Sickle cell anemia, an orphan disease of African Americans, is noted for its extensive morbidity and high mortality. Only one FDA approved drug is available for its pathophysiologically-based treatment. This agent, hydroxyurea, works through its ability to induce fetal hemoglobin (HbF) expression, which thwarts sickle hemoglobin polymerization. Not all patients respond to this treatment, so additional HbF inducing drugs are needed. Our goal is to create the technology for developing high throughput sickle cell anemia-specific induced pluripotent stem cells (iPS) and characterize their directly differentiated progeny. Using a novel excisable reprogramming vector we will generate 'clinical grade' human iPS cells free of any residual reprogramming transgenes. These directly differentiated sickle iPS cells will be used to produce an unlimited supply of erythroid-lineage cells to better understand HbF genetic regulation and perform pre-clinical small molecule drug screens. Specifically, we hypothesize: 1) that 'clinical grade' disease-specific iPS cells can be efficiently and reproducibly derived from peripheral blood cells and induced to normal erythroid differentiation, which includes the expected the spectrum of p-like globin gene expression; 2) major HbF quantitative trait loci impact globin gene expression during embryonic, fetal, and adult erythropoiesis; 3) patients with markedly elevated HbF levels serve as natural models to identify and characterize genetic variations affecting HbF production; 4) high-potency inducers of HbF, either singly or in combination can be studied in iPS-derived erythroid precursor cells.
Our aims are: 1) implement an efficient and 'scalable' system for the production of sickle cell anemia-specific iPS cells and use this to recapitulate erythroid-lineage ontogeny in vitro; 2) identify developmental gene expression profile differences between erythroid precursors that produce primarily HbF and those that produce primarily HbA or HbS; 3) determine the effects of the known major HbF quantitative trait loci on globin gene expression in iPS cells; 4) search for novel HbF genetic modifiers associated with HbF levels by examining gene expression in iPS derived erythroid cells; 5) determine which novel therapeutics discovered in high throughput screens can enhance and maintain high level HBG expression in iPS-derived sickle erythroid cells. Ultimately, we hope to translate these findings into clinically efficacious treatments.
We will make stem cells from the blood of patients with sickle cell anemia to learn how genes that make hemoglobin that is beneficial to these patients are regulated, and how these cells might be used for their treatment.
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