C3orf58, a Novel Paracrine Protein, Stimulates Cardiomyocyte Cell Cycle Progression Through the PI3K-AKT-CDK7 Pathway
Rationale: The regenerative capacity of the heart is markedly diminished shortly after birth coinciding with overall withdrawal of cardiomyocytes from cell cycle. Consequently, the adult mammalian heart has limited capacity to regenerate after injury. The discovery of factors that can induce cardiomyocyte proliferation is therefore of high interest and has been the focus of extensive investigation over the past years.
Objective: We have recently identified C3orf58 as a novel Hypoxia and Akt induced Stem cell Factor (HASF) secreted from mesenchymal stem cells that can promote cardiac repair through cytoprotective mechanisms. Here, we tested the hypothesis that HASF can also contribute to cardiac regeneration by stimulating cardiomyocyte division and proliferation.
Methods and Results: Neonatal ventricular cardiomyocytes were stimulated in culture for seven days with purified recombinant HASF protein. Compared to control untreated cells, HASF-treated neonatal cardiomyocytes exhibited 60% increase in DNA synthesis as measured by BrdU incorporation. These results were confirmed by immunofluorescence confocal microscopy showing a 50-100% increase in the number of cardiomyocytes in the mitotic and cytokinesis phases. Importantly, in vivo cardiac overexpression of HASF in a transgenic mouse model resulted in enhanced level of DNA synthesis and cytokinesis in neonatal and adult cardiomyocytes. These proliferative effects were modulated by a PI3K-AKT-CDK7 pathway as revealed by the use of PI3K pathway specific inhibitors and silencing of the Cdk7 gene.
Conclusions: Our studies support the hypothesis that HASF induces cardiomyocyte proliferation via a PI3K-AKT-CDK7 pathway. The implications of this finding may be significant for cardiac regeneration biology and therapeutics.
- Received January 28, 2013.
- Revision received June 5, 2013.
- Accepted June 19, 2013.