The Hippo-YAP pathway is highly conserved and plays a pivotal role in cardiomyocyte cell cycle re-entry. Hippo deficiency enhances cardiomyocyte regeneration and heart functional recovery while reducing scar formation after myocardial infarction in adult mice[
31,
32]. The Hippo-deficient cardiomyocytes express higher levels of proliferative and stress response genes, such as
Park2[
32]. YAP, the inactivated downstream effector of Hippo, is abundant in neonatal heart tissue but not in adult heart tissue. Recent studies found YAP to be a key regulator for cardiac development and regeneration in mice[
33-
35]. Similar to inhibiting Hippo, activation of YAP results in less scar formation and improved heart function after myocardial infarction at postnatal days 7 and 28 as well as adult stages[
35,
36]. In Erb-B2 receptor tyrosine kinase (ErbB2)-overexpressed mice, YAP mediated a robust epithelial-mesenchymal transition (EMT)-like regeneration by interacting with the cytoskeleton and altering the mechanical characteristics of the cell[
33]. In addition, non-coding RNAs make up a major part of the complex regulatory signaling network. Eulalio
et al.[
37] found that miR-199a and miR-590 can effectively induce cell cycle re-entry of cardiomyocytes
in vitro as well as in neonatal and adult mice. In murine myocardial infarction models, overexpression of miR-199a and miR-590
via single-dose injection of synthetic RNA promotes cardiac regeneration and recovery of cardiac function[
37,
38]. Recently, Gabisonia
et al.[
39] found that, using infarcted pig hearts, miR-199a was shown to facilitate cardiac repair and increase muscle mass and contractility. Follow-up studies on miR-199a have identified potential downstream signaling, such as CD151[
40], mechanistic target of rapamycin (mTOR)[
41] and Wnt2[
42]. Cardiac-specific overexpression of miR-128 in neonatal mice attenuates cardiomyocyte proliferation and functional recovery after myocardial infarction. miR-128 regulates cardiomyocyte cell cycle re-entry
via SUZ12, a chromatin modifier that targets p27, cyclin E, and CK2[
43]. Overexpression of miR-195 (a member of miR-15) leads to reduced proliferation and hypertrophy of cardiomyocytes, while inhibition of the miR-15 family increases cardiomyocyte proliferation after myocardial infarction in adult mice. The downstream target of miR-195 includes cell cycle genes, mitochondrial genes, and inflammatory genes[
44]. Similarly, miR-1/-133a is also a negative regulator of cardiomyocyte cell cycle re-entry in the adult heart. Short-term deletion of miR-1/ -133a protects against myocardial infarction. However, long-term deficiency leads to heart failure[
45]. circNfix, a circular RNA, is up-regulated in the adult hearts of humans and mice. Knocking down circNfix releases suppression on downstream cyclinA2 and cyclinB1 and increases miR-214 activity, leading to enhanced cardiomyocyte proliferation and recovery after injury[
46]. miR-152 has been found to be a target of Toll-like receptor 3 (TLR3) and induces cardiomyocyte proliferation by regulating cell cycle proteins downstream of YAP1[
47]. Recent study shows that FAM122A, an endogenous inhibitor of protein phosphatase 2A, is a novel regulator in the mesendodermal specification and cardiac differentiation
via Hippo and Wnt signaling pathways[
48]. In the first step, RNA-binding protein LIN28a stimulates the formation of new cardiomyocytes and prevents cardiomyocyte apoptosis[
49]. Activation of YAP promotes progenitor regeneration by triggering LIN28a transcription[
50].