Background:
Extensive research has characterized the embryonic development of a four-chambered heart in mammals. After birth, mammalian cardiomyocytes undergo a transition characterized by a final cell cycle with nuclear division (karyokinesis) in the absence of cytoplasmic division (cytokinesis), generating mature binucleated cardiomyocytes. Downregulation of pro-proliferative signaling and epigenetic changes permanently ‘lock’ cardiomyocytes out of the cell cycle, and nearly all subsequent growth is accomplished via cellular hypertrophy. Before this transition, cardiomyocytes exhibit robust proliferative potential, but afterward are unable to divide.
Rationale & Hypothesis:
Recent evidence suggests that non-coding RNAs influence early neonatal cardiac development and hypertrophy. We hypothesize that transient expression of regulatory miRNAs may impact the neonatal heart’s transition from proliferation to hypertrophy.
Results:
Cardiac mRNA and miRNA were systematically analyzed using microarrays to identify targets that were transiently and significantly changing after birth. Through our analysis we identified three primary ontogenies significantly changing: metabolism, extracellular matrix remodeling, and cell cycle regulation.
Global analysis of micro-RNA expression patterns during perinatal heart development identified miR-205 as a novel candidate for modulating cardiomyocyte maturation. We observed miR-205 expression undergoing a 20-fold increase from 1-day postpartum (1D) to 5D, returning to prenatal levels by 10D. It is expressed in cardiomyocytes of the epicardium, the primary location of fetal cardiomyocyte proliferation. MiR-205 targets two important cell cycle regulators: Pten phosphatase of the PI3K/AKT pathway, and Yap1 in the Hippo pathway. Both pathways have proven to be essential for proper heart development. Previous research showed that germline deletion of miR-205 results in death at 5D.
To define its role in the heart, we generated an αMHC-Cre postnatal miR-205 cardiac-specific deletion mouse model. Systematic characterization of miR-205-/- hearts confirmed miR-205’s interaction with Pten and Yap1 by western blot and immunohistochemistry. Postnatal miR-205-/- hearts exhibit Hippo pathway dysregulation, increased cardiomyocyte number, more actively cycling cardiomyocytes beyond 7D, and no difference in binucleation.
We also generated a DOX-inducible cardiac-specific miR-205 over-expression mouse model. Perinatal miR-205OE hearts expedited the transitional period, with more cardiomyocytes present at 5D and no difference at 14D. These hearts show increased Hippo signaling immediately after birth, suggesting compensatory mechanisms to ensure sufficient cardiomyocyte number.
Conclusions:
Our data strongly supports miR-205 as a regulator of cardiomyocyte maturation in the neonatal heart, by promoting the neonatal cardiomyocyte transition from hyperplastic to hypertrophic growth. In turn, miR-205’s antiproliferative properties originate in part from suppressing the expression of Pten and Yap1.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/39809 |
| Date | 06 November 2019 |
| Creators | Weldrick, Jonathan |
| Contributors | Megeney, Lynn, Burgon, Patrick |
| 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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