In Humanized Sickle Cell Mice, Imatinib Protects Against Sickle Cell-Related Injury.

Drug repurposing is a valuable strategy for rare diseases. Sickle cell disease (SCD) is a rare hereditary hemolytic anemia accompanied by acute and chronic painful episodes, most often in the context of vaso-occlusive crisis (VOC). Although progress in the knowledge of pathophysiology of SCD have allowed the development of new therapeutic options, a large fraction of patients still exhibits unmet therapeutic needs, with persistence of VOCs and chronic disease progression. Here, we show that imatinib, an oral tyrosine kinase inhibitor developed for the treatment of chronic myelogenous leukemia, acts as multimodal therapy targeting signal transduction pathways involved in the pathogenesis of both anemia and inflammatory vasculopathy of humanized murine model for SCD. In addition, imatinib inhibits the platelet-derived growth factor-B-dependent pathway, interfering with the profibrotic response to hypoxia/reperfusion injury, used to mimic acute VOCs. Our data indicate that imatinib might be considered as possible new therapeutic tool for chronic treatment of SCD.

Peroxiredoxin-2: A Novel Regulator of Iron Homeostasis in Ineffective Erythropoiesis.

AIMS: Iron overload (IO) is a life-threatening complication of chronic hemolytic disorders such as ß-thalassemia. IO results in severe cellular oxidative damage, leading to organ failure. Peroxiredoxin-2 (Prx2), a typical 2-cysteine-(Cys)-peroxiredoxin, is an important component of the cytoprotective system, but its response to IO is still to be fully defined. RESULTS: We studied the effects of IO on Prx2-knockout mice (Prx2-/-). The absence of Prx2 enhanced toxicity due to IO on erythropoiesis. We found that IO failed to induce the typical hepcidin (Hamp) upregulation in Prx2-/- mice due to its failure to activate the signal transducer and activator of transcription-3 (STAT3) with intact Jak2 signaling. In Prx2-/- mice, the loss of Hamp response was also observed after administration of a single dose of oral iron. When lipopolysaccharide (LPS) was used to explore IL6-STAT3 activation in Prx2-/- mice, STAT3 activation and Hamp upregulation were once again defective. Treatment with PEP-fusion-recombinant-Prx2 (PEP Prx2) significantly increased STAT3 activation with upregulation of Hamp expression in both IO- and LPS-exposed Prx2-/- mice. We also confirmed the beneficial effects of PEP Prx2 on Hamp expression through STAT3 activation in ß-thalassemic mice. INNOVATION: We propose that Prx2 plays a key role in responding to cytotoxicity of IO, directly targeting STAT3-transcriptional factor in a Jak2-independent fashion and regulating Hamp in response to canonical stimuli. CONCLUSION: Collectively, our data highlight a novel role of Prx2 in iron homeostasis. Prx2 is a key cytoprotector against IO that is induced either by iron supplementation or due to chronic hemolysis as in ß-thalassemia. Prx2 is required to support STAT3 transcriptional activity and regulation of Hamp expression. Antioxid. Redox Signal. 28, 1-14.

Abnormal modulation of cell protective systems in response to ischemic/reperfusion injury is important in the development of mouse sickle cell hepatopathy.

BACKGROUND: Sickle cell disease, a genetic red cell disorder inherited in an autosomal recessive manner, occurs throughout the world. Hepatic dysfunction and liver damage may be present in sickle cell disease, but the pathogenesis of these conditions is only partially understood. DESIGN AND METHODS: Transgenic mice with sickle cell disease (SAD mice) and wild-type mice were exposed to an ischemic/reperfusion stress. The following parameters were evaluated: hematologic profile, transaminase and bilirubin levels, liver histopathology, and mRNA levels of nuclear factor-κB p65, endothelial nitric oxide synthase, inducible nitric oxide synthase, heme oxygenase-1 and phosphodiesterase-1, -2, -3, and -4 genes in hepatocytes obtained by laser-capture microdissection. Immunoblotting was used to analyze the expression of the following proteins: nuclear factor-κB p65 and phospho-nuclear factor-κB p65, heme oxygenase-1, biliverdin reductase, heat shock protein-70, heat shock protein-27 and peroxiredoxin-6. A subgroup of SAD mice was treated with the phosphodiesterase-4 inhibitor rolipram (30 mg/Kg/day by gavage) during the ischemic/reperfusion protocol. RESULTS: In SAD mice the ischemic/reperfusion stress induced liver damage compatible with sickle cell disease hepatopathy, which was associated with: (i) lack of hypoxia-induced nuclear factor-κB p65 activation; (ii) imbalance in the endothelial/inducible nitric oxide synthase response to ischemic/reperfusion stress; (iii) lack of hypoxia-induced increased expression of heme oxygenase-1/biliverdin reductase paralleled by a compensatory increased expression of heat shock proteins 70 and 27 and peroxiredoxin-6; and (iv) up-regulation of the phosphodiesterase-1, -2, -3, and -4 genes. In SAD mice the phosphodiesterase-4 inhibitor rolipram attenuated the ischemic/reperfusion-related microcirculatory dysfunction, reduced the inflammatory cell infiltration and induced the heme oxygenase-1/biliverdin reductase cytoprotective systems. CONCLUSIONS: In SAD mice, sickle cell hepatopathy is associated with perturbed nuclear factor-κB p65 signaling with an imbalance of endothelial/inducible nitric oxide synthase levels, lack of heme oxygenase-1/biliverdin reductase expression and up-regulation of two novel cytoprotective systems: heat shock protein-27 and peroxiredoxin-6.