Abstract 1112: Re-isolation and Functional Characterization of Cardiomyocytes after Implantation of Bone Marrow Stromal Cells or Neonatal Cardiomyocytes in Rat Heart

Abstract

Background: Replacement of cardiac muscle is a key goal of cell therapy, but uncertainty exists about whether cell implantation strategies actually generate true functioning cardiomyocytes. We therefore aimed to re-isolate implanted bone marrow stromal cells (BMSCs) to determine their functional characteristics ex vivo . Neonatal cardiomyocytes (NCMs), in which the myocyte phenotype was established before implantation, were used as a gold standard. Methods: NCMs from GFP-transgenic rats were injected into the hearts of nude rats (n=4), and re-isolated after 1, 2 or 4 weeks. These were compared with adult myocytes, and with myocytes from 2 and 4 week-old (2W-O and 4W-O) rats. labelled myocytes detected 2 weeks after implantation of DiI and iron-labelled BMSCs (2W-BI) into infarcted rat hearts (n=4) were studied. Results: GFP-labelled myocytes approaching the adult morphology (rod-shaped, with defined sarcomeres) were not detected until 2 weeks after implantation of NCMs (2W-I), and were significantly shorter than adult myocytes in cell length (52 ± 5μm, n=10 vs. 99 ± 9μm, n=9, p<0.001), but the similar length to those from 2W-O (56 ± 3μm, n=15). Contraction amplitude (% shortening) was significantly lower and time to 50 % relaxation (R50) longer for the re-isolated cells compared with adult. By 4 weeks after implantation (4W-I), re-isolated myocytes were close to the adult phenotype, although cell length (64 ± 5μm, n=20, p<0.01) showed immature characteristics. After implantation of BMSCs, DiI-labelled myocytes were detected in only 4/10 rats and then at low levels (0.4–21 per 10,000). Labelled myocytes, isolated 2 weeks after implantation of BMSCs, had similar length (101 ± 20, n=21), contraction amplitude and beat duration to adult myocytes. Conclusions: Implanted NCMs mature within the heart over a period of at least 4 weeks. The adult phenotype of labelled myocytes after BMSC implantation is inconsistent with a process of transdifferentiation and maturation.