Novel function of the P2y/cysteinyl-leukotriene receptor going in. Recruitment of circulating and resident myofibroblast progenitors following acute myocardial infarction

Background - GPR17 is a Gi-coupled dual receptor activated by uracil-nucleotides and cysteinyl-leukotrienes, families of signaling molecules massively released into hypoxic tissues. In the normal heart GPR17 expression has been reported, while its role during ischemia is totally unknown. Aims and Results - To investigate GPR17 expression in mice hearts, before or after myocardial infarction (MI) induction, immunofluorescence was set up. In non ischemic hearts, GPR17 protein was confined into small cell groups localized between myocytes. These cells expressed the stem cell antigen-1 (Sca-1). At 24, 48 and 72 hrs post-MI, cell clusters expressing GPR17 were found to infiltrate the MI border zone and penetrate into the ischemic area. They expressed Sca-1, the myofibroblast/mesenchymal marker CD44 and the hematopoietic lineage marker CD45. Interestingly, not all cells expressing GPR17 also expressed CD45, suggesting a dual origin of GPR17+ cells recruited after MI. A flow-sorting experiment was performed to separate Sca-1+/CD45+ from Sca-1+/CD45- cells at 48 hrs post-MI. RT-PCR showed that both cellular populations expressed GPR17, thus confirming their dual origin. A clonogenic Sca-1+ cell line was derived from non-ischemic hearts. In addition to CD44, these cells expressed mesenchymal markers CD29 and CD105, but not endothelial and hematopoietic markers, and showed a side population phenotype. Sca-1+ cells expressed GPR17 RNA/protein and were able to differentiate into cardiac lineage cells and myofibroblasts in culture. To investigate GPR17 functions, Sca-1+ cells were treated with receptor agonists UDP-Glucose (10nM) and LTD4 (100nM). These ligands did not rescue cells from hypoxia-induced apoptosis. By contrast, they enhanced CSCs migratory activity (3.1±0.8 and 1.7±0.2, folds vs. control; P< .05 paired t-test). Finally, addition of GPR17 antagonists montelukast and cangrelor abolished this migratory effect. Conclusions - The present results indicate a role of dual GPR17 receptor in early homing of Sca-1+ cardiac stem cells-derived and circulatory stem cells-derived myofibroblasts into the infarcted myocardium. These findings have implications for the pharmacologic control of heart remodeling at early times after infarction.