Myocardial infarction causes irreversible loss of cardiomyocytes (CMs) and often leads to heart failure. To
replace the lost cells, we identified a combination of cell-cycle regulators that induces stable cytokinesis in adult
post-mitotic cells. Overexpression of cyclin-dependent kinase 1 (CDK1), CDK4, cyclin B1, and cyclin D1 (referred
to as 4F) promotes cell division in post-mitotic mouse, rat, and human cardiomyocytes. The high efficiency of
this protocol in inducing myocyte renewal provides new opportunities for understanding the mechanisms involved
in cardiomyocyte proliferation. One of the most interesting findings related to this discovery was the confirmation
of a link between metabolic reprogramming and cardiomyocyte proliferation. Although in proliferating cells there
is a strong correlation between metabolic changes and cellular proliferation, it remains unclear how metabolism
influences the proliferative potential of cardiomyocytes. During the past 2 years, in collaboration with Dr. Hill’s
group, I have generated preliminary data which indicate that cardiomyocyte proliferation is associated with
marked reprogramming in energy metabolism. In proliferating cardiomyocytes isolated from lineage tracing
(MADM) mice, RNA-seq data indicate profound downregulation of fatty acid oxidation genes and upregulation of
biosynthetic pathway enzyme expression; in human iPSC-derived cardiomyocytes (hiPSC-CMs), 4F expression
decreases mitochondrial respiration and catabolic activities. Using stable isotope-resolved metabolomics
(SIRM), we demonstrate that 4F-infected hiPS-CMs show significant elevation in 13C labeled intermediates or
end products of the hexosamine biosynthetic pathway (HBP), serine biosynthesis pathway (SBP), and pentose
phosphate pathway (PPP). In line with these findings, our results also demonstrate that augmenting the carbon
availability for these biosynthetic pathways by overexpressing phosphoenolpyruvate carboxykinase (PCK1 or
PCK2) augments the ability of cardiomyocytes to proliferate. These data suggest that higher biosynthetic
pathway flux may be required for cardiomyocyte proliferation. Informed by these results, we propose the general
hypothesis that activation of ancillary biosynthetic pathways of glucose metabolism are required for
cardiomyocyte proliferation. We suggest that higher biosynthetic pathway flux is required for building block
synthesis and may be important for regulating pro-proliferative gene programs. During this project we will
delineate the importance of each biosynthetic pathway in influencing cardiomyocyte proliferation. First, using
pharmacological and virus-based approaches, we will determine the specific contribution of the HBP, SBP and
PPP pathways to myocyte proliferation. In addition, we will investigate the influence of increasing the carbon flux
in biosynthetic pathway through overexpression of PCK1, or PCK2 on cardiac function and repair in vivo. The
aims of this project are: Specific Aim 1: Delineate the contribution of each biosynthetic pathway on cardiomyocyte
proliferation. Specific Aim 2: Investigate the functional efficacy of increasing carbon flux in biosynthetic pathways
on cardiac repair in vivo.