Abstract 17569: The Reserve Respiratory Capacity in Cardiac Myocytes is Regulated by Metabolic Substrates, Hypoxia, and miR-199a
Preconditioning of the heart to ischemia is one of the most effective measures in reducing the damage inflicted by ischemia. An aspect of ischemia preconditioning that has not been investigated is its effect on fatty acid and glucose metabolism; in particular, its effect on the reserve respiratory capacity (RRC) of the myocytes. Under normal conditions the cell runs on a fraction of its bioenergetic capacity, and the difference between its basal and maximum respiratory capacity is the RRC. A reduction in RRC has been associated with cell death and neurodegenerative disease; however, we have no knowledge regarding RRC regulation in cardiac myocytes during health or disease. We hypothesized that RRC is regulated in the myocytes by hypoxia and regulators of metabolism. To test this, we monitored the oxygen consumption rate (OCR) and the extracellular acidification rate (ECAR) in real time in neonatal cardiac myocytes under different conditions, and after incubating them with various reagents to assess mitochondrial function. Our data show that myocytes, under normoxic conditions, had a 200% of basal RRC when palmitate was the source of energy. In contrast, there was no RRC in the presence of glucose, which induced a surge in glycolysis. After 24 h incubation in < 1% O2, RCC is completely obliterated in the presence of either substrate; basal OCR is reduced by ~30%; glucose increases glycolysis to levels equivalent to normal cells, however, it reduces OCR to ~10% of basal levels; while palmitate is more effective in sustaining OCR during the reoxygenation period. Since miR-199a, Hif-1α, and their targets play major roles in hypoxia preconditioning and metabolism, we tested their roles in regulating RCC. Our results show that miR-199a reduces glucose oxidation while increasing glycolysis, glucose-, and fatty acid-dependent RRC. These effects are partly mediated by Pdk1, Glut3, and G0s2, which are transcriptionally-induced by antimiR-199a via Hif-1α in myocytes. In conclusion, our study shows that the RRC in myocytes favors fatty acids and is exhausted by hypoxia. Furthermore, inhibiting miR-199a and upregulating Hif-1α, has a positive effect on RRC, which potentially mediates the hypoxia preconditioning effects of these molecules.
- © 2013 by American Heart Association, Inc.