This application focuses on the special emphasis area of nutritional and metabolic factors in aging. The primary goal is to study alterations in adipose tissue metabolism as the animal ages, specifically the role of adipose tissue derived tumor necrosis factor-alpha (TNFalpha). TNFalpha mRNA has recently been found in adipose tissue. Additionally, elevated production was associated with insulin resistant states. TNFalpha is known to decrease adipose tissue lipoprotein lipase activity (ATLPL) predominantly through transcriptional mechanisms. Moreover, infusions of TNFalpha increase plasma free fatty acids and produce hypertriglyceridemia. Plasma glucose is also increased due to decreased glucose transport and increased hepatic glucose output. Therefore, many of actions of TNFalpha promote insulin resistance. Because insulin resistance increases with aging, we hypothesize that adipose tissue TNFalpha production increases with age diminishing insulin action in adipose tissue. Since insulin resistance is a risk factor for both coronary heart disease and diabetes, this is an important area for study. This project will investigate the biology of TNFalpha in adipose tissue by several approaches. After defining the age-dependent differences in TNFalpha production in different adipose tissue depots, a longitudinal study will be carried out to document the timetable in which elevated TNFalpha is seen in aging. Measurements of glucose uptake and ATLPL activity will be used to assess the relationship between TNFalpha and insulin resistance. Nuclear run-on experiments will be used to determine if the increase in adipose tissue TNFalpha with age is due to increases in TNFalpha gene transcription.
The second aim i s to study the effect of diet on the regulation of TNFalpha in adipose tissue in aging. Experiments will include short term regulation of TNFalpha by meals and long term regulation by energy restriction. Thirdly, transgenic mice will be used to examine if overexpression of TNFalpha in adipose tissue produces local and systemic insulin resistance, and reduce longevity. Overall, alterations in adipose tissue metabolism with aging may have important systemic effects. Increases in adipose tissue-derived TNFalpha could mediate these aging-dependent metabolic effects.
| Morin, C L; Gayles, E C; Podolin, D A et al. (1998) Adipose tissue-derived tumor necrosis factor activity correlates with fat cell size but not insulin action in aging rats. Endocrinology 139:4998-5005 |
| Morin, C L; Eckel, R H; Marcel, T et al. (1997) High fat diets elevate adipose tissue-derived tumor necrosis factor-alpha activity. Endocrinology 138:4665-71 |
| Morin, C L; Pagliassotti, M J; Windmiller, D et al. (1997) Adipose tissue-derived tumor necrosis factor-alpha activity is elevated in older rats. J Gerontol A Biol Sci Med Sci 52:B190-5 |
