Nonhematopoietic Nrf2 Deficiency Worsens Chronic Intravascular Hemolysis but Not Cardiomyopathy in Transgenic Sickle Cell Mice

Background: Cardiopulmonary complications are the leading causes of death in sickle cell disease (SCD). Cardiac complications in SCD include left ventricular (LV) hypertrophy and LV systolic or diastolic dysfunction. In SCD, intravascular hemolysis (IVH) contributes to multiorgan damage, but its role in cardiac injury is unknown. We previously reported that nonhematopoietic deficiency of nuclear factor erythroid-2-related factor 2 (Nrf2), a transcription factor that controls antioxidative and anti-inflammatory genes, worsens the severity of IVH in SCD mice. Here, we first sought to determine if Townes transgenic SCD mice develop an abnormal cardiac phenotype, utilizing a cross-sectional study of varying-aged mice to test the hypothesis that these mice develop an age-related cardiomyopathy. Second, we determined whether IVH associated with absence of Nrf2 in the nonhematopoietic system worsens SCD cardiomyopathy. Methods: To identify a SCD cardiac phenotype, we performed echocardiography in a cross sectional cohort of Townes transgenic sickle cell mice (SS) and matched AA controls of varying ages (1-10 months). LV echocardiography dimensions were normalized to body weight. To determine the role of IVH and Nrf2 on the SCD cardiac phenotype, we transplanted whole bone marrow cells from SS mice to irradiated Nrf2-/- mice or C57BL/6 (Nrf2+/+) mice, to generate bone marrow chimeric sickle mice with Nrf2 deficiency in nonhematopoietic tissues (SSNHNrf2-/-) or chimeric sickle controls (SSNrf2+/+), respectively. Serial echocardiography was performed for up to 10 months, and hearts were harvested post-mortem for histology and molecular studies. Results: Cross-sectional study: Echocardiography showed cardiac abnormalities, most pronounced by 10 months, in the SS (n=8-9) compared to AA mice (n=9-13), respectively: LV hypertrophy was evidenced by a larger LV internal diameter (0.16 ± 0.01 vs. 0.13 ± 0.10 mm/g, p=0.005), higher LV mass index (5.2 ± 0.5 vs. 4.0 ±0.2 mg/g, p=0.02) and higher post-mortem heart weight (7.8 ± 0.3 vs. 5.2 ± 0.2 mg/g, p