Short-Time Survival and Engraftment of Bone Marrow Stromal Cells in an Ectopic Model of Bone Regeneration

Abstract

In tissue-engineered applications bone marrow stromal cells (BMSCs) are combined with scaffolds to target bone regeneration; animal models have been devised and the cells' long-term engraftment has been widely studied. However, in regenerated bone, the cell number is severely reduced with respect to the initially seeded BMSCs. This reflects the natural low cellularity of bone but underlines the selectivity of the differentiation processes. In this respect, we evaluated the short-term survival of BMSCs, transduced with the luciferase gene, after implantation of cell-seeded scaffolds in a nude mouse model. Cell proliferation/survival was assessed by bioluminescence imaging: light production was decreased by 30% on the first day, reaching a 50% loss within 48 h. Less than 5% of the initial signal remained after 2 months in vivo. Apoptotic BMSCs were detected within the first 2 days of implantation. Interestingly, the initial frequency of clonogenic progenitors matched the percentage of in vivo surviving cells. Cytokines and inflammation may contribute to the apoptotic onset at the implant milieu. However, preculturing cells with tumor necrosis factor alpha enhanced survival, allowing detection of 8.1% of the seeded BMSCs 2 months after implantation. Thus culturing conditions may reduce the apoptotic overload of seeded osteoprogenitors, strengthening the constructs' osteogenic potential.

Transplanted Umbilical Cord Mesenchymal Stem Cells Modify the In Vivo Microenvironment Enhancing Angiogenesis and Leading to Bone Regeneration

“…At variance with UC-MSCs, it is widely accepted that BMMSCs are able to directly engraft, differentiate, and deposit new bone [40], although only 10% of the adult implanted BM-MSCs remain in the ectopic implants after 14 days [46].…”

“…In particular, fetal MSCs have gained much attention as tools capable of activating the endogenous repair mechanisms of the host by furnishing a burst of paracrine factors [44,46]. Such an effect has been demonstrated despite their rapid clearance from the site of implantation and confirms that their physical existence at the site throughout the entire time required for repair to take place is not necessary to ensure complete healing.…”

Signals Between Cells and Matrix Mediate Bone Regeneration

“…Thus, even in young fetal tissues osteoprogenitors consist of only a very small fraction of bone tissue and usually reside in a well-protected niche. Moreover, during seeding, grafting and transfer of cells to the wounded area there is loss of cells through apoptosis or cytotoxic effects of mediators in the wound area (Giannoni et al 2009). Regeneration efforts focus on the ability to deliver mesenchymal stem cells to the wound, which will differentiate to the osteoblastic lineage.…”

In VivoBioluminescent Tracking of Mesenchymal Stem Cells Within Large Hydrogel Constructs

“…1,2 Endogenous cells are typically situated within 200 mm of a vascular network and rely on diffusion for their nutrient and oxygen supplies. 3 Cells implanted within tissue engineering constructs, however, in the absence of prevascularized networks, may initially experience physiologically abnormal oxygen tension and a reduced transport of nutrients and waste to and from the implantation site.…”

“…BLI signal shows a linear relationship with viable cell number with little influence from variations in cell seeding density or time in culture. 1,11 In 3D cell culture systems, BLI signal is affected by a range of additional variables such as luciferin transport kinetics and light scattering properties of the construct. 10,12 BLI measured from cells seeded within constructs of significantly different material properties has been found to differ in magnitude, but to be linearly correlated to Luc content when evaluated in vitro.…”