No abstract

Sickle cell disease (SCD) is an inherited disorder caused by a point mutation in the β-globin gene, leading to the production of abnormally shaped red blood cells. Sickle cells are prone to hemolysis and thereby release free heme into plasma, causing oxidative stress and inflammation that in turn result in damage to multiple organs. The transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2) is a master regulator of the antioxidant cell-defense system. Here we show that constitutive Nrf2 activation by ablation of its negative regulator Keap1 (kelch-like ECH-associated protein 1) significantly improves symptoms in SCD model mice. SCD mice exhibit severe liver damage and lung inflammation associated with high expression levels of proinflammatory cytokines and adhesion molecules compared with normal mice. Importantly, these symptoms subsided after Nrf2 activation. Although hemolysis and stress erythropoiesis did not change substantially in the Nrf2-activated SCD mice, Nrf2 promoted the elimination of plasma heme released by sickle cells' hemolysis and thereby reduced oxidative stress and inflammation, demonstrating that Nrf2 activation reduces organ damage and segregates inflammation from prevention of hemolysis in SCD mice. Furthermore, administration of the Nrf2 inducer CDDO-Im (2-cyano-3, 12 dioxooleana-1, 9 diene-28-imidazolide) also relieved inflammation and organ failure in SCD mice. These results support the contention that Nrf2 induction may be an important means to protect organs from the pathophysiology of sickle cell-induced damage.

Chromosomal rearrangements between 3q21 and 3q26 induce inappropriate expression by recruiting a-distal hematopoietic enhancer (G2DHE) to the proximity of the gene, leading to myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). The acquisition of G2DHE by the gene reciprocally deprives this enhancer of 1 of the 2 alleles, resulting in a loss-of-function genetic reduction in abundance. Because haploinsufficiency is strongly associated with MDS and AML, we asked whether misexpression and haploinsufficiency both contributed to the observed leukemogenesis by using a 3q21q26 mouse model that recapitulates the G2DHE-driven misexpression, but in this case, it was coupled to a heterozygous germ line deletion. Of note, the heterozygous deletion promoted the -provoked leukemic transformation, resulting in early onset of leukemia. The 3q21q26 mice suffered from leukemia in which B220 cells and/or Gr1 leukemic cells occupied their bone marrows. We found that the B220Gr1c-Kit population contained leukemia-initiating cells and supplied Gr1 leukemia cells in the 3q21q26 leukemia. When expression levels in the B220Gr1c-Kit cells were decreased as a result of heterozygous deletion or spontaneous phenomenon, myeloid differentiation of the B220Gr1c-Kit cells was suppressed, and the cells acquired induced proliferation as well as B-lymphoid-primed characteristics. Competitive transplantation analysis revealed that heterozygous deletion confers selective advantage to EVI1-expressing leukemia cell expansion in recipient mice. These results demonstrate that both the inappropriate stimulation of and the loss of 1 allele equivalent of expression contribute to the acceleration of leukemogenesis.

Inflammation can be defined as a protective immune response against harmful exogenous and endogenous stimuli. Nevertheless, prolonged or autoimmune inflammatory responses are likely to cause pathological states that are associated with a production of inflammation-associated molecules along with reactive oxygen species (ROS). Kelch-like ECH-associated protein 1-nuclear factor erythroid 2-related factor 2 (KEAP1-NRF2) signaling provides a cell protection mechanism against oxidative insults when endogenous stress defense mechanisms are imbalanced. Understanding the roles of the KEAP1-NRF2 system in inflammation caused by various types of stimuli may aid in the development of new therapies. Recent Advances: There have been tremendous advances in understanding the mechanism by which the KEAP1-NRF2 pathway abrogates inflammation. In addition to the well-established ROS-dependent pathway, recent studies have provided evidence of the direct repression of the transcription of pro-inflammatory cytokine genes, such as IL1b and IL6 (encoding Interleukin-1β and Interleukin-6, respectively). Further, the expanding functions of NRF2 have elicited interest in the development of therapeutic modalities for inflammatory diseases, including multiple sclerosis and sickle cell disease. Critical Issues and Future Directions: Despite progress in the understanding of molecular mechanisms supporting the roles that NRF2 plays during inflammation, the relationship between NRF2 and other transcription factors and mediators of inflammation still remains ambiguous. Further studies are required to address the effects of functional polymorphisms in KEAP1 and NRF2 that modify susceptibility to specific disease-related inflammation. Comprehensive analyses in the future should explore tissue- or cell-type specific NRF2 activation to elaborate effects of NRF2 induction. Antioxid. Redox Signal. 00, 000-000.