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

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 8

TSP-deficient platelets release higher amounts of SDF-1 after stimulation.

Options: View larger image (or click on image) Download as PowerPoint
TSP-deficient platelets release higher amounts of SDF-1 after stimulati...
(A) SDF-1 levels in carefully collected platelet-poor plasma were measured. However, most samples contained SDF-1 below detection level. An average concentration of less than 250 pg/ml was calculated for both WT and TSP-DKO animals (n = 6). (B) Retro-orbital blood from the same animals as in A was collected and incubated for clot formation, and serum was harvested after centrifugation. SDF-1 in the serum was higher in TSP-DKO than in WT blood. However, this difference did not reach a level of significance (2.3 ng/ml in WT versus 2.8 ng/ml in TSP-DKO serum; P = 0.08) but reflected the elevated platelet levels found in TSP-DKO mice. Importantly, these results strongly suggest that platelets are the major source of serum SDF-1. (C) PRP underwent analysis by aggregometry, and SDF-1 released upon stimulation with different platelet agonists was examined. Stimulation of 10 μg/ml collagen followed by 10 μmol adenosine resulted in the strongest aggregation. Interestingly, TSP-DKO platelets secreted twice as much total SDF-1 as WT platelets under these conditions (5 pg/ml in WT versus 11.5 pg/ml in TSP-DKO). PRP was pooled from n = 3–4 animals, experiment was repeated 3 times, *P < 0.05.