Therapeutic targeting of the stem cell niche in experimental hindlimb ischemia

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Abstract

Background The custom microenvironment 'vascular niche' is a potential therapeutic target for several pathophysiological conditions. Osteoblasts regulate the hematopoietic stem cell niche, and activation of the parathyroid hormone (PTH) receptor can increase the number of cells mobilized into the bloodstream.

Methods C57Bl/6 mice were randomly assigned treatment with granulocyte-colony stimulating factor (G-CSF), PTH, G-CSF plus PTH or saline. All mice underwent hindlimb ischemia. Blood flow was measured by laser Doppler imaging. Indices of capillary activity were determined by electron microscopy in muscle tissue. CD34+ and Ki67+ cells were detected and evaluated by immunofluorescence, apoptosis by TUNEL, surface antigen and endothelial progenitor cells by fluorescence-activated cell sorting analysis, and vascular endothelial growth factor-164 and angiopoietin-1 expression by reverse-transcriptase polymerase chain reaction. Frozen bone marrow sections were stained for antigen-specific B cells and fibronectin and analyzed by confocal laser scanning microscopy.

Results Following mobilization induced by G-CSF treatment, mice also treated with PTH showed increases in blood flow, capillary density, nitrite/nitrate release, angiogenic factors and circulating progenitor cells, as well as reduced apoptosis, fibrosis, oxidative stress and inflammation in ischemic muscles. Furthermore, hematopoietic antigen-specific B cells in the bone marrow were also increased by G-CSF alone and in combination with PTH.

Conclusions PTH might increase the efficiency of hematopoietic stem-cell-based therapy in a recognized model of peripheral ischemia. Our translational experimental therapeutic targeting of the vascular niche points to novel clinical targets for the hematopoietic stem-cell treatment of ischemic vascular diseases.

Key Points

  • The vascular niche is a potential therapeutic target for peripheral arterial disease

  • We present a translational research study investigating whether targeting the niche with parathyroid hormone (PTH) might improve stem cell-based therapy in an experimental model of hindlimb ischemia that would be relevant to the clinical use of hematopoietic stem-cell-driven angiogenesis

  • After mobilization induced by granulocyte-colony stimulating factor (G-CSF), mice also receiving PTH showed increased blood flow, capillary density, nitrite/nitrate release, angiogenic factors and circulating progenitor cells together with reduced apoptosis, fibrosis, oxidative stress and inflammation in ischemic muscles

  • Our translational study could stimulate clinical trials aimed at increasing the effectiveness of hematopoietic stem cell therapy in peripheral arterial disease by targeting the hematopoietic stem cell niche with PTH

  • In a recent phase I clinical trial,38 PTH (up to 100µg for 14 days) was tolerated well and there was no dose-limiting toxicity; thus, the clinical efficacy of PTH will need to be tested in a larger phase II study

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Figure 1: Laser Doppler determination of blood flow.
Figure 2: Effects of therapy on angiogenesis.
Figure 3: Changes in concentrations of circulating cells, RNA expression and bone marrow B-cell staining after therapy.
Figure 4: Apoptotic and inflammatory effects of therapy.
Figure 5: Proposed mechanisms involved in beneficial effects of PTH in peripheral ischemia.

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Acknowledgements

These studies were supported by grants from the following institutions: Ministero dell'Università e Ricerca Scientifica PRIN 2006 to C Napoli and PRIN 2005 to A Giovane; Fondation Jerome Lejeune to C Napoli; NIH to S Williams-Ignarro, A Giordano, LJ Ignarro and C Napoli; Regione Campania 2007 to ML Balestrieri and C Napoli; Sbarro Research Institute to A Giordano; Ricerca di Ateneo 2006 and Camera di Commercio to the University of Sannio for FP Mancini and E Varricchio; and research funds of the University of Salerno to MF Tecce.

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Correspondence to Claudio Napoli.

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The authors declare no competing financial interests.

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Napoli, C., William-Ignarro, S., Byrns, R. et al. Therapeutic targeting of the stem cell niche in experimental hindlimb ischemia. Nat Rev Cardiol 5, 571–579 (2008) doi:10.1038/ncpcardio1214

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