Measurement of oxygen tension within mesenchymal stem cell spheroids.
Spheroids formed of mesenchymal stem cells (MSCs) exhibit increased cell survival and trophic factor secretion compared with dissociated MSCs, making them therapeutically advantageous for cell therapy. Presently, there is no consensus for the mechanism of action. Many hypothesize that spheroid formation potentiates cell function by generating a hypoxic core within spheroids of sufficiently large diameters. The purpose of this study was to experimentally determine whether a hypoxic core is generated in MSC spheroids by measuring oxygen tension in aggregates of increasing diameter and correlating oxygen tension values with cell function. MSC spheroids were formed with 15 000, 30 000 or 60 000 cells per spheroid, resulting in radii of 176 ± 8 µm, 251 ± 12 µm and 353 ± 18 µm, respectively. Oxygen tension values coupled with mathematical modelling revealed a gradient that varied less than 10% from the outer diameter within the largest spheroids. Despite the modest radial variance in oxygen tension, cellular metabolism from spheroids significantly decreased as the number of cells and resultant spheroid size increased. This may be due to adaptive reductions in matrix deposition and packing density with increases in spheroid diameter, enabling spheroids to avoid the formation of a hypoxic core. Overall, these data provide evidence that the enhanced function of MSC spheroids is not oxygen mediated.
Department of Biomedical Engineering, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Kaitlin C
KC
Murphy
Department of Biomedical Engineering, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Ben P
BP
Hung
Department of Biomedical Engineering, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Stephen
S
Browne-Bourne
Department of Biomedical Engineering, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Dejie
D
Zhou
Department of Biomedical Engineering, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Jessica
J
Yeung
Department of Anatomy, Physiology, and Cell Biology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Damian C
DC
Genetos
Department of Biomedical Engineering, School of Veterinary Medicine, University of California, Davis, CA 95616, USA jkleach@ucdavis.edu.|Department of Orthopaedic Surgery, School of Medicine, University of California, Davis, Sacramento, CA 95817, USA.
J Kent
0000-0002-1673-3335
JK
Leach
D006801:Humans; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D018874:Spheroids, Cellular / Q000166:cytology / Q000378:metabolism*
D010100:Oxygen
diffusion; hypoxia; mesenchymal stem cell; oxygen tension; spheroid