Bone Marrow-Derived Mesenchymal Stem Cells (BMSCs)-Exosome Carrying MiRNA-312 Inhibits Sevoflurane-Induced Cardiomyocyte Apoptosis Through Activation of Phosphatidylinositol 3-Kinase/Protein Kinase B (PI3K/AKT) Pathway

This study was to explore the mechanism by how exosomes (exo) derived from BMSCs affects cardiomyocyte apoptosis. BMSCs were isolated and incubated with cardiomyocytes while the cardiomyocytes were exposed to sevoflurane or DMSO treatment. Apoptotic cells were calculated and level of apoptosis related proteins was detected by Western blot. Through transfection with microRNA-(miRNA)-312 inhibitor, we evaluated the effect of BMSC-exo on the sevoflurane-induced apoptosis. Sevoflurane significantly inhibited the viability of cardiomyocytes and induced cardiomyocyte apoptosis. Besides, sevoflurane decreased the expression of miR-312 and enhanced Bax expression in cardiomyocytes through restraining the phosphorylation of MAPK/ERK. Treatment with BMSC-exo, however, activated MAPK/ERK signaling by up-regulating miR-312, thereby inhibiting cardiomyocyte apoptosis, promoting cardiomyocyte proliferation, and elevating the level of Bcl-2. In conclusion, BMSC-exo-derived miR-312 inhibits sevoflurane-induced cardiomyocyte apoptosis by activating PI3K/AKT signaling pathway.

The Insulin-Like Growth Factor Signalling Pathway in Cardiac Development and Regeneration

Insulin and Insulin-like growth factors (IGFs) perform key roles during embryonic development, regulating processes of cell proliferation and survival. The IGF signalling pathway comprises two IGFs (IGF1, IGF2), two IGF receptors (IGFR1, IGFR2), and six IGF binding proteins (IGFBPs) that regulate IGF transport and availability. The IGF signalling pathway is essential for cardiac development. IGF2 is the primary mitogen inducing ventricular cardiomyocyte proliferation and morphogenesis of the compact myocardial wall. Conditional deletion of the Igf1r and the insulin receptor (Insr) genes in the myocardium results in decreased cardiomyocyte proliferation and ventricular wall hypoplasia. The significance of the IGF signalling pathway during embryonic development has led to consider it as a candidate for adult cardiac repair and regeneration. In fact, paracrine IGF2 plays a key role in the transient regenerative ability of the newborn mouse heart. We aimed to review the current knowledge about the role played by the IGF signalling pathway during cardiac development and also the clinical potential of recapitulating this developmental axis in regeneration of the adult heart.

FUCCI-based live imaging platform reveals cell cycle dynamics and identifies pro-proliferative compounds in human iPSC-derived cardiomyocytes

One of the major goals in cardiac regeneration research is to replace lost ventricular tissue with new cardiomyocytes. However, cardiomyocyte proliferation drops to low levels in neonatal hearts and is no longer efficient in compensating for the loss of functional myocardium in heart disease. We generated a human induced pluripotent stem cell (iPSC)-derived cardiomyocyte-specific cell cycle indicator system (TNNT2-FUCCI) to characterize regular and aberrant cardiomyocyte cycle dynamics. We visualized cell cycle progression in TNNT2-FUCCI and found G2 cycle arrest in endoreplicating cardiomyocytes. Moreover, we devised a live-cell compound screening platform to identify pro-proliferative drug candidates. We found that the alpha-adrenergic receptor agonist clonidine induced cardiomyocyte proliferation in vitro and increased cardiomyocyte cell cycle entry in neonatal mice. In conclusion, the TNNT2-FUCCI system is a valuable tool to characterize cardiomyocyte cell cycle dynamics and identify pro-proliferative candidates with regenerative potential in the mammalian heart.

Phosphoproteomic Analysis Reveals Downstream PKA Effectors of AKAP Cypher/ZASP in the Pathogenesis of Dilated Cardiomyopathy

Background: Dilated cardiomyopathy (DCM) is a major cause of heart failure worldwide. The Z-line protein Cypher/Z-band alternatively spliced PDZ-motif protein (ZASP) is closely associated with DCM, both clinically and in animal models. Our earlier work revealed Cypher/ZASP as a PKA-anchoring protein (AKAP) that tethers PKA to phosphorylate target substrates. However, the downstream PKA effectors regulated by AKAP Cypher/ZASP and their relevance to DCM remain largely unknown.Methods and Results: For the identification of candidate PKA substrates, global quantitative phosphoproteomics was performed on cardiac tissue from wild-type and Cypher-knockout mice with PKA activation. A total of 216 phosphopeptides were differentially expressed in the Cypher-knockout mice; 31 phosphorylation sites were selected as candidates using the PKA consensus motifs. Bioinformatic analysis indicated that differentially expressed proteins were enriched mostly in cell adhesion and mRNA processing. Furthermore, the phosphorylation of β-catenin Ser675 was verified to be facilitated by Cypher. This phosphorylation promoted the transcriptional activity of β-catenin, and also the proliferative capacity of cardiomyocytes. Immunofluorescence staining demonstrated that Cypher colocalised with β-catenin in the intercalated discs (ICD) and altered the cytoplasmic distribution of β-catenin. Moreover, the phosphorylation of two other PKA substrates, vimentin Ser72 and troponin I Ser23/24, was suppressed by Cypher deletion.Conclusions: Cypher/ZASP plays an essential role in β-catenin activation via Ser675 phosphorylation, which modulates cardiomyocyte proliferation. Additionally, Cypher/ZASP regulates other PKA effectors, such as vimentin Ser72 and troponin I Ser23/24. These findings establish the AKAP Cypher/ZASP as a signalling hub in the progression of DCM.

A Bibliometric and Visualized Analysis of Cardiac Regeneration Over a 20-Year Period

Background: Recent research has suggested that cardiac regeneration may have the widely applicable potential of treating heart failure (HF). A comprehensive understanding of the development status of this field is conducive to its development. However, no bibliometric analysis has summarized this field properly. We aimed to analyze cardiac regeneration-related literature over 20 years and provide valuable insights.Methods: Publications were collected from the Web of Science Core Collection (WoSCC). Microsoft Excel, VOSviewer, CiteSpace, and alluvial generator were used to analyze and present the data.Results: The collected 11,700 publications showed an annually increasing trend. The United States and Harvard University were the leading force among all the countries and institutions. The majority of articles were published in Circulation Research, and Circulation was the most co-cited journal. According to co-citation analysis, burst detection and alluvial flow map, cardiomyocyte proliferation, stem cells, such as first-and second-generation, extracellular vesicles especially exosomes, direct cardiac reprogramming, macrophages, microRNAs, and inflammation have become more and more popular recently.Conclusions: Cardiac regeneration remains a research hotspot and develops rapidly. How to modify cardiac regeneration endogenously and exogenously may still be the hotspot in the future and should be discussed more deeply.

Thyroid hormone-dependent regulation of metabolism and heart regeneration

While adult zebrafish and newborn mice possess a robust capacity to regenerate their hearts, this ability is generally lost in adult mammals. The logic behind the diversity of cardiac regenerative capacity across the animal kingdom is not well understood. We have recently reported that animal metabolism is inversely correlated to the abundance of mononucleated diploid cardiomyocytes in the heart, which retain proliferative and regenerative potential. Thyroid hormones are classical regulators of animal metabolism, mitochondrial function, and thermogenesis and a growing body of scientific evidence demonstrates that these hormonal regulators also have direct effects on cardiomyocyte proliferation and maturation. We propose that thyroid hormones dually control animal metabolism and cardiac regenerative potential through distinct mechanisms, which may represent an evolutionary tradeoff for the acquisition of endothermy and loss of heart regenerative capacity. In this review, we describe the effects of thyroid hormones on animal metabolism and cardiomyocyte regeneration, and highlight recent reports linking the loss of mammalian cardiac regenerative capacity to metabolic shifts occurring after birth.

RRM2 Improves Cardiomyocyte Proliferation after Myocardial Ischemia Reperfusion Injury through the Hippo-YAP Pathway

Objective. Ribonucleotide reductase M2 (RRM2) as an enzyme that catalyzes the deoxyreduction of nucleosides to deoxyribonucleoside triphosphate (dNTP) has been extensively studied, and it plays a crucial role in regulating cell proliferation. However, its role in ischemia-reperfusion injury (I/RI) is still unclear. Methods. SD rats were used as the research object to detect the expression of RRM2 in the myocardium by constructing an I/RI model. At the same time, primary SD neonatal rat cardiomyocytes were extracted, and hypoxia/reoxygenation (H/R) treatment simulated the I/RI model. Using transfection technology to overexpress RRM2 in cardiomyocytes, quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) was used to detect the expression of RRM2, Cell Counting Kit-8 (CCK-8) assay was used to detect cell viability, and immunofluorescence staining was used to detect Ki67 and EdU-positive cells. Western blot (WB) technology was used to detect YAP and its phosphorylation expression. Results. qRT-PCR results indicated that the expression of RRM2 was inhibited in the model group, and cardiomyocytes overexpressing RRM2 can obviously promote the proliferation of primary cardiomyocytes and improve the damage of cardiac structure and function caused by I/R. At the same time, RRM2 can promote the increase of YAP protein expression and the increase of Cyclin D1 mRNA expression. Conclusion. RRM2 expression was downregulated in myocardial tissue with I/R. After overexpression of RRM2, cardiomyocyte proliferation was upregulated and the Hippo-YAP signaling pathway was activated.