Abstract 1916: miR-34a Induces Senescence of Human Cardiac Progenitor Cells
The objective of this work was to establish whether telomeric shortening and p53 promote senescence of human cardiac progenitor cells (hCPCs) by negatively influencing their growth, migration and survival. We raised the hypothesis that p53-mediated transcriptional repression of a cluster of genes modulating the functional competence of hCPCs may be achieved by upregulation of specific microRNAs (miRs). MiRs are small RNAs that control the post-transcriptional expression of proteins by interfering with the stability and/or the translation of target mRNAs. To identify miRs regulated by p53, hCPCs were exposed to doxorubicin (DOXO) which enhanced phosphorylation and nuclear translocation of p53. The expression of miR-21, miR-29b and miR-30a-5p did not differ in DOXO-treated and untreated hCPCs. However, the quantity of miR-34a was significantly higher in hCPCs characterized by activation of p53. Notably, miR-34b and miR-34c were essentially undetectable in these cells. By employing a web-based target-prediction program, we found that putative targets of miR-34a include cell cycle regulators, members of the Notch pathway, the longevity gene Sirt1 and multiple ligand-receptor systems involved in cell migration. To establish the function of miR-34a, hCPCs were infected with a lentiviral vector carrying miR-34a (miR-34a-hCPCs). By Q-RT-PCR, miR-34a-hCPCs showed decreased transcript levels of c-Met, semaphorin (Sema) 4F, EphA4 receptor, Numb, Notch1, Jagged1 and Sirt1. Transcript levels of Sema4B, 4C and 5B and thymosin β4 did not differ in the two cell groups. With respect to cells transduced with an empty vector, overexpression of miR-34a decreased proliferation and increased apoptosis of hCPCs. Also, the migratory response to HGF was attenuated in miR-34a-hCPCs. HGF was used because hCPCs possess the c-Met receptor and HGF mobilizes hCPCs in vitro and in vivo. Thus, miR-34a-hCPCs acquired functional aspects of cellular aging. However, telomere shortening and upregulation of p53 and p16INK4a were not present in miR-34a-hCPCs documenting the crucial role of this miR in the induction of the hCPC aging phenotype. In conclusion, miR-34a is a downstream effector of p53 and a critical determinant of p53-mediated hCPC senescence.