One of the most widely accepted theories in aging research is the free radical or oxidative stress theory of aging, which argues that the age-related loss of physiological function and age-related increase in pathology are due to the progressive accumulation of oxidative damage. Although this theory is currently one of the most popular explanations for how aging occurs at the biochemical/molecular level, most of the evidence in support of this theory is correlative. Over the past decade our laboratory has measured the lifespans of more than 15 different transgenic and knockout mice with alterations in the antioxidant defense system. Except for mice lacking Cu/ZnSOD, none of the transgenic or knockout mice showed a decrease in lifespan even though these mice showed increased resistance or sensitivity to oxidative stress. These data, which were obtained with aging colonies of mice maintained under optimal husbandry conditions, seriously call into the question the role that oxidative damage/stress plays in the aging process in mammals. However, when transgenic or knockout mice are breed to various age-related disease models (e.g., models of atherosclerosis, Alzheimer's disease, and amyotrophic lateral sclerosis), we observed that the alterations in the antioxidant defense system had an impact on the progression of these diseases as predicted by the oxidative stress theory of aging. More recently, we found that overexpressing Cu/ZnSOD increased the lifespan and reduced the age-related pathology in an obese strain of rats. Based on these observations, we propose that under optimal husbandry conditions, which minimize stress and trauma from infectious agents and other agents (e.g., inflammation), oxidative stress/damage plays a minimal role in longevity and the aging process. However, when mice are maintained under stressful conditions that accelerate aging, alterations in the antioxidant defense system will have an impact on longevity and pathology. In the revised application, we will test the hypothesis that overexpressing Cu/ZnSOD will retard aging and reduce oxidative stress/damage when mice are fed a high-fat diet to induce life-long, a low-grade inflammatory-stress. This hypothesis will be tested in the following Specific Aims: 1. To determine whether overexpressing Cu/ZnSOD alters the lifespan and pathology of high-fat fed vs. low- fat fed mice. 2. To determine whether overexpressing Cu/ZnSOD alters the age-related decline in physiological function in high-fat fed vs. low-fat fed mice. In this Specific Aim, we will measure 3 age-sensitive physiological processes to assess the physiological function of the transgenic and WT mice on the low- and high-fat diets: cardiac function, neuromuscular function, and cognition. 3. To determine whether overexpressing Cu/ZnSOD alters the levels of oxidative stress and inflammation in high-fat fed vs. low-fat fed mice. In this Specific Aim, we will determine whether reduced inflammation and oxidative damage play a role in the mechanism underlying increased lifespan/reduced pathology by measuring markers of inflammation, oxidative damage, expression profiles in tissues of the transgenic and WT mice fed a high-fat or low-fat diet. 4. To determine whether alterations in Cu/ZnSOD expression specifically in adipose tissue provide protection against high-fat induced stress. Transgenic mice overexpressing Cu/ZnSOD in adipose tissue and conditional knockout mice lacking Cu/ZnSOD in adipose tissue will be generated and the effect of these manipulations on various markers of inflammation and oxidative damage in tissues of the mice fed a high- or low-fat diet will be determined.
We hypothesize that environment is a critical factor in the role that oxidative stress/damage plays in aging. In an environment with minimal stress oxidative damage plays little, if any role;aging arises from other factors. However, when an organism is exposed to chronic stress because of the environment and/or genetic manipulation, oxidative stress/damage plays a major role in aging. The effect of overexpressing Cu/ZnSOD will be tested in mice that are maintained over their lifespan under a chronic stress. Such an approach will not only allow us to test our hypothesis, but will provide a model that is more relevant to what humans encounter in their normal environment. These data would provide very important clues in treating and preventing age-related pathological changes associated with metabolic syndrome in the human population.