Cardiac-Specific Overexpression of Oxytocin Receptor Leads to Cardiomyopathy in Mice

Background: Oxytocin (Oxt) and its receptor (Oxtr) gene system has been implicated in cardiomyogenesis and cardioprotection; however, effects of chronic activation of Oxtr are not known. We generated and investigated transgenic (TG) mice that overexpress Oxtr specifically in the heart. Methods and Results: Cardiac-specific overexpression of Oxtr was obtained by having the alpha-major histocompatibility complex promoter drive the mouse Oxtr gene (alpha-Mhc-Oxtr). Left ventricular (LV) function and remodeling were assessed by magnetic resonance imaging and echocardiography. In alpha-Mhc-Oxtr TG mice, LV ejection fraction was severely compromised at 14 weeks of age compared with wild-type (WT) litter mates (25 +/- 6% vs 63 +/- 3%; P < .001). LV end-diastolic volume was larger in the TG mice (103 +/- 6 mu L vs 67 +/- 5 mu L; P < .001). alpha-Mhc-Oxtr TG animals displayed cardiac fibrosis, atrial thrombus, and increased expression of pro-fibrogenic genes. Mortality of alpha-Mhc-Oxtr TG animals was 45% compared with 0% (P < .0001) of WT littermates by 20 weeks of age. Most cardiomyocytes of alpha-Mhc-Oxtr TG animals but not WT littermates (68.0 +/- 12.1% vs 5.6 +/- 2.4%; P = .008) were positive in staining for nuclear factor of activated T cells (NEAT). To study if thrombin inhibitor prevents thrombus formation, a cohort of 7-week-old alpha-Mhc-Oxtr TG mice were treated for 12 weeks with AZD0837, a potent thrombin inhibitor. Treatment with AZD0837 reduced thrombus formation (P < .05) and tended to attenuate fibrosis and increase survival. Conclusions: Cardiac-specific overexpression of Oxtr had negative consequences on LV function and survival in mice. The present findings necessitate further studies to investigate potential adverse effects of chronic Oxt administration. We provide a possible mechanism of Oxtr overexpression leading to heart failure by nuclear factor of activated T cell signaling. The recapitulation of human heart failure and the beneficial effects of the antithrombin inhibitor render the alpha-Mhc-Oxtr TG mice a promising tool in drug discovery for heart failure.