E2F2 expression induces proliferation of terminally differentiated cardiomyocytes in vivo.
OBJECTIVE
In previous experiments we have demonstrated that expression of the transcription factors E2F2 and E2F4 is sufficient to induce proliferation of isolated primary cardiomyocytes from newborn rats and mice. We now wanted to analyse whether E2F2 or E2F4 are also able to promote cell cycle progression of adult cardiomyocytes in vivo, which unlike cardiomyocytes from newborn rodents lack the ability to undergo cell proliferation.


RESULTS
E2F2 or E2F4 was expressed in hearts of mice at different developmental stages using adenoviral vectors. Effects regarding proliferation, hypertrophy, and apoptosis were analysed on histological sections, and quantitative assessment of cell cycle regulatory genes was performed by real-time PCR (polymerase chain reaction) and western blot. We found that both E2F2 and E2F4 can stimulate hypertrophic cell growth of cardiomyocytes. However, only directed expression of E2F2 but not of E2F4 was sufficient to induce proliferation of cardiomyocytes. Expression of E2F2 in vivo did not increase the percentage of apoptotic cardiomyocytes but down-regulated the expression of the pro-apoptotic genes caspase-6 and apaf-1. Further analysis of the cell cycle regulatory machinery revealed that expression of E2F2 caused a strong induction of cyclin A and E while the expression of cyclin-dependent kinase inhibitors (CKIs) such as p21 was not affected.


CONCLUSIONS
We conclude that a limited induction of cardiomyocyte cell proliferation can be achieved by E2F2-mediated stimulation of cyclin A and E expression without a reduction of CKIs.
Ebelt
Henning
H
Department of Medicine III, University of Halle-Wittenberg, Ernst-Grube-Strasse 40, 06097 Halle, Germany. henning.ebelt@medizin.uni-halle.de
Zhang
Ying
Y
Kampke
Alexander
A
Xu
Jia
J
Schlitt
Axel
A
Buerke
Michael
M
Müller-Werdan
Ursula
U
Werdan
Karl
K
Braun
Thomas
T
D000818:Animals; D017209:Apoptosis; D002453:Cell Cycle; D002454:Cell Differentiation; D049109:Cell Proliferation; D019925:Cyclin A / Q000378:metabolism; D056743:Cyclin D3; D019927:Cyclin E / Q000378:metabolism; D050756:Cyclin-Dependent Kinase Inhibitor Proteins / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism; D050703:E2F2 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D050704:E2F4 Transcription Factor / Q000378:metabolism; D017930:Genes, Reporter; D006984:Hypertrophy; D051379:Mice; D008822:Mice, Transgenic; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D014162:Transfection
C534697:Ccnd3 protein, mouse; C534698:Ccnd3 protein, rat; D019925:Cyclin A; D056743:Cyclin D3; D019927:Cyclin E; D050756:Cyclin-Dependent Kinase Inhibitor Proteins; D016213:Cyclins; D050703:E2F2 Transcription Factor; D050704:E2F4 Transcription Factor