Transplantation of Neonatal Mouse Cardiac Macrophages into Adult Mice

In an injured neonatal myocardium, macrophages facilitate cardiomyocyte proliferation and angiogenesis and promote heart regeneration. The present study ...

Peking Union Medical College

Heart failure represents a challenging clinical and public health problem and is associated with significant morbidity and mortality. Mechanistically, loss of cardiomyocytes leads to decompensated ventricular remodeling, which eventually progresses to cardiac failure. Regenerative medicine aimed to supplement functional cardiomyocytes is supposedly a promising approach for the effective treatment of heart failure. Over the past decades, investigations on heart regeneration have revealed the regulating networks of cardiomyocyte proliferation. Recently, the research effort has been directed to non-cardiomyocytes for heart regeneration, including cardiac fibroblasts, epicardial cells, endothelial cells, stem/progenitor cells, and immune cells. Cardiac fibroblasts not only substantially influence the composition of extracellular matrix deposition which is vital for the function and proliferation of cardiomyocytes, but also directly convert into cardiomyocytes. The epicardium is functionally important since it is involved in the cardiac development and regeneration via epicardial-mesenchymal transformation. Moreover, several immune cell lineages are found to be interspersed in heart tissue. Immune cell infiltration in combination with inflammatory reaction is found to stimulate the regenerative response in neonatal mouse heart after injury. In this review, we presented and discussed recent development in the studies on non-cardiomyocytes that directly regulate cardiomyocyte proliferation and differentiation during postnatal cardiac regeneration, with an attempt to provide information on the potential targets for the treatment of heart failure.

Non-Cardiomyocytes in Heart Regeneration.

Long noncoding RNAs (lncRNAs) play important roles in the regulation of genes involved in cell proliferation. We have previously sought to more globally understand the differences of lncRNA expression between human fetal heart and adult heart to identify some functional lncRNAs which involve in the process of heart repair. We found that a highly conserved long noncoding RNA NR_045363 was mainly expressed in cardiomyocytes and rarely in non-cardiomyocytes. NR_045363 overexpression in 7-day-old mice heart could improve cardiac function and stimulate cardiomyocyte proliferation after myocardial infarction. Furthermore, NR_045363 knockdown inhibited proliferation of primary embryonic cardiomyocytes, while NR_045363 overexpression enhanced DNA synthesis and cytokinesis in neonatal cardiomyocytes in vitro. Mechanistic analysis revealed that NR_045363 promoted cardiomyocyte proliferation through interaction with miR-216a, which regulated the JAK2-STAT3 pathway. Our results showed that NR_045363 is a potent lncRNA modulator essential for cardiomyocyte proliferation.

A long noncoding RNA NR_045363 controls cardiomyocyte proliferation and cardiac repair.

Platelet-derived growth factor receptor (PDGFR) signaling is involved in proliferation and survival in a wide array of cell types. The role of PDGFR signaling in heart regeneration is still unknown. We find that PDGFR-β signaling decreases in myocardium with age and that conditional activation PDGFR-β in cardiomyocytes promotes heart regeneration. Employing RNA sequencing, we show that the enhancer of zeste homolog 2 (Ezh2) can be upregulated by PDGFR-β signaling in primary cardiomyocytes. Conditional knockout of Ezh2 blocks cardiomyocyte proliferation and H3K27me3 modification during neonatal heart regeneration with Ink4a/Arf upregulation, even in mice with myocyte-specific conditional activation of PDGFR-β. We also show that PDGFR-β controls EZH2 expression via the phosphatidylinositol 3-kinase (PI3K)/p-Akt pathway in cardiomyocytes. Gene therapy with adeno-associated virus serotype 9 (AAV9) encoding activated PDGFR-β enhances adult heart regeneration and systolic function. Our data demonstrate that the PDGFR-β/EZH2 pathway is critical for promoting cardiomyocyte proliferation and heart regeneration, providing a potential target for cardiac repair.

PDGFR-β Signaling Regulates Cardiomyocyte Proliferation and Myocardial Regeneration.

Transplantation of murine neonatal cardiac macrophage improves adult cardiac repair.

The neonatal heart completely regenerates after apical resection (AR), providing a desirable research model to study the mechanism of cardiac regeneration and cardiomyocyte proliferation. However, AR-induced neonatal heart regenerative phenomenon is controversial due to the variation of operative details in different laboratories. Here, we provide an optimized AR operation procedure with stable regeneration and high survival rate by achieving heart exposure, normalizing myocardium cut-offs, and reducing operation duration. We also established a whole-heart-slice approach to estimate the myocardial regeneration after the AR operation, which ensures no false-negative/positive results. The combination of the optimized AR operation and the whole-heart-slice analysis provides a stable system to study neonatal heart regeneration and cardiomyocyte proliferation in situ.

Achieving stable myocardial regeneration after apical resection in neonatal mice.

A key cause of the high mortality of cardiovascular diseases is the cardiomyocyte inability to renew after cardiac injury. As a promising strategy to supplement functional myocytes for cardiac repair, there is a pressing need to understand the cellular and molecular mechanisms of heart regeneration.

gp130 Controls Cardiomyocyte Proliferation and Heart Regeneration.

Myeloid-derived growth factor (Mydgf), a paracrine protein secreted by bone marrow-derived monocytes and macrophages, was found to protect against cardiac injury following myocardial infarction (MI) in adult mice. We speculated that Mydgf might improve heart function  myocardial regeneration, which is essential for discovering the target to reverse heart failure.  Two genetic mouse lines were used: global Mydgf knockout () and  mice. Two models of cardiac injury, apical resection was performed in neonatal and MI was performed in adult mice. Quantitative reverse transcription-polymerase chain reaction, western blot and flow cytometry were performed to study the protein expression. Immunofluorescence was performed to detect the proliferation of cardiomyocytes. Heart regeneration and cardiac function were evaluated by Masson's staining and echocardiography, respectively. RNA sequencing was employed to identify the key involved in Mydgf-induced cardiomyocyte proliferation. Mydgf recombinant protein injection was performed as a therapy for cardiac repair post MI in adult mice.  Mydgf expression could be significantly induced in neonatal mouse hearts after cardiac injury. Unexpectedly, we found that Mydgf was predominantly expressed by endothelial cells rather than macrophages in injured neonatal hearts. Mydgf deficiency impeded neonatal heart regeneration and injury-induced cardiomyocyte proliferation. Mydgf recombinant protein promoted primary mouse cardiomyocyte proliferation. Employing RNA sequencing and functional verification, we demonstrated that c-Myc/FoxM1 pathway mediated Mydgf-induced cardiomyocyte expansion. Mydgf recombinant protein improved cardiac function in adult mice after MI injury with inducing cardiomyocyte proliferation.  Mydgf promotes cardiomyocyte proliferation by activating c-Myc/FoxM1 pathway and improves heart regeneration both in neonatal and adult mice after cardiac injury, providing a potential target to reverse cardiac remodeling and heart failure.

Yandong Li

Peking Union Medical College

Transplantation of Neonatal Mouse Cardiac Macrophages into Adult Mice