In rodents, TCDD treatment causes a general depletion of body fat with a parallel increase in serum triglycerides and diabetic-like insulin resistance. Mouse embryo fibroblast (MEF) lines can be induced to differentiate to fat cells (adipocytes) by a hormonal mixture (IDM) containing insulin (I), a glucocorticoid (dexamethasone [D]) and a means to elevate cAMP (methylisobutylxanthine [M]) in combination with a stimulant for the peroxisome proliferation activation receptor-type gamma2 (PPARgamma2), usually a thiazolidinedione (TZD). Previous work has shown that a pre-adipocyte line 3T3-LI undergoes this differentiation without TZD and this is blocked by TCDD at an early stage. We have shown that the TZD stimulated adipogenesis in primary MEF's and equivalent cell lines is also blocked by TCDD. In contrast MEF's cultured from mice deficient in the Ah-receptor (AhR(-/-)EF) no longer respond to TCDD, consistent with the AhR being required in this suppression. MEF's express a form of cytochrome P450 (CYPlBl) that is expressed constitutively under AhR control and which is highly induced TCDD. MEF's from CYPlBl-deficient mice are completely converted to fat cells with IDM stimulation without the need for external PPARgamma2 stimulation. The proposed research addresses the role of the AhR in regulating PPARgamma2 and CYPlBl during normal adipogenesis and in inhibiting this process when activated by TCDD. We will test the hypothesis that TCDD inhibits the increased activity of PPARgamma2 following IDM/TZD stimulation, which is critical to the initiation of differentiation. The research will focus on effects of endogenous AhR and TCDD specifically during the period of proliferative arrest (2 days after IDM stimulation) where nuclear regulatory factors such as c/EBPbeta and SREBP-1 stimulate expression of PPARgamma2. This will be linked to measurement of other potential early initiators of the differentiation pathway that respond to PPARgamma2 (RB-family proteins, PP2Ac immunophilins). We will establish that these effects correlate with the subsequent progression of adipogenesis after a further 5 days. We will further test the possibility that CYPlBl checks adipogenesis by metabolizing an endogenous activator of PPARgamma2 and that elevation of this process by TCDD contributes to the anti-adipogenic effect. This research will provide insight into general mechanisms through which TCDD alters differentiation, as well as provide a noel approach to the mechanism of adipogenesis and the action of TZD drugs, now a treatment for Type II disease.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK055302-04
Application #
6517559
Study Section
Special Emphasis Panel (ZRG4-ALTX-1 (01))
Program Officer
Haft, Carol R
Project Start
1999-03-15
Project End
2003-02-28
Budget Start
2002-03-01
Budget End
2003-02-28
Support Year
4
Fiscal Year
2002
Total Cost
$192,747
Indirect Cost
Name
University of Wisconsin Madison
Department
Public Health & Prev Medicine
Type
Schools of Earth Sciences/Natur
DUNS #
161202122
City
Madison
State
WI
Country
United States
Zip Code
53715
Hanlon, Paul R; Cimafranca, Melissa A; Liu, Xueqing et al. (2005) Microarray analysis of early adipogenesis in C3H10T1/2 cells: cooperative inhibitory effects of growth factors and 2,3,7,8-tetrachlorodibenzo-p-dioxin. Toxicol Appl Pharmacol 207:39-58
Cho, Young C; Zheng, Wenchao; Yamamoto, Megumi et al. (2005) Differentiation of pluripotent C3H10T1/2 cells rapidly elevates CYP1B1 through a novel process that overcomes a loss of Ah Receptor. Arch Biochem Biophys 439:139-53
Hanlon, Paul R; Zheng, Wenchao; Ko, Alex Y et al. (2005) Identification of novel TCDD-regulated genes by microarray analysis. Toxicol Appl Pharmacol 202:215-28
Cimafranca, Melissa A; Hanlon, Paul R; Jefcoate, Colin R (2004) TCDD administration after the pro-adipogenic differentiation stimulus inhibits PPARgamma through a MEK-dependent process but less effectively suppresses adipogenesis. Toxicol Appl Pharmacol 196:156-68
Cho, Young C; Zheng, Wenchao; Jefcoate, Colin R (2004) Disruption of cell-cell contact maximally but transiently activates AhR-mediated transcription in 10T1/2 fibroblasts. Toxicol Appl Pharmacol 199:220-38
Barnes, David M; Hanlon, Paul R; Kircher, Emily A (2003) Effects of inorganic HgCl2 on adipogenesis. Toxicol Sci 75:368-77