Bone marrow transplantation modulates tissue macrophage phenotype and enhances cardiac recovery after subsequent acute myocardial infarction.

BACKGROUND: Bone marrow transplantation (BMT) is commonly used in experimental studies to investigate the contribution of BM-derived circulating cells to different disease processes. During studies investigating the cardiac response to acute myocardial infarction (MI) induced by permanent coronary ligation in mice that had previously undergone BMT, we found that BMT itself affects the remodelling response. METHODS AND RESULTS: Compared to matched naive mice, animals that had previously undergone BMT developed significantly less post-MI adverse remodelling, infarct thinning and contractile dysfunction as assessed by serial magnetic resonance imaging. Cardiac rupture in male mice was prevented. Histological analysis showed that the infarcts of mice that had undergone BMT had a significantly higher number of inflammatory cells, surviving cardiomyocytes and neovessels than control mice, as well as evidence of significant haemosiderin deposition. Flow cytometric and histological analyses demonstrated a higher number of alternatively activated (M2) macrophages in myocardium of the BMT group compared to control animals even before MI, and this increased further in the infarcts of the BMT mice after MI. CONCLUSIONS: The process of BMT itself substantially alters tissue macrophage phenotype and the subsequent response to acute MI. An increase in alternatively activated macrophages in this setting appears to enhance cardiac recovery after MI.

Impact of a selfish B chromosome on chromatin dynamics and nuclear organization in Nasonia.

B chromosomes are centric chromosomal fragments present in thousands of eukaryotic genomes. Because most B chromosomes are non-essential, they can be lost without consequence. In order to persist, however, some B chromosomes can impose strong forms of intra-genomic conflict. An extreme case is the paternal sex ratio (PSR) B chromosome in the jewel wasp Nasonia vitripennis. Transmitted solely via the sperm, PSR 'imprints' the paternal chromatin so that it is destroyed during the first mitosis of the embryo. Owing to the haplo-diploid reproduction of N. vitripennis, PSR-induced loss of the paternal chromatin converts embryos that should become females into PSR-transmitting males. This conversion is key to the persistence of PSR, although the underlying mechanisms are largely unexplored. We assessed how PSR affects the paternal chromatin and then investigated how PSR is transmitted efficiently at the cellular level. We found that PSR does not affect progression of the paternal chromatin through the cell cycle but, instead, alters its normal Histone H3 phosphorylation and loading of the Condensin complex. PSR localizes to the outer periphery of the paternal nucleus, a position that we propose is crucial for it to escape from the defective paternal set. In sperm, PSR consistently localizes to the extreme anterior tip of the elongated nucleus, while the normal wasp chromosomes localize broadly across the nucleus. Thus, PSR may alter or bypass normal nuclear organizational processes to achieve its position. These findings provide new insights into how selfish genetic elements can impact chromatin-based processes for their survival.

Wharton's Jelly-Mesenchymal Stem Cell-Engineered Conduit for Pediatric Translation in Heart Defect.

The materials available for the right ventricular outflow tract (RVOT) reconstruction in patients with tetralogy of fallot (TOF)/pulmonary atresia come with the severe limitation of long-term degeneration and lack of growth potential, causing right ventricular dysfunction, aneurysm formation, and arrhythmias, thus necessitating several high-risk reoperations throughout patients' lives. In this study, we evaluated the capacity of mesenchymal stem cells (MSCs) derived from the Wharton's Jelly (WJ-MSCs), the gelatinous inner portion of the umbilical cord, to grow and recellularize an extracellular matrix (ECM) graft in our optimized xeno-free, good manufacturing practice-compliant culture system. WJ-MSCs were phenotypically and functionally characterized by flow cytometry and multilineage differentiation capacity, respectively. The typical MSC immunophenotype and functional characteristics were retained in our xeno-free culture system, as well as the capacity to grow and engraft onto a naturally occurring scaffold. WJ-MSCs, from both human and swine source, showed excellent capacity to recellularize ECM graft producing a living cell-seeded construct. In addition, we have provided an in vivo proof of concept of feasibility of the cellularized conduit, engineered with swine WJ-MSCs, to be used in a novel porcine model of main pulmonary artery reconstruction, where it showed good integration within the host tissue. Our study indicates that the addition of WJ-MSCs to the ECM scaffold can upgrade the material, converting it into a living tissue, with the potential to grow, repair, and remodel the RVOT. These results could potentially represent a paradigm shift in pediatric cardiac intervention toward new modalities for effective and personalized surgical restoration of pulmonary artery and RVOT function in TOF/pulmonary atresia patients. Impact Statement The materials available for pulmonary artery reconstruction in pediatric patients with Congenital Heart Defect come with the limitation of long-term degeneration and lack of growth, thus necessitating several reoperations. Here, we describe a novel approach combining perinatal stem cells and naturally occurring scaffold to create a living tissue engineered conduit that showed good growth potential in a pulmonary artery reconstruction porcine model. We envision this approach is of great interest and relevance in tissue engineering field applied to cardiovascular regenerative medicine, as it may open up new avenues for correction of congenital cardiac defects, with remarkable medical and social benefits.

Amnion-Based Scaffold with Enhanced Strength and Biocompatibility for In Vivo Vascular Repair.

IMPACT STATEMENT: This study aimed at developing an amnion-based scaffold suitable for vascular tissue engineering applications and in vivo usage. We successfully produced a multilayered scaffold with improved biomechanical properties and biocompatibility for in vivo vascular implantation. Our approach not only offers an allogeneic "off-the-shelf" solution for clinical use but also it provides the possibility of personalized medicine using a patient's own amnion and stem cells for the production of tissue engineered grafts for reconstructive heart surgery.

Successful Reconstruction of the Right Ventricular Outflow Tract by Implantation of Thymus Stem Cell Engineered Graft in Growing Swine.

Graft cellularization holds great promise in overcoming the limitations associated with prosthetic materials currently used in corrective cardiac surgery. In this study, the authors evaluated the advantages of graft cellularization for right ventricular outflow tract reconstruction in a novel porcine model. After 4.5 months from implantation, improved myocardial strain, better endothelialization and cardiomyocyte incorporation, and reduced fibrosis were observed in the cellularized grafts compared with the acellular grafts. To the authors' knowledge, this is the first demonstration of successful right ventricular outflow tract correction using bioengineered grafts in a large animal model.

Reconstruction of the pulmonary artery by a novel biodegradable conduit engineered with perinatal stem cell-derived vascular smooth muscle cells enables physiological vascular growth in a large animal model of congenital heart disease.

Lack of growth potential of available grafts represents a bottleneck in the correction of congenital heart defects. Here we used a swine small intestinal submucosa (SIS) graft functionalized with mesenchymal stem cell (MSC)-derived vascular smooth muscle cells (VSMCs), for replacement of the pulmonary artery in piglets. MSCs were expanded from human umbilical cord blood or new-born swine peripheral blood, seeded onto decellularized SIS grafts and conditioned in a bioreactor to differentiate into VSMCs. Results indicate the equivalence of generating grafts engineered with human or swine MSC-derived VSMCs. Next, we conducted a randomized, controlled study in piglets (12-15 kg), which had the left pulmonary artery reconstructed with swine VSMC-engineered or acellular conduit grafts. Piglets recovered well from surgery, with no casualty and similar growth rate in either group. After 6 months, grafted arteries had larger circumference in the cellular group (28.3 ±â€¯2.3 vs 18.3 ±â€¯2.1 mm, P < 0.001), but without evidence of aneurism formation. Immunohistochemistry showed engineered grafts were composed of homogeneous endothelium covered by multi-layered muscular media, whereas the acellular grafts exhibited a patchy endothelial cell layer and a thinner muscular layer. RESULTS: show the feasibility and efficacy of pulmonary artery reconstruction using clinically available grafts engineered with allogeneic VSMCs in growing swine.

Canonical Wnt5b Signaling Directs Outlying Nkx2.5+ Mesoderm into Pacemaker Cardiomyocytes.

Pacemaker cardiomyocytes that create the sinoatrial node are essential for the initiation and maintenance of proper heart rhythm. However, illuminating developmental cues that direct their differentiation has remained particularly challenging due to the unclear cellular origins of these specialized cardiomyocytes. By discovering the origins of pacemaker cardiomyocytes, we reveal an evolutionarily conserved Wnt signaling mechanism that coordinates gene regulatory changes directing mesoderm cell fate decisions, which lead to the differentiation of pacemaker cardiomyocytes. We show that in zebrafish, pacemaker cardiomyocytes derive from a subset of Nkx2.5+ mesoderm that responds to canonical Wnt5b signaling to initiate the cardiac pacemaker program, including activation of pacemaker cell differentiation transcription factors Isl1 and Tbx18 and silencing of Nkx2.5. Moreover, applying these developmental findings to human pluripotent stem cells (hPSCs) notably results in the creation of hPSC-pacemaker cardiomyocytes, which successfully pace three-dimensional bioprinted hPSC-cardiomyocytes, thus providing potential strategies for biological cardiac pacemaker therapy.

Thymus-Derived Mesenchymal Stem Cells for Tissue Engineering Clinical-Grade Cardiovascular Grafts.

Mesenchymal stem cells (MSCs) are attractive tools for regenerative medicine because of their multidifferentiation potential and immunomodulation capacity. In congenital heart defect surgical correction, replacement grafts lacking growth potential are commonly used. Tissue engineering promises to overcome the limitations of these grafts. In this study, we hypothesized that human thymus-derived MSCs are a suitable tool to tissue engineer a living vascular graft with good integration and patency once implanted in vivo. Human thymus-derived MSCs (hT-MSCs) were identified by the expression of MSC markers and mesenchymal differentiation potential. When cultured onto natural scaffold to produce tissue-engineered graft, hT-MSCs exhibited great proliferation potential and the ability to secrete their own extracellular matrix. In addition, when implanted in vivo in a piglet model of left pulmonary grafting, the engineered graft exhibited good integration within the host tissue, indicating potential suitability for corrective cardiovascular surgery. The optimized xeno-free, good manufacturing practices-compliant culture system proved to be optimum for large-scale expansion of hT-MSCs and production of tissue-engineered cardiovascular grafts, without compromising the quality of cells. This study demonstrated the feasibility of engineering clinical-grade living autologous replacement grafts using hT-MSCs and proved the compatibility of these grafts for in vivo implantation in a left pulmonary artery position.

Expansion and characterization of neonatal cardiac pericytes provides a novel cellular option for tissue engineering in congenital heart disease.

BACKGROUND: Living grafts produced by combining autologous heart-resident stem/progenitor cells and tissue engineering could provide a new therapeutic option for definitive correction of congenital heart disease. The aim of the study was to investigate the antigenic profile, expansion/differentiation capacity, paracrine activity, and pro-angiogenic potential of cardiac pericytes and to assess their engrafting capacity in clinically certified prosthetic grafts. METHODS AND RESULTS: CD34(pos) cells, negative for the endothelial markers CD31 and CD146, were identified by immunohistochemistry in cardiac leftovers from infants and children undergoing palliative repair of congenital cardiac defects. Following isolation by immunomagnetic bead-sorting and culture on plastic in EGM-2 medium supplemented with growth factors and serum, CD34(pos)/CD31(neg) cells gave rise to a clonogenic, highly proliferative (>20 million at P5), spindle-shape cell population. The following populations were shown to expresses pericyte/mesenchymal and stemness markers. After exposure to differentiation media, the expanded cardiac pericytes acquired markers of vascular smooth muscle cells, but failed to differentiate into endothelial cells or cardiomyocytes. However, in Matrigel, cardiac pericytes form networks and enhance the network capacity of endothelial cells. Moreover, they produce collagen-1 and release chemo-attractants that stimulate the migration of c-Kit(pos) cardiac stem cells. Cardiac pericytes were then seeded onto clinically approved xenograft scaffolds and cultured in a bioreactor. After 3 weeks, fluorescent microscopy showed that cardiac pericytes had penetrated into and colonized the graft. CONCLUSIONS: These findings open new avenues for cellular functionalization of prosthetic grafts to be applied in reconstructive surgery of congenital heart disease.