Adipose tissue-derived tumor necrosis factor-alpha activity is elevated in older rats.
High levels of adipose tissue-derived tumor necrosis factor-alpha (AT-TNF) mRNA and protein have previously been associated with genetic models of obesity and insulin resistance. Because there are endogenous TNF inhibitors it is unknown if AT-TNF activity is also increased. We hypothesized that AT-TNF activity would increase in older animals because of an accumulation of fat mass. We chose to study 2 different-aged male Fischer 344 rats, 3-month-old (young) and 14-month-old (mature) because fat mass should be quite different but insulin action on glucose metabolism similar. Indeed, mature rats had over 1.5-fold more fat mass, but whole body insulin resistance, as estimated by fasting plasma insulin, was similar to young rats. Mature rats had twice as much AT-TNF activity as the young in both the epididymal (EPI) and retroperitoneal (Retro) fat pads (p < .0005). AT-TNF correlated with fasting plasma insulin in Retro only (r = .48, p = .04). AT-TNF activity strongly correlated with cell size in both EPI and Retro (r = .79 and .81, respectively, p < .0001). Because cytokines can be regulated at several levels, AT-TNF activity, protein, and mRNA were measured. AT-TNF protein levels were higher in young rats, suggesting that these animals may secrete an inhibitor that reduces AT-TNF activity. There were no significant differences in AT-TNF mRNA between groups. Since TNF has been shown to affect several key genes in tissue culture, mRNA for lipoprotein lipase, hormone-sensitive lipase, and Glut4 were measured. No differences were found between groups. In summary, AT-TNF activity increased in mature animals in relation to adipose cell size.
Morin
C L
CL
Division of Endocrinology, Metabolism, and Diabetes, University of Colorado, Denver, USA. Catherine.Morin@UCHSC.EDU
Pagliassotti
M J
MJ
Windmiller
D
D
Eckel
R H
RH
D017667:Adipocytes / Q000166:cytology; D000273:Adipose Tissue / Q000033:anatomy & histology / Q000166:cytology / Q000378:metabolism*; D000375:Aging / Q000378:metabolism*; D000818:Animals; D001835:Body Weight; D002452:Cell Count; D008071:Lipoprotein Lipase / Q000378:metabolism; D008297:Male; D009929:Organ Size; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D008071:Lipoprotein Lipase