Sickle cell disease (SCD) and some types of b-thalassemia that are caused by defects in the adult form of hemoglobin manifest shortly after birth, when the switch from the fetal to the adult form of hemoglobin is complete. Even a partial reversal of this switch is associated with an improved course of these diseases. We employed a newly improved CRISPR-Cas9 platform to carry out a kinase domain-focused genetic screen to identify potentially druggable molecules that repress fetal hemoglobin (HbF) production. This screen uncovered HRI (also known as EIF2AK1), an erythroid-specific protein kinase that regulates protein translation. Depletion of HRI elevates HbF levels in human erythroid cells with few additional perturbations. HRI loss reduces the expression of the major HbF repressor BCL11A, and restoration of BCL11A expression partially restores HbF repression. Moreover, HRI depletion reduces sickling of SCD-derived human erythroid cells in culture.
In Aim 1 we will comprehensively dissect HRI function by assessing the transcriptome and proteome of HRI-depleted cells. The goals of Aim 2 are to study the mechanism by which HRI regulates BCL11A, identify additional HRI regulated HbF repressors, and examine the global impact of HRI on protein translational control in primary human erythroid cells.
Aim 3 will explore synergies with previously known HbF inducers both using a candidate approach, and by unbiased genetic screens for novel synergies.
In Aim 4 we will examine the effects of HRI loss on SCD by generating HRI-deficient humanized SCD mouse models. In sum, these studies explore the role of HRI in human red cell biology and examine HRI as target for pharmacologic HbF induction alone or in combination with mechanistically distinct HbF inducers.
This application seeks to study the biological functions and mechanism of action of a newly identified molecule called HRI that we found to regulate the expression of the fetal form of hemoglobin. Raising fetal hemoglobin in patients with sickle cell disease and some forms of thalassemia improves outcomes and has been an important therapeutic goal in the field for many years. The enzyme we discovered is expressed specifically in red blood cell precursors and is expected to be targetable with small molecules.
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