Hematopoietic Progenitor Cell Mobilization by Granulocyte Colony-Stimulating Factor and Erythropoietin in the Absence of Matrix Metalloproteinase-9

Sequential morphological characteristics of murine fetal liver hematopoietic microenvironment in Swiss Webster mice

Embryonic hematopoiesis occurs via dynamic development with cells migrating into various organs. Fetal liver is the main hematopoietic organ responsible for hematopoietic cell expansion during embryologic development. We describe the morphological sequential characteristics of murine fetal liver niches that favor the settlement and migration of hematopoietic cells from 12 days post-coitum (dpc) to 0 day post-partum. Liver sections were stained with hematoxylin and eosin, Lennert’s Giemsa, Sirius Red pH 10.2, Gomori’s Reticulin, and Periodic Acid Schiff/Alcian Blue pH 1.0 and pH 2.5 and were analyzed by bright-field microscopy. Indirect imunohistochemistry for fibronectin, matrix metalloproteinase-1 (MMP-1), and MMP-9 and histochemistry for naphthol AS-D chloroacetate esterase (NCAE) were analyzed by confocal microscopy. The results showed that fibronectin was related to the promotion of hepatocyte and trabecular differentiation; reticular fibers did not appear to participate in fetal hematopoiesis but contributed to the physical support of the liver after 18 dpc. During the immature phase, hepatocytes acted as the fundamental stroma for the erythroid lineage. The appearance of myeloid cells in the liver was related to perivascular and subcapsular collagen, and NCAE preceded MMP-1 expression in neutrophils, an occurrence that appeared to contribute to their liver evasion. Thus, the murine fetal liver during ontogenesis shows two different phases: one immature and mainly endodermic (<14 dpc) and the other more developed (endodermic-mesenchymal; >15 dpc) with the maturation of hepatocytes, a better definition of trabecular pattern, and an increase in the connective tissue in the capsule, portal spaces, and liver parenchyma. The decrease of hepatic hematopoiesis (migration) coincides with hepatic maturation.

Mechanisms of G-CSF-mediated hematopoietic stem and progenitor mobilization

Under normal conditions, the great majority of hematopoietic stem/progenitors cells (HSPCs) reside in the bone marrow. The number of HSPCs in the circulation can be markedly increased in response to a number of stimuli, including hematopoietic growth factors, myeloablative agents and environmental stresses such as infection. The ability to 'mobilize' HSPCs from the bone marrow to the blood has been exploited clinically to obtain HSPCs for stem cell transplantation and, more recently, to stimulate therapeutic angiogenesis at sites of tissue ischemia. Moreover, there is recent interest in the use of mobilizing agents to sensitize leukemia and other hematopoietic malignancies to cytotoxic agents. Key to optimizing clinical mobilizing regimens is an understanding of the fundamental mechanisms of HSPC mobilization. In this review, we discuss recent advances in our understanding of the mechanisms by which granulocyte colony-stimulating factor (G-CSF), the prototypical mobilizing agent, induces HSPC mobilization.

AMD3100 synergizes with G-CSF to mobilize repopulating stem cells in Fanconi anemia knockout mice

Fanconi anemia (FA) is a heterogeneous inherited disorder characterized by a progressive bone marrow (BM) failure and susceptibility to myeloid leukemia. Genetic correction using gene-transfer technology is one potential therapy. A major hurdle in applying this technology in FA patients is the inability of granulocyte colony-stimulating factor (G-CSF) to mobilize sufficient numbers of hematopoietic stem (HSC)/progenitor cells (HPC) from the BM to the peripheral blood. Whether the low number of CD34(+) cells is a result of BM hypoplasia or an inability of G-CSF to adequately mobilize FA HSC/HPC remains incompletely understood. Here we use competitive repopulation of lethally irradiated primary and secondary recipients to show that in two murine models of FA, AMD3100 synergizes with G-CSF resulting in a mobilization of HSC, whereas G-CSF alone fails to mobilize stem cells even in the absence of hypoplasia.

Matrix metalloproteinase inhibitors as therapy for inflammatory and vascular diseases

Matrix metalloproteinases (MMPs) have outgrown the field of extracellular-matrix biology and have progressed towards being important regulatory molecules in cancer and inflammation. This rise in status was accompanied by the development of various classes of inhibitors. Although clinical trials with synthetic inhibitors for the treatment of cancer were disappointing, recent data indicate that the use of selective inhibitors might lead to new therapies for acute and chronic inflammatory and vascular diseases. In this Review, we compare the major classes of MMP inhibitors and advocate that future drug discovery should be based on crucial insights into the differential roles of specific MMPs in pathophysiology obtained with animal models, including knockout studies.