Résumé :
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Cell therapy has emerged as a promising therapeutic option for heart failure. To such an aim, optimisation of cell engraftment is mandatory. Both cell survival and secure differentiation are likely to require an extracellular scaffold. Using nanotechnology, we engineered biocompatible polypeptide and polysacharide multilayer films (PEMS). These included Poly (L-lysine) hydrobromide (PLL) and Hyaluronan (HA). Crosslinking of films using different amounts of dimethylaminopropyl carbodiimide (EDC) defines their stiffness. We found that the most plastic cells (i.e, embryonic stem cells) respond to the force exerted by their attachment to the film. This force is translated into induction of a mesodermal cardiogenic genetic program. Indeed, stem cells cultured on PEMS (PLL/HA) with increasing stiffness turned on expression of mesodermal genes. This was associated with changes in cell shape. Real time RT-PCR revealed that the most rigid films (EDC:100), mimicking the infarction scar, induced a 4, 7, 6, 4.5 fold increase in expression of Brachyury, Myocardin, Tbx6 and Mesp1,2, respectively, in comparison with the non cross-linked ones. In fact, more the films were cross-linked and in turn stiff, more the cells adhered, changed their shape and expressed mesodermal cardiogenic genes. Expression of the protein Brachyury was also observed in cells grown on rigid films (from EDC 40). Furthermore, the proliferation rate of cells also increased with the level of stiffness. Our study shows that the stiffness of films is crucial for the differentiation of stem cells towards mesodermal cardiac lineage. By exerting traction forces on a substrate, stem cells sense the stiffness and show dissimilar morphology and adhesive properties translated in gene transcription. Biocompatible nanofilms might represent in the future a mean to secure a cell product in therapy of heart failure.
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