Study on the roles of endothelial PLD2 in hypoxic response and pathological angiogenesis

다국어 초록 (Multilingual Abstract)

Aberrant regulation of the proliferation, survival, and migration of endothelial cells (ECs) is closely related to the abnormal angiogenesis occurs in hypoxia-induced pathological situations, such as cancer and vascular retinopathy. Hypoxic conditions and the subsequent upregulation of hypoxia-inducible factor-1α (HIF-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, I investigated the potential roles of PLD2 in ECs under hypoxia and in hypoxia-induced pathological angiogenesis in vivo. Here, I report that Pld2 knockout (KO) endothelial cells exhibited decreased hypoxia-induced cellular responses in survival, migration, and thus vessel sprouting. 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 KO mice (eKO). Pld2 eKO retinae showed decreased neovascular tuft formation despite a larger avascular region. Tumor growth and tumor blood vessel formation were also reduced in Pld2 eKO. Analysis of hypoxia-induced gene expression revealed that PLD2 deficiency disrupted the upregulation of HIF-1α target genes including VEGF, PFKFB3, HMOX-1, and NTRK2. Consistent with this, PLD2 contributed to hypoxia-induced HIF-1α expression at the translational level.
Aberrant regulation of the proliferation, survival, and migration of endothelial cells (ECs) is closely related to the abnormal angiogenesis occurs in hypoxia-induced pathological situations, such as cancer and vascular retinopathy. Hypoxic conditions and the subsequent upregulation of hypoxia-inducible factor-1α (HIF-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, I investigated the potential roles of PLD2 in ECs under hypoxia and in hypoxia-induced pathological angiogenesis in vivo. Here, I report that Pld2 knockout (KO) endothelial cells exhibited decreased hypoxia-induced cellular responses in survival, migration, and thus vessel sprouting. 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 KO mice (eKO). Pld2 eKO retinae showed decreased neovascular tuft formation despite a larger avascular region. Tumor growth and tumor blood vessel formation were also reduced in Pld2 eKO. Analysis of hypoxia-induced gene expression revealed that PLD2 deficiency disrupted the upregulation of HIF-1α target genes including VEGF, PFKFB3, HMOX-1, and NTRK2. Consistent with this, PLD2 contributed to hypoxia-induced HIF-1α expression at the translational level.

목차 (Table of Contents)

• Chapter 1. Research Background
• 1.1 Angiogenesis and diseases 1
• 1.1.1 Vascular system 1
• 1.1.2 Angiogenesis and pathological condition 2
• 1.1.3 Cellular functions of endothelial cells for angiogenesis 2
• 1.2 Hypoxia and angiogenesis 5
• 1.2.1 Hypoxia and HIF-1α-mediated cellular response 5
• 1.2.2 Regulatory mechanisms for HIF-1α expression 5
• 1.2.3 HIF-1α in angiogenesis 8
• 1.3 Phospholipase D 9
• 1.3.1 General features of PLD 9
• 1.3.2 Roles of PLD in signaling pathways and cellular functions 11
• 1.3.3 In vivo pathophysiological roles of PLD 11
• 1.4 References 13
• Chapter 2. Endothelial functions of phospholipase D2 in pathological angiogenesis
• 2.1 Introduction 22
• 2.2 Materials and Methods 24
• 2.3 Results 31
• 2.3.1 Generation of Pld2 knockout mice 31
• 2.3.2 PLD2 is required for survival, migration and sprouting of endothelial cells under hypoxic condition 33
• 2.3.3 Ablation of Pld2 decreases retinal angiogenesis and oxygen-induced retinopathy 37
• 2.3.4 Tumor growth and tumor angiogenesis is decrease in endothelial-specific Pld2 knockout mice 44
• 2.4 Discussion 51
• 2.5 Reference 54
• Chapter 3. Role of PLD2 in hypoxia-induced expression of HIF-1α.
• 3.1 Introduction 58
• 3.2 Materials and Methods 60
• 3.3 Results 65
• 3.3.1 Hypoxia-response gene expression is decreased in Pld2 KO endothelial cells 65
• 3.3.2 PLD2 plays a positive role in translational control of HIF-1α expression during hypoxia 71
• 3.4 Discussion 76
• 3.5 Reference 80
• Conclusions 86
• 요약문 88
• 감사의 글 (Acknowledgement) 91