Abstract 11257: Fatty Acid Binding Protein 4 and Fatty Acid Translocase are Induced by Notch Signaling via Induction of PPARγ in Capillary Endothelial Cells in Heart After Long Time Fasting
Notch signaling, a pathway for cell fate determination, controls multiple aspects of vascular function. We have reported that fatty acid binding protein 4 (FABP4) and FA translocase (FAT/CD36) are target genes of PPARγ in endothelial cells (EC) of muscle type continuous capillary and that FABP4/5 expressed in capillary endothelial cells facilitate FA transport from circulation into cardiac muscle through continuous endothelial layer (we term this function trans-endothelial FA transport). Here we show that Notch signaling induces capillary expression of FABP4 and FAT/CD36 in a PPARγ-dependent manner in vivo and in vitro. FABP4, FAT/CD36 as well as PPARγ were induced by overexpression of Notch1 dominant active form (NICD) and further enhanced by pioglitazone (Pio), a synthetic PPARγ ligand, in human cardiac microvessel endothelial cells (HCMEC). The induction of FABP4 and FAT/CD36 was markedly reduced by pretreatment with siPPARγ. Activation of Notch signaling was found to facilitate uptake of FA into HCMEC; 14C-palmitic acid uptake was stimulated by overexpression of NICD plus Pio and the increase in the uptake was partially inhibited by pre-treatment of cells with siRNAs for PPARγ, FABP4 and FAT/CD36. Co-culture of HCMEC with cells expressing a Notch ligand Dll4, but not Jagged1, induced expression of FABP4 and FAT/CD36. Consistent with this, FABP4, FAT/CD36 as well as Notch components (Notch1 and Dll4) were strongly expressed in capillary ECs in hearts. The luciferase reporter constructs of both FABP4 and FAT/CD36 promoters were markedly trans-activated by NICD plus pioglitazone. The trans-activation was reduced by mutation of the PPAR responsive elements or pretreatment with siRNA for PPARγ. We further found that capillary expression of FABP4 and FAT/CD36 in hearts was enhanced by fasting in a time-dependent manner (0, 24- and 48-hour fasting) in wild type mice and that the increase was reduced by an inhibitor of Notch signaling (γ-secretase inhibitor; Ly411575, 10 mg/kg for three days) in Notch1 (+/-) mice. These findings suggest that Notch-PPARγ-pathway and their target genes may play a crucial role in trans-endothelial FA transport to supply adequate FA into FA-consuming organs such as hearts, especially under fasting condition.
- © 2012 by American Heart Association, Inc.