Abstract 14123: Activated Macrophages Release Delta-like 4: A Potential New Biomarker of Cardiometabolic Disorders
Background: We previously demonstrated that the Notch ligand Delta-like 4 (Dll4), a transmembrane protein, promotes macrophage activation and cardiometabolic disorders. ADAM17, a potent transmembrane protease, cleaves transmembrane proteins to release the soluble forms. We recently found that activated macrophages release the extracellular domain of Dll4. The present study has explored the underlying release mechanisms and tested hypothesis that blood Dll4 levels associate with atherosclerotic plaque burden.
Method and Results: LPS significantly increased Dll4 in the supernatant of cultured mouse peritoneal macrophages in time- and dose-dependent manners. Inhibition of ADAM17 by siRNA-mediated silencing inhibited LPS-induced Dll4 release, while silencing of ADAM10, another ADAM protease implicated in Notch signaling, had no significant effect on soluble Dll4 release. LPS increased the number of microparticles and ultracentrifugation to remove microparticles reduced Dll4 levels in culture supernatant. In the microparticle pellet, full-length Dll4 was detected by Western blotting. These findings indicate that macrophages may release Dll4 as a soluble form mediated by ADAM17 and in microparticles. Further, Dll4 was detected in plasma by ELISA. Plasma Dll4 levels were lower in ADAM17-deficient mice compared to wild-type mice (10.8±6.7 vs. 17.9±6.3 ng/mL, n=11, p < 0.05). In hyperlipidemic LDL receptor deficient (Ldlr-/-) mice, plasma Dll4 levels were higher than normolipidemic wild-type mice (Figure A, N=10-14) and positively associated with plasma triglyceride and cholesterol levels. In addition, plasma Dll4 levels correlated with lipid content in the aorta of Ldlr-/- mice (oil red O stain, Figure B, r=0.47, p<0.05).
Conclusion: These results indicate that macrophages can release Dll4 via ADAM17-mediated shedding and through microparticle release. Plasma Dll4 concentrations may serve as a novel biomarker of cardiometabolic disorders.
- © 2013 by American Heart Association, Inc.