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(Circulation Research. 2005;97:337.)
© 2005 American Heart Association, Inc.

Molecular Medicine

Thrombopoietin Gene Transfer–Mediated Enhancement of Angiogenic Responses to Acute Ischemia

Hideki Amano, Neil R. Hackett, Shahin Rafii, Ronald G. Crystal

From the Department of Genetic Medicine (H.A., S.R., R.G.C.) and Belfer Gene Therapy Core Facility (N.R.H., R.G.C.), Weill Medical College of Cornell University, New York.

Correspondence to Dr Ronald G. Crystal, Dept of Genetic Medicine, Weill Medical College of Cornell University, 515 E 71st St, S-1000, New York, NY 10021. E-mail geneticmedicine{at}med.cornell.edu

The development of new blood vessels is a complex process, likely requiring the synergy of multiple angiogenic mediators. This study focuses on the proximal angiogenic response using the platelet as a complex carrier of critical mediators of angiogenesis. Platelet levels are controlled by circulating levels of thrombopoietin (TPO) functioning to activate megakaryocyte differentiation and platelet release through the c-mpl receptor. We hypothesized that TPO gene transfer should enhance correction of experimental ischemia by providing increased levels of platelets and hence platelet-derived mediators of angiogenesis. To evaluate this hypothesis, we dissected the role of the TPO–c-mpl–megakaryocyte–platelet pathway in the angiogenic response using a model of acute hindlimb ischemia of wild-type, TPO^–/–, and c-mpl^–/– mice. The data demonstrate that infusion of platelets will enhance the angiogenic response in wild-type mice and that the endogenous angiogenic response is blunted in TPO^–/– and c-mpl^–/– mice. Consistent with this observation, adenovirus (Ad)-mediated transfer of TPO (AdTPO) enhanced the correction of ischemia in wild-type and TPO^–/–, but not c-mpl^–/–, mice. Local versus systemic administration of AdTPO showed that the effect of TPO gene transfer was systemic, not local, and it could be replaced by gene transfer of VEGF, one of the many mediators of angiogenesis carried by the platelets, even in the absence of components in the TPO–c-mpl–megakaryocyte–platelet pathway.

Key Words: angiogenesis • thrombopoietin • platelets • megakaryocyte • gene therapy