Salubrinal induces fetal hemoglobin expression via the stress-signaling pathway in human sickle erythroid progenitors and sickle cell disease mice

Abstract

Sickle cell disease (SCD) is an inherited blood disorder caused by a mutation in the HBB gene leading to hemoglobin S production and polymerization under hypoxia conditions leading to vaso-occlusion, chronic hemolysis, and progressive organ damage. This disease affects ~100,000 people in the United States and millions worldwide. An effective therapy for SCD is fetal hemoglobin (HbF) induction by pharmacologic agents such as hydroxyurea, the only Food and Drug Administration-approved drug for this purpose. Therefore, the goal of our study was to determine whether salubrinal (SAL), a selective protein phosphatase 1 inhibitor, induces HbF expression through the stress-signaling pathway by activation of p-eIF2α and ATF4 trans-activation in the γ-globin gene promoter. Sickle erythroid progenitors treated with 24µM SAL increased F-cells levels 1.4-fold (p=0.021) and produced an 80% decrease in reactive oxygen species. Western blot analysis showed SAL enhanced HbF protein by 1.6-fold (p=0.0441), along with dose-dependent increases of p-eIF2α and ATF4 levels. Subsequent treatment of SCD mice by a single intraperitoneal injection of SAL (5mg/kg) produced peak plasma concentrations at 6 hours. Chronic treatments of SCD mice with SAL mediated a 2.3-fold increase in F-cells (p=0.0013) and decreased sickle erythrocytes supporting in vivo HbF induction.

Pharmacological Induction of Fetal Hemoglobin in β-Thalassemia and Sickle Cell Disease: An Updated Perspective

“…Hahn et al on the other hand showed that in normal erythroid precursors, SAL might prevent dephosphorylation of p-eIF2α, resulting in increased HbF production by a post-transcriptional mechanism [144]. Lopez et al investigated whether SAL can induce HbF expression through the stresssignaling pathway by the activation of p-eIF2α and ATF4 trans-activation in the γ-globin gene promoter [148]. In sickle erythroid precursors, SAL (24 µM) increased F cells and significantly reduced oxidative stress, and increased levels of p-eIF2α and ATF4 [148].…”

“…Lopez et al investigated whether SAL can induce HbF expression through the stresssignaling pathway by the activation of p-eIF2α and ATF4 trans-activation in the γ-globin gene promoter [148]. In sickle erythroid precursors, SAL (24 µM) increased F cells and significantly reduced oxidative stress, and increased levels of p-eIF2α and ATF4 [148]. In humanized SCD mice, a single intraperitoneal injection of SAL (at a dose of 5 mg/kg for four weeks) mediated a 2.3-fold increase in F cells and reduced the percentage of sickle erythrocytes and erythrocyte ROS production [148].…”

“…In sickle erythroid precursors, SAL (24 µM) increased F cells and significantly reduced oxidative stress, and increased levels of p-eIF2α and ATF4 [148]. In humanized SCD mice, a single intraperitoneal injection of SAL (at a dose of 5 mg/kg for four weeks) mediated a 2.3-fold increase in F cells and reduced the percentage of sickle erythrocytes and erythrocyte ROS production [148]. Although the study did not report an additive effect when SAL was used in combination with HU, it was concluded that SAL was as effective as HU [148].…”