title: Telomere-independent cellular senescence in human fetal cardiomyocytes.
abstract: Fetal cardiomyocytes have been proposed as a potential source of cell-based therapy for heart failure. This study examined cellular senescence in cultured human fetal ventricular cardiomyocytes (HFCs). HFCs were isolated and identified by immunocytochemistry and RT-PCR. Cells were found to senesce after 20-25 population doublings, as determined by growth arrest, morphological changes and senescence-associated beta-galactosidase activity. Using the telomeric repeat amplification protocol assay, telomerase activity was undetectable in primary HFCs. Cells were transduced to express the human reverse transcriptase subunit (hTERT) of telomerase. This resulted in greatly increased telomerase activity, but no significant lifespan extension. Analysis of telomere length in primary HFCs revealed that the senescent phenotype was not accompanied by telomere shortening. Telomeres in hTERT-positive cells were elongated in comparison with primary cells, and elongation was retained in senescent cells. Levels of the tumor suppressor protein p16INK4A increased in all senescent cells whether telomerase-positive or -negative. Senescence was accompanied by a decline in transcript levels of the polycomb gene Bmi-1, Ets1 and Ets2 transcription factors, and Id1, Id2 and Id3 helix-loop-helix proteins, suggesting roles for these genes in maintenance of cardiomyocyte proliferative capacity. In addition to offering novel insights into the behavior of human fetal cardiomyocytes in culture, these findings have implications for the development of a cell-based therapy for cardiac injury using primary fetal heart tissue.
authors.affiliation: UCSD Cancer Center, 9500 Gilman Drive, La Jolla, CA 92093-0816, USA. ajball@ucsd.edu
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Ball
authors.forename: Fred
authors.initials: F
authors.lastname: Levine
mesh_terms: D015687:Cell Hypoxia / Q000502:physiology; D049109:Cell Proliferation; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000502:physiology*; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics; D005333:Fetus / Q000166:cytology; D015870:Gene Expression / Q000235:genetics; D006801:Humans; D051798:Inhibitor of Differentiation Protein 1; D051797:Inhibitor of Differentiation Protein 2; D051796:Inhibitor of Differentiation Proteins; D032383:Myocytes, Cardiac / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D009363:Neoplasm Proteins / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics; D063150:Polycomb Repressive Complex 1; D050784:Proto-Oncogene Protein c-ets-1; D050787:Proto-Oncogene Protein c-ets-2; D011518:Proto-Oncogene Proteins / Q000235:genetics; D050783:Proto-Oncogene Proteins c-ets; D012097:Repressor Proteins / Q000235:genetics; D019098:Telomerase / Q000235:genetics / Q000378:metabolism; D016615:Telomere / Q000378:metabolism / Q000502:physiology*; D015534:Trans-Activators / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: C069077:BMI1 protein, human; D019941:Cyclin-Dependent Kinase Inhibitor p16; D004268:DNA-Binding Proteins; C494041:ETS1 protein, human; C494069:ETS2 protein, human; C497453:ID1 protein, human; C497450:ID2 protein, human; D051798:Inhibitor of Differentiation Protein 1; D051797:Inhibitor of Differentiation Protein 2; D051796:Inhibitor of Differentiation Proteins; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D050784:Proto-Oncogene Protein c-ets-1; D050787:Proto-Oncogene Protein c-ets-2; D011518:Proto-Oncogene Proteins; D050783:Proto-Oncogene Proteins c-ets; D012097:Repressor Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C075640:ID3 protein, human; D063150:Polycomb Repressive Complex 1; D019098:Telomerase; D001616:beta-Galactosidase