AIBP Limits Angiogenesis Through γ-Secretase-Mediated Upregulation of Notch Signaling.

Abstract

Angiogenesis improves perfusion to the ischemic tissue after acute vascular obstruction. Angiogenesis in pathophysiological settings reactivates signaling pathways involved in developmental angiogenesis. We showed previously that AIBP (apolipoprotein A-I [apoA-I]-binding protein)-regulated cholesterol efflux in endothelial cells controls zebra fish embryonic angiogenesis. This study is to determine whether loss of AIBP affects angiogenesis in mice during development and under pathological conditions and to explore the underlying molecular mechanism. In this article, we report the generation of AIBP knockout (<i>Apoa1bp</i>^-/-) mice, which are characterized of accelerated postnatal retinal angiogenesis. Mechanistically, AIBP triggered relocalization of γ-secretase from lipid rafts to nonlipid rafts where it cleaved Notch. Consistently, AIBP treatment enhanced DLL4 (delta-like ligand 4)-stimulated Notch activation in human retinal endothelial cells. Increasing high-density lipoprotein levels in <i>Apoa1bp</i>^-/- mice by crossing them with apoA-I transgenic mice rescued Notch activation and corrected dysregulated retinal angiogenesis. Notably, the retinal vessels in <i>Apoa1bp</i>^-/- mice manifested normal pericyte coverage and vascular integrity. Similarly, in the subcutaneous Matrigel plug assay, which mimics ischemic/inflammatory neovascularization, angiogenesis was dramatically upregulated in <i>Apoa1bp</i>^-/- mice and associated with a profound inhibition of Notch activation and reduced expression of downstream targets. Furthermore, loss of AIBP increased vascular density and facilitated the recovery of blood vessel perfusion function in a murine hindlimb ischemia model. In addition, AIBP expression was significantly increased in human patients with ischemic cardiomyopathy. Our data reveal a novel mechanistic connection between AIBP-mediated cholesterol metabolism and Notch signaling, implicating AIBP as a possible druggable target to modulate angiogenesis under pathological conditions.