Thrombospondin, a negative modulator of megakaryocytopoiesis.
The effects of native thrombospondin (TSP), an 18 kd recombinant protein comprising residues 1-174 of TSP (TSP1-174) with heparin-binding domain and a fusion protein comprising residues 559-669 of TSP (TSP559-669) on murine hematopoiesis, were studied by using different in vitro culture systems. TSP by itself did not show an inhibitory effect on colony-forming unit-megakaryocyte (CFU-MK) growth in a serum-free agar system and on the growth of colony-forming unit-granulocyte and macrophage (CFU-GM) in a plasma clot system. It was, however, found that in the plasma clot culture system when using aplastic anemia serum as the source of thrombopoietin or C-Mpl ligand (TPO), TSP and TSP1-174, but not TSP559-669, were able to inhibit the growth of CFU-MK from unfractionated and lineage negative (Lin-) bone marrow cells in a dose-dependent manner. A statistically significant suppression was seen at 1 microg/ml of TSP and 5 microg/ml of TSP1-174. This inhibitory effect of TSP was further found in both the serum-free agar system and the plasma clot system without aplastic anemia serum, where megakaryocyte colony growth was stimulated by recombinant TPO, basic fibroblast growth factor (bFGF), or interleukin-3 (IL-3). In a methylcellulose system, where a combination of stem cell factor (SCF), IL-3, and granulocyte/macrophage colony-stimulating factor (GM-CSF) were used, TSP inhibited the growth of colony-forming unit-granulocyte-erythroblast, megakaryocyte, and macrophage (CFU-GEMM) but not CFU-GM and burst-forming unit-erythroblast (BFU-E). Interestingly, this inhibitory effect of TSP on megakaryocyte colony growth could be counteracted by Fraxiparin, a low-molecular-weight heparin. These results demonstrate that TSP is a negative modulator of megakaryocytopoiesis and suggest that its inhibitory effect is at least partially mediated by N-terminal heparin-binding domain.
Chen
Y Z
YZ
Institut des Vaisseaux et du Sang, University VII of Paris, France.
Incardona
F
F
Legrand
C
C
Momeux
L
L
Caen
J
J
Han
Z C
ZC
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D006098:Granulocytes / Q000166:cytology / Q000187:drug effects; D006410:Hematopoiesis / Q000187:drug effects*; D006412:Hematopoietic Stem Cells / Q000166:cytology; D008533:Megakaryocytes / Q000187:drug effects*; D008562:Membrane Glycoproteins / Q000494:pharmacology*; D051379:Mice; D008807:Mice, Inbred BALB C; D010446:Peptide Fragments / Q000494:pharmacology; D013234:Stem Cells / Q000166:cytology / Q000187:drug effects; D019699:Thrombospondins
D008562:Membrane Glycoproteins; D010446:Peptide Fragments; D019699:Thrombospondins