immunohistochemistry reveals the presence of dot-like stainings around many of these plaques. In order to determine the nature of ubiquitinated deposits, we performed an immunogold electron microscope study on autoptic samples from the cerebellum of a GSS patient. Both pre- and post-embedding staining methods showed Ubq-positive dense bodies and filamentous structures, belonging to dystrophic neurites. They are analogous to ubiquitinated neuritic processes described around cerebellar amyloid plaques of Alzheimer's disease (AD). These results suggest that amyloid deposition is responsible for the degeneration of adjacent axon terminals in both AD and GSS.

Neuronal inclusions of Parkinson's disease

Two distinct neuronal inclusions occur in Parkinson's disease. The Lewy body is the diagnostic hallmark and is recognized by its eosinophilic body and unstained halo. It can be found in specific regions of the nervous system, where its frequency, size, shape, and structure differ. Large neurons of the dorsal vagal nucleus and sympathetic ganglia often contain particularly large quantities of Lewy-body-like matter. It consists of filament in the outer part and electron dense material in the core, the outer part staining with silver and with antibodies to neurofilament and tubulin. The pale body is restricted to the substantia nigra and locus ceruleus. It does not react with conventional stains, silver, or neurofilament antibodies, and has a homogeneous structure with a granular and vesicular surface texture. It contains sparse granular matter, vacuoles, and filaments, surrounded by melanin. The Lewy body and pale body may be juxtaposed or contiguous in some cells, but their distinct appearances and structures indicate that they are separate inclusions.

Activation of polyubiquitin gene expression during developmentally programmed cell death

Ubiquitin, a highly conserved 76 amino acid protein, plays a role in targeting intracellular proteins for degradation. Ubiquitin expression was examined during the developmentally programmed atrophy and degeneration of the intersegmental muscles (ISMs) in the hawk-moth, Manduca sexta. A clone containing nine repeats of the ubiquitin coding sequence was isolated from an ISM cDNA library and was used as a probe to examine polyubiquitin expression during development. When the ISMs became committed to degenerate, polyubiquitin gene expression increased dramatically. Injection of 20-hydroxyecdysone, which delays degeneration in this system, prevented the increase in polyubiquitin mRNA. The expression of polyubiquitin occurred without apparent activation of the cell's heat shock response. These data suggest that ubiquitin plays a role in programmed cell death.

Isolation and quantitation of ubiquitin from rat brain

A fast and sensitive method for the isolation and quantitation of cytoplasmic ubiquitin from brain by reversed-phase high-performance liquid chromatography is described. Cytosol from brain tissue was obtained by differential centrifugation and, after perchloric acid treatment, the sample was concentrated and ubiquitin was quantitatively isolated by means of a single chromatographic run. The amino acid composition, molecular weight, and primary structure of the pure protein were identified. The addition of monoiodinated 125I-ubiquitin to the sample as an internal standard indicated high native ubiquitin recovery. Statistical analysis carried out on different preparations and standardization of the chromatographic system indicated both the accuracy and the reproducibility of the method.

Ubiquitin in Chlamydomonas reinhardii. Distribution in the cell and effect of heat shock and photoinhibition on its conjugate pattern

Ubiquitin, a highly conserved 76-amino-acid protein, is involved in the response of many types of eukaryotic cells to stress but little is known about its role in lower plants. In the present study we have investigated the distribution of ubiquitin in the unicellular alga Chlamydomonas reinhardii as well as the effect of heat and light stress on its conjugation to cellular proteins. Immunoelectron microscopy shows that ubiquitin is located in the chloroplast, nucleus, cytoplasm, pyrenoid and on the plasma membrane. The location of ubiquitin within chloroplasts has not been observed previously. In immunoblots of whole cell extracts with an antibody to ubiquitin a prominent conjugate band with an apparent molecular mass of 29 kDa and a broad region of high-molecular-mass conjugates (apparent molecular mass greater than 45 kDa) were observed. Exposure of cells to a 41.5 degrees C heat shock in both the dark and light caused the disappearance of the 29-kDa conjugate and an increase in the high-molecular-mass conjugates. After step down to 25 degrees C the 29-kDa conjugate reappeared while the levels of high-molecular-mass conjugates decreased. In light, the recovery of the 29-kDa band was more rapid than in the dark. Photoinhibition alters the ubiquitin conjugation pattern similarly to heat shock, but to a lesser degree. These observations imply that, in Chlamydomonas, ubiquitin has a role in the chloroplast and in the response to heat and light stress.

Ubiquitinated filamentous inclusions in spinal cord of patients with motor neuron disease

The ultrastructural localization of ubiquitin (Ubq) in spinal cord of 2 cases of amyotrophic lateral sclerosis was studied, using immunoperoxidase and immunogold labeling on Vibratome sections or on sections cut from paraffin blocks. Two different types of ubiquitinated cytoplasmic inclusions were observed: (1) bundles composed of 10-15 nm filaments; (2) small rounded bodies without a limiting membrane. A panel of antibodies to neurofilaments (NFs) did not stain the ubiquitinated bundles, and decorated only axonal swellings. Ubq-positive filamentous deposits could be identified with inclusions previously described ultrastructurally. The absence of staining with antibodies to NFs might be due to abnormalities of the filaments, possibly because of a dysfunction of the ubq proteolytic system.

The structure of the human gene encoding protein gene product 9.5 (PGP9.5), a neuron-specific ubiquitin C-terminal hydrolase

Database search using a bovine thymus ubiquitin C-terminal hydrolase sequence indicated 54% sequence identity with the abundant human neuron-specific protein gene product 9.5 (PGP9.5), which was then shown to possess the same activity [Wilkinson, Lee, Deshpande, Duerksen-Hughes, Boss & Pohl (1989) Science 246, 670-673]. A yeast counterpart of the enzyme is also known. The human PGP9.5 gene, described here, spans 10 kb, contains nine exons and displays 5' features some common to many genes and some common with neurofilament neuron-specific enolase and Thy-1-antigen gene 5' regions.

ATP-induced loss of Alz-50 immunoreactivity with the A68 proteins from Alzheimer brain is mediated by ubiquitin

The Alz-50 immunoreactive proteins, designated A68, are detected by electrophoretic blot analysis of 100,000 x g pellet fractions of brain tissue from individuals with Alzheimer disease (AD). In exploring the biochemical nature of these proteins, we have found that a preincubation of such fractions with 5 mM ATP results in loss of Alz-50 immunoreactivity on immunoblots. The loss of antigenicity is complete after a 1-hr incubation at 37 degrees C and is stringently dependent on ATP. Hydrolysis of ATP is required, since the inhibition is not supported by the nonhydrolyzable analog adenosine 5'-[gamma-thio]triphosphate (ATP[gamma S]) and is prevented when the ATPase inhibitors o-vanadate and oligomycin are present. Upon further characterization, it was found that certain protease inhibitors, phenylmethylsulfonyl fluoride, antipain, tosylphenylalanine chloromethyl ketone, and aprotonin prevent the loss of the epitope. This suggests that hydrolysis of ATP is coupled with proteolysis of A68, leading to loss of Alz-50 immunoreactivity. Since a variety of proteins are believed to be degraded by an ATP/ubiquitin-dependent pathway, a possible role for ubiquitin (Ub) in this effect was investigated. Two polyclonal antibodies against Ub protected A68 from proteolysis and were also effective in immunoprecipitating A68 after incubation with ATP in the presence of Ub and phenylmethylsulfonyl fluoride. The proteolysis of A68 was also blocked by hemin, an inhibitor of the protease that cleaves Ub-protein conjugates. Taken together, these findings indicate that loss of Alz-50 immunoreactivity with A68 is due to ATP-dependent/Ub-mediated proteolysis. This mechanism may be relevant to the physiological role for A68 in AD or it may simply represent an attempt to abort an aberrant protein.

Glial cytoplasmic inclusions in the CNS of patients with multiple system atrophy (striatonigral degeneration, olivopontocerebellar atrophy and Shy-Drager syndrome)

Glial cytoplasmic inclusions (GCIs) were demonstrated by silver staining, immunocytochemistry and by electron microscopy in the central nervous system (CNS) of 11 patients with various combinations of striatonigral degeneration, olivopontocerebellar atrophy and Shy-Drager syndrome. Although their configuration in light microscope can sometimes resemble neurofibrillary tangles, their cellular localisation, measurements, ultrastructure, immunocytochemical characteristics and regional distribution all differ from these Alzheimer type changes. The majority of GCIs were localized in the white matter and appeared to be accompanied by an increase in the number of interfascicular oligodendroglial cells and pallor or loss of myelin staining. Our histological, ultrastructural and immunocytochemical findings all indicate that the cells which contain GCIs are oligodendrocytes and the inclusions themselves are composed of tubular structures. The presence of the until now unknown GCIs in all the 11 CNS, but not in age- and sex-matched control brains, indicates that GCI is a cellular change characteristic of multiple system atrophy and the three syndromes are various manifestations of the same disease.

Inclusion bodies in motor cortex and brainstem of patients with motor neurone disease are detected by immunocytochemical localisation of ubiquitin

Histological sections of cerebral motor cortex, brainstem, and spinal cord from 10 cases of clinically diagnosed motor neurone disease (MND) and 10 control cases were examined by conventional histology and immunocytochemical methods to localise ubiquitin. Intracytoplasmic inclusion bodies were identified in motor neurones of hypoglossal nuclei and appeared specific for MND. Similar inclusions were found in both large pyramidal cells and small neurones in the motor cortex, and were restricted to 4 cases having the amyotrophic lateral sclerosis form of MND with severe degeneration of corticospinal tracts. As reported in earlier studies, cellular inclusion bodies were identified in motor neurones of spinal cord from cases of MND but not in control material. Ubiquitin inclusions in motor neurones appear to be markers for the degenerative process causing neuronal loss in MND and there appears to be a close association between the anatomical location of inclusions and clinical manifestations of disease.

Pick bodies in the locus ceruleus

In classical Pick's disease with typical Pick bodies, inclusions resembling those present in the cerebral cortex are frequently found in the locus ceruleus. In three such cases Pick bodies were studied by light and electron microscopy and compared with Lewy bodies, inclusions more commonly found in this location. In contrast to the situation in the cerebral cortex, nerve cells with multiple Pick bodies were often found in the locus ceruleus, but in other respects definite light and electron microscopic differences between Pick bodies and Lewy bodies were present. Pick bodies were slightly basophilic and never had a central core or a peripheral halo. They were intensely argyrophilic. Differences in immunocytochemical reactions were especially marked with antibodies to tau and to paired helical filaments. Pick bodies displayed an intense reaction with these two antibodies, contrasting with that of Lewy bodies, which either lacked reactivity or reacted in a peripheral band. By electron microscopy the Pick bodies were composed of random filaments with smooth contour, whereas typical Lewy bodies had fuzzy deposits on filaments that radiated from a central core. Pick bodies in the locus ceruleus therefore maintained their immunocytochemical and electron microscopic characteristics and did not take on the character of Lewy bodies. Such differences point to a different pathogenesis and perhaps etiology of these two types of inclusions and attest to the marked difference clinically and pathologically between Pick's and Parkinson's diseases.