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 3

TSP deficiency enhances megakaryocyte repopulation of the bone marrow and platelet production after myelosuppression.

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TSP deficiency enhances megakaryocyte repopulation of the bone marrow an...
(A) After 250 mg/kg of 5-FU treatment, WT mice experienced pancytopenia followed by rebound thrombocytosis. Platelets reverted to normal around day 24. TSP-DKO mice displayed a more rapid regeneration, with 8.9 × 105 platelets/μl compared with 4.77 × 105 platelets/μl in WT animals on day 7. Furthermore, rebound thrombocytosis was exaggerated, with platelets reaching 5.5 × 106/μl compared with 2.9 × 106/μl in WT controls on day 14 (n = 6, P = 0.006). *P < 0.05. (B) Leukocytes and (C) hemoglobin concentrations did not show significant differences between TSP-DKO and WT mice (n = 6). (D) TSP-DKO mice had higher numbers of megakaryocytes at all time points following 5-FU injection (P < 0.05). While megakaryocytes reached their lowest levels on day 7 in WT mice, megakaryocyte concentration returned to normal levels in TSP-DKO mice on day 7 (P < 0.0003). (E) After 5-FU injection, endothelial cell mass plummeted to about 2% of hematopoietic marrow surface area and reverted to normal around day 14. In TSP-DKO mice, the overall course of these changes was similar to that in WT mice. However, MECA32-positive surface area never decreased to less than 4.9% (day 7 after 5-FU injection; P < 0.005). (F and G) The same femoral marrow as represented in E stained with H&E (F) and anti-citrulline antibody (G). DAB was counterstained with hematoxylin. TSP-DKO marrow showed extreme megakaryocytosis at day 10 after 5-FU injection. Green arrows indicate megakaryocytes. Original magnification, ×400.