Ubiquitin in Alzheimer and other Neurodegenerative Diseases. In: Perry G, editor. Alterations in the Neuronal Cytoskeleton in Alzheimer Disease. Boston: Springer US; 1988. pp. 53-9. [DOI: 10.1007/978-1-4613-1657-2_5]

Odorants as cell-type specific activators of a heat shock response in the rat olfactory mucosa

Heat shock, or stress, proteins (HSPs) are induced in response to conditions that cause protein denaturation. Activation of cellular stress responses as a protective and survival mechanism is often associated with chemical exposure. One interface between the body and the external environment and chemical or biological agents therein is the olfactory epithelium (OE). To determine whether environmental odorants affect OE HSP expression, rats were exposed to a variety of odorants added to the cage bedding. Odorant exposure led to transient, selective induction of HSP70, HSC70, HSP25, and ubiquitin immunoreactivities (IRs) in supporting cells and subepithelial Bowman's gland acinar cells, two OE non-neuronal cell populations involved with inhalant biotransformation, detoxification, and maintenance of overall OE integrity. Responses exhibited odor specificity and dose dependency. HSP70 and HSC70 IRs occurred throughout the apical region of supporting cells; ubiquitin IR was confined to a supranuclear cone-shaped region. Electron microscopic examination confirmed these observations and, additionally, revealed odor-induced formation of dense vesicular arrays in the cone-like regions. HSP25 IR occurred throughout the entire supporting cell cytoplasm. In contrast to classical stress responses, in which the entire array of stress proteins is induced, no increases in HSP40 and HSP90 IRs were observed. Extended exposure to higher odorant doses caused prolonged activation of the same HSP subset in the non-neuronal cells and severe morphological damage in both supporting cells and olfactory receptor neurons (ORNs), suggesting that non-neuronal cytoprotective stress response mechanisms had been overwhelmed and could no longer adequately maintain OE integrity. Significantly, ORNs showed no stress responses in any of our studies. These findings suggest a novel role for these HSPs in olfaction and, in turn, possible involvement in other normal neurophysiological processes.

Ubiquitin and ubiquitin-protein conjugates in PC12h cells: changes during neuronal differentiation

Ubiquitin and ubiquitin-protein conjugates in PC12h cells were detected with in vitro [125I]ubiquitination, and quantified by immunoblotting. These levels were altered by nerve growth factor (NGF), which promotes neuronal differentiation. (i) Levels of high molecular weight (HMW) ubiquitin-protein conjugates ranging from 40 to 1,000 kDa were increased by 2 days of NGF treatment, and remained high up to 10 days of NGF treatment. (ii) Ubiquitin and a 23-kDa conjugate tended to be decreased from days 2 to 10 of NGF treatment. 10-Day culture with 10 nM staurosporine, n protein kinase inhibitor, that blocks NGF-induced neurite outgrowth suppressed the NGF-induced increases in levels of HMW conjugates. Cyclic AMP and forskolin, both of which promote neurite outgrowth, mimicked the NGF-induced changes in ubiquitin and HMW conjugates, but phorbol ester and epidermal growth factor had little effect. These findings suggest that changes in ubiquitin-protein conjugates are closely coupled with neuronal differentiation.

Modified Bielschowsky stain and immunohistochemical studies on striatal plaques in Alzheimer's disease

The nature of senile plaques (SP) in the striatum in 14 cases of Alzheimer's disease (AD) was investigated with the modified Bielschowsky stain and immunohistochemistry using antibodies to a beta amyloid synthetic peptide, ubiquitin, tau protein, and paired helical filaments (PHF). Striatal SP, composed of beta amyloid deposits with or without neuritic elements, were demonstrated in all AD cases examined. Compact and perivascular amyloid deposits were concentrated in the ventral striatum, including the nucleus accumbens. Many diffuse amyloid deposits in the ventral striatum contained ubiquitin-positive granular elements, presumably representing dystrophic neurites, whereas most of those in the dorsal striatum did not have such elements. On the other hand, most compact amyloid deposits in both ventral and dorsal striatum had ubiquitin immunoreactivity. Dystrophic neurites with tau or PHF immunoreactivity were detected particularly around compact amyloid deposits. Our results indicate that the ventral striatum, which is closely affiliated with the limbic system, is frequently affected by amyloid deposits with dystrophic neurites, and suggest that the ventral striatum is particularly vulnerable to AD. Furthermore, our results suggest that amyloid deposits, especially compact deposits, may induce dystrophic neurites.

Ubiquitin immunoelectron microscopy of dystrophic neurites in cerebellar senile plaques of Alzheimer's disease

Senile plaques are present in the cerebellum of most Alzheimer patients. They are composed of beta-amyloid deposits lacking neurites detectable with immunocytochemistry for neurofilament, tau and paired helical filament proteins. Recent studies, however, have shown that cerebellar plaques usually contain round structures that are reactive with ubiquitin antibodies. In this immunoelectron microscopic study, the nature of these structures is explored. Ubiquitin-positive structures in cerebellar senile plaques were composed of degenerating neurites that contained membranous and vesicular dense bodies, but no paired helical filaments. A minority of the neurites contained finely granular material. Thus, cerebellar plaques are associated with neuritic degeneration, and the neurites in cerebellar plaques resemble dystrophic neurites in senile plaques of non-demented elderly subjects and subjects with non-Alzheimer dementias. They differ from some of the neurites in senile plaques in the neocortex in Alzheimer's disease by the absence of paired helical filaments. These results suggest that the same mechanisms involved in the generation of dystrophic neurites in pathological aging are involved in generating dystrophic neurites in the cerebellum in Alzheimer's disease.

Immunochemical properties of ubiquitin conjugates in the paired helical filaments of Alzheimer disease

Immunocytochemical and peptide sequencing studies indicate that the regulatory protein ubiquitin (Ub) is incorporated into the paired helical filaments (PHF) of Alzheimer disease. In this study, we showed that some antibodies raised to PHF recognize epitopes of Ub. Analysis of the Ub sequences recognized by the antibodies raised to PHF, along with the known specificity of several monoclonal antibodies raised to artificial Ub conjugates, indicates the immunochemical representation of Ub residues 34-76 in PHF. The Ub epitopes recognized by antibodies raised to PHF are distinct from those recognized by antibodies raised to artificial Ub conjugates in two respects. First, antibodies that are raised to PHF and that recognize Ub react with PHF equally, whether denatured or not, whereas those raised to artificial Ub conjugates show greater reaction after denaturation. Second, mapping of the epitopes recognized by two monoclonal antibodies to PHF onto Ub indicates a distinction in the Ub residues recognized, compared with monoclonal antibodies raised to artificial Ub conjugates. The proximity of their epitopes to the site of conjugation, as well as their affinity for PHF polypeptides, suggests that the PHF antibodies that recognize Ub may be directed specifically to Ub epitopes defined by the protein conjugated to Ub.

Diffuse Lewy body disease: light and electron microscopic immunocytochemistry of senile plaques

The nature of senile plaques (SP) in 27 cases of diffuse Lewy body disease (LBD) was investigated using immunocytochemistry and antibodies to beta amyloid protein synthetic peptides (BetaSP), ubiquitin (UBQ), paired helical filaments (PHF; Ab39) and a 68-kDa protein in Alzheimer brains (Alz50). Lewy bodies were present in widespread areas of the neocortex of all cases and were more easily detected with ubiquitin immunocytochemistry than with conventional stains. All cases had neocortical SP, but only six cases had neocortical neurofibrillary tangles (NFT). SP were very numerous in most cases and were usually "pale", "diffuse" or "very primitive" plaques with thioflavin S fluorescent microscopy. SP in diffuse LBD were immunostained with BetaSP. Several cases had extensive amyloid angiopathy that was also immunoreactive with BetaSP. SP in diffuse LBD were characterized by amyloid deposits with few or no neuritic elements that could be detected with thioflavin S, Bielschowsky's stain or double staining with BetaSP and Bodian's silver stain. They differed from plaques in Alzheimer's disease by lack of PHF-type neurites that could be stained with Ab39. In diffuse LBD, SP contained PHF-type neurites only in areas coexistent with NFT. Some SP had round, granular neurites that were immunoreactive with UBQ, but weakly argyrophilic with Bodian's stain and nonfluorescent with thioflavin S. Diffuse LBD lacked significant neuritic change in the neuropil that could be detected with UBQ, Ab39 and Alz50. The latter finding is a characteristic feature that distinguishes Alzheimer's disease from diffuse LBD.