Specific features of stromal cells isolated from both layers of subcutaneous adipose tissue : roles of their secretion on angiogenesis and neurogenesis

In recent years, mesenchymal stromal cells have become a hot topic in the scientific community in the field of tissue regeneration, thanks to their trophic and immunomodulatory properties. In particular, adipose tissue-derived mesenchymal stromal cells (AD-MSCs) are increasingly used in plastic surgery, as well as in basic and clinical research. Despite the diversity of tissue engineering approaches and research into skin substitutes, the management of chronic wounds remains a major public health challenge. Recent literature shows that the effects of these cells are mainly linked to their paracrine secretion: in the culture supernatant or via exosomes. Subcutaneous abdominal adipose tissue (AAT) is divided into two layers: the superficial layer (sAAT) and the deep layer (dAAT). However, it is not clear whether each layer has similar characteristics relevant to the regenerative potential of AD-MSCs. The first line of work was to compare the characteristics of AD-MSCs (obtained by enzymatic digestion of abdominoplasty) by flow cytometry, proliferation assay and differentiation assay into mesodermal cells. A comparison of their immunosuppressive properties was also carried out. Following an exhaustive literature review on AD-MSCs, we set out to compare the effects of these cells and their secretory products on their angiogenic and neurostimulatory capacities. We began by comparing the secretory profile of AD-MSCs using Proteom Profiller®. Following these results, we turned our attention to the effects of the complete secretome and exosomes on endothelial cell migration and vascular network formation, from the angiogenic point of view, and on axonal regrowth after injury and neuritic growth from a neuromodulatory point of view. First, our results show that there is indeed a difference between the two layers of the AT, notably on AD-MSCs proliferation in favor of sAAT and on adipogenic differentiation in favor of dAAT. Phenotypic analysis of the vascular stromal fraction revealed that the superficial layer was more pure, with fewer hematopoietic cells and more AD-MSCs. Next, analysis of exosome characteristics obtained by differential ultracentrifugation showed no significant differences between the two layers. Analysis of the cytokine content of the complete supernatant and exosomes detected no differences either. With regard to angiogenesis, we found that the secretome was deleterious to vascular network formation and endothelial cell migration compared with the control. Exosomes had minor pro-angiogenic effects, but therefore more important than the complete secretome. With regard to neuritogenesis, exosomes again had more interesting effects than the secretome. Moreover, exosomes obtained from dAAT-derived AD-MSCs were significantly more interesting than those obtained from sAAT-derived AD-MSCs for neuritic growth alone. Thus, they appear to be more effective on neuromodulation, whereas no exosomes of the two layer have any significant impact on endothelial function. In all cases, exosomes possess more important properties than the complete secretome. In conclusion, some-significant differences between the two layers and between the secretion products were highlighted, suggesting different clinical prospects depending on the layer harvested.