The ability to genotype millions of polymorphisms in thousands of individuals and to sequence entire genomes affords the opportunity to understand how human diversity is associated with many diseases and longevity. It is also possible to direct the differentiation of patient-specific induced pluripotent stem cells, or iPSCs to erythroid progenitors that mature to produce hemoglobin. Both genomics and new iPSC technology can be used to study the molecular basis of phenotypic heterogeneity. This knowledge will then allow the development of predictive networks and genetic risk scores that can be used prognostically and point to functional studies of interesting variants and novel pathways that might can lead to new treatment options. We are taking this approach to the study of hemoglobin disorders focusing on sickle cell disease.
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.
This collection, from Dr. Martin Steinberg (Boston University), used erythroid cells from patient-specific iPSCs to study genetic factors modulating the severity of sickle cell anemia and its responsiveness to treatment. This study was largely centered on this feature of the disease where the quantitative trait loci evaluated affect fetal hemoglobin (HbF) expression.
The iPS cell lines in this collection were banked and characterized in the laboratory of Dr. Gustavo Mostoslavsky, Boston University.
This collection contains over 40 cell lines. Individuals giving rise to iPSC lines were of African American or Arab descent. Disease states for the subjects include sickle cell anemia as well as no reported diagnoses. Age of donors range from 3-45 years.