Specific Deletion of Keap1 in Endothelial Cells or/and Macrophages of SCD Mice Induces Nrf2 to Protect Tissues Against Oxidative Insults

Sickle cell disease (SCD) model mice frequently suffer from hemolysis. Endothelial cells face hemolysis, and they activate inflammatory cells following their own activation. Heme and iron discharge into blood stream enhanced by the following ischemia reperfusion injury as consequence of intermittent vaso-occlusion, jeopardize functions of SCD mouse organs. Transcription factor Nrf2 regulates expression of the genes involved in antioxidant cell defense. The roles that Nrf2 plays in pathological conditions in association with oxidative insults make the Nrf2 pathway attractive for developing new drugs for SCD treatment. Recently, we demonstrated that systemic Nrf2 induction significantly relieves inflammation and organ damage of SCD mice, while hemolysis is still unaffected (PNAS 2015). To examine the mechanisms underlying the contribution of Nrf2, we analyzed SCD mice by means of cell type-specific activation of Nrf2 through conditional loss of its repressor Keap1. We generated compound SCD mice with Keap1 floxed and cell-specific Cre expression alleles (SCD::Keap1F/F::Tie1-Cre and SCD::Keap1F/F::LysM-Cre mice targeting endothelial cells and macrophages, respectively). In lungs of SCD::Keap1F/F::Tie1-Cre mice, expression of Nrf2 and Nrf2-target genes were upregulated, while expression of inflammatory cytokines were significantly repressed. In both genotypes, necrosis and inflammation of liver and lungs were significant improvement, compared to littermates control mice. Plasma leucocytes counts, plasma heme level, total bilirubin and indirect bilirubin levels, were significantly reduced in both genotypes compared to controls, and these levels were slightly higher in the SCD::Keap1F/F::LysM-Cre mice compared to SCD::Keap1F/F::Tie1-Cre mice. 8-OHdG staining of lungs showed smaller number of positive cells in SCD::Keap1F/F::Tie1-Cre mice. These results indicate that Nrf2 activation in both endothelial cells and macrophages contributes to relieve chronic complications of SCD.