Macrophage 12(S)-HETE Enhances Angiotensin II–Induced Contraction by a BLT2 (Leukotriene B 4 Type-2 Receptor) and TP (Thromboxane Receptor)-Mediated Mechanism in Murine Arteries

12/15-LO (12/15-lipoxygenase), encoded by Alox15 gene, metabolizes arachidonic acid to 12(S)-HETE (12-HETE). Macrophages are the major source of 12/15-LO among immune cells, and 12/15-LO plays a crucial role in development of hypertension. Global Alox15- or macrophage-deficient mice are resistant to Ang II (angiotensin II)–induced hypertension. This study tests the hypothesis that macrophage 12(S)-HETE contributes to Ang II–mediated arterial constriction and thus to development of Ang II–induced hypertension. Ang II constricted isolated abdominal aortic and mesenteric arterial rings. 12(S)-HETE (100 nmol/L) alone was without effect; however, it significantly enhanced Ang II–induced constriction. The presence of wild-type macrophages also enhanced the Ang II–induced constriction, while Alox15 −/− macrophages did not. Using this model, pretreatment of aortic rings with inhibitors, receptor agonists/antagonists, or removal of the endothelium, systematically uncovered an endothelium-mediated, Ang II receptor-2–mediated and superoxide-mediated enhancing effect of 12(S)-HETE on Ang II constrictions. The role of superoxide was confirmed using aortas from p47 phox−/− mice where 12(S)-HETE failed to enhance constriction to Ang II. In cultured arterial endothelial cells, 12(S)-HETE increased the production of superoxide, and 12(S)-HETE or Ang II increased the production of an isothromboxane-like metabolite. A TP (thromboxane receptor) antagonist inhibited 12(S)-HETE enhancement of Ang II constriction. Both Ang II–induced hypertension and the enhancing effect of 12(S)-HETE on Ang II contractions were eliminated by a BLT2 (leukotriene B 4 receptor-2) antagonist. These results outline a mechanism where the macrophage 12/15-LO pathway enhances the action of Ang II. 12(S)-HETE, acting on the BLT2, contributes to the hypertensive action of Ang II in part by promoting endothelial synthesis of a superoxide-derived TP agonist.

Roles of Thromboxane Receptor Signaling in Enhancement of Lipopolysaccharide-Induced Lymphangiogenesis and Lymphatic Drainage Function in Diaphragm

Objective: Thromboxane is an arachidonic acid metabolite that exerts its actions through a G-protein–coupled receptor with 7 transmembrane domains. Although an arachidonic acid metabolite, prostaglandin E2 was reported to enhance lymphangiogenesis, little is known on other arachidonic acid metabolites. In the present study, we investigated the roles of TP (thromboxane prostanoid) signaling in facilitating lymphangiogenesis during inflammation. Approach and Results: Inflammation was induced by repeated intraperitoneal injections of lipopolysaccharide, and lymphangiogenesis essential for draining peritoneal fluids was estimated in the diaphragm. Lipopolysaccharide induced lymphangiogenesis in the diaphragm in a time-dependent manner in wild-type mice. Compared with wild-type mice, lipopolysaccharide-induced lymphangiogenesis in TP-deficient (TP −/− ) mouse diaphragm tissues was suppressed, and this was accompanied by reduced drainage function from the peritoneal cavity. TP-positive macrophages and T cells were accumulated in the diaphragm and produced VEGF (vascular endothelial growth factor)-C and VEGF-D in a TP-dependent manner. Removal of macrophages and T cells resulted in reduced lymphangiogenesis and lowered expressions of VEGF-C and VEGF-D. Furthermore, TP −/− bone marrow chimeric mice exhibited reduced lymphangiogenesis. TP knockout specific to macrophages and T cells also led to reduced lymphangiogenesis and drainage function in mice with lipopolysaccharide injections. Conclusions: The present results suggest that TP signaling exerts prolymphangiogenic activity by acting on macrophages and T cells accumulated during inflammation and that TP signaling represents a novel target for controlling lymphangiogenesis.