Faber JE. Effect of mini-tyrosyl-tRNA synthetase on ischemic angiogenesis, leukocyte recruitment, and vascular permeability. Am J Physiol Regul Integr Comp Physiol 295: R1138 -R1146, 2008. First published August 27, 2008 doi:10.1152/ajpregu.90519.2008, the N-terminal domain of tyrosyl-tRNA synthetase, is a recently identified protein released by endothelial cells that exhibits angiogenic and leukocyte chemoattractant, ELR-motif (Glu-Leu-Arg)-dependent activities in vitro. We sought to determine whether exogenous mini-TyrRS exerts these and other cytokine-like actions in physiological and pathological settings in vivo. High-dose mini-TyrRS (600 g ⅐ kg Ϫ1 ⅐ day Ϫ1 ) augmented while low-dose mini-TyrRS (3 g ⅐ kg Ϫ1 ⅐ day Ϫ1 ), unexpectedly, inhibited angiogenesis in the ischemic mouse ear. Enhanced angiogenesis was associated with increased CD45-and CD4-positive leukocyte accumulation. Mini-TyrRS also had biphasic actions on both basal and mustard oil-evoked and VEGF-evoked leakage of Evan's blue dye-albumin in nonischemic ear and in endothelial cell monolayers, that is, low-dose inhibited and high-dose augmented leakage. Mutation of the ELR motif of mini-TyrRS abolished the above activities. Mini-TyrRS was reduced (immunoblot) in extracts of ischemic calf muscle and in thoracic aorta explants exposed to hypoxia or VEGF. Inhibition of VEGF with a soluble Flt1 "trap" protein abolished this hypoxic-induced reduction in mini-TyrRS in aorta explants. These data show that mini-TyrRS has dose-dependent biphasic effects on ischemic angiogenesis and vascular permeability in vivo, that is, antiangiogenic and antipermeability activities at low concentration and proangiogenic, propermeability activities at high concentrations. hypoxia; ischemia; vascular endothelial growth factor AMINOACYL-TRNA SYNTHETASES, which catalyze the aminoacylation of tRNA molecules, are essential for encoding genetic information during translation (22,(32)(33)(34)(35). In higher eukaryotes, aminoacyl-tRNA synthetases associate with other polypeptides to form supramolecular multienzyme complexes. The eukaryotic tRNA synthetases consist of a core enzyme, which is closely related to the prokaryotic counterpart of the tRNA synthetase, and an additional domain that is appended to the amino-terminal or carboxyl-terminal end of the core enzyme. Human tyrosyl-tRNA synthetase (TyrRS), for example, has a carboxyl-terminal domain that is not part of the prokaryotic and lower eukaryotic TyrRS molecules. The synthetase also has an N-terminal domain that is cleaved by several endogenous enzymes, yielding mini-tyrosyl tRNA synthetase (mini-TyrRS).Mini-TyrRS has recently been shown to possess cytokinelike actions, leading to its inclusion in a growing family of aminoacyl tRNA synthetase (AARS) multifunction cytokinelike proteins and peptides (22,(32)(33)(34)(35). Mini-TyrRS stimulates neutrophil activation and chemotaxis in vitro and is angiogenic in endothelial cell cultures and in chick chorioallantoic membrane (CAM) and mouse matrigel implants (22,(32)(33)(34)...