Heart failure (HF) is a major cause of death in the United States. Current pharmacological treatments and implantable cardiac assist devices may contribute to improving symptoms of HF on the short term but they are insufficient to restore and maintain cardiac integrity and function on the long term. Autologous stem cell therapy has been introduced as a promising alternative approach to current therapies for HF. However, the reparative responses of either endogenous or adoptively transferred stem cells are limited due to extremely poor engraftment rates and increased susceptibility to cell death in the unfavorable necrotic environment. Hence, genetic modification and ex vivo expansion of stem cells from diverse origins, including cardiac-derived progenitor cells (CPCs), have been pursued to improve their growth and survival capabilities and eventually promote superior regeneration in vivo. Extracellular nucleotides released during cardiac ischemia initiate inflammatory and regenerative responses required for the healing of injured myocardium through the activation of multiple transmembrane nucleotide receptors, including P2Y2 receptor (P2Y2R), a G protein-coupled receptor that is equipotently activated by ATP and UTP. In addition to its established cardioprotective responses in both rodent animal models and human cardiomyocytes, P2Y2R agonists ATP and UTP are potent stimulants of human hematopoietic stem cell (hHSC) proliferation and migration. ATP also induces the differentiation of human bone-marrow derived mesenchymal stem cells (hMSCs). Nonetheless, the physiological roles of extracellular nucleotides in CPCs have not been adequately addressed. This proposal aims to explore the physiological responses mediated by P2 nucleotide receptors with a focus on the P2Y2R in CPCs and identify the underlying mechanisms. Research strategy involves initial in vitro characterization of P2Y2R-mediated responses in mouse and human CPCs using pharmacological as well as loss- and gain-of- function studies. The in vitro findings will be extended in vivo by overexpressing P2Y2R in human CPCs prior to adoptive transfer in infarcted mouse myocardium, which we hypothesize improves CPC-mediated reparative potential of injured myocardium following myocardial infarction. We also hypothesize that P2Y2R-induced regenerative responses in CPCs involve the activation of Hippo signaling pathway that is known to be regulated by various G protein-coupled receptors. This provides a novel direct link between extracellular nucleotides released during cardiac ischemia, extracellular matrix sensing and Hippo signaling that has been recently introduced as an important regulator for cardiac regeneration following injury.
Autologous stem cell therapy represents a promising alternative approach to current inefficient therapies for heart failure. Genetic modification and e vivo expansion of stem cells prior to adoptive transfer has been attempted to enhance the growth and survival capabilities of transplanted stem cells in the unfavorable necrotic environment. Since previous published reports have shown that P2Y2 nucleotide receptor (P2Y2R) activation induces cardioprotective responses both in rodent animal models and human cardiomyocytes in addition to regenerative responses in stem cells from diverse origins, we hypothesize that P2Y2R plays similar roles in cardiac-derived progenitor cells (CPCs) and its overexpression improves CPC-mediated repair of injured myocardium.
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