Thrombopoietic activity of recombinant human interleukin-11 in nonhuman primates with ACNU-induced thrombocytopenia

Angptl4 is upregulated under inflammatory conditions in the bone marrow of mice, expands myeloid progenitors, and accelerates reconstitution of platelets after myelosuppressive therapy

BACKGROUND

Upon inflammation, myeloid cell generation in the bone marrow (BM) is broadly enhanced by the action of induced cytokines which are produced locally and at multiple sites throughout the body.

METHODS

Using microarray studies, we found that Angptl4 is upregulated in the BM during systemic inflammation.

RESULTS

Recombinant murine Angptl4 (rmAngptl4) stimulated the proliferation of myeloid colony-forming units (CFUs) in vitro. Upon repeated in vivo injections, rmAngptl4 increased BM progenitor cell frequency and this was paralleled by a relative increase in phenotypically defined granulocyte-macrophage progenitors (GMPs). Furthermore, in vivo treatment with rmAngptl4 resulted in elevated platelet counts in steady-state mice while allowing a significant acceleration of reconstitution of platelets after myelosuppressive therapy. The administration of rmAngptl4 increased the number of CD61(+)CD41(low)-expressing megakaryocytes (MK) in the BM of steady-state and in the spleen of transplanted mice. Furthermore, rmAngptl4 improved the in vitro differentiation of immature MKs from hematopoietic stem and progenitor cells. Mechanistically, using a signal transducer and activator of transcription 3 (STAT3) reporter knockin model, we show that rmAngptl4 induces de novo STAT3 expression in immature MK which could be important for the effective expansion of MKs after myelosuppressive therapy.

CONCLUSION

Whereas the definitive role of Angptl4 in mediating the effects of lipopolysaccharide (LPS) on the BM has to be demonstrated by further studies involving multiple cytokine knockouts, our data suggest that Angptl4 plays a critical role during hematopoietic, especially megakaryopoietic, reconstitution following stem cell transplantation.

CD41+/CD45+Cells Without Acetylcholinesterase Activity Are Immature and a Major Megakaryocytic Population in Murine Bone Marrow

Murine megakaryocytes (MKs) are defined by CD41/CD61 expression and acetylcholinesterase (AChE) activity; however, their stages of differentiation in bone marrow (BM) have not been fully elucidated. In murine lineage-negative (Lin(-))/CD45(+) BM cells, we found CD41(+) MKs without AChE activity (AChE(-)) except for CD41(++) MKs with AChE activity (AChE(+)), in which CD61 expression was similar to their CD41 level. Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs could differentiate into AChE(+), with an accompanying increase in CD41/CD61 during in vitro culture. Both proplatelet formation (PPF) and platelet (PLT) production for Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs were observed later than for Lin(-)/CD41(++)/CD45(+)/AChE(+) MKs, whereas MK progenitors were scarcely detected in both subpopulations. GeneChip and semiquantitative polymerase chain reaction analyses revealed that the Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs are assigned at the stage between the progenitor and PPF preparation phases in respect to the many MK/PLT-specific gene expressions, including beta1-tubulin. In normal mice, the number of Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs was 100 times higher than that of AChE(+) MKs in BM. When MK destruction and consequent thrombocytopenia were caused by an antitumor agent, mitomycin-C, Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs led to an increase in AChE(+) MKs and subsequent PLT recovery with interleukin-11 administration. It was concluded that MKs in murine BM at least in part consist of immature Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs and more differentiated Lin(-)/CD41(++)/CD45(+)/AChE(+) MKs. Immature Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs are a major MK population compared with AChE(+) MKs in BM and play an important role in rapid PLT recovery in vivo.

Nonhuman primate embryonic stem cells as a preclinical model for hematopoietic and vascular repair

Stem cell-based regenerative medicine therapies have been touted recently as a novel therapeutic approach to treat and cure a wide range of diseases. Both adult and embryonic stem (ES) cells can serve as important sources of precursor cells to derive more mature cells potentially utilized for clinical applications. Nonhuman primates have proven useful as a preclinical model, as demonstrated in studies of hematopoietic cell transplantation, gene therapy, and other areas. The derivation of nonhuman primate ES cells now provides an optimal resource to characterize and test ES cell-based therapies prior to trials with human ES cells. This review describes work to define strategies and mechanisms to derive blood and endothelial cells from nonhuman primate ES cells isolated from various species. Preclinical testing that solely relies on studies of putative therapeutic cells derived from mouse ES cells transplanted into other mice, or analyses of human ES cell-derived cells transplanted into immunodeficient or immunosuppressed rodents may not be predictive of efficacy in subsequent human trials. However, future testing using nonhuman primate ES cell-derived therapeutic cells done as an allogeneic transplant may best predict success for subsequent studies using human ES cells. Therefore, additional research on nonhuman primate ES cells, in addition to work on mouse and human ES cells, is greatly needed to facilitate clinical translation of new stem cell treatments.