Our Research
The Clinical Problem:
Diminished megakaryocyte production is a serious problem in cancer patients who have received intensive, bone marrow toxic (myeloablative) chemotherapy. After standard chemotherapy and after bone marrow transplantation, delayed recovery of platelet counts, due to poor marrow megakaryocyte recovery, represents one of the most common and intractable complications. This complication results in many of patients receiving large numbers of platelet transfusions, a treatment that provides only transient benefits, is costly, and exposes patients to infectious and alloimmunization risks. Although effective treatments have emerged to boost marrow production of red cells and neutrophils, no effective treatments exist to boost marrow production of platelets. Thrombopoietin, the major growth factor for megakaryocytes, shows no clinical efficacy in accelerating marrow megakaryocyte recovery in myeloablated patients. Effective treatments will need to target the earliest phases of megakaryocyte development in the human marrow, enhancing the numbers of megakaryocytic precursors by promoting increased lineage commitment. Mechanistic dissection of megakaryocytic lineage commitment, the main goal of our research, will ultimately enable rational design of treatments to boost post-therapy megakaryocyte and platelet recovery.
The Scientific Problem:
During hematopoietic development in the bone marrow, megakaryocytes arise from a bipotent progenitor cell known as the BFU-E/Mk or the MEP. This progenitor gives rise both to the megakaryocytic and erythroid lineages; the abbreviation MEP stands for Megakaryocyte-Erythroid-Progenitor. The signals that determine lineage choice, megakaryocytic versus erythroid, remain essentially unknown. Many of the key transcription factors that program megakaryocytic development also program erythroid development. Paradoxically, the repetoire of genes expressed in megakaryocytic development shows little overlap with the repetoire of genes expressed in erythroid development. Understanding the basic mechanisms of megakaryocytic-erythroid lineage divergence will therefore elucidate a mammalian developmental strategy in which striking cellular diversity can be acheived using limited signaling and transcriptional pathways.
The Strategies Employed:
The goal is to understand megakaryocytic lineage commitment of normal human bone marrow cells. Therefore, one key model system consists of using primary human hematopoietic progenitor cells. Gene expression and lineage commitment in these cells can be studied by multiparametric flow cytometry, immunoblot, and RNA analysis. Genes of interest can be introduced into these cells by retroviral transduction. In vivo function of these cells will eventually be assayed by engraftment in immunodeficient NOD-SCID mice. For basic biochemical studies looking at the functioning of signaling and transcriptional complexes, multiple cell line model systems are used for initial characterization. For more physiologic testing of function, murine embryonic stem cell and knock-in mice will eventually be employed.