Cardiac and Pulmonary Inflammatory Responses by Intermittent Hypoxia in C57BL/6N and C57BL/6J Mouse Strains

Abstract

Introduction: Mouse inbred lines C57BL/6N (6N) and C57BL/6J (6J) are both widely used as animal models of obstructive sleep apnea (OSA), which is characterized by intermittent hypoxia (IH). In the current study, we investigated the degree of susceptibility to IH on cardiac and pulmonary inflammation between the two sub-strains. Methods: Equal numbers of 13-week old male mice of 6N (n = 8; Strain code: 027; Charles River, NCI Research Models and Services, Frederick, Maryland, USA) and 6J (n=8; Stock #000664; Jackson Laboratories, Bar Harbor, Maine, USA) sub-strains were randomly subjected to intermittent normoxia (IN) or IH (IH30; thirty hypoxic events per hour; BioSpherix, USA) for one week. Between different groups, the pro-inflammatory mediators cytokine-induced neutrophil chemoattractant 1 (CINC-1), interleukin (IL)-6 and monocyte chemoattractant protein-1 (MCP-1) in heart and lung homogenates were measured by ELISA. Results: In both sub-strains, IH caused significant elevations of CINC-1 in heart and lung homogenates of both strains (6N heart: 113.1 ± 20.5 pg/mg protein vs. 60.5 ± 8.8 pg/mg protein for IH and IN group respectively, p < 0.05; 6J heart: 114.7 ± 10.3 pg/mg protein vs. 73.4 ± 8.7 pg/mg protein for IH and IN group respectively, p < 0.01) (6N lung: 81.7 ± 9.4 pg/mg protein vs. 57.8 ± 3.5 pg/mg protein for IH and IN group respectively, p < 0.05; 6J lung: 55.6 ± 2.7 pg/mg protein vs. 46.2 ± 2.7 pg/mg protein for IH and IN respectively, p < 0.05). However, there was a differential IH-mediated elevations of IL-6 in lung homogenates of both strains but not in heart homogenates (6N lung: 8.0 ± 0.6 pg/mg protein vs. 5.5 ± 0.5 pg/mg protein for IH and IN group respectively, p < 0.01; 6J lung: 7.5 ± 0.7 pg/mg protein vs. 5.5 ± 0.4 pg/mg protein for IH and IN respectively, p < 0.05). IH caused no difference in heart and lung MCP-1 level of either strain. Conclusion: Our data revealed that the genetic difference between 6N and 6J mice has similar impact on IH-induced cardiac and pulmonary inflammation. CINC-1 is expected to be an excellent tool for investigating neutrophil-mediated inflammatory diseases due to cardiopulmonary sequelae of obstructive sleep apnoea. †Equal contributors Acknowledgement: This study was supported by the generous donation from Shun Tak District Min Yuen Tong of Hong Kong and Stanley Ho Matching Grant.