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Maintenance of the hematopoietic system is dependent upon the proper regulation and orchestrated functions of the hematopoietic stem cell (HSC) pool. A number of extrinsic signaling pathways and intrinsic regulators have been found to regulate HSC processes. However a full understanding of the ability of HSC to balance the processes of self-renewal, quiescence, and lineage specification is not yet clear. We therefore set out to identify novel HSC regulators by comparative gene expression analysis of whole genome transcriptomes generated for long-term (LT)-HSC (Hoechst low/- Lin- Sca1+ cKit+ CD34-), short-term (ST)-HSC (Hoechst low/- Lin- Sca1+ cKit+ CD34+), and non-HSC (Hoechst+) of the bone marrow. These studies identified IGF2 as one of the most differentially expressed genes within LT-HSC, suggesting a potential role for IGF2 in the regulation of HSC. Using a combination of lentiviral-mediated overexpression and knockdown experiments, we found IGF2 to confer enhanced self-renewal in vitro and in vivo. Overexpression of IGF2 resulted in an increased percentage of multi-lineage colonies within colony-forming unit (CFU) assays without affecting lineage specification. In vivo, serial bone marrow transplantation revealed that IGF2 within HSC enhances short-term and long-term donor contribution. Analysis of the expression of key cell cycle regulators revealed that IGF2 induced upregulation of p57 expression specifically within HSC. This upregulation could be attributed to differences in the methylation status of the p57 promoter in HSC compared to other progenitor and mature blood cell populations. p57, a member of the Cip/Kip family of cyclin dependent kinase inhibitors, has recently been shown to be required for the regulation of HSC quiescence and long-term self-renewal. Analysis of bone marrow obtained from primary and secondary transplant recipients showed that overexpression of IGF2 resulted in an increased percentage of quiescent HSC. Treatment of HSC overexpressing IGF2 with LY294002, a PI3K-Akt inhibitor, prevented IGF2-mediated upregulation of p57 expression. These findings demonstrate that within HSC, IGF2 induces p57 expression through activation of the PI3K-Akt pathway to regulate HSC quiescence. We have identified a novel role for IGF2 in HSC function, providing new insights into the biology of HSC and opening potential platforms for the development of better therapies involving HSC-mediated hematopoietic reconstitution.

Aging of the hematopoietic system promotes various immune and systemic disorders and is driven in-part by dysfunction of life-long self-renewing hematopoietic stem cells (HSC). Autophagy is required for the benefit associated with activation of conserved longevity signaling programs and is essential for HSC function in response to various stressors. With age, some HSCs basally increase autophagy flux and maintain inert metabolic activity. This autophagy-activated subset is responsible for the residual regenerative capacity of old stem cells, but the mechanisms promoting autophagy activation in HSC aging remain unknown. Here, we demonstrate that autophagy is a response to chronic inflammation in the aging HSC niche. Chronic inflammation impairs glucose metabolism in young and old HSCs (oHSC) by impeding AKT-FOXO intracellular signaling networks. We find that autophagy enables metabolic adaptation of oHSCs to non-glucose energy substrates for functional maintenance. Notably, water-only fasting transiently further activates autophagy in oHSCs, and upon refeeding normalizes glucose uptake and glycolytic flux as well as regenerative output. Our results demonstrate that inflammation-driven glucose hypometabolism impairs oHSC regenerative capacity, that autophagy activation metabolically adapts oHSCs to an inflamed niche, and that autophagy is a modulable node to restore glycolytic and regenerative capacity during stem cell aging.

Indiana University-Purdue University Indianapolis (IUPUI) / The hematopoietic system is highly proliferative, making hematopoietic stem and progenitor cells (HSPC) sensitive to radiation damage. Total body irradiation and chemotherapy, as well as the risk of radiation accident, create a need for countermeasures that promote recovery of hematopoiesis. Substantive damage to the bone marrow from radiation exposure results in the hematopoietic syndrome of the acute radiation syndrome (HS-ARS), which includes life-threatening neutropenia, lymphocytopenia, thrombocytopenia, and possible death due to infection and/or hemorrhage. Given adequate time to recover, expand, and appropriately differentiate, bone marrow HSPC may overcome HS-ARS and restore homeostasis of the hematopoietic system. Prostaglandin E2 (PGE2) is known to have pleiotropic effects on hematopoiesis, inhibiting apoptosis and promoting self-renewal of hematopoietic stem cells (HSC), while inhibiting hematopoietic progenitor cell (HPC) proliferation. We assessed the radiomitigation potential of modulating PGE2 signaling in a mouse model of HS-ARS. Treatment with the PGE2 analog 16,16 dimethyl PGE2 (dmPGE2) at 24 hours post-irradiation resulted in increased survival of irradiated mice compared to vehicle control, with greater recovery in HPC number and colony-forming potential measured at 30 days post-irradiation. In a sublethal mouse model of irradiation, dmPGE2-treatment at 24 hours post-irradiation is associated with enhanced recovery of HSPC populations compared to vehicle-treated mice. Furthermore, dmPGE2-treatment may also act to promote recovery of the HSC niche through enhancement of osteoblast-supporting megakaryocyte (MK) migration to the endosteal surface of bone. A 2-fold increase in MKs within 40 um of the endosteum of cortical bone was seen at 48 hours post-irradiation in mice treated with dmPGE2 compared to mice treated with vehicle control. Treatment with the non-steroidal anti-inflammatory drug (NSAID) meloxicam abrogated this effect, suggesting an important role for PGE2 signaling in MK migration. In vitro assays support this data, showing that treatment with dmPGE2 increases MK expression of the chemokine receptor CXCR4 and enhances migration to its ligand SDF-1, which is produced by osteoblasts. Our results demonstrate the ability of dmPGE2 to act as an effective radiomitigative agent, promoting recovery of HSPC number and enhancing migration of MKs to the endosteum where they play a valuable role in niche restoration.

Indiana University-Purdue University Indianapolis (IUPUI) / FMS-like tyrosine receptor kinase-internal tandem duplications (FLT3-ITDs) are the most frequent deleterious mutations found in acute myeloid leukemia (AML) and portend a poor prognosis. Currently, AML patients typically achieve disease remission, yet undergo high rates of disease relapse, implying a residual post-treatment reservoir of resistant malignancy-initiating cells. This begs for new therapeutic approaches to be discovered, and suggests that targeting multiple cellular compartments is needed for improved therapeutic approaches. We have shown that the protein tyrosine phosphatase, Shp2, associates physically FLT3-ITD at tyrosine 599 (Y599) and positively regulates aberrant STAT5 activation and leukemogenesis. We also demonstrated that genetic disruption of Ptpn11, the gene encoding Shp2, increased malignancy specific survival of animals transplanted with FLT3-ITD-transduced cells, suggesting that Shp2 may regulate the function of the malignancy-initiating cell. Taken together, I hypothesized that inhibiting Shp2 can target both FLT3-ITD+ AML tumor cells as well as FLT3-ITD-expressing hematopoietic stem cells. To study this hypothesis, I employed two validation models including genetic inhibition of Shp2 interaction with FLT3-ITD in 32D cells or genetic disruption of Shp2 in FLT3-ITD-expressing HSCs. Using FLT3-ITD-expressing 32D cells as an AML tumor model, I found that mutating the Shp2 binding site on FLT3-ITD (Y599) reduced proliferation in vitro and increased latency to leukemia onset in vivo. Further, pharmacologic inhibition of Shp2 preferentially reduced proliferation of FLT3-ITD+ primary AML samples compared to FLT3-ITD- samples, and cooperated with inhibition of the lipid kinase, phospho-inositol-3-kinase (PI3K), and of the tyrosine kinase, Syk, to reduce proliferation of both FLT3-ITD+ and FLT3-ITD- AML samples. To evaluate the stem cell compartment, I crossed a murine locus-specific knock-in of FLT3-ITD with Shp2flox/flox; Mx1-Cre mice to generate FLT3-ITD; Shp2+/- mice and found that Shp2 heterozygosity dramatically inhibits hematopoietic stem cell engraftment in competitive transplant assays. Further, I found that lineage negative cells from FLT3-ITD; Shp2+/- mice demonstrated increased senescence compared to control mice, suggesting that Shp2 may regulate senescence in FLT3-ITD-expressing hematopoietic stem cells. Together, these findings indicate a cooperative relationship between the tyrosine phosphatase, Shp2, and the kinases PI3K and Syk in AML tumor cells, and indicate that Shp2 plays a positive role in the stem cell compartment to promote stem cell function of the malignancy-initiating cell in AML. Therefore, targeting Shp2 may hold therapeutic benefit for patients with FLT3-ITD+ AML.

京都大学 / 0048 / 新制・論文博士 / 博士(医学) / 乙第12815号 / 論医博第2077号 / 新制||医||1004(附属図書館) / 31302 / 京都大学大学院医学研究科医学専攻 / (主査)教授 山田 亮, 教授 小川 誠司, 教授 竹内 理 / 学位規則第4条第2項該当 / Doctor of Medical Science / Kyoto University / DFAM

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Indiana University-Purdue University Indianapolis (IUPUI) / Hematopoietic cell transplantation (HCT) is an important modality used to treat patients with hematologic diseases and malignancies. A better understanding of the biological processes controlling hematopoietic cell functions such as migration/homing, proliferation and self-renewal is required for improving HCT therapies. This study focused on the role of two biologically relevant proteins, dipeptidylpeptidase IV (DPPIV/CD26) and Ras homologue enriched in brain 2 (Rheb2), in modulating hematopoietic cell engraftment. The first goal of this study was to determine the role of the protein DPPIV/CD26 in modulating the engraftment of human umbilical cord blood (hUCB) CD34+ stem/progenitor cells using a NOD/SCID mouse xenograft model, and based upon previous work demonstrating a role for this enzyme in Stromal-Derived Factor-1/CXCL12 mediated migration and homing. Related to this first goal, pretreatment with an inhibitor of DPPIV/CD26 peptidase activity increased engraftment of hUCB CD34+ cells in vivo in recipient Non Obese Diabetic/Severe Combined Immunodeficiency (NOD/SCID) mice while not disturbing their differentiation potential following transplantation. These results support using DPPIV/CD26 inhibition as a strategy for enhancing the efficacy of cord blood transplantation. The second goal was to determine, by overexpression, the role of the Rheb2 in affecting the balance between proliferation and in vivo repopulating activity of mouse hematopoietic cells. Rheb2 is known to activate the mammalian target of rapamycin (mTOR) pathway, a pathway important in hematopoiesis. Rheb2 overexpression increased the proliferation and mTOR signaling of two hematopoietic cell lines, 32D and BaF3, in response to delayed IL-3 addition. In primary mouse hematopoietic cells, Rheb2 overexpression enhanced the proliferation and expansion of hematopoietic progenitor cells (HPCs) and phenotypic hematopoietic stem cells (HSCs) in vitro. In addition, HPC survival was enhanced by Rheb2 overexpression. Using in vivo competitive repopulation assays, Rheb2 overexpression transiently expanded immature HPC/HSC populations shortly after transplantation, but reduced the engraftment of total transduced cells. These findings support previous work showing that signaling proteins able to enhance the proliferative status of hematopoietic stem cells often cause exhaustion of self-renewal and repopulating ability. These studies of hematopoietic engraftment modulated by both of these molecules provide information which may be important to future work on HCT.

Vitamin-C (Vit-C) has been shown to modulate hematopoietic stem cells and leukemia stem cell frequency in-vivo. Herein, Vit-C analogue, L-ascorbic acid 2-phosphate (AA2P), was investigated as a new potential HSC expansion agonist. Cord blood CD34+ cells were expanded in cultures with or without AA2P. AA2P induced a 2-fold increase in the expansion of stem and progenitor subsets including lymphoid-primed multi-potential progenitors (p<0.05, n=3) and functional colony forming progenitors. The functional properties of AA2P grafts was evaluated with a xenotransplant model. Superior platelet levels in the periphery (p<0.05) and human bone marrow engraftment (median 75% hCD45+ cells for AA2P Vs. 48% for PBS control at week-22, n=3, p<0.05) was detected in AA2P cohorts Vs. control. In summary, my results demonstrate that AA2P is a new stem and progenitor expansion agonist with AA2P-expanded stem and progenitor cells capable of increased engraftment and higher platelet recovery. These findings may aid to overcome cord blood limitations; thereby, improving clinical relevance.

Acute myeloid leukemia (AML) is a fatal cancer of the human hematopoietic system characterized by the rapid accumulation of non-functional, immature hematopoietic cells in the bone marrow (BM) and peripheral blood (PB) of affected patients. Limited sources of safe hematopoietic stem/progenitor cells (HSPCs) for transplantation and incomplete mechanistic understandings of disease initiation, progression and maintenance have impeded advances in therapy required for improvement of long-term AML patient survival rates. Toward addressing these unmet clinical needs, the ability to generate induced pluripotent stem cells (iPSCs) from human somatic cells may provide platforms from which to develop patient-specific (autologous) cell-based therapies and disease models. However, the ability to generate iPSCs from human AML patient somatic cells had not been investigated prior to this dissertation. Accordingly, I hypothesized that cellular reprogramming of human AML patient somatic cells to iPSCs is possible and will enable derivation of autologous sources of normal and dysfunctional hematopoietic progenitor cells (HPCs). I first postulated that reprogramming AML patient fibroblasts (AML Fibs) to pluripotency would provide a novel source of normal autologous HPCs. Our findings revealed that AML patient-specific iPSCs devoid of leukemia-associated aberrations found in the matched bone marrow (BM) could be generated from AML Fibs, and demonstrated that this cellular platform allowed for the derivation of healthy HPCs capable of normal differentiation to mature myeloid lineages in vitro. During the tenure of these experiments we also redefined conventional reprogramming methods by discovering that OCT4 transcription factor delivery combined with culture in pluripotent-supportive media was minimally sufficient to induce pluripotency in AML and normal Fibs. Toward capturing and modeling the molecular heterogeneity observed across human AML samples in vitro, we next asked whether reprogramming of AML patient leukemic cells would enable generation of iPSCs and derivative HPCs that recapitulated dysfunctional differentiation features of primary disease. Our results demonstrated that conventional reprogramming conditions were insufficient to induce pluripotency in leukemic cells, but that generation of AML iPSCs could be reproducibly achieved in one AML sample when reprogramming conditions were modified. These AML iPSCs and their derivative HPCs harboured and expressed the leukemia-associated aberration found in the BM leukemic cells and similarly possessed dysfunctional differentiation capacities. Together, this body of works provides the proof of principle that cellular reprogramming can be applied on a personalized basis to generate normal and dysfunctional HPCs from AML patient somatic cells. These foundational findings should motivate additional studies aimed at developing iPSC-based cell therapies and disease models toward improving AML patient quality of life and long-term survival rates. / Thesis / Doctor of Philosophy (PhD)