Aberrant expression of insulin-like growth factor-2 (IGF-2) in Philadelphia chromosome negative chronic myeloproliferative disorders

Insulin-like growth factor 2 modulates murine hematopoietic stem cell maintenance through upregulation of p57

Hematopoietic stem cells (HSC) rely on a highly regulated molecular network to balance self-renewal and lineage specification to sustain life-long hematopoiesis. Despite a plethora of studies aimed at identifying molecules governing HSC fate, our current knowledge of the genes responsible is limited. We have found insulin-like growth factor 2 (IGF2) to be expressed predominantly within long-term HSCs. This study examines IGF2 expression patterns and the effects of the gene in HSCs. Through the overexpression and knockdown of IGF2 within purified HSCs, we report that IGF2 expression increases HSC-derived multilineage colonies in vitro and enhances hematopoietic contribution in vivo on competitive bone marrow transplantation. The effects of IGF2 are mediated by direct upregulation of the CDKi p57, exclusively within long-term HSCs, via activation of the PI3K-Akt pathway. Increased expression of p57 resulted in a concomitant increase in HSCs in the G0/G1 stage of the cell cycle. Analysis of genomic DNA methylation revealed that HSCs exhibited a hypomethylated state within the promoter region of the CDKN1C (p57) gene, providing a potential mechanism for the exclusive effects of IGF2 within HSCs. Our studies indicate a novel role for IGF2 in regulating HSC cell cycle and illustrate potential novel therapeutic targets for hematologic diseases.

Global cytokine analysis in myeloproliferative disorders

Recently developed human cytokine array membranes combine the individual assets of enzyme-linked immunosorbent assay, enhanced chemiluminescence, and the high-throughput of microspot in order to detect multiple plasma cytokines simultaneously. We employed such a system to evaluate the presence and quantity of 79 different cytokines in the plasma of 20 patients with myeloproliferative disorders (MPDs) that were not on active therapy: 10 with primary myelofibrosis (PMF), 5 with polycythemia vera (PV), and 5 with essential thrombocythemia (ET). Compared to healthy controls, patients with PMF, but not those with either PV or ET, displayed significantly higher levels of tissue inhibitor of metalloproteinase (TIMP-1), macrophage inflammatory protein-1beta (MIP-1beta), and insulin-like growth factor binding factor-2 (IGFBP-2) (p=0.013, 0.028 and 0.02, respectively). These results constitute an important conformation for the pathogenetic role of these cytokines in PMF.

Stromal cell lines from the aorta-gonado-mesonephros region are potent supporters of murine and human hematopoiesis

OBJECTIVE

The hematopoietic system is nurtured by a supportive stroma environment allowing maintenance and differentiation of hematopoietic stem cells (HSC). However, only a limited number of these stromal cell clones support hematopoiesis in the absence of cytokine supplementation. So far, only two bone marrow-derived stromal cell lines (OP9 and S17) are capable of inducing hematopoietic differentiation of totipotent murine and human embryonic stem cells (ESC). Here, the potential of more than 100 stromal cell lines developed from the aorta-gonado-mesonephros (AGM) region was investigated in supporting adult and embryonic hematopoiesis. In addition, extensive phenotypic analysis should elucidate possible mechanisms involved in maintenance of hematopoietic stem cell function.

METHODS

More than 100 stromal cell clones derived from the AGM region of E10.5 mouse embryos were isolated. Hematopoietic stem cell support was tested for adult murine and human cord blood hematopoietic stem cells and hematopoietic cells derived from murine ESC. Genotypic and phenotypic characterization was performed including gene array analysis.

RESULTS

It was demonstrated that multiple clones showed high efficiency in supporting maintenance and expansion of primitive murine and human hematopoietic progenitors. In addition, we demonstrated for the first time that AGM stromal cell lines are also potent inducers of hematopoietic differentiation of murine ESC. Microarray analysis of AGM lines revealed a characteristic genotype with expression of genes involved in regulating hematopoiesis as well as mesodermal and early B cell development.

CONCLUSION

These AGM stromal cell lines may be of value in elucidating molecular mechanisms regulating early stem cell development and hematopoietic differentiation from ES-derived mesoderm.

Statins in the treatment of polycythaemia vera and allied disorders: An antithrombotic and cytoreductive potential?

Thrombohaemorrhagic complications are major clinical problems in the classical chronic Ph-negative myeloproliferative disorders (CMPDs), polycytaemia vera (PV), essential thrombocythaemia (ET) and idiopathic myelofibrosis (IMF), contributing significantly to morbidity and mortality. Pathophysiologically these disorders are characterized by clonal myeloproliferation, myeloaccumulation and a propensity to develop myelofibrosis and neoangiogenesis in both the bone marrow and spleen. Based upon in vitro and in vivo studies of the effects of statins (antithrombotic, antiproliferative, proapoptotic and antiangiogenic), this review focuses on the translation of these effects into potential clinical benefits of statin therapy in patients with CMPDs.

Genetic and Functional Characterization of Isolated Stromal Cell Lines from the Aorta-Gonado-Mesonephros Region

The hematopoietic system interacts with a supportive stromal environment allowing maintenance and differentiation of hematopoietic stem cells (HSCs). The aorta-gonado-mesonephros (AGM) region serves as a unique embryonic microenvironment, generating the first adult repopulating HSCs in the mouse embryo. To eludicate factors involved in hematopoietic support and induction of hematopoietic differentiation, we isolated more than 100 stromal cell clones derived from the AGM region of embryonic day (E) 10.5 mouse embryos for functional and genetic analysis. Selected isolated AGM stromal cell lines are highly efficient in supporting maintenance and expansion of mouse and human hematopoietic stem and progenitor cells. In addition, we can demonstrate for the first time that AGM stromal cell lines are also potent inducers of hematopoietic differentiation of murine embryonic stem cells. Stromal gene array analysis has identified genes that could play a role in hematopoietic support.