Rationale/Background: The adult mammalian heart has a very limited potential for regeneration due to cardiomyocyte cell cycle withdrawal which occurs shortly after birth. One potential avenue to repair the heart following stress/injury is to reprogram pre-existing cardiomyocytes to re-enter the cell cycle. The E2F family is a group of transcription factors which ubiquitously regulate the cell cycle, but it has previously been difficult to fully appreciate their role in the post-natal myocardium due to either redundancy or embryonic lethality of genetic models. Thus we generated a dominant negative model of the E2F/Rb pathway via expression of the unique transcriptional repressor E2F6 in postnatal myocardium. E2F6 transgenic (Tg) mice developed dose dependent Dilated Cardiomyopathy (DCM) and sudden death without hypertrophy or apoptosis. This was accompanied by the partial loss of E2F3 (critical for cardiac development) and connexin-43 important for metabolic and electrical coupling.
Methods/Results: In this thesis E2F6-Tg mice were examined for markers of cardiac differentiation/ function and exposed to stressors to evaluate the capacity for the E2F pathway to regulate cardiomyocyte growth (isoproterenol) and death (doxorubicin and cobalt chloride). E2F6-Tg mice were twice as sensitive to isoproterenol as their Wt counterparts due to the observed activation of a β2-adrenergic survival pathway. Cardiac hypertrophy in E2F6-Tg mice was accompanied by the rescue of E2F3 expression. Treatment of neonatal cardiomyocytes isolated from Wt and E2F6-Tg pups with cobalt chloride revealed a protective effect for E2F6 against apoptosis. Doxorubicin exposure led to the loss of E2F6 protein and abolished its protective effect. Examination of neonatal hearts and cardiomyocytes isolated from them demonstrated a shift in the cell cycle and metabolic profiles of E2F6-Tg myocardium. Tg cardiomyocytes show decreased glycolysis and a dramatic increase in the regulator of ketolysis, β-hydroxybutyrate dehydrogenase (BDH1), prior to DCM. The substrate of BDH1 (β-hydroxybutyrate) was demonstrated to influence the levels of CX-43 in cardiomyocytes. E2F6 also deregulated expression of T-cap which has been linked to human DCM.
Conclusions: I provide evidence that the E2F pathway can regulate growth, death, and differentiation through a variety of mechanisms which link the cell cycle and metabolism to growth and survival to critically govern post-natal cardiac function. Furthermore, I reveal a new biomarker (BDH1) for early DCM which may be useful in diagnosis/ treatment of idiopathic cases of disease.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/36014 |
| Date | January 2017 |
| Creators | Major, Jennifer Lynn |
| Contributors | Tuana, Balwant |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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