title: Cardiomyocyte bridging between hearts and bioengineered myocardial tissues with mesenchymal transition of mesothelial cells.
abstract: BACKGROUND
  For the reconstruction of 3-dimensional (3D) tissues, we exploited an original method of tissue engineering that layers individual cell sheets harvested from temperature-responsive culture dishes. Stacked cardiomyocyte sheets demonstrated electrical and morphologic communication, resulting in synchronously beating myocardial tissue. When these bioengineered 3D tissue grafts are transplanted onto damaged hearts, gap junction communication between graft and host is likely critical for synchronized beating and functional improvement. In this study, these graft-to-heart morphologic communications were examined.
  
  
  METHODS
  Neonatal rat cardiomyocyte sheets were harvested from temperature-responsive culture dishes and layered to create 3D tissues. These constructs were then transplanted onto infarcted rat hearts. Histologic analyses and transmission electron microscopy (TEM) were performed to examine morphologic communications. The passage of small molecules through functional gap junctions was also detected using a dye-transfer assay.
  
  
  RESULTS
  Transplanted cardiomyocytes bridged between the grafts and hearts in intact areas. Connexin-43 staining and TEM revealed the existence of gap junctions and intercalated disks between the bridging cardiomyocytes. Furthermore, it was confirmed that a low-molecule fluorescent dye, calcein, was transferred from the grafts to the hearts via the bridging cardiomyocytes. Immunohistochemistry with anti-intercellular adhesion molecule-1 antibodies revealed that mesothelial cells in the epicardium scattered and transdifferentiated into mesenchymal cells between the graft and host.
  
  
  CONCLUSIONS
  The direct attachment of layered cardiomyocyte sheets on the heart surface promotes mesothelial cell transdifferentiation and cardiomyocyte bridging, leading to functional communication via gap junctions. These results indicate that these bioengineered myocardial tissues may improve damaged heart function via synchronized beating.
authors.affiliation: Institute of Advanced Biomedical Engineering and Science, Tokyo Women's Medical University, Tokyo, Japan.
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Sekine
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Shimizu
authors.forename: Seiichi
authors.initials: S
authors.lastname: Kosaka
authors.forename: Eiji
authors.initials: E
authors.lastname: Kobayashi
authors.forename: Teruo
authors.initials: T
authors.lastname: Okano
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002450:Cell Communication; D004195:Disease Models, Animal; D004847:Epithelial Cells / Q000502:physiology; D005109:Extracellular Matrix / Q000648:ultrastructure; D005347:Fibroblasts / Q000637:transplantation; D005452:Fluoresceins; D005456:Fluorescent Dyes; D017629:Gap Junctions / Q000502:physiology; D006329:Heart Conduction System / Q000502:physiology* / Q000648:ultrastructure; D018799:Intercellular Adhesion Molecule-1 / Q000032:analysis; D008648:Mesoderm / Q000166:cytology; D046529:Microscopy, Electron, Transmission; D009203:Myocardial Infarction / Q000473:pathology / Q000503:physiopathology; D009206:Myocardium / Q000166:cytology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D023822:Tissue Engineering; D016378:Tissue Transplantation / Q000379:methods
chemical_list: D005452:Fluoresceins; D005456:Fluorescent Dyes; D018799:Intercellular Adhesion Molecule-1; C085925:calcein AM