Involvement of a gut-retina axis in protection against dietary glycemia-induced age-related macular degeneration.

Age-related macular degeneration (AMD) is the major cause of blindness in developed nations. AMD is characterized by retinal pigmented epithelial (RPE) cell dysfunction and loss of photoreceptor cells. Epidemiologic studies indicate important contributions of dietary patterns to the risk for AMD, but the mechanisms relating diet to disease remain unclear. Here we investigate the effect on AMD of isocaloric diets that differ only in the type of dietary carbohydrate in a wild-type aged-mouse model. The consumption of a high-glycemia (HG) diet resulted in many AMD features (AMDf), including RPE hypopigmentation and atrophy, lipofuscin accumulation, and photoreceptor degeneration, whereas consumption of the lower-glycemia (LG) diet did not. Critically, switching from the HG to the LG diet late in life arrested or reversed AMDf. LG diets limited the accumulation of advanced glycation end products, long-chain polyunsaturated lipids, and their peroxidation end-products and increased C3-carnitine in retina, plasma, or urine. Untargeted metabolomics revealed microbial cometabolites, particularly serotonin, as protective against AMDf. Gut microbiota were responsive to diet, and we identified microbiota in the Clostridiales order as being associated with AMDf and the HG diet, whereas protection from AMDf was associated with the Bacteroidales order and the LG diet. Network analysis revealed a nexus of metabolites and microbiota that appear to act within a gut-retina axis to protect against diet- and age-induced AMDf. The findings indicate a functional interaction between dietary carbohydrates, the metabolome, including microbial cometabolites, and AMDf. Our studies suggest a simple dietary intervention that may be useful in patients to arrest AMD.

Dietary and donepezil modulation of mTOR signaling and neuroinflammation in the brain.

Recent clinical and laboratory evidences suggest that high fat diet (HFD) induced obesity and its associated metabolic syndrome conditions promotes neuropathology in aging and age-related neurological disorders. However, the effects of high fat diet on brain pathology are poorly understood, and the effective strategies to overcome these effects remain elusive. In the current study, we examined the effects of HFD on brain pathology and further evaluated whether donepezil, an AChE inhibitor with neuroprotective functions, could suppress the ongoing HFD induced pathological changes in the brain. Our data demonstrates that HFD induced obesity results in increased neuroinflammation and increased AChE activity in the brain when compared with the mice fed on low fat diet (LFD). HFD administration to mice activated mTOR pathway resulting in increased phosphorylation of mTOR(ser2448), AKT(thr308) and S6K proteins involved in the signaling. Interestingly, donepezil administration with HFD suppressed HFD induced increases in AChE activity, and partially reversed HFD effects on microglial reactivity and the levels of mTOR signaling proteins in the brain when compared to the mice on LFD alone. However, gross levels of synaptic proteins were not altered in the brain tissues of mice fed either diet with or without donepezil. In conclusion, these results present a new insight into the detrimental effects of HFD on brain via microglial activation and involvement of mTOR pathway, and further demonstrates the possible therapeutic role for donepezil in ameliorating the early effects of HFD that could help preserve the brain function in metabolic syndrome conditions.

Elevated adiponectin prevents HIV protease inhibitor toxicity and preserves cerebrovascular homeostasis in mice.

HIV protease inhibitors are key components of HIV antiretroviral therapies, which are fundamental in the treatment of HIV infection. However, the protease inhibitors are well-known to induce metabolic dysfunction which can in turn escalate the complications of HIV, including HIV associated neurocognitive disorders. As experimental and epidemiological data support a therapeutic role for adiponectin in both metabolic and neurologic homeostasis, this study was designed to determine if increased adiponectin could prevent the detrimental effects of protease inhibitors in mice. Adult male wild type (WT) and adiponectin-overexpressing (ADTg) mice were thus subjected to a 4-week regimen of lopinavir/ritonavir, followed by comprehensive metabolic, neurobehavioral, and neurochemical analyses. Data show that lopinavir/ritonavir-induced lipodystrophy, hypoadiponectinemia, hyperglycemia, hyperinsulinemia, and hypertriglyceridemia were attenuated in ADTg mice. Furthermore, cognitive function and blood-brain barrier integrity were preserved, while loss of cerebrovascular markers and white matter injury were prevented in ADTg mice. Finally, lopinavir/ritonavir caused significant increases in expression of markers of brain inflammation and decreases in synaptic markers in WT, but not in ADTg mice. Collectively, these data reinforce the pathophysiologic link from metabolic dysfunction to loss of cerebrovascular and cognitive homeostasis; and suggest that preservation and/or replacement of adiponectin could prevent these key aspects of HIV protease inhibitor-induced toxicity in clinical settings.

Prolonged diet induced obesity has minimal effects towards brain pathology in mouse model of cerebral amyloid angiopathy: implications for studying obesity-brain interactions in mice.

Cerebral amyloid angiopathy (CAA) occurs in nearly every individual with Alzheimer's disease (AD) and Down's syndrome, and is the second largest cause of intracerebral hemorrhage. Mouse models of CAA have demonstrated evidence for increased gliosis contributing to CAA pathology. Nearly two thirds of Americans are overweight or obese, with little known about the effects of obesity on the brain, although increasingly the vasculature appears to be a principle target of obesity effects on the brain. In the current study we describe for the first time whether diet induced obesity (DIO) modulates glial reactivity, amyloid levels, and inflammatory signaling in a mouse model of CAA. In these studies we identify surprisingly that DIO does not significantly increase Aß levels, astrocyte (GFAP) or microglial (IBA-1) gliosis in the CAA mice. However, within the hippocampal gyri a localized increase in reactive microglia were increased in the CA1 and stratum oriens relative to CAA mice on a control diet. DIO was observed to selectively increase IL-6 in CAA mice, with IL-1ß and TNF-α not increased in CAA mice in response to DIO. Taken together, these data show that prolonged DIO has only modest effects towards Aß in a mouse model of CAA, but appears to elevate some localized microglial reactivity within the hippocampal gyri and selective markers of inflammatory signaling. These data are consistent with the majority of the existing literature in other models of Aß pathology, which surprisingly show a mixed profile of DIO effects towards pathological processes in mouse models of neurodegenerative disease. The importance for considering the potential impact of ceiling effects in pathology within mouse models of Aß pathogenesis, and the current experimental limitations for DIO in mice to fully replicate metabolic dysfunction present in human obesity, are discussed. This article is part of a Special Issue entitled: Animal Models of Disease.

Aging is associated with hypoxia and oxidative stress in adipose tissue: implications for adipose function.

As a part of aging there are known to be numerous alterations which occur in multiple tissues of the body, and the focus of this study was to determine the extent to which oxidative stress and hypoxia occur during adipose tissue aging. In our studies we demonstrate for the first time that aging is associated with both hypoxia (38% reduction in oxygen levels, Po(2) 21.7 mmHg) and increases reactive oxygen species in visceral fat depots of aging male C57Bl/6 mice. Interestingly, aging visceral fat depots were observed to have significantly less change in the expression of genes involved in redox regulation compared with aging subcutaneous fat tissue. Exposure of 3T3-L1 adipocytes to the levels of hypoxia observed in aging adipose tissue was sufficient to alter multiple aspects of adipose biology inducing increased levels of in insulin-stimulated glucose uptake and decreased lipid content. Taken together, these data demonstrate that hypoxia and increased levels of reactive oxygen species occur in aging adipose tissue, highlighting the potential for these two stressors as potential modulators of adipose dysfunction during aging.

Amino acid analog toxicity in primary rat neuronal and astrocyte cultures: implications for protein misfolding and TDP-43 regulation.

Amino acid analogs promote translational errors that result in aberrant protein synthesis and have been used to understand the effects of protein misfolding in a variety of physiological and pathological settings. TDP-43 is a protein that is linked to protein aggregation and toxicity in a variety of neurodegenerative diseases. This study exposed primary rat neurons and astrocyte cultures to established amino acid analogs (canavanine and azetidine-2-carboxylic acid) and showed that both cell types undergo a dose-dependent increase in toxicity, with neurons exhibiting a greater degree of toxicity compared with astrocytes. Neurons and astrocytes exhibited similar increases in ubiquitinated and oxidized protein following analog treatment. Analog treatment increased heat shock protein (Hsp) levels in both neurons and astrocytes. In neurons, and to a lesser extent astrocytes, the levels of TDP-43 increased in response to analog treatment. Taken together, these data indicate that neurons exhibit preferential toxicity and alterations in TDP-43 in response to increased protein misfolding compared with astrocytes.

Diet-induced metabolic disturbances as modulators of brain homeostasis.

A number of metabolic disturbances occur in response to the consumption of a high fat western diet. Such metabolic disturbances can include the progressive development of hyperglycemia, hyperinsulemia, obesity, metabolic syndrome, and diabetes. Cumulatively, diet-induced disturbances in metabolism are known to promote increased morbidity and negatively impact life expectancy through a variety of mechanisms. While the impact of metabolic disturbances on the hepatic, endocrine, and cardiovascular systems is well established there remains a noticeable void in understanding the basis by which the central nervous system (CNS) becomes altered in response to diet-induced metabolic dysfunction. In particular, it remains to be fully elucidated which established features of diet-induced pathogenesis (observed in non-CNS tissues) are recapitulated in the brain, and identification as to whether the observed changes in the brain are a direct or indirect effect of peripheral metabolic disturbances. This review will focus on each of these key issues and identify some critical experimental questions which remain to be elucidated experimentally, as well as provide an outline of our current understanding for how diet-induced alterations in metabolism may impact the brain during aging and age-related diseases of the nervous system.

Activation of PERK kinase in neural cells by proteasome inhibitor treatment.

Inhibition of the proteasome proteolytic pathway occurs as the result of normal aging, as well as in a variety of neurodegenerative conditions, and is believed to promote cellular toxicity in each of these conditions through diverse mechanisms. In the present study, we examined whether proteasome inhibition alters the protein kinase receptor-like endoplasmic reticulum kinase (PERK). Our studies demonstrate that proteasome inhibitors induce the transient activation of PERK in both primary rat neurons as well as the N2a neural cell line. Experiments with siRNA to PERK demonstrated that the modulation of PERK was not significant involved in regulating toxicity, ubiquitinated protein levels, or ribosome perturbations in response to proteasome inhibitor treatment. Surprisingly, PERK was observed to be involved in the up-regulation of p38 kinase following proteasome inhibitor treatment. Taken together, these data demonstrate the ability of proteasome inhibition to activate PERK and demonstrate evidence for novel cross-talk between PERK and the activation of p38 kinase in neural cells following proteasome inhibition. Taken together, these data have implications for understanding the basis by which proteasome inhibition alters neural homeostasis, and the basis by which cell signaling cascades are regulated by proteasome inhibition.

Intersection between metabolic dysfunction, high fat diet consumption, and brain aging.

Deleterious neurochemical, structural, and behavioral alterations are a seemingly unavoidable aspect of brain aging. However, the basis for these alterations, as well as the basis for the tremendous variability in regards to the degree to which these aspects are altered in aging individuals, remains to be elucidated. An increasing number of individuals regularly consume a diet high in fat, with high-fat diet consumption known to be sufficient to promote metabolic dysfunction, although the links between high-fat diet consumption and aging are only now beginning to be elucidated. In this review we discuss the potential role for age-related metabolic disturbances serving as an important basis for deleterious perturbations in the aging brain. These data not only have important implications for understanding the basis of brain aging, but also may be important to the development of therapeutic interventions which promote successful brain aging.

Autophagic receptor p62 protects against glycation-derived toxicity and enhances viability.

Diabetes and metabolic syndrome are associated with the typical American high glycemia diet and result in accumulation of high levels of advanced glycation end products (AGEs), particularly upon aging. AGEs form when sugars or their metabolites react with proteins. Associated with a myriad of age-related diseases, AGEs accumulate in many tissues and are cytotoxic. To date, efforts to limit glycation pharmacologically have failed in human trials. Thus, it is crucial to identify systems that remove AGEs, but such research is scanty. Here, we determined if and how AGEs might be cleared by autophagy. Our in vivo mouse and C. elegans models, in which we altered proteolysis or glycative burden, as well as experiments in five types of cells, revealed more than six criteria indicating that p62-dependent autophagy is a conserved pathway that plays a critical role in the removal of AGEs. Activation of autophagic removal of AGEs requires p62, and blocking this pathway results in accumulation of AGEs and compromised viability. Deficiency of p62 accelerates accumulation of AGEs in soluble and insoluble fractions. p62 itself is subject to glycative inactivation and accumulates as high mass species. Accumulation of p62 in retinal pigment epithelium is reversed by switching to a lower glycemia diet. Since diminution of glycative damage is associated with reduced risk for age-related diseases, including age-related macular degeneration, cardiovascular disease, diabetes, Alzheimer's, and Parkinson's, discovery of methods to limit AGEs or enhance p62-dependent autophagy offers novel potential therapeutic targets to treat AGEs-related pathologies.

Proteasome inhibition modulates kinase activation in neural cells: relevance to ubiquitination, ribosomes, and survival.

In this study we examined whether established signal transduction cascades, p44/42 mitogen-activated protein kinase (ERK1/2) and Jun N-terminal kinases (JNK) pathways, are altered in N2a neural cells in response to proteasome inhibition. Additionally, we sought to elucidate the relative contribution of these signal transduction pathways to the multiple downstream effects of proteasome inhibition. Our data indicate that ERK1/2 and JNK are activated in response to proteasome inhibition. Washout of proteasome inhibitor (MG132) results in an enhancement of ERK1/2 activation and amelioration of JNK activation. Treatment with an established MAPK inhibitor resulted in an increase in proteasome inhibitor toxicity, and incubation with JNK inhibitor was observed to attenuate proteasome inhibitor toxicity significantly. Subsequent studies demonstrated that inhibition of ERK1/2 and JNK activity does not alter the gross increase in ubiquitinated protein following proteasome inhibitor administration. Similarly, ERK1/2 and JNK activity do not appear to play a role in the disruption of polysomes following proteasome inhibitor administration in neural cells. Together these data indicate that ERK1/2 and JNK activation may play differential roles in modulating neurochemical disturbances and neurotoxicity induced by proteasome inhibition.

The db mutation improves memory in younger mice in a model of Alzheimer's disease.

Alzheimer's disease (AD) is the most common age-related neurodegenerative disease, while obesity is a major global public health problem associated with the metabolic disorder type 2 diabetes mellitus (T2DM). Chronic obesity and T2DM have been identified as invariant risk factors for dementia and late-onset AD, while their impacts on the occurrence and development of AD remain unclear. As shown in our previous study, the diabetic mutation (db, Leprdb/db) induces mixed or vascular dementia in mature to middle-aged APPΔNL/ΔNL x PS1P264L/P264L knock-in mice (db/AD). In the present study, the impacts of the db mutation on young AD mice at 10 weeks of age were evaluated. The db mutation not only conferred young AD mice with severe obesity, impaired glucose regulation and activated mammalian target of rapamycin (mTOR) signaling pathway in the mouse cortex, but lead to a surprising improvement in memory. At this young age, mice also had decreased cerebral Aß content, which we have not observed at older ages. This was unlikely to be related to altered Aß synthesis, as both ß- and γ-secretase were unchanged. The db mutation also reduced the cortical IL-1ß mRNA level and IBA1 protein level in young AD mice, with no significant effect on the activation of microglia and astrocytes. We conclude that the db mutation could transitorily improve the memory of young AD mice, a finding that may be partially explained by the relatively improved glucose homeostasis in the brains of db/AD mice compared to their counterpart AD mice, suggesting that glucose regulation could be a strategy for prevention and treatment of neurodegenerative diseases like AD.

Aging and dietary restriction effects on ubiquitination, sumoylation, and the proteasome in the heart.

Dietary restriction (DR), in the absence of malnutrition, is the only intervention known to reliably increase average and maximal lifespan in a variety of organisms including mammals. Because the effects of DR on the heart are poorly understood, in the present study we examined the effects of DR on the ubiquitin-proteasome pathway (UPP) in the heart. In these studies we observed that DR significantly reduced age-related impairments in proteasome-mediated protein degradation, and reduced age-related increases in ubiquitinated, oxidized, and sumoylated protein in the heart. Interestingly, DR did not significantly increase the expression of 20S proteasome subunits or the proteasome maturation factor (POMP-1). These data demonstrate for the first time the effects of aging and DR on proteasome biogenesis and sumoylation in the heart. Cumulatively, our data indicate that DR has many beneficial effects towards the UPP in the heart, and suggests that a preservation of the UPP may be a potential mechanism by which DR mediates beneficial effects on the cardiovascular system.

Adipose-specific ablation of Nrf2 transiently delayed high-fat diet-induced obesity by altering glucose, lipid and energy metabolism of male mice.

Nuclear factor E2-related factor 2 (NRF2) is a well-known master controller of the cellular adaptive antioxidant and detoxification response. Recent studies demonstrated altered glucose, lipid and energy metabolism in mice with a global Nrf2 knockout. In the present study, we aim to determine the effects of an adipose-specific ablation of Nrf2 (ASAN) on diet-induced obesity (DIO) in male mice. The 6-week-old adipose-specific Nrf2 knockout (NK) and its Nrf2 control (NC) mice were fed with either control diet (CD) or high-fat diet (HFD) for 14 weeks. NK mice exhibited transiently delayed body weight (BW) growth from week 5 to week 11 of HFD feeding, higher daily physical activity levels and preferential use of fat over carbohydrates as a source of energy at week 8 of the CD-feeding period. After 14 weeks of feeding, NK mice showed comparable results with NC mice with respect to the overall BW and body fat content, but exhibited reduced blood glucose, reduced number but increased size of adipocytes, accompanied with elevated expression of many genes and proteins in the visceral fat related to glucose, lipid and energy metabolism (e.g. Fgf21, Pgc1a). These results indicated that NRF2 is an important mediator for glucose, lipid and energy metabolism in adipose tissue, and ASAN could have beneficial effect for prevention of DIO during the early development of mice.

Oxidative stress, neurodegeneration, and the balance of protein degradation and protein synthesis.

Oxidative stress occurs in a variety of disease settings and is strongly linked to the development of neuron death and neuronal dysfunction. Cells are equipped with numerous pathways to prevent the genesis, as well as the consequences, of oxidative stress in the brain. In this review we discuss the various forms and sources of oxidative stress in the brain and briefly discuss some of the complexities in detecting the presence of oxidative stress. We then focus the review on the interplay between the diverse cellular proteolytic pathways and their roles in regulating oxidative stress in the brain. Additionally, we discuss the involvement of protein synthesis in regulating the downstream effects of oxidative stress. Together, these components of the review demonstrate that the removal of damaged proteins by effective proteolysis and the synthesis of new and protective proteins are vital in the preservation of brain homeostasis during periods of increased levels of reactive oxygen species. Last, studies from our laboratory and others have demonstrated that protein synthesis is intricately linked to the rates of protein degradation, with impairment of protein degradation sufficient to decrease the rates of protein synthesis, which has important implications for successfully responding to periods of oxidative stress. Specific neurodegenerative diseases, including Alzheimer disease, Parkinson disease, amyotrophic lateral sclerosis, and stroke, are discussed in this context. Taken together, these findings add to our understanding of how oxidative stress is effectively managed in the healthy brain and help elucidate how impairments in proteolysis and/or protein synthesis contribute to the development of neurodegeneration and neuronal dysfunction in a variety of clinical settings.

Obesity increases cerebrocortical reactive oxygen species and impairs brain function.

Nearly two-thirds of the population in the United States is overweight or obese, and this unprecedented level of obesity will undoubtedly have a profound impact on overall health, although little is currently known about the effects of obesity on the brain. The objective of this study was to investigate cerebral oxidative stress and cognitive decline in the context of diet-induced obesity (DIO). We demonstrate for the first time that DIO induces higher levels of reactive oxygen species (ROS) in the brain and promotes cognitive impairment. Importantly, we also demonstrate for the first time in these studies that both body weight and adiposity are tightly correlated with the level of ROS. Interestingly, ROS were not correlated with cognitive decline in this model. Alterations in the antioxidant/detoxification Nrf2 pathway, superoxide dismutase, and catalase activity levels were not significantly altered in response to DIO. However, a significant impairment in glutathione peroxidase was observed in response to DIO. Taken together, these data demonstrate for the first time that DIO increases the levels of total and individual ROS in the brain and highlight a direct relationship between the amount of adiposity and the level of oxidative stress within the brain. These data have important implications for understanding the negative effects of obesity on the brain and are vital to understanding the role of oxidative stress in mediating the effects of obesity on the brain.

Role of physiological levels of 4-hydroxynonenal on adipocyte biology: implications for obesity and metabolic syndrome.

Lipid peroxidation products such as 4-hydroxynonenal (HNE) are known to be increased in response to oxidative stress, and are known to cause dysfunction and pathology in a variety of tissues during periods of oxidative stress. The aim of the current study was to determine the chronic (repeated HNE exposure) and acute effects of physiological concentrations of HNE toward multiple aspects of adipocyte biology using differentiated 3T3-L1 adipocytes. Our studies demonstrate that acute and repeated exposure of adipocytes to physiological concentrations of HNE is sufficient to promote subsequent oxidative stress, impaired adipogenesis, alter the expression of adipokines, and increase lipolytic gene expression and subsequent increase in free fatty acid (FFA) release. These results provide an insight in to the role of HNE-induced oxidative stress in regulation of adipocyte differentiation and adipose dysfunction. Taken together, these data indicate a potential role for HNE promoting diverse effects toward adipocyte homeostasis and adipocyte differentiation, which may be important to the pathogenesis observed in obesity and metabolic syndrome.

Mutant amyloid precursor protein differentially alters adipose biology under obesogenic and non-obesogenic conditions.

Mutations in amyloid precursor protein (APP) have been most intensely studied in brain tissue for their link to Alzheimer's disease (AD) pathology. However, APP is highly expressed in a variety of tissues including adipose tissue, where APP is also known to exhibit increased expression in response to obesity. In our current study, we analyzed the effects of mutant APP (E693Q, D694N, K670N/M671L) expression toward multiple aspects of adipose tissue homeostasis. These data reveal significant hypoleptinemia, decreased adiposity, and reduced adipocyte size in response to mutant APP, and this was fully reversed upon high fat diet administration. Additionally, mutant APP was observed to significantly exacerbate insulin resistance, triglyceride elevations, and macrophage infiltration of adipose tissue in response to a high fat diet. Taken together, these data have significant implications for linking mutant APP expression to adipose tissue dysfunction and global changes in endocrine and metabolic function under both obesogenic and non-obesogenic conditions.

Proteasome alterations during adipose differentiation and aging: links to impaired adipocyte differentiation and development of oxidative stress.

Intracellular proteins are degraded by a number of proteases, including the ubiquitin-proteasome pathway (UPP). Impairments in the UPP occur during the aging of a variety of tissues, although little is known in regards to age-related alterations to the UPP during the aging of adipose tissue. The UPP is known to be involved in regulating the differentiation of a variety of cell types, although the potential changes in the UPP during adipose differentiation have not been fully elucidated. How the UPP is altered in aging adipose tissue and adipocyte differentiation and the effects of proteasome inhibition on adipocyte homeostasis and differentiation are critical issues to elucidate experimentally. Adipogenesis continues throughout the life of adipose tissue, with continual differentiation of preadipocytes essential to maintaining tissue function during aging, and UPP alterations in mature adipocytes are likely to directly modulate adipose function during aging. In this study we demonstrate that aging induces alterations in the activity and expression of principal components of the UPP. Additionally, we show that multiple changes in the UPP occur during the differentiation of 3T3-L1 cells into adipocytes. In vitro data link observed UPP alterations to increased levels of oxidative stress and altered adipose biology relevant to both aging and differentiation. Taken together, these data demonstrate that changes in the UPP occur in response to adipose aging and adipogenesis and strongly suggest that proteasome inhibition is sufficient to decrease adipose differentiation, as well as increasing oxidative stress in mature adipocytes, both of which probably promote deleterious effects on adipose aging.

Increased protein hydrophobicity in response to aging and Alzheimer disease.

Increased levels of misfolded and damaged proteins occur in response to brain aging and Alzheimer disease (AD), which presumably increase the amount of aggregation-prone proteins via elevations in hydrophobicity. The proteasome is an intracellular protease that degrades oxidized and ubiquitinated proteins, and its function is known to be impaired in response to both aging and AD. In this study we sought to determine the potential for increased levels of protein hydrophobicity occurring in response to aging and AD, to identify the contribution of proteasome inhibition to increased protein hydrophobicity, and last to identify the contribution of ubiquitinated and oxidized proteins to the pool of hydrophobic proteins. In our studies we identified that aging and AD brain exhibited increases in protein hydrophobicity as detected using Bis ANS, with dietary restriction (DR) significantly decreasing age-related increases in protein hydrophobicity. Affinity chromatography purification of hydrophobic proteins from aging and AD brains identified increased levels of oxidized and ubiquitinated proteins in the pool of hydrophobic proteins. Pharmacological inhibition of the proteasome in neurons, but not astrocytes, resulted in an increase in protein hydrophobicity. Taken together, these data indicate that there is a relationship between increased protein oxidation and protein ubiquitination and elevations in protein hydrophobicity within the aging and the AD brain, which may be mediated in part by impaired proteasome activity in neurons. Our studies also suggest a potential role for decreased oxidized and hydrophobic proteins in mediating the beneficial effects of DR.