SAT-LB124 Phosphatidylcholine Transfer Protein Interacts With PPARδ to Modulate Activity

Abstract

Obesity is one of the largest public health crises in the USA. Obesity can be lethal due to the development of cardiovascular complications such as, hypertension, heart attack, and stroke. Recently, peroxisome proliferator-activated receptor δ (PPARδ), the least-characterized member of the PPAR family of nuclear receptors (NRs), has shown great promise in treating obesity and associated cardiovascular complications. Recent reports have shown that PPARδ activation is tuned, in part, through an interaction with fatty acid binding protein 5 (FABP5) in a polyunsaturated Fatty acids (PUFAs) dependent manner. This enhancement is thought to occur due to ligand transfer, however, FABP5 only binds a subset of reported PPARδ ligands. To find other candidate lipid transport proteins (LTPs), we performed a protein complementation assay (PCA) between LTPs and NRs. We uncovered a novel interaction between PPARδ and phosphatidylcholine transfer protein (PC-TP), sensitive to cellular nutrient levels. Preliminary data show that this interaction opposes canonical PPARδ signaling, leading to a decrease in PPARδ transactivation in cells and isolated mice livers. This led me to hypothesize that PC-TP senses nutrient status through membrane composition. Specific PC molecular species drive PC-TP translocation to inhibit PPARδ transactivation of genes. Utilizing our novel PCA assay I have shown that the interaction is modulated in part by cellular levels of methionine and choline, as cells cultured in media depleted of methionine and choline (MCD) show a decreased in the interaction. Using the same assay, I have shown a requirement of full length PPARδ for the interaction with PC-TP. This analysis will be complimented by mutagenesis and chemical perturbations aimed to alter PC-TP and PPARδ function. Additionally, I have assayed the in vivo relevance of PC-TP interaction with PPARδ using livers harvested from PCTP-/- and littermate control mice fed a variety of diets. Preliminary RNA-seq characterization, show interesting alterations in gene expression that suggest more complex regulation between PC-TP and PPARδ in vivo. MCD, which was shown to reduce the inhibitory interaction between PC-TP and PPARδ in vitro, seems to lead to an increased effect on PPARδ transactivation when PC-TP is depleted. Analysis comparing the effect of diet within each genotype shows a loss of differential PPARδ regulation for both CHEA and KEGG analysis when comparing WT to PCTP -/- mice supporting a role for PC-TP in differential PPARδ regulation caused by MCD diet. These studies will further the understanding of how lipid homeostasis is sensed and maintained through PPARδ by interactions with two separate LTPs.