Increased Ischemia-Induced Angiogenesis in the Staggerer Mouse, a Mutant of the Nuclear Receptor Ror

Ror is an orphan nuclear receptor. In homozygous staggerer mutant mice (Rora), a deletion within the Rora gene leads to an overexpression of inflammatory cytokines. Because inflammation and hypoxia are 2 key stimuli of ischemia-induced angiogenesis, we studied the role of Ror in this setting. Ischemia was induced by ligation of the right femoral artery in C57BL/6 Rora / and Rora mice. After 3 and 28 days, angiogenesis was evaluated by microangiography, measurement of capillary density using immunohistochemistry (anti-CD31), and measurement of blood flow by laser Doppler imaging. At day 3, angiographic score and blood flow were similar in Rora mice and in Rora / littermates. Conversely, at day 28, Rora mice showed a significant 2-fold increase in angiographic score and a 3-fold increase in capillary density within the ischemic hindlimb compared with control. Functionally, this coincided with a significant rise in leg perfusion in Rora mice (0.83 0.05 for ischemic/nonischemic leg perfusion ratio) compared with Ror / mice (0.66 0.04, P 0.05). In addition, more extensive angiogenesis in Rora mice correlated with an increased expression of eNOS protein by 83 12% and 71 24% at 3 and 28 days, respectively (P 0.05), whereas the level of the antiangiogenic cytokine IL-12 was significantly reduced by 38 10% at day 28 (P 0.05). Conversely, no changes in VEGF expression were observed. Our study identifies for the first time a new role for Ror as a potent negative regulator of ischemia-induced angiogenesis. (Circ Res. 2001;89:1209-1215.)