Multiple-site activation of the cysteinyl leukotriene receptor 2 is required for exacerbation of ischemia/reperfusion injury.

Objective Transgenic overexpression of the human cysteinyl leukotriene receptor 2 (CysLT(2)R) in murine endothelium exacerbates vascular permeability and ischemia/reperfusion injury. Here, we explore the underlying mechanisms of CysLT(2)R activation-mediated inflammation and delineate the relative contributions of endogenous murine CysLT(2)R and the transgene-derived receptor. Approach and Results We created a novel mouse with only endothelial-expressed CysLT(2)R (endothelium-targeted overexpression mice [EC]/CysLT(2)R-knockout mice [KO]) by crossing EC with KO to dissect the role of endothelial CysLT(2)R in tissue injury. Surprisingly, we discovered that damage in EC/KO mice was not elevated (24% versus 47% EC) after ischemia/reperfusion. We examined vascular permeability and leukocyte recruitment/rolling responses in the cremaster vasculature after cysteinyl leukotriene (cysLT) stimulation. Mice possessing transgenic endothelial CysLT(2)R overexpression, whether EC or EC/KO, when stimulated with cysLTs, exhibited vascular hyperpermeability, declining leukocyte flux, and a transient increase in slow-rolling leukocyte fraction. Mice lacking endogenous CysLT(2)R (both KO [203 cells/min] EC/KO [24 +/- 3]) showed lower-rolling leukocyte flux versus wild-type (38 +/- 6) and EC (35 +/- 6) mice under unstimulated conditions. EC/KO mice differed from EC counterparts in that vascular hyperpermeability was not present in the absence of exogenous cysLTs. Conclusions These results indicate that endothelial and nonendothelial CysLT(2)R niches have separate roles in mediating inflammatory responses. Endothelial receptor activation results in increased vascular permeability and leukocyte slow-rolling, facilitating leukocyte transmigration. Nonendothelial receptors, likely located on resident/circulating leukocytes, facilitate endothelial receptor activation and leukocyte transit. Activation of both receptor populations is required for injury exacerbation.