Abstract Body: Introduction
The heart is a metabolically intense organ, utilizing oxidative phosphorylation for ATP in adults. When injured, a metabolic shift occurs to rely on inefficient glycolytic ATP, further propagating heart dysfunction and contributing to fibrosis. The very young heart equivalently utilizes glycolytic ATP, but also uniquely possess an ability to repair after injury. We sought to determine how changes to mitochondrial oxidative phosphorylation can be linked to organ repair in the young pediatric heart, and poor heart function and fibrosis in the adult, and determine if mitochondrial signaling and tissue repair could be transferred from the pediatric heart to the damaged adult organ.

Methods
We collected 100 cardiac tissue samples from children undergoing open heart surgery, with isolation of cardiac progenitor cells from each explant. In culture, total secreted biomolecules of the stem cells (secretome) were collected. Matured stem cell-derived cardiomyocyte (iPSC-CM) tissues were placed under hypoxia (1% oxygen) and treated with each patient’s secretome with metabolic and functional analysis. Secretome composition was determined using mass spectrometry. Sprague-Dawley rats underwent LAD ligation with peri-infarct secretome injection. Cardiac function was analysed using echocardiography.

Results
Secretome treatment improved tissue contractility, mitochondrial mass and polarization, basal and maximal respiration, and ATP/ADP ratio (all p < 0.01). Mitochondria from treated cells were less fragmented (EM imaging), with a decreased pDRP1/DRP1 ratio (p < 0.05). Shot-gun mass spectrometry found over 400 over-represented proteins, with metabolic regulation seen as a hub of the identified proteins. Of the metabolic proteins, enolase-1 (ENO1) was significantly in over abundance. To validate ENO1, we generated a Lenti virus construct and over-expressed the protein in iPSC-CMs under hypoxic conditions. We found ENO1 improved tissue contractility, mitochondrial polarization, basal and maximal respiration (all p < 0.05). Recominant ENO1 encapsulated into lipid nanoparticles (LNP) showed similar improved iPSC-CM contractile function and mitochondrial polarization and structure.

Conclusion
We have shown how metabolic regulators from the pediatric heart can provide a transferable benefit to injured cardiomyocytes. Future studies will deliver loaded LNPs into the hearts of porcine models with ischemic cardiac injury, towards a novel metabolic therapy for heart failure.