Inhibition of proteasome activity is sufficient to induce neuron degeneration and death; however, altered proteasome activity in a neurodegenerative disorder has not been demonstrated. In the present study, we analyzed proteasome activity in shortpostmortem-interval autopsied brains from 16 Alzheimer's disease (AD) and nine age-and sex-matched controls. A significant decrease in proteasome activity was observed in the hippocampus and parahippocampal gyrus (48%), superior and middle temporal gyri (38%), and inferior parietal lobule (28%) of AD patients compared with controls. In contrast, no significant decrease in proteasome activity was observed in either the occipital lobe or the cerebellum. The loss of proteasome activity was not associated with a decrease in proteasome expression, suggesting that the proteasome may become inhibited in AD by a posttranslational modification. Together, these data indicate a possible role for proteasome inhibition in the neurodegeneration associated with AD. Key Words: Alzheimer's disease-Amyloid ␤-peptide-Neurodegeneration-Oxidative stress-Proteasome-Ubiquitin. J. Neurochem. 75, 436 -439 (2000).The proteasome is a large, ϳ700-kDa complex, which is present in all cells of the CNS (Coux et al., 1996;Tanaka, 1998;Tanaka and Chiba, 1998). The proteasome is composed of 28 individual ␣-and ␤-subunits, which are arranged in four rings, with each ring composed of either seven ␣-or seven ␤-subunits. The two inner rings of the proteasome are composed of the ␤-subunits, which possess the proteolytic sites, whereas the ␣-subunits function to stabilize the proteasome complex. Caplike structures can bind to the 20S proteasome to form a larger, ϳ2,000-kDa 26S proteasome complex. The proteasome is responsible for the majority of cellular proteolysis (Rock et al., 1994) and has been best characterized for its role in the ubiquitin-ATP-dependent proteolytic pathway (Hershko and Ciechanover, 1992). In addition to ubiquitinated proteins, the proteasome degrades multiple substrates that are important in maintaining neuronal homeostasis, including the catabolism of oxidized, damaged, and aggregated proteins (Grune et al., 1997;Tanaka, 1998;Tanaka and Chiba, 1998). Since its discovery, the proteasome has been demonstrated in several cellular functions, including differentiation, proliferation, and apoptosis (Tanaka, 1998;Tanaka and Chiba, 1998); however, the role of the proteasome in the CNS has not been determined.Recent studies implicate a possible role for proteasome inhibition in neuron degeneration and death that occurs in Alzheimer's disease (AD). Proteasome activity is inhibited by the application of amyloid ␤-peptide and exposure to oxidative stress (Gregori et al., 1995;Grune et al., 1995;Reinheckel et al., 1998), both of which are believed to contribute to the progression of AD (Markesbery, 1997;Mattson, 1997). Also, pharmacologic inhibition of the proteasome is sufficient to induce neuron degeneration and death (Lopes et al., 1997;Boutillier et al., 1999;Qiu et al., 2000).In spi...

Oxidative stress is implicated in neuronal apoptosis that occurs in physiological settings and in neurodegenerative disorders. Superoxide anion radical, produced during mitochondrial respiration, is involved in the generation of several potentially damaging reactive oxygen species including peroxynitrite. To examine directly the role of superoxide and peroxynitrite in neuronal apoptosis, we generated neural cell lines and transgenic mice that overexpress human mitochondrial manganese superoxide dismutase (MnSOD). In cultured pheochromocytoma PC6 cells, overexpression of mitochondria-localized MnSOD prevented apoptosis induced by Fe2+, amyloid beta-peptide (Abeta), and nitric oxide-generating agents. Accumulations of peroxynitrite, nitrated proteins, and the membrane lipid peroxidation product 4-hydroxynonenal (HNE) after exposure to the apoptotic insults were markedly attenuated in cells expressing MnSOD. Glutathione peroxidase activity levels were increased in cells overexpressing MnSOD, suggesting a compensatory response to increased H2O2 levels. The peroxynitrite scavenger uric acid and the antioxidants propyl gallate and glutathione prevented apoptosis induced by each apoptotic insult, suggesting central roles for peroxynitrite and membrane lipid peroxidation in oxidative stress-induced apoptosis. Apoptotic insults decreased mitochondrial transmembrane potential and energy charge in control cells but not in cells overexpressing MnSOD, and cyclosporin A and caspase inhibitors protected cells against apoptosis, demonstrating roles for mitochondrial alterations and caspase activation in the apoptotic process. Membrane lipid peroxidation, protein nitration, and neuronal death after focal cerebral ischemia were significantly reduced in transgenic mice overexpressing human MnSOD. The data suggest that mitochondrial superoxide accumulation and consequent peroxynitrite production and mitochondrial dysfunction play pivotal roles in neuronal apoptosis induced by diverse insults in cell culture and in vivo.

C57Bl/6 mice were administered a high fat, Western diet (WD, 41% fat) or a very high fat lard diet (HFL, 60% fat), and evaluated for cognitive ability using the Stone T-maze and for biochemical markers of brain inflammation. WD consumption resulted in significantly increased body weight and astrocyte reactivity, but not impaired cognition, microglial reactivity, or heightened cytokine levels. HFL increased body weight, and impaired cognition, increased brain inflammation, and decreased BDNF. Collectively, these data suggest that while different diet formulations can increase body weight, the ability of high fat diets to disrupt cognition is linked to brain inflammation.

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Alzheimer's disease (AD) is a progressive and devastating disorder that is often preceded by mild cognitive impairment (MCI). In the present study, we report that in multiple cortical areas of MCI and AD subjects, there is a significant impairment in ribosome function that is not observed in the cerebellum of the same subjects. The impairment in ribosome function is associated with a decreased rate and capacity for protein synthesis, decreased ribosomal RNA and tRNA levels, and increased RNA oxidation. No alteration in the level of initiation factors was observed in the brain regions exhibiting impairments in protein synthesis. Together, these data indicate for the first time that impairments in protein synthesis may be one of the earliest neurochemical alterations in AD and directly demonstrate that the polyribosome complex is adversely affected early in the development of AD. These data have important implications for AD studies involving proteomics and studies analyzing proteolysis in AD, indicate that oxidative damage may contribute to decreased protein synthesis, and suggest a role for alterations in protein synthesis as a novel contributor to the onset and development of AD.

Glutamate transporters are involved in the maintenance of synaptic glutamate concentrations. Because of its potential neurotoxicity, clearance of glutamate from the synaptic cleft may be critical for neuronal survival. Inhibition of glutamate uptake from the synapse has been implicated in several neurodegenerative disorders. In particular, glutamate uptake is inhibited in Alzheimer's disease (AD); however, the mechanism of decreased transporter activity is unknown. Oxidative damage in brain is implicated in models of neurodegeneration, as well as in AD. Glutamate transporters are inhibited by oxidative damage from reactive oxygen species and lipid peroxidation products such as 4‐hydroxy‐2‐nonenal (HNE). Therefore, we have investigated a possible connection between the oxidative damage and the decreased glutamate uptake known to occur in AD brain. Western blots of immunoprecipitated HNE‐immunoreactive proteins from the inferior parietal lobule of AD and control brains suggest that HNE is conjugated to GLT‐1 to a greater extent in the AD brain. A similar analysis of beta amyloid (Aβ)‐treated synaptosomes shows for the first time that Aβ1–42 also increases HNE conjugation to the glutamate transporter. Together, our data provide a possible link between the oxidative damage and neurodegeneration in AD, and supports the role of excitotoxicity in the pathogenesis of this disorder. Furthermore, our data suggests that Aβ may be a possible causative agent in this cascade.

Oxidative damage occurs in the brain of subjects with mild cognitive impairment, suggesting that oxidative damage may be one of the earliest events in the onset and progression of Alzheimer disease.

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