Coordinated Changes of Mitochondrial Biogenesis and Antioxidant Enzymes during Osteogenic Differentiation of Human Mesenchymal Stem Cells

¹ Institute of Biochemistry and Molecular Biology, National Yang-Ming University, Taipei 112, Taiwan
² Institute of Biopharmaceutical Sciences, National Yang-Ming University, Taipei 112, Taiwan
³ Institute of Clinical Medicine, National Yang-Ming University, Taipei 112, Taiwan; and Department of Medical Research and Education, Taipei Veterans General Hospital, Taipei 112, Taiwan

^* To whom correspondence should be addressed. E-mail: joeman{at}ym.edu.tw.

	Abstract

The multi-differentiation ability of mesenchymal stem cells (MSCs) holds great promise for cell therapy. Numerous studies have focused on the establishment of differentiation protocols while little attention has been paid to the metabolic changes during the differentiation process. Mitochondria, the powerhouse of mammalian cells, vary in their number and function in different cell types with different energy demands; but how these variations are associated with cell differentiation remains elusive. In this study, we investigated the changes of mitochondrial biogenesis and bioenergetic function using human MSCs (hMSCs) because of their well-defined differentiation potentials. Upon osteogenic induction, the copy number of mitochondrial DNA, protein subunits of the respiratory enzymes, oxygen consumption rate, and intracellular ATP content were increased, indicating the upregulation of aerobic mitochondrial metabolism. On the other hand, undifferentiated hMSCs showed higher levels of glycolytic enzymes and lactate production rate, suggesting that hMSCs rely more on glycolysis for energy supply in comparison with hMSC-differentiated osteoblasts. In addition, we observed a dramatic decrease of intracellular reactive oxygen species (ROS) as a consequence of upregulation of two antioxidant enzymes, Mn-dependent superoxide dismutase and catalase. Finally, we found that exogenous H₂O₂ and mitochondrial inhibitors could retard the osteogenic differentiation. These findings suggested an energy production transition from glycolysis to oxidative phosphorylation in hMSCs upon osteogenic induction. Meanwhile, antioxidant enzymes were concurrently upregulated to prevent the accumulation of intracellular ROS. Together, our findings suggest that coordinated regulation of mitochondrial biogenesis and antioxidant enzymes occurs synergistically during osteogenic differentiation of hMSCs.