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

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.

Lysophosphatidic acid (LPA), a bioactive phospholipid released by activated platelets, can induce platelet shape changes and aggregation, which may play an important role in thrombosis. In contrast, the interaction of LPA with neutrophils in thrombosis has not been studied. Recently, neutrophil extracellular traps (NETs) have been shown to bind plasma proteins and activate platelets, which promotes thrombosis.

Lysophosphatidic acid promotes thrombus stability by inducing rapid formation of neutrophil extracellular traps: A new mechanism of thrombosis.

Neonatal mouse hearts can regenerate completely in 21 days after cardiac injury, providing an ideal model to exploring heart regenerative therapeutic targets. The oxidative damage by Reactive Oxygen Species (ROS) is one of the critical reasons for the cell cycle arrest of cardiomyocytes (CMs), which cause mouse hearts losing the capacity to regenerate in 7 days or shorter after birth. As an antioxidant, hydrogen sulfide (HS) plays a protective role in a variety of diseases by scavenging ROS produced during the pathological processes. In this study, we found that blocking HS synthesis by PAG (HS synthase inhibitor) suspended heart regeneration and CM proliferation with ROS deposition increase after cardiac injury (myocardial infarction or apex resection) in 2-day-old mice. NaHS (a HS donor) administration improved heart regeneration with CM proliferation and ROS elimination after myocardial infarction in 7-day-old mice. NaHS protected primary neonatal mouse CMs from HO-induced apoptosis and promoted CM proliferation  SOD2-dependent ROS scavenging. The oxidative DNA damage in CMs was reduced with the elimination of ROS by HS. Our results demonstrated for the first time that HS promotes heart regeneration and identified NaHS as a potent modulator for cardiac repair.

Hydrogen Sulfide Promotes Cardiomyocyte Proliferation and Heart Regeneration  ROS Scavenging.

 Lysophosphatidic acid (LPA) is a small glycerophospholipid that acts as a potent extracellular signal in various biological processes and diseases. Our previous work demonstrated that the expression of the LPA receptors LPA and LPA is elevated in the early postnatal heart. However, the role of this stage-specific expression of LPA and LPA in the heart is unknown.  By using LPA and LPA knockout mice, and neonatal SD rats treated with Ki16425 (LPA/LPA inhibitor), we found that the number of proliferating cardiomyocytes, detected by coimmunostaining pH3, Ki67 or BrdU with cardiac troponin T, was significantly decreased in the LPA knockout mice and the Ki16425-treated rats but not in the LPA knockout mice during the first week of postnatal life. Using a myocardial infarction (MI) model, we found that cardiac function and the number of proliferating cardiomyocytes were decreased in the neonatal LPA KO mice and increased in the AAV9-mediated cardiac-specific LPA overexpression mice. By using lineage tracing and AAV9-LPA, we further found that LPA overexpression in adult mice enhances cardiac function and heart regeneration as assessed by pH3-, Ki67-, and Aurora B-positive cardiomyocytes and clonal cardiomyocytes after MI. Genome-wide transcriptional profiling and additional mechanistic studies showed that LPA induces cardiomyocyte proliferation through the PI3K/AKT, BMP-Smad1/5, Hippo/YAP and MAPK/ERK pathways , whereas only ERK was confirmed to be activated by LPA-LPA signaling .  Our study reports that LPA-mediated LPA signaling is a crucial factor for cardiomyocyte proliferation in the early postnatal heart. Cardiac-specific LPA overexpression improved cardiac function and promoted cardiac regeneration after myocardial injury induced by MI. This finding suggested that activation of LPA potentially through AAV-mediated gene therapy might be a therapeutic strategy to improve the outcome after MI.

LPA-mediated lysophosphatidic acid signaling promotes postnatal heart regeneration in mice.

Loss of Phosphatase and Tensin Homolog Promotes Cardiomyocyte Proliferation and Cardiac Repair After Myocardial Infarction.

Cardiac fibrosis occurs in most cardiac diseases, which reduces cardiac muscle compliance, impairs both systolic and diastolic heart function and, ultimately, leads to heart failure. Long noncoding RNAs (lncRNAs) have recently emerged as important regulators of a variety of biological processes; however, little is known about the expression and function of lncRNAs in cardiac fibrosis. Using unbiased transcriptome profiling in a mouse model of myocardial infarction (MI), we identified a cardiac fibroblast-enriched lncRNA (AK048087) named cardiac fibroblast-associated transcript (), which is significantly elevated after MI. Silencing  expression by small interfering RNAs (siRNAs) or lentiviral short hairpin RNAs (shRNAs) resulted in suppression of fibrosis-related gene expression and transdifferentiation of myofibroblasts into cardiac fibroblasts. Depletion of  by lentiviral shRNAs in mouse hearts significantly attenuated cardiac fibrosis induced by MI or isoproterenol-infusion. Importantly, inhibition of  ameliorated cardiac function following cardiac injury. RNA pull-down followed by mass spectrometry analyses identified COTL1 (coactosin-like 1) as one of the  interacting proteins. Mechanistically,  competitively inhibits the COTL1 interaction with TRAP1 (transforming growth factor-β receptor-associated protein 1), which enhances TGF-β signaling by augmenting SMAD2/SMAD4 complex formation. Therefore, our study identifies  as a novel cardiac fibroblast-enriched lncRNA that regulates cardiac fibroblast activation in response to pathophysiological stress.  could serve as a potential therapeutic target for the prevention of cardiac fibrosis and cardiac diseases.

Jianqiu Pei

Peking Union Medical College

Transplantation of Neonatal Mouse Cardiac Macrophages into Adult Mice