Lysyl oxidase-like protein-2 regulates sprouting angiogenesis and type IV collagen assembly in the endothelial basement membrane

Sprouting angiogenesis is associated with extensive extracellular matrix (ECM) remodeling. The molecular mechanisms involved in building the vascular microenvironment and its impact on capillary formation remain elusive. We therefore performed a proteomic analysis of ECM from endothelial cells maintained in hypoxia, a major stimulator of angiogenesis. Here, we report the characterization of lysyl oxidase-like protein-2 (LOXL2) as a hypoxia-target expressed in neovessels and accumulated in the endothelial ECM. LOXL2 belongs to the lysyl oxidase family of secreted enzymes involved in ECM crosslinking. Knockdown experiments in Tg(fli1:egfp)y1 zebrafish embryos resulted in lack of intersegmental vessel circulation and demonstrated LOXL2 involvement in proper capillary formation. Further investigation in vitro by loss and gain of function experiments confirmed that LOXL2 was required for tubulogenesis in 3D fibrin gels and demonstrated that this enzyme was required for collagen IV assembly in the ECM. In addition, LOXL2 depletion down-regulated cell migration and proliferation. These data suggest a major role for LOXL2 in the organization of endothelial basal lamina and in the downstream mechanotransductive signaling. Altogether, our study provides the first evidence for the role of LOXL2 in regulating angiogenesis through collagen IV scaffolding. (Blood. 2011;118(14):3979-3989)