Abstract 5208: The role of platelet-type arachidonate 12-lipoxyganse in murine lungs exposed to a fibrogenic dose of irradiation
Authors: Chung Eun Joo , White Ayla , Citrin Deborah 
Published: July 2017

Introduction: Ionizing radiation (RT) is employed in the treatment of approximately half of patients with cancer, including those with thoracic malignancies. Exposure of tumor adjacent normal lung may result in injury and fibrosis. Arachidonate lipoxygenase oxidizes arachidonic acid, yielding hydroperoxyl derivatives including hydroperoxyeicosatetraenoic acids (HPETEs) and the reduced form, hydroxyeicosatetraeonic acids (HETEs). Arachidonate lipoxygenases are classified as 5-, 8-, 12-, or 15-LOX, according to the site of oxygen insertion within arachidonic acid. There are two isoforms of arachidonate 12-lipoxygnases in mammals, the platelet-type (12S-LOX; gene ALOX12), and the epidermal-type (12R-LOX; gene ALOX12B). Recently, we found an increased expression 12S-LOX in murine lungs exposed to a fibrogenic dose of irradiation. We hypothesized that 12S-LOX would be required for radiation-induced pulmonary fibrosis (RIPF).

Methods: C57/BL6 mice (n&gt;3 per group) were exposed to thoracic RT (0 Gy, 5 Gy, 17.5 Gy, or 6x5 Gy). Levels of 12S-LOX mRNA and protein were assessed in isolated various cell types from lungs (In Vitro) and in lung tissues (In Vivo) after RT with an immunohistochemical assay and quantitative PCR. Levels of chemokine ligands mRNA were assessed in isolated primary pneumocytes exposed to 17.5 Gy or 12S-HETE. Differential polarization of bone marrow-derived macrophage cultures with/without 12S-HETE was examined by quantitative PCR of polarization markers. Activity of arginase-1 was measured in lung tissue lysates at 16 weeks after RT.

Results: An increase of 12S-LOX protein was observed in type2 pneumocytes at 8 weeks after exposure with fibrogenic doses of RT (17.5 Gy and 5x6 Gy) compared to low dose RT (5 Gy) or controls (0 Gy). 12S-LOX mRNA was significantly induced in type2 pneumocytes at 3 days after receiving fibrogenic doses compared to other cell types in murine lung. Chemokine ligands including CCL2, which are responsible for bone marrow-derived monocytes recruitment, were induced in primary pneumocytes treated with RT or 12S-HETE. Treatment with 12S-HETE (150 nM) augmented arginase-1 expression significantly in bone marrow-derived macrophages cultured with IL-4. Macrophages expressing active arginase-1 accumulated in murine lungs at 16 weeks after thoracic irradiation with fibrogenic doses.

Conclusion: These studies demonstrate that type2 pneumocytes express 12S-LOX in response to RT with fibrogenic doses of radiation, and increased 12S-LOX contributes to the accumulation of alternatively activated macrophages in irradiated murine lungs. 12S-LOX may serve as a novel therapeutic target in mitigating RIPF.

Citation Format: Eun Joo Chung, Ayla White, Deborah Citrin. The role of platelet-type arachidonate 12-lipoxyganse in murine lungs exposed to a fibrogenic dose of irradiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5208. doi:10.1158/1538-7445.AM2017-5208