Ischemia in myocardial and peripheral tissues is a leading cause of heart failure and tissue necrosis in the United States. Ischemic diseases are clinically treated with drug administration and surgery, which still meet many challenges for treatment on a permanent basis. Recently, revascularization therapy to rebuild the vascular network of ischemic tissue via angiogenesis, vasculogenesis or both is being extensively studied to restore blood perfusion in various tissues. A variety of stem and progenitor cells are promising revascularization medicines in conjunction with several angiogenic cytokines and growth factors. Commonly, these cells are transplanted via intracoronary injection, but the therapeutic efficacy of transplanted cells is greatly reduced by a significant loss of cells due to the absence of the signals to guide the cells to the injured endothelium. The objectives of this proposed study are to develop a nano-sized cell guidance molecule and attach it to the transplanted cells, so the transplanted cells can pinpoint the injured endothelium and subsequently improve blood perfusion of ischemic tissue. We hypothesize that a hyper-branched poly(glycerol) linked with both epitopes binding with transplanted cells and those binding with vascular cell adhesion molecules (VCAM)-1 will precisely guide transplanted cells to the injured endothelium because the endothelial injury stimulates endothelial cells to over-express VACM-1. Ultimately, this tuning of cell guidance will significantly improve restoration of blood perfusion in the ischemic tissue. We will examine this hypothesis using endothelial progenitor cells (EPCs) derived from a porcine cord blood. The oligopeptide containing RGD sequence (RGD peptide) will be used as the EPC-binding epitope and that containing VHSPNKK sequence (VHSPNKK peptide) will be used as the VCAM1- binding epitope. The oligopeptide structure will be varied to improve the binding affinity to cells and VCAM-1. These two oligopeptides will be chemically linked to the poly(glycerol). The degree of oligopeptides substitution to poly(glycerol) will be further optimized with in vitro analysis. Specifically, we will use a fluorescence resonance energy transfer (FRET) technique we previously developed to quantify the number of poly(glycerol) bound to EPCs. We will complete this proposed study by first functionalizing poly(glycerol) with RGD peptides [RGD- poly(glycerol)] and analyzing the amount of poly(glycerol) bound with EPCs (Aim 1), secondly modifying RGD-poly(glycerol) with VHSPNKK peptides [RGD-poly(glycerol)-VHSPNKK] and analyzing its ability to guide EPCs to the synthetic endothelium (Aim 2) and finally demonstrate the function of bioactive poly(glycerol) in vivo using the immunodeficient mouse with an ischemic hindlimb (Aim 3). This study will be performed through the interdisciplinary collaboration between a tissue engineer (Kong, investigator), chemist (Zimmerman) and biologist (Schook). Kong and Zimmerman's groups are responsible for the synthesis of bioactive poly(glycerol) and evaluation of its ability to enhance the transplanted cell adhesion to the target ischemic tissue in vitro and in vivo. The cell isolation from a cord blood and characterization will be evaluated by the Schook group. We believe that the successful completion of this proposed study will significantly minimize the loss of transplanted cells and improve the therapeutic potency of EPCs for repairing ischemic tissue. Results from our in vitro and in vivo studies will be readily translated into the large scale preclinical and clinical trials, and aid the expedition of cell-based neovascularization therapies to the clinical setting. Finally, this design strategy of a cell guidance system and quantitative analysis of the molecular binding with cells and target tissue will be widely applicable to a broad array of stem and progenitor cells for the treatment of many diseases.
The successful completion of this proposed study will create a precision cell guidance system that will greatly improve the regenerative efficacy of therapeutic cells and expedite the use of cells in clinical treatment of ischemic disease. Specifically, the through in vitro and in vivo analysis of cell guidance system will expedite the translation of the results of this study into the clinical trials. In the end, this study will aid saving a number of patients who suffer from the ischemic disorders of myocardial and peripheral tissues.
