Dianne Deplewski, MD

My laboratory studies the molecular mechanism of PPAR? action in the adipocyte. Adipocytes and PPAR? are central players in the control of energy balance and whole body lipid homeostasis. PPAR? signaling pathways impact both cellular and systemic lipid metabolism and have links to obesity, diabetes and cardiovascular disease. In addition, evidence from studies of human populations shows a connection between PPAR? and insulin sensitivity (the antidiabetic drugs, thiazolidinediones, are ligands for PPAR?).

One aspect of our research focuses on the significance of the N-terminus of PPAR?, and the importance of ligand-independent coactivator binding to the N-terminus. There is evidence from several studies that the N-terminus of PPAR? is important in its overall function. For example, two human mutations have been described in the N-terminus of PPAR? that affect overall PPAR? activity. In addition, the N-terminus harbors the only coding difference between PPAR?1 and PPAR?2. We have been performing in vitro mapping of coactivator binding to the N-terminus of PPAR?1 verses PPAR?2, using various mutants which have been described in humans (Pro12Ala and Pro115Gln) and truncation constructs. In addition, we are utilizing the technique of RNA interference to differentiate the roles of the coactivators CBP and p300, on activation of the N-terminus of PPAR?. We have also generated a mouse model in which various floxed genes can be knocked out specifically in adipose tissue at various stages of development, and plan to use this model to further study the role of CBP and p300 in adipocytes in vivo. The exact role played by PPAR? in adipogenesis and insulin action is still unclear, especially the specific roles of PPAR?1 and PPAR?2. Thus, we are studying the physiologic significance of PPAR?1 and PPAR?2 expression in adipocytes in vitro using RNA interference, and in vivo through the development of novel transgenic mice models.

Figure: Differentiation of preadipocytes in vitro. Confluent 3T3-L1 preadipocytes were induced to differentiate following incubation with DMEM/10% FBS with 3-isobutyl-1-methylxanthine (IBMX), dexamethasone and insulin. Cells were fixed with calcium formalin and stained with Oil Red O which stains lipid droplets red.