Search

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.

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 UPP during adipose differentiation have not been fully elucidated. Simultaneously elucidating how the UPP is altered in aging adipose tissue and adipocyte differentiation, and determining 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 pre-adipocytes essential to maintaining tissue function during aging, while UPP alterations in mature adipocytes is likely to directly modulate adipose function during aging. In the current 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 increase oxidative stress in mature adipocytes, both of which likely promote deleterious effects on adipose aging.

Increased levels of misfolded and damaged proteins occur in response to brain aging and Alzheimer’s disease (AD), which presumably increases the amount of aggregation prone proteins via elevations in hydrophobicity. The proteasome is an intracellular protease which degrades oxidized and ubiquitinated proteins, with the function of the proteasome known to be impaired in response to both aging and AD. In the present study we sought to determine the potential for increased levels of protein hydrophobicity occurring in response to aging and AD, identify the contribution of proteasome inhibition to increased protein hydrophobicity, and lastly to identify the contribution of ubiquitinated and oxidized proteins to the pool of hydrophobic proteins. In our studies we identified that aging and AD 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 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.