Thymosin ß4 and prothymosin α promote cardiac regeneration post-ischaemic injury in mice.

AIMS: The adult mammalian heart is a post-mitotic organ. Even in response to necrotic injuries, where regeneration would be essential to reinstate cardiac structure and function, only a minor percentage of cardiomyocytes undergo cytokinesis. The gene programme that promotes cell division within this population of cardiomyocytes is not fully understood. In this study, we aimed to determine the gene expression profile of proliferating adult cardiomyocytes in the mammalian heart after myocardial ischaemia, to identify factors to can promote cardiac regeneration. METHODS AND RESULTS: Here, we demonstrate increased 5-ethynyl-2'deoxyuridine incorporation in cardiomyocytes 3 days post-myocardial infarction in mice. By applying multi-colour lineage tracing, we show that this is paralleled by clonal expansion of cardiomyocytes in the borderzone of the infarcted tissue. Bioinformatic analysis of single-cell RNA sequencing data from cardiomyocytes at 3 days post ischaemic injury revealed a distinct transcriptional profile in cardiomyocytes expressing cell cycle markers. Combinatorial overexpression of the enriched genes within this population in neonatal rat cardiomyocytes and mice at postnatal day 12 (P12) unveiled key genes that promoted increased cardiomyocyte proliferation. Therapeutic delivery of these gene cocktails into the myocardial wall after ischaemic injury demonstrated that a combination of thymosin beta 4 (TMSB4) and prothymosin alpha (PTMA) provide a permissive environment for cardiomyocyte proliferation and thereby attenuated cardiac dysfunction. CONCLUSION: This study reveals the transcriptional profile of proliferating cardiomyocytes in the ischaemic heart and shows that overexpression of the two identified factors, TMSB4 and PTMA, can promote cardiac regeneration. This work indicates that in addition to activating cardiomyocyte proliferation, a supportive environment is a key for regeneration to occur.

In Vivo Retention Quantification of Supramolecular Hydrogels Engineered for Cardiac Delivery.

Recent advances in the field of cardiac regeneration show great potential in the use of injectable hydrogels to reduce immediate flush-out of injected factors, thereby increasing the effectiveness of the encapsulated drugs. To establish a relation between cardiac function and retention of the drug-encapsulating hydrogel, a quantitative in vivo imaging method is required. Here, the supramolecular ureido-pyrimidinone modified poly(ethylene glycol) (UPy-PEG) material is developed into a bioactive hydrogel for radioactive imaging in a large animal model. A radioactive label is synthesized, being a ureido-pyrimidinone moiety functionalized with a chelator (UPy-DOTA) complexed with the radioactive isotope indium-111 (UPy-DOTA-111 In) that is mixed with the hydrogel. Additionally, bioactive and adhesive properties of the UPy-PEG hydrogel are increased by supramolecular introduction of a UPy-functionalized recombinant collagen type 1-based material (UPy-PEG-RCPhC1). This method enables in vivo tracking of the nonbioactive and bioactive supramolecular hydrogels and quantification of hydrogel retention in a porcine heart. In a small pilot, cardiac retention values of 8% for UPy-PEG and 16% for UPy-PEG-RCPhC1 hydrogel are observed 4 h postinjection. This work highlights the importance of retention quantification of hydrogels in vivo, where elucidation of hydrogel quantity at the target site is proposed to strongly influence efficacy of the intended therapy.

Non-coding RNAs in endothelial cell signalling and hypoxia during cardiac regeneration.

Heart failure (HF) as a result of myocardial infarction (MI) is the leading cause of death worldwide. In contrast to the adult mammalian heart, which has low regenerative capacity, newborn mammalian and zebrafish hearts can completely regenerate after injury. Cardiac regeneration is considered to be mediated by proliferation of pre-existing cardiomyocytes (CMs) mainly located in a hypoxic niche. To find new therapies to treat HF, efforts are being made to understand the molecular pathways underlying the regenerative capacity of the heart. However, the multicellularity of the heart is important during cardiac regeneration as not only CM proliferation but also the restoration of the endothelium is imperative to prevent progression to HF. It has recently come to light that signalling from non-coding RNAs (ncRNAs) and extracellular vesicles (EVs) plays a role in the healthy and the diseased heart. Multiple studies identified differentially expressed ncRNAs after MI, making them potential therapeutic targets. In this review, we highlight the molecular interactions between endothelial cells (ECs) and CMs in cardiac regeneration and when the heart loses its regenerative capacity. We specifically emphasize the role of ncRNAs and cell-cell communication via EVs during cardiac regeneration and neovascularisation.

Follistatin-like 1 in Cardiovascular Disease and Inflammation.

Follistatin-like 1 (FSTL1), a secreted glycoprotein, has been shown to participate in regulating developmental processes and to be involved in states of disease and injury. Spatiotemporal regulation and posttranslational modifications contribute to its specific functions and make it an intriguing candidate to study disease mechanisms and potentially develop new therapies. With cardiovascular diseases as the primary cause of death worldwide, clarification of mechanisms underlying cardiac regeneration and revascularization remains essential. Recent findings on FSTL1 in both acute coronary syndrome and heart failure emphasize its potential as a target for cardiac regenerative therapy. With this review, we aim to shed light on the role of FSTL1 specifically in cardiovascular disease and inflammation.