Mesenchymal stem cells from adipose tissue (ASCs) in pre-clinical models : tissue engineering for bone regeneration

The loss of bone due to trauma, infection, tumors and congenital deficiency is still one of the most important issues in orthopedic surgery. An innovative approach to solve this problem includes tissue engineering techniques, a new interdisciplinary field for the development of biological substitutes to restore or repair damaged tissues by the combination of cells, scaffolds and bioactive factors. In particular, musculoskeletal tissue regeneration often requires the use of cells and bio-degradable or bio-absorbable scaffolds which should possess either adequate mechanical properties, to match the site of implantation, and interconnecting pores to allow cellular infiltration, graft integration and vascularisation. In the last years, our laboratory has been studying in vitro human mesenchymal stem cells isolated from adipose tissue (hASCs, human Adipose-derived Stem Cells) for future clinical applications. With the aim of evaluating the potential of hASCs to regenerate osteocondral defects in pre-clinical models, we focused our attention on the characterization and differentiation towards the osteogenic lineage of ASCs isolated from adipose tissue of rabbit (rbASCs) and pig (pASCs), which may be considered good pre-clinical models in the orthopedic field. These two cell populations showed a high proliferative and clonogenic ability and a good self-renewal potential at the undifferentiated state comparable to the human ASCs. The differentiation of rbASCs and pASCs towards the osteogenic lineage is efficient as showed by an increase of alkaline phosphatase activity (ALP), of calcified extracellular matrix deposition and of the expression of bone specific proteins in comparison to undifferentiated cells. Furthermore, either undifferentiated or differentiated rbASCs and pASCs, were seeded on hydroxyapatite: almost 80% of cells adhered on the scaffold and they properly colonized it. In a 3-D environment, both ASC cells expressed bone specific markers after three weeks of differentiation. Our study suggests that autologous ASCs, alone or together with proper biomaterials, may be a suitable approach to repair critical bone defects in pre-clinical models.