Epicardial transplantation of atrial appendage micrograft patch salvages myocardium after infarction

Advanced Cardiac Patches for the Treatment of Myocardial Infarction

Myocardial infarction is a cardiovascular disease characterized by a high incidence rate and mortality. It leads to various cardiac pathophysiological changes, including ischemia/reperfusion injury, inflammation, fibrosis, and ventricular remodeling, which ultimately result in heart failure and pose a significant threat to global health. Although clinical reperfusion therapies and conventional pharmacological interventions improve emergency survival rates and short-term prognoses, they are still limited in providing long-lasting improvements in cardiac function or reversing pathological progression. Recently, cardiac patches have gained considerable attention as a promising therapy for myocardial infarction. These patches consist of scaffolds or loaded therapeutic agents that provide mechanical reinforcement, synchronous electrical conduction, and localized delivery within the infarct zone to promote cardiac restoration. This review elucidates the pathophysiological progression from myocardial infarction to heart failure, highlighting therapeutic targets and various cardiac patches. The review considers the primary scaffold materials, including synthetic, natural, and conductive materials, and the prevalent fabrication techniques and optimal properties of the patch, as well as advanced delivery strategies. Last, the current limitations and prospects of cardiac patch research are considered, with the goal of shedding light on innovative products poised for clinical application.

Hydrogels for Cardiac Restorative Support: Relevance of Gelation Mechanisms for Prospective Clinical Use

PURPOSE OF REVIEW

Cardiac tissue regenerative strategies have gained much traction over the years, in particular those utilizing hydrogels. With our review, and with special focus on supporting post-myocardial infarcted tissue, we aim to provide insights in determining crucial design considerations of a hydrogel and the implications these could have for future clinical use.

RECENT FINDINGS

To date, two hydrogel delivery strategies are being explored, cardiac injection or patch, to treat myocardial infarction. Recent advances have demonstrated that the mechanism by which a hydrogel is gelated (i.e., physically or chemically cross-linked) not only impacts the biocompatibility, mechanical properties, and chemical structure, but also the route of delivery of the hydrogel and thus its effect on cardiac repair. With regard to cardiac regeneration, various hydrogels have been developed with the ability to function as a delivery system for therapeutic strategies (e.g., drug and stem cells treatments), as well as a scaffold to guide cardiac tissue regeneration following myocardial infarction. However, these developments remain within the experimental and pre-clinical realm and have yet to transition towards the clinical setting.

Nonthrombogenic Roles of the Left Atrial Appendage: JACC Review Topic of the Week

The atrial appendage (LAA) is a well-established source of cardioembolism in patients with atrial fibrillation. Therefore, research involving the LAA has largely focused on its thrombogenic attribute and the utility of its exclusion in stroke prevention. However, recent studies have highlighted several novel functions of the LAA that may have important therapeutic implications. In this paper, we provide a concise overview of the LAA anatomy and summarize the emerging data on its nonthrombogenic roles.

Use of left atrial appendage as an autologous tissue source for epicardial micrograft transplantation during LVAD implantation

We report here the first clinical use of the left atrial appendage (LAA) for epicardial micrograft transplantation during left ventricular assist device (LVAD) implantation. Previously, a sample from the right atrial appendage (RAA) has been available for processing and administering micrograft therapy in cardiac surgery. Both LAA and RAA are rich sources of various types of myocardial cells and are capable of providing both paracrine and cellular support to the failing myocardium. The surgical approach of LAA micrografting facilitates epicardial micrograft therapy dose escalation and treatment of larger myocardial areas than done previously. Moreover, as collection of treated vs. untreated tissues from the recipient heart is possible following LVAD implantation at the time of heart transplantation, the evaluation of the therapy's mechanism of action can be further deciphered at cellular and molecular levels. This LAA modification of the epicardial micrografting technique has the overall potential to facilitate the adoption of cardiac cell therapy during heart surgery.

Biomaterials-Based Cell Therapy for Myocardial Tissue Regeneration

Cardiovascular diseases (CVDs) have been the leading cause of death worldwide during the past several decades. Cell loss is the main problem that results in cardiac dysfunction and further mortality. Cell therapy aiming to replenish the lost cells is proposed to treat CVDs especially ischemic heart diseases which lead to a big portion of cell loss. Due to the direct injection's low cell retention and survival ratio, cell therapy using biomaterials as cell carriers has attracted more and more attention because of their promotion of cell delivery and maintenance at the aiming sites. In this review, the three main factors involved in cell therapy for myocardial tissue regeneration: cell sources (somatic cells, stem cells, and engineered cells), chemical components of cell carriers (natural materials, synthetic materials, and electroactive materials), and categories of cell delivery materials (patches, microspheres, injectable hydrogels, nanofiber and microneedles, etc.) are systematically summarized. An introduction of the methods including magnetic resonance/radionuclide/photoacoustic and fluorescence imaging for tracking the behavior of transplanted cells in vivo is also included. Current challenges of biomaterials-based cell therapy and their future directions are provided to give both beginners and professionals a clear view of the development and future trends in this area.

Epicardial transplantation of autologous atrial appendage micrografts: evaluation of safety and feasibility in pigs after coronary artery occlusion

Objectives. Several approaches devised for clinical utilization of cell-based therapies for heart failure often suffer from complex and lengthy preparation stages. Epicardial delivery of autologous atrial appendage micrografts (AAMs) with a clinically used extracellular matrix (ECM) patch provides a straightforward therapy alternative. We evaluated the operative feasibility and the effect of micrografts on the patch-induced epicardial foreign body inflammatory response in a porcine model of myocardial infarction. Design. Right atrial appendages were harvested and mechanically processed into AAMs. The left anterior descending coronary artery was ligated to generate acute infarction. Patches of ECM matrix with or without AAMs were transplanted epicardially onto the infarcted area. Four pigs received the ECM and four received the AAMs patch. Cardiac function was studied by echocardiography both preoperatively and at 3-week follow-up. The primary outcome measures were safety and feasibility of the therapy administration, and the secondary outcome was the inflammatory response to ECM. Results. Neither AAMs nor ECM patch-related complications were detected during the follow-up time. AAMs patch preparation was feasible according to time and safety. Inflammation was greatly reduced in AAMs when compared with ECM patches as measured by the amount of infiltrated inflammatory cells and area of inflammation. Immunohistochemistry demonstrated an increased CD3+ cell density in the AAMs patch infiltrate. Conclusions. Epicardial AAMs transplantation demonstrated safety and clinical feasibility. The use of micrografts significantly inhibited ECM-induced foreign body inflammatory reactivity. Transplantation of AAMs shows good clinical applicability as adjuvant therapy to cardiac surgery and can suppress acute inflammatory reactivity.

Emerging roles of the RNA modifications N6-methyladenosine and adenosine-to-inosine in cardiovascular diseases

Cardiovascular diseases lead the mortality and morbidity disease metrics worldwide. A multitude of chemical base modifications in ribonucleic acids (RNAs) have been linked with key events of cardiovascular diseases and metabolic disorders. Named either RNA epigenetics or epitranscriptomics, the post-transcriptional RNA modifications, their regulatory pathways, components, and downstream effects substantially contribute to the ways our genetic code is interpreted. Here we review the accumulated discoveries to date regarding the roles of the two most common epitranscriptomic modifications, N6-methyl-adenosine (m6A) and adenosine-to-inosine (A-to-I) editing, in cardiovascular disease.

N6-methyladenosine modulates long non-coding RNA in the developing mouse heart

Long non-coding RNAs (lncRNAs) were reported to potentially play a regulatory role in the process of myocardial regeneration in the neonatal mouse. N6-methyladenosine (m⁶A) modification may play a key role in myocardial regeneration in mice and regulates a variety of biological processes through affecting the stability of lncRNAs. However, the map of m⁶A modification of lncRNAs in mouse cardiac development still remains unknown. We aimed to investigate the differences in the m⁶A status of lncRNAs during mouse cardiac development and reveal a potential role of m⁶A modification modulating lncRNAs in cardiac development and myocardial regeneration during cardiac development in mice. Methylated RNA immunoprecipitation sequencing (MeRIP-seq) and RNA sequencing (RNA-seq) of the heart tissue in C57BL/6 J mice at postnatal day 1 (P1), P7 and P28 were performed to produce stagewise cardiac lncRNA m⁶A-methylomes in a parallel timeframe with the established loss of an intrinsic cardiac regeneration capacity and early postnatal development. There were significant differences in the distribution and abundance of m⁶A modifications in lncRNAs in the P7 vs P1 mice. In addition, the functional role of m⁶A in regulating lncRNA levels was established for selected transcripts with METTL3 silencing in neonatal cardiomyocytes in vitro. Based on our MeRIP-qPCR experiment data, both lncGm15328 and lncRNA Zfp597, that were not previously associated with cardiac regeneration, were found to be the most differently methylated at P1-P7. These two lncRNAs sponged several miRNAs which further regulated multiple mRNAs, including some of which have previously been linked with cardiac regeneration ability. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis revealed that differential m⁶A modifications were more enriched in functions and cellular signalling pathways related to cardiomyocyte proliferation. Our data suggested that the m⁶A modification on lncRNAs may play an important role in the regeneration of myocardium and cardiac development.

The graphical abstract of the potential mechanism of m⁶A modulates long non-coding RNA in the developing mouse heart.

Structural and Functional Support by Left Atrial Appendage Transplant to the Left Ventricle after a Myocardial Infarction

The left atrial appendage (LAA) of the adult heart has been shown to contain cardiac and myeloid progenitor cells. The resident myeloid progenitor population expresses an array of pro-regenerative paracrine factors. Cardiac constructs have been shown to inhibit deleterious remodeling of the heart using physical support. Due to these aspects, LAA holds promise as a regenerative transplant. LAAs from adult mT/mG mice were transplanted to the recipient 129X1-SvJ mice simultaneously as myocardial infarction (MI) was performed. A decellularized LAA patch was implanted in the control group. Two weeks after MI, the LAA patch had integrated to the ventricular wall, and migrated cells were seen in the MI area. The cells had two main phenotypes: small F4/80+ cells and large troponin C+ cells. After follow-up at 8 weeks, the LAA patch remained viable, and the functional status of the heart improved. Cardiac echo demonstrated that, after 6 weeks, the mice in the LAA-patch-treated group showed an increasing and statistically significant improvement in cardiac performance when compared to the MI and MI + decellularized patch controls. Physical patch-support (LAA and decellularized LAA patch) had an equal effect on the inhibition of deleterious remodeling, but only the LAA patch inhibited the hypertrophic response. Our study demonstrates that the LAA transplantation has the potential for use as a treatment for myocardial infarction. This method can putatively combine cell therapy (regenerative effect) and physical support (inhibition of deleterious remodeling).

Thrombospondin-4 Is a Soluble Dermal Inflammatory Signal That Selectively Promotes Fibroblast Migration and Keratinocyte Proliferation for Skin Regeneration and Wound Healing

Thrombospondin-4 (THBS4) is a non-structural extracellular matrix molecule associated with tissue regeneration and a variety of pathological processes characterized by increased cell proliferation and migration. However, the mechanisms of how THBS4 regulates cell behavior as well as the pathways contributing to its effects have remained largely unexplored. In the present study we investigated the role of THBS4 in skin regeneration both in vitro and in vivo. We found that THBS4 expression was upregulated in the dermal compartment of healing skin wounds in humans as well as in mice. Application of recombinant THBS4 protein promoted cutaneous wound healing in mice and selectively stimulated migration of primary fibroblasts as well as proliferation of keratinocytes in vitro. By using a combined proteotranscriptomic pathway analysis approach we discovered that β-catenin acted as a hub for THBS4-dependent cell signaling and likely plays a key role in promoting its downstream effects. Our results suggest that THBS4 is an important contributor to wound healing and its incorporation into novel wound healing therapies may be a promising strategy for treatment of cutaneous wounds.

Epicardial Transplantation of Autologous Cardiac Micrografts During Coronary Artery Bypass Surgery

Background: Cardio-regenerative cell therapies offer additional biologic support to coronary artery bypass surgery (CABG) and are aimed at functionally repairing the myocardium that suffers from or is damaged by ischemia. This non-randomized open-label study assessed the safety and feasibility of epicardial transplantation of atrial appendage micrografts (AAMs) in patients undergoing CABG surgery. Methods: Twelve consecutive patients destined for CABG surgery were included in the study. Six patients received AAMs during their operation and six patients were CABG-operated without AAMs transplantation. Data from 30 elective CABG patients was collected for a center- and time-matched control group. The AAMs were processed during the operation from a biopsy collected from the right atrial appendage. They were delivered epicardially onto the infarct scar site identified in preoperative late gadolinium enhancement cardiac magnetic resonance imaging (CMRI). The primary outcome measures at the 6-month follow-up were (i) patient safety in terms of hemodynamic and cardiac function over time and (ii) feasibility of therapy administration in a clinical setting. Secondary outcome measures were left ventricular wall thickness, change in myocardial scar tissue volume, changes in left ventricular ejection fraction, plasma concentrations of N-terminal pro-B-type natriuretic peptide levels, NYHA class, number of days in hospital and changes in the quality of life. Results: Epicardial transplantation of AAMs was safe and feasible to be performed during CABG surgery. CMRI demonstrated an increase in viable cardiac tissue at the infarct site in patients receiving AAMs treatment. Conclusions and Relevance: Transplantation of AAMs shows good clinical applicability as performed during cardiac surgery, shows initial therapeutic effect on the myocardium and has the potential to serve as a delivery platform for cardiac gene therapies. Trial Registration:ClinicalTrials.gov, identifier: NCT02672163.

Epitranscriptomics of Ischemic Heart Disease-The IHD-EPITRAN Study Design and Objectives

Epitranscriptomic modifications in RNA can dramatically alter the way our genetic code is deciphered. Cells utilize these modifications not only to maintain physiological processes, but also to respond to extracellular cues and various stressors. Most often, adenosine residues in RNA are targeted, and result in modifications including methylation and deamination. Such modified residues as N-6-methyl-adenosine (m6A) and inosine, respectively, have been associated with cardiovascular diseases, and contribute to disease pathologies. The Ischemic Heart Disease Epitranscriptomics and Biomarkers (IHD-EPITRAN) study aims to provide a more comprehensive understanding to their nature and role in cardiovascular pathology. The study hypothesis is that pathological features of IHD are mirrored in the blood epitranscriptome. The IHD-EPITRAN study focuses on m6A and A-to-I modifications of RNA. Patients are recruited from four cohorts: (I) patients with IHD and myocardial infarction undergoing urgent revascularization; (II) patients with stable IHD undergoing coronary artery bypass grafting; (III) controls without coronary obstructions undergoing valve replacement due to aortic stenosis and (IV) controls with healthy coronaries verified by computed tomography. The abundance and distribution of m6A and A-to-I modifications in blood RNA are charted by quantitative and qualitative methods. Selected other modified nucleosides as well as IHD candidate protein and metabolic biomarkers are measured for reference. The results of the IHD-EPITRAN study can be expected to enable identification of epitranscriptomic IHD biomarker candidates and potential drug targets.

A Novel Autologous Micrografts Technology in Combination with Negative Pressure Wound Therapy (NPWT) for Quick Granulation Tissue Formation in Chronic/Refractory Ulcer

Negative pressure wound therapy (NPWT) has been commonly used over the years for a wide range of chronic/refractory lesions. Alternatively, autologous micrografting technology is recently becoming a powerful modality for initiating wound healing. The case presented is of a patient with a lower leg ulcer that had responded poorly to NPWT alone for three weeks. Consequently, the patient was put on a combination therapy of NPWT and micrografting. After injection of a dermal tissue micrografts suspension into the entire wound bed, NPWT was performed successively for two weeks, resulting in fresh granulation tissue formation. Thereafter, the autologous skin graft was taken well. This case study indicates that for a chronic/refractory ulcer patient with poor NPWT outcome, combination therapy using micrografting treatment and NPWT could rapidly initiate and enhance granulation tissue formation, creating a favorable bedding for subsequent skin grafting.