MicroRNA-155 prevents necrotic cell death in human cardiomyocyte progenitor cells via targeting RIP1

To improve regeneration of the injured myocardium, cardiomyocyte progenitor cells (CMPCs) have been put forward as a potential cell source for transplantation therapy. Although cell transplantation therapy displayed promising results, many issues need to be addressed before fully appreciating their impact. One of the hurdles is poor graft-cell survival upon injection, thereby limiting potential beneficial effects. Here, we attempt to improve CMPCs survival by increasing microRNA-155 (miR-155) levels, potentially to improve engraftment upon transplantation. Using quantitative PCR, we observed a 4-fold increase of miR-155 when CMPCs were exposed to hydrogen-peroxide stimulation. Flow cytometric analysis of cell viability, apoptosis and necrosis showed that necrosis is the main cause of cell death. Overexpressing miR-155 in CMPCs revealed that miR-155 attenuated necrotic cell death by 40 ± 2.3%via targeting receptor interacting protein 1 (RIP1). In addition, inhibiting RIP1, either by pre-incubating the cells with a RIP1 specific inhibitor, Necrostatin-1 or siRNA mediated knockdown, reduced necrosis by 38 ± 2.5% and 33 ± 1.9%, respectively. Interestingly, analysing gene expression using a PCR-array showed that increased miR-155 levels did not change cell survival and apoptotic related gene expression. By targeting RIP1, miR-155 repressed necrotic cell death of CMPCs, independent of activation of Akt pro-survival pathway. MiR-155 provides the opportunity to block necrosis, a conventionally thought non-regulated process, and might be a potential novel approach to improve cell engraftment for cell therapy.