MSCs for Tissue Engineered Tracheas and Enhanced Fracture Healing

For all my readers who have ever broken a bone, this one’s for you.

Setting a broken bone properly can lead to the healing of a broken bone, but large fractures that generate gaps in bones are very hard to heal. Stem cell therapy in combination with small protein molecules called cytokines has the potential to improve bone repair, since cytokines summon resident stem cells to migrate and home to the injured site. Having said that, the engraftment, participation and recruitment of other cells within the regenerating tissue are equally important.

To stimulate stem cell-mediated healing, University College London scientists over-expressed the SDF-1 protein in mesenchymal stem cells. Since SDF-1 is a stem cell-recruitment protein, it seems reasonable to suspect that these engineered cells would effectively increase the migration of native cells to the site of fracture and enhance bone repair.

Once they made SDF-1-expressing mesenchymal stem cells, Chih-Yuan Ho and colleagues showed that these cells increased the migration of non-transfected cells in a cell culture system.

Once these SDF-1-expressing mesenchymal stem cells were implanted into rats with large bone defects, bone marrow mesenchymal stem cells that over-expressed SDF-1 showed significantly more new bone formation within the gap and less bone mineral loss at the areas next to the defect site during the early bone healing stage.

Thus, SDF-1 plays an important role in accelerating fracture repair and contributing to bone repair, at least in this rat model. SDF-1 does this by recruiting more host stem cells to the defect site and encouraging their differentiation into bone cells, which go on to produce good-quality bone.  This paper appeared the the journal Tissue Engineering, Part A.

In a second paper that appeared in the Annals of Biomedical Engineering, mesenchymal stem cells were used to tissue engineer tracheae. In this case a biocompatible scaffold was seeded various with various cells and this strategy could be a solution for tracheal reconstruction.

Yoo Seob Shin and colleagues seeded mesenchymal stem cells (MSCs) on a scaffold made from pig cartilage powder (PCP). The PCP was made with minced and decellularized pig joint cartilage and was molded into a 5 × 12 mm (height × diameter) scaffold. Mesenchymal stem cells from the bone marrow of young rabbits were grown in culture and then cultured with the PCP scaffold. After 7 weeks in culture, these tracheal implants were transplanted on a 5 × 10 mm tracheal defect in six rabbits, which were evaluated 6 and 10 weeks after the operation.

None of the six rabbits showed any sign of respiratory distress, and endoscopic examination of these tissue engineered tracheae showed that the a normal-looking respiratory epithelium completely covered the regenerated trachea. These trachea also displayed no signs of collapse or blockage.

The tissue engineered tracheae were also scanned and modeled on a computer model (luminal contour). The reconstructed areas of the trachea were the right width and dimensions compared to normal adjacent trachea and were not narrow.

Detailed microscopic tissue examinations of the tissue engineered tracheae showed that the new cartilage was successfully produced by the seeded mesenchymal stem cells and there was only a minimal degree of inflammation or granulation tissue that forms on the surfaces of wounds during the healing process. This shows that the implants did not trigger a massive inflammatory response that damaged resident or implanted tissue.

The outer surfaces of tracheal cells are decorated with tiny beating hairs called cilia that constantly beat to clear particles from the respiratory system. There are also cells that secrete mucus, which acts like fly paper for invading pollutants, particles or microorganisms. in the tissue engineered tracheae, ciliary beating frequency of the regenerated epithelium was not significantly different from the normal adjacent mucosa.

Thus, mesenchymal stem cells from bone marrow seeded on a PCP scaffold successfully restored not only the shape but also the function of the trachea without any signs of graft rejection.

Bones and trachea – mesenchymal stem cells pack a powerful healing punch!!