Dysregulation of transcription factors and chromatin architecture in Trisomy 21 hematopoietic disorders

About This Grant

PROJECT SUMMARY/ABSTRACT Human hematopoiesis requires a complex interplay of genes, transcription factors, and epigenetic modifiers that regulate lineage commitment and maturation. Trisomy 21 (T21), the chromosomal abnormality underlying Down syndrome, is associated with genome-wide gene dysregulation and baseline hematopoietic abnormalities such as polycythemia and thrombocytopenia. Transient abnormal myelopoiesis (TAM) and myeloid leukemia of Down syndrome (ML-DS) are related disorders unique to Down syndrome that arise from a megakaryocyte-erythroid progenitor with blocked differentiation. TAM and ML-DS are characterized by a megakaryocyte (MK) surface marker signature and mutations in the hematopoietic transcription factor GATA1, resulting in exclusive expression of the truncated GATA1s isoform. ML-DS is additionally characterized by “third-hit” mutations in regulators of epigenetics or chromatin structure, such as in the cohesin complex member STAG2. Individuals with germline GATA1s mutations without T21 develop cytopenia(s) without leukemic predisposition, emphasizing the role of chromosome 21-encoded genes, such as the transcription factor RUNX1, in the progression from T21 to TAM to ML-DS. However, the underlying mechanisms remain incompletely understood. This proposal employs a novel isogenic human induced pluripotent stem cell (iPSC) system to isolate the individual and synergistic roles of T21, GATA1s, RUNX1 isoforms, and STAG2 loss in hematopoiesis. My data suggest that T21 and GATA1s synergistically lead to enhanced megakaryopoiesis and cytokine-independent proliferation, a hallmark of myeloproliferative disorders, and that dysregulation of RUNX1 may contribute to this phenotype. STAG2 loss combined with T21 and GATA1s further enhances megakaryopoiesis and results in dysplasia. This proposal builds upon these data through two specific aims: 1) Determine how GATA1s and RUNX1 co-regulate megakaryopoiesis and 2) Determine how STAG2 loss further perturbs hematopoiesis in T21/GATA1s cells. The aims seek to produce medically relevant knowledge on normal and Down syndrome hematopoiesis by combining established and cutting-edge techniques in assessing chromatin architecture, MK biology, and transcriptional regulation. This proposal describes a 5-year training plan for the applicant, Dr. Kaoru Takasaki, to transition to an independent research career in pediatric hematology as a physician-scientist with expertise in the dysregulation of transcription factors and chromatin structure at the intersection between normal and abnormal hematopoiesis. She will be supported by two mentors, Dr. Stella Chou, an international expert on hematopoiesis, and Dr. Mortimer Poncz, a global expert in platelets and MKs, as well as an advisory committee with complementary expertise in epigenetics, chromatin structure, and iPSC disease modeling. Dr. Takasaki’s research and training will take place in the resource-rich environments of the Children’s Hospital of Philadelphia and the University of Pennsylvania that will provide an outstanding foundation to embark on an independent physician-scientist career.