Stem Cells Harvested from Bone Marrow and Adipose Tissue Demonstrate Equivalent Healing but Through Different Mechanisms in a Murine Model of Irradiated Mandibular Fracture Healing
Kavitha Ranganathan, MD, Alexandra Luby, BS, Noah S. Nelson, BS, Alicia Snider, MD, Alexis Donneys, MD, Russell Ettinger, MD, Joseph J. Rodriguez, MD, Lauren Buchman, N/A, Benjamin Levi, MD, Steven R. Buchman, MD.
University of Michigan, Ann Arbor, MI, USA.
PURPOSE: The difficulty of harvest and relative scarcity of bone marrow stromal cells (BMSCs) has limited the widespread use and clinical application of this technology, thereby necessitating inquiry into other therapies including adipose-derived stromal cells (ASCs). The goal of this study was to compare the ability of ASCs and BMSCs to heal mandibular defects and understand the mechanism through which this occurs. We hypothesize that ASCs will enhance fracture healing by improving vasculogenesis, while BSMCs will directly affect osteogenesis.
METHODS: Male Lewis rats were radiated (35Gy), and subsequently underwent mandibular osteotomy with external fixation with implantation of two million BMSCs (n=12) or ASCs (n=16) marked with Green fluorescent protein (GFP). After 40 days, union rates were evaluated using microCT. Confocal microscopy visualized the contribution of ASCs/BMSCs to the bone regenerate. Quantitative polymerase chain reaction of ASCs/BMSCs compared expression of osteogenic and vasculogenic genes. Coculture of ASCs (n=3) or BMSCs (n=3) with human umbilical vein endothelial cells (HUVECs) was performed in vitro in transwells to measure tubule formation as a marker of vasculogenesis.
RESULTS: ASC-implantation resulted in higher union rates than BMSC-implantation (union rate: 94% vs. 66%). These cells contribute indirectly to fracture healing, as GFP was not visualized at the site. (Fig. 1A) BMSCs expressed osteogenic genes including osteopontin to a significantly greater degree than did ASCs, while ASCs expressed greater levels of vascular endothelial growth factor. (Fig. 1B) This translated to greater tubule formation among HUVECs co-cultured with ASCs than with BMSCs (64.3±7.3 vs. 23.3±2.6, p=0.0008), and increased vasculogenesis in vivo in mandibles after ASC implantation. (Fig. 1C-D)
CONCLUSIONS: ASCs heal fracture defects better than BMSCs. This effect is likely mediated by indirect modulation of vasculogenesis, rather than by a direct effect on osteogenesis. Clinicians interested in cell-based therapies for irradiated bone injury should consider ASCs as a promising option, given their abundance, ease of acquisition, and improved fracture healing.
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