Mémoire
| Résumé : | The mesenchymal stem/stromal cells (MSCs) have the ability to differentiate in vitro into osteoblasts, chondrocytes or adipocytes when they are properly stimulated. This explains the interest that they provoke in the research field of the regenerative medicine and cellular therapy. It is therefore important to define how the process of differentiation is controlled. The MSCs can be isolated from different tissues: bone marrow, adipose tissue, umbilical cord,…, and they can be easily maintained in cell culture thanks to their power of self-renewal. Because easily to harvest, the main cellular model of MSCs used in the host laboratory is the model of MSCs isolated from the adipose tissue (ATMSCs). The cellular communication between MSCs and macrophages has been extensively studied but mainly in one way, MSCs to macrophages. In the host laboratory, it has been previously shown that in the presence of resident peritoneal macrophages (M0), the differentiation of ATMSCs into osteoblasts is inhibited. This result suggests that macrophages release inhibitory factors of differentiation. The aim of our Master Thesis was to study if this inhibitory function of macrophages could be dependent on their phenotype. We investigated the influence of three types of macrophages: pro-inflammatory (M1 macrophages generated following an IFNγ+LPS pre-treatment), anti-inflammatory (M2 macrophages generated by an IL-4 stimulation), and “foam cells” i.e. pathological macrophages overloaded with oxidized-LDL, known to be involved in the pathogenesis of atherosclerosis. Because IFNγ+LPS and IL-4 stimulations as well as oxidized-LDL treatment affected the process of differentiation of the ATMSCs, we first developed an appropriate experimental protocol. We choose to study the effect of supernatants collected from cultures of the different types of macrophages on the osteoblastogenesis of ATMSCs. Our data showed that the supernatant of M1 and M2 macrophages were unable to block the osteoblastogenic differentiation of ATMSCs on the contrary of M0 supernatants. But, the supernatants of “foam cells” favoured the entry of ATMSCs into osteoblastogenesis. This could be linked to the fact that atherosclerotic plaques often exhibit ectopic vascular calcification. Our results have shown that the ability of macrophages to control the osteoblastogenesis is dependent on their phenotype. |
