Phospholipase Cγ Activation Drives Increased Production of Autotaxin in Endothelial Cells and Lysophosphatidic Acid-Dependent Regression

Abstract

We previously reported that vascular endothelial growth factor (VEGF)-dependent activation of phospholipase C␥1 (PLC␥) regulated tube stability by competing with phosphoinositide 3-kinase (PI3K) for their common substrate. Here we describe an additional mechanism by which PLC␥ promoted regression of tubes and blood vessels. Namely, it increased the level of autotaxin (ATX), which is a secreted form of lysophospholipase D that produces lysophosphatidic acid (LPA). LPA promoted motility of endothelial cells, leading to disorganization/regression of tubes in vitro. Furthermore, mice that under-or overexpressed members of this intrinsic destabilization pathway showed either delayed or accelerated, respectively, regression of blood vessels. We conclude that endothelial cells can be instructed to engage a PLC␥-dependent intrinsic destabilization pathway that results in the production of soluble regression factors such as ATX and LPA. These findings are likely to potentiate ongoing efforts to prevent, manage, and eradicate numerous angiogenesis-based diseases such as proliferative diabetic retinopathy and solid tumors.

Lactate Engages Receptor Tyrosine Kinases Axl, Tie2, and Vascular Endothelial Growth Factor Receptor 2 to Activate Phosphoinositide 3-Kinase/Akt and Promote Angiogenesis

“…For instance, although the amount of VEGF produced by endothelial cells does not substantially contribute to the circulating level of VEGF (and is therefore considered to be small), it is nonetheless essential (38). Similarly, endogenously produced lysophosphatidic acid makes a vital contribution to instructing regression of endothelial cell tubes (39). These findings raise the possibility that angiomodulators that are produced by endothelial cells in response to lactate may make an important contribution to the angiogenic response despite the relative small quantity.…”

Thematic Review Series: Phospholipases: Central Role in Lipid Signaling and Disease Autotaxin, a lysophospholipase D with pleomorphic effects in oncogenesis and cancer progression

“…It has been shown that ATX regulates both prenatal lymphatic vessel formation in mice and zebrafi sh ( 79,80 ) and generates directional cues that direct primitive hematopoiesis and hemangioblast formation ( 81 ). Importantly, ATX can drive either vessel regression ( 82 ) or maturation ( 80 ) depending on the experimental context. It is likely that compartmentalization of ATX and its lipid substrates greatly infl uences biological function and activity because it generates high concentrations of lipid substrate in proximity to the membrane.…”

Insulin-like Growth Factor 1 (IGF-1) Stabilizes Nascent Blood Vessels

“…We prepared HMREC tube lysates as described previously (10,12,21). Briefly, medium was removed, and the collagen gel sandwich was digested with two gel volumes of collagenase (type I from Clostridium histolyticum, Sigma-Aldrich) in Hanks' buffered salt solution supplemented with 100 M Na 3 VO 4 .…”

“…Murine Retinal Explants-We prepared retinal explants as described previously (10,12,22). Immediately after euthanasia, the eyes were enucleated and kept in PBS.…”

“…Image Analysis and Quantification-For tube assays and retinal explants, image acquisition and data quantification were performed as described previously (10,12). Briefly, phase-contrast images at ϫ100 magnification were acquired with a Nikon Eclipse TE2000-S inverted microscope (Melville, NY) equipped with Diagnostic Instruments RT Slider charge-coupled device camera.…”