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 6

TSPs are deposited perivascularly in ischemic musculature.

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TSPs are deposited perivascularly in ischemic musculature. (A) Left: WT ...
(A) Left: WT mice underwent ligation of the left femoral artery. Shortly after the surgical procedure, ischemic tissue of the affected limb’s gastrocnemius muscle was harvested. Immunohistochemical analysis of the ischemic areas showed deposition of TSP in and around microvessels (black arrows). Note the perivascular location of freshly deposited TSPs along with inflammatory cells infiltrating the ischemic musculature. Importantly, there was no detectable staining on nonischemic musculature. Paraffin-embedded section from a representative field of WT gastrocnemius after femoral vessel ligation, stained with DAB and counterstained with hematoxylin. Scored at original magnification, ×400. IHL, ischemic hind limb. Right: RNA was extracted from ischemic gastrocnemius tissue, and TSP1 mRNA levels were compared with those at steady state. A strong increase in relative expression of TSP1 was found at the mRNA level (2–ΔCt × 10,000). This finding is in line with previous observations in skin healing models, where TSP1 mRNA is thought to be derived from invading hematopoietic cells. RQ, relative expression. (B) TSP-DKO mice 3 days after ischemic hind limb surgery received a single transfusion with 300 × 106 WT platelets. Seven days later, TSPs were deposited perivascularly only in ischemic musculature (red arrows). Frozen section, representative field of ischemic TSP-DKO gastrocnemius muscle, stained for TSPs with Cy2-conjugated secondary antibody and Hoechst 33342 nuclear stain. Scored at original magnification, ×400. As an internal control for autofluorescence and background staining, nonischemic musculature of the contralateral, nonischemic gastrocnemius muscle stained for TSP is shown. Original magnification, ×200.