Metabolic Requirement of Adipose-Derived Stem Cells for Bone Tissue Engineering

The repair of massive bone defects using autologous adipose-derived adult stem (ADAS) cells in a tissue-engineered scaffold has been proposed. Scaffold materials currently in use do not initially provide sufficient mechanical strength for load bearing. One technique for avoiding mechanical damage to these constructs while they are developing is to implant them intramuscularly, allow them to mature, and then surgically transfer them to the required functional site. During the initial implantation period, these constructs are initially devoid of a vascular supply, and thus the implanted cells are in a potentially hypoxic environment which may adversely affect cell function and viability. ADAS cells are typically cultured in vitro at atmospheric oxygen tension (20% oxygen) and little is known about the metabolism of ADAS cells in anoxic environments (0.1% oxygen) or at physiologic oxygen tensions (2–10%). The authors characterized the metabolism of ADAS cells at 20%, 5%, and 0.1% oxygen while differentiating in control, osteogenic, or adipogenic media. Under these conditions, cellular proliferation (as measured by a fluorescent assay for total DNA), oxygen consumption rate (assessed with the BD-oxygen biosensor system fluorescent microplate), and change in glucose and lactate osteogenic conditions. ADAS cells in adipogenic media had lower oxygen consumption, and higher lactate production and glucose consumption at normoxic conditions, compared to the control and osteogenic differentiation media. These cells proliferated more slowly at 20%, 5%, and 0.1% oxygen relative to cells cultured in osteogenic or control media. ADAS cells in osteogenic media had higher oxygen consumption rates than cells cultured in control and adipogenic media and proliferated more slowly than control media cultured cells. Five percent hypoxia increased lactate production and glucose consumption in osteogenic media cultured cells. The metabolism of ADAS cells exposed to osteogenic differentiation conditions was primarily aerobic, while the cells in adipogenic media were primarily anaerobic. ADAS cells in osteogenic conditions appear to adapt to hypoxia by increasing anaerobic glycolysis, allowing them to survive under hypoxic conditions in the presence of glucose.