Normal Hematopoietic Stem Cell Biology
A major focus of Dr. Goodell’s laboratory is the molecular regulation of hematopoietic stem cells (HSC). Her laboratory has sought to identify the genes that are responsible for maintaining the quiescent state of HSC, as well as their self renewal. A single injection of the chemotherapeutic agent 5-Fluoruracil (5FU) kills rapidly dividing progenitors in the bone marrow, and activates HSC, causing some to differentiate, regenerating the hematopoietic system, and others to self-renew. Using microarrays to examine gene expression changes over a time-course of activation, the laboratory has identified cohorts of genes that appear to be involved in activating self-renewal of the HSC (Venezia et al PLoS 2004 [PMID: 15459755]). The laboratory is now examining the role of specific genes in the self-renewal and activation cycle.
A long-term goal of these studies is to elucidate the genes required for HSC self-renewal, with the goal of determining conditions that would allow HSC to be expanded in vitro without differentiation, a long-sought goal of hematological research that could have enormous impact on the practice of bone marrow transplantation. A second major goal is to broadly understand growth regulation of normal stem cells, with the expectation that insights into regulation of normal stem cells would also apply to regulation of quiescence and activation of putative tumor stem cells.
Generation of hematopoietic cells from human embryonic stem cells
Human ES (hES) cells can expand indefinitely and differentiate to all known somatic cells types, including blood. Human bone marrow stem cells made from hES could be used for bone marrow transplantation to make patients histocompatible to additional therapeutic cell types made from hES. Hematopoietic components differentiate from hES, albeit only inefficiently. The laboratory is investigating genes that may regulate hematopoietic differentiation from hES, with a view to either selecting differentiating hematopoietic cells, or enhancing hematopoietic differentiation by forced expression of specific hematopoietic regulators.
Hematopoietic stem cells in aging
Stem cells replenish the cells of aging tissues, and can thus act as a barrier against some of the affects of age. However, hematopoietic stem cells from older mice have been shown to have diminished function, suggesting that they themselves may age. The Goodell laboratory is examining the molecular changes in hematopoietic stem cells that may account for these functional changes, by profiling gene expression in purified stem cells over a time-course of aged mice. Many broad changes are observed, including some seen in other aging systems. Current efforts will are directed to identifying genes that are regulate the aging process, as opposed to those that are simple markers of aging.
Identification of Putative Tumor Stem Cells
Dr. Goodell developed a method for the identification of normal murine hematopoietic stem cells, based on the efficient and specific efflux of the fluorescent DNA-binding dye Hoechst 33342. This so-called “side population” or “SP” method has now been widely applied by many investigators in attempt to identify stem cells in other tissues and species. Recently, the laboratories of Dr. Goodell and Dr. Malcolm Brenner have collaborated to determine whether the SP phenotype is a property of tumor-maintaining cells from acute myeloid leukemia (AML), showing that a subset of freshly-derived of AML lines could be established by isolating SP cells, and that these lines were capable of being passaged in NOD/SCID mice (Wulf et al, Blood 2001 [PMID: 11493466]).
More recently, the laboratories of Goodell and Brenner have also collaborated to examine the SP phenotype in fresh neuroblastomas (Hirschmann-Jax, PNAS 2004 [PMID: 15381773]). They found the SP phenotype to be characteristic of 15 of 23 neuroblastomas, and a subset of cell lines from other tumors. The SP phenotype itself has been linked to broad drug efflux properties (PMID: 15655356). Thus, the SP may mark a tumor-maintaining “stem cell” that should be examined in other tumor types. The laboratories are continuing to collaborate to examine the SP phenotype in a wide variety of tumors, and to determine whether tumor SP cells are tumor “stem cells.”