A procardiogenic piRNA orchestrates cardiomyogenic commitment of embryonic and adult stem cells in vitro and in vivo

P-element-Induced Wimpy Testis (PIWI)–interacting RNAs (piRNAs) are not only expressed in germline cells but are also present in somatic cells of the cardiovascular system, including cardiomyocytes (CMs), as well as in embryonic stem cells (ESCs) and cardiac stem cells (CSCs). This expression suggests a potential role for piRNAs in regulating stem cell function and cardiac regeneration, possibly through mechanisms involving genome rearrangement and epigenetic programming.

We evaluated the potential role of piRNAs in ESC and CSC myogenic commitment.

Data obtained from piRNA expression profile (piRNome) in cloned mouse CSCs were matched with those obtained from mouse ESCs and compared to fetal and adult CMs. Furthermore, we compared their piRNome during in vitro myogenic differentiation. Bioinformatics identified a set of differentially expressed piRNAs whereby few of them were highly expressed in CMs but very faintly expressed in undifferentiated CSCs and ESCs.

As result of this analysis, we focused on one of this piRNA that we named as myo-piRNA-1, whose expression progressively increased during the commitment of CSC-derived CMs and ESC-derived CMs (hereafter CSCs-CMs or ESC-CMs respectively). To investigate whether myo-piRNA-1 is mechanistically relevant in cardiomyogenic differentiation we performed loss of function assays by transfecting differentiating ESCs and CSCs with a specific myo-piRNA-1 inhibitor. Interestingly cardiac-specific gene levels were significantly reduced in the inhibitor-transfected cells compared to scramble transfected cells and the treated cells show poorly defined sarcomeric structures. The methylome analysis by Infinium Mouse Methylation BeadChip established that myo-piRNA-1 mimic and inhibitor inversely modulate methylation of the promoters of major cardiac genes. Finally, right after permanent coronary ligation in vivo, GFPpos ESC-CMs + myo-piRNA-1 mimic and/or Tomatopos CSC-CM + myo-piRNA-1 mimic were injected intramyocardially and 28 days post myocardial infarction both cell products populated islands of remuscularized tissue with amelioration of cardiac function when compared to matched controls.

Overall, myo-piRNA-1 plays a critical procardiogenic role in cardiomyogenic commitment and regeneration, promoting the acquisition of the cardiomyocyte phenotype from both embryonic and adult stem cells in vitro and in vivo.