Wasting syndrome is one of the most consistently observed effects of TCDD in many animal species. In the past period we have found that TCDD causes suppression of not only lipoprotein lipase (LPL) but glucose transporters (GLUT), fatty acid binding proteins and many other gene expressions involved in lipogenesis and adipogenesis. The combined effect of these effects are serum hyperlipidemia, hypoinsulinemia and cellular starvation. In this project period we will address the question on the basic mechanism of TCDD's antiIipogenic action and toxicological significance of such actions. The main question we raise first is how TCDD induces simultaneously these many changes in a coordinated manner to turn adipocytes to a lipolytic mode. Our hypothesis is that one of the major Causes for the above changes is the activation of mitotic nuclear transcription factors such as AP-1 through TCDD-induced increases in growth factor signaling, and that such a stimulation of mitotic program works antagonistically to lipogenic and adipogenic cellular program through """"""""cross-talking"""""""" among nuclear transcription factors. To this end we propose to study, using mainly guinea pig adipose tissue and mouse 3T3- L1 preadipocytes as in vivo and in vitro models, respectively: (1) TCDD's effects on the DNA binding activities of growth factor-activated and lipogenesis-related transcription factors in guinea pig adipose tissue using gel mobility assay, (2) repeat the same in 3T3-L1 preadipocytes in vitro and assess TCDD's effects on adipocyte differentiation processes, (3) the role of CCAAT enhancer binding protein (C/EBPalpha), a nuclear factor known to regulate many adipogenic gene expressions in toxic action of TCDD both in vivo and in vitro, (4) the changes in 125I-TNF-alpha binding and its nuclear signal transducer, NFkappaB at various stages of 3T3-L1 differentiation to determine the role of TNFalpha in TCDD's action, and (5) TCDD's effects on nuclear modulators of the GLUT4 gene expression in 3T3-L1 cells. Our strategy is to closely follow the experimental design and approaches of successful studies demonstrating """"""""cross-talking"""""""" among key factors. Furthermore, we plan to study: (6) toxicological significance of TCDD-induced reduction in GLUTs by studying vitamin C uptake, which has been recently shown to be transported by GLUTs [15S], and relate the finding to lipid peroxidation in the guinea pig adipose tissue. Finally (7) we will integrate the data, carry out critical tests to determine the roles, the scope and the limit of this route of action mechanism of TCDD that is mediated by growth factor signaling and """"""""cross-talking"""""""" among nuclear transcription factors.
Showing the most recent 10 out of 40 publications
