Kurre Lab Current Projects
Hematopoietic Stem Cell Biology
A small subset of hematopoietic cells is responsible for homeostatic maintenance of blood and immune cell production in the bone marrow. Asymmetric division (self-renewal and differentiation) is one of their key properties and producing an apparent developmental hierarchy and a paradigm for stem cell research. Our research is focused on the critical interaction between hematopoietic stem cells and the microenvironment during homeostatic conditions and their impact on disease pathophysiology in bone marrow failure. Using murine transplantation and cell culture models we are sytematically studying select bone marrow populations.
We are particularly interested in bone marrow derived mesenchymal stromal cell precursors (MSC) and strategies that would allow the direct therapeutic manipulation of these and other cells in the microvenvironment.
Intra-hematopoietic cell fusion and genetic variation
Hematopoietic cells have previously been shown to fuse with heterogeneous cell types: hepatocytes, neurons, as well as epithelial cells of the intestine. Following several murine bone marrow transplants, we observed a small population of hematopoietic cells co-expressing unique cellular markers from both donor and host parental cells. Unlike previous observations, these cells were exclusively hematopoietic in nature. We developed single nucleotide polymorphism (SNP) PCR and interphase fluorescent in situ hybridization (FISH) strategies to confirm that these hybrid cells contained genetic material from both parental cells. Our PCR studies revealed that hematopoietic cell fusion products have a variety of unexpected genetic rearrangements. When we examined redundant parental markers in individual cells, we observed gain or loss of individual markers. (Figure). In spite of the genetic rearrangements, we did not observe any evidence of malignant transformation in the animals, even following serial transplantation of fused cells. These results were surprising because current dogma holds that genetic rearrangements in hematopoietic cells lead to cancer development. Based on our observations we conclude that hematopoietic cells may undergo intra-hematopoietic cell fusion, which leads to non-pathogenic genetic variation in the hematopoietic system. Our current studies are now focused on examining the integrity of DNA in fused hematopoietic cells and determining a mechanism by which hematopoietic cells fuse.
Replication deficient particles access the cell through a series of steps involving no specific (receptor independent) receptor dependent mechanisms. Previous work demonstrated the limitations posed by cell surface receptor expression and, by implication, heterologous pseudotyping with the cognate envelope. In the context of more recent studies using vesicular stomatitis virus G envelope protein we have identified additional aspects of the initial cell-vector interaction that reveal cell specific, cell entry kinetics associated with the complexity of the fibronectin extracellular matrix (Figure). Experiments are ongoing to understand how transduction of stem cell target population can be further optimized in light of these findings.
Ex vivo culture of HIV-derived lentivirus particles is generally thought to result in non specific attachment, receptor mediated binding, followed by uptake of the particle by the cell and proviral integration, or degradation via lysosomal / proteasomal mechanisms. Studies in the laboratory over the past years suggest that additional non-degradative cytoplasmic fates may exist. Based on extensive experiments a model (Figure) is now emerging whereby a minority of particles are capable of cytoplasmic persistence in association with key marker proteins of an exosomal pathway. And while DC-SIGN mediated uptake of native HIV particles can lead to exosomal sequestration by dendritic cells and ' trans-infection' of T-cells, our observation offers no apparent cell type restriction, suggesting a generally conserved cellular mechanism. The underlying biology and potential therapeutic implications of these studies are subject of ongoing investigation.
Fanconi Anemia | Genetics and Biology
Bone marrow failure is the most common cause of morbidity and mortality from Fanconi anemia (FA), a recessively inherited disorder resulting from mutations in one of at least 15 genes that cooperate in a DNA repair pathway. The underlying etiology is thought to reflect an accelerated postnatal exhaustion of the hematopoietic stem and progenitor cell (HSPC) pool. However, laboratory evidence of compromised hematopoietic function in patients generally precedes symptoms of cytopenia, and several other mesodermal-derived organ systems show defects with prenatal onset, including the skeletal system, heart, kidneys, and others.
Although spontaneous bone marrow failure does not occur in most murine models of FA, animals recapitulate impaired repopulating ability, characteristic cell cycle abnormalities, and impaired cytokine responses. The fetal liver provides a unique microenvironment for development of definitive hematopoietic function and serves as a site of massive HSPC expansion. Our ongoing studies suggest that bone marrow failure begins early during development with a progressive deficiency in progenitor number and function. Results contrast with a conventional model of postnatal stem cell attrition and may impact the development of preemptive therapies for FA patients.