Endothelial Deletion of Phospholipase D2 Reduces Hypoxic Response and Pathological Angiogenesis

Abstract

A ngiogenesis involves complex endothelial cell (EC) behaviors, such as proliferation, survival, migration, and tube formation. The most important stimulus promoting angiogenesis is tissue hypoxia. Hypoxia mediates several processes in ECs that are required for each step of angiogenesis.1 Hypoxia-induced angiogenesis is closely related to pathological situation. The dysregulation of these EC behaviors and thus abnormal angiogenesis are critically associated with hypoxia-induced pathological angiogenesis that occurs during the course of several diseases, such as cancer and vascular retinopathy.2,3 Therefore, identification of specific molecules involved in hypoxia-induced angiogenesis will facilitate studies to clarify the various molecular mechanisms involved in pathological angiogenesis and may aid the discovery of novel angiogenic drug targets.© 2014 American Heart Association, Inc. Objective-Aberrant regulation of the proliferation, survival, and migration of endothelial cells (ECs) is closely related to the abnormal angiogenesis that occurs in hypoxia-induced pathological situations, such as cancer and vascular retinopathy. Hypoxic conditions and the subsequent upregulation of hypoxia-inducible factor-1α and target genes are important for the angiogenic functions of ECs. Phospholipase D2 (PLD2) is a crucial signaling mediator that stimulates the production of the second messenger phosphatidic acid. PLD2 is involved in various cellular functions; however, its specific roles in ECs under hypoxia and in vivo angiogenesis remain unclear. In the present study, we investigated the potential roles of PLD2 in ECs under hypoxia and in hypoxia-induced pathological angiogenesis in vivo. Approach and Results-Pld2 knockout ECs exhibited decreased hypoxia-induced cellular responses in survival, migration, and thus vessel sprouting. Analysis of hypoxia-induced gene expression revealed that PLD2 deficiency disrupted the upregulation of hypoxia-inducible factor-1α target genes, including VEGF, PFKFB3, HMOX-1, and NTRK2. Consistent with this, PLD2 contributed to hypoxia-induced hypoxia-inducible factor-1α expression at the translational level. The roles of PLD2 in hypoxia-induced in vivo pathological angiogenesis were assessed using oxygen-induced retinopathy and tumor implantation models in endothelial-specific Pld2 knockout mice. Pld2 endothelial-specific knockout retinae showed decreased neovascular tuft formation, despite a larger avascular region. Tumor growth and tumor blood vessel formation were also reduced in Pld2 endothelial-specific knockout mice. Cellular responses to hypoxic stress are mediated by multiple mechanisms. Hypoxia-inducible factor-1 (HIF-1) is the most prominent factor that mediates cellular responses to hypoxia by inducing the expression of several target genes. Conclusions-Our 1Because HIF-1 activation is preferentially modulated by changes in the amount of the HIF-1α subunit, several factors and mechanisms have been suggested. Among these, the regulation of HIF-1α degradation through post-translat...

The phospholipase D superfamily as therapeutic targets

“…Metastasizing tumor cells also need to interact with platelets to achieve efficient colonization at distant sites [57], and this is hindered in mice lacking PLD1 due to the blunted platelet activation described above; hence there are at least two roles for PLD1 in the tumor environment [31]. Related roles for PLD2 have also been described in hypoxia-induced Hif1-α expression and VEGF secretion by endothelial cells, which similarly results in a reduction of tumor neovascularization and growth when PLD2 is absent, although to a lesser extent than in the absence of PLD1 [58]. Inhibiting both PLD1 and PLD2 may both address redundancy and target non-overlapping roles as well.…”

Thematic Review Series: Phospholipases: Central Role in Lipid Signaling and Disease

“…In a human breast cancer xenograft model, it was shown that increased PLD2 expression in tumor cells suppresses apoptosis, ultimately facilitating tumor growth and chemoresistance ( 68 ). PLD2 may also play roles in the tumor environment similar to those previously reported for PLD1 ( 39 ), because PLD2 ablation from endothelial cells suppresses their hypoxiainduced Hif1-␣ expression and VEGF secretion, reducing proximal tumor neovascularization and growth ( 67 ). Although the overall expression levels of PLD2 may vary in tumors, there is a signifi cant correlation between PLD2 expression level and tumor size ( P < 0.05), as well as with survival of patients with colorectal carcinoma ( P < 0.05) ( 78 ).…”

Intestinal Epithelial Cell-Specific Deletion of PLD2 Alleviates DSS-Induced Colitis by Regulating Occludin

“…Specific pathogen-free Villin-Cre mice (on the C57BL/6 genetic background) were purchased from the Jackson Laboratory. Pld2 floxed mice were generated as previously described 53 . The Pld2 IEC KO mice were generated by breeding Pld2 fl/fl mice with Villin-Cre mice.…”