adrenomedullin and Retinal-Neovascularization

Adrenomedullin (ADM) was originally identified as an endogenous peptide having vasodilating functions. Following that, ADM has been shown to possess pleiotropic functions including angiogenic potency. The vascular function of ADM is mainly regulated by a receptor activity-modifying protein 2 (RAMP2). However, pathophysiological roles of ADM-RAMP2 system in retinal angiogenesis remain to be clarified. We analyzed (1) a oxygen-induced retinopathy (OIR) model using heterozygous ADM and RAMP2 knockout mice (ADMJ+/- and RAMP2+/-, respectively), (2) proliferation and migration of retinal endothelial cells in vitro, (3) retinal angiogenesis during developmental stage using drug-inducible endothelial cell-specific RAMP2 knockout mice (DI-E-RAMP2-/-), and (4) an OIR model treated with intravitreal injection of anti-ADM antibody. We found that ADM mRNA expression was upregulated under hypoxic conditions in OIR model. In ADM+/-, pathological neovascularization as well as VEGF and eNOS mRNA expression was suppressed. In addition, proliferation and migration effects of ADM on retinal endothelial cells were confirmed in vitro. We found that ADM-RAMP2 system also plays important roles in retinal vascular development, and Notch signaling is possibly involved. Finally, we revealed that intravitreal injection of anti-ADM antibody reduced pathological retinal angiogenesis in OIR model. From these results, we clarified that ADM-RAMP2 system plays important roles in both the pathological and physiological retinal angiogenesis. ADM-RAMP2 system is a hopeful new therapeutic method for controlling pathological retinal angiogenesis in ocular diseases.

Topics: Adrenomedullin; Animals; Humans; Hypoxia; Neovascularization, Physiologic; Receptor Activity-Modifying Protein 2; Retina; Retinal Neovascularization

Adrenomedullin (ADM) is an endogenous peptide first identified as a strong vasodilating molecule. We previously showed that in mice, homozygous knockout of ADM (ADM(-/-)) or its receptor regulating protein, RAMP2 (RAMP2(-/-)), is embryonically lethal due to abnormal vascular development, thereby demonstrating the importance of ADM and its receptor signaling to vascular development. ADM expression in the retina is strongly induced by ischemia; however, its role in retinal pathophysiology remains unknown. Here, we analyzed oxygen-induced retinopathy (OIR) using heterozygous ADM and RAMP2 knockout mice models (ADM(+/-) or RAMP2(+/-), respectively). In addition, we analyzed the role of the ADM-RAMP2 system during earlier stages of retinal angiogenesis using an inducible endothelial cell-specific RAMP2 knockout mouse line (DI-E-RAMP2(-/-)). Finally, we assessed the ability of antibody-induced ADM blockade to control pathological retinal angiogenesis in OIR. In OIR, neovascular tufts, avascular zones, and hypoxic areas were all smaller in ADM(+/-) retinas compared with wild-type mice. ADM(+/-) retinas also exhibited reduced levels of VEGF and eNOS expression. DI-E-RAMP2(-/-) showed abnormal retinal vascular patterns in the early stages of development. However, ADM enhanced the proliferation and migration of retinal endothelial cells. Finally, we found intravitreal injection of anti-ADM antibody reduced pathological retinal angiogenesis. In conclusion, the ADM-RAMP2 system is crucially involved in retinal angiogenesis. ADM and its receptor system are potential therapeutic targets for controlling pathological retinal angiogenesis.

Topics: Adrenomedullin; Animals; Antibodies, Monoclonal; Cell Hypoxia; Cell Movement; Cell Proliferation; Cells, Cultured; Endothelial Cells; Fetal Development; Gene Expression Regulation; Intravitreal Injections; Mice; Mice, Inbred C57BL; Mice, Knockout; Receptor Activity-Modifying Protein 2; Retina; Retinal Neovascularization; Retinal Vessels; RNA, Messenger

Hypoxia inducible factor (HIF) plays a critical role in cellular adaptation to hypoxia by regulating the expression of essential genes. Pathological activation of this pathway leads to the expression of pro-angiogenic factors during the neovascularization in cancer and retinal diseases. Little is known about the epigenetic regulations during HIF-mediated transcription and activation of pro-angiogenic genes in oxygen-dependent retinal diseases. Here, we show that hypoxia induces the expression of a number of histone lysine demethylases (KDMs) in retinal pigment epithelial cells. Moreover, we show that the expression of pro-angiogenic genes (ADM, GDF15, HMOX1, SERPE1 and SERPB8) is dependent on KDMs under hypoxic conditions. Further, treating the cells with a general KDM inhibitor blocks the expression of these pro-angiogenic genes. Results from these studies identify a new layer of epigenetic transcription regulation under hypoxic conditions and suggest that specific inhibitors of KDMs such as JMJD1A can be a new therapeutic approach to treat diseases caused by the hypoxia induced neovascularization in cancer and retinal diseases.

Topics: Adrenomedullin; Amino Acids, Dicarboxylic; Cell Hypoxia; Cell Line, Tumor; Epigenesis, Genetic; Growth Differentiation Factor 15; Heme Oxygenase-1; Histone Demethylases; Humans; Oxygen; Retinal Neovascularization; Retinal Pigment Epithelium