Hemolysis-driven IFNα production impairs erythropoiesis by negatively regulating EPO signaling in sickle cell disease.

Disordered erythropoiesis is a feature of many hematologic diseases including sickle cell disease (SCD). However, very little is known about erythropoiesis in SCD. Here we show that while bone marrow (BM) erythroid progenitors and erythroblasts in thalassemia mice Hbbth3/+were increased more than 2 fold, they were expanded by only ~40% in Townes sickle mice (SS). We further show that the colony forming ability of SS erythroid progenitors was decreased and EPO/EPOR signaling was impaired in SS erythroid cells. Furthermore, SS mice exhibited reduced responses to EPO. Injection of mice with red cell lysates or hemin, mimicking hemolysis in SCD, led to suppression of erythropoiesis and reduced EPO/EPOR signaling, indicating hemolysis, a hallmark of SCD, can contribute to the impaired erythropoiesis in SCD. In vitro hemin treatment did not affect Stat5 phosphorylation, suggesting hemin-induced erythropoiesis suppression in vivo is via an indirect mechanism. Treatment with IFNα, which is upregulated by hemolysis and elevated in SCD, led to suppression of mouse BM erythropoiesis in vivo and human erythropoiesis in vitro along with inhibition of Stat5 phosphorylation. Notably, in sickle erythroid cells, IFN-I signaling was activated and the expression of CISH, a negative regulator of EPO/EPOR signaling, was increased. CISH deletion in human erythroblasts partially rescued IFNa-mediated impairment of cell growth and EPOR signaling. Knocking out Ifnar1 in SS mice rescued the defective BM erythropoiesis and improved EPO/EPOR signaling. Our findings identify an unexpected role of hemolysis on the impaired erythropoiesis in SCD through inhibition of EPO/EPOR signaling via a heme-IFNα-CISH axis.