Role of growth factors and oxygen to limit hypertrophy and impact of high magnetic nanoparticles dose during stem cell chondrogenesis.

Due to an unmet clinical need of curative treatments for osteoarthritic patients, tissue engineering strategies that propose the development of cartilage tissue replacements from stem cells have emerged. Some of these strategies are based on the internalization of magnetic nanoparticles into stem cells to then initiate the chondrogenesis via magnetic compaction. A major difficulty is to drive the chondrogenic differentiation of the cells such as they produce an extracellular matrix free of hypertrophic collagen. An additional difficulty has to be overcome when nanoparticles are used, knowing that a high dose of nanoparticles can limit the chondrogenesis. We here propose a gene-based analysis of the effects of chemical factors (growth factors, hypoxia) on the chondrogenic differentiation of human mesenchymal stem cells both with and without nanoparticles. We focus on the synthesis of two of the most important constituents present in the cartilaginous extracellular matrix (Collagen II and Aggrecan) and on the expression of collagen X, the signature of hypertrophic cartilage, in order to provide a quantitative index of the type of cartilage produced (i.e. hyaline, hypertrophic). We demonstrate that by applying specific environmental conditions, gene expression can be directed toward the production of hyaline cartilage, with limited hypertrophy. Besides, a combination of the growth factors IGF-1, TGF-β3, with a hypoxic conditioning remarkably reduced the impact of high nanoparticles concentration.