Abstract 5552: Notch-peroxisome Proliferator Activated Receptor Gamma 2 Pathway Regulates Transendothelial Fatty Acid Transport via Induction of Fatty Acid Binding Protein 4 and Fatty Acid Translocase in Capillary Endothelial Cells in Heart
Notch signaling, an evolutionarily conserved pathway for cell fate determination, is essential for normal vascular development and maintenance as well as other multiple aspects of vascular function. We have reported that fatty acid binding protein 4 (FABP4), also known as aP2, is a potential candidate of Notch target genes in capillary endothelial cells (EC) of heart, skeletal muscle and adipose tissue. Given that FABP4 is well known as an adipocyte-specific marker and downstream of PPAR-γ, we hypothesized that Notch signaling may regulate several genes abundant in adipocyte via induction of peroxisome proliferator activated receptor-γ (PPAR-γ). Here we show that Notch signaling induces several adipocyte-related genes in capillary EC via induction of PPAR-γ2, an isoform known to play a major role in adipocyte differentiation. Overexpression of Notch intracellular domain (NICD), an activated form of Notch, in human cardiac microvessel endothelial cells (HCMEC) induced expression of FABP4, lipoprotein lipase (LPL), but not fatty acid translocase (FAT/CD36). The induction was accompanied by expression of PPAR-γ2, but not PPAR-γ1. Administration of synthetic PPAR-γ ligands, thiazolidindione (TZD), markedly enhanced expression of these genes including even FAT/CD36. Their induction was mediated by PPAR-γ2 because their expression by NICD plus TZD was abolished by administration of GW9662, a PPAR-γ inhibitor. Of importance, the gene induction by NICD and the enhancement by TZD were not observed in other cells such as human umbilical vein EC and 3T3L1 fibroblast/adipocyte, suggesting capillary EC-specific effect of Notch-PPAR-γ pathway. The gene induction was observed in HCMEC when co-cultured with cells expressing Dll4, a Notch ligand, in the presence of TZD. Consistent with these findings, these genes including a Notch receptor Notch1, Dll4, FABP4 and FAT/CD36 were co-localized in capillary EC. Given that long chain fatty acids are central source of energy metabolism in heart, skekletal muscle and adipocyte, adipocyte-related genes such as FABP4 and FAT/CD36 induced by Notch-PPAR pathway in capillary EC may play a crucial role in fatty acid transport system through endothelial layer to supply adequate fatty acids to the fatty acid-burning organs.