Thrombospondins deployed by thrombopoietic cells determine angiogenic switch and extent of revascularization
Hans-Georg Kopp, … , Aaron J. Marcus, Shahin Rafii
Hans-Georg Kopp, … , Aaron J. Marcus, Shahin Rafii
Published December 1, 2006
Citation Information: J Clin Invest. 2006;116(12):3277-3291. https://doi.org/10.1172/JCI29314.
View: Text | PDF
Research Article Vascular biology Article has an altmetric score of 3

Thrombospondins deployed by thrombopoietic cells determine angiogenic switch and extent of revascularization

Abstract

Thrombopoietic cells may differentially promote or inhibit tissue vascularization by releasing both pro- and antiangiogenic factors. However, the molecular determinants controlling the angiogenic phenotype of thrombopoietic cells remain unknown. Here, we show that expression and release of thrombospondins (TSPs) by megakaryocytes and platelets function as a major antiangiogenic switch. TSPs inhibited thrombopoiesis, diminished bone marrow microvascular reconstruction following myelosuppression, and limited the extent of revascularization in a model of hind limb ischemia. We demonstrate that thrombopoietic recovery following myelosuppression was significantly enhanced in mice deficient in both TSP1 and TSP2 (TSP-DKO mice) in comparison with WT mice. Megakaryocyte and platelet levels in TSP-DKO mice were rapidly restored, thereby accelerating revascularization of myelosuppressed bone marrow and ischemic hind limbs. In addition, thrombopoietic cells derived from TSP-DKO mice were more effective in supporting neoangiogenesis in Matrigel plugs. The proangiogenic activity of TSP-DKO thrombopoietic cells was mediated through activation of MMP-9 and enhanced release of stromal cell–derived factor 1. Thus, TSP-deficient thrombopoietic cells function as proangiogenic agents, accelerating hemangiogenesis within the marrow and revascularization of ischemic hind limbs. As such, interference with the release of cellular stores of TSPs may be clinically effective in augmenting neoangiogenesis.

Authors

Hans-Georg Kopp, Andrea T. Hooper, M. Johan Broekman, Scott T. Avecilla, Isabelle Petit, Min Luo, Till Milde, Carlos A. Ramos, Fan Zhang, Tabitha Kopp, Paul Bornstein, David K. Jin, Aaron J. Marcus, Shahin Rafii

×

Figure 1

In the bone marrow, TSP1 is expressed in megakaryocytes and platelets and on endosteal surfaces.

Options: View larger image (or click on image) Download as PowerPoint
In the bone marrow, TSP1 is expressed in megakaryocytes and platelets an...
An antibody raised against citrullinated proteins results in robust and specific megakaryocyte staining. (A) Megakaryocytes (red arrows) are highly immunoreactive for TSPs. Representative images of WT bone marrow at steady state are shown. Sections were stained for TSPs. Original magnification, ×400. Inset provides a lower magnification overview of WT bone marrow; original magnification, ×200. Sections shown in A and B were counterstained with hematoxylin. (B) In addition, TSP immunoreactivity was demonstrated on endosteal osseous surfaces (green arrows) and platelets (black arrow). This would be in line with previous reports in which TSP1 has been shown to be a cytoadhesive molecule for hematopoietic stem cells. On the other hand, hematopoietic cells other than megakaryocytes and platelets did not stain with the same antibody. Frozen bone marrow section at steady state is shown. Original magnification, ×1,000. (C) WT murine steady state bone marrow was stained with an antibody against CD41 and the anti-citrulline antibody. While anti-CD41 binding was visualized with a Cy2-labeled secondary antibody (green), the anti-citrulline antibody was detected with a Cy3-labeled secondary antibody (red). It is obvious that both antibodies bind to megakaryocytes. However, the anti-citrulline antibody results in more robust and stronger staining results. Original magnification, ×100. (D) Murine megakaryocytes differentiated in culture costained with anti-CD41a and anti-citrulline as above. The merged view shows that both antibodies bind to megakaryocytes. Cytospin from in vitro–differentiated lineage negative murine bone marrow cells is shown. Original magnification, ×1,000.