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

Rationale: 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. Objective: 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. Methods and Results: In this article, we report the generation of AIBP knockout (Apoa1bp^-/-) 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 Apoa1bp^-/- mice by crossing them with apoA-I transgenic mice rescued Notch activation and corrected dysregulated retinal angiogenesis. Notably, the retinal vessels in Apoa1bp^-/- 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 Apoa1bp^-/- 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. Conclusions: 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.