Molecular determinants of fetal hemoglobin induction by hydroxyurea to treat sickle cell disease

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Project Summary Highly proliferative cells need to coordinate their gene expression programs with cellular metabolism and nutrient availability. However, we have a poor understanding of the transcriptional responses that arise when cells are limited in nucleotides, which are products of metabolism, and the machinery that initiates these programs. This is a critical need because nucleotide synthesis inhibitors are used as treatment for many diseases. One condition that is treated with a nucleotide synthesis inhibitor is sickle cell disease (SCD), a genetic blood disorder that causes significant morbidity and mortality in millions worldwide due to a mutation in beta-globin that causes red blood cells to sickle. Decades ago, the ribonucleotide reductase inhibitor hydroxyurea (HU), which blocks nucleotide synthesis, was found to induce expression of gamma-globin, which is normally expressed in the fetus as a component of fetal hemoglobin (HbF). Since HbF can functionally replace adult hemoglobin, it masks the effect of the beta-globin mutation and prevents sickling if present in red blood cells at sufficient levels. Unfortunately, the ability of HU to induce HbF is heterogeneous; many patients only have a partial response, and some do not respond at all. Progress in improving SCD therapy has been hampered by our lack of mechanistic understanding of how HU induces HbF. The objective of my proposal is to unravel the link between nucleotide limitation and HbF induction and identify genes that modulate this transcriptional response, using modern tools in genetics and metabolism. In Aim 1, I will determine how nucleotide limitation and replication stress caused by HU induces HbF in erythroid progenitors, and whether this occurs through the known transcriptional repressors of gamma-globin. In Aim 2, I will determine the degree of nucleotide depletion and replication stress in physiological contexts, such as primary erythroid cells and bone marrow, where HbF is induced. Finally, in Aim 3, I will use lineage barcoding strategies to detect gene expression differences that determine whether individual cells induce HbF in response to HU, with the goal of identifying genes whose genetic or pharmacologic modulation could improve the efficacy of HU in vivo. I anticipate that these proposed experiments will reveal the mechanism by which HU reactivates HbF and inform novel strategies to improve treatment of patients with SCD. More broadly, it will provide insight into how highly proliferative cells can coordinate a clinically efficacious transcriptional program in response to nucleotide limitation. My training plan leverages the rich resources of MIT, Boston Children’s Hospital, and Harvard Medical School to perform cutting-edge research and obtain clinical training. I have also outlined activities designed to facilitate substantial scientific career development and cultivate mentors who are physician scientists. Overall, my research proposal and career development plan are focused on providing me with the training and proficiencies needed to further my development as a physician scientist.