Acetoacetate is a more efficient energy-yielding substrate for human mesenchymal stem cells than glucose and generates fewer reactive oxygen species

• Published in: The international journal of biochemistry & cell biology Vol. 88; pp. 75 - 83
• Main Authors: Board, Mary, Lopez, Colleen, van den Bos, Christian, Callaghan, Richard, Clarke, Kieran, Carr, Carolyn
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 01.07.2017; Elsevier
• Subjects: Acetoacetate; Acetoacetates - metabolism; Acetoacetates - pharmacology; Adenosine Triphosphate - biosynthesis; Adipocytes - cytology; Adipocytes - drug effects; Aerobiosis - drug effects; Anaerobiosis - drug effects; Biomarkers - metabolism; Cell Differentiation - drug effects; Chondrocytes - cytology; Chondrocytes - drug effects; Energy Metabolism - drug effects; Glucose - metabolism; Glucose - pharmacology; Glutamine - metabolism; Glycolysis; Glycolysis - drug effects; Humans; Iridoids - pharmacology; Mesenchymal Stem Cells - cytology; Mesenchymal Stem Cells - drug effects; Mesenchymal Stem Cells - metabolism; Osteocytes - cytology; Osteocytes - drug effects; Oxidation; Oxidation-Reduction - drug effects; Oxidative Stress - drug effects; Pyruvic Acid - metabolism; Reactive Oxygen Species - metabolism; ROS; Stem cells; Uncoupling Protein 2 - antagonists & inhibitors; Uncoupling Protein 2 - metabolism; p2; p5; ROS; Stem cells; Glycolysis; Oxidation; hMS; Acetoacetate
• ISSN: 1357-2725; 1878-5875
• DOI: 10.1016/j.biocel.2017.05.007

Energy yielding pathways of human mesenchymal stem cells Glucose is consumed by both the glycolytic and the oxidative pathways. Pyruvate, acetoacetate and glutamine are oxidised by hMSCs. Exogenous substrates are shown in boxes with solid lines, pathway intermediates in boxes with dashed lines and products in boxes with dotted lines. Arrows showing routes of entry of exogenous substrates into pathways are weighted to represent rates of utilisation (not to scale). [Display omitted] •Human mesenchymal stem cells oxidise acetoacetate 35 times faster than glucose.•Oxidation of acetoacetate reduces ROS-production 45-fold compared with glucose.•Acetoacetate plus pyruvate is the optimal substrate combination for ATP-production.•Culture of hMSCs in 20% oxygen upregulates energy metabolism 2-fold. Stem cells have been assumed to demonstrate a reliance on anaerobic energy generation, suited to their hypoxic in vivo environment. However, we found that human mesenchymal stem cells (hMSCs) have an active oxidative metabolism with a range of substrates. More ATP was consistently produced from substrate oxidation than glycolysis by cultured hMSCs. Strong substrate preferences were shown with the ketone body, acetoacetate, being oxidised at up to 35 times the rate of glucose. ROS-generation was 45-fold lower during acetoacetate oxidation compared with glucose and substrate preference may be an adaptation to reduce oxidative stress. The UCP2 inhibitor, genipin, increased ROS production with either acetoacetate or glucose by 2-fold, indicating a role for UCP2 in suppressing ROS production. Addition of pyruvate stimulated acetoacetate oxidation and this combination increased ATP production 27-fold, compared with glucose alone, which has implications for growth medium composition. Oxygen tension during culture affected metabolism by hMSCs. Between passages 2 and 5, rates of both glycolysis and substrate-oxidation increased at least 2-fold for normoxic (20% O2)- but not hypoxic (5% O2)-cultured hMSCs, despite declining growth rates and no detectable signs of differentiation. Culture of the cells with 3-hydroxybutyrate abolished the increased rates of these pathways. These findings have implications for stem cell therapy, which necessarily involves in vitro culture of cells, since low passage number normoxic cultured stem cells show metabolic adaptations without detectable changes in stem-like status.