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.
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Research Article Vascular biology

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

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Figure 2

TSP-DKO mice display increased bone marrow microvascular and megakaryocyte density as well as higher peripheral platelet levels compared with WT mice.

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TSP-DKO mice display increased bone marrow microvascular and megakaryoc...
(A and B) Marrow sinusoidal microvasculature was quantified in WT (A) and TSP-DKO (B) mice after immunostaining against panendothelial cell antigen clone MECA32. Note that absolute number of cross-sectioned sinusoids (black arrows) is higher in TSP-DKO animals. Representative marrow sections at steady state are shown at original magnification, ×400. DAB was counterstained with hematoxylin. (C) TSP-DKO marrow has a higher sinusoidal microvascular density than WT marrow: 36 ± 0.7 versus 25 ± 1.4 sinusoidal vessels per field. Scored at original magnification, ×400. HPF, high-power field. *P < 0.005. (D) WT marrow, stained for TSPs. Note that only megakaryocytes and platelets are stained. Red arrows indicate differentiated, multinucleated megakaryocytes. Original magnification, ×400. DAB was counterstained with hematoxylin. (E) Megakaryocytes in TSP-DKO marrow are abundant at steady state and can be stained with an antibody against citrullinated proteins. This antibody stained megakaryocytes at the same level of differentiation as the TSP antibody (red arrows). Original magnification, ×400. DAB was counterstained with hematoxylin. (F) TSP-DKO megakaryocyte density is almost twice as high as that in WT marrow: 21 ± 1.2 versus 0 ± 0.5 megakaryocytes per field. Scored at original magnification, ×400. **P < 6 × 10–6. (G) Leukocyte counts at steady state (n = 6). Difference was not significant. (H) Analysis of hemoglobin concentration (n = 6) showed similar results. (I) TSP-DKO mice displayed significantly elevated platelet counts compared with WT controls: 1,495,000 ± 37,000/μl versus 1,305,000 ± 53,000/μl. #P < 0.05. n = 6.