Thrombopoietin‐induced CXC chemokines, NAP‐2 and PF4, suppress polyploidization and proplatelet formation during megakaryocyte maturation

The mechanism of megakaryopoiesis, proplatelet formation (PPF) and platelet (PLT) production is not fully elucidated. Lactoferrin (LF) has been reported to have many biological functions including cell proliferation and differentiation, and the LF receptor is present on megakaryocytic cells. In the present study, we examined the effect of human LF (hLF) on PLT production from primary megakaryocytes (MKs). At first, we developed a PLT production system derived from human CD34 ؉ cells by thrombopoietin (TPO) stimulation. Because the number of proplatelets, PLTs and CD41؉ MKs was remarkebly increased after day 5, we employed the TPO-induced CD34 ؉ cells on day 5. Then, the effect of hLF on PLT production from human primary MKs was examined. In the range of 3-30 m mg/ml, hLF significantly inhibited PLT production up to about 60%. However, it did not significantly change the intensity of CD41 expression in MKs and the ploidy of MKs. In addition, it did not inhibit MK progenitors. These results suggest that LF directly inhibits PLT production from matured MKs, but does not inhibit megakaryopoiesis, including proliferation/maturation processes.

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“…25) In the present study, we observed that neutrophils surrounded MKs in BM (Fig. 5A) and strongly aggregated with MKs (Fig.…”

Section: Discussionsupporting

confidence: 66%

Lactoferrin Inhibits Platelet Production from Human Megakaryocytes in Vitro

Matsumura-Takeda

Ishida

Sogo

et al. 2008

Biological & Pharmaceutical Bulletin

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“…18,38 We tested the effect of CXCL7 peptides (LDGF, ␤-TG, and NAP-2) on the in vitro production of megakaryocytes from CFU-Megs. In our studies, NAP-2 not only decreased megakaryocyte colony numbers but also reduced the number of cells per colony, confirming the reports that NAP-2 limits megakaryocyte growth in vitro.…”

Section: Discussionmentioning

confidence: 99%

Monocyte-derived CXCL7 peptides in the marrow microenvironment

Pillai

Iwata

Awaya

et al. 2006

Blood

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The marrow microenvironment consists of several different interacting cell types, including hematopoietic-derived monocyte/macrophages and nonhematopoieticderived stromal cells. Gene-expression profiles of stromal cells and monocytes cultured together differ from those of each population alone. Here, we report that CXCL7 gene expression, previously described as limited to the megakaryocyte lineage, is expressed by monocytes cocultured with stromal cells. CXCL7 gene expression was confirmed by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR), and secretion of protein was detected by enzyme-linked immunosorbent assay (ELISA) and Western blot. At least 2 stromal-derived activities, one yet to be identified, were required for optimal expression of CXCL7 by monocytes. NAP-2, the shortest form of CXCL7 detected in the coculture media, was confirmed to decrease the size and number of CFU-Meg colonies. The propeptide LDGF, previously reported to be mitogenic for fibroblasts, was not secreted by stimulated monocytes. The recombinant form of LDGF produced in a prokaryotic expression system did not have biologic activity in our hands. The monocytic source of CXCL7 was also detected by immunohistochemistry in normal bone marrow biopsies, indicating an in vivo function. We conclude that stromal-stimulated monocytes can serve as an additional source for CXCL7 peptides in the microenvironment and may contribute to the local regulation of megakaryocytopoiesis. ( IntroductionHematopoietic regulation takes place within the marrow microenvironment (ME), which is defined by function as a complex of cells and cell products critical for the maintenance and regulation of stem cells and their progeny. The ME contains mesenchymal cells (eg, fibroblasts, adipocytes, and smooth muscle, all referred to as stromal cells); it also contains hematopoietic-derived monocytes/ macrophages. Primary long-term cultures (LTCs) of marrow stroma have been used to approximate the ME in vitro. 1 The model has proven useful for identifying cells and factors that play a role in supporting hematopoiesis. However, the heterogeneity of the cell types that comprise a functional LTC have led many investigators to generate stromal cell lines to dissect ME functional components. [2][3][4] We have previously reported on immortalized stromal lines generated by transducing human stromal cells with E6/E7 genes from human papilloma virus (HPV). 5,6 Two of these lines have been studied and characterized in detail. One, designated HS27a, supports maintenance of early hematopoietic progenitors in "cobblestone areas" and does not secrete growth factors. The other, designated HS5, does not support cobblestone areas but does secrete copious amounts of growth factors. These lines have hence been hypothesized to represent cell types that contribute to functionally distinct niches.Monocyte-derived macrophages have long been known as critical components of both the in vivo and in vitro ME. In vivo, the macrophage can function as the "nurse cell" of the ery...

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“…Of interest, in this upregulated list (Supplementary Table S1) are secreted gene products such as Cxcl7, Cxcl4 and Thrombospondin 1. Cxcl7 and Cxcl4 block megakaryocyte development, 22 while Cxcl4 also supports the survival and chemosensitivity of hematopoietic cells. 23 Thrombospondin 1 promotes granulocytic 24 and blocks megakaryocyte differentiation.…”

Section: Identification Of Genes Altered By Aml1-eto9a In Microarraymentioning

confidence: 99%

The multi-functional cellular adhesion molecule CD44 is regulated by the 8;21 chromosomal translocation

Wang

et al. 2007

Leukemia

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The 8;21 translocation is a common chromosomal abnormality in acute myeloid leukemia (AML). We recently identified a naturally occurring leukemogenic splice variant, AML1-ETO9a (acute myeloid leukemia-1 transcription factor and the eighttwenty-one corepressor-9a), of t(8;21). To understand the leukemic potential of AML1-ETO9a, we performed microarray analysis with the murine multipotential hematopoietic FDCPmix A4 cell line. We identified changes in expression of various genes including CD44. CD44 is a type I transmembrane protein and functions as the major cellular adhesion molecule for hyaluronic acid, a component of the extracellular matrix. CD44 is expressed in most human cell types and is implicated in myeloid leukemia pathogenesis. We show that the presence of AML1-ETO9a significantly increased the expression of CD44 at both RNA and protein levels. Furthermore, the CD44 promoter is bound by AML1-ETO9a and AML1-ETO at the chromatin level. In addition, in the AML1-ETO9a leukemia mouse model CD44 is regulated in a cell context-dependent manner. Thus, our observations suggest that AML1-ETO and its splice variant AML1-ETO9a are able to regulate the expression of the CD44 gene, linking the 8;21 translocation to the regulation of a cell adhesion molecule that is involved in the growth and maintenance of the AML blast/stem cells.

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Thrombopoietin‐induced CXC chemokines, NAP‐2 and PF4, suppress polyploidization and proplatelet formation during megakaryocyte maturation

Abstract: Background : We previously reported that the express-

Cited by 13 publications

References 26 publications

Lactoferrin Inhibits Platelet Production from Human Megakaryocytes in Vitro

Lactoferrin Inhibits Platelet Production from Human Megakaryocytes in Vitro

Monocyte-derived CXCL7 peptides in the marrow microenvironment

The multi-functional cellular adhesion molecule CD44 is regulated by the 8;21 chromosomal translocation

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